Background: It has been postulated that systemic infection with pathogens such as Porphyromonas gingivalis (Pg) elevates the inflammatory response and increases susceptibility to atherosclerosis. We hypothesized that Doxycycline would be beneficial in diet- and/or Pg-induced atherosclerosis given its role in various cell functions and matrix remodeling.
Methods and results: ApoE+/- mice were inoculated weekly with Pg and treated with either Doxycycline or saline; animals were fed either a high-fat or chow diet. Animals were euthanized at 14 or 24 weeks and histomorphometric analysis of atheromatous lesions in proximal aorta, levels of SAA and serum cytokine profiling were performed. Histomorphometric analysis demonstrated that in non-infected mice fed a high fat diet, Doxycycline treatment resulted in a reduction of mean lesions from 10.5%+/-.49 to 1.09%+/-0.102 (p<0.05) at 14 weeks and a reduction from 21.5%+/-6.49 to 8.26%+/-0.162 (p=0.106) at 24 weeks. Chow-fed Pg mice treated with Doxyclycline also resulted in a reduction from 0.62%+/-0.128 to 0.0%+/-0.0 (p<0.05) at 14 weeks and a reduction from 0.92%+/-0.23 to 0.0%+/-0.0 (p<0.05) at 24 weeks. Administration of Doxycycline to mice fed a high fat diet and Pg-inoculated resulted in a reduction of mean percentage of atheromatous lesions from 16.46%+/-1.69 to 1.141%+/-0.23 (p<0.05) at 14 weeks and a reduction from 25.27%+/-1.734 to 0.428%+/-0.033 (p<0.05) at 24 weeks. At this timepoint, SAA levels in Pg-infected animals were reduced by five-fold and three-fold in Doxycycline-treated chow and high fat-diet groups, respectively. Cytokine antibody arrays revealed a marked reduction in the levels of pro-inflammatory cytokines in Doxycycline-treated groups whether Pg-infected or fed a high fat diet while anti-inflammatory cytokines were not affected. Consistent with the role of Doxycycline on matrix proteases, at 24 weeks MMP-9 Serum levels were markedly reduced by 60% (p<0.05) and 30% (p<0.05) with Doxycycline treatment in Pg-infected high fat and chow diet groups, respectively.
Conclusions: Doxycycline decreases pro-inflammatory cytokines and results in reduction of atherosclerosis in ApoE+/-Pg-inoculated and/or high fat diet fed mice.