P-CB-17 | Microbicidal 405-nm violet-blue light inactivates Leishmania parasites in ex vivo human platelets stored in plasma

Background/Case Studies
Violet-blue light of 405 nm in the visible spectrum has been shown to be an effective microbicidal tool. Unlike UV-A, -B or -C irradiation, 405 nm light is less toxic on the host cells while effective in killing microbes. To date, the violet-blue light has been shown to be effective against several blood-borne pathogens including bacteria, HIV-1, and Trypanosoma cruzi.

Study Design/Methods
Apheresis-collected human platelets concentrates (PCs) stored in plasma, from six screened donors were used. The FDA Research Involving Human Subjects Committee approved the use of human platelets for the research. Platelets from three donors were each inoculated with Leishmania donovani promastigotes at high titer (10E6/mL). Six Teruflex® T-150 transfer bags containing 40 mL each of parasite-spiked platelets were prepared per donor. Three bags were used as controls (no 405 nm light exposure wrapped in tinfoil) and other three bags were treated with the light at an irradiance of 54 J/cm2/h for 5 h. Similarly, three PCs from a separate set of donors were inoculated with lower titer of parasites (10E3/mL) reflecting a physiological parasitemia level. All bags were placed in a closed LED source emitting narrowband 405 nm light, and maintained at 22°C, on a shaker incubator set at 60 rpm. Ten samples from each bag at 0 hr and 5 hr time points were enumerated for viable parasites using Neubauer hematocytometer chamber.

Results/Findings
Relative to controls, in the high titer-spiked 5-h light-treated samples, parasite counts were near zero, suggesting parasite inactivation. Similar results were observed with lower titer-spiked 5-h light-treated samples. The observed parasite inactivation associated with 5 hrs light treatment demonstrates that the treatment was able to exert microbicidal effect on Leishmania in ex vivo platelets. Based on previous reports, this is perhaps achieved through photoexcitation of porphyrins and flavins present in the plasma which induces reactive oxygen species (ROS) that cause damage to pathogens.

Conclusions
This study revealed promising microbicidal role of the violet-blue light on Leishmania in ex vivo platelets stored in plasma and warrants further studies involving in vivo animal model to validate the results obtained from in vitro experiments.