Effect of high-fat diet on glucose homeostasis and gene expression in glucokinase knockout mice

Aim: We have generated a heterozygous glucokinase knockout mouse (gk^del/wt), upon which we investigated the effect of high‐fat diet (HFD) with respect to metabolic control and both hepatic and β‐cell gene expression. We also investigated the in vitro efficacy of a glucokinase activator (GKA) on glucose‐stimulated insulin secretion (GSIS) in gk^del/wtmouse islets. Methods: Male gk^del/wtand gk^wt/wtmice were grouped (n = 8–10) at 10 weeks of age and fed HFD or chow diet (CD) for 10 weeks. Multiple parameters including blood glucose, plasma insulin and glucose tolerance were assessed. Further animal groups were used for in vitro GSIS and islet and liver gene expression analysis. Results and Conclusions: gk^del/wtmice showed early‐onset persistent hyperglycaemia, raised glycated haemoglobin levels, impaired GSIS and glucose tolerance but no change in plasma cholesterol, non‐esterified fatty acids or triglyceride levels. After HFD feeding, insulin levels of gk^del/wtmice were less than half that of gk^wt/wtmice, although they were equivalent to gk^wt/wtmice on CD. While gk^wt/wtmice maintained moderate hyperglycaemia, gk^del/wtmice became overtly diabetic, with worsened glucose tolerance. A GKA (GKA50) increased GSIS, at 10 mM glucose, in gk^del/wtmice to an extent at least as great as that seen in gk^wt/wtmice on both CD and HFD. gk^del/wtmice showed only a small number of changes in gene expression compared with gk^wt/wtmice. We propose the high fat–fed gk^del/wtmouse as a model of type 2 diabetes and report retained efficacy of a GKA on in vitro GSIS.     

Pregnancy outcome in patients with raised blood glucose due to a heterozygous glucokinase gene mutation

Aim To assess determinants of fetal growth in the offspring of pregnant women with hyperglycaemia due to a heterozygous glucokinase (GCK) gene mutation. Methods Details of gestational age at delivery, fetal birth weight and maternal antenatal treatment were collected from patients and retrospective case note review of 82 offspring born to 42 women with GCK gene mutations and 31 offspring born to 13 unaffected normoglycaemic women with an affected partner. Fetal genotype was determined using direct sequencing from either a mouth swab or a blood sample. Results In mothers with GCK mutations, non‐mutation‐carrying offspring were heavier than mutation‐carrying offspring (corrected birth weight 3.9 ± 0.6 vs. 3.2 ± 0.8 kg; P < 0.001) and more likely to be macrosomic (> 4.0 kg; 39% vs. 7%, P = 0.001). There was no difference in corrected birth weight between offspring of insulin‐ and diet‐treated women (3.7 ± 0.7 vs. 3.8 ± 0.6 kg; P = 0.1), although insulin‐treated mothers delivered earlier (37.5 ± 1.7 vs. 38.9 ± 2.3 weeks; P < 0.001) due to increased obstetric intervention. Conclusions Offspring of women with GCK mutations are at increased risk of macrosomia and its obstetric consequences. Fetal birth weight is predominantly altered by fetal genotype and not treatment of maternal hyperglycaemia with insulin. This probably reflects the large effect of a fetal GCK mutation on fetal insulin secretion and the difficulty in reducing the regulated maternal glycaemia caused by a glucose sensing defect in people with GCK mutations.     

Clinical characteristics of mutation carriers in a large family with glucokinase diabetes (MODY2)

Aims To investigate the prevalence and clinical characteristics of heterozygotes of the glucokinase gene mutations G264S and IVS8+2 in the extended pedigree of two patients with permanent neonatal diabetes as a result of glucokinase deficiency (IVS8+2 homozygosity and IVS8+2/G264S compound heterozygosity). Methods Eighty‐eight first, second and third degree family members of the two patients with permanent neonatal diabetes were genotyped. Clinical, laboratory and historical data were collected via chart reviews. Results Thirty‐one IVS8+2 and three G264S heterozygotes were identified. Of these, 18/34 (52.9%) had diabetes and 9/34 (26.5%) impaired fasting glucose (IFG), compared with 1/54 (1.9%) with diabetes and 2/54 (3.7%) with IFG in the non‐carrier group. Odds ratio for heterozygotes was 70.4 (95% CI 16.9–293.5 and P < 0.001). Mean body mass index of heterozygotes (> 18 years of age) who had diabetes was 27.1 ± 2.66, compared with 23.18 ± 4.72 for heterozygotes with normal glucose levels (P < 0.05). While none of the non‐carrier women had gestational diabetes, eight of the 10 heterozygotes developed gestational diabetes. Inheritance of a glucokinase mutation by the fetus from a carrier mother resulted in a significant reduction in birthweight (3600 ± 570 vs. 2970 ± 390grams, P < 0.05). Conclusions These data support the association between carriage of GCK gene mutations, G264S and IVS8+2, and the development of diabetes, impaired fasting glucose and reduced birthweight. Moreover, in heterozygotes, a clear correlation between body mass index and the development of diabetes was observed. These findings underline the need for surveillance and prevention in individuals at risk.     

The efficacy and safety of glucokinase activators for the treatment of type-2 diabetes mellitus: A protocol for systematic review and meta-analysis

Background:Glucokinase activators are a novel family of glucose-lowering agents used for the treatment of type-2 diabetes mellitus (T2DM). Glucokinase activators blind to GK activate the enzyme allosterically. Treatment with different GKAs has been shown to reduce fasting and postprandial glucose in patients with type 2 diabetes. We compared the efficacy/safety of glucokinase activators in T2DM patients through a meta-analysis.Methods:We searched PubMed, Excerpt Medica Database, and Cochrane Central Register of Controlled Trials databases for articles published before December 30, 2020. Two independent reviewers extracted the information from article. The quality of articles were assessed by 2 independent reviewers using the 5 items of scale proposed by Jadad. We computed the weighted mean difference and 95% confidence interval (CI) for a change from baseline to the study endpoint for glucokinase activators vs placebo. Egger test and Begg test were used to assess the possible publication bias caused by the tendency of published studies to be positive.Results:The present meta-analysis will compare the efficacy and safety of glucokinase activators and placebo for the treatment of T2DM.Conclusions:This meta-analysis will provide advanced evidence on the efficacy and safety of glucokinase activators for the treatment of T2DM.Ethics and dissemination:Ethical approval and patient consent are not required because this study is a literature-based study. This systematic review and meta-analysis will be published in a peer-reviewed journalPROSPERO registration number:CRD42021220364.     

The efficacy and safety of glucokinase activators for the treatment of type-2 diabetes mellitus: A meta-analysis

Background:Glucokinase activators (GKAs) are a novel family of glucose-lowering agents used for the treatment of type-2 diabetes mellitus. Treatment with different GKAs has been shown to reduce blood glucose levels in these patients. We compared the efficacy/safety of GKAs in patients with type-2 diabetes mellitus through a meta-analysis.Methods:We searched the PubMed, Excerpt Medica Database, and Cochrane Central Register of Controlled Trials databases for articles published before December 30, 2020. We computed the weighted mean difference (WMD) and 95% confidence interval (CI) for the change from baseline to the study endpoint for GKA versus placebo treatments.Results:A total of 4 articles (5 studies) were included in the meta-analysis. GKAs were associated with reductions in glycated hemoglobin levels from baseline (WMD, −0.3%; 95% CI, −0.466% to −0.134%). No significant difference between GKA and placebo treatment was observed in the results of fasting plasma glucose levels from baseline (WMD 0.013 mmol/L; 95% CI, −0.304–0.33 mmol/L). A significantly higher change in 2-hour postprandial plasma glucose (2-h PPG) levels (WMD −2.434 mmol/L; 95% CI, −3.304 to −1.564 mmol/L) was observed following GKA than placebo treatment. GKAs were associated with a higher prevalence of causing hypoglycemic events than placebo treatment (risk difference [RD], 0.06; 95% CI 0.013–0.106). GKAs had no association with the risk of developing adverse effects (RD, 0.038; 95% CI, −0.03–0.106) and serious adverse events (RD, 0.01; 95% CI, −0.004–0.023).Conclusions:GKAs were more effective for postprandial blood glucose control. However, these agents showed a significantly high risk of causing hypoglycemia.PROSPERO registration number:CRD42021220364.     

Glucokinase mutations in young children with hyperglycemia

BACKGROUND: The etiology of mild hyperglycemia without ketoacidosis in young children is often unknown. Maturity onset diabetes of youth (MODY) is a form of diabetes mellitus (DM) characterized by fasting hyperglycemia without evidence for autoimmune destruction of beta-cells. METHODS: We genetically analyzed four families of young children with fasting hyperglycemia with family histories of diabetes for mutations in the genes for hepatocyte nuclear factor 4 alpha (HNF4alpha), glucokinase (GCK), and hepatocyte nuclear factor 1 alpha (HNF1alpha), the genes responsible for MODY1, MODY2, and MODY3, respectively. RESULTS: We identified mutations in GCK (Gly258Asp, Arg303Trp, and Arg191Gln) in three of the four families. Molecular genetic characterization in these children clarified the etiology and prognosis of the hyperglycemia and allowed discontinuation of insulin therapy in one family. CONCLUSIONS: We conclude that molecular evaluation for MODY in children with mild fasting hyperglycemia without ketosis with family histories of diabetes can provide important prognostic information to guide therapy and exclude preclinical type 1 diabetes mellitus.     

Assessment of insulin sensitivity in glucokinase-deficient subjects

Summary The chronic hyperglycaemia of glucokinase-deficient diabetes results from a glucose-sensing defect in pancreatic beta cells and abnormal hepatic glucose phosphorylation. We have evaluated the contribution of insulin resistance to this form of chronic hyperglycaemia. Insulin sensitivity, assessed by the homeostasis model assessment (HOMA) method in 35 kindreds with glucokinase mutations, was found to be significantly decreased in 125 glucokinase-deficient subjects as compared to 141 unaffected first-degree relatives. Logistic regression analysis showed that in glucokinase-deficient subjects a decrease in insulin sensitivity was associated with deterioration of the glucose tolerance status. A euglycaemic hyperin-sulinaemic clamp was performed in 14 glucokinase-deficient subjects and 12 unrelated control subjects. In six patients and six control subjects the clamp was coupled to dideutero-glucose infusion to measure glucose turnover. Average glucose infusion rates (GIR) at 1 and 5 mU · kg body weight · min^–1 insulin infusion rates were significantly lower in (the glucokinase-deficient) patients than in control subjects. Although heterogeneous results were observed, in 8 out of the 14 patients GIRs throughout the experiment were lower than 1 SD below the mean of the control subjects. Hepatic glucose production at 1 mU · kg body weight^–1 · min^–1 insulin-infusion rate was significantly higher in patients than in control subjects. In conclusion, insulin resistance correlates with the deterioration of glucose tolerance and contributes to the hyperglycaemia of glucokinase-deficient diabetes. Taken together, our results are most consistent with insulin resistance being considered secondary to the chronic hyperglycaemia and/or hypoinsulinaemia of glucokinase-deficiency. Insulin resistance might also result from interactions between the unbalanced glucose metabolism and susceptibility gene(s) to low insulin sensitivity likely to be present in this population.Abbreviations NIDDM Non-insulin-dependent diabetes mellitus - HGP hepatic glucose production - GCK glucokinase - IIR insulin infusion rate - GIR glucose infusion rate - MFH mild fasting hyperglycaemia - NGT normal glucose tolerance - IGT impaired glucose tolerance - HOMA homeostasis model assessment - ANOVA analysis of variance - MODY maturity-onset diabetes of the young     

Genetic and clinical characteristics of maturity-onset diabetes of the young

Genetic factors play an important role in various forms of diabetes mellitus (DM), but inheritance is complex and interacts with environmental factors. Although in most cases type 2 DM (T2DM) and T1DM are polygenic disorders, several monogenic forms have been identified. Among them, maturity-onset diabetes of the young (MODY) has been the most intensively investigated. MODY is a group of six different forms of monogenic diabetes, characterized by insulin secretion defects in pancreatic beta-cells, supposed to be responsible for 2-5% of all cases of diabetes. The most common are MODY2 and MODY3, caused by mutations in the genes encoding glucokinase and hepatocyte nuclear factor 1-alpha respectively. MODY2 is characterized by glucose sensing defects, leading to an increase in insulin secretion threshold. This causes lifelong sustained and mild hyperglycaemia from birth, most often in non-diabetic levels. Diagnosis is incidental in most cases. These patients are asymptomatic, seldom need treatment and rarely present chronic complications. MODY3 is characterized by a severe insulin secretion defect in response to glucose. Diagnosis is made usually in adolescence and early adulthood, often by osmotic symptoms. Hyperglycaemia is progressive, and patients frequently need treatment with oral drugs or insulin some time in their follow up. This group seems to have a marked sensitivity to sulphonylureas compared to other types of diabetes. The recognition of MODY as a monogenic disorder and a thorough understanding of its pathophysiology are important for correct diagnosis and treatment, with great impact on prognosis. Besides, the study of these forms of diabetes brings important contributions to the understanding of glucose homeostasis as a whole.     

Hypothalamic arcuate nucleus glucokinase regulates insulin secretion and glucose homeostasis

Aims

To investigate the role of arcuate glucokinase (GK) in the regulation of glucose homeostasis.

Materials and methods

A recombinant adeno‐associated virus expressing either GK or an antisense GK construct was used to alter GK activity specifically in the hypothalamic arcuate nucleus (arc). GK activity in this nucleus was also increased by stereotactic injection of the GK activator, compound A. The effect of altered arc GK activity on glucose homeostasis was subsequently investigated using glucose and insulin tolerance tests.

Results.

Increased GK activity specifically within the arc increased insulin secretion and improved glucose tolerance in rats during oral glucose tolerance tests. Decreased GK activity in this nucleus reduced insulin secretion and increased glucose levels during the same tests. Insulin sensitivity was not affected in either case. The effect of arc GK was maintained in a model of type 2 diabetes.

Conclusions

These results demonstrate a role for arc GK in systemic glucose homeostasis.     

Exendin‐4 ameliorates diabetic symptoms through activation of glucokinase

Background: Glucagon‐like peptide‐1 (GLP‐1) and its stable analogue exendin‐4 maintain glucose homeostasis by modulating insulin secretion from pancreatic β‐cells and controlling hepatic glucose output. Glucokinase (GK), by catalysing the first step in glycolysis, plays an important role in glucose‐stimulated insulin secretion and hepatic glucose metabolism. In the present study, we investigated the effects of exendin‐4 on GK in high fat‐fed and alloxan‐treated diabetic mice. Methods: The effects of alloxan (5, 10 and 20 μmol/L) on insulin release from isolated murine islets, as well as glycogen synthesis by isolated murine hepatocytes, were assessed. The effects of exendin‐4 (10 nmol/kg, twice daily for 4 weeks) were assessed in high fat‐fed, alloxan (50 mg/kg, i.v.)‐treated C57 mice. Glucokinase activity was assessed in the same model. Results: Pretreatment with exendin‐4 attenuated alloxan‐induced decreases in insulin release and glycogen synthesis in islets and hepatocytes. The alloxan‐induced decrease in the GK activity in islets and hepatocytes was also ameliorated by exendin‐4 treatment. Pretreatment with the GLP‐1 receptor antagonist exendin‐9 (100 nmol/L) blocked the effects of exendin‐4 on the liver and pancreas. Treatment of high‐fat fed, alloxan‐treated diabetic mice with exendin‐4 (10 nmol/L, i.p.) reduced the severity of diabetic symptoms. Specifically, exendin‐4 treatment reduced serum glucose by 50% and %HbA1c by 24% compared with control and significantly decreased HOMA‐IR by 39% and increased HOMA‐β by 150%. In addition, exendin‐4 treatment significantly reduced body weight by 6.8% and serum triglycerides by 35%. Conclusions: The results indicate that glucose‐stimulated insulin release and glycogen synthesis are decreased by alloxan due to reduced GK activity. These findings provide further insight into the mechanism by which exendin‐4 regulates glucose homeostasis.     

Hepatic glucose uptake,gluconeogenesis and the regulation of glycogen synthesis

Hepatic glycogen is replenished during the absorptive period postprandially. This repletion is prompted partly by an increased hepatic uptake of glucose by the liver, partly by metabolite and hormonal signals in the portal vein, and partly by an increased gluconeogenic flux to glycogen (glyconeogenesis). There is some evidence that the direct formation of glycogen from glucose and that formed by gluconeogenic pathways is linked. This includes: (i) the inhibition of all glycogen synthesis, in vivo, when gluconeogenic flux is blocked by inhibitors; (ii) a dual relationship between glucose concentrations, lactate uptake by the liver and glycogen synthesis (by both pathways) which indicates that glucose sets the maximal rates of glycogen synthesis while lactate uptake determines the actual flux rate to glycogen; (iii) the decrease of both gluconeogenesis and glycogen synthesis by the biguanide, metformin; and (iv) correlations between increased gluconeogenesis and liver glycogen in obese patients and animal models. The degree to which the liver extracts portal glucose is not entirely agreed upon although a preponderance of evidence points to about a 5% extraction rate, following meals, which is dependent on a stimulation of glucokinase. This enzyme may be linked to the expression of other enzymes in the gluconeogenic pathway. Perivenous cells in the liver may induce additional gluconeogenesis in the periportal cells by increasing glycolytically produced lactate. A number of potential mechanisms therefore exist which could link glycogen synthesis from glucose and gluconeogenic substrate. Copyright © 2001 John Wiley & Sons, Ltd.     

Linkage analysis of the glucokinase locus in familial Type 2 (non-insulin-dependent) diabetic pedigrees

Summary Glucokinase is among the few genes which may play a key role in both insulin secretion and insulin action. Glucokinase is present in pancreatic beta cells where it may have a key role in the glucose sensing mechanism, and it is present in hepatocytes, where it may participate in glucose flux. Glucokinase defects have recently been implicated in maturity-onset diabetes of the young. To examine the hypothesis that glucokinase plays a key role in the predisposition to common familial Type 2 (non-insulin-dependent) diabetes mellitus, we typed 399 members of 18 Utah pedigrees with multiple Type 2 diabetic individuals for two markers in the 5 and 3 flanking regions of the glucokinase gene. Linkage analysis was performed under both dominant and recessive models. We also repeated these analyses with individuals with impaired glucose tolerance who were considered affected if their stimulated (2-h) glucose exceeded age-specific normal levels for 95 % of the population. Under several dominant models, linkage was significantly excluded, and under recessive models log of the odds (LOD) score was less than –1. We were also unable to demonstrate statistical support for the hypothesis that a small subgroup of pedigrees had glucokinase defects, but the most suggestive pedigree (individual pedigree LOD 1.8–1.9) ranked among the youngest and leanest in our cohort. We can exclude a major role for glucokinase in familial Type 2 diabetes, but our data cannot exclude a role for this locus in a minority of pedigrees. Further testing of the hypothesis that glucokinase defects contribute to diabetes in a small proportion of Type 2 diabetic pedigrees must await thorough sequence analysis of the glucokinase gene, including regulatory regions, particularly from pedigrees with positive LOD scores.     

Impact of patient characteristic factors on the dynamics of liver glucose metabolism: Evaluation of multiparametric imaging with dynamic whole-body 18F-fluorodeoxyglucose-positron emission tomography

Aims

To assess the impact of various patient characteristics on the dynamics of liver glucose metabolism using automated multiparametric imaging with whole-body dynamic ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET).

Materials and Methods

We retrospectively enrolled 540 patients who underwent whole-body dynamic FDG-PET. Three quantitative indices representing hepatic glucose metabolism [mean standardized uptake value normalized by lean body mass (SULmean), metabolic glucose rate (kinetic index) and distribution volume (DV)] were measured from multiparametric PET images produced automatically based on the Patlak plot model. Patient characteristics including age, sex, body mass index, fasting time, blood glucose level, and the presence of diabetes mellitus (DM) or hepatic steatosis (HS) were collected. We examined the correlations between the characteristic factors and three quantitative indices using multiple regression analysis.

Results

The success rate of kinetic analysis using multiparametric PET imaging was 93.3% (504/540). Hepatic SULmean was significantly correlated with age (p < .001), sex (p < .001) and blood glucose level (p = .002). DV was significantly correlated with age (p = .033), sex (p < .001), body mass index (p = .002), fasting time (p = .043) and the presence of HS (p = .002). The kinetic index was significantly correlated with age (p < .001) and sex (p = .004). In the comparison of the healthy, DM and HS groups, patients with DM had a significantly increased SULmean, whereas patients with HS had a significantly decreased DV.

Conclusions

Our results showed that liver glucose metabolism was influenced by various patient characteristic factors. Multiparametric FDG-PET imaging can be used to analyse the kinetics of liver glucose metabolism in routine clinical practice.