Pharmaceutical study on the risk of endocrine disrupting chemicals based on the regulation of ketone body metabolism

乙酰乙酰辅酶a合成酶（Acetoacetyl-CoA synthetase， AACS, acetoacetate-CoA ligase, EC 6.2.1.16）是一种酮体利用酶，其生理作用尚不清楚。为了研究AACS在人体内的组织分布，从HepG2细胞中分离编码AACS的cDNA。从开放阅读框中推断出的人AACS氨基酸序列与大鼠AACS同源性较高（89.3%），与细菌AACS同源性较低（43.7%）。AACS mRNA在肾脏、心脏和大脑中表达量高，而在肝脏中表达量低，并且AACS在人脑中的表达谱与3-羟基-3-甲基甲酰基辅酶a还原酶的表达谱非常相似。接下来，为了研究AACS的生理作用，我们研究了链脲佐菌素（STZ）诱导的糖尿病大鼠对AACS酶活性的影响。在STZ给药72小时，肝酶比活性下降到初始活性的23%。而STZ处理对非肝组织的酶活性影响不显著。4%胆胺和0.4%普伐他汀均饲喂3 d，可显著提高糖尿病大鼠肝脏AACS活性，降低血浆酮体水平。上述结果提示，AACS在调节大鼠肝脏酮体利用中具有重要作用，这些降胆固醇药物具有弥补糖尿病条件下酮体利用受损的能力。然后研究了雌二醇和双酚A对AACS活性的影响。两种物质均可降低大鼠或MCF-7细胞中的AACS活性。而在不表达雌激素受体的MCF-7/Adr^R细胞中，AACS活性不受双酚A的影响，提示双酚A对AACS表达的作用是由雌激素受体介导的。

Acetoacetyl-CoA synthetase (AACS, acetoacetate-CoA ligase, EC 6.2.1.16) is a ketone body-utilizing enzyme, the physiological role of which remains unclear yet. In order to investigate the tissue distribution of AACS in human, cDNA encoding AACS was isolated from HepG2 cells. Amino acid sequence of human AACS deduced from the open reading frame showed high homology (89.3 %) with that of rat AACS and much less homology (43.7 %) with that of bacterial AACS. The expression level of the AACS mRNA was high in kidney, heart and brain, but low in liver, and the expression profile of AACS in the human brain was quite similar to that of 3-hydroxy-3-methylgmtaryl-CoA reductase. Next, in order to investigate the physiological role of AACS, effects of streptozotocin (STZ)-induced diabetes on the enzyme activity was investigated in rats. At 72 hr of the STZ administration, hepatic enzyme specific activity decreased to 23 % of its initial activity. However, the enzyme activities in non-hepatic tissues were not significantly affected by the STZ treatment. Feeding of rats with both 4% cholestyramine and 0.4 % pravastatin for 3 days remarkably increased the hepatic AACS activity and decreased the plasma ketone bodies level in the diabetic rats. These results suggest that AACS has important roles in the regulation of ketone body utilization in rat liver and that these hypocholesterolemic agents have the ability to remedy the impaired utilization of ketone bodies under the diabetic condition. Then, effects of administration of estradiol and bisphenol A on the AACS activity was investigated. AACS activity in the rat or MCF-7 cells was decreased by both substances. However, AACS activity in MCF-7/Adr^R cells, which does not express estrogen receptor, was not affected by bisphenol A, suggesting that bisphenol A action on the AACS expression is mediated by estrogen receptor.