The roles of orexins on sleep/wakefulness, energy homeostasis and intestinal secretion

Abstract Orexins, or hypocretins, are peptides originally found in the hypothalamus, and have been shown to be involved in the stabilization and maintenance of sleep and wakefulness. In addition, these peptides are known for their actions on energy homeostasis by increased heat production or physical activity. Previous results suggest them to be also involved in peripheral actions on the regulation of intestinal secretion, depending on the subject’s nutritional status (fasted-fed). Orexin-A and Orexin-B peptides, are derived from the prepro-orexin precursor protein. These ligands bind to two G-protein-coupled receptors, orexin-1 and -2 -receptors. Despite intensive research, the role of orexins has not yet been clarified. The aim of the present study was to investigate the role of orexins and their receptors on sleep and wake patterns, energy homeostasis and intestinal secretion. The effects of orexins on sleep and wakefulness, and energy homeostasis were studied in a novel transgenic mouse line, overexpressing the human prepro-orexin gene. The overexpression of prepro-orexin and orexin-A was confirmed in the hypothalami of transgenic mice. The transgenic mice showed a significant reduction in their REM sleep during day and night time, and differences in their vigilance states in the light/dark transition periods. In addition, the mice demonstrated a significantly elevated day time food intake at room temperature, and an increased metabolic heat production independent of uncoupling protein 1 mediated thermogenesis in brown adipose tissue. Instead, transgenic mice showed increased levels of uncoupling protein 2 in white adipose tissue. Furthermore, transgenic mice significantly decreased their total locomotor activity during the first two nights in response to cold exposure (+4°C). The effect of orexins and their receptors on duodenal HCO3– secretion were studied after an overnight (16 h) food deprivation in an in situ perfused organ. Fasting decreased the expression of orexin receptors in rat duodenal mucosa and in acutely isolated duodenal enterocytes. Furthermore, food deprivation abolished OXA induced duodenal mucosal HCO3– secretion in rats, and intracellular calcium signalling in isolated rat and human duodenal enterocytes. In conclusion, the present thesis demonstrates that orexins inhibit REM sleep. In addition, peptides affect increasingly on metabolic heat production, independent of uncoupling protein 1 mediated thermogenesis. Furthermore, the orexin system has a significant role in duodenal bicarbonate secretion, which is regulated by the presence of food in the intestine

Effect of physical activity on plasma PCSK9 in subjects with high risk for type 2 diabetes

Abstract Background: Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a liver serine protease regulating LDL cholesterol metabolism. PCSK9 binds to LDL receptors and guides them to lysosomes for degradation, thus increasing the amount of circulating LDL cholesterol. The aim of the study was to investigate associations between physical activity and plasma PCSK9 in subjects with high risk for type 2 diabetes (T2D). Methods: Sixty-eight subjects from both genders with a high risk for T2D were included to a randomized controlled trial with a 3-month physical activity intervention. Physical activity intensities and frequencies were monitored throughout the intervention using a hip worn portable accelerometer. The plasma was collected before and after intervention for analysis of PCSK9 and cardiovascular biomarkers. Results: Plasma PCSK9 did not relate to physical activity although number of steps were 46% higher in the intervention group than in the control group (p < 0.029). Total cholesterol was positively correlated with plasma PCSK9 (R = 0.320, p = 0.008), while maximal oxygen uptake was negatively associated (R = −0.252, p = 0.044). After the physical activity intervention PCSK9 levels were even stronger inversely associated with maximal oxygen uptake (R = −0.410, p = 0.0008) and positively correlated with HDL cholesterol (R = 0.264, p = 0.030). Interestingly, plasma PCSK9 levels were higher in the beginning than at the end of the study. Conclusion: The low physical activity that our subjects with high risk for T2D could perform did not influence plasma PCSK9 levels. Intervention with higher physical activities might be more effective in influencing PCSK9 levels

Polydextrose changes the gut microbiome and attenuates fasting triglyceride and cholesterol levels in Western diet fed mice

Abstract Obesity and dyslipidemia are hallmarks of metabolic and cardiovascular diseases. Polydextrose (PDX), a soluble fiber has lipid lowering effects. We hypothesize that PDX reduces triglycerides and cholesterol by influencing gut microbiota, which in turn modulate intestinal gene expression. C57BL/6 male mice were fed a Western diet (WD) ±75 mg PDX twice daily by oral gavage for 14 days. Body weight and food intake were monitored daily. Fasting plasma lipids, caecal microbiota and gene expression in intestine and liver were measured after 14 days of feeding. PDX supplementation to WD significantly reduced food intake (p < 0.001), fasting plasma triglyceride (p < 0.001) and total cholesterol (p < 0.05). Microbiome analysis revealed that the relative abundance of Allobaculum, Bifidobacterium and Coriobacteriaceae taxa associated with lean phenotype, increased in WD + PDX mice. Gene expression analysis with linear mixed-effects model showed consistent downregulation of Dgat1, Cd36, Fiaf and upregulation of Fxr in duodenum, jejunum, ileum and colon in WD + PDX mice. Spearman correlations indicated that genera enriched in WD + PDX mice inversely correlated with fasting lipids and downregulated genes Dgat1, Cd36 and Fiaf while positively with upregulated gene Fxr. These results suggest that PDX in mice fed WD promoted systemic changes via regulation of the gut microbiota and gene expression in intestinal tract

Metabolomics analysis of plasma and adipose tissue samples from mice orally administered with polydextrose and correlations with cecal microbiota

Abstract Polydextrose (PDX) is a branched glucose polymer, utilized as a soluble dietary fiber. Recently, PDX was found to have hypolipidemic effects and effects on the gut microbiota. To investigate these findings more closely, a non-targeted metabolomics approach, was exploited to determine metabolic alterations in blood and epididymal adipose tissue samples that were collected from C57BL/6 mice fed with a Western diet, with or without oral administration of PDX. Metabolomic analyses revealed significant differences between PDX- and control mice, which could be due to differences in diet or due to altered microbial metabolism in the gut. Some metabolites were found in both plasma and adipose tissue, such as the bile acid derivative deoxycholic acid and the microbiome-derived tryptophan metabolite indoxyl sulfate, both of which increased by PDX. Additionally, PDX increased the levels of glycine betaine and l-carnitine in plasma samples, which correlated negatively with plasma TG and positively correlated with bacterial genera enriched in PDX mice. The results demonstrated that PDX caused differential metabolite patterns in blood and adipose tissues and that one-carbon metabolism, associated with glycine betaine and l-carnitine, and bile acid and tryptophan metabolism are associated with the hypolipidemic effects observed in mice that were given PDX

Pancreatic secretory trypsin inhibitor (SPINK1) gene mutation in patients with acute alcohol pancreatitis (AAP) compared to healthy controls and heavy alcohol users without pancreatitis

Abstract Only 3–5% of heavy alcohol users develop acute alcohol pancreatitis (AAP). This suggests that additional triggers are required to initiate the inflammatory process. Genetic susceptibility contributes to the development of AAP, and SPINK1 mutation is a documented risk factor. We investigated the prevalence of the SPINK1(N34S) mutation in patients with AAP compared to heavy alcohol users who had never suffered an episode of pancreatitis. Blood samples for the mutational analysis from patients with first episode (n = 60) and recurrent AAP (n = 43) and from heavy alcohol users without a history of AAP (n = 98) as well as from a control population (n = 1914) were obtained. SPINK1 mutation was found in 8.7% of the patients with AAP. The prevalence was significantly lower in healthy controls (3.4%, OR 2.72; 1.32–5.64) and very low in alcoholics without pancreatitis (1.0%, OR 9.29; 1.15–74.74). In a comparison adjusted for potential cofounders between AAP patients and alcoholics, SPINK1 was found to be an independent marker for AAP. The prevalence of the SPINK1 mutation is overrepresented in AAP patients and very low in alcoholics without pancreatitis. This finding may play a role in understanding the variable susceptibility to AAP found in heavy alcohol users