Biomedical subjects

D L Knook

Publications and source records attributed to D L Knook.

117 records · Page 7Linked to original sources

PubMedDate not supplied

Respiratory activities of hepatocytes isolated from rats of various ages. A brief note.

The ratio between the oxygen consumption of isolated hepatocytes in the presence of an inhibitor of oxidative phosphorylation (oligomycin, atractyloside) and in the presence of an uncoupler (dinitrophenol) is used as an estimation of the respiratory control ratio of mitochondria inside the isolated liver parenchymal cell. No significant age-related decline in the functional integrity of the mitochondria could be detected.

Aging↗

PubMedDate not supplied

The effect of age on protein synthesis by isolated liver parenchymal cells.

The protein synthesizing capacity of liver parenchymal cells isolated from 3-, 12-, 24-, 31- and 36-month-old rats was determined by the incorporation of 14C-leucine. Conditions for optimum protein synthesis included the use of an enriched medium (modified Waymouth's MB 752/1) and cell suspension concentrations ranging from 0.25 to 4 X 10(6) cells/ml medium. The cells were incubated with a dose of 6 micronmol leucine/ml medium for 2 h at 37 degrees C under an atmosphere of 95% O2 and 5% CO2. With parenchymal cells isolated from 3-month-old rats, a leucine incorporation rate of 14.4 nmol leucine/h/10(6) cells was found. The capacity of the parenchymal cells to synthesize protein decreased between 3 and 12 months, remained constant between 12 and 24 months and increased between 24 and 26 months. Degradation of newly synthesized proteins or reutilization of 14C-leucine did not occur during the incubation period. The ratio between albumin and total protein synthesis as a function of age was determined. This ratio did not change between 3 and 24 months but there was a significant increase between 24 and 36 months. The increase in total protein synthesis in late age may be due to a compensation by the liver for a more pronounced proteinuria, increased proteolysis or an accumulation of "altered" proteins.

Aging↗

PubMedDate not supplied

Aging and multiple forms of acid phosphatase in isolated rat liver cells.

Purified suspensions of highly viable parenchymal, endothelial and Kupffer cells were prepared from the livers of young (3 months of age) and old (33-34 months of age) female rats. In the cell suspensions, the activities of the multiple forms of acid phosphatase were determined with the substrates 4-methylumbelliferyl phosphate, 1-naphthyl phosphate and p-nitrophenyl phosphate. Most specific enzyme activities increased during aging, but the preference to hydrolyse any of the three substrates did not change. The small age-related changes in effects of the inhibitors fluoride and alloxan were not uniform for the the three liver cell types. The pattern for multiple forms of acid phosphatase obtained after isoelectric focusing did not change with age for Kupffer cells, while one of the two major forms of the enzyme almost disappeared in endothelial cells from old rats. With age, a very pronounced heterogeneous pattern was observed for the enzyme forms in the long-lived parenchymal cells. The increase in heterogeneity in multiple forms of acid phosphatase in aging parenchymal cells may be the result of post-translational modifications.

Acid Phosphatase↗

PubMedDate not supplied

The reticuloendothelial system and aging: a review.

This review represents an attempt to summarize and evaluate the literature data on the changes occurring in the reticuloendothelial system (RES) during aging. The RES is briefly introduced with emphasis on cellular composition, function, physiology, regulation and the methods employed for assessment of its functions. The age-related changes in the RES are discussed in terms of endocytotic capacity, antimicrobial and antitumor activity and morphology. In addition, the cooperation between the RES and the immune system in the defence of the body against disease agents is discussed in relation to the increased susceptibility to infectious diseases and tumorigenesis in both man and experimental animals during aging.

Aging↗

PubMedDate not supplied

Kinetics of ultraviolet induced DNA excision repair in rat and human fibroblasts.

To obtain more information on the well-documented low excision-repair capacity of rodent cells in comparison with human cells, we have studied this form of DNA repair in UV-irradiated human and rat skin fibroblasts. For this purpose, we have determined (i) unscheduled DNA synthesis (UDS), using autoradiography, (ii) the number and size of repaired sites with the bromodeoxyuridine (BrdU) photolysis assay and (iii) the removal of Micrococcus luteus UV-endonuclease susceptible sites (ESS). We found rat cells to be quite capable of performing DNA-repair synthesis, as demonstrated by both UDS and BrdU photolysis, whereas they almost completely lacked the capacity to remove pyrimidine dimers, as indicated by the persistence of ESS. This discrepancy will be discussed in terms of the types of mechanisms by which mammalian cells may recognize and remove UV-induced photoproducts.

Animals↗

PubMedDate not supplied

Decreased DNA repair capacity in familial, but not in sporadic Alzheimer's disease.

Using the alkaline filter elution technique we determined the induction and disappearance of DNA single-strand breaks (SSB) in freshly isolated peripheral blood lymphocytes (PBL) from 43 Alzheimer's disease (AD) patients and 48 normal, healthy age- and sex-matched control subjects following in vitro exposure to N-ethyl-N-nitrosourea (ENU). The mean percentage SSB disappearance in PBL from control subjects at 1 h after ENU treatment was 41.4 +/- 2.9%; this was not significantly different from that found in samples from AD patients which had no (n = 16) or one (n = 12) first-degree relative with dementia (42.5 +/- 8.2% and 43.0 +/- 4.4%, respectively; p greater than 0.75). However, in PBL of 15 AD patients with at least two first-degree relatives with dementia the mean percentage SSB disappearance was 23.6 +/- 5.8%, which was significantly lower than that found in controls (p less than 0.01) or in the other AD patients (p less than 0.02).

Aged↗

PubMedDate not supplied

Mortality risk in men is associated with a common mutation in the methylene-tetrahydrofolate reductase gene (MTHFR).

An elevated level of homocysteine in plasma is associated with the occurrence of cardiovascular disease. A common ala-to-val mutation in the methylenetetrahydrofolate reductase gene (MTHFR) is associated with an elevated level of plasma homocysteine. We studied the possible detrimental effects of the MTHFR mutation on mortality. Within a population-based study in the city of Leiden, the Netherlands, we first compared the MTHFR genotype distribution among 365 elderly subjects aged 85 years and over born in Leiden, and 250 young subjects aged 18 to 40 years whose families originated from the same geographical region. Second, the complete cohort of 666 subjects aged 85 years and over was followed over a period of 10 years for all-cause and cause-specific mortality and stratified according to MTHFR genotype. The frequency of the MTHFR mutation was significantly lower in the elderly than in the young (0.30 and 0.36, respectively; P = 0.03). The difference in genotype distribution was only present in men. The estimated mortality risk up to 85 years in men carrying the vallval genotype was 3.7 (95% confidence interval (CI), 1.3-10.9). Over the age of 85, mortality in men with the vallval genotype was increased 2.0-fold (95% CI, 1.1-3.9) and appeared to be attributable to cancer rather than cardiovascular causes of death. Among women aged 85 years and over, no deleterious effect of the MTHFR mutation was observed. In conclusion, the MTHFR mutation is associated with increased mortality in men in middle and old age, but not in women.

Adolescent↗

PubMedDate not supplied

Characterization in vitro of interaction of human apolipoprotein E-free high density lipoprotein with human hepatocytes.

Characterization of the interaction of iodinated apolipoprotein (apo) E-free high density lipoprotein (HDL) with cultured human hepatocytes provides evidence for a saturable, Ca2(+)-independent, high affinity binding site with an apparent km value of 20 micrograms/ml of apolipoprotein. Nitrated HDL and low density lipoprotein (LDL) did not compete for the binding of HDL, in contrast to very low density lipoprotein (VLDL). It is suggested that VLDL competition is exerted by the presence of apo Cs. Degradation of HDL was relatively low and in some cases not detectable. In cases where degradation was found, inhibitors of the lysosomal pathway of protein degradation had no effect, while LDL degradation was inhibited more than 80%. In the presence of 10 microM of monensin, the cell-association of HDL was unaffected, but the degradation was inhibited by 30%. Under similar conditions, LDL association was inhibited by 40% and LDL degradation, by 90%. Incubation of human hepatocytes with fluorescently labeled HDL (Dil-HDL) revealed (in contrast to Dil-LDL) mainly strong membrane-bound fluorescence and hardly any labeling of small intracellular vesicles. It is concluded that human hepatocytes possess a specific high affinity site for human HDL with recognition properties similar to those described earlier on rat hepatocytes. No evidence that the binding of HDL is actively coupled to uptake and lysosomal degradation could be obtained, indicating that binding of LDL and HDL to human hepatocytes is coupled differently to intracellular pathways.

Ammonium Chloride↗

PubMedDate not supplied

Kupffer cells and the acute phase response: the effect of aging.

Aging is associated with a significant increase in the susceptibility to scepsis and endotoxin induced shock in both man and experimental animals. In this study, some metabolic, heamodynamic and other pathophysiological factors possibly involved in the increased mortality of aged rats after endotoxin administration were investigated. The results indicate that older rats display an overall decrease in the capacity to maintain homeostasis after endotoxin challenge, which is expressed by severe disregulation of body temperature (hypothermia), glucose metabolism (hypoglycemia), tissue perfusion (fibrinolytic and anti-fibrinolytic factors) and severe tissue damage. Although a slight decrease in the clearance of endotoxin from the circulation was noted in old rats, alterations in the secondary response, evoked by stimulated macrophages and other cells appear to be more important in the age-related increase in susceptibility.

Acute-Phase Reaction↗