A sensitive HPLC method for the quantification of free and total p-cresol in patients with chronic renal failure

It is generally recognized that the uremic syndrome results in a depression of immune function, but the uremic solutes responsible remain largely unidentified. In this study, the effect of 18 known uremic retention solutes, including urea and creatinine, on hexose monophosphate shunt (HMS)-dependent glucose-1-C14 utilization (G1C-U), chemiluminescence production (CL-P) and flow cytometric parameters (FCP) of respiratory burst and phagocytosis were evaluated in granulocytes and/or monocytes. Among the compounds studied, only p-cresol depressed whole blood respiratory burst reactivity (G1C-U, CL-P) dose dependently at concentrations currently encountered in end-stage renal disease (ESRD) (P < 0.05 from 5 micrograms/ml on). The effect of p-cresol was enhanced by increasing incubation times from 10 to 120 minutes. HMS activity of isolated packed erythrocytes remained unaffected. FCP of respiratory burst activity (Bursttest, expressed as log fluorescence units, LFU) revealed a marked depression in the presence of p-cresol (from 700 +/- 167 to 291 +/- 128 LFU for granulocytes, from 278 +/- 102 to 146 +/- 52 LFU for monocytes, P < 0.01), whereas particle ingestion (Phagotest) remained unaffected. Cell-free myeloperoxidase activity was also markedly depressed in the presence of p-cresol. Polarity based HPLC-elution of a standard solution containing all the solutes studied, using a gradient from 100% formic acid to 100% methanol during 60 minutes, revealed elution of p-cresol after 46.6 minutes, pointing to its relative hydrophobicity. Conjugation of p-cresol to p-cresylsulfate anihilated the depressive effect of p-cresol on granulocyte function, and at the same time caused a shift in HPLC-elution pattern to a less lipophilic range.(ABSTRACT TRUNCATED AT 250 WORDS)

In the presence of sublethal concentrations of phenol, 4-chlorophenol, and p-cresol in the growth medium, cells of Escherichia coli modified the fatty acid composition of their lipids. The results of these changes was an increase in the degree of saturation of lipids probably in order to compensate an increase of fluidity of the membrane induced by the phenols. Supplementation of the growth medium with saturated fatty acids could also enhance the degree of lipid saturation due to the incorporation of the acyl chains in the phospholipids. At the same time the growth of cells was less inhibited than in unsupplemented cells. The increase of tolerance of cells by manipulating the lipid composition indicates that the membrane structure plays a crucial role in the mode of action of phenols.