武汉云克隆科技股份有限公司

Abstract:

Background:

Physical frailty and loss of mobility in elderly individuals lead to reduced independence, quality of life, and

increased mortality. Vitamin B12 deficiency has been linked to several age-related chronic diseases, including in the

musculo-skeletal system, where vitamin B12 deficiency is generally believed to be linked to poor nutritional intake. In the present study, we asked whether aging and frailty associate with altered vitamin B12 homeostasis in humans and investigated the underlying molecular mechanisms using preclinical models.

Methods:

We analysed a subset of the Singapore Longitudinal Aging Study and stratified 238 participants based on age

and Fried frailty criteria. Levels of methyl-malonic acid (MMA), a marker for vitamin B12 deficiency, and amnionless, the vitamin B12 co-receptor that anchors the vitamin B12 transport complex to the membrane of epithelial cells, were measured in plasma. In addition, vitamin B12 levels and the molecular mechanisms of vitamin B12 uptake and excretion

were analysed in ileum, kidney, liver, and blood using a rat model of natural aging where nutritional intake is fully

controlled.

Results:

We demonstrate that aging and frailty are associated with a higher prevalence of functional vitamin B12 deficiency

that can be detected by increased levels of MMA in blood (ρ = 0.25; P = 0.00013). The decline in circulating vitamin B12 levels is recapitulated in a rat model of natural aging where food composition and intake are stable. At the molecular level, these perturbations involve altered expression of amnionless in the ileum and kidney. Interestingly, we demonstrate that amnionless can be detected in serum where its levels increase during aging in both rodents and human (P = 3.3e-07 and 9.2e-07, respectively). Blood amnionless levels negatively correlate with vitamin B12 in rats (r 2 = 0.305; P = 0.0042) and positively correlate with the vitamin B12 deficiency marker MMA in humans (ρ = 0.22; P = 0.00068).

Conclusions :

Our results demonstrate that aging and frailty cause intrinsic vitamin B12 deficiencies, which can occur

independently of nutritional intake. Mechanistically, vitamin B12 deficiency involves the physio-pathological decline of both the intestinal uptake and the renal reabsorption system for vitamin B12. Finally, amnionless is a novel biomarker which can detect perturbed vitamin B12 bioavailability during aging and physical frailty.

摘要：

目的：

身体虚弱、丧失行动能力的老年人的独立性和生活质量降低、死亡率升高。维生素B12缺乏症与几种年龄相关的慢性疾病有关，包括肌肉—骨骼系统，此系统中，维生素B12缺乏症通常被认为与营养不良有关。在本研究中，我们探究衰老和虚弱是否与人体内维生素B12稳态改变有关，并利用临床前模型探讨其潜在的分子机制。

方法：

我们分析了新加坡纵向老龄化研究的一个子集，并根据年龄和虚弱标准对238名参与者进行了分层。血浆中甲基丙二酸(MMA)水平可作为维生素B12缺乏症的标志，无羊膜蛋白是维生素B12的共受体，它将维生素B12转运复合物锚定在上皮细胞膜上。此外，采用完全控制营养摄入的自然衰老大鼠模型分析回肠、肾脏、肝脏和血液中维生素B12水平与维生素B12摄取和排泄的分子机制。

结果：

我们发现衰老和虚弱与功能性维生素B12缺乏症的较高患病率有关，可以通过血液中MMA水平的增加来检测功能性维生素B12缺乏症（ρ=0.25；P=0.00013）。在食物组成和摄取量稳定的自然衰老的大鼠模型中循环维生素B12水平下降。在分子水平上，这些微扰包括回肠和肾脏无羊膜蛋白的表达改变。有趣的是，我们发现在老鼠和人类的血清中，老化过程中无羊膜含量都会增加（P=3.3e-07和9.2e-07）。大鼠血液中无羊膜蛋白水平与维生素B12呈负相关（r 2 = 0.305；P = 0.0042），人血液中无羊膜蛋白水平与维生素B12缺乏标志物MMA呈正相关（ρ= 0.22；P = 0.00068）。

结论：

结果表明衰老和脆弱导致内在维生素B12缺乏与营养摄入无关。维生素B12缺乏症包括维生素B12肠道摄取和肾再吸收系统的生理病理下降。最后，无羊膜蛋白可以作为一种新的生物标记，在衰老和虚弱时检测维生素B12的生物利用度。

使用试剂原文信息：AMN measurements in human serum were performed by sandwich Enzyme-Linked Immunosorbent Assay (Cloud-Clone Corp. #SEC295Hu).