The potential relationship between gasotransmitters and oxidative stress, inflammation and apoptosis in lead-induced hepatotoxicity in rats.

The interrelationship between gasotransmitters and oxidative stress, inflammation and apoptosis in lead-induced hepatotoxicity was investigated in this study. On prolonged exposure, lead was accumulated in liver tissue of rats and impaired liver function and structure as assessed by measurement of the serum hepatic function markers and by histopathological examination. The accumulated metal induced oxidative stress, inflammation and apoptosis in the liver. Also, it increased nitric oxide (NO) production and decreased hydrogen sulfide (H2S) level and heme oxygenase (HO-1) concentration in liver tissue. Decreasing of NO production by L-N(G)-nitroarginine methyl ester (L-NAME) and increasing of H2S level by sodium hydrosulfide (NaHS) and carbon monoxide (CO) level by carbon monoxide-releasing molecule-A1 (CORM-A1) inhibited lead-induced impairment of liver function and structure. Concomitantly, these agents inhibited lead intoxication-induced oxidative stress, inflammation, apoptosis, nitrosative stress and reduction of HO-1 concentration and H2S level. Furthermore, concurrent treatment with these agents inhibited lead intoxication-induced increase in the protein expressions of inducible NO synthase, tumor necrosis factor-alpha, interleukin-1beta and caspase-3 as well as decrease in protein expressions of HO-1 and cystathionine-γ-lyase in the liver. NO donor, l-arginine and H2S and CO biosynthesis inhibitors, trifluoro-DL-alanine and zinc deutroporphyrin, respectively aggravated the toxic effects of lead. These results indicate, for the first time, that there is an interrelationship between gasotransmitters and lead-induced hepatotoxicity. The ability of L-N AME, NaHS and CORM-A1 to provide protective effects against lead-induced hepatotoxicity may positively correlate, to their ability to suppress hepatic oxidative stress, nitrosative stress, inflammation and apoptosis.

The interrelationship between gasotransmitters and lead-induced renal toxicity in rats.

This study explored the role of gasotransmitters in lead-induced nephrotoxicity. Long-term exposure of rats to lead resulted in its accumulation in kidney. The accumulated metal impaired kidney function and structure. Lead intoxication resulted in oxidative stress, inflammation and apoptosis in kidney. In addition, it resulted in nitric oxide (NO) overproduction and decrease in hydrogen sulfide (H2S) level and heme oxygenase (HO-1) concentration in kidney. Inhibition of NO overproduction by L-N(G)-nitroarginine methyl ester (L-NAME) and increasing of H2S level by sodium hydrosulfide (NaHS) and CO level by carbon monoxide-releasing molecule-A1 (CORM-A1) inhibited lead-induced impairment of kidney function and structure. These agents inhibited lead-intoxication induced oxidative stress, inflammation, apoptosis, nitrosative stress and reduction of H2S level and HO-1 concentration. Also, concomitant treatment with these agents inhibited lead intoxication-induced increase in protein expressions of inducible NO synthase (iNOS), tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1ß) and caspase-3 as well as decrease in protein expressions of HO-1 and cystathionine- γ-lyase (CSE) in kidney. The NO donor, L-arginine and the H2S and CO biosynthesis inhibitors, trifluoro-DL-alanine and zinc deutroporphyrin, respectively produced opposite effects and aggravated the toxic effects of lead. These results demonstrate, for the first time, that gasotransmitters play an important role in lead-induced nephrotoxicity.

Protective effect of the standardized leaf extract of Ginkgo biloba (EGb761) against hypertension-induced renal injury in rats.

BACKGROUND: Ginkgo biloba leaves extract has been widely used worldwide to protect against oxidative stress-induced cell damage and improves blood circulation. METHODS: The potential protective role of the standardized leaf extract of Ginkgo biloba (EGb761) on hypertension-induced renal injury was investigated in rats. Hypertension was induced in rats by L-NAME. RESULT: Repeated treatment with EGb761 produced progressive reductions in the systolic, diastolic and mean arterial blood pressure. Also, EGb761 increased the progressive reductions in blood pressure induced by losartan. Hypertension-induced marked elevation of renal malondialdehyde (MDA) and nitrite levels and reduction of reduced glutathione (GSH) level were inhibited by EGb761. In addition, hypertension-induced increases in tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interleukin-1ß (IL-1ß)) levels in renal tissues were inhibited by EGb761. Also, treatment with EGb761 inhibited hypertension-induced decrease in endothelial nitric oxide synthase (eNOS) protein expression and increase in the protein expressions of inducible NO synthase (iNOS), TNF-α, IL-6 and IL-1B in the kidney tissues. EGb761 enhanced losartan effects on renal tissues oxidative stress, nitrite, and inflammatory markers levels and on protein expressions of eNOS, iNOS, TNF-α, IL-6 and IL-1B. effects. CONCLUSIONS: These results indicate that EGb761 has the ability to protect against hypertension-induced renal injury.

Protective effect of the standardized extract of ginkgo biloba (EGb761) against hypertension with hypercholesterolemia-induced renal injury in rats: Insights in the underlying mechanisms.

The potential protective role of the standardized leaf extract of ginkgo biloba (EGb761) on hypertension with hypercholesterolemia-induced renal injury was investigated in rats. Hypertension was induced by L-N(G)-nitroarginine methyl ester (L-NAME) and hypercholesterolemia was induced by feeding rats with a diet containing 1% cholesterol. In these animals repeated treatment with EGb761 produced a progressive reduction in the systolic, diastolic and mean arterial blood pressure (BP). EGb761 increased the progressive reduction in the systolic, diastolic and mean arterial BP induced by repeated administration of losartan with simvastatin. EGb761 corrected the compromised serum lipid profile and enhanced the effect of losartan with simvastatin on lipid profile. EGb761 protected against hypertension with hypercholesterolemia-induced renal injury as assessed by measurement of serum renal function markers and by histopathological examination. EGb761 enhanced the renoprotective effect of losartan with simvastatin in these rats. Concomitantly, hypertension with hypercholesterolemia-induced elevation of renal tissue malondialdehyde (MDA) and nitrite levels and reduction of intracellular reduced glutathione (GSH) level were inhibited by repeated treatment with EGb761. In addition, hypertension with hypercholesterolemia-induced increases in tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interleukin-1ß (IL-1ß) levels in renal tissues were inhibited by treatment with EGb761. Also, EGb761 inhibited hypertension with hypercholesterolemia-induced decrease in endothelial nitric oxide synthase (eNOS) protein expression and increase in the protein expressions of inducible NO synthase (iNOS), TNF-α, IL-6 and IL-1ß in the kidney tissues. Losartan with simvastatin produced similar effects on renal tissues oxidative stress, nitrite and inflammatory markers levels and on protein expressions of eNOS, iNOS, TNF-α, IL-6 and IL-1ß. EGb761 enhanced losartan with simvastatin effects. These results indicate that EGb761 has the ability to protect against hypertension with hypercholesterolemia-induced renal injury. The ability of EGb761 to provide this renoprotective effect may positively correlate, besides its antihypertensive and antihypercholesterolemic effects, to its ability to suppress renal oxidative stress, nitrosative stress and inflammation.

A potential mechanism for the ameliorative effect of thymoquinone on pentylenetetrazole-induced kindling and cognitive impairments in mice.

Cognitive dysfunction is commonly observed in epileptic patients. Pentylenetetrazole (PTZ) kindling is a well established animal model which simulates clinical epilepsy. This study evaluated the potential role of glutamate, oxidative stress and nitric oxide (NO) overproduction in pentylenetetrazole (PTZ)-induced kindling and associated cognitive impairments in mice and effect of thymoquinone on these parameters. Repeated treatment of mice with a subconvulsive dose of PTZ (35mg/kg i.p.) once every alternate-day for 12 injections induced kindling. PTZ-kindled mice showed learning and memory impairments as assessed by acquisition and probe trials of Morris water maze and step-through latency of passive avoidance tests. Concurrently, the brain glutamate, malondialdehyde and nitrite levels were increased while the brain intracellular reduced glutathione level and glutathione peroxidase activity were decreased in PTZ-kindled mice. Also, the brain inducible but not neuronal NO synthase mRNA and protein expressions were increased in PTZ-kindled mice. Treatment of mice with thymoquinonne (5, 10 and 20mg/kg i.p.) along with alternate-day subconvulsive dose of PTZ produced dose-dependent protection against PTZ-induced kindling and learning and memory impairments. Moreover, treatment of mice with thymoquinonne (20mg/kg) inhibited the biochemical alterations induced by PTZ in the brain except the elevation of brain glutamate level. The associated increase in brain inducible NO synthase mRNA and protein expressions were also inhibited. These results suggest that glutamate, and subsequent oxidative stress and NO overproduction, via inducible NO synthase, play an important role in the pathophysiology of PTZ-induced kindling and cognitive impairments in mice. Thymoquinone dose-dependently protects against PTZ-induced kindling and cognitive impairments. Inhibition of PTZ-induced brain oxidative stress and NO overproduction, via increase the expression and activity of inducible NO synthase, may play an important role in thymoquinone action.

Protective effect of citicoline against aluminum-induced cognitive impairments in rats.

The potential protective effect of citicoline on aluminum chloride-induced cognitive deficits was investigated in rats. In a Morris water maze, administration of aluminum chloride to rats for 90 days resulted in increased escape latency to reach the platform and decreased swimming speed in acquisition trials. Similarly, in probe trials, the time required to reach the hidden platform was increased and the time spent in the target quadrant was reduced. Also, administration of aluminum chloride to rats for 90 days increased the reference and working memory errors and time required to end the task in the radial arm maze. In addition, this treatment decreased the step-through latency in the passive avoidance test. Concurrently, treatment of rats with aluminum chloride for 90 days increased hippocampal glutamate, malondialdehyde, and nitrite levels and decreased intracellular reduced glutathione level. In the citicoline-treated group, aluminum chloride-induced learning and memory impairments as assessed by the Morris water maze, radial arm maze, and passive avoidance tests were inhibited. At the same time, treatment of rats with citicoline prevented the biochemical alterations induced by aluminum chloride in the hippocampus. It can be concluded that elevation of hippocampal glutamate level with consequent oxidative stress and nitric oxide (NO) overproduction may play an important role in aluminum-induced cognitive impairments. Also, our results suggest, for the first time, that citicoline can protect against the development of these cognitive deficits through inhibition of aluminum-induced elevation of glutamate level, oxidative stress, and NO overproduction in the hippocampus.

Effect of simvastatin on the antihypertensive activity of losartan in hypertensive hypercholesterolemic animals and patients: role of nitric oxide, oxidative stress, and high-sensitivity C-reactive protein.

This study investigated whether simvastatin has antihypertensive activity and can enhance the antihypertensive effect of losartan in hypertensive hypercholesterolemic animals and patients. Hypertension and hypercholesterolemia were induced in rats by L-NAME and cholesterol-enriched diet, respectively. In these animals, repeated administration of simvastatin decreased the systolic blood pressure, enhanced its progressive reductions induced by repeated administration of losartan, and corrected the compromised lipid profile. Concomitantly, repeated administration of simvastatin, losartan, or simvastatin in combination with losartan to these animals increased nitric oxide (NO) production and decreased the elevated serum malondialdehyde (MDA) and high-sensitivity C-reactive protein (hs-CRP) levels. Effects of combined treatment were greater than those of simvastatin or losartan alone. In hypertensive hypercholesterolemic patients, repeated administration of losartan decreased systolic and diastolic blood pressure, increased NO production, and decreased the elevated serum MDA and hs-CRP levels. Addition of simvastatin to losartan therapy enhanced these effects and corrected the compromised lipid profile. Simvastatin inhibited the contractile responses of isolated aortic rings induced by angiotensin II and enhanced the inhibitory effect of losartan on this preparation. l-arginine and acetylcholine enhanced, while L-NAME inhibited the effects of simvastatin, losartan, and their combination on these contractile responses. Thus, simvastatin exerts antihypertensive effect in hypertensive hypercholesterolemic animals and enhances the antihypertensive effect of losartan in hypertensive hypercholesterolemic animals and patients. Besides, its cholesterol-lowering effect, the ability of simvastatin to ameliorate endothelial dysfunction through increasing NO bioavailability and through suppression of oxidative stress and vascular inflammation may play an important role in these effects.

Role of oxidative stress and inducible nitric oxide synthase in morphine-induced tolerance and dependence in mice. Effect of alpha-lipoic acid.

In this study, the possible role of oxidative stress and nitric oxide (NO) synthase isoforms in the development of morphine tolerance and dependence, and effect of alpha-lipoic acid on these parameters were investigated in mice. The development of morphine tolerance as measured by the hot plate test and dependence, as assessed by naloxone-precipitated withdrawal manifestations, produced an increase in brain glutamate and malondialdehyde (MDA) levels and NO production as well as a decrease in brain intracellular reduced glutathione (GSH) level and glutathione peroxidase (GSH-Px) activity. Also, the development of these syndromes increased inducible but not neuronal NO synthase mRNA and protein expressions in mice brain. Co-administration of alpha-lipoic acid (α-LA) inhibited the development of morphine tolerance and dependence, their associated biochemical alterations, except elevation of brain glutamate level, and their associated increase in brain inducible NO synthase mRNA and protein expressions. The inhibitory effect of α-LA on morphine-induced tolerance and dependence and on naloxone-induced biochemical alterations in morphine-dependent mice was enhanced by concurrent administration of the NMDA receptor antagonist, dizocilpine, the antioxidant, N-acetylcysteine or the selective inducible NO synthase inhibitor, aminoguanidine. On the other hand, this inhibitory effect of α-LA was not changed by concurrent administration of the selective neuronal NO synthase inhibitor, 7-nitroindazole but antagonized by concurrent administration of the NO precursor, L-arginine. These results suggest that α-LA through inhibition of morphine-induced oxidative stress and increase in the expression and activity of inducible NO synthase in the brain can attenuate the development of morphine tolerance and dependence.

Inhibition of brain oxidative stress and inducible nitric oxide synthase expression by thymoquinone attenuates the development of morphine tolerance and dependence in mice.

In this study, the effect of thymoquinone on morphine-induced tolerance and dependence in mice was investigated. Repeated administration of thymoquinone along with morphine attenuated the development of morphine tolerance, as measured by the hot plate test, and dependence, as assessed by naloxone-precipitated withdrawal manifestations. Concurrently, morphine-induced progressive increase in brain malondialdehyde (MDA) level and nitric oxide (NO) production as well as progressive decrease in brain intracellular reduced glutathione (GSH) level and glutathione peroxidase (GSH-Px) activity were inhibited by co-administration of thymoquinone. Morphine-induced progressive increase in brain glutamate level was not inhibited by concomitant administration of thymoquinone. Similarly, co-administration of thymoquinone inhibited naloxone-induced increase in brain MDA level, NO overproduction and decrease in brain intracellular GSH level and GSH-Px activities but it did not inhibit naloxone-induced elevation of brain glutamate level in morphine-dependent mice. The inhibitory effect of thymoquinone on morphine-induced tolerance and dependence on naloxone-induced biochemical alterations in morphine-dependent mice was enhanced by concurrent i.p. administration of the NMDA receptor antagonist, dizocilpine, the antioxidant, N-acetylcysteine or the NO synthase inhibitor, L-N (G)-nitroarginine methyl ester. On the other hand, this inhibitory effect of thymoquinone was antagonized by concurrent i.p. administration of NO precursor, L-arginine. In addition, concomitant administration of thymoquinone inhibited morphine tolerance and dependence-induced increase in inducible but not in neuronal NO synthase mRNA expression in mice brain. These results demonstrate that inhibition of morphine-induced oxidative stress, increase in the expression of brain inducible NO synthase and NO overproduction by thymoquinone can attenuate the development of morphine tolerance and dependence.

Involvement of glutamate, oxidative stress and inducible nitric oxide synthase in the convulsant activity of ciprofloxacin in mice.

This study investigated the potential convulsive activity of ciprofloxacin in mice and the possible mechanism(s) of this activity. Intraperitoneal (i.p.) administration of ciprofloxacin into mice resulted in convulsive seizures in a dose-dependent manner. The clonic median convulsant dose (CD(50)) of ciprofloxacin in mice was increased by pretreatment with dizocilpine, alpha-lipoic acid or aminoguanidine, not changed by pretreatment with 7-nitroindazole and decreased by pretreatment with L-arginine and fenbufen. The increase in nitric oxide (NO) production and malondialdehyde (MDA) level as well as the decrease in intracellular reduced glutathione (GSH) level and glutathione peroxidase (GSH-Px) activity induced by the estimated clonic CD(50) of ciprofloxacin in mice brain was inhibited by pretreatment with dizocilpine, alpha-lipoic acid or aminoguanidine. These biochemical alterations were not changed by pretreatment with 7-nitroindazole but enhanced by pretreatment with L-arginine. The elevation induced by the clonic CD(50) of ciprofloxacin in brain glutamate level was not changed by pretreatment with MK-801, alpha-lipoic acid, aminoguanidine or L-arginine. Combined treatment of mice with fenbufen and ciprofloxacin produced elevation of brain NO production and glutamate and MDA levels as well as inhibition of brain intracellular GSH level and GSH-Px activity. In addition, i.p. administration of the clonic CD(50) of ciprofloxacin produced an increase in inducible but not in neuronal NO synthase mRNA and protein expressions in mice brain. These results suggest that elevation of brain glutamate levels with consequent oxidative stress and increase in the expression and activity of brain inducible NO synthase may play a pivotal role in ciprofloxacin-induced convulsive seizures.

Simvastatin enhances the antihypertensive effect of ramipril in hypertensive hypercholesterolemic animals and patients. Possible role of nitric oxide, oxidative stress, and high sensitivity C-reactive protein.

In this study, the effects of simvastatin on the blood pressure and on the antihypertensive activity of ramipril in hypertensive hypercholesterolemic animals and patients were evaluated. In hypertensive hypercholesterolemic animals, repeated administration of simvastatin slightly but significantly decreased the systolic blood pressure, enhanced its progressive reductions induced by repeated administration of ramipril and corrected the compromised lipid profile. Concomitantly, repeated administration of simvastatin, ramipril or simvastatin in combination with ramipril to these animals, increased nitric oxide (NO) production and decreased the elevated serum malondialdehyde (MDA) and high sensitivity C-reactive protein (hs-CRP) levels. The effects of combined treatment were greater than those of simvastatin or ramipril alone. In hypertensive hypercholesterolemic patients, repeated administration of ramipril decreased systolic and diastolic blood pressure, increased NO production, and decreased the elevated serum MDA and hs-CRP levels. Addition of simvastatin to ramipril therapy enhanced these effects and corrected the compromised lipid profile. Simvastatin but not ramipril inhibited the contractile responses of isolated aortic rings induced by angiotensin 11. l-arginine and acetylcholine enhanced, while l-NAME inhibited effects of simvastatin, and simvastatin in combination with ramipril on these contractile responses. These findings suggest that simvastatin exerts antihypertensive effect and enhances the antihypertensive effect of ramipril in hypertensive hypercholesterolemic animals and patients. In addition to its cholesterol-lowering effect, the ability of simvastatin to ameliorate endothelial dysfunction through increasing NO bioavailability and through suppression of oxidative stress and vascular inflammation and its ability to enhance the effect of ramipril on these parameters may play a pivotal role in these effects.

Protective effect of Nigella sativa oil against tramadol-induced tolerance and dependence in mice: role of nitric oxide and oxidative stress.

Nigella sativa seed extracts and its oil have been exploited for their various health benefits. In this study, the effects of N. sativa oil on tramadol-induced tolerance and dependence and possible mechanism(s) of these effects were investigated, for the first time, in mice. Repeated administration of N. sativa oil (4 ml/kg, p.o.) along with tramadol (50mg/kg, s.c.) inhibited the development of tramadol tolerance, as measured by the hot plate test, and dependence as assessed by naloxone (5mg/kg, i.p.)-precipitated withdrawal manifestations. Concomitantly, nitric oxide overproduction and increase in brain malondialdehyde level induced by repeated administration of tramadol to mice or by administration of naloxone to tramadol-dependent mice were inhibited by co-administration of the oil. Also, the decrease in brain intracellular reduced glutathione level and glutathione peroxidase activity induced by both treatments was inhibited by co-administration of the oil. The increase in brain glutamate level induced by both treatments was not inhibited by concurrent administration of the oil. The inhibitory effect of N. sativa oil on tramadol-induced tolerance and dependence was enhanced by concurrent i.p. administration of the NMDA receptor antagonist, dizocilpine (0.25mg/kg). Also, the inhibitory effect of the oil on naloxone-induced biochemical alterations in tramadol-dependent mice was enhanced by concurrent administration of dizocilpine. Similarly, concurrent i.p. administration of the NO synthase inhibitor, L-N(G)-nitroarginine methyl ester (10mg/kg) or the antioxidant, N-acetylcysteine (50mg/kg) enhanced these inhibitory effects of N. sativa oil. On the other hand, these effects were antagonized by concurrent i.p. administration of the NO precursor, L-arginine (300 mg/kg). These results provide evidence that N. sativa oil appears to have a therapeutic potential in tramadol tolerance and dependence through blockade of NO overproduction and oxidative stress induced by the drug.

Alpha-lipoic acid protects against potassium cyanide-induced seizures and mortality.

This study was proposed to investigate the potential protective effect of alpha-lipoic acid (α-LA) against potassium cyanide (KCN)-induced seizures and lethality in mice. The intraperitoneal ED(50) value of KCN, as measured by induction of clonic and tonic seizures was increased by pretreatment of mice with α-LA (25, 50 and 100 mg/kg) intraperitoneally in a dose-dependent manner. Similarly, the intraperitoneal LD(50) value of KCN, based on 24h mortality, was increased by pretreatment with α-LA in a dose-dependent manner. Intraperitoneal injection of the estimated ED(50) of KCN (4.8 mg/kg) into mice increased, 1h later, nitric oxide (NO) production and brain glutamate and malondialdehyde (MDA) levels. The estimated ED(50) of KCN also decreased brain intracellular reduced glutathione (GSH) level and glutathione peroxidase (GSH-Px) activity in these animals. Administration of the estimated LD(50) of KCN (6 mg/kg) produced, 24h later, similar marked biochemical alterations in surviving animals. Pretreatment of mice with α-LA inhibited; dose-dependently KCN (ED(50) and LD(50))-induced an increase in NO production and brain MDA level as well as a decrease in brain intracellular GSH level and GSH-Px activity. The elevation induced by KCN in brain glutamate level was not inhibited by α-LA. It can be concluded that the protective effect of α-LA against KCN-induced seizures and lethality may be due to inhibition of NO overproduction and maintenance of intracellular antioxidant defense mechanisms.

Blockade of nitric oxide overproduction and oxidative stress by Nigella sativa oil attenuates morphine-induced tolerance and dependence in mice.

The effects of Nigella sativa oil on morphine-induced tolerance and dependence in mice and possible mechanism(s) of these effects were investigated, for the first time, in this study. Repeated administration of Nigella sativa oil (4 ml/kg, p.o.) along with morphine (5 mg/kg, s.c.) attenuated the development of tolerance, as measured by the hot plate test, and dependence, as assessed by naloxone (5 mg/kg, i.p.)-precipitated withdrawal manifestations. Concomitantly, nitric oxide overproduction and increase in brain malondialdehyde level induced by repeated administration of morphine to mice or by administration of naloxone to morphine-dependent mice were inhibited by co-administration of the oil. Also, the decrease in brain intracellular reduced glutathione level and glutathione peroxidase activity induced by both treatments were inhibited by co-administration of the oil. The increase in brain glutamate level induced by both treatments was not inhibited by concurrent administration of the oil. The inhibitory effect of the oil on morphine-induced tolerance and dependence and on naloxone-induced biochemical alterations in morphine-dependent mice was enhanced by concurrent i.p. administration of the NMDA receptor antagonist, dizocilpine (0.25 mg/kg). Similarly, concurrent i.p. administration of the NO synthase inhibitors; L-N (G)-nitroarginine methyl ester (10 mg/kg), aminoguanidine (20 mg/kg) and 7-nitroindazole (25 mg/kg) or the antioxidant, N-acetylcysteine (50 mg/kg) enhanced this inhibitory effect of the oil. On the other hand, this effect was antagonized by concurrent i.p. administration of the nitric oxide precursor, L-arginine (300 mg/kg). These results provide evidence that Nigella sativa oil, through inhibition of morphine-induced NO overproduction and oxidative stress, appears to have a therapeutic potential in opioid tolerance and dependence.

The potential protective role of alpha-lipoic acid against acetaminophen-induced hepatic and renal damage.

The potential protective role of alpha-lipoic acid (alpha-LA) in acetaminophen (APAP)-induced hepatotoxicity and nephrotoxicity was investigated in rats. Pretreatment of rats with alpha-LA (100mg/kg) orally protected markedly against hepatotoxicity and nephrotoxicity induced by an acute oral toxic dose of APAP (2.5 g/kg) as assessed by biochemical measurements and by histopathological examination. None of alpha-LA pretreated animals died by the acute toxic dose of APAP. Concomitantly, APAP-induced profound elevation of nitric oxide (NO) production and oxidative stress, as evidenced by increasing of lipid peroxidation level, reducing of glutathione peroxidase (GSH-Px) activity and depleting of intracellular reduced glutathione (GSH) level in liver and kidney, were suppressed by pretreatment with alpha-LA. Similarly, daily treatment of rats with a smaller dose of alpha-LA (25mg/kg) concurrently with a smaller toxic dose of APAP (750 mg/kg) for 1 week protected against APAP-induced hepatotoxicity and nephrotoxicity. This treatment also completely prevented APAP-induced mortality and markedly inhibited APAP-induced NO overproduction and oxidative stress in hepatic and renal tissues. These results provide evidence that inhibition of NO overproduction and maintenance of intracellular antioxidant status may play a pivotal role in the protective effects of alpha-LA against APAP-induced hepatic and renal damage.

Role of nitric oxide and reduced glutathione in the protective effects of aminoguanidine, gadolinium chloride and oleanolic acid against acetaminophen-induced hepatic and renal damage.

The potential protective role of aminoguanidine (AG), gadolinium chloride (GdCl(3)) and oleanolic acid (OA) in acetaminophen (APAP)-induced hepatotoxicity and nephrotoxicity was investigated in rats. Pretreatment of rats with AG (50mg/kg) orally, GdCl(3) (10mg/kg) intramuscularly or OA (25mg/kg) intramuscularly protected markedly against hepatotoxicity and nephrotoxicity induced by an acute oral toxic dose of APAP (2.5g/kg) as assessed by biochemical measurements and by histopathological examination. None of AG-, GdCl(3)- or OA-pretreated animals died by the acute toxic dose of APAP. Concomitantly, pretreatment of rats with these agents suppressed the profound elevation of nitric oxide (NO) production and obvious reduction of intracellular reduced glutathione (GSH) levels in liver and kidney induced by the acute toxic dose of APAP. Similarly, daily treatment of rats with a smaller dose of AG (10mg/kg), GdCl(3) (3mg/kg) or OA (5mg/kg) concurrently with a smaller toxic dose of APAP (750mg/kg) for 1 week protected against APAP-induced hepatotoxicity and nephrotoxicity. This treatment also completely prevented APAP-induced mortality and markedly inhibited APAP-induced NO overproduction as well as hepatic and renal intracellular GSH levels reduction. These results provide evidence that inhibition of NO overproduction and consequently maintenance of intracellular GSH levels may play a pivotal role in the protective effects of AG, GdCl(3) and OA against APAP-induced hepatic and renal damages.

Attenuation of morphine tolerance and dependence by aminoguanidine in mice.

The effect of aminoguanidine, an inducible nitric oxide synthase (iNOS) inhibitor, on morphine-induced tolerance and dependence in mice was investigated in this study. Acute administration of aminoguanidine (20 mg/kg, p.o.) did not affect the antinociceptive effect of morphine (10 mg/kg, s.c.) as measured by the hot plate test. Repeated administration of aminoguanidine along with morphine attenuated the development of tolerance to the antinociceptive effect of morphine. Also, the development of morphine dependence as assessed by naloxone-precipitated withdrawal manifestations was reduced by co-administration of aminoguanidine. The effect of aminoguanidine on naloxone-precipitated withdrawal was enhanced by concurrent administration of the non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, dizocilpine (0.25 mg/kg, i.p.) or the non-specific nitric oxide synthase (NOS) inhibitor, l-N(G)-nitroarginine methyl ester (l-NAME; 5 mg/kg, i.p.) and antagonized by concurrent administration of the nitric oxide (NO) precursor, l-arginine (50 mg/kg, p.o.). Concomitantly, the progressive increase in NO production, but not in brain glutamate level, induced by morphine was inhibited by repeated administration of aminoguanidine along with morphine. Similarly, co-administration of aminoguanidine inhibited naloxone-induced NO overproduction, but it did not inhibit naloxone-induced elevation of brain glutamate level in morphine-dependent mice. The effect of aminoguanidine on naloxone-induced NO overproduction was potentiated by concurrent administration of dizocilpine or l-NAME and antagonized by concurrent administration of l-arginine. These results provide evidence that blockade of NO overproduction, the consequence of NMDA receptor activation, by aminoguanidine, via inhibition of iNOS, can attenuate the development of morphine tolerance and dependence.

Antidiabetic activity and toxicity of Zizyphus spina-christi leaves.

The effect of the butanol extract of Zizyphus spina-christi (L.), Willd (Rhamnaceae) leaves and its major saponin glycoside, christinin-A, on the serum glucose and insulin levels was studied in non-diabetic control, type-I (insulin-dependent) and type-II (non-insulin-dependent) diabetic rats. Pretreatment either with 100 mg/kg butanol extract or christinin-A potentiated glucose-induced insulin release in non-diabetic control rats. In type-II but not in type-I diabetic rats pretreatment with the butanol extract or christinin-A improved the oral glucose tolerance and potentiated glucose-induced insulin release. Treatment either with 100 mg/kg butanol extract or christinin-A reduced the serum glucose level and increased the serum insulin level of non-diabetic control and type-II diabetic rats but not of type-I diabetic rats. Effects of the butanol extract and christinin-A were similar. Pretreatment of non-diabetic control and type-II diabetic rats either with 100 mg/kg butanol extract or christinin-A enhanced the glucose lowering and insulinotropic effects of 5 g/kg glibenclamide. The hyperglycemic and hypoinsulinemic effects of 30 mg/kg diazoxide in non-diabetic control and type-II diabetic rats were inhibited and antagonized, respectively by pretreatment with the butanol extract or christinin-A. The relaxant effects of different concentrations of diazoxide on the isolated norepinephrine-contracted aortic strips were inhibited by 100 micromol/l christinin-A or 10 micromol/l glibenclamide. The combination of glibenclamide and christinin-A led to complete inhibition of the relaxant effects of different concentrations of diazoxide. At a dose level much higher than that required to produce satisfactory insulinotropic and hypoglycemic effects, the butanol extract of Zizyphus spina-christi leaves produced a depressant effect on the central nervous system in rats. Treatment of rats with 100mg/kg butanol extract for 3 months produced no functional or structural disturbances in liver and kidney and no haematological changes. In addition, the oral LD50 of the butanol extract in mice was 3820 mg/kg, while that of glibenclamide was 3160 mg/kg. Thus, Zizyphusspina-christi leaves appears to be a safe alternative to lower blood glucose. The safe insulinotropic and subsequent hypoglycemic effects of Zizyphus spina-christi leaves may be due to a sulfonylurea-like activity.