Biomarkers of Oxidative Stress

Introduction

Oxidative stress is a process when either larger amount of oxidants (reactive oxygen or nitrogen species) is formed or inhibition of antioxidant mechanisms of cells occurs. Sies defined oxidative stress as an imbalance between the concentration of oxidants and antioxidants in favour of oxidants which can lead to cell damage1.

The term reactive oxygen species (ROS) includes free oxygen radicals (•HO, HO2•, RO•, RO2• and O2) and other reactive oxygen compounds (H2O2 and HOCl) which do not have a free electron and are formed from free radicals. In addition to ROS, reactive nitrogen species (RNS) exist as well – for example NO or ONOO.

Oxidants in cells (e.g. NO or H2O2) are used by immune system to eliminate pathogens, in cell signaling or they are formed in mitochondria. However, in high concentration they oxidize nucleic acids, proteins and phospholipids. That leads to pathological changes in the physiology of cells2.

There are number of antioxidant mechanisms for removing oxidants in cells (e.g. vitamins or enzymes). They can either prevent oxidant formation or transform them into more stable and less reactive products.

ROS and RNS are very unstable and therefore it is not possible to study their concentration in vivo. However, specific molecules – so called biomarkers – are formed in oxidative stress. These substances are present in body fluids (blood plasma, cerebrospinal fluid, urine, exhaled breath condensate) and can be used in the diagnostics of diseases connected with oxidative stress.

Biomarkers of oxidative stress can be determined also in samples collected from healthy people where they are formed due to aging, pollution etc. As a consequence of pathological process, their concentration in body fluids is many times higher. Diseases connected with oxidative stress are e.g. neurodegenerative diseases (Alzheimer’s and Parkinson’s disease) or lung diseases (COPD, lung cancer etc.).

Mechanism of disease formation is described in Figure 1. With high concentration of oxidants, deficiency of antioxidants or damage of antioxidant mechanism, oxidative stress occurs. When the adaptation of immune system is not sufficient nucleic acids, proteins and phospholipids can be damaged. Thus, tissues are damaged and disease occurs3.



Figure 1: Mechanism of oxidative stress disease formation3.

Research activities and interests

The level of organism damage by oxidative stress is determined on the basis of the concentration of biomarkers – substances that are formed by oxidants in body fluids (exhaled breath condensate, urine, blood plasma, cerebrospinal fluid). 8-iso Prostaglandin F and other prostaglandins, dienes, alkanes, aldehydes (malondialdehyde, 4-hydroxy-2-trans-nonenal, 4-hydroxy-2-trans-hexenal, n-aliphatic aldehydes C6-C13) and saturated and unsaturated ketones are formed by oxidation of unsaturated fatty acids (mainly ω-3 a ω-6 presented in phospholipide membranes). By reaction with proteins (amino acids) o-tyrosine, 3-nitrotyrosine, 3-chlortyrosine, o,o’-dityrosine and other biomarkers are formed. By oxidation of nucleic acids 8-hydroxyguanine, 8-hydroxyguanosine, 8-hydroxy-2’-deoxyguanosine a 5-hydroxymethyluracil are formed (Figure 2).



Figure 2: Products of reactive oxygen species (ROS) activity in organism.

The aim of work within this study is a development and validation of analytical methods for the determination of biomarkers in various body fluids using HPLC-MS techniques. These methods are used in clinical studies where concentration levels of biomarkers in healthy subjects and in people with diseases related to oxidative stress (e.g. asbestosis, silicosis, lung cancer etc.) are compared.

References

1. Sies, H. Oxidative Stress. Academic Press, London, 1985.
2.  Stadtman E. R. Curr. Med. Chem. 2004, 11 (7), 1105.
3. Dalle-Donne I., Giustarini D., Colombo R., Rossi R., Milzani A. Trend Mol. Med. 2003, 9 (4), 169.