Aim: To define the clinical significance of asymmetric dimethylarginine (ADMA) and that of methylenetetrahydrofolate reductase (MTHFR) gene polymorphism as factors of endothelial dysfunction (ED) in the development of early kidney injury in obese patients.
Subjects and methods: The investigation included 86 patients (64 men and 22 women aged 44 +/- 11 years) with abdominal obesity. Along with physical examination, the authors determined albuminuria, calculated glomerular filtration rate (GFR) using the Modification of Diet in Renal Disease (MDRD) formula, estimated insulin resistance markers (fasting plasma insulin and C-peptide concentrations and homeostatic model assessment (HOMA) index), as well as serum ADMA levels by enzyme immunoassay in all the patients. C677T polymorphism in the MTHFR gene was studied by allele-specific polymerase chain reaction and restriction fragment length polymorphism analysis. Kidney injury (chronic kidney disease (CKD)) was diagnosed using the Kidney Disease Outcomes Quality Initiative (KDOQI) criteria. Early vascular remodeling was determined from the increased intima-media thickness (IMT) of the common carotid artery (CCA).
Results: CKD was diagnosed in 27(31%) patients. The latter, unlike the patients with CKD, were observed to have more pronounced obesity (body mass index (BMI) 36.8 +/- 8.0 and 32.0 +/- 4.7 kg/m2, respectively (p < 0.001)), waist circumference (119 +/- 18 and 109 +/- 11 cm (p = 0.002)), higher levels of C-peptide (1348 +/- 363 and 1028 +/- 363 pmol/I; p < 0.001), insulin (16.9 +/- 7.3 and 11.7 +/- 5.5 microU/ ml; p < 0.001), and HOMA index (4.3 +/- 1.7 and 2.9 +/- 1.5; p < 0.001). In the patients with Stage IIIa CKD, ADMA concentrations (0.77 +/- 0.19 micromol/l) was higher than in those with Stages I (0.58 +/- 0.11 micromol/l; p = 0.048) and II (0.61 +/- 0.13 micromol/l; p = 0.071). An association between ADMA concentrations, CCA IMT, and estimated GFR was revealed in the patients with CKD. The predictors of an estimated GFR reduction in obesity were elevated serum concentrations of ADMA, uric acid, insulin, and HOMA index. The combination of obstructive sleep apnea syndrome and metabolic syndrome increased the risk of CKD by 2.1-fold (95% confidence interval, 1.06-3.14). Evaluation of the impact of MTHFR gene polymorphism on kidney injury in obesity disclosed that the patients with homozygous carriage of the abnormal T allele of the MTHFR gene had a higher risk for Stages I-IIIa CKD (2.60 with 95% confidence interval, 1.32-3.88), more marked obesity and hyperinsulinemia, and increased serum ADMA concentrations.
Conclusion: Insulin resistance and ED hold a central position in the pathogenesis of CKD in obese patients. The mechanisms of the atherosclerotic vascular remodeling associated with elevated serum ADMA concentrations are of paramount importance in the progression of early-stage CKD. The homozygous carriage of the abnormal T allele of the MTHFR gene increases the risk of Stages I-IIIa by more than twice.