Distribution of purine nucleotides in uremic fluids and tissues

There are almost 100 different substances called uremic toxins. In this study, we analyze all findings concerning the new family of uremic compounds--nicotinamide end products: N-methyl-2-pyridone-5-carboxamide (Met2PY), N-methyl-4-pyridone-5-carboxamide, newly described 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside (4PYR) and 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside triphosphate (4PYTP). After few years of studies, we have found that these substances have higher plasma concentration in patients with chronic renal failure (CRF) in comparison with the healthy population. We noted a 40-fold increase in plasma 4PYR concentration in patients with CRF. This increment correlates significantly with the decline of kidney function measured as an increase of serum creatinine concentration and decrease of estimated glomerular filtration rate. Tested compounds are present and measurable in physiological fluids and tissues. We found higher saliva Met2PY concentration in patients with CRF in comparison with controls. Saliva Met2PY correlated negatively with estimated glomerular filtration rate and positively with serum creatinine concentration. One-third of studied group had higher concentration of Met2PY in the saliva than in plasma, and this segment of patients may be called as "good excretors." In rats with experimental CRF, we found that both Met2PY and N-methyl-4-pyridone-5-carboxamide accumulated in selected tissues. We also demonstrated formation of 4PYTP in intact human erythrocytes during incubation with the precursor 4PYR. Incubation with 4PYR leads to lowering concentration of adenosine-5'-triphosphate. 4PYTP formation may be a way to remove 4PYR from the circulation and save adenosine-5'-triphosphate depletion. Summarizing, end products of the nicotinamide family are members of uremic toxins; however, exact pathophysiological role of these compounds in the development of uremic syndrome needs further studies.