Hippocampus hypoxia-inducible factor-1 alpha and heme oxygenase-1 expression in the delayed encephalopathy after acute carbon monoxide poisoning rat model

Abstract

Objective To research the expression of hypoxia-inducible factor-1 alpha (HIF-1α) and heme oxygenase-1 (HO-1) in hippocampus of rats with delayed encephalopathy after acute carbon monoxide poisoning (DEACMP) and its functions. Methods One hundred and fifty-six rats were selected and randomly divided into several groups: group CO of 60 rats, group air control (AC) of 60 rats and group blank control (BC) of 36 rats according to the random number table method, and then randomly divided into six subgroups after exposure, 1, 3, 7, 14, 21 and 28 d. The expression of HIF-1α and HO-1 in rat hippocampus was detected by Western blotting and immunohistochemistry method, the expression of iron ion was detected by the blue staining, the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay staining was used to detect the apoptosis of cells, the Morris water maze was used to analyze the behavioral changes of rats, the changes of cell morphology in the hippocampus were observed and the carboxyhemoglobin (HbCO) concentration in arterial blood was monitored. Results The expression of HIF-1α, HO-1 and iron in hippocampus of rats in group CO increased and reached a peak at the third day (HIF-1α: 7.4±1.0, HO-1: 9.8±0.9, iron: 44.60±1.77), and then decreased, with the peak of apoptosis delayed at the 7th to the 14th day(7 d: 19.4±1.0; 14 d: 17.8±1.0). The difference of the same time points between the group AC (HIF-1α: 1.7±0.7, HO-1: 2.1±0.4, apoptosis: 4.2±1.0) and the group BC (HIF-1α: 2.0±0.5, HO-1: 2.1±0.4, apoptosis: 3.9±0.6) was statistically significant (F=77.86, 228.77, 258.54, all P<0.05). The difference between each peak value and that at other time points in the same group was statistically significant. The water maze test showed that the memory cognitive function and behavioral changes of rats declined in the 14th day. The pyramidal cells in the hippocampus were found degenerated and necrotic through morphological observation. The concentration of HbCO in rats′ aorta was above 50% for 16 hours throughout the exposure. Conclusions The increase of HIF-1α in the rat′s hippocampus resulted in the increase of the downstream target gene HO-1 under hypoxia stress with acute severe CO toxicity. The excessive expression of the both and metabolic products promoting the delayed apoptosis of pyramidal cells in the hippocampus may be a mechanism of DEACMP. Key words: Carbon monoxide poisoning; Hippocampus; Rats; Hypoxia-inducible factor 1, alpha subunit; Heme oxygenase-1