Adaptive changes in renal mitochondrial redox status in diabetic nephropathy

Renal Glutathione: Dual roles as antioxidant protector and bioactivation promoter

The tripeptide glutathione (GSH) possesses two key structural features, namely the nucleophilic sulfur and the γ-glutamyl isopeptide bond. The former allows GSH to serve as a critical antioxidant and anti-electrophile. The latter allows GSH to translocate throughout the systemic circulation without being degraded. The kidneys exhibit several unique processes for handling GSH. This includes the extraction of 80% of plasma GSH, in part by glomerular filtration but mostly by transport across the basolateral plasma membrane. Studies on the protective effect of exogenous GSH are summarized, showing the different inherent susceptibility of proximal tubular and distal tubular cells and the impact on pathological or disease states, including hypoxia, diabetic nephropathy, and compensatory renal growth associated with uninephrectomy. Studies on mitochondrial GSH transport show the coordination between the citric acid cycle and oxidative phosphorylation in generating driving forces for both plasma membrane and mitochondrial carriers. The strong protective effects of increasing expression and activity of these carriers against oxidants and mitochondrial toxicants are summarized. Although GSH plays a cytoprotective role in most situations, two distinct exceptions to this are presented. In contrast to expectations, overexpression of the mitochondrial 2-oxoglutarate carrier markedly increased cell death from exposure to the nephrotoxic chemotherapeutic drug cisplatin (CDDP). Another key example of GSH serving a bioactivation role in the kidneys, rather than a detoxification role, is the metabolism of halogenated alkenes such as trichloroethylene (TCE). Although considerable research has gone into this topic, unanswered questions and emerging topics remain and are discussed.

Pharmacological Targeting of Mitochondria in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) in the United States and many other countries. DKD occurs through a variety of pathogenic processes that are in part driven by hyperglycemia and glomerular hypertension, leading to gradual loss of kidney function and eventually progressing to ESRD. In type 2 diabetes, chronic hyperglycemia and glomerular hyperfiltration leads to glomerular and proximal tubular dysfunction. Simultaneously, mitochondrial dysfunction occurs in the early stages of hyperglycemia and has been identified as a key event in the development of DKD. Clinical management for DKD relies primarily on blood pressure and glycemic control through the use of numerous therapeutics that slow disease progression. Because mitochondrial function is key for renal health over time, therapeutics that improve mitochondrial function could be of value in different renal diseases. Increasing evidence supports the idea that targeting aspects of mitochondrial dysfunction, such as mitochondrial biogenesis and dynamics, restores mitochondrial function and improves renal function in DKD. We will review mitochondrial function in DKD and the effects of current and experimental therapeutics on mitochondrial biogenesis and homeostasis in DKD over time. SIGNIFICANCE STATEMENT: Diabetic kidney disease (DKD) affects 20% to 40% of patients with diabetes and has limited treatment options. Mitochondrial dysfunction has been identified as a key event in the progression of DKD, and pharmacologically restoring mitochondrial function in the early stages of DKD may be a potential therapeutic strategy in preventing disease progression.

Effects of fermented red bean extract on nephropathy in streptozocin-induced diabetic rats

Background

The antioxidant effects of Bacillus subtilis-fermented red bean (natto-red bean) extract (NRBE) in young (6 weeks old) Sprague–Dawley rats and aged (12 months old) mice had been reported previously.

Objective

To evaluate the antioxidant and anti-inflammatory effects of NRBE in the kidneys of streptozocin-induced diabetic rats.

Design

Normal control rats and diabetic rats were orally gavaged with saline and low-dose NRBE (100 mg/kg body weight [BW]), medium-dose NRBE (200 mg/kg BW), and high-dose NRBE (500 mg/kg BW), for 12 weeks and then sacrificed. Concentration of fasting glucose, adiponectin, renal function markers, antioxidative markers, and pro-inflammatory markers were measured.

Results

Oral administration of 50% ethanolic extract of NRBE with a dosage of 100 mg/kg BW, 200 mg/kg BW, or 500 mg/kg BW could improve the symptoms of kidney enlargement and renal function. Supplementation of NRBE can effectively inhibit the formation of renal reactive oxygen species and advanced-glycation end-products and increase renal glutathione content and serum adiponectin. A low dose of NRBE (100 mg/kg BW) decreased fasting blood sugar and renal interleukin (IL)-6 expression. Serum C-reactive protein, renal tumor necrosis factor-α, and monocyte chemoattractant protein-1 concentrations were decreased, and renal superoxide dismutase activity was increased in the medium-dose NRBE group. Twenty-four hour creatinine clearance and urinary albumin excretion also improved by medium-dose NRBE supplementation. In NRBE, total phenols and flavonoids were 6.3 mg gallic acid equivalent/g and 12.02 mg rutin equivalent/g, respectively, and kampherol was the major active antioxidant compound.

Conclusion

This study demonstrated that appropriate amount of NRBE, 200 mg/kg BW in rats, could prevent diabetic nephropathy by improving antioxidant status and inhibiting inflammation in renal tissue.

Dillenia indica L. attenuates diabetic nephropathy via inhibition of advanced glycation end products accumulation in STZ-nicotinamide induced diabetic rats

The present study was aimed to evaluate advanced glycation end products (AGEs) inhibitory activity of alcohol and hydro-alcohol extract (DAE and DHE) of Dillenia indica L. (Family: Dilleniaceae) and its potential in treatment of diabetic nephropathy by targeting markers of oxidative stress. D. indica was evaluated for its in vitro inhibitory activity against formation of AGEs by using bovine serum albumin. Diabetes was induced in male Wistar rats by streptozotocin (65 mg/kg i.p.) 15 min after nicotinamide (230 mg/kg, i.p.) administration. Diabetic rats were treated with different doses of extracts (100, 200 and 400 mg/kg) to analyze their nephroprotective effect. Tissue antioxidant enzymes level was measured along with the formation of AGEs in kidney to assess the effect of D. indica in ameliorating oxidative stress. D. indica showed significant inhibition of AGEs formation in vitro. D. indica produced significant attenuation in the glycemic status, renal parameter, lipid profile and level of antioxidant enzymes proving efficacy in diabetic nephropathy. Moreover, D. indica produced significant reduction in the formation of AGEs in kidneys. The present study concludes that D. indica as a possible therapeutic agent against diabetic nephropathy.

Mitochondrial Glutathione in Diabetic Nephropathy

Although there are many etiologies for diabetic nephropathy (DN), one common characteristic of all cases involves mitochondrial oxidative stress and consequent bioenergetic dysfunction. As the predominant low-molecular-weight, intramitochondrial thiol reductant, the mitochondrial glutathione (mtGSH) pool plays important roles in how this organelle adapts to the chronic hyperglycemia and redox imbalances associated with DN. This review will summarize information about the processes by which this important GSH pool is regulated and how manipulation of these processes can affect mitochondrial and cellular function in the renal proximal tubule. Mitochondria in renal proximal tubular (PT) cells do not appear to synthesize GSH de novo but obtain it by transport from the cytoplasm. Two inner membrane organic anion carriers, the dicarboxylate carrier (DIC; Slc25a10) and 2-oxoglutarate carrier (OGC; Slc25a11) are responsible for this transport. Genetic modulation of DIC or OGC expression in vitro in PT cells from diabetic rats can alter mitochondrial function and susceptibility of renal PT cells to oxidants, with overexpression leading to reversion of bioenergetic conditions to a non-diabetic state and protection of cells from injury. These findings support the mtGSH carriers as potential therapeutic targets to correct the underlying metabolic disturbance in DN.

Glutathione Levels and Susceptibility to Chemically Induced Injury in Two Human Prostate Cancer Cell Lines

More aggressive prostate cancer cells (PCCs) are often resistant to chemotherapy. Differences exist in redox status and mitochondrial metabolism that may help explain this phenomenon. Two human PCC lines, PC-3 cells (more aggressive) and LNCaP cells (less aggressive), were compared with regard to cellular glutathione (GSH) levels, susceptibility to either oxidants or GSH depletors, and expression of several proteins involved in apoptosis and stress response to test the hypothesis that more aggressive PCCs exhibit higher GSH concentrations and are relatively resistant to cytotoxicity. PC-3 cells exhibited 4.2-fold higher GSH concentration than LNCaP cells but only modest differences in acute cytotoxicity were observed at certain time points. However, only LNCaP cells underwent diamide-induced apoptosis. PC-3 cells exhibited higher levels of Bax and caspase-8 cleavage product but lower levels of Bcl-2 than LNCaP cells. However, LNCaP cells exhibited higher expression of Fas receptor (FasR) but also higher levels of several stress response and antioxidant proteins than PC-3 cells. LNCaP cells also exhibited higher levels of several mitochondrial antioxidant systems, suggesting a compensatory response. Thus, significant differences in redox status and expression of proteins involved in apoptosis and stress response may contribute to PCC aggressiveness.

Protective role of NAD(P)H:quinone oxidoreductase 1 (NQO1) in cisplatin-induced nephrotoxicity

Although cisplatin is widely used as an anti-cancer agent, its use is significantly limited because of its tendency to induce nephrotoxicity through poorly understood mechanisms. NAD(P)H:quinone oxidoreductase 1 (NQO1) is well known to regulate ROS generation. The purpose of this study was to investigate whether NQO1 modulates cisplatin-induced renal failure associated with NADPH oxidase (NOX)-derived ROS production in an animal model. NQO1-/- mice were treated with cisplatin (18 mg/kg) and renal function, oxidative stress, and tubular apoptosis were assessed. NQO1-/- mice showed increased blood urea nitrogen and creatinine levels, tubular damage, oxidative stress, and apoptosis. In accordance with these results, the cellular NADPH/NADP ratio and NOX activity were markedly increased in the kidneys of NQO1-/- mice compared to NQO1+/+ mice. In addition, activation of NQO1 by βL treatment significantly improved renal dysfunction and reduced tubular cell damage, oxidative stress, and apoptosis. This study demonstrates that NQO1 protects cells against renal failure induced by cisplatin, and that this effect is mediated by decreased NOX activity via cellular NADPH/NADP modulation. These results provide convincing evidence that NQO1 might be beneficial for ameliorating renal failure induced by cisplatin.

Mitochondrial glutathione in toxicology and disease of the kidneys

The tripeptide glutathione (GSH), comprised of the amino acids l-cysteine, glycine, and l-glutamate, is found in all cells of aerobic organisms and plays numerous, critical roles as an antioxidant and nucleophile in regulating cellular homeostasis and drug metabolism. GSH is synthesized exclusively in the cytoplasm of most cells by two ATP-dependent reactions. Despite this compartmentation, GSH is found in other subcellular compartments, including mitochondria. As the GSH molecule has a net negative charge at physiological pH, it cannot cross cellular membranes by diffusion. Rather, GSH is a substrate for a variety of anion and amino acid transporters. Two organic anion carriers in the inner membrane of renal mitochondria, the dicarboxylate carrier (DIC; Slc25a10) and the 2-oxoglutarate carrier (OGC; Slc25a11), are responsible for most of the transport of GSH from cytoplasm into mitochondrial matrix. Genetic manipulation of DIC and/or OGC expression in renal cell lines demonstrated the ability to produce sustained increases in mitochondrial GSH content, which then protected these cells from cytotoxicity due to several oxidants and mitochondrial toxicants. Several diseases and pathological states are associated with mitochondrial dysfunction and oxidative stress, suggesting that the mitochondrial GSH pool may be a therapeutic target. One such disease that is of particular concern for public health is diabetic nephropathy. Another chronic, pathological state that is associated with bioenergetic and redox changes is compensatory renal hypertrophy that results from reductions in functional renal mass. This review summarizes pathways of mitochondrial GSH transport and discusses studies on its manipulation in toxicological and pathological states.