Antioxidant, Anti-Inflammatory, and Microbial-Modulating Activities of Essential Oils: Implications in Colonic Pathophysiology

Abstract

Essential oils (EOs) are a complex mixture of hydrophobic and volatile compounds synthesized from aromatic plants, most of them commonly used in the human diet. In recent years, many studies have analyzed their antimicrobial, antioxidant, anti-inflammatory, immunomodulatory and anticancer properties in vitro and on experimentally induced animal models of colitis and colorectal cancer. However, there are still few clinical studies aimed to understand their role in the modulation of the intestinal pathophysiology. Many EOs and some of their molecules have demonstrated their efficacy in inhibiting bacterial, fungi and virus replication and in modulating the inflammatory and oxidative processes that take place in experimental colitis. In addition to this, their antitumor activity against colorectal cancer models makes them extremely interesting compounds for the modulation of the pathophysiology of the large bowel. The characterization of these EOs is made difficult by their complexity and by the different compositions present in the same oil having different geographical origins. This review tries to shift the focus from the EOs to their individual compounds, to expand their possible applications in modulating colon pathophysiology.

Keywords: anti-inflammatory; antioxidant; bowel; colorectal cancer; essential oils; microbial-modulating.

Figure 1

Multiple effects of essential oils, generally extracted by distillation from aromatic plants, on the gastrointestinal system. These effects have been obtained both from essential oils as they are and from their single bioactive compounds. The anti-tumor action of essential oils (EOs) is due both to the single effects shown in the figure and to specific actions directed against colorectal cancer cells.

Figure 2

Intestinal anti-inflammatory effects of essential oils (EOs). Pro-inflammatory stimuli, such as chemicals (Dextran Sulphate Sodium (DSS), Acetic Acid, Trinitrobenzenesulfonic acid (TNBS)), bacterial toxins (such as Lipopolysaccharide (LPS)) or pathobionts infections increase the inflammatory response into the gut, with increased expression of Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-kβ) or Myeloperoxydase (MPO) enzyme. Recruitment and activation of immune cells increase cellular and histological damages that mainly involve the large bowel. EOs and their single components act at multiple levels, counteracting inflammation and consequently decreasing damages to the intestinal mucosa and to the intestinal wall. EO, essential oil; PPARγ, peroxisome proliferator-activated receptor-gamma; COX-2, Cyclooxygenase-2; ROS, reactive oxygen species.

Figure 3

Antioxidant effect of essential olis (EOs) in the gut. The chronic low-grade inflammation or dysbiosis that very soon occurs into the gut and in the gut wall increases the level of reactive oxygen species (ROS). Their increased levels are effectively counteracted by EOs that are able to reduce the activity and expression of enzymes, such as Myeloperoxydase (MPO), Cyclooxygenase-2 (COX-2) or inducible Nitric oxide synthase(iNOS), which are the ones most responsible for ROS production and for the oxidative damages related to them.