Effects of Cannabidiol, Hypothermia, and Their Combination in Newborn Rats With Hypoxic-Ischemic Encephalopathy

Therapeutic hypothermia is well-established as a standard treatment for infants with hypoxic-ischemic encephalopathy but it is only partially effective. The potential for combination treatments to augment hypothermic neuroprotection has major relevance. Our aim was to assess the effects of treating newborn rats following hypoxic-ischemic (HI) injury with cannabidiol (CBD) at 0.1 or 1 mg/kg i.p., in normothermic (37.5°C) and hypothermic (32.0°C) conditions, from 7 (neonatal phase) to 37 days old (juvenile phase). Placebo or CBD were administered at 0.5, 24 and 48 h after HI injury. Two sensorimotor (rotarod and cylinder rearing), and two cognitive (novel object recognition and T-maze) tests were conducted 30 days after HI. The extent of brain damage was determined by magnetic resonance imaging, histological evaluation, magnetic resonance spectroscopy, amplitude-integrated electroencephalography and Western blotting. At 37 days, the HI insult produced impairments in all neurobehavioral score (cognitive and sensorimotor tests), brain activity (electroencephalography), neuropathological score (temporoparietal cortexes and CA1 layer of hippocampus), lesion volume, magnetic resonance biomarkers of brain injury (metabolic dysfunction, excitotoxicity, neural damage and mitochondrial impairment), oxidative stress and inflammation (TNFα). We observed that CBD or hypothermia (to a lesser extent than CBD) alone improved cognitive and motor functions, as well as brain activity. When used together, CBD and hypothermia ameliorated brain excitotoxicity, oxidative stress and inflammation, reduced brain infarct volume, lessened the extent of histological damage, and demonstrated additivity in some parameters. Thus, coadministration of CBD and hypothermia could complement each other in their specific mechanisms to provide neuroprotection.

Significance StatementCannabidiol and hypothermia act on some common processes related to hypoxic-ischemic brain damage, modulating excitotoxicity, inflammation and oxidative stress. The two therapies in combination do not compete against each other in modulating these processes, but rather produce additive neuroprotective effects. Furthermore, in the instances where there was not an additive effect, combination of cannabinoid with hypothermia often resulted in a significantly superior profile compared to hypothermia alone, being a promising observation for the clinic. These results justify interest in cannabidiol for developing a combined treatment with hypothermia to increase the number of hypoxic-ischemic infants that benefit from treatment.