Botanical Drugs as an Emerging Strategy in Inflammatory Bowel Disease: A Review

Abstract

Crohn's disease and ulcerative colitis are the two most common categories of inflammatory bowel disease (IBD), which are characterized by chronic inflammation of the intestine that comprises the patients' life quality and requires sustained pharmacological and surgical treatments. Since their aetiology is not completely understood, nonfully efficient drugs have been developed and those that show effectiveness are not devoid of quite important adverse effects that impair their long-term use. Therefore, many patients try with some botanical drugs, which are safe and efficient after many years of use. However, it is necessary to properly evaluate these therapies to consider a new strategy for human IBD. In this report we have reviewed the main botanical drugs that have been assessed in clinical trials in human IBD and the mechanisms and the active compounds proposed for their beneficial effects.

Figure 1

Physiopathology of IBD. (a) The intestine is the largest mucosal surface exposed to the external environment. It constitutes an interface between the host and the luminal contents, which include nutrients and the highest count of resident microbes. Thus, the intestinal immune system meets more antigens than any other part of the body and it must discriminate between invasive organisms and harmless antigens, such as food, proteins, and commensal bacteria, to prevent infections or preserve the homeostasis. This intestinal homeostasis depends on the dynamic interaction between the microbiota, the intestinal epithelial cells, and the resident immune cells, which coordinate a response that keeps the balance between immunity and tolerance. (b) A breakdown of this balance triggers the chronic inflammatory process that characterizes inflammatory bowel disease. There are often several preexisting conditions that lead to the disease: first of all, a genetic susceptibility of the intestinal immune system to distinguish an environmental antigen presented within the gastrointestinal tract; secondly, the contact with the antigen; finally, usually due to an alteration of the permeability, the antigen is presented to the gastrointestinal mucosal immune system through its paracellular passage, which triggers the inflammatory cascade. During early inflammation, luminal antigens activate the different innate immune cells located in the intestine, including natural killer cells, mast cells, neutrophils, macrophages, and dendritic cells, and maintained inflammatory reaction promotes the activation of the adaptive immune response. Abnormally activated effector CD4+ T helper (Th) cells synthesize and release different inflammatory mediators that generate an amplified inflammation that originates from chronic tissue injury and epithelial damage.

Figure 2

Chemical structures of Aloe vera compounds.

Figure 3

Chemical structures of Andrographis paniculata compounds.

Figure 4

Chemical structures of Artemisia absinthium compounds.

Figure 5

Chemical structure of boswellic acid.

Figure 6

Chemical structures of Cannabis sativa compounds.

Figure 7

Chemical structure of curcumin.