High Density Lipoproteins Inhibit Oxidative Stress-Induced Prostate Cancer Cell Proliferation.

Recent evidence suggests that oxidative stress can play a role in the pathogenesis and the progression of prostate cancer (PCa). Reactive oxygen species (ROS) generation is higher in PCa cells compared to normal prostate epithelial cells and this increase is proportional to the aggressiveness of the phenotype. Since high density lipoproteins (HDL) are known to exert antioxidant activities, their ability to reduce ROS levels and the consequent impact on cell proliferation was tested in normal and PCa cell lines. HDL significantly reduced basal and H2O2-induced oxidative stress in normal, androgen receptor (AR)-positive and AR-null PCa cell lines. AR, scavenger receptor BI and ATP binding cassette G1 transporter were not involved. In addition, HDL completely blunted H2O2-induced increase of cell proliferation, through their capacity to prevent the H2O2-induced shift of cell cycle distribution from G0/G1 towards G2/M phase. Synthetic HDL, made of the two main components of plasma-derived HDL (apoA-I and phosphatidylcholine) and which are under clinical development as anti-atherosclerotic agents, retained the ability of HDL to inhibit ROS production in PCa cells. Collectively, HDL antioxidant activity limits cell proliferation induced by ROS in AR-positive and AR-null PCa cell lines, thus supporting a possible role of HDL against PCa progression.

Minimum amino acid residues of an α-helical peptide leading to lipid nanodisc formation.

Nanodiscs are a relatively new class of nanoparticles composed of amphiphilic α-helical scaffold peptides and a phospholipid bilayer, and find potential applications in various fields. In order to identify the minimum number of amino acid residues of an amphiphilic α-helical peptide that leads to nanodisc formation, seven peptides differing in lengths (22-, 18-, 14-, 12-, 10-, 8-, and 6-mers) that mimic and modify the C-terminal domain of apoA-I (residues 220-241) were synthesized. At a concentration of 0.3 mM, the 6- and 8-mer peptides did not present any surface activity. In case of the 10-mer peptide, the aqueous surface tension initially decreased and reached a constant value of 51.9 mN/m with the 14-, 18-, and 22-mer peptides. Moreover, upon mixing the surface-active peptides (14-, 18-, and 22-mers) with dipalmitoylphosphatidylcholine (DMPC) liposomes (2.5:1, peptide : DMPC), the turbid DMPC liposome solution rapidly became transparent. Further analysis of this solution by negative-stain transmission electron microscopy (NS-TEM) indicated the presence of disk-like nanostructures. The average diameter of the nanodiscs formed was 9.5 ± 2.7 nm for the 22-mer, 8.1 ± 2.7 nm for the 18-mer, and 25.5 ± 8.5 nm for the 14-mer peptides. These results clearly demonstrate that the surface properties of peptides play a critical role in nanodisc formation. Furthermore, the minimum length of an amphiphilic peptide from the C-terminal of apoA-I protein that can lead to nanodisc formation is 14 amino acid residues.

Apolipoprotein A-I mimetic peptides.

PURPOSE OF REVIEW: To review published data related to the potential applicability of apolipoprotein A-I mimetic peptides. RECENT FINDINGS: Despite a wealth of information on HDL-C levels and risk for cardiovascular disease (CVD), little evidence is present to suggest that raising HDL-C levels per se will result in CVD risk reduction. Rather, increasing HDL functionality might be a more successful strategy to reverse the process of atherosclerosis. In as such, apoA-I mimetic peptides, either in single or tandem formulation, hold great promise. Evidence gathered over the last years has provided insight in the extent to which mimetics influence several cardio metabolic pathways. ApoA-I mimetics have shown to have anti-inflammatory, antioxidant, and antiatherogenic effects. Direct comparisons between different mimetics have provided insight in factors influencing the differential beneficial consequences of these peptides. Data derived from recent studies suggest that mimetics might gain their position as a therapeutic intervention in the treatment of septicaemia, transplantation rejection, diabetes and auto-immune diseases. SUMMARY: This review provides a summary of the current literature on the potential application of apoA-I mimetics as therapeutic agents. There is increasing evidence that these mimetics should be considered as a promising supplement to current strategies. Results from human studies addressing the in-vivo effects of the different apoA-I mimetics are eagerly awaited.

Anti-inflammatory and cardioprotective activities of synthetic high-density lipoprotein containing apolipoprotein A-I mimetic peptides.

Apolipoprotein A-I (apoA-I) mimetic peptides may represent an alternative to apoA-I for large-scale production of synthetic high-density lipoproteins (sHDL) as a therapeutic agent. In this study, the cardioprotective activity of sHDL made with either L37pA peptide or its d-stereoisomer, D37pA, was compared to sHDL made with apoA-I. The peptides were reconstituted with palmitoyl-oleoyl-phosphatidylcholine, which yielded sHDL particles comparable to apoA-I sHDL in diameter, molecular weight, and alpha-helical content. Pretreatment of endothelial cells with either peptide sHDL reduced tumor necrosis factor alpha-stimulated vascular cell adhesion molecule-1 expression to the same extent as apoA-I sHDL. In an isolated rat heart model of ischemia/reperfusion (I/R) injury, L37pA and D37pA sHDL significantly reduced postischemic cardiac contractile dysfunction compared to the saline control, as indicated by a 49.7 +/- 6.4% (L37pA; P < 0.001) and 53.0 +/- 9.1% (D37pA; P < 0.001) increase of left ventricular-developed pressure (LVDP) after reperfusion and by a 45.4 +/- 3.4% (L37pA; P < 0.001) and 49.6 +/- 2.6% (D37pA; P < 0.001) decrease of creatine kinase (CK) release. These effects were similar to the 51.3 +/- 3.0% (P < 0.001) increase of LVDP and 51.3 +/- 3.0 (P < 0.001) reduction of CK release induced by apoA-I sHDL. Consistent with their cardioprotective effects, all three types of sHDL particles mediated an approximate 20% (P < 0.001) reduction of cardiac tumor necrosis factor alpha (TNFalpha) content and stimulated an approximate 35% (P < 0.05) increase in postischemic release of prostacyclin. In summary, L37pA and D37pA peptides can form sHDL particles that retain a similar level of protective activity as apoA-I sHDL on the endothelium and the heart; thus, apoA-I mimetic peptides may be useful therapeutic agents for the prevention of cardiac I/R injury.

Oral administration of an Apo A-I mimetic Peptide synthesized from D-amino acids dramatically reduces atherosclerosis in mice independent of plasma cholesterol.

When apolipoprotein A-I mimetic peptides synthesized from either D- or L-amino acids were given orally to LDL receptor-null mice, only the peptide synthesized from D-amino acids was stable in the circulation and enhanced the ability of HDL to protect LDL against oxidation. The peptide synthesized from L-amino acids was rapidly degraded and excreted in the urine. When a peptide synthesized from D-amino acids (D-4F) was administered orally to LDL receptor-null mice on a Western diet, lesions decreased by 79%. When added to the drinking water of apoE-null mice, D-4F decreased lesions by approximately 75% at the lowest dose tested (0.05 mg/mL). The marked reduction in lesions occurred independent of changes in total plasma or HDL-cholesterol.

Studies of synthetic peptides of human apolipoprotein A-I containing tandem amphipathic alpha-helixes.

In mature human apolipoprotein A-I (apo A-I), the amino acid residues 1-43 are encoded by exon 3, whereas residues 44-243 are encoded by exon 4 of the apo A-I gene. The region encoded by exon 4 of the apo A-I gene contains 10 tandem amphipathic alpha-helixes; their location and the class to which they belong are as follows: helix 1 (44-65, class A1), helix 2 (66-87, class A1), helix 3 (88-98, class Y), helix 4 (99-120, class Y), helix 5 (121-142, class A1), helix 6 (143-164, class A1), helix 7 (165-186, class A1), helix 8 (187-208, class A1), helix 9 (209-219, class Y), and helix 10 (220-241, class Y). To examine the effects of multiple tandem amphipathic helixes compared to individual helixes of apo A-I on lipid association, we have studied lipid-associating properties of the following peptides: Ac-44-87-NH2 (peptide 1-2), Ac-66-98-NH2 (peptide 2-3), Ac-66-120-NH2 (peptide 2-3-4), Ac-88-120-NH2 (peptide 3-4), Ac-99-142-NH2 (peptide 4-5), Ac-121-164-NH2 (peptide 5-6), Ac-143-186-NH2 (peptide 6-7), Ac-165-208-NH2 (peptide 7-8), Ac-187-219-NH2 (peptide 8-9), and Ac-209-241-NH2 (peptide 9-10). To study lipid-associating properties of the region encoded by exon 3 of the apo A-I gene, 1-33-NH2 (peptide G) has also been studied. The results of the present study indicate that, among the peptides studied, peptides 1-2 and 9-10 possess significantly higher lipid affinity than the other peptides, with peptide 9-10 having higher lipid affinity than peptide 1-2, as evidenced by (i) higher helical content in the presence of 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), (ii) faster rate of association with DMPC multilamellar vesicles (MLV), (iii) greater reduction in the enthalpy of gel to liquid-crystalline phase transition of DMPC MLV, (iv) higher exclusion pressure from an egg yolk phosphatidylcholine monolayer, and (v) higher partitioning into 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine MLV. A comparison of the free energies of lipid association (DeltaG) of the peptides studied here with those studied previously by us [Palgunachari, M. N. , et al. (1996) Arterioscler. Thromb. Vasc. Biol. 16, 328-338] indicates that, except for the peptides 4-5 and 5-6, other peptides possess higher lipid affinities compared to constituent helixes. However, the lipid affinities of the peptides studied here are neither higher than nor equal to the sum of the lipid affinities of the constituent helixes. This indicates the absence of cooperativity among the adjacent amphipathic helical domains of apo A-I for lipid association. As indicated by DeltaG, the lipid affinity of peptide 4-5 is higher than peptide 5 but lower than peptide 4; the lipid affinity of peptide 5-6 is lower than both peptides 5 and 6. Implications of these results for the structure and function of apo A-I are discussed.