Apolipoprotein B-48: comparison of fasting concentrations measured in normolipidaemic individuals using SDS-PAGE, immunoblotting and ELISA

Raised levels of chylomicrons and chylomicron remnants, which circulate following a meal, have been implicated in the development of atherosclerosis. Apolipoprotein (apo) B-48 is exclusively associated with chylomicron particles and provides a specific direct measurement of the number of intestinally derived lipoproteins in the circulation. The quantification of apo B-48 in biological samples is difficult due to the very low concentration in plasma, structural similarity to the N-terminal 48% of apo B-100 and lack of an appropriate standard for apo B-48. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), followed by coomassie blue staining, has been used for many years to measure apo B-48 levels in triacylglycerol (TAG)-rich lipoprotein samples. The raising of antiserum to apo B-48 has led to development of more sensitive and specific methods including immunoblotting and enzyme-linked immunosorbant assays (ELISAs). This has enabled direct measurement of apo B-48 in plasma without the need for separation into TAG-rich lipoproteins. A high degree of variability was observed in the apo B-48 concentrations reported in the literature both within and between the SDS-PAGE, immunoblotting and ELISA methods. (C) 2004 Elsevier Ireland Ltd. All rights reserved.

Plant- and marine-derived n-3 polyunsaturated fatty acids have differential effects on fasting and postprandial blood lipid concentrations and on the susceptibility of LDL to oxidative modification in moderately hyperlipidemic subjects

Background: Dietary a-linolenic acid (ALA) can be converted to long-chain n-3 polyunsaturated fatty acids (PUFAs) in humans and may reproduce some of the beneficial effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on cardiovascular disease risk factors. Objective: This study aimed to compare the effects of increased dietary intakes of ALA and EPA+DHA on a range of atherogenic risk factors. Design: This was a placebo-controlled, parallel study involving 150 moderately hyperlipidemic subjects randomly assigned to 1 of 5 interventions: 0.8 or 1.7 g EPA+DHA/d, 4.5 or 9.5 g ALA/d, or an n-6 PUFA control for 6 mo. Fatty acids were incorporated into 25 g of fat spread and 3 capsules to be consumed daily. Results: The change in fasting or postprandial lipid, glucose, or insulin concentrations or in blood pressure was not significantly different after any of the n-3 PUFA interventions compared with the n-6 PUFA control. The mean (+/-SEM) change in fasting triacylglycerols after the 1.7-g/d EPA+DHA intervention (-7.7 +/- 4.99%) was significantly (P < 0.05) different from the change after the 9.5-g/d ALA intervention (10.9 +/- 4.5%). The ex vivo susceptibility of LDL to oxidation was higher after the 1.7-g/d EPA+DHA intervention than after the control and ALA interventions (P < 0.05). There was no significant change in plasma a-tocopherol concentrations or in whole plasma antioxidant status in any of the groups. Conclusion: At estimated biologically equivalent intakes, dietary ALA and EPA+DHA have different physiologic effects.

Impact of menstrual cycle phase on insulin sensitivity measures and fasting lipids

There is evidence to suggest that insulin sensitivity may vary in response to changes in sex hormone levels. However, the results Of human studies designed to investigate changes in insulin sensitivity through the menstrual cycle have proved inconclusive. The aims of this Study were to 1) evaluate the impact of menstrual cycle phase on insulin sensitivity measures and 2) determine the variability Of insulin sensitivity measures within the same menstrual cycle phase. A controlled observational study of 13 healthy premenopausal women, not taking any hormone preparation and having regular menstrual cycles, was conducted. Insulin sensitivity (Si) and glucose effectiveness (Sg) were measured using an intravenous glucose tolerance test (IVGTT) with minimal model analysis. Additional Surrogate measures Of insulin sensitivity were calculated (homoeostasis model for insulin resistance [HOMA IR], quantitative insulin-to-glucose check index [QUICKI] and revised QUICKI [rQUICKI]), as well as plasma lipids. Each woman was tested in the luteal and follicular phases of her Menstrual cycle, and duplicate measures were taken in one phase of the cycle. No significant differences in insulin sensitivity (measured by the IVGTT or Surrogate markers) or plasma lipids were reported between the two phases of the menstrual cycle or between duplicate measures within the same phase. It was Concluded that variability in measures of insulin sensitivity were similar within and between menstrual phases.

Interactions between age and apoE genotype on fasting and postprandial triglycerides levels

Objective The influences of genetic determinants on the magnitude of postprandial lipaemia are presently unclear. Here the impact of the common apolipoprotein (apo)E epsilon mutation on the postprandial triglyceride (TG) response is determined, along with an assessment of genotype penetrance according to age, body mass index and gender. Methods and results Healthy adults (n = 251) underwent a postprandial investigation, in which blood samples were taken at regular intervals after a test breakfast (0 min, 49 g fat) and lunch (330 min, 29 g fat) until 480 min after the test breakfast. There was a significant impact of apoE genotype on fasting total cholesterol (TC), (P = 0.027), LDL-cholesterol (LDL-C), (P = 0.008), and %LDL3 (P = 0.001), with higher and lower levels in the E4 and E2 carriers respectively relative to the E3/E3 genotype. Reflective of a higher fasting TG (P = 0.001), a significantly higher area under the curve for the postprandial TG response (TG AUC) was evident in the E4 carriers relative to the E3/E3 group (P = 0.038). In the group as a whole, a significant age × genotype interaction was observed for fasting TC (P = 0.021). In the participants >50 years there was a significant impact of genotype on TC (P = 0.005), LDL-C (P = 0.001) and TAG AUC (P = 0.028). Conclusions It is possible that an exaggerated postprandial lipaemia contributes to the increased coronary heart disease risk associated with carriers of the E4 allele; an effect which is more evident in older adults.

The effect of the daily intake of inulin on fasting lipid, insulin and glucose concentrations in middle-aged men and women

The present study was carried out to examine the effect of the daily intake of 10 g inulin on fasting blood lipid, glucose and insulin levels in healthy middle-aged men and women with moderately raised total plasma cholesterol (TC) and triacylglycerol (TAG) levels. This study was a doubleblind randomized placebo-controlled parallel study in which fifty-four middle-aged subjects received either inulin or placebo for a period of 8 weeks. Fasting blood samples were collected before the supplementation period (baseline samples 1 and 2, separated by 1 week) and at weeks 4 and 8, with a follow-up at week 12. Compared with baseline values, insulin concentrations were significantly lower at 4 weeks (P,0×01) in the inulin group. There was a trend for TAG values, compared with baseline, to be lower in the inulin group at 8 weeks (P,0×08) returning to baseline concentrations at week 12. On comparison of the inulin and placebo groups, the fasting TAG responses over the 8-week test period were shown to be significantly different (P,0×05, repeated measures ANOVA), which was largely due to lower plasma TAG levels in the inulin group at week 8. The percentage change in TAG levels in the inulin group during the 8-week study was shown to correlate with the initial TAG level of the subjects (rs -0×499, P = 0×004). We therefore conclude that the daily addition of 10 g inulin to the diet significantly reduced fasting insulin concentrations during the 8-week test period and resulted in lower plasma TAG levels, particularly in subjects in whom fasting TAG levels were greater than 1×5 mmol/l. These data support findings from animal studies that fructans influence the formation and/or degradation of TAG-rich lipoprotein particles, and the insulin data are also consistent with recent studies showing attenuation of insulin levels in fructan-treated rats.

Greater impairment of postprandial triacylglycerol than glucose response in metabolic syndrome subjects with fasting hyperglycaemia

Abstract Objective: Studies have started to question whether a specific component or combinations of metabolic syndrome (MetS) components may be more important in relation to cardiovascular disease risk. Our aim was to examine the impact of the presence of raised fasting glucose as a MetS component on postprandial lipaemia. Methods: Men classified with the MetS underwent a sequential test meal investigation, in which blood samples were taken at regular intervals after a test breakfast (t=0 min) and lunch (t=330 min). Lipids, glucose and insulin were measured in the fasting and postprandial samples. Results: MetS subjects with 3 or 4 components were subdivided into those without (n=34) and with (n=23) fasting hyperglycaemia (≥ 5.6 mmol/l), irrespective of the combination of components. Fasting lipids and insulin were similar in the two groups, with glucose significantly higher in the men with glucose as a MetS component (P<0.001). Following the test meals, there was a higher maximum concentration (maxC), area under the curve (AUC) and incremental AUC (P≤0.016) for the postprandial triacylglycerol (TAG) response in men with fasting hyperglycaemia. Greater glucose AUC (P<0.001) and insulin maxC (P=0.010) was also observed in these individuals after the test meals. Multivariate regression analysis revealed fasting glucose to be an important predictor of the postprandial TAG and glucose response. Conclusion: Our data analysis has revealed a greater impairment of postprandial TAG than glucose response in MetS subjects with raised fasting glucose. The worsening of postprandial lipaemic control may contribute to the greater CVD risk reported in individuals with MetS component combinations which include hyperglycaemia.

Preoperative predictors for postoperative problems in heart transplantation: psychiatric and psychosocial considerations

The psychiatric and psychosocial evaluation of the heart transplant candidate can identify particular predictors for postoperative problems. These factors, as identified during the comprehensive evaluation phase, provide an assessment of the candidate in context of the proposed transplantation protocol. Previous issues with compliance, substance abuse, and psychosis are clear indictors of postoperative problems. The prolonged waiting list time provides an additional period to evaluate and provide support to patients having a terminal disease who need a heart transplant, and are undergoing prolonged hospitalization. Following transplantation, the patient is faced with additional challenges of a new self-image, multiple concerns, anxiety, and depression. Ultimately, the success of the heart transplantation remains dependent upon the recipient's ability to cope psychologically and comply with the medication regimen. The limited resource of donor hearts and the high emotional and financial cost of heart transplantation lead to an exhaustive effort to select those patients who will benefit from the improved physical health the heart transplant confers.

The Ventral Premammillary Nucleus Links Fasting-Induced Changes in Leptin Levels and Coordinated Luteinizing Hormone Secretion

Physiological conditions of low leptin levels like those observed during negative energy balance are usually characterized by the suppression of luteinizing hormone (LH) secretion and fertility. Leptin administration restores LH levels and reproductive function. Leptin action on LH secretion is thought to be mediated by the brain. However, the neuronal population that mediates this effect is still undefined. The hypothalamic ventral premammillary nucleus (PMV) neurons express a dense concentration of leptin receptors and project to brain areas related to reproductive control. Therefore, we hypothesized that the PMV is well located to mediate leptin action on LH secretion. To test our hypothesis, we performed bilateral excitotoxic lesions of the PMV in adult female rats. PMV-lesioned animals displayed a clear disruption of the estrous cycle, remaining in anestrus for 15-20 d. After apparent recovery of cyclicity, animals perfused in the afternoon of proestrus showed decreased Fos immunoreactivity in the anteroventral periventricular nucleus and in gonadotropin releasing hormone neurons. PMV-lesioned animals also displayed decreased estrogen and LH secretion on proestrus. Lesions caused no changes in mean food intake and body weight up to 7 weeks after surgery. We further tested the ability of leptin to induce LH secretion in PMV-lesioned fasted animals. We found that complete lesions of the PMV precluded leptin stimulation of LH secretion on fasting. Our findings demonstrate that the PMV is a key site linking changing levels of leptin and coordinated control of reproduction.

beta-ADRENERGIC ACTIVITY PRESERVES GLUT4 PROTEIN IN GLYCOLYTIC FIBERS IN FASTING

Glucose transporter 4 (GLUT4) expression in adipose tissue decreases during fasting. In skeletal muscle, we hypothesized that GLUT4 expression might be maintained in a beta-adrenergic-dependent way to ensure energy disposal for contractile function. Herein we investigate beta-blockade or beta-stimulation effects on GLUT4 expression in oxidative (soleus) and glycolytic [extensor digitorum longus (EDL)] muscles of fasted rats. Fasting increased GLUT4 mRNA in soleus (24%) and EDL (40%) but the protein content increased only in soleus (30%). beta 1-beta 2-, and beta 1-beta 2-beta 3-blockade decreased (20-30%) GLUT4 mRNA content in both muscles, although GLUT4 protein decreased only in EDL. When mRNA and GLUT4 protein regulations were discrepant, changes in the mRNA poly(A) tail length were detected, indicating a posttranscriptional modulation of gene expression. These results show that beta-adrenergic activity regulates GLUT4 gene expression in skeletal muscle during fasting, highlighting its participation in preservation of GLUT4 protein in glycolytic muscle. Muscle Nerve 40: 847-854, 2009

Opposite effects of fasting on TGF-beta 3 and T beta RI distribution in the gastric mucosa of suckling and early weanling rats

Objective: Our aim was to evaluate the effects of a dietary regimen (suckling or early weaning) and feeding status (fed or fasted) on the distribution of transforming growth factor-beta 3 (TGF-beta 3) and TGF receptor-I (T beta RI) in the gastric epithelium of pups Methods: Wistar rats were used At 15 d, half of the pups were separated from dams and fed with hydrated powered chow On day 17, suckling and early weanling rats were subjected to fasting (17 h). Four different conditions were established. suckling fed and fasted and early weanling fed and fasted At 18 d stomachs were collected under anesthesia and were fixed in 4% formaldehyde for immunohistochemistry The number of immunostained epithelial cells per microscopic field was determined for TGF-beta 3 and T beta RI in longitudinal sections from the gastric mucosa Results: We found that during suckling, fasting reduced the number of immunolabeled cells per field of both molecules when compared with the fed group (P < 0.05), whereas in early weaning, food restriction increased TGF-beta 3 and T beta RI distributions (P < 0.05) We also observed that TGF-beta 3 and T beta RI were more concentrated in parietal cells in the upper gland in suckling pups, whereas after early weaning these were displaced to parietal and chief cells at the bottom of the gland Conclusion: Suckling and early weaning directly influence TGF-beta 3 and T beta RI distributions in the gastric epithelium in response to fasting, such that early weaning anticipates the effects observed in adult rats. Furthermore, the differential concentrations of TGF-beta 3 and T beta RI indicate that they might be important for cell proliferation events in growth control (C) 2010 Elsevier Inc. All rights reserved

Fasting differentially regulates plasma corticosterone-binding globulin, glucocorticoid receptor, and cell cycle in the gastric mucosa of pups and adult rats

Ogias D, de Andrade Sa ER, Kasai A, Moisan M, Alvares EP, Gama P. Fasting differentially regulates plasma corticosterone-binding globulin, glucocorticoid receptor, and cell cycle in the gastric mucosa of pups and adult rats. Am J Physiol Gastrointest Liver Physiol 298: G117-G125, 2010. First published October 15, 2009; doi:10.1152/ajpgi.00245.2009.-The nutritional status influences gastric growth, and interestingly, whereas cell proliferation is stimulated by fasting in suckling rats, it is inhibited in adult animals. Corticosterone takes part in the mechanisms that govern development, and its effects are regulated in particular by corticosterone-binding globulin (CBG) and glucocorticoid receptor (GR). To investigate whether corticosterone activity responds to fasting and how possible changes might control gastric epithelial cell cycle, we evaluated different parameters during the progression of fasting in 18- and 40-day-old rats. Food restriction induced higher corticosterone plasma concentration at both ages, but only in pups did CBG binding increase after short-and long-term treatments. Fasting also increased gastric GR at transcriptional and protein levels, but the effect was more pronounced in 40-day-old animals. Moreover, in pups, GR was observed in the cytoplasm, whereas, in adults, it accumulated in the nucleus after the onset of fasting. Heat shock protein (HSP) 70 and HSP 90 were differentially regulated and might contribute to the stability of GR and to the high cytoplasmic levels in pups and elevated shuttling in adult rats. As for gastric epithelial cell cycle, whereas cyclin D1 and p21 increased during fasting in pups, in adults, cyclin E slowly decreased, concomitant with higher p27. In summary, we demonstrated that corticosterone function is differentially regulated by fasting in 18-and 40-day-old rats, and such variation might attenuate any possible suppressive effects during postnatal development. We suggest that this mechanism could ultimately increase cell proliferation and allow regular gastric growth during adverse nutritional conditions.

Fasting activates the gene expression of UCP3 independent of genes necessary for lipid transport and oxidation in skeletal muscle

Fasting triggers a complex array of adaptive metabolic and hormonal responses including an augmentation in the capacity for mitochondrial fatty acid (FA) oxidation in skeletal muscle. This study hypothesized that this adaptive response is mediated by increased mRNA of key genes central to the regulation of fat oxidation in human skeletal muscle. Fasting dramatically increased UCP3 gene expression, by 5-fold at 15 h and 10-fold at 40 h. However the expression of key genes responsible for the uptake, transport, oxidation, and re-esterification of FA remained unchanged following 15 and 40 h of fasting. Likewise there was no change in the mRNA abundance of transcription factors. This suggests a unique role for UCP3 in the regulation of FA homeostasis during fasting as adaptation to 40 h of fasting does not require alterations in the expression of other genes necessary for lipid metabolism.

Association of television viewing with fasting and 2-h postchallenge plasma glucose levels in adults without diagnosed diabetes

OBJECTIVE—We examined the associations of television viewing time with fasting plasma glucose (FPG) and 2-h postchallenge plasma glucose (2-h PG) levels in Australian adults.

RESEARCH DESIGN AND METHODS—A total of 8,357 adults aged >35 years who were free from diagnosed diabetes and who attended a population-based cross-sectional study (Australian Diabetes, Obesity and Lifestyle Study [AusDiab]) were evaluated. Measures of FPG and 2-h PG were obtained from an oral glucose tolerance test. Self-reported television viewing time (in the previous week) was assessed using an interviewer-administered questionnaire. Homeostasis model assessment (HOMA) of insulin sensitivity (HOMA-%S) and ß-cell function (HOMA-%B) were calculated based on fasting glucose and insulin concentrations.

RESULTS—After adjustment for confounders and physical activity time, time spent watching television in women was positively associated with 2-h PG, log fasting insulin, and log HOMA-%B and inversely associated with log HOMA-%S (P < 0.05) but not with FPG. No significant associations were observed with glycemic measures in men. The ß-coefficients across categories of average hours spent watching television per day (<1.0, 1.0–1.9, 2.0–2.9, 3.0–3.9, and ≥4.0) for 2-h PG in women were 0 (reference), 0.009, 0.047, 0.473, and 0.501, respectively (P for trend = 0.02).

CONCLUSIONS—Our findings highlight the unique deleterious relationship of sedentary behavior (indicated by television viewing time) and glycemic measures independent of physical activity time and adiposity status. These relationships differed according to sex and type of glucose measurement, with the 2-h PG measure being more strongly associated with television viewing. The findings suggest an important role for reducing sedentary behavior in the prevention of type 2 diabetes and cardiovascular disease, especially in women.