Differential Effects of Oral and Intravenous Lipid Administration on Key Molecules Related to Energy Homeostasis

CONTEXT

The spectrum of lipid-induced changes in the secretion of hormones important in energy homeostasis has not yet been fully elucidated.

OBJECTIVE

To identify potential incretin-like effects in response to lipid administration, we examined the short-term effect of iv vs oral lipids on key molecules regulating energy homeostasis. Design, Intervention, and Participants: After a 10-hour overnight fast, 26 subjects were randomized to receive an oral lipid load, a 10% iv lipid emulsion, a 20% iv lipid emulsion, or an iv saline infusion. We obtained blood samples at 30-minute intervals for the first 2 hours and hourly thereafter for a total of 6 hours.

MAIN OUTCOME MEASURES

Circulating levels of insulin, glucose, c-peptide, free fatty acids, incretins (glucagon-like peptide-1, gastric inhibitory polypeptide), glucagon, peptide YY, ghrelin, fibroblast growth factor 21, fetuin A, irisin, omentin, and adiponectin were measured.

RESULTS

Oral lipid ingestion resulted in higher glucagon-like peptide-1, gastric inhibitory polypeptide, glucagon, and peptide YY levels, compared with the other three groups (incremental area under the curve P = .003, P < .001, P < .001, P < .001, respectively). The 20% lipid emulsion, leading to higher free fatty acid levels, resulted in greater insulin, c-peptide, and fibroblast growth factor 21 responses compared with placebo and the other two groups (incremental area under the curve P = .002, P = .005, P < .001, P < .001, respectively). Omentin, adiponectin, fetuin A, and irisin levels were not affected by either mode of lipid administration.

CONCLUSIONS

Metabolic responses to lipids depend on the route of administration. Only iv lipids trigger a dose-dependent fibroblast growth factor 21 secretion, which is nonglucagon mediated. Intravenous lipids also induce hyperinsulinemia without concurrent decreases in glucose, a phenomenon observed in insulin-resistant states. Orally administered lipids mostly affect gastrointestinal tract-secreted molecules important in glucose and energy homeostasis such as glucagon, incretins, and peptide YY.

Irisin mRNA and circulating levels in relation to other myokines in healthy and morbidly obese humans

OBJECTIVE

Skeletal muscle is considered to be an endocrine organ that secretes a number of myokines including follistatin (FST), myostatin (MSTN), activin A, and the newly identified irisin. Irisin's biology and function exhibit similarities with the functions of the FST-MSTN-activin A axis. It remains unknown whether there is any interplay among these molecules. The aim of this study is to examine potential associations of irisin with the FST, MSTN, and activin A axis.

METHODS

Two observational studies were performed to evaluate the associations of irisin with the other three peptides. Study A included 150 healthy males aged 18.48±0.16 years with BMI 23.18±3.75 kg/m(2). Fasting serum samples were used to measure the levels of the molecules of interest. Study B included 14 morbidly obese individuals, candidates for bariatric surgery, aged 53.14±8.93 years with BMI 50.18±10.63 kg/m(2). Blood samples were obtained after an overnight fast. Eight out of the 14 participants consented to an optional thigh biopsy during their bariatric surgery. Using the above blood and tissue samples, we measured circulating levels and muscle mRNA of irisin, FST, MSTN, and activin A.

RESULTS

We report that FNDC5 mRNA in muscle is positively correlated with FST mRNA expression in morbidly obese subjects (ρ=0.93, P<0.001). We also found that circulating irisin is positively correlated with FST circulating levels among lean subjects (ρ=0.17, P=0.05) while this association was suggestive among the obese (ρ=0.56, P=0.07).

CONCLUSION

The newly identified myokine irisin may be positively associated with FST at both the mRNA and circulating protein level.

Metformin and sulfonylureas in relation to cancer risk in type II diabetes patients: a meta-analysis using primary data of published studies

INTRODUCTION

Accumulating evidence suggests that patients with type 2 diabetes mellitus (T2DM) and hyperinsulinemia are at increased risk for developing malignancies. It remains to be fully elucidated whether use of metformin, an insulin sensitizer, and/or sulfonylureas, insulin secretagogues, affect cancer incidence in subjects with T2DM.

MATERIAL & METHODS

We performed a meta-analysis using PubMed, of randomized control trials (RCTs), cohorts, and case-control studies published through July 2012 that assess effects of metformin and/or sulfonylurea sulfonylureas on cancer risk at any site, in subjects with T2DM. Fixed and random effects meta-analysis models were used, and the effect size was summarized as relative risk (RR) for RCTs/cohorts and as odds ratio (OR) for the case-control studies.

RESULTS

Analysis of 24 metformin studies in subjects with T2DM showed that metformin use is associated with reduced risk for the development of cancer, in both cohort (RR=0.70 [95% CI=0.67-0.73]) and case-control studies (OR=0.90 [95% CI=0.84-0.98]), but this finding was not supported by RCTs (RR=1.01[95% CI=0.81-1.26]). Data from 18 sulfonylurea studies in subjects with T2DM showed that sulfonylurea use is associated with an increase in all-cancer risk, in cohort studies (RR=1.55 [95% CI=1.48 -1.63]), though data from RCTs (RR=1.17 [95% CI=0.95-1.45]) and case-control studies (OR=1.02 [95% CI=0.93-1.13]) failed to demonstrate a statistically significant effect.

CONCLUSIONS

This analysis using pooled primary data demonstrates that metformin use reduces, while sulfonylurea use may be associated with an increased cancer risk in subjects with T2DM. These findings need to be confirmed in large-scale RCTs before they are translated into clinical practice.

FNDC5 and irisin in humans: I. Predictors of circulating concentrations in serum and plasma and II. mRNA expression and circulating concentrations in response to weight loss and exercise

OBJECTIVE

In mouse, PGC1-α overexpression in muscle stimulates an increase in expression of FNDC5, a membrane protein that is cleaved and secreted as a newly identified hormone, irisin. One prior study has shown that FNDC5 induces browning of subcutaneous fat in mice and mediates beneficial effects of exercise on metabolism, but a more recent study using gene expression arrays failed to detect a robust increase in FNDC5 mRNA in human muscles from exercising subjects. No prior study has reported on the physiological regulation and role of circulating irisin and FNDC5 in humans.

MATERIALS/METHODS

A. FNDC5 gene expression studies: We first examined tissue distribution of FNDC5 in humans. B. Cross-sectional studies: Predictors of FNDC5 mRNA expression levels were examined in muscle tissues from 18 healthy subjects with a wide range of BMI. Assays were optimized to measure circulating FNDC5 and irisin levels, and their associations with anthropometric and metabolic parameters were analyzed in two cross-sectional studies that examined 117 middle-aged healthy women and 14 obese subjects, respectively. C. Interventional studies: The effect of weight loss on FNDC5 mRNA and/or circulating irisin levels was examined in 14 obese subjects before and after bariatric surgery. The effect of acute and chronic exercise was then assessed in 15 young healthy adults who performed intermittent sprint running sessions over an 8 week period.

RESULTS

Tissue arrays demonstrated that in humans, the FNDC5 gene is predominantly expressed in muscle. Circulating irisin was detected in the serum or plasma of all subjects studied, whereas circulating FNDC5 was detected in only a distinct minority of the subjects. Cross-sectional studies revealed that circulating irisin levels were positively correlated with biceps circumference (used as a surrogate marker of muscle mass herein), BMI, glucose, ghrelin, and IGF-1. In contrast, irisin levels were negatively correlated with age, insulin, cholesterol, and adiponectin levels, indicating a possible compensatory role of irisin in metabolic regulation. Multivariate regression analysis revealed that biceps circumference was the strongest predictor of circulating irisin levels underlying the association between irisin and metabolic factors in humans at baseline. Both muscle FNDC5 mRNA levels and circulating irisin levels were significantly downregulated 6 months after bariatric surgery. Circulating irisin levels were significantly upregulated 30 min after acute exercise and were correlated mainly with ATP levels and secondarily with metabolites related to glycolysis and lipolysis in muscle.

CONCLUSIONS

Similar to mice, the FNDC5 gene is expressed in human muscle. Age and muscle mass are the primary predictors of circulating irisin, with young male athletes having several fold higher irisin levels than middle-aged obese women. Circulating irisin levels increase in response to acute exercise whereas muscle FNDC5 mRNA and circulating irisin levels decrease after surgically induced weight loss in parallel to decrease in body mass. Further studies are needed to study the regulation of irisin levels and its physiological effects in humans and to elucidate the mechanisms underlying these effects.

Short-term walnut consumption increases circulating total adiponectin and apolipoprotein A concentrations, but does not affect markers of inflammation or vascular injury in obese humans with the metabolic syndrome: data from a double-blinded, randomized, placebo-controlled study

Long-term consumption of walnuts is associated with lower cardiovascular disease risk in epidemiological studies, possibly through improvements in lipid profile and endothelial function. It remains to be elucidated how soon after initiation of walnut consumption beneficial effects on lipid profile and biomarkers of inflammation or vascular injury can be observed. Fifteen obese subjects (9 men and 6 women; age, 58 ± 2.5 years; body mass index, 36.6 ± 1.7 kg/m(2)) with the metabolic syndrome participated as inpatients in a randomized, double-blinded, placebo-controlled crossover study involving short-term placebo or walnut-enriched diet (48 g/d for 4 days). Apolipoproteins and markers of inflammation and vascular injury were measured before and after consumption of the experimental diets. Consumption of walnuts was associated with a statistically significant increase in serum apolipoprotein A concentrations (P = .03), but did not affect circulating levels of fetuin A, resistin, C-reactive protein, serum amyloid A, soluble intercellular adhesion molecules 1 and 3, soluble vascular cell adhesion protein 1, interleukins 6 and 8, tumor necrosis factor α, E-selectin, P-selectin, and thrombomodulin. Four days of walnut consumption (48 g/d) leads to mild increases in apolipoprotein A concentrations, changes that may precede and lead to the beneficial effects of walnuts on lipid profile in obese subjects with the metabolic syndrome.

Circulating clusterin (apolipoprotein J) levels do not have any day/night variability and are positively associated with total and LDL cholesterol levels in young healthy individuals

CONTEXT

Clusterin has been associated with several pathologies, including cardiovascular disease and neoplasias. However, little is known about its physiology and its association with metabolic and anthropometric parameters in humans.

OBJECTIVE

The aim of the study was to examine whether circulating clusterin levels exhibit a day/night variation pattern and whether clusterin is associated with anthropometric and metabolic parameters.

DESIGN

Study A was a frequent sampling study to evaluate potential periodicity in clusterin secretion. Study B was an observational study to evaluate the cross-sectional and prospective associations of clusterin with anthropometric and metabolic parameters.

PARTICIPANTS

Study A participants were healthy males (n = 6) and females (n = 6), aged 22.3 ± 3.1 and 22.8 ± 3.4 yr, respectively. Study B participants were 186 healthy males aged 18.4 ± 0.14 yr. Ninety-one of the study B subjects were studied again 2 yr later and clusterin's associations with change of anthropometric and metabolic parameters were thus investigated prospectively.

INTERVENTION

Samples in study A were collected every 15 min during an overnight admission, and subsequently pooled every hour. Samples in study B were collected during a screening visit.

MAIN OUTCOME MEASURE

Circulating clusterin levels were measured.

RESULTS

In study A, spectral domain and cosinor regression analysis failed to reveal any day/night variation pattern. In study B, clusterin was positively correlated with total and low-density lipoprotein cholesterol (r = 0.23, P = 0.002; and r = 0.20, P = 0.005). Baseline clusterin did not predict change of any anthropometric, biochemical, or metabolic parameters prospectively.

CONCLUSIONS

We report for the first time that circulating clusterin does not have a day/night variation pattern in healthy young individuals. Clusterin levels are associated with total and low-density lipoprotein cholesterol cross-sectionally but do not predict short-term changes in metabolic parameters in healthy young males.

Energy deprivation alters in a leptin- and cortisol-independent manner circulating levels of activin A and follistatin but not myostatin in healthy males

CONTEXT

Activin A, myostatin, and follistatin have recently emerged as important regulatory molecules of reproduction and the musculoskeletal system. Little is known, however, about their day/night patterns of secretion and their physiological regulation by energy availability.

OBJECTIVE

The objective of the study was to explore day/night patterns of secretion and assess whether energy deprivation alters circulating levels of activin A, myostatin, follistatin, and cortisol and to examine whether leptin may mediate this effect. DESIGN, SETTING AND PATIENTS, AND INTERVENTIONS: Seven healthy lean men (aged 23.2 ± 3.7 yr, body mass index 23.6 ± 1.7 kg/m(2)) were studied for 72 h under three different conditions: on their baseline/isocaloric diet and in a complete fasting state with administration of either placebo or metreleptin. The two fasting studies were randomized and double blinded. Blood samples were obtained every 15 min from 0800 h on d 3 until 0800 h on d 4 and pooled hourly.

MAIN OUTCOME MEASURES

Serum concentrations of activin A, myostatin, follistatin, cortisol, and leptin were measured.

RESULTS

In contrast to cortisol, we demonstrated no day/night pattern of activin A, myostatin, and follistatin secretion. Activin A concentrations decreased significantly in response to energy deprivation (P < 0.01). Follistatin and cortisol concentrations increased significantly (P < 0.01 and P < 0.01, respectively). Myostatin remained unaffected (P = 0.40). Leptin administration reversed cortisol response (P < 0.01) but failed to alter activin A, follistatin, or myostatin concentrations.

CONCLUSIONS

Unlike cortisol, there is no day/night variation in the concentrations of activin A, myostatin, and follistatin in healthy young males. Although energy deprivation-induced cortisol changes are leptin mediated, the changes in follistatin and activin A concentrations occur through a leptin-independent pathway.