Gutiérrez José María, Rucavado Alexandra, Escalante Teresa, Díaz Cecilia
Instituto Clodomiro Picado, Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica.
Toxicon. 2005 Jun 15;45(8):997-1011. doi: 10.1016/j.toxicon.2005.02.029. Epub 2005 Apr 18.
Zinc-dependent metalloproteinases are responsible for the hemorrhagic activity characteristic of viperid snake venoms. Snake venom metalloproteinases (SVMPs) are classified in various groups (P-I-IV), according to their domain composition. P-III SVMPs, comprising metalloproteinase, disintegrin-like and cysteine-rich domains, exert more potent hemorrhagic activity than P-I SVMPs, which present only the metalloproteinase domain. SVMPs degrade various components of the basement membrane and are also able to hydrolyze endothelial cell membrane proteins, such as integrins and cadherins, involved in cell-matrix and cell-cell adhesion. In addition, disintegrin-like and cysteine-rich domains interact with endothelial cell integrins, interfering with their adhesion to extracellular matrix. Hemorrhage induced by SVMPs is an extremely rapid event in vivo, with capillary endothelial cells showing drastic structural alterations within few minutes. In contrast, observations in cell culture conditions do not evidence such rapid endothelial cell damage. Instead, the main effect is detachment and rounding of these cells; it is only after several hours of incubation that cells show evidence of apoptotic damage. This apparent discrepancy between in vivo and in vitro observations can be explained if biophysical forces operating on microvessels in vivo are taken into consideration. It is proposed that SVMP-induced hemorrhage occurs in vivo by a 'two-step' mechanism. Initially, SVMPs degrade basement membrane and adhesion proteins, thus weakening the capillary wall and perturbing the interactions between endothelial cells and the basement membrane. Then, transmural pressure acting on the weakened capillary wall causes distention. As a consequence, endothelial cells become very thin, until the integrity of the capillary wall is lost at some points, where extravasation occurs. In addition, endothelial cells become more susceptible to blood flow-dependent shear stress, which further contributes to capillary wall disruption.
锌依赖性金属蛋白酶是蝰蛇科蛇毒出血活性的关键因素。蛇毒金属蛋白酶（SVMPs）根据其结构域组成可分为不同类别（P-I-IV）。P-III类SVMPs包含金属蛋白酶、解整合素样和富含半胱氨酸结构域，其出血活性比仅含金属蛋白酶结构域的P-I类SVMPs更强。SVMPs可降解基底膜的各种成分，还能水解参与细胞-基质和细胞-细胞黏附的内皮细胞膜蛋白，如整合素和钙黏蛋白。此外，解整合素样和富含半胱氨酸结构域与内皮细胞整合素相互作用，干扰其与细胞外基质的黏附。在体内，SVMPs诱导的出血是一个极其迅速的过程，几分钟内毛细血管内皮细胞就会出现剧烈的结构改变。相比之下，在细胞培养条件下的观察并未发现如此迅速的内皮细胞损伤。相反，主要影响是这些细胞的脱离和变圆；只有在孵育数小时后，细胞才会出现凋亡损伤的迹象。如果考虑到体内微血管上作用的生物物理力，就可以解释体内和体外观察结果之间的这种明显差异。有人提出，SVMPs诱导的出血在体内是通过“两步”机制发生的。首先，SVMPs降解基底膜和黏附蛋白，从而削弱毛细血管壁，扰乱内皮细胞与基底膜之间的相互作用。然后，作用于薄弱毛细血管壁的跨壁压力导致扩张。结果，内皮细胞变得非常薄，直到毛细血管壁在某些点失去完整性，发生渗漏。此外，内皮细胞对血流依赖性剪切应力变得更加敏感，这进一步导致毛细血管壁破坏。
