A Therapeutic Role for Apolipoprotein-E in the Germ Theory of Alzheimer's Dementia

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Abstract: A Therapeutic Role for Apolipoprotein-E in the Germ Theory of AD P. gingivalis is the keystone bacteria of periodontal disease, the 6th most common infectious disease worldwide. Half of all Americans over the age of 30 and 70% of those over age 65 suffer some degree of P. gingivalis infection associated with gum disease. In a study of 6800 patients with gum disease that were followed for up to 26 years, those that developed gingivitis and then periodontal disease were linked to a significantly increased risk of dementia including Alzheimer's dementia. Tooth loss, a frequent outcome of periodontal disease, was also associated with an increased the risk of dementia. P. gingivalis products including lipopolysaccharide, cysteine proteases known as gingipains, and 16S rRNA from P. gingivalis have all been found in the brains of Alzheimer's patients. Since P. gingivalis is found in the mouth, the blood and is known to invade non-oral tissues including the brain, then strategies to reduce P. gingivalis numbers and activities including reducing brain inflammation, are beginning to show positive effects on outcomes associated with AD in animal models and in the clinic. We recently discovered that small mimetics of Apolipoprotein-E (ApoE-mimetics) inhibited the growth and killed P. gingivalis bacteria. Other groups have reported similar anti-bacterial activities of ApoE-mimetics including our ApoE-mimetics. These anti-bacterial activities appear to correlate with anti-inflammatory activities of ApoE-mimetics reported by us and other groups. We reported that these ApoE-mimetics extended lifespan in mice subjected to whole body sepsis using a caecal ligation and puncture model. We also reported that these ApoE-mimetics cross the blood brain barrier where they reduce brain inflammation in multiple models of Alzheimer's disease. In this grant, we propose to preferentially kill P. gingivalis by a unique strategy. This strategy involves a targeting ligand that specifically binds to a unique cell surface protein on P. gingivalis that, when conjugated with our anti-bacterial ApoE-mimetics, provides a “targeted” anti-bacterial agent. We refer to the “P. gingivalis targeting motif” as a “gingi-tif” and the conjugation with an ApoE-mimetic with as an “ApoE-gingitif”. As proof- of-principle, we now show that the ApoE-gingitif known as RGN2002 retains bacterial killing activity and preferentially targets P. gingivalis killing over killing of commensal bacteria (Figure 9 and Table 2). We will synthesize additional ApoE-gingitif and gingitif-ApoE conjugates and use them to measure the minimum inhibitory concentrations (MICs) against P. gingivalis. We will also use these ApoE-gingitif and gingitif-ApoE conjugates to measure MICs against a non-pathogenic commensal bacteria also found in the mouth. The ratio of the MICs for killing pathogenic P. gingivalis versus non-pathogenic commensal bacteria will provide a quantitation of the preferential killing of P. gingivalis, which we call a “Preference Ratio.” (Table 2). Once our in vitro screen has selected an appropriate ApoE-gingitif or gingitif-ApoE conjugate, then we will test these conjugates in a whole mouse model of P. gingivalis infection. Since oral delivery of P. gingivalis resulted in increased amyloid beta peptide 1-42, increased phosphorylated-tau and increased cytokines, which are all found in Alzheimer's patient's brains, we will measure these products in the brains of P. gingivalis infected mice with and without ApoE-gingitif or gingitif-ApoE conjugate treatment. These results will permit us to determine the efficacy of this targeted “ApoE-gingitif-strategy” to reduce brain inflammation and pathology associated with AD and P. gingivalis infections.