L.A. Silva-Torres1,2, C. Vélez3, J. Vargas-Vidot4, J.G. Ortiz1, B. Zayas1,3. 1Pharmacology and Toxicology Department, School of Medicine, Medical Science Campus, University of Puerto Rico, United States; 2Puerto Rico Institute of Forensic Science, United States; 3School of Environmental Affairs, Universidad Metropolitana, United States; 4Iniciativa Comunitaria, United States
BACKGROUND: The use of xylazine in Puerto Rico and worldwide as a drug of abuse and its combination with cocaine and/or heroin has increase in recent years. Xylazine is approved by FDA for animal use only. Clinical findings reported that xylazine users presented limb skin lesions, ulcerations and greater physiological deterioration than heroin users only. The aim of this study was to assess the cytotoxicity of xylazine on endothelial cells, as this is the first tissue affected upon administration. METHODS: Human umbilical vein endothelial cells in culture were treated with xylazine, cocaine, heroin and their combinations from 10 nM to 400 μM at 24, 48 and 72 hours exposure periods. IC50 was determined applying a fluorometric assay for viability determination. The Annexin V assay was also implemented as well as activation of caspases 8 and 9 in order to determine apoptosis as the cell death mechanism. RESULTS: Results indicated IC50 values at 24 hours as follow: xylazine 62 μM, cocaine 202 μM, heroin 278 μM and the combination of the three drugs 55 μM. Similar IC50s was observed at 48 and 72 hours. The Annexin V positive results as well as the positive activation of caspases 8 and 9 strongly suggest apoptosis as the cell death mechanism. CONCLUSIONS: The study demonstrated that xylazine inhibits endothelial cell proliferation at lower concentrations than cocaine and heroin. These findings support that xylazine use increase the toxicity of cocaine and heroin when used in combination and induce cell death by apoptosis. Key words: xylazine, cocaine, heroin, apoptosis, drug abuse.