CONFORMATIONAL CHANGES IN PRORENIN DURING RENIN INHIBITION IN VITRO AND IN VIVO AS ASSESSED BY A CHEMOLUMINESCENCE IMMUNOASSAY: PP.24.469

Abstract

We have previously shown that the renin inhibitor, aliskiren, induce changes in the conformation of prorenin in vitro and influence the quantification of active renin by the Cisbio and the Nichols immunoradiometric assays. The difference between the two assays depended on incubation time in vitro. Objective: to test whether such phenomenon occurs with a shorter incubation time (30–40 min) using the chemoluminescence DiaSorin Liaison® immunoassay by comparison to the Cisbio assay (3 h incubation). Methods: Immunoreactive active renin concentrations were measured 1) in plasma samples taken from 5 healthy subjects incubated with aliskiren 10 nM to 1 mM in vitro for < 1 h and 24 h (DiaSorin) and for 3 h and 24 h (Cisbio), and 2) in plasma samples collected in a single oral dose crossover study comparing aliskiren (300 mg) and valsartan (160 mg), in 16 normotensive subjects. Results: Aliskiren added to plasma samples in vitro increased active renin immunoreactivity in both assays. The increase was significant from 10 μM aliskiren onwards (+107% [95%CI:39;208] in the DiaSorin assay and +183% [95%CI:42;465] in the Cisbio assay, p < 0.0001) and reached +144% (95%CI:64;263) and +246.8% (95%CI:74;592) at 1 mM aliskiren, respectively. 24 h incubation amplified the magnitude of the phenomenon which started to be significant at lower aliskiren concentration (100 nM) in both assays. In the crossover study, the two assays gave similar values for plasma active renin concentration before treatment and following valsartan administration (intraclass coefficient for agreement between the 2 assays:0.84 [95%CI:0.60;0.94]). However, a Bland-Altman plot showed a systematic bias towards higher values (1.76 times higher [95% CI:1.66;1.87]) in the DiaSorin than in the Cisbio assay following aliskiren administration. Conclusion: Even with a short incubation time, aliskiren at high concentration interfere with the recognition of active renin molecules by the monoclonal antibodies used in the DiaSorin assay. Careful consideration must be given to the methodology used for quantifying immunoreactive plasma active renin when patients are treated with aliskiren.