Saponins are natural glycosides which possess a wide range of pharmacological properties including cytotoxic activity. In this review, the recent studies (2005–2009) concerning the cytotoxic activity of saponins have been summarized. The correlations between the structure and the cytotoxicity of both steroid and triterpenoid saponins have been described as well as the most common mechanisms of action.

Erucic acid (EA) is monounsaturated fatty acid (22:1 n-9), synthesized in the seeds of many plants from the Brassicaceae family, with Brassica napus, B. rapa, or B. carinata considered as its richest source. As the compound has been blamed for the poisoning effect in Toxic Oil Syndrome, and some data indicated its cardiotoxicity to rats, EA has been for decades classified as toxic substance, the use of which should be avoided. However, the cardiac adverse effects of EA have not been confirmed in humans, and the experiments in animal models had many limitations. Thus, the aim of this review was to present the results of the so far published studies on both toxic, and pharmacological properties of EA, trying to answer the question on its future medicinal use. Despite the ambiguous and relatively small data on toxic and beneficial effects of EA it seems that the compound is worth investigating. Further research should be particularly directed at the verification EA toxicity, more in-depth studies on its neuroprotective and cytotoxic properties, but also its use in combination with other drugs, as well as its role as a drug carrier.

Quercetin is one of the most common, naturally occurring flavonoids, structurally classified to the flavonol subfamily. This compound, found in many edible and medicinal plants either as a free or glycosidated form, has been scientifically exploited for many years, and one could hardly expect it could be a hero of some additional story. Commonly recognized as an anti-inflammatory agent, quercetin not only limits capillary vessel permeability by inhibiting hyaluronidase but also blocks cyclooxygenases and lipoxygenases. As a typical flavonoid, it is also known for its antioxidant effect, which was confirmed by many in vitro and in vivo studies. Throughout the years, numerous other activities were reported for quercetin, including antidiabetic, anti-proliferative, or anti-viral. Of note, recent data have revealed its potential role as a therapeutic agent for several central nervous system disorders. This review provides an overview of available experimental data on quercetin and its complexes with respect to central nervous system diseases, with a main focus on some aspects that were not discussed previously, such as anti-anxiolytic effects, anti-Huntington’s disease activity, or therapeutic potential in brain cancer. Moreover, quercetin’s protective role in some of these diseases is discussed, especially as an anti-neuroinflammatory agent. Bearing in mind the poor bioavailability of this compound, possible options that would enhance its delivery to the site of action are also presented.

This review is focused on the comparison of the biological and pharmacological activities of usnic acid enantiomers. Most of the available data refer to (+)-usnic acid, while the left-handed isomer has been less often significantly studied. Special attention was paid to the experiments comparing both (+)- and (−)-usnic acid at the same time, the results of which indicated interesting differences, however no tendency as to which enantiomer was more potent could be observed. Nevertheless, more studies, especially on (−)-usnic acid, are needed to give a final explanation for the similarities and differences between both usnic acid enantiomers. These should be especially directed to steric structure–activity relationship of the enantiomers, tested under the same experimental conditions, which may help to explain the possible mechanisms of their actions.

Background: Atranorin, a compound with the depside structure, is one of the most common lichen secondary metabolites, characteristic for numerous lichen families but rarely found in some mosses and higher plants. Over the years various biological properties of atranorin were examined. Objective: This review summarizes the studies on atranorin, focusing on a number of biological activities in different fields. The literature describes anti-inflammatory, analgesic, as well as wound healing, antibacterial, antifungal, cytotoxic, antioxidant, antiviral, and immunomodulatory activities of the depside. Furthermore, lack of toxicity of atranorin was confirmed in the animals' in vivo assays. Conclusion: In conclusion, atranorin seems to be an interesting lichen substance, which needs to be investigated in more detail in order to allow further applications, e.g. in pharmacy, medicine or cosmetology.