MRI study of myelin-protective effect of betulonic acid amide in a mouse model of multiple sclerosis

With appearance of non-invasive imaging techniques (MRI and optical coherence tomography), it has become possible to detect early degenerative changes in the central nervous system in patients with multiple sclerosis (MS) caused by demyelination, inflammation, axonal loss, usually hidden by symptoms of acute inflammation. The possibility of early diagnosis shifts the focus in the search for effective MS treatments to the agents that enhance remyelination. The inducers of the Nrf2 transcription factor signaling pathway, such as pentacyclic triterpenoids which exhibit neuroprotective properties in MS models, are of great interest in this regard. Amide of betulonic acid (ABA), a lupane triterpenoid with pronounced cytoprotective activity, was synthesized in Novosibirsk Institute of Organic Chemistry of the SB RAS, and was studied in vivo models of toxic and inflammatory genesis. The aim of the work was to evaluate the myelin-protective properties of ABA in a model of toxic demyelination caused by cuprizon. Material and methods . The experiment was carried out on fifty C57Bl/6 male mice 8 weeks aged. All animals, except intact group, received 0.3 % aqueous solution of cuprizon instead of drinking water. ABA was administered orally at the doses of 50 and 100 mg/kg five times a week for 8 weeks at the same time of the cuprizone drinking. Control animals received a water-tween mixture. The reference group was subcutaneously injected twice a week with 17b-estradiol (Sigma-Aldrich, USA) at a dose of 0.2 µg per mouse in mineral oil (0.1 ml). The intact group was not manipulated. The myelin-protective effect was evaluated versus control as the changes in the area of the corpus callosum of the brain, which was determined on T2-weighted images using MRI on an ultra-high-field 11.7 T BioSpec 117/16 USR tomograph (Bruker BioSpin, FRG). Before MRI, the animals were anesthetized with a mixture of oxygen and isoflurane (200 ml/min, 1.5 % isoflurane). Results and their discussion . It is found that 8-week exposure to cuprizon causes a 60 % decrease in the area of the corpus callosum in the control group relative to intact mice. Administration of ABA at a dose of 50 mg / kg reduces myelin loss by 33 % (p<0.001), and at a dose of 100 mg / kg – by 20 % (p < 0.01) compared with the control. 17b-estradiol reduces the demyelinating effect of cuprizon by 17 % (p < 0.05). At the same time, significant differences in the area of the corpus callosum with intact animals persist in all experimental groups. Thus, ABA and 17b-estradiol have similar myelin-protective effects, although the remyelination mechanisms of these agents are obviously different. The potential significance of ABA as a myelin-protective agent is due to its ability to activate intracellular signaling cascades associated with antioxidant and anti-inflammatory effects. Conclusions. The data obtained indicate the ability of ABA to stimulate remyelination processes, prolonging it in conditions of chronic demyelination caused by long cuprizon exposition. The myelin-protective effect of ABA is dose-dependent, which is confirmed by literature data concerning the dose dependence of the properties of lupane triterpenoids as regulators of various intracellular signaling pathways.