Department of Pediatrics, Eastern Virginia Medical School, Norfolk, VA, USA.
J Transl Med. 2012 Mar 5;10:35. doi: 10.1186/1479-5876-10-35.
Diabetic patients are at increased risk for bacterial infections; these studies provide new insight into the role of the host defense complement system in controlling bacterial pathogens in hyperglycemic environments.
The interactions of complement C3 with bacteria in elevated glucose were assayed for complement activation to opsonic forms, phagocytosis and bacterial killing. C3 was analyzed in euglycemic and hyperglycemic conditions by mass spectrometry to measure glycation and structural differences.
Elevated glucose inhibited S. aureus activation of C3 and deposition of C3b and iC3b on the bacterial surface. S. aureus-generated C5a and serum-mediated phagocytosis by neutrophils were both decreased in elevated glucose conditions. Interestingly, elevated glucose increased the binding of unactivated C3 to S. aureus, which was reversible on return to normal glucose concentrations. In a model of polymicrobial infection, S. aureus in elevated glucose conditions depleted C3 from serum resulting in decreased complement-mediated killing of E. coli. To investigate the effect of differing glucose concentration on C3 structure and glycation, purified C3 incubated with varying glucose concentrations was analyzed by mass spectrometry. Glycation was limited to the same three lysine residues in both euglycemic and hyperglycemic conditions over one hour, thus glycation could not account for observed changes between glucose conditions. However, surface labeling of C3 with sulfo-NHS-biotin showed significant changes in the surface availability of seven lysine residues in response to increasing glucose concentrations. These results suggest that the tertiary structure of C3 changes in response to hyperglycemic conditions leading to an altered interaction of C3 with bacterial pathogens.
These results demonstrate that hyperglycemic conditions inhibit C3-mediated complement effectors important in the immunological control of S. aureus. Mass spectrometric analysis reveals that the glycation state of C3 is the same regardless of glucose concentration over a one-hour time period. However, in conditions of elevated glucose C3 appears to undergo structural changes.
糖尿病患者发生细菌感染的风险增加；这些研究为宿主防御补体系统在控制高血糖环境中的细菌病原体方面的作用提供了新的见解。
在高葡萄糖环境中，检测补体 C3 与细菌的相互作用，以评估补体向调理形式的激活、吞噬作用和细菌杀伤作用。通过质谱分析在正常血糖和高血糖条件下的 C3，以测量糖基化和结构差异。
高葡萄糖抑制金黄色葡萄球菌激活 C3 和 C3b 和 iC3b 在细菌表面的沉积。在高葡萄糖条件下，金黄色葡萄球菌产生的 C5a 和血清介导的中性粒细胞吞噬作用均降低。有趣的是，高葡萄糖增加了未激活的 C3 与金黄色葡萄球菌的结合，在恢复正常葡萄糖浓度时这种结合是可逆的。在混合细菌感染模型中，高葡萄糖条件下的金黄色葡萄球菌从血清中耗尽 C3，导致补体介导的大肠杆菌杀伤减少。为了研究不同葡萄糖浓度对 C3 结构和糖基化的影响，用质谱分析了在不同葡萄糖浓度下孵育的纯化 C3。在 1 小时内，糖基化仅限于正常血糖和高血糖条件下的三个赖氨酸残基，因此糖基化不能解释两种葡萄糖条件之间的变化。然而，用 sulfo-NHS-biotin 对 C3 进行表面标记显示，随着葡萄糖浓度的增加，C3 的七个赖氨酸残基的表面可及性发生了显著变化。这些结果表明，C3 的三级结构在高血糖条件下发生变化，导致 C3 与细菌病原体的相互作用发生改变。
这些结果表明，高血糖条件抑制了 C3 介导的补体效应物，这些效应物在金黄色葡萄球菌的免疫控制中很重要。质谱分析显示，在 1 小时的时间内，无论葡萄糖浓度如何，C3 的糖基化状态都是相同的。然而，在高血糖条件下，C3 似乎发生了结构变化。
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