Hypoxia Induces Intestinal Isocitrate Dehydrogenase Expression and Enhances 13C-Octanoate Metabolism in Healthy Mountaineers After Rapid Ascent to 4559 M

Abstract

Background: Bacterial lipopolysaccharide (LPS) is an established animal model to study the innate immune response to gram-negative bacteria mimicking symptoms of infection including reduction of food intake. We previously reported that LPS decreased acyl ghrelin associated with decreased concentrations of circulating ghrelin-O-acyltransferase (GOAT) likely contributing to the anorexigenic effect. In addition, we recently described the prominent expression of the novel anorexigenic hormone, nucleobindin2 (NUCB2)/nesfatin-1 in gastric X/A-like cells co-localized with ghrelin in different pools of vesicles. Aim: To investigate whether LPS would affect gastric and circulating NUCB2/nesfatin-1 concentration. Methods: Ad libitum fed male Sprague-Dawley rats were equipped with an intravenous (IV) catheter placed in the right jugular vein and allowed to recover for four days. LPS was injected intraperitoneally (IP, 100μg/kg) and blood was withdrawn before and at 2, 5, 7 and 24h post injection and processed for NUCB2/nesfatin-1 measurement by radioimmunoassay (n= 5/group). Gastric corpus was collected at different time points to measure NUCB2 mRNA expression by quantitative RT-PCR and NUCB2/nesfatin-1 protein concentration by Western blot. Results: Injection of LPS significantly increased plasma NUCB2/nesfatin-1 concentrations by 55% compared to vehicle at 2h post injection (248.5 ± 45.5 vs. 161.2 ± 14.3 pg/ ml, P<0.05), whereas at all other time points (5, 7, 24h) no significant alterations were observed. The plasma NUCB2/nesfatin-1 increase at 2h was associated with an increased corpus NUCB2 mRNA expression compared to vehicle (1.22 ± 0.11 vs. 0.58 ± 0.17 pg/ml, P<0.01), whereas NUCB2 mRNA was not detectable in white blood cells. Likewise, gastric NUCB2 protein concentration was increased by 62% after LPS compared to vehicle (concentration normalized to housekeeping protein β-actin: 1.17 ± 0.06 vs. 0.72 ± 0.05, P<0.01). Conclusions: These data show that NUCB2 production and release are increased under conditions of inflammation in response to LPS. The stomach is likely to represent the source of NUCB2/nesfatin-1 as gastric mRNA and protein content was increased at the same time indicating stimulated production, whereas NUCB2 mRNA was not detectable in circulating white blood cells. These changes are in opposition to those observed for ghrelin and support the assumption of a differential regulation of these two food intake regulatory peptides derived from the same cell. The decrease of ghrelin and the increase of nesfatin-1 may act in concert to decrease food intake giving rise to the potential benefits of stimulating ghrelin and reducing nesfatin-1 signaling under conditions of inflammation. Acknowledgement: VA Merit Award (NWGL), Center grant DK-41301 (Animal Core, YT)