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

Concentric remodeling and the metabolic-associated steatotic liver disease in patients with type 1 diabetes: an exploratory study

INTRODUCTION

Diabetic cardiomyopathy in young patients with type 1 diabetes (T1D) usually presents as asymptomatic diastolic heart dysfunction with left ventricle (LV) remodeling. Its prevalence seems to be underestimated. One of the factors seemingly influencing LV remodeling is a metabolic-associated steatotic liver disease (MASLD), which was extensively investigated in patients with type 2 diabetes but not with T1D. This study aimed to describe the correlation between MASLD risk and relative wall thickness (RWT) in young patients with T1D without heart failure symptoms or treatment.

MATERIALS AND METHODS

Study participants were recruited at the inpatient diabetology department, in admission order. Patients underwent a set of laboratory tests and echocardiographic examinations. The risk of MASLD was estimated using fatty liver index (FLI). Acquired data was then statistically analyzed.

RESULTS

The study group consisted of 55 patients. 25 participants had RWT > 0.42, suggesting LV remodeling. Study participants did not differ in HbA1c, NT-proBNP, HDL, LDL, non-HDL, and uric acid concentrations. However, patients with RWT > 0.42 had higher FLI (40.97 vs. 13.82, p < 0.01) and BMI (27.3 vs. 22.5, p < 0.01) and differed in transaminase concentrations. Moreover, patients with RWT > 0.42 had significantly higher LV mass index (85.6 vs. 68.2 g/m2) and altered mitral ring velocities. In univariable logistic regression, FLI correlated with LV remodeling risk (OR 1.028, p = 0.05). The optimal cutoff point for FLI predicting the RWT > 0.42 was 26.38 (OR 10.6, p = 0.04, sensitivity 0.857, specificity 0.657).

CONCLUSIONS

FLI correlates with RWT in patients with T1D independently of diabetes metabolic control and hypothetically may support recognizing T1D patients with a higher risk of LV remodeling.

Dysglycemia and liver lipid content determine the relationship of insulin resistance with hepatic OXPHOS capacity in obesity

BACKGROUND & AIMS

Hepatic mitochondrial respiration is higher in steatosis, but lower in overt type 2 diabetes. We hypothesized that hepatic OXPHOS capacity increases with a greater degree of insulin resistance in obesity, independent of other metabolic diseases.

METHODS

We analysed 65 humans without diabetes (BMI 50±7 kg/m2, HbA1c 5.5±0.4%) undergoing bariatric surgery. MASLD stages were assessed by histology, whole-body insulin sensitivity (PREDIcted-M index) by oral glucose tolerance tests, and maximal ADP-stimulated mitochondrial OXPHOS capacity by high-resolution respirometry of liver samples.

RESULTS

Prediabetes was present in 30 participants, and MASLD in 46 participants. Thereof, 25 had metabolic dysfunction-associated steatohepatitis (MASH), and seven had F2-F3 fibrosis. While simple regression did not detect an association of insulin sensitivity with hepatic OXPHOS capacity, interaction analyses revealed that the regression coefficient of OXPHOS capacity depended on fasting plasma glucose (FPG) and liver lipid content. Interestingly, the respective slopes were negative for FPG ≤100 mg/dl, but positive for FPG >100 mg/dl. Liver lipid content displayed similar behavior, with a threshold value of 24%. Post-challenge glycemia affected the association between insulin sensitivity and OXPHOS capacity normalized for citrate synthase activity. Presence of prediabetes affected hepatic insulin signaling, mitochondrial dynamics and fibrosis prevalence, while the presence of MASLD related to higher biomarkers of hepatic inflammation, cell damage and lipid peroxidation in people with normal glucose tolerance.

CONCLUSIONS

Rising liver lipid contents and plasma glucose concentrations, even in the non-diabetic range, are associated with a progressive decline of hepatic mitochondrial adaptation in people with obesity and insulin resistance. CLINTRIALS.

GOV IDENTIFIER

NCT01477957.

Alterations of hepatic energy metabolism in murine models of obesity, diabetes and fatty liver diseases

BACKGROUND

Disturbed hepatic energy metabolism contributes to non-alcoholic fatty liver (NAFLD), but the development of changes over time and obesity- or diabetes-related mechanisms remained unclear.

METHODS

Two-day old male C57BL/6j mice received streptozotocin (STZ) or placebo (PLC) and then high-fat (HFD) or regular chow diet (RCD) from week 4 (W4) to either W8 or W16, yielding control [CTRL = PLC + RCD], diabetes [DIAB = STZ + RCD], obesity [OBES = PLC + HFD] and diabetes-related non-alcoholic steatohepatitis [NASH = STZ + HFD] models. Mitochondrial respiration was measured by high-resolution respirometry and insulin-sensitive glucose metabolism by hyperinsulinemic-euglycemic clamps with stable isotope dilution.

FINDINGS

NASH showed higher steatosis and NAFLD activity already at W8 and liver fibrosis at W16 (all p < 0.01 vs CTRL). Ballooning was increased in DIAB and NASH at W16 (p < 0.01 vs CTRL). At W16, insulin sensitivity was 47%, 58% and 75% lower in DIAB, NASH and OBES (p < 0.001 vs CTRL). Hepatic uncoupled fatty acid oxidation (FAO)-associated respiration was reduced in OBES at W8, but doubled in DIAB and NASH at W16 (p < 0.01 vs CTRL) and correlated with biomarkers of unfolded protein response (UPR), oxidative stress and hepatic expression of certain enzymes (acetyl-CoA carboxylase 2, Acc2; carnitine palmitoyltransferase I, Cpt1a). Tricarboxylic acid cycle (TCA)-driven respiration was lower in OBES at W8 and doubled in DIAB at W16 (p < 0.0001 vs CTRL), which positively correlated with expression of genes related to lipolysis.

INTERPRETATION

Hepatic mitochondria adapt to various metabolic challenges with increasing FAO-driven respiration, which is linked to dysfunctional UPR, systemic oxidative stress, insulin resistance and altered lipid metabolism. In a diabetes model, higher TCA-linked respiration reflected mitochondrial adaptation to greater hepatic lipid turnover.

FUNDING

Funding bodies that contributed to this study were listed in the acknowledgements section.

Impaired Hepatic Mitochondrial Capacity in Nonalcoholic Steatohepatitis Associated With Type 2 Diabetes

OBJECTIVE

Individuals with type 2 diabetes are at higher risk of progression of nonalcoholic fatty liver (steatosis) to steatohepatitis (NASH), fibrosis, and cirrhosis. The hepatic metabolism of obese individuals adapts by upregulation of mitochondrial capacity, which may be lost during the progression of steatosis. However, the role of type 2 diabetes with regard to hepatic mitochondrial function in NASH remains unclear.

RESEARCH DESIGN AND METHODS

We therefore examined obese individuals with histologically proven NASH without (OBE) (n = 30; BMI 52 ± 9 kg/m2) or with type 2 diabetes (T2D) (n = 15; 51 ± 7 kg/m2) as well as healthy individuals without liver disease (CON) (n = 14; 25 ± 2 kg/m2). Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamps with d-[6,6-2H2]glucose. Liver biopsies were used for assessing mitochondrial capacity by high-resolution respirometry and protein expression.

RESULTS

T2D and OBE had comparable hepatic fat content, lobular inflammation, and fibrosis. Oxidative capacity in liver tissue normalized for citrate synthase activity was 59% greater in OBE than in CON, whereas T2D presented with 33% lower complex II-linked oxidative capacity than OBE and higher H2O2 production than CON. Interestingly, those with NASH and hepatic fibrosis score ≥1 had lower oxidative capacity and antioxidant defense than those without fibrosis.

CONCLUSIONS

Loss of hepatic mitochondrial adaptation characterizes NASH and type 2 diabetes or hepatic fibrosis and may thereby favor accelerated disease progression.

Hepatic energy metabolism in a family with a glucokinase gene mutation and dysglycemia

Carriers heterozygous for the D124N (c.370, GAC > AAC in exon 4) variant of GCK not only exhibit reduced insulin-secretion, but also impaired adipose insulin sensitivity, which may shift fatty acids towards the liver. This could contribute to increased hepatic lipid-accumulation and alterations of liver energy metabolism resulting in dysglycemia. ClinicalTrial.gov registration no: NCT01055093.

Novel Antidiabetic Strategies and Diabetologists' Views in Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide with high prevalence, especially in individuals with obesity and type 2 diabetes. Among individuals with type 2 diabetes, the severe insulin resistant subgroup has the greatest risk of NAFLD, likely due to dysfunctional adipose tissue mass but also genetic factors, and may progress earlier to inflammatory and profibrotic nonalcoholic steatohepatitis (NASH). NASH has been associated with increased liver-related as well as cardiovascular morbidity and mortality. International diabetes associations recommend certain screening and treatment strategies for NASH in type 2 diabetes, which, however, bear several limitations such as lack of accurate noninvasive diagnostic tools and targeted treatments. Currently, antihyperglycemic drug concepts based on glucagon-like peptide-1 receptor agonists and sodium glucose cotransporter 2 inhibitors offer metabolic as well as cardiorenal benefits and provide treatment options for both hyperglycemia and NASH in type 2 diabetes.

Allopurinol ameliorates liver injury in type 1 diabetic rats through activating Nrf2

Hyperglycemia-induced oxidative stress plays important roles in the development of non-alcoholic fatty liver disease (NAFLD), which is a common complication in diabetic patients. The Nrf2-Keap1 pathway is important for cell antioxidant protection, while its role in exogenous antioxidant mediated protection against NAFLD is unclear. We thus, postulated that antioxidant treatment with allopurinol (ALP) may attenuate diabetic liver injury and explored the underlying mechanisms. Control (C) and streptozotocin (STZ)-induced diabetes rats (D) were untreated or treated with ALP for 4 weeks starting at 1 week after diabetes induction. Serum levels of alanine aminotransferase (ALT) and aspartate transaminase (AST), production of lipid peroxidation product malondialdehyde (MDA), and serum superoxide dismutase (SOD) were detected. Liver protein expressions of cleaved-caspase 3, IL-1β, nuclear factor-erythroid-2-related factor-2 (Nrf2), heme oxygenase-1 (HO-1), P62, Kelch-like ECH-associated protein 1 (Keap1), and LC3 were analyzed. In vitro, cultured rat normal hepatocytes BRL-3A were grouped to normal glucose (5.5 mM, NG) or high glucose (25 mM, HG) and treated with or without allopurinol (100 µM) for 48 h. Rats in the D group demonstrated liver injury evidenced as increased serum levels of ALT and AST. Diabetes increased apoptotic cell death, enhanced liver protein expressions of cleaved-caspase 3 and IL-1β with concomitantly increased production of MDA while serum SOD content was significantly reduced (all P < 0.05 vs C). In the meantime, protein levels of Nrf2, HO-1, and P62 were reduced while Keap1 and LC3 were increased in the untreated D group as compared to control (P < 0.05 vs C). And all the above alterations were significantly attenuated by ALP. Similar to our findings obtained from in vivo study, we got the same results in in vitro experiments. It is concluded that ALP activates the Nrf2/p62 pathway to ameliorate oxidative stress and liver injury in diabetic rats.

Non-alcoholic fatty liver disease in type 2 diabetes - A specific entity?

Individuals with obesity or type 2 diabetes (T2D) have an increased risk of developing non-alcoholic fatty liver disease (NAFLD). In insulin-resistant states, altered adipose tissue function may be the initial abnormality underlying NAFLD. Hepatic lipid oversupply interferes with insulin signalling and mitochondrial function. In obese individuals, adaptation of hepatic mitochondrial respiration fails with the progression of NAFLD and can activate pro-inflammatory pathways. T2D as well as type 1 diabetes are associated with altered hepatic mitochondrial function. Screening for NAFLD remains challenging especially in those with diabetes because liver enzymes are often in the normal range and the performance of NAFLD scores is limited. Patients with T2D and severe insulin-resistant diabetes (SIRD) have the highest prevalence of NAFLD at diagnosis and the greatest risk of progression. In this subgroup, the single-nucleotide-polymorphism (SNP) rs738409(G) of the patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene is associated with high liver fat content and adipose tissue insulin resistance. This frequent SNP is also known to be associated with lean NAFLD so that genetic testing for this and other SNPs could improve future screening strategies to identify high-risk individuals. Although lifestyle modifications are effective, this approach is limited owing to difficulties with compliance and several classes of drugs are being tested to treat NAFLD. Antihyperglycaemic drugs such as glucagon-like peptide 1 receptor agonists (GLP-1 RA), sodium-glucose cotransporter 2 inhibitors (SGLT2i) and pioglitazone are promising and halt the progression of NAFLD. In conclusion, although NAFLD in diabetes may not be a separate entity, there are specific features to its pathogenesis and clinical management.

Associations among perfluorooctanesulfonic/perfluorooctanoic acid levels, nuclear receptor gene polymorphisms, and lipid levels in pregnant women in the Hokkaido study

The effect of interactions between perfluorooctanesulfonic (PFOS)/perfluorooctanoic acid (PFOA) levels and nuclear receptor genotypes on fatty acid (FA) levels, including those of triglycerides, is not clear understood. Therefore, in the present study, we aimed to analyse the association of PFOS/PFOA levels and single-nucleotide polymorphisms (SNPs) in nuclear receptors with FA levels in pregnant women. We analysed 504 mothers in a birth cohort between 2002 and 2005 in Japan. Serum PFOS/PFOA and FA levels were measured using liquid chromatography-tandem mass spectrometry and gas chromatography-mass spectrometry. Maternal genotypes in PPARA (rs1800234; rs135561), PPARG (rs3856806), PPARGC1A (rs2970847; rs8192678), PPARD (rs1053049; rs2267668), CAR (rs2307424; rs2501873), LXRA (rs2279238) and LXRB (rs1405655; rs2303044; rs4802703) were analysed. When gene-environment interaction was considered, PFOS exposure (log₁₀ scale) decreased palmitic, palmitoleic, and oleic acid levels (log₁₀ scale), with the observed β in the range of - 0.452 to - 0.244; PPARGC1A (rs8192678) and PPARD (rs1053049; rs2267668) genotypes decreased triglyceride, palmitic, palmitoleic, and oleic acid levels, with the observed β in the range of - 0.266 to - 0.176. Interactions between PFOS exposure and SNPs were significant for palmitic acid (P_int = 0.004 to 0.017). In conclusion, the interactions between maternal PFOS levels and PPARGC1A or PPARD may modify maternal FA levels.

Early changes in hepatic energy metabolism and lipid content in recent-onset type 1 and 2 diabetes mellitus

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is associated with abnormal mitochondrial capacity. While oxidative capacity can be increased in steatosis, hepatic ATP decreases in long-standing diabetes. However, longitudinal studies on diabetes-related NAFLD and its relationship to hepatic energy metabolism are lacking.

METHODS

This prospective study comprised volunteers with type 1 (T1DM, n = 30) and type 2 (T2DM, n = 37) diabetes. At diagnosis and 5 years later, we used ¹H/³¹P magnetic resonance spectroscopy to measure hepatocellular lipid (HCL), γATP and inorganic phosphate (Pi) concentrations, and to assess adipose tissue volumes. Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamps.

RESULTS

At diagnosis, individuals with T2DM had higher HCL and adipose tissue volumes, but lower whole-body insulin sensitivity than those with T1DM, despite comparable glycemic control. NAFLD was present in 38% of individuals with T2DM and 7% with T1DM. After 5 years, visceral adipose tissue only increased in individuals with T2DM, while HCL almost doubled in this group (p <0.001), resulting in a 70% prevalence of NAFLD (independent of diabetes treatment). Changes in HCL correlated with adipose tissue volume and insulin resistance (r = 0.50 and r = 0.44, both p <0.05). Pi decreased by 17% and 10% in individuals with T2DM and T1DM (p <0.05), respectively. In T1DM, HCL did not change, whereas γATP decreased by 10% and correlated negatively with glycated hemoglobin (r = -0.56, p <0.05).

CONCLUSIONS

The rapid increase in HCL during the early course of T2DM likely results from enlarging adipose tissue volume and insulin resistance in response to impaired hepatic mitochondrial adaptation. The decrease of phosphorus metabolites in T1DM may be due to pharmacological insulin supply.

LAY SUMMARY

Previous studies suggested that the impaired function of mitochondria, the power plants of cells, can promote fatty liver and type 2 diabetes mellitus. This study now shows that during the first 5 years of type 2 diabetes the increase in body fat content rapidly leads to a doubling of liver fat content, whereas the energy metabolism of the patients' livers progressively declines. These data suggest that fat tissue mass and liver mitochondria have an important role in the development of fatty liver disease in humans with diabetes.

CLINICAL TRIAL NUMBER

NCT01055093.

In vivo absolute quantification of hepatic γ-ATP concentration in mice using 31 P MRS at 11.7 T

Measurement of ATP concentrations and synthesis in humans indicated abnormal hepatic energy metabolism in obesity, non-alcoholic fatty liver disease (NAFLD) and Type 2 diabetes. Further mechanistic studies on energy metabolism require the detailed phenotyping of specific mouse models. Thus, this study aimed to establish and evaluate a robust and fast single voxel ³¹ P MRS method to quantify hepatic γ-ATP concentrations at 11.7 T in three mouse models with different insulin sensitivities and liver fat contents (72-week-old C57BL/6 control mice, 72-week-old insulin resistant sterol regulatory-element binding protein-1c overexpressing (SREBP-1c⁺ ) mice and 10-12-week-old prediabetic non-obese diabetic (NOD) mice). Absolute quantification was performed by employing an external reference and a matching replacement ATP phantom with 3D image selected in vivo spectroscopy ³¹ P MRS. This single voxel ³¹ P MRS method non-invasively quantified hepatic γ-ATP within 17 min and the repeatability tests provided a coefficient of variation of 7.8 ± 1.1%. The mean hepatic γ-ATP concentrations were markedly lower in SREBP-1c⁺ mice (1.14 ± 0.10 mM) than in C57BL/6 mice (2.15 ± 0.13 mM; p < 0.0002) and NOD mice (1.78 ± 0.13 mM; p < 0.006, one-way ANOVA test). In conclusion, this method allows us to rapidly and precisely measure hepatic γ-ATP concentrations, and thereby to non-invasively detect abnormal hepatic energy metabolism in mice with different degrees of insulin resistance and NAFLD. Thus, this ³¹ P MRS will also be useful for future mechanistic as well as therapeutic translational studies in other murine models.

Distinct alterations of gut morphology and microbiota characterize accelerated diabetes onset in nonobese diabetic mice

The rising prevalence of type 1 diabetes (T1D) over the past decades has been linked to lifestyle changes, but the underlying mechanisms are largely unknown. Recent findings point to gut-associated mechanisms in the control of T1D pathogenesis. In nonobese diabetic (NOD) mice, a model of T1D, diabetes development accelerates after deletion of the Toll-like receptor 4 (TLR4). We hypothesized that altered intestinal functions contribute to metabolic alterations, which favor accelerated diabetes development in TLR4-deficient (TLR4^-/-) NOD mice. In 70-90-day-old normoglycemic (prediabetic) female NOD TLR4^+/+ and NOD TLR4^-/- mice, gut morphology and microbiome composition were analyzed. Parameters of lipid metabolism, glucose homeostasis, and mitochondrial respiratory activity were measured in vivo and ex vivo Compared with NOD TLR4^+/+ mice, NOD TLR4^-/- animals showed lower muscle mass of the small intestine, higher abundance of Bacteroidetes, and lower Firmicutes in the large intestine, along with lower levels of circulating short-chain fatty acids (SCFA). These changes are associated with higher body weight, hyperlipidemia, and severe insulin and glucose intolerance, all occurring before the onset of diabetes. These mice also exhibited insulin resistance-related abnormalities of energy metabolism, such as lower total respiratory exchange rates and higher hepatic oxidative capacity. Distinct alterations of gut morphology and microbiota composition associated with reduction of circulating SCFA may contribute to metabolic disorders promoting the progression of insulin-deficient diabetes/T1D development.

Correlates of Insulin-Stimulated Glucose Disposal in Recent-Onset Type 1 and Type 2 Diabetes

CONTEXT AND OBJECTIVE

Not only type 2 diabetes (T2D), but also type 1 diabetes (T1D), can be associated with insulin resistance, as assessed using insulin-stimulated whole-body glucose disposal (M-value). We hypothesized that different factors would affect the M-value at the onset of T1D and T2D.

DESIGN AND PATIENTS

We examined 132 patients with T1D or T2D matched for sex, age, and body mass index with a known diabetes duration of <12 months. Multivariable linear regression analyses were applied to test the associations between glycemic control, blood lipid levels, adiponectin, and proinflammatory immune mediators and the M-value, obtained from the hyperinsulinemic-euglycemic clamp.

RESULTS

Despite comparable age, body mass index, and near-normoglycemic control, the mean M-value was lower in those with T2D than in those with T1D. Patients with T1D had a lower waist/hip ratio and serum triglycerides but higher serum adiponectin than patients with T2D. However, the circulating proinflammatory markers were not different. Even with adjustments for glucose-lowering treatments, the fasting blood glucose correlated negatively with the M-value in both groups. However, gamma-glutamyl transferase-independently of any treatments-correlated negatively only in T2D. In contrast, serum adiponectin correlated positively with the M-values.

CONCLUSIONS

Fasting glycemia correlated with insulin-stimulated glucose disposal in both diabetes types. However, altered liver and adipose tissue function were associated with insulin-stimulated glucose disposal only in T2D, underpinning the specific differences between these diabetes types.

Reduced hepatocellular lipid accumulation and energy metabolism in patients with long standing type 1 diabetes mellitus

The prevalence of obesity and metabolic syndrome increases in patients with type 1 diabetes mellitus (T1DM). In the general population this is linked with ectopic lipid accumulation in liver (HCL) and skeletal muscle (IMCL), representing hallmarks in the development of insulin resistance. Moreover, hepatic mitochondrial activity is lower in newly diagnosed patients with T1DM. If this precedes later development of diabetes related fatty liver disease is currently not known. This study aims to investigate energy metabolism in liver (k_ATP) and skeletal muscle (k_CK) and its impact on HCL, IMCL, cardiac fat depots and heart function in 10 patients with long standing T1DM compared to 11 well-matched controls by ³¹P/¹H magnetic resonance spectroscopy. HCL was almost 70% lower in T1DM compared to controls (6.9 ± 5% vs 2.1 ± 1.3%; p = 0.030). Also k_ATP was significantly reduced (0.33 ± 0.1 s^-1 vs 0.17 ± 0.1 s^-1; p = 0.018). In T1DM, dose of basal insulin strongly correlated with BMI (r = 0.676, p = 0.032) and HCL (r = 0.643, p = 0.045), but not with k_ATP. In the whole cohort, HCL was significantly associated with BMI (r = 0.615, p = 0.005). In skeletal muscle k_CK was lower in patients with T1DM (0.25 ± 0.05 s^-1 vs 0.31 ± 0-04 s^-1; p = 0.039). No significant differences were found in IMCL. Cardiac fat depots as well as heart function were not different. Our results in patients with long standing T1DM show that HCL is lower compared to matched controls, despite reduced energy metabolism in liver and skeletal muscle.

Interorgan Metabolic Crosstalk in Human Insulin Resistance

Excessive energy intake and reduced energy expenditure drive the development of insulin resistance and metabolic diseases such as obesity and type 2 diabetes mellitus. Metabolic signals derived from dietary intake or secreted from adipose tissue, gut, and liver contribute to energy homeostasis. Recent metabolomic studies identified novel metabolites and enlarged our knowledge on classic metabolites. This review summarizes the evidence of their roles as mediators of interorgan crosstalk and regulators of insulin sensitivity and energy metabolism. Circulating lipids such as free fatty acids, acetate, and palmitoleate from adipose tissue and short-chain fatty acids from the gut effectively act on liver and skeletal muscle. Intracellular lipids such as diacylglycerols and sphingolipids can serve as lipotoxins by directly inhibiting insulin action in muscle and liver. In contrast, fatty acid esters of hydroxy fatty acids have been recently shown to exert a series of beneficial effects. Also, ketoacids are gaining interest as potent modulators of insulin action and mitochondrial function. Finally, branched-chain amino acids not only predict metabolic diseases, but also inhibit insulin signaling. Here, we focus on the metabolic crosstalk in humans, which regulates insulin sensitivity and energy homeostasis in the main insulin-sensitive tissues, skeletal muscle, liver, and adipose tissue.

Enhancement of Adiponectin Ameliorates Nonalcoholic Fatty Liver Disease via Inhibition of FoxO1 in Type I Diabetic Rats

Nonalcoholic fatty liver disease (NAFLD) is a common liver disease which has been previously shown to be associated with type 2 diabetes mellitus (T2DM). Recent research has indicated that type 1 diabetes mellitus (T1DM) is also involved in the development of nonalcoholic fatty liver disease, whereas the underlying mechanisms are largely unknown. Forkhead box O1 (FoxO1) and adiponectin (APN) have been proposed to play an important role in the processes in NAFLD in T1DM. We herein investigated the effects of FoxO1 and APN on the development of NAFLD and the underlying mechanism in streptozotocin-induced T1DM. Serum liver enzymes AST, ALT, and triglyceride (TG) were determined by commercially available kits. Blood glucose levels were measured by the OneTouch Ultra glucose meter. Relevant protein expression was tested by Western blot analysis. Results showed that serum AST, ALT, and TG were all significantly increased in T1DM rats, which was ameliorated by application of APN or selective inhibition of FoxO1 with AS1842856. Moreover, APN and AS1842856 both decreased the expression of liver nuclear FoxO1 which was significantly increased in diabetic rats. However, the inhibition of FoxO1 did not alter the expression of APN and its receptors. We also found that Akt1 expression was significantly declined in diabetic rat which was restored by APN and moderately and significantly increased by FoxO1 inhibition. It is concluded that APN ameliorates NAFLD via inhibition of FoxO1 through Akt1/FoxO1 signaling pathway.

Linking Metabolic Disease With the PGC-1α Gly482Ser Polymorphism

Peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) is a highly conserved transcriptional coactivator enriched in metabolically active tissues including liver, adipose, pancreas, and muscle. It plays a role in regulating whole body energy metabolism and its deregulation has been implicated in type 2 diabetes (T2D). A single nucleotide variant of the PPARGC1A gene (rs8192678) is associated with T2D susceptibility, relative risk of obesity and insulin resistance, and lower indices of β cell function. This common polymorphism is within a highly conserved region of the bioactive protein and leads to a single amino acid substitution (glycine 482 to serine). Its prevalence and effects on metabolic parameters appear to vary depending on factors including ethnicity and sex, suggesting important interactions between genetics and cultural/environmental factors and associated disease risk. Interestingly, carriers of the serine allele respond better to some T2D interventions, illustrating the importance of understanding functional impacts of genetic variance on PGC-1α when targeting this pathway for personalized medicine. This review summarizes a growing body of literature surrounding possible links between the PGC-1α Gly482Ser single nucleotide polymorphism and diabetes, with focus on key clinical findings, affected metabolic systems, potential molecular mechanisms, and the influence of geographical or ethnic background on associated risk.

[The informative value of non-invasive liver fibrosis markers in patients with nonalcoholic fatty liver disease]

AIM

To estimate the diagnostic and informative value of clinical and laboratory parameters in the development and progression of liver fibrosis in patients with nonalcoholic fatty liver disease (NAFLD) to enhance efficiency of their treatment.

SUBJECTS AND METHODS

An open-label case-control study included 77 patients with NAFLD. Clinical and laboratory examinations were done. To search for additional noninvasive fibrosis markers, the investigators studied the serum concentrations of insulin, leptin, adiponectin, matrix metalloproteinase-9 (MMP-9) and its inhibitors, such as tissue inhibitor of matrix metalloproteinases 1 (TIMP-1) and TIMP-2. All the patients underwent elastometry to assess the degree of liver fibrosis with the Metavir scale with the use of a Fibroscan machine.

RESULTS

The serum levels of low-density lipoproteins, glucose, MMP-9, and leptin proved to be most informative in assessing the progression of the initial stages (1-2) of fibrosis, as were the increased liver size detected by physical examination, systolic blood pressure, carbohydrate metabolic disorders, alanine/aspartate aminotransferase levels, waist-to-hip ratio, TIMP-1, and TIMP-2 in evaluating the progression of Stage II fibrosis 2 to Stage 3.

CONCLUSION

The clinical and laboratory parameters can serve as reliable noninvasive markers that reflect the progression of fibrotic changes in liver tissue.

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.

Estrogen Signals Through Peroxisome Proliferator-Activated Receptor-γ Coactivator 1α to Reduce Oxidative Damage Associated With Diet-Induced Fatty Liver Disease

BACKGROUND & AIMS

Inefficient fatty acid oxidation in mitochondria and increased oxidative damage are features of non-alcoholic fatty liver disease (NAFLD). In rodent models and patients with NAFLD, hepatic expression of peroxisome proliferator-activated receptor-γ (PPARG) coactivator 1α (PPARGC1A or PGC1A) is inversely correlated with liver fat and disease severity. A common polymorphism in this gene (rs8192678, encoding Gly482Ser) has been associated with NAFLD. We investigated whether reduced expression of PGC1A contributes to development of NAFLD using mouse models, primary hepatocytes, and human cell lines.

METHODS

HepG2 cells were transfected with variants of PPARGC1A and protein and messenger RNA levels were measured. Mice with liver-specific hemizygous or homozygous disruption of Ppargc1a (Ppargc1af/+Alb-cre+/0 and Ppargc1af/f Alb-cre+/0 mice, respectively) were fed regular chow (control) or a high-fat diet supplemented with 30% d-fructose in drinking water (obesogenic diet) for 25-33 weeks. Liver tissues were analyzed by histology and by immunoblotting. Primary hepatocytes were analyzed for insulin signaling, reactive oxygen species, and estrogen response. Luciferase reporter expression was measured in transfected H2.35 cells expressing an estrogen receptor reporter gene, estrogen receptor 1, and/or PGC1A/B.

RESULTS

The serine 482 variant of the human PGC1A protein had a shorter half-life than the glycine 482 variant when expressed in HepG2 cells. Liver tissues from mice with liver-specific hemizygous disruption of Ppargc1a placed on an obesogenic diet expressed increased markers of inflammation and fibrosis and decreased levels of antioxidant enzymes compared with the Ppargc1a+/+ on the same diet. Oxidative damage was observed in livers from Ppargc1af/+Alb-cre+/0 mice of each sex, in a cell-autonomous manner, but was greater in livers from the female mice. Expression of PGC1A in H2.35 cells coactivated estrogen receptor 1 and was required for estrogen-dependent expression of genes that encode antioxidant proteins. These findings could account for the increased liver damage observed in female Ppargc1af/+Alb-cre+/0 mice; while, compensatory increases in PPARG coactivator 1β could prevent oxidative damage associated with complete loss of PGC1A expression in Ppargc1af/fAlb-cre+/0 female mice.

CONCLUSIONS

In mice, loss of estrogen signaling contributes to oxidative damage caused by low levels of PGC1A in liver, exacerbating steatohepatitis associated with diets high in fructose and fat.