Research Article: Platelet Activating Factor Contributes to Vascular Leak in Acute Dengue Infection

Date Published: February 3, 2015

Publisher: Public Library of Science

Author(s): Chandima Jeewandara, Laksiri Gomes, N. Wickramasinghe, Danuta Gutowska-Owsiak, Dominic Waithe, S. A. Paranavitane, N. L. A. Shyamali, Graham S. Ogg, Gathsaurie Neelika Malavige, Aravinda M de Silva. http://doi.org/10.1371/journal.pntd.0003459

Abstract: BackgroundAlthough plasma leakage is the hallmark of severe dengue
infections, the factors that cause increased vascular permeability have not been identified. As platelet activating factor (PAF) is associated with an increase in vascular permeability in other diseases, we set out to investigate its role in acute dengue infection.Materials and MethodsPAF levels were initially assessed in 25 patients with acute dengue infection to determine if they were increased in acute dengue. For investigation of the kinetics of PAF, serial PAF values were assessed in 36 patients. The effect of dengue serum on tight junction protein ZO-1 was determined by using human endothelial cell lines (HUVECs). The effect of dengue serum on and trans-endothelial resistance (TEER) was also measured on HUVECs.ResultsPAF levels were significantly higher in patients with acute dengue (n = 25; p = 0.001) when compared to healthy individuals (n = 12). In further investigation of the kinetics of PAF in serial blood samples of patients (n = 36), PAF levels rose just before the onset of the critical phase. PAF levels were significantly higher in patients with evidence of vascular leak throughout the course of the illness when compared to those with milder disease. Serum from patients with dengue significantly down-regulated expression of tight junction protein, ZO-1 (p = 0.004), HUVECs. This was significantly inhibited (p = 0.004) by use of a PAF receptor (PAFR) blocker. Serum from dengue patients also significantly reduced TEER and this reduction was also significantly (p = 0.02) inhibited by prior incubation with the PAFR blocker.ConclusionOur results suggest the PAF is likely to be playing a significant role in inducing vascular leak in acute dengue infection which offers a potential target for therapeutic intervention.

Partial Text: Dengue is thought to infect 390 million individuals per year resulting in approximately 96 million clinically apparent infections[1]. The annual burden of dengue has been estimated to be 750,000 disability adjusted life years (DALYs)[2] which is higher than the global burden of 17 other disease conditions, including upper respiratory tract infections, hepatitis and Japanese Encephalitis[3]. It has been declared a priority infection by the WHO, UNICEF and World Bank[4]. Currently there are no effective antiviral drugs to treat acute infection, nor a licensed vaccine to prevent infection.

In the initial phase of the study, 25 adult patients with clinical features suggestive of dengue infection, admitted to a general medical ward in a tertiary care hospital (Colombo South Teaching Hospital) in Colombo during the year 2013, were enrolled following informed written consent. 16 of these patients developed DHF and 9 had DF. 12 dengue-seropositive healthy individuals were also recruited for the initial assays of lipid mediators.

Serum samples for analysis of PAF, PAF-AH and soluble PAF-Receptor was obtained on day 5–6 of illness. In the initial analysis of all 25 patients with acute dengue infection and healthy individuals, PAF levels were significantly higher in patients (p = 0.002) when compared to healthy individuals. Although not significant (p = 0.15), PAF levels were higher in patients with DHF (median 335.2, Inter quartile range 4.7 to 443.1 ng/ml) when compared to those with DF (median 47.63, IQR 0 to 111.6 ng/ml) (Fig. 1A). Since high PAF values could be either due to increased production or reduced breakdown, we also analysed PAF—acetyl hydrolase (PAF-AH) levels in these patients. PAF-AH is the enzyme that breaks down PAF [26]. PAF-AH levels have been shown to be low in some diseases such as asthma and anaphylaxis and thus thought to contribute to disease pathogenesis by reduced breakdown of PAF [27,28]. We found that PAF-AH levels were significantly higher (p<0.0001) in patients with acute dengue when compared to healthy individuals. The PAF-AH levels were significantly higher (p = 0.01) in those with DHF (median 112.6, IQR 88.35 to 151.1 ng/ml) when compared to those with DF (median 85.35, IQR 73.2 to 98.3 ng/ml) (Fig. 1B) suggesting that high PAF values were not due to reduced breakdown of PAF. We also assessed soluble PAF-Receptor levels in serum and found that there was no difference in PAF-R levels in patients with acute dengue or in healthy individuals (Fig. 1C). In this study we have investigated the role of PAF as a mediator of vascular leak in acute dengue infection. We found that PAF levels were significantly elevated in patients with dengue infection, as well as its principle breakdown enzyme PAF-AH, which suggested that the increase in PAF was likely due to increased production rather than reduced breakdown. We also found that PAF levels were significantly higher in patients with DHF throughout the course of the acute disease when compared to those with DF, although huge inter-individual variations in PAF levels were observed. PAF has been shown to be important in vascular leak in dengue mice models and PAFR−/− mice were shown to have milder clinical disease [21]. The role of PAF in human dengue infection has only been investigated in the context of in vitro studies where mononuclear leucocytes of dengue immune donors were found to produce more PAF than non-immune donors [29]. Source: http://doi.org/10.1371/journal.pntd.0003459

 

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