Polymorphisms of the UDP-glucuronosyl transferase 1A genes are associated with adverse events in cancer patients receiving irinotecan-based chemotherapy.

A prodrug, irinotecan (CPT-11), is a semisynthetic derivative of camptothecin. It inhibits topoisomerase I and is used for treatment of lung, stomach, and colon cancers in Japan. The active form of CPT-11, SN-38, causes the adverse events such as neutropenia and diarrhea. Since SN-38 is metabolized to non-toxic SN-38-glucuronide by hepatic uridine diphosphate glucuronosyl transferase (UGT) 1A enzymes, UGT1A enzyme activities may influence adverse events of CPT-11. UGT1A enzymes consist of three isozymes (1A1, 1A7, 1A9), and their genes are characterized by polymorphisms. Here, to identify the genetic factors that affect the adverse events of CPT-11, we determined the polymorphism in three UGT 1A isozyme genes in 45 inpatients with lung, colon, or stomach cancer. The univariate and multivariate analysis of patients' physiological and genetic factors revealed that one or more genotypes of UGT1A1*6/*28, UGT1A7*3/*3, and UGT1A9*1/*1 may enhance the adverse events. Each of the first two genotypes is expected to generate the enzyme with low catalytic activity. The UGT1A9*1 represents the wild-type allele, which however provides the lower catalytic activity, compared to the UGT1A9*22 variant that is common in this study population. Indeed, four (67%) out of six patients who carry one or more of the above-mentioned genotypes suffered from adverse events, leading to the discontinuation of chemotherapy or the decreased dose of CPT-11. By contrast, only six (15%) out of 39 patients with other genotypes suffered from adverse events. In conclusion, UGT1A1*6/*28, UGT1A7*3/*3, and UGT1A9*1/*1 should be taken into consideration as markers for preventing severe adverse events of CPT-11 administration.

Polychlorinated biphenyl-mediated decrease in serum thyroxine level in rodents.

Effects of Kanechlor-500 (KC500), a commercial polychlorinated biphenyl mixture, on the levels of serum thyroid hormones such as total thyroxine (T(4)) and triiodothyronine were examined in male mice, hamsters, rats, and guinea pigs. Four days after a single intraperitoneal injection of KC500, significant decreases in the levels of the serum total T(4) and free T(4) occurred in all the animals examined, whereas a significant decrease in the level of serum triiodothyronine was observed only in guinea pigs among the animals examined. In addition, no significant change in the level of serum thyroid-stimulating hormone was observed in any of the rodents examined. A significant increase in the activity of hepatic T(4)-UDP-glucuronosyltransferase after the KC500 administration occurred only in guinea pigs, whereas the increase in the amount of biliary [(125)I]T(4) glucuronide after an intravenous injection of [(125)I]T(4) to the KC500-pretreated animals occurred only in rats. On the other hand, in all the rodents examined, KC500-pretreatment promoted the clearance of [(125)I]T(4) from the serum and led to a significant increase in the steady-state distribution volumes of [(125)I]T(4). Likewise, its pretreatment raised the concentration ratio (K(p) value) of the liver to serum and the liver distribution of [(125)I]T(4) in all the rodents tested. The present findings indicate that for the first time the KC500-mediated decrease in the serum T(4) level in mice, hamsters, rats and guinea pigs occurs mainly through an increase in the accumulation level of T(4) in the liver.

The decrease in level of serum thyroxine by 2,2',4,5,5'-pentachlorobiphenyl in rats and mice: no correlation with formation of methylsulfonyl metabolites.

A relationship between formation of methylsulfonyl (MeSO2) metabolites of 2,2',4,5,5'-pentachlorobiphenyl (PentaCB) and decrease in serum thyroxine (T4) level was examined in the rats and mice after a single i.p. injection of PentaCB (342 micromol/kg body weight). In either rats or mice, levels of the 3- and 4-MeSO2 metabolites of PentaCB in the liver and feces increased in a time-dependent fashion up to 8 days after PentaCB-treatment. However, there was a marked difference between rats and mice in the amount of the metabolites formed, and the cumulative amount of the either MeSO2 metabolite for 8 days after PentaCB treatment in the liver was 4 to 15 times higher in mice than in rats. On the other hand, a 40 to 60% decrease in level of serum total T4 occurred in both rats and mice at 1 day after PentaCB treatment, and the decrease was retained up to 8 days after PentaCB treatment. Thus, there was a marked difference between rats and mice in the formation of MeSO2 metabolites from PentaCB but not a significant difference between rats and mice in PentaCB-induced decrease in the level of serum total T4, indicating that PentaCB-induced decrease in the level of serum total T4 is not necessarily dependent on the MeSO2 metabolites formed.

A possible mechanism for decrease in serum thyroxine level by polychlorinated biphenyls in Wistar and Gunn rats.

We have previously demonstrated that in mice, the decrease in serum thyroxine (T(4)) level by polychlorinated biphenyls (PCBs) occurs without an increase in the UDP-glucuronosyltransferase (T(4)-UDP-GT) for T(4) glucuronidation, although the PCB-induced decrease in rats is generally thought to occur through induction of T(4)-UDP-GT, UGT1A1, and UGT1A6. In the present study, to further clarify the relationship between the decrease in serum T(4) level and the increase in UGT1A activity by PCB in rats, we examined the relationship using Wistar rats and Gunn rats, a mutant strain of Wistar rats deficient in UGT1A isoforms. The serum total T(4) level was markedly decreased not only in the Wistar rats but also in the Gunn rats 4 days after treatment with a PCB, Kanechlor-500 (KC500, 100 mg/kg) or 2,2',4,5,5'-pentachlorobiphenyl (PentaCB, 112 mg/kg), and there was no significant difference in magnitude of the decrease between the two rat strains. At the same time, the level and activity of T(4)-UDP-GT were significantly increased by treatment with either KC500 or PentaCB in Wistar rats but not in Gunn rats. In addition, no significant change in the level of serum total triiodothyronine (T(3)) and thyroid-stimulating hormone by the KC500 treatment was observed in either Wistar or Gunn rats. Furthermore, significant decrease in the activity of hepatic type-I deiodinase, which mediates the deiodization of T(4) and T(3), by treatment with KC500 or PentaCB was observed in both Wistar and Gunn rats. From the serum of KC500- or PentaCB-treated Wistar and Gunn rats, mono- and di-hydroxylated PCB metabolites, which would bind to T(4) binding serum protein (transthyretin), were detected. In conclusion, the present results suggest that the decrease in serum total T(4) level by either KC500 or PentaCB in Gunn rats was not dependent on the increase in hepatic T(4)-UDP-GT activity. The findings further suggest that the PCB-mediated decrease in serum T(4) level might occur, at least in part, through formation of the hydroxylated PCB metabolites. Furthermore, even in Wistar rats, the PCB-mediated decrease in serum T(4) level might occur not only through the increase in hepatic T(4)-UDP-GT but also via formation of hydroxylated PCB metabolites.

Effects of polychlorinated biphenyls, kanechlor-500, on serum thyroid hormone levels in rats and mice.

Effects of a commercial polychlorinated biphenyls mixture, Kanechlor-500 (KC500), on the levels of serum thyroid hormones such as total thyroxine (T4) and triiodothyronine (T3) were examined comparatively in male Wistar rats and ddy mice. Serum T4 levels were significantly decreased in both rats and mice 4 days after a single ip injection of KC500 (100 mg/kg body weight), whereas decreased levels of T3 were observed in mice but not in rats. In addition, no significant change in the level of serum thyroid stimulating hormone was observed in either rats or mice. Hepatic UDP-glucuronosyltransferases (UDP-GTs) UGT1A1 and UGT1A6, which efficiently mediate glucuronidation of T4 and promote the excretion of the hormones, were induced by KC500 in rats but not in mice. Hepatic microsomal cytochrome P450 (P450) content and the microsomal activity for 7-ethoxy-, 7-pentoxy-, and 7-benzoyloxy-resorufin dealkylations were significantly increased by KC500 in both rats and mice, although the magnitude of increase in the enzyme activities was higher in rats than in mice. The difference in the increase in the activity of microsomal enzymes, including UDP-GT and P450, between KC500-treated rats and mice was not correlated with that in the level of hepatic methylsulfonyl-PCB metabolites. In the present study, we found for the first time that the decrease in serum T4 levels by KC-500 in mice occurred without increase in hepatic UDP-GTs, UGT1A1 and UGT1A6, responsible for T4 glucuronidation. The present findings further suggested that although the decrease in serum T4 levels in KC500-treated rats would occur at least in part through the induction of the UDP-GTs, it might not be dependent on only the increase in the enzymes.