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Biomedical subjects

M McLean

Publications and source records attributed to M McLean.

At least 73 records · Page 4Linked to original sources
PubMed1995

DH element reading frame selection is influenced by an Ig heavy chain transgene, but not by bcl-2.

Mouse B cell precursors containing Ig DHJH junctions in one particular reading frame are selectively lost during B cell development. In this register, arbitrarily referred to as reading frame 2, DHJH junctions give rise to an open reading frame starting upstream of the DH element and including the DHJH-peptide fused to the constant region of IgM. Expression of this protein, called D mu, has been strongly implicated in the loss of B cell precursors containing reading frame 2 DHJH junctions. In an attempt to elucidate the means of D mu counterselection, we have examined the reading frame distribution of DHJH junctions in peripheral B cells from mice transgenic for either the human bcl-2 oncogene or for a functionally rearranged Ig mu heavy chain. In bcl-2 transgenic mice, reading frame 2 accounted for < 5% of the DHJH junctions in peripheral B cells, a value not significantly different from controls. Reading frames 1 and 3 were equally represented among the remaining junctions. By contrast, the reading frame distribution of endogenous DHJH junctions in splenic B cells from Ig mu heavy chain transgenic mice showed no evidence of bias against D mu encoding DHJH junctions. Reading frames 2 and 3 accounted for 27% and 30% of the sequenced DHJH junctions, respectively, and the remaining 43% were reading frame 1. Thus although the presence of BCL-2 cannot prevent the selective loss of reading frame 2 DHJH B cells, a functional mu heavy chain can. These results suggest that D mu-expressing B cell precursors may be selectively lost because of the premature and inappropriate cessation of heavy chain gene rearrangement rather than because of the induction of an apoptotic process which can be blocked by BCL-2.

Animals↗
PubMed1995

The gene for neuronal apoptosis inhibitory protein is partially deleted in individuals with spinal muscular atrophy.

The spinal muscular atrophies (SMAs), characterized by spinal cord motor neuron depletion, are among the most common autosomal recessive disorders. One model of SMA pathogenesis invokes an inappropriate persistence of normally occurring motor neuron apoptosis. Consistent with this hypothesis, the novel gene for neuronal apoptosis inhibitory protein (NAIP) has been mapped to the SMA region of chromosome 5q13.1 and is homologous with baculoviral apoptosis inhibitor proteins. The two first coding exons of this gene are deleted in approximately 67% of type I SMA chromosomes compared with 2% of non-SMA chromosomes. Furthermore, RT-PCR analysis reveals internally deleted and mutated forms of the NAIP transcript in type I SMA individuals and not in unaffected individuals. These findings suggest that mutations in the NAIP locus may lead to a failure of a normally occurring inhibition of motor neuron apoptosis resulting in or contributing to the SMA phenotype.

Amino Acid Sequence↗
PubMed1995

B1 and B2 cells differ in their potential to switch immunoglobulin isotype.

The ability of purified B1a (Ly-1 B) and B2 cells to switch immunoglobulin isotype was assessed by limiting dilution analysis in two in vitro culture systems. When stimulated in the presence of interleukins-4 and -5 by either lipopolysaccharide or CD40 ligand, the frequency of IgG1 precursors in the B1a population was at most one third that of IgM precursors. In B2 cells, however, the frequency of IgG1 precursors was up to seven times that of IgM precursors. B1a cells were shown to respond to interleukin-4 by virtue of up-regulating major histocompatibility complex class II expression when exposed to the cytokine, precluding non-responsiveness as a reason for not switching to IgG1. Indeed, interleukin-4 was found to specifically induce transcription of the germ-line IgG1 constant region locus in B1a cells as it did in B2 cells. Collectively these results suggest that the ability of B1 cells to respond to isotype switch commitment factors such as interleukin-4 may be secondary to the production of IgM by these cells.

Animals↗
PubMed1995

Electron transfer from cytochrome b5 to cytochrome c.

The reaction of cytochrome b5 with cytochrome c has become a very prominent system for investigating fundamental questions regarding interprotein electron transfer. One of the first computer modeling studies of electron transfer and protein/protein interaction was reported using this system. Subsequently, numerous studies focused on the experimental determination of the features which control protein/protein interactions. Kinetic measurements of the intracomplex electron transfer reaction have only appeared in the last 10 years. The current review will provide a summary of the kinetic measurements and a critical assessment of the interpretation of these experiments.

Amino Acid Sequence↗
PubMed1995

Cellular interactions and metabolism of aflatoxin: an update.

The aflatoxins are a group of closely related mycotoxins that are widely distributed in nature. The most important of the group is aflatoxin B1 (AFB1), which has a range of biological activities, including acute toxicity, teratogenicity, mutagenicity and carcinogenicity. In order for AFB1 to exert its effects, it must be converted to its reactive epoxide by the action of the mixed function mono-oxygenase enzyme systems (cytochrome P450-dependent) in the tissues (in particular, the liver) of the affected animal. This epoxide is highly reactive and can form derivatives with several cellular macromolecules, including DNA, RNA and protein. Cytochrome P450 enzymes may additionally catalyse the hydroxylation (to AFQ1 and AFM1) and demethylation (to AFP1) of the parent AFB1 molecule, resulting in products less toxic than AFB1. Conjugation of AFB1 to glutathione (mediated by glutathione S-transferase) and its subsequent excretion is regarded as an important detoxification pathway in animals. Resistance to AFB1 toxicity has been interpreted in terms of levels and activities of these detoxifying pathways. This article reviews the multiple reactions and effects attributed to aflatoxin, with particular reference to the interaction of aflatoxin with nucleic acids and proteins, and the contribution this mycotoxin has in disease development and in the promotion of hepatocellular carcinoma (HCC). The anti-mutagenic properties of several dietary factors are also considered in this article. Undoubtedly, the most important aspect of aflatoxin action is its putative role in the development of human cancer, in particular, HCC. Recently, there has been a renewed interest in this aspect and experimental evidence is rapidly accumulating at the molecular level, indicating aflatoxin as an important consideration in the aetiology of human HCC.

Abnormalities, Drug-Induced↗
PubMed1995

A placental clock controlling the length of human pregnancy.

We report the existence of a 'placental clock', which is active from an early stage in human pregnancy and determines the length of gestation and the timing of parturition and delivery. Using a prospective, longitudinal cohort study of 485 pregnant women we have demonstrated that placental secretion of corticotropin-releasing hormone (CRH) is a marker of this process and that measurement of the maternal plasma CRH concentration as early as 16-20 weeks of gestation identifies groups of women who are destined to experience normal term, preterm or post-term delivery. Further, we report that the exponential rise in maternal plasma CRH concentrations with advancing pregnancy is associated with a concomitant fall in concentrations of the specific CRH binding protein in late pregnancy, leading to a rapid increase in circulating levels of bioavailable CRH at a time that coincides with the onset of parturition, suggesting that CRH may act directly as a trigger for parturition in humans.

Biological Clocks↗
PubMed1995

Organization of the Saccharomyces cerevisiae actin gene UAS: functional significance of reiterated REB1 binding sites and AT-rich elements.

The upstream activation sequence (UAS) in the Saccharomyces cerevisiae actin gene promoter contains three different motifs, specifically two AT-rich tracts, two binding sites for the yeast protein REB1, and an Mlul site. Synthetic UAS elements containing individual motifs, or combinations of them, were inserted in place of the natural UAS, and assayed using a lacZ reporter gene. The REB1 binding sites were found to be essential for, and sufficient to restore partial, UAS activity. AT-rich tracts alone were inactive. Multimerization of a REB1 binding site created a UAS that in galactose is more active, but in glucose less active, than a UAS having a single REB1 site with one AT-rich tract. In general, transcription during growth in galactose or glycerol/lactate responds more to multimerization of motifs. The results suggest that the natural actin promoter UAS retains activity on these alternative carbon sources because of reiteration of sequence elements within it; the additional elements appear to be redundant when cells are grown on glucose. The Mlul site, which is present upstream of a number of yeast genes involved in DNA synthesis and confers cell cycle periodicity to those genes, contributes to the activity of the synthetic UAS elements, but not in a cell-cycle-dependent manner.

Actins↗
PubMed1995

Genomic rearrangements in childhood spinal muscular atrophy: linkage disequilibrium with a null allele.

Autosomal recessive childhood onset spinal muscular atrophy has been mapped to chromosome 5q13. We report the analysis of a polymorphic microsatellite which shows linkage disequilibrium with the disease. The linkage disequilibrium is observed with a null allele which is seen as the non-inheritance of alleles from one or both parents. The inheritance of a null allele was observed in 26 out of 36 (72%) informative childhood onset spinal muscular atrophy (SMA) families tested, of all types of severity and from a variety of ethnic backgrounds. In seven families segregating for the severe Werdnig-Hoffmann or SMA type I, no alleles were inherited from either parent using this microsatellite. This null allele may represent a deletion which is either closely associated with, or causes, the disease.

Alleles↗
PubMed1994

A multicopy dinucleotide marker that maps close to the spinal muscular atrophy gene.

Spinal muscular atrophy (SMA) is a common autosomal recessive disorder resulting in loss of motor neurons. The interval containing the SMA gene has been defined by linkage analysis as 5qcen-D5S435-SMA-D5S557-5qter. We have isolated a new dinucleotide repeat marker, CATT1, that lies between these two closest markers. The marker CATT1 has 16 alleles and is highly polymorphic. The marker can have 1 to 4 (or more) copies per chromosome, giving rise to individuals with up to 8 (or more) alleles. All of the subloci map between the markers D5S557 and D5S435 and lie in close proximity to one another. The marker CATT1 is linked to the SMA gene with a lod score of Zmax = 34.42 at theta = 0 and crosses all available recombinants. Certain alleles occurred more frequently in either the SMA or normal populations, indicating significant allelic association between CATT1 and the SMA locus. Haplotype analysis combining U.S. and Canadian SMA families reveals that one haplotype group (VII) occurs significantly more frequently in the SMA population than in the normal. This confirms the allelic association of CATT1 with the SMA locus.

Alleles↗
PubMed1994

The variation of small bowel volume within the pelvis before and during adjuvant radiation for rectal cancer.

Prior to adjuvant postoperative radiation therapy for carcinoma of the rectum, 21 consecutive patients had small bowel barium studies to determine whether there was an optimal interval between ingestion of barium sulphate and imaging, and whether the volume of small bowel within the posterior pelvis was constant throughout the course of treatment. It was found that the optimum interval prior to imaging after ingestion of barium was 1.5-2 h. For seven patients there was no, or minimal, small bowel visualised within the posterior pelvis at any time. For six patients there was an apparently fixed loop of bowel within the posterior pelvis at simulation, both before and during treatment. For a further eight, the small bowel was mobile and the volume of bowel within the posterior pelvis was reduced by bladder distension. Seven of these eight patients had repeat studies during the course of treatment and in five the difference between the appearance of the small bowel with the bladder full and empty was lost. It is concluded that the displacement of small bowel from the posterior pelvis by bladder distension may not be reliably maintained throughout a course of pelvic radiation.

Barium Sulfate↗
PubMed1994

Incidence of Guillain-Barré syndrome in Ontario and Quebec, 1983-1989, using hospital service databases.

To determine the incidence of Guillain-Barré syndrome (GBS) in the Canadian provinces of Ontario and Quebec during 1983-1989 and to demonstrate the feasibility of measuring the incidence of GBS through internal record linkage of Canadian hospital service data, we conducted a record linkage study. This study used the databases of the Hospital Medical Records Institute and the Ministère de la santé et des services sociaux du Québec. We extracted records containing the International Classification of Diseases, 9th revision, code for GBS or a diagnosis likely to harbor misclassified GBS cases from each database and linked them internally using computerized algorithms. We identified a total of 1,302 and 1,031 incident cases of GBS admitted to Ontario and Quebec hospitals, respectively. The calculated mean annual GBS incidence rate in each province, after age and sex standardization to the 1986 Canadian census population, was 2.02 per 100,000 person-years in Ontario and 2.30 per 100,000 person-years in Quebec. Chart reviews revealed that the false-positive diagnosis rate might be as high as 0.26 per 100,000 person-years in Ontario and 0.21 per 100,000 person-years in Quebec. With adjustment for these false-positive rates, the incidence rate of GBS becomes 1.51 per 100,000 person-years and 1.78 per 100,000 person-years in Ontario and Quebec, respectively. In both provinces, the incidence rate was higher in older age strata (70-80 years) and in males. We saw no seasonal or geographic pattern.

Adolescent↗
PubMed1994

Corticotrophin-releasing hormone and beta-endorphin in labour.

The objectives of this study were to determine whether the maternal plasma corticotrophin-releasing hormone (CRH) concentration influences the amount of uterine contractility induced by infused oxytocin during induction of labour, and secondly to assess changes in CRH and beta-endorphin in response to stress during labour. Serial plasma CRH and beta-endorphin measurements were made in 40 women undergoing induction of labour and correlated with uterine contractility, cervical dilatation, length of labour, analgesic usage and fetal distress. The plasma CRH concentration did not change throughout labour. In subjects receiving infused oxytocin there was a significant positive correlation between plasma CRH and the amount of uterine activity, and a high plasma CRH level was associated with shorter labour. The plasma beta-endorphin level rose with progressive cervical dilatation and fell after epidural anaesthesia. The plasma CRH level did not correlate with the plasma beta-endorphin level or rise with fetal distress. We conclude that high levels of maternal plasma CRH are associated with an increase in the uterine contractile response to infused oxytocin. The maternal plasma CRH level does not vary in response to maternal or fetal stress, but beta-endorphin secretion does rise in response to the stress of labour and is influenced by pain perception.

Adult↗
PubMed1993

Development of an isotope-selective high-performance liquid chromatography detector using chemical-reaction-interface mass spectrometry: application to deuterated cortisol metabolites in urine.

An isotope-selective detector for HPLC based on the particle-beam-interface and the chemical-reaction-interface mass spectrometer (CRIMS) principle is described. This paper focuses on the selective detection of deuterium-labeled analytes. The CRIMS product HD is detected as has been previously described for GC-CRIMS. The analytical performance was not affected by analyte structure or solvent composition. Deuterium detection was linear from 20 ng to 490 ng using 2H3-labeled cortisol. Based on this method, the fractional abundance of three labeled metabolites of cortisol were determined in the urine of a patient infused with tracer amounts of deuterated cortisol.

Chromatography, High Pressure Liquid↗
PubMed1993

Intracomplex electron transfer between ruthenium-65-cytochrome b5 and position-82 variants of yeast iso-1-cytochrome c.

We tested the idea that the aromatic ring on the invariant residue Phe-82 in cytochrome c acts as an electron-transfer bridge between cytochrome c and cytochrome b5. Ru-65-cyt b5 was prepared by labeling the single sulfhydryl group on T65C cytochrome b5 with [4-(bromomethyl)-4'-methylbipyridine][bis(bipyridine)]ruthenium 2+ as previously described [Willie, A., Stayton, P.S., Sligar, S.G., Durham, B., & Millett, F. (1992) Biochemistry 31, 7237-7242]. Laser excitation of the complex formed between Ru-65-cyt b5 and Saccharomyces cerevisiae iso-1-cytochrome c at low ionic strength results in rapid electron transfer from the excited-state Ru(II*) to the heme group of Ru-65-cyt b5 followed by biphasic electron transfer to the heme group of cytochrome c with rate constants of (1.0 +/- 0.2) x 10(5) s-1 and (2.0 +/- 0.04) x 10(4) s-1. Variants of iso-1-cytochrome c substituted at Phe-82 with Tyr, Gly, Leu, and Ile have fast-phase rate constants of 0.4, 1.9, 2.1, and 2.0 x 10(5) s-1 and slow-phase rate constants of 5.3, 3.5, 2.4, and 2.0 x 10(3) s-1, respectively. Increasing the ionic strength to 50 mM results in single-phase intracomplex electron transfer with rate constants of 3.8, 3.1, 3.0, 5.0, and 4.5 x 10(4) s-1 for the wild-type, Tyr, Gly, Leu, and Ile variants, respectively. These results demonstrate that an aromatic side chain at residue 82 is not needed for rapid electron transfer with cytochrome b5. Furthermore, two conformational forms of the complex are present at low ionic strength with fast and slow electron-transfer rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome c Group↗
PubMed1993

Pilot study of accelerated hyperfractionated thoracic radiation therapy in patients with unresectable stage III non-small cell lung carcinoma.

BACKGROUND: The primary goal of this study was to determine the incidence of severe or greater acute radiation toxicity, and secondarily, response, survival, and local control in patients with unresectable Stage IIIA or B non-small cell lung cancer treated with accelerated hyperfractionated thoracic radiation therapy (AHTRT). METHODS: From September, 1989 through March, 1990, 21 evaluable patients with unresectable Stage IIIA or B non-small cell lung cancer were treated with AHTRT, using 6000 cGy in 40 fractions of 150 cGy twice daily, 6 hours between fractions, with a 2-week break midway through treatment. RESULTS: Two patients (9.5%) had acute Grade 3 radiation esophagitis requiring intravenous hydration, and two patients (9.5%) had acute Grade 3 radiation pneumonitis requiring oxygen and steroids. Only one patient had chronic toxicity, a Grade 3 radiation pneumonitis. Five patients (24%) achieved a complete response, whereas eight (38%) had a partial response or regression. With minimum follow-up of nearly 3 years, 3 patients are alive and 18 are dead. The median survival time and 1-, 2-, and 3-year survival rates were 10.8 months, 48%, 29%, and 14%, respectively. Local control was achieved in 11 of 21 (52%) patients. CONCLUSIONS: This AHTRT regimen can be given with an acceptable incidence of acute radiation toxicity. Response, survival, and local control rates in this unfavorable group of patients are encouraging. A North Central Cancer Treatment Group Phase III study of standard thoracic radiation therapy (6000 cGy in 30 fractions of 200 cGy daily) versus AHTRT (+/- chemotherapy) is now open.

Aged↗