Sirtuins in Adipose Tissue Metabolism

Obesity, a complex metabolic disorder linked to the development of several diseases, is characterized by both hypertrophy and hyperplasia of adipocytes. While white adipose tissue (WAT) is an energy storage site, brown adipose tissue (BAT) activation generates heat from nutrients by non-shivering thermogenesis. The human orthologue of silencing information regulator 2 (Sir2) which was recognized as a regulator of life span in S. cerevisiae, includes seven sirtuins which are NAD+-dependent protein deacetylases distributed in different subcellular compartments. Sirtuins, particularly Sirt1, have emerged as important nutrient sensors and regulators of metabolism. Sirt1 has been shown to play a role in retarding the expansion of WAT while stimulating both differentiation and activation of brown adipose tissue as well as browning of WAT. This chapter focuses on the role of sirtuins in adipose tissue biology, their implications in obesity and potential as therapeutic targets

Xanthine analogues and adipose tissue metabolism

Obesity has been increasing in the last decades and is one of the most prolific health concern worldwide. Methylxanthines, such as caffeine (1,3,7-trimethylxanthine), theophylline (1,3-dimethylxanthine), and theobromine (3,7-dimethylxanthine), have demonstrated potential anti-obesity properties. These natural compounds are widely distributed in the human diet, especially food products such as coffee, tea, and chocolate. In fact, caffeine is known to modulate glucose and fatty acid metabolism and its consumption seems to be inversely associated with body weight increase. Based on methylxanthines chemical structure, several xanthine analogues have been synthetized. We hypothesized that one of those compounds, 8-(3-phenylpropyl)-1,3,7-triethylxanthine, may have a promising anti-obesity potential. Our study aims to characterize the modulation conferred by 8-(3-phenylpropyl)-1,3,7-triethylxanthine in the metabolic and oxidative profile of adipocytes in order to evaluate its potential as a pharmacological option to address obesity and its complications. For this purpose, the anti-obesogenic potential of 8-(3-phenylpropyl)-1,3,7-triethylxanthine was evaluated in mouse preadipocyte cell line 3T3-L1, using synthetic caffeine for comparative purposes. Cells were cultured in the presence of increasing concentrations of caffeine or 8-(3-phenylpropyl)-1,3,7-triethylxanthine (0.1, 1, 10 and 100 µM) and the cytotoxic profile was accessed spectrophotometrically by reduction of tetrazolium salt (MTT) and quantification of released lactate dehydrogenase (LDH). The metabolites in culture medium were identified and quantified by proton nuclear magnetic resonance (1H-NMR) and cells were collected for analysis of the oxidative profile. Our results show that 8-(3-phenylpropyl)-1,3,7-triethylxanthine presented no cytotoxicity at all studied concentrations. When compared with caffeine, 8-(3-phenylpropyl)-1,3,7-triethylxanthine significantly increased glucose, pyruvate, and glutamine consumption, and lactate, alanine, and acetate production. These findings illustrate that 8-(3-phenylpropyl)-1,3,7-triethylxanthine has a high potential to act as a metabolic modulator, even when compared with caffeine. Additionally, 8-(3-phenylpropyl)-1,3,7-triethylxanthine promoted an antioxidant environment, decreasing protein oxidation, and protecting against oxidative stress-induced damage. Thus, 8-(3-phenylpropyl)-1,3,7-triethylxanthine appears as a promising candidate for new and safe anti-obesity drug design.A obesidade tem aumentado nas últimas décadas e é um dos problemas de saúde mais preocupantes a nível mundial. As metilxantinas, como é o caso da cafeína (1,3,7-trimetilxantina), teofilina (1,3-dimetilxantina) e teobromina (3,7-dimetilxantina), demonstraram propriedades anti-obesogénicas bastante promissoras. Estes compostos naturais encontram-se bastante difundidos na dieta humana, nomeadamente no café, no chá e no chocolate. De entre estes fitoquímicos, a cafeína é descrita como moduladora do metabolismo da glucose e ácidos gordos, assim como o seu consumo aparenta ser inversamente proporcional ao aumento de peso corporal. Com base na estrutura química das metilxantinas, vários compostos análogos têm sido sintetizados. Foi colocada a hipótese de que um desses compostos, a 8-(3-fenilpropil)-1,3,7-trietilxantina, poderia apresentar um potencial anti-obesogénico bastante elevado. Deste modo, o nosso projeto visou avaliar os efeitos desta nova molécula no perfil metabólico e oxidativo de adipócitos, com o objetivo de avaliar o seu potencial como opção farmacológica para o tratamento da obesidade e suas complicações. Para este fim, foi utilizada como modelo in vitro a linha celular de pré-adipócitos de rato 3T3-L1 e a cafeína, de origem sintética, para fins comparativos. As células foram incubadas na presença de concentrações crescentes de cafeína e 8-(3-fenilpropil)-1,3,7-trietilxantina (0.1, 1, 10 e 100 µM) e o perfil citotóxico de ambos os compostos foi avaliado espectrofotometricamente pela redução do sal de tetrazólio (MTT) e quantificação de lactato desidrogenase (LDH) libertada. Os metabolitos presentes no meio de cultura foram identificados e quantificados recorrendo à ressonância magnética nuclear de protão (1H-NMR) e as células foram recolhidas para a caracterização do perfil oxidativo. Os nossos resultados demonstram que a 8-(3-fenilpropil)-1,3,7-trietilxantina não induziu citotoxicidade em nenhuma das concentrações estudadas. Comparativamente à cafeína, este composto aumentou significativamente o consumo de glucose, piruvato e glutamina, assim como a produção de lactato, alanina e acetato. Estes resultados ilustram o elevado potencial da 8-(3-fenilpropil)-1,3,7-trietilxantina como modulador metabólico, mesmo quando comparado com a cafeína. Adicionalmente, a 8-(3-fenilpropil)-1,3,7-trietilxantina promoveu um efeito antioxidante, diminuindo os níveis de oxidação proteica e protegendo contra os danos causados pelo stress oxidativo. Em suma, a 8-(3-fenilpropil)-1,3,7-trietilxantina apresenta-se como um ótimo candidato para o design de fármacos anti-obesidade seguros e inovadores

Role of AMP-activated protein kinase in adipose tissue metabolism and inflammation

AMPK (AMP-activated protein kinase) is a key regulator of cellular and whole-body energy balance. AMPK phosphorylates and regulates many proteins concerned with nutrient metabolism, largely acting to suppress anabolic ATP-consuming pathways while stimulating catabolic ATP-generating pathways. This has led to considerable interest in AMPK as a therapeutic target for the metabolic dysfunction observed in obesity and insulin resistance. The role of AMPK in skeletal muscle and the liver has been extensively studied, such that AMPK has been demonstrated to inhibit synthesis of fatty acids, cholesterol and isoprenoids, hepatic gluconeogenesis and translation while increasing fatty acid oxidation, muscle glucose transport, mitochondrial biogenesis and caloric intake. The role of AMPK in the other principal metabolic and insulin-sensitive tissue, adipose, remains poorly characterized in comparison, yet increasing evidence supports an important role for AMPK in adipose tissue function. Obesity is characterized by hypertrophy of adipocytes and the development of a chronic sub-clinical pro-inflammatory environment in adipose tissue, leading to increased infiltration of immune cells. This combination of dysfunctional hypertrophic adipocytes and a pro-inflammatory environment contributes to insulin resistance and the development of Type 2 diabetes. Exciting recent studies indicate that AMPK may not only influence metabolism in adipocytes, but also act to suppress this pro-inflammatory environment, such that targeting AMPK in adipose tissue may be desirable to normalize adipose dysfunction and inflammation. In the present review, we discuss the role of AMPK in adipose tissue, focussing on the regulation of carbohydrate and lipid metabolism, adipogenesis and pro-inflammatory pathways in physiological and pathophysiological conditions

A computational model of postprandial adipose tissue lipid metabolism derived using human arteriovenous stable isotope tracer data

Given the association of disturbances in non-esterified fatty acid (NEFA) metabolism with the development of Type 2 Diabetes and Non-Alcoholic Fatty Liver Disease, computational models of glucose-insulin dynamics have been extended to account for the interplay with NEFA. In this study, we use arteriovenous measurement across the subcutaneous adipose tissue during a mixed meal challenge test to evaluate the performance and underlying assumptions of three existing models of adipose tissue metabolism and construct a new, refined model of adipose tissue metabolism. Our model introduces new terms, explicitly accounting for the conversion of glucose to glyceraldehye-3-phosphate, the postprandial influx of glycerol into the adipose tissue, and several physiologically relevant delays in insulin signalling in order to better describe the measured adipose tissues fluxes. We then applied our refined model to human adipose tissue flux data collected before and after a diet intervention as part of the Yoyo study, to quantify the effects of caloric restriction on postprandial adipose tissue metabolism. Significant increases were observed in the model parameters describing the rate of uptake and release of both glycerol and NEFA. Additionally, decreases in the model’s delay in insulin signalling parameters indicates there is an improvement in adipose tissue insulin sensitivity following caloric restriction.</p

Dydrogesterone and norethisterone regulate expression of lipoprotein lipase and hormones-sensitive lipase in human subcutaneous abdominal adipocytes

Aim: In premenopausal women, hyper-androgenicity is associated with central obesity and an increased cardiovascular risk. We investigated the effects of dydrogesterone (DYD)(a non-androgenic progestogen) and norethisterone (NET)(an androgenic progestogen) on lipoprotein lipase (LPL), hormone-sensitive lipase (HSL) and glycerol release in adipocytes isolated from subcutaneous abdominal adipose tissue. Methods: Adipose tissue was obtained from 12 non-diabetic women, mean age 51 years (range 37-78) and mean BMI 25.4kg/m2 (range 20.3-26.4). Adipocytes were treated with increasing doses of DYD and NET for 48 hours prior to protein extraction. Effects on lipogenesis and lipolysis were assessed using western blotting to determine the expression of key enzymes, LPL (56kDa) and HSL (84kDa) respectively. Measurement of glycerol release into the medium provided an assessment of lipolytic activity. Results: Expression of LPL was increased by DYD and NET (mean protein expression relative to control ± SEM); with greatest effect at 10-8M for DYD: 2.32±0.51(p0.05). Conclusions: DYD and NET significantly increased LPL expression relative to control whilst significantly reducing HSL expression. At the concentrations studied, similar effects were observed with the androgenic NET and the non-androgenic DYD despite differing effects on the lipid profile when taken in combination with estrogen. Further work in this area may improve knowledge about the effects of different progestogens on body fat distribution and enable progestogen use to be tailored to the individual to achieve maximal benefits

Sirtuins 1–7 expression in human adipose-derived stem cells from subcutaneous and visceral fat depots: influence of obesity and hypoxia

The sirtuin family comprises seven NAD+-dependent deacetylases which control the overall health of organisms through the regulation of pleiotropic metabolic pathways. Sirtuins are important modulators of adipose tissue metabolism and their expression is higher in lean than obese subjects. At present, the role of sirtuins in adipose-derived stem cells has not been investigated yet. Therefore, in this study, we evaluated the expression of the complete panel of sirtuins in adipose-derived stem cells isolated from both subcutaneous and visceral fat of non-obese and obese subjects. We aimed at investigating the influence of obesity on sirtuins' levels, their role in obesity-associated inflammation, and the relationship with the peroxisome proliferator-activated receptor delta, which also plays functions in adipose tissue metabolism. The mRNA levels in the four types of adipose-derived stem cells were evaluated by quantitative polymerase chain reaction, in untreated cells and also after 8 h of hypoxia exposure. Correlations among sirtuins' expression and clinical and molecular parameters were also analyzed. We found that sirtuin1-6 exhibited significant higher mRNA expression in visceral adipose-derived stem cells compared to subcutaneous adipose-derived stem cells of non-obese subjects. Sirtuin1-6 levels were markedly reduced in visceral adipose-derived stem cells of obese patients. Sirtuins' expression in visceral adipose-derived stem cells correlated negatively with body mass index and C-reactive protein and positively with peroxisome proliferator-activated receptor delta. Finally, only in the visceral adipose-derived stem cells of obese patients hypoxia-induced mRNA expression of all of the sirtuins. Our results highlight that sirtuins' levels in adipose-derived stem cells are consistent with protective effects against visceral obesity and inflammation, and suggest a transcriptional mechanism through which acute hypoxia up-regulates sirtuins in the visceral adipose-derived stem cells of obese patients

PET imaging during hypoglycaemia to study adipose tissue metabolism

Contains fulltext : 205513.pdf (publisher's version ) (Open Access)BACKGROUND: Disturbances in adipose tissue glucose uptake may play a role in the pathogenesis of type 2 diabetes, yet its examination by 2-deoxy-2-[(18) F]fluorodeoxyglucose ([(18) F]FDG) PET/CT is challenged by relatively low uptake kinetics. We tested the hypothesis that performing [(18) F]FDG PET/CT during a hypoglycaemic clamp would improve adipose tissue tracer uptake to allow specific comparison of adipose tissue glucose handling between people with or without type 2 diabetes. DESIGN: We enrolled participants with or without diabetes who were at least overweight, to undergo a hyperinsulinaemic hypoglycaemic clamp or a hyperinsulinaemic euglycaemic clamp (n = 5 per group). Tracer uptake was quantified using [(18) F]FDG PET/CT. RESULTS: Hypoglycaemic clamping increased [(18) F]FDG uptake in visceral adipose tissue of healthy participants (P = 0.002). During hypoglycaemia, glucose uptake in visceral adipose tissue of type 2 diabetic participants was lower as compared to healthy participants (P < 0.0005). No significant differences were observed in skeletal muscle, liver or pancreas. CONCLUSIONS: The present findings indicate that [(18) F]FDG PET/CT during a hypoglycaemic clamp provides a promising new research tool to evaluate adipose tissue glucose metabolism. Using this method, we observed a specific impairment in visceral adipose tissue [(18) F]FDG uptake in type 2 diabetes, suggesting a previously underestimated role for adipose tissue glucose handling in type 2 diabetes

The Effect of Heat Stress and Beta-Adrenergic Agonists on Fatty Acid Mobilization and Their Individual and Interacting Impact on the Adipose Transcriptome of Ruminant Livestock

Heat stress reduces livestock efficiency, induces inflammation, and alters adipose tissue metabolism through stress-induced epinephrine acting on beta-adrenoreceptors (β-AR). Supplementation of beta-adrenergic agonists (β-AA) improve livestock growth and carcass traits, also by acting on β-AR located in skeletal muscle and adipose tissue. The binding of β-AR in adipose tissue results in changes in adipose tissue metabolism including increased lipolysis and decreased fatty acid synthesis. Due to their similar effects on stress response pathways, the possible interaction of heat stress and β-AA could negatively impact animal well-being. The purpose of the first study was to understand how ractopamine (RAC), a beta-one adrenergic agonist, and heat stress alter the subcutaneous adipose tissue transcriptome in sheep, and to identify interaction between the two. Based on differential expression and pathway analysis, the interaction of RAC and heat stress was predicted to alter adipose tissue metabolism and inflammation, but physiological data did not show a negative impact due to interaction. The second study investigated possible interaction of zilpaterol hydrochloride (ZH), a beta-two adrenergic agonist, and heat stress in subcutaneous adipose tissue transcriptome in beef cattle. Transcriptomic evidence suggests that ZH did not exacerbate the negative effects of heat stress and instead moderated heat stress-induced inflammation and oxidative stress. The purpose of the third study was to understand the effects of chronic heat stress and ZH supplementation on fatty acid mobilization in ex vivo visceral adipose tissue with and without stimulation of the adipose tissue with epinephrine. All treatment groups responded to stimulation by epinephrine, with no interaction of heat stress and ZH being apparent. Heat stress decreased fatty acid concentration while ZH increased it. Overall, these findings indicate that while the interaction of heat stress and β-AA in ruminant adipose may impact gene expression, there was no evidence of a detriment to animal well-being based on the parameters measured; in fact, β-AA supplementation may moderate many negative effects of heat stress. Advisor: Jessica L. Peterse