Polybacterial Periodontal Pathogens Alter Vascular and Gut BH4/nNOS/NRF2-Phase II Enzyme Expression.

Keith Channon,Pandu Gangula,Kalpana Ravella,Lakshmyya Kesavalu,Ashley Hale,Janet Southerland,Sasanka Chukkapalli,Shanthi Srinivasan,Mercedes Rivera,Wenhui Hu

doi:10.1371/journal.pone.0129885

Abstract

Periodontal disease is a highly prevalent chronic inflammatory disease and is associated with complex microbial infection in the subgingival cavity. Recently, American Heart Association supported a century old association between periodontal disease and atherosclerotic vascular disease. We have recently shown that polybacterial periodontal infection led to aortic atherosclerosis and modulation of lipid profiles; however the underlying mechanism(s) has not been yet demonstrated. Altered nitric oxide (NO) synthesis and tetrahydrobiopterin (BH4), a cofactor for nitric oxide synthases (NOS) has long been shown to be associated with vascular dysfunction and gastrointestinal motility disorders. We sought to examine the mechanism of periodontal infection leading to altered vascular and gastrointestinal smooth muscle relaxation, focusing on the BH4/nNOS pathways. In addition, we also have investigated how the antioxidant system (NRF2-Phase II enzyme expression) in vascular and GI specimens is altered by oral infection. Eight week old male ApoEnull mice were either sham-infected or infected orally for 16 weeks with a mixture of major periodontal bacteria Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia to induce experimental periodontitis. Serum, vascular (mesenteric), stomach, and colon specimens were collected at the end of periodontal pathogen infection. Bacterial infection induced significant (p<0.05) reductions in the levels of BH4,in ratio of BH4:BH2+B and also in nitric oxide levels compared to sham-infected controls. In addition, we identified a significant (p<0.05) reduction in eNOS dimerization, nNOS dimerization and protein expression of BH4 biosynthesis enzymes; GCH-1, DHFR and NRF2 & Phase II enzymes in infected mice versus controls in both mesenteric artery and colon tissues. However, we found no differences in nNOS/BH4 protein expression in stomach tissues of infected and sham-infected mice. This suggests that a polybacterial infection can cause significant changes in the vascular and colonic BH4/nNOS/NRF2 pathways which might lead to impaired vascular relaxation and colonic motility.

Highlights

Periodontal diseases (PD) are among the most common chronic infections of humans, affecting up to an estimated 5–20% of the global population and are associated with a polymicrobial subgingival bio-film
We found reduced nitric oxide (NO) levels in serum from ApoEnull mice with established periodontitis, in comparison to sham-infected ApoEnull mice
Since vascular BH4/neuronal NO synthase (nNOS)/NRF2 protein expression is altered in orally infected mice, we examined if the BH4/nNOS/ NRF2 pathway is impaired in all 3 regions of colon; if so, this could lead to a reduced colonic motility

Summary

Introduction

Periodontal diseases (PD) are among the most common chronic infections of humans, affecting up to an estimated 5–20% of the global population and are associated with a polymicrobial subgingival bio-film. Reduced NO bioavailability as well as an impaired NO-mediated vasodilation, as a result of endothelial nitric oxide synthase (eNOS) uncoupling and increased reactive oxygen species (ROS), has been known to play a detrimental role in cardiovascular pathologies [21]. Most importantly PD is associated with endothelial dysfunction in patients with coronary artery disease through a decrease in NO bioavailability [22]. We hypothesize that periodontitis leads to vascular endothelial dysfunction and suppression of antioxidants through impairment of BH4/ nNOS/NRF2 pathway which leads to elevated vascular inflammation. This in turn might impair gut BH4/nNOS/NRF2 pathway, leading to altered colonic motility. Since NO is the principal inhibitory neurotransmitter and controls the peristaltic movements of the gut, we investigated changes in the expression of these pathways in all 3 regions of colon (proximal, mid and distal colon) [24]

Ethics Statement

Results

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