The antioxidative activity of a total of 92 phenolic extracts from edible and nonedible plant materials (berries, fruits, vegetables, herbs, cereals, tree materials, plant sprouts, and seeds) was examined by autoxidation of methyl linoleate. The content of total phenolics in the extracts was determined spectrometrically according to the Folin-Ciocalteu procedure and calculated as gallic acid equivalents (GAE). Among edible plant materials, remarkable high antioxidant activity and high total phenolic content (GAE > 20 mg/g) were found in berries, especially aronia and crowberry. Apple extracts (two varieties) showed also strong antioxidant activity even though the total phenolic contents were low (GAE < 12.1 mg/g). Among nonedible plant materials, high activities were found in tree materials, especially in willow bark, spruce needles, pine bark and cork, and birch phloem, and in some medicinal plants including heather, bog-rosemary, willow herb, and meadowsweet. In addition, potato peel and beetroot peel extracts showed strong antioxidant effects. To utilize these significant sources of natural antioxidants, further characterization of the phenolic composition is needed.

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Thymoquinone (TQ), a component of black seed essential oil, is known to induce apoptotic cell death and oxidative stress, however, the direct involvement of oxidants in TQ-induced cell death has not been established yet. Here, we show that TQ inhibited the proliferation of a panel of human colon cancer cells (Caco-2, HCT-116, LoVo, DLD-1 and HT-29), without exhibiting cytotoxicity to normal human intestinal FHs74Int cells. Further investigation in DLD-1 revealed that apoptotic cell death is the mechanism for TQ-induced growth inhibition as confirmed by flow cytometry, M30 cytodeath and caspase-3/7 activation. Apoptosis was induced via the generation of reactive oxygen species (ROS) as evidenced by the abrogation of TQ apoptotic effect in cells preincubated with the strong antioxidant N-acetyl cysteine (NAC). TQ increased the phosphorylation states of the mitogen-activated protein kinases (MAPK) JNK and ERK, but not of p38. Their activation was completely abolished in the presence of NAC. Using PD98059 and SP600125, specific ERK and JNK inhibitors, the two kinases were found to possess pro-survival activities in TQ-induced cell death. These data present evidence linking the pro-oxidant effects of TQ with its apoptotic effects in colon cancer and prove a protective role of MAPK.

Natural derived or originated compounds still play a major role as drugs, and as lead structures for the development of synthetic molecules. About 50% of the drugs introduced to the market during the last 20 years are derived directly or indirectly from small biogenic molecules. In the future, natural products will continue to play a major role as active substances, model molecules for the discovery and validation of drug targets. A multidisciplinary approach to drug discovery involving the generation of truly novel molecular diversity from natural product sources, combined with total and combinatorial synthetic methodologies provides the best solution to increase the productivity in drug discovery and development. Screening for new drugs in plants implies the screening of extracts for the presence of novel compounds and an investigation of their biological activities. It is currently estimated that approximately 420,000 plant species exist in nature. For the purpose of lead discovery, or for the scientific validation of a traditional medicinal plant or a phytopharmaceutical, active principals in complex matrices need to be identified. Therefore, the interfacing of biological and chemical assessment becomes the critical issue. Drug discovery from plants can be guided by epidemiologic studies facilitated with computer assisted HPLC microfractionation and microplate technology. Epidemiologic studies have shown that high dietary flavonoid intake may be associated with decreased risk for cardiovascular disease. Chlamydia pneumoniae is a common human pathogen and epidemiological and clinical studies have shown a connection between chronic C. pneumoniae infection, atherosclerosis and the risk of myocardial infarction. We will present here the detection of natural compounds active against C. pneumoniae as an example.

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Quinones are a class of natural and synthetic compounds that have several beneficial effects. Quinones are electron carriers playing a role in photosynthesis. As vitamins, they represent a class of molecules preventing and treating several illnesses such as osteoporosis and cardiovascular diseases. Quinones, by their antioxidant activity, improve general health conditions. Many of the drugs clinically approved or still in clinical trials against cancer are quinone related compounds. Quinones have also toxicological effects through their presence as photoproducts from air pollutants. Quinones are fast redox cycling molecules and have the potential to bind to thiol, amine and hydroxyl groups. The aforementioned properties make the analytical detection of quinones problematic. However, recent advances of the available analytical techniques along with the possibility of using labeled compound facilitate their detection hence allowing a better understanding of their action. This review summarizes the current knowledge with respect to the oxido-reductive and electrophilic properties of quinones as well as to the analytical tools used for their analysis. It includes a general introduction about the physiological, and therapeutical functions of quinones. A number of studies are reported to cover the chemical reactivity in an attempt to understand quinones as biologically active compounds. Data ranging from normal analytical methods to study quinones derived from plant or biological matrices to the use of labeled compounds are presented. The examples illustrate how chemical, biological and analytical knowledge can be integrated to have a better understanding of the mode of action of the quinones.