Biomedical subjects

M Poot

Publications and source records attributed to M Poot.

77 records · Page 5Linked to original sources

PubMed1984

Glutathione content of cultured human fibroblasts during in vitro ageing.

The glutathione level of cultured human fibroblasts was determined with a micromodification of a spectrophotometric glutathione cycling method. There was a slight increase in reduced glutathione (GSH) content during in vitro ageing of normal human fibroblasts. Fibroblasts from patients with Werner's syndrome or ceroid lipofuscinosis (Spielmeyer-Vogt syndrome) and healthy individuals exhibited similar patterns of GSH levels during in vitro ageing. The GSH content of non-proliferating confluent cultures of normal fibroblasts and of proliferating normal fibroblasts was identical. Moreover, autofluorescent "aged" cells isolated by cell sorting did not differ in GSH content from the non-autofluorescent cells in the same culture. It was concluded that the GSH content does not play a role in in vitro ageing, nor in the accumulation of autofluorescent material in human skin fibroblasts.

Cell Survival↗

PubMed1984

In vitro DNA replication in association with the nuclear matrix of permeable mammalian cells.

DNA replication has been studied in in vitro cultured bovine liver cells permeabilized in 0.02% Triton X-100. The Km for TTP was 20 microM. The initial incorporation rate at 10 microM TTP concentration was about 12% of the in vivo synthesis and declined very strongly within 1 h. A similar decline of the incorporation rate was found at 0.12 microM TTP concentration. DNAase I digestion of DNA-matrix complexes obtained from isolated nuclei in 2 M NaCl revealed that newly replicated DNA was preferentially bound to the nuclear matrix. A similar digestion with S1 nuclease caused a selective release of short duplexes of Okazaki fragments with the complementary parental strand. The results show that in vivo replication continues in permeabilized cells in an almost unchanged way, except for a gradual decline of its rate which is mainly due to inactivation of one or more essential components.

Animals↗

PubMed1980

Nucleic acids and related enzymes. Secretion of four alkaline DNases by plasmodia of Physarum polycephalum.

In plasmodia of Physarum polycephalum, DNase activity with a preference for native DNA was found in a pattern of three or four isoenzymes. During growth a constant specific activity of approx. 0.3 unit of DNase activity per mg protein was found in the plasmodia, with a broad maximum during the G2-phase in the naturally synchronous flat cultures. Under conditions of starvation or sclerotization, DNase activity was secreted by the plasmodia in amounts which were up to ten times higher than the internal level of enzyme activity. Purification of the secreted DNase activity to high purity by three simple chromatographic steps showed that four different DNase isoenzymes existed which were identical with the intracellular ones. The relative abundances of the various isoenzyme forms inside and outside the plasmodia seemed to be slightly different. The possible functions of the DNase activities are discussed.

Cell Cycle↗

PubMed1979

Measurement of DNA-excision repair in suspensions of freshly isolated rat hepatocytes after exposure to some carcinogenic compounds: its possible use in carcinogenicity screening.

When suspensions of freshly isolated rat hepatocytes were exposed to a number of carcinogenic compounds, it was possible to measure an increased UDS by a rapid procedure via liquid-scintillation counting. For a number of carcinogenic compounds and some of their non-carcinogenic structural analogues a good correlation between the carcinogenic property and the ability to induce UDS was demonstrable. Out of 12 carcinogenic compounds, belonging to several different chemical classes, 10 gave rise to an increased UDS, whereas only 2 compounds, the polycyclic aromatic hydrocarbons benzo[alpha]pyrene and benz[alpha]anthracene, did not. All 4 noncarcinogenic compounds tested were negative. Possibly this method can be of value as a routine screening test, in combination with other short-term test systems, thus improving the predictive value of screening in vitro with respect to carcinogenicity.

Animals↗

PubMedDate not supplied

Oxidants and antioxidants in proliferative senescence.

In terms of the amount of experimental research it has generated the free radical theory of ageing is one of the most popular hypotheses to explain this ubiquitous phenomenon. From the theory two postulates were derived: either cellular defence mechanisms against free radical-dependent oxidants deteriorate during ageing of cells, or essential, unrepairable damages are imparted to the cell by oxidants regardless of the activity of antioxidant defence systems. The many reports dealing with a putative breakdown in antioxidant defence systems failed to positively support this postulate. However, a minor depletion in cellular glutathione by exposure to a model lipophilic peroxide led to a significant decrement in DNA and protein synthesis. In other words, the glutathione redox cycle is intrinsically fallible with respect to defending the cellular DNA replication system against this model lipophilic peroxide. Interestingly, after ageing in culture cells a partial uncoupling of the NADPH-producing and -consuming systems tends to take place. Experiments involving the addition of antioxidants to the culture medium have failed to significantly extend the lifespan of cultured diploid somatic cells. The level of antioxidants appears to be a modulator rather than a primary determinant of cellular ageing in culture. Several lines of evidence suggest that DNA damages accumulate during ageing of the organism, but no oxidant-related DNA damage has been pinpointed in the cultured cell system. Human mutants with defects in antioxidant enzymes have not shown conclusive signs of accelerated ageing. Cells from patients with Werner's syndrome (progeria of the adult), on the other hand, do not suffer from a defect in their antioxidant defence system, nor do they accumulate more than normal amounts of autofluorescent products resulting from lipid peroxidation. The recent finding that Werner's syndrome constitutes a mutator phenotype may prompt the comparison of oxidant- and ageing-related mutation spectra in order to investigate a mutational theory of ageing as a new derivative from the free radical hypothesis.

Animals↗