Oxidative metabolic activity of boar spermatozoa: a system for assessing anti-glycolytic activity of potential inhibitors in vitro

Carcinogenicity of Monochloro-1,2-Propanediol (α-Chlorohydrin, 3-MCPD)

3-Monochloro-1,2-propanediol (3-MCPD) is a by-product found in trace amounts, generally less than 1 mg/kg (<1 ppm), in hydrolyzed vegetable protein produced through acid hydrolysis. In a chronic study with F344 rats, high doses of 3-MCPD produced benign renal tumors in both sexes and Leydig-cell and mammary tumors in males. 3-MCPD is genotoxic in vitro, but there is no evidence of genotoxicity in vivo. There is some question about the mechanism responsible for the carcinogenicity of 3-MCPD in certain species. Here we present a critical review of the toxicological, metabolic, and mechanistic data on 3-MCPD. On the basis of this review, the tumors reported in F344 rats are concluded to have developed as a result of nongenotoxic mechanisms and are considered not to be relevant to humans exposed to trace amounts of 3-MCPD. This conclusion was based on the lack of carcinogenicity of 3-MCPD in mice or Sprague-Dawley rats; the benign nature of the tumors involved; the dependence of the Leydig-cell and mammary tumors on species-and strain-dependent mechanisms involving chronic changes in hormone balance; the association of the renal tumors with chronic nephropathy and nephrotoxicity; and differences between bacterial and mammalian systems in the metabolism of 3-MCPD that likely account for its genotoxic activity in certain in vitro test systems. At trace levels in foods, 3 MCPD is considered not to pose a carcinogenic risk to humans.

The toxicity of 3-chloropropane-1,2-dipalmitate in Wistar rats and a metabonomics analysis of rat urine by ultra-performance liquid chromatography-mass spectrometry

3-Monochloropropane-1,2-diol(3-MCPD) fatty acid esters can release free 3-MCPD in a certain condition. Free 3-MCPD is a well-known food contaminant and is toxicological well characterized, however, in contrast to free 3-MCPD, the toxicological characterization of 3-MCPD fatty acid esters is puzzling. In this study, toxicological and metabonomics studies of 3-chloropropane-1,2-dipalmitate(3-MCPD dipalmitate) were carried out based on an acute oral toxicity test, a 90-day feeding test and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) analysis. The LD50 value of 3-MCPD dipalmitate was determined to be 1780 mg/kg body weight (bw) for Wistar rats. The results of the 90-day feeding test in male Wistar rats showed that 3-MCPD dipalmitate caused a significant increase in blood urea nitrogen and creatinine in the high-dose group (267 mg/kg bw/day) compared to control rats. Renal tubular epithelium cell degeneration and renal tubular hyaline cast accumulation were the major histopathological changes in rats administered 3-MCPD dipalmitate. Urine samples obtained after the 90-day feeding test and analyzed by UPLC-MS showed that the differences in metabolic profiles between control and treated rats were clearly distinguished by partial least squares-discriminant analysis (PLS-DA) of the chromatographic data. Five metabolite biomarkers which had earlier and significant variations had been identified, they were first considered to be the early, sensitive biomarkers in evaluating the effect of 3-MCPD dipalmitate exposure, and the possible mechanism of these biomarkers variation was elucidated. The combination of histopathological examination, clinical chemistry and metabolomics analyses in rats resulted in a systematic and comprehensive assessment of the long-term toxicity of 3-MCPD dipalmitate.

Glycolytic enzyme activity is essential for domestic cat (Felis catus) and cheetah (Acinonyx jubatus) sperm motility and viability in a sugar-free medium

We have previously reported a lack of glucose uptake in domestic cat and cheetah spermatozoa, despite observing that these cells produce lactate at rates that correlate positively with sperm function. To elucidate the role of glycolysis in felid sperm energy production, we conducted a comparative study in the domestic cat and cheetah, with the hypothesis that sperm motility and viability are maintained in both species in the absence of glycolytic metabolism and are fueled by endogenous substrates. Washed ejaculates were incubated in chemically defined medium in the presence/absence of glucose and pyruvate. A second set of ejaculates was exposed to a chemical inhibitor of either lactate dehydrogenase (sodium oxamate) or glyceraldehyde-3-phosphate dehydrogenase (alpha-chlorohydrin). Sperm function (motility and acrosomal integrity) and lactate production were assessed, and a subset of spermatozoa was assayed for intracellular glycogen. In both the cat and cheetah, sperm function was maintained without exogenous substrates and following lactate dehydrogenase inhibition. Lactate production occurred in the absence of exogenous hexoses, but only if pyruvate was present. Intracellular glycogen was not detected in spermatozoa from either species. Unexpectedly, glycolytic inhibition by alpha-chlorohydrin resulted in an immediate decline in sperm motility, particularly in the domestic cat. Collectively, our findings reveal an essential role of the glycolytic pathway in felid spermatozoa that is unrelated to hexose metabolism or lactate formation. Instead, glycolytic enzyme activity could be required for the metabolism of endogenous lipid-derived glycerol, with fatty acid oxidation providing the primary energy source in felid spermatozoa.

Control of glycolysis in mature boar spermatozoa: effect of pH in vitro

The glycolytic pathway in boar sperm is sensitive to pH, which decreases as lactate is produced from either glucose or fructose in vitro. The build up of lactate appears to be due to the saturation of mitochondrial lactate transporters, which causes the cytoplasmic pH to fall. Phosphofructokinase has been shown to be sensitive to this drop in pH rather than to the build up of lactate ions or ATP, thereby controlling the rate of glycolysis in vitro.

The anti-glycolytic activity of 3-bromopyruvate on mature boar spermatozoa in vitro

Mature epididymal boar spermatozoa converted fructose, glycerol and glycerol-3-phosphate to carbon dioxide, but in the presence of 0.5 mM 3-bromopyruvate, these oxidations were inhibited while that of lactate was unaffected. Inhibition of the oxidation of these substrates results in a decrease in the content of ATP and the accumulation of dihydroxyacetone phosphate and fructose-1,6-bisphosphate. Examination of the activities of the enzymes within stage two of the glycolytic pathway showed that glyceraldehyde-3-phosphate dehydrogenase and 3-phosphoglycerate kinase were immediately inhibited by 3-bromopyruvate in a competitive manner. We now report the action of 3-bromopyruvate on the metabolic activity of boar spermatozoa. At a concentration of 0.5 mM, this compound selectively inhibits stage two of the glycolytic pathway and becomes yet another specific inhibitor of spermatozoal metabolism.

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

The dichloro-analogue of D-fructose 1,6-bisphosphate, 1,6-dichloro-1,6-dideoxy-D-fructose, is a weak substrate for boar sperm aldolase which converts it to (S)-3-chlorolactaldehyde and 3-chloro-1-hydroxypropanone in vitro. Production of these chloro-trioses leads to the strong inhibition of glyceraldehyde-3-phosphate dehydrogenase, the weak inhibition of triosephosphate isomerase and the transient inhibition of aldolase.

Intracellular signal transduction mechanisms of rat epididymal spermatozoa and their relationship to motility and metabolism

The role of intracellular signal transduction mechanisms in regulating the motility and metabolism of rat spermatozoa in undiluted caudal epididymal fluid (CEF) was examined. Samples of CEF containing immotile spermatozoa were exposed to drugs and other agents that either stimulate signal transduction pathways or mimic the action of their second messengers. Under these conditions, sperm motility in 25-30 nl of CEF was stimulated by calcium ions (Ca2+), N2,2'-O-dibutyrylguanosine 3':5'-cyclic monophosphate (dibutyryl cGMP), cyclic adenosine 3':5'-monophosphate (cAMP), N6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate (dibutyryl cAMP), 8-bromoadenosine 3':5'-cyclic monophosphate (8-bromo cAMP), caffeine, theophylline and bicarbonate ions (HCO3-). Other agents such as magnesium ions (Mg2+), veratridine, phospholipase C (PLC), ionophore A23187, 1,2-dioctenoyl-sn-glycerol (DAG), phorbol 12-myristate 13-acetate, phospholipase A2 (PLA2), arachidonic acid, and melittin did not significantly influence motility. In the presence of radiolabelled energy substrates, untreated (immotile) spermatozoa in samples of CEF utilised D-[U-14C]glucose and [1-14C]acetate as exogenous energy sources for oxidative metabolism. No detectable 14C-lactate was produced, and none of the drugs altered the rate of glycolytic or oxidative metabolism. The findings suggest that the motility of rat caudal epididymal spermatozoa is regulated by Ca2+ and the guanylate cyclase and adenylate cyclase pathways, but not through the PLC and PLA2 pathways. Also, their metabolism of exogenous substrate was uncoupled from the induction of motility, and their oxidative capacity exceeded the rate of flux of glucose-carbon through the glycolytic pathway.

The male antifertility activity of 6-chloro-6-deoxyglucose

6-Chloro-6-deoxy[U-14C]glucose is not metabolised by mature boar spermatozoa nor has it any specific inhibitory action on their metabolic activity in vitro. The compound is metabolised by the male rat and the identification of two urinary metabolites as alpha-chlorohydrin and 3-chlorolactate confirmed that (S)-3-chlorolactaldehyde is produced by this species in vivo. A tissue distribution study revealed that radioactivity from 6-chloro-6-deoxy[U-14C]glucose was more concentrated in rat caudal spermatozoa than in any other of the major tissues.