Spironolactone improves nephropathy by enhancing glucose-6-phosphate dehydrogenase activity and reducing oxidative stress in diabetic hypertensive rat

The NADPH Link between the Renin Angiotensin System and the Antioxidant Mechanisms in Dopaminergic Neurons

The renin angiotensin system (RAS) has several components including signaling peptides, enzymes, and membrane receptors. The effort in characterizing this system in the periphery has led to the approval of a class of antihypertensives. Much less is known about RAS in the central nervous system. The production of RAS peptides and the expression of several RAS enzymes and receptors in dopaminergic neurons of the substantia nigra has raised expectations in the therapy of Parkinson's disease, a neurodegenerative condition characterized by lack of dopamine in the striatum, the motor control region of the mammalian brain. On the one hand, dopamine production requires reducing power. On the other hand, reducing power is required by mechanisms involved in REDOX homeostasis. This review focuses on the potential role of RAS in the regulation of neuronal/glial expression of glucose-6-phosphate dehydrogenase, which produces the NADPH required for dopamine synthesis and for reactive oxygen species (ROS) detoxification. It is known that transgenic expression of the gene coding for glucose-6-phosphate dehydrogenase prevents the death of dopaminergic nigral neurons. Signaling via angiotensin II G protein-coupled receptors, AT1 or AT2, leads to the activation of protein kinase A and/or protein kinase C that in turn can regulate glucose-6- phosphate dehydrogenase activity, by Ser/Thr phosphorylation/dephosphorylation events. Long-term effects of AT1 or AT2 receptor activation may also impact on the concentration of the enzyme via activation of transcription factors that participate in the regulation of gene expression in neurons (or glia). Future research is needed to determine how the system can be pharmacologically manipulated to increase the availability of NADPH to neurons degenerating in Parkinson's disease and to neuroprotective glia.

Haloxyfop-P-methyl induces immunotoxicity and glucose metabolism disorders and affects the Nrf2/ARE pathway mediated antioxidant system in Chiromantes dehaani

Haloxyfop-P-methyl is used extensively in agricultural production, and its metabolites in soil have potentially toxic effects on aquatic ecosystems. In this study, we explored the toxicity of haloxyfop-P-methyl on Chiromantes dehaani. The results of the 21-day toxicity test showed that haloxyfop-P-methyl decreased the weight gain (WG), specific growth rate (SGR) and hepatosomatic index (HSI). In glucose metabolism, haloxyfop-P-methyl reduced pyruvate, lactate, lactate dehydrogenase and succinate dehydrogenase, but enhanced glucose-6-phosphate dehydrogenase and hexokinase. Furthermore, expression of glucose metabolism-related genes was upregulated. We cloned the full-length CdG6PDH gene, which contains a 1587 bp ORF that encoded a 528 amino acid polypeptide. In antioxidant system, haloxyfop-P-methyl increased glutathione, thioredoxin reductase and thioredoxin peroxidase activities and activated the Nrf2/ARE pathway through upregulation of ERK, JNK, PKC and Nrf2. In immunity, low concentrations haloxyfop-P-methyl, or short-term exposure, upregulated the expression of immune-related genes and enhanced immune-related enzymes activity, while high concentrations or long-term exposure inhibited immune function. In summary, haloxyfop-P-methyl inhibited the growth performance, disrupted glucose metabolism, activated the antioxidant system, and led to immunotoxicity. The results deepen our understanding of the toxicity mechanism of haloxyfop-P-methyl and provide basic biological data for the comprehensive assessment of the risk of haloxyfop-P-methyl to the environment and humans.

All-trans retinoic acid inhibits oxidative stress via ACE2/Ang (1-7)/MasR pathway in renal tubular epithelial cells stimulated with high glucose

The aim of this study was to investigate the effects of all-trans retinoic acid (atRA) on oxidative stress in renal tubular epithelial cells induced by high glucose (HG) and its potential mechanism. We investigated the effects of atRA in HG-induced renal epithelial cell line HK-2. Seven groups were designed for this experiment: negative control, mannitol, high-glucose (HG), HG combined with a low concentration of atRA, HG combined with a middle concentration of atRA, HG combined with a high concentration of atRA, and HG combined with captopril. After 48 h of incubation, oxidative stress factor expression in the supernatant was detected by enzyme-linked immunosorbent assay. Reactive oxygen species and cell apoptosis expression were assessed by flow cytometry. NADPH oxidase, fibrosis factor, and angiotensin-converting enzyme 2/angiotensin (1-7)/mas receptor (ACE2/Ang (1-7)/MasR) pathway-related protein expressions were determined by western blot analysis. The expressions of oxidative stress factors, NADPH oxidase components, and fibrosis factors were significantly higher after HG treatment. Apoptosis of HK2 cells in the HG group was also significantly higher. AtRA could reverse the above abnormal changes in a concentration-dependent manner. HG significantly promoted the expression of ACE, Ang II, and Ang II type 1 receptor (AT1R), whereas it inhibited the expression of ACE2, Ang (1-7), and MasR. With the elevation of concentration, atRA could gradually suppress the expression of ACE, Ang II, and AT1R, but facilitate ACE2, Ang (1-7), and MasR. These results were statistically significant. AtRA could significantly inhibit oxidative stress and apoptosis of renal tubular epithelial cells induced by HG. The mechanism may inhibit the ACE/Ang II/AT1R pathway and/or activate ACE2/Ang (1-7)/MasR pathway.

Integrated physiological and transcriptome analysis reveals potential toxicity mechanism of haloxyfop-P-methyl to Chiromantes dehaani

Haloxyfop-P-methyl is widely used in controlling gramineous weeds, including the invasive plant Spartina alterniflora. However, the mechanism of its toxicity to crustaceans is unclear. In this study, we adopted transcriptome analysis combined with physiologic changes to investigate the response of estuarine crab (Chiromantes dehaani) to haloxyfop-P-methyl. The results showed that the median lethal concentration (LC₅₀) of C. dehaani to haloxyfop-P-methyl at 96 h was 12.886 mg/L. Antioxidant system analysis indicated that MDA, CAT, GR, T-GSH, and GSSG might be sensitive biomarkers that characterize the oxidative defense response of the crab. In total, 782 differentially expressed genes were identified, including 489 up-regulated and 293 down-regulated genes. Glutathione metabolism, detoxification response and energy metabolism were significantly enriched, revealing the potential toxic mechanism of haloxyfop-P-methyl to C. dehaani. These results provide a theoretical foundation for further research on haloxyfop-P-methyl toxicity to crustaceans.

Benefits of the Non-Steroidal Mineralocorticoid Receptor Antagonist Finerenone in Metabolic Syndrome-Related Heart Failure with Preserved Ejection Fraction

The mineralocorticoid receptor (MR) plays an important role in the development of chronic kidney disease (CKD) and associated cardiovascular complications. Antagonizing the overactivation of the MR with MR antagonists (MRA) is a therapeutic option, but their use in patients with CKD is limited due to the associated risk of hyperkalemia. Finerenone is a non-steroidal MRA associated with an improved benefit-risk profile in comparison to steroidal MRAs. In this study, we decided to test whether finerenone improves renal and cardiac function in male hypertensive and diabetic ZSF1 rats as an established preclinical HFpEF model. Finerenone was administered at 10 mg/kg/day for 12 weeks. Cardiac function/hemodynamics were assessed in vivo. ZSF1 rats showed classical signs of CKD with increased BUN, UACR, hypertrophy, and fibrosis of the kidney together with characteristic signs of HFpEF including cardiac fibrosis, diastolic dysfunction, and decreased cardiac perfusion. Finerenone treatment did not impact kidney function but reduced renal hypertrophy and cardiac fibrosis. Interestingly, finerenone ameliorated diastolic dysfunction and cardiac perfusion in ZSF1 rats. In summary, we show for the first time that non-steroidal MR antagonism by finerenone attenuates cardiac diastolic dysfunction and improves cardiac perfusion in a preclinical HFpEF model. These cardiac benefits were found to be largely independent of renal benefits.

Mineralocorticoid receptor antagonists in diabetic kidney disease - mechanistic and therapeutic effects

Chronic kidney disease (CKD) is the leading complication in type 2 diabetes (T2D) and current therapies that limit CKD progression and the development of cardiovascular disease (CVD) include angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers and sodium-glucose co-transporter 2 (SGLT2) inhibitors. Despite the introduction of these therapeutics, an important residual risk of CKD progression and cardiovascular death remains in patients with T2D. Mineralocorticoid receptor antagonists (MRAs) are a promising therapeutic option in diabetic kidney disease (DKD) owing to the reported effects of mineralocorticoid receptor activation in inflammatory cells, podocytes, fibroblasts, mesangial cells and vascular cells. In preclinical studies, MRAs consistently reduce albuminuria, CKD progression, and activation of fibrotic and inflammatory pathways. DKD clinical studies have similarly demonstrated that steroidal MRAs lead to albuminuria reduction compared with placebo, although hyperkalaemia is a major secondary effect. Non-steroidal MRAs carry a lower risk of hyperkalaemia than steroidal MRAs, and the large FIDELIO-DKD clinical trial showed that the non-steroidal MRA finerenone also slowed CKD progression and reduced the risk of adverse cardiovascular outcomes compared with placebo in patients with T2D. Encouragingly, other non-steroidal MRAs have anti-albuminuric properties in DKD. Whether or not combining MRAs with other renoprotective drugs such as SGLT2 inhibitors might provide additive protective effects warrants further investigation.

The mineralocorticoid receptor in chronic kidney disease

Chronic kidney disease (CKD) is a major public health concern, affecting approximately 10% of the population worldwide. CKD of glomerular or tubular origin leads to the activation of stress mechanisms, including the renin angiotensin aldosterone system and mineralocorticoid receptor (MR) activation. Over the last two decades, blockade of the MR has arisen as a potential therapeutic approach against various forms of kidney disease. In this review, we summarize the experimental studies that have shown a protective effect of MR antagonists (MRAs) in non-diabetic and diabetic CKD animal models. Moreover, we review the main clinical trials that have shown the clinical application of MRAs to reduce albuminuria and, importantly, to slow CKD progression. Recent evidence from the FIDELIO trial showed that the MRA finerenone can reduce hard kidney outcomes when added to the standard of care in CKD associated with type 2 diabetes. Finally, we discuss the effects of MRAs relative to those of SGLT2 inhibitors, as well as the potential benefit of combination therapy to maximize organ protection.

Mineralocorticoid Receptor Antagonists in Diabetic Kidney Disease

Diabetes mellitus is a global health issue and main cause of chronic kidney disease. Both diseases are also linked through high cardiovascular morbidity and mortality. Diabetic kidney disease (DKD) is present in up to 40% of diabetic patients; therefore, prevention and treatment of DKD are of utmost importance. Much research has been dedicated to the optimization of DKD treatment. In the last few years, mineralocorticoid receptor antagonists (MRA) have experienced a renaissance in this field with the development of non-steroidal MRA. Steroidal MRA have known cardiorenal benefits, but their use is limited by side effects, especially hyperkalemia. Non-steroidal MRA still block the damaging effects of mineralocorticoid receptor overactivation (extracellular fluid volume expansion, inflammation, fibrosis), but with fewer side effects (hormonal, hyperkalemia) than steroidal MRA. This review article summarizes the current knowledge and newer research conducted on MRA in DKD.

Suppression of Adenosine Deaminase and Xanthine Oxidase Activities by Mineralocorticoid and Glucocorticoid Receptor Blockades Restores Renal Antioxidative Barrier in Oral Contraceptive-Treated Dam

OBJECTIVE

We tested the hypothesis that postpartum combined oral contraceptive (COC) treatment would induce oxidative stress via the adenosine deaminase-xanthine oxidase pathway in the kidney. We also sought to determine whether mineralocorticoid receptor (MR) or glucocorticoid receptor (GR ) blockade would suppress the activities of ADA and xanthine oxidase caused by postpartum COC treatment in the kidney.

METHODS

Twenty-four Wistar dams were randomly assigned to 4 groups (n = 6/group). Dams received vehicle (po), COC (1.0 μg ethinylestradiol and 5.0 μg levonorgestrel; po), COC with GR blockade (mifepristone; 80.0 mg/kg; po), and COC with MR blockade (spironolactone; 0.25 mg/kg; po) daily between 3rd and 11th week postpartum.

RESULTS

Data showed that postpartum COC caused increased plasma creatinine and urea, increased renal triglyceride/high-density lipoprotein ratio, free fatty acid accumulation, alanine aminotransferase, gamma-glutamyltransferase, uric acid, and activities of renal XO and ADA. On the other hand, postpartum COC resulted in decreased plasma albumin, renal glutathione, and Na+-K+-ATPase activity with no effect on lactate production. However, MR or GR blockade ameliorated the alterations induced by postpartum COC treatment. The present results demonstrate that MR or GR blockade ameliorates postpartum COC-induced increased activities of ADA and xanthine oxidase and restores glutathione-dependent antioxidative defense.

CONCLUSION

These findings implicate the involvements of GR and MR in renal dysfunctions caused by COC in dams via disrupted glutathione antioxidative barrier.

Acetate causes renoprotection like androgen and mineralocorticoid receptors blockade in testosterone-exposed pregnant rats

The kidney plays a critical role in human health and deviation from its normal function can lead to severe morbidity and mortality. Exposure to excess testosterone in women has been linked to several disorders, including kidney disorder and acting undoubtedly through androgen receptor (AR), whereas the involvement of mineralocorticoid receptor (MR) is unclear. Likewise, the renal effect of sodium acetate (SAc) during late gestational exposure to testosterone is not well known. We hypothesized that SAc or MR blockade would protect the kidney of testosterone-exposed pregnant rats against glutathione and adenosine depletion. Twenty-five pregnant Wistar rats were treated (sc) with olive oil, testosterone propionate (0.5 mg/kg) singly or in combination with SAc (200 mg/kg; p.o.), androgen receptor (AR) blocker, flutamide (Flu; 7.5 mg/kg; p.o.) or (MR) blocker, eplerenone (Eple; 0.5 mg/kg) between gestational days 14 and 19. Glutathione, adenosine and nitric oxide were decreased while uric acid (UA), xanthine oxidase (XO), malondialdehyde (MDA), lactate dehydrogenase activity and free fatty acids were increased in the kidneys of gestational rats exposed to testosterone. Also, plasma urea and creatinine were elevated. SAc and Eple reversed tested testosterone-induced effects in gestational rats. The exposure to testosterone impairs renal antioxidant defense via AR and MR during late gestation in pregnant rats. The study also provides evidence that sodium acetate protects the kidneys of gestational testosterone-exposed rats against defective antioxidant defense in like manner as MR or AR antagonist.

Role of mineralocorticoid receptor antagonists in kidney diseases

Mineralocorticoid receptor (MR) antagonists, for example, spironolactone and eplerenone, are in clinical use to treat hypertension. Increasing evidence suggests that mineralocorticoid receptor activation causes the pathogenesis and progression of chronic kidney disease. Aldosterone-induced MR activation increases inflammation, fibrosis, and oxidative stress in the kidney. MR antagonists (MRAs) have demonstrated therapeutic actions in chronic kidney disease (CKD), diabetic nephropathy (DN), renal fibrosis, and drug-induced renal injury in preclinical and clinical studies. We have summarized and discussed these studies in this review. The nonsteroidal MRA, esaxerenone, recently received approval for the treatment of hypertension. It has also shown a positive therapeutic effect in phase 3 clinical trials in patients with DN. Other nonsteroidal MRA such as apararenone, finerenone, AZD9977, and LY2623091 are in different clinical trials in patients with hypertension suffering from renal or hepatic fibrotic diseases. Hyperkalemia associated with MRA therapy has frequently led to the discontinuation of the treatment. The new generation nonsteroidal MRAs like esaxerenone are less likely to cause hyperkalemia at therapeutic doses. It appears that the nonsteroidal MRAs can provide optimum therapeutic benefit for patients suffering from kidney diseases.

Blood pressure reduction and RAAS inhibition in diabetic kidney disease: therapeutic potentials and limitations

Diabetic kidney disease (DKD) affects approximately one-third of patients with diabetes and taking into consideration the high cardiovascular risk burden associated to this condition a multifactorial therapeutic approach is traditionally recommended, in which glucose and blood pressure control play a central role. The inhibition of renin–angiotensin–aldosterone RAAS system represent traditionally the cornerstone of DKD. Clinical outcome trials have demonstrated clinical significant benefit in slowing nephropathy progression mainly in the presence of albuminuria. Thus, international guidelines mandate their use in such patients. Given the central role of RAAS activity in the pathogenesis and progression of renal and cardiovascular damage, a more profound inhibition of the system by the use of multiple agents has been proposed in the past, especially in the presence of proteinuria, however clinical trials have failed to confirm the usefulness of this therapeutic approach. Furthermore, whether strict blood pressure control and pharmacologic RAAS inhibition entails a favorable renal outcome in non-albuminuric patients is at present unclear. This aspect is becoming an important issue in the management of DKD since nonalbuminuric DKD is currently the prevailing presenting phenotype. For these reasons it would be advisable that blood pressure management should be tailored in each subject on the basis of the renal phenotype as well as related comorbidities. This article reviews the current literature and discusses potentials and limitation of targeting the RAAS in order to provide the greatest renal protection in DKD.

The Pentose Phosphate Pathway Dynamics in Cancer and Its Dependency on Intracellular pH

The Pentose Phosphate Pathway (PPP) is one of the key metabolic pathways occurring in living cells to produce energy and maintain cellular homeostasis. Cancer cells have higher cytoplasmic utilization of glucose (glycolysis), even in the presence of oxygen; this is known as the "Warburg Effect". However, cytoplasmic glucose utilization can also occur in cancer through the PPP. This pathway contributes to cancer cells by operating in many different ways: (i) as a defense mechanism via the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) to prevent apoptosis, (ii) as a provision for the maintenance of energy by intermediate glycolysis, (iii) by increasing genomic material to the cellular pool of nucleic acid bases, (iv) by promoting survival through increasing glycolysis, and so increasing acid production, and (v) by inducing cellular proliferation by the synthesis of nucleic acid, fatty acid, and amino acid. Each step of the PPP can be upregulated in some types of cancer but not in others. An interesting aspect of this metabolic pathway is the shared regulation of the glycolytic and PPP pathways by intracellular pH (pHi). Indeed, as with glycolysis, the optimum activity of the enzymes driving the PPP occurs at an alkaline pHi, which is compatible with the cytoplasmic pH of cancer cells. Here, we outline each step of the PPP and discuss its possible correlation with cancer.

The Ascent of Mineralocorticoid Receptor Antagonists in Diabetic Nephropathy

Diabetic nephropathy is defined as a decline in the renal function and an increase in the amount of albuminuria (>300 mg/day). The interruption of the renin-angiotensin-aldosterone system (RAAS) by well-established therapies such as angiotensin-converting enzyme inhibitor, angiotensin receptor blockers, calcium channel blockers or diuretics has been beneficial in reducing the progression of renal diseases; however, there is an increase in the levels of aldosterone due to the aldosterone escape phenomenon. Newer and novel approaches to counteract this aldosterone breakthrough while accentuating the anti-hypertensive and anti-proteinuric effects of these agents would be ideal and mineralocorticoid receptor antagonists fit in this slot perfectly. This review attempted to evaluate the safety and efficacy of and mineralocorticoid receptor antagonists for diabetic nephropathy. Presently mineralocorticoid receptor antagonists such as spironolactone, eplerenone and finerenone are being investigated as both monotherapies and as additional therapies. Clinical studies have shown that these drugs have been effective in the reduction of blood pressure, urinary-albumin-excretion and estimated glomerular filtration rate. The commonly observed adverse effects are hyperkalemia, gynaecomastia and vaginal bleeding, that are bothersome with spironolactone seems to be avoidable if these patients are switched to non-steroidal and mineralocorticoid receptor antagonists such as finerenone and eplerenone. Most of the studies have only evaluated the short-term effects of mineralocorticoid receptor antagonists on diabetic nephropathy. Hard outcomes such as cardiovascular events, creatinine doubling, progression to end-stage renal disease, mortality and the need for temporary or permanent dialysis need to be studied with these molecules.

Downregulation of glucose-6-phosphate dehydrogenase contributes to diabetic neuropathic pain through upregulation of toll-like receptor 4 in rats

Background and aim

Diabetic neuropathic pain is a refractory and disabling complication of diabetes mellitus. The pathogenesis of the diabetic neuropathic pain is still unclear, and treatment is insufficient. The aim of this study is to investigate the roles of glucose-6-phosphate dehydrogenase (G6PD) and toll-like receptor 4 (TLR4) in neuropathic pain in rats with diabetes.

Methods

Type 1 diabetes model was induced by intraperitoneal injection of streptozotocin (STZ, 75 mg/kg) in adult female Sprague-Dawley rats. Paw withdrawal threshold and paw withdrawal latency of rats were measured by von Frey filaments and thermal radiation, respectively. The expressions of G6PD and TLR4 in L4-L6 dorsal root ganglions (DRGs) were measured by western blotting and quantitative real-time polymerase chain reaction analysis. Fluorescent immunohistochemistry was employed to detect expressions of G6PD and TLR4 and co-location of G6PD with TLR4.

Results

The mRNA and protein expression levels of G6PD in DRGs were significantly decreased in diabetic rats when compared with age-matched control rats. Upregulation of G6PD by intrathecal injection of G6PD overexpression adenovirus markedly attenuated hindpaw pain hypersensitivity of diabetic rats. The mRNA and protein expression levels of TLR4 in DRGs of diabetic rats were significantly increased when compared with control rats. Intrathecal injection of TLR4-selective inhibitor CLI-095 attenuated diabetic pain in dose- and time-dependent manners. Furthermore, G6PD and TLR4 were co-localized in DRG neurons. Intrathecal injection of G6PD overexpression adenovirus greatly reduced TLR4 expression, while intrathecal injection of CLI-095 had no significant effect on G6PD expression in diabetic rats.

Conclusions

Our results suggest that decrease in G6PD expression was involved in diabetic peripheral neuropathic pain, which was most likely through upregulation of TLR4 expression in the DRGs of rats.

D-ribose is elevated in T1DM patients and can be involved in the onset of encephalopathy

Although many mechanisms have been proposed for diabetic encephalopathy in type 2 diabetes mellitus (T2DM), the risk factors for cognitive impairment in type 1 diabetes mellitus (T1DM) are less clear. Here, we show that streptozotocin (STZ)-induced T1DM rats showed cognitive impairment in both Y maze and Morris water maze assays, accompanied with D-ribose was significantly increased in blood and urine, in addition to D-glucose. Furthermore, advanced glycation end products (AGE), Tau hyperphosphorylation and neuronal death in the hippocampal CA4/DG region were detected in T1DM rats. The expression and activity of transketolase (TKT), an important enzyme in the pentose shunt, were decreased in the brain, indicating that TKT may be involved in D-ribose metabolism in T1DM. Support for these change was demonstrated by the activation of TKT with benfotiamine (BTMP) treatment. Decreased D-ribose levels but not D-glucose levels; markedly reduced AGE accumulation, Tau hyperphosphorylation, and neuronal death; and improved cognitive ability in T1DM rats were shown after BTMP administration. In clinical investigation, T1DM patients had high D-ribose levels in both urine and serum. Our work suggests that D-ribose is involved in the cognitive impairment in T1DM and may provide a potentially novel target for treating diabetic encephalopathy.

Mineralocorticoid receptor antagonists and kidney diseases: pathophysiological basis

Chronic kidney disease (CKD) represents a global health concern, and its prevalence is increasing. The ultimate therapeutic option for CKD is kidney transplantation. However, the use of drugs that target specific pathways to delay or halt CKD progression, such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and sodium-glucose co-transporter-2 (SGLT-2) inhibitors is limited in clinical practice. Mineralocorticoid receptor activation in nonclassical tissues, such as the endothelium, smooth muscle cells, inflammatory cells, podocytes, and fibroblasts may have deleterious effects on kidney structure and function. Several preclinical studies have shown that mineralocorticoid receptor antagonists (MRAs) ameliorate or cure kidney injury and dysfunction in different models of kidney disease. In this review, we present the preclinical evidence showing a benefit of MRAs in acute kidney injury, the transition from acute kidney injury to CKD, hypertensive and diabetic nephropathy, glomerulonephritis, and kidney toxicity induced by calcineurin inhibitors. We also discuss the molecular mechanisms responsible for renoprotection related to MRAs that lead to reduced oxidative stress, inflammation, fibrosis, and hemodynamic alterations. The available clinical data support a benefit of MRA in reducing proteinuria in diabetic kidney disease and improving cardiovascular outcomes in CKD patients. Moreover, a benefit of MRAs in kidney transplantation has also been observed. The past and present clinical trials describing the effect of MRAs on kidney injury are presented, and the risk of hyperkalemia and use of other options, such as potassium binding agents or nonsteroidal MRAs, are also addressed. Altogether, the available preclinical and clinical data support a benefit of using MRAs in CKD, an approach that should be further explored in future clinical trials.

Antioxidant Defense Mechanisms in Erythrocytes and in the Central Nervous System

Differential antioxidant action is found upon comparison of organ/tissue systems in the human body. In erythrocytes (red blood cells), which transport oxygen and carbon dioxide through the circulatory system, the most important issue is to keep hemoglobin in a functional state that requires maintaining the haem group in ferrous (Fe²⁺) state. Conversion of oxidized Fe³⁺ back into Fe²⁺ in hemoglobin needs a special mechanism involving a tripeptide glutathione, glucose-6-phosphate dehydrogenase, and glucose and NADPH as suppliers of reducing power. Fava beans are probably a good resource to make the detox innate system more robust as the pro-oxidant molecules in this food likely induce the upregulation of members of such mechanisms. The central nervous system consumes more oxygen than the majority of human tissues, i.e., 20% of the body's total oxygen consumption and, therefore, it is exposed to a high level of oxidative stress. This fact, together with the progressive age-related decline in the efficiency of the antioxidant defense system, leads to neuronal death and disease. The innate mechanism operating in the central nervous system is not well known and seems different to that of the erythrocytes. The strategies of antioxidant intervention in brain will be reviewed here.

Glucose 6-phosphate dehydrogenase and the kidney

PURPOSE OF REVIEW

Glucose 6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of the pentose phosphate pathway. G6PD is the main source of the essential cellular reductant, NADPH. The purpose of this review is to describe the biochemistry of G6PD and NADPH, cellular factors that regulate G6PD, normal physiologic roles of G6PD, and the pathogenic role altered G6PD/NADPH plays in kidney disease.

RECENT FINDINGS

NADPH is required for many essential cellular processes such as the antioxidant system, nitric oxide synthase, cytochrome p450 enzymes, and NADPH oxidase. Decreased G6PD activity and, as a result, decreased NADPH level have been associated with diabetic kidney disease, altered nitric oxide production, aldosterone-mediated endothelial dysfunction, and dialysis-associated anemia. Increased G6PD activity is associated with all cancers including kidney cancer. Inherited G6PD deficiency is the most common mutation in the world that is thought to be a relatively mild disorder primarily associated with anemia. Yet, intriguing studies have shown an increased prevalence of diabetes mellitus in G6PD-deficient people. It is not known if G6PD-deficient people are at more risk for other diseases.

SUMMARY

Much more research needs to be done to determine the role of altered G6PD activity (inherited or acquired) in the pathogenesis of kidney disease.

MicroRNA‑146a/NAPDH oxidase4 decreases reactive oxygen species generation and inflammation in a diabetic nephropathy model

The present study investigated the role of microRNA (miR)‑146a in a diabetic nephropathy (DN) model, and its molecular mechanism. DN mice were given intraperitoneal injections of streptozotocin (55 mg/kg/day) for 5 consecutive days as an in vivo DN model. The HK‑2 human kidney cell line were exposed to 45% D‑glucose as an in vitro DN model. Firstly, it was demonstrated that miR‑146a expression was inhibited and NAPDH oxidase 4 (Nox4) was increased in DN mice. In HK‑2 cells, overexpression of miR‑146a inhibited Nox4 protein expression and decreased reactive oxygen species (ROS) generation, oxidative stress and inflammation, and suppressed vascular cell adhesion molecule‑1 (VCAM‑1) and intracellular adhesion molecule‑1 (ICAM‑1) protein expression. Nacetylcysteine, a Nox4 inhibitor, was demonstrated to inhibit ROS generation, suppress VCAM‑1 and ICAM‑1 protein expression, and decrease oxidative stress and inflammation in HK‑2 cells following overexpression of miR‑146a. In conclusion, these results indicated that miR‑146a/Nox4 decreases ROS generation and inflammation and prevents DN. Therefore, miR‑146a may represent a novel anti‑inflammatory and ‑oxidative modulator of DN.

Euterpe oleracea Mart. seed extract protects against renal injury in diabetic and spontaneously hypertensive rats: role of inflammation and oxidative stress

PURPOSE

Euterpe oleracea Mart. (açaí) seed extract (ASE), through its anti-hypertensive, antioxidant and anti-inflammatory properties, may be useful to treat or prevent human diseases. Several evidences suggest that oxidative stress and inflammation contribute to the pathogenesis of diabetic nephropathy; therefore, we tested the hypothesis that ASE (200 mg/kg^-1day^-1) prevents diabetes and hypertension-related oxidative stress and inflammation, attenuating renal injury.

METHODS

Male rats with streptozotocin (STZ)-induced diabetes (D), and spontaneously hypertensive rats with STZ-induced diabetes (DH) were treated daily with tap water or ASE (D + ASE and DH + ASE, respectively) for 45 days. The control (C) and hypertensive (H) animals received water.

RESULTS

The elevated serum levels of urea and creatinine in D and DH, and increased albumin excretion in HD were reduced by ASE. Total glomeruli number in D and DH, were increased by ASE that also reduced renal fibrosis in both groups by decreasing collagen IV and TGF-β1 expression. ASE improved biomarkers of renal filtration barrier (podocin and nephrin) in D and DH groups and prevented the increased expression of caspase-3, IL-6, TNF-α and MCP-1 in both groups. ASE reduced oxidative damage markers (TBARS, carbonyl levels and 8-isoprostane) in D and DH associated with a decrease in Nox 4 and p47 subunit expression and increase in antioxidant enzyme activity in both groups (SOD, catalase and GPx).

CONCLUSION

ASE substantially reduced renal injury and prevented renal dysfunction by reducing inflammation, oxidative stress and improving the renal filtration barrier, providing a nutritional resource for prevention of diabetic and hypertensive-related nephropathy.

SGK1 inhibits cellular apoptosis and promotes proliferation via the MEK/ERK/p53 pathway in colitis

AIM: To investigate the role of serum-and-glucocorticoid-inducible-kinase-1 (SGK1) in colitis and its potential pathological mechanisms.

METHODS: SGK1 expression in mucosal biopsies from patients with active Crohn’s disease (CD) and normal controls was detected by immunohistochemistry. We established an acute colitis model in mice induced by 2,4,6-trinitrobenzene sulfonicacid, and demonstrated the presence of colitis using the disease activity index, the histologic activity index and hematoxylin and eosin staining. The cellular events and potential mechanisms were implemented with small interference RNA and an inhibitor of signaling molecule (i.e., U0126) in intestinal epithelial cells (IECs). The interaction between SGK1 and the signaling molecule was assessed by co-immunoprecipitation.

RESULTS: SGK1 expression was significantly increased in the inflamed epithelia of patients with active CD and TNBS-induced colitis model (0.58 ± 0.055 vs 0.85 ± 0.06, P < 0.01). At the cellular level, silencing of SGK1 by small interference RNA (siSGK1) significantly inhibited the phosphorylation of mitogen-activated protein kinase kinase 1 (MEK1) and the downstream molecule extracellular signal regulated protein kinase (ERK) 1/2, which induced the upregulation of p53 and Bcl-2-associated X protein, mediating the subsequent cellular apoptosis and proliferation in IECs. Cells treated with MEK1 inhibitor (i.e., U0126) before siSGK1 transfection showed a reversal of the siSGK1-induced cellular apoptosis.

CONCLUSION: Our data suggested that SGK1 may protect IECs in colitis from tumor necrosis factor-α-induced apoptosis partly by triggering MEK/ERK activation.

Spironolactone improves endothelial dysfunction in streptozotocin-induced diabetic rats

Endothelial dysfunction is a critical initiator for developing diabetic vascular complications. Substantial clinical and experimental evidence suggests that aldosterone plays a crucial role in its pathogenesis. The present study aimed to investigate the effect of the mineralocorticoid receptor (MR) blocker, spironolactone, on diabetes-associated endothelial dysfunction and address the underlying mechanism(s) involved in this setting. Diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ) to rats and spironolactone was orally administered (50 mg/kg/day). Our results showed a marked increase in aortic malondialdehyde (MDA) level and upregulation of the catalytic NADPH oxidase subunit, NOX2 gene expression alongside reducing catalase enzyme capacity, and the serum nitric oxide (NO) bioavailability in diabetic rats. This was associated with a significant reduction in endothelial nitric oxide synthase (eNOS) immunoreactivity and gene expression in diabetic aorta. The transforming growth factor-β (TGF-β) protein and the MR gene expression levels were significantly increased in the diabetic rat aorta. Moreover, the diabetic aorta showed a marked impairment in acetylcholine-mediated endothelium-dependent relaxation. Additionally, spironolactone significantly inhibited the elevated MDA, TGF-β, NOX2, and MR levels alongside correcting the dysregulated eNOS expression and the defective antioxidant function as well as NO bioavailability. Spironolactone markedly reversed the impaired endothelial function in the diabetic aorta. Collectively, our study demonstrates that spironolactone ameliorated the vascular dysfunction of diabetic aorta, at least partially via its anti-inflammatory and anti-oxidative effects alongside correcting the dysregulated eNOS and TGF-β expression. Thus, blockade of MR may represent a useful therapeutic approach against diabetic vasculopathy.

The role of the renin-angiotensin-aldosterone system in the pathobiology of pulmonary arterial hypertension (2013 Grover Conference series)

Pulmonary arterial hypertension (PAH) is associated with aberrant pulmonary vascular remodeling that leads to increased pulmonary artery pressure, pulmonary vascular resistance, and right ventricular dysfunction. There is now accumulating evidence that the renin-angiotensin-aldosterone system is activated and contributes to cardiopulmonary remodeling that occurs in PAH. Increased plasma and lung tissue levels of angiotensin and aldosterone have been detected in experimental models of PAH and shown to correlate with cardiopulmonary hemodynamics and pulmonary vascular remodeling. These processes are abrogated by treatment with angiotensin receptor or mineralocorticoid receptor antagonists. At a cellular level, angiotensin and aldosterone activate oxidant stress signaling pathways that decrease levels of bioavailable nitric oxide, increase inflammation, and promote cell proliferation, migration, extracellular matrix remodeling, and fibrosis. Clinically, enhanced renin-angiotensin activity and elevated levels of aldosterone have been detected in patients with PAH, which suggests a role for angiotensin and mineralocorticoid receptor antagonists in the treatment of PAH. This review will examine the current evidence linking renin-angiotensin-aldosterone system activation to PAH with an emphasis on the cellular and molecular mechanisms that are modulated by aldosterone and may be of importance for the pathobiology of PAH.

Antioxidant N-acetylcysteine protects pancreatic β-cells against aldosterone-induced oxidative stress and apoptosis in female db/db mice and insulin-producing MIN6 cells

Previous studies have shown that primary aldosteronism is associated with glucose-related metabolic disorders. However, the mechanisms by which aldosterone (ALDO) triggers β-cell dysfunction remains unclear. This study aimed to investigate whether oxidative stress is involved in and whether the antioxidant N-acetylcysteine (NAC) or the mineralocorticoid receptor antagonist spironolactone (SPL) could prevent or delay β-cell damage in vivo and in vitro. As expected, 8 weeks after ALDO treatment, 12-week-old female diabetic db/db mice exhibited impaired oral glucose tolerance, decreased β-cell mass, and heightened levels of oxidative stress marker (urinary 8-hydroxy-2'-deoxyguanosine). NAC reversed these symptoms completely, whereas SPL treatment did so only partially. After exposure to ALDO, the mouse pancreatic β-cell line MIN6 exhibited decreased viability and increased caspase-3 activity, as well as reduced expression of Bcl-2/Bax and p-AKT, even if mineralocorticoid receptor was completely suppressed with small interfering RNA. NAC, but not SPL, suppressed oxidative stress in MIN6 cells, as revealed by the decrease in inducible NOS levels and expression of the proteins p22-phox and p67-phox. These findings suggest that oxidative stress may be involved in ALDO-induced β-cell dysfunction and that NAC, but not SPL, may protect pancreatic β-cells of mice from ALDO-induced oxidative stress and apoptosis in a manner independent of its receptor.

The effects of aldosterone on diet-induced fatty liver formation in male C57BL/6 mice: comparison of adrenalectomy and mineralocorticoid receptor blocker

OBJECTIVE

Obesity, diabetes, fatty liver, and hypertension are major determinants of the metabolic syndrome. The effects of aldosterone and mineralocorticoid receptor blockers on fatty liver are largely unknown. The aim of the present study was to evaluate the relationships between aldosterone and the development of fatty liver.

MATERIALS AND METHODS

In our experiments, we performed adrenalectomy (ADX) or administered 100 mg/kg/day eplerenone, a specific mineralocorticoid receptor blocker, to male C57BL/6 mice fed with a 60% fat diet for 20 weeks.

RESULTS

High-fat diet led to metabolic syndrome as indicated by increased body weight, elevated systolic blood pressure, impaired glucose tolerance, elevated insulin levels, and development of fatty liver. A marked reduction of aldosterone by ADX or blockade of aldosterone interaction with its receptor by eplerenone, which increased serum aldosterone considerably, resulted in reduced blood pressure, and reduced serum insulin and levels of triglycerides. However, differential effects were found on reduction of blood glucose to normal levels, which was observed only in ADX. Neither ADX nor eplerenone affected fatty liver formation or body weight. In cultured hepatocytes, triglyceride loading induced by high glucose, oleic acid or very low density lipoprotein was not affected by aldosterone, spironolactone or eplerenone.

CONCLUSION

Our results suggest that whereas aldosterone might be involved in some of the diet-induced insulin and glucose metabolic effects, it played no role in the development of fatty liver.

Therapeutic potential of serum and glucocorticoid inducible kinase inhibition

INTRODUCTION

Expression of serum-and-glucocorticoid-inducible kinase-1 (SGK1) is low in most cells, but dramatically increases under certain pathophysiological conditions, such as glucocorticoid or mineralocorticoid excess, inflammation with TGFβ release, hyperglycemia, cell shrinkage and ischemia. SGK1 is activated by insulin and growth factors via phosphatidylinositide-3-kinase, 3-phosphoinositide-dependent kinase and mammalian target of rapamycin. SGK1 sensitive functions include activation of ion channels (including epithelial Na(+) channel ENaC, voltage gated Na(+) channel SCN5A transient receptor potential channels TRPV4 - 6, Ca(2+) release activated Ca(2+) channel Orai1/STIM1, renal outer medullary K(+) channel ROMK, voltage gated K(+) channels KCNE1/KCNQ1, kainate receptor GluR6, cystic fibrosis transmembrane regulator CFTR), carriers (including Na(+),Cl(-) symport NCC, Na(+),K(+),2Cl(-) symport NKCC, Na(+)/H(+) exchangers NHE1 and NHE3, Na(+), glucose symport SGLT1, several amino acid transporters), and Na(+)/K(+)-ATPase. SGK1 regulates several enzymes (e.g., glycogen synthase kinase-3, ubiquitin-ligase Nedd4-2) and transcription factors (e.g., forkhead transcription factor 3a, β-catenin, nuclear factor kappa B).

AREAS COVERED

The phenotype of SGK1 knockout mice is mild and SGK1 is apparently dispensible for basic functions. Excessive SGK1 expression and activity, however, contributes to the pathophysiology of several disorders, including hypertension, obesity, diabetes, thrombosis, stroke, fibrosing disease, infertility and tumor growth. A SGK1 gene variant (prevalence ∼ 3 - 5% in Caucasians and ∼ 10% in Africans) is associated with hypertension, stroke, obesity and type 2 diabetes. SGK1 inhibitors have been developed and shown to reduce blood pressure of hyperinsulinemic mice and to counteract tumor cell survival.

EXPERT OPINION

Targeting SGK1 may be a therapeutic option in several clinical conditions, including metabolic syndrome and tumor growth.