Dietary methyl content regulates opioid responses in mice

De-Yong Liang,^1,2 Yuan Sun,^1,2 J David Clark<sup>1,2

1</sup>Department of Anesthesiology, Veterans Affairs Palo Alto Health Care System, Palo Alto, ²Stanford University School of Medicine, Stanford, CA, USA

Background: Large interindividual differences in clinical responses to opioids and the variable susceptibility to abuse of this class of drugs make their use problematic. We lack a full understanding of the factors responsible for these differences. Dietary factors including methyl donor content have been noted to alter multiple physiological and behavioral characteristics of laboratory animals. The purpose of this research was to determine the effects of dietary methyl donor content on opioid responses in mice.
Methods: Groups of male C57BL/6J mice were treated with high and low methyl donor diets either in the perinatal period or after weaning. Analgesic responses to morphine, as well as tolerance, opioid-induced hyperalgesia, and physical dependence were assessed.
Results: Mice fed high and low methyl donor diets showed equal weight gain over the course of the experiments. Exposure to a high methyl donor diet in the perinatal period enhanced physical dependence. Dietary methyl donor content also altered analgesic responses to low doses of morphine when the dietary treatments were given to the mice after weaning. Opioid-induced hyperalgesia was unaltered by dietary methyl donor content.
Conclusion: High and low methyl donor diet treatment has selective effects on opioid responses depending on the timing of exposure. These findings suggest that examination of DNA methylation patterns in specific brain regions linked to opioid analgesia and dependence may provide specific explanations for dietary effects on opioid responses.

Keywords: opioid, methylation, tolerance, hyperalgesia, dependence