Free radicals are chemical particles containing one or more unpaired electrons, which may be part of the molecule. They cause the molecule to become highly reactive. The free radicals are also known to play a dual role in biological systems, as they can be either beneficial or harmful for living systems. It is clear that there are numerous mechanisms participating on the protection of a cell against free radicals. In this review, our attention is paid to metallothioneins (MTs) as small, cysteine-rich and heavy metal-binding proteins, which participate in an array of protective stress responses. The mechanism of the reaction of metallothioneins with oxidants and electrophilic compounds is discussed. Numerous reports indicate that MT protects cells from exposure to oxidants and electrophiles, which react readily with sulfhydryl groups. Moreover, MT plays a key role in regulation of zinc levels and distribution in the intracellular space. The connections between zinc, MT and cancer are highlighted.

Traditional supplements of selenium generally have a low degree of absorption and increased toxicity. Therefore, it is imperative to develop innovative systems as transporters of selenium compounds, which would raise the bioavailability of this element and allow its controlled release in the organism. Nanoscale selenium has attracted a great interest as a food additive especially in individuals with selenium deficiency, but also as a therapeutic agent without significant side effects in medicine. This review is focused on the incorporation of nanotechnological applications, in particular exploring the possibilities of a more effective way of administration, especially in selenium-deficient organisms. In addition, this review summarizes the survey of knowledge on selenium nanoparticles, their biological effects in the organism, advantages, absorption mechanisms, and nanotechnological applications for peroral administration.

Detection of DNA fragments in situ using the terminal deoxyribonucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling (TUNEL) assay is increasingly applied to investigate active cell death (apoptosis). We studied the specificity of the assay in well-defined models of apoptosis and necrosis as well as in postmortem autolysis in rat liver. During involution of liver hyperplasia, which follows stopping treatment with the hepatomitogens cyproterone acetate (CPA) or nafenopin (NAF), numerous apoptotic hepatocytes could be observed with TUNEL-positive chromatin residues. A similar TUNEL-positive reaction appeared in necrotic hepatocytes after a cytotoxic dose of carbon tetrachloride (CCl4) or N-nitrosomorpholine (NNM). Also, in insufficiently fixed, autolytic livers TUNEL-positive nuclei were observed. Thus, DNA fragmentation is common to different kinds of cell death; its detection in situ should not be considered a specific marker of apoptosis.