Metabolite interpretation
Potential metabolites (M1 to M13) identified from the
MetabolitePilotTM software (Sciex) are reported inTable 1 . The molecular ions that were detected in negative
controls (including 0-minute incubations, negative co-factor controls,
and negative ivermectin controls) were excluded from the list.
Percentage scores were based on three parameters including mass
accuracy, mass defect (Sleno, 2012; Zhang et al., 2009), and MS/MS
spectrum (for details see supplementary material). Chemical structures
and biotransformation sites of the metabolites (M1 to M13) were
interpreted based on two fragment ions for IVM-B1a, m/z
307.2 and 551.3. IVM-B1a metabolites without ion m/z
307.2 indicated that biotransformation occurred in the spiroketal. The
presence of ion m/z 307.2 without ion m/z 551.3 indicated that
biotransformation occurred in the cyclohexene cyclic ether, and
metabolites with changed molecular ions with presence of both ions m/z
307.2 and 551.3 indicated that biotransformation occurred in the
disaccharide moiety. Identical results were observed for
IVM-B1b metabolites, but with ions m/z 293.2 and 537.3.
Interpretations of M1 to M13 are detailed in Table 2. The
60-min microsome reactions for pure IVM-B1a and
IVM-B1b substrates confirmed an identical transformation
pattern of both compounds (Tables S1 ).