Comparative study on antioxidative and macrophage-stimulating activities of polyguluronic acid (PG) and polymannuronic acid (PM) prepared from alginate.

The antioxidant and macrophage-stimulating activities of polyguluronic acid (PG) and polymannuronic acid (PM) prepared from alginate were examined. A chemiluminescence (CL) method using a luminol analog, L-012, showed that both PM and PG scavenge superoxide produced by hypoxanthine-xanthine oxidase system in a concentration-dependent manner. At 100 μg/ml, PG showed slightly stronger superoxide scavenging activity than PM. In an electron spin resonance (ESR)-spin trapping method in which the Fenton reaction was used as hydroxyl radical generation system, we found that both PM and PG showed potent hydroxyl radical scavenging activity to a similar extent. Because PM and PG showed no chelating activity on Fe(2+), it was confirmed that PM and PG can directly scavenge hydroxyl radical. No significant scavenging activity of PM and PG toward hydrogen peroxide was observed. Interestingly, the macrophage-stimulation activity of PG as measured by nitric oxide (NO)-production from mouse macrophage cell line RAW264.7 cells was evidently stronger than that of PM. Our results suggest that RAW264.7 cells might be able to distinguish the conformational differences between PM and PG, and respond differently to them, whereas the effects of such structural differences between PM and PG on the radical scavenging activities may not be so significant.