Equality in satisfaction, perceived need, and utilization of dental care in a 50-year old Swedish population.

Satisfaction with dental care, perceived need for dental care, and dental care utilization were analyzed as to equality in geographical, socio-economic, and gender distributions. The study base was a cross-sectional mail questionnaire sent in 1992 to all 50-year old persons (totally 8890) in Orebro and Ostergötland counties in Sweden. Measures of the variables were all based on self-assessments. The response rate was 71.3%. The results showed no large inequalities as to satisfaction, except the aspect travel time for rural residents. They also had higher perceived need for dental care. For utilization of dental care, workers were relatively fewer among "high" consumers. Controlling for socio-economic group, there were twice as many men than women among "low" consumers. In conclusion, there was relative equality in the dental care delivery in this 50-year old Swedish population, with some remaining social differences, primarily socio-economically contingent.

Radioprotective effect of N-acetylcysteine in vitro using the induction of DNA breaks as end-point.

Cultures of Chinese hamster cells were treated with N-acetylcysteine (NAC) and irradiated under hypoxic or aerobic conditions. Protection factors (PFs) were calculated using the yield of DNA breaks as a measure of the radiation response. With NAC up to 50 mmol dm-3, the PF values were smaller for aerobically- than for hypoxically-irradiated cells. In contrast with NAC concentrations > 100 mmol dm-3, the PF values for aerobically-irradiated cells were larger than those for hypoxic cells. This reversal is in agreement with the predictions of a modified competition model, the 'X-model'. The value of X (the ratio of reparable to non-reparable damage) was calculated to be close to 5 for the NAC-treated cells, i.e. about 18% of the radiation damage was not reparable. The increase of the total non-protein bound thiols (NPSH) and GSH content after NAC treatment was measured both in whole cells and isolated nuclei. Measurement of the cellular NPSH content showed a continuous increase with increasing NAC concentrations in the medium, independent of treatment time. In contrast, the amount of intracellular and intranuclear GSH increased with prolonged incubation time with NAC. No quantitative relationship was found between PF values and cellular NPSH or GSH content.

Radioprotection by dithiothreitol (DTT) at varying oxygen concentrations: predictions of a modified competition model and theory evaluation.

Cultures of Chinese hamster cells were treated with dithiothreitol (DTT) at varying concentrations, and exposed to radiation aerobically or at various oxygen tensions. The extent of radioprotection by DTT was calculated using the yield of DNA strand breaks as a measure of the radiation response. The curve of protection factors (PF) had a specific pattern, characterized by low PF values at low and high oxygen tensions with a peak at an intermediate tension. The peak value of the PF was increased and shifted to higher oxygen tensions as DTT concentrations increased. The experimentally observed pattern of the PF curves is incompatible with the Alper model of the competition hypothesis, which assumes that the entire radiation injury can be modified by sensitizers or protectors. On the other hand, the pattern is consistent with a model (X model) which is based upon a modification of the original hypothesis and assumes two types of radiation injury, only one of which is modifiable.

Radiosensitization by oxygen and radioprotection by thiols: analysis of the combined action according to a modified competition model.

Cultures of Chinese hamster fibroblasts were treated with dithiothreitol (DTT) and irradiated under aerobic or hypoxic conditions. Protection factors (PF) and oxygen enhancement ratios (OER) were calculated with DNA breakage as the criterion of the radiation effects, and related to the intracellular concentration of non-protein-bound thiols (NPSH). When the increment of the cellular NPSH was in a low concentration range, the PF values were smaller for aerobically than for hypoxically irradiated cells. In contrast, in the case of cells with a large increase in NPSH concentration, the PF values for the hypoxically irradiated cells were smaller. As a consequence the PF curve of the hypoxically and aerobically exposed cells crossed, and OER values followed a bell-shaped curve with respect to increasing cellular NPSH concentrations. The observations could be explained by assuming a competition between the damage-restituting and damage-fixing reactants, and postulating that only a certain proportion of the damaged targets is reparable.

Cellular glutathione content and K values. II.

After exposure to radiation in the presence of different oxygen concentrations, the OER values were determined for human fibroblasts cell strains with differing intrinsic GSH content, and cells depleted of GSH to different extent by treatment with BSO. The yield of DNA single-strand breaks was used as the measure of radiosensitivity. The K values were found to be related specifically to the GSH concentration in the cell nuclei. A good agreement was found between the experimental observations and the prediction of a variant of the competition model in which a second type of damage, not influenced by oxygen, was included.

Cellular glutathione content and K values.

The K values for two cell strains with differing intrinsic GSH concentrations have been measured with the yield of DNA breaks as end-point of the radiation effect. The K value of the strain with reduced GSH content was decreased (1.59 microM O2) in comparison to the K value (3.01 microM O2) for the strain with a normal GSH content. The significance of the observation is discussed in relation to competition models. All variants of the competition model agree in predicting a reduction of K, if GSH is reduced.

Specificity of endogenous glutathione in determining the oxygen enhancement of cellular radiosensitivity.

Oxygen enhancement ratios (OER) determined with single-strand DNA breaks as end-point of radiation effect were lower for cells with genetically determined glutathione (GSH) deficiency, than for cells depleted of GSH artificially to a corresponding degree by treatment with buthionine sulfoximine (BSO). In view of a considerable non-protein thiol (NPSH) accumulation found in both cases, the difference can be attributed to different NPSH components. Those in the BSO-treated cells having the capacity to substitute for GSH in the processes which define OER. As an alternative explanation, the particular location of GSH in GSH-proficient cells in close contact with the critical radiation target can be considered. At these sites, as indicated by measurements of NPSH in isolated nuclei, BSO may not deplete thiols as efficiently as at other sites. Observations on a persisting difference found between the OER of genetically GSH-deficient and proficient cells after treatment with dithiothreitol (DTT) can also be given a spatial explanation, assuming that exogenous thiols may not reach the critical sites in the nucleus in efficient concentrations.