Explicit role of peroxisome proliferator-activated receptor gamma in gallic acid-mediated protection against ischemia-reperfusion-induced acute kidney injury in rats.

BACKGROUND: Gallic acid is a polyphenolic compound and is reported to be renoprotective because of its antioxidant activity in various preclinical studies. Gallic acid has been reported to activate peroxisome proliferator-activated receptor gamma (PPAR-γ) in vitro. However, the relevance of the interplay between gallic acid and PPAR-γ in various pathologic conditions is yet to be established in vivo. The present study investigated the protective role of gallic acid against ischemia-reperfusion-induced acute kidney injury (AKI) and the possible involvement of PPAR-γ in gallic acid-mediated renoprotection. MATERIALS AND METHODS: The AKI was induced in rats through bilateral clamping of renal arteries for 40 min followed by reperfusion for 24 h. The AKI was assessed by the quantification of creatinine clearance, blood urea nitrogen, uric acid, potassium level, fractional excretion of sodium, and urinary microproteins. The oxidative stress in renal tissues was quantified in terms of myeloperoxidase activity, thiobarbituric acid reactive substances, superoxide anion generation, and reduced glutathione level. The histopathologic changes in renal tissues were assessed by hemotoxylin and eosin staining. The rats were administered gallic acid (50, 100, and 200 mg/kg) orally for 7 d before subjecting them to AKI. RESULTS: The renal ischemia-reperfusion induced significant changes in plasma, urinary, and tissue parameters. The administration of gallic acid at three dose levels offered a significant protection against renal ischemia-reperfusion-induced AKI. The prior treatment with PPAR-γ antagonist, bisphenol A diglycidyl ether, significantly abolished the renoprotective effect of gallic acid that confirms the involvement of PPAR-γ in gallic acid-mediated renoprotection. CONCLUSIONS: It is concluded that the activation of PPAR-γ significantly contributes toward gallic acid-mediated protection against ischemia-reperfusion-induced AKI.

Involvement of progesterone receptors in ascorbic acid-mediated protection against ischemia-reperfusion-induced acute kidney injury.

BACKGROUND: Ascorbic acid (AA) is an established antioxidant and has been used for treatment of various disorders. Recent reports suggest that administration of AA increases the level of steroids such as progesterone in the body. The present study investigated the protective role of progesterone against ischemia-reperfusion-induced acute kidney injury (AKI) and possible involvement of progesterone receptors in AA-mediated renoprotection in rats. MATERIALS AND METHODS: The male rats were subjected to bilateral renal ischemia for 40 min followed by reperfusion for 24 h to induce AKI. The rats were treated with progesterone (5 and 10 mg/kg, intraperitoneally) and AA (500 mg/kg, intraperitoneally for 1, 2, and 5 d) before AKI. In separate groups, mifepristone, the progesterone receptor antagonist was administered to rats before progesterone (10 mg/kg) and AA treatment (5 d). Various parameters including creatinine clearance, serum urea, uric acid, potassium level, fractional excretion of sodium, lactate dehydrogenase, and microproteinuria were used to assess kidney injury. Moreover, renal tissues were subjected to quantification of oxidative stress and evaluation of histopathologic changes. RESULTS: The exogenous administration of progesterone afforded protection against AKI in a dose-dependent manner that was abolished by mifepristone. The administration of AA for 1, 2, and 5 d induced significant increase in serum progesterone levels and afforded protection against AKI. The antioxidant and renoprotective effect of AA was abolished by prior treatment with mifepristone. CONCLUSIONS: It is concluded that exogenous administration of progesterone exerts significant antioxidant and renoprotective effect. Moreover, the progesterone receptors find their explicit involvement in AA-mediated renoprotection against ischemia-reperfusion-induced AKI in rats.

Involvement of peroxisome proliferator-activated receptor gamma in vitamin D-mediated protection against acute kidney injury in rats.

BACKGROUND: Vitamin D has been reported as renoprotective agents in various studies. Recently, a few in vitro studies highlighted cross talk between vitamin D and peroxisome proliferator-activated receptor gamma (PPAR-γ). The present study investigated the activation of PPAR-γ as novel mechanism in vitamin D-mediated protection against ischemia reperfusion-induced acute kidney injury (AKI) in rats. MATERIALS AND METHODS: The AKI was induced by clamping renal pedicles for 40 min followed by reperfusion for 24 h. The AKI was assessed by measuring creatinine clearance, serum urea, uric acid level, and lactate dehydrogenase activity. Moreover, serum potassium, calcium level, fractional excretion of sodium, and microproteinuria were measured in rats. The oxidative stress in renal tissues was assessed by quantification of thiobarbituric acid-reactive substances, superoxide anion generation, reduced glutathione level, and catalase and myeloperoxidase activities. The hematoxylin-eosin staining was carried out to observe histopathologic changes in renal tissues. Vitamin D (0.25, 0.5, and 1 µg/kg) was administered for 7 d before subjecting rats to renal ischemia reperfusion injury (IRI). RESULTS: The renal IRI in rats induced significant changes in serum, urinary, and oxidative stress parameters in renal tissues. Moreover, hematoxylin-eosin staining revealed marked damage produced by IRI in renal tissues. The administration of vitamin D at 0.5 µg/kg dose afforded maximum protection against renal IRI. The prior treatment with PPAR-γ antagonist bisphenol A diglycidyl ether significantly attenuated protective effect of vitamin D, thus confirming involvement of PPAR-γ in vitamin D-mediated renoprotection. CONCLUSIONS: It is concluded that activation of PPAR-γ significantly contributes toward vitamin D-mediated protection against ischemia reperfusion-induced AKI.

Role of GABAergic activity of sodium valproate against ischemia-reperfusion-induced acute kidney injury in rats.

Gamma amino butyric acid (GABA) has been reported to be renoprotective in various preclinical studies. Sodium valproate (SVP) is documented to protect against renal injury through its histone deacetylase-inhibiting activity. The present study investigated the involvement of GABAA receptors and the role of GABAergic activity of SVP against ischemia-reperfusion-induced acute kidney injury (AKI) in rats. The rats were subjected to bilateral renal ischemia for 40 min followed by reperfusion for 24 h to induce AKI. The creatinine clearance, serum urea, uric acid, lactate dehydrogenase, potassium, fractional excretion of sodium, and microproteinuria were measured to assess kidney injury. The thiobarbituric acid-reactive substances, reduced glutathione level, myeloperoxidase, and catalase activity were assayed to assess oxidative stress in renal tissues along with hematoxylin-eosin staining to observe histopathological changes. The ischemia-reperfusion-induced AKI witnessed an increase in serum parameters, microproteinuria, oxidative stress, and histopathological changes in renal tissues. Picrotoxin aggravated ischemia-reperfusion injury-induced AKI confirming the role of GABAA receptors in AKI. The SVP treatment afforded protection against AKI that was blocked by concurrent treatment with picrotoxin. Hence, it is concluded that regulation of GABAA receptors is important for management of AKI. Moreover, the GABAergic activity of SVP is important for its renoprotective effect.

Why are there so few key mutant clones? The influence of stochastic selection and blocking on affinity maturation in the germinal center.

A small number of key somatic mutations lead to high-affinity binding in the anti-hapten immune responses to 2-phenyl-5-oxazolone (phOx) and (4-hydroxy-3-nitrophenyl)acetyl (NP). Affinity maturation models of the germinal center hold that B cells carrying these key mutations are preferentially selected for expansion within the germinal centers. However, additional factors are required to account for some quantitative aspects of affinity maturation in vivo. Radmacher et al. have shown that key mutants are observed in vivo significantly less frequently than expected by these models. To account for this finding, they propose that selection is a stochastic process where key mutants may be overlooked by positive selection or recruited out of the germinal center. While acknowledging that a minimal amount of stochastic selection is probably unavoidable in the germinal center, we instead propose a structural explanation for this key mutant discrepancy. This model is based on the existence of a large number of blocking mutations whose presence can prevent the ability of key mutations to confer high-affinity binding. Using mathematical modeling and computer simulation, we show that in addition to reconciling the key mutant discrepancy, the blocking model accounts for other aspects of experimental data that are not predicted by the stochastic selection model. In particular, the blocking model is consistent with the observation that key mutants generally exhibit a higher number of mutations per sequence in the phOx response, but a lower number in the NP response.