瘦素、脂肪酸对大鼠胰岛细胞解偶联蛋白2 mRNA表达的影响

以瘦素、脂肪酸作用于体外培养的大鼠胰岛细胞，以甘油三酯含量，解偶联蛋白2 mRNA表达水平为指标，显示瘦素通过外周途径调节产热，脂肪酸可损害胰岛功能。     

Regulation of rat heart triacylglycerol ester hydrolases by free fatty acids,fatty acyl CoA and fatty acyl carnitine

The regulation of triacylglycerol ester hydrolase (TG lipase) activity was studied in a pH 5.2 precipitate fraction from rat hearts. Neutral TG lipase activity (assayed at pH 7.5) was measured with both ethanolic and glycerol-dispersed triolein substrate preparations; acid lipase activity was determined at pH 5 with a glycerol-dispersed triolein substrate preparation containing lecithin. Neutral TG lipase activity was inhibited by free fatty acids (oleic acid) and by fatty acyl CoA compounds (oleoyl CoA, palmitoyl CoA); concentrations required for half-maximal inhibition were 100 μm and 20 to 25 μm, respectively. Palmitoyl carnitine resulted in an increase in neutral TG lipase activity. The inhibition of neutral TG lipase activity by oleoyl CoA could be prevented by increasing the content of albumin in the assay, and was reduced when the triolein substrate concentration was increased. Fatty acyl CoA compounds also inhibited acid TG lipase activity, but palmitoyl carnitine was the most effective inhibitor (concentration for half-maximal inhibition of 30 μm). The inhibition of neutral TG lipase activity by fatty acyl CoA is consistent with the observation that metabolic interventions that increase tissue levels of fatty acyl CoA result in an inhibition of rates of cardiac lipolysis.     

Short-chain fatty acids stimulate leptin production in adipocytes through the G protein-coupled receptor GPR41

Leptin is an adipose-derived hormone that regulates a wide variety of physiological processes, including feeding behavior, metabolic rate, sympathetic nerve activity, reproduction, and immune response. Circulating leptin levels are tightly regulated according to energy homeostasis in vivo. Although mechanisms for the regulation of leptin production in adipocytes are not well understood, G protein-coupled receptors may play an important role in this adipocyte function. Here we report that C2-C6 short-chain fatty acids, ligands of an orphan G protein-coupled receptor GPR41, stimulate leptin expression in both a mouse adipocyte cell line and mouse adipose tissue in primary culture. Acute oral administration of propionate increases circulating leptin levels in mice. The concentrations of short-chain fatty acids required to stimulate leptin production are within physiological ranges, suggesting the relevance of this pathway in vivo.     

Leptin controls the fate of fatty acids in isolated rat white adipocytes

Leptin directly increases the rate of exogenous glucose and fatty acids oxidation in isolated adipocytes. However, the effects of leptin on fatty acid metabolism in white adipose tIssue have not been examined in detail. Here, we report that in adipocytes incubated for 6 h in the presence of leptin (10 ng/ml), the insulin-stimulated de novo fatty acid synthesis was inhibited by 36% (P<0.05), while the exogenous oxidation of acetic and oleic acids was increased by 50% and 76% respectively. Interestingly, leptin did not alter the oxidation of intracellular fatty acids. Leptin-incubated cells presented a 16-fold increase in the incorporation of oleic acid into triglyceride (TG) and a 123% increase in the intracellular TG hydrolysis (as measured by free fatty acids release). Fatty acid-TG cycling was not affected by leptin. By employing fatty acids radiolabeled with (3)H and (14)C, we could determine the concomitant influx of fatty acids (incorporation of fatty acids into TG) and efflux of fatty acids (intracellular fatty acids oxidation and free fatty acids release) in the incubated cells. Leptin increased by 30% the net efflux of fatty acids from adipocytes. We conclude that leptin directly inhibits de novo synthesis of fatty acids and increases the release and oxidation of fatty acids in isolated rat adipocytes. These direct energy-dissipating effects of leptin may play an important role in reducing accumulation of fatty acids into TG of rat adipose cells.     

The nicotinic acid analogue acipimox increases plasma leptin and decreases free fatty acids in type 2 diabetic patients

The effect of 3 days of intensive treatment with acipimox, an antilipolytic nicotinic acid derivative, on plasma leptin levels was studied in eight patients with Type 2 diabetes mellitus in a double-blind, placebo-controlled, cross-over study. Acipimox reduced plasma free fatty acids (FFA) markedly and lowered plasma triglycerides, glucose and insulin. Plasma leptin levels were elevated in all eight patients during 3 days of acipimox treatment (mean increase+/-s.e.: 2.38+/-0.57ng/ml, P<0.005) and the 24h mean effect of acipimox on leptin levels increased during the experimental period (P<0.03). The effect on plasma insulin and glucose resembled a mirror image of the effect on plasma leptin during 3 days of treatment. The suggestion that leptin mediates insulin resistance and may be involved in the development of the diabetic syndrome cannot be supported by the present results. It has been reported that FFA stimulates leptin secretion. Surprisingly, despite a markedly reduced FFA level, leptin concentration increased in the present study. We suggest that a primary acipimox effect is to increase leptin secretion, and that this prevails over the reduced FFA stimulus.     

The role of endogenous catecholamine in the depressive effects of free fatty acids on isolated,perfused rat hearts

Summary Langendorff perfusion of hearts with 0.5 mM palmitate complexed with albumin in a molar ratio of six showed a depression of contractility to about 505 of control values. The coronary flow rate was enhanced and no arrhythmias occured. This decrease in contractility during fatty acid perfusion was irreversible since reperfusion with control medium containing 11 mM glucose as substrate did not lead to a recovery in contractile behaviour, while coronary flow rates reached values equal to, or below control levels. The deleterious effects of palmitate were partly overcome by adding 11 mM glucose to the fatty acid containing medium. No significant change in energy charge of ventricular tissue was observed after a thirty minute recirculating perfusion with palmitate when compared with the energy charge of hearts perfused with palmitate plus 11 mM glucose.In hearts, depleted from their endogenous catecholamines by preperfusion with tyramine, the fatty acid induced decrease in contractility was significantly less compared with control hearts during perfusion with palmitate. Reperfusion of tyramine-pretreated hearts with control medium was followed by a slow recovery of contractility. Hearts, preloaded with [³H]-norepinephrine showed a sudden release of radioactivity in the perfusate upon introduction of 0.5 mM palmitate, while no release occurred upon introduction of 0.5 mM palmitate in the presence of 11 mM glucose. These findings suggest that catecholamines released from endogenous stres may play an important role in the depressive actions of fatty acids. The role of the intracellular levels of fatty acids and their possible ionophoric role in the release of catecholamines is discussed in relation to thedeterioration of myocardial function. Prostaglandin E₁, of which ionophoric properties have also been shown, added instead of fatty acids, was found to have a similar effect.

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Die Rolle von endogenen Katecholaminen in der depressiven Wirkung von freien Fettsäuren auf isolierte, perfundierte Rattenherzen

Zusammenfassung Die Kontraktilität des retrograd perfundierten Rattenherzens wird um 50% herabgesetzt, wenn 0,5 mM Palmitinsäure, komplexiert mit 0,08 mM Albumin, im Perfusionsmedium vorhanden ist. Die Fettsäureperfusion erhöht die Koronardurchströmungsgeschwindigkeit, während keine Rhythmusstörungen beobachtet wurden. Die fettsäureinduzierte Kontraktilitätssenkung war nicht umkehrbar, weil nachträgliche Durchströmung mit 11 mM Glukose anstatt Fettsäure die Kontraktilität nicht verbesserte. Wenn Glukose während der Fettsäuredurchströmung zu gleicher Zeit hinzugefügt wurde, war die schädliche Wirkung der Fettsäure beschränkt. Nach halbstündiger Durchströmung mit Palmitinsäure als einzigem Brennstoff war der Gehalt energiereicher Adeninnukleotide unverändert, obwohl eine geringe Herabsetzung des Kreatinphosphatgehaltes beobachtet wurde. Wenn Herzen während 15 Minuten mit Tyramine präperfundiert wurden, um die endogenen Katecholamine zu entfernen, hatte Palmitatdurchströmung nur einen kleinen Effekt auf die Kontraktilität, während die geringe Herabsetzung reversibel war, wenn eine nachträgliche Durchströmung mit Glukose erfolgte. Diese Beobachtung machte uns auf die Möglichkeit aufmerksam, daß Fettsäure die endogenen Katecholamine mobilisieren. Wenn Herzen mit [³H]-Norepinephrin in der frühen Perfusionszeit aufgeladen wurden, stellte sich heraus, daß nachher die Radioaktivität auf asymptotische Weise aus dem Herzen freigemacht wurde. Wenn Palmitinsäure (mit Albumin im 61-Molar-Verhältnis) angeboten wurde, wurde plötzlich viel mehr Radioaktivität freigemacht, was nicht geschieht, wenn zu gleicher Zeit Glukose angeboten wurde. Diese Befunde deuten darauf, daß freie Fettsäuren endogene Katecholamine mobilisieren können. Es ist möglich, daß die ionophoren Eigenschaften von Fettsäure dabei eine wesentliche Rolle spielen, weil wir auch fanden, daß Prostaglandin E₁ (dessen Rolle als ionophore Verbindung bewiesen wurde) den gleichen Effekt zeigte wie Fettsäure, während bakterielle Ionophore, wie X-537 A, in der Literatur auch Katecholamine mobilisierende Eigenschaften zeigten.

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With 4 figures and 1 table

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Support was obtained from the Dutch Heart Foundation     

Intracellular pH in adipocytes: effects of free fatty acid diffusion across the plasma membrane, lipolytic agonists, and insulin.

The main function of white adipose tissue is to store nutrient energy in the form of triglycerides. The mechanism by which free fatty acids (FFA) move into and out of the adipocyte has not been resolved. We show here that changes in intracellular pH (pH1) in adipocytes correlate with the movement of FFA across cellular membranes as predicted by the Kamp and Hamilton model of passive diffusion of FFA. Exposure of fat cells to lipolytic agents or external FFA results is a rapid intracellular acidification that is reversed by metabolism of the FFA or its removal by albumin. In contrast, insulin causes an alkalinization of the cell, consistent with its main function to promote esterification. Inhibition of Na+/H+ exchange in adipocytes does not prevent the changes in pHi caused by FFA, lipolytic agents, or insulin. A fatty acid dimer, which diffuses into the cell but is not metabolized, causes an irreversible acidification. Taken together, the data suggest that changes in pHi occur in adipocytes in response to the passive diffusion of un-ionized FFA (flip-flop) into and out of the cell and in response to their metabolism and production within the cell. These changes in pHi may, in turn, modulate hormonal signaling and metabolism with significant impact on cell function.     

Metabolism of free fatty acids in fatty tissue

Hyperlipacidaemias play a role as etiological partial factor in the pathogenesis of various acute and chronic functional disturbances and are essentially the sequel of a disturbed metabolism of the free fatty acids of the fatty tissue. With regard to its clinical relevance a survey is given of the free fatty acid metabolism of the fatty tissue and its free fatty acid net balance as resultants from lipolysis and triglyceride synthesis is described. The author deals with the regulation of the lipolysis by cyclic mononucleotides, adenosine triphosphate, adenosine, fatty acids, ions, beta-hydroxybutyrate, lactate as well as hormones and finally with the control of the triglyceride synthesis.     

瘦素对游离脂肪酸致大鼠胰岛β细胞脂毒性的保护作用

目的 探讨瘦素对于游离脂肪酸(FFA)导致的大鼠胰岛β细胞脂毒性的保护作用。方法体外分离Wistar大鼠胰岛进行培养,根据培养液中加入不同物质而分为4组:(1)对照组,(2)瘦素组,(3)FFA组,(4)FFA+瘦素组。培养72h后测定胰岛内甘油三酯(TG)含量,基础状态及葡萄糖刺激下胰岛素分泌情况,并用RT-PCR方法检测胰岛β细胞内脂肪酸氧化酶-肉毒碱软脂酰转移酶Ⅰ(CPT-Ⅰ)、脂肪酸合成酶-乙酰辅酶A羧化酶(ACC)以及过氧化质体增殖物激活受体α(PPARα)和PPARγ的mRNA表达情况 结果 (1)FFA使胰岛内TG含量增加(P<0.01),瘦素使胰岛内TG含量减少(P<0.01)。(2)瘦素抑制基础状态及高糖负荷后胰岛素分泌(均P<0.01);FFA使基础胰岛素分泌增加而高糖负荷后胰岛素分泌的增高幅度明显低于对照组(均P<0.01)。(3)瘦素使CPT-Ⅰ和PPARα表达增加(分别P<0.01和P<0.05),ACC和PPARγ表达减少(均P<0.01);FFA使CPT-Ⅰ和ACC表达增加,PPARα和PPARγ表达减少(均P<0.01)。结论 FFA使胰岛内TC聚集增加,基础状态胰岛素分泌增加而高糖负荷后胰岛素分泌减少,形成高胰岛素血症。而瘦素可以通过PPARα和PPARγ途径使胰岛内脂肪酸氧化酶表达增加,脂肪酸合成酶表达减少,胰岛内TG聚集减少,同时抑制胰岛素分泌,减轻高胰岛素血症,从而起到对于FFA导致的大鼠胰     

Temporal patterns of circulating leptin levels in lean and obese adolescents: relationships to insulin, growth hormone, and free fatty acids rhythmicity

Alterations in nutritional status, such as obesity, markedly influence insulin, leptin, GH secretion, and free fatty acid (FFA) levels. We measured every hour for 24 h circulating leptin, insulin, GH, and FFA levels in lean and obese adolescents to determine: 1) the impact of adolescent obesity on the diurnal changes in leptin concentrations; and 2) the temporal relationships between the diurnal patterns of circulating leptin levels and insulin, GH, and FFA levels. During puberty, we found that the 24-h profile of circulating plasma leptin levels follows a bimodal pattern with minimal concentrations occurring early in the afternoon and a nocturnal elevation starting after midnight and culminating early morning. The time course of the diurnal variation in leptin levels in the obese adolescents was not different from that in lean controls. Of note, however, in obese girls leptin 24-h excursion and leptin night to day ratio were lower than those found in lean girls. In obese adolescents, mean GH levels varied significantly less during the day and night than lean controls. During the day, there were distinct preprandial increases and postprandial decreases in FFA levels, whereas after midnight FFA levels rose in both lean and obese adolescents. A significant positive correlation was found between mean plasma insulin levels between 0800 h and 2000 h and peak in leptin in lean and obese girls and boys (r = 0.63, P: < 0.001). Peak leptin was inversely correlated with the area under the nocturnal GH levels in all groups (r = -0.31, P: < 0.0003), whereas it was positively correlated with the nocturnal peak in FFA levels (r = 0.45, P: < 0.004). In summary, we report in obese adolescent girls a blunted relative diurnal excursion in leptin levels. This abnormal rhythmicity may, in part, explain their leptin resistance state. The nocturnal rise in leptin was paralleled by a nocturnal rise in GH and FFA levels. Additional studies are needed to test the potential link between the adipose-derived peptide and GH axis in humans.     

Acute regulation of adiponectin by free fatty acids

Little is known about the acute regulation of adiponectin in humans. In animal studies, adiponectin increases the clearance of free fatty acids (FFA) from the circulation by increasing skeletal uptake and oxidation of lipid, thereby regulating the FFA concentration. However, it is unknown if FFA regulate adiponectin. The aim of the present study was to investigate the effect of an acute reduction in free fatty acids on adiponectin concentration in healthy subjects. Ten normal male subjects were admitted for 2 inpatient visits and randomized to receive either acipimox (500 mg orally at 2 am and again at 6 am) or placebo on the first visit and vice versa on the second visit. Adiponectin, FFA, insulin and glucose were measured at 7:45 am. FFA concentrations were significantly lower after acipimox than placebo administration (0.08 +/- 0.02 mEq/L v 0.35 +/- 0.53 mEq/L, P <.05). Adiponectin concentrations were also significantly lower after acipimox than placebo administration (7.4 +/- 1.2 microg/mL v 10.3 +/- 1.7 microg/mL, P <.05). The change in FFA between acipimox and placebo correlated significantly with the change in adiponectin (r = 0.66, P <.05), eg, the larger the reduction in FFA in response to acipimox, the larger the reduction in adiponectin. These results suggest that acute lowering of FFA is associated with decreased adiponectin concentrations.     

Diazepam in acute myocardial infarction. Clinical effects and effects on catecholamines, free fatty acids, and cortisol.

Diazepam is a valuable drug in cases of acute myocardial infarction. The 10 mg intravenous loading dose and the subsequent 15 mg oral dose of diazepam administered three times daily produced safe, pleasant sedation, and reduced the need for analgesics. A much reduced excretion of catecholamines was recorded. It is presumed that diazepam causes a lower stress reaction, which is beneficial in diminishing the incidence of malignant arrhythmias and preventing the existing myocardial injury from spreading.     

Acute stimulation of leptin concentrations in humans during hyperglycemic hyperinsulinemia. Influence of free fatty acids and fasting

OBJECTIVE: To assess the acute regulation of leptin concentrations by insulin, glucose and free fatty acids (FFAs). DESIGN: Four protocols: saline control experiment (CON); hyperglycemic clamps (approximately 8.3 mmol/l, 120 min) after an overnight fast (12 FAST); after a 36 h fast (36 FAST); and after a 36 h fast during which Intralipid/heparin was given over the last 24 h (36 FAST+FFA). SUBJECTS: Lean, young, healthy volunteers; control group (n=6), experimental group (n=6). MEASUREMENTS: Serum leptin concentrations. RESULTS: Glucose and insulin concentrations were similar during the three clamp protocols. Average FFAs during the last 60 min of the clamp were 671+/-68 microM (CON),109+/-15 microM (12 FAST), 484+/-97 microM (36 FAST) and 1762+/-213 microM (36 FAST+FFA). Leptin concentrations decreased similarly during 36 FAST and 36 FAST+FFA. Leptin concentrations at 120 min (expressed as percentage of mean basal value) were 0.82+/-0.02 (CON), 0.93+/-0.08 (12 FAST) (P=0.29), 1.19+/-0.06 (36 FAST) (P<0.01) and 1.44+/-0.12 (36 FAST+FFA) (P<0.01). CONCLUSION: During a one-day fast leptin concentrations decrease regardless of maintainance of an isocaloric balance. During acute hyperinsulinemic hyperglycemia leptin concentrations increase only after a preceding fast. This increase was most pronounced during simultaneous elevation of FFAs. Overall, our findings are compatible with the hypothesis that leptin secretion may be coupled to triglyceride synthesis rather than to the absolute lipid content of the adipocyte. International Journal of Obesity (2001) 25, 138-142     

肥胖人群中血清瘦素、游离脂肪酸和脂联素水平的相互关系

目的 测定肥胖人群中血清瘦素、游离脂肪酸(FFA)和脂联素的血清水平及分析其相互之间的关系。方法 20名正常非肥胖对照和63名体重指数>25kg/m~2的超重肥胖个体进入研究,后者按其血糖水平又分为单纯性肥胖组(38例)和2型糖尿病组(25例)。所有研究对象均分别完成口服葡萄糖耐量试验和减少样本数的静脉葡萄糖耐量试验(FSIVGTT)。使用SPSS10.0统计软件包统计分析血清胰岛素、瘦素、游离脂肪酸和脂联素在各组人群间的水平差异以及与肥胖度和胰岛素敏感指数等指标的关系。结果 肥胖患者的血清瘦素和FFA水平均显著高于正常对照,唯血清脂联素水平显著低于正常对照[瘦素:单纯肥胖(15.55±1.87)μg/L,糖尿病肥胖(13.41±5.07)μg/Lvs正常对照(2.83±0.70)μg/L,均P<0.001;FFA:单纯肥胖(670.5±239.8)μmol/L,糖尿病肥胖(780.8±381.7)μmol/Lvs正常对照(393.2±152.1)μmol/L,P<0.001和P<0.01;脂联素:单纯肥胖(9.11±2.16)μg/L,糖尿病肥胖(4.25±1.59)μg/Lvs正常对照(12.14±3.57)μg/L,P<0.01和P<0.001]。在以胰岛素敏感指数为应变量的多元回归方程中,脂联素、空腹胰岛素、FFA和腰臀比(WHR)进入方程(r~=0.28,P<0.001)。结论 肥胖人群的血清瘦素、FFA水平显著高于正常人群,血清脂联素水平则与之相反;肥胖度是影响     

Direct apoptotic effects of free fatty acids on human endothelial cells

Background and aimEndothelial cell injury is a key event in the pathogenesis of diabetes-associated atherosclerosis and vascular complications. Increased apoptosis may contribute to the loss of endothelial integrity and leads to cardiovascular disease. This study was designed to elucidate whether high levels of free fatty acids (FFA) cause apoptosis and if so what is the possible role of insulin signaling alteration(s) in determining this effect.Methods and resultsIn human umbilical vein endothelial cells (HUVECs) cultured for 72 h with high levels of FFA, apoptotic cells, detected by Annexin V-FITC and PI, were increased. Then we observed a decrease of Bcl-2/Bax ratio (pro-apoptotic condition), measured by RT–PCR and Western blot. As the Akt pathway is involved in insulin signaling and apoptosis, we investigated whether Akt mediated FFA apoptotic effects. HUVECs exposed to FFA showed an equal amount of total Akt protein content compared to controls. In HUVECs, FFA induced a significant decrease in phosphorylated active Akt. Furthermore, phosphorylated eNOS (active form) was decreased and cleaved caspase-9 (active form) was increased. These alterations were prevented when insulin at 10⁻⁸ M was added in culture medium containing FFA. The insulin anti-apoptotic effect was prevented by Ly29400, a PI3K/Akt inhibitor.ConclusionHigh levels of FFA cause HUVECs apoptosis through Akt inhibition; insulin can prevent these effects. Inappropriate FFA elevation may affect vascular endothelium by impairing cell survival via activation of apoptosis, thus contributing to the development of cardiovascular disease in Type 2 diabetic patients.     

Effect of dialysis on serum carnitine,free fatty acids,and triglyceride levels in man and the rat

Serum free carnitine, free fatty acid and triglyceride values were followed in patients with end-stage renal disease on maintenance dialysis therapy. During dialysis a decrease in serum carnitine was documented. Whereas the elevated triglyceride concentration remained constant, there was a sharp rise in free fatty acids during the dialysis procedure. This pattern occurred whether patients were subjected to hemodialysis or intermittent peritoneal dialysis. Peritoneal dialysis was performed in a rat model and produced results similar to those observed in human subjects. Furthermore, it could be demonstrated that peritoneal dialysis initiated the hypertriglyceridemia in the otherwise normal animal within a short time period. Whereas the abnormalities observed in carnitine and fatty acid metabolism may or may not be causally related in rat or man, they both seem to result from dialysis therapy.     

Obesity and free fatty acids: double trouble.

The socio-economic impact of obesity, one of the most prevalent medical disorders in Western society, is mainly due to its association with a higher risk of coronary heart disease. It is likely that atherosclerosis develops against a background of obesity as a result of the insulin resistance that is invariably present in overweight and obese subjects. Fasting plasma lipids may be normal in obese subjects, but they are usually affected by postprandial hyperlipidemia, which is probably due to competition between chylomicrons and VLDL for the same metabolic pathways. The basis for the impaired clearance of atherogenic chylomicron remnants is the fact that obesity causes hepatic apo B-VLDL overproduction, and thus leads to competition with chylomicrons and their remnants at the lipolytic pathway (lipoprotein lipase and hepatic lipase) and receptor level (LDL-receptor and remnant-receptor). The overproduction of VLDL is probably caused by an enhanced hepatic flux of free fatty acids in both the postprandial (from the lipolysis of triglyceride rich particles) and postabsorptive states (from adipocytes). Weight reduction by means of life-style changes, supported by medical interventions with inhibitors of intestinal fat absorption (e.g. Orlistat) or appetite suppressants (e.g. Sibutramine), is essential in order to decrease the risk of atherosclerosis. Furthermore, improvement of risk factors can be achieved by means of fibrate treatment to modulate fasting and postprandial triglyceride levels. Treatment with cholesterol synthesis inhibitors ("statins") may reduce hepatic VLDL production and increase the clearance of atherogenic remnants by upregulating LDL-receptors, thus leading to improved fasting lipid levels and enhanced clearance of chylomicron remnants. Finally, the use of thiazolidinedione derivatives to improve insulin sensitivity may be one of the options for reducing the risk of atherosclerosis in obese subjects.