Early detection and prognosis of CM patients with a higher risk for fatal outcome is necessary for better clinical case management and improvement of treatment outcome. It is anticipated that a better understanding of mechanisms contributing to CM-associated death will help in the development of novel adjunctive therapies to reduce mortality associated with CM. Currently there is no reliable biological test that can predict CM or its associated complications, including mortality and post recovery neurological deficits. This study reveals that in Indian CM patients ANG-2 and ANG-2/ANG-1 ratios had high levels of sensitivity and specificity (area under the ROC curve close to 1) in discriminating CMNS from MM patients. However, ANG-2 levels differentiated CMNS from CMS with high sensitivity, but moderate levels of specificity.
Other studies demonstrated ANG-1 as a good biomarker in differentiating CM from MM among Thai adults, but not in Ugandan children . Yeo et al. reported that ANG-2 is a better marker of severe malaria associated deaths than lactate in Indonesian adults . Among Ugandan children higher levels of ANG-1 were found to be associated with a reduced risk of death . However, in our study population ANG-1 levels were not good prognostic indicators by themselves in as much as this study observed a decrease in ANG-1 levels with disease severity. Interestingly, in a recent study conducted with Malawian children, ANG-1 levels were significantly down regulated among CM patients with retinopathy compared to those without retinopathy, uncomplicated malaria patients and those with non-malarial encephalopathy . It is thought that differences in the epidemiology of malaria between Asia and Africa, genetic differences in these two distinct populations and other factors (e.g. age, etc.) may explain these inconsistencies.
Consistent with earlier studies [15, 18, 20, 21, 24], this study highlight the potential involvement of ANG-1 and ANG-2 in the pathogenesis of CM in endemic setting of Central India. The breach of blood brain barrier is believed to be an important component in the pathogenesis of CM [25, 26] but a recent histologic study conducted in Vietnamese adults who died of CM did not support such a hypothesis . In the Vietnamese study, no significant correlation between vascular injury and death associated with CM was evident . Overall, these findings suggest pathogenesis of CM is multifactorial and complex .
Platelets and PMP were described to enhance PRBCs sequestration to EC and this is associated with accumulation of host inflammatory cells [12, 13]. Resultant inflammation may lead to CM pathology which may results in excess release of ANG-2 (from the Wiebel-Palade bodies) and loosening of endothelial tight junctions. vWF (mediate platelet/PRBCs sequestration) and IL-8 which are co-packed with ANG-2 are also seen elevated in severe malaria [12, 24].
Also angiogenic expression of molecules are variable among African CM children during acute and convalescence stages [18, 20, 27]. Interestingly platelet and infected red blood cells which adhere to brain endothelial cells and placenta during malarial pathology have recently been reported to alter gene expression of EC and syncytiotrophoblast respectively [29, 30]. This in-turn may result in EC apoptosis (via TNF, TGF-beta signaling) and inhibition of angiogenesis in placental pathology (via VEGF) [29, 30]. Thus studies related to histopathology of internal vital organs in addressing oedema and heamorrhages need to be done to better understand parasite- dependent host's pathogenic/protective pathways in CM.