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Biomedical subjects

M Fox

Publications and source records attributed to M Fox.

At least 163 records · Page 9Linked to original sources
PubMed1987

The in vitro lifespan of MRC-5 cells is shortened by 5-azacytidine-induced demethylation.

The minor base 5-methylcytosine (5mC) in DNA may be important for the regulation of gene expression. Random loss of 5mC may occur during pre-replicative DNA synthesis in mortal cell strains, and thus give rise to biochemical aberrations in aging cells. 5-Azacytidine (5azaC) was used to induce loss of 5mC in DNA of human diploid fibroblasts (MRC-5) in an attempt to accelerate in vitro senescence. The 5mC content of DNA was measured by incorporation of [3H]uridine into dividing cells, hydrolysis of DNA and separation of bases by HPLC. In untreated MRC-5 cells, 5mC was 3.6% of the total cytosine (C+5mC) at population doubling (PD) 20 (28% of lifespan) and fell to 1.6% at PD 67 (97% of lifespan). A single pulse treatment with 5azaC (1 microgram/ml) induced demethylation and shortened the lifespan by 10% (6.8 PDs loss). Pulse-treated cells showed temporary growth inhibition, though they subsequently regained normal growth rate and morphology. However, uniform treatment with 0.1 microgram/ml 5azaC between PD 20 and 23 produced no immediate growth inhibition, but a 22% loss of 5mC and 25% decrement in lifespan (16.6 PDs loss). The present results indicate that 5mC levels fall during normal aging of MRC-5 cells and accelerated 5mC loss shortens the in vitro lifespan of these cells. Hypomethylation may thus be responsible for some aspects of in vitro aging.

5-Methylcytosine↗
PubMed1987

Protection of Chinese hamster cells against the cytotoxic and mutagenic effects of alkylating agents by transfection of the Escherichia coli alkyltransferase gene and a truncated derivative.

The cytotoxic and mutagenic effects of various monofunctional and bifunctional alkylating agents have been assessed in V79 Chinese hamster cells that express either the entire O6-alkylguanine (O6AG) and alkylphosphotriester alkyltransferase (ATase) gene (clone 8 cells) or a truncated form that codes only for O6AG ATase activity (clone SB cells). Protection ratios, as determined by D37 values, were greater for clone 8 cells than for SB cells. Significant protection against the mutagenic effects of N-methyl-N-nitrosourea and ethylmethanesulphonate at the hypoxanthine phosphoribosyltransferase (HPRT) locus was observed in clone 8 and SB cells. Streptozotocin and the haloethyl nitrosoureas, chlorozotocin and bis-chloroethylnitrosourea were less efficient in inducing HPRT-deficient mutants and a smaller degree of protection was afforded by the transfected genes. This is possibly due to the propensity of these compounds to induce multi-locus deletions. Southern analysis of DNA from clone 8 and SB cells indicated the presence of multiple copies of the plasmid integrated into clone 8 cells but few copies in clone SB cells. The copy number did not change but ATase levels fell when cells were grown in the absence of G418.

Alkylating Agents↗
PubMed1987

Cortical and vascular prostaglandin synthesis during renal allograft rejection in the rat.

Alterations in local prostacyclin and thromboxane synthesis could mediate the changes in vascular perfusion and platelet deposition in acutely rejecting renal allografts and prostaglandin E2 (PGE2) has been implicated in the regulation of the immune response. 6-Keto-prostaglandin F1 alpha (6 KetoPGF1 alpha), thromboxane B2 (TxB2) (the stable degradation products of prostacyclin and thromboxane A2 [TxA2], respectively) and PGE2 were measured in incubates of cortical slices taken from rat renal allografts or isografts one to seven days after transplantation. 6 KetoPGF1 alpha and TxB2 synthesis was also measured in incubates of blood vessels supplying and transplanted with the kidney in these animals. During the phase of cellular rejection (3-5 days), TxB2 synthesis was selectively elevated in allografted renal cortex, renal artery, renal vein, and abdominal aorta in comparison with isografted tissues. There was also a small but significant rise in cortical PGE2 synthesis at this time, but vascular and cortical 6 KetoPGF1 alpha production remained unchanged. Renal infarction, occurring 7 days after transplantation, was accompanied by a nonspecific rise in the synthesis of all three prostaglandins by renal cortical slices. Increased tissue TxA2 synthesis may contribute to local thrombosis and decreased graft perfusion during acute rejection, thereby potentiating graft destruction.

6-Ketoprostaglandin F1 alpha↗
PubMed1987

Shedding of oocysts in immunocompetent individuals infected with Cryptosporidium.

In June 1985, we investigated an outbreak of cryptosporidiosis at a day-care center in Florida. Through day-care center-wide stool screening, 33% (28/84) of the children and 22% (4/18) of the staff members submitting stool specimens were found to have cryptosporidiosis. Children 12-35 months of age and their teachers were at highest risk. All but 1 of the Cryptosporidium-positive patients reported diarrhea, which lasted between 1-44 days. Serial stool specimens were obtained from 8 infected individuals (5 children and 3 adults). Duration of oocyst shedding ranged from 8 to more than 50 days and continued in 5 individuals after diarrhea ceased. No relationship was found between duration of oocyst shedding and the age of the patient or duration or severity of diarrhea. Results of the investigation indicate that infected individuals may continue to excrete oocysts and, therefore, may remain infectious for days or weeks after gastrointestinal symptoms disappear.

Adult↗
PubMed1986

Primary tracheoesophageal puncture for voice restoration.

A 93 percent success rate of voice restoration after primary tracheoesophageal puncture was achieved in 15 patients. Patients were usually able to talk within 3 weeks after laryngectomy. Male patients without chronic obstructive lung disease achieved better results. The incidence of complication after this procedure were not significantly different from a group of 111 patients who underwent laryngectomy alone. Finally, early speech acquisition provides a substantial psychologic boost for the patient undergoing total laryngectomy.

Adult↗
PubMed1986

Effect of dietary phosphorus concentration and electrolyte balance on the growth performance of broiler chickens.

The performance of 1680 male and female broiler chickens given diets with either a low (4.7-4.3 g/kg) or high (8.9-8.2 g/kg) content of inorganic phosphorus and four (150, 200, 250 and 300 mEq/kg) electrolyte balances (Na+K-Cl) was measured from 1-d-old to 49 d of age. Diets with the higher concentration of inorganic phosphorus reduced body weight gains in the starter (P less than 0.01) and finisher (P less than 0.05) phases but the efficiency of food utilisation was reduced only in the starter phase (P less than 0.05). The reduction in body weight gain was greater in males than in females. The growth depression caused by the higher concentration of inorganic phosphorus in the finisher diets was partially alleviated by increasing the electrolyte balance to either 250 or 300 mEq/kg diet. The higher concentration of inorganic phosphorus significantly reduced the dressing percentage and increased the abdominal fat pad weight and litter moisture content. Electrolyte balance had no significant effects on efficiency of food utilisation, abdominal fat pad weights or litter moisture content. Neither the dietary concentration of phosphorus nor the electrolyte balance had a significant effect on mortality or ash content of the tibia.

Animal Nutritional Physiological Phenomena↗
PubMed1986

Molecular analysis of X-ray-induced mutants at the HPRT locus in V79 Chinese hamster cells.

Spontaneous and X-ray-induced mutants at the hypoxanthine phosphoribosyl transferase (HPRT) locus have been isolated from V79 Chinese hamster cells and characterized at the biochemical and cytogenetic levels. Fourteen spontaneous and 24 X-ray-induced clones were azaguanine and thioguanine resistant, did not grow in HAT medium (AZRTGRHATS) and failed to incorporate significant levels of [14C]hypoxyanthine. Cytogenetic analysis of two spontaneous and eight X-ray-induced mutants revealed no major X chromosome rearrangements. In two induced mutants, one of which was hypotetraploid (mode 35-39) with 2 X chromosomes, the short arm of the chromosome (Xp) was slightly shorter than normal. A third mutant was hyperdiploid (mode 22-23) compared with the parental clone (mode 21). When compared with wild-type clones, no other cytogenetic changes were evident in the remaining mutants. Analysis at the DNA level using a Chinese hamster HPRT cDNA probe showed major deletion of HPRT sequences in two and partial deletion in another two induced mutants. In two of the mutants with deletions of HPRT sequences there was a visible shortening of the Xp arm. In the other six mutants two spontaneous and four induced) no karyotypic changes or alterations in restriction fragment patterns were detected suggesting that they carry small deletions or point mutations at the HPRT locus.

Animals↗
PubMed1986

A comparison of cell survival, mutation and persistence of putative promutagenic lesions in Chinese hamster cells exposed to BNU or MNU.

The ability of N-n-butyl-N-nitrosourea (BNU) and N-methyl-N-nitrosourea (MNU) to induce cytotoxicity and mutation has been compared in the Chinese hamster cell lines V79A-2 and V79/79. The kinetics of cytotoxicity is resolvable into two phases, a rapid phase occurring within 1 h at pH 7.4 and 37 degrees C that is probably due to alkylation and a phase of progressive cytotoxicity involving long-lived species. The latter component is larger with BNU than with MNU. Using short-term exposure in which alkylation toxicity predominates, mutations were observed at two loci. Thioguanine-resistant mutants were induced at similar frequencies in V79A-2 and V79/79 but more ouabain-resistant mutants were induced in V79A-2 than in V79/79. Fewer mutants were induced at each locus per surviving cell by BNU compared with MNU. The major potentially miscoding adduct, O6-alkylguanine, was measured by radioimmunoassay and its persistence determined. The methyl adduct persists in V79A-2 but is removed with a half time of approximately 7 h in V79/79. In contrast, the butyl adduct was removed from both V79A-2 and V79/79 with half times of 28 and 19 h, respectively. No O6-alkylguanine DNA alkyltransferase (AT) activity could be detected in extracts of either cell line. Thus Chinese hamster cells appear to repair O6-alkylguanine by a mechanism(s) other than by AT.

Alkylation↗
PubMed1986

Renal neoplasia and acquired cystic kidney disease in patients receiving long-term dialysis.

Acquired cystic disease (ACD) is a recently described phenomenon occurring in the native kidneys of patients treated with long-term dialysis. Renal cell carcinoma is being diagnosed with increasing frequency in patients with chronic renal failure. In most, but not all, instances the cancers develop in association with ACD. Careful microscopic examination of end-stage kidneys undergoing dialysis discloses cysts lined with hyperplastic cells. Papillary hyperplasia of cyst epithelium is recorded in virtually every detailed pathology report of tumors arising in ACD and is the likely pathogenetic basis for the development of renal tumors in cystic kidneys undergoing dialysis. The pathology of ACD and its related neoplasms is reviewed. An estimate is made of the incidence of ACD and renal cell carcinoma in patients receiving dialysis by tabulating data from studies published in medical journals. Acquired cystic disease is found in approximately 35% of patients treated by long-term hemodialysis. Renal cell carcinoma occurs in approximately 5.8% of cases of ACD. Most of the cancers are found incidentally at autopsy or by examination of kidneys from bilateral nephrectomies and are of little clinical significance, but occasional cases present aggressive neoplasms that metastasize and cause the deaths of patients.

Age Factors↗
PubMed1985

The effects of pyrimidine nucleotides on alkylating agent induced cytotoxicity and spontaneous and induced mutation to purine analog resistance in V79 cells.

Exposure of three V79 cell lines to dT after treatment with monofunctional alkylating agents resulted in potentiation of alkylation induced cytotoxicity. The degree of potentiation achieved was dependent on the concentration and duration of exposure to dT and was reversed by equimolar concentrations of dCyd. Exposure to dT after UV or X-irradiation or treatment with HN2 or MMC did not affect the cytotoxic response. dT exposure at non-cytotoxic concentrations did not affect DNA synthesis as measured by [3H]-dT incorporation when allowance was made for reductions in specific activity of labelled thymidine. However, dT post treatment reversed the alkylation induced inhibition of DNA synthesis. Toxic concentrations of dT caused an increase in frequency of TGR colonies but this increase was shown to be due to effects of dT on cell growth rate, and differential sensitivity ot HGPRT- and HGPRT+ cells. The frequency of spontaneous and alkylation induced AZR and to a lesser extent TGR colonies was also increased by non-toxic dT concentrations. Evidence was obtained which suggests that this increase is more likely to be due to alterations in the selective efficiency of the purine analogs than alterations in coding fidelity due to altered dNTP pools.

Alkylating Agents↗