Influence of catecholamines on proteins and erythrocytes

A mammal (including humans) exposed to a stressful situation responds with different reactions. Catecholamines (epinephrine and norepinephrine) are frontline hormones to enable an individual to overcome these situations. In addition to rapid enzymatic degradation, catecholamines are known to form adducts with different proteins. We hypothesise that these modified proteins have an extended lifespan, an impaired function and accumulate in the body. Therefore, the present study will explore the fate and the biological consequences of these adducts using the rat as a model animal for mammals. We will investigate the accumulation of catecholamine adducts in various organs and tissues, the changes in the lifespan of two representative plasma proteins (albumin and -globulin) loaded with catecholamines, and the impact of catecholamine excess on erythrocytes. Radiolabelled epinephrine and norepinephrine will serve as trace substances in the proposed experiments. Our hypothesis is based on the fact that binding of catecholamines to thiols, present as cysteinyl residues of proteins or peptides like glutathione, leads to their oxidative modification and is a source of reactive oxygen species. Furthermore, these modifications result in impaired functionality and may reduce degradation and therefore facilitate accumulation of the affected proteins. It is well known that the catecholamine dopamine, for example, forms adducts non-enzymatically in the brain with cysteinyl residues of various proteins. The formed adducts are associated with Parkinson`s disease and other disorders of the central nervous system. Adduct formation in the blood between the related catecholamines, epinephrine and norepinephrine, has also been described, but the biological consequences remain unknown. Furthermore, accumulation of catecholamines in erythrocytes has been proven. However, information about the binding of catecholamines to haemoglobin or to other proteins or peptides of erythrocytes and its physiological implication is scarce. Although the toxicity of the formed compounds has drawn some attention, basic aspects of the lifespan, degradation, excretion and/or accumulation of the modified proteins remain unclear. Therefore this study will provide basic knowledge that will be crucial to understanding the negative effects of long- term stress in animals as well as in humans and will lay the foundation for establishing new methods for evaluating the cumulative effects of stressful situations.

Catecholamines (CA) are frontline hormones that enable an organism to overcome stressful situations. In addition to rapid enzymatic inactivation, CA bind non-enzymatically and irreversible to proteins and form adducts. Furthermore, accumulation of CA in erythrocytes has been proven, however the metabolic fate inside the cells and the physiological impact of these CA adducts are still unclear, as in vivo studies are rare and data in the literature give conflicting information. We therefore collected basic data about the distribution of CA adducts in various tissues including plasma and erythrocytes over 21 days in the rat as a model animal after repeated intravenous administration of 3H-adrenaline (A) and 3H-noradrenaline (NA). In addition, we checked if heavily catecholaminated serum albumin or erythrocytes show an altered half-life. In all animals radioactivity in plasma and erythrocytes increased from Day 1 (24 h after first injection) to Day 7 (24 h after last injection). While in plasma radioactivity decreased then slowly to values close to background activity 3 weeks after the last injection, radioactivity in erythrocytes remained higher until the end of the experiment. In all sampled tissues together a total of 1% to 3% of the injected radioactivity could still be found (highest concentrations in hair, adrenals and kidneys, lowest in fat and brain) after two weeks. Afterwards radioactivity declined depending on the metabolism of the respective organ, only in hair samples similar high amounts of radioactivity remained present even after 4 weeks. We also compared the half-life of rat serum albumin or erythrocytes labelled with radioactive A or NA as a tracer (control groups) or loaded additionally with unlabelled A or NA. In control groups as well as in the experimental groups radioactivity slowly decreased until the end of the experiment. There were no significant differences between both groups throughout the whole experiments. Besides providing basic knowledge about the distribution of CA in the body after chronically elevated CA, this study did not find a physiological effect of CA adducts (unchanged half-life of proteins and erythrocytes). However, the present project showed for the first time deposition and accumulation of CA in the hair, suggesting that hair might be used for evaluating the cumulative effects of stressful situations.