Christian A. Drevon

Leptin stimulates human osteoblastic cell proliferation, de novo collagen synthesis, and mineralization: Impact on differentiation markers, apoptosis, and osteoclastic signaling

Anabolic hormones, mechanical loading, and the obese protein leptin play separate roles in maintaining bone mass. We have previously shown that leptin, as well as its receptor, are expressed by normal human osteoblasts. Consequently, we have investigated how leptin affects proliferation, differentiation, and apoptosis of human osteoblasts. Iliac crest osteoblasts, incubated with either leptin (100 ng/ml), calcitriol (1,25(OH)2D3; 10−9 M) or 1–84 human parathyroid hormone (PTH; 10−8 M), were cultured for 35 consecutive days and assayed for expression of various differentiation‐related marker genes (as estimated by RT‐PCR), de novo collagen synthesis, proliferation, in vitro mineralization, and osteoclast signaling. The effects of leptin on protection against retinoic acid (RA; 10−7 M) induced apoptosis, as well as transition into preosteocytes, were also tested. Leptin exposure enhanced cell proliferation and collagen synthesis over both control condition and PTH exposure. Leptin inhibited in vitro calcified nodule production after 1–2 weeks in culture, however, subsequent to 4–5 weeks, leptin significantly stimulated mineralization. The mineralization profile throughout the entire incubation period was almost undistinguishable from the one induced by PTH. In comparison, 1,25(OH)2D3 generally reduced proliferation and collagen production rates, whereas mineralization was markedly enhanced. Leptin exposure (at 2 and 5 weeks) significantly enhanced the expression of TGFβ, IGF‐I, collagen‐Iα, ALP, and osteocalcin mRNA. Leptin also protected against RA‐induced apoptosis, as estimated by soluble DNA fractions and DNA laddering patterns subsequent to 10 days of culture. The expression profiles of Bax‐α and Bcl‐2 mRNAs indicated that leptin per se significantly protected against apoptosis throughout the entire incubation period. Furthermore, the osteoblast marker OSF‐2 was diminished, whereas the CD44 osteocyte marker gene expression was stimulated, indicating a transition into preosteocytes. In terms of osteoclastic signaling, leptin significantly augmented the mRNA levels of both interleukin‐6 (IL‐6) and osteoprotegerin (OPG). In summary, continuous leptin exposure of iliac crest osteoblasts, promotes collagen synthesis, cell differentiation and in vitro mineralization, as well as cell survival and transition into preosteocytes. Leptin may also facilitate osteoblastic signaling to the osteoclast.

Genetic Control of Obesity and Gut Microbiota Composition in Response to High-Fat, High-Sucrose Diet in Mice

Obesity is a highly heritable disease driven by complex interactions between genetic and environmental factors. Human genome-wide association studies (GWAS) have identified a number of loci contributing to obesity; however, a major limitation of these studies is the inability to assess environmental interactions common to obesity. Using a systems genetics approach, we measured obesity traits, global gene expression, and gut microbiota composition in response to a high-fat/high-sucrose (HF/HS) diet of more than 100 inbred strains of mice. Here we show that HF/HS feeding promotes robust, strain-specific changes in obesity that are not accounted for by food intake and provide evidence for a genetically determined set point for obesity. GWAS analysis identified 11 genome-wide significant loci associated with obesity traits, several of which overlap with loci identified in human studies. We also show strong relationships between genotype and gut microbiota plasticity during HF/HS feeding and identify gut microbial phylotypes associated with obesity.

The effects of acute and chronic exercise on PGC‐1α, irisin and browning of subcutaneous adipose tissue in humans

Irisin was first identified as a peroxisome proliferator‐activated receptor γ co‐activator‐1α (PGC‐1α) dependent myokine with the potential to induce murine brown‐fat‐like development of white adipose tissue. In humans, the regulatory effect of training on muscle FNDC5mRNA expression and subsequently irisin levels in plasma is more controversial. We recruited 26 inactive men (13 normoglycaemic and normal weight, controls; and 13 slightly hyperglycaemic and overweight, pre‐diabetes group) aged 40–65 years for a 12‐week intervention of combined endurance and strength training with four sessions of training per week. Before and after the 12‐week intervention period, participants were exposed to an acute endurance workload of 45 min at 70% of VO2max, and muscle biopsies were taken prior to and after exercise. Skeletal muscle mRNA for PGC1A and FNDC5 correlated and both PGC1A and FNDC5mRNA levels increased after 12 weeks of training in both control and pre‐diabetes subjects. Circulating irisin was reduced in response to 12 weeks of training, and was increased acutely (~1.2‐fold) just after acute exercise. Plasma concentration of irisin was higher in pre‐diabetes subjects compared with controls. There was little effect of 12 weeks of training on selected browning genes in subcutaneous adipose tissue. UCP1mRNA did not correlate with FNDC5 expression in subcutaneous adipose tissue or skeletal muscle or with irisin levels in plasma. We observed no enhancing effect of long‐term training on circulating irisin levels, and little or no effect of training on browning of subcutaneous white adipose tissue in humans.

Evidence against a Beneficial Effect of Irisin in Humans

Brown adipose tissue has gained interest as a potential target to treat obesity and metabolic diseases. Irisin is a newly identified hormone secreted from skeletal muscle enhancing browning of white fat cells, which improves systemic metabolism by increasing energy expenditure in mice. The discovery of irisin raised expectations of its therapeutic potential to treat metabolic diseases. However, the effect of irisin in humans is unclear. Analyses of genomic DNA, mRNA and expressed sequence tags revealed that FNDC5, the gene encoding the precursor of irisin, is present in rodents and most primates, but shows in humans a mutation in the conserved start codon ATG to ATA. HEK293 cells transfected with a human FNDC5 construct with ATA as start codon resulted in only 1% full-length protein compared to human FNDC5 with ATG. Additionally, in vitro contraction of primary human myotubes by electrical pulse stimulation induced a significant increase in PGC1α mRNA expression. However, FNDC5 mRNA level was not altered. FNDC5 mRNA expression in muscle biopsies from two different human exercise studies was not changed by endurance or strength training. Preadipocytes isolated from human subcutaneous adipose tissue exhibited differentiation to brite human adipocytes when incubated with bone morphogenetic protein (BMP) 7, but neither recombinant FNDC5 nor irisin were effective. In conclusion, our findings suggest that it is rather unlikely that the beneficial effect of irisin observed in mice can be translated to humans.

Effect of Supplementing Pregnant and Lactating Mothers With n-3 Very-Long-Chain Fatty Acids on Children's IQ and Body Mass Index at 7 Years of Age

OBJECTIVES. Arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3) are essential for brain growth and cognitive development. We have reported that supplementing pregnant and lactating women with n-3 very-long-chain polyunsaturated fatty acids promotes higher IQ scores at 4 years of age as compared with maternal supplementation with n-6 polyunsaturated fatty acids. In our present study, the children were examined at 7 years of age with the same cognitive tests as at 4 years of age. We also examined the relation between plasma fatty acid pattern and BMI in children, because an association between arachidonic acid and adipose tissue size has been suggested. METHODS. The study was randomized and double-blinded. The mothers took 10 mL of cod liver oil or corn oil from week 18 of pregnancy until 3 months after delivery. Their children were tested with the Kaufman Assessment Battery for Children at 7 years of age, and their height and weight were measured. RESULTS. We did not find any significant differences in scores on the Kaufman Assessment Battery for Children test at 7 years of age between children whose mothers had taken cod liver oil (n = 82) or corn oil (n = 61). We observed, however, that maternal plasma phospholipid concentrations of α-linolenic acid (18:3n-3) and docosahexaenoic acid during pregnancy were correlated to sequential processing at 7 years of age. We observed no correlation between fatty acid status at birth or during the first 3 months of life and BMI at 7 years of age. CONCLUSION. This study suggests that maternal concentration of n-3 very-long-chain polyunsaturated fatty acids during pregnancy might be of importance for later cognitive function, such as sequential processing, although we observed no significant effect of n-3 fatty acid intervention on global IQs. Neonatal fatty acid status had no influence on BMI at 7 years of age.

Intake of Flavonoid-Rich Wine, Tea, and Chocolate by Elderly Men and Women Is Associated with Better Cognitive Test Performance

In a cross-sectional study, we examined the relation between intake of 3 common foodstuffs that contain flavonoids (chocolate, wine, and tea) and cognitive performance. 2031 participants (70-74 y, 55% women) recruited from the population-based Hordaland Health Study in Norway underwent cognitive testing. A cognitive test battery included the Kendrick Object Learning Test, Trail Making Test, part A (TMT-A), modified versions of the Digit Symbol Test, Block Design, Mini-Mental State Examination, and Controlled Oral Word Association Test. Poor cognitive performance was defined as a score in the highest decile for the TMT-A and in the lowest decile for all other tests. A self-reported FFQ was used to assess habitual food intake. Participants who consumed chocolate, wine, or tea had significantly better mean test scores and lower prevalence of poor cognitive performance than those who did not. Participants who consumed all 3 studied items had the best test scores and the lowest risks for poor test performance. The associations between intake of these foodstuffs and cognition were dose dependent, with maximum effect at intakes of approximately 10 g/d for chocolate and approximately 75-100 mL/d for wine, but approximately linear for tea. Most cognitive functions tested were influenced by intake of these 3 foodstuffs. The effect was most pronounced for wine and modestly weaker for chocolate intake. Thus, in the elderly, a diet high in some flavonoid-rich foods is associated with better performance in several cognitive abilities in a dose-dependent manner.

Inhibition by insulin of resistin gene expression in 3T3-L1 adipocytes.

Expression of the gene encoding resistin, a low molecular weight protein secreted from adipose tissue postulated to link obesity and type II diabetes, was examined in 3T3‐L1 adipocytes. Resistin mRNA was detected in 3T3‐L1 cells by day 3 following induction of differentiation into adipocytes; by day 4 the level of resistin mRNA peaked and remained high. The PPARγ activators, rosiglitazone or darglitazone, reduced the level of resistin mRNA. Dexamethasone upregulated resistin mRNA level, but no effect was observed with the β3‐adrenoceptor agonist, BRL 37344. A substantial reduction in resistin mRNA level was observed with insulin, which induced decreases at physiological concentrations. Insulin may be a major inhibitor of resistin production, and this does not support a role for resistin in insulin resistance.

Effects of dietary fat modification on insulin sensitivity and on other risk factors of the metabolic syndrome--LIPGENE: a European randomized dietary intervention study.

Background:Excessive energy intake and obesity lead to the metabolic syndrome (MetS). Dietary saturated fatty acids (SFAs) may be particularly detrimental on insulin sensitivity (SI) and on other components of the MetS.Objective:This study determined the relative efficacy of reducing dietary SFA, by isoenergetic alteration of the quality and quantity of dietary fat, on risk factors associated with MetS.Design:A free-living, single-blinded dietary intervention study.Subjects and Methods:MetS subjects (n=417) from eight European countries completed the randomized dietary intervention study with four isoenergetic diets distinct in fat quantity and quality: high-SFA; high-monounsaturated fatty acids and two low-fat, high-complex carbohydrate (LFHCC) diets, supplemented with long chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs) (1.2 g per day) or placebo for 12 weeks. SI estimated from an intravenous glucose tolerance test (IVGTT) was the primary outcome measure. Lipid and inflammatory markers associated with MetS were also determined.Results:In weight-stable subjects, reducing dietary SFA intake had no effect on SI, total and low-density lipoprotein cholesterol concentration, inflammation or blood pressure in the entire cohort. The LFHCC n-3 PUFA diet reduced plasma triacylglycerol (TAG) and non-esterified fatty acid concentrations (P<0.01), particularly in men.Conclusion:There was no effect of reducing SFA on SI in weight-stable obese MetS subjects. LC n-3 PUFA supplementation, in association with a low-fat diet, improved TAG-related MetS risk profiles.

Effect of dietary supplementation with eicosapentaenoic acid in the treatment of atopic dermatitis

The effects of a dietary supplement of n‐3 fatty acids in patients with atopic dermatitis were investigated in a 12‐week, double‐blind study. The experimental group received 10 g of fish oil daily, of which about 1.8 g was eicosapentaenoic acid. This amount of eicosapentaenoic acid can be obtained from a daily intake of fat fish. The controls received an iso‐energetic placebo supplement containing olive oil. Compliance was monitored by gas‐chromatographic analysis of the fatty acid pattern in serum phospholipids. Results favoured the experimental group with regard to scale (P < 0.05), itch (P < 0.05) and overall subjective severity (P < 0.02) as compared to the controls.

Adiponectin is reduced in gestational diabetes mellitus in normal weight women

Background.  Adiponectin is an adipose tissue‐derived protein counteracting insulin resistance and inflammation. We have compared women with gestational diabetes mellitus (GDM; n = 22) and normal pregnancies (controls; n = 29) to evaluate whether adiponectin represents a link between endocrine function of adipose tissue and the development of diabetes during pregnancy.