18碳多元不飽和脂肪酸改善脂毒性誘導HK2腎小管細胞損傷的功效與相關機制

過量脂質在腎臟中異位堆積所引發的脂毒性會導致腎小管上皮細胞損傷，進而引發發炎反應、細胞凋亡與纖維化等病理變化，已被認為是胰島素阻抗與肥胖導致腎臟疾病發生的重要機制之一。在第2型糖尿病(type 2 diabetes mellitus, T2DM)的病理發展中，胰島素阻抗高血糖造成異位脂質沉積於肝臟、肌肉與胰臟等與糖尿病慢性併發症發生的重要危險因子，組織，例如: 腎臟中脂質沉積在糖尿病微血管併發症糖尿病腎病變(diabetic kidney disease, DKD)的發展中扮演關鍵角色研究發現。研究發現，18碳多元不飽和脂肪酸(18-carbon chain polyunsaturated fatty acids, 18C-PUFAs)，如:亞麻油酸(Linoleic Acid, LA)、α-次亞麻油酸(Alpha-linolenic acid, LNA)與γ-次亞麻油酸(Gamma-Linolenic Acid, GLA)具有抗發炎、抗氧化與調節脂質等多重生理功能。GLA 更被證實具有抑制腎臟發炎與纖維化、延緩腎臟病變進展的潛力。本研究結果顯示，介入18C-PUFAs即LA、GLA與LNA，可有效減少棕櫚酸(palmitic acid, PA)誘導之人類腎小管上皮細胞HK-2中之油脂堆積量降低，並抑制脂質合成相關因子 sterol regulatory element-binding protein 1(SREBP-1)和脂肪酸合成酶(fatty acid synthase, FAS)及，提升乙醯輔酶A羧化酶(acetyl-CoA carboxylase, ACC)之磷酸化表現。此外，18C-PUFAs 可顯著改善 PA 誘導之促發炎因子腫瘤壞死因子-α(tumor necrosis factor-α, TNF-α)與介白素-6(interleukin-6, IL-6)之 mRNA 表現，並降低cleaved caspase-7 與多腺苷酸二磷酸核糖聚合酶(poly (ADP-ribose) polymerase, PARP)表現，減緩細胞凋亡現象。研究亦發現，18C-PUFAs 可下調腎小管間質纖維化相關指標α-平滑肌動蛋白(α-smooth muscle actin, α-SMA)、纖維連接蛋白(fibronectin)與第四型膠原蛋白(collagen IV)之 mRNA 表現，顯示18C-PUFAs具緩解腎小管間質纖維化功效。此外，相較於單獨處理PA，添加18C-PUFAs可提升自噬相關蛋白microtubule-associated protein 1 light chain 3-II(LC3-II)表現，並降低p62/sequestosome 1蛋白質表現，顯示其能透過促進自噬活性以發揮保護腎小管細胞的作用。綜合實驗結果可知，LA、GLA與LNA 不僅可減少PA誘導之HK-2細胞內脂質堆積與發炎反應，亦可透過促進自噬途徑，進一步降低脂毒性所造成的腎小管纖維化與細胞凋亡，顯示18C-PUFAs對於腎臟具有多重保護效應。

Excess lipid accumulation in the kidney, known as ectopic lipid deposition, can trigger lipotoxicity, which causes damage to renal tubular epithelial cells and subsequently induces pathological processes such as inflammation, apoptosis, and fibrosis. This has been recognized as one of the key mechanisms through which insulin resistance and obesity contribute to the development of kidney diseases. In the pathogenesis of type 2 diabetes mellitus (T2DM), insulin resistance and hyperglycemia lead to ectopic lipid deposition in organs such as the liver, muscle, and pancreas—factors that are closely associated with the progression of chronic diabetic complications. In particular, lipid accumulation in the kidney has been identified as a critical factor in the development of diabetic kidney disease (DKD), a major microvascular complication of diabetes. Studies had shown that 18-carbon chain polyunsaturated fatty acids (18C-PUFAs), such as linoleic acid (LA), alpha-linolenic acid (LNA), and gamma-linolenic acid (GLA), exhibit multiple biological functions, including anti-inflammatory, antioxidant, and lipid-regulatory properties. Notably, GLA has been demonstrated to inhibit renal inflammation and fibrosis, suggesting its potential to delay the progression of kidney disease. Our experimental results showed that treatment with 18C-PUFAs—specifically LA, GLA, and LNA—significantly reduced palmitic acid (PA)-induced lipid accumulation in human renal tubular epithelial HK-2 cells. Moreover, 18C-PUFAs suppressed the expression of lipid synthesis-related factors, including sterol regulatory element-binding protein 1 (SREBP-1) and fatty acid synthase (FAS), while enhancing the phosphorylation of acetyl-CoA carboxylase (ACC). In addition, 18C-PUFAs significantly reduced the PA-induced mRNA expression of pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and decreased the protein expression levels of cleaved caspase-7 and poly (ADP-ribose) polymerase (PARP), thereby attenuated apoptosis. This study also found that 18C-PUFAs downregulated the mRNA expression of renal interstitial fibrosis markers, including α-smooth muscle actin (α-SMA), fibronectin, and collagen IV, indicating their anti-fibrotic effects. Furthermore, compared to PA treatment alone, the addition of 18C-PUFAs increased the expression of the autophagy-related protein microtubule-associated protein 1 light chain 3-II (LC3-II) and decreased the expression of p62/sequestosome 1, suggesting that 18C-PUFAs exert protective effects on renal tubular cells by promoting autophagic activity. In summary, LA, GLA, and LNA not only reduce PA-induced lipid accumulation and inflammatory responses in HK-2 cells, but also alleviate renal tubular fibrosis and apoptosis by enhancing autophagy. These findings indicate that 18C-PUFAs have multiple protective effects on the kidney.