Effect of myo-inositol on peripheral-nerve function in diabetes

Potential Metabolite Biomarkers of Multiple Sclerosis from Multiple Biofluids

Multiple sclerosis (MS) is a chronic and progressive neurological disorder without a cure, but early intervention can slow disease progression and improve the quality of life for MS patients. Obtaining an accurate diagnosis for MS is an arduous and error-prone task that requires a combination of a detailed medical history, a comprehensive neurological exam, clinical tests such as magnetic resonance imaging, and the exclusion of other possible diseases. A simple and definitive biofluid test for MS does not exist, but is highly desirable. To address this need, we employed NMR-based metabolomics to identify potentially unique metabolite biomarkers of MS from a cohort of age and sex-matched samples of cerebrospinal fluid (CSF), serum, and urine from 206 progressive MS (PMS) patients, 46 relapsing-remitting MS (RRMS) patients, and 99 healthy volunteers without a MS diagnosis. We identified 32 metabolites in CSF that varied between the control and PMS patients. Utilizing patient-matched serum samples, we were able to further identify 31 serum metabolites that may serve as biomarkers for PMS patients. Lastly, we identified 14 urine metabolites associated with PMS. All potential biomarkers are associated with metabolic processes linked to the pathology of MS, such as demyelination and neuronal damage. Four metabolites with identical profiles across all three biofluids were discovered, which demonstrate their potential value as cross-biofluid markers of PMS. We further present a case for using metabolic profiles from PMS patients to delineate biomarkers of RRMS. Specifically, three metabolites exhibited a variation from healthy volunteers without MS through RRMS and PMS patients. The consistency of metabolite changes across multiple biofluids, combined with the reliability of a receiver operating characteristic classification, may provide a rapid diagnostic test for MS.

B vitamins as a treatment for diabetic pain and neuropathy

WHAT IS KNOWN AND OBJECTIVE

B vitamin therapy is a common treatment for diabetic pain and neuropathy, yet its use remains controversial in patients lacking B vitamin deficiencies. The aim of this review was to summarize the current evidence for the efficacy of B vitamin therapy in diabetic patients with neuropathy.

COMMENT

We screened the English literature for clinical studies evaluating B vitamins as a therapy for pain and neuropathy in diabetic patients. We selected 43 relevant studies for qualitative analysis based on our selection criteria. Our survey of the literature revealed substantive heterogeneity with respect to efficacies of reported outcomes, as well as study design. Most beneficial outcomes were reported against baseline measures, with few positive comparisons against placebo. This highlights the need for larger, placebo-controlled studies.

WHAT IS NEW AND CONCLUSION

B vitamins should be considered a plausible therapy for diabetic neuropathy, but its overall efficacy remains uncertain and requires further study.

Understanding Diabetic Neuropathy: Focus on Oxidative Stress

Diabetic neuropathy is one of the clinical syndromes characterized by pain and substantial morbidity primarily due to a lesion of the somatosensory nervous system. The burden of diabetic neuropathy is related not only to the complexity of diabetes but also to the poor outcomes and difficult treatment options. There is no specific treatment for diabetic neuropathy other than glycemic control and diligent foot care. Although various metabolic pathways are impaired in diabetic neuropathy, enhanced cellular oxidative stress is proposed as a common initiator. A mechanism-based treatment of diabetic neuropathy is challenging; a better understanding of the pathophysiology of diabetic neuropathy will help to develop strategies for the new and correct diagnostic procedures and personalized interventions. Thus, we review the current knowledge of the pathophysiology in diabetic neuropathy. We focus on discussing how the defects in metabolic and vascular pathways converge to enhance oxidative stress and how they produce the onset and progression of nerve injury present in diabetic neuropathy. We discuss if the mechanisms underlying neuropathy are similarly operated in type I and type II diabetes and the progression of antioxidants in treating diabetic neuropathy.

Efficient production of myo-inositol in Escherichia coli through metabolic engineering

BACKGROUND

The biosynthesis of high value-added compounds using metabolically engineered strains has received wide attention in recent years. Myo-inositol (inositol), an important compound in the pharmaceutics, cosmetics and food industries, is usually produced from phytate via a harsh set of chemical reactions. Recombinant Escherichia coli strains have been constructed by metabolic engineering strategies to produce inositol, but with a low yield. The proper distribution of carbon flux between cell growth and inositol production is a major challenge for constructing an efficient inositol-synthesis pathway in bacteria. Construction of metabolically engineered E. coli strains with high stoichiometric yield of inositol is desirable.

RESULTS

In the present study, we designed an inositol-synthesis pathway from glucose with a theoretical stoichiometric yield of 1 mol inositol/mol glucose. Recombinant E. coli strains with high stoichiometric yield (> 0.7 mol inositol/mol glucose) were obtained. Inositol was successfully biosynthesized after introducing two crucial enzymes: inositol-3-phosphate synthase (IPS) from Trypanosoma brucei, and inositol monophosphatase (IMP) from E. coli. Based on starting strains E. coli BW25113 (wild-type) and SG104 (ΔptsG::glk, ΔgalR::zglf, ΔpoxB::acs), a series of engineered strains for inositol production was constructed by deleting the key genes pgi, pfkA and pykF. Plasmid-based expression systems for IPS and IMP were optimized, and expression of the gene zwf was regulated to enhance the stoichiometric yield of inositol. The highest stoichiometric yield (0.96 mol inositol/mol glucose) was achieved from recombinant strain R15 (SG104, Δpgi, Δpgm, and RBSL5-zwf). Strain R04 (SG104 and Δpgi) reached high-density in a 1-L fermenter when using glucose and glycerol as a mixed carbon source. In scaled-up fed-batch bioconversion in situ using strain R04, 0.82 mol inositol/mol glucose was produced within 23 h, corresponding to a titer of 106.3 g/L (590.5 mM) inositol.

CONCLUSIONS

The biosynthesis of inositol from glucose in recombinant E. coli was optimized by metabolic engineering strategies. The metabolically engineered E. coli strains represent a promising method for future inositol production. This study provides an essential reference to obtain a suitable distribution of carbon flux between glycolysis and inositol synthesis.

Nutritional composition and antioxidant activity of Spanish and Virginia groundnuts (Arachis hypogaea L.): a comparative study

Kernels of sixty groundnut genotypes comprising thirty each of Spanish and Virginia groups were characterized and compared for the content of oil, protein, phenols and antioxidant activity along with their fatty acid and sugars profiles. The antioxidant activity for Virginia genotypes was ranged from 12.5 to 16.5 μM Trolox equivalent activity for Spanish genotypes ranged from 6.8-15.2 μM. Amongst Virginia types, the highest oleic acid/linoleic acid (O/L) ratio of 2.38 was observed for NRCG 12312 while from Spanish group the highest O/L ratio of 1.24 was observed for NRCG 12731. The sucrose content for Virginia genotypes ranged from 38.5 to 69.0 mg/g while it was 27.9 to 53.3 mg/g for Spanish genotypes. Average myo-inositol content was higher for Spanish genotypes (0.8-2.1 mg/g) compared to Virginia (0.4-1.8 mg/g) while the reverse was true for stachayose content (Spanish: 3.5-7.9 mg/g; Virginia: 4.6-10.3 mg/g). Thus, Virginia genotypes could be preferred to Spanish genotypes for better oil stability and antioxidant activity.

Potential role and therapeutic interests of myo-inositol in metabolic diseases

Several inositol isomers and in particular myo-inositol (MI) and D-chiro-inositol (DCI), were shown to possess insulin-mimetic properties and to be efficient in lowering post-prandial blood glucose. In addition, abnormalities in inositol metabolism are associated with insulin resistance and with long term microvascular complications of diabetes, supporting a role of inositol or its derivatives in glucose metabolism. The aim of this review is to focus on the potential benefits of a dietary supplement of myo-inositol, by far the most common inositol isomer in foodstuffs, in human disorders associated with insulin resistance (polycystic ovary syndrome, gestational diabetes mellitus or metabolic syndrome) or in prevention or treatment of some diabetic complications (neuropathy, nephropathy, cataract). The relevance of such a nutritional strategy will be discussed for each context on the basis of the clinical and/or animal studies. The dietary sources of myo-inositol and its metabolism from its dietary uptake to its renal excretion will be also covered in this review. Finally, the actual insights into inositol insulin-sensitizing effects will be addressed and in particular the possible role of inositol glycans as insulin second messengers.

Is prenatal myo-inositol deficiency a mechanism of CNS injury in galactosemia?

Classic Galactosemia due to galactose-1-phosphate uridyltransferase (GALT) deficiency is associated with apparent diet-independent complications including cognitive impairment, learning problems and speech defects. As both galactose-1-phosphate and galactitol may be elevated in cord blood erythrocytes and amniotic fluid despite a maternal lactose-free diet, endogenous production of galactose may be responsible for the elevated fetal galactose metabolites, as well as postnatal CNS complications. A prenatal deficiency of myo-inositol due to an accumulation of both galactose-1- phosphate and galactitol may play a role in the production of the postnatal CNS dysfunction. Two independent mechanisms may result in fetal myo-inositol deficiency: competitive inhibition of the inositol monophosphatase1 (IMPA1)-mediated hydrolysis of inositol monophosphate by high galactose-1- phosphate levels leading to a sequestration of cellular myo-inositol as inositol monophosphate and galactitol-induced reduction in SMIT1-mediated myo-inositol transport. The subsequent reduction of myo-inositol within fetal brain cells could lead to inositide deficiencies with resultant perturbations in calcium and protein kinase C signaling, the AKT/mTOR/ cell growth and development pathway, cell migration, insulin sensitivity, vescular trafficking, endocytosis and exocytosis, actin cytoskeletal remodeling, nuclear metabolism, mRNA export and nuclear pore complex regulation, phosphatidylinositol-anchored proteins, protein phosphorylation and/or endogenous iron "chelation". Using a knockout animal model we have shown that a marked deficiency of myo-inositol in utero is lethal but the phenotype can be rescued by supplementing the drinking water of the pregnant mouse. If myo-inositol deficiency is found to exist in the GALT-deficient fetal brain, then the use of myo-inositol to treat the fetus via oral supplementation of the pregnant female may warrant consideration.

Chronic treatment with D-chiro-inositol prevents autonomic and somatic neuropathy in STZ-induced diabetic mice

AIM

D-chiro-inositol (DCI) has been shown to prevent and reverse endothelial dysfunction in diabetic rats and rabbits. The present study evaluates the preventive effect of DCI on experimental diabetic neuropathy (DN).

METHODS

Streptozotocin-induced (STZ) diabetic mice were treated by oral gavage for 60 days with DCI (20 mg/kg/12 h) or saline (NaCl 0.9%; 0.1 ml/10 g/12 h; Diab) and compared with euglycaemic groups treated with saline (0.1 ml/10 g/12 h; Eugly). We compared the response of the isolated sciatic nerve, corpora cavernosa or vas deferens to electrical stimulation.

RESULTS

The electrically evoked compound action potential of the sciatic nerve was greatly blunted by diabetes. The peak-to-peak amplitude (PPA) was decreased from 3.24 ± 0.7 to 0.9 ± 0.2 mV (p < 0.05), the conduction velocity (CV) of the first component was reduced from 46.78 ± 4.5 to 26.69 ± 3.8 ms (p < 0.05) and chronaxy was increased from 60.43 ± 1.9 to 69.67 ± 1.4 ms (p < 0.05). These parameters were improved in nerves from DCI-treated mice (p < 0.05). PPA in the DCI group was 5.79 ± 0.8 mV (vs. 0.9 ± 0.2 mV-Diab; p < 0.05) and CV was 45.91 ± 3.6 ms (vs. 26.69 ± 3.8 ms-Diab; p < 0.05). Maximal relaxation of the corpus cavernosum evoked by electrical stimulation (2-64 Hz) in the Diab group was 36.4 ± 3.8% compared to 65.4 ± 2.8% in Eugly and 59.3 ± 5.5% in the DCI group (p < 0.05). Maximal contraction obtained in the vas deferens was 38.0 ± 9.2% in Eugly and 11.5 ± 2.6% in Diab (decrease of 69.7%; p < 0.05), compared to 25.2 ± 2.3% in the DCI group (p < 0.05 vs. diabetic). Electron microscopy of the sciatic nerves showed prevention of neuronal damage.

CONCLUSIONS

DCI has a neuroprotective action in both autonomic and somatic nerves in STZ-induced DN.

Impairment, disability, or handicap in peripheral neuropathy: analysis of the use of outcome measures in clinical trials in patients with peripheral neuropathies

Outcome measures can be classified into measures of impairment, disability, and handicap. To investigate the biological effect of treatment, measures of impairment are appropriate. Studies investigating whether patients benefit from treatment in terms of improvement of functional health, however, require disability or handicap measures. In a review of the medical literature between 1978 and 1993, 73 controlled intervention studies in patients with peripheral neuropathies were found. Disability or handicap measures were used in two of 54 studies in patients with diabetic neuropathy, in two of six studies in patients with chronic inflammatory demyelinating polyneuropathy, in none of five studies in a mixed group of patients, and in all eight studies in patients with Guillain-Barré syndrome. The limited use of disability and handicap measures in patients with diabetic and mixed neuropathies can be explained by the experimental nature of most studies. In four of six studies, however, in patients with chronic inflammatory demyelinating polyneuropathy or neuropathy associated with monoclonal gammopathy that were designed to assess effectiveness of treatment, the choice of outcome measures was not appropriate. It is concluded that in the design of intervention studies in patients with peripheral neuropathy more attention should be paid to a proper choice of suitable outcome measures to assess the effectiveness of treatment.

Inositol and inositol 1,4,5-trisphosphate content of Down syndrome fibroblasts exhibiting enhanced inositol uptake

Fibroblasts from individuals with Down syndrome (DS; trisomy 21) exhibit increased inositol uptake. Here we examine the relationship between this increase in uptake and mass levels of free inositol and inositol 1,4,5-trisphosphate (IP3) in DS fibroblasts. We report that human fibroblasts contain high levels of free inositol which are not significantly affected by the increase in inositol uptake associated with DS. In addition, increased uptake is accompanied by increased efflux of radiolabelled inositol from DS cells. Neither basal nor bradykinin-stimulated IP3 levels in DS cells differ significantly from normal values. This work highlights the usefulness of the DS cells in uncovering the role of transport across the plasma membrane in cellular inositol homeostasis.

The effects of lithium discontinuation and the non-effect of oral inositol upon thyroid hormones and cortisol in patients with bipolar affective disorder

Thyroid and adrenal function was assessed in euthymic bipolar patients, stable on prophylactic lithium for at least 1 year, before and after lithium discontinuation in a randomised double-blind placebo-controlled trial. All hormonal measurements were within the reference range, but a significant increase (P less than 0.001) in plasma thyroxine (T4) levels and a decrease (P less than 0.01) in TSH levels were observed 1 month after lithium withdrawal; cortisol concentrations showed a non-significant decrease in the same period. No relationship could be demonstrated between the magnitude of the change in hormone levels and the probability of relapse of manic symptoms. In the second part of this study, inositol was added for 11 days to the diets of bipolar patients being treated with prophylactic lithium and normal controls. No modification was shown in T4 and TSH in either group before or after inositol administration. Inositol did not alleviate other side-effects such as tremor and thirst in the patient group. This result suggests that short-term dietary inositol is not equivalent to lithium withdrawal and is of no value in reducing hormonal and other adverse effects of lithium prophylaxis.

A defect in sodium-dependent amino acid uptake in diabetic rabbit peripheral nerve. Correction by an aldose reductase inhibitor or myo-inositol administration

A myo-inositol-related defect in nerve sodium-potassium ATPase activity in experimental diabetes has been suggested as a possible pathogenetic factor in diabetic neuropathy. Because the sodium-potassium ATPase is essential for other sodium-cotransport systems, and because myo-inositol-derived phosphoinositide metabolites regulate multiple membrane transport processes, sodium gradient-dependent amino acid uptake was examined in vitro in endoneurial preparations derived from nondiabetic and 14-d alloxan diabetic rabbits. Untreated alloxan diabetes reduced endoneurial sodium-gradient dependent uptake of the nonmetabolized amino acid 2-aminoisobutyric acid by greater than 50%. Administration of an aldose reductase inhibitor prevented reductions in both nerve myo-inositol content and endoneurial sodium-dependent 2-aminoisobutyric acid uptake. Myo-inositol supplementation that produced a transient pharmacological elevation in plasma myo-inositol concentration, but did not raise nerve myo-inositol content, reproduced the effect of the aldose reductase inhibitor on endoneurial sodium-dependent 2-aminoisobutyric acid uptake. Phorbol myristate acetate, which acutely normalizes sodium-potassium ATPase activity in diabetic nerve, did not acutely correct 2-aminoisobutyric uptake when added in vitro. These data suggest that depletion of a small myo-inositol pool may be implicated in the pathogenesis of defects in amino acid uptake in diabetic nerve and that rapid correction of sodium-potassium ATPase activity with protein kinase C agonists in vitro does not acutely normalize sodium-dependent 2-aminoisobutyric acid uptake.

Biochemical manifestations of diabetes mellitus in microscopic layers of the cornea and retina

Biochemical evidence of glucose toxicity was found in the retinal and corneal layers of diabetic rabbits. It can be reasonably assumed that the observed changes are causally related to the morphological and physiological diabetic pathologies of the retinal and corneal cells. Intracellular glucose is greatly increased, and the polyol pathway activity appears to be enhanced, resulting in an accumulation of intracellular sorbitol, which can be assumed to be oxidized to fructose. Accompanying the alterations of glucose metabolism are disturbances in myoinositol and Na+ handling by the affected structures. The detailed relationship of the observed metabolic effects of hyperglycemia to changes in cellular ion handling and the observed morphological and functional disturbances has yet to be elucidated. The morphologically and functionally discrete populations of RPE and CEN cells, which are readily amenable to experimental manipulation in situ and in cell culture may serve as unique models for systematic examination of the causes and the consequences of diabetes leading to ocular complications in particular and to the complications of other more complex tissues such as nerve and kidney. The present data show that the findings in one population of cells may not be completely reproducible in another as can be seen in the diverse myoinositol responses of the retinal and corneal layers to diabetes mellitus. The diverse responses perhaps reflect unique adaptive capabilities of individual tissues to the diabetic condition. It is a challenge for complications research to fully appreciate diverse responses of various tissues to persistent glucose intoxication and to delineate meticulously the time courses of such heterogeneous responses, which might result in debilitating pathology in certain cases but in a compensated chronic disease state in others. The corneal endothelium and the RPE are relatively resilient structures compared with the mural and endothelial cells of the retinal microvessels which are destroyed by the diabetic condition. Factors and components that protect tissues against the persistent effects of hyperglycemia need to be uncovered. Success in such an endeavor could be of benefit in the management of diabetic complications.

Clinical aspects of diabetic neuropathies

Diabetic neuropathy is a common complication of diabetes that may be associated both with considerable morbidity (painful polyneuropathy, neuropathic ulceration) and mortality (autonomic neuropathy). The epidemiology and natural history of diabetic neuropathy is clouded with uncertainty, largely due to confusion in the definition and measurement of this disorder. We have reviewed a variety of the clinical manifestations associated with somatic and autonomic neuropathy and discussed current views related to the management of the different abnormalities. Although unproven, the best evidence suggests that near normal control of blood glucose in the early years following onset of diabetes may help delay the development of clinically significant nerve impairment. Intensive therapy to achieve normalization of blood glucose may also lead to reversibility of early diabetic neuropathy, but again this is unproven. Our ability to manage successfully the many different manifestations of diabetic neuropathy depends ultimately on our success in uncovering the pathogenic processes underlying this disorder. The recent resurgence of interest in the vascular hypothesis, for example, has opened up new avenues of investigation for therapeutic intervention. Paralleling our increased understanding of the pathogenesis of diabetic neuropathy, there must be refinements in our ability to measure quantitatively the different types of defects that occur in this disorder. These tests must be validated and standardized to allow comparability between studies and more meaningful interpretation of study results.

Management of peripheral neuropathy in diabetes mellitus. Recent research findings and their therapeutic implications

Peripheral neuropathy in diabetes begins as a physiologic aberration related to hyperglycemia and its subsequent effects of endoneurial hypoxia, elevated sorbitol levels, and decreased myoinositol levels. Resultant decreases in sodium-potassium-adenosine triphosphatase levels ultimately lead to structural alterations at the nodes of Ranvier. Aldose reductase inhibitors and dietary myoinositol supplementation are being used in long-term clinical studies to monitor the possibility that they may prevent or reverse these abnormalities. In the meantime, symptomatic treatment remains the mainstay of management.

Recent advances in the pathogenesis of diabetic neuropathy

Recent advances in the understanding of the pathogenesis of diabetic neuropathy have been made in six areas. There is support for the notion that a reduction in nerve free myoinositol may be responsible in part for the nerve conduction slowing in diabetic neuropathy. There is further evidence of microvascular abnormalities, including morphometric evidence of multifocal fiber loss and of capillary changes in biopsied sural nerve. There is evidence of endoneurial hypoxia, including the findings of reduced nerve blood flow and endoneurial oxygen tensions in chronic experimental diabetic neuropathy (EDN). The major mechanisms of resistance to ischemic conduction failure (RICF) is the marked increase in nerve energy substrates. Recent studies provide certain insights into clinical characteristics of human diabetic neuropathy (HDN), including the asymmetric pattern of HDN, the paradox between liability to pressure palsies and RICF, and insulin-related acute painful neuropathy. The suggested pathogenetic scheme incorporates the notion that once hypoxia is established, it may start a vicious cycle of further capillary damage and escalating hypoxia.

New therapies for the chronic complications of older diabetic patients

Recently, four biochemical mechanisms have been implicated in the pathogenesis of certain late complications of diabetes mellitus. All of these mechanisms (altered polyol pathway activity, disrupted myo-inositol metabolism, increased vascular permeability, and increased nonenzymatic glycosylation of proteins) are activated by exposure of tissues to hyperglycemia. There is evidence to suggest that the development of retinopathy, nephropathy, and neuropathy is directly related to the level of glycemia in patients with diabetes mellitus. Whether strict glycemic control will prevent or reverse diabetic complications is the subject of the Diabetes Control and Complications Trial. Until the results of that study are reported, and until euglycemia can be achieved in all diabetic patients, the search will continue for other pharmacologic agents that might prevent the development of complications. Therapies that are currently under investigation include administration of aldose reductase inhibitors and supplementation of dietary myo-inositol. It is too early to conclude whether such therapies will prove useful in the prevention or reversal of diabetic complications.

A sodium-pump defect in diabetic peripheral nerve corrected by sorbinil administration: relationship to myo-inositol metabolism and nerve conduction slowing

Nerve conduction slowing, a hallmark of both experimental and human diabetic neuropathy, is improved or corrected by aldose reductase inhibitors such as sorbinil. Recent animal experiments attribute acutely reversible nerve conduction slowing in diabetes to a myo-inositol (MI)-related defect in the nerve Na-K-ATPase (which generates the transmembrane sodium and potassium potentials necessary for nerve impulse conduction and the sodium gradient necessary for sodium-dependent uptake of substrates). This MI-related abnormality in Na-K-ATPase function is currently viewed as a cyclic, metabolic defect involving sequential alteration of Na-dependent MI uptake, MI content, MI incorporation into membrane phospholipids, and phospholipid-dependent Na-K-ATPase function in peripheral nerve. Aldose reductase inhibitors have been shown to normalize both nerve MI content and nerve Na-K-ATPase activity. These observations suggest that the acute effects of aldose reductase inhibitors on nerve conduction in both diabetic animals and patients may be mediated by correction of an underlying MI-related nerve Na-K-ATPase defect. Furthermore, this sorbinil-corrected Na-K-ATPase defect in diabetic nerve may contribute to other biochemical, functional, and structural abnormalities present in patients with diabetic peripheral neuropathy.

Diabetic autonomic neuropathy

The incidence of autonomic dysfunction as a complication of diabetes mellitus is reported to be as high as 20% to 40%. Symptoms of diabetic autonomic neuropathy (DAN) are often vague, and signs difficult to detect on routine physical examination. The early diagnosis of DAN is possible by utilizing several simple noninvasive tests, which may also be helpful in localizing the lesion(s) to specific autonomic pathways. DAN may affect multiple organ systems, to include cardiovascular, gastrointestinal, genitourinary and/or neuroendocrine, and may, in fact, be life-threatening. The same metabolic disturbances of somatic peripheral nerve may also be responsible for DAN. Like somatosensory neuropathy, definitive therapy for DAN is not yet satisfactory, although multiple chemotherapeutic agents have been tried and warrant further investigation.

Treatment of peripheral neuropathies

There are three general approaches to treatment of peripheral neuropathy. First, an attempt should be made to reverse the pathophysiological process if its nature can be elucidated. Second, nerve metabolism can be stimulated and regeneration encouraged. Third, even if the neuropathy itself cannot be improved, symptomatic therapy can be employed. This review outlines the options available for each approach.

A double blind placebo controlled trial of mixed gangliosides in diabetic peripheral and autonomic neuropathy

Twenty-six patients with signs or symptoms of diabetic neuropathy who also had motor or sensory neurophysiological abnormalities, were intensively studied in the first double-blind, placebo controlled trial of a ganglioside mixture in the U.K. (Cronassial, Fidia Farmaceutici, Abano Terme, Italy; 6 weeks of 20 mg daily intramuscularly). Diabetes control was good in both groups and there was no deterioration in either group during the course of the trial. Of the five neurophysiological parameters measured - the motor nerve compound action potential, motor nerve conduction velocity and minimum f wave latency of the common peroneal nerve and the sensory action potential and conduction velocity of the sural nerve - only the mean motor nerve action potential and conduction velocity increased though the changes were not significant. Four patients showed improvements of greater than 1.0 mV after treatment with Cronassial while none of the placebo group did so (p less than 0.05). Of the four patients who showed dramatic improvements in motor nerve action potentials, three also showed improvements in motor nerve conduction velocity. There were no significant changes in three tests of autonomic function after Cronassial therapy (orthostatic tilt reactions, single deep breath and Valsalva maneuver). Four patients in the Cronassial group (not those showing neurophysiological improvement) but only one in the placebo group reported marked improvements in their symptomatic complaints after treatment. We conclude that Cronassial is a promising new drug for the treatment of diabetic peripheral neuropathy with clear benefits for some patients.

Influence of glucoregulation with continuous subcutaneous insulin infusion on nerve conduction velocity and beat to beat variation in diabetics

Limited and contrasting data are available on the relationship between metabolic control and diabetic neuropathy. In eight type I diabetics peripheral and autonomic neuropathy were studied, first in conditions of poor metabolic control and then after one and three months during which an improved control of glycemic levels had been obtained by continuous subcutaneous insulin infusion. Autonomic neuropathy was investigated by evaluating beat to beat variation during deep breathing; peripheral neuropathy by measuring maximum motor conduction velocity of peroneal and median nerves and sensory conduction velocity of median nerve. Our data showed significant improvement of motor conduction velocity in both nerves studied, whilst sensory conduction velocity did not show any significant variation. The changes observed in beat to beat variation in five subjects with initially abnormal scores might reflect an improvement in autonomic nervous function, even if long-term studies are needed.

Oral supplementation of myoinositol: effects on peripheral nerve function in human diabetics and on the concentration in plasma, erythrocytes, urine and muscle tissue in human diabetics and normals

28 young diabetics with short disease duration participated in a double-blind study by taking 6 g of myoinositol or placebo daily for 2 months. The aim was to demonstrate a possible beneficial effect of this compound on subclinical diabetic neuropathy. Measurement of vibratory perception threshold, motor and sensory conduction velocity and amplitude of nerve potential did not disclose any effect of the myoinositol given. In accordance with this, no indication for a lack of myoinositol in human diabetic blood or tissue could be found. The concentration of myoinositol in the plasma and erythrocyte of 4 human diabetics was normal or high, even though the loss of urinary myoinositol was greater than in the case of 4 normals. Further, an analysis of the content of free and lipid-bound myoinositol in muscle biopsies taken from the 4 diabetics did not give any indication of deficiency. The content of myoinositol in their muscle tissue remained uninfluenced by oral supplementation of myoinositol.

Sodium- and energy-dependent uptake of myo-inositol by rabbit peripheral nerve. Competitive inhibition by glucose and lack of an insulin effect

Experimental diabetes consistently reduces the concentration of free myo-inositol in peripheral nerve, which usually exceeds that of plasma by 90-100-fold. This phenomenon has been explicitly linked to the impairment of nerve conduction in the acutely diabetic streptozocin-treated rat. However, the mechanism by which acute experimental diabetes lowers nerve myo-inositol content and presumably alters nerve myo-inositol content and presumably alters nerve myo-inositol metabolism is unknown. Therefore, the effects of insulin and elevated medium glucose concentration of 2-[3H]myo-inositol uptake were studied in a metabolically-defined in vitro peripheral nerve tissue preparation derived from rabbit sciatic nerve, whose free myo-inositol content is reduced by experimental diabetes. The results demonstrate that myo-inositol uptake occurs by at least two distinct transport systems in the normal endoneurial preparation. A sodium- and energy-dependent saturable transport system is responsible for at least 94% of the measured uptake at medium myo-inositol concentrations approximating that present in plasma. This carrier-mediated transport system has a high affinity for myo-inositol (Kt = 63 microM), and is not influenced acutely by physiological concentrations of insulin; it is, however, inhibited by hyperglycemic concentrations of glucose added to the incubation medium in a primarily competitive fashion. Thus, competitive inhibition of peripheral nerve myo-inositol uptake by glucose may constitute a mechanism by which diabetes produces physiologically significant alterations in peripheral nerve myo-inositol metabolism.

The nutritional significance, metabolism, and function of myo-inositol and phosphatidylinositol in health and disease

Recent advances in nutritional and biochemical research have substantiated the importance of inositol as a dietary and cellular constituent. The processes involved in the metabolism of inositol and its derivatives in mammalian tissues have been characterized both in vivo and at the enzyme level. Biochemical functions elucidated for phosphatidylinositol in biological membranes include the mediation of cellular responses to external stimuli, nerve transmission, and the regulation of enzyme activity through specific interactions with various proteins. Inositol deficiency in animals has been shown to produce an accumulation of triglyceride in liver, intestinal lipodystrophy, and other abnormalities. The metabolic mechanisms giving rise to these latter phenomena have been extensively studied as a function of dietary inositol. Altered metabolism of inositol has been documented in patients with diabetes mellitus, chronic renal failure, galactosemia, and multiple sclerosis. A moderate increase in plasma and nerve inositol levels by dietary supplementation has been suggested as a means of treating diabetic neuropathy, although excessively high levels, such as are found in uremic patients, may be neurotoxic. A thorough consideration of the biochemical functions of inositol and a further characterization of various diseases with the aid of appropriate animal models may suggest a possible role for inositol and other dietary components in their prevention and treatment

Effects of aldose reductase inhibitor treatment in diabetic polyneuropathy - a clinical and neurophysiological study

The efficacy of treatment with an aldose reductase inhibitor (1,3-dioxo-1 H-benz-de-isoquinoline-2(3H)-acetic acid, AY-22,284, Alrestatin) on peripheral nerve function in diabetic polyneuropathy was assessed. Thirty patients with long-standing diabetes and slight to moderate neuropathy participated in the double-blind placebo trial. Clinical examination, sensory threshold determinations for vibratory, tactile and thermal stimuli, conduction velocity measurements and studies of automatic function were performed to evaluate the treatment. Significant differences favouring Alrestatin over placebo were found for many of the measured variables, whereas no changes occurred on placebo. The apparent improvement of neuropathy occurred despite persisting hyperglycaemia. The results indicate that aldose reductase inhibitor treatment may be of value in diabetic polyneuropathy, and provide support for the sorbitol pathway hypothesis of diabetic polyneuropathy.

Nerve conduction velocity in experimental diabetes in the rat and rabbit

Tibial motor nerve conduction velocity was measured in rats, before and two months after the induction of diabetes with streptozotocin. A second group of diabetic animals was also administered 1% dietary myoinositol supplements. An analysis of variance was performed on these data. Myoinositol supplements had no effect whatsoever. The period of diabetes had a statistically significant and quantitatively marginal effect (a decrease of 2.2 m s-1) on conduction velocity. This is considerably less than in previous reports. The reasons for this are discussed. Tibial motor nerve conduction velocity was also measured in a group of alloxan-diabetic rabbits two months after the induction of diabetes and in an age-matched control group. Conduction velocity was again slightly but significantly less in the diabetic animals.