Molecular Imaging of Gingipain Activity in Advanced Periodontitis

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PROJECT SUMMARY This objective of this proposal is an activatable photoacoustic contrast agent to map and measure the gingipain proteases released by P. gingivalis during periodontitis. While P. gingvalis is easy to measure with PCR it cannot mapped in the mouth. Here, photoacoustic ultrasound will be used to report the quantity and location of gingipains released by P. gingivalis and improve diagnosis and response to therapy. We are motivated by studies showing that dental pain dramatically decreases quality of life but that nearly 50% of Americans have some form of periodontitis. Our rationale is that current approaches to monitoring oral health only measure the results and symptoms of gingipains (tooth loss, pocket depth, etc.). We argue that by imaging and measuring a molecular cause of periodontal disease—i.e., the gingipains secreted by P. gingivalis—new insights will be gained into the basic biology of this condition as well as better diagnostic and treatment-monitoring plans. This improved diagnostic insight will better guide therapy, and non-invasive imaging will increase patient compliance ultimately translating into earlier and better treatment of periodontitis. The workflow will include two parts: Aim 1 will build the contrast agent and validate it with recombinant gingipains, bacterial culture, and saliva from healthy subjects. Aim 2 will test the probe with gingival crevicular fluid (GCF) samples collected by Dr. Chen during routine cleanings. We will resuspend these samples and quantitate the gingipains using the probe validated in Aim 1. We hypothesize that the photoacoustic signal of our probe will increase linearly with gingipain concentration in vitro. We hypothesize that photoacoustic imaging can stratify GCF samples as a function of oral health status. This approach is innovative because this contrast agent will be the first molecular imaging technique for periodontal disease. It will detect disease prior to anatomical damage. As such, we will be able to map and measure the extent of pathogenic activity caused by P. gingivalis in the subgingival space in real time. It will also triage the disease in early stages. Current periodontal charting can only assess pocket depths and bleeding on probing, but detection of early- stage pathogenic activity will allow easy and inexpensive intervention to lower the clinical burden of periodontitis and improve patient outcomes. The clinical impact is a tool to detect early-stage changes in the oral microbiota to guide/monitor therapy. This technique could also answer questions about the impact of gingipains on inflammation, immune loading, pocket deepening, and alveolar bone loss in situ. We all well positioned to perform this work because of Dr. Jokerst’s skills in photoacoustic contrast media and Dr. Chen’s leadership position at the USC School of Dentistry; we have already published together on related research.