Kandiah Sivarajah

Arachidonic acid-dependent metabolism of (±) trans-7,8-dihydroxy-7,8- dihydro-benzo[a]pyrene (BP-7,8 diol) to 7,10/8,9 tetrols

The environmental pollutant benzo [alpyrene (BP) is not carcinogenic per se but requires metabolic activation by the cytochrome P-450-dependent monoxygenase system for the manifestation of carcinogenic activity [ 1,2]. The activation of BP results in the generation of reactive metabolites which can covalently bind to DNA. The covalent binding of some reactive BP intermediates to DNA is implicated with carcinogenesis [3,4]. Recent evidence suggests that the diol epoxides are the ultimate carcinogenic form of BP [4,5]. The pathway of diol epoxide formation involves epoxidation and hydration of BP catalyzed by the cytochrome P-450 monooxygenase system-dependent and epoxide hydrase . We have reported that BP, BP-7,8-diol and 7,12dimethyl benzanthracene are oxidized by guinea pig lung microsomes during prostaglandin (PC) biosynthesis to reactive metabolites which can covalently bind to tissue protein and nucleic acids [6]. The nature of the metabolites of BP-7,8-diol formed during PG biosynthesis is not known. The metabolites of NP-7,8-diol but not BP formed during PG biosynthesis by ram seminal vesicle microsomes are highly mutagenic to Salmonella typhimurium [7]. Therefore, we have investigated the nature of the metabolites generated from BP-7,8diol during PG biosynthesis in guinea pig lung (GPL) and ram seminal vesicle (RSV) microsomes. Our studies indicate 7,10/89-BP tetrol as the major metabolite formed by both tissues.

Peroxidative oxidation of bilirubin during prostaglandin biosynthesis.

The peroxidative oxidation of bilirubin has been characterized in the ram seminal vesicle microsomal system. The oxidation was monitored by following the loss in absorbance of bilirubin at 440 nm. Bilirubin behaves as a peroxidase substrate for prostaglandin H synthase. The oxidation may be initiated by the addition of arachidonic acid or peroxides to incubations containing ram seminal vesicle microsomes and bilirubin, and is sensitive to inhibition by reduced glutathione. The arachidonate-dependent oxidation, but not the peroxide-initiated case, is inhibited by indomethacin. Similar results were obtained using microsomal preparations from mouse, rat, and pig lungs. Spectral and chromatographic examination of the products of bilirubin oxidation in the ram seminal vesicle system demonstrate that biliverdin is produced in this system by the dehydrogenation of bilirubin, but that this product accounts for only about 15% of the bilirubin consumed. Biliverdin itself is not oxidized in this system. At least three highly polar, fluorescent products also are formed from bilirubin. Though not identified, these polar products differ markedly in chromatographic behavior from the major fluorescent products obtained following the singlet oxygen oxidation or the autoxidation of bilirubin.

Cooxidation of steroidal and non-steroidal estrogens by purified prostaglandin synthase results in a stimulation of prostaglandin formation

Estrone (E1), estradiol (E2), the catechol estrogens 2-OHE1 and 2-OHE2, and diethylstilbestrol (DES) were incubated with purified prostaglandin synthase (PHS) in vitro in the presence of arachidonic acid and their PHS-catalyzed cooxidation was determined. 2-OHE1, 2-OHE2, and DES were extensively metabolized by PHS peroxidase activity, E1 and E2 to a lesser extent. The cooxidation of the estrogens is accompanied by an increased prostaglandin formation and an increase in cyclooxygenase activity in vitro; progesterone and nylestriol are without effect. Prostaglandins have been proposed to play a role in events related to early estrogen action in tissues such as the uterus. The cooxidation of estrogens and their metabolites by prostaglandin hydroperoxidase might represent one type of interaction between the hormones and the arachidonic acid cascade that could lead to changes in prostaglandins.

An electron spin resonance study of a novel radical cation produced during the horseradish peroxidase-catalyzed oxidation of tetramethylhydrazine

Summary The one-electron oxidation of tetramethylhydrazine by the horseradish peroxidase/hydrogen peroxide system forms a novel stable radical cation. The steady-state concentration of the tetramethylhydrazine radical cation increases with the hydrazine concentration, but depends on neither the enzyme concentration nor the hydrogen peroxide concentration. A mechanism involving the enzymatic one-electron oxidation of the tetramethylhydrazine radical cation to a dication is proposed to account for the enzyme independency. Incubations containing horseradish peroxidase, hydrogen peroxide and tetramethylhydrazine produced formaldehyde which was found to increase with either HRP or tetramethylhydrazine concentration. The cation radical, the dication, and the imine (the deprotonated dication) are proposed as intermediates in the mechanism of formaldehyde production.

An ESR Study of the Oxidation and Reduction of Bisulfite (Hydrated Sulfur Dioxide) in Biological Systems

Sulfur dioxide is recognized as a major air pollutant, particularly near large cities (Rall, 1974), while the ionized forms, bisulfite and sulfite, are found as preservatives in food and wine. In the lung, sulfur dioxide is hydrated rapidly according to the following equation,

Xenobiotic Metabolism by Prostaglandin Endoperoxide Synthetase

{H_2}O + S{O_2} \rightleftharpoons HSO_3^ - + {H^ + }

An electron spin resonance study of o-semiquinones formed during the enzymatic and autoxidation of catechol estrogens.

with the equilibrium constant 1.07 × 102 mole/liter. The bisulfite anion is a weak acid which dissociates according to the reaction,