**1. Introduction**

442 Biochemistry

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Treatment of free radical pathologies by antioxidants has been substantiated by studies in animal models of diseases. However, so far the therapy of oxidative stress-related diseases has not found satisfactory application in clinical practice. This may be due to an insufficient efficacy of the antioxidants available, their unsuitable pharmacokinetics, lack of selectivity, presence of adverse side effects, their toxicity, etc. Thus, new antioxidants have to be identified. In numerous studies searching for novel antioxidant compounds, trolox, a water soluble analogue of alpha-tocopherol, is commonly utilized as a reference antioxidant. Chemically, trolox represents a carboxylic acid chromane (Fig. 1A). Due to its good water solubility, this antioxidant has been broadly used as a standard when screening antioxidant efficacy of other prospectively active compounds in studies involving chemical, subcellular, cellular and tissue models of oxidative stress mediated injury (Aruoma, 2003; Huang et al., 2005; Prior et al., 2005). On the other hand, a fairly large and specific group of substances with beneficial antioxidant effects is derived from indole structure (Suzen, 2007). This puts a demand on the reassessment of the suitability of a phenol-type reference trolox, particularly in studies on screening of nitrogen heterocyclic antioxidants.

The pyridoindole stobadine (Fig. 1A) has been found out to be an effective chain-breaking antioxidant scavenging a variety of reactive oxygen species (Kagan et al., 1993; Steenken et al., 1992; Stefek & Benes, 1991). The input of stobadine into the literary data on indole-type antioxidants comprises more than two hundred PubMed references. Several comprehensive reviews cover stobadine action as determined in a variety of models including simple chemical systems, biological models at subcellular, cellular or organ level, followed by extensive studies in vivo in a number of free-radical disease models, and that also in comparison with other drugs (Horakova et al., 1994; Horakova & Stolc, 1998; Juranek et al., 2010; Stolc et al., 1997; Stefek et al., 2010). The main goal of the present paper is to provide an overview on the current data of the indole-type antioxidant stobadine and to compare them with those of the phenol-type antioxidant trolox.
