HDL functionality in South Asians as compared to white Caucasians

BACKGROUND AND AIMS

South Asians have an exceptionally high risk of developing cardiovascular disease compared to white Caucasians. A contributing factor might be dysfunction of high density lipoprotein (HDL). We aimed to compare HDL function in different age groups of both ethnicities.

METHODS AND RESULTS

HDL functionality with respect to cholesterol efflux, anti-oxidation and anti-inflammation was determined using fasting, apoB-depleted, plasma samples from South Asian and white Caucasian neonates (n = 14 each), adolescent healthy men (n = 12 each, 18-25 y), and adult overweight men (n = 12 each, 40-50 y). Adolescents were subjected to a 5-day high fat high calorie diet (HCD) and adults to an 8-day very low calorie diet (LCD). Additionally, HDL composition was measured in adolescents and adults using (1)H-NMR spectroscopy. Anti-oxidative capacity was lower in South Asian adults before LCD (19.4 ± 2.1 vs. 25.8 ± 1.2%, p = 0.045, 95%-CI = [0.1; 12.7]) and after LCD (16.4 ± 2.4 vs. 27.6 ± 2.7%, p = 0.001, 95%-CI = [4.9; 17.5]). Anti-inflammatory capacity was reduced in South Asian neonates (23.8 ± 1.2 vs. 34.9 ± 1.3%, p = 0.000001, 95%-CI = [-14.6; -7.5]), and was negatively affected by an 8-day LCD only in South Asian adults (-12.2 ± 4.3%, p = 0.005, 95%-CI = [-5.9; -1.2]). Cholesterol efflux capacity was increased in response to HCD in adolescents (South Asians: +6.3 ± 2.9%, p = 0.073, 95%-CI = [-0.02; 0.46], Caucasians: +11.8 ± 3.4%, p = 0.002, 95%-CI = [0.17;0.65]) and decreased after LCD in adults (South Asians: -10.3 ± 2.4%, p < 0.001, 95%-CI = [-0.57; -0.20], Caucasians: -13.7 ± 1.9%, p < 0.00001, 95%-CI = [-0.67; -0.33]). Although subclass analyses of HDL showed no differences between ethnicities, cholesterol efflux correlated best with cholesterol and phospholipid within small HDL compared to other HDL subclasses and constituents.

CONCLUSION

Impaired HDL functionality in South Asians may be a contributing factor to their high CVD risk.

CLINICAL TRIAL REGISTRATION

NTR 2473 (URL: http://www.trialregister.nl/).

Hematopoietic α7 nicotinic acetylcholine receptor deficiency increases inflammation and platelet activation status, but does not aggravate atherosclerosis

BACKGROUND

The autonomic nervous system attenuates inflammation through activation of the α7 nicotinic acetylcholine receptor (α7nAChR), a pathway termed the cholinergic anti-inflammatory reflex. Interestingly, α7nAChR is expressed on immune cells and platelets, both of which play a crucial role in the development of atherosclerosis.

OBJECTIVE

To investigate the role of hematopoietic α7nAChR in inflammation and platelet function in atherosclerotic ldlr(-/-) mice and to identify its consequences for atherosclerotic lesion development.

METHODS

Bone marrow from α7nAChR(-/-) mice or wild-type littermates was transplanted into irradiated ldlr(-/-) mice. After a recovery period of 8 weeks, the mice were fed an atherogenic Western-type diet for 7 weeks.

RESULTS

Hematopoietic α7nAChR deficiency clearly increased the number of leukocytes in the peritoneum (2.6-fold, P < 0.001), blood (2.9-fold; P < 0.01), mesenteric lymph nodes (2.0-fold; P < 0.001) and spleen (2.2-fold; P < 0.01), indicative of an increased inflammatory status. Additionally, expression of inflammatory mediators was increased in peritoneal leukocytes (TNFα, 1.6-fold, P < 0.01; CRP, 1.8-fold, P < 0.01) as well as in the spleen (TNFα, 1.6-fold, P < 0.01). The lack of α7nAChR on platelets from these mice increased the expression of active integrin αIIb β3 upon stimulation by ADP (1.9-fold, P < 0.01), indicating increased activation status, while incubation of human platelets with an α7nAChR agonist decreased aggregation (-35%, P < 0.05). Despite the large effects of hematopoietic α7nAChR deficiency on inflammatory status and platelet function, it did not affect atherosclerosis development or composition of lesions.

CONCLUSIONS

Hematopoietic α7nAChR is important for attenuation of inflammatory responses and maintaining normal platelet reactivity, but loss of hematopoietic α7nAChR does not aggravate development of atherosclerosis.

Exendin-4 decreases liver inflammation and atherosclerosis development simultaneously by reducing macrophage infiltration

BACKGROUND AND PURPOSE

The aetiology of inflammation in the liver and vessel wall, leading to non-alcoholic steatohepatitis (NASH) and atherosclerosis, respectively, shares common mechanisms including macrophage infiltration. To treat both disorders simultaneously, it is highly important to tackle the inflammatory status. Exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, reduces hepatic steatosis and has been suggested to reduce atherosclerosis; however, its effects on liver inflammation are underexplored. Here, we tested the hypothesis that exendin-4 reduces inflammation in both the liver and vessel wall, and investigated the common underlying mechanism.

EXPERIMENTAL APPROACH

Female APOE*3-Leiden.CETP mice, a model with human-like lipoprotein metabolism, were fed a cholesterol-containing Western-type diet for 5 weeks to induce atherosclerosis and subsequently treated for 4 weeks with exendin-4.

KEY RESULTS

Exendin-4 modestly improved dyslipidaemia, but markedly decreased atherosclerotic lesion severity and area (-33%), accompanied by a reduction in monocyte adhesion to the vessel wall (-42%) and macrophage content in the plaque (-44%). Furthermore, exendin-4 reduced hepatic lipid content and inflammation as well as hepatic CD68⁺ (-18%) and F4/80⁺ (-25%) macrophage content. This was accompanied by less monocyte recruitment from the circulation as the Mac-1⁺ macrophage content was decreased (-36%). Finally, exendin-4 reduced hepatic chemokine expression in vivo and suppressed oxidized low-density lipoprotein accumulation in peritoneal macrophages in vitro, effects dependent on the GLP-1 receptor.

CONCLUSIONS AND IMPLICATIONS

Exendin-4 reduces inflammation in both the liver and vessel wall by reducing macrophage recruitment and activation. These data suggest that exendin-4 could be a valuable strategy to treat NASH and atherosclerosis simultaneously.

The insulin sensitizing effect of topiramate involves KATP channel activation in the central nervous system

BACKGROUND AND PURPOSE

Topiramate improves insulin sensitivity, in addition to its antiepileptic action. However, the underlying mechanism is unknown. Therefore, the present study was aimed at investigating the mechanism of the insulin-sensitizing effect of topiramate both in vivo and in vitro.

EXPERIMENTAL APPROACH

Male C57Bl/6J mice were fed a run-in high-fat diet for 6 weeks, before receiving topiramate or vehicle mixed in high-fat diet for an additional 6 weeks. Insulin sensitivity was assessed by hyperinsulinaemic-euglycaemic clamp. The extent to which the insulin sensitizing effects of topiramate were mediated through the CNS were determined by concomitant i.c.v. infusion of vehicle or tolbutamide, an inhibitor of ATP-sensitive potassium channels in neurons. The direct effects of topiramate on insulin signalling and glucose uptake were assessed in vivo and in cultured muscle cells.

KEY RESULTS

In hyperinsulinaemic-euglycaemic clamp conditions, therapeutic plasma concentrations of topiramate (∼4 μg·mL(-1) ) improved insulin sensitivity (glucose infusion rate + 58%). Using 2-deoxy-D-[(3) H]glucose, we established that topiramate improved the insulin-mediated glucose uptake by heart (+92%), muscle (+116%) and adipose tissue (+586%). Upon i.c.v. tolbutamide, the insulin-sensitizing effect of topiramate was completely abrogated. Topiramate did not directly affect glucose uptake or insulin signalling neither in vivo nor in cultured muscle cells.

CONCLUSION AND IMPLICATIONS

In conclusion, topiramate stimulates insulin-mediated glucose uptake in vivo through the CNS. These observations illustrate the possibility of pharmacological modulation of peripheral insulin resistance through a target in the CNS.

Sex-specific effects of naturally occurring variants in the dopamine receptor D2 locus on insulin secretion and type 2 diabetes susceptibility

AIMS

Modulation of dopamine receptor D2 (DRD2) activity affects insulin secretion in both rodents and isolated pancreatic β-cells. We hypothesized that single nucleotide polymorphisms in the DRD2/ANKK1 locus may affect susceptibility to type 2 diabetes in humans.

METHODS

Four potentially functional variants in the coding region of the DRD2/ANKK1 locus (rs1079597, rs6275, rs6277, rs1800497) were genotyped and analysed for type 2 diabetes susceptibility in up to 25 000 people (8148 with type 2 diabetes and 17687 control subjects) from two large independent Dutch cohorts and one Danish cohort. In addition, 340 Dutch subjects underwent a 2-h hyperglycaemic clamp to investigate insulin secretion. Since sexual dimorphic associations related to DRD2 polymorphisms have been previously reported, we also performed a gender-stratified analysis.

RESULTS

rs1800497 at the DRD2/ANKK1 locus was associated with a significantly increased risk for type 2 diabetes in women (odds ratio 1.14 (1.06-1.23); P = 4.1*10⁴) but not in men (odds ratio 1.00 (95% CI 0.93-1.07); P = 0.92) or the combined group. Although rs1800497 was not associated with insulin secretion, we did find another single nucleotide polymorphism in this locus, rs6275, to be associated with increased first-phase glucose-stimulated insulin secretion in women (P = 5.5*10⁴) but again not in men (P = 0.34).

CONCLUSION

The present data identify DRD2/ANKK1 as a potential sex-specific type 2 diabetes susceptibility gene.

APOE*3Leiden.CETP transgenic mice as model for pharmaceutical treatment of the metabolic syndrome

AIMS

This study aimed to investigate systematically (i) the appropriate dietary conditions to induce the features of the MetS in APOE*3Leiden.humanCholesteryl Ester Transfer Protein (E3L.CETP) mice and (ii) whether the response of this model to different antidiabetic and hypolipidemic drugs is similar as in humans.

METHODS

Male obese, IR and dyslipidemic E3L.CETP mice were treated with antidiabetic drugs rosiglitazone, liraglutide or an experimental 11β-hydroxysteroid-dehydrogenase-1 (HSD-1) inhibitor, or with hypolipidemic drugs atorvastatin, fenofibrate or niacin for 4-6 weeks. The effects on bw, IR and plasma and liver lipids were assessed.

RESULTS

Rosiglitazone, liraglutide and HSD-1 inhibitor significantly decreased glucose and insulin levels or IR. Liraglutide and HSD-1 inhibitor also decreased bw. Atorvastatin, fenofibrate and niacin improved the dyslipidemia and fenofibrate and niacin increased high-density lipoprotein (HDL) cholesterol. In addition, hepatic triglycerides were significantly decreased by treatment with rosiglitazone and liraglutide, while hepatic cholesterol esters were significantly decreased by rosiglitazone and atorvastatin.

CONCLUSIONS

We conclude that the E3L.CETP mouse is a promising novel translational model to investigate the effects of new drugs, alone or in combination, that affect IR, diabetic dyslipidemia and non-alcoholic fatty liver disease (NAFLD).

Effects of high fat diet on the Basal activity of the hypothalamus-pituitary-adrenal axis in mice: a systematic review

Hypothalamus-pituitary-adrenal-axis activity is suggested to be involved in the pathophysiology of the metabolic syndrome. In diet-induced obesity mouse models, features of the metabolic syndrome are induced by feeding high fat diet. However, the models reveal conflicting results with respect to the hypothalamus-pituitary-adrenal-axis activation. The aim of this review was to assess the effects of high fat feeding on the activity of the hypothalamus-pituitary-adrenal-axis in mice. PubMed, EMBASE, Web of Science, the Cochrane database, and Science Direct were electronically searched and reviewed by 2 individual researchers. We included only original mouse studies reporting parameters of the hypothalamus-pituitary-adrenal-axis after high fat feeding, and at least 1 basal corticosterone level with a proper control group. Studies with adrenalectomized mice, transgenic animals only, high fat diet for less than 2 weeks, or other interventions besides high fat diet, were excluded. 20 studies were included. The hypothalamus-pituitary-adrenal-axis evaluation was the primary research question in only 5 studies. Plasma corticosterone levels were unchanged in 40%, elevated in 30%, and decreased in 20% of the studies. The effects in the peripheral tissues and the central nervous system were also inconsistent. However, major differences were found between mouse strains, experimental conditions, and the content and duration of the diets. This systematic review demonstrates that the effects of high fat feeding on the basal activity of the hypothalamus-pituitary-adrenal-axis in mice are limited and inconclusive. Differences in experimental conditions hamper comparisons and accentuate the need for standardized evaluations to discern the effects of diet-induced obesity on the hypothalamus-pituitary-adrenal-axis.

The dopamine receptor D2 agonist bromocriptine inhibits glucose-stimulated insulin secretion by direct activation of the alpha2-adrenergic receptors in beta cells

Treatment with the dopamine receptor D2 (DRD2) agonist bromocriptine improves metabolic features in obese patients with type 2 diabetes by a still unknown mechanism. In the present study, we investigated the acute effect of bromocriptine and its underlying mechanism(s) on insulin secretion both in vivo and in vitro. For this purpose, C57Bl6/J mice were subjected to an intraperitoneal glucose tolerance test (ipGTT) and a hyperglycemic (HG) clamp 60min after a single injection of bromocriptine or placebo. The effects of bromocriptine on glucose-stimulated insulin secretion (GSIS), cell membrane potential and intracellular cAMP levels were also determined in INS-1E beta cells. We report here that bromocriptine increased glucose levels during ipGTT in vivo, an effect associated with a dose-dependent decrease in GSIS. During the HG clamp, bromocriptine reduced both first-phase and second-phase insulin response. This inhibitory effect was also observed in INS-1E beta cells, in which therapeutic concentrations of bromocriptine (0.5-50nM) decreased GSIS. Mechanistically, neither cellular energy state nor cell membrane depolarization was affected by bromocriptine whereas intracellular cAMP levels were significantly reduced, suggesting involvement of G-protein-coupled receptors. Surprisingly, the DRD2 antagonist domperidone did not counteract the effect of bromocriptine on GSIS, whereas yohimbine, an antagonist of the alpha2-adrenergic receptors, completely abolished bromocriptine-induced inhibition of GSIS. In conclusion, acute administration of bromocriptine inhibits GSIS by a DRD2-independent mechanism involving direct activation of the pancreatic alpha2-adrenergic receptors. We suggest that treatment with bromocriptine promotes beta cells rest, thereby preventing long-lasting hypersecretion of insulin and subsequent beta cell failure.

The dual PPARalpha/gamma agonist tesaglitazar blocks progression of pre-existing atherosclerosis in APOE*3Leiden.CETP transgenic mice

BACKGROUND AND PURPOSE

We have evaluated the effects of a peroxisome proliferator-activated receptor (PPAR)alpha/gamma agonist on the progression of pre-existing atherosclerotic lesions in APOE*3Leiden.cholesteryl ester transfer protein (E3L.CETP) transgenic mice.

EXPERIMENTAL APPROACH

E3L.CETP mice were fed a high-cholesterol diet for 11 weeks to induce atherosclerosis, followed by a low-cholesterol diet for 4 weeks to obtain a lower plasma total cholesterol level of approximately 10 mmol.L(-1). Mice were divided into three groups, which were either killed before (baseline) or after an 8 week treatment period with low-cholesterol diet without (control) or with the PPARalpha/gamma agonist tesaglitazar (10 microg.kg(-1).day(-1)). Atherosclerosis was assessed in the aortic root.

KEY RESULTS

Treatment with tesaglitazar significantly reduced plasma triglycerides, total cholesterol, CETP mass and CETP activity, and increased high-density lipoprotein-cholesterol. At baseline, substantial atherosclerosis had developed. During the 8 week low-cholesterol diet, atherosclerosis progressed in the control group with respect to lesion area and severity, whereas tesaglitazar inhibited lesion progression during this period. Tesaglitazar reduced vessel wall inflammation, as reflected by decreased monocyte adhesion and macrophage area, and modified lesions to a more stabilized phenotype, with increased smooth muscle cell content in the cap and collagen content.

CONCLUSIONS AND IMPLICATIONS

Dual PPARalpha/gamma agonism with tesaglitazar markedly improved the atherogenic triad by reducing triglycerides and very low-density lipoprotein-cholesterol and increasing high-density lipoprotein-cholesterol and additionally reduced cholesterol-induced vessel wall activation. These actions resulted in complete inhibition of progression and stabilization of pre-existing atherosclerotic lesions in E3L.CETP mice.

Leptin deficiency per se dictates body composition and insulin action in ob/ob mice

Obese humans are often insulin- and leptin resistant. Since leptin can affect glucose metabolism, it is conceivable that a lack of leptin signal transduction contributes to insulin resistance. It remains unclear whether leptin affects glucose metabolism via peripheral and/or central mechanistic routes. In the present study, we aimed: (i) to determine the relative contributions of lack of leptin signal transduction and adiposity to insulin resistance and (ii) to establish the impact of central leptin action on glucose metabolism. To address the first point, ob/ob mice were subjected to severe calorie restriction, so that their body weight became similar to that of wild-type mice. Insulin sensitivity was measured in obese ob/ob, lean (food restricted) ob/ob and lean, weight-matched wild-type mice. To address the second point, leptin (or vehicle) was i.c.v. infused to the lateral cerebral ventricle of ob/ob mice and insulin sensitivity was determined. Hyperinsulinaemic euglyceamic clamps were used to quantify insulin sensitivity. Food restriction barely affected body composition, although it profoundly curtailed body weight. Insulin suppressed hepatic glucose production (HGP) to a greater extent in lean ob/ob than in obese ob/ob mice, but its impact remained considerably less than in wild-type mice (% suppression: 11.8 +/- 8.9 versus 1.3 +/- 1.1 versus 56.6 +/- 13.0%/nmol, for lean, obese ob/ob and wild-type mice, respectively; P < 0.05). The insulin-mediated glucose disposal (GD) of lean ob/ob mice was also in between that of obese ob/ob and wild-type mice (37.5 +/- 21.4 versus 25.1 +/- 14.6 versus 59.6 +/- 17.3 mumol/min/kg/nmol of insulin, respectively; P < 0.05 wild-type versus obese ob/ob mice). Leptin infusion acutely enhanced both hepatic insulin sensitivity (insulin-induced inhibition of HGP) and insulin-mediated GD (9.1 +/- 2.4 versus 5.0 +/- 2.7%/nmol of insulin, and 25.6 +/- 5.6 versus 13.6 +/- 4.8 mumol/min/kg/nmol of insulin, respectively; P < 0.05 for both comparisons) in ob/ob mice. Both a lack of leptin signals and adiposity may contribute to insulin resistance in obese individuals. Diminution of central leptin signalling can critically affect glucose metabolism in these individuals.

Dynamics of insulin signalling in liver during hyperinsulinemic euglycaemic clamp conditions in vivo and the effects of high-fat feeding in male mice

Insulin is an important regulator of hepatic carbohydrate, lipid, and protein metabolism, and the regulation of these processes by insulin is disturbed under conditions of insulin resistance and type 2 diabetes. Despite these alterations, the impact of insulin resistance on insulin signalling in the liver is not well defined. Variations in time and dose of insulin stimulation as well as plasma glucose levels may underlie this. The present study aimed at determining the dynamics of activation of hepatic insulin signalling in vivo at insulin concentrations resembling those achieved after a meal, and addressing the effects of high-fat feeding. An unexpected finding of this study was the biphasic activation pattern of the IRS-PI3K-PKB/Akt pathway. Our findings indicate that the first burst of activation contributes to regulation of glucose metabolism. The physiological function of the second peak is still unknown, but may involve regulation of protein synthesis. Finally, high-fat feeding caused hepatic insulin resistance, as illustrated by a reduced suppression of hepatic glucose production. A sustained increased phosphorylation of the serine/threonine kinases p70S6kinase and Jun N-terminal kinase in the absence of insulin may underlie the abrogated phosphorylation of the IRS proteins and their downstream targets.

Gut-brain axis: regulation of glucose metabolism

Obesity and type II diabetes mellitus have reached epidemic proportions. From this perspective, knowledge about the regulation of satiety and food intake is more important than ever. The gut releases several peptides upon feeding, which affect hypothalamic pathways involved in the regulation of satiety and metabolism. Within the hypothalamus, there are complex interactions between many nuclei of which the arcuate nucleus is considered as one of the most important hypothalamic centres that regulates food intake. The neuropeptides, which are present in the hypothalamus and are involved in regulating food intake, also play a key role in regulating glucose metabolism and energy expenditure. In synchrony with the effects of those neuropeptides, gastrointestinal hormones also affect glucose metabolism and energy expenditure. In this review, the effects of the gastrointestinal hormones ghrelin, cholecystokinin, peptide YY, glucagon-like peptide, oxyntomodulin and gastric inhibitory polypeptide on glucose and energy metabolism are reviewed. These gut hormones affect glucose metabolism at different levels: by altering food intake and body weight, and thereby insulin sensitivity; by affecting gastric delay and gut motility, and thereby meal-related fluctuations in glucose levels; by affecting insulin secretion, and thereby plasma glucose levels, and by affecting tissue specific insulin sensitivity of glucose metabolism. These observations point to the notion of a major role of the gut-brain axis in the integrative physiology of whole body fuel metabolism.

Sustained activation of the mammalian target of rapamycin nutrient sensing pathway is associated with hepatic insulin resistance, but not with steatosis, in mice

AIMS/HYPOTHESIS

Activation of nutrient sensing through mammalian target of rapamycin (mTOR) has been linked to the pathogenesis of insulin resistance. We examined activation of mTOR-signalling in relation to insulin resistance and hepatic steatosis in mice.

MATERIALS AND METHODS

Chronic hepatic steatosis and hepatic insulin resistance were induced by high-fat feeding of male C57BL/6Jico mice for 6 weeks. In addition, acute hepatic steatosis in the absence of insulin resistance was induced by pharmacological blockade of beta-oxidation using tetradecylglycidic acid (TDGA). mTOR signalling was examined in liver homogenates.

RESULTS

High-fat feeding caused obesity (p<0.001), hepatic steatosis (p<0.05) and hepatic insulin resistance (p<0.05). The phosphorylation of mTOR and its downstream targets p70S6 kinase and S6 ribosomal protein was two-fold higher in mice on a high-fat diet than in mice fed standard chow (all p<0.05) and associated with enhanced rates of protein synthesis. Acute induction of hepatic steatosis with TDGA had no effect on mTOR activity. The increased activity of the mTOR pathway in livers from mice on a high-fat diet could not be ascribed to diet-induced alterations in known modulators of mTOR activity such as circulating plasma leucine levels, phosphorylation of protein kinase B and AMP-activated protein kinase, and changes in mitochondrial function.

CONCLUSIONS/INTERPRETATION

High-fat diet induces increase of the mTOR nutrient sensing pathway in association with hepatic insulin resistance, but not with hepatic lipid accumulation as such.

Macrophage low-density lipoprotein receptor-related protein deficiency enhances atherosclerosis in ApoE/LDLR double knockout mice

OBJECTIVE

In vitro studies implicate that the low-density lipoprotein receptor (LDLR)-related protein (LRP) in macrophages has a pro-atherogenic potential. In the present study, we investigated the in vivo role of macrophage specific LRP in atherogenesis independent of its role in the uptake of lipoproteins.

METHODS AND RESULTS

We generated macrophage-specific LRP-deficient mice on an apoE/LDLR double-deficient background. Macrophage LRP deletion did not affect plasma cholesterol and triglyceride levels, lipoprotein distribution, and blood monocyte counts. Nevertheless, macrophage LRP deficiency resulted in a 1.8-fold increase in total atherosclerotic lesion area in the aortic root of 18-week-old mice. Moreover, LRP deficiency also resulted in a relatively higher number of advanced lesions. Whereas macrophage and smooth muscle cell content did not differ between LRP-deficient mice and control littermates, a 1.7-fold increase in collagen content and 2.3-fold decrease in relative number of CD3+ T cells were observed in lesions from macrophage specific LRP-deficient mice.

CONCLUSIONS

Our data demonstrate that independent of its role in lipoprotein uptake, absence of LRP in macrophages resulted in more advanced atherosclerosis and in lesions that contained more collagen and less CD3+ T cells. In contrast to previous in vitro studies, we conclude that macrophage LRP has an atheroprotective potential and may modulate the extracellular matrix in the atherosclerotic lesions.

Mdm2, but not Mdm4, protects terminally differentiated smooth muscle cells from p53-mediated caspase-3-independent cell death

p53 is a potent inhibitor of cell growth and an inducer of apoptosis. During embryonic development, Mdm2 and Mdm4 inhibit the growth suppressive activities of p53. However, whether tight surveillance of p53 activity is required in quiescent cells is unknown. To test this, conditional inactivation of mdm2 and mdm4 was carried out in smooth muscle cells (SMCs). Upon SMC-specific inactivation of mdm2, and not of mdm4, mice rapidly became ill and died. Necropsy showed small intestinal dilation, and histological analyses indicated a severe reduction in the number of intestinal SMCs. Increased p53 levels and activity were detected in the remaining SMCs, and the phenotype was completely rescued on a p53-null background. Interestingly, intestinal SMCs are caspase-3-negative and therefore did not undergo caspase-3-dependent apoptotic cell death. Together, Mdm2, but not Mdm4, prevents accumulation of active p53 in quiescent SMCs and thereby the induction of p53-mediated caspase-3-independent cell death.

Ghrelin differentially affects hepatic and peripheral insulin sensitivity in mice

AIMS/HYPOTHESIS

This study was conducted to evaluate the effects of ghrelin on insulin's capacity to suppress endogenous glucose production and promote glucose disposal in mice. To establish whether the growth hormone secretagogue (GHS) receptor can mediate the putative effect of ghrelin on the action of insulin, we also determined the metabolic effects of growth hormone releasing peptide 6 (GHRP-6), a specific GHS receptor agonist. In addition, we explored the biological significance of des-ghrelin (unacylated ghrelin) in this experimental context.

MATERIALS AND METHODS

Vehicle (n=8), ghrelin (n=9), GHRP-6 (n=9), des-ghrelin (n=8) or a combination of des-ghrelin and ghrelin (n=7) were infused i.v. for 3 h. Simultaneously, endogenous glucose production and glucose disposal were measured by (14)C-glucose dilution during a hyperinsulinaemic-euglycaemic clamp. Tissue-specific glucose uptake in muscle and adipose tissue was measured using (3)H-2-deoxyglucose.

RESULTS

During hyperinsulinaemia, glucose disposal was 31% higher in mice treated with ghrelin than in those treated with vehicle (77+/-16 and 59+/-8 micromol kg(-1) h(-1), respectively, p<0.05). This was in accordance with enhanced 2-deoxyglucose uptake in muscle in ghrelin-treated animals. In contrast, endogenous glucose production was less effectively suppressed by insulin during ghrelin infusion (46+/-22 vs 71+/-11% in controls, p<0.05). GHRP-6 did not affect insulin action. Des-ghrelin hampered insulin's capacity to inhibit endogenous glucose production, whereas it did not affect glucose disposal. The restraining effects of des-ghrelin and ghrelin on hepatic insulin action were abolished by simultaneous administration of both peptides.

CONCLUSIONS/INTERPRETATION

Ghrelin hampers insulin's capacity to suppress endogenous glucose production, whereas it reinforces the action of insulin on glucose disposal, independently of food intake and body weight. These metabolic effects are unlikely to be mediated by the GHS receptor. Furthermore, simultaneous administration of des-ghrelin abolishes the inhibitory effect of ghrelin on hepatic insulin action.

High fat diet induced hepatic insulin resistance is not related to changes in hypothalamic mRNA expression of NPY, AgRP, POMC and CART in mice

The hypothalamic circuitry, apart from its impact on food intake, modulates insulin sensitivity to adapt metabolic conditions in the face of environmental fluctuations in nutrient availability. The purpose of the present study was to investigate the effects of 2 weeks high fat feeding in wildtype mice on (1) insulin sensitivity and triglyceride accumulation in liver and muscle in relation to (2) mRNA expression levels of Neuropeptide Y (NPY), Agouti-related protein (AgRP), pro-opiomelanocortin (POMC), and cocaine- and amphetamine-regulated transcript (CART) in the hypothalamus. Two weeks of high fat feeding induced hepatic insulin resistance in the presence of increased hepatic triglyceride accumulation. In muscle, however, 2 weeks of high fat feeding did not result in changes in insulin sensitivity or in triglyceride content. mRNA expression levels of NPY, AgRP, POMC, and CART in the hypothalamus were not different between the groups. This study shows that 2 weeks of high fat feeding in mice does not affect mRNA expression levels of NPY, AgRP, POMC or CART, in the whole hypothalamus, despite induction of hepatic, but not peripheral, insulin resistance. Therefore, a major physiological role of these neuroendocrine factors in the induction of hepatic insulin resistance during a high fat diet seems less likely.

Efficient targeting of adenoviral vectors to integrin positive vascular cells utilizing a CAR-cyclic RGD linker protein

Vascular smooth muscle (VSMC) and endothelial cells (EC) are particularly resistant to infection by type 5 adenovirus (Ad) vectors. To overcome this limitation and target Ad vectors to ubiquitously expressed alpha(V)beta(3/5) integrins, we have generated a linker protein consisting of the extracellular domain of the coxsackie adenovirus receptor (CAR) connected via avidin to a biotinylated cyclic (c) RGD peptide. After optimization of CAR to cRGD and to Ad coupling, infection of mouse heart endothelial cells (H5V) could be augmented significantly, as demonstrated by 600-fold increased transgene expression levels. In EOMAs, a hemangioendothelioma-derived cell line, the fraction of infected cells was enhanced 4- to 6-fold. Furthermore, the fraction of infected primary mouse VSMC was increased from virtually 0% to 25%. Finally, in human umbilical vein endothelial cells, the number of GFP positive cells was enhanced from 2% to 75%. In conclusion, CAR-cRGD is a versatile and highly efficient construct to target Ad vectors to both transformed and primary VSMC and EC.

Intracerebroventricular administration of melanotan II increases insulin sensitivity of glucose disposal in mice

AIMS/HYPOTHESIS

The present study was conducted to evaluate the effects of central administration of melanotan II (MTII), a melanocortin-3/4 receptor agonist, on hepatic and whole-body insulin sensitivity, independent of food intake and body weight.

METHODS

Over a period of 24 h, 225 ng of MTII was injected in three aliquots into the left lateral ventricle of male C57Bl/6 mice. The animals had no access to food. The control group received three injections of distilled water. Whole-body and hepatic insulin sensitivity were measured by hyperinsulinaemic-euglycaemic clamp in combination with [(3)H]glucose infusion. Glut4 mRNA expression was measured in skeletal muscle.

RESULTS

Plasma glucose and insulin concentrations under basal and hyperinsulinaemic conditions were similar in MTII- and placebo-treated mice. Endogenous glucose production (EGP) and glucose disposal in the basal state were significantly higher in MTII-treated mice than in the control group (71+/-22 vs 43+/-12 micromol.min(-1).kg(-1), p<0.01). During hyperinsulinaemia, glucose disposal was significantly higher in MTII-treated mice (151+/-20 vs 108+/-20 micromol.min(-1).kg(-1), p<0.01). In contrast, the inhibitory effect of insulin on EGP was not affected by MTII (relative decrease in EGP: 45+/-27 vs 50+/-20%). Glut4 mRNA expression in skeletal muscle was significantly increased in MTII-treated mice (307+/-94 vs 100+/-56%, p<0.01).

CONCLUSIONS/INTERPRETATION

Intracerebroventricular administration of MTII acutely increases insulin-mediated glucose disposal but does not affect the capacity of insulin to suppress EGP in C57Bl/6 mice. These data indicate that central stimulation of melanocortin-3/4 receptors modulates insulin sensitivity in a tissue-specific manner, independent of its well-known impact on feeding and body weight.

The B domain of coagulation factor VIII interacts with the asialoglycoprotein receptor

BACKGROUND

Coagulation factor VIII (FVIII) is a heavily glycosylated heterodimeric plasma protein that consists of a heavy (domains A1-A2-B) and light chain (domains A3-C1-C2). It has been well established that the clearance of FVIII from the circulation involves mechanisms that are sensitive to the low-density lipoprotein receptor (LDLR) family antagonist receptor-associated protein (RAP), including LDLR-related protein. Because FVIII clearance in the presence of a bolus injection of RAP still occurs fairly efficient, also RAP-independent mechanisms are likely to be involved.

OBJECTIVES

In the present study, we investigated the interaction of FVIII with the endocytic lectin asialoglycoprotein receptor (ASGPR) and the physiological relevance thereof.

METHODS AND RESULTS

Surface plasmon resonance studies demonstrated that FVIII dose-dependently bound to ASGPR with high affinity (Kd approximately 2 nM). FVIII subunits were different in that only the heavy chain displayed high-affinity binding to ASGPR. Studies employing a FVIII variant that lacks the B domain revealed that FVIII-ASGPR complex assembly is driven by structure elements within the B domain of the heavy chain. The FVIII heavy chain-ASGPR interaction required calcium ions and was inhibited by soluble D-galactose. Furthermore, deglycosylation of the FVIII heavy chain by endoglycosidase F completely abrogated the interaction with ASGPR. In clearance experiments in mice, the FVIII mean residence time was prolonged by the ASGPR-antagonist asialo-orosomucoid (ASOR).

CONCLUSIONS

We conclude that asparagine-linked oligosaccharide structures of the FVIII B domain recognize the carbohydrate recognition domains of ASGPR and that an ASOR-sensitive mechanism, most likely ASGPR, contributes to the catabolism of coagulation FVIII in vivo.

No effect of C-reactive protein on early atherosclerosis development in apolipoprotein E*3-leiden/human C-reactive protein transgenic mice

OBJECTIVE

C-reactive protein (CRP) has been associated with risk of cardiovascular disease. It is not clear whether CRP is causally involved in the development of atherosclerosis. Mouse CRP is not expressed at high levels under normal conditions and increases in concentration only several-fold during an acute phase response. Because the dynamic range of human CRP is much larger, apolipoprotein E*3-Leiden (E3L) transgenic mice carrying the human CRP gene offer a unique model to study the role(s) of CRP in atherosclerosis development.

METHODS AND RESULTS

Atherosclerosis development was studied in 15 male and 15 female E3L/CRP mice; E3L transgenic littermates were used as controls. The mice were fed a hypercholesterolemic diet to induce atherosclerosis development. Cholesterol exposure did not differ between E3L/CRP and E3L mice. Plasma CRP levels were on average 10.2+/-6.5 mg/L in male E3L/CRP mice, 0.2+/-0.1 mg/L in female E3L/CRP mice, and undetectable in E3L mice. Quantification of atherosclerosis showed that lesion area in E3L/CRP mice was not different from that in E3L mice.

CONCLUSIONS

This study demonstrates that mildly elevated levels of CRP in plasma do not contribute to the development of early atherosclerosis in hypercholesterolemic E3L/CRP mice.

Hepatic steatosis: a mediator of the metabolic syndrome. Lessons from animal models

Epidemiological studies in humans, as well as experimental studies in animal models, have shown an association between visceral obesity and dyslipidemia, insulin resistance, and type 2 diabetes mellitus. Recently, attention has been focused on the excessive accumulation of triglycerides (TG) in the liver as part of this syndrome. In this review, important principles of the pathophysiological involvement of the liver in the metabolic syndrome obtained in rodent models are summarized. We focus on non-alcoholic causes of steatosis, because the animal experiments we refer to did not include alcohol as an experimental condition. In general, there is continuous cycling and redistribution of non-oxidized fatty acids between different organs. The amount of TG in an intrinsically normal liver is not fixed but can readily be increased by nutritional, metabolic, and endocrine interactions involving TG/free fatty acid (FFA) partitioning and TG/FFA metabolism. Several lines of evidence indicate that hepatic TG accumulation is also a causative factor involved in hepatic insulin resistance. Complex interactions between endocrine, metabolic, and transcriptional pathways are involved in TG-induced hepatic insulin resistance. Therefore, the liver participates passively and actively in the metabolic derangements of the metabolic syndrome. We speculate that similar mechanisms may also be involved in human pathophysiology.

White adipose tissue: getting nervous

Neuroendocrine research has altered the traditional perspective of white adipose tissue (WAT) as a passive store of triglycerides. In addition to fatty acids, WAT produces many hormones and can therefore be designated as a traditional endocrine gland actively participating in the integrative physiology of fuel and energy metabolism, eating behaviour and the regulation of hormone secretion and sensitivity. WAT is controlled by humoral factors, para- and intracrine factors and by neural regulation. Sympathetic nerve fibres innervate WAT and stimulate lipolysis, leading to the release of glycerol and free fatty acids. In addition, recent research in rats has clearly shown a functional parasympathetic innervation of WAT. There appears to be a distinct somatotopy within the parasympathetic nuclei: separate sets of autonomic neurones in the brain stem innervate either the visceral or the subcutaneous fat compartment. We therefore propose that the central nervous system (CNS) plays a major role in the hitherto unexplained regulation of body fat distribution. Parasympathectomy induces insulin resistance with respect to glucose and fatty acid uptake in the innervated fat depot and has selective effects on local hormone synthesis. Thus, the CNS is involved not only in the regulation of hormone production by WAT, but also in its hormone sensitivity. The developments in this research area are likely to increase our insights in the pathogenesis of metabolic disorders such as hypertriglyceridemia, diabetes mellitus type 2 and lipodystrophy syndromes.

Long term efficacy and safety of atorvastatin in the treatment of severe type III and combined dyslipidaemia

BACKGROUND

Fibric acid derivatives and HMG-CoA reductase inhibitors are effective in combination for treating patients with familial dysbetalipoproteinaemia and severe combined dyslipidaemia, but combination therapy affects compliance and increases the risk of side effects.

AIM

To evaluate the efficacy and safety of monotherapy with atorvastatin, an HMG-CoA reductase inhibitor with superior efficacy in lowering low density lipoprotein cholesterol and triglyceride concentrations, in patients with dysbetalipoproteinaemia and severe combined dyslipidaemia.

METHODS

Atorvastatin was tested as single drug treatment in 36 patients with familial dysbetalipoproteinaemia and 23 patients with severe combined dyslipidaemia.

RESULTS

After 40 weeks of 40 mg atorvastatin treatment decreases in total cholesterol, triglycerides, and apolipoprotein B of 40%, 43%, and 41%, respectively, were observed in the combined dyslipidaemia group, and of 46%, 40%, and 43% in the dysbetalipoproteinaemic patients. Target concentrations of total cholesterol (< 5 mmol/l) were reached by 63% of the patients, and target concentrations of triglycerides (< 3.0 mmol/l) by 66%. Treatment with atorvastatin was well tolerated and no serious side effects were reported.

CONCLUSIONS

Atorvastatin is very effective as monotherapy in the treatment of familial dysbetalipoproteinaemia and severe combined dyslipidaemia.

Inhibition of accelerated atherosclerosis in vein grafts by placement of external stent in apoE*3-Leiden transgenic mice

OBJECTIVE

Vein grafts fail because of the development of intimal hyperplasia and accelerated atherosclerosis. Placement of an external stent around vein grafts resulted in an inhibition of intimal hyperplasia in several animal studies. Here, we assess the effects of external stenting on accelerated atherosclerosis in early vein grafts in carotid arteries in hypercholesterolemic apolipoprotein E*3-Leiden transgenic mice.

METHODS AND RESULTS

Venous interposition grafting was performed in apolipoprotein E*3-Leiden mice fed standard chow or a highly cholesterol-rich diet for 4 weeks. After engraftment, external stents with different inner diameters (0.4 or 0.8 mm) were placed. In unstented vein grafts in hypercholesterolemic mice, thickening up to 50 times the original thickness, with foam cell-rich lesions, calcification, and necrosis, was observed within 28 days. The atherosclerotic lesions observed show high morphological resemblance to atherosclerotic lesions observed in human vein grafts. In stented vein grafts in hypercholesterolemic mice, no foam cell accumulation or accelerated atherosclerosis was observed. Compared with unstented vein grafts, stenting of vein grafts in a hypercholesterolemic environment resulted in a 94% reduction of vessel wall thickening. These effects were independent of stent size.

CONCLUSIONS

Extravascular stent placement results in strong inhibition of accelerated vein graft atherosclerosis in hypercholesterolemic transgenic mice and thereby provides a perspective for therapeutic intervention in vein graft diseases.

Effect of the APOE-491A/T promoter polymorphism on apolipoprotein E levels and risk of Alzheimer disease: The Rotterdam Study

The apolipoprotein E (APOE) gene is involved in lipid transport. A common polymorphism in this gene with the APOE*2, APOE*3, and APOE*4 alleles influences plasma levels of apolipoprotein E and cholesterol. Besides its role in lipid transport, the APOE*4 allele is a genetic risk factor for Alzheimer disease (AD). Recently, a polymorphism in the APOE promoter region was found to be involved in plasma apolipoprotein E levels and was found associated with AD. We studied the effect of this -491A/T promoter polymorphism on plasma apolipoprotein E levels and risk for AD in a population-based case-control study. We found that there was a modest but statistically significant effect of the -491A/T polymorphism on plasma apolipoprotein E levels independent of the APOE genotype. The lowest plasma levels were measured for the AA genotype, highest levels for the TT genotype, and intermediate levels for the heterozygotes. There was a small effect of the -491 AA genotype on AD risk that disappeared after adjusting for APOE genotypes. Our data suggest that the -491A/T polymorphism has an APOE genotype-independent effect on plasma apolipoprotein E levels but no APOE-independent effect on AD risk.

The effect of tibolone on the lipoprotein profile of postmenopausal women with type III hyperlipoproteinemia

OBJECTIVE

To investigate the short-term effect of treatment with tibolone on plasma lipid and lipoprotein levels in postmenopausal women with type III hyperlipoproteinemia (HLP).

DESIGN AND INTERVENTION

Patients were randomized to receive, in a double-blind cross-over fashion, a fixed dose of tibolone, 2.5 mg once daily or placebo for 8 weeks. The two treatment periods were separated by a wash-out period of 6 weeks. At each visit body weight and blood pressure were determined. Before and after each treatment period, fasting venous blood samples were obtained from the patients for biochemical measurements.

SETTING

The Leiden University Medical Center.

SUBJECTS

Postmenopausal women with type III HLP (aged < or = 65 years) were recruited from the Lipid Clinics of the Leiden University Medical Center, the Amsterdam Medical Center, the Utrecht Medical Center and the University Hospital Rotterdam. Five out of 25 women with type III HLP were eligible to be included in the study. Four of the five included patients completed the study according to the protocol. One patient was excluded from blinded therapy because total cholesterol levels increased above 20 mmol L(-1).

MAIN OUTCOME MEASURES

A significant reduction of plasma triglyceride, total cholesterol, VLDL cholesterol and VLDL triglyceride levels.

RESULTS

Plasma triglyceride and total cholesterol levels decreased from 6.82 +/- 3.58 to 2.45 +/- 1.36 mmol L(-1) and from 13.53 +/- 3.64 to 6.61 +/- 2.03 mmol L(-1), respectively (both P < 0.05). The body mass index remained unchanged. The glycated haemoglobin percentage decreased significantly from 5.8 to 5.3%. Treatment with tibolone resulted in a profound reduction in plasma apolipoprotein E, VLDL cholesterol and VLDL triglyceride levels (mean reductions of 66, 77 and 70%, respectively, P < 0.05).

CONCLUSIONS

Tibolone is a valuable adjuvant to current therapy in postmenopausal women with type III HLP.

Identification of differentially regulated genes in mildly hyperlipidemic ApoE3-Leiden mice by use of serial analysis of gene expression

Although genes determining lipoprotein homeostasis and atherosclerosis are the subject of intensive investigation, only a subset of these genes is known at present. Hence, we do not have sufficient knowledge to explain the genetic basis of hyperlipidemia in the majority of subjects. Our aim was to identify novel genes and pathways underlying lipoprotein homeostasis by using serial analysis of gene expression. The liver expression profile of mild hyperlipidemic apolipoprotein E3-Leiden (E3L) transgenic mice was compared with that of the wild-type C57BL/6JIco (B6) mice. Over 18 000 liver transcripts of B6 as well as E3L mice were analyzed, representing >9400 unique genes. One hundred seventy-five genes showed altered expression between the strains (P<0.05). Although several of these genes belonged to known metabolic pathways, such as lipoprotein metabolism, detoxification processes, glycolysis, and the acute-phase response, most were novel. Differential gene expression of 8 of 10 genes tested could be confirmed by Northern blot analysis. This inventory of differentially expressed genes will provide a unique basis for detailed studies to gain more insight into their role in lipoprotein homeostasis and atherosclerosis.

Protection from obesity and insulin resistance in mice overexpressing human apolipoprotein C1

Apolipoprotein (APO) C1 is a 6.6-kDa protein present in plasma and associated with lipoproteins. Using hyperinsulinemic-euglycemic clamp tests, we previously found that in APOC1 transgenic mice, the whole-body insulin-mediated glucose uptake is increased concomitant with a decreased fatty acid uptake. These latter results are confirmed in the present study, showing that APOC1 transgenic mice exhibit a 50% reduction in the uptake of the fatty acid analog 15-(p-iodophenyl)-3-(R,S)-methyl pentadecanoic acid in white adipose tissue stores. We next investigated whether APOC1 overexpression can modulate the initiation and/or development of obesity and insulin resistance. When crossbred on the genetically obese ob/ob background, APOC1 transgenic mice were fully protected from the development of obesity compared with ob/ob only mice, as reflected by a strong reduction in body weight (21 +/- 4 vs. 44 +/- 7 g), total adipose tissue stores (15 +/- 3 vs. 25 +/- 3% body wt), and average adipocyte size (7,689 +/- 624 vs. 15,295 +/- 1,289 microm(2)). Although less pronounced, APOC1 overexpression also reduced body weight on a wild-type background, solely due to a reduction in adipose tissue. Furthermore, despite elevated plasma free fatty acid and triglyceride levels, APOC1 overexpression significantly improved insulin sensitivity in ob/ob mice, as demonstrated by a strong reduction in plasma glucose and insulin levels, as well as a better performance in the glucose tolerance test. In conclusion, a marked reduction in the uptake of fatty acids into adipocytes may underlie the protection from obesity and insulin resistance in transgenic mice overexpressing human APOC1.

Stimulation of the in vivo production of very low density lipoproteins by apolipoprotein E is independent of the presence of the low density lipoprotein receptor

Apolipoprotein (apo) E stimulates the secretion of very low density lipoproteins (VLDLs) by an as yet unknown mechanism. Recently, a working mechanism for apoE was proposed (Twisk, J., Gillian-Daniel, D. L., Tebon, A., Wang, L., Barrett, P. H., and Attie, A. D. (2000) J. Clin. Invest. 105, 521-532) in which apoE prevents the inhibitory action of the low density lipoprotein receptor (LDLr) by binding to it. We have first tested whether this newly described effect of the LDLr on VLDL secretion, obtained in vitro, is also observed in vivo. In LDLr knockout mice (LDLr-/-), the production of VLDL triglycerides and apoB was 30% higher than that in controls. Also the ratio of apoB100:apoB48 secretion was increased in the LDLr-/- mice. The composition of nascent VLDL was similar in both strains. To test whether the action of apoE depends on the presence of the LDLr, VLDL production was measured in LDLr-/- and apoE-/- LDLr-/- mice. Deletion of apoE on a LDLr-/- background still caused a 50% decrease of VLDL triglycerides and apoB production. The composition of nascent VLDL was again similar for both strains. We conclude that the effect of apoE on hepatic VLDL production is independent of the presence of the LDLr.

In muscle-specific lipoprotein lipase-overexpressing mice, muscle triglyceride content is increased without inhibition of insulin-stimulated whole-body and muscle-specific glucose uptake

In patients with type 2 diabetes, a strong correlation between accumulation of intramuscular triclycerides (TGs) and insulin resistance has been found. The aim of the present study was to determine whether there is a causal relation between intramuscular TG accumulation and insulin sensitivity. Therefore, in mice with muscle-specific overexpression of human lipoprotein lipase (LPL) and control mice, muscle TG content was measured in combination with glucose uptake in vivo, under hyperinsulinemic-euglycemic conditions. Overexpression of LPL in muscle resulted in accumulation of TGs in skeletal muscle (85.5 +/- 33.3 vs. 25.7 +/- 23.1 micromol/g tissue in LPL and control mice, respectively; P < 0.05). During the hyperinsulinemic clamp study, there were no differences in plasma glucose, insulin, and FFA concentrations between the two groups. Moreover, whole-body, as well as skeletal muscle, insulin-mediated glucose uptake did not differ between LPL-overexpressing and wild-type mice. Surprisingly, whole-body glucose oxidation was decreased by approximately 60% (P < 0.05), whereas nonoxidative glucose disposal was increased by approximately 50% (P < 0.05) in LPL-overexpressing versus control mice. In conclusion, overexpression of human LPL in muscle increases intramuscular TG accumulation, but does not affect whole-body or muscle-specific insulin-mediated uptake, findings that argue against a simple causal relation between intramuscular TG content and insulin resistance.

Apolipoprotein C-III deficiency accelerates triglyceride hydrolysis by lipoprotein lipase in wild-type and apoE knockout mice

Previous studies with hypertriglyceridemic APOC3 transgenic mice have suggested that apolipoprotein C-III (apoC-III) may inhibit either the apoE-mediated hepatic uptake of TG-rich lipoproteins and/or the lipoprotein lipase (LPL)-mediated hydrolysis of TG. Accordingly, apoC3 knockout (apoC3(-/-)) mice are hypotriglyceridemic. In the present study, we attempted to elucidate the mechanism(s) underlying these phenomena by intercrossing apoC3(-/-) mice with apoE(-/-) mice to study the effects of apoC-III deficiency against a hyperlipidemic background. Similar to apoE(+/+) apoC3(-/-) mice, apoE(-/-)apoC3(-/-) mice exhibited a marked reduction in VLDL cholesterol and TG, indicating that the mechanism(s) by which apoC-III deficiency exerts its lipid-lowering effect act independent of apoE. On both backgrounds, apoC3(-/-) mice showed normal intestinal lipid absorption and hepatic VLDL TG secretion. However, turnover studies showed that TG-labeled emulsion particles were cleared much more rapidly in apoC3(-/-) mice, whereas the clearance of VLDL apoB, as a marker for whole particle uptake by the liver, was not affected. Furthermore, it was shown that cholesteryl oleate-labeled particles were also cleared faster in apoC3(-/-) mice. Thus the mechanisms underlying the hypolipidemia in apoC3(-/-) mice involve both a more efficient hydrolysis of VLDL TG as well as an enhanced selective clearance of VLDL cholesteryl esters from plasma. In summary, our studies of apoC3(-/-) mice support the concept that apoC-III is an effective inhibitor of VLDL TG hydrolysis and reveal a potential regulating role for apoC-III with respect to the selective uptake of cholesteryl esters.

Raman spectroscopic evaluation of the effects of diet and lipid-lowering therapy on atherosclerotic plaque development in mice

Quantitative characterization of atherosclerotic plaque composition with standard histopathological methods remains limited to sectioned plaques. Raman spectroscopy enables nondestructive quantification of atherosclerotic plaque composition. We used Raman spectroscopy to study the effects of diet and lipid-lowering therapy on plaque development in apolipoprotein (APO) E*3-Leiden transgenic mice. Raman spectra were obtained over the full width and entire length of the ascending aorta and aortic arch. Spectra were modeled to calculate the relative dry weights of cholesterol and calcium salts, and quantitative maps of their distribution were created. In male mice (n=20) that received a high-fat/high-cholesterol (HFC) diet for 0, 2, 4, or 6 months, Raman spectroscopy showed good correlation between cholesterol accumulation and total serum cholesterol exposure (r approximately 0.87, P<0.001). In female mice (n=10) that were assigned to an HFC diet, with or without 0.01% atorvastatin, a strong reduction in cholesterol accumulation (57%) and calcium salts (97%) (P<0.01) was demonstrated in the atorvastatin-treated group. In conclusion, Raman spectroscopy can be used to quantitatively study the size and distribution of depositions of cholesterol and calcification in APOE*3-Leiden transgenic mice. This study encourages Raman spectroscopy for the quantitative investigation of atherosclerosis and lipid-lowering therapy in larger animals or humans in vivo.

Protection from obesity in mice lacking the VLDL receptor

It has previously been reported that mice lacking the VLDL receptor (VLDLR-/-) exhibit normal plasma lipid levels and a modest decrease in adipose tissue mass. In the present study, the effect of VLDLR deficiency on profound weight gain was studied in mice. Obesity was induced either by feeding of a high-fat, high-calorie (HFC) diet or by crossbreeding mice onto the genetically obese ob/ob background. After 17 weeks of HFC feeding, VLDLR-/- mice remained lean, whereas their wild-type littermates (VLDLR+/+) became obese. Similarly, the weight gain of ob/ob mice was less profound in the absence of the VLDLR. Moreover, VLDLR deficiency led to increased plasma triglycerides after HFC feeding. The protection from obesity in VLDLR-/- mice involved decreased peripheral uptake of fatty acids, because VLDLR-/- mice exhibited a significant reduction in whole-body free fatty acid uptake, with no clear differences in food intake and fat absorption. These observations were supported by a strong decrease in average adipocyte size in VLDLR-/- mice of both obesity models, implying reduced adipocyte triglyceride storage in the absence of the VLDLR. These results suggest that the VLDLR plays a role in the delivery of VLDL-derived fatty acids into adipose tissue.

Apolipoprotein E and carotid artery atherosclerosis: the Rotterdam study

BACKGROUND AND PURPOSE

Carotid artery atherosclerosis is a strong predictor for future stroke. It is yet unclear whether the apolipoprotein E polymorphism (APOE) is related to atherosclerosis in the carotid arteries. The aim of the present study was to investigate the role of APOE in carotid artery atherosclerosis.

METHODS

A population-based cross-sectional study was performed on 5401 subjects. Atherosclerosis was noninvasively assessed by the common carotid artery intima-media wall thickness and the presence of plaques in the carotid arteries. The relationship of the 6 APOE genotypes with these 2 indicators was studied with linear and logistic regression analysis, respectively, with adjustments for age and sex.

RESULTS

Carriers of the E2E3 genotype had a thinner intima-media wall thickness (mean difference, -0.02 mm; 95% CI, -0.03 to -0.01 mm) and fewer plaques (odds ratio for >3 plaques at 6 sites, 0.6; 95% CI, 0.4 to 0.8) than the most common group, E3E3. The E4E4 group had slightly more atherosclerosis, but this was not statistically significant. Adjusting for the level of the apolipoprotein E protein (apoE) in serum or total or HDL cholesterol did not essentially change these findings.

CONCLUSIONS

Our results suggest that APOE*4 is not an important risk factor for carotid artery atherosclerosis. The inverse relationship of E2E3 with carotid artery atherosclerosis seems to be independent of serum apoE and total and HDL cholesterol levels. However, the low frequency, together with the small effects, implies that any protective effect of E2E3 on carotid artery atherosclerosis is limited.

The amino-terminal 1-185 domain of apoE promotes the clearance of lipoprotein remnants in vivo. The carboxy-terminal domain is required for induction of hyperlipidemia in normal and apoE-deficient mice

Apolipoprotein E (apoE) promotes receptor-mediated catabolism of apoE-containing lipoprotein remnants. Impairments in remnant clearance are associated with type III hyperlipoproteinemia and premature atherosclerosis. In humans, apoE plasma levels correlate with plasma triglyceride levels, suggesting that excess apoE may also affect plasma triglyceride levels. We have used adenovirus-mediated gene transfer in mice to map the domains of apoE required for cholesterol and triglyceride clearance, in vivo. Adenovirus expressing apoE3 and apoE4 at doses of (1-2) x 10(9) pfu increased plasma cholesterol and triglyceride levels in normal C57BL6 mice and failed to normalize the high cholesterol levels of apoE-deficient mice due to induction of hypertriglyceridemia. In contrast, an adenovirus expressing the truncated apoE 1-185 form normalized the cholesterol levels of E(-)(/)(-) mice and did not cause hypertriglyceridemia. Northern blot analysis of hepatic RNA from mice expressing the full-length and the truncated apoE forms showed comparable steady-state apoE mRNA levels of the full-length apoE forms that cause hyperlipidemia and the truncated apoE forms that do not cause hyperlipidemia. The findings suggest that the amino-terminal residues 1-185 of apoE are sufficient for the clearance of apoE-containing lipoprotein remnants by the liver, whereas domains of the carboxy-terminal one-third of apoE are required for apoE-induced hyperlipidemia.

Dietary vegetable oil and wood derived plant stanol esters reduce atherosclerotic lesion size and severity in apoE*3-Leiden transgenic mice

The hypolipidemic and anti-atherosclerotic effects of vegetable oil- and wood-based dietary plant stanol esters were compared in female apoE*3-Leiden transgenic mice at relevant plasma cholesterol levels. The plant stanol esters derived from vegetable oil (sitostanol 65.7%, campestanol 30.1%) had different contents of sitostanol and campestanol than the plant stanol esters derived from wood (sitostanol 87.6%, campestanol 9.5%) or from a mixture of vegetable oil and wood (sitostanol 73.0%, campestanol 24.7%). The mice (10 per group) received for 38 weeks a control diet or diets containing 1.0% (w/w) plant stanol esters derived from either vegetable oil, wood or a mixture of both. Vegetable oil (-46%), wood (-42%) and vegetable oil/wood (-51%) plant stanol esters decreased the plasma cholesterol levels (P<0.0001) by reducing the cholesterol content in plasma very low density-, intermediate density- and to a lesser extent in low density-lipoprotein. Plant stanol ester feeding did not change plasma triglyceride levels. Dietary plant stanol esters reduced the atherosclerotic lesion area by 91+/-13% (vegetable oil), 97+/-4% (wood) and 78+/-34% (vegetable oil/wood) (P<0.0001) and the severity from regular intimal fatty streaks/mild plaques (on average type 2--3 lesions) in controls to individual intimal foam cells (<type 1 lesions) in the treatment groups (P<0.0001). Plant stanol esters had no effect on adherence of monocytes to the vessel wall. Feeding of plant stanol esters dramatically reduced, independent of its sources, the extent and severity of atherosclerotic lesions, by decreasing VLDL-, IDL- and to a lesser extent LDL-cholesterol in apoE*3-Leiden transgenic mice.

Mice expressing only the mutant APOE3Leiden gene show impaired VLDL secretion

Apolipoprotein E (apoE)-deficient mice develop hepatic steatosis and show impaired very low density lipoprotein (VLDL)-triglyceride (TG) secretion. These effects are normalized on the introduction of the human APOE3 gene. To assess whether this apoE effect is isoform specific, we studied hepatic lipid metabolism in mice expressing either APOE3 or the mutant APOE3Leiden on apoe-/- or apoe+/- backgrounds. The transgenes were expressed mainly in periportal hepatocytes, as revealed by in situ hybridization. Mice expressing APOE3Leiden, on the apoe-/- and apoe+/- backgrounds, had fatty livers, which were absent in APOE3/apoe-/- mice. APOE3Leiden/apoe-/- mice showed a strongly reduced VLDL-TG secretion compared with APOE3/apoe-/- mice (48+/-14 versus 82+/-10 micromol/kg per hour, respectively). The presence of a single mouse apoe allele increased VLDL-TG secretion in APOE3Leiden/apoe+/- mice (121+/-43 micromol/kg per hour) compared with APOE3Leiden/apoe-/- mice. These results show that APOE3Leiden does not prevent development of a fatty liver and does not normalize VLDL-TG secretion in mice with an apoE-deficient background. The presence of a single mouse apoe allele is sufficient to normalize the APOE3Leiden-associated reduction of VLDL-TG secretion but does not prevent steatosis. We conclude that apoE-mediated stimulation of VLDL secretion is isoform specific.

Apolipoprotein E protects against neuropathology induced by a high-fat diet and maintains the integrity of the blood-brain barrier during aging

SUMMARY

The present study provides evidence that chronic intake of a high-fat diet induces a dramatic extravasation of immunoglobulins, indicating alterations in blood-brain barrier (BBB) functioning, in the brains of apolipoprotein E (apoE)-knockout mice, but not of C57Bl/6 control mice. Using sodium fluorescein as a marker for the permeability of the BBB, we found additional support for age-related disturbances of BBB function in apoE-knockout mice. Behavioral analysis of apoE-knockout mice compared with C57Bl/6 mice indicated that they were also less efficient in acquiring the spatial Morris water maze task. Furthermore, apoE-knockout mice are known to develop severe atherosclerosis, which is exacerbated with a high-fat diet. We therefore compared the apoE-knockout mice with the apoE3-Leiden transgenic mice, which are known to develop atherosclerosis. However, apoE3-Leiden mice that were kept on a high-fat, high-cholesterol diet and that developed atherosclerosis to an extent similar to the apoE-knockout mice, showed no signs of BBB disturbances. These results indicate for the first time that apoE plays an essential role in the maintenance of the integrity of the BBB during aging and that it protects the brain from neuropathology induced by a high-fat diet. We therefore hypothesize that the role of apoE in the maintenance of the integrity of the BBB may be the mechanism by which apoE affects the progression of neurodegeneration, as seen in Alzheimer's disease.

Domains of apolipoprotein E contributing to triglyceride and cholesterol homeostasis in vivo. Carboxyl-terminal region 203-299 promotes hepatic very low density lipoprotein-triglyceride secretion

Apolipoprotein (apo) E has been implicated in cholesterol and triglyceride homeostasis in humans. At physiological concentration apoE promotes efficient clearance of apoE-containing lipoprotein remnants. However, high apoE plasma levels correlate with high plasma triglyceride levels. We have used adenovirus-mediated gene transfer in apoE-deficient mice (E(-)/-) to define the domains of apoE required for cholesterol and triglyceride homeostasis in vivo. A dose of 2 x 10(9) plaque-forming units of apoE4-expressing adenovirus reduced slightly the cholesterol levels of E(-)/- mice and resulted in severe hypertriglyceridemia, due to accumulation of cholesterol and triglyceride-rich very low density lipoprotein particles in plasma. In contrast, the truncated form apoE4-202 resulted in a 90% reduction in the plasma cholesterol levels but did not alter plasma triglyceride levels in the E(-)/- mice. ApoE secretion by cell cultures, as well as the steady-state hepatic mRNA levels in individual mice expressing apoE4 or apoE4-202, were similar. In contrast, very low density lipoprotein-triglyceride secretion in mice expressing apoE4, but not apoE4-202, was increased 10-fold, as compared with mice infected with a control adenovirus. The findings suggest that the amino-terminal 1-202 region of apoE4 contains the domains required for the in vivo clearance of lipoprotein remnants. Furthermore, the carboxyl-terminal 203-299 residues of apoE promote hepatic very low density lipoprotein-triglyceride secretion and contribute to apoE-induced hypertriglyceridemia.

Living up to a name: the role of the VLDL receptor in lipid metabolism

The VLDL receptor (VLDLR) is a member of the LDL receptor family. The VLDLR was hypothesized to mediate fatty acid entry into peripheral tissues, on the basis of its expression in tissues that are active in fatty acid metabolism and its capacity to bind apolipoprotein-E-rich VLDL in vitro. This hypothesis initially proved difficult to confirm, because VLDLR-knockout mice were reported to display normal plasma lipid levels. Moreover, studies in VLDLR-knockout mice that were also deficient in a second LDL receptor family member, the apolipoprotein E receptor 2, indicated a role for the VLDLR in neuronal migration during brain development. However, in accordance with what the term VLDLR suggests, recent studies using VLDLR-deficient and transgenic mice have provided compelling evidence that the VLDLR does indeed play a role in VLDL-triglyceride metabolism, and that it is important for triglyceride storage in the adipocyte.

Dietary plant stanol esters reduce VLDL cholesterol secretion and bile saturation in apolipoprotein E*3-Leiden transgenic mice

Dietary plant stanols lower serum cholesterol levels in humans and in hyperlipidemic rodents, mainly by inhibition of the intestinal cholesterol absorption. We used female apolipoprotein E*3-Leiden transgenic mice to investigate the consequences of this effect on serum lipid levels and hepatic lipid metabolism. Five groups of 6 or 7 mice received for 9 weeks a diet containing 0.25% cholesterol and 0.0%, 0.25%, 0.5%, 0.75%, or 1.0% (wt/wt) plant stanols (sitostanol 88% [wt/wt], campestanol 10% [wt/wt]) esterified to fatty acids. Compared with the control diet, plant stanol ester treatment dose-dependently reduced serum cholesterol levels by 10% to 33% (P<0.05), mainly in very low density lipoproteins (VLDLs), intermediate density lipoproteins, and low density lipoproteins. Furthermore, 1.0% of the dietary plant stanols significantly decreased the liver contents of cholesteryl esters (-62%), free cholesterol (-31%), and triglycerides (-38%) but did not change the hepatic VLDL-triglyceride and VLDL-apolipoprotein B production rates. However, plant stanol ester feeding significantly decreased the amounts of cholesteryl esters and free cholesterol incorporated in nascent VLDLs by 72% and 30%, respectively, resulting in a net 2-fold decreased VLDL cholesterol output. Liver mRNA levels of low density lipoprotein receptors, 3-hydroxy-3-methylglutaryl coenzyme A synthase, cholesterol 7alpha-hydroxylase, and sterol 27-hydroxylase were not changed by plant stanol ester feeding. Nevertheless, the serum lathosterol-to-cholesterol ratio was significantly increased by 23%, indicating that dietary plant stanol esters increased whole-body cholesterol synthesis. Plant stanol esters also significantly decreased the cholesterol saturation index in bile by 55%. In conclusion, in apolipoprotein E*3-Leiden transgenic mice, plant stanol ester feeding dose-dependently lowered serum cholesterol levels as a result of a reduced secretion of VLDL cholesterol. This was caused by a decreased hepatic cholesterol content that also resulted in a lowered biliary cholesterol output, indicative of a reduced lithogenicity of bile in these mice.

Effective generation of very low density lipoprotein receptor transgenic mice by overlapping genomic DNA fragments: high testis expression and disturbed spermatogenesis

The generation of functional transgenes via microinjection of overlapping DNA fragments has previously been reported to be successful, but it is still not a widely applied approach. Here we show that the method is very reliable, and should be considered, in case a single large insert clone of the desired gene is not available. In the present study, two large DNA fragments consisting of overlapping cosmids, together constituting the human very low density lipoprotein receptor (VLDLR) gene (35 kb), were used to generate VLDLR transgenic (VLDLR-Tg) mice. Three transgenic founders were born, of which two (strain #2 and #3) generated transgenic offspring. Using Fiber-FISH analysis, the integration site was shown to contain at least 44 and 64 DNA fragments in mouse strains #2 and #3, respectively. This copy number resulted in integration sites of 1.5 and 2.5 megabase in size. Notably, over 90% of the fragments in both mouse strains #2 and #3 were flanked by their complementary fragment. In line with this observation, Southern blot analysis demonstrated that the correct recombination between fragments predominated in the transgenic insertion. Human VLDLR expression was detected in testis, kidney and brain of both mouse strains. Since this pattern did not parallel the endogenous VLDLR expression, some crucial regulatory elements were probably not present in the cosmid clones. Human VLDLR expression in testis was detected in germ cells up to the meiotic stage by in situ mRNA analysis. Remarkably, in the F1 generation of both VLDLR-Tg mouse strains the testis was atrophic and giant cells were detected in the semineferous tubuli. Furthermore, male VLDLR-Tg mice transmitted the transgene to their progeny with low frequencies. This could imply that VLDLR overexpression in the germ cells disturbed spermatogenesis.

Macrophage p53 deficiency leads to enhanced atherosclerosis in APOE*3-Leiden transgenic mice

Cell proliferation and cell death (either necrosis or apoptosis) are key processes in the progression of atherosclerosis. The tumor suppressor gene p53 is an essential gene in cell proliferation and cell death and is upregulated in human atherosclerotic plaques, both in smooth muscle cells and in macrophages. In the present study, we investigated the importance of macrophage p53 in the progression of atherosclerosis using bone marrow transplantation in APOE*3-Leiden transgenic mice, an animal model for human-like atherosclerosis. APOE*3-Leiden mice were lethally irradiated and reconstituted with bone marrow derived from either p53-deficient (p53(-/-)) or control (p53(+/+)) donor mice. Reconstitution of mice with p53(-/-) bone marrow did not result in any hemopoietic abnormalities as compared with p53(+/+) transplanted mice. After 12 weeks on an atherogenic diet, APOE*3-Leiden mice reconstituted with p53(-/-) bone marrow showed a significant (P=0.006) 2.3-fold increase in total atherosclerotic lesion area as compared with mice reconstituted with p53(+/+) bone marrow. Although likely a secondary effect of the increased lesion area, p53(-/-) transplanted mice also showed significantly more lesion necrosis (necrotic index, 1.1+/-1.3 versus 0.2+/-0.7; P=0.04) and lesion macrophages (macrophage area, 79.9+/-40.0 versus 39.7+/-27.3x10(3) micrometer(2) per section; P=0.02). These observations coincided with a tendency toward decreased apoptosis (terminal deoxynucleotidyl transferase end-labeling [TUNEL]-positive nuclei going from 0.42+/-0.39 to 0.14+/-0.15%, P=0.071), whereas the number of proliferating cells (5'-bromo-2'-deoxyuridine-positive nuclei) was not affected (3.75+/-0.98 versus 4.77+/-2.30%; P=0.59). These studies indicate that macrophage p53 is important in suppressing the progression of atherosclerosis and identify a novel therapeutic target for regulating plaque stability.

Acyl-CoA:cholesterol acyltransferase inhibitor avasimibe reduces atherosclerosis in addition to its cholesterol-lowering effect in ApoE*3-Leiden mice

BACKGROUND

The present study investigated whether the ACAT inhibitor avasimibe can reduce atherogenesis independently of its cholesterol-lowering effect in ApoE*3-Leiden mice.

METHODS AND RESULTS

Two groups of 15 female ApoE*3-Leiden mice were put on a high-cholesterol (HC) diet; 1 group received 0.01% (wt/wt) avasimibe mixed into the diet. The HC diet resulted in a plasma cholesterol concentration of 18.7+/-2.6 mmol/L. Addition of avasimibe lowered plasma cholesterol by 56% to 8.1+/-1.2 mmol/L, caused mainly by a reduction of and composition change in VLDL and LDL. In a separate low-cholesterol (LC) control group, plasma cholesterol was titrated to a level comparable to that of the avasimibe group (10.3+/-1.4 mmol/L) by lowering the amount of dietary cholesterol. After 22 weeks of intervention, atherosclerosis in the aortic root area was quantified. Treatment with avasimibe resulted in a 92% reduction of lesion area compared with the HC control group. Compared with the LC control, avasimibe reduced lesion area by 78%. After correction for the slight difference in cholesterol exposure between the LC control and avasimibe groups, the effect of avasimibe on lesion area (73% reduction) remained highly significant. In addition, monocyte adherence to the endothelium, free cholesterol accumulation, and lesion severity were reduced by avasimibe treatment.

CONCLUSIONS

Treatment with avasimibe potently lowered plasma cholesterol levels in ApoE*3-Leiden mice and considerably reduced atherosclerotic lesion area in addition to its cholesterol-lowering effect. Because monocyte adherence to the endothelium and lesion severity were also reduced by avasimibe, treatment with avasimibe may result in higher plaque stability and therefore a reduced risk of plaque rupture.

Hyperlipidaemia is associated with increased insulin-mediated glucose metabolism, reduced fatty acid metabolism and normal blood pressure in transgenic mice overexpressing human apolipoprotein C1

AIMS/HYPOTHESIS

Insulin resistance for glucose metabolism is associated with hyperlipidaemia and high blood pressure. In this study we investigated the effect of primary hyperlipidaemia on basal and insulin-mediated glucose and on non-esterified fatty acid (NEFA) metabolism and mean arterial pressure in hyperlipidaemic transgenic mice overexpressing apolipoprotein C1 (APOC1). Previous studies have shown that APOC1 transgenic mice develop hyperlipidaemia primarily because of an impaired hepatic uptake of very low density lipoprotein (VLDL).

METHODS

Basal and hyperinsulinaemic (6 mU.kg-1.min-1), euglycaemic (7 mmol/l) clamps with 3(-)3H-glucose or 9,10(-)3H-palmitic acid infusions and in situ freeze clamped tissue collection were carried out.

RESULTS

The APOC1 mice showed increased basal plasma cholesterol, triglyceride, NEFA and decreased glucose concentrations compared with wild-type mice (7.0 +/- 1.2 vs 1.6 +/- 0.1, 9.1 +/- 2.3 vs 0.6 +/- 0.1, 1.9 +/- 0.2 vs 0.9 +/- 0.1 and 7.0 +/- 1.0 vs 10.0 +/- 1.1 mmol/l, respectively, p < 0.05). Basal whole body glucose clearance was increased twofold in APOC1 mice compared with wild-type mice (18 +/- 2 vs 10 +/- 1 ml.kg-1.min-1, p < 0.05). Insulin-mediated whole body glucose uptake, glycolysis (generation of 3H2O) and glucose storage increased in APOC1 mice compared with wild-type mice (339 +/- 28 vs 200 +/- 11; 183 +/- 39 vs 128 +/- 17 and 156 +/- 44 vs 72 +/- 17 mumol.kg-1.min-1, p < 0.05, respectively), corresponding with a twofold to threefold increase in skeletal muscle glycogenesis and de novo lipogenesis from 3-(3)H-glucose in skeletal muscle and adipose tissue (p < 0.05). Basal whole body NEFA clearance was decreased threefold in APOC1 mice compared with wild-type mice (98 +/- 21 vs 314 +/- 88 ml.kg-1.min-1, p < 0.05). Insulin-mediated whole body NEFA uptake, NEFA oxidation (generation of 3H2O) and NEFA storage were lower in APOC1 mice than in wild-type mice (15 +/- 3 vs 33 +/- 6; 3 +/- 2 vs 11 +/- 4 and 12 +/- 2 vs 22 +/- 4 mumol.kg-1.min-1, p < 0.05) in the face of higher plasma NEFA concentrations (1.3 +/- 0.3 vs 0.5 +/- 0.1 mmol/l, p < 0.05), respectively. Mean arterial pressure and heart rate were similar in APOC1 vs wild-type mice (82 +/- 4 vs 85 +/- 3 mm Hg and 459 +/- 14 vs 484 +/- 11 beats.min-1).

CONCLUSIONS/INTERPRETATION

1) Hyperlipidaemic APOC1 mice show reduced NEFA and increased glucose metabolism under both basal and insulin-mediated conditions, suggesting an intrinsic defect in NEFA metabolism. Primary hyperlipidaemia alone in APOC1 mice does not lead to insulin resistance for glucose metabolism and high blood pressure.