Sasanka S. Chukkapalli

Background: Cardiovascular disease (CVD) remains the leading global cause of mortality, with endothelial dysfunction as an early driver of pathology. Periodontal disease (PD) and its pathogen Porphyromonas gingivalis (Pg) are increasingly associated with metabolic disturbances and vascular injury, yet the combined impact of microbial and dietary stressors has not been mechanistically defined. Methods: In this 24-week study, mice were subjected to chronic Pg infection with or without a high-fat diet (HFD). Metabolic profiling, cytokine analyses, molecular signaling assessments, and ex vivo vascular reactivity studies were performed to evaluate systemic and vascular outcomes. Results: Pg infection induced metabolic alterations and vascular inflammation, while HFD alone caused obesity, insulin resistance, dyslipidemia, and impaired endothelial relaxation. Combined Pg infection and HFD produced the most severe phenotype, with synergistically elevated cytokines, heightened TLR4/NF-κB activation, marked suppression of PPARγ and Nrf2 signaling, reduced eNOS expression, and diminished nitric oxide bioavailability. Cinnamaldehyde (CNM) supplementation improved metabolic indices, reduced inflammatory cytokines, restored PPARγ and Nrf2 activation, enhanced Akt-mediated eNOS phosphorylation, and normalized endothelial-dependent vasorelaxation. Conclusions: Pg infection and HFD act as synergistic metabolic and vascular stressors that accelerate endothelial dysfunction through coordinated disruption of PPARγ/Akt/eNOS and Nrf2 pathways, while CNM provides substantial protective effects.

Schematic representation of established biomarkers and various methods developed for diagnosing PD. Created with https://www.BioRender.com.

Porphyromonas gingivalis (Pg), a Gram-negative oral pathogen, promotes and accelerates periodontitis-associated gut disorders. Intestinal epithelial barrier dysfunction is crucial in the pathogenesis of intestinal and systemic diseases. In this study, we sought to elucidate the protective role of cinnamaldehyde (CNM, an activator of Nrf2) against P. gingivalis (W83) and Pg-derived lipopolysaccharide (Pg-LPS) induced intestinal epithelial barrier dysfunction via antioxidative mechanisms in IEC-6 cells. IEC-6 (ATCC, CRL-1592) cells were pretreated with or without CNM (100 µM), in the presence or absence of P. gingivalis (strain W83, 10⁹ MOI) or Pg-LPS (1, 10, and 100 µg/mL), respectively, between 0–72 h time points by adopting a co-culture method. Intestinal barrier function, cytokine secretion, and intestinal oxidative stress protein markers were analyzed. P. gingivalis or Pg-LPS significantly (p < 0.05) increased reactive oxygen species (ROS) and malondialdehyde (MDA) levels expressing oxidative stress damage. Pg-LPS, as well as Pg alone, induces inflammatory cytokines via TLR-4 signaling. Furthermore, infection reduced Nrf2 and NAD(P)H quinone dehydrogenase 1 (NQO1). Interestingly, inducible nitric oxide synthase (iNOS) protein expression significantly (p < 0.05) increased with Pg-LPS or Pg infection, with elevated levels of nitric oxide (NO). CNM treatment suppressed both Pg- and Pg-LPS-induced intestinal oxidative stress damage by reducing ROS, MDA, and NO production. Furthermore, CNM treatment significantly upregulated the expression of tight junction proteins via increasing the phosphorylation levels of PI3K/Akt/Nrf2 suppressing inflammatory cytokines. CNM protected against Pg infection-induced intestinal epithelial barrier dysfunction by activating the PI3K/Akt-mediated Nrf2 signaling pathway in IEC-6 cells.