Inhibition of Monoacylglycerol Lipase by NSD1819 as an Effective Strategy for the Endocannabinoid System Modulation against Neuroinflammation-Related Disorders

Abstract

Neuroinflammation is a key pathological event shared by different diseases affecting the nervous system. Since the underlying mechanism of neuroinflammation is a complex and multifaceted process, current pharmacological treatments are unsatisfactory-a reason why new therapeutic approaches are mandatory. In this context, the endocannabinoid system has proven to possess neuroprotective and immunomodulatory actions under neuroinflammatory status, and its modulation could represent a valuable approach to address different inflammatory processes. To this aim, we evaluated the efficacy of a repeated treatment with NSD1819, a potent β-lactam-based monoacylglycerol lipase inhibitor in a mouse model of neuroinflammation induced by lipopolysaccharide (LPS) injection. Mice were intraperitoneally injected with LPS 1 mg/kg for five consecutive days to induce systemic inflammation. Concurrently, NSD1819 (3 mg/kg) was daily per os administered from day 1 until the end of the experiment (day 11). Starting from day 8, behavioral measurements were performed to evaluate the effect of the treatment on cognitive impairments, allodynia, motor alterations, anhedonia, and depressive-like behaviors evoked by LPS. Histologically, glial analysis of the spinal cord was also performed. The administration of NSD1819 was able to completely counteract thermal and mechanical allodynia as highlighted by the Cold plate and von Frey tests, respectively, and to reduce motor impairments as demonstrated by the Rota rod test. Moreover, the compound was capable of neutralizing the memory loss in the Passive avoidance test, and reducing depressive-like behavior in the Porsolt test. Finally, LPS stimulation caused a significant glial cells activation in the dorsal horn of the lumbar spinal cord that was significantly recovered by NSD1819 repeated treatment. In conclusion, NSD1819 was able to thwart the plethora of symptoms evoked by LPS, thus representing a promising candidate for future applications in the context of neuroinflammation and related diseases.

Keywords: 2-AG; LPS; MGL inhibitor; depression; glial cells; memory; neuroinflammation; pain.

Figure 1

The structures of endocannabinoids AEA (1) and 2-AG (2), the natural cannabinoid Δ9-THC (3), and the title compound NSD1819 (4).

Scheme 1

Reagents and conditions: (a) 4-amino-1-benzylpiperidine, EtOH, 80 °C, 2 h, quantitative yield; (b) triphosgene, dry DCM, 50 °C, 0.5 h then TEA, 50 °C, 12 h, 60%; (c) H₂, Pd/C 10%, MeOH, 25 °C, 2 h, quantitative yield; (d) 1H-1,2,4-triazole, phosgene (20% in toluene), DMAP, dry DCM, 25 °C, 12 h, 63%.

Figure 2

Effect of NSD1819 on LPS-induced thermal and mechanical allodynia. LPS (1 mg/kg) was intraperitoneally injected for five consecutive days (from 1 to 5). NSD1819 was suspended in 1% carboxymethylcellulose sodium salt (CMC) and daily orally administered starting from day 1 until the end of the experiment. Control animals were treated with vehicles. On day 8, 16 h after the last administration of the compound, (a) thermal and (b) mechanical allodynia were assessed by the Cold plate and von Frey tests, respectively. Data are expressed as the mean ± S.E.M. of values from 8 mice analyzed in 2 different experimental sets. ** p < 0.01 vs. vehicle + vehicle; ^^ p < 0.01 vs. LPS + vehicle.

Figure 3

Effect of NSD1819 on LPS-induced motor alterations. LPS (1 mg/kg) was intraperitoneally injected for five consecutive days (from 1 to 5). NSD1819 was suspended in 1% carboxymethylcellulose sodium salt (CMC) and daily orally administered starting from day 1 until the end of the experiment. Control animals were treated with vehicles. On day 8, 16 h after the last administration of the compound, the motor coordination was assessed by the Rota rod test. Data are expressed as the mean ± S.E.M. of values from 8 mice analyzed in 2 different experimental sets. * p < 0.05 vs. vehicle + vehicle; ^ p < 0.05 vs. LPS + vehicle.

Figure 4

Effect of NSD1819 on LPS-induced depressive-like behavior. LPS (1 mg/kg) was intraperitoneally injected for five consecutive days (from 1 to 5). NSD1819 was suspended in 1% carboxymethylcellulose sodium salt (CMC) and daily orally administered starting from day 1 until the end of the experiment. Control animals were treated with vehicles. On day 8, 16 h after the last administration of the compound, the depressive-like behavior was assessed by the Porsolt test. Data are expressed as the mean ± S.E.M. of values from 8 mice analyzed in 2 different experimental sets. ** p < 0.01 vs. vehicle + vehicle; ^^ p < 0.01 vs. LPS + vehicle.

Figure 5

Effect of NSD1819 on LPS-induced memory loss. LPS (1 mg/kg) was intraperitoneally injected for five consecutive days (from 1 to 5). NSD1819 was suspended in 1% carboxymethylcellulose sodium salt (CMC) and daily orally administered starting from day 1 until the end of the experiment. Control animals were treated with vehicles. On day 8, 16 h after the last administration of the compound, the memory was assessed by the Passive avoidance test. Data are expressed as the mean ± S.E.M. of values from 8 mice analyzed in 2 different experimental sets. ** p < 0.01 vs. vehicle + vehicle; ^^ p < 0.01 vs. LPS + vehicle.

Figure 6

Effect of NSD1819 on LPS-induced glia cell activation in the dorsal horn of the lumbar spinal cord (L4–L5). LPS (1 mg/kg) was intraperitoneally injected for five consecutive days (from 1 to 5). NSD1819 was suspended in 1% carboxymethylcellulose sodium salt (CMC) and daily orally administered, starting from day 1 until the end of the experiment. Control animals were treated with vehicles. At the end of the behavioral experiments and 16 h after the last administration of the compound, animals were sacrificed, and the lumbar spinal cord was collected. GFAP and Iba-1 antibodies were used as marker for astrocytes and microglia, respectively. Representative images of merged GFAP-or Iba-1-labeled cells (red), plus DAPI-labeled cell nuclei (blue) at 40× magnification are shown (scale bar = 50 μm). Histograms show the quantitative analysis of GFAP and Iba-1 fluorescence intensity and the number of GFAP- and Iba-1 positive cells/optic field. Data are expressed as the mean ± S.E.M. of values from 8 mice analyzed in 2 different experimental sets. ** p < 0.01 vs. vehicle + vehicle; ^^ p < 0.01 vs. LPS + vehicle.