Regulation of the intestinal immune system by flavonoids and its utility in chronic inflammatory bowel disease

Flavonoids are phytochemicals which can regulate the activity of the intestinal immune system. In patients with chronic inflammatory bowel disease (IBD) there is an overexpression and imbalance of the components of the inflammatory immune reactions which are chronically activated. Suppression of inflammation can be achieved by anti-inflammatory drugs which are used in clinical medicine but these can cause serious side effects. Flavonoids can have natural immunosuppressive properties and inhibit the activation of immune cells and its effectors (chemokines, TNF-, cytokines). Phytochemicals such as flavonoids bind to the nuclear Ah (aryl hydrocarbon) -receptor thereby stimulating protective enzyme activities. As shown by clinical evidence in patients and by experimental work some flavonoids (apigenin, epigallocatechin gallate) were effective in the inhibition of inflammation. Instead of or additionally to anti-inflammatory drugs flavonoids can be used in IBD patients to treat the over-reactive immunologic system. This is accomplished by upregulation of the Ah-receptor. Flavonoids interact with toll-like receptors expressing on the surface of immune cells, then they were internalized to the cytosol and transferred into the nucleus, where they were attached to the Ah-receptor. The Ah-receptor binds to the Ah-R nuclear translocator and via Ah response element beneficial protective enzymes and cytokines are induced, leading to upregulation of the anti-inflammatory system.

Disparities of conjugating protective enzyme activities in the colon of patients with adenomas and carcinomas

AIM: To investigate the metabolic enzymatic capacity of the colon mucosa to detoxify noxious carcinogenic compounds.

METHODS: We investigated the activity of 2 conjugating enzymes-the microsomal uridine glucuronosyltransferase (UGT) and the cytosomal glutathione S-transferase (GST) in the uninvolved mucosa of the colon transversum and sigmoideum in patients with adenomatous polyps and colorectal cancer. Biopsies were taken from the mucosa during colonoscopies which were done for clinical (diagnostic) reasons. After storage, the biopsy material was homogenized and after differential centrifugation the enzyme assays were performed with 4-nitrophenol (UGT) and 1-chloro 2,4-dinitrobenzene (GST) as substrates.

RESULTS: About 48 patients were included of which 28 had adenomas and 20 had colorectal carcinomas confirmed by histopathology. Enzyme activities were expressed as nmol/mg per minute protein for the GST and as pmol/mg per minute protein for the UGT. Analysis of variance (F-test) indicated that both enzymes were more widely distributed in adenoma than in cancer patients. The means ± SD were smaller for cancer patients: GST for adenomas 268 ± 152 vs 241 ± 69 for carcinomas and UGT for adenomas 197 ± 200 vs 150 ± 86 for carcinomas.

CONCLUSION: Compared to patients with adenomatous colon polyps those with colorectal carcinoma exhibited a lower capacity of detoxifying enzyme metabolism and their activities clustered over a smaller range.

Emerging role of bioflavonoids in gastroenterology: Especially their effects on intestinal neoplasia

Flavonoids, secondary plant products which could be essential for normal physiology in humans and animals, may be the vitamins of the next century. Flavonoids belong to the polyphenols and possess antioxidative, anti-inflammatory, antimutagenic and anticarcinogenic properties. Among the various flavonoid species, tea flavonoids such as apigenin (from camomile) and epigallocatechin gallate (EGCG from green tea) can be used for the prevention of intestinal neoplasia, especially for adenoma and cancer prevention in the gastrointestinal tract. Numerous experimental studies with molecular and biological end points support the therapeutic efficacy of bioflavonoids. Clinical studies with cohorts and case-control trials suggest that flavonoids are effective in tertiary bioprevention but, as yet, there are no controlled randomized clinical trials. Flavonoids can inhibit inflammatory pathways and could be useful for chronic inflammatory bowel diseases. Flavonoid deficiency syndromes could be therapeutic targets in the future.

[Colorectal cancer prevention by flavonoids]

BACKGROUND

Valid, sustained and safe clinical means of colorectal cancer prevention are still lacking, but they are urgently needed to lower the incidence of colorectal cancer. Dietary factors and phytochemicals such as flavonoids play an important role for prevention.

METHODS

A selective search of the literature using PubMed was performed with the following key words: flavonoids, cancer, therapy, colorectal cancer focused on clinical queries. Results of clinical studies including the authors' own were compared.

RESULTS

In vivo and in vitro studies with animals, cell cultures and subcellular components provide ample evidence for antimutagenic and anticarcinogenic effects of flavonoids as shown for multiple biological and molecular endpoints. Isoflavonoids in vitro have been shown to induce proliferation of breast cancer cells. Epidemiologic trials (cohort, case-control and cross-sectional studies) yielded inconsistent results for flavonoid protection. Systematic reviews and meta-analyses support the protective role of tea flavonoids on adenoma incidence. An interventional pilot study with sustained flavonoid supplementation was shown to reduce the rate of neoplasia in patients with resected colorectal cancer.

CONCLUSION

Selected flavonoids possess antimutagenic and anticarcinogenic properties and could reduce the incidence of colorectal neoplasias as shown in epidemiologic trials. Randomized controlled clinical studies with flavonoid intervention are necessary to provide evidence for their role in colorectal cancer prevention.