Phenotyping SULT in Man: a Simple Metric Using Paracetamol as Probe

Abstract

Introduction Sulfotransferase enzymes (SULT) catalyze sulfoconjugation of drugs, as well as endogenous mediators and environmental xenobiotics. To address the scarce evidence on sulfonation activity from clinical research, we developed a clinical metabolic phenotyping method using paracetamol as a probe substrate. Sulfonation accounts for up to 35% of the total paracetamol metabolism in humans and is mediated mainly by the activity of SULT1A1 and SULT1A3 (phenol sulfotransferases), in liver and small intestine respectively. Our aim was to estimate sulfonation capability of phenolic compounds and study its intraindividual variability in man. Population and Methods: This study was approved by the Portuguese National Ethics Committee. We recruited a population of 36 healthy adults (12 men and 24 women, 12 on oral contraceptives). Subjects received 1 g of oral paracetamol on three different occasions. Paracetamol and its metabolites (paracetamol sulfate, paracetamol glucuronate, paracetamol cysteine-S-conjugate and paracetamol mercapturate) were measured in plasma and spot urine samples using liquid chromatography-high resolution mass spectrometry. Paracetamol sulfonation index (PSI) was used to express SULT activity. PSI was calculated for urine (uPSI) and for plasma (pPSI) samples. We tested differences between groups using ANOVA and we used Pearson's correlation coefficient. Results The frequency distribution histograms of pPSI and uPSI were positively skewed in the studied population (Figure 1). The mean pPSI and uPSI were 0.43 (range 0.34 to 0.60) and 0.40 (range 0.31 to 0.55) respectively (Figure 2). PSI showed low intraindividual variability (mean coefficient of variation was 10% for pPSI and 13% for uPSI). There was a good correlation between values in plasma and spot urine samples (Pearson r=0.79). Urinary PSI was independent of factors not related to SULT activity, such as urine pH or eGFR. Gender and oral contraceptive intake had no impact on PSI. Discussion Our SULT phenotyping method is a simple non-invasive procedure requiring urine spot samples, using the safe and convenient drug paracetamol as a probe substrate, and with low intraindividual coefficient of variation. Although it will not give us mechanistic information, it will provide us an empirical measure of an individual's sulfonator status. To the best of our knowledge, our method provides the first in vivo empirical measure of an individual's phenol sulfonation capability and of its intraindividual variability.