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

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.

Manual acupuncture for treatment of diabetic peripheral neuropathy: a systematic review of randomized controlled trials

OBJECTIVE

Manual acupuncture has commonly been used in China, either alone or in combination with conventional medicine, to treat diabetic peripheral neuropathy (DPN). The objective of this study was to perform a systematic review to evaluate the potential benefits and harms of manual acupuncture for DPN to justify its clinical use.

METHODS

We searched for published and unpublished randomized controlled trials of manual acupuncture for DPN till 31 March 2013. Revman 5.2 software was used for data analysis with effect estimate presented as relative risk (RR) and mean difference (MD) with a 95% confidence interval (CI).

RESULTS

A total of 25 trials involving 1649 participants were included. The methodological quality of included trials was generally poor. Meta-analysis showed that manual acupuncture had better effect on global symptom improvement compared with mecobalamin (RR 1.31, 95%CI 1.21 to 1.42), vitamin B1 and B12 (RR 1.55, 95%CI 1.33 to 1.80), and no treatment (RR 1.56, 95%CI 1.31 to 1.85), and that the combination of manual acupuncture and mecobalamin had better effect compared with mecobalamin alone on global symptom improvement (RR 1.56, 95%CI 1.28 to 1.90). Adverse events were not reported in any trials. The asymmetric funnel plot suggested publication bias.

CONCLUSIONS

Despite the number of trials of manual acupuncture for DPN and their uniformly positive results, no clinically relevant conclusions can be drawn from this review due to the trials' high risks of bias and the possibility of publication bias. Clearly defined and internationally acknowledged outcome measures are required for future study. There remains an urgent need for training Chinese researchers in conducting unbiased trials as well as prospectively registering all initiated Chinese trials to avoid publication bias.

Diabetic neuropathy part 1: overview and symmetric phenotypes

Diabetes is the most common cause of neuropathy in United States and neuropathies are the most common complication of diabetes mellitus, affecting up to 50% of patients with type 1 and type 2 diabetes mellitus. Symptoms usually include numbness, tingling, pain, and weakness. Dizziness with postural changes can be seen with autonomic neuropathy. Metabolic, vascular, and immune theories have been proposed for the pathogenesis of diabetic neuropathy. Axonal damage and segmental demyelination can be seen with diabetic neuropathies. Management of diabetic neuropathy should begin at the initial diagnosis of diabetes and mainly requires tight and stable glycemic control.

Vitamin B for treating peripheral neuropathy

BACKGROUND

Vitamin B is frequently used for treating peripheral neuropathy but its efficacy is not clear.

OBJECTIVES

The objective of this review was to assess the effects of vitamin B for treating generalised peripheral neuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Trials Register (searched August 2005), MEDLINE (January 1966 to September 2005), EMBASE (January 1980 to September 2005), Philippine databases (searched September 2005) and reference lists of articles. We also contacted manufacturers and researchers in the field.

SELECTION CRITERIA

Randomised and quasi-randomised trials where vitamin B was compared with placebo or another treatment in generalised peripheral neuropathy.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. We contacted study authors for additional information.

MAIN RESULTS

Thirteen studies involving 741 participants with alcoholic or diabetic neuropathy were included. In the comparison of vitamin B with placebo, two small trials showed no significant short-term benefit in pain intensity while one of the trials showed a small significant benefit in vibration detection from oral benfotiamine, a derivative of thiamine. In the larger of two trials comparing different doses of vitamin B complex, there was some evidence that higher doses resulted in a significant short-term reduction in pain and improvement in paraesthesiae, in a composite outcome combining pain, temperature and vibration, and in a composite outcome combining pain, numbness and paraesthesiae. There was some evidence that vitamin B is less efficacious than alpha-lipoic acid, cilostazol or cytidine triphosphate in the short-term improvement of clinical and nerve conduction study outcomes but the trials were small. There were few minor adverse effects reported.

AUTHORS' CONCLUSIONS

There are only limited data in randomised trials testing the efficacy of vitamin B for treating peripheral neuropathy and the evidence is insufficient to determine whether vitamin B is beneficial or harmful. One small trial in alcoholic peripheral neuropathy reported slightly greater improvement in vibration perception threshold with oral benfotiamine for eight weeks than placebo. In another small study, a higher dose of oral vitamin B complex for four weeks was more efficacious than a lower dose in reducing symptoms and signs. Vitamin B administered by various routes for two to eight weeks was less efficacious than alpha-lipoic acid, cilostazol or cytidine triphosphate in short-term improvement of clinical and nerve conduction study outcomes. Vitamin B is generally well-tolerated.

PTEN hamartomatous tumor syndromes (PHTS): rare syndromes with great relevance to common cancers and targeted drug development

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a tumor suppressor gene located on chromosome 10q22-23 that negatively regulates the pro-survival PI3K/Akt/mTOR pathway by functioning as a lipid phosphatase. Signaling through this pathway promotes cellular transformation and survival as well as resistance to chemotherapy and radiation. Loss of PTEN function is commonly observed in human cancers through somatic mutation, hypermethylation, and/or enhanced degradation. PTEN hamartomatous tumor syndromes (PHTS) are a collection of rare clinical syndromes marked by germline PTEN loss. Compared to the general population, PHTS patients have an increased risk of developing certain cancers and can develop benign tumors in virtually any organ. These patients provide a unique opportunity to examine the role of PTEN in human tumorigenesis, as well as study genotype-phenotype relationships. Because these patients are at higher risk of developing malignancies and have no established medical therapies, early screening, surveillance, and preventive care are important issues. Inhibitors of the PI3K/Akt/mTOR pathway that are being developed as cancer therapeutics could provide new therapeutic options for these rare patients, and could be credentialed as pathway inhibitors prior to testing in the general oncology population.

A sensitive assay of red blood cell sorbitol level by high performance liquid chromatography: potential for diagnostic evaluation of diabetes

BACKGROUND

The level of sorbitol within erythrocyte or other tissue is increased during diabetic complications such as neuropathy, retinopathy, and nephropathy and is thus considered as an indicator for the diagnosis and monitoring the diabetic status. A highly sensitive method of estimation of RBC sorbitol may be very useful in determining the state of diabetes. In this study a high performance liquid chromatography method was developed to analyze RBC sorbitol level.

METHOD

Benzoylation was used for the precolumn derivatization of RBC polyol prior to analyze by HPLC using C-18 reversed phase column and UV detector.

RESULTS

The sensitivity was 5 ng/ml using standard sorbitol. The linearity was highly satisfactory up to 2.5 mug/ml which was adequate to measure RBC sorbitol in both diabetic and normal subjects. The values were significantly higher for the diabetic patient compared to normal. Within-run assay CVs were <10% and <14% for between-run.

CONCLUSION

This method could be useful in estimating RBC sorbitol content for the clinical evaluation of diabetic patients.

Diabetic neuropathy: pathogenesis and therapy

Diabetic neuropathies are complex, heterogeneous disorders that encompass a wide range of abnormalities affecting both peripheral and autonomic nervous systems, causing considerable morbidity and mortality. Treatment should be based upon the underlying etiology and not symptoms alone, although symptomatic therapy is needed. Neuropathies may be focal or diffuse, proximal or distal, and involve somatic and autonomic nerves. Focal syndromes are classified as (1) entrapment syndromes or (2) mononeuropathies. Entrapment syndromes are treated by means of relieving compression within confined spaces. Mononeuropathies are due to a vascular insult and resolve spontaneously. They are best treated by supportive therapy. Proximal neuropathies are usually due to an inflammatory, vasculitic, or autoimmune condition and are best treated with specific therapies for the underlying disorder based on biopsy findings. Therapies for distal polyneuropathies include metabolic treatments (e.g., aldose reductase inhibitors, aminoguanidine, gamma-linolenic acid), autoimmune therapies, and nerve growth factors. No definitive treatment is available for painful diabetic neuropathy. Several medications have been used, among them tricyclic antidepressants, antiepileptic drugs, phenothiazines, calcitonin, local anesthetics, nonsteroidal anti-inflammatory drugs, and dextromethorphan. Nonpharmacologic therapies include surgical sympathectomy, spinal cord blockade, electrical spinal cord stimulation, and prostaglandin.

Dietary factors in human colorectal cancer

Colorectal cancer is a significant cause of mortality in Western societies. The progression of the disease from normal colonic epithelium to the acquisition of the malignant phenotype is accompanied by numerous genetic and epigenetic alterations. Compelling experimental and epidemiological evidence indicates that diet and nutrition are key factors in the modulation of colorectal cancer. A salient case in point is the recent observation that a dietary regimen based on a Western-style diet provokes in the rodent colon the appearance of preneoplastic lesions in the absence of any genotoxic insult. This review mainly describes dietary factors that inhibit the development and progression of colorectal cancer. Much is unknown about the precise mechanisms of action of chemically disparate nutrients and how they interfere with the development and progression of this disease. Current knowledge about this important issue is summarized. We believe that continuing scrutiny and precise assessment of the benefits (and potential risks) of nutrients in the treatment and prevention of colorectal cancer will prove significant to controlling this devastating disease.

Dietary myoinositol results in lower urine glucose and in lower postprandial plasma glucose in obese insulin resistant rhesus monkeys

In a previous study, D-chiroinositol added to a meal (0.5 g/kg) resulted in significantly lower postprandial plasma glucose concentrations without an increase in insulin concentrations in obese insulin-resistant monkeys. The present report describes the effects of another isomer of inositol, myoinositol, on postprandial plasma glucose and insulin concentrations and on urine glucose concentrations in 6 similarly insulin-resistant monkeys. The three 5 day study periods included a control period (liquid diet ad libitum) and 2 experimental periods (liquid diet ad libitum with either 1.5 g/kg/day myoinositol or D-chiroinositol added). Twenty-four hour urine samples were collected during each 5 day period. On the sixth day of each period the monkeys were anesthetized 110 min after completing either the control meal (15 ml/kg) or the experimental meals (1.5 g/kg myoinositol or D-chiroinositol) and plasma samples were obtained at 120, 150, 180, 210, 240, 270 and 300 min. The plasma glucose concentration was lower after the meal with myoinositol compared to the control meal at 120, 150 and 180 min (p's < 0.05). The plasma insulin concentration was lower after the meal with myoinositol compared to the control meal at 150 and 180 min (p's < 0.05). In addition, 24 hour urine glucose concentrations were lower during the myoinositol diet compared to the control diet (p < 0.001). The plasma glucose concentration was lower after the meal with D-chiroinositol compared to the control meal at 150, 240, 270 and 300 min (p's < or = 0.05). In obese insulin-resistant monkeys, myoinositol added to the diet lowers urine glucose concentrations and both myoinositol and D-chiroinositol added to a meal lower postprandial plasma glucose concentrations without increasing postprandial insulin concentrations. Therefore, myoinositol, like D-chiroinositol, may be a useful agent for reducing meal-induced hyperglycemia without inducing hyperinsulinemia in insulin-resistant subjects.

Chalcones, myo-inositol and other novel inhibitors of pulmonary carcinogenesis

The objective of the studies reported here has been to find novel chemopreventive agents effective against carcinogenesis of the lung. In particular, identification of suppressing agents, i.e., compounds preventing the evolution of the neoplastic process, has been sought. For this purpose, inhibition of pulmonary neoplasia in female A/J mice given the test agent starting one week after the last administration of three doses of benzo[a]pyrene has been employed as the experimental model. Under these conditions, chalcone, 4'-methoxychalcone,myo-inositol, dexamethasone, and "terpeneless" orange oil added to the diet suppressed pulmonary adenoma formation. Chalcone and 4'-methoxychalcone are open chain flavonoids, neither of these compounds occurs naturally, and their mechanism of action is not known. myo-Inositol is a naturally occurring compound of particular interest because of its exceedingly low toxicity. Dexamethasone is a potent glucocorticoid. Amongst its biological properties is the capacity to induce maturation of Type 2 alveolar cells and to stimulate production of surfactant by these cells. "Terpeneless" orange oil is a fraction of orange oil consisting predominantly of compounds with carbonyl or hydroxyl groups. The constituent or constituents responsible for the inhibitory effects observed is not known. The above studies are in an early phase of development and their ramifications remain to be determined.

Ziskind-Somerfeld Research Award 1993. Biochemical, behavioral, and clinical studies of the role of inositol in lithium treatment and depression

Lithium (Li) reduces brain inositol levels by inhibiting the enzyme inositol monophosphatase. The enzyme inositol-1-phosphatase was measured in human red blood cells of controls, Li-free bipolar patients, and Li-treated bipolar patients and was found to be reduced by 80% in Li-treated bipolars, thus supporting the concept that chronic Li at therapeutic concentrations inhibits this enzyme. Two behaviors in rats caused by Li, reduction of rearing, and Li-pilocarpine seizures, are reversed by intracerebroventricular replenishment of inositol. The reversal is stereospecific to the naturally occurring myo-inositol; whereas the stereoisomer L-chiro-inositol is ineffective. The reversal is dose-dependent, requiring a dose consistent with known quantities of brain inositol depletion; and is time-dependent, as inositol must be given 1-8 h before stimulation. High-dose peripheral inositol also reverses the limbic seizures induced by Li-pilocarpine, and using gas chromatography was shown to increase brain inositol levels that had been reduced by Li treatment. Low-dose inositol could be shown to reverse a peripheral Li-induced side effect, polyuria/polydipsia, in rats and in patients treated with Li. A higher dose of inositol markedly reduced Hamilton Depression Ratings in 9 of 11 unipolar major depressive disorder patients previously unresponsive to tricyclics, in an open design, but had no effect on chronic schizophrenics in a controlled double-blind randomized crossover trial. A new inositol monophosphatase inhibitor, a fungal product originally discovered as a complement inhibitor, was found to act like Li and lower the seizure threshold for subconvulsant doses of pilocarpine. These data suggest that inositol monophosphatase inhibition is a key mechanism of Li's therapeutic action and that design of new inositol monophosphatase inhibitors may be a practical strategy to create new compounds with Li-like therapeutic effects.

[Role of polyols in the development of diabetic complications. Value of aldose-reductase inhibitors]

The evidence of sorbitol excess in the crystalline lens of alloxan-diabetic rats has led to anticipate the role of the enzyme aldose-reductase in the pathogenesis of the diabetic cataract. In addition, a number of experimental works have more recently shown the involvement of myoinositol deficiency, which probably results from the sorbitol accumulation. These metabolic pathways are most likely implicated in the pathogenesis of diabetic neuropathy and perhaps additionally in that of microangiopathy. The synthesis of several aldose-reductase inhibitors (AR inhibitors) confirmed experimentally these hypothesis. By reducing the activity of the enzyme aldose-reductase, these substances suppress the adverse metabolic consequences of polyol accumulation, myositol deficiency and dysfunction of the Na+/K+ ATPase dependent sodium activity. Although different experimentations showed that the AR inhibitors could prevent in animals the development of experimental cataract as well as the early functional or later anatomic abnormalities of the diabetic retinopathy and nephropathy, the clinical trials did not clearly support these experimental results in humans. On the other hand, the AR inhibitors were proved to exhibit some efficacy in the early stage of diabetic neuropathy and in incipient nephropathy where they delay the development of albustix positive proteinuria. However, the benefit of an early treatment with AR inhibitors should be confirmed by long term prospective studies, which could also assess the safety of these drugs in chronic administration.

Diabetic autonomic neuropathy

One of the earliest manifestations of diabetic neuropathy is denervation of the cardiovascular system; loss of heart rate variability may have a prevalence as high as 21.5% in diabetic patients, and declines at 1 beat/min/year, which is 3 times faster than in normal subjects. The cause of this neuropathy is unknown: attempts at decreasing the excess quantities of sorbitol, glucose and fructose in nerve tissue have lead to little functional improvement in man. Nerve ischaemia and immunological damage have stimulated increased interest lately, the latter particularly because of the structural homology of nerve growth factor and insulin. Symptoms from autonomic neuropathy are rare. When present they may well be intermittent, but never remit; they rarely progress or become disabling. One uncommon consequente of loss of sympathetic vascular tone is postural hypotension. This may result from failure of splanchnic vasoconstriction on standing. Food and insulin can greatly exacerbate the postural blood pressure fall. Reduced vascular tone in the neuropathic foot leads to increased arterio-venous shunt flow. The local reflex control of this shunt flow is also abnormal: paradoxical vasoconstriction occurs in response to local skin heating and postural reflexes are reduced. This high shunt flow together with its abnormal vascular control may be important in the pathogenesis of neuroarthropathy and foot ulceration. The prognosis of patients with autonomic neuropathy is better than previously reported. Abnormal heart rate variability alone is of no prognostic value. The presence of symptoms, in particular postural hypotension, significantly reduces survival. The majority of deaths however, result from concurrent renal disease and macrovessel atheroma.

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.

The effect of aldose reductase inhibition on erythrocyte polyols and galactitol accumulation in diabetic patients

Erythrocyte sorbitol level has previously been used as a measure of the efficacy of aldose reductase inhibitors, but its value is limited by fluctuations related to variations in blood glucose concentration. The aim of the study was to compare sorbitol content with the ability to accumulate galactitol during ex vivo incubation with galactose, of erythrocytes taken from diabetic patients following administration of a single 600 mg dose of the aldose reductase inhibitor, ponalrestat. Twelve patients were studied in a placebo-controlled crossover trial. Blood glucose levels were not statistically different during the placebo and ponalrestat treatment periods except at 1 h after the dose was taken (10.6 +/- 6.7 vs 7.7 +/- 4.6 mmol l-1 (+/- SD), p less than 0.05). Ponalrestat reduced erythrocyte sorbitol concentrations compared with placebo at 3, 5 and 7 h (0.82 +/- 0.36, 0.69 +/- 0.23, and 0.83 +/- 0.35 mg l-1 vs 1.79 +/- 0.67, 1.68 +/- 0.65, and 1.57 +/- 0.59 mg l-1 respectively, p less than 0.005) and 24 h post-dose (1.57 + 0.45 vs 2.01 + 0.73 mg l-1, p less than 0.05). Ponalrestat also reduced erythrocyte galactitol accumulation at 3, 5 and 24 h post-dose from 5.53 +/- 2.41, 5.43 +/- 1.89, and 5.42 +/- 1.96 mg l-1 2-h-1 to 1.47 +/- 0.30, 1.76 +/- 0.41, and 4.12 +/- 0.72 mg l-1 2-h-1 respectively, p less than 0.01. Galactitol accumulation rate appeared to be a less variable parameter than erythrocyte sorbitol and was not influenced by fluctuations in blood glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve glucose, fructose, sorbitol, myo-inositol, and fiber degeneration and regeneration in diabetic neuropathy

We measured the alcohol sugars in sural nerves from 11 controls, 21 conventionally treated patients with diabetes and neuropathy, and 4 diabetics without neuropathy. The results were related to metabolic control and to clinical, neuropathological, and morphometric abnormalities in the nerves. The mean endoneurial glucose, fructose, and sorbitol values were higher in diabetic patients than in controls. Linear regression analysis revealed that nerve sorbitol content in the diabetics was inversely related to the number of myelinated fibers (P = 0.003). Mean nerve levels of myo-inositol were not decreased in the diabetic patients, with or without neuropathy, and were not associated with any of the neuropathological end points of diabetes. Our results indicate that myo-inositol deficiency is not part of the pathogenesis of human diabetic neuropathy, as had been hypothesized. Other accumulated alcohol sugars, however, were increased in diabetes and were associated with the severity of neuropathy. On repeat biopsy, six diabetics, treated for a year with the aldose reductase inhibitor sorbinil, had decreased endoneurial levels of sorbitol (P less than 0.01) and fructose (0.05 less than P less than 0.1), but unchanged levels of myo-inositol.

Inositol supplementation in respiratory distress syndrome: relationship between serum concentration, renal excretion, and lung effluent phospholipids

Inositol or placebo was given to 48 small preterm infants with respiratory distress syndrome (mean birth weight 1365 g, gestational age 30.1 weeks) between 48 hours and 10 days of age. The dose of inositol, 40 mg/kg every 6 hours, was at least as high as amounts received in full preterm human milk feedings. Serum inositol concentration increased between days 2 and 3 from a mean of 566 mumol/L to 823 mumol/L in the infants given supplement and fell from 451 mumol/L to 292 mumol/L in the controls. On day 16, serum inositol values remained higher in the infants given supplement than in those given placebo (mean 334 mumol/L vs 146 mumol/L, P = 0.014). The infants who developed bronchopulmonary dysplasia had significantly higher renal inositol clearance, lower inositol intake, and lower serum inositol concentrations. Inositol supplementation increased the saturated phosphatidylcholine/sphingomyelin ratio in tracheal aspirates. According to these results, supplementation with inositol in preterm infants leads to a rise in serum inositol concentration and improvement in the surfactant phospholipids. Inositol deserves further study as a dietary supplement for immature preterm infants who do not receive full human milk feeds.

Sorbitol, phosphoinositides, and sodium-potassium-ATPase in the pathogenesis of diabetic complications

During the past decade, our appreciation of the original experiments with myo-inositol supplementation in diabetic rats has greatly expanded. The effects of myo-inositol on nerve conduction are now explained by concepts that were largely unappreciated in 1976, including the fundamental role of phosphoinositide metabolism in cell regulation and the importance of the activity of sodium-potassium-ATPase in nerve conduction. Aldose reductase inhibitors firmly link defects in myo-inositol metabolism to activation of the polyol pathway in diabetes; the resulting "sorbitol-myo-inositol hypothesis" has been extended from its application to the lenses and peripheral nerves to most of the tissues involved with diabetic complications. These biochemical mechanisms provide a new framework within which to explore the complex interactions between hyperglycemia and the vascular, genetic, and environmental variables in the pathogenesis of diabetic complications. It is anticipated that these endeavors will result in the appearance of new classes of therapeutic agents, the first of which--the aldose reductase inhibitors--has emerged from the laboratory and is now undergoing extensive clinical testing. These efforts are very likely to result in the appearance of new treatment methods that may dramatically lighten the burden of chronic complications in patients with diabetes.

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.

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.

myo-Inositol and sorbitol in erythrocytes from diabetic patients before and after sorbinil treatment

Erythrocytes from diabetic patients before and after treatment with the aldose reductase inhibitor, sorbinil, were analyzed by a capillary gas chromatographic method for sorbitol and myo-inositol. The mean erythrocyte sorbitol level in the diabetic patients was significantly higher than in the control subjects (13.1 +/- 0.9 and 5.2 +/- 0.3 nmol/ml erythrocytes, respectively, mean +/- SEM, p less than 0.001). The mean erythrocyte myo-inositol level in diabetic patients was not different from that in control subjects (43.2 +/- 2.9 and 40.5 +/- 1.9 nmol/ml erythrocytes, respectively). Sorbinil treatment reduced the elevated sorbitol levels in the diabetic patients to normal or slightly below normal, but did not affect the erythrocyte myo-inositol concentration. It is concluded that the erythrocyte is not a suitable model to monitor a possible effect of sorbinil on myo-inositol concentration in less accessible tissues.

Treatment of painful diabetic polyneuropathy with mixed gangliosides

We studied 18 patients with painful diabetic neuropathy in a double-blind study of 40 mg per day of mixed gangliosides. Diabetes control was maintained throughout by analysis of serum glucose and glycosylated hemoglobin levels. Median motor and sensory, and peroneal motor conductions we evaluated in placebo and treated groups before and after a treatment period of three months. All conductions were performed by one technician on a TECA-4 EMG machine with surface temperature controlled at 37 degrees C. There was a definite improvement in nerve conductions in the treated group, particularly noted in the median sensory conductions. We have demonstrated a difference between right and left-sided conductions in the same patients confirming that this illness, at least from an electrophysiological point of view is asymmetric. Clinical improvement was variable but when present was dramatic. Side effects of this drug were minimal. Half of the patient complained of a transient increase in pain during the first two weeks of treatment. No patient stopped the drug because of this complaint. We conclude that in this three-month study mixed gangliosides caused a significant improvement in some nerve conductions without significant side effects. Further studies seem warranted to determine the nature and extent of this effect.

Diabetic neuropathy

Peripheral nerve disorders are important late complications of diabetes mellitus. Polyneuropathy, which may involve varying proportions of sensory, motor, and autonomic fibers, is considered the consequence of metabolic derangements that result from chronic hyperglycemia. Symmetrical proximal motor neuropathy ("diabetic amyotrophy") also may have a metabolic basis. Mononeuropathies in diabetes may have an ischemic or compressive cause. Advances have been made in understanding the biochemical basis for diabetic polyneuropathy. The treatment of symptomatic diabetic neuropathy should be directed toward long-term normalization of blood glucose until more specific therapies become available.