Severe hyperchylomicronemia in two infants with novel APOC2 gene mutation.

Background Familial apo C-II deficiency is a rare hereditary disorder frequently caused by lipoprotein lipase (LPL) and APOC2 gene mutations. To date, less than 30 patients with familial apo C-II deficiency with 24 different mutations have been identified in the literature. Here, we describe two familial chylomicronemia syndrome cases in infants with two novel mutations of the APOC2 gene. Case presentation Case 1, a 46-day-old female, was admitted to our hospital for evaluation due to the lipemic appearance of the blood sample. A clinical examination revealed hepatomegaly and lipemia retinalis. Triglyceride level of 6295 mg/dL was decreased with a strict low-fat diet, medium-chain triglycerides (MCT) oil-rich formula and omega-3 fatty acid supplementation. Due to low adherence to the diet, TG elevation was detected and fresh frozen plasma (10 mL/kg/day) was administered for 2 days. A novel homozygous p.Q25X (c.73C>T) mutation in the APOC2 gene was detected. Case 2, a 10-month-old female patient, referred to our center for the differential diagnosis of hyperlipidemia as her blood sample could not be assessed due to its lipemic appearance. Laboratory examinations showed a TG level of 4520 mg/dL which was reduced with a low-fat diet, MCT oil-rich formula and omega-3 fatty acid supplementation. Hepatosteatosis and splenomegaly were determined using abdominal sonography. A novel homozygous IVS2+6T>G (c.55+6T>G) mutation in the APOC2 gene was identified. Conclusions We describe two novel homozygous mutations (p.Q25X [c.73C>T] and IVS2+6T>G [c.55+6T>G]) in the APOC2 gene in infants with hyperchylomicronemia. To the best of our knowledge, Case 1 is the youngest patient with familial apo C-II deficiency in the literature to date.

Creation of Apolipoprotein C-II (ApoC-II) Mutant Mice and Correction of Their Hypertriglyceridemia with an ApoC-II Mimetic Peptide.

Apolipoprotein C-II (apoC-II) is a cofactor for lipoprotein lipase, a plasma enzyme that hydrolyzes triglycerides (TGs). ApoC-II deficiency in humans results in hypertriglyceridemia. We used zinc finger nucleases to create Apoc2 mutant mice to investigate the use of C-II-a, a short apoC-II mimetic peptide, as a therapy for apoC-II deficiency. Mutant mice produced a form of apoC-II with an uncleaved signal peptide that preferentially binds high-density lipoproteins (HDLs) due to a 3-amino acid deletion at the signal peptide cleavage site. Homozygous Apoc2 mutant mice had increased plasma TG (757.5 ± 281.2 mg/dl) and low HDL cholesterol (31.4 ± 14.7 mg/dl) compared with wild-type mice (TG, 55.9 ± 13.3 mg/dl; HDL cholesterol, 55.9 ± 14.3 mg/dl). TGs were found in light (density < 1.063 g/ml) lipoproteins in the size range of very-low-density lipoprotein and chylomicron remnants (40-200 nm). Intravenous injection of C-II-a (0.2, 1, and 5 µmol/kg) reduced plasma TG in a dose-dependent manner, with a maximum decrease of 90% occurring 30 minutes after the high dose. Plasma TG did not return to baseline until 48 hours later. Similar results were found with subcutaneous or intramuscular injections. Plasma half-life of C-II-a is 1.33 ± 0.72 hours, indicating that C-II-a only acutely activates lipolysis, and the sustained TG reduction is due to the relatively slow rate of new TG-rich lipoprotein synthesis. In summary, we describe a novel mouse model of apoC-II deficiency and show that an apoC-II mimetic peptide can reverse the hypertriglyceridemia in these mice, and thus could be a potential new therapy for apoC-II deficiency.

Effects of 3-thia fatty acids on expression of some lipid related genes in Atlantic salmon (Salmo salar L.).

In this study, the effects of in vivo administration of 3-thia fatty acids (FAs) on lipid metabolism in muscle and liver of Atlantic salmon were investigated. Prior to analysis, the fish were kept in tanks supplied with 5 degrees C seawater for 20 weeks. The fish were fed fish meal and fish oil (FO)-based diets supplemented with either nothing (FO), or 0.3% and 0.6% of the 3-thia FAs dodecylthioacetic acid (DTA) and tetradecylthioacetic acid (TTA) respectively. The fish grew from an initial weight of 110 g to 220 g in the FO group and to approximately 160 g in the 3-thia FA groups. There was a significant higher mortality (66%) in fish fed 0.6% TTA than in fish fed the 0.3% DTA (15%) and FO diets (15%). None of the 3-thia FA diets affected the lipid content of the salmon muscle. The liver index, however, was significantly higher and the total liver fat content lower in the TTA group than in the FO group. Both DTA and TTA were incorporated into the lipid fraction of muscle and liver (0.4% to 0.9%). There were no major differences in the total FA composition of liver and muscle between the dietary groups; except for a small increase of n-3 polyunsaturated FAs (PUFAs) in liver of the DTA group. The mRNA expression of peroxisome proliferator-activated receptor (PPAR) alpha, apolipoprotein AI (ApoAI), apolipoprotein CII (ApoCII) and low-density lipoprotein receptor (LDL-R) was down-regulated in liver of the salmon fed 0.3% DTA. PPARalpha and ApoAI transcripts were also reduced in liver of salmon fed 0.6% TTA. Additionally, the hepatic lipoprotein lipase (LPL) mRNA level was 3.8 fold increased in TTA fish relative to the FO group. In muscle there were no significant changes in gene expression pattern of any of the genes investigated. This is the first report on the effects of 3-thia FAs on gene expression in Atlantic salmon.

Farnesoid X-activated receptor induces apolipoprotein C-II transcription: a molecular mechanism linking plasma triglyceride levels to bile acids.

The farnesoid X-activated receptor (FXR; NR1H4), a member of the nuclear hormone receptor superfamily, induces gene expression in response to several bile acids, including chenodeoxycholic acid. Here we used suppression subtractive hybridization to identify apolipoprotein C-II (apoC-II) as an FXR target gene. Retroviral expression of FXR in HepG2 cells results in induction of the mRNA encoding apoC-II in response to several FXR ligands. EMSAs demonstrate that recombinant FXR and RXR bind to two FXR response elements that are contained within two important distal enhancer elements (hepatic control regions) that lie 11 kb and 22 kb upstream of the transcription start site of the apoC-II gene. A luciferase reporter gene containing the hepatic control region or two copies of the wild-type FXR response element was activated when FXR-containing cells were treated with FXR ligands. In addition, we report that hepatic expression of both apoC-II and phospholipid transfer protein mRNAs increases when mice are fed diets supplemented with cholic acid, an FXR ligand, and this induction is attenuated in FXR null mice. Finally, we observed decreased plasma triglyceride levels in mice fed cholic acid- containing diets. These results identify a mechanism whereby FXR and its ligands lower plasma triglyceride levels. These findings may have important implications in the clinical management of hyperlipidemias.

Hypobetalipoproteinemia associated with apo B-48.4, a truncated protein only 14 amino acids longer than apo B-48.

Familial hypobetalipoproteinemia is an autosomal codominant trait that can be caused by mutations in the apo B gene. Here we report a novel apo B gene mutation causing hypobetalipoproteinemia, that is associated with the synthesis of a truncated apo B protein in a young healthy male subject and his mother. The mutation is an A deletion at position 6627 of the apo B cDNA leading to a truncated protein of 2166 amino acids (apo B-48.4). This truncated apo B was detected mainly in VLDL, LDL and in trace amounts in HDL, but not in the lipoprotein deficient plasma fraction. Affected family members present with elevated levels of HDL-cholesterol, mainly due to an increase in HDL2 particles. Postprandial triglycerides and retinyl esters in the d < 1.006 g/ml lipoprotein in the proband showed a normal response to an oral fat load compared to a group of eight matched healthy controls. In summary this novel mutation is associated with hypobetalipoproteinemia with a normal fat absorption as expected for a protein with a length similar to that of apo B-48.

Dietary monounsaturated and polyunsaturated fatty acids are comparable in their effects on hepatic apolipoprotein mRNA abundance and liver lipid concentrations when substituted for saturated fatty acids in cynomolgus monkeys.

Although studies have shown that saturated and polyunsaturated fats can mediate plasma lipid and apolipoprotein (apo) concentrations at the mRNA level, there is little data on the role of monounsaturated fats. We determined hepatic lipid and apo mRNA levels in 10 cynomolgus monkeys fed three diets that provided 30% of energy as fat with 0.1% cholesterol by weight and differed solely by the substitution of saturated, mono- and polyunsaturated fats as 60% of total fat energy. Total, LDL, and HDL cholesterol, as well as LDL apo B, HDL apo A-I and HDL total apo C concentrations, were reduced with the mono- and polyunsaturated fat diets relative to the saturated fat diet. Although fat saturation did not significantly affect hepatic apo A-I, B, C-II, or E mRNA abundance, hepatic apo C-III mRNA concentrations were uniformly lower (-23%, P < 0.01) with the mono- and polyunsaturated fat diets than with the saturated fat diet. Interestingly, liver triglycerides were significantly elevated with the monounsaturated fat diet relative to the saturated fat diet, but no other differences in hepatic lipids were noted among diets. Hepatic triglyceride composition was shown to reflect dietary fatty acid composition, with liver triglycerides enriched in myristic and palmitic fatty acids during the saturated fat diet, oleic acid during the monounsaturated fat diet and linoleic acid during the polyunsaturated fat diet. We conclude that dietary monounsaturated fats are comparable to polyunsaturated fats in their effects on hepatic lipid and apo mRNA levels in this species, with both unsaturated fats significantly reducing only hepatic apo C-III mRNA abundance relative to saturated fat.

Multivitamin supplementation of adult omnivores and lactovegetarians: circulating levels of vitamin A, D and E, lipids, apolipoproteins and selenium.

Serum levels of fat-soluble vitamins, lipids, apolipoproteins, total protein, hemoglobin, iron, and selenium were determined in healthy Finnish adults during a 7-month period beginning in January and ending in August. The subjects were either omnivores or established lactovegetarians, who had consumed their respective diets for at least 6 months prior to the study. Half of the subjects in both groups received daily multivitamin supplementation and the other half served as controls. In the beginning, the lactovegetarians differed from the omnivores in having lower serum levels of protein, apolipoproteins A-I and C-II, and higher levels of standardized alpha-tocopherol. During the study, serum retinol and standardized alpha-tocopherol (in March and May), as well as apolipoproteins A-I and C-II, and selenium decreased in the omnivores and 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, cholesterol, HDL-cholesterol, and the HDL-cholesterol/cholesterol ratio increased. Apolipoprotein B decreased and then increased. In the lactovegetarians, serum selenium and protein decreased during the study, whereas retinol and alpha-tocopherol stayed higher than in the omnivores. Consumption of the lactovegetarian diet was accompanied by lower circulating levels of cholesterol and selenium and higher levels of retinol and standardized alpha-tocopherol than the mixed diet. Multivitamin supplementation may have value especially for omnivores in northern countries, like Finland, in providing better retinol, alpha-tocopherol, vitamin D, and selenium status in late winter and early spring.

Serum selenium is related to low-density lipoproteins in healthy children but not in children with diabetes.

The serum concentrations of selenium in 13 healthy children and 27 children with type 1 diabetes mellitus were evaluated in relation to serum lipoprotein and apolipoprotein concentrations. In healthy children a correlation was found between serum selenium and both serum cholesterol (r = 0.56; p less than 0.05) and serum triglycerides (r = 0.56; less than 0.05) and their low-density lipoprotein (LDL) + very low-density lipoprotein (VLDL) fractions (r = 0.60 and 0.56 respectively; p less than 0.05), but not their high-density lipoprotein fractions. Associations were also found between selenium and apolipoproteins, especially A II and C II (r = 0.57; p less than 0.05). In diabetic children serum selenium was significantly correlated with apolipoproteins A II and Apo C II, but not with any lipoprotein or lipid or any of their fractions. This study supports the hypothesis that serum selenium is an integral part of the defence system against degradation products associated with LDL and VLDL in young healthy humans. These associations were not found in diabetes, which might suggest that the defence system against lipid peroxidation is less effective in this disease.

Postprandial distribution of apolipoproteins C-II and C-III in normal subjects and patients with mild hypertriglyceridemia: comparison of meals containing corn oil and medium-chain triglyceride oil.

Five healthy male subjects and five patients with mild hypertriglyceridemia were studied following the administration of 800-kcal liquid meals containing 40% of energy from fat, 40% from carbohydrate, and 20% from protein. On the first day of the study, the fat source was corn oil (long-chain triglyceride), whereas medium-chain triglyceride (MCT) oil was used the second day. Meals were infused into the duodenum using a peristaltic pump. Plasma samples, obtained at hourly intervals for 8 hours, were analyzed for glucose, cholesterol, triglyceride, and apolipoproteins C-II and C-III. The distribution of apoC-II and apoC-III between ultracentrifugally-separated triglyceride-rich lipoproteins (TRL) and high-density lipoproteins (HDL) was also evaluated. The patient group had significantly elevated fasting levels of triglyceride, apoC-II and apoC-III, as well as much greater lipemic response to the meal containing corn oil. In both groups, TRL apoC-II and apoC-III levels were positively correlated with the triglyceride level as it increased following the corn oil meal. These correlations were also observed in the normal subjects when the MCT oil meal was administered, even though changes in plasma triglycerides were minimal. In normal subjects, whole plasma levels of apoC-II and apoC-III decreased significantly following the meal containing corn oil, whereas no net changes occurred following the MCT oil meal. In hypertriglyceridemic subjects, small decreases in plasma apoC-II and apoC-III levels occurred after both meals, although the changes in apoC-II were not statistically significant. The tendency for decreased plasma apoC levels following alimentary lipemia confirms previous reports, and provides further data to support the concept that some apoC is cleared from plasma in association with TRL remnants. The finding that mildly hypertriglyceridemic subjects responded similarly to both conventional fat and MCT may indicate that their rates of remnant clearance were similar following the two meals.

Metabolic disorders of serum lipoproteins in endotoxin-poisoned mice: the role of high density lipoprotein (HDL) and triglyceride-rich lipoproteins.

A study was performed to clarify the role of serum lipoproteins, especially high density lipoprotein (HDL) and triglyceride-rich lipoproteins in endotoxemic or endotoxin-poisoned animals. The level of HDL-cholesterol decreased markedly in mouse serum 18-24 hr postintoxication, while the amount of low density lipoprotein (LDL)-cholesterol in the sera of poisoned mice was about 175% of that of the controls. Serum lecithin-cholesterol acyltransferase activity in the poisoned mice decreased slightly for 3-6 hr after endotoxin injection, but became markedly increased at 18-24 hr as compared with that in the controls. The amount of serum very low density lipoprotein (VLDL) showed a marked increase in the poisoned mice 8-24 hr postintoxication. The HDL fraction in the electrophoretic patterns of serum was reduced according to the dose of endotoxin 18 hr postintoxication. The HDL fraction in mice injected with lead acetate plus endotoxin was markedly lower than that in the poisoned mice. When streptozotocin-diabetic mice were injected with endotoxin, the HDL fraction was higher than that in the endotoxin-poisoned mice. In endotoxin-poisoned mice a correlation was observed between the lipid peroxide and LDL levels in the serum. In disk electrophoretic patterns, the HDL fraction in mice given vitamin E-supplemented diet showed a higher level than that in mice given a normal diet. Lipoprotein lipase (LPL) activity in poisoned mice significantly decreased to 59% of the control value 18 hr postintoxication, but hepatic triglyceride lipase activity was only slightly increased in endotoxin-poisoned mice. In analysis of HDL apoprotein peptide in serum lipoprotein, the apo C-II peptide level was clearly lower in mouse serum 18 hr postintoxication than that in the controls. These results suggest that the decrease in LPL activity in endotoxin-poisoned mice may be closely related to a decrease in the apo C-II peptide level, and also that it plays an important part in HDL and triglyceride-rich lipoprotein metabolism in the poisoned mice.