膳食中缺鋅對吳郭魚肝臟細胞色素P4501A活性及表現之影響

Influence of Dietary Zinc Deficiency on Hepatic Cytochrome P4501A Activity and Expression in Tilapia (Oreochromis, niloticus x O. aureus)

本研究主要探討膳食中缺鋅對吳郭魚肝臟的細胞色素P4501A(cytochrome P4501A, CYP1A)活性及表現之影響。吳郭魚隨機分為缺鋅組(zinc-deficiency group)及對飼組(pair-fed control)分別餵食缺鋅飼料（5 mg Zn/kg飼料）及基礎飼料（46 mg Zn/kg飼料）。經八週的飼養實驗後，每組各隨機選取6尾吳郭魚進行分折。發現兩組吳郭魚的增重率。肝體比沒有明顯差異，但缺鋅組之吳郭魚血漿中的鋅濃度則明顯低於對飼組。肝臟中之總CYP含量及相關之單加氧酶(monooxygenases)活性亦顯現無差異的情況，說明鱔食中缺乏鋅對吳郭魚之肝臟中的總CYP含量及相關酵素的活性似乎沒有影響。進一步將此二組的吳郭魚分別施打不同劑量之五氯酚(pentachlorophenol, PCP)，則發現兩組吳郭魚肝臟中aryl hydrocarbon hydroxylase(AHH)及ethoyresorufin-O-deethylase(EROD)之活性均可被PCP誘發。但在較高劑量的PCP下，PCP所誘導的AHH及EROD活性，則是缺鋅組比對飼組為低。同時以反轉錄聚合酶連鎖反應檢測(reverse transcription-polymerase chain reaction assay, PT-PCR assay)進行CYP1A mRNA表現的分析，發現缺鋅組之吳郭魚肝臟CYP1A mRNA的表現與對飼組比較，缺鋅組之CYP1A mRNA的表現似乎受到壓抑。顯示鋅似乎在CYP1A表現的調控上具有特殊之功能。其機制為何？有待更進一步的探討。

The present study investigated the effect of dietary zinc deficiency on hepatic cytochrome P45O1A (CYP1A) activity and expression in tilapia. The fish were given randomly assigned to either a zinc-deficient dietary group (5 mg Zn/kg diet) or a pair-fed control (46 mg Zn/kg diet). After 8 weeks of the feeding trial, six fish were randomly removed from each dietary group for analysis. Compared with the pair-fed control, zinc deficiency reduced plasma zinc concentration but no effect on the body weight gain, relative liver weight, total CYP content and NADPH-cytochrome C reductase activity in tilapia. CYP-mediated monooxygenase activities, which were indicated by aryl hydrocarbon hydroxylase (AHH), ethoxycoumarin-O-deethylase (ECOD), 7-ethoxyresorufin-O-deethylase (EROD). aniline-4-hydroxylase (A4H) and aminopyrine-N-hydroxylase (APNH), were also not affected by dietary zinc deficiency. The fish of each dietary group was further injected individually with graded doses of pentachlorophenol (PCP), and levels of hepatic CYP1A mRNA and CYP1A-mediated monooxygenase activities were determined, Hepatic CYP1A-mediated ARK and EROD were significantly inducible by PCP in tilapia from the two groups. When treated with higher doses of PCP, the PCP-induced AHH and EROD activities were decreased in dietary zinc deficient tilapia. Moreover, reverse transcription-polymerase chain reaction assay (RT-PCR assay) revealed an inhibition of CYP1A mRNA expression in zinc-deficient tilapia, These results indicate that dietary zinc deficiency reduced the hepatic gene expression of the CYP1A in tilapia.