Renal antioxidant enzymes and glutathione redox status in leptin-induced hypertension

The complex effects of adipokines in the patients with kidney disease

Kidney diseases are categorized as the highest prevalent ones with worldwide noticeable incidence. They cause accelerated cardiovascular diseases and noticeable mortalities. Adipose tissue and its messengers, adipokines, are reported to have the highest relationship with end-stage renal diseases or chronic kidney diseases. Over recent years, with shifting of scientists’ mindset from a simple overview of adipose tissue as a fat store to the complex paradigm of this issue as a multipotential secretory organ, the importance of studies on this tissue has emerged.

Adiponectin, leptin, nitric oxide, and C-reactive protein levels in kidney transplant recipients: comparison with the hemodialysis and chronic renal failure

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of mortality and morbidity in patients with chronic kidney disease (CKD) including kidney transplant recipients (KTR). Secondary lipid metabolism disorders, endothelial dysfunction, and inflammation enhance the risk of CVD development in these patients. The aim of the present study was to investigate the lipid profile, adiponectin, leptin, nitric oxide (NO), and high sensitivity C-reactive protein (hs-CRP) levels in KTR and to compare these parameters with those of the patients with chronic renal failure (CRF), hemodialysis (HD) patients, and healthy controls.

METHODS

Serum adiponectin and leptin levels were measured by radioimmunoassay; hs-CRP was determined immunoturbidimetrically. Determination of NO was based on the Griess reaction.

RESULTS

Compared with the control group, serum NO and adiponectin levels were significantly higher in the KTR, CRF, and HD groups; hs-CRP levels were significantly higher in the KTR and HD groups; leptin levels were significantly higher in the KTR. In addition, serum NO level was significantly higher in the KTR compared to CRF cases. Adiponectin correlated positively with high density lipoprotein-cholesterol in the control and patient groups. A positive correlation was observed between hs-CRP and NO in the KTR and the patients with CRF. Serum adiponectin levels were inversely correlated with hs-CRP and leptin in the HD group.

CONCLUSION

KTR suffer from inflammation and accompanying changes in levels of adipocytokines and NO which contribute to the increased risk of CVD in these patients.

Renal hemodynamic and morphological changes after 7 and 28 days of leptin treatment: the participation of angiotensin II via the AT1 receptor

The role of hyperleptinemia in cardiovascular diseases is well known; however, in the renal tissue, the exact site of leptin’s action has not been established. This study was conducted to assess the effect of leptin treatment for 7 and 28 days on renal function and morphology and the participation of angiotensin II (Ang II), through its AT₁ receptor. Rats were divided into four groups: sham, losartan (10 mg/kg/day, s.c.), leptin (0.5 mg/kg/day for the 7 days group and 0.25 mg/kg/day for the 28 days group) and leptin plus losartan. Plasma leptin, Ang II and endothelin 1 (ET-1) levels were measured using an enzymatic immuno assay. The systolic blood pressure (SBP) was evaluated using the tail-cuff method. The renal plasma flow (RPF) and the glomerular filtration rate (GFR) were determined by p-aminohippuric acid and inulin clearance, respectively. Urinary Na⁺ and K⁺ levels were also analyzed. Renal morphological analyses, desmin and ED-1 immunostaining were performed. Proteinuria was analyzed by silver staining. mRNA expression of renin-angiotensin system (RAS) components, TNF-α and collagen type III was analyzed by quantitative PCR. Our results showed that leptin treatment increased Ang II plasma levels and progressively increased the SBP, achieving a pre-hypertension state. Rats treated with leptin 7 days showed a normal RPF and GFR, but increased filtration fraction (FF) and natriuresis. However, rats treated with leptin for 28 showed a decrease in the RPF, an increase in the FF and no changes in the GFR or tubular function. Leptin treatment-induced renal injury was demonstrated by: glomerular hypertrophy, increased desmin staining, macrophage infiltration in the renal tissue, TNF-α and collagen type III mRNA expression and proteinuria. In conclusion, our study demonstrated the progressive renal morphological changes in experimental hyperleptinemia and the interaction between leptin and the RAS on these effects.

Adipokines promote chronic kidney disease

The rapid growth in obesity worldwide contributes to an increase in metabolic syndrome and obesity-related kidney disease with an enhanced increased risk for chronic kidney disease, finally progressing to end-stage renal disease. Adipose tissue is a highly active endocrine organ secreting numerous factors that contribute to renal and cardiovascular complications. In renal damage, various adipokines are involved through mediating endothelial dysfunction, inducing oxidative stress and inflammation as well as stimulating renal sympathetic nervous activity, and it reduces cancellous bone but conversely increases cortical bone. Adipokines may also be involved in the development of renal anaemia. A balance exists between more protective adipokines (adiponectin) and factors mediating pathophysiological effects (angiotensin II, TNFα). Obesity may cause a disruption of this delicate balance, thereby inducing renal disease. Consequently, weight reduction and lifestyle changes affecting all components of the metabolic syndrome are essential to disrupt this vicious cycle.

Association between glutathione S-transferase M1 polymorphism and urinary sodium excretion in a Brazilian population

BACKGROUND

Null genotypes of glutathione S-transferase (GST) exhibit the absence of enzymatic activity and are associated with increased cardiovascular risk. Recent reports have related both lower and higher urinary sodium excretion (USE) to higher cardiovascular risk. Here we investigate the impact of GSTM1 and GSTT1-null polymorphisms on USE in a Brazilian population.

METHODS

We cross-sectionally evaluated 1,308 subjects from the city of Vitoria, Brazil, based on clinical history, physical examination, anthropometry, analysis of laboratory parameters, measurement of USE, and GST polymorphisms genotyping.

RESULTS

The frequency of GST M1, T1, and double-deletion polymorphisms was 51%, 22%, and 11%, respectively. Individuals with the GSTM1-null genotype had lower USE than those with the non-null genotype (92.1±52.3 vs. 102.8 ± 6 0.7 mEq/12h; P < 0.001). Linear regression analysis adjusted for confounding factors revealed that the GSTM1-null genotype was independently associated with USE (P = 0.001). In addition, diastolic blood pressure and triglyceride levels were higher in GSTM1-null individuals than in non-null individuals in the highest tertile of USE. Finally, the presence of GSTT1-null or double-deleted genotypes did not influence USE or affect the interactions between USE and the variables studied.

CONCLUSIONS

Deletion of GSTM1 was associated with low USE and modulated the interaction between sodium intake and blood pressure in Brazilian subjects. These novel findings may provide a new unexplored link between sodium regulation and GST homeostasis.

Leptin and the Regulation of Renal Sodium Handling and Renal Na-Transporting ATPases: Role in the Pathogenesis of Arterial Hypertension

Leptin, an adipose tissue hormone which regulates food intake, is also involved in the pathogenesis of arterial hypertension. Plasma leptin concentration is increased in obese individuals. Chronic leptin administration or transgenic overexpression increases blood pressure in experimental animals, and some studies indicate that plasma leptin is elevated in hypertensive subjects independently of body weight. Leptin has a dose- and time-dependent effect on urinary sodium excretion. High doses of leptin increase Na(+) excretion in the short run; partially by decreasing renal Na(+),K(+)-ATPase (sodium pump) activity. This effect is mediated by phosphatidylinositol 3-kinase (PI3K) and is impaired in animals with dietary-induced obesity. In contrast to acute, chronic elevation of plasma leptin to the level observed in patients with the metabolic syndrome impairs renal Na(+) excretion, which is associated with the increase in renal Na(+),K(+)-ATPase activity. This effect results from oxidative stress-induced deficiency of nitric oxide and/or transactivation of epidermal growth factor receptor and subsequent stimulation of extracellular signal-regulated kinases. Ameliorating "renal leptin resistance" or reducing leptin level and/or leptin signaling in states of chronic hyperleptinemia may be a novel strategy for the treatment of arterial hypertension associated with the metabolic syndrome.

Regulation of hypoxia inducible factor-1α expression by the alteration of redox status in HepG2 cells

Hypoxia inducible factor-1 (HIF-1) has been considered as a critical transcriptional factor in response to hypoxia. It can increase P-glycoprotein (P-Gp) thus generating the resistant effect to chemotherapy. At present, the mechanism regulating HIF-1α is still not fully clear in hypoxic tumor cells. Intracellular redox status is closely correlated with hypoxic micro-environment, so we investigate whether alterations in the cellular redox status lead to the changes of HIF-1α expression. HepG2 cells were exposed to Buthionine sulphoximine (BSO) for 12 h prior to hypoxia treatment. The level of HIF-1α expression was measured by Western blot and immunocytochemistry assays. Reduce glutathione (GSH) concentrations in hypoxic cells were determined using glutathione reductase/5,5^'-dithiobis-(2-nitrob-enzoic acid) (DTNB) recycling assay. To further confirm the effect of intracellular redox status on HIF-1α expression, N-acetylcysteine (NAC) was added to culture cells for 8 h before the hypoxia treatment. The levels of multidrug resistance gene-1 (MDR-1) and erythropoietin (EPO) mRNA targeted by HIF-1α in hypoxic cells were further determined with RT-PCR, and then the expression of P-Gp protein was observed by Western blotting. The results showed that BSO pretreatment down-regulated HIF-1α and the effect was concentration-dependent, on the other hand, the increases of intracellular GSH contents by NAC could partly elevate the levels of HIF-1α expression. The levels of P-Gp (MDR-1) and EPO were concomitant with the trend of HIF-1α expression. Therefore, our data indicate that the changes of redox status in hypoxic cells may regulate HIF-1α expression and provide valuable information on tumor chemotherapy.

Obesity is the major contributor to vascular dysfunction and inflammation in high-fat diet hypertensive rats

Obesity and hypertension are the two major risk factors that contribute to the progression of end-stage renal disease. To examine whether hypertension further exacerbates oxidative stress and vascular dysfunction and inflammation in obese rats, four groups of male Sprague-Dawley rats were fed either a normal (7% fat) or high-fat (36% fat) diet for 6 weeks and osmotic pumps were implanted to deliver ANG (angiotensin II) or vehicle for an additional 4 weeks.Treatment with the high-fat diet did not alter ANG-induced hypertension compared with the normal diet (174 +/- 6 compared with 170 +/- 5 mmHg respectively). Treatment with the high-fat diet increased body weight gain and plasma leptin levels and induced insulin resistance in normotensive and ANG-induced hypertensive rats. Plasma TBARS (thiobarbituric acid-reacting substances), a measure of oxidative stress, were elevated in high-fat diet-fed rats compared with controls (11.2 +/-1 compared with 8.4 +/- nmol/ml respectively) and was increased further in ANG-induced hypertensive rats fed a high-fat diet (18.8 +/-2.2 nmol/ml). Urinary nitrite excretion was also decreased in rats fed a high-fat diet without or with ANG infusion compared with controls. Afferent arteriolar relaxation to acetylcholine was impaired in rats fed the high-fat diet without or with ANG infusion. Renal cortical TNF-alpha(tumour necrosis factor-alpha), COX-2(cyclo-oxygenase-2) and phospho-IKK (inhibitor of nuclear factor k B kinase) expression increased in high-fat diet-fed rats compared with normal diet-fed rats. The increases in phospho-IKK and COX-2 expression were elevated further in ANG-induced hypertensive rats fed the high-fat diet.These results suggest that ANG-induced hypertension exacerbates oxidative stress and renal inflammation without further impairment in vascular dysfunction in high-fat diet-induced obesity.

N-acetylcysteine inhibits hyperglycemia-induced oxidative stress and apoptosis markers in diabetic neuropathy

Several studies have indicated the involvement of oxidative stress in the development of diabetic neuropathy. In the present study, we have targeted oxidative stress mediated nerve damage in diabetic neuropathy using N-acetyl-l-cysteine (NAC), a potent antioxidant. After 8 weeks, streptozotocin-induced diabetic rats developed neuropathy which was evident from decreased tail-flick latency (thermal hyperalgesia). This was accompanied by decreased motor coordination as assessed by performance on rota-rod treadmill. Na(+) K(+) ATPase, a biochemical marker of development of diabetic neuropathy, was significantly inhibited in sciatic nerve of diabetic animals. NAC treatment at a daily dose between 1.4 and 1.5 g/kg body weight to diabetic animals for 7 weeks in drinking water ameliorated hyperalgesia, improved motor coordination and reversed reduction in Na(+) K(+) ATPase activity. There was an increase in lipid peroxidation in sciatic nerve of diabetic animals along with decrease in phospholipid levels, while NAC treatment attenuated lipid peroxidation and restored phospholipids to control levels. This was associated with decrease in glutathione and protein thiols. The activities of antioxidant enzymes; superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase and glutathione-S-transferase were reduced in sciatic nerve of diabetic animals. Cytochrome c release and active caspase 3 were markedly increased in nerve from diabetic animals suggesting activation of apoptotic pathway. NAC treatment significantly ameliorated decrease in antioxidant defense and prevented cytochrome c release and caspase 3 activation. Electron microscopy revealed demyelination, Wallerian degeneration and onion-bulb formation in sciatic nerve of diabetic rats. NAC on the other hand was able to reverse structural deficits observed in sciatic nerve of diabetic rats. Our results clearly demonstrate protective effect of NAC is mediated through attenuation of oxidative stress and apoptosis, and suggest therapeutic potential of NAC in attenuation of diabetic neuropathy.

Curcumin eliminates leptin's effects on hepatic stellate cell activation via interrupting leptin signaling

Nonalcoholic steatohepatitis (NASH) is commonly found in patients with obesity and is often accompanied with abnormally elevated levels of plasma leptin, i.e. hyperleptinemia. A relatively high population of NASH patients develops hepatic fibrosis, even cirrhosis. Hepatic stellate cells (HSCs) are the major effector cells during liver fibrogenesis and could be activated by leptin. The antioxidant curcumin, a phytochemical from turmeric, has been shown to suppress HSC activation in vitro and in vivo. This project is to evaluate the effect of curcumin on leptin-induced HSC activation and to elucidate the underlying mechanisms. We hypothesize that curcumin abrogates the stimulatory effect of leptin on HSC activation by interrupting leptin signaling and attenuating leptin-induced oxidative stress. Curcumin eliminates the stimulatory effects of leptin on regulating expression of genes closely relevant to HSC activation. Curcumin interrupts leptin signaling by reducing phosphorylation levels of leptin receptor (Ob-R) and its downstream intermediators. In addition, curcumin suppresses gene expression of Ob-R in HSCs, which requires the activation of endogenous peroxisome proliferator-activated receptor-gamma and de novo synthesis of glutathione. In conclusion, our results demonstrate that curcumin abrogates the stimulatory effect of leptin on HSC activation in vitro by reducing the phosphorylation level of Ob-R, stimulating peroxisome proliferator-activated receptor-gamma activity, and attenuating oxidative stress, leading to the suppression of Ob-R gene expression and interruption of leptin signaling. These results provide novel insights into therapeutic mechanisms of curcumin in inhibiting HSC activation and intervening liver fibrogenesis associated with hyperleptinemia in NASH patients.