A Study on Multiple Facets of Apolipoprotein A1 Milano

For several strategies formulated to prevent atherosclerosis, Apolipoprotein A1 Milano (ApoA1M) remains a prime target. ApoA1M has been reported to have greater efficiency in reducing the incidence of coronary artery diseases. Furthermore, recombinant ApoA1M based mimetic peptide exhibits comparatively greater atheroprotective potential, offers a hope in reducing the burden of atherosclerosis in in vivo model system. The aim of this review is to emphasize on some of the observed ApoA1M structural and functional effects that are clinically and therapeutically meaningful that might converge on the basic role of ApoA1M in reducing the chances of glycation assisted ailments in diabetes. We also hypothesize that the nonenzymatic glycation prone arginine amino acid of ApoA1 gets replaced with cysteine residue and the rate of ApoA1 glycation may decrease due to change substitution of amino acid. Therefore, to circumvent the effect of ApoA1M glycation, the related mechanism should be explored at the cellular and functional levels, especially in respective experimental disease model in vivo.

HDL therapy today: from atherosclerosis, to stent compatibility to heart failure

Epidemiologically, high-density lipoprotein (HDL) cholesterol levels have been inversely associated to cardiovascular (CV) events, although a Mendelian Randomisation Study had failed to establish a clear causal role. Numerous atheroprotective mechanisms have been attributed to HDL, the main being the ability to promote cholesterol efflux from arterial walls; anti-inflammatory effects related to HDL ligands such as S1P (sphingosine-1-phosphate), resolvins and others have been recently identified. Experimental studies and early clinical investigations have indicated the potential of HDL to slow progression or induce regression of atherosclerosis. More recently, the availability of different HDL formulations, with different phospholipid moieties, has allowed to test other indications for HDL therapy. Positive reports have come from studies on coronary stent biocompatibility, where the use of HDL from different sources reduced arterial cell proliferation and thrombogenicity. The observation that low HDL-C levels may be associated with an enhanced risk of heart failure (HF) has also suggested that HDL therapy may be applied to this condition. HDL infusions or apoA-I gene transfer were able to reverse heart abnormalities, reduce diastolic resistance and improve cardiac metabolism. HDL therapy may be effective not only in atherosclerosis, but also in other conditions, of relevant impact on human health.Key messagesHigh-density lipoproteins have as a major activity that of removing excess cholesterol from tissues (particularly arteries).Knowledge on the activity of high-density lipoproteins on health have however significantly widened.HDL-therapy may help to improve stent biocompatibility and to reduce peripheral arterial resistance in heart failure.

Cholesterol transport system: An integrated cholesterol transport model involved in atherosclerosis

Atherosclerosis, the pathological basis of most cardiovascular disease (CVD), is closely associated with cholesterol accumulation in the arterial intima. Excessive cholesterol is removed by the reverse cholesterol transport (RCT) pathway, representing a major antiatherogenic mechanism. In addition to the RCT, other pathways are required for maintaining the whole-body cholesterol homeostasis. Thus, we propose a working model of integrated cholesterol transport, termed the cholesterol transport system (CTS), to describe body cholesterol metabolism. The novel model not only involves the classical view of RCT but also contains other steps, such as cholesterol absorption in the small intestine, low-density lipoprotein uptake by the liver, and transintestinal cholesterol excretion. Extensive studies have shown that dysfunctional CTS is one of the major causes for hypercholesterolemia and atherosclerosis. Currently, several drugs are available to improve the CTS efficiently. There are also several therapeutic approaches that have entered into clinical trials and shown considerable promise for decreasing the risk of CVD. In recent years, a variety of novel findings reveal the molecular mechanisms for the CTS and its role in the development of atherosclerosis, thereby providing novel insights into the understanding of whole-body cholesterol transport and metabolism. In this review, we summarize the latest advances in this area with an emphasis on the therapeutic potential of targeting the CTS in CVD patients.

Resident and Monocyte-Derived Macrophages in Cardiovascular Disease

Macrophages are ubiquitous cells that reside in all major tissues. Counter to long-held beliefs, we now know that resident macrophages in many organs are seeded during embryonic development and self-renew independently from blood monocytes. Under inflammatory conditions, those tissue macrophages are joined and sometimes replaced by recruited monocyte-derived macrophages. Macrophage function in steady state and disease depends on not only their developmental origin but also the tissue environment. Here, we discuss the ontogeny, function, and interplay of tissue-resident and monocyte-derived macrophages in various organs contributing to the development and progression of cardiovascular disease.

Apo A-I (Apolipoprotein A-I) Vascular Gene Therapy Provides Durable Protection Against Atherosclerosis in Hyperlipidemic Rabbits

OBJECTIVE

Gene therapy that expresses apo A-I (apolipoprotein A-I) from vascular wall cells has promise for preventing and reversing atherosclerosis. Previously, we reported that transduction of carotid artery endothelial cells with a helper-dependent adenoviral (HDAd) vector expressing apo A-I reduced early (4 weeks) fatty streak development in fat-fed rabbits. Here, we tested whether the same HDAd could provide long-term protection against development of more complex lesions.

APPROACH AND RESULTS

Fat-fed rabbits (n=25) underwent bilateral carotid artery gene transfer, with their left and right common carotids randomized to receive either a control vector (HDAdNull) or an apo A-I-expressing vector (HDAdApoAI). Twenty-four additional weeks of high-fat diet yielded complex intimal lesions containing lipid-rich macrophages as well as smooth muscle cells, often in a lesion cap. Twenty-four weeks after gene transfer, high levels of apo A-I mRNA (median ≥250-fold above background) were present in all HDAdApoAI-treated arteries. Compared with paired control HDAdNull-treated arteries in the same rabbit, HDAdApoAI-treated arteries had 30% less median intimal lesion volume (P=0.03), with concomitant reductions (23%-32%) in intimal lipid, macrophage, and smooth muscle cell content (P≤0.05 for all). HDAdApoAI-treated arteries also had decreased intimal inflammatory markers. VCAM-1 (vascular cell adhesion molecule-1)-stained area was reduced by 36% (P=0.03), with trends toward lower expression of ICAM-1 (intercellular adhesion molecule-1), MCP-1 (monocyte chemoattractant protein 1), and TNF-α (tumor necrosis factor-α; 13%-39% less; P=0.06-0.1).

CONCLUSIONS

In rabbits with severe hyperlipidemia, transduction of vascular endothelial cells with an apo A-I-expressing HDAd yields at least 24 weeks of local apo A-I expression that durably reduces atherosclerotic lesion growth and intimal inflammation.

Synchrotron radiation circular dichroism spectroscopy reveals structural divergences in HDL-bound apoA-I variants

Apolipoprotein A-I (apoA-I) in high-density lipoprotein (HDL) provides cardiovascular protection. Synchrotron radiation circular dichroism (SRCD) spectroscopy was used to analyze the dynamic solution structure of the apoA-I protein in the apo- and HDL-states and the protein structure conversion in HDL formation. Wild-type apoA-I protein was compared to human variants that either are protective (R173C, Milano) or lead to increased risk for ischaemic heart disease (A164S). Comparable secondary structure distributions in the HDL particles, including significant levels of beta strand/turn, were observed. ApoA-I Milano in HDL displayed larger size heterogeneity, increased protein flexibility, and an altered lipid-binding profile, whereas the apoA-I A164S in HDL showed decrease thermal stability, potentially linking the intrinsic HDL propensities of the variants to disease risk.

Genetic control of apoprotein A-I and atheroprotection: some insights from inbred strains of mice

PURPOSE OF REVIEW

Previous epidemiological studies and studies in experimental animals have provided strong evidence for the atheroprotective effect of HDL and its major apoprotein, apolipoprotein A-I (apoA-I). Identification of genetic loci associating apoA-I/HDL with cardiovascular disease is needed to establish a causal relationship.

RECENT FINDINGS

Pharmacological interventions to increase apoA-I or HDL cholesterol levels in humans are not associated with reduction in atherosclerosis. Genome wide association study (GWAS) studies in humans and hybrid mouse diversity panel (HMDP) studies looking for genetic variants associated with apoA-I or HDL cholesterol levels with cardiovascular disease and atherosclerosis have not provided strong evidence for their atheroprotective function.

SUMMARY

These findings indicate that GWAS and HMDP studies identifying possible genetic determinants of HDL and apoA-I function are needed.

The phenomenon of atherosclerosis reversal and regression: Lessons from animal models

Studies in non-rodent and murine models showed that atherosclerosis can be reversed. Atherosclerosis progression induced by high-fat or cholesterol-rich diet can be reduced and reversed to plaque regression after switching to a normal diet or through administration of lipid-lowering agents. The similar process should exist in humans after implementation of lipid-lowering therapy and as a result of targeting of small rupture-prone plaques that are major contributors for acute atherosclerotic complications. Lowering of low density lipoprotein (LDL) cholesterol and the activation of reverse cholesterol transport lead to a decline in foam cell content, to the depletion of plaque lipid reservoirs, a decrease in lesional macrophage numbers through the activation of macrophage emigration and, probably, apoptosis, dampening plaque inflammation, and the induction of anti-inflammatory macrophages involved in clearance of the necrotic core and plaque healing. By contrast, plaque regression is characterized by opposite events, leading to the retention of atherogenic LDL and oxidized LDL particles in the plaque, an increased flux of monocytes, the immobilization of macrophages in the intimal vascular tissues, and the propagation of intraplaque inflammation. Transfer of various apolipoprotein (apo) genes to spontaneously hypercholesterolemic mice deficient for either apoE or LDL receptor and, especially, the implementation of the transplantation murine model allowed studying molecular mechanisms of atherosclerotic regression, associated with the depletion of atherogenic lipids in the plaque, egress of macrophages and phenotypic switch of macrophages from the proinflammatory M1 to the anti-inflammatory M2.