A model-based approach to assess the exposure-response relationship of Lorenzo's oil in adrenoleukodystrophy.

ABSTRACT

AIMS: X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder, most commonly affecting boys, associated with increased very long chain fatty acids (C260) in all tissues, causing cerebral demyelination and adrenocortical insufficiency. Certain monounsaturated long chain fatty acids including oleic and erucic acids, known as Lorenzo's oil (LO), lower plasma C260 levels. The aims of this study were to characterize the effect of LO administration on plasma C260 concentrations and to determine whether there is an association between plasma concentrations of erucic acid or C260 and the likelihood of developing brain MRI abnormalities in asymptomatic boys. METHODS: Non-linear mixed effects modelling was performed on 2384 samples collected during an open label single arm trial. The subjects (n = 104) were administered LO daily at ~2-3 mg kg(-1) with a mean follow-up of 4.88 ± 2.76 years. The effect of erucic acid exposure on plasma C260 concentrations was characterized by an inhibitory fractional Emax model. A Weibull model was used to characterize the time-to-developing MRI abnormality. RESULTS: The population estimate for the fractional maximum reduction of C260 plasma concentrations was 0.76 (bootstrap 95% CI 0.73, 0.793). Our time-to-event analyses showed that every mg l(-1) increase in time-weighted average of erucic acid and C260 plasma concentrations was, respectively, associated with a 3.7% reduction and a 753% increase in the hazard of developing MRI abnormality. However, the results were not significant (P = 0.5344, 0.1509, respectively). CONCLUSIONS: LO administration significantly reduces the abnormally high plasma C260 concentrations in X-ALD patients. Further studies to evaluate the effect of LO on the likelihood of developing brain MRI abnormality are warranted.