Introduction: Diabetic nephropathy accounts for more than 20% of the cases of chronic renal failure. For many patients, the method of renal replacement therapy is chronic ambulatory peritoneal dialysis (CAPD). Diabetes, through glucose autooxidation and production of free radicals, causes protein glycation. Products of protein glycation increase the concentrations of proinflammatory cytokines. The tumor necrosis factor (TNF) is one of the most important cytokines of cellular response and inflammation. Its level is increased in chronic renal failure. Numerous polymorphisms have been identified within and around the TNF gene, which is located on chromosome 6. Single nucleotide polymorphisms, such as a polymorphism at a position -308, probably have a direct influence on the TNF production. Myeloperoxidase (MPD) is a heme enzyme, participating in oxygen mechanisms of microorganism killing by phagocytes. Chronic renal failure patients show a significant reduction in the intracellular myeloperoxidase level. In the promoter region of myeloperoxidase gene, at position -463, G to A transition has been found, which causes a decreased gene expression. The aim of the present study was an analysis of genetic basis of TNF and myeloperoxidase production in dialyzed patients with diabetic nephropathy.
Subjects and methods: The study group consisted of 37 diabetic nephropathy patients treated with peritoneal dialysis. The control subjects were 58 dialyzed patients with other primary renal diseases and 115 healthy individuals. TNF and myeloperoxidase gene polymorphisms were detected by polymerase chain reaction (PCR) and amplification products were digested with the NcoI and AciI restriction enzymes respectively. ELISA determined the TNF and MPO levels in plasma.
Results: We haven't found significant differences in TNF genotype and allele frequencies between the groups; however, diabetic nephropathy patients seemed to have a lower frequency of TNF1/TNF1 genotype. In diabetic nephropathy patients, the median TNF plasma level was 43.8 pg/mL, and in other renal diseases it was 36.8 pg/ mL. The difference was significant (p<0.05). The differences in TNF levels between both groups and the control group (1.7 pg/mL) were highly significant (p<0.001). There was a statistically significant difference in MPO genotype frequencies between patients with diabetic nephropathy and patients with other renal diseases (p<0.05). GG and AA genotypes were significantly more common in patients with diabetic nephropathy. The genotype distribution in patients with other renal diseases was similar to the distribution in the control group. Median plasma MPO level in diabetic nephropathy patients was similar to patients with other renal diseases. A significantly lower level (p<0.05) was observed in the control group. In diabetic nephropathy, we have also observed a correlation between the MPO genotype and an earlier onset of the disease. For the TNF genotype, we haven't found such a relationship. There was also no relationship between the TNF and MPO genotypes and time to end-stage renal disease (ESRD). There were no differences in the frequency of peritonitis between patients with diabetic nephropathy and dialyzed patients with other renal diseases.
Discussion: In conclusion, we found that in diabetic nephropathy patients molecular variants of TNF are more frequent than in nondiabetic patients with chronic renal failure and these changes might be associated with altered ability to TNF synthesis. Analysis of the myeloperoxidase genotypes showed significant difference in genotype distribution in dialyzed patients with diabetic nephropathy. This, however, requires further studies to confirm the relationship with the disease.