Increased risk of type 3c diabetes mellitus after acute pancreatitis warrants a personalized approach including diabetes screening

BACKGROUND

Acute pancreatitis (AP) is a frequent cause of hospitalization with long-term health consequences, including type 3c diabetes mellitus (DM). The incidence and risk factors for new-onset morbidities after AP need to be clarified to inform a personalized medicine approach.

METHODS

Using a longitudinal electronic healthcare record-linkage analysis, all patients admitted to hospital in Scotland with a first episode of AP between 1 April 2009 and 31 March 2012 and followed for a minimum of 5 years after their index AP admission were identified. All new-onset morbidity with specific focus on type 3c DM were analysed and, using time-split multiple regression.

RESULTS

A total of 2047 patients were included. AP requiring critical care was followed by 2 years of heightened risk (HR 5.24) of developing type 3c DM, increased risk of new-onset cardiac disease (HR 1.61), and renal disease (HR 2.96). The additional risk conferred by critical care AP had a negative interaction with time, whereas additional risk associated with male sex and a non-gallstone aetiology was long lasting.

CONCLUSION

Based on these findings, a personalized approach to include type 3c DM screening for a minimum of 2 years for individuals who required critical care when hospitalized with AP is recommended.

INCREASED MORTALITY IN PATIENTS WITH PRIMARY HYPERPARATHYROIDISM: DOES SURGERY MAKE A DIFFERENCE?

Objective: Primary hyperparathyroidism (PHPT) is functionally characterized by an inappropriately raised secretion of parathyroid hormone, leading to raised serum calcium levels. Some patients are referred for parathyroidectomy, and some are managed conservatively. The aim of the audit was to compare the mortality outcomes between the two groups. Methods: We retrospectively identified a cohort of inpatients with a main or secondary diagnosis of PHPT between 1986 and 2010 and followed them up to the end of 2011. The risk of mortality in PHPT patients compared to the background general population was estimated by calculating standardized mortality ratios (SMRs), adjusting for age, sex, and person-years at risk. Mortality in surgically treated patients was compared to conservatively treated patients using Cox regression, taking account of the Charlson Comorbidity Index. Results: A total of 2,589 patients (77.9% females) were diagnosed with PHPT in Scotland over this period. Of patients diagnosed with PHPT, 41.6% (1,077/2,589) had died by the end of 2011. The SMR was 1.58 (95% confidence interval [CI], 1.48 to 1.67). A total of 54.8% of the patients underwent surgery (SMR, 1.30; 95% CI, 1.18 to 1.43), while the rest were treated "conservatively" (SMR, 1.88; 95% CI, 1.73 to 2.03) (P<.001). When other significant variables including the Charlson Comorbidity Index were taken into account in the final model, the hazard ratio for the "conservatively" managed group was reduced to 1.49 (95% CI, 1.30 to 1.70; P<.0001). Conclusion: Our study confirmed that inpatients diagnosed with PHPT have increased mortality. The risk of mortality was lower in those treated surgically compared with patients treated conservatively. Abbreviations: CI = confidence interval; HR = hazard ratio; PHPT = primary hyperparathyroidism; PTX = parathyroidectomy; SMR = standard mortality ratio; SMR01 = Scottish Morbidity Records.

The impact of cancer on subsequent chance of pregnancy: a population-based analysis

STUDY QUESTION

What is the impact of cancer in females aged ≤39 years on subsequent chance of pregnancy?

SUMMARY ANSWER

Cancer survivors achieved fewer pregnancies across all cancer types, and the chance of achieving a first pregnancy was also lower.

WHAT IS KNOWN ALREADY

The diagnosis and treatment of cancer in young females may be associated with reduced fertility but the true pregnancy deficit in a population is unknown.

STUDY DESIGN, SIZE, DURATION

We performed a retrospective cohort study relating first incident cancer diagnosed between 1981 and 2012 to subsequent pregnancy in all female patients in Scotland aged 39 years or less at cancer diagnosis (n = 23 201). Pregnancies were included up to end of 2014. Females from the exposed group not pregnant before cancer diagnosis (n = 10 271) were compared with general population controls matched for age, deprivation quintile and year of diagnosis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Scottish Cancer Registry records were linked to hospital discharge records to calculate standardized incidence ratios (SIR) for pregnancy, standardized for age and year of diagnosis. Linkage to death records was also performed. We also selected women from the exposed group who had not been pregnant prior to their cancer diagnosis who were compared with a matched control group from the general population. Additional analyses were performed for breast cancer, Hodgkin lymphoma, leukaemia, cervical cancer and brain/CNS cancers.

MAIN RESULTS AND THE ROLE OF CHANCE

Cancer survivors achieved fewer pregnancies: SIR 0.62 (95% CI: 0.60, 0.63). Reduced SIR was observed for all cancer types. The chance of achieving a first pregnancy was also lower, adjusted hazard ratio = 0.57 (95% CI: 0.53, 0.61) for women >5 years after diagnosis, with marked reductions in women with breast, cervical and brain/CNS tumours, and leukaemia. The effect was reduced with more recent treatment period overall and in cervical cancer, breast cancer and Hodgkin lymphoma, but was unchanged for leukaemia or brain/CNS cancers. The proportion of pregnancies that ended in termination was lower after a cancer diagnosis, and the proportion ending in live birth was higher (78.7 vs 75.6%, CI of difference: 1.1, 5.0).

LIMITATIONS, REASONS FOR CAUTION

Details of treatments received were not available, so the impact of specific treatment regimens on fertility could not be assessed. Limited duration of follow-up was available for women diagnosed in the most recent time period.

WIDER IMPLICATIONS OF THE FINDINGS

This analysis provides population-based quantification by cancer type of the effect of cancer and its treatment on subsequent pregnancy across the reproductive age range, and how this has changed in recent decades. The demonstration of a reduced chance of pregnancy across all cancer types and the changing impact in some but not other common cancers highlights the need for appropriate fertility counselling of all females of reproductive age at diagnosis.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by NHS Lothian Cancer and Leukaemia Endowments Fund. Part of this work was undertaken in the MRC Centre for Reproductive Health which is funded by the MRC Centre grant MR/N022556/1. RAA has participated in Advisory Boards and/or received speaker’s fees from Beckman Coulter, IBSA, Merck and Roche Diagnostics. He has received research support from Roche Diagnostics, Ansh labs and Ferring. The other authors have no conflicts to declare.

Survival and new-onset morbidity after critical care admission for acute pancreatitis in Scotland: a national electronic healthcare record linkage cohort study

INTRODUCTION

Severe acute pancreatitis (AP) requiring critical care admission (ccAP) impacts negatively on long-term survival.

OBJECTIVE

To document organ-specific new morbidity and identify risk factors associated with premature mortality after an episode of ccAP.

DESIGN

Cohort study.

SETTING

Electronic healthcare registries in Scotland.

PARTICIPANTS

The ccAP cohort included 1471 patients admitted to critical care with AP between 1 January 2008 and 31 December 2010 followed up until 31 December 2014. The population cohort included 3450 individuals from the general population of Scotland frequency-matched for age, sex and social deprivation.

METHODS

Record linkage of routinely collected electronic health data with population matching.

PRIMARY AND SECONDARY OUTCOME MEASURES

Patient demographics, comorbidity (Charlson Comorbidity Index), acute physiology, organ support and other critical care data were linked to records of mortality (death certificate data) and new-onset morbidity. Kaplan-Meier and Cox regression analyses were used to identify risk factors associated with mortality.

RESULTS

310 patients with AP died during the index admission. Outcomes were not ascertained for five patients, and the deprivation quintile was not known for six patients. 340 of 1150 patients in the resulting postdischarge ccAP cohort died during the follow-up period. Greater comorbidity measured by the Charlson score, prior to ccAP, negatively influenced survival in the hospital and after discharge. The odds of developing new-onset diabetes mellitus after ccAP compared with the general population were 10.70 (95% CI 5.74 to 19.94). A new diagnosis of myocardial infarction, stroke, heart failure, liver disease, peptic ulcer, renal failure, cancer, peripheral vascular disease and lung disease was more frequent in the ccAP cohort than in the general population.

CONCLUSIONS

The persistent deleterious impact of severe AP on long-term outcome and survival is multifactorial in origin, influenced by pre-existing patient characteristics and acute episode features. Further mechanistic and epidemiological investigation is warranted.

Perinatal risks in female cancer survivors: A population-based analysis

Background/objectives

Advances in cancer management have resulted in improved survival rates, particularly in children and young adults. However, treatment may adversely affect reproductive outcomes among female cancer survivors. The objective of this study was to investigate their risk of adverse perinatal outcomes compared to the general population.

Design/methods

We performed a population-based analysis, including all female cancer survivors diagnosed before the age of 40 years between 1981 and 2012. Pregnancy and perinatal complications were identified through linkage of the Scottish Cancer Registry with hospital discharge records based on the Community Health Index (CHI) database. We compared 1,629 female cancer survivors with a first ever singleton pregnancy after diagnosis, with controls matched on age, deprivation quintile, and year of cancer diagnosis selected from the general population (n = 8,899). Relative risks and 95%-confidence intervals of perinatal risks were calculated using log-binomial regression.

Results

Survivors were more likely to give birth before 37 weeks of gestation (relative risk (RR]) 1.32, 95%-CI 1.10–1.59), but did not show an increased risk of low birth weight (<2.5kg: RR 1.15, 95%-CI 0.94–1.39), and were less likely to give birth to offspring small for gestational age (RR 0.81, 95%-CI 0.68–0.98). Operative delivery and postpartum haemorrhage were more common but approached rates in controls with more recent diagnosis. The risk of congenital abnormalities was not increased (RR 1.01, 95%-CI 0.85–1.20).

Conclusion

Cancer survivors have an increased risk of premature delivery and postpartum haemorrhage, but their offspring are not at increased risk for low birth weight or congenital abnormalities. In recent decades there has been a normalisation of delivery method in cancer survivors, nevertheless careful management remains appropriate particularly for those diagnosed in childhood.

Primary hyperparathyroidism: Increasing prevalence, social deprivation, and surgery

OBJECTIVE

To measure the increasing incidence of primary hyperparathyroidism (PHPT) in Scotland, to determine the relationship between PHPT and deprivation, and to investigate the relationship between parathyroidectomy (PTX) and social deprivation.

METHODS

We retrospectively identified a cohort of patients diagnosed with PHPT between 1986 and 2013 from the Scottish Morbidity Records (SMR01) database. The diagnosis of PHPT was made in accordance with the International Classification of Diseases code.

RESULTS

Between the years 1986 and 2013, 4002 patients were diagnosed with PHPT. There was a significant increase in the incidence of PHPT in this period (p < 0.0001), an association between the incidence of PHPT and deprivation (p < 0.0001) plus an association between a lower rate of PTX and deprivation (p < 0.001).

CONCLUSION

The increase in incidence of PHPT may be due to a combination of increased awareness of PHPT, easier diagnosis, and an ageing population. The lower rate of PTX in relation to deprivation may reflect comorbidities, age, and uncertainty about the long-term benefits of PTX in asymptomatic patients.

Risk of hospitalization and death following prostate biopsy in Scotland

OBJECTIVE

To investigate the risk of hospitalization and death following prostate biopsy.

STUDY DESIGN

Retrospective cohort study.

METHODS

Our study population comprised 10,285 patients with a record of first ever prostate biopsy between 2009 and 2013 on computerized acute hospital discharge or outpatient records covering Scotland. Using the general population as a comparison group, expected numbers of admissions/deaths were derived by applying age-, sex-, deprivation category-, and calendar year-specific rates of hospital admissions/deaths to the study population. Indirectly standardized hospital admission ratios (SHRs) and mortality ratios (SMRs) were calculated by dividing the observed numbers of admissions/deaths by expected numbers.

RESULTS

Compared with background rates, patients were more likely to be admitted to hospital within 30 days (SHR 2.7; 95% confidence interval 2.4, 2.9) and 120 days (SHR 4.0; 3.8, 4.1) of biopsy. Patients with prior co-morbidity had higher SHRs. The risk of death within 30 days of biopsy was not increased significantly (SMR 1.6; 0.9, 2.7), but within 120 days, the risk of death was significantly higher than expected (SMR 1.9; 1.5, 2.4). The risk of death increased with age and tended to be higher among patients with prior co-morbidity. Overall risks of hospitalization and of death up to 120 days were increased both in men diagnosed and those not diagnosed with prostate cancer.

CONCLUSIONS

Higher rates of adverse events in older patients and patients with prior co-morbidity emphasizes the need for careful patient selection for prostate biopsy and justifies ongoing efforts to minimize the risk of complications.

Pharmacogenetics of human cytosolic sulfotransferases

Cytosolic sulfotransferases (SULTs) are phase II detoxification enzymes that are involved in the biotransformation of a wide variety of structurally diverse endo- and xenobiotics, including many therapeutic agents and endogenous steroids. Single-nucleotide polymorphisms (SNPs) in SULTs have functional consequences on the translated protein. For the most part, these SNPs are fairly uncommon in the population, but some, most notably for SULT isoform 1A1, are commonly found and have been associated with cancer risk for a variety of tumor sites and also with response to therapeutic agents. SNPs in the hydroxysteroid sulfotransferase, SULT2A1, have been identified in African-American subjects and influence the ratio of plasma DHEA:DHEA-S. This modification could potentially influence cancer risk in steroidogenic tissues. SNPs in many SULTs are ethnically distributed, another factor that could influence SULT pharmacogenetics. Finally, genetic variation has also been identified in 3'-phosphoadenoside 5'-phosphosulfate synthetase (PAPPS), the enzymes responsible for producing the obligatory cosubstrate for all sulfotransferases. Taken together, this variability could substantially influence the disposition of drugs metabolized by SULTs. Elucidation of the basis and effect of variability in sulfation could greatly impact individualized therapy in the future.

Validity of an ELISA for N-acetyltransferase-2 (NAT2) phenotyping

A competitive antigen ELISA was previously developed for NAT2 phenotyping, using caffeine as the probe drug. The ELISA phenotypes by measuring the ratio of 5-acetamido-6-amino-3-methyluracil (AAMU) and 1-methylxanthine (1X) after transformation of 5-acetamido-6-formylamino-3-methyluracil (AFMU) to AAMU, in contrast to capillary electrophoresis high-pressure liquid chromatography (HPLC) which phenotype by measuring the AFMU/1X ratio. The ELISA phenotyping was previously determined in 30 samples and correlated well with phenotypes determined by capillary electrophoresis (29/30). The correlation was extended with the standard HPLC methodology by expanding the data set by 146 in order to test the validity of the ELISA methodology. The correlation with HPLC in this larger sample size was 96%; whereas the correlation between the two methods for determination of 1X was high (r(2)=0.90), that for determination of AAMU by ELISA and AFMU by HPLC was low (r(2)=0.53). The poor correlation between the two methodologies could not be attributed to the age of urine samples, nor to a significant decomposition of AFMU in the body prior to collection of the urine sample. The addition of a simple caffeine metabolite extraction method, originally developed for HPLC analysis of metabolites, to the ELISA phenotyping protocol produced a methodology with absolute correlation to the standard HPLC method.

Relationship of phenol sulfotransferase activity (SULT1A1) genotype to sulfotransferase phenotype in platelet cytosol

Sulfation catalysed by human cytosolic sulfotransferases is generally considered to be a detoxification mechanism. Recently, it has been demonstrated that sulfation of heterocyclic aromatic amines by human phenol sulfotransferase (SULT1A1) can result in a DNA binding species. Therefore, sulfation capacity has the potential to influence chemical carcinogenesis in humans. To date, one genetic polymorphism (Arg213His) has been identified that is associated with reduced platelet sulfotransferase activity. In this study, data on age, race, gender, SULT1A1 genotype and platelet SULT1A1 activity were available for 279 individuals. A simple colorimetric phenotyping assay, in conjunction with genotyping, was employed to demonstrate a significant correlation (r = 0.23, P < 0.01) of SULT1A1 genotype and platelet sulfotransferase activity towards 2-naphthol, a marker substrate for this enzyme. There was also a difference in mean sulfotransferase activity based on gender (1.28 nmol/min/mg, females; 0.94 nmol/min/mg, males, P = 0.001). DNA binding studies using recombinant SULT1A1*1 and SULT1A1*2 revealed that SULT1A1*1 catalysed N-hydroxy-aminobiphenyl (N-OH-ABP) DNA adduct formation with substantially greater efficiency (5.4 versus 0.4 pmol bound/mg DNA/20 min) than the SULT1A1*2 variant. A similar pattern was observed with 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5b]pyridine (N-OH-PhIP) (4.6 versus 1.8 pmol bound/mg DNA/20 min).

An allele-specific polymerase chain reaction method for the determination of the D85Y polymorphism in the human UDP-glucuronosyltransferase 2B15 gene in a case-control study of prostate cancer

BACKGROUND

UDP-glucuronosyltransferase 2B15 (UGT2B15) catalyzes the inactivation of dihydrotestosterone (DHT) by forming the DHT-glucuronide and is expressed in normal and hyperplastic prostate tissue. Alterations in the activity of this enzyme could be a major contributing factor to the bioavailability of androgens in target tissue such as the prostate.

METHODS

A polymorphism (D85 to Y85) has been identified in the UGT2B15 gene that results in a 50% reduction in enzyme activity. Previously, detection of the polymorphic nucleotide has required direct sequencing. We have developed and validated an allele-specific polymerase chain reaction (PCR) assay to identify the polymorphic base pair in the UGT2B15 gene. This assay was used to examine the distribution of the UGT2B15 polymorphism in a small case-control group (64 cases and 64 controls) from a prostate cancer study.

RESULTS

The results of this analysis show that prostate cancer patients were significantly more likely to be homozygous for the lower activity D85 UGT2B15 allele than control individuals (41% versus 19%, respectively, odds ratio = 3.0 (95% confidence intervals 1.3-6.5)).

CONCLUSIONS

These results suggest that individuals who are homozygous for the lower activity allele may be at increased risk for developing prostate cancer.

Cancer therapy and polymorphisms of cytochromes P450

Cytochrome P450 (CYP) enzymes are important in the metabolism of some endogenous compounds, environmental and dietary xenobiotics and many drugs. Many of these enzymes have genetic polymorphisms that produce significant changes in metabolic activity, however the function of other polymorphisms is unknown. Genetic polymorphisms have important influences on variability in human pharmacokinetics, including intra-individual differences in drug toxicity, drug interactions and response to chemotherapy. Other factors that influence drug metabolism include differences in enzyme expression due to differences in age, gender, smoking status, exposure to dietary or environmental xenobiotics or co-administration of other drugs. In addition, some xenobiotics and drugs can directly inhibit or induce the activity of CYPs. All of these factors can produce differences in metabolic capacities among individuals which can produce toxicity in some patients and sub-effective dosing in others. Maximum clinical benefit will require a more complete understanding of the influence of these polymorphisms on allele function and their interaction with inducers and inhibitors of enzyme expression or activity. This effort will permit the pharmacogenetic screening of patients before the administration of drugs and result in the identification of individuals who are prone to adverse reactions or poor response, resulting in more effective individualized therapy.

In vivo human metabolism of [2-14C]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

To better understand the interactions of the pathways of activation and detoxification on the metabolism of the putative carcinogen, PhIP, we administered a dose of 70-84 microg [2-14C] PhIP (17.5 [microCi 14C) 48-72 h before scheduled colon surgery. Blood and urine collected for the next 48-72 h was evaluated by linear accelerator mass spectroscopy (AMS) and scintillation counting LC-MS to identify specific PhIP metabolites. The thermostable phenol sulfotransferase (SULT1A1) phenotype was correlated with the 4'-PhIP-SO4 levels in the urine at 0-4 h (R = 0.86, P = 0.059). The CYP1A2 activity had a negative correlation with PhIP serum levels at 1 h (R = 0.94, P = 0.06) and a positive correlation with urine N-OH-PhIP levels at 0-4 h (R = 0.85, P = 0.15). This low level radioisotope method of determining the influence of phenotype on metabolism will significantly improve our understanding of the interrelationships of these pathways and provide a critical foundation for the development of individual risk assessment.

DNA and protein adduct formation in the colon and blood of humans after exposure to a dietary-relevant dose of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

Epidemiology studies have indicated that certain dietary components, including well-cooked meat, are risk determinants for colon cancer. Cooked meat can contain significant quantities of heterocyclic aromatic amines (HCAs), which have been established as carcinogens in laboratory animals. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is usually the most mass-abundant HCA, with concentrations up to 480 ppb. We used accelerator mass spectrometry to establish whether DNA and protein adducts can be detected in humans exposed to a quantity of PhIP comparable with levels of exposure that occur in the diet. Five human volunteers were administered a dietary-relevant dose of [14C]PhIP (70-84 microg) 48-72 h before surgery for removal of colon tumors. Blood samples were collected at various time points, and albumin, hemoglobin, and WBC DNA were extracted for analysis by accelerator mass spectrometry. Tissue samples were collected during surgery and used to assess either tissue available doses of [14C]PhIP or adduct levels. The results of this study show: (a) PhIP is activated to a form that will bind to albumin, hemoglobin, and WBC DNA in peripheral blood. WBC DNA adducts were unstable and declined substantially over 24 h; (b) PhIP is bioavailable to the colon, with levels in normal tissue in the range 42-122 pg PhIP/g tissue; and (c) PhIP binds to both protein and DNA in the colon. DNA adduct levels in the normal tissue were 35-135 adducts/10(12) nucleotides, which was significantly lower than tumor tissue. The results of this study demonstrate that PhIP is bioavailable to the human colon following defined dietary-relevant doses and forms DNA and protein adducts.

The identification of [2-(14)C]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine metabolites in humans

[2-(14)C]2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine ([14C]PhIP), a putative human carcinogenic heterocyclic amine found in well-done cooked meat, was administered orally to three colon cancer patients undergoing a partial colonectomy. Forty-eight to seventy-two hours prior to surgery, subjects received a 70-84 microg dose of 14C. Urine and blood were analyzed by HPLC for PhIP and PhIP metabolites. Metabolites were identified based on HPLC co-elution with authentic PhIP metabolite standards, mass spectral analysis and susceptibility to enzymatic cleavage. In two subjects, approximately 90% of the administered [14C]PhIP dose was eliminated in the urine, whereas in the other, only 50% of the dose was found in the urine. One subject excreted three times more radioactivity in the first 4 h than did the others. Twelve radioactive peaks associated with PhIP were detected in the urine samples. The relative amount of each metabolite varied by subject, and the amounts of each metabolite within subjects changed over time. In all three subjects the most abundant urinary metabolite was identified as 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine-N2-glucuron ide (N-hydroxy-PhIP-N2-glucuronide), accounting for 47-60% of the recovered counts in 24 h. PhIP accounted for <1% of the excreted radiolabel in all three patients. Other metabolites detected in the urine at significant amounts were 4-(2-amino-1-methylimidazo[4,5-b]pyrid-6-yl)phenyl sulfate, N-hydroxy-PhIP-N3-glucuronide and PhIP-N2-glucuronide. In the plasma, N-hydroxy-PhIP-N2-glucuronide accounted for 60, 18 and 20% of the recovered plasma radioactivity at 1 h post PhIP dose in subjects 1, 2 and 3 respectively. Plasma PhIP was 56-17% of the recovered dose at 1 h post exposure. The relatively high concentration of N-hydroxy-PhIP-N2-glucuronide and the fact that it is an indicator of bioactivation make this metabolite a potential biomarker for PhIP exposure and activation. Determining the relative differences in PhIP metabolites among individuals will indicate metabolic differences that may predict individual susceptibility to carcinogenic risk from this suspected dietary carcinogen.

Photoaffinity labeling studies of the human recombinant UDP-glucuronosyltransferase, UGT1*6, with 5-azido-UDP-glucuronic acid

Recombinant human liver UDP-glucuronosyltransferase (UGT), UGT1*6, which catalyzes the glucuronidation of small phenols, previously expressed in a V79 cell line (1) was photolabeled with [beta-32P]5N3UDP-glucuronic acid ([beta-32P]5N3UDP-GlcUA). Two polypeptides with an approximate molecular weight of 54 kDa were extensively photolabeled in the recombinant cell line while the nontransfected cell line showed no photoincorporation in this area. The identity of the two polypeptides as UGTs, which correspond to two different glycosylation forms of the same enzyme, was confirmed by Western blot using a polyclonal monospecific antibody directed against the 120 amino acids of the N-terminal end of UGT1*6. Preincubation with UDP-glucuronic acid (UDP-GlcUA) inhibited the photoincorporation of the probe into the polypeptides indicating competition of both the photoprobe and the nucleotide-sugar for the same binding site. It was further shown that photoincorporation of [beta-32P]5N3UDP-GlcUA into the UDP-GlcUA-binding site was saturable. The lack of photoincorporation of a related photoprobe, [beta-32P]5N3UDP-glucose ([beta-32P]5N3UDP-Glc), into UGT1*6 demonstrated specificity of this enzyme for UDP-GlcUA. In enzymatic assays, unlabeled 5N3UDP-GlcUA was shown to be an effective cosubstrate of the glucuronidation of 4-nitrophenol catalyzed by UGT1*6. The studies were further extended by demonstrating that photolabeling of UGT1*6 was inhibited by several active site-directed inhibitors. Finally, photoaffinity labelling was used in the purification of the labeled UGT1*6 using preparative gel electrophoresis. In conclusion, we have demonstrated that photoaffinity labeling with [beta-32P]5N3UDP-GlcUA is an effective tool for the characterization of enzymes such as recombinant UGTs that use UDP-GlcUA.

Glucuronidation of all-trans-retinoic acid and 5,6-epoxy-all-trans-retinoic acid. Activation of rat liver microsomal UDP-glucuronosyltransferase activity by alamethicin

The effects of detergent, alamethicin (a channel-forming peptide), and the inducers phenobarbital and 3-methylcholanthrene on glucuronidation of all-trans-retinoic acid (atRA) and 5,6-epoxy-atRA have been investigated using liver microsomes from Sprague-Dawley and Fischer 344 rats. Conditions for enzymatic glucuronidation were optimized for substrate concentration, protein, and time by using atRA and Sprague-Dawley microsomes. With detergent-activated Sprague-Dawley microsomes, 5,6-epoxy-atRA was shown to be a significantly better substrate than atRA for microsomal glucuronidation (263 vs. 116 pmol/mg/min for 5,6-epoxy-atRA and atRA, respectively). The product of incubation of microsomes with atRA and UDP-glucuronic acid was identified as a glucuronide by beta-glucuronidase hydrolysis and by HPLC analysis. Alamethicin was shown to be a highly effective activator of glucuronidation activity; atRA and 5,6-epoxy-atRA glucuronidation rates were increased 2- and 3-fold, respectively, compared with detergent activation. Alamethicin (but not detergent) significantly increased retinoid glucuronidation by microsomes from Fischer 344 rats treated with phenobarbital and 3-methylcholanthrene, compared with untreated controls. The two compounds were equally effective inducers of activity, although 5,6-epoxy-atRA was again the better substrate. The same control and induced Fischer rat microsomes were photolabeled with [32P]5-azido-UDP-glucuronic acid in the absence or presence of detergent, two concentrations of alamethicin, and a 10-fold molar excess of unlabeled UDP-glucuronic acid. Photoincorporation into microsomal proteins from detergent-disrupted induced microsomes was 2-3 times greater than that of controls. Alamethicin increased photoincorporation of the probe into UDP-glucuronosyltransferase proteins an additional 1.5-2-fold in control and induced microsomes, compared with the respective detergent-activated samples.

Two kinetically-distinct components of UDP-glucuronic acid transport in rat liver endoplasmic reticulum

Previous studies have documented the presence of protein-mediated transport of UDP-glucuronic acid (UDP-GlcUA) in rat liver endoplasmic reticulum (ER). Measurement of uptake at varying concentrations of high specific activity [beta-32P]UDP-GlcUA has revealed the presence of a two component UDP-GlcUA transporting system. Transport at low substrate concentrations occurred predominantly via a high affinity component (K(m) = 1.6 microM), whereas a low affinity component (K(m) = 38 microM) predominated at high substrate concentrations. The K(m) for the high affinity system is in agreement with that previously published, while the low affinity component is a new finding. The uptake of UDP-GlcUA was temperature-sensitive, time dependent, and saturable for both components. The high affinity transport was affected by trans-stimulation and cis-inhibition by UDP-N-acetylglucosamine (UDP-GlcNAc); however, the same concentrations of UDP-GlcNAc had less effect on the low affinity system. In order to further study the two transport components, various inhibitors of anion transport carriers were tested. The high affinity component was strongly inhibited by 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) and furosemide, while the low affinity system was less sensitive to these reagents. Dose-dependent inhibition by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) was found for both transport systems. Probenecid was found to be a weak inhibitor of both components of the UDP-GlcUA uptake. Finally, the major metabolite of 3'-azido-3'-deoxythymidine, 3'-azido-3'-deoxythymidine monophosphate (AZTMP), was able to inhibit the uptake of UDP-GlcUA by both components. The results indicate the presence of two carrier-mediated UDP-glucuronic acid transporting components in rat liver ER.

Photoaffinity labeling of human recombinant sulfotransferases with 2-azidoadenosine 3',5'-[5'-32P]bisphosphate

Photoaffinity labeling with 2-azidoadenosine 3', 5'-[5'-32P]bisphosphate was used to identify and characterize adenosine 3',5'-bisphosphate-binding proteins in human liver cytosol and recombinant sulfotransferase proteins. The sulfotransferases investigated in these studies were the human phenol sulfotransferases, HAST1, -3, and -4, dehydroepiandrosterone sulfotransferase, and estrogen sulfotransferase. The cDNAs for these enzymes have been previously cloned and expressed in COS-7 cells or Escherichia coli. Photoaffinity labeling of all proteins was highly dependent on UV irradiation, was protected by co-incubation with unlabeled adenosine 3',5'-bisphosphate and phosphoadenosine phosphosulfate, and reached saturation at concentrations above 10 microM. To verify that the 31 35-kDa photolabeled proteins were indeed sulfotransferases, specific antibodies known to recognize human sulfotransferases were used for Western blot analyses of photolabeled proteins. It was shown unequivocally that the proteins in the 31-35-kDa region recognized by the antibodies also photoincorporated 2-azidoadenosine 3',5'-[5'-32P]bisphosphate. This is the first application of photoaffinity labeling with 2-azidoadenosine 3',5'-[5'-32P]bisphosphate for the characterization of recombinant human sulfotransferases. Photoaffinity labeling will be also useful in the purification and functional identification of other adenosine 3',5'-bisphosphate-binding proteins and to determine amino acid sequences at or near their active sites.

Value of Tomography in Lesions of the Main Bronchi and their Larger Sub-divisions

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