No abstract

Ozone (O3), the major oxidant of photochemical smog, is thought to be genotoxic and a potential respiratory carcinogen or promoter of carcinogenic processes. Because of oxidative reactions with the mucus in the upper airway, O3 reaction products are able to penetrate into the tracheobronchial epithelial (TE) cells. The carcinogenic effects of O3 on the TE cells are especially of interest since most previous studies have focused on the morphology or permeability changes of tracheas only. Therefore, the objective of this study was to examine the potential O3 genotoxicity in TE cells after an in vivo exposure, using DNA strand breaks as an index. Two-month-old male Dunkin-Hartley guinea pigs, specific pathogen free, 4 in each group, were exposed to 1.0 ppm O3 for 0, 12, 24, 48, 72, or 96 h. Animals exposed to filtered air without O3 exposure were used as controls. After O3 exposure, the trachea with two main bronchi was removed from each animal, and TE cells were isolated and employed for determination of DNA strand breaks by fluorometric analysis of DNA unwinding (FADU). The statistical significance level was set at alpha = .05. Compared with controls, ozone exposure did not alter the TE cell yield or viability, but caused an increase in protein content in tracheal lavage and an increase in DNA strand breaks. The amount of DNA left in the alkali lysate of TE cells found at 72 h exposure was significantly decreased from controls for 3 different alkali incubation times. An increase of the double-stranded DNA left in the alkali lysate of TE cells was observed at 96 h of exposure and approached the value of 24 h of exposure. The same pattern was seen with all 3 different alkali incubation times at 15 degrees C. One Qd unit was estimated to correspond to 100 strand breaks per cell. The Qd was also used as an indicator for O3 damage. Compared to controls, the Qd increases significantly after 1 ppm O3 exposure for 72 h, regardless of the alkali incubation time at 15 degrees C.

No abstract

Dot hybridization of messenger RNA (mRNA) and complementary DNA (cDNA) has been used to measure the relative levels of albumin and alpha-fetoprotein mRNA in liver of rats fed for 5 d a fat-free (carbohydrate-rich) diet, a high fat diet or a basal diet, all three of which were isonitrogenous. The level of albumin mRNA in rats fed the fat-free (carbohydrate-rich) diet was 30 to 45% of the level in animals fed the basal 4% fat diet. The concentration of another mRNA, that for alpha-fetoprotein, remained unchanged. It has been established by others that albumin mRNA levels and albumin synthesis are diminished in response to low levels of dietary protein. We show that albumin mRNA levels are lower than those observed in animals fed the basal 4% fat diet, even when dietary protein is adequate (30% wt/wt), if the nonprotein calories are derived solely from carbohydrate.

Chemical composition of liver chromatin was determined for rats fed a complete stock diet, or a diet lacking protein or fat. High carbohydrate, fat-free (diet 1) and low carbohydrate, protein-free (diet 2) diets were selected because they elicit structural alteration in chromatin as measured by incubation with micrococcal nuclease (E.C. 3.1.4.7). In the present study, either dietary treatment caused an increase in mass ratios of RNA:DNA and nonhistone:DNA, relative to control ratios. The nonhistone-DNA ratios in liver of rats fed diet 1 or diet 2 were 2.4-fold and 3.5-fold, respectively, larger than control ratios. The histone:DNA ratio remained relatively constant among all three dietary treatments. Liver nuclei were purified from rats fed each dietary treatment and were solubilized in 9 M urea. The nuclear proteins were analyzed by two-dimensional electrophoresis and visualized with a silver treatment that stains proteins in color. The electrophoretograms presented show preferentially proteins with low molecular weights and acidic pIs, two characteristics of nonhistones. The two-dimensional protein patterns are nearly identical for nuclear proteins from all three treatments. Analysis of the electrophoretograms indicates that the diet-induced increased nonhistone:DNA ratios are apparently not attributable to new species of protein, but rather to increased relative abundance of many proteins in the existing populations.