Effects of α-lipoic acid on neurovascular function in diabetic rats: interaction with essential fatty acids

Summary Elevated oxidative stress and impaired n-6 essential fatty acid metabolism contribute to defective nerve conduction velocity (NCV) and perfusion in diabetic rats, which may be corrected by free radical scavenger and γ-linolenic acid (GLA) treatments. α-Lipoic acid (LPA) has antioxidant actions and both LPA racemate (racLPA) and GLA treatments produced benefits in clinical neuropathy trials. The aims were to study LPA action on neurovascular function in diabetic rats and to investigate potential interactions for co-treatment with GLA and other essential fatty acids. After 6 weeks of diabetes, 2 weeks of racLPA treatment corrected 20 % sciatic motor and 14 % saphenous sensory NCV deficits. The ED₅₀ for motor NCV restoration was approximately 38 mg kg^–1 day^–1. racLPA also corrected a 49 % diabetic deficit in sciatic endoneurial blood flow. R and S-LPA enantiomers were equipotent in correcting NCV and blood flow deficits. Treatment of diabetic rats with low doses (20 mg kg^–1 day^–1) of racLPA and GLA, while having modest effects on their own, showed evidence of marked synergistic action in joint treatment, completely correcting motor NCV and blood flow deficits. This was also noted for the novel compound, SOC0150, which contains equimolar proportions of LPA and GLA (ED₅₀ 9.3 mg kg^–1 day^–1, containing 3.5 mg LPA). NCV effects also showed marked synergism when racLPA:GLA ratios were varied over a 1:3–3:1 range. In contrast, a compound containing LPA and the n-3 component, docosahexaenoic acid, showed similar activity to LPA alone. Thus, LPA-GLA interactions yield drug combinations and compounds with an order of magnitude increase in efficacy against experimental diabetic neuropathy and are worthy of consideration for clinical trials. [Diabetologia (1998) 41: 390–399] Received: 22 September 1997 and in revised form: 26 November 1997     

Reduced nerve blood flow in diabetic rats: relationship to nitric oxide production and inhibition of aldose reductase

This study examined links between impaired nitric oxide production in the sciatic endoneurium, nerve blood flow, and polyol pathway flux, to test the hypothesis that reduced nerve blood flow might be compromised by competition for NADPH between aldose reductase and nitric oxide synthase. Sciatic nerves of streptozotocin-diabetic rats showed reduced laser Doppler flux (by 51 % or 63 %; both p<0.05)—indicative of reduced nerve blood flow—and reduced motor nerve conduction velocity (17 % in two experiments; p<0.05). Acute interruption of nitric oxide production in the sciatic nerves of control rats, via endoneurial injection of Nω-nitro-D -arginine methyl ester ( L -NAME), caused a local reduction (of 64 %; p<0.001) in nerve Doppler flux. This was reversed by either L -arginine or sodium nitroprusside. The response to L -NAME was greatly reduced in diabetic rats (only 22 % reduction; p<0.01), though both L -arginine and SNP caused marked increases in flux. Chronic inhibition of aldose reductase in diabetic rats (with either sorbinil or imirestat at a range of doses) had little effect on resting sciatic nerve Doppler flux, though both inhibitors normalized conduction velocity. Both aldose reductase inhibitors reduced sorbitol pathway intermediates in a dose-related manner. These findings do not support the proposition that aldose reductase inhibitors normalise conduction velocity by mechanisms dependent upon either normalization of endoneurial nitric oxide or nerve blood flow. Instead, a mechanism based upon more direct effects on axon or Schwann cell function is favoured. © 1998 John Wiley & Sons, Ltd.     

Aldose reductase inhibition,nerve perfusion,oxygenation and function in streptozotocin-diabetic rats: Dose-response considerations and independence from a myo-inositol mechanism

Summary We examined the effects of aldose reductase inhibition on nerve biochemistry and function, blood flow and endoneurial oxygenation in experimental diabetes mellitus. After 1 month untreated diabetes in rats, treatment with the novel sulphonylnitromethane aldose reductase inhibitor, ZENECA ZD5522, prevented a progressive increase in sciatic nerve resistance to hypoxic conduction failure (p<0.05). Motor conduction velocity deficits after 4 months untreated diabetes were rapidly returned to normal within 12 days (p<0.0001) by ZD5522 treatment. Following 2-months untreated diabetes, examination of 1 month ZD5522 treatment dose-response relationships for correction of nerve sorbitol and fructose accumulations and reduction in myo-inositol concentration, sciatic motor and saphenous sensory conduction velocity and sciatic blood flow by laser-Doppler flowmetry revealed poor agreement between nerve function and biochemical indices. In addition, polyol accumulation differed between sciatic and saphenous nerves, the latter showing ten-fold lower sorbitol concentrations. Laser-Doppler blood flow was 60% decreased by untreated diabetes (p<0.001) and there was a strong correlation between ZD5522-mediated increases in blood flow and conduction velocity (p<0.0001). Measurement of nutritive endoneurial blood flow by microelectrode polarography and hydrogen clearance showed 44% and 45% deficits for 1 and 2 months untreated diabetes (p<0.001) that were prevented by ponalrestat and ZD5522 treatments, respectively. In contrast, 2 months myo-inositol treatment from diabetes induction did not prevent reduction in blood flow or sciatic motor conduction velocity. A 37% reduction in endoneurial oxygen tension after 2 months diabetes (p<0.001) was completely prevented by ZD5522 treatment (p< 0.001). The data show that a very high degree of polyol pathway blockade is necessary to correct nerve functional deficits and that aldose reductase inhibitors have a neurovascular action that does not depend on restoration of nerve myo-inositol.Abbreviations ARI aldose reductase inhibitor - ED₅₀ 50% effective dose - EMG electromyogram - Na⁺-K⁺-ATPase sodium potassium adenosine triphosphatase - NCV nerve conduction velocity - NO nitric oxide - RHCF resistance to hypoxic conduction failure     

Essential fatty acid treatment — effects on nerve conduction,polyol pathway and axonal transport in streptozotocin diabetic rats

Summary This study was designed to examine the effect of dietary supplementation with essential fatty acids (evening primrose oil — 5% weight:weight added to the diet) on acute neurophysiological and neurochemical defects in streptozotocin-diabetic rats. Diabetic rats, which were not given evening primrose oil, showed highly significant elevations of nerve sorbitol and fructose combined with a depletion of nerve myo-inositol. In those animals there was also a 40% reduction (p<0.02) in the accumulation of axonally transported substance P-like immunoreactivity proximal to a 12 h sciatic nerve ligature together with reduced motor nerve conduction velocity (13% [p<0.001] and 20% [p<0.001] in two separate experiments). Treatment of other diabetic rats with evening primrose oil prevented completely the development of the motor nerve conduction velocity deficit without affecting sorbitol, fructose or myo-inositol levels or the deficit in axonal transport of substance P. In a second experiment, treatment of diabetic rats with evening primrose oil was associated with significant attenuation of the conduction velocity deficit, but not complete prevention.     

The potential contribution of endothelin-1 to neurovascular abnormalities in streptozotocin-diabetic rats

Summary Abnormal vascular endothelium function may contribute to the reduced nerve perfusion implicated in the aetiology of neuropathy in diabetes mellitus. The aim was to test the hypothesis that a powerful vasoconstrictor, endothelin-1, could be involved in nerve dysfunction in streptozotocin-diabetic rats. After 6 weeks of untreated diabetes, rats were implanted with osmotic minipumps which continuously delivered the endothelin-1 antagonist, BQ-123, to the circulation via a jugular vein cannula. Sciatic motor conduction velocity, monitored serially, was increased after 4 days, treatment (p=0.028), and reached asymptote by 9–11 days (p=0.0001), when the degree of amelioration was approximately 60% of the initial diabetic deficit. Treatment of non-diabetic rats for 13 days with BQ-123 had no significant effect on motor conduction velocity. Sensory saphenous nerve conduction velocity was measured acutely after 20 days, BQ-123 treatment. The amelioration of a sensory deficit was approximately 80% (p<0.001); the resultant conduction velocity value was not significantly different from that of a non-diabetic control group. After 20 days, treatment, sciatic nutritive endoneurial blood flow was measured by microelectrode polarography and hydrogen clearance. A 48% deficit with untreated diabetes (p<0.001) was 64% ameliorated by BQ-123 treatment (p<0.001). In non-diabetic rats, BQ-123 treatment had no effect on blood flow. We conclude that endothelin-1 does not seem to be involved in the control of nerve blood flow in non-diabetic rats; however, it makes a major contribution to the perfusion deficit in experimental diabetes. This has deleterious consequences for nerve conduction, and it is possible that endothelin-1 receptor blockade may have therapeutic potential in diabetic patients.Abbreviations ED₅₀ 50% effective dose - EMG electromyogram - ET endothelin-1 - NCV nerve conduction velocity - NO nitric oxide     

Impaired contraction and relaxation in aorta from streptozotocin-diabetic rats: Role of polyol pathway

Summary The effects of 3 months streptozotocin-induced diabetes mellitus on contraction and relaxation of aorta were examined in vitro. A further diabetic group was treated with a novel sulphonylnitromethane-based aldose reductase inhibitor for 3 months following diabetes induction. Diabetes resulted in reduced maximal tension production, particularly for responses to phenylephrine (p < 0.001) and serotonin (p < 0.001). However, with aldose reductase inhibitor treatment, responses were in the non-diabetic range. The ratio of maximum contractions to noradrenaline and phenylephrine were 28 % elevated by diabetes (p < 0.01), which may suggest increased ₂-adrenoreceptor-mediated responses. Endothelium-independent relaxation to glyceryl trinitrate was unaffected by diabetes or treatment. By contrast, there were 38 % deficits in endothelium-dependent relaxation to acetylcholine (p < 0.001) and Ca²⁺ ionophore A23187 (p < 0.001) with diabetes which were prevented by aldose reductase inhibitor treatment (p < 0.001). A 121 % shift in the concentration giving a 50% maximum effect for acetylcholine towards lower sensitivity with diabetes (p < 0.001) was also largely corrected by treatment (p < 0.001). A non-diabetic group treated with aldose reductase inhibitor showed a 30 % decrease in the 50 % effective concentration for acetylcholine (p < 0.05). A 15 % deficit in maximum relaxation to the ATP-sensitive K⁺ channel opener cromakalim for the diabetic group (p < 0.001) was prevented by aldose reductase inhibitor treatment (p < 0.01). We conclude that there are polyol pathway related abnormalities for contraction, some aspects of endothelium-independent relaxation, but particularly for endothelium-dependent relaxation in aorta from chronic streptozotocin-diabetic rats. If found in the appropriate circulatory beds, these could potentially contribute to the putative vascular basis of some of the complications of diabetes. Their amelioration could account for many of the beneficial effects of aldose reductase inhibitors.     

Comparison of the effects of inhibitors of aldose reductase and sorbitol dehydrogenase on neurovascular function, nerve conduction and tissue polyol pathway metabolites in streptozotocin-diabetic rats

Summary Aldose reductase inhibitors (ARIs) attenuate diabetic complications in several tissues, including lens, retina, kidney, blood vessels, striated muscle and peripheral nerve. However, it is unclear whether their action in diabetes mellitus depends directly on inhibiting the conversion of glucose to sorbitol by aldose reductase or indirectly by reducing the sorbitol available for subsequent metabolism to fructose by sorbitol dehydrogenase. To identify the polyol pathway step most relevant to complications, particularly neuropathy, we compared the biochemical effects of a sorbitol dehydrogenase inhibitor, WAY-135 706, (250 mg · kg⁻¹· day⁻¹) and an ARI, WAY-121 509, (10 mg · kg⁻¹· day⁻¹) on a variety of tissues, and their effects on nerve perfusion and conduction velocity. After 6 weeks of untreated streptozotocin diabetes, rats were treated for 2 weeks. Sorbitol was elevated 2.1–32.6-fold by diabetes in lens, retina, kidney, aorta, diaphragm, erythrocytes and sciatic nerve; this was further increased (1.6–8.2-fold) by WAY-135 706 whereas WAY-121 509 caused a marked reduction. Fructose 1.6–8.0-fold elevated by diabetes in tissues other than diaphragm, was reduced by WAY-135 706 and WAY-121 509, except in the kidney. Motor and sensory nerve conduction velocities were decreased by 20.2 and 13.9 %, respectively with diabetes. These deficits were corrected by WAY-121 509, but WAY-135 706 was completely ineffective. A 48.6 % diabetes-induced deficit in sciatic nutritive endoneurial blood flow was corrected by WAY-121 509, but was unaltered by WAY-135 706. Thus, despite profound sorbitol dehydrogenase inhibition, WAY-135 706 had no beneficial effect on nerve function. The data demonstrate that aldose reductase activity, the first step in the polyol pathway, makes a markedly greater contribution to the aetiology of diabetic neurovascular and neurological dysfunction than does the second step involving sorbitol dehydrogenase. [Diabetologia (1997) 40: 271–281] Received: 13 August 1996 and in final revised form: 6 December 1996     

Effects of an extracellular metal chelator on neurovascular function in diabetic rats

Abstract Aims/hypothesis. Increased oxidative stress has been causally linked to diabetic neurovascular complications, which are attenuated by antioxidants. There are several possible sources of reactive oxygen species in diabetes. Our aim was to assess the contribution of free radicals, produced by transition metal catalysed reactions, to early neuropathic changes. To this end, we examined, firstly, the effects of an extracellular high molecular weight chelator, hydroxyethyl starch-deferoxamine, which is expected to be confined to vascular space, on nerve perfusion and conduction deficits in diabetic rats and, secondly, the action of a single chelator dose. Methods. Diabetes was induced by streptozotocin. In vivo measurements comprised sciatic nerve motor conduction velocity and endoneurial perfusion, monitored by hydrogen clearance microelectrode polarography. Results. We found that 8 weeks of diabetes reduced sciatic blood flow and conduction velocity by 48.3 % and 19.9 % respectively. Two weeks of intravenous treatment corrected these deficits. Starch vehicle was ineffective. The time-course of action of a single hydroxyethyl starch-deferoxamine injection was examined in diabetic rats. There was a rapid increase in nerve blood flow on day 1, which remained within the non-diabetic range for 9 days before declining to the diabetic level at day 27. In contrast, conduction velocity changes were slower, reaching the non-diabetic range at day 6 and declining to the diabetic level at day 27. Conclusion/interpretation. Extracellular transition metal catalysed reactions play a major role in the neurovascular deficits of experimental diabetes. Given the long-lasting effect of a single treatment, extracellular metal chelator therapy could be suitable for further assessment in clinical trials. [Diabetologia (2001) 44: 621–628] Received: 30 October 2000 and in revised form: 12 January 2001     

Vascular factors and metabolic interactions in the pathogenesis of diabetic neuropathy

Diabetes mellitus is a major cause of peripheral neuropathy, commonly manifested as distal symmetrical polyneuropathy. This review examines evidence for the importance of vascular factors and their metabolic substrate from human and animal studies. Diabetic neuropathy is associated with risk factors for macrovascular disease and with other microvascular complications such as poor metabolic control, dyslipidaemia, body mass index, smoking, microalbuminuria and retinopathy. Studies in human and animal models have shown reduced nerve perfusion and endoneurial hypoxia. Investigations on biopsy material from patients with mild to severe neuropathy show graded structural changes in nerve microvasculature including basement membrane thickening, pericyte degeneration and endothelial cell hyperplasia. Arterio-venous shunting also contributes to reduced endoneurial perfusion. These vascular changes strongly correlate with clinical defects and nerve pathology. Vasodilator treatment in patients and animals improves nerve function. Early vasa nervorum functional changes are caused by the metabolic insults of diabetes, the balance between vasodilation and vasoconstriction is altered. Vascular endothelium is particularly vulnerable, with deficits in the major endothelial vasodilators, nitric oxide, endothelium-derived hyperpolarising factor and prostacyclin. Hyperglycaemia and dyslipidaemia driven oxidative stress is a major contributor, enhanced by advanced glycation end product formation and polyol pathway activation. These are coupled to protein kinase C activation and ω-6 essential fatty acid dysmetabolism. Together, this complex of interacting metabolic factors accounts for endothelial dysfunction, reduced nerve perfusion and function. Thus, the evidence emphasises the importance of vascular dysfunction, driven by metabolic change, as a cause of diabetic neuropathy, and highlights potential therapeutic approaches. [Diabetologia (2001) 44: 1973–1988] Received: 19 March 2001 and in revised form: 15 June 2001     

Anti-oxidant and pro-oxidant effects on nerve conduction velocity,endoneurial blood flow and oxygen tension in non-diabetic and streptozotocin-diabetic rats

Summary Increased oxygen free radical activity, coupled with reduced protection against oxidative stress, could play a role in the aetiology of neurovascular abnormalities in experimental diabetes mellitus. To test this hypothesis, non-diabetic and streptozotocin-diabetic rats were treated with the anti-oxidant probucol or the pro-oxidant primaquine. One-month diabetes caused 21.4 % and 13.6 % reduction in sciatic motor and saphenous sensory conduction velocity (p<0.001). These deficits were prevented by probucol treatment (p<0.001). After 1-month untreated diabetes, conduction velocity deficits were reversed by a further month of probucol treatment (p<0.001). For non-diabetic rats, primaquine treatment caused a 12.9 % reduction in motor conduction velocity (p<0.001), which was prevented by probucol treatment (p<0.001). Primaquine treatment did not affect diabetic rats. Sciatic nerve nutritive endoneurial blood flow, measured using microelectrode polarography and hydrogen clearance, was 48.0 % reduced by 2-month diabetes (p<0.001). This was completely prevented by probucol treatment (p<0.001). Primaquine treatment did not affect blood flow in diabetic rats. However, in non-diabetic rats it caused a 30.0 % reduction (p<0.01) which was prevented by probucol treatment (p<0.05). Sciatic endoneurial oxygen tensions were also measured by microelectrode polarography. Mean tension was 38.8 % reduced by diabetes (p<0.001). This was prevented by probucol treatment. Non-diabetic rats given primaquine treatment showed a 21.7 % reduction in endoneurial oxygen tension (p<0.01). The data suggest that vascular-mediated nerve dysfunction in diabetes depends on oxidative stress, and that similar effects in non-diabetic rats may be produced by pro-oxidant treatment. This provides evidence for the potentially important role of oxygen free radical activity in diabetic neuropathy. [Diabetologia (1994) 37: 449–459] Received: 13 September 1993 and in revised form: 19 November 1993     

Effects of natural free radical scavengers on peripheral nerve and neurovascular function in diabetic rats

Summary Increased generation of reactive oxygen species, coupled with impaired endogenous scavenging mechanisms, plays a prominent role in the aetiology of neurovascular abnormalities in experimental diabetes mellitus. We examined the efficacy of the natural anti-oxidants vitamins C, E and -carotene in preventing nerve conduction and nutritive blood flow deficits in streptozotocin-diabetic rats. One month of diabetes caused a 19.1% reduction in sciatic motor conduction velocity (p<0.001). This was approximately prevented 80–90% by high-dose (1000 mg · kg^–1 · day^–1) vitamin E and -carotene treatments (p<0.001). Vitamin C had lesser effects; the maximum protection found for motor conduction velocity was 36% using a dose of 150 mg · kg^–1 · day^–1 (p<0.001). High dose (500 mg · kg^–1 · day^–1) vitamin C had a lesser effect on conduction than intermediate doses. Joint vitamin C and lower dose (500 mg · kg^–1 · day^–1) vitamin E treatment had a predominantly additive preventive effect against nerve dysfunction. Resistance to hypoxic conduction failure for sciatic nerve in vitro was markedly increased by diabetes and this remained relatively unaffected by treatment. Sciatic nutritive endoneurial blood flow, measured using microelectrode polarography and hydrogen clearance, was reduced 46.1% by 1 month of diabetes (p<0.001). This was prevented to the extent of 87%, 36% and 98% by vitamins E, C and -carotene, respectively (p<0.01). These data emphasize the role of oxidative stress in the development of early neurovascular changes in experimental diabetes and show that naturally available scavengers have a neuroprotective action.Abbreviations NCV Nerve conduction velocity - NO nitric oxide - ROS reactive oxygen species     

Essential fatty acid treatment prevents nerve ischaemia and associated conduction anomalies in rats with experimental diabetes mellitus

Summary In rats with 6 weeks streptozotocin-diabetes there was a 53% reduction in sciatic nerve laser Doppler flux compared to controls (p<0.01). Treatment of a parallel group of diabetic rats with evening primrose oil, by dietary admixture throughout the protocol, prevented this ischaemia (Doppler flux was 91% of evening primrose oil-treated controls and was not significantly different). There were no differences in systemic arterial pressure. In another experiment evening primrose oil markedly antagonised the development of exaggerated resistance to anoxic conduction failure in sciatic nerves from diabetic rats. The resistance to anoxia of nerves from non-diabetic rats was also reduced by evening primrose oil. These observations suggest that the sciatic nerves of diabetic rats with short-term streptozotocin-diabetes are markedly ischaemic and that this ischaemia is involved in the development of increased resistance to anoxic/ischaemic conduction failure in diabetic nerve. The findings also promote evening primrose oil as a potential treatment to prevent nerve ischaemia.     

Protein kinase C effects on nerve function, perfusion, Na+,K+-ATPase activity and glutathione content in diabetic rats

Abstract Aims//hypothesis. Increased protein kinase C activity has been linked to diabetic vascular complications in the retina and kidney, which were attenuated by protein kinase C antagonist treatment. Neuropathy has a vascular component, therefore, the aim was to assess whether treatment with WAY151 003 or chelerythrine, inhibitors of protein kinase C regulatory and catalytic domains respectively, could correct nerve blood flow, conduction velocity, Na⁺,K⁺-ATPase, and glutathione deficits in diabetic rats. Methods. Diabetes was induced by streptozotocin. Sciatic nerve conduction velocity was measured in vivo and sciatic endoneurial perfusion was monitored by microelectrode polarography and hydrogen clearance. Glutathione content and Na⁺,K⁺-ATPase activity were measured in extracts from homogenised sciatic nerves. Results. After 8 weeks of diabetes, sciatic blood flow was 50 % reduced. Two weeks of WAY151 003 (3 or 100 mg/kg) treatment completely corrected this deficit and chelerythrine dose-dependently improved nerve perfusion. The inhibitors dose-dependently corrected a 20 % diabetic motor conduction deficit, however, at high doses ( > 3.0 mg/kg WAY151003; > 0.1 mg/kg chelerythrine) conduction velocity was reduced towards the diabetic level. Sciatic Na⁺,K⁺-ATPase activity, 42 % reduced by diabetes, was partially corrected by low but not high dose WAY151 003. In contrast, only a very high dose of chelerythrine partially restored Na⁺,K⁺-ATPase activity. A 30 % diabetic deficit in sciatic glutathione content was unchanged by protein kinase C inhibition. The benefits of WAY151 003 on blood flow and conduction velocity were blocked by nitric oxide synthase inhibitor co-treatment. Conclusion/interpretation. Protein kinase C contributes to experimental diabetic neuropathy by a neurovascular mechanism rather than through Na⁺,K⁺-ATPase defects. [Diabetologia (1999) 42: 1120–1130] Received: 21 December 1998 and in final revised form: 23 April 1999     

Pharmacological manipulation of vascular endothelium function in non-diabetic and streptozotocin-diabetic rats: effects on nerve conduction,hypoxic resistance and endoneurial capillarization

Summary We examined the potential for some of the abnormalities of vascular endothelium found in diabetes mellitus to cause neuropathic changes. Non-diabetic rats were treated for 2 months with the cyclo-oxygenase inhibitor flurbiprofen (5 mg·kg⁻¹·day⁻¹) to reduce prostacyclin production, the nitric oxide synthase inhibitor N^G-nitro-L-arginine (5 or 25 mg·kg⁻¹·day⁻¹), or combined treatment. There were dose-dependent reductions in sciatic motor and saphenous sensory conduction velocity. The two inhibitors acted synergistically, thus, the 5–6% motor conduction deficits (p<0.01) produced by either flurbiprofen or N^G-nitro-l-arginine (5 mg·kg⁻¹·day⁻¹) increased to 17% (p<0.001) for combined treatment. With N^G-nitro-l-arginine (25 mg·kg⁻¹·day⁻¹) and flurbiprofen, motor and sensory conduction velocity were reduced by 23% (p<0.001) and 12% (p<0.001), respectively, matching the deficits following 2-month streptozotocin diabetes. N^G-nitro-l-arginine (25 mg·kg⁻¹·day⁻¹) and flurbiprofen together produced a 13% prolongation of the time taken for 80% hypoxic conduction failure in vitro (p<0.05) and a 10% reduction in sciatic capillary density. A second investigation tested an alternative hypothesis that overproduction of nitric oxide was responsible for vascular-related complications in diabetes, the prediction being that N^G-nitro-L-arginine (5 mg·kg⁻¹·day⁻¹) would prevent nerve dysfunction. However, rather than prophylaxis during 2-month streptozotocin diabetes, treatment exacerbated nerve abnormalities. Thus, N^G-nitro-L-arginine worsened (8%,p<0.001) the motor conduction deficit, there was an 11% increase in hypoxic conduction failure time (p<0.01) and an 11% reduction in endoneurial capillary density (p<0.01). We conclude that overproduction of nitric oxide is unlikely to be involved in the aetiology of experimental diabetic neuropathy. However, endothelial dysfunction resulting in impaired nitric oxide and prostacyclin synthesis could make a substantial contribution.     

Effects of interleukin‐6 treatment on neurovascular function,nerve perfusion and vascular endothelium in diabetic rats

Aim: Interleukin‐6 (IL‐6), a member of the neuropoietic cytokine family, participates in neural development and has neurotrophic activity. Recent research has also indicated actions to improve vasa nervorum function in diabetes. Both these facets are potentially relevant for treatment of diabetic neuropathy. The aim of this study was to determine whether IL‐6 treatment corrected changes in neurovascular function in streptozotocin‐induced diabetic rats. Methods: After 1 month of diabetes, rats were given IL‐6 for 1 month. The rats were subjected to sensory testing and measurements of nerve conduction velocities and nerve blood flow by hydrogen clearance microelectrode polarography. Further groups were used to study responses of the isolated gastric fundus and renal artery. Results were statistically analysed using ANOVA and post hoc tests. Results: Diabetic rats showed mechanical hyperalgesia, thermal hyperalgesia, and tactile allodynia. The former was unaffected by IL‐6 treatment, whereas the latter two measures were corrected. Immunohistochemical staining of dorsal root ganglia for IL‐6 did not reveal any changes with diabetes or treatment. The results showed that 22 and 17.4% slowing of sciatic motor and saphenous sensory nerve conduction velocities, respectively, with diabetes were improved by IL‐6. Sciatic endoneurial perfusion was halved by diabetes and corrected by IL‐6. A 40.6% diabetic deficit in maximal non‐adrenergic, non‐cholinergic relaxation of gastric fundus to nerve stimulation was unaffected by IL‐6. Renal artery endothelium‐dependent relaxation was halved by diabetes, the endothelium‐derived hyperpolarizing factor (EDHF) component being severely attenuated. IL‐6 did not affect nitric oxide‐mediated vasorelaxation, but markedly improved EDHF responses. Conclusions: IL‐6 improved aspects of small and large nerve fibre and vascular endothelium dysfunction in diabetic rats. The functional benefits related to increased nerve blood flow via an EDHF mechanism, and IL‐6 could have therapeutic potential in diabetic neuropathy and vasculopathy, which should be further evaluated.     

冠状动脉慢血流患者一氧化氮和内皮素1浓度的变化

目的探讨冠状动脉慢血流(coronary slow flow,CSF)患者的血管内皮功能。方法选择因胸痛行冠状动脉造影的患者40例,根据造影结果分为CSF组20例和对照组20例。2组分别于静息和多巴酚丁胺负荷试验结束时立即抽取血标本,检测血浆内皮素1、血清NO浓度,并进行比较。结果 CSF组静息时血浆内皮素1浓度较对照组升高,但差异无统计学意义(P>0.05),而药物负荷试验后血浆内皮素1浓度较对照组明显升高,差异有统计学意义[(37.60±6.93)ng/L vs(14.16±5.73)ng/L,P<0.01]。CSF组静息时和药物负荷试验后血清NO浓度均明显低于对照组,差异有统计学意义[(42.36±9.72)μmol/L vs(50.39±9.77)μmol/L,(24.88±9.28)μmol/L vs(61.06±8.20)μmol/L,P<0.01)]。结论 CSF患者无论静息或者药物负荷状态下均存在内皮素1及NO平衡失调,负荷状态下这种平衡失调现象更加明显。     

Advanced glycation end products-cytokine-nitric oxide sequence pathway in the development of diabetic nephropathy: aminoguanidine ameliorates the overexpression of tumour necrosis factor-α and inducible nitric oxide synthase in diabetic rat glomeruli

Aims/hypothesis. Advanced glycation end products are believed to contribute to diabetic microvascular complications by inducing glomerular damage but their role has not been fully clarified. In this study, we explain their central role in the induction of inducible nitric oxide synthase and production of nitric oxide (NO) in streptozotocin-induced diabetic rat glomeruli. Methods. Localization of carboxymethyllysine, which is one of the chemical components of advanced glycation end products, glomerular expression of inducible nitric oxide synthase and urinary excretion and glomerular production of NO₂ ^–/NO₃ ^– were examined at 0, 26, 51, and 52 weeks after the induction of diabetes. Therapeutic effects of aminoguanidine were also examined. Results. Carboxymethyllysine was detected in the mesangial area in glomeruli and it progressively accumulated during 52 weeks of observation. Immunohistochemistry and hybridization studies in situ showed that the number of inducible nitric oxide synthase-positive cells was notably increased in diabetic rat glomeruli at 52 weeks. Further, this augmented expression paralleled intraglomerular expression of TNF-α and NO₂ ^–/NO₃ ^– in diabetic rat glomeruli. Treatment with aminoguanidine reduced the expression of TNF-α, inducible nitric oxide synthase and intraglomerular NO₂ ^–/NO₃ ^– production. It also ameliorated proteinuria in diabetic rats. Conclusion/interpretation. This study showed that carboxymethyllysine possibly enhances the expression of inducible nitric oxide synthase by stimulating the expression of TNF-α in diabetic rat glomeruli. The carboxymethyllysine-cytokine-NO sequence pathway could be one of the major mechanisms in the development of diabetic nephropathy. [Diabetologia (1999) 42: 878–886] Received: 11 September 1998 and in revised form: 28 December 1998