高脂飲食與奇異果對小鼠急性發炎反應的影響

Abstract

本實驗欲以LPS (lipopolysaccharides)致急性發炎的小鼠模式，探討肥胖對急性發炎反應的影響，再觀察攝食奇異果是否能改善因肥胖所造成的不良影響。 首先，先探討肥胖對急性發炎小鼠存活率的影響，以高油飲食誘發小鼠肥胖後，腹腔注射15 mg/kg BW LPS誘發C57BL/6J小鼠急性發炎，觀察小鼠生命期，並於小鼠死亡時測定腦部、肝臟和脂肪組織mRNA的表現量。結果顯示，肥胖會降低急性發炎早期小鼠的存活率，增加腦部MCP-1、IL-1RA的RNA表現量及降低IL-10 RNA的表現，增加肝臟中IL-12、NOS2 RNA的表現；增加脂肪組織中的巨噬細胞聚集，並降低IL-10、Foxp3和Ym1的RNA表現量。接著，為了解肥胖急性發炎小鼠血清、腦部、肝臟、脂肪組織中發炎相關指標的變化，於注射LPS後2、6、9、12小時犧牲小鼠。結果顯示，注射後6小時血清IL-6、IL-1β、MCP-1達分泌高峰，腦部促發炎介質的RNA表現量皆達高峰。 進一步為觀察餵食奇異果10週後對發炎相關指標的影響，於注射LPS後6小時犧牲測得結果顯示，攝食奇異果可降低血清TNF-α和IL-6濃度，減少脾臟細胞分泌TNF-α，並增加IL-10的分泌；降低肝臟的MCP-1 RNA表現量；有減少體內脂肪重量的潛力，及降低脂肪組織leptin、F4/80 RNA 表現量，並增加MRC1、IL-10 RNA的表現。最後，肥胖小鼠餵食奇異果8週後進行觀察生命期的急性發炎實驗。結果顯示，奇異果並未延長小鼠生命期，對死亡時發炎相關指標亦無影響。由急性發炎肥胖小鼠生命期和相關指標的相關性，歸納出血清、腦部和肝臟的IL-6、MCP-1，血清和腦部的IL-1RA，以及血清和肝臟的IFN-γ，皆為急性發炎反應的重要指標。 綜合上述結果推論，肥胖對急性發炎反應的影響仍有待商榷，但已證實發炎反應的嚴重程度為影響急性發炎小鼠生命期的關鍵。奇異果能提升脾臟調節發炎反應的能力，減緩肝臟及脂肪組織的發炎反應，並能減少脂肪的形成。雖然未觀察到奇異果延長生命期的功效，但證實Ym1與存活時數有顯著正相關。Ym1能成為調控發炎反應食材的作用標的。

In this study, we used a LPS-induced acute inflammation murine model to investigate the effects of obesity on acute inflammatory response, and then analyze the effects of kiwifruits on inflammation. First, to analyze the effects of obesity on acute inflammation, high-fat diet-induced obese (DIO) C57BL/6J mice were intraperitoneally injected with a 15 mg/ kg body weight (BW) LPS to provoke acute inflammation, and the survival of mice was observed. The results showed that obesity increases the mortality in early stage of acute inflammation. Obese mice had both higher MCP-1 and IL-1RA mRNA expression in the brain and higher liver IL-12 and NOS2 mRNA expression. Obesity could not only decrease IL-10 mRNA expression in the brain, and also increase macrophages aggregation, and reduce IL-10, Foxp3 and Ym1 mRNA expression in adipose tissue. To understand the immune responses of LPS-challenged obese mice, mice were sacrificed at 2, 6, 9, 12 hours after LPS injection. The results indicated that obese mice had the highest serum IL-6, IL-1β, and MCP-1 levels, as well as the highest mRNA expression of pro-inflammatory mediators in the brain at 6 hours after LPS challenge. Then, to investigate the effects of kiwifruits on inflammation, mice were sacrificed at 6 hours post LPS injection after kiwifruit feeding for ten weeks. The results indicated that kiwifruit consumption lowered serum TNF-α and IL-6 levels, decrease TNF-α secretion by splenocytes, and reduce MCP-1 mRNA expression in liver. In addition, kiwifruit increased IL-10 secretion by splenocytes and tend to reduce fat mass. Intake of kiwifruits could not only decrease the mRNA expression of leptin and F4/80, but also increase MRC1 and IL-10 mRNA expression in adipose tissue. To confirm the effect of kiwifruits on life span of LPS-challenged obese mice, mice fed high-fat diet supplemented kiwifruit for eight weeks were injected with LPS and the life span was observed. The results showed that kiwifruit could not affect the survival time, nor inflammation-related indicators detected at the moment of LPS-induced death. In our studies, it is confirmed that IL-6 and MCP-1 in the serum, brain, and liver, as well as IL-1RA in the serum and brain are important indicators of acute inflammation. Also, IFN-γ in serum and liver is one of important indicators of acute inflammation. To summarize, it is controversial that obesity reduce the mortality of acute inflammation, but the key factor of the mortality is the severity of inflammation. Kiwifruit can enhance the regulatory ability of splenocytes, decrease the inflammation in the liver and adipose tissue. Furthermore, kiwifruit tend to reduce adipose tissue. Although our studies didn’t observed that kiwifruit can extend the life span of LPS-challenged mice, but we confirmed that Ym1 is significantly positive correlated with the survival rate in all the models. Ym1 may be become an important target for evaluation of anti-inflammatory agents.