Efficacy and safety of the combined metabolic medication, containing inosine, nicotinamide, riboflavin and succinic acid, for the treatment of diabetic neuropathy: a multicenter randomized, double-blind, placebo-controlled parallel group clinical trial (CYLINDER).

INTRODUCTION: Antioxidants may have positive impact on diabetic polyneuropathy (DPN), presumably due to alleviation of oxidative stress. We aimed to evaluate the efficacy and safety of combination of antioxidants: succinic acid, inosine, nicotinamide, and riboflavin (SINR) in the treatment of DPN. RESEARCH DESIGN AND METHODS: In a double-blind, placebo-controlled clinical trial, men and women aged 45-74 years with type 2 diabetes and symptomatic DPN, with initial Total Symptom Score (TSS) ˃5, were randomized into experimental (n=109) or placebo (n=107) group. Patients received study medication/placebo intravenously for 10 days, followed by oral administration for 75 days. Statistical significance was defined as a two-tailed p<0.05. RESULTS: In SINR group, mean TSS change after 12 weeks was -2.65 (±1.46) vs -1.73 (±1.51) in the placebo group (p<0.0001; t-test). Reduction of symptoms in the SINR group was achieved regardless of hemoglobin A1c levels, but better results were observed in patients with initial TSS <7.5. The analysis of TSS subscores revealed statistically significant between-group differences by dynamics of the intensity of paresthesia and of numbness starting from day 11 (p=0.035 and p=0.001, respectively; mixed model); by day 57, statistically significant between-group differences were detected also by dynamics of burning intensity (p=0.005; mixed model). Study limitations are small effect size, moderate proportion of patients with severe DPN symptoms, subjective assessment of outcomes, exclusion of participants who received injectable glucose-lowering medications other than insulins, and patients with uncontrolled and type 1 diabetes. CONCLUSIONS: The combination of SINR effectively alleviates DPN symptoms in patients with type 2 diabetes. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Registry (NCT04649203; Unique Protocol ID: CTF-III-DM-2019).

The Role of Oxidative Stress in Diabetic Neuropathy: Generation of Free Radical Species in the Glycation Reaction and Gene Polymorphisms Encoding Antioxidant Enzymes to Genetic Susceptibility to Diabetic Neuropathy in Population of Type I Diabetic Patients.

Diabetic neuropathy (DN) represents the main cause of morbidity and mortality among diabetic patients. Clinical data support the conclusion that the severity of DN is related to the frequency and duration of hyperglycemic periods. The presented experimental and clinical evidences propose that changes in cellular function resulting in oxidative stress act as a leading factor in the development and progression of DN. Hyperglycemia- and dyslipidemia-driven oxidative stress is a major contributor, enhanced by advanced glycation end product (AGE) formation and polyol pathway activation. There are several polymorphous pathways that lead to oxidative stress in the peripheral nervous system in chronic hyperglycemia. This article demonstrates the origin of oxidative stress derived from glycation reactions and genetic variations within the antioxidant genes which could be implicated in the pathogenesis of DN. In the diabetic state, unchecked superoxide accumulation and resultant increases in polyol pathway activity, AGEs accumulation, protein kinase C activity, and hexosamine flux trigger a feed-forward system of progressive cellular dysfunction. In nerve, this confluence of metabolic and vascular disturbances leads to impaired neural function and loss of neurotrophic support, and over the long term, can mediate apoptosis of neurons and Schwann cells, the glial cells of the peripheral nervous system. In this article, we consider AGE-mediated reactive oxygen species (ROS) generation as a pathogenesis factor in the development of DN. It is likely that oxidative modification of proteins and other biomolecules might be the consequence of local generation of superoxide on the interaction of the residues of L-lysine (and probably other amino acids) with α-ketoaldehydes. This phenomenon of non-enzymatic superoxide generation might be an element of autocatalytic intensification of pathophysiological action of carbonyl stress. Glyoxal and methylglyoxal formed during metabolic pathway are detoxified by the glyoxalase system with reduced glutathione as co-factor. The concentration of reduced glutathione may be decreased by oxidative stress and by decreased in situ glutathione reductase activity in diabetes mellitus. Genetic variations within the antioxidant genes therefore could be implicated in the pathogenesis of DN. In this work, the supporting data about the association between the -262T > C polymorphism of the catalase (CAT) gene and DN were shown. The -262TT genotype of the CAT gene was significantly associated with higher erythrocyte catalase activity in blood of DN patients compared to the -262CC genotype (17.8 ± 2.7 × 10(4) IU/g Hb vs. 13.5 ± 3.2 × 10(4) IU/g Hb, P = 0.0022). The role of these factors in the development of diabetic complications and the prospective prevention of DN by supplementation in formulations of transglycating imidazole-containing peptide-based antioxidants (non-hydrolyzed carnosine, carcinine, n-acetylcarcinine) scavenging ROS in the glycation reaction, modifying the activity of enzymic and non-enzymic antioxidant defenses that participate in metabolic processes with ability of controlling at transcriptional levels the differential expression of several genes encoding antioxidant enzymes inherent to DN in Type I Diabetic patients, now deserve investigation.

A splice variant of GNB3 and peripheral polyneuropathy in type 1 diabetes.

Abnormalities in G protein-mediated signal transduction could be involved in the pathogenesis of diabetic polyneuropathy (DPN). Here we test whether the GNB3 C825T variant confers susceptibility to DPN in type 1 diabetes (T1D) mellitus. The C825T marker of GNB3 was genotyped in genomic DNA from blood isolated from a total of 213 Russian T1D patients 100 of whom had DPN. Compared to carriers of the wild-type genotype C/C, diabetic subjects with genotypes T/T had significantly increased risk to develop DPN (Odds Ratio (OR) of 4.4 (p = 0.001). The adjustment for confounders (age, sex, body mass index, cigarette smoking, and level of reduced glutathione) resulted in increase of the OR value up to 4.72 (p = 8.9 x 10;{-3}). The further adjustment for hypertension abolished the association between the GNB3 C825T variant and DPN (OR = 1.95, p = 0.18). Non-complicated subjects homozygous for T/T showed decreased levels of reduced glutathione (T/T: 69 +/- 19 vs. C/T: 74 +/- 19 vs. C/C: 77 +/- 17 micromol/l, p = 0.009). Compared to other GNB3 variants, carriers of the T/T genotype had elevated systolic blood pressure (SBP) in complicated (T/T: 115.8 +/- 9.1 vs. C/T: 113.3 +/- 8.2 vs. C/C: 109.5 +/- 8.7 mm/Hg, p = 0.036) and non-complicated T1D patients (T/T: 118.1 +/- 8.4 vs. C/T: 116.9 +/- 7.9 vs. C/C: 112.1 +/- 7.2 mm/Hg, p = 0.02). However, the significance of association between the C825T polymorphism was lost after adjustment for confounding risk factors. In conclusion, the 825T allele of GNB3 is likely to accelerate the development of DPN through primary effects to SBP and hypertension in subgroups of diabetic patients with impaired neurovascular function and advanced oxidative stress.

Leu54Phe and Val762Ala polymorphisms in the poly(ADP-ribose)polymerase-1 gene are associated with diabetic polyneuropathy in Russian type 1 diabetic patients.

Poly(ADP-ribose) polymerase-1 (PARP-1) is an ubiquitous DNA-binding protein involved in the cellular response to various genotoxic agents. Excessive PARP-1 activation is known to lead to the depletion of intracellular NAD+ and ATP pools and hence to threat cell survival. Therefore, PARP-1 could be involved in neuronal death and contribute to the development of diabetic polyneuropathy (DPN). This study addressed the association of Leu54Phe and Val762Ala polymorphisms of PARP-1 with DPN in Russian type 1 diabetic (T1D) patients. Eighty-six T1D patients with severe DPN and 93 T1D patients with no clinical signs of DPN have been studied by a polymerase chain reaction restriction fragment length polymorphism approach. Using Fisher's exact test revealed the association of the Phe54 and Val762 variants of PARP-1 (odds ratio (OR), 1.66 and 2.88, respectively) with increased risk of DPN in T1D. These results suggest that the PARP1 gene is involved in the pathogenesis of diabetic neuropathy in a Russian population. Additionally, a logistic regression analysis revealed a significant association between the neurological variances such as vibration detection threshold (OR, 2.08), vibration and temperature perception thresholds (OR, 1.32 and 1.67, respectively), and sensory and motor nerve conduction velocities (OR, 2.34 and 2.58, respectively), with DPN.