Thiazolidinedione ameliorates renal injury in experimental diabetic rats through anti-inflammatory effects mediated by inhibition of NF-kappaB activation

Nuclear factor κB-dependent anti-inflammatory effects of s-allyl cysteine and s-propyl cysteine in kidney of diabetic mice

Renal protection of s-allyl cysteine (SAC) and s-propyl cysteine (SPC) in diabetic mice against inflammatory injury was examined. Each agent at 0.5 and 1 g/L was added to the drinking water for 10 weeks. SAC or SPC intake significantly reduced the plasma blood urea nitrogen level and increased creatinine clearance (P < 0.05). These treatments significantly lowered the renal level of reactive oxygen species, nitric oxide, interleukin-6, tumor necrosis factor-α, and prostaglandin E(2) in diabetic mice (P < 0.05). Renal mRNA expression of inducible nitric oxide synthase, cyclooxygenase-2, protein kinase C (PKC)-α, PKC-β, and PKC-γ was enhanced in diabetic mice (P < 0.05); however, SAC or SPC treatments dose dependently declined mRNA expression of these factors (P < 0.05). Nuclear factor κB (NF-κB) activity, mRNA expression, and protein production in kidney of diabetic mice were significantly increased (P < 0.05). SAC or SPC intake dose dependently suppressed NF-κB activity, NF-κB p65 mRNA expression, and protein level (P < 0.05). Diabetes also enhanced renal protein expression of mitogen-activated protein kinase (P < 0.05). SAC and SPC, only at a high dose, significantly suppressed protein production of p-p38 and p-ERK1/2 (P < 0.05). Renal mRNA expression and protein generation of peroxisome proliferator-activated receptor (PPAR)-α and PPAR-γ were significantly down-regulated in diabetic mice (P < 0.05), but the intake of SAC or SPC at high dose up-regulated PPAR-α and PPAR-γ (P < 0.05). These findings support that SAC and SPC are potent anti-inflammatory agents against diabetic kidney diseases.

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

Pharmaceutical agonists of peroxisome proliferator-activated receptors (PPARs) are widely used in the management of type 2 diabetes, chiefly as lipid-lowering agents and oral hypoglycaemic agents. Although most of the focus has been placed on their cardiovascular effects, both positive and negative, these agents also have significant renoprotective actions in the diabetic kidney. Over and above action on metabolic control and effects on blood pressure, PPAR agonists also appear to have independent effects on a number of critical pathways that are implicated in the development and progression of diabetic kidney disease, including oxidative stress, inflammation, hypertrophy, and podocyte function. This review will examine these direct and indirect actions of PPAR agonists in the diabetic kidney and explore recent findings of clinical trials of PPAR agonists in patients with diabetes.

The effects of rosiglitazone on osteoblastic differentiation, osteoclast formation and bone resorption

Rosiglitazone has the potential to activate peroxisome proliferator-activated receptor-γ (PPARγ), which in turn can affect bone formation and resorption. However, the mechanisms by which rosiglitazone regulates osteoclastic orosteoblastic differentiation are not fully understood. This study examines how rosiglitazone affects osteoclast formation, bone resorption and osteoblast differentiation from mouse bone marrow. Rosiglitazone treatment not only inhibited the formation of tartrate-resistant acid phosphatase-positive cells, but also prevented pit formation by bone marrow cells in a dose- and time-dependent manner. Rosiglitazone also suppressed the receptor activator of nuclear factor (NF)-κB ligand (RANKL) receptor(RANK) expression but increased PPARγ2 expression in the cells. In addition, rosiglitazone diminished RANKL induced activation of NF-κB-DNA binding by blocking IκBαphosphorylation. Furthermore, it reduced collagen and osteocalcin levels to nearly zero and prevented mRNA expression of osteoblast-specific proteins including runtrelated transcription factor-2, osteocalcin, and type I collagen.However, mRNA levels of adipocyte-specific marker, aP2, were markedly increased in the cells co-incubated with rosiglitazone. These results suggest that PPARγ activation by rosiglitazone inhibits osteoblast differentiation with increased adipogenesis in bone marrow cells and also may prevent osteoclast formation and bone resorptionin the cells.

The effects of anti-inflammatory and anti-angiogenic DNA vaccination on diabetic nephropathy in rats

Inflammation and angiogenesis play a crucial role in the pathomechanism of diabetic nephropathy. Monocyte chemoattractant protein 1 (MCP) is a key regulator of the immune system in kidneys, and its inhibition with a dominant-negative mutant lacking the N-terminal amino acids 2-8 (7ND) reduces renal fibrosis. Angiomotin (Amot) is a novel angiogenesis modulator. We studied the effects of inhibition of Amot and MCP using DNA vaccination on incipient diabetic nephropathy in rats. Plasmid DNA (with either 7ND or human Amot) was electroporated twice into hind-limb muscles of rats with streptozotocin-induced diabetes mellitus. Sham-electroporated diabetic rats and healthy animals served as controls. After 4 months, renal histology and biochemical analyses were performed. In sham-electroporated diabetic rats, glomerular histology revealed pathological changes. 7ND and Amot treatments reduced glomerular hypertrophy and periodic acid-Schiff positivity. In both treated groups, the expression of profibrotic (transforming growth factor-β, collagen 1), proinflammatory (interleukin-6, tumor necrosis factor-α), and proangiogenic (vascular endothelial growth factor) genes in the renal cortex was lower than in the diabetic group without treatment. The mentioned renoprotective effects could be mediated via higher total antioxidant capacity and improved glycemic control. Anti-angiogenic and anti-inflammatory DNA vaccination ameliorates the progression of glomerular pathology in an animal model of diabetic nephropathy.

Losartan and pioglitazone ameliorate nephropathy in experimental metabolic syndrome rats

It is well known that metabolic syndrome (MS) is a risk factor for proteinuria and chronic kidney disease. Losartan (angiotensin II receptor blocker, ARB) and pioglitazone (peroxisome proliferator-activated receptor-γ, PPARγ agonist) have been shown to confer renoprotection. However, to date, whether or not an ARB and a PPARγ agonist have synergistic renoprotective effects remains controversial. Thus, the present study was designed to evaluate a combined treatment with losartan and pioglitazone in Sprague-Dawley rats fed with a high-fat, high-salt (HFS) diet and 20% sucrose solution for 16 weeks, an animal model of MS accompanying with renal lesions. Losartan, pioglitazone, and their combination were orally administered in the MS rats from 8 weeks to the end of this study. At 16 weeks, the MS rats showed the elevation in systolic blood pressure (SBP), urinary albumin excretion (UAE), and glomerulosclerosis (GS) score, but creatinine clearance, urinary protein excretion, and score of tubulointerstitial damage were not affected. Renal vascular endothelial growth factor (VEGF) protein level, mRNA and protein expression, which were respectively measured by enzyme-linked immunosorbent assay (ELISA), reverse transcription-polymerase chain reaction (RT-PCR), and Western blot analysis, were obviously decreased in the MS rats. Treatment with the combination of losartan and pioglitazone provided synergistic effects in reducing the SBP, UAE, and GS score when compared with monotherapy. These effects were not associated with ameliorated the downregulation of renal VEGF expression. Our data suggest that combined treatment with losartan and pioglitazone may offer additional advantages in treating MS nephropathy.

Renal epidermal growth factor receptor: its role in sodium and water homeostasis in diabetic nephropathy

1. Volume expansion is observed in animal and human models of diabetic nephropathy, which is in a large part a result of disordered renal tubular cell sodium and water transport. 2. Sodium transport in the proximal tubule is increased in diabetes mellitus as a result of enhanced activity of the sodium-hydrogen exchanger-3 (NHE3), the key transporter for transcellular reabsorption of sodium. Transactivation of the epidermal growth factor receptor (EGFR) by factors inherent in the milieu of diabetes mellitus increases serum glucocorticoid regulated kinase-1 (Sgk1), a key regulator of NHE3. 3. Enhanced sodium and water reabsorption, occurring as a consequence of endogenous or pharmacological stimulation of the peroxisome proliferator-activated receptor gamma is Sgk1 mediated. 4. EGFR inhibitors, which are currently used clinically to treat malignancies, might have potential in attenuating the cellular mechanisms responsible for thiazolidinedione (TZD)-mediated sodium and water transport in diabetes. 5. In the present review, the authors focus on the importance of the EGFR in sodium and water uptake in the proximal tubule in the environment of pathophysiological and pharmacological influences.

Curcumin ameliorates macrophage infiltration by inhibiting NF-κB activation and proinflammatory cytokines in streptozotocin induced-diabetic nephropathy

Background

Chronic inflammation plays an important role in the progression of diabetic nephropathy (DN) and that the infiltration of macrophages in glomerulus has been implicated in the development of glomerular injury. We hypothesized that the plant polyphenolic compound curcumin, which is known to exert potent anti-inflammatory effect, would ameliorate macrophage infiltration in streptozotocin (STZ)-induced diabetic rats.

Methods

Diabetes was induced with STZ (55 mg/kg) by intraperitoneal injection in rats. Three weeks after STZ injection, rats were divided into three groups, namely, control, diabetic, and diabetic treated with curcumin at 100 mg/kg/day, p.o., for 8 weeks. The rats were sacrificed 11 weeks after induction of diabetes. The excised kidney was used to assess macrophage infiltration and expression of various inflammatory markers.

Results

At 11 weeks after STZ injection, diabetic rats exhibited renal dysfunction, as evidenced by reduced creatinine clearance, increased blood glucose, blood urea nitrogen and proteinuria, along with marked reduction in the body weight. All of these abnormalities were significantly reversed by curcumin. Hyperglycemia induced the degradation of IκBα and NF-κB activation and as a result increased infiltration of macrophages (52%) as well as increased proinflammatory cytokines: TNF-α and IL-1β. Curcumin treatment significantly reduced macrophage infiltration in the kidneys of diabetic rats, suppressed the expression of above proinflammatory cytokines and degradation of IκBα. In addition, curcumin treatment also markedly decreased ICAM-1, MCP-1 and TGF-β₁ protein expression. Moreover, at nuclear level curcumin inhibited the NF-κB activity.

Conclusion

Our results suggested that curcumin treatment protect against the development of DN in rats by reducing macrophage infiltration through the inhibition of NF-κB activation in STZ-induced diabetic rats.

Glucagon-like peptide-1 receptor agonist ameliorates renal injury through its anti-inflammatory action without lowering blood glucose level in a rat model of type 1 diabetes

AIMS/HYPOTHESIS

Glucagon-like peptide-1 (GLP-1) has various extra-pancreatic actions, in addition to its enhancement of insulin secretion from pancreatic beta cells. The GLP-1 receptor is produced in kidney tissue. However, the direct effect of GLP-1 on diabetic nephropathy remains unclear. Here we demonstrate that a GLP-1 receptor agonist, exendin-4, exerts renoprotective effects through its anti-inflammatory action via the GLP-1 receptor without lowering blood glucose.

METHODS

We administered exendin-4 at 10 μg/kg body weight daily for 8 weeks to a streptozotocin-induced rat model of type 1 diabetes and evaluated their urinary albumin excretion, metabolic data, histology and morphometry. We also examined the direct effects of exendin-4 on glomerular endothelial cells and macrophages in vitro.

RESULTS

Exendin-4 ameliorated albuminuria, glomerular hyperfiltration, glomerular hypertrophy and mesangial matrix expansion in the diabetic rats without changing blood pressure or body weight. Exendin-4 also prevented macrophage infiltration, and decreased protein levels of intercellular adhesion molecule-1 (ICAM-1) and type IV collagen, as well as decreasing oxidative stress and nuclear factor-κB activation in kidney tissue. In addition, we found that the GLP-1 receptor was produced on monocytes/macrophages and glomerular endothelial cells. We demonstrated that in vitro exendin-4 acted directly on the GLP-1 receptor, and attenuated release of pro-inflammatory cytokines from macrophages and ICAM-1 production on glomerular endothelial cells.

CONCLUSIONS/INTERPRETATION

These results indicate that GLP-1 receptor agonists may prevent disease progression in the early stage of diabetic nephropathy through direct effects on the GLP-1 receptor in kidney tissue.

The citrus flavonoid hesperidin induces p53 and inhibits NF-κB activation in order to trigger apoptosis in NALM-6 cells: involvement of PPARγ-dependent mechanism

BACKGROUND

Hesperidin, a flavanone present in citrus fruits, has been identified as a potent anticancer agent because of its proapoptotic and antiproliferative characteristics in some tumor cells. However, the precise mechanisms of action are not entirely understood.

AIM

The main purpose of this study is to investigate the involvement of peroxisome proliferator-activated receptor-gamma (PPARγ) in hesperidin's anticancer actions in human pre-B NALM-6 cells, which expresses wild-type p53.

METHODS

The effects of hesperidin on cell-cycle distribution, proliferation, and caspase-mediated apoptosis were examined in NALM-6 cells in the presence or absence of GW9662. The expression of peroxisome proliferator-activated receptor-gamma (PPARγ), p53, phospho-IκB, Bcl-2, Bax, and XIAP proteins were focused on using the immunoblotting assay. The transcriptional activities of PPARγ and nuclear factor-kappaB (NF-κB) were analyzed by the transcription factor assay kits. The expression of PPARγ and p53 was analyzed using the RT-PCR method.

RESULTS

Hesperidin induced the expression and transcriptional activity of PPARγ and promoted p53 accumulation and downregulated constitutive NF-κB activity in a PPARγ-dependent and PPARγ-independent manner. The growth-inhibitory effect of hesperidin was partially reduced when the cells preincubated with PPARγ antagonist prior to the exposure to hesperidin.

CONCLUSIONS

The findings of this study clearly demonstrate that hesperidin-mediated proapoptotic and antiproliferative actions are regulated via both PPARγ-dependent and PPARγ-independent pathways in NALM-6 cells. These data provide the first evidence that hesperidin could be developed as an agent against hematopoietic malignancies.

PPARγ and chronic kidney disease

Peroxisome proliferator-activated receptor-γ (PPARγ) agonists, exemplified by the thiazolidinediones (TZDs), have been used extensively for their beneficial effects to improve insulin sensitivity and lipid metabolism in type 2 diabetic patients. PPARγ receptors are part of the steroid hormone nuclear receptor family and, when activated by agonist binding, can affect numerous target genes expressing PPAR response elements. Results from experimental studies and a limited number of studies in humans suggest that PPARγ agonists have manifold effects beyond those on dysmetabolic syndrome. These potentially beneficial actions are mediated via renal parenchymal and infiltrating cells and modulate fibrotic, inflammatory, immune, proliferative, reactive oxygen and mitochondrial injury pathways. Thus, the potential benefits of TZDs in chronic kidney disease impact numerous pathogenic pathways. This review will focus on evidence of the effects of TZDs in nondiabetic chronic kidney disease in experimental and human disease settings.

Activation of peroxisome proliferator-activated receptor delta inhibits streptozotocin-induced diabetic nephropathy through anti-inflammatory mechanisms in mice

OBJECTIVE

Activation of the nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR)-δ has been shown to improve insulin resistance, adiposity, and plasma HDL levels. Several studies have reported that activation of PPARδ is atheroprotective; however, the role of PPARδ in renal function remains unclear. Here, we report the renoprotective effects of PPARδ activation in a model of streptozotocin-induced diabetic nephropathy.

RESEARCH DESIGN AND METHODS

Eight-week-old male C57BL/6 mice were divided into three groups: 1) nondiabetic control mice, 2) diabetic mice, and 3) diabetic mice treated with the PPARδ agonist GW0742 (1 mg/kg/day). GW0742 was administered by gavage for 8 weeks after inducing diabetes.

RESULTS

GW0742 decreased urinary albumin excretion without altering blood glucose levels. Macrophage infiltration, mesangial matrix accumulation, and type IV collagen deposition were substantially attenuated by GW0742. The gene expression of inflammatory mediators in the kidney cortex, such as monocyte chemoattractant protein-1 (MCP-1) and osteopontin (OPN), was also suppressed. In vitro studies demonstrated that PPARδ activation increased the expression of anti-inflammatory corepressor B-cell lymphoma-6, which subsequently suppressed MCP-1 and OPN expression.

CONCLUSIONS

These findings uncover a previously unrecognized mechanism for the renoprotective effects of PPARδ agonists and support the concept that PPARδ agonists may offer a novel therapeutic approach for the treatment of diabetic nephropathy.

Renal PPARγ mRNA expression increases with impairment of renal function in patients with chronic kidney disease

AIM

Peroxisome proliferator-activated receptor gamma (PPARγ) is generally accepted as renoprotective factor in type 2 diabetes mellitus, and PPARγ agonists have been reported to reduce albuminuria. However, little is known about renal PPARγ expression in chronic kidney disease, and especially human data are scarce. We hypothesized that renal PPARγ expression is associated with extent of proteinuria, kidney function, histological diagnosis and inflammatory mediators. Therefore, we investigated PPARγ mRNA expression in human kidney biopsies.

METHODS

We quantified PPARγ mRNA as well as the expression of macrophage chemoattractant protein-1, transforming growth factor beta-1 and interleukin-6 in 64 human kidney biopsies from patients with chronic kidney disease and mild-to-marked proteinuria of diverse aetiology. We measured renal function, and macrophage invasion was quantified by CD68 and vascularization by CD34 immunostaining.

RESULTS

PPARγ mRNA expression correlated inversely with renal function. Higher blood pressure levels were associated with higher PPARγ expression levels. PPARγ mRNA expression correlated significantly (P<0.001) with macrophage chemoattractant protein-1 mRNA expression and showed a negative trend with transforming growth factor beta-1 mRNA expression. No differences in PPARγ expression were detected with regard to extent of proteinuria, histological diagnosis, macrophage invasion, interleukin-6 expression, and age or body mass index.

CONCLUSIONS

PPARγ expression increases with loss of renal function and may be an important factor in maintaining normal renal function serving as a key protective mechanism to renal injury.

Additive effect of PPAR-γ agonist and ARB in treatment of experimental IgA nephropathy

Our recent in vitro study demonstrated peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist potentiated the anti-inflammatory effect of angiotensin receptor blocker (ARB) in tubular epithelial cell under milieu mimicking IgA nephropathy (IgAN). Here we studied the therapeutic effect of combining a PPAR-γ agonist, rosiglitazone (Ros), with an ARB, losartan (Los), in experimental IgAN induced in Lewis rats by oral and intravenous immunization with bovine gamma-globulin (BGG). The rats were randomly divided into six groups: control, IgAN, IgAN with unilateral nephrectomy (IgAN/1K), and IgAN/1K receiving Ros, Los, or Ros + Los. Medication was given 1 week after nephrectomy until killing. Rats developing IgAN had hematuria, mesangial hypercellularity with IgA deposition, glomerular damage, and tubulointerstitial infiltration of CD25+ leukocytes accompanied by increased renal expression of TGF-β, AngII receptor subtype-1 (ATR1) and ICAM-1. The renal histopathology, albuminuria, and renal expression of TGF-β, ATR1 and ICAM-1 worsened with unilateral nephrectomy. Ros or Los reduced the renal expression of PCNA, TGF-β, ATR1, and ICAM-1 in IgAN rats with nephrectomy. Despite no difference between rats treated with monotherapy, combined therapy offered additive effect with decreased renal expression of TGF-β, ATR1 and ICAM-1 and attenuation of renal injury. Our animal study suggests combined PPAR-γ agonist and ARB holds promise for future therapy for IgAN.

Hydrochloride pioglitazone decreases urinary cytokines excretion in type 2 diabetes

OBJECTIVE

To observe the effects of hydrochloride pioglitazone on urinary cytokine excretion in type 2 diabetes and to explore its possible reno-protective mechanisms.

DESIGN

Subjects and Methods. Ninety-eight patients with type 2 diabetes and a fasting blood glucose (FBG) levels between 7.0 and 13.0 mm and glycated haemoglobin A1c (HbA1c) ≥ 7.0% were assigned randomly to receive either the pioglitazone (DP group) or a sulphonylurea (DS group). Another 49 healthy individuals were chosen as normal controls (group NC). At the start of the study and after 12 weeks of treatment, urinary cytokines including monocyte chemoattractant protein-1 (MCP-1), transforming growth factor-β1 (TGF-β1) and vascular endothelial growth factor were measured and were expressed as a ratio of urinary creatinine excretion. Urinary albumin/creatinine ratio, FBG and HbA1c were determined at the same time.

RESULTS

The excretion of each urinary cytokine, corrected for urinary creatinine, was significantly increased in both groups of patients with diabetes, compared with normal controls, and after a 12-week treatment were significantly decreased by both therapies but the effect of pioglitazone was statistically greater than with sulphonylureas. Urinary albumin/UCr and both systolic and diastolic blood pressure were decreased significantly by pioglitazone (P < 0.01 or P < 0.05) but not by sulphonylurea treatment (P < 0.05), while there was no significant difference in FBG or HbA1c between two groups. There was a positive correlation between the excretion of cytokines and urinary albumin /UCr (all P < 0.01).

CONCLUSIONS

This study indicates that pioglitazone reduces urinary albumin excretion by a mechanism that is at least partly independent of blood sugar control. The correlation of urinary albumin excretion with improvement in urinary cytokines suggests that this reno-protective effect of piogliazone in diabetes may be related to local reduction in cytokine activity within the kidney.

The roles of Kruppel-like factor 6 and peroxisome proliferator-activated receptor-γ in the regulation of macrophage inflammatory protein-3α at early onset of diabetes

Macrophage inflammatory protein-3 alpha (MIP-3α) is known to be upregulated early in the development of diabetic nephropathy (DN). However, the transcriptional regulation of MIP-3α is unknown. We previously demonstrated that the transcription factors KLF6 and PPAR-γ play key roles in regulating renal fibrotic and inflammatory responses to factors inherent in diabetes mellitus. Hence we determined the role of these transcription factors in regulating MIP-3α expression. HK-2 cells and STZ-induced diabetic rats were used. siRNAs, over-expressing constructs and CHIP promoter binding assays were used to determine the role of KLF6 and PPAR-γ in MIP-3α transcriptional regulation. KLF6 overexpression increased MIP-3α which was inhibited by concurrent exposure to PPAR-γ agonists. PPAR-γ agonists attenuated high glucose-induced MIP-3α secretion. Furthermore, MIP-3α secretion was up-regulated in PPAR-γ silenced cells, suggesting both KLF6 and PPAR-γ antagonistically regulate high glucose-induced MIP-3α secretion. The CHIP promoter binding assay confirmed that PPAR-γ binds to the MIP-3α promoter and negatively regulates MIP-3α expression. PPAR-γ agonists increased the binding activity of the PPAR-γ-MIP-3α promoter. In contrast, promoter binding activity decreased in KLF6 over-expressing cells. PPAR-γ decreased in KLF6 over-expressing cells and increased in KLF6 silenced cells, while PPAR-γ siRNA had no effect on KLF6 expression, suggesting that KLF6 acted upstream of PPAR-γ in the regulation of MIP-3α. In diabetic rats, renal MIP-3α and the macrophage marker ED-1 expression increased, which was inhibited by exposure to PPAR-γ agonists. The recognition of MIP-3α as a significant pathogenic mediator in diabetic nephropathy reaffirms the increasingly recognized role of inflammation in the progression of DN. Targeting pro-inflammatory chemokine MIP-3α and its signaling pathways will provide novel strategy to treat diabetic kidney disease.

Antifibrotic effects of pioglitazone at low doses on the diabetic rat kidney are associated with the improvement of markers of cell turnover, tubular and endothelial integrity, and angiogenesis

BACKGROUND/AIMS

Pioglitazone and other thiazolidinediones are renoprotective in diabetic nephropathy at doses that normalize glycemia, presumably as a consequence of glycemic control. However, low doses of pioglitazone that did not normalize glycemia in rat models of type 2 diabetes prevented tubulointerstitial fibrosis and glomerulosclerosis through counteracting inflammation, oxidative stress, cell cycle arrest, and fibrosis. The current work tested whether this low-dose treatment also reduces other fibrosis and inflammation factors in the diabetic kidney and prevents tubular cell loss, endothelial damage, and abnormal angiogenesis.

METHODS

ZDF fa/fa rats (ZDF) were fed for 4 months chow with 0.001% pioglitazone, and the untreated ZDF and the non-diabetic lean Zucker rats (LZR) received regular chow. Proteinuria, creatinine clearance, blood pressure, and renal quantitative histopathology markers were determined.

RESULTS

Correction of renal function in ZDF by pioglitazone, occurring with a glycemia >250 mg/dl, was accompanied by normalization of the renal levels of connective tissue growth factor and fibronectin (fibrosis), TNF-α, interleukin-6 and MCP-1 (inflammation), megalin (tubular cells), the PCNA/caspase-3 ratio (positive cell turnover), VEGF (abnormal angiogenesis), and the ratio between eNOS and iNOS (endothelial dysfunction).

CONCLUSION

This supports mechanisms for the renoprotective effects of pioglitazone in diabetes additional to glycemic control.

Targeting inflammation-induced obesity and metabolic diseases by curcumin and other nutraceuticals

Extensive research within the past two decades has revealed that obesity, a major risk factor for type 2 diabetes, atherosclerosis, cancer, and other chronic diseases, is a proinflammatory disease. Several spices have been shown to exhibit activity against obesity through antioxidant and anti-inflammatory mechanisms. Among them, curcumin, a yellow pigment derived from the spice turmeric (an essential component of curry powder), has been investigated most extensively as a treatment for obesity and obesity-related metabolic diseases. Curcumin directly interacts with adipocytes, pancreatic cells, hepatic stellate cells, macrophages, and muscle cells. There, it suppresses the proinflammatory transcription factors nuclear factor-kappa B, signal transducer and activators of transcription-3, and Wnt/beta-catenin, and it activates peroxisome proliferator-activated receptor-gamma and Nrf2 cell-signaling pathways, thus leading to the downregulation of adipokines, including tumor necrosis factor, interleukin-6, resistin, leptin, and monocyte chemotactic protein-1, and the upregulation of adiponectin and other gene products. These curcumin-induced alterations reverse insulin resistance, hyperglycemia, hyperlipidemia, and other symptoms linked to obesity. Other structurally homologous nutraceuticals, derived from red chili, cinnamon, cloves, black pepper, and ginger, also exhibit effects against obesity and insulin resistance.

Diabetes and inflammation: fundamental aspects and clinical implications

AIM

The aim of this paper is to provide the fundamental background of the inflammation theory associated with type 2 diabetes, to discuss the clinical consequences of low-grade inflammation, particularly in terms of cardiovascular risk, and to infer some clinical therapeutic strategies deriving from drugs that already exist or are in development.

METHODS

This non-exhaustive work is the result of a Pubmed(®) research, based on requests including the following keywords: diabetes, inflammation, innate immunity, obesity, reticulum endoplasmic stress, cytokines, endothelial dysfunction.

RESULTS

Obesity and type 2 diabetes are linked with a low-grade inflammation state that reflects the activation of innate immunity where metabolic, environmental and genetic factors are implicated. The role of endoplasmic reticulum stress and unfold protein response is underlined. Inflammation markers are predictive for the risk to develop diabetes, and are associated with an increased cardiovascular risk. While lifestyle modifications are followed by an improvement in inflammation markers, treatments inferred from the inflammation theory are of great interest, although quite moderate effects on glycaemic control have been observed with some of them.

CONCLUSION

The development of molecules targeting different inflammatory mechanisms could lead in diabetic patients to improvement of both glycaemia and cardiovascular prognosis.

Additive antifibrotic effects of pioglitazone and candesartan on experimental renal fibrosis in mice

AIM

To examine the additive protective effects of the peroxisome proliferator-activated receptor-gamma agonist pioglitazone (Pio) and the angiotensin II receptor blocker candesartan (Cand) in a murine model of renal fibrosis: mice with unilateral ureteral obstruction (UUO).

METHODS

Mice were randomly assigned into four groups that after UUO received i.p. injections of either Pio (10 mg/kg/day), Cand (1 mg/kg/day), Cand + Pio or vehicle for 10 days. Physiological parameters, the degree of renal fibrosis and molecules related to renal fibrosis were analysed, and sham-operated mice were used as controls.

RESULTS

Total collagen assay showed prominent renal fibrosis in the vehicle-treated mice, significantly attenuated renal fibrosis in the Cand-treated and the Pio-treated mice, and further attenuated renal fibrosis in the (Cand + Pio)-treated mice. Real-time reverse transcription polymerase chain reaction revealed that this attenuation pattern was also evident in the expression of the mRNA for transforming growth factor-beta, collagens I and III, and plasminogen activator inhibitor-1.

CONCLUSION

Pioglitazone and candesartan have additive protective effects on renal fibrosis due to UUO in mice, suggesting that their use in combination would be an effective treatment for chronic kidney disease.

Relationship between oxidative stress and inflammatory cytokines in diabetic nephropathy

The prevalence of diabetes has dramatically increased worldwide due to the vast increase in the obesity rate. Diabetic nephropathy is one of the major complications of type 1 and type 2 diabetes and it is currently the leading cause of end-stage renal disease. Hyperglycemia is the driving force for the development of diabetic nephropathy. It is well known that hyperglycemia increases the production of free radicals resulting in oxidative stress. While increases in oxidative stress have been shown to contribute to the development and progression of diabetic nephropathy, the mechanisms by which this occurs are still being investigated. Historically, diabetes was not thought to be an immune disease; however, there is increasing evidence supporting a role for inflammation in type 1 and type 2 diabetes. Inflammatory cells, cytokines, and profibrotic growth factors including transforming growth factor-β (TGF-β), monocyte chemoattractant protein-1 (MCP-1), connective tissue growth factor (CTGF), tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), interleukin-6 (IL-6), interleukin-18 (IL-18), and cell adhesion molecules (CAMs) have all been implicated in the pathogenesis of diabetic nephropathy via increased vascular inflammation and fibrosis. The stimulus for the increase in inflammation in diabetes is still under investigation; however, reactive oxygen species are a primary candidate. Thus, targeting oxidative stress-inflammatory cytokine signaling could improve therapeutic options for diabetic nephropathy. The current review will focus on understanding the relationship between oxidative stress and inflammatory cytokines in diabetic nephropathy to help elucidate the question of which comes first in the progression of diabetic nephropathy, oxidative stress, or inflammation.

KIOM-79 prevents xylose-induced lens opacity and inhibits TGF-beta2 in human lens epithelial cells cultured under high glucose

AIM OF THE STUDY

To investigate the effects of KIOM-79 in preventing the development of diabetic complications, such as cataracts.

MATERIALS AND METHODS

The inhibitory effects of KIOM-79 were assessed in a model of xylose-induced lens opacity and on changes mediated by high levels of glucose in human lens epithelial (HLE-B3) cells.

RESULTS

In lenses treated with KIOM-79, opacity was significantly improved and glutathione (GSH) was increased compared to controls. In HLE-B3 cells treated with KIOM-79, high glucose-mediated increases in TGF-beta2, alphaB-crystallin, and fibronectin were significantly inhibited in a dose-dependent manner. KIOM-79 decreased the phosphorylation of p-Smad2/3, pp38MAPK, pp44/42, and NF-kappaB signaling in cells grown under high glucose conditions.

CONCLUSION

KIOM-79 is protective against lens opacity and protects HLE-B3 cells from the toxic effects of high glucose. Therefore, KIOM-79 may provide a potential therapeutic approach for preventing diabetic complications, such as cataracts.

Hydrochloride pioglitazone decreases urinary TGF-beta1 excretion in type 2 diabetics

BACKGROUND

Thiazolidinediones (TZDs) exert a number of direct reno-protection beyond its hypoglycaemic effect in type 2 diabetics, which may be partly related to its anti-fibrosis and anti- inflammatory action.

MATERIALS AND METHODS

A total of 98 type 2 diabetics with fasting blood glucose (FBG) between 7.0 and 13.0 mmol L(-1) and glycated haemoglobin A1c (HbA1c) > or = 7.0% were randomly assigned to add pioglitazone (group DP) or sulfonylurea (group DS) for 12 weeks. FBG, HbA1c, serum creatinine (SCr) and blood urea nitrogen (BUN), and urinary TGF-beta1, albumin (UALB) and creatinine (UCr) were determined at the basal and the 12th week.

RESULTS

Fasting blood glucose, HbA1c and urinary TGF-beta1/UCr ratio (UTCR) were obviously decreased in both groups after 12 weeks treatment; UALB/UCr ratio (UACR) decreased obviously in group DP (P < 0.01), while slightly in group DS. UACR and UTCR in group DP were significantly lower than those in group DS after treatment, while FBG and HbA1c had no statistical differences between the two groups. In addition, UTCR had positive correlation with UACR (r = 0.367, P < 0.01).

CONCLUSIONS

Pioglitazone decreases urinary TGF-beta1 excretion in type 2 diabetics, which may be partly contributed to its direct reno-protection.

Homocysteine and Hypertension in Diabetes: Does PPARgamma Have a Regulatory Role?

Dysfunction of macro- and microvessels is a major cause of morbidity and mortality in patients with cardio-renovascular diseases such as atherosclerosis, hypertension, and diabetes. Renal failure and impairment of renal function due to vasoconstriction of the glomerular arteriole in diabetic nephropathy leads to renal volume retention and increase in plasma homocysteine level. Homocysteine, which is a nonprotein amino acid, at elevated levels is an independent cardio-renovascular risk factor. Homocysteine induces oxidative injury of vascular endothelial cells, involved in matrix remodeling through modulation of the matrix metalloproteinase (MMP)/tissue inhibitor of metalloproteinase (TIMP) axis, and increased formation and accumulation of extracellular matrix protein, such as collagen. In heart this leads to increased endothelial-myocyte uncoupling resulting in diastolic dysfunction and hypertension. In the kidney, increased matrix accumulation in the glomerulus causes glomerulosclerosis resulting in hypofiltration, increased renal volume retention, and hypertension. PPARγ agonist reduces tissue homocysteine levels and is reported to ameliorate homocysteine-induced deleterious vascular effects in diabetes. This review, in light of current information, focuses on the beneficial effects of PPARγ agonist in homocysteine-associated hypertension and vascular remodeling in diabetes.

Rosiglitazone inhibits proliferation of renal proximal tubular cells via down-regulation of ERK and Akt

Rosiglitazone has been reported to exert the protective effect against acute renal failure in animal models. However, the underlying mechanisms by which it protects the damaged kidney cells are poorly understood. The present study was therefore undertaken to examine the effect of rosiglitazone on cell proliferation and to determine its molecular mechanism in opossum kidney (OK) cells, an established renal proximal tubular cell line. Rosiglitazone treatment inhibited cell proliferation in a dose- and time-dependent manner, and such effects were not associated with induction of cell death. The anti-proliferative effect of rosiglitazone was accompanied by the cell cycle arrest at the G1 phase. Western blot analysis data showed that rosiglitazone caused down-regulation of extracellular signal-regulated kinase (ERK) and Akt pathway. Transfection of constitutively active forms of MEK (an upstream kinase of ERK) and Akt prevented the proliferation inhibition induced by rosiglitazone. Rosiglitazone facilitated the recovery of cells after cisplatin-mediated injury. Taken together, these data suggest that rosiglitazone induces inhibition of cell proliferation through ERK and Akt-dependent cell cycle arrest at the G1 phase. The cell cycle arrest may play a protective role in kidney cells by preventing injured cells from progressing in the cell cycle.

Transgenic overexpression of GLUT1 in mouse glomeruli produces renal disease resembling diabetic glomerulosclerosis

Previous work identified an important role for hyperglycemia in diabetic nephropathy (The Diabetes Control and Complications Trial Research Group. N Engl J Med 329: 977-986, 1993; UK Prospective Diabetes Study Group. Lancet 352: 837-853, 1998), and increased glomerular GLUT1 has been implicated. However, the roles of GLUT1 and intracellular glucose have not been determined. Here, we developed transgenic GLUT1-overexpressing mice (GT1S) to characterize the roles of GLUT1 and intracellular glucose in the development of glomerular disease without diabetes. GLUT1 was overexpressed in glomerular mesangial cells (MC) of C57BL6 mice, a line relatively resistant to diabetic nephropathy. Blood pressure, blood glucose, glomerular morphometry, matrix proteins, cell signaling, transcription factors, and selected growth factors were examined. Kidneys of GT1S mice overexpressed GLUT1 in glomerular MCs and small vessels, rather than renal tubules. GT1S mice were neither diabetic nor hypertensive. Glomerular GLUT1, glucose uptake, mean capillary diameter, and mean glomerular volume were all increased in the GT1S mice. Moderately severe glomerulosclerosis (GS) was established by 26 wk of age in GT1S mice, with increased glomerular type IV collagen and fibronectin. Modest increases in glomerular basement membrane thickness and albuminuria were detected with podocyte foot processes largely preserved, in the absence of podocyte GLUT1 overexpression. Activation of glomerular PKC, along with increased transforming growth factor-beta1, VEGFR1, VEGFR2, and VEGF were all detected in glomeruli of GT1S mice, likely contributing to GS. The transcription factor NF-kappaB was also activated. Overexpression of glomerular GLUT1, mimicking the diabetic GLUT1 response, produced numerous features typical of diabetic glomerular disease, without diabetes or hypertension. This suggested GLUT1 may play an important role in the development of diabetic GS.

Inflammatory cytokines as predictive markers for early detection and progression of diabetic nephropathy

Diabetic nephropathy is a major complication of diabetes mellitus and the leading cause of end-stage renal disease. Both hyperglycemia and hypertension (systemic and/or intraglomerular) are established causal factors for diabetic nephropathy. Nonetheless, there is growing evidence that activated innate immunity and inflammation are also contributing factors to the pathogenesis of diabetic nephropathy. This notion is based on increasing evidence indicating that both cytokines-chemokines and pro-fibrotic growth factors are important players in the progression of diabetic nephropathy, effectively accelerating and exacerbating inflammatory and fibrotic processes leading to end-stage renal disease. In this review, we focus on several predominant cytokines-chemokines as potential predictive markers for diabetic nephropathy. These cytokines-chemokines may also be helpful as biomarkers to monitor the progression of the disease and the impact of interventional modalities aimed at halting eventual manifestation of end-stage renal disease in diabetic patients.

Residual microvascular risk in diabetes: unmet needs and future directions

The burden of microvascular disease in patients with type 2 diabetes mellitus continues to escalate worldwide. Current standards of care reduce but do not eliminate the risk of diabetic retinopathy, nephropathy or neuropathy in these patients. Correction of atherogenic dyslipidemia, which is characterized by elevated triglyceride levels and low levels of HDL cholesterol, might provide additional benefit. Whereas promising data have been published with respect to fibrate therapy for maculopathy, fenofibrate for diabetic retinopathy, and statin or fibrate therapy for diabetic nephropathy, further studies are warranted to define optimal management strategies for reducing the residual microvascular risk. Such strategies are especially relevant in cases of diabetic peripheral neuropathy, where even optimal care fails to affect disease progression. Identification of those factors that are most relevant to residual diabetes-related microvascular risk is a priority of an ongoing multinational epidemiological study. In this Review, we highlight an urgent need to address the issue of microvascular residual risk in patients with or at risk of type 2 diabetes mellitus.

KIOM-79 prevents S100b-induced TGF-beta1 and fibronectin expression in mouse mesangial cells

AIM OF THE STUDY

In this study, we investigated whether KIOM-79 inhibits transforming growth factor-beta 1 (TGF-beta1) and fibronectin expression in mouse mesangial cells cultured under S100b, a specific ligand of the receptor for advanced glycation end products (RAGE).

MATERIALS AND METHODS

Cell counting kit (CCK-8) assay was employed to evaluate the viability of KIOM-79-treated mesangial cells. The effect of KIOM-79 on S100b-induced TGF-beta1 and fibronectin expression was investigated using RT-PCR, ELISA, and Western blot on mesangial cells.

RESULTS

KIOM-79 (up to 50 microg/ml) appeared to have no effect on cell viability. S100b induced an increase in the expression TGF-beta1 and fibronectin. Expression of TGF-beta1 and fibronectin was inhibited significantly by KIOM-79 treatment in mesangial cells. KIOM-79 also inhibited the expression of NF-kB and inactivated p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) 1/2 in mesangial cells. KIOM-79 pretreatment inhibited increased malondialdehyde (a product of lipid peroxidation and a marker for oxidative stress) levels in S100b-induced mesangial cells.

CONCLUSIONS

These data demonstrate that KIOM-79 inhibits expression of TGF-beta1 and fibronectin through inactivation of MAPK/ERK1/2 signaling, reduction in malondiadehyde levels, and inhibition of NF-kB in mesangial cells cultured under diabetic conditions. KIOM-79 could be beneficial for preventing of the development of diabetic complications such as nephropathy.

Long-term effects of rosiglitazone on the progressive decline in renal function in patients with type 2 diabetes

BACKGROUND/AIMS

Thiazolidinediones reduce urinary albumin excretion and may prevent the development of renal injury. We evaluated the long-term effects of rosiglitazone on the progression of renal dysfunction in patients with type 2 diabetes mellitus.

METHODS

We enrolled patients with type 2 diabetes mellitus who initially had normal or mildly impaired renal function, defined as an estimated glomerular filtration rate (eGFR) of 60-120 mL/min per 1.73 m2, and normoalbuminuria. Patients were divided into two groups according to their use of rosiglitazone during 3 years of follow-up: those treated with rosiglitazone (rosiglitazone group, n=52) and those treated without rosiglitazone (control group, n=85). Progression of renal dysfunction was defined as a decrease in eGFR of >or=9 mL/min per 1.73 m2 after 3 years.

RESULTS

A greater difference was observed in the decrease in eGFR between the rosiglitazone and control groups after 3 years (3.8+/-9.9 vs. 12.6+/-10.5 mL/min per 1.73 m2, p<0.001). Seventeen of 52 (32.7%) patients in the rosiglitazone group and 53 of 85 (62.3%) patients in the control group showed progression of renal dysfunction (p=0.001). The progressors had a longer duration of diabetes (6.7+/-5.9 vs. 3.9+/-4.1 years, p=0.002), higher HbA1c levels (7.4+/-1.8 vs. 6.8+/-1.3%, p=0.023), and less frequent use of rosiglitazone (24.2 vs. 52.2%, p<0.001) compared to non-progressors. Multiple logistic regression analysis revealed that the use of rosiglitazone was a significant and independent predictor of the progression of renal dysfunction.

CONCLUSIONS

This study suggests that rosiglitazone treatment slows the progressive deterioration of renal function in patients with type 2 diabetes.

Rosiglitazone prevents high glucose-induced vascular endothelial growth factor and collagen IV expression in cultured mesangial cells

Peroxisome proliferator-activated receptor (PPARγ), a ligand-dependent transcription factor, negatively modulates high glucose effects. We postulated that rosiglitazone (RSG), an activator of PPARγ prevents the upregulation of vascular endothelial growth factor (VEGF) and collagen IV by mesangial cells exposed to high glucose. Primary cultured rat mesangial cells were growth-arrested in 5.6 mM (NG) or 25 mM D-glucose (HG) for up to 48 hours. In HG, PPARγ mRNA and protein were reduced within 3 h, and enhanced ROS generation, expression of p22^phox, VEGF and collagen IV, and PKC-ζ membrane association were prevented by RSG. In NG, inhibition of PPARγ caused ROS generation and VEGF expression that were unchanged by RSG. Reduced AMP-activated protein kinase (AMPK) phosphorylation in HG was unchanged with RSG, and VEGF expression was unaffected by AMPK inhibition. Hence, PPARγ is a negative modulator of HG-induced signaling that acts through PKC-ζ but not AMPK and regulates VEGF and collagen IV expression by mesangial cells.

Crosstalk between peroxisome proliferator-activated receptor-gamma and angiotensin II in renal tubular epithelial cells in IgA nephropathy

Our recent study suggested that peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist attenuates inflammatory response in activated tubular epithelial cells in IgA nephropathy (IgAN). Here, we explore thiazolidinediones as new therapeutic additives to established treatment regime of renin angiotensin blockade in IgAN. Human proximal tubular epithelial cells (PTEC) were pretreated with PPAR-gamma agonist, rosiglitazone, and/or angiotensin II (AngII) type 1 receptor (ATR1) blocker (ARB), losartan, followed by activation with the conditioned medium collected from human mesangial cells incubated with pIgA1 (IgA-HMC) from patients with IgAN. IgA-HMC conditioned medium up-regulated expression of ICAM-1, IL-6 and ATR1 and activated NF-kappaB and ERK1/2 in PTEC. Dual treatment of rosiglitazone and losartan provided synergistic effect in reducing ICAM-1, IL-6 and ATR1 expression and NF-kappaB and ERK1/2 activation induced by the conditioned media when compared with monotherapy. Our data suggest that rosiglitazone trans-represses AngII signaling and may offer additional potential when combined with ARB in treating IgAN.

Historical chronology of basic and clinical research in diabetic nephropathy and contributions of Japanese scientists

The most problematic issue in clinical nephrology worldwide is the relentless and progressive increase in patients with end-stage renal disease (ESRD). Diabetic nephropathy has considerable impact on society in the areas of public health and social economy; many scientists are involved in research for the elucidation of the pathogenesis of diabetic nephropathy and for the prevention and cure of the disease. In contrast, diabetic nephropathy was a neglected or ignored disease in the historical era, and few dedicated physicians recognized the disease process of diabetic nephropathy. In this review, we look back on the history of basic and clinical research on diabetic nephropathy and survey the recent progress of the research, especially focusing on the contribution of Japanese scientists.

Felodipine downregulates serum interleukin-18 levels in rats with fructose-induced metabolic syndrome

OBJECTIVE

Human studies suggest that calcium-channel blockers have cardiovascular protection besides reducing blood pressure, and interleukin-18 (IL-18) levels which are elevated in obese population are associated with metabolic syndrome (MetS). The purpose of this research was to study the change of serum IL-18 levels and the effect of felodipine on it in high-fructose diet-fed rats.

METHODS

In this research, 30 Wistar male rats were randomized into 3 groups. A control group (no.=12) was fed with normal feeds, and high-fructose diet was given to a fructose group and a flodioine group (no.=9 in each group). All animals were fed for a period of 32 weeks, during which body weight and systolic blood pressure (BP) were measured once every 4 weeks. Felodipine (5 mg/kg/d) was then administered by gavage daily for 6 weeks to the felodipine group. Before and after treatment with felodipine, fasting plasma lipid, blood glucose, plasma insulin, and serum IL-18 were detected.

RESULTS

Body weight, systolic BP, triglycerides, fasting insulin, and the R-value of homeostasis model (HOMA-R) were significantly increased in high-fructose rats (p<0.01). Serum IL-18 levels were elevated and had significant positive correlation with HOMA-R in rats with fructose-induced MetS (p<0.01). We also found that felodipine may decrease HOMA-R and serum IL-18 levels besides reducing blood pressure (p<0.05, p<0.01).

CONCLUSION

IL-18 plays an important role in the development of MetS, while felodipine exerts an anti-inflammatory effect on rats with fructose-induced MetS by downregulating serum IL-18 levels.

Renoprotective effect of total glucosides of paeony (TGP) and its mechanism in experimental diabetes

Total glucosides of paeony (TGP), extracted from the root of Paeonia lactiflora pall, has been shown to have ant-inflammatory and antioxidative actions. The aims of this study were to elucidate the renoprotective effect of TGP and its mechanism in experimental diabetes. Streptozotocin-induced diabetic rats were treated with TGP for 8 weeks. Treatment with TGP at 50, 100, and 200 mg/kg significantly lowered 24-h urinary albumin excretion rate in diabetic rats. TGP treatment in all doses markedly attenuated glomerular volume, and treatment with TGP at 100 and 200 mg/kg markedly reduced indices for tubulointerstitial injury in diabetic rats. Western blot analysis showed that the expressions of 1 alpha (IV) collagen, intercellular adhesion molecule (ICAM)-1, interleukin (IL)-1, tumor necrosis factor (TNF)-alpha, NF-kappaB p65, and 3-nitrotyrosine (3-NT) protein were increased in the kidneys of diabetic rats; the increases in these proteins were all dose-dependently and significantly inhibited by TGP treatment. The expression of nephrin protein was significantly reduced in the kidneys from diabetic rats and markedly increased by TGP treatment. The expression of transforming growth factor (TGF)-beta1 protein in the kidney was also significantly increased in diabetic rats, which was significantly inhibited by treatment with TGP at all doses. Our data suggest that TGP treatment ameliorates early renal injury via the inhibition of expression of ICAM-1, IL-1, TNF-alpha, and 3-NT in the kidneys of diabetic rats.

PPARgamma in Kidney Physiology and Pathophysiology

Involvement of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) in kidney physiology has been explored recently. Synthetic PPARγ ligands can ameliorate the diabetic kidney disease through different mechanisms, involving inhibition of mesangial cell growth, reduction of mesangial matrix, and cytokine production of glomerular cells as well as promoting endothelial cell survival within the kidney glomeruli. Activation of PPARγ has additional profibrotic consequences, which can contribute to wound healing in diabetic glomerulonephritis. Beside many beneficial effects, PPARγ activation, however, can lead to severe water retention, a common side effect of thiazolidinedione therapy. This unwanted effect is due to the activation of PPARγ in the mesonephric distal collecting system, where PPARγ positively regulates sodium and water resorbtion leading to the expansion of interstitial fluid volume. Recent studies indicate that PPARγ is also involved in the normal kidney development, renal lipid metabolism, and activation of the renin-angiotensin system. In this paper, we give a synopsis of the current knowledge on PPARγ functions in kidney phyisology and pathophysiology.

Alpha-tocopherol modulates human umbilical vein endothelial cell expression of Cu/Zn superoxide dismutase and catalase and lipid peroxidation

Recent studies suggest the potential of alpha-tocopherol as a gene regulator, possibly through peroxisome proliferator-activated receptor gamma (PPARgamma) activation due to the structural similarity of alpha-tocopherol to a PPARgamma ligand, troglitazone. Other investigators have suggested that a link exists between induction of the antioxidant enzymes Cu/Zn superoxide dismutase (SOD) and catalase and PPARgamma activation. This study was designed to examine whether alpha-tocopherol modulates expression of Cu/Zn SOD and catalase in human umbilical vein endothelial cells through redox-sensitive transcription factors, PPARgamma, and nuclear factor-kappaB (NF-kappaB). Alpha-tocopherol treatments showed significant increases in both PPARgamma (1.4- to 2.2-fold, P < .01) and NF-kappaB p50 (1.3- to 1.5-fold, P < .005) DNA binding activities compared with vehicle control. Significant increases in Cu/Zn SOD mRNA levels (6.0-fold, P < .005) and catalase mRNA (8.0-fold, P < .005) and its protein levels (2.3-fold, P < .005) and lipid peroxidation levels (5.3-fold, P < .005) were observed at the lowest concentration (10 mumol/L) of alpha-tocopherol treatments. Both mRNA and protein levels of these 2 antioxidant enzymes were positively associated with lipid peroxidation (P < .05). Alpha-tocopherol may play a role not only in preventing against oxidative damage as an exogenous antioxidant by scavenging free radicals and superoxide but also in modulating the expression of the endogenous antioxidant enzymes as a gene regulator through PPARgamma and NF-kappaB in the vascular cells. The alpha-tocopherol-mediated gene expression is either stimulatory or inhibitory, depending on its oxidative status or its concentrations.

Role of PPARgamma in renoprotection in Type 2 diabetes: molecular mechanisms and therapeutic potential

DN (diabetic nephropathy) is a chronic disease characterized by proteinuria, glomerular hypertrophy, decreased glomerular filtration and renal fibrosis with loss of renal function. DN is the leading cause of ESRD (end-stage renal disease), accounting for millions of deaths worldwide. TZDs (thiazolidinediones) are synthetic ligands of PPARgamma (peroxisome-proliferator-activated receptor gamma), which is involved in many important physiological processes, including adipose differentiation, lipid and glucose metabolism, energy homoeostasis, cell proliferation, inflammation, reproduction and renoprotection. A large body of research over the past decade has revealed that, in addition to their insulin-sensitizing effects, TZDs play an important role in delaying and preventing the progression of chronic kidney disease in Type 2 diabetes. Although PPARgamma activation by TZDs is in general considered beneficial for the amelioration of diabetic renal complications in Type 2 diabetes, the underlying mechanism(s) remains only partially characterized. In this review, we summarize and discuss recent findings regarding the renoprotective effects of PPARgamma in Type 2 diabetes and the potential underlying mechanisms.

Intervention with cilostazol attenuates renal inflammation in streptozotocin-induced diabetic rats

AIMS

An inflammatory reaction is commonly found in the pathogenesis of diabetic nephropathy (DN). Cilostazol, a type 3 phosphodiesterase (PDE) inhibitor, has been previously reported to be anti-inflammatory, independent of an anti-platelet property. In the present study, we evaluated the hypothesis that cilostazol has protective effects on diabetic nephropathy by modulating the inflammatory process.

MAIN METHODS

Cilostazol was administered (27 or 9 mg kg(-1)d(-1)) to streptozotocin (STZ)-induced diabetic rats for eight weeks. We studied the kidney expression of vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1 by immunofluorescence, western blotting and real-time PCR. The renal monocyte chemoattractant protein (MCP)-1 and vascular endothelial growth factor (VEGF) levels were examined by ELISA. The nuclear factor (NF)-kappaB-DNA binding activity was assessed by electrophoresis mobility shift assay (EMSA).

KEY FINDINGS

Our results showed cilostazol inhibited diabetes-induced hypertrophy of the glomeruli and infiltration of inflammatory cells, as well as the increase in the VCAM-1 and ICAM-1 mRNA and protein expression, and MCP-1 and VEGF contents in the kidneys. Consistent with these findings, cilostazol attenuated the enhanced activation of NF-kappaB in diabetic rats.

SIGNIFICANCE

These results demonstrate that the renoprotective effects of cilostazol may be mediated by its anti-inflammatory actions, including inhibition of NF-kappaB activation and the subsequent decrease in proinflammatory factors, such as VCAM-1, ICAM-1, MCP-1 and VEGF expression in kidneys of diabetic rats.

Renoprotective effect of rosiglitazone through the suppression of renal intercellular adhesion molecule-1 expression in streptozotocin-induced diabetic rats

OBJECTIVE

To observe the effect of rosiglitazone on serum intercellular adhesion molecule-1 (SICAM-1) level, urinary excretion of ICAM-1, and renal expression of ICAM-1, and investigate its possible renoprotective mechanisms in diabetic rats.

METHOD

Twenty-four Wistar Rats were divided into 3 groups: non-diabetic control rats (group A, no.=8), streptozotocin-induced diabetic rats (group B, no.=8), and diabetic rats treated with rosiglitazone (group C, no.=8). Rats in group C were treated with rosiglitazone (5 mg x kg(-1) x d(-1)) 1 week after the establishment of diabetic model, group A and B were treated with corresponding sodium chloride. Peripheral blood glucose was tested weekly. Glycosylated hemoglobin (HbA1c) and SICAM-1 as well as urinary albumin excretion rate (UAER), urinary retinol binding-protein (URBP) excretion rate, and urinary ICAM-1 (UICAM- 1) excretion rate were tested at the 8th week, and the renal tissues of all rats were obtained for evaluating kidney/body weight ratio, observing pathologic change via electron microscope, and for examining the expression of ICAM-1 mRNA by reverse transcriptase-PCR.

RESULTS

At the 8th week, the blood glucose, HbA1c levels, UAER, URBP excretion rate, kidney/body weight ratio and serum, urinary ICAM-1 levels all increased significantly in group B and group C in comparison with group A; however, the above-mentioned parameters in group C (except the blood glucose and HbA1c levels) were much lower than those in group B. In addition, both SICAM-1 and UICAM-1 were highly correlated with the UAER, URBP level, and kidney/body weight ratio in all rats; renal pathological lesions observed by electron microscope in group C were much lighter than those of group B; compared with group A, the expression of ICAM-1 mRNA was markedly up-regulated in group B and group C, and rosiglitazone was able to decrease the expression of ICAM-1 mRNA in the renal tissue.

CONCLUSION

Rosiglitazone could definitely protect against the renal injury of diabetic rats, which may be partly associated with decreasing the expression of ICAM-1 in the renal tissue, reducing ICAM-1 productions in both serum and urine.

Present and future drug treatments for chronic kidney diseases: evolving targets in renoprotection

At present, there are no specific cures for most of the acquired chronic kidney diseases, and renal transplantation is limited by organ shortage, therefore present efforts are concentrated on the prevention of progression of renal diseases. There is robust experimental and clinical evidence that progression of chronic nephropathies is multifactorial; however, intraglomerular haemodynamic changes and proteinuria play a key role in this process. With a focus on renoprotection, we first examine more established therapies--such as those that modulate the renin-angiotensin-aldosterone system--that can be used for the treatment of proteinuric renal diseases. We then discuss examples of novel drugs and biologics that might be used to target the inflammatory and profibrotic process, and glomerular injury, highlighting results from recent clinical trials.

Rosiglitazone reduces renal and plasma markers of oxidative injury and reverses urinary metabolite abnormalities in the amelioration of diabetic nephropathy

Recent studies suggest that thiazolidinediones ameliorate diabetic nephropathy (DN) independently of their effect on hyperglycemia. In the current study, we confirm and extend these findings by showing that rosiglitazone treatment prevented the development of DN and reversed multiple markers of oxidative injury in DBA/2J mice made diabetic by low-dose streptozotocin. These diabetic mice developed a 14.2-fold increase in albuminuria and a 53% expansion of renal glomerular extracellular matrix after 12 wk of diabetes. These changes were largely abrogated by administration of rosiglitazone beginning 2 wk after the completion of streptozotocin injections. Rosiglitazone had no effect on glycemic control. Rosiglitazone had similar effects on insulin-treated diabetic mice after 24 wk of diabetes. Podocyte loss and glomerular fibronectin accumulation, other markers of early DN, were prevented by rosiglitazone in both 12- and 24-wk diabetic models. Surprisingly, glomerular GLUT1 levels did not increase and nephrin levels did not decrease in the diabetic animals; neither changed with rosiglitazone. Plasma and kidney markers of protein oxidation and lipid peroxidation were significantly elevated in the 24-wk diabetic animals despite insulin treatment and were reduced to near-normal levels by rosiglitazone. Finally, urinary metabolites were markedly altered by diabetes. Of 1,988 metabolite features identified by electrospray ionization time of flight mass spectrometry, levels of 56 were altered more than twofold in the urine of diabetic mice. Of these, 21 were returned to normal by rosiglitazone. Thus rosiglitazone has direct effects on the renal glomerulus to reduce reactive oxygen species accumulation to prevent type 1 diabetic mice from development of DN.

Tissue-specific expression of PPAR mRNAs in diabetic rats and divergent effects of cilostazol

Cilostazol and ligands of peroxisome proliferator-activated receptors (PPARs) have been effectively used to alleviate diabetic complications, but the common and tissue-specific expression patterns of PPARs in different tissues in diabetic patients and those treated with cilostazol have not been reported. Here, we aimed to assess the effects of diabetes and cilostazol on mRNA expression of PPARalpha and PPARgamma in the aorta, renal cortex, and retina of diabetic rats treated with cilostazol for 8 weeks. PPARalpha mRNA expression showed uniform downregulation in all these tissues in diabetic rats, and this effect was reversed by cilostazol treatment. Surprisingly, PPARgamma mRNA expression was reduced in the renal cortex and retina, yet increased in the aorta of diabetic rats, although cilostazol still reversed these changes. Interestingly, cilostazol, a well-known phosphodiesterase 3 inhibitor and cAMP elevator, augmented cAMP content only in the aorta, but showed no significant effects in the renal cortex of diabetic rats. In conclusion, mRNA expression of PPARs is tissue-specific in diabetes and may be differently affected by cilostazol, possibly because of its tissue-specific effects on cAMP content.