A New Enzyme Immunoassay for the Quantitative Determination of Classical Autotaxins (ATXα, ATXβ, and ATXγ) and Novel Autotaxins (ATXδ and ATXε).

Background: Autotaxin (ATX) is a secreted enzyme that converts lysophosphatidylcholine to lysophosphatidic acid, a potent bioactive lipid mediator, through its lysophospholipase D activity. Although five alternative splicing isoforms of ATX have been identified as ATXα, ATXβ, ATXγ, ATXδ, and ATXε and the expression patterns of each isoform differ among several tissues, the clinical significance of each isoform remains to be elucidated.

Methods: Anti-ATXβ and anti-ATXδ monoclonal antibodies were produced by immunization with recombinant human ATXβ and ATXδ expressed using a baculovirus system, respectively. We then developed enzyme immunoassays to measure the serum concentrations of "classical ATX" (ATXα, ATXβ, and ATXγ) and "novel ATX" (ATXδ and ATXε) antigens and evaluated the usefulness of these assays using human serum samples.

Results: The with-run and between-run precision, interference, detection limit, and linearity studies for the present assay were well validated. In healthy subjects, the serum concentrations of classical ATX and novel ATX were significantly (P < 0.01) higher in women than in men, while the ratios of classical ATX or novel ATX to total ATX were not different between women and men. The concentrations of both classical ATX and novel ATX in normal pregnant subjects and patients with chronic liver diseases or follicular lymphoma were significantly higher than those in healthy subjects, while the ratio of both ATX isoforms to total ATX did not vary among these groups.

Conclusions: We have developed a new enzyme immunoassay to determine the concentrations of classical ATX and novel ATX in human serum. These assays may be helpful for elucidating the distinct functional roles of each ATX isoform, which are largely unknown at present.