Stratified analyses for selecting appropriate target patients with diabetic peripheral neuropathy for long-term treatment with an aldose reductase inhibitor, epalrestat

Activation of 20-HETE Synthase Triggers Oxidative Injury and Peripheral Nerve Damage in Type 2 Diabetic Mice

Diabetic Peripheral Neuropathy (DPN), highly prevalent among patients with diabetes, is characterized by peripheral nerve dysfunction. Reactive Oxygen Species (ROS) overproduction has been suggested to orchestrate diabetic complications including DPN. Untargeted antioxidant therapy has exhibited limited efficacy, highlighting a critical need to explore ROS sources altered in a cell-specific manner in DPN. Cytochromes P450 (CYP) enzymes are prominent sources of ROS. Particularly, the 20-HETE synthase, CYP4A, is reported to mediate diabetes-induced renal, retinal, and cardiovascular injuries. This work investigates the role of CYP4A/20-HETE in DPN and their mechanisms of action. Non-obese type 2 Diabetic mice (MKR) were used and treated with a CYP4A-inhibitor (HET0016) or AMPK-activator (Metformin). Peripheral nerves of MKR mice reflect increased CYP4A and 20-HETE levels, concurrent with altered myelin proteins and sensorimotor deficits. This was associated with increased ROS production and altered Beclin-1 and LC3 protein levels, indicative of disrupted autophagic responses in tandem with AMPK inactivation. AMPK activation via Metformin restored nerve integrity, reduced ROS production, and regulated autophagy. Interestingly, similar outcomes were revealed upon HET0016 treatment whereby ROS production, autophagic responses, and AMPK signaling were normalized in diabetic mice. Altogether, the results highlight hyperglycemia-mediated oxidative injury in DPN through a novel CYP4A/20-HETE/AMPK pathological axis. PERSPECTIVE: To our knowledge, this is the first study to highlight the role of CYPs/20-HETE-induced oxidative injury in the pathogenesis of diabetic peripheral neuropathy. Targeting the identified pathological axis CYP4A/20-HETE/AMPK may be of clinical potential in predicting and alleviating peripheral nerve injury in patients with Type 2 Diabetes Mellitus.

Aldose Reductase and the Polyol Pathway in Schwann Cells: Old and New Problems

Aldose reductase (AR) is a member of the reduced nicotinamide adenosine dinucleotide phosphate (NADPH)-dependent aldo-keto reductase superfamily. It is also the rate-limiting enzyme of the polyol pathway, catalyzing the conversion of glucose to sorbitol, which is subsequently converted to fructose by sorbitol dehydrogenase. AR is highly expressed by Schwann cells in the peripheral nervous system (PNS). The excess glucose flux through AR of the polyol pathway under hyperglycemic conditions has been suggested to play a critical role in the development and progression of diabetic peripheral neuropathy (DPN). Despite the intensive basic and clinical studies over the past four decades, the significance of AR over-activation as the pathogenic mechanism of DPN remains to be elucidated. Moreover, the expected efficacy of some AR inhibitors in patients with DPN has been unsatisfactory, which prompted us to further investigate and review the understanding of the physiological and pathological roles of AR in the PNS. Particularly, the investigation of AR and the polyol pathway using immortalized Schwann cells established from normal and AR-deficient mice could shed light on the causal relationship between the metabolic abnormalities of Schwann cells and discordance of axon-Schwann cell interplay in DPN, and led to the development of better therapeutic strategies against DPN.

(-)-Kusunokinin as a Potential Aldose Reductase Inhibitor: Equivalency Observed via AKR1B1 Dynamics Simulation

(-)-Kusunokinin performed its anticancer potency through CFS1R and AKT pathways. Its ambiguous binding target has, however, hindered the next development phase. Our study thus applied molecular docking and molecular dynamics simulation to predict the protein target from the pathways. Among various candidates, aldo-keto reductase family 1 member B1 (AKR1B1) was finally identified as a (-)-kusunokinin receptor. The predicted binding affinity of (-)-kusunokinin was better than the selected aldose reductase inhibitors (ARIs) and substrates. The compound also had no significant effect on AKR1B1 conformation. An intriguing AKR1B1 efficacy, with respect to the known inhibitors (epalrestat, zenarestat, and minalrestat) and substrates (UVI2008 and prostaglandin H₂), as well as a similar interactive insight of the enzyme pocket, pinpointed an ARI equivalence of (-)-kusunokinin. An aromatic ring and a γ-butyrolactone ring shared a role with structural counterparts in known inhibitors. The modeling explained that the aromatic constituent contributed to π-π attraction with Trp111. In addition, the γ-butyrolactone ring bound the catalytic His110 using hydrogen bonds, which could lead to enzymatic inhibition as a consequence of substrate competitiveness. Our computer-based findings suggested that the potential of (-)-kusunokinin could be furthered by in vitro and/or in vivo experiments to consolidate (-)-kusunokinin as a new AKR1B1 antagonist in the future.

Point-of-care nerve conduction device predicts the severity of diabetic polyneuropathy: A quantitative, but easy-to-use, prediction model

Aims/Introduction

A gold standard in the diagnosis of diabetic polyneuropathy (DPN) is a nerve conduction study. However, as a nerve conduction study requires expensive equipment and well‐trained technicians, it is largely avoided when diagnosing DPN in clinical settings. Here, we validated a novel diagnostic method for DPN using a point‐of‐care nerve conduction device as an alternative way of diagnosis using a standard electromyography system.

Materials and Methods

We used a multiple regression analysis to examine associations of nerve conduction parameters obtained from the device, DPNCheck™, with the severity of DPN categorized by the Baba classification among 375 participants with type 2 diabetes. A nerve conduction study using a conventional electromyography system was implemented to differentiate the severity in the Baba classification. The diagnostic properties of the device were evaluated using a receiver operating characteristic curve.

Results

A multiple regression model to predict the severity of DPN was generated using sural nerve conduction data obtained from the device as follows: the severity of DPN = 2.046 + 0.509 × ln(age [years]) − 0.033 × (nerve conduction velocity [m/s]) − 0.622 × ln(amplitude of sensory nerve action potential [µV]), r = 0.649. Using a cut‐off value of 1.3065 in the model, moderate‐to‐severe DPN was effectively diagnosed (area under the receiver operating characteristic curve 0.871, sensitivity 70.1%, specificity 87.7%, positive predictive value 83.0%, negative predictive value 77.3%, positive likelihood ratio 5.67, negative likelihood ratio 0.34).

Conclusions

Nerve conduction parameters in the sural nerve acquired by the handheld device successfully predict the severity of DPN.

Targeting the NADPH Oxidase-4 and Liver X Receptor Pathway Preserves Schwann Cell Integrity in Diabetic Mice

Diabetes triggers peripheral nerve alterations at a structural and functional level, collectively referred to as diabetic peripheral neuropathy (DPN). This work highlights the role of the liver X receptor (LXR) signaling pathway and the cross talk with the reactive oxygen species (ROS)-producing enzyme NADPH oxidase-4 (Nox4) in the pathogenesis of DPN. Using type 1 diabetic (T1DM) mouse models together with cultured Schwann cells (SCs) and skin biopsies from patients with type 2 diabetes (T2DM), we revealed the implication of LXR and Nox4 in the pathophysiology of DPN. T1DM animals exhibit neurophysiological defects and sensorimotor abnormalities paralleled by defective peripheral myelin gene expression. These alterations were concomitant with a significant reduction in LXR expression and increase in Nox4 expression and activity in SCs and peripheral nerves, which were further verified in skin biopsies of patients with T2DM. Moreover, targeted activation of LXR or specific inhibition of Nox4 in vivo and in vitro to attenuate diabetes-induced ROS production in SCs and peripheral nerves reverses functional alteration of the peripheral nerves and restores the homeostatic profiles of MPZ and PMP22. Taken together, our findings are the first to identify novel, key mediators in the pathogenesis of DPN and suggest that targeting LXR/Nox4 axis is a promising therapeutic approach.

Diabetic neuropathy and the sensory neuron: New aspects of pathogenesis and their treatment implications

Diabetic polyneuropathy (DPN) continues to be generally considered as a "microvascular" complication of diabetes mellitus alongside nephropathy and retinopathy. The microvascular hypothesis, however, might be tempered by the concept that diabetes directly targets dorsal root ganglion sensory neurons. This neuron-specific concept, supported by accumulating evidence, might account for important features of DPN, such as its early sensory neuron degeneration. Diabetic sensory neurons develop neuronal atrophy alongside a series of messenger ribonucleic acid (RNA) changes related to declines in structural proteins, increases in heat shock protein, increases in the receptor for advanced glycation end-products, declines in growth factor signaling and other changes. Insulin is recognized as a potent neurotrophic factor, and insulin ligation enhances neurite outgrowth through activation of the phosphoinositide 3-kinase-protein kinase B pathway within sensory neurons and attenuates phenotypic features of experimental DPN. Several interventions, including glucagon-like peptide-1 agonism, and phosphatase and tensin homolog inhibition to activate growth signals in sensory neurons, or heat shock protein overexpression, prevent or reverse neuropathic abnormalities in experimental DPN. Diabetic sensory neurons show a unique pattern of microRNA alterations, a key element of messenger RNA silencing. For example, let-7i is widely expressed in sensory neurons, supports their growth and is depleted in experimental DPN; its replenishment improves features of DPN models. Finally, impairment of pre-messenger RNA splicing in diabetic sensory neurons including abnormal nuclear RNA metabolism and structure with loss of survival motor neuron protein, a neuron survival molecule, and overexpression of CWC22, a splicing factor, offer further novel insights. The present review addresses these new aspects of DPN sensory neurodegeneration.

Study on degradation kinetics of epalrestat in aqueous solutions and characterization of its major degradation products under stress degradation conditions by UHPLC-PDA-MS/MS

Drug stability is closely related to drug safety and needs to be considered in the process of drug production, package and storage. To investigate the stability of epalrestat, a carboxylic acid derivative, a reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed in this study and applied to analyzing the degradation kinetics of epalrestat in aqueous solutions in various conditions, such as different pH, temperatures, ionic strengths, oxidation and irradiation. The calibration curve was A = 1.6 × 10⁵ C-1.3 × 10³ (r = 0.999) with the liner range of 0.5-24 μg/mL, the intra-day and inter-day precision was less than 2.0%, as was the repeatibility. The average accuracy for different concentrations was more than 98.5%, indicating that perfect recoveries were achieved. Degradation kinetic parameters such as degradation rate constants (k), activation energy (Ea) and shelf life (t _0.9 ) under different conditions were calculated and discussed. The results indicated that the degradation behavior of epalrestat was pH-dependent and the stability of epalrestat decreased with the rised irradiation and ionic strength; however, it was more stable in neutral and alkaline conditions as well as lower temperatures. The results showed that the degradation kinetics of epalrestat followed first-order reaction kinetics. Furthermore, the degradation products of epalrestat under stress conditions were identified by UHPLC-PDA-MS/MS, with seven degradation products being detected and four of them being tentatively identified.

Epalrestat Stimulated Oxidative Stress, Inflammation, and Fibrogenesis in Mouse Liver

Epalrestat (EPS), an aldose reductase inhibitor, is widely prescribed to manage diabetic neuropathy. It is generally believed that EPS is beneficial to diabetic patients because it can protect endothelial cells, Schwann cells, or other neural cells from oxidative stress. However, several clinical studies revealed that EPS therapy led to liver dysfunction, which limited its clinical applications. Currently, the underlying mechanism by which EPS causes liver dysfunction is unknown. This study aimed to investigate the mechanism responsible for EPS-induced liver injury. In mouse liver, EPS 1) increased oxidative stress, indicated by increased expression of manganese superoxide dismutase, Ho-1, and Nqo1, 2) induced inflammation, indicated by infiltration of inflammatory cells, and induced expression of tumor necrosis factor-alpha, CD11b, and CD11c, as well as 3) predisposed to induce fibrosis, evidenced by increased mRNA and protein expression of early profibrotic biomarker genes procollagen I and alpha-smooth muscle actin, and by increased collagen deposition. In cultured mouse and human hepatoma cells, EPS treatment induced oxidative stress, decreased cell viability, and triggered apoptosis evidenced by increased Caspase-3 cleavage/activation. In addition, EPS increased mRNA and protein expression of cytoglobin in mouse liver, indicating that EPS activated hepatic stellate cells (HSCs). Furthermore, EPS treatment in cultured human HSCs increased cell viability. In summary, EPS administration induced oxidative stress and inflammation in mouse liver, and stimulated liver fibrogenesis. Therefore, cautions should be exercised during EPS therapy.

Aldo-Keto Reductase Family 1 Member B10 Inhibitors: Potential Drugs for Cancer Treatment

Cytosolic NADPH-dependent reductase AKR1B10 is a member of the aldo-keto reductase (AKR) superfamily. This enzyme is normally expressed in the gastrointestinal tract. However, it is overexpressed in many solid tumors, such as hepatocarcinoma, lung cancer and breast cancer. AKR1B10 may play a role in the formation and development of carcinomas through multiple mechanisms including detoxification of cytotoxic carbonyls, modulation of retinoic acid level, and regulation of cellular fatty acid synthesis and lipid metabolism. Studies have suggested that AKR1B10 may be a useful biomarker for cancer diagnosis and a potential target for cancer treatment. Over the last decade, a number of AKR1B10 inhibitors including aldose reductase inhibitors (ARIs), endogenous substances, natural-based derivatives and synthetic compounds have been developed, which could be novel anticancer drugs. This review provides an overview on related articles and patents about AKR1B10 inhibitors, with a focus on their inhibition selectivity and mechanism of function.

Reactive oxygen species: sources, consequences and targeted therapy in type 2 diabetes

Oxidative stress has been considered as a central mediator in the progression of diabetic complication. The intracellular reactive oxygen species (ROS) leads to oxidative stress and it is raised from the mitochondria as well as by activation of five major pathways: increased polyol pathway flux, activation of protein kinase C (PKC) pathway, increased formation of advanced glycation end products (AGEs), over activity of hexosamine pathway and increased production of angiotensin II. The increased ROS through these pathways leads to β-cell dysfunction and insulin resistance, responsible for cell damage and death. This review not only highlights the sources of ROS production and their involvement in the progression of diabetes, but also emphasizes on pharmacological interventions and targeting of ROS in type 2 diabetes. This review summarizes the ROS as potential therapeutic targets, based on a putative mechanism in the progression of the diabetes. It also summarizes current knowledge of ROS activation in type 2 diabetes as well as ROS as a possible target for its treatment. Eventually, it would be a promising target for various strategies and drugs to modulate ROS levels in diabetes.

Glucotoxic Mechanisms and Related Therapeutic Approaches

Neuropathy is the earliest and commonest complication of diabetes. With increasing duration of diabetes, frequency and severity of neuropathy are worsened. Long-term hyperglycemia is therefore implicated in the development of this disorder. Nerve tissues require glucose energy to function and survive. Upon excessive glucose entry into the peripheral nerve, the glycolytic pathway and collateral glucose-utilizing pathways are overactivated and initiate adverse effects on nerve tissues. During hyperglycemia, flux through the polyol pathway, formation of advanced glycation end-products, production of free radicals, flux into the glucosamine pathway, and protein kinase C activity are all enhanced to negatively influence nerve function and structure. Suppression of these aberrant metabolic pathways has succeeded in prevention and inhibition of the development of neuropathy in animal models with diabetes. Satisfactory results were not attained, however, in patients with diabetes and further clinical trials are required. In this review, the author summarizes the hitherto proposed theories on the pathogenesis of diabetic neuropathy related to glucose metabolism and future prospects for the effective treatment of neuropathy.

Effects of aldose reductase inhibitor on microneurographically assessed peripheral sympathetic nerve activity in rats

Autonomic neuropathy, one of the serious complications of diabetes, decreases quality of life. Aldose reductase inhibitor (ARI) blocks sorbitol production, and results in prevention of damage of nerve fibers. Beneficial effects of ARI have usually been confirmed through nerve conduction velocity tests in motor and sensory nerves. On the other hand, few reports have dealt with the effects of ARI on the small fiber activity such as sympathetic nerve one. In the present study, we administered eparlestat, ARI orally for 3weeks, to streptozotocin-induced diabetic (STZ+ARI) rats, and then recorded peripheral sympathetic nervous signal detected with microneurographic technique. Action potentials (APs) and bursts of APs were detected from the recorded signal, and their rates and incidences (=rates/heart rate) were compared with those in non-diabetic control (normal) and ARI-untreated streptozotocin-induced diabetic (STZ) rats. While streptozotocin and/or epalrestat did not influence burst parameters in all the three groups, AP parameters in the STZ+ARI and normal groups were higher than those in the STZ group. However, response of AP parameters to the intravenous glucose administration (IVGA) was not large in the STZ+ARI group, similar to that of the STZ group and different from that of the normal group in which AP parameters increased after IVGA. The results suggest that epalrestat may prevent sympathetic nerve activity (SNA) from reduction under hyperglycemic and insulin-depleted conditions, that enhancement of SNA was not induced after IVGA under that condition, and that AP parameters might be useful to assess the degree of neuropathy.

Inhibitory activities of selected Kampo formulations on human aldose reductase

BACKGROUND

Diabetes complications include various symptoms such as diabetic neuropathy and cognitive disorders. Aldose reductase (AR) is the rate-limiting enzyme of the polyol pathway and is one of the causal factors of diabetes complications. In this study, the bioactivities of eight selected Kampo formulations that are currently in clinical use for diabetes complications were assessed using human AR (hAR) inhibitory activity as the primary parameter to explore the possibilities of novel clinical applications of these formulations in the treatment of diabetes complications.

METHODS

The hAR inhibitory activities of four Kampo formulations that are clinically used for diabetic neuropathy, four Kampo formulations that are used for cognitive disorders, and a total of 21 component crude drugs were measured. Furthermore, the hAR inhibitory activity of Glycyrrhizae Radix preparata was measured to determine the effect of frying, which is one of the specific processing of Glycyrrhizae Radix. hAR inhibitory activity was determined by measuring the rate of decline in the absorbance of NAPH at 340 nm using 0.5 mM NADPH, 10 mM D,L-glyceraldehyde, and 3.6 mU/mL hAR in phosphate buffer solution (0.2 M, pH 6.2).

RESULTS

All of the Kampo formulations exhibited significant hAR inhibitory activity; Chotosan exhibited particularly strong activity. Among the 21 crude drugs tested, adequate inhibitory activities were found for the following, in descending order of activity: Glycyrrhizae Radix > Paeoniae Radix > Chrysanthemi Flos > Cinnamomi Cortex > Phellodendri Cortex > Uncariae Uncis cum Ramulus > Bupleuri Radix. Glycyrrhizae Radix preparata exhibited an inhibitory activity that was nearly identical to that of Glycyrrhizae Radix.

CONCLUSIONS

Despite their seemingly different treatment objectives, all of the Kampo formulations that are clinically used for diabetes complications demonstrated significant hAR inhibitory activity. This activity might underlie the characteristic multi-target effects of Kampo formulations. Although the overall effect of a Kampo formulation is certainly difficult to evaluate based on specific herbal medications or components, the approach as taken in this study might nonetheless contribute to further advancement in the development of new drugs via the review of proper usage and re-examination of the chemical compounds from a new perspective.

Mechanism of diabetic neuropathy: Where are we now and where to go?

Neuropathy is the most common complication of diabetes. As a consequence of longstanding hyperglycemia, a downstream metabolic cascade leads to peripheral nerve injury through an increased flux of the polyol pathway, enhanced advanced glycation end‐products formation, excessive release of cytokines, activation of protein kinase C and exaggerated oxidative stress, as well as other confounding factors. Although these metabolic aberrations are deemed as the main stream for the pathogenesis of diabetic microvascular complications, organ‐specific histological and biochemical characteristics constitute distinct mechanistic processes of neuropathy different from retinopathy or nephropathy. Extremely long axons originating in the small neuronal body are vulnerable on the most distal side as a result of malnutritional axonal support or environmental insults. Sparse vascular supply with impaired autoregulation is likely to cause hypoxic damage in the nerve. Such dual influences exerted by long‐term hyperglycemia are critical for peripheral nerve damage, resulting in distal‐predominant nerve fiber degeneration. More recently, cellular factors derived from the bone marrow also appear to have a strong impact on the development of peripheral nerve pathology. As evident from such complicated processes, inhibition of single metabolic factors might not be sufficient for the treatment of neuropathy, but a combination of several inhibitors might be a promising approach to overcome this serious disorder. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00070.x, 2010)

Recent advances in the management of diabetic distal symmetrical polyneuropathy

There is now little doubt that poor blood glucose control is an important risk factor for the development of diabetic peripheral neuropathy (DPN). Furthermore, traditional cardiovascular risk factors for macrovascular disease appear to be associated with an increased risk of DPN. The recently established International Expert Group on Diabetic Neuropathy has recommended new criteria for the diagnosis of DPN in the context of clinical and research settings. Studies in experimental diabetes examining the pathogenesis of DPN have identified a number of metabolic abnormalities including polyol pathway hyperactivity, increased advanced glycation end‐point formation, alterations in the protein kinase C beta pathway through diacylglycerol and oxidative stress. There is now strong evidence implicating nerve ischemia as the cause of DPN. Studies in human and animal models have shown reduced nerve perfusion and endoneurial hypoxia. These endoneurial microvascular changes strongly correlate with clinical severity and the degree of nerve‐fiber pathology. Unfortunately, many compounds that have been effective in animal models of neuropathy have not been successful in human diabetic neuropathy. The only compounds found to be efficacious in human diabetic neuropathy, and are in clinical use, are the anti‐oxidant, α‐lipoic acid and the aldose reductase inhibitor, epalrestat. Overall, the evidence emphasizes the importance of vascular dysfunction, driven by metabolic change, in the etiology of DPN, and highlights potential therapeutic approaches. Epidemiological data on diabetic painful neuropathic pain (DPNP) are limited. In one population‐based study, the prevalence of DPNP, as assessed by a structured questionnaire and examination, was estimated at 16%. It was notable that, of these patients, 12.5% had never reported symptoms to their doctor and 39% had never received treatment for their pain. Thus, despite being common, DPNP continues to be underdiagnosed and undertreated. Pharmacological treatment of DPNP include tricyclic compounds, serotonin noradrenalin reuptake inhibitors, the anti‐oxidant α‐lipoic acid, anticonvulsants, opiates, membrane stabilizers, topical capsaicin and so on. Management of the patient with DPNP must be tailored to individual requirements and will depend on the presence of other comorbidities. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00083.x)

Strategies for preventing type 2 diabetes: an update for clinicians

Diabetes is a major and growing public health challenge which threatens to overwhelm medical services in the future. Type 2 diabetes confers significant morbidity and mortality, most notably with target organ damage to the eyes, kidneys, nerves and heart. The magnitude of cardiovascular risk associated with diabetes is best illustrated by its position as a coronary heart disease risk equivalent. Complications related to neuropathy are also vast, often working in concert with vascular abnormalities and resulting in serious clinical consequences such as foot ulceration. Increased understanding of the natural history of this disorder has generated the potential to intervene and halt pathological progression before overt disease ensues, after which point management becomes increasingly challenging. The concept of prediabetes as a formal diagnosis has begun to be translated from the research setting to clinical practice, but with continually updated guidelines, varied nomenclature, emerging pharmacotherapies and an ever-changing evidence base, clinicians may be left uncertain of best practice in identifying and managing patients at the prediabetic stage. This review aims to summarize the epidemiological data, new concepts in disease pathogenesis and guideline recommendations in addition to lifestyle, pharmacological and surgical therapies targeted at stopping progression of prediabetes to diabetes. While antidiabetic medications, with newer anti-obesity medications and interventional bariatric procedures have shown some promising benefits, diet and therapeutic lifestyle change remains the mainstay of management to improve the metabolic profile of individuals with glucose dysregulation. New risk stratification tools to identify at-risk individuals, coupled with unselected population level intervention hold promise in future practice.

Novel drugs and their targets in the potential treatment of diabetic retinopathy

Diabetic retinopathy (DR) is the most common complication of diabetes. It causes vision loss, and the incidence is increasing with the growth of the diabetes epidemic worldwide. Over the past few decades a number of clinical trials have confirmed that careful control of glycemia and blood pressure can reduce the risk of developing DR and control its progression. In recent years, many treatment options have been developed for clinical management of the complications of DR (e.g., proliferative DR and macular edema) using laser-based therapies, intravitreal corticosteroids and anti-vascular endothelial growth factors, and vitrectomy to remove scarring and hemorrhage, but all these have limited benefits. In this review, we highlight and discuss potential molecular targets and new approaches that have shown great promise for the treatment of DR. New drugs and strategies are based on targeting a number of hyperglycemia-induced metabolic stress pathways, oxidative stress and inflammatory pathways, the renin-angiotensin system, and neurodegeneration, in addition to the use of stem cells and ribonucleic acid interference (RNAi) technologies. At present, clinical trials of some of these newer drugs in humans are yet to begin or are in early stages. Together, the new therapeutic drugs and approaches discussed may control the incidence and progression of DR with greater efficacy and safety.

Long-term clinical effects of epalrestat, an aldose reductase inhibitor, on progression of diabetic neuropathy and other microvascular complications: multivariate epidemiological analysis based on patient background factors and severity of diabetic neuropathy

AIMS

The goal of the study was to evaluate the efficacy of epalrestat, an aldose reductase inhibitor, on diabetic retinopathy and diabetic nephropathy, based on analysis of the results of the Aldose Reductase Inhibitor-Diabetes Complications Trial, a 3-year multicentre comparative clinical trial of conventional therapy (control group) and epalrestat therapy (epalrestat group) in Japanese patients with mild diabetic neuropathy.

METHODS

The subjects of the study were patients enrolled in the Aldose Reductase Inhibitor-Diabetes Complications Trial for whom data for major patient characteristics, severity of diabetic neuropathy at the end of the study and time-courses of diabetic retinopathy and diabetic nephropathy were available (57 and 52 patients from the control and epalrestat groups, respectively). Progression of diabetic retinopathy/nephropathy (a primary endpoint) in relation to major patient characteristics, severity of diabetic neuropathy at the end of the study (assessed from the mean of z-scores in four neurological function tests) and epalrestat treatment were analysed using univariate analysis and multiple logistic regression analysis.

RESULTS

Progression of diabetic retinopathy/nephropathy was significantly inhibited in the epalrestat group compared with the control group (odds ratio = 0.323, P = 0.014) and was dependent on the severity of diabetic neuropathy at the end of the study (odds ratio = 2.131, P = 0.025).

CONCLUSIONS

Epalrestat prevented progression of diabetic neuropathy and retinopathy/nephropathy. The effect on diabetic retinopathy/nephropathy may have occurred indirectly because of the prevention of progression of diabetic neuropathy, in addition to the inhibitory action of epalrestat on aldose reductase.

Protein kinase C beta inhibitor prevents diabetic peripheral neuropathy, but not histopathological abnormalities of retina in Spontaneously Diabetic Torii rat

Spontaneously Diabetic Torii (SDT) rat shows severe ocular complications such as tractional retinal detachment. In the present study, effect of protein kinase C beta (PKCbeta) inhibitor JTT-010 was evaluated to clarify the involvement of PKCbeta in complications of SDT rat. SDT rats were administered JTT-010 (10 or 50 mg/kg/day) for 48 weeks. SDT rats showed delayed oscillatory potentials in electroretinogram. Delayed motor nerve conduction velocity, decreased coefficients of variation of R-R intervals in electrocardiogram and thermal hypoalgesia were also observed. These functional disorders were prevented by administration of JTT-010. Abnormal retinal vascular was formed and the optic disc was protruded in SDT rat; however, JTT-010 did not prevent these hyperglycaemia-induced retinal abnormalities. These findings indicate that PKCbeta is intimately involved in diabetic complications; however, it seems that other factor(s) are primary contributors to histopathological abnormalities in retina. Therefore, PKCbeta inhibitors require concurrent administration of antihyperglycaemic drugs to achieve maximum effect on diabetic complications.

[Pathophysiology and treatment for diabetic neuropathy]

Diabetic neuropathy (DN) is the most frequent among peripheral neuropathies. Since its pathophysiology is so complicated, neither classification nor therapeutic management of DN has been established. Sensory/autonomic polyneuropathy (DP) is the main type of DN. Since diabetic patients occasionally have one or more subtypes of DN and/or other polyneuropathy including treatable neuropathy like CIDP, the treatment for DP has to be conducted after excluding the possibility of other conditions. Glycemic control is most essential to prevent the development of DP. However, it is practically difficult to keep HbA1c under 6.5% so that drinking and smoking better be restricted and blood pressure be properly maintained to retard the progression of DP. Aldose reductase inhibitor is only one commercially available drug for DP and its efficacy must be evaluated by nerve function tests along with subjective symptoms. More vigorous therapeutic procedure is expected by obtaining not only more potential drugs based on pathogenic mechanisms but also the technique targeting of DNA/siRNA of given peptides at dorsal root ganglion neurons.