Diabetic neuropathy

Aldo-keto reductase and sorbitol dehydrogenase enzymes in Egyptian diabetic patients with and without proliferative diabetic retinopathy

BACKGROUND

Activation of the polyol pathway due to increased aldo-keto reductase (AKR) activity has been implicated in the development of diabetic complications, including proliferative diabetic retinopathy (PDR); however, the relationship between hyperglycaemia-induced activation of the polyol pathway in the retina and PDR is still uncertain.

METHODS

This study was conducted on 73 individuals, who were categorised into three groups: healthy individuals as normal control (15 age-matched subjects), diabetic patients treated with oral hypoglycaemic drugs (OHD, 34 patients), six of whom (17.7 per cent) were diagnosed with PDR and the rest were diagnosed with non-proliferative diabetic retinopathy (NPDR) and diabetic patients treated with insulin (INS, 24 patients), 12 of whom (50 per cent) were diagnosed with PDR and the rest had NPDR.

RESULTS

The AKR level in diabetic subjects showed a significant increase compared with the normal controls. Interestingly, AKR levels were significantly increased in the INS compared with the OHD group. Also the AKR level was significantly increased in the patients with proliferative compared with the non-proliferative retinopathy in both the insulin and oral diabetic groups. The sorbitol dehydrogenase (SDH) level in diabetic patients showed a significant decrease compared with the normal control level. Interestingly, the SDH level was significantly decreased in the INS compared with the OHD group. Also, the SDH level was significantly decreased in patients with proliferative compared with non-proliferative retinopathy in both INS and OHD groups. The HbA(1c) level in both INS and OHD subjects showed a significant increase compared with normal controls. In addition, the triglyceride level in insulin proliferative retinopathy showed a significant increase compared with other groups.

CONCLUSIONS

The AKR level was significantly increased in patients with proliferative compared with non-proliferative retinopathy in both insulin and oral diabetic groups. The SDH level was significantly decreased in patients with proliferative compared with non-proliferative retinopathy in both insulin and oral diabetic groups. Both AKR and SDH could be used as indicators for diabetic control.

A comparative profile of methanol extracts of Allium cepa and Allium sativum in diabetic neuropathy in mice

Introduction:

Diabetic Neuropathy (DN) is a major microvascular complication of uncontrolled diabetes. This may result from increased oxidative stress that accompanies diabetes. Hence plants with antioxidant action play an important role in management of diabetes and its complications.

Materials and Methods:

This study was designed to evaluate preventive as well as curative effect of methanol extracts of outer scales and edible portions of two plants with established antioxidant action - Allium cepa and Allium sativum, in induced DN in albino mice. Mice were divided into control, diabetic and test extracts treated groups. Test extracts were administered daily at a dose of 200 mg/kg p.o. for 21 days, in the preventive group prior to onset of DN, and in the curative group after the onset of DN. Hyperalgesia and oxidative stress markers were assessed. STZ-diabetic mice showed a significant thermal hyperalgesia (as assessed by the tail-flick test), indicating development of DN.

Results:

Treatment with test extracts prevented loss in body weight, decreased plasma glucose level, and significantly ameliorated the hyperalgesia, TBARS, serum nitrite and GSH levels in diabetic mice.

Conclusion:

Methanol extract of outer scales of onion has shown most significant improvement; may be due to higher content of phenolic compounds in outer scales of A. cepa.

Human cerebral neuropathology of Type 2 diabetes mellitus

The cerebral neuropathology of Type 2 diabetes (CNDM2) has not been positively defined. This review includes a description of CNDM2 research from before the 'Pubmed Era'. Recent neuroimaging studies have focused on cerebrovascular and white matter pathology. These and prior studies about cerebrovascular histopathology in diabetes are reviewed. Evidence is also described for and against the link between CNDM2 and Alzheimer's disease pathogenesis. To study this matter directly, we evaluated data from University of Kentucky Alzheimer's Disease Center (UK ADC) patients recruited while non-demented and followed longitudinally. Of patients who had come to autopsy (N = 234), 139 met inclusion criteria. These patients provided the basis for comparing the prevalence of pathological and clinical indices between well-characterized cases with (N = 50) or without (N = 89) the premortem diagnosis of diabetes. In diabetics, cerebrovascular pathology was more frequent and Alzheimer-type pathology was less frequent than in non-diabetics. Finally, a series of photomicrographs demonstrates histopathological features (including clinical-radiographical correlation) observed in brains of persons that died after a history of diabetes. These preliminary, correlative, and descriptive studies may help develop new hypotheses about CNDM2. We conclude that more work should be performed on human material in the context of CNDM2.

Effects of cytidine 5'-diphosphocholine (CDP-choline) on the thermal nociceptive threshold in streptozotocin-induced diabetic mice

Neuropathy accompanied by abnormal sensory perception is the most common complication in insulin-dependent and -independent diabetes mellitus. Since there are very few effective therapeutic regimens for sensory abnormalities in diabetes, we examined the effect of cytidine 5'-diphosphocholine (CDP)-choline on the thermal nociceptive threshold in streptozotocin-induced diabetic mice using the tail-flick test. Diabetic mice showed a shorter tail-flick latency at 1-4 weeks after streptozotocin treatment and a longer tail-flick latency after 8-12 weeks. This hyper- and hypoalgesia in diabetic mice was almost completely inhibited by daily treatment with CDP-choline (100 mg/kg/day, p.o.) beginning on the day of streptozotocin treatment. Daily treatment with CDP-choline beginning 5 weeks after streptozotocin treatment attenuated the development of hypoalgesia. Diabetic mice showed a significant increase in Na(+)-K(+)-ATPase activity at 3 weeks after streptozotocin treatment, whereas Na(+)-K(+)-ATPase activity was decreased at 12 weeks after treatment. These alterations were normalized by daily treatment with CDP-choline (100 mg/kg/day, p.o.) beginning the day of streptozotocin treatment. These results provide evidence to support the therapeutic potency of CDP-choline on the development of thermal hyper- and hypoalgesia and the progression of thermal hypoalgesia in diabetic mice. Moreover, these effects of CDP-choline may result from the normalization of Na(+)-K(+)-ATPase activity.

Comparison of clinical evaluation and neurosensory testing in the early diagnosis of superimposed entrapment neuropathy in diabetic patients

Diabetic patients are more susceptible to the development of entrapment neuropathy than nondiabetics. Since these patients suffer from a slowly progressing diabetic polyneuropathy, standard neurosensory and motor tests of nerve function are not sufficient in the diagnosis of superimposed nerve compression. This is most evident in the early stages of compression when quantitative diagnosis is important for making decisions on surgical decompression. We evaluated the validity of computer-assisted pressure-specified sensory device (PSSD) testing in the early detection of superimposed entrapment in diabetic neuropathy in comparison with standard clinical tests. Twenty-five diabetic patients with complaints of peripheral nerve dysfunction were evaluated by clinical tests and PSSD. Out of those, nerve entrapment was detected in 15 patients (60%) (9 in late and 6 in early stage) by neurosensory PSSD testing. Standard clinical tests were confirmative in 33.3% of these cases (44% of late and 16.7% of early stage). Out of 144 evaluated nerves, 50 were diagnosed with entrapment (24 in late and 26 in early stage) using PSSD. Clinically, diagnosis was confirmed in 16% of entrapped nerves (20.8% of late and 11.5% of early stage). Average diabetes duration in patients with entrapment diagnosed using PSSD was significantly shorter than for those diagnosed clinically (4.14 +/- 2.04 vs. 7.2 +/- 1.3, respectively; P = 0.005). Among evaluated factors, mean age and diabetes duration were found to be significantly shorter in patients with entrapment than in those with advanced diffused changes (54.47 +/- 13.07 vs. 67.10 +/- 14.2; P = 0.019 and 5.33 +/- 3.74 vs.14.22 +/- 8.17; P = 0.006; respectively). Our results revealed higher sensitivity of PSSD in comparison with standard clinical tests in the detection of early-stage entrapment in patients with diabetes. To assess accuracy of PSSD in the proper patients' qualification for surgery, further prospective, postoperative studies are needed.

Restoration of ultrastructural and biochemical changes in alloxan-induced diabetic rat sciatic nerve on treatment with Na3VO4 and Trigonella--a promising antidiabetic agent

Vanadium has been reported to have broad pharmacological activity both in vitro and in vivo. Vanadium compound, sodium orthovanadate, Na3VO4, is well known for its hypoglycaemic effects. However, Na3VO4 exerts these effects at relatively high doses (0.6 mg/ml) and exhibit several toxic effects. In the present study lower doses of Na3VO4 (0.2 mg/ml) are combined with Trigonella foenum graecum seed powder (TSP), another hypoglycaemic agent, to reduce its toxicity without compromising its antidiabetic potential. The efficacy of the lower doses of Na3VO4 has been investigated in restoring the altered glucose metabolism and histological structure in the sciatic nerves in 21 and 60 days alloxan diabetic rats. A portion of the glucose was found to be channelled from the normal glycolytic route to polyol pathway, evident by the reduced hexokinase activity and increased polyol pathway enzymes aldose reductase and sorbitol dehydrogenase activity causing accumulation of sorbitol and fructose in diabetic conditions. Ultrastructural observation of the sciatic nerve showed extensive demylination and axonal loss after eight weeks of diabetes induction. Blood glucose levels increased in diabetic rats were normalized with the lower dose of vanadium and Trigonella treatment. The treatment of the diabetic rats with vanadium and Trigonella prevented the activation of the polyol pathway and sugar accumulations. The sciatic nerves were also protected against the structural abnormalities found in diabetes with Trigonella foenum graecum as well as Na3VO4. Results suggest that lower doses of Na3VO4 may be used in combination with TSP as an efficient antidiabetic agent to effectively control the long-term complications of diabetes in tissues like peripheral nerve.

F-wave and H-reflex alterations in recently diagnosed diabetic patients

OBJECTIVE

To explore the frequency of F-wave and H-reflex alterations in recently diagnosed type 2 diabetes mellitus patients and to determine if the alterations are dependent on the levels of glycemia.

METHODS

A cross-sectional study was carried out on 50 asymptomatic patients, with a mean age of 45.4 +/- 9.8 years and a disease evolution of less than 10 years. Patients were classified as either normoglycemic (7 mmol/L; n = 20) or hyperglycemic (7 mmol/L; n = 30). H-reflex (HR), F-wave (FW), and nerve-conduction measurements (NCM) between the diabetic and non-diabetic (control) groups were compared.

RESULTS

The H-reflex was absent in 22% of the patients, while the M-component of this reflex was altered in 58% of patients. The F-wave was altered in 12% of the patients. The motor nerve compound action potential showed a diminution in amplitude (26% of patients, n = 13), area (32%, n = 16), and conduction velocity (20%, n = 10). No positive correlation between glycemia levels and the above alterations was found.

CONCLUSIONS

This study demonstrated that asymptomatic diabetic patients showed a high incidence of subclinical neurophysiological abnormalities.

Changes in aorta alpha1-adrenoceptor number and affinity during one year of streptozotocin-induced diabetes in rats

alpha(1)-Adrenoceptor function and density in isolated thoracic aorta were measured during the course of streptozotocin-induced diabetes in rats. Diabetes was induced by a single tail vein injection of streptozotocin (60 mg/kg) and was verified by four measures (blood glucose level, increase in food intake, increase in water intake, and characteristic weight changes). Diabetes produced a significant increase in isolated aorta sensitivity to alpha(1)-adrenoceptor activation, manifested as a significant (p < 0.05) decrease in the A(50) value for phenylephrine and an increase in the A(50) (control)/A(50) (diabetic) ratio (1.2, 1.7, and 2.0, respectively) with increasing length of diabetes (4, 12 and 52 weeks). There was a large and biphasic change in receptor density (B(max)), without a significant change (p > 0.05) in either agonist (phenylephrine) or antagonist (prazosin) affinities (K(A) and pA(2) values, respectively). These results suggest compensatory mechanisms in receptor number and abnormalities in 2nd messenger transduction and can help direct efforts for improving antihypertensive or other pharmacological therapy for diabetic patients.

The effects of occupational exposure to chlorpyrifos on the peripheral nervous system: a prospective cohort study

AIMS

To determine whether chronic occupational exposure to chlorpyrifos at levels associated with various aspects of manufacturing produced a clinically evident or subclinical peripheral neuropathy.

METHODS

Clinical and quantitative nerve conduction study (NCS) examinations were performed on two occasions on chlorpyrifos manufacturing workers who had measurable chlorpyrifos exposure and a referent group. Baseline evaluations were performed on 53 of 66 eligible chlorpyrifos subjects and on 60 of 74 eligible referent subjects; one-year evaluations were completed on 111 of the 113 subjects evaluated at baseline.

RESULTS

Chlorpyrifos and referent groups differed significantly in measures of 3,5,6 trichloro-2-pyridinol excretion and plasma butyrylcholinesterase (BuChE) activity, indicating substantially higher exposures among chlorpyrifos subjects. Few subjects had clinically important neurological symptoms or signs. NCS results were comparable to control values, and there were no significant group differences in NCS results at baseline, one year, or change over one year. No chlorpyrifos subject fulfilled conventional criteria for confirmed peripheral neuropathy at baseline or one-year examinations. The odds ratios for developing any diagnosable level of peripheral neuropathy among the chlorpyrifos subjects was not increased at baseline or at one year compared to referents at baseline. Mixed regression models used to evaluate subclinical group-by-time interactions showed numerous significant NCS differences attributable to near-nerve temperature differences among all subjects between the baseline and one-year examinations, but only a few disparate effects related to group.

CONCLUSIONS

Chronic chlorpyrifos exposure during the manufacturing process sufficient to produce biological effects on BuChE activity was not associated with clinically evident or subclinical peripheral neuropathy at baseline or with measurable deterioration among chlorpyrifos subjects compared to referents after one year of additional exposure.

Absence of sensory neuropathy among workers with occupational exposure to chlorpyrifos

Several studies have reported the occurrence of sensory neuropathy with exposure to chlorpyrifos and other organophosphorus insecticides, at levels not associated with overt toxicity. We evaluated 113 chemical workers, including 53 of 66 (80%) eligible chlorpyrifos workers and 60 of 74 (81%) randomly selected referent workers, to identify evidence of sensory neuropathy or subclinical neuropathy. Compared to referents, chlorpyrifos subjects had significantly longer duration of work in chlorpyrifos-exposed areas (9.72 vs. 0.01 years; P < 0.0001), greater cumulative chlorpyrifos exposure (64.16 vs. 0.69 mg/m(3). day; P < 0.0001), higher urine 3,5,6-trichloro-2-pyridinol (TCP) excretion (108.6 vs. 4.3 microg/g creatinine; P < 0.0001), and lower plasma butyrylcholinesterase (BuChE) activity (7281 vs. 8176 mU/ml; P = 0.003). Despite exposures among chlorpyrifos subjects to levels at which well-described physiological effects on B-esterases exist, the frequency of symptoms or signs of neuropathy did not differ significantly between groups, and the only 2 subjects fulfilling criteria for confirmed neuropathy were both in the referent group. Mean nerve conduction study results were comparable to established control values and did not differ significantly between groups. We found no evidence of sensory neuropathy or isolated peripheral abnormalities among subjects with long-term chlorpyrifos exposure at levels known to be associated with the manufacturing process.

Pyridoxine and pyridoxamine inhibits superoxide radicals and prevents lipid peroxidation, protein glycosylation, and (Na+ + K+)-ATPase activity reduction in high glucose-treated human erythrocytes

Vitamin B(6) (pyridoxine) supplementation has been found beneficial in preventing diabetic neuropathy and retinopathy, and the glycosylation of proteins. Oxygen radicals and oxidative damage have been implicated in the cellular dysfunction and complications of diabetes. This study was undertaken to test the hypothesis that pyridoxine (P) and pyridoxamine (PM) inhibit superoxide radical production, reduce lipid peroxidation and glycosylation, and increase the (Na+ + K+)-ATPase activity in high glucose-exposed red blood cells (RBC). Superoxide radical production was assessed by the reduction of cytochrome C by glucose in the presence and absence of P or PM in a cell-free buffered solution. To examine cellular effects, washed normal human RBC were treated with control and high glucose concentrations with and without P or PM. Both P and PM significantly lowered lipid peroxidation and glycated hemoglobin (HbA(1)) formation in high glucose-exposed RBC. P and PM significantly prevented the reduction in (Na+ + K+)-ATPase activity in high glucose-treated RBC. Thus, P or PM can inhibit oxygen radical production, which in turn prevents the lipid peroxidation, protein glycosylation, and (Na+ + K+)-ATPase activity reduction induced by the hyperglycemia. This study describes a new biochemical mechanism by which P or PM supplementation may delay or inhibit the development of complications in diabetes.

Lipoic acid decreases lipid peroxidation and protein glycosylation and increases (Na(+) + K(+))- and Ca(++)-ATPase activities in high glucose-treated human erythrocytes

Lipoic acid supplementation has been found to be beneficial in preventing neurovascular abnormalities in diabetic neuropathy. Insufficient (Na(+) + K(+))-ATPase activity has been suggested as a contributing factor in the development of diabetic neuropathy. This study was undertaken to test the hypothesis that lipoic acid reduces lipid peroxidation and glycosylation and can increase the (Na(+) + K(+))- and Ca(++)-ATPase activities in high glucose-exposed red blood cells (RBC). Washed normal human RBC were treated with normal (6 mM) and high glucose concentrations (45 mM) with 0-0.2 mM lipoic acid (mixture of S and R sterioisomers) in a shaking water bath at 37 degrees C for 24 h. There was a significant stimulation of glucose consumption by RBC in the presence of lipoic acid both in normal and high glucose-treated RBC. Lipoic acid significantly lowered the level of glycated hemoglobin (GHb) and lipid peroxidation in RBC exposed to high glucose concentrations. High glucose treatment significantly lowered the activities of (Na(+) + K(+))- and Ca(++)-ATPases of RBC membranes. Lipoic acid addition significantly blocked the reduction in activities of (Na(+) + K(+))- and Ca(++)-ATPases in high glucose- treated RBC. There were no differences in lipid peroxidation, GHb and (Na(+) + K(+))- and Ca(++)-ATPase activity levels in normal glucose-treated RBC with and without lipoic acid. Thus, lipoic acid can lower lipid peroxidation and protein glycosylation, and increase (Na(+) + K(+))- and Ca(++)-ATPase activities in high-glucose exposed RBC, which provides a potential mechanism by which lipoic acid may delay or inhibit the development of neuropathy in diabetes.

Neuropathic gait shows only trends towards increased variability of sagittal plane kinematics during treadmill locomotion

Patients with diabetes mellitus (DM) and peripheral neuropathy (PN) are at greater risk of falling and of suffering injuries during falls. It has been hypothesized that PN leads to changes in gait variability that may account for this increased risk. The purpose of this investigation was to analyze the variability of the sagittal plane kinematics of diabetic neuropathic (NP), diabetic non-neuropathic (NNP) and age- and weight-matched control subjects (Control) during motorized treadmill walking at constant speed. While there were distinct trends towards increased variability within the three diagnostic groups (NP > NNP > Control) for several measures of gait variability, most of these trends were not statistically significant. We hypothesize that motorized treadmill walking may be inherently less variable than overground walking and that statistical measures of variability may not be sufficient to fully characterize stride-to-stride variability in human locomotion.

Impact of diabetes on CNS: role of signal transduction cascade

Diabetic neuropathy is the most common secondary complication of diabetes mellitus. Several pathogenetic factors have been proposed for diabetic neuropathy. The present investigation was undertaken to study different components of signal transduction from discrete brain regions from streptozotocin-induced diabetic rats. Rats were sacrificed after 1 and 3 months of induction of diabetes, and a control group was also studied in parallel to ascertain the specificity of diabetes-associated changes. Blood glucose level and protein content of discrete brain regions were also estimated. Signal transduction cascade components like protein kinase A, protein kinase C, cAMP, phospholipase C, phospholipase A2, diacylglycerol and inositol phosphate levels were assayed in control and diabetic groups of rats. Significant attenuation in phosphoinositide metabolism along with activation of protein kinase activities were observed. These findings provide evidence to suggest a mechanism linking changes in signal transduction cascade, which is observed in 1- and 3-month diabetic rats, which ultimately leads to development of diabetic neuropathy.

Nerve growth factor (NGF) and diabetic neuropathy in the rat: morphological investigations of the sural nerve, dorsal root ganglion, and spinal cord

A number of functions for nerve growth factor (NGF) have been described over the past years, including its role for neuronal function and regeneration during toxic or metabolic neuropathies. In order to further assess the effects of NGF on the somatosensory system in diabetic neuropathy, the sural nerve, dorsal root ganglia (DRG), and dorsal horn of the spinal cord were investigated by morphological and quantitative methods in rats after 12 weeks of uncontrolled streptozotocin-induced diabetes mellitus. The results from our study suggest a twofold effect of NGF: (1) In sural nerve treatment with NGF (0.1 or 0.5 mg/kg) for 12 weeks was able to reverse distinct diabetes-related alterations in myelinated nerve fiber morphology, such as myelin thickness. These changes occurred in the entire myelinated population of sensory nerves and were not restricted to nociceptive nerve fibers. (2) The NGF effect on neurotransmitters of the sensory, nociceptive system was reflected by increased CGRP and substance P content in the DRG and in the dorsal horn of the spinal cord. No change of trkA receptor immunostaining was seen in DRGs of diabetic rats; however, a reduction of trkA immunoreactivity of DRG neurons was noted after long-term NGF treatment of healthy controls. The data demonstrate that NGF regulates a number of neuronal parameters along peripheral and central parts of the somatosensory pathway in the adult. This neurotrophic support may be essential for inducing functionally significant regenerative mechanisms in diabetic neuropathy.

A simplified diagnostic test for ambulatory screening of peripheral diabetic neuropathy

The reliability and reproducibility of Michigan Neuropathy Screening Instrument (MNSI), a recently proposed simple test for ambulatory screening of peripheral diabetic neuropathy (PDN), was evaluated on 80 diabetic patients. MNSI was carried out by two diabetologists and repeated after a week. It consisted of the sum of scores varying from 0 to 1 for each abnormality revealed in foot appearance, achilles reflexes presence and vibratory threshold (VPT) by tuning fork (maximum score = 8). Then patients had to go to neurologist for PDN diagnosis by a quantitative neurological examination and electrophysiological evaluation, the so named Michigan Diabetic Neuropathy Score (MDNS) and the results compared with MNSI score according to one of the two observers. The inter-observer reproducibility of MNSI was 88.75% the within observer reproducibility was 95 and 94%, respectively, for each observer with good correlation between the two measurements (P < 0.001). The MNSI score of 2.5 as a cut-off appeared to be reliable for ambulatory screening of suspected PDN (false positive and false negative = 2.5%; specificity and sensitivity = 75% and 78.6%, respectively). In conclusion MNSI by using 2.5 score as cut-off may be considered a rapid, simple, reproducible and reliable test for rapid ambulatory screening of PDN from the diabetologists.

Susceptibility to diabetic neuropathy in patients with insulin dependent diabetes mellitus is associated with a polymorphism at the 5' end of the aldose reductase gene

OBJECTIVES

There is evidence that the polyol pathway is involved in the pathogenesis of diabetic neuropathy. Aldose reductase (ALR2) is the first and rate limiting enzyme of this pathway and recent studies have suggested that polymorphisms in and around the gene are associated with the development of diabetic microvascular disease. The aim was to examine the role of ALR2 in the susceptibility to diabetic neuropathy in patients with insulin dependent diabetes mellitus (IDDM).

METHODS

One hundred and fifty nine British white patients with IDDM and 102 normal healthy controls were studied using the polymerase chain reaction to test for a highly polymorphic microsatellite marker 2.1 kilobase (kb) upstream of the initiation site of the ALR2 gene.

RESULTS

Seven alleles were detected (Z-6, Z-4, Z-2, Z, Z+2, Z+4, and Z+6). There was a highly significant decrease in the frequency of the Z+2 allele in those patients with overt neuropathy compared with those with no neuropathy after 20 years duration of diabetes (14.1% v 38.2%, chi2 =17.3, p<0.00001). A similar difference was also found between the neuropathy group and those patients who have had diabetes for < five years with no overt neuropathy (14.1% v 30.2%, chi2=9.0, p<0.0025). The neuropathy group also had a significant decrease in the frequency of the Z/Z+2 genotype compared with those patients who have no neuropathy after 20 years duration of diabetes (14.0% v 44.7%, chi2=13.0, p<0.0005).

CONCLUSION

These results suggest that the aldose reductase gene is intimately involved in the pathogenesis of diabetic neuropathy.

Nodal Na(+)-channel displacement is associated with nerve-conduction slowing in the chronically diabetic BB/W rat: prevention by aldose reductase inhibition

Chronic nerve conduction showing in experimental diabetic neuropathy has been associated with decreased nodal Na+ permeability and an ultrastructurally identifiable loss of axo-glial junctions, which comprise the paranodal voltage channel barrier separating nodal Na+ channels from paranodal K+ channels. In human and experimental diabetic neuropathy these structural changes of the paranodal apparatus correlate closely with the nerve conduction defect. The present immunocytochemical study of the alpha-subunit of the Na+ channel examined whether the breach of the voltage channel barrier may account for a shift in the distribution of Na+ channels explaining decreased nodal Na+ permeability. Biobreeding Wistar (BB/W) rats diabetic for 4-8 months showed a progressive redistribution of nodal Na+ channels across the paranodal barrier into the paranodal and internodal domains which was associated with chronic nerve conduction slowing. The present data suggest that structural damage to the paranodal barrier system in diabetic nerve facilitates the lateral displacement of Na+ channels from the nodal axolemma thereby diminishing their nodal density and the nodal Na+ permeability associated with the chronic nerve conduction defect in experimental diabetes. These abnormalities were prevented by the treatment with an aldose reductase inhibitor, belonging to a class of drugs that, in neuropathic patients, improves nerve-conduction velocity and repairs axo-glial dysjunction of the paranodal apparatus.

Enteric neuropeptides in streptozotocin-diabetic rats; effects of insulin and aldose reductase inhibition

The aim of the present study was to determine whether diabetes-induced changes in the distribution of enteric neuropeptides, could be prevented in 12-week streptozotocin-diabetic rats, by rigorous control of glycaemia, using daily adminstration of insulin, or an aldose reductase inhibitor (ponalrestat). The pattern of distribution of nerve fibres and cell bodies, containing immunoreactive vasoactive intestinal polypeptide (VIP), galanin (GAL), calcitonin gene-related peptide (CGRP) and substance P was examined in the myenteric plexus of ileum from control, untreated diabetic, insulin-treated diabetic and aldose reductase inhibitor-treated diabetic rats. The increase in VIP- and GAL-like immunoreactivity, seen in the myenteric plexus of untreated diabetic rat ileum, was not present in the myenteric plexus of ileum from insulin- and aldose reductase inhibitor-treated diabetic rats. With CGRP-like immunoreactive fibres, there was a clear decrease in the ileum of untreated diabetic rats. This was prevented by insulin treatment, but aldose reductase inhibitor treatment had no effect. No alterations in substance P-like immunoreactivity were seen in the myenteric plexus of ileum from any of the groups investigated. Generally, the similarity of effect of ponalrestat and insulin on VIP and galanin expression in this study supports a primary effect of insulin via glycaemic control. The dissimilarity of the effect of the two treatments on CGRP expression may imply a neurotrophic effect of insulin, although there are certainly consequences of hyperglycaemia other than exaggerated flux through the polyol pathway.

C-peptide stimulates rat renal tubular Na+, K(+)-ATPase activity in synergism with neuropeptide Y

This study was performed in order to test the hypothesis that the connecting peptide of proinsulin, C-peptide, might in itself possess biological activity. Renal tubular Na+, K(+)-ATPase, which is a well-established target for many peptide hormones, was chosen as a model. Rat C-peptide (I) was found to stimulate Na+, K(+)-ATPase activity in single, proximal convoluted tubules dissected from rat kidneys. C-peptide increased the Na+ affinity of the enzyme and all subsequent studies were performed at non-saturating Na+ concentrations. C-peptide stimulation of Na+, K(+)-ATPase activity occurred in a concentration-dependent manner in the dose range 10(-8)-10(-6) mol/l. The presence of neuropeptide Y, 5 x 10(-9) mol/l, enhanced this effect and stimulation of Na+, K(+)-ATPase activity then occurred in the C-peptide dose range 10(-11)-10(-8) mol/l. C-peptide stimulation of Na+, K(+)-ATPase activity was abolished in tubules pretreated with pertussis toxin. It was also abolished in the presence of FK 506, a specific inhibitor of the Ca2(+)-calmodulin-dependent protein phosphatase 2B. These results indicate that C-peptide stimulates Na+, K(+)-ATPase activity, probably by activating a receptor coupled to a pertussis toxin-sensitive G-protein with subsequent activation of Ca2(+)-dependent intracellular signalling pathways.

Antioxidants in peripheral nerve

Oxidative stress and antioxidants have been related in a wide variety of ways with nervous tissue. This review attempts to gather the most relevant information related to a) the antioxidant status in non pathologic nervous tissue; b) the hypothesis and evidence for oxidative stress (considered as the disequilibrium between prooxidants and antioxidants in the cell) as the responsible mechanism of diverse neurological diseases; and c) the correlation between antioxidant alterations and neural function, in different experimental neuropathies. Decreased antioxidant availability has been observed in different neurological disorders in the central nervous system, for example, Parkinson's disease, Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis, cerebral ischaemia, etc. Moreover, the experimental manipulation of the antioxidant defense has led in some cases to interesting experimental models in which electrophysiological alterations are associated with the metabolic modifications induced. In view of the electrophysiological and biochemical effects of some protein kinase C inhibitors on different neural experimental models, special attention is dedicated to the role of this kinase in peripheral nervous tissue. The nervous tissue, central as well as peripheral, has two main special features that are certainly related to its antioxidant metabolism: the lipid-enriched membrane and myelin sheaths, and cellular excitability. The former explains the importance of the glutathione (GSH)-conjugating activity towards 4-hydroxy-nonenal, a biologically active product of lipid peroxidation, present in nervous tissue and in charge of its inactivation. The impairment of the latter by oxidative damage or experimental manipulation of antioxidant metabolism is discussed. Work on different experimental neuropathies from author's laboratory has been primarily used to provide information about the involvement of free radical damage and antioxidants in peripheral nerve metabolic and functional impairment.

The aetiology of diabetic neuropathy: the combined roles of metabolic and vascular defects

A combination of metabolic and vascular defects have been implicated in the pathogenesis of diabetic neuropathy. Animal studies have demonstrated that a reduction in nerve blood flow may be an important early defect and that vasodilators can prevent or ameliorate nerve dysfunction. The potential factors contributing to nerve ischaemia include structural defects in the endoneurial microvasculature together with rheological abnormalities, abnormalities in vasoactive agents which regulate nerve blood flow including nitric oxide and the eicosanoids, and alterations in tone of the autonomic innervation of the nerve vasculature. The principle metabolic defects which have been implicated include disruption of the polyol pathway, altered lipid metabolism, advanced glycosylated end-product formation, increased oxidative stress, and diabetes-induced defects in growth factors. The demonstration that activation of the polyol pathway in experimental diabetes may affect nerve blood flow, and conversely that vasoactive agents appear to be important in regulating some aspects of nerve metabolism, has highlighted the interdependence of the metabolic and vascular defects in the pathogenesis of this condition. Thus, selective intervention aimed at a key defect early in this cascade may subsequently correct a number of later abnormalities offering therapeutic hope in this chronic debilitating complication.

Natural course of diabetic peripheral neuropathy in spontaneous-onset diabetic Chinese hamsters

We investigated metabolic and pathological changes in the peripheral nerve of the spontaneous-onset diabetic Chinese hamster. Electrophysiological examination revealed that the motor nerve conduction velocity was significantly decreased at 10 months and afterwards, however, the F-wave latency was significantly increased at 5 months and afterwards. Concerning sciatic nerve contents of sorbitol, myo- and scyllo-inositol, the content of sorbitol was not significantly increased at 5 months, but, myo- and scyllo-inositol were significantly decreased at 5 months and thereafter. At 10 and 15 months, however, sciatic nerve content of sorbitol was significantly increased. On morphological examination, loss of large myelinated fiber and reciprocal increase in degenerative fiber were also seen in sciatic nerve, but not in tibial nerve, at 5 months. At 15 months, these morphological changes were also found in the tibial as well as the sciatic nerve. Thus, we may hypothesize that F-wave latency is useful in the detection of initial diabetic neuropathy, and that the initial pathological changes in diabetic neuropathy of diabetic Chinese hamsters are predominantly found in the proximal site of peripheral nerves.

The effects of goshajinkigan, a herbal medicine, on subjective symptoms and vibratory threshold in patients with diabetic neuropathy

Goshajinkigan, a herbal medicine, has long been used in Japan to alleviate the subjective symptoms of diabetic neuropathy; however, its effects have not been confirmed objectively. We evaluated its effects on subjective symptoms and on vibration sensation in patients with diabetic neuropathy. The oral administration of 7.5 g/day of Goshajinkigan for 3 months (treatment period) relieved subjective symptoms of numbness in 9 of 13 patients. When the drug was discontinued for 2 months as a washout period, the subjective symptom worsened in 7 of 13 patients. Chi-square analysis revealed significant effects of Goshajiniagan on subjective symptoms (P < 0.001 for numbness and P < 0.05 for cold sensation). Vibration sensation was evaluated by measuring vibratory threshold using an SMV-5 vibrometer. There were significant changes in vibratory thresholds by paired t-test (P < 0.05) both in the upper and the lower extremities during the treatment and washout periods. Chi-square analysis also revealed a significant effect of Goshajinkigan on vibratory threshold (P < 0.01). There was no significant change in glycosylated hemoglobin as a whole during the study. These observations confirm that Goshajinkigan relieves subjective symptoms and demonstrate that it improves vibration sensation in patients with diabetic neuropathy.

Treatment of non-insulin-dependent diabetes mellitus and its complications. A state of the art review

Non-insulin-dependent diabetes mellitus (NIDDM) is a major health problem which occurs predominantly in the older population; 16.8% of persons over age 65 years have NIDDM. The total health costs of NIDDM are in excess of $US20 billion annually. The primary objective in the treatment of NIDDM is to achieve normoglycaemia, without aggravating coexisting abnormalities. Common abnormalities include obesity, hypertension, retinopathy, nephropathy and neuropathies. Diet, and consequent bodyweight reduction, is the cornerstone of therapy for NIDDM. Total calorie intake should be limited, while the percentage of calories from carbohydrates should be increased and that from fats and cholesterol should be decreased. Exercise may also help to reduce bodyweight. Sulphonylurea drugs stimulate insulin secretion from beta-cells, and may be a useful adjunct to nonpharmacological therapy. Failure to respond to sulphonylurea drugs may be primary (25 to 30% of initially treated patients) or secondary (5 to 10% per year). It is not clear which is the most effective pharmacological intervention in such cases. Options include switching to or combining therapy with insulin, a biguanide, or other insulin-sparing antihyperglycaemic agents, e.g. alpha-glucosidase inhibitors, thiazolidinediones, chloroquine or hydroxychloroquine, or fibric acid derivatives such as clofibrate. Other experimental agents include the fatty acid oxidation inhibitors and dichloroacetate. Specific agents, such as antihypertensives, lipid lowering agents and sorbitol inhibitors, may be needed to prevent the complications arising from the spectrum of clinical and metabolic abnormalities which arise from insulin resistance.

Influence of diabetes on mortality in acute myocardial infarction: data from the GISSI-2 study

OBJECTIVES

This study was conducted to determine the role of insulin-dependent and noninsulin-dependent diabetes in the prognosis of patients after myocardial infarction and treatment with fibrinolytic agents.

BACKGROUND

Several studies have shown that diabetic patients have a high mortality rate after acute myocardial infarction. However, the impact of diabetes on survival in patients treated with fibrinolytic agents is still undefined. It is also not known whether the type of diabetes or gender affects prognosis.

METHODS

We analyzed prevalence and prognostic significance of a history of diabetes in patients enrolled in the GISSI-2 study, all of whom received fibrinolytic agents. The incidence of deaths in the hospital and at 6 months after study entry was computed for patients without diabetes and for insulin-dependent and noninsulin-dependent diabetic patients; relative risks were evaluated by univariate and multivariate analysis.

RESULTS

Information on diabetic status was available for 11,667 patients, 94.2% of those randomized in the GISSI-2 study. The prevalence of diabetes was higher in women than in men (8.75% vs. 1.85%, p < 0.01 for insulin-dependent and 23.7% vs. 13.8%, p < 0.01 for noninsulin-dependent diabetic patients). The type of fibrinolytic agent did not affect mortality rates; the increase in in-hospital mortality of diabetic patients was moderate and similar for men with insulin- and noninsulin-dependent diabetes (8.7% and 10.1%, respectively, vs. 5.8% in nondiabetic patients); in women, mortality was markedly higher for insulin-dependent and only slightly higher for noninsulin-dependent diabetic patients (24.0% and 15.8%, respectively, vs. 13.9% for nondiabetic patients). The adjusted relative risks were 1.9 (95% confidence interval 1.2 to 2.9) for insulin-dependent diabetic women and 1.4 (95% confidence interval 1.1 to 1.8) for noninsulin-dependent diabetic men. The mortality rate after discharge showed a similar gender difference, and in insulin-dependent diabetic women, prognosis was ominous even in the absence of left ventricular damage before discharge.

CONCLUSIONS

A history of diabetes is associated with a worse prognosis after myocardial infarction, even in patients treated with fibrinolytic agents. Gender and type of diabetes appear to be critical in affecting survival. In men, both insulin-dependent and noninsulin-dependent diabetes are associated with a moderately higher mortality rate; in women, insulin-dependent diabetes is, in itself, a strong risk factor for death after myocardial infarction.

Impairment of central motor conduction in diabetic patients

In 70 patients with diabetes mellitus (DM) we recorded the motor evoked potentials (MEPs) following magnetic stimulation of the motor cortex and spinal roots. Central motor conduction time (CMCT) was determined as the difference between MEP latencies after cortical and spinal stimulation. The mean CMCTs for the biceps, thenar and tibialis anterior muscles were prolonged in the DM group, as compared to normal controls, and 21 patients exceeded the CMCT upper confidence limit for at least one muscle. CMCT changes and peripheral conduction velocity abnormalities occurred independently and were related to different clinical parameters. We conclude that a subclinical impairment of central motor conduction is present in 30% of DM patients, independently from the occurrence of a diabetic peripheral neuropathy and possibly reflecting different pathophysiological mechanisms.

Decreased glutathione peroxidase activity in sciatic nerve of alloxan-induced diabetic mice and its correlation with blood glucose levels

The effect of alloxan-induced diabetes on glutathione peroxidase (GSH-Px) activity in sciatic nerve of mice has been studied. We have found, 7 days after alloxan treatment, a significant decrease in this enzymatic activity in the cytosol of sciatic nerve of diabetic mice, and moreover, that these changes remained unaltered up to 21 days after alloxan injection. No modification in the glutathione content of sciatic nerve of diabetic mice was observed throughout the experiment when compared with controls. The decrease in GSH-Px activity in this tissue shows a good correlation with the increase of blood glucose levels throughout the experiment. It is hypothesized whether a combination of mechanisms could be involved in this decrease of GSH-Px activity and if oxygen radicals might be the common mediators of these processes.

Insulin-like growth factor I: a mitogen for rat Schwann cells in the presence of elevated levels of cyclic AMP

To develop effective procedures for improving the regeneration of peripheral nerves and for preventing the formation of neurofibromas, it is necessary to identify the different mitogens that stimulate the proliferation of Schwann cells. Insulin-like growth factor I (IGF-I), which is a potent autocrine growth factor in many tissues, is synthesized by proliferating Schwann cells. However, the role of IGF-I in stimulating their division is still uncertain. Here we show that nanomolar concentrations of IGF-I stimulate the growth of Schwann cells in primary culture. IGF-I alone was uneffective, but in the presence of forskolin (5 microM) or dibutyryl cyclic AMP (dbcAMP, 10 microM), it became a potent mitogen. Neither IGF-II nor epidermal growth factor (EGF) were effective even in the presence of forskolin. Insulin also stimulated Schwann cell proliferation in the presence of forskolin, but only at micromolar concentration. Receptors for IGF-I were visualized on the Schwann cell surface by indirect immunofluorescence staining using anti-human IGF-I receptor antibodies. Their presence was also assessed by binding assays using [125I]-IGF-I as a ligand. Scatchard analysis showed a single class of high-affinity receptors (Kd = 1.5 nM). Competitions studies with unlabeled IGF-I or insulin indicated a half-maximal displacement of [125I]-IGF-I by IGF-I at about 5 nM, while insulin was about 500-fold less effective. The number of binding sites for IGF-I was increased by exposing cells for 3 days to forskolin (-forskolin: about 5,100; + forskolin: about 12,200 binding sites/cell).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hyperglycemia and the aldose reductase inhibitor tolrestat on sural nerve biochemistry and morphometry in advanced diabetic peripheral polyneuropathy. The Tolrestat Study Group

Tolrestat is a well tolerated nonhydantoin aldose reductase inhibitor that has been reported to improve nerve conduction in diabetic animals and humans. Its effects on nerve biochemistry and structure have not been studied in patients with diabetic neuropathy. Patients with advanced diabetic neuropathy treated with long-term open-label tolrestat were randomly assigned to continuation on drug treatment or to placebo-controlled drug withdrawal for 12 months. At the end of this period, sural nerve biopsies were obtained for measurement of glucose, sorbitol, and fructose content, and for detailed morphometric analysis. Tolrestat ameliorated the glucose-mediated increase in sorbitol and fructose in sural nerve tissue. No statistically significant differences in nerve morphometry emerged between the two groups; however, both treatment groups exhibited increased nerve-fiber regeneration and normalization of axo-glial dysfunction and segmental demyelination following long-term tolrestat treatment. These findings are similar to those previously reported in a placebo-controlled sequential nerve biopsy study with the aldose reductase inhibitor sorbinil. Thus tolrestat is a biochemically effective aldose reductase inhibitor in human diabetic nerve with potential therapeutic efficacy for diabetic neuropathy.

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

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.

Neuropathies associated with diabetes

Diabetic neuropathy is the most frequent complication of diabetes and the leading cause of polyneuropathy in the Western world. A distal symmetric predominantly sensory polyneuropathy is the most common of the diverse neuropathies that occur secondary to diabetes. Pain is often the most bothersome and difficult to treat symptom of diabetic neuropathy. Autonomic neuropathy is a frequent feature of diabetic neuropathy and the source of many significant problems including postural hypotension, gastroparesis, diarrhea, constipation, neurogenic bladder, and male impotence. Physicians need to be familiar with the multiple, less common forms of diabetic neuropathy, as these often mimic other medical or neurologic conditions. The cause of diabetic neuropathy is not determined, but abundant evidence suggests that both metabolic and ischemic nerve injury are likely factors. These should not be considered mutually exclusive causes of diabetic neuropathy as both factors likely operate to different degrees to produce the clinical spectrum of neuropathies that are seen in diabetes. Although no effective treatment exists to cure diabetic neuropathy, improvement is possible with glycemic control and symptomatic therapy.

Inhibition of protein kinase C restores Na+,K(+)-ATPase activity in sciatic nerve of diabetic mice

We have tested if inhibition of protein kinase C is able to prevent and/or to restore the decrease of Na+,K(+)-ATPase activity in the sciatic nerve of alloxan-induced diabetic mice. Mice were made diabetic by subcutaneous injection of 200 mg of alloxan/kg of body weight. The activity of Na+,K(+)-ATPase decreased rapidly (43% after 3 days) and slightly thereafter (58% at 11 days). We show that intraperitoneal injection of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), an inhibitor of protein kinase C, prevents completely the loss of Na+,K(+)-ATPase activity produced by alloxan. Also, H7 injected into diabetic mice, 4-9 days after the injection of alloxan, restores the activity of the enzyme. The amount of activity recovered depends on the dose of H7 administered; complete recovery was reached with injection of 15 mg of H7/kg of body weight. The effect of H7 is transient, with a half-life of approximately 1 h.

Aldose reductase inhibitors as pathobiochemical probes

In tissues susceptible to damage from chronic diabetes, excess glucose is metabolized by aldose reductase (AR) to sorbitol. Originally, AR-catalyzed sorbitol formation (and accumulation) was found in the diabetic lens; the cataractogenicity of this process was proven by preventing cataract formation with an AR inhibitor (ARI). These findings were extended to the hypothesis that, in diabetic tissues, excessive intracellular sorbitol formation initiates a cascade of metabolic abnormalities which gradually progress to loss of functional and structural integrity. The pivotal role of AR as a trigger for such abnormalities was established by preventing their occurrence in diabetic animals treated with an ARI. By inference, this led to the concept that inhibition of AR should prevent, arrest, and, possibly, reverse the development of late diabetic sequelae. In addition to motivating drug-oriented research, the ARI concept provided a rationale for the use of ARIs as experimental tools to probe the pathogenesis of diabetic complications. By helping to elucidate the metabolic, functional, and structural ramifications of the AR-catalyzed disposal of excess glucose in diabetic schemes, and in addition, by helping to define the applicability of animal models for the study of early functional pathogenic alterations occurring in diabetic subjects, ARIs may enable the discrimination in diabetic tissue of arrestible and reversible from the irreversible abnormalities.

Ophthalmoplegia with headache. Be aware of diabetes

Cranial neuropathy affecting the eyes is a possible symptom of type II diabetes. In this article, Dr Dickerman describes a case in which diabetes was diagnosed in a 63-year-old woman who presented with unilateral headache and eye pain.

Polyol pathway activity in nervous tissues of diabetic and galactose-fed rats: effect of dietary galactose withdrawal or tolrestat intervention therapy

Enhanced polyol pathway activity resulting in an accumulation of sorbitol and a depletion of myoinositol in nervous tissues has been proposed to be important in development of diabetic neuropathies. This investigation demonstrated that in two models of diabetic complications, streptozocin (STZ)-induced diabetic rats and galactose-fed rats, 5 weeks of disease led to an accumulation of sorbitol or galactitol, respectively, in three cranial nerves (the optic (II), trigeminal (V), and vagus (X) nerves), as well as the sciatic nerve, cerebral cortex, and retina. In both models, the cranial nerves and cerebral cortex contained lower levels of accumulated polyol than the sciatic nerve. In addition, myoinositol depletion was observed in the sciatic nerve only. In a second galactose-fed rat study, returning 5-week galactose-fed rats to a normal diet for 6 weeks led to complete elimination of galactitol from the optic nerve, sciatic nerve, and retina and normalization of the sciatic nerve myoinositol concentration. Similarly, continuing the galactose diet for 6 more weeks (ie, a total of 11 weeks) as well as administration of the aldose reductase inhibitor (ARI) tolrestat (20 and 40 mg/kg/day), caused the sciatic nerve to contain a normal myoinositol concentration and a galactitol concentration that was 95% below the level observed in galactose-fed controls. In the optic nerve and retina, tolrestat was less effective, resulting in 69-78% lower galactitol levels. In conclusion, these findings indicate that sorbitol and galactitol accumulate in cranial nerves, brain, and retina without a concomitant decrease in myoinositol. Either withdrawal of the galactose diet or intervention with tolrestat normalized polyol levels in the sciatic nerve.(ABSTRACT TRUNCATED AT 250 WORDS)