The adipsin-acylation stimulating protein system and regulation of intracellular triglyceride synthesis.

We have previously characterized an activity from human plasma that markedly stimulates triglyceride synthesis in cultured human skin fibroblasts and human adipocytes. Based on its in vitro activity we named the active component acylation stimulating protein (ASP). The molecular identity of the active serum component has now been determined. NH2-terminal sequence analysis, ion spray ionization mass spectroscopy, and amino acid composition analysis all indicate that the active purified protein is a fragment of the third component of plasma complement, C3a-desArg. As well, reconstitution experiments with complement factors B, D, and complement C3, the components necessary to generate C3a, have confirmed the identity of ASP as C3a. ASP appears to be the final effector molecule generated by a novel regulatory system that modulates the rate of triglyceride synthesis in adipocytes.

Impaired response of fibroblasts from patients with hyperapobetalipoproteinemia to acylation-stimulating protein.

Acylation-stimulating protein (ASP) is a small, basic, human plasma protein that markedly stimulates triglyceride synthesis in human adipocytes and cultured human skin fibroblasts. The present studies examine the response to ASP of cultured skin fibroblasts from normal subjects patients with hyperapobetalipoproteinemia, patients with familial hypercholesterolemia, and patients with hypertriglyceridemia without hyperapobetalipoproteinemia. Triglyceride synthesis induced by ASP did not differ significantly among the normals, the patients with familial hypercholesterolemia, and the patients with hypertriglyceridemia with normal low density lipoprotein (LDL) apolipoprotein B levels; however, on average, it was markedly reduced in the patients with hyperapobetalipoproteinemia. In all groups studied, evidence of specific saturable binding of radioiodinated ASP was present. Binding, however, was significantly reduced in the groups with hyperapobetalipoproteinemia whereas the other three groups were indistinguishable. By contrast, LDL-specific binding was reduced only in the patients with familial hypercholesterolemia. There was a significant direct relation between the degree of ASP binding and the triglyceride synthesis inducible by ASP. In addition, with the exception of the patients with familial hypercholesterolemia, there was an inverse relation between both ASP-specific binding and ASP-induced triglyceride synthesis in fibroblasts to LDL levels in plasma whereas no relation was evident to plasma high density lipoprotein and very low density lipoprotein.

Acylation-stimulating protein (ASP) regulates glucose transport in the rat L6 muscle cell line.

Acylation-stimulating protein (ASP), a human plasma protein, is a potent stimulator of triglyceride synthesis and glucose transport in both human adipocytes and fibroblasts. The purpose of the present in vitro study was to examine the effect of ASP on glucose transport in muscle cells. ASP stimulated 2-deoxy-glucose transport (2-DG) in differentiated rat L6 myotubes in a time (30 min to 24 h) and concentration dependent manner (97% increase). The magnitude of the ASP effect on glucose transport was comparable to the time- and concentration-dependent effects seen with insulin (125% increase), but was additive to insulin, pointing to involvement of differential signalling pathways. ASP stimulation was dependent on cell differentiation in that glucose transport increased by only 12% in myoblasts, comparable to the effect of insulin in myoblasts (15% increase) demonstrating selective responsiveness of the differentiated myotubes to ASP and insulin. The mechanism for the ASP induced increase in glucose transport was also examined. ASP increased the Vmax for 2-DG transport by 183% (4.02 vs. 1.42 nmol/mg cell protein/30 s; ASP vs. Control, respectively). This could be explained by an increased translocation of glucose transporters (GLUT 1, GLUT 4 and GLUT 3) to the plasma membrane surface as demonstrated by Western analysis (+43% P < 0.05, +30% P < 0.05, and +49% P < 0.05, respectively). The effects of ASP were equal to those of insulin (+47%, +26% and +53% for GLUT 1, GLUT 4 and GLUT 3, respectively) and in all cases were paralleled by comparable glucose transport increases under the same incubation conditions. After long-term stimulation (24 h), Western analysis indicated that ASP had a permissive effect on insulin stimulated increases in total GLUT3 and GLUT4 cellular transporter content. These results suggest that muscle is also responsive to ASP and that ASP may play a role in glucose metabolism in both muscle and adipose tissue.

Critical review of acylation-stimulating protein physiology in humans and rodents.

In the last few years, there has been increasing interest in the physiological role of acylation-stimulating protein (ASP). Recent studies in rats and mice, in particular in C3 (-/-) mice that are ASP deficient, have advanced our understanding of the role of ASP. Of note, the background strain of the mice influences the phenotype of delayed postprandial triglyceride clearance in ASP-deficient mice. Administration of ASP in all types of lean and obese mice studied to date, however, enhances postprandial triglyceride clearance. On the other hand, regardless of the background strain, ASP-deficient mice demonstrate reduced body weight, reduced leptin and reduced adipose tissue mass, suggesting that ASP deficiency results in protection against development of obesity. In humans, a number of studies have examined the relationship between ASP, obesity, diabetes and dyslipidemia as well as the influence of diet, exercise and pharmacological therapy. While many of these studies have small subject numbers, interesting observations may help us to better understand the parameters that may influence ASP production and ASP action. The aim of the present review is to provide a comprehensive overview of the recent literature on ASP, with particular emphasis on those studies carried out in rodents and humans.

Differences in mRNA expression of the proteins secreted by the adipocytes in human subcutaneous and visceral adipose tissues.

We have investigated the difference in gene expression of six proteins secreted by adipocytes in paired biopsies from visceral and abdominal subcutaneous adipose tissue in nine individuals with various degrees of obesity. The mRNAs levels of leptin, TNFalpha, angiotensinogen, acylation stimulating protein (ASP), cholesterol ester transfer protein (CETP) and phospholipid transfer protein (PLTP) were quantified by RT-competitive PCR. ASP and angiotensinogen mRNA levels were higher in the visceral fat, whereas the mRNA levels of leptin and CETP were higher in the subcutaneous depot. TNFalpha mRNA expression was similar in the two sites. For angiotensinogen, the difference was more pronounced in the subjects with body mass index (BMI) lower than 30 kg/m(2) whereas for ASP, CETP and leptin, the difference was observed regardless the BMI of the subjects. PLTP mRNA levels in subcutaneous, but not in the visceral, adipose tissue were positively related to the BMI of the subjects. These results strongly suggest that visceral and subcutaneous adipocytes may have different properties in the production of bioactive molecules.

Serum C3 but not plasma acylation-stimulating protein is elevated in Finnish patients with familial combined hyperlipidemia.

A trapping defect of fatty acids due to impaired function of acylation-stimulating protein (ASP) has been suggested as one mechanism underlying the metabolic abnormalities in familial combined hyperlipidemia (FCHL). The study aimed at defining the role of ASP and complement C3 in 35 Finnish FCHL families. There was no difference in plasma ASP levels between the 66 hypertriglyceridemic FCHL patients and their 84 normotriglyceridemic relatives. No response in plasma ASP could be observed after a fatty meal in 10 FCHL patients or in 10 control subjects. In familial correlation analyses, C3 exhibited a significant sibling-sibling correlation. The FCHL patients had higher serum C3 levels than their unaffected relatives (P<0.001). Furthermore, serum C3 levels correlated significantly with several lipid parameters. The correlations between ASP and lipid variables were weaker than those of C3. These analyses suggest that common genes might contribute to the regulation of serum C3, triglycerides, HDL-C, free fatty acids, and insulin. The present data do not support the hypothesis that defects of the ASP pathway are reflected in plasma lipoproteins or in impaired plasma lipid clearance postprandially.

Delayed and exaggerated postprandial complement component 3 response in familial combined hyperlipidemia.

Very low density lipoprotein overproduction is the major metabolic characteristic in familial combined hyperlipidemia (FCHL). Peripheral handling of free fatty acids (FFAs) in vitro may be impaired in FCHL by decreased action of acylation-stimulating protein (ASP), which is identical to the immunologically inactive complement component 3a (C3adesArg). Because decreased FFA uptake by impaired complement component 3 (C3) response (as the precursor for ASP) may result in enhanced FFA flux to the liver in FCHL, we have evaluated postprandial C3 changes in vivo in FCHL patients. Accordingly, 10 untreated FCHL patients and 10 matched control subjects underwent an oral fat loading test. Fasting plasma C3 and ASP levels were higher in FCHL patients (1.33+/-0.09 g/L and 70.53+/-4.37 mmol/L, respectively) than in control subjects (0.91+/-0.03 g/L and 43.21+/-8.96 mmol/L, respectively; P=0.01 and P<0.05). In control subjects, C3 concentrations increased significantly after 4 hours (to 1.03+/-0.04 g/L). In FCHL, plasma C3 was unchanged after 4 hours. The earliest postprandial C3 rise in FCHL patients occurred after 8 hours (1.64+/-0.12 g/L). The maximal apolipoprotein B-48 concentration was reached after 6 hours in FCHL patients and control subjects. Postprandial FFA and hydroxybutyric acid (as a marker of hepatic FFA oxidation) were significantly higher in FCHL patients than in control subjects, and the early postprandial C3 rise was negatively correlated with the postprandial FFA and hydroxybutyric acid concentrations. The present data suggest an impaired postprandial plasma C3 response in FCHL patients, most likely as a result of a delayed response by C3, as the precursor for the biologically active ASP, acting on FFA metabolism. Therefore, an impaired postprandial C3 response may be associated with impaired peripheral postprandial FFA uptake and, consequently, lead to increased hepatic FFA flux and very low density lipoprotein overproduction.

Plasma acylation stimulating protein concentration and subcutaneous adipose tissue C3 mRNA expression in nondiabetic and type 2 diabetic men.

We studied the effect of an oral fat load on plasma acylation stimulating protein (ASP) concentrations in 9 lean healthy (age 59+/-2 years, body mass index [BMI] 23.2+/-0.4 kg/m(2); both mean+/-SEM), 9 obese nondiabetic (58+/-2 years, BMI 29.4+/-0.5 kg/m(2)), and 12 type 2 diabetic (60+/-2 years, BMI 29.6+/-1.0 kg/m(2)) men. Because ASP is a cleavage product of complement protein C3 (C3adesArg) and its secretion is regulated by insulin, we also examined the subcutaneous adipose tissue expression of C3 mRNA before and after a 240-minute euglycemic hyperinsulinemic clamp in a subgroup of these men. Plasma ASP concentration and adipose tissue C3 mRNA expression were higher in the obese groups than in the lean men. Plasma ASP concentration did not change significantly after the fat load. Fasting plasma ASP concentration and C3 mRNA expression were correlated negatively with insulin sensitivity and positively with the magnitude of postprandial lipemia in nondiabetic but not in type 2 diabetic men. The expression of C3 mRNA was not regulated by insulin. These data suggest that ASP is associated with whole-body glucose and lipid metabolism in nondiabetic individuals, whereas metabolic disturbances in diabetes may overcome the regulatory role of ASP in lipid and glucose metabolism.

The ability of Sephadex to activate human complement is suppressed in specifically substituted functional Sephadex derivatives.

The capacity of Sephadex and of chemically substituted Sephadex derivatives to activate human complement was examined by incubating polymer particles in normal human serum (NHS) under conditions that allow classical and/or alternative pathway activation, and by determining complement consumption or generation of C3a antigen in serum. Sephadex was found to activate complement in NHS, mainly through the alternative pathway. The complement-activating capacity of Sephadex was directly related to the surface area of polymer that could interact with serum. Substitution of hydroxyl groups of Sephadex with carboxymethyl (CM) groups suppressed the complement-activating capacity of the polymer in a dose-dependent fashion so that Sephadex bearing an average of one or more CM groups per saccharidic unit exhibited no complement-activating ability. Blocking of CM groups on CM sephadex with amide bonds did not restore a complement-activating capacity to the polymer, indicating that intact hydroxyl groups of the sugar units are required for complement activation by Sephadex. CM Sephadex was also found to adsorb C3adesArg which bound to the polymer with a calculated affinity of 1 x 10(6) l x M-1. Substitution of Sephadex with carboxymethyl and benzylamide sulphonate groups which confers to the polymer the capacity to catalyse thrombin inactivation on its surface also suppressed the complement-activating capacity of Sephadex. Sephadex derivatives that lack complement-activating properties and adsorb anaphylatoxins may provide useful models for the design of cellulosic membranes and biomaterials with blood compatible properties.

A critical evaluation of the putative role of C3adesArg (ASP) in lipid metabolism and hyperapobetalipoproteinemia.

The acylation stimulating protein, ASP is a small, basic serum protein capable of stimulating triglyceride synthesis in cultured fibroblasts and adipocytes. Sequence analysis of ASP has shown that ASP is identical to C3adesArg the inactive fragment of the complement anaphylatoxin peptide, C3a. It has been proposed that C3adesArg (ASP) can be generated by mature adipocytes secreting the three complement proteins: complement protein C3, factor B and factor D (adipsin). There have also been indications that adipocytes may express a specific C3adesArg (ASP)-receptor that is distinct from the recently cloned C3a-receptor. This suggests that C3adesArg (ASP) acts as an adipocyte autocrine and that it plays a central role in the metabolism of adipose tissue. Based on these observations a hypothesis for the etiology of hyperapobetalipoproteinemia (hyperapoB) has been proposed. Hyperapobetalipoproteinemia (hyperapoB), is a familial lipoprotein disorder characterized by increased hepatic secretion of very low density lipoprotein (VLDL) and low density lipoprotein (LDL) particles. If C3adesArg (ASP) function in the adipose tissue is impaired, a reduced rate of triglyceride synthesis will follow, generating an increased flux of fatty acids to the liver. In response to an increased flow of fatty acids, the liver will increase its production of VLDL particles yielding the phenotype of hyperapoB. This review critically assesses this hypothesis and the potential role of C3adesArg (ASP) as a major determinant for triglyceride synthesis in the light of data collected in vitro and in vivo.

Insulin action and insulinemia are closely related to the fasting complement C3, but not acylation stimulating protein concentration.

OBJECTIVE: An elevated C3 concentration has been reported in people with obesity, type 2 diabetes, hypertension, and dyslipidemia, and has been proposed to play a role in the development of atherosclerosis. We hypothesized that an elevated C3 concentration might be linked to insulin resistance and/or hyperinsulinemia, abnormalities commonly observed in association with the above conditions. RESEARCH DESIGN AND METHODS: Fasting concentrations of C3 and acylation stimulating protein (ASP, C3adesarg), a cleavage product of C3 recently found to stimulate glucose uptake in vitro, were measured in 33 healthy nondiabetic Pima Indians (14 women and 19 men; age 27 +/- 1 and body fat 33 +/- 1%, means +/- SEM). Subjects were characterized for body composition dual-energy X-ray absorptiometry, insulin action (insulin-stimulated glucose disposal [M], hyperinsulinemic glucose clamp), and glucose tolerance (75-g oral glucose tolerance test). RESULTS: Fasting C3 and ASP concentrations were positively correlated (r = 0.43, P < 0.05). Fasting C3 concentration was closely related to percent body fat (r = 0.77), M (r = -0.75), and fasting insulin concentration (r = 0.72) (all P < 0.0001). Fasting C3 concentrations remained significantly related to M and fasting insulin after adjusting for percent body fat (partial r = -0.53 and 0.33, both P < 0.05). In subjects with impaired glucose tolerance, fasting C3 concentrations were higher than in those with normal glucose tolerance--a difference that remained after adjustment for percent body fat and M. We found that fasting ASP concentrations were significantly related to percent body fat (r = 0.37, P < 0.05), but not to M or fasting insulin. CONCLUSIONS: In Pima Indians, fasting C3 concentration is closely related to adiposity, insulin action, and fasting insulin levels and may thus be a mediator for the postulated link between obesity, insulin resistance, hyperinsulinemia, and possibly atherosclerosis.

Complement peptides C3a- and C5a-induced mediator release from dissociated human skin mast cells.

The complement peptides C3a and C5a have been shown previously to release histamine from human basophils but not human lung mast cells. As skin mast cells differ from those of the lung in both immunocytochemical and functional properties, we examined the ability of these anaphylatoxins to release preformed and newly generated mediators from human dispersed skin mast cells. In concentration-response studies, both C3a and C5a released histamine in a concentration related manner with C5a being 40-50 times more potent. However, the extent of histamine, 15-20%, was considerably less than that released from basophils. This was not due to catabolism of the peptides by mast cell proteases, mast cell supernatants that contained C5a being effective in releasing basophil histamine. Removal of the C-terminal arginine from C3a and C5a abolished their activity on skin mast cells. In time-course studies, histamine release induced by C3a and C5a was complete within 15 seconds. Complement-induced histamine release is a non-cytotoxic process as evidenced by 2-deoxy-D-glucose and antimycin A, inhibitors of glycolysis and oxidative phosphorylation, respectively. In contrast to IgE-dependent stimulation, anaphylatoxin-induced histamine release from human skin mast cells is independent of extracellular calcium. Both C3a and C5a at concentrations that induced 10-16% net histamine release caused a negligible release of the newly generated mediator, PGD2. The results suggest that C3a and C5a stimulate human skin mast cells in a manner similar to substance P and related basic secretagogues. However, the activation site for C3a and C5a appears to be different to that for substance P as the substance P antagonist (D-Pro4, D-Trp7,9,10) SP4-11 inhibited histamine release stimulated by substance P but not that induced by C3a and C5a.

Reduced body weight, adipose tissue, and leptin levels despite increased energy intake in female mice lacking acylation-stimulating protein.

Acylation-stimulating protein (ASP) is a potent lipogenic protein produced by adipocytes. In vitro studies have shown that ASP increases triglyceride synthesis and glucose transport in both murine and human adipocytes. Our initial study indicated that complement C3-deficient (-/-) mice (and, therefore, ASP deficient) demonstrated altered dietary postprandial triglyceride clearance. In the present study we examined the phenotype of female mice longitudinally on different diets. Female C3(-/-) mice on both low (10% of energy) and high (40% of energy) fat diets displayed an average reduction in total body weight of 10.1+/-0.5% (P < 0.0003, by ANOVA) compared with the C3(+/+) littermates. Reductions in white adipose tissue mass accounted for most of this weight difference (59% reduction; P < 0.01 on low fat diet). Plasma leptin levels were significantly reduced in C3(-/-) mice on both high (P < 0.001) and low fat diets (P < 0.01). This reduction was significant even after adjusting for the reduced body weight and body fat (P < 0.001). Leptin reductions in the C3(-/-) were greater on the high fat diet and were associated with increased food intake (18+/-2% increase; P < 0.001). Furthermore, there was a decrease in basal glucose levels and basal insulin levels [12.8% decrease in glucose at 14 weeks (HF; P < 0.05) and 41% decrease in insulin at 26 weeks (HF; P < 0.05)]. These in vivo experiments demonstrate that female mice lacking ASP have marked alterations of body weight, adiposity, plasma leptin, and plasma insulin levels. Decreased adiposity and leptin levels occurred in the ASP-deficient animals despite increased energy intake, suggesting that energy expenditure was elevated in these animals. Thus, ASP appears to have an important role in the regulation of energy balance in mice.

Studies of adipose tissue metabolism in human immunodeficiency virus-associated lipodystrophy.

We studied aspects of metabolism in subcutaneous adipose tissue (SAT) in 40 human immunodeficiency virus (HIV)-infected subjects with and without lipodystrophy and in healthy control subjects. HIV-infected subjects without lipodystrophy had less SAT and visceral adipose tissue (VAT). Glycerol release was higher in both HIV-infected groups, especially those without fat redistribution. Tumor necrosis factor (TNF) release from SAT and serum soluble TNF receptor 2 concentrations were significantly higher in HIV-infected individuals with lipodystrophy. The absolute production of acylation-stimulating protein (ASP) and the percentage conversion of the complement protein to ASP were significantly lower in HIV-infected subjects with lipodystrophy. Further studies are needed to dissect the factors that mediate lipoatrophy in HIV infection.

Examination of several potential mechanisms for the negative outcome in a clinical stroke trial of enlimomab, a murine anti-human intercellular adhesion molecule-1 antibody: a bedside-to-bench study.

BACKGROUND AND PURPOSE: Enlimomab, a murine monoclonal anti-human intercellular adhesion molecule (ICAM)-1 antibody, had a negative outcome in a multicenter acute-stroke trial. We did a bedside-to-bench study in standardized rat stroke models to explore mechanisms for these untoward results. METHODS: After focal brain ischemia in Wistar rats and spontaneously hypertensive rats (SHR), we administered murine anti-rat ICAM-1 antibody (1A29), subclass-matched murine immunoglobulin (IgG1), or vehicle intravenously. To examine whether rat anti-mouse antibodies were generated against the mouse protein and whether these were deleterious, we sensitized Wistar rats with 1A29 or vehicle 7 days before surgery. Infarct volume, tissue myeloperoxidase activity, neutrophil CD11b expression, and microvascular E-selectin, P-selectin, and ICAM-1 expression were examined 48 hours after surgery. Complement activation was serially assessed for 2 hours after a single injection of either 1A29 or vehicle. RESULTS: 1A29 treatment did not significantly reduce infarct size in either strain. 1A29 sensitization augmented infarct size and generated rat anti-mouse antibodies. Although 1A29 inhibited neutrophil trafficking shown by reduction in brain myeloperoxidase activity, circulating neutrophils were activated and displayed CD11b upregulation. Complement was activated in 1A29-sensitized Wistar rats and 1A29-treated SHR. E-selectin (SHR), endothelial P-selectin (Wistar and SHR), and ICAM-1 (SHR) were upregulated in animals treated with 1A29. CONCLUSIONS: Administration to rats of a murine antibody preparation against ICAM-1, 1A29, elicits the production of host antibodies against the protein, activation of circulating neutrophils, complement activation, and sustained microvascular activation. These observations provide several possible mechanisms for central nervous system-related clinical deterioration that occurred when Enlimomab was given in acute ischemic stroke.

Increased fasting plasma acylation-stimulating protein concentrations in nephrotic syndrome.

Acylation-stimulating protein (ASP) is an adipocyte-derived protein that has recently been suggested to play an important role in the regulation of lipoprotein metabolism and triglyceride (TG) storage. ASP also appears to have a role in the regulation of energy balance. In addition to its role as a hormonal regulator of body weight and energy expenditure, leptin is now implicated as a regulatory molecule in lipid metabolism. However, little is known about the alterations in fasting plasma ASP and leptin concentrations in the nephrotic syndrome. As hyperlipidemia is one of the most striking manifestations of the nephrotic syndrome, we have investigated fasting plasma ASP and leptin levels and their relation to lipid levels in this syndrome. Twenty-five patients with untreated nephrotic syndrome and 25 age-, sex-, and body mass index-matched healthy controls were included in the study. Fasting plasma lipoproteins, TG, total cholesterol, lipoprotein(a), apolipoprotein AI (apoAI), apoB, urinary protein, plasma albumin, third component of complement (C3), ASP, and leptin levels were measured in both groups. Total cholesterol, TG, low and very low density lipoproteins, lipoprotein(a), apoB, and urinary protein levels were increased in the patient group, whereas plasma albumin, high density lipoprotein cholesterol, and apoAI levels were decreased compared with those in the control group (P < 0.001). Plasma ASP levels were significantly higher in the patient group compared with the control subjects (133.72 +/- 65.14 vs. 29.93 +/- 12.68 nmol/liter; P < 0.001), whereas leptin (2.69 +/- 2.06 vs. 3.99 +/- 2.99 ng/ml; P = 0.118) and C3 (1.01 +/- 0.25 vs. 1.06 +/- 0.23 g/liter; P = 0.662) levels were not significantly different between the two groups. Plasma leptin levels were correlated with body mass index in both nephrotic patients (r(s) = 0.86; P < 0.001) and controls (r(s) = 0.98; P < 0.001), but were not correlated with the other parameters. Fasting ASP concentrations showed no correlation with body mass index, proteinuria, plasma albumin, leptin, or any lipid parameter in either group, but C3 levels (in patient group: r(s) = 0.92; P < 0.001; in control group: r(s) = 0.68; P < 0.001). Our findings showed that plasma ASP levels were significantly elevated, whereas leptin levels were normal in the nephrotic syndrome. Increased ASP levels in the setting of dyslipidemia in the nephrotic syndrome raise the possibility of an ASP receptor defect in adipocytes, which also suggests the existence of so-called ASP resistance. Moreover, it is possible that ASP activity is maximal, but cannot keep up with increased rates of lipid production by the liver. Thus, further studies are needed to elucidate the mechanism or source (adipocytes, the liver, or both) of elevated ASP concentrations in the nephrotic syndrome.

Plasma acylation-stimulating protein, adiponectin, leptin, and ghrelin before and after weight loss induced by gastric bypass surgery in morbidly obese subjects.

We examined fasting plasma insulin, acylation-stimulating protein (ASP), leptin, adiponectin, ghrelin, and metabolic/cardiovascular risk profile before and 15 +/- 6 months after isolated Roux-en-Y gastric bypass surgery in 50 morbidly obese subjects. Average preoperative plasma lipids were mostly normal, whereas ASP, insulin, and leptin were elevated, and adiponectin and ghrelin were decreased. Postoperatively, body weight decreased significantly (-36.4 +/- 9.6%) and was best predicted by preoperative adiponectin concentration in weight-stable subjects (r = -0.59; P = 0.02). Plasma lipids and insulin resistance improved, leptin and ASP decreased (-76.3 +/- 14.6% and -35.9 +/- 52.2%; P < 0.001), and adiponectin increased (50.1 +/- 47.0%; P < 0.001). The decrease in apolipoprotein B was best predicted by the decrease in ASP (r = 0.55; P = 0.009), whereas the improved postoperative insulin sensitivity was best predicted by the increase in adiponectin (r = 0.70; P = 0.01). Despite bypassing 95% of the stomach and isolating the fundus from contact with ingested nutrients, circulating ghrelin did not decrease after surgery. In fact, plasma ghrelin increased postoperatively in the subset of subjects undergoing active weight loss (+60.5 +/- 23.2%; P < 0.001); ghrelin, however, remained unchanged in weight-stable subjects. In summary, 1) preoperative adiponectin concentrations may be predictive of the extent of weight loss; 2) changes in ASP and adiponectin are predictive of decreased apolipoprotein B and improved insulin action, respectively; and 3) plasma ghrelin increases after gastric bypass surgery in patients experiencing active weight loss.

Improved glycemic control increases fasting plasma acylation-stimulating protein and decreases leptin concentrations in type II diabetic subjects.

Acylation-stimulating protein is an adipocyte-derived protein that has recently been suggested to play an important role in the regulation of triglyceride storage. To date, little information has been reported with regard to fasting acylation-stimulating protein levels and its relation to metabolic control, leptin, and/or lipids in subjects with diabetes mellitus. We therefore evaluated fasting acylation-stimulating protein, leptin, and lipid levels before and 4 months after improving glycemic control with sulfonylurea treatment in a group of poorly controlled obese women with type 2 diabetes and in age- and body mass index-matched nondiabetic obese women. Fasting plasma acylation-stimulating protein (49.67 +/- 19.73 vs. 48.49 +/- 20.70 nmol/liter) and leptin concentrations (33.7 +/- 23.2 vs. 26.2 +/- 10.6 ng/ml) were not significantly different between the groups. Improvement of glycemic control produced parallel falls in fasting blood glucose and hemoglobin A1c. Plasma leptin concentrations were also significantly reduced (33.69 +/- 23.2 vs. 22.73 +/- 11.26 ng/ml; P = 0.036), whereas fasting acylation-stimulating protein concentrations were significantly increased after treatment (48.49 +/- 20.70 vs. 72,82 +/- 29,72 nmol/liter; P = 0.004). Nevertheless, lipids and apolipoprotein B did not significantly improve. We could not find any correlation between elevated acylation-stimulating protein levels and changes in body mass index, glucose, insulin, hemoglobin A1c, leptin, or lipid levels. Similarly, the decrement in circulating leptin levels observed after treatment did not correlate with changes in the levels of glucose, insulin, hemoglobin A1c, or any lipid parameters. We conclude that improved glycemic control increases fasting acylation-stimulating protein and decreases leptin concentrations, but not corrects critical lipid abnormalities in type 2 obese diabetic subjects. Moreover, altered plasma acylation-stimulating protein levels are not associated with changes in body mass index or lipid, leptin, insulin, or glucose levels. Thus, our findings suggest that improved glycemic control or insulin resistance is not responsible for abnormal fatty acid trapping, and failure of lipids to improve after treatment in our patients is consistent with the acylation-stimulating protein resistance concept.

Human acylation stimulating protein enhances triacylglycerol biosynthesis in plant microsomes.

Diacylglycerol acyltransferase has a universal role in catalyzing the acyl-CoA-dependent formation of triacylglycerol in microorganisms, animals and plants. Acylation stimulating protein, from human blood, is known to enhance diacylglycerol acyltransferase activity and triacylglycerol biosynthesis in human adipocytes. In the current study, acylation stimulating protein was also shown to enhance diacylglycerol acyltransferase activity in microsomes from cell suspension cultures of oilseed rape. Enzyme stimulation occurred over the pH range of 6-9 but the degree of stimulation decreased with increasing ionic strength at pH 7.4. Varying acyl-CoA concentration did not affect the degree of stimulation. Membranes from triacylglycerol producing cells in plants and humans may have similar binding sites for acylation stimulating protein which have been preserved during molecular evolution. The results suggest that human acylation stimulating protein may be useful in modifying lipid biosynthesis in plants.

Addition of glucose to an oral fat load reduces postprandial free fatty acids and prevents the postprandial increase in complement component 3.

BACKGROUND: Elevated fasting plasma concentrations of complement component 3 (C3) are associated with elevated fasting and postprandial triacylglycerol concentrations, insulin resistance, obesity, and coronary artery disease. C3 is the central component of the complement system and the precursor of acylation-stimulating protein (ASP). Insulin and ASP are principal determinants of free fatty acid (FFA) trapping by adipose tissue. OBJECTIVE: Because controversy exists concerning postprandial changes in C3 and because meal composition may influence complement activation, we studied postprandial lipemia in relation to changes in plasma C3. DESIGN: After an overnight fast, 6 healthy men ( +/- SD age: 23 +/- 2 y) underwent 4 oral liquid challenges: fat (50 g/m(2) body surface), glucose (37.5 g/m(2)), fat and glucose (mixed test), and water (as a control test) in a random, crossover design. RESULTS: Plasma ASP concentrations did not change postprandially in any test. Changes in C3 concentration were observed only after the fat challenge: elevated concentrations occurred between 1 and 3 h, and a maximum increase of 11% occurred at 2 h (P = 0.05). Postprandial triacylglycerolemia did not differ significantly between the fat and mixed tests. The FFA response after the fat challenge was the highest of all the tests (P < 0.05 for all comparisons) and was accompanied by an increase in ketone bodies (maximum at 6 h); this increase did not occur after the mixed test, which suggests less hepatic FFA delivery. CONCLUSIONS: When glucose is added to an oral fat load, the postprandial FFA response is reduced, and the fat-specific increase in C3 is prevented. After ingestion of fat without glucose, the lack of insulin response may lead to C3-mediated peripheral FFA trapping, which probably serves as a backup system in case of insufficient or inefficient insulin-dependent FFA trapping.