Increased Plasma Apo Research Articles

Strong effects of the ABCA1 agonist CS6253 on Amyloidβ42/40 ratio and lipoproteins in cynomolgus monkeys

AbstractBackgroundATI has discovered a novel molecule, CS6253, for hereditary Apolipoprotein E4 (ApoE4) associated Alzheimer’s disease (AD), which is highly differentiated from other molecules in development by its focus on cholesterol transport. CS6253 is a 26mer peptide optimized for ATP binding cassette transporter A1 (ABCA1) mediated cholesterol efflux, in the brain a rate‐limiting step in cholesterol transport from cells to ApoE. ABCA1 activity, as well as CS6253 in AD mouse models, is associated with improvement in AD pathology.In preparation for human studies, we investigated the effects of the ABCA1 agonist peptide CS6253 on amyloid‐β peptides (Aβ) and lipoproteins in plasma and cerebrospinal fluid (CSF) of cynomolgus monkeys, a species with amyloid and lipoprotein metabolism similar to humans.MethodsCS6253 peptide was injected intravenously to cynomolgus monkeys at various doses in three different studies, 1) a pharmacokinetics (PK) study, 2) a dose‐range finding (DRF) study, and 3) a 30‐day Good Laboratory Practice (GLP) toxicology study. Plasma and CSF samples were collected at several time points before and after treatment. Levels of cholesterol, triglyceride (TG), lipoprotein particles, apolipoproteins, and Aβ were measured using ELISA, ion‐mobility analysis, and asymmetric flow field flow fractionation (AF4). The relationship between the change in levels of these biomarkers was analyzed using multiple linear regression models and linear mixed‐effects models.ResultsCS6253 intravenous injection, within minutes, induced an increase in small, plasma high‐density lipoprotein (HDL) particles. Plasma TG, ApoE, and Aβ42/40 ratio were transiently increased following CS‐6253 intravenous injection, and a non‐significant decrease in CSF APP and Aβ42 was observed. CS‐6253 in plasma displaced ApoE from HDL to intermediate‐density‐ and low density‐lipoprotein (IDL/LDL) sized particles paralleled by transient reductions in total cholesterol and HDL‐cholesterol. In contrast to plasma, CS6253 had no effect on the assessed CSF apolipoproteins or lipids.ConclusionsIn cynomolgus monkeys administration of the ABCA1 agonist CS6253 transiently increased plasma ApoE and TGs which was paralleled by plasma Aβ42/40 ratio increase, providing a strong rationale for following these markers in ensuing human studies.

Plasma ApoE elevations are associated with NAFLD: The PREVEND Study.

Non-alcoholic fatty liver disease (NAFLD) is featured by increased plasma very low density lipoproteins (VLDL). The extent to which plasma apolipoprotein E (ApoE) levels are elevated in NAFLD is unclear. We determined whether plasma ApoE is elevated in subjects with suspected NAFLD. Plasma ApoE and genotypes were determined in 6,762 participants of the Prevention of Renal and Vascular End-Stage Disease (PREVEND) cohort. A Fatty Liver Index (FLI) ≥ 60 was used as a proxy of NAFLD. A total of 1,834 participants had a FLI ≥ 60, which coincided with increased triglycerides, non-HDL cholesterol, ApoB and ApoE (all P<0.001). In multivariable linear regression analysis, plasma ApoE levels were positively associated with an elevated FLI when taking account of ApoE genotypes and other clinical and laboratory covariates (fully adjusted model: β = 0.201, P<0.001). Stratified analysis for ApoE genotypes (ApoE ε3ε3 homozygotes, ApoE ε2 carriers, and ApoE ε3ε4 and ε4ε4 carriers combined), also showed positive associations of plasma ApoE levels with an elevated FLI in each group (all P<0.001). In conclusion, it is suggested that NAFLD is characterized by increased plasma ApoE levels, even when taking account of the various ApoE genotypes. Increased plasma ApoE may contribute to altered VLDL metabolism and to increased atherosclerosis susceptibility in NAFLD.

Differential Methylation in APOE (Chr19; Exon Four; from 44,909,188 to 44,909,373/hg38) and Increased Apolipoprotein E Plasma Levels in Subjects with Mild Cognitive Impairment.

Background: Biomarkers are essential for identification of individuals at high risk of mild cognitive impairment (MCI) for potential prevention of dementia. We investigated DNA methylation in the APOE gene and apolipoprotein E (ApoE) plasma levels as MCI biomarkers in Colombian subjects with MCI and controls. Methods: In total, 100 participants were included (71% women; average age, 70 years; range, 43–91 years). MCI was diagnosed by neuropsychological testing, medical and social history, activities of daily living, cognitive symptoms and neuroimaging. Using multivariate logistic regression models adjusted by age and gender, we examined the risk association of MCI with plasma ApoE and APOE methylation. Results: MCI was diagnosed in 41 subjects (average age, 66.5 ± 9.6 years) and compared with 59 controls. Elevated plasma ApoE and APOE methylation of CpGs 165, 190, and 198 were risk factors for MCI (p < 0.05). Higher CpG-227 methylation correlated with lower risk for MCI (p = 0.002). Only CpG-227 was significantly correlated with plasma ApoE levels (correlation coefficient = −0.665; p = 0.008). Conclusion: Differential APOE methylation and increased plasma ApoE levels were correlated with MCI. These epigenetic patterns require confirmation in larger samples but could potentially be used as biomarkers to identify early stages of MCI.

The Effect of Natural LCAT Mutations on the Biogenesis of HDL.

We have investigated how the natural LCAT[T147I] and LCAT[P274S] mutations affect the pathway of biogenesis of HDL. Gene transfer of WT LCAT in LCAT(-/-) mice increased 11.8-fold the plasma cholesterol, whereas the LCAT[T147I] and LCAT[P274S] mutants caused a 5.2- and 2.9-fold increase, respectively. The LCAT[P274S] and the WT LCAT caused a monophasic distribution of cholesterol in the HDL region, whereas the LCAT[T147I] caused a biphasic distribution of cholesterol in the LDL and HDL region. Fractionation of plasma showed that the expression of WT LCAT increased plasma apoE and apoA-IV levels and shifted the distribution of apoA-I to lower densities. The LCAT[T147I] and LCAT[P274S] mutants restored partially apoA-I in the HDL3 fraction and LCAT[T147I] increased apoE in the VLD/IDL/LDL fractions. The in vivo functionality of LCAT was further assessed based on is its ability to correct the aberrant HDL phenotype that was caused by the apoA-I[L159R]FIN mutation. Co-infection of apoA-I(-/-) mice with this apoA-I mutant and either of the two mutant LCAT forms restored only partially the HDL biogenesis defect that was caused by the apoA-I[L159R]FIN and generated a distinct aberrant HDL phenotype.

Abstract 30: Apolipoprotein CIII Sialylation is a Critical Determinant of Liver Triglyceride Metabolism

Apolipoprotein (apo) CIII inhibits lipoprotein lipase (LPL) activity and remnant particle uptake in the liver by the lipolysis stimulated receptor (LSR); and therefore modulates liver and systemic lipid metabolism. Although post-translational modifications of apo CIII lead to asialylated, mono- or di-sialylated variants, the biological relevance of these sialylations is not known. Our objectives were to determine the association of apo C-III sialylation with plasma triglycerides and liver fat content in vivo, and to evaluate the effect of apo CIII sialylation on lipid uptake in liver cells or LPL activity in vitro. In 209 obese non-diabetic adolescent Hispanic participants, apo CIII variants in plasma were measured using mass spectrometric immunoassay. Increased plasma apo C-III sialylation (di- to mono-sialylated apo CIII ratio) was associated with lower triglyceride levels (r=-0.43, p&lt;0.001) and liver fat (by MRI, r=-0.27, p&lt;0.001) independent of total apo CIII concentrations. Higher plasma concentrations of the mono-, but not the di-sialylated variant, were associated with higher triglycerides concentrations (r=0.53, p&lt;0.001). In HepG2 liver cells, immunoprecipitated apo CIII from VLDL of participants in the upper quartile of plasma apo CIII sialylation less effectively inhibited LSR-mediated VLDL uptake compared to apo CIII from those in the lower quartile of apo CIII sialylation (28% difference, p=0.02). This difference in inhibition was abolished by removal of sialic acid with neuraminidase. Apo CIII isolated from VLDL of participants with different level of apo CIII sialylation showed similar capacity to inhibit fatty acid release by LPL of control VLDL. VLDL particles with higher apo CIII sialylation also demonstrated a two-fold increase in ApoE. We conclude that a greater apo CIII sialylation together with particle enrichment in apo E allow for more efficient VLDL liver uptake and less liver fat accumulation. The measurement of plasma apo CIII sialylation may be a useful index of triglyceride metabolism and risk of fatty liver.

ApoE3[K146N/R147W] acts as a dominant negative apoE form that prevents remnant clearance and inhibits the biogenesis of HDL

The K146N/R147W substitutions in apoE3 were described in patients with a dominant form of type III hyperlipoproteinemia. The effects of these mutations on the in vivo functions of apoE were studied by adenovirus-mediated gene transfer in different mouse models. Expression of the apoE3[K146N/R147W] mutant in apoE-deficient (apoE(-/-)) or apoA-I-deficient (apoA-I(-/-))×apoE(-/-) mice exacerbated the hypercholesterolemia and increased plasma apoE and triglyceride levels. In apoE(-/-) mice, the apoE3[K146N/R147W] mutant displaced apoA-I from the VLDL/LDL/HDL region and caused the accumulation of discoidal apoE-containing HDL. The WT apoE3 cleared the cholesterol of apoE(-/-) mice without induction of hypertriglyceridemia and promoted formation of spherical HDL. A unique property of the truncated apoE3[K146N/R147W]202 mutant, compared with similarly truncated apoE forms, is that it did not correct the hypercholesterolemia. The contribution of LPL and LCAT in the induction of the dyslipidemia was studied. Treatment of apoE(-/-) mice with apoE3[K146N/R147W] and LPL corrected the hypertriglyceridemia, but did not prevent the formation of discoidal HDL. Treatment with LCAT corrected hypertriglyceridemia and generated spherical HDL. The combined data indicate that the K146N/R147W substitutions convert the full-length and the truncated apoE3[K146N/R147W] mutant into a dominant negative ligand that prevents receptor-mediated remnant clearance, exacerbates the dyslipidemia, and inhibits the biogenesis of HDL.

Both Targeted Mass Spectrometry and Flow Sorting Analysis Methods Detected the Decreased Serum Apolipoprotein E Level in Alzheimer's Disease Patients

Apolipoprotein E (ApoE) polymorphism has been appreciated as a valuable predictor of Alzheimer disease (AD), and the associated ε4 allele has been recognized as an indicator of susceptibility to this disease. However, serum ApoE levels have been a controversial issue in AD, due to the great variability regarding the different target detection methods, ethnicity, and the geographic variations of cohorts. The aim of this study was to validate serum ApoE levels in relation to AD, particularly using two distinct detection methods, liquid chromatography-selected reaction monitoring (SRM) mass spectrometry and microsphere-based fluorescence-activated cell sorting (FACS) analysis, to overcome experimental variations. Also, comparison of serum ApoE levels was performed between the level of protein detection by FACS and peptide level by SRM in both control and AD patients. Results from the two detection methods were cross-confirmed and validated. Both methods produced fairly consistent results, showing a significant decrease of serum ApoE levels in AD patients relative to those of a control cohort (43 control versus 45 AD, p < 0.0001). Significant correlation has been revealed between results from FACS and SRM (p < 0.0001) even though lower serum ApoE concentration values were measured in protein by FACS analysis than in peptide-level detections by SRM. Correlation study suggested that a decrease of the serum ApoE level in AD is related to the mini-mental state exam score in both results from different experimental methods, but it failed to show consistent correlation with age, gender, or clinical dementia rating.

Modulation of lipid metabolism with the overexpression of NPC1L1 in mouse liver

Niemann-Pick C1-like 1 protein (NPC1L1), a transporter crucial in intestinal cholesterol absorption, is expressed in human liver but not in murine liver. To elucidate the role of hepatic NPC1L1 on lipid metabolism, we overexpressed NPC1L1 in murine liver utilizing adenovirus-mediated gene transfer. C57BL/6 mice, fed on normal chow with or without ezetimibe, were injected with NPC1L1 adenovirus (L1-mice) or control virus (Null-mice), and lipid analyses were performed five days after the injection. The plasma cholesterol levels increased in L1-mice, and FPLC analyses revealed increased cholesterol contents in large HDL lipoprotein fractions. These fractions, which showed α-mobility on agarose electrophoresis, were rich in apoE and free cholesterol. These lipoprotein changes were partially inhibited by ezetimibe treatment and were not observed in apoE-deficient mice. In addition, plasma and VLDL triglyceride (TG) levels decreased in L1-mice. The expression of microsomal triglyceride transfer protein (MTP) was markedly decreased in L1-mice, accompanied by the reduced protein levels of forkhead box protein O1 (FoxO1). These changes were not observed in mice with increased hepatic de novo cholesterol synthesis. These data demonstrate that cholesterol absorbed through NPC1L1 plays a distinct role in cellular and plasma lipid metabolism, such as the appearance of apoE-rich lipoproteins and the diminished VLDL-TG secretion.

Decreased apoE within lipoprotein classes in the nephrotic syndrome is due to diluted apoE pool

Hyperlipidemia in nephrotic syndrome (NS) results from decreased clearance of triglyceride rich lipoproteins (TGLs). VLDL and HDL from NS rats have reduced apolipoprotein E (apoE) content despite increased plasma apoE levels. Lipoprotein lipase (LpL) is decreased in both NS and the Nagase Analbuminemic Rat (NAR). However, NAR have nearly normal lipid levels and TGLs clearance. ApoE, a ligand for the VLDL receptor, is depleted from NS VLDL rats, while normal or increased in NAR VLDL suggesting that the difference in VLDL apoE contributes to defective clearance. It is unknown whether decreased apoE was a consequence of decreased binding to VLDL. Plasma apoE was measured by ELISA. Apo E clearance was measured 7 Control, 7 NS and 9 NAR male rats using 125I labeled apoE. Apo E affinity was measured in 6 Control and 5 NS rats using spin labeled E4 binding with electron spin resonance and nonlinear regression. Apo E levels were significantly greater in plasma NS than in NAR and greater in both than in Control. However, VLDL and HDL from NS had significantly less apoE per mole of PL than those isolated from NAR or Control. ApoE clearance was significantly lower in NS than in NAR and Control, entirely accounting for the increased plasma levels of apoE. Binding of apoE did not differ by lipoprotein class or by group. Decreased apoE within lipoprotein classes in the nephrotic syndrome is due to diluted apoE pool. (Supported by the Department of Veteran's Affairs)

Molecular etiology of a dominant form of type III hyperlipoproteinemia caused by R142C substitution in apoE4

We have used adenovirus-mediated gene transfer in apolipoprotein (apo)E(-/-) mice to elucidate the molecular etiology of a dominant form of type III hyperlipoproteinemia (HLP) caused by the R142C substitution in apoE4. It was found that low doses of adenovirus expressing apoE4 cleared cholesterol, whereas comparable doses of apoE4[R142C] greatly increased plasma cholesterol, triglyceride, and apoE levels, caused accumulation of apoE in VLDL/IDL/LDL region, and promoted the formation of discoidal HDL. Co-expression of apoE4[R142C] with lecithin cholesterol acyltransferase (LCAT) or lipoprotein lipase (LPL) in apoE(-/-) mice partially corrected the apoE4[R142C]-induced dyslipidemia. High doses of C-terminally truncated apoE4[R142C]-202 partially cleared cholesterol in apoE(-/-) mice and promoted formation of discoidal HDL. The findings establish that apoE4[R142C] causes accumulation of apoE in VLDL/IDL/LDL region and affects in vivo the activity of LCAT and LPL, the maturation of HDL, and the clearance of triglyceride-rich lipoproteins. The prevention of apoE4[R142C]-induced dyslipidemia by deletion of the 203-299 residues suggests that, in the full-length protein, the R142C substitution may have altered the conformation of apoE bound to VLDL/IDL/LDL in ways that prevent triglyceride hydrolysis, cholesterol esterification, and receptor-mediated clearance in vivo.

Lipoprotein(a) accelerates atherosclerosis in uremic mice

Uremic patients have increased plasma lipoprotein(a) [Lp(a)] levels and elevated risk of cardiovascular disease. Lp(a) is a subfraction of LDL, where apolipoprotein(a) [apo(a)] is disulfide bound to apolipoprotein B-100 (apoB). Lp(a) binds oxidized phospholipids (OxPL), and uremia increases lipoprotein-associated OxPL. Thus, Lp(a) may be particularly atherogenic in a uremic setting. We therefore investigated whether transgenic (Tg) expression of human Lp(a) increases atherosclerosis in uremic mice. Moderate uremia was induced by 5/6 nephrectomy (NX) in Tg mice with expression of human apo(a) (n = 19), human apoB-100 (n = 20), or human apo(a) + human apoB [Lp(a)] (n = 15), and in wild-type (WT) controls (n = 21). The uremic mice received a high-fat diet, and aortic atherosclerosis was examined 35 weeks later. LDL-cholesterol was increased in apoB-Tg and Lp(a)-Tg mice, but it was normal in apo(a)-Tg and WT mice. Uremia did not result in increased plasma apo(a) or Lp(a). Mean atherosclerotic plaque area in the aortic root was increased 1.8-fold in apo(a)-Tg (P = 0.025) and 3.3-fold (P = 0.0001) in Lp(a)-Tg mice compared with WT mice. Plasma OxPL, as detected with the E06 antibody, was associated with both apo(a) and Lp(a). In conclusion, expression of apo(a) or Lp(a) increased uremia-induced atherosclerosis. Binding of OxPL on apo(a) and Lp(a) may contribute to the atherogenicity of Lp(a) in uremia.

Liver-specific Deficiency of Serine Palmitoyltransferase Subunit 2 Decreases Plasma Sphingomyelin and Increases Apolipoprotein E Levels

Sphingomyelin (SM) is one of the major lipid components of plasma lipoproteins. Serine palmitoyltransferase (SPT) is the key enzyme in SM biosynthesis. Mice totally lacking in SPT are embryonic lethal. The liver is the major site for plasma lipoprotein biosynthesis, secretion, and degradation, and in this study we utilized a liver-specific knock-out approach for evaluating liver SPT activity and also its role in plasma SM and lipoprotein metabolism. We found that a deficiency of liver-specific Sptlc2 (a subunit of SPT) decreased liver SPT protein mass and activity by 95 and 92%, respectively, but had no effect on other tissues. Liver Sptlc2 deficiency decreased plasma SM levels (in both high density lipoprotein and non-high density lipoprotein fractions) by 36 and 35% (p < 0.01), respectively, and increased phosphatidylcholine levels by 19% (p < 0.05), thus increasing the phosphatidylcholine/SM ratio by 77% (p < 0.001), compared with controls. This deficiency also decreased SM levels in the liver by 38% (p < 0.01) and in the hepatocyte plasma membranes (based on a lysenin-mediated cell lysis assay). Liver-specific Sptlc2 deficiency significantly increased hepatocyte apoE secretion and thus increased plasma apoE levels 3.5-fold (p < 0.0001). Furthermore, plasma from Sptlc2 knock-out mice had a significantly stronger potential for promoting cholesterol efflux from macrophages than from wild-type mice (p < 0.01) because of a greater amount of apoE in the circulation. As a result of these findings, we believe that the ability to control liver SPT activity could result in regulation of lipoprotein metabolism and might have an impact on the development of atherosclerosis.

Sphingomyelin Synthase 2 Is One of the Determinants for Plasma and Liver Sphingomyelin Levels in Mice

It has been proposed that plasma sphingomyelin (SM) plays a very important role in plasma lipoprotein metabolism and atherosclerosis. Sphingomyelin synthase (SMS) is the last enzyme for SM de novo biosynthesis. Two SMS genes, SMS1 and SMS2, have been cloned and characterized. To evaluate the in vivo role of SMS2 in SM metabolism, we prepared SMS2 knockout (KO) and SMS2 liver-specific transgenic (LTg) mice and studied their plasma SM and lipoprotein metabolism. On a chow diet, SMS2 KO mice showed a significant decrease in plasma SM levels (25%, P<0.05), but no significant changes in total cholesterol, total phospholipids, or triglyceride, compared with wild-type (WT) littermates. On a high-fat diet, SMS2 KO mice showed a decrease in plasma SM levels (28%, P<0.01), whereas SMS2LTg mice showed a significant increase in those levels (29%, P<0.05), but no significant changes in other lipids, compared with WT littermates. Atherogenic lipoproteins from SMS2LTg mice displayed a significantly stronger tendency toward aggregation after mammalian sphingomyelinase treatment, compared with controls. Moreover, SMS2 deficiency significantly increased plasma apoE levels (2.0-fold, P<0.001), whereas liver-specific SMS2 overexpression significantly decreased those levels (1.8-fold, P<0.01). Finally, SMS2 KO mouse plasma promoted cholesterol efflux from macrophages, whereas SMS2LTg mouse plasma prevented it. We therefore believe that regulation of liver SMS2 activity could become a promising treatment for atherosclerosis.

Phosphatidylinositol acts through mitogen-activated protein kinase to stimulate hepatic apolipoprotein A-I secretion

Phosphatidylinositol (PI) has been shown to stimulate reverse cholesterol transport in animal models and to increase plasma apolipoprotein (apo) A-I levels and high-density lipoprotein cholesterol in human subjects. The objective of this study was to determine the molecular mechanism through which PI stimulates apo A-I secretion in hepatic cells. PI (12 μmol/L) significantly stimulates apo A-I secretion from HepG2 cells over 24 hours. The stimulation in apo A-I secretion is completely blocked by phospholipase C inhibitors (D609 and U73122) and the Ras inhibitor sulindac sulfide. Apolipoprotein A-I secretion is augmented with a protein kinase C agonist (dioctanoyl glycerol) and inhibited by a protein kinase C inhibitor (dioleoyl ethylene glycol). The PI-induced apo A-I secretion is unaffected by PI-3-kinase inhibitors but is sensitive to mitogen-activated protein kinase (MAPK) inhibitors. Whereas the p38MAPK inhibitor SB203580 has no effect on PI-induced apo A-I secretion, the MAPK kinase 1/2 inhibitor U0126 and the c-Jun- N-terminal kinase/stress-activated protein kinase inhibitor SP600125 block PI-induced apo A-I secretion. PI also increased extracellular-regulated protein kinase 1 and 2 phosphorylation in HepG2 cells in a time-dependent manner. PI does not appear to stimulate apo A-I gene transcription, as cellular apo A-I messenger RNA levels remained unchanged over the 24-hour incubation. However, PI significantly decreases apo A-I binding and degradation in HepG2 cells. Collectively, the data suggest that PI acts through MAPK pathways to increase plasma apo A-I levels by protecting it from reuptake and degradation.

Dyslipidaemia as predictor of progressive renal failure and the impact of treatment with atorvastatin

In patients with chronic renal disease, other lipid markers than total cholesterol or low density lipoprotein (LDL)-cholesterol are probably more appropriate to detect a potential lipid-related risk for progression to renal failure. Statin therapy might be protective. From 1999 to 2001, 177 consecutive patients with renal disease from our out-patient clinic were included and 169 could be followed-up for a mean period of 4.1 years. Seventy-two progressive patients (end-stage chronic renal disease or >5 ml/min/year decrease of creatinine clearance) were compared in 97 patients with stable or slowly progressive disease (<5 ml/min/year decrease). Throughout the study all patients were treated according to nephrology guidelines. Atorvastatin was instituted in patients with elevated LDL-cholesterol (LDL-C) after the baseline determinations Proteinuria, mean arterial pressure and the type of underlying renal disease were independently associated with progressive renal disease. After adjustment for these factors and whether or not statin therapy was started, an increase in plasma apo B concentration was the most predictive lipid parameter for renal failure. An increase in apo B from 0.77 g/l (10th percentile) to 1.77 g/l (90th percentile) was associated with progressive loss of renal function, represented by an odds ratio of 2.63 (95% CI: 1.02-6.76; P = 0.045). Treatment with atorvastatin in the dyslipidaemic patients to lower LDL-C, was also accompanied by a reduction of proteinuria in this group (P < 0.001). The patients who reached the target level for LDL-C of <2.6 mmol/l in response to atorvastatin showed less often progression than patients with higher LDL-C (P = 0.010). A high apo B at baseline appeared to be the strongest risk factor among various lipid parameters for progression of renal failure during the following years. Atorvastatin, aimed at lowering LDL-C, reduced proteinuria. Renal outcome was better in patients with the lowest LDL-C on treatment.

Transcriptional control of apolipoprotein A-I gene expression in diabetes.

Cardiovascular disease continues to be the leading cause of mortality in diabetes. One of the factors contributing to the increased risk is the high prevalence rate of low plasma concentrations of HDL cholesterol. Multiple potential mechanisms account for the cardioprotective effects of HDL and its main protein apolipoprotein (apo) A-I. The reduced plasma concentrations of HDL could be the result of increased fractional clearance of HDL and reduced expression of apo A-I. In animal models of diabetes and in cell cultures treated with high concentrations of glucose, apo A-I expression is reduced. In this review we will discuss the alterations in transcriptional control of apo A-I in diabetes. The role of select nutritional and hormonal alterations commonly found in diabetes will be reviewed. Specifically, we will review the literature on the effect of hyperglycemia, hypoinsulinemia, and ketoacidosis, as well as the role of various mediators of insulin resistance, such as fatty acids, cytokines, and prostanoids, on apo A-I promoter activity. Identifying the mechanisms that modulate apo A-I gene expression will aid in the new development of therapeutic agents that increase plasma apo A-I and HDL concentrations.

Dietary Mono- and Polyunsaturated Fatty Acids Similarly Increase Plasma Apolipoprotein A-IV Concentrations in Healthy Men and Women

We investigated the effect of dietary fatty acid composition on plasma apolipoprotein (apo) A-IV concentrations. Plasma apo A-IV concentrations were measured by ELISA in plasma of 48 healthy men and women in a controlled dietary study. First, all participants consumed a 2-wk baseline diet rich in saturated fatty acids (SFA). Then, they were randomly assigned to one of three dietary treatments, which contained refined olive oil [rich in monounsaturated fatty acids (MUFA), n = 17], rapeseed oil [rich in MUFA and alpha-linolenic acid [18:3(n-3)], n = 13], or sunflower oil [rich in (n-6) PUFA, n = 18] as the principal source of fat for 4 wk. The plasma concentrations of apo A-IV increased when subjects consumed the diets rich in unsaturated fatty acids, by 16% or 13.0 mg/L [F((2,76)) = 12.874, P < 0.001 by repeated-measures ANOVA]. The increase was not affected by diet group affiliation, gender or apo A-IV genotype. In conclusion, diets rich in unsaturated fatty acids, independent of the degree of unsaturation, gender and apo A-IV genotype, increase plasma apo A-IV concentrations compared with a baseline diet rich in SFA in healthy men and women.

Effect of leptin on intestinal apolipoprotein AIV in response to lipid feeding.

We determined apolipoprotein AIV (apo AIV) content in intestinal epithelial cells using immunohistochemistry when leptin was administered intravenously. Most of the apo AIV immunoreactivity in the untreated intestine was located in the villous cells as opposed to the crypt cells. Regional distribution of apo AIV immunostaining revealed low apo AIV content in the duodenum and high content in the jejunum that gradually decreases caudally toward the ileum. Intraduodenal infusion of lipid (4 h) significantly increased apo AIV immunoreactivity in the jejunum and ileum. Simultaneous intravenous leptin infusion plus duodenal lipid infusion markedly suppressed apo AIV immunoreactivity. Duodenal lipid infusion increased plasma apo AIV significantly (measured by ELISA), whereas simultaneous leptin infusion attenuated the increase. These findings suggest that leptin may regulate circulating apo AIV by suppressing apo AIV synthesis in the small intestine.

Reduction of Isoprostanes and Regression of Advanced Atherosclerosis by Apolipoprotein E

Apolipoprotein E is a multifunctional protein synthesized by hepatocytes and macrophages. Plasma apoE is largely liver-derived and known to regulate lipoprotein metabolism. Macrophage-derived apoE has been shown to reduce the progression of atherosclerosis in mice. We tested the hypothesis that liver-derived apoE could directly induce regression of pre-existing advanced atherosclerotic lesions without reducing plasma cholesterol levels. Aged low density lipoprotein (LDL) receptor-deficient (LDLR(-/-)) mice were fed a western-type diet for 14 weeks to induce advanced atherosclerotic lesions. One group of mice was sacrificed for evaluation of atherosclerosis at base line, and two other groups were injected with a second generation adenoviruses encoding human apoE3 or a control empty virus. Hepatic apoE gene transfer increased plasma apoE levels by 4-fold at 1 week, and apoE levels remained at least 2-fold higher than controls at 6 weeks. There were no significant changes in plasma total cholesterol levels or lipoprotein composition induced by expression of apoE. The liver-derived human apoE gained access to and was retained in arterial wall. Compared with base-line mice, the control group demonstrated progression of atherosclerosis; in contrast, hepatic apoE expression induced highly significant regression of advanced atherosclerotic lesions. Regression of lesions was accompanied by the loss of macrophage-derived foam cells and a trend toward increase in extracellular matrix of lesions. As an index of in vivo oxidant stress, we quantitated the isoprostane iPF(2 alpha)-VI and found that expression of apoE markedly reduced urinary, LDL-associated, and arterial wall iPF(2 alpha)-VI levels. In summary, these results demonstrate that liver-derived apoE directly induced regression of advanced atherosclerosis and has anti-oxidant properties in vivo that may contribute to its anti-atherogenic effects.

Human growth hormone increases apo(a) expression in transgenic mice.

Levels of Lp(a), an atherogenic lipoprotein that circulates in human plasma, are increased by the administration of growth hormone (GH). Many of the physiological effects of GH are mediated through insulin-like growth factor-1 (IGF-1), but ironically, IGF-1 treatment of humans is associated with a fall in plasma Lp(a) levels. To glean insight into the mechanism responsible for the GH-associated increase in plasma levels of Lp(a), we administered recombinant human GH (rhGH) to mice expressing a 370-kb human genomic fragment containing the apo(a) gene, 40 kb of 5'-, and 200 kb of 3'-flanking sequence [YAC-apo(a) transgenic mice]. The plasma levels of apo(a) and hepatic levels of apo(a) mRNA rose dramatically in the post-pubertal male mice in response to rhGH treatment. To determine whether the increase in plasma apo(a) was mediated by IGF-1, we treated castrated and noncastrated YAC-apo(a) transgenic mice with a continuous infusion of IGF-1 (100 microg/d) for 2 weeks, and plasma levels of apo(a) fell by approximately 50%. Thus the effects of rhGH and IGF-1 administration on plasma levels of apo(a) in the YAC-apo(a) transgenic mice simulate those seen in humans. The coordinate changes in apo(a) mRNA and plasma levels of apo(a) in response to rhGH and IGF-1 strongly suggest that these 2 hormones have independent effects on the transcription of the apo(a) gene.