Evaluation of saphenous venipuncture and modified tail-clip blood collection in mice.

The purpose of this study was to evaluate the effects of 2 methods of blood collection in unanesthetized mice. The saphenous venipuncture method was compared with a modified tail-clip technique that requires minimal restraint. Mice were evaluated through behavioral observation and plasma corticosterone levels. The results showed that the 2 methods produced similar corticosterone responses and that the tail-clip method produced fewer behavioral reactions. In addition, the effects of saphenous venipuncture method appeared to be dependent on the handler's technical expertise. When a series of 4 blood collections were performed over 1 wk, the 2 methods yielded similar corticosterone levels that did not increase over time. Some of the behavioral signs appeared to increase over the series of blood collections obtained by the saphenous venipuncture method. Serial complete blood counts showed that the tail vessels yielded higher total white blood cell, neutrophil, and lymphocyte counts than did the saphenous vein. Neither method appeared to cause stress-associated changes in the leukogram after serial blood collection. Overall, the effects of modified tail-clip method were similar to those of the saphenous venipuncture method in unanesthetized mice.

Taurine reverses neurological and neurovascular deficits in Zucker diabetic fatty rats.

Increased oxidative stress is implicated in the pathogenesis of diabetic peripheral neuropathy (DPN). However, the efficacy of antioxidant therapy on DPN complicating type 2 diabetes remains unexplored. We therefore determined the ability of the antioxidant taurine to reverse deficits of hind limb sciatic motor and digital sensory nerve conduction velocity (NCV), nerve blood flow (NBF), and sensory thresholds in hyperglycemic Zucker diabetic fatty (ZDF) rats. Experimental groups comprised lean nondiabetic (ND), ND treated with taurine (ND + T), untreated ZDF diabetic (D), and D rats treated with taurine (D + T). Compared to ND rats, 23%, 15% and 56% deficits of motor NCV, sensory NCV and NBF, respectively as well as thermal and mechanical hyperalgesia were reversed by taurine. An 84% deficit of dorsal root ganglion neuron calcitonin gene-related peptide in D rats was prevented by taurine. In summary, the antioxidant taurine reverses neurological and neurovascular deficits in experimental type 2 diabetes.

Topical pretreatment of diabetic rats with all-trans retinoic acid improves healing of subsequently induced abrasion wounds.

In the current study, rats were made diabetic with streptozotocin (STZ) and maintained for 8 weeks, during which time they were treated topically on alternative days with a solution of 0.1% all-trans retinoic acid in a vehicle of 70:30% ethanol/propylene glycol. STZ-induced diabetic rats treated with vehicle served as controls. Additional nondiabetic rats were treated with all-trans retinoic acid or vehicle in parallel. At the end of the 8-week period, rats from all four treatment groups were subjected to abrasion wound formation. Wounds healed more rapidly in vehicle-treated nondiabetic skin than in vehicle-treated diabetic skin (96% of the wound surface area closed in nondiabetic rats within 6 days vs. 41% closed in diabetic rats). Wounds in all-trans retinoic acid-treated diabetic skin healed more rapidly than wounds in vehicle-treated diabetic skin (85% of the wound surface area closed in all-trans retinoic acid-treated diabetic rats vs. 41% closed in vehicle-treated diabetic rats). At the histological level, recently healed skin from vehicle-treated diabetic rats was shown to contain a thin, wispy provisional matrix in which many of the embedded cells were rounded and some were pycnotic. In contrast, a much denser provisional matrix with large numbers of embedded spindle-shaped cells was observed in healed wounds from diabetic skin that had been pretreated with all-trans retinoic acid. The all-trans retinoic acid-treated diabetic skin was histologically similar to vehicle-treated (or all-trans retinoic acid-treated) skin from nondiabetic animals. In light of these findings, we suggest that prophylactic use of retinoid-containing preparations might be useful in preventing the development of nonhealing skin ulcers resultant from minor traumas in at-risk skin.

Role for nitrosative stress in diabetic neuropathy: evidence from studies with a peroxynitrite decomposition catalyst.

Nitrosative stress, that is, enhanced peroxynitrite formation, has been documented in both experimental and clinical diabetic neuropathy (DN), but its pathogenetic role remains unexplored. This study evaluated the role for nitrosative stress in two animal models of type 1 diabetes: streptozotocin-diabetic mice and diabetic NOD mice. Control (C) and streptozotocin-diabetic (D) mice were treated with and without the potent peroxynitrite decomposition catalyst FP15 (5 mg kg(-1) d(-1)) for 1 wk after 8 wk without treatment. Sciatic nerve nitrotyrosine (a marker of peroxynitrite-induced injury) and poly(ADP-ribose) immunoreactivities were present in D and absent in C and D+FP15. FP15 treatment corrected sciatic motor and hind-limb digital sensory nerve conduction deficits and sciatic nerve energy state in D, without affecting those variables in C. Nerve glucose and sorbitol pathway intermediate concentrations were similarly elevated in D and D+FP15 vs C. In diabetic NOD mice, a 7-day treatment with either 1 or 3 mg kg(-1) d(-1) FP15 reversed increased tail-flick latency (a sign of reduced pain sensitivity); the effect of the higher dose was significant as early as 3 days after beginning of the treatment. In conclusion, nitrosative stress plays a major role in DN in, at least, type 1 diabetes. This provides the rationale for development of agents counteracting peroxynitrite formation and promoting peroxynitrite decomposition, and their evaluation in DN.

Role of poly(ADP-ribose) polymerase activation in diabetic neuropathy.

Oxidative and nitrosative stress play a key role in the pathogenesis of diabetic neuropathy, but the mechanisms remain unidentified. Here we provide evidence that poly(ADP-ribose) polymerase (PARP) activation, a downstream effector of oxidant-induced DNA damage, is an obligatory step in functional and metabolic changes in the diabetic nerve. PARP-deficient (PARP(-/-)) mice were protected from both diabetic and galactose-induced motor and sensory nerve conduction slowing and nerve energy failure that were clearly manifest in the wild-type (PARP(+/+)) diabetic or galactose-fed mice. Two structurally unrelated PARP inhibitors, 3-aminobenzamide and 1,5-isoquinolinediol, reversed established nerve blood flow and conduction deficits and energy failure in streptozotocin-induced diabetic rats. Sciatic nerve immunohistochemistry revealed enhanced poly(ADP-ribosyl)ation in all experimental groups manifesting neuropathic changes. Poly(ADP-ribose) accumulation was localized in both endothelial and Schwann cells. Thus, the current work identifies PARP activation as an important mechanism in diabetic neuropathy and provides the first evidence for the potential therapeutic value of PARP inhibitors in this devastating complication of diabetes.

Diabetes-induced overexpression of endothelin-1 and endothelin receptors in the rat renal cortex is mediated via poly(ADP-ribose) polymerase activation.

We hypothesize that poly (ADP-ribosyl)ation, that is, poly (ADP-ribose) polymerase (PARP)-dependent transfer of ADP-ribose moieties from NAD to nuclear proteins, plays a role in diabetic nephropathy. We evaluated whether PARP activation is present and whether two unrelated PARP inhibitors, 3-aminobenzamide (ABA) and 1,5-isoquinolinediol (ISO), counteract overexpression of endothelin-1 (ET-1) and ET receptors in the renal cortex in short-term diabetes. The studies were performed in control rats and streptozotocin-diabetic rats treated with/without ABA or ISO (30 and 3 mg x kg(-1) x day(-1), intraperitoneally, for 2 weeks after 2 weeks of diabetes). Poly (ADP-ribose) immunoreactivity was increased in tubuli, but not glomeruli, of diabetic rats and this increase was corrected by ISO, whereas ABA had a weaker effect. ET-1 concentration (ELISA) was increased in diabetic rats, and this elevation was blunted by ISO. ET-1, ET(A), and ET(B) mRNA (ribonuclease protection assay), but not ET-3 mRNA (RT/PCR), abundance was increased in diabetic rats, and three variables were, at least, partially corrected by ISO. ABA produced a trend towards normalization of ET-1 concentration and ET-1, ET(A), and ET(B) mRNA abundance, but the differences with untreated diabetic group were not significant. Poly(ADP-ribosyl)ation is involved in diabetes-induced renal overexpression of ET-1 and ET receptors. PARP inhibitors could provide a novel therapeutic approach for diabetic complications including nephropathy, and other diseases that involve the endothelin system.

Aldose reductase inhibitor fidarestat prevents retinal oxidative stress and vascular endothelial growth factor overexpression in streptozotocin-diabetic rats.

The study addressed the role for aldose reductase (AR) in 1) retinal oxidative stress and vascular endothelial growth factor (VEGF) overexpression in early diabetes, and 2) high glucose-induced oxidative stress in retinal endothelial cells. In vivo experiments were performed on control rats and diabetic rats treated with or without low or high dose of the AR inhibitor (ARI) fidarestat (2 or 16 mg. kg(-1). day(-1)). In vitro studies were performed on bovine retinal endothelial cells (BREC) cultured in either 5 or 30 mmol/l glucose with or without 1 micro mol/l fidarestat. Intracellular reactive oxygen species were assessed using the 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (H(2)DCFDA) probe and flow cytometry. Both low and high doses of fidarestat (i.e., the doses that partially and completely inhibited sorbitol pathway hyperactivity) arrested diabetes-induced retinal lipid peroxidation. This was achieved due to upregulation of the key antioxidative defense enzyme activities rather than changes in reduced glutathione, oxidized glutathione, ascorbate and dehydroascorbate concentrations, and the glutathione and ascorbate redox states. Diabetes-associated 2.1-fold VEGF protein overexpression (enzyme-linked immunosorbent assay; ELISA) was dose-dependently prevented by fidarestat, whereas total VEGF mRNA and VEGF-164 mRNA (RT-PCR) abundance were not affected by either diabetes or the ARI. In BREC, fidarestat corrected hyperglycemia-induced increase in H(2)DCFDA fluorescence but not oxidative stress caused by three different pro-oxidants in normoglycemic conditions. In conclusion, increased AR activity contributes to retinal oxidative stress and VEGF protein overexpression in early diabetes. The findings justify the rationale for evaluation of fidarestat on diabetic retinopathy.