Macrophage polarization M1 vs. M2 dynamics in periodontal tissues

Macrophages in periodontal tissues adopt a spectrum of activation states, with classically-activated (M1) and alternatively-activated (M2) subsets dominating the pro-inflammatory and reparative phases of periodontitis, respectively. In healthy tissues, resident macrophages contribute to homeostasis and microbial surveillance, but in disease conditions, dysbiotic biofilms trigger shifts toward an M1-dominant milieu that exacerbates inflammation and bone loss [9, 10]. Conversely, M2 macrophages secrete anti-inflammatory mediators and pro-resolving factors that restrain tissue destruction, promote efferocytosis, and support osteoblast activity to restore the periodontium [11, 12].

G protein-coupled receptors (GPCRs) mediated signalling

SCFAs signal through distinct GPCRs. Acetate primarily activates GPR43 [free fatty acid receptor 2 (FFAR2)], whereas propionate and butyrate also engage GPR41 (FFAR3), with butyrate showing preferential activity at GPR109A [5]. These receptors are expressed across multiple immune cell populations, including neutrophils, monocytes/macrophages, dendritic cells, and T lymphocytes, where they initiate anti-inflammatory signalling cascades [15]. Activation of GPR43 enhances neutrophil movement to sites of infection and aids microbial clearance, while at the same time reducing pro-inflammatory cytokines such as IL-6, IL-12, and TNF-α through macrophage-dependent mechanisms [16]. Similarly, activation of GPR109A by butyrate promotes tolerogenic dendritic cells that support Treg development and help limit systemic inflammation. In addition, SCFA signalling through GPCRs regulates inflammasome activity, as GPR43-dependent calcium signalling controls NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome assembly and IL-1β release without triggering pyroptotic cell death under normal conditions [17].

HDAC inhibition & epigenetic regulation

Due to their small size and ability to enter cells and the nucleus, SCFAs—especially butyrate—act as inhibitors of class I and II HDACs. This leads to increased histone acetylation at genes involved in immune regulation, such as forkhead box P3 (FOXP3) and IL-10, promoting the differentiation of naïve CD4⁺ T cells into Tregs with anti-inflammatory functions [3]. At the same time, butyrate suppresses Th17 and Th1 cell development, reducing IL-17 and IFN-γ production in inflammatory settings. In innate immune cells, including macrophages and dendritic cells, HDAC inhibition decreases the expression of pro-inflammatory mediators such as nitric oxide synthase 2 (Nos2), IL-6, IL-12, and TNF, thereby favouring a more tolerogenic, anti-inflammatory phenotype [4].

Mucosal barrier & innate sensor regulation

SCFAs, particularly butyrate, play a central role in preserving the integrity of the intestinal epithelial barrier, the body’s first line of defence against invading pathogens and luminal antigens. One mechanism involves the stabilization of hypoxia-inducible factor-1α (HIF-1α), a transcription factor that supports epithelial survival under hypoxic conditions [18]. Stabilized HIF-1α enhances the expression of genes critical for barrier maintenance, including those regulating tight junction proteins such as claudin-1, occludin, and zonula occludens-1 (ZO-1) [19]. By reinforcing these junctional structures, SCFAs reduce microbial translocation and the risk of systemic inflammation [20]. Beyond barrier stabilization, butyrate directly influences host microbe interactions by inducing antimicrobial peptides (AMPs), such as RegIIIγ and β-defensins, without disrupting commensal communities. This induction occurs via GPR43 signalling, which activates downstream mitogen-activated protein kinase (MAPK) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathways in epithelial cells [21].

SCFAs also fine-tune innate immune sensors by modulating inflammasome activity. Through calcium-dependent signalling downstream of GPR41/43, they regulate NLRP3 inflammasome assembly. This regulation prevents excessive IL-1β production, a potent pro-inflammatory cytokine capable of driving tissue injury and systemic inflammation if unchecked. In this way, SCFAs function as molecular brakes on innate immune hyperactivation, preserving their protective roles while limiting pathological outcomes [22].

Neutrophil activation and innate clearance

SCFAs also influence neutrophil biology, a cornerstone of the innate immune response. Neutrophils are among the first immune cells recruited to infection or injury sites, where they eliminate pathogens. Acetate, propionate, and butyrate activate GPR43 (FFAR2), a receptor abundantly expressed on neutrophils, to regulate their migration and effector functions [23]. Engagement of GPR43 enhances neutrophil chemotaxis, allowing precise navigation toward chemokine gradients and microbial signals within inflamed tissues [24]. This targeted recruitment facilitates rapid deployment of innate defence at the site of infection [25]. In addition to recruitment, SCFAs boost neutrophil effector functions. They increase phagocytic activity and enhance the oxidative burst by promoting reactive oxygen species (ROS) production, thereby strengthening microbial killing [26]. SCFAs also stimulate the formation of neutrophil extracellular traps (NETs), web-like DNA structures coated with antimicrobial proteins that immobilize and kill microbes [27]. However, excessive neutrophil activation and ROS release can damage host tissues, disrupting epithelial integrity and perpetuating inflammation. This duality is evident in inflammatory bowel disease (IBD), where uncontrolled neutrophil responses contribute to mucosal erosion and tissue injury. SCFAs appear to balance these opposing outcomes by supporting efficient pathogen clearance while restraining pathological inflammation, thereby sustaining neutrophil function in a protective, rather than destructive, manner [28].

Macrophages and monocytes

Experimental studies using RAW 264.7 macrophages and primary human monocytes demonstrate that exposure to SCFAs, particularly butyrate, significantly modulates their inflammatory responses. Butyrate suppresses LPS or P. gingivalis-induced expression of Nos2, IL-1β, TNF-α, and CXCL2, key mediators driving periodontal tissue destruction. These findings suggest that SCFAs dampen inflammatory cascades that would otherwise accelerate alveolar bone loss and connective tissue breakdown. Interestingly, butyrate does not act in a strictly suppressive manner; at low concentrations, it can paradoxically elevate IL-1β production, indicating a biphasic, dose-dependent effect that underscores the fine balance between protective and pathogenic immune outcomes in the periodontal niche [41, 42]. SCFAs also shape macrophage polarization, favoring a shift from a pro-inflammatory M1-like phenotype toward an anti-inflammatory M2-like state. This reprogramming is mediated by HDAC inhibition and GPCR signalling, which attenuate NF-κB activity while enhancing IL-10 secretion. These epigenetic and metabolic changes drive a transition from glycolysis to oxidative phosphorylation, reinforcing tolerogenic and tissue-protective functions [43]. Nevertheless, persistently high levels of SCFAs, as observed in advanced periodontitis, may exert cytotoxic or dysregulatory effects, complicating their protective role [44]. Figure 2 illustrates how gut microbial balance influences macrophage-mediated immune regulation through SCFA signalling. Under eubiotic conditions, SCFAs foster an anti-inflammatory M2 phenotype, reinforcing neuroimmune stability and mitigating periodontal tissue damage. Conversely, dysbiosis disrupts SCFA availability, skewing macrophages toward a pro-inflammatory M1 state that amplifies systemic inflammation and periodontal disease progression.

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Figure 2. Comparative illustration of macrophage responses under gut eubiosis versus dysbiosis. During eubiosis, microbial fermentation of dietary fibers produces SCFAs that promote M2 macrophage polarization through GPR43/GPR109A signalling and HDAC inhibition, enhancing IL-10 and TGF-β secretion. These anti-inflammatory mediators support neuroprotection and contribute to reduced periodontal inflammation. In contrast, gut dysbiosis and the consequent depletion of SCFAs drive macrophage M1 polarization, leading to elevated TNF-α, IL-6, and IL-12 levels that exacerbate systemic and periodontal inflammation. SCFA: short-chain fatty acid; IL: interleukin; TGF-β: transforming growth factor beta; TNF-α: tumor necrosis factor-α; ROS: reactive oxygen species; HDAC: histone deacetylase. “Comparative illustration of macrophage responses under gut eubiosis versus dysbiosis” created in BioRender. Kumar, A. (2026) https://BioRender.com/ulv3rl0 is licensed under CC BY 4.0.

Gingival fibroblasts and epithelial cells

Fibroblasts and epithelial cells, essential for maintaining periodontal structure and barrier integrity, are highly susceptible to SCFA toxicity. At concentrations in the 1–5 mM range, butyrate and propionate impair fibroblast proliferation by inducing G0/G1 or G2/M cell cycle arrest through downregulation of cyclin B1, Cdc2, and Cdc25C, thereby disrupting tissue repair and regenerative capacity [45]. SCFA exposure also increases ROS generation, causing DNA and protein damage, thus triggering apoptosis through mitochondrial and caspase-dependent pathways. Recent reports further implicate butyrate in ferroptosis induction via ferritinophagy, linking iron-dependent cell death to periodontal oxidative stress [40]. Epithelial keratinocytes display similar vulnerabilities. In Ca9-22 cells, elevated SCFAs induce apoptosis, pyroptosis, and autophagy, accompanied by loss of tight junction proteins such as occludin and E-cadherin. This barrier disruption facilitates deeper bacterial penetration into the gingival tissues. Clinical studies confirm that butyrate levels in GCF are higher in periodontitis patients compared to healthy individuals, directly correlating with epithelial barrier breakdown [46, 47].

Neutrophils and dendritic cells

SCFAs strongly influence neutrophil function through GPR43 activation. Acetate, propionate, and butyrate act as ligands to drive chemotaxis via PI3Kγ, Rac2, and MAPK signalling, enhancing recruitment to infected sites. While this supports microbial clearance, excessive signalling leads to hyper recruitment, elevated ROS release, and protease activity; factors contributing to periodontal tissue injury [29]. Supporting this, GPR43-deficient mice exhibit uncontrolled neutrophil accumulation, elevated cytokine release, and aggravated inflammation during microbial challenge, emphasizing SCFA GPR43 signalling as a checkpoint for neutrophil homeostasis [48]. NETs are released during NETosis and serve as an important barrier against periodontal pathogens, but when NET formation is exaggerated or dysregulated, it contributes to tissue destruction by releasing proteases, histones, and ROS that damage epithelium and alveolar bone [49, 50].

In dendritic cells, butyrate induces a tolerogenic phenotype characterized by reduced major histocompatibility complex class II (MHC-II) and co-stimulatory molecule expression alongside increased IL-10 production. These tolerogenic dendritic cells promote Treg differentiation while suppressing Th1 and Th17 responses, contributing to immune tolerance within the periodontium. Thus, SCFAs orchestrate dual outcomes, enhancing localized innate defence yet promoting systemic immune regulation through dendritic cell programming [51].

Adaptive T cell responses

Gut-derived SCFAs also regulate adaptive immunity by influencing CD4⁺ T cell differentiation. Butyrate enhances the generation of Tregs via HDAC inhibition, upregulating FOXP3 and IL-10 expression, hallmark features of an anti-inflammatory phenotype. Simultaneously, SCFAs attenuate Th1 and Th17 polarization, thereby reducing secretion of IL-17 and IFN-γ [3, 4]. Epigenetically, SCFAs increase acetylation at the FOXP3 promoter while repressing RORγt, the master regulator of Th17 differentiation, thus stabilizing Treg development and limiting pro-inflammatory effector responses in periodontal tissues. Importantly, these protective effects are Treg-dependent; in Treg-deficient settings, SCFAs fail to confer immunoregulation [4].

To translate these findings therapeutically, novel delivery approaches such as SCFA-loaded nanoparticles or liposomal butyrate are under development. These systems sustain Treg-promoting and anti-inflammatory effects while minimizing cytotoxicity, offering promise as adjunctive strategies in managing periodontal and systemic inflammatory diseases [52]. Thus, SCFAs have a significant impact on key immune cell populations relevant to periodontal health, as summarized in Table 2.

Dietary fiber and probiotics

Increasing dietary intake of fermentable fibers, such as inulin and resistant starch, enhances colonic SCFA production, reinforcing barrier integrity and anti-inflammatory immune responses [56]. In preclinical models, high fiber diets reduce systemic inflammation and attenuate experimental periodontal bone loss by elevating butyrate levels. Similarly, administration of butyrate-producing probiotics, including Faecalibacterium prausnitzii and Clostridium butyricum raise systemic SCFA concentrations and diminishes inflammatory pathology in models of arthritis and periodontitis, highlighting their potential as adjuncts in periodontal care [57].

SCFA supplementation

Direct SCFA delivery is being explored to bypass variability in host microbiota composition. Encapsulation techniques and prodrugs such as tributyrin allow systemic butyrate release while minimizing local cytotoxicity. In vitro, lipid-encapsulated butyrate supports dose-dependent Treg differentiation and reduces epithelial cell damage. Although human studies in periodontal disease remain limited, early phase trials in other inflammatory conditions suggest that SCFA supplementation is both safe and immunomodulatory [58].

Biomarkers and personalized therapies

SCFA levels may serve as useful biomarkers for both local and systemic immune homeostasis. In periodontal pockets, elevated butyrate and propionate in gingival crevicular fluid reflect microbial dysbiosis and tissue activity, whereas fecal or serum SCFA levels correlate with gut microbial resilience and lower inflammatory burden. Longitudinal studies are required to validate these signatures and to develop microbiome-targeted, personalized strategies for managing periodontal disease [59].

Although several routes exist to harness SCFAs for periodontal benefit, their comparative feasibility and readiness for clinical translation differ markedly. Dietary fiber/prebiotic approaches are the most advanced in humans. Animal and small clinical studies show that increasing fermentable fiber reliably raises systemic SCFA production and can reduce inflammatory biomarkers, but effects on periodontal endpoints are variable and slow to appear because of individual differences in baseline microbiota and adherence [60]. Probiotic strategies (including Clostridium butyricum strains) have demonstrated efficacy in rodent periodontitis models and show promise for restoring butyrogenic taxa, yet human evidence is limited and strain-, dose-, and formulation-dependent [37]. Direct systemic SCFA supplementation or prodrugs offers controlled dosing and proof-of-principle immunomodulation in preclinical models (including bone-protective effects), but rapid host absorption/metabolism and uncertain safety at therapeutic doses complicate translation [38]. Local, targeted periodontal delivery (mucoadhesive hydrogels, microparticles, nanoparticles) is attractive because it limits systemic exposure and can concentrate agents at the diseased site; however, the periodontal pocket’s fluid flow, salivary washout, and the small, highly diffusible nature of SCFAs require advanced encapsulation chemistries and mucoadhesive strategies to achieve sustained, sub-toxic release—most such platforms are still at the preclinical/proof-of-concept stage [61]. Engineered SCFA-bearing nanocarriers and enzyme-responsive SCFA pro-materials are emerging preclinical options that promise tuned pharmacokinetics and site-specific release but face formulation complexity, biocompatibility testing, and regulatory hurdles before human trials [62].

Mechanistic insights for therapy