Effects of supplemented isoenergetic diets varying in cereal fiber and protein content on the bile acid metabolic signature and relation to insulin resistance.

Bile acids (BA) are potent metabolic regulators influenced by diet. We studied effects of isoenergetic increases in the dietary protein and cereal-fiber contents on circulating BA and insulin resistance (IR) in overweight and obese adults. Randomized controlled nutritional intervention (18 weeks) in 72 non-diabetic participants (overweight/obese: 29/43) with at least one further metabolic risk factor. Participants were group-matched and allocated to four isoenergetic supplemented diets: control; high cereal fiber (HCF); high-protein (HP); or moderately increased cereal fiber and protein (MIX). Whole-body IR and insulin-mediated suppression of hepatic endogenous glucose production were measured using euglycaemic-hyperinsulinemic clamps with [6-62H2] glucose infusion. Circulating BA, metabolic biomarkers, and IR were measured at 0, 6, and 18 weeks. Under isoenergetic conditions, HP-intake worsened IR in obese participants after 6 weeks (M-value: 3.77 ± 0.58 vs. 3.07 ± 0.44 mg/kg/min, p = 0.038), with partial improvement back to baseline levels after 18 weeks (3.25 ± 0.45 mg/kg/min, p = 0.089). No deleterious effects of HP-intake on IR were observed in overweight participants. HCF-diet improved IR in overweight participants after 6 weeks (M-value 4.25 ± 0.35 vs. 4.81 ± 0.31 mg/kg/min, p = 0.016), but did not influence IR in obese participants. Control and MIX diets did not influence IR. HP-induced, but not HCF-induced changes in IR strongly correlated with changes of BA profiles. MIX-diet significantly increased most BA at 18 weeks in obese, but not in overweight participants. BA remained unchanged in controls. Pooled BA concentrations correlated with fasting fibroblast growth factor-19 (FGF-19) plasma levels (r = 0.37; p = 0.003). Higher milk protein intake was the only significant dietary predictor for raised total and primary BA in regression analyses (total BA, p = 0.017; primary BA, p = 0.011). Combined increased intake of dietary protein and cereal fibers markedly increased serum BA concentrations in obese, but not in overweight participants. Possible mechanisms explaining this effect may include compensatory increases of the BA pool in the insulin resistant, obese state; or defective BA transport.

Circulating triacylglycerols but not pancreatic fat associate with insulin secretion in healthy humans.

BACKGROUND: Loss of adequate insulin secretion for the prevailing insulin resistance is critical for the development of type 2 diabetes and has been suggested to result from circulating lipids (triacylglycerols [TG] or free fatty acids) and/or adipocytokines or from ectopic lipid storage in the pancreas. This study aimed to address whether circulating lipids, adipocytokines or pancreatic fat primarily associates with lower insulin secretion. SUBJECTS/METHODS: Nondiabetic persons (n=73), recruited from the general population, underwent clinical examinations, fasting blood drawing to measure TG and adipocytokines and oral glucose tolerance testing (OGTT) to assess basal and dynamic insulin secretion and sensitivity indices. Magnetic resonance imaging and 1H-magnetic resonance spectroscopy were used to measure body fat distribution and ectopic fat content in liver and pancreas. RESULTS: In age-, sex- and BMI-adjusted analyses, total and high-molecular-weight adiponectin were the strongest negative predictors of fasting beta-cell function (BCF; ß=-0.403, p=0.0003 and ß=-0.237, p=0.01, respectively) and adaptation index (AI; ß=-0.210, p=0.006 and ß=-0.133, p=0.02, respectively). Circulating TG, but not pancreatic fat content, related positively to BCF (ß=0.375, p<0.0001) and AI (ß=0.192, p=0.003). Similar results were obtained for the disposition index (DI). CONCLUSIONS: The association of serum lipids and adiponectin with beta-cell function may represent a compensatory response to adapt for lower insulin sensitivity in nondiabetic humans.

Amino Acid and Fatty Acid Levels Affect Hepatic Phosphorus Metabolite Content in Metabolically Healthy Humans.

Objective: Hepatic energy metabolism negatively relates to insulin resistance and liver fat content in patients with type 2 diabetes, but its role in metabolically healthy humans is unclear. We hypothesized that intrahepatocellular γ-adenosine triphosphate (γATP) and inorganic phosphate (Pi) concentrations exhibit similar associations with insulin sensitivity in nondiabetic, nonobese volunteers. Design: A total of 76 participants underwent a four-point sampling, 75-g oral glucose tolerance test (OGTT), as well as in vivo31P/1H magnetic resonance spectroscopy. In 62 of them, targeted plasma metabolomic profiling was performed. Pearson correlation analyses were performed for the dependent variables γATP and Pi. Results: Adjusted for age, sex, and body mass index (BMI), hepatic γATP and Pi related to 2-hour OGTT glucose (r = 0.25 and r = 0.27, both P < 0.05), and Pi further associated with nonesterified fatty acids (NEFAs; r = 0.28, P < 0.05). However, neither γATP nor Pi correlated with several measures of insulin sensitivity. Hepatic γATP correlated with circulating leucine (r = 0.42, P < 0.001) and Pi with C16:1 fatty acids palmitoleic acid and C16:1w5 (r = 0.28 and 0.30, respectively, P < 0.01), as well as with δ-9-desaturase index (r = 0.33, P < 0.05). Only the association of γATP with leucine remained important after correction for multiple testing. Leucine and palmitoleic acid, together with age, sex, and BMI, accounted for 26% and for 15% of the variabilities in γATP and Pi, respectively. Conclusions: Specific circulating amino acids and NEFAs, but not measures of insulin sensitivity, partly affect hepatic phosphorus metabolites, suggesting mutual interaction between hepatic energy metabolism and circulating metabolites in nondiabetic humans.

Acute dietary fat intake initiates alterations in energy metabolism and insulin resistance.

BACKGROUND: Dietary intake of saturated fat is a likely contributor to nonalcoholic fatty liver disease (NAFLD) and insulin resistance, but the mechanisms that initiate these abnormalities in humans remain unclear. We examined the effects of a single oral saturated fat load on insulin sensitivity, hepatic glucose metabolism, and lipid metabolism in humans. Similarly, initiating mechanisms were examined after an equivalent challenge in mice. METHODS: Fourteen lean, healthy individuals randomly received either palm oil (PO) or vehicle (VCL). Hepatic metabolism was analyzed using in vivo 13C/31P/1H and ex vivo 2H magnetic resonance spectroscopy before and during hyperinsulinemic-euglycemic clamps with isotope dilution. Mice underwent identical clamp procedures and hepatic transcriptome analyses. RESULTS: PO administration decreased whole-body, hepatic, and adipose tissue insulin sensitivity by 25%, 15%, and 34%, respectively. Hepatic triglyceride and ATP content rose by 35% and 16%, respectively. Hepatic gluconeogenesis increased by 70%, and net glycogenolysis declined by 20%. Mouse transcriptomics revealed that PO differentially regulates predicted upstream regulators and pathways, including LPS, members of the TLR and PPAR families, NF-κB, and TNF-related weak inducer of apoptosis (TWEAK). CONCLUSION: Saturated fat ingestion rapidly increases hepatic lipid storage, energy metabolism, and insulin resistance. This is accompanied by regulation of hepatic gene expression and signaling that may contribute to development of NAFLD.REGISTRATION. ClinicalTrials.gov NCT01736202. FUNDING: Germany: Ministry of Innovation, Science, and Research North Rhine-Westfalia, German Federal Ministry of Health, Federal Ministry of Education and Research, German Center for Diabetes Research, German Research Foundation, and German Diabetes Association. Portugal: Portuguese Foundation for Science and Technology, FEDER - European Regional Development Fund, Portuguese Foundation for Science and Technology, and Rede Nacional de Ressonância Magnética Nuclear.

Inflammatory markers are associated with cardiac autonomic dysfunction in recent-onset type 2 diabetes.

OBJECTIVE: Cardiovascular autonomic neuropathy is a common but underestimated diabetes-related disorder. Associations between cardiovascular autonomic dysfunction and subclinical inflammation, both risk factors of diabetic comorbidities and mortality, have been proposed in non-diabetic populations, while data for type 1 and type 2 diabetes are conflicting. Our aim was to investigate associations between inflammation-related biomarkers and cardiac autonomic dysfunction in patients with diabetes. METHODS: We characterised the associations between seven biomarkers of subclinical inflammation and cardiac autonomic dysfunction based on heart rate variability and cardiovascular autonomic reflex tests (CARTs) in 161 individuals with type 1 and 352 individuals with type 2 diabetes (time since diagnosis of diabetes <1 year). Analyses were adjusted for age, sex, anthropometric, metabolic and lifestyle factors, medication and cardiovascular comorbidities. RESULTS: In individuals with type 2 diabetes, higher serum interleukin (IL)-18 was associated with lower vagal activity (p≤0.015 for association with CARTs), whereas higher levels of total and high-molecular-weight adiponectin showed associations with very low frequency power, an indicator of reduced sympathetic activity (p≤0.014). Higher levels of soluble intercellular adhesion molecule-1 were associated with indicators of both lower vagal (p=0.025) and sympathetic (p=0.008) tone, soluble E-selectin with one indicator of lower vagal activity (p=0.047). Serum C-reactive protein and IL-6 were also related to cardiac autonomic dysfunction, but these associations were explained by confounding factors. No consistent associations were found in individuals with type 1 diabetes. CONCLUSIONS: Biomarkers of inflammation were differentially associated with diminished cardiac autonomic dysfunction in recent-onset type 2 diabetes.

Variants in Genes Controlling Oxidative Metabolism Contribute to Lower Hepatic ATP Independent of Liver Fat Content in Type 1 Diabetes.

Type 1 diabetes has been recently linked to nonalcoholic fatty liver disease (NAFLD), which is known to associate with insulin resistance, obesity, and type 2 diabetes. However, the role of insulin resistance and hyperglycemia for hepatic energy metabolism is yet unclear. To analyze early abnormalities in hepatic energy metabolism, we examined 55 patients with recently diagnosed type 1 diabetes. They underwent hyperinsulinemic-normoglycemic clamps with [6,6-(2)H2]glucose to assess whole-body and hepatic insulin sensitivity. Hepatic γATP, inorganic phosphate (Pi), and triglyceride concentrations (hepatocellular lipid content [HCL]) were measured with multinuclei magnetic resonance spectroscopy ((31)P/(1)H-MRS). Glucose-tolerant humans served as control (CON) (n = 57). Whole-body insulin sensitivity was 44% lower in patients than in age- and BMI-matched CON. Hepatic γATP was 15% reduced (2.3 ± 0.6 vs. 2.7 ± 0.6 mmol/L, P < 0.001), whereas hepatic Pi and HCL were similar in patients when compared with CON. Across all participants, hepatic γATP correlated negatively with glycemia and oxidized LDL. Carriers of the PPARG G allele (rs1801282) and noncarriers of PPARGC1A A allele (rs8192678) had 21 and 13% lower hepatic ATP concentrations. Variations in genes controlling oxidative metabolism contribute to a reduction in hepatic ATP in the absence of NAFLD, suggesting that alterations in hepatic mitochondrial function may precede diabetes-related liver diseases.

Sfrp5 associates with beta-cell function in humans.

BACKGROUND: Secreted frizzled-related protein (Sfrp)5 improves insulin sensitivity, but impairs beta-cell function in rodents. However, the relationship between Sfrp5, insulin sensitivity and secretion in humans is currently unclear. Therefore, the aim of the study was to characterize the associations between serum Sfrp5 and indices of insulin sensitivity and beta-cell function from dynamic measurements using oral glucose tolerance tests (OGTT) in humans. MATERIAL AND METHODS: This study enrolled 194 individuals with nonalcoholic fatty liver disease (NAFLD), who were diagnosed based on ultrasound and liver transaminases and underwent a frequent sampling 75-g OGTT. Fasting serum Sfrp5 was measured by ELISA. Associations were assessed with several indices of insulin sensitivity and beta-cell function derived from glucose, insulin and C-peptide concentrations during the OGTT. RESULTS: Circulating Sfrp5 associated inversely with the insulinogenic index based on C-peptide (rs = -0·244, P = 0·001), but not with the insulinogenic index based on insulin levels (rs = -0·007, P = 0·926) after adjustment for age, sex and body mass index. Sfrp5 inversely correlated only with QUICKI as a marker of insulin sensitivity in the model adjusted for age and sex (rs = -0·149, P = 0·039). These associations were not influenced by the additional adjustment for hepatic steatosis index. CONCLUSIONS: The inverse association of serum Sfrp5 with beta-cell function suggests a detrimental role of Sfrp5 for insulin secretion also in humans. The severity of NAFLD does not appear to affect this relationship. The weak association between serum Sfrp5 and insulin sensitivity was partially explained by body mass.

Adiponectin, markers of subclinical inflammation and nerve conduction in individuals with recently diagnosed type 1 and type 2 diabetes.

OBJECTIVE: Subclinical inflammation has been implicated in the development of diabetic sensorimotor polyneuropathy (DSPN), but studies using electrophysiological assessment as outcomes are scarce. Therefore, we aimed to investigate associations of biomarkers reflecting different aspects of subclinical inflammation with motor and sensory nerve conduction velocity (NCV) in individuals with diabetes. DESIGN AND METHODS: Motor and sensory NCV was assessed in individuals with recently diagnosed type 2 (n=352) or type 1 diabetes (n=161) from the baseline cohort of the observational German Diabetes Study. NCV sum scores were calculated for median, ulnar and peroneal motor as well as median, ulnar and sural sensory nerves. Associations between inflammation-related biomarkers, DSPN and NCV sum scores were estimated using multiple regression models. RESULTS: In type 2 diabetes, high serum interleukin (IL)-6 was associated with the presence of DSPN and reduced motor NCV. Moreover, higher levels of high-molecular weight (HMW) adiponectin, total adiponectin and their ratio were associated with prevalent DSPN and both diminished motor and sensory NCV, whereas no consistent associations were observed for C-reactive protein, IL18, soluble intercellular adhesion molecule-1 and E-selectin. In type 1 diabetes, only HMW and total adiponectin showed positive associations with motor NCV. CONCLUSIONS: Our results point to a link between IL6 and both DSPN and slowed motor NCV in recently diagnosed type 2 diabetes. The reverse associations between adiponectin and NCV in type 1 and type 2 diabetes are intriguing, and further studies should explore whether they may reflect differences in the pathogenesis of DSPN in both diabetes types.

Effect of Low-Energy Diets Differing in Fiber, Red Meat, and Coffee Intake on Cardiac Autonomic Function in Obese Individuals With Type 2 Diabetes.

OBJECTIVE: The autonomic nervous system (ANS) regulates both the cardiovascular system and energy balance and is disturbed in diabetes and obesity. The effect of different approaches of caloric restriction on ANS function has not been assessed in individuals with diabetes. Thus, we sought to determine whether low-energy diets differing in fiber, red meat, and coffee intake exert differential effects on cardiac autonomic function. RESEARCH DESIGN AND METHODS: In this randomized parallel-group pilot trial, obese patients with type 2 diabetes were randomly allocated to consume either a diet high in cereal fiber, free of red meat, and high in coffee (n = 13) or a diet low in fiber, high in red meat, and coffee free (n = 15) over 8 weeks. Eight measures of heart rate variability (HRV) indicating vagal and/or sympathetic modulation over 3 h and inflammatory markers were determined during a hyperinsulinemic-euglycemic clamp. RESULTS: After 8 weeks, both dietary interventions resulted in a mean weight loss of 5-6 kg, a mean decline in heart rate of 4-6 bpm, and improvement in vagally mediated HRV. However, the changes in HRV parameters from baseline to 8 weeks did not differ between the groups. In the entire study cohort, incremental HRV from baseline to 8 weeks was associated with enhanced oxidative glucose utilization (P < 0.05), but not with insulin sensitivity and inflammatory markers. CONCLUSIONS: In obese patients with type 2 diabetes, energy restriction per se over 8 weeks contributed to improved cardiac vagal function in relation to improved oxidative glucose utilization. This preliminary finding should be verified in a confirmatory trial.

Intake of Lactobacillus reuteri improves incretin and insulin secretion in glucose-tolerant humans: a proof of concept.

OBJECTIVE: Ingestion of probiotics can modify gut microbiota and alter insulin resistance and diabetes development in rodents. We hypothesized that daily intake of Lactobacillus reuteri increases insulin sensitivity by changing cytokine release and insulin secretion via modulation of the release of glucagon-like peptides (GLP)-1 and -2. RESEARCH DESIGN AND METHODS: A prospective, double-blind, randomized trial was performed in 21 glucose-tolerant humans (11 lean: age 49 ± 7 years, BMI 23.6 ± 1.7 kg/m(2); 10 obese: age 51 ± 7 years, BMI 35.5 ± 4.9 kg/m(2)). Participants ingested 10(10) b.i.d. L. reuteri SD5865 or placebo over 4 weeks. Oral glucose tolerance and isoglycemic glucose infusion tests were used to assess incretin effect and GLP-1 and GLP-2 secretion, and euglycemic-hyperinsulinemic clamps with [6,6-(2)H2]glucose were used to measure peripheral insulin sensitivity and endogenous glucose production. Muscle and hepatic lipid contents were assessed by (1)H-magnetic resonance spectroscopy, and immune status, cytokines, and endotoxin were measured with specific assays. RESULTS: In glucose-tolerant volunteers, daily administration of L. reuteri SD5865 increased glucose-stimulated GLP-1 and GLP-2 release by 76% (P < 0.01) and 43% (P < 0.01), respectively, compared with placebo, along with 49% higher insulin (P < 0.05) and 55% higher C-peptide secretion (P < 0.05). However, the intervention did not alter peripheral and hepatic insulin sensitivity, body mass, ectopic fat content, or circulating cytokines. CONCLUSIONS: Enrichment of gut microbiota with L. reuteri increases insulin secretion, possibly due to augmented incretin release, but does not directly affect insulin sensitivity or body fat distribution. This suggests that oral ingestion of one specific strain may serve as a novel therapeutic approach to improve glucose-dependent insulin release.

Adaptation of hepatic mitochondrial function in humans with non-alcoholic fatty liver is lost in steatohepatitis.

The association of hepatic mitochondrial function with insulin resistance and non-alcoholic fatty liver (NAFL) or steatohepatitis (NASH) remains unclear. This study applied high-resolution respirometry to directly quantify mitochondrial respiration in liver biopsies of obese insulin-resistant humans without (n = 18) or with (n = 16) histologically proven NAFL or with NASH (n = 7) compared to lean individuals (n = 12). Despite similar mitochondrial content, obese humans with or without NAFL had 4.3- to 5.0-fold higher maximal respiration rates in isolated mitochondria than lean persons. NASH patients featured higher mitochondrial mass, but 31%-40% lower maximal respiration, which associated with greater hepatic insulin resistance, mitochondrial uncoupling, and leaking activity. In NASH, augmented hepatic oxidative stress (H2O2, lipid peroxides) and oxidative DNA damage (8-OH-deoxyguanosine) was paralleled by reduced anti-oxidant defense capacity and increased inflammatory response. These data suggest adaptation of the liver ("hepatic mitochondrial flexibility") at early stages of obesity-related insulin resistance, which is subsequently lost in NASH.

Serum Chemerin Concentrations Associate with Beta-Cell Function, but Not with Insulin Resistance in Individuals with Non-Alcoholic Fatty Liver Disease (NAFLD).

The novel adipokine chemerin has been related to insulin-resistant states such as obesity and non alcoholic fatty liver disease (NAFLD). However, its association with insulin resistance and beta cell function remains controversial. The main objective was to examine whether serum chemerin levels associate with insulin sensitivity and beta cell function independently of body mass index (BMI), by studying consecutive outpatients of the hepatology clinics of a European university hospital. Individuals (n=196) with NAFLD were stratified into persons with normal glucose tolerance (NGT; n=110), impaired glucose tolerance (IGT; n=51) and type 2 diabetes (T2D; n=35) and the association between serum chemerin and measures of insulin sensitivity and beta cell function as assessed during fasting and during oral glucose tolerance test (OGTT) was measured. Our results showed that serum chemerin positively associated with BMI (P=0.0007) and C peptide during OGTT (P<0.004), but not with circulating glucose, insulin, lipids or liver enzymes (all P>0.18). No BMI independent relationships of chemerin with fasting and OGTT derived measures of insulin sensitivity were found (P>0.5). Chemerin associated positively with fasting beta cell function as well as the OGTT derived insulinogenic index IGI_cp and the adaptation index after adjustment for age, sex and BMI (P=0.002-0.007), and inversely with the insulin/C peptide ratio (P=0.007). Serum chemerin neither related to the insulinogenic index IGI_ins nor the disposition index. In conclusion, circulating chemerin is likely linked to enhanced beta cell function but not to insulin sensitivity in patients with NAFLD.

Characterization of the peak at 2.06 ppm in (31) P magnetic resonance spectroscopy of human liver: phosphoenolpyruvate or phosphatidylcholine?

High field MR scanners can resolve a metabolite resonating at 2.06 ppm in the in vivo proton-decoupled liver (31) P MR spectrum. Traditionally this peak has been assigned to phosphoenolpyruvate (PEP), the key metabolite for gluconeogenesis. However, recent evidence supported the assignment to biliary phosphatidylcholine (PtdCh), which is produced in the liver and stored in the gall bladder. To elucidate the respective contributions of PtdCh and PEP to the in vivo resonance at 2.06 ppm (PEP-PtdCh), we made phantom measurements that confirmed that both biliary PtdCh and PEP resonate approximately at 2 ppm. The absolute quantification of PEP-PtdCh yielded concentrations ranging from 0.6 to 2.0 mmol/l, with mean coefficients of variation of 4.8% for intraday and 7.2% for interday reproducibility in healthy volunteers. The T1 relaxation time of PEP-PtdCh was 0.97 ± 0.30 s in the liver and 0.44 ± 0.11 s in the gallbladder. Ingestion of a mixed meal decreased the concentration of PtdCh-PEP by approximately 12%. In the retrospective analysis, PEP-PtdCh was 68% higher in the liver of subjects with gallbladder infiltration of the volume of interest (VOI) compared with those without gallbladder infiltration. PEP-PtdCh was also significantly higher in the liver of cholecystectomy patients compared with volunteers without gallbladder infiltration, which suggests increased intrahepatic bile fluid as a compensation for gall bladder removal. These results show that liver PtdCh is the major component of the resonance at 2.06 ppm and that careful VOI positioning is mandatory to avoid interference from the gallbladder.

Differential Patterns and Determinants of Cardiac Autonomic Nerve Dysfunction during Endotoxemia and Oral Fat Load in Humans.

UNLABELLED: The autonomic nervous system (ANS) plays an important role in regulating the metabolic homeostasis and controlling immune function. ANS alterations can be detected by reduced heart rate variability (HRV) in conditions like diabetes and sepsis. We determined the effects of experimental conditions mimicking inflammation and hyperlipidemia on HRV and heart rate (HR) in relation to the immune, metabolic, and hormonal responses resulting from these interventions. Sixteen lean healthy subjects received intravenous (i.v.) low-dose endotoxin (lipopolysaccharide [LPS]), i.v. fat, oral fat, and i.v. glycerol (control) for 6 hours, during which immune, metabolic, hormonal, and five HRV parameters (pNN50, RMSSD, low-frequency (LF) and high-frequency (HF) power, and LF/HF ratio) were monitored and energy metabolism and insulin sensitivity (M-value) were assessed. LPS infusion induced an increase (AUC) in HR and LF/HF ratio and decline in pNN50 and RMSSD, while oral fat resulted in elevated HR and a transient (hours 1-2) decrease in pNN50, RMSSD, and HF power. During LPS infusion, ΔIL-1ra levels and ΔIL-1ra and ΔIL-1ß gene expression correlated positively with ΔLF/HF ratio and inversely with ΔRMSSD. During oral fat intake, ΔGLP-1 tended to correlate positively with ΔHR and inversely with ΔpNN50 and ΔRMSSD. Following LPS infusion, lipid oxidation correlated positively with HR and inversely with pNN50 and RMSSD, whereas HRV was not related to M-value. In conclusion, suppression of vagal tone and sympathetic predominance during endotoxemia are linked to anti-inflammatory processes and lipid oxidation but not to insulin resistance, while weaker HRV changes in relation to the GLP-1 response are noted during oral fat load. TRIAL REGISTRATION: ClinicalTrials.gov NCT01054989.

Pancreatic adipose tissue infiltration, parenchymal steatosis and beta cell function in humans.

AIMS/HYPOTHESIS: This study aimed to perform a comprehensive analysis of interlobular, intralobular and parenchymal pancreatic fat in order to assess their respective effects on beta cell function. METHODS: Fifty-six participants (normal glucose tolerance [NGT] (n = 28), impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT) (n = 14) and patients with type 2 diabetes (n = 14)) underwent a frequent-sampling OGTT and non-invasive magnetic resonance imaging (MRI; whole-body and pancreatic) and proton magnetic resonance spectroscopy ((1)H-MRS; liver and pancreatic fat). Total pancreatic fat was assessed by a standard 2 cm(3) (1)H-MRS method, intralobular fat by 1 cm(3) (1)H-MRS that avoided interlobular fat within modified DIXON (mDIXON) water images, and parenchymal fat by a validated mDIXON-MRI fat-fraction method. RESULTS: Comparison of (1)H-MRS techniques revealed an inhomogeneous distribution of interlobular and intralobular adipose tissue, which increased with decreasing glucose tolerance. mDIXON-MRI measurements provided evidence against uniform steatosis, revealing regions of parenchymal tissue void of lipid accumulation in all participants. Total (r = 0.385, p < 0.01) and intralobular pancreas adipose tissue infiltration (r = 0.310, p < 0.05) positively associated with age, but not with fasting or 2 h glucose levels, BMI or visceral fat content (all p > 0.5). Furthermore, no associations were found between total and intralobular pancreatic adipose tissue infiltration and insulin secretion or beta cell function within NGT, IFG/IGT or patients with type 2 diabetes (all p > 0.2). CONCLUSIONS/INTERPRETATION: The pancreas does not appear to be another target organ for abnormal endocrine function because of ectopic parenchymal fat storage. No relationship was found between pancreatic adipose tissue infiltration and beta cell function, regardless of glucose tolerance status.

Effects of intranasal insulin on hepatic fat accumulation and energy metabolism in humans.

Studies in rodents suggest that insulin controls hepatic glucose metabolism through brain-liver crosstalk, but human studies using intranasal insulin to mimic central insulin delivery have provided conflicting results. In this randomized controlled crossover trial, we investigated the effects of intranasal insulin on hepatic insulin sensitivity (HIS) and energy metabolism in 10 patients with type 2 diabetes and 10 lean healthy participants (CON). Endogenous glucose production was monitored with [6,6-(2)H2]glucose, hepatocellular lipids (HCLs), ATP, and inorganic phosphate concentrations with (1)H/(31)P magnetic resonance spectroscopy. Intranasal insulin transiently increased serum insulin levels followed by a gradual lowering of blood glucose in CON only. Fasting HIS index was not affected by intranasal insulin in CON and patients. HCLs decreased by 35% in CON only, whereas absolute hepatic ATP concentration increased by 18% after 3 h. A subgroup of CON received intravenous insulin to mimic the changes in serum insulin and blood glucose levels observed after intranasal insulin. This resulted in a 34% increase in HCLs without altering hepatic ATP concentrations. In conclusion, intranasal insulin does not affect HIS but rapidly improves hepatic energy metabolism in healthy humans, which is independent of peripheral insulinemia. These effects are blunted in patients with type 2 diabetes.

Evidence for a direct effect of the NAD+ precursor acipimox on muscle mitochondrial function in humans.

Recent preclinical studies showed the potential of nicotinamide adenine dinucleotide (NAD(+)) precursors to increase oxidative phosphorylation and improve metabolic health, but human data are lacking. We hypothesize that the nicotinic acid derivative acipimox, an NAD(+) precursor, would directly affect mitochondrial function independent of reductions in nonesterified fatty acid (NEFA) concentrations. In a multicenter randomized crossover trial, 21 patients with type 2 diabetes (age 57.7 ± 1.1 years, BMI 33.4 ± 0.8 kg/m(2)) received either placebo or acipimox 250 mg three times daily dosage for 2 weeks. Acipimox treatment increased plasma NEFA levels (759 ± 44 vs. 1,135 ± 97 µmol/L for placebo vs. acipimox, P < 0.01) owing to a previously described rebound effect. As a result, skeletal muscle lipid content increased and insulin sensitivity decreased. Despite the elevated plasma NEFA levels, ex vivo mitochondrial respiration in skeletal muscle increased. Subsequently, we showed that acipimox treatment resulted in a robust elevation in expression of nuclear-encoded mitochondrial gene sets and a mitonuclear protein imbalance, which may indicate activation of the mitochondrial unfolded protein response. Further studies in C2C12 myotubes confirmed a direct effect of acipimox on NAD(+) levels, mitonuclear protein imbalance, and mitochondrial oxidative capacity. To the best of our knowledge, this study is the first to demonstrate that NAD(+) boosters can also directly affect skeletal muscle mitochondrial function in humans.

Low-energy diets differing in fibre, red meat and coffee intake equally improve insulin sensitivity in type 2 diabetes: a randomised feasibility trial.

AIMS/HYPOTHESIS: Epidemiological studies have found that a diet high in fibre and coffee, but low in red meat, reduces the risk for type 2 diabetes. We tested the hypothesis that these nutritional modifications differentially improve whole-body insulin sensitivity (primary outcome) and secretion. METHODS: Inclusion criteria were: age 18-69 years, BMI ≥ 30 kg/m(2), type 2 diabetes treated with diet, metformin or acarbose and known disease duration of ≤ 5 years. Exclusion criteria were: HbA1c >75 mmol/mol (9.0%), type 1 or secondary diabetes types and acute or chronic diseases including cancer. Patients taking any medication affecting the immune system or insulin sensitivity, other than metformin, were also excluded. Of 59 patients (randomised using randomisation blocks [four or six patients] with consecutive numbers), 37 (54% female) obese type 2 diabetic patients completed this controlled parallel-group 8-week low-energy dietary intervention. The participants consumed either a diet high in cereal fibre (whole grain wheat/rye: 30-50 g/day) and coffee (≥ 5 cups/day), and free of red meat (L-RISK, n = 17) or a diet low in fibre (≤ 10 g/day), coffee-free and high in red meat (≥ 150 g/day) diet (H-RISK, n = 20). Insulin sensitivity and secretion were assessed by hyperinsulinaemic-euglycaemic clamp and intravenous glucose tolerance tests with isotope dilution. Whole-body and organ fat contents were measured by magnetic resonance imaging and spectroscopy. RESULTS: Whole-body insulin sensitivity increased in both groups (mean [95% CI]) (H-RISK vs L-RISK: 0.8 [0.2, 1.4] vs 1.0 [0.4, 1.7]mg kg(-1) min(-1), p = 0.59), while body weight decreased (-4.8% [-6.1%, -3.5%] vs -4.6% [-6.0%, -3.3%], respectively). Hepatic insulin sensitivity remained unchanged, whereas hepatocellular lipid content fell in both groups (-7.0% [-9.6%, -4.5%] vs -6.7% [-9.5%, -3.9%]). Subcutaneous fat mass (-1,553 [-2,767, -340] cm(3) vs -751 [-2,047; 546] cm(3), respectively) visceral fat mass (-206 [-783, 371] cm(3) vs -241 [-856, 373] cm(3), respectively) and muscle fat content (-0.09% [-0.16%, -0.02%] vs -0.02% [-0.10%, 0.05%], respectively) decreased similarly. Insulin secretion remained unchanged, while the proinflammatory marker IL-18 decreased only after the L-RISK diet. CONCLUSIONS/INTERPRETATION: No evidence of a difference between both low-energy diets was identified. Thus, energy restriction per se seems to be key for improving insulin action in phases of active weight loss in obese type 2 diabetic patients, with a potential improvement of subclinical inflammation with the L-RISK diet. TRIAL REGISTRATION: Clinicaltrials.gov NCT01409330. FUNDING: This study was supported by the Ministry of Science and Research of the State of North Rhine-Westphalia (MIWF NRW), the German Federal Ministry of Health (BMG), the Federal Ministry for Research (BMBF) to the Center for Diabetes Research (DZD e.V.) and the Helmholtz Alliance Imaging and Curing Environmental Metabolic Diseases (ICEMED).

Modulation of amino acid metabolic signatures by supplemented isoenergetic diets differing in protein and cereal fiber content.

CONTEXT: Amino-acid (AA) metabolic signatures differ in insulin-resistant (IR) obese vs normal-weight subjects, improve after weight loss, and seem to predict the risk of type 2 diabetes. It is unknown whether weight-maintaining dietary measures aimed at influencing IR alter AA signatures of high-risk subjects. SETTING AND DESIGN: In the randomized controlled Protein, Fiber and Metabolic Syndrome (ProFiMet) trial we investigated effects of four isoenergetic, moderately fat-reduced diets varying in protein and cereal-fiber contents on complete AA metabolic signatures in 76 group-matched overweight or obese high-risk subjects. We analyzed the relation of whole-body and hepatic IR with AA signatures, body fat composition and liver fat, after 0, 6, and 18 weeks of dietary intervention. Discrimination between diets was further enhanced by providing tailored dietary supplements for twice-daily consumption over 18 weeks in all groups. RESULTS: Baseline AA, including branched-chain signatures significantly related to IR, liver fat, and visceral fat mass. Isoenergetic variation of protein and cereal-fiber dietary contents, but not fat restriction, significantly influenced IR, whereas the relation of AA with IR changed with all diets. The tryptophan ratio was significantly suppressed in obese vs overweight participants, but increased after 6 weeks of high cereal-fiber intake to a nonobese phenotype. Modeling analyses revealed diet-induced alterations of complex AA profiles to relate to 70% and 62% of changes in whole-body and hepatic IR. CONCLUSIONS: We demonstrate that relatively short-term isoenergetic changes in the diet significantly alter the relation of AA signatures with IR, with possible implications on the determination and treatment of diabetes risk.