麩醯胺補充對於imiquimod誘導小鼠乾癬樣皮膚發炎之影響

Abstract

乾癬(psoriasis)是一種自體免疫功能失調引起的慢性皮膚發炎疾病，其特徵是過度增生的角質細胞以及浸潤的T細胞、樹突細胞、巨噬細胞及嗜中性白血球，並對患者的生活品質有不良影響。乾癬的發病機制雖然尚未完全釐清，但已知T細胞在疾病的起始與發展階段扮演主要的致病因子之一。麩醯胺 (Glutamine；GLN) 具有抗氧化、抗發炎、免疫調節的作用，且乾癬患者血漿及血清中麩醯胺顯著較低。因此，本研究使用imiquimod (IMQ)誘發小鼠乾癬樣皮膚炎的動物模式，探討飲食中補充麩醯胺對於乾癬的保護效果。本實驗將雄性C57BL/6J小鼠隨機分為三組 (n=8/組)：控制 (NC)組、IMQ誘發乾癬 (P)組、IMQ誘導並補充GLN (PG)組。NC組和P組所有小鼠給予AIN-93G飼料，PG組則於飼料中添加麩醯胺 (GLN取代30%總胺基酸氮含量)，經15天餵養後，連續6天以Aldara乳膏 (5% IMQ) 塗抹於P組及PG組小鼠背部皮膚誘發乾癬樣皮膚炎，誘發期間持續給予飼料介入麩醯胺。實驗結果發現，與NC組相比，P組小鼠背部皮膚出現紅斑、脫屑、增厚等典型乾癬樣皮膚炎反應，且呈現更高的乾癬面積暨嚴重程度指數(psoriasis area severity index , PASI)，以及血液中嗜中性白血球、促發炎單核球、抗發炎單核球、T細胞、輔助型T細胞17 (helper T cell 17, Th17) 及調節型T細胞比例顯著提升。將P組和PG組做比較，發現飼料中補充麩醯胺可顯著降低IMQ誘導的乾癬嚴重程度的PASI指數、血中嗜中性白血球及Th17細胞比例。補充麩醯胺可顯著降低IMQ誘發的背部皮膚之嗜中性白血球比例與促發炎因子如interleukin (IL)-17A、IL-23、C-X-C motif chemokine ligand 1的mRNA表現量。在組織學方面觀察到補充麩醯胺降低了IMQ誘導引起的表皮增厚，降低角質層的厚度、減少角化不全及角化過度；免疫化學染色方面觀察到，補充麩醯胺降低了皮膚中T細胞及嗜中性白血球的浸潤。綜合上述結果推論，飲食補充GLN能可藉由調節Th17細胞比例、降低發炎激素及趨化因子的表現量，而改善IMQ誘導小鼠乾癬樣皮膚發炎反應。Psoriasis is an immune-mediated chronic inflammatory skin disease characterized by hyperproliferative keratinocytes and infiltration of T cells, dendritic cells, macrophages and neutrophils, which has great negative impact on patients’ quality oflife. Although the pathogenesis of psoriasis is not fully understood, there is evidence suggesting that T cells play a dominant pathogenic role in the initiation and development of psoriasis. Glutamine (GLN) possesses antioxidant, anti-inflammatory, and immunoregulatory properties. Glutamine has been found at lower levels in the serum and plasma of psoriasis patients. Therefore, we conducted imiquimod (IMQ)-induced psoriasis-like mouse model to explore the protective role of GLN in psoriasis. Thirty male C57BL/6J mice were randomly divided into three groups (n=10 in each group): the normal control (NC), IMQ-induced psoriasis (P), and IMQ-induced psoriasis with glutamine supplementation (PG) group. All animals in the NC and P groups were fed an AIN-93 semi-purified diet, while PG group received a semi-purified diet that casein was replaced by Gln, which provided 30% of total amino acid nitrogen. Three groups were fed the respective diets for 15 days, and then P and PG group were topical treated for 6 days with Aldara cream (5% IMQ) to induce psoriasis-like dermatitis. Results showed that the P group emerged typical psoriasis-like inflammatory responses on back, such as erythema, scaling and thickening, and exerted higher psoriasis area severity index (PASI) scores, increased percentage of neutrophils, inflammatory monocyte, anti-inflammatory monocyte, T cells, T helper (Th)17 cells, and regulatory T (Treg) cells in blood, as compared to NC group. GLN supplementation significantly reduced IMQ-induced PASI scores, and the percentage of neutrophils and Th17 cells in blood. GLN supplementation also significantly reduced the percentage of neutrophils and the mRNA levels of proinflammatory mediators (interleukin (IL)-17A, IL-23, C-X-C motif chemokine ligand 1) in the back skin by IMQ induction. Besides, the results of histological observation indicated GLN decreased IMQ-induced epidermal hyperplasia, thinning of the stratum corneum, parakeratosis, and hyperkeratosis. In conclusion, these results suggested that dietary GLN supplementation alleviates IMQ-induced psoriatic inflammation by modulating the percentage of Th17 in the blood, reducing the expression of inflammatory mediator and chemokines.