Platelet Phenol Sulfotransferase Research Articles

L-DOPA biotransformation: correlations of dosage, erythrocyte catechol O-methyltransferase and platelet SULT1A3 activities with metabolic pathways in Parkinsonian patients.

The objectives of this study were to determine (1) the effects of dose and drug absorption on pathways of biotransformation of L-DOPA in Parkinsonian patients treated with Sinemet, and (2) the extent to which genetically-determined variations in the activities of erythrocyte catechol O-methyltransferase and/or platelet phenol sulfotransferase might be reflected in individual differences in L-DOPA metabolism. In the 19 patients studied, there were negative correlations between dosage or absorption and extent of O-methylation and of sulfation of L-DOPA or its metabolites. Levels of activity for erythrocyte COMT were also reflected in individual variation in the metabolism of L-DOPA. In contrast, differences in platelet phenol sulfotransferase were not reflected in differences in sulfation of L-DOPA or of its metabolites. If such a relationship did exist, it might have been obscured by the effects of high dosage of L-DOPA, effects which might have resulted from a deficiency of the sulfation cosubstrate 3'-phosphoadenosine 5'-phosphosulfate in patients taking higher doses of drug.

Gender-Related Seasonality of Human Platelet Phenolsulfotransferase Activity

This study focused on the investigation of the possible effect of gender and season on the activity of the thermolabile and thermostable forms of platelet phenolsulfotransferase (PST) in a group of 23 healthy, drug-free volunteers of both sexes. The results showed a different seasonal profile of PST activity in men and women: in men, PST seasonal rhythms revealed a shallow profile with higher values in both the spring and summer than in the autumn. Conversely, in women, the PST seasonality showed a profile consisting overall of a main peak in the summer. Also, significant gender-dependent correlations were found between the photoperiod length and PST values. Our findings should stimulate further investigation into gender-dependent molecular mechanisms underlying the regulation of the metabolism of endogenous and xenobiotic agents, such as monoamines and phenols, which are the substrates of PST.

39-116 - Gender X seasonality effect on platelet phenolsulfotransferase

39-116 - Gender X seasonality effect on platelet phenolsulfotransferase

Platelet sulfotransferase in different psychiatric disorders

The aim of our study was to measure and compare platelet phenolsulfotransferase (PST) activity in patients affected by different psychiatric disorders and in healthy volunteers. The results showed that the activity of both of the two forms of PST was significantly higher in 30 patients with obsessive-compulsive disorder and in 25 manic patients than in 20 healthy volunteers. On the contrary, normal values were found in 11 dysthymic patients, 12 bipolar depressives, and 14 patients with panic disorder, whereas lower values were found in 12 unipolar depressives and 30 patients with migraine. It would therefore seem that different neuropsychiatric disorders are associated with different levels of PST activity.

Deuterium-labelled p-tyramine challenge test and phenolsulfotransferase activity in depressed patients — failure to replicate decreased p-tyramine conjugation in depression

1. 1. Depressed and normal subjects were challenged with deuterium-labelled p-tyramine and urine was collected for 3 h. 2. 2. Urinary excretion of conjugated p-tyramine was not significantly different between normal, melancholic and non-melancholic depressed subjects. 3. 3. Platelet phenolsulfotransferase activity to p-tyramine (p < 0.05) and to phenol (p 0.005) were significantly lower in the depressed patients.

Immunohistochemical Detection of Phenol Sulfotransferase‐Containing Neurons in Human Brain

Using antibodies raised against human platelet phenol sulfotransferase (PST), immunohistochemical studies were performed to determine the cellular localization of PST in several areas of human brain. In the hippocampus PST immunoreactivity was localized in both the pyramidal and nonpyramidal neurons and was in greatest abundance in the CA2 and CA3 areas. In the striatum the immunoreactivity was most predominant in the large neurons of the globus pallidus and in the medulla the staining was scattered throughout the neurons of the raphe nucleus and the reticular formation. The selective presence of PST in the neurons of the CNS raises the issue as to the role of this enzyme in sulfating neurotransmitters because PST has been shown to be capable of conjugating a variety of neurotransmitters including the catecholamines as well as the tyrosine moiety of a number of small peptides such as enkephalin and cholecystokinin.

Sulfation pharmacogenetics: correlation of human platelet and small intestinal phenol sulfotransferase.

Phenol sulfotransferase (PST) catalyzes the sulfate conjugation of phenolic drugs. All human tissues studied contain a thermostable (TS) form of PST, which catalyzes the sulfate conjugation of "simple" phenols such as p-nitrophenol, and a thermolabile (TL) form, which catalyzes the sulfation of dopamine and other monoamines. In the present study we tested the hypothesis that genetically controlled levels of TS and TL PST activity in the platelet, as well as inherited variations in the thermal stability of platelet TS PST, might reflect those same characteristics of the enzyme in the less accessible tissue, human small intestinal mucosa. Platelet TS and TL PST activities and TS PST thermal stability were measured in blood samples from 45 randomly selected healthy subjects, and 14 of those subjects were selected to have intestinal biopsies performed. There was a significant correlation between levels of platelet and jejunal mucosal TS PST activity (rs = 0.574, p less than 0.030), but there was not a significant correlation between levels of TL PST activity in the two tissues (rs = 0.265, p = 0.368). There was also a significant correlation between the trait of TS PST thermal stability in the two tissues (rs = 0.828, p less than 0.0001). These observations suggest that inherited variations in TS PST activity and thermal stability in an easily obtained tissue, the platelet, might be used to predict individual differences of those properties of the enzyme in the human small intestine, an organ that plays an important role in drug metabolism.

Is the platelet phenolsulfotransferase involved in the sulfoconjugation of plasma catecholamines?

Catecholamines are predominantly present in the sulfoconjugated forms in human plasma. Phenolsulfotransferase (EC 2.8.2.1), which catalyses the sulfation of phenolic compounds, is widely distributed in human tissues. In blood, a phenolsulfotransferase, more specific for catecholamine sulfation is found exclusively in platelets. Free and sulfoconjugated catecholamines were measured in plasma and platelets of healthy volunteers and compared with those present in patients with uremia or pheochromocytoma to determine the ability of platelet phenolsulfotransferase to sulfurylate plasma catecholamines. In patients with pheochromocytoma, the rise in free and sulfoconjugated plasma catecholamines is accompanied by a simultaneous rise of these molecules in platelets. In uremia, where the level of plasma catecholamines is normal, the rise in the sulfoconjugates is not accompanied by a concomitant increase in either free or sulfoconjugated catecholamines in platelets. Platelet phenolsulfotransferase activity remains unchanged in pheochromocytoma and uremia. These data indicate that the platelet phenolsulfotransferase is involved in the sulfation of the catecholamines present in platelets, but its contribution, if any, to the high level of sulfoconjugated catecholamines found in plasma is negligible. This assertion is confirmed by our observations in thrombocytopenic patients. Indeed, despite the very low number of platelets and the absence of plasma phenolsulfotransferase activity, thrombocytopenic patients have normal plasma levels of free and sulfoconjugated catecholamines.

Lung phenol sulfotransferases: Thermal stability of human and bovine enzymes

Phenol sulfotransferase (PST) from human and bovine lung was purified about 1000-fold and the activity was measured with different acceptor substrates. Human lung PST catalyzes sulfation of both exo- and endogenous phenols, but the bovine lung enzyme only exogenous phenols. This difference in substrate specificity seems to be related to the presence of at least two different molecular forms of the enzyme: a thermostable and a thermolabile form in human lung, and two thermostable forms in bovine lung. Like the human platelet PST, the thermostable form from human lung is active with low concentrations of phenol ( K m = 45 μM) and the thermolabile form with dopamine and high concentrations of phenol ( K m = 909 μM). Bovine lung, which shows no catecholamine sulfating activity, contains two thermostable phenol sulfotransferases, both active with phenol but differing in their affinity to this substrate ( K m = 40 μM and 335 μM, respectively).

Human pituitary phenol sulfotransferase: biochemical properties and activities of the thermostable and thermolabile forms.

Pituitary tissue contains phenol sulfotransferase (PST), the enzyme that catalyzes the sulfate conjugation of monoamine neurotransmitters. We carried out these studies with pituitaries obtained 21.3 +/- 3.0 h postmortem (mean +/- SEM; n = 21) to determine whether the biochemical properties and variations in levels of human pituitary PST activities were similar to those of PST in platelets from control subjects. PST in the human platelet has been studied thoroughly because of the possibility that platelet PST might reflect levels of PST activity in other tissues such as the pituitary and brain. Our results demonstrated 2 forms of the pituitary enzyme that were similar to the thermostable (TS) and thermolabile (TL) forms of platelet PST with regard to assay conditions, pH optima, Km values for multiple substrates, responses to 2,6-dichloro-4-nitrophenol (DCNP), and thermal stability properties. Pituitary samples also were obtained at autopsy 6.3 +/- 0.33 h (mean +/- SEM; n = 3) after death to determine the effects of storage at 4 degrees C on PST activities. After storage for 6-18 h, 83-99.6% of the TS PST activity remained and 44-66.9% of the TL PST activity remained. Pituitary TS PST activity in samples obtained within 12.1 +/- 3.25 h after death was 121.0 +/- 49.1 units/mg protein (mean +/- SEM; n = 7) with a range from 9.7 to 367.6. TL PST activity was 35.6 +/- 11.6 units/mg protein (mean +/- SEM; n = 6) with a range from 6.1 to 80.7. Wide variations of both enzyme activities were also present in 3 pituitary tumor samples.(ABSTRACT TRUNCATED AT 250 WORDS)

The platelet phenolsulfotransferase is not indispensable for the sulfoconjugation of plasma catecholamines.

To investigate the role of platelets, a proposed primary site of catecholamine sulfoconjugation, we determined plasma free and sulfoconjugated catecholamines and platelet phenolsulfotransferase activity in severe platelet defficiency states. We found that even in the presence of very low platelet counts, the plasma concentrations of sulfoconjugated catecholamines were within normal limits. Although the platelet phenolsulfotransferase activity expressed per number of platelets was normal there was a considerable decrease of the total platelet phenolsulfotransferase activity. This suggests that the platelet phenolsulfotransferase is not indispensable for the sulfoconjugation of catecholamines and this process can occur elsewhere. A preliminary finding of lower platelet phenolsulfotransferase activity in platelet deficiency states with reduced platelet generation (because of reduced megakaryocytes) than in those states with a decreased platelet survival, suggests that the phenolsulfotransferase is synthesised in the megakaryocytes and the platelets are only carriers of this enzyme.

Sulfate and methyldopa metabolism: Metabolite patterns and platelet phenol sulfotransferase activity

Sulfate conjugation catalyzed by phenol sulfotransferase (PST) is the major metabolic pathway for methyldopa. Methyldopa is also O-methylated in a reaction catalyzed by catechol-O-methyltransferase (COMT). Our studies were performed to determine whether sodium sulfate alters methyldopa metabolism. Methyldopa powder, 3.5 mg/kg, was taken with and without sodium sulfate, 13.25 mg/kg, by 24 subjects in a randomized, crossover design. Compared with results obtained when only methyldopa was taken, sodium sulfate taken with methyldopa increased the proportion of drug excreted as methyldopa sulfate expressed as the percentage of all urinary metabolites (66.0% +/- 5.3% and 50.1% +/- 7.5%; means +/- SD). The percentage of free methyldopa excreted also decreased (17.1% +/- 3.7% and 27.3% +/- 5.5%). Platelet PST and red blood cell COMT activities were measured in blood samples from these subjects. When sodium sulfate was taken with methyldopa, there was a significant correlation between platelet PST activities and percentages of metabolites excreted as methyldopa sulfate (r = 0.545; P less than 0.01). This correlation was not significant when methyldopa was taken alone (r = -0.340; P greater than 0.10). There was a significant correlation between red blood cell COMT activities and the proportion of urinary metabolites excreted as 3-O-methyl-alpha-methyldopa when methyldopa was taken alone (r = 0.532; P less than 0.01) but not when it was taken with sodium sulfate (r = 0.153; P greater than 0.20). Our data support the conclusion that variation in sulfate availability may be one factor responsible for individual differences in the metabolism of clinically used doses of methyldopa.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte catechol-O-methyltransferase, platelet monoamine oxidase, and platelet phenol sulfotransferase activities in patients with prolactin-secreting pituitary adenomas.

Dopamine is metabolized by oxidative deamination catalyzed by monoamine oxidase, O-methylation catalyzed by catechol-O-methyltransferase, and sulfate conjugation catalyzed by phenol sulfotransferase. This study was performed to determine whether platelet monoamine oxidase, red blood cell catechol-O-methyltransferase and platelet phenol sulfotransferase enzymatic activities in patients with prolactinomas were quantitatively different from the same enzyme activities in blood samples from normal subjects. The mean enzyme activities in blood samples from 22 women with histologically proven prolactinomas were compared to the mean enzyme activities in blood samples from 32 normal women. The blood levels of these 3 enzymatic activities were not significantly different between the two groups (P greater than 0.4). If the regulation of these catecholamine-metabolizing enzyme activities in blood elements reflects the regulation of the enzymes in the hypothalamic-hypophyseal region, these results suggest that a defect in the regulation of dopamine-metabolizing enzymes is not associated with the pathogenesis of prolactinomas.

Human platelet phenol sulfotransferase: familial variation in thermal stability of the TS form.

Phenol sulfotransferase (PST) catalyzes the sulfate conjugation of catechol and phenolic drugs and xenobiotic compounds. Platelets and other tissues contain at least two forms of PST, forms that have been designated the "TL" and the "TS" forms. We measured the thermal stability of platelet TS PST in blood samples from 218 randomly selected unrelated subjects by heating platelet homogenates at 44 degrees C for 15 min. Thermal stability was expressed as the ratio of the enzyme activity remaining after preincubation to that in an unheated sample, a heated/control (H/C) ratio. The frequency distribution of H/C ratios for this population sample was bimodal, with a nadir at an H/C ratio of 0.33. Of the 218 subjects studied, 29 (13.3%) had thermolabile TS PST (H/C less than 0.33). Platelet samples were then obtained from subjects with thermolabile and thermostable TS platelet PST. PST activity in these platelet samples had similar apparent Km constants for substrates. IC50 values for inhibition of TS PST by 2,6-dichloro-4-nitrophenol in these samples were also nearly identical. The results of experiments in which platelet homogenates from subjects with thermolabile and thermostable TS PST were mixed and the results of experiments in which platelet homogenates were subjected to gel filtration chromatography were compatible with the conclusion that individual differences in TS PST thermal stability were properties of PST itself. Finally, there was a significant familial aggregation of the trait of thermolabile TS PST when H/C ratios were measured in platelet homogenates from 231 members of 49 randomly selected families.

Human platelet phenol sulfotransferase: stability of two forms of the enzyme with time and presence of a racial difference

Thermolabile (TL) and thermostable (TS) forms of human platelet phenol sulfotransferase (PST) were measured over various periods of time. TL PST was assayed with dopamine as the substrate and TS PST was measured with phenol and with p-nitrophenol. Levels of TL and TS PST from the same subjects did not change significantly over 1 day, 1 week, 4 weeks, and 8.5 months. Interassay coefficients of variation of PST activities over 3–4 weeks measured in samples from 8–12 subjects with dopamine, phenol and p-nitrophenol were 13.96%, 13.60% and 13.30%, respectively. There was a significant correlation between PST activity measured in the same samples with phenol and with p-nitrophenol ( r = 0.946, n = 18, p < 0.0001). TS PST activity measured with p-nitrophenol was significantly higher ( p < 0.0001) in platelets from 51 black subjects than the level of TS PST in samples from 52 white subjects (0.72 ± 0.06 vs 0.42 ± 0.04 units/10 8 platelets, respectively; mean ± SEM). These results demonstrate the ‘stability’ of the levels of both forms of the enzyme with time. They also point out the usefulness of a reproducible assay for the detection of a racial difference in the levels of TS PST.

Platelet phenol sulfotransferase and erythrocyte catechol-O-methyltransferase activities: correlation with methyldopa metabolism.

Methyldopa is metabolized by sulfate conjugation catalyzed by phenol sulfotransferase (PST), O-methylation catalyzed by catechol-O-methyltransferase (COMT), and decarboxylation catalyzed by aromatic L-amino acid decarboxylase. These experiments were performed to determine whether individual variations in red blood cell (RBC) COMT and platelet PST activities might reflect variations in the metabolism of methyldopa in man. Methyldopa, 3.5 mg/kg, was taken orally by 28 subjects. Blood samples were obtained from these subjects for the assay of platelet PST and RBC COMT activities, and a 24-hr urine sample was collected for the measurement of methyldopa and its major metabolites. Human platelets contain two independently regulated forms of PST. One form is thermolabile (TL), and the other is thermostable (TS). Methyldopa and alpha-methyldopamine are substrates for the TL but not for the TS form of PST. The results of the experiment showed significant correlations between TL platelet PST activity and the proportion of alpha-methyldopamine excreted as a sulfate conjugate, and between RBC COMT activity and the proportion of methyldopa excreted as an O-methyl metabolite. There was no significant correlation, however, between TL platelet PST activity, and the proportion of methyldopa itself excreted as a sulfate conjugate. These results are compatible with the conclusion that differences among subjects in drug metabolizing enzyme activities are one factor responsible for wide individual variations in methyldopa metabolism in man.

Thermolabile and thermostable human platelet phenol sulfotransferase. Substrate specificity and physical separation.

Human platelets contain at least two forms of phenol sulfotransferase (PST), a thermolabile (TL) form for which dopamine is a substrate and a thermostable (TS) form for which micromolar concentrations of phenol can serve as substrate. At higher concentrations phenol is also a substrate for the TL form. Studies of the regulation and the possible clinical value of measurements of platelet PST have been hampered because there is no specific substrate for the TS form of the enzyme. The purposes of these experiments were to determine whether there might be a better substrate than phenol for use in measurement of the activity of the TS form of platelet PST, and to attempt to physically separate the two forms of the platelet enzyme. The results of substrate kinetic, thermal stability, and inhibitor studies performed with platelet homogenates were all compatible with the conclusion that p-nitrophenol and 6-OH-melatonin were substrates for both the TS and TL forms of platelet PST. Norepinephrine, epinephrine and 5-OH-tryptamine were substrates for only the TL form. The apparent Km constants of the two forms of PST for p-nitrophenol differed by 7,100-fold when measured in platelet homogenates. This difference was 200 times greater than that which has been reported for phenol. Therefore, p-nitrophenol is the preferred substrate for measurement of the TS PST activity if interference by the TL activity is to be avoided. This information made it possible to use p-nitrophenol as a substrate in experiments designed to separate the two forms of platelet PST.(ABSTRACT TRUNCATED AT 250 WORDS)

Human platelet phenol sulfotransferase: partial purification and detection of two forms of the enzyme.

To begin to study the usefulness of platelet phenol sulfotransferase (PST) as a possible measure of the enzyme activity in other organs such as the brain, we purified human platelet PST 36-120-fold. Activity toward 3-methoxy-4-hydroxyphenylglycol (MHPG), dopamine, 5-hydroxytryptamine (5-HT), and phenol eluted in the same Sephadex G-100 and Affi-Gel Blue column fractions. Specific activities of the enzyme with MHPG, dopamine, 5-HT, and phenol as substrates were 1198, 1068, 401, and 408 units/mg protein, respectively. Optimal assay conditions were established for each substrate. Apparent Km values were 598 microM, 21 microM, 19 microM, and 500 microM for MHPG, dopamine, phenol, and 5-HT, respectively. Apparent Km values for 3'-phosphoadenosine-5'-phosphosulfate (PAPS) with the same four substrates ranged from 0.11 to 0.25 microM. The pH optima were 6.3 for phenol, 6.8 for dopamine, and 7.0 for MHPG and 5-HT. An additional pH optimum at 8.6 was present for 5-HT. A thermolabile form of the enzyme measured with dopamine and 5-HT, as well as a thermostable form measured with phenol, were present. Dichloronitrophenol (10(-5) M) noncompetitively inhibited the thermostable enzyme activity by 96% but decreased the thermolabile activity by only 36%. These studies provide the basis for a more accurate comparison of human platelet PST with the enzyme in the human brain and in other tissues.

Platelet phenol sulfotransferase activity: correlation with sulfate conjugation of acetaminophen.

Human platelets contain two independently regulated forms of the drug conjugating enzyme, phenol sulfotransferase (PST). One form of platelet PST activity is relatively thermolabile (TL) and the other is relatively thermostable (TS). Acetaminophen is a substrate for both the TS and TL forms of PST. Our aim was to determine whether individual variations in platelet PST activity might reflect variations in teh sulfate conjugation of oral acetaminophen. Platelet PST activity was measured in blood samples from 29 randomly selected subjects. There was no significant correlation between the independently regulated activities of the TS and TL forms of PST in the platelets of these subjects (r = 0.16, P less than 0.4). Each of the 29 subjects ingested 10 mg/kg acetaminophen and 24-hr urinary excretions of acetaminophen, acetaminophen glucuronide, and acetaminophen sulfate were measured. Average 24-hr urinary excretions of acetaminophen, acetaminophen glucuronide, and acetaminophen sulfate were 2.3%, 46.9%, and 35.0% of the total dose of drug. There were significant correlations between the activities of both the TS and TL forms of platelet PST and the excretion of acetaminophen sulfate expressed as a percentage of the dose of the drug (r = 0.62, P less than 0.001; r = 0.456, P less than 0.02). The correlation coefficient between the TS activity and the excretion of acetaminophen sulfate was significant when the excretion of sulfate conjugate was expressed as a percentage of the sum of acetaminophen plus conjugated metabolites excreted (r = 0.565, P less than 0.002). Our data demonstrate that relative levels of platelet PST activity reflect individual variations in the urinary excretion of the sulfate conjugate of acetaminophen.