The apolipoprotein C-II variant apoC-IILys19→Thr is not associated with dyslipidemia in an affected kindred

The rare apolipoprotein C-II (apoC-II) mutation, apoC-II_Lys19→Thr, also known as apoC-II-v, has been found previously in association with hyperlipoproteinemia. From a lipid clinic screening we identified three unrelated individuals who had the apoC-II_Lys19→Thr mutation. Among eight family members of one proband, we have found another four who were affected. None of the inviduals in this kindred is dyslipidemic and there is no difference in lipid levels between affected and unaffected family members. Therefore, we conclude that the presence of this apolipoprotein variant by itself has no effect on lipoprotein levels. In addition, the apolipoprotein E (apoE) isoform, apoE4 does not have a synergistic effect on lipoprotein levels in this kindred, in contrast to observations on the interaction of apoE4 with another apoC-II mutant (apoC-II_Toronto). The single nucleotide substitution that causes the apoC-II_Lys19→Thr variant introduces a previously unrecognized restriction site (for Mae III), that provides for easy screening.     

Ultrastructural and biochemical studies on the intestinal absorption of a medium-chain triglyceride (MCT), tricaprylin

The intestinal absorption of a medium-chain triglyceride (MCT) was studied by electron microscopy and biochemical analysis. In jejunal absorptive cells of rats fed tricaprylin, the smooth endoplasmic reticulum in the apical cytoplasm appeared to increase in number and contained one or two particles about 40–80 nm in diameter that were less electron dense and similar in size and profile to very low density lipoprotein. Similar particles were also observed packed in the dilated Golgi sacs and in the extended intercellular spaces. These particles were remarkably increased in number as compared with those in fasted rats. Biochemical analysis of lymph from the main intestinal lymph duct showed that caprylate was apparently demonstrated only in the lymph of rats given tricaprylin at the maximum rate 3h after oral administration. The study strongly suggests that medium-chain triglyceride is at least in part transported via lacteal, possibly in the form of very low density lipoprotein.     

Formaldehyde alters triglyceride synthesis and very low-density lipoprotein secretion in a time-dependent manner

Formaldehyde is a common indoor air pollutant that is toxic to the liver. This study aimed to investigate the effects of formaldehyde on triglyceride metabolism in human hepatocellular carcinoma cells (HepG2). Cell viability was detected using a MTT (3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide) assay. Following treatment with different concentrations of formaldehyde for 24 and 48 h, the intra and extra-hepatocellular triglyceride (TG) content was determined using a chemical-enzymatic method; Western blotting was used to detect the levels of fatty acid synthesis and VLDL-related proteins. Our results showed that cell viability significantly decreased after formaldehyde treatment (0.5–12.5 mM, 24/48 h). Extracellular TG levels in the hepatocytes increased after formaldehyde treatment at 0.004 mM–0.1 mM for 24 h. SREBP-1c, ACC, FASN, and MTP, CES3 and DGAT1 proteins increased significantly after 24 h of formaldehyde treatment. Intracellular TG levels decreased for 48 h treatment of formaldehyde. AMPKα increased significantly in all tested groups and p-AMPK increased significantly after 0.1 mM formaldehyde treatment for 48 h. Our results indicated that short–term formaldehyde exposure balances triglyceride metabolism by promoting hepatocellular TG synthesis and VLDL secretion; Long-term formaldehyde disturbs the TG metabolism balance in the hepatocytes.     

巨噬细胞氧化修饰极低密度脂蛋白及Cu2+修饰的极低密度脂蛋白对单核细胞与内皮细胞粘附的影响

极低密度脂蛋白(VLDL)与小鼠腹腔巨噬细胞温育24小时和48小时后,其硫代巴比妥酸反应物质值明显高于无细胞对照组,琼脂糖电泳速度也加快,两者一致。结果说明小鼠腹腔巨噬细胞可以氧化修饰极低密度脂蛋白。VLDL在体外用Cu~(2+)修饰后。硫代巴比妥酸反应物质明显增加,琼脂糖凝股电泳速度加快。比较正常的VLDL(n—VLDL)及Cu~(2+)氧化的VLDL(Ox—VLDL)对内皮细胞粘附单核细胞的影响时,发现在所用各种浓度下,Ox—VLDL单核细胞的粘附率比n—VLDL组大得多(P<0.0001),说明VLDL被氧化后明显增加单核细胞与内皮细胞的粘附。     

Apolipoprotein C in Type 2 (non-insulin-dependent) diabetic patients with hypertriglyceridaemia

Summary The composition of apolipoprotein C of the very low density lipoproteins (VLDL) was examined in 23 treated Type 2 (non-insulin-dependent) diabetic patients, who had elevated VLDL concentrations. Apolipoprotein C was separated by isoelectric focussing into apolipoprotein C-II which is known as the specific activator of lipoprotein lipase, and three apolipoprotein C-III fragments. A regulatory role has been ascribed to the ratio of apolipoprotein C-II to apolipoprotein C-III in the removal of plasma triglycerides. In our diabetic group, the composition of apolipoprotein C of the VLDL particles was not different from that of a healthy control group. In particular, the above apolipoprotein ratio and the relative amounts of apolipoprotein C-III fragments were normal. Hypertriglyceridaemia in these diabetic subjects does not seem to be related to alterations in the apolipoprotein C composition.     

Normal metabolism of apolipoprotein B100-containing lipoproteins despite qualitative abnormalities in type 1 diabetic men

Aims/hypothesis Type 1 diabetic subjects are at increased risk of cardiovascular disease and exhibit multiple qualitative abnormalities of apolipoprotein (apo) B100-containing lipoproteins. This stable isotope kinetic experiment was designed to study whether these abnormalities are associated with changes in the synthesis and fractional catabolic rates of VLDL-, IDL- and LDL-apoB100.Methods Using a bolus followed by a 16-h constant infusion of ¹³C-leucine, we performed a kinetic study in eight men with type 1 diabetes treated with a continuous subcutaneous insulin infusion administered by an external pump and in seven healthy men, in the fed state.Results The mean HbA₁c level in the type 1 diabetic patients was 8.00±1.48%. Plasma triglyceride, and total, LDL and HDL cholesterol levels were similar in patients and control subjects. VLDL were less triglyceride rich in type 1 diabetic patients than in control subjects (VLDL triglyceride : apoB 6.91±0.81 vs 8.29±1.24 mmol/g, p=0.05). Conversely, the IDL and LDL of the type 1 diabetic patients contained relatively higher levels of triglycerides (IDL triglycerides : apoB 2.16±0.36 vs 1.57±0.30 mmol/g, p<0.01; LDL triglycerides : apoB 0.27±0.06 vs 0.16±0.04 mmol/g, p<0.05). The apoB100 pool size, production and fractional catabolic rates in the two groups of subjects were similar for all lipoprotein fractions.Conclusions/interpretation Despite qualitative abnormalities, especially abnormalities of triglyceride content, the metabolism of apoB100-containing lipoproteins is not altered in type 1 diabetic men with fair glycaemic control with continuous subcutaneous insulin infusion. The high risk of atherosclerosis in these patients cannot be explained by kinetic abnormalities of apoB100-containing lipoproteins.     

Familial homozygous hypobetalipoproteinemia

An apparently new form of abetalipoproteinemia, homozygous hypobetalipoproteinemia, was studied in progeny of a mating of two parents each heterozygous for familial hypobetalipoproteinemia, which was characterized by three-generation vertical transmission on both maternal and paternal sides of the family. The two children, with an apparent homozygous form of hypobetalipoproteinemia, had, in addition to abetalipoproteinemia, acanthocytosis, intestinal etpithelial and hepatic steatosis and steatorrhea. No low desity lipoprotein (LDL) was detected by immunodiffusion with antisera to LDL or apoLDL. The defects in apolipoproteins in these two children were the same as those reported in children with abetalipoproteinemia inherited as an autosomal recessive trait. The genetic defect of hypobetalipoproteinemia, when homozygous, can lead to all of the known clinical and biochemical features of abetalipoproteinemia.     

Increased lipolysis by secretory phospholipase A(2) group V of lipoproteins in diabetic dyslipidaemia

Background. Lipolysis of lipoproteins by secretory phospholipase A₂ group V (sPLA₂‐V) promotes inflammation, lipoprotein aggregation and foam cell formation – all considered as atherogenic mechanisms. Objective. In this study, we compared the susceptibility to sPLA₂‐V lipolysis of VLDL and LDL from individuals with type 2 diabetes and the metabolic syndrome (T2D‐MetS) and from healthy controls. Design. VLDL and LDL were isolated from 38 T2D‐MetS subjects and 38 controls, treated pair‐wise. Extent of sPLA₂‐V lipolysis was measured as release of nonesterified free fatty acids (NEFA). In a subset of the subjects, lipoprotein composition was determined as a relationship between lipid and apolipoprotein components. Results. Mean paired increase in sPLA₂‐V lipolysis after 1 h for T2D‐MetS versus control was 2.0 μmol NEFA l^?1 for VLDL (P = 0.004) and 0.75 μmol NEFA l^?1 for LDL (P = 0.001). There were also substantial differences in lipoprotein composition between the groups. T2D‐MetS VLDL had higher triglyceride and cholesterol contents than control VLDL. T2D‐MetS LDL was smaller and contained more triglycerides and less cholesterol than control LDL. Both VLDL and LDL from T2D‐MetS subjects also contained more apolipoprotein CIII per particle. Conclusion. VLDL and LDL from T2D‐MetS individuals were more susceptible to sPLA₂‐V lipolysis than those from control individuals. This may result in elevated levels of NEFA and lysophosphatidylcholine, both in circulation and in LDL, possibly contributing to the elevated inflammatory state and increased risk of cardiovascular diseases seen in these individuals.     

A case control study on HDL associated PON1 enzyme level in Northern Indian type 2 diabetes mellitus patients

Aim

To evaluate the serum paraoxonase 1 activity and determine its association with duration in type 2 Diabetes mellitus patients.

Biochemical and immunohistochemical changes in delta-9-tetrahydrocannabinol-treated type 2 diabetic rats

The regulation of glucose, lipid metabolism and immunoreactivities of insulin and glucagon peptides by delta-9-tetrahydrocannabinol (Δ⁹-THC) in diabetes were examined in an experimental rat model. Male Sprague-Dawley rats were divided into four groups: (1) control, (2) Δ⁹-THC treated, (3) diabetic, and (4) diabetic + Δ⁹-THC. The type 2 diabetic rat model was established by intraperitoneal (i.p.) injection of nicotinamide (85 mg/kg body weight) followed after 15 min by i.p. injection of streptozotocin (STZ) at 65 mg/kg of body weight. Δ⁹-THC and Δ⁹-THC treated diabetic groups received 3 mg/kg/day of Δ⁹-THC for 7 days. The immunolocalization of insulin and glucagon peptides was investigated in the pancreas using a streptavidin–biotin–peroxidase technique. High density lipoprotein cholesterol (HDL), low density lipoprotein cholesterol (LDL), very low density lipoprotein cholesterol (VLDL), triglycerides (TG), total cholesterol (TC) and total protein (TP) levels were measured in serum. Total islet area percent of insulin immunoreactive cells slightly changed in diabetic + Δ⁹-THC rats compared to diabetic animals. However, the area percent of glucagon immunoreactive cells showed a decrease in diabetic + Δ⁹-THC rats compared to that of diabetic animals alone. Serum TC, HDL and LDL levels of diabetes + Δ⁹-THC group showed a decrease compared to the diabetic group. These results indicate that Δ⁹-THC may serve a protective role against hyperlipidemia and hyperglycemia in diabetic rats.