The protective role of 5-hydroxymethyl-2-furfural (5-HMF) against acute hypobaric hypoxia

Abstract

Our previous study showed that pretreatment with 5-hydroxymethyl-2-furfural (5-HMF) led to protection against hypoxic injury via a p-ERK-mediated pathway in vitro. Whether the protection of 5-HMF against hypoxia is effective in vivo is unknown. The present study is aimed to verify the role of 5-HMF in acute hypobaric hypoxia using Kunming mice as an in vivo model and further investigate the underlying mechanisms. Mice pretreated with or without 5-HMF for 1 h were exposed to acute hypobaric hypoxic condition for 6 h and then the survival time, the survival rate, the permeability of blood-brain barrier (BBB), the histological analysis in hippocampus and cortex, and the phosphorylation level of mitogen-activated protein kinases (ERK, JNK, and p38) were investigated. The results showed that 5-HMF significantly increased the survival time and the survival rate of mice. Accordingly, pretreatment with 5-HMF markedly attenuated acute hypobaric hypoxia-induced permeability of BBB (P < 0.01). In addition, the cellular damage extent of the hippocampus and the cortex induced by hypoxia for 6 h was also attenuated by pretreatment with 5-HMF, especially in the hippocampus CA1 region. Furthermore, the activation of ERK rather than JNK and p38 was involved in the protection of 5-HMF against acute hypobaric hypoxia. In summary, 5-HMF enhanced the survival capability of mice and decreased acute hypoxic damage to the brain, which may be associated with the effects on BBB and p-ERK.

Fig. 1

Kaplan–Meier survival plots of conscious mice exposed to lethal acute hypobaric hypoxia after 100 mg/kg 5-HMF administration. Mice were exposed to simulated acute hypobaric hypoxia at 9,500 m (lethal hypoxia) at a velocity of about 45 m/s at 21°C in a decompression chamber after 1 h of 5-HMF administration. Mice were monitored for survival for 15 min immediately after exposure to acute hypobaric hypoxia. Control mice received vehicle alone 1 h before being exposed to acute hypobaric hypoxia. ^**p < 0.01, versus control. Control group: n = 14; 100 mg/kg 5-HMF group: n = 12

Fig. 2

Effect of 5-HMF on BBB permeability under acute hypobaric hypoxia using Evans blue in mice. The animals were exposed to normoxia or simulated sublethally acute hypobaric hypoxia of 8,300 m in a decompression chamber for 6 h after 1 h of 100 mg/kg 5-HMF or vehicle administration. The Evans blue extravasation assay was used to evaluate the BBB permeability and it was measured as described in the “Materials and methods” section. The hypoxia group demonstrated a significantly higher concentration of Evans blue in brain tissue than the control group. 5-HMF treatment decreased Evans blue extravasation in hypoxia-stressed group. The Evans blue extravasation is converted using a standardized curve to quantify the amount of Evans blue per brain weight (ng/mg). All data were expressed as means ± SD, n = 5; ^**p < 0.01, versus normoxia control; ^#p < 0.05, versus hypoxia control. Nor normoxia, Hyp hypoxia, 5-HMF 100 mg/kg 5-HMF

Fig. 3

Prevention of acute hypobaric hypoxia-induced cellular damage or death in cortex and hippocampus by 100 mg/kg 5-HMF pretreatment 1 h before exposure to sublethally acute hypobaric hypoxia. The animals were exposed to normoxia or simulated sublethally acute hypobaric hypoxia of 8,300 m in a decompression chamber for 6 h after 1 h of 100 mg/kg 5-HMF or vehicle administration. Representative HE stains (n = 5) in the CA1 region of hippocampus (a–d) and the cortex (e–h) with low magnification insets in the upper right corners in the different conditions are shown. The box indicates the source of the high magnification image. a, e Normoxia control; b, f 5-HMF administration in normoxia; c, g hypoxia control; d, h 5-HMF administration in hypoxia. Nor normoxia, Hyp hypoxia, 5-HMF 100 mg/kg 5-HMF

Fig. 4

Effect of 5-HMF pretreatment on the level of p-ERK protein. The animals were exposed to normoxia or simulated sublethally acute hypobaric hypoxia of 8,300 m in a decompression chamber for 6 h after 1 h of 100 mg/kg 5-HMF or vehicle administration. Whole tissue extracts from cortex and hippocampus were analyzed with western blotting. Representative results showed that the levels of p-ERK, not T-ERK, increased in the cortex (a) and hippocampus (c) of mice in response to hypoxic exposure. And 5-HMF treatment decreased the levels of p-ERK in hypoxia-stressed group. Quantitative analysis (b, d) verified an increase of p-ERK in the cortex and hippocampus of mice under hypoxia and an decrease of p-ERK in the 5-HMF treated hypoxia group. All data were expressed as means ± SD, n = 4; ^*p < 0.05, versus normoxia control; ^#p < 0.05, ^##p < 0.01, versus hypoxia control. Nor normoxia, Hyp hypoxia, 5-HMF 100 mg/kg 5-HMF, p-ERK phosphorylated ERK, T-ERK total protein of ERK

Fig. 5

Effect of 5-HMF pretreatment on the level of p-JNK protein. The animals were exposed to normoxia or simulated sublethally acute hypobaric hypoxia of 8,300 m in a decompression chamber for 6 h after 1 h of 100 mg/kg 5-HMF or vehicle administration. Whole-tissue extracts from cortex and hippocampus were analyzed with western blotting. Representative results and quantitative analysis showed that the levels of p-JNK did not change significantly in the cortex (a, b) and hippocampus (c, d) of mice under hypoxia. And 5-HMF treatment did not change the levels of p-JNK in hypoxia-stressed group. All data were expressed as means ± SD, n = 4. Nor normoxia, Hyp hypoxia, 5-HMF 100 mg/kg 5-HMF, p-p38 phosphorylated JNK, T-p38 total protein of JNK

Fig. 6

Effect of 5-HMF pretreatment on the level of p-p38 protein. The animals were exposed to normoxia or simulated sublethally acute hypobaric hypoxia of 8,300 m in a decompression chamber for 6 h after 1 h of 100 mg/kg 5-HMF or vehicle administration. Whole-tissue extracts were analyzed with western blotting. Representative results and quantitative analysis showed that the levels of p-p38 did not change significantly in the cortex (a, b) and hippocampus (c, d) of mice under hypoxia. And 5-HMF treatment did not change the levels of p-p38 in hypoxia-stressed group. All data were expressed as means ± SD, n = 4. Nor normoxia, Hyp hypoxia, 5-HMF 100 mg/kg 5-HMF, p-p38 phosphorylated p38, T-p38 total protein of p38