Low mitochondrial number and activity have been suggested as underlying factors in obesity, type 2 diabetes, and metabolic syndrome. However, the stage at which mitochondrial dysfunction manifests in ...adipose tissue after the onset of obesity remains unknown. Here we examined subcutaneous adipose tissue (SAT) samples from healthy monozygotic twin pairs, 22.8-36.2 years of age, who were discordant (ΔBMI >3 kg/m(2), mean length of discordance 6.3 ± 0.3 years, n = 26) and concordant (ΔBMI <3 kg/m(2), n = 14) for body weight, and assessed their detailed mitochondrial metabolic characteristics: mitochondrial-related transcriptomes with dysregulated pathways, mitochondrial DNA (mtDNA) amount, mtDNA-encoded transcripts, and mitochondrial oxidative phosphorylation (OXPHOS) protein levels. We report global expressional downregulation of mitochondrial oxidative pathways with concomitant downregulation of mtDNA amount, mtDNA-dependent translation system, and protein levels of the OXPHOS machinery in the obese compared with the lean co-twins. Pathway analysis indicated downshifting of fatty acid oxidation, ketone body production and breakdown, and the tricarboxylic acid cycle, which inversely correlated with adiposity, insulin resistance, and inflammatory cytokines. Our results suggest that mitochondrial biogenesis, oxidative metabolic pathways, and OXPHOS proteins in SAT are downregulated in acquired obesity, and are associated with metabolic disturbances already at the preclinical stage.
A carbohydrate-restricted diet is a widely recommended intervention for non-alcoholic fatty liver disease (NAFLD), but a systematic perspective on the multiple benefits of this diet is lacking. Here, ...we performed a short-term intervention with an isocaloric low-carbohydrate diet with increased protein content in obese subjects with NAFLD and characterized the resulting alterations in metabolism and the gut microbiota using a multi-omics approach. We observed rapid and dramatic reductions of liver fat and other cardiometabolic risk factors paralleled by (1) marked decreases in hepatic de novo lipogenesis; (2) large increases in serum β-hydroxybutyrate concentrations, reflecting increased mitochondrial β-oxidation; and (3) rapid increases in folate-producing Streptococcus and serum folate concentrations. Liver transcriptomic analysis on biopsy samples from a second cohort revealed downregulation of the fatty acid synthesis pathway and upregulation of folate-mediated one-carbon metabolism and fatty acid oxidation pathways. Our results highlight the potential of exploring diet-microbiota interactions for treating NAFLD.
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•A low-carbohydrate diet (LCD) improves liver fat metabolism in NAFLD patients•The LCD promotes rapid shifts in the gut microbiota composition of NAFLD patients•The LCD-induced microbial changes are associated with increased circulating folate•The LCD increases folate-dependent one-carbon metabolism gene expression in liver
Mardinoglu et al. use multi-omics to investigate the effects of a carbohydrate-restricted diet in obese NAFLD patients. They show that the diet improves liver fat metabolism, promotes rapid shifts in the gut microbiota, increases circulating folate, and upregulates expression of genes involved in folate-dependent one-carbon metabolism in the liver.
To elucidate the molecular mechanisms underlying non‐alcoholic fatty liver disease (NAFLD), we recruited 86 subjects with varying degrees of hepatic steatosis (HS). We obtained experimental data on ...lipoprotein fluxes and used these individual measurements as personalized constraints of a hepatocyte genome‐scale metabolic model to investigate metabolic differences in liver, taking into account its interactions with other tissues. Our systems level analysis predicted an altered demand for NAD+ and glutathione (GSH) in subjects with high HS. Our analysis and metabolomic measurements showed that plasma levels of glycine, serine, and associated metabolites are negatively correlated with HS, suggesting that these GSH metabolism precursors might be limiting. Quantification of the hepatic expression levels of the associated enzymes further pointed to altered de novo GSH synthesis. To assess the effect of GSH and NAD+ repletion on the development of NAFLD, we added precursors for GSH and NAD+ biosynthesis to the Western diet and demonstrated that supplementation prevents HS in mice. In a proof‐of‐concept human study, we found improved liver function and decreased HS after supplementation with serine (a precursor to glycine) and hereby propose a strategy for NAFLD treatment.
Synopsis
Personalized modeling and metabolic measurements identified altered GSH and NAD+ metabolism as a prevailing feature in NAFLD. These findings suggested a potential treatment strategy for NAFLD patients based on increased oxidation of fat and increased synthesis of GSH.
We developed personalized genome‐scale metabolic models for NAFLD patients.
We found that altered GSH and NAD+ metabolism is a prevailing feature in NAFLD.
Plasma and liver levels of glycine and serine were lower in NAFLD patients.
Supplementation of precursors for glutathione and NAD+ decreased HS in mice.
Serine supplementation decreased liver fat and improved markers of liver function in humans.
Personalized modeling and metabolic measurements identified altered GSH and NAD+ metabolism as a prevailing feature in NAFLD. These findings suggested a potential treatment strategy for NAFLD patients based on increased oxidation of fat and increased synthesis of GSH.
Nonalcoholic fatty liver disease (i.e., increased intrahepatic triglyceride IHTG content), predisposes to type 2 diabetes and cardiovascular disease. Adipose tissue lipolysis and hepatic de novo ...lipogenesis (DNL) are the main pathways contributing to IHTG. We hypothesized that dietary macronutrient composition influences the pathways, mediators, and magnitude of weight gain-induced changes in IHTG.
We overfed 38 overweight subjects (age 48 ± 2 years, BMI 31 ± 1 kg/m
, liver fat 4.7 ± 0.9%) 1,000 extra kcal/day of saturated (SAT) or unsaturated (UNSAT) fat or simple sugars (CARB) for 3 weeks. We measured IHTG (
H-MRS), pathways contributing to IHTG (lipolysis (
H
glycerol) and DNL (
H
O) basally and during euglycemic hyperinsulinemia), insulin resistance, endotoxemia, plasma ceramides, and adipose tissue gene expression at 0 and 3 weeks.
Overfeeding SAT increased IHTG more (+55%) than UNSAT (+15%,
< 0.05). CARB increased IHTG (+33%) by stimulating DNL (+98%). SAT significantly increased while UNSAT decreased lipolysis. SAT induced insulin resistance and endotoxemia and significantly increased multiple plasma ceramides. The diets had distinct effects on adipose tissue gene expression.
Macronutrient composition of excess energy influences pathways of IHTG: CARB increases DNL, while SAT increases and UNSAT decreases lipolysis. SAT induced the greatest increase in IHTG, insulin resistance, and harmful ceramides. Decreased intakes of SAT could be beneficial in reducing IHTG and the associated risk of diabetes.
NAD+ is a redox-active metabolite, the depletion of which has been proposed to promote aging and degenerative diseases in rodents. However, whether NAD+ depletion occurs in patients with degenerative ...disorders and whether NAD+ repletion improves their symptoms has remained open. Here, we report systemic NAD+ deficiency in adult-onset mitochondrial myopathy patients. We administered an increasing dose of NAD+-booster niacin, a vitamin B3 form (to 750–1,000 mg/day; clinicaltrials.govNCT03973203) for patients and their matched controls for 10 or 4 months, respectively. Blood NAD+ increased in all subjects, up to 8-fold, and muscle NAD+ of patients reached the level of their controls. Some patients showed anemia tendency, while muscle strength and mitochondrial biogenesis increased in all subjects. In patients, muscle metabolome shifted toward controls and liver fat decreased even 50%. Our evidence indicates that blood analysis is useful in identifying NAD+ deficiency and points niacin to be an efficient NAD+ booster for treating mitochondrial myopathy.
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•Mitochondrial myopathy patients have NAD+ deficiency in muscle and blood•Niacin is an efficient NAD+ booster in humans•Niacin improves muscle strength and fatty liver in mitochondrial myopathy•Niacin boosts muscle mitochondrial biogenesis and respiratory chain activity in humans
Pirinen et al. report that niacin, a vitamin B3, can efficiently rescue NAD+ levels in the muscle and blood of patients with mitochondrial myopathy, improving disease signs and muscle strength. NAD+ levels increased also in healthy subjects. The evidence suggests that niacin is an effective NAD+ booster in humans.
Background: Cross-sectional studies have identified a high intake of simple sugars as an important dietary factor predicting nonalcoholic fatty liver disease (NAFLD).Objective: We examined whether ...overfeeding overweight subjects with simple sugars increases liver fat and de novo lipogenesis (DNL) and whether this is reversible by weight loss.Design: Sixteen subjects BMI (kg/m2): 30.6 ± 1.2 were placed on a hypercaloric diet (>1000 kcal simple carbohydrates/d) for 3 wk and, thereafter, on a hypocaloric diet for 6 mo. The subjects were genotyped for rs739409 in the PNPLA3 gene. Before and after overfeeding and after hypocaloric diet, metabolic variables and liver fat (measured by proton magnetic resonance spectroscopy) were measured. The ratio of palmitate (16:0) to linoleate (18:2n−6) in serum and VLDL triglycerides was used as an index of DNL.Results: Carbohydrate overfeeding increased weight (±SEM) by 2% (1.8 ± 0.3 kg; P < 0.0001) and liver fat by 27% from 9.2 ± 1.9% to 11.7 ± 1.9% (P = 0.005). DNL increased in proportion to the increase in liver fat and serum triglycerides in subjects with PNPLA3-148IIbut not PNPLA3-148MM. During the hypocaloric diet, the subjects lost 4% of their weight (3.2 ± 0.6 kg; P < 0.0001) and 25% of their liver fat content (from 11.7 ± 1.9% to 8.8 ± 1.8%; P < 0.05).Conclusions: Carbohydrate overfeeding for 3 wk induced a >10-fold greater relative change in liver fat (27%) than in body weight (2%). The increase in liver fat was proportional to that in DNL. Weight loss restores liver fat to normal. These data indicate that the human fatty liver avidly accumulates fat during carbohydrate overfeeding and support a role for DNL in the pathogenesis of NAFLD. This trial was registered at www.hus.fi as 235780.
Aims/hypothesis
Low mitochondrial activity in adipose tissue is suggested to be an underlying factor in obesity and its metabolic complications. We aimed to find out whether mitochondrial measures ...are downregulated in obesity also in isolated adipocytes.
Methods
We studied young adult monozygotic (MZ) twin pairs discordant (
n
= 14, intrapair difference ΔBMI ≥ 3 kg/m
2
) and concordant (
n
= 5, ΔBMI < 3 kg/m
2
) for BMI, identified from ten birth cohorts of 22- to 36-year-old Finnish twins. Abdominal body fat distribution (MRI), liver fat content (magnetic resonance spectroscopy), insulin sensitivity (OGTT), high-sensitivity C-reactive protein, serum lipids and adipokines were measured. Subcutaneous abdominal adipose tissue biopsies were obtained to analyse the transcriptomics patterns of the isolated adipocytes as well as of the whole adipose tissue. Mitochondrial DNA transcript levels in adipocytes were measured by quantitative real-time PCR. Western blots of oxidative phosphorylation (OXPHOS) protein levels in adipocytes were performed in obese and lean unrelated individuals.
Results
The heavier (BMI 29.9 ± 1.0 kg/m
2
) co-twins of the discordant twin pairs had more subcutaneous, intra-abdominal and liver fat and were more insulin resistant (
p
< 0.01 for all measures) than the lighter (24.1 ± 0.9 kg/m
2
) co-twins. Altogether, 2538 genes in adipocytes and 2135 in adipose tissue were significantly differentially expressed (nominal
p
< 0.05) between the co-twins. Pathway analysis of these transcripts in both isolated adipocytes and adipose tissue revealed that the heavier co-twins displayed reduced expression of genes relating to mitochondrial pathways, a result that was replicated when analysing the pathways behind the most consistently downregulated genes in the heavier co-twins (in at least 12 out of 14 pairs). Consistently upregulated genes in adipocytes were related to inflammation. We confirmed that mitochondrial DNA transcript levels (12S RNA, 16S RNA,
COX1
,
ND5
,
CYTB
), expression of mitochondrial ribosomal protein transcripts and a major mitochondrial regulator
PGC-1α
(also known as
PPARGC1A
) were reduced in the heavier co-twins’ adipocytes (
p
< 0.05). OXPHOS protein levels of complexes I and III in adipocytes were lower in obese than in lean individuals.
Conclusions/interpretation
Subcutaneous abdominal adipocytes in obesity show global expressional downregulation of oxidative pathways, mitochondrial transcripts and OXPHOS protein levels and upregulation of inflammatory pathways.
Data availability
The datasets analysed and generated during the current study are available in the figshare repository,
https://dx.doi.org/10.6084/m9.figshare.3806286.v1
Purpose
Neurofilament light (NfL) is a biomarker reflecting neurodegeneration and acute neuronal injury, and an increase is found following hypoxic brain damage. We assessed the ability of plasma NfL ...to predict outcome in comatose patients after out-of-hospital cardiac arrest (OHCA). We also compared plasma NfL concentrations between patients treated with two different targets of arterial carbon dioxide tension (PaCO
2
), arterial oxygen tension (PaO
2
), and mean arterial pressure (MAP).
Methods
We measured NfL concentrations in plasma obtained at intensive care unit admission and at 24, 48, and 72 h after OHCA. We assessed neurological outcome at 6 months and defined a good outcome as Cerebral Performance Category (CPC) 1–2 and poor outcome as CPC 3–5.
Results
Six-month outcome was good in 73/112 (65%) patients. Forty-eight hours after OHCA, the median NfL concentration was 19 (interquartile range IQR 11–31) pg/ml in patients with good outcome and 2343 (587–5829) pg/ml in those with poor outcome,
p
< 0.001. NfL predicted poor outcome with an area under the receiver operating characteristic curve (AUROC) of 0.98 (95% confidence interval CI 0.97–1.00) at 24 h, 0.98 (0.97–1.00) at 48 h, and 0.98 (0.95–1.00) at 72 h. NfL concentrations were lower in the higher MAP (80–100 mmHg) group than in the lower MAP (65–75 mmHg) group at 48 h (median, 23 vs. 43 pg/ml,
p
= 0.04). PaCO
2
and PaO
2
targets did not associate with NfL levels.
Conclusions
NfL demonstrated excellent prognostic accuracy after OHCA. Higher MAP was associated with lower NfL concentrations.
Background & Aims Our aims were to develop a method to accurately predict non-alcoholic fatty liver disease (NAFLD) and liver fat content based on routinely available clinical and laboratory data and ...to test whether knowledge of the recently discovered genetic variant in the PNPLA3 gene (rs738409) increases accuracy of the prediction. Methods Liver fat content was measured using proton magnetic resonance spectroscopy in 470 subjects, who were randomly divided into estimation (two thirds of the subjects, n = 313) and validation (one third of the subjects, n = 157) groups. Multivariate logistic and linear regression analyses were used to create an NAFLD liver fat score to diagnose NAFLD and liver fat equation to estimate liver fat percentage in each individual. Results The presence of the metabolic syndrome and type 2 diabetes, fasting serum (fS) insulin, fS-aspartate aminotransferase (AST), and the AST/alanine aminotransferase ratio were independent predictors of NAFLD. The score had an area under the receiver operating characteristic curve of 0.87 in the estimation and 0.86 in the validation group. The optimal cut-off point of −0.640 predicted increased liver fat content with sensitivity of 86% and specificity of 71%. Addition of the genetic information to the score improved the accuracy of the prediction by only <1%. Using the same variables, we developed a liver fat equation from which liver fat percentage of each individual could be estimated. Conclusions The NAFLD liver fat score and liver fat equation provide simple and noninvasive tools to predict NAFLD and liver fat content.
Preterm birth at very low birth weight (VLBW, < 1500 g) is associated with an accumulation of cardiovascular and metabolic risk factors from childhood at least to middle age. Small-scale studies ...suggest that this could partly be explained by increased visceral or ectopic fat. We performed magnetic resonance imaging on 78 adults born preterm at VLBW in Finland between 1978 and 1990 and 72 term same-sex siblings as controls, with a mean age of 29 years. We collected T1-weighted images from the abdomen, and magnetic resonance spectra from the liver, subcutaneous abdominal adipose tissue, and tibia. The adipose tissue volumes of VLBW adults did not differ from their term siblings when adjusting for age, sex, and maternal and perinatal factors. The mean differences were as follows: subcutaneous - 0.48% (95% CI - 14.8%, 16.3%), visceral 7.96% (95% CI - 10.4%, 30.1%), and total abdominal fat quantity 1.05% (95% CI - 13.7%, 18.4%). Hepatic triglyceride content was also similar. VLBW individuals displayed less unsaturation in subcutaneous adipose tissue (- 4.74%, 95% CI - 9.2%, - 0.1%) but not in tibial bone marrow (1.68%, 95% CI - 1.86%, 5.35%). VLBW adults displayed similar adipose tissue volumes and hepatic triglyceride content as their term siblings. Previously reported differences could thus partly be due to genetic or environmental characteristics shared between siblings. The VLBW group displayed less unsaturation in subcutaneous abdominal adipose tissue, suggesting differences in its metabolic activity and energy storage.
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