Anti-ulcerant kynurenic acid molecules intercalated Mg/Al-layered double hydroxide and its release study

Kynurenic acid (KYNA) is a product of the tryptophan metabolism and it possess also anti- ulcerant properties, however, the application of KYNA for the treatment of gastroduodenal ulceration is limited, because the concentration of KYNA is very low in human gastric fluid (0.01 mu M). The intercalation of KYNA molecules into biocompatible Mg-Al layered double hydroxides (LDH) lamellae could solve this problem. For this purpose Mg-Al LDH with 114.96 +/- 0.48 m(2)/g BET surface area and + 0.641 meq/g specific surface charge was synthesized. The intercalation of the anionic target molecules into positively charged LDH layers was carried out with simply ion- exchange reaction. The structure of the obtained KYNA/LDH hybrid materials were studied by powdered X-ray diffraction (PXRD) and Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy verifying that the KYNA molecules prefer creating a paraffin type monolayer arrangement. Due to the intercalation process the (003) reflection peaks of initial LDH (2 Theta = 11.39 degrees, d((0 < b > 03)) = 0.775 nm) shift to lower angles (2 Theta = 4.11 degrees, d = 2.146 nm). That means, that the basal space value (Delta(dL) ) of the KYNA-LDH sample was 1.436 nm. The total amount of the intercalated KYNA molecules into LDH layers was measured by fluorescence spectroscopy method. According to the results the drug- loading capacity was about 120 mg KYNA/g LDH. This similar to 12% KYNA content of the hybrid materials was also evidenced by thermogravimetric measurements, because the thermal decomposition of the bio-hybrid materials was examined by thermogravimetry (TG) analysis. Our experimental data confirm that the anti- ulcerant KYNA molecules can be safely loaded and stored into LDH's layers forming a new bio-active hybrid material. In addition we also presented by PXRD and gravimetric measurements that prepared LDH layers were almost completely dissolved (similar to 83 wt%) in the applied simulated gastric fluid (SGF) media (pH = 1.5) under 60 min and the encapsulated KYNA molecules released from the destroyed interlayers. Finally, the measured KYNA drug release profile from the bioactive composite material was also presented in SGF media. According to the results 18% of the loaded KYNA molecules were released during 6 h.