Many inflammatory bowel diseases (IBD) such as Chron's (CD) or ulcerative colitis (UC) are considered autoimmune diseases caused by the body's immune system attacking the gastrointestinal tract. This is thought to trigger colitis, the medical term used to describe colonic and often intestinal inflammation. Specifically, a failure to regulate T cell responses are believed to trigger the inflammation of the intestinal or colonic mucosa in these disorders.
Researchers have begun to suspect intestinal microflora inhabiting the mucosae play a significant role in the development of IBD and colitis. Patients suffering from IBD have been shown to have higher concentrations of mucosal bacteria that increase progressively with symptom severity. The mucosae are thin membranes that are found throughout the body in areas where internal organs and tissues are exposed to external environments. They possess unique immune systems that are tightly regulated and hyporesponsive, or unresponsive to most antigens, due to the high antigen loads they come into contact with (Neurath et al., 2007). Because the mucosae are so sensitive to inflammatory damage, disruption of the hyporesponsive state can have devestating effects.
Phloretin is a type of flavonoid found mainly in apples and strawberries that has antioxidative and anticarcinogenic properties, as well as biological roles in estrogen hormonal activity and cardiovascular disease prevention. If the roles of phloretin weren't already diverse enough, researchers have also recently found flavonoids can inhibit the biofilm formation of pathogenic E. coli O157:H7. Bacterial biofilms are aggregates of bacteria that aggregate together and adhere to a surface. This might explain another recent study that found phloretin is capable of reducing the expression of many inflammatory proteins and receptors in human colon epithelial cells.
Recently, this relationship between phloretin and biofilm formation was further investigated by a team of researchers hoping interested in whether phloretin's inhibitory effect on biofilm formation could have a therapeutic effect on patients of IBD (Lee et al., 2011).They found phloretin was able to differentiate between commensal and pathogenic E.coli biofilms, reducing biofilm formation in pathogenic E. coli strains but enhancing biofilm formation in nonpathogenic strains. Phloretin, but not the antioxidants vitamin C or vitamin E, successfully inhibited E. coli O157:H7 biofilm formation without preventing planktonic cell growth. Drugs that mediate their effects through cell toxicity can lead to bacterial drug resistance through natural selection of the bacteria immune to the drugs effects. Phloretin's effect on E. coli O157:H7 cells was completely nontoxic, with planktonic cells showing identical growth rates in the presence and absence of Phloretin.
Phloretin appeared to mediate this reduction in pathogenic biofilm formation in part through it's suppressive effects on AI-2 expression. AI-2 is important for E. coli quorum sensing, a system that allows bacteria to coordinate gene expression with local population densities. When AI-2 was suppressed by Phloretin, biofilm formation was significantly attenuated. Phloretin was also found to prevent pathogenic biofilm formation by reducing expression of fimbria and curli genes, which are both considered virulence attributes, or indicators of pathogenicity. Fimbria are the protein appendages that adhere bacteria to each other or surfaces on host cells while curli simply link bacterial cells together.
The importance of these genes in pathologic biofilm formation was demonstrated in culture using HT-29 human colonic epithelial cells. E. coli O157:H7 cells were more adhesive than E. coli K-12 BW25113 cells and attached to the epithelial cells in greater numbers. Phloretin treatment was found to not only to reduce the adhesiveness of E. coli O157:H7 strains without influencing the adhesiveness of E. coli K-12 BW25113 cells, but also to reduce the number of E. coli O157:H7 bound to the HT029 surface.
The researchers also used the HT-29 cell cultures to test whether phloretin could prevent intestinal inflammation through a cell culture model of colitis. TNF-a is a cell signaling molecule that is involved in IBD and known to cause inflammation, partly by triggering white blood cells to travel to the site of inflammation, bind to the mucosa and divide into inflammatory response cells that enhance the immune response. While TNF-a induced monocytes to adhere to the HT-29 cells, phloretin inhibited this activity, which can be expected to have a dampening effect on the inflammatory immune response.
Enteroaggressive E. coli fimbriae-dependent colonization has been found to occur in the mucosa of both small and large bowels, triggering colitis. While this hasn't been demonstrated yet in IBD specifically, researchers tested the possibility of whether a link could exist between E. coli O157:H7 biofilm formation and IBD by testing in vitro whether Phloretin could reduce IBD symptoms in a rat disease model for colitis. In rats treated with TNBS, typical physiological symptoms of IBD were eliciited, including a significant loss of body weight contrasted by a large increase in colon tissue weights. Additionally, a large number of inflammatory cells originating from monocytes appeared to have migrated to the colon as expected in an inflammatory response.
Rats given TNBS but then later administered phloretin were able to recover their normal body and colon weights. In accord with that, the number of inflammatory migratory cells that had previous filled the colon was suppressed to almost the same level of those mice given placebo treatmetns. This suggests phloretin's therapeutic potential is not just preventative, but can actually restore the inflammatory balance in IBD diseases. Even more exciting was the discovery that phloretin significantly outperformed than the drug currently prescribed to IBD patients, 5-ASA, in every aspect of the TNBS-induced inflammatory response.
Other studies have also suggested polyphenols can have a therapeutic effect in Chron's patients by reducing inflammation (Skyberg et al., 2011). Rather than focusing on the microflora of the colon, these studies looked at how polyphenols suppress T cell activation to prevent colitis but the biology behind the studies fits together well. These findings together suggest phloretin may be a useful treatment for inhibition of pathogenic intestinal microflora. Not only does it alleviate symptoms to a greater degree then the current leading drug on the market for IBD, it also is capable of distinguishing between pathogenic and commensal E. coli. strains and acts through nontoxic mechanisms, eliminating the threat of antimicrobial resistance
Lee, J., Regmi, S., Kim, J., Cho, M., Yun, H., Lee, C., Lee, J. (2011). Apple flavonoid phloretin inhibits escherichia coli O157:H7 biofilm formation and ameliorates colon inflammation in rats. Immunity and Infection, 79(12), 4819-4829.
Neurath, M., Finotto, S., & Glimcher, L. (2002). The role of Th1/Th2 polarization in mucosal immunity. Nature Medicine, 8(6), 567-573.
Skyberg, J., Robinson, A., Golden, S., Rollins, F., Callis, G., Huarte, E., Kochetkova, M., Jutila D., Pascual, W. (2011). Apple polyphenols require T cells to ameliorate dextran sulfate sodium-induced colitis and dampen proinflammatory cytokine expression. Leukocyte Biology, 2011, 90(6): 1043.