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Am J Physiol Heart Circ Physiol 286: H667-H676, 2004; doi:10.1152/ajpheart.00690.2003
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Vasoactive effects of methylamine in isolated human blood vessels: role of semicarbazide-sensitive amine oxidase, formaldehyde, and hydrogen peroxide

D. J. Conklin,1 H. R. Cowley,2 R. J. Wiechmann,3 G. H. Johnson,3 M. B. Trent,4 and P. J. Boor4

1Division of Cardiology, Department of Medicine, University of Louisville, Louisville, Kentucky 40202; 2Department of Biology, University of Wisconsin, and 3Department of Cardiothoracic Surgery, Luther Hospital/Midelfort Clinic, Eau Claire, Wisconsin 54702; and 4Department of Pathology, University of Texas Medical Branch at Galveston, Galveston, Texas 77555-0609

Submitted 18 July 2003 ; accepted in final form 14 October 2003


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
It is hypothesized that methylamine (MA) and semicarbazide-sensitive amine oxidase (SSAO) activity are involved in the cardiovascular complications in human diabetics. To test this, we 1) determined the acute vasoactive effects of MA (1–1,000 µmol/l) in uncontracted and norepinephrine (NE; 1 µmol/l)-precontracted human blood vessels used for coronary artery bypass grafts [left internal mammary artery (LIMA), radial artery (RA), and right saphenous vein (RSV)]; 2) tested whether MA effects in LIMA and RSV were dependent on SSAO activity using the SSAO inhibitor semicarbazide (1 mmol/l, 15 min); 3) determined the effects of MA metabolites formaldehyde and hydrogen peroxide in LIMA and RSV; 4) tested whether the MA response was nitric oxide, prostaglandin, or hyperpolarization dependent; 5) measured the LIMA and RSV cGMP levels after MA exposure; and 6) quantified SSAO activity in LIMA, RA, and RSV. In NE-precontracted vessels, MA stimulated a biphasic response in RA and RSV (rapid contraction followed by prolonged relaxation) and dominant relaxation in LIMA (mean ± SE, %relaxation: 55.4 ± 3.9, n = 30). The MA-induced relaxation in LIMA was repeatable, nontoxic, and age independent. Semicarbazide significantly blocked MA-induced relaxation (%inhibition: 82.5 ± 4.8, n = 7) and SSAO activity (%inhibition: 98.1 ± 1.3, n = 26) in LIMA. Formaldehyde (%relaxation: 37.3 ± 18.6, n = 3) and H2O2 (%relaxation: 55.6 ± 9.0, n = 9) at 1 mmol/l relaxed NE-precontracted LIMA comparable with MA. MA-induced relaxation in LIMA was nitric oxide, prostaglandin, and possibly cGMP independent and blocked by hyperpolarization. We conclude that vascular SSAO activity may convert endogenous amines, like MA, to vasoactive metabolites.

amine metabolism; coronary artery bypass grafts; diabetes; H2O2

A CURRENT HYPOTHESIS STATES that chronic methylamine (MA) exposure induces vascular injury and promotes vascular disease, including atherosclerosis, in humans via semicarbazide-sensitive amine oxidase-mediated (SSAO) metabolism of MA to injurious metabolites: formaldehyde, H2O2, and ammonia (NH3) (19, 50–52). Recent clinical and experimental studies support such a relationship. Altered plasma MA levels, MA excretion, and elevated plasma SSAO activity are present in human diseases associated with chronic vascular pathology [e.g., diabetes mellitus and uremia (Refs. 3, 5, 6, 27, and 49; for reviews, see Refs. 19 and 51)]. In the case of Type I diabetes, SSAO plasma levels increase at the onset of disease (6) and plasma SSAO activity positively correlates with the amount of glycosylated hemoglobin, an indicator of the severity of complications in human diabetics (5, 43). Similarly, plasma SSAO activity is elevated within 2 wk after streptozotocin-induced diabetes in rats (22). Thus much circumstantial evidence links MA levels and SSAO activity to the development of vascular pathology in diabetic humans, and recently the suggestion has been made that therapeutic inhibition of SSAO could slow the progression of vascular disease (17, 19, 51, 53).

MA is a ubiquitous primary amine derived from a multitude of sources and is preferentially metabolized by SSAO compared with other amine oxidases (16, 33, 47). Methylamine is both an exogenous (present in cigarette smoke and wine and foods) and an endogenous amine, and it is a metabolic end product of diverse compounds, including epinephrine, carbamate insecticides, creatine, nicotine, and sarcosine (35, 38, 48). MA metabolism in rats and humans appears to be due largely to SSAO activity (16, 34). For example, MA excretion is elevated in rats after the administration of SSAO inhibitors (34) and in humans after the consumption of creatinine, certain fish and seafood, and some fruits and vegetables (38). Moreover, MA is metabolized by vascular homogenates, including the rat aorta and human umbilical artery, to formaldehyde (9, 39). Finally, SSAO inhibitors prevent MA toxicity in cultured endothelial cells (47). Thus present evidence supports the concept that MA, exogenous and endogenous, is converted to metabolites, formaldehyde and H2O2, by endogenous SSAO activity.

The plasma and tissue forms of the SSAO (EC 1.4.3.6 [EC] ) enzymes are distinct from the monoamine oxidases (MAO), diamine oxidases, and polyamine oxidases (33). The copper-containing SSAOs share common features including insensitivity to MAO inhibitors (e.g., clorgyline, deprenyl), preference for aliphatic amines and the aromatic benzylamine, and inhibition by carbonyl-containing compounds, such as semicarbazide, for which the most current name is derived (33, 47). SSAO activity is present in all mammalian cardiovascular tissues tested, including plasma/serum, the aorta, and the heart with the most concentrated SSAO activity present in the mammalian aorta, including those of the human and rat (11, 13, 14, 32, 33, 37, 39, 44). This high level of SSAO activity in the cardiovascular tissues implies functionality, although a specific function for the SSAO enzyme has yet to be established (7, 33, 51).

To better understand the contribution of MA and vascular SSAO activity to human vascular physiology and pathophysiology, we studied the acute vascular effects of MA in isolated human blood vessels of patients undergoing coronary artery bypass surgery. We tested whether MA-induced vascular effects were dependent on blood vessel SSAO activity by using the SSAO inhibitor semicarbazide. Additionally, we assessed the role of age, endothelial function, and contribution of nitric oxide and prostaglandins in the MA effects in the left internal mammary artery (LIMA). Finally, we measured the SSAO activity present in the three human blood vessel types examined, the LIMA, radial artery (RA), and right saphenous vein (RSV).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Human Subjects and Blood Vessels

Research involving humans and animals in this study adhered to the ethical priniciples put forth in federal guidelines and the American Physiological Society "Guiding Principles in the Care and Use of Animals" and was approved by the local Institutional Review Board and Institutional Animal Care and Use Committee. Consenting adult humans [age (means ± SE): all, 62.8 ± 1.8 yr; men, 59.9 ± 2.4 yr ({approx}77% of total); women, 71.9 ± 1.9 yr] undergoing coronary artery bypass graft (CABG) surgery at Luther Hospital/Midelfort Clinic (Eau Claire, WI) between 2000 and 2003 were the source of the blood vessels (Institutional Review Board No. T-4028). Unused sections of the LIMA, left and right RA, and RSV were placed in lactated Ringer solution and refrigerated (4°C) at the hospital. Vessels were retrieved between 4 and 16 h after surgery, cleaned of blood, staples, thread, and extraneous tissue, and placed in fresh physiological saline solution (PSS) with glucose (pH 7.4, 4°C). All vessel experiments were begun within 24 h of surgical removal.

Vascular Ring Physiology

The human blood vessel segments used were free of overt trauma and relatively free of luminal thrombi and adventitial hematomas. The majority of vessels of each vessel type were uniform in size, but there was variation, and the exact location from where each vessel segment was removed was unknown (e.g., ankle vs. knee region of the RSV). The segment ends were trimmed, and approximately 2- to 3-mm segments ("rings") were cut. Rings were hung on stainless steel hooks in PSS bubbled with 20% O2-5% CO2 (balance N2)at37°C. One hook was connected to an isometric strain-gauge transducer (Kent Scientific; Litchfield, CT), whereas the other was attached to a fixed support rod. Transducer signals were fed into a PowerLab analog-to-digital converter and recorded on a personal computer using Chart software (version 3.4.9, iWorx; Dover, NH).

Rat thoracic aortas (TA) were taken from CO2-euthanized 12- to 14-wk-old male Sprague-Dawley rats and ~1-yr-old male Wistar rats, placed in cold PSS, and treated as previously reported (13).

All rings were subjected to the same four initials steps in sequence. Rings were equilibrated to a specified tension for 30 min in the bath [1 g for the RSV and rat TA or 3 g for the LIMA and RA (15)]. Rings were stimulated with 100 mmol/l potassium (HI K+)-PSS to test for viability. Rings were washed three times with PSS over 30 min and reequilibrated to resting tension (3x PSS). Rings were contracted with norepineprine (NE; 1 or 10 µmol/l, control NE) and then stimulated with ACh (1 µmol/l) to test for the presence of an EDRF [nitric oxide (NO{bullet})] response before experimentation [i.e., a contraction and relaxation (C/R) cycle].

Following the standard protocol, each ring was assigned one of four experimental protocols.

After all treatments and 3x PSS washouts, rings were precontracted with HI K+, followed by exposure to ACh (1 µmol/l) and then sodium nitroprusside (SNP; 100 µmol/l). ACh and SNP exposure assessed vessel responsiveness to endogenous and exogenous NO{bullet}, respectively. To test for MA hyperpolarization, a subset of HI K+-precontracted rings were exposed to MA, formaldehyde, or H2O2 (1 mmol/l, 10 min) followed by ACh and SNP addition (in LIMA only). The experimental duration was typically 4–6 h.

Vessel contractions were normalized as a percentage of the control NE contraction. Vessel relaxations were calculated as the percent reduction of the agonist-induced contractions (i.e., NE or HI K+). Cumulative concentration-response curves were used to interpolate the apparent effective concentration producing 50% relaxation (NE-precontracted vessels) or contraction (uncontracted and NE-precontracted vessels; %responses were pooled). Relaxation half-times (t1/2; in s) were calculated for MA (1 mmol/l) and ACh (1 µmol/l) relaxations in NE-precontracted LIMA and for SNP (100 µmol/l) relaxations in HI K+-precontracted LIMA.

cGMP ELISA Assay

To ascertain whether cGMP was involved in MA relaxation, we used longer segments of LIMA and RSV (0.5–1.0 cm, 100–150 mg total) exposed to MA or SNP. The percent relaxation and cGMP level for each vessel were quantified. Briefly, vessel segments were contracted with HI K+ solution, followed by 3x PSS and a C/R cycle (as above). Next, they were precontracted with 1 or 10 µmol/l NE and, when stable, exposed to MA (1 mmol/l) or SNP (100 µmol/l). After the response was allowed to plateau (20–40 min), vessels were wrapped in aluminum foil, frozen in liquid nitrogen, and stored at –80°C until analysis. Unstimulated LIMA and RSV (n = 5 vessels, patient matched) vessels were used for baseline measurement of cGMP.

Vessel segments were minced on ice and cold homogenized in 0.1 mol/l HCl (25–30 strokes, 0.1 g vessel wet wt/1 ml HCl). A homogenate subsample (50 µl) was frozen for protein analysis, and the remaining samples were centrifuged (14,000 g, 20 min). Supernatants were processed for cGMP analysis according to the ELISA kit manufacturer's instructions (DirectCyclic GMP Kit, Assay Designs; Ann Arbor, MI) using the acetylated and overnight incubation protocols. Protein was determined with the Bio-Rad Protein Dye Concentrate reagent (Hercules, CA) using BSA as the standard (Sigma; St. Louis, MO).

SSAO Assay

Standard assay protocols for measurement of SSAO activity radiometrically using [14C]benzylamine hydrochloride (BZA; 1 µmol/l; 59 µCi/mmol, Amersham; Rockford, IL) as the substrate were followed (13, 32). Blood vessel segments were homogenized in Sorensen's Na+-K+-PBS (0.1 M, pH7.8) at a ratio of 1 g of sample per 30 ml of buffer using a hand-held glass homogenizer. The homogenate was centrifuged, and 30 µl of supernatant were used in each assay. The SSAO final assay volume was 245 µl with [14C]BZA in PBS (1 µmol/l) and deprenyl in PBS (1 µmol/l). After a 30-min incubation at 37°C, the assay was stopped by the addition of 2 mmol/l citric acid (150 µl). The assay volume was extracted (extraction efficiency assumed at >95% with no correction) with toluene-ethyl acetate (1:1, 1 ml), and an aliquot (100 µl) of the organic layer was counted (3 min) by liquid scintillation (Beta-fluor, National Diagnostics; Atlanta, GA). All samples were run in duplicate or triplicate.

SSAO activity was measured in homogenized human LIMA (means ± SE patient age, 66.1 ± 2.0 yr, n = 27), RA (58.1 ± 2.5 yr, n = 12), and RSV (66.4 ± 0.6 yr, n = 5) with or without semicarbazide (1, 10, 100, or 1,000 µmol/l, 20-min preincubation) at 37°C. Protein was determined with the Bio-Rad Protein Dye Concentrate reagent using BSA in saline as the standard (Sigma). SSAO activity was calculated as nanomoles of BZA substrate metabolized per 30 min per milligram of protein. Semicarbazide inhibition was calculated as a percentage of the control SSAO activity (i.e., without semicarbazide = 100%).

Chemicals and Solutions

PSS was composed of the following (in mmol/l): 130 NaCl, 4.7 KCl, 1.17 MgSO4{bullet}7H2O, 1.18 KH2PO4, 14.9 NaHCO3, 2.0 CaCl2, and 5.0 glucose; pH 7.4. HI K+-PSS was composed of the following (in mmol/l): 34.7 NaCl, 100 KCl, 1.17 MgSO4{bullet}7H2O, 1.18 KH2PO4, 14.9 NaHCO3, 2.0 CaCl2, and 5.0 glucose; pH 7.4. All other chemicals were purchased from Sigma and dissolved in distilled water except for Indo, which was dissolved in 0.1 mol/l NaHCO3 in 0.1 N NaOH.

Statistics

Values are reported as means ± SE. Statistical comparisons between two groups were performed with Student's paired or unpaired t-tests and between more than two groups using one-way ANOVA with posttest comparisons using the Student-Newman-Keuls test (SigmaStat, SPSS; Chicago, IL). Statistical significance was assumed at P <= 0.05.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
MA, Formaldehyde, and H2O2 Effects in Isolated Human Blood Vessels and Rat TA

In preliminary tests, MA (1 mmol/l, 10 min) exposure in NE-precontracted human vessels produced biphasic responses, i.e., initial contraction, followed by prolonged relaxation, in RA and RSV and predominately strong relaxation in LIMA (4 of 30 LIMA were weakly contracted; Fig. 1A). MA-induced contractions in RA and RSV were significantly greater than those in LIMA, whereas MA-induced relaxations were significantly greater in LIMA and RA than in RSV (Fig. 1A and Table 1).



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  		Fig. 1. Methylamine (MA) produced vessel-specific responses in human blood vessels. A: quantification of maximum MA-induced responses showed MA predominately relaxed left internal mammary arteries (LIMA; n = 35) but produced a notable biphasic response, contraction first (+) followed by relaxation (–), in both radial arteries (RA; n = 9) and right saphenous veins (RSV; n = 21), although the relaxation in RA was significantly greater than that in RSV. B: typical MA (1–1,000 µmol/l) cumulative concentration-response curves in norepinephrine (NE; 1 µmol/l)-precontracted isolated human blood vessels (LIMA, RA, and RSV) from one patient. C: MA responses were plotted as percentage of the maximum response to determine the sensitivity of vessels to MA. The apparent effective concentration producing a 50% response (apparent EC50) was determined from concentration-response curves for both the MA-induced contractions and relaxations observed in NE-precontracted vessels. Values are means ± SE; n, number of vessels. * or {dagger}, Significant difference from other vessels of same category (i.e., + or –).

 

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  		Table 1. Contraction or relaxation responses in NE-precontracted isolated human blood vessels and the rat thoracic aorta after 10-min exposure to 1 mmol/l MA, formaldehyde, or H2O2

 

Unlike human blood vessel responses to 1 mmol/l MA, NE-precontracted rat TA were minimally affected by MA, and these responses appeared further blunted in TA of older rats. In contrast, vigorous biphasic responses to 1 mmol/l H2O2 were present in both young and old rat TA alike and were similar to the 1 mmol/l H2O2-induced responses in human LIMA (Table 1). Formaldehyde (1 mmol/l, 10 min) produced either minimal contraction or relatively strong relaxation, whereas no biphasic responses were observed in any blood vessel tested (Table 1). Formaldehyde-induced relaxations were slow in onset and prolonged in duration, and overt toxicity was seen in only 2 of 18 rat TA and in none of the 6 human vessels exposed, i.e., toxicity was the near-complete loss of a tension response to HI K+ after 3x PSS washout after the formaldehyde exposure.

Vessel sensitivities to MA, formaldehyde, or H2O2 were comparable between toxicants and between vessels (Fig. 1C and Table 2). RA were significantly more sensitive to MA-induced contraction than to MA-induced relaxation, whereas LIMA were more sensitive to H2O2-induced relaxation compared with RSV (Table 2). Similarly, RSV were more sensitive to MA-induced relaxation than to H2O2-induced relaxation (i.e., Fig. 1, B and C, and Table 2). Of the six human vessels tested (3 LIMA and 3 RSV), no vessel responded to formaldehyde at <1 mmol/l (note the same apparent EC50 values for all formaldehyde-induced responses; Table 2).


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  		Table 2. Apparent effective concentrations producing EC50 in isolated human blood vessels to cumulative concentrations (1–1,000 mmol/l) of MA, formaldehyde, and H2O2

 

MA Relaxation in Isolated Human LIMA

Because the MA-induced relaxation was the dominant response in the LIMA and because LIMA was the most frequently obtained blood vessel type, we further studied mechanisms of the MA relaxation in LIMA only. MA exposure (1 mmol/l, 10 min) inhibited or reduced NE contractions equally in unstimulated or NE-precontracted LIMA (means ± SE; %reduction of NE-contraction: MA pre-NE, 53 ± 7; MA post-NE, 61 ± 5, n = 5 and 9 vessels, respectively; Fig. 2). The MA-induced relaxation in NE-precontracted LIMA was repeatable, reversible, and nontoxic. In NE-precontracted LIMA, a second MA relaxation was indistinguishable from the first, and a third MA relaxation also was elicited (means ± SE; %relaxation: first relaxation, 72.0 ± 7.5; second relaxation, 60.8 ± 12.6; third relaxation, 82.1, n = 5, 5, and 1 vessels, respectively). MA exposure had no observable long-lasting inhibitory or toxic effects in any vessel.



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  		Fig. 2. Representative tracings of MA (1 mmol/l, 10 min) effects on NE (1-induced µmol/l) contractions in LIMA. MA exposure occurred as a pre- or posttreatment to NE contraction. Occasionally, MA pretreatment slightly reduced baseline tension.

 

Semicarbazide Pretreatment Inhibited MA Relaxation in Isolated Human LIMA

The MA-induced relaxation in LIMA appeared dependent on vascular SSAO activity because semicarbazide pretreatment (1 mmol/l, 15 min) significantly reduced the MA-induced relaxation but had no effect on NE-induced contraction or ACh-induced relaxation (Fig. 3, A and B). Also, MA-induced relaxations in NE-precontracted LIMA were slowly reversed within 10 min of the addition of 1 mmol/l semicarbazide (mean ± SE; %reversal: 63.0 ± 15.8, n = 2). Moreover, semicarbazide pretreatment appeared specific because the final vessel responses to HI K+, ACh, and SNP were not statistically different between paired LIMA vessels exposed to MA alone or semicarbazide plus MA (Table 3). Similarly, semicarbazide pretreatment (1 mmol/l, 15 min) completely blocked MA responses in RSV without effect on subsequent reactivity (data not shown; n = 2).



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  		Fig. 3. A: representative tracings of responses of control and semicarbazide (Semi; 1 mmol/l, >15 min)-pretreated isolated LIMA rings from one patient to NE (1 µmol/l), MA (1 mmol/l, 10 min), and ACh (1 µmol/l). B: Semi significantly blocked MA-induced relaxation but had no effect on NE contraction and ACh relaxation in LIMA rings (n = 8–9). Values are means ± SE and are presented as a percentage of the control NE-induced contractions; n, number of vessels. *Significant difference from MA control.

 

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  		Table 3. Vascular responses were intact after MA exposure or after Semi + MA exposure in isolated human LIMA

 

ACh, Nitric Oxide, and Prostanoids in MA-induced Relaxation in LIMA

ACh-induced relaxations were most often present in LIMA compared with RA or RSV (ACh addition usually produced small contraction in RSV; data not shown). The percent MA-induced relaxation was vessel specific and, in general, was associated with the ACh response, i.e., LIMA had the strongest ACh and MA relaxations, RSV had the strongest MA contractions and the weakest ACh and MA relaxations, and RA produced both strong MA contractions (equal to RSV) and strong ACh and MA relaxations (equal to LIMA; see Fig. 1A).

Despite the general positive association between ACh-induced relaxation and MA-induced relaxation observed across vessels, these two responses were not correlated within LIMA. In LIMA, the MA relaxation, on average, was greater than two times stronger than the ACh-induced relaxation regardless of the order of addition (i.e., means ± SE; ACh added before or after MA: pre-MA ACh, 25 ± 6%; post-MA ACh, 14 ± 6%, n = 21 and 20 vessels, respectively). More specifically, the percent MA relaxation was not correlated with the percent ACh relaxation or with patient age (a variable that was significantly correlated with the percent ACh relaxation in LIMA; Fig. 4A). L-NAME pretreatment (200 µmol/l, 20 min) in a subset of LIMA rings possessing a relatively strong ACh relaxation significantly inhibited the ACh-induced relaxation but had no effect on the MA-induced relaxation (Fig. 4C). In addition, neither Indo alone (100 µmol/l, 20 min) nor L-NAME + Indo pretreatment affected the MA-induced relaxation in NE-precontracted LIMA (Fig. 4C). Furthermore, the mean relaxation t1/2 for MA-induced relaxation was significantly longer in duration than the t1/2 for either ACh-induced relaxation in NE-precontracted LIMA or the SNP-induced relaxation in HI K+-precontracted LIMA (means ± SE; MA, 139.9 ± 35.8 s; ACh, 64.2 ± 7.34 s; SNP, 78.3 ± 6.6 s, n = 9, 9, and 8 vessels, respectively).



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  		Fig. 4. Relationships among MA (1 mmol/l, 10 min)-induced relaxation, ACh (1 µmol/l)-induced relaxation, and age in isolated NE (1 µmol/l)-precontracted LIMA (n = 20) were investigated. A: percent MA-induced relaxation was not correlated with the percent ACh-induced relaxation (R2 = 0.0001) or patient age, although ACh relaxation and patient age were significantly correlated (R2 = 0.23, P = 0.014). B: LIMA were pretreated with the nitric oxide synthase inhibitor N{omega}-nitro-L-arginine methyl ester (L-NAME; 200 µmol/l, 20 min), indomethacin (Indo; 100 µmol/l, 20 min), or L-NAME + Indo. L-NAME pretreatment significantly reduced ACh-induced relaxation in a subset of LIMA (n = 9) with strong ACh-induced relaxations (ACh control; >=15% relaxation) but had no effect on MA-induced relaxation (MA + L-NAME). Values are means ± SE; n, number of vessels. *Significantly different from all other treatments.

 

We determined whether the MA-, formaldehyde-, or H2O2-induced relaxations were dependent on hyperpolarization. MA, formaldehyde, or H2O2 exposure (1 mmol/l, 10 min) in HI K+-precontracted LIMA typically resulted in small, sustained contractions (e.g., MA treated: 6 of 9 responses were relatively small contractions, <10% increase in tension; H2O2 treated: 5 of 6 responses were <25% increase in tension). H2O2 produced significantly greater contractions than MA but not formaldehyde due to a few relatively large MA-stimulated relaxations (i.e., in 3 of 9 LIMA), whereas no relaxations were observed in any of the formaldehyde- or H2O2-exposed LIMA (means ± SE; percent HI K+ tension: MA, 1.7 ± 3.9; formaldehyde, 12.9 ± 2.4; H2O2, 21.1 ± 7.7, n = 9, 3, and 6 vessels, respectively). Notably, two of the three MA relaxations, including the two strongest, were in LIMA from females. The subsequent relaxations of the HI K+-precontracted LIMA produced by ACh and SNP, respectively, were not significantly different between the MA-, formaldehyde-, and the H2O2-treated vessels (data not shown).

Role of cGMP in MA-induced Relaxation in Human LIMA

Because most vascular relaxations depend on cGMP production in vascular smooth muscle cells, we investigated the role of cGMP in MA-induced relaxation in LIMA and RSV. SNP (100 µmol/l) stimulated a statistically significant three-fold increase in cGMP levels (in pmol/mg protein) in NE-precontracted RSV, and the cGMP level was also increased in SNP-stimulated LIMA (%relaxation: 100; cGMP, 1.520, n = 1 vessel) but not in RA (%relaxation: 73.9; cGMP, 0.099, n = 1 vessel) (Table 4). However, 1 mmol/l MA exposure failed to significantly elevate cGMP in either NE-precontracted LIMA or RSV despite producing significant, long-lasting relaxations (Table 4). A strong positive correlation was observed in LIMA between the MA-induced %relaxation and the %B/Bo value (i.e., used to interpolate cGMP levels; r2 = 0.70, n = 9), but a weaker relationship was present when the picomole cGMP levels were normalized to protein levels (r2 = 0.48, n = 9; data not shown).


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  		Table 4. Vascular relaxations and cGMP levels after MA or SNP exposure in NE-precontracted human LIMA and RSV

 

Human Blood Vessel SSAO Activity, Patient Age, and SSAO Inhibition

Mean SSAO activities were similar among all three human blood vessel types (Fig. 5A). For the age range examined, SSAO activity was not correlated with patient age for any vessel (Fig. 5B) but was significantly correlated between patient-matched LIMA and RSV (r2 = 0.76, P = 0.054, n = 5 vessels; data not shown) and similarly inhibited by semicarbazide (1, 10, 100, and 1,000 µmol/l) in all three blood vessel types (Fig. 5C; IC50: LIMA, 16.7 ± 19.5 µmol/l; RA, 21.2 ± 11.2 µmol/l; RSV, 14.7 ± 13.3 µmol/l, n = 25, 10, and 5 vessels, respectively).



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  		Fig. 5. A: Semicarbazide-sensitive amine oxidase (SSAO) activity was similar between the homogenized human blood vessels (LIMA, n = 26; RA, n = 12; and RSV, n = 5). B: SSAO activity in human blood vessels was not correlated with the age of the patient (R2 = 0.0002). C: Semicarbazide inhibition of SSAO activity in homogenized human LIMA (n = 26), RA (n = 12), and RSV (n = 5) was concentration dependent; however, no differences between vessels in the Semicarbazide concentrations producing 50% inhibition (IC50) were detected. Blood vessel homogenates were preincubated with Semicarbazide (1, 10, 100, and 1,000 µmol/l; 20 min) and assayed at 37°C. Values are means ± SE and are presented as a percentage of control vessel SSAO activity (i.e., without Semi); n, number of vessels.

 


   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
This is the first report of the acute vasoactive effects of MA in isolated human blood vessels. Several of our findings clearly appear at odds with the proposed role of MA as a potent vascular toxicant in humans. We find the most prominent effect of MA in isolated human blood vessels is a generally robust yet benign relaxation. This relaxation, highly expressed in LIMA, is dependent on vascular SSAO activity and, more importantly, is reversible and repeatable. It is quite distinct from the SSAO-dependent, yet quite injurious, actions of allylamine, a wellknown cardiovascular toxicant, or from effects of the {alpha},{beta}-unsaturated aldehyde acrolein in isolated rat TA, rat coronary arteries, and human blood vessels, where both agents produce vasospasm in rat coronary arteries (12, 13). Our present findings in isolated human blood vessels, while somewhat surprising, suggest that vascular SSAO activity (and possibly MA) may be a source of vasoactive signaling molecules that generally relax blood vessels.

MA Responses in Human CABG Vessels Are Dependent on Vascular SSAO Activity

MA effects in isolated human LIMA are clearly dependent on vascular SSAO activity. Data from several experiments support this conclusion. The pretreatment of isolated LIMA with semicarbazide (1 mmol/l, >15 min before the addition of MA) significantly inhibits MA responses. The inhibition was specific for SSAO activity, because semicarbazide pretreatment had no direct or indirect effects on vascular function. Moreover, semicarbazide pretreatment and posttreatment inhibition of MA relaxation in LIMA precludes a nonspecific mechanism of action of MA [e.g., MA does not directly block adrenergic receptors (31)].

We show here, for the first time, that three human blood vessels used as CABG vessels possess similar levels of relatively abundant, age-independent (age range = 45–81 yr) amine oxidase activity that is inhibited by semicarbazide in a concentration-dependent manner (Refs. 13 and 37; although our reported inhibition in human saphenous vein appears more sensitive, IC50 = 500 vs. 14.7 µmol/l, Ref. 37 vs. present study, respectively). Recently, we found similarly abundant SSAO activity in homogenized human coronary arteries of accident victims aged 7–71 yr (13). Human aortic SSAO activity was ~10 times more concentrated than in human coronary arteries, LIMA, RA, RSV, and other human blood vessels but was also age independent (23, 32). Similarly the age of rats (12–14 vs. 52 wk) had little effect on TA responses to MA exposure in our present study. So whereas age and perhaps atherosclerosis (23) appear to have little effect on SSAO expression in the blood vessel wall, the factors important in the regulation of overall SSAO expression (e.g., genetic, diabetes, environmental, etc.) remain to be identified (5, 6, 19, 51).

Dependence on SSAO activity is a hallmark of allylamine cardiovascular toxicity in vivo, in isolated blood vessels, and in cultured cardiovascular cells (2, 8, 52). The cellular toxicity of MA, in contrast, has a more complicated history because MA toxicity is orders of magnitude less toxic than allylamine in cultured cardiovascular cells (14, 30, 52). Whereas allylamine and MA are relatively similar substrates for homogenized rat aortic SSAO activity [Kms = 145.2 and 246.7 µmol/l, respectively (47)], human blood vessels have strikingly different Kms for MA [e.g., cerebral microvessels, 22 µM (Ref. 11); umbilical artery, 832 µM (see Ref. 33 for a review)]. While the disparity in toxicity between these two amines is likely due to the metabolism of allylamine to acrolein and MA to the less toxic formaldehyde, it is likely that affinity and catalytic rates and, thus, specificity of various SSAOs for different amines vary dramatically from site to site (11, 33, 51). However, biological activity is not predictable solely based on substrate availability and Km. In our present study, for example, rat aortic responses were minimal in the presence of 1 mmol/l MA despite the fact that the rat aorta possessed high SSAO activity and an adequate affinity (9, 32). Nonetheless, substrate specificity and distribution of SSAOs are likely important to the potential contribution of MA to differential cardiovascular pathology in humans [e.g., atherosclerosis, retinopathy, nephropathy, and coronary artery disease (51)].

Mechanism of Action of MA Responses in Human LIMA

Because effects of MA in LIMA and RSV appear dependent on SSAO activity, it follows that the effects of MA are likely due to one or more of MA's metabolites: formaldehyde, H2O2, and NH3. The MA responses in LIMA and RSV were similar, qualitatively and quantitatively, to both formaldehyde- and H2O2-induced responses. For example, H2O2 (1 mmol/l) pretreatment inhibits subsequent NE contractions in rabbit aorta, whereas in precontracted vessels H2O2 induces contractions, relaxations, or biphasic responses dependent on the blood vessel type (25, 28, 40). More specifically, H2O2 induced biphasic responses in rat TA and human RA and RSV that are similar in appearance to our MA responses in isolated RA and RSV (Ref. 28 and present study). In the arteries, however, weak contractions are similar for MA and formaldehyde exposures, whereas H2O2 is much more efficacious. Notably, vasospasm occurs more often in human RA and RSV compared with LIMA, and our general reactivity findings are consistent with these data (10, 24). Additionally, MA, formaldehyde, and H2O2 effects generally are reversible at 1 mmol/l in the rabbit aorta, rat TA, and human blood vessels (Refs. 25, 28, and 40 and present study). Finally, the apparent EC50s for MA, formaldehyde, and H2O2 in all three human vessels are very similar (approximate range = 200–300 µmol/l), although formaldehyde responses are only observed at 1 mmol/l. Thus we conclude that both formaldehyde and H2O2 produced by SSAO metabolism of MA contribute to the MA-induced vascular responses in human LIMA.

MA-, formaldehyde-, and H2O2-induced relaxation in LIMA may be dependent on vascular smooth muscle cell membrane hyperpolarization via activation of K+ channels because HI K+ precontraction decreases their ability to stimulate relaxation. Hyperpolarization is used in H2O2-induced relaxation of the rat aorta and porcine coronary artery (4, 28), and K+ channels may act as redox-sensitive targets for H2O2 as proposed in the mechanism of hypoxic pulmonary vasoconstriction and hypoxia-induced vasodilation (see Ref. 1 for a review). Moreover, H2O2 is considered an EDHF in human mesenteric arteries but not in the carbachol-induced relaxation in human RA (21, 36). In addition, the relaxation (and generally low toxicity) observed with 1 mmol/l formaldehyde in human blood vessels, while surprising, is not without precedent because formaldehyde (660 µmol/l) relaxes NE-precontracted but not 25 mmol/l KCl-depolarized rabbit aortas by inhibition of Ca2+ influx and NE inactivation in vitro (42). However, we cannot rule out that the strong depolarizing stimulus used in the present study (i.e., 100 mmol/l KCl) may have inhibited relaxation pathways stimulated during NE-precontraction by MA, formaldehyde, and H2O2.

Regardless of which specific metabolite is involved, MA-induced relaxation clearly appears independent of endothelial NO{bullet} or prostanoid release in human LIMA. This conclusion is supported by the observation that inhibition of endothelial nitric oxide synthase activity with L-NAME significantly reduced the ACh relaxation but had no effect on the MA relaxation. Yet, if the endothelium is involved, it perhaps is releasing an EDHF in response to MA metabolites. Hamilton et al. (21) propose that blood vessels with reduced EDRF capacity compensate with enhanced EDHF production. Because no inverse relationship was observed between ACh and MA relaxations in LIMA from patients with significantly reduced EDRF, we favor the more likely role of formaldehyde or H2O2 generated at the vascular smooth muscle cell plasma membrane [i.e., the location of SSAO (44)] acting as autocrine and/or paracrine factor(s).

It is unclear whether MA-induced relaxations are dependent on increased cGMP. While the MA-induced relaxation in RSV appears cGMP independent, there is a weak positive association between cGMP levels and the %relaxation to MA in LIMA. However, even though many relaxations are mediated by cGMP, it is possible that the formation of formaldehyde and/or H2O2 at the vascular smooth muscle cell plasma membrane directly relax(es) vessels by activation of K+ channels, thiol oxidation, inhibition of Ca2+ influx, adrenergic inactivation, or some combination of these mechanisms.

Implications for Human Health: Pharmacological and Toxicological Considerations

In the present study, MA at 1–1,000 µmol/l had no easily observable adverse effects in isolated human blood vessels. However, it is clear that massive MA exposure can be lethal in humans. As a result of an accidental spill of purified liquid MA, 35 Chinese persons of 7–71 yr of age and a nearly equal male-to-female distribution were hospitalized 7 to 8 h postexposure with 6 resulting fatalities (46). Overt toxicity in these patients included significant cardiovascular symptoms of tachycardia and low or "unmeasurable" blood pressure and pulse. These symptoms are consistent with the scenario of severe systemic hypotension, accompanied by reflex tachycardia, declining cerebral perfusion, and ultimate coma (10 of 35 people suffered light to deep coma). On the basis of the MA-induced prolonged and robust relaxation in LIMA, RA, and RSV blood vessels in our study, one might predict severe hypotension would follow a systemic, high-level MA dose [assuming the MA relaxation occurs in the resistance vessels–a testable hypothesis that is supported by the ubiquitous presence of SSAO activity in human conductance and resistance blood vessels (11, 13, 23, 32, 39)].

With the exception of an acute toxic exposure, reaching a toxic level dosage of MA in humans is unlikely. Although MA is present in a variety of common exogenous sources, including wine, cigarette smoke, a variety of foods, and as a metabolite of nicotine, it is unlikely that anyone could reach acute toxic doses by these paths (35, 38, 48), because the estimated normal human plasma [MA] = <1–5 µmol/l and the uremic human plasma [MA] = 10–20 µmol/l (3, 45). Even though [MA] in plasma is elevated in diabetic humans, especially those with chronic renal dysfunction, it is unlikely to exceed 50 µmol/l (27, 49). Some red wines possess up to 5 mg/l MA (35), which could elevate plasma MA levels by ~30 µmol/l in a 70-kg male assuming the consumption of 1 liter of wine and 100% absorption. Our data suggest that exposure of isolated human blood vessels to 80 µmol/l MA would produce a very modest vascular relaxation.

It has been suggested that treatment of human diabetics with a SSAO inhibitor, such as aminoguanidine, may provide vascular protection by inhibiting SSAO activity, diminishing amine metabolism, subsequent aldehyde and adduct formation, and reducing advanced glycation end products (AGEs) (17, 20, 37, 48). However, it is unclear how a SSAO inhibitor would affect the variety of cardiovascular and noncardiovascular pools of SSAO activity, including adipose and gastrointestinal tract smooth muscle, where the function of SSAO also remains undetermined (18). For example, the SSAO protein homolog vascular adhesion protein-1 (VAP-1) expressed in endothelial and vascular smooth muscle cells mediates lymphocyte binding (26, 41). Whereas previous studies detect little to no SSAO activity in endothelial cell cultures (50), purified human and bovine brain microvessels possess concentrated SSAO activity with relatively high affinity for MA (11). Thus endothelial cell VAP-1 may contribute to overall vascular SSAO enzymatic activity and also to nonenzymatic functions associated with amine binding, a pathway we cannot rule out in the present study. Moreover, there are no specific inhibitors for each tissue-specific pool of SSAO activity (Refs. 17 and 37 and L. Sayre, unpublished observations), and thus we should tread cautiously because the effects of SSAO inhibition or overexpression of SSAO in developing rats are detrimental to vascular tissue (19, 29) and remain unknown in the adult, although treatment of Parkinson's patients with carbidopa or hydralazine may indicate limited systemic toxicity (for reviews, see Refs. 19 and 51).


   ACKNOWLEDGMENTS
 
We thank University of Wisconsin-Eau Claire undergraduates J. Frey, M. Garney, K. Hall, D. Kranig, G. Liebsch, E. Moritz, and N. Xiong for technical assistance. We thank the staff in the Departments of Cardiothoracic Surgery and Pathology at Luther Hospital/Midelfort Clinic (Eau Claire, WI). We also thank Dr. Yu Xiao Chun of Hong Kong University for article translation.

Part of this work appeared in Experimental Biology 2002 (Abstract 378.5).

GRANTS

This work was supported by National Institutes of Health (NIH) Academic Research Enhancement Award Grant 1 R15 ES-011141-01 (to D. J. Conklin), University of Wisconsin-Eau Claire Office of Research and Sponsored Programs, the Ronald E. McNair Postbaccalaureate Scholar Program, NIH Grant HL-65416 (to P. Boor), and NIH Grant R03 AGI-8094 (to P. Boor).


   FOOTNOTES
 

Address for reprint requests and other correspondence: D. J. Conklin, Div. of Cardiology, Dept. of Medicine, Baxter II, 421C, Univ. of Louisville, Louisville, KY 40202 (E-mail: dj.conklin{at}louisville.edu).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Archer S and Michelakis E. The mechanism(s) of hypoxic pulmonary vasoconstriction: potassium channels, redox O2 sensors, and controversies. News Physiol Sci 17: 131–137, 2002.
  2. Awasthi S and Boor PJ. Semicarbazide protection from in vivo oxidant injury of vascular tissue by allylamine. Toxicol Lett 66: 157–163, 1993.
  3. Baba S, Watanabe Y, Gejyo F, and Arakawa M. High-performance liquid chromatographic determination of serum aliphatic amines in chronic renal failure. Clin Chim Acta 136: 48–56, 1984.
  4. Barlow RS and White RE. Hydrogen peroxide relaxes porcine coronary arteries by stimulating BKCa channel activity. Am J Physiol Heart Circ Physiol 275: H1283–H1289, 1998.
  5. Boomsma F, Derkx FH, van den Meiracker AH, Man in't Veld AJ, and Schalekamp MA. Plasma semicarbazide-sensitive amine oxidase activity is elevated in diabetes mellitus and correlates with glycosylated haemoglobin. Clin Sci (Lond) 88: 675–679, 1995.
  6. Boomsma F, van den Meiracker AH, Winkel S, Aanstoot HJ, Batstra MR, Man in't Veld AJ, and Bruining GJ. Circulating semicarbazide-sensitive amine oxidase is raised both in Type I (insulin-dependent), in Type II (non-insulin-dependent) diabetes mellitus and even in childhood Type I diabetes at first clinical diagnosis. Diabetologia 42: 233–237, 1999.
  7. Boor PJ, Hysmith RM, and Sanduja R. A role for a new vascular enzyme in the metabolism of xenobiotic amines. Circ Res 66: 249–252, 1990.
  8. Boor PJ and Nelson TJ. Allylamine cardiotoxicity: III. Protection by semicarbazide and in vivo derangements of monoamine oxidase. Toxicology 18: 87–102, 1980.
  9. Boor PJ, Trent MB, Lyles GA, Tao M, and Ansari GAS. Methylamine metabolism to formaldehyde by vascular semicarbazide-sensitive amine oxidase. Toxicology 73: 251–258, 1992.
  10. Cable DG, Caccitolo JA, Pfeifer EA, Daly RC, Dearani JA, Mullany CJ, O'Brien T, Orszulak TA, and Schaff HV. Endothelial regulation of vascular contraction in radial and internal mammary arteries. Ann Thorac Surg 67: 1083–1090, 1999.
  11. Castillo V, Lizcano JM, and Unzeta M. Presence of SSAO in human and bovine meninges and microvessels. Neurobiology (Bp) 7: 263–272, 1999.
  12. Conklin DJ and Boor PJ. Allylamine cardiovascular toxicity: evidence for aberrant vasoreactivity. Toxicol Appl Pharmacol 148: 245–251, 1998.
  13. Conklin DJ, Boyce CL, Trent MB, and Boor PJ. Amine metabolism: a novel path to coronary artery vasospasm. Toxicol Appl Pharmacol 175: 149–159, 2001.
  14. Conklin DJ, Langford SD, and Boor PJ. Serum and cellular semicarbazide-sensitive amine oxidase in amine metabolism and cardiovascular toxicity. Toxicol Sci 46: 386–392, 1998.
  15. Cracowski JL, Stanke-Labesque F, Sessa C, Hunt M, Chavanon O, Devillier P, and Bessard G. Functional comparison of the human isolated femoral artery, internal mammary artery, gastroepiploic artery, and saphenous vein. Can J Physiol Pharmacol 77: 770–776, 1999.
  16. Dar MS, Morselli PL, and Bowman ER. The enzymatic systems involved in the mammalian metabolism of methylamine. Gen Pharmacol 16: 557–560, 1985.
  17. Ekblom J. Potential therapeutic value of drugs inhibiting semicarbazide-sensitive amine oxidase: vascular cytoprotection in diabetes mellitus. Pharmacol Res 37: 87–92, 1998.
  18. Enrique-Tarancon G, Marti L, Morin N, Lizcano JM, Unzeta M, Sevilla L, Camps M, Palacin M, Testar X, Carpene C, and Zorzano A. Role of semicarbazide-sensitive amine oxidase on glucose transport and GLUT4 recruitment to the cell surface in adipose cells. J Biol Chem 273: 8025–8032, 1998.
  19. Göktürk C, Garpenstrand H, Nilsson J, Nordquist J, Oreland L, and Forsberg-Nilsson K. Studies on semicarbazide-sensitive amine oxidase in patients with diabetes mellitus and in transgenic mice. Biochim Biophys Acta 1647: 88–91, 2001.
  20. Gronvall JLE, Garpenstrand H, Oreland L, and Ekblom J. Autoradiographic imaging of formaldehyde adducts in mice: possible relevance for vascular damage in diabetes. Life Sci 63: 759–768, 1998.
  21. Hamilton CA, McPhaden AR, Berg G, Pathi V, and Dominiczak AF. Is hydrogen peroxide an EDHF in human radial arteries? Am J Physiol Heart Circ Physiol 280: H2451–H2455, 2001.
  22. Hayes BE and Clarke DE. Semicarbazide-sensitive amine oxidase activity in streptozotocin diabetic rats. Res Commun Chem Pathol Pharmacol 69: 71–83, 1990.
  23. Hayes BE, Ostrow PT, and Clarke DE. Benzylamine oxidase in normal and atherosclerotic human aortae. Exp Mol Pathol 38: 243–254, 1983.
  24. He GW. Arterial grafts for coronary artery bypass grafting: biological characteristics, functional classification, and clinical choice. Ann Thorac Surg 67: 277–284, 1999.
  25. Iesaki T, Okada T, Yamaguchi H, and Ochi R. Inhibition of vasoactive amine induced contractions of vascular smooth muscle by hydrogen peroxide in rabbit aorta. Cardiovasc Res 28: 963–968, 1994.
  26. Jaakkola K, Kaunismaki K, Tohka S, Yegutkin G, Vanttinen E, Havia T, Pellinlemi LJ, Virolainen M, Jalkanen S, and Salmi M. Human vascular adhesion protein-1 in smooth muscle cells. Am J Pathol 155: 1953–1965, 1999.
  27. Kapeller-Adler R and Toda K. Uber das vorkommen von monomethylamine im harn. Biochem Z 248: 403–425, 1932.
  28. Karasu C. Increased activity of H2O2 in aorta isolated from chronically streptozotocin-diabetic rats: effects of antioxidant enzymes and enzyme inhibitors. Free Radic Biol Med 27: 16–27, 1999.
  29. Langford SD, Trent MB, Balakumaran A, and Boor PJ. Developmental vasculotoxicity associated with inhibition of semicarbazide-sensitive amine oxidase. Toxicol Appl Pharmacol 155: 237–244, 1999.
  30. Langford SD, Trent MB, and Boor PJ. Cultured vascular smooth muscle cells are resistant to methylamine toxicity: no correlation to semicarbazide-sensitive amine oxidase. Cardiovasc Toxicol 1: 51–60, 2001.
  31. Lebrun P, Atwater I, Rosario LM, Herchuelz A, and Malaisse WJ. Dissociation by methylamine of insulin release from glucose-induced electrical activity in isolated mouse islets of Langerhans. Metabolism 34: 1122–1127, 1985.
  32. Lewinsohn R, Heinrich Bohm K, Glover V, and Sandler M. A benzylamine oxidase distinct from monoamine oxidase B–widespread distribution in man and rat. Biochem Pharmacol 27: 1857–1863, 1978.
  33. Lyles GA. Mammalian plasma and tissue-bound semicarbazide-sensitive amine oxidase: biochemical, pharmacological and toxicological aspects. Int J Biochem Cell Biol 28: 259–274, 1996.
  34. Lyles GA and McDougall SA. The enhanced daily excretion of urinary methylamine in rats treated with semicarbazide or hydralazine may be related to the inhibition of semicarbazide-sensitive amine oxidase activities. J Pharm Pharmacol 41: 97–100, 1989.
  35. Mafra I, Herbert P, Santos L, Barros P, and Alves A. Evaluation of biogenic amines in some Portuguese quality wines by HPLC fluorescence detection of OPA derivatives. Am J Enol Vitic 50: 128–132, 1990.
  36. Matoba T, Shimokawa H, Kubota H, Morikawa K, Fujiki T, Kunihiro I, Mukai Y, Hirakawa Y, and Takeshita A. Hydrogen peroxide is an endothelium-derived hyperpolarizing factor in human mesenteric arteries. Biochem Biophys Res Commun 290: 909–913, 2002.
  37. Meszaros Z, Csanyi A, Vallus G, Szombathy T, Karadi I, and Magyar K. Inhibitor sensitivity of human serum and vascular semicarbazide-sensitive amine oxidases. Neurobiology (Bp) 8: 215–223, 2000.
  38. Mitchell SC and Zhang AQ. Methylamine in human urine. Clin Chim Acta 312: 107–114, 2001.
  39. Precious E, Gunn CE, and Lyles GA. Deamination of methylamine by semicarbazide-sensitive amine oxidase in human umbilical artery and rat aorta. Biochem Pharmacol 37: 707–713, 1988.
  40. Rodriguez-Martinez MA, Garcia-Cohen EC, Baena AB, Gonzalez R, Salaices M, and Marin J. Contractile responses elicited by hydrogen peroxide in aorta from normotensive and hypertensive rats. Endothelial modulation and mechanisms involved. Br J Pharmacol 125: 1329–1335, 1998.
  41. Salmi M, Yegutkin GG, Lehvonen R, Koskinen K, Salminen T, and Jalkanen S. A cell surface amine oxidase directly controls lymphocyte migration. Immunity 14: 265–276, 2001.
  42. Tani T. [Relaxation of vascular smooth muscle induced by formaldehyde.] Nippon Yakurigaku Zasshi 77: 221–230, 1981.
  43. Thornalley PJ, McLellan AC, Lo TWC, Benn J, and Sonksen PH. Negative association between erythrocyte reduced glutathione concentration and diabetic complications. Clin Sci (Lond) 91: 575–582, 1996.
  44. Wibo M, Duong AT, and Godfraind T. Subcellular location of semicarbazide-sensitive amine oxidase in rat aorta. Eur J Biochem 112: 87–94, 1980.
  45. Wingender W. High-performance liquid chromatographic method for the quantitative analysis of a synthetic copolymer with antitumor activity (copovithane) and methylamine in human plasma and urine. J Chromot 273: 319–326, 1983.
  46. Yang GH, Wang YM, Chen L, and Yin JY. Emergency treatment and care of 35 patients with monomethylamine poisoning. Chung-Hua Hu Li Tsa Chih Chinese J Nurs 30: 83–85, 1995.
  47. Yu P. Oxidative deamination of aliphatic amines by rat aorta semicarbazide-sensitive amine oxidase. J Pharm Pharmacol 42: 882–884, 1990.
  48. Yu PH. Increase of formation of methylamine and formaldehyde in vivo after administration of nicotine and the potential cytotoxicity. Neurochem Res 23: 1205–1210, 1998.
  49. Yu PH and Dyck RF. Impairment of methylamine clearance in uremic patients and its nephropathological implications. Clin Nephrol 49: 299–302, 1998.
  50. Yu PH, Lai CT, and Zuo DM. Formation of formaldehyde from adrenaline in vivo; a potential risk factor for stress-related angiopathy. Neurochem Res 22: 615–620, 1997.
  51. Yu PH, Wright S, Fan EH, Lun ZR, and Gubisne-Harberle D. Physiological and pathological implications of semicarbazide-sensitive amine oxidase. Biochim Biophys Acta 1647: 193–199, 2003.
  52. Yu PH and Zuo DM. Oxidative deamination of methylamine by semicarbazide-sensitive amine oxidase leads to cytotoxic damage in endothelial cells. Possible consequences for diabetes. Diabetes 42: 594–603, 1993.
  53. Yu PH and Zuo DM. Aminoguanidine inhibits semicarbazide-sensitive amine oxidase activity: implications for advanced glycation and diabetic complications. Diabetologia 40: 1243–1250, 1997.



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