Gene therapy for dyslipidemia: a review of gene replacement and gene inhibition strategies

Lipid-Lowering Medications for Managing Dyslipidemia: A Narrative Review

Dyslipidemia refers to the change in the normal levels of one or more lipid components in the bloodstream, which include triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C). Dyslipidemia represents a substantial source of danger for cardiovascular disease (CVD). Effectively managing dyslipidemia involves a thorough strategy that includes changing one's lifestyle and using medications that are specifically designed to target the complex processes involved in lipid metabolism. Lipid-lowering treatments play a crucial role in this approach, providing a wide range of medications that are developed to specifically target different components of dyslipidemia. Statins are the main drug among these medications. Other drugs that are used with statin or as monotherapy include fibrates, omega-3 fatty acids (OM3FAs), ezetimibe, bile acid sequestrants, proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors, and bempedoic acid. Using the PubMed database, we reviewed the literature about dyslipidemia, drugs used for treating dyslipidemia, their efficacy parameters, and common adverse events. We also reviewed the international guidelines for treating dyslipidemia and discussed the future of lipid-lowering medications. More trials and experiments are still required to verify the effectiveness of many lipid-lowering drugs and to know their common adverse events to be able to manage them properly.

Current Diagnosis and Management of Abetalipoproteinemia

Abetalipoproteinemia (ABL) is a rare autosomal recessive disorder caused by biallelic pathogenic mutations in the MTTP gene. Deficiency of microsomal triglyceride transfer protein (MTTP) abrogates the assembly of apolipoprotein (apo) B-containing lipoprotein in the intestine and liver, resulting in malabsorption of fat and fat-soluble vitamins and severe hypolipidemia. Patients with ABL typically manifest steatorrhea, vomiting, and failure to thrive in infancy. The deficiency of fat-soluble vitamins progressively develops into a variety of symptoms later in life, including hematological (acanthocytosis, anemia, bleeding tendency, etc.), neuromuscular (spinocerebellar ataxia, peripheral neuropathy, myopathy, etc.), and ophthalmological symptoms (e.g., retinitis pigmentosa). If left untreated, the disease can be debilitating and even lethal by the third decade of life due to the development of severe complications, such as blindness, neuromyopathy, and respiratory failure. High dose vitamin supplementation is the mainstay for treatment and may prevent, delay, or alleviate the complications and improve the prognosis, enabling some patients to live to the eighth decade of life. However, it cannot fully prevent or restore impaired function. Novel therapeutic modalities that improve quality of life and prognosis are awaited. The aim of this review is to 1) summarize the pathogenesis, clinical signs and symptoms, diagnosis, and management of ABL, and 2) propose diagnostic criteria that define eligibility to receive financial support from the Japanese government for patients with ABL as a rare and intractable disease. In addition, our diagnostic criteria and the entry criterion of low-density lipoprotein cholesterol (LDL-C) ＜15 mg/dL and apoB ＜15 mg/dL can be useful in universal or opportunistic screening for the disease. Registry research on ABL is currently ongoing to better understand the disease burden and unmet needs of this life-threatening disease with few therapeutic options.

PEGylated helper-dependent adenoviral vector expressing human Apo A-I for gene therapy in LDLR-deficient mice

Helper-dependent adenoviral (HD-Ad) vectors have great potential for gene therapy applications; however, their administration induces acute toxicity that impairs safe clinical applications. We previously observed that PEGylation of HD-Ad vectors strongly reduces the acute response in murine and primate models. To evaluate whether PEGylated HD-Ad vectors combine reduced toxicity with the correction of pathological phenotypes, we administered an HD-Ad vector expressing the human apolipoprotein A-I (hApoA-I) to low-density lipoprotein (LDL)-receptor-deficient mice (a model for familial hypercholesterolemia) fed a high-cholesterol diet. Mice were treated with high doses of HD-Ad-expressing apo A-I or its PEGylated version. Twelve weeks later, LDL levels were lower and high-density lipoprotein (HDL) levels higher in mice treated with either of the vectors than in untreated mice. After terminal killing, the areas of atherosclerotic plaques were much smaller in the vector-treated mice than in the control animals. Moreover, the increase in pro-inflammatory cytokines was lower and consequently the toxicity profile better in mice treated with PEGylated vector than in mice treated with the unmodified vector. This finding indicates that the reduction in toxicity resulting from PEGylation of HD-Ad vectors does not impair the correction of pathological phenotypes. It also supports the clinical potential of these vectors for the correction of genetic diseases.

Gene therapy for lipoprotein lipase deficiency

PURPOSE OF REVIEW

The present review summarizes the clinical development of adeno-associated viral vector (AAV)1-lipoprotein lipase (LPL)S447X gene therapy (alipogene tiparvovec) for lipoprotein lipase deficiency. Lipoprotein lipase deficiency is a rare inherited disease characterized by severe hypertriglyceridaemia, chylomicronaemia and risk of recurrent pancreatitis or other complications. AAV1-LPLS447X gene therapy is based on the rationale that by adding episomal copies of functional LPL genes into muscle cells lacking active LPL, metabolic function could be improved or restored.

RECENT FINDINGS

AAV1-LPLS447X is a nonreplicating and nonintegrating AAV of serotype 1 designed to deliver and express the human LPL gene variant S447X. The clinical development programme for AAV1-LPLS447X consisted of two observational studies, three open-label interventional studies and one case note review analysis. Intramuscular administration of AAV1-LPLS447X was generally well tolerated and was associated with reduction in overall pancreatitis incidence and signs of clinical improvement up to 2 years after administration. Results of interventional studies suggest that markers of postprandial metabolism could be more accurate than fasting plasma triglyceride concentration to monitor the effect of AAV1-LPLS447X .

SUMMARY

The overall benefit-risk ratio of AAV1-LPLS447X gene therapy appears positive to date, particularly for the patients presenting the highest risk of complications.

Treatment of familial hypercholesterolemia: is there a need beyond statin therapy?

Familial hypercholesterolemia (FH) is a genetic lipid disorder that is characterized by severely elevated cholesterol levels and premature cardiovascular disease. Both the heterozygous and homozygous forms of FH require aggressive cholesterol-lowering therapy. Statins alone frequently do not lower these patients' cholesterol to therapeutic levels, and some patients are intolerant to statins. Combination or monotherapy with other current pharmacotherapies are options, but even with these some FH patients do not meet their low-density lipoprotein (LDL) cholesterol goals. In the cases of statin intolerance, LDL apheresis may be another treatment option. There are currently several novel therapies in development for LDL lowering that target either production or catabolism of LDL, plaque regression, and potentially gene transfer. We conclude that there is a need beyond statins for patients with FH, especially in cases of statin intolerance, and when even the highest doses of statin do not get patients to goal cholesterol levels.