Effects of fenofibrate, a PPAR-α ligand, on the haemodynamics of glycerol-induced renal failure in rats

Novel Function for Bilirubin as a Metabolic Signaling Molecule: Implications for Kidney Diseases

Bilirubin is the end product of the catabolism of heme via the heme oxygenase pathway. Heme oxygenase generates carbon monoxide (CO) and biliverdin from the breakdown of heme, and biliverdin is rapidly reduced to bilirubin by the enzyme biliverdin reductase (BVR). Bilirubin has long been thought of as a toxic product that is only relevant to health when blood levels are severely elevated, such as in clinical jaundice. The physiologic functions of bilirubin correlate with the growing body of evidence demonstrating the protective effects of serum bilirubin against cardiovascular and metabolic diseases. Although the correlative evidence suggests a protective effect of serum bilirubin against many diseases, the mechanism by which bilirubin offers protection against cardiovascular and metabolic diseases remains unanswered. We recently discovered a novel function for bilirubin as a signaling molecule capable of activating the peroxisome proliferator-activated receptor α (PPARα) transcription factor. This review summarizes the new finding of bilirubin as a signaling molecule and proposes several mechanisms by which this novel action of bilirubin may protect against cardiovascular and kidney diseases.

Effect of fenofibrate on proliferation of SMMC-7721 cells via regulating cell cycle

Liver cancer is a malignant cancer with great harmfulness. Fenofibrate is a peroxisome proliferation activated receptor (PPARα) agonist widely used in the treatment of dyslipidemia. Previous studies have shown that fenofibrate may promote cell proliferation, but the underlying mechanism has not been fully characterized. The aim of this study was to investigate the role of PPARα agonist fenofibrate in cell proliferation of SMMC-7721 cells compared with that of THLE-2 cells. SMMC-7721 and THLE-2 cells were treated with different concentrations of fenofibrate. Cell proliferation was analyzed by MTT, using flow cytometry for cell cycle analysis, and CyclinD1, Cyclin-dependent kinases2 (CDK2) and Proliferating Cell Nuclear Antigen (PCNA) were analyzed by Western blotting. RT-qPCR method was used to assess CDK2, CyclinD1 and PCNA mRNA levels. The results showed that 10^-9-10^-4 mol/L fenofibrate could induce cell growth and 10^-4, 10^-5, 10^-6 mol/L fenofibrate could reduce the number of G0/G1 phase cells and increased in the number of cells in S and G2/M phase of cell cycle in SMMC-7721 cells. Furthermore, fenofibrate could significantly increase the expression of cell cycle related protein (CyclinD1, CDK2)and cell proliferation related proteins (PCNA). The use of PPARα inhibitor MT886 inhibited cell cycle progression and promote tumor cell apoptosis. But fenofibrate had no obvious effect on THLE-2 cells. These results revealed the effect of fenofibrate on the cell cycle of liver cancer cells, and provided a reasonable explanation for studying how fenofibrate promotes cell proliferation.

Acute kidney injury induced by glycerol is worsened by orchiectomy and attenuated by testosterone replacement

Although several studies have demonstrated that the male gender represents an independent risk factor for renal disease, evidence shows that androgens exert renal protective actions. The findings are controversial and no studies have evaluated the effects of orchiectomy and testosterone replacement on glycerol-induced renal injury. Male Wistar rats were submitted to orchiectomy or sham surgery and divided into four groups: SC, sham control rats injected with NaCl; SG, sham rats injected with glycerol; OG, orchiectomized rats injected with glycerol; OGT, orchiectomized rats injected with glycerol and testosterone. Testosterone was administered daily for 14 days in the OGT group. After 11 days of testosterone replacement in the OGT group, SC rats were submitted to a saline injection, while SG, OG and OGT rats received glycerol. All rats were euthanized three days after injections. OG rats presented higher serum creatinine and urea, and sodium excretion, compared to SC and SG, while testosterone attenuated these changes. Acute tubular necrosis was also mitigated by testosterone. Renal immunostaining for macrophages, lymphocytes and NF-κB was higher in OG compared to SC and SG. In addition, renal interleukin-1β, Caspase 3 and AT1 gene expression was higher in OG rats compared to SG. Testosterone attenuated these alterations, except the NF-κB immunostaining. The renal NO was lower in OG rats compared to SG. Only the OG rats presented decreases in serum NO and renal HO-1, and increased TNF-α, angiotensinogen and AT1 expression compared to SC. We conclude that orchiectomy worsened glycerol-induced kidney injury, while testosterone attenuated this renal damage.

Fenofibrate attenuates ischemia reperfusion-induced acute kidney injury and associated liver dysfunction in rats

Ischemia/reperfusion (I/R) is one of the common reasons for acute kidney injury (AKI) and we need to develop effective therapies for treating AKI. We investigated the role of fenofibrate against I/R-induced AKI and associated hepatic dysfunction in rats. In male wistar albino rats, renal pedicle occlusion for 40 min and 24 h reperfusion resulted in AKI. I/R-induced AKI was demonstrated by measuring serum creatinine, creatinine clearance, urea, uric acid, potassium, fractional excretion of sodium and urinary microproteins. Oxidative stress in rat kidneys was quantified by assaying superoxide anion generation, thiobarbituric acid reactive substances, and reduced glutathione levels. AKI-induced hepatic damage was quantified by assaying serum aminotransferases, alkaline phosphatase and bilirubin levels. Moreover, serum cholesterol, high density lipoprotein and triglycerides were quantified. Hematoxylin-eosin staining of renal and hepatic tissues was done and the kidney and liver injury scores were determined. Immunohistology of endothelial nitric oxide synthase (eNOS) was done in rat kidneys. Fenofibrate was administered for 1 week before subjecting rats to AKI. In separate group, the nitric oxide synthase inhibitor, L-nitroarginine methyl ester (L-NAME) was administered prior to fenofibrate treatment. In I/R group, significant alteration in the serum/urine parameters indicated AKI and hepatic dysfunction along with marked increase in kidney and liver injury scores. Treatment with fenofibrate attenuated AKI and associated hepatic dysfunction. Moreover, I/R-induced decrease in renal eNOS expression was abrogated by fenofibrate. Pre-treatment with L-NAME abolished fenofibrate mediated reno- and hepato-protective effects. In conclusion, fenofibrate attenuates I/R-induced AKI and associated hepatic dysfunction putatively through modulation of eNOS expression.

Bilirubin, a new therapeutic for kidney transplant?

In patients with end-stage renal disease, kidney transplantation has been associated with numerous benefits, including increased daily activity, and better survival rates. However, over 20% of kidney transplants result in rejection within five years. Rejection is primarily due to a hypersensitive immune system and ischemia/reperfusion injury. Bilirubin has been shown to be a potent antioxidant that is capable of potentially reversing or preventing damage from reactive oxygen species generated from ischemia and reperfusion. Additionally, bilirubin has several immunomodulatory effects that can dampen the immune system to promote organ acceptance. Increased bilirubin has also been shown to have a positive impact on renal hemodynamics, which is critical post-transplantation. Lastly, bilirubin levels have been correlated with biomarkers of successful transplantation. In this review, we discuss a multitude of potentially beneficial effects that bilirubin has on kidney acceptance of transplantation based on numerous clinical trials and animal models. Exogenous bilirubin delivery or increasing endogenous levels pre- or post-transplantation may have therapeutic benefits.

Fibrate treatment of eEOCs in murine AKI

BACKGROUND

Early endothelial outgrowth cells (eEOCs) protect mice from acute kidney injury (AKI). Peroxisome proliferator-activated receptor-alpha (PPAR-α) has been shown to mediate renoprotective effects under different experimental conditions. The aim of the study was to investigate consequences of fibrate treatment of murine eEOCs in a cell-based therapeutic approach to AKI.

METHODS

Male C57/Bl6N mice, subjected to unilateral renal ischemia (40 min) post-uninephrectomy, were systemically injected with 0.5 × 10(6) untreated or fenofibrate (FF 1, 5, 10 or 50 μm)/clofibrate (CF 1 mm) pretreated syngeneic murine eEOCs. Renal function and morphology were analyzed 48 h later. Cellular consequences of eEOC treatment with fibrates (FF 1, 5, 10, 50 μm, CF 1 mm) were evaluated using different in vitro assays (direct cell migration, apoptosis/necrosis, ELISA studies).

RESULTS

Administration of untreated eEOCs did not protect mice from AKI. Injection of eEOCs treated with CF (1 mm) or FF 50 μm did not result in any protection from ischemia-induced renal dysfunction. In vitro analysis showed reduced cellular secretion of vasoprotective vascular endothelial growth factor (VEGF), an effect that was more pronounced with CF; FF increased percentages of apoptotic/necrotic eEOCs, and both substances failed to stimulate migration of cultured cells. With lower FF concentrations (1, 5, 10 μm) cell survival was increased and 10 μm FF stimulated VEGF secretion. In vivo administration of FF-treated eEOCs (10 μm) also did not result in any renoprotective effect.

CONCLUSION

PPAR-α activation using fibrates does not stimulate renoprotective effects of syngeneic murine eEOCs in ischemic AKI, although lower fibrate concentrations significantly activate eEOCs in vitro.