Crosstalk between proteinuria, plasma oxalic acid and inflammation in glomerulonephritis patients: an exploratory study

In the present exploratory cross-sectional cohort study, we evaluated whether plasma and urine oxalate concentrations in patients with primary glomerulonephritis depend not only on the glomerular filtration rate but also on the proteinuria level and influence the inflammatory response. Methods. We enrolled 100 participants, including 76 patients with glomerulonephritis having chronic kidney disease stage (CKD) 1–3b (69.7% of them with nephrotic syndrome) and 24 healthy volunteers. We excluded patients with diabetes, cardiovascular disease and those with glomerulonephritis with an estimated GFR (eGFR) < 30 mL/min/1.73 m2. In addition to routine hematological and biochemical tests, plasma oxalate concentration, urinary oxalate excretion, and serum interleukin (IL)-6 and monocyte chemoattractant protein-1 (MCP-1) levels were assessed in all study participants. Results. We observed that plasma oxalic acid concentration was significantly higher in patients with glomerulonephritis (19.0 [5.9–45.2] µmol/L) than in healthy volunteers (5.5 [3.8–7.3] µmol/L, p < 0.0001). Moreover, nephrotic proteinuria was significantly associated with plasma oxalic acid elevation independent of the patients' age, sex, glomerular filtration rate, and body mass index (odds ratio = 1.42, 95% confidence interval = 1.13–1.77, p = 0.002). In turn, the increased plasma oxalic acid concentration was associated with high levels of serum IL-6 and MCP-1, which may be cardiovascular risk factors in patients with primary glomerulonephritis. Conclusions. Nephrotic proteinuria was significantly associated with the elevation of plasma oxalic acid concentration and hyperoxaluria in glomerulonephritis patients with CKD stages 1–3b. Plasma oxalate at least partly promotes inflammation, which may be a cardiovascular risk factor in patients with glomerulonephritis in the early stages of CKD. Future studies should recruit at least 156 participants to confirm our preliminary results, validate nephrotic proteinuria as a risk factor for oxalate metabolism violation or determine the role of impaired oxalate homeostasis in clinical outcomes in patients with glomerulonephritis.