Role of Peroxisome Proliferator-Activated Receptor α in Diabetic Nephropathy

Oxidative stress, inflammation, and steatosis elucidate the complex dynamics of HgCl2 induced liver damage in Channa punctata

Water bodies are highly pollution-prone areas in which mercury (Hg) is considered as a major menace to aquatic organisms. However, the information about the toxicity of mercuric chloride (HgCl2) in a vital organ such as the liver of fish is still inadequate. This study aimed to assess the impact of mercuric chloride (HgCl2) exposure on the liver of Channa punctata fish over 15, 30, and 45 days, at two different concentrations (0.039 mg/L and 0.078 mg/L). Mercury is known to be a significant threat to aquatic life, and yet, information regarding its effects on fish liver remains limited. The results of this study demonstrate that exposure to HgCl2 significantly increases oxidative stress markers, such as lipid peroxidation (LPO) and protein carbonyls (PC), as well as the levels of serum glutamic-oxaloacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGPT) in the fish. Additionally, the transcriptional and protein analysis of specific genes and molecules associated with necroptosis and inflammation, such as ABCG2, TNF α, Caspase 3, RIPK 3, IL-1β, Caspase-1, IL-18, and RIPK1, confirm the occurrence of necroptosis and inflammation in the liver. Histopathological and ultrastructural examinations of the liver tissue further reveal a significant presence of liver steatosis. Interestingly, the upregulation of PPARα suggests that the fish's body is actively responding to counteract the effects of liver steatosis. This study provides a comprehensive analysis of oxidative stress, biochemical changes, gene expression, protein profiles, and histological findings in the liver tissue of fish exposed to mercury pollution in freshwater environments.

Metformin mitigates renal dysfunction in obese insulin-resistant rats via activation of the AMPK/PPARα pathway

Insulin signaling and lipid metabolism are disrupted by long-term consumption of a high-fat diet (HFD). This disruption can lead to insulin resistance, dyslipidemia and subsequently renal dysfunction as a consequence of the inactivation of the AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-α (PPARα) or AMPK/PPARα pathways. We investigated the impact of metformin on the prevention of renal dysfunction through the modulation of AMPK-regulated PPARα-dependent pathways in insulin-resistant rats induced by a HFD. Male Wistar rats were fed a HFD for 16 weeks to induce insulin resistance. After insulin resistance had been confirmed, metformin (30 mg/kg) or gemfibrozil (50 mg/kg) was given orally for 8 weeks. Evidence of insulin resistance, dyslipidemia, lipid accumulation and kidney injury were observed in HF rats. Impairment of lipid oxidation, energy metabolism and renal organic anion transporter 3 (Oat3) expression and function were demonstrated in HF rats. Metformin can stimulate the AMPK/PPARα pathways and suppress sterol regulatory element-binding transcription factor 1 (SREBP1) and fatty acid synthase (FAS) signaling (SREBP1/FAS) to enable the regulation of lipid metabolism. Renal inflammatory markers and renal fibrosis expression induced by a HFD were more effectively reduced after metformin treatment than after gemfibrozil treatment. Interestingly, renal Oat3 function and expression and kidney injury were improved following metformin and gemfibrozil treatment. Renal cluster of differentiation 36 (CD36) or sodium glucose cotransporter type 2 (SGLT2) expression did not differ after treatment with metformin or gemfibrozil. Metformin and gemfibrozil could reduce the impairment of renal injury in obese conditions induced by a HFD through the AMPK/PPARα-dependent pathway. Interestingly, metformin demonstrated greater efficacy than gemfibrozil in attenuating renal lipotoxicity through the AMPK-regulated SREBP1/FAS signaling pathway.

The Proteome of Circulating Large Extracellular Vesicles in Diabetes and Hypertension

Hypertension and diabetes induce vascular injury through processes that are not fully understood. Changes in extracellular vesicle (EV) composition could provide novel insights. Here, we examined the protein composition of circulating EVs from hypertensive, diabetic and healthy mice. EVs were isolated from transgenic mice overexpressing human renin in the liver (TtRhRen, hypertensive), OVE26 type 1 diabetic mice and wild-type (WT) mice. Protein content was analyzed using liquid chromatography-mass spectrometry. We identified 544 independent proteins, of which 408 were found in all groups, 34 were exclusive to WT, 16 were exclusive to OVE26 and 5 were exclusive to TTRhRen mice. Amongst the differentially expressed proteins, haptoglobin (HPT) was upregulated and ankyrin-1 (ANK1) was downregulated in OVE26 and TtRhRen mice compared with WT controls. Conversely, TSP4 and Co3A1 were upregulated and SAA4 was downregulated exclusively in diabetic mice; and PPN was upregulated and SPTB1 and SPTA1 were downregulated in hypertensive mice, compared to WT mice. Ingenuity pathway analysis identified enrichment in proteins associated with SNARE signaling, the complement system and NAD homeostasis in EVs from diabetic mice. Conversely, in EVs from hypertensive mice, there was enrichment in semaphroin and Rho signaling. Further analysis of these changes may improve understanding of vascular injury in hypertension and diabetes.

A comprehensive insight into the molecular and cellular mechanisms of the effects of Propolis on preserving renal function: a systematic review

BACKGROUND

The present systematic review is conducted, focusing on the existing evidence of Propolis's effects due to its various health benefits, mainly antioxidant and anti-inflammatory properties on preserving renal function.

METHODS

A systematic search of PubMed, Scopus, Embase, ProQuest, and Google Scholar was undertaken for relevant papers published from the start until January 2021.

RESULTS

This review revealed that Propolis affects fasting blood sugar (FBS), postprandial blood glucose, advanced glycation end products (AGEs) concentrations, malondialdehyde (MDA) levels, urinary concentrations of reactive oxygen metabolites (Tbars), total oxidant status (TOS), oxidative stress index (OSI), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation favorably. The findings on hemoglobin A1C (HbA1C), insulin, homeostasis model assessment of insulin resistance (HOMA-IR), β-cell function (HOMA-β), quantitative insulin sensitivity check index (QUICKI), and lipid profile were controversial. Moreover, a significant reduction in renal nuclear factor kappa B (NF-κB), serum immunoglobulins, renal ED-1+ cells, and urinary monocyte chemoattractant protein-1 (MCP-1) following Propolis supplementation has been reported, while the results on interleukin-6 (IL-6), tumor necrosis factor α (TNF-α), nitric oxide (NO), nitric oxide synthetase (NOS), and high sensitivity C-reactive protein (hs-CRP) were controversial. Furthermore, included studies showed its anti- proteinuria and kidney restoring effects.

CONCLUSION

In this review, both human and animal studies provide us evidences that Propolis could potentially improve the glycemic status, oxidative stress, renal tissue damage, and renal function. Further studies are needed to determine the underlying mechanisms.

APX-115, a pan-NADPH oxidase inhibitor, protects development of diabetic nephropathy in podocyte specific NOX5 transgenic mice

NADPH oxidases (NOXs) are comprised of different isoforms, NOX1 to 5 and Duox1 and 2, and they trigger diabetic nephropathy (DN) in the patients with diabetes mellitus. Recently, it was shown that, compared to the other isoforms, the expression of NOX5 was increased in the patients with DN and, NOX5 has been suggested to be important in the development of therapeutic agents. The effect of pan-NOX inhibition by APX-115 has also been investigated in type 2 diabetic mice. However, since NOX5 is absent in mice, we evaluated the effect of pan-NOX inhibition by APX-115 in Nox5 transgenic mouse. Wild type and renal podocyte specific NOX5 transgenic mice (NOX5 pod+) were fed with high-fat diet (60% kcal fat) and treated with APX-115 (60 mg/kg) by oral gavage for 14 weeks. APX-115 significantly improved pancreatic beta cell function by decreased fasting blood glucose levels and increased insulin levels. Further, the total serum cholesterol, triglycerides, and urinary albumin/creatinine levels were also significantly decreased by APX-115 treatment. Increased NOX5 mRNA expressions, increased desmin levels, and reduced podocin protein expressions in the kidney of NOX5 pod + mice were also significantly restored to normal levels by APX-115 treatment. Moreover, APX-115 inhibited the expression of inflammation-related proteins such as TRAF6. Collectively, these data suggest that APX-115 might be a promising therapeutic agent for the treatment of DN because of its pan-NOX inhibitory activity, including its NOX5 inhibitory activity, and also owing to its anti-inflammatory effect.

AMPK allostery: A therapeutic target for the management/treatment of diabetic nephropathy

Diabetic nephropathy (DN) is a chronic complication of diabetes mellitus (DM) with approximately 30-40% of patients with DM developing nephropathy, and it is the leading cause of end-stage renal diseases and diabetic morbidity. The pathogenesis of DN is primarily associated with irregularities in the metabolism of glucose and lipid leading to hyperglycemia-induced oxidative stress, which has been a major target together with blood pressure regulation in the control of DN progression. However, the regulation of 5' adenosine monophosphate-activated protein kinase (AMPK), a highly conserved protein kinase for maintaining energy balance and cellular growth and repair has been implicated in the development of DM and its complications. Therefore, targeting AMPK pathway has been explored as a therapeutic strategy for the treatment of diabetes and its complication, although most of the mechanisms have not been fully elucidated. In this review, we discuss the structure of AMPK relevant to understanding its allosteric regulation and its role in the pathogenesis and progression of DN. We also identify therapeutic agents that modulate AMPK and its downstream targets with their specific mechanisms of action in the treatment of DN.

Fenofibrate decreased microalbuminuria in the type 2 diabetes patients with hypertriglyceridemia

Background

This study was to research the efficacy of fenofibrate in the treatment of microalbuminuria in the patients with type 2 diabetes mellitus (T2DM) and hypertriglyceridemia.

Methods

Type 2 diabetic patients (56) with microalbuminuria and hypertriglyceridemia aged 30 to 75 were randomly divided into the fenofibrate treatment group(n = 28) and the control group (n = 28) for 180 days. Urinary microalbumin /creatinine ratio (UACR) and other metabolic parameters were compared at baseline, during treatment and after treatment.

Results

After 180 days, the reduction of level of fasting blood glucose (FBG) and glycosylated hemoglobin (HbA1c) between two groups showed no difference. In the treatment group, uric acid (UA) (296.42 ± 56.41 vs 372.46 ± 72.78), triglyceride (TG) [1.51(1.17, 2.06) vs 3.04(2.21, 3.29)], and UACR [36.45 (15.78,102.41) vs 129.00 (53.00, 226.25)] were significantly decreased compared with the baseline. The high-density lipoprotein cholesterol (HDL-C) levels were significantly increased (1.22 ± 0.26 vs 1.09 ± 0.24) compared with the baseline. The decrease in UACR [− 44.05(− 179.47, − 12.16) vs − 8.15(− 59.69, 41.94)]in treatment group was significantly higher compared with the control group. The decrease in UACR was positively associated with the decreases in TG (r = 0.447, P = 0.042) and UA (r = 0.478, P = 0.024) after fenofibrate treatment.

Conclusion

In the patients with hypertriglyceridemia and type 2 diabetes mellitus, fenofibrate can improve microalbuminuria and do not increase the deterioration of glomerular filtration rate.

Trial registration

ClinicalTrials.gov identifier: NCT02314533, 2014.12.9

Greater efficacy of atorvastatin versus a non-statin lipid-lowering agent against renal injury: potential role as a histone deacetylase inhibitor

Statins, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors have been shown to improve diabetic nephropathy. However, whether they provide protection via Histone deacetylases (HDAC) inhibition is not clear. We conducted a comparative evaluation of Atorvastatin (AT) versus the non-statin cholesterol-lowering drug, Ezetimibe (EZT) on severity of diabetic nephropathy. Streptozotocin-treated male Wistar rats were fed a cholesterol-supplemented diet and gavaged daily with vehicle, AT or EZT. Control rats received normal diet and gavaged vehicle (n = 8-9/group). Diabetes increased blood glucose, urine albumin-to-creatinine ratio (ACR), kidney pathology and HDAC activity, and reduced renal E-cadherin levels. Both AT and EZT reduced circulating cholesterol, attenuated renal pathology, and did not lower blood glucose. However, AT was significantly more effective than EZT at reducing kidney pathology and HDAC activity. Chromatin immunoprecipitation revealed a significantly higher association of acetylated H3 and H4 with the E-cadherin promoter in kidneys from AT-, relative to EZT- or vehicle-treated rats. Moreover, we demonstrated a direct effect of AT, but not EZT, on HDAC-inhibition and, H3 and H4- acetylation in primary glomerular mesangial cells. Overall, both AT and EZT attenuated diabetic nephropathy; however, AT exhibited greater efficacy despite a similar reduction in circulating cholesterol. HDAC-inhibition may underlie greater efficacy of statins in attenuating kidney injury.

Peroxisome proliferator-activated receptor α-dependent renoprotection of murine kidney by irbesartan

Activation of renal peroxisome proliferator-activated receptor α (PPARα) is renoprotective, but there is no safe PPARα activator for patients with chronic kidney disease (CKD). Studies have reported that irbesartan (Irbe), an angiotensin II receptor blocker (ARB) widely prescribed for CKD, activates hepatic PPARα. However, Irbe's renal PPARα-activating effects and the role of PPARα signalling in the renoprotective effects of Irbe are unknown. Herein, these aspects were investigated in healthy kidneys of wild-type (WT) and Ppara-null (KO) mice and in the murine protein-overload nephropathy (PON) model respectively. The results were compared with those of losartan (Los), another ARB that does not activate PPARα. PPARα and its target gene expression were significantly increased only in the kidneys of Irbe-treated WT mice and not in KO or Los-treated mice, suggesting that the renal PPARα-activating effect was Irbe-specific. Irbe-treated-PON-WT mice exhibited decreased urine protein excretion, tubular injury, oxidative stress (OS), and pro-inflammatory and apoptosis-stimulating responses, and they exhibited maintenance of fatty acid metabolism. Furthermore, the expression of PPARα and that of its target mRNAs encoding proteins involved in OS, pro-inflammatory responses, apoptosis and fatty acid metabolism was maintained upon Irbe treatment. These renoprotective effects of Irbe were reversed by the PPARα antagonist MK886 and were not detected in Irbe-treated-PON-KO mice. These results suggest that Irbe activates renal PPARα and that the resultant increased PPARα signalling mediates its renoprotective effects.

Anthocyanin-rich Seoritae extract ameliorates renal lipotoxicity via activation of AMP-activated protein kinase in diabetic mice

BACKGROUND

Anthocyanins are major constituents of food colours and have been reported to possess anti-diabetic activities for potential medicinal use. The precise role of anthocyanins in diabetic nephropathy is poorly understood. We investigated whether anthocyanin-rich Seoritae extract (SE) can potentially prevent oxidative stress and lipotoxicity, which are the main causes of renal damage in diabetic nephropathy, via activation of AMP-activated protein kinase (AMPK) and the consequent effects on its target molecules.

METHODS

Four groups of male C57BLKS/J db/m and db/db mice were used. Diabetic and non-diabetic mice were orally administered 10 mg/kg body weight SE daily for 12 weeks, starting at 8 weeks of age.

RESULTS

db/db mice treated with anthocyanins showed decreased albuminuria. Anthocyanins ameliorated intra-renal lipid concentrations in db/db mice with improvement of glomerular matrix expansion and inflammation, which was related to increased phosphorylation of AMPK and activation of peroxisome proliferator-activated receptor (PPAR) α and PPARγ, and inhibited the activity of acetyl-CoA carboxylase and sterol regulatory element-binding protein 1. Anthocyanins reversed diabetes-induced increases in renal apoptosis and oxidative stress. In cultured human glomerular endothelial cells, anthocyanins prevented high glucose-induced oxidative stress and apoptosis through activation of AMPK in the same manner.

CONCLUSIONS

The results revealed that anthocyanins ameliorated diabetic nephropathy in db/db mice via phosphorylation of AMPK, the major energy-sensing enzyme, and the consequent effects on its target molecules, which appeared to prevent lipotoxicity-related apoptosis and oxidative stress in the kidney.

Fenofibrate and dipyridamole treatments in low-doses either alone or in combination blunted the development of nephropathy in diabetic rats

Low-doses of fenofibrate and dipyridamole have pleiotropic renoprotective actions in diabetic rats. This study investigated their combined effect relative to their individual treatments and lisinopril in rats with diabetic nephropathy. Streptozotocin (55mg/kg, i.p., once)-administered diabetic rats were allowed for 10 weeks to develop nephropathy. Diabetic rats after 10 weeks developed nephropathy with discernible renal structural and functional changes as assessed in terms of increase in kidney weight to body weight ratio (KW/BW), and elevations of serum creatinine, urea and uric acid, which accompanied with elevated serum triglycerides and decreased high-density lipoproteins. Hematoxylin-eosin, periodic acid Schiff and Masson trichrome staining confirmed renal pathological changes in diabetic rats that included glomerular capsular wall distortion, mesangial cell expansion, glomerular microvascular condensation, tubular damage and degeneration and fibrosis. Low-dose fenofibrate (30mg/kg, p.o., 4 weeks) and low-dose dipyridamole (20mg/kg, p.o., 4 weeks) treatment either alone or in combination considerably reduced renal structural and functional abnormalities in diabetic rats, but without affecting the elevated glucose level. Fenofibrate, but not dipyridamole, significantly prevented the lipid alteration and importantly the uric acid elevation in diabetic rats. Lisinopril (5mg/kg, p.o., 4 weeks, reference compound), prevented the hyperglycemia, lipid alteration and development of diabetic nephropathy. Lipid alteration and uric acid elevation, besides hyperglycemia, could play key roles in the development of nephropathy. Low-doses of fenofibrate and dipyridamole treatment either alone or in combination markedly prevented the diabetes-induced nephropathy. Their combination was as effective as to their individual treatment, but not superior in preventing the development of diabetic nephropathy.

Diabetic kidney disease: from epidemiology to clinical perspectives

With worldwide epidemic of diabetes mellitus, diabetic nephropathy which is one of the major causes of microvascular complication has become a serious concern in Korea as well as the rest of the world. In view of its significance, there is an urgent and paramount need for proper managements that could either deter or slow the progression of diabetic nephropathy. Despite advances in care, ever increasing number of patients suffering from diabetic kidney disease and from end-stage renal disease implies that the current management is not adequate in many aspects. The reasons for these inadequacies compromise lack of early diagnosis, failure to intervene with timely and aggressive manner, and lack of understanding on the kind of interventions required. Another issue equally important for the adequate care of patients with diabetic nephropathy is an understanding of past, present and future epidemiology of diabetic nephropathy which serves, especially in Korea, as a material determining standard diagnosis and treatment and a national health-policy decision.

Peroxisome proliferator-activated receptor agonists in a battle against the aging kidney

As aging is a complex phenomenon characterized by intraindividual and interindividual diversities in the maintenance of the homeostatic condition of cells and tissues, changes in renal function are not uniform and depend on associated diseases and environmental factors. Multiple studies have investigated the possible underlying mechanisms of age-related decline in kidney function. Evolutionary, molecular, cellular and systemic theories have been postulated to explain the primary disease independent age-related changes and adaptive responses. As peroxisome proliferator-activated receptors (PPARs) are involved in a broad spectrum of biological processes, PPAR activation might have an effect on the prevention of cell senescence. In this review, we will focus on the experimental and clinical evidence of PPAR agonists in a battle against the aging kidney.

Age-associated molecular changes in the kidney in aged mice

BACKGROUND

Aging is a multifactorial process characterized by a progressive decline in physiological function. Decreased kidney function is associated with cardiovascular disease and mortality. Therefore, increasing our insight into kidney aging by understanding the anatomic, physiologic, and pathologic changes of aging in the kidney is important to prevent disastrous outcomes in elderly people.

METHODS

Male two-, 12-, and 24-month-old C57/BL6 mice were used in this study. We measured histological change, oxidative stress, and aging-related protein expression in the kidneys.

RESULTS

Twenty-four-month-old mice displayed increased albuminuria. Creatinine clearance decreased with aging, although this was not statistically significant. There were increases in mesangial volume and tubulointerstitial fibrosis in 24-month-old mice. There were also increases in F4/80 expression and in apoptosis detected by TUNEL assay. Urine isoprostane excretion increased with aging and SOD1 and SOD2 were decreased in 24-month-old mice. Oxidative stress may be mediated by a decrease in Sirt1, PGC-1α, ERR-1α, and PPARα expression. Klotho expression also decreased.

CONCLUSIONS

Our results demonstrate that Sirt1 was decreased with aging and may relate to changed target molecules including PGC-1α/ERR-1α signaling and PPARα. Klotho can also induce oxidative stress. Pharmacologically targeting these signaling molecules may reduce the pathologic changes of aging in the kidney.

Differential effects of low-dose fenofibrate treatment in diabetic rats with early onset nephropathy and established nephropathy

We have previously shown that low-dose fenofibrate treatment has an ability to prevent diabetes-induced nephropathy in rats. We investigated here the comparative pre- and post-treatment effects of low-dose fenofibrate (30 mg/kg/day p.o.) in diabetes-induced onset of nephropathy. Rats were made diabetics by single administration of streptozotocin (STZ, 55 mg/kg i.p.). The development of diabetic nephropathy was assessed biochemically and histologically. Moreover, lipid profile and renal oxidative stress were assessed. Diabetic rats after 8 weeks of STZ-administration developed apparent nephropathy by elevating serum creatinine, blood urea nitrogen and microproteinuria, and inducing glomerular-capsular wall distortion, mesangial expansion and tubular damage and renal oxidative stress. Fenofibrate (30 mg/kg/day p.o., 4 weeks) pretreatment (4 weeks after STZ-administration) markedly prevented diabetes-induced onset of diabetic nephropathy, while the fenofibrate (30 mg/kg/day p.o., 4 weeks) post-treatment (8 weeks after STZ-administration) was less-effective. However, both pre-and post fenofibrate treatments were effective in preventing diabetes-induced renal oxidative stress and lipid alteration in diabetic rats though the pretreatment was slightly more effective. Conversely, both pre-and post fenofibrate treatments did not alter elevated glucose levels in diabetic rats. It may be concluded that diabetes-induced oxidative stress and lipid alteration, in addition to a marked glucose elevation, play a detrimental role in the onset of nephropathy in diabetic rats. The pretreatment with low-dose fenofibrate might be a potential therapeutic approach in preventing the onset of nephropathy in diabetic subjects under the risk of renal disease induction. However, low-dose fenofibrate treatment might not be effective in treating the established nephropathy in diabetic subjects.