Introduction
Trimethylamine N-oxide (TMAO), a gut flora-derived metabolite from dietary choline, has emerged as an indicator of atherosclerosis [
1]. Circulatory TMAO has been associated with increased cardiovascular risk by disrupting enterohepatic cholesterol and bile acid metabolism, upregulating macrophage scavenger receptor expression, and promoting endothelial dysfunction, oxidative stress, and inflammation [
2‐
4]. It activates nuclear factor kappa B (NF-κB), leading to the elevated expression of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and IL-1β [
5] through IL-1-related pro-inflammatory pathways [
2,
3]. Simultaneously, TMAO suppresses anti-inflammatory cytokines like IL-10 [
6], further contributing to systemic inflammation and atherosclerosis progression. Additionally, TMAO can contribute to inflammatory processes by enhancing macrophage chemotaxis and increasing the expression of inflammatory cytokines like TNF-α [
7,
8], which plays a crucial role in immune responses and inflammation and has been demonstrated as a crucial participant also during the development of periodontal diseases [
9]. Interestingly, TMAO has been detected in cerebrospinal fluid [
10] and has been implicated in neurodegenerative diseases, including Alzheimer’s [
11] and Parkinson’s [
12], through its role in amyloid-beta aggregation and tau protein stabilization [
13]. A clinical study has highlighted elevated circulating TMAO levels in periodontitis, correlating with
in-vitro endothelial dysfunction [
3]. Additionally, TMAO’s association with oral pathogens, such as
Porphyromonas gingivalis and
Aggregatibacter actinomycetemcomitans in myocardial infarction patients, underscores its potential link to oral dysbiosis [
14]. However, the precise role of TMAO in the local (salivary) versus systemic (serum) levels associated with periodontitis remains poorly defined.
According to the literature, in both in vitro and in vivo studies, elevated TMAO levels have been linked to periodontal disease and its systemic effects [
3,
8,
15‐
17]. In vivo studies in mice demonstrate that periodontitis-induced gut dysbiosis increases plasma TMAO [
16], exacerbating atherosclerosis [
17], endothelial dysfunction, and systemic inflammation via IL-6 and FMO3 upregulation [
8,
15]. In vitro studies confirm that TMAO impairs endothelial progenitor cell function, induces pyroptosis, and promotes inflammatory responses [
3], suggesting a mechanistic link between periodontitis, TMAO metabolism, and cardiovascular risk. While studies have explored the interplay between periodontitis and cardiovascular risk via circulating TMAO levels, limited attention has been given to salivary TMAO levels to evaluate its contribution to periodontal inflammation [
3,
14]. Unlike serum TMAO, salivary TMAO offers a novel, non-invasive diagnostic approach that can be integrated into routine clinical evaluations. This perspective underscores the unique value of salivary biomarkers, particularly for localized inflammatory conditions like periodontitis, and highlights their potential in bridging oral and systemic health diagnostics. This study aims to evaluate the independent effects of periodontitis on TMAO and TNF-α levels in saliva and serum. By focusing on salivary TMAO, the study provides novel insights into its potential as a localized biomarker and highlights its diagnostic utility in non-invasive clinical applications, advancing our understanding of its link to cardiovascular disease pathways.
Discussion
Our study provides new insights into the role of salivary trimethylamine N-oxide (TMAO) as a biomarker for periodontitis, demonstrating elevated salivary and serum TMAO levels in individuals with periodontitis compared to healthy controls. This finding suggests that TMAO is not only a systemic metabolite associated with cardiovascular disease but may also be involved in localized inflammatory responses within the oral cavity. While previous research has primarily focused on circulating TMAO in relation to systemic diseases [
3,
14], particularly cardiovascular conditions, our findings highlight its potential relevance within the oral cavity and periodontal inflammatory processes. The significant correlation between salivary TMAO and clinical periodontal parameters, including probing depth (PD), clinical attachment loss (CAL), and bleeding on probing (BOP), suggests that TMAO may be influenced by local periodontal inflammation.
Biomarker-based diagnostic methods provide significant advantages in identifying individuals at risk for disease onset or progression, offering insights beyond traditional clinical parameters such as gingival bleeding, clinical attachment loss, and radiographic bone loss [
4,
25]. In periodontology, point-of-care (PoC) tests have facilitated the rapid detection of periodontal diseases by analyzing biomarkers in oral fluids—including saliva, oral rinse, and gingival crevicular fluid—without requiring laboratory-based assessments [
26,
27]. Among these, the active-matrix metalloproteinase-8 (aMMP-8) PoC test has been extensively studied and has demonstrated a strong ability to differentiate periodontitis patients from periodontally healthy individuals [
28‐
31]. However, its accuracy may be influenced by systemic conditions, such as Crohn’s disease (CD), where reported sensitivity and specificity values have been lower compared to systemically healthy individuals [
32]. While aMMP-8 remains a well-established biomarker for assessing periodontal disease, TMAO has emerged as another potential biomarker that may provide complementary insights, particularly in the context of systemic inflammatory conditions. Unlike aMMP-8, which primarily indicates periodontal tissue degradation, TMAO is associated with broader inflammatory pathways. As a catalytically active and tissue-destructive enzyme, MMP-8 plays a key role in progressive periodontal lesions [
26], whereas TMAO has been implicated in endothelial dysfunction, oxidative stress, and inflammatory gene expression [
3,
8,
15]. Given that TMAO is recognized for its systemic effects, including modulation of nitric oxide (NO) bioavailability and superoxide-driven oxidative stress [
4], its presence in saliva may provide a link between oral and systemic inflammation.
A key finding in our study was that ordinal regression analyses revealed a significant association between higher salivary TNF-α and TMAO levels and increased odds of having periodontitis, even after adjusting for age. This suggests that these biomarkers may serve as independent indicators of periodontal disease risk, beyond the influence of aging-related inflammatory changes. Given that TNF-α is a well-established pro-inflammatory cytokine involved in periodontal destruction [
33], its association with TMAO levels and periodontitis status further supports the role of inflammatory-metabolic interactions in periodontal pathogenesis.
One possible explanation for the observed elevation in salivary TMAO is its interaction with oral microbiota. It is well established that TMAO is derived from the microbial metabolism of dietary precursors such as choline, betaine, and carnitine, which are subsequently oxidized in the liver [
34]. Oral bacteria, particularly periodontopathogens, have been implicated in TMAO metabolism, with evidence suggesting that species like
Porphyromonas gingivalis and
Fusobacterium nucleatum may enhance TMA production, thereby contributing to local and systemic TMAO accumulation [
8]. Previous in vivo studies have demonstrated that exposure to P. gingivalis can increase circulating TMAO levels and promote endothelial dysfunction, further reinforcing the link between oral dysbiosis, TMAO production, and systemic inflammation [
15]. The significant correlation observed between plaque index (PI) and salivary TMAO in our study indirectly supports the notion that bacterial load influences TMAO metabolism, highlighting the need for future microbiome-integrated analyses.
In addition to its potential microbial origins, TMAO is recognized for its pro-inflammatory properties. Our study found a significant positive correlation between TMAO and TNF-α, a key cytokine involved in periodontal and systemic inflammation [
33,
35‐
39]. TNF-α plays a crucial role in periodontal destruction by promoting osteoclastogenesis, matrix metalloproteinase activation, and soft tissue degradation [
40]. Elevated TNF-α levels in saliva and serum have been consistently reported in patients with periodontitis [
41,
42], particularly in stage III and IV disease [
43]. Experimental studies suggest that TMAO may directly stimulate TNF-α production via NF-κB activation [
38,
39], contributing to an amplified inflammatory response. These findings suggest that TMAO may not merely be a metabolic byproduct but an active participant in the inflammatory cascade, potentially influencing disease progression.
After evaluating differences in TMAO and TNF-α levels between groups, we further examined the correlation between salivary and serum levels of these molecules. The strong correlation between salivary and systemic TMAO concentrations reinforces the potential of salivary diagnostics as a surrogate for systemic inflammatory status. While serum TMAO has been widely associated with cardiovascular disease risk [
15], with meta-analyses reporting its predictive value for atherosclerosis and major adverse cardiovascular events [
44], our study specifically excluded individuals with diagnosed cardiovascular disease. The observation that TMAO was elevated in periodontitis patients suggests that periodontal inflammation alone may contribute to increased TMAO production. This aligns with previous reports indicating that TMAO levels can be influenced by chronic inflammatory conditions [
38,
39], independent of classical cardiovascular risk factors.
One of the key strengths of this study is its controlled evaluation of salivary and serum TMAO and TNF-α levels, which allowed for the isolation of periodontitis-associated changes from potential systemic confounders. By excluding individuals with known cardiovascular disease and other systemic disorders, we were able to specifically assess the relationship between periodontal inflammation and TMAO metabolism. Additionally, the use of both salivary and serum samples enhances the translational relevance of our findings, supporting the potential application of salivary TMAO as a non-invasive biomarker in periodontal disease monitoring.
However, several limitations should be noted. First, the cross-sectional design of the study limits causal inferences regarding the relationship between TMAO, TNF-α, and periodontal disease progression. Longitudinal studies tracking TMAO levels over time in individuals with periodontitis would help determine whether TMAO serves as a predictive biomarker for disease progression or resolution following periodontal therapy. Second, while our findings suggest a microbial contribution to TMAO levels, we did not directly analyze the composition of the oral microbiome. Given the emerging evidence linking periodontopathogens to TMA metabolism, future research integrating metagenomic and metabolomic approaches could provide deeper insights into the interplay between oral bacteria, host metabolism, and inflammatory pathways.
Conclusions
This study contributes to the growing body of evidence suggesting that salivary TMAO may serve as a potential biomarker for periodontal inflammation, demonstrating strong correlations between TMAO, TNF-α, and clinical periodontal parameters. Importantly, ordinal regression analyses confirmed that higher salivary TNF-α and TMAO levels were significantly associated with higher odds of periodontitis, even after adjusting for age, reinforcing their relevance as potential indicators of periodontal disease risk. While aMMP-8 has been widely studied as an indicator of periodontal tissue degradation, TMAO appears to provide complementary information, reflecting broader inflammatory pathways that may bridge oral and systemic health. However, given the complexity of TMAO metabolism and its interactions with microbial and host inflammatory responses, further studies are needed to determine its specificity and utility in clinical practice. Future research should focus on longitudinal studies, in vitro and in vivo mechanistic analyses, and microbiome-metabolome integrations to better understand TMAO’s role in periodontitis pathogenesis and its potential application in personalized periodontal diagnostics and therapeutic strategies.
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