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Biomedical subjects

R Clarke

Publications and source records attributed to R Clarke.

At least 55 records · Page 3Linked to original sources
PubMed2000

Characterization of the human and mouse HEY1, HEY2, and HEYL genes: cloning, mapping, and mutation screening of a new bHLH gene family.

Many basic helix-loop-helix (bHLH) transcription factors are known as key regulators of embryonic development or differentiation in various species. We have isolated and characterized three new hairy-related bHLH transcription factor genes from mouse and human (hairy and Enhancer-of-split related with YRPW motif; HEY1, HEY2, and HEYL). All three HEY genes have a similar genomic structure with five exons. Together with a highly related Drosophila homologue, they form a new bHLH gene subfamily that is different from both hairy and the known vertebrate Hes and Her genes. While the overall structure with the bHLH domain, Orange domain, and WRPW motif is similar, the last motif is changed to KPYRPWG in Hey1/2 and absent in HeyL. This and other sequence features suggest Hey proteins to have unique functional properties. The genes were mapped by fluorescence in situ hybridization and RH mapping to the following human chromosomes: (HEY1) 8q21, (HEY2) 6q21, and (HEYL) 1p34.3. Based on expression patterns and map location, HEY genes are candidates for several human or mouse disease loci. However, initial screening of DNA from affected individuals for two human disorders and four mouse mutants did not reveal any diagnostic alterations in the coding regions.

Amino Acid Sequence↗
PubMed2000

Development of an immobilized P-glycoprotein stationary phase for on-line liquid chromatographic determination of drug-binding affinities.

The membrane transporter P-glycoprotein (PGP) has been immobilized on an immobilized artificial membrane (IAM) LC stationary phase. The resulting PGP-IAM phase retained the ability of the native PGP to bind the known PGP-ligand vinblastine. Displacement studies using other known PGP ligands, verapamil and cyclosporin A, demonstrated that there was selective binding between vinblastine and the immobilized PGP transporter. The binding affinity (Kd value) of vinblastine for the PGP-IAM was determined to be 19+/-20 and 71+/-11 nM on two separate columns. These values are consistent with previously reported values of 9+/-2, 8+/-2, and 37+/-10 nM, which were obtained using native membranes. The Kd values obtained on the PGP-IAM for cyclosporin A and verapamil were 492+/-21 and 172+/-29 microM, respectively. These results were higher than the corresponding Kd values obtained using native membranes, but the relative affinities vinblastine > cyclosporin A >> verapamil are consistent in both approaches. During several months of experiments and storage, the PGP-IAM was found to be reproducible and stable. The stationary phase appears to be useful in the on-line screening for PGP ligands.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Identification of twenty alternatively spliced estrogen receptor alpha mRNAs in breast cancer cell lines and tumors using splice targeted primer approach.

Estrogen receptor (ER) alpha splice variant transcript profiles were analyzed by RT PCR in six ER positive breast cancer cell lines, MCF-7, T47D, ZR-75, LCC1, LCC2 and LCC9, three ER negative cell lines, MDA-MB-435, MDA-MB-235 and LCC6, and three ER positive malignant breast tumors using targeted primers which specifically anneal to the splice junctions of exon 2Delta, exon 3Delta, exons 2-3Delta, exon 4Delta, exon 5Delta, exon 6Delta and exon 7Delta. The partner primers were chosen such that largest possible transcripts were amplified between exons 1 and 8. The results described here show that each splice specific primer amplified not only the single exon deleted transcript but also a number of related transcripts that have deletions in various combinations of exons. The exon 2Delta specific primer amplified five transcripts that have deletions in exon 2, exons 2 and 7, exons 2, 5, and 7, exons 2 and 4-5, and exons 2 and 4-6. The exon 3Delta specific primer amplified two transcripts that have deletions in exon 3, and exons 3 and 7. The exon 2-3Delta specific primer amplified three products that have deletions in exons 2-3, exons 2-3 and 7 and exons 2-3, 5 and 7. The exon 4Delta specific primer amplified two products that have deletions in exon 4, and exons 4 and 7. The exon 5Delta specific primer amplified three transcripts, that have deletions in exon 5, exons 5 and 2, and exons 5, and 2-3. The 6Delta specific primer amplified only one transcript that has a deletion in exon 6. The 7Delta specific primer amplified four transcripts, that have deletions in exon 7, exons 7 and 4, exons 7 and 3-4, and exons 7 and 3-5. None of the above splice specific primers amplified the wild type ER sequences. The six ER positive cell lines differed in the patterns of the variant transcripts and among the three ER negative cell lines analyzed, only MDA-MB-435 showed the presence of exon 2Delta and exon 4Delta transcripts. Analyses in the tumor samples indicated that the above transcripts are extensively modified.

Alternative Splicing↗
PubMed2000

Use of the atypical antipsychotics Olanzapine and Risperidone in adults with intellectual disability.

The present study was designed to monitor the use of atypical antipsychotics in adults with intellectual disability and to evaluate the clinical effectiveness of these drugs. Twenty-one patients were commenced on an atypical antipsychotic: 12 on Olanzapine and nine on Risperidone. The ICD-10 diagnoses of the subjects were mild (13 cases) or moderate (8 cases) mental retardation, and psychiatric disorders (17 cases) with significant impairment of behaviour in 10 cases. Tolerability was good for 15 patients experiencing minimum or no side-effects, and medication was only stopped as a result of side-effects in one case. Clinical global outcome was rated as minimally improved or better for 16 cases. The present findings suggest that the atypical antipsychotics Olanzapine and Risperidone are well tolerated by patients with intellectual disability and psychiatric disorders, and are broadly effective against target symptoms.

Adult↗
PubMed2000

Vitamin supplements and cardiovascular risk: review of the randomized trials of homocysteine-lowering vitamin supplements.

Epidemiological studies have shown that higher blood homocysteine levels appear to be associated with higher risks of coronary, cerebral, and peripheral vascular disease and are inversely related to blood levels of folate and of vitamin B12 and vitamin B6. However, observational studies cannot exclude the possibility that elevated homocysteine levels may be associated with some other factor, rather than being causally related to vascular disease. Large-scale clinical trials of sufficient dose and duration of treatment are required to test this hypothesis, but there was substantial uncertainty about the optimal vitamin regimen to test in such trials. A meta-analysis of 12 randomized trials of vitamin supplements to lower homocysteine levels was carried out to determine the optimal dose of folic acid required to lower homocysteine levels and to assess whether vitamin B12 or vitamin B6 had additive effects. This meta-analysis demonstrated that reductions in blood homocysteine levels were greater at higher pretreatment blood homocysteine levels and at lower pretreatment folate concentrations. After standardization for a pretreatment homocysteine concentration of 12 micromol/L and folate concentration of 12 nmol/L (approximate average concentrations for western populations), dietary folic acid reduced homocysteine levels by 25% (95% confidence interval [CI]: 23 to 28%) with similar effects in a daily dosage range of 0.5 to 5 mg. Vitamin B12 (mean 0.5 mg) produced an additional reduction in blood homocysteine of 7%, whereas vitamin B6 (mean 16.5 mg) did not have any significant effect. Hence, in typical populations, daily supplementation with both 0.5 to 5 mg folic acid and about 0.5 mg vitamin B12 would be expected to reduce homocysteine levels by one quarter to one third (from about 12 micromol/L to about 8 to 9 micromol/L). Large-scale randomized trials of such regimens are now required to determine whether lowering homocysteine levels by folic acid and vitamin B12, with or without added vitamin B6, reduces the risk of vascular disease.

Adult↗
PubMed2000

The perceived utility of six selected measures of consumer outcomes proposed for routine use in Australian mental health services.

OBJECTIVE: This paper aims to assess the utility of six measures of consumer outcomes: the Behaviour and Symptom Identification Scale, the Mental Health Inventory (MHI), the Medical Outcomes Study 36-Item Short-Form Survey, the Health of the Nation Outcome Scales, the Life Skills Profile (LSP) and the Role Functioning Scale previously recommended for the routine assessment in Australian mental health services. METHOD: Consumers and service providers were invited through focus group discussions and surveys to describe the perceived utility of these selected measures. RESULTS: All six measures were rated favourably. The qualitative and quantitative findings suggest that the MHI elicited the most positive results of the consumer measures. No observer-rated scale was clearly preferred. CONCLUSION: The qualitative feedback obtained indicated that process and context issues may be as important to the successful use of routine instruments for the measurement of consumer outcomes in clinical practice as the choice of instrument.

Adult↗
PubMed2000

Interleukin-1 levels in the supernatant of conditioned media of embryos grown in autologous endometrial coculture: correlation with outcome after in vitro fertilization.

PROBLEM: To determine if interleukin (IL)-1 produced by autologous endometrial coculture (AECC) was associated with outcome in patients with a history of multiple in vitro fertilization (IVF) failures. METHOD OF STUDY: The conditioned media (CM) from AECC cells exposed or non-exposed to human embryos was analyzed for IL-1. RESULTS: Embryos grown on AECC demonstrated a significant improvement in number of blastomeres and fragmentation (frag) when compared to embryos grown in conventional media without ECC (6.4 +/- 1.3 vs. 5.5 +/- 1.2 blastomeres and 14.6 +/- 9.3%, vs. 18.4 +/- 9.8% frag; P< 0.008 and 0.003, respectively). When IL-1alpha and IL-1beta were undetectable in the CM, the embryos grown in ECC were of improved quality as compared to the embryos grown only in conventional media. Conversely, IL-1ra levels in the CM were positively associated with embryo quality. Exposure or non-exposure to an embryo did not result in differing levels of IL-1alpha, IL-1beta, or IL-1ra in the CM. IL-1beta levels were negatively associated with clinical pregnancy outcome (3.3 pg/mL (pregnant, n = 12) vs. 27.1 pg/mL (not pregnant, n = 17); P = 0.008, Mann Whitney U-test). IL-1alpha and IL-1ra levels were not associated with outcome. CONCLUSIONS: We have demonstrated a significant improvement in blastomere number and frag with ECC. The presence of IL-1beta in the CM was negatively associated with embryonic development and clinical pregnancy. The presence of IL-1alpha in the CM was negatively associated with embryonic development and the presence of IL-1ra in the CM was positively associated with embryonic development. Whether IL-1beta itself interferes with successful outcome after embryo transfer or if it is a marker for undetected endometritis in the biopsy specimens remains to be determined.

Adult↗
PubMed2000

Re-survey of the Whitehall study of London civil servants: changes in risk factors for cardiovascular disease during 29 years of follow-up.

BACKGROUND: Substantial uncertainty persists about the relevance of blood pressure and cholesterol to the risk of cardiovascular disease in the elderly. OBJECTIVE: To investigate the determinants of cardiovascular risk in old age, and the relevance of such risk factors when recorded in middle and old age. METHODS: A re-survey in 1997 of 8537 survivors of a cohort of men who were originally examined in 1967-1970 when aged 40-69 years. RESULTS: Completed questionnaires were received from 7050 (82%) of the survivors, and blood pressure and blood samples from 5427 (64%). The response rate declined with increasing age, was inversely related to markers of socioeconomic status in 1967-70 and in 1997, and was lower in those who had been current smokers or had a higher blood pressure level in 1967-70. After excluding those with reported cardiovascular disease (25% of respondents), the mean levels of total cholesterol and apolipoprotein B were lower in older age groups, whereas apolipoprotein A1 levels did not vary much with age. Among those with risk factors recorded both in 1967-70 and 1997, the prevalence of smoking had declined by two-thirds (32% in 1970 and 12% in 1997), the prevalence of diabetes had increased (0.3% versus 4.5%), and the mean systolic blood pressure had increased by 16 mmHg (130 versus 146 mmHg), but the diastolic blood pressure had not changed materially (80 versus 81 mmHg), and the measured levels of total cholesterol had increased by 0.5 mmol/l (although that change may be artefactual). CONCLUSION: Follow-up of vital status in this cohort should permit an assessment of the relevance of risk factors recorded in middle and old age to cardiovascular disease in old age.

Adult↗
PubMed2000

Effect of cisapride on the QT interval in infants with gastroesophageal reflux.

OBJECTIVE: We prospectively studied the effect of cisapride per se on QT interval in young infants (3-6 months) with gastroesophageal reflux (GER) in a controlled setting. STUDY DESIGN: The infants diagnosed with GER and deemed to require therapy with cisapride were divided into 2 groups. Group A comprised infants with GER who underwent an electrocardiogram (ECG) before initiation of therapy with cisapride in the dose of 1 mg per kg per 24 hours, divided into 3 doses. They were reweighed after 7 to 10 days, and the dose was adjusted for their new weight. A repeat ECG was performed after approximately 2 weeks (12-18 days) of therapy. The QT interval was measured in each ECG and then the corrected QT interval was calculated by Bazett's formula. Group B comprised infants with GER who had already been on therapy with cisapride for over 1 month. All infants in group B received cisapride in an approximate dose of 1 mg per kg per 24 hours (.8-1.1 mg/kg/24 hours) given in 3 divided doses. They underwent only 1 ECG, ie, at 1 to 4 months after initiation of therapy. The measurement of the actual dose of cisapride was demonstrated to every parent and a marked measuring syringe was provided. The following categories of infants were not included: those with any underlying cardiopulmonary, renal, or hepatic problem; those with a history of apnea; those using a macrolide antibiotic or azole antifungal at any stage during the study; and infants hospitalized for any reason during the course of the study. RESULTS: Cisapride therapy in the dose of 1 mg/kg/day frequently resulted in a slight increase in the QT interval (pretreatment: 390 +/- 18 milliseconds; posttreatment: 400 +/- 20 milliseconds) but the increase was still below the accepted upper limit of 440 milliseconds and not statistically significant. Even with prolonged therapy, the pattern of change in QT interval was similar to that with therapy for 2 weeks. Overall, 2 of 100 (2%) infants developed a prolongation of corrected QT interval beyond the normal range (456 and 486 milliseconds). Neither infant had evidence of any arrhythmia or conduction defect on ECG. No additional factor could be identified in either infant to explain prolongation of the QT interval. CONCLUSION: Our experience suggests that cautious cisapride therapy in young infants in a modest dose does not result in arrhythmias or conduction defects. We recommend that: 1) the dose of cisapride in infants be <1.2 mg/kg/day and preferably between.8 and 1 mg/kg/day; 2) the right measure of the dose be actually demonstrated to the parents; and 3) parents be provided a list of drug interactions with cisapride. One should think twice before denying the use of an effective drug simply because of the need for closer monitoring and extra time spent for parent education.

Cisapride↗
PubMed2000

Maternal exposure to tamoxifen during pregnancy increases carcinogen-induced mammary tumorigenesis among female rat offspring.

Tamoxifen is under investigation as a potential chemopreventive agent in women of child-bearing age who are at an increased risk to develop breast cancer. However, because tamoxifen may act as an estrogen in the fetus and high fetal estrogenic activity, in turn, may increase subsequent breast cancer risk, we wanted to determine the effects of a maternal exposure to tamoxifen during pregnancy on offspring's susceptibility to mammary tumorigenesis. Pregnant rats were injected s.c. with 20 microg of tamoxifen or oil vehicle daily during days 15 and 20 of gestation. In utero exposure to tamoxifen caused abnormalities in the development and function of the reproductive track, including a delayed puberty onset and changes in uterine wet weights. The tamoxifen-exposed offspring, treated with 7,12-dimethylbenz[a]antracene (DMBA) at the age of 45 days, developed an increased incidence of mammary tumors. In week 18 after DMBA administration, 50% of the vehicle-controls had developed mammary tumors, whereas tumor incidence in the tamoxifen group was 95%. In addition, a significantly higher number of tumors in the tamoxifen-exposed group kept growing (rather than stopped growing or regressed) than in the control group. Furthermore, histopathological examination revealed that the mammary tumors in the tamoxifen offspring were less differentiated and exhibited a more aggressive phenotype, compared with the tumors growing in the controls. These results suggest that a maternal exposure to tamoxifen during pregnancy acts as an estrogen in the fetal mammary gland and increases the susceptibility to breast cancer among female offspring.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2000

Evaluation of novel assays in clinical chemistry: quantification of plasma total homocysteine.

BACKGROUND: There is a need for systematic evaluation of methods before their release to the market. We addressed this problem in novel homocysteine assays as part of an European Demonstration Project involving six centers in four countries. METHODS: Two immunological methods for measurement of plasma total homocysteine (P-tHcy), the fluorescence polarization immunoassay (FPIA) and the enzyme immunoassay (EIA), were compared with two comparison methods, HPLC and gas chromatography-mass spectrometry (GC-MS). All laboratories performed the following procedures: (a) familiarization; (b) determination of linearity and precision by analyzing five plasma samples with interrelated concentrations for 20 days; (c) correlation using patients' samples; and (d) assessment of long-term performance. RESULTS: Both immunological methods were linear for P-tHcy between 5 and 45 micromol/L. The intralaboratory imprecision (CV) was <5% for FPIA and <9% for EIA used with a sample processor. The bias was -2% to 3% for FPIA and 2-4% for EIA used with a sample processor. CONCLUSIONS: The immunological methods provide results with little bias compared with HPLC and GC-MS. The imprecision of the assays must be considered in the context of their intended use(s).

Fluorescence Polarization Immunoassay↗
PubMed1999

Underestimation of risk associations due to regression dilution in long-term follow-up of prospective studies.

In prospective studies, disease rates during follow-up are typically analyzed with respect to the values of factors measured during an initial baseline survey. However, because of "regression dilution," this generally tends to underestimate the real associations of disease rates with the "usual" levels of such risk factors during some particular exposure period. The "regression dilution ratio" describes the ratio of the steepness of the uncorrected association to that of the real association. To assess the relevance of the usual value of a risk factor during particular exposure periods (e.g., first, second, and third decades) to disease risks, regression dilution ratios can be derived by relating baseline measurements of the risk factor to replicate measurements from a reasonably representative sample of study participants after an interval equivalent to about the midpoint of each exposure period (e.g., at 5, 15, and 25 years, respectively). This report illustrates the impact of this time interval on the magnitude of the regression dilution ratios for blood pressure and blood cholesterol. The analyses were based on biennial remeasurements over 30 years for participants in the Framingham Study (Framingham, Massachusetts) and a 26-year resurvey for a sample of men in the Whitehall Study (London, England). They show that uncorrected associations of disease risk with baseline measurements underestimate the strength of the real associations with usual levels of these risk factors during the first decade of exposure by about one-third, the second decade by about one-half, and the third decade by about two-thirds. Hence, to correct appropriately for regression dilution, replicate measurements of such risk factors may be required at varying intervals after baseline for at least a sample of participants.

Adult↗
PubMed1999

Use of hierarchical models for meta-analysis: experience in the metabolic ward studies of diet and blood cholesterol.

Overviews that combine single effect estimates from published studies generally use a summary statistic approach where the effect of interest is first estimated within each study and then averaged across studies in an appropriately weighted manner. Combining multiple regression coefficients from publications is more problematic, particularly when there are differences in study design and inconsistent reporting of effect sizes and standard errors. This paper describes the use of a hierarchical model in such circumstances. Its use is illustrated in a meta-analysis of the metabolic ward studies that have investigated the effect of changes in intake of various dietary lipids on blood cholesterol. These studies all reported average blood cholesterol for groups of individuals who were studied on one or more diets. Thirty-one studies had randomized cross-over designs, 12 had matched parallel group designs, 12 had non-randomized Latin square designs and 16 had other uncontrolled designs. The hierarchical model allowed the different types of comparison (within-group between-diet, between matched group) that were made in the various studies to each contribute to the overall estimates in an appropriately weighted manner by distinguishing between-study variation, within-study between-matched-group variation and within-group between-diet variation. The hierarchical models do not require consistent specification of effect sizes and standard errors and hence have particular utility in combining results from published studies where the relationships between a dependent variable and two or more predictors have been investigated using heterogeneous methods of analysis.

Cholesterol↗