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Comparison of Two Commercial Preparations of Curcumin using the Caco-2 in vitro Assay of Human Intestinal Permeability

Objectives: The transport of curcuminoids in Caco-2 cell monolayers, which are widely used as an in vitro model of drug permeability in the human small intestine, was investigated. The formulations tested demonstrated two distinct methods for enhancing the intestinal absorption and bioavailability of curcumin: a curcumin– phospholipid complex and a turmerone/piperine-enhanced curcumin product. 
Design and outcome measures: Two unique formulations representing distinct approaches to maximizing curcumin bioavailability were compared with each other and with standard control compounds. Outcomes evaluated included apparent permeability, which reflects the ability of drug molecules to penetrate the intestinal tract; percentage recovery of compound through the Caco-2 monolayer; and efflux ratio, which is generally considered to reflect the role of efflux proteins in expelling compounds from the intestinal lumen. 
Results: In our widely used Caco-2 cell model experiments, the absorption of curcumin from each unique commercial formulation was equivalent at the single concentration tested. Furthermore, curcumin efflux was substantially reduced in the turmerone/piperine formula, though the difference between formulations was not significant. This reduction of curcumin efflux was expected on the basis of reports of piperine’s P-glycoprotein-inhibitory activity. 
Conclusion: The results of the present experiment strongly suggest that the incorporation of turmerones and piperine into curcumin preparations may be a simple way to improve the poor bioavailability of curcumin, which has previously been shown to be improved by the formulation of curcumin into curcumin–phospholipid complexes.