The potential of liposomes as dental drug delivery systems.

The potential of liposomes as a drug delivery system for use in the oral cavity has been investigated. Specifically targeting for the teeth, the in vitro adsorption of charged liposomal formulations to hydroxyapatite (HA), a common model substance for the dental enamel, has been conducted. The experiments were performed in human parotid saliva to simulate oral-like conditions. It was observed, however, that precipitation occurred in tubes containing DPPC/DPTAP or DPPC/DPPG-liposomes in parotid saliva with no HA present, indicating that constituents of parotid saliva reacted with the liposomes. The aggregation reactions of liposome-parotid saliva mixtures were examined by turbidimetry and by atomic force microscopy. Negatively charged DPPC/DPPS and DPPC/PI-liposomes were additionally included in these experiments. The initial turbidity of positive DPPC/DPTAP-liposomes in parotid saliva was very high, but decreased markedly after 30 min. AFM images showed large aggregates of micelle-like globules known to be present in saliva. The turbidity of the various negatively charged liposome and parotid saliva mixtures stayed relatively constant throughout the measuring time; however, their initial turbidities were different; mixtures with DPPC/DPPG-liposomes were the most turbid and DPPC/DPPA-liposomes the least. Pyrophosphate (PP) was added to the various liposome-parotid saliva mixtures to examine the effect of Ca(2+) on the interactions. The effect of PP treatment of the negatively charged liposome-parotid saliva mixtures was most pronounced with DPPC/DPPG-liposome mixtures where it caused a sudden drop in turbidity. For positive DPPC/DPTAP liposome and parotid saliva mixtures, the effect of PP was minimal. These experiments showed that saliva constituents may interact with liposomes. An appropriate liposomal drug delivery system intended for use in the oral cavity seems to be dependent on the liposomal formulation. Based on the present results, negatively charged DPPC/DPPA-liposomes seem to be most suitable for use in the oral cavity as they were found to be the least reactive with the components of parotid saliva.