Effects of beta-ionone on the expression of cytochrome P450s and NADPH-cytochrome P450 reductase in Sprague Dawley rats

Study on the developmental toxicity of β-ionone in the rat

β-ionone (BIO) is used in fragrances, toiletries and non-cosmetic products, and as a flavor food additive. Notwithstanding the widespread human exposure, there are limited data on the reproductive toxicity of BIO. This study evaluated the developmental toxicity of BIO (0, 125, 250, 500 and 1000 mg/kg body weight/day) given orally to rats on days 6-15 of gestation (GD6-15). C-section was on GD21 and implantations, living and dead fetuses and resorptions were recorded. Fetuses were weighed, and examined for external abnormalities and skeleton and visceral anomalies. The embryotoxicity of a single oral dose of BIO (1000 mg/kg body wt) given on GD11 was evaluated as well. At the highest dose, BIO reduced weight gain and produced chromodacryorrhea and other signs of toxicity. BIO did not increase the frequency of malformations nor did it retard fetal growth. Nonetheless, BIO decreased the pregnancy rate in the group of females exposed on GD6-15, and increased the resorption rate in those treated on GD11 only. In conclusion, except for a higher embryolethality at a maternally toxic dose, BIO caused no embryotoxic effect over the dose range tested and the study NOAEL for maternal and developmental toxicity was 500 mg of BIO/ kg of body weight/day.

Carotenoid oxidation products as stress signals in plants

Carotenoids are known to play important roles in plants as antioxidants, accessory light-harvesting pigments, and attractants for pollinators and seed dispersers. A new function for carotenoids has recently emerged, which relates to the response of plants to environmental stresses. Reactive oxygen species, especially singlet oxygen, produced in the chloroplasts under stress conditions, can oxidize carotenoids leading to a variety of oxidized products, including aldehydes, ketones, endoperoxides and lactones. Some of those carotenoid derivatives, such as volatile β-cyclocitral, derived from the oxidation of β-carotene, are reactive electrophile species that are bioactive and can induce changes in gene expression leading to acclimation to stress conditions. This review summarizes the current knowledge on the non-enzymatic oxidation of carotenoids, the bioactivity of the resulting cleavage compounds and their functions as stress signals in plants.

Nonenzymic carotenoid oxidation and photooxidative stress signalling in plants

Carotenoids play a crucial protective role in photosynthetic organisms as quenchers of singlet oxygen ((1)O(2)). This function occurs either via a physical mechanism involving thermal energy dissipation or via a chemical mechanism involving direct oxidation of the carotenoid molecule. The latter mechanism can produce a variety of aldehydic or ketonic cleavage products containing a reactive carbonyl group. One such molecule, the volatile β-carotene derivative β-cyclocitral, triggers changes in the expression of (1)O(2)-responsive genes and leads to an enhancement of photooxidative stress tolerance. Thus, besides their well-known functions in light harvesting and photoprotection, carotenoids can also play a role through their nonenzymic oxidation in the sensing and signalling of reactive oxygen species and photooxidative stress in photosynthetic organisms. Enzymic carotenoid oxidation does not seem to play a significant role in this phenomenon. Elucidation of the carotenoid-mediated (1)O(2) signalling pathway could provide new targets for improving photooxidative stress tolerance of plants.

Effects of a new neuroprotective agent KR-31378 on liver cytochrome P450s in male Sprague Dawley rats

The effects of KR-31378, a neuroprotective agent for ischemia-reperfusion damage, on liver microsomal cytochrome P450s (CYPs) were investigated in male Sprague Dawley rats. When rats were treated orally with KR-31378 for 7 consecutive days, CYP3A-selective erythromycin N-demethylase (ERDM) activity was significantly induced in a dose-dependent manner. In Western immunoblotting, CYP 3A proteins were clearly induced by treatment with KR-31378. Within 24 h after treatment with 80 mg/kg of KR-31378, ERDM activity was induced in liver microsomes in accompanied by induction of the level of CYP 3A proteins. The present results suggest that KR-31378 might modulate the expression of CYP 3A enzymes in humans.

In vivo effects of Panax ginseng extracts on the cytochrome P450-dependent monooxygenase system in the liver of 2,3,7,8-tetrachlorodibenzo-p-dioxin-exposed guinea pig

The effects of the subchronic administration of Panax ginseng extracts were examined on the hepatic cytochrome P450-dependent monooxygenase system of guinea pigs pre-exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Panax ginseng extracts were intraperitoneally administered to guinea pigs at 100 mg/kg/day for 14 days from 1 week after a single intraperitoneal injection of 1 microg of TCDD/kg of body weight. TCDD treatment increased the total cytochrome P450 content 2.86-fold, and this was remarkably inhibited by the administration of Panax ginseng extracts. Treatment with ginseng extract alone also decreased the contents of cytochrome P450 by 33%, but both TCDD and ginseng extracts had no effect on cytochrome b(5) content. The administration of TCDD resulted in a 1.73-fold increase in microsomal NADPH-cytochrome P450 reductase activity in the guinea pig liver, and this was significantly inhibited by ginseng extracts, but treatment with ginseng extracts alone had no effect on its activity, and no statistical changes in the activity of NADPH-cytochrome b(5) reductase were observed in guinea pig liver due to TCDD and/or ginseng extract administration. Compared to the control, ECOD activity remarkably (1.76-fold) increased after TCDD administration, but this increase was completely inhibited by treatment with ginseng extract. Treatment with ginseng extract alone resulted in a 50% reduction of ECOD activity. TCDD administration remarkably induced benzphetamine demethylation (BPDM) activity, while ginseng extract also slightly increased the enzyme's activity, but the induction attributed to ginseng extracts was not statistically significant. Even though administration of ginseng extracts slightly inhibited TCDD-induced BPDM activity, the inhibition was not statistically significant. These results indicate that ginseng extract exerts different effect on the induction of P450 isozymes. From these results, we suggest that Panax ginseng extracts may act as an inhibitor of CYP1A rather than that of CYP2B.

Induction of cytochrome P450 1A and 2B by alpha- and beta-ionone in Sprague Dawley rats

Beta-lonone has been reported to induce the cytochrome P450 (P450) 281 in rats. In this study, the effects of beta-ionone and an isomer, alpha-ionone, on liver P450 1A and 2B expression in Sprague Dawley rats were investigated. Subcutaneous administration of alpha- and beta-ionone 72 and 48 hr prior to sacrificing the animals induced the liver microsomal P450 1A and 2B proteins. P450 2B1 induction was associated with the accumulation of its corresponding mRNA. Induction by beta-ionone was much higher than that by a-ionone in both the mRNA and protein levels. When the route of administration was compared, P450 2B was induced more strongly after oral administration compared to that after subcutaneous injection. A single oral dose of 100, 300 and 600 mg/kg of alpha- and beta-ionone for 24 h induced P450 2B1-selective pentoxyresorufin O-depentylase activity comparably in a dose-dependent manner. In addition, alpha- and beta-ionone induced the P450 1A and 2B proteins. These results suggest that alpha- and beta-ionone might be potent P450 281 inducers in rats, and that both ionones may be useful for examining the role of metabolic activation in chemical-induced toxicity where metabolic activation is required.

Role of metabolic activation by cytochrome P450 in thioacetamide-induced suppression of antibody response in male BALB/c mice

Effects of thioacetamide on antibody response to sheep red blood cells were investigated in male BALB/c mice. When mice were treated intraperitoneally with thioacetamide once, the antibody response was significantly suppressed at 200 mg/kg with hepatotoxicity. When mice were treated intraperitoneally with thioacetamide for 7 consecutive days, the antibody response was suppressed at 50 mg/kg without hepatotoxicity. To determine the possible role of metabolic activation by cytochrome P450 in thioacetamide-induced suppression of antibody response, mice were pretreated with phenobarbital intraperitoneally for 3 days, followed by intraperitoneal administration of 100 mg/kg of thioacetamide for 3 days. The elevated activities of serum aspartate aminotransferase and alanine aminotransferase by thioacetamide were potentiated by phenobarbital pretreatment. The suppression of antibody response by thioacetamide was potentiated by phenobarbital. In liver microsomes, the activities of P450 2B-specific enzymes were induced by phenobarbital. Our present results suggest that thioacetamide may require metabolic activation by P450 to its immunosuppressive form(s).

Pretreatment of male BALB/c mice with beta-ionone potentiates thioacetamide-induced hepatotoxicity

A possible role of metabolic activation by cytochrome P450 (P450) in thioacetamide-induced hepatotoxicity was investigated in male BALB/c mice. The mice were pretreated with the P450 inducer, beta-ionone, subcutaneously at 600 mg/kg, 72 and 48 h prior to an intraperitoneal administration of either 100 or 200 mg/kg of thioacetamide. The elevated activities of serum alanine aminotransferase and serum aspartate aminotransferase by thioacetamide were greatly potentiated by the pretreatment with beta-ionone. Moreover, the potentiation of thioacetamide-induced hepatotoxicity was also observed in the histopathological examination of livers. The hepatic necrosis by thioacetamide was potentiated when mice were pretreated with beta-ionone. In liver microsomes, the activities of P450 2B-specific pentoxyresorufin O-depentylase and benzyloxyresorufin O-debenzylase were significantly induced by the treatment with beta-ionone. Beta-ionone also induced other P450-associated monooxygenases. Because the pretreatment with beta-ionone was not hepatotoxic at the dose inducing P450s. our present results suggest that beta-ionone may be a useful model inducer of P450 enzyme(s) in studying toxic mechanism of certain chemicals which require metabolic activation by P450s in mice.