Pa. Haughan et al., EFFECTS OF AN AZASTEROL INHIBITOR OF STEROL 24-TRANSMETHYLATION ON STEROL BIOSYNTHESIS AND GROWTH OF LEISHMANIA-DONOVANI PROMASTIGOTES, Biochemical journal, 308, 1995, pp. 31-38
Leishmania donovani promastigotes were cultured in the presence of an
azasterol (20-piperidin-2-yl-5 alpha-pregnane-3 beta,20-diol) to deter
mine the effects on sterol biosynthesis and cell proliferation. Inhibi
tion of growth increased gradually with azasterol concentrations up to
5 mu g/ml; concentrations of azasterol exceeding 5 mu g/ml were letha
l, Sterol biosynthesis was affected by the azasterol when administered
at concentrations as low as 100 pg/ml. The primary site of action was
the alkylation at C-24 of a Delta(24)-sterol precursor. The 24-alkyla
ted sterols [ergosta-5,7,24(24(1))-trien-3 beta-ol and ergosta-5,7,22-
trien-3 beta-ol] of the protozoan were replaced by Delta(24)-cholesta-
type sterols which then accumulated in the cells, Administration of th
e azasterol together with a bis-triazole inhibitor of the 14 alpha-met
hylsterol 14-demethylase reaction, which operates in sterol biosynthes
is, resulted in depletion of 24-alkylsterols and their replacement wit
h predominantly 14 alpha-methylsterols lacking a 24-alkyl group. Conti
nuous subculture of promastigotes in the presence of the azasterol res
ulted in gradual depletion of 24-alkylsterols and their complete repla
cement by Delta(24)-cholesta-type sterols. Transfer of the azasterol-t
reated cells to medium lacking azasterol resulted in a gradual restora
tion, after several subcultures, of the normal 24-alkylsterol pattern.
The results indicate that, although 24-alkylsterols are normally prod
uced by the protozoan, it can nevertheless survive with sterols posses
sing only the cholestane skeleton. Thus there is no absolute requireme
nt for 24-alkylsterols to fulfil some essential 'sparking' role associ
ated with cell growth in promastigotes.