Nitrones, Old Fellows for New Therapies in Ischemic Stroke

Recent Advances on Nitrones Design for Stroke Treatment

The recent advances of tetramethylpyrazine nitrones and quinolylnitrones for the treatment of stroke have been reviewed and compared with other agents, showing promising therapeutic applications. As a result of a functional transformation of natural product ligustrazine, (Z)-N-tert-butyl-1-(3,5,6-trimethylpyrazin-2-yl)methanimine oxide (6) is a multitarget small nitrone showing potent thrombolytic activity and free radicals scavenging power, in addition to nontoxicity and blood-brain barrier permeability. Similarly, antioxidant (Z)-N-tert-butyl-1-(2-chloro-6-methoxyquinolin-3-yl)methanimine oxide (17) is a novel agent for cerebral ischemia therapy as it is able to scavenge different types of free radical species, showing strong neuroprotection and reduced infarct size.

5-Aryl-2-(3,5-dialkyl-4-hydroxyphenyl)-4,4-dimethyl-4H-imidazole 3-Oxides and Their Redox Species: How Antioxidant Activity of 1-Hydroxy-2,5-dihydro-1H-imidazoles Correlates with the Stability of Hybrid Phenoxyl-Nitroxides

Cyclic nitrones of the imidazole series, containing a sterically hindered phenol group, are promising objects for studying antioxidant activity; on the other hand, they can form persistent hybrid phenoxyl-nitroxyl radicals (HPNs) upon oxidation. Here, a series of 5-aryl-4,4-dimethyl-4H-imidazole 3-oxides was obtained by condensation of aromatic 2-hydroxylaminoketones with 4-formyl-2,6-dialkylphenols followed by oxidation of the initially formed N-hydroxy derivatives. It was shown that the antioxidant activity of both 1-hydroxy-2,5-dihydroimidazoles and 4H-imidazole 3-oxides increases with a decrease in steric volume of the alkyl substituent in the phenol group, while the stability of the corresponding HPNs generated from 4H-imidazole 3-oxides reveals the opposite tendency.

Quinolinyl Nitrone RP19 Induces Neuroprotection after Transient Brain Ischemia

There is a need to develop additional effective therapies for ischemic stroke. Nitrones, which were first developed as reactive oxygen species (ROS)-trapping compounds, have been proposed as neuroprotective agents for ischemic stroke, a ROS-related disorder. The previous reported ROS-trapping compound, quinolyl nitrone RP19, is here being assayed to induce neuroprotection to ischemia-reperfusion injury in three experimental ischemia models: (i) oxygen-glucose deprivation (OGD) on primary neuronal cultures; (ii) transient global cerebral ischemia in four-vessel occlusion model; and (iii) transient focal cerebral ischemia in middle cerebral artery occlusion (tMCAO) model. RP19 (50 μM) induced long-term neuroprotection at 5 days of recovery after OGD in primary neuronal cultures, evaluated by cell viability assay, and decreased both ROS formation and lipid peroxidation upon recovery after OGD. Furthermore, treatment of animals with RP19 at the onset of reperfusion after either global or focal ischemia, at the dose range that was demonstrated to be neuroprotective in neuronal cultures, decreased neuronal death and apoptosis induction, reduced the size of infarct, and improved the neurological deficit scores after 48 h or 5 days of reperfusion after ischemia. The molecule proposed, quinolyl nitrone RP19, induced substantial neuroprotection on experimental ischemia in neuronal cells, and against ischemic injury following transient brain ischemia in treated animals. This molecule may have potential therapeutic interest in ischemic stroke and to reduce the reoxygenation-induced injury after induced reperfusion.