Apolipoprotein B100 biogenesis: a complex array of intracellular mechanisms regulating folding, stability, and lipoprotein assembly.

Apolipoprotein B100 (apoB) is a large amphipathic lipid-binding protein that is synthesized by hepatocytes and used to assemble and stabilize very low density lipoproteins (VLDL). It may have been derived through evolution from other lipid-associating proteins such as microsomal triglyceride transfer protein or vitellogenin. The correct folding of apoB requires assistance from chaperone proteins in co-translational lipidation, disulfide bond formation, and glycosylation.

Palmitate enhances protein tyrosine phosphatase 1B (PTP1B) gene expression at transcriptional level in C2C12 skeletal muscle cells.

The factors responsible for regulating PTP1B expression in certain metabolic states have been unclear. We investigated the effects of palmitate on PTP1B gene transcription in C2C12 myotubes and myotubes co-cultured with J774A.1 macrophages.

Sleep-disordered breathing is increased in obese adolescents with craniopharyngioma compared with obese controls.

Context: Retrospective studies suggest that adolescents with craniopharyngioma and hypothalamic obesity have increased sleep-disordered breathing (SDB).

Objectives: The objectives of this study were to compare the prevalence of SDB in adolescents with craniopharyngioma-related obesity compared with body mass index (BMI)-matched controls and to explore possible relationships between SDB, insulin resistance, and adipocytokines.

Design: This was a cross-sectional study of obese craniopharyngioma and obese control adolescents.

Protein tyrosine phosphatase-1B (PTP-1B) knockdown improves palmitate-induced insulin resistance in C2C12 skeletal muscle cells.

Insulin resistance is the central defect in type 2 diabetes and obesity. During the development of insulin resistance a lipid accumulation is accompanied by increased PTP-1B expression in the muscle. The aim of this study was to examine the effects of PTP-1B knockdown on insulin signaling and insulin resistance in the presence or absence of palmitate in C2C12 skeletal muscle cells.

Proteomic profiling of intestinal prechylomicron transport vesicle (PCTV)-associated proteins in an animal model of insulin resistance (94 char).

Intestinal overproduction of apolipoprotein B (apoB)-48-containing chylomicrons is increasingly recognized as an underlying factor in metabolic dyslipidemia commonly observed in insulin-resistant states. Enhanced chylomicron assembly and secretion has been documented in animal models of insulin resistance, but the underlying mechanistic factors are unknown. Chylomicron assembly occurs through a series of complex vesicular interactions involving prechylomicron transport vesicles (PCTVs), which transport lipids from the endoplasmic reticulum (ER) to the Golgi.

Elevated lactate in ethylene glycol poisoning: True or false?

Background: There have been an increasing number of reports on false increase of lactate in ethylene glycol poisoning. We recently encountered two cases of ethylene glycol poisoning with very high blood lactate concentrations on ABL blood gas analyzers.

Methods: Patient plasma lactate concentrations were measured on different chemistry instruments in addition to ABL analyzer.

Strong induction of PCSK9 gene expression through HNF1alpha and SREBP2: mechanism for the resistance to LDL-cholesterol lowering effect of statins in dyslipidemic hamsters.

We investigated the role of proprotein convertase subtilisin/kexin type 9 (PCSK9) in the resistance of dyslipidemic hamsters to statin-induced LDL-cholesterol (LDL-C) reduction and the molecular mechanism by which statins modulated PCSK9 gene expression in vivo. We utilized the fructose diet-induced dyslipidemic hamsters as an in vivo model and rosuvastatin to examine its effects on liver PCSK9 and LDL receptor (LDLR) expression and serum lipid levels. We showed that rosuvastatin induced PCSK9 mRNA to a greater extent than LDLR mRNA in the hamster liver.

Pharmacological management of metabolic syndrome and its lipid complications.

Obesity epidemic has been spread all over the world in the past few decades and has caused a major public health concern due to its increasing global prevalence. Obese individuals are at higher risks of developing dyslipidemic characteristics resulting in increased triglyceride and LDL-cholesterol content and reduced HDL-cholesterol levels. This disorder has profound implications as afflicted individuals have been demonstrated to be at increased risk of development of hypertension, atherosclerosis, type 2 diabetes and cardiovascular diseases.

The glucagon-like peptide 1 receptor is essential for postprandial lipoprotein synthesis and secretion in hamsters and mice.

Aims/hypothesis: Glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors attenuate postprandial lipaemia through mechanisms that remain unclear. As dyslipidaemia is a contributing risk factor for cardiovascular disease in type 2 diabetes, we examined the mechanisms linking pharmacological and physiological regulation of GLP-1 action to control of postprandial lipid metabolism.

Methods: Postprandial lipid synthesis and secretion were assessed in normal and fructose-fed hamsters and in wild-type mice that were treated with or without sitagliptin.

Laboratory quality regulations and accreditation standards in Canada.

Objectives: To review the current status of laboratory quality regulations and accreditation standards in Canada.

Design And Methods: The review is written based on information collected by survey questionnaires, a comprehensive review of available websites, and personal communications.

Results: Accreditation of medical laboratories in Canada is regulated by provincial health authorities.

Free fatty acid-induced muscle insulin resistance and glucose uptake dysfunction: evidence for PKC activation and oxidative stress-activated signaling pathways.

In the present study, we examined the effects of free fatty acids (FFAs) on insulin sensitivity and signaling cascades in the C2C12 skeletal muscle cell culture system. Our data clearly manifested that the inhibitory effects of PKC on insulin signaling may at least in part be explained by the serine/threonine phosphorylation of IRS-1. Both oleate and palmitate treatment were able to increase the Serine(307) phosphorylation of IRS-1.

A national survey on pediatric critical values used in clinical laboratories across Canada.

Objective: Notification of critical values to clinical staff is an important post-analytical process in all acute care clinical laboratories. No data are available however on how laboratories obtain or establish critical values, particularly in pediatric settings. This study was designed to examine and compare critical values used for pediatric patients in biochemistry laboratories in Canada and assess potential interlaboratory variability.

Proteomic profiling of the prechylomicron transport vesicle involved in the assembly and secretion of apoB-48-containing chylomicrons in the intestinal enterocytes.

Intracellular assembly of chylomicrons (CM) occurs in intestinal enterocytes through a series of complex vesicular interactions. CM are transported from the ER to the Golgi using a specialized vesicular compartment called the prechylomicron transport vesicle (PCTV). In this study, PCTVs were isolated from the enteric ER of the Syrian Golden hamster, and characterized using 2-DE and MS.

Clinical laboratory reference intervals in pediatrics: the CALIPER initiative.

Objective And Rationale: Reference intervals provided on laboratory reports are essential for appropriate interpretation of test results, and can significantly impact clinical decision-making and the quality of patient care. Careful determination and/or validation of reference intervals by the laboratory for use in the patient population it serves are therefore important to ensure their proper utility. Unfortunately, critical gaps currently exist in accurate and up-to-date pediatric reference intervals for accurate interpretation of laboratory tests performed in children and adolescents.

Metabolic effects of dietary cholesterol in an animal model of insulin resistance and hepatic steatosis.

Although the atherogenic role of dietary cholesterol has been well established, its diabetogenic potential and associated metabolic disturbances have not been reported. Diet-induced hamster models of insulin resistance and dyslipidemia were employed to determine lipogenic and diabetogenic effects of dietary cholesterol. Metabolic studies were conducted in hamsters fed diets rich in fructose (40%), fat (30%), and cholesterol (0.

Hepatic insulin resistance, metabolic syndrome and cardiovascular disease.

Background: The metabolic syndrome is a constellation of common metabolic disorders that is associated with cardiovascular disease. Insulin resistance has a central role in the pathophysiology of metabolic syndrome.

Recent Advances: It is now commonly accepted that chronic inflammation associated with visceral obesity induces insulin resistance in the liver.

LXRalpha activation perturbs hepatic insulin signaling and stimulates production of apolipoprotein B-containing lipoproteins.

Liver X receptor-alpha (LXRalpha) is considered a master regulator of hepatic lipid metabolism; however, little is known about the link between LXR activation, hepatic insulin signaling, and very low-density lipoprotein (VLDL)-apolipoprotein B (apoB) assembly and secretion. Here, we examined the effect of LXRalpha activation on hepatic insulin signaling and apoB-lipoprotein production. In vivo activation of LXRalpha for 7 days using a synthetic LXR agonist, TO901317, in hamsters led to increased plasma triglyceride (TG; 3.

Insulin sensitivity and secretion in children and adolescents with hypothalamic obesity following treatment for craniopharyngioma.

Background: Craniopharyngioma (CP), a tumour occurring in the hypothalamic-pituitary area, results in morbid obesity in 25-60% of affected children. It has been suggested that abnormalities of insulin secretion and/or insulin action due to hypothalamic injury may be associated with weight gain and the metabolic syndrome in this population.

Aim: To evaluate: (i) insulin secretion (IS) and insulin sensitivity (Si); (ii) features of the metabolic syndrome (MS) and (iii) factors involved in risk for diabetes and heart disease in obese youth treated for CP.

Glucagon-like peptide-2 increases intestinal lipid absorption and chylomicron production via CD36.

Background & Aims: Excessive postprandial lipemia is a prevalent condition that results from intestinal oversecretion of apolipoprotein B48 (apoB48)-containing lipoproteins. Glucagon-like peptide-2 (GLP-2) is a gastrointestinal-derived intestinotropic hormone that links nutrient absorption to intestinal structure and function. We investigated the effects of GLP-2 on intestinal lipid absorption and lipoprotein production.

Does the Macroduct collection system reliably define sweat chloride concentration in subjects with intermediate results?

Objectives: The sweat test remains the current diagnostic gold standard for CF disease. Many CF testing centres have switched from the Gibson and Cooke to the Macroduct. Since the validity and sensitivity of Macroduct has not been tested in patients with intermediate sweat chloride concentrations, we compared both methods simultaneously including subjects expected to have intermediate results.

Apolipoprotein B100 acts as a molecular link between lipid-induced endoplasmic reticulum stress and hepatic insulin resistance.

Unlabelled: Accumulation of unfolded and misfolded proteins in the endoplasmic reticulum (ER) results in ER stress and lipid overload-induced ER stress has been implicated in the development of insulin resistance. Here, evidence is provided for a molecular link between hepatic apolipoprotein B100 (apoB100), induction of ER stress, and attenuated insulin signaling. First, in vivo upregulation of hepatic apoB100 by a lipogenic diet was found to be closely associated with ER stress and attenuated insulin signaling in the liver.

Glucosamine-induced endoplasmic reticulum stress attenuates apolipoprotein B100 synthesis via PERK signaling.

Glucosamine impairs hepatic apolipoprotein B100 (apoB100) production by inducing endoplasmic reticulum (ER) stress and enhancing cotranslational and posttranslational apoB100 degradation (Qiu, W., R. K.

Microsomal proteomics.

Proteomic profiling of subcellular compartments has many advantages over traditional proteomic approaches using whole cell lysates as it allows for detailed proteome analysis of a specific organelle and corresponding functional characteristics. The microsome is a critical, membranous compartment involved in the synthesis, sorting, and secretion of proteins as well as other metabolic functions. This chapter will describe detailed methods for the isolation of microsomal organelles including the ER, Golgi, and prechylomicron transport vesicle (PCTV), a recently identified vesicular system involved in intestinal lipoprotein assembly and secretion.

Insulin stimulates the expression of carbohydrate response element binding protein (ChREBP) by attenuating the repressive effect of Pit-1, Oct-1/Oct-2, and Unc-86 homeodomain protein octamer transcription factor-1.

The carbohydrate response element binding protein (ChREBP) has been recognized as a key controller of hepatic lipogenesis. Whereas the function of ChREBP has been extensively investigated, mechanisms underlying its transcription remain largely unknown, although ChREBP production is elevated in a hyperinsulinemic mouse model. We located a conserved Pit-1, Oct-1/Oct-2, and Unc-86 (POU) protein binding site (ATGCTAAT) within the proximal promoter region of human ChREBP.