Platelet Phenolsulphotransferase Research Articles

Platelet phenolsulphotransferase activity in patients with dementia of Alzheimer type

Human blood platelets are more and more regarded as a reliable model of nerve cells, and some biochemical alterations found in platelet enzyme activities and receptor binding parameters may be related to analogous changes occuring in the central nervous system. Platelet phenol‐sulphotransferase activity has been evaluated in some neurological disorders, such as Parkinson's disease and headache. In the present work we determined phenolsulphotransferase activity in platelets of 36 patients with dementia of Alzheimer type, and compared such activity values with those of 36 sex‐ and age‐matched healthy controls. Patients showed a significantly higher platelet phenolsulphotransferase activity than control subjects, both with dopamine and with phenol as substrates. Moreover, a significant positive correlation was found between platelet enzyme activity and severity of illness. These findings are discussed in terms of the biochemical abnormalities found in the central nervous system of demented subjects, and in terms of the possible pathogenetic involvement of an altered phenolsulphotransferase activity (and, in general, of a modified monoamine metabolism) in such derangements of biochemical systems often occuring in dementia of Alzheimer type.

Dietary modulation of human platelet phenolsulphotransferase activity.

1. The mammalian phenolsulphotransferase enzymes are known to play a major role in both the detoxification and possibly the activation of pre-carcinogenic phenols and aromatic amines. 2. Vegetable cytosol preparations were tested in vitro for their ability to affect the sulphation of two reference compounds (rho-nitrophenol and dopamine, which are selective substrates for the phenol and monoamine forms of phenolsulphotransferase respectively), and to act as substrates for the enzymes in comparison with the same reference compounds. 3. The majority of cytosols greatly decreased (> 80%) the sulphation of either or both the reference compounds. This effect may have been due to either enzyme inhibition or substrate binding. 4. Whereas some of the cytosols were sulphated under the assay conditions, most were not. Additionally, it was found that a cytosol that decreased the sulphation of the two reference compounds was not necessarily poorly sulphated itself. 5. It is concluded that dietary factors have the potential to play a major role in modulating the sulphation detoxification pathway, and have wide ranging implications with regard to adverse drug reactions.

Reduced platelet phenolsulphotransferase activity towards dopamine and 5-hydroxytryptamine in migraine.

The sulphation of the neurotransmitters dopamine and 5-hydroxytryptamine, and of the prototypical xenobiotic 4-nitrophenol, by phenolsulphotransferases was measured in platelet homogenates prepared from a group of migraine sufferers and a group of control subjects. The activity of the M form of phenolsulphotransferase, responsible for the sulphation of dopamine and 5-hydroxytryptamine was significantly reduced in the migraine population, by 28% with dopamine as substrate and by 20% with 5-hydroxytryptamine. The activity of the P form of the enzyme towards 4-nitrophenol was the same in both groups. We also report that the selective inhibition of P form phenolsulphotransferase by red wine is much more potent than previously thought, with a 2000-fold dilution of dealcoholised red wine having the ability to inhibit sulphation by this enzyme by 50%. Our findings suggest that a reduced capacity for sulphation and inactivation of biogenic amines and catecholamines may be related to susceptibility to migraine.

The human phenolsulphotransferase polymorphism is determined by the level of expression of the enzyme protein.

We have examined the expression of platelet phenolsulphotransferase (PST) in 60 individuals. Using an antibody which recognizes both forms of PST present in man (P-PST and M-PST), we determined that the polymorphism of platelet P-PST activity is determined by the level of expression of the enzyme protein. The implications for susceptibility to adverse drug reactions and chemical carcinogenesis are discussed.

Effect of dopamine and dopamine-antagonist infusion on blood platelet count, size and release reaction in hypertensive and normotensive subjects

To examine the effect of dopamine on in vivo platelet function and a possible platelet contribution to the clearance of dopamine we measured platelet count, platelet size and plasma concentration of the platelet specific protein beta-thromboglobulin (BTG) in groups of 40 year old untreated hypertensive and normotensive men. One hypertensive (n = 10) and one normotensive (n = 10) group received dopamine infusion at doses from 0.5 to 2.0 micrograms/kg/min which increased plasma dopamine 100-fold from baseline. Two other groups of hypertensive (n = 10) and normotensive (n = 11) subjects received 10 mg of the dopamine antagonist metoclopramide intravenously, upon which serum prolactin concentration increased 10-fold. No significant effect on platelet function in any group was observed during these interventions. Platelet phenol-sulphotransferase may contribute to dopamine conjugation. However, the selected platelet parameters correlated only weakly with dopamine kinetics during the infusion. Neither dopamine nor a dopamine antagonist altered the selected platelet parameters, nor did these parameters influence the clearance of dopamine during a short-lasting pharmacological infusion.

Platelet phenolsulphotransferase activity and 'abdominal migraine'.

Low platelet phenolsulphotransferase activity has been reported in adult patients with dietary sensitive migraine. Platelet activity of this enzyme was therefore measured in children having 'abdominal migraine' with probable dietary trigger and in controls. No significant difference was found in activity between the two groups. There was no significant correlation between platelet phenolsulphotransferase activity and age.

Effect of pregnancy on human platelet monoamine oxidase and phenolsulphotransferase M and P

SummaryThere were no significant changes in platelet phenolsulphotransferase M and monoamine oxidase activities in pregnant women compared with controls and women postpartum, although mean monoamine oxidase values were about 10 per cent higher during pregnancy. Platelet phenosulphotransferase P activity tended to decline during pregnancy and rose substantially postpartum. Mean values postpartum were higher than those in the pregnant group as a whole (P > 0.01) and in women during the last trimester of pregnancy (P > 0.01). If these platelet findings reflect changes elsewhere in the body, they might imply that women towards the end of pregnancy are more sensitive and women postpartum less sensitive to the action of drugs that are inactivated by sulphoconjugation.

Human platelet phenolsulphotransferase M and P: substrate specificities and correlation with in vivo sulphoconjugation of paracetamol and salicylamide.

Human platelet phenolsulphotransferase exists in two functional forms. M and P. In this study the substrate specificity of the two forms has been further delineated by correlating activities in different individuals with various substrates. m-Tyramine, noradrenaline, adrenaline, 5-hydroxytryptamine, p-hydroxyamphetamine, isoprenaline, salbutamol and l-naphthol were all specific substrates for the M form of the enzyme. Paracetamol, a mixed substrate, was predominantly metabolized by the M form. Salicylamide at 5 microM was a substrate for the P form but became and M substrate at higher concentration. Phenol itself, a specific substrate for phenolsulphotransferase P at 10 microM, also became an M substrate at 1 mM concentration. These substrate specificities were confirmed with the selective inhibitor, dichloronitrophenol. In this study, we measured phenolsulphotransferase activity in platelets from 13 individuals selected on the basis of their wide variation in ability to sulphoconjugate paracetamol and salicylamide in vivo. There was no significant relationship between the in vivo pattern with either drug and the activity of platelet phenolsulphotransferase assayed with paracetamol or salicylamide respectively.

Platelet phenolsulphotransferase activity in Parkinson's disease.

Mean platelet phenolsulphotransferase activity was significantly increased in L-dopa-treated parkinsonian patients compared with controls. The degree of rise was associated with dose of and duration of treatment with L-dopa and may thus represent an adaptive increase to circulating dopamine. Alternatively, the increase may reflect changes supervening with duration of illness.

Sulphate conjugation of p-hydroxytriamterene by platelet phenol sulphotransferase: assay conditions and correlation with metabolism in man.

1 Sulphate conjugation catalyzed by phenol sulphotransferase (PST) is an important pathway in the metabolism of many drugs including triamterene. Variations in PST activity in an easily obtained tissue such as the platelet might reflect individual differences in the sulphate conjugation in other organs and tissues. Human platelets contain at least two forms of PST, a thermolabile (TL) form for which dopamine is a substrate and a thermostable (TS) form for which low concentrations of p-nitrophenol serve as a substrate. 2 p-OH-triamterene, the major metabolite of triamterene, is conjugated with sulphate in vivo. p-OH-triamterene was a substrate for platelet PST with an apparent Michaelis-Menten value of 26 microM. Thermal stability studies indicated that p-OH-triamterene was a substrate for only the TS form of platelet PST. 3 When platelet homogenates from 29 individual subjects were tested, there was a significant correlation between PST activities measured with 4 microM p-nitrophenol and with p-OH-triamterene (r = 0.985, P less than 0.0001) but not between activities measured with dopamine and with p-OH-triamterene (r = 0.023, P greater than 0.2). These results confirmed that p-OH-triamterene was a substrate for only the TS form of human platelet PST. 4 The same 29 subjects were treated with 1 mg/kg of triamterene orally. 24-h urinary excretions of triamterene, p-OH-triamterene and p-OH-triamterene sulphate averaged 15.3%, 6.3% and 78.4%, respectively, of the total of triamterene plus measured metabolites excreted. The excretion of triamterene plus the two metabolites averaged 43.1 +/- 2.6% (mean +/- s.e. mean) of the ingested dose. There was not a significant correlation between the proportion of p-OH-triamterene excreted as sulphate conjugate and the activities of either the TS or TL forms of platelet PST activity.

Alpha-Methyldopa, alpha-methyldopamine an alpha-methylnoradrenaline: substrates for the thermolabile form of human platelet phenol sulphotransferase.

1 Sulphate conjugation catalyzed by phenol sulphotransferase (PST) is an important pathway in the catabolism of alpha-methyldopa (MD). Variations in PST activity in an easily obtained tissue such as the human platelet might reflect individual differences in the sulphate conjugation of MD in other organs and tissues. There are at least two forms of human platelet PST, a thermolabile form for which dopamine is a substrate and a thermostable form for which low concentrations of phenol can serve as a substrate. 2 MD, alpha-methyldopamine (MDA) and alpha-methylnoradrenaline (MNA) were tested as substrates for human platelet PST. All three were substrates for the thermolabile form of the enzyme and none were substrates for the thermostable form of PST. Apparent Michaelis-Menten (Km) values for MD, MDA and MNA were 5.5, 0.014 and 0.28 mM, respectively. Apparent Km values for 3'-phosphoadenosine-5'-phosphosulphate, the sulphate donor for the reaction, were 0.08, 0.13 and 0.10 microM, respectively, for the three catechol substrates. The pH optima for the reaction were 7.5 for MD and 6.5 for both MDA and MNA. 3 When platelet homogenates from 20 individual subjects were tested, there were significant correlations between PST activities measured with dopamine and those measured with MD, MDA and MNA (r = 0.54, 0.98 and 0.93, P less than 0.02, less than 0.001, and less than 0.001, respectively), but not between activities measured with low concentrations of phenol and those measured with MD, MDA and MNA (r = 0.021, 0.045 and 0.046, respectively). There results were also compatible with the conclusion that MD, MDA and MNA were substrates for the thermolabile form of platelet PST. 4 These observations will make it possible to test the hypothesis that variations in the activity of the thermolabile form of platelet PST may reflect individual differences in the sulphate conjugation of MD, MDA and MNA.

PLATELET PHENOLSULPHOTRANSFERASE DEFICIENCY IN DIETARY MIGRAINE

Patients with dietary migraine were found to have significantly lower levels of platelet phenolsulphotransferase activity than either migrainous patients without a history of dietary provocation or normal controls. Of the two known human variants of this enzyme, the phenol-inactivating P form, for which no endogenous substrate has so far been identified, was more severely involved than the M enzyme, which inactivates monoamines (including tyramine). Such commonly implicated, dietary triggering agents as chocolate and cheese may contain as-yet-unidentified phenolic substrates of phenolsulphotransferase P; if the platelet enzyme deficiency were mirrored by low gut activity, abnormally large amounts of potentially toxic substances might gain access to the circulation in consequence.

A genetic study of platelet phenolsulphotransferase activity in normal and schizophrenic twins

In a series of 19 identical and 16 fraternal twin pairs, the activities of the two forms of the enzyme, phenolsulphotransferase, denominated M and P, were investigated in blood platelets. Both were shown to be under a high degree of genetic control. No differences were found between 11 schizophrenic patients from discordant twin pairs, compared with their well cotwins and 12 male and female volunteer twin pairs, for either form of the enzyme.

Human platelet phenolsulphotransferase: Separate control of the two forms and activity range in depressive illness

Human phenolsulphotransferase exists in two forms, one specific for dopamine and tyramine, termed “M” and one for phenol, termed “P”. In this study we have shown that these two forms are under separate control by correlating their activities in different individuals using different substrates. There was a highly significant correlation between the activities with dopamine, p-tyramine and 4-hydroxy-3-methoxyphenylglycol, but no significant correlation between the activities with any of these three substrates and that with phenol. Neither age nor sex had any effect on platelet phenolsulphotransferase “M” or “P” activities. Nor was there any significant correlation between platelet monoamine oxidase activity and phenolsulphotransferase “M” or “P” activities. Human platelet phenolsulphotransferase “M” was found to be unstable at temperatures above 35°C and it lost substantial activity when stored deep frozen in isotonic saline. However it was stable for up to four months when stored in isotonic sucrose or 10 mmol/1 phosphate buffer (pH 7.4). Phenolsulphotransferase “M” and “P” activities were measured in platelets from depressed patients of a diagnostic type characterized by low output of tyramine- O-sulphate after oral tyramine loading but their enzyme activities were not different from those in two control groups.

Sulphate conjugation of biologically active monoamines and their metabolites by human platelet phenolsulphotransferase

The substrate specificity of phenolsulphotransferase in human platelets has been studied using a wide range of biogenic amines and their metabolites. Substantially differing activities were observed at 30 μmol/l; the enzyme was more active towards the catecholamines and their alcoholic metabolites than the corresponding acids (with the exception of 3,4-dihydroxyphenylacetic acid which did not appear to be a substrate) and the relative order was not changed by dialysis to remove possible low molecular mass inhibitors. However, most of the V values were similar to each other, reflecting a large variation in K m values, ranging from 0.3 μmol/l for 3-methoxytyramine to 3700 μmol/l for 4-hydroxy-3-methoxymandelic acid. All substrates showed substrate inhibition. Dopamine, noradrenaline and adrenaline all had a high affinity for the enzyme, with K m values of 3.0, 5.0 and 2.7 μmol/l respectively. These values are considerably lower than those for monoamine oxidase and the relative importance of oxidation and sulphoconjugation of these amines in vivo may be concentration dependent. Human platelet phenolsulphotransferase appears different from the rat enzyme, but similar to that described by others in human brain. The platelet should be a useful source of enzyme for clinical studies.

Human platelet phenol sulphotransferase: Assay procedure, substrate and tissue correlations

Procedures for the precise assay of human platelet phenol sulphotransferase activity were determined. The coefficient of variation of the assay was 5.8% when the enzyme activity was expressed per 10 8 platelets, and was 9.4% when it was expressed per mg soluble platelet protein. Mean platelet phenol sulphotransferase (PST) activity in samples from 102 randomly selected adults was 1.2 ± 0.4 units/10 8 platelets (mean ± S.D.), with a range from 0.2 to 2.9. The mean activity for umbilical cord blood platelet PST was 0.93 ± 0.3 units/10 8 platelets (mean ± S.D., n = 27). The substrate used routinely for the assay was 3-methoxy-4-hydroxyphenylglycol (MHPG). There was a significant correlation between the formation of MHPG sulfate by individual platelet preparations and the formation of sulfated product with each of the following substrates: tyramine ( r = 0.92, n = 21); dopamine ( r = 0.82, n = 16); 5-hydroxytryptamine ( r = 0.94, n = 20); acetaminophen ( r = 0.77, n = 17); and alphamethyldopa ( r = 0.77, n = 17) ( p < 0.001 for each). Platelet PST activity correlated significantly with human renal cortex PST activity ( r = 0.54, n = 20, p < 0.02). The correlation coefficient between platelet PST activity and jejunal mucosal enzyme activity in eight patients was 0.67. These results raise the possibility that human platelet PST activity measured with MHPG as substrate might reflect the enzyme activity in other tissues and the degree of sulfate conjugation of a variety of substrates.