The effects of selected health supplements on drug intestinal epithelial permeation

Abstract

With the growing popularity of health supplement usage to support and maintain a healthy body there is an increasing concern for possible drug-drug and drug-supplement interactions because health supplements are not subjected to the demanding pre-market clinical testing as registered prescription drugs. During this study emphasis was placed on 5 selected commercially available health supplements (acetyl-L-carnitine, berberine, chondroitin sulfate, D-glucosamine and silymarin) and their modulating effects on the intestinal permeation of a model compound. Rhodamine-123 (RH-123), which is a known substrate of the active efflux transporter P-glycoprotein (P-gp), was used to assess the membrane permeation modulating effects of the selected commercially available health supplements. The bi-directional transport studies were conducted with RH-123 in the presence and absence of the selected health supplements across excised pig intestinal tissue using a Sweetana-Grass diffusion chamber apparatus. Over a period of 2 hours samples of 180μl were withdrawn at 20 min intervals. The RH-123 concentration in each sample was determined by using a validated fluorescence spectroscopic method on the Spectramax Paradigm® plate reader. Lucifer yellow was used to conduct a transport study to prove that the mounting technique of the excised pig intestinal tissue did not affect the viability and integrity of the tissue. All the transport experiments were conducted in triplicate at two different concentrations (a low and high concentration) of each of the selected health supplements. The bi-directional transport studies were conducted, and the resultant data was used to calculate the percentage transport and apparent permeability coefficient (Papp) values. The Papp values were then used to calculate efflux ratio (ER) values. Trans-epithelial electrical resistance (TEER) was also measured at the beginning (T0) and end (T120) of each transport experiment using a Warner Instruments® EC-825A epithelial voltage clamp. If the TEER values decreased it may be considered indicative of permeation altering effects based on changes in the membrane integrity due to the presence of the selected health supplements which may have mediated changes in the tight junction integrity. The study conducted with RH-123 in the presence of acetyl-L-carnitine (ALC) rendered a statistically significant increase in transport of RH-123 in the absorptive (apical to basolateral) direction when compared to the negative control (RH-123 alone). Berberine showed a statistically significant decrease between the secretory (basolateral to apical) direction and the negative control and RH-123 in the presence of the low concentration (0.000566% w/v) berberine. The ER values of RH-123 in the presence of either berberine or chondroitin sulfate (CS) indicated that the possible transport mechanism of RH-123 transport could be via paracellular transport or passive diffusion while the ER value of RH-123 in the presence of D-glucosamine indicated a possible inhibition of P-gp related efflux. The transport of RH-123 in the secretory direction (BL-AP) in the presence of silymarin showed an increase in RH-123 transport when compared to the negative control (RH-123 alone). The ER values for the transport of RH-123 in the presence of a high silymarin concentration (0.272% w/v) showed possible inhibitory effects on P-gp related efflux. The ex vivo pharmacokinetic interactions obtained during this study proved that the selected health supplements may indeed induce membrane permeation altering effects when administered in conjunction with prescription drugs. Further in vivo studies should be conducted to investigate the clinical significance of these results.