The PPARα ligand fenofibrate: meeting multiple targets in diabetic nephropathy

Carnosic acid improves diabetic nephropathy by activating Nrf2/ARE and inhibition of NF-κB pathway

BACKGROUND

Diabetic nephropathy (DN), one of the most serious complications of diabetes, is the leading cause of morbidity and mortality of end-stage renal disease. Our previous research found that carnosic acid (CA) or rosemary extract can effectively improve glucose and lipid metabolism disorder by inhibiting SREBPs.

PURPOSE

In this study, we aimed to explore the therapeutic effects of CA on the DN.

METHODS

The mice glomerular mesangial cells (mGMCs) were used to evaluate the anti-oxidative and anti-inflammation effects of CA under high glucose (HG) condition. Furthermore, db/db mice and streptozotocin (STZ)-induced diabetic mice were used to investigate the effects of CA against DN in vivo.

RESULTS

The results showed that CA activated Nrf2, inhibited NF-κB pathway and regulated related downstream genes in mGMC under HG condition. A 14-week treatment of mice with CA reduced water uptake and urine volume, attenuated diabetes-induced albuminuria, increased urine creatinine, and subsequently improved the glomerular sclerosis and mesangial expansion in db/db mice. Similarly, a 20-week oral administration of CA improved kidney damage in STZ-induced diabetic mice. In addition, CA inhibited the expression of profibrotic factors, such as TGF-β1, fibronectin and E-cadherin. Compared to irbesartan, CA exerted better glucose lowering effect, and in kidney, CA was more potent to reduce fibronectin and E-cadherin expression. In all the animal experiment, CA did not lead to abnormal damages to other tissues.

CONCLUSION

These findings suggest that CA is a safe compound which exerts the protective effects on diabetes-induced kidney complications.

Perfluorooctanoic acid and chronic kidney disease: Longitudinal analysis of a Mid-Ohio Valley community

INTRODUCTION

Perfluorooctanoic acid (PFOA) is an environmentally persistent chemical found at low-levels in the serum of almost all U.S. residents. Chronic kidney disease (CKD) has been positively associated with serum PFOA in prior cross-sectional studies and in one occupational mortality study, while other investigations have found no association between kidney function and PFOA.

METHODS

We conducted a longitudinal analysis of chronic kidney disease among adults, aged ≥20 years, (N=32,254) in a Mid-Ohio Valley community cohort, exposed to high PFOA levels from contaminated drinking water. Estimated retrospective yearly serum PFOA concentrations (1951-2011) were previously modeled in this population. Information about lifetime history of CKD diagnosis was collected during surveys in 2008-2011; self-reported CKD diagnoses were validated through medical record review. Using a Cox proportional hazards model, we retrospectively examined the association between validated adult onset CKD, and modeled PFOA exposure, from time of first exposure. We also analyzed data for the cohort prospectively, among people with no CKD diagnosis prior to enrollment in a baseline survey in 2005-2006. Both the full cohort and a non-diabetic subset were analyzed, retrospectively and prospectively.

RESULTS

Neither in retrospective nor in prospective analyses did we find a significant (α=0.05) trend between PFOA exposure and CKD. In the full cohort, estimated hazard ratios by quintile of cumulative serum PFOA in the retrospective analysis were 1.00 (referent), 1.26, 1.12, 1.12 and 1.24 (trend test for log cumulative exposure: p=0.80).

CONCLUSION

Our analyses suggest that CKD is not associated with exposure to PFOA.

Mammalian tribbles homologs at the crossroads of endoplasmic reticulum stress and Mammalian target of rapamycin pathways

In 2000, investigators discovered Tribbles, a Drosophila protein that coordinates morphogenesis by inhibiting mitosis. Further work has delineated Xenopus (Xtrb2), Nematode (Nipi-3), and mammalian homologs of Drosophila tribbles, which include TRB1, TRB2, and TRB3. The sequences of tribbles homologs are highly conserved, and despite their protein kinase structure, to date they have not been shown to have kinase activity. TRB family members play a role in the differentiation of macrophages, lymphocytes, muscle cells, adipocytes, and osteoblasts. TRB isoforms also coordinate a number of critical cellular processes including glucose and lipid metabolism, inflammation, cellular stress, survival, apoptosis, and tumorigenesis. TRB family members modulate multiple complex signaling networks including mitogen activated protein kinase cascades, protein kinase B/AKT signaling, mammalian target of rapamycin, and inflammatory pathways. The following review will discuss metazoan homologs of Drosophila tribbles, their structure, expression patterns, and functions. In particular, we will focus on TRB3 function in the kidney in podocytes. This review will also discuss the key signaling pathways with which tribbles proteins interact and provide a rationale for developing novel therapeutics that exploit these interactions to provide better treatment options for both acute and chronic kidney disease.

Fibrates: therapeutic potential for diabetic nephropathy?

Despite intensive glucose-lowering treatment and advanced therapies for cardiovascular risk factors, such as hypertension and dyslipidaemia, diabetes mellitus with its macro- and microvascular complications remains a major health problem. Especially diabetic nephropathy is a leading cause of morbidity and mortality, and its prevalence is increasing. Peroxisome proliferator-activated receptor-α (PPAR-α), a member of a large nuclear receptor superfamily, is expressed in several tissues including the kidney. Recently, experimental data have suggested that PPAR-α activation plays a pivotal role in the regulation of fatty acid oxidation, lipid metabolism, inflammatory and vascular responses, and might regulate various metabolic and intracellular signalling pathways that lead to diabetic microvascular complications. This review examines the role of PPAR-α activation in diabetic nephropathy and summarises data from experimental and clinical studies on the emerging therapeutic potential of fibrates in diabetic nephropathy.

Evaluation of the incidence and risk factors for development of fenofibrate-associated nephrotoxicity

BACKGROUND

Fenofibrate-associated nephrotoxicity has been described in two randomized controlled trials and several observational studies. However, little is known regarding its incidence and the population(s) at risk.

OBJECTIVE

This study aims to quantify the incidence and identify potential risk factors for development of nephrotoxicity in patients receiving fenofibrate.

METHODS

A retrospective, observational study was conducted in the South Texas Veterans Health Care System. Data were collected regarding baseline demographics, concurrent medical conditions, medications, laboratory results, and fenofibrate use.

RESULTS

Within 6 months after initiation of fenofibrate in 428 patients, 115 (27%) experienced an increase in serum creatinine of ≥ 0.3 mg/dL. Any renal disease (P = .001), chronic kidney disease (P = .01), and diabetes (P = .02) were significantly more prevalent in patients with fenofibrate-associated nephrotoxicity. Patients with nephrotoxicity had significantly greater serum creatinine (1.2 [SD 0.3] vs. 1.1 mg/dL [SD 0.3], P = .0002) and lower estimated glomerular filtration rate (72 [SD 20] vs 81 mL/min/1.73 m² [SD 20], P < .0001) at baseline. These patients also had greater use of calcium channel blockers (P = .0003), furosemide (P = .02), and angiotensin-converting enzyme inhibitors (P = .02). The incidence of nephrotoxicity was significantly greater in patients initiated on high-dose versus those on low-dose fenofibrate (P = .002). In a multivariable regression model, renal disease (P = .02), high-dose fenofibrate (P = .001), and dihydropyridine calcium channel blocker use (P = .02) were determined to be independent predictors of development of increased serum creatinine on fenofibrate.

CONCLUSION

This observational study suggests fenofibrate-associated nephrotoxicity occurs more frequently than previously reported, particularly in patients with renal disease and in those receiving high-dose fenofibrate or concomitant calcium channel blockers.

Can drug screening lead to candidate therapies for testing in diabetic neuropathy?

A key mechanism of dorsal root ganglia (DRG) neuron injury in high glucose is mitochondrial overload leading to oxidative stress. We screened selected compounds for the ability to prevent hyperglycemia-induced mitochondrial superoxide in primary sensory DRG neurons. Twenty five out of 1,040 compounds decreased both mitochondrial superoxide and subsequent neuronal injury. These data both validate our screening strategy and indicate further mechanistic evaluation of drug hits and related compounds. Such studies may lead to the design of rational therapeutic approaches for this severe complication of diabetes.

Diabetes and the endothelium

Abnormal endothelial function plays a pivota role in the pathogenesis of diabetic complications. Due to lack of autoregulation of glucose transport in the presence of high extracellular glucose concentrations, intracellular hyperglycaemia induces a series of metabolic changes that ultimately lead to the genesis of both microvascular complications (the hallmark of chronic hyperglycaemic states) and macrovascular damage. In type 2 diabetes, the abnormalities associated with insulin resistance and the metabolic syndrome phenotype (such as high blood pressure, dyslipidaemia, abnormal levels of circulating adipokines and free fatty acids e.g.) also contribute to accelerate the endothelial damage sustained as a result of chronic exposure to hyperglycaemia. Only recently was a unifying theory proposed to account for the four major abnormal pathways activated by chronic hyperglycaemia and thought to damage the endothelial cell and to trigger the downstream micro- and macrovascular complications associated with diabetes mellitus. This pathophysiological sequence revolves around the metabolic abnormalities triggered as a result of overproduction of superoxide by the mitochondrial electron transport chain and subsequent inhibition of the key glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase by increased activity of nuclear poly(ADP-ribose)polymerase.

New Potential Agents in Treating Diabetic Kidney Disease

Despite the worldwide epidemic of chronic kidney disease complicating diabetes mellitus, current therapies directed against nephroprogression are limited to angiotensin conversion or receptor blockade. Nonetheless, additional therapeutic possibilities are slowly emerging. The diversity of therapies currently in development reflects the pathogenic complexity of diabetic nephropathy. The three most important candidate drugs currently in development include a glycosaminoglycan, a protein kinase C (PKC) inhibitor and an inhibitor of advanced glycation. In targeting primary mechanisms by which hyperglycaemia contributes to diabetic complications, these drugs could provide risk reduction complementary to the partial reduction proven for ACE inhibitors and angiotensin II receptor antagonists (angiotensin receptor blockers). Glycosaminoglycans act to restore glycoproteins present in reduced amounts in the glomerular basement membrane and mesangium of diabetic animal models. Components of the drug sulodexide prevent pathological changes and proteinuria in diabetic rats. Reductions in albuminuria, a hallmark of early diabetic kidney disease, have been reported in initial human trials. In the US, a multicentre phase II study has been completed, with an interim analysis indicating reduction in urinary albumin losses. Pivotal phase II trials have begun in patients with type 2 diabetes. A second metabolic pathway of diabetic complications is overexpression of PKC. Several activators of this family of intracellular kinases have been identified and PKC activation may result in tissue damage through a variety of mechanisms. In animal models, the inhibitor ruboxistaurin reduces albuminuria, diabetic histological changes and kidney injury. Like sulodexide, drug development of ruboxistaurin has reached completion of a phase II evaluation with mixed results. The third metabolic target is the nonenzymatic formulation of advanced glycation end-products (AGEs) through well described biochemical pathways. Multiple pathways lead to AGE accumulation in tissues in diabetes and diverse AGE products are formed. AGE deposition has been implicated in animal models of diabetic nephropathy. The leading AGE inhibitor currently in development is pyridoxamine, which has multiple actions that inhibit glycation. Pyridoxamine is an efficient AGE inhibitor in experimental diabetes. A phase II study in diabetic patients with nephropathy reported mixed efficacy results and a favourable safety profile. Phase III evaluation of pyridoxamine has not begun. These three classes of potential therapies, if successfully developed, will confirm that diabetic kidney disease has entered the era of biochemical treatments.