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.

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

Background: Amyloid-β (Aβ) is found in circulation and cerebrospinal fluid (CSF), predominantly associated with lipoproteins. However, in a lipid environment it is possible that a masking of Aβ epitopes and/or an altered conformation of Aβ leads to an underestimation of Aβ concentrations.

Methods: We generated lipoprotein-like lipid emulsions containing a known amount of Aβ and compared immunoreactivity with an equimolar amount of Aβ solubilized in an aqueous medium.

Results: We found that Aβ exists primarily as a dimer and a monomer within an aqueous and lipid environment, respectively. We also showed that lipids bind tightly to Aβ, 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 Aβ in plasma and CSF may have significantly underestimated the pool of lipoprotein-bound Aβ.

New insights into cardiovascular disease risk in subjects with visceral obesity

Obese insulin resistant individuals often present with a dyslipidemic phenotype characterised by hypertriglyceridemia, low HDL cholesterol levels, essentially normal total- and LDL-cholesterol, but a propensity for smaller, denser LDL particles. We have reported that concentrations of chylomicrons are two to three folds greater than in age-matched lean controls. We have recently observed that in lean free-living subjects the flux of chylomicrons over a 12h period was just 25% greater in these subjects than basal chylomicron production. Constitutive secretion of chylomicrons appears to be of greater relevance to arterial exposure than postprandial fluctuations. Insulin critically regulates the metabolism of very low density lipoprotein (VLDL) and hence it would be expected that the hormone is also involved in the regulation of chylomicron metabolism. Impaired insulin action may therefore be responsible for the associated hyperchylomicronaemia. In this review we examine the hypothesis that insulin chronically modulates chylomicron metabolism and present evidence suggesting that hyperchylomicronaemia primarily results from impaired chylomicron production.

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.

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.

Three-dimensional immunofluorescent double labelling using polyclonal antibodies derived from the same species: enterocytic colocalization of chylomicrons with Golgi apparatus

Double immunolabelling is a useful technique to determine cellular colocalization of proteins, but is prone to false-positive staining because of cross-reactivity between antibodies. In this study, we established a simple and quick method to demonstrate the immunofluorescent double labelling with two rabbit-derived polyclonal antibodies. The principle used was to establish a dilution of primary antibody for the first protein of interest, which would only be detectable following biotin-avidin amplification. Thereafter, the second protein of interest was assessed via standard secondary antibody detection, ensuring no cross-reactivity with the first protein antibody-antigen complex. We successfully demonstrated the three-dimensional colocalization of enterocytic apolipoprotein B, an equivocal marker of intestinal lipoproteins with Golgi apparatus. Colocalization of apo B and Golgi apparatus (75.2 +/- 8.5%) is consistent with the purported mode of secretion of these macromolecules.

Effect of an acute hyperinsulinaemic clamp on post-prandial lipaemia in subjects with insulin resistance

BACKGROUND

Obese, insulin-resistant individuals have raised levels of intestinal and hepatic lipoproteins. Insulin decreases the production of hepatic lipoproteins in vivo and so this study aimed to investigate whether an acute hyperinsulinaemic, euglycaemic clamp could correct fasting and post-prandial dyslipidaemia.

SUBJECTS AND METHODS

In a randomized, cross-over design, post-prandial lipaemia was compared in subjects infused either with insulin to achieve a steady-state concentration of 100 mU L(-1) or with saline. Nine obese (Body Mass Index > 26 kg m(-2); waist : hip > 1.0) insulin-resistant (Homeostatic Model Assessment score > 2.0) male subjects were given an oral fat load 3 h after the infusions began, and sampling continued for 6 h. Plasma apoB-48, triglyceride and nonesterified fatty acid (NEFA) were measured hourly.

RESULTS

Average steady-state serum insulin levels during the hyperinsulinaemic clamp were 123 +/- 4.4 mU L(-1). A paired analysis showed no net effect of insulin on post-prandial chylomicron metabolism when calculated as the (apoB-48) incremental area under the curve (IAUC). However, there was a trend towards a delay in the apoB-48 peak, consistent with possible changes in the rates of chylomicron biogenesis, lipolysis and/or clearance. Similarly, post-prandial lipaemia (depicted as triglyceride IAUC) was similar for subjects infused with insulin or saline, but the peak post-prandial response was delayed during insulin infusion. The NEFA were rapidly decreased by 83% after 3 h of insulin infusion.

CONCLUSIONS

In obesity and insulin resistance, short-term changes in plasma insulin do not appreciably exert a regulatory effect on exogenously-derived post-prandial lipoproteins. The data suggest that hyperchylomicronaemia in insulin-resistant subjects is a result of chronic aberrations in insulin-mediated regulation of post-prandial lipid metabolism.

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.

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 effect of metformin and rosiglitazone on postprandial lipid metabolism in obese insulin-resistant subjects

INTRODUCTION

Obese insulin-resistant individuals exhibit a dyslipidaemia due to raised levels of both hepatically and intestinally derived lipoproteins. However, little is known about the related dysregulation of intestinally derived lipoproteins. We examined whether the insulin-sensitizing agents, metformin and rosiglitazone, improve intestinal lipoprotein metabolism in obese insulin-resistant individuals.

METHODS

Thirty male obese (body mass index > 26; waist circumference > 100 cm) insulin-resistant [homeostasis model assessment (HOMA) score > 2.0] subjects were randomized to either a metformin (1 g bd), rosiglitazone (4 mg bd) or control treatment group for a period of 8 weeks. Fasting and postprandial lipid metabolism was studied before and after the intervention period.

RESULTS

Metformin and rosiglitazone both significantly improved insulin sensitivity, but this was not paralleled by improvement in dyslipidaemia. With rosiglitazone relative to control there was a significant (p < 0.05) increase in the area under the apolipoprotein (apo) B48 curve following the oral fat load and a decrease in the ratio of triglyceride to apo B48 levels postprandially following rosiglitazone treatment.

CONCLUSION

In obese insulin-resistant subjects metformin and rosiglitazone both improve insulin sensitivity, as measured by HOMA, without improvement in lipid metabolism. Rosiglitazone may have a detrimental effect on chylomicron metabolism by an increase in postprandial apo B48 levels, and this requires further investigation.

The acute effects of olive oil v. cream on postprandial thermogenesis and substrate oxidation in postmenopausal women

The influence of the source of dietary fat on postprandial thermogenesis and substrate oxidation rates, was examined in twelve postmenopausal women aged 57-73 years, with BMI 21.9-38.3 kg/m(2). A single blind, randomised, paired comparison of two high-fat, isoenergetic, mixed test meals was conducted. The major source of fat was either cream (CREAM) or extra virgin olive oil (EVOO). RMR, diet-induced thermogenesis (DIT) and substrate oxidation rates over 5 h were measured by indirect calorimetry. There were no differences in body weight, RMR, fasting carbohydrate or fat oxidation rates between the two occasions. DIT (EVOO 97 (SD 46) v. CREAM 76 (SD 69) kJ/5 h and EVOO 5.2 (SD 2.5) v. CREAM 4.1 (SD 3.7)% energy) did not differ between the two test meals. The postprandial increase in carbohydrate oxidation rates, relative to their respective fasting values (DeltaCOX), was significantly lower following the EVOO meal (EVOO 10.6 (SD 8.3) v. CREAM 17.5 (SD 10) g/5 h; paired t test, P=0.023), while postprandial fat oxidation rates (DeltaFOX) were significantly higher (EVOO 0.0 (SD 4.4) v. CREAM -3.6 (sd 4.0) g/5 h; P=0.028). In the eight obese subjects, however, DIT was significantly higher following the EVOO meal (EVOO 5.1 (SD 2.0) v. CREAM 2.5 (sd 2.9) %; P=0.01). This was accompanied by a significantly lower DeltaCOX (EVOO 10.9 (SD 9.9) v. CREAM 17.3 (SD 10.5) g/5 h; P=0.03) and significantly higher DeltaFOX (EVOO 0.11 (SD 4.4) v. CREAM -4.1 (SD 4.5) g/5 h, P=0.034). The present study showed that olive oil significantly promoted postprandial fat oxidation and stimulated DIT in abdominally obese postmenopausal women.

Chylomicron remnant metabolism studied with a new breath test in postmenopausal women with and without type 2 diabetes mellitus

OBJECTIVES

The kinetic basis for the effect of type 2 diabetes mellitus (DM) on postprandial lipoproteins has not been fully established. We investigated chylomicron remnant metabolism using a stable isotope breath test and fasting measurements of plasma apolipoprotein (apo) B-48 and apoC-III concentrations in postmenopausal women with and without type 2 DM.

PATIENTS

Twenty-four postmenopausal women without DM and 14 postmenopausal women with diet-controlled DM of similar age and body mass index (BMI) were studied in the postabsorptive state.

METHODS

The fractional catabolic rate (FCR) of an intravenously injected chylomicron remnant-like emulsion was determined from the appearance of 13CO2 in the breath using isotope-ratio mass spectrometry and multicompartmental modelling. apoB-48, a marker of particle number of intestinal lipoproteins, was determined immunoelectrophoretically. apoC-III was measured by immunoturbidimetric assay.

RESULTS

Compared with the nondiabetic women, the women with DM had significantly higher plasma apoB-48 concentration (16.40 +/- 1.18 mg/l vs. 13.0 +/- 0.9 mg/l; mean +/- standard error mean; P = 0.021), higher plasma apoC-III concentration (204.24 +/- 15.18 mg/l vs. 170.74 +/- 10.75 mg/l; P = 0.042) and lower FCR of the chylomicron remnant-like emulsion (0.06 +/- 0.05 pools/h vs. 0.12 +/- 0.02 pools/h; P < 0.001). In the diabetic patients, the FCR of the emulsion was correlated significantly with plasma apoB-48 levels (r = -0.641, P = 0.007) but not with apoC-III levels.

CONCLUSIONS

In postmenopausal women, diabetes mellitus appears to decrease the catabolism of chylomicron remnants and result in an accumulation of these particles in plasma. This may chiefly be due to decreased clearance by hepatic receptors related to an effect of insulin resistance. Impairment in the catabolism of chylomicron remnants may contribute to increased risk of atherosclerosis in postmenopausal women with type 2 diabetes mellitus.

Effect of Simvastatin on markers of triglyceride-rich lipoproteins in familial hypercholesterolaemia

BACKGROUND

We have previously shown elevated fasting plasma concentrations of intestinal remnants, as reflected by apolipoprotein (apo) B-48 and remnant-like particle-cholesterol (RLP-C) in patients with heterozygous familial hypercholesterolaemia (FH). We now investigate the effect of an HMG-CoA reductase inhibitor (simvastatin) on chylomicron remnant metabolism using the measurement of fasting apoB-48 and RLP-C in FH patients after long- and short-term simvastatin therapy and after a wash-out period. We also piloted the response of a breath test, involving the measurement of the fractional catabolic rate (FCR) of an intravenously injected chylomicron remnant-like emulsion labeled with cholesteryl (13)C-oleate.

METHODS

Fifteen FH patients were studied after > 6 months 40 mg day(-1) simvastatin treatment (long-term), a wash-out period (4 weeks), and 4 weeks of simvastatin treatment (short-term). Apolipoprotein B-48 was determined by SDS-PAGE and Western blotting/enhanced chemiluminescence and RLP-C by an immunoseparation assay. The FCR of the chylomicron remnant-like emulsion was determined from the appearance of (13)CO(2) in the breath and by multicompartmental mathematical modelling.

RESULTS

Both long- and short-term treatment with simvastatin were associated with decreases in the plasma concentration of apoB-48 (P < 0.05) and RLP-C (P < 0.001), but there was no significant change in the FCR of the emulsion.

CONCLUSIONS

We suggest that long- and short-term treatments with simvastatin have comparable effects in decreasing the plasma concentration of triglyceride-rich remnants in heterozygous FH, as measured by fasting apoB-48 and RLP-C. The mechanisms for this may involve decreased production of hepatic and possibly intestinal lipoproteins, and/or up-regulation of hepatic receptor clearance pathways, but these changes are apparently not associated with a change in remnant clearance as measured kinetically by the (13)CO(2) breath test.

Effect of dietary cholesterol oxidation products on the plasma clearance of chylomicrons in the rat

Oxidized cholesterols in the diet have been shown to exacerbate arterial cholesterol deposition and the development of atherosclerosis in animal models. Dietary oxidized cholesterols are absorbed through the intestine and incorporated into lymph chylomicrons. The aim of this study was to investigate the effect of oxidized cholesterols on the metabolism of nascent chylomicrons in vivo. It was shown that oxidized cholesterols markedly delay the clearance of chylomicrons from plasma compared to rats given TG alone. However, there was no difference in the clearance of chylomicrons containing oxidized cholesterols vs. purified cholesterol, although the presence of oxysterols did appear to exacerbate the removal of these particles from circulation. The impaired clearance of chylomicrons containing oxidized cholesterols was not due to impaired lipolysis and slower conversion to the remnant form. Moreover, the incorporation of oxidized cholesterols did not alter the hepatic or splenic uptake of chylomicrons compared to chylomicrons isolated from rats given purified cholesterol or TG alone. Collectively, the results of this study suggest that the exacerbated delay in clearance of chylomicron remnants enriched with oxysterols may be due to impaired uptake by tissues other than the liver and spleen. Apolipoprotein (apo) analysis showed that oxysterol incorporation reduced the apoE content and altered the apoC phenotype of chylomicrons, which may have an impact on the removal of chylomicron remnants from plasma. In conclusion, dietary oxysterols appear to have the potential to adversely affect chylomicron metabolism. Therefore, further investigations in humans are required to determine whether dietary oxidized cholesterols found in cholesterol-rich processed foods delay the clearance of postprandial remnants, which may contribute to and exacerbate the development of atherosclerosis.