Four hypotheses on mitochondria’s role in the development and regulation of oxidative stress in the normal state, cell pathology and reversion of tumor cells

Stress-associated radiation effects in pygmy wood mouse Apodemus uralensis (Muridae, Rodentia) populations from the East-Urals Radioactive Trace

This work is based on the comparative analysis of data obtained in the course of monitoring pygmy wood mouse populations (Apodemus uralensis Pallas, 1811) in the East-Urals Radioactive Trace (EURT) area and background territories. The effect of population size and its interaction with the radioactivity on biochemical parameters in the spleen and adrenal glands was studied. The concentrations of total lipids, proteins, DNA and RNA, activity of glucose-6-phosphate isomerase and catalase as well as the level of lipid peroxidation (LPO) were evaluated. The functional-metabolic shifts seen with large population sizes were characterized by delipidisation of adrenocortical cells, increased LPO as the main mechanism for steroidogenesis, growth of the protein components of the adrenal glands to maintain their hyperfunction, as well as immunosuppression associated with the restriction of carbohydrates providing splenocytes, reduction of DNA synthesis, and the development of a pro-/antioxidant imbalance. Reactivity of the neuroendocrine and hematopoietic systems of animals experiencing a high population density was higher in the EURT zone compared with the reference group. This difference can be explained by the additional stress from the chronic radiation exposure. The level of LPO, catalase activity, and DNA/protein ratio in the spleen and the total protein content in the adrenal glands were the most sensitive to the interaction of population size and radiation exposure. The harmful effect (distress) of the interaction of non-radiation and radiation factors can manifest when there is a population abundance above 30 ind./100 trap-day and a radiation burden which exceeds the lower boundary of the Derived Consideration Reference Levels, which is above 0.1 mGy/day.

Variability of salivary markers of oxidative stress and antioxidant status in young healthy individuals

OBJECTIVES

Salivary advanced glycation end-products (AGEs), advanced oxidation protein products (AOPP), total antioxidant capacity (TAC), and ferric reducing ability of saliva (FRAS) are increased in various diseases. Little data exist for these markers in the healthy population. The aim of this study was to assess the inter-individual and intra-individual variability of AGEs, AOPP, TAC, and FRAS in the saliva of young healthy individuals.

METHODS

Unstimulated saliva samples were collected from 16 females and 18 males daily over a period of 30 days. Markers were measured using spectrophotometric and spectrofluorometric microplate-based methods.

RESULTS

All salivary markers measured were significantly higher in men than in women (P < 0.05 for AGEs; P < 0.001 for AOPP, TAC, and FRAS). The inter-individual variability was approximately 60% for AGEs and AOPP and 30-40% for TAC and FRAS in both genders. The inter-individual variability of FRAS was higher in men vs. women (P < 0.01). Intra-individual variability ranged from 20% for TAC, to 30% for AGES and FRAS and 45% for AOPP.

DISCUSSION

Intra-individual variability of salivary AGEs, AOPP, TAC, and FRAS indicates that their use is currently limited to large cohort studies. Identifying the underlying factors related to the high inter-individual and intra-individual variability is needed. Sex differences should be considered in future studies.

Dioscorin pre-treatment protects A549 human airway epithelial cells from hydrogen peroxide-induced oxidative stress

Hydrogen peroxide (H(2)O(2)) is a highly reactive oxygen species involved in lung and bronchial epithelium injury. Increased H(2)O(2) levels have been reported in expired breath condensates of patients with inflammatory airway diseases such as chronic obstructive pulmonary disease. Protecting airway epithelial cells from oxidative stress is an important task in the prevention and management of airway diseases. Previous studies demonstrate that yam (Dioscorea batatas Decne) has antioxidant and anti-trypsin activities. This study evaluated the validity of dioscorin in vitro. The results showed that dioscorin attenuated the alteration of H(2)O(2) on G2/M cell cycle arrest. This might be associated with the activation of IκB and subsequent inactivation of NF-κB. Furthermore, dioscorin suppressed IL-8 secretion and reduced changes of adhesion molecule expressions in H(2)O(2)-injured A549 cells. These results help in understanding the potential of traditional Chinese herbal medicine as treatment for airway inflammatory diseases.

Striated muscle fiber apoptosis after experimental tendon lesion in a rat model

Tendon lesions induce muscular atrophy, the nature of which has not yet been clearly related to lesion etiology and entity. In the present study, tendon and muscle alterations were assessed after experimental tendon lesion of the Infraspinatus muscle in young rats. The consequences of lesions differed on the basis of both extension and injured tissue vascularization, that is apoptosis and/or degeneration, differing mainly by energy demands: apoptosis requires high energy levels (proportional to vascular supply), but degeneration does not. It is well known that tendons are poorly supplied with blood compared with muscular masses, which are abundantly vascularized. Five weeks after tendon surgical section, tendon/muscle samples were taken for TUNEL and transmission electron microscopy. The structural results reported here identified different tendon/muscle alterations: degeneration of tendon without signs of apoptosis, and atrophy of muscle fibers due only to apoptosis. This led to the formulation of the following hypothetical sequence of events: a tendon lesion, not recovering quickly due to the poor tendon blood supply, results in degeneration of the injured tendon, which, in turn, induces a partial disuse of the muscle mass, which consequently atrophies (proportionally to the severity of tendon lesion) by striated muscular fiber apoptosis. The authors suggest that the different behavior of the two tissues depends on the marked difference in their vascularization.

Mitochondrial concept of leukemogenesis: key role of oxygen-peroxide effects

Background and hypothesis

The high sensitivity of hematopoietic cells, especially stem cells, to radiation and to pro-oxidative and other leukemogenic agents is related to certain of their morphological and metabolic features. It is attributable to the low (minimal) number of active mitochondria and the consequently slow utilization of O₂ entering the cell. This results in an increased intracellular partial pressure of O₂ (pO₂) and increased levels of reactive oxygen (ROS) and nitrogen (RNS) species, and a Δ(PO – AO) imbalance between the pro-oxidative (PO) and antioxidative (AO) constituents.

Proposed mechanism

Because excessive O₂ is toxic, we suggest that hematopoietic cells exist in a kind of unstable dynamic balance. This suggestion is based on the idea that mitochondria not only consume O₂ in the process of ATP production but also constitute the main anti-oxygenic stage in the cell's protective antioxidative system. Variations in the mitochondrial base capacity (quantity and quality of mitochondria) constitute an important and highly efficient channel for regulating the oxidative stress level within a cell.

The primary target for leukemogenic agents is the few mitochondria within the hematopoietic stem cell. Disturbance and weakening of their respiratory function further enhances the initial pro-oxidative state of the cell. This readily results in peroxygenation stress, creating the necessary condition for inducing leukemogenesis. We propose that this is the main cause of all related genetic and other disorders in the cell. ROS, RNS and peroxides act as signal molecules affecting redox-sensitive transcription factors, enzymes, oncogenes and other effectors. Thereby, they influence the expression and suppression of many genes, as well as the course and direction of proliferation, differentiation, leukemogenesis and apoptosis.

Differentiation of leukemic cells is blocked at the precursor stage. While the transformation of non-hematopoietic cells into tumor cells starts during proliferation, hematopoietic cells become leukemic at one of the interim stages in differentiation, and differentiation does not continue beyond that point. Proliferation is switched to differentiation and back according to a trigger principle, again involving ROS and RNS. When the leukemogenic Δ_L(PO – AO) imbalance decreases in an under-differentiated leukemia cell to the differentiation level Δ_D(PO – AO), the cell may continue to differentiate to the terminal stage.

Conclusion

The argument described in this article is used to explain the causes of congenital and children's leukemia, and the induction of leukemia by certain agents (vitamin K3, benzene, etc.). Specific research is required to validate the proposals made in this article. This will require accurate and accessible methods for measuring and assessing oxidative stress in different types of cells in general, and in hematopoietic cells in particular, in their different functional states.

Intracellular redox status and oxidative stress: implications for cell proliferation, apoptosis, and carcinogenesis

Oxidative stress can be defined as the imbalance between cellular oxidant species production and antioxidant capability. Reactive oxygen species (ROS) are involved in a variety of different cellular processes ranging from apoptosis and necrosis to cell proliferation and carcinogenesis. In fact, molecular events, such as induction of cell proliferation, decreased apoptosis, and oxidative DNA damage have been proposed to be critically involved in carcinogenesis. Carcinogenicity and aging are characterized by a set of complex endpoints, which appear as a series of molecular reactions. ROS can modify many intracellular signaling pathways including protein phosphatases, protein kinases, and transcription factors, suggesting that the majority of the effects of ROS are through their actions on signaling pathways rather than via non-specific damage of macromolecules; however, exact mechanisms by which redox status induces cells to proliferate or to die, and how oxidative stress can lead to processes evoking tumor formation are still under investigation.

Downregulation of multiple stress defense mechanisms during differentiation of human embryonic stem cells

Evolutionary theory predicts that cellular maintenance, stress defense, and DNA repair mechanisms should be most active in germ line cells, including embryonic stem cells that can differentiate into germ line cells, whereas it would be energetically unfavorable to keep these up in mortal somatic cells. We tested this hypothesis by examining telomere maintenance, oxidative stress generation, and genes involved in antioxidant defense and DNA repair during spontaneous differentiation of two human embryonic stem cell lines. Telomerase activity was quickly downregulated during differentiation, probably due to deacetylation of histones H3 and H4 at the hTERT promoter and deacetylation of histone H3 at hTR promoter. Telomere length decreased accordingly. Mitochondrial superoxide production and cellular levels of reactive oxygen species increased as result of increased mitochondrial biogenesis. The expression of major antioxidant genes was downregulated despite this increased oxidative stress. DNA damage levels increased during differentiation, whereas expression of genes involved in different types of DNA repair decreased. These results confirm earlier data obtained during mouse embryonic stem cell differentiation and are in accordance with evolutionary predictions.