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Biomedical subjects

G M Martin

Publications and source records attributed to G M Martin.

At least 127 records · Page 7Linked to original sources
PubMed1989

Genetic modulation of the senescent phenotype in Homo sapiens.

While it is important to search for unifying mechanisms of aging among a variety of model systems, evolutionary arguments suggest that the pathophysiological details of senescence may be, to some extent, species specific. Moreover, in species that are characterized by extensive genetic heterogeneity, such as our own, one is likely to find kindreds with both "private" and "public" markers of aging. Crude estimates of the number of loci with the potential to modulate aspects of the senescent phenotype of man suggest that thousands of genes could be involved. No single locus appears to modulate all features. Some affect predominantly a single aspect ("unimodal progeroid syndromes"); familial Alzheimer's disease is discussed as a prototype. Linkage studies indicate genetic heterogeneity for autosomal dominant forms of the disease. Some loci affect multiple aspects of the phenotype ("segmental progeroid disorders"); the prototype is Werner's syndrome, an autosomal recessive. Cells from homozygotes behave like mutator strains and undergo accelerated senescence in vitro. Elucidation of the biochemical genetic basis of such abiotrophic disorders may shed light on specific aging processes in man.

Aging↗
PubMed1988

Direct evidence of intercellular sharing of glutathione via metabolic cooperation.

Intracellular glutathione (GSH) content and cell density are known to be two important determinants of cell sensitivity to free radicals and radiation. We have investigated intercellular sharing of GSH via metabolic cooperation (MC) by measuring the GSH content of Chinese hamster V79 cells under conditions that varied MC among cells. GSH was measured by flow cytometry with monochlorobimane, which becomes fluorescent after conjugation to GSH by GSH-S-transferase. High-performance liquid chromatography was used to confirm the accuracy of GSH measurements by flow cytometry. Several lines of evidence indicate sharing of GSH or its precursor gamma-glutamylcysteine via MC. These include a cell density-dependent heterogeneity in GSH content, reconstitution of GSH in GSH-depleted cells by coculture with nondepleted cells (except when the depleted cells were MC deficient), and decreased equilibration of GSH among GSH-depleted cells and nondepleted cells when an inhibitor of MC (phorbol myristate acetate) was present. The equilibration of GSH among GSH-depleted cells and nondepleted cells in coculture was not inhibitable by acivicin, suggesting that this form of intercellular sharing of GSH does not rely on gamma-glutamyltransferase-mediated extracellular transport of GSH.

Animals↗
PubMed1988

A novel class of unstable 6-thioguanine-resistant cells from dog and human kidneys.

Thioguanine-resistant primary clones were grown from single cell suspensions obtained from dog and human kidneys by enzymatic digestion. In medium containing a relatively high concentration (10 micrograms/ml) of thioguanine, thioguanine-resistant primary clones arose from each source at frequencies ranging from 10(-4) to 10(-5). A reduction in total hypoxanthine uptake was found in the thioguanine-resistant primary clones which had developed in thioguanine medium, consistent with a reduction in hypoxanthine phosphoribosyltransferase activity. When these thioguanine-resistant primary clones were subsequently grown in the absence of thioguanine and assayed for the thioguanine-resistant phenotype and hypoxanthine phosphoribosyltransferase activity, it was found that most were now thioguanine-sensitive and yielded cell-free extracts with substantial amounts of hypoxanthine phosphoribosyltransferase activity. In contrast, thioguanine-resistant human clones grown continuously in the presence of thioguanine yielded cell-free extracts with little or no detectable hypoxanthine phosphoribosyltransferase activity. Southern blot analysis demonstrated no structural alterations in the hypoxanthine phosphoribosyltransferase gene in thioguanine-resistant primary human kidney clones. These results suggest that a novel mechanism(s) for thioguanine resistance and the control of hypoxanthine phosphoribosyltransferase expression may occur in dog and human kidney cells.

Animals↗
PubMed1988

Glucocorticoids attenuate taste aversions produced by toxins in rats.

Conditioned taste aversions (CTAs) develop if toxicosis is induced after an animal eats or drinks. Usually, if a second drug is administered after consumption and prior to the toxin, it either adds to the CTA produced by the toxin or else has no noticeable effect. However, glucocorticoids (dexamethasone, cortisol, methylprednisolone, and prednisolone) attenuate CTAs produced by cyclophosphamide. Dexamethasone was tested most extensively and is also effective against CTAs produced by carmustine, cisplatin, copper sulfate, cytarabine, dactinomycin, doxorubicin, lithium chloride, and mechlorethamine. Delta-9 THC, domperidone, haloperidol, metoclopramide, and scopolamine were ineffective against CTAs produced by cyclophosphamide, although they are used medically for palliative purposes. Prochlorperazine attenuated CTAs but to a much smaller extent than the glucocorticoids. These results are interpreted as cross-validation of recent reports that glucocorticoids alleviate clinically observed distress produced by cancer chemotherapies.

Animals↗
PubMed1988

Morphine preexposure attenuates the aversive properties of opiates without preexposure to the aversive properties.

Evidence that action on peripheral opiate receptors is necessary to produce aversive effects with morphine, enabled us to determine whether preexposure to these aversive effects is necessary for the later attenuation of morphine's aversive properties. We found that blockade of the aversive effects of morphine with the peripheral antagonist methylnaltrexone during morphine preexposure had no effect on the later attenuated development of conditioned taste aversions to morphine. Moreover, in the same rat morphine preexposure did not affect the development of a place preference to an environment paired with injections of morphine. The results suggest that an effect of central opiate action is able to attenuate the later peripheral aversive, but not the central rewarding, effects of morphine.

Animals↗
PubMed1988

Constitutional genetic markers of aging.

Constitutional genetic markers of aging can be defined as members of that subset of genes that modulate the times of onset and/or the rates of progression of one or more of the processes of aging, or the response of the target cells, tissues and organisms to a particular process. These genetic factors are classified into: (1) those that control changes in structure and function that may be universally expressed in aging organisms or that are expressed in large taxonomic groups of organisms ("public markers") and (2) those that control changes that are species specific or that reflect polymorphisms or mutations within a species ("private markers"). Both spontaneous and experimentally induced genetic variation can identify and characterize such genetic elements. Recommendations for implementing such a program of research include (1) particularization of the aging phenotype, (2) further development of nonmammalian models amenable to genetic analysis, (3) systematic search for relevant spontaneous mutations in Mus musculus, (4) utilization of recombinant inbred, chimeric, transgenic and interspecific mice and (5) investigations of genetic concomitants of speciation.

Aging↗
PubMed1988

Life table analysis and pathologic observations in male mice of a long-lived hybrid strain (Af X C57BL/6)F1.

We have utilized a long-lived (Af X C57BL/6)F1 hybrid strain of mice for a variety of aging studies. In this report we have characterized the life expectancy and pattern of spontaneous deaths in 202 mice, malignant and nonmalignant lesions in 64 male mice dying spontaneously, and organ weights and lesions in 39 male mice killed at selected ages. The maximum age observed was 41.5 months. The principal causes of death were malignant lymphoma and alveologenic neoplasms, which were present in 56.3% and 45.3%, respectively, of the mice dying spontaneously. A variety of other neoplastic and non-neoplastic lesions that are not infrequently seen in older mice were observed in these mice. Neoplasms seen in these mice that are rare in other mice included disseminated mast cell tumors in two mice and gastric adenocarcinoma in one mouse. In comparing the diseases observed in this hybrid strain with those reported for the parent strains, there was an incidence of malignant lymphoma similar to the C57BL/6 parent, an incidence of alveologenic neoplasms intermediate between the parent strains, and a markedly reduced incidence of amyloidosis. This study provides a detailed background of baseline hematologic and morphologic data in a long-lived hybrid of two commonly used strains of mice.

Actuarial Analysis↗
PubMed1987

Flow cytometry and scrape-loading/dye transfer as a rapid quantitative measure of intercellular communication in vitro.

We describe two flow cytometric assays performed on populations of cells which have been stained with various fluorescent tracer molecules by the scrape-loading technique. One assay uses a simple one-color analysis on a flow cytometer by quantitating the fluorescence intensity of scrape-loaded lucifer yellow CH (LY) in individual cells. The other assay utilizes a two-color analysis on a cell sorter whereby cells which are initially loaded (donors) are identified by their uptake of both rhodamine isothiocyanate-dextran and LY, whereas the recipients of dye transfer are identified as having LY only. Agents which have been shown to inhibit intercellular communication in other assays exhibit similar blocking activity in LY transfer and this is readily quantitated by flow cytometry. The two-color analysis has the added advantage of being able to identify both donors and recipients in a highly quantitative manner.

Cell Communication↗
PubMed1987

Murine "housekeeping" enzyme (genetic locus: Idh-1) is regulated in an allele-specific manner.

The murine "housekeeping" enzyme, cytosolic NADP-isocitrate dehydrogenase (E.C.1.1.1.42) (genetic locus: Idh-1), exhibited a complex pattern of allele-specific expression. Protein electrophoresis on cellulose-acetate gels and determination of relative enzymatic activity by means of densitometry revealed that in heart tissue (but not liver tissue) of certain hybrid crosses the AA-homodimer was underrepresented relative to total enzymatic activity, and the degree of underrepresentation changed during development. In mixtures of homozygous tissue extracts of heart tissue (but not liver tissue) the AA-homodimer was underrepresented relative to the BB-homodimer. Relative activity of allelic isozymes varied as a function of tissue (heart versus liver), age, and the parental source of the Idh-1 alpha allele, but did not vary as a function of sex. Allele-specific expression was also exhibited in kidney tissue of the same animals. In adult male kidney tissue extracts from heterozygotes, the AA-homodimer was underrepresented relative to total enzymatic activity; in adult female kidney tissue extracts from heterozygotes, a more codominant phenotype was observed. Tissue extracts from immature hybrid animals exhibited a phenotype midway between the adult male and adult female phenotypes. Tissue extracts from castrated males exhibited a phenotype equivalent to that seen in females. Relative activity of allelic isozymes in kidney varied as a function of age and sex, but did not vary as a function of the parental source of the Idh-1 alpha allele. While cytosolic NADP-IDH is a "housekeeping" enzyme, expressed in multiple tissues of the mouse, differences in the relative intensities of allelic isozyme bands provide evidence for tissue- and stage-specific regulatory variation.

Alleles↗
PubMed1987

Aphidicolin-resistant mutator strains of mouse teratocarcinoma.

From among a series of stable, aphidicolin-resistant mutant strains of mouse teratocarcinoma, derived from a multipotent parental line (PSA-1-80), three were selected for further study on the basis of their comparatively high degrees of resistance and elevated frequencies of spontaneous forward mutation to 6-thioguanine and ouabain resistance. Fluctuation tests confirmed that they were mutator strains. Since each of the three mutants was isolated after multiple rounds of selection, and since a variety of biochemical abnormalities were observed, it is likely that a number of mechanisms, probably consisting of overlapping subsets, determine the phenotypes. Abnormalities in the metabolism of the nucleotide substrates for polymerization are likely to be of major importance in mutants designated Aph-2 and Aph-3, as there were marked alterations in the dCTP and dATP pool sizes. The specific activity of DNA polymerase alpha was also increased. For the case of Aph-3, which exhibited the greatest (400-fold) increase in resistance to aphidicolin, a mutation in the structural gene for DNA polymerase alpha may be an additional important component, since in vitro assays revealed that the isolated enzyme was resistant to aphidicolin. For the case of Aph-1 however, only minor alterations in dNTP pools were observed, and there was no increase in the specific activity of DNA polymerase alpha or in the aphidicolin resistance of the isolated DNA polymerase alpha, suggesting yet another mechanism(s) underlying the aphidicolin resistance/mutator phenotype. All three mutants formed subcutaneous tumors in syngeneic mice; both Aph-1 and Aph-2 were multipotent; whereas Aph-3 was nullipotent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Association of an apolipoprotein CII allele with familial dementia of the Alzheimer type.

In order to identify the genetic locus responsible for familial dementia of the Alzheimer type (DAT), we are studying 10 families in which DAT appears to be inherited as an autosomal dominant trait. Genotypes for a TaqI restriction fragment length polymorphism (RFLP) at the apolipoprotein CII locus were determined for the following groups: affected and unaffected DAT family members, DAT subjects with no family history of the disease, and normal control subjects. The control group included 103 individuals from our study and 123 from the study of Wallis et al. (Hum. Genet., 68 (1984) 286). The frequency of the TaqI fast (F) allele in the affected familial DAT subjects (0.64 +/- 0.08) differed significantly from that for the control group (0.39 +/- 0.02) (Z = 2.87, P less than 0.005). In contrast, the F-allele frequency for the unaffected family members was 0.31 +/- 0.09, which was similar to that of the combined control group (Z = 0.78, P greater than 0.40). Subsequently, genotypes were determined for two other polymorphisms at the Apo CII locus: a BanI RFLP and a BglI RFLP. For these two polymorphisms, the allele frequencies for the familial DAT subjects differed from the unaffected control groups but the differences were smaller and not statistically significant. These data suggest a previously unrecognized association between the Apo CII TaqI F-allele and familial DAT.

Aged↗
PubMed1987

Interactions of aging and environmental agents: the gerontological perspective.

This article attempts to briefly review the current status of knowledge of biogerontology as a basis for a beginning set of discussions on the potential roles of environmental agents in the modulation of rates of aging in man. The article has tried to summarize "what the toxicologist should know about gerontology," whereas a companion review, by Dr. Jerry Williams, summarizes "what the gerontologist should know about toxicity." The review begins by defining some basic terminology, including introduction of the term "gerontogens" for those putative environmental agents that may in fact modulate the times of onset and/or rates of development of specific aspects of the senescent phenotype. That phenotype is then briefly described from the level of populations to the level of molecules, including an organ systems approach with emphasis on what is observed in humans. Among the important points that emerge from this description are: the variety of phenotypic alterations; the multiplicity of phenotypic alterations in any one aged individual; the special vulnerability in humans of the arterial system; the loss of proliferative homeostasis; the decline in the efficiency of enzyme adaptation; the decline in protein synthesis; the increasing evidence of post-translational modifications of proteins and DNA; the evidence for chromosomal instability (and, therefore, the potential importance of environmental clastogens). Arguments for a genetic basis for differential rates of aging are then developed, and a number of "genotropic" theories of aging are tabulated (i.e., those theories that invoke crucial roles for alterations of the genomes of somatic cells, whether changes in gene expression, gene structure, or both). It is concluded that no single theory is supported by a preponderance of evidence. Because aging appears to involve numerous processes and is highly polygenic in its determination, it is likely that a number of different mechanisms are responsible for the phenotypic alterations and that different individuals exhibit various patterns of aging based upon their specific inheritance and environmental experiences. At this early stage in the development of experimental approaches to the study of environmental-genetic interactions in the genesis of different aspects of senescence, the most vital issue involves the question of suitable model systems. Clearly, a number of different model systems will be required. A selection of these is tabulated based upon their amenability to a reasonable degree of genetic definition and genetic manipulation. Only by controlling the genotype can the environmental influences be properly assessed.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1986

Resistance to paraquat in a mammalian cell line.

Paraquat-resistant variants were isolated in Chinese hamster ovary (CHO) cells by stepwise increases in paraquat concentrations. Three series of selective experiments gave variants which appeared to be using one or several different mechanisms of resistance. In all variants tested (PQ-1, PQ-2, PQ-3, PQ-2X and PQ-3X of series 1), radioactively labeled paraquat was taken up by the cells. These variants exhibited no unusual resistance to either oxygen or radiation, nor were increases found in the activities of free-radical scavenging enzymes. They had extra DNA (3-12%) and an unusual acrocentric marker chromosome which was common to all of the variants but never observed in the parental cells. Double minutes were observed in 29% of metaphases of the PQ-3 variant. One of the resistant lines exhibited evidence of an intrinsic chromosomal instability, a phenotype that could conceivably facilitate gene amplification. Selection series 2 and 3 were designed to further evaluate gene amplification as a mechanism of resistance. These variants exhibited high frequencies (40-100%) of tetraploidy or hypotetraploidy with loss of chromosomes and varying frequencies of double minutes (10-75% of metaphases). In two of the variants the same marker chromosome which was observed in the series 1 variants was seen. Two other lines exhibited a variant of this marker, incorporating it into a metacentric chromosome. It may be that gene amplification facilitates resistance to paraquat and that both stable and unstable methods of amplifying genes are used.

Animals↗
PubMed1986

Differentiation alters the unstable expression of adenine phosphoribosyltransferase in mouse teratocarcinoma cells.

Three multipotent mouse teratocarcinoma stem lines, all exhibiting unstable expression for the purine salvage enzyme adenine phosphoribosyltransferase (APRT) were used for the isolation of differentiated cell lines from neoplasms developed in syngeneic mice. Two of the stem cell lines (DAP1B and DAP1C) exhibited homozygous deficiencies for APRT expression while the third stem cell line (E140) exhibited a heterozygous deficiency (Turker, M.S., Smith, A.C., and Martin, G.M.; Somat. Cell Mol. Genet.; 10:55-69; 1984). A total of 16 morphologically differentiated cell lines were established from these neoplasms; most were no longer tumorigenic. Differentiated cell lines derived from the E140-induced tumors segregated homozygous deficient mutants in a single step, consistent with their retention of the heterozygous deficient state. Differentiated homozygous deficient cell lines gave rise to phenotypic revertants at very high frequencies (10(-1) to 10(-2)). The majority of these putative revertants, however, yielded cell-free extracts with little or no detectable APRT activity. These putative revertants were capable of adenine salvage and were therefore termed APRT pseudorevertants. Since the APRT pseudorevertant phenotype was only observed in the differentiated progeny of the APRT deficient stem cell lines, we conclude that this change in the nature of the revertant phenotype was a consequence of cellular differentiation.

Adenine↗