Background and Objective: It is generally accepted that the inhibition
of sebum excretion has a predictive value for anti-acne activity, Whe
reas oral 13-cis-retinoic acid (13-cis-RA) decreases sebum excretion,
it has not been shown so far if oral all-trans-retinoic acid (tretinoi
n, tRA) does so, The aim of this exploratory study was to investigate
the effect of oral tRA on the sebum excretion rate (SER) in young male
subjects. Methods: 12 healthy volunteers with a baseline SER above 1.
0 mu g/cm(2)/min were treated with 20 mg/day tRA for 4 weeks, The SER
was measured at weeks 2 and 4, Adverse reactions were recorded. Result
s: The mean SER varied from 1.56 at baseline to 1.65 at week 2 and to
1.49 mu g/cm(2)/min at week 4. Comparison with values obtained in the
same subjects previously treated with either 13-cis-RA or 9-cis-retino
ic acid indicated that tRA less sebosuppressive. Mucocutaneous reactio
ns and headache were the most frequent side effects of oral tRA. Concl
usion: The lack of effect on the SER suggests that oral tRA would prob
ably be ineffective against acne, The fact that, of the three isomers
tested, only 13-cis-RA (which does not bind to nuclear receptors) show
s activity may suggest that sebosuppression is not nuclear receptor me
diated. We discuss other hypotheses related to pharmacokinetics.