Cytomorphological changes in liver cells exposed to allyl and benzyl isothiocyanate and their cysteine and glutathione conjugates

Enhancing the fungicidal activity of amphotericin B via vacuole disruption by benzyl isothiocyanate, a cruciferous plant constituent

Amphotericin B (AmB), a typical polyene macrolide antifungal agent, is widely used to treat systemic mycoses. In the present study, we show that the fungicidal activity of AmB was enhanced by benzyl isothiocyanate (BITC), a cruciferous plant-derived compound, in the budding yeast, Saccharomyces cerevisiae. In addition to forming a molecular complex with ergosterol present in fungal cell membranes to form K⁺ -permeable ion channels, AmB has been recognized to mediate vacuolar membrane disruption resulting in lethal effects. BITC showed no effect on AmB-induced plasma membrane permeability; however, it amplified AmB-induced vacuolar membrane disruption in S. cerevisiae. Furthermore, the BITC-enhanced fungicidal effects of AmB significantly decreased cell viability due to the disruption of vacuoles in the pathogenic fungus Candida albicans. The application of the combinatorial antifungal effect of AmB and BITC may aid in dose reduction of AmB in clinical antifungal therapy and consequently decrease side effects in patients. These results also have significant implications for the development of vacuole-targeting chemotherapy against fungal infections.

Radiations and biodegradation techniques for detoxifying Carica papaya seed oil for effective dietary and industrial use

Benzyl isothiocyanate (BITC) is toxic in high concentration. The capacity of Aspergillus niger, microwave and ultraviolet radiations to reduce the BITC levels in Carica papaya Linn seed oil were assessed in vitro. BITC at different concentrations were periodically exposed to microwave and ultraviolet radiations for 30 min and 10 h, respectively; and to identify Aspergillus niger for 4 days. Microwave radiation significantly reduced (p < 0.05) BITC levels (0.0272, 0.0544, and 0.0816 μmol) to 12.19, 8.99 and 27.5 % respectively within 15 min. Ultraviolet radiation significantly reduced (p < 0.05) BITC levels at all the concentrations. A. niger significantly increased (p < 0.05) BITC degradation on days 2 and 4 at 0.816, 1.36 and 2.72 nmol. Glutathione activity was significantly increased (p < 0.05) while glutathione S-transferase activity significantly reduced (p < 0.05) at all concentrations on days 3 and 4 respectively. The three techniques are possible models for improving the dietary consumption of the oil.

Preclinical evaluation of 4-methylthiobutyl isothiocyanate on liver cancer and cancer stem cells with different p53 status

Isothiocyanates from plants of the order Brassicales are considered promising cancer chemotherapeutic phytochemicals. However, their selective cytotoxicity on liver cancer has been barely researched. Therefore, in the present study, we systematically studied the chemotherapeutic potency of 4-methylthiobutyl isothiocyanate (MTBITC). Selective toxicity was investigated by comparing its effect on liver cancer cells and their chemoresistant subpopulations to normal primary hepatocytes and liver tissue slices. Additionally, in a first assessment, the in vivo tolerability of MTBITC was investigated in mice. Growth arrest at G2/M and apoptosis induction was evident in all in vitro cancer models treated with MTBITC, including populations with cancer initiating characteristics. This was found independent from TP53; however cell death was delayed in p53 compromised cells as compared to wt-p53 cells which was probably due to differential BH3 only gene regulation i. e. Noxa and its antagonist A1. In normal hepatocytes, no apoptosis or necrosis could be detected after repeated administration of up to 50 µM MTBITC. In mice, orally applied MTBITC was well tolerated over 18 days of treatment for up to 50 mg/kg/day, the highest dose tested. In conclusion, we could show here that the killing effect of MTBITC has a definite selectivity for cancer cells over normal liver cells and its cytotoxicity even applies for chemoresistant cancer initiating cells. Our study could serve for a better understanding of the chemotherapeutic properties of isothiocyanates on human liver-derived cancer cells.

Tocolytic and toxic activity of papaya seed extract on isolated rat uterus

Carica papaya L. seeds extracted with 80% ethanol (EEPS) caused concentration-dependent tocolysis of uterine strips isolated from gravid and non-gravid rats. Prostaglandin F2alpha and oxytocin-induced contractions of the isolated rat uterus were also inhibited in a concentration-dependent fashion by EEPS. Recoveries of the uterine activity after EEPS-induced uterine quiescence were very weak. Higher concentration of EEPS caused prompt uterine quiescence, which was also significantly irreversible. Pre-incubation of the rat uterus in Ringer Locke solution containing 10 mg/ml of EEPS for 1 hour prior to suspension in tissue baths led to significant depression of the spontaneous and KCl (60 mM)-induced uterine contractions relative to the solvent control (P<0.05). Cross sections of EEPS-pretreated non-gravid rat uterus (stained with hematoxyline and eosin) examined under light microscope revealed degeneration of the endometrium and myometrium with obvious cytoplasmic vacuolation indicating that EEPS could have direct toxic effect on the uterine tissues. Previous workers have reported benzyl isothiocyanate (BITC) as the main bioactive and anthelmintic compound in different extracts of papaya seeds. Using electron impact ionization methods, the presence of BITC in EEPS was also shown in this study. Mass spectra of both EEPS and standard BITC showed a base peak of benzyl/tropylium ion at m/z 91 (indicative of an aromatic compound) and the molecular ion peak of BITC (m/z 149). Our earlier studies have demonstrated BITC-induced functional and morphological derangement of isolated uterus. We thus conclude that at high concentration, EEPS is capable of causing irreversible uterine tocolysis probably due to the damaging effect of BITC (its chief phytochemical) on the myometrium.

Quantitative microscopy of hepatic changes induced by phenethyl isothiocyanate in Fischer-344 rats fed either a cereal-based diet or a purified diet

Hepatic changes induced by phenethyl isothiocyanate (PEITC) in the liver of rats were determined by quantitative microscopy. Groups of male Fischer-344 rats were fed either a standard, cereal-based diet (Wayne rodent meal) or a purified diet (AIN-76A) containing PEITC at concentrations of 0.75 and 6.0 mmol/kg for 13 wk. Severe hepatic lipidosis was observed in control rats fed the purified diet. Addition of PEITC to the purified diet significantly reduced lipid content in hepatocytes. In contrast, lipid content in the liver of the rats fed the cereal-based diet containing PEITC was greater than in control rats maintained on the same diet. In addition, dose-related reductions in hepatocyte, lipid droplet, peroxisome, and mitochondrial volumes were observed in PEITC-treated rats fed the cereal-based diet. These results indicate that PEITC exerts differential effects on the liver of rats fed either the cereal-based or purified diet.

Selective toxicity of compounds naturally present in food toward the transformed phenotype of human colorectal cell line HT29

It has previously been observed that allyl isothiocyanate, a compound naturally present in the diet, is more cytotoxic toward the human colorectal adenocarcinoma cell line HT29 in its control transformed state than after exposure to sodium butyrate or to dimethylformamide, which slow growth and induce differentiation (detransformation). In the present study, a range of other dietary compounds were assayed for such selective toxicity. These compounds were chosen as constituents of foodstuffs that have been identified from epidemiologic studies as being potentially antitumorigenic and also as having anticarcinogenic activity in experimental models. Benzyl and phenethyl isothiocyanate, benzyl thiocyanate, and quercetin showed decreased toxicity towards HT29 after detransformation of the cells by one or both treatments, whereas no change was observed in the sensitivity to diallyl sulfide or diallyl disulfide. It is proposed that the presence of such selectively toxic compounds in the diet may inhibit the development of tumors by interfering with the growth of preneoplastic lesions while having little effect on normal cells. The cumulative effects of these inhibitions may contribute to the chemopreventive properties of the parent foodstuffs observed in epidemiologic studies.

Glutathione conjugation as a mechanism for the transport of reactive metabolites

From this and other chapters in this volume, it should be clear that GSH conjugation no longer represents a mechanism for the detoxication of xenobiotics or their metabolites. Although the majority of conjugations with GSH do facilitate the efficient excretion of xenobiotics from the body, many examples now exist where this process results in enhanced biological reactivity (Monks et al., 1990a; Monks and Lau, 1992, 1994). The number of examples in which GSH conjugation plays an important role in the generation of biologically reactive intermediates is expanding rapidly and GSH-dependent toxicity is manifested in many diverse ways. As emphasized in this chapter, GSH can act as a transport form for reactive metabolites, permitting the delivery of such metabolites to target tissues distal to the site of the initial conjugation. This type of GSH conjugate may be important in the mutagenic, carcinogenic, nephrotoxic, embryotoxic, cataractogenic, methemoglobinemic, and neurotoxic properties of a variety of redox active compounds (Monks and Lau, 1992).

Subacute oral toxicity study of benzyl isothiocyanate in rats

The subacute toxicity of benzyl isothiocyanate (BITC) was investigated in male rats given oral doses of 0, 50, 100 and 200 mg/kg body weight/day for 4 weeks. Body weight gain and food consumption were decreased with increasing doses of BITC. Haematological changes of toxicological relevance were observed in the highest dose group. BITC administration resulted in increased serum cholesterol level in all treatment groups and decreased serum triglycerides level at 200 mg/kg. Renal dysfunction was indicated by reduced urine volume, proteinuria and enhanced urinary lactate dehydrogenase activity. BITC exposure also affected the weights of various organs and caused histological changes in the ductus choledochus, liver, ileum and mesenteric lymph nodes.

N-acetylcysteine-conjugated pyrrole identified in rat urine following administration of two pyrrolizidine alkaloids, monocrotaline and senecionine

This report demonstrates that an Ehrlich-reagent-positive metabolite of monocrotaline and senecionine is excreted in the urine of male rats as an N-acetylcysteine conjugate of (+/-)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (NAC-DHP). Isolation of the metabolite employed an initial organic extraction followed by HPLC separation of remaining urinary components using a reverse-phase, polymer-based, PRP-1 column. Fast-atom-bombardment tandem mass spectrometry was used to identify the metabolite. This finding suggests that reactive metabolites of pyrrolizidine alkaloids generated in the liver can survive the aqueous environment of the circulatory system as glutathione conjugates or mercapturic acids.

Glutathione S-transferases in relation to their role in the biotransformation of xenobiotics

The glutathione S-transferases (GST) are a family of isoenzymes serving a major role in the biotransformation of many reactive compounds. The isoenzymes from rat, man and mouse are divided into three classes, alpha, mu and pi, on the basis of similar structural and enzymatic properties. In view of the fact that the individual isoenzymes demonstrate differential though overlapping substrate selectivities, the extent to which biotransformation occurs is dependent on the actual profile of isoenzymes present. Consequently, both genetic factors as well as external factors causing changes in the levels or activities of individual isoenzymes are of relevance with respect to an individual's susceptibility towards electrophilic compounds. This review article deals with a number of determinants of GST isoenzyme patterns and/or activities, including tissue distribution, developmental patterns, hormonal influences, induction and inhibition. In addition, current knowledge on specific properties of class alpha, class mu and class pi isoenzymes is presented.

Short-term toxicity study of allyl isothiocyanate in rats

Allyl isothiocyanate (AITC) was given in doses of 0, 10, 20, or 40 mg/kg (5 days/week) by oral intubation to male rats for up to 6 weeks. The highest dosage level caused a decrease in body weight, thymus weight, blood glucose and serum globulin levels. Haematological examination revealed an increased percentage of neutrophils and a decreased percentage of lymphocytes after treatment for 2 weeks. Increased liver and adrenal weights were found in all test groups. Renal dysfunction was indicated by increased urinary aspartate amino-transferase activity, reduced urine volume and changes in the specific gravity of the urine. Histopathological changes were observed in the kidneys of animals at dosages of 20 and 40 mg/kg and in the livers of animals at the highest dosage level.

Effects of carbamoylating agents on tumor metabolism

Carbamoylation of macromolecules occurs by the displacement of hydrogen on several groups, but the most stable addition at neutral pH is on amino groups. This reaction occurs predominantly with proteins and results from the administration in vivo of inorganic cyanate or organic isocyanates. The latter act more rapidly, but also are more rapidly hydrolyzed in aqueous solution. This instability has been a factor limiting study of the pharmacological properties of organic isocyanates. However, organic isocyanates are released from some nitrosoureas of value in cancer therapy such as 1,3-bis(2-chlorethyl)-1-nitrosourea (BCNU) and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU). The carbamoylating activities of BCNU and CCNU are generally considered less significant than their alkylating activity in the action of these drugs on tumors, but carbamoylation may serve to inhibit DNA repair. There is evidence that carbamoylating agents can exert selective inhibitory effects on metabolite uptake and macromolecular synthesis in neoplastic tissues. Such selectivity is much more notable in vivo than in vitro. In the case of cyanate, the selectivity in vivo has been variously attributed to a requirement for metabolic activation, to selective effects on circulation in solid tumors, and to diminished pH in tumors. It is the distinction between such factors and the identification of critical cellular targets which provide major challenges in present studies on the effects of carbamoylating agents on tumor metabolism.