Therapy for diabetic neuropathy: an overview

The Predictors of Painful Diabetic Neuropathy and Its Effect on Quality of Life

BACKGROUND

Knowing the prevalence and predictors of neuropathic pain and its impacts on the quality of life (QoL) using measurement tools is important for good diabetes management. In Turkish society, neuropathic pain, its predictors and its impact on the quality of life of diabetics are not considered enough.

OBJECTIVES

This study examined the prevalence and predictors of neuropathic pain and its impacts on the quality of life in diabetics in Rize Province, Turkey.

DESIGN

This study was designed as a cross-sectional, correlational study.

SETTING

Data collected through face-to-face interviews. The sample size was determined using the formula [n= N t²pq / d² (N-1) + t²pq].

PARTICIPANT

The sample of the study consisted of 122 people with diabetes who visited the diabetes outpatient clinic of the hospital.

METHODS

A Personal Information Form, Douleur Neuropathique en 4 questions (DN4), and Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) were used to collect data. Pain intensity was measured using Visual Analogue Scale (VAS) RESULTS: The prevalence of the diagnosed painful diabetic polyneuropathy (PDPN) was found to be 22.9%. On the other hand, the prevalence of the undiagnosed PDPN was found to be 44.3% according to DN4 and 27.9% according to LANSS. The VAS pain score was determined as 1.99±1.20 (range: 1-5). In the people with PDPN, nephropathy was seen 4.514 times more frequently according to DN4 and 7.217 times more frequently according to LANSS. Painful diabetic peripheral neuropathy had negative effects on all dimensions of QoL except for social function and mental health (p <0.05).

CONCLUSIONS

It is important for nurses to determine the prevalence and predictive factors of PDPN in their region and to evaluate the effect of pain on the quality of life of diabetics. Nurses should attempt to increase the quality of life of people with diabetes by reducing the predictors affecting pain.

Vibrotactile perception on the sole of the foot in an older group of people with normal glucose tolerance and type 2 diabetes

OBJECTIVES

To evaluate vibrotactile sense in an older group of people with normal glucose tolerance and type 2 diabetes relative to other sensory tests.

METHODS

Vibration perception thresholds on the sole of the foot (Multifrequency vibrametry and Biothesiometer) were compared to the results from evaluation of touch (monofilament), electrophysiology (sural nerve) and thermal sensation (Thermotest®).

RESULTS

Vibration perception and temperature thresholds, as well as sural nerve function, differed between normal glucose tolerance and type 2 diabetes. Measuring vibration perception thresholds at lower frequencies with multifrequency vibrametry versus biothesiometer provided correlations similar to sural nerve amplitude. Temperature thresholds correlated with vibration perception thresholds and sural nerve function. Monofilaments revealed pathology in only a few participants with type 2 diabetes.

CONCLUSIONS

In an older group of people, vibration perception thresholds show a correlation similar to sural nerve amplitude on tactile and non-tactile surfaces. Measuring a vibration perception threshold on a tactile surface in type 2 diabetes provides no clear advantage over measuring it on the medial malleolus. In older type 2 diabetes subjects, both large and small diameter nerve fibers are affected.

New Perspective in Diabetic Neuropathy: From the Periphery to the Brain, a Call for Early Detection, and Precision Medicine

Diabetic peripheral neuropathy (DPN) is a common chronic complication of diabetes mellitus. It leads to distressing and expensive clinical sequelae such as foot ulceration, leg amputation, and neuropathic pain (painful-DPN). Unfortunately, DPN is often diagnosed late when irreversible nerve injury has occurred and its first presentation may be with a diabetic foot ulcer. Several novel diagnostic techniques are available which may supplement clinical assessment and aid the early detection of DPN. Moreover, treatments for DPN and painful-DPN are limited. Only tight glucose control in type 1 diabetes has robust evidence in reducing the risk of developing DPN. However, neither glucose control nor pathogenetic treatments are effective in painful-DPN and symptomatic treatments are often inadequate. It has recently been hypothesized that using various patient characteristics it may be possible to stratify individuals and assign them targeted therapies to produce better pain relief. We review the diagnostic techniques which may aid the early detection of DPN in the clinical and research environment, and recent advances in precision medicine techniques for the treatment of painful-DPN.

Triglyceride-lowering effect of the aldose reductase inhibitor cemtirestat-another factor that may contribute to attenuation of symptoms of peripheral neuropathy in STZ-diabetic rats

Hyperglycemia is considered a key risk factor for development of diabetic complications including neuropathy. There is strong scientific evidence showing a primary role of aldose reductase, the first enzyme of the polyol pathway, in the cascade of metabolic imbalances responsible for the detrimental effects of hyperglycemia. Aldose reductase is thus considered a significant drug target. We investigated the effects of cemtirestat, a novel aldose reductase inhibitor, in the streptozotocin-induced rat model of uncontrolled type 1 diabetes in a 4-month experiment. Markedly increased sorbitol levels were recorded in the erythrocytes and the sciatic nerve of diabetic animals. Osmotic fragility of red blood cells was increased in diabetic animals. Indices of thermal hypoalgesia were significantly increased in diabetic rats. Tactile allodynia, recorded in diabetic animals in the early stages, turned to mechanical hypoalgesia by the end of the experiment. Treatment of diabetic animals with cemtirestat (i) reduced plasma triglycerides and TBAR levels; (ii) did not affect the values of HbA1c and body weights; (iii) reversed erythrocyte sorbitol accumulation to near control values, while sorbitol in the sciatic nerve was not affected; (iv) ameliorated indices of the erythrocyte osmotic fragility; and (v) attenuated the symptoms of peripheral neuropathy more significantly in the middle of the experiment than at the end of the treatment. Taking into account the lipid metabolism as an interesting molecular target for prevention or treatment of diabetic peripheral neuropathy, the triglyceride-lowering effect of cemtirestat should be considered in future studies. The most feasible mechanisms of triglyceride-lowering action of cemtirestat were suggested.

Association between HbA1c and peripheral neuropathy in a 10-year follow-up study of people with normal glucose tolerance, impaired glucose tolerance and Type 2 diabetes

AIMS

To explore the association between HbA_1c and sural nerve function in a group of people with normal glucose tolerance, impaired glucose tolerance or Type 2 diabetes.

METHODS

We conducted a 10-year follow-up study in 87 out of an original 119 participants. At study commencement (2004), 64 men and 55 women (mean age 61.1 years) with normal glucose tolerance (n=39), impaired glucose tolerance (n=29), or Type 2 diabetes (n=51) were enrolled. At the 2014 follow-up (men, n=46, women, n=41; mean age 71.1 years), 36, nine and 42 participants in the normal glucose tolerance, impaired glucose tolerance and Type 2 diabetes categories, respectively, were re-tested. Biometric data and blood samples were collected, with an electrophysiological examination performed on both occasions.

RESULTS

At follow-up, we measured the amplitude of the sural nerve in 74 of the 87 participants. The mean amplitude had decreased from 10.9 μV (2004) to 7.0 μV (2014; P<0.001). A 1% increase in HbA_1c was associated with a ~1% average decrease in the amplitude of the sural nerve, irrespective of group classification. Crude and adjusted estimates ranged from -0.84 (95% CI -1.32, -0.37) to -1.25 (95% CI -2.31, -0.18). Although the mean conduction velocity of those measured at both occasions (n=73) decreased from 47.6 m/s to 45.8 m/s (P=0.009), any association with HbA_1c level was weak. Results were robust with regard to potential confounders and missing data.

CONCLUSIONS

Our data suggest an association between sural nerve amplitude and HbA_1c  at all levels of HbA_1c . Decreased amplitude was more pronounced than was diminished conduction velocity, supporting the notion that axonal degeneration is an earlier and more prominent effect of hyperglycaemia than demyelination.

Acrolein Scavenger Hydralazine Prevents Streptozotocin-Induced Painful Diabetic Neuropathy and Spinal Neuroinflammation in Rats

Diabetes-induced neuropathic pain (DNP) substantially influences people's life qualities. Hyperglycemia-induced excess free radicals have been considered as the most critical mechanisms underlying DNP. As an unsaturated aldehyde and a reactive product of lipid peroxidation, acrolein plays critical roles in diabetic nephropathy and inflammatory pain. We sought to determine whether acrolein is involved in DNP in this study. Diabetes was induced by a single intraperitoneal (i.p.) injection of 60 mg/kg streptozotocin (STZ). An acrolein scavenger hydralazine (5 mg/kg) was administered through a daily injection for 4 weeks, starting immediately within 30 min after STZ injection. Western blot showed that hydralazine could effectively inhibit STZ-induced upregulation of acrolein in the spinal dorsal horn on day 7-28 after STZ injection. Behavioral tests showed that STZ injection induced significant mechanical allodynia and thermal hyperalgesia, which could be alleviated by hydralazine. Immunofluorescent histochemistry and Western blot showed that STZ induced significant microglial activation. ELISA data indicated upregulation of inflammatory cytokines IL-1β and TNF-α expression in the spinal dorsal horn. Furthermore, hydralazine effectively attenuated microglial activation and expression of inflammatory mediators. Our data indicate that acrolein might be involved in the development of neuroinflammation and behavioral consequences of DNP. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1858-1864, 2017. © 2017 Wiley Periodicals, Inc.

Nicotinamide Riboside Opposes Type 2 Diabetes and Neuropathy in Mice

Male C57BL/6J mice raised on high fat diet (HFD) become prediabetic and develop insulin resistance and sensory neuropathy. The same mice given low doses of streptozotocin are a model of type 2 diabetes (T2D), developing hyperglycemia, severe insulin resistance and diabetic peripheral neuropathy involving sensory and motor neurons. Because of suggestions that increased NAD⁺ metabolism might address glycemic control and be neuroprotective, we treated prediabetic and T2D mice with nicotinamide riboside (NR) added to HFD. NR improved glucose tolerance, reduced weight gain, liver damage and the development of hepatic steatosis in prediabetic mice while protecting against sensory neuropathy. In T2D mice, NR greatly reduced non-fasting and fasting blood glucose, weight gain and hepatic steatosis while protecting against diabetic neuropathy. The neuroprotective effect of NR could not be explained by glycemic control alone. Corneal confocal microscopy was the most sensitive measure of neurodegeneration. This assay allowed detection of the protective effect of NR on small nerve structures in living mice. Quantitative metabolomics established that hepatic NADP⁺ and NADPH levels were significantly degraded in prediabetes and T2D but were largely protected when mice were supplemented with NR. The data justify testing of NR in human models of obesity, T2D and associated neuropathies.

Retinal Failure in Diabetes: a Feature of Retinal Sensory Neuropathy

Physiologic adaptations mediate normal responses to short-term and long-term stresses to ensure organ function. Organ failure results if adaptive responses fail to resolve persistent stresses or maladaptive reactions develop. The retinal neurovascular unit likewise undergoes adaptive responses to diabetes resulting in a retinal sensory neuropathy analogous to other sensory neuropathies. Vision-threatening diabetic retinal neuropathy results from unremitting metabolic and inflammatory stresses, leading to macular edema and proliferative diabetic retinopathy, states of "retinal failure." Current regulatory strategies focus primarily on the retinal failure stages, but new diagnostic modalities and understanding of the pathophysiology of diabetic retinopathy may facilitate earlier treatment to maintain vision in persons with diabetes.

Effect of combination therapy consisting of enalapril, α-lipoic acid, and menhaden oil on diabetic neuropathy in a high fat/low dose streptozotocin treated rat

We have previously demonstrated that treating diabetic rats with enalapril, an angiotensin converting enzyme (ACE) inhibitor, α-lipoic acid, an antioxidant, or menhaden oil, a natural source of omega-3 fatty acids can partially improve diabetic peripheral neuropathy. In this study we sought to determine the efficacy of combining these three treatments on vascular and neural complications in a high fat fed low dose streptozotocin treated rat, a model of type 2 diabetes. Rats were fed a high fat diet for 8 weeks followed by a 30 mg/kg dose of streptozotocin. Eight weeks after the onset of hyperglycemia diabetic rats were treated with a combination of enalapril, α-lipoic acid and menhaden oil. Diabetic rats not receiving treatment were continued on the high fat diet. Glucose clearance was impaired in diabetic rats and significantly improved with treatment. Diabetes caused steatosis, elevated serum lipid levels, slowing of motor and sensory nerve conduction, thermal hypoalgesia, reduction in intraepidermal nerve fiber profiles, decrease in cornea sub-basal nerve fiber length and corneal sensitivity and impairment in vascular relaxation to acetylcholine and calcitonin gene-related peptide in epineurial arterioles of the sciatic nerve. Treating diabetic rats with the combination of enalapril, α-lipoic acid and menhaden oil reversed all these deficits to near control levels except for motor nerve conduction velocity which was also significantly improved compared to diabetic rats but remained significantly decreased compared to control rats. These studies suggest that a combination therapeutic approach may be most effective for treating vascular and neural complications of type 2 diabetes.