RAGE modulatory effects on cytokines network and histopathological conditions in malarial mice

Highlights

• Survival of malarial mice did not improved prior to RAGE-related drugs treatment.

• Parasitaemia levels in malarial mice were reduced upon RAGE-related drugs treatment.

• RAGE-related drugs treatment modified cytokine network.

• RAGE-related drugs treatment improved histological conditions in malarial mice.

Abstract

This study was aimed at investigating the involvement of Receptor for Advanced Glycation End Products (RAGE) during malaria infection and the effects of modulating RAGE on the inflammatory cytokines release and histopathological conditions of affected organs in malarial animal model. Plasmodium berghei (P. berghei) ANKA-infected ICR mice were treated with mRAGE/pAb and rmRAGE/Fc Chimera drugs from day 1 to day 4 post infection. Survival and parasitaemia levels were monitored daily. On day 5 post infection, mice were sacrificed, blood were drawn for cytokines analysis and major organs including kidney, spleen, liver, brain and lungs were extracted for histopathological analysis. RAGE levels were increased systemically during malaria infection. Positive correlation between RAGE plasma concentration and parasitaemia development was observed. Treatment with RAGE related drugs did not improve survival of malaria-infected mice. However, significant reduction on the parasitaemia levels were recorded. On the other hand, inhibition and neutralization of RAGE production during the infection significantly increased the plasma levels of interleukin (IL-4, IL-17A, IL-10 and IL-2) and reduced interferon (IFN)-γ secretion. Histopathological analysis revealed that all treated malarial mice showed a better outcome in histological assessment of affected organs (brain, liver, spleen, lungs and kidney). RAGE is involved in malaria pathogenesis and targeting RAGE could be beneficial in malaria infected host in which RAGE inhibition or neutralization increased the release of anti-inflammatory cytokines (IL-10 and IL-4) and reduce pro-inflammatory cytokine (IFNγ) which may help alleviate tissue injury and improve histopathological conditions of affected organs during the infection.

Introduction

Malaria is a blood borne disease caused by intracellular parasites belonging to the Plasmodium genus (Yotoko and Elisei, 2006). Until now, there are five Plasmodium species responsible for malaria infection in human viz P. falciparum, P. ovale, P. vivax, P. malariae, and P. knowlesi (Singh et al., 2004; Singh and Daneshvar, 2013). An estimation of more than 216 million cases and 445,000 deaths were recorded in 2016 due to malaria infection with 99% of deaths caused by P. falciparum. Most of malaria cases occur in African regions, followed by Southeast Asia and the Eastern Mediterranean regions, with children aged less than 5 years are prone to this parasitic infection (WHO, 2016).

Briefly, the pathogenesis of the malaria begins with the invasion of host cells by the parasite, followed by continuous multiplication and proliferation of parasites in the host causing cerebral malaria or severe anaemia in humans (Miller et al., 1994). Cerebral malaria (CM) is a life-threatening encephalopathy, caused by P. falciparum. It is characterized by sequestration and cytoadhesion of parasitized red blood cells (PRBC), within the microvasculature, and accompany with elevated release of cytokines, mainly pro-inflammatory cytokines (Clark and Rockett, 1994; Artavanis-Tsakonas and Riley, 2002).

One the most severe pathogenesis of malaria is inflammation, in which exacerbation of inflammatory response elicited towards parasite invasion can lead to malaria susceptibility, severe immunopathological conditions, septic shock and multi organ failure due to end organ damage (Plebanski and Hill, 2000). High levels of pro-inflammatory cytokines followed by hyper-inflammation seen in multiple organs such as brain, kidneys, lungs, spleen and livers were closely linked with the development of severe malaria (Lyke et al., 2004; Artavanis-sakonas et al., 2003). Hence, an appropriate immunomodulator which can reduce and limit the exaggeration immune response production is believed to reduce the mortality and morbidity of malaria infection.

The receptor for advanced glycation end-products (RAGE) is a cellular receptor which belongs to the immunoglobulin superfamily. It has a variable (V-type) and two constant (C-type) immunoglobulin-like domains. RAGE is usually found at low levels in normal adult cells and tissues involved in the innate immune system viz endothelial cells, monocytes, neutrophils, macrophages, T and B lymphocytes and dendritic cells (Bierhaus et al., 2006; Chen et al., 2004; Moser et al., 2007). RAGE is imperative in the regulation of innate immunity by inducing the Th-1 type response and involved in the signal transduction from pathogen substrates to cell activation during the onset and perpetuation of inflammation. Blocking of RAGE signal transduction pathway for example, increased the survival of animals in experimental sepsis (Wang et al., 1999; Yang et al., 2004). Besides that, inhibition of RAGE signaling also decreased inflammatory responses in infectious models of diseases such as E. coli and S. pneumonia (van Zoelen et al., 2009). In addition, a review by Chuah et al. (2013) suggests that targeting RAGE might help curbing the hyper-inflammatory responses that occur in many inflammation-associated conditions (Chuah et al., 2013).

Accumulating evidence have shown that the host immune response to malaria infection is often characterized by dominant pro-inflammatory responses and Th1 cell development (Stevenson and Riley, 2004; Riley et al., 2006). The mechanism to eliminate parasitized cells is mediated by pro-inflammatory cytokines and Th1-like cellular responses are necessary in clearance of malarial parasites (Artavanis-Tsakonas and Riley, 2002). Notably, previous studies on murine models and human T cells reported that RAGE appears to be implicated in activation and differentiation of T cells (Chen et al., 2008; Akirav et al., 2012). These results are consistent with a more recent study which further described the role of RAGE in modulating T cell responses following immune activation (Akirav et al., 2014). However, the role of RAGE on the course of malaria infection still remains obscure and needs to be investigated. Hence, in this study, we attempt to investigate the involvement of RAGE during malaria infection and the effects of its inhibition and neutralization on the inflammatory cytokines release and histopathological conditions during the infection to further elucidate its role in the pathogenesis of malaria. With all the previous accumulated evidence on the role and importance of RAGE in immune system regulation during pathological conditions, we believe that RAGE may involve and play important roles during malaria infection and modulating its release and production would produce positive outcomes in the infected host.