Aim: 

In the present study we have evaluated the effect of melatonin treatment on caspase activity evoked by increases in cytosolic free calcium concentration ([Ca²⁺]_c) in neutrophils and lymphocytes from leukemia rats.

Methods: 

Leukemia was induced in rats by intraperitoneal injection with 5-10 x 10⁷ human leukemia cells HL-60 and melatonin (20 mg/ml) was given in drinking water for 14-16 weeks ad libitum. At the end of treatment, neutrophils and lymphocytes were isolated and caspase-3 and -9 activities were determined from the cleavage of the respective specific fluorogenic substrates and measured with a fluorescence spectrophotometer.

Results: 

Our results show that the % of blood lymphocytes in leukemia rats was reduced by melatonin treatment compared with control group. The treatment of neutrophils and lymphocytes from leukemia rats with the specific inhibitor of calcium reuptake thapsigargin (TG, 1 mM for 60 min) was able to increase the caspase-3 and -9 activities. However, when the cells were obtained from leukemia rats treated previously with melatonin, the caspase activities induced by TG were significantly reduced.

Conclusion: 

Our results suggest that melatonin is able to reduce the caspase-3 and -9 activities induced by increases in cytosolic free calcium concentration ([Ca²⁺]_c) in neutrophils and lymphocytes from leukemia rats.

Supported by MEC-DGI grant BFU2007-60091. M.P. Terrón is beneficiary of a grant by Junta de Extremadura (REI07004).