Charles Lavigne

Functional significance of skeletal muscle adiponectin production, changes in animal models of obesity and diabetes, and regulation by rosiglitazone treatment

Endocrine effects of adipose-derived adiponectin on skeletal muscle have been shown to account, at least in part, for the anti-diabetic effects of this adipokine. Recently, the concept of myokines has gained credence, and the potential for skeletal muscle to produce adiponectin has been suggested. Here we demonstrated an increased level of adiponectin mRNA and protein expression as well as protein secretion in response to rosiglitazone treatment in L6 muscle cells. This correlated with the ability of rosiglitazone to enhance insulin sensitivity for stimulation of protein kinase B (Akt) phosphorylation and glucose transport; rosiglitazone also corrected high-glucose-induced insulin resistance in L6 cells. Overexpression of adiponectin confirmed the functional significance of local production of adiponectin in muscle cells via elevated glucose uptake and increased insulin sensitivity. In obese diabetic db/db mice, there was a change in the adiponectin expression profile in soleus and extensor digitorum longus (EDL) muscle with less high molecular weight (HMW) and more medium (MMW)/low (LMW) molecular weight species detected. Induction of obesity and insulin resistance in rats by feeding a high-fat high-sucrose diet also led to decreased muscle HMW adiponectin content that could be corrected by rosiglitazone treatment. In summary, we show the ability of skeletal muscle cells to produce adiponectin, which can mediate autocrine metabolic effects, thus establishing adiponectin as a bona fide myokine. We also demonstrate that skeletal muscle adiponectin production is altered in animal models of obesity and diabetes and that these changes can be corrected by rosiglitazone.

Differential effects of various fish proteins in altering body weight, adiposity, inflammatory status, and insulin sensitivity in high-fat-fed rats.

Mounting evidence suggests that the benefits of fish consumption are not limited to the well-appreciated effects of omega-3 fatty acids. We previously demonstrated that cod protein protects against the development of diet-induced insulin resistance. The goal of this study was to determine whether other fish protein sources present similar beneficial effects. Rats were fed a high-fat, high-sucrose diet containing protein from casein or fish proteins from bonito, herring, mackerel, or salmon. After 28 days, oral glucose tolerance tests or hyperinsulinemic-euglycemic clamps were performed; and tissues and plasma were harvested for biochemical analyses. Despite equal energy intake among all groups, the salmon-protein-fed group presented significantly lower weight gain that was associated with reduced fat accrual in epididymal white adipose tissue. Although this reduction in visceral adiposity was not associated with improved glucose tolerance, we found that whole-body insulin sensitivity for glucose metabolism was improved using the very sensitive hyperinsulinemic-euglycemic clamp technique. Importantly, expression of both tumor necrosis factor-α and interleukin-6 was reduced in visceral adipose tissue of all fish-protein-fed groups when compared with the casein-fed control group, suggesting that fish proteins carry anti-inflammatory properties that may protect against obesity-linked metabolic complications. Interestingly, consumption of the salmon protein diet was also found to raise circulating salmon calcitonin levels, which may underlie the reduction of weight gain in these rats. These data suggest that not all fish protein sources exert the same beneficial properties on the metabolic syndrome, although anti-inflammatory actions appear to be common.

Fish oil and argan oil intake differently modulate insulin resistance and glucose intolerance in a rat model of dietary-induced obesity

We investigated the potential metabolic benefits of fish oil (FO) or vegetable argan oil (AO) intake in a dietary model of obesity-linked insulin resistance. Rats were fed a standard chow diet (controls), a high-fat/high-sucrose (HFHS) diet, or an HFHS diet in which 6% of the fat was replaced by either FO or AO feeding, respectively. The HFHS diet increased adipose tissue weight and insulin resistance as revealed by increased fasting glucose and exaggerated glycemic and insulin responses to a glucose tolerance test (intraperitoneal glucose tolerance test). Fish oil feeding prevented fat accretion, reduced fasting glycemia, and normalized glycemic or insulin responses to intraperitoneal glucose tolerance test as compared with HFHS diet. Unlike FO consumption, AO intake failed to prevent obesity, yet restored fasting glycemia back to chow-fed control values. Insulin-induced phosphorylation of Akt and Erk in adipose tissues, skeletal muscles, and liver was greatly attenuated in HFHS rats as compared with chow-fed controls. High-fat/high-sucrose diet-induced insulin resistance was also confirmed in isolated hepatocytes. Fish oil intake prevented insulin resistance by improving or fully restoring insulin signaling responses in all tissues and isolated hepatocytes. Argan oil intake also improved insulin-dependent phosphorylations of Akt and Erk; and in adipose tissue, these responses were increased even beyond values observed in chow-fed controls. Taken together, these results strongly support the beneficial action of FO on diet-induced insulin resistance and glucose intolerance, an effect likely explained by the ability of FO to prevent HFHS-induced adiposity. Our data also show for the first time that AO can improve some of the metabolic and insulin signaling abnormalities associated with HFHS feeding.

Validation of the Use of Peripheral Blood Mononuclear Cells as Surrogate Model for Skeletal Muscle Tissue in Nutrigenomic Studies

Peripheral blood mononuclear cells (PBMCs) offer a significant promise for gene expression analyses as a substitute for tissues that are not easily accessible. The objective of this study was to validate the use of PBMCs for gene expression analysis as a marker of nutritional intervention as an alternative to skeletal muscle tissue (SMT) biopsies. We performed a transcriptome comparison of PBMCs versus SMT after an 8-week supplementation with n-3 polyunsaturated fatty acid (PUFA) in 16 obese and insulin-resistant subjects. Expression levels of 48,803 transcripts were assessed by the Human-6 v3 Expression BeadChips (Illumina, San Diego, CA). In SMT, 36,738 (75%) transcripts were detected, whereas 34,182 (70%) transcripts were detected in PBMCs. Further, 88% (32,341) of these transcripts were coexpressed in both tissues. Importantly, a strong correlation (r = 0.84, p < 0.0001) was observed between transcript expression levels of PBMCs and SMT after n-3 PUFA supplementation. In conclusion, PBMCs express the majority of transcripts expressed in SMT subsequent to n-3 PUFA supplementation and their expression levels are comparable. In the interest of practicalities and cost, these results support the use of PBMCs as a surrogate model for SMT gene expression in nutrigenomic studies. Further research on PBMC and SMT gene expression in response to other nutritional exposures is warranted.

Lean-seafood intake reduces cardiovascular lipid risk factors in healthy subjects: results from a randomized controlled trial with a crossover design,

BACKGROUND Observational studies have strongly indicated an association between fish consumption and reduced risk of cardiovascular disease, but data from randomized controlled trials have been inconclusive. OBJECTIVE Our primary outcome in this study was to elucidate the potentials of the 2 main dietary protein sources lean seafood and nonseafood to modulate fasting and postprandial lipids in healthy subjects. We hypothesized that lean-seafood intake would reduce cardiovascular lipid risk factors in healthy subjects more than would the intake of nonseafood protein sources. DESIGN This study was a randomized controlled trial with a crossover design. After 3-wk run-in periods and separated by a 5-wk washout period, 20 healthy subjects (7 men and 13 women) consumed 2 balanced diets that varied in main protein sources (60% of total dietary proteins from lean-seafood or nonseafood sources for 4 wk). At days 1 and 28 of each intervention, fasting and postprandial blood samples were collected before and after consumption, respectively, of test meals with cod or lean beef. RESULTS Relative to the nonseafood intervention, the lean-seafood intervention reduced fasting (relative difference by diets: 0.31 mmol/L; P = 0.03) and postprandial (P = 0.01) serum triacylglycerol concentrations. The lower serum triacylglycerol concentration was associated with reduced fasting triacylglycerol in chylomicrons and very-low-density lipoproteins (VLDLs) (P = 0.004), reduced fasting VLDL particle size (P = 0.04), and a reduced postprandial concentration of medium-sized VLDL particles (P = 0.02). The lean-seafood intervention prevented the elevated ratio of total cholesterol to HDL cholesterol in the fasted serum (P = 0.03) and postprandial serum (P = 0.01) that was observed after the nonseafood intervention. CONCLUSION The dietary protein source determines fasting and postprandial lipids in healthy individuals in a manner that may have an effect on the long-term development of cardiovascular disease. This study was registered at clinicaltrials.gov as NCT01708681.

Responses of plasma lipoproteins and sex hormones to the consumption of lean fish incorporated in a prudent-type diet in normolipidemic men

Objective: The effects of lean fish on plasma lipoproteins, postheparin plasma lipolytic activities and sex hormones were examined in 11 normolipidemic male subjects. Methods: This study was a randomized crossover trial of two isoenergetic prudent-type diets, lean fish diet and beef, pork, veal, eggs and milk (nonfish) diet. Experimental diets provided approximately 11800 kJ—18% as proteins, 50% as carbohydrates, 32% as lipids [ratio of polyunsaturated to saturated fatty acids (P:S) of 1:1 compared with 0.5:1 in preexperimental diet], and 260 mg cholesterol/day. Results: Compared with the nonfish diet, the lean fish diet induced higher plasma total and LDL apolipoprotein (apo) B and apo B:apo A-1 ratio, indicating that the substitution of lean fish for beef, veal, pork, eggs and milk provides little benefits with regard to plasma apo B concentrations in a low-fat high P:S diet. Moreover, triglycerides:apo B and cholesterol:apo B ratios of VLDL were lower following the lean fish diet than the nonfish diet, suggesting the presence of smaller very low-density lipoprotein (VLDL) particles following the consumption of lean fish. Higher plasma concentrations of sex hormone-binding globulin (SHBG), HDL2 cholesterol and HDL2:HDL3 cholesterol ratio were found with the lean fish diet compared with the nonfish diet. Negative correlations between plasma postheparin lipoprotein lipase (LPL) activity and VLDL triglycerides (n = 11, r = −0.53, p = 0.02), and between plasma postheparin LPL activity and VLDL triglycerides:apo B ratio (n = 11, r = −0.64, p = 0.02) were also observed following the lean fish diet. Conclusion: These results suggest that the effects of substituting lean fish for beef, veal, pork, eggs and milk on plasma lipoproteins may be partly associated with variations in plasma sex hormone status and plasma LPL activity in normolipidemic men.

Effects of Dietary Fibre Mixtures on Glucose and Lipid Metabolism and on Mineral Absorption in the Rat

Four diets containing different mixtures of dietary fibre (DF) were tested in the rat to verify the effects of fibre source and fibre level on plasma glucose, insulin and lipids and on apparent intestinal absorption of minerals. Diets Puri5 and Puri 10 contained 5 and 10% of total DF from pectin and cellulose. Diets Bran 5 and Bran 10 supplied 5 and 10% DF from oat bran and wheat bran. A fifth diet with 5% cellulose was used as a control. Ten rats were fed each diet for 4 weeks. On days 3, 17 and 28, feces were collected and analyzed for Fe, Zn, Ca and Mg. On day 29, blood samples were collected in portal vein and abdominal aorta in fasted and fed rats from each group. All diets had similar effects on plasma insulin and triglycerides. Compared to Bran diets, Puri diets induced higher portal glucose (p < 0.01) and lower plasma cholesterol (p < 0.03) in fed rats. The apparent absorption of Fe, Zn and Mg was higher (p < 0.05) in rats fed Puri diets than in those fed Bran diets. For Ca, the difference was significant only on day 3. In this study, only the apparent absorption of Fe was affected (p < 0.01) by fibre level (5 > 10%). This indicates that in fibre mixtures, the source rather than the amount of fibre generally affects absorptive and metabolic parameters.

Fish nutrients decrease expression levels of tumor necrosis factor-α in cultured human macrophages

Numerous studies have demonstrated the beneficial effects of fish consumption on inflammatory markers. Until now, these beneficial effects of fish consumption have been mostly linked to the omega-3 fatty acids (FA). The objective of the present study was to examine, in vitro, whether expression levels of genes involved in the inflammatory response differ in human macrophages incubated with casein hydrolysates (CH) or fish protein hydrolysates (FPH) in the presence or absence of omega-3 FA compared with omega-3 FA alone. Peripheral blood monocytes differentiated into macrophages from 10 men were incubated in the presence of omega-3 FA (10 microM eicosapentaenoic acid and 5 microM docosahexaenoic acid) or CH or FPH (10, 100, 1,000 microg) with or without omega-3 FA for 48 h. Results demonstrate that expression levels of tumor necrosis factoralpha (TNFalpha) had a tendency to be lower after the addition of FPH alone or CH with omega-3 FA compared with omega-3 FA treatment. Furthermore, the combination of FPH and omega-3 FA synergistically decreased expression levels of TNFalpha compared to treatment with omega-3 FA or FPH alone. No difference on gene expression levels of interleukin-6 was observed between treatments. In conclusion, these preliminary results suggest that the anti-inflammatory effects of fish consumption can be explained by a synergistic effect of the omega-3 FA with the protein components of fish on TNFalpha expression and therefore contribute to the beneficial effects of fish consumption. Hence, follow-up studies should be performed to confirm the effects of a diet rich in FPH and omega-3 FA on serum proinflammatory cytokine concentrations.

Lean‐seafood intake decreases urinary markers of mitochondrial lipid and energy metabolism in healthy subjects: Metabolomics results from a randomized crossover intervention study

SCOPE Proteins constitute an important part of the human diet, but understanding of the effects of different dietary protein sources on human metabolism is sparse. We aimed to elucidate diet-induced metabolic changes through untargeted urinary metabolomics after four weeks of intervention with lean-seafood or nonseafood diets. It is shown that lean-seafood intake reduces urinary excretion of metabolites involved in mitochondrial lipid and energy metabolism possibly facilitating a higher lipid catabolism in healthy subjects. METHODS In a randomized controlled trial with crossover design, 20 healthy subjects consumed two balanced diets that varied in main protein sources for 4 weeks. Morning spot urine samples were collected before and after each intervention period. Untargeted metabolomics based on (1) H NMR spectroscopy and LC-MS analyses were applied to characterize the urinary metabolic response to the interventions. RESULTS The lean-seafood diet period reduced the urinary level of l-carnitine, 2,6-dimethylheptanoylcarnitine, and N-methyl-2-pyridone-5-carboxamide, relative to the nonseafood period. The dietary analysis revealed that the higher urinary level of trimethylamine-N-oxide after the lean-seafood diet period and guanidinoacetate and 3-methylhistidine after the nonseafood diet period was related to the endogenous content of these compounds in the diets. CONCLUSIONS Our data reveal that 4 weeks of lean-seafood intake reduces urinary excretion of metabolites involved in mitochondrial lipid and energy metabolism possibly facilitating a higher lipid catabolism in healthy subjects after the lean-seafood intake.

Effects of a Supplementation of n-3 Polyunsaturated Fatty Acids with or without Fish Gelatin on Gene Expression in Peripheral Blood Mononuclear Cells in Obese, Insulin-Resistant Subjects

Aim: To investigate gene expression changes in peripheral blood mononuclear cells (PBMCs) following an n-3 polyunsaturated fatty acid (PUFA) and n-3 PUFA plus fish gelatin (+FG) supplementation. Methods: A transcriptome comparison of 8-week supplementation with n-3 PUFA and n-3 PUFA+FG was carried out in PBMCs of 16 obese insulin-resistant subjects. Results: Erythrocyte n-3 PUFA concentration increased and plasma triglycerides decreased significantly without altering inflammatory parameters after both supplementations. n-3 PUFA supplementation changed the expression of 805 genes, whereas n-3 PUFA+FG supplementation altered the expression of 184 genes. Three genes were commonly changed: fatty acid desaturase 1, free fatty acid receptor 3, and ectodysplasin. Pathway analyses indicate changes in gene expression via the nuclear receptor peroxisome proliferator-activated receptor α pathway after both supplementations. Further, the extent of modifications in the expression of genes implicated in the inflammatory pathways – the oxidative stress response mediated by nuclear factor (erythroid-derived 2)-like 2, nuclear transcription factor ĸB, oxidative stress, and hypoxia-inducible factor signaling – was different after each supplementation. Conclusion: Although n-3 PUFA and n-3 PUFA+FG supplementations have a distinct impact on gene expression levels, the consequences on biochemical parameters and metabolic pathways were comparable after both supplementations.