Effects of dietary N-(4-hydroxyphenyl)retinamide on N-nitrosomethylbenzylamine metabolism and esophageal tumorigenesis in the Fischer 344 rat

BACKGROUND

9-cis-Retinoic acid (9-cis-RA) and N-(4-hydroxyphenyl)retinamide (4-HPR) are effective chemopreventive agents against epithelial tumors in the oral cavity, breast, and prostate. We tested the inhibitory activity of these retinoids against N-nitrosomethylbenzylamine (NMBA)-induced tumorigenesis in the rat esophagus.

METHODS

Male Fischer 344 rats were randomly assigned to receive diets either lacking or containing 9-cis-RA or 4-HPR for 1 week before tumor initiation with NMBA and then for the duration of the study. NMBA metabolism, O(6)-methylguanine adduct formation, and cytochrome P450 messenger RNA (mRNA) expression in the esophagi of the rats were studied to investigate the mechanisms by which dietary 4-HPR affects tumorigenesis. All statistical tests were two-sided.

RESULTS

Dietary 4-HPR resulted in a dose-dependent and statistically significant enhancement (P<.05) of tumorigenesis in response to NMBA. In two different tumor bioassays, the mean tumor multiplicity for rats fed the highest concentration of dietary 4-HPR (0.8 g/kg diet) was increased by 5.9 tumors (95% confidence interval [CI] = 1.7 to 10.1 tumors) and 6.7 tumors (95% CI = 5.6 to 7.8 tumors) compared with the mean tumor multiplicity for rats that received the control diet lacking 4-HPR. Animals fed diets containing 9-cis-RA displayed no statistically significant increase in tumorigenesis. Compared with animals fed a diet lacking 4-HPR, animals fed 4-HPR had increased NMBA metabolism in esophageal explant cultures and had higher levels of O(6)-methylguanine DNA adducts and CYP2A3 mRNA in their esophagi.

CONCLUSIONS

Dietary 4-HPR enhances tumorigenesis in response to NMBA in the rat esophagus by increasing tumor initiation events. Dietary 4-HPR may exert paradoxical effects at some sites, such as the aerodigestive tract, by modulating the bioactivation of carcinogens in target tissues.

Wear of materials used in dentistry: a review of the literature

This is a review of the literature concerning wear related to the following materials used in dentistry: dental amalgam, composite resins, and glass-ionomer cements, as well as natural tooth substance. Discussions are included on both in vivo and in vitro studies in which various methods were used to help determine wear resistance.

Velocity of sound in liquid argon at high pressures and temperatures

Measurements were made of the velocity of sound in liquid argon in the temperature range 86–146 °K and at pressures up to 65 atm. The velocity versus pressure isotherms are steeper and more curved at the higher temperatures. At any one pressure, the velocity is a smoothly decreasing function of temperature. Analysis of the results using existing density data showed that the specific heat ratio, γ, decreases with pressure and increases with temperature in this range. The coefficient in Rao's relation was found to increase with temperature at constant pressure, while that in the relation due to Carnevale and Litovitz exhibited no definite trend with temperature or pressure.

Sound velocity in the inert gas liquids and the law of corresponding states

Velocity of sound was measured to an accuracy of 0.1% in liquid argon, krypton, and xenon under saturated vapor conditions by a resonance ultrasonic technique. Measurements in argon and krypton were from their normal boiling points to close to their critical points, while those in xenon were from its triple point to close to its critical point. Adiabatic compressibilities of these liquids were calculated in the temperature regions for which density data were available.Analysis of the results indicates that such velocity data can provide a precise test of the principle of corresponding states, in its classical and quantum forms. The corresponding states principle holds quite well in the above liquids when subjected to this test.The velocity data in all cases agree more closely with tunnel model calculations than with cell model calculations.

Velocity of sound in liquid CF4

The velocity of sound in liquid CF4has been measured in the temperature range from its triple point to its normal boiling point. Measurements have been made with an ultrasonic interferometer, consisting of barium titanate ceramic in tubular form, to an accuracy of 0.4% or better. The adiabatic compressibility has also been calculated for the corresponding temperature range using available density data. No other velocity of sound or compressibility data for CF4are available for comparison. Comparisons with other liquids by the method of corresponding states show similarity between CF4and CCl4, but not between CF4and methane or argon.