Safety evaluation of amylomaltase from Thermus aquaticus.

A recombinant amylomaltase, MQ-01, obtained by cultivation of Bacillus subtilis expressing the amylomaltase gene from Thermus aquaticus is to be used in the production of enzymatically-synthesized glycogen; which is intended for use as a food ingredient. In order to establish the safety of MQ-01, the enzyme was subjected to standard toxicological testing. In a battery of standard Salmonella typhimurium strains (TA98, TA100, TA1535, and TA1537) and in Escherichia coli WP2 uvrA, both with and without metabolic activation, MQ-01 failed to exhibit mutagenic activity. Similarly, MQ-01 did not display clastogenic properties in Chinese hamster lung fibroblast cells (CHL/IU), in an in vitro chromosomal aberration assay. In a 13-week subchronic toxicity study in rats, oral administration of MQ-01 at doses of up to 15 mL/kg body weight/day (corresponding to approximately 1230 mg/kg body weight/day) did not produce compound-related clinical signs or toxicity, changes in body weight gain, food consumption, hematology, clinical chemistry, urinalysis, organ weights, or in any gross and microscopic findings. The results of this study support the safety of MQ-01 in food production.

Characterization of cytochrome P450 expression in murine embryonic stem cell-derived hepatic tissue system.

An in vitro system for liver organogenesis from murine embryonic stem (ES) cells has been recently established. This system is expected to be applied to the development of a new drug metabolism assay system that uses ES cells as a substitute for animal experiments. The objective of this study was to elucidate the drug metabolism profiles of the murine ES cell-derived hepatic tissue system compared with those of primary cultures of murine adult and fetal hepatocytes. The expression of the genes of the cytochrome P450 (P450) family, such as Cyp2a5, Cyp2b10, Cyp2c29, Cyp2d9, Cyp3a11, and Cyp7a1, was observed in the murine ES cell-derived hepatic tissue system at 16 days and 18 days after plating (A16 and A18). To investigate the activities of these P450 family enzymes in the murine ES cell-derived hepatic tissue system at A16 and A18, testosterone metabolism in this system was analyzed. Testosterone was hydroxylated to 6beta-hydroxytestosterone (6beta-OHT), 16alpha-OHT, 2alpha-OHT, and 2beta-OHT in this system, and was not hydroxylated to 15alpha-OHT, 7alpha-OHT, and 16beta-OHT. This metabolism profile was similar to that of fetal hepatocytes and different from that of adult hepatocytes. Furthermore, pretreatment with phenobarbital resulted in a 2.5- and 2.6-fold increase in the production of 6beta-OHT and 16beta-OHT. Thus, evidence for drug metabolic activities in relation to P450s has been demonstrated in this system. These results in this system would be a stepping stone of the research on the development and differentiation to adult liver.