Diabetes medication associates with DNA methylation of metformin transporter genes in the human liver

Patterns of paternal medication dispensation around the time of conception

BACKGROUND

Past research on the safety of prenatal exposure to medications has focused on maternal use during gestation, with limited research into the potential effects of paternal use during the spermatogenic period preceding conception. Knowing the most common medications used by fathers around the time of conception can inform research priorities in this field.

OBJECTIVES

To identify the most common medications dispensed to fathers in the preconception period.

METHODS

Within the MarketScan research database of commercially insured individuals in the United States from 2011 to 2020, we identified pregnancies, estimated the date of conception, linked each pregnancy to the father using family enrolment information and required minimum enrolment period and prescription benefits. Then, we described the use of prescription medications by the father during the 90 days before conception based on pharmacy dispensation claims.

RESULTS

Of 4,437,550 pregnancies, 51.6% were linked with a father. Among the 1,413,762 pregnancies connected with a father that also met the inclusion criteria, the most common classes of medications dispensed were psychotropics (8.66%), antibiotics (7.21%), and analgesics (6.82%). The most frequently dispensed medications were amoxicillin (3.75%), azithromycin (3.15%), fluticasone (2.70%) and acetaminophen/hydrocodone (2.70%). Some fathers filled prescriptions for medications associated with foetal embryopathy when used by the mother, including mycophenolate (0.04%), methotrexate (0.03%) and isotretinoin (0.02%).

CONCLUSIONS

More than a third of fathers filled at least one prescription medication in the preconception period, and several of them are known to be embryotoxic, emphasizing the necessity for further investigation into the potential teratogenicity of paternal exposure.

Paternal Use of Metformin During the Sperm Development Period Preceding Conception and Risk for Major Congenital Malformations in Newborns

BACKGROUND

Metformin is the most used oral antidiabetic medication. Despite its established safety profile, it has known antiandrogenic and epigenetic modifying effects. This raised concerns about possible adverse developmental effects caused by genomic alterations related to paternal use of metformin during the spermatogenesis period preceding conception.

OBJECTIVE

To assess the potential adverse intergenerational effect of metformin by examining the association between paternal metformin use during spermatogenesis and major congenital malformations (MCMs) in newborns.

DESIGN

Nationally representative cohort study.

SETTING

A large Israeli health fund.

PARTICIPANTS

383 851 live births linked to fathers and mothers that occurred in 1999 to 2020.

MEASUREMENTS

MCMs and parental cardiometabolic conditions were ascertained using clinical diagnoses, medication dispensing information, and laboratory test results. The effect of metformin use on MCMs was estimated using general estimating equations, accounting for concurrent use of other antidiabetic medications and parental cardiometabolic morbidity.

RESULTS

Compared with unexposed fathers, the prevalence of cardiometabolic morbidity was substantially higher among fathers who used metformin during spermatogenesis, and their spouses. Whereas the crude odds ratio (OR) for paternal metformin exposure in all formulations and MCMs was 1.28 (95% CI, 1.01 to 1.64), the adjusted OR was 1.00 (CI, 0.76 to 1.31). Within specific treatment regimens, the adjusted OR was 0.86 (CI, 0.60 to 1.23) for metformin in monotherapy and 1.36 (CI, 1.00 to 1.85) for metformin in polytherapy, a treatment that was more common in patients with more poorly controlled diabetes.

LIMITATION

Laboratory test results for hemoglobin A1c to assess underlying diabetes severity were available only for a subset of the cohort.

CONCLUSION

Paternal use of metformin in monotherapy does not increase the risk for MCMs. Association for metformin in polytherapy could potentially be explained by worse underlying parental cardiometabolic risk profile.

PRIMARY FUNDING SOURCE

None.

DNA methylation and type 2 diabetes: a systematic review

OBJECTIVE

DNA methylation influences gene expression and function in the pathophysiology of type 2 diabetes mellitus (T2DM). Mapping of T2DM-associated DNA methylation could aid early detection and/or therapeutic treatment options for diabetics.

DESIGN

A systematic literature search for associations between T2DM and DNA methylation was performed. Prospero registration ID: CRD42020140436.

METHODS

PubMed and ScienceDirect databases were searched (till October 19, 2023). Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and New Castle Ottawa scale were used for reporting the selection and quality of the studies, respectively.

RESULT

Thirty-two articles were selected. Four of 130 differentially methylated genes in blood, adipose, liver or pancreatic islets (TXNIP, ABCG1, PPARGC1A, PTPRN2) were reported in > 1 study. TXNIP was hypomethylated in diabetic blood across ethnicities. Gene enrichment analysis of the differentially methylated genes highlighted relevant disease pathways (T2DM, type 1 diabetes and adipocytokine signaling). Three prospective studies reported association of methylation in IGFBP2, MSI2, FTO, TXNIP, SREBF1, PHOSPHO1, SOCS3 and ABCG1 in blood at baseline with incident T2DM/hyperglycemia. Sex-specific differential methylation was reported only for HOOK2 in visceral adipose tissue (female diabetics: hypermethylated, male diabetics: hypomethylated). Gene expression was inversely associated with methylation status in 8 studies, in genes including ABCG1 (blood), S100A4 (adipose tissue), PER2 (pancreatic islets), PDGFA (liver) and PPARGC1A (skeletal muscle).

CONCLUSION

This review summarizes available evidence for using DNA methylation patterns to unravel T2DM pathophysiology. Further validation studies in diverse populations will set the stage for utilizing this knowledge for identifying early diagnostic markers and novel druggable pathways.

Metformin: From Diabetes to Cancer-Unveiling Molecular Mechanisms and Therapeutic Strategies

Metformin, a widely used anti-diabetic drug, has garnered attention for its potential in cancer management, particularly in breast and colorectal cancer. It is established that metformin reduces mitochondrial respiration, but its specific molecular targets within mitochondria vary. Proposed mechanisms include inhibiting mitochondrial respiratory chain Complex I and/or Complex IV, and mitochondrial glycerophosphate dehydrogenase, among others. These actions lead to cellular energy deficits, redox state changes, and several molecular changes that reduce hyperglycemia in type 2 diabetic patients. Clinical evidence supports metformin's role in cancer prevention in type 2 diabetes mellitus patients. Moreover, in these patients with breast and colorectal cancer, metformin consumption leads to an improvement in survival outcomes and prognosis. The synergistic effects of metformin with chemotherapy and immunotherapy highlights its potential as an adjunctive therapy for breast and colorectal cancer. However, nuanced findings underscore the need for further research and stratification by molecular subtype, particularly for breast cancer. This comprehensive review integrates metformin-related findings from epidemiological, clinical, and preclinical studies in breast and colorectal cancer. Here, we discuss current research addressed to define metformin's bioavailability and efficacy, exploring novel metformin-based compounds and drug delivery systems, including derivatives targeting mitochondria, combination therapies, and novel nanoformulations, showing enhanced anticancer effects.

Metformin-mediated epigenetic modifications in diabetes and associated conditions: Biological and clinical relevance

An intricate interplay between genetic and environmental factors contributes to the development of type 2 diabetes (T2D) and its complications. Therefore, it is not surprising that the epigenome also plays a crucial role in the pathogenesis of T2D. Hyperglycemia can indeed trigger epigenetic modifications, thereby regulating different gene expression patterns. Such epigenetic changes can persist after normalizing serum glucose concentrations, suggesting the presence of a 'metabolic memory' of previous hyperglycemia which may also be epigenetically regulated. Metformin, a derivative of biguanide known to reduce serum glucose concentrations in patients with T2D, appears to exert additional pleiotropic effects that are mediated by multiple epigenetic modifications. Such modifications have been reported in various organs, tissues, and cellular compartments and appear to account for the effects of metformin on glycemic control as well as local and systemic inflammation, oxidant stress, and fibrosis. This review discusses the emerging evidence regarding the reported metformin-mediated epigenetic modifications, particularly on short and long non-coding RNAs, DNA methylation, and histone proteins post-translational modifications, their biological and clinical significance, potential therapeutic applications, and future research directions.

Impact of individual factors on DNA methylation of drug metabolism genes: A systematic review

Individual differences in drug response have always existed in clinical treatment. Many non-genetic factors show non-negligible impacts on personalized medicine. Emerging studies have demonstrated epigenetic could connect non-genetic factors and individual treatment differences. We used systematic retrieval methods and reviewed studies that showed individual factors' impact on DNA methylation of drug metabolism genes. In total, 68 studies were included, and half (n = 36) were cohort studies. Six aspects of individual factors were summarized from the perspective of personalized medicine: parental exposure, environmental pollutants exposure, obesity and diet, drugs, gender and others. The most research (n = 11) focused on ABCG1 methylation. The majority of studies showed non-genetic factors could result in a significant DNA methylation alteration in drug metabolism genes, which subsequently affects the pharmacokinetic processes. However, the underlying mechanism remained unknown. Finally, some viewpoints were presented for future research.

DNA methylation partially mediates antidiabetic effects of metformin on HbA1c levels in individuals with type 2 diabetes

AIMS

Despite metformin being used as first-line pharmacological therapy for type 2 diabetes, its underlying mechanisms remain unclear. We aimed to determine whether metformin altered DNA methylation in newly-diagnosed individuals with type 2 diabetes.

METHODS AND RESULTS

We found that metformin therapy is associated with altered methylation of 26 sites in blood from Scandinavian discovery and replication cohorts (FDR<0.05), using MethylationEPIC arrays. The majority (88%) of these 26 sites were hypermethylated in patients taking metformin for ∼3 months compared to controls, who had diabetes but had not taken any diabetes medication. Two of these blood-based methylation markers mirrored the epigenetic pattern in muscle and adipose tissue (FDR<0.05). Four type 2 diabetes-associated SNPs were annotated to genes with differential methylation between metformin cases and controls, e.g., GRB10, RPTOR, SLC22A18AS and TH2LCRR. Methylation correlated with expression in human islets for two of these genes. Three metformin-associated methylation sites (PKNOX2, WDTC1 and MICB) partially mediate effects of metformin on follow-up HbA1c levels. When combining methylation of these three sites into a score, which was used in a causal mediation analysis, methylation was suggested to mediate up to 32% of metformin's effects on HbA1c.

CONCLUSION

Metformin-associated alterations in DNA methylation partially mediates metformin's antidiabetic effects on HbA1c in newly-diagnosed individuals with type 2 diabetes.

Epigenetics of the Pathogenesis and Complications of Type 2 Diabetes Mellitus

Epigenetics of type 2 diabetes mellitus (T2DM) has widened our knowledge of various aspects of the disease. The aim of this review is to summarize the important epigenetic changes implicated in the disease risks, pathogenesis, complications and the evolution of therapeutics in our current understanding of T2DM. Studies published in the past 15 years, from 2007 to 2022, from three primary platforms namely PubMed, Google Scholar and Science Direct were included. Studies were searched using the primary term 'type 2 diabetes and epigenetics' with additional terms such as 'risks', 'pathogenesis', 'complications of diabetes' and 'therapeutics'. Epigenetics plays an important role in the transmission of T2DM from one generation to another. Epigenetic changes are also implicated in the two basic pathogenic components of T2DM, namely insulin resistance and impaired insulin secretion. Hyperglycaemia-i nduced permanent epigenetic modifications of the expression of DNA are responsible for the phenomenon of metabolic memory. Epigenetics influences the development of micro-and macrovascular complications of T2DM. They can also be used as biomarkers in the prediction of these complications. Epigenetics has expanded our understanding of the action of existing drugs such as metformin, and has led to the development of newer targets to prevent vascular complications. Epigenetic changes are involved in almost all aspects of T2DM, from risks, pathogenesis and complications, to the development of newer therapeutic targets.

Adipose cell-free DNA in diabetes

Cancer-associated necrosis is a well-known source of cell-free DNA (cfDNA). However, the origins of cfDNA are not strictly limited to cancer. Additionally, dietary exposure induces apoptosis-induced proliferation in adipocytes, leading to the release of cfDNA. The genetic information derived from cfDNA as a result of apoptosis-induced proliferation contains specific methylation patterns in adipose tissue that can be used as a marker to detect the risk of developing Type 2 diabetes Mellitus (T2DM) in the future. cfDNA is superior to peripheral blood leukocytes (PBL) and whole blood samples for reflecting tissue pathology due to the frequent use of PBL and whole blood samples that do not match tissue pathology. The difficulty of demonstrating that cfDNA is derived from adipose tissue. We propose several promising techniques by analyzing cfDNA derived from adipose tissue to detect T2DM risk. First, adipose-specific genes such as ADIPOQ and Leptin were utilized. Second, MCTA-Seq, EpiSCORE, deconvolution, multiplexing, and automated machine learning (AutoML) were used to determine the proportion of total methylation in related genes.

Pharmacoepigenetics in type 2 diabetes: is it clinically relevant?

Data generated over nearly two decades clearly demonstrate the importance of epigenetic modifications and mechanisms in the pathogenesis of type 2 diabetes. However, the role of pharmacoepigenetics in type 2 diabetes is less well established. The field of pharmacoepigenetics covers epigenetic biomarkers that predict response to therapy, therapy-induced epigenetic alterations as well as epigenetic therapies including inhibitors of epigenetic enzymes. Not all individuals with type 2 diabetes respond to glucose-lowering therapies in the same way, and there is therefore a need for clinically useful biomarkers that discriminate responders from non-responders. Blood-based epigenetic biomarkers may be useful for this purpose. There is also a need for a better understanding of whether existing glucose-lowering therapies exert their function partly through therapy-induced epigenetic alterations. Finally, epigenetic enzymes may be drug targets for type 2 diabetes. Here, I discuss whether pharmacoepigenetics is clinically relevant for type 2 diabetes based on studies addressing this topic.

Effect of metformin on the epigenetic age of peripheral blood in patients with diabetes mellitus

Background: Metformin has been proven to have an antiaging effect. However, studies on how metformin affects global epigenetic regulation and its effect on the epigenetic clock in diabetes mellitus (DM) patients are limited. This study aims to investigate the impact of metformin on the epigenetic age in subjects with type 2 DM.

Results: We collected the peripheral blood of the metformin group and the no-metformin group of the 32 DM patients. Three previously established epigenetic clocks (Hannum, Horvath, and DNAmPhenoAge) were used to estimate the epigenetic age acceleration of the two groups. We defined biological age acceleration for each group by comparing the estimated biological age with the chronological age. Results were presented as follows: 1) all three epigenetic clocks were strongly correlated with chronological age. 2) We found a strong association between metformin intake and slower epigenetic aging by Horvath’s clock and Hannum’s clock.

Conclusions: Here, we found an association between metformin intake and slower epigenetic aging.

The role of maternal DNA methylation in pregnancies complicated by gestational diabetes

Diabetes in pregnancy is associated with adverse pregnancy outcomes and poses a serious threat to the health of mother and child. Although the pathophysiological mechanisms that underlie the association between maternal diabetes and pregnancy complications have not yet been elucidated, it has been suggested that the frequency and severity of pregnancy complications are linked to the degree of hyperglycemia. Epigenetic mechanisms reflect gene-environment interactions and have emerged as key players in metabolic adaptation to pregnancy and the development of complications. DNA methylation, the best characterized epigenetic mechanism, has been reported to be dysregulated during various pregnancy complications, including pre-eclampsia, hypertension, diabetes, early pregnancy loss and preterm birth. The identification of altered DNA methylation patterns may serve to elucidate the pathophysiological mechanisms that underlie the different types of maternal diabetes during pregnancy. This review aims to provide a summary of existing knowledge on DNA methylation patterns in pregnancies complicated by pregestational type 1 (T1DM) and type 2 diabetes mellitus (T2DM), and gestational diabetes mellitus (GDM). Four databases, CINAHL, Scopus, PubMed and Google Scholar, were searched for studies on DNA methylation profiling in pregnancies complicated with diabetes. A total of 1985 articles were identified, of which 32 met the inclusion criteria and are included in this review. All studies profiled DNA methylation during GDM or impaired glucose tolerance (IGT), while no studies investigated T1DM or T2DM. We highlight the increased methylation of two genes, Hypoxia‐inducible Factor‐3α (HIF3α) and Peroxisome Proliferator-activated Receptor Gamma-coactivator-Alpha (PGC1-α), and the decreased methylation of one gene, Peroxisome Proliferator Activated Receptor Alpha (PPARα), in women with GDM compared to pregnant women with normoglycemia that were consistently methylated across diverse populations with varying pregnancy durations, and using different diagnostic criteria, methodologies and biological sources. These findings support the candidacy of these three differentially methylated genes as biomarkers for GDM. Furthermore, these genes may provide insight into the pathways that are epigenetically influenced during maternal diabetes and which should be prioritized and replicated in longitudinal studies and in larger populations to ensure their clinical applicability. Finally, we discuss the challenges and limitations of DNA methylation analysis, and the need for DNA methylation profiling to be conducted in different types of maternal diabetes in pregnancy.

Lifestyle and NR3C1 exon 1F gene methylation is associated with changes in glucose levels and insulin resistance

AIMS

the present study aimed to investigate how glucose and insulin levels may be associated with changes in NR3C1 gene methylation levels in adults.

MAIN METHODS

375 volunteers users of the Brazilian Public Unified Health System (SUS) were recruited to assess socioeconomic status, lifestyle, anthropometric data, blood glucose and serum cortisol levels, insulin resistance, and NR3C1 gene methylation assessment. Factors associated with glucose levels and insulin resistance were investigated using multivariate analysis GLzM at 5 % significance (p < 0.05).

KEY FINDINGS

our results verified that glucose levels and insulin resistance were directly related to NR3C1 gene methylation and age, while not being overweight and obese and no tobacco consumption were indirectly related to glucose levels and insulin resistance.

SIGNIFICANCE

habits and lifestyle may influence NR3C1 gene regulation, revealing the complexity of environmental impacts on NR3C1 methylation. Furthermore, associated risk factors must be taken into account in epigenetic studies as they directly interfere with blood glucose levels and insulin resistance.

Epigenetics of type 2 diabetes mellitus and weight change - a tool for precision medicine?

Pioneering studies performed over the past few decades demonstrate links between epigenetics and type 2 diabetes mellitus (T2DM), the metabolic disorder with the most rapidly increasing prevalence in the world. Importantly, these studies identified epigenetic modifications, including altered DNA methylation, in pancreatic islets, adipose tissue, skeletal muscle and the liver from individuals with T2DM. As non-genetic factors that affect the risk of T2DM, such as obesity, unhealthy diet, physical inactivity, ageing and the intrauterine environment, have been associated with epigenetic modifications in healthy individuals, epigenetics probably also contributes to T2DM development. In addition, genetic factors associated with T2DM and obesity affect the epigenome in human tissues. Notably, causal mediation analyses found DNA methylation to be a potential mediator of genetic associations with metabolic traits and disease. In the past few years, translational studies have identified blood-based epigenetic markers that might be further developed and used for precision medicine to help patients with T2DM receive optimal therapy and to identify patients at risk of complications. This Review focuses on epigenetic mechanisms in the development of T2DM and the regulation of body weight in humans, with a special focus on precision medicine.

DNA methylation level of the gene encoding thioredoxin-interacting protein in peripheral blood cells is associated with metabolic syndrome in the Japanese general population

Metabolic syndrome (MetS) is cluster of metabolic diseases, including abdominal obesity, hyperglycemia, high blood pressure, and dyslipidemia, that directly escalate the risk of type 2 diabetes, heart disease, and stroke. Thioredoxin-interacting protein (TXNIP) is a binding protein for thioredoxin, a molecule that is a key inhibitor of cellular oxidation, and thus regulates the cellular redox state. Epigenetic alteration of the TXNIP-encoding locus has been associated with components of MetS. In the present study, we sought to determine whether the level of TXNIP methylation in blood is associated with MetS in the general Japanese population. DNA was extracted from the peripheral blood cells of 37 subjects with and 392 subjects without MetS. The level of TXNIP methylation at cg19693031 was assessed by the bisulfite-pyrosequencing method. We observed that TXNIP methylation levels were lower in MetS subjects (median 74.9%, range 71.7-78.4%) than in non-MetS subjects (median 77.7%, range 74.4-80.5%; p = 0.0024). Calculation of the confounding factor-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for hypomethylation revealed that subjects with MetS exhibited significantly higher ORs for hypomethylation than did those without MetS (OR, 2.92; 95% CI, 1.33-6.62; p = 0.009). Our findings indicated that lower levels of TXNIP methylation are associated with MetS in the general Japanese population. Altered levels of DNA methylation in TXNIP at cg19693031 might play an important role in the pathogenesis of MetS.

Determinants in Tailoring Antidiabetic Therapies: A Personalized Approach

Diabetes has become a pandemic as the number of diabetic people continues to rise globally. Being a heterogeneous disease, it has different manifestations and associated complications in different individuals like diabetic nephropathy, neuropathy, retinopathy, and others. With the advent of science and technology, this era desperately requires increasing the pace of embracing precision medicine and tailoring of drug treatment based on the genetic composition of individuals. It has been previously established that response to antidiabetic drugs, like biguanides, sulfonylureas, dipeptidyl peptidase-4 (DPP-4) inhibitors, glucagon-like peptide 1 (GLP-1) agonists, and others, depending on variations in their transporter genes, metabolizing genes, genes involved in their action, etc. Responsiveness of these drugs also relies on epigenetic factors, including histone modifications, miRNAs, and DNA methylation, as well as environmental factors and the lifestyle of an individual. For precision medicine to make its way into clinical procedures and come into execution, all these factors must be reckoned with. This review provides an insight into several factors oscillating around the idea of precision medicine in type-2 diabetes mellitus.

Genomic imprinting of the IGF2R/AIR locus is conserved between bovines and mice

Genomic imprinting is an epigenetic phenomenon that leads to genes monoallelically expressed in a parent-of-origin-specific manner and plays an important role in the embryonic development and postnatal growth of mammals. Imprinted genes usually occur in clusters in a chromosomal region and are regulated by a cis-acting imprinting control region that involves differential DNA methylation modification. Igf2r, Slc22a2 and Slc22a3 are three maternally expressed genes on mouse chromosome 17. The paternally expressed long noncoding RNA (lncRNA) Air and the nonimprinted gene Slc22a1 are also located in the imprinted region. Comparative characterization of imprinted clusters between species is useful for us to understand the biological significance and epigenetic regulating mechanism of genomic imprinting. The aim of this study was to analyze the allelic expression pattern of AIR and SLC22A1-3 genes in cattle and to determine the role of DNA methylation in regulating gene expression. Allelic expression analysis was performed in bovine adult tissues and term placenta using an SNP-based approach. We found that IGF2R, AIR and SLC22A3 were monoallelically expressed in all detected bovine somatic tissues, including heart, liver, spleen, lung, kidney, muscle, fat and brain. In bovine placenta, IGF2R and SLC22A3 are maternally expressed; however, the AIR gene is paternally expressed. Tissue-specific monoallelic expression of SLC22A2 is detected in bovines, with monoallelic expression in the spleen and brain but biallelic expression in kidney tissues. SLC22A1 is only detected in bovine liver and kidney tissues and is biallelicly expressed, which is consistent with the imprint expression in mice. To determine the possible role of DNA methylation in regulating the monoallelic/imprinted expression of bovine IGF2R, AIR, SLC22A2, and SLC22A3 genes, we analyzed the DNA methylation status of CpG islands in the first exon of SLC22A2, the promoter region of SLC22A3 and region 2 in the second intron of the IGF2R gene by bisulfite sequencing. Two differentially methylated regions (DMRs) were detected in the first exon of bovine SLC22A3 and the common regions of IGF2R and AIR. This suggests that DNA methylation is involved in the regulation of monoallelic/imprinted expression of IGF2R, AIR and SLC22A3 genes in cattle.

An interferon-related signature characterizes the whole blood transcriptome profile of insulin-resistant individuals—the CODAM study

Background

Worldwide, the prevalence of obesity and insulin resistance has grown dramatically. Gene expression profiling in blood represents a powerful means to explore disease pathogenesis, but the potential impact of inter-individual differences in a cell-type profile is not always taken into account. The objective of this project was to investigate the whole blood transcriptome profile of insulin-resistant as compared to insulin-sensitive individuals independent of inter-individual differences in white blood cell profile.

Results

We report a 3% higher relative amount of monocytes in the insulin-resistant individuals. Furthermore, independent of their white blood cell profile, insulin-resistant participants had (i) higher expression of interferon-stimulated genes and (ii) lower expression of genes involved in cellular differentiation and remodeling of the actin cytoskeleton.

Conclusions

We present an approach to investigate the whole blood transcriptome of insulin-resistant individuals, independent of their DNA methylation-derived white blood cell profile. An interferon-related signature characterizes the whole blood transcriptome profile of the insulin-resistant individuals, independent of their white blood cell profile. The observed signature indicates increased systemic inflammation possibly due to an innate immune response and whole-body insulin resistance, which can be a cause or a consequence of insulin resistance. Altered gene expression in specific organs may be reflected in whole blood; hence, our results may reflect obesity and/or insulin resistance-related organ dysfunction in the insulin-resistant individuals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12263-021-00702-7.

Extrinsic and intrinsic factors influencing metabolic memory in type 2 diabetes

Direct and indirect influence of pathological conditions in Type 2 Diabetes (T2D) on vasculature manifests in micro and/or macro vascular complications that act as a major source of morbidity and mortality. Although preventive therapies exist to control hyperglycemia, diabetic subjects are always at risk to accrue vascular complications. One of the hypotheses explained is 'glycemic' or 'metabolic' memory, a process of permanent epigenetic change in different cell types whereby diabetes associated vascular complications continue despite glycemic control by antidiabetic drugs. Epigenetic mechanisms including DNA methylation possess a strong influence on the association between environment and gene expression, thus indicating its importance in the pathogenesis of a complex disease such as T2D. The vascular system is more prone to environmental influences and present high flexibility in response to physiological and pathological challenges. DNA methylation based epigenetic changes during metabolic memory are influenced by sustained hyperglycemia, inflammatory mediators, gut microbiome composition, lifestyle modifications and gene-nutrient interactions. Hence, understanding underlying mechanisms in manifesting vascular complications regulated by DNA methylation is of high clinical importance. The review provides an insight into various extrinsic and intrinsic factors influencing the regulation of DNA methyltransferases contributing to the pathogenesis of vascular complications during T2D.

Expression Profiles of Circulating microRNAs in South African Type 2 Diabetic Individuals on Treatment

Aim: The influence of disease duration and anti-diabetic treatment on epigenetic processes has been described, with limited focus on interactions with microRNAs (miRNAs). miRNAs have been found to play key roles in the regulation of pathways associated with type 2 diabetes mellitus (T2DM), and expression patterns in response to treatment may further promote their use as therapeutic targets in T2DM and its associated complications. We therefore aimed to investigate the expressions of circulating miRNAs (miR-30a-5p, miR-1299, miR-182-5p, miR-30e-3p and miR-126-3p) in newly diagnosed and known diabetics on treatment, in South Africa.

Methods: A total of 1254 participants with an average age of 53.8years were included in the study and classified according to glycaemic status (974 normotolerant, 92 screen-detected diabetes and 188 known diabetes). Whole blood levels of miR-30a-5p, miR-1299, miR-182-5p, miR-30e-3p and miR-126-3p were quantitated using RT-qPCR. Expression analysis was performed and compared across groups.

Results: All miRNAs were significantly overexpressed in subjects with known diabetes when compared to normotolerant individuals, as well as known diabetics vs. screen-detected (p<0.001). Upon performing regression analysis, of all miRNAs, only miR-182-5p remained associated with the duration of the disease after adjustment for type of treatment (OR: 0.127, CI: 0.018–0.236, p=0.023).

Conclusion: Our findings revealed important associations and altered expression patterns of miR-30a-5p, miR-1299, miR-182-5p, miR-30e-3p and miR-126-3p in known diabetics on anti-diabetic treatment compared to newly diagnosed individuals. Additionally, miR-182-5p expression decreased with increasing duration of T2DM. Further studies are, however, recommended to shed light on the involvement of the miRNA in insulin signalling and glucose homeostasis, to endorse its use as a therapeutic target in DM and its associated complications.

Polysaccharides of vinegar-baked radix bupleuri promote the hepatic targeting effect of oxymatrine by regulating the protein expression of HNF4α, Mrp2, and OCT1

ETHNOPHARMACOLOGICAL RELEVANCE

Vinegar-baked Radix Bupleuri (VBRB) is a processed form of Bupleurum chinense DC. As a well-known meridian-guiding drug, it is traditionally used as a component of traditional Chinese medicine formulations indicated for the treatment of liver diseases. However, the liver targeting component in VBRB remains unclear. Therefore, this study aims to explore the efficacy and mechanism of PSS (polysaccharides in Vinegar-baked Radix Bupleuri) in enhancing liver targeting.

MATERIALS AND METHODS

Drug distribution of OM alone or combined with PSS was investigated in vivo. Relative uptake efficiency (RUE) and relative targeting efficiency (RTE) were calculated to evaluate liver targeting efficiency. The mRNA and protein expression of organic cation transporter 1 (OCT1), multi-drug resistance protein 2 (Mrp2), and hepatocyte nuclear factor 4α (HNF4α) in the liver were determined by q-PCR and Western blot. Then, AZT, the inhibitor of OCT1 and BI6015, the inhibitor of HNF4α were used to investigate regulatory mechanisms involved in the uptake of OM in the cell. At last, the role of PSS in the anti-hepatitis B virus (HBV) was explored on HepG2.2.15.

RESULTS

PSS increased the AUC of OM in the liver and increase the RUE and RTE in the liver which indicated a liver targeting enhancing effect. The mRNA and protein expression of OCT1 was increased while Mrp2 and HNF4α decreased. PSS could increase the uptake of OM in HepG2 by increasing the protein expression of HNF4α and OCT1, while inhibited Mrp2. Moreover, PSS combined with OM could enhance the anti-HBV effect of OM.

CONCLUSION

PSS enhanced the liver targeting efficiency and the underlying mechanism related to up-regulating the expression of OCT1 and HNF4α, while down-regulating of Mrp2. These results suggest that PSS may become a potential excipient and provide a new direction for new targeted research.

Regulation Mechanisms of Expression and Function of Organic Cation Transporter 1

The organic cation transporter 1 (OCT1) belongs together with OCT2 and OCT3 to the solute carrier family 22 (SLC22). OCTs are involved in the movement of organic cations through the plasma membrane. In humans, OCT1 is mainly expressed in the sinusoidal membrane of hepatocytes, while in rodents, OCT1 is strongly represented also in the basolateral membrane of renal proximal tubule cells. Considering that organic cations of endogenous origin are important neurotransmitters and that those of exogenous origin are important drugs, these transporters have significant physiological and pharmacological implications. Because of the high expression of OCTs in excretory organs, their activity has the potential to significantly impact not only local but also systemic concentration of their substrates. Even though many aspects governing OCT function, interaction with substrates, and pharmacological role have been extensively investigated, less is known about regulation of OCTs. Possible mechanisms of regulation include genetic and epigenetic modifications, rapid regulation processes induced by kinases, regulation caused by protein–protein interaction, and long-term regulation induced by specific metabolic and pathological situations. In this mini-review, the known regulatory processes of OCT1 expression and function obtained from in vitro and in vivo studies are summarized. Further research should be addressed to integrate this knowledge to known aspects of OCT1 physiology and pharmacology.

Identifying Shared Risk Genes between Nonalcoholic Fatty Liver Disease and Metabolic Traits by Cross-Trait Association Analysis

Nonalcoholic fatty liver disease (NAFLD) generally co-occurs with metabolic disorders, but it is unclear which genes have a pleiotripic effect on NAFLD and metabolic traits. We performed a large-scale cross-trait association analysis to identify the overlapping genes between NAFLD and nine metabolic traits. Among all the metabolic traits, we found that obesity and type II diabetes are associated with NAFLD. Then, a multitrait association analysis among NAFLD, obesity and type II diabetes was conducted to improve the overall statistical power. We identified 792 significant variants by a cross-trait meta-analysis involving 100 pleiotripic genes. Moreover, we detected another two common genes by a genome-wide gene test. The results from the pathway enrichment analysis show that the 102 shared risk genes are enriched in cancer, diabetes, insulin secretion, and other related pathways. This study can help us understand the molecular mechanisms underlying comorbid NAFLD and metabolic disorders.

Restoration of mRNA Expression of Solute Carrier Proteins in Liver of Diet-Induced Obese Mice by Metformin

Metformin (MET), the most common medicine for type 2 diabetes (T2DM), improves insulin sensitivity by targeting the liver, intestine and other organs. Its impact on expression of the solute carrier (Slc) transporter genes have not been reported in the mechanism of insulin sensitization. In this study, we examined Slc gene expression in the liver and colon of diet-induced obese (DIO) mice treated with MET by transcriptomic analysis. There were 939 differentially expressed genes (DEGs) in the liver of DIO mice vs lean mice, which included 34 Slc genes. MET altered 489 DEGs in the liver of DIO mice, in which 23 were Slc genes. Expression of 20 MET-responsive Slc DEGs was confirmed by qRT-PCR, in which 15 Slc genes were altered in DIO mice and their expressions were restored by MET, including Slc2a10, Slc2a13, Slc5a9, Slc6a14, Slc7a9, Slc9a2, Slc9a3, Slc13a2, Slc15a2, Slc26a3, Slc34a2, Slc37a1, Slc44a4, Slc51b and Slc52a3. While, there were only 97 DEGs in the colon of DIO mice with 5 Slc genes, whose expression was not restored by MET. The data suggest that more genes were altered in the liver over the colon by the high fat diet (HFD). There were 20 Slc genes with alteration confirmed in the liver of DIO mice and 15 of them were restored by MET, which was associated with improvement of insulin sensitivity and obesity. The restoration may improve the uptake of glucose, amino acids, mannose, fructose, 1,5-anhydro-D-glucitol and bumetanide in hepatocytes of the liver of DIO mice. The study provides new insight into the mechanism of metformin action in insulin sensitization and obesity.

Epigenetics of Hepatic Insulin Resistance

Insulin resistance (IR) is largely recognized as a unifying feature that underlies metabolic dysfunction. Both lifestyle and genetic factors contribute to IR. Work from recent years has demonstrated that the epigenome may constitute an interface where different signals may converge to promote IR gene expression programs. Here, we review the current knowledge of the role of epigenetics in hepatic IR, focusing on the roles of DNA methylation and histone post-translational modifications. We discuss the broad epigenetic changes observed in the insulin resistant liver and its associated pathophysiological states and leverage on the wealth of 'omics' studies performed to discuss efforts in pinpointing specific loci that are disrupted by these changes. We envision that future studies, with increased genomic resolution and larger cohorts, will further the identification of biomarkers of early onset hepatic IR and assist the development of targeted interventions. Furthermore, there is growing evidence to suggest that persistent epigenetic marks may be acquired over prolonged exposure to disease or deleterious exposures, highlighting the need for preventative medicine and long-term lifestyle adjustments to avoid irreversible or long-term alterations in gene expression.

Reading between the (Genetic) Lines: How Epigenetics is Unlocking Novel Therapies for Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune condition where the body’s immune cells destroy their insulin-producing pancreatic beta cells leading to dysregulated glycaemia. Individuals with T1D control their blood glucose through exogenous insulin replacement therapy, often using multiple daily injections or pumps. However, failure to accurately mimic intrinsic glucose regulation results in glucose fluctuations and long-term complications impacting key organs such as the heart, kidneys, and/or the eyes. It is well established that genetic and environmental factors contribute to the initiation and progression of T1D, but recent studies show that epigenetic modifications are also important. Here, we discuss key epigenetic modifications associated with T1D pathogenesis and discuss how recent research is finding ways to harness epigenetic mechanisms to prevent, reverse, or manage T1D.

Genome-Wide DNA Methylation and LncRNA-Associated DNA Methylation in Metformin-Treated and -Untreated Diabetes

Metformin, which is used as a first line treatment for type 2 diabetes mellitus (T2DM), has been shown to affect epigenetic patterns. In this study, we investigated the DNA methylation and potential lncRNA modifications in metformin-treated and newly diagnosed adults with T2DM. Genome-wide DNA methylation and lncRNA analysis were performed from the peripheral blood of 12 screen-detected and 12 metformin-treated T2DM individuals followed by gene ontology (GO) and KEGG pathway analysis. Differentially methylated regions (DMRs) observed showed 22 hypermethylated and 11 hypomethylated DMRs between individuals on metformin compared to screen-detected subjects. Amongst the hypomethylated DMR regions were the SLC gene family, specifically, SLC25A35 and SLC28A1. Fifty-seven lncRNA-associated DNA methylation regions included the mitochondrial ATP synthase-coupling factor 6 (ATP5J). Functional gene mapping and pathway analysis identified regions in the axon initial segment (AIS), node of Ranvier, cell periphery, cleavage furrow, cell surface furrow, and stress fiber. In conclusion, our study has identified a number of DMRs and lncRNA-associated DNA methylation regions in metformin-treated T2DM that are potential targets for therapeutic monitoring in patients with diabetes.

Hypomethylation of IL1RN and NFKB1 genes is linked to the dysbalance in IL1β/IL-1Ra axis in female patients with type 2 diabetes mellitus

Inflammation has received considerable attention in the pathogenesis of type 2 diabetes mellitus (T2DM). Supporting this concept, enhanced expression of interleukin (IL)-1β and increased infiltration of macrophages are observed in pancreatic islets of patients with T2DM. Although IL-1 receptor antagonist (IL-1Ra) plays a major role in controlling of IL-1β-mediated inflammation, its counteraction effects and epigenetic alterations in T2DM are less studied. Thus, we aimed to analyze the DNA methylation status in IL1RN, RELA (p65) and NFKB1 (p50) genes in peripheral blood mononuclear cells (PBMCs) from treated T2DM patients (n = 35) and age-/sex- matched healthy controls (n = 31). Production of IL-1β and IL-1Ra was analyzed in plasma and supernatants from LPS-induced PBMCs. Immunomodulatory effects of IL-1β and IL-1Ra were studied on THP-1 cells. Average DNA methylation level of IL1RN and NFKB1 gene promoters was significantly decreased in T2DM patients in comparison with healthy controls (P< 0.05), which was associated with the increased IL-1Ra (P< 0.001) and IL-1β (P = 0.039) plasma levels in T2DM patients. Negative association between average methylation of IL1RN gene and IL-1Ra plasma levels were observed in female T2DM patients. Methylation of NFKB1 gene was negatively correlated with IL-1Ra levels in the patients and positively with IL-1β levels in female patients. LPS-stimulated PBMCs from female patients failed to raise IL-1β production, while the cells from healthy females increased IL-1β production in comparison with unstimulated cells (P< 0.001). Taken together, the findings suggest that hypomethylation of IL1RN and NFKB1 gene promoters may promote the increased IL-1β/IL-1Ra production and regulate chronic inflammation in T2DM. Further studies are necessary to elucidate the causal direction of these associations and potential role of IL-1Ra in anti-inflammatory processes in treated patients with T2DM.

The Importance of Precision Medicine in Type 2 Diabetes Mellitus (T2DM): From Pharmacogenetic and Pharmacoepigenetic Aspects

BACKGROUND

Type 2 Diabetes Mellitus (T2DM) is a worldwide disorder as the most important challenges of health-care systems. Controlling the normal glycaemia greatly profit long-term prognosis and gives explanation for early, effective, constant, and safe intervention.

MATERIAL AND METHODS

Finding the main genetic and epigenetic profile of T2DM and the exact molecular targets of T2DM medications can shed light on its personalized management. The comprehensive information of T2DM was earned through the genome-wide association study (GWAS) studies. In the current review, we represent the most important candidate genes of T2DM like CAPN10, TCF7L2, PPAR-γ, IRSs, KCNJ11, WFS1, and HNF homeoboxes. Different genetic variations of a candidate gene can predict the efficacy of T2DM personalized strategy medication.

RESULTS

SLCs and AMPK variations are considered for metformin, CYP2C9, KATP channel, CDKAL1, CDKN2A/2B and KCNQ1 for sulphonylureas, OATP1B, and KCNQ1 for repaglinide and the last but not the least ADIPOQ, PPAR-γ, SLC, CYP2C8, and SLCO1B1 for thiazolidinediones response prediction.

CONCLUSION

Taken everything into consideration, there is an extreme need to determine the genetic status of T2DM patients in some known genetic region before planning the medication strategies.

DNA methylation: a cause and consequence of type 2 diabetes

DNA methylation is a relatively stable epigenetic modification that can regulate and stabilize gene expression patterns and hence establish cell identity. Because metabolic intermediates are key factors of DNA methylation and demethylation, perturbations in metabolic homeostasis can trigger alterations in cell-specific patterns of DNA methylation and contribute to disease development, including type 2 diabetes (T2D). During the past decade, genome-wide DNA methylation studies of T2D have expanded our knowledge of the molecular mechanisms underlying T2D. This review summarizes case-control studies of the DNA methylome of T2D and discusses DNA methylation as both a cause and consequence of T2D. Therefore, DNA methylation has potential as a promising T2D biomarker that can be applied to the development of therapeutic strategies for T2D.

Insights into the Role of DNA Methylation and Protein Misfolding in Diabetes Mellitus

Background:

Diabetes mellitus is a metabolic disorder that is characterized by impaired glucose tolerance resulting from defects in insulin secretion, insulin action, or both. Epigenetic modifications, which are defined as inherited changes in gene expression that occur without changes in gene sequence, are involved in the etiology of diabetes.

Methods:

In this review, we focused on the role of DNA methylation and protein misfolding and their contribution to the development of both type 1 and type 2 diabetes mellitus.

Results:

Changes in DNA methylation in particular are highly associated with the development of diabetes. Protein function is dependent on their proper folding in the endoplasmic reticulum. Defective protein folding and consequently their functions have also been reported to play a role. Early treatment of diabetes has proven to be of great benefit, as even transient hyperglycemia may lead to pathological effects and complications later on. This has been explained by the theory of the development of a metabolic memory in diabetes. The basis for this metabolic memory was attributed to oxidative stress, chronic inflammation, non-enzymatic glycation of proteins and importantly, epigenetic changes. This highlights the importance of linking new therapeutics targeting epigenetic mechanisms with traditional antidiabetic drugs.

Conclusion:

Although new data is evolving on the relation between DNA methylation, protein misfolding, and the etiology of diabetes, more studies are required for developing new relevant diagnostics and therapeutics.

Significantly altered peripheral blood cell DNA methylation profile as a result of immediate effect of metformin use in healthy individuals

BACKGROUND

Metformin is a widely prescribed antihyperglycemic agent that has been also associated with multiple therapeutic effects in various diseases, including several types of malignancies. There is growing evidence regarding the contribution of the epigenetic mechanisms in reaching metformin's therapeutic goals; however, the effect of metformin on human cells in vivo is not comprehensively studied. The aim of our study was to examine metformin-induced alterations of DNA methylation profiles in white blood cells of healthy volunteers, employing a longitudinal study design.

RESULTS

Twelve healthy metformin-naïve individuals where enrolled in the study. Genome-wide DNA methylation pattern was estimated at baseline, 10 h and 7 days after the start of metformin administration. The whole-genome DNA methylation analysis in total revealed 125 differentially methylated CpGs, of which 11 CpGs and their associated genes with the most consistent changes in the DNA methylation profile were selected: POFUT2, CAMKK1, EML3, KIAA1614, UPF1, MUC4, LOC727982, SIX3, ADAM8, SNORD12B, VPS8, and several differentially methylated regions as novel potential epigenetic targets of metformin. The main functions of the majority of top-ranked differentially methylated loci and their representative cell signaling pathways were linked to the well-known metformin therapy targets: regulatory processes of energy homeostasis, inflammatory responses, tumorigenesis, and neurodegenerative diseases.

CONCLUSIONS

Here we demonstrate for the first time the immediate effect of short-term metformin administration at therapeutic doses on epigenetic regulation in human white blood cells. These findings suggest the DNA methylation process as one of the mechanisms involved in the action of metformin, thereby revealing novel targets and directions of the molecular mechanisms underlying the various beneficial effects of metformin.

TRIAL REGISTRATION

EU Clinical Trials Register, 2016-001092-74. Registered 23 March 2017, https://www.clinicaltrialsregister.eu/ctr-search/trial/2016-001092-74/LV .

Changes in tramadol enantioselective pharmacokinetics and metabolism in rats with experimental diabetes treated or not with insulin

This study aimed to investigate the impact of diabetes treated or not with insulin in the enantioselective pharmacokinetics of tramadol (trans-T) and its phase 1 metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2). The CYP2D inhibitor quinidine was used to simulate the poor metabolizer phenotype. Male Wistar rats were divided into groups: control, quinidine (80-mg/kg quinidine intraperitoneally 4 h before trans-T), diabetic (45-mg/kg STZ i.v.), diabetes + insulin (2 IU/day insulin for 12 days), diabetes + quinidine and diabetes + insulin + quinidine. All animals (n = 6, per sampling time) received 20-mg/kg trans-T orally. The kinetic disposition of trans-T is enantioselective in control with higher AUC of (+)-trans-T than for its antipode. Quinidine reduced AUC ratios (+)-M1/(+)-trans-T and (-)-M1/(-)-trans-T compared to Control. Diabetes increased plasma concentrations of (+)-trans-T, (-)-trans-T, (+)-M1, (-)-M1 and (+)-M2 compared to control, but without changing AUC ratios M1/trans-T or M2/trans-T. Insulin reverted the effect of diabetes only for (-)-trans-T. The simulated diabetes in CYP2D poor metabolizers showed reduced metabolic ratios for M1 enantiomers. In conclusion, diabetes resulted in higher plasma concentrations of the active (+)-trans-T, (-)-trans-T and (+)-M1, suggesting down-regulation of CYP3A and OCT1. The glycemic control of diabetes by insulin reduces partially the impact of diabetes on trans-T pharmacokinetics.

Epigenetic effects of metformin: From molecular mechanisms to clinical implications

There is a growing body of evidence that links epigenetic modifications to type 2 diabetes. Researchers have more recently investigated effects of commonly used medications, including those prescribed for diabetes, on epigenetic processes. This work reviews the influence of the widely used antidiabetic drug metformin on epigenomics, microRNA levels and subsequent gene expression, and potential clinical implications. Metformin may influence the activity of numerous epigenetic modifying enzymes, mostly by modulating the activation of AMP-activated protein kinase (AMPK). Activated AMPK can phosphorylate numerous substrates, including epigenetic enzymes such as histone acetyltransferases (HATs), class II histone deacetylases (HDACs) and DNA methyltransferases (DNMTs), usually resulting in their inhibition; however, HAT1 activity may be increased. Metformin has also been reported to decrease expression of multiple histone methyltransferases, to increase the activity of the class III HDAC SIRT1 and to decrease the influence of DNMT inhibitors. There is evidence that these alterations influence the epigenome and gene expression, and may contribute to the antidiabetic properties of metformin and, potentially, may protect against cancer, cardiovascular disease, cognitive decline and aging. The expression levels of numerous microRNAs are also reportedly influenced by metformin treatment and may confer antidiabetic and anticancer activities. However, as the reported effects of metformin on epigenetic enzymes act to both increase and decrease histone acetylation, histone and DNA methylation, and gene expression, a significant degree of uncertainty exists concerning the overall effect of metformin on the epigenome, on gene expression, and on the subsequent effect on the health of metformin users.

DNA methylation landscapes in the pathogenesis of type 2 diabetes mellitus

Although genetic variations and environmental factors are vital to the development and progression of type 2 diabetes mellitus (T2DM), emerging literature suggest that epigenetics, especially DNA methylation, play a key role in the pathogenesis of T2DM by affecting insulin secretion of pancreatic β cells and the body’s resistance to insulin. Previous studies have elucidated how DNA methylation interacted with various factors in T2DM pathogenesis. This review summarized the role of related methylation genes in insulin-sensitive organs, such as pancreatic islets, skeletal muscle, liver, brain and adipose tissue, as well as peripheral blood cells, comparing the tissue similarity and specificity of methylated genes, aiming at a better understanding of the pathogenesis of T2DM and providing new ideas for the personalized treatment of this metabolism-associated disease.

Altered DNA methylation in liver and adipose tissues derived from individuals with obesity and type 2 diabetes

Background

Obesity is a well-recognized risk factor for insulin resistance and type 2 diabetes (T2D), although the precise mechanisms underlying the relationship remain unknown. In this study we identified alterations of DNA methylation influencing T2D pathogenesis, in subcutaneous and visceral adipose tissues, liver, and blood from individuals with obesity.

Methods

The study included individuals with obesity, with and without T2D. From these patients, we obtained samples of liver tissue (n = 16), visceral and subcutaneous adipose tissues (n = 30), and peripheral blood (n = 38). We analyzed DNA methylation using Illumina Infinium Human Methylation arrays, and gene expression profiles using HumanHT-12 Expression BeadChip Arrays.

Results

Analysis of DNA methylation profiles revealed several loci with differential methylation between individuals with and without T2D, in all tissues. Aberrant DNA methylation was mainly found in the liver and visceral adipose tissue. Gene ontology analysis of genes with altered DNA methylation revealed enriched terms related to glucose metabolism, lipid metabolism, cell cycle regulation, and response to wounding. An inverse correlation between altered methylation and gene expression in the four tissues was found in a subset of genes, which were related to insulin resistance, adipogenesis, fat storage, and inflammation.

Conclusions

Our present findings provide additional evidence that aberrant DNA methylation may be a relevant mechanism involved in T2D pathogenesis among individuals with obesity.

Electronic supplementary material

The online version of this article (10.1186/s12881-018-0542-8) contains supplementary material, which is available to authorized users.

DNA methylation in the pathogenesis of type 2 diabetes in humans

Background

Type 2 diabetes (T2D) is a multifactorial, polygenic disease caused by impaired insulin secretion and insulin resistance. Genome-wide association studies (GWAS) were expected to resolve a large part of the genetic component of diabetes; yet, the single nucleotide polymorphisms identified by GWAS explain less than 20% of the estimated heritability for T2D. There was subsequently a need to look elsewhere to find disease-causing factors. Mechanisms mediating the interaction between environmental factors and the genome, such as epigenetics, may be of particular importance in the pathogenesis of T2D.

Scope of Review

This review summarizes knowledge of the impact of epigenetics on the pathogenesis of T2D in humans. In particular, the review will focus on alterations in DNA methylation in four human tissues of importance for the disease; pancreatic islets, skeletal muscle, adipose tissue, and the liver. Case–control studies and studies examining the impact of non-genetic and genetic risk factors on DNA methylation in humans will be considered. These studies identified epigenetic changes in tissues from subjects with T2D versus non-diabetic controls. They also demonstrate that non-genetic factors associated with T2D such as age, obesity, energy rich diets, physical activity and the intrauterine environment impact the epigenome in humans. Additionally, interactions between genetics and epigenetics seem to influence the pathogenesis of T2D.

Conclusions

Overall, previous studies by our group and others support a key role for epigenetics in the growing incidence of T2D.