Anti-proliferative activity and apoptotic effect of tick salivary gland extracts on human HeLa cells.

OBJECTIVES: The anti-proliferative and apoptotic potential of salivary gland extracts (SGE) of unfed and partially fed adult ixodid ticks were screened using human HeLa cells.

METHODS: Cell growth inhibition activity of SGE was measured by the MTT assay. Cell cycle analysis and quantification of DNA fragmentation was performed by DNA staining with propidium iodide. Annexin V-FITC was used to detect apoptotic cells.

RESULTS: SGE of all ticks examined suppressed HeLa cell proliferation in a dose dependent manner. Extracts from 2-day fed R. appendiculatus females (IC(50) 0.22 mg/ml SGE soluble protein) and 9-day fed A. variegatum females (IC(50) 0.30 mg/ml) were most potent. Species-specific differences in the anti-proliferative effects of SGE were revealed, suggesting that the amount of active compounds in tick salivary glands change during feeding. Total apoptosis (about 12%) and no significant alteration in cell cycle were confirmed for SGE of A. variegatum and R. appendiculatus, and additionally SGE of 5-day fed I. ricinus females (IC(50) 0.64 mg/ml).

CONCLUSIONS: The study shows that tumour cell growth suppressant(s) and/or apoptotic triggers are present in tick salivary glands, however, further research into the characteristics and mode of action of such natural substances is necessary.