A disadvantage of many apoA-I mimetic peptides is that they require end blocking to be effective, which precludes its synthesis by living organisms. Large-scale production of the peptides for therapeutic use would therefore be too expensive. In a search for apoA-I mimetic peptides that do not require end blocking, 6 F yielded promising results.
L-6 F has been shown to possess antioxidant and anti-inﬂammatory properties in several mice models (Chattopadhyay et al. 2013; Navab et al. 2013). Given that the small intestine may be an important site of action for apoA-I mimetic peptides, the observed reduction in plasma levels of the proinﬂammatory and proatherogenic lipid lysophosphatidic acid (LPA) following administration of L-6 F is of particular interest. Feeding LDL-R knockout mice a Western diet does result in changes in intestinal gene expression and proinﬂammatory and hypercholesterolemic changes in serum. Similar changes were observed when mice were fed unsaturated LPA. Administration of L-6 F reduced intestinal LPA levels and prevented the Western diet-mediated proatherogenic changes in intestinal gene expression. In addition, when L-6 F was administered to mice on chow supplemented with LPA, intestinal levels of unsaturated LPA were signiﬁcantly reduced, and this decrease correlated with reduced systemic inﬂammation and hypercholesterolemia (Chattopadhyay et al. 2013; Navab et al. 2013). Thus, reducing levels of intestinal LPA may be an important mechanism of action for L-6 F.
To enable the large-scale production of the peptide, transgenic, 6 F expressing tomatoes have been developed. Feeding LDL-R knockout mice a Western diet with and without transgenic tomatoes expressing 6 F improved an array of biomarkers of inﬂammation and antioxidant status and signiﬁcantly reduced aortic lesion area compared to controls following 13 weeks of treatment (Chattopadhyay et al. 2013).
The peptide 5A is synthesized by replacing 5 amino acids of the apoA-I mimetic peptide 37pA with alanine residues, thereby decreasing its lipid afﬁnity. Although 37pA effectively induces cholesterol efﬂux, its high lipid afﬁnity is associated with cytotoxicity because of adverse effects on the integrity of the plasma membrane (Remaley et al. 2003). As a result of the amino acid substitutions, 5A is less cytotoxic and induces cholesterol efﬂux more speciﬁcally through ATP-binding cassette transporter A1 (ABCA1) (Sethi et al. 2008).
The 5A-phospholipid complex has been shown to induce cholesterol efﬂux both through ABCA1 and ATP-binding cassette transporter G1 (ABCG1). Administration of a single intravenous dose of a 5A-phospholipid complex was shown to enhance reverse cholesterol transport, as evidenced by a ﬂux of cholesterol from peripheral cells to plasma, an increased amount of cholesterol and phospholipids in the HDL fraction, and an enhanced fecal sterol and bile acid secretion (Amar et al. 2010). In addition, 5A has been shown to possess anti-inﬂammatory and antioxidant properties (Tabet et al. 2010). To mimic acute inﬂammation, a nonocclusive collar was placed around the carotid artery in rabbits following infusion with 5A-phospholipid. Treatment with 5A-phospholipid signiﬁcantly reduced the expression of proinﬂammatory endothelial adhesion molecules and neutrophil inﬁltration compared to placebo, and this effect of 5A infusion was similar to the effect observed after infusing lipid-free apoA-I or recombinant HDL.
In the same rabbit model, it was shown that 5A-phospholipid reduced the production of radical oxygen species (ROS), such as O2(Tabet et al. 2010).
The ability of 5A-phospholipid to inhibit the formation of atherosclerosis in vivo has been demonstrated in apolipoprotein E (apoE) knockout mice. Treatment with 30 mg/kg of intravenous 5A-phospholipid three times per week for 13 weeks resulted in 30 % reduction in aortic plaque area in both young apoE knockout mice and older apoE knockout mice with established lesions. The efﬁciency of the complex to inhibit plaque formation was shown to be dependent on the constitution of the phospholipid component. Reconstituting 5A with a sphingomyelincontaining combination of phospholipids enhanced its anti-atherosclerotic properties. When apoE knockout mice were treated with this complex using the same dosing regimen as used in the previously described experiments, there was a superior 54 % reduction in aortic lesions compared to controls.
In addition to its potent anti-atherosclerotic effects, 5A has been shown to reduce airway inﬂammation in murine models of asthma (Yao et al. 2011). Thus, the therapeutic potential of 5A extends beyond atherosclerotic cardiovascular disease.
As of yet, 5A has not been tested in humans. However, the ﬁrst clinical trial is planned in the near future.