A pooled analysis of nine studies in one institution to assess effects of whole heart irradiation in rat models

Abstract

Purpose

Over the years, animal models of local heart irradiation have provided insight into mechanisms of and treatments for radiation-induced heart disease in human populations. However, it is not completely clear which manifestations of radiation injury are most commonly seen after whole heart irradiation, and whether certain biological factors impact experimental results. Combining 9 homogeneous studies in rat models of whole heart irradiation from one laboratory, we sought to identify experimental and/or biological factors that impact heart outcomes. We evaluated the usefulness of including (1) heart rate and (2) bodyweight as covariates when analyzing biological parameters, and (3) we determined which echocardiography, histological, and immunohistochemistry parameters are most susceptible to radiation effects. Finally, (4) as an educational example, we illustrate a hypothetical sample size calculation for a study design commonly used in evaluating radiation modifiers, using the pooled estimates from the 9 rat studies only for context. The results may assist investigators in the design and analyses of pre-clinical studies of whole heart irradiation.

Materials and Methods

We made use of data from 9 rat studies from our labs, 8 published elsewhere in 2008–2017, and one unpublished study. Echocardiography, histological, and immunohistochemical parameters were collected from these studies. Using mixed effects analysis of covariance models, we estimated slopes for heart rate and bodyweight and estimated the radiation effect on each of the parameters.

Results

Bodyweight was related to most echocardiography parameters, and heart rate had an effect on echocardiography parameters related to the diameter of the left ventricle. For some parameters, there was evidence that heart rate and bodyweight relationships with the parameter depended on whether the rats were irradiated. Radiation effects were found in systolic measures of echocardiography parameters related to the diameter of the left ventricle, with ejection fraction and fractional shortening, with atrial wall thickness, and with histological measures of capillary density, collagen deposition, and mast cells infiltration in the heart.

Conclusion

Accounting for bodyweight, as well as heart rate, in analyses of echocardiography parameters should reduce variability in estimated radiation effects. Several echocardiography and histological parameters were particularly susceptible to whole heart irradiation, showing robust effects compared to sham-irradiation. Lastly, we provide an example approach for a sample size calculation that will contribute to a rigorous study design and reproducibility in experiments studying radiation modifiers.

Keywords:

• Radiation-induced heart disease
• power calculations
• echocardiography

Acknowledgements

The authors thank Jeffrey Jonkman, PhD, of Grinnell College for his helpful comments on this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Center for Advancing Translational Science of the National Institutes of Health (NIH) under grant UL1TR003107 and by the National Institute of General Medical Sciences (NIGMS) of the NIH under grant P20 GM109005. CL and MB were also supported by University of Arkansas for Medical Sciences/College of Pharmacy under a Seed Grant. RDL received support in preparing the manuscript from the Center for Childhood Obesity Prevention funded by grant P20 GM109096 awarded by the NIGMS of the NIH. CB is supported by R01 HL147884.

Notes on contributors

Reid D. Landes

Reid D. Landes is a Professor of Biostatistics. He received his MSc in biometry from the University of Nebraska-Lincoln and a PhD in statistics from Iowa State University. Among various roles, he finds his role as IACUC statistician particularly rewarding. Reid likes thinking about good experiment designs in animal studies.

Chenghui Li

Chenghui Li, PhD, is an Associate Professor in the Division of Pharmaceutical Evaluation, University of Arkansas for Medical Sciences College of Pharmacy, Little Rock, AR, USA.

Vijayalakshmi Sridharan

Vijayalakshmi Sridharan received her PhD in Biochemistry and Molecular Biology from the University of Madras in India. She completed postdoctoral fellowships at the Medical University of South Carolina and the University of Arkansas for Medical Sciences (UAMS). She is currently a Research Instructor in the UAMS Division of Radiation Health.

Carmen Bergom

Carmen Bergom received her PhD and MD from the Medical College of Wisconsin. She is an Associate Professor of Radiation Oncology at Washington University School of Medicine in St Louis, MO, USA.

Marjan Boerma

Marjan Boerma received her PhD in radiation biology from Leiden University, the Netherlands and followed this with a postdoctoral fellowship at the University of Arkansas for Medical Sciences (UAMS). She serves as the director of the UAMS Department of Pharmaceutical Sciences, Division of Radiation Health.