Abstract
BackgroundMicroglia initiates and sustains the inflammatory reaction that drives the pathogenesis of pneumococcal meningitis. The expression of the G-protein cannabinoid receptor type 2 (CB2) in the brain is low, but is upregulated in glial cells during infection. Its activation down-regulates pro-inflammatory processes, driving microglia towards an anti-inflammatory phenotype. CB2 agonists are therefore therapeutic candidates in inflammatory conditions like pneumococcal meningitis. We evaluated the effects of JWH-133, a specific CB2 agonist on microglial cells, inflammation, and damage driven by S. pneumoniae in vitro and in experimental pneumococcal meningitis.Materials/methodsPrimary mixed glial cultures were stimulated with live or heat-inactivated S. pneumoniae, or lipopolysaccharide and treated with JWH-133 or vehicle. Nitric oxide and cytokines levels were measured in the supernatant. In vivo, pneumococcal meningitis was induced by intracisternal injection of live S. pneumoniae in 11 days old Wistar rats. Animals were treated with antibiotics (Ceftriaxone, 100 mg/kg, s.c. bid) and JWH-133 (1 mg/kg, i.p. daily) or vehicle (10% Ethanol in saline, 100 µl/25g body weight) at 18 h after infection. Brains were harvested at 24 and 42 h post infection (hpi) for histological assessment of hippocampal apoptosis and cortical damage and determination of cyto/chemokines in tissue homogenates. Microglia were characterized using Iba-1 immunostaining. Inflammation in brain homogenates was determined using membrane-based antibody arrays.Results In vitro, nitric oxide and cytokines levels were significantly lowered by JWH-133 treatment. In vivo, clinical parameters were not affected by the treatment. JWH-133 significantly lowered microglia activation assessed by quantification of cell process length and endpoints per microglia. Animals treated with JWH-133 demonstrated significantly lower parenchymal levels of chemokines (CINC-1, CINC-2α/β, and MIP-3α), TIMP-1, and IL-6 at 24 hpi, and CINC-1, MIP-1α, and IL-1α at 42 hpi. Quantitative analysis of brain damage did not reveal an effect of JWH-133.ConclusionsJWH-133 attenuates microglial activation and downregulates the concentrations of pro-inflammatory mediators in pneumococcal infection in vitro and in vivo. However, we didn’t observe a reduction in cortical or hippocampal injury. This data provides evidence that inhibition of microglia by adjuvant CB2 agonists therapy effectively downmodulates neuroinflammation but does not reduce brain damage in experimental pneumococcal meningitis
Highlights
In bacterial meningitis an overshooting inflammatory reaction in the central nervous system contributes to the pathophysiology of the disease including the development of brain damage
Pneumococcal meningitis is characterized by a high rate of mortality and morbidity, even when patients are treated with efficient antibiotic therapy
Mixed glial cultures consisting of microglial and astroglial cells were isolated from infant rat brains at postnatal day 3 (P3) as previously described (Muri et al, 2019b)
Summary
In bacterial meningitis an overshooting inflammatory reaction in the central nervous system contributes to the pathophysiology of the disease including the development of brain damage. In particular children, are left with several long-lasting disabilities, the most frequent being hearing loss, and cognitive impairments, including learning and memory deficits, as well as focal neurological deficits (Edmond et al, 2010; Agyeman et al, 2014; Lucas et al, 2016; Muri et al, 2019a). The causes of these different sequelae have been deduced from the histological analyses of tissues of deceased patients or from experimental models. Inflammation in brain homogenates was determined using membrane-based antibody arrays
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