β-carbolines that enhance GABAA receptor response expressed in oligodendrocytes promote remyelination in an in vivo rat model of focal demyelination

Abstract

Demyelination is typically followed by a remyelination process through mature oligodendrocytes (OLs) differentiated from precursor cells (OPCs) recruited into the lesioned areas, however, this event usually results in uncompleted myelination. Potentiation of the remyelination process is an important target for designing effective therapeutic strategies against white matter loss. Here, it was evaluated the remyelinating effect of different β-carbolines that present differential allosteric modulation on the GABAA receptor expressed in OLs. For this, we used a focalized demyelination model in the inferior cerebellar peduncle (i.c.p.) of rats (DRICP model), in which, demyelination by ethidium bromide (0.05%) stereotaxic injection was confirmed histologically by staining with Black-Gold II (BGII) and toluidine blue. In addition, a longitudinal analysis with diffusion-weighted magnetic resonance imaging (dMRI) was made by computing fractional anisotropy (FA), apparent diffusion coefficient (ADC) and diffusivity parameters to infer i.c.p. microstructural changes. First, dMRI analysis revealed FA decreases together with ADC and radial diffusivity (RD) increases after demyelination, which correlates with histological BGII observations. Then, we evaluated the effect produced by three allosteric GABAA receptor modulators, the N-butyl-β-carboline-3-carboxylate (β-CCB), ethyl 9H-pyrido [3,4-b]indole-3-carboxylate (β-CCE), and 4-ethyl-6,7-dimethoxy-9H-pyrido [3,4-b]indole-3-carboxylic acid methyl ester (DMCM). The results indicated that daily systemic β-CCB (1 mg/Kg) or β-CCE (1 mg/Kg) administration for 2 weeks, but not DMCM (0.35 mg/Kg), in lesioned animals increased FA and decreased ADC or RD, suggesting myelination improvement. This was supported by BGII staining analysis that showed a recovery of myelin content. Also, it was quantified by immunohistochemistry both NG2+ and CC1+ cellular population in the different experimental sceneries. Data indicated that either β-CCB or β-CCE, but not DMCM, produced an increase in the population of CC1+ cells in the lesioned area. Finally, it was also calculated the g-ratio of myelinated axons and observed a similar value in those lesioned animals treated with β-CCB or β-CCE compared to controls. Thus, using the DRICP model, it was observed that either β-CCB or β-CCE, positive modulators of the GABAA receptor in OLs, had a potent promyelinating effect.

N-butyl-β-carboline-3-carboxylate (β-CCB) systemic administration promotes remyelination in the cuprizone demyelinating model in mice

“…In the cerebral cortex ( mctx ), β-CCB did not have a clear effect, whereas in some areas of the hippocampus it exhibited a mild effect. Thus, the promyelinating character of β-CCB was confirmed in a model of generalized demyelination, supporting the idea that β-carbolines have the potential to be used as therapeutic drugs against demyelinating diseases, as it has been shown elsewhere 12 , this promyelinating action could be explained by its potentiating effect on the oligodendroglial GABA A R.…”

“…Previous studies have shown that β-CCB potentiates the response of GABA A Rs expressed in OPCs and OLs in culture, and that it has a promyelinating effect in a model of focal demyelination of the rat icp 3 , 5 , 8 , 12 . Identification of white matter structures that seem to undergo CPZ-induced demyelination, as assessed by MRI metrics and histology, allowed us to evaluate a generalized promyelinating effect of β-CCB.…”

“…Before proceeding with this analysis, we examined the areas that had been demyelinated by CPZ using BGII staining and, more importantly, we confirmed the promyelinating effect of β-CCB in several brain regions. It has been previously described that β-CCB has a promyelinating effect on focal demyelination in the rat icp 5 , 12 . Here, we show that the β-CCB treatment in mice demyelinated by CPZ intake promotes the recovery of myelin content in various structures.…”

“…In this context, the promyelinating effect of β-CCB administrated in vivo may occur through GABA response potentiation in the oligodendroglial lineage (see also ref. 12 ). Therefore, to identify a possible direct effect of β-CCB, we performed an immunolabeling analysis of OPC and mature OL populations using the NG2 and CC1 markers, respectively 1 , 31 , 32 (Fig.…”

“…We have previously shown that β-CCB treatment promotes remyelination in a focal demyelination model 5 , 12 . Here, we investigated whether the effect of β-CCB extends to other regions in the CNS.…”