Low-density lipoprotein augments interleukin-1-induced vascular adhesion molecule expression in human endothelial cells

IL-1β Induces LDL Transcytosis by a Novel Pathway Involving LDLR and Rab27a

BACKGROUND

In early atherosclerosis, circulating LDLs (low-density lipoproteins) traverse individual endothelial cells by an active process termed transcytosis. The CANTOS trial (Canakinumab Antiinflammatory Thrombosis Outcome Study) treated advanced atherosclerosis using a blocking antibody for IL-1β (interleukin-1β); this significantly reduced cardiovascular events. However, whether IL-1β regulates early disease, particularly LDL transcytosis, remains unknown.

METHODS

We used total internal reflection fluorescence microscopy to quantify transcytosis by human coronary artery endothelial cells exposed to IL-1β. To investigate transcytosis in vivo, we injected wild-type and knockout mice with IL-1β and LDL to visualize acute LDL deposition in the aortic arch.

RESULTS

Exposure to picomolar concentrations of IL-1β induced transcytosis of LDL but not of albumin by human coronary artery endothelial cells. Surprisingly, expression of the 2 known receptors for LDL transcytosis, ALK-1 (activin receptor-like kinase-1) and SR-BI (scavenger receptor BI), was unchanged or decreased. Instead, IL-1β increased the expression of the LDLR (LDL receptor); this was unexpected because LDLR is not required for LDL transcytosis. Overexpression of LDLR had no effect on basal LDL transcytosis. However, knockdown of LDLR abrogated the effect of IL-1β on transcytosis rates while the depletion of Cav-1 (caveolin-1) did not. Since LDLR was necessary but overexpression had no effect, we reasoned that another player must be involved. Using public RNA sequencing data to curate a list of Rab (Ras-associated binding) GTPases affected by IL-1β, we identified Rab27a. Overexpression of Rab27a alone had no effect on basal transcytosis, but its knockdown prevented induction by IL-1β. This was phenocopied by depletion of the Rab27a effector JFC1 (synaptotagmin-like protein 1). In vivo, IL-1β increased LDL transcytosis in the aortic arch of wild-type but not Ldlr-/- or Rab27a-deficient mice. The JFC1 inhibitor nexinhib20 also blocked IL-1β-induced LDL accumulation in the aorta.

CONCLUSIONS

IL-1β induces LDL transcytosis by a distinct pathway requiring LDLR and Rab27a; this route differs from basal transcytosis. We speculate that induction of transcytosis by IL-1β may contribute to the acceleration of early disease.

Expression of adenosine 5'-monophosphate-Activated protein kinase (AMPK) in ovine testis (Ovis aries): In vivo regulation by nutritional state

In the present study, we identified AMPK and investigated its potential role in steroidogenesis in vivo in the ovine testis in response to variation in nutritional status (fed control vs. restricted). We performed immunoblotting to show that both active and non-active forms of AMPK exist in ovine testis and liver. In testis, we confirmed these results by immunohistochemistry. We found a correlation between ATP (Adenosine-Triphosphate) levels and the expression of AMPK in liver. Also, low and high caloric diets induce isoform-dependent AMPK expression, with an increase in α2, ß1ß2 and γ1 activity levels. Although the restricted group exhibited an increase in lipid balance, only the triglyceride and HC-VLDL (Cholesterol-Very low density lipoprotein) fractions showed significant differences between groups, suggesting an adaptive mechanism. Moreover, the relatively low rate of non-esterified fatty acid released into the circulation implies re-esterification to compensate for the physiological need. In the fed control group, AMPK activates the production of testosterone in Leydig cells; this is, in turn, associated with an increase in the expression of 3ß-HSD (3 beta hydroxy steroid deshydrogenase), p450scc (Cholesterol side-chain cleavage enzyme) and StAR (Steroidogenic acute regulatory protein) proteins induced by decreased MAPK ERK½ (Extracellular signal-regulated kinase -Mitogen-activated protein kinase) phosphorylation. In contrast, in the restricted group, testosterone secretion was reduced but intracellular cholesterol concentration was not. Furthermore, the combination of high levels of lipoproteins and emergence of the p38 MAP kinase pathway suggest the involvement of pro-inflammatory cytokines, as confirmed by transcriptional repression of the StAR protein. Taken together, these results suggest that AMPK expression is tissue dependent.

Carnosic acid prevents the migration of human aortic smooth muscle cells by inhibiting the activation and expression of matrix metalloproteinase-9

The migration and matrix metalloproteinase (MMP) activation of vascular smooth muscle cells may play key roles in the development of atherosclerosis. Carnosic acid (CA) is a phenolic compound found in herbs, including rosemary and sage. Previous studies indicated that CA possesses antioxidant activityin vitro. In this study, we investigated the effects of CA on TNF-α-induced cell migration, the formation of intracellular reactive oxygen species, the translocation of NF-κB and the activation and expression of MMP-9 in human aortic smooth muscle cells (HASMC). The Matrigel migration assay showed that CA (10 and 20 μmol/l) effectively inhibited TNF-α-induced migration of HASMC as compared with the control group. To explain this inhibitory effect, MMP-9 was assayed by gelatin zymography and Western blot. The results indicated that CA inhibited MMP-9 activity and expression. Furthermore, the production of reactive oxygen species and the nuclear translocation of NF-κB p50 and p65 induced by TNF-α were dose-dependently suppressed by CA pretreament. These results indicate that CA has anti-inflammatory properties and may prevent the migration of HASMC by suppressing MMP-9 expression through down-regulation of NF-κB.

Vascular cell adhesion molecule-1: a viable therapeutic target for atherosclerosis?

Atherosclerosis is now well recognised as a chronic inflammatory process which may ultimately lead to myocardial infarction, stroke and peripheral vascular disease. The role of inflammation in the pathogenesis of atherosclerosis has lead to interest in developing therapies that target vascular inflammation. Leucocytes play a key role during atherosclerotic plaque development. Activated vascular endothelium expresses vascular cell adhesion cell molecule-1 (VCAM-1), a member of the adhesion molecule superfamily, to which monocytes and lymphocytes can bind. These inflammatory cells can then move through the endothelium by diapedesis and release cytokines and enzymes, important components in the progression of the lesion. Researchers have demonstrated that the extent of atherosclerotic lesions is significantly reduced in animal models with decreased VCAM-1 expression. VCAM-1 has therefore been identified as a potential anti-inflammatory therapeutic target, the hypothesis being that reduced expression of VCAM-1 will slow the development of atherosclerosis. Succinobucol (AGI-1067), an anti-oxidant compound also capable of inhibiting VCAM-1 gene expression, is an example of such an agent and is currently being investigated in a phase III cardiovascular end-point trial due to report in 2007. If the results are positive, further investigations should derive to what extent blockade of VCAM-1 by succinobucol, rather than its other effects, accounts for the reduction in vascular events.

Systemic inflammatory markers in acute coronary syndrome: association with cardiovascular risk factors and effect of early lipid lowering

BACKGROUND

Evidence for statin therapy in prevention of coronary artery disease is overwhelming. In spite of theoretical benefits, any additional advantage of its early introduction in the management of acute coronary syndrome is, however, uncertain. We therefore investigated differences between plasma levels of the systemic inflammatory markers intercellular adhesion molecule-1, vascular cell adhesion molecule-1, E-selectin, C-reactive protein and interleukin-6 in patients presenting with unstable angina or acute myocardial infarction, and assessed whether the 30-day levels of these markers are influenced by early instigation of the HMG-CoA reductase inhibitor pravastatin.

MATERIALS AND METHODS

170 (134 male) patients presenting with acute coronary syndrome, but without previous statin therapy, participated. Blood was taken within 24 h of onset of ischaemic pain and again at 30 days. In all, 87 (71 male) participants were treated with pravastatin (20-40 mg daily) and 83 (63 male) with a matched placebo.

RESULTS

At presentation, interleukin-6 was higher in males than in females (P=0.008) and lower in those with a pre-existing history of myocardial infarction (P=0.038). C-reactive protein and interleukin-6 were greater in myocardial infarction, but this difference was lost at 30 days. Thirty-day changes in all parameters were inversely related to level at presentation but not to treatment with pravastatin. Hypertension (P=0.011) and smoking (P=0.042) were associated with elevation of C-reactive protein with no difference between unstable angina or acute myocardial infarction. The effect of these individual factors was cumulative.

CONCLUSIONS

Interleukin-6 was greater in acute myocardial infarction than in unstable angina; E-selectin was positively associated with a previous myocardial infarction and inversely related to age. We found no effect of early introduction of pravastatin on systemic inflammatory markers 30 days after acute coronary syndrome.

Inflammation meets oxidation: NF-kappaB as a mediator of initial lesion development in atherosclerosis

Transcription factor nuclear factor-kappaB (NF-kappaB) and its target genes are involved in the pathogenesis of atherosclerosis, in addition to many other diseases. Monocyte recruitment into subendothelial space is primarily mediated by NF-kappaB-dependent gene expression, and this event is a crucial milestone, because it is nearly impossible to reverse the progression of the lesion after this point. Recent advances in our understanding of atherosclerosis as a disease of childhood enforces the necessity of developing novel approaches for prevention and treatment. Here, the authors address NF-kappaB as a major therapeutic target, especially for preventive measures, in the light of two main hypotheses of atherosclerosis: oxidation and inflammation.

Calcium mobilization and Rac1 activation are required for VCAM-1 (vascular cell adhesion molecule-1) stimulation of NADPH oxidase activity

VCAM-1 (vascular cell adhesion molecule-1) plays an important role in the regulation of inflammation in atherosclerosis, asthma, inflammatory bowel disease and transplantation. VCAM-1 activates endothelial cell NADPH oxidase, and this oxidase activity is required for VCAM-1-dependent lymphocyte migration. We reported previously that a mouse microvascular endothelial cell line promotes lymphocyte migration that is dependent on VCAM-1, but not on other known adhesion molecules. Here we have investigated the signalling mechanisms underlying VCAM-1 function. Lymphocyte binding to VCAM-1 on the endothelial cell surface activated an endothelial cell calcium flux that could be inhibited with anti-alpha4-integrin and mimicked by anti-VCAM-1-coated beads. VCAM-1 stimulation of calcium responses could be blocked by an inhibitor of intracellular calcium mobilization, a calcium channel inhibitor or a calcium chelator, resulting in the inhibition of NADPH oxidase activity. Addition of ionomycin overcame the calcium channel blocker suppression of VCAM-1-stimulated NADPH oxidase activity, but could not reverse the inhibitory effect imposed by intracellular calcium blockage, indicating that both intracellular and extracellular calcium mobilization are required for VCAM-1-mediated activation of NADPH oxidase. Furthermore, VCAM-1 specifically activated the Rho-family GTPase Rac1, and VCAM-1 activation of NADPH oxidase was blocked by a dominant negative Rac1. Thus VCAM-1 stimulates the mobilization of intracellular and extracellular calcium and Rac1 activity that are required for the activation of NADPH oxidase.

Cellular adhesion molecules and cardiovascular disease. Part II. Their association with conventional and emerging risk factors, acute coronary events and cardiovascular risk prediction

The role of cellular adhesion molecules in the patho-genesis of atherosclerosis has now been clearly demonstrated. Plasma levels of adhesion molecules, which have been shed from the cell surface, have also been associated with the presence of clinical atherosclerotic disease, cardiovascular risk factors and acute coronary syndromes. However, there is little consensus in the literature, including between the large well-designed population studies. This may be explained either by unrecognized confounding factors or, alternatively, by the unpredictable relationship between cell surface expression and activity of cellular adhesion molecules and their shedding into the plasma under different circumstances. Probably for the latter reasons, there is at present little evidence that the measurement of circulating adhesion molecules is likely to offer any additional benefit for individual patients above the assessment of conventional cardiovascular risk factors in the assessment of either the extent of, or future risk from, cardiovascular disease.

Differential effects of fenofibrate versus atorvastatin on the concentrations of E-selectin and vascular cellular adhesion molecule-1 in patients with type 2 diabetes mellitus and mixed hyperlipoproteinemia: a randomized cross-over trial

Background

Diabetic dyslipoproteinemia is characterized by hypertriglyceridemia, low HDL-cholesterol and often elevated LDL-cholesterol and is a strong risk factor for atherosclerosis. Adhesion molecule levels are elevated both in hyperlipoproteinemia and diabetes mellitus. It is unclear whether fibrate or statin therapy has more beneficial effects on adhesion molecule concentrations.

Methods

Atorvastatin (10 mg/d) was compared to fenofibrate (200 mg/d) each for 6 weeks separated by a 6 week washout period in 11 patients (6 male, 5 female; 61.8 ± 8.2 years; body mass index 29.8 ± 3.1 kg/m²) with type 2 diabetes mellitus (HbA_1c 7.3 ± 1.1 %) and mixed hyperlipoproteinemia using a randomized, cross-over design. Fasting blood glucose, HbA₁c, lipid parameters, E-selectin, ICAM-1, VCAM-1, and fibrinogen concentrations were determined before and after each drug.

Results

Glucose and HbA₁c concentrations remained unchanged during the whole study period. LDL cholesterol was reduced during atorvastatin therapy, triglycerides were lowered more effectively with fenofibrate. Comparison of pre- and postreatment concentrations of E-selectin showed a reduction during atorvastatin (-7 %, p = 0.11) and fenofibrate (-10 %, p < 0.05) therapy. Atorvastatin treatment reduced VCAM-1 levels by 4% (p < 0.05), while VCAM-1 concentrations remained unchanged (+1%, ns) during fenofibate therapy. However, direct comparisons of post-treatment levels during both forms of therapy were not of statistical significance. ICAM-1 levels were not influenced by either form of therapy.

Conclusions

In addition to the different beneficial effects on lipid metabolism, both drugs appear to lower adhesion molecule plasma concentrations in a different manner in patients with type 2 diabetes and mixed hyperlipoproteinemia. Our observations should be confirmed in a larger cohort of such patients.

Role of pro-atherogenic adhesion molecules and inflammatory cytokines in patients with coronary artery disease and diabetes mellitus type 2

Accelerated progression of atherosclerosis in coronary, carotid, cerebral, and peripheral arteries is a phenomenon observed in diabetes mellitus. Pathophysiologic mechanisms are slowly being understood. Pro-atherogenic adhesion molecules and inflammatory cytokines are involved in this process. This review addresses current concepts of atherogenesis and focuses on alterations of adhesion molecule and cytokine expression and their regulation in diabetic patients. Molecules are being discussed in both the normoglycemic and hyperglycemic states, with a focus on their atherogenic role in diabetes mellitus. Understanding the mechanisms that underlie disease progression will help to identify high-risk patients, which is a prerequisite for new treatment strategies aiming at an attenuation of disease progression in diabetic patients.

Time course of plasma adhesion molecules in acute coronary syndromes

BACKGROUND

Atherosclerosis is an inflammatory process in which adhesion molecules play an intimate role in both the initiation and progression of lesions. It is postulated that they also play a role in the presentation of acute coronary syndromes and that plasma levels thereafter may be of potential prognostic significance. The stability of sample levels under different laboratory conditions is unknown.

METHODS

Stability of plasma levels was assessed in six healthy subjects under four different laboratory conditions. The time course of levels was studied in 57 patients with acute chest pain, 21 of non-cardiac aetiology, 23 unstable angina and 13 acute myocardial infarction, at mean times of 2.3, 8.2 and 17.3 h after the onset of pain. Samples were assayed for intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), P-selectin, E-selectin and C-reactive protein (CRP).

RESULTS

ICAM-1, VCAM-1, P-selectin and E-selectin levels did not differ under different laboratory conditions. Levels were similar at presentation in patients with acute chest pain of non-cardiac aetiology, unstable angina or acute myocardial infarction (median levels ICAM-1 269 microg/l, VCAM-1 379 microg/l, P-selectin 167 microg/l and E-selectin 53 microg/l). Levels did not change in the 24 h following the onset of pain. CRP levels did not differ at presentation between groups (median level 2.1 mg/l), but rose more than 12 h after the onset of pain in the group with acute myocardial infarction (P < 0.05).

CONCLUSION

Adhesion molecule levels are stable under normal laboratory sample handling conditions. Levels do not change in the 24 h following the onset of chest pain of non-cardiac or acute ischaemic aetiology.

Abnormalities in apo B-containing lipoproteins in diabetes and atherosclerosis

Atherosclerosis is the major cause of death in patients with diabetes. Low-density lipoprotein (LDL) being the most important cholesterol-carrying lipoprotein has been studied extensively in both diabetes and non-diabetes. This paper reviews the literature but also focuses on the precursors of LDL and in particular the postprandial apo B-containing lipoproteins. Abnormalities in the postprandial lipoproteins and alteration in chylomicron assembly and clearance are discussed and the evidence presented suggesting the importance of dysregulation of these lipoproteins in atherosclerotic progression. The relationship between chylomicron production in the intestine and hepatic release of very low-density lipoproteins (VLDL) is explored, as is the interrelationship between clearance rates of these lipoproteins. The size of LDL influences its atherogenicity. VLDL composition and size in relation to its influence on LDL is discussed. The effect of diet on the composition of lipoproteins and the relationship between fatty acid composition and clearance is reviewed. Evidence that diabetic control beneficially alters lipoprotein composition is presented suggesting how improved diabetic control may reduce atherosclerosis. The review concludes with a discussion on the effect of the apo B-containing lipoproteins and their modification through glycation and oxidation on macrophage and endothelial function.