MTII administered peripherally reduces fat without invoking apoptosis in rats

The melanocortin (MC) system in the brain is believed to be an important downstream effector of leptin signaling; interference with MC functioning results in severe obesity. Melanotan II (MTII), an MC3/4-receptor agonist, produces similar behavioral and metabolic outcomes to those observed after leptin treatments, which enhance apoptosis in specific fat depots. To determine whether MTII also mediates adipose apoptosis induced by leptin treatment, two groups of rats (n=8) received MTII (2 mg/kg, i.p.) or saline (2 ml/kg) once daily for 4 days and had free access to food and water, and a third group was injected with saline and pair-fed (PF) to MTII treated rats. Food intake, water intake, body temperature, and body weight were measured daily. MTII reduced food and water intake and body weight gain (P<.05) and decreased body temperature compared to PF and saline-treated control groups. Retroperitoneal white adipose tissue (WAT) mass and epididymal WAT mass were reduced 46.3% and 21.1%, respectively (P<.05), after MTII, but not after PF, compared with the saline control rats. Both MTII- (25.0%) and PF (33.3%)-treated rats had decreased brown fat weight (P<.05), whereas muscle mass remained unchanged. Free fatty acid concentrations in serum were not different between MTII and control groups, but increased by 56.4% in PF group. DNA fragmentation assay did not support a role for MTII as an apoptotic signal in any of the fat tissues tested. These results show that in addition to reducing food intake and inhibiting body weight gain, intraperitoneal administration of MTII reduces fat mass, most likely by accelerated lipid mobilization, but not by apoptosis.     

Current concepts of the molecular structure and metabolism of human apolipoproteins and lipoproteins

Summary During the last few years major advances have occurred in our knowledge of the structure, function, and metabolism of the plasma lipoproteins. Twelve human apolipoproteins have been isolated and characterized. The primary structure of apolipoproteins A-I, A-II, C-I, C-II, and C-III have been elucidated. The primary structure of these apolipoproteins contains no unique sequences, however the primary structure of several of the apolipoproteins contain segments which can be modeled into amphipathic helices. The helical segments may be important in protein-protein as well as protein-lipid interactions. The molecular properties of the apolipoproteins have been investigated and shown to undergo self-association with major increases in conformation. The molecular organization of the plasma lipoprotein particle has been studied, and an iceberg-sea model has been proposed. This model emphasizes the micellar organization of the phospholipids, and the possibility of secondary, tertiary as well as quaternary structure of the apolipoprotein associated with the lipoprotein particle.The metabolism of plasma lipoproteins has been extensively analyzed over the last several years. Two general types of apolipoprotein-lipoprotein particle interactions have been recognized. The first type involves a quasi-irreversible interaction between the apolipoprotein and lipoprotein particle, and is exemplified by apolipoprotein B. The second type of interaction is a reversible apolipoprotein-lipoprotein particle interaction. Apolipoproteins A-I, A-II, C-I, C-II, C-III, and E are examples of the reversible interaction. Within this framework two major apoB-lipoprotein particle cascades have been proposed. Apo B-triglyceride rich lipoproteins including chylomicrons and hepatic VLDL undergo sequential triglyceride hydrolysis. Following triglyceride hydrolysis chylomicrons are converted to remnants with hydrated densities principally of VLDL and IDL. Liver apoB-VLDL is converted initially to IDL and finally to LDL. Apolipoproteins which undergo reversible interactions are present in virtually all density fractions and the distribution of these apolipoproteins is determined by the laws of mass action.With these concepts rapid progress has been made in our understanding of apolipoprotein-lipoprotein biochemistry, physiology, and clinical disorders of lipoproteins and atherosclerosis. The next several years will undoubtedly provide further insights into the structure, function, and metabolism of plasma lipoproteins.Based upon the acceptance address to the Kuratorium für die Verleihung des Heinrich-Wieland-Preises, München, October 31, 1980     

Adipocyte responses to adrenaline and insulin in active and former sportsmen

Summary The rates of lipolysis and lipogenesis in adipocytes, isolated from biopsy samples of subcutaneous fat, was assessed by estimation of glycerol release during a 30-min incubation, and of the incorporation of¹³C-glucose into lipids during a 1-h incubation at 37° C, respectively. The subjects were six highly-qualified, active endurance sportsmen, eight former endurance sportsmen of international class, and six untrained young men. In the active sportsmen the basal rate of lipolysis was about half of that in the previously-active sportsmen and the untrained subjects, but after the addition of adrenaline (10^–4 or 5 × 10^–4 mol · l^–1) the lipolysis rate was the highest. No differences were observed in the lipolytic rates in the former sportsmen compared to the untrained subjects. Gases of a comparatively high level of lipogenesis were found in the trained subjects. The addition of insulin (9 U · ml^–1) to isolated adipocytes caused a significant augmentation of individual rates of lipogenesis in the active sportsmen and the untrained persons but not in the previously-active sportsmen. In comparison with the active sportsmen, the previously active sportsmen revealed an increased basal rate of lipolysis and a reduced sensitivity to the lipogenic action of insulin. These findings suggest that these changes may have had significance in avoiding an increase of adipose tissue after a decrease in energy expenditure due to a change in physical activity.     

溶脂抽脂术对乳腺癌手术保护肋间臂神经的探讨

目的：探讨利用腋下溶脂、抽脂术对乳腺癌开放性手术中保护肋间臂神经的效果。 方法：对比乳腺癌改良根治手术中先采用溶脂、抽脂术观察组（29例）和未采用溶脂、抽脂术对照组（31例）对肋间臂神经损伤的发生情况,评估两者预防肋间臂神经损伤的效果。 结果：观察组中1例在溶脂过程中直接损伤肋间臂神经,1例溶脂不理想,致手术时误断肋间臂神经;对照组中8例误伤肋间臂神经。 结论：在开放性乳腺癌手术中先行溶脂、抽脂术以行保护肋间臂神经是可行的、有效的,如术者能在熟练掌握该技术。     

Adipose tissue distribution and risk of metabolic disease: does thiazolidinedione-induced adipose tissue redistribution provide a clue to the answer?

The relative effect of visceral and subcutaneous obesity on the risk of chronic metabolic disease has been a matter of long-term dispute. While ample data support either of the fat depots being causative or associative, valid argument for one depot often automatically belittles the other. Paradigms such as the visceral/portal hypothesis and the acquired lipodystrophy/ectopic fat storage and endocrine hypothesis have been proposed. Nevertheless, neither hypothesis alone explains the entire pathophysiological setting. Treatment of diabetes with thiazolidinediones selectively increases fat partitioning to the subcutaneous adipose depot but does not change visceral fat accumulation. This is in contrast to the preferential visceral fat mobilisation by diet and exercise. Surgical removal of visceral or subcutaneous adipose tissue yields relatively long-lasting metabolic improvement only when combined with procedures that ameliorate adipose tissue cell composition. These studies illustrate that human adipose tissue in different anatomic locations does not work in isolation, and that there is a best-fit relationship in terms of volume and function among different fat depots that needs to be met to maintain the systemic energy balance and to prevent the complications related to obesity.     

Human adipose triglyceride lipase (PNPLA2) is not regulated by obesity and exhibits low in vitro triglyceride hydrolase activity

Aims/hypothesis The recent identification of murine adipose triglyceride lipase (ATGL, now known as patatin-like phospholipase domain containing 2 [PNPLA2]), gene product of Pnpla2, has questioned the unique role of hormone sensitive lipase (HSL, now known as LIPE), gene product of Lipe, in fat cell lipolysis. Here, we investigated human ATGL and HSL adipose tissue gene expression and in vitro lipase activity.Subjects, materials and methods Levels of mRNA in adipose tissue from healthy obese and non-obese subjects were measured and lipase activity and adipocyte lipolytic capacity determined. HSL and ATGL cDNAs were transfected into Cos-7 cells and the relative tri- and diglyceride hydrolase activities were measured.Results Obesity was associated with a decreased subcutaneous and increased omental adipose tissue level of HSL mRNA. Subcutaneous HSL mRNA content was normalised upon weight reduction. In contrast, ATGL mRNA levels were unaffected by obesity and weight reduction. A high adipose tissue lipase activity was associated with increased maximal lipolysis and increased HSL, but not with ATGL mRNA levels. The in vitro triglyceride hydrolase activity of HSL was markedly higher than that of ATGL and contrary to HSL, ATGL was devoid of diglyceride hydrolase activity. The use of a selective HSL-inhibitor resulted in complete inhibition of HSL-mediated tri- and diglyceride hydrolase activity. The pH profile of human white adipose tissue triolein hydrolase activity was identical to that of HSL but differed from the ATGL profile.Conclusions/interpretation HSL, but not ATGL gene expression shows a regulation according to obesity status and is associated with increased adipose tissue lipase activity. Moreover, HSL has a higher capacity than ATGL to hydrolyse triglycerides in vitro.     

Adrenaline-induced "oxygen-wastage" and enzyme release from working rat heart. Effects of calcium antagonism, beta-blockade, nicotinic acid and coronary artery ligation

Adrenaline in a high dose (10⁻⁶m) caused the following harmful effects on mechanical and biochemical parameters of the isolated working rat heart: (i) loss of efficiency of mechanical work from 4.48 ± 0.20 to 3.24 ± 0.13 joules per ml O₂ (P < 0.001), so that much more oxygen was required to do the same amount of work (“oxygen-wastage”); (ii) a decreased cardiac output despite increased power production (from 14.2 ± 0.7 to 18.9 ± 0.8 mW/g, (P < 0.001); (iii) a marked release of lactate dehydrogenase (value 10 min after adrenaline: 558 ± 113 mU/g/min; vs control: 16 ± 2); and (iv) a decreased myocardial content of ATP. Interventions to counter the deleterious effects of adrenaline were: calcium antagonism, β-blockade, an antilipolytic agent, and a combination of calcium antagonism and an antilipolytic agent. From this, two separate aspects emerged. First, mechanical function as measured by cardiac output and power production was markedly improved by calcium antagonism which completely reversed the impairment of function caused by the high dose of adrenaline. β-blockade had also a less marked protective effect on mechanical function. Secondly, enzyme release was most effectively inhibited by the combination of calcium antagonism and inhibition of lipolysis or by propranolol. The inefficiency of work (“oxygen-wastage”) was β-mediated and Ca²⁺-dependent, whereas enzyme release was predominantly Ca²⁺-dependent and partially dependent on lipolysis. Hence the effects of β-blockade in inhibition of the adrenaline-provoked enzyme release could be ascribed to a combination of calcium-antagonism and inhibition of lipolysis.     

Metabolismo di cellule adipose umane isolate in vitro. III. Effetto lipolitico del N6-2′-O-dibutirriladenosin-3′,5′-monofosfato ciclico (db-cAMP)

Riassunto Lo N⁶-2-O-dibutirriladenosin-3,5-monofosfato ciclico (db-cAMP) si è dimostrato una sostanza efficace nel promuovere la lipolisi in cellule adipose umane isolatein vitro. L'aumento della liberazione di glicerolo e di acidi grassi nel mezzo di incubazione è osservabile alle concentrazioni 1 mM e 0,2 mM. Alla concentrazione 0,04 mM, il db-cAMP non svolge una sicura azione lipolitica. L'insulina umana, presente nel mezzo di incubazione alla concentrazione di 500 µU/ml, non è in grado di inibire la lipolisi stimolata dal db-cAMP (0,2 mM).

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Summary It has been shown that cyclic N⁶-2-O-dibutyryl adenosin-3,5-monophosphate (db-cAMP) is a powerful lipolytic agent on isolated human fat cells incubatedin vitro. Increased glycerol and fatty acid release into the medium becomes evident with concentrations 1 mM and 0.2 mM of db-cAMP. No significant lipolytic effect is apparent at the concentration of 0.04 mM. When human insulin is added to the incubating medium at the concentration of 500 µU/ml, no inhibition of db-cAMP stimulated lipolysis is demonstrable.

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Zusammenfassung Das zyklische N⁶-2-O-Dibutyryladenosin-3,5-Monophosphat (db-cAMP) hat sich als eine zur Förderung der Lipolyse inin vitro isolierten menschlichen Fettzellen wirksame Substanz erwiesen. Schon bei Konzentrationen von 1 mM und 0,2 mM lässt sich im Inkubationsmedium eine erhöhte Freisetzung von Glyzerol und Fettsäuren nachweisen. Bei Konzentrationen von 0,04 mM hat db-cAMP keine sichere lipolytische Wirkung. Die Anwesenheit von menschlichem Insulin in Konzentrationen von 500 µU/ml im Inkubationsmedium ist nicht imstande die von db-cAMP (0,2 mM) stimulierte Lipolyse zu hemmen.

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Resumen El N⁶-2-O-dibutirriladenosin-3,5-monofosfato cíclico (db-cAMP) ha demostrado ser una substancia eficaz y capaz de promover la lipólisis en células adiposas humanas aisladasin vitro. En las concentraciones 1 mM y 0,2 mM, se puede observar una liberación de glicerol y ácidos grasos mayor en el medio de incubación. A la concentración de 0,04 mM, el db-cAMP no desarrolla una acción lipolítica segura. La insulina humana, presente en el medio de incubación a la concentración de 500 µU/ml, no es capaz de inhibir la lipólisis estimulada por el db-cAMP (0,2 mM).

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Résumé Le N⁶-2-O-dibutyryladenosin-3,5-monophosphate cyclique (db-cAMP) s'est démontré une substance qui stimule efficacement la lipolyse dans les adipocytes humains isolésin vitro. L'augmentation de la libération de glycérol et d'acides gras dans le milieu d'incubation s'observe aux concentrations 1 mM et 0,2 mM. À la concentration 0,04 mM, le db-cAMP n'explique pas une action lipolytique sure. L'insuline humaine, présente dans le milieu d'incubation à la concentration de 500 µU/ml, n'est pas capable d'inhiber la lipolyse stimulée par le db-cAMP (0,2 mM).

     

Effect of beta-adrenergic stimulation on whole-body and abdominal subcutaneous adipose tissue lipolysis in lean and obese men

Aims/hypothesis Obesity is characterised by increased triacylglycerol storage in adipose tissue. There is in vitro evidence for a blunted beta-adrenergically mediated lipolytic response in abdominal subcutaneous adipose tissue (SAT) of obese individuals and evidence for this at the whole-body level in vivo. We hypothesised that the beta-adrenergically mediated effect on lipolysis in abdominal SAT is also impaired in vivo in obese humans. Methods We investigated whole-body and abdominal SAT glycerol metabolism in vivo during 3 h and 6 h [²H₅]glycerol infusions. Arterio–venous concentration differences were measured in 13 lean and ten obese men after an overnight fast and during intravenous infusion of the non-selective beta-adrenergic agonist isoprenaline [20 ng (kg fat free mass)⁻¹ min⁻¹]. Results Lean and obese participants showed comparable fasting glycerol uptake by SAT (9.7 ± 3.4 vs 9.3 ± 2.5% of total release, p = 0.92). Furthermore, obese participants showed an increased whole-body beta-adrenergically mediated lipolytic response versus lean participants. However, their fasting lipolysis was blunted [glycerol rate of appearance: 7.3 ± 0.6 vs 13.1 ± 0.9 μmol (kg fat mass)⁻¹ min⁻¹, p < 0.01], as was the beta-adrenergically mediated lipolytic response per unit SAT [Δ total glycerol release: 140 ± 71 vs 394 ± 112 nmol (100 g tissue)⁻¹ min⁻¹, p < 0.05] compared with lean participants. Net triacylglycerol flux tended to increase in obese compared with lean participants during beta-adrenergic stimulation [Δ net triacylglycerol flux: 75 ± 32 vs 16 ± 11 nmol (100 g tissue)⁻¹ min⁻¹, p = 0.06]. Conclusions/interpretation We demonstrated in vivo that beta-adrenergically mediated lipolytic response is impaired systematically and in abdominal SAT of obese versus lean men. This may be important in the development or maintenance of increased triacylglycerol stores and obesity.     

Distinct long-term regulation of glycerol and non-esterified fatty acid release by insulin and TNF-α in 3T3-L1 adipocytes

Aims/hypothesis. Adipose tissue lipolysis plays a central part in total body fuel metabolism. Our study was to assess the long-term regulation of glycerol and non-esterified fatty acid (NEFA) release by insulin or TNF-α.¶Methods. Fully differentiated 3T3-L1 adipocytes were exposed for up to 22 h to insulin or TNF-α.¶Results. Long-term insulin treatment resulted in increased basal glycerol release, reaching sixfold at 22 h with 1 nmol/l insulin. Partial inhibition was observed by pharmacologically inhibiting phosphatidylinositol 3-kinase or the mitogen-activated kinase kinase – extracellular signal-regulated kinase cascades. This represented 50–60 % of the response induced by 1 nmol/l TNF-α and approximately 40 % of the glycerol release maximally stimulated by isoproterenol (1 μmol/l, 30 min). The cellular mechanism seemed to be distinct from that of TNF-α: First, glycerol release in response to long-term insulin was progressive with time and did not display a lag-time characteristic of the effect of TNF-α. Second, pretreatment and co-treatment of the cells with troglitazone greatly inhibited TNF-α-induced glycerol release (128.5 ± 10.2 to 35.4 ± 2.1 nmol/mg protein per h) but not the effect of insulin, which was exaggerated. Third, hormone-sensitive lipase protein content was decreased (45 %) by TNF-α but not following long-term insulin. Finally, TNF-α was associated with NEFA release to the medium, whereas long-term insulin treatment was not. Moreover, glycerol release during isoproterenol-stimulated lipolysis was additive to the effect of long-term insulin, whereas NEFA release was inhibited by nearly 90 %.¶Conclusions interpretation. Contradictory to its short-term inhibitory effect, long-term insulin stimulates glycerol release with concomitant stimulation of NEFA re-esterification. [Diabetologia (2001) 44: 55–62]