Human albumin attenuates Mincle-associated early neuroinflammatory injury in subarachnoid hemorrhage rats

Abstract

Objective To investigate the protective role of human serum albumin in treatment of monocyte-inducible C-type lectin (Mincle)-associated neuroinflammation in subarachnoid hemorrhage (SAH) rats and its underlying mechanisms. Methods Vascular perforation model was used to induce SAH. Ninety-two male SD rats were randomly assigned to sham (n=23), vehicle (n=23), low-dose albumin (0.63 g/kg, n=23) and high-dose albumin (1.25 g/kg, n=23) groups. Saline and albumin were intravenously injected into rats two hours after surgery. Modified Garcia scale was employed to assess neurological functions. Iba-1 and myeloperoxidase (MPO) staining was used to examine the activation of microglial cells and infiltration of neutrophils. Real-time PCR was applied to determine the changes of IL-1β, inducible nitric oxide synthase, CD11b, monocyte chemoattractant protein-1, cytokine-induced neutrophil chemoattractant-1 and CXC motif chemokine ligand-2 mRNA levels. Co-immunoprecipitation was conducted to assess the binding ability of albumin with Mincle. Immunoblotting was carried out to evaluate protein levels of Minlce, Syk and p-Syk. SAH severity measurement was performed before conductions of all the experiments. Results SAH severity scores were 11.4±1.6, 12.8±2.5 and 11.2±3.2 in the vehicle, low-dose albumin and high-dose albumin groups, respectively, without statistically significant difference among groups (F=0.694, P=0.516). Neurological score was 7.5±2.9 in the vehicle group, while the low-dose albumin (14.6±2.2) and high-dose albumin groups (13.6±2.7) exhibited better neurological perfomance (P<0.01). Immunostaining showed that albumin significantly inhibited the activation of microglia, and reduced the percentage of MPO positive cells from 20.7%±1.9% in the vehicle group to 12.1%±2.1% in the low-dose albumin group and 9.8%±0.9% in the high-dose albumin group (F=32.216, P=0.001). mRNA levels of pro-inflammatory cytokines and chemotactic factors were also suppressed by albumin (P<0.05). The results of co-immunoprecipitation displayed that albumin could directly bind Mincle and disrupt the association between Mincle and SAP130. Immunoblotting demonstrated that albumin depressed the protein levels of Mincle, Syk and p-Syk. Conclusion Human serum albumin can inhibit Mincle/Syk-induced neuroinflammation via directly binding Mincle receptor in SAH rats. Key words: Subarachnoid hemorrhage; Albumins; Neuroinflammation; Neuroprotection