Gymnastics participation is associated with skeletal benefits in the distal forearm: a 6-month study using peripheral Quantitative Computed Tomography

OBJECTIVES

Musculoskeletal development of the upper limbs during exposure to weight-bearing loading is under-researched during early pubescent growth. The purpose was to assess the changes in upper body musculoskeletal strength in young girls following 6 months of non-elite gymnastics participation.

METHODS

Eighty-four girls, 6-12 years were divided into groups based on gymnastics participation: high-training (HGYM, 6-16 hr/wk), low-training (LGYM, 1-5 hr/wk), and non-gymnasts (NONGYM). Volumetric BMD, bone geometry, estimated bone strength and muscle size were assessed at the non-dominant forearm (4% and 66% radius and ulna) with pQCT. DXA assessed aBMD and body composition. Tests for explosive power, muscle strength, and endurance were also performed.

RESULTS

Interaction effects were observed in all variables at the 4% radius. At the 66% ulna, HGYM and LGYM had greater bone mass, size and bone strength than NONGYM, furthermore a dose-response relationship was observed at this location. Body composition was better for HGYM than LGYM and NONGYM, however muscle function was better for HGYM and LGYM than NONGYM.

CONCLUSION

The greatest changes were obtained with more than one gymnastics class per week. Separating gymnastics participation-related changes from those associated with normal growth and development remains difficult, particularly at the 4% radius.

Non-elite gymnastics participation is associated with greater bone strength, muscle size, and function in pre- and early pubertal girls

Recent reports indicate an increase in forearm fractures in children. Bone geometric properties are an important determinant of bone strength and therefore fracture risk. Participation in non-elite gymnastics appears to contribute to improving young girls' musculoskeletal health, more specifically in the upper body.

INTRODUCTION

The primary aim of this study was to determine the association between non-elite gymnastics participation and upper limb bone mass, geometry, and strength in addition to muscle size and function in young girls.

METHODS

Eighty-eight pre- and early pubertal girls (30 high-training gymnasts [HGYM, 6-16 hr/ wk], 29 low-training gymnasts [LGYM, 1-5 h r/wk] and 29 non-gymnasts [NONGYM]), aged 6-11 years were recruited. Upper limb lean mass, BMD and BMC were derived from a whole body DXA scan. Forearm volumetric BMD, bone geometry, estimated strength, and muscle CSA were determined using peripheral QCT. Upper body muscle function was investigated with muscle strength, explosive power, and muscle endurance tasks.

RESULTS

HGYM showed greater forearm bone strength compared with NGYM, as well as greater arm lean mass, BMC, and muscle function (+5% to +103%, p < 0.05). LGYM displayed greater arm lean mass, BMC, muscle power, and endurance than NGYM (+4% to +46%, p < 0.05); however, the difference in bone strength did not reach significance. Estimated fracture risk at the distal radius, which accounted for body weight, was lower in both groups of gymnasts. Compared with NONGYM, HGYM tended to show larger skeletal differences than LGYM; yet, the two groups of gymnasts only differed for arm lean mass and muscle CSA.

CONCLUSION

Non-elite gymnastics participation was associated with musculoskeletal benefits in upper limb bone geometry, strength and muscle function. Differences between the two gymnastic groups emerged for arm lean mass and muscle CSA, but not for bone strength.

Skeletal differences at the ulna and radius between pre-pubertal non-elite female gymnasts and non-gymnasts

OBJECTIVE

To compare skeletal parameters between the ulna and radius in pre-pubertal non-elite gymnasts and non-gymnasts.

METHODS

Fifty-eight non-elite artistic gymnasts, aged 6-11 years, were compared with 28 non-gymnasts for bone mineral content (BMC), total and cortical bone area (ToA, CoA), trabecular and cortical volumetric density (TrD, CoD) and estimated bone strength (BSI and SSIp), obtained by pQCT at the distal and proximal forearm.

RESULTS

Gymnasts had greater estimated bone strength than non-gymnasts at both sites of the forearm. At the distal forearm, the gymnastics-induced skeletal benefits were greater at the radius than ulna (Z-scores for BMC, TrD and BSI +0.40 to +0.61 SD, p<0.05 vs. +0.15 to +0.48 SD, NS). At the proximal forearm, the skeletal benefits were greater at the ulna than the radius (Z-scores for BMC, ToA, CoA and SSIp +0.59 to +0.82 SD, p<0.01 vs. +0.35 (ToA) and +0.43 SD (SSIp), p<0.01).

CONCLUSION

Skeletal benefits at the distal and proximal forearm emerged in young non-elite gymnasts. Benefits were larger when considering skeletal parameters at both the ulna and radius, than the radius alone as traditionally performed with pQCT. These findings suggest the ulna is worth investigating in future studies aiming to accurately quantify exercise-induced skeletal adaptations.

Calcium and vitamin-D supplementation on bone structural properties in peripubertal female identical twins: a randomised controlled trial

A randomised controlled trial was used in assessing the impact of 6 months of daily calcium and vitamin-D supplementation on trabecular and cortical bone acquisition at distal tibial and radial sites using peripheral quantitative computed tomography (pQCT). Daily supplementation was associated with increased bone density and bone strength at the distal tibia and radius.

INTRODUCTION

pQCT has not been used to assess bone responses to calcium and vitamin-D supplementation on peripubertal children. This randomised controlled trial aimed to assess the impact of a 6-month daily calcium and vitamin-D supplementation on trabecular and cortical bone acquisition at distal tibial and radial sites using pQCT.

METHODS

Twenty pairs of peripubertal female identical twins, aged 9 to 13 years, were randomly assigned to receive either 800 mg of calcium and 400 IU of vitamin D3, or a matched placebo. Bone structural properties at the distal tibia and distal radius were acquired at baseline and 6 months.

RESULTS

The calcium-supplemented group showed greater gains in trabecular density, trabecular area and strength strain index at the 4% of distal tibial and radial sites compared with the placebo group (p=0.001). Greater gains in cortical area at the 38% and 66% of tibial sites were also found in twins receiving the calcium supplement (p=0.001).

CONCLUSIONS

Daily supplementation for a period of 6 months was associated with increased trabecular area, trabecular density and strength strain index at the ultra-distal tibia and radius and increased cortical area at tibial mid-shaft.

Assessment of bone strength at differentially-loaded skeletal regions in adolescent middle-distance runners

Bone adaptations to loading extend beyond mineral accrual to geometric markers of bone strength. Available technology and regional differences in cortical bone dictate how bone strength is reported. Examination of bone strength at two differentially-loaded skeletal sites using hip structure analysis (HSA) and bone strength index (BSI) is under-explored in adolescent sporting populations. The purpose of this study was to compare HSA at the femoral neck and BSI at the distal tibia in adolescent middle-distance runners and age- and gender-matched controls. Four groups of 20 adolescents aged 14-18 years were composed of male and female middle-distance runners, and male and female controls. Distal tibial BSI was calculated using data from dual energy X-ray absorptiometry (DXA) and magnetic resonance imaging (MRI). Calculations for femoral neck strength were acquired from DXA-derived HSA software. Female athletes displayed greater distal tibial BSI than controls t(38)=3.4, p=0.002, but femoral neck bone measures did not differ. In males, no group differences were found at either the distal tibia or femoral neck. In conclusion, exposure to similar high training loads may advantage female adolescent athletes more than male adolescent athletes compared with less active peers in bone strength at the distal tibia.

A challenge to fitness testing in primary schools

We challenge the tradition of fitness testing in schools on the basis of purpose, procedures and outcomes. A number of assumptions about validity of selected tests are raised. The need to be able to track fitness through childhood into adulthood is challenged with limited scientific evidence of longitudinal tracking. Supporters of wide-scale fitness testing of children in schools include researchers whose intention is to promote public health awareness and policy. But a variety of confounding factors can affect field-based testing and lower the confidence in intra and inter group comparisons. Confounders include variability in motivation, familiarisation, external conditions, group dynamics, self-efficacy in testing, and perceived value of testing and likely outcomes. With acknowledged limitations, a more appropriate context for fitness testing for young people who have a strong commitment to physical activity may lie more in a professionally delivered sports-specific setting rather than in large-scale school-based testing. Given the less than desirable participation in activity outside of school and the distressing prevalence of childhood overweight and obesity, it is unlikely that fitness testing experiences will provide children with much needed positive encouragement for lifelong physical activity. Alternative strategies for school-based assessment of the promotion of child health through physical activity are proposed.

Bone strength index in adolescent girls: does physical activity make a difference?

BACKGROUND

Bone strength index (BSI) combines bone mineral and bone biomechanical properties to measure resistance to bending. This index may have greater clinical significance than the more often described markers of bone mineral content (BMC), areal density, or geometry alone and, in turn, may show a stronger relation to fracture risk. The BSI is the product of volumetric cortical bone mineral density (BMD) and cross sectional moment of inertia within a region of interest. Calculations combine dual energy x ray absorptiometry and magnetic resonance imaging technologies and provide a useful, non-invasive measure of in vivo bone strength.

OBJECTIVES

(a) To compare BSI in adolescent female middle distance runners and age matched controls; (b) to examine factors predictive of BSI in adolescent girls.

METHODS

Twenty adolescent female middle distance runners (mean (SD) age 16 (1.7) years, physical activity 8.9 (2.1) hours a week) and 20 female controls (age 16 (1.8) years, physical activity 2.0 (0.07) hours a week) were recruited. To calculate BSI, a region of interest representing 10% of the mid-distal tibia was analysed for dual energy x ray absorptiometry derived BMC and was combined with bone geometry and biomechanical properties obtained by magnetic resonance imaging assessments. Potential predictors of BSI were also examined.

RESULTS

Independent t tests showed that BMC (p = 0.028), cortical bone volume (p = 0.002), volumetric cortical BMD (p = 0.004), cross sectional moments of inertia (p = 0.005), and BSI (p = 0.002) were higher in the distal tibia of athletes than of controls. The strongest predictor of BSI was hours of physical activity a week (R2 = 0.46).

CONCLUSIONS

Athletes habitually exposed to high training loads displayed greater BSI at the distal tibia than controls. The results further confirm BSI as a significant and discerning marker in musculoskeletal health in adolescent girls engaged in high and low mechanical loading.

Musculoskeletal health in elite male adolescent middle-distance runners

The impact of high training volumes on musculoskeletal adaptations of male adolescents is poorly understood. We compared bone mineral content (BMC) of total body, lumbar spine and proximal femur using Dual X-ray Absorptiometry (Lunar Prodigy, GE Medical Systems, Madison WI) in elite level (n=20), male adolescent middle distance runners (mean 16.8 yrs, range 14-18 yrs) and age-matched (n=20) controls. Athletes averaged 14 hrs of physical activity per week and controls reported participating in physical activity an average of two hrs per week. Total body mass was 10.97 kg less in athletes than controls (p=0.005). Within the total body mass difference, fat tissue mass of athletes was 10.93 kg less in athletes than controls (p= 0.001). Multiple regression analysis identified total body lean mass and total body fat mass as the strongest predictors of total body BMC (R2 0.71). After adjusting for lean tissue mass per kg of body weight (p=0.07), no difference in BMC was detected. Lower limb muscle strength and macronutrient intakes were also measured but no between group differences were found. The number of weeks of training and/or competition missed through injury was not associated with total body BMC (R2=0.19) among athletes. Our results imply high training volumes in middle distance running are not detrimental to musculoskeletal health and are associated with positive body composition profiles in elite adolescent male athletes.

Digital electron microscopic examination of human sural nerve biopsies

Diabetic peripheral polyneuropathy is characterized by axonal degeneration and regeneration as well as by Schwann cell and microvascular changes. These changes have been described at both the light (LM) and the electron microscopic (EM) levels; however, EM has not been applied to large clinical trials. Our goal was to adapt the rigorous techniques used for quantifying human biopsies with LM image analysis to accommodate ultrastructural analyses. We applied digital image capture and analysis to the ultrastructural examination of axons in sural nerve biopsies from diabetic patients enrolled in a multicenter clinical trial. The selection of sural nerve biopsies was based on the quality of specimen fixation, absence of physical distortion, and nerve fascicle size (> or =100,000; < or =425,000 microm2). Thin sections were collected on formvar-coated slot grids, stabilized with carbon and scanned on a Phillips CM100 transmission electron microscope. Digital images were captured with a Kodak Megaplus 1.6 camera. A montage was constructed using software derived from aerial mapping applications, and this virtual image was viewed by EM readers. Computer-assisted analyses included identification and labeling of individual axons and axons within regenerating clusters. The average density of regenerating myelinated axon clusters per mm2 was 65.8 +/- 5.1, range of 0-412 (n = 193). These techniques increase the number of samples that may be analyzed by EM and extend the use of this technique to clinical trials using tissue biopsies as a primary endpoint.

Glycemic control is related to the morphological severity of diabetic sensorimotor polyneuropathy

OBJECTIVE

The aim of the current study was to determine the independent clinical risk factors for predicting morphological severity of distal diabetic sensorimotor polynecuropathy (DSP) as determined by fiber density (FD) on sural nerve biopsy.

RESEARCH DESIGN AND METHODS

A total of 89 patients with both type 1 and type 2 diabetes, ascertained from a large therapeutic randomized clinical trial, were included in this observational cohort study. Morphological severity of DSP was expressed as the myelinated FD in the sural nerve biopsy General linear models were used to assess the relationship between the morphological severity of DSP and various clinical risk factors.

RESULTS

Glycated hemoglobin (GHb) was significantly related to FD in univariate and multivariate regression analyses. This relationship was present in models in which GHb was handled either as a continuous variable or as a categorical variable with the highest significance level, with a GHb cutoff level of 9%. After dividing patients into groups with optimal to moderate GHb < or = 9%) and suboptimal (GHb >9%) glycemic control, the difference in FD between the two groups ranged between 3,461 and 2,334 per mm2. FD was also significantly related to duration of diabetes and age of the patient.

CONCLUSIONS

The severity of peripheral DSP expressed by morphological criteria was significantly related to glycemic control in type 1 and type 2 diabetic patients. Inconsistent with previously published electrophysiological data demonstrating a correlation between height and conduction velocity, increasing height is not associated with morphological severity. Based on the results of the present study, it might be hypothesized that improving glycemic control will lessen severity of DSP in terms of FD loss in subjects with diabetes.

Regulation of glucose transport in cultured Schwann cells

Glucose is the major source of metabolic energy in the peripheral nerve. Energy derived from glucose is mostly utilized for axonal repolarization. One route by which glucose may reach the axon is by crossing the Schwann cells that initially surround the axons. Considering the ability of neurons to control many glial cell functions, we postulated that Schwann cell glucose transporters might be transiently regulated by axonal contact. Glucose transport was studied in a cultured, differentiated rat Schwann cell line stably expressing SV40 T antigen regulated by a synthetic mouse metallothionein promoter. 3[H]-2-deoxy-D-glucose uptake was measured in cultured cells in basal and in various experimental conditions. Glucose transporter gene expression was determined after RNA isolation from cultured cells through Northern and RNAse protection assay. In vitro, Schwann cells were found to express high-affinity, insulin-insensitive, facilitative glucose transporters and predominantly GLUT1 mRNA. Schwann cell 2-deoxyglucose uptake was increased by axolemmal membranes or forskolin but unchanged by elevated glucose levels. Regulation of Schwann cell glucose transporters by axolemma and their resistance to glucose-induced down-regulation suggest extrinsic rather than intrinsic regulation that might enhance Schwann cell vulnerability to glucotoxicity.

Evaluation of alpha(1)-adrenoceptor antagonist on diabetes-induced changes in peripheral nerve function, metabolism, and antioxidative defense

The role for nerve blood flow (NBF) vs. other factors in motor nerve conduction (MNC) slowing in short-term diabetes was assessed by evaluating alpha(1)-adrenoceptor antagonist prazosin on NBF, MNC, as well as metabolic imbalances and oxidative stress in the neural tissue. Control and diabetic rats were treated with or without prazosin (5 mg.kg(-1).d(-1) for 3 wk). NBF was measured by hydrogen clearance. Both endoneurial vascular conductance and MNC velocity were decreased in diabetic rats vs. controls, and this decrease was prevented by prazosin. Free NAD(+):NADH ratios in mitochondrial cristae, matrix, and cytosol assessed by metabolite indicator method, as well as phosphocreatine levels and phosphocreatine/creatine ratios, were decreased in diabetic rats, and this reduction was ameliorated by prazosin. Neither diabetes-induced accumulation of two major glycation agents, glucose and fructose, as well as sorbitol and total malondialdehyde plus 4-hydroxyalkenals nor depletion of myo-inositol, GSH, and taurine or decrease in (Na/K)-ATP-ase activity were affected by prazosin. In conclusion, decreased NBF, but not metabolic imbalances or oxidative stress in the neural tissue, is a key mechanism of MNC slowing in short-term diabetes. Further experiments are needed to estimate whether preservation of NBF is sufficient for prevention of nerve dysfunction and morphological abnormalities in long-standing diabetes or whether the aforementioned metabolic imbalances closely associated with impaired neurotropism are of greater importance in advanced than in early diabetic neuropathy.

Early changes in lipid peroxidation and antioxidative defense in diabetic rat retina: effect of DL-alpha-lipoic acid

This study was designed to (1) evaluate retinal lipid peroxidation in early diabetes by the method specific for free malondialdehyde and 4-hydroxyalkenals, (2) identify impaired antioxidative defense mechanisms and (3) assess if enhanced retinal oxidative stress in diabetes is prevented by the potent antioxidant, DL-alpha-lipoic acid. The groups included control and streptozotocin-diabetic rats treated with or without DL-alpha-lipoic acid (100 mg kg(-1) day(-1), i.p., for 6 weeks). All parameters were measured in individual retinae. 4-Hydroxyalkenal concentration was increased in diabetic rats (2.63+/-0.60 vs. 1.44+/-0.30 nmol/mg soluble protein in controls, P<0.01), and this increase was prevented by DL-alpha-lipoic acid (1.20+/-0.88, P<0.01 vs. untreated diabetic group). Malondialdehyde, reduced glutathione (GSH) and oxidized glutathione (GSSG) concentrations were similar among the groups. Superoxide dismutase, glutathione peroxidase (GSHPx), glutathione reductase (GSSGRed) and glutathione transferase (GSHTrans) activities were decreased in diabetic rats vs. controls. Quinone reductase was upregulated in diabetic rats, whereas catalase and cytoplasmic NADH oxidase activities were unchanged. DL-alpha-Lipoic acid prevented changes in superoxide dismutase and quinone reductase activities induced by diabetes without affecting the enzymes of glutathione metabolism. In conclusion, accumulation of 4-hydroxyalkenals is an early marker of oxidative stress in the diabetic retina. Increased lipid peroxidation occurs in the absence of GSH depletion, and is prevented by DL-alpha-lipoic acid.

Effects of DL-alpha-lipoic acid on peripheral nerve conduction, blood flow, energy metabolism, and oxidative stress in experimental diabetic neuropathy

Experimental diabetic peripheral neuropathy (DPN) is marked by impaired nerve conduction velocity (NCV), reduced nerve blood flow (NBF), and a variety of metabolic abnormalities in peripheral nerve that have been variously ascribed to hyperglycemia, abnormal fatty acid metabolism, ischemic hypoxia, and/or oxidative stress. Some investigators propose that NCV slowing in experimental DPN can be explained entirely on the basis of nerve energy depletion secondary to reduced NBF. This article reports highly selective effects of administration of the antioxidant DL-alpha-lipoic acid (LA) to streptozotocin-injected diabetic rats. LA improved digital sensory but not sciatic-tibial motor NCV, corrected endoneurial nutritive but not composite NBF, increased the mitochondrial oxidative state without correcting nerve energy depletion, and enhanced the accumulation of polyol pathway intermediates without worsening myo-inositol or taurine depletion. These studies implicate oxidative stress as an important pathophysiological factor in experimental DPN. They reveal complex interrelationships among nerve perfusion, energy metabolism, osmolyte content, conduction velocity, and oxidative stress that may reflect the heterogeneous and compartmentalized composition of peripheral nerve.

Sorbitol and myo-inositol levels and morphology of sural nerve in relation to peripheral nerve function and clinical neuropathy in men with diabetic, impaired, and normal glucose tolerance

AIMS

Sorbitol and myo-inositol levels and morphology of sural nerve were compared with nerve function and clinical neuropathy in men with diabetic, impaired (IGT), and normal glucose tolerance.

METHODS

After neurography of sural nerve and determinations of sensory thresholds for vibration, warm and cold on the foot, whole nerve sural nerve biopsy was performed in 10 men with Type 1 diabetes mellitus, 10 with IGT, and 10 with normal glucose tolerance. Polyol levels were assessed by gas-liquid chromatography/mass spectrometry.

RESULTS

Sural nerve amplitudes were significantly lower and sorbitol levels significantly higher in diabetic patients (median (interquartile range)) (3.7 (3.5) microV and 643 (412) pmol/mg protein, respectively) both compared with IGT (11.3 (10.6)microV; P = 0.04 and 286 (83) pmol/mg protein; P = 0.0032, respectively) and normally glucose tolerant (10.0 (11.6); P = 0.0142 and 296 (250) pmol/mg protein; P = 0.0191, respectively) subjects. There were no differences in nerve morphology between the three groups. Nerve myo-inositol levels correlated, however, positively with cluster density (rs = 0.56; P = 0.0054). In diabetic and IGT subjects, sural nerve amplitudes (2.6 (3.8) vs. 12.1 (10.6) microV; P = 0.0246) and myelinated nerve fibre density (MNFD; 4,076 (1091) vs. 5,219 (668) nerve fibres/mm2; P = 0.0021) were significantly lower in nine subjects with clinical neuropathy than in 10 without.

CONCLUSIONS

Nerve degeneration (i.e. MNFD) correlated with clinical neuropathy but not with glucose tolerance status whereas nerve myo-inositol levels positively correlated with signs of nerve regeneration (i.e. increased cluster density).

Evaluation of a sorbitol dehydrogenase inhibitor on diabetic peripheral nerve metabolism: a prevention study

AIMS/HYPOTHESIS

Studies of the role of sorbitol dehydrogenase in nerve functional deficits induced by diabetes reported contradictory results. We evaluated whether sorbitol dehydrogenase inhibition reduces metabolic abnormalities and enhances oxidative stress characteristic of experimental diabetic neuropathy.

METHODS

Control and streptozotocin-diabetic rats were treated with or without sorbitol dehydrogenase inhibitor (SDI)-157 (100 mg x kg(-1) x day(-1), in the drinking water, for 3 weeks). Sciatic nerve free mitochondrial (cristae and matrix) and cytosolic NAD(+): NADH ratios were calculated from the beta-hydroxybutyrate, glutamate and lactate dehydrogenase systems. Concentrations of metabolites, e. g. sorbitol pathway intermediates and variables of energy state were measured in individual nerves spectrofluorometrically by enzymatic procedures.

RESULTS

The flux through sorbitol dehydrogenase (manifested by nerve fructose concentrations) was inhibited by 53 % and 74 % in control and diabetic rats treated with SDI compared with untreated control and diabetic groups. Free NAD(+):NADH ratios in mitochondrial cristae, matrix and cytosol were decreased in diabetic rats compared with controls and reduction in either of the three variables was not prevented by sorbitol dehydrogenase inhibitor. Phosphocreatine concentrations and phosphocreatine:creatine ratios were decreased in diabetic rats compared with controls and were further reduced by the inhibitor. Malondialdehyde plus 4-hydroxyalkenals concentration was increased and reduced gluthathione concentration was reduced in diabetic rats compared with the control group, and changes in both variables were further exacerbated by sorbitol dehydrogenase inhibitor. Neither NAD-redox and energy states nor lipid aldehyde and reduced gluthathione concentrations were affected by treatment with the inhibitor in control rats.

CONCLUSION/INTERPRETATION

Inhibition of sorbitol dehydrogenase does not offer an effective approach for prevention of oxidation and metabolic imbalances in the peripheral nerve that is induced by diabetes and is adverse rather than beneficial. [Diabetologia (1999) 42: 1187-1194]

Effect of aldose reductase inhibition on nerve conduction and morphometry in diabetic neuropathy. Zenarestat Study Group

OBJECTIVE

To determine whether the aldose reductase inhibitor (ARI) zenarestat improves nerve conduction velocity (NCV) and nerve morphology in diabetic peripheral polyneuropathy (DPN).

METHODS

A 52-week, randomized, placebo-controlled, double-blinded, multiple-dose, clinical trial with the ARI zenarestat was conducted in patients with mild to moderate DPN. NCV was measured at baseline and study end. Contralateral sural nerve biopsies were obtained at 6 weeks and at the study's end for nerve sorbitol measurement and computer-assisted light morphometry to determine myelinated nerve fiber density (number of fibers/mm2 cross-sectional area) in serial bilateral sural nerve biopsies.

RESULTS

Dose-dependent increments in sural nerve zenarestat level and sorbitol suppression were accompanied by significant improvement in NCV. In a secondary analysis, zenarestat doses producing >80% sorbitol suppression were associated with a significant increase in the density of small-diameter (<5 microm) sural nerve myelinated fibers.

CONCLUSIONS

Aldose reductase pathway inhibition improves NCV slowing and small myelinated nerve fiber loss in DPN in humans, but >80% suppression of nerve sorbitol content is required. Thus, even low residual levels of aldose reductase activity may be neurotoxic in diabetes, and potent ARIs such as zenarestat may be required to stop or reverse progression of DPN.

2-Chloroadenosine reverses hyperglycemia-induced inhibition of phosphoinositide synthesis in cultured human retinal pigment epithelial cells and prevents reduced nerve conduction velocity in diabetic rats

The effect of the adenosine (AD) analog 2-chloroadenosine (C-AD) on glucose-induced inhibition of phosphoinositide synthesis was studied in human retinal pigment epithelial (RPE) cells by monitoring the level of the phosphatidylinositol (PI) synthase substrate, cytidine diphosphate diglyceride (CDP-DG). In high-aldose reductase (AR)-expressing RPE 91 cells, C-AD decreased CDP-DG at 5 mmol/L glucose and reversed the increase by 20 mmol/L glucose. AD deaminase (ADA), which inactivates endogenously released AD, potentiated the hyperglycemia-induced increase in CDP-DG. Theophylline, an AD-A1 and AD-A2 receptor antagonist, caused an increase in CDP-DG at 20 mmol/L glucose. C-AD did not alter CDP-DG in low-AR-expressing RPE 45 cells, but did decrease CDP-DG after cells were conditioned in 300 mmol/L glucose for 1 week (which induces AR). The mechanism by which AD regulates PI synthase in cells with high AR activity is unknown, but it is independent of Gi or Gs proteins, adenylate cyclase and phospholipase C (PLC) activation, myo-inositol (MI) uptake, or MI efflux. Administration of C-AD to streptozotocin-induced diabetic rats prevented the slowing of motor nerve conduction velocity (MNCV). Thus, AD derivatives, which reverse a glucose-induced deficit in phosphoinositide metabolism, might serve as a useful pharmacological tool to intervene in hyperglycemia-induced diabetic complications.

Glucose-induced oxidative stress and programmed cell death in diabetic neuropathy

The Diabetes Control and Complications Trial (DCCT) established the importance of hyperglyemia and other consequences of insulin deficiency in the pathogenesis of diabetic neuropathy, but the precise mechanisms by which metabolic alterations produce peripheral nerve fiber damage and loss remain unclear. Emerging data from human and animal studies suggest that glucose-derived oxidative stress may play a central role, linking together many of the other currently invoked pathogenetic mechanisms such as the aldose reductase and glycation pathways, vascular dysfunction, and impaired neurotrophic support. These relationships suggest combinations of pharmacological interventions that may synergistically protect the peripheral nervous system (PNS) against the metabolic derangements of diabetes mellitus.

Alternate splicing in human Na+-MI cotransporter gene yields differentially regulated transport isoforms

myo-Inositol is a ubiquitous intracellular organic osmolyte and phosphoinositide precursor maintained at millimolar intracellular concentrations through the action of membrane-associated Na+-myo-inositol cotransporters (SMIT). Functional cloning and expression of a canine SMIT cDNA, which conferred SMIT activity in Xenopus oocytes, predicted a 718-amino acid peptide homologous to the Na+-glucose cotransporter with a potential protein kinase A phosphorylation site and multiple protein kinase C phosphorylation sites. A consistent approximately 1.0- to 13.5-kb array of transcripts hybridizing with this cDNA are osmotically induced in a variety of mammalian cells and species, yet SMIT activity appears to vary among different tissues and species. An open reading frame on human chromosome 21 (SLC5A3) homologous to that of the canine cDNA (96.5%) is thought to comprise an intronless human SMIT gene. Recently, this laboratory ascribed multiply sized, osmotically induced SMIT transcripts in human retinal pigment epithelial cells to the alternate utilization of several 3'-untranslated SMIT exons. This article describes an alternate splice donor site within the coding region that extends the open reading frame into the otherwise untranslated 3' exons, potentially generating novel SMIT isoforms. In these isoforms, the last putative transmembrane domain is replaced with intracellular carboxy termini containing a novel potential protein kinase A phosphorylation site and multiple protein kinase C phosphorylation sites, and this could explain the heterogeneity in the regulation and structure of the SMIT.

Acute effects of adrenergic-mediated ischemia on nerve conduction in subjects with type 2 diabetes

Several lines of evidence support peripheral nerve ischemia as a contributing factor in the etiology of human diabetic neuropathy. We questioned whether diabetic subjects with relatively normal nerve function in the baseline state would be more likely than healthy control subjects to show either improvement of ulnar nerve function with acute intraarterial infusion of nitroprusside (vasodilation) or be more sensitive than control subjects to worsening of nerve function with acute intraarterial infusion of norepinephrine (vasoconstriction). We measured forearm blood flow (FABF) using venous occlusion plethysmography and assessed ulnar nerve function at baseline and during two intrabrachial artery infusions. Six nondiabetic control subjects (mean age, 56 years) and 11 subjects with type 2 diabetes (mean age, 58 years) in good general health participated. Only three type 2 diabetic subjects had peripheral sensory neuropathy, which was mild. Among control subjects, there was no significant change in sensory distal latency, motor distal latency, motor proximal latency, or sensory or motor conduction velocity during norepinephrine infusion. In contrast, among type 2 diabetic subjects, there was a significant increase in sensory (baseline vnorepinephrine, 2.73+/-0.10 v 2.94+/-0.10 milliseconds [MS], P< or =.01) and motor distal latencies (baseline v norepinephrine, 2.90+/-0.06 v 3.18+/-0.1 ms, P< or =.001) and motor proximal latency (baseline v norepinephrine, 7.15+/-0.18 v 7.60+/-0.23 ms, P<.01) and a decrease in sensory conduction velocity (baseline v norepinephrine, 52.1+/-2.0 v 47.7+/-1.6 m/s, P<.01) during norepinephrine infusion. There were no consistent changes in nerve function during nitroprusside infusion in either group. In summary, we found that subjects with type 2 diabetes, but not control subjects, demonstrate a decrement in nerve function with vasoconstriction during intraarterial infusion of norepinephrine, but no consistent change during nitroprusside-induced vasodilation. These findings suggest there may be enhanced sensitivity of nerve function to ischemia in type 2 diabetic subjects with mild or absent clinical neuropathy.

Diabetes-induced changes in lens antioxidant status, glucose utilization and energy metabolism: effect of DL-alpha-lipoic acid

The study was aimed at evaluating changes in lens antioxidant status, glucose utilization, redox state of free cytosolic NAD(P)-couples and adenine nucleotides in rats with 6-week streptozotocin-induced diabetes, and to assess a possibility of preventing them by DL-alpha-lipoic acid. Rats were divided into control and diabetic groups treated with and without DL-alpha-lipoic acid (100 mg x kg body weight(-1) x day(-1), i.p.). The concentrations of glucose, sorbitol, fructose, myo-inositol, oxidized glutathione, glycolytic intermediates, malate, alpha-glycerophosphate, and adenine nucleotides were assayed in individual lenses spectrofluorometrically by enzymatic methods, reduced glutathione and ascorbate--colorimetrically, and taurine by HPLC. Free cytosolic NAD+:NADH and NADP+:NADPH ratios were calculated from the lactate dehydrogenase and malic enzyme systems. Sorbitol pathway metabolites were found to increase, and antioxidant concentrations were reduced in diabetic rats compared with controls. The profile of glycolytic intermediates (increase in glucose 6-phosphate and fructose 6-phosphate, decrease in fructosel,6-diphosphate, increase in dihydroxyacetone phosphate, 3-phosphoglycerate, phosphoenolpyruvate, pyruvate, and no change in lactate), and 5.9-fold increase in alpha-glycerophosphate suggest diabetes-induced inhibition of glycolysis. Free cytosolic NAD+:NADH ratios, ATP levels, ATP/ADP x inorganic phosphate (Pi), and adenylate charge were reduced in diabetic rats while free cytosolic NADP+:NADPH ratios were elevated. Diabetes-induced changes in the concentrations of antioxidants, key glycolytic intermediates, free cytosolic NAD+:NADH ratios, and energy status were partially prevented by DL-alpha-lipoic acid, while sorbitol pathway metabolites and free cytosolic NADP+:NADPH ratios remained unaffected. In conclusion, diabetes-induced impairment of lens antioxidative defense, glucose intermediary metabolism via glycolysis, energy status and redox changes are partially prevented by DL-alpha-lipoic acid. The findings support the important role of oxidative stress in lens metabolic imbalances in diabetes.

Specific impairment of endothelium-dependent vasodilation in subjects with type 2 diabetes independent of obesity

In subjects with type 2 diabetes in whom an impaired response to an endothelial-dependent vasodilator has been characterized, the populations have also been at least moderately obese. Obesity has been characterized as an independent predictor of endothelial dysfunction in nondiabetic subjects. We hypothesized that in normotensive subjects with type 2 diabetes compared with age-matched control subjects, 1) endothelium-dependent vasodilation, as demonstrated by the forearm blood flow (FABF) response to intraarterial acetylcholine, would be decreased; 2) endothelium-independent vasodilation, as demonstrated by the FABF response to intraarterial nitroprusside, would be similar; 3) the degree of insulin resistance, as measured by the insulin sensitivity index (SI), would predict greater impairment in the FABF response to acetylcholine; and 4) these relationships would be independent of obesity. We measured FABF by venous occlusion plethysmography during brachial arterial infusions of the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator nitroprusside in 20 control and 17 subjects with type 2 diabetes. We measured SI using the frequently sampled i.v. glucose tolerance test. Among the diabetic relative to the control subjects we identified a decrease in the acetylcholine-mediated percent increase in FABF (P = 0.02). Using the absolute FABF response to acetylcholine and including adjustments for body mass index and other covariates, the overall group difference remained and was noted to be greatest in those subjects who had lower baseline FABFs. In contrast, no significant difference in the nitroprusside-mediated increase in the percent change FABF was identified between groups (P = 0.30). Finally, the degree of insulin resistance, as measured by SI, did not independently predict greater impairment of the FABF response to acetylcholine. This study is the first to identify specific endothelial cell dysfunction that remains significant after adjustment for obesity in a population of normotensive subjects with type 2 diabetes.

Human Na(+)-myo-inositol cotransporter gene: alternate splicing generates diverse transcripts

Na(+)-myo-inositol cotransport activity generally maintains millimolar intracellular concentrations of myo-inositol and specifically promotes transepithelial myo-inositol transport in kidney, intestine, retina, and choroid plexus. Glucose-induced, tissue-specific myo-inositol depletion and impaired Na(+)-myo-inositol cotransport activity are implicated in the pathogenesis of diabetic complications, a process modeled in vitro in cultured human retinal pigment epithelium (RPE) cells. To explore this process at the molecular level, a human RPE cDNA library was screened with a canine Na(+)-dependent myo-inositol cotransporter (SMIT) cDNA. Overlapping cDNAs spanning 3569 nt were cloned. The resulting cDNA sequence contained a 2154-nt open reading frame, 97% identical to the canine SMIT amino acid sequence. Genomic clones containing SMIT exons suggested that the cDNA is derived from at least five exons. Hypertonic stress induced a time-dependent increase, initially in a 16-kb transcript and subsequently in 11.5-, 9.8-, 8.5-, 3.8-, and approximately 1.2-kb SMIT transcripts, that was ascribed to alternate exon splicing using exon-specific probes and direct cDNA sequencing. The human SMIT gene is a complex multiexon transcriptional unit that by alternate exon splicing generates multiple SMIT transcripts that accumulate differentially in response to hypertonic stress.

Pathogenesis of diabetic neuropathy

Diabetes mellitus affects over 14 million people in the United States and the number of diabetics is increasing by 5% per year. Diabetic neuropathy (DN) is a common complication of diabetes and occurs in approximately 50% of diabetic patients over time. Clinical trials have proven that hyperglycemia almost certainly conditions the development of DN. Despite this fact, we still do not understand the mechanism(s) underlying DN. Several possible etiologies have been proposed including altered metabolism of polyol, lipids, or amino acids, vascular insufficiency, increased superoxide-induced free radical formation, impaired axonal transport or reduced neurotrophism. Accumulating evidence suggests that these defects are likely interrelated and that their interaction(s) within the diabetic milieu are responsible for the development and progression of DN. In this review we will discuss these theories, their interrelationships and how, collectively, these ideas may begin to explain the etiology of DN.

Protein kinase and Ca2+ modulation of myo-inositol transport in cultured retinal pigment epithelial cells

The acute regulation of inwardly directed Na(+)-myo-inositol (MI) cotransporter activity and basal and volume-sensitive MI efflux by protein kinases C (PKC) and A (PKA), cytosolic Ca2+, and phosphoinositide (PI) turnover were characterized in cultured human retinal pigment epithelial cells using 2-[3H]MI and liquid scintillation spectrometry. Kinetic analysis revealed two distinct Na(+)-MI cotransporter components differing in apparent Michaelis constant and maximal velocity. Composite Na(+)-MI cotransport activity was stimulated by PKA activation, the muscarinic agonist carbachol, and the Ca2+ ionophore A-23187 and was inhibited by PKC activation. PKC activation also increased MI efflux, but only the volume-sensitive component, whereas PKA activation increased both basal and volume-sensitive MI efflux. These studies implicate PKC as a negative modulator of MI content through Na(+)-MI cotransport inhibition and potentiation of volume-sensitive MI efflux. PKA is a positive modulator of both Na(+)-MI cotransport and basal and volume-sensitive MI efflux. Cytosolic Ca2+ release through receptor-mediated PI hydrolysis may facilitate Na(+)-MI cotransport activity.

A multicenter study on the prevalence of diabetic neuropathy in Italy. Italian Diabetic Neuropathy Committee

OBJECTIVE

The prevalence of neuropathy, a common complication of diabetes, was determined in diabetic patients recruited from 109 outpatient diabetes clinics in Italy.

RESEARCH DESIGN AND METHODS

Neuropathy was diagnosed using the Diabetic Neuropathy Index (DNI), a standardized examination developed for use in the outpatient setting. A total of 8,757 diabetic patients were studied, 51.2% men and 48.8% women, with average and median ages of 56 and 58 years, respectively.

RESULTS

Of the 8,757 patients, 32.3% had neuropathy, defined as a positive score of > 2 points on the DNI. A total of 2,033 (49.6% men and 50.4% women) were administered the Diabetic Neuropathy Score (DNS), the second component of the screening program, by a neurologist. This component consists of a quantitative neurological examination and nerve conduction studies that together provide a summated score. A total of 335 patients (16.5%) were not neuropathic, and 395 (19.4%) had borderline, 453 (22.3%) mild, 592 (29.1%) moderate, and 258 (12.7%) severe neuropathy. The concordance between a positive score on the DNI and a DNS indicating neuropathy was 83.5%. The severity of neuropathy increased with both age and disease duration. Of patients with neuropathy, 64.1% had an average age between 58 and 59 years with a disease duration between 12.4 +/- 8.4 years (mild neuropathy) and 15.6 +/- 9.7 years (severe neuropathy).

CONCLUSIONS

Neuropathy is a common complication of diabetes and, in this study, was present in 32.3% of all patients. An increased awareness of the high prevalence of neuropathy can lead to early therapeutic intervention and possible prevention of later neuropathic complications, such as infection and foot ulcers.

Supplemental myo-inositol prevents L-fucose-induced diabetic neuropathy

Nerve myo-inositol depletion, which has been implicated in the pathogenesis of acute experimental diabetic neuropathy, can be reproduced in normal rats by feeding diets enriched in L-fucose, a competitive inhibitor of sodium-dependent myo-inositol transport. Previously, we reported that L-fucose feeding for 6 weeks reproduces the effect of experimental diabetes on nerve Na+-K+-ATPase activity and conduction velocity, which can be prevented by simultaneous dietary myo-inositol supplementation. To further validate this model of myo-inositol depletion, we examined the effects of long-term (24-week) L-fucose feeding and dietary myo-inositol supplementation on nerve Na+-K+-ATPase, nerve conduction velocity, and myelinated nerve fiber pathology. After 24 weeks of L-fucose enriched (10 or 20%) diets, nerve myo-inositol levels and Na+-K+-ATPase activity decreased significantly (P < 0.05) and were associated with a 25-30% reduction in nerve conduction velocity, all of which were completely prevented by 1% dietary myo-inositol. Twenty percent L-fucose diet resulted in significant axonal atrophy, paranodal swelling (P < 0.001), and paranodal demyelination (P < 0.005), without increasing Wallerian degeneration or nerve fiber loss, a pattern qualitatively similar to that seen in early murine diabetic neuropathy. Dietary myo-inositol supplementation prevented these structural changes and increased nodal remyelination, supporting a role of myo-inositol depletion in the genesis of early diabetic neuropathy. The L-fucose model system may therefore serve as an experimental tool to elucidate the pathophysiological role of isolated myo-inositol depletion and its consequences in the multifactorial pathogenesis of diabetic neuropathy.

Glucose transporters in rat peripheral nerve: paranodal expression of GLUT1 and GLUT3

Peripheral nerve depends on glucose oxidation to energize the repolarization of excitable axonal membranes following impulse conduction, hence requiring high-energy demands by the axon at the node of Ranvier. To enter the axon at this site, glucose must be transported from the endoneurial space across Schwann cell plasma membranes and the axolemma. Such transport is likely to be mediated by facilitative glucose transporters. Although immunohistochemical studies of peripheral nerves have detected high levels of the transporter GLUT1 in endoneurial capillaries and perineurium, localization of glucose transporters to Schwann cells or peripheral axons in vivo has not been documented. In this study, we demonstrate that the GLUT1 transporter is expressed in the plasma membrane and cytoplasm of myelinating Schwann cells around the nodes of Ranvier and in the Schmidt-Lanterman incisures, making them potential sites of transcellular glucose transport. No GLUT1 was detected in axonal membranes. GLUT3 mRNA was expressed only at low levels, but GLUT3 polypeptide was barely detected by immunocytochemistry or immunoblotting in peripheral nerve from young adult rats. However, in 13-month-old rats, GLUT3 polypeptide was present in myelinated fibers, endoneurial capillaries, and perineurium. In myelinated fibers, GLUT3 appeared to be preferentially expressed in the paranodal regions of Schwann cells and nodal axons, but was also present in the internodal aspects of these structures. The results of the present study suggest that both Schwann cell GLUT1 and axonal and Schwann cell GLUT3 are involved in the transport of glucose into the metabolically active regions of peripheral axons.

Acetyl-L-carnitine deficiency as a cause of altered nerve myo-inositol content, Na,K-ATPase activity, and motor conduction velocity in the streptozotocin-diabetic rat

Defective metabolism of long-chain fatty acids and/or their accumulation in nerve may impair nerve function in diabetes by altering plasma or mitochondrial membrane integrity and perturbing intracellular metabolism and energy production. Carnitine and its acetylated derivatives such as acetyl-L-carnitine (ALC) promote fatty acid beta-oxidation in liver and prevent motor nerve conduction velocity (MNCV) slowing in diabetic rats. Neither the presence nor the possible implications of putative ALC deficiency have been definitively established in diabetic nerve. This study explored sciatic nerve ALC levels and the dose-dependent effects of ALC replacement on sciatic nerve metabolites, Na,K-ATPase, and MNCV after 2 and 4 weeks of streptozotocin-induced diabetes (STZ-D) in the rat. ALC treatment that increased nerve ALC levels delayed (to 4 weeks) but did not prevent nerve myo-inositol (MI) depletion, but prevented MNCV slowing and decreased ouabain-sensitive (but not -insensitive) ATPase activity in a dose-dependent fashion. However, ouabain-sensitive ATPase activity was also corrected by subtherapeutic doses of ALC that did not increase nerve ALC or affect MNCV. These data implicate nerve ALC depletion in diabetes as a factor contributing to alterations in nerve intermediary and energy metabolism and impulse conduction in diabetes, but suggest that these alterations may be differentially affected by various degrees of ALC depletion.

Primary preventive and secondary interventionary effects of acetyl-L-carnitine on diabetic neuropathy in the bio-breeding Worcester rat

The abnormalities underlying diabetic neuropathy appear to be multiple and involve metabolic neuronal and vasomediated defects. The accumulation of long-chain fatty acids and impaired beta-oxidation due to deficiencies in carnitine and/or its esterified derivatives, such as acetyl-L-carnitine, may have deleterious effects. In the present study, we examined, in the diabetic bio-breeding Worcester rat, the short- and long-term effects of acetyl-L-carnitine administration on peripheral nerve polyols, myoinositol, Na+/K+ -ATPase, vasoactive prostaglandins, nerve conduction velocity, and pathologic changes. Short-term prevention (4 mo) with acetyl-L-carnitine had no effects on nerve polyols, but corrected the Na+/K+ -ATPase defect and was associated with 63% prevention of the nerve conduction defect and complete prevention of structural changes. Long-term prevention (8 mo) and intervention (from 4 to 8 mo) with acetyl-L-carnitine treatment normalized nerve PGE(1) whereas 6-keto PGF(1-alpha) and PGE(2) were unaffected. In the prevention study, the conduction defect was 73% prevented and structural abnormalities attenuated. Intervention with acetyl-L-carnitine resulted in 76% recovery of the conduction defect and corrected neuropathologic changes characteristic of 4-mo diabetic rats. Acetyl-L-carnitine treatment promoted nerve fiber regeneration, which was increased two-fold compared to nontreated diabetic rats. These results demonstrate that acetyl-L-carnitine has a preventive effect on the acute Na+/- K+_ATPase defect and a preventive and corrective effect on PGE1 in chronically diabetic nerve associated with improvements of nerve conduction velocity and pathologic changes.

Modulation of basal nitric oxide-dependent cyclic-GMP production by ambient glucose, myo-inositol, and protein kinase C in SH-SY5Y human neuroblastoma cells

Defective tissue perfusion and nitric oxide production and altered myo-inositol metabolism and protein kinase C activation have been invoked in the pathogenesis of diabetic complications including neuropathy. The precise cellular compartmentalization and mechanistic interrelationships of these abnormalities remain obscure, and nitric oxide possesses both neurotransmitter and vasodilator activity. Therefore the effects of ambient glucose and myo-inositol on nitric oxide-dependent cGMP production and protein kinase C activity were studied in SH-SY5Y human neuroblastoma cells, a cell culture model for peripheral cholinergic neurons. D-Glucose lowered cellular myo-inositol content, phosphatidylinositol synthesis, and phosphorylation of an endogenous protein kinase C substrate, and specifically reduced nitric oxide-dependent cGMP production a time- and dose-dependent manner with an apparent IC50 of approximately 30 mM. The near maximal decrease in cGMP induced by 50 mM D-glucose was corrected by the addition of protein kinase C agonists or 500 microM myo-inositol to the culture medium, and was reproduced by protein kinase C inhibition or downregulation, or by myo-inositol deficient medium. Sodium nitroprusside increased cGMP in a dose-dependent fashion, with low concentrations (1 microM) counteracting the effects of 50 mM D-glucose or protein kinase C inhibition. The demonstration that elevated D-glucose diminishes basal nitric oxide-dependent cGMP production by myo-inositol depletion and protein kinase C inhibition in peripheral cholinergic neurons provides a potential metabolic basis for impaired nitric oxide production, nerve blood flow, and nerve impulse conduction in diabetes.

Frequency of median mononeuropathy in patients with mild diabetic neuropathy in the early diabetes intervention trial (EDIT). Tolrestat Study Group For Edit (Early Diabetes Intervention Trial)

We used electrophysiologic criteria to identify median mononeuropathy (MM) at the nondominant wrist among 414 patients enrolled in a multicenter study of patients with mild diabetic neuropathy according to consensus recommendations. Patients with absent sural or peroneal responses or greater than mild symptoms of carpal tunnel syndrome were ineligible. Ninety-five of 414 participants (23%) fulfilled criteria for MM, independent of diabetes type. Patients with MM had a longer duration of diabetes than remaining patients, independent of age, and patients with MM and type II diabetes were more likely to be female (34% vs. 19%; P = 0.008), shorter (165.7 vs. 172.7 cm; P = 0.001), and have a higher body mass index (32.5 vs. 29.1; P = 0.0008) than remaining type II patients. Sural or peroneal conduction abnormalities did not influence the frequency of MM. These results suggest that patients with diabetic neuropathy require special consideration with regard to the evaluation of suspected carpel tunnel syndrome.

Nerve conduction measures in mild diabetic neuropathy in the Early Diabetes Intervention Trial: the effects of age, sex, type of diabetes, disease duration, and anthropometric factors. Tolrestat Study Group for the Early Diabetes Intervention Trial

We evaluated nerve conduction measures at baseline from 429 patients enrolled in a multicenter diabetic neuropathy study. We defined neuropathy by using recently proposed recommendations but included only patients who had measurable sural and peroneal responses and quantitative vibration thresholds. Patients with type II diabetes were older than type I patients (54.5 versus 39.1 years), were heavier (body mass index [BMI] of 30.9 versus 25.5 kg/m2, and in general had lower evoked amplitudes. The effects of diabetes type upon nerve conduction measures disappeared when age and BMI were included in regression models. The men had lower amplitudes and conduction velocities and longer latencies than the women. The effect of gender was greatly reduced when height was included in the regression models, but gender continued to be a significant predictor of median sensory amplitude, most conduction velocities, and most latencies in these models. The relationships between nerve conduction measures and age, sex, and anthropometric factors were similar for patients with type II, but not those with type I, diabetes to the relationships reported for normal subjects. This may be a result of greater homogeneity with respect to degree of neuropathy for type II patients than for type I patients. These findings are important in designing and interpreting clinical studies of diabetic neuropathy.

Single-fiber electromyography in diabetic peripheral polyneuropathy

In this study we examined the value of single-fiber electromyography (SFEMG) in assessing the degree of reinnervation in diabetic patients with clinical neuropathy. Relationships between reinnervation and the degree of metabolic control, and/or duration of diabetes were examined. Thirty-six insulin-dependent diabetics and 54 non-insulin-dependent diabetics underwent SFEMG examination of the tibialis anterior muscle, as well as conventional nerve conduction studies of the upper and lower limbs. All patients examined exhibited some abnormality of SFEMG even in the presence of normal nerve conduction studies found in 18% of patients. In diabetic patients, the jitter in the tibialis anterior muscle correlated positively with glycosylated hemoglobin; whereas lower limb nerve conduction studies did not correlate with this measure of diabetic control. These data suggest that SFEMG is a sensitive measure of nerve function and reinnervation and that it may reflect the dynamic changes in metabolic status in diabetic patients.

Components of variance for vibratory and thermal threshold testing in normal and diabetic subjects

Quantitative sensory testing (QST) is commonly used in the assessment of diabetic neuropathy. However, little data are available on the reliability of tactile and thermal testing devices. Reproducibility of QST measures between centers has not been previously reported. This study was designed to validate QST testing procedures and determine if these devices are suitable for large scale multicenter clinical trials. Finger and toe vibratory (Vf, Vt) and thermal (Tf, Tt) thresholds were determined for ten normal individuals by a two-alternative forced-choice procedure using the Optacon Tactile Tester (OTT) and Thermal Sensitivity Tester (TST). Threshold measurements were reproducible between technologists and had a day-to-day coefficient of variation of Vf 20%, Vt 23%, Tf 41%, and Tt 95%. Thresholds were determined for 140 normal individuals at six centers. Mean threshold values between centers were not significantly different. Center-to-center coefficients of variation (CV) were Vf 44%, Vt 45%, Tf 47%, and Tt 87%. There was no significant difference in threshold measures with regard to sex, side studied, presence of calluses, or skin temperature. Vf thresholds significantly correlated with age (p < 0.01). There was no correlation between either vibratory or thermal thresholds in normal individuals, and nerve conduction velocities (NCV). Thermal and vibratory thresholds were determined for 98 diabetic patients. Diabetic subjects without clinical evidence of neuropathy were not significantly different from normal individuals, but diabetic patients with neuropathy had increased thresholds compared to normals (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Diabetic neuropathy in the elderly

Neuropathy is the most common symptomatic chronic complication in diabetic patients and accounts for substantial morbidity in the diabetic population. It is predominently a disease of the older diabetic population, and shows a progressive course with limb amputation as the final end-point of the disease. Pathologically the disorder is characterised by progressive degeneration as well as impaired regenerative ability of peripheral nerve fibers, resulting in a progressive loss and dying-back of the longest nerve fibres innervating the distal limbs. These changes are associated with progressive impairment of nerve function leading to impaired sensitivity in the limbs, which sometimes is associated with troublesome pain. Qualitatively similar but much milder functional and structural changes occur during normal aging processes, which potentially could make elderly diabetic patients more susceptible to an additional hyperglycaemic insult. The mechanisms underlying the development of diabetic neuropathy involve hyperglycaemia-induced metabolic abnormalities of peripheral nerve fibres and the supporting nutritive vascular supply. One of the major abnormalities involves activation of the polyol pathway with subsequent impairments in nerve function and vascular supply. Since hyperglycaemia appears to be the major culprit in the development of diabetic neuropathy, good glycaemic control is paramount in the long term treatment of diabetic patients to attenuate the development and/or progression of the disorder. Furthermore, elimination of risk factors such as obesity, smoking and excessive alcohol (ethanol) consumption, as well as patient education, are all important factors in the care of diabetic patients. In symptomatic neuropathic patients, including those with painful neuropathy, symptomatic and palliative measures are often effective. Stepwise addition of antidepressants to simple analgesics has proven to be effective in patients with troublesome pain. During recent years a class of drugs have been developed that inhibits the activation of the polyol pathway in diabetic nerves. These so-called aldose reductase inhibitors hold promise for a targeted treatment regimen in the near future. The aldose reductase inhibitors are already available in several European countries and in Japan.

Transphosphatidylation of sugar alcohols and its implications for the pathogenesis of diabetic complications

Glucose-induced sorbitol accumulation and attendant alterations in cellular myo-inositol and phosphoinositide metabolism have been invoked in the pathogenesis of diabetic complications; however, direct effects of sorbitol on membrane phospholipid composition or metabolism have never been evaluated. Phospholipase D catalyses the transphosphatidylation of ethanol into phosphatidylcholine to yield phosphatidylethanol, an "abnormal" phospholipid whose content in rat brain is increased by chronic ethanol ingestion. Analogous transphosphatidylation of sorbitol or other polyols whose concentration is elevated in diabetes was explored in vitro and in glucose-exposed cultured human retinal pigment epithelial cells. Phosphatidylcholine and varying concentrations of sorbitol, galactitol, mannitol and glucose were incubated with peanut phospholipase D in sodium acetate buffer for varying time periods. Thin layer chromatography revealed new phospholipid bands whose hydrolysis by phospholipase D liberated a water-soluble compound that cochromatographed with sorbitol on gas-liquid chromatography, and whose concentration increased in a time- and concentration-dependent fashion. Identical transphosphatidylation activity was demonstrated in a rat brain synaptosomal fraction. Phospholipase D hydrolysis of lipids from human retinal pigment epithelial cells constitutively overexpressing the aldose reductase gene yielded a sorbitol-like compound whose appearance was increased by glucose exposure and was decreased by an aldose reductase inhibitor. Thus, glucose-induced aldose reductase inhibitor sensitive sorbitol accumulation might induce the formation of "phosphatidylsorbitol" through a transphosphatidyl mechanism that may contribute to altered membrane phospholipid metabolism in diabetes.

A practical two-step quantitative clinical and electrophysiological assessment for the diagnosis and staging of diabetic neuropathy

OBJECTIVE

Early diagnosis of distal symmetric sensorimotor polyneuropathy, a common complication of diabetes, may decrease patient morbidity by allowing for potential therapeutic interventions. We have designed an outpatient program to facilitate diagnosis of diabetic neuropathy.

RESEARCH DESIGN AND METHODS

Patients are initially administered a brief questionnaire and screening examination, designated the Michigan Neuropathy Screening Instrument (MNSI). Diabetic neuropathy is confirmed in patients with a positive assessment by a quantitative neurological examination coupled with nerve conduction studies, designated the Michigan Diabetic Neuropathy Score (MDNS). In this study, 56 outpatients with confirmed type I or II diabetes were administered the standardized quantitative components required to diagnose and stage diabetic neuropathy according to the San Antonio Consensus Statement (1) and the Mayo Clinic protocol (2). These same patients were then assessed with the MNSI and the MDNS.

RESULTS

Of 29 patients with a clinical MNSI score > 2, 28 had neuropathy. Twenty-eight patients with an MDNS of > or = 7 had neuropathy, while 21 non-neuropathic patients had a score < or = 6. Of 35 patients with diabetic neuropathy, 34 had > or = 2 abnormal nerve conductions. Twenty-one normal patients and one patient with neuropathy had < or = 1 abnormal nerve conduction.

CONCLUSIONS

The results indicate that the MNSI is a good screening tool for diabetic neuropathy and that the MDNS coupled with nerve conductions provides a simple means to confirm this diagnosis.

The linked roles of nitric oxide, aldose reductase and, (Na+,K+)-ATPase in the slowing of nerve conduction in the streptozotocin diabetic rat

Metabolic and vascular factors have been invoked in the pathogenesis of diabetic neuropathy but their interrelationships are poorly understood. Both aldose reductase inhibitors and vasodilators improve nerve conduction velocity, blood flow, and (Na+,K+)-ATPase activity in the streptozotocin diabetic rat, implying a metabolic-vascular interaction. NADPH is an obligate cofactor for both aldose reductase and nitric oxide synthase such that activation of aldose reductase by hyperglycemia could limit nitric oxide synthesis by cofactor competition, producing vasoconstriction, ischemia, and slowing of nerve conduction. In accordance with this construct, N-nitro-L-arginine methyl ester, a competitive inhibitor of nitric oxide synthase reversed the increased nerve conduction velocity afforded by aldose reductase inhibitor treatment in the acutely diabetic rat without affecting the attendant correction of nerve sorbitol and myo-inositol. With prolonged administration, N-nitro-L-arginine methyl ester fully reproduced the nerve conduction slowing and (Na+,K+)-ATPase impairment characteristic of diabetes. Thus the aldose reductase-inhibitor-sensitive component of conduction slowing and the reduced (Na+,K+)-ATPase activity in the diabetic rat may reflect in part impaired nitric oxide activity, thus comprising a dual metabolic-ischemic pathogenesis.

Effects of glucose on sorbitol pathway activation, cellular redox, and metabolism of myo-inositol, phosphoinositide, and diacylglycerol in cultured human retinal pigment epithelial cells

Sorbitol (aldose reductase) pathway flux in diabetes perturbs intracellular metabolism by two putative mechanisms: reciprocal osmoregulatory depletion of other organic osmolytes e.g., myo-inositol, and alterations in NADPH/NADP+ and/or NADH/NAD+. The "osmolyte" and "redox" hypotheses predict secondary elevations in CDP-diglyceride, the rate-limiting precursor for phosphatidylinositol synthesis, but through different mechanisms: the "osmolyte" hypothesis via depletion of intracellular myo-inositol (the cosubstrate for phosphatidylinositol-synthase) and the "redox" hypothesis through enhanced de novo synthesis from triose phosphates. The osmolyte hypothesis predicts diminished phosphoinositide-derived arachidonyl-diacylglycerol, while the redox hypothesis predicts increased total diacylglycerol and phosphatidic acid. In high aldose reductase expressing retinal pigment epithelial cells, glucose-induced, aldose reductase inhibitor-sensitive CDP-diglyceride accumulation and inhibition of 32P-incorporation into phosphatidylinositol paralleled myo-inositol depletion (but not cytoplasmic redox, that was unaffected by glucose) and depletion of arachidonyl-diacylglycerol. 3 mM pyruvate added to the culture medium left cellular redox unaltered, but stimulated Na(+)-dependent myo-inositol uptake, accumulation, and incorporation into phosphatidylinositol. These results favor myo-inositol depletion rather than altered redox as the primary cause of glucose-induced aldose reductase-related defects in phospholipid metabolism in cultured retinal pigment epithelial cells.

Noninvasive assessment of cardiac diabetic neuropathy by carbon-11 hydroxyephedrine and positron emission tomography

OBJECTIVES

The purpose of this investigation was to evaluate the sympathetic nervous system of the heart by positron emission tomographic (PET) imaging in patients with diabetes mellitus with and without diabetic autonomic neuropathy.

BACKGROUND

The clinical assessment of cardiac involvement in diabetic autonomic neuropathy has been limited to cardiovascular reflex testing. With the recent introduction of radiolabeled catecholamines such as carbon (C)-11 hydroxyephedrine, the sympathetic innervation of the heart can be specifically visualized with PET imaging.

METHODS

Positron emission tomographic imaging was performed with C-11 hydroxyephedrine and rest myocardial blood flow imaging with nitrogen-13 ammonia. Three patient groups were studied, including healthy volunteers as control subjects, diabetic patients with normal autonomic function testing and diabetic patients with varying severity of autonomic neuropathy. Homogeneity of cardiac tracer retention as well as absolute tracer retention was determined by relating myocardial tracer retention to an arterial C-11 activity input function.

RESULTS

Abnormal regional C-11 hydroxyephedrine retention was seen in seven of eight patients with autonomic neuropathy. Relative tracer retention was significantly reduced in apical, inferior and lateral segments. The extent of the abnormality correlated with the severity of conventional markers of autonomic dysfunction. Absolute myocardial tracer retention index measurements showed a 45 +/- 21% decrease in distal compared with proximal myocardial segments in autonomic neuropathy (0.069 +/- 0.037 min-1 vs. 0.13 +/- 0.052 min-1, p = 0.02).

CONCLUSIONS

This study demonstrates a heterogeneous pattern of neuronal abnormalities in patients with diabetic cardiac neuropathy. The extent of this abnormality correlated with the severity of neuropathy assessed by conventional tests. Future studies in larger groups of patients are required to define the relative sensitivity of this imaging approach in detecting cardiac neuropathy and to determine the clinical significance of these scintigraphic findings in comparison with conventional markers of autonomic innervation.