Interindividual variability of the human hepatic sulphotransferases.

The variability among subjects of the hepatic activities of O-sulphotransferase towards dopamine, p-nitrophenol, testosterone and ethinyloestradiol and of N-sulphotransferase with 1,2,3,4-tetrahydroisoquinoline (TIQ) as substrate is described. The rates of testosterone and TIQ sulphation were higher in men than women whereas those of ethinyloestradiol, dopamine and p-nitrophenol were similar in both sexes. The sulphotransferase activities towards p-nitrophenol and dopamine were positively skewed whereas those towards ethinyloestradiol approached normality. The coefficients of variations for the sulphotransferase activities ranged between 34% and 62% indicating a considerable variability among subjects. The rates of dopamine-, TIQ- and p-nitrophenol-sulphation were measured in the mucosa of the human intestine, and the duodenum/liver ratios were 10, 0.9 and 0.1, respectively. Thus the contribution of the intestine in the sulphation of xenobiotics is substrate dependent.

Glutathione conjugation with 1-chloro-2,4-dinitrobenzene (CDNB): interindividual variability in human liver, lung, kidney and intestine.

The rate of glutathione conjugation with 1-chloro-2,4-dinitrobenzene (CDNB) was measured in specimens of human liver (n = 93), sigmoid colon (n = 56), renal cortex (n = 67) and lung (n = 68). In the liver there was a weak but significant (r = - 0.247 p = 0.017) negative correlation between the activity of glutathione transferase and the liver donor's age. Such a correlation was not found in the renal cortex, lung and colon. In the renal cortex and in lung the rate of glutathione conjugation with CDNB was a little but significantly (p < 0.05) higher in women than men, whereas no sex-dependent difference was observed in the liver and colon. The distribution of glutathione transferase activity was polymorphic in the mucosa of colon and renal cortex of men but not in that of women. Smoking seems not to affect the glutathione conjugation rate with CDNB in lung. The activity of glutathione transferase was 2-, 6-, and 7-fold greater in liver than in the renal cortex, lung and colon, respectively. There was a large interindividual variability of the hepatic glutathione transferase activity, and because this variability, 15% of the population studied catalyzed the glutathione conjugation with CDNB at a rate similar to those of the renal cortex and duodenum. The subjects with low expression of the hepatic glutathione transferase should be more exposed to the effects of toxic and carcinogenic compounds.

Human brain sulphotransferase and glucuronyltransferase.

The activities of cytosolic sulphotransferase (ST) and microsomal glucuronyltransferase (GT) were measured with 1-naphthol as the substrate in three frontal cortex, three temporal cortex, one parietal cortex, one occipital cortex and two cerebellar cortex specimens from human brain. The average activity was 11.7 +/- 4.2 pmol/min/mg protein/(ST) and 26.8 +/- 13.6 pmol/min/mg protein (GT). The kinetics of ST were studied varying the concentration of 1-naphthol in five brain specimens (temporal cortex, temporal subcortex, occipital cortex, cerebellum cortex and frontal cortex) whereas those of GT were studied in a sample obtained by pooling the microsomal fractions from the following eight brain tissues: one frontal cortex, four temporal cortex, one parietal cortex and two cerebellar cortex specimens. The Km of the first and second enzyme was 1.55 +/- 0.47 microM (mean +/- s.d.) and 121 microM, respectively. The Vmax values were 13.70 +/- 8.16 (mean +/- s.d.) pmol/min/mg protein (ST) and 103 pmol/min/mg protein (GT). Vmax/Km was ten times higher for ST than GT. These data suggest that ST is the predominant pathway at low concentrations of 1-naphthol whereas at higher concentrations, GT becomes the predominant pathway.

Human liver sulphotransferase and UDP-glucuronosyltransferase: structure-activity relationship for phenolic substrates.

1. Human liver sulphotransferase and UDP-glucuronosyltransferase were studied with phenol, methyl-, ethyl-, propyl-, butyl-, phenyl-, nitro-, amino-phenols and hydroxybenzoic acids as substrates. 2. The Michaelis-Menten constants (Km) and the maximum velocities of reaction (Vmax) of sulphotransferase and UDP-glucuronosyltransferase for each substrate were measured. 3. The Km values for sulphotransferase varied over 5000-fold whereas they varied over 25-fold for UDP-glucuronosyltransferase. 4. Sulphotransferase and UDP-glucuronosyltransferase have different structure-activity relationships with phenolic substrates.

Interindividual variability in the glucuronidation and sulphation of ethinyloestradiol in human liver.

1. Glucuronidation and sulphation of ethinyloestradiol (EE2) was studied in human liver. Microsomal glucuronyltransferase activity was measured in 110 livers whose donors were 71 women and 39 men. Enzyme activity ranged between 12.6 and 242 pmol min-1 mg-1 protein, i.e. over a 19-fold range and the mean (+/- s.d.) glucuronyltransferase activity was 96.8 +/- 47.9 pmol min-1 mg-1 protein. 2. Cytosolic sulphotransferase activity was measured in 138 livers whose donors were 90 women and 48 men. Enzyme activity ranged between 14.4 and 98.2 pmol min-1 mg-1 protein, i.e. over a 7-fold range, and the mean (+/- s.d.) sulphotransferase activity was 43.7 +/- 18.6 pmol min-1 mg-1 protein. 3. Human liver glucuronyltransferase and sulphotransferase activities showed a unimodal distribution pattern. Enzyme activities were neither sex-related nor age-dependent. Sulphotransferase activity did not correlate with glucuronyltransferase activity (n = 80) suggesting that the two enzymes are independently regulated. The ratio of specific glucuronyltransferase to sulphotransferase activity ranged between 0.15 and 8.0 (mean +/- s.d., 2.44 +/- 1.51) and was unimodally distributed.

Conjugation of benzoic acid with glycine in human liver and kidney: a study on the interindividual variability.

1. The rate of conjugation of benzoic acid with glycine was measured in the homogenates of 110 specimens of human liver and in 67 specimens of human renal cortex. 2. The assay for the formation of benzoyl glycine consisted of measuring the formation of benzoyl glycine from (14C) benzoic acid and glycine in the presence of coenzyme A and ATP. 3. In human liver, the mean (+/- SD) and coefficient of variation for the formation rate of benzoyl glycine were 254 +/- 90.5 nmol min-1 per g liver and 36%, respectively. There was a weak, but significant, negative correlation (r = -0.339, p < 0.001) between the rate of formation of benzoyl glycine and the liver donor's age. 4. In the human kidney, the rate of benzoyl glycine formation was normally distributed. The mean (+/- SD) and coefficient of variation were 321 +/- 99.3 nmol min-1 per g kidney and 31%, respectively. 5. These in vitro results are consistent with the view that the in vivo rate of conjugation of carboxylic acid with glycine varies among subjects and is normally distributed.

Cytosolic epoxide hydrolase in humans: development and tissue distribution.

Cytosolic epoxide hydrolase activity was measured towards trans-stilbene oxide in 41 human adult livers, in 40 fetal livers, in 17 placentas and in fetal and adult lungs, kidneys and gut. The cytosolic epoxide hydrolase activity was measurable in all specimens investigated. The rate of formation of trans-stilbene glycol (pmol/min per mg protein, mean +/- SD) was 55.2 +/- 89.6 (fetal liver). 303.2 +/- 73.2 (adult liver) and 18.8 +/- 13.1 (placenta) In the fetal extrahepatic tissues, the cytosolic epoxide hydrolase activity was 70.0 +/- 9.4 (adrenals), 47.6 +/- 7.2 (gut), 69.4 +/- 22.5 (kidneys) and 43.2 +/- 19.2 (lungs) pmol/min per mg protein, whereas in the adult tissues it was 131.2 +/- 63.1 (kidneys), 27.8 +/- 20.3 (intestine), 8.5 +/- 2.8 (lungs) and 7.2 +/- 4.2 (urinary bladder) pmol/min per mg protein.

Valpromide is a poor inhibitor of the cytosolic epoxide hydrolase.

The effect of the antiepileptics valpromide and sodium valproate on the cytosolic epoxide hydrolase was studied in human fetal liver, kidneys and adrenals and from human adult liver and kidneys. Trans-stilbene oxide was used as substrate. Valpromide (10 mM) lowered the activity of the epoxide hydrolase to one half of the control in all organs studied. Sodium valproate (10 mM) was less powerful as an inhibitor than valpromide; however, it exerted a significant inhibition in all tissues studied.

Human liver budesonide sulphotransferase is inhibited by testosterone and correlates with by testosterone sulphotransferase.

Budesonide, a corticosteroid used in the treatment of asthma and allergic reactions, is almost entirely cleared by metabolism in man. We describe the sulphation of budesonide in human liver and lung and provide evidences that the sulphation of budesonide is catalysed by testosterone sulphotransferase. A rapid and reproducible radiometric assay for budesonide sulphotransferase is described. Liver specimens were obtained from 35 men and 65 women and lung specimens from 2 women and 17 men. The average hepatic budesonide sulphation rate was significantly higher in men (41.1 pmol.min-1.ml-1) than women (28.2 pmol.min-1.mg-1). In the lung, the mean budesonide sulphation rate was 5.0 pmol.min-1.mg-1. Testosterone strongly inhibited the hepatic sulphation of budesonide, whereas p-nitrophenol and dopamine were poor inhibitors; the IC50 was 7.0 uM (testosterone), 320 uM (p-nitrophenol) and 510 uM (dopamine). The hepatic rates of testosterone, p-nitrophenol and dopamine sulphation were measured in the same samples assayed for budesonide sulphotransferase. There was a correlation between the hepatic rates of budesonide and testosterone sulphation (P < 0.001; r = 0.810). The activity of testosterone sulphotransferase was significantly greater in men than women (22.0 vs. 17.2 pmol.min-1.mg-1), whereas those of dopamine and p-nitrophenol sulphotransferase were not sex dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Conjugation pathways in liver disease.

1. The activities of microsomal glucuronyltransferase and thiomethyltransferase, and those of cytosolic sulphotransferase, acetyltransferase, glutathione transferase and thiomethyltransferase were measured in abnormal (cirrhosis and chronic hepatitis) and normal livers. 2. Glucuronyltransferase and sulphotransferase were investigated with 2-naphthol and ethinyloestradiol as substrates. p-Aminobenzoic acid, benzo(a)pyrene-4,5-epoxide and 2-mercaptoethanol were the substrates of acetyltransferase, glutathione transferase and thiomethyltransferase, respectively. 3. Enzyme activities are expressed as nmol min-1 incubation mg-1 protein and the averages (+/- s.d.) are given. With 2-naphthol as substrate, the glucuronyltransferase activity was 6.55 +/- 4.10 (abnormal liver, n = 33) and 7.81 +/- 4.02 (normal liver, n = 26) (NS); whereas sulphotransferase activity was 0.28 +/- 0.18 (abnormal liver, n = 35) and 0.68 +/- 0.43 (normal liver, n = 26) (P less than 0.01). Glucuronyltransferase activity towards ethinyloestradiol was 102.5 +/- 56.9 (abnormal liver, n = 30) and 107 +/- 59.9 (normal liver, n = 26) (NS), whereas sulphotransferase activity was 57.2 +/- 36.0 (abnormal liver, n = 35) and 122 +/- 67.6 (normal liver, n = 28) (P less than 0.01). Acetyltransferase activity was 0.84 +/- 0.83 (abnormal liver, n = 35) and 3.84 +/- 1.65 (normal liver, n = 26) (P less than 0.01). Glutathione transferase activity was 0.83 +/- 0.68 (abnormal liver, n = 35) and 2.90 +/- 1.59 (normal liver, n = 25) (P less than 0.01) and thiomethyltransferase activity was 1.00 +/- 0.69 (abnormal liver, n = 34) and 3.99 +/- 1.49 (normal liver, n = 25) (P less than 0.01). 4. Liver disease lowers the activities towards the substrates studied of sulphotransferase, acetyltransferase, glutathionetransferase and thiomethyltransferase but not that of glucuronyltransferase.(ABSTRACT TRUNCATED AT 250 WORDS)

Profile of drug-metabolizing enzymes in human ileum and colon.

Six patients (4 women and 2 men, age between 60 and 90 years), subjected to right hemicolectomy, were gut donors. The mucosa was isolated from the last portion of the ileum and the first portion of the colon. Tissue specimens were free from pathological changes. The activities of the enzymes of phase I (NADPH cytochrome c reductase, ethoxycoumarin O-deethylase, aminopyrine N-demethylase, microsomal epoxide hydrolase, cytosolic epoxide hydrolase, glutathione reductase and glutathione peroxidase) and the enzymes of phase II (glutathionetransferase, glucuronyltransferase, acetyltransferase, thioltransferase, sulphotransferase and glyoxalase) were measured in the microsomal or cytosolic fractions obtained from ileum and colon mucosa. The activity in the ileum was higher than in the colon for NADPH cytochrome c reductase (p less than 0.05) and cytosolic epoxide hydrolase (p less than 0.001) (phase I enzymes), and glutathionetransferase (p less than 0.02), sulphotransferase (p less than 0.05) and glyoxalase (p less than 0.02) (phase II enzymes). The other enzymes had similar activities in two mucosa. The distribution pattern of drug metabolizing enzymes cannot be considered as a single pattern in human ileum and colon because of the observed enzyme-dependent differences.

Profile of drug-metabolizing enzymes in the cortex and medulla of the human kidney.

The cortex and medulla were isolated from kidneys whose donors (5 men and 1 woman, aged between 44 and 68 years) were undergoing nephrectomy to remove a tumor. Kidneys with normal architecture for at least two thirds of the organ were included in the study. Tissue specimens used in our experiments were free from pathological changes. The activities of the following enzymes of phase I NADPH cytochrome c reductase, aminopyrine N-demethylase, ethoxycoumarin O-deethylase, ethoxyresorufin O-deethylase, microsomal and cytosolic epoxide hydrolases, glutathione reductase and glutathione peroxidase, and those of the following enzymes of phase II glutathione transferase, glucuronyl transferase, sulphotransferase, acetyltransferase, thiomethyltransferase, thiopurinemethyltransferase, thioltransferase and glyoxalase were measured. The activity in renal cortex was significantly higher than in medulla for NADPH cytochrome c reductase, cytosolic epoxide hydrolase, glutathione reductase and glutathione peroxidase (phase I enzymes), and glutathione transferase, acetyltransferase, thiomethyltransferase, thiopurinemethyltransferase, thioltransferase and glyoxalase (phase II enzymes). The other enzymes had similar activity in cortex and medulla. The distribution pattern of drug-metabolizing enzymes in the human kidney cannot be considered as a single pattern because of the observed enzyme-dependent differences between cortex and medulla.