Evaluation of chylomicron effect on ASP production in 3T3-L1 adipocytes

C3 and alternative pathway components are associated with an adverse lipoprotein subclass profile: The CODAM study

BACKGROUND

Plasma lipoproteins contain heterogeneous subclasses. Previous studies on the associations of the complement system with lipids and lipoproteins are mainly limited to the major lipid classes, and associations of complement with lipoprotein subclass characteristics remain unknown.

OBJECTIVE

We investigated the associations of C3 and other components of the alternative complement pathway with plasma lipoprotein subclass profile.

METHODS

Plasma complement concentrations (complement component 3 [C3], properdin, factor H, factor D, MASP-3, C3a, Bb), and lipoprotein subclass profile (as measured by nuclear magnetic resonance spectroscopy) were obtained in 523 participants (59.6 ± 6.9 years, 60.8% men) of the Cohort on Diabetes and Atherosclerosis Maastricht (CODAM) study. Multiple linear regression was used to investigate the associations of C3 (primary determinant) and other alternative pathway components (secondary determinants) with characteristics (particle concentration and size [main outcomes], and lipid contents [secondary outcomes]) of 14 lipoprotein subclasses, ranging from extremely large VLDL to small HDL (all standardized [std] values).

RESULTS

Participants with higher C3 concentrations had more circulating VLDL (stdβs ranging from 0.27 to 0.36), IDL and LDL (stdβs ranging from 0.14 to 0.17), and small HDL (stdβ = 0.21). In contrast, they had fewer very large and large HDL particles (stdβs = -0.36). In persons with higher C3 concentrations, all lipoprotein subclasses were enriched in triglycerides. Similar but weaker associations were observed for properdin, factor H, factor D, and MASP-3, but not for C3a and Bb.

CONCLUSIONS

The alternative complement pathway, and most prominently C3, is associated with an adverse lipoprotein subclass profile that is characterized by more triglyceride-enriched lipoproteins but fewer large HDL.

Acylation stimulating protein, complement C3 and lipid metabolism in ketosis-prone diabetic subjects

Background

Ketosis-prone diabetes (KPDM) is new-onset diabetic ketoacidosis without precipitating factors in non-type 1 diabetic patients; after management, some are withdrawn from exogenous insulin, although determining factors remain unclear.

Methods

Twenty KPDM patients and twelve type 1 diabetic patients (T1DM), evaluated at baseline, 12 and 24 months with/without insulin maintenance underwent a standardized mixed-meal tolerance test (MMTT) for 2 h.

Results

At baseline, triglyceride and C3 were higher during MMTT in KPDM vs. T1DM (p<0.0001) with no differences in non-esterified fatty acids (NEFA) while Acylation Stimulating Protein (ASP) tended to be higher. Within 12 months, 11 KPDM were withdrawn from insulin treatment (KPDM-ins), while 9 were maintained (KPDM+ins). NEFA was lower in KPDM-ins vs. KPDM+ins at baseline (p = 0.0006), 12 months (p<0.0001) and 24 months (p<0.0001) during MMTT. NEFA in KPDM-ins decreased over 30–120 minutes (p<0.05), but not in KPDM+ins. Overall, C3 was higher in KPDM-ins vs KPDM+ins at 12 months (p = 0.0081) and 24 months (p = 0.0019), while ASP was lower at baseline (p = 0.0024) and 12 months (p = 0.0281), with a decrease in ASP/C3 ratio.

Conclusions

Notwithstanding greater adiposity in KPDM-ins, greater NEFA decreases and lower ASP levels during MMTT suggest better insulin and ASP sensitivity in these patients.

Association of immune and metabolic receptors C5aR and C5L2 with adiposity in women

Adipose tissue receptors C5aR and C5L2 and their heterodimerization/functionality and interaction with ligands C5a and acylation stimulating protein (ASP) have been evaluated in cell and rodent studies. Their contribution to obesity factors in humans remains unclear. We hypothesized that C5a receptors, classically required for host defense, are also associated with adiposity. Anthropometry and fasting blood parameters were measured in 136 women divided by body mass index (BMI): normal/overweight (≤30 kg/m(2); n = 34), obese I (≤45 kg/m(2); n = 33), obese II (≤51 kg/m(2); n = 33), and obese III (≤80 kg/m(2); n = 36). Subcutaneous and omental adipose tissue C5aR and C5L2 expression were analysed. C5L2 expression was comparable between subcutaneous and omental across all BMI groups. Plasma ASP and ASP/omental C5L2 expression increased with BMI (P < 0.001 and P < 0.01, resp.). While plasma C5a was unchanged, C5aR expression decreased with increasing BMI in subcutaneous and omental tissues (P < 0.01 and P < 0.05, resp.), with subcutaneous omental depots. Omental C5L2/C5aR ratio increased with BMI (P < 0.01) with correlations between C5L2/C5aR and waist circumference, HDL-C, and adiponectin. Tissue and BMI differences in receptors and ligands, particularly in omental, suggest relationship to metabolic disturbances and highlight adipose-immune interactions.

A new recombinant pituitary adenylate cyclase-activating peptide-derived peptide efficiently promotes glucose uptake and glucose-dependent insulin secretion

The recombinant peptide, DBAYL, a promising therapeutic peptide for type 2 diabetes, is a new, potent, and highly selective agonist for VPAC2 generated through site-directed mutagenesis based on sequence alignments of pituitary adenylate cyclase-activating peptide (PACAP), vasoactive intestinal peptide (VIP), and related analogs. The recombinant DBAYL was used to evaluate its effect and mechanism in blood glucose metabolism and utilization. As much as 28.9 mg recombinant DBAYL peptide with purity over 98% can be obtained from 1 l of Luria-Bertani medium culture by the method established in this study and the prepared DBAYL with four mutations (N10Q, V18L, N29Q, and M added to the N-terminal) were much more stable than BAY55-9837. The half-life of recombinant DBAYL was about 25 folds compared with that of BAY55-9837 in vitro. The bioactivity assay of DBAYL showed that it displaced [(125)I]PACAP38 and [(125)I]VIP from VPAC2 with a half-maximal inhibitory concentration of 48.4 ± 6.9 and 47.1 ± 4.9 nM, respectively, which were significantly lower than that of BAY55-9837, one established VPAC2 agonists. DBAYL enhances the cAMP accumulation in CHO cells expressing human VPAC2 with a half-maximal stimulatory concentration (EC(50)) of 0.68 nM, whereas the receptor potency of DBAYL at human VPAC1 (EC(50) of 737 nM) was only 1/1083 of that at human VPAC2, and DBAYL had no activity toward human PAC1 receptor. Western blot analysis of the key proteins of insulin receptor signaling pathway: insulin receptor substrate 1 (IRS-1) and glucose transporter 4 (GLUT4) indicated that the DBAYL could significantly induce the insulin-stimulated IRS-1 and GLUT4 expression more efficiently than BAY55-9837 and VIP in adipocytes. Compared with BAY55-9837 and PACAP38, the recombinant peptide DBAYL can more efficiently promote insulin release and decrease plasma glucose level in Institute of Cancer Research (ICR) mice. These results suggested that DBAYL could efficiently improve glucose uptake and glucose-dependent insulin secretion by VPAC2-mediated effect.

CD55 deficiency protects against atherosclerosis in ApoE-deficient mice via C3a modulation of lipid metabolism

Atherosclerosis, the leading cause of death in the Western world, is driven by chronic inflammation within the artery wall. Elements of the complement cascade are implicated in the pathogenesis, because complement proteins and their activation products are found in the atherosclerotic plaque. We examined the role of CD55, a membrane inhibitor of the complement component 3 (C3) convertase, which converts C3 into C3a and C3b, in atherosclerosis. CD55-deficient (CD55^−/−) mice were crossed onto the atherosclerosis-prone apolipoprotein E (apoE)-deficient (apoE^−/−) background. High fat–fed male apoE^−/−/CD55^−/− mice were strongly protected from developing atherosclerosis compared with apoE^−/− controls. Lipid profiling showed significantly lower levels of triglycerides, nonesterified fatty acids, and cholesterol in apoE^−/−/CD55^−/− mice than that in controls after high-fat feeding, whereas body fat in apoE^−/−/CD55^−/− mice content was increased. Plasma levels of C3 fell, whereas concentrations of C3adesArg (alias acylation stimulating protein; ASP), produced by serum carboxypeptidase N–mediated desargination of C3a, increased in nonfasted high fat–fed apoE^−/−/CD55^−/− mice, indicating complement activation. Thus, complement dysregulation in the absence of CD55 provoked increased C3adesArg production that, in turn, caused altered lipid handling, resulting in atheroprotection and increased adiposity. Interventions that target complement activation in adipose tissue should be explored as lipid-decreasing strategies.