Abstract
A series of 17 proanthocyanidins and structurally related compounds was tested for activity against Leishmania donovani amastigotes and promastigotes in vitro. Most of the polyphenols significantly inhibited the intracellular survival of L. donovani amastigotes (EC50 0.8—10.6 nM) when compared with the antileishmanial drug Pentostam® (EC50 10.6 nM), but all were inactive against the extracellular form (EC50 7.8 to >86 nM). Noteworhy is that all compounds exhibited only moderate or no cytotoxicity against the murine host cells (EC50 7.8 to >56 nM; >25 μg/ml). These polyphenols were further evaluated for immunomodulatory effects on macrophage functions, including release of nitric oxide (NO), tumor necrosis factor-α (TNF) and interferon (IFN)-like properties using several functional assays. The results showed that all compounds induced murine RAW 264.7 cells only moderately to release NO (7—26 μM) relative to the reference stimulus IFN-γ/LPS (119 μM). The TNF-inducing potential of the polyphenols producing 50% lysis in murine L929 cells ranged from absent to 138 U/ml at the host cell subtoxic concentration of 50 μg/ml. The highest TNF-inducing activity was associated with those flavan-3-ols with galloyl groups (98—127 U/ml). For proanthocyanidins, it appeared that an increase in the flavanyl chain length did not enhance the induction of TNF-release (32—86 U/ml and below detection limits for oligomers and polymers, respectively). With interferon-like activities, phylloflavan and a prodelphinidin polymer showed appreciable cytoprotective effects, as reflected by the inhibition of the cytopathic effect of encephalomyocarditis virus on L929 fibroblast cells (38 and 36 U/ml, respectively). All remaining compounds displayed only negligible or moderate protective effects at subtoxic concentrations up to 25 μg/ml (<5 to 12 U/ml). These results indicate that proanthocyanidins and related compounds have favorable antileishmanial activity in vitro and might be considered as beneficial immunological response modifiers provided there are no bioavailability problems.
