Graduation Date

Spring 5-4-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Pharmaceutical Sciences

First Advisor

Dong Wang

Abstract

Periodontitis is an inflammatory disease induced by complex interactions between the host immune system and pathogens that affect the integrity of teeth-supporting tissues. To prevent disease progression and thus preserve the alveolar bone structure, simultaneous anti-inflammatory and osteogenic intervention is essential. Hence, simvastatin (SIM) and a glycogen synthase kinase 3 beta inhibitor (BIO) were selected as anti-inflammatory and osteogenic agents.

First, SIM is a HMG-CoA reductase inhibitor widely prescribed for hypercholesterolemia. It has been reported to ameliorate inflammation and promote osteogenesis. Its clinical applications on these potential secondary indications, however, have been hampered by its lack of osteotropicity and poor water solubility. To address this challenge, we proposed to design and evaluate the therapeutic efficacy of a novel simvastatin prodrug with better water solubility and bone affinity. The prodrug (SIM-PPi) was synthesized by directly conjugating a SIM trimer to a pyrophosphate (PPi). It was characterized and evaluated in vitro for its water solubility, osteotropicity, toxicity, anti-inflammatory, and osteoinductive properties. It was then tested for anti-inflammatory and osteoinductive properties in vivo by three weekly injections into gingiva of a ligature-induced experimental periodontitis rat model. In vitro studies showed that SIM-PPi has greatly improved water-solubility of SIM and shows strong binding to hydroxyapatite (HA). In macrophage culture, SIM-PPi inhibited LPS-induced pro-inflammatory cytokines (IL-1β, IL-6). In osteoblast culture, it was found to significantly increase alkaline phosphatase (ALP) activity with accelerated mineral deposition, confirming the osteogenic potential of SIM-PPi. When tested in vivo on an experimental periodontal bone-loss model, SIM-PPi exhibited a superior prophylactic effect compared to dose equivalent SIM in reducing inflammatory cells and in preserving the alveolar bone structure, as shown in the histological and micro-CT data.

Second, a glycogen synthase kinase 3 beta inhibitor (BIO) is a potent inflammation modulator and osteogenic agent. However, its lack of osteotropicity, poor water solubility, and potential long-term side effects have hampered its clinical applications. To address these limitations, pyrophosphorylated Pluronic F127 was synthesized to prepare a novel, injectable and thermosensitive hydrogel (PF127) that could effectively release BIO to exert its therapeutic effects locally. Comparing to F127 hydrogel, PF127 hydrogels exhibited strong binding to hydroxyapatite (HA) discs as a function of PPi content. Additionally, BIO’s solubility in PF127 solution compared to F127 was greatly improved and proportionally to the polymer concentration. When tested in vivo on an experimental periodontal bone-loss rat model, PF127-BIO hydrogel exhibited a superior prophylactic effect in preserving alveolar bone structure and preventing periodontal inflammation, as shown by the micro-CT and histological data, respectively.

Altogether, these two delivery strategies (SIM-PPi prodrug and PF127 hydrogel) with excellent bone binding may have the potential to be further developed for better clinical management of bone loss associated with periodontitis.

Available for download on Thursday, April 22, 2021

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