Apolipoprotein A1 levels and its association with NS1 in the pathogenesis of acute dengue

Background The dengue NS1 antigen is a secretory protein and was shown to associate with apolipoprotein A1 (ApoA1). Therefore, we sought to investigate the changes in ApoA1 levels in patients with varying severity of acute dengue and then proceeded to investigate how ApoA1 and NS1 interactions affect cytokine production from primary human monocytes. Methodology/Principal Findings Serial measurements of ApoA1, viral loads, NS1 antigen levels and lipid profiles were done in adult patients with dengue fever (DF= 21) and dengue haemorrhagic fever (DHF =28). To investigate the effect of ApoA1-NS1 interactions in cytokine production from primary human monocytes, cells were harvested from healthy individuals (n=6) and co-cultured with varying concentrations of ApoA1 and levels of IL-6 and TNF-α measured in culture supernatants. The ApoA1 levels were significantly lower in patients with DHF on day 5 of illness (p=0.04) compared to those with DF. ApoA1 levels did not show any correlation with either the NS1 antigen levels or the viral loads in patients with DF or DHF, although they did significantly and inversely correlate with liver transaminases, AST (Spearmans R=-0.55, p <0.0001) and ALT (Spearmans R=-0.49, p<0.0001) in patients with DF. However, a significant correlation was not seen between ApoA1 levels and AST levels (Spearmans R=-0.45, p=0.09) in patients with DHF and ALT levels (Spearman’s R=0.0.5, p=0.64). HDL and LDL levels were significantly lower on day 5 of the illness in patients with DHF compared to those with DF. Co-culture of NS1 and ApoA1 resulted in an increased IL-6 production (but not TNFα) in culture supernatants in a dose dependent manner. Conclusions/Significance HDL, LDL and ApoA1 levels were significantly lower in those who have severe dengue, especially in the critical phase and ApoA1 levels inversely correlated with the extent of rise in liver enzymes. While co-culture of ApoA1 with NS1 in primary human monocytes induced high IL-6 levels in a dose dependent manner, this was not seen for TNFα suggesting that the interaction of ApoA1 with NS1 could give rise to different outcomes. Author summary The dengue NS1 antigen is a secretory protein and was shown to associate with apolipoprotein A1 (ApoA1). Therefore, we sought to investigate the changes in ApoA1 levels in patients with varying severity of acute dengue and then proceeded to investigate how ApoA1 and NS1 interactions affect cytokine production from primary human monocytes. Serial measurements of ApoA1, viral loads, NS1 antigen levels and lipid profiles were done in adult patients with dengue fever (DF) and dengue haemorrhagic fever (DHF). HDL, LDL and ApoA1 levels were significantly lower in those who have severe dengue, especially in the critical phase and ApoA1 levels inversely correlated with the extent of rise in liver enzymes. While co-culture of ApoA1 with NS1 in primary human monocytes induced high IL-6 levels in a dose dependent manner, this was not seen for TNFα, suggesting that the interaction of ApoA1 with NS1 could give rise to different outcomes. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement We are grateful to the Centre for Dengue Research, and the UK Medical Research Council for funding. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Not Applicable The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval was obtained by the Ethics Review Committee of the Faculty of Medical Sciences, University of Sri Jayewardenepura. All patients and healthy individuals were recruited following informed written consent. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Not Applicable I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Not Applicable I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Not Applicable All relevant data are within the manuscript and its Supporting Information files.