研究背景与目的:

我国已成为世界上老龄化速度最快，老年人口最多的国家之一。老龄化问题给我国医疗保健带来了严峻的挑战。一直以来，炎症、氧化应激均为衰老研究中的热点。高糖状态时体内衰老加速，炎症、氧化应激水平增加，但当前机制未明。通过探索不同糖耐量水平人群中衰老标志物端粒长度（LTL）及线粒体拷贝数（mtDNAcn）的关联及炎症、氧化应激在两者作用中的影响，能够为糖代谢异常人群中衰老加速的机制提供新线索。糖化血红蛋白（HbA1c）对衰老疾病指示和预测能力近来出现争议。寻找新的评价糖代谢与衰老指标，有利于衰老的个性化管理。血红蛋白糖基化个体差异（即血红蛋白糖基化指数（HGI））是炎症及代谢疾病的预测指标之一。对HGI与衰老、炎症及氧化应激关系的研究，可为衰老研究管理提供新的便于监测的指标。饮食作为体内糖基化产物重要来源以及炎症、氧化应激的关键影响因素是延缓衰老的有效管理手段之一。但目前尚缺乏基于中国居民饮食习惯的膳食模型以评价膳食的炎症潜力及饮食与衰老的关联。本研究拟建立基于我国饮食习惯的经验性膳食炎症评价模型，并探索其与衰老的关联，为健康老龄化提供评价及管理的新思路。综上，本研究将从机制、标志物、膳食管理等多角度全面探索不同糖代谢状态人群中衰老与炎症、氧化应激的关系。

研究方法:

本研究人群来自“北京昌平农村社区2型糖尿病管理项目”的基线人群。通过调查问卷获取患者一般人口学资料，24小时回顾法收集饮食数据。采集空腹生化指标及HbA1c。进行75g口服葡萄糖耐量试验(OGTT)，采集0、30、60、120分钟血糖（PG）、胰岛素（INS）、C肽（C-P）。通过聚合酶链式反应测定确定端粒长度(LTL)和线粒体DNA拷贝数(mtDNAcn)。测量了肿瘤坏死因子α(TNFα)和白介素-6(IL-6)、8-羟基脱氧鸟苷(8-oxo-dG)、超氧化物歧化酶活力值(SOD活力值)和谷胱甘肽还原酶(GR)。

研究结果:

1.不同糖耐量水平人群中衰老标志物间的关系及炎症、氧化应激在其中的作用

共纳入450名研究对象，根据OGTT试验结果分为糖代谢正常（NGT，n=193）及糖代谢异常（AGM，n=257）组。Spearman相关分析显示LTL、mtDNAcn与TNFα、IL-6以及SOD活力值相关。糖代谢异常与短端粒对mtDNAcn减少呈现正向交互作用（S 1.14,95%CI(1.07,4.91)）。LTL与mtDNAcn在AGM组呈正相关（r=0.214，p=0.001），但在NGT组无显著相关性。线性回归校正炎症指标后，LTL与mtDNAcn的关联消失（p=0.087）。中介效应分析显示TNFα在LTL与mtDNAcn的关联中发挥完全中介效应。

2.血红蛋白糖基化个体差异与衰老及炎症、氧化应激的关联

共纳入434名研究对象。HGI为实测HbA1c和依据空腹血糖（FPG）预测的HbA1c之差。将研究对象按照HGI三分位进行分组。高HGI组LTL较短，TNFα、SOD活力值、HbA1c水平较高。相关性分析显示HGI独立于HbA1c，与LTL（r=-0.25，p<0.001）及TNFα（r=0.19，p<0.001）相关。HGI与mtDNAcn无统计学关联。利用多元线性回归分析校正混杂因素后，HGI（β=-0.238,p=0.015）和TNFα（β=-0.020，p<0.001）均与LTL关联。有序Logistics回归分析显示，低、中HGI组有更长LTL的可能性分别是高HGI组的5.29倍（OR 5.29,95%CI（2.45,11,41），p<0.001）和2.41倍(OR 2.41, 95% CI (1.35, 4.30),P =0.003)。中介效应分析显示TNFα在HGI与LTL的关系中发挥中介效应，其中介效应可达30.39%。

3.经验性炎症膳食模式与衰老及炎症、氧化应激的关系

共纳入388名研究对象。根据膳食调查问卷计算膳食平衡指数（DBI）相关指数、基于西方饮食的经验性炎症饮食指数（EDIP）。利用降秩回归(RRR)开发中国经验性炎症饮食指数（CEDII）。研究对象按照CEDII三分位进行分组。高CEDII组以精制谷物等碳水化合物及肉蛋类蛋白质高摄入，低脂肪摄入的饮食模式中TNFα、IL-6更高，LTL、mtDNAcn更低。相关性分析显示CEDII与TNFα（r=0.32，p<0.001）、IL-6（r=0.14，p=0.012）、SOD活力值（r=0.13，p=0.020）正相关，与LTL(-0.15, p=0.003)及mtDNAcn(r=-0.18,p<0.001)负相关。DBI衍生指数、EDIP与炎症及衰老指标无相关性。线性回归分析校正年龄、性别、糖脂代谢、能量摄入等混杂因素后CEDII与LTL（β=-0.332，p=0.024）及mtDNAcn（p=-0.072，p=0.026）仍呈负向关联。亚组分析表明在在糖脂代谢及高血压人群中高CEDII饮食，LTL缩短风险更高。

研究结论:

1.炎症和氧化应激在端粒和线粒体功能障碍中发挥重要作用。在糖耐量异常人群中观察到伴随端粒磨损，线粒体功能障碍加重。端粒-线粒体相互作用可能是糖耐量异常人群不同于糖耐量正常人的衰老机制之一。TNFα在其中发挥完全中介效应。

2.发现血红蛋白糖基化个体差异是独立于HbA1c的端粒磨损预测指标，HGI有望成为老龄化综合管理的评价指标之一。TNFα部分介导两者之间的关联。本研究并未发现HGI与mtDNAcn间的关联。

3.开发中国经验性炎症饮食模型。体内高炎症的膳食模式以精制谷物等碳水化合物及肉蛋类蛋白质高摄入，低脂肪摄入的为特征。反映炎症的膳食模式与衰老进程关联。在代谢异常人群中两者关联更明显。相比之下，DBI衍生指数、EDIP与炎症及衰老指标无相关性。CEDII对健康老龄化的综合管理具有一定指导意义。

本研究发现了糖耐量异常人群存在异常的端粒和线粒体的相互作用，提示了衰老加速的可能机制。证明了血红蛋白糖基化的个体差异与个体衰老关联，为评价衰老进程提供新的指标。建立了适用于我国评价膳食炎症潜力模型的，构建了膳食、炎症、衰老的桥梁，为衰老个性化管理提供了新策略。

Background:

China is rapidly transforming into an aging society and houses the largest elderly population in the world. The problem of ageing will inevitably give rise to formidable healthcare and socio-economic challenges. Recent studies have focused on the association of inflammation, oxidative stress and ageing. Type 2 diabetes mellitus(T2DM) is a leading risk factor for ageing and high levels of inflammation and oxidative stress. However, the underlying mechanisms are not well understood. This study evaluated the relationship between leukocyte telomere length (LTL) and mitochondrial DNA copy number (mtDNAcn) in subjects with different glucose tolerance statuses，in order to elucidate the underlying mechanisms of accelerated ageing in subjects with abnormal glucose metabolism. In addition, we investigated whether the indicators of oxidative stress and inflammation were involved and identified mediators among them. Hemoglobin A1c(HbA1c) is not consistently correlated with aging disorders in recent studies. Identification of a novel marker of glycemia and ageing will be useful. Interindividual differences in hemoglobin glycation（the hemoglobin glycation index（HGI））is correlated with inflammation and metabolic diseases. Thus, we also illustrated links between HGI and aging biomarkers, and explored the potential role of inflammation and oxidative stress in the correlations, in an effort to provide a potential indicator of ageing. Diet patterns contribute to advanced glycation end products (AGEs) and therefore increase inflammation and oxidative stress, which might be effective strategies for improvement in ageing. This study sought to develop a Chinese empirical dietary inflammatory index(CEDII) that assesses Chinese diet quality based on its inflammatory potential and examine whether the index was associated with an accelerated aging process，in order to provide intervention strategies for mitigating the health burden in aging societies. This study will illustrate the correlation of inflammation, oxidative stress and ageing from perspectives of mechanism, monitoring and treatment strategies.

Methods:

This study was a community-based cross-sectional study that was conducted in the Nankou community of Changping, Beijing. Dietary intake was collected based on 24-h dietary recalls. Participants performed a standardized 75 g oral glucose tolerance test (OGTT), and the levels of plasma glucose（PG）, insulin（INS） and C-peptide（C-P） were measured at fasting and at 30,60 and 120 minutes. LTL and mtDNAcn were determined by polymerase chain reaction assay. Tumor necrosis factor α(TNFα) and interleukin-6(IL-6), 8-oxo-2'-deoxyguanosine (8-oxo-dG), superoxide dismutase (SOD) activities, and glutathione reductase (GR) were measured.

Result:

1. Interaction between telomeres and mitochondria in subjects with different glucose tolerance statuses, and the roles of inflammation and oxidative stress in the relationship.

A total of 450 subjects were included and divided into two groups according to a 75g OGTT: the abnormal glucose metabolism (AGM, n = 257) group and the normal glucose tolerance (NGT, n = 193) group. LTL and mtDNAcn were both inversely related to TNFα, IL-6, and SOD activity. Interaction between glucose metabolism and telomere length on mtDNAcn was significant（S 1.14,95%CI(1.07,4.91)）. In the AGM, LTL was correlated with mtDNAcn (r =0.214, p =0.001), but no correlation was found in the NGT. The association between LTL and mtDNAcn was weakened after adjusting for inflammatory factors in the AGM (p=0.087) according to linear regressions. Mediation analysis demonstrated that TNFα was a significant mediator in the telomere-mitochondrial interactome in the AGM.

2. Associations of HGI, ageing, inflammation and oxidative stress

A total of 434 subjects were included. The HGI was calculated as the difference between the measured and predicted hemoglobin A1c (HbA1c). The population was categorized into tertiles of the HGI. Participants in the high HGI group reported a shorter LTL, higher levels of TNFα, SOD activities, and HbA1c. Correlation analyses demonstrated that HGI was correlated with LTL (r =-0.25, P <0.001) and TNFα (r = 0.19, P <0.001) regardless of HbA1c levels. No relationship was found between HGI and mtDNAcn. HGI (β =-0.238, p=0.015) and TNFα (β = -0.020, P <0.001) were proved to be correlated with LTL independently, using multiple linear regression analysis. Ordinal logistic regression models showed that compared with subjects of the high HGI group, the possibility of a higher-level LTL was 5.29-fold in the low HGI group (OR 5.29, 95% CI (2.45, 11.41), P <0.001), 2.41-fold in the moderate HGI group (OR 2.41, 95% CI (1.35, 4.30), P =0.003) after controlling for confounding variables. Mediation analyses indicated that TNFα accounted for 30.39% of the effects of the HGI on LTL.

3. Associations of diet patterns, aging, inflammation and oxidative stress.

A total of 388 subjects were enrolled. the Chinese Diet Balance Index（DBI）and its derivatives, as well as the empirical dietary inflammatory pattern (EDIP) based on the western diet, were calculated for assessing dietary quality in different aspects. Chinese empirical dietary inflammatory index(CEDII) was derived using reduced-rank regression(RRR) according to Chinese diet patterns. The population was categorized into tertiles of the CEDII. High CEDII group was characterized by high intakes of refined grains, red meat and eggs, and less intakes of fat. This pattern predicted higher levels of TNFα, IL-6, shorter LTL and less mtDNAcn. CEDII was positively related to TNFα（r=0.32，p<0.001）, IL-6（r=0.14，p=0.012） and SOD activities（r=0.13，p=0.020）, but negatively associated with LTL(-0.15, p=0.003) and mtDNAcn(r=-0.18,p<0.001). Neither  DBI nor EDIP was correlated with biomarkers of inflammation or ageing. High CEDII scores were associated with short LTL and decreased mtDNAcn using multivariate linear regression with adjustment for age, sex, HbA1c, lipid profiles, and daily energy intake. The stratified analysis demonstrated that the high CEDII group had an increased risk of short LTL in subjects with abnormal glucose, lipid and blood pressure.

Conclusion:

1. Inflammation and oxidative stress may play vital roles in telomere shortening and mitochondrial dysfunction. The article suggested for the first time that there was a significant positive correlation between LTL and mtDNAcn in the subjects with hyperglycemia, which might be a potential mechanism for accelerated aging of the AGM. The relationship was completely mediated by TNFα.

2. HGI was negatively related to telomere attrition, independent of HbA1c, which indicated that HGI might be a predictor of ageing. TNFα acted as a mediator of the relationship between HGI and LTL. No correlation between HGI and mtDNAcn was found.

3. We developed a Chinese empirical dietary inflammatory index(CEDII). Dietary pattern high in refined grains, red meat and eggs, and low in fat, was associated with higher proinflammatory potential. High CEDII scores were correlated with an increased risk of ageing. Compared with indexes related to DBI and EDIP, CEDII was much more effective to assess inflammation and ageing potential of diet patterns.

This study was the first to report the abnormal interaction between telomeres and mitochondria in people with abnormal glucose tolerance, indicating a potential mechanism of accelerated aging. In this article, individual differences in hemoglobin glycation were originally demonstrated to be correlated with ageing as a new marker. It was the first time to establish a model for evaluating dietary inflammation of Chinese dietary patterns, which built a bridge between diet, inflammation and aging, and provided a new strategy for individualized management of ageing.