Increased protein kinase C (PKC) activity has been implicated in the pathogenesis of diabetic retinopathy and nephropathy. However, the role of PKC in diabetic neuropathy remains unclear. The present study was conducted to compare the effect of PKC inhibition by a PKC-beta-selective inhibitor, LY333531 (LY), on diabetic nerve dysfunction with that of an aldose reductase inhibitor, NZ-314 (NZ). Streptozotocin-induced diabetic rats were treated with or without LY and/or NZ for 4 weeks, and motor nerve conduction velocity (MNCV), coefficient of variation of R-R interval (CVR-R), sciatic nerve blood flow (SNBF), peak latencies of oscillatory potentials on electroretinogram, PKC activities in membranous and cytosolic fractions of sciatic nerves, and polyol contents in the tail nerves were measured. Untreated diabetic rats demonstrated delayed MNCV, decreased CVR-R, reduced SNBF, and prolonged peak latencies of oscillatory potentials. Treatment with LY as well as NZ prevented all these deficits in diabetic rats. There were no significant differences in PKC activities in membranous or cytosolic fractions of sciatic nerves between normal and diabetic rats. Treatment with neither LY nor NZ altered PKC activities. Nerve myo-inositol depletion in diabetic rats was ameliorated not only by NZ, but also by LY. These observations suggest that inhibition of PKC-beta by LY may have a beneficial effect in preventing the development of diabetic nerve dysfunction, and that this effect may be mediated through its action on the endoneurial micro-vasculature.

OBJECTIVE-Mesenchymal stem cells (MSCs) have been reported to secrete various cytokines that exhibit angiogenic and neurosupportive effects. This study was conducted to investigate the effects of MSC transplantation on diabetic polyneuropathy (DPN) in rats.RESEARCH DESIGN AND METHODS-MSCs were isolated from bone marrow of adult rats and transplanted into hind limb skeletal muscles of rats with an 8-week duration of streptozotocin (STZ)-induced diabetes or age-matched normal rats by unilateral intramuscular injection. Four weeks after transplantation, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) productions in transplanted sites, current perception threshold, nerve conduction velocity (NCV), sciatic nerve blood flow (SNBF), capillary number-to-muscle fiber ratio in soleus muscles, and sural nerve morphometry were evaluated.RESULTS-VEGF and bFGF mRNA expression were significantly increased in MSC-injected thigh muscles of STZ-induced diabetic rats. Furthermore, colocalization of MSCs with VEGF and bFGF in the transplanted sites was confirmed. STZ-induced diabetic rats showed hypoalgesia, delayed NCV, decreased SNBF, and decreased capillary number-to-muscle fiber ratio in soleus muscles, which were all ameliorated by MSC transplantation. Sural nerve morphometry showed decreased axonal circularity in STZ-induced diabetic rats, which was normalized by MSC transplantation. D iabetic polyneuropathy (DPN) is the most common complication of diabetes. It is estimated that ϳ20 -30% of diabetic patients are affected by symptomatic DPN (1). Generally, DPN develops symmetrically in a length-dependent fashion, with dying back or dropout of the longest nerve fibers; both myelinated and unmyelinated, large and small are affected. Diabetic patients suffer from various symptoms of DPN, such as spontaneous pain, hyperalgesia, and diminished sensation (2). It has been shown that tight glycemic control is effective in slowing the progression of DPN but cannot completely prevent it (3). Therefore, additional therapeutic strategies are required. CONCLUSIONS-TheseNeural cell degeneration and decreased nerve blood flow (NBF) have been recognized as pathophysiologically characteristic features of DPN (4). Therefore, therapeutic agents that could act as both neurotrophic and angiogenic factors would be useful for the treatment of DPN even at an advanced stage. We previously demonstrated that local administration of basic fibroblast growth factor (bFGF) by intramusclar injection with crosslinked gelatin hydrogel improved the impaired nerve functions of streptozotocin (STZ)-induced diabetic rats, including amelioration of decreased NBF, hypoalgesia, and the delayed motor nerve conduction velocity (MNCV) on the treated side of sciatictibial nerves and that these effects were maintained for at least 30 days (5). Schratzberger et al. (6) showed that vascular endothelial growth factor (VEGF) gene transfer significantly increased the NCV and NBF as well as the vascular densities in muscle and peripheral nerv...

Diabetic neuropathy is based on the impairment of nerve blood flow and the metabolic disorder. Although the vasodilating agents and anticoagulants improve nerve function and symptoms in diabetic neuropathy, more effective treatments are needed. Because endothelial progenitor cells (EPCs) have been identified in adult human peripheral blood, many studies have shown that transplantation of EPCs improves circulation to ischemic tissues. In this study, we have demonstrated that therapeutic neovascularization using human umbilical cord blood-derived EPCs reversed diabetic neuropathy. EPCs were isolated and expanded on day 7 of culture from cord blood mononuclear cells. Unilateral intramuscular injection of EPCs into hindlimb skeletal muscles significantly ameliorated impaired sciatic motor nerve conduction velocity and sciatic nerve blood flow in the EPC-injected side of streptozotocin-induced diabetic nude rats compared with the saline-injected side of diabetic nude rats. Histological study revealed an increased number of microvessels in hindlimb skeletal muscles in the EPC-injected side of diabetic rats. These findings suggest that transplantation of EPCs from cord blood may be a useful treatment for diabetic neuropathy.

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OBJECTIVEThe therapeutic potential of exendin-4, an agonist of the glucagon-like peptide-1 receptor (GLP-1R), on diabetic polyneuropathy (DPN) in streptozotocin (STZ)-induced diabetic mice was investigated.RESEARCH DESIGN AND METHODSThe presence of the GLP-1R in lumbar dorsal root ganglion (DRG) was evaluated by immunohistochemical analyses. DRG neurons were dissected from C57BL6/J mice and cultured with or without Schwann cell–conditioned media in the presence or absence of GLP-1 (7–37) or exendin-4. Then neurite outgrowth was determined. In animal-model experiments, mice were made diabetic by STZ administration, and after 12 weeks of diabetes, exendin-4 (10 nmol/kg) was intraperitoneally administered once daily for 4 weeks. Peripheral nerve function was determined by the current perception threshold and motor and sensory nerve conduction velocity (MNCV and SNCV, respectively). Sciatic nerve blood flow (SNBF) and intraepidermal nerve fiber densities (IENFDs) also were evaluated.RESULTSThe expression of the GLP-1R in DRG neurons was confirmed. GLP-1 (7–37) and exendin-4 significantly promoted neurite outgrowth of DRG neurons. Both GLP-1R agonists accelerated the impaired neurite outgrowth of DRG neurons cultured with Schwann cell–conditioned media that mimicked the diabetic condition. At the doses used, exendin-4 had no effect on blood glucose or HbA1c levels. Hypoalgesia and delayed MNCV and SNCV in diabetic mice were improved by exendin-4 without affecting the reduced SNBF. The decreased IENFDs in sole skins of diabetic mice were ameliorated by exendin-4.CONCLUSIONSOur findings indicate that exendin-4 ameliorates the severity of DPN, which may be achieved by its direct actions on DRG neurons and their axons.

a b s t r a c tIn this study we aimed to identify the physiological roles of G protein-coupled receptor 84 (GPR84) in adipose tissue, together with medium-chain fatty acids (MCFAs), the specific ligands for GPR84. In mice, high-fat diet up-regulated GPR84 expression in fat pads. In 3T3-L1 adipocytes, co-culture with a macrophage cell line, RAW264, or TNFa remarkably enhanced GPR84 expression. In the presence of TNFa, MCFAs down-regulated adiponectin mRNA expression in 3T3-L1 adipocytes. Taken together, our results suggest that GPR84 emerges in adipocytes in response to TNFa from infiltrating macrophages and exacerbates the vicious cycle between adiposity and diabesity.

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Diabetes mellitus is one of the major risk factors for atherosclerosis and is associated with an increased incidence of coronary heart diseases and cerebrovascular diseases [1,2]. The high prevalence of these macrovascular diseases in diabetic patients can be explained by hyperglycaemia in itself [3] as well as by the increased frequency of conventional risk factors such as hypertension, hyperlipidemia, obesity, and smoking.The proliferation of vascular smooth muscle cells is one of the characteristic features of atherosclerosis [4]. According to previous reports [4,5], platelet-derived growth factor (PDGF) plays an important part in the accelerated proliferation of smooth muscle Diabetologia (2001) Abstract Aims/hypothesis. The protein kinase C (PKC), platelet-derived growth factor (PDGF) and polyol pathway play important parts in the hyperproliferation of smooth muscle cells, a characteristic feature of diabetic macroangiopathy. The precise mechanism, however, remains unclear. This study investigated the relation between polyol pathway, protein kinase C and platelet-derived growth factor in the development of diabetic macroangiopathy. Methods. Smooth muscle cells were cultured with 5.5 or 20 mmol/l glucose with or without an aldose reductase inhibitor, epalrestat, or a PKC-b specific inhibitor, LY333 531. Protein kinase C activities, the expression of PKC-bII isoform and PDGF-b receptor protein, free cytosolic NAD + :NADH ratio, the contents of reduced glutathione, and proliferation activities were measured. Results. Smooth muscle cells cultured with 20 mmol/l glucose showed statistically significant increases in protein kinase C activities, the expression of PKCbII isoform and PDGF-b receptor protein, and proliferation activities, compared with smooth muscle cells cultured with 5.5 mmol/l glucose. Although epalrestat and LY333 531 inhibited protein kinase C activation induced by glucose to the same degree, the effects of epalrestat on proliferation activities and expression of the PDGF-b receptor were more prominent than those of LY333 531. Epalrestat improved the glucose-induced decrease in free cytosolic NAD + :NADH ratio and reduced glutathione content, but LY333 531 did not. The increased expression of membranous PKC-bII isoform was normalized by epalrestat. Conclusion/interpretation. These observations suggest that polyol pathway hyperactivity contributes to the development of diabetic macroangiopathy through protein kinase C, PDGF-b receptor, and oxidative stress, and that an aldose reductase inhibitor has a therapeutic value for this complication. [Diabetologia (2001) 44: 480±487]