Inhibition of atherosclerosis in apolipoprotein-E-deficient mice following muscle transduction with adeno-associated virus vectors encoding human apolipoprotein-E

An artificial virus-like triblock protein shows low in vivo humoral immune response and high stability

The use of viral vectors for in vivo gene therapy can be severely limited by their immunogenicity. Non-viral vectors may represent an alternative, however, reports analyzing their immunogenicity are still lacking. Here, we studied the humoral immune response in a murine model triggered by artificial virus-like particles (AVLPs) carrying plasmid or antisense DNA. The AVLPs were assembled using a family of modular proteins based on bioinspired collagen-like and silk-like sequences that produce virus-like particles. We compared our AVLPs against an Adeno Associated Virus 1 (AAV), a widely used viral vector for in vivo gene delivery that has been approved by the FDA and EMA for gene therapy. We found that a 1000-fold higher mass of AVLPs than AAV are necessary to obtain similar specific antibody titters. Furthermore, we studied the stability of AVLPs against relevant biological reagents such as heparin and fetal bovine serum to ensure nucleic acid protection in biological media. Our study demonstrates that the AVLPs are stable in physiological conditions and can overcome safety limitations such as immunogenicity. The scarce humoral immunogenicity and high stability found with AVLPs suggest that they have potential to be used as stealth non-viral gene delivery systems for in vivo studies or gene therapy.

Adenovirus-Based Transient Expression Systems for Peritoneal Membrane Research

Background

Peritoneal membrane research has provided important insights into the physiology and pathophysiology of this tissue that is of vital importance for peritoneal dialysis patients. Among the various tools and methodologies used to study the peritoneum, we have extensively used adenovirus-mediated gene transfer.

Methods

A literature review was carried out. Information from reviewed papers was combined with the authors’ experience and results.

Results

We have used first-generation adenoviruses that are simple to construct and can infect a wide range of dividing and nondividing cell types. These vectors are restricted, however, in that they provide only a short duration of transgene expression and may elicit an inflammatory response. Modifications to this technology with helper-dependent adenovirus may circumvent these problems but with increased complexity of construction. Adenovirus-mediated gene transfer has been used to evaluate the effect of several cytokines and growth factors on peritoneal membrane physiology. We have used intraperitoneal delivery of transforming growth factor-β to generate an experimental model system of resolving peritoneal fibrosis and epithelial mesenchymal transdifferentiation. We have studied the effects of the inflammatory cytokines interleukin-1β and tumor necrosis factor alpha on the peritoneum, and have shown that antiangiogenic factors such as sFLT-1 and angiostatin can reduce the damaging effects of exposure to peritoneal dialysis solutions in an animal model.

Conclusions

The use of recombinant adenoviruses to genetically modify cells and tissues is now a common laboratory research tool. This technique has provided important advances in our understanding of the peritoneal membrane.

Effects of High Fat Feeding and Diabetes on Regression of Atherosclerosis Induced by Low-Density Lipoprotein Receptor Gene Therapy in LDL Receptor-Deficient Mice

We tested whether a high fat diet (HFD) containing the inflammatory dietary fatty acid palmitate or insulin deficient diabetes altered the remodeling of atherosclerotic plaques in LDL receptor knockout (Ldlr^-/-) mice. Cholesterol reduction was achieved by using a helper-dependent adenovirus (HDAd) carrying the gene for the low-density lipoprotein receptor (Ldlr; HDAd-LDLR). After injection of the HDAd-LDLR, mice consuming either HFD, which led to insulin resistance but not hyperglycemia, or low fat diet (LFD), showed regression compared to baseline. However there was no difference between the two groups in terms of atherosclerotic lesion size, or CD68+ cell and lipid content. Because of the lack of effects of these two diets, we then tested whether viral-mediated cholesterol reduction would lead to defective regression in mice with greater hyperglycemia. In both normoglycemic and streptozotocin (STZ)-treated hyperglycemic mice, HDAd-LDLR significantly reduced plasma cholesterol levels, decreased atherosclerotic lesion size, reduced macrophage area and lipid content, and increased collagen content of plaque in the aortic sinus. However, reductions in anti-inflammatory and ER stress-related genes were less pronounced in STZ-diabetic mice compared to non-diabetic mice. In conclusion, HDAd-mediated Ldlr gene therapy is an effective and simple method to induce atherosclerosis regression in Ldlr^-/- mice in different metabolic states.

Gene transfer of apolipoprotein A-V improves the hypertriglyceridemic phenotype of apoa5 (-/-) mice

OBJECTIVE

Apolipoprotein (apo) A-V is a low abundance protein with a profound influence on plasma triacylglycerol levels. In human populations, single nucleotide polymorphisms and mutations in APOA5 positively correlate with hypertriglyceridemia. As an approach to preventing the deleterious effects of chronic hypertriglyceridemia, apoA-V gene therapy has been pursued.

METHODS AND RESULTS

Recombinant adeno-associated virus (AAV) 2/8 harboring the coding sequence for human apoA-V or a control AAV2/8 was transduced into hypertriglyceridemic apoa5 (-/-) mice. After injection of 1×10(12) viral genome AAV2/8-apoA-V, maximal plasma levels of apoA-V protein were achieved at 3 to 4 weeks, after which the concentration slowly declined. Complementing the appearance of apoA-V was a decrease (50±6%) in plasma triacylglycerol content compared with apoa5 (-/-) mice treated with AAV2/8-β-galactosidase. After 8 weeks the mice were euthanized and plasma lipoproteins separated. AAV2/8-apoA-V-transduced mice displayed a dramatic reduction in very low-density lipoprotein triacylglycerol content. Vector generated apoA-V in plasma associated with both very low-density lipoprotein and high-density lipoprotein fractions.

CONCLUSIONS

Taken together, the data show that gene transfer of apoA-V improves the severe hypertriglyceridemia phenotype of apoa5 (-/-) mice. Given the prevalence of hypertriglyceridemia, apoA-V gene therapy offers a potential strategy for maintenance of plasma triacylglycerol homeostasis.

Apolipoprotein E mimetic is more effective than apolipoprotein A-I mimetic in reducing lesion formation in older female apo E null mice

OBJECTIVE

The apolipoprotein E mimetic peptide Ac-hE18A-NH(2), capable of reducing plasma cholesterol and possessing anti-inflammatory properties, was compared with the well-studied anti-atherogenic apoA-I mimetic peptide 4F for reducing lesion formation in female apoE null mice with already existing lesions.

METHODS AND RESULTS

In initial experiments, Ac-hE18A-NH(2) was administered retro-orbitally two or three times weekly for 6-8 weeks, while peptide 4F was administered intraperitoneally every day for the same period. Age matched controls were injected with saline every day. At the end of the treatment period, plasma cholesterol levels of Ac-hE18A-NH(2) administered mice were significantly lower than in 4F and control mice. However, both 4F and Ac-hE18A-NH(2) showed reduced lesion areas in en face lesion analysis to a similar extent compared to the control group, while paraoxonase-1 (PON-1) activity was increased only in the Ac-hE18A-NH(2) group. In the third experiment, both peptides were administered at the same dose, frequency, and route of administration. The reduction in en face lesions with Ac-hE18A-NH(2) was significantly greater than the 4F and control groups, although lesions in 4F-treated mice were also significantly reduced compared with controls. Both peptide groups had significantly reduced plasma lipid hydroperoxides, but only the Ac-hE18A-NH(2) group had significantly reduced serum amyloid A levels. HDL and plasma inflammatory indices were significantly reduced in both peptide groups compared with controls.

CONCLUSIONS

Although both peptides had similar anti-inflammatory properties, Ac-hE18A-NH(2) was more effective in inhibiting lesions than 4F at the same dose, frequency, and route of administration, perhaps due to its cholesterol reducing properties.

Gene therapy in skeletal muscle mediated by adeno-associated virus vectors

Adeno-associated virus (AAV) is the most promising gene delivery vehicle for muscle-directed gene therapy. AAV's natural tropism to muscle cells, long-term persistent transgene expression, multiple serotypes, as well as its minimal immune response have made AAV vectors well suited for muscle-directed gene therapy. AAV vector-mediated gene delivery to augment muscle structural proteins, such as dystrophin and sarcoglycans, offers great hope for muscular dystrophy patients. In addition, muscle can be used as a therapeutic platform for AAV vectors to express nonmuscle secretory/regulatory pathway proteins for diabetes, atherosclerosis, hemophilia, cancer, etc. AAV vector can be delivered into both skeletal muscle and cardiac muscle by means of local, regional, and systemic administrations. Successful animal studies have led to several noteworthy clinical trials involving muscle-directed gene therapy. In this chapter, we describe the basic methodology that is currently utilized in the area of AAV-mediated muscle-directed gene therapy. These methods include vector delivery route, vector dosage, detection of transgene expression by immunostaining and western blot, determination of vector copy numbers and quantification of mRNA expression, as well as potential immune responses involved in AAV delivery. Technical details and tips leading to successful experimentation are also discussed.

Adeno-associated virus serotypes 7 and 8 outperform serotype 9 in expressing atheroprotective human apoE3 from mouse skeletal muscle

Intramuscular injection of adeno-associated viral (AAV) vectors is potentially a safe, minimally invasive procedure for the long-term gene expression of circulating antiatherogenic proteins. Here, we compare secretion and atheroprotective effects of human apoE3 after injection of 3 pseudotyped AAV vectors (AAV2/7, AAV2/8, or AAV2/9), driven by the CMV enhancer/chicken β-actin (CAG) promoter, into skeletal muscle of hyperlipidemic apolipoprotein E-deficient (apoE⁻/⁻) mice. Vector viabilities were verified by transducing cultured C2C12 mouse myotubes and assessing secretion of human apoE3 protein. Both hind limb tibialis anterior muscles of female C57BL/6 apoE⁻/⁻ mice, 2 months old and fed a high-fat diet, were each injected with 1 x 10¹⁰ vector genomes of AAV vector. Identical noninjected mice served as controls; and blood was collected at weeks 0, 1, 2, 4, and 13. At termination (13 weeks), the brachiocephalic artery was excised; and after staining sections, plaque morphometry and fractional lipid content were quantified by computerized image analysis. Intramuscular injection of AAV2/7 and AAV2/8 vectors produced up to 2 μg human apoE3 per milliliter plasma, just below the threshold to reverse dyslipoproteinemia. AAV2/9 was notably less effective, mice having a 3-fold lower level of plasma apoE3 at 13 weeks and a 50% greater burden of atherosclerotic plaque lipid in their brachiocephalic arteries. We conclude that although vector refinement is needed to exploit fully apoE3 atheroprotective functions, AAV2/7 and AAV2/8 are promising gene transfer vectors for muscle-based expression of antiatherogenic circulating proteins.

Standardization of models and methods used to assess nanoparticles in cardiovascular applications

Nanotechnology has the potential to revolutionize the management and treatment of cardiovascular disease. Controlled drug delivery and nanoparticle-based molecular imaging agents have advanced cardiovascular disease therapy and diagnosis. However, the delivery vehicles (dendrimers, nanocrystals, nanotubes, nanoparticles, nanoshells, etc.), as well as the model systems that are used to mimic human cardiac disease, should be questioned in relation to their suitability. This review focuses on the variations of the biological assays and preclinical models that are currently being used to study the biocompatibility and suitability of nanomaterials in cardiovascular applications. There is a need to standardize appropriate models and methods that will promote the development of novel nanomaterial-based cardiovascular therapies.

LXR promotes the maximal egress of monocyte-derived cells from mouse aortic plaques during atherosclerosis regression

We have previously shown that mouse atherosclerosis regression involves monocyte-derived (CD68+) cell emigration from plaques and is dependent on the chemokine receptor CCR7. Concurrent with regression, mRNA levels of the gene encoding LXRalpha are increased in plaque CD68+ cells, suggestive of a functional relationship between LXR and CCR7. To extend these results, atherosclerotic Apoe-/- mice sufficient or deficient in CCR7 were treated with an LXR agonist, resulting in a CCR7-dependent decrease in plaque CD68+ cells. To test the requirement for LXR for CCR7-dependent regression, we transplanted aortic arches from atherosclerotic Apoe-/- mice, or from Apoe-/- mice with BM deficiency of LXRalpha or LXRbeta, into WT recipients. Plaques from both LXRalpha and LXRbeta-deficient Apoe-/- mice exhibited impaired regression. In addition, the CD68+ cells displayed reduced emigration and CCR7 expression. Using an immature DC line, we found that LXR agonist treatment increased Ccr7 mRNA levels. This increase was blunted when LXRalpha and LXRbeta levels were reduced by siRNAs. Moreover, LXR agonist treatment of primary human immature DCs resulted in functionally significant upregulation of CCR7. We conclude that LXR is required for maximal effects on plaque CD68+ cell expression of CCR7 and monocyte-derived cell egress during atherosclerosis regression in mice.

StAR overexpression decreases serum and tissue lipids in apolipoprotein E-deficient mice

Cholesterol metabolism as initiated by mitochondrial sterol 27-hydroxylase (CYP27A1) is a ubiquitous pathway capable of synthesizing multiple key regulatory oxysterols involved in lipid homeostasis. Previously we have shown that the regulation of its activities within hepatocytes is highly controlled by the rate of mitochondrial cholesterol delivery. In the present study, we hypothesized that increasing expression of the mitochondrial cholesterol delivery protein, steroidogenic acute regulatory protein (StAR), is able to lower lipid accumulation in liver, aortic wall, as well as in serum in a well-documented animal model, apolipoprotein E-deficient (apoE(-/-)) mice. ApoE(-/-) mice, characterized by increased serum, liver, and endothelial cholesterol and triglyceride levels by 3 months of age, were infected with recombinant cytomegalovirus (CMV)-StAR adenovirus to increase StAR protein expression. Six days following infection, serum total cholesterol and triglycerides had decreased 19 and 30% (P < 0.01), respectively, with a compensatory 40% (P < 0.01) increase in serum HDL-cholesterol in increased StAR expressing mice as compared to controls (no or control virus). Histologic and biochemical analysis of the liver demonstrated not only a dramatic decrease in cholesterol ( downward arrow25%; P < 0.01), but an even more marked decrease in triglyceride ( downward arrow56%; P < 0.01) content. En bloc Sudan IV staining of the aorta revealed a >80% (P < 0.01) decrease in neutral lipid staining. This study demonstrates for the first time a possible therapeutic role of the CYP27A1-initiated pathway in the treatment of dyslipidemias.

Human apolipoprotein E expression from mouse skeletal muscle by electrotransfer of nonviral DNA (plasmid) and pseudotyped recombinant adeno-associated virus (AAV2/7)

Plasma apolipoprotein E (apoE) has multiple atheroprotective actions. However, although liver-directed adenoviral gene transfer of apoE reverses hypercholesterolemia and inhibits atherogenesis in apoE-deficient (apoE(-/-)) mice, safety considerations have revived interest in nonviral DNA (plasmid) and nonpathogenic adeno-associated viral (AAV) vectors. Here, we assess the effectiveness of these two delivery vehicles by minimally invasive intramuscular injection. First, we constructed AAV2-based expression plasmids harboring human apoE3 cDNA, driven by two muscle-specific promoters (CK6 and C5-12) and one ubiquitous promoter (CAG); each efficiently expressed apoE3 in transfected cultured C2C12 mouse myoblasts, although muscle-specific promoters were active only in differentiated multinucleate myotubes. Second, a pilot study verified that electrotransfer of the CAG-driven plasmid (p.CAG.apoE3) into tibialis anterior muscles, pretreated with hyaluronidase, of apoE(-/-) mice significantly enhanced (p < 0.001) local intramuscular expression of apoE3. However, in a 7-day experiment, the CK6- and C5-12-driven plasmids produced less apoE3 in muscle than did p.CAG.apoE3 (0.61 +/- 0.38 and 0.45 +/- 0.38 vs. 13.38 +/- 7.46 microg of apoE3 per muscle, respectively), but plasma apoE3 levels were below our detection limit (<15 ng/ml) in all mice and did not reverse the hyperlipidemia. Finally, we showed that intramuscular injection of a cross-packaged AAV serotype 7 viral vector, expressing human apoE3 from the CAG promoter, resulted in increasing levels of apoE3 in plasma over 4 weeks, although the concentration reached (1.40 +/- 0.35 microg/ml) was just below the threshold level needed to reduce the hypercholesterolemia. We conclude that skeletal muscle can serve as an effective secretory platform to express the apoE3 transgene, but that improved gene transfer vectors are needed to achieve full therapeutic levels of plasma apoE3 protein.

Gene therapy for lipoprotein disorders

Existing approaches to the treatment of refractory hypercholesterolaemia, severe hypertriglyceridaemia, low levels of high-density lipoprotein cholesterol and certain inherited disorders of intracellular lipid metabolism are ineffective in a substantial number of patients. Somatic gene therapy is considered to be a potential approach to the therapy of several of these lipid disorders. In many cases preclinical proof-of-principle studies have already been performed, and in one (homozygous familial hypercholesterolaemia) a clinical trial has been conducted. Other clinical gene therapy trials for dyslipidaemia are likely to be initiated within the next several years.

Gene therapy of atherosclerosis

Atherosclerosis and related diseases are the leading cause of death in Western world. The disease process begins with the formation of fatty streaks already during the first decade of life but does not manifest clinically until several decades later. Gene therapy is a potential new way to target multiple factors playing a role in the development and progression of atherosclerosis. A great number of genes involved in the development of atherosclerosis have been identified and have been tested both in vitro and in vivo as potential new targets for therapy. Pre-clinical experiments have shown the feasibility and safety of several gene therapy applications for the treatment of atherosclerosis and clinical trials have also provided evidence for the applicability of gene therapy for the treatment of cardiovascular diseases. In this review we discuss vectors and potential gene therapy approaches for intervention and therapy of atherosclerosis.

Serial Studies of Mouse Atherosclerosis by In Vivo Magnetic Resonance Imaging Detect Lesion Regression After Correction of Dyslipidemia

Objective— We determined the effects of sustained normocholesterolemia on advanced mouse atherosclerosis and whether changes in plaque size and composition can be detected noninvasively by MRI.

Methods and Results— Aortic arch segments containing advanced lesions from apolipoprotein E–deficient (apoE−/−) mice (total cholesterol 1281±97 mg/dL) were transplanted into syngeneic wild-type (WT; 111±11 mg/dL) or apoE−/− (702±74 mg/dL) recipient mice on chow diet. Mice underwent serial MRI at 3, 5, 7, and 9 weeks after transplantation. Compared with 3 weeks, correction of dyslipidemia in WT recipient mice resulted in a monotonic decrease (regression) in arterial wall volume, whereas in apoE−/− recipient mice, further plaque progression was noted ( P <0.05). MRI and histological measurements were closely correlated ( R =0.937). The lesional content of macrophages decreased >90% ( P <0.001), and smooth muscle cells increased in the WT recipient mice. In vivo T 1 -, T 2 -, and proton density–weighted images of the mouse thoracic aorta differentiated intraplaque lipid and collagen.

Conclusions— Plaque changes can be noninvasively monitored by serial in vivo MRI of a mouse regression model. Our ability to image the thoracic aorta and perform in vivo plaque characterization will further enhance atherosclerosis studies.

Applied gene therapy in preclinical models of vascular injury

Atherosclerosis remains the major cause of morbidity and mortality in Western countries. Atherothrombotic complications, including vascular occlusions and severe narrowing of nutrient blood vessels in the cerebral, coronary, or peripheral circulation, usually require invasive revascularization strategies. As molecular mediators contributing to these complications are being identified in more representative experimental injury models, and as gene transfer platforms and vectors acquire improved safety and efficacy profiles, there is ground for cautious optimism that gene-based interventions will likely reduce the clinical burden of these diseases. Increased generation of reactive oxygen species in diseased atherosclerotic vessels has been implicated in vasospasm, exaggerated neointima formation, and enhanced thrombosis. Ex vivo pressurized vascular gene transfer in venous bypass grafts using antisense oligonucleotides directed against cell-cycle control genes can modify the venous graft's phenotype and confer clinical benefit with improved long-term graft survival. Alternatively, percutaneous intra-arterial gene transfer is feasible, but at relatively low transgene expression levels. Although this may suffice in the case of secreted gene products with marked paracrine or bystander effects, including nitric oxide synthase and heme oxygenase-1, drug- and gene-eluting stents may provide the preferred future vehicle for well-controlled, quantifiable, and safe vascular gene transfer. Continued efforts to improve gene transfer technology in diseased human vessels and to increase our understanding of molecular targets are required before the full therapeutic potential of vascular gene therapy can be realized.

Gene Therapy for Cardiovascular Disease

The last decade has seen substantial advances in the development of gene therapy strategies and vector technology for the treatment of a diverse number of diseases, with a view to translating the successes observed in animal models into the clinic. Perhaps the overwhelming drive for the increase in vascular gene transfer studies is the current lack of successful long-term pharmacological treatments for complex cardiovascular diseases. The increase in cardiovascular disease to epidemic proportions has also led many to conclude that drug therapy may have reached a plateau in its efficacy and that gene therapy may represent a realistic solution to a long-term problem. Here, we discuss gene delivery approaches and target diseases.