癸酸降低脂多醣活化巨噬細胞株前列腺素E2生成之機制探討

Capric Acid Inhibits the Production of PGE2 by LPS-Activated Macrophage Cell Line

黃懿寧(Yi-Ning Huang)

指導教授 ： 黃青真

國立臺灣大學/生命科學院/微生物與生化學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.01683

摘要

癸酸 (capric acid) 為中鏈脂肪酸 (medium-chain fatty acid)之一，具有抗菌、抗微生物與抗病毒等功效。之前研究指出，癸酸 (capric acid) 可以抑制脂多醣 (LPS) 活化巨噬細胞。本實驗的目的即試圖找出癸酸抑制PGE2產生的機制。癸酸抑制LPS刺激PGE2生成具有劑量效應，其IC50約為8.9 μM；但並不會改變 COX-2蛋白質表現。癸酸於 LPS 刺激後添加，仍可以有效的降低 PGE2 生成。在 LPS刺激之前，先給予癸酸預處理，則不會減少PGE2生成量。
為了驗證基質的獲取是否為限制因子，故在LPS刺激18小時之後，移除培養液再加入外源性的arachidonic acid (AA)，癸酸抑制PGE2 生成的效果依然存在，但抑制程度較低。表示癸酸的抑制效果可能部分來自於降低COX-2酵素活性，另一部份則推測可能源自降低細胞內源性基質獲取。以酵素動力學分析，capric acid對於AA為一種non-competitive inhibition的關係。
以純化酵素為模式，發現 0.5-5 μM 癸酸可降低COX-2之酵素活性達27%；進一步的測試 eroxidase 的活性，癸酸處理亦具有抑制COX-2 活性效應。
本研究結果推論：癸酸降低PGE2生成是經由抑制酵素轉換以及降低酵素的基質獲取。

關鍵字

癸酸 ； 發炎 ； 前列腺素E2

並列摘要

Capric acid, a member of medium-chain fatty acid, has antibacterial, antimicrobial and antivirus functions. Previous study has indicated that capric acid inhibits PGE2 production in the LPS-stimulated RAW264.7 macrophage cell line. The aim of this study has to examine the mechanism on how capric acid inhibits PGE2 production.
Capric acid inhibited PGE2 production in the LPS imulated RAW264.7 cells in a dose-dependent manner. However, capric acid did not change the COX-2 protein expression as etected by Western Blot Analysis. The inhibition of Capric acid on PGE2 production was also observed when Capric acid and LPS were added simultaneously (p<0.05). Capric acid pretreatment did not result in a reduction in PGE2 production after cells were treated with LPS. To test whether substrate availability could be a limiting factor, medium was supplement with arachidonic acid (AA) after cells were treated with LPS for 18 hours. It was found that the inhibition of PGE2 production could be reduced to a great extent by the supplementation of AA, implying Capric acid might inhibit LPS-stimulated PGE2 production by limiting the substrate availability. However, when capric acid was included in the AA supplemented medium, a slight inhibition of PGE2 production could still be observed (p<0.0001). Kinetic study suggested a non-competitive inhibition before capric acid and AA on PGE2 production in the LPS-stimulated macrophage cells. The effect of capric acid on the activity of purified COX-2 enzyme was also examined. Results showed that Capric acid significantly inhibited COX-2 enzyme activity at a concentration of 0.5, 1 and 5 μM (p<0.05). Capric acid also slightly inhibited the peroxidase activity of the purified COX-2 enzyme.
In conclusion, the present study suggests that Capric acid decreases PGE2 production by inhibition of enzymatic conversion and by reduction of substrate availability for COX-2.

並列關鍵字

capric acid ； inflammation ； PGE2

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