Pathogenesis of diabetic neuropathy: the role of the n-6 essential fatty acids and their eicosanoid derivatives

Supplementation of Dihomo-γ-Linolenic Acid for Pollen-Induced Allergic Symptoms in Healthy Subjects: A Randomized, Double-Blinded, Placebo-Controlled Trial

Dihomo-γ-linolenic acid (DGLA) is an n-6 polyunsaturated fatty acid that has been shown to have anti-inflammatory and anti-allergic effects in mice and cell study. To date, however, no human intervention study has examined the effects of DGLA. Therefore, we investigated the effects of DGLA on pollen-induced allergic symptoms in healthy adults. We performed a randomized, double-blind, placebo-controlled, parallel-group study comprising healthy Japanese men and women. Each subject received four 250 mg capsules providing 314 mg DGLA/day (DGLA group, n = 18) or olive oil (placebo group, n = 15) for 15 weeks. The primary outcomes, classification of the severity of allergic rhinitis symptoms (CSARS), and the Japanese Rhino-conjunctivitis Quality of Life Questionnaire (JRQLQ) served as symptom scores during the pollen season. In the DGLA group, the cedar pollen associated symptoms of sneezing and a blocked nose in the CSARS were significantly lower than those in the placebo group (p < 0.05, p < 0.01, respectively). Significant trends were observed the symptoms of runny nose in the CSARS and total symptom score (TSS) in the JRQLQ for cedar pollen (p < 0.1). To our knowledge, this is the first study to report the effects of DGLA in humans, and the results suggest that DGLA is effective in reducing allergic symptoms caused by pollen.

Canine Diabetes Mellitus Associated Ocular Disease

Diabetes mellitus (DM) is a commonly encountered disease in companion animal veterinary practice. Ocular complications in dogs with DM are thought to be common but there are no reports of the overall incidence of DM-associated ocular disease. Some complications, such as cataracts and ocular surface disease, can lead to vision loss and significant morbidity among DM patients, therefore early recognition and intervention are essential for successful outcomes. The purpose of this article is to provide a review of several currently known or suspected ocular diseases associated with DM.

Protective effect of Umbelliferone on membranous fatty acid composition in streptozotocin-induced diabetic rats

Umbelliferone (UMB), a natural antioxidant, is benzopyrone in nature, and it is present in the fruits of golden apple and bitter orange. Earlier we evaluated and reported the effect of Umbelliferone on antidiabetic, antioxidant and antihyperlipidemic properties, and this study was designed to evaluate the effect of Umbelliferone on membrane fatty acid composition and histopathology of liver and kidney of control and streptozotocin (STZ) diabetic rats. Male albino Wistar rats (180-200 g) were made diabetic by an intraperitonial administration of STZ (40 mg/kg). The control and diabetic rats were treated with Umbelliferone and glibenclamide dissolved in 10% dimethyl sulfoxide for 45 days. Diabetic rats had decreased insulin and increased glucose, and increased levels of thiobarbituric acid reactive substances, lipid hydroperoxides and conjugated dienes. The levels of palmitic, stearic and oleic acids increased and the levels of linolenic and arachidonic acids decreased in diabetic rats as compared with control rats. Thus, the saturated fatty acids and monounsaturated fatty acids increased and the polyunsaturated fatty acids decreased in diabetic rats. Diabetic rats had decreased liver weight and increased activities of alanine transaminase and aspartate transaminase; increased kidney weight and urine albumin, and decreased levels of urea, uric acid and creatinine in the urine. Histopathological studies of liver and kidney in diabetic rats showed fatty changes surrounding portal triad; enlargement of lining cells of tubules, fatty infiltration, large area of hemorrhage and lymphocyte infiltration. Treatment with Umbelliferone and glibenclamide reversed these changes to near normalcy. Our results showed that Umbelliferone has a protective effect on membrane fatty acid composition of liver and kidney as supported by antioxidant and antihyperlipidemic effects of Umbelliferone reported earlier as evidenced by improved histopathological changes, hepatic and nephritic markers, indicating recovery from the risk of diabetic complications.

Relationships between Heart Rate Variability and Urinary Albumin Excretion in Patients with Type 2 Diabetes

BACKGROUND

Although in type 1 diabetes the close association between heart rate variability and urinary albumin excretion (UAE) is recognized even in patients with normoalbuminuria, this association has not yet been fully established in patients with type 2 diabetes. Therefore, we investigated the association in patients with type 2 diabetes.

PATIENTS AND METHODS

All the hospital's 185 inpatients with type 2 diabetes were prospectively enrolled. Heart rate variability was evaluated by coefficients of variance of RR intervals (CVRR).

RESULTS

The mean age, duration of diabetes, and hemoglobin A1C of the patients were 59.7+/-9.9 years, 10.4+/-7.8 years, and 9.7+/-2.3%, respectively. An analysis of the patients showed a significant negative correlation between CVRR and log10-transformed (log) UAE (R=-0.3340, P <0.0001). CVRR showed a significant negative correlation with age, duration of diabetes, hemoglobin AIC, systolic blood pressure, diastolic blood pressure, and triglyceride level. Log UAE showed a significant positive correlation with body mass index, hemoglobin A1C, systolic blood pressure, diastolic blood pressure, total cholesterol, and triglyceride level. In the macroalbuminuric group (UAE above 300 mg/g creatinine; n=57), although CVRR showed a significant negative correlation with log UAE (R=-0.3571, P= 0.0064), but in normoalbuminuric (UAE below 30 mg/g Cr; n=79) and in microalbuminuric groups (30 to 300 mg/g Cr; n = 49), CVRR and log UAE showed no correlation.

CONCLUSIONS

Our data suggest that in type 2 diabetes, the association between CVRR and UAE is significant only in patients with macroalbuminuria.

Pain in diabetic neuropathy case study: whole patient management

Painful diabetic peripheral neuropathy (DPN) is described as a superficial burning pain associated with other positive and/or negative sensory systems affecting the feet and lower extremities. It is one of the most commonly encountered neuropathic pain syndromes in clinical practice. Presentation may be complicated by multiple symptoms, including allodynia, hyperalgesia, other less well characterized dysesthesias, and serious disruption of social functioning and mood. Peripheral nerve function may deteriorate, which can account for patient reports of diminution of pain after several years of follow-up. Although current understanding holds that the pathogenesis of DPN is multifactorial in nature, long-term studies have shown that rigorous glycemic control is the most relevant factor in clinical intervention and can delay the onset and slow the progression of neuropathy. In addition to glycemic control, other treatment approaches must be examined in order to restore quality of life for patients experiencing painful DPN. Differential diagnosis is required to isolate DPN from other unexplained chronic pain. Neurologic testing in painful DPN is an area of active research and is used to assess the neurologic pathways giving rise to the pain, the degree of neural damage and the degree of subclinical damage. Current treatment options for DPN include mainly antidepressants and anticonvulsants, with other agents such as tramadol, dextromethorphan and memantine being employed or studied. This review article includes a case study of a patient with painful DPN to demonstrate the current management strategies for this neuropathic pain syndrome.

Acetyl-L-carnitine (levacecarnine) in the treatment of diabetic neuropathy. A long-term, randomised, double-blind, placebo-controlled study

OBJECTIVE

To assess the efficacy and tolerability of acetyl-L-carnitine (levacecarnine; LAC) versus placebo in the treatment of diabetic neuropathy, mainly by evaluating the effects of treatment on electrophysiological parameters and pain symptoms.

DESIGN

This was a multicentre (n = 20), randomised, double-blind, placebo-controlled, parallel-group study.

PATIENTS

333 patients meeting clinical and/or neurophysiological criteria for diabetic neuropathy were enrolled.

INTERVENTIONS

Patients were randomised to treatment with LAC or placebo. LAC (or placebo) was started intramuscularly at a dosage of 1000 mg/day for 10 days and continued orally at a dosage of 2000 mg/day for the remainder of the study (355 days). MAIN OUTCOME PARAMETERS AND RESULTS: The main efficacy parameter was the effect of treatment on 6- and 12-month changes from baseline in nerve conduction velocity (NCV) and amplitude in the sensory (ulnar, sural and median) and motor (median, ulnar and peroneal) nerves. The effect of treatment on pain was also evaluated by means of a visual analogue scale (VAS). Among the 294 patients with impaired electrophysiological parameters at baseline, those treated with LAC showed a statistically significant improvement in mean NCV and amplitude compared with placebo (p < 0.01). The greatest changes in NCV (at 12 months) were observed in the sensory sural nerve (7 m/sec in the LAC group vs +1.0 m/sec in the placebo group), sensory ulnar nerve (+2.9 vs +0.1 m/sec, respectively) and motor peroneal nerve (+2.7 vs -0.2 m/sec), whereas the greatest changes in amplitude were recorded in the motor peroneal nerve (+2.2 vs +0.1 mV). After 12 months of treatment, mean VAS scores for pain were significantly reduced from baseline by 39% in LAC-treated patients (p < 0.0 vs baseline) compared with 8% in placebo recipients. LAC was well tolerated over the study period.

CONCLUSIONS

LAC was effective and well tolerated in improving neurophysiological parameters and in reducing pain over a 1-year period. LAC is, therefore, a promising treatment option in patients with diabetic neuropathy.

Electrophysiologic measures of diabetic neuropathy: mechanism and meaning

Whole nerve electrophysiologic procedures afford a battery of measures that can provide a noninvasive and objective index of the onset and progression of diabetic polyneuropathy (DPN). Advances in physiologic procedures, digital hardware, and mathematical models have allowed assessment of activity in slower conducting fibers, as well as measures that reflect changes in refractory periods and threshold excitability. These expanded options can augment standard measures of maximal conduction velocity and compound amplitude and greatly enhance the sensitivity of whole nerve measure to both structural (e.g. demyelination) and "nonstructural" (e.g. redistribution of ion channels) deficits associated with DPN. The mechanisms underlying the physiologic events in DPN are multifactorial and their sequence in complex, with different mechanisms contributing to change at overlapping, but distinct points in the progression. Factors influencing early change in velocity may differ from those contributing to chronic deficits and these mechanisms may also differ in their response to various putative therapies. This review attempts to summarize the pattern of whole nerve electrophysiologic change associated with DPN, outlines the strengths and limitations of the various measures that are feasible, and discusses the specific impact of know pathophysiologic mechanisms on these end points.

New developments in the diagnosis of diabetic neuropathy

The development of new treatments to slow or arrest the progression of diabetic polyneuropathy (DPN) has increased the importance of the early and accurate identification of this complication. It is likely that effective intervention will be possible only during the subclinical or early phase of dysfunction. Accurate diagnosis of DPN is a formidable task because of the diversity of presentations, involvement of different nerve fiber types, and the common dissociation of symptoms from objective measures of neural function. Several diagnostic tools are available or in development, each with strengths and limitations. Electrophysiology is a sensitive, objective, and targeted measure of DPN, but it reflects, almost exclusively, the activity of large-caliber, myelinated axons. Newly refined skin-punch biopsy procedures use morphometric and immunohistochemical methods to examine thinly myelinated and unmyelinated nerve fibers. The integrity, density, and distribution of these fibers may provide a sensitive index of small-fiber distal axonopathy. Improvements in quantitative sensory testing include better control of stimulation characteristics and the use of computer-assisted testing algorithms (e.g., CASE IV), as well as the ability to examine a distal to proximal gradient of sensation (Physitemp NTE-2a). Composite scales, which combine the assessment of signs, symptoms, electrophysiology, and specific quantitative sensory measures, have also been proposed and, in some cases, validated. The existing diagnostic tools and newly emerging methods provide a battery of tests that can be used to assess multiple aspects of neural function and increase sensitivity to detect the onset and progression of DPN.

Restoration of nitric oxide production by aldose reductase inhibitor in human endothelial cells cultured in high-glucose medium

The effects of elevated glucose and aldose reductase inhibitor (ARI:ONO-2235) on nitric oxide (NO) production in cultured human umbilical endothelial cells (HUVEC) were evaluated. Aldose reductase and nitric oxide synthase(NOS) share NADPH as an obligate cofactor, therefore it is suggested that the enhanced of glucose flux (27.5 mM) by aldose reductase inhibited NO production by blunting NOS activity. However, the addition of ONO-2235 (100 microM) prevented the inhibition of [NO2-] production. Since ARI decreases glucose-mediated inhibition of NO production in HUVEC. this agent might ameliorate endothelial function associated with diabetes.

Long-term effects of eicosapentaenoic acid on diabetic peripheral neuropathy and serum lipids in patients with type II diabetes mellitus

The present study was undertaken to investigate the efficacy of a new, highly purified (purity greater than 91%), ethyl esterification product from natural eicosapentaenoic acid (EPA-E, C20:5 omega 3) in patients with type II diabetes mellitus (NIDDM). Hemodynamic changes were assessed at the level of the dorsalis pedis artery using an ultrasonic color Doppler duplex system before and after oral administration of EPA-E at a dose of 1800 mg/day for 48 weeks. The cross-sectional area of the dorsalis pedis artery increased significantly from 2.5 +/- 0.2 to 3.9 +/- 0.4 mm2 (48 weeks, mean +/- SE, p < 0.05). Moreover, EPA-E improved the clinical symptom (coldness, numbness) as well as the vibration perception threshold sense of the lower extremities [from 32.1 +/- 8.5 to 16.1 +/- 4.8 (48 weeks) microns]. A significant decrease of serum triglycerides was also noted by EPA-E administration. Furthermore, significant decrease of the excretion of albumin in urine [from 24.4 +/- 3.3 to 13.9 +/- 1.8 (48 weeks) mg/g.Cr, p < 0.05]. The results of this study suggest that EPA-E has significant beneficial effects on diabetic neuropathy and serum lipids as well as other diabetic complications such as nephropathy and macroangiopathy.

Neurotropin prevents neurophysiological abnormalities and ADP-induced hyperaggregability in rats with streptozotocin-induced diabetes

Neurotropin, a non-proteinaceous extract from the inflamed dermis of rabbits inoculated with vaccinia virus, was administered for 8 weeks to rats with streptozotocin-induced diabetes. The physiological and biochemical changes of the nerves were studied as well as ADP-induced platelet aggregation. Neurotropin improved the caudal motor nerve conduction velocity, R-R variability, sciatic nerve blood flow, and platelet hyperaggregability in diabetic rats, despite having no effect on sorbitol and fructose accumulation or myoinositol depletion in the sciatic nerve. The correlation between nerve conduction velocity, R-R variability, nerve blood flow, and platelet aggregation were significant between each two parameters (p < 0.0001). Thus, the mechanism of action of neurotropin differed from that of aldose reductase inhibitors. These findings suggest that vascular factors may play an important role in the development of diabetic neuropathy, and that neurotropin may be useful for the treatment of this condition.

The estrogen connection: the etiological relationship between diabetes, cancer, rheumatoid arthritis and psychiatric disorders

For some considerable time, there has been a growing awareness that defective essential fatty acid metabolism plays a causal role in the pathogenesis of both schizophrenia and non-insulin-dependent diabetes mellitus (NIDDM) but the influence of defective essential fatty acid metabolism in the pathogenesis of rheumatoid arthritis and cancer is less well appreciated. An EFA deficiency, or defective EFA metabolism, negatively influences prostaglandin synthesis and glucose regulation and transport. Moreover, defective EFA metabolism negatively influences estrogen availability which contributes to the observed gender bias some of these illnesses manifest. While fluctuations of estrogen are known to contribute to the pathogenesis of these conditions, so also do fluctuations of IGF-II and there is some suggestion that IGF-II and insulin may well be inversely regulated. In addition, insulin-dependent diabetes mellitus (IDDM), rheumatoid arthritis, and schizophrenia are thought to be autoimmune disorders, while cancer is associated with immune system failure. Consequently, this paper aims to examine the pathophysiological similarities and differences between mental illness, diabetes, rheumatoid arthritis and cancer in respect of which the causal relationship that obtains between essential fatty acids, estrogen, IGF-II, glucose regulation and autoimmunity will be addressed.

Prevention of abnormalities in motor nerve conduction and nerve blood-flow by a prostacyclin analog, beraprost sodium, in streptozotocin-induced diabetic rats

The effects of the prostacyclin analog beraprost sodium on motor nerve function and nerve blood-flow were examined in streptozotocin-induced diabetic rats. Oral administration of beraprost sodium 0.1 mg/kg/day for 8 wks significantly (P < 0.001) improved caudal motor nerve conduction velocity and sciatic nerve blood-flow, both of which are impaired in diabetic rats. Beraprost sodium did not affect glucose, sorbitol, or fructose levels in the sciatic nerve. However, a decreased content of cyclic AMP in the sciatic nerve and higher level of thromboxane B2 in the thoracic aorta of diabetic rats, as compared with those in normal rats, were reversed by the treatment with beraprost sodium (P < 0.01). Results suggest that beraprost sodium may have value in treating diabetic neuropathy, mainly by improving endoneurial blood-flow.

Long-term complications of diabetes mellitus, Part I: Retinopathy, nephropathy, neuropathy

Diabetic retinopathy, nephropathy, and neuropathy occur infrequently in small animals, but are capable of causing significant disease. The clinical and histopathologic findings seen with these late complications of diabetes are discussed. The pathogenesis of these disorders is most likely multifactorial; metabolic alterations secondary to the hyperglycemic state, and microvascular changes seen with diabetes have both been implicated. Current treatment consists of aggressive control of the hyperglycemia, as research continues into the pathology of the late complications in attempts to find a definitive therapy.

Effect of a potent new aldose reductase inhibitor, (5-(3-thienyltetrazol-1-yl)acetic acid (TAT), on diabetic neuropathy in rats

(5-(3-Thienyl)tetrazol-1-yl)acetic acid (TAT), a novel potent aldose reductase inhibitor, was administered for 4 weeks to rats with streptozotocin-induced diabetes. Physiological and biochemical studies were subsequently conducted on rat nerve tissue and erythrocyte sorbitol content was estimated. Sciatic nerve blood flow (SNBF) was markedly lower (about 43.4%) in untreated diabetic (DC) rats than in non-diabetic controls (NC). A significant delay in caudal motor nerve conduction velocity (MNCV) and significantly higher glucose, sorbitol and fructose values were observed in the sciatic nerve, accompanied by a markedly higher sorbitol concentration in erythrocytes. In contrast, TAT-treated diabetic groups (DT-10, DT-40 and DT-200) had significantly higher SNBF, MNCV and sciatic nerve myo-inositol values and lower sciatic nerve sorbitol and fructose levels and erythrocyte sorbitol concentration than the DC group. There were good correlations between SNBF and MNCV (r = 0.672, P < 0.001) and between SNBF and erythrocyte sorbitol (r = 0.455, P < 0.003). These findings suggest that both vascular and metabolic factors play an important role in diabetic neuropathy and the effect of aldose reductase inhibitors on diabetic neuropathy may be mediated by at least these two factors.

The efficacy of aldose reductase inhibitors in the management of diabetic complications. Comparison with intensive insulin treatment and pancreatic transplantation

Recently, aldose reductase inhibitors (ARIs) have been registered in several countries for the improvement of glycaemic control. However, their efficacy is still controversial. ARIs inhibit the enhanced flux of glucose through the polyol pathway. As such, they can never be more effective than normoglycaemia, and so their potential benefits and limitations should be considered relative to the effects of prolonged euglycaemia. The clinical effects of ARIs can be put into perspective by assessing the effects of improved glycaemic control attained in randomised trials of intensive insulin treatment [such as the Diabetes Control and Complications Trial (DCCT)] and after pancreatic transplantation. Although direct comparison of these 3 interventions is hampered by differences in patient populations, duration and methods of follow-up and in the potency of ARIs, the effects of these 3 metabolic interventions and their course in time appear remarkably similar. For neuropathy, all 3 interventions induce an increase in average motor nerve conduction velocity of approximately 1 m/sec during the first months of treatment. At the same time, improvement of painful symptoms may occur. These changes probably largely represent a metabolic amelioration of the condition of the nerves. Around the second year of treatment with all 3 forms of metabolic improvement, an acceleration of nerve conduction of a similar magnitude occurs, with signs of structural nerve regeneration and some sensory recuperation. Experience with ARIs in nephropathy is still limited, but similar improvements in glomerular filtration rate and, less consistently, in urinary albumin excretion were found during short term normoglycaemia produced by all 3 forms of treatment. Comparison of a small number of studies, however, shows differences between intensive insulin regimens, pancreatic transplantation and ARIs in effects on retinopathy. Retinopathy often temporarily deteriorates in the early phases of improved glycaemic control, but this is not noted with ARIs. New microaneurysm formation was slightly reduced in a single long term study with the ARI sorbinil, but the preventive effects on the overall levels of retinopathy seemed less strong than in normoglycaemia trials of similar duration. However, the pharmacodynamic effects on inhibiting the polyol pathway differ among ARIs, and the half-life of the inhibiting effect of sorbinil may have been too short for a complete reduction of polyol pathway activity. The trials of prolonged intensive insulin therapy and pancreatic transplantation have demonstrated that very strict metabolic control must be maintained continuously for many years before a significant reduction of complications can be demonstrated.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of gamma linolenic acid in the prevention and treatment of diabetic neuropathy

A substantial disturbance of the metabolism of the n-6 essential fatty acids (EFAs) exists in both human and experimental diabetes mellitus. The process of conversion of dietary linoleic acid to gammalinolenic, dihomogammalinolenic and arachidonic acids, and other polyunsaturates is inadequate in diabetic patients. Disturbances of these EFAs and the 1- and 2-series prostaglandins derived from them cause a variety of microvascular, haemorheological, and other abnormalities leading to reduced blood flow and neural hypoxia. This will in turn produce an escalating cycle of further hypoxia through the generation of oxygen-free radicals and aggravation of neural capillary endothelial damage. Endoneurial hypoxia impairs axonal transport, produces demyelination, and reduces neural ATP-ase activity. Furthermore, depletion of polyunsaturated fatty acids derived from n-6 pathway may lead to abnormalities of myelin turnover, membrane-bound proteins (such as enzymes and receptors) and other axonal structural abnormalities. The disorders postulated here may synergistically interact with the metabolic changes described in both the glycosylation and the myoinositol hypotheses and may have important implications in the approach to treat diabetic neuropathy.

Prostacyclin release in experimental diabetes: effects of evening primrose oil

Alterations in release of endothelium-derived vasomotor agents could underlie microvascular and neuropathic complications in diabetes. This study examined release of the potent vasodilator prostacyclin, measured as immunoreactive 6-keto prostaglandin F1 alpha, from rat lung, kidney and peripheral nerve. Tissues were taken from control and streptozotocin-diabetic rats which had been treated for 8 weeks with either evening primrose oil (EPO) or, as a control for lipid intake, coconut oil (CO). Lung and kidney slices were incubated in the presence of acetylcholine (ACh), the calcium ionophore 4-Br-A23187, arachidonic acid (AA) or without agonist (basal). Segments of sciatic nerve, with their epineuria punctured, were incubated with or without 4-Br-A23187. Basal prostacyclin release from the lung was significantly higher in rats treated with EPO irrespective of diabetic state (increased by 60% in controls and by 77% in diabetics). Levels were reduced in CO-diabetics compared to EPO-controls (53% reduction) and CO-controls (30% reduction), although this did not reach statistical significance in the latter. Basal prostacyclin release was also significantly reduced in the kidney from CO-diabetics (40% reduction compared to CO-controls and 56% reduction compared to EPO-controls). In the presence of AA, lung prostacyclin release was significantly lower in CO-diabetic rats compared to all other groups (40% reduction compared to EPO-diabetics and 60% compared to both control groups) but there were no differences in renal release between any group. Prostacyclin release by nerves from CO-diabetic rats was significantly reduced (by 91-93%) compared to all other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of gamma-linolenic acid in diabetic neuropathy

EF4 is an entirely new approach to the management of diabetic neuropathy. EF4 (providing gamma-linolenic acid or gamolenic acid, GLA) has been shown to reverse existing diabetic neuropathy in trials in seven centres. Diabetic animals and humans have a reduced ability to convert dietary linoleic acid to GLA. GLA and its metabolites are required for normal neuronal structure and function and a normal microcirculation. The lack of GLA and its metabolites may play a major role in the development of the neuropathy. EF4 helps to correct the biochemical defects, restores levels of GLA metabolites towards normal and produces highly significant clinical and neurophysiological improvements in diabetic neuropathy.