A novel dual-epitope ELISA reveals heterogeneity of circulating lipoprotein lipase: distinguishing intact LPL from total LPL

BACKGROUND: Conventional immunoassays measure total circulating lipoprotein lipase (LPL) but do not distinguish molecular species retaining both terminal regions. We developed a dual-epitope E LISA that measures LPL simultaneously recognized through defined N- and C-terminal epitopes, operationally termed "intact LPL." METHODS: The F1A/R23B ELISA was evaluated using recombinant full-length LPL, analytical validation, immunoblotting, reciprocal immunoprecipitation-immunoblotting, post-heparin kinetics, LPL activity measurements, and ex vivo tetrahydrolipstatin treatment. Clinical analyses included healthy volunteers (n = 19), patients with multifactorial chylomicronemia syndrome (MCS; n = 170), and patients with GPIHBP1 autoantibody syndrome (n = 17). RESULTS: The assay showed a detection limit of 0.01 ng/mL, good dilutional linearity, and intra- and inter-assay coefficients of variation below 7%. An approximately 55-kDa plasma species was recognized through both terminal regions, whereas 30-35-kDa N-terminal-reactive species demonstrated molecular heterogeneity. Intact LPL represented a minority of total LPL immunoreactivity and broadly paralleled LPL activity after heparin administration in two individuals. In healthy participants, intact LPL and the intact-to-total LPL ratio decreased significantly. In MCS, pancreatitis history was associated with higher triglyceride (TG)/intact LPL ratios, although intact LPL alone did not differ significantly. Patients with GPIHBP1 autoantibody syndrome had markedly reduced intact LPL concentrations and intact-to-total LPL ratios. CONCLUSIONS: The F1A/R23B ELISA distinguishes an LPL species retaining both antibody-defined terminal regions from conventional total LPL immunoreactivity. These findings demonstrate biochemical heterogeneity of circulating LPL under the specific experimental and clinical conditions examined in this study. Prospective studies are required to establish the incremental clinical value of intact LPL measurement.