Integration of hepatic drug transporters and phase II metabolizing enzymes: Mechanisms of hepatic excretion of sulfate, glucuronide, and glutathione metabolites

The liver is the primary site of drug metabolism in the body. Typically, metabolic conversion of a drug results in inactivation, detoxification, and enhanced likelihood for excretion in urine or feces. Sulfation, glucuronidation, and glutathione conjugation represent the three most prevalent classes of phase II metabolism, which may occur directly on the parent compounds that contain appropriate structural motifs, or, as is usually the case, on functional groups added or exposed by phase I oxidation. These three conjugation reactions increase the molecular weight and water solubility of the compound, in addition to adding a negative charge to the molecule. As a result of these changes in the physicochemical properties, phase II conjugates tend to have very poor membrane permeability, and necessitate carrier-mediated transport for biliary or hepatic basolateral excretion into sinusoidal blood for eventual excretion into urine. This review summarizes sulfation, glucuronidation, and glutathione conjugation reactions, as well as recent progress in elucidating the hepatic transport mechanisms responsible for the excretion of these conjugates from the liver. The discussion focuses on alterations of metabolism and transport by chemical modulators, and disease states, as well as pharmacodynamic and toxicological implications of hepatic metabolism and/or transport modulation for certain active phase II conjugates. A brief discussion of issues that must be considered in the design and interpretation of phase II metabolite transport studies follows.     

Phosphatidylinositol 3-kinase inhibition by LY294002 radiosensitizes human cervical cancer cell lines.

PURPOSE: The phosphatidylinositol 3-kinase (PI3K) catalytic subunit is amplified in cervical cancers, implicating PI3K in cervical carcinogenesis. We evaluated the radiosensitizing effect of PI3K inhibition by LY294002 on clonogenic survival, growth characteristics, and gene expression in cervical cancer cell lines (HeLa and CaSki). EXPERIMENTAL DESIGN: Cervical cancer cells were treated separately and concurrently with the PI3K inhibitor LY294002 (10 micromol/L) and radiation (2 Gy) with serial analysis of cell count, apoptosis, and flow cytometry. PI3K inhibition was assessed by protein analysis of phosphorylated Akt. Clonogenic assays were done with varying doses of radiation and LY294002 and varied time points of administration of LY294002 proximate to the radiation dose. Surviving fractions and dose modification factors (DMF) were calculated. Each experiment was done in triplicate and analyzed using ANOVA regression analysis and Dunnett's t Test. Microarray gene expression analysis was done on the HeLa cell line. RESULTS: PI3K inhibition with LY294002 alone did not decrease cell survival. However, treatment with LY294002 significantly radiosensitized HeLa and CaSki cell lines with DMFs (1 log cell kill) of 1.95 and 1.37, respectively. Compared with post-irradiation, pretreatment produced more radiosensitization (P < 0.0001). DMFs were 2.2, 2.0, 2.0, and 1.2 for LY294002 added at 6, 2, and 0.5 hours before irradiation and 6 hours after irradiation, respectively. LY294002 pretreatment in irradiated HeLa cells led to altered gene expression. CONCLUSIONS: Although LY294002 alone did not produce cytotoxic effects, PI3K inhibition with LY294002 produced significant radiosensitization, showed significant time-dependent effects, increased apoptosis, and altered gene expression. These findings support future investigation of PI3K inhibitors in combination with radiation therapy for carcinoma of the cervix.     

Variation in DNA repair genes ERCC2, XRCC1, and XRCC3 and risk of follicular lymphoma.

The reasons for the positive association between skin cancer and non-Hodgkin's lymphoma are not known but may be due to common susceptibility involving suboptimal DNA repair. Therefore, we investigated selected polymorphisms and haplotypes in three DNA repair genes, previously associated with skin cancer and DNA repair capacity, in risk of follicular lymphoma, including possible gene interaction with cigarette smoking and sun exposure. We genotyped 19 single nucleotide polymorphisms (SNP) in the ERCC2, XRCC1, and XRCC3 genes in 430 follicular lymphoma patients and 605 controls within a population-based case-control study in Denmark and Sweden. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using unconditional logistic regression and haplotype associations were assessed with a global score test. We observed no associations between variation in the ERCC2 and XRCC1 genes and follicular lymphoma risk. In XRCC3, increased risk of follicular lymphoma was suggested for rare homozygotes of three SNPs [Rs3212024: OR, 1.8 (95% CI, 1.1-2.8); Rs3212038: OR, 1.5 (95% CI, 1.0-2.4); Rs3212090: OR, 1.5 (95% CI, 1.0-2.5)]. These results were strengthened in current cigarette smokers. However, evidence of differences in XRCC3 haplotype distributions between follicular lymphoma cases and controls was weak, both overall and in current smokers. We conclude that polymorphic variation in the XRCC3 gene, but not in ERCC2 or XRCC1, may be of importance for susceptibility to follicular lymphoma, perhaps primarily in current smokers. The link between skin cancer and follicular lymphoma is unlikely to be mediated through common variation in the studied DNA repair gene polymorphisms.     

Effect of soy phytoestrogens on hot flashes in postmenopausal women with breast cancer: a randomized, controlled clinical trial.

PURPOSE: Vasomotor symptoms, such as hot flashes and night sweats, in breast cancer survivors are often worsened by chemotherapy and tamoxifen, and/or the discontinuation of hormone replacement therapy at diagnosis. This study evaluated the acceptability and effectiveness of a soy beverage containing phytoestrogens as a treatment for hot flashes in postmenopausal women with breast cancer. METHODS: A randomized, placebo-controlled, double-blind clinical trial was conducted in postmenopausal women with moderate hot flashes who were previously treated for early-stage breast cancer. Women were stratified for tamoxifen use and randomized to a soy beverage (n = 59) containing 90 mg of isoflavones or to a placebo rice beverage (n = 64). Women recorded the number and severity of hot flashes daily with a daily menopause diary for 4 weeks at baseline and for 12 weeks while consuming 500 mL of a soy or placebo beverage. RESULTS: There were no significant differences between the soy and placebo groups in the number of hot flashes or hot flash scores. However, presumably because of a strong placebo effect, both groups had significant reductions in hot flashes. Mild gastrointestinal side effects were experienced by both groups but occurred with greater frequency and severity with soy. The mean serum genistein concentration at 6 weeks was significantly higher in women who consumed soy (0.61 +/- 0.43 micromol/L) compared with placebo (0.43 +/- 0.37 micromol/L) (P =.02). Overall acceptability and compliance were high and similar in both groups. CONCLUSION: The soy beverage did not alleviate hot flashes in women with breast cancer any more than did a placebo. Future research into other compounds is recommended to identify safe and effective therapies for hot flashes in breast cancer survivors.     

Is there a role for Notch signalling in human breast cancer?

Aberrant Notch signalling has been observed in several human cancers, including acute T-cell lymphoblastic leukaemia and cervical cancer, and is strongly implicated in tumourigenesis. Unregulated Notch signalling in the mouse mammary gland leads to tumour formation. These results raise the possibility that Notch signalling might play a role in human breast cancer. There are currently few reports that address this question directly and this appears to be an area worthy of further investigation.     

Patient selection before endopyelotomy: can it improve the outcome?

OBJECTIVE: To compare endopyelotomy and primary reconstructive procedures in patients with pelvi-ureteric junction (PUJ) obstruction and with risk factors for endopyelotomy failure. PATIENTS AND METHODS: Nineteen patients (eight female and 11 male, mean age 34.5 years, range 15-82) underwent endoluminal ultrasonography (US) before treatment for PUJ obstruction; the US findings were used to direct the treatment. Patients with unavoidable crossing vessels, massive hydronephrosis and crossing vessels associated with previous failed endopyelotomy were selected for reconstructive surgery. The clinical results of these patients (group 1) were compared with 12 consecutive patients who had undergone endopyelotomy before the use of endoluminal ultrasonography (group 2). RESULTS: Imaging detected 17 crossing vessels in 13 of the 19 patients. Six patients underwent primary reconstructive surgery and 13 underwent endopyelotomy. The endoluminal US findings changed treatment in some way in nine patients. Endopyelotomy was successful in 12 of the 13 patients and reconstructive surgery successful in five of six patients. The success after endopyelotomy improved from eight in 12 patients in group 2 to 12 of 13 in group 1 (P = 0.16, NS). CONCLUSIONS: Endoluminal US can be used to select patients in whom endopyelotomy is likely to fail. Using primary reconstructive procedures in these patients might improve the overall outcome, but these preliminary findings need to be confirmed in a larger study.     

Comparison of vaginal length after iliococcygeus fixation and sacrospinous ligament fixation

OBJECTIVE: To compare vaginal length after iliococcygeus fixation (ICF) and sacrospinous ligament fixation (SSLF). METHODS: A retrospective cohort study was performed on patients undergoing ICF or SSLF. Sixty-seven patients were identified and, of these, only 46 had complete data sets, leaving 23 patients in either group eligible for study. RESULTS: There were no significant differences in demographic data between the 2 groups. Mean vaginal length measurements were not significantly different before and after the ICF procedure (7.7+/-0.9 cm vs 7.6+/-0.8 cm, respectively; P=0.68). However, the mean vaginal length was significantly shortened following SSLF (7.9+/-0.8 cm vs 7.1+/-1.1 cm, P=0.001). The mean vaginal lengths preoperatively (7.7+/-0.9 cm vs 7.9+/-0.8 cm, P=0.51) and postoperatively (7.6+/-0.8 cm vs 7.1+/-1.1 cm, P=0.07) were similar. CONCLUSION: Iliococcygeus fixation does not significantly shorten vaginal length at the time of vaginal vault suspension, whereas the sacrospinous ligament fixation procedure does shorten vaginal length.     

The changing pattern of infant mortality in the US: The role of prenatal factors and their obstetrical implications

Infant mortality is one of the leading public health problems in the United States today. During the first half of this century the decline in infant mortality resulted largely from a reduction in postneonatal deaths (2–11 months after birth). Since 1950, two-thirds of all infant deaths have occurred in the neonatal period (1st month after birth). Since 1981, the rate of decline in the infant mortality rate has slowed due to a deterioration in the distribution of birthweights and a slowed improvement in birthweight-specific mortality rates. The role of birthweight is central to this issue, because low birthweight (LBW, < 2500 g) is a major determinant of death in the first year of life, particularly during the neonatal period. Stated another way, less than 0.5% of infants with birthweights > 2500 g die during the first year of life compared to 10.2% of infants with birthweights <2500 g and 45.3% with birthweights < 1500 g (very low birthweight, VLBW). These effects are magnified when evaluated on a race-specific basis: the rate of LBW is twice as high and the rate of VLBW is three times as high for black infants compared to white infants. Reducing the rates of VLBW and LBW, particularly among blacks, holds the greatest potential for future reductions in infant mortality in the United States. The important role of maternal factors in the antecedents of infant mortality (VLBW, LBW, intrauterine growth retardation, preterm birth) have been clearly and repeatedly demonstrated. Some of these factors, such as maternal race, adverse obstetrical history and low level of education, are not amenable to change during pregnancy. Other factors, such as cessation of smoking, higher maternal weight gain and the initiation of early prenatal care have been shown to improve the course and outcome of pregnancy and subsequently result in reduced infant mortality.