Serum amyloid A is found on ApoB-containing lipoproteins in obese humans with diabetes.

OBJECTIVE: In murine models of obesity/diabetes, there is an increase in plasma serum amyloid A (SAA) levels along with redistribution of SAA from high-density lipoprotein (HDL) to apolipoprotein B (apoB)-containing lipoprotein particles, namely, low-density lipoprotein and very low-density lipoprotein. The goal of this study was to determine if obesity is associated with similar SAA lipoprotein redistribution in humans. DESIGN AND METHODS: Three groups of obese individuals were recruited from a weight loss clinic: healthy obese (n = 14), metabolic syndrome (MetS) obese (n = 8), and obese with type 2 diabetes (n = 6). Plasma was separated into lipoprotein fractions by fast protein liquid chromatography, and SAA was measured in lipid fractions using enzyme-linked immunosorbent assay and Western blotting. RESULTS: Only the obese diabetic group had SAA detectable in apoB-containing lipoproteins, and SAA reverted back to HDL with active weight loss. CONCLUSIONS: In human subjects, SAA is found in apoB-containing lipoprotein particles only in obese subjects with type 2 diabetes, but not in healthy obese or obese subjects with MetS.

Elevated IgG levels against specific bacterial antigens in obese patients with diabetes and in mice with diet-induced obesity and glucose intolerance.

High fat diets increase the risk for insulin resistance by promoting inflammation. The cause of inflammation is unclear, but germfree mouse studies have implicated commensal gut bacteria. We tested whether diet-induced obesity, diabetes, and inflammation are associated with anti-bacterial IgG. Blood from lean and obese healthy volunteers or obese patients with diabetes were analyzed by ELISA for IgG against extracts of potentially pathogenic and pro-biotic strains of Escherichia coli (LF-82 and Nissle), Bacteroides thetaiotaomicron, and Lactobacillus acidophilus, and for circulating tumor necrosis factor α (TNFα). C57Bl/6 mice were fed low- or high-fat diets (10% or 60% kcal from fat) for 10 weeks and tested for anti-bacterial IgG, bodyweight, fasting glucose, and inflammation. Obese diabetic patients had significantly more IgG against extracts of E. coli LF-82 compared with lean controls, whereas IgG against extracts of the other bacteria was unchanged. Circulating TNFα was elevated and correlated with IgG against the LF-82 extract. Mice fed high-fat diets had increased fasting glucose levels, elevated TNFα and neutrophils, and significantly more IgG against the LF-82 extracts. Diabetes in obesity is characterized by increased IgG against specific bacterial antigens. Specific commensal bacteria may mediate inflammatory effects of high-fat diets.

Nascent HDL formation by hepatocytes is reduced by the concerted action of serum amyloid A and endothelial lipase.

Inflammation is associated with significant decreases in plasma HDL-cholesterol (HDL-C) and apoA-I levels. Endothelial lipase (EL) is known to be an important determinant of HDL-C in mice and in humans and is upregulated during inflammation. In this study, we investigated whether serum amyloid A (SAA), an HDL apolipoprotein highly induced during inflammation, alters the ability of EL to metabolize HDL. We determined that EL hydrolyzes SAA-enriched HDL in vitro without liberating lipid-free apoA-I. Coexpression of SAA and EL in mice by adenoviral vector produced a significantly greater reduction in HDL-C and apoA-I than a corresponding level of expression of either SAA or EL alone. The loss of HDL occurred without any evidence of HDL remodeling to smaller particles that would be expected to have more rapid turnover. Studies with primary hepatocytes demonstrated that coexpression of SAA and EL markedly impeded ABCA1-mediated lipidation of apoA-I to form nascent HDL. Our findings suggest that a reduction in nascent HDL formation may be partly responsible for reduced HDL-C during inflammation when both EL and SAA are known to be upregulated.

ATP binding cassette G1-dependent cholesterol efflux during inflammation.

ATP binding cassette transporter G1 (ABCG1) mediates the transport of cellular cholesterol to HDL, and it plays a key role in maintaining macrophage cholesterol homeostasis. During inflammation, HDL undergoes substantial remodeling, acquiring lipid changes and serum amyloid A (SAA) as a major apolipoprotein. In the current study, we investigated whether remodeling of HDL that occurs during acute inflammation impacts ABCG1-dependent efflux. Our data indicate that lipid free SAA acts similarly to apolipoprotein A-I (apoA-I) in mediating sequential efflux from ABCA1 and ABCG1. Compared with normal mouse HDL, acute phase (AP) mouse HDL containing SAA exhibited a modest but significant 17% increase in ABCG1-dependent efflux. Interestingly, AP HDL isolated from mice lacking SAA (SAAKO mice) was even more effective in promoting ABCG1 efflux. Hydrolysis with Group IIA secretory phospholipase A(2) (sPLA(2)-IIA) significantly reduced the ability of AP HDL from SAAKO mice to serve as a substrate for ABCG1-mediated cholesterol transfer, indicating that phospholipid (PL) enrichment, and not the presence of SAA, is responsible for alterations in efflux. AP human HDL, which is not PL-enriched, was somewhat less effective in mediating ABCG1-dependent efflux compared with normal human HDL. Our data indicate that inflammatory remodeling of HDL impacts ABCG1-dependent efflux independent of SAA.

High-density lipoprotein and the acute phase response.

PURPOSE OF REVIEW: Inflammation and the concomitant acute phase response induce marked changes in the lipoprotein profile, particularly the high-density lipoprotein (HDL) fraction. The present review describes the transfer proteins and lipases that remodel HDL and regulate its plasma levels, discusses the changes occurring in their activities during inflammation, and the influence of this altered remodeling on HDL function. The review will also discuss the contribution of the ATP-binding-membrane-cassette transporters to the protective actions of HDL. RECENT FINDINGS: Studies using different models showed that remodeling of acute phase HDL in vitro generates pre-beta migrating particles capable of cholesterol efflux. Induction of the acute phase response in humans resulted in a reduction of HDL phospholipids without a change in HDL-cholesterol. However, the capacity of HDL to promote cholesterol efflux ex vivo was impaired. Studies with ATP-binding-membrane-cassette transporter A1 and ATP-binding-membrane-cassette transporter G1 knockout mice demonstrated anti-inflammatory roles for these transporters by virtue of reducing cell-membrane-free cholesterol and lipid raft content, thus attenuating proinflammatory signaling pathways. SUMMARY: It is well known that HDL has anti-inflammatory properties that are diminished during inflammation. Acute phase HDL contains serum amyloid A that can be liberated during remodeling by cholesteryl ester transfer protein and secretory phospholipase A2, or other inflammatory factors. The ability of serum amyloid A and apolipoprotein A-I to promote cholesterol efflux may confer protective effects during the acute phase response.

SR-BI selective lipid uptake: subsequent metabolism of acute phase HDL.

OBJECTIVE: The purpose of this study was to investigate the interaction of SAA and SR-BI in remodeling of acute phase HDL (AP HDL). METHODS AND RESULTS: We used SAA and SR-BI adenoviral vector expression models to study the interaction between these entities. SR-BI processing of mouse AP HDL generated progressively smaller discreet HDL particles with distinct apolipoprotein compositions. SR-BI actions segregated apolipoproteins with the smallest particles containing only apoA-I. Larger remnants contained apoA-I, apoA-II, and SAA. Small apoA-I only particles failed to associate with preformed HDL, whereas larger remnants readily did. The presence of SAA on SR-BI-processed HDL particles propelled apoA-I to a small lipid-poor form and accelerated apoA-I catabolism. CONCLUSIONS: Data indicate that after core and surface HDL lipid perturbation by SR-BI, SAA propels apoA-I to a small lipid-poor form while accelerating HDL metabolism.

Scavenger receptor class B type I protein as an independent predictor of high-density lipoprotein cholesterol levels in subjects with hyperalphalipoproteinemia.

CONTEXT: In mice, scavenger receptor class B, type I (SR-BI) receptor protein deficiency is associated with elevated high-density lipoprotein (HDL)-cholesterol (HDL-C) levels. OBJECTIVE: Our objective was to determine the relationship between SR-BI protein and HDL-C levels in humans. DESIGN: This was a prospective study of adults with hyperalphalipoproteinemia. Fasting blood was obtained for lipid and lipoprotein measurement, genomic DNA, and monocyte-derived macrophages. SR-BI protein levels were measured by Western blots, and SR-BI activity was measured by cholesteryl ester (CE) uptake of each donor's radiolabeled HDL with their monocyte-derived macrophages, or by degradation and specific cell association of dual-labeled HDL in vitro. SETTING: The study was performed in a tertiary university teaching hospital. RESULTS: The mean age was 57.2 +/- 10.9 yr (n = 65). SR-BI protein levels were inversely associated with HDL-C levels (P < 0.002), HDL particle size (P < 0.05), and positively associated with CE uptake (P < 0.004); there was no association with plasma apolipoprotein levels. SR-BI protein levels (P = 0.01) were independent predictors of HDL-C levels. Subjects who were carriers of the A allele for the rs4238001 (glycine to serine at position 2) polymorphism [single nucleotide polymorphism (SNP)] had lower SR-BI protein levels (P = 0.01), whereas carriers of the C allele for the rs2278986 SNP also had lower SR-BI protein levels (P = 0.02). Body mass index (P = 0.05), rs4238001 (P = 0.01), and rs2278986 (P = 0.01) SNPs were independent predictors of SR-BI protein levels. In vitro studies of murine macrophages stably expressing the glycine to serine at position 2 SNP showed less degradation (P < 0.0004) and specific cell association (P < 0.0004) of [(125)I, (3)H]-CE-labeled HDL. CONCLUSIONS: SR-BI protein has an independent effect on HDL-C levels in women with hyperalphalipoproteinemia. Two SNPs were significantly associated with lower SR-BI protein levels.

HDL remodeling during the acute phase response.

OBJECTIVE: The purpose of this study was to examine the interactive action of serum amyloid A (SAA), group IIA secretory phospholipase A(2) (sPLA(2)-IIA), and cholesteryl ester transfer protein (CETP) on HDL remodeling and cholesterol efflux during the acute phase (AP) response elicited in humans after cardiac surgery. METHODS AND RESULTS: Plasma was collected from patients before (pre-AP), 24 hours after (AP-1 d), and 5 days after cardiac surgery (AP-5 d). SAA levels were increased 16-fold in AP-1 d samples. The activity of sPLA(2)-IIA was increased from 77.7+/-38.3 U/mL (pre-AP) to 281.4+/-57.1 U/mL (AP-1 d; P<0.001). CETP mass and activity reduction was commensurate to the reduction of HDL cholesterol levels. The combined action of SAA, sPLA(2)-IIA, and CETP in vitro markedly remodeled HDL with the generation of lipid-poor apoA-I from both pre-AP and AP-1 d HDL. The net result of this remodeling was a relative preservation of ABCA1- and ABCG1-dependent cholesterol efflux during the acute phase response. CONCLUSIONS: Our results show that the many and complex changes in plasma proteins during the acute phase response markedly remodel HDL with functional implications, particularly the relative retention of cholesterol efflux capacity.

Dietary fish oil alters cardiomyocyte Ca2+ dynamics and antioxidant status.

The n-3 polyunsaturated fatty acids (PUFAs) found in fish oil (FO) have been shown to protect against reperfusion arrhythmias, a manifestation of reperfusion injury, which is believed to be induced by the formation of reactive oxygen species (ROS) and intracellular calcium (Ca2+) overload. Adult rats fed a diet supplemented with 10% FO had a higher proportion of myocardial n-3 PUFAs and increased expression of antioxidant enzymes compared with the saturated fat (SF)-supplemented group. Addition of hydrogen peroxide (H2O2) to cardiomyocytes isolated from rats in the SF-supplemented group increased the proportions of cardiomyocytes contracting in an asynchronous manner, increased the rate of Ca2+ influx, and increased the diastolic and systolic [Ca2+]i compared with the FO group. H2O2 exposure increased the membrane fluidity of cardiomyocytes from the FO group. These results demonstrate that dietary FO supplementation is associated with a reduction in the susceptibility of myocytes to ROS-induced injury and this may be related to membrane incorporation of n-3 PUFAs, increased antioxidant defenses, changes in cardiomyocyte membrane fluidity, and the ability to prevent rises in cellular Ca2+ in response to ROS.

Apolipoproteins regulate the kinetics of endothelial lipase-mediated hydrolysis of phospholipids in reconstituted high-density lipoproteins.

Endothelial lipase (EL) is a newly identified member of the triglyceride lipase gene family that hydrolyzes high-density lipoprotein (HDL) phospholipids. This study investigates the ability of the major apolipoproteins of rHDL to regulate the kinetics of EL-mediated phospholipid hydrolysis in well-characterized, homogeneous preparations of spherical rHDL. The rHDL contained either apoA-I as the only apolipoprotein, (A-I)rHDL, apoA-II as the only apolipoprotein, (A-II)rHDL, or apoA-I as well as apoA-II, (A-I/A-II)rHDL. The rHDL were comparable in terms of size and lipid composition and contained cholesteryl esters (CE) as their sole core lipid. Phospholipid hydrolysis was quantitated as the mass of nonesterified fatty acids (NEFA) released from the rHDL during incubation with EL. The V(max) of phospholipid hydrolysis for (A-I/A-II)rHDL [391.9 +/- 12.9 nmol of NEFA formed (mL of EL)(-1) h(-1)] was greater than (A-I)rHDL [152.8 +/- 4.7 nmol of NEFA formed (mL of EL)(-1) h(-1)]. The energy of activation (E(a)) for the hydrolysis reactions was calculated to be 52.1 and 34.8 kJ mol(-1) for (A-I)rHDL and (A-I/A-II)rHDL, respectively. Minimal phospholipid hydrolysis was observed for the (A-II)rHDL. Kinetic analysis showed that EL has a higher affinity for the phospholipids in (A-I)rHDL [K(m)(app) = 0.10 +/- 0.01 mM] than in (A-I/A-II)rHDL [K(m)(app) = 0.27 +/- 0.03 mM]. Furthermore, (A-I)rHDL is a competitive inhibitor of the EL-mediated phospholipid hydrolysis of (A-I/A-II)rHDL. These results establish that apolipoproteins are major determinants of the kinetics of EL-mediated phospholipid hydrolysis in rHDL.

Dietary fish oil increases acetylcholine- and eicosanoid-induced contractility of isolated rat ileum.

The long-chain (n-3) polyunsaturated fatty acids (PUFA) have been reported to exhibit health benefits and healing properties for the gastrointestinal tract. The aim of this study was to investigate the effects of dietary fish oil supplementation on the in vitro contractility of gut tissue. Rats (9 wk old) were fed synthetic diets supplemented with 170 g/kg Sunola oil (SO; 850 g/kg as oleic acid [18:1(n-9)]) or with 100 g/kg of the SO replaced by saturated animal fat (SF) or fish oil (FO) for 4 wk. In the colon, there was no difference in the sensitivity (50% effective concentration) or the maximal contraction among the three dietary groups induced by acetylcholine or 8-iso-prostaglandin (PG)E(2) with the rat colon being relatively insensitive to the thromboxane mimetic U-46619. However, in the ileum, the FO group had greater maximal contractions induced by acetylcholine and 8-iso-PGE(2) compared with the SO and SF groups (P < 0.05), and greater maximal contractions induced by PGE(2), PGF(2alpha) and U-46619 compared with the SF group (P < 0.05). FO feeding increased the incorporation of (n-3) PUFA (eicosapentaenoic [20:5(n-3)], docosapentaenoic [22:5(n-3)] and docosahexaenoic acids [22:6(n-3) primarily at the expense of (n-6) PUFA (linoleic [18:2(n-6)] and arachidonic acids [20:4(n-6)]) in the ileum and colon phospholipid fatty acids (P < 0.05). The FO group had a lower cecal digesta pH (P < 0.001) and a greater butyrate concentration than the SF group (P < 0.05). These results suggest that dietary (n-3) PUFA may modulate the contractility of the small intestine.