Modulation of Glucokinase Regulatory Protein: A Double-Edged Sword?

Genetic evidence for the effects of glucokinase activation on frailty-related outcomes: A Mendelian randomisation study

AIMS

We aimed to use the Mendelian randomisation (MR) design to investigate the potential causal effects of glucokinase (GK) activation on frailty-related outcomes and to explore the potential mediating effects of metabolic and inflammatory biomarkers.

MATERIALS AND METHODS

Seventeen independent single-nucleotide polymorphisms (SNPs) located within the GCK gene and significantly correlated with the glycated haemoglobin (HbA1c) level were used as genetic proxies for the effect of GK activation. We employed two-sample MR analysis to assess the relationship between genetically proxied GK activation and multifactorial frailty-related outcomes (frailty index, grip strength, walking pace, appendicular lean mass [ALM] and telomere length) We also explored the potential mediating effects using two-step MR.

RESULTS

Genetically proxied GK activation was significantly associated with a lower frailty index (beta: -0.161 per 1% decrease in HbA1c level due to GK activation, 95% confidence interval: -0.282 to -0.040, false discovery rate-adjusted p = 0.011). Additionally, GK activation showed significant associations with increased grip strength, higher ALM, faster walking pace and longer telomere length. GK activation also demonstrated a significant indirect effect on total grip strength and telomere length by reducing C-reactive protein levels (proportion of mediation: 6.79% to 8.21%).

CONCLUSION

Our study provides genetic evidence supporting the causal effects of GK activation on lowering the risk of frailty. These findings suggest that GK activators (GKAs) may aid in the management of frailty and sarcopaenia in people with diabetes; however, future randomized controlled trials are necessary to validate these results and establish their clinical applicability.

Effects of coding variants in the glucokinase regulatory protein gene on hepatic glucose and triglyceride metabolism suggest a gene regulatory function of glucokinase

BACKGROUND

Regulation of glucose metabolism after a meal is the major task of hepatic glucokinase (GCK). Inhibition and nuclear retention of glucokinase during fasting is achieved by glucokinase regulatory protein (GKRP). Compounds disrupting the GCK-GKRP interaction alter glucose but not triglyceride levels, whilst GKRP coding alleles lower glucose but elevate triglycerides. The aim of this study was to identify yet unknown functions of GKRP by examining human variants both rare (p.Q234P, p.H438Y) and common (p.P446L).

METHODS

Fluorescently labelled human GKRP variant and GCK proteins were expressed in hepatoma cells or primary mouse hepatocytes to investigate the subcellular localization of both proteins, cellular glucose uptake, and triglyceride levels. Mutational effects on GKRP protein structure were analyzed with PyMOL. Nuclear-to-cytoplasmic distribution of the GCK-GKRP complex was modeled in MATLAB.

RESULTS

Nuclear localization of the GKRP variants was decreased compared to wild-type. Only H438Y-GKRP still evoked WT-like GCK nuclear accumulation. Nuclear localization of Q234P-GKRP was most impaired and depended on the presence of GCK, which, supported by structural analyses, could stabilize its conformation. Nonetheless, inhibition of glucose uptake was least impaired with Q234P-GKRP. Triglyceride contents related to the glucose uptake of hepatoma cells were disproportionately high for cells expressing wild-type or H438Y-GKRP, the two variants that induced higher nuclear sequestration of GCK.

CONCLUSIONS

Our results, supported by a modeling approach, suggest that GKRP-mediated nuclear localization of GCK has a function in liver metabolism beyond GCK inhibition and sequestration. This needs further elucidation given that GKRP disruptors have been proposed for antihyperglycemic therapy.

Evaluating the Overall Safety of Glucokinase Activators in Patients with Type 2 Diabetes Mellitus

Purpose

This study aimed to assess the overall clinical adverse events (AEs) associated with glucokinase activators (GKAs) in patients with type 2 diabetes mellitus (T2DM).

Methods

We searched MEDLINE, EMBASE, Cochrane Library, and ClinicalTrials.gov databases from their dates of inception to June 6, 2023, for randomized controlled trials (RCTs) that reported safety data for GKAs in patients with T2DM. A random-effects model was used to obtain a summary odds ratio (OR) with associated 95% Confidence Intervals (CIs). Pre-specified subgroup analyses were conducted according to individual GKAs (dorzagliatin and all other GKAs), various controls, follow-up duration, mean duration of diabetes, and the location of clinical research.

Results

17 RCTs enrolling 4,918 patients (3,196 patients received GKAs and 1,722 patients received placebo or other hypoglycemic drugs) were identified. Among the 17 RCTs, dorzagliatin, AZD1656 and MK-0941 in three trials (1,541 patients), five trials (885 patients), and three trials (798 patients), respectively. GKA treatment was associated with a higher risk of any AEs (OR 1.220, 95% CI 1.072-1.389), mild AEs (OR 1.373, 95% CI 1.085-1.738), hyperlipidemia (OR 1.532, 95% CI 1.071-2.189), and hyperuricemia (OR 2.768, 95% CI 1.562-4.903) compared to patients in the control groups. The higher risks of any AEs were mainly attributed to dorzagliatin and MK-0941 and mild AEs mainly attributed to dorzagliatin. Notably, dorzagliatin had significant effects on the occurrence of hyperlipidemia (OR 1.476, 95% CI 1.025-2.126) and hyperuricemia (OR 2.727, 95% CI 1.523-4.883) in the subgroup analyses. No significant effects were detected from other GKAs when regarding hyperlipidemia and hyperuricemia.

Conclusion

The results of our meta-analysis indicated that GKAs were associated with a higher risk of any AEs, mild AEs, hyperlipidemia, and hyperuricemia. Further subgroup analyses revealed that the increased occurrence of hyperlipidemia, and hyperuricemia mainly originated from dorzagliatin treatment.

Compromised chronic efficacy of a glucokinase activator AZD1656 in mouse models for common human GCKR variants

Glucokinase activators (GKAs) have been developed as blood glucose lowering drugs for type 2 diabetes. Despite good short-term efficacy, several GKAs showed a decline in efficacy chronically during clinical trials. The underlying mechanisms remain incompletely understood. We tested the hypothesis that deficiency in the liver glucokinase regulatory protein (GKRP) as occurs with common human GCKR variants affects chronic GKA efficacy. We used a Gckr-P446L mouse model for the GCKR exonic rs1260326 (P446L) variant and the Gckr-del/wt mouse to model transcriptional deficiency to test for chronic efficacy of the GKA, AZD1656 in GKRP-deficient states. In the Gckr-P446L mouse, the blood glucose lowering efficacy of AZD1656 (3 mg/kg body wt) after 2 weeks was independent of genotype. However after 19 weeks, efficacy was maintained in wild-type but declined in the LL genotype, in conjunction with raised hepatic glucokinase activity and without raised liver lipids. Sustained blood glucose lowering efficacy in wild-type mice was associated with qualitatively similar but more modest changes in the liver transcriptome compared with the P446L genotype, consistent with GKA therapy representing a more modest glucokinase excess than the P446L genotype. Chronic treatment with AZD1656 in the Gckr-del/wt mouse was associated with raised liver triglyceride and hepatocyte microvesicular steatosis. The results show that in mouse models of liver GKRP deficiency in conjunction with functional liver glucokinase excess as occurs in association with common human GCKR variants, GKRP-deficiency predisposes to declining efficacy of the GKA in lowering blood glucose and to GKA induced elevation in liver lipids.

Exploring the Impact of Astaxanthin Supplementation in Conjunction with a 12-Week CrossFit Training Regimen on Selected Adipo-Myokines Levels in Obese Males

OBJECTIVE

Obesity is associated with an exacerbated metabolic condition that is mediated through impairing balance in the secretion of some adipo-myokines. Therefore, the objective of the present study was to explore the impact of astaxanthin supplementation in conjunction with a 12-week CrossFit training regimen on some selected adipo-myokines, insulin insensitivity, and serum lipid levels in obese males.

MATERIAL AND METHODS

This study is a randomized control trial design; 60 obese males were randomly divided into four groups of 15, including the control group (CG), supplement group (SG), training group (TG), and combined training and supplement group (TSG). The participants were subjected to 12 weeks of astaxanthin (AST) supplementation [20 mg/d capsule, once/d] or CrossFit training or a combination of both interventions. The training regimen comprised 36 sessions of CrossFit, each lasting 60 min, conducted three times per week. The metabolic indices, body composition, anthropometrical, cardio-respiratory, and also some plasma adipo-myokine factors, including decorin (DCN), activin A, myostatin (MST), transforming growth factor (TGF)-β1, and follistatin (FST), were examined 12 and 72 h before the initiation of the main interventional protocols, and then 72 h after the final session of the training protocol.

RESULTS

There was no significant difference in the baseline data between the groups (p > 0.05). There were significant interactions between group x time for DCN (η2 = 0.82), activin A (η2 = 0.50), FST (η2 = 0.92), MST (η2 = 0.75), and TGFB-1 (η2 = 0.67) (p < 0.001 for all the variables). Significantly changes showed for DCN in TSG compared to TG and SG and also TG compared to SG (p = 0.0001); for activin A in SG compared to TG (p = 0.01) and TSG (p = 0.002); for FST in SG compared to TG and TSG (p = 0.0001), also in TSG compared to TG (p = 0.0001); for MST in SG, TG, and TSG compared to CG (p = 0.0001) and also in TSG compared to SG (p = 0.0001) and TG (p = 0.001); for TGFB-1 in SG, TG, and TSG compared to CG (p = 0.0001) and also TSG compared to SG (p = 0.0001) and TG (p = 0.001).

CONCLUSIONS

The 12-week CrossFit training concurrent with AST supplementation reduced anthropometric and metabolic factors and also serum lipid levels while producing positive changes in body composition and cardiovascular factors. Increased FST and DCN and reduced activin A, MST, and TGF-β1 were other affirmative responses to both interventions.

Hormone and reproductive factors and risk of systemic lupus erythematosus: a Mendelian randomized study

Systemic lupus erythematosus (SLE) is an autoimmune and inflammatory disease with a risk associated with hormonal and reproductive factors. However, the potential causal effects between these factors and SLE remain unclear. A two-sample Mendelian randomization study was conducted using the published summary data from the genome-wide association study database. Five independent genetic variants associated with hormonal and reproductive factors were selected as instrumental variables: age at menarche, age at natural menopause, estradiol, testosterone, and follistatin. To estimate the causal relationship between these exposure factors and disease outcome, we employed the inverse-variance weighted, weighted median, and MR-Egger methods. In addition, we carried out multiple sensitivity analyses to validate model assumptions. Inverse variance weighted showed that there was a causal association between circulating follistatin and SLE risk (OR = 1.38, 95% CI 1.03 to 1.86, P = 0.033). However, no evidence was found that correlation between AAM (OR = 1.04, 95% CI 0.77 to 1.40, P = 0.798), ANM (OR = 0.99, 95% CI 0.92 to 1.06, P = 0.721), E2 (OR = 1.40, 95% CI 0.14 to 13.56, P = 0.772), T (OR = 1.25, 95% CI 0.70 to 2.28, P = 0.459), and SLE risk. Our study revealed that elevated circulating follistatin associates with an increased risk of SLE. This finding suggests that the regulatory signals mediated by circulating follistatin may provide a potential mechanism relevant to the treatment of SLE.

Impaired GK-GKRP interaction rather than direct GK activation worsens lipid profiles and contributes to long-term complications: a Mendelian randomization study

BACKGROUND

Glucokinase (GK) plays a key role in glucose metabolism. In the liver, GK is regulated by GK regulatory protein (GKRP) with nuclear sequestration at low plasma glucose level. Some GK activators (GKAs) disrupt GK-GKRP interaction which increases hepatic cytoplasmic GK level. Excess hepatic GK activity may exceed the capacity of glycogen synthesis with excess triglyceride formation. It remains uncertain whether hypertriglyceridemia associated with some GKAs in previous clinical trials was due to direct GK activation or impaired GK-GKRP interaction.

METHODS

Using publicly available genome-wide association study summary statistics, we selected independent genetic variants of GCKR and GCK associated with fasting plasma glucose (FPG) as instrumental variables, to mimic the effects of impaired GK-GKRP interaction and direct GK activation, respectively. We applied two-sample Mendelian Randomization (MR) framework to assess their causal associations with lipid-related traits, risks of metabolic dysfunction-associated steatotic liver disease (MASLD) and cardiovascular diseases. We verified these findings in one-sample MR analysis using individual-level statistics from the Hong Kong Diabetes Register (HKDR).

RESULTS

Genetically-proxied impaired GK-GKRP interaction increased plasma triglycerides, low-density lipoprotein cholesterol and apolipoprotein B levels with increased odds ratio (OR) of 14.6 (95% CI 4.57-46.4) per 1 mmol/L lower FPG for MASLD and OR of 2.92 (95% CI 1.78-4.81) for coronary artery disease (CAD). Genetically-proxied GK activation was associated with decreased risk of CAD (OR 0.69, 95% CI 0.54-0.88) and not with dyslipidemia. One-sample MR validation in HKDR showed consistent results.

CONCLUSIONS

Impaired GK-GKRP interaction, rather than direct GK activation, may worsen lipid profiles and increase risks of MASLD and CAD. Development of future GKAs should avoid interfering with GK-GKRP interaction.

Metabolomic and genetic architecture of gestational diabetes subtypes

AIMS/HYPOTHESIS

Physiological gestational diabetes mellitus (GDM) subtypes that may confer different risks for adverse pregnancy outcomes have been defined. The aim of this study was to characterise the metabolome and genetic architecture of GDM subtypes to address the hypothesis that they differ between GDM subtypes.

METHODS

This was a cross-sectional study of participants in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study who underwent an OGTT at approximately 28 weeks' gestation. GDM was defined retrospectively using International Association of Diabetes and Pregnancy Study Groups/WHO criteria, and classified as insulin-deficient GDM (insulin secretion <25th percentile with preserved insulin sensitivity) or insulin-resistant GDM (insulin sensitivity <25th percentile with preserved insulin secretion). Metabolomic analyses were performed on fasting and 1 h serum samples in 3463 individuals (576 with GDM). Genome-wide genotype data were obtained for 8067 individuals (1323 with GDM).

RESULTS

Regression analyses demonstrated striking differences between the metabolomes for insulin-deficient or insulin-resistant GDM compared to those with normal glucose tolerance. After adjustment for covariates, 33 fasting metabolites, including 22 medium- and long-chain acylcarnitines, were uniquely associated with insulin-deficient GDM; 23 metabolites, including the branched-chain amino acids and their metabolites, were uniquely associated with insulin-resistant GDM; two metabolites (glycerol and 2-hydroxybutyrate) were associated with the same direction of association with both subtypes. Subtype differences were also observed 1 h after a glucose load. In genome-wide association studies, variants within MTNR1B (rs10830963, p=3.43×10-18, OR 1.55) and GCKR (rs1260326, p=5.17×10-13, OR 1.43) were associated with GDM. Variants in GCKR (rs1260326, p=1.36×10-13, OR 1.60) and MTNR1B (rs10830963, p=1.22×10-9, OR 1.49) demonstrated genome-wide significant association with insulin-resistant GDM; there were no significant associations with insulin-deficient GDM. The lead SNP in GCKR, rs1260326, was associated with the levels of eight of the 25 fasting metabolites that were associated with insulin-resistant GDM and ten of 41 1 h metabolites that were associated with insulin-resistant GDM.

CONCLUSIONS/INTERPRETATION

This study demonstrates that physiological GDM subtypes differ in their metabolome and genetic architecture. These findings require replication in additional cohorts, but suggest that these differences may contribute to subtype-related adverse pregnancy outcomes.

Comprehensive genetic study of the insulin resistance marker TG:HDL-C in the UK Biobank

Insulin resistance (IR) is a well-established risk factor for metabolic disease. The ratio of triglycerides to high-density lipoprotein cholesterol (TG:HDL-C) is a surrogate marker of IR. We conducted a genome-wide association study of the TG:HDL-C ratio in 402,398 Europeans within the UK Biobank. We identified 369 independent SNPs, of which 114 had a false discovery rate-adjusted P value < 0.05 in other genome-wide studies of IR making them high-confidence IR-associated loci. Seventy-two of these 114 loci have not been previously associated with IR. These 114 loci cluster into five groups upon phenome-wide analysis and are enriched for candidate genes important in insulin signaling, adipocyte physiology and protein metabolism. We created a polygenic-risk score from the high-confidence IR-associated loci using 51,550 European individuals in the Michigan Genomics Initiative. We identified associations with diabetes, hyperglyceridemia, hypertension, nonalcoholic fatty liver disease and ischemic heart disease. Collectively, this study provides insight into the genes, pathways, tissues and subtypes critical in IR.

Observational and genetic analyses clarify the relationship between type 2 diabetes mellitus and gallstone disease

Background

The relationship between type 2 diabetes mellitus (T2DM) and gallstone disease (GSD) have been incompletely understood. We aimed to investigate their phenotypic and genetic associations and evaluate the biological mechanisms underlying these associations.

Methods

We first evaluated the phenotypic association between T2DM and GSD using data from the UK Biobank (n>450,000) using a prospective observational design. We then conducted genetic analyses using summary statistics from a meta-analysis of genome-wide association studies of T2DM, with and without adjusting for body mass index (BMI) (Ncase=74,124, Ncontrol=824,006; T2DMadjBMI: Ncase=50,409, Ncontrol=523,897) and GSD (Ncase=43,639, Ncontrol=506,798).

Results

A unidirectional phenotypic association was observed, where individuals with T2DM exhibited a higher GSD risk (hazard ratio (HR)=1.39, P<0.001), but not in the reverse direction (GSD→T2DM: HR=1.00, P=0.912). The positive T2DM-GSD genetic correlation (rg=0.35, P=7.71×10-23) remained even after adjusting for BMI (T2DMadjBMI: rg=0.22, P=4.48×10-10). Mendelian randomization analyses provided evidence of a unidirectional causal relationship (T2DM→GSD: odds ratio (OR)=1.08, P=4.6×10-8; GSD→T2DM: OR=1.02, P=0.48), even after adjusting for important metabolic confounders (OR=1.02, P=0.02). This association was further corroborated through a comprehensive functional analysis reflected by 23 pleiotropic single nucleotide polymorphisms, as well as multiple neural and motor-enriched tissues.

Conclusion

Through comprehensive observational and genetic analyses, our study clarified the causal relationship between T2DM and GSD, but not in the reverse direction. These findings might provide new insights into prevention and treatment strategies for T2DM and GSD.

Interaction between the GCKR rs1260326 variant and serum HDL cholesterol contributes to HOMA-β and ISIMatusda in the middle-aged T2D individuals

This study aims to investigate the correlations between islet function/ insulin resistance and serum lipid levels, as well as to assess whether the strength of such correlations is affected by the GCKR rs1260326 variant in healthy and T2D individuals. We performed an oral glucose tolerance test (OGTT) on 4889 middle-aged adults, including 3135 healthy and 1754 T2D individuals from the REACTION population study in the Nanjing region. We also measured their serum lipid levels and genotyped for rs1260326. We found that serum high-density lipoprotein (HDL) cholesterol and triglyceride (TG) levels were independently correlated with indexes of islet function (HOMA-β and IGI [insulinogenic index]) and insulin resistance (HOMO-IR and ISIMatsuda) in both healthy and T2D individuals. The correlations were significantly decreased in T2D individuals, with significant heterogeneities compared to healthy controls (I2 > 75%, Phet < 0.05). Although no correlation was observed between serum total cholesterol (TC) level and islet function/ insulin resistance in healthy controls, significant correlations were found in T2D individuals, with significant heterogeneity to healthy controls in the correlation with ISIMatsuda(I2 = 85.3%, Phet = 0.009). Furthermore, we found significant interactions of the GCKR rs1260326 variant for the correlations between serum HDL cholesterol and HOMA-β/ISIMatsuda in T2D subjects (P = 0.015 and 0.038, respectively). These findings illustrate that distinct correlations between serum lipid levels and islet function/ insulin resistance occurred in T2D subjects compared to healthy individuals. Common gene variants, such as rs1260326, might interact substantially when studied in specific populations, especially T2D disease status.

GCKR and ADIPOQ gene polymorphisms in women with gestational diabetes mellitus

AIMS

To investigate the associations of GCKR and ADIPOQ variants with the risk of gestational diabetes mellitus (GDM) in Chinese women.

METHODS

GCKR rs1260326, ADIPOQ rs266729, and rs1501299 were selected and genotyped in 519 GDM patients and 498 controls. Candidate SNPs were genotyped using multiplex polymerase chain reaction (PCR) combined with next-generation sequencing methods, and the association of these SNPs with GDM was analyzed.

RESULTS

We found that GCKR rs1260326 was significantly associated with an increased risk of GDM in the allele model, the codominant model (CC vs. TT), the dominant model, the recessive model, and the genotypic model distributions (p = 0.0029, p = 0.0022, p = 0.0402, p = 0.0038, and p = 0.0028, respectively). The rs1260326 polymorphism was shown to be associated with 1 h-OGTT level and gravidity in GDM patients (CC vs. TT: p = 0.0475 and p = 0.0220, respectively). Diastolic blood pressure (DBP) was significantly higher in the GDM patients with the rs266729 GG genotype compared to those with the CC or CG genotype (p = 0.0444 and p = 0.0339, respectively). The DBP of the GDM patients with the rs1501299 GT genotype was lower than that of those with the GG genotype (p = 0.0197). There was a weak linkage disequilibrium value between the GCKR and ADIPOQ SNPs.

CONCLUSIONS

The genes GCKR and ADIPOQ may be involved in the pathophysiology of GDM.

Shared genetic basis informs the roles of polyunsaturated fatty acids in brain disorders

The neural tissue is rich in polyunsaturated fatty acids (PUFAs), components that are indispensable for the proper functioning of neurons, such as neurotransmission. PUFA nutritional deficiency and imbalance have been linked to a variety of chronic brain disorders, including major depressive disorder (MDD), anxiety, and anorexia. However, the effects of PUFAs on brain disorders remain inconclusive, and the extent of their shared genetic determinants is largely unknown. Here, we used genome-wide association summary statistics to systematically examine the shared genetic basis between six phenotypes of circulating PUFAs (N = 114,999) and 20 brain disorders (N = 9,725-762,917), infer their potential causal relationships, identify colocalized regions, and pinpoint shared genetic variants. Genetic correlation and polygenic overlap analyses revealed a widespread shared genetic basis for 77 trait pairs between six PUFA phenotypes and 16 brain disorders. Two-sample Mendelian randomization analysis indicated potential causal relationships for 16 pairs of PUFAs and brain disorders, including alcohol consumption, bipolar disorder (BIP), and MDD. Colocalization analysis identified 40 shared loci (13 unique) among six PUFAs and ten brain disorders. Twenty-two unique variants were statistically inferred as candidate shared causal variants, including rs1260326 (GCKR), rs174564 (FADS2) and rs4818766 (ADARB1). These findings reveal a widespread shared genetic basis between PUFAs and brain disorders, pinpoint specific shared variants, and provide support for the potential effects of PUFAs on certain brain disorders, especially MDD, BIP, and alcohol consumption.

Evaluating the distinct pleiotropic effects of omega-3 fatty acids on type 2 diabetes mellitus: a mendelian randomization study

BACKGROUND

Observational studies and conventional Mendelian randomization (MR) studies showed inconclusive evidence to support the association between omega-3 fatty acids and type 2 diabetes. We aim to evaluate the causal effect of omega-3 fatty acids on type 2 diabetes mellitus (T2DM), and the distinct intermediate phenotypes linking the two.

METHODS

Two-sample MR was performed using genetic instruments derived from a recent genome-wide association study (GWAS) of omega-3 fatty acids (N = 114,999) from UK Biobank and outcome data obtained from a large-scale T2DM GWAS (62,892 cases and 596,424 controls) in European ancestry. MR-Clust was applied to determine clustered genetic instruments of omega-3 fatty acids that influences T2DM. Two-step MR analysis was used to identify potential intermediate phenotypes (e.g. glycemic traits) that linking omega-3 fatty acids with T2DM.

RESULTS

Univariate MR showed heterogenous effect of omega-3 fatty acids on T2DM. At least two pleiotropic effects between omega-3 fatty acids and T2DM were identified using MR-Clust. For cluster 1 with seven instruments, increasing omega-3 fatty acids reduced T2DM risk (OR: 0.52, 95%CI 0.45-0.59), and decreased HOMA-IR (β = - 0.13, SE = 0.05, P = 0.02). On the contrary, MR analysis using 10 instruments in cluster 2 showed that increasing omega-3 fatty acids increased T2DM risk (OR:1.10; 95%CI 1.06-1.15), and decreased HOMA-B (β = - 0.04, SE = 0.01, P = 4.52 × 10^-5). Two-step MR indicated that increasing omega-3 fatty acid levels decreased T2DM risk via decreasing HOMA-IR in cluster 1, while increased T2DM risk via decreasing HOMA-B in cluster 2.

CONCLUSIONS

This study provides evidence to support two distinct pleiotropic effects of omega-3 fatty acids on T2DM risk influenced by different gene clusters, which could be partially explained by distinct effects of omega-3 fatty acids on insulin resistance and beta cell dysfunction. The pleiotropic feature of omega-3 fatty acids variants and its complex relationships with T2DM need to be carefully considered in future genetic and clinical studies.

The GCKR-P446L gene variant predisposes to raised blood cholesterol and lower blood glucose in the P446L mouse-a model for GCKR rs1260326

OBJECTIVES

The Glucokinase Regulatory Protein GKRP, encoded by GCKR, enables acute regulation of liver glucokinase to support metabolic demand. The common human GCKR rs1260326:Pro446 > Leu variant within a large linkage disequilibrium region associates with pleiotropic traits including lower Type 2 diabetes risk and raised blood triglycerides and cholesterol. Whether the GCKR-P446 > L substitution is causal to the raised lipids is unknown. We determined whether mouse GKRP phenocopies the human GKRP:P446 > L substitution and studied a GKRP:P446L knockin mouse to identify physiological consequences to P446 > L.

METHODS

GKRP-deficient hepatocytes were transfected with adenoviral vectors for human or mouse GKRP:446 P or 446 L for cellular comprehensive analysis including transcriptomics consequent to P446 > L. Physiological traits in the diet-challenged P446L mouse were compared with pleiotropic associations at the human rs1260326 locus. Transcriptomics was compared in P446L mouse liver with hepatocytes overexpressing glucokinase or GKRP:446 P/L.

RESULTS

1. P446 > L substitution in mouse or human GKRP similarly compromises protein expressivity of GKRP:446 L, nuclear sequestration of glucokinase and counter-regulation of gene expression. 2. The P446L knockin mouse has lower liver glucokinase and GKRP protein similar to human liver homozygous for rs1260326-446 L. 3. The diet-challenged P446L mouse has lower blood glucose, raised blood cholesterol and altered hepatic cholesterol homeostasis consistent with relative glucokinase-to-GKRP excess, but not raised blood triglycerides.

CONCLUSIONS

Mouse GKRP phenocopies the human GKRP:P446 > L substitution despite the higher affinity for glucokinase of human GKRP. The diet-challenged P446L mouse replicates several traits found in association with the rs1260326 locus on chromosome 2 including raised blood cholesterol, lower blood glucose and lower liver glucokinase and GKRP protein but not raised blood triglycerides.

Evaluation of efficacy and safety of glucokinase activators-a systematic review and meta-analysis

Aims

Glucokinase activators (GKAs) promote the activity of glucokinase (GK) and is under development for the treatment of diabetes. The efficacy and safety of GKAs require evaluation.

Methods

This meta-analysis included randomized controlled trials (RCTs) with a duration of at least 12 weeks conducted in patients with diabetes. The primary objective of this meta-analysis was the difference of hemoglobin A1c (HbA1c) change from baseline to study end between GKA groups and placebo groups. Risk of hypoglycemia and laboratory indicators were also evaluated. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated for the continuous outcomes, and odds ratios (ORs) and 95% CI were calculated for the risk of hypoglycemia.

Results

Data from 13 RCTs with 2,748 participants treated with GKAs and 2,681 control participants were analyzed. In type 2 diabetes, the level of HbA1c decreased greater in patients with GKA treatment compared with placebo (WMD = -0.339%, 95% CI -0.524 to -0.154%, P < 0.001). The OR comparing GKA versus placebo was 1.448 for risk of hypoglycemia (95% CI 0.808 to 2.596, P = 0.214). The WMD comparing GKA versus placebo was 0.322 mmol/L for triglyceride (TG) levels (95% CI 0.136 to 0.508 mmol/L, P = 0.001). When stratified by drug type, selectivity, and study duration, a significant difference was found between groups. In type 1 diabetes, the result of HbA1c change and lipid indicators showed no significant difference between the TPP399 group and the placebo group.

Conclusions

In patients with type 2 diabetes, GKA treatment was associated with a better glycemic control but a significant elevation in TG concentration in general. The efficacy and safety varied with drug type and selectivity.

Systematic review registration

International Prospective Register of Systematic Reviews, identifier CRD42022378342.

Efficacy and safety of novel dual glucokinase activator dorzagliatin in type-2 diabetes A meta-analysis

BACKGROUND & AIMS

Glucokinase has a critical role in regulating glucose homeostasis in humans, and has been a target for diabetes drug development since 1990s. Dorzagliatin is a novel allosteric dual glucokinase activator targeting both pancreatic and hepatic glucokinase. No meta-analysis has analysed the efficacy and safety of dorzagliatin in type-2 diabetes (T2DM). We undertook this meta-analysis to address this knowledge-gap.

METHODS

Electronic databases were searched for RCTs involving T2DM patients receiving dorzagliatin in intervention arm, and placebo/active comparator in control arm. Primary outcome was to evaluate changes in HbA1c. Secondary outcomes were to evaluate alterations in blood glucose parameters, lipids, insulin-resistance and adverse events.

RESULTS

From initially screened 17 articles, data from 3 RCTs (1333 patients) was analysed. Over 12-24 weeks use, dorzagliatin had significantly higher lowering of HbA1c [MD -0.66% (95%CI: -0.74 to -0.59); P < 0.01; I² = 99%], fasting glucose [MD -32.03 mg/dl (95%CI: 45.12 to -18.94); P < 0.01; I² = 100%], 2-h post-prandial glucose [MD -43.49 mg/dl (95%CI: -46.26 to -40.72); P < 0.01; I² = 90%] along with greater number of patients achieving HbA1c<7% [OR 6.01 (95% CI: 2.50-14.46); P < 0.01; I² = 83%], as compared to placebo. Dorzagliatin was associated with significant elevation of triglycerides [MD 0.43 mmol/L (95%CI:0.30-0.56); P < 0.01; I² = 0%], greater occurrence of hyperlipidaemia [RR 1.52 (95% CI:1.05-2.18); P = 0.03; I² = 0%], and increase in body-weight [MD 0.40 kg (95%CI:0.06-0.75); P = 0.03; I² = 0%], compared to placebo. The occurrence of total-adverse-events [RR 1.43 (95%CI:1.11-1.83); P < 0.01; I² = 0%] but not severe adverse-events [RR 0.92 (95%CI:0.54-1.57); P = 0.76; I² = 0%] was significantly higher with dorzagliatin.

CONCLUSION

Dorzagliatin has good glycaemic efficacy and well tolerated over 6-months use. Mild increase in body-weight, serum triglycerides and overall adverse events remain issues of concern warranting further evaluation in longer clinical trials with active controls.

Effect of common genetic variants on the risk of cirrhosis in non-alcoholic fatty liver disease during 20 years of follow-up

BACKGROUND AND AIMS

Several genotypes associate with a worse histopathological profile in patients with non-alcoholic fatty liver disease (NAFLD). Whether genotypes impact long-term outcomes is unclear. We investigated the importance of PNPLA3, TM6SF2, MBOAT7 and GCKR genotype for the development of severe outcomes in NAFLD.

METHOD

DNA samples were collected from 546 patients with NAFLD. Advanced fibrosis was diagnosed by liver biopsy or elastography. Non-alcoholic steatohepatitis (NASH) was histologically defined. Additionally, 5396 controls matched for age, sex and municipality were identified from population-based registers. Events of severe liver disease and all-cause mortality were collected from national registries. Hazard ratios (HRs) adjusted for age, sex, body mass index and type 2 diabetes were estimated with Cox regression.

RESULTS

In NAFLD, the G/G genotype of PNPLA3 was associated with a higher prevalence of NASH at baseline (odds ratio [OR] 3.67, 95% CI = 1.66-8.08), but not with advanced fibrosis (OR 1.81, 95% CI = 0.79-4.14). After up to 40 years of follow-up, the PNPLA3 G/G genotype was associated with a higher rate of severe liver disease (adjusted hazard ratio [aHR] 2.27, 95% CI = 1.15-4.47) compared with the C/C variant. NAFLD patients developed cirrhosis at a higher rate than controls (aHR 9.00, 95% CI = 6.85-11.83). The PNPLA3 G/G genotype accentuated this rate (aHR 23.32, 95% = CI 9.14-59.47). Overall mortality was not affected by any genetic variant.

CONCLUSION

The PNPLA3 G/G genotype is associated with an increased rate of cirrhosis in NAFLD. Our results suggest that assessment of the PNPLA3 genotype is of clinical relevance in patients with NAFLD to individualize monitoring and therapeutic strategies.

Association between de novo lipogenesis susceptibility genes and coronary artery disease

BACKGROUND AND AIMS

Coronary artery disease (CAD) is the principal cause of death in individuals with non-alcoholic fatty liver disease (NAFLD). The aim of this study was to use genetic epidemiology to study the association between de novo lipogenesis (DNL), one of the major pathways leading to NAFLD, and CAD risk.

METHODS AND RESULTS

DNL susceptibility genes were used as instruments and selected using three approaches: 1) genes that are associated with both high serum triglycerides and low sex hormone-binding globulin, both downstream consequences of DNL (unbiased approach), 2) genes that have a known role in DNL (biased approach), and 3) genes that have been associated with serum fatty acids, used as a proxy of DNL. Gene-CAD effect estimates were retrieved from the meta-analysis of CARDIoGRAM and the UK Biobank (∼76014 cases and ∼264785 controls). Effect estimates were clustered using a fixed-effects meta-analysis. Twenty-two DNL susceptibility genes were identified by the unbiased approach, nine genes by the biased approach and seven genes were associated with plasma fatty acids. Clustering of genes selected in the unbiased and biased approach showed a statistically significant association with CAD (OR:1.016, 95%CI:1.012; 1.020 and OR:1.013, 95%CI:1.007; 1.020, respectively), while clustering of fatty acid genes did not (OR:1.004, 95%CI:0.996-1.011). Subsequent exclusion of potential influential outliers did reveal a statistically significant association (OR:1.009, 95%CI:1.000; 1.018).

CONCLUSIONS

DNL susceptibility genes are associated with an increased risk of CAD. These findings suggest that DNL may be involved in the pathogenesis of CAD and favor further development of strategies that target NAFLD through DNL.

Chronotherapy with a glucokinase activator profoundly improves metabolism in obese Zucker rats

Circadian rhythms play a critical role in regulating metabolism, including daily cycles of feeding/fasting. Glucokinase (GCK) is central for whole-body glucose homeostasis and oscillates according to a circadian clock. GCK activators (GKAs) effectively reduce hyperglycemia, but their use is also associated with hypoglycemia, hyperlipidemia, and hepatic steatosis. Given the circadian rhythmicity and natural postprandial activation of GCK, we hypothesized that GKA treatment would benefit from being timed specifically during feeding periods. Acute treatment of obese Zucker rats with the GKA AZD1656 robustly increased flux into all major metabolic pathways of glucose disposal, enhancing glucose elimination. Four weeks of continuous AZD1656 treatment of obese Zucker rats improved glycemic control; however, hepatic steatosis and inflammation manifested. In contrast, timing AZD1656 to feeding periods robustly reduced hepatic steatosis and inflammation in addition to improving glycemia, whereas treatment timed to fasting periods caused overall detrimental metabolic effects. Mechanistically, timing AZD1656 to feeding periods diverted newly synthesized lipid toward direct VLDL secretion rather than intrahepatic storage. In line with increased hepatic insulin signaling, timing AZD1656 to feeding resulted in robust activation of AKT, mTOR, and SREBP-1C after glucose loading, pathways known to regulate VLDL secretion and hepatic de novo lipogenesis. In conclusion, intermittent AZD1656 treatment timed to feeding periods promotes glucose disposal when needed the most, restores metabolic flexibility and hepatic insulin sensitivity, and thereby avoids hepatic steatosis. Thus, chronotherapeutic approaches may benefit the development of GKAs and other drugs acting on metabolic targets.

Fructose 1-phosphate, an evolutionary signaling molecule of abundancy

Evidence is accumulating that specifically fructose exerts adverse cardiometabolic effects in humans. Recent experimental studies have shown that fructose not only serves as a substrate for, among others, intrahepatic lipid formation, but also has a signaling function. It is postulated that fructose 1-phosphate (F1-P) has evolved as a signaling molecule of abundancy that stimulates nutrient absorption, lipid storage, and reproduction. Such a role would provide an explanation for why fructose contributes to the pathogenesis of evolutionary mismatch diseases, including nonalcoholic fatty liver disease (NAFLD), cardiovascular disease, polycystic ovary syndrome (PCOS), and colorectal cancer, in the current era of nutritional abundance. It is anticipated that reducing F1-P, by either pharmacological inhibition of ketohexokinase (KHK) or societal measures, will mitigate the risk of these diseases.

Evaluating the impact of glucokinase activation on risk of cardiovascular disease: a Mendelian randomisation analysis

BACKGROUND

Glucokinase activators (GKAs) are an emerging class of glucose lowering drugs that activate the glucose-sensing enzyme glucokinase (GK). Pending formal cardiovascular outcome trials, we applied two-sample Mendelian randomisation (MR) to investigate the impact of GK activation on risk of cardiovascular diseases.

METHODS

We used independent genetic variants in or around the glucokinase gene meanwhile associated with HbA_1c at genome-wide significance (P < 5 × 10^-8) in the Meta-Analyses of Glucose and Insulin-related traits Consortium study (N = 146,806; European ancestry) as instrumental variables (IVs) to mimic the effects of GK activation. We assessed the association between genetically proxied GK activation and the risk of coronary artery disease (CAD; 122,733 cases and 424,528 controls), peripheral arterial disease (PAD; 7098 cases and 206,541 controls), stroke (40,585 cases and 406,111 controls) and heart failure (HF; 47,309 cases and 930,014 controls), using genome-wide association study summary statistics of these outcomes in Europeans. We compared the effect estimates of genetically proxied GK activation with estimates of genetically proxied lower HbA_1c on the same outcomes. We repeated our MR analyses in East Asians as validation.

RESULTS

Genetically proxied GK activation was associated with reduced risk of CAD (OR 0.38 per 1% lower HbA_1c, 95% CI 0.29-0.51, P = 8.77 × 10^-11) and HF (OR 0.54 per 1% lower HbA_1c, 95% CI 0.41-0.73, P = 3.55 × 10^-5). The genetically proxied protective effects of GKA on CAD and HF exceeded those due to non-targeted HbA_1c lowering. There was no causal relationship between genetically proxied GK activation and risk of PAD or stroke. The estimates in sensitivity analyses and in East Asians were generally consistent.

CONCLUSIONS

GKAs may protect against CAD and HF which needs confirmation by long-term clinical trials.

Novel insights in intestinal and hepatic fructose metabolism: from mice to men

PURPOSE OF REVIEW

The rise in fructose consumption in parallel with the current epidemic of obesity and related cardiometabolic disease requires a better understanding of the pathophysiological pathways that are involved.

RECENT FINDINGS

Animal studies have shown that fructose has various effects on the intestines that subsequently affect intrahepatic lipid accumulation and inflammation. Fructose adversely affects the gut microbiome - as a producer of endotoxins and intermediates of de novo lipogenesis - and intestinal barrier function. Furthermore, intestinal fructose metabolism shields fructose away from the liver. Finally, fructose 1-phosphate (F1-P) serves as a signal molecule that promotes intestinal cell survival and, consequently, intestinal absorption capacity. Intervention and epidemiological studies have convincingly shown that fructose, particularly derived from sugar-sweetened beverages, stimulates de novo lipogenesis and intrahepatic lipid accumulation in humans. Of interest, individuals with aldolase B deficiency, who accumulate F1-P, are characterized by a greater intrahepatic lipid content. First phase II clinical trials have recently shown that reduction of F1-P, by inhibition of ketohexokinase, reduces intrahepatic lipid content.

SUMMARY

Experimental evidence supports current measures to reduce fructose intake, for example by the implementation of a tax on sugar-sweetened beverages, and pharmacological inhibition of fructose metabolism to reduce the global burden of cardiometabolic disease.

The genetic interactions between non-alcoholic fatty liver disease and cardiovascular diseases

The ongoing debate on whether non-alcoholic fatty liver disease (NAFLD) is an active contributor or an innocent bystander in the development of cardiovascular disease (CVD) has sparked interests in understanding the common mediators between the two biologically distinct entities. This comprehensive review identifies and curates genetic studies of NAFLD overlapping with CVD, and describes the colinear as well as opposing correlations between genetic associations for the two diseases. Here, CVD described in relation to NAFLD are coronary artery disease, cardiomyopathy and atrial fibrillation. Unique findings of this review included certain NAFLD susceptibility genes that possessed cardioprotective properties. Moreover, the complex interactions of genetic and environmental risk factors shed light on the disparity in genetic influence on NAFLD and its incident CVD. This serves to unravel NAFLD-mediated pathways in order to reduce CVD events, and helps identify targeted treatment strategies, develop polygenic risk scores to improve risk prediction and personalise disease prevention.

Serum sex hormone-binding globulin levels are reduced and inversely associated with intrahepatic lipid content and saturated fatty acid fraction in adult patients with glycogen storage disease type 1a

PURPOSE

De novo lipogenesis has been inversely associated with serum sex hormone-binding globulin (SHBG) levels. However, the directionality of this association has remained uncertain. We, therefore, studied individuals with glycogen storage disease type 1a (GSD1a), who are characterized by a genetic defect in glucose-6-phosphatase resulting in increased rates of de novo lipogenesis, to assess the downstream effect on serum SHBG levels.

METHODS

A case-control study comparing serum SHBG levels in patients with GSD1a (n = 10) and controls matched for age, sex, and BMI (n = 10). Intrahepatic lipid content and saturated fatty acid fraction were quantified by proton magnetic resonance spectroscopy.

RESULTS

Serum SHBG levels were statistically significantly lower in patients with GSD1a compared to the controls (p = 0.041), while intrahepatic lipid content and intrahepatic saturated fatty acid fraction-a marker of de novo lipogenesis-were significantly higher in patients with GSD1a (p = 0.001 and p = 0.019, respectively). In addition, there was a statistically significant, inverse association of intrahepatic lipid content and saturated fatty acid fraction with serum SHBG levels in patients and controls combined (β: - 0.28, 95% CI: - 0.47;- 0.09 and β: - 0.02, 95% CI: - 0.04;- 0.01, respectively).

CONCLUSION

Patients with GSD1a, who are characterized by genetically determined higher rates of de novo lipogenesis, have lower serum SHBG levels than controls.

A multiancestry genome-wide association study of unexplained chronic ALT elevation as a proxy for nonalcoholic fatty liver disease with histological and radiological validation

Nonalcoholic fatty liver disease (NAFLD) is a growing cause of chronic liver disease. Using a proxy NAFLD definition of chronic elevation of alanine aminotransferase (cALT) levels without other liver diseases, we performed a multiancestry genome-wide association study (GWAS) in the Million Veteran Program (MVP) including 90,408 cALT cases and 128,187 controls. Seventy-seven loci exceeded genome-wide significance, including 25 without prior NAFLD or alanine aminotransferase associations, with one additional locus identified in European American-only and two in African American-only analyses (P < 5 × 10-8). External replication in histology-defined NAFLD cohorts (7,397 cases and 56,785 controls) or radiologic imaging cohorts (n = 44,289) replicated 17 single-nucleotide polymorphisms (SNPs) (P < 6.5 × 10-4), of which 9 were new (TRIB1, PPARG, MTTP, SERPINA1, FTO, IL1RN, COBLL1, APOH and IFI30). Pleiotropy analysis showed that 61 of 77 multiancestry and all 17 replicated SNPs were jointly associated with metabolic and/or inflammatory traits, revealing a complex model of genetic architecture. Our approach integrating cALT, histology and imaging reveals new insights into genetic liability to NAFLD.

Targeting human Glucokinase for the treatment of type 2 diabetes: an overview of allosteric Glucokinase activators

Diabetes mellitus is a worldwide impacting disorder and the ratio through which the number of diabetic patients had increased worldwide, puts medical professionals to serious stress for its effective management. Due to its polygenic origin and involvement of multiple genes to its pathophysiology, leads to understanding of this ailment more complex. It seems that current interventions, such as dietary changes, life style changes and drug therapy such as oral hypoglycaemics and insulin, are unable to halt the trend. There are various novel and emerging targets on which the researchers are paying attention to combat with this ailment successfully. Human glucokinase (GK) enzyme is one of these novel and emerging targets for management of diabetes. Its availability in the pancreas and liver cells makes this target more lucrative. GK's presence in the pancreatic and hepatic cells plays a very important function for the management of glucose homoeostasis. Small molecules that activate GK allosterically provide an alternative strategy for restoring/improving glycaemic regulation, especially in type 2 diabetic patients. Although after enduring many setbacks in the development of the GK activators, interest has been renewed especially due to introduction of novel dual acting GK activator dorzagliatin, and a novel hepato-selective GK activator, TTP399. This review article has been formulated to discuss importance of GK in glucose homeostasis, recent updates on small molecules of GK activators, clinical status of GK activators and challenges in development of GK activators.

Type 2 Diabetes Partitioned Polygenic Scores Associate With Disease Outcomes in 454,193 Individuals Across 13 Cohorts

OBJECTIVE

Type 2 diabetes (T2D) has heterogeneous patient clinical characteristics and outcomes. In previous work, we investigated the genetic basis of this heterogeneity by clustering 94 T2D genetic loci using their associations with 47 diabetes-related traits and identified five clusters, termed β-cell, proinsulin, obesity, lipodystrophy, and liver/lipid. The relationship between these clusters and individual-level metabolic disease outcomes has not been assessed.

RESEARCH DESIGN AND METHODS

Here we constructed individual-level partitioned polygenic scores (pPS) for these five clusters in 12 studies from the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium and the UK Biobank (n = 454,193) and tested for cross-sectional association with T2D-related outcomes, including blood pressure, renal function, insulin use, age at T2D diagnosis, and coronary artery disease (CAD).

RESULTS

Despite all clusters containing T2D risk-increasing alleles, they had differential associations with metabolic outcomes. Increased obesity and lipodystrophy cluster pPS, which had opposite directions of association with measures of adiposity, were both significantly associated with increased blood pressure and hypertension. The lipodystrophy and liver/lipid cluster pPS were each associated with CAD, with increasing and decreasing effects, respectively. An increased liver/lipid cluster pPS was also significantly associated with reduced renal function. The liver/lipid cluster includes known loci linked to liver lipid metabolism (e.g., GCKR, PNPLA3, and TM6SF2), and these findings suggest that cardiovascular disease risk and renal function may be impacted by these loci through their shared disease pathway.

CONCLUSIONS

Our findings support that genetically driven pathways leading to T2D also predispose differentially to clinical outcomes.

Elevated circulating follistatin associates with an increased risk of type 2 diabetes

The hepatokine follistatin is elevated in patients with type 2 diabetes (T2D) and promotes hyperglycemia in mice. Here we explore the relationship of plasma follistatin levels with incident T2D and mechanisms involved. Adjusted hazard ratio (HR) per standard deviation (SD) increase in follistatin levels for T2D is 1.24 (CI: 1.04–1.47, p < 0.05) during 19-year follow-up (n = 4060, Sweden); and 1.31 (CI: 1.09–1.58, p < 0.01) during 4-year follow-up (n = 883, Finland). High circulating follistatin associates with adipose tissue insulin resistance and non-alcoholic fatty liver disease (n = 210, Germany). In human adipocytes, follistatin dose-dependently increases free fatty acid release. In genome-wide association study (GWAS), variation in the glucokinase regulatory protein gene (GCKR) associates with plasma follistatin levels (n = 4239, Sweden; n = 885, UK, Italy and Sweden) and GCKR regulates follistatin secretion in hepatocytes in vitro. Our findings suggest that GCKR regulates follistatin secretion and that elevated circulating follistatin associates with an increased risk of T2D by inducing adipose tissue insulin resistance.

Follistatin promotes in type 2 diabetes (T2D) pathogenesis in model animals and is elevated in patients with T2D. Here the authors report that plasma follistatin associates with increased risk of incident T2D in two longitudinal cohorts, and show that follistatin regulates insulin-induced suppression lipolysis in cultured human adipocytes.

Sex hormone-binding globulin: biomarker and hepatokine?

Over the past decade, there have been important breakthroughs in our understanding of the regulation and function of sex hormone-binding globulin (SHBG). A recent genome-wide association and Mendelian randomization study has provided new insights at the population level. Thorough study of genetic variants affecting serum SHBG has identified de novo lipogenesis as one of the mechanistic links between the metabolic syndrome and reduced serum SHBG levels in humans. Furthermore, careful deduction of the Mendelian randomization results suggests a direct, causal role for SHBG in the pathogenesis of type 2 diabetes, as a hepatokine, in women. These findings prompt the development of SHBG-raising therapies as a means to prevent or treat disorders such as type 2 diabetes and polycystic ovary syndrome.

Relationship between AGT rs2493132 polymorphism and the risk of coronary artery disease in patients with NAFLD in the Chinese Han population

Objective

To investigate the relationship between angiotensin (AGT) rs2493132 gene polymorphism and the risk of developing non-alcoholic fatty liver disease (NAFLD) and coronary artery disease (CAD) in the Chinese Han population.

Methods

Polymerase chain reaction was performed to determine AGT genotypes. Anthropometric and clinical data were investigated and statistically analyzed in the clinical laboratory department of Qingdao Municipal Hospital.

Results

The AGT rs2493132 CT + TT genotype was an important risk factor for CAD in patients with NAFLD and NAFLD + CAD in healthy controls. The AGT rs2493132 T allele increased the risk of NAFLD + CAD in healthy controls. The AGT rs2493132 CT + TT genotype and T allele also significantly increased the risk of CAD in patients with NAFLD after adjustments for age, sex, and body mass index. In addition, AGT rs2493132 T allele carriers showed higher total cholesterol (TC) and low-density lipoprotein (LDL) levels compared with non-carriers.

Conclusions

The AGT rs2493132 CT + TT genotype and T allele significantly increased the risk of developing CAD in patients with NAFLD in the Chinese Han population. The AGT rs2493132 T allele was associated with increased serum TC and LDL levels.

SIRT2 ablation inhibits glucose-stimulated insulin secretion through decreasing glycolytic flux

Rationale: Sirtuins are NAD⁺-dependent protein deacylases known to have protective effects against age-related diseases such as diabetes, cancer, and neurodegenerative disease. SIRT2 is the only primarily cytoplasmic isoform and its overall role in glucose homeostasis remains uncertain.

Methods: SIRT2-knockout (KO) rats were constructed to evaluate the role of SIRT2 in glucose homeostasis. The effect of SIRT2 on β-cell function was detected by investigating the morphology, insulin secretion, and metabolomic state of islets. The deacetylation and stabilization of GKRP in β-cells by SIRT2 were determined by western blot, adenoviral infection, and immunoprecipitation.

Results: SIRT2-KO rats exhibited impaired glucose tolerance and glucose-stimulated insulin secretion (GSIS), without change in insulin sensitivity. SIRT2 deficiency or inhibition by AGK2 decreased GSIS in isolated rat islets, with lowered oxygen consumption rate. Adenovirus-mediated overexpression of SIRT2 enhanced insulin secretion from rat islets. Metabolomics analysis revealed a decrease in metabolites of glycolysis and tricarboxylic acid cycle in SIRT2-KO islets compared with control islets. Our study further demonstrated that glucokinase regulatory protein (GKRP), an endogenous inhibitor of glucokinase (GCK), was expressed in rat islets. SIRT2 overexpression deacetylated GKRP in INS-1 β-cells. SIRT2 knockout or inhibition elevated GKRP protein stability in islet β-cells, leading to an increase in the interaction of GKRP and GCK. On the contrary, SIRT2 inhibition promoted the protein degradation of ALDOA, a glycolytic enzyme.

Conclusions: SIRT2 ablation inhibits GSIS through blocking GKRP protein degradation and promoting ALDOA protein degradation, resulting in a decrease in glycolytic flux.

NAFLD, and cardiovascular and cardiac diseases: Factors influencing risk, prediction and treatment

BACKGROUND AND AIM

Non-alcoholic fatty liver disease (NAFLD), affecting up to around 30% of the world's adult population, causes considerable liver-related and extrahepatic morbidity and mortality. Strong evidence indicates that NAFLD (especially its more severe forms) is associated with a greater risk of all-cause mortality, and the predominant cause of mortality in this patient population is cardiovascular disease (CVD). This narrative review aims to discuss the strong association between NAFLD and increased risk of cardiovascular, cardiac and arrhythmic complications. Also discussed are the putative mechanisms linking NAFLD to CVD and other cardiac/arrhythmic complications, with a brief summary of CVD risk prediction/stratification and management of the increased CVD risk observed in patients with NAFLD.

RESULTS

NAFLD is associated with an increased risk of CVD events and other cardiac complications (left ventricular hypertrophy, valvular calcification, certain arrhythmias) independently of traditional CVD risk factors. The magnitude of risk of CVD and other cardiac/arrhythmic complications parallels the severity of NAFLD (especially liver fibrosis severity). There are most likely multiple underlying mechanisms through which NAFLD may increase risk of CVD and cardiac/arrhythmic complications. Indeed, NAFLD exacerbates hepatic and systemic insulin resistance, promotes atherogenic dyslipidaemia, induces hypertension, and triggers synthesis of proatherogenic, procoagulant and proinflammatory mediators that may contribute to the development of CVD and other cardiac/arrhythmic complications.

CONCLUSION

Careful assessment of CVD risk is mandatory in patients with NAFLD for primary prevention of CVD, together with pharmacological treatment for coexisting CVD risk factors.

Glucose metabolism-related gene polymorphisms as the risk predictors of type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a complex polygenic metabolic disease characterized by elevated blood glucose. Multiple environmental and genetic factors can increase the risk of T2DM and its complications, and genetic polymorphisms are no exception. This review is mainly focused on the related genes involved in glucose metabolic, including G6PC2, GCK, GCKR and OCT3. In this review, we have summarized the results reported globally and found that the genetic variants of GCK and OCT3 genes is a risk factor for T2DM while G6PC2 and GCKR genes are controversial in different ethnic groups. Hopefully, this summary could possibly help researchers and physicians understand the mechanism of T2DM so as to diagnose and even prevent T2DM at early time.

Chronic glucokinase activator treatment activates liver Carbohydrate response element binding protein and improves hepatocyte ATP homeostasis during substrate challenge

AIM

To test the hypothesis that glucokinase activators (GKAs) induce hepatic adaptations that alter intra-hepatocyte metabolite homeostasis.

METHODS

C57BL/6 mice on a standard rodent diet were treated with a GKA (AZD1656) acutely or chronically. Hepatocytes were isolated from the mice after 4 or 8 weeks of treatment for analysis of cellular metabolites and gene expression in response to substrate challenge.

RESULTS

Acute exposure of mice to AZD1656 or a liver-selective GKA (PF-04991532), before a glucose tolerance test, or challenge of mouse hepatocytes with GKAs ex vivo induced various Carbohydrate response element binding protein (ChREBP) target genes, including Carbohydrate response element binding protein beta isoform (ChREBP-β), Gckr and G6pc. Both glucokinase activation and ChREBP target gene induction by PF-04991532 were dependent on the chirality of the molecule, confirming a mechanism linked to glucokinase activation. Hepatocytes from mice treated with AZD1656 for 4 or 8 weeks had lower basal glucose 6-phosphate levels and improved ATP homeostasis during high substrate challenge. They also had raised basal ChREBP-β mRNA and AMPK-α mRNA (Prkaa1, Prkaa2) and progressively attenuated substrate induction of some ChREBP target genes and Prkaa1 and Prkaa2.

CONCLUSIONS

Chronic GKA treatment of C57BL/6 mice for 8 weeks activates liver ChREBP and improves the resilience of hepatocytes to compromised ATP homeostasis during high-substrate challenge. These changes are associated with raised mRNA levels of ChREBP-β and both catalytic subunits of AMP-activated protein kinase.

Genome-wide association study of non-alcoholic fatty liver and steatohepatitis in a histologically characterised cohort☆

BACKGROUND & AIMS

Genetic factors associated with non-alcoholic fatty liver disease (NAFLD) remain incompletely understood. To date, most genome-wide association studies (GWASs) have adopted radiologically assessed hepatic triglyceride content as the reference phenotype and so cannot address steatohepatitis or fibrosis. We describe a GWAS encompassing the full spectrum of histologically characterised NAFLD.

METHODS

The GWAS involved 1,483 European NAFLD cases and 17,781 genetically matched controls. A replication cohort of 559 NAFLD cases and 945 controls was genotyped to confirm signals showing genome-wide or close to genome-wide significance.

RESULTS

Case-control analysis identified signals showing p values ≤5 × 10^-8 at 4 locations (chromosome [chr] 2 GCKR/C2ORF16; chr4 HSD17B13; chr19 TM6SF2; chr22 PNPLA3) together with 2 other signals with p <1 × 10^-7 (chr1 near LEPR and chr8 near IDO2/TC1). Case-only analysis of quantitative traits showed that the PNPLA3 signal (rs738409) had genome-wide significance for steatosis, fibrosis and NAFLD activity score and a new signal (PYGO1 rs62021874) had close to genome-wide significance for steatosis (p = 8.2 × 10^-8). Subgroup case-control analysis for NASH confirmed the PNPLA3 signal. The chr1 LEPR single nucleotide polymorphism also showed genome-wide significance for this phenotype. Considering the subgroup with advanced fibrosis (≥F3), the signals on chr2, chr19 and chr22 maintained their genome-wide significance. Except for GCKR/C2ORF16, the genome-wide significance signals were replicated.

CONCLUSIONS

This study confirms PNPLA3 as a risk factor for the full histological spectrum of NAFLD at genome-wide significance levels, with important contributions from TM6SF2 and HSD17B13. PYGO1 is a novel steatosis modifier, suggesting that Wnt signalling pathways may be relevant in NAFLD pathogenesis.

LAY SUMMARY

Non-alcoholic fatty liver disease is a common disease where excessive fat accumulates in the liver and may result in cirrhosis. To understand who is at risk of developing this disease and suffering liver damage, we undertook a genetic study to compare the genetic profiles of people suffering from fatty liver disease with genetic profiles seen in the general population. We found that particular sequences in 4 different areas of the human genome were seen at different frequencies in the fatty liver disease cases. These sequences may help predict an individual's risk of developing advanced disease. Some genes where these sequences are located may also be good targets for future drug treatments.

Metabolomic and genetic associations with insulin resistance in pregnancy

AIMS/HYPOTHESIS

Our study aimed to integrate maternal metabolic and genetic data related to insulin sensitivity during pregnancy to provide novel insights into mechanisms underlying pregnancy-induced insulin resistance.

METHODS

Fasting and 1 h serum samples were collected from women in the Hyperglycemia and Adverse Pregnancy Outcome study who underwent an OGTT at ∼28 weeks' gestation. We obtained targeted and non-targeted metabolomics and genome-wide association data from 1600 and 4528 mothers, respectively, in four ancestry groups (Northern European, Afro-Caribbean, Mexican American and Thai); 1412 of the women had both metabolomics and genome-wide association data. Insulin sensitivity was calculated using a modified insulin sensitivity index that included fasting and 1 h glucose and C-peptide levels after a 75 g glucose load.

RESULTS

Per-metabolite and network analyses across the four ancestries identified numerous metabolites associated with maternal insulin sensitivity before and 1 h after a glucose load, ranging from amino acids and carbohydrates to fatty acids and lipids. Genome-wide association analyses identified 12 genetic variants in the glucokinase regulatory protein gene locus that were significantly associated with maternal insulin sensitivity, including a common functional missense mutation, rs1260326 (β = -0.2004, p = 4.67 × 10^-12 in a meta-analysis across the four ancestries). This SNP was also significantly associated with multiple fasting and 1 h metabolites during pregnancy, including fasting and 1 h triacylglycerols and 2-hydroxybutyrate and 1 h lactate, 2-ketoleucine/ketoisoleucine and palmitoleic acid. Mediation analysis suggested that 1 h palmitoleic acid contributes, in part, to the association of rs1260326 with maternal insulin sensitivity, explaining 13.7% (95% CI 4.0%, 23.3%) of the total effect.

CONCLUSIONS/INTERPRETATION

The present study demonstrates commonalities between metabolites and genetic variants associated with insulin sensitivity in the gravid and non-gravid states and provides insights into mechanisms underlying pregnancy-induced insulin resistance. Graphical abstract.

Single Nucleotide Polymorphisms Related to Lipoprotein Metabolism Are Associated with Blood Lipid Changes following Regular Avocado Intake in a Randomized Control Trial among Adults with Overweight and Obesity

BACKGROUND

Avocados are rich in unsaturated fat and fiber; clinical trials have investigated their effects on metabolic disease. There is high variability in individual changes following avocado consumption, which may be in part due to individual genetic differences.

OBJECTIVE

Secondary analyses of the Persea americana for Total Health (PATH) Study were used to examine how single nucleotide polymorphisms (SNPs) impact blood lipid changes following a daily meal containing avocado compared with control.

METHODS

Adults (n = 115, 37% male) aged 25-45 y with overweight and obesity were randomly assigned to receive a daily isocaloric meal with (intervention) or without (control) a standardized amount (males: 175 g; females: 140 g) of avocado for 12 wk. Control meals were higher in saturated fat (17% of energy compared with 7%) and lower in fiber (4 g compared with 16 g) than intervention meals. Whole venous blood was taken at baseline and 12 wk to determine total cholesterol (TC), high-density lipoprotein (HDL) cholesterol, and triglyceride (TG) concentrations. Seventeen SNPs in 10 genes related to lipoprotein metabolism were genotyped. Effects of SNP, diet, and SNP-diet interactions were determined using general linear models.

RESULTS

No group-by-time effects were detected for changes in TC (P = 0.96), HDL cholesterol (P = 0.28), or TG (P = 0.06) over 12 wk. Three SNP-diet interactions were associated with final TC concentrations: ANGPTL3-rs10889337 (P = 0.01), ANGPTL4-rs2278236 (P = 0.02), and CD36-rs10499859 (P = 0.01). SNPs in GCKR and LPL were associated with TC changes (P = 0.01). The interaction between GCKR-rs1260326 and diet was such that C-homozygotes receiving avocado (n = 23) had final TC concentrations that were significantly lower than the C-homozygotes in the control group (n = 20) (P = 0.02).

CONCLUSIONS

Results from these exploratory analyses indicate that avocado consumption may help manage dyslipidemia in adults with overweight and obesity; however, effectiveness may differ by genetic profile. Understanding the role of genetic variation in variability following dietary intervention can potentially inform personalized nutrition recommendations.

Noninvasive Evaluation of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver diseases and can progress to advanced fibrosis and end-stage liver disease. Thus, intensive research has been performed to develop noninvasive methods for the diagnosis of nonalcoholic steatohepatitis (NASH) and fibrosis. Currently, no single noninvasive tool covers all of the stages of pathologies and conditions of NAFLD, and the cost and feasibility of known techniques are also important issues. Blood biomarkers for NAFLD may be useful to select subjects who need ultrasonography (US) screening for NAFLD, and noninvasive tools for assessing fibrosis may be helpful to exclude the probability of significant fibrosis and to predict advanced fibrosis, thus guiding the decision of whether to perform liver biopsy in patients with NAFLD. Among various methods, magnetic resonance-based methods have been shown to perform better than other methods in assessing steatosis as well as in detecting hepatic fibrosis. Many genetic markers are associated with the development and progression of NAFLD. Further well-designed studies are needed to determine which biomarker panels, imaging studies, genetic marker panels, or combinations thereof perform well for diagnosing NAFLD, differentiating NASH and fibrosis, and following-up NAFLD, respectively.

Recent advances in the pathogenesis of hereditary fructose intolerance: implications for its treatment and the understanding of fructose-induced non-alcoholic fatty liver disease

Hereditary fructose intolerance (HFI) is a rare inborn disease characterized by a deficiency in aldolase B, which catalyzes the cleavage of fructose 1,6-bisphosphate and fructose 1-phosphate (Fru 1P) to triose molecules. In patients with HFI, ingestion of fructose results in accumulation of Fru 1P and depletion of ATP, which are believed to cause symptoms, such as nausea, vomiting, hypoglycemia, and liver and kidney failure. These sequelae can be prevented by a fructose-restricted diet. Recent studies in aldolase B-deficient mice and HFI patients have provided more insight into the pathogenesis of HFI, in particular the liver phenotype. Both aldolase B-deficient mice (fed a very low fructose diet) and HFI patients (treated with a fructose-restricted diet) displayed greater intrahepatic fat content when compared to controls. The liver phenotype in aldolase B-deficient mice was prevented by reduction in intrahepatic Fru 1P concentrations by crossing these mice with mice deficient for ketohexokinase, the enzyme that catalyzes the synthesis of Fru 1P. These new findings not only provide a potential novel treatment for HFI, but lend insight into the pathogenesis of fructose-induced non-alcoholic fatty liver disease (NAFLD), which has raised to epidemic proportions in Western society. This narrative review summarizes the most recent advances in the pathogenesis of HFI and discusses the implications for the understanding and treatment of fructose-induced NAFLD.

Metabolic control analysis of hepatic glycogen synthesis in vivo

Hepatic glycogen synthesis plays a critical role in maintaining normal glucose homeostasis; however, the rate-controlling step regulating this process is unknown. Applying metabolic control analysis in vivo, we show that the regulation of insulin-stimulated hepatic glycogen synthesis under both normal and pathophysiological conditions of fatty liver-associated hepatic insulin resistance is controlled at the glucokinase (GCK) step through GCK translocation.

Multiple insulin-regulated enzymes participate in hepatic glycogen synthesis, and the rate-controlling step responsible for insulin stimulation of glycogen synthesis is unknown. We demonstrate that glucokinase (GCK)-mediated glucose phosphorylation is the rate-controlling step in insulin-stimulated hepatic glycogen synthesis in vivo, by use of the somatostatin pancreatic clamp technique using [¹³C₆]glucose with metabolic control analysis (MCA) in three rat models: 1) regular chow (RC)-fed male rats (control), 2) high fat diet (HFD)-fed rats, and 3) RC-fed rats with portal vein glucose delivery at a glucose infusion rate matched to the control. During hyperinsulinemia, hyperglycemia dose-dependently increased hepatic glycogen synthesis. At similar levels of hyperinsulinemia and hyperglycemia, HFD-fed rats exhibited a decrease and portal delivery rats exhibited an increase in hepatic glycogen synthesis via the direct pathway compared with controls. However, the strong correlation between liver glucose-6-phosphate concentration and net hepatic glycogen synthetic rate was nearly identical in these three groups, suggesting that the main difference between models is the activation of GCK. MCA yielded a high control coefficient for GCK in all three groups. We confirmed these findings in studies of hepatic GCK knockdown using an antisense oligonucleotide. Reduced liver glycogen synthesis in lipid-induced hepatic insulin resistance and increased glycogen synthesis during portal glucose infusion were explained by concordant changes in translocation of GCK. Taken together, these data indicate that the rate of insulin-stimulated hepatic glycogen synthesis is controlled chiefly through GCK translocation.

Non-alcoholic fatty liver disease and cardiovascular disease: assessing the evidence for causality

Non-alcoholic fatty liver disease (NAFLD) is highly prevalent among individuals with type 2 diabetes. Although epidemiological studies have shown that NAFLD is associated with cardiovascular disease (CVD), it remains unknown whether NAFLD is an active contributor or an innocent bystander. Plasma lipids, low-grade inflammation, impaired fibrinolysis and hepatokines are potential mediators of the relationship between NAFLD and CVD. The Mendelian randomisation approach can help to make causal inferences. Studies that used common variants in PNPLA3, TM6SF2 and GCKR as instruments to investigate the relationship between NAFLD and coronary artery disease (CAD) have reported contrasting results. Variants in PNPLA3 and TM6SF2 were found to protect against CAD, whereas variants in GCKR were positively associated with CAD. Since all three genes have been associated with non-alcoholic steatohepatitis, the second stage of NAFLD, the question of whether low-grade inflammation is an important mediator of the relationship between NAFLD and CAD arises. In contrast, the differential effects of these genes on plasma lipids (i.e. lipid-lowering for PNPLA3 and TM6SF2, and lipid-raising for GCKR) strongly suggest that plasma lipids account for their differential effects on CAD risk. This concept has recently been confirmed in an extended set of 12 NAFLD susceptibility genes. From these studies it appears that plasma lipids are an important mediator between NAFLD and CVD risk. These findings have important clinical implications, particularly for the design of anti-NAFLD drugs that also affect lipid metabolism.

Association between lncRNA and GCKR gene in type 2 diabetes mellitus

OBJECTIVE

To screen long non-coding RNA (lncRNA) related to glucokinase regulatory protein gene (GCKR), its differential expression was analyzed in patients with Type 2 diabetes mellitus (T2DM) and control samples. The correlation of lncRNA with GCKR was verified and its potential value as a molecular marker of T2DM was assessed.

METHODS

Lymphocyte RNA was extracted from five patients with T2DM and five patients with non-T2DM. The expression profiles of circulating lncRNAs and mRNAs were obtained by microarray. Bioinformatics analysis was used to screen lncRNAs associated with the GCKR gene in 127 patients with T2DM and 130 patients with non-T2DM were selected. The expression levels of the GCKR gene and lncRNA (ENST00000588707.1 and TCONS_00004187) in the T2DM group and control group were verified by real-time PCR. Additionally, a correlation analysis was conducted. The value of circulating ENST00000588707.1 and TCONS_00004187 as biomarkers for the diagnosis of T2DM was performed by receiver operating characteristic curve analysis.

RESULTS

We identified 68 lncRNAs and 74 mRNAs differentially expressed from the expression profile. Compared with the control group, the expression levels of the GCKR gene and lncRNA ENST00000588707.1 and TCONS_00004187 in the T2DM group were significantly lower (P < 0.05). The correlation analysis revealed that ENST00000588707.1 and TCONS_00004187 were correlated with GCKR gene expression and glycolipid metabolism (P < 0.05). ROC analysis showed that the area under the curve value of ENST00000588707.1 between T2DM patients and non-T2DM patients was 0.816 (95% CI: 0.764-0.869, sensitivity 72.0%, specificity 80.3%) and the AUC value of TCONS_00004187 was 0.826 (95% CI: 0.774-0.879, sensitivity 81.6%, specificity 61.3%).

CONCLUSION

lncRNA ENST0000588707.1 and TCONS_00004187 could serve as potential biomarkers for T2DM, which could involve in glycolipid metabolism by regulating the GCKR gene.

Targeted sequencing of candidate genes of dyslipidemia in Punjabi Sikhs: Population-specific rare variants in GCKR promote ectopic fat deposition

Dyslipidemia is a well-established risk factor for cardiovascular diseases. Although, advances in genome-wide technologies have enabled the discovery of hundreds of genes associated with blood lipid phenotypes, most of the heritability remains unexplained. Here we performed targeted resequencing of 13 bona fide candidate genes of dyslipidemia to identify the underlying biological functions. We sequenced 940 Sikh subjects with extreme serum levels of hypertriglyceridemia (HTG) and 2,355 subjects were used for replication studies; all 3,295 participants were part of the Asian Indians Diabetic Heart Study. Gene-centric analysis revealed burden of variants for increasing HTG risk in GCKR (p = 2.1x10-5), LPL (p = 1.6x10-3) and MLXIPL (p = 1.6x10-2) genes. Of these, three missense and damaging variants within GCKR were further examined for functional consequences in vivo using a transgenic zebrafish model. All three mutations were South Asian population-specific and were largely absent in other multiethnic populations of Exome Aggregation Consortium. We built different transgenic models of human GCKR with and without mutations and analyzed the effects of dietary changes in vivo. Despite the short-term of feeding, profound phenotypic changes were apparent in hepatocyte histology and fat deposition associated with increased expression of GCKR in response to a high fat diet (HFD). Liver histology of the GCKRmut showed severe fatty metamorphosis which correlated with ~7 fold increase in the mRNA expression in the GCKRmut fish even in the absence of a high fat diet. These findings suggest that functionally disruptive GCKR variants not only increase the risk of HTG but may enhance ectopic lipid/fat storage defects in absence of obesity and HFD. To our knowledge, this is the first transgenic zebrafish model of a putative human disease gene built to accurately assess the influence of genetic changes and their phenotypic consequences in vivo.

An intronic variant in the GCKR gene is associated with multiple lipids

Previous studies have shown that an intronic variant rs780094 of the GCKR gene (glucokinase regulatory protein) is significantly associated with several metabolites, but the associations of this genetic variant with different lipids is largely unknown. Therefore, we applied metabolomics approach to measure metabolites in a large Finnish population sample (METSIM study) to investigate their associations with rs780094 of GCKR. We measured metabolites by mass spectrometry from 5,181 participants. P < 5.8 × 10-5 was considered as statistically significant given 857 metabolites included in statistical analyses. We found novel negative associations of the T allele of GCKR rs780094 with serine and threonine, and positive associations with two metabolites of tryptophan, indolelactate and N-acetyltryptophan. Additionally, we found novel significant positive associations of this genetic variant with 12 glycerolipids and 19 glycerophospholipids. Significant negative associations were found for three glycerophospholipids (all plasmalogen-cholines), and two sphingolipids. Significant novel associations were also found with gamma-glutamylthreonine, taurocholenate sulfate, and retinol. Our study adds new information about the pleiotropy of the GCKR gene, and shows the associations of the T allele of GCKR rs780094 with lipids.

Characterization of Glucokinase Catalysis from a Pseudo-Dimeric View

Glucose phosphorylation by glucokinase exhibits a sigmoidal dependency on substrate concentration regardless of its simple structure. Dimorph mechanism suggested the existence of two enzymatic states with different catalytic properties, which has been shown to be plausible by structural analysis. However, the dimorph mechanism gives rise to a complicated or non-explicit non-closed mathematical form. It is neither feasible to apply the dimorph mechanism in effector characterizations. To improve the area of glucokinase study with stronger theoretical support and less complication in computation, we proposed the investigation of the enzyme from a pseudo-dimeric angle. The proposed mechanism started from the idealization of two monomeric glucokinase as a dimeric complex, which significantly simplified the glucose phosphorylation kinetics, while the differences in enzyme reconfiguration caused by variable substrates and effectors have been successfully characterized. The study presented a simpler and more reliable way in studying the properties of glucokinase and its effectors, providing guidelines of effector developments for hyperglycemia and hypoglycemia treatment.

Functional Variant in the GCKR Gene Affects Lactate Levels Differentially in the Fasting State and During Hyperglycemia

The rs780094 single nucleotide polymorphism (SNP; C/T) of glucokinase regulatory protein gene (GCKR) is a regulatory genetic variant that has been associated with lactate levels in the fasting state. However, the association of this locus with lactate during hyperglycemia, and the mechanisms underlying these associations remain unknown. We investigated the association of rs780094 with lactate levels in a frequently sampled oral glucose tolerance test in humans and evaluated the effect of increasing GCKR expression on lactate production in liver cells. The C allele of rs780094 was associated with lower lactate levels in fasting but increased lactate level during hyperglycemia independently of insulin levels. Increased expression of GKRP induced higher lactate level in HepG2 cells and in human primary hepatocytes (HPH) upon glucose stimulation by increasing the amount of GCK. Glucagon induced the expression of GCKR in HepG2 and HPH cells. Our results suggest that the association of rs780094 with lactate levels may involve differential GCKR expression between the carriers of the C and T alleles.

Association of common gene variants in glucokinase regulatory protein with cardiorenal disease: A systematic review and meta-analysis

Background

Small-molecules that disrupt the binding between glucokinase and glucokinase regulatory protein (GKRP) in the liver represent a potential new class of glucose-lowering drugs. It will, however, take years before their effects on clinically relevant cardiovascular endpoints are known. The purpose of this study was to estimate the effects of these drugs on cardiorenal outcomes by studying variants in the GKRP gene (GCKR) that mimic glucokinase-GKRP disruptors.

Methods

The MEDLINE and EMBASE databases were searched for studies reporting on the association between GCKR variants (rs1260326, rs780094, and rs780093) and coronary artery disease (CAD), estimated glomerular filtration rate (eGFR), and chronic kidney disease (CKD).

Results

In total 5 CAD studies (n = 274,625 individuals), 7 eGFR studies (n = 195,195 individuals), and 4 CKD studies (n = 31,642 cases and n = 408,432 controls) were included. Meta-analysis revealed a significant association between GCKR variants and CAD (OR:1.02 per risk allele, 95%CI:1.00–1.04, p = 0.01). Sensitivity analyses showed that replacement of one large, influential CAD study by two other, partly overlapping studies resulted in similar point estimates, albeit less precise (OR:1.02; 95%CI:0.98–1.06 and OR: 1.02; 95%CI: 0.99–1.04). GCKR was associated with an improved eGFR (+0.49 ml/min, 95%CI:0.10–0.89, p = 0.01) and a trend towards protection from CKD (OR:0.98, 95%CI:0.95–1.01, p = 0.13).

Conclusion

This study suggests that increased glucokinase-GKRP disruption has beneficial effects on eGFR, but these may be offset by a disadvantageous effect on coronary artery disease risk. Further studies are warranted to elucidate the mechanistic link between hepatic glucose metabolism and eGFR.