Human apoE isoforms differentially regulate brain amyloid-β peptide clearance

The apolipoprotein E (APOE) ε4 allele is the strongest genetic risk factor for late-onset, sporadic Alzheimer's disease (AD). The APOE ε4 allele markedly increases AD risk and decreases age of onset, likely through its strong effect on the accumulation of amyloid-β (Aβ) peptide. In contrast, the APOE ε2 allele appears to decrease AD risk. Most rare, early-onset forms of familial AD are caused by autosomal dominant mutations that often lead to overproduction of Aβ(42) peptide. However, the mechanism by which APOE alleles differentially modulate Aβ accumulation in sporadic, late-onset AD is less clear. In a cohort of cognitively normal individuals, we report that reliable molecular and neuroimaging biomarkers of cerebral Aβ deposition vary in an apoE isoform-dependent manner. We hypothesized that human apoE isoforms differentially affect Aβ clearance or synthesis in vivo, resulting in an apoE isoform-dependent pattern of Aβ accumulation later in life. Performing in vivo microdialysis in a mouse model of Aβ-amyloidosis expressing human apoE isoforms (PDAPP/TRE), we find that the concentration and clearance of soluble Aβ in the brain interstitial fluid depends on the isoform of apoE expressed. This pattern parallels the extent of Aβ deposition observed in aged PDAPP/TRE mice. ApoE isoform-dependent differences in soluble Aβ metabolism are observed not only in aged but also in young PDAPP/TRE mice well before the onset of Aβ deposition in amyloid plaques in the brain. Additionally, amyloidogenic processing of amyloid precursor protein and Aβ synthesis, as assessed by in vivo stable isotopic labeling kinetics, do not vary according to apoE isoform in young PDAPP/TRE mice. Our results suggest that APOE alleles contribute to AD risk by differentially regulating clearance of Aβ from the brain, suggesting that Aβ clearance pathways may be useful therapeutic targets for AD prevention.

Effects of Moderate and Subsequent Progressive Weight Loss on Metabolic Function and Adipose Tissue Biology in Humans with Obesity

Although 5%-10% weight loss is routinely recommended for people with obesity, the precise effects of 5% and further weight loss on metabolic health are unclear. We conducted a randomized controlled trial that evaluated the effects of 5.1% ± 0.9% (n = 19), 10.8% ± 1.3% (n = 9), and 16.4% ± 2.1% (n = 9) weight loss and weight maintenance (n = 14) on metabolic outcomes. 5% weight loss improved adipose tissue, liver and muscle insulin sensitivity, and β cell function, without a concomitant change in systemic or subcutaneous adipose tissue markers of inflammation. Additional weight loss further improved β cell function and insulin sensitivity in muscle and caused stepwise changes in adipose tissue mass, intrahepatic triglyceride content, and adipose tissue expression of genes involved in cholesterol flux, lipid synthesis, extracellular matrix remodeling, and oxidative stress. These results demonstrate that moderate 5% weight loss improves metabolic function in multiple organs simultaneously, and progressive weight loss causes dose-dependent alterations in key adipose tissue biological pathways.

Absence of an effect of liposuction on insulin action and risk factors for coronary heart disease

BACKGROUND

Liposuction has been proposed as a potential treatment for the metabolic complications of obesity. We evaluated the effect of large-volume abdominal liposuction on metabolic risk factors for coronary heart disease in women with abdominal obesity.

METHODS

We evaluated the insulin sensitivity of liver, skeletal muscle, and adipose tissue (with a euglycemic-hyperinsulinemic clamp procedure and isotope-tracer infusions) as well as levels of inflammatory mediators and other risk factors for coronary heart disease in 15 obese women before and 10 to 12 weeks after abdominal liposuction. Eight of the women had normal glucose tolerance (mean [+/-SD] body-mass index, 35.1+/-2.4), and seven had type 2 diabetes (body-mass index, 39.9+/-5.6).

RESULTS

Liposuction decreased the volume of subcutaneous abdominal adipose tissue by 44 percent in the subjects with normal glucose tolerance and 28 percent in those with diabetes; those with normal oral glucose tolerance lost 9.1+/-3.7 kg of fat (18+/-3 percent decrease in total fat, P=0.002), and those with type 2 diabetes lost 10.5+/-3.3 kg of fat (19+/-2 percent decrease in total fat, P<0.001). Liposuction did not significantly alter the insulin sensitivity of muscle, liver, or adipose tissue (assessed by the stimulation of glucose disposal, the suppression of glucose production, and the suppression of lipolysis, respectively); did not significantly alter plasma concentrations of C-reactive protein, interleukin-6, tumor necrosis factor alpha, and adiponectin; and did not significantly affect other risk factors for coronary heart disease (blood pressure and plasma glucose, insulin, and lipid concentrations) in either group.

CONCLUSIONS

Abdominal liposuction does not significantly improve obesity-associated metabolic abnormalities. Decreasing adipose tissue mass alone will not achieve the metabolic benefits of weight loss.

Insulin resistance drives hepatic de novo lipogenesis in nonalcoholic fatty liver disease

BACKGROUNDAn increase in intrahepatic triglyceride (IHTG) is the hallmark feature of nonalcoholic fatty liver disease (NAFLD) and is decreased by weight loss. Hepatic de novo lipogenesis (DNL) contributes to steatosis in individuals with NAFLD. The physiological factors that stimulate hepatic DNL and the effect of weight loss on hepatic DNL are not clear.METHODSHepatic DNL, 24-hour integrated plasma insulin and glucose concentrations, and both liver and whole-body insulin sensitivity were determined in individuals who were lean (n = 14), obese with normal IHTG content (n = 26), or obese with NAFLD (n = 27). Hepatic DNL was assessed using the deuterated water method corrected for the potential confounding contribution of adipose tissue DNL. Liver and whole-body insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp procedure in conjunction with glucose tracer infusion. Six subjects in the obese-NAFLD group were also evaluated before and after a diet-induced weight loss of 10%.RESULTSThe contribution of hepatic DNL to IHTG-palmitate was 11%, 19%, and 38% in the lean, obese, and obese-NAFLD groups, respectively. Hepatic DNL was inversely correlated with hepatic and whole-body insulin sensitivity, but directly correlated with 24-hour plasma glucose and insulin concentrations. Weight loss decreased IHTG content, in conjunction with a decrease in hepatic DNL and 24-hour plasma glucose and insulin concentrations.CONCLUSIONSThese data suggest hepatic DNL is an important regulator of IHTG content and that increases in circulating glucose and insulin stimulate hepatic DNL in individuals with NAFLD. Weight loss decreased IHTG content, at least in part, by decreasing hepatic DNL.TRIAL REGISTRATIONClinicalTrials.gov NCT02706262.FUNDINGThis study was supported by NIH grants DK56341 (Nutrition Obesity Research Center), DK20579 (Diabetes Research Center), DK52574 (Digestive Disease Research Center), and RR024992 (Clinical and Translational Science Award), and by grants from the Academy of Nutrition and Dietetics Foundation, the College of Natural Resources of UCB, and the Pershing Square Foundation.

Alterations in adipose tissue and hepatic lipid kinetics in obese men and women with nonalcoholic fatty liver disease

BACKGROUND & AIMS

Steatosis in patients with nonalcoholic fatty liver disease (NAFLD) is due to an imbalance between intrahepatic triglyceride (IHTG) production and export. The purpose of this study was to evaluate TG metabolism in adipose tissue and liver in NAFLD.

METHODS

Fatty acid, VLDL-TG, and VLDL-apolipoprotein B-100 (apoB100) kinetics were assessed by using stable isotope tracers in 14 nondiabetic obese subjects with NAFLD (IHTG, 22.7% +/- 2.0%) and 14 nondiabetic obese subjects with normal IHTG content (IHTG, 3.4% +/- 0.4%), matched on age, sex, body mass index, and percent body fat.

RESULTS

Compared with the normal IHTG group, the NAFLD group had greater rates of palmitate release from adipose tissue into plasma (85.4 +/- 6.6 and 114.1 +/- 8.1 micromol/min, respectively; P = .01) and VLDL-TG secretion (11.4 +/- 1.1 and 24.3 +/- 3.1 micromol/min, respectively; P = .001); VLDL-apoB100 secretion rates were not different between groups. The increase in VLDL-TG secretion was primarily due to an increased contribution from "nonsystemic" fatty acids, presumably derived from lipolysis of intrahepatic and intra-abdominal fat and de novo lipogenesis. VLDL-TG secretion rate increased linearly with increasing IHTG content in subjects with normal IHTG but reached a plateau when IHTG content was >/=10% (r = 0.618, P < .001).

CONCLUSIONS

Obese persons with NAFLD have marked alterations in both adipose tissue (increased lipolytic rates) and hepatic (increased VLDL-TG secretion) TG metabolism. Fatty acids derived from nonsystemic sources are responsible for the increase in VLDL-TG secretion. However, the increase in hepatic TG export is not adequate to normalize IHTG content.

Amyloid β concentrations and stable isotope labeling kinetics of human plasma specific to central nervous system amyloidosis

INTRODUCTION

Cerebrospinal fluid analysis and other measurements of amyloidosis, such as amyloid-binding positron emission tomography studies, are limited by cost and availability. There is a need for a more practical amyloid β (Aβ) biomarker for central nervous system amyloid deposition.

METHODS

We adapted our previously reported stable isotope labeling kinetics protocol to analyze the turnover kinetics and concentrations of Aβ38, Aβ40, and Aβ42 in human plasma.

RESULTS

Aβ isoforms have a half-life of approximately 3 hours in plasma. Aβ38 demonstrated faster turnover kinetics compared with Aβ40 and Aβ42. Faster fractional turnover of Aβ42 relative to Aβ40 and lower Aβ42 and Aβ42/Aβ40 concentrations in amyloid-positive participants were observed.

DISCUSSION

Blood plasma Aβ42 shows similar amyloid-associated alterations as we have previously reported in cerebrospinal fluid, suggesting a blood-brain transportation mechanism of Aβ. The stability and sensitivity of plasma Aβ measurements suggest this may be a useful screening test for central nervous system amyloidosis.

Tau Kinetics in Neurons and the Human Central Nervous System

We developed stable isotope labeling and mass spectrometry approaches to measure the kinetics of multiple isoforms and fragments of tau in the human central nervous system (CNS) and in human induced pluripotent stem cell (iPSC)-derived neurons. Newly synthesized tau is truncated and released from human neurons in 3 days. Although most tau proteins have similar turnover, 4R tau isoforms and phosphorylated forms of tau exhibit faster turnover rates, suggesting unique processing of these forms that may have independent biological activities. The half-life of tau in control human iPSC-derived neurons is 6.74 ± 0.45 days and in human CNS is 23 ± 6.4 days. In cognitively normal and Alzheimer's disease participants, the production rate of tau positively correlates with the amount of amyloid plaques, indicating a biological link between amyloid plaques and tau physiology.

Tauroursodeoxycholic Acid may improve liver and muscle but not adipose tissue insulin sensitivity in obese men and women

OBJECTIVE

Insulin resistance is commonly associated with obesity. Studies conducted in obese mouse models found that endoplasmic reticulum (ER) stress contributes to insulin resistance, and treatment with tauroursodeoxycholic acid (TUDCA), a bile acid derivative that acts as a chemical chaperone to enhance protein folding and ameliorate ER stress, increases insulin sensitivity. The purpose of this study was to determine the effect of TUDCA therapy on multiorgan insulin action and metabolic factors associated with insulin resistance in obese men and women.

RESEARCH DESIGN AND METHODS

Twenty obese subjects ([means +/- SD] aged 48 +/- 11 years, BMI 37 +/- 4 kg/m2) were randomized to 4 weeks of treatment with TUDCA (1,750 mg/day) or placebo. A two-stage hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotopically labeled tracer infusions and muscle and adipose tissue biopsies were used to evaluate in vivo insulin sensitivity, cellular factors involved in insulin signaling, and cellular markers of ER stress. RESULTS Hepatic and muscle insulin sensitivity increased by approximately 30% (P < 0.05) after treatment with TUDCA but did not change after placebo therapy. In addition, therapy with TUDCA, but not placebo, increased muscle insulin signaling (phosphorylated insulin receptor substrate(Tyr) and Akt(Ser473) levels) (P < 0.05). Markers of ER stress in muscle or adipose tissue did not change after treatment with either TUDCA or placebo.

CONCLUSIONS

These data demonstrate that TUDCA might be an effective pharmacological approach for treating insulin resistance. Additional studies are needed to evaluate the target cells and mechanisms responsible for this effect.

Resveratrol supplementation does not improve metabolic function in nonobese women with normal glucose tolerance

Resveratrol has been reported to improve metabolic function in metabolically abnormal rodents and humans, but it has not been studied in nonobese people with normal glucose tolerance. We conducted a randomized, double-blind, placebo-controlled trial to evaluate the metabolic effects of 12 weeks of resveratrol supplementation (75 mg/day) in nonobese, postmenopausal women with normal glucose tolerance. Although resveratrol supplementation increased plasma resveratrol concentration, it did not change body composition, resting metabolic rate, plasma lipids, or inflammatory markers. A two-stage hyperinsulinemic-euglycemic clamp procedure, in conjunction with stable isotopically labeled tracer infusions, demonstrated that resveratrol did not increase liver, skeletal muscle, or adipose tissue insulin sensitivity. Consistent with the absence of in vivo metabolic effects, resveratrol did not affect its putative molecular targets, including AMPK, SIRT1, NAMPT, and PPARGC1A, in either skeletal muscle or adipose tissue. These findings demonstrate that resveratrol supplementation does not have beneficial metabolic effects in nonobese, postmenopausal women with normal glucose tolerance.

WNT-LRP5 signaling induces Warburg effect through mTORC2 activation during osteoblast differentiation

WNT signaling controls many biological processes including cell differentiation in metazoans. However, how WNT reprograms cell identity is not well understood. We have investigated the potential role of cellular metabolism in WNT-induced osteoblast differentiation. WNT3A induces aerobic glycolysis known as Warburg effect by increasing the level of key glycolytic enzymes. The metabolic regulation requires LRP5 but not β-catenin and is mediated by mTORC2-AKT signaling downstream of RAC1. Suppressing WNT3A-induced metabolic enzymes impairs osteoblast differentiation in vitro. Deletion of Lrp5 in the mouse, which decreases postnatal bone mass, reduces mTORC2 activity and glycolytic enzymes in bone cells and lowers serum lactate levels. Conversely, mice expressing a mutant Lrp5 that causes high bone mass exhibit increased glycolysis in bone. Thus, WNT-LRP5 signaling promotes bone formation in part through direct reprogramming of glucose metabolism. Moreover, regulation of cellular metabolism may represent a general mechanism contributing to the wide-ranging functions of WNT proteins.

Effect of sleep on overnight cerebrospinal fluid amyloid β kinetics

Sleep disturbances are associated with future risk of Alzheimer disease. Disrupted sleep increases soluble amyloid β, suggesting a mechanism for sleep disturbances to increase Alzheimer disease risk. We tested this response in humans using indwelling lumbar catheters to serially sample cerebrospinal fluid while participants were sleep-deprived, treated with sodium oxybate, or allowed to sleep normally. All participants were infused with ¹³ C₆ -leucine to measure amyloid β kinetics. We found that sleep deprivation increased overnight amyloid β38, amyloid β40, and amyloid β42 levels by 25 to 30% via increased overnight amyloid β production relative to sleeping controls. These findings suggest that disrupted sleep increases Alzheimer disease risk via increased amyloid β production. Ann Neurol 2018;83:197-204.

Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women

In rodents, obesity and aging impair nicotinamide adenine dinucleotide (NAD⁺) biosynthesis, which contributes to metabolic dysfunction. Nicotinamide mononucleotide (NMN) availability is a rate-limiting factor in mammalian NAD⁺ biosynthesis. We conducted a 10-week, randomized, placebo-controlled, double-blind trial to evaluate the effect of NMN supplementation on metabolic function in postmenopausal women with prediabetes who were overweight or obese. Insulin-stimulated glucose disposal, assessed by using the hyperinsulinemic-euglycemic clamp, and skeletal muscle insulin signaling [phosphorylation of protein kinase AKT and mechanistic target of rapamycin (mTOR)] increased after NMN supplementation but did not change after placebo treatment. NMN supplementation up-regulated the expression of platelet-derived growth factor receptor β and other genes related to muscle remodeling. These results demonstrate that NMN increases muscle insulin sensitivity, insulin signaling, and remodeling in women with prediabetes who are overweight or obese (clinicaltrial.gov NCT03151239).

Association between specific adipose tissue CD4+ T-cell populations and insulin resistance in obese individuals

BACKGROUND & AIMS

An increased number of macrophages in adipose tissue is associated with insulin resistance and metabolic dysfunction in obese people. However, little is known about other immune cells in adipose tissue from obese people, and whether they contribute to insulin resistance. We investigated the characteristics of T cells in adipose tissue from metabolically abnormal insulin-resistant obese (MAO) subjects, metabolically normal insulin-sensitive obese (MNO) subjects, and lean subjects. Insulin sensitivity was determined by using the hyperinsulinemic euglycemic clamp procedure.

METHODS

We assessed plasma cytokine concentrations and subcutaneous adipose tissue CD4(+) T-cell populations in 9 lean, 12 MNO, and 13 MAO subjects. Skeletal muscle and liver samples were collected from 19 additional obese patients undergoing bariatric surgery to determine the presence of selected cytokine receptors.

RESULTS

Adipose tissue from MAO subjects had 3- to 10-fold increases in numbers of CD4(+) T cells that produce interleukin (IL)-22 and IL-17 (a T-helper [Th] 17 and Th22 phenotype) compared with MNO and lean subjects. MAO subjects also had increased plasma concentrations of IL-22 and IL-6. Receptors for IL-17 and IL-22 were expressed in human liver and skeletal muscle samples. IL-17 and IL-22 inhibited uptake of glucose in skeletal muscle isolated from rats and reduced insulin sensitivity in cultured human hepatocytes.

CONCLUSIONS

Adipose tissue from MAO individuals contains increased numbers of Th17 and Th22 cells, which produce cytokines that cause metabolic dysfunction in liver and muscle in vitro. Additional studies are needed to determine whether these alterations in adipose tissue T cells contribute to the pathogenesis of insulin resistance in obese people.

Randomized trial of exercise effect on intrahepatic triglyceride content and lipid kinetics in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) and alterations in hepatic lipoprotein kinetics are common metabolic complications associated with obesity. Lifestyle modification involving diet-induced weight loss and regular exercise decreases intrahepatic triglyceride (IHTG) content and very low density lipoprotein (VLDL) triglyceride (TG) secretion rate. The aim of this study was to evaluate the weight loss-independent effect of following the physical activity guidelines recommended by the Department of Health and Human Services on IHTG content and VLDL kinetics in obese persons with NAFLD. Eighteen obese people (body mass index [BMI]: 38.1 ± 4.6 kg/m(2)) with NAFLD were randomized to 16 weeks of exercise training (45%-55% VO(2peak) , 30-60 minutes × 5 days/week; n = 12) or observation (control; n = 6). Magnetic resonance spectroscopy and stable isotope tracer infusions in conjunction with compartmental modeling were used to evaluate IHTG content and hepatic VLDL-TG and apolipoprotein B-100 (apoB-100) secretion rates. Exercise training resulted in a 10.3% ± 4.6% decrease in IHTG content (P < 0.05), but did not change total body weight (103.1 ± 4.2 kg before and 102.9 ± 4.2 kg after training) or percent body fat (38.9% ± 2.1% before and 39.2% ± 2.1% after training). Exercise training did not change the hepatic VLDL-TG secretion rate (17.7 ± 3.9 μmol/min before and 16.8 ± 5.4 μmol/min after training) or VLDL-apoB-100 secretion rate (1.5 ± 0.5 nmol/min before and 1.6 ± 0.6 nmol/min after training).

CONCLUSION

Following the Department of Health and Human Services recommended physical activity guidelines has small but beneficial effects on IHTG content, but does not improve hepatic lipoprotein kinetics in obese persons with NAFLD.

Amyloid-β efflux from the central nervous system into the plasma

OBJECTIVE

The aim of this study was to measure the flux of amyloid-β (Aβ) across the human cerebral capillary bed to determine whether transport into the blood is a significant mechanism of clearance for Aβ produced in the central nervous system (CNS).

METHODS

Time-matched blood samples were simultaneously collected from a cerebral vein (including the sigmoid sinus, inferior petrosal sinus, and the internal jugular vein), femoral vein, and radial artery of patients undergoing inferior petrosal sinus sampling. For each plasma sample, Aβ concentration was assessed by 3 assays, and the venous to arterial Aβ concentration ratios were determined.

RESULTS

Aβ concentration was increased by ∼7.5% in venous blood leaving the CNS capillary bed compared to arterial blood, indicating efflux from the CNS into the peripheral blood (p < 0.0001). There was no difference in peripheral venous Aβ concentration compared to arterial blood concentration.

INTERPRETATION

Our results are consistent with clearance of CNS-derived Aβ into the venous blood supply with no increase from a peripheral capillary bed. Modeling these results suggests that direct transport of Aβ across the blood-brain barrier accounts for ∼25% of Aβ clearance, and reabsorption of cerebrospinal fluid Aβ accounts for ∼25% of the total CNS Aβ clearance in humans. Ann Neurol 2014;76:837-844.

Gastric bypass and banding equally improve insulin sensitivity and β cell function

Bariatric surgery in obese patients is a highly effective method of preventing or resolving type 2 diabetes mellitus (T2DM); however, the remission rate is not the same among different surgical procedures. We compared the effects of 20% weight loss induced by laparoscopic adjustable gastric banding (LAGB) or Roux-en-Y gastric bypass (RYGB) surgery on the metabolic response to a mixed meal, insulin sensitivity, and β cell function in nondiabetic obese adults. The metabolic response to meal ingestion was markedly different after RYGB than after LAGB surgery, manifested by rapid delivery of ingested glucose into the systemic circulation, by an increase in the dynamic insulin secretion rate, and by large, early postprandial increases in plasma glucose, insulin, and glucagon-like peptide-1 concentrations in the RYGB group. However, the improvement in oral glucose tolerance, insulin sensitivity, and overall β cell function after weight loss were not different between surgical groups. Additionally, both surgical procedures resulted in a similar decrease in adipose tissue markers of inflammation. We conclude that marked weight loss itself is primarily responsible for the therapeutic effects of RYGB and LAGB on insulin sensitivity, β cell function, and oral glucose tolerance in nondiabetic obese adults.

Stimulation of muscle protein synthesis by long-term insulin infusion in severely burned patients

OBJECTIVE

To determine if long-term (7 days) infusion of insulin can ameliorate altered protein kinetics in skeletal muscle of severely burned patients and to investigate the hypothesis that changes in protein kinetics during insulin infusion are associated with an increased rate of transmembrane amino acid transport from plasma into the intracellular free amino acid pool.

SUMMARY BACKGROUND DATA

In critically ill patients, vigorous nutritional support alone may often fail to entirely curtail muscle catabolism; insulin stimulates muscle protein synthesis in normal volunteers.

METHODS

Nine patients with severe burns were studied once during enteral feeding alone (control period), and once after 7 days of high-dose insulin. The order of treatment with insulin was randomized. Data were derived from a model based on a primed-continuous infusion of L-[15N]phenylalanine, sampling of blood from the femoral artery and vein, and biopsies of the vastus lateralis muscle.

RESULTS

Net leg muscle protein balance was significantly (p < 0.05) negative during the control period. Exogenous insulin eliminated this negative balance by stimulating protein synthesis approximately 350% (p < 0.01). This was made possible in part by a sixfold increase in the inward transport of amino acids from blood (p < 0.01). There was also a significant increase in leg muscle protein breakdown. The new rates of synthesis, breakdown, and inward transport during insulin were in balance, such that there was no difference in the intracellular phenylalanine concentration from the control period. The fractional synthetic rate of protein in the wound was also stimulated by insulin by approximately 50%, but the response was variable and did not reach significance.

CONCLUSIONS

Exogenous insulin may be useful in promoting muscle protein synthesis in severely catabolic patients.

Effects of Dietary Fructose Restriction on Liver Fat, De Novo Lipogenesis, and Insulin Kinetics in Children With Obesity

BACKGROUND & AIMS

Consumption of sugar is associated with obesity, type 2 diabetes mellitus, nonalcoholic fatty liver disease, and cardiovascular disease. The conversion of fructose to fat in liver (de novo lipogenesis [DNL]) may be a modifiable pathogenetic pathway. We determined the effect of 9 days of isocaloric fructose restriction on DNL, liver fat, visceral fat (VAT), subcutaneous fat, and insulin kinetics in obese Latino and African American children with habitual high sugar consumption (fructose intake >50 g/d).

METHODS

Children (9-18 years old; n = 41) had all meals provided for 9 days with the same energy and macronutrient composition as their standard diet, but with starch substituted for sugar, yielding a final fructose content of 4% of total kilocalories. Metabolic assessments were performed before and after fructose restriction. Liver fat, VAT, and subcutaneous fat were determined by magnetic resonance spectroscopy and imaging. The fractional DNL area under the curve value was measured using stable isotope tracers and gas chromatography/mass spectrometry. Insulin kinetics were calculated from oral glucose tolerance tests. Paired analyses compared change from day 0 to day 10 within each child.

RESULTS

Compared with baseline, on day 10, liver fat decreased from a median of 7.2% (interquartile range [IQR], 2.5%-14.8%) to 3.8% (IQR, 1.7%-15.5%) (P < .001) and VAT decreased from 123 cm³ (IQR, 85-145 cm³) to 110 cm³ (IQR, 84-134 cm³) (P < .001). The DNL area under the curve decreased from 68% (IQR, 46%-83%) to 26% (IQR, 16%-37%) (P < .001). Insulin kinetics improved (P < .001). These changes occurred irrespective of baseline liver fat.

CONCLUSIONS

Short-term (9 days) isocaloric fructose restriction decreased liver fat, VAT, and DNL, and improved insulin kinetics in children with obesity. These findings support efforts to reduce sugar consumption. ClinicalTrials.gov Number: NCT01200043.

Increased in vivo amyloid-β42 production, exchange, and loss in presenilin mutation carriers

Alzheimer's disease (AD) is hypothesized to be caused by an overproduction or reduced clearance of amyloid-β (Aβ) peptide. Autosomal dominant AD (ADAD) caused by mutations in the presenilin (PSEN) gene have been postulated to result from increased production of Aβ42 compared to Aβ40 in the central nervous system (CNS). This has been demonstrated in rodent models of ADAD but not in human mutation carriers. We used compartmental modeling of stable isotope labeling kinetic (SILK) studies in human carriers of PSEN mutations and related noncarriers to evaluate the pathophysiological effects of PSEN1 and PSEN2 mutations on the production and turnover of Aβ isoforms. We compared these findings by mutation status and amount of fibrillar amyloid deposition as measured by positron emission tomography (PET) using the amyloid tracer Pittsburgh compound B (PIB). CNS Aβ42 to Aβ40 production rates were 24% higher in mutation carriers compared to noncarriers, and this was independent of fibrillar amyloid deposits quantified by PET PIB imaging. The fractional turnover rate of soluble Aβ42 relative to Aβ40 was 65% faster in mutation carriers and correlated with amyloid deposition, consistent with increased deposition of Aβ42 into plaques, leading to reduced recovery of Aβ42 in cerebrospinal fluid (CSF). Reversible exchange of Aβ42 peptides with preexisting unlabeled peptide was observed in the presence of plaques. These findings support the hypothesis that Aβ42 is overproduced in the CNS of humans with PSEN mutations that cause AD, and demonstrate that soluble Aβ42 turnover and exchange processes are altered in the presence of amyloid plaques, causing a reduction in Aβ42 concentrations in the CSF.

Effects of Diet versus Gastric Bypass on Metabolic Function in Diabetes

BACKGROUND

Some studies have suggested that in people with type 2 diabetes, Roux-en-Y gastric bypass has therapeutic effects on metabolic function that are independent of weight loss.

METHODS

We evaluated metabolic regulators of glucose homeostasis before and after matched (approximately 18%) weight loss induced by gastric bypass (surgery group) or diet alone (diet group) in 22 patients with obesity and diabetes. The primary outcome was the change in hepatic insulin sensitivity, assessed by infusion of insulin at low rates (stages 1 and 2 of a 3-stage hyperinsulinemic euglycemic pancreatic clamp). Secondary outcomes were changes in muscle insulin sensitivity, beta-cell function, and 24-hour plasma glucose and insulin profiles.

RESULTS

Weight loss was associated with increases in mean suppression of glucose production from baseline, by 7.04 μmol per kilogram of fat-free mass per minute (95% confidence interval [CI], 4.74 to 9.33) in the diet group and by 7.02 μmol per kilogram of fat-free mass per minute (95% CI, 3.21 to 10.84) in the surgery group during clamp stage 1, and by 5.39 (95% CI, 2.44 to 8.34) and 5.37 (95% CI, 2.41 to 8.33) μmol per kilogram of fat-free mass per minute in the two groups, respectively, during clamp stage 2; there were no significant differences between the groups. Weight loss was associated with increased insulin-stimulated glucose disposal, from 30.5±15.9 to 61.6±13.0 μmol per kilogram of fat-free mass per minute in the diet group and from 29.4±12.6 to 54.5±10.4 μmol per kilogram of fat-free mass per minute in the surgery group; there was no significant difference between the groups. Weight loss increased beta-cell function (insulin secretion relative to insulin sensitivity) by 1.83 units (95% CI, 1.22 to 2.44) in the diet group and by 1.11 units (95% CI, 0.08 to 2.15) in the surgery group, with no significant difference between the groups, and it decreased the areas under the curve for 24-hour plasma glucose and insulin levels in both groups, with no significant difference between the groups. No major complications occurred in either group.

CONCLUSIONS

In this study involving patients with obesity and type 2 diabetes, the metabolic benefits of gastric bypass surgery and diet were similar and were apparently related to weight loss itself, with no evident clinically important effects independent of weight loss. (Funded by the National Institutes of Health and others; ClinicalTrials.gov number, NCT02207777.).

Associations between free fatty acids, cumulus oocyte complex morphology and ovarian function during in vitro fertilization

OBJECTIVE

To determine if follicular free fatty acid (FFA) levels are associated with cumulus oocyte complex (COC) morphology.

DESIGN

Prospective cohort study.

SETTING

University in vitro fertilization (IVF) practice.

PATIENT(S)

A total of 102 women undergoing IVF.

INTERVENTION(S)

Measurement of FFAs in serum and ovarian follicular fluid.

MAIN OUTCOME MEASURE(S)

Total and specific follicular and serum FFA levels, correlations between follicular and serum FFAs, and associations between follicular FFA levels and markers of oocyte quality, including COC morphology.

RESULT(S)

Predominant follicular fluid and serum FFAs were oleic, palmitic, linoleic, and stearic acids. Correlations between follicular and serum FFA concentrations were weak (r=0.252, 0.288, 0.236, 0.309, respectively for specific FFAs; r=0.212 for total FFAs). A receiver operating characteristic curve determined total follicular FFAs≥0.232 μmol/mL distinguished women with a lower versus higher percentage of COCs with favorable morphology. Women with elevated follicular FFAs (n=31) were more likely to have COCs with poor morphology than others (n=71; OR 3.3, 95% CI1.2-9.2). This relationship held after adjusting for potential confounders, including age, body mass index, endometriosis, and amount of gonadotropin administered (β=1.2; OR 3.4, 95% CI 1.1-10.4).

CONCLUSION(S)

Elevated follicular FFA levels are associated with poor COC morphology. Further work is needed to determine what factors influence follicular FFA levels and if these factors impact fertility.

Sucralose affects glycemic and hormonal responses to an oral glucose load

OBJECTIVE

Nonnutritive sweeteners (NNS), such as sucralose, have been reported to have metabolic effects in animal models. However, the relevance of these findings to human subjects is not clear. We evaluated the acute effects of sucralose ingestion on the metabolic response to an oral glucose load in obese subjects.

RESEARCH DESIGN AND METHODS

Seventeen obese subjects (BMI 42.3 ± 1.6 kg/m(2)) who did not use NNS and were insulin sensitive (based on a homeostasis model assessment of insulin resistance score ≤ 2.6) underwent a 5-h modified oral glucose tolerance test on two separate occasions preceded by consuming either sucralose (experimental condition) or water (control condition) 10 min before the glucose load in a randomized crossover design. Indices of β-cell function, insulin sensitivity (SI), and insulin clearance rates were estimated by using minimal models of glucose, insulin, and C-peptide kinetics.

RESULTS

Compared with the control condition, sucralose ingestion caused 1) a greater incremental increase in peak plasma glucose concentrations (4.2 ± 0.2 vs. 4.8 ± 0.3 mmol/L; P = 0.03), 2) a 20 ± 8% greater incremental increase in insulin area under the curve (AUC) (P < 0.03), 3) a 22 ± 7% greater peak insulin secretion rate (P < 0.02), 4) a 7 ± 4% decrease in insulin clearance (P = 0.04), and 5) a 23 ± 20% decrease in SI (P = 0.01). There were no significant differences between conditions in active glucagon-like peptide 1, glucose-dependent insulinotropic polypeptide, glucagon incremental AUC, or indices of the sensitivity of the β-cell response to glucose.

CONCLUSIONS

These data demonstrate that sucralose affects the glycemic and insulin responses to an oral glucose load in obese people who do not normally consume NNS.

Age and amyloid effects on human central nervous system amyloid-beta kinetics

OBJECTIVE

Age is the single greatest risk factor for Alzheimer's disease (AD), with the incidence doubling every 5 years after age 65. However, our understanding of the mechanistic relationship between increasing age and the risk for AD is currently limited. We therefore sought to determine the relationship between age, amyloidosis, and amyloid-beta (Aβ) kinetics in the central nervous system (CNS) of humans.

METHODS

Aβ kinetics were analyzed in 112 participants and compared to the ages of participants and the amount of amyloid deposition.

RESULTS

We found a highly significant correlation between increasing age and slowed Aβ turnover rates (2.5-fold longer half-life over five decades of age). In addition, we found independent effects on Aβ42 kinetics specifically in participants with amyloid deposition. Amyloidosis was associated with a higher (>50%) irreversible loss of soluble Aβ42 and a 10-fold higher Aβ42 reversible exchange rate.

INTERPRETATION

These findings reveal a mechanistic link between human aging and the risk of amyloidosis, which may be owing to a dramatic slowing of Aβ turnover, increasing the likelihood of protein misfolding that leads to deposition. Alterations in Aβ kinetics associated with aging and amyloidosis suggest opportunities for diagnostic and therapeutic strategies. More generally, this study provides an example of how changes in protein turnover kinetics can be used to detect physiological and pathophysiological changes and may be applicable to other proteinopathies.

Effect of fenofibrate and niacin on intrahepatic triglyceride content, very low-density lipoprotein kinetics, and insulin action in obese subjects with nonalcoholic fatty liver disease

CONTEXT

Nonalcoholic fatty liver disease is associated with risk factors for cardiovascular disease, particularly increased plasma triglyceride (TG) concentrations and insulin resistance. Fenofibrate and extended release nicotinic acid (Niaspan) are used to treat hypertriglyceridemia and can affect fatty acid oxidation and plasma free fatty acid concentrations, which influence intrahepatic triglyceride (IHTG) content and metabolic function.

OBJECTIVE

The objective of the study was to determine the effects of fenofibrate and nicotinic acid therapy on IHTG content and cardiovascular risk factors. EXPERIMENTAL DESIGN AND MAIN OUTCOME MEASURES: We conducted a randomized, controlled trial to determine the effects of fenofibrate (8 wk, 200 mg/d), Niaspan (16 wk, 2000 mg/d), or placebo (8 wk) on IHTG content, very low-density lipoprotein (VLDL) kinetics, and insulin sensitivity.

SETTING AND PARTICIPANTS

Twenty-seven obese subjects with nonalcoholic fatty liver disease (body mass index 36 +/- 1 kg/m(2), IHTG 23 +/- 2%) were studied at Washington University.

RESULTS

Neither fenofibrate nor Niaspan affected IHTG content, but both decreased plasma TG, VLDL-TG, and VLDL-apolipoprotein B concentrations (P < 0.05). Fenofibrate increased VLDL-TG clearance from plasma (33 to 54 ml/min; P < 0.05) but not VLDL-TG secretion. Niaspan decreased VLDL-TG secretion (27 to 15 micromol/min; P < 0.05) without affecting clearance. Both fenofibrate and Niaspan decreased VLDL-apolipoprotein B secretion (1.6 to 1.2 and 1.3 to 0.9 nmol/min, respectively; P < 0.05). Niaspan reduced hepatic, adipose tissue, and muscle insulin sensitivity (P < 0.05), whereas fenofibrate had no effect on insulin action.

CONCLUSIONS

Fenofibrate and Niaspan decrease plasma VLDL-TG concentration without altering IHTG content. However, the mechanism responsible for the change in VLDL-TG concentration is different for each drug; fenofibrate increases plasma VLDL-TG clearance, whereas nicotinic acid decreases VLDL-TG secretion.

Rate of production of plasma and very-low-density lipoprotein (VLDL) apolipoprotein C-III is strongly related to the concentration and level of production of VLDL triglyceride in male subjects with different body weights and levels of insulin sensitivity

Overweight individuals with reduced insulin sensitivity often have mild to moderate hypertriglyceridemia. To investigate the role of apolipoprotein (apo)C-III metabolism in the etiology of hypertriglyceridemia in these individuals, we investigated 10 male subjects with different body weights (body mass index, 24-34 kg/m(2)) and insulin sensitivity (homeostasis model assessment, 4.7-35.0). Total plasma and very-low-density lipoprotein (VLDL) apoC-III kinetics, as well as VLDL triglyceride (TG) and VLDL apoB kinetics, were measured with iv injected stable isotopes. The apoC-III, TG, and apoB levels in VLDL ranged from 2.9-18.2 mg/dl, 0.49-2.89 mmol/liter, and 6.7-29.3 mg/dl, respectively. Mean production rates (PRs) were: VLDL apoC-III, 20.2 +/- 4.1 micromol/d (range, 8.0-44.8); VLDL TG, 26.9 +/- 4.6 mmol/d (range, 10.2-51.1); and VLDL apoB, 4.4 +/- 0.8 micromol/d (range, 1.5-9.1). VLDL apoC-III PRs were significantly correlated with body mass index, homeostasis model assessment, and plasma TG (r = 0.66, P < 0.05; r = 0.80, P < 0.01; r = 0.95, P < 0.001, respectively). Similar correlations were found for plasma apoC-III PRs (r = 0.70, P < 0.05; r = 0.67, P < 0.05; r = 0.80, P < 0.01, respectively). Fractional catabolic rates (FCRs) were not significantly related to metabolic variables. VLDL TG levels were strongly related to VLDL apoC-III levels (r = 0.99, P < 0.001) and VLDL apoC-III PRs (r = 0.94, P < 0.001). VLDL apoC-III levels were more strongly correlated with VLDL TG PRs (r = 0.81, P < 0.01) than with VLDL TG FCRs or VLDL apoB FCRs (r = -0.53, P = 0.12; r = -0.37, P = 0.29). These results suggest that increased hepatic production of VLDL apoC-III is characteristic of subjects with higher body weights and lower levels of insulin sensitivity and is strongly related to the plasma concentration and level of production of VLDL TG.