Hypoxia caused by
ischemia induces
acidosis and neuroexcitotoxicity, resulting in neuronal death in the central nervous system (CNS).
Monoacylglycerol lipase (MAGL) is a modulator of
2-arachidonoylglycerol (2-AG), which is involved in retrograde inhibition of
glutamate release in the
endocannabinoid system. In the present study, we used positron emission tomography (PET) to monitor MAGL-positive neurons and
neuroinflammation in the brains of ischemic rats. Additionally, we performed PET imaging to evaluate the
neuroprotective effects of an MAGL inhibitor in an ischemic injury model. Methods: Ischemic-injury rat models were induced by intraluminal right
middle cerebral artery occlusion (MCAO). PET studies of the brains of the ischemic rats were performed at several experimental time points (pre-occlusion, days 2, 4, and 7 after the MCAO surgery) using [11C]
SAR127303 for MAGL and [18F]FEBMP for 18 kDa translocator
protein (TSPO, a hall-mark of
neuroinflammation). Medication using
minocycline (a well-known
neuroprotective agent) or KML29 (a potent MAGL inhibitor) was given immediately after the MCAO surgery and then daily over the subsequent three days. Results: PET imaging of the ischemic rats using [11C]
SAR127303 showed an acute decline of radioactive accumulation in the ipsilateral side at two days after MCAO surgery (ratio of the area under the curve between the ipsilateral and contralateral sides: 0.49 ± 0.04 in the cortex and 0.73 ± 0.02 in the striatum). PET imaging with [18F]FEBMP, however, showed a moderate increase in accumulation of radioactivity in the ipsilateral hemisphere on day 2 (1.36 ± 0.11), and further increases on day 4 (1.72 ± 0.15) and day 7 (1.99 ± 0.06). Treatment with
minocycline or KML29 eased the decline in radioactive accumulation of [11C]
SAR127303 for MAGL (
minocycline-treated group: 0.82 ± 0.06 in the cortex and 0.81 ± 0.05 in the striatum; KML29-treated group: 0.72 ± 0.07 in the cortex and 0.88 ± 0.04 in the striatum) and increased uptake of [18F]FEBMP for TSPO (
minocycline-treated group: 1.52 ± 0.21 in the cortex and 1.56 ± 0.11 in the striatum; KML29-treated group: 1.63 ± 0.09 in the cortex and 1.50 ± 0.17 in the striatum). In MCAO rats,
minocycline treatment showed a
neuroprotective effect in the sensorimotor cortex suffering from severe hypoxic injury, whereas KML29 treatment saved neurons in the striatum, including bundles of myelinated axons. Conclusions: PET imaging allowed visualization of the different
neuroprotective effects of
minocycline and KML29, and indicated that combination
pharmacotherapy using these drugs may be an effective
therapy in acute
ischemia.