Changes in circulating adiponectin, leptin, glucose and C-peptide in patients with ketosis-prone diabetes.

AIMS: To evaluate circulating adipokines in people with ketosis-prone diabetes, a heterogeneous disorder characterized by unprovoked ketoacidosis in people with previously unrecognized diabetes. METHODS: Patients presenting with ketoacidosis with no previous diabetes diagnosis were compared with patients with previously established Type 1 diabetes. Baseline assessments of autoimmune status (A+/A-), and ß-cell function (B+/B-), as well as leptin and adiponectin levels during a standardized mixed-meal tolerance test of 120 min, were performed. In all, 20 patients with heterogeneous ketosis-prone diabetes and 12 patients with Type 1 diabetes were evaluated at baseline, 12 and 24 months. RESULTS: At baseline, during a mixed-meal tolerance test, glucose and adiponectin concentrations were lower in patients with ketosis-prone diabetes than in those with Type 1 diabetes (P = 0.0023 and P < 0.0001, respectively), whereas C-peptide concentrations were higher, with no significant difference in leptin concentrations. Within 12 months, 11 patients with ketosis-prone diabetes (all A-/B+) were discontinued from insulin treatment (ketosis-prone diabetes - insulin group), while nine patients (four A-B-, four A+B- and one A-B+) were maintained on insulin (ketosis-prone diabetes + insulin group). Fasting C-peptide levels increased significantly over 24 months in the ketosis-prone diabetes - insulin group (P = 0.01), while HbA1c levels decreased (P < 0.0001). Overall, the ketosis-prone diabetes - insulin group had a higher BMI (P = 0.018), yet a lower fasting glucose concentration (P = 0.003) compared with the ketosis-prone diabetes + insulin group. Over 24 months, the mixed-meal tolerance test area-under-the-curve of C-peptide increased in the ketosis-prone diabetes - insulin group, with no change in ketosis-prone diabetes + insulin (P < 0.0001). At 24 months, in spite of the higher BMI in the ketosis-prone diabetes - insulin group, mixed-meal tolerance test glucose and leptin concentrations were significantly lower (P < 0.0001 and P = 0.017, respectively), while adiponectin levels were higher (P = 0.023) compared with the ketosis-prone diabetes + insulin group. CONCLUSIONS: In spite of the higher BMI in the ketosis-prone diabetes - insulin group, lower leptin and higher adiponectin levels may contribute to improved ß-cell function and insulin sensitivity, as evidenced by lower glucose and higher C-peptide levels. This allows insulin therapy to be withdrawn.

Relationships among acylation-stimulating protein, insulin resistance, lipometabolism, and fetal growth in gestational diabetes mellitus women.

The aim of this study was to investigate the potential relationship between acylation-stimulating protein (ASP), insulin resistance, lipometabolism, the intrauterine metabolic environment and fetal growth in well-controlled gestational diabetes mellitus (GDM) women. A total of 55 well-controlled GDM women, 66 pregnant women with normal glucose tolerance (NGT) and their newborns, were included in this study. Fasting maternal and cord blood ASP, serum lipid profiles, glucose level, insulin level, HOMA-IR, in addition to neonatal anthropometry data, were measured. Maternal blood ASP in GDM is higher than that in NGT. In the GDM group, maternal blood ASP has a positive correlation with TG, FFA and HOMA-IR. Maternal and cord blood ASP levels of LGA fetuses correlate with elevated birth weight and SF4. Similarly, cord blood ASP levels of LGA fetuses also correlate with birth weight and SF4 in the NGT group. The maternal blood ASP level of GDM mothers is associated with lipometabolism, insulin resistance and LGA fetal growth. Nevertheless, the cord blood ASP level correlates with FFA of GDM mothers, LGA fetal growth of GDM and NGT mothers. ASP may be a biomarker for evaluating insulin resistance of GDM and LGA fetal growth.

Effect of secretin on preadipocyte, differentiating and mature adipocyte functions.

OBJECTIVE: Several gastrointestinal peptides are now recognized to have target functions beyond the intestinal wall, including effects on adipocytes. Secretin (SEC), one of the first identified, has not been evaluated in this context. METHODS: Using cultured 3T3-L1 preadipocytes, adipocytes and primary rat adipocytes we evaluated the effect of SEC on cell proliferation, mitochondrial activity, differentiation, triglyceride (TG) synthesis, lipolysis as well expression of the SEC receptor (SCTR) in rodent and human adipose tissues. RESULTS: In preadipocytes, SEC significantly increased mitochondrial activity (115%; P<0.01), thymidine incorporation (149.7%; P<0.05) and C/EBPß expression (123.4%; P<0.05). During standard differentiation, SCTR mRNA increased up to a maximum of ninefold (P<0.001). In human adipose tissue, SCTR correlated with body mass index and plasma insulin, and SCTR mRNA expression was also detected in rat adipose tissues. SEC supplementation during differentiation enhanced TG accumulation (+138%; P<0.01). In mature adipocytes, SEC increased fatty acid (FA) uptake (186%; P<0.01), adiponectin and monocyte chemotactic protein-1 secretion (+142% and +149%, respectively; P<0.05) and mRNA expression of PPARγ (+206%; P<0.01), FABP4 (+164%; P<0.001), DGAT-1 (+144%; P<0.01), adiponectin (+138%; P<0.001) and CD36 (+149%; P<0.05). In primary rat adipocytes, SEC also increased FA uptake (137%; P<0.05). Pretreatment with a SEC antagonist impaired SEC-induced FA uptake and cAMP accumulation. SEC treatment simultaneously stimulated lipolysis measured as glycerol release in 3T3-L1 adipocytes and rat adipose tissue. CONCLUSION: The present results suggest that SEC is a potent modulator of adipocyte functions, demonstrating overall a role in enhanced substrate cycling.

Randomized clinical trial of the impact of insulin therapy on liver function in patients undergoing major liver resection.

BACKGROUND: Postoperative liver dysfunction is the major source of morbidity and mortality in patients undergoing partial hepatectomy. This study tested the benefits of a metabolic support protocol based on insulin infusion, for reducing liver dysfunction following hepatic resection. METHODS: Consecutive consenting patients scheduled for liver resection were randomized to receive preoperative dextrose infusion followed by insulin therapy using the hyperinsulinaemic normoglycaemic clamp protocol (n = 29) or standard therapy (control group, n = 27). Patients in the insulin therapy group followed a strict dietary regimen for 24 h before surgery. Intravenous dextrose was started at 2 mg per kg per min the night before and continued until surgery. Hyperinsulinaemic therapy for a total of 24 h was initiated at 2 munits per kg per min at induction of anaesthesia, and continued at 1 munit per kg per min after surgery. Normoglycaemia was maintained (3.5-6.0 mmol/l). Control subjects received no additional dietary supplement and a conventional insulin sliding scale during fasting. All patients were tested serially to evaluate liver function using the Schindl score. Liver tissue samples were collected at two time points during surgery to measure glycogen levels. RESULTS: Demographics were similar in the two groups. More liver dysfunction occurred in the control cohort (liver dysfunction score range 0-8 versus 0-4 with insulin therapy; P = 0.031). Median (interquartile range) liver glycogen content was 278 (153-312) and 431 (334-459) µmol/g respectively (P = 0.011). The number of complications rose with increasing severity of postoperative liver dysfunction (P = 0.032) CONCLUSION: The glucose-insulin protocol reduced postoperative liver dysfunction and improved liver glycogen content. REGISTRATION NUMBER: NCT00774098 (http://www.clinicaltrials.gov).

The beta-1 adrenergic antagonist, atenolol, decreases acylation stimulating protein, exercise capacity and plasma free fatty acids in men with type 2 diabetes.

BACKGROUND AND AIMS: Atenolol is a beta-1 adrenergic antagonist commonly prescribed for the treatment of systemic hypertension or coronary artery disease yet its use in individuals with type 2 diabetes mellitus (T2DM) is controversial due to potentially negative side effects on insulin resistance. Non-esterified fatty acid (NEFA) metabolism is altered in T2DM especially under conditions of metabolic stress such as exercise or the postprandial state. We evaluated atenolol effects on circulating NEFA and related hormones in men with T2DM during acute cardiorespiratory exercise in both the fasting and postprandial state, including the adipokine acylation stimulating protein (ASP) which stimulates adipose tissue NEFA uptake. METHODS AND RESULTS: Ten men with T2DM underwent four 1-h exercise sessions at 60% of their maximal oxygen uptake (VO(2max)) under the following conditions: 1) fasting (F), and 2) 2 h postprandial (PP) without medication; and 3) fasting (F-Atenolol), and 4) 2 h postprandial (PP-Atenolol) after a one-week treatment with atenolol. Results were tested for the effects of atenolol via two-way ANOVA for the F vs F-Atenolol and PP vs PP-Atenolol states separately. Atenolol treatment decreased fasting and postprandial glycerol (p < 0.0001) and NEFA (p < 0.0001), postprandial epinephrine (p = 0.048), postprandial cortisol (p = 0.02), postprandial ASP (p = 0.04) and postprandial dopamine (p < 0.004). CONCLUSION: Atenolol alters fatty acid metabolism and associated metabolic hormones including ASP during exercise in men with T2DM and its effects are more apparent during conditions of stress such as the postprandial state, acute exercise and obesity.

Growth patterns during childhood and the relationship with acylation-stimulating protein.

BACKGROUND/OBJECTIVES: Acylation-stimulating protein (ASP) is an adipose tissue-derived hormone, which stimulates glucose and free fatty acid (FFA) uptake into adipocytes. Changes in ASP metabolism are associated with alterations in lipid metabolism. As postnatal catch-up growth has been associated with dyslipidaemia in later life, we investigated the association between ASP and birth size, adult size and different growth patterns during childhood. METHODS: The associations were investigated by multiple regression analyses in 285 young adults, aged 18-24. Subsequently, differences in ASP were analysed in four clinically relevant subgroups, young adults either born small for gestational age with short stature (SGA-S) or with catch-up growth (SGA-CU), or born appropriate for gestational age with idiopathic short stature (ISS) or with normal stature (controls). RESULTS: Weight gain during childhood, particularly fat accumulation, was positively related to ASP levels in early adulthood, independent of birth size, age and gender. Foetal growth, reflected by birth size, was not related to ASP levels. Between the subgroups, no differences in ASP were found, but SGA-CU and ISS subjects had significantly higher levels of FFA. CONCLUSION: Exaggerated weight gain during childhood, but not foetal growth, contributes to alterations in ASP metabolism, which may be associated with impaired FFA uptake and delayed triglycerides clearance. Therefore, exaggerated weight gain during childhood should be prevented.

Serum resistin correlates with central obesity but weakly with insulin resistance in Chinese children and adolescents.

OBJECTIVE: Resistin has been linked with obesity and hypothesized as a potential marker of insulin resistance in addition to being linked with acute inflammation. However, these links are still highly controversial in humans. Our goal was to examine resistin levels in relation to obesity, insulin resistance and inflammation markers in a large population of Asian children and adolescents. METHODS: Children and adolescents (n=3472) aged 6-18 years, boys (n=1765) and girls (n=1707), were assessed for body size parameters, pubertal development, blood lipids, glucose, insulin, resistin, C-reactive protein (CRP), adiponectin and complement C3 (C3) levels. RESULTS: Resistin increased with central obesity in both genders but not with simple adiposity in boys. Several markers associated with central obesity correlated in a gender-specific fashion with plasma resistin. Waist circumference, fat-mass percentage, waist-to-height ratio and body mass index (BMI) positively correlated with resistin in both genders. Blood lipids such as triglycerides, nonesterified fatty acids (NEFA) and low-density lipoprotein cholesterol, diastolic and systolic blood pressure correlated positively with resistin in boys. NEFA, high-density lipoprotein cholesterol (negatively) and inflammation markers, such as CRP and C3, positively correlated with resistin in girls. There was no correlation between resistin and adiponectin, and no association of adiponectin with resistin quintiles in either boys or girls. In both boys and girls, resistin tended to decrease with age, with girls having higher levels than boys. Few indices of insulin resistance were linked with plasma resistin in either gender. CONCLUSION: In this population, plasma resistin levels are a weak biochemical marker of metabolic dysfunction defined by central obesity, adiposity and inflammation and does not predict insulin resistance. Only a small proportion of resistin variation can be explained by factors related to metabolic syndrome, suggesting that resistin is not strongly implicated in a concentration-dependent fashion in any of the examined pathologies.

Regulation of leptin, adiponectin and acylation-stimulating protein by hyperinsulinaemia and hyperglycaemia in vivo in healthy lean young men.

AIM: Both type 1 and 2 diabetes are associated with differential regulation of leptin, adiponectin and ASP. Our aim was to examine whether or not acute hyperinsulinaemia and/or hyperglycaemia per se have differential regulation of these hormones in healthy subjects. METHODS: We examined changes in leptin, adiponectin and ASP concentrations and subcutaneous white adipose tissue mRNA expression with 3-hour hyperinsulinaemic (HI, n=10), hyperglycaemic (HG, n=7) and hyperinsulinaemic-hyperglycaemic (HGHI, n=8) clamps in healthy lean young men. As somatostatin was used for the HG and HGHI clamps, a control somatostatin clamp was carried out (n=4). Changes in the expression of HKII and p85alpha Pi3K were examined as positive controls for the induction of gene expression by the insulin pathway. RESULTS: HI, HG and HGHI clamps increased expression of HKII and p85alpha Pi3K while somatostatin did not. The HI clamp decreased serum adiponectin (-15%, P<0.001) and increased serum leptin (+11%, P=0.031), while the HG clamp reduced serum leptin (-20%, P=0.003). The HGHI clamp increased serum ASP (+21%, P=0.047) and expression of C3 (+26%, P=0.018) and leptin (+50%, P=0.024). Interestingly, the control somatostatin clamp suppressed both serum leptin (-17%, P=0.043) and adiponectin (-7%, P=0.020). CONCLUSION: HG and/or HI per se regulated the concentrations and expression of leptin, adiponectin and ASP in healthy lean young men, suggesting a contribution to dysregulation of these hormones in diabetes.

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.

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.

Increased levels of acylation-stimulating protein in interleukin-6-deficient (IL-6(-/-)) mice.

IL-6-deficient (IL-6(-/-)) mice develop obesity at 6-7 months of age. To elucidate the mechanisms of this mature-onset obesity, global gene expression profiles of 3-month-old preobese IL-6(-/-) were compared with those of IL-6(+/+) mice using DNA arrays. Genes that were up-regulated in IL-6(-/-) mice included the factors transthyretin and properdin in white adipose tissue and adipsin in muscle. These factors have been shown to influence the formation of acylation-stimulating protein (ASP), a cleavage product of complement C3. ASP stimulates the synthesis of triacylglycerol in adipocytes, and ASP-deficient mice are resistant to diet-induced obesity. In line with the increases in transthyretin, properdin, and adipsin, ASP levels in serum were increased by 31-54% in IL-6(-/-) compared with IL-6(+/+) mice. Furthermore, IL-6 replacement treatment in IL-6(-/-) mice decreased ASP levels significantly by 25-60%. In conclusion, ASP levels are increased in preobese IL-6(-/-) mice. This increase may result in increased triacylglycerol formation and uptake in IL-6(-/-) adipocytes and thereby contribute to the development of obesity in IL-6(-/-) mice.

Lifestyle behaviours and components of energy balance as independent predictors of ghrelin and adiponectin in young non-obese women.

AIM: Dysregulation of the normal levels of ghrelin, leptin and adiponectin in young non-obese subjects could promote food intake, diabetes and cardiovascular disease in later stages of life. Little information is available on how plasmatic concentrations of these hormones may be influenced by eating habits and/or components of energy balance in a young population, which if known, could facilitate their voluntary regulation. METHODS: In this cross-sectional study we examined the predictors of fasting plasma ghrelin, adiponectin and leptin in a population of well-characterized young non-obese women (N = 63). Energy intake was assessed by 24-hour dietary recall, resting metabolic rate (RMR) by indirect calorimetry, physical activity energy expenditure (PAEE) by tri-axial accelerometer, physical fitness by VO(2 peak), and eating behaviors by self administrated questionnaire. RESULTS: Lower RMR and higher HDL-cholesterol were independent predictors of higher plasma ghrelin explaining 17.6% of its variation even after correcting for BMI. Higher total or central fat mass was the only predictor of higher plasma leptin, and no other variable added any power to the prediction equation. Finally, higher energy intake and waist circumference and lower PAEE predicted lower plasma adiponectin in young non-obese women, explaining 43% of the variation in its concentrations even after correcting for total or central fat mass. CONCLUSION: Components of the energy balance (ie: energy intake and/or expenditure) influence adiponectin and ghrelin circulating levels. That is, higher energy intake and lower physical activity independently predict lower adiponectin concentrations, whereas lower resting metabolic rate independently predicts higher ghrelin levels in young non-obese women. Prospective studies are needed to examine whether circulating concentrations of ghrelin and adiponectin can be voluntarily regulated by lifestyle interventions.

Characterization and modulation of LP(a) in human hepatoma HEPG2 cells.

HepG2 cells have been widely used to study factors which affect the secretion of apoB100 lipoprotein particles. The objectives of this study were to determine if Lp(a) particles were present in conditioned medium from HepG2 cells and if so, was this accumulation affected by factors which alter apoB100 lipoprotein metabolism. The data demonstrate that Lp(a) accumulated in the medium in a time dependent manner over a 48 h incubation period. Ultracentrifugation fractionation and Western blot analysis demonstrated that lipoprotein particles containing apo(a) in complex with apoB100 were present at a density consistent with human plasma Lp(a). Incubation of the HepG2 cells with LDL or VLDL caused increases in Lp(a) accumulation in the medium (+33% +/- 14%, P NS and 56% +/- 21%, P < 0.05, respectively). In contrast, apo(a) mRNA decreased (-17% +/- 3%, P < 0.01 for both LDL and VLDL incubation). Increasing concentrations of amino acids in the medium resulted in progressively less Lp(a) and apoB100 in the medium, the effect being greater on apoB100. ApoB100 mRNA levels decreased with incubation of HepG2 cells with amino acids (-22% +/- 10%, P < 0.06) whereas apo(a) mRNA levels increased significantly (+47% +/- 14%, P < 0.005). Taken together, our data show that HepG2 cells express mRNA for apo(a), and accumulate Lp(a) in the medium. The close correlation of medium Lp(a) levels with medium apoB100 levels, and not with apo(a) mRNA levels, suggests that medium Lp(a) accumulation may be a function of lipoprotein synthesis and secretion and is consistent with extracellular assembly of Lp(a) lipoprotein particles.

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.

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.

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.

Acylation stimulating protein and triacylglycerol synthesis: potential drug targets?

Triacylglycerol storage in adipose tissue is mediated by a host of transporters, enzymes and binding proteins. Additionally, several hormones (both autocrine and endocrine) are known to interact with cell surface receptors and modulate triacylglycerol synthesis (such as acylation stimulating protein, ASP). The many proteins involved contribute to the robustness of the system and, in most cases, deletion of a single gene is not deleterious and adipose tissue is preserved. On the other hand, this does not mean that gene disruption is not without effect, and in fact often results in a leaner, and presumably "healthier" mouse. These insights provide valuable indications for potential drug tools to delay and/or reverse obesity. In this review we examine the potential of ASP as a candidate target. ASP deficiency in mice decreases adipose tissue mass, increases insulin sensitivity and energy expenditure even in obese ob/ob mice, suggesting that partial interference of ASP action could be advantageous. ASP interacts with a specific cell surface receptor present in adipose tissue and certain structural components, such as the tightly folded core region, are implicated in activity. We propose that interference of the ASP-receptor interaction using an antagonist offers future prospect for an anti-obesity target.

Effect of moderate hypertriglyceridemia on the relation of plasma total and LDL apo B levels.

The risk of premature coronary artery disease is related to an important degree to the number of particles of low density lipoproteins (LDL) in plasma, an estimate given by measurement of LDL apo B. In clinical practise, though it is total, not LDL apo B, which is measured. The purpose of the present study therefore was to compare plasma total and LDL apo B in the presence and absence of moderate hypertriglyceridemia. The results demonstrate that within the range of plasma triglyceride levels examined, i.e., values of triglyceride up to 500 mg/dl, there is close correspondence between total and LDL apo B, with the latter more than 90% of the former. VLDL composition was also examined and two patterns found in hypertriglyceridemic patients: those with normal apo B had markedly lipid enriched VLDL while those with elevated apo B had VLDL which was normal in composition except for a moderate increase in triglyceride content. Thus total apo B within the circumstances studied reflects principally LDL apo B. Moreover measurement of apo B allows distinction between two different forms of hypertriglyceridemia, only one of which - that with an increased LDL particle number - has previous work shown to be associated with increased coronary risk. Total apo B, therefore, provides additional information not available from conventional plasma and lipoprotein lipids which allows more precise physiologic classification and may lead to more rational choice of pharmacologic therapy in normolipidemic and hypertriglyceridemic patients.

Divergent responses of the liver to increased delivery of glucose or fatty acids: implications for the pathogenesis of type IV hyperlipoproteinemia.

This study examines the patterns of response of primary cultures of hamster hepatocytes to increased delivery of glucose or oleate. Increased glucose in the medium produced: (1) increased triglyceride in the cells and the medium; (2) no change in cholesterol ester in the cells or the medium; (3) no change in apo B100 secreted into the medium; (4) more apo B100 particles within the VLDL range with an increase in the VLDL triglyceride to apo B100 ratio. By contrast, increased oleate in the medium resulted in: (1) increased triglyceride in the cells and the medium; (2) increased cholesterol ester in the cells and the medium; and (3) increased apo B100 secreted into the medium. Important differences in the intracellular metabolism of triglyceride and cholesterol ester were also documented. Under all circumstances, there was substantially more radiolabelled triglyceride (overall eight times more) in the cell than in the medium, indicating that up to 90% of the newly synthesized triglyceride enters the cellular pool rather than being secreted with apo B100. By contrast, almost half of the newly synthesized cholesterol ester molecules were secreted with apo B100, pointing to an equal probability of entering the cell storage pool as opposed to being secreted. The data establish therefore two patterns of response of the liver to increased triglyceride synthesis depending on whether the substrate drive is glucose or oleate.

Effects of albumin on lipid synthesis, apo B-100 secretion, and LDL catabolism in HepG2 cells.

This study examines the effects of extracellular albumin on hepatic apo B-100 metabolism. To do so, a transformed human liver cell line, HepG2, was used as a hepatocyte model and the concentration of albumin in the medium was varied between 0 and 5 g%. Apo B-100 and apo A1 concentrations in the medium were determined by specific enzyme-linked immunoassay (ELISA) and intracellular synthesis of cholesterol ester and triglyceride were determined by addition of appropriate radiolabels to the medium. The data demonstrate that the reduction of extracellular albumin concentration resulted in increased apo B-100 concentration in the medium. Apo A1 secretion, however, was unaffected. While the differences in apo B-100 concentration in the medium were statistically significant (33% +/- 7%, P < 0.0025, 0 g% albumin compared to 5 g% albumin in the medium), the absolute magnitude of the effect under these conditions was relatively modest. Nevertheless, the changes were consistent and evident over incubation periods as long as 8 days. Of interest, although triglyceride synthesis was unaffected, cholesterol ester synthesis changed such that as albumin concentration decreased, synthesis of cholesterol ester increased paralleling the changes in apo B-100 (170% +/- 9%, P < 0.005). These findings were extended by studying interventions which altered cholesterol ester synthesis. Addition of the compound 58-035 (5 micrograms/ml, a specific inhibitor of acylcholesterol acyltransferase activity) resulted in substantial inhibition of cholesterol ester synthesis (39% to 66%, P < 0.025 and P < 0.005, respectively) and apo B-100 concentrations in the medium which decreased by 20% to 28%, P < 0.025. Triglyceride synthesis, in contrast, increased significantly by 32% P < 0.025. Therefore, addition of 58-035 confirmed the previous findings of a parallel relation between cholesterol ester synthesis and apo B-100 concentration in the medium. Nonetheless, albumin still had an additional inhibitory effect on cholesterol ester and apo B-100 secretion. Of interest, when chylomicron remnants (25 micrograms/ml cholesterol), which cause apo B-100 secretion to increase by more than threefold, were added to the medium, albumin now had a more pronounced absolute effect on apo B-100 secretion with a 48% inhibition observed as albumin was increased from 0 to 5 g% in the medium (P < 0.0125). The effect of extracellular albumin on the low density lipoprotein (LDL) pathway was also examined. No differences in non-specific cell association component were detected.(ABSTRACT TRUNCATED AT 400 WORDS)