Oral Supplementation with Benzylamine Delays the Onset of Diabetes in Obese and Diabetic db-/- Mice

Substrates of semicarbazide-sensitive amine oxidase (SSAO) exert insulin-like actions in adipocytes. One of them, benzylamine (Bza) exhibits antihyperglycemic properties in several rodent models of diabetes. To further study the antidiabetic potential of this naturally occurring amine, a model of severe type 2 diabetes, the obese db-/- mouse, was subjected to oral Bza administration. To this end, db-/- mice and their lean littermates were treated at 4 weeks of age by adding 0.5% Bza in drinking water for seven weeks. Body mass, fat content, blood glucose and urinary glucose output were followed while adipocyte insulin responsiveness and gene expression were checked at the end of supplementation, together with aorta nitrites. Bza supplementation delayed the appearance of hyperglycemia, abolished polydypsia and glycosuria in obese/diabetic mice without any detectable effect in lean control, except for a reduction in food intake observed in both genotypes. The improvement of glucose homeostasis was observed in db-/- mice at the expense of increased fat deposition, especially in the subcutaneous white adipose tissue (SCWAT), without sign of worsened inflammation or insulin responsiveness and with lowered circulating triglycerides and uric acid, while NO bioavailability was increased in aorta. The higher capacity of SSAO in oxidizing Bza in SCWAT, found in the obese mice, was unaltered by Bza supplementation and likely involved in the activation of glucose utilization by adipocytes. We propose that Bza oxidation in tissues, which produces hydrogen peroxide mainly in SCWAT, facilitates insulin-independent glucose utilization. Bza could be considered as a potential agent for dietary supplementation aiming at preventing diabetic complications

Histamine oxidation in mouse adipose tissue is controlled by the AOC3 gene-encoded amine oxidase.

International audienceINTRODUCTION: Histaminergic status can modify adipose tissue (AT) development: histamine-free mice exhibit visceral obesity, and treatments with H3-antagonists reduce body weight gain. However, direct histamine effects on AT remain poorly documented: it has been observed that histamine stimulates lipolysis in rodent adipocytes when its oxidation by amine oxidases (AOs) is blocked by inhibitors such as semicarbazide. OBJECTIVE: The aim of this work was to study the influence of AOC3 gene invalidation, encoding for semicarbazide-sensitive AO (SSAO), on histamine oxidation and on histamine lipolytic activity in AT. MATERIALS AND METHODS: Expression of AOC- and MAO-encoding genes was determined by real-type PCR in wild-type (WT) and SSAO-deficient (AOC3-KO) mice. Lipolysis was assessed by glycerol release in isolated adipocytes and AO activity by substrate-induced hydrogen peroxide formation in kidney, ileum and AT. RESULTS: The expression levels of the genes encoding AOC1, AOC2 or MAOA and MAOB were not modified in the AT of AOC3-KO mice. In WT mice, histamine oxidation was lower than that of the reference SSAO-substrate benzylamine in AT, but not in ileum. The order of magnitude regarding benzylamine oxidation was AT > ileum >> kidney. In AOC3-KO mice, benzylamine oxidation was abolished in all tissues, while histamine oxidation was abolished in AT but not in ileum. Histamine was inactive on lipolysis in WT but stimulated lipolysis in fat cells from AOC3-KO mice, without reaching the maximal intensity of beta-adrenergic stimulation. CONCLUSION: Histamine was mainly oxidized by diamine oxidase (AOC1 product) in intestine, but by SSAO (AOC3 product) in AT. When protected from its oxidation by SSAO in AT, histamine moderately activated lipolysis in adipocytes in AOC3-KO mice

Transition from metabolic adaptation to maladaptation of the heart in obesity: role of apelin.

International audienceBackground/Objectives:Impaired energy metabolism is the defining characteristic of obesity-related heart failure. The adipocyte-derived peptide apelin has a role in the regulation of cardiovascular and metabolic homeostasis and may contribute to the link between obesity, energy metabolism and cardiac function. Here we investigate the role of apelin in the transition from metabolic adaptation to maladaptation of the heart in obese state.Methods:Adult male C57BL/6J, apelin knock-out (KO) or wild-type mice were fed a high-fat diet (HFD) for 18 weeks. To induce heart failure, mice were subjected to pressure overload after 18 weeks of HFD. Long-term effects of apelin on fatty acid (FA) oxidation, glucose metabolism, cardiac function and mitochondrial changes were evaluated in HFD-fed mice after 4 weeks of pressure overload. Cardiomyocytes from HFD-fed mice were isolated for analysis of metabolic responses.Results:In HFD-fed mice, pressure overload-induced transition from hypertrophy to heart failure is associated with reduced FA utilization (P<0.05), accelerated glucose oxidation (P<0.05) and mitochondrial damage. Treatment of HFD-fed mice with apelin for 4 weeks prevented pressure overload-induced decline in FA metabolism (P<0.05) and mitochondrial defects. Furthermore, apelin treatment lowered fasting plasma glucose (P<0.01), improved glucose tolerance (P<0.05) and preserved cardiac function (P<0.05) in HFD-fed mice subjected to pressure overload. In apelin KO HFD-fed mice, spontaneous cardiac dysfunction is associated with reduced FA oxidation (P<0.001) and increased glucose oxidation (P<0.05). In isolated cardiomyocytes, apelin stimulated FA oxidation in a dose-dependent manner and this effect was prevented by small interfering RNA sirtuin 3 knockdown.Conclusions:These data suggest that obesity-related decline in cardiac function is associated with defective myocardial energy metabolism and mitochondrial abnormalities. Furthermore, our work points for therapeutic potential of apelin to prevent myocardial metabolic abnormalities in heart failure paired with obesity.International Journal of Obesity advance online publication, 12 August 2014; doi:10.1038/ijo.2014.122

Chronic benzylamine administration in the drinking water improves glucose tolerance, reduces body weight gain and circulating cholesterol in high-fat diet-fed mice.

International audienceBenzylamine is found in Moringa oleifera, a plant used to treat diabetes in traditional medicine. In mammals, benzylamine is metabolized by semicarbazide-sensitive amine oxidase (SSAO) to benzaldehyde and hydrogen peroxide. This latter product has insulin-mimicking action, and is involved in the effects of benzylamine on human adipocytes: stimulation of glucose transport and inhibition of lipolysis. This study examined whether chronic, oral administration of benzylamine could improve glucose tolerance and the circulating lipid profile without increasing oxidative stress in overweight and pre-diabetic mice. The benzylamine diffusion across the intestine was verified using everted gut sacs. Then, glucose handling and metabolic markers were measured in mice rendered insulin-resistant when fed a high-fat diet (HFD) and receiving or not benzylamine in their drinking water (3600micromol/(kgday)) for 17 weeks. HFD-benzylamine mice showed lower body weight gain, fasting blood glucose, total plasma cholesterol and hyperglycaemic response to glucose load when compared to HFD control. In adipocytes, insulin-induced activation of glucose transport and inhibition of lipolysis remained unchanged. In aorta, benzylamine treatment partially restored the nitrite levels that were reduced by HFD. In liver, lipid peroxidation markers were reduced. Resistin and uric acid, surrogate plasma markers of metabolic syndrome, were decreased. In spite of the putative deleterious nature of the hydrogen peroxide generated during amine oxidation, and in agreement with its in vitro insulin-like actions found on adipocytes, the SSAO-substrate benzylamine could be considered as a potential oral agent to treat metabolic syndrome

Effect of EPA on adipokines and APJ mRNA expression in adipose tissue.

<p>(A) Leptin, (B) Adiponectin, (C) Apelin and (D) APJ expression in total adipose tissue of ND (n = 12), HFD (n = 14) and HFD+EPA mice (n = 14). Results represent mean ±SEM **p<0.01, ***p<0.001</p

Protective effect of EPA supplementation on the HFD-induced obesity.

<p>(A) Body weight in mice after 10-week feeding with a ND (n = 12), HFD (n = 14) or HFD+EPA(n = 14). Results represent mean ±SEM. *p<0.05, **p<0.01, ***p<0.001 vs ND; and ### p<0.001 vs HFD, ns: not significant. (B) fat and lean mass and (C) fat pads weights of subcutaneous (Subcut), perigonadal (Perigon) and mesenteric (Mes) adipose tissue in mice fed for 10 weeks with a ND or N (n = 12), HFD or H (n = 14) or HFD+EPA or E (n = 14) Results represent mean ±SEM. ***p<0.001, (D) Representative photographs of H&E staining of liver section of mice fed the different diets for 10 weeks (bar = 200 µm).</p

Protective effect of EPA supplementation on the HFD-induced impaired glucose metabolism.

<p>(A) Glycemia and (B) insulinemia in 6 h-fasted mice fed a ND (n = 12), a HFD (n = 14) or a HFD+EPA (n = 14) after 10 weeks. Results represent mean ±SEM. ***p<0.001, (C) OGTT curves and area under the curve (AUC) of glycemia monitored during OGTT performed on 6 h fasted (during light period) mice after 9 weeks of diet in ND (n = 4), HFD (n = 6) and HFD+EPA (n = 6) mice. Results represent mean ±SEM. *p<0.05, **p<0.01, ***p<0.001 vs ND; and ## p<0.01, ### p<0.001 vs HFD.</p

EPA induces in vivo and in vitro expression of the apelin/APJ system in muscle.

<p>(A) Apelin and (B) APJ mRNA expression in soleus muscle of ND (n = 7), HFD (n = 10) and HFD+EPA (n = 5). Results represent mean ±SEM **p<0.01, ***p<0.001, ns: not significant. (C) Apelin mRNA expression and (D) secretion in differentiated C2C12 cells treated with the indicated EPA concentrations or the corresponding BSA content for 24 hours after 12-hour serum deprivation. Data are mean ±SEM n = 4–5 in each condition. *p<0.05, **p<0.01 ***p<0.001. (E) Effect of 100 µM EPA in the absence or in the presence of the PI3K inhibitor LY294002 (20 µM) or the ERK 1/2 inhibitor U0126 (20 µM) for 24 h after 12-hour serum deprivation on apelin mRNA expression and (F) secretion in differentiated C2C12 cells. Results represent mean ±SEM (n = 4–5 in each condition) *p<0.05, **p<0.01, ns: not significant.</p

Effect of EPA on muscle lipid metabolism.

<p>(A) Intramuscular triglycerides content in red gastrocnemius of ND (n = 9), HFD (n = 10) and HFD+EPA (n = 10) mice. (B) ¹⁴C-palmitate complete β-oxidation and mRNA expression of (C) CPT1b and (D) UCP3 in soleus muscle of ND (n = 9), HFD (n = 6–10) and HFD+EPA mice (n = 6–10). Results are mean ±SEM and were normalized to the ND group (100%) for B, C and D, *p<0.05, **p<0.01, ***p<0.001</p

Plasma lipid composition.

<p>SFA (Saturated Fatty Acids), MUFAs (Mono-Unsaturated Fatty Acids) and PUFAs (Poly-Unsaturated Fatty Acids) were measured by gas-liquid chromatography in plasma of fasted mice after 10 weeks feeding with ND (black column, n = 6), HFD (white column, n = 12) or HFD+EPA (grey column, n = 9). Data are expressed as mean ±SEM. *p<0.05, **p<0.01, ***p<0.001 vs ND; # p<0.05, ## p<0.01, ### p<0.001 vs HFD. ns: not significant</p