Effects of the peroxynitrite decomposition catalyst, FeTMPyP, on function of corpus cavernosum from diabetic mice

Peroxynitrite, the reaction product of nitric oxide and superoxide, may contribute to vascular tissue oxidant stress in diabetes mellitus. The aim was to establish whether the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) could improve nitric oxide-dependent autonomic nerve and microvascular penile function in the diabetic mouse. Diabetes was induced by streptozotocin; duration was 6 weeks. Intervention FeTMPyP treatment (25 mg kg(-1) day(-1)) was given for 2 weeks following 4 weeks untreated diabetes. Corpus cavernosum were isolated in organ baths for measurement of agonist or electrical stimulation-evoked nerve-mediated tension responses. Maximum nitrergic nerve-mediated relaxation of phenylephrine-precontracted cavernosum was approximately 35% reduced by diabetes; FeTMPyP treatment reversed this deficit by 45%. The concentration response-curve for nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was attenuated by diabetes; FeTMPyP restored the deficit to the nondiabetic range. Sensitivity (EC50) to the nitric oxide donor, sodium nitroprusside, was reduced by approximately 0.56 log10 M units in diabetes; however, FeTMPyP treatment failed to significantly reverse this deficit. Therefore, the peroxynitrite mechanism contributes to nitric oxide-dependent diabetic autonomic neuropathy and vasculopathy and may be a potential target for clinical trials using peroxynitrite decomposition catalysts.     

Neuroprotective effects of FeTMPyP: a peroxynitrite decomposition catalyst in global cerebral ischemia model in gerbils.

Peroxynitrite involvement has been implicated in the neuronal damage. In the present study, we have investigated the neuroprotective effects of peroxynitrite decomposition catalyst (FeTMPyP) on global cerebral ischemia. Global cerebral ischemia-reperfusion (IR) injury was produced by 5 min occlusion of both common carotid arteries followed by reperfusion of 96 h in the adult male Mongolian gerbils. The extent of injury was assessed behaviorally by measuring neurological functions, locomotor activity, passive avoidance test and by histopathological evaluation of extent of damage to CA1 hippocampal pyramidal region. FeTMPyP (1 and 3 mgkg(-1), i.p., administered 30 min prior to ischemia) treatment improved the neurological functions, reduced the hyperlocomotion and memory impairment in IR challenged gerbils. The loss of neurons from the pyramidal layer of the CA1 region caused by global IR injury was attenuated with FeTMPyP. FeTMPyP also inhibited lipid peroxidation as evident from reduction in brain malondialdehyde levels. These results suggest that peroxynitrite decomposition catalyst may be effective neuroprotective agent for global cerebral ischemia.     

Blockade of adenosine A2A receptor counteracts neuropeptide-S-induced hyperlocomotion in mice

Neuropeptide S (NPS) is the endogenous ligand of a G-protein-coupled receptor named as NPSR. Behavioral effects have been recently attributed to NPS, i.e. hyperlocomotion, anxiolysis, and wakefulness. However, little is known about the mechanisms by which NPS evokes such biological actions. The present study aimed to investigate the role played by the adenosine A_2A and A₁ receptors in hyperlocomotion induced by NPS. Spontaneous locomotion was assessed in an activity cage for 30 min in mice acutely treated with caffeine (a nonselective adenosine receptor antagonist), ZM241385 (a selective A_2A receptor antagonist), or CPT (a selective A₁ receptor antagonist) before NPS challenge (0.1 nmol, i.c.v.), which induce hyperlocomotion in mice. The pretreatment with caffeine (3 mg/kg, i.p.), in an inactive dose per se, prevented the increase in locomotion evoked by NPS. The co-administration of NPS (0.1 nmol, i.c.v.) and ZM241385 (0.1 pmol, i.c.v.) counteracted hyperlocomotion evoked by NPS. The co-administration of NPS and CPT (0.1 pmol, i.c.v.) slightly facilitated the increase in locomotion evoked by NPS alone. In summary, the pharmacological blockade of A_2A receptors significantly attenuated the stimulatory effects of NPS. By contrast, the antagonism of A₁ receptors facilitated NPS-induced hyperlocomotion in mice, but we cannot rule out a merely additive effect of two stimulatory systems in the brain. Altogether, this is the first evidence of a putative role played by A_2A and A₁ receptors in modulating hyperlocomotion induced by NPS.     

Central action of cesium chloride in streptozotocin-diabetic mice

The changes in the pharmacological responses to cesium were examined in streptozotocin(STZ)-induced diabetic mice. An acute administration of cesium chloride (10 mEqCs⁺/kg IP) to non-diabetic control mice elicited increased salivation and inhibition of respiration followed by death in about half of the animals examined. These effects of cesium were diminished in STZ-diabetic mice. LD₅₀ for acute cesium was higher in STZ-diabetic mice (14.3 mEq/kg) than non-diabetic buffer controls (11.7 mEq/kg); however, subchronic administration of cesium did not decrease the LD₅₀ in STZ-diabetic mice. The sleeping time induced by pentobarbital was reduced in STZ-diabetic mice and the reduction of the pentobarbital-induced hypnosis was reversed by subchronic cesium pretreatment but not by acute cesium administration. Methamphetamine-induced mortality was increased in STZ-diabetic mice and acute administration of cesium decreased the toxicity in both control and diabetic mice. Inhibition of locomotor activity elicited by acute single injection of cesium chloride was observed in both STZ-diabetic and non-diabetic mice. These results indicate that responses to cesium as well as centrally-acting drugs are affected differentially in STZ-diabetic mice.     

Changes in pentobarbital hypnosis and hepatic metabolism in streptozotocin-diabetic mice

The present study deals with the hypnotic effect of pentobarbital (Pento) in relation to its metabolism in hepatic microsomes in streptozotocin (STZ, 170 mg/kg, i.p.) injected mice. Liver weight (mg/10 g body wt.) of STZ-treated mice was larger than that of the controls throughout the experimental period. Although the shortening of sleeping time induced by Pento (60 mg/kg, i.p.) was always observed, Pento-metabolizing enzyme activity (by the method of Kato et al., 1964) increased in mice with diabetes for 2 and 4 weeks but decreased in mice with diabetes for 8 weeks. Induction following phenobarbital (100 mg/kg, s.c.) and inhibition by SKF 525-A (10 mg/kg, i.p.) of hepatic metabolizing enzyme were found in both control and mice with diabetes for 2, 4 and 8 weeks, but these were not definitely correlated to their hepatic Pento-metabolizing enzyme activities. STZ-induced hyperglycemia and shortening of sleeping time by Pento were completely prevented by the pretreatment with nicotinamide (500 mg/kg, i.p.). NPH-insulin injection partially decreased hyperglycemia in STZ-diabetic mice, but sleeping time by Pento was not significantly affected. These results suggest that the hyposensitivity to Pento in STZ-diabetic mice is partially related to an abnormality of metabolism in liver such as the hyperglycemic state.     

Changes in arachidonic acid-induced respiratory distress in streptozotocin-diabetic mice]

Using streptozotocin (STZ)-diabetic mice, we examined the respiratory distress induced by arachidonic acid. Male ddY mice were made diabetic by injecting STZ (170 mg/kg, i.p.) 2 weeks prior to the experiment. Control mice received the vehicle (citrate buffer, pH 4.6). The duration of respiratory distress was observed by a slow i.v.-injection of sodium arachidonic acid (AA) into the caudal vein of mice at the dose of 50 mg/kg. Aspirin was i.p.-administered 30 min before AA. OKY-046 (specific thromboxane A2 (TXA2) synthetase inhibitor), OP-41483 (stable prostacyclin analog) and 9, 11 epithia-11, 12-methano-TXA2 (STA2, stable TXA2 analog) were i.v.-administered 30 min before AA. The duration of respiratory distress induced by AA was significantly reduced in STZ-diabetic mice. Aspirin (10-50 mg/kg) and OKY-046 (25-100 mg/kg) enhanced the AA-induced respiratory distress in STZ-diabetic mice. OP-41483 (1-100 micrograms/kg) reduced the AA-induced effect in both control and STZ-diabetic mice. STA2 (10 micrograms/kg) enhanced the AA-induced effect in both control and STZ-diabetic mice. ONO-1078 (1-10 mg/kg) did not affect the AA-induced effect in both control and STZ-diabetic mice. TMK-688 (0.01-1 mg/kg) reduced the AA-induced effect in the control mice, but not in the STZ-diabetic mice. These results suggest an involvement of leukotriene in the respiratory response to AA in diabetic mice, especially when cyclooxygenase and TXA2 synthetase are inhibited.     

The hyperalgesic effect of naloxone is attenuated in streptozotocin-diabetic mice

In mice with streptozotocin-induced hyperglycemia, nociception was tested after naloxone administration in hot plate and tail immersion tests. The choice of these two tests was to include a supra-spinal nociceptive reflex indicative of higher cognitive process (hot-plate test) as well as a reflex which predominantly represents lower spinal motor mechanisms (tail immersion test). Naloxone-induced hyperalgesia was attenuated in both tests in mice with streptozotocin-induced diabetes. In mice with hyperglycemia induced by intraperitoneal dextrose administration, naloxone hyperalgesia was significantly enhanced in the hot plate test. The basal nociceptive threshold in streptozotocintreated animals was decreased in the immersion but not in the hot plate test. These results indicate that hyperglycemia per se does not adequately explain the changes in naloxone hyperalgesia in experimental models of diabetes. They also suggest that acute hyperglycemia may modify the interaction of endogenous opioid peptides with their receptors only at supra-spinal sites. However, chronic hyperglycemia appears to affect endogenous opioid peptides both at spinal and supra-spinal levels and their interaction with the opiate receptors.     

Poly(ADP-ribose) polymerase (PARP) inhibition counteracts multiple manifestations of kidney disease in long-term streptozotocin-diabetic rat model

Evidence for the important role for poly(ADP-ribose) polymerase (PARP) in the pathogenesis of diabetic nephropathy is emerging. We previously reported that PARP inhibitors counteract early Type 1 diabetic nephropathy. This study evaluated the role for PARP in kidney disease in long-term Type 1 diabetes. Control and streptozotocin-diabetic rats were maintained with or without treatment with the PARP inhibitor 10-(4-methyl-piperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de] anthracen-3-one (GPI-15,427, Eisai Inc.), 30 mg kg⁻¹ d⁻¹, for 26 weeks after first 2 weeks without treatment. PARP activity in the renal cortex was assessed by Western blot analysis of poly(ADP-ribosyl)ated proteins. Urinary albumin, isoprostane, and 8-hydroxy-2′-deoxyguanosine excretion, and renal concentrations of transforming growth factor-β₁, vascular endothelial growth factor, soluble intercellular adhesion molecule-1, fibronectin, and nitrotyrosine were evaluated by ELISA, and urinary creatinine and renal lipid peroxidation products by colorimetric assays. PARP inhibition counteracted diabetes-associated increase in renal cortex poly(ADP-ribosyl)ated protein level. Urinary albumin, isoprostane, and 8-hydroxy-2′-deoxyguanosine excretions and urinary albumin/creatinine ratio were increased in diabetic rats, and all these changes were at least partially prevented by GPI-15,427 treatment. PARP inhibition counteracted diabetes-induced renal transforming growth factor-β₁, vascular endothelial growth factor, and fibronectin, but not soluble intercellular adhesion molecule-1 and nitrotyrosine, accumulations. Lipid peroxidation product concentrations were indistinguishable among control and diabetic rats maintained with or without GPI-15,427 treatment. In conclusion, PARP activation plays an important role in kidney disease in long-term diabetes. These findings provide rationale for development and further studies of PARP inhibitors and PARP inhibitor-containing combination therapies, for prevention and treatment of diabetic nephropathy.     

The radical scavenger edaravone counteracts diabetes in multiple low-dose streptozotocin-treated mice

Edaravone is a potent scavenger of hydroxyl radicals and attenuates oxidative damage-related neurodegenerative diseases. Previous studies suggest that oxidative stress plays a key role in the pathogenesis of diabetes. The present study examined the effect of edaravone on diabetes in multiple low-dose streptozotocin-treated mice. Mice treated with low-doses of streptozotocin for five consecutive days showed progressive hyperglycemia and an increased incidence of diabetes. Daily treatment with edaravone during the streptozotocin injections counteracted the multiple low-dose streptozotocin-induced hyperglycemia in a dose-dependent manner. Edaravone protected against the multiple low-dose streptozotocin-induced reduction in pancreatic insulin. The suppressive effects of edaravone were also observed when it was administered after the last injection of streptozotocin. Histochemical examination showed that multiple low-dose streptozotocin treatment caused mononuclear cell infiltration in pancreatic islets, followed by hyperglycemia, and that edaravone significantly inhibited the multiple low-dose streptozotocin-induced insulitis. Multiple low-dose streptozotocin treatment also increased the lipid peroxidation product thiobarbituric acid reactive substance in pancreatic tissues of mice, and this effect was completely inhibited by edaravone. These findings suggest that edaravone, even after streptozotocin treatment, counteracts the development of multiple low-dose streptozotocin-induced diabetes by scavenging free radicals, which are possible mediators of the immune destruction of islet beta cells.     

Anti-hyperglycemic effect of fangchinoline isolated from Stephania tetrandra Radix in streptozotocin-diabetic mice

Kampo medicine, Stephania tetrandra Radix (Stephania) in Boi-ogi-to increases the blood insulin level and falls the blood glucose level in streptozotocin (STZ)-diabetic ddY mice. These actions of Stephania are potentiated by Astragalus membranaceus Bunge Radix (Astragali) in Boi-ogi-to (Liu et al., J. Traditional Med., 17, 253-260, 2000). In the present study, actions of bis-benzylisoquinoline alkaloids isolated from Stephania were investigated in the hyperglycemia of STZ-diabetic mice. A main bis-benzylisoquinoline alkaloid, fangchinoline (0.3-3 mg/kg) significantly fell the blood glucose level of the diabetic mice in a dose-dependent manner. The effect of fangchinoline was 3.9-fold greater than that of water extract of Stephania. However, another main compound, tetrandrine (1-100 mg/kg) did not have any effect. The water extract of Astragali did not affect singly but potentiated the anti-hyperglycemic action of fangchinoline (0.3 mg/kg). Out of used compounds (1 mg/kg) isolated from Stephania, fangchinoline, fangchinoline 2'-N-alpha-oxide and 2'-N-norfangchinoline, which are substituted with 7-hydroxy side chain for 7-O-methyl side chain, decreased to near 50% of high blood glucose level. In addition, tetrandrine 2'-N-beta-oxide, tetrandrine 2'-N-alpha-oxide, tetrandrine 2-N-beta-oxide, fangchinoline 2'-N-alpha-oxide, which are added to 2- or 2'-N-oxide side chain, also decreased to near 50% of the high blood glucose level. In conclusion, fangchinoline but not tetrandrine from Stephania shows the anti-hyperglycemic action in the STZ-diabetic mice. The demethylation of 7-O-position and/or addition of 2- or 2'-N-oxide side chain in bis-benzylisoquinoline compounds in Stephania have a role for the induction of the anti-hyperglycemic actions.     

Neuroprotective efficacy and therapeutic time window of peroxynitrite decomposition catalysts in focal cerebral ischemia in rats

Free radicals have been implicated in cerebral ischemia reperfusion (IR) injury. Massive production of nitric oxide and superoxide results in continuous formation of peroxynitrite even several hours after IR insult. This can produce DNA strand nicks, hydroxylation and/or nitration of cytosolic components of neuron, leading to neuronal death. Peroxynitrite decomposition catalysts 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron (III) (FeTMPyP) and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) (FeTPPS) have been demonstrated to protect neurons in in vitro cultures; however, their neuroprotective efficacy in cerebral IR injury has not been explored. In the present study, we investigated the efficacy and the therapeutic time window of FeTMPyP and FeTPPS in focal cerebral ischemia (FCI). FCI was induced according to the middle cerebral artery occlusion (MCAO) method. After 2 h of MCAO and 70 h of reperfusion, the extent of neurological deficits, infarct and edema volume were measured in Sprague-Dawley rats. FeTMPyP and FeTPPS were administered at different time points 2, 6, 9 and 12 h post MCAO. FeTMPyP and FeTPPS (3 mg kg(-1), i.v.) treatment at 2 and 6 h post MCAO produced significant reduction in infarct volume, edema volume and neurological deficits. However, treatment at latter time points did not produce significant neuroprotection. Significant reduction of peroxynitrite in blood and nitrotyrosine in brain sections was observed on FeTMPyP and FeTPPS treatment. As delayed treatment of FeTMPyP and FeTPPS produced neuroprotection, we tested whether treatment had any influence over the apoptotic neuronal death. DNA fragmentation and in situ nick end-labeling assays showed that FeTMPyP and FeTPPS treatment reduced IR injury-induced DNA fragmentation. In conclusion, peroxynitrite decomposition catalysts (FeTMPyP and FeTPPS) produced prominent neuroprotection even if administered 6 h post MCAO and the neuroprotective effect is at least in part due to the reduction of peroxynitrite and apoptosis.     

Reduction of blood glucose level by orexins in fasting normal and streptozotocin-diabetic mice

The influence of chronic arthritic pain on two endogenous opioid peptides, dynorphin B and [Met5]enkephalin-Arg6-Phe7, and multiple opioid receptors in discrete brain, lumbar spinal cord and pituitary pools was investigated. Using radioimmunoassay and receptor binding assay, we examined the changes in regional opioid peptide levels and opioid receptor activity due to chronic inflammation in adjuvant arthritic rats. At 4 weeks post-inoculation, increased levels of immunoreactive dynorphin B and [Met5]enkephalin-Arg6-Phe7 were measured in tissues of arthritic rats compared with controls. No significant changes in mu-, delta- or kappa-opioid receptors were seen after chronic inflammation. Taken together, these results indicate that in chronic arthritis, opioid receptor changes do not follow the peptide alterations of pro-dynorphin and pro-enkephalin systems. Thus, dynamic modification and modulation of nociceptive information takes place during chronic inflammation. This supports the key role of the central nervous system in chronic inflammatory pain conditions.     

Protective effects of a superoxide dismutase mimetic and peroxynitrite decomposition catalysts in endotoxin-induced intestinal damage.

1. The relative contributions of superoxide anion (O2-) and peroxynitrite (PN) were evaluated in the pathogenesis of intestinal microvascular damage caused by the intravenous injection of E. coli lipopolysaccharide (LPS) in rats. The superoxide dismutase mimetic (SODm) SC-55858 and the active peroxynitrite decomposition catalysts 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5-disulphonatophenyl)-por phyrinato iron (III) and 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)-porphyrinato iron (III) (FeTMPS, FeTMPyP respectively) were used to assess the roles of O2- and PN respectively. 2. The intravenous injection of LPS elicited an inflammatory response that was characterized by a time-dependent infiltration of neutrophils, lipid peroxidation, microvascular leakage (indicative of microvascular damage), and epithelial cell injury in both the duodenum and jejunum. 3. Administration of the SODm SC-55858, FeTMPS or FeTMPyP at 3 h post LPS reduced the subsequent increase in microvascular leakage, lipid peroxidation and epithelial cell injury. Inactive peroxynitrite decomposition catalysts exhibited no protective effects. Only, SC-55858 inhibited neutrophil infiltration. 4. Our results suggest that O2 and peroxynitrite play a significant role in the pathogenesis of duodenal and intestinal injury during endotoxaemia and that their remoyal by SODm and peroxynitrite decomposition catalysts offers a novel approach to the treatment of septic shock or clinical conditions of gastrointestinal inflammation. Furthermore, the remarkable protection of the intestinal epithelium by these agents suggests their use during chemo- and radiation therapy, cancer treatments characterized by gastrointestinal damage. Potential mechanisms through which these radicals evoke damage are discussed.     

Effect of trapidil on neuropathy in diabetic mice

Long term oral administration of trapidil at the doses of 20 and 60 mg/kg/day restored the decrease in motor nerve conduction velocity in genetically diabetic mice (C57BL/KsJ db+/db+). Trapidil also suppressed the increase in sorbitol content and the decrease in myoinositol content in the sciatic nerve. The elevation of serum total cholesterol level and the decrease in the ratio of serum HDL-cholesterol level to total cholesterol level were suppressed by trapidil. The blood glucose level and the serum triglyceride level were not affected by the drug administration. These results suggest that trapidil may restore the decrease in nerve conduction velocity in diabetic mice through amelioration of the metabolite abnormalities in nerve and microcirculatory disorders.     

Decreased sensory neuropeptide release in isolated bronchi of rats with cisplatin-induced neuropathy

We studied if attenuated neurogenic bronchoconstriction was associated with a change in sensory neuropeptide release in preparations from rats with cisplatin-induced neuropathy. Electrical field stimulation (100 stimuli, 20 V, 0.1 ms, 20 Hz) induced an increase in the release of somatostatin, calcitonin gene-related peptide (CGRP) and substance P determined by radioimmunoassay from baseline 0.18+/-0.01, 0.17+/-0.01 and 0.86+/-0.02, to 0.59+/-0.02, 1.77+/-0.04 and 5.96 fmol/mg wet tissue weight, respectively, in organ fluid of tracheal tubes from rats. This was significantly attenuated to post-stimulation values of 0.36+/-0.02, 0.45+/-0.02, 4.68+/-0.24 fmol/mg wet tissue weight for somatostatin, CGRP, and substance P, respectively, with a significant decrease in field stimulation-induced contraction of bronchial preparations from animals 11 days after a 5-day treatment period with cisplatin (1.5 mg/kg i.p. once a day). The cisplatin-treated animals developed sensory neuropathy characterized by a 40% decrease in femoral nerve conduction velocity. The results show that a decrease in tracheo-bronchial sensory neuropeptide release associates with feeble bronchomotor responses in rats with cisplatin-induced sensory neuropathy.     

Protein kinase C beta inhibition and aorta and corpus cavernosum function in streptozotocin-diabetic mice

Increased activity of the beta-isoform of protein kinase C (PKC) has been linked to the vascular and neural complications of diabetes mellitus. Treatment with the PKCbeta inhibitor, (s)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16,21-dimetheno-1H,13H-dibenzo[e,k]pyrrolo[3,4-h][1,4,13]oxadiazacyclohexadecene-1,3(2H)-dione, (LY333531), improves somatic nerve function and blood flow in diabetic rats. The aim was to assess whether LY333531 treatment could prevent nitric oxide-dependent autonomic nerve and vascular dysfunction in a diabetic mouse model. Diabetes was induced by streptozotocin; duration was 4 weeks. Aorta and corpus cavernosum were isolated and mounted in organ baths and agonist or electrical stimulation-evoked nerve-mediated tension responses were examined. Maximum nitric oxide-mediated endothelium-dependent relaxation of phenylephrine-precontracted aorta and cavernosum to acetylcholine were more than 30% reduced by diabetes. LY333531 treatment (10 mg kg(-1) day(-1)) completely prevented the diabetic deficit in cavernosum, and 75% prevented the deficit in aorta. Maximum nitric oxide-dependent non-adrenergic, non-cholinergic (NANC) nerve-mediated relaxation of phenylephrine-precontracted cavernosum was approximately 43% reduced by diabetes; LY333531 attenuated the deficit by 44%. For diabetic aorta, but not cavernosum, sensitivity (EC50) to phenylephrine-mediated contraction was increased by approximately 0.85 log10 M units; LY333531 treatment completely prevented this effect. Thus, PKCbeta activation contributes to nitric oxide-dependent vascular and autonomic nerve dysfunction in diabetic mice and could prove suitable for further study in clinical trials of diabetic autonomic neuropathy and vasculopathy.     

Influence of ganglioside treatment on acrylamide neuropathy in mice. A morphometric study

Female CBA/J mice were given oral doses of 40 mg/kg acrylamide 3 times weekly for 7 or 11 weeks in order to induce peripheral neuropathy. Half the animals were concurrently treated with 20 mg/kg, subcutaneously, of a ganglioside mixture (Cronassial). The other half received physiological saline and served as control. At the end of 7 or 11 weeks, the tibial nerves were removed and examined histomorphometrically. Every animal had developed a neuropathy. However, the mice treated with the ganglioside mixture showed on both the examination dates a substantially larger proportion of small sprouting nerve fibres than the control. It was concluded from this that treatment with gangliosides stimulated the regenerative potential of the damaged nerves.     

Prevention and reversal of motor and sensory peripheral nerve conduction abnormalities in streptozotocin-diabetic rats by the prostacyclin analogue iloprost

Summary The effects of the prostacyclin analogue iloprost on nerve function were examined in streptozotocin-diabetic rats. Rats were treated either with iloprost from induction of diabetes over 2 months in a preventive experiment, or for 1 month following a 1 month untreated period of diabetes in a reversal experiment. One and 2 months untreated diabetic control, non-diabetic control, and iloprost-treated non-diabetic groups were also used.Diabetes of 1 month duration caused a 21% (P < 0.001) reduction in sciatic motor conduction velocity and a 14% (P (0.001) deficit in saphenous sensory conduction. This was not significantly changed over a subsequent month without treatment. Diabetic rats given iloprost treatment in both preventive and reversal studies had motor and sensory conduction velocities not significantly different from those of non-diabetic controls, but greater than for untreated diabetes (P < 0.01). Iloprost treatment did not have a significant effect on nerve conduction in non-diabetic rats. The time taken for sciatic nerve compound action potential amplitude to be reduced by 80% under hypoxic conditions in vitro was progressively elevated by 19% and 57% after 1 and 2 months diabetes respectively. Iloprost treatment significantly attenuated this for both preventive (47%, P < 0.001) and reversal (50%, P < 0.001) studies. There was no effect on hypoxic resistance for non-diabetic rats. In the preventive group there was a 28010 increase in sciatic nerve endoneurial capillary density (P < 0.001), a lesser effect (16%, P < 0.05) in the reversal group, and no effect in non-diabetic rats. Sciatic nerve sorbitol, fructose and myo-inositol levels were measured in 2 month diabetic control and reversal iloprost-treated groups. Treatment had no significant effect on the elevation of polyol pathway metabolites or myo-inositol concentration.We conclude that iloprost treatment may compensate for reduced prostacyclin production by vasa nervorum. Although short durations of experimental diabetes do not result in the severe degenerative changes found in clinical neuropathy, it is nevertheless possible that iloprost may have therapeutic potential for vascular-related diabetic complications. Correspondence to N. E. Cameron at the above address     

Effect of mexiletine on vincristine-induced painful neuropathy in mice

In the present study, we examined the effect of mexiletine on vincristine-induced thermal hyperalgesia in mice. Mice were intraperitoneally treated with vincristine at a dose of 0.05 mg/kg one day after the measurement of the pre-drug latency in the tail-flick test, and then treated with a dose of 0.125 mg/kg twice a week for 6 weeks. In vincristine-treated mice, a significant decrease in tail-flick latency developed at 6 weeks after treatment. Pretreatment with mexiletine, at doses of 3, 10 and 30 mg/kg, i.p., dose-dependently increased the tail-flick latency in vincristine-treated mice. A significant reduction of the tail-flick latency was observed when the tail-flick latency was examined 60 min after i.t. administration of NG-nitro-L-arginine methyl ester (L-NAME, 30 nmol), a nitric oxide synthase (NOS) inhibitor, in naive mice. This L-NAME-induced thermal hyperalgesia was dose-dependently attenuated by pretreatment with mexiletine (10 and 30 mg/kg, i.p.), 10 min before the injection of L-NAME. The duration of nociceptive behavioral response induced by fenvalerate, at a dose of 0.1 microg, i.t., was significantly increased by pretreatment with L-NAME (30 nmol, i.t.). Intrathecal pretreatment with L-arginine (300 pmol) significantly reversed the L-NAME-induced enhancement of fenvalerate-induced nociceptive responses. The present study demonstrates that systemic mexiletine can effectively attenuate vincristine-induced thermal hyperalgesia. Furthermore, these results suggest that blockade of nitric oxide-induced enhancement of nociceptive transmission, in which tetrodotoxin-resistant sodium channels play an important role, may participate in the antinociceptive effect of mexiletine on vincristine-induced thermal hyperalgesia.