Sahar M. El-Gowilly

Role of oxidative stress and nitric oxide in the protective effects of α-lipoic acid and aminoguanidine against isoniazid-rifampicin-induced hepatotoxicity in rats.

Despite the great efficacy of isoniazid (INH) and rifampicin (RIF) combination, in the treatment of tuberculosis, hepatotoxicity is the most common serious complication. The potential protective effect of alpha-lipoic acid and aminoguanidine; against combination-induced hepatotoxicity was investigated in the present study. Administration of INH-RIF combination (50 mg/kg each for 14 days) resulted in an elevation of serum hepatic marker enzymes and a significant increase in lipid profile parameters. Combinations treatment increased lipid peroxidation products, decreased glutathione content, superoxide dismutase, catalase and myeloperoxidase activities. Furthermore, liver total nitrite level was significantly increased in INH-RIF treated rats. Co-administration of either alpha-lipoic acid or aminoguanidine significantly ameliorate combination-induced alterations in hepatic marker enzymes. These effects were directly linked to a greater decrease in the combination-induced elevation in lipid peroxidation products and total nitrite levels. Furthermore, co-administration of alpha-lipoic acid and aminoguanidine restore superoxide dismutase, catalase and myeloperoxidase activities and maintained the imbalance in the glutathione level. Additionally, such beneficial effect of alpha-lipoic acid was linked to a marked lipid-lowering effect. Histopathological examination revealed preservation of liver integrity of the protected groups compared to combination-treated rats alone.

Regional and endothelial differences in cyclosporine attenuation of adenosine receptor-mediated vasorelaxations.

Abstract: The present study investigated the acute effects of the immunosuppressant drug cyclosporine A on vasorelaxations evoked via activation of adenosine receptors in the phenylephrine-preconstricted rat perfused kidney and isolated aorta. The roles of endothelial relaxing factors in this interaction were also evaluated. The adenosine analogue 5′-N-ethylcarboxamidoadenosine (NECA; kidney, 6 × 10−9−1 × 10−7 mol; aorta, 1 × 10−9−1 × 10−5 M) elicited dose-dependent vasorelaxations. In the perfused kidney, NECA responses were similarly and significantly attenuated by NG-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor) or tetraethylammonium (K+ channel blocker) versus no effect for diclophenac (cyclooxygenase inhibitor). NECA relaxations in the aorta were reduced by the three inhibitors; the reduction in the response evoked by the highest dose of NECA (1 × 10−5 M) amounted to 37.7 ± 2.0% (L-NAME), 19.8 ± 1.7% (tetraethylammonium), and 29.4 ± 1.1% (diclophenac). A combination of the three inhibitors almost abolished NECA relaxations in the two preparations. Cyclosporine (2 μM) reduced NECA relaxations in the two preparations. In the aorta, cyclosporine attenuation of NECA responses was significantly reduced after exposure to L-NAME or diclophenac but not tetraethyl-ammonium, suggesting selective involvement of nitric oxide and vasodilator prostanoids in the interaction. In contrast, the cyclosporine attenuation of NECA responses in the kidney was reduced by L-NAME or tetraethylammonium. L-arginine, a nitric oxide substrate, partially restored NECA relaxations in cyclosporine-treated preparations. These findings demonstrate that cyclosporine attenuates endothelium-dependent vasorelaxations elicited via activation of adenosine receptors and highlight the interesting possibility that the relative contribution of the endothelial relaxing factors to cyclosporine-NECA interaction is largely region dependent.

Pharmacological characterization of cellular mechanisms of the renal vasodilatory effect of nicotine in rats

Nicotine causes vasodilation in the renal vasculature through as yet unidentified mechanism. This study investigated the role of endothelial and non-endothelial factors in the vasodilatory action of nicotine in the rat isolated kidney. Nicotine vasodilation in phenylephrine-preconstricted perfused kidneys was evaluated in the absence and presence of drugs that interfere with nitric oxide synthase (NOS), K+ channels, cholinergic or adrenergic activity. Nicotine infusion (5 x 10(-5), 1 x 10(-4), and 5 x 10(-4) M) produced concentration-dependent decreases in the renal perfusion pressure, which continued for 20 min with a peak depressor effect observed at approximately 3 min. Nicotine vasodilation was associated with increases in norepinephrine and NO metabolites (nitrite/nitrate, NOx) levels in the renal effluent. Chemical denudation of the endothelium with 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propane-sulfonate (CHAPS), or inhibition of NOS (NG-nitro-L-arginine, L-NNA), or guanylate cyclase (methylene blue) almost abolished the renal vasodilatory action of nicotine. Nicotine vasodilation was also significantly attenuated after selective blockade of ATP-sensitive (K(ATP), glibenclamide) or inward rectifier (Kir, BaCl2) K+ channels but remained unaltered after blockade of large-conductance calcium-activated (BKCa, tetraethylammonium, TEA) or voltage-dependent (Kv, 4-aminopyridine) K+ channels. Hexamethonium (ganglionic blocker), propranolol (beta-adrenceptor blocker), guanethidine (adrenergic neuron blocker), atropine (muscarinic antagonist) or the use of kidneys preconstricted with 80 mM KCl reduced the vasodepressor action of nicotine. Finally, exposure to diclophenac or neostigmine had no effect on nicotine vasodilation. Together, these findings implicate endothelial NOS and KATP and Kir channels in the renal vasodepressor effect of nicotine. Further, the sympathetic-dependent NO-mediated neurogenic vasodilation apparently contributes, at least partly, to nicotine vasodilation.

Estrogen dependence of the renal vasodilatory effect of nicotine in rats: role of α7 nicotinic cholinergic receptor/eNOS signaling

AIMS We recently reported that acute exposure to nicotine vasodilates the renal vasculature of male rats via facilitation of endothelial nitric oxide synthase (eNOS). In this study, we investigated whether this effect of nicotine is sexually dimorphic and the role of estrogen in modulating the nicotine effect. MAIN METHODS Nicotine-evoked vasodilation was evaluated in phenylephrine-preconstricted perfused kidneys obtained from male, proestrus female, ovariectomized (OVX) and estrogen-replaced OVX (OVXE(2)) rats. KEY FINDINGS Nicotine infusion (5×10(-5), 1×10(-4), and 5×10(-4) M) produced greater concentration-dependent reductions in the renal perfusion pressure (RPP) in an isolated kidney from proestrus females than from males. Inhibition of NOS by N(G)-nitro-L-arginine abolished the nicotine-evoked reduction in RPP and abolished the gender difference in the nicotine effect. Nicotine vasodilation was also attenuated in kidneys isolated from OVX and diestrus rats, models characterized by reduced estrogen levels. Further, estrogen or L-arginine supplementation in OVX rats largely restored the renal vasodilatory response to nicotine. Estrogen receptor blockade by tamoxifen abrogated the enhanced nicotine-evoked vasodilation elicited by E(2) in OVX rats. The nitrite/nitrate levels and protein expressions of eNOS and α(7) nicotinic cholinergic receptor (α(7) nAChRs) were significantly higher in renal tissues of OVXE(2) compared with OVX rats, suggesting a facilitatory effect for E(2) on α(7) nAChRs/eNOS signaling. SIGNIFICANCE Estrogen-dependent facilitation of NOS signaling mediates the enhanced vasodilator capacity of nicotine in the renal vasculature of female rats. Preliminary evidence also suggests a potential role for α(7) nAChRs in this estrogen-dependent phenomenon.

EXACERBATION BY NICOTINE OF THE CYCLOSPORINE A‐INDUCED IMPAIRMENT OF β‐ADRENOCEPTOR‐MEDIATED RENAL VASODILATION IN RATS

1 Nicotine is implicated in smoking‐related renovascular impairment and worsening of existing nephropathies. In the present study, we investigated whether nicotine aggravates the deleterious effect of the immunosuppressant drug cyclosporine A (CsA) on renal vasodilation induced by the β‐adrenoceptor agonist isoprenaline. 2 Bolus isoprenaline (0.03–8.0 µmol) elicited dose‐dependent vasodilation of phenylephrine‐preconstricted perfused kidneys that was attenuated by infusion at 5 mL/min of nicotine (5 × 10−4 mol/L) or CsA (2 µmol/L). Further, chronic administration of nicotine (0.4 mg/kg per day) or CsA (20 mg/kg per day) for 3 weeks reduced isoprenaline‐induced vasodilation and elevated plasma urea and creatinine concentrations, effects that were magnified when both nicotine and CsA were administered concurrently. 3 The role of endothelial and smooth muscle signalling in the acute nicotine/CsA renovascular interaction was investigated. Vasodilation caused by 0.25 µmol isoprenaline was attenuated by 6 µmol/L propranolol and 10 mmol/L tetraethylammonium (TEA), potentiated by 100 µmol/L hexamethonium and 7 µmol/L diclophenac, and virtually abolished in 80 mmol/L KCl‐preconstricted tissues. NG‐Nitro‐l‐arginine (l‐NNA; 200 µmol/L), methylene blue (10 µmol/L), 3‐[(3‐cholamidopropyl)‐dimethyl‐ammonio]‐1‐propane‐sulphonate (CHAPS; 0.2% for 30 s), nifedipine (750 nmol/L), atropine (1 µmol/L) and SQ22536 (an adenylyl cyclase inhibitor; 3 × 10−5 mol/L) had no effect on isoprenaline responses. 4 Nicotine (5 × 10−4 mol/L) reduced isoprenaline‐induced vasodilation and this effect was potentiated by concurrent CsA (2 µmol/L) infusion. Nicotine‐induced impairment of the vasodilator response to isoprenaline was reduced by hexamethonium and potentiated by l‐NNA, methylene blue, CHAPS and nifedipine. Alternatively, CsA exacerbation of the nicotine–isoprenaline interaction was abolished by propranolol, l‐NNA, methylene blue, CHAPS, l‐arginine, TEA and nifedipine. 5 In summary, nicotine and CsA produce additive impairment of kidney function and β‐adrenoceptor‐mediated renovascular control, nitric oxide (NO)–cGMP signalling tonically restrains nicotine‐induced impairment of isoprenaline vasodilation and the endothelial NO–K+ pathway modulates the aggravating effect of CsA on nicotine–isoprenaline interactions.

Role of adenosine A2A receptor signaling in the nicotine-evoked attenuation of reflex cardiac sympathetic control

Baroreflex dysfunction contributes to increased cardiovascular risk in cigarette smokers. Given the importance of adenosinergic pathways in baroreflex control, the hypothesis was tested that defective central adenosinergic modulation of cardiac autonomic activity mediates the nicotine-baroreflex interaction. Baroreflex curves relating changes in heart rate (HR) to increases or decreases in blood pressure (BP) evoked by i.v. doses (1-16μg/kg) of phenylephrine (PE) and sodium nitroprusside (SNP), respectively, were constructed in conscious rats; slopes of the curves were taken as measures of baroreflex sensitivity (BRS). Nicotine (25 and 100μg/kg i.v.) dose-dependently reduced BRS(SNP) in contrast to no effect on BRS(PE). BRS(SNP) was also attenuated after intracisternal (i.c.) administration of nicotine. Similar reductions in BRS(SNP) were observed in rats pretreated with atropine or propranolol. The combined treatment with nicotine and atropine produced additive inhibitory effects on BRS, an effect that was not demonstrated upon concurrent exposure to nicotine and propranolol. BRS(SNP) was reduced in preparations treated with i.c. 8-phenyltheophylline (8-PT, nonselective adenosine receptor antagonist), 8-(3-Chlorostyryl) caffeine (CSC, A(2A) antagonist), or VUF5574 (A(3) antagonist). In contrast, BRS(SNP) was preserved after blockade of A(1) (DPCPX) or A(2B) (alloxazine) receptors or inhibition of adenosine uptake by dipyridamole. CSC or 8-PT abrogated the BRS(SNP) depressant effect of nicotine whereas other adenosinergic antagonists were without effect. Together, nicotine preferentially impairs reflex tachycardia via disruption of adenosine A(2A) receptor-mediated facilitation of reflex cardiac sympathoexcitation. Clinically, the attenuation by nicotine of compensatory sympathoexcitation may be detrimental in conditions such as hypothalamic defense response, posture changes, and ventricular rhythms.

Estrogen Provokes the Depressant Effect of Chronic Nicotine on Vagally Mediated Reflex Chronotropism in Female Rats

We recently reported that acute nicotine impairs reflex tachycardic activity in estrogen-depleted, but not estrogen-repleted, female rats, suggesting a restraining influence for estrogen against the nicotine effect. In this study, we tested whether the baroreflex-protective effect of estrogen can be replicated when nicotine was administered chronically. We also report on the dose dependence and autonomic modulation of the nicotine-baroreflex interaction. The effects of nicotine (0.5, 1, or 2 mg/kg/day for 14 days) on baroreflex curves relating changes in heart rate to increases [phenylephrine (PE)] or decreases [sodium nitroprusside (SNP)] in blood pressure were evaluated in sham-operated (SO), ovariectomized (OVX), and estrogen-replaced OVX (OVXE2) rats. Slopes of the curves were taken as a measure of baroreflex sensitivity (BRSPE and BRSSNP). In SO rats, both reflex bradycardic and tachycardic responses were attenuated by nicotine in a dose-related fashion. In nicotine-treated rats, blockade of β-adrenergic (propranolol), but not muscarinic (atropine), receptors caused additional reductions in reflex chronotropic responses, implying that nicotine selectively impairs reflex vagal activity. OVX selectively decreased BRSPE but not BRSSNP and abolished the nicotine-induced impairment of either response. These effects of OVX were reversed after treatment with estrogen or the estrogen receptor modulator raloxifene. In atropine-treated rats, comparable BRS values were demonstrated in all rat preparations regardless of the estrogen or nicotine milieu. Collectively, the inhibition of vagal activity accounts for the depressant effect of chronic nicotine on baroreflex activity. Furthermore, contrary to nicotines acute effects, the baroreflex-attenuating effect of chronic nicotine is exacerbated by estrogen.

Comparable renovascular protective effects of moxonidine and simvastatin in rats exposed to cigarette smoke

Renovascular impairment plays a major role in smoking-induced nephrotoxicity. This study investigated the effect of the imidazoline I(1)-receptor/alpha(2)-adrenoceptor agonist moxonidine, as compared to the lipid lowering drug simvastatin, on abnormalities induced by cigarette smoke (CS) in renovascular reactivity. Six rat groups were used: control, CS (twice a day for 6weeks), simvastatin, moxonidine, CS+simvastatin, and CS+moxonidine. CS exposure increased plasma urea and creatinine and reduced plasma and renal nitrate/nitrite (NOx). In isolated perfused phenylephrine-preconstricted kidneys of CS rats, vasodilator responses to carbachol or isoprenaline, but not papaverine, were attenuated. Nitric oxide synthase (NOS) inhibition by N(G)-nitro-L-arginine (L-NNA) reduced carbachol vasodilations in control but not CS kidneys, suggesting the impairment of NOS activity by CS. Simultaneous administration of moxonidine or simvastatin abolished CS-induced abnormalities in indices of renal function, NOx, and vasodilations caused by carbachol or isoprenaline. The possibility whether alterations in antioxidant or lipid profiles contributed to the interaction was investigated. CS increased renal malondialdyde and decreased glutathione, and glutathione peroxidase, superoxide dismutase and catalase activities. Further, CS reduced plasma HDL and increased cholesterol, triglycerides, and LDL. Simvastatin or moxonidine abolished the deleterious CS effects on antioxidant activity; the lipid profile was normalized by simvastatin only. These findings highlight that renovascular dysfunction caused by CS and the underlying oxidative damage is evenly attenuated by moxonidine and simvastatin.

Central estrogenic pathways protect against the depressant action of acute nicotine on reflex tachycardia in female rats

We have previously shown that acute exposure of male rats to nicotine preferentially attenuates baroreceptor-mediated control of reflex tachycardia in contrast to no effect on reflex bradycardia. Here, we investigated whether female rats are as sensitive as their male counterparts to the baroreflex depressant effect of nicotine and whether this interaction is modulated by estrogen. Baroreflex curves relating reflex chronotropic responses evoked by i.v. doses (1-16 μg/kg) of phenylephrine (PE) or sodium nitroprusside (SNP), were constructed in conscious freely moving proestrus, ovariectomized (OVX), and estrogen (50 μg/kg/day s.c., 5 days)-replaced OVX (OVXE₂) rats. Slopes of the curves were taken as a measure of baroreflex sensitivity (BRS(PE) and BRS(SNP)). Nicotine (100 μg/kg i.v.) reduced BRS(SNP) in OVX rats but not in proestrus or OVXE₂ rats. The attenuation of reflex tachycardia by nicotine was also evident in diestrus rats, which exhibited plasma estrogen levels similar to those of OVX rats. BRS(PE) was not affected by nicotine in all rat preparations. Experiments were then extended to determine whether central estrogenic receptors modulate the nicotine-BRS(SNP) interaction. Intracisteral (i.c.) treatment of OVX rats with estrogen sulfate (0.2 μg/rat) abolished the BRS(SNP) attenuating effect of i.v. nicotine. This protective effect of estrogen disappeared when OVX rats were pretreated with i.c. ICI 182,780 (50 μg/rat, selective estrogen receptor antagonist). Together, these findings suggest that central neural pools of estrogen receptors underlie the protection offered by E₂ against nicotine-induced baroreceptor dysfunction in female rats.

PPARγ dependence of cyclosporine-isoprenaline renovascular interaction: roles of nitric oxide synthase and heme oxygenase.

We previously showed that cyclosporine (CSA) impairs renal vasodilations caused by β-adrenoceptor activation. This study investigated whether the peroxisome proliferator-activated receptor gamma (PPARγ) and related nitric oxide synthase (NOS)/heme oxygenase (HO) signaling mediates the CSA-β-adrenoceptor interaction. The vasodilatory response elicited by a bolus injection of isoprenaline (1 μmole) in phenylephrine-preconstricted perfused kidneys of rats was reduced after prior infusion of zinc protoporphyrin IX (ZnPP, HO inhibitor) or GW9662 (PPARγ antagonist), suggesting the involvement of PPARγ and HO-derived CO in the isoprenaline response. In contrast, the inhibition of NOS activity by NG-nitro-l-arginine methyl ester had no effect on isoprenaline responses. CSA (5 μM) significantly attenuated isoprenaline vasodilations, an effect that was abolished in the presence of GW9662 and accentuated by ZnPP. Also, supplementation with the PPARγ agonist pioglitazone or with l-arginine or hemin, substrates for NOS and HO, respectively, eliminated the unfavorable effect of CSA on isoprenaline vasodilations. The protection conferred by pioglitazone against CSA-evoked attenuation of isoprenaline vasodilations was maintained in NG-nitro-l-arginine methyl ester-treated kidneys and disappeared after treatment with ZnPP or GW9662. In conclusion, the activation of the HO/CO/PPARγ cascade is probably the cellular mechanism that underlies the beneficial effect of pioglitazone on the CSA-isoprenaline interaction. Further, the facilitation of the HO/CO or NOS/NO pathway seems to offset this harmful effect of CSA.