Binding of the monoacylglycerol lipase (MAGL) radiotracer [3H]T-401 in the rat brain after status epilepticus

OBJECTIVES

Monoacylglycerol lipase (MAGL) is a cytosolic serine hydrolase considered a potential novel drug target for the treatment of CNS disorders including epilepsy. Here we examined MAGL levels in a rat model of epilepsy.

METHODS

Autoradiography has been used to validate the binding properties of the MAGL radiotracer, [3H]T-401, in the rat brain, and to explore spatial and temporal changes in binding levels in a model of temporal lobe epilepsy model using unilateral intra-hippocampal injections of kainic acid (KA) in rats.

RESULTS

Specific and saturable binding of [3H]T-401 was detected in both cortical grey and subcortical white matter. Saturation experiments revealed a KD in the range between 15 nM and 17 nM, and full saturation was achieved at concentrations around 30 nM. The binding could be completely blocked with the cold ligand (Ki 44.2 nM) and at higher affinity (Ki 1.27 nM) with another structurally different MAGL inhibitor, ABD 1970. Bilateral reduction in [3H]T-401 binding was observed in the cerebral cortex and the hippocampus few days after status epilepticus that further declined to a level of around 30% compared to the control. No change in binding was observed in either the hypothalamus nor the white matter at any time point. Direct comparison to [3H]UCB-J binding to synaptic vesicle glycoprotein 2 A (SV2A), another protein localized in the pre-synapse, revealed that while binding to MAGL remained low in the chronic phase, SV2A was increased significantly in some cortical areas.

SIGNIFICANCE

These data show that MAGL is reduced in the cerebral cortex and hippocampus in a chronic epilepsy model and indicate that MAGL inhibitors may further reduce MAGL activity in the treatment resistant epilepsy patient.

Synaptic vesicle glycoprotein 2A (SV2A) levels in the cerebral cortex in patients with Alzheimer's disease: a radioligand binding study in postmortem brains

Histological and biochemical analyses in postmortem tissues have demonstrated neurodegenerative changes in the cerebral cortex in patients with Alzheimer's disease (AD), and it has been suggested that this represents a loss of synapses. PET imaging of the (pre)synaptic vesicular glycoprotein 2A (SV2A) has demonstrated a reduction in synapse density in AD in the hippocampus but not consistently in the neocortex. This investigation examines the level of [³H]UCB-J binding in postmortem cortical tissue from patients with AD and matched healthy controls using autoradiography. Among the neocortical areas examined, the binding was significantly lower only in the middle frontal gyrus in AD compared to matched controls. No differences were observed in the parietal, temporal, or occipital cortex. The binding levels in the frontal cortex in the AD cohort displayed large variability among subjects, and this revealed a highly significant negative association with the age of the patient. These results demonstrate low UCB-J binding in the frontal cortex of patients with AD, and this biomarker correlates negatively with age, which may further indicate that SV2A could be an important biomarker in AD patients.

Transient receptor potential (TRP) channels mRNA transcripts in the lumbar intervertebral discs: biomarkers for inflammation, pain, disability, and clinical outcome

Transient receptor potential (TRP) channels are widely expressed cation channels that play an essential role in mediating Ca2+ homeostasis and are considered potential regulators of inflammatory pain. This study investigates the expression of the TRP channel subtypes TRPV1, TRPV4, TRPC6, TRPM2, TRPM8 in lumbar intervertebral disc (IVD) biopsies from patients with chronic low back pain (LBP). We determined the expression of these TRP channel subtypes in the annulus fibrosus (AF) and the nucleus pulposus (NP) from 46 patients with LBP undergoing 1-2 level lumbar fusion surgery for degenerative disc disease. The mRNA transcripts were analyzed using quantitative real-time polymerase chain reaction (RT-qPCR), and the expression levels were compared against visual analog scale (VAS) and oswestry disability index (ODI) scores (0-100) for pain and disability. A significant positive correlation was demonstrated between VAS score and the mRNA expression of TRPV1, TRPC6, TRPM2, TRPM8 in the AF. We also found a significant positive correlation between ODI scores and expression of TRPV1 and TRPM8. Further, there is a significant positive correlation between TNF-α and TRPV1, TRPM2 and TRPM8 expression in the AF, and IL-6 to TRPV1 in the NP. Interestingly, when investigating treatment response via a 12-month postoperative follow-up ODI, we found a significant correlation between only TRPV1 expression at baseline and the follow-up ODI scores, which indicates this marker could predict the effectiveness of surgery. These results strongly suggest an association between pain, inflammatory mediators, and TRP channel expression in lumbar disc biopsies of patients with chronic LBP.

Characterization of the Novel P2X7 Receptor Radioligand [3H]JNJ-64413739 in Human Brain Tissue

Radioligands targeting microglia cells have been developed to identify and determine neuroinflammation in the living brain. One recently discovered ligand is JNJ-64413739 that binds selectively to the purinergic receptor P2X7R. The expression of P2X7R is increased under inflammation; hence, the ligand is considered useful in the detection of neuroinflammation in the brain. [¹⁸F]JNJ-64413739 has been evaluated in healthy subjects with positron emission tomography; however, the in vitro binding properties of the ligand in human brain tissue have not been investigated. Therefore, the purpose of this study was to measure B_max and K_d of [³H]JNJ-64413739 using autoradiography on human cortical tissue sections resected from a total of 48 patients with treatment-resistant epilepsy. Correlations between the specific binding of [³H]JNJ-64413739 with age, sex, and duration of disease were explored. Finally, to examine the relationship between P2X7R and TSPO availability, specific binding of [³H]JNJ-64413739 and [¹²³I]CLINDE was examined in the same tissue. The binding was measured in both cortical gray and subcortical white matter. Saturation revealed a K_d (5 nM) value similar between gray and white matter but a larger B_max in the white than in the gray matter. The binding was completely displaced by the cold ligand and structurally different P2X7R ligands. The variability in saturable binding among the samples was found to be 38% in gray and white matter but was not correlated to either age, sex, or the duration of the disease. Interestingly, there was no significant correlation between [³H]JNJ-64413739 and [¹²³I]CLINDE binding. These data demonstrate that [³H]JNJ-64413739 is a suitable radioligand for evaluating the distribution and expression of the P2X7R in the human brain.

Expression profile of synaptic vesicle glycoprotein 2A, B, and C paralogues in temporal neocortex tissue from patients with temporal lobe epilepsy (TLE)

Synaptic vesicle glycoprotein-2 (SV2) is a family of proteins consisting of SV2A, SV2B, and SV2C. This protein family has attracted attention in recent years after SV2A was shown to be an epileptic drug target and a perhaps a biomarker of synaptic density. So far, the anatomical localization of these proteins in the rodent and human brain have been reported, but co-expression of SV2 genes on a cellular level, their expressions in the human brain, comparison to radioligand binding, any possible regulation in epilepsy are not known. We have here analyzed the expression of SV2 genes in neuronal subtypes in the temporal neocortex in selected specimens by using single nucleus-RNA sequencing, and performed quantitative PCR in populations of temporal lobe epilepsy (TLE) patients and healthy controls. [3H]-UCB-J autoradiography was performed to analyze the correlation between the mRNA transcript and binding capacity to SV2A. Our data showed that the SV2A transcript is expressed in all glutamatergic and GABAergic cortical subtypes, while SV2B expression is restricted to only the glutamatergic neurons and SV2C has very limited expression in a small subgroup of GABAergic interneurons. The level of [3H]-UCB-J binding and the concentration of SV2A mRNA is strongly correlated in each patient, and the expression is lower in the TLE patients. There is no relationship between SV2A expression and age, sex, seizure frequency, duration of epilepsy, or whether patients were recently treated with levetiracetam or not. Collectively, these findings point out a neuronal subtype-specific distribution of the expression of the three SV2 genes, and the lower levels of both radioligand binding and expression further emphasize the significance of these proteins in this disease.

N1H- and N1-Substituted Phenylguanidines as α7 Nicotinic Acetylcholine (nACh) Receptor Antagonists: Structure-Activity Relationship Studies

We previously reported that N-(3-chlorophenyl)guanidine (1) represents a novel α7 nicotinic ACh (nACh) receptor antagonist chemotype. In the present study, a small series of compounds was synthesized with the intent to investigate the structure-activity relationship (SAR). Preliminary data suggested that the N-methyl analog of 1, 2, was several times more potent. Therefore, the chloro group at the aryl 3-position of 1 and its N₁-methyl counterpart 2 were replaced with a number of substituents considering the electronic, lipophilic, and steric nature of the substituents. The potencies of the compounds to inhibit acetylcholine (ACh)-induced responses were obtained in Xenopus laevis oocytes expressing human α7 nicotinic ACh receptors (nAChRs) using a two-electrode voltage-clamp assay. We found that the nature of the 3-position substituents had relatively little (i.e., <10-fold) effect on potency, and the presence of an N₁-isopropyl substituent was tolerated. Here, we report the first SAR investigation of this novel α7 nAChR antagonist chemotype.

Low back pain scores correlate with the cytokine mRNA level in lumbar disc biopsies: a study of inflammatory markers in patients undergoing lumbar spinal fusion

PURPOSE

The molecular mechanism behind pain in degenerative disc disease (DDD) and chronic low back pain (LBP) patients is largely unknown. This present study examines the association of LBP and disability to mediators of the inflammatory cascade, as indexed by mRNA gene expression of pro-inflammatory cytokine markers in the intervertebral disc (IVD).

METHODS

Biopsies of the annulus fibrosus (AF) and the nucleus pulposes (NP) from patients with DDD undergoing 1-2 level fusion surgery at L4/L5 or L5/S1 were obtained from total of 34 patients [9 M, 25 F] with average age of 53 [32-63]. The mRNA expression of TNF-α, IL-1β, and IL-6 in the AF and NP was analyzed using quantitative real-time polymerase chain reaction (RT-qPCR), and the expression level of these markers was correlated to the visual analogue scale (VAS) and Oswestry Disability Index (ODI) scores (0-100) for pain and disability.

RESULTS

We report a statistically significant positive correlation between pain intensity (VAS score) and the expression of TNF-α in both the AF (r = 0.54, p = 0.001) and NP (r = 0.40, p = 0.02), similarly with IL-1β in AF (r = 0.37, p = 0.02) and IL-6 in NP (r = 0.40, p = 0.02). In addition, we found significant positive correlation observed between disability score (ODI) and expression of IL-6 in both AF (r = 0.36, p = 0.03) and NP (r = 0.41, p = 0.01).

CONCLUSION

We conclude that the intensity of LBP and disability is associated with the level of inflammation in the disc.

Anti-Inflammatory Effect of Alpha7 Nicotinic Acetylcholine Receptor Modulators on BV2 Cells

OBJECTIVE

The development of neuroinflammation shares numerous risk factors and involves many complex interactions which contribute to disease pathology. An important cell type in neuroinflammation is the active microglia cell - the resident immune cell of the CNS. There is increasing need to understand how these pathways related to neuroinflammation work and how they can be regulated. Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated receptors and widely distributed in the brain. The α7 nAChR is a penta-homomeric receptor and is one of the nAChRs expressed in microglia. This study was first designed to characterize the effects of lipopolysaccharide (LPS) on BV2 culture cells, a cell line of murine microglia origin, on release of inflammatory markers and to characterize the inhibitory effects of α7 nAChR modulators in these cells.

METHODS

First, the BV2 cell cultures were functionally validated by exposing them to LPS for 4-24 h and then examining the release of tumor necrosis factor-alpha (TNF-α) using ELISA and nitric oxide (NO) release using the Griess assay, respectively. Next, α7 nAChR modulators with different pharmacological profiles were applied dose-dependently to study their effects on LPS-induced release of NO and TNF-α.

RESULTS

The time-course and dose-response curve revealed that LPS dose-dependently activated (EC50 = 2.5 ng/mL) BV2 cells releasing TNF-α at 4 h, followed by release of NO that occurred first at 8-h time point. The α7 nAChR subunit mRNA was identified in the BV2 cells. The pharmacology studies showed the α7 nAChR selective modulators NS6740 and TQS reduced NO and cytokine release from BV2 cell cultures.

CONCLUSION

We here identified the dose- and time-dependent effects of LPS in BV2 cell cultures on several inflammatory readouts and showed that α7 nAChR modulators with little or no ion channel activity inhibited this anti-inflammatory mechanism.