壳寡糖是一种从有壳海洋生物中提取的天然氨基多糖，因其广泛的生理活性，近年来在代谢相关脂肪性肝病领域备受关注。壳寡糖通过抑制脂质生成、调控炎症反应、缓解氧化应激、改善胰岛素抵抗、调节肠道菌群等多重机制，显著改善非酒精性脂肪肝症状。具体机制包括抑制转录因子的表达、激活腺苷酸活化蛋白激酶（AMPK）信号通路促进脂肪酸氧化、抑制磷脂酰肌醇3激酶/蛋白激酶B/磷酸化哺乳动物雷帕霉素靶蛋白（PI3K/AKT/mTOR）等信号通路的活性。本文系统综述壳寡糖在代谢相关脂肪性肝病的改善作用及其机制研究，旨在为其临床应用和药物开发提供科学依据。

代谢相关脂肪性肝病（metabolic dysfunction-associated fatty liver disease，MASLD），原称非酒精性脂肪性肝病（non-alcoholic fatty liver disease，NAFLD），是指在无过量酒精摄入的基础上，合并1项或多项心血管代谢危险因素的脂肪性肝病 [1-3]。随着生活方式的改变和饮食结构的调整，MASLD已成为影响全球约25%人口健康的重大公共卫生问题[4-6]。

MASLD根据病理特征和疾病进展可分为三个主要阶段：①单纯性脂肪肝（simple steatosis）：以肝细胞脂肪变性为主要特征，无明显炎症反应和纤维化改变；②代谢相关脂肪性肝炎（metabolic dysfunction-associated steatohepatitis，MASH）：在脂肪变性基础上伴有肝细胞损伤、炎症细胞浸润和气球样变；③代谢相关脂肪性肝纤维化/肝硬化：疾病进展至纤维组织增生和肝脏结构改建阶段。

目前，尽管美国食品药品监督局已正式批准新药Rezdiffra用于治疗该病[7-8]，但其临床有效率仅25%~30%，且价格昂贵[9]。当前治疗仍以生活方式调整，以及使用减肥药物、降血糖药物、他汀类降血脂药物、降血压药物和水飞蓟素等药物治疗、手术治疗为主[10]。然而，上述治疗都有一定的局限性，迫切需要开发更多安全性高、疗效佳的药物。

壳寡糖（chitooligosaccharides，COS）作为一种天然的氨基多糖，由虾蟹壳中提取的壳聚糖经过酶解、酸解或物理化学降解获得的低分子量寡糖，是由2~10个D-氨基葡萄糖（或少量N-乙酰-氨基葡萄糖）通过β-1,4-糖苷键连接而成[11-12]。其为一种带正电荷的碱性、水溶性多糖，能够与带负电的细胞膜或生物大分子相互作用，具有抗菌、抗肿瘤、抗氧化、抗炎、降脂、减肥、降血糖等生理活性[13-15]。作为一种新兴的海洋药物，COS近年来在生物医药领域受到广泛关注。随着中国海洋强国战略的深入推进，国家为海洋药物的开发提供了政策支持，《“十四五”海洋经济发展规划》明确提出，要发展海洋生物医药，鼓励海洋医药关键技术攻关，支持COS等创新药物的研发。然而，与传统药物相比，目前COS的应用研究较为有限，特别是在治疗MASLD方面的应用研究尚处于起步阶段。基于此，本文就COS对MASLD作用机制的研究展开综述，以期为COS用于MASLD治疗提供参考。

1 MASLD的发病机制

MASLD的发病机制复杂且尚不明确，1998年Day等[16]首次提出“二次打击学说”，认为“一次打击”主要是胰岛素抵抗（insulin resistance，IR），通过促使外周脂肪分解和引起高胰岛素血症增加肝细胞脂肪酸合成，并增加肝脏对损害因子的敏感性。氧化应激则是“二次打击”，通过过量的活性氧（reactive oxygen species，ROS）引发脂质过氧化，进而激活线粒体解偶联蛋白和细胞因子及凋亡相关因子Fas配体，诱发炎症、肝纤维化和肝硬化，甚至肝癌[17]。然而“二次打击”学说未能解释遗传易感个体中多种因素的协同作用[18-21]。2008年，Jou等[22]提出“第三次打击”假说，认为氧化应激和细胞因子的分泌异常导致肝细胞的迅速死亡，坏死组织释放化学因子，激活免疫细胞，加速肝脏病变。随着研究的深入，2010年，Tilg等[23]提出的“多重打击”学说被广泛接受，认为MASLD发病机制是IR、遗传易感性、肠道菌群、脂肪组织分泌因子等多因素协同作用的结果，导致脂肪变性、炎症、氧化应激等多重病理过程的发生。

2 COS改善MASLD的作用和机制

2.1 抑制脂质生成

肝脏是脂质代谢的核心器官，负责调控游离脂肪酸（free fatty acid，FFA）的摄取、转化及代谢。FFA通过脂肪组织的脂解、膳食摄入以及从头脂肪合成（de novo lipogenesis，DNL）进入肝脏，并进一步转化为甘油三酯（triglyceride，TG），通过极低密度脂蛋白（very low-density lipoprotein，VLDL）运输或通过线粒体β氧化分解以提供能量 [24-26]。当FFA摄取过量或代谢失衡时，TG的过度积累导致肝脂肪沉积，引发MASLD。此过程涉及脂肪酸合成酶（fatty acid synthase，FAS）和硬脂酰辅酶A去饱和酶（stearoyl-coA desaturase，SCD）等脂质代谢关键酶的异常激活，其活性增加会加剧脂质在肝脏中的堆积。研究表明，COS能够有效抑制FAS和SCD的表达，并有效降低肝脏内TG和血清总胆固醇（total cholesterol，TC）积累[14, 27-30]。不同研究的结果存在一定差异。沈欣[31]和Deng等 [32]研究发现，COS通过减少肝脏和血清中的TG水平有效缓解脂质沉积，但对TC水平的影响不明显。王健[33]研究表明，COS可降低体内外MASLD模型TG的作用，但该研究未表明，COS的分子量、聚合度及其与降脂作用之间的关系。此外Cao等 [34]对不同分子量的COS（1  000  Da和3  000  Da）在HepG2细胞中清除脂质积累的能力比较研究显示，两种分子量COS均可降低油酸钠诱导的脂质积累及细胞内TG含量，且剂量呈依赖性，其中低分子量COS（1 000 Da）效果更显著。Li等[35]发现COS（GLcN）2~6能改善脂质积累，其中壳二糖通过减少FFA的摄取和TG的合成抑制脂质生成，对脂质变性调节有最佳作用。如表1所示，不同分子量聚合度的COS在MASLD代谢干预中存在差异。

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  表格1 不同分子量或聚合度COS在MASLD脂质代谢干预中的作用

  Table 1.The role of COS with different molecular weights and degree of polymerization in lipid metabolism intervention in MASLD

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此外，COS通过下调固醇调节元件结合蛋白-1c（sterol regulatory element-binding protein-1c，SREBP-1c）表达，抑制脂质合成并促进脂肪酸氧化。在正常生理条件下，SREBP-1c通过调节FAS和乙酰辅酶A羧化酶（acetyl coenzyme A carboxylase，ACC）等关键基因的表达，维持脂肪酸合成与分解的动态平衡。然而，在患者中，SREBP-1c的过度激活导致脂质代谢失衡 [37]。COS还可通过上调过氧化物酶体增殖物激活受体（peroxisome proliferator-activated receptor，PPAR）γ和脂肪酸相关的基因如肉碱棕榈转移酶1A（carnitine palmitoyl transferase 1A，CPT1A）的表达，增强脂肪酸的β氧化能力，从而改善肝脏脂质代谢紊乱[19, 38-39]。Yang等[40]进一步指出，COS通过下调甾醇反应元件结合蛋白2（sterol-response element binding protein 2，SREBP-2）的表达，抑制胆固醇合成酶的活性，减少胆固醇积累。此外，Jiang等[41]研究表明，COS通过上调胆固醇7α-羟化酶（cholesterol 7α-hydroxylase，CYP7A1）、肝脏X受体α（liver X receptor α，LXRα）和PPARα的表达，促进胆固醇转化为胆汁酸，并通过下调3-羟基-3-甲基戊二酰辅酶A还原酶（3-hydroxy-3-methylglutaryl coenzyme A reductase，HMGCR）和SREBP2及上调低密度脂蛋白受体（low density lipoprotein receptor，LDLR）的表达，减少胆固醇从头合成，改善胆固醇代谢。既往研究发现[42]，COS有效降低关键的成脂转录因子CCAAT/增强子结合蛋白（CCAAT/enhancer binding protein，CCAAT/EBP）α和PPARγ的mRNA表达水平，抑制脂质合成。沈欣等[31]进一步研究表明，COS通过抑制转移酶2（diacylgiycerol O-acyltransferase 2，DGAT2）、LXRα、PPARγ、孕烯醇酮X受体（pregnenolone X receptor，PXR）和分化簇36（cluster of differentiation 36，CD36）的mRNA和蛋白表达水平，减少FFA吸收及TG合成。

褐色脂肪（brown adipose tissue，BAT）在调节能量代谢和脂肪分解中发挥关键作用。研究表明[15-43]，COS通过激活 BAT中热生成基因解耦联蛋白1（uncoupling protein 1，UCP1）和PPARγ共激活因子1α（peroxiseome proliferator-activated receptor gamma coactivaror 1α，PGC- 1α）的表达，增强热生成能力，促进能量消耗并减少脂肪积累。

COS还通过信号通路进一步调节脂质代谢。研究表明COS可激活腺苷酸活化蛋白激酶（amp-activated protein kinase，AMPK）信号通路，增加ACC表达，减少脂肪合成并促进FFA氧化[37, 44-45]。Zhang等[42]研究发现COS通过抑制磷脂酰肌醇3-激酶（phosphatidylinositol 3-kinase，PI3K） /蛋白激酶B（protein kinase B，AKT）/哺乳动物雷帕霉素靶蛋白（mammalian target of rapamycin，mTOR）信号通路，减少脂肪生成和储存，改善脂质代谢。该通路在细胞增殖、代谢和生存调节中发挥重要作用，与MASLD的发病机制密切相关[46-48]。这些结果表明，COS不仅能在细胞水平抑制脂质的积累，还通过调控信号通路改善MASLD。

2.2 调节肠道菌群

肠道菌群是肠道微生态系统的重要组成部分，其基因数量远超宿主基因，能够编码多种降解酶，如胆汁酸水解酶和碳水化合物降解酶等，在宿主代谢、免疫调节及炎症应答中发挥关键作用。COS通过调节肠道菌群的丰度和结构，促进乳酸菌、双歧杆菌等有益菌增殖，同时抑制克雷伯氏菌等潜在致病菌的生长[49]。此外，COS通过调控短链脂肪酸（short-chain fatty acid，SCFA）及胆汁酸代谢，有助于缓解肝脏脂质蓄积和相关代谢紊乱[50-51]。

高脂高糖饮食（high-fat high-sugar diet，HFHSD）可导致肠道菌群多样性下降，并增加有害菌的相对丰度，引发肠屏障受损和全身代谢紊乱，这一肠道菌群失调现象与MASLD发生和发展密切相关[52-53]。多项研究表明，COS通过改善肠道菌群结构和多样性，促进有益菌如乳酸菌、双歧杆菌的增殖，同时抑制克雷伯氏菌和Mucispirillum等潜在有害菌的生长，从而恢复肠道微生态平衡[54-56]。此外，COS还可下调厚壁菌门和拟杆菌门（firmicutes/bacteroidetes，F/B）比值，进一步纠正肠道菌群失衡。并通过上调紧密连接蛋白（如ZO-1和Claudin-1）的表达，增强肠道屏障功能，降低肠道内脂多糖（lipolysaccharide，LPS）透过血液循环的风险，进而缓解肝脏脂质积累和炎症反应[15, 54-55]。

SCFA是肠道菌群的重要代谢产物，主要包括乙酸、丙酸和丁酸，对维持肠道稳态、调节能量代谢、改善免疫功能以及降低血脂水平发挥重要作用，与MASLD的病理调控密切相关。HFHSD引起的肠道菌群失调常导致SCFA水平下降，削弱肠道屏障功能，加剧肝脏脂质过度蓄积 [57-59]。研究表明COS干预可显著提升SCFA水平，尤其是丁酸水平，增强肠上皮细胞的氧化磷酸化活性，激活AMPK/PPARγ信号通路，促进肝脏脂肪酸β氧化，缓解肝脏脂肪蓄积[15, 42, 55-60]。此外，SCFA还能调节炎症反应，降低促炎因子（如白细胞介素-6（interleukin-6，IL-6）、肿瘤坏死因子-α（tumor necrosis factor-α，TNF-α）水平，进而减轻MASLD引发的炎症[54-60]。COS在调节肠道菌群结构的同时，还可影响菌群-免疫互作网络，最新研究发现[61]，COS干预可以减少白色念珠菌等条件致病真菌的丰度，恢复肠道菌群稳态，并促进巨噬细胞由促炎性M1型向抗炎性M2型极化协同调控免疫反应，进一步遏制MASLD进展。

2.3 调控炎症反应

炎症反应是MASLD向MASH进展的关键驱动因素。COS通过调控炎症信号通路，抑制肝脏慢性炎症反应[27, 62-63]。

在MASLD患者中，肠道屏障功能受损导致LPS进入血液，并通过激活肝脏中的Toll样受体4（Toll-like receptor 4，TLR4），诱导LPS/TLR4/NF-κB炎症通路，促使肝细胞和免疫细胞释放促炎因子，如TNF-α、白细胞介素-1β（interleukin-1β，IL-1β）和IL-6，从而加剧炎症反应[63-65]。Feng等[55]研究表明，COS能够在HFHSD诱导MASLD小鼠中调控LPS/TLR4/NF-κB炎症通路，抑制炎症信号传导，减轻肝脏的炎症反应。Wang[66]及Qian等 [15]的研究进一步表明，COS通过抑制NF-κB炎症通路，可降低TNF-α、IL-6和IL-1β等炎症因子的水平，从而缓解肝脏炎症反应。此外，COS还通过激活核因子E2相关因子2（nuclear factor erythroid 2-related factor 2，Nrf-2）抗氧化信号通路，增强肝脏的抗氧化能力，缓解氧化应激对肝脏的损害。综上所述，COS通过抑制LPS/TLR4/NF-κB通路和降低TNF-α、IL-6和IL-1β炎症因子水平，同时通过激活Nrf-2信号通路增强抗氧化能力，缓解肝脏炎症反应，改善MASLD。

2.4 缓解氧化应激

氧化应激是MASLD发展中的关键病理机制之一。ROS是氧化代谢的中间产物，其平衡由抗氧化和氧化系统共同维持[67]。过量的TG、TC和FFA会加速ROS的生成，导致肝脏氧化应激和脂质过氧化，进而损伤肝细胞并加剧炎症反应和肝纤维化，促进MASLD的进展[37, 68-69]。肝脏是ROS生成的主要场所，也是其主要作用靶点[70]。总超氧化物歧化酶（total superoxide dismutase，T-SOD）、谷胱甘肽过氧化物酶（glutathione peroxidase，GSH-PX）和过氧化氢酶（catalase，CAT）是关键抗氧化酶，在维持肝脏氧化还原平衡中发挥重要作用。T-SOD是清除ROS的关键酶，其活性在ROS过度积累时降低，导致肝细胞损伤加重[71]。GSH-Px是内源性抗氧化系统的重要组成部分，可通过消除ROS缓解肝脏氧化应激[72]。CAT可通过催化过氧化氢分解为水和氧，减少ROS的积累，从而保护肝细胞免受氧化应激损伤[73]。Qian等[15]研究发现，COS干预可提高MASLD小鼠肝脏中T-SOD和GSH-Px的活性，并降低丙二醛（malondialdehyde，MDA）水平。MDA是脂质过氧化的标志物，其升高反映脂质过氧化加剧。COS的抗氧化作用可减少脂质过氧化对肝细胞的损伤，缓解肝脏氧化应激。Li等[38]研究也进一步证实，COS增加了FFA刺激的HepG2细胞中T-SOD、GSH-Px和CAT等抗氧化酶的活性，从而缓解了肝脏氧化应激。

Nrf2/抗氧化反应元件（antioxidant response element，ARE）信号通路是宿主抗氧化反应的关键调控通路之一。Nrf2是抗氧化基因表达的主要调控因子。在氧化应激条件下，Nrf2从细胞质转位至细胞核，与ARE结合，促进抗氧化基因的表达，增强宿主抗氧化能力[74]。Tao等[75]研究表明COS可通过上调抗氧化酶的基因表达缓解肝脏氧化应激，同时激活Nrf2通路增强肝脏的抗氧化防御。以上研究表明COS通过提高T-SOD、GSH-PX和CAT等关键抗氧化酶的活性，并激活Nrf2/ARE通路，增强肝脏抗氧化防御，改善MASLD。

2.5 改善IR

IR导致肝脏对胰岛素反应能力下降，引起葡萄糖和脂质代谢紊乱，导致肝脏脂肪积累[76- 78]。研究表明，COS在改善IR具有显著作用[79]。刘永健[56]通过HFHSD诱导的MASLD小鼠模型发现，COS能改善小鼠的IR及高血糖状态，恢复代谢平衡。MASLD通常伴随慢性炎症，肝脏内NF-κB信号通路的激活会加剧IR。研究发现，COS通过抑制NF-κB炎症信号的传导，减少TNF-α、IL-6等促炎因子的释放，缓解炎症并改善IR[75, 80]。COS可通过激活AMPK通路改善能量代谢。AMPK是能量代谢的关键调控因子，能量不足时被激活，可促进脂肪酸氧化，抑制脂质生成并增加葡萄糖的摄取[80-81]。在MASLD发展过程中，沉默信息调节因子2相关酶1（silent information regulator factor 2 related enzyme 1，SIRT1）的表达与IR密切相关。Veličković等[82]研究表明，高糖饮食喂养9周的大鼠，NF-κB和c-Jun氨基末端激酶（c-Jun N-terminal kinase，JNK）通路被激活，同时α-AMPK/AMPK降低，SIRT1表达增加，胰岛素敏感性下降。COS通过调节AMPK通路抑制SIRT1表达，减少炎症信号传导，恢复胰岛素的敏感性。此外，COS还可调控胰岛β细胞的丝裂原活化蛋白激酶（mitogen-activated protein kinase，MAPK）和PI3K/AKT信号通路 ，促进胰岛素基因表达与分泌，提高胰岛素敏感性，缓解IR，改善肝脏及全身代谢紊乱[43-83]。COS改善MASLD的作用机制图见图1。

综上，COS作为多功能天然活性物质，展现出多通路协同调控潜力，具体见图2。AMPK作为核心能量感应器，在COS刺激下被激活，既能调控mTOR信号，抑制脂质生成与异常细胞代谢，又能通过抑制SREBP-1c活性，进一步减少FFA合成与TG积累。同时COS还可激活PI3K/Akt信号通路，增强胰岛素敏感性，AMPK和PI3K/AKT信号通路二者在改善肝脏代谢紊乱呈正协同关系。COS还通过促进肠道有益菌增值，增加丁酸等SCFAs产生产量，进一步通过“肠道菌群-SCFA-AMPK轴”持续激活AMPK信号通路，这一调控轴不仅改善脂代谢，还能降低炎症反应，形成正向调节回路。在炎症调节方面，COS激活AMPK可间接抑制TLR/NF-κB通路，降低促炎因子水平，同时激活Nrf2/ARE通路，增强抗氧化防御系统。COS通过AMPK为核心枢纽，协调调控多条关键通路，减轻MASLD进展。

• 
  图1 COS改善MASLD的作用机制

  Figure 1.Mechanism of Action of in COS Ameliorating MASLD

  注：↑表示激活/上调，↓表示抑制/下调。

  

• 
  图2 多通路协同改善MASLD作用机制图

  Figure 2.Schematic illustration of the mechanism of multi-channel synergy for enhancing MASLD performance

  

3 结语

目前针对MASLD的治疗，现有的治疗方式尚未取得满意疗效[84]。寻找新的治疗突破口是现阶段面临的重大挑战，COS作为一种天然多糖，通过大量体内外实验，对缓解MASLD具有良好的效果，可以通过抑制脂质生成、调节肠道菌群、调控炎症反应和缓解氧化应激，并可以通过改善IR从而发挥降脂作用。

与现有NASLD治疗策略相比，COS在作用机制展现出多靶点协同优势。GLP-1受体主要通过增强肠促胰岛素信号，改善葡萄糖代谢与控制体重，间接降低肝脂，但胃肠道不良反应发生率高，且患者耐受性较差[85-86]；FXR激动剂则通过调控胆汁酸及脂质代谢发挥作用，但易引发血脂异常[87]；PPAR激动剂可通过促进脂肪酸氧化及抗炎通路干预MASLD进程，研究显示其可降低肝脏硬度，但对脂肪含量改善有限，且存在心血管负荷增加风险[88]。COS在动物模型中可降低肝脂30%~50%，在脂质代谢方面具有可比性[89-92]。同时，COS在抗炎、抗氧化和肠道微生物调节方面显示出更广泛的生物学活性，且在目前的动物研究中未见明显毒性，具有良好的发展前景[93]。然而，目前COS对缓解MASLD的研究仍有许多问题和挑战亟待解决。一是COS的临床转化仍面临一系列关键挑战，COS的生物利用度较低，且受分子量和脱乙酰度的影响明显，须通过纳米载体、缓释制剂等技术优化其体内稳定性和生物可利用性。二是用于MASLD的临床使用案例较少，仍局限于体外细胞研究和动物实验，缺乏系统的人体剂量探索与长期安全性评估，需要开展多中心、随机对照临床研究，明确MASLD人群的有效剂量、安全范围与治疗窗口。三是COS治疗MASLD脂质代谢、改善IR和减少炎症反应中的分子机制尚未完全阐明，尤其是对关键信号通路如AMPK、SREBP-1/PPARs等以及与其他代谢调节因子之间的相互作用的研究尚未完全清晰，治疗靶点尚未明确，未来研究应进一步解析其具体分子机制，特别是AMPK、Nrf2等信号通路的作用靶点，同时研究不同信号通路之间的相互作用。四是目前大多数COS相关研究仍以整体MASLD作为研究对象，对不同病程阶段（如单纯性脂肪肝、代谢相关性脂肪肝炎及肝纤维化/肝硬化）的靶向作用机制研究较为欠缺。考虑到MASLD具有明确的疾病进展过程，各阶段在病理机制、治疗敏感性及干预目标上均存在差异，未来研究应加强分期分型机制探索，明确COS在不同MASLD阶段的作用特点、分子靶点及潜在效益，以期为制定更精准、个体化的干预策略提供理论支持。

综上所述，COS作为一种多靶点天然活性物质，在缓解MASLD方面具有良好的研究基础和发展潜力。未来需在分子机制解析、剂型优化及临床验证方面进一步推进，特别关注其在MASLD不同进展阶段的靶向差异，为MASLD的精准治疗提供新思路。

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