Acid diterpenes from Copaiba oleoresin (Copaifera langsdorffii): Chemical and plasma stability and intestinal...

Copaiba oleoresin has been used in folk medicine in the treatment of bronchitis, syphilis, skin diseases and ulcers due to its anti-inflammatory and antiseptic activities, but there is no information about major compounds oral absorption to support the traditional use.

Considering the potential of copalic (CA) and kaurenoic acid (KA) - major biological activity (in vitro) diterpenes found in the oleoresin, this study aimed to evaluate the intestinal permeability of CA and KA using Caco-2 cells model as predictive test for oral drug absorption.

Chemical stability at pH 1.2 and 7.4 and plasma stability were evaluated to mimic physiological conditions of the gastrointestinal tract. The intestinal permeability of CA and KA was evaluated in Caco-2 cells in the presence and absence of the P-glycoprotein inhibitor verapamil.

CA and KA were rapidly degraded at pH 1.2 (0.2 M Clark-Lubs buffer). At pH 7.4 (0.1 M phosphate buffer), CA was stable for up to 24 h and KA for up to 6 h. In human plasma, CA and KA can be considered stable for 24 h and 12 h at 37 °C, respectively. Caco-2 cells were considered viable when incubated with CA or KA in the range of 3.9-250 μM for 24 h. CA and KA exhibited moderate apparent permeability (P_app) of 4.67 (±0.08) × 10^-6 cm/s and 4.66 (±0.04) × 10^-6 cm/s, respectively. Simultaneous incubation with verapamil showed that P-glycoprotein does not play a relevant role on CA and KA oral absorption, with P_app of 4.48 (±0.26) × 10^-6 cm/s and 5.37 (±0.72) × 10^-6 cm/s observed for CA and KA, respectively.

The oral absorption of both CA and KA is driven by mainly passive permeability, is not limited by p-glycoprotein, but enteric-coated dosage forms should be used to avoid chemical instability in the gastric pH.