Anti-Diabetic Properties of Honokiol are Facilitated by Improving High Glucose-Induced IL-10 Hyporesponsiveness and Enhancing ABCA1-Mediated Cholesterol Efflux Through AKT Pathway

Objective: There is growing evidence suggests that chronic yet low-grade inflammation brought on by hyperglycemia is closely linked to various complications of diabetes. The goal of this study was to assess the prospective therapeutic potential of Honokiol, a natural immunomodulatory compound, against inflammation and cholesterol efflux in an in vitro setting under hyperglycemic environment. Methods: The study employed RAW 264.7 macrophage cell line to investigate the therapeutic potential of Honokiol. The cytotoxicity of Honokiol on cells was detected by MTT assay. The anti-diabetic activity of Honokiol was evaluated by studying concentration of pro-inflammatory (TNF-α) and anti-inflammatory (IL-10) cytokine by ELISA and cholesterol efflux assay by Amplex Red method secreted by cells following treatment with glucose and/or Honokiol. The role of ATP binding cassette transporter-A1 (ABCA1) was assessed by siRNA-mediated knockdown of ABCA1 in cells cultured in high glucose condition. Immunoblot analysis (P-STAT3, P-AKT and ABCA1) and RT-PCR (P-STAT3, P-AKT and ABCA1) were employed for studying the expression of various proteins and mRNA respectively. Results: Research indicated that IL-10, recognized as an anti-inflammatory cytokine was not as effective in suppressing the production of TNF-α stimulated by lipopolysaccharide (LPS) in cultured RAW 264.7 cells exposed with high glucose (30 mM) indicated that IL-10 hyporesponsiveness may lead to chronic inflammation. Treatment with Honokiol (20 μM) significantly improved the IL-10 function which was linked to an elevated expression of SH2 domain-containing inositol 5ʹ-phosphatase 1 (SHIP1) and thus, a lower phosphorylation level of AKT (a serine/threonine kinase) was observed. AKT activation was significantly inhibited by pretreatment with 3α-aminocholestane, a SHIP1 inhibitor (SHIPi), validating our findings. Application of Honokiol showed a substantial decline in TNF-α production in RAW 264.7 cells and scenario was reversed by SHIPi treatment, emphasizing the importance of the SHIP1 pathway in the reduction of inflammation associated with hyperglycemia. Additionally, a significant rise in cholesterol efflux, facilitated by ATP binding cassette transporter-A1 (ABCA1), crucial for diminishing complexity in hyperglycemic states, was observed in macrophages subjected to Honokiol treatment. Conclusions: In summary, anti-diabetic properties of Honokiol may be linked to the mitigation of IL-10 hyporesponsiveness, which relies on the SHIP1-mediated suppression of AKT activity and the facilitation of cholesterol efflux via increased ABCA1 expression.