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Long-chain bases (sphingosine, dihydrosphingosine, and phytosphingosine) are present in the oral cavity and have potent antimicrobial activity against oral pathogens. However, little is known about their cytotoxicity for oral cells, an important step in considering their potential as future antimicrobial agents for oral infections.
In this study, primary oral keratinocytes, primary oral fibroblasts, dendritic cells, and oral squamous cell carcinoma cells were exposed to 10.0-640.0 µM long-chain bases and glycerol monolaurate (GML) in cell culture medium containing resazurin (e.g., Alamar Blue, Invitrogen Corp., Carlsbad, CA). Cell metabolism was assessed at 48 hours by the reduction of resazurin to resorufin. Percent cytotoxicity was defined as the median fluorescence intensity (MFI) of resazurin in cell culture media of cells treated with dilutions of long-chain bases/MFI of resazurin in cell culture media of untreated cells x 100, and the lethal dose 50 (LD50) was determined from the dose response curve where the 50 percent cytotoxicity intercepts with the long-chain base concentration on the x-axis.
For all cells, the LD50 (mean µM + std err) of sphingosine, dihydrosphingosine, phytosphingosine, and GML were 69.7 (1.7), 29.2 (1.7), 20.6 (1.7), and 134.3 (1.7), respectively. Primary oral keratinocytes were more resistant to long chain bases, whereas oral fibroblasts, dendritic cells, and oral squamous cell carcinoma cells were more susceptible.
Overall, long chain bases have LD50 for oral keratinocytes, oral fibroblasts, dendritic cells, and oral squamous cell carcinoma cells that are considerably higher than the minimal inhibitory concentrations for oral pathogens, a finding important to their future potential as therapeutics for prevention or treatment of periodontal disease infections.