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

From complement to complosome in non-alcoholic fatty liver disease: When location matters

Non-alcoholic fatty liver disease (NAFLD) is a growing public health threat and becoming the leading cause of liver transplantation. Nevertheless, no approved specific treatment is currently available for NAFLD. The pathogenesis of NAFLD is multifaceted and not yet fully understood. Accumulating evidence suggests a significant role of the complement system in the development and progression of NAFLD. Here, we provide an overview of the complement system, incorporating the novel concept of complosome, and summarise the up-to-date evidence elucidating the association between complement dysregulation and the pathogenesis of NAFLD. In this process, the extracellular complement system is activated through various pathways, thereby directly contributing to, or working together with other immune cells in the disease development and progression. We also introduce the complosome and assess the evidence that implicates its potential influence in NAFLD through its direct impact on hepatocytes or non-parenchymal liver cells. Additionally, we expound upon how complement system and the complosome may exert their effects in relation with hepatic zonation in NAFLD. Furthermore, we discuss the potential therapeutic implications of targeting the complement system, extracellularly and intracellularly, for NAFLD treatment. Finally, we present future perspectives towards a better understanding of the complement system's contribution to NAFLD.

Role of Complement and Complement-Related Adipokines in Regulation of Energy Metabolism and Fat Storage

Adipose tissue releases many cytokines and inflammatory factors described as adipokines. In obesity, adipokines released from expanding adipose tissue are implicated in disease progression and metabolic dysfunction. However, mechanisms controlling the progression of adiposity and metabolic complications are not fully understood. It has been suggested that expanding fat mass and sustained release of inflammatory adipokines in adipose tissue lead to hypoxia, oxidative stress, apoptosis, and cellular damage. These changes trigger an immune response involving infiltration of adipose tissue with immune cells, complement activation and generation of factors involved in opsonization and clearance of damaged cells. Abundant evidence now indicates that adipose tissue is an active secretory source of complement and complement-related adipokines that, in addition to their inflammatory role, contribute to the regulation of metabolic function. This article highlights advances in knowledge regarding the role of these adipokines in energy regulation of adipose tissue through modulating lipogenic and lipolytic pathways. Several adipokines will be discussed including adipsin, Factor H, properdin, C3a, Acylation-Stimulating Protein, C1q/TNF-related proteins, and response gene to complement-32 (RGC-32). Interactions between these factors will be described considering their immune-metabolic roles in the adipose tissue microenvironment and their potential contribution to progression of adiposity and metabolic dysfunction. The differential expression and the role of complement factors in gender-related fat partitioning will also be addressed. Identifying lipogenic adipokines and their specific autocrine/paracrine roles may provide means for adipose-tissue-targeted therapeutic interventions that may disrupt the vicious circle of adiposity and disease progression. © 2019 American Physiological Society. Compr Physiol 9:1411-1429, 2019.

The complement system in human cardiometabolic disease

The complement system has been implicated in obesity, fatty liver, diabetes and cardiovascular disease (CVD). Complement factors are produced in adipose tissue and appear to be involved in adipose tissue metabolism and local inflammation. Thereby complement links adipose tissue inflammation to systemic metabolic derangements, such as low-grade inflammation, insulin resistance and dyslipidaemia. Furthermore, complement has been implicated in pathophysiological mechanisms of diet- and alcohol induced liver damage, hyperglycaemia, endothelial dysfunction, atherosclerosis and fibrinolysis. In this review, we summarize current evidence on the role of the complement system in several processes of human cardiometabolic disease. C3 is the central component in complement activation, and has most widely been studied in humans. C3 concentrations are associated with insulin resistance, liver dysfunction, risk of the metabolic syndrome, type 2 diabetes and CVD. C3 can be activated by the classical, the lectin and the alternative pathway of complement activation; and downstream activation of C3 activates the terminal pathway. Complement may also be activated via extrinsic proteases of the coagulation, fibrinolysis and the kinin systems. Studies on the different complement activation pathways in human cardiometabolic disease are limited, but available evidence suggests that they may have distinct roles in processes underlying cardiometabolic disease. The lectin pathway appeared beneficial in some studies on type 2 diabetes and CVD, while factors of the classical and the alternative pathway were related to unfavourable cardiometabolic traits. The terminal complement pathway was also implicated in insulin resistance and liver disease, and appears to have a prominent role in acute and advanced CVD. The available human data suggest a complex and potentially causal role for the complement system in human cardiometabolic disease. Further, preferably longitudinal studies are needed to disentangle which aspects of the complement system and complement activation affect the different processes in human cardiometabolic disease.

The role of the complement system in metabolic organs and metabolic diseases

Emerging evidence points to a close crosstalk between metabolic organs and innate immunity in the course of metabolic disorders. In particular, cellular and humoral factors of innate immunity are thought to contribute to metabolic dysregulation of the adipose tissue or the liver, as well as to dysfunction of the pancreas; all these conditions are linked to the development of insulin resistance and diabetes mellitus. A central component of innate immunity is the complement system. Interestingly, the classical view of complement as a major system of host defense that copes with infections is changing to that of a multi-functional player in tissue homeostasis, degeneration, and regeneration. In the present review, we will discuss the link between complement and metabolic organs, focusing on the pancreas, adipose tissue, and liver and the diverse effects of complement system on metabolic disorders.

Up-regulation of the complement system in subcutaneous adipocytes from nonobese, hypertriglyceridemic subjects is associated with adipocyte insulin resistance

BACKGROUND

Dysfunctional adipose tissue plays an important role in the etiology of the metabolic syndrome, type 2 diabetes, and dyslipidemia. However, the molecular mechanisms underlying adipocyte dysfunction are incompletely understood.

AIM

The aim of the study was to identify differentially regulated pathways in sc adipocytes of dyslipidemic subjects.

METHODS

Whole-genome expression profiling was conducted on sc adipocytes from a discovery group of nine marginally overweight subjects with familial combined hyperlipidemia (FCHL) and nine controls of comparable body sizes as well as two independent confirmation groups. In this study, FCHL served as a model of familial insulin resistance and dyslipidemia, in the absence of frank obesity.

RESULTS

Functional analyses and gene set enrichment analysis using the Kyoto Encyclopedia of Genes and Genomes or a custom pathway database identified the complement system and complement regulators as one of the top up-regulated pathways in FCHL [false discovery rate (FDR) < 1E-30]. Higher adipocyte complement expression in FCHL was confirmed in the appropriate confirmation group. Higher complement gene expression was associated with lower adipocyte insulin receptor substrate-1 expression as marker of adipocyte insulin resistance, independent of age, sex, or disease status, and this association was corroborated in the two confirmation groups. Additionally, complement gene expression was associated with triglycerides in the discovery set and with triglycerides and/or waist circumference in the confirmation groups. Complement pathway up-regulation did not appear to be driven by hypertriglyceridemia because a 40% pharmacological reduction in triglycerides did not affect complement expression.

CONCLUSIONS

These findings point to an up-regulation of a complement-related transcriptome in sc adipocytes under metabolically stressed conditions, even in the absence of overt obesity. Such up-regulation may subsequently influence downstream processes, including macrophage infiltration into adipose tissue and adipocyte insulin resistance.

Complement C3 and cleavage products in cardiometabolic risk

This review summarizes available evidence on the role of serum complement component 3 (C3), produced by liver, adipocytes and activated macrophages at inflammation sites, and C3 cleavage products linking lipoproteins and metabolism to immunity. C3 and cleavage products are modified in several associated metabolic disorders including obesity, insulin resistance, type-2 diabetes, dyslipidemia, and cardiovascular diseases. Circulating C3 is independently and linearly associated with serum triglycerides, C-reactive protein (CRP), waist circumference and in some populations inversely with current smoking. The complement cascade is activated during myocardial ischemia and likely mediates immune and inflammatory responses in ischemic myocardium. Serum complement activation is elevated in unstable rather than stable angina pectoris suggesting added contribution to damage extension in acute coronary syndromes. In logistic regression models for incident metabolic syndrome (MetS), increasing C3 concentrations predicted MetS in women, after adjusting for continuous values of 3 major MetS components and other confounders, with a relative risk similar in magnitude to an established component suggesting elevated C3 likely constitutes part of the cluster of MetS in women. C3 interacts with MetS in men for independently conferring risk of incident type-2 diabetes and coronary heart disease (CHD). In women, though C3 is equally predictive of cardiometabolic risk, it is less so additively to MetS components or to CRP. Evidence suggests that circulating C3 might serve as a signal for an immune process that enhances - via mediation of increased apolipoprotein (apo) E levels - the development of dysfunctional apoA-I particles rendering them diabetogenic and atherogenic in populations prone to MetS or subsets of populations harboring impaired glucose tolerance. C3 activation also leads to production of chemoattractants C3a and C5a, and acylation stimulating protein (ASP, C3adesArg), a lipogenic hormone, which contribute additionally to the metabolic phenotypes generated. These observations have clinical and public health implications.

The association of 83 plasma proteins with CHD mortality, BMI, HDL-, and total-cholesterol in men: applying multivariate statistics to identify proteins with prognostic value and biological relevance

In this study, we applied the multivariate statistical tool Partial Least Squares (PLS) to analyze the relative importance of 83 plasma proteins in relation to coronary heart disease (CHD) mortality and the intermediate end points body mass index, HDL-cholesterol and total cholesterol. From a Dutch monitoring project for cardiovascular disease risk factors, men who died of CHD between initial participation (1987-1991) and end of follow-up (January 1, 2000) (N = 44) and matched controls (N = 44) were selected. Baseline plasma concentrations of proteins were measured by a multiplex immunoassay. With the use of PLS, we identified 15 proteins with prognostic value for CHD mortality and sets of proteins associated with the intermediate end points. Subsequently, sets of proteins and intermediate end points were analyzed together by Principal Components Analysis, indicating that proteins involved in inflammation explained most of the variance, followed by proteins involved in metabolism and proteins associated with total-C. This study is one of the first in which the association of a large number of plasma proteins with CHD mortality and intermediate end points is investigated by applying multivariate statistics, providing insight in the relationships among proteins, intermediate end points and CHD mortality, and a set of proteins with prognostic value.

Selenium intake reduces serum C3, an early marker of metabolic syndrome manifestations, in healthy young adults

OBJECTIVES

To evaluate the associations between serum complement factor 3 (C3) and several anthropometrical, biochemical and lifestyle features in healthy young adults, emphasizing on the putative effect of selenium intake on C3 concentrations.

METHODS

This study enrolled 100 healthy young adults aged 18-34 years. Anthropometric and blood pressure measurements and lifestyle features were analyzed. Fasting blood samples were collected for the measurement of glucose, total cholesterol, HDL-cholesterol, LDL-cholesterol, triacylglycerols and C3 concentrations. Nail samples were collected for the analysis of selenium concentrations.

RESULTS

Values of BMI (P=0.034), sum of skinfold thicknesses (STs) (P=0.021), body fat mass (BFM) (P=0.023), percentage of overweight subjects (P=0.007), serum triacylglycerols (P=0.012) and nail selenium (P=0.001) were significantly different between subjects above and below the median of serum C3 concentrations. The following correlations with serum C3 were identified tricipital ST (P=0.033), sum of STs (P=0.012), BMI (P=0.008), BFM (P=0.018), waist-to-height ratio (P=0.016), serum glucose (P=0.045), serum triacylglycerols (P=0.001) and nail selenium (P=0.006). Circulating C3 showed a positive association with several adiposity markers such as BMI (P=0.001), waist circumference (P=0.006), waist-to-height ratio (P=0.002), BFM (P=0.025), as well as serum glucose (P=0.027) and triacylglycerols (P<0.001), whereas nail selenium was a statistically significant negative predictor of C3 concentrations (P=0.018).

CONCLUSIONS

C3 seems to be related with selenium status and several anthropometrical and biochemical measurements linked to metabolic syndrome in apparently healthy young adults. These findings suggest a possible role for selenium intake in the modulation of C3, whose assessment may be an early marker of metabolic syndrome manifestations.

Increased plasma acylation-stimulating protein in pediatric proteinuric renal disease

Hyperlipidemia has been well recognized as a striking feature of nephrotic syndrome and other renal diseases. However, the underlying pathophysiological mechanisms still have not yet been elucidated. In this study, we evaluated acylation-stimulating protein (ASP) and complement component 3 (C3) in children (n=48) with various forms of proteinuric renal disease [nephrotic syndrome, acute poststreptococcal infection glomerulonephritis (APSGN), and lupus nephritis (LN)] in comparison with age- and gender-matched controls (n=279). In children with proteinuric renal disease, various aberrations in plasma lipids were noted, including increased triglyceride, cholesterol, and low-density lipoprotein cholesterol (LDL-C) (all p<0.0001). Whereas C3 was not altered in children with nephrotic syndrome (1.05+/-0.05 g/L vs. 1.29+/-0.04 controls), the decrease was pronounced in children with LN and APSGN (0.42+/-0.11, p<0.05 and 0.30+/-0.06, p<0.001, respectively). Plasma C3 correlated positively with lipid parameters [triglyceride, cholesterol, LDL-C, apolipoprotein B (apoB), high-density lipoprotein cholesterol (HDL-C) and apoA1] and inversely with total protein, blood urea nitrogen, and creatinine. By contrast, plasma ASP was significantly elevated in all proteinuric renal diseases (101.4+/-7.1 nmol/L nephrotic syndrome, 90.9+/-14.1 LN, and 81.8+/-7.2 APSGN vs. 44.3+/-1.5 controls, p<0.05 to p<0.001), and this increase was correlated with changes in lipid parameters (triglycerides and apoA1). In summary, these results demonstrate alterations in C3 and ASP that may contribute to or compensate for dyslipidemia.

Metformin decreases circulating acylation-stimulating protein levels in polycystic ovary syndrome

AIM

There are no studies that examine the circulating acylation-stimulating protein (ASP) levels in patients with polycystic ovary syndrome (PCOS). The present study was designed to determine the ASP levels in PCOS and to evaluate the effect of metformin on plasma fasting ASP concentrations.

METHODS

Twenty women with PCOS and 20 healthy controls matched for age and body mass index (BMI) were included in the study. We determined ASP and other biochemical parameters before and after treatment.

RESULTS

Baseline levels of plasma ASP, complement 3 (C3), waist-to-hip ratio (WHR), homeostasis model assessment-insulin resistance index (HOMA-IR), fasting insulin, triglycerides (TG) and very-low-density lipoprotein cholesterol (VLDL-C) were significantly higher in patients than in controls. After 3 months of metformin treatment, BMI, WHR, ASP, C3, fasting glucose, fasting insulin, HOMA-IR, total cholesterol, TG, VLDL-C and free testosterone decreased significantly, whereas apolipoprotein A-I and high-density lipoprotein cholesterol increased significantly.

CONCLUSIONS

The major novel information of the present study is that ASP and C3 values are markedly increased in non-obese patients with PCOS, with a decrease evidenced with metformin treatment.

Relationships among acylation stimulating protein, adiponectin and complement C3 in lean vs obese type 2 diabetes

OBJECTIVE

The purpose of this study was to determine the relationships between adipocyte hormones acylation stimulating protein (ASP), adiponectin, complement C3 (C3) (ASP precursor) and insulin, C-reactive protein (CRP), lipid profiles and insulin resistance in lean vs obese type 2 diabetes subjects.

SUBJECTS

Lean type 2 diabetes subjects (DL n = 27) vs obese type 2 diabetes subjects (DO n = 55) were compared to age-matched nondiabetic groups (Obese, OB n = 55 and control, CTL n = 50).

RESULTS

The DO group demonstrated significant increases in plasma ASP and C3 with decreases in plasma adiponectin as compared to CTL. Interestingly, these increases in ASP and C3 were as high, or greater, in the DL group in spite of normal weight. By contrast adiponectin in the DL group was comparable to CTL, in spite of marked insulin resistance. C3 correlated with insulin, glucose and homeostasis model assessment of insulin resistance (HOMA-IR); ASP correlated with body mass index (BMI), glucose, insulin and plasma lipid parameters (non-esterified fatty acids (NEFA), triglyceride, cholesterol and apolipoprotein B). Adiponectin correlated with BMI, glucose, NEFA, triglyceride, high-density lipoprotein cholesterol and apolipoprotein A1 but not HOMA-IR, ASP or C3. CRP correlated only with HOMA-IR.

CONCLUSION

Increased ASP and C3 are both associated with diabetes and related lipid factors but are not regulated coordinately. Adiponectin appears to be more closely related to body size (decreased in obese subjects) than insulin resistance in these subjects.

Regulation of Complement C3 Expression by the Bile Acid Receptor FXR

The farnesoid X receptor (FXR; NR1H4) is an intracellular bile acid-sensing transcription factor that plays a critical role in the regulation of synthesis and transport of bile acids as well as lipid metabolism. Although the reciprocal relationship between bile acid and triglyceride levels is well known, the mechanism underlying this link is not clearly defined. In this study, we demonstrate that FXR regulates the expression of at least two secreted factors, complement component C3 and FGF15, the rat ortholog of FGF19, known to influence lipid metabolism. The analysis of the human complement C3 gene reveals the presence of functional FXR response elements in the proximal promoter of C3. Furthermore, rats given a single dose of an FXR agonist exhibit an increase in the plasma concentration of complement C3 protein. These studies demonstrate a mechanism by which FXR, a nuclear receptor with a limited tissue expression pattern, regulates secretion of factors that ultimately can affect lipid metabolism in an endocrine or paracrine manner.

Diabetes, lipids, and adipocyte secretagogues

That obesity is associated with insulin resistance and type II diabetes mellitus is well accepted. Overloading of white adipose tissue beyond its storage capacity leads to lipid disorders in non-adipose tissues, namely skeletal and cardiac muscles, pancreas, and liver, effects that are often mediated through increased non-esterified fatty acid fluxes. This in turn leads to a tissue-specific disordered insulin response and increased lipid deposition and lipotoxicity, coupled to abnormal plasma metabolic and (or) lipoprotein profiles. Thus, the importance of functional adipocytes is crucial, as highlighted by the disorders seen in both "too much" (obesity) and "too little" (lipodystrophy) white adipose tissue. However, beyond its capacity for fat storage, white adipose tissue is now well recognised as an endocrine tissue producing multiple hormones whose plasma levels are altered in obese, insulin-resistant, and diabetic subjects. The consequence of these hormonal alterations with respect to both glucose and lipid metabolism in insulin target tissues is just beginning to be understood. The present review will focus on a number of these hormones: acylation-stimulating protein, leptin, adiponectin, tumour necrosis factor alpha, interleukin-6, and resistin, defining their changes induced in obesity and diabetes mellitus and highlighting their functional properties that may protect or worsen lipid metabolism.

Detection of retained microbubbles in carotid arteries with real-time low mechanical index imaging in the setting of endothelial dysfunction

OBJECTIVES

We sought to determine if intravenously injected microbubbles would be retained by the carotid arteries (CAs) in the setting of endothelial dysfunction (ED) using a linear transducer equipped with a low mechanical index pulse sequence scheme (PSS).

BACKGROUND

Microbubbles normally pass freely through large and small vessels but are retained in regions with ED. New high-frequency low mechanical index PSS can potentially be utilized to image these retained microbubbles.

METHODS

Intravenous albumin- and lipid-encapsulated microbubbles were administered in seven pigs while imaging the CAs before and after a 20% intralipid infusion to induce hypertriglyceridemia. The degree of microbubble retention was quantified by measuring endothelial acoustic intensity (AI) after clearance of free-flowing microbubbles. Microbubble adherence was also evaluated after selective balloon injury of the CAs. The CA diameter responses to acetylcholine were quantified.

RESULTS

After induction of hypertriglyceridemia, adherence of albumin-encapsulated microbubbles was visually evident in all CAs, and endothelial AI increased significantly (p < 0.001 compared with baseline). The CA responses to acetylcholine went from vasodilation at baseline to vasoconstriction during hypertriglyceridemia. Endothelial AI also increased in the balloon-stretched vessels (p < 0.01 compared with uninjured vessels) after albumin-encapsulated microbubble injection, with a ring of microbubbles selectively adhering to the injured segment. This retention was not observed with lipid-encapsulated microbubbles. Scanning electron microscopy confirmed that albumin-coated microbubbles adhered to endothelial cells.

CONCLUSIONS

Retention of intravenously injected albumin microbubbles occurs in the setting of both global and regional ED in large vessels and can be noninvasively imaged with high-frequency low mechanical index PSS.

Evidence for a complex risk profile in obese postmenopausal Turkish women with hypertriglyceridaemia and elevated apolipoprotein B

The aim of the present study was to examine possible pathophysiological relationships among a wide array of proatherogenic risk factors in postmenopausal women. Fasting lipids, apoB (apolipoprotein B), BMI (body mass index) and waist circumference were measured in 178 women (59.4±7.2 years) from the Turkish Adult Risk Factor Study. Fasting levels of complement C3, insulin, SHBG (sex hormone-binding globulin), cortisol, oestradiol, testosterone and DHEA-S (dehydroepiandrosterone sulphate) were also determined. This is the first study to examine the relationships of all these variables with apoB. In the first of two different approaches, three groups of obese women were compared. Group 1 comprised women who were normolipidaemic with normal apoB; group 2, women who were hypertriglyceridaemic, but with normal apoB; and group 3, women who were hypertriglyceridaemic with elevated apoB. Complement C3, fasting insulin and glucose were significantly higher and HDL-C (high-density lipoprotein-cholesterol) and SHBG levels were significantly lower in group 3 than in group 1. In the former group, the testosterone/SHBG ratio tended to be higher, indicating more free testosterone, than in group 1. The mean risk score in group 3 and the odds ratio for coronary disease by logistic regression analysis were significantly higher, 2.56 (confidence intervals, 1.12–5.85; P=0.026), compared with the two other groups combined. In examining the whole group, apoB levels correlated significantly with a wider array of pro-atherogenic risk factors than did LDL-C (low-density lipoprotein-cholesterol), particularly being linked to complement C3 and glucose, as well as the risk score. Complement C3 demonstrated the widest associations and was significantly linked with BMI, waist circumference, insulin, glucose, fibrinogen, triacylglycerols (triglycerides) and apoB and was inversely correlated with HDL-C and SHBG. SHBG was also correlated inversely with a wide spectrum of risk variables. In summary, in Turkish women, apoB was linked with a complex array of proatherogenic risk factors, and hypertriglyceridaemia with elevated apoB was associated with a higher risk of coronary disease.

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.

Lipaemia, Inflammation and Atherosclerosis

Atherosclerosis is the major cause of death in the world. Fasting and postprandial hyperlipidaemia are important risk factors for coronary heart disease (CHD). Recent developments have undoubtedly indicated that inflammation is pathophysiologically closely linked to atherogenesis and its clinical consequences. Inflammatory markers such as C-reactive protein (CRP), leucocyte count and complement component 3 (C3) have been linked to CHD and to hyperlipidaemia and several other CHD risk factors. Increases in these markers may result from activation of endothelial cells (CRP, leucocytes, C3), disturbances in adipose tissue fatty acid metabolism (CRP, C3), or from direct effects of CHD risk factors (leucocytes). It has been shown that lipoproteins, triglycerides, fatty acids and glucose can activate endothelial cells, most probably as a result of the production of reactive oxygen species. Similar mechanisms may also lead to leucocyte activation. Increases in triglycerides, fatty acids and glucose are common disturbances in the metabolic syndrome and are most prominent in the postprandial phase. People are in a postprandial state most of the day, and this phase is proatherogenic. Inhibition of the activation of leucocytes, endothelial cells, or both, is an interesting target for intervention, as activation is obligatory for adherence of leucocytes to the endothelium, thereby initiating atherogenesis. Potential interventions include the use of unsaturated long-chain fatty acids, polyphenols, antioxidants, angiotensin converting enzyme inhibitors and high-dose aspirin, which have direct anti-inflammatory and antiatherogenic effects. Furthermore, peroxisome proliferator activating receptor gamma (PPARgamma) agonists and statins have similar properties, which are in part independent of their lipid-lowering effects.

Effects of atorvastatin on fasting and postprandial complement component 3 response in familial combined hyperlipidemia

VLDL overproduction by enhanced hepatic FFA flux is a major characteristic of familial combined hyperlipidemia (FCHL). The postprandial complement component 3 (C3) response has been associated with impaired postprandial FFA metabolism in FCHL. We investigated the effects of 16 weeks of treatment with atorvastatin on postprandial C3 and lipid changes in 12 FCHL patients. Atorvastatin significantly lowered fasting plasma C3 and triglyceride (TG) in FCHL. Fasting TG and insulin sensitivity were the best predictors of fasting and postprandial C3. Postprandial triglyceridemia and C3 response, estimated as area under the curve (AUC), were significantly lowered by atorvastatin by 19% and 12%, respectively, albeit still elevated, compared with 10 matched controls. Postprandial FFA-AUC and postheparin plasma lipolytic activities remained unchanged after atorvastatin, suggesting no major effect on lipolysis. After atorvastatin, postprandial hydroxybutyric acid-AUC, which was elevated in untreated FCHL patients, was decreased, reaching values similar to those in controls. The present data show reduction of postprandial hepatic FFA flux in FCHL by atorvastatin, providing an additional mechanistic explanation for the reduction of VLDL secretion reported previously for atorvastatin. This was accompanied by a decrease in fasting plasma C3 concentrations and a blunted postprandial C3 response to an acute oral fat load.

Fasting acylation-stimulating protein is predictive of postprandial triglyceride clearance

Postprandial plasma triglyceride (ppTG) and NEFA clearance were stratified by plasma acylation-stimulating protein (ASP) and gender to determine the contribution of fasting ASP in a normal population (70 men; 71 women). In the highest ASP tertile only, ASP decreased over 8 h (90 +/- 9.7 nM to 70 +/- 5.9 nM, P<0.05 males; 61.9 +/- 4.0 nM to 45.6 +/- 6.2 nM, P<0.01 females). Fasting ASP correlated positively with ppTG response. ppTG (P<0.0001, 2-way ANOVA, both genders) and NEFA levels progressively increased from lowest to highest ASP tertile, with the greatest differences in males. By stepwise multiple regression, the best prediction of ppTG was: (fasting ASP + apolipoprotein B + insulin + TG; r=0.806) for men and (fasting ASP + total cholesterol; r=0.574) for women. Leptin, body mass index, and other fasting variables did not improve the prediction. Thus, in men and women, ASP significantly predicted ppTG and NEFA clearance and, based on lower ASP, women may be more ASP sensitive than men. Plasma ASP may be useful as a fasting variable that will provide additional information regarding ppTG and NEFA clearance.

Acylation-stimulating protein precursor proteins in adipose tissue in human obesity

Recent reports have suggested a link between acylation-stimulating protein (ASP) and complement C3 with obesity, insulin resistance, coronary artery disease, and hyperlipidemia. Our aim was to examine the mRNA expression of C3 and other factors related to ASP production (such as factor B and adipsin) in adipose tissue. The influence of gender and obesity was examined in subcutaneous (SC) and omental (OM) tissues from 16 males and 16 females with body mass index (BMI) from 20 to 54 kg/m(2). The results demonstrate that factor B mRNA expression is higher in males than females in both SC and OM tissues. In female SC tissue, C3 and adipsin mRNA decrease with increasing BMI (r = 0.557, P =.025 and r = 0.717 P =.002, respectively), with no change in factor B. By contrast, in males there was a pronounced increase in C3, adipsin, and factor B in OM tissue with increasing BMI (r = 0.759 P =.001, r = 0.650 P =.006, and r = 0.568 P =.022, respectively). Of note, however, in both men and women there was a marked increase in the OM/SC ratio of C3 and adipsin with increasing BMI. These results suggest that in female SC adipose tissue, there is downregulation of factors related to ASP production in obesity, perhaps to limit further expansion of adipose tissue. In males, there is increased expression in OM tissue. In addition, relative OM/SC expression increases with obesity and these changes may contribute to the development of visceral 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.

Genetic influences contributing to LDL particle size in familial combined hyperlipidaemia

The nature of the genetic and environmental factors influencing low density lipoprotein (LDL) particle size in patients with familial combined hyperlipidaemia (FCHL) is under debate. We measured LDL peak particle size in 553 subjects belonging to 48 Finnish FCHL families. Individuals with high triglyceride (TG) concentrations (phenotype IV) or combined hyperlipidaemia (phenotype IIB) had significantly smaller LDL particles than those with hypercholesterolaemia (phenotype IIA) or unaffected subjects (P<0.001). In stepwise regression analyses, serum TGs (r(2)=43%, P<0.001) and high density lipoprotein cholesterol (HDL-C) (r(2)=4.5%, P<0.001) were the only significant predictors of LDL peak particle size. Familial correlations support the conclusion that LDL peak particle size is familial, and most probably influenced by genes in these families. Segregation analysis of LDL peak particle size, a quantitative trait, was performed to model this genetic influence. Our results suggest a polygenic background for LDL size with a recessive major gene that may contribute to large LDL peak particle size in women. Serum TG and HDL-C concentrations predict the majority of variations in LDL particle size.