Lawrence J. Coppey

Slowing of motor nerve conduction velocity in streptozotocin-induced diabetic rats is preceded by impaired vasodilation in arterioles that overlie the sciatic nerve.

Diabetes mellitus produces marked abnormalities in motor nerve conduction, but the mechanism is not clear. In the present study we hypothesized that in the streptozotocin (STZ)-induced diabetic rat impaired vasodilator function in arterioles that provide circulation to the region of the sciatic nerve is associated with reduced endoneural blood flow (EBF) and that these defects precede slowing of motor nerve conduction velocity, and thereby may contribute to nerve dysfunction. As early as three days after the induction of diabetes endoneural blood flow was reduced in the STZ-induced diabetic rat. Furthermore, after 1 week of diabetes acetylcholine- induced vasodilation was found to be impaired. This was accompanied by an increase in the superoxide level in arterioles that provide circulation to the region of the sciatic nerve as well as changes in the level of other markers of oxidative stress including an increase in serum levels of thiobarbituric acid reactive substances and a decrease in lens glutathione level. In contrast to the vascular related changes that occur within 1 week of diabetes, motor nerve conduction velocity and sciatic nerve Na+/k+ ATPase activity were significantly reduced following 2 and 4 weeks of diabetes, respectively. These studies demonstrate that changes in vascular function in the STZ-induced diabetic rat precede the slowing of motor nerve conduction velocity (MNCV) and are accompanied by an increase in superoxide levels in arterioles that provide circulation to the region of the sciatic nerve.

Effect of M40403 treatment of diabetic rats on endoneurial blood flow, motor nerve conduction velocity and vascular function of epineurial arterioles of the sciatic nerve

To further explore the effect of antioxidants in preventing diabetes‐induced vascular and neural dysfunction we treated streptozotocin‐induced diabetic rats daily with subcutaneous injections of 10 mg kg−1 of M40403 (n=11) and compared the results obtained from 17 control rats and 14 untreated diabetic rats. M40403 is a manganese(II) complex with a bis(cyclo‐hexylpyridine)‐substituted macrocyclic ligand that was designed to be a selective functional mimetic of superoxide dismutase. Thus, M40403 provides a useful tool to evaluate the roles of superoxide in disease states. Treatment with M40403 significantly improved diabetes‐induced decrease in endoneurial blood flow, acetylcholine‐mediated vascular relaxation in arterioles that provide circulation to the region of the sciatic nerve, and motor nerve conduction velocity (P<0.05). M40403 treatment also reduced the appearance of superoxide in the aorta and epineurial vessels and peroxynitrite in epineurial vessels. Treating diabetic rats with M40403 reduced the diabetes‐induced increase in thiobarbituric acid reactive substances in serum but did not prevent the decrease in lens glutathione level. Treating diabetic rats with M40403 did not improve sciatic nerve Na+/K+ ATPase activity or the sorbitol, fructose or myo‐inositol content of the sciatic nerve. These studies provide additional evidence that diabetes‐induced oxidative stress and the generation of superoxide and perhaps peroxynitrite may be partially responsible for the development of diabetic vascular and neural complications.

Antioxidants attenuate myocyte apoptosis in the remote non-infarcted myocardium following large myocardial infarction

OBJECTIVE Increased oxidative stress and myocyte apoptosis co-exist in the remote non-infarcted myocardium (RM) following a large myocardial infarction. We proposed that these phenomena are causally related. METHODS AND RESULTS On day 3 after induction of myocardial infarction, Sprague-Dawley rats were randomized to receive probucol and pyrrolidine dithiocarbamate (MI-T), or vehicle only (MI) for 7 weeks. Control rats (C) received vehicle. At 7 weeks, lipidperoxidation within the RM was assessed by measuring thiobarbituric acid reactive substances, which were significantly increased in MI vs. C, while MI-T was not different from C. There was a significant increase in cardiac myocytes positive for in situ TdT-UTP nick-end labeling within the RM in MI vs. C, which was inhibited in MI-T. Furthermore, internucleosomal DNA fragmentation was clearly demonstrated on agarose gels from RM in the MI group, while it was much less apparent on gels from RM in the C and MI-T groups. Western blot analysis showed a significant increase in p53, Bax and caspase-3 protein expression within the RM of MI vs. C, all of which were inhibited in the MI-T group. Furthermore, there was evidence for an increase in caspase-3 activity within the RM from MI vs. C, which was normalized in the MI-T group. CONCLUSIONS Long-term treatment with the antioxidants probucol and pyrrolidine dithiocarbamate attenuates oxidative stress, myocyte apoptosis, caspase-3 like activity and the expression of p53, bax and caspase-3 within RM in rats after a large myocardial infarction.

Preventing Superoxide Formation in Epineurial Arterioles of the Sciatic Nerve from Diabetic Rats Restores Endothelium-dependent Vasodilation

We have previously reported that in streptozotocin-induced diabetic rats that increased formation of superoxide and peroxynitrite is associated with impairment in vascular relaxation in epineurial arterioles of the sciatic nerve. In this study we demonstrate that pretreating epineurial arterioles from diabetic rats in vitro with f -lipoic acid, dihydrolipoic acid, tempol or arginine restores acetylcholine-mediated vascular relaxation to near the reactivity observed in vessels from control rats. Suggesting that increased oxidative stress and reduction in nitric oxide availability is partially responsible for the impairment in endothelium-dependent vasodilation observed in epineurial arterioles from diabetic rats. In contrast, pretreating epineurial arterioles from diabetic rats with aminoguanidine or allopurinol had no effect. Studies designed to investigate the source of superoxide formation provided results suggesting that complex I of the mitochondrial electron transport chain and NAD(P)H oxidase are responsible for the increase in superoxide formation observed with epineurial arterioles from the sciatic nerve. Pretreating epineurial arterioles from diabetic rats with the protein kinase C inhibitor bisindolymaleimide I (GF 109203X) improved acetylcholine-mediated vascular relaxation but did not prevent the increase in superoxide formation suggesting that activation of protein kinase C by oxidative stress is downstream of superoxide formation. These studies imply that increased superoxide formation via the mitochondrial electron transport chain and perhaps NAD(P)H oxidase is partially responsible for reduced vascular reactivity observed in epineurial arterioles of the sciatic nerve from diabetic rats.

Changes in endoneurial blood flow, motor nerve conduction velocity and vascular relaxation of epineurial arterioles of the sciatic nerve in ZDF-obese diabetic rats

We have previously reported that in streptozotocin‐induced diabetic rats, reduction in endoneurial blood flow (EBF) and impairment of acetylcholine‐mediated vascular relaxation of arterioles that provide circulation to the sciatic nerve precedes slowing of motor nerve conduction velocity (MNCV). However, in animal models of type 2 diabetes it is unknown whether slowing of MNCV is accompanied by vascular dysfunction.

Acetylcholine-induced arteriolar dilation is reduced in streptozotocin-induced diabetic rats with motor nerve dysfunction

Diabetes mellitus produces marked abnormalities in motor nerve conduction, but the mechanism is not clear. In the present study we hypothesized that in the streptozotocin (STZ)‐induced diabetic rat impaired vasodilator function is associated with reduced endoneural blood flow (EBF) which may contribute to nerve dysfunction. We examined whether diabetes‐induced reductions in sciatic nerve conduction velocity and EBF were associated with impaired endothelium‐dependent dilation in adjacent arterioles. We measured motor nerve conduction velocity (MNCV) in the sciatic nerve using a non‐invasive procedure, and sciatic nerve nutritive blood flow using microelectrode polarography and hydrogen clearance. In vitro videomicroscopy was used to quantify arteriolar diameter responses to dilator agonists in arterioles overlying the sciatic nerve. MNCV and EBF in 4‐week‐STZ‐induced diabetic rats were decreased by 22% and 49% respectively. Arterioles were constricted with U46619 and dilation to acetylcholine (ACh), aprikalim, or sodium nitroprusside (SNP) examined. All agonists elicited dose‐dependent dilation in control and diabetic rats, although ACh‐induced dilation was significantly reduced in diabetic rats. Treating vessels from normal or diabetic rats with indomethacin (INDO) alone did not significantly affect ACh‐induced relaxation. However, ACh‐induced vasodilation was significantly reduced by treatment with KCl or Nω‐nitro‐L‐arginine (LNNA) alone. Combining LNNA and KCl further reduced ACh‐induced dilation in these vessels. Diabetes causes vasodilator dysfunction in a microvascular bed that provides circulation to the sciatic nerve. These studies imply that ACh‐induced dilation in these vessels is mediated by multiple mechanisms that may include the endothelial‐dependent production of nitric oxide and endothelial‐derived hyperpolarizing factor. This impaired vascular response is associated with neural dysfunction.

Attenuation of Vascular/Neural Dysfunction in Zucker Rats Treated With Enalapril or Rosuvastatin

Objective: Obese Zucker rats, animal model for the metabolic syndrome, develop a diabetes‐like neuropathy that is independent of hyperglycemia. The purpose of this study was to determine whether drugs used to treat cardiovascular dysfunction in metabolic syndrome also protect nerve function.

Diet-induced obesity in Sprague–Dawley rats causes microvascular and neural dysfunction

The objective of this study was to determine the effect of diet‐induced obesity (DIO) on microvascular and neural function.

Vascular and neural dysfunction in Zucker diabetic fatty rats: a difficult condition to reverse.

Aim:  We had previously demonstrated that vascular and neural dysfunction in Zucker diabetic fatty (ZDF) rats is progressive. In this study, we sought to determine whether monotherapy of ZDF rats can reverse the vascular and nerve defects.

Treatment of Zucker diabetic fatty rats with AVE7688 improves vascular and neural dysfunction.

Aim:  Vasopeptidase inhibitors are drugs that inhibit angiotensin‐converting enzyme and neutral endopeptidase (NEP). The latter is a protease that degrades vasoactive peptides and is increased in diabetes. We have previously shown that treating streptozotocin‐induced diabetic rats, an animal model of type 1 diabetes, with AVE7688, a vasopeptidase inhibitor, improves neurovascular and neural function. In this study, we determined the effect of treating Zucker diabetic fatty (ZDF) rats, an animal model of type 2 diabetes, with AVE7688 on vascular and neural function.