Positive Health Online

Abstract

HOSTANSKA and colleagues, Department of Internal Medicine, University Hospital Zürich, Switzerland, analysed the anticarcinogenic activities of total extracts of fresh versus dried Hypericum perforatum (St. John's wort) on human tumour cells in vitro, and compared these activities in the dark and after exposure to white light illumination .

Background

Hypericum p. extracts are effective in the treatment of mild-to-moderate depression . Further, the component hypericin demonstrates light-dependent cell toxicity (phototoxicity) and can be used in the form of phototherapy as an anticancer agent .

Methodology

The tumour cells examined were K562, U937 (leukaemia cells lines) and LN229 glioblastoma cell lines. Effects of the Hypericum p. extracts and of hypericin in the dark and after exposure to 7.5 J/cm2 white light illumination were compared with those on normal human astrocytes (NHAs). Toxicity was assessed by calculation of LC50 values, and growth retardation by calculation of GI50 values. The mechanism of cytotoxicity/growth inhibition was determined by examining treated tumour cells under the light microscope and also by investigating phosphatidylserine exposure on the outer plasma membrane using Annexin-V binding with flow cytometry after 24 hours. Finally, the hyperforin contents of fresh versus dried Hypericum p. extracts were compared and evaluated with respect to their growth inhibition activities both in the dark and after white light exposure .

Results

Non-illuminated Hypericum p. extracts showed low cytotoxicity: the LC50 was between 1.9 and 4.1 mg/ml (corresponding to 10.3-17.3 M hypericin and 114.4-190.7 M hyperforin) after 48 hours of treatment. However, non-illuminated Hypericum p. extracts did show dose-dependent growth inhibition of tumour cells: the GI50 values for the fresh and dried plant extracts respectively were 0.43-1.77 mg/ml (2.3-9.7 M hypericin, 26.1-106.7 M hyperforin) and 0.59-3.03 mg/ml (2.5-12.8 M hypericin, 24.2-124.7 M hyperforin). Fresh Hypericum p. extracts showed more potent growth inhibition of the leukaemia cell lines K562 and U937 than of LN229 cells or NHAs: the GI50 values were about 7-fold lower than the corresponding LC50 values for K562 and U937 cells, but were almost the same as the LC50 values for LN229 cells and NHAs. After 48 hours' treatment, GI50 values for K562 and U937 cells were 432 and 799 g/ml respectively, compared with 1767 and 2900 g/ml respectively for LN229 cells and NHAs (p<0.05). Light-exposed Hypericum p. extracts showed greater cytotoxicity and growth inhibition than non-illuminated extracts: LC50 and GI50 values were reduced to values that corresponded with LC50 and GI50 values for phototoxic hypericin of 3.7-7.4 and 1.3-3.5 M respectively. Light exposure also increased the growth inhibition activity of Hypericum p. extracts on glioblastoma LN229 cells: after light exposure, the GI50 for LN229 cells was 582 g/ml compared with 1050 g/ml for NHAs (p=0.006). Light microscopic examination of treated tumour cells and Annexin-V binding studies confirmed that Hypericum p. extracts caused apoptosis ('programmed cell death') of cells in the absence of illumination . Fresh Hypericum p. extracts were found to contain 47% more hypericin than dried extracts, and the GI50 values for non-illuminated fresh plant extract in K562, U937 and LN229 cell lines respectively were 73%, 77% and 58% of those of the dried extract (p<0.05). Under 7.5 J/ cm2 white light illumination, fresh and dried Hypericum p. extracts displayed similar growth inhibitory and cytotoxic effects ; this was a result of the phototoxic activity of hypericin (corresponding concentrations being in the range 1.3-3.5 M).

Conclusion

Hypericum p. extracts show growth inhibition and cytotoxic (apoptotic) activities that are not dependent on light exposure ; however, light exposure potentiates these activities. The constituent hyperforin appears to be at least partly responsible for these effects in the dark .

References

Hostanska K et al. Aqueous ethanolic extract of St. John's wort (Hypericum perforatum L.) induces growth inhibition and apoptosis in human malignant cells in vitro. Die Pharmazie 57 (5): 323-31. May 2002.