Detergent Sclerosants Stimulate Leukocyte Apoptosis and Oncosis

The objective was to investigate the effects of the detergent sclerosants sodium tetradecyl sulfate (STS) and polidocanol (POL) on human leukocytes at sublytic concentrations.

Leukocytes were isolated and labelled with antibodies to assess for apoptosis and examined with confocal microscopy and flow cytometry. Isolated leukocyte count and viability was assessed using trypan blue, and propidium iodide staining. Phosphatidylserine (PS) exposure, a universal hallmark to measure cell apoptosis, was identified by flow cytometry using lactadherin. Caspases 3, 8, and 9, and Bax activation, as well as inhibitory assays with pan-caspase (Z-VAD-FMK) and Bax (BI-6C9) were assessed to determine apoptotic pathways. Porimin activation was used to assess cell permeability.

Up to 40% of leukocytes maintained membrane integrity at sublytic concentrations (≤0.15%) of sclerosants. The remaining 60% did not maintain membrane integrity but were not completely lysed. PS exposure was increased with both STS and POL exhibiting a dose- and time-dependant trend. While activation of caspases 3, 8, and 9, as well as Bax activation, were increased in leukocytes stimulated with low concentrations of STS, only caspases 3 and 9 and Bax were increased with POL. Inhibitory assays demonstrated caspases 3, 8, and 9, and Bax inhibition at low concentrations with both STS and POL. Both agents increased the leukocyte activation of porimin at all concentrations. On confocal microscopy, stains for caspases 3, 8, and 9, and Bax were increased for both STS and POL. Porimin stain was markedly positive for both STS and POL.

Both sclerosants induced leukocyte apoptosis at sublytic concentrations. STS activated both extrinsic and intrinsic pathways of apoptosis, while POL stimulated the intrinsic pathway of apoptosis only. Both agents induced oncosis. Based on these results, STS appears to have a greater effect than POL.