Health from Herbs? Antioxidant Studies on Selected Lamiaceae Herbs in vitro and in Humans

High dietary intake of fruits and vegetables has been linked to protection against chronic diseases, of which cardiovascular diseases (CVD) are the major cause of death in Finland. One of the hypotheses underlying the mechanism behind this effect is the antioxidant action of several dietary factors, including vitamins C and E, carotenoids and polyphenolic compounds. Polyphenols are consumed in large quantities in plant rich diets and observations on their antioxidant potency in vitro have made them a hot research topic during the past twenty years. The present study deals with the antioxidant activity of selected members of the plant family Lamiaceae – sage (Salvia officinalis L.), thyme (Thymus vulgaris L.), rosemary (Rosmarinus officinalis L.) and two oregano species (Origanum vulgare L., Origanum onites L.). Due to the abundance of various phenolic compounds in these herbs, they are considered as a potential source of health-beneficial natural components with usage as healthpromoting dietary supplements. The applicability of hydrodistillation, methanolic and ethanolic extraction, and pressurised hot-water extraction (PHWE) to extract phenolic antioxidants from sage was studied. Based on the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging activity of the different extracts, PHWE was the most effective technique. The hydrodistillation method was chosen for the further production of study extracts due to sensory properties of the extracts suitable for human consumption. The technique was also easily applicable in a larger scale production. The in vitro antioxidant properties of water extracts from sage, rosemary, thyme and oregano (O. vulgare) were characterised using three radical scavenging assays, a reductive capacity assay and a human low-density lipoprotein (LDL) oxidation assay. The total phenolic content of these extracts was determined. Depending on the method used, the extracts showed varying degrees of antioxidant activity. The absorption and metabolism of oregano (O. onites) extract in humans was evaluated by analysing the urinary excretion of phenolic metabolites using liquid chromatographic methods. The excretion of phenolic metabolites in urine was markedly increased following a single ingestion of O. onites extract, and the pattern of urinary metabolites suggested effective metabolism to take place. The in vitro antioxidant activity of phenolic constituents and human metabolites of O. onites were studied in DPPH and LDL oxidation assays. The phenolic acids from O. onites showed a range of antioxidant activity in the assays used, and some degree of activity was observed for many of the aglycone forms of their human metabolites. In a double-blinded, placebo-controlled clinical trial, the effects of oregano (O. vulgare) extract consumption on different biomarkers of antioxidant capacity and lipid peroxidation were studied in healthy men. No shortor long term effects on the antioxidant parameters followed were observed. This work revealed several aspects on the problematic nature of studies on antioxidants. Even though these extracts and their constituents seem promising antioxidant candidates in vitro and are at least to some extent available in the body, they lack effects on an array of lipid peroxidation and antioxidant capacity parameters in vivo. The findings suggest that their potential health-beneficial effects on humans are not mediated via direct antioxidant action. However, the epidemiologically observed association between the high intake of polyphenol rich fruits and vegetables and the decreased risk of CVD, as well as accumulating in vitro evidence on several bioactivities of polyphenols support the theory that polyphenols may have favourable effects on human health mediated via some other mechanisms.