Tom B. Mulvey

Postprandial response of adiponectin, interleukin-6, tumor necrosis factor-α, and C-reactive protein to a high-fat dietary load

OBJECTIVE Circulating levels of adiponectin are low in obesity and metabolic disorders associated with increasing fat mass including insulin resistance and dyslipidemia. Body fat stores may be positively related to intake of dietary fat, but little is known of mechanisms by which serum adiponectin may be regulated through diet. We investigated acute effects of a high-fat load and changes in fatty acid saturation on circulating adiponectin and associated mediators of inflammation including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and C-reactive protein (CRP). METHODS A high-fat test meal (59 +/- 4 g fat; 71% of energy as fat) containing a high ( approximately 71:29) or low ( approximately 55:45) ratio of saturated:unsaturated fatty acids was given at breakfast on two occasions. Blood samples were collected at 0 (baseline), 1, 3, and 6 h for measurement of adiponectin, IL-6, TNF-alpha, and high-sensitivity CRP. A fat-exclusion lunch, snack, and dinner were also given and blood samples collected at 10 and 24 h. RESULTS Eighteen healthy, lean men completed the trial. There was no evidence of acute change in circulating adiponectin in response to the lipid bolus or a differential effect of fatty acid saturation on adiponectin, high-sensitivity CRP, or IL-6 (P > 0.05). IL-6 increased over 6 h on both treatments (time, P < 0.05). TNF-alpha decreased on the high saturated:unsaturated fatty acid treatment (treatment by time, P < 0.05). There were no significant correlations between circulating adiponectin and insulin on either dietary treatment in these normoglycemic subjects. CONCLUSION Acute changes in the content of saturated and unsaturated fatty acids had no adverse effect on postprandial circulation of the adipose-related factors adiponectin, IL-6, TNF-alpha, or high-sensitivity CRP.

Trifluoroacetate, a contaminant in purified proteins, inhibits proliferation of osteoblasts and chondrocytes

Peptides purified by HPLC are often in the form of a trifluoroacetate (TFA) salt, because trifluoroacetic acid is used as a solvent in reversed-phase HPLC separation. However, the potential effects of this contaminant in culture systems have not been addressed previously. TFA (10-8 to 10-7 M) reduced cell numbers and thymidine incorporation into fetal rat osteoblast cultures after 24 h. Similar effects were found in cultures of articular chondrocytes and neonatal mouse calvariae, indicating that the effect is not specific to one cell type or to one species of origin. When the activities of the TFA and hydrochloride salts of amylin, amylin-(1-8), and calcitonin were compared in osteoblasts, cell proliferation was consistently less with the TFA salts of these peptides, resulting in failure to detect a proliferative effect or wrongly attributing an antiproliferative effect. This finding is likely to be relevant to all studies of purified peptides in concentrations above 10-9 M in whatever cell or tissue type. Such peptides should be converted to a hydrochloride or biologically equivalent salt before assessment of their biological effects is undertaken.Peptides purified by HPLC are often in the form of a trifluoroacetate (TFA) salt, because trifluoroacetic acid is used as a solvent in reversed-phase HPLC separation. However, the potential effects of this contaminant in culture systems have not been addressed previously. TFA (10(-8) to 10(-7) M) reduced cell numbers and thymidine incorporation into fetal rat osteoblast cultures after 24 h. Similar effects were found in cultures of articular chondrocytes and neonatal mouse calvariae, indicating that the effect is not specific to one cell type or to one species of origin. When the activities of the TFA and hydrochloride salts of amylin, amylin-(1-8), and calcitonin were compared in osteoblasts, cell proliferation was consistently less with the TFA salts of these peptides, resulting in failure to detect a proliferative effect or wrongly attributing an antiproliferative effect. This finding is likely to be relevant to all studies of purified peptides in concentrations above 10(-9) M in whatever cell or tissue type. Such peptides should be converted to a hydrochloride or biologically equivalent salt before assessment of their biological effects is undertaken.

Lipid-lowering effects of a modified butter-fat: a controlled intervention trial in healthy men

Objective: To investigate the lipid-lowering potential of a butter-fat modified through manipulations in bovine feeding to increase the unsaturated:saturated fatty acid ratio.Design: Double-blind, randomised, cross-over intervention trial.Setting: University of Auckland Human Nutrition Unit, New Zealand.Subjects: Twenty healthy, male subjects.Intervention: A residential trial in which all foods and beverages were provided during two intervention periods, comprising 3 weeks of high unsaturated ‘modified’ vs 3 weeks of saturated ‘control’ butter feeding separated by a 4 week washout. Diets were of typical composition of 39 percentage energy (en%) fat (20 en% butter-fat), 48 en% CHO, 13 en% protein.Results: There was a significant decrease in both total (P<0.05, −7.9%) and LDL-cholesterol (P<0.01, −9.5%) during modified butter feeding. There was no significant effect of treatment on a range of other risk factors including HDL-cholesterol, triglyceride, apolipoprotein A or B, nonesterified fatty acids (NEFA), haemostatic clotting factor VII and fibrinogen or glucose (P>0.05). Subjects were maintained in energy balance and there was no significant change in body weight during intervention. Butter-fat composition alone differed between treatments.Conclusions: A significant improvement in cardiovascular risk can be achieved by moderate changes in dietary fatty acid profile, achieved through a common and well accepted food source, butter-fat.Sponsorship: New Zealand Dairy Board, Wellington; Auckland Uniservices Ltd, Auckland; Maurice & Phyllis Paykel Trust, Auckland, New Zealand.

Dissociation of the effects of amylin on osteoblast proliferation and bone resorption

This study assesses the structure-activity relationships of the actions of amylin on bone. In fetal rat osteoblasts, only intact amylin and amylin-(1-8) stimulated cell proliferation (half-maximal concentrations 2.0 x 10(-11) and 2.4 x 10(-10) M, respectively). Amylin-(8-37), COOH terminally deamidated amylin, reduced amylin, and reduced amylin-(1-8) (reduction results in cleavage of the disulfide bond) were without agonist effect but acted as antagonists to the effects of both amylin and amylin-(1-8). Calcitonin gene-related peptide-(8-37) also antagonized the effects of amylin and amylin-(1-8) on osteoblasts but was substantially less potent in this regard than amylin-(8-37). In contrast, inhibition of bone resorption in neonatal mouse calvariae only occurred with the intact amylin molecule and was not antagonized by any of these peptides. The rate of catabolism of the peptides in calvarial cultures was not accelerated in comparison with that of intact amylin. This dissociation of the actions of amylin suggests that it acts through two separate receptors, one on the osteoclast (possibly the calcitonin receptor) and a second on the osteoblast.This study assesses the structure-activity relationships of the actions of amylin on bone. In fetal rat osteoblasts, only intact amylin and amylin-(1-8) stimulated cell proliferation (half-maximal concentrations 2.0 × 10-11 and 2.4 × 10-10 M, respectively). Amylin-(8-37), COOH terminally deamidated amylin, reduced amylin, and reduced amylin-(1-8) (reduction results in cleavage of the disulfide bond) were without agonist effect but acted as antagonists to the effects of both amylin and amylin-(1-8). Calcitonin gene-related peptide-(8-37) also antagonized the effects of amylin and amylin-(1-8) on osteoblasts but was substantially less potent in this regard than amylin-(8-37). In contrast, inhibition of bone resorption in neonatal mouse calvariae only occurred with the intact amylin molecule and was not antagonized by any of these peptides. The rate of catabolism of the peptides in calvarial cultures was not accelerated in comparison with that of intact amylin. This dissociation of the actions of amylin suggests that it acts through two separate receptors, one on the osteoclast (possibly the calcitonin receptor) and a second on the osteoblast.

Effect of high-fat meals and fatty acid saturation on postprandial levels of the hormones ghrelin and leptin in healthy men

Objective:Ghrelin and leptin play a role in control of food intake and adiposity but mechanisms regulating these hormones in man are poorly defined and evidence that dietary fats may have adverse effects is inconclusive. We investigated whether high-fat meals, which differed in saturated fatty acid (SFA) content acutely modified these hormones.Design:Randomised, double-blind, crossover trial. A high-fat (HF) test meal (59±4 g fat; 71% of energy as fat) was given for breakfast on two occasions. Meals comprised either high (∼70:30) or low (∼55:45) saturated:unsaturated fatty acid (SFA:USFA) ratio. Fasting and postprandial measurements of serum total ghrelin (RIA), leptin (enzyme-linked immunosorbent assay (ELISA)) and insulin (RIA) were made over 6 h. Postprandial measurements were also made at 10 and 24 h following a fat-exclusion lunch, snack and dinner.Subjects:A total of 18 lean, healthy men.Results:There was no significant effect of the fatty meal (time, P>0.05), nor a differential effect of SFA:USFA ratio (treatment*time, P>0.05) on ghrelin over 6 h. Leptin decreased in response to both HF treatments (time, P<0.001) but increased SFA content did not further inhibit hormone secretion (treatment*time, P>0.05). There was no significant correlation between ghrelin or leptin and circulating insulin (P>0.05).Conclusion:We conclude that HF diets may adversely effect serum leptin, although the circadian decrease may account in part for this response. Increasing dietary SFAs had no deleterious effects on leptin or total ghrelin.

No evidence of an effect of alterations in dietary fatty acids on fasting adiponectin over 3 weeks.

Objective: Little is known about the effects of alterations in fatty acid classes on adiponectin, a hormone secreted by the adipocyte known to be important in the development of diabetes and cardiovascular disease (CVD). Any factor, including diet, that may positively influence adiponectin gene expression or increase circulating levels might be useful for improving such metabolic abnormalities. We investigated the effects of alterations in dietary fatty acid saturation on fasting serum adiponectin and associated peptides.

Effect of moderate changes in dietary fatty acid profile on postprandial lipaemia, haemostatic and related CVD risk factors in healthy men

Objective: To investigate the effect of moderate changes in dietary fatty acid profile on postprandial risk factors for cardiovascular disease (CVD).Design: Double-blind, randomised, crossover, intervention trial.Setting: University of Auckland Human Nutrition Unit, New Zealand.Subjects: A total of 18 lean healthy men.Interventions: A dairy butter fat modified to reduce the saturated:unsaturated fatty acid ratio and a conventional high saturated butter fat were given on two separate occasions as a high-fat test meal (59±4 g fat; 71 en% fat) at breakfast. A fat exclusion lunch, dinner and snacks were also given. Blood samples were collected at 0 (baseline), 1, 3, 6, 10 and 24 h.Results: Maximum peak in total triacylglycerol (TAG) occurred 3 h postprandially and was highest on modified treatment (diet, P<0.05) due predominantly to increased TAG within the chylomicron-rich fraction. Transient peaks in total-, LDL- and HDL-cholesterol occurred postprandially, but did not differ between dietary treatments (P>0.05). There were no differential effects of diet on postprandial free fatty acids, apo A, apo B, glucose, insulin, amylin or haemostatic clotting factors (P>0.05).Conclusions: In a group of healthy young men, replacement of 16% of total saturated fatty acids by mono- and polyunsaturated fats within a dairy lipid did not induce postprandial changes in CVD risk that may be considered beneficial for health.Sponsorship: Fonterra, Wellington; New Zealand.