Our study was designed to assess the fecal and urinary excretion of 3 aflatoxin B 1 (AFB 1 ) metabolites, aflatoxins M 1 (AFM 1 ) and Q 1 (AFQ 1 ) and aflatoxin B 1 -N 7 -guanine (AFB-N 7 -guanine) that are produced by the predominant forms of cytochrome P450 enzymes responsible for the biotransformation of AFB 1 . Fecal and urinary AFM 1 , AFQ 1 and urinary AFB-N 7 -guanine were assessed in 83 young Chinese males selected from a larger population (n = 300) based on detectable urinary AFM 1 . The concentration of fecal AFQ 1 (median 137 ng/g fresh weight, IQR 9.1 to 450) was approximately 60 times higher than that of AFM 1 (2.3 ng/g, IQR 0.0 to 7.3). In urine, the median AFQ 1 was 10.4 ng/ml (IQR 3.4 to 23.3), and the median AFM 1 and AFB-N 7 -guanine 0.04 ng/ml (IQR 0.01 to 0.33) and 0.38 ng/ml (IQR 0.0 to 2.15), respectively. A subgroup (n = 14) with hepatitis B virus (HBV) infection had significantly higher fecal concentrations of AFQ 1 ( p = 0.043) and AFM 1 ( p = 0.001) than those who were hepatitis B-virus antigen (HBsAg) negative, and the respective differences in urinary AFQ 1 and AFM 1 concentrations approached statistical significance ( p = 0.054, p = 0.138). Our study demonstrates that AFQ 1 is excreted in urine and feces at higher levels than AFM 1 , and feces are an important route of excretion of these AFB 1 metabolites. AFQ 1 should be further assessed for its predictive value as a marker for exposure and risk of dietary aflatoxins. The most serious health effect of dietary exposure to aflatoxins is hepatocellular carcinoma. The etiology of this disease also involves chronic infection with hepatitis B and C viruses (HBV and HCV), and a significant synergistic interaction between aflatoxin exposure and hepatitis B virus has been reported. 2,3After oral uptake AFB 1 is efficiently absorbed and metabolized prior to excretion by fecal and urinary routes (Fig. 1). Absorbed AFB 1 and its metabolites are excreted in urine, while elimination to feces is a route for both the unabsorbed AFB 1 and biliary excretion of metabolites formed from the absorbed toxin. Animal studies have shown that under normal conditions 50% of the orally administered dose of AFB 1 is quickly absorbed from the duodenal region of the small intestine 4 and enters the liver through the hepatic portal blood supply.5 AFB 1 is concentrated in the liver and to a lesser extent in kidney, 6 and it is also found in the mesenteric venous blood as free AFB 1 or its water-soluble metabolites.Members of the cytochrome P450 (CYP) enzyme family, CYP1A2, CYP3A4 and CYP2A6 have been shown to be responsible for the metabolism of the absorbed aflatoxins 7,8 (Fig. 1). These enzymes convert AFB 1 to its carcinogenic form, AFB-8,9-epoxide, which is covalently bound to DNA 9 and serum albumin, 10 forming aflatoxin B 1 -N 7 -guanine (AFB-N 7 -guanine) and lysine adducts, respectively. These enzymes also oxidize AFB 1 to various other derivatives, including aflatoxin M 1 (AFM 1 ), aflatoxin Q 1 (AFQ 1 ), aflatoxin P 1 as well as a reduced aflatoxin species...

ABSTRACT:Passive permeability and active efflux are parallel processes in transcellular flux. Therefore, the observed kinetics of a transporter substrate depends on both of these factors. The transporter expression has been shown to affect both the apparent K m and V max values. Kinetic parameters can be obtained from various experimental settings, but these do not necessarily reflect the situation in transcellular flux. Kinetic absorption models need reliable estimates of saturable kinetics when accurate in silico predictions are to be made. The effect of increasing P-glycoprotein expression on apparent transport kinetics was studied using quinidine and digoxin as model compounds. The intracellular concentrations of drugs during the transport process were also measured. A dynamic simulation model was constructed to study the observed data. The apparent K m and V max values increased as the P-glycoprotein expression increased. Simulations reproduced the shift in both kinetic parameters as a function of efflux pump expression. In addition, the apparent K m value showed a strong inverse relationship to the passive permeability. In contrast, the apparent V max value reached a maximum at intermediate passive permeability and declined above and below this passive permeability. The true V max and K m values were never reached. The shift in K m was assigned to a decrease in intracellular concentration at the Pglycoprotein interaction site with both experimental and simulation data. In conclusion, the apparent kinetic parameters in transcellular permeability assays depend on passive permeability and efflux pump activity. Therefore, parameters that are obtained from in vitro assays should be cautiously applied to in vivo predictions.

The hydroxysteroid (17beta) dehydrogenase (HSD17B)12 gene belongs to the hydroxysteroid (17β) dehydrogenase superfamily, and it has been implicated in the conversion of estrone to estradiol as well as in the synthesis of arachidonic acid (AA). AA is a precursor of prostaglandins, which are involved in the regulation of female reproduction, prompting us to study the role of HSD17B12 enzyme in the ovarian function. We found a broad expression of HSD17B12 enzyme in both human and mouse ovaries. The enzyme was localized in the theca interna, corpus luteum, granulosa cells, oocytes, and surface epithelium. Interestingly, haploinsufficiency of the HSD17B12 gene in female mice resulted in subfertility, indicating an important role for HSD17B12 enzyme in the ovarian function. In line with significantly increased length of the diestrous phase, the HSD17B females gave birth less frequently than wild-type females, and the litter size of HSD17B12 females was significantly reduced. Interestingly, we observed meiotic spindle formation in immature follicles, suggesting defective meiotic arrest in HSD17B12 ovaries. The finding was further supported by transcriptome analysis showing differential expression of several genes related to the meiosis. In addition, polyovular follicles and oocytes trapped inside the corpus luteum were observed, indicating a failure in the oogenesis and ovulation, respectively. Intraovarian concentrations of steroid hormones were normal in HSD17B12 females, whereas the levels of AA and its metabolites (6-keto prostaglandin F1alpha, prostaglandin D, prostaglandin E, prostaglandin F, and thromboxane B) were decreased. In conclusion, our study demonstrates that HSD17B12 enzyme plays an important role in female fertility through its role in AA metabolism.

Objective: The aim of this study was to characterize the expression of hydroxysteroid (17β) dehydrogenase type 12 (HSD17B12), an enzyme involved in the synthesis of arachidonic acid (AA), in ovarian cancer, and to study its coexpression with its upstream and downstream enzymes in the AA pathway, namely elongation of very long chain fatty acids protein 5 (ELOVL5) and cyclooxygenase-2 (COX-2), respectively. Materials and Methods: Samples from benign and malignant ovarian neoplastic lesions were immunohistochemically stained with HSD17B12, ELOVL5, and COX-2. The staining intensities were quantified with the QuantCenter program, and the results were confirmed with visual inspection. Statistical significances were calculated with the Student t test, the Mann-Whitney test, linear regression, or ANOVA. Results: The expression of the HSD17B12, ELOVL5, and COX-2 enzymes increased according to the grade of the endometrioid ovarian adenocarcinomas. In contrast, in serous adenocarcinomas, staining with ELOVL5 was constantly weak, whereas the expression of HSD17B12 and COX-2 increased with the grade or FIGO stage of the cancer, respectively. Conclusions: The expression of HSD17B12 increased along with the severity of ovarian cancer, and the expression mimicked COX-2 expression and intensity. This further suggests the involvement of HSD17B12 in AA production, and its coexpression with COX-2 indicates a role for the enzyme in the increased prostaglandin production during ovarian cancer progression.