Interaction of phenols with delta 9 terminal desaturase and other cyanide-sensitive factors in chicken liver microsomes

2 Final Report on the Safety Assessment of p-Aminophenol, m-Aminophenol, and o-Aminophenol

p-Aminophenol (PAP), m-Aminophenol (MAP), and o-Aminophenol (OAP) are used in permanent (oxidative) hair dyes at concentrations from 0.1 to 5%. In vivo and in vitro skin absorption studies indicated that 11% of the dermally applied 14C-PAP was detected in the excreta, viscera, and skin of the test animals. The oral LD50s of PAP, MAP, and OAP in rats ranged from 600 to 1300 mg/kg. Topical application of PAP at concentrations up to 8.00 g/kg to the skin of New Zealand white (NZW) rabbits produced no skin irritation and no mortality. PAP, MAP, and OAP were irritating to eyes of NZW rabbits at a concentration of 2.5%. MAP at 3% was nonsensitizing in guinea pigs; PAP at 2% sensitized 9 of 10 guinea pigs. Neither PAP nor MAP produced photosensitization in guinea pigs. No treatment-related toxicity was found in three separate four-generation chronic dermal toxicity and reproduction studies of hair dye formulations containing the three Aminophenols. Additional studies on the pure ingredients were also nonteratogenic; embryotoxicity was reported. A range of results was obtained from studies assessing the mutagenic activity of the Aminophenols. PAP tested positive in six of eight mutagenicity tests. MAP and OAP gave positive results in two of eight and five of seven mutagenicity tests, respectively. Oxidative hair dye formulations containing PAP, MAP, and OAP did not produce gross or microscopic alterations or have carcinogenic effects after chronic topical application to mice. Feeding of OAP-HCl and PAP to rats at a dose of 8 mmol/kg produced neither hepatic cirrhosis nor neoplastic lesions. A 3% solution of MAP in an aqueous vehicle was neither a significant irritant nor sensitizer in two clinical studies. A variety of epidemiological studies have not indicated that occupational exposure to, and personal use of, hair dyes containing the Aminophenols presented a carcinogenic risk. A discussion of the significance of the mutagenic data in the safety assessment and the potential for human effects is presented. On the basis of the available animal and clinical data presented in this report it is concluded that p-, m-, and o-Aminophenols are safe as cosmetic ingredients in the present practices of use and concentrations.

The regulation of stearoyl-CoA desaturase (SCD)

The stearoyl-CoA desaturase gene family encodes stearoyl-CoA desaturase, the key enzyme involved in the biosynthesis of unsaturated fatty acids, as well as in the regulation of this process. Because of the important role that the SCD gene product plays in fat cell metabolism, future studies on SCD1 gene expression could provide new insights into the role of fatty acids in cellular regulation, metabolism, and gene expression both in normal and disease states. In addition, the SCD gene family can be used as a model to study mechanisms of cellular differentiation, tissue-specific gene expression, and dietary and hormonal regulation of gene expression.

Stearoyl-coenzyme A desaturase activity in the mammary gland and liver of lactating rats

Stearoyl-CoA desaturase activity in microsomes from lactating rat mammary gland is very low (0.05-0.15 nmol/min/mg of protein) regardless of lactating time. In such microsomes, reductase activities and content of cytochrome b5 are several-fold lower than in normal rat liver microsomes. Preincubation of the mammary microsomes with purified terminal desaturase gives a 55-fold stimulation of stearoyl-CoA desaturase activity, whereas preincubation with cytochrome b5 has no effect. However, preincubation of mammary microsomes with both cytochrome b5 and terminal desaturase results in a 200-fold stimulation of overall desaturation. These observations suggest that negligible stearoyl-CoA desaturase activity in lactating rat mammary microsomes is due to a cytochrome b5 content and the absence of terminal enzyme. The hepatic stearoyl-CoA desaturase activity increases 9-fold during lactation. There is little or no change in the NADH-cytochrome c reductase activity or in the concentrations of cytochrome b5 during this period, but the activity of the terminal desaturase increases with the increase of overall desaturation. These results suggest that liver is one of the more important sources of oleic acid for milk triglycerides.