PubMed Health⌕ Search

Biomedical subjects

M J Ord

Publications and source records attributed to M J Ord.

At least 19 recordsLinked to original sources
PubMed1990

Changes in muntjac fibroblasts associated with the acquisition of cadmium resistance. A pre-resistance, transitional and post-resistance study.

A series of cell lines with different levels of resistance to continuous cadmium exposure has been developed from an immortal but non-transformed muntjac fibroblast cell line. Concentrations accepted in their culture medium range from 0.1 microM for the cadmium sensitive parent line to 5 microM for the intermediate "cadmium-tolerant" line, to 5, 10, 20 and 50 microM for the four "cadmium-resistant" lines. The present paper follows the morphological changes which accompanied the development of resistance through a 20-month pre-resistance period, a relatively abrupt 6-week transitional period and a 3-year post-resistance period, during which time levels of cadmium resistance were increased. Initial changes which led to the cadmium-tolerant CR5 cell line included (i) increased efficiency in autophagocytosing damaged cell components and in ridding the cell of residual waste materials, (ii) a reduction in fluid filled vacuoles and (iii) improved recycling and/or replacement of cadmium-damaged cell membrane. With the advent of cadmium resistance the intracellular damage necessitating these activities disappeared, yet the series of changes which occurred included a massive build-up of Golgi and the appearance of a trans-Golgi tubular network in addition to cytoskeletal and membrane changes. Though metallothionein levels are greater in the cadmium-resistant variants, their increase appears inadequate on their own to account for the high levels of resistance. The post-resistance changes which accompanied each step-up in cadmium resistance included further membrane and glycocalyx changes, in addition to continued increases in Golgi bodies and tubular network. This paper details the morphological changes which occurred throughout the 5-year period, tests the direct dependence of each on the presence of cadmium and examines their possible contribution to a cadmium protective mechanism.

Animals↗
PubMed1989

The mutagenic and carcinogenic properties of three second generation antitumour platinum compounds: a comparison with cisplatin.

The cytotoxicity, mutagenicity and transforming potentials of three second generation platinum compounds have been investigated in mammalian cells. All the compounds showed positive response in two assay systems in Chinese hamster V 79 cells, i.e. measurement of mutation induction at the HGPRT locus and of DNA damage as indicated by sister chromatid exchange frequencies. At equitoxic doses, the compounds in order of decreasing mutagenicities were cisplatin, spiroplatin, carboplatin and iproplatin. The BHK transformation assay reflected a similar order in the potential carcinogenicity of the drugs. Cisplatin was highly carcinogenic, followed by spiroplatin. In comparison, carboplatin and iproplatin were potentially weak carcinogens.

Animals↗
PubMed1988

Cadmium induced changes in cell organelles: an ultrastructural study using cadmium sensitive and resistant muntjac fibroblast cell lines.

A detailed electron microscopy study of cadmium sensitive and resistant muntjac fibroblast cell lines has identified a wide range of intracellular damage following exposure to cadmium. Damaged organelles included cell membrane, mitochondria, Golgi cisternae and tubular network, chromatin, nucleoli, microfilaments and ribosomes. Although cell membrane damage was generally the earliest indication of adverse cadmium action, particularly with continuous cadmium exposures, cells could tolerate extensive membrane loss. Mitochondrial distortion and some damage to Golgi was also tolerated. The turning point at which cadmium became lethal was generally marked by a cascade of events which included damage to both nuclear and cytoplasmic components. These results for fibroblasts are discussed and compared with damage reported in other types of cells.

Animals↗
PubMed1988

Parallel development of cadmium resistance and in vitro transformation in cultured Indian muntjac cells.

The development of cadmium resistance in an Indian muntjac cell line has been investigated. The parent cell line is highly sensitive to cadmium ions. Resistance was obtained by continuous growth of cells in low levels of cadmium with stepwise increments. Four cell lines were developed with resistances of between 50- and 200-fold greater than that of the parental line. Early in the development of resistance an unstable cell line displaying extensive chromosomal rearrangement and an elevated sister chromatid exchange frequency was identified. The more stable resistant lines produced from this original cell line have normal karyotypes. Having passed through the initial period of genome rearrangement the resultant cells acquired several characteristics of morphologically transformed cells. It is concluded that long-term exposure to low levels of cadmium can transform cells in vitro concurrently with their acquiring cadmium resistance.

Animals↗
PubMed1985

The ability of bifunctional and monofunctional pyrrole compounds to induce sister-chromatid exchange (SCE) in human lymphocytes and mutations in Salmonella typhimurium.

The ability to induce sister-chromatid exchange (SCE) in human lymphocytes and mutations in Salmonella typhimurium has been assessed for 4 pyrrole compounds. Three of the compounds, 2,3-bishydroxymethyl-1-methylpyrrole (BHMP), 2-hydroxymethyl-1-methylpyrrole (2HMP) and 3-hydroxymethyl-1-methylpyrrole (3HMP) are synthetic pyrrolic alcohols; the fourth compound, dehydroretronecine (DHR) is a metabolite of several naturally occurring pyrrolizidine alkaloids. The activity of these compounds was compared with that of mitomycin C (MMC) and decarbamoyl mitomycin C (DCMMC), chemicals related structurally to the pyrrole compounds. All 6 compounds caused an increase in the numbers of SCEs. Whereas the bifunctional pyrroles, DHR and BHMP, and the mitomycins, MMC and DCMMC, increased levels of SCEs by 8-12 times control levels, the monofunctional pyrroles gave increases of only 2 times. Three of the 4 pyrrole compounds (DHR, BHMP and 3HMP) induced mutations in the Salmonella typhimurium base substitution strain TA92, the fourth (2HMP) was not found to be mutagenic in any of the 8 strains used. The mitomycins induced mutations in the frameshift strain TA94 in addition to the base substitution strain TA92, with DCMMC always more mutagenic and less cytotoxic than MMC. All bifunctional compounds induced more mutations and were less cytotoxic in strains containing an efficient excision-repair system. With the pyrrole compounds numbers of SCEs and mutations were only increased when using chemical concentrations significantly higher than those required for the mitomycins: more than twice as high to produce significant numbers of SCEs and more than 100 times as high to produce equal numbers of mutations.

Humans↗
PubMed1985

Novobiocin inhibition of DNA excision repair may occur through effects on mitochondrial structure and ATP metabolism, not on repair topoisomerases.

Novobiocin inhibits DNA topoisomerases. It also inhibits excision repair of DNA photodamage, blocking both repair synthesis and the earlier step of incision at u.v. damage sites (as measured by the accumulation of DNA strand breaks in u.v.-irradiated interphase cells treated with DNA synthesis inhibitors such as hydroxyurea or cytosine arabinoside). It has been supposed, therefore, that novobiocin affects repair by blocking a putative topoisomerase step prior to incision. But we find that novobiocin also has a marked dose- and time-dependent effect on mitochondria: in cells exposed to novobiocin, mitochondria swell and their cristae become disrupted, and the intracellular ATP:ADP ratio is lowered, though the membrane potential is maintained as judged by rhodamine 123 fluorescence. Mitotic cells are more resistant to mitochondrial disruption by novobiocin than are interphase cells. This correlates with a relative resistance of u.v.-irradiated mitotic cells to the inhibition of incision by novobiocin. The chromosomal decondensation that results from the accumulation of DNA breaks due to incision when u.v.-irradiated mitotic cells are treated with hydroxyurea and cytosine arabinoside is largely suppressed by novobiocin. Furthermore, the suppression of induced strand break accumulation is partly due to a suppression by novobiocin of the uptake and phosphorylation of cytosine arabinoside; breaks accumulated in u.v.-irradiated cells in the presence of aphidicolin, an inhibitor of DNA polymerase alpha that does not require phosphorylation, are less novobiocin-sensitive. We conclude that the effects of novobiocin on excision repair are more likely to be due to a non-specific effect on ATP metabolism than to a specific effect on a repair-related topoisomerase.

Adenosine Triphosphate↗
PubMed1982

Correlation of mitochondrial form and function in vivo: microinjection of substrate and nucleotides.

Microinjection of adenine nucleotides and substrates into the cytoplasm of Amoeba proteus followed by EM examination has been used in an attempt to relate alterations in mitochondrial morphology with functional changes. Contracted mitochondria with dark matrix and wide cristae (Type I), and expanded mitochondria with light matrix and narrower cristae (Type II) coexist in normal active amoebae, but their numbers can be varied according to different cell activity states. Following injection of ATP, the mitochondria of the amoebae showed a time-dependent movement towards a predominately Type II form, whilst injections of ADP produced predominately the Type I form. Injection of succinate or deionised water, even in large amounts, had little effect on the numbers of Type I and Type II forms. The change induced by ATP was of long duration; that induced by ADP was influenced by both concentration injected and the cell's substrate levels. With 3 mM solutions of ADP the mitochondrial population was primarily of Type I organelles; higher ADP concentrations or the simultaneous injection of succinate, however, resulted in a switch with time to increased proportions of Type II mitochondria. The results extend the findings of previous in vivo and in vitro mitochondrial studies and are discussed in the light of these.

Adenosine Diphosphate↗
PubMed1981

Correlations of DNA damage and repair with nuclear and chromosomal damage in HeLa cells caused by methylnitrosamides.

N-Methyl-N-nitrosourethan induces breaks or alkali-labile sites in cellular DNA, many if not all of which are repaired rapidly. Other DNA lesions are repaired by an excision process. Hydroxyurea and 1-beta-D-arabinofuranosylcytosine cause an accumulation of DNA breaks after N-methyl-N-nitrosourethan treatment, probably by inhibiting the DNA-synthetic (but not the nucleolytic) stage of excision repair. Chromosome damage (fragmentation or attenuation of interphase chromosomes and decondensation and radial rearrangement of metaphase chromosomes) is present soon after treatment with N-methyl-N-nitrosourethan and is not reversed during further incubation. It is apparently associated with the longer-lived DNA lesions, probably those which are removed by excision, and is enhanced by incubation with hydroxyurea and 1-beta-D-arabinofuranosylcytosine. N-Methyl-N-nitrosourethan also inhibits cellular protein and the loss of nucleolar structure. N-Methyl-N-nitrosourea is less potent than N-methyl-N-nitrosourethan in causing DNA or chromosome damage and is less cytotoxic.

Cell Cycle↗
PubMed1979

Morphological alterations in the mitochondria of Amoeba proteus induced by uncoupling agents.

Ultrastructural changes in mitochondrial morphology were observed in amoebae exposed to the uncoupling agents dinitrophernol (DNP), pentachlorophenol (PCP), and m-chlorocarbonyl cyanide phenylhydrazone (CCCP). These alterations occurred with rapidity and were present before whole-cell activity changes could be detected. They included changes in profile shape and overall dimensions, matrix density changes, and alterations to the cristal membranes, so that distinction between control Type I and Type II conformations was eliminated and a form with intermediate characters generated. It is proposed that, in producing these altered forms, the uncoupling agents are acting by suppressing the control functional states of the mitochondria. At the end of the uncoupler treatment all alterations were shown to be reversible, i.e. in cells transferred back to normal culture medium, mitochondrial profiles identical to those in control cells were again evident with time. These effects on the mitochondria could be produced whether the uncoupler was introduced externally by total cell exposure, or to the inside of the cell by microinjection. The importance of precisely defining conditions for treatments and at disrupting cell activity was evident. Thus, an uncoupler, which is a weak acid, proved to be more effective in whole cell treatments if applied at a pH near to it pKa - so ensuring its penetration across the outer cell membrane.

Amoeba↗
PubMed1978

A capillary technique for cloning Amoeba from single cells.

Each amoeba is placed in a drop of approximately 40 microliter of a balanced 'medium + food' solution introduced into the central region of a 7 cm long capillary tube which has first been fused at one end. Such amoebae divide to form clones of 20-30 cells without changing capillaries, though additional food may be required after 7-10 days. Experiments on damage induced by chemicals, cell cycle sensitivities and nuclear/cytoplasmic inheritance, which may involve the cloning of some 2-3,000 or more cells can be carried out with comparative ease. Apart from research, the capillary cloning technique has proved useful in the teaching laboratory. It is adaptable, and can be used for Protozoa other than amoebae, even for requiring sterile conditions.

Amoeba↗
PubMed1976

A study of the change in DNA synthesis of S phase cells treated with N-methyl-N-nitrosourethane: a study using Amoeba proteus as a single cell model.

The present experiments using Amoeba proteus as a single cell model show that DNA synthesis continues during and after exposure of S phase cell to N-methyl-N'-nitrosourethane (MNU). At sublethal dose levels which caused long division delays, division and growth abnormalities and mutations, the amount of [3h] thymidine ([3h]Tdr) incorporated was decreased by 20-30%; at dose levels which killed all S phase cells it was inhibited by up to 90%. There was a direct correlation between the dose of MNU used and the degree of inhibition of [3H]Tdr incorporated. The effect was rapid, mainly taking place within 20 min of treatment. Amoeba heterokaryons (HKs) were used to examine the rate of DNA synthesis of treated and untreated nuclei in the same cytoplasm, i.e. where the nuclei would have the same [h]tdr intake, the same thymidine kinase (TK) activity and the same endogenous precursor pools. Direct comparison of the nuclear DNA synthetic activity in this way revealed less difference between treated and untreated nuclei than comparisons made using the nuclear grain counts from treated and untreated amoebae. This suggested that much of the decrease in [3H]Tdr incorporation by MNU-treated S phase cells was due to a change in the cytoplasm and/or the cell membrane, rather than to nuclear damage. Thus MNU-treated nuclei were able to synthesize DNA at a near normal rate when they could draw on the resources of untreated cytoplasm, while the rate of DNA synthesis of control nuclei decreased when they occupied cytoplasm which had been exposed to high doses of MNU. These studies suggest that nuclear sites of damage were only involved when lethal doses of MNU had been used.

Amoeba↗