Department of Medicine, University of California, San Diego, California, United States of America.
Department of Cellular & Molecular Medicine, Glycobiology Research and Training Center, University of California, San Diego, California, United States of America.
PLoS One. 2018 Jun 18;13(6):e0197464. doi: 10.1371/journal.pone.0197464. eCollection 2018.
N-glycolylneuraminic acid (Neu5Gc) is a non-human red-meat-derived sialic acid immunogenic to humans. Neu5Gc can be metabolically incorporated into glycan chains on human endothelial and epithelial surfaces. This represents the first example of a "xeno-autoantigen", against which circulating human "xeno-autoantibodies" can react. The resulting inflammation ("xenosialitis") has been demonstrated in human-like Neu5Gc-deficient mice and contributed to carcinoma progression via antibody-mediated inflammation. Anti-Neu5Gc antibodies have potential as biomarkers for diseases associated with red meat consumption such as carcinomas, atherosclerosis, and type 2 diabetes.
ELISA assays measured antibodies against Neu5Gc or Neu5Gc-glycans in plasma or serum samples from the Nurses' Health Studies, the Health Professionals Follow-up Study, and the European Prospective Investigation into Cancer and Nutrition, including inter-assay reproducibility, stability with delayed sample processing, and within-person reproducibility over 1-3 years in archived samples. We also assessed associations between antibody levels and coronary artery disease risk (CAD) or red meat intake. A glycan microarray was used to detected antibodies against multiple Neu5Gc-glycan epitopes. A nested case-control study design assessed the association between total anti-Neu5Gc antibodies detected in the glycan array assay and the risk of colorectal cancer (CRC).
ELISA assays showed a wide range of anti-Neu5Gc responses and good inter-assay reproducibility, stability with delayed sample processing, and within-person reproducibility over time, but these antibody levels did not correlate with CAD risk or red meat intake. Antibodies against Neu5Gc alone or against individual Neu5Gc-bearing epitopes were also not associated with colorectal cancer (CRC) risk. However, a sialoglycan microarray study demonstrated positive association with CRC risk when the total antibody responses against all Neu5Gc-glycans were combined. Individuals in the top quartile of total anti-Neu5Gc IgG antibody concentrations had nearly three times the risk compared to those in the bottom quartile (Multivariate Odds Ratio comparing top to bottom quartile: 2.98, 95% CI: 0.80, 11.1; P for trend = 0.02).
Further work harnessing the utility of these anti-Neu5Gc antibodies as biomarkers in red meat-associated diseases must consider diversity in individual antibody profiles against different Neu5Gc-bearing glycans. Traditional ELISA assays for antibodies directed against Neu5Gc alone, or against specific Neu5Gc-glycans may not be adequate to define risk associations. Our finding of a positive association of total anti-Neu5Gc antibodies with CRC risk also warrants confirmation in larger prospective studies.
N-羟乙酰神经氨酸（Neu5Gc）是一种非人类红肉衍生的唾液酸，对人类具有免疫原性。Neu5Gc 可以代谢掺入到人类内皮细胞和上皮细胞表面的聚糖链中。这代表了第一个“异种自身抗原”的例子，针对该抗原，循环中的人类“异种自身抗体”可以发生反应。在类似人类的 Neu5Gc 缺陷型小鼠中已经证明了由此产生的炎症（“异种唾液炎”），并且通过抗体介导的炎症促进了癌的进展。抗-Neu5Gc 抗体具有作为与红肉消费相关疾病（如癌、动脉粥样硬化和 2 型糖尿病）的生物标志物的潜力。
ELISA 检测法测量了来自护士健康研究、健康专业人员随访研究和欧洲前瞻性癌症与营养研究的血浆或血清样本中针对 Neu5Gc 或 Neu5Gc-聚糖的抗体，包括检测内的重现性、延迟样本处理的稳定性以及在 1-3 年内存档样本中的个体内重现性。我们还评估了抗体水平与冠状动脉疾病（CAD）风险或红肉摄入量之间的关联。使用聚糖微阵列检测针对多种 Neu5Gc-聚糖表位的抗体。巢式病例对照研究设计评估了聚糖阵列测定中检测到的总抗-Neu5Gc 抗体与结直肠癌（CRC）风险之间的关联。
ELISA 检测法显示出广泛的抗-Neu5Gc 反应和良好的检测内重现性、延迟样本处理的稳定性以及随时间的个体内重现性，但这些抗体水平与 CAD 风险或红肉摄入量无关。针对 Neu5Gc 本身或针对单个 Neu5Gc 结合表位的抗体也与结直肠癌（CRC）风险无关。然而，唾液酸聚糖微阵列研究表明，当组合所有 Neu5Gc-聚糖的总抗体反应时，与 CRC 风险呈正相关。与最低四分位相比，总抗-Neu5Gc IgG 抗体浓度处于最高四分位的个体的风险几乎增加了三倍（最高四分位与最低四分位相比的多变量优势比：2.98，95%置信区间：0.80，11.1；趋势 P 值=0.02）。
为了将这些抗-Neu5Gc 抗体作为红肉相关疾病的生物标志物加以利用，进一步的工作必须考虑针对不同 Neu5Gc 结合聚糖的个体抗体谱的多样性。针对 Neu5Gc 本身或针对特定 Neu5Gc-聚糖的传统 ELISA 检测法可能不足以确定风险关联。我们发现总抗-Neu5Gc 抗体与 CRC 风险呈正相关，这一发现也需要在更大的前瞻性研究中得到证实。
