Sample preparation with sucrose cryoprotection dramatically alters Zn distribution in the rodent hippocampus, as revealed by elemental mapping.

Transition metal ions (Fe, Mn, Cu, Zn) are essential for healthy brain function, but altered concentration, distribution, or chemical form of the metal ions has been implicated in numerous brain pathologies. Currently, it is not possible to image the cellular or sub-cellular distribution of metal ions in vivo and therefore, studying brain-metal homeostasis largely relies on ex vivo in situ elemental mapping. Sample preparation methods that accurately preserve the in vivo elemental distribution are essential if one wishes to translate the knowledge of elemental distributions measured ex vivo toward increased understanding of chemical and physiological pathways of brain disease. The choice of sample preparation is particularly important for metal ions that exist in a labile or mobile form, for which the in vivo distribution could be easily distorted by inappropriate sample preparation. One of the most widely studied brain structures, the hippocampus, contains a large pool of labile and mobile Zn. Herein, we describe how sucrose cryoprotection, the gold standard method of preparing tissues for immuno-histochemistry or immuno-fluorescence, which is also often used as a sample preparation method for elemental mapping studies, drastically alters hippocampal Zn distribution. Based on the results of this study, in combination with a comparison against the strong body of published literature that has used either rapid plunge freezing of brain tissue, or sucrose cryo-protection, we strongly urge investigators in the future to cease using sucrose cryoprotection as a method of sample preparation for elemental mapping, especially if Zn is an analyte of interest.

Antihypertensive agents do not prevent blood-brain barrier dysfunction and cognitive deficits in dietary-induced obese mice.

BACKGROUND: While vascular risk factors including Western-styled diet and obesity are reported to induce cognitive decline and increase dementia risk, recent reports consistently suggest that compromised integrity of cerebrovascular blood-brain barrier (BBB) may have an important role in neurodegeneration and cognitive deficits. A number of studies report that elevated blood pressure increases the permeability of BBB. METHODS: In this study, we investigated the effects of antihypertensive agents, candesartan or ursodeoxycholic acid (UDCA), on BBB dysfunction and cognitive decline in wild-type mice maintained on high fat and fructose (HFF) diet for 24 weeks. RESULTS: In HFF-fed mice, significantly increased body weight with elevated blood pressure, plasma insulin and glucose compared with mice fed with low-fat control chow was observed. Concomitantly, significant disruption of BBB and cognitive decline were evident in the HFF-fed obese mice. Hypertension was completely prevented by the coprovision of candesartan or UDCA in mice maintained on HFF diet, while only candesartan significantly reduced the body weight compared with HFF-fed mice. Nevertheless, BBB dysfunction and cognitive decline remained unaffected by candesartan or UDCA. CONCLUSIONS: These data conclusively indicate that modulation of blood pressure and/or body weight may not be directly associated with BBB dysfunction and cognitive deficits in Western diet-induced obese mice, and hence antihypertensive agents may not be effective in preventing BBB disruption and cognitive decline. The findings may provide important mechanistical insights to obesity-associated cognitive decline and its therapy.

Biostatistical analysis of quantitative immunofluorescence microscopy images.

Semiquantitative immunofluorescence microscopy has become a key methodology in biomedical research. Typical statistical workflows are considered in the context of avoiding pseudo-replication and marginalising experimental error. However, immunofluorescence microscopy naturally generates hierarchically structured data that can be leveraged to improve statistical power and enrich biological interpretation. Herein, we describe a robust distribution fitting procedure and compare several statistical tests, outlining their potential advantages/disadvantages in the context of biological interpretation. Further, we describe tractable procedures for power analysis that incorporates the underlying distribution, sample size and number of images captured per sample. The procedures outlined have significant potential for increasing understanding of biological processes and decreasing both ethical and financial burden through experimental optimization.

Vitamin D & endothelial function.

There is increasing interest in the extra-skeletal roles of vitamin D for health and well-being. Poor vitamin D status has been associated with obesity, cardiovascular disease, type 2 diabetes and mental health. Endothelial dysfunction may underscore insulin resistance and hence predispose to both cardiovascular disease (CVD) and type 2 diabetes. The objective of this review was to gain an appreciation of the recent causative evidence linking vitamin D and endothelial function. The PubMed database was searched from 2009 to date. Key words used were vitamin D, supplementation, systemic inflammation, endothelium, endothelial dysfunction and humans. Selected articles were restricted to the English language and to randomized control trials (RCTs) of vitamin D supplementation with direct measures of endothelial function. Final inclusion was based on a quality rating ≥ 3, based on the Jadad score. Ten RCTs met these criteria and were summarized for their outcomes. Only two studies showed an improvement in flow mediated dilatation with vitamin D. Three other studies reported decreases in C-reactive protein, platelet activation inhibitor-1, tissue plasminogen activator or B type natriuretic peptide. Recent evidence from good quality RCTs did not support a beneficial effect of vitamin D on vascular reactivity. Future intervention studies may need to target a higher vitamin D status and longer duration to determine whether the vitamin has a regulatory role in endothelial function.

Aging-related changes in blood-brain barrier integrity and the effect of dietary fat.

BACKGROUND: Disturbances in blood-brain barrier (BBB) integrity contribute to the onset and progression of neurodegenerative diseases including Alzheimer's disease (AD) and vascular dementia (VaD). Aging is positively associated with AD and VaD risk, but this may reflect comorbidities or the effects of other chronic modulators of vascular function such as diet. OBJECTIVE: To explore putative synergistic effects of aging with diet, in this study genetically unmanipulated mice were maintained on diets enriched in saturated fatty acids (SFA) or cholesterol and compared to mice provided with low-fat (LF) feed formula. METHODS: The functional integrity of the BBB was assessed following 3, 6 and 12 months of dietary intervention commenced at 6 weeks of age, by determining the brain parenchymal extravasation of immunoglobulin G (IgG). RESULTS: Mice maintained on the SFA- or cholesterol-enriched diet showed significant parenchymal IgG abundance following 3 months of feeding, concomitant with diminished expression of the tight junction protein occludin. LF control mice had essentially no evidence of BBB disturbances. Six months of SFA feeding exacerbated the difference in IgG abundance compared to the LF mice. At 12 months of feeding, the control LF mice also had significant parenchymal IgG that was comparable to mice fed the SFA- or cholesterol-enriched diet for 3 months. However, there may have been an adaptation to the fat-enriched diets because SFA and cholesterol did not exacerbate IgG parenchymal accumulation beyond 6 months of feeding. CONCLUSION: Collectively, the study suggests that diets enriched in SFA or cholesterol accelerate the onset of BBB dysfunction that otherwise occurs with aging.

Increased risk of cardiovascular disease in Type 1 diabetes: arterial exposure to remnant lipoproteins leads to enhanced deposition of cholesterol and binding to glycated extracellular matrix proteoglycans.

AIMS: To determine fasting and postprandial metabolism of apolipoprotein B48 (apoB48) remnant lipoproteins in subjects with Type 1 diabetes and the relationship to progressive cardiovascular disease, and to investigate the impact of remnant lipoprotein cholesterol accumulation associated with arterial wall biglycan using a rodent model of Type 1 diabetes. METHODS: Normolipidaemic subjects (n = 9) with long-standing Type 1 diabetes (and advanced cardiovascular disease) and seven healthy control subjects were studied. Fasting and postprandial apoB48 concentration was determined following a sequential meal challenge. A rodent model of streptozotocin-induced diabetes was used to investigate the ex vivo retention of fluorescent-conjugated remnants. Binding of remnant lipoproteins to human recombinant biglycan was assessed in vitro. RESULTS: A significantly higher concentration of fasting plasma apoB48 remnants was observed in patients with Type 1 diabetes compared with control subjects. Patients with Type 1 diabetes exhibited a greater total plasma apoB48 area under the curve (AUC) and an increased incremental AUC following a second sequential meal compared with control subjects. The arterial retention of remnants ex vivo and associated cholesterol was increased sevenfold in Type 1 diabetes rats relative to controls. Remnants were shown to bind with significant affinity to human biglycan in vitro and a further 2.3-fold increased binding capacity was observed with glycated biglycan. Remnants were shown to colocalize with both arterial biglycan and glycated matrix proteins in the Type 1 diabetes rodent model. CONCLUSION: Impaired metabolism of remnant lipoproteins associated with enhanced binding to proteoglycans appears to contribute to the arterial cholesterol deposition in Type 1 diabetes. Our findings support the hypothesis that impaired remnant metabolism may contribute to accelerated progression of atherosclerosis in the hyperglycaemic and insulin-deficient state.

Elemental characterisation of the pyramidal neuron layer within the rat and mouse hippocampus.

A unique combination of sensitivity, resolution, and penetration make X-ray fluorescence imaging (XFI) ideally suited to investigate trace elemental distributions in the biological context. XFI has gained widespread use as an analytical technique in the biological sciences, and in particular enables exciting new avenues of research in the field of neuroscience. In this study, elemental mapping by XFI was applied to characterise the elemental content within neuronal cell layers of hippocampal sub-regions of mice and rats. Although classical histochemical methods for metal detection exist, such approaches are typically limited to qualitative analysis. Specifically, histochemical methods are not uniformly sensitive to all chemical forms of a metal, often displaying variable sensitivity to specific "pools" or chemical forms of a metal. In addition, histochemical methods require fixation and extensive chemical treatment of samples, creating the strong likelihood for metal redistribution, leaching, or contamination. Direct quantitative elemental mapping of total elemental pools, in situ within ex vivo tissue sections, without the need for chemical fixation or addition of staining reagents is not possible with traditional histochemical methods; however, such a capability, which is provided by XFI, can offer an enormous analytical advantage. The results we report herein demonstrate the analytical advantage of XFI elemental mapping for direct, label-free metal quantification, in situ within ex vivo brain tissue sections. Specifically, we definitively characterise for the first time, the abundance of Fe within the pyramidal cell layers of the hippocampus. Localisation of Fe to this cell layer is not reproducibly achieved with classical Perls histochemical Fe stains. The ability of XFI to directly quantify neuronal elemental (P, S, Cl, K, Ca, Fe, Cu, Zn) distributions, revealed unique profiles of Fe and Zn within anatomical sub-regions of the hippocampus i.e., cornu ammonis 1, 2 or 3 (CA1, CA2 or CA3) sub-regions. Interestingly, our study reveals a unique Fe gradient across neuron populations within the non-degenerating and pathology free rat hippocampus, which curiously mirrors the pattern of region-specific vulnerability of the hippocampus that has previously been established to occur in various neurodegenerative diseases.

Chylomicron amyloid-beta in the aetiology of Alzheimer's disease.

Alzheimer's disease is characterized by inflammatory proteinaceous deposits comprised principally of the protein amyloid-beta (Abeta). Presently, the origins of cerebral amyloid deposits are controversial, though pivotal for the prevention of Alzheimer's disease. Recent evidence suggests that in blood, Abeta may serve as a regulating apoprotein of the triglyceride-rich-lipoproteins and we have found that the synthesis of Abeta in enterocytes and thereafter secretion as part of the chylomicron cascade is regulated by dietary fats. It is our contention that chronically elevated plasma levels of Abeta in response to diets rich in saturated fats may lead to disturbances within the cerebrovasculature and exaggerated blood-to-brain delivery of circulating Abeta, thereby exacerbating amyloidosis. Consistent with this hypothesis we show that enterocytic Abeta is increased concomitant with apolipoprotein B48. Furthermore, cerebral extravasation of immunoglobulin G, a surrogate marker of plasma proteins is observed in a murine model of Alzheimer's disease maintained on a saturated-fat diet and there is diminished expression of occludin within the cerebrovasculature, an endothelial tight junction protein.

Plasma lipoprotein beta-amyloid in subjects with Alzheimer's disease or mild cognitive impairment.

BACKGROUND: Plasma amyloid beta-peptide (Abeta) can compromise the blood-brain barrier, contributing to cerebrovascular alterations and amyloid angiopathy in Alzheimer's disease (AD). The objectives of this study were to investigate the distribution of lipoprotein-bound plasma-Abeta isoforms. METHODS: This involved a case-control study of subjects with AD or amnestic mild cognitive impairment (MCI) versus controls. Lipoprotein Abeta distribution was determined in fasted plasma. For assessment of chylomicron homeostasis in the postabsorptive state, subjects were bled 4 h after a low-fat meal. The main outcome measures were plasma lipoprotein Abeta isoform distribution and lipid homeostasis. RESULTS: We found the majority of plasma Abeta to be associated with triglyceride-rich lipoproteins (TRLs) encompassing chylomicrons, VLDL and IDL. For all lipoprotein groups, Abeta1-40 was the predominant isoform, accounting for approximately 50% of the total. Thereafter, equivalent amounts of the isoforms 1-42, 2-40, 1-38, 1-37 and 1-39 were found. Abeta1-37, Abeta1-38 and Abeta2-40 isoforms were significantly enriched within the TRL fraction of AD/MCI subjects and similar trends were observed for isoforms Abeta1-39, Abeta1-40 and Abeta1-42. Lipoprotein-Abeta was inversely associated with plasma total- and LDL cholesterol. AD/MCI subjects were not dyslipidaemic, however, there was evidence of accumulation of chylomicrons in the postabsorptive state. CONCLUSIONS: Our data show that Abeta was found to be associated with plasma lipoproteins, especially those enriched with triglyceride. We find that Abeta may be increased in normolipidaemic AD subjects, commensurate with possible disturbances in postprandial lipoprotein homeostasis.

Long-Term Supplementation of Microencapsulated ursodeoxycholic Acid Prevents Hypertension in a Mouse Model of Insulin Resistance.

Hypertension is a significant comorbidity associated with insulin resistance and type-2 diabetes. Limited evidence show that ursodeoxycholic acid (UDCA) has some anti-hypertensive effects. However, the potential effect of UDCA on hypertension induced by type-2 diabetic insulin resistance has not been reported. In C57Bl6 wild-type mice, insulin resistance was induced by the chronic ingestion of diet enriched in fat and fructose (HFF). HFF mice were randomized to treatment with UDCA or candersartan incorporated into the diet to achieve an ingested dose of approximately 70 mg/kg/day of UDCA or 3 mg/kg/day respectively. Systolic and diastolic blood pressure were measured with tail-cuff method. At 4 weeks of dietary treatment systolic and diastolic blood pressure were comparable in HFF and low-fat (LF) control mice. Co-administration of candesartan at 4 weeks significantly decreased systolic and diastolic blood pressure, UDCA showed no anti-hypertensive effect at 4 weeks. At 24 weeks of dietary intervention, HFF fed mice had substantially elevated systolic blood pressure compared to LF controls. The provision of UDCA substantially attenuated the dietary HFF induced increase in systolic blood pressure concomitant with significantly lower plasma angiotensin II. The anti-hypertensive effect of UDCA in HFF mice was comparable to candesartan. The data suggests that long term supplementation of UDCA effectively lowers hypertension in a dietary induced model of type-2 diabetic insulin resistance.

The effect of chronic consumption of red wine polyphenols on vascular function in postmenopausal women.

OBJECTIVE: To elucidate whether the chronic consumption of dealcoholised red wine (DRW) (polyphenol-rich component) and/or red wine (RW) improves vascular function in hypercholesterolaemic postmenopausal women. DESIGN, SUBJECTS AND INTERVENTION: A randomised parallel-arm study. Forty-five hypercholesterolaemic postmenopausal women were randomised into either water, DRW or RW group for 6 weeks following a 4 week washout. Fasting measures of central haemodynamic parameters, arterial wave reflection and endothelial nitric oxide were taken at 0 and 6 weeks. SETTING: Clinic in the School of Public Health, Curtin University. RESULTS: There were no significant between group differences in arterial stiffness as measured by augmentation index (AIx) and augmentation pressure (AP). However, a significant within group decrease in AIx (-9%, P=0.02) and AP (-12%, P=0.02) was observed following DRW consumption. No significant changes were observed in central haemodynamic parameters and endothelial nitric oxide levels following DRW and RW consumption, compared to water. CONCLUSIONS: Neither the chronic consumption of DRW nor RW improved markers of arterial stiffness, compared to control. However, the significant within group improvements in these indices following the consumption of DRW cannot be overlooked and warrant further investigation.

Resolution of non-psychogenic epileptic-like seizures utilizing a vasodilatory and anti-inflammatory dietary intervention.

A young female subject with ineffective pharmacological regulation of chronic vasoconstrictive-induced epilectic-like seizures was effectively treated with a dietary regimen targeted to promote vasodilatation and attenuate vascular inflammation. The intervention consisted of complete cessation of caffeinated beverages, supplementation with L-arginine to promote vasodilatation, consumption of foods rich in phytoestrogens, minimization of foods enriched with saturated fatty acids, supplementation with vitamin D concomitant with increased ingestion of dairy milk and supplementation with aged garlic extract.

Binding and uptake of chylomicron remnants by cultured arterial smooth muscle cells from normal and Watanabe-heritable-hyperlipidemic rabbits.

Chylomicron remnants (RM's) may be involved in atherogenesis because they can be delivered to the subendothelial space of arterial vessels and serve as substrate for arterial cells. A number of proteins may bind RM's, however, the quantitative significance of these is not established. The aim of this study was to identify the primary RM binding site of arterial smooth muscle cells (SMC's). At 4 degrees C, SMC's displayed saturable high affinity binding of RM's. In receptor competition studies, LDL inhibited binding of RM's by almost 60% suggesting involvement of the apolipoprotein B100/E receptor. Unlabeled RM's were more effective with an EC50 significantly less than for unlabeled LDL. Furthermore, at 37 degrees C RM uptake was three times greater than LDL, consistent with greater affinity of the apolipoprotein B100/E receptor for lipoproteins containing apolipoprotein E. In SMC's from homozygote Watanabe heritable hyperlipidemic (WHHL) rabbits, the binding and degradation of chylomicron remnants was severely impaired. SMC's from cross-bred WHHL rabbits exhibited levels of binding and degradation intermediate between homozygote WHHL rabbits and controls. We confirmed that the apolipoprotein B100/E receptor is the primary mechanism by which arterial smooth muscle cells bind and degrade RM's using a polyclonal antibody which specifically recognises the receptor. In the presence of the antibody, RM binding and degradation were inhibited by 90%.

Effects of sphingomyelin and phosphatidylcholine acyl chains on the clearance of triacylglycerol-rich lipoproteins from plasma. Studies with lipid emulsions in rats.

Series of lipid emulsions were prepared as physical models of lymph chylomicrons. The emulsion phospholipid was systematically varied with respect to sphingomyelin, in 0-100% mixtures with egg yolk phosphatidylcholine (EYPC). In other emulsions, the phospholipid was systematically varied with respect to dipalmitoylphosphatidylcholine (DPPC) in 0-100% mixtures with 1-palmitoyl-2-oleoylphosphatidylcholine (POPC). All emulsions contained unlabeled free cholesterol, radiolabeled triolein (TO) and radiolabeled cholesteryl oleate (CO). The emulsions were injected into conscious rats to measure the clearances of emulsion TO and CO and the capture of lipid radioactivity by selected organs. The emulsions containing EYPC or POPC were metabolized similarly to lymph chylomicrons, consistent with rapid lipoprotein lipase-mediated hydrolysis of emulsion TO followed by hepatic uptake of the CO in the triglyceride-depleted emulsion remnants. Emulsions stabilized with either 1-oleoyl-2-stearoyl- or 1-stearoyl-2-oleoylphosphatidylcholine (OSPC or SOPC) were metabolized similarly. Increasing amounts of sphingomyelin in EYPC emulsions progressively slowed the removal of TO and CO labels from plasma. With 50% sphingomyelin clearance was very slow, while emulsion clearance was negligible with 100% sphingomyelin. Emulsions containing 20% of DPPC in POPC were metabolized similarly to 100% POPC, but 40% or more of DPPC progressively slowed the removal from plasma of both TO and CO. With 100% DPPC clearance was characterized by a rapid initial removal of about 30% of the injected material, followed by a second phase when removal was negligible, suggesting lack of hydrolysis of triacylglycerols by lipoprotein lipase. Changes in the apolipoproteins associated with the emulsions probably mediated the observed changes in clearance.

Defective plasma clearance of chylomicron-like lipid emulsions in Watanabe heritable hyperlipidemic rabbits.

Human patients with familial hypercholesterolemia (FH) and Watanabe heritable hyperlipidemic rabbits (WHHL), while lacking normal receptors recognizing low-density lipoproteins (LDL), are said to have normal clearance of chylomicrons. In the present study, emulsions with a similar lipid composition to chylomicrons were injected intravenously in homozygous WHHL rabbits and normal control rabbits fed diet with low or high cholesterol. Radioactive labels tracing emulsion triolein and cholesteryl oleate were both removed rapidly from the bloodstream, with the removal rate of triolein always faster than that of cholesteryl oleate. This pattern was similar to the clearance of normal chylomicrons in rabbits or rats, and was consistent with the formation of remnant lipoproteins after hydrolysis of emulsion triolein by lipoprotein lipase, followed by hepatic uptake of the remnants. The removal of cholesteryl oleate was significantly slower in WHHL rabbits than in normal controls, suggesting that the absence of LDL receptor function led to impaired remnant clearance. Measured in post-heparin plasma, the activity of lipoprotein lipase was decreased in WHHL rabbits, but this was not associated with clear evidence of defective lipolysis of emulsion triolein. Apolipoprotein E did not appear to be deficient in WHHL rabbits. Plasma devoid of lipoproteins less than 1.006 g/ml from WHHL and normal control rabbits transferred similar amounts of apolipoprotein E to chylomicron-like emulsions after incubation. Impaired clearance of chylomicron remnants possibly contributes to the hypertriglyceridemia of WHHL rabbits and to accelerated atherogenesis when the function of LDL receptors is defective.

Plasma triacylglycerol secretion in sheep. Paradoxical effects of fasting and alloxan diabetes.

Plasma triacylglycerol and phospholipid concentrations were increased in fasting and diabetic sheep compared with fed animals. Secretion was measured in these animals using Triton WR1339 to block lipoprotein lipase. Triacylglycerol secretion was lowest in fed animals and, unlike non-ruminant species, increased by fasting and diabetes. These changes were in proportion to plasma free fatty acid concentration. However, no effect of Triton was found on plasma phospholipids under any of the conditions studied. It is suggested that the low rate of triacylglycerol secretion in normal animals is due to the limiting membrane found in the liver sinusoid of the sheep and that the greater rate in fasting and diabetes reflects the increased mass of intrahepatic triacylglycerol.

Hypertriglyceridemia is exacerbated by slow lipolysis of triacylglycerol-rich lipoproteins in fed but not fasted streptozotocin diabetic rats.

Hydrolysis by endothelial lipases of triacylglycerol-rich lipoproteins of diabetic origin were compared to lipoproteins of non-diabetic origin. The plasma lipoprotein fraction of density < 1.006 g/ml, including chylomicrons and VLDL, were incubated in vitro with post-heparin plasma (PHP) lipases. The lipoproteins of diabetic origin were hydrolysed at a significantly slower rate than lipoproteins from normal rats by the lipoprotein lipase component of PHP. However, if rats were fasted for 16 h prior to lipoprotein recovery, no differences in rates of VLDL hydrolysis were observed. Slower hydrolysis of lipoproteins of diabetic origin reflected a decrease in the apolipoprotein CII/CIII ratio and other changes in the apolipoprotein profile. To assess whether diabetic rats were less able to clear triacylglycerol independent of changes in the nature of the lipoproteins, we monitored the clearance of chylomicron-like lipid emulsions in hepatectomized rats. In vivo, emulsion triacylglycerol hydrolysis was not slowed due to diabetes. However, control and diabetic rats, which had been fasted for 16 h, cleared triacylglycerol at about twice the rate of fed rats. Triacylglycerol secretion rates in diabetic and control rats were similar, whether fed or fasted. We conclude that in streptozocin diabetic rats, hypertriglyceridemia was not due to overproduction of chylomicron- or VLDL-triacylglycerol, nor to decreased endothelial lipase activities. Rather, in fed diabetic rats, the triacylglycerol-rich lipoproteins are poorer substrates for lipoprotein lipase. This may lead to slower formation of remnants which would exacerbate slow remnant removal. VLDL of diabetic origin were hydrolysed as efficiently as VLDL from control donors, suggesting that in the fed state the lipolytic defect may be specific for chylomicrons.

A low-protein diet exacerbates postprandial chylomicron concentration in moderately dyslipidaemic subjects in comparison to a lean red meat protein-enriched diet.

OBJECTIVE: To investigate whether altering energy intake as red meat protein or carbohydrate modifies chylomicron homeostasis and postprandial lipaemia. DESIGN: Randomized single-blind dietary intervention trial. SETTING: School of Public Health, Division of Health Science, Curtin University, Perth, Western Australia. SUBJECTS: A total of 20 moderately hypertriglyceridaemic but otherwise healthy subjects were recruited and completed the study. INTERVENTION: Participants consumed an isocaloric weight maintenance diet low in protein (14, 53 and 30% of energy as protein, carbohydrate and fat, respectively) or high in protein (25, 35 and 30% energy as protein, carbohydrate and fat) for a period of 6 weeks. Fasting plasma lipids and postprandial lipoprotein studies (triglyceride and apolipoprotein B48) following an oral fat challenge were carried out at the start and conclusion of the dietary intervention period. RESULTS: Consumption of the low- or high-protein diet had no significant effect on fasting plasma or postprandial lipaemia, the latter determined as the incremental area under the triglyceride curve following a fat challenge. However, subjects who consumed a low-protein diet for 6 weeks had a substantially exaggerated postprandial chylomicron response, indicated as the area under the apo B48 curve following a fat challenge. The change in postprandial chylomicron kinetics could not be explained by changes in insulin sensitivity, which appeared to be similar before and after intervention with either diet. CONCLUSIONS: Daily moderate consumption of a lean red meat protein-enriched diet attenuates postprandial chylomicronaemia in response to ingestion of a fatty meal.

The immunodetection of lipoprotein-bound amyloid-beta is attenuated because of the presence of lipids.

BACKGROUND: Amyloid-beta (Abeta) is found in circulation and cerebrospinal fluid (CSF), predominantly associated with lipoproteins. However, in a lipid environment it is possible that a masking of Abeta epitopes and/or an altered conformation of Abeta leads to an underestimation of Abeta concentrations. METHODS: We generated lipoprotein-like lipid emulsions containing a known amount of Abeta and compared immunoreactivity with an equimolar amount of Abeta solubilized in an aqueous medium. RESULTS: We found that Abeta exists primarily as a dimer and a monomer within an aqueous and lipid environment, respectively. We also showed that lipids bind tightly to Abeta, blocking detection of the monomeric form and substantially attenuating detection of the dimeric form of the protein. CONCLUSION: It is possible that studies that have quantified the concentration of Abeta in plasma and CSF may have significantly underestimated the pool of lipoprotein-bound Abeta.

Retention of chylomicron remnants by arterial tissue; importance of an efficient clearance mechanism from plasma.

Atherosclerosis is thought to begin with the trapping of cholesterol rich lipoproteins within the intima of arterial vessels. Thereafter a complex inflammatory cascade involving recruitment and transformation of leukocytes, accumulation of sterols in macrophages and cellular proliferation, can lead to a progressive occlusion in blood flow, or an unstable arterial lesion prone to prothrombotic events. Primary intervention strategies aimed at reducing atherogenesis are designed to achieve reductions in sterol rich lipoproteins, primarily low density lipoproteins, given the hypothesis that decreased exposure will attenuate the rate of arterial cholesterol accumulation. Epidemiological evidence has clearly identified a positive relationship between poor dietary (fat) habits and the onset and progression of atherosclerosis. However lipoproteins which mediate the transport of dietary lipid, that is chylomicrons, are not normally considered to be directly involved in atherogenesis, because of their larger size and inability to efficiently penetrate arterial tissue. In contrast, this article reviews recent evidence which suggests that once chylomicrons are hydrolysed to their remnant form, the triglyceride depleted chylomicron remnants penetrate arterial tissue and moreover, become preferentially trapped within the subendothelial space as concentrated focii. Ongoing studies demonstrate that significant chylomicron remnant accumulation can occur in a number of primary and secondary lipid disorders and in normolipidemic subjects with coronary artery disease. Chylomicron remnant dyslipidemia in conditions prone to premature atherosclerosis is consistent with the putative atherogenicity of these particles and can be explained by increased arterial exposure to cholesterol rich chylomicron remnants.