Alvito P. Alvares

Enhanced phenacetin metabolism in human subjects fed charcoal‐broiled beef

There were marked individual differences in the plasma levels of phenacetin after oral administration of a 900‐mg dose to 9 normal volunteers eating their customary home diet. Feeding a diet that contained charcoal‐broiled beeffor 4 days prior to the administration of phenacetin markedly decreased the plasma levels of this drug without appreciably influencing the plasma concentrations of phenacetins metabolite, N‐acetyl‐p‐aminophenol (APAP), or the plasma half‐life of phenacetin. The average peak concentration of phenacetin in plasma, after a 900‐mg oral dose, fell from 1,628 ng/ml, when the subjects were fed a control diet for 7 days, to 352 ng/ml after they were fed the same diet which contained charcoal‐broiled beeffor 4 days. The average peak concentration of phenacetin rose to 1,885 ng Iml after the subjects were subsequently fed the control diet for 7 days. The ratios of the average concentrations of APAP in plasma to those of phenacetin markedly increased after the charcoal‐broiled beef diet. The results suggest that a diet containing charcoal‐broiled beef enhances the metabolism of phenacetin in the gastrointestinal tract and/or during its first pass through the liver. This effect greatly decreases the bioavailability of phenacetin.

Effect of charcoal‐broiled beef on antipyrine and theophylline metabolism

Eight healthy volunteers were sequentially fed a control diet, a charcoal‐broiled beef‐containing diet, and the control diet a second time. The mean plasma half‐lives (t½) of antipyrine and theophylline were each decreased by 22% after the subjects were fed the charcoal‐broiled beef‐containing diet. The mean plasma t½s for these drugs returned to control values when the subjects were fed the control diet for a second time. Considerable individuality occurred in the responsiveness of the subjects to the charcoal‐broiled beef‐containing diet. The decreases in antipyrine plasma t½s among the 8 subjects ranged from 5% to 39%, and the decreases in theophylline t½S ranged from 0% to 42%.

Gel electrophoresis of partially purified cytochromes P450 from liver microsomes of variously-treated rats

Liver microsomes and partially purified cytochromes P450 prepared from untreated animals or those injected with phenobarbital, or 3-methylcholanthrene, or polychlorinated biphenyls, were subjected to slab-gel SDS-electrophoresis. There were observed marked differences, after these treatments, in the gel-electrophoresis patterns of the induced cytochromes P450 in the microsomes and partially purified preparations.

DRUG METABOLISM IN NORMAL CHILDREN, LEAD POISONED CHILDREN AND NORMAL ADULTS

Drug‐metabolizing capacities were determined in 10 normal adults and 10 children in the age range from 1 to 8 years. Among the latter, 2 were normal and 8 had biochemical evidence of lead poisoning but no clinical expression of plumbism. There were no differences between the 2 normal children and the 8 lead‐poisoned children in their capacities to metabolize two test drugs, antipyrine and phenylbutazone. The mean antipyrine half‐life in the whole group of 10 children, 6.63 hr, was significantly lower than the mean half‐life of 13.58 obtained in adults. The mean phenylbutazone half‐lives in the children and adults, 1.68 and 3.16 days, respectively, also differed significantly. Thus children in the age range studied appear to metabolize drugs at almost twice the rate of adults, which differs from findings in animals in which drug‐metabolizing capacities increase with maturation. In two other children who showed clinical as well as biochemical manifestations of acute plumbism, antipyrine half‐lives were significantly longer than normal and therapy with EDT A led to restitution toward normal.

Induction of Benzo[α]pyrene Hydroxylase in Human Skin

Foreskins from children who were circumcised 2 to 4 days after birth contain an enzyme system that hydroxylates the carcinogen benzo[α]pyrene. When foreskin was cultured for 16 hours in the presence of 10 micromolar benz[α]anthracene, a two- to fivefold increase in activity of benzo[α]pyrene hydroxylase was obtained. An evaluation of the basal activity and inducibility of carcinogen-metabolizing enzymes in human tissues may provide a means of determining the ability of different individuals to metabolize carcinogens.

Studies on the hydroxylation of 3,4-benzpyrene by hepatic microsomes: Effect of albumin on the rate of hydroxylation of 3,4-benzpyrene☆

Abstract The enzyme system which hydroxylates 3,4-benzpyrene was studied using 9000 g supernatant and microsomes from livers of untreated rats and 3-methylcholanthrene-treated rats. When 9000 g supernatant obtained from less than 10 mg of liver is used as the enzyme source, the rate of formation of hydroxy-3,4-benzpyrene was proportional to tissue concentration. In contrast, when microsomes obtained from less than 10 mg of liver were used, the rate of reaction was not linear with tissue concentration. However, linearity could be obtained if albumin was added to the reaction mixture. The kinetic constants for 3,4-benzpyrene hydroxylase obtained with liver microsomes, in the presence of albumin, were similar to those previously reported using 9000 g supernatant in the absence of albumin. Evidence is presented which shows that the addition of albumin or liver microsomes to the incubation mixture used for the assay of 3,4-benzpyrene hydroxylase activity resulted in an increase in the amount of 3,4-benzpyrene solubilized.

Antipyrine: Radioimmunoassay in plasma and saliva following administration of a high dose and a low dose

A simple and sensitive radioimmunoassay has been developed for the determination of antipyrine levels in plasma and salim of man. Antiserum to antipyrine was obtained from rabbits immunized with an immunogen prepared by covalently coupling N‐(4‐antipyrinyl)‐succinamic acid to bovine serum albumin (BSA). The radioimmunoassay can detect antipyrine levels as low as 10 ng/ml of plasma or saliva, using a 0.1‐ml sample. This contrasts with the sensitivity of a commonly used spectrophotometric method that can measure about 4,000 ng/ml using a 2‐ml plasma sample. Agreement between the radioimmunoassay and spectrophotometric assay of antipyrine was excellent for plasma (r = 0.98) and saliva (r = 0.97) when samples were analyzed from 6 subjects receiving 18 mg/kg of antipyrine. The correlation between plasma and saliva antipyrine half‐lives using the radioimmunoassay and an 18 mg/kg dose of antipyrine was r = 0.90 (p < 0.005). After a dose of 1.8 mg/kg of antipyrine, the drug disappeared monoexponentially from plasma and salim for at least 51 hr, and the correlation between plasma half‐life and saliva half‐life was r = 0.97 (p < 0.001) in the 6 subjects. Excellent agreement was also observed between half‐lives after the high and low doses of antipyrine (r = 0.99, p < 0.001 for plasma and r = 0.98, p < 0.001 for saliva).

The inducing properties of polychlorinated biphenyls on hepatic monooxygenases.

The polychlorinated biphenyls (PCBs) represent a newly recognized and widely distributed category of environmental pollutants whose biologic impact on animals and man may be both substantial and highly detrimental. The pharmacologic effects of these agents on enzymes in the liver which metabolize drugs and other foreign compounds. such as carcinogens. are powerful and long lasting. PCBs mimic the effects produced on these enzymes by drugs. such as phenobarbital. and carcinogens. such as 3‐methylcholanthrene. They are potent inducers of cytochromes P‐450 and P‐448 and associated enzymic activities. Further. these chemicals can cross the placental barrier and be transmitted through maternal milk to the newborn infant causing marked increases in drug biotransformation enzymes in the fetus and the neonate. Studies with the use of microscope immersion oils containing PCBs show that application of minute amounts of these oils to the skin of experimental animals results in a marked induction of the drugand carcinogen‐metabolizing enzymes. These findings suggest that even trivial skin exposure to chemicals. such as PCBs. can have significant and perhaps harmful biologic effects in man.

Induction of aryl hydrocarbon hydroxylase by polychlorinated biphenyls in the foeto‐placental unit and neonatal livers during lactation

Polychlorinated biphenyls (PCBs) have been widely used as industrial chemicals in a variety of commercial and domestic products. They also constitute a major component of microscope immersion oils. Residues of PCBs have been widely found in tissues of fish and wild life and contamination of human adipose tissue [ 1,2] and of human milk [3] has been previously reported. Recent studies from this laboratory [4] have shown that PCBs are potent inducers of the hepatic mixed function oxidase system, enhancing the metabolism of a variety of substrates and causing marked increases in the concentration of cytochrome P-450, effects similar to the barbiturate class of inducing chemicals. PCBs also cause several fold increases in hepatic aryl hydrocarbon hydroxylase [4] , the enzyme involved in the metabolism of chemical carcinogens, such as benzo(a)pyrene. In this respect, PCBs share a number of properties of the carcinogen type of inducers of microsomal enzymes, including that of inducing the synthesis of cytochrome P-448 [4]. Since PCBs have been found in human adipose tissue and in human milk, it was of interest to determine the effects of these chemicals on the fetal environment as well as their possible effects on neonatal liver enzymes as mediated by the transmission of these chemicals through maternal milk. In this regard, the effects of the PCBs were compared to those of phenobarbital and the polycyclic hydrocarbon carcinogen, 3-methylcholanthrene (3-MC).

Effect of storage of frozen liver microsomal preparations on the hydroxylation of testosterone and pentobarbital and the N-demethylation of ethylmorphine

Abstract The activity of the liver microsomal enzyme systems responsible for the hydroxylation of testosterone in the 7α-, 16α- and 6β-positions is differentially affected by storage of microsomal preparations at −15°. The 16α-hydroxylase activity decreased upon storage of microsomal suspensions or lyophilized preparations for 20 days, but was not affected when the microsomes were stored as a pellet. In contrast, the 7α- hydroxylase activity remained essentially unchanged while the 6β-hydroxylase activity decreased in all three microsomal preparations. The stability of pentobarbital hydroxylase and ethylmorphine N -demethylase was similar to that obtained for testosterone 16α-hydroxylase. The differential effects of storage of liver microsomal preparations on the hydroxylation of testosterone in the 6β-, 7α- and 16α-positions suggest that a single cytochrome cannot alone determine the specificity of the three hydroxylation reactions. In addition, the results suggest that when storage of microsomes for more than 1 day is absolutely necessary, microsomes should be stored as a pellet rather than as a suspension or as a lyophilized powder.