Merton Sandler

Multiple forms of phenolsulphotransferase in human tissues: Selective inhibition by dichloronitrophenol

Evidence is presented for two functional forms of phenolsulphotransferase in human tissues: (1) activity ratios, using dopamine and phenol as substrates, varied 30-fold between different tissues, whereas the dopamine to tyramine activity ratio was relatively constant; (2) incubation at 37 degrees caused a selective decrease in activity towards dopamine compared with phenol; and (3) phenol sulphoconjugation was selectively inhibited by dichloronitrophenol and pentachlorophenol compared with that of dopamine and tyramine. The two forms, which have been designated M (monoamines) and P (phenol), were both present in platelets, jejunum, adrenal and brain.

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.

Gut flora and the origin of some urinary aromatic phenolic compounds.

The concentration of several phenolic acids and alcohols was measured in urine from germ-free and specific pathogen-free (SPF) rats before and after inoculation with faecal microorganisms, and from conventional rats before and after gut sterilization. The rate of excretion of benzoic acid, phenylacetic acid, and m- and p-hydroxyphenylpropionic acid in the germ-free animals was markedly increased after inoculation. Some acids showed no increase, including the endogenously generated homovanillic, vanilmandelic and p-hydroxyphenyllactic acids. Most others sought showed a small but significant increase. Some of the compounds excreted by the germ-free animals may have been in the food pellets, either as such or as precursors. The pattern was somewhat different in the SPF rats. The excretion of p-hydroxyphenylpropionic, p-hydroxyphenylacetic and m-hydroxyphenylacetic acids was initially much higher than in the germ-free animals and their excretion decreased after inoculation, presumably because of an altered pattern of gut flora. This work quantifies the effect of gut flora in the formation of some of the more important phenolic acids found in rat urine.

In vitro inhibition of phenolsulphotransferase by food and drink constituents

Several natural and synthetic food and drink constituents were tested in vitro for their inhibitory actions on phenolsulphotransferase P and M (PST P, PST M) and monoamine oxidase A and B (MAO A, MAO B). Cyanidin 3-rutinoside, a simple anthocyanin, (+)-catechin, a flavanol, and carmoisine, a synthetic food colorant, were found to be particularly potent, reversible inhibitors of PST P. All inhibited this enzyme by 100% at a concentration of 5 microM and had an IC50 in the microM range. The effects of these compounds on PST M and MAO A and B were less pronounced. There was a considerable difference in the inhibitory ability of different purified anthocyanins but all were selective for PST P. Several other phenolic food colorants were also found to be specific inhibitors of PST P, though less potent in their actions. Tartrazine, a non-phenolic food colorant, had little effect. The phenolic extracts from two red wines were also found selectively to inhibit PST P in vitro, suggesting that it is within this fraction that these inhibitors are to be found. PST is an important enzyme involved in the inactivation of a wide range of exogenous and endogenous phenols. If such a degree of inhibition were to occur in vivo, potentially toxic concentrations of some phenolic substrates might result.

Anxiolytic Activity of Intraventricularly Administered Atrial Natriuretic Peptide in the Rat

Rat atrial natriuretic peptide (ANP) was investigated for putative anxiolytic activity in rats, following intracerebroventricular (ICV) administration. ANP in doses of 200 and 500 ng/rat induced significant anxiolysis, comparable with that of lorazepam (0.5 mg/kg, IP) in a variety of anxiety models (open-field, elevated plus-maze, social interaction, and novelty-induced feeding suppression tests). Isatin, an endogenous anxiogenic indole, shown to be an antagonist of ANP in vitro, significantly inhibited the anxiolytic effect of ANP in the elevated plus-maze test in subanxiogenic doses. The anxiolytic action of ANP was unaffected by flumazenil, a benzodiazepine receptor antagonist. Conversely, the anxiolytic action of lorazepam was antagonized by flumazenil but not by isatin. The data indicate that ANP may function as an endogenous anximodulator, which may act in conjunction with isatin independently of benzodiazepine receptors. These results strengthen the evidence for links between physiological systems involved in anxiety and those in natriuresis.

Migraine and depression: Biological aspects

There is a considerable overlap in migraine and depression incidence, and both conditions may be associated with low levels of 5-hydroxytryptamine (5-HT). During a migraine attack there is evidence for low levels of platelet 5-HT and possibly also low Vmax for 5-HT uptake; both these findings are also associated with the depressed state. Both conditions can be treated by tricyclic and monoamine oxidase inhibiting antidepressants. However, there are also clear differences: migraine attacks are brief and self limiting. Part of the migraine cascade occurs outside the blood brain barrier, presumably involving blood vessels and, unlike depression, migraine attacks can be ameliorated by drugs which only act peripherally. In addition, migraine patients, especially males, often have permanently low levels of platelet monoamine oxidase activity, whereas patients with unipolar depression tend to have raised levels of this marker. This low enzyme activity may reflect part of the vulnerability to migraine, often associated in the prodromal phase with agitation or hyperactivity. Migraine may form part of a family of brief recurrent self-limiting disorders, which involve disturbances of both mood and monoamines; during the headache phase of the attack, the links with depression are most apparent.

Rat brain monoamine oxidase A and B inhibitory (tribulin) activity during drug withdrawal anxiety.

Morphine (10 mg/kg), ethanol (8% w/v, 2 ml/kg), nicotine (0.1 mg/kg), cannabis extract (200 mg/kg), lorazepam (10 mg/kg) and ondansetron (0.1 mg/kg) were each administered to rats twice daily i.p. for 14 days and the anxiogenic response following their withdrawal was monitored by the elevated plus-maze test 24 h later. Brains were removed and endogenous monoamine oxidase (MAO) A and B inhibitory activity (tribulin) levels measured on day 14 and 24 h after drug withdrawal in different groups of animals. Morphine, ethanol, lorazepam and nicotine withdrawal was associated with significant anxiety and corresponding increase in brain tribulin activity, particularly its MAO A inhibitory component. Cannabis and ondansetron withdrawal were neither associated with anxiety or change in tribulin levels. The investigation supports the postulated role of tribulin as an endogenous correlate of anxiety, its MAO A inhibitory component accounting for a major part of this effect.

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

The substrate specificity of phenosulphotransferase in human platelets has been studied using a wide range of biogenic amines and their metabolites. Substantially differing activities were observed at 30 mumol/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 if Km values, ranging from 0.3 mumol/l for 3-methoxytyramine to 3700 mumol/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 Km values of 3.0, 5.0 and 2.7 mumol/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.

Decreased urinary output of conjugated tyramine is associated with lifetime vulnerability to depressive illness

In a group of normal pregnant women whose psychiatric histories were unknown, those with the lowest output of urinary tyramine (free plus conjugated) after an oral tyramine load had a significantly higher lifetime incidence of depressive illness compared with those with the highest output. as none of the women were suffering from depression at the time of tyramine loading, it seems likely that this decreased excretion of tyramine is associated in some way with vulnerability to depressive illness, whether puerperal or nonpuerperal.

Phenolsulphotransferase in Human Tissue: Evidence for Multiple Forms

We have examined human platelet phenolsulphotransferase (PST) with a wide range of different substrates and compared its activity pattern with that of enzyme in other sites in the human body. The main finding was that the dopamine/phenol activity ratio varied considerably from tissue to tissue, ranging from 5.6 in the jejunum to 0.18 in the adrenal, pointing to the presence of more than one enzyme. Further evidence for the presence of two forms of PST has been obtained by the use of the inhibitor, dichloronitrophenol (DCNP), which selectively inhibited phenol- compared with dopamine-conjugating activity in both platelet and brain. We therefore propose that the two forms of the enzyme be denoted PST P (for phenol) and PST M (for monoamine and monoamine metabolites) respectively. The specific activity of the enzymes towards both phenol and dopamine varied considerably in the different human tissues examined, both being most active in the jejunum and least in the brain. The high activity in the intestine supports the view that the enzymes are important in dealing with exogenous phenols.