Butyrate and its multifarious effects

By Pauline Paap, Orffa Additives, the Netherlands

Energy supply to intestinal epithelial cells is important due to the fact that the mammalian intestinal mucosa is one of the most rapidly replicating tissues in the body. For example, studies in rodents demonstrate that the small intestinal epithelium is completely replaced every two to three days. Thereby, the colonic epithelium is permanently in close association with microbes and their product, meaning there is a constant immunological challenge. This makes the barrier defence function of the epithelial layer of great importance. Butyrate is seen as the most important energy source for intestinal epithelial cells and numerous studies indicate the importance of butyrate in sodium and water absorption, influence on epithelial cell proliferation and differentiation, villi development and in improving gut defence systems. In addition, butyrate strengths the barrier function, has antimicrobial potency and positively influences the immune system. In this article we highlight some of the documented effects of butyrate and the need for extra supplementation in animal (pet) diets.

Production of butyrate

Butyrate is naturally present in the colon as a result of microbial fermentation of dietary fibre. It is formed by colon bacteria such as Clostridium, Eubacterium and Butyrivibrio, that ferment the fibres in short-chain fatty acids (SCFA’s), such as acetate, propionate and butyrate. The colon is able to ferment dietary fibre into butyrate at very high concentrations. Whereas most other cell types utilise glucose as their primary energy source, colonocytes (colonic epithelial cells) have a great capacity to rapidly metabolise butyrate into energy for the animal. In the small intestine, microbial formation of butyrate is low or absent. Nevertheless, cells in the small intestine also express the transporter to bring butyrate into the cells, as shown in a study from 2006. Healthy growing piglets that were fed butyrate demonstrated that targeting butyrate into the small intestine improves villi development, gut morphology and function. You can say that the synthesis of many key components of the intestinal epithelial tissue depends on butyrate metabolism. Only small quantities of butyrate will reach the general peripheral blood circulation and liver.

Multifarious effects

Butyrate not only provides energy to cells, it also shows many beneficial ‘side effects’. For example, in contrast to the trophic effect on normal healthy colonocytes, butyrate decreases proliferation and differentiation of tutor cell lines and can finally induce apoptosis; programmed cell death. Butyrate has the ability to influence the gene expression, thereby inducing early apoptosis in cancer cells. Its opposite is seen in normal, healthy cells, where butyrate activates gene expression for cell proliferation and maturation. Several epidemiological studies support the protective role of dietary fibre and its breakdown product butyrate against colonic cancer. These contradictory patterns of butyrate of stimulating cell growth and differentiation of normal cells and apoptosis (early cell death) of tumour cells, represents the so called ‘butyrate paradox’. Butyrate also has a role as an anti-inflammatory agent, primarily via inhibition of nuclear factor kB (NF-kB) activation in colonic epithelial cells. NF-kB regulates many cellular genes involved in early inflammatory responses. The activity of NF-kB is frequently deregulated in colon cancer and in inflammatory bowel diseases (IBDs). Clinical studies show beneficial effects of butyrate administration, directly or via dietary fibre, on inflammation and symptoms in patients with ulcerative colitis (UC, form of IBD). It has been demonstrated that supplemented butyrate is effective in the treatment of mild to moderate Crohn’s disease. A daily dose of oral butyrate resulted in reduction of the clinical signs and inflammatory parameters in the large intestine. Finally as major precursor for de novo lipids synthesis used for the cell membrane, butyrate contributes the maintenance of barrier and transporter functions of the gut. Especially for butyrate there are indications that it increases the defence barrier of the colon mucosa by stimulation of the formation of mucin glycoproteins. These mucin glycoproteins are essential in the mucus layer which protects the intestinal epithelium. Studies showed an important role of butyrate in intestinal wound healing through its positive effect on the tight junctions and gut integrity.

Antimicrobial activity

Extensive use of antibiotics leads to the emergence of antimicrobial resistance, which is not only an issue in livestock, but also in pet animals. Companion animals are in close contact with humans which increase the risk on zoonotic transmission, moreover, difficult to treat infections, use of antimicrobials which are also important in human medicine and limited control on antibiotic treatments increase concerns for public health. Groups of opportunistic pathogens in pet animals include staphylococci, enterococci, Escherichia coli and Salmonella. Antimicrobial peptides (like defensins and cathelicidins) are essential effector molecules of the innate immune system and are of great importance in bacterial host defence. These peptides, also mentioned host defence peptides (HDP’s), possess broad-spectrum antimicrobial activities against bacteria, protozoa, enveloped viruses and fungi. HDP’s can bind to different types of microbial membranes, cause membrane disruption which results in microbial death. This first line of defence and their natural broad-spectrum against microbes, makes the up regulation of HDP’s an interesting approach as alternative or adjunct therapy to antibiotic treatment.

Effect on host defence system

A recent study revealed a novel role for butyrate in the host defence system. Results from this study in chickens showed that butyrate increases the antibacterial activity of host immune cells by up-regulation of an array of HDP’s in vitro and in vivo. This immune defence was coupled with a minimum impact on immune cell activation and inflammation. More importantly, oral supplementation of butyrate resulted in a significant reduction of Salmonella enteritidis after infection. Same results of butyrate were seen in other studies in mammals. After antibiotic treatment of Shigella-infected patients, adjunct therapy of sodium butyrate significantly increased the expression of a specific HDP (cathelicidin LL-37) in the rectal epithelium. Accompanied by early improvement of rectal inflammation and reduction of pro-inflammatory cytokines in the stool compared to the control group. Oral butyrate treatment in Shigella infected rabbits resulted in reduced clinical illness, less severity of inflammation in the colon, significant up-regulation of antimicrobials (HDP’s) in the gut and early reduction of Shigella ­count in the faeces. Another mechanistic explanation on the antimicrobial efficacy of butyrate is discussed by the research group of Van Immerseel (2006). An early step in the pathogenesis of bacteria, like Salmonella, is the interaction between the bacteria and host cells. At low doses butyrate down regulates expression of invasion genes in Salmonella, thereby reducing the ability of the bacteria to attach to host cells of the intestinal epithelium, becoming invasive and virulent. Other studies confirm the efficacy butyrate on inhibition of pathogen colonisation of E. coli and in particular Salmonella.

Proper coating needed

Fibres are a source for butyrate production by the animal itself, but diet with too large amounts of fermentable fibres can have negative effects on faecal characteristics such as loose stools and flatulence. Secondly, intestinal infections, chronic inflammatory disorders and use of antibiotics negatively affect the colonic microflora and may result in reduced production of butyrate. Butyrate is therefore available as metal salts (Na, K, Mg or Ca salt) to add to animal diets, in particular pet food formulations. It is possible to supplement the diet in order to enhance levels of butyrate in various regions of the large intestine. Uncoated butyrate is directly available and will immediately be absorbed in the first part of the digestive tract before reaching the large intestine. In order to exert the influence in the large intestine, dietary butyrate should slowly be released over the gastro intestinal tract. The aim of a coating or encapsulation is to have a targeted release in the whole digestive tract. The protective lipid matrix used for micro-encapsulation of organic acids allows slow-release of active ingredients over the digestive tract, preventing the immediate disappearance of the ingredient (Figure 1). The type of coating influences the release of butyrate over the digestive tract. Proper coating should not be decomposed in the stomach but gradually released in the presence of fat degrading enzymes. By the use of a dissolution test the release rate of sodium butyrate is tested and analysed. This is done by simulating the same conditions of the stomach and intestinal tract. By testing a coated butyrate product (Excential Butycoat), all butyrate is passing the stomach and is gradually released in the intestinal fluid (Internal research by Orffa, 2012).

Effect on Salmonella and smell

Studies in swine and chickens showed that coated butyrate is superior to uncoated butyric acid in reducing intestinal Salmonella colonisation. Environmental contamination and transmission of Salmonella to other uninfected animals was reduced in the coated butyrate group. The researchers suggest that uncoated butyrate is taken up by the cells in the upper digestive tract, whereas coated butyric acid will influence the colonisation of Salmonella bacteria at the site of the  colonisation, i.e., in the gut. In addition to targeted release of SCFA over the digestive tract, coating reduces the typical unpleasant smell of butyrate. Although preferred by some animal species, most pet owners do not prefer the smell of butyrate in pet food. Wageningen University tested the effect of extrusion on odour properties of Excential Butycoat (micro-encapsulated sodium butyrate 30%) in a commercial dog food formulation. During the extrusion process and after packaging of the kibbles, there was no clear difference observed in smell between the control diets and diets with the coated butyrate.

Conclusion

Butyrate is essential as an energy source for epithelial cells and vital intestinal function. Diverse beneficial effects of butyrate on animal health can be achieved by the use of dietary fibres and by direct addition of butyrate to the diet. Butyrate is an important factor in the development of the gastrointestinal tract, but newborn animals produce only small quantities of butyrate and the production increases during the development of the hindgut. So supplementation of milk formula and starter diets with butyrate contribute to enhanced development of the intestinal mucosa and improvement of digestive processes in neonatal calves and piglets. The use of coated butyrate may play a role in preventing certain types of diarrhoea in animals and create less odour in pet stools. Use of proper micro-encapsulated butyrate results in targeted release of the SCFA over the digestive tract. It also reduced the typical smell of butyrate during production and in the feeding of butyrate containing diets to pet animals.

References are available on request

AllAboutFeed issue 22, No 1 2014