Oxidative stress is caused by ROS produced within an organism by endogenous or exogenous sources and is a major cause of stress to cells or tissues. In human medicine, oxidative stress is known to be harmful to the body. Therefore, the human body has developed a redox (oxidation and reduction) regulating system, which acts defensively against oxidative stress. Within this system, TRX has an important role in maintaining homeostasis in response to oxidative stress.
Thioredoxin is now known to be a class of small redox proteins. Thioredoxin-1 is a small redox-active protein (12 kDa) consisting of 105 amino acids,1 which is ubiquitously expressed in tissues of humans and other animals. Thioredoxin was originally identified in Escherichia coli as an electron donor for ribonucleotide reductase, an essential enzyme for DNA synthesis.2 Human TRX was cloned independently as an ADF in 1989.3 In humans, TRX is a defensive protein induced by various stresses and has antioxidative, antiapoptotic, and anti-inflammatory effects.4 Thioredoxin is present in all cells, including prokaryotes and fungi,1 and is induced as a defensive protein by various stimuli such as UV light, radiation, ischemia and reperfusion injury, chemotherapy, infection, and inflammation.4–6 In human medicine, TRX has an important role in inflammation during viral infection by HIV or hepatitis C virus as well as autoimmune and cardiovascular disease.7–11 Thioredoxin expression is expected to influence the diagnosis of these disorders and their prognosis as well as be useful for treatment evaluation. Additionally, TRX might be useful for treatment of acute respiratory distress syndrome, acute lung injury, and contact dermatitis.12,13
Thus, in human medicine, TRX is generally recognized as an oxidative stress marker with clinical applicability.14,15 In veterinary medicine, similar to human medicine, oxidative stress is likely involved in various diseases of animals, and TRX is expected to be a clinically applicable biostress marker and useful therapeutic agent for disorders associated with oxidative stress. However, to our knowledge, there have been no studies evaluating TRX in veterinary medicine. Measurements of plasma TRX-1 concentrations in companion animals such as dogs and cats have not been investigated.
We previously reported immune cross-reactivity between humans and dogs by demonstrating that a rabbit antibody directed against human TRX (ADF) could also detect canine ADF by immunohistostaining.14 Furthermore, antibodies directed against canine ADF successfully reacted with human ADF in a sensitive ELISA.15
The purpose of the study reported here was to determine whether TRX can be used as a valid biomarker for oxidative stress in dogs. Our intent was to measure plasma and urine TRX-1 concentrations in dogs to evaluate the clinical diagnostic application of an ELISA with cross-reactive anti-human TRX antibodies for use in clinical veterinary practice. Because TRX is an oxidative stress marker in humans, we hypothesized that 100% O2–induced hyperoxia would induce oxidative stress in dogs and that increases in TRX-1 concentrations in dog urine and plasma samples could be measured by ELISA with human anti-TRX antibodies that are cross-reactive with canine TRX.
Supported in part by the Nippon Veterinary and Life Science University.
The authors thank Drs. Hajime Nakamura and Masayuki Iwano and Kenji Kasuno for technical advice.
The authors have no conflicts of interest to declare.
Adult T-cell leukemia-derived factor
Reactive oxygen species
Madin-Darby Canine Kidney cells, ATCC, Manassas, Va.
Protease inhibitor cocktail, Complete Mini, Roche Applied Science, Tokyo, Japan.
15% to 20% Tris-HCl gels, Bio Craft, Tokyo, Japan.
Immobilon-P membranes, Millipore, Tokyo, Japan.
Horseradish peroxidase-conjugated anti-mouse IgG, Promega, Tokyo, Japan.
Enhanced chemiluminescence substrate, SuperSignal West Femto Maximum Sensitivity Substrate, Thermo Scientific, Tokyo, Japan.
Beagles, Kitayama Labs, Nagano, Japan.
Artificial respirator, Kimura Ika Kougyou, Tokyo, Japan.
Venous catheter, Terumo, Tokyo, Japan.
6F Catheter, Atom Medical, Tokyo, Japan.
Sandwich TRX ELISA, Redox Bioscience Corp, Kyoto, Japan.
ELISA reader, BioRad Laboratories, Calif.
Hitachi 7180, Hitachi, Tokyo, Japan.
ICR-001, Techno Medica, Yokohama, Japan.
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