Chaman Lal Kaul

Neuroprotective efficacy and therapeutic time window of peroxynitrite decomposition catalysts in focal cerebral ischemia in rats

Free radicals have been implicated in cerebral ischemia reperfusion (IR) injury. Massive production of nitric oxide and superoxide results in continuous formation of peroxynitrite even several hours after IR insult. This can produce DNA strand nicks, hydroxylation and/or nitration of cytosolic components of neuron, leading to neuronal death. Peroxynitrite decomposition catalysts 5,10,15,20‐tetrakis(N‐methyl‐4′‐pyridyl)porphyrinato iron (III) (FeTMPyP) and 5,10,15,20‐tetrakis(4‐sulfonatophenyl)porphyrinato iron (III) (FeTPPS) have been demonstrated to protect neurons in in vitro cultures; however, their neuroprotective efficacy in cerebral IR injury has not been explored. In the present study, we investigated the efficacy and the therapeutic time window of FeTMPyP and FeTPPS in focal cerebral ischemia (FCI). FCI was induced according to the middle cerebral artery occlusion (MCAO) method. After 2 h of MCAO and 70 h of reperfusion, the extent of neurological deficits, infarct and edema volume were measured in Sprague–Dawley rats. FeTMPyP and FeTPPS were administered at different time points 2, 6, 9 and 12 h post MCAO. FeTMPyP and FeTPPS (3 mg kg−1, i.v.) treatment at 2 and 6 h post MCAO produced significant reduction in infarct volume, edema volume and neurological deficits. However, treatment at latter time points did not produce significant neuroprotection. Significant reduction of peroxynitrite in blood and nitrotyrosine in brain sections was observed on FeTMPyP and FeTPPS treatment. As delayed treatment of FeTMPyP and FeTPPS produced neuroprotection, we tested whether treatment had any influence over the apoptotic neuronal death. DNA fragmentation and in situ nick end‐labeling assays showed that FeTMPyP and FeTPPS treatment reduced IR injury‐induced DNA fragmentation. In conclusion, peroxynitrite decomposition catalysts (FeTMPyP and FeTPPS) produced prominent neuroprotection even if administered 6 h post MCAO and the neuroprotective effect is at least in part due to the reduction of peroxynitrite and apoptosis.

Neuroprotective effect of 4-amino-1,8-napthalimide, a poly(ADP ribose) polymerase inhibitor in middle cerebral artery occlusion-induced focal cerebral ischemia in rat.

In the present study, neuroprotective effect of 4-amino-1,8-napthalimide (4-ANI), a poly(ADP-ribose) polymerase (PARP) inhibitor was investigated in middle cerebral artery occlusion (MCAo)-induced focal ischemia. Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion followed by 22 h of reperfusion. After 22 h of reperfusion rats were evaluated for cerebral infarction, neurological deficits, brain NAD levels, and in situ terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL). Focal ischemia produced significant infarct volume (201 +/- 14 mm3), neurological scores (2 +/- 0.5) and 28 +/- 4.5% brain NAD depletion. Ischemia was associated with increased in TUNEL positive cells in brain sections indicating DNA fragmentation. 4-ANI treatment (1 and 3 mg/kg, i.p.) significantly decreased infarct volume to 35 +/- 7% and 70 +/- 6%, respectively. Neurological functions were also significantly improved at these doses. 4-ANI (3 mg/kg) completely reversed brain NAD depletion and significantly reduced the increase in the number of TUNEL positive cells. Nevertheless, 4-ANI treatment did not alter cerebral blood flow and blood pressure. Our study suggests 4-ANI is a potent neuroprotective agent in focal cerebral ischemia and its neuroprotective effects may be attributed to reduction of NAD depletion and DNA fragmentation.

Effects of adenosine and adenosine A2A receptor agonist on motor nerve conduction velocity and nerve blood flow in experimental diabetic neuropathy

Abstract This study examined the effects of chronic administration of adenosine and CGS 21680 hydrochloride (adenosine A2A receptor agonist) on motor nerve conduction velocity (MNCV), nerve blood flow (NBF) and histology of sciatic nerve in animal model of diabetic neuropathy. Adenosinergic agents were administered for 2 weeks after 6 weeks of streptozotocin-induced (50 mg/kg i.p.) diabetes in male Sprague–Dawley rats. Significant reduction in sciatic MNCV and NBF were observed after 8 weeks in diabetic animals in comparison with control (non diabetic) rats. Adenosine (10 mg/kg, i.p.) significantly improved sciatic MNCV and NBF in diabetic rats. The protective effect of adenosine on MNCV and NBF was completely reversed by theophylline (50 mg/kg, i.p.), a non-selective adenosine receptor antagonist, suggesting that the adenosine effect was mediated via adenosinergic receptors. CGS 21680 (0.1 mg/kg, i.p.) significantly improved NBF; however, MNCV was not significantly improved in diabetic rats. At a dose of 1 mg/kg, neither MNCV nor NBF was improved by CGS 21680 in diabetic rats. ZM 241385 (adenosine A2A receptor antagonist) prevented the effect of CGS 21680 (0.1 mg/kg, i.p.). Histological changes observed in sciatic nerve were partially improved by the adenosinergic agents in diabetic rats. Results of the present study, suggest the potential of adenosinergic agents in the therapy of diabetic neuropathy.

Neuroprotective effect of combination of poly (ADP-ribose) polymerase inhibitor and antioxidant in middle cerebral artery occlusion induced focal ischemia in rats

Abstract We have investigated the neuroprotective potential of combination of poly (ADP-ribose) polymerase inhibitor (nicotinamide or 3-aminobenzamide) and antioxidant (melatonin) in middle cerebral artery occlusion (MCAo) induced focal ischemia in rats. MCAo of 2 h followed by 22 h reperfusion produced large volume of cerebral infarction (mean ± SEM 211.38 ± 8.35 mm3), volume of edema (60 ± 2 mm3) and neurological deficits (4.45 ± 0.25). Combination of nicotinamide (500 mg kg–1, i.p.) and melatonin (10 mg kg–1 , i.p.) significantly decreased infarct volume to 48 ± 2.58 mm3 as compared to their individual drug (nicotinamide 76 ± 12.49 mm3, melatonin 76.17 ± 1.24 mm3). A significant improvement was observed in edema volume and neurological deficits with this combination. Combination of 3-aminobenzamide (20 mg kg–1, i.p.) and melatonin (10 mg kg–1, i.p.) also produced similar reduction in infarction, edema and neurological score. These results indicate that the combination of poly (ADP-ribose) polymerase inhibitor and antioxidant produce enhanced neuroprotection. Clinical availability and wide therapeutic margin of nicotinamide and melatonin make them a promising drug combination for clinical evaluation in stroke patients.

Role of L-type Ca2+ channels in attenuated morphine antinociception in streptozotocin-diabetic rats.

The role of L-type Ca2+ channels in morphine antinociception was studied in streptozotocin-induced diabetic and control rats, using [3H]PN200-110 [isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-methoxycabonylpyridine-3-caboxylate] binding (0.005-1.0 nmol/l) and rat whole brain membranes, to determine if the attenuation of morphine antinociception was related to alterations in dihydropyridine-sensitive Ca2+ channel binding characteristics. The tail-flick antinociceptive effect of morphine (4 mg/kg, i.p.) was significantly reduced in diabetic rats in comparison to that in controls. Nimodipine (0.1-3 mg/kg, i.p.) did not produce antinociception but significantly potentiated the morphine response in control rats. Nimodipine (0.3-3 mg/kg, i.p.) reversed the attenuation of morphine antinociception in a dose-dependent manner in diabetic rats. Moreover, insulin (2 U/kg, s.c.) [correction of mu/kg] reversed the attenuated morphine antinociception in streptozotocin-diabetic rats. A significant increase in the Bmax (+41%) of [3H]PN200-110 binding was observed in diabetic rat brain membranes compared to that in control rats. However, there was no change in affinity (Kd) value of [3H]PN200-110. The reduced morphine response in diabetic rats, in accordance with up-regulation of dihydropyridine sites, may be due to an increased Ca2+ influx through L-type channels. These results suggest a functional role of L-type Ca2+ channels in morphine antinociception and the diabetic state may lead to alterations in their density.

Evaluation of bioequivalence of isoniazid and pyrazinamide in three and four drugs fixed dose combinations using WHO simplified protocol.

The reliable supply of quality drugs in the form of fixed dose combination (FDC) is an essential part of tuberculosis treatment. The objective of this investigation was to evaluate whether the World Health Organization (WHO) simplified screening protocol for the bioequivalence assessment of rifampicin can be used for the evaluation of other components of FDC so as to ensure the bioavailability of all drugs at tissue site. These bioequivalence studies were conducted on 20 and 22 healthy male volunteers for evaluation of three and four drugs FDC formulations, respectively. Both studies were conducted as randomized, open, crossover trials and sampling schedule was upto 8h according to WHO recommended protocol for evaluation of rifampicin bioequivalence. The bioequivalence of isoniazid and pyrazinamide were estimated using AUC(0-8), AUC(0-alpha), and C(max). FDC formulation was considered bioequivalent to separate formulations for isoniazid and pyrazinamide if bioequivalence limit fall in between 0.80 and 1.25. Bioequivalence estimates of AUC(0-8) and AUC(0-alpha) for isoniazid and all the three pharmacokinetic measures of pyrazinamide were within the acceptable limits, whereas C(max) of isoniazid from four drugs FDC was outside the limit when evaluated by two-way ANOVA. After evaluation of isoniazid and pyrazinamide based on their pharmacokinetics, it was found that C(max) is being affected by limited sampling time points of WHO protocol. Further, AUC was a robust parameter unaffected by sampling schedule adopted. The WHO simplified protocol for assessment of rifampicin is also suitable for evaluating bioequivalence of isoniazid and pyrazinamide from FDC formulations. However, for comparison of rate of absorption by means of C(max), careful evaluation of concentration-time profile along with pharmacokinetics is necessary before final judgment.

Enhancement of α-adrenoceptor-mediated responses in prostate of testosterone-treated rat

Abstract The present study was undertaken to investigate the effect of testosterone on the α-adrenoceptor-mediated contractile responses in ventral lobe of rat prostate. Contractile responses to various α-adrenoceptor agonists (phenylephrine, A61603 (N-[5-(4,5-dihydro-1H-imidazol-2-yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl] methanesulphonamide), clonidine, guanfacine, ST587 ((2,3-dihydro-benzo[1,4]dioxin-2-ylmethyl)-[2-(2,6-dimethoxy-phenoxy)-ethyl]-amine) and xylazine) were tested in prostate strips obtained from control and testosterone (3 mg/kg, s.c. 5 days a week for 15 days—10 doses total)-treated rats. Dose–response curves for α-adrenoceptor agonists in testosterone-treated animals showed a leftward shift, indicating increased sensitivity of tissue to α-adrenoceptor agonists. To find the mechanism of increased sensitivity, KA value and receptor reserve of phenylephrine were estimated. Neither the KA value nor the receptor reserve of phenylephrine was altered in testosterone-treated rats. The concentration–occupancy curve for A61603 was shifted leftward and the KA value for A61603 decreased about four-fold. The KB value of 2-(2,6-dimethoxyphenoxyethyl) aminomethyl-1,4-benzodioxane (WB4101) was not altered, however, the KB value for prazosin was decreased ∼5.5-fold. These findings indicate that the testosterone-mediated increase in sensitivity of prostate to α-adrenoceptor agonists is due to alterations in the α1-adrenoceptor pool.

In vitro evaluation of food effect on the bioavailability of rifampicin from antituberculosis fixed dose combination formulations.

Rifampicin is one of the major first line anti-tuberculosis drugs used in the therapy of tuberculosis. In literature, there are conflicting reports regarding effect of food on the bioavailability of rifampicin. In vitro, effect of food on the bioavailability can be studied by simulating in vivo conditions in dissolution fluid hence, to understand the variable effect of food on rifampicin release, dissolution studies were done by simulating in vivo conditions after meal intake. In this study, we assessed the effect of hydrodynamic stress in presence of food and meal composition on two rifampicin containing fixed dose combination formulations by carrying out dissolution at different agitation rates (simulation of fasted and fed state) as well as in the presence of different percentage of oil (fatty food). Agitation intensity as well as presence of oil did not had any influence on rifampicin release from formulation A. This formulation had shown excellent release characteristics at all the conditions studied. Whereas, formulation B showed agitation rate dependent release and also release was affected in presence of oil. Hence, it is concluded that food may not have any effect on the release of rifampicin from the formulation and subsequently on its bioavailability if the formulation has excellent release profile (>85% release in 10 min). Further, effect of food on the rifampicin release was a function of dosage form characteristics such as disintegration time and dissolution rate, which will subsequently affect the release behavior of a formulation in presence of food.

Sympathetic nervous system and experimental diabetes: role of adrenal medullary hormones

The sympathetic nervous system is of major importance in the regulation of various physiological functions. The present review discusses the mechanisms which control glucose homeostasis and the role of the sympathetic nervous system in experimental diabetes with special emphasis on the role of adrenal medullary hormones, over-activity of the sympathetic nervous system and its relationship to hypertension in the diabetic state and the effect of stress. The chapter also reviews the ability of various drugs and pharmacological agents to produce hyperglycemia in experimental animals and how this information can be used in screening new chemical entities and in differentiating the mode of action of these agents.