A whole blood-based, flow cytometric assay was used to simultaneously assess phagocytosis and oxidative burst. Calcein-AM stained Candida albicans (DSM 1386) were used as target organisms. Oxidative burst was measured by addition of dihydroethidium (DHE). Target organisms and whole blood were co-incubated and analyzed after 0, 2, 4, 6, 10, and 30 min. Intracellular killing of the target organisms was evaluated by determining the number of surviving yeast cells after co-incubation of C. albicans and human whole blood. EPs® 7630 was applied in therapeutically relevant concentrations between 0 and 30 μg/ml.
Compared with controls EPs® 7630 increased the number of phagocytosing PBP during the observed time points between 2 and 10 min in a concentration-dependent manner, with a maximum enhancement of 56 % at 2 min (p=0.002). The application of EPs® 7630 also led to a significant increase in the number of burst-active PBP for all time points observed beyond 2 min (p<0.001). The maximum augmentation was 120 % after application of 30 μg/ml EPs® 7630 at 4 min. Using a microbiological assay, intracellular killing was also enhanced by EPs® 7630. This was expressed by a significant reduction in the number of surviving target organisms (p<0.001). The maximum reduction in viable yeast cells (−31 % ) was observed after co-incubation for 120 min with the highest concentration of EPs® 7630 (30 μg/ml).
In conclusion, the positive effects of EPs® 7630 on phagocytosis, oxidative burst, and intracellular killing of yeast cells as test organisms are important components of the compound's biological activity. Our findings constitute a valuable contribution to understanding the clinical effects of EPs® 7630.