肥胖性铁缺乏/缺铁性贫血的病因机制及干预措施研究

Obese children are at greater risk of iron deficiency (ID) or iron deficiency anemia(IDA) and with decreased response to oral iron therapy, mainly due to intestinal iron absorption being inhibited by the elevated systemic hepcidin in obesity. Hence, it is of great importance to clarify the reason why obese individuals have higher circulating hepcidin concentrations. It has been well established that the normal cause of obesity involves leptin resistance, and the elevated plasma hepcidin levels are positively correlated with leptin levels in obese people. Our initial research found that leptin administration down-regulates hepcidin expression in mice liver in vivo, possibly through activating nuclear transcription factors Egr1(early growth response factor 1)、AP1(activator protein 1) and HIF1α(hypoxia inducible factor 1-α)to enhancing the production of GDF15 and TMPRSS6, the negative regulators of hepcidin gene expression. Hence we hypothesized that leptin may be involved in the regulation of intestinal iron absorption by restricting the expression level of liver hepcidin, and that malabsorption of iron and the resulting iron deficiency or iron deficiency anemia in obesity may be caused by leptin resistance under which leptin has little or no effect on controlling hepcidin expression with the result that plasm hepcidin concentration increased. This programme focused on verifying these hypotheses by means of animal experiments and human clinical trials. For animal testing, the wild-type C57BL/6J mice and the leptin-deficient ob/ob mice will be used to establish animal models of:(ⅰ)obesity with leptin resistance, (ii)obesity without leptin resistance and (iii) non-obese leptin resistance.The effects of leptin and leptin resistance on hepcidin gene expression in vivo and the molecular pathways involved be analysed, the animals' iron absorption capacity be evaluated as well.For clinical study, 300 children with simple obesity will be enrolled into a randomized, double-blind, controlled trial to investigate the effects of acupuncture on decreasing leptin resistance and hepcidin levels. Through carrying out this research programme, it is expected that a substantive progress in the understanding of etiology of obesity-induced ID/IDA will be achieved.

肥胖儿童易患铁缺乏甚至贫血，主要由于其铁调素水平升高抑制铁的吸收所致。因此阐明肥胖引起铁调素升高的机理是有效防治肥胖性铁缺乏之关键。已知瘦素抵抗是肥胖发生的基本原因，而肥胖者血铁调素水平与瘦素抵抗程度正相关。我们初步研究发现瘦素注射可抑制铁调素基因表达,并可能是通过激活转录因子Egr1、AP1、HIF1α继而诱导铁调素负性调节子GDF15、TMPRSS6生成增加来实现的。据此本项目提出瘦素抵抗致铁调素升高和铁吸收障碍假说，认为体内存在瘦素-铁调素调节系统以约束铁调素水平保障铁吸收，在肥胖并瘦素抵抗情况下，瘦素通过上述途径维持铁调素稳态作用减弱或消失，导致铁调素升高。为验证该假说，拟通过野生型C57小鼠和瘦素缺失的ob/ob小鼠建立肥胖并瘦素抵抗、肥胖无瘦素抵抗和非肥胖瘦素抵抗动物模型，并通过针刺改善肥胖儿童瘦素抵抗和铁吸收效应的随机对照试验,对肥胖诱发铁缺乏的病因机制及干预措施进行深入探析

肥胖动物和人铁缺乏（ID）或缺铁性贫血（IDA）的发生率高于正常体重者，并且这种肥胖性ID/IDA对于补铁治疗的效果较差，其原因是肥胖者肠道铁吸收下降。本项目利用C57BL/6J小鼠和瘦素缺陷型ob/ob小鼠，建立肥胖并瘦素抵抗、肥胖无瘦素抵抗、非肥胖瘦素抵抗动物模型，结合外源性瘦素刺激干预，运用Western blot和免疫组化等方法，研究肥胖性ID/IDA发生的原因及分子机制，并通过人体针灸减肥随机对照临床试验，探讨针刺减肥对肥胖性ID/IDA的辅助治疗作用及机理。研究发现：（1）肥胖性铁吸收障碍的发生环节可能在于肠粘膜细胞铁的释放障碍，是由于脂肪源性铁调素（hepcidin）分泌增多诱使十二指肠膜铁转运蛋白（ferroportin）表达减少所致。（2）瘦素具有调节（促进）铁吸收作用，其机理可能与抑制铁调素基因表达有关。铁调素作为肠铁吸收的关键负性调节因子，其表达受到多种转录因子的精密调控，瘦素可能通过激活转录因子AP-1（C-JUN）而促进GDF15表达增加，后者抑制铁调素基因表达。肥胖状态下存在有瘦素抵抗，导致瘦素诱导的AP-1和GDF15表达下降，抑制铁调素效应减弱而致铁调素升高，铁吸收减少。（3）持续高瘦素刺激并不能引发瘦素抵抗，提示肥胖状态下的高瘦素水平应是瘦素抵抗的结果，而不是瘦素抵抗发生的原因。肥胖性瘦素抵抗的特征主要是瘦素的PI3K/Akt信号通路活性受抑制，而抑制蛋白PTP1B是其中主要的作用因子，肥胖状态下PTP1B表达量增高。（4）针灸具有改善肥胖性铁吸收不良的作用，增强口服铁剂对于肥胖性ID/IDA的治疗效果，其机理可能与改善肥胖患者的瘦素抵抗及瘦素-铁调素调节系统的作用有关，因此，针刺减肥可作为肥胖性ID/IDA的一种有效的辅助治疗措施。本项目的这些研究结果对于肥胖性ID/IDA的防治具有学术理论价值和实践应用意义。