Expression of T helper cell-associated inflammatory mediator mRNAs in cells of bronchoalveolar lavage fluid samples and oxygen concentration in arterial blood samples from healthy horses exposed to hyperbaric oxygen.

This research investigates how exposure to highly concentrated oxygen under pressure, known as hyperbaric oxygen therapy, affects inflammatory markers in the lungs of healthy horses. The study finds that the therapy does not increase inflammation, but does briefly raise oxygen levels in the blood.

Objective and Animal Subjects

• The primary objective of this study was to monitor and evaluate the expression of mRNA of inflammatory mediators in bronchoalveolar lavage fluid samples. These mediators are associated with T helper (Th)1, Th2, and Th17 cells.
• The second aim was to observe the changes in arterial blood oxygen concentration during and after HBO therapy.
• A total of eight healthy horses took part in this research project.

Study Procedures

• The researchers used a randomized controlled crossover design for the study.
• Each horse was subjected to 100% oxygen at a maximum of 3 atmospheres absolute daily for 10 days. As a control, they also exposed horses to ambient air at atmospheric pressure in the HBO chamber for an equivalent amount of time.
• Bronchoalveolar lavage fluid samples were collected on the first and tenth day of the experiment.
• After verifying candidate reference genes, relative mRNA expressions of various innate inflammatory, Th1 cell, Th2 cell (including eotaxin-2), Th17 cell, and regulatory cytokines were evaluated using quantitative PCR assays.
• In three horses, arterial blood samples were collected for blood gas analysis during separate HBO therapy sessions.

Results

• The optimal combination of reference genes that was obtained consisted of glyceraldehyde-3-phosphate dehydrogenase, hypoxanthine ribosyltransferase, and ribosomal protein L32.
• Compared to the initial findings on day 0, the expression of eotaxin-2 mRNA reduced significantly (0.12-fold decrease) on the tenth day after the horses had undergone HBO therapy.
• The percentage of neutrophils in bronchoalveolar lavage fluid samples was significantly lower on day 10 when the horses received HBO therapy.
• The oxygen concentration in the arterial blood (Pao2) values rapidly increased to more than 800 mm Hg but reverted to normal levels immediately after the HBO sessions ended.

Conclusions and Clinical Relevance

• The results of the study indicated that HBO therapy does not increase mRNA expression of inflammatory cytokines, but it reduces the transcription of eotaxin-2 mRNA.
• The increase in the Pao2 value was found to be transient with no cumulative effects after HBO therapy.