Table 1.
Number of features retained throughout the successive data-processing steps for the different methodologies employed.
LC-MS based analyses were performed both in the positive and negative electrospray ionization mode (referred to as ESI+ and ESI-, respectively).
Fig 1.
Selection of biomarkers associated to onchocerciasis.
(A) Results for plasma lipids PI(16:0/14:0) and PC(12:0/14:0) in the different groups. (B) Results for plasma metabolites hypoxanthine and inosine in the different groups. (C) Results for urine metabolites cinnamoylglycine and hippuric acid in the different groups. All results are expressed in peak area. Abbreviations: NP: Nodule Positive; NEC: Non-Endemic Control; LF: Lymphatic Filariasis.
Table 2.
Comparison between untargeted and targeted analysis of candidate biomarkers.
Correlation curves were prepared on log-transformed data based on peak area from the untargeted analysis (X) and concentration (ng/mL) of the targeted analysis (Y) and correlation coefficients (r2) were calculated. Based on the data of the targeted analysis, ROC analysis was performed with NP and NEC as cases and controls, respectively and AUC was calculated.
Fig 2.
Validation of biomarkers associated to onchocerciasis.
Results for the three new biomarkers (plasma hypoxanthine and inosine; and urine CCG) and for NATOG that have been obtained on the nodule positive individuals (NP, blue), endemic controls (EC, purple), LF patients (LF, green), non-endemic controls (NEC, red) and healthy controls from Belgium (HC, orange). For each plot, the grey zone indicates the zone between limit of detection (LOD) and limit of quantification (LOQ), the dashed line indicates the biomarker-specific cutoff and the yellow zone indicates the zone between 0.5 log times the cut-off and the maximum value observed for the specific biomarker. In case of NATOG, the cutoff (4.63 μg/mL = 13 μM) and maximum value (98.3 μg/mL = 276 μM) was derived from the data published by Globisch and colleagues [27]. NATOG data were previously obtained on the same sample set (doi: 10.1186/s13071-016-1582-6) [28]. For each marker, the percentage of positive samples in the group considered to be infected (i.e. sensitivity) and the percentage of negative samples in the group considered to be not infected (i.e. specificity), is indicated. For CCG and NATOG, which are onchocerciasis specific biomarkers, the LF group was plotted separately from the other control samples to highlight specificity.
Table 3.
Diagnostic characteristics of the biomarkers, as determined on the validation sample set.
Sensitivity for filarial markers was based on NP, LF and EC, while specificity was based on NEC and HC. For onchocerciasis markers, sensitivity was based on NP and EC, with specificity based on NEC, HC and LF.
Fig 3.
Levels of plasma hypoxanthine, plasma inosine, and urine CCG in a non-endemic population from Kenya, compared to the positive and negative population from the validation study.
The dashed lines indicate the biomarker-specific cutoffs. The percentage of positive samples in each group is indicated as well as P-value of Chi square analysis for each metabolite comparing the Kenyan population with the negative and positive validation set, respectively.
Fig 4.
The percentage of individuals that were urine CCG positive stratified according to their peptide serology status OvMP-1, OvMP-23 and OvNMP-48 [39].
Red bars indicate number of samples positive for urine CCG, blue bars indicate number of samples negative for urine CCG. For each peptide the P-value of Chi square analysis is indicated.