Interleukin-6 Dynamics as a Predictor of the Renal Dysfunction Formation and a Criterion of the Effectiveness of the Nephroprotective Strategy in Early Rheumatoid Arthritis

Rheumatoid arthritis is one of the most severe chronic human diseases, characterized by pronounced inflammation with proliferation of the synovial membrane of the joints, damage of the internal organs and systems, long-term persistent inflammation activity and gradual destruction of the structure of the joints and periarticular tissues. The purpose of the work was to study the prognostic significance of interleukin-6 over-expression in the formation of nephropathy and to evaluate the adequacy of nephroprotective therapy in the early rheumatoid arthritis. Material and methods. This study included 35 patients aged over 18 with early rheumatoid arthritis. The average age of patients was 50.71 ± 2.25 (from 18 to 76 years), 80% of women, the average duration of the disease at the time of the initial study was 9.21 ± 0.43 months. Results and discussion. The equation for calculating the personal probability of the presence of subclinical renal dysfunction was calculated by using the formula p = 1/1 + e – z, where z – 15.625 + 0.045 IL-6 (the sensitivity of the proposed method was about 83%, which is quite high and indicates clinical approbation of the obtained mathematical model for a qualitative prediction of the risk of nephropathy formation in rheumatoid arthritis). The predicted IL-6 level decreased by 28.24% (p <0.05) compared with the baseline values. Therapy with the drug "Actemra", in addition to a reliable clinical effect, was characterized by high nephroprotective activity. Thus, the decrease in microproteins excretion in the urine were 22.17% and 31.92% for microalbumin and β2-microglobulin, respectively (p<0.05 in all cases). At the same time, a statistically significant increase in the renal functional reserve was observed without a decrease in the initial level of glomerular filtration by endogenous creatinine clearance. We also noted a regression of the glomerular membrane porosity. Increased urinary excretion of albumin in patients with rheumatoid arthritis without concomitant kidney disease was detected in 76% of patients, which far exceeded the general population. The tubulointerstitial involvement was documented in 82% of patients in this group. The increase in the markers of tubular dysfunction is ahead of the increase in the level of the traditional marker of glomerular damage - urinary albumin excretion. As the pathological process progresses, the growth of glomerular and tubular dysfunction runs in parallel. Conclusions. The logistic regression method investigated the dependence of the dichotomous variable (presence or absence of violation of the functional status of the kidneys) from the autonomous regressor, which was considered to be a potential predictor associated with the risk of formation of nephropathy. The obtained data allows to consider IL-6 not only a subclinical predictor of renal function impairment, but also a potential marker for evaluating the nephroprotective effect of therapy in patients with early rheumatoid arthritis.