Physico-chemistry and Cytotoxicity of Tenofovir-Loaded Acid Phosphatase-Responsive Chitosan Nanoparticles

This study assesses the in vitro release of tenofovir (TFV)-loaded triphosphate (TPP) cross-linked chitosan nanoparticles (NPs) catalyzed by human prostatic acid phosphatase (hPAP) for 24 h. The physico-chemical characterization of the NPs included particle mean diameter (PMD), zeta potential (ζ), percent drug encapsulation efficiency (% EE), Fourier transform infra-red (FTIR) spectroscopy, powder X-ray diffractometry analysis (PXRD), and drug release kinetics. The first-order rate constant (k) and activation energy (E_a) of the cross-link (TPP) are determined by the integrated rate law and Arrhenius's equations. The hPAP Michaelis-Menten constant (Km) is determined by the Lineweaver-Burk's equation. The NP's safety profile is evaluated on vaginal epithelial cells (VK2/E6E7). The lyophilized drug-loaded NPs' PMD, ζ, and PDI are 149.97 nm, 4.4 mV, and 0.3, respectively. The % EE after lyophilization is 93.7 ± 4.4%. These NPs released drug at faster rate (63% of TFV within 6 h) under the enzyme's influence. The similarity and difference factors of drug release profiles (absence vs presence of hPAP) are 56.5 and 40.3, respectively. The hPAP's Km value of 0.019 mM suggests it has a good affinity for TPP at physiological pH ~ 7.4. The enhanced hydrolysis of TPP or degradation of chitosan NPs is fundamentally due to a decrease of TPP's activation energy by hPAP. In fact, the E_a value is 22.50 ± 3.06 kJ/mol or 16.33 ± 0.62 kJ/mol in the absence or presence of hPAP, respectively. The NPs are non-cytotoxic to the treated vaginal cell line. These hPAP-responsive NPs are promising topical nanomicrobicides for HIV/AIDS prevention.