Differing Collagen Responses in the Right and Left Ventricle Following Postnatal Hyperoxia Exposure

Abstract

BackgroundPreterm birth affects approximately 1 in 10 pregnancies, and extreme preterm birth is associated with a 17‐fold increased risk of heart failure during childhood and early adulthood. Whether this is related to increase cardiac fibrosis is currently unknown. The objective of this study was to determine if fibrosis is present in an animal model of cardiomyopathy of prematurity using postnatal hyperoxia exposure.MethodsPostnatal hyperoxia exposure in an immature rat heart was used to mimic the relative hyperoxia exposure premature infants experience at birth. Timed‐pregnant Sprague Dawley rats (Rattus norvegicus) were allowed to deliver naturally, and pups randomized to either postnatal hyperoxia (85% FIO2) or normoxia (21%) exposure from 0–14 days of life. Dams were rotated daily to prevent maternal oxygen toxicity. On day 21 of life, cardiac tissue was harvested and prepped for Masson’s trichrome blue stain. Additional hearts were resected and the right ventricle (RV) and left ventricle (LV) were flash frozen. The trichrome stained tissue was analyzed using ImageJ to determine the percent of image that was collagen, and colorimetric collagen assays that measured the hydroxyproline were ran on the flash frozen tissue. Results were compared with t‐tests, with p<0.05 used to determine significance.ResultsOverall, presence of cardiac fibrosis was low. In the LV, trichrome analysis demonstrated no difference between the hyperoxic and normoxic groups (4.56x10−4% vs 3.01x10−4 %, p=0.58). Similarly, the collagen assay showed no difference between the hyperoxic and normoxic LV (1.24 ±0.20 μg/g vs 1.01 ±0.34 μg/g, p=0.231). However, in the RV there was decreased percent fibrosis in hyperoxia relative to normoxia (2.69x10‐3 % vs 4.88x10‐3 %, p=0.03). The collagen assay showed similar results of a trend towards decreased collagen in hyperoxic RV compared to the normoxic RV (2.01±0.45μg/g vs 2.57±0.27μg/g, p =0.09).ConclusionThese results appear to suggest that cardiac fibrosis is not a prominent feature in the animal model of cardiomyopathy of prematurity. Whether this is true for humans born preterm merits further study in the function and structure of the human heart throughout its development. The increased risk of heart failure could be caused by factors other than collagen deposition, or collagen deposition that occurs later in life. Further testing is required to fully understand the relationship between hyperoxygenation and long‐term heart health.Support or Funding InformationUniversity of Wisconsin Clinical and Translational Science Award program, through the NIH National Center for Advancing Translational Sciences grant NIH UL1TR000427