SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Lipoprotein lipase

133

Excessive circulating triglycerides due to reduction or loss of lipoprotein lipase activity contribute to hypertriglyceridemia and increased risk for pancreatitis. The only gene therapy treatment for lipoprotein lipase deficiency decreases pancreatitis but minimally reduces hypertriglyceridemia. Synthesized in multiple tissues including striated muscle and adipose tissue, lipoprotein lipase is trafficked to blood vessel endothelial cells where it is anchored at the plasma membrane and hydrolyzes triglycerides into free fatty acids. We conditionally knocked out lipoprotein lipase in differentiated striated muscle tissue lowering striated muscle lipoprotein lipase activity causing hypertriglyceridemia. We then crossed lipoprotein lipase striated muscle knockout mice with mice possessing a conditional avian retroviral receptor gene and injected mice with either a human lipoprotein lipase retrovirus or an mCherry control retrovirus. Post-heparin plasma lipoprotein lipase activity increased for three weeks following human lipoprotein lipase retroviral infection compared to mCherry infected mice. Human lipoprotein lipase infected mice had significantly lower blood triglycerides compared to mCherry controls and were comparable to wild-type blood triglyceride levels. Thus, targeted delivery of human lipoprotein lipase into striated muscle tissue identifies a potential therapeutic target for lipoprotein lipase deficiency.

Concepts: Gene, Cell, Fatty acid, Heart, Triglyceride, Tissues, Lipid, Lipoprotein lipase

28

Homozygous lipoprotein lipase (LPL) deficiency is an ultra-orphan disease associated with increased rates of pancreatitis. Current treatments based on acute plasmapheresis allied with ultra-low fat diets are inadequate as responses to fibrates or other triglyceride-lowering therapies tend to be poor. Alipogene tiparvovec is an adeno-associated virus type I (AAV1) gene therapy using a hyper-functional LPL serine(447)-stop (S447X) insert administered intramuscularly under general anaesthetic with allied immunosuppression. Treatment results in histological muscle expression of LPL allied with a transient 40% reduction in triglycerides and improvements in postprandial chylomicron triglyceride content. Alipogene tiparvovec is the first possibly curative treatment for LPL deficiency.

Concepts: Cholesterol, Metabolism, Virus, Triglyceride, Lipoprotein, Lipid, Lipase, Lipoprotein lipase

2

Rare monogenic hyperchylomicronemia is caused by loss-of-function mutations in genes involved in the catabolism of triglyceride-rich lipoproteins, including the lipoprotein lipase gene, LPL. Clinical hallmarks of this condition are eruptive xanthomas, recurrent pancreatitis and abdominal pain. Patients with LPL deficiency and severe or recurrent pancreatitis are eligible for the first gene therapy treatment approved by the European Union. Therefore the precise molecular diagnosis of familial hyperchylomicronemia may affect treatment decisions. We present a 57-year-old male patient with excessive hypertriglyceridemia despite intensive lipid-lowering therapy. Abdominal sonography showed signs of chronic pancreatitis. Direct DNA sequencing and cloning revealed two novel missense variants, c.1302A>T and c.1306G>A, in exon 8 of the LPL gene coexisting on the same allele. The variants result in the amino-acid exchanges p.(Lys434Asn) and p.(Gly436Arg). They are located in the carboxy-terminal domain of lipoprotein lipase that interacts with the glycosylphosphatidylinositol-anchored HDL-binding protein (GPIHBP1) and are likely of functional relevance. No further relevant mutations were found by direct sequencing of the genes for APOA5, APOC2, LMF1 and GPIHBP1. We conclude that heterozygosity for damaging mutations of LPL may be sufficient to produce severe hypertriglyceridemia and that chylomicronemia may be transmitted in a dominant manner, at least in some families.

Concepts: DNA, Protein, Gene, Mutation, Molecular biology, Point mutation, Pancreatitis, Lipoprotein lipase

1

Alipogene tiparvovec (Glybera┬«) is a gene therapy product approved in Europe under the ‘exceptional circumstances’ pathway as a treatment for lipoprotein lipase deficiency (LPLD), a rare genetic disease resulting in chylomicronemia and a concomitantly increased risk of acute and recurrent pancreatitis, with potentially lethal outcome. This retrospective study analyzed the frequency and severity of pancreatitis in 19 patients with LPLD up to 6-years following a single treatment with alipogene tiparvovec. An independent adjudication board of 3 pancreas experts, blinded to patient identification and to pre- or post-gene therapy period, performed a retrospective review of data extracted from the patients' medical records and categorized LPLD-related acute abdominal pain events requiring hospital visits and/or hospitalizations based on the adapted 2012 Atlanta diagnostic criteria for pancreatitis. Both entire disease time period data and data from an equal time period before and after gene therapy were analyzed. Events with available medical record information meeting the Atlanta diagnostic criteria were categorized as definite pancreatitis; events treated as pancreatitis but with variable levels of laboratory and imaging data were categorized as probable pancreatitis and acute abdominal pain events. A reduction of approximately 50% was observed in all 3 categories of the adjudicated post-gene therapy events. Notably, no severe pancreatitis and only 1 intensive-care unit (ICU) admission were observed in the post-alipogene tiparvovec period. However, important inter- and intra-individual variations in the pre- and post-gene therapy incidence of events were observed. There was no relationship between the post-treatment incidence of events and the number of LPL gene copies injected, the administration of immunosuppressive regimen or the percent of TG decrease achieved at 12 weeks (primary end point in the prospective clinical studies). Although a causal relationship cannot be established and despite the limited number of individuals evaluated, results from this long-term analysis suggest that alipogene tiparvovec was associated with a lower frequency and severity of pancreatitis events, and a consequent overall reduction in healthcare-resource utilization up to 6 years post-treatment.

Concepts: Genetics, Medical terms, Hospital, Abdominal pain, Wavelength, Pancreatitis, Lipoprotein lipase, Lipoprotein lipase deficiency

1

Hypertriglyceridemia is an independent risk factor for cardiovascular disease, and plasma triglycerides (TGs) correlate strongly with plasma apolipoprotein C-III (ApoC-III) levels. Antisense oligonucleotides (ASOs) for ApoC-III reduce plasma TGs in primates and mice, but the underlying mechanism of action remains controversial. We determined that a murine-specific ApoC-III-targeting ASO reduces fasting TG levels through a mechanism that is dependent on low-density lipoprotein receptors (LDLRs) and LDLR-related protein 1 (LRP1). ApoC-III ASO treatment lowered plasma TGs in mice lacking lipoprotein lipase (LPL), hepatic heparan sulfate proteoglycan (HSPG) receptors, LDLR, or LRP1 and in animals with combined deletion of the genes encoding HSPG receptors and LDLRs or LRP1. However, the ApoC-III ASO did not lower TG levels in mice lacking both LDLR and LRP1. LDLR and LRP1 were also required for ApoC-III ASO-induced reduction of plasma TGs in mice fed a high-fat diet, in postprandial clearance studies, and when ApoC-III-rich or ApoC-III-depleted lipoproteins were injected into mice. ASO reduction of ApoC-III had no effect on VLDL secretion, heparin-induced TG reduction, or uptake of lipids into heart and skeletal muscle. Our data indicate that ApoC-III inhibits turnover of TG-rich lipoproteins primarily through a hepatic clearance mechanism mediated by the LDLR/LRP1 axis.

Concepts: Cholesterol, Atherosclerosis, Cardiovascular disease, Low density lipoprotein receptor gene family, Lipid, Heparan sulfate, Apolipoprotein B, Lipoprotein lipase

0

Type I hyperlipoproteinemia, also known as familial chylomicronemia syndrome (FCS), is a rare autosomal recessive disorder caused by variants in LPL, APOC2, APOA5, LMF1 or GPIHBP1 genes. The aim of this study was to identify novel variants in the LPL gene causing lipoprotein lipase deficiency and to understand the molecular mechanisms.

Concepts: Allele, Lipoprotein lipase, Lipoprotein lipase deficiency

0

Lipoprotein lipase (LPL) deficiency is an autosomal recessive genetic disorder characterized by extreme hypertriglyceridemia, with no cure presently available. The purpose of this study was to test the possibility of using cell therapy to alleviate LPL deficiency.

Concepts: Genetics, Disease, Genetic disorder, Allele, Gregor Mendel, Phenylketonuria, Lipoprotein lipase, Lipoprotein lipase deficiency

0

Lipoprotein lipase deficiency (LPLD) is an autosomal recessive inherited disorder caused by loss-of-function mutations in genes involved in the lipoprotein lipase pathway. It is characterised by chylomicronaemia, severe hypertriglyceridaemia and an increased risk of recurrent pancreatitis that often requires hospitalisation. This research aimed to improve our understanding of the debilitating impact that LPLD has on the daily lives of patients and their families.

Concepts: DNA, Genetics, Genetic disorder, Mutation, Life, Pancreatitis, Lipoprotein lipase, Lipoprotein lipase deficiency

0

Familial Chylomicronemia Syndrome (FCS) is a rare genetic disorder that is caused by a decrease or an absence of lipoprotein lipase activity. FCS is characterized by marked accumulation of chylomicrons and extreme hypertriglyceridemia, which have major effects on both physical and mental health. To date, there have been no systematic efforts to characterize the impact of chylomicronemia on FCS patients' lives. In particular, the impact of FCS on the burden of illness (BoI) and quality of life (QoL) has not been fully described in the literature.

Concepts: Lipoprotein lipase

0

Exercise lowers plasma triglyceride levels, but the physiological mechanisms remain not fully elucidated. Lipoprotein lipase (LPL) is a key enzyme in facilitating fatty acid uptake from lipoproteins. Since exercise increase the efficiency of VLDL-TG oxidation, we hypothesized that muscle LPL activity would be a rate-limiting step and predict VLDL-TG FA oxidation during exercise.

Concepts: Cholesterol, Metabolism, Fatty acid, Triglyceride, Fatty acid metabolism, Lipid, Lipase, Lipoprotein lipase