PLMI Blog

As of 2024, chronic disease is shown to affect at least 129 million individuals in the US (1). A growing body of research demonstrates the connection between chronic disease and nitric oxide (NO) production, a critical molecule that governs an array of biological processes integral to systemic and overall health. The state of the oral and gut microbiome are also key players in regulating NO synthesis and have a pivotal influence on chronic disease.

Connecting the Dots with NO

With a fleeting life of nearly a second, NO is a gaseous signaling molecule involved in modulating integral cellular functions that underlie health including inflammation, GI motility, endothelial function, oxidative stress, immunity, and insulin signaling (2-4). NO levels are influenced by oral and GI microbiome health, as bacteria in these ecosystems can synthesize NO. Low levels of NO can impede a multitude of regulatory processes in the body, making one more susceptible to developing chronic disease.

The intricate relationship among the oral microbiome, gut health, NO production, and chronic disease highlights the complex microbial interactions that influence systemic health, revealing connections that warrant further exploration for improved treatments.

Let’s explore these connections.

Oral Microbiome – The oral microbiome exhibits diverse microbial composition; hosting an ecosystem of bacteria, fungi, and viruses. It harbors more than 700 different types of these microorganisms, playing a crucial role in maintaining oral health, with vast implications beyond the mouth (5). The oral microbiome can initiate oral and systemic disease, similar to microbial shifts observed in the (GI) tract (6).

Oral microbiota have been linked to various systemic diseases, as they have the capability to spread throughout the body (6). The oral microbiota actively communicates with the host via bi-directional interactions across the oral cavity and systemic organs. A number of chronic health conditions have been shown to correlate with systemic disease as a result of disruptions in microbial balance (7). Oral microbiota contribute to systemic diseases by triggering inflammatory responses through the migration of oral microbes to other organs and tissues (8).

Gut Health – The gut microbiome consists of approximately 10^13–10^14 microorganisms that establish a symbiotic relationship with the host – regulating metabolism, GI motility, inflammation, digestion, and immune function (9). There is growing evidence that disturbances in the gut microbiome, (as in dysbiosis) are associated with various chronic diseases. Recent research has linked gut microbiota function to a range of chronic diseases. Recognizing the significance of the oral-systemic connection is crucial for advancing strategies to prevent and treat GI disorders effectively (10-14).

(NO) Production – NO functions as a crucial signaling molecule involved in diverse physiological regulatory processes. It is synthesized in various tissues, including endothelial cells and certain bacteria. NO has roles enhancing oxygen delivery to cells, while also serving vital antioxidant functions by counteracting free radicals and helping to modulate healthy levels of inflammation. This is significant as inflammation is implicated in the etiology of nearly all chronic diseases (3).

CONNECTION AND MECHANISMS

Oral Microbiome and NO Production

The oral cavity plays a key role in producing (NO) via the nitrate-nitrite-NO pathway, supported by beneficial bacteria. Distinct bacteria in the oral microbiome can produce NO, particularly from dietary nitrate. NO can then be absorbed into the bloodstream and affect systemic NO levels. Within the oral cavity, various bacterial species have the ability to convert nitrate into nitrite, an important precursor to the signaling molecule NO (9).

The oral microbiome is integral as it can trigger both oral and systemic diseases. Similar to the GI tract, changes in oral microbial ecology can promote pathogenic conditions. The nitrate-nitrite-NO pathway, facilitated by commensal bacteria in the oral cavity, underscores the oral microbiome’s role in NO production.

Saliva, essential for oral health, contains antimicrobial enzymes that support and defend against external bacteria throughout the body. This interconnected system highlights how the oral microbiome influences chronic diseases through NO-mediated pathways (2). Individuals generate over 1000 mL of saliva daily, nearly all of which reaches the GI tract. This makes oral microbiota crucial for maintaining gut ecosystem stability (7).

Recent research highlights the role of oral bacteria in the nitrogen cycle by converting salivary nitrate to nitrite. Upon ingestion, nitrite undergoes enzymatic and non-enzymatic processes to form NO. As NO serves as a crucial signaling molecule with antimicrobial properties, and acts as a potent vasodilator and protective agent in all tissues, this underscores that the composition and activity of oral bacteria play a significant role in chronic disease regulation (9).

The oral microbiome is dynamic and influential in health and chronic disease. This ecosystem is highly responsive to internal and external factors. The composition of the oral microbiome holds significant implications for overall health, including its impact on metabolic regulation.

Understanding the oral microbiome offers insights into optimizing health outcomes, particularly with relevance to chronic disease (9). These insights underscore the critical role of the oral microbiome in influencing various aspects of chronic disease and overall health, with NO serving as a central link connecting these imperative physiological functions (2, 6).

Gut Microbiome and NO Production

Microbiota residing in the gut microbiome can also produce NO. The gut microbiome’s composition and health influence this process, impacting systemic NO levels, and thus vascular function and overall systemic health. There is a 45% overlap between the bacteria in the oral cavity and in the GI tract (15).

The gut microbiome plays a significant role in NO production through several mechanisms:

Nitrate Reduction: Dietary nitrate can be converted into nitrite by symbiotic bacteria.  Nitrite undergoes non-enzymatic synthesis to form NO (16). Nitrite is then further reduced to NO either in the mouth or after absorption into the bloodstream. Tiso and Schechter (2015) demonstrated that various commensal bacteria in the oral cavity and gut, (Veillonella and Prevotella species) are capable of reducing nitrate to nitrite, thus contributing to systemic NO production (17).

NOS Regulation: Gut bacteria influence the expression and activity of NOS enzymes, responsible for NO synthesis. Yang et al. (2015) demonstrated that gut microbiota-derived metabolites, such as short-chain fatty acids, can enhance the expression of endothelial nitric oxide synthase (eNOS) in endothelial cells, thereby increasing NO production (18).

Metabolite Production: Gut microbes produce various metabolites that can affect NO signaling pathways and cardiovascular health indirectly. Research findings have demonstrated that gut microbiota-produced TMAO can modulate endothelial function and NO signaling, potentially influencing cardiovascular health (19-20).

Nutrition: Dietary nitrate intake from vegetables (such as spinach and beetroot) can enhance NO bioavailability through microbial conversion to nitrite and NO synthesis, as evidenced in the literature (21). Beyond modifying the gut microbiome composition, probiotic supplementation has been associated with various benefits, including enhanced immune function, reduced blood pressure, improved blood glucose levels and insulin sensitivity, and beneficial effects on total cholesterol and LDL levels (22-25).

The gut microbiome’s composition and activity are intricately linked to NO production through its ability to metabolize dietary nitrate, regulate NOS enzymes, produce NO-related metabolites, and influence systemic NO levels. This interplay underscores the importance of microbiome health in cardiovascular and metabolic processes mediated by NO.

Impact on Chronic Disease

Dysbiosis in the oral or gut microbiome can lead to reduced NO production or altered metabolism of nitrate, potentially contributing to chronic disease. For example, reduced NO availability can impair vascular function, increase inflammation, and affect immune responses, all of which are implicated in chronic disease development.

Research over the past 15 years has shown that mouthwash use decreases levels of salivary and plasma nitrite, crucial for NO-dependent biological effects. One study demonstrated that 7 days of mouthwash use changed the oral microbiota, leading to increased acidity in the oral environment and reduced nitrite levels in healthy individuals (26-27). Another study also found that using mouthwash for 7 days resulted in reduced levels of salivary and plasma nitrite, accompanied by elevated systolic and diastolic blood pressure (28). These changes can lead to a less favorable oral environment due to altered microbial composition and reduced nitrite availability.

Clinical Implications

Maintaining a healthy oral and gut microbiome through balanced nutrition, informed oral hygiene practices, and probiotic supplementation may support optimal NO production. This approach helps mitigate the risk of chronic diseases associated with endothelial dysfunction, inflammation, and oxidative stress. NO production declines with age and is influenced by factors such as diet, stress, and the use of mouthwash and medications. Regular exercise, quality sleep, sun exposure, and nourishing the microbiome with diverse, nutrient-dense foods can all optimize NO production.

Adding nitrate-rich beetroot juice has been demonstrated to modify the oral microbiome, as observed in several studies (29-31). Most studies indicate an increase in the relative abundance of Neisseria and Rothia in saliva following nitrate supplementation (29, 31). Substantial evidence suggests that consuming a diet rich in nitrates can contribute to improved oral health. Doel et al. found that children who harbor more nitrate-reducing bacteria, such as Veillonella atypica demonstrated enhanced nitrate reduction and a notably lower risk of experiencing dental caries (32). Further studies have indicated that adults and children with higher levels of salivary nitrite also tend to have a reduced incidence of dental caries (33-34).

Research demonstrated that a two week regimen of nitrate-rich lettuce juice elevated levels of Rothia and Neisseria bacteria and reduced gingival inflammation in patients (35-36). Unlike treatments involving antibiotics or mouthwash, this approach appears to address the underlying cause of the condition, while also maintaining the nitrate-nitrite-NO pathway from the gut to saliva.

The oral and gut microbiome play critical roles in NO production, which in turn affects various integral processes that regulate health. Understanding these connections underscores the importance of microbial balance in both oral and gut ecosystems for maintaining systemic health.

Join us for this event, The Gateway to Healing: Uncovering the Intersection of the Oral Microbiome, Gut Health, and Chronic Disease on August 27th, from 5 to 7 pm PST with Dr. Chris Easton, Dr. Haroldo Magarinos, and Jeffrey Bland, PhD. The interconnectedness of the oral microbiome, gut health, and chronic disease will be discussed with emphasis on the significant overlap between oral and gut microbial communities and NO synthesis, providing valuable clinical insights.

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