Curcumin, Lupeol and Piperine Inhibit the Bacterial Triggers of some Autoimmune Inflammatory Diseases and Potentiate the Activity of Conventional Antibiotics

Background: Curcumin, lupeol and piperine are phytochemical constituents of multiple plants that are used traditionally to treat inflammation, including for treating autoimmune inflammatory diseases. Despite this, relatively few studies have examined the ability of these compounds to inhibit the etiological events of these diseases by examining their ability to inhibit their bacterial triggers. Methods: The ability of curcumin, lupeol and piperine to inhibit the growth of some bacterial triggers of selected autoimmune inflammatory diseases was screened using disc diffusion assays and quantified by liquid dilution MIC assays. The ΣFIC of the pure plant compound/conventional antibiotic combinations was determined and used to classify the class of interaction. Toxicity was evaluated using the Artemia nauplii cytotoxicity assay. Results: Curcumin, lupeol and piperine strongly inhibited the growth of several bacterial triggers of autoimmune diseases, with MIC values as low as 178 µg/mL against some bacteria. Furthermore, combining these compounds with conventional antibiotics resulted in significant potentiation of the inhibitory activity for some combinations, with one synergistic and nineteen additive combinations detected. Notably, three antagonistic combinations were also noted. None of the individual components (nor the combinations) were significantly toxic in the ALA toxicity assay. Conclusion: Curcumin, lupeol and piperine inhibit the growth of some bacterial triggers of rheumatoid arthritis, ankylosing spondylitis, multiple sclerosis and rheumatic fever. Additionally, these compounds substantially potentiated the effects of some conventional antibiotics against these bacteria. Further in vivo studies to determine the anti-inflammatory and antibacterial mechanisms are warranted.