Fetotoxicity and reproductive effects of monocrotaline in pregnant rats

Sex difference in monocrotaline-induced developmental toxicity and fetal hepatotoxicity in rats

Pyrrolizidine alkaloids (PAs) are a class of hepatic toxins widely existing in plants. Cytochromes P450 (CYP) mediates PA bioactivation and toxicities in mammals. It has been reported that PAs can induce developmental toxicity, but systematic research is lacking. In this study, we investigated developmental toxicity of monocrotaline (MCT) in rats. Pregnant rats were administered with MCT (20 mg/kg) intragastrically from gestation day 9 to 20, followed by determination of changes in fetal growth, hepatic morphology, serum biochemical indices, and indicators of hepatocytes apoptosis. MCT was found to induce developmental toxicity and fetal hepatotoxicity, particularly in female fetuses. Metabolic activation was also studied by examination of bioactivation efficiency of MCT in fetal liver microsomes, serum MCT, pyrrole-protein adduction derived from MCT, and hepatic CYP3 A expression of fetuses in vivo. Male fetuses showed greater basal MCT bioactivation than that of female fetuses, but continuous exposure to MCT caused a selective CYP3 A induction in female fetuses, which may contribute to the sex difference in MCT-induced developmental toxicity.

Prenatal exposure to pyrrolizidine alkaloids induced hepatotoxicity and pulmonary injury in fetal rats

Hepatic and pulmonary toxicity in fetal rats induced by pyrrolizidine alkaloids (PAs) was investigated. Retrorsine (RTS) or monocrotaline (MCT) was intragastrically administered during pregnancy. The reduction of body and tail lengths was consistent with body weight loss in PA-exposed fetuses, and pathological lesions in liver and lung were observed only in fetuses. Both PAs reduced fetal serum transaminase activities. The GSH/GSSG ratio, GSH peroxidase and superoxide dismutase activities also decreased but glutathione S-transferase activity increased in fetal lung, especially for MCT. The pyrrole-protein adducts in fetal liver and lung could be detected, and those adducts in RTS fetal lungs were about 65% of those in MCT group. In conclusion, prenatal PAs exposure induced fetal hepatic and pulmonary toxicities through the generation of pyrrole metabolites and oxidative injury. The difference on fetal pulmonary redox homeostasis between two PAs groups might be associated with the content of PAs migrated to fetal lungs.

Maternal-Fetal Disposition and Metabolism of Retrorsine in Pregnant Rats

Pyrrolizidine alkaloids (PAs) are extensively synthesized by plants, are commonly present in herbs and foodstuffs, and exhibit hepatotoxicity requiring metabolic activation by cytochrome P450 3A to form the electrophilic metabolites-pyrrolic esters. PAs also cause embryo toxicity, but the metabolic profiles of PAs in fetus and placenta have been far from clear. In this study, we determined the basal metabolic activation of retrorsine (RTS) in rat maternal liver, placenta, and fetal liver in vitro and examined the fetal toxicity and bioactivation of RTS in vivo. Detection of microsomal RTS metabolites in vitro showed that the basal metabolic activity of fetal liver and placenta to RTS was much weaker than that of maternal liver. In addition, a higher rate of pyrrolic ester formation was found in normal male fetal liver compared with that of female pups. In vivo exposure to RTS caused fetal growth retardation, as well as placental and fetal liver injury. Little difference in serum RTS was observed in dams and fetuses, but the content of pyrrole-protein adduction in the fetal liver was much lower than that in maternal liver, which was consistent with basal metabolic activity. Unexpectedly, compared with basal metabolism in fetal liver, exposure to RTS during middle and late pregnancy caused an opposite gender difference in RTS metabolism and CYP3A expression in the fetal liver. For the first time, our study showed that RTS can permeate the placenta barrier and entering fetal circulation, whereas the intrauterine pyrrolic metabolite was generated mainly by fetal liver but not transported from the maternal circulation. Induction of CYP3A by RTS was gender-dependent in the fetal liver, which was probably responsible for RTS-induced fetal hepatic injury, especially for female pups.

Synergistic effects of pyrrolizidine alkaloids and lipopolysaccharide on preterm delivery and intrauterine fetal death in mice

Preterm birth is the leading cause of death for newborn infants, and lipopolysaccharide (LPS) is commonly used to induce preterm delivery in experimental animals. Pyrrolizidine alkaloids (PAs) are widespread and occur in foods, herbs, and other plants. This study was to investigate the synergistic effects of LPS and two representative PAs, retrorsine (RTS) and monocrotaline (MCT), on preterm delivery and fetal death. Pregnant Kunming mice were divided into seven groups: control, RTS, MCT, LPS, RTS+LPS and two MCT+LPS groups. Animals in PAs and PAs+LPS groups were dosed intragastrically with RTS (10mg/kg) or MCT (20 mg/kg or 60 mg/kg) from gestational day (GD) 9 to GD16; mice given LPS were injected intraperitoneally with 150 μg/kg on GD15.5. Latencies to delivery, numbers of pups live and dead at birth were recorded, and livers of live neonates were collected. The incidence of LPS-induced preterm birth was enhanced in dams pretreated with MCT, and combination of PAs and LPS increased fetal mortality from PAs. The enhancement of LPS-induced preterm delivery and fetal demise in animals exposed chronically to PAs and other substances found in foods and beverages consumed widely by humans merits further focused investigation.

The Role of Astrocytes in Metabolism and Neurotoxicity of the Pyrrolizidine Alkaloid Monocrotaline, the Main Toxin of Crotalaria retusa

The metabolic interactions and signaling between neurons and glial cells are necessary for the development and maintenance of brain functions and structures and for neuroprotection, which includes protection from chemical attack. Astrocytes are essential for cerebral detoxification and present an efficient and specific cytochrome P450 enzymatic system. Whilst Crotalaria (Fabaceae, Leguminosae) plants are used in popular medicine, they are considered toxic and can cause damage to livestock and human health problems. Studies in animals have shown cases of poisoning by plants from the genus Crotalaria, which induced damage to the central nervous system. This finding has been attributed to the toxic effects of the pyrrolizidine alkaloid (PA) monocrotaline (MCT). The involvement of P450 enzymatic systems in MCT hepatic and pulmonary metabolism and toxicity has been elucidated, but little is known about the pathways implicated in the bioactivation of these systems and the direct contribution of these systems to brain toxicity. This review will present the main toxicological aspects of the Crotalaria genus that are established in the literature and recent findings describing the mechanisms involved in the neurotoxic effects of MCT, which was extracted from Crotalaria retusa, and its interaction with neurons in isolated astrocytes.

Lack of protective action of cysteine against the fetotoxic effect of monocrotaline

Monocrotaline (MCT), a pyrrolizidine alkaloid present in Crotalaria species, has hepatotoxic, nephrotoxic, pneumotoxic and fetotoxic effects. However, the toxic effects of exposure to MCT in adult rats can be prevented by cysteine. Thus, the present study was conducted to evaluate the possible prevention by cysteine of the toxic effects of MCT on pregnant rats. Thirty-six pregnant rats were used. The females in the experimental groups were fed ration containing 0.02% MCT, 0.02% MCT + 1% cysteine, or 1% cysteine from day 6 to day 21 of pregnancy; the control group was fed only common ration for the same period of time. All rats were killed on day 21 of pregnancy and their blood was collected for determination of liver and kidney function. General toxicity to pregnant dams was assessed. Fetuses were removed by caesarian section and embryofetotoxic parameters were examined. Results showed impaired body weight gain in rats fed MCT, with or without cysteine supplementation. Plasma levels of AST, ALT, LDH, GGT, urea and creatinine were increased in MCT animals compared to controls. The pathology study revealed lesions only in dams from the MCT group. The weights of the placentas and fetuses of the MCT and MCT + cysteine groups were significantly lower than those of the control group. Thus, the present data suggests some protective action of 1% of cysteine in ration against the toxic effects of MCT on the dams but not on the litter.