IDF21-0406 Genetic variants in the Carnosine-Carnosinase system and their impact on diabetic nephropathy

Abstract

Background: The role of carnosine-carnosinase system in diabetic nephropathy has been established through various studies in animal models. It has been proven that low carnosinase secretion promotes high circulating carnosine levels which acts as a protective factor against adverse effects of hyperglycemia on renal cells. While genetic variants in the carnosinase gene (CNDP1) could influence carnosinase concentration, variants in the carnosine synthase gene (CARNS1) which synthesizes carnosine and variants in the SLC15A4 and SLC15A2 genes which are involved in the renal transport of carnosine could influence carnosine concentration thereby causing nephropathy. Aim: To study the association of genetic variants in the carnosine-carnosinase system (CARNS1, CNDP1, SLC15A4 and SLC15A2) with nephropathy and their influence on carnosinase levels in south Indian population. Method: Study Participants: 580 type 2 diabetes individuals without nephropathy (DM) and 597 type 2 diabetes individuals with nephropathy (DN) from Dr. Mohan’s Diabetes Specialities Centre, Chennai, India. Methodology: Genomic DNA was extracted from blood samples using phenol chloroform method. A total of 27 SNPs from the four genes were genotyped using MassARRAY. The levels of carnosinase in serum was measured in 116 DM and 93 DN participants using commercially available ELISA kit. Results: The D18S880 repeat polymorphism (5-8 repeats of Leucine) in CNDP1 gene and rs1626067 SNP of CARNS1 gene showed significant association with DN. The odds ratio for DN after adjusting for potential confounders such as age, sex, BMI, HbA1c, duration of diabetes and systolic blood pressure for the 6L/XL genotype of D18S880 and the GA genotype of rs1626067 as compared to their respective homozygous normal genotypes was 0.67 (95%CI: 0.48-0.94, p=0.022) and 0.68 (95% CI:0.49-0.93, p=0.016) respectively. The levels of carnosinase (mean±SE in picogram/mL) was significantly higher in DN (3.07±0.19) compared to DM group (2.48±0.13, p=0.038). Discussion: This study gains significance as the role of genetic variants in the carnosine-carnosinase system in DN remains largely unexplored. Most of the studies so far have focussed only on the CNDP1 gene. The association of D18S880 Leucine repeat with DN is significant as it is present in the signal peptide region of CNDP1 gene and may play a role in the secretion of carnosinase. The association of rs1626067 SNP in CARNS1 with DN has not been reported so far. This SNP is positioned in the 3́UTR region of CARNS1 and hence could alter the binding of transcription factors and have a regulatory effect. The significant difference in serum carnosinase levels between DM and DN groups was an interesting finding. When the groups were further stratified based on the genotypes, the sample size was less than 50 in each group and was not sufficiently powered to study the correlation of enzyme levels and genotypes. Measuring the levels and activity of carnosinase in larger number of samples will help identify whether the genetic variations influence the enzyme levels. If found, targeted dietary intervention studies giving carnosine supplements to those carrying the susceptible alleles can be undertaken to alleviate the burden of nephropathy.