Pharmacological and therapeutic effects of short-chain fatty acids in gastrointestinal and extra-intestinal disorders: evaluation of metabolic, hormonal and inflammatory parameters

The short chain fatty acid (SCFA) butyrate, a main end product of microbial fermentation of dietary fibers in human intestine, plays an important role in the maintenance of intestinal homeostasis and overall health status. The effects exerted by butyrate are multiple and involve several distinct mechanisms of action including epigenetic modifications owing to its inhibitory effects on histone deacetylases, inhibition of NF-κB signaling, or direct agonism on the free fatty acid receptors. At intestinal level, butyrate is the major energy source for colonocytes and acts regulating epithelial cell proliferation, defense barrier, visceral sensitivity and motility, preventing and inhibiting colonic carcinogenesis. Recent experimental evidence has suggested potential extra-intestinal therapeutic applications of butyrate, including the treatment of systemic diseases, among these not only metabolic and inflammatory disorders but also cystic fibrosis, urea cycle enzyme deficiency, X-linked adrenoleukodystrophy. Data from literature and clinical evidence of several research groups show a wide spectrum of possibilities for potential therapeutic use of butyrate by oral administration without having serious adverse effects. Some butyrate-based products are marketed, but their spread is still very limited and greatly understaffed in view of the wide spectrum of possible indications, especially in chronic diseases, where it is possible to predict a lasting use of the compound. The main problem is the availability of butyrate formulations that could overcome the main limitations to the use of butyrate in the therapeutic field, namely its instability and poor palatability. In fact, the unpleasant taste and odour make oral administration of butyrate extremely difficult, especially in children. On the basis of its characteristics, butyrate can be considered a “postbiotic” being a non-viable bacterial metabolic product obtained from probiotic microorganisms that have biologic activity in the host. The direct use of postbiotics, such as butyrate, may be potential alternatives to the use of live probiotic organisms or to dietary fiber intake as prebiotics exerting several and similar beneficial regulatory effects on host biological functions. Even if a growing number of studies has revealed new mechanisms and effects of butyrate with a wide range of potential clinical applications from the intestinal tract to peripheral tissues, more data are needed to elucidate the efficacy of butyrate in gastrointestinal and extra-intestinal diseases and new solutions for an easier administration. To date, several studies have evaluated butyrate effectiveness in several animal models of colitis. In humans few studies have been performed probably due to low compliance for the oral route (for its rancid taste) or rectal enemas administration (for its cumbersome application to the patient and irritability due to acid property). Here, about its intestinal effects, we examined the efficacy of oral butyrate and its derivative N-(1-carbamoyl-2-phenyl-ethyl) butyramide (FBA), as preventive or therapeutic treatment in a murine model of DSS-induced colitis. Both compounds are able to recover the imbalance between pro-inflammatory and anti-inflammatory mediators, altered in colitis and restore gut permeability, avoiding bacterial translocation and modulating immune cell recruitment. Butyrate anti-inflammatory effects are associated not only to the reduction in neutrophil infiltration and HDAC9 transcription in colonic mucosa, but also the restoration of PPAR-γ expression and inhibition of NF-kB activation, protecting colonocytes from inflammation. Alterations in the microbiota have now been implicated in the pathogenesis of some diseases, including food allergy. Intestinal microbiota influences immune system network and impairs its regulatory functions. Allergic infants exhibit an accelerated evolution of microbiota more typical of the adult one with a significantly reduced abundance of butyrate-producing species, such as Lactobacillales and Bifidobacteriales, and increased abundance of Clostridiales. Animal models of food allergy have emerged as tool for identifying mechanisms involved in the development of sensitization to normally harmless food allergens, as well as delineating the critical immune components of the effect or phase of allergic reactions to food. One of the critical advantages of using mouse models to study food allergy is that allergic sensitization or tolerance can be induced to specific allergens under controlled environmental conditions within defined genetic backgrounds, which is not possible in human subjects. This aspect of mouse models allows extensive and precise investigations into the mechanisms involved in disease etiology and responsible for loss of tolerance in patients, identifying new targets and efficacious therapies. Increasing evidence from several mouse models indicates that alterations in regulatory T (Treg) cell function and environmental factors, such as microbiota, are likely important contributors to allergic sensitization and food allergy. Here, we used a model of cow's milk allergy (CMA) induced in mice. In this experimental model of CMA the preventive and therapeutic effects of oral sodium butyrate administration were evaluated. Butyrate was able to suppress acute skin response to the β-lactoglobulin (BLG) allergen, one of the most important cow’s milk proteins, and to reduce anaphylactic symptoms and immediate immune response. Furthermore, butyrate ability to improve gut permeability was also shown, reducing plasma levels of FITC-Dextran evaluated after oral administration. Butyrate reduced ear swelling, hypersensitivity symptoms and limited the decrease of body temperature after BLG challenge. Moreover, butyrate decreased the innate immune response, reducing IgE and IL-4 levels. About butyrate extra-intestinal effect, our study was focused on osteoarthritis (OA), the most common form of arthritis worldwide, whose development is increased by aging, obesity and biomechanical injury. It is a cartilage degenerative disease where chondrocytes play a central role. In fact, in OA chondrocyte phenotype changes and apoptosis and extracellular matrix degradation occur. Using an in vitro model, we demonstrated the effect of sodium butyrate in reducing inflammatory mediators and pathways in chondrocytes activated by IL-1, and, more interestingly, we showed that its chemoattractant activity is mediated by GPR43. Butyrate, not only reduced pro-inflammatory cytokines and adipokines involved in OA, but also decreased the expression of several adhesion molecules, inhibiting inflammatory and anti-apoptotic pathways. We also show the butyrate capability to reduce MMPs production and the loss of collagen type 2, suggesting an improvement of cartilage disruption. Interestingly, butyrate anti-inflammatory effects were associated to its capability to stimulate neutrophil recruitment, increasing the expression of important chemokines (Ccl3 and Cx3cl1) and anti-inflammatory protein AnxA1, suggesting butyrate pro-resolving activity during inflammatory response. The novelty of our data is the involvement of GPR43 in the chemoattractant activity of butyrate in IL-1-stimulated chondrocytes. In fact, butyrate failed to induce the expression of Cx3cl1 and AnxA1 in GPR43-silenced cells, missing its chemoattractant effect. The pro-resolving effect of butyrate was also analyzed in two models of wound healing induced by doxorubicin or mechanical damage. In tissue repair the immediate goal is to achieve tissue integrity, homeostasis and wound healing. Tissue injury causes the immediate onset of acute inflammation. The healing process involves three phases that overlap in time and space: inflammation, tissue formation, and tissue remodeling. Synthesis, remodeling, and deposition of structural extracellular matrix molecules and soluble mediators, are indispensable for initiating repair and progression into the healing state. In our study, we demonstrated that butyrate and FBA treatments accelerate and promote wound resolution process. In our experimental models, we showed that butyrate and its derivative FBA reduced the repair time when used systemically (by oral administration) or topically (by intradermal injection). This protective effect appeared to be time- and concentration-dependent. In summary, we have demonstrated the multiple protective effect of butyrate in limiting molecular events underlying the onset of several inflammatory-based pathologies, suggesting a potential clinical relevance for this compound. In particular, we have also showed the efficacy of its synthetic derivative N-(1-carbamoyl-2-phenyl-ethyl) butyramide or FBA, demonstrating that it could represent an alternative therapeutic option to sodium butyrate, sharing a comparable efficacy, but better palatability and compliance