Protection Of Curcumin Supplementation Against High Fructose-induced Hippocampus Inflammation And Its MechanismResearch In Mice

OBJECTIVE:Obesity induces the activation of astrocytes and microglia, aggregation, neuroinflammation, contributing to nerve injury. CX3CL1-CX3CR1 (Chemokine (C-X3-C motif) ligand 1-chemokine (C-X3-C motif) receptor 1) axis as the significant signaling pathway has been proven to play an important role in glial activation and inflammatory responses. Previous findings found that high-fructose intake may lead to rats’ nerve inflammation. However, the underlying molecular mechanism is still not fully understood. Curcumin as a natural production performs role of anti-neuroinflammation and neuroprotection in rats. In view of such situation, we constructed fructose-fed mice model to study whether CX3CL1-CX3CR1 axis effects glial activation and how curcumin inhibits nerve injury and the underlying mechanisms by which they may suppress high-fructose fed mice neuroinflammation.METHODS:Mice were received 10% fructose feed per day, curcumin was supplied at 20,40 and 80 mg/kg to feed for 4 weeks and 30 mg/kg pioglitazone was used to evaluate as positive drug. Oral glucose tolerance test (OGTT) and blood pressure were performed to evaluate insulin resistance and blood level in mice. The levels of tumor necrosis factor-a (TNF-a), interleukin-1β(IL-1β), interleukin-6 (IL-6) and CX3CL1 of liver tissue, astroglials and serum were measured by ELISA methods. The real-time quantitive PCR was used to investigate the dynamic changes of TNF-α、 IL-1β、IL-6、CX3CL1、CX3CR1、 Glial fibrillary acidic protein (GFAP)、Ionized calcium binding adapter molecule(Iba-1) and Monocyte chemotactic protein 1 (MCP-1) mRNA expression during 0-8 weeks in hippocampus tissue. Also, it will be performed to test TNF-α、IL-1β、IL-6、CX3CL1、CX3CR1、GFAP、Iba-1 and MCP-1 mRNA expression in astrocyte and microglial cocluture. Additionally, Mice hippocampus tissues were stained with immunofluorescent assay to observe histopathological changes.RESULTS:Results from our research illustrated that high-fructose intake is capable of inducing metabolic syndrome and systemic inflammation. CX3CL1 expression was significantly up regulated in serum and liver tissue. Pro-inflammatory cytokines including TNF-a and IL-1β in mice hippocampus tissues were sharply increased during the earlier stage, then changed to be steady. Meanwhile, CX3CL1 and CX3CR1 levels were up regulated with extend of experimental time before 28 days, and then lower than a normal level at the terminal time. These changes were consisting with GFAP expression. Furthermore, according to results of immunofluorescence, we found that there were no obvious changes in CX3CL1, neuron and astrocytes in fructose-fed mice’s hippocampus CA area. Of note, CX3CL1 expression, neuro and astrocytes were decreased in DG area. These results illustrated that in fructose-fed mice, the CX3CL1-CX3CR1 axis was significantly activated via occurring of systemic inflammation. Of note, chronic inflammation of hippocampus can lead to DG area neuronal injury and the synthesis of CX3CL1 and GFAP function decline in astrocyte. Curcumin supplement has ability to inhibit neuroinflammation of hippocampus tissues and physiological indicators.It showed a beneficial effect on high fructose-induced nerve injury by suppressing inflammation in mice, which is relative with the improvement of insulin resistance, blood pressure, nerve inflammation factors, peripheral inflammation and the level of CX3CL1. Moreover, curcumin suppresses the activation and inflammatory development of hippocampus DG and CA neurons, microglia and astrocytes via inhibition ofnuclear factor kB (NF-κB) activation of signaling pathway and its phosphorylation, reducing CX3CL1-CX3CR1 activation.Fructose could up-regulate the GFAP and CX3CL1 expression in astrocytes. But in the co-culture of astrocytes and microglia, CX3CL1 expression and fructose-incubated time is not in a typical time-dependent manner. In the earlier stage, CX3CL1 and CX3CR1 expression were significantly increased with fructose incubation, and then in the later stage, CX3CL1 level was down-regulated and consistent with GFAP trends. Pro-inflammatory cytokines of TNF-α and IL-1β were steadily increased with the same trend of Iba-1 expression. Our in vitro experiments further demonstrated that in the incipient stage, fructose could activate astrocytes, microglia and construct activation responses of CX3CL1-CX3CR1 axis, promote release of inflammatory cytokines. But in the later stage, due to excessive damage of astrocytes, the production of CXCL1 and GFAP function were significantly declined. Moreover, curcumin is capable of suppressing glia activation and CX3CL1-CX3CR1 responses, further inhibiting pro-inflammatory cytokines, contributing to the protection of astrocytes.CONCLUSION:In this study, fructose could lead to metabolic syndrome in mice, activation of glial in hippocampus, CX3CL1-CX3CR1 axis responses and pro-inflammatory cytokines release. Curcumin with nerve protective effect inhibits nerve inflammation, insulin resistance, glial cell activation and aggregation via down-regulating CX3CL1-CX3CR1 activation responses between astrocytes and microglia.