Inhibition of glycolysis in boar spermatozoa by 1,6-dichloro-1,6-dideoxy-D-fructose

CYP2E1-Catalyzed Oxidation Contributes to the Sperm Toxicity of 1-Bromopropane in Mice1

1-bromopropane (1-BrP) induces dose- and time-dependent reproductive organ toxicity and reduced sperm motility in rodents. The contribution of cytochrome P4502E1 (CYP2E1) to both 1-BrP metabolism and the induction of male reproductive toxicity was investigated using wild-type (WT) and Cyp2e1-/- mice. In gas uptake inhalation studies, the elimination half-life of [1,2,3-(13)C]-1-BrP was longer in Cyp2e1-/- mice relative to WT (3.2 vs. 1.3 h). Urinary metabolites were identified by 13C nuclear magnetic resonance. The mercapturic acid of 1-bromo-2-hydroxypropane (2OHBrP) was the major urinary metabolite in WT mice, and products of conjugation of 1-BrP with glutathione (GSH) were insignificant. The ratio of GSH conjugation to 2-hydroxylation increased 5-fold in Cyp2e1-/- mice relative to WT. After 1-BrP exposure, hepatic GSH was decreased by 76% in WT mice vs. 47% in Cyp2e1-/- mice. Despite a 170% increase in 1-BrP exposure in Cyp2e1-/- vs. WT mice, sperm motility in exposed Cyp2e1-/- mice did not change relative to unexposed matched controls. This suggests that metabolites produced through CYP2E1-mediated oxidation may be responsible for 1-BrP-induced sperm toxicity. Both 1-BrP and 2OHBrP inhibited the motility of sperm obtained from WT mice in vitro. However, only 2OHBrP reduced the motility of sperm obtained from Cyp2e1-/- mice in vitro, suggesting that conversion of parent compound to 2OHBrP within the spermatozoa may contribute, at least in part, to reduced motility. Overall, these data suggest that metabolism of 1-BrP is mediated in part by CYP2E1, and activation of 1BrP via this enzyme may contribute to the male reproductive toxicity of this chemical.

Lack of antifertility properties of novel halogenated glycolytic inhibitors and the urinary excretion and metabolism of 1,6-dichloro-1,6-dideoxy-D-fructofuranose in the male rat

The antifertility action of (R,S)-alpha-chlorohydrin administered orally to male rats was compared with that of several novel chlorinated compounds known to inhibit glycolysis and the kinematics of rat sperm in vitro. Oral gavage of 1,6-dichloro-1,6-dideoxy-D-fructofuranose (dichlorodideoxyfructose, DCF), 1-chloro-3-hydroxypropanone, its dimethylketal and bromopyruvate did not reduce the fertility of male rats below that of controls at the equivalent antifertility dose of (R,S)-alpha-chlorohydrin (5 mg/kg/day) or higher. As anticipated for a compound cleaved to products of (S)-chirality even high doses of DCF (200 mg/kg) showed no effect on renal function. 36Cl-Labelled DCF administered orally to male rats was eliminated only slowly in the urine (16% of the ingested dose excreted in 96 h). In the first 8 h, approximately 50% of DCF was excreted unchanged, 30% was excreted as 3-chlorolactate (BCLA), the oxidation product 3-chlorolactaldehyde and 25% as Cl-. By 24 h little DCF remained and the major metabolite (70%) was BCLA and 20% Cl-. The high rate of dechlorination is most likely responsible for the low antifertility action of DCF.

A re-appraisal of the post-testicular action and toxicity of chlorinated antifertility compounds

Some 30 years ago, alpha-chlorohydrin and some analogues were considered as close to the ideal contraceptive which acted rapidly and reversibly on the post-testicular maturation of spermatozoa. Despite their early promise, research funding was withdrawn only 5 years later because of what were considered to be unacceptable side-effects in primates. The literature on the toxic effects of these contraceptive agents was reviewed and was found to be wanting in respect to the rigour of scientific methods applied (impure compounds were used, inappropriate target populations were studied, excessive doses were employed, abstracts were cited from which no full publications subsequently arose). These compounds remain the closest approach yet to non-hormonal contraceptives for males and have led to the synthesis of related compounds which have a similar antifertility action but with much diminished toxicity. If toxicity remains a problem, a range of other compounds now known to have a similar antifertility action, should be investigated.

Metabolism of 36Cl-ornidazole after oral application to the male rat in relation to its antifertility activity

1. The antimycotic ornidazole (a male antifertility agent in rats) was synthesized incorporating 36Cl in the chloropropyl sidechain and its metabolism was investigated in the male rat after oral ingestion. 2. Blood levels of radioactivity were low over the first 24 h and there was no tissue accumulation of radioactivity over 48 h. 3. Most of the excreted radioactivity (20% of the ingested dose) appeared in the urine within the first 24 h. 4. Three major compounds were detected in 0-24-h urine samples and were characterized as ornidazole (13% of total radioactivity), Cl- (22%) and 3-chlorolactate (30%), the oxidation product of 3-chlorolactaldehyde. 5. No polyuria or glucosuria was observed following the oral administration of ornidazole, suggesting that any (R)-3-chlorolactate produced was insufficient to affect renal metabolism. 6. Conversion of ornidazole initially to (R, S)-alpha-chlorohydrin or ultimately to the glycolytic inhibitor (S)-3-chlorolactaldehyde could explain its antifertility action in the male rat.