The renoprotective actions of peroxisome proliferator-activated receptors agonists in diabetes

A review on the phytochemistry and pharmacology of the herb Scoparia dulcis L. for the potential treatment of metabolic syndrome

This review discusses the chemical constituents and pharmacological effects of Scoparia dulcis L. (S. dulcis) plants. So far, approximately 160 compounds have been identified from S. dulcis, among which 115 compounds may be related to the treatment of metabolic syndrome. Extracts of S. dulcis have effects of reducing fasting blood glucose level, increasing the plasma insulin level, and stimulating insulin secretion to treat diabetes. They also produce antihyperlipidemic effects by increasing serum high-density lipoprotein levels, the anti-atherogenic index of plasma, and HMG-CoA reductase activity. The chemical composition of glutinol and glutinone, isolated from S. dulcis, provide potential anti-inflammatory effects. These compounds can also reduce total cholesterol, triacylglycerol, and low-density lipoprotein (LDL)-cholesterol and increase high-density lipoprotein (HDL)-cholesterol to provide the anti-atherosclerotic effect. S. dulcis exerts anti-arthritic properties through its effect on cytokine levels, significantly reducing IFN-γ and IL-6 levels and elevating IL-10 levels. The extracts carry out hepatoprotective effect by preventing the descent of the antioxidative enzymes of superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GRd), and glutathione-S-transferase (GST). Therefore, S. dulcis provides new potential for medicine given its numerous therapeutic properties and can be promoted as a complementary or alternative therapy for patients with chronic conditions.

This review discusses the chemical constituents and pharmacological effects of S. dulcis plants. S. dulcis provides new potential for medicine and can be promoted as a complementary or alternative therapy for patients with chronic conditions.

Association between PPARγrs1801282 polymorphism with diabetic nephropathy and type-2 diabetes mellitus susceptibility in south India and a meta-analysis

BACKGROUND

Diabetic Nephropathy (DN) is a major complication of Type 2 Diabetes Mellitus (T2DM) with high morbidity rates worldwide.

OBJECTIVE

To determine the association of PPARγ rs1801282 polymorphism in T2DM and DN in south Indian population.

METHODS

We have conducted a case-control study to test the association of rs1801282 polymorphism with T2DM and DN in 424 subjects (DN=128; T2DM=148 and controls=148) belonging to the south Indian population using ARMS-PCR and Sanger sequencing method. Further, a meta-analysis was performed for rs1801282 polymorphism from the published literature retrieved from various electronic databases to determine the susceptibility among T2DM and DN across various ethnic populations under five genetic models.

RESULTS

The genotyping of rs1801282 polymorphism showed significant (p-value<0.05) association with DN and T2DM compared to controls. In the meta-analysis, no significant association (p-value>0.05) was noticed for rs1801282 with DN vs. controls in homozygote, heterozygote, allelic, recessive and dominant genetic models. However, a significant association was observed between rs1801282 SNP and T2DM under heterozygote (Jj vs JJ) genetic model with OR=0.56, (95%CI [0.43-0.74]), p≤0.0001 of Asian and Caucasian populations.

CONCLUSION

Overall analysis suggests that the rs1801282 polymorphism might be associated with DN and T2DM. More case-control studies on the PPARγ gene with a larger sample size including all the confounding factors are required to corroborate the findings from this meta-analysis.

Association between PPARγrs1801282 polymorphism with diabetic nephropathy and type-2 diabetes mellitus susceptibility in south India and a meta-analysis

BACKGROUND

Diabetic Nephropathy (DN) is a major complication of Type 2 Diabetes Mellitus (T2DM) with high morbidity rates worldwide.

OBJECTIVE

To determine the association of PPARγ rs1801282 polymorphism in T2DM and DN in south Indian population.

METHODS

We have conducted a case-control study to test the association of rs1801282 polymorphism with T2DM and DN in 424 subjects (DN=128; T2DM=148 and controls=148) belonging to the south Indian population using ARMS-PCR and Sanger sequencing method. Further, a meta-analysis was performed for rs1801282 polymorphism from the published literature retrieved from various electronic databases to determine the susceptibility among T2DM and DN across various ethnic populations under five genetic models.

RESULTS

The genotyping of rs1801282 polymorphism showed significant (p-value<0.05) association with DN and T2DM compared to controls. In the meta-analysis, no significant association (p-value>0.05) was noticed for rs1801282 with DN vs. controls in homozygote, heterozygote, allelic, recessive and dominant genetic models. However, a significant association was observed between rs1801282 SNP and T2DM under heterozygote (Jj vs JJ) genetic model with OR=0.56, (95%CI [0.43-0.74]), p≤0.0001 of Asian and Caucasian populations.

CONCLUSION

Overall analysis suggests that the rs1801282 polymorphism might be associated with DN and T2DM. More case-control studies on the PPARγ gene with a larger sample size including all the confounding factors are required to corroborate the findings from this meta-analysis.

Augmentation of cadmium-induced oxidative cytotoxicity by pioglitazone in renal tubular epithelial cells

The aim of this study was to examine whether a peroxisome proliferator-activated receptor (PPAR)-γ agonist could affect cadmium (Cd)-induced cytotoxicity via the increased expression of megalin, one of the uptake pathways, using renal epithelial LLC-PK1 cells. The treatment with 1 µM Cd for 24 h was not cytotoxic; however, when the cells were pretreated with 0.1 µM pioglitazone for 12 h and then exposed to 1 µM Cd for 24 h, significant accumulation of Cd and cytotoxicity were detected, with an increase in megalin mRNA expression. In addition, pretreatment with pioglitazone significantly increased the Cd-induced generation of hydrogen peroxide and cell apoptosis. The augmented Cd-induced cytotoxicity and apoptosis on preincubation with pioglitazone were inhibited by prior treatment with GW 9662 (PPAR-γ antagonist). These findings suggest that a PPAR-γ agonist could augment Cd-induced oxidative injury and cell apoptosis, possibly dependent on the expression level of the uptake pathway.

Maintenance of Kidney Metabolic Homeostasis by PPAR Gamma

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that control the transcription of specific genes by binding to regulatory DNA sequences. Among the three subtypes of PPARs, PPARγ modulates a broad range of physiopathological processes, including lipid metabolism, insulin sensitization, cellular differentiation, and cancer. Although predominantly expressed in adipose tissue, PPARγ expression is also found in different regions of the kidney and, upon activation, can redirect metabolism. Recent studies have highlighted important roles for PPARγ in kidney metabolism, such as lipid and glucose metabolism and renal mineral control. PPARγ is also implicated in the renin-angiotensin-aldosterone system and, consequently, in the control of systemic blood pressure. Accordingly, synthetic agonists of PPARγ have reno-protective effects both in diabetic and nondiabetic patients. This review focuses on the role of PPARγ in renal metabolism as a likely key factor in the maintenance of systemic homeostasis.

Overexpression of heart-type fatty acid binding protein enhances fatty acid-induced podocyte injury

Deregulated lipid metabolism is a characteristic of metabolic diseases including type 2 diabetes and obesity, and likely contributes to podocyte injury and end-stage kidney disease. Heart-type fatty acid binding protein (H-FABP) was reported to be associated with lipid metabolism. The present study investigated whether H-FABP contributes to podocyte homeostasis. Podocytes were transfected by lentiviral vector to construct a cell line which stably overexpressed H-FABP. Small interfering RNA capable of effectively silencing H-FABP was introduced into podocytes to construct a cell line with H-FABP knockdown. Certain groups were treated with palmitic acid (PA) and the fat metabolism, as well as inflammatory and oxidative stress markers were measured. PA accelerated lipid metabolism derangement, inflammatory reaction and oxidative stress in podocytes. Overexpression of H-FABP enhanced the PA-induced disequilibrium in podocytes. The mRNA and protein expression levels of acyl-coenzyme A oxidase 3 and monocyte chemotactic protein 1, and the protein expression levels of 8-hydroxy-2'-deoxyguanosine and 4-hydroxynonenal were upregulated in the H-FABP overexpression group, while the mRNA and protein expression of peroxisome proliferator activated receptor α was downregulated. Knockdown of H-FABP inhibited the PA-induced injury and lipid metabolism derangement, as well as the inflammatory reaction and oxidative stress in podocytes. These results indicated that overexpression of H-FABP enhances fatty acid-induced podocyte injury, while H-FABP inhibition may represent a potential therapeutic strategy for the prevention of lipid metabolism-associated podocyte injury.

Antidiabetic Properties, Bioactive Constituents, and Other Therapeutic Effects of Scoparia dulcis

This review discusses the antidiabetic activities of Scoparia dulcis as well as its antioxidant and anti-inflammatory properties in relation to the diabetes and its complications. Ethnomedical applications of the herb have been identified as treatment for jaundice, stomach problems, skin disease, fever, and kidney stones, reproductory issues, and piles. Evidence has been demonstrated through scientific studies as to the antidiabetic effects of crude extracts of S. dulcis as well as its bioactive constituents. The primary mechanisms of action of antidiabetic activity of the plant and its bioactive constituents are through α-glucosidase inhibition, curbing of PPAR-γ and increased secretion of insulin. Scoparic acid A, scoparic acid D, scutellarein, apigenin, luteolin, coixol, and glutinol are some of the compounds which have been identified as responsible for these mechanisms of action. S. dulcis has also been shown to exhibit analgesic, antimalarial, hepatoprotective, sedative, hypnotic, antiulcer, antisickling, and antimicrobial activities. Given this evidence, it may be concluded that S. dulcis could be promoted among the masses as an alternative and complementary therapy for diabetes, provided further scientific studies on the toxicological and pharmacological aspects are carried out through either in vivo or clinical means.

Effects of combination PPARγ agonist and angiotensin receptor blocker on glomerulosclerosis

We previously observed that high-dose angiotensin receptor blocker (ARB) can induce regression of existing glomerulosclerosis. We also found that proliferator-activated recepto-γ (PPARγ) agonist can attenuate glomerulosclerosis in a nondiabetic model of kidney disease, with specific protection of podocytes. We now assessed effects of combination therapy with ARB and pioglitazone on established glomerulosclerosis. Sprague-Dawley male rats underwent 5/6 nephrectomy (5/6 Nx) at week 0 and renal biopsy at week 8. Rats were randomized to groups with equal starting moderate glomerulosclerosis, and treated with ARB, PPARγ agonist (pioglitazone), combination or vehicle from weeks 8 to 12. Body weight, systolic blood pressure (SBP), and urinary protein (UP) were measured at intervals. In rats with established sclerosis, SBP, UP, and GS were equal in all groups at week 8 before treatment by study design. Untreated control rats had hypertension, decreased GFR, and progressive proteinuria and glomerulosclerosis at week 12. Only combination therapy significantly ameliorated hypertension and proteinuria. ARB alone or pioglitazone alone had only numerically lower SBP and UP than vehicle at week 12. Both pioglitazone alone and combination had significantly less decline in GFR than vehicle. Combination-induced regression of glomerulosclerosis in more rats from weeks 8 to 12 than ARB or pioglitazone alone. In parallel, combination treatment reduced plasminogen activator inhibitor-1 expression and macrophage infiltration, and preserved podocytes compared with vehicle. These results were linked to increased AT2 receptor and Mas1 mRNA in the combination group. PPARγ agonists in combination with ARB augment regression of glomerulosclerosis, with downregulation of injurious RAAS components vs PPARγ alone, with increased anti-fibrotic/healing RAAS components, enhanced podocyte preservation, and decreased inflammation and profibrotic mechanisms.

Sodium Intake Regulates Glucose Homeostasis through the PPARδ/Adiponectin-Mediated SGLT2 Pathway

High sodium intake is a major risk factor for developing hypertension in diabetes. Promotion of sodium excretion reduces cardiometabolic lesions in diabetes. However, the interaction between sodium intake and glucose homeostasis remains elusive. Here, we report that high sodium intake remarkably increased natriuresis in wild-type mice, but this effect was blunted in adipose-specific PPARδ knockout mice and diabetic mice. PPARδ activation in perirenal fat by agonist or high sodium intake inhibited renal sodium-glucose cotransporter 2 (SGLT2) function, which is mediated by increased production of adipose adiponectin. In addition, high salt intake-induced natriuresis was impaired in diabetic states because of renal SGLT2 dysfunction. Type 2 diabetic patients with uncontrolled hyperglycemia had less natriuresis that was correlated to their plasma adiponectin levels. Our findings provide insights into the distinctive role of the PPARδ/adiponectin/SGLT2 pathway in the regulation of sodium and glucose homeostasis.

ACE2, angiotensin-(1-7) and Mas receptor axis in inflammation and fibrosis

Recent advances have improved our understanding of the renin-angiotensin system (RAS). These have included the recognition that angiotensin (Ang)-(1-7) is a biologically active product of the RAS cascade. The identification of the ACE homologue ACE2, which forms Ang-(1-7) from Ang II, and the GPCR Mas as an Ang-(1-7) receptor have provided the necessary biochemical and molecular background and tools to study the biological significance of Ang-(1-7). Most available evidence supports a counter-regulatory role for Ang-(1-7) by opposing many actions of Ang II on AT₁ receptors, especially vasoconstriction and proliferation. Many studies have now shown that Ang-(1-7) by acting via Mas receptor exerts inhibitory effects on inflammation and on vascular and cellular growth mechanisms. Ang-(1-7) has also been shown to reduce key signalling pathways and molecules thought to be relevant for fibrogenesis. Here, we review recent findings related to the function of the ACE2/Ang-(1-7)/Mas axis and focus on the role of this axis in modifying processes associated with acute and chronic inflammation, including leukocyte influx, fibrogenesis and proliferation of certain cell types. More attention will be given to the involvement of the ACE2/Ang-(1-7)/Mas axis in the context of renal disease because of the known relevance of the RAS for the function of this organ and for the regulation of kidney inflammation and fibrosis. Taken together, this knowledge may help in paving the way for the development of novel treatments for chronic inflammatory and renal diseases.

Bioactive diterpenoids and flavonoids from the aerial parts of Scoparia dulcis

Six new diterpenoids, 4-epi-7α-O-acetylscoparic acid A (1), 7α-hydroxyscopadiol (2), 7α-O-acetyl-8,17β-epoxyscoparic acid A (3), neo-dulcinol (4), dulcinodal-13-one (5), and 4-epi-7α-hydroxydulcinodal-13-one (6), and a new flavonoid, dillenetin 3-O-(6″-O-p-coumaroyl)-β-D-glucopyranoside (10), along with 12 known compounds, were isolated from the aerial parts of Scoparia dulcis. The 7S absolute configuration of the new diterpenoids 1-4 and 6 was deduced by comparing their NOESY spectra with that of a known compound, (7S)-4-epi-7-hydroxyscoparic acid A (7), which was determined by the modified Mosher's method. The flavonoids scutellarein (11), hispidulin (12), apigenin (15), and luteolin (16) and the terpenoids 4-epi-scopadulcic acid B (9) and betulinic acid (19) showed more potent α-glucosidase inhibitory effects (with IC50 values in the range 13.7-132.5 μM) than the positive control, acarbose. In addition, compounds 1, 11, 12, 15, 16, and acerosin (17) exhibited peroxisome proliferator-activated receptor gamma (PPAR-γ) agonistic activity, with EC50 values ranging from 0.9 to 24.9 μM.

Does combined peroxisome proliferator-activated receptors-agonist and pravastatin therapy attenuate the onset of diabetes-induced experimental nephropathy?

OBJECTIVES

To investigate the combined effects of rosiglitazone and pravastatin on renal functions in early streptozotocin induced diabetic nephropathy (DN).

METHODS

This study was carried out at King Khalid University Hospital Animal House, Riyadh, Saudi Arabia from August 2013 to February 2014. Fifty male Wistar rats were assigned to normal control rats and diabetic rats that received saline, rosiglitazone, pravastatin, or rosiglitazone+pravastatin for 2 months. Their weight range was 230-250 gm, and age range was from 18-20 weeks. At the end of experiment, creatinine clearance, and urinary albumin to creatinine ratio (ACR) were measured. Blood samples were analyzed for transferrin, glycosylated hemoglobin (HbA1c), lipid profile, tumor necrosis factor-alpha (TNF-α), intercellular adhesion molecule-1 (ICAM-1), and lipid peroxide.

RESULTS

Rosiglitazone treatment increased creatinine clearance and plasma transferrin, and decreased urinary ACR, HbA1c, plasma TNF-α, ICAM-1, and serum lipid peroxide levels without affecting the altered lipid profile. Pravastatin treatment produced similar results and normalized the lipid alteration. The combination of rosiglitazone and pravastatin was more effective in attenuating the diabetes-induced nephropathy compared with treatment with either drug alone.

CONCLUSION

The combination strategy of rosiglitazone and pravastatin may provide a potential synergistic renoprotective effect against DN by improving renal functions and reducing indices of DN. 

Diabetic nephropathy: diagnosis and treatment

Nephropathy remains a major cause of morbidity and a key determinant of mortality in patients with type 1 or type 2 diabetes mellitus. Research is ongoing to identify biomarkers that in addition to albuminuria and glomerular filtration rate assist in the prediction and monitoring of renal disease in diabetes mellitus. Current strategies to treat this condition focus on intensification of glycaemic control and excellent control of blood pressure using regimens based on blockade of the renin-angiotensin system. Other approaches to control blood pressure and afford renoprotection are under active clinical investigation, including renal denervation and endothelin receptor antagonism. With increasing understanding of the underlying pathophysiological processes implicated in diabetic nephropathy, new specific renoprotective treatment strategies are anticipated to become available over the next few years.

Peroxisome proliferator-activated receptor δ agonist, HPP593, prevents renal necrosis under chronic ischemia

The Goldblatt’s 2 kidney 1 clip (2K1C) rat animal model of renovascular hypertension is characterized by ischemic nephropathy of the clipped kidney. 2K1C rats were treated with a specific peroxisome proliferator-activated receptor δ (PPARδ) agonist, HPP593. Clipped kidneys from untreated rats developed tubular and glomerular necrosis and massive interstitial, periglomerular and perivascular fibrosis. HPP593 kidneys did not exhibit any histochemical features of necrosis; fibrotic lesions were present only in perivascular areas. Necrosis in the untreated clipped kidneys was associated with an increased oxidative stress, up regulation and mitochondrial translocation of the pro-death protein BNIP3 specifically in tubules. In the kidneys of HPP593-treated rats oxidative stress was attenuated and BNIP3 protein decreased notably in the mitochondrial fraction when compared to untreated animals. In untreated clipped kidneys, mitochondria were dysfunctional as revealed by perturbations in the levels of MCAD, COXIV, TFAM, and Parkin proteins and AMPK activation, while in HPP593-treated rats these proteins remained at the physiological levels. Nuclear amounts of oxidative stress-responsive proteins, NRF1 and NRF2 were below physiological levels in treated kidneys. Mitochondrial biogenesis and autophagy were inhibited similarly in both treated and untreated 2K1C kidneys as indicated by a decrease in PGC1-α and deficiency of the autophagy-essential proteins LC3-II and ATG5. However, HPP593 treatment resulted in increased accumulation of p62 protein, an autophagic substrate and an enhancer of NRF2 activity. Therefore, inhibition of BNIP3 activation by the preservation of mitochondrial function and control of oxidative stress by PPARδ is the most likely mechanism to account for the prevention of necrotic death in the kidney under conditions of persistent ischemia.

Effects of the dual PPAR-α/γ agonist aleglitazar on glycaemic control and organ protection in the Zucker diabetic fatty rat

AIMS

To evaluate the effects of aleglitazar, a dual peroxisome proliferator-activated receptor-α/γ agonist, on the development of diabetes-related organ dysfunction, in relation to glycaemic and lipid changes, in Zucker diabetic fatty (ZDF) rats.

METHODS

Six-week-old, male ZDF rats received aleglitazar 0.3 mg/kg/day or vehicle as food admix for 13 weeks (n = 10 per group). Age-matched male Zucker lean rats served as non-diabetic controls. Plasma and renal markers were measured at several time points. Histopathology and quantitative immunohistochemistry were performed at 13 weeks.

RESULTS

Glycated haemoglobin (5.4 vs. 9.2%) and blood glucose (8.3 ± 0.3 vs. 26.1 ± 1.0 mmol/l) were significantly reduced at 12 weeks with aleglitazar versus vehicle-treated ZDF rats (both p < 0.01), while aleglitazar preserved near-normal plasma insulin levels. Aleglitazar prevented the development of hypertriglyceridaemia (1.4 ± 0.1 vs. 8.5 ± 0.9 mmol/l) and reduced plasma non-esterified fatty acids (0.09 ± 0.02 vs. 0.26 ± 0.04 mmol/l) relative to vehicle-treated animals (both p < 0.01). Urinary glucose and protein concentrations were significantly reduced at 13 weeks with aleglitazar versus vehicle-treated rats (both p < 0.01). Consistent with its effect on glycaemic control, aleglitazar protected β-cell morphology, as evidenced by preservation of islet integrity, and reduction of β-cell apoptosis and islet fibrosis. Aleglitazar prevented renal glomerular hypertrophy, podocyte degeneration, glomerulosclerosis, tubulo-interstitial lesions and development of cataracts.

CONCLUSIONS

Aleglitazar strongly improved glycaemic and lipid parameters while protecting key tissues, including the pancreas, kidneys and eyes, against diabetes-associated structural and functional changes in the ZDF rat.

Examining the safety of PPAR agonists - current trends and future prospects

INTRODUCTION

The peroxisome proliferator-activated receptor (PPAR)-α and -γ agonists, fibrates and glitazones, are effective treatments for dyslipidemia and type 2 diabetes mellitus, respectively, but exhibit class-related, as well as compound-specific safety characteristics.

AREAS COVERED

This article reviews the profiles of PPAR-α, PPAR-γ, and dual PPAR-α/γ agonists with regard to class-related and compound-specific efficacy and adverse effects. We explore how learnings from first-generation drugs are being applied to develop safer PPAR-targeted therapies.

EXPERT OPINION

The finding that rosiglitazone may increase risk for cardiovascular events has led to regulatory guidelines requiring demonstration of cardiovascular safety in appropriate outcome trials for new type 2 diabetes mellitus drugs. The emerging data on the possibly increased risk of bladder cancer with pioglitazone may prompt the need for post-approval safety studies for new drugs. Since PPAR-α and -γ affect key cardiometabolic risk factors (diabetic dyslipidemia, insulin resistance, hyperglycemia, and inflammation) in a complementary fashion, combining their benefits has emerged as a particularly attractive option. New PPAR-targeted therapies that balance the relative potency and/or activity toward PPAR-α and -γ have shown promise in retaining efficacy while reducing potential side effects.