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Am J Physiol Heart Circ Physiol 293: H1737-H1744, 2007. First published June 8, 2007; doi:10.1152/ajpheart.00269.2007
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Statins prevent cholinesterase inhibitor blockade of sympathetic {alpha}7-nAChR-mediated currents in rat superior cervical ganglion neurons

Mansoor Mozayan1 and Tony J. F. Lee1,2

1Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois; and 2Tzu Chi University Center for Vascular Medicine, College of Life Sciences, Neuro-Medical Scientific Center, Tzu Chi General Hospital, Tzu Chi University, Hualien, Taiwan

Submitted 5 March 2007 ; accepted in final form 4 June 2007


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Statins are reported to be beneficial in treating a multitude of disorders including dementia due to Alzheimer disease (AD) and vascular dementia (VaD) with varying, yet-to-be determined mechanisms of actions. Although cholinesterase inhibitors (ChEIs) are still recommended as the primary drug of choice for AD and related diseases, their efficacy is frequently questioned. We recently reported that {alpha}7-neuronal acetylcholine nicotinic receptor ({alpha}7-nAChR)-mediated neurogenic vasodilation of porcine cerebral arteries was blocked by ChEIs, and this blockade was prevented by statin pretreatment. The exact mechanism of interaction between ChEIs and statins remains unclear. Activation of {alpha}7-nAChRs located on perivascular postganglionic sympathetic nerve terminals releases norepinephrine, which then acts on presynaptic beta2-adrenoceptors located on neighboring nitrergic nerve terminals, resulting in nitric oxide release and vasodilation. The present study, therefore, was designed to determine whether interaction of ChEIs and statins occurs at the {alpha}7-nAChR level. We examined effects of concurrent application of ChEIs and statins on {alpha}7-nAChR-mediated inward currents in primary neuronal cultures of rat superior cervical ganglion cells, the origin of the perivascular sympathetic innervation to the cerebral arteries. The results indicated that physostigmine, neostigmine, and galantamine inhibited choline- and nicotine-induced whole cell currents in a concentration-dependent manner. This inhibition, which was noncompetitive in nature, was prevented by concurrent application of mevastatin and lovastatin in a concentration-dependent manner. These results suggest that statins protect {alpha}7-nAChR function directly at the receptor level. Since {alpha}7-nAChR is neuroprotective, having beneficial effects on memory and cerebral vascular function, its functional inhibition by ChEIs may explain in part the limitation of its effectiveness in AD and VaD therapy. Protection of {alpha}7-nAChR function from ChEI inhibition by concurrent administration of statins may provide an alternative strategy in improving the efficacy of AD and VaD therapy.

vascular dementia; galantamine; lovastatin

STATINS WERE INITIALLY INTRODUCED as novel hypolipidemic agents by virtue of their inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase enzyme, the rate-limiting enzyme of cholesterol synthesis, in the liver (7). By inhibiting the synthesis of new cholesterol, statins also decrease the hepatic production of low-density lipoprotein (LDL) and upregulate the expression of hepatic LDL receptors, resulting in lower concentrations of circulating LDL cholesterol. However, not only have statins become the primary treatment for lowering LDL cholesterol, but they have also been shown to decrease the morbidity and mortality associated with cardiovascular diseases (35, 36).

In various cross-sectional studies, use of these hypolipidemic and cardioprotective statins has been associated with a decrease in the prevalence (14, 31, 46) and progression (40) of Alzheimer disease (AD). Although the hypolipidemic and pleiotropic effects of statins have been identified, the exact mechanism of their protective action in AD is still unknown. Their neuroprotective role could be due to their immunomodulatory (43), anti-inflammatory (47), or antioxidant (2) effects via multiple pathways unrelated to cholesterol metabolism (11, 42). Because of these and other yet unidentified effects, statins are beneficial and are used in the management of AD and vascular dementia (VaD). The primary drug of choice for AD therapy, however, is still cholinesterase inhibitors (ChEIs).

AD is characterized by a cholinergic deficit, and ChEIs, by decreasing the breakdown of synaptic acetylcholine, would increase the concentration and prolong the duration of action of acetylcholine, resulting in increased cholinergic neurotransmission. On the basis of this hypothesis ChEIs were introduced in the treatment of AD. However, fewer than half of patients receiving ChEIs achieve a clinically significant response (1, 10, 12), which may be due to ChEIs having additional effects other than inhibiting cholinesterase enzyme.

ChEIs have been shown to block the neuronal acetylcholine nicotinic receptors (nAChRs) in the striatum (3), muscle nAChR expressed in COS cells (41), and the {alpha}7-nAChR-mediated cerebral nitrergic vasodilation in porcine cerebral arteries (25). On activation by choline and nicotine, these {alpha}7-nAChRs located on the cerebral perivascular postganglionic sympathetic nerves mediate a calcium influx causing the vesicular release of norepinephrine from the sympathetic neuron. This norepinephrine then acts on the beta2-receptors on the neighboring parasympathetic nitrergic perivascular neuron to induce the release of the vasodilator nitric oxide (NO) (20, 38, 48). ChEIs inhibit this {alpha}7-nAChR-mediated vasorelaxation pathway, which, as we showed recently (25), is prevented by statins. However, the exact site of this preventive action by statins and its effect on the {alpha}7-nAChR remained undetermined. Hence, to study the effects of ChEIs and statins on the {alpha}7-nAChR directly, we examined the effects of concurrent application of ChEIs and statins on choline- and nicotine-induced whole cell currents in rat superior cervical ganglion (SCG) neurons. The results indicated that ChEIs inhibited the {alpha}7-nAChR-mediated currents in a concentration-dependent manner, and this inhibition was prevented by concurrent application of statins.


   MATERIALS AND METHODS
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 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
SCG cell culture. Primary SCG neuronal cultures were prepared from male Sprague-Dawley rats (4–8 wk old) euthanized with pentobarbital sodium. The experimental procedure was approved by the laboratory animal care and use committee of Southern Illinois University School of Medicine. Freshly dissected SCGs were placed in cold Hibernate A (Invitrogen, Carlsbad, CA) solution (22) and cut into small pieces. The ganglia were then transferred to Mg2+/Ca2+-free Hanks’ balanced salt solution containing papain (2 U/ml; Sigma-Aldrich, St. Louis, MO), collagenase D (1.2 mg/ml; Roche Diagnostics, Indianapolis, IN), and dispase (4.8 mg/ml; Invitrogen) and were incubated for 50 min at 37°C. Cells were released by gentle trituration with a fire-polished glass pipette at the end of the incubation. The cell suspension was centrifuged at 300 g for 5 min. The pellet was gently resuspended in Neurobasal culture medium (Invitrogen) containing B27 (1:50 dilution; Invitrogen), 0.5 mM L-glutamine, 25 µM L-glutamate, and nerve growth factor (50 ng/ml; Alomone Labs, Jerusalem, Israel). All media and Hanks’ balanced salt solution contained 100 U/ml penicillin and 100 U/ml streptomycin. The single-cell suspension was plated onto a four-well culture plate with a poly-D-lysine (50 µg/ml; Sigma-Aldrich)-coated glass coverslip (12-mm diameter; Fisher Scientific, Fair Lawn, NJ) in each well and incubated with air containing 5% CO2 at 37°C. The growth medium was changed once on day 2. The SCG cells were stained with anti-rabbit Neurofilament 200 (Sigma-Aldrich) as a marker of neuronal cells (22).

Whole cell electrophysiology. Cells were used 2–5 days after plating. The gigaseal patch-clamp technique was used to record whole cell currents as described previously (22). In brief, a glass coverslip containing cultured neurons was transferred from the growth medium to a recording chamber containing the extracellular recording solution (in mM: 140 NaCl, 2.5 KCl, 1 MgCl2, 2 CaCl2, 10 glucose, and 10 HEPES, pH 7.35 and 300–310 mosmol/kgH2O) on a phase-contrast microscope (Nikon TMD-Diaphot). Recording electrodes were prepared from capillary glass (PG52151-4, World Precision Instruments, Sarasota, FL). After filling with intracellular solution [in mM: 145 K-gluconate, 10 KCl, 1 EGTA, 10 HEPES, 5 K-ATP, and 0.25 GTP (pH 7.35)], electrode impedance in the extracellular recording solution was 4–6 M{Omega}.

Data acquisition and analysis were performed with Axopatch 200B, Digidata 1322A, and pCLAMP 9.0 (Axon Instruments). The traces were filtered at 5 kHz and sampled at 10 kHz.

A controlled SF-77B Perfusion Fast-Step (Warner Instrument, Hamden, CT) solution exchange system was used for rapid application of drugs onto SCG neurons. This system used a three-barreled glass perfusion head. External drug application was delivered by gravity flow from a linear array of quartz tubes. The distance from the perfusion head to the cell was ~200 µm with flow controlled manually by a micromanipulator. The duration of each recording was 20 s. During the first 2 s the cells were perfused with control extracellular solution only. This was followed by a 17-s application of experimental drugs and a final application of control extracellular solution for 1 s at the end of the recording.

Nicotine (0.1–30 mM) or choline (0.3–30 mM) was applied for 17 s, and the inward current was measured in the presence and absence of ChEIs and statins. All drugs were added simultaneously without any preincubation. To avoid development of tachyphylaxis by repeated applications of nicotinic agonists, the cells were washed for 5 min with extracellular solution before the next application. The recording chamber was continuously perfused, and cells were exposed to a constant flow of bath solution into the bath between drug applications at 2 ml/min and room temperature.

Drugs and statistical analysis. The following drugs were used: (–)-nicotine, choline chloride, {alpha}-bungarotoxin ({alpha}-BGTX), physostigmine, and neostigmine (all from Sigma-Aldrich), galantamine (Tocris, Ellisville, MO), and mevastatin sodium and lovastatin sodium (Calbiochem, La Jolla, CA). All drugs, unless otherwise stated, were dissolved in deionized water.

Results are expressed as means ± SE. Statistical analysis was evaluated by ANOVA and Student's t-test for paired or unpaired samples as appropriate. The P < 0.05 level of probability was accepted as significant.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Choline- and nicotine-evoked whole cell currents in cultured rat SCG neurons. Cultured rat SCG cells contain dense {alpha}7-nAChRs (37). With the use of the gigaseal patch-clamp technique to record whole cell currents, quantitative analysis of primary neuronal cultures of rat SCG cells indicated that choline and nicotine (0.1-mM) evoked inward currents in a concentration-dependent manner (Fig. 1). These choline- and nicotine-evoked currents were characterized by a rapid onset of action and rapid desensitization. The EC50 values of choline- and nicotine-evoked currents were 2.16 (0.92–5.06) mM and 2.54 (1.56–4.15) mM, respectively (n = 5 or 6). These choline- and nicotine-evoked inward currents did not undergo tachyphylaxis. On repeated applications of agonist, in 5-min intervals, the amplitude of choline- and nicotine-evoked currents remained stable and exhibited no rundown for up to 60 min, when whole cell recordings were obtained with an ATP/GTP-containing pipette solution (Figs. 2 and 3). Furthermore, these choline- and nicotine-evoked currents were blocked by {alpha}-BGTX (a preferential {alpha}7-nAChR antagonist; 10 and 100 nM) in a concentration-dependent manner (Figs. 2 and 3). This blockade was completely reversible after {alpha}-BGTX was washed off (Figs. 2 and 3).


Figure 1
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  		Fig. 1. Concentration-response relationship for choline and nicotine in cultured rat superior cervical ganglion (SCG) neurons. A: representative tracing of inward whole cell currents evoked by choline (0.1–30 mM) in rat SCG neurons that were clamped at –60 mV. Choline induced a concentration-dependent inward current that had a maximum amplitude at 10 mM. B: summary of concentration-response relationships for choline- and nicotine-evoked currents in cultured rat SCG neurons. Choline (0.1–30 mM) and nicotine (0.1–30 mM) evoked a concentration-dependent inward current in rat SCG neurons that were clamped at –60 mV. Data are expressed as % of the current amplitude evoked by 30 mM choline or 30 mM nicotine in each neuron. EC50 values for choline- and nicotine-evoked currents were 2.16 (0.92–5.06) and 2.54 (1.56–4.15) mM, respectively. Points represent means ± SE; n, no. of neurons for each agonist.

 

Figure 2
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  		Fig. 2. Choline-evoked currents in rat SCG neurons do not undergo tachyphylaxis and are mediated by {alpha}7-neuronal acetylcholine nicotinic receptor ({alpha}7-nAChR). A: representative tracing showing that choline-evoked currents did not run down on repeated applications of choline (10 mM) and were reversibly blocked by the selective {alpha}7-nAChR antagonist {alpha}-bungarotoxin ({alpha}-BGTX) in rat SCG neurons. B: summary showing that the peak amplitudes of choline-evoked currents after 3 consecutive applications of choline in a rat SCG neuron were not different (n = 7). The choline-evoked current was dose-dependently blocked by {alpha}-BGTX (10–100 nM), and this blockade was readily reversed after the antagonists were washed off (recovery; Rec). The neurons were held at –60 mV. The amplitudes of inward currents were calculated as % of that evoked by 10 mM choline and are expressed as means ± SE; n, no. of cells examined. **P < 0.01, significant difference from respective controls (Con).

 

Figure 3
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  		Fig. 3. Nicotine-evoked currents in rat SCG neurons do not undergo tachyphylaxis and are mediated by {alpha}7-nAChR. A: representative tracing showing that nicotine-evoked currents did not run down on repeated applications of nicotine (10 mM) and were reversibly blocked by the selective {alpha}7-nAChR antagonist {alpha}-BGTX in rat SCG neurons. B: summary showing that the peak amplitudes of nicotine-evoked currents after 3 consecutive applications of nicotine in a rat SCG neuron are not different (n = 5). The nicotine-evoked current was concentration-dependently blocked by {alpha}-BGTX (10–100 nM), and this blockade was readily reversed after the antagonists were washed off. The neurons were held at –60 mV. The amplitudes of inward currents were calculated as % of that evoked by 10 mM nicotine and are expressed as means ± SE; n, no. of cells examined. **P < 0.01, significant difference from respective controls.

 
ChEIs inhibited choline- and nicotine-evoked whole cell currents in primary rat SCG neurons in a dose-dependent manner. The peak currents elicited by choline and nicotine (10 mM) were attenuated by physostigmine (0.1–30 µM) in a concentration-dependent manner (Fig. 4) in the rat SCG neurons. This blockade by physostigmine was completely reversible after physostigmine was washed off (Fig. 4A). The IC50 values for physostigmine inhibition of choline- and nicotine-evoked current were 1.83 (0.49–6.81) µM and 5.08 (1.31–19.66) µM, respectively. Similarly, neostigmine (0.1–30 µM) and galantamine (0.3–100 µM) also inhibited choline and nicotine (10 mM)-evoked currents in a concentration-dependent manner (Fig. 4, B and C). The IC50 values for neostigmine inhibition of choline- and nicotine-evoked current were 8.03 (3.8–16.96) µM and 11.02 (2.72–44.71) µM, respectively. The IC50 values for galantamine inhibition of choline- and nicotine-evoked current were 2.95 (0.43–20.46) 10–5 M and 4.78 (1.02–22.43) 10–5 M, respectively. Physostigmine, neostigmine, or galantamine alone did not evoke a whole cell current in rat SCG cells (data not shown).


Figure 4
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  		Fig. 4. Effects of cholinesterase inhibitors (ChEIs) on choline- and nicotine-induced currents in rat SCG neurons. A: representative tracing showing effect of physostigmine (Physo, 0.1–30 µM) on inward currents evoked by choline (10 mM) in a single rat SCG neuron. Physostigmine inhibits the choline-evoked currents in a concentration-dependent manner, and this inhibition was completely reversible on wash off of physostigmine. B and C: summaries of ChEI inhibition of choline- and nicotine-induced inward currents in SCG neurons, respectively. The effect of ChEIs on whole cell currents evoked by choline (10 mM) and nicotine (10 mM) in a single rat SCG neuron clamped at –60 mV is shown. Physostigmine (0.1–30 µM), neostigmine (0.1–30 µM), and galantamine (0.3–100 µM) inhibit choline (B)- and nicotine (C)-evoked responses in a concentration-dependent manner, and this inhibition was completely reversible on wash off of the antagonists. Data are expressed as % of the current amplitude evoked by choline (10 mM) and nicotine (10 mM) in each neuron. Points represent mean ± SE response amplitudes; n, no. of neurons for each agonist examined.

 
ChEI inhibition of choline-evoked whole cell currents is noncompetitive in nature. Physostigmine (30 µM) inhibited the peak currents elicited by choline (0.1–30 mM) (Fig. 5, A and B) in the rat SCG neurons. The inhibition of choline-evoked currents was greater at higher doses of choline, resulting in a decrease in the efficacy of choline. The EC50 values for choline-evoked currents in the presence and absence of physostigmine were 1.53 (1.15–2.03) mM and 2.71 (1.56–4.73) mM, respectively. Neostigmine (30 µM, Fig. 5B) and galantamine (100 µM, Fig. 5C) exhibited a similar effect. The EC50 values for choline-evoked currents in the presence and absence of neostigmine were 1.68 (1.01–2.77) mM and 2.56 (1.18–5.55) mM, respectively. The EC50 values for choline-evoked current in the presence and absence of galantamine were 1.59 (0.85–2.99) mM and 2.08 (1.09–3.96) mM, respectively. The EC50 values for choline-evoked currents were not significantly different in the presence or absence of ChEIs. Since ChEIs decreased the efficacy of choline-evoked currents without affecting their EC50, it suggests that the nature of ChEI inhibition is noncompetitive.


Figure 5
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  		Fig. 5. Effects of ChEI inhibition of choline-induced currents in rat SCG neuron. A: representative tracing of currents evoked by choline (0.1–30 mM) in a single rat SCG neuron in the absence (Control) and presence of physostigmine (30 µM). Physostigmine inhibition of choline-evoked inward currents was greater at higher concentrations of choline, suggesting a noncompetitive nature of the inhibition. B–D: summary of ChEI inhibition of choline-evoked inward currents in the SCG neurons. Physostigmine (30 µM; B), neostigmine (Neo, 30 µM; C), and galantamine (Gal, 100 µM; D) inhibited choline (0.1–30 mM)-evoked currents in rat SCG neurons. This inhibition was greater at higher doses of choline, resulting in a decrease in the efficacy of choline. Data are expressed as % of the current amplitude evoked by choline (10 mM) in each neuron. Points represent mean ± SE response amplitudes; n, no. of neurons for each dose of choline examined.

 
Concurrent application of statins prevented ChEI inhibition of choline-evoked inward currents in a concentration-dependent manner. The inhibition of choline-evoked inward currents by physostigmine (30 µM), neostigmine (30 µM), and galantamine (100 µM) was prevented by concurrent application of mevastatin (1 and 10 µM; Fig. 6, A–D) and lovastatin (1 and 10 µM; Fig. 6, E–G) in a concentration-dependent manner. Similarly, the inhibition of nicotine-evoked inward currents by physostigmine (30 µM), neostigmine (30 µM), and galantamine (100 µM) was also prevented by concurrent administration with mevastatin (1 and 10 µM; Fig. 7, A–D) and lovastatin (1 and 10 µM; Fig. 7, E–G) in a concentration-dependent manner. Mevastatin and lovastatin alone did not affect choline- or nicotine-evoked currents (n = 5; data not shown).


Figure 6
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  		Fig. 6. Effects of statins on ChEI inhibition of choline-evoked currents in rat SCG neurons. A: representative tracing demonstrating concentration-dependent prevention of physostigmine (30 µM) inhibition of choline-evoked inward current in rat SCG neurons by mevastatin (Meva, 1–10 µM). B–D: summary of effects of mevastatin on ChEI inhibition of choline-evoked currents in rat SCG neuron. Concurrent administration of mevastatin (1–10 µM) prevented the inhibition of choline-evoked currents by physostigmine (30 µM, n = 5; B), neostigmine (30 µM, n = 6; C), and galantamine (100 µM, n = 6; D) in a concentration-dependent manner. E–G: summary of effects of lovastatin on ChEI inhibition of choline-evoked currents in rat SCG neuron. Similarly, concurrent administration of lovastatin (1–10 µM) prevented the inhibition of choline-evoked currents by physostigmine (30 µM, n = 5; E), neostigmine (30 µM, n = 6; F), and galantamine (100 µM, n = 6; G) in a concentration-dependent manner. Data are expressed as % of the current amplitude evoked by choline (10 mM) in each neuron. Values are means ± SE; n, no. of experiments. #P < 0.05, significant inhibition from control. *P < 0.05 and **P < 0.01, significant difference from ChEI treatment.

 

Figure 7
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  		Fig. 7. Effects of statins on ChEI inhibition of nicotine-evoked currents in rat SCG neurons. A: representative tracing demonstrating concentration-dependent prevention of physostigmine (30 µM) inhibition of nicotine-evoked inward currents in rat SCG neurons by mevastatin (1–10 µM). B–D: summary of effects of mevastatin on ChEI inhibition of nicotine-evoked currents in rat SCG neuron. Concurrent administration of mevastatin (1–10 µM) prevented the inhibition of nicotine-evoked current by physostigmine (30 µM, n = 6; B), neostigmine (30 µM, n = 6; C), and galantamine (100 µM, n = 6; D) in a concentration-dependent manner. E–G: summary of effects of lovastatin on ChEI inhibition of nicotine-evoked currents in rat SCG neuron. Similarly, concurrent administration of lovastatin (1–10 µM) prevented the inhibition of nicotine-evoked current by physostigmine (30 µM, n = 6; E), neostigmine (30 µM, n = 5; F), and galantamine (100 µM, n = 6; G) in a concentration-dependent manner. Data are expressed as % of the current amplitude evoked by nicotine (10 mM) in each neuron. Values are means ± SE; n, no. of experiments. #P < 0.05, significant inhibition from control. *P < 0.05 and **P < 0.01, significant difference from ChEI treatment.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The novel finding in this study is that the concurrent application of statins prevented ChEI inhibition of the {alpha}7-nAChR directly. The interaction of these two drugs commonly used in the treatment of AD and related VaD with focus on the {alpha}7-nAChR may answer questions regarding the unpredictability of response to ChEI therapy in some patients. The {alpha}7-nAChR, which is evolutionarily the oldest nAChR (18), has neuroprotective effects that have been demonstrated in vitro (15) and in vivo (26, 27) resulting in improvements in cognition and memory (21, 24). It is also located on the cerebral perivascular postganglionic sympathetic nerves, where it mediates choline- and nicotine-induced nitrergic neurogenic vasodilation in porcine and feline cerebral arteries at the base of the brain (20, 38, 48). ChEIs have been shown to block this {alpha}7-nAChR-mediated vasorelaxation in porcine cerebral arteries, which was prevented by pretreatment with statins (25). On activation by nicotinic agonist, nicotine or choline, the presynaptic sympathetic perivascular neurons release norepinephrine, which then acts on presynaptic beta2-adrenoceptors located on the neighboring nitrergic nerve terminals, resulting in release of NO and vasodilation (20, 37, 38). Since the adrenergic innervation in the cerebral circulation originates in the SCG in all species including the pig and rat (19), the present study localized the site of action of ChEIs and statins to the {alpha}7-nAChR on the rat SCG directly. Our recent findings indeed indicate that statins prevent beta-amyloid inhibition of {alpha}7-nAChR-mediated cerebral vasodilation (39), suggesting that statins may prevent decrease in cerebral blood flow due to beta-amyloid.

The aim of ChEI therapy in AD is to increase activity of the nicotinic receptors, by increasing the synaptic concentration of acetylcholine. This is based on the observation that nicotinic receptor agonists improve (45) while their antagonists impair (28) cognitive function. This effect is mediated to a significant extent by {alpha}7-nAChRs present in the hippocampus, which plays a major role in cognitive function (8, 44). Furthermore, since nicotine, a nonspecific {alpha}7-nAChR agonist, and AR-R17779, an {alpha}7-nAChR-specific agonist, consolidate memory (4), these agonists have beneficial effects on memory and learning (21, 24). Inhibition of these receptors by the {alpha}7-nAChR antagonist methyllycaconitine, in turn, results in impaired memory (9). It also has been speculated that {alpha}7-nAChR is neuroprotective against beta-amyloid, a major constituent of senile plaques in AD, and neurotoxicity due to beta-amyloid can be prevented by nicotinic agonists in cortical neurons through activation of the {alpha}7-nAChR (16). Furthermore, the perivascular sympathetic {alpha}7-nAChR, by regulating cerebral nitrergic vasorelaxation (38, 39), plays an important role in central nervous system vascular function. This is an important consideration in dementia patients who have decreased cerebral blood flow, which is positively correlated with degree of cognitive impairment (13, 29).

In the present study the three ChEIs studied inhibited the {alpha}7-nAChR noncompetitively. This ChEI blockade of {alpha}7-nAChR would be counterintuitive to the principle for which they were administered. By blocking the {alpha}7-nAChR they would prevent its beneficial neuroprotective, vasodilatory, and cognitive effects. This may explain the decreased efficacy of ChEIs in dementia, especially AD and VaD. There is much discussion about the effects of ChEIs in the treatment of AD. Three of the most commonly used ChEIs, i.e., galantamine (30), donepezil (32, 33), and rivastigmine (34), have demonstrated beneficial effects on cognition compared with placebo. Based on these and other reports, the American Academy of Neurology's practice parameter has recommended that although these drugs have a small average degree of benefit ChEIs should be considered in patients with mild to moderate AD (6). On the other hand, the National Institute for Health and Clinical Excellence (NICE), the body that advises on the use of treatments by the UK National Health Service, initially recommended that ChEIs should not be used to treat AD (17). However, the latest guidelines do recommend ChEIs, but only for cases of moderate severity (23), and NICE is examining whether ChEIs are more effective only in certain groups of people. Thus, although ChEIs are effective and produce small improvements, the practical and clinical effectiveness of these drugs remains controversial.

The present study further demonstrated that statins prevented ChEI inhibition of the {alpha}7-nAChR directly. This effect, which was seen on concurrent administration of lovastatin and mevastatin with ChEIs, strongly suggests that statins act directly on the {alpha}7-nAChR to prevent ChEI inhibition and this effect is most likely independent of any intermediate second messenger pathway. The possibility that statins directly inactivate ChEIs can be excluded, because our previous reports (25) clearly demonstrated that statins preferentially prevent the ChEI-mediated inhibition of nicotine- and choline-induced relaxation but not the ChEI-mediated inhibition of relaxation induced by other stimuli.

The finding of the present study is limited by our lack of understanding of the precise mechanism of action of ChEIs and statins in AD and VaD. Although ChEIs are beneficial in the early stages of AD, there have been reports that cholinergic deficits may not be present in the early stages of this disease (5). Furthermore, ChEIs, by increasing synaptic acetylcholine, act as cholinergic agonists and could potentially desensitize the receptors rather than activate them. In the present study we observed that the ChEIs actually inhibited the receptor.

This novel finding that statins act directly on the {alpha}7-nAChR identifies yet another beneficial effect of statins in dementia. Besides being hypolipidemic, statins had been observed to improve cognition and improve dementia of AD and VaD by cholesterol-dependent and -independent mechanisms. In this study, although statins themselves did not have an effect on {alpha}7-nAChRs, they prevented the probable adverse effects of ChEIs on coadministration. The inhibition of {alpha}7-nAChRs by ChEIs may be the limiting factor in subjects who do not respond or only respond minimally. Coadministration of statins with ChEIs would improve the efficacy of AD and VaD therapy by preventing the potentially adverse effects of ChEIs.


   GRANTS
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 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This work was supported by National Heart, Lung, and Blood Institute Grants HL-27763 and HL-47574, Tzu Chi Foundation, Tzu Chi University, National Science Council (NSC92-2320B-320-025, 93-2745-B-320-004-URD, and NSC-95-2320-B-320-013-MY2), and Southern Illinois University.


   FOOTNOTES
 

Address for reprint requests and other correspondence: T. J. F. Lee, Dept. of Pharmacology, Southern Illinois Univ. School of Medicine, PO Box 19629; Springfield, IL 62794-9629 (e-mail: tlee{at}mail.tcu.edu.tw)

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
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 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. AD2000 Collaborative Group. Long-term donepezil treatment in 565 patients with Alzheimer's disease (AD2000): randomised double-blind trial. Lancet 363: 2105–2115, 2004.[CrossRef][Web of Science][Medline]
  2. Chen L, Haught WH, Yang B, Saldeen TG, Parathasarathy S, Mehta JL. Preservation of endogenous antioxidant activity and inhibition of lipid peroxidation as common mechanisms of antiatherosclerotic effects of vitamin E, lovastatin and amlodipine. J Am Coll Cardiol 30: 569–575, 1997.[Abstract]
  3. Clarke PB, Reuben M, el-Bizri H. Blockade of nicotinic responses by physostigmine, tacrine and other cholinesterase inhibitors in rat striatum. Br J Pharmacol 111: 695–702, 1994.[Web of Science][Medline]
  4. Colrain IM, Mangan GL, Pellett OL, Bates TC. Effects of post-learning smoking on memory consolidation. Psychopharmacology (Berl) 108: 448–451, 1992.[CrossRef][Medline]
  5. Davis KL, Mohs RC, Marin D, Purohit DP, Perl DP, Lantz M, Austin G, Haroutunian V. Cholinergic markers in elderly patients with early signs of Alzheimer disease. JAMA 281: 1401–1406, 1999.[Abstract/Free Full Text]
  6. Doody RS, Stevens JC, Beck C, Dubinsky RM, Kaye JA, Gwyther L, Mohs RC, Thal LJ, Whitehouse PJ, DeKosky ST, Cummings JL. Practice parameter: management of dementia (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology 56: 1154–1166, 2001.[Abstract/Free Full Text]
  7. Endo A, Kuroda M, Tsujita Y. ML-236A, ML-236B, and ML-236C, new inhibitors of cholesterogenesis produced by Penicillium citrinium. J Antibiot (Tokyo) 29: 1346–1348, 1976.[Medline]
  8. Fabian-Fine R, Skehel P, Errington ML, Davies HA, Sher E, Stewart MG, Fine A. Ultrastructural distribution of the alpha7 nicotinic acetylcholine receptor subunit in rat hippocampus. J Neurosci 21: 7993–8003, 2001.[Abstract/Free Full Text]
  9. Felix R, Levin ED. Nicotinic antagonist administration into the ventral hippocampus and spatial working memory in rats. Neuroscience 81: 1009–1017, 1997.[CrossRef][Web of Science][Medline]
  10. Grady D. Minimal benefit is seen in drugs for Alzheimer's. New York Times, April 7, 2004.
  11. Hirai A, Nakamura S, Noguchi Y, Yasuda T, Kitagawa M, Tatsuno I, Oeda T, Tahara K, Terano T, Narumiya S, Kohn LD, Saito Y. Geranylgeranylated rho small GTPase(s) are essential for the degradation of p27Kip1 and facilitate the progression from G1 to S phase in growth-stimulated rat FRTL-5 cells. J Biol Chem 272: 13–16, 1997.[Abstract/Free Full Text]
  12. Ibach B, Haen E. Acetylcholinesterase inhibition in Alzheimer's Disease. Curr Pharm Des 10: 231–251, 2004.[CrossRef][Web of Science][Medline]
  13. Jagust WJ, Budinger TF, Reed BR. The diagnosis of dementia with single photon emission computed tomography. Arch Neurol 44: 258–262, 1987.[Abstract/Free Full Text]
  14. Jick H, Zornberg GL, Jick SS, Seshadri S, Drachman DA. Statins and the risk of dementia. Lancet 356: 1627–1631, 2000.[CrossRef][Web of Science][Medline]
  15. Kaneko S, Maeda T, Kume T, Kochiyama H, Akaike A, Shimohama S, Kimura J. Nicotine protects cultured cortical neurons against glutamate-induced cytotoxicity via {alpha}7-neuronal receptors and neuronal CNS receptors. Brain Res 765: 135–140, 1997.[CrossRef][Web of Science][Medline]
  16. Kihara T, Shimohama S, Sawada H, Kimura J, Kume T, Kochiyama H, Maeda T, Akaike A. Nicotinic receptor stimulation protects neurons against beta-amyloid toxicity. Ann Neurol 42: 159–163, 1997.[CrossRef][Web of Science][Medline]
  17. Kmietowicz Z. NICE proposes to withdraw Alzheimer's drugs from NHS. BMJ 330: 495, 2005.[Free Full Text]
  18. Le Novere N, Changeux JP. The ligand gated ion channel database. Nucleic Acids Res 27: 340–342, 1999.[Abstract/Free Full Text]
  19. Lee TJF, Kinkead LR, Sarwinski S. Norepinephrine and acetylcholine transmitter mechanisms in large cerebral arteries of the pig. J Cereb Blood Flow Metab 2: 439–450, 1982.[Web of Science][Medline]
  20. Lee TJF, Zhang W, Sarwinski S. Presynaptic beta2-adrenoceptors mediate nicotine-induced NOergic dilation in porcine basilar arteries. Am J Physiol Heart Circ Physiol 279: H808–H816, 2000.[Abstract/Free Full Text]
  21. Levin ED, Bettegowda C, Blosser J, Gordon J. AR-R17779, an alpha7 nicotinic agonist, improves learning and memory in rats. Behav Pharmacol 10: 675–680, 1999.[Web of Science][Medline]
  22. Liu J, Evans MS, Brewer GJ, Lee TJF. N-type Ca2+ channels in cultured rat sphenopalatine ganglion neurons: an immunohistochemical and electrophysiological study. J Cereb Blood Flow Metab 20: 183–191, 2000.[CrossRef][Web of Science][Medline]
  23. Mayor S. NICE recommends drugs for moderate Alzheimer's disease. BMJ 332: 195, 2006.[Free Full Text]
  24. Meyer EM, Tay ET, Papke RL, Meyers C, Huang GL, de Fiebre CM. 3-[2,4-Dimethoxybenzylidene]anabaseine (DMXB) selectively activates rat alpha7 receptors and improves memory-related behaviors in a mecamylamine-sensitive manner. Brain Res 768: 49–56, 1997.[CrossRef][Web of Science][Medline]
  25. Mozayan M, Chen MF, Si M, Yi Chen P, Premkumar LS, Lee TJF. Cholinesterase inhibitor blockade and its prevention by statins of sympathetic alpha7-nAChR-mediated cerebral nitrergic neurogenic vasodilation. J Cereb Blood Flow Metab 26: 1562–1576, 2006.[CrossRef][Web of Science][Medline]
  26. Nanri M, Kasahara N, Yamamoto J, Miyake H, Watanabe H. GTS-21, a nicotinic agonist, protects against neocortical neuronal cell loss induced by the nucleus basalis magnocellularis lesion in rats. Jpn J Pharmacol 74: 285–289, 1997.[Medline]
  27. Nanri M, Yamamoto J, Miyake H, Watanabe H. Protective effect of GTS-21, a novel nicotinic receptor agonist, on delayed neuronal death induced by ischemia in gerbils. Jpn J Pharmacol 76: 23–29, 1998.[CrossRef][Medline]
  28. Newhouse PA, Potter A, Corwin J, Lenox R. Age-related effects of the nicotinic antagonist mecamylamine on cognition and behavior. Neuropsychopharmacology 10: 93–107, 1994.[Web of Science][Medline]
  29. O'Brien JT, Eagger S, Syed GM, Sahakian BJ, Levy R. A study of regional cerebral blood flow and cognitive performance in Alzheimer's disease. J Neurol Neurosurg Psychiatry 55: 1182–1187, 1992.[Abstract/Free Full Text]
  30. Raskind MA, Peskind ER, Wessel T, Yuan W. Galantamine in AD: a 6-month randomized, placebo-controlled trial with a 6-month extension. The Galantamine USA-1 Study Group. Neurology 54: 2261–2268, 2000.[Abstract/Free Full Text]
  31. Rockwood K, Kirkland S, Hogan DB, MacKnight C, Merry H, Verreault R, Wolfson C, McDowell I. Use of lipid-lowering agents, indication bias, and the risk of dementia in community-dwelling elderly people. Arch Neurol 59: 223–227, 2002.[Abstract/Free Full Text]
  32. Rogers SL, Doody RS, Mohs RC, Friedhoff LT. Donepezil improves cognition and global function in Alzheimer disease: a 15-week, double-blind, placebo-controlled study. Donepezil Study Group. Arch Intern Med 158: 1021–1031, 1998.[Abstract/Free Full Text]
  33. Rogers SL, Farlow MR, Doody RS, Mohs R, Friedhoff LT. A 24-week, double-blind, placebo-controlled trial of donepezil in patients with Alzheimer's disease. Donepezil Study Group. Neurology 50: 136–145, 1998.[Abstract/Free Full Text]
  34. Rosler M, Anand R, Cicin-Sain A, Gauthier S, Agid Y, Dal-Bianco P, Stahelin HB, Hartman R, Gharabawi M. Efficacy and safety of rivastigmine in patients with Alzheimer's disease: international randomised controlled trial. BMJ 318: 633–638, 2001.
  35. Scandinavian Simvastatin Survival Study Group. Randomised trial of cholesterol lowering in 4444 patients with coronary heart disease: the Scandinavian Simvastatin Survival Study (4S). Lancet 344: 1383–1389, 1994.[CrossRef][Web of Science][Medline]
  36. Shepherd J, Cobbe SM, Ford I, Isles CG, Lorimer AR, MacFarlane PW, McKillop JH, Packard CJ. Prevention of coronary heart disease with pravastatin in men with hypercholesterolemia. West of Scotland Coronary Prevention Study Group. N Engl J Med 333: 1301–1307, 1995.[Abstract/Free Full Text]
  37. Si ML, Lee TJF. Presynaptic {alpha}7-nicotinic acetylcholine receptors mediate nicotine-induced nitric oxidergic neurogenic vasodilation in porcine basilar arteries. J Pharmacol Exp Ther 298: 122–128, 2001.[Abstract/Free Full Text]
  38. Si ML, Lee TJF. {alpha}7-Nicotinic acetylcholine receptors on cerebral perivascular sympathetic nerves mediate choline-induced nitrergic neurogenic vasodilation. Circ Res 91: 62–69, 2002.[Abstract/Free Full Text]
  39. Si ML, Long C, Yang DI, Chen MF, Lee TJF. Statins prevent beta-amyloid inhibition of sympathetic alpha7-nAChR-mediated nitrergic neurogenic dilation in porcine basilar arteries. J Cereb Blood Flow Metab 25: 1573–1585, 2005.[CrossRef][Web of Science][Medline]
  40. Simons M, Schwarzler F, Lutjohann D, von Bergmann K, Beyreuther K, Dichgans J, Wormstall H, Hartmann T, Schulz JB. Treatment with simvastatin in normocholesterolemic patients with Alzheimer's disease: a 26-week randomized, placebo-controlled, double-blind trial. Ann Neurol 52: 346–350, 2002.[CrossRef][Web of Science][Medline]
  41. Svobodova L, Krusek J, Hendrych T, Vyskocil F. Allosteric modulation of the nicotinic acetylcholine receptor by physostigmine. Ann NY Acad Sci 1048: 355–358, 2005.[CrossRef][Web of Science][Medline]
  42. Tatsuno I, Tanaka T, Oeda T, Yasuda T, Kitagawa M, Saito Y, Hirai A. Geranylgeranylpyrophosphate, a metabolite of mevalonate, regulates the cell cycle progression and DNA synthesis in human lymphocytes. Biochem Biophys Res Commun 241: 376–382, 1997.[CrossRef][Web of Science][Medline]
  43. Weitz-Schmidt G, Welzenbach K, Brinkmann V, Kamata T, Kallen J, Bruns C, Cottens S, Takada Y, Hommel U. Statins selectively inhibit leukocyte function antigen-1 by binding to a novel regulatory integrin site. Nat Med 7: 687–692, 2001.[CrossRef][Web of Science][Medline]
  44. Whiteaker P, Davies AR, Marks MJ, Blagbrough IS, Potter BV, Wolstenholme AJ, Collins AC, Wonnacott S. An autoradiographic study of the distribution of binding sites for the novel alpha7-selective nicotinic radioligand [3H]-methyllycaconitine in the mouse brain. Eur J Neurosci 11: 2689–2696, 1999.[CrossRef][Web of Science][Medline]
  45. Wilson AL, Langley LK, Monley J, Bauer T, Rottunda S, McFalls E, Kovera C, McCarten JR. Nicotine patches in Alzheimer's disease: pilot study on learning, memory, and safety. Pharmacol Biochem Behav 51: 509–514, 1995.[CrossRef][Web of Science][Medline]
  46. Wolozin B, Kellman W, Ruosseau P, Celesia GG, Siegel G. Decreased prevalence of Alzheimer disease associated with 3-hydroxy-3-methyglutaryl coenzyme A reductase inhibitors. Arch Neurol 57: 1439–1443, 2000.[Abstract/Free Full Text]
  47. Youssef S, Stuve O, Patarroyo JC, Ruiz PJ, Radosevich JL, Hur EM, Bravo M, Mitchell DJ, Sobel RA, Steinman L, Zamvil SS. The HMG-CoA reductase inhibitor, atorvastatin, promotes a Th2 bias and reverses paralysis in central nervous system autoimmune disease. Nature 420: 78–84, 2002.[CrossRef][Medline]
  48. Zhang W, Edvinsson L, Lee TJF. Mechanism of nicotine-induced neurogenic vasodilation in the porcine basilar artery. J Pharmacol Exp Ther 284: 790–797, 1998.[Abstract]



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