The effect of an aldose reductase inhibitor (Epalrestat) on diabetic nephropathy in rats

Metabolomics and molecular dynamics unveil the therapeutic potential of epalrestat in diabetic nephropathy

Diabetic nephropathy (DN) is one of the leading clinical causes of end-stage renal failure. The classical aldose reductase (AR) inhibitor epalrestat shows beneficial effect on renal dysfunction induced by DN, with metabolic profile and molecular mechanisms remains to be investigated further. In the current study, integrated untargeted metabolomics, network pharmacology and molecular dynamics approaches were applied to explore the therapeutic mechanisms of epalrestat against DN. Firstly, untargeted serum and urine metabolomics analysis based on UPLC-Q-TOF-MS was performed, revealed that epalrestat could regulate the metabolic disorders of amino acids metabolism, arachidonic acid metabolism, pyrimidine metabolism and citrate cycle metabolism pathways after DN. Subsequently, metabolomics-based network analysis was carried out to predict potential active targets of epalrestat, mainly involving AGE-RAGE signaling pathway, TNF signaling pathway and HIF-1 signaling pathway. Moreover, a 100 ns molecular dynamics approach was employed to validate the interactions between epalrestat and the core targets, showing that epalrestat could form remarkable tight binding with GLUT1 and NFκB than it with AR. Surface-plasmon resonance assay further verified epalrestat could bind GLUT1 and NFκB proteins specifically. Overall, integrated system network analysis not only demonstrated that epalrestat could attenuate DN induced metabolic disorders and renal injuries, but also revealed that it could interact with multi-targets to play a synergistic regulatory role in the treatment of DN.

Diabetic nephropathy: A twisted thread to unravel

Diabetic nephropathy (DN), a persistent microvascular problem of diabetes mellitus is described as an elevated level of albumin excretion in urine and impaired renal activity. The morbidity and mortality of type-1 diabetics and type-2 diabetics due to end stage renal disease is also a result of the increased prevalence of DN. DN typically occurs as a consequence of an association among metabolic and hemodynamic variables, activating specific pathways leading to renal injury. According to current interventions, intensive glucose regulation decreases the threat of DN incidence and growth, and also suppressing the renin-angiotensin system (RAS) is a significant goal for hemodynamic and metabolism-related deformities in DN. However, the pathogenesis of DN is multifactorial so novel approaches other than glucose and blood pressure control are required for treatment. This review briefly summarizes the reported pathogenesis of DN, current interventions for its treatment, and possible novel interventions to unweave the thread of DN.

Multifunctional agents based on benzoxazolone as promising therapeutic drugs for diabetic nephropathy

Diabetic nephropathy (DN) is resulted from activations of polyol pathway and oxidative stress by abnormal metabolism of glucose, and no specific medication is available. We designed a novel class of benzoxazolone derivatives, and a number of individuals were found to have significant antioxidant activity and inhibition of aldose reductase of the key enzyme in the polyol pathway. The outstanding compound (E)-2-(7-(4-hydroxy-3-methoxystyryl)-2-oxobenzo[d]oxazol-3(2H)-yl)acetic acid was identified to reduce urinary proteins in diabetic mice suggesting an alleviation in the diabetic nephropathy, and this was confirmed by kidney hematoxylin-eosin staining. Further investigations showed blood glucose normalization, declined in the polyol pathway and lipid peroxides, and raised glutathione and superoxide dismutase activity. Thus, we suggest a therapeutic function of the compound for DN which could be attributed to the combination of hypoglycemic, aldose reductase inhibition and antioxidant.

QM/MM analysis, synthesis and biological evaluation of epalrestat based mutual-prodrugs for diabetic neuropathy and nephropathy

Herein, a quantum mechanics/molecular mechanics (QM/MM) based biotransformation study was performed on synthetically feasible mutual-prodrugs of epalrestat which have been identified from an in-house database developed by us. These prodrugs were submitted to quantum polarized ligand docking (QPLD) with the CES1 enzyme followed by MM-GBSA calculation. Electronic aspects of transition state of these prodrugs were also considered to study the catalytic process through density functional theory (DFT). ADMET analysis of prodrugs was then carried out to assess the drug-likeness. On the basis of in-silico results, the best five prodrugs were synthesized and further evaluated for their neuroprotective and nephroprotective potential in high-fat diet-streptozotocin (HFD-STZ) induced diabetes in rat model. Clinically relevant molecular manifestations of diabetic complications (DC) including aldose reductase (ALR2) activity and oxidative stress markers such as reduced glutathione (GSH), catalase (CAT), and thiobarbituric acid reactive substances (TBARS) were determined in blood plasma as well as tissues of the brain and kidneys. The histopathological examination of these organs was also carried out to see the improvement in structural deformities caused due to neuropathy and nephropathy. Finally, in-vivo pharmacokinetic study was performed for the best two prodrugs to assess the improvement in biopharmaceutical attributes of parent drugs. Overall, EP-G-MFA and EP-MFA have significantly reduced the hyperglycemia-induced ALR2 activity, levels of oxidative stress markers, and manifested about a two-fold increase in the biological half-life (T_1/2) of parent drugs. The overall findings of this study suggest that methyl ferulate conjugated prodrugs of epalrestat may be considered as potential protective agents in diabetic neuropathy and nephropathy.

The aldose reductase inhibitor epalrestat exerts nephritic protection on diabetic nephropathy in db/db mice through metabolic modulation

Epalrestat is an inhibitor of aldose reductase in the polyol pathway and is used for the management of diabetic neuropathy clinically. Our pilot experiments and accumulated evidences showed that epalrestat inhibited polyol pathway and reduced sorbitol production, and suggested the potential renal protection effects of epalrestat on diabetic nephropathy (DN). To evaluate the protective effect of epalrestat, the db/db mice were used and exposed to epalrestat for 8 weeks, both the physiopathological condition and function of kidney were examined. For the first time, we showed that epalrestat markedly reduced albuminuria and alleviated the podocyte foot process fusion and interstitial fibrosis of db/db mice. Metabolomics was employed, and metabolites in the plasma, renal cortex, and urine were profiled using a gas chromatography-mass spectrometry (GC/MS)-based metabolomic platform. We observed an elevation of sorbitol and fructose, and a decrease of myo-inositol in the renal cortex of db/db mice. Epalrestat reversed the renal accumulation of the polyol pathway metabolites of sorbitol and fructose, and increased myo-inositol level. Moreover, the upregulation of aldose reductase, fibronectin, collagen III, and TGF-β1 in renal cortex of db/db mice was downregulated by epalrestat. The data suggested that epalrestat has protective effects on DN, and the inhibition of aldose reductase and the modulation of polyol pathway in nephritic cells be a potentially therapeutic strategy for DN.

Aldo-Keto Reductases: Multifunctional Proteins as Therapeutic Targets in Diabetes and Inflammatory Disease

Aldose reductase (AR) is an NADPH-dependent aldo-keto reductase that has been shown to be involved in the pathogenesis of several blinding diseases such as uveitis, diabetic retinopathy (DR) and cataract. However, possible mechanisms linking the action of AR to these diseases are not well understood. As DR and cataract are among the leading causes of blindness in the world, there is an urgent need to explore therapeutic strategies to prevent or delay their onset. Studies with AR inhibitors and gene-targeted mice have demonstrated that the action of AR is also linked to cancer onset and progression. In this review we examine possible mechanisms that relate AR to molecular signaling cascades and thus explain why AR inhibition is an effective strategy against colon cancer as well as diseases of the eye such as uveitis, cataract, and retinopathy.

Diabetic Kidney Disease: Pathophysiology and Therapeutic Targets

Diabetes is a worldwide epidemic that has led to a rise in diabetic kidney disease (DKD). Over the past two decades, there has been significant clarification of the various pathways implicated in the pathogenesis of DKD. Nonetheless, very little has changed in the way clinicians manage patients with this disorder. Indeed, treatment is primarily centered on controlling hyperglycemia and hypertension and inhibiting the renin-angiotensin system. The purpose of this review is to describe the current understanding of how the hemodynamic, metabolic, inflammatory, and alternative pathways are all entangled in pathogenesis of DKD and detail the various therapeutic targets that may one day play a role in quelling this epidemic.

Therapeutic strategies of diabetic nephropathy: recent progress and future perspectives

Diabetic nephropathy (DN) is one of the most common complications of diabetes with high mortality rates worldwide. The treatment of DN has posed a formidable challenge to the scientific community. Simple control of risk factors has been insufficient to cope with the progression of DN. During the process of anti-DN drug discovery, multiple pathogeneses such as oxidative stress, inflammation and fibrosis should all be considered. In this review, the pathogenesis of DN is summarized. The major context focuses on a few small molecules toward the pathogenesis available in animal models and clinical trials for the treatment of DN. The perspectives of novel anti-DN agents and the future directions for the prevention of DN are discussed.

Diabetic nephropathy - complications and treatment

Diabetic nephropathy is a significant cause of chronic kidney disease and end-stage renal failure globally. Much research has been conducted in both basic science and clinical therapeutics, which has enhanced understanding of the pathophysiology of diabetic nephropathy and expanded the potential therapies available. This review will examine the current concepts of diabetic nephropathy management in the context of some of the basic science and pathophysiology aspects relevant to the approaches taken in novel, investigative treatment strategies.

H2S donors attenuate diabetic nephropathy in rats: Modulation of oxidant status and polyol pathway

BACKGROUND

Sulfurous mineral water and its main active ingredient sodium hydrosulfide (NaHS) are major sources of H2S. The present study aimed to explore their protective effect on one of the serious long-term complications of diabetes; diabetic nephropathy.

METHODS

Sulfurous mineral water (as drinking water), NaHS (14 μmol/kg/day; ip), and gliclazide (10mg/kg; po) were administered daily for 6 weeks to streptozotocin (STZ)-diabetic rats.

RESULTS

STZ-induced diabetes was associated with body weight reduction, hyperglycemia, overproduction of glycated hemoglobin, as well as decline in serum insulin, C-peptide, and insulin like growth factor-I. Besides, diabetes impaired kidney functions and imposed oxidative and nitrosative stress as manifested by elevated contents of renal thiobarbituric acid reactive substances and nitric oxide, parallel to reduced glutathione content. These deleterious effects were antagonized by sulfurous water and to a better extent by NaHS. Activities of myeloperoxidase and sorbitol dehydrogenase were not altered by STZ or any of the treatments. However, STZ-induced diabetes was accompanied by an increment of aldose reductase which was only mitigated by gliclazide and NaHS. Histopathological examination of kidney sections corroborated the biochemical findings.

CONCLUSION

This study suggests a novel therapeutic approach for diabetic nephropathy using H2S donors.

Effects of Allium victorialis leaf extracts and its single compounds on aldose reductase, advanced glycation end products and TGF-β1 expression in mesangial cells

Background

Accumulating evidences suggest that aldose reductase (AR) inhibitors and advanced glycation end product (AGE) formation inhibitors may prevent chronic hyperglycemia-induced long-term complication in diabetes. Transforming growth factor-beta1 (TGF-β1) plays an important role in the development of diabetic nephropathy. Allium species have been utilized in folk medicine throughout the world for the treatment of various physical disorders. However, the benefits of Allium victorialis (A. victorialis) against diabetic complications, especially nephropathy, have yet to be explored. In the present study, we investigated the protective effect of the compounds isolated from A. victorialis leaf on diabetic nephropathy.

Methods

In vitro AR activity, AGEs formation, and AGE-receptor for AGEs (RAGE) binding in human RAGE (hRAGE)-overexpressing cells were tested. High glucose-induced transforming growth factor-beta1 (TGF-β1) expression was also examined in mouse kidney mesangial cells (MMCs) cultured under high glucose.

Results

Of the isolated eight compounds from A. victorialis leaf extracts tested, quercitrin exhibited the most pronounced inhibitory effects on AR activity (IC₅₀ value of 0.17 μM) and AGEs formation (IC₅₀ value of 4.20 μM). Furthermore, quercitrin disrupted AGE-RAGE binding in a concentration-dependent manner in hRAGE-overexpressing cells. Additionally, of the eight compounds tested, ferulic acid significantly reduced high glucose-induced TGF-β1 expression and secretion in MMCs.

Conclusions

Our results suggest that active compounds isolated from A. victorialis leaf exhibit inhibitory effects on AR activity in rat lenses and AGE formation. Further, ferulic acid reduces TGF-β1 mRNA expression and secretion in MMCs under diabetic conditions. Thus, A. victorialis is a good candidate for the development of treatments for diabetic nephropathy.

Association of 276G>T adiponectin gene polymorphism to plasma adiponectin and albuminuria in type 2 diabetic patients

PURPOSE

The 276G>T polymorphism of the adiponectin (ADIPOQ) gene has been correlated with plasma adiponectin, type 2 diabetes (T2D) and its complications. Studies of the role of 276G>T polymorphism in the prevalence of T2D kidney disease are few and contradictory; ethnic differences might play a role. We aimed to assess the relationship of this polymorphism with albuminuria in a cohort of Caucasian T2D patients.

METHODS

Consecutive T2D outclinic patients were screened and included upon informed consent; exclusion criteria were glomerular filtration rate (GFR)<30 ml/min, acute intercurrent illness and urinary tract infection. History, standard laboratory evaluation, total plasma adiponectin and genotyping for the 276 ADIPOQ locus were obtained.

RESULTS

One hundred and three T2D patients were included. Forty-three (41.7%) of them had GG genotype, 50 (48.5%) had GT and 10 (9.7%) had TT genotype. Plasma adiponectin was significantly higher in TT-allele carriers (19.03±3.46 μg/ml) than in GT (10.14±1.78 μg/ml) and GG carriers (8.71±1.60 μg/ml), P=0.003. Adiponectin was higher in albuminuric (13.97±2.07 μg/ml) than in normoalbuminuric patients (6.91±0.88 μg/ml), P=0.004. The prevalence of T allele was higher in normoalbuminuric patients [36 (69.2%) GT+TT carriers] than in albuminuric ones [24 (47.1%)], P=0.02. Logistic regression identified the following as predictors of albuminuria: GG genotype: P=0.003 (OR 4.2; CI 1.61-10.96); low GFR: P=0.003 (OR 0.97; CI 0.95-0.99); and high plasma adiponectin: P=0.012 (OR 1.07; CI 1.01-1.14).

CONCLUSIONS

Our data suggest that 276G>T polymorphism of the ADIPOQ gene is associated with plasma adiponectin levels. By influencing adiponectinemia, 276G>T polymorphism might predict the presence of albuminuria in Caucasian T2D patients.

Genetic deficiency of aldose reductase counteracts the development of diabetic nephropathy in C57BL/6 mice

AIMS/HYPOTHESIS

The aim of the study was to investigate the effects of genetic deficiency of aldose reductase in mice on the development of key endpoints of diabetic nephropathy.

METHODS

A line of Ar (also known as Akr1b3)-knockout (KO) mice, a line of Ar-bitransgenic mice and control C57BL/6 mice were used in the study. The KO and bitransgenic mice were deficient for Ar in the renal glomeruli and all other tissues, with the exception of, in the bitransgenic mice, a human AR cDNA knockin-transgene that directed collecting-tubule epithelial-cell-specific AR expression. Diabetes was induced in 8-week-old male mice with streptozotocin. Mice were further maintained for 17 weeks then killed. A number of serum and urinary variables were determined for these 25-week-old mice. Periodic acid-Schiff staining, western blots, immunohistochemistry and protein kinase C (PKC) activity assays were performed for histological analyses, and to determine the levels of collagen IV and TGF-β1 and PKC activities in renal cortical tissues.

RESULTS

Diabetes-induced extracellular matrix accumulation and collagen IV overproduction were completely prevented in diabetic Ar-KO and bitransgenic mice. Ar deficiency also completely or partially prevented diabetes-induced activation of renal cortical PKC, TGF-β1 and glomerular hypertrophy. Loss of Ar results in a 43% reduction in urine albumin excretion in the diabetic Ar-KO mice and a 48% reduction in the diabetic bitransgenic mice (p < 0.01).

CONCLUSIONS/INTERPRETATION

Genetic deficiency of Ar significantly ameliorated development of key endpoints linked with early diabetic nephropathy in vivo. Robust and specific inhibition of aldose reductase might be an effective strategy for the prevention and treatment of diabetic nephropathy.

Aldose reductase and cardiovascular diseases, creating human-like diabetic complications in an experimental model

Hyperglycemia and reduced insulin actions affect many biological processes. One theory is that aberrant metabolism of glucose via several pathways including the polyol pathway causes cellular toxicity. Aldose reductase (AR) is a multifunctional enzyme that reduces aldehydes. Under diabetic conditions AR converts glucose into sorbitol, which is then converted to fructose. This article reviews the biology and pathobiology of AR actions. AR expression varies considerably among species. In humans and rats, the higher level of AR expression is associated with toxicity. Flux via AR is increased by ischemia and its inhibition during ischemia reperfusion reduces injury. However, similar pharmacological effects are not observed in mice unless they express a human AR transgene. This is because mice have much lower levels of AR expression, probably insufficient to generate toxic byproducts. Human AR expression in LDL receptor knockout mice exacerbates vascular disease, but only under diabetic conditions. In contrast, a recent report suggests that genetic ablation of AR increased atherosclerosis and increased hydroxynonenal in arteries. It was hypothesized that AR knockout prevented reduction of toxic aldehydes. Like many in vivo effects found in genetically manipulated animals, interpretation requires the reproduction of human-like physiology. For AR, this will require tissue specific expression of AR in sites and at levels that approximate those in humans.

Polyol pathway and RAGE: a central metabolic and signaling axis in diabetic complications

There are multiple metabolic and molecular consequences of hyperglycemia. This review will focus on the roles of the polyol pathway and the receptor for advanced glycation end products (RAGE) in the pathogenesis of diabetic complications. The lead enzyme of the polyol pathway, aldose reductase, transduces maladaptive effects of hyperglycemia by multiple mechanisms, at least in part via the generation of the products of nonenzymatic glycation of proteins, the advanced glycation end products (AGEs). Furthermore, seminal shifts in metabolic flux in the intracellular space stimulated by aldose reductase action activate signal transduction pathways, which alter gene expression and change cellular phenotype. Among the ligands of the multi-ligand receptor RAGE are the AGEs. AGE-RAGE stimulation mediates vascular and target cell dysfunction. The intersection and interdependence of the polyol pathway-RAGE connection suggest that targeting this axis may provide benefit in reducing the complications of diabetes.

Regulation of glucose uptake in mesangial cells stimulated by high glucose: role of angiotensin II and insulin

Mesangial cells (MCs) play a central role in the pathogenesis of diabetic nephropathy (DN). MC dysfunction arises from excessive glucose uptake through insulin-independent glucose transporter (GLUT1). The role of the insulin-dependent transporter (GLUT4) remains unknown. This study evaluated the effect of high glucose on GLUT1, GLUT4, and fibronectin expression levels. Glucose uptake was determined in the absence and presence of insulin. Angiotensin II has been implicated as a mediator of MC abnormalities in DN, and its effects on the GLUTs expression were evaluated in the presence of losartan. MCs were exposed to normal (NG, 10 mM) or high (HG, 30 mM) glucose for 1, 4, 12, 24, and 72 hrs. Glucose uptake was elevated from 1 hr up to 24 hrs of HG, but returned to NG levels after 72 hrs. HG induced an early (1-, 4-, and 12-hrs) rise in GLUT1 expression, returning to NG levels after 72 hrs, whereas GLUT4 was overexpressed at later timepoints (24 and 72 hrs). HG during 4 hrs induced a 40% rise in glucose uptake, which was unaffected by insulin. In contrast, after 72 hrs, glucose uptake was increased by 50%, only under insulin stimulus. Losartan blunted the effects of HG on GLUT1, GLUT4, and fibronectin expression and on glucose uptake. Results suggest that MCs can be highly susceptible to the HG environment since they uptake glucose in both an insulin-independent and insulin-dependent manner. The beneficial effects of angiotensin II inhibition in DN may also involve a decrease in the rate of glucose uptake by MCs.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Association of aldose reductase gene Z+2 polymorphism with reduced susceptibility to diabetic nephropathy in Caucasian Type 1 diabetic patients

AIMS

The Z-2 allele of the (AC)n polymorphism in the aldose reductase gene (ALR2) confers increased risk of microvascular diabetic complications, whereas the Z+2 allele has been proposed to be a marker of protection. However data are conflicting. Therefore, we investigated whether this polymorphism is associated with diabetic nephropathy and retinopathy in Type 1 diabetes mellitus in a large case-control study and a family-based analysis.

METHODS

A total of 431 Type 1 diabetic patients with diabetic nephropathy and 468 patients with longstanding Type 1 diabetes and persistent normoalbuminuria were genotyped for the case-control study. In addition, 102 case trios and 98 control trios were genotyped for a family-based study.

RESULTS

Thirteen different alleles were identified. In the case-control study, the Z+2 allele frequency was significantly higher in the normoalbuminuric diabetic than in patients with diabetic nephropathy (0.17 vs. 0.11, P = 0.008), suggesting a protective function of the Z+2 allele. No significant increase in the frequency of the putative risk allele Z-2 was found in patients with diabetic nephropathy vs. controls (0.39 vs. 0.36). No association with diabetic retinopathy was found. Although the results of the transmission of the Z-2 and Z+2 alleles in the independent family-based study were consistent with the association study, the number of informative families was limited and thus differences were not statistically significant.

CONCLUSIONS

The Z+2 allele of the ALR2 promoter polymorphism is associated with a reduced susceptibility to diabetic nephropathy in Danish Type 1 diabetic patients, suggesting a minor role for the polyol pathway in the pathogenesis of diabetic kidney disease. No association of the ALR2 polymorphism with diabetic retinopathy was found.

Glucose, glycation, and RAGE: implications for amplification of cellular dysfunction in diabetic nephropathy

Receptor for advanced glycation endproducts (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. Driven by rapid accumulation and expression of key ligands such as advanced glycation endproducts (AGE) and S100/calgranulins in diabetic tissues, upregulation and activation of RAGE magnifies cellular perturbation in tissues affected by hyperglycemia, such as the large blood vessels and the kidney. In the diabetic glomerulus, RAGE is expressed principally by glomerular visceral epithelial cells (podocytes). Blockade of RAGE in the hyperglycemic db/db mouse suppresses functional and structural alterations in the kidney, in the absence of alterations in blood glucose. Recent studies in homozygous RAGE null mice support a key role for RAGE in glomerular perturbation in diabetes. Importantly, beyond diabetes, studies in other settings of glomerulopathies support a critical RAGE-dependent pathway in podocytes linked to albuminuria, mesangial expansion, and glomerular sclerosis. A new paradigm is proposed in glomerular injury, and it is suggested that blockade of the RAGE axis may provide a novel means to prevent irreparable glomerular injury in diabetes and other sclerosing glomerulopathies.

Analysis of the association between diabetic nephropathy and polymorphisms in the aldose reductase gene in Type 1 and Type 2 diabetes mellitus

AIMS

To investigate the association between polymorphisms of the aldose reductase gene and diabetic nephropathy in both Type 1 and Type 2 diabetes mellitus, and to carry out a meta-analysis of published results.

METHODS

We have investigated the role of two aldose reductase polymorphisms in four independent cohorts of cases and controls (two each with Type 1 and Type 2 diabetes) drawn from two ethnic populations, including 471 patients with nephropathy and 494 control diabetic patients without nephropathy. A C/T transition at position -106, and a (CA)n microsatellite marker 2.1 kb from the start site of the aldose reductase gene were genotyped in nephropathic patients and non-nephropathic controls from each cohort.

RESULTS

Carriage of the -106 T allele was significantly associated with diabetic nephropathy in three of the four study groups. The Mantel-Haenszel combined odds ratio was 2.22 (95% CI 1.69, 2.94), P = 1.05 x 10(-8). We found no evidence for association of the microsatellite marker with nephropathy, despite moderate levels of disequilibrium between the two markers. Meta-analysis of published data yielded no evidence for association of the microsatellite marker with diabetic nephropathy in Type 2 diabetes, but varying degrees of association with diabetic nephropathy in Type 1 diabetes.

CONCLUSIONS

Meta-analyses provide more convincing evidence of a role for the ALR2-106 marker than for the microsatellite marker in diabetic nephropathy (DN). More studies are now required to confirm these results and to establish whether the ALR2-106 polymorphism has a functional role in DN.

Long-term effect of epalrestat, an aldose reductase inhibitor, on the development of incipient diabetic nephropathy in Type 2 diabetic patients

The aim of the present study was to elucidate the long-term effect of epalrestat, an aldose reductase inhibitor (ARI), on renal function in patients with type 2 diabetes mellitus showing microalbuminuria. Patients were allocated to two groups (cases and controls) matched for age, BMI, and the extent of urinary albumin excretion (UAE). Thirty-five type 2 diabetic patients presenting microalbuminuria were included in this study: cases were treated with epalrestat (150 mg/day) for 5 years. No significant changes were found in blood pressure, HbA1c, and total cholesterol in either group during the observation period. In the control group, UAE increased significantly (P<.01) from 82+/-12 mg/g Cr at the baseline to 301+/-111 mg/g Cr at the end of the study, while UAE remained unchanged, 81+/-15 mg/g Cr at the baseline and 87+/-19 mg/g Cr at the end of the study, in the epalrestat-treated group. Reciprocal creatinine measured by an enzyme assay decreased significantly (P<.01) in both groups; however, the reduction rate in the epalrestat-treated group was significantly (P<.05) smaller than that in the control group. These results suggest the potential usefulness of ARIs in preventing the progression of incipient diabetic nephropathy in patients with type 2 diabetes mellitus.

Immunohistochemical characterization of glomerular PDGF B-chain and PDGF beta-receptor expression in diabetic rats

Platelet-derived growth factor (PDGF) was found to contribute to the pathophysiological process in the development and progression of glomerulosclerosis characterized by mesangial cell proliferation and accumulation of extracellular matrix. To examine the role of PDGF in the development of diabetic nephropathy, we conducted immunohistochemical analysis for PDGF B-chain (PDGF-B) and PDGF beta-receptor (PDGFR-beta) in the glomeruli of streptozotocin-induced diabetic rats. At 2, 4, and 12 weeks after the onset of diabetes, the expression of PDGF-B in glomeruli of diabetic rats was increased significantly as compared to control or diabetic rats treated with insulin. Similar changes were observed on PDGFR-beta immunostaining. The immunostaining of mirror sections revealed the existence of PDGF-B or PDGFR-beta not only in mesangial cells but also in visceral epithelial cells. Glomerular volume was significantly increased in diabetes. This early glomerular abnormality was prevented by an inhibition of PDGF system with trapidil as well as by the treatment of insulin. Our results suggest that the activation of the PDGF system in glomerular cells might play an important role in the development of early glomerular lesion in diabetes.

Protective effect of an aldose reductase inhibitor against bone loss in galactose-fed rats: possible involvement of the polyol pathway in bone metabolism

Many patients with diabetes mellitus show a moderate reduction in bone mass. Our recent in vitro studies showed that sustained exposure of osteoblast-like MG-63 cells to high glucose by itself impairs their functions partly via the polyol pathway. To investigate the role of hyperglycemia in the etiology of diabetic osteopenia in vivo separately from insulin deficiency, we determined whether epalrestat, an aldose reductase (AR) inhibitor (ARI), lessens the abnormalities in calcium (Ca) metabolism in galactose-fed rats. Weight gain was impaired in the rats, which was not altered by epalrestat. Galactose feeding temporarily enhanced bone resorption as reflected by increased biochemical markers for bone resorption (urinary excretion of pyridinoline [PYR] and deoxypyridinoline [DPYR]) at 1 to 3 months, which were significantly decreased by epalrestat. Epalrestat also restored the positive correlation between a bone-formation marker (serum osteocalcin [OC]) and a bone-resorption marker (urinary DPYR excretion) at 6.5 months. Histomorphometric analysis of bone performed 6.5 months after galactose feeding showed that both the bone volume and osteoblast numbers in the tibia, which were significantly suppressed by galactose feeding, were partly restored to a significant extent by the simultaneous administration of epalrestat. In summary, epalrestat partially protected against the development of osteoblast dysfunction and reduced the temporary increase in biochemical markers for bone resorption induced by galactose feeding, with a resultant increase in bone volume, suggesting that the polyol pathway may be intimately involved in the development of abnormal bone metabolism in galactose-fed rats.