Pharmacokinetic and pharmacodynamic of dexamethasone - butyrate loaded solid lipid nanoparticles

Erica Imbalzano1, Elisabetta Muntoni1, Loredana Serpe1, Federica Foglietta1, Roberto Canaparo1, Paolo Gasco2, Gian Paolo Zara1. 1University of Torino, Scienza e Tecnologia del Farmaco 10125, Italy, 2Nanovector s.r.l., Enviroument Park, Italy

Glucocorticoids can be highly effective in treating inflammatory diseases, but their systemic application is limited because of a high incidence of serious adverse effects. Thus, it is considered desirable to develop glucocorticoid preparations efficacious at the target site, but with weak systemic side-effects. Butyrate, a short chain fatty acid normally present in the body, has been used for the treatment of various inflammatory diseases. However the infrequent application is not due to side-effects or general toxicity, but to the extremely short half life of butyric salts derivatives, which impairs any long-lasting effect in vivo. Currently, we have developed an alternative delivery system, by entrapment dexamethasone and butyrate (dexa-but) in solid lipid nanoparticles (SLN). The aim of the work is to evaluate the in vitro pharmacological effects and the in vivo kinetic of this new formulation for the oral administration of dexamethasone in association with butyrate.

Methods: In vitro we evaluated the capacity of dexa-but SLN at different concentrations of the combined drugs (i.e., 100 ng/ml - 10 μM; 10 ng/ml - 1 μM and 1 ng/ml - 0,1 μM, respectively dexamethasone and butyrate) to improve the anti-inflammatory activity of the drugs alone studying the effects on cytokines secretion of rat peripheral mononuclear blood cells (PMBC) exposed to lipopolisaccaride (LPS). PBMC were cultured in RPMI 1640 medium containing 10% (v/v) fetal calf serum, L-glutamine, streptomycin, penicillin and 1 μg/ml of LPS for 24 h at 37 °C, 5% CO2. The concentrations of IL-1beta, TNF-alfa and IL-10 in culture supernatants of rat PMBC were measured using an ELISA assay after 24 h exposure. Statistical comparisons between treatment groups were performed with analysis of variance (two-way ANOVA) and the threshold of significance was calculated by the Bonferroni’s test. In vivo male albino rats (Wistar derived strain) weighing 350-450 g were used. Dexa-but SLN and dexamethasone standard reference solution 3 mg/Kg were administered directly into the duodenal lumen through a cannula surgically implanted. Blood samples at different time were collected through an implanted cannula into the jugular vein 24 h after surgery. The drug plasma concentrations were determined by revearsed-phase HPLC method with UV detection.

Results: The secretion of IL-1beta (p<0.01 and p<0.05 vs free dexamethasone and free butyrate, respectively) and TNF-alfa (p<0.01 and p<0.001 vs free dexamethasone and free butyrate, respectively) was significantly decreased while the secretion of IL-10 (p<0.05 and p<0.001 vs free dexamethasone and free butyrate, respectively) was significantly increased by dexa-but SLN at the lowest concentration tested, i.e. dexamethasone 1 ng/ml and butyrate 0.1 μM. Moreover, no cytotoxic effects have been reported at the concentration tested able to inhibit cytokines production. In vivo gastrointestinal bioavailability of dexamethasone was significantly improved after dexa-but SLN compared with dexamethasone standard reference solution. Cmax after 45 minutes and AUCinf were greater after dexa-but SLN than after dexamethasone standard reference solution.

Conclusion: The new formulation of dexamethasone and butyrate incorporated in solid lipid nanoparticles improved the anti-inflammatory activity in comparison with the effect of each individual drug. Gastrointestinal bioavailability of dexamethasone was increased with the new formulation

Therefore, dexa-but SLN formulation may offer an alternative means of administering dexamethasone with important advantages over the existing formulations to treat chronic inflammatory diseases.