Expression of Nitric Oxide Synthase and Nitric Oxide Levels in Peripheral Blood Cells and Oxidized Low-Density Lipoprotein Levels in Saliva as Early Markers of Severe Dengue

Abstract

Background. Severe dengue (SD), experienced by only a fraction of dengue patients, can be lethal. Due to the lack of early markers that can predict the evolution of SD, all dengue patients have to be monitored under hospital care. We discovered early oxidative stress markers of SD to identify patients who can benefit from early intervention before the symptoms appear. Methods. The expression of inducible nitric oxide synthase (iNOS) in peripheral blood cells (PBC), nitric oxide (NO), and oxidized low-density lipoprotein (oxLDL) levels in plasma and saliva collected at early stages of dengue infection from 20 nonsevere dengue fever (DF) patients and 20 patients who later developed SD were analyzed in a retrospective nested case-control study. Results. The expression of iNOS is significantly ( $P<0.05$ ) lower in patients who developed SD than in DF patients at admission within 4 days from fever onset. Median plasma NO concentration within 4 days from fever onset is also significantly ( $P<0.05$ ) lower in patients who developed SD ( $17.9\pm 1.6\mu \text{mol}/\text{L}$ ) than DF ( $23.0\pm 2.1\mu \text{mol}/\text{L}$ ). Median oxLDL levels in plasma within 3 days from fever onset is significantly ( $P<0.05$ ) lower in patients who developed SD ( $509.4\pm 224.1\text{ng}/\text{mL}$ ) than DF ( $740.0\pm 300.0\text{ng}/\text{mL}$ ). Median salivary oxLDL levels are also significantly ( $P<0.05$ ) lower in patients who developed SD ( $0.8\pm 0.5\text{ng}/\text{mL}$ ) than DF ( $3.6\pm 2.6\text{ng}/\text{mL}$ ) within 4 days from fever onset. Conclusions. These findings suggest that the expression of iNOS (73% sensitivity, 86% specificity) and plasma NO (96% sensitivity, 61% specificity at 22.3 μmol/L; $P<0.05$ ) may serve as early markers of SD within 3 days from fever onset. Salivary oxLDL levels may serve as early noninvasive markers of SD with a sensitivity and specificity, respectively, of 57% and 91% at 0.9 ng/mL; 76% and 55% at 2.3 ng/mL; and 100% and 50% at 4.6 ng/mL ( $P<0.05$ ) within 4 days from fever onset.