In vivo inhibition of glucocorticoid-inducible gene expression by dimethylnitrosamine in rat liver.

Sprague-Dawley rats were pretreated with a single i.p. injection of either 2.25 mL/kg of phosphate-buffered saline (PBS) or 22.5 mg/kg of dimethylnitrosamine (DMN) followed 2 hr later by a single i.p. injection of either 1.35 mg/kg of dexamethasone (DEX) or the vehicle, a 50% ethanol solution, both delivered in a volume of 3 mL/kg. RNA levels of the hormone-inducible, specialized liver function genes, tyrosine aminotransferase (TAT) and glutamine synthetase (GS), were monitored 4, 5, 6, 7, 8, and 10 hr after the DEX injection. Maximal induction of both the TAT (26-fold) and GS (6-fold) RNAs occurred 6 hr after DEX administration in PBS-pretreated animals. Pretreatment with DMN caused at least a 42% inhibition of DEX-induced RNA accumulation at every time point examined, with greater than 90% inhibition occurring when the genes were maximally induced at 6 hr. This inhibition was not due to any alterations of the glucocorticoid receptors as DMN had no effect on the binding affinity or amounts of glucocorticoid receptors present in rat hepatic cytosols. These results suggest that chemical carcinogens such as DMN may affect normal gene function in vivo by inhibiting the cellular response to hormone receptors mediating differentiation-associated, specialized cell functions.

Increased metallothionein gene expression in 5-aza-2'-deoxycytidine-induced resistance to cadmium cytotoxicity.

The pyrimidine analog, 5-azacytidine (AZA-CR), has been shown to increase the expression of the metallothionein (MT) gene and to induce tolerance to cadmium toxicity. Since incorporation into DNA of AZA-CR appears to be required for this effect, the deoxynucleoside of AZA-CR should also be effective. Therefore, this study was undertaken to assess the effect of 5-aza-2'-deoxycytidine (AZA-CdR) pretreatment on cadmium-induced cytotoxicity and MT expression in cultured cells. TRL 1215 cells in log phase of growth were exposed to AZA-CdR (0.4, 0.8, 4.0, 8.0 microM) followed 48 h later by the addition of cadmium (10 microM). MT concentrations were measured 24 h after the addition of cadmium. AZA-CdR alone caused modest, dose-related increases in MT levels (2.3-fold maximum), while cadmium alone resulted in a 9.5-fold increase. Pretreatment with AZA-CdR in combination with cadmium caused a 19--24-fold increase in cellular MT at all doses of AZA-CdR. Addition of the DNA synthesis inhibitor, hydroxyurea (HU), to the incubation medium during AZA-CdR exposure prevented the enhancing effect of the analog on cadmium induction of MT accumulation. Time course studies revealed that AZA-CdR pretreatment reduced the time required for cadmium to induce MT levels from 4--8 h to 0--2 h. AZA-CdR pretreated cells placed in suspension with cadmium (125 microM) showed a marked reduction in cadmium-induced cytotoxicity as reflected by reduced glutamic-oxaloacetic transaminase (GOT) loss. Uptake studies showed that AZA-CdR pretreatment had no effect on cadmium transport during the initial phases of exposure, indicating that an alteration in the toxicokinetics of the metal did not account for the reduction in toxicity. AZA-CdR did, however, cause hypomethylation of the MT-I gene. These results suggest that AZA-CdR pretreatment induces tolerance to cadmium toxicity by increasing the genetic expression of MT possibly through hypomethylation of the MT gene.

Simultaneous multicomponent drug determinations with a vidicon spectrometer.

A vidicon spectrometer, useful for absorption spectrophotometry over the 210-800-nm spectral region and capable of scanning a portion of this region at repetition rates of 250 scans/sec, was applied for the simultaneous determination of multicomponent drug formulations without a separation. Results are reported for two drug preparations containing two and four active components. The average of ratios of determined to expected values for the six active components contained in both formulations was 99.2% based on the specified tablet contents. Relative standard errors for the analyses were less than 3%. Other potential applications of the vidicon spectrometer are discussed briefly.

Application of a vidicon spectrometer for simultaneous multicomponent drug determinations.

A rapid scanning vidicon spectrometer has been evaluated for the simultaneous determination of drugs in mixtures, without a separation step. Spectral data in the ultraviolet region are collected on-line with a small computer at repetition rates of 100 scans per second. Absorbance data at several wavelengths are processed by matrix equations to resolve them into the concentration of each component in each mixture. Results are reported for two-component mixtures of procainamide and N-acetylprocainamide in serum, for two-component aqueous mixtures of butabarbital and seconbarbital, and for seven-component aqueous mixtures of phenobarbital, diphenylhydantoin, aminophylline, acetaminophen, salicylamide, phenylbutazone, and secobarbital. We conclude that the computer-inter-faced vidicon spectrometer is a viable tool for simultaneous multicomponent determinations.

Applications of a Vidicon spectrometer to analytical problems in clinical chemistry.

This report discusses characteristics of a custom-designed vidicon spectrometer and evaluates its applicability to several clinical analysis problems. Data show that the vidicon detector response is linear with intensity over about four orders of magnitude and that the uncertainty in absorbance measurements can approach 0.001 absorbance units in the range from 0 to 2 absorbance units. Applications include the enzymatic determination of glucose, the determination of lactate dehydrogenase, and determinations of barbital, chlordiazepoxide, and glutethimide. Capabilities of the instrument system for first-derivative spectroscopy are also discussed. The discussion included a critical evaluation of the potential advantages and limitations of the concept.