Insulin resistance induced by hyperinsulinemia coincides with a persistent alteration at the insulin receptor tyrosine kinase domain

Rice Protein Peptides Ameliorate DSS-Induced Cognitive Impairment and Depressive Behavior in Mice by Modulating Phenylalanine Metabolism and the BDNF/TRKB/CREB Pathway

Rice protein peptide (RPP) has been reported to alleviate the symptoms of dextran sulfate sodium (DSS)-induced colitis, but its potential protective effect and fundamental neurobiological mechanisms against DSS-induced inflammatory bowel disease (IBD), coupled with depression and cognitive impairment, remain unclear. In this study, RPP treatment in DSS-induced mice inhibited decreases in body weight and colon length and improved intestinal barrier function and behavioral performance. RPP treatment enhanced phenylalanine and tyrosine metabolism in the brains of mice, and it upregulated metabolites such as l-dopa, phenylethylamine, and 3,4-dihydroxyphenylacetate. Additionally, RPP treatment enhanced the brain-derived neurotrophic factor (BDNF) by upregulating the BDNF/TrkB/CREB signaling pathway. Spearman's correlation analysis revealed that the phenylalanine and tyrosine contents in the brain were significantly negatively correlated with the BDNF/TrkB/CREB signaling pathway and behavioral performance. In conclusion, this study suggested that RPP may serve as a unique nutritional strategy for preventing IBD and its associated cognitive impairment and depression symptoms.

Insulin promotes the bone formation capability of human dental pulp stem cells through attenuating the IIS/PI3K/AKT/mTOR pathway axis

BACKGROUND

Insulin has been known to regulate bone metabolism, yet its specific molecular mechanisms during the proliferation and osteogenic differentiation of dental pulp stem cells (DPSCs) remain poorly understood. This study aimed to explore the effects of insulin on the bone formation capability of human DPSCs and to elucidate the underlying mechanisms.

METHODS

Cell proliferation was assessed using a CCK-8 assay. Cell phenotype was analyzed by flow cytometry. Colony-forming unit-fibroblast ability and multilineage differentiation potential were evaluated using Toluidine blue, Oil red O, Alizarin red, and Alcian blue staining. Gene and protein expressions were quantified by real-time quantitative polymerase chain reaction and Western blotting, respectively. Bone metabolism and biochemical markers were analyzed using electrochemical luminescence and chemical colorimetry. Cell adhesion and growth on nano-hydroxyapatite/collagen (nHAC) were observed with a scanning electron microscope. Bone regeneration was assessed using micro-CT, fluorescent labeling, immunohistochemical and hematoxylin and eosin staining.

RESULTS

Insulin enhanced the proliferation of human DPSCs as well as promoted mineralized matrix formation in a concentration-dependent manner. 10- 6 M insulin significantly up-regulated osteogenic differentiation-related genes and proteins markedly increased the secretion of bone metabolism and biochemical markers, and obviously stimulated mineralized matrix formation. However, it also significantly inhibited the expression of genes and proteins of receptors and receptor substrates associated with insulin/insulin-like growth factor-1 signaling (IIS) pathway, obviously reduced the expression of the phosphorylated PI3K and the ratios of the phosphorylated PI3K/total PI3K, and notably increased the expression of the total PI3K, phosphorylated AKT, total AKT and mTOR. The inhibitor LY294002 attenuated the responsiveness of 10- 6 M insulin to IIS/PI3K/AKT/mTOR pathway axis, suppressing the promoting effect of insulin on cell proliferation, osteogenic differentiation and bone formation. Implantation of 10- 6 M insulin treated DPSCs into the backs of severe combined immunodeficient mice and the rabbit jawbone defects resulted in enhanced bone formation.

CONCLUSIONS

Insulin induces insulin resistance in human DPSCs and effectively promotes their proliferation, osteogenic differentiation and bone formation capability through gradually inducing the down-regulation of IIS/PI3K/AKT/mTOR pathway axis under insulin resistant states.

Impact of Serotonin Transporter Absence on Brain Insulin Receptor Expression, Plasma Metabolome Changes, and ADHD-like Behavior in Mice fed a Western Diet

The impaired function of the serotonin transporter (SERT) in humans has been linked to a higher risk of obesity and type 2 diabetes, especially as people age. Consuming a "Western diet" (WD), which is high in saturated fats, cholesterol, and sugars, can induce metabolic syndrome. Previous research indicated that mice carrying a targeted inactivation of the Sert gene (knockout, KO) and fed a WD display significant metabolic disturbances and behaviors reminiscent of ADHD. These abnormalities might be mediated via a dysfunction in insulin receptor (IR) signaling, which is also associated with adult ADHD. However, the impact of Sert deficiency on IR signaling and systemic metabolic changes has not been thoroughly explored. In this study, we conducted a detailed analysis of locomotor behavior in wild-type (WT) and KO mice fed a WD or control diet. We investigated changes in the blood metabolome and examined, via PCR, the expression of insulin receptor A and B isoforms and key regulators of their function in the brain. Twelve-month-old KO mice and their WT littermates were fed a WD for three weeks. Nuclear magnetic resonance spectroscopy analysis of plasma samples showed that KO mice on a WD had higher levels of lipids and lipoproteins and lower levels of glucose, lactate, alanine, valine, and isoleucine compared to other groups. SERT-KO mice on the control diet exhibited increased brain levels of both IR A and B isoforms, accompanied by a modest increase in the negative regulator ENPP. The KO mice also displayed anxiety-like behavior and reduced exploratory activity in an open field test. However, when the KO animals were fed a WD, the aberrant expression levels of IR isoforms in the KO mice and locomotor behavior were ameliorated indicating a complex interaction between genetic and dietary factors that might contribute to ADHD-like symptoms. Overall, our findings suggest that the lack of Sert leads to a unique metabolic phenotype in aged mice, characterized by dysregulated IR-related pathways. These changes are exacerbated by WD in the blood metabolome and are associated with behavioral abnormalities.

The antioxidant, antidiabetic, and antihyperlipidemic effects of the polyphenolic extract from Salvia blancoana subsp. mesatlantica on induced diabetes in rats

Currently, several studies have demonstrated the benefits of medicinal plants in managing type 2 diabetes. In this work, we evaluated the beneficial effects of the polyphenolic extract (PESB) from Salvia blancoana subsp. mesatlantica in the management of hypercaloric-feeding and small-dose alloxan-brought type 2 diabetes in rats. We analyzed the chemical constituents of the extract, including flavones and flavonols content, to understand its biological action. The antioxidant activities were evaluated by total antioxidant action, scavenging effect of the free radical DPPH, and reducing power. The obtained results showed that the value of TFC was estimated at 31.90 ± 0.34 mgEQ/g in the PESB extract. The total antioxidant capacity was estimated at 593.51 ± 4.09 mg (EAA)/g, the value of DPPH IC50 was 7.3 ± 0.00 μg/mL, and the value of EC50 of reducing power was estimated at 6.43 ± 0.01 μg/mL. In total, 14 phenolic compounds were identified and the naringin was the most dominant (63.19%) while the vanillin was the less recorded (0.10%). Serum glucose decreased significantly (p < 0.05) in rats given PESB (100 mg/kg) after four weeks. Glibenclamide (GLB) and PESB reduced HbA1c and increased plasma insulin in diabetic rats, restoring HOMA-β and HOMA-IR levels to near-normal. Additionally, diabetic rats treated with GLB or PESB showed statistically equivalent results to those of non-diabetic rats regarding hepatic enzymes, renal and lipid markers, as well as cardiovascular indices. The weight loss was significantly lower in diabetic rats receiving a dose of PESB (100 mg/kg), and GLB compared to corresponding untreated diabetic rats (p < 0.01). PESB and GLB showed a prominent protective function in the pancreas, liver, and kidney tissues. This investigation demonstrates the capacity of extracts from leaves of S. blancoana subsp. mesatlantica to manage diabetes mellitus due to their richness in a wide range of bioactive compounds. Therefore, more investigations are required to estimate the safety of the plant use.

A rare case report of reversible glucose counterregulation in an insulinoma patient with type 2 diabetes

CONTEXT

Insulinoma is a neuroendocrine tumor derived from pancreatic β -cells whose clinical manifestation is recurrent hypoglycemia. Insulinoma in a patient with preexisting diabetes is extraordinarily rare, and the unmasking of type 2 diabetes (T2DM) after insulinoma surgery is even rarer.

CASE REPORT

This article reports a 49-year-old male patient with insulinoma that masked the diagnosis of T2DM. The patient was admitted to the hospital with symptoms of hypoglycemia, such as repeated sweating, palpitations, and asthenia for over 4 years. The patient was diagnosed with insulinoma after completing relevant examinations. The emergence of hyperglycemia after the removal of insulinoma is attributable to the coexistence of T2DM. Surprisingly, a reversible decrease in cortisol levels was observed during the diagnostic process. We searched the previously published reports of this type of case from PubMed to determine why type 2 diabetes was covered by insulinoma and why glucocorticoids decreased.

CONCLUSIONS

The diagnosis of T2DM in the patient after surgery may be related to increased food intake and insulin resistance induced by hyperinsulinemia caused by long-term hypoglycemia. The reversible decrease in cortisol levels, not adrenocortical insufficiency during the diagnostic process, may be caused by a transient abnormality in glucose counterregulation.

Metabolic syndrome and pharmacotherapy outcomes in patients with type 2 diabetes mellitus

Background

Metabolic syndrome is a group of metabolic abnormalities that increase predisposition to several diseases including ischemic heart disease and diabetes mellitus. The study aimed to investigate metabolic syndrome among patients with type-2 diabetes mellitus (DM), and its impact on pharmacotherapy outcomes.

Methods

An observational cross-sectional study was performed on 910 patients with type-2 DM between June and December 2023. Fasting blood sugar, triglycerides, high-density lipoproteins (HDL), blood pressure, and abdominal obesity were measured. Metabolic syndrome was identified according to the National Cholesterol Education Program Adult Treatment Panel III criteria. Pharmacotherapy outcomes were assessed according to American Association of Clinical Endocrinologists and American Diabetes Association guidelines using the ability to achieve adequate glycemic control and normal levels of blood pressure and fasting plasma lipoproteins.

Results

In total, 87.5% of type-2 DM patients had metabolic syndrome; the prevalence increased with age and was higher among females. Metabolic syndrome showed the following distribution of risk factors: insulin resistance (100%), low HDL (95.3%), elevated blood pressure (83%), triglycerides dyslipidemia (80.1%), and abdominal obesity (62.5%). Majority of the patients had either 5 or 4 risk factors of metabolic syndrome. The most common comorbidities were dyslipidemia (97.7%) and hypertension (83%). Treatment outcomes were insufficient where adequate glycemic control was only achieved in 12% of type-2 DM patients, and proper management of comorbid dyslipidemia and hypertension was achieved in 29% and 40.9% of patients, respectively. Adequate blood pressure control was less achieved in patients with metabolic syndrome (34.4%) than those without metabolic syndrome (77.2%). Similarly, dyslipidemia was less controlled in patients with metabolic syndrome (26.9%) than in those without metabolic syndrome (47.3%).

Conclusion

Pharmacotherapy outcomes were inadequate for most patients with type-2 diabetes mellitus. Adopting early preventive and therapeutic interventions for metabolic syndrome is advised to improve treatment outcomes of the comorbid dyslipidemia and hypertension.

Double diabetes-when type 1 diabetes meets type 2 diabetes: definition, pathogenesis and recognition

Currently, the differentiation between type 1 diabetes (T1D) and type 2 diabetes (T2D) is not straightforward, and the features of both types of diabetes coexist in one subject. This situation triggered the need to discriminate so-called double diabetes (DD), hybrid diabetes or type 1.5 diabetes, which is generally described as the presence of the insulin resistance characteristic of metabolic syndrome in individuals diagnosed with T1D. DD not only raises the question of proper classification of diabetes but is also associated with a significantly greater risk of developing micro- and macroangiopathic complications, which was independent of glycaemic control. When considering the global obesity pandemic and increasing incidence of T1D, the prevalence of DD may also presumably increase. Therefore, it is of the highest priority to discover the mechanisms underlying the development of DD and to identify appropriate methods to prevent or treat DD. In this article, we describe how the definition of double diabetes has changed over the years and how it is currently defined. We discuss the accuracy of including metabolic syndrome in the DD definition. We also present possible hypotheses connecting insulin resistance with T1D and propose possible methods to identify individuals with double diabetes based on indirect insulin resistance markers, which are easily assessed in everyday clinical practice. Moreover, we discuss adjuvant therapy which may be considered in double diabetic patients.

Diabetic Encephalopathy: Role of Oxidative and Nitrosative Factors in Type 2 Diabetes

Diabetes mellitus is a set of complex metabolic disorders characterized by chronic hyperglycaemic condition due to defective insulin secretion (Type 1) and action (Type 2), which leads to serious micro and macro-vascular damage, inflammation, oxidative and nitrosative stress and a deranged energy homeostasis due to imbalance in the glucose and lipid metabolism. Moreover, patient with diabetes mellitus often showed the nervous system disorders known as diabetic encephalopathy. The precise pathological mechanism of diabetic encephalopathy by which it effects the central nervous system directly or indirectly causing the cognitive and motor impairment, is not completely understood. However, it has been speculated that like other extracerebellar tissues, oxidative and nitrosative stress may play significant role in the pathogenesis of diabetic encephalopathy. Therefore, the present review aimed to explain the possible association of the oxidative and nitrosative stress caused by the chronic hyperglycaemic condition with the central nervous system complications of the type 2 diabetes mellitus induced diabetic encephalopathy.

Insulin and aging - a disappointing relationship

Experimental studies in animal models of aging such as nematodes, fruit flies or mice have observed that decreased levels of insulin or insulin signaling promotes longevity. In humans, hyperinsulinemia and concomitant insulin resistance are associated with an elevated risk of age-related diseases suggestive of a shortened healthspan. Age-related disorders include neurodegenerative diseases, hypertension, cardiovascular disease, and type 2 diabetes. High ambient insulin concentrations promote increased lipogenesis and fat storage, heightened protein synthesis and accumulation of non-functional polypeptides due to limited turnover capacity. Moreover, there is impaired autophagy activity, and less endothelial NO synthase activity. These changes are associated with mitochondrial dysfunction and oxidative stress. The cellular stress induced by anabolic activity of insulin initiates an adaptive response aiming at maintaining homeostasis, characterized by activation of the transcription factor Nrf2, of AMP activated kinase, and an unfolded protein response. This protective response is more potent in the long-lived human species than in short-lived models of aging research resulting in a stronger pro-aging impact of insulin in nematodes and fruit flies. In humans, resistance to insulin-induced cell stress decreases with age, because of an increase of insulin and insulin resistance levels but less Nrf2 activation. These detrimental changes might be contained by adopting a lifestyle that promotes low insulin/insulin resistance levels and enhances an adaptive response to cellular stress, as observed with dietary restriction or exercise.

Effect of Insulin on Bone Formation Ability of Rat Alveolar Bone Marrow Mesenchymal Stem Cells

The alveolar bone marrow mesenchymal stem cells (ABM-MSCs) play an important role in oral bone healing and regeneration. Insulin is considered to improve impaired oral bones due to local factors, systemic factors and pathological conditions. However, the effect of insulin on bone formation ability of ABM-MSCs still needs to be elucidated. The aim of this study was to determine the responsiveness of rat ABM-MSCs to insulin and to explore the underlying mechanism. We found that insulin promoted ABM-MSCs proliferation in a concentration-dependent manner, in which 10-6 M insulin exerted the most significant effect. 10-6 M insulin significantly promoted the type I collagen (COL-1) synthesis, alkaline phosphatase (ALP) activity, osteocalcin (OCN) expression, and mineralized matrix formation in ABM-MSCs, significantly enhanced the gene and protein expressions of intracellular COL-1, ALP, and OCN. Acute insulin stimulation significantly promoted insulin receptor (IR) phosphorylation, IR substrate-1 (IRS-1) protein expression, and mammalian target of rapamycin (mTOR) phosphorylation, but chronic insulin stimulation decreased these values, while inhibitor NT219 could attenuate these responses. When seeded on β-tricalcium phosphate (β-TCP), ABM-MSCs adhered and grew well, during the 28-day culture period, ABM-MSCs+β-TCP +10-6 M insulin group showed significantly higher extracellular total COL-1 amino-terminus prolongation peptide content, ALP activity, OCN secretion, and Ca and P concentration. When implanted subcutaneously in severe combined immunodeficient mice for 1 month, the ABM-MSCs+β-TCP +10-6 M insulin group obtained the most bone formation and blood vessels. These results showed that insulin promoted the proliferation and osteogenic differentiation of ABM-MSCs in vitro, and enhance osteogenesis and angiogenesis of ABM-MSCs in vivo. Inhibition studies demonstrated that the insulin-induced osteogenic differentiation of ABM-MSCs was dependent of insulin/mTOR signaling. It suggests that insulin has a direct anabolic effect on ABM-MSCs.

Sex hormone-binding globulin (SHBG) mitigates ER stress and improves viability and insulin sensitivity in adipose-derived mesenchymal stem cells (ASC) of equine metabolic syndrome (EMS)-affected horses

BACKGROUND

Equine metabolic syndrome (EMS), which encompasses insulin resistance, low-grade inflammation and predisposition to laminitis is a critical endocrine disorder among the most prevalent conditions affecting horses from different breeds. According to the most recent research, low human sex hormone-binding globulin (SHBG) serum levels correlate with an increased risk of obesity, insulin resistance and diabetes, and may contribute to overall metabolic dysregulations. This study aimed to test whether exogenous SHBG could protect EMS affected adipose-derived stromal stem cells (EqASCEMS) from apoptosis, oxidative stress, ER stress and thus improve insulin sensitivity.

METHODS

EqASCEMS wells were treated with two different concentrations (50 and 100 nM) of exogenous SHBG, whose biocompatibility was tested after 24, 48 and 72 h of incubation. Several parameters including cell viability, apoptosis, cell cycle, reactive oxygen species levels, ER stress, Pi3K/MAPK activation and insulin transducers expression were analysed.

RESULTS

Obtained data demonstrated that exogenous SHBG treatment significantly promoted ASCs cells proliferation, cell cycle and survival with reduced expression of p53 and p21 pro-apoptotic mediators. Furthermore, SHBG alleviated the oxidative stress caused by EMS and reduced the overaccumulation of intracellular ROS, by reducing ROS + cell percentage and regulating gene expression of endogenous antioxidant enzymes (Sod 1, Cat, GPx), SHBG treatment exhibited antioxidant activity by modulating total nitric oxide (NO) levels in EMS cells as well. SHBG treatment dampened the activation of ER stress sensors and effectors in EqASCEMS cells via the upregulation of MiR-7a-5p, the decrease in the expression levels of ATF-6, CHOP and eiF2A and the restoration of PDIA3 chaperone protein levels. As a consequence, SHBG application substantially improved insulin sensitivity through the modulation of Pi3K/Akt/Glut4 insulin signalling cascades.

CONCLUSION

Our results suggest that the SHBG is endowed with crucial beneficial effects on ASCs metabolic activities and could serve as a valuable therapeutic target for the development of efficient EMS treatment protocols. Video Abstract.

Bitter melon extract suppresses metastatic breast cancer cells (MCF-7 cells) growth possibly by hindering glucose uptake

Breast cancer is one of the most commonly diagnosed cancers among women, however the complete cure for metastatic breast cancer is lacking due to poor prognosis. There has been an increasing trend of dietary modifications including consumption of natural food for the prevention of cancer. One of the popular natural foods is bitter melon. Bitter melon grows in tropical and subtropical areas. Some of the beneficial effects of bitter melon towards disease including cancer have been reported at the whole body/organismal level. However, specific cellular mechanisms by which bitter melon exerts beneficial effects in breast cancer are lacking. In this study, we used a human metastatic breast cancer cell line, MCF-7 cell, to study if bitter melon alters glucose clearance from the culture medium. We co-cultured MCF-7 cells with bitter melon extract in the presence and absence of supplemented insulin and subsequently measured MCF-7 cells viability. In this study, we report a noble finding that bitter melon extract exerts cytotoxic effects on MCF-7 cells possibly via inhibition of glucose uptake. Our findings show that insulin rescues MCF-7 cells from the effects of bitter melon extract.

Molecular Mechanisms for the Vicious Cycle between Insulin Resistance and the Inflammatory Response in Obesity

The comprehensive anabolic effects of insulin throughout the body, in addition to the control of glycemia, include ensuring lipid homeostasis and anti-inflammatory modulation, especially in adipose tissue (AT). The prevalence of obesity, defined as a body mass index (BMI) ≥ 30 kg/m², has been increasing worldwide on a pandemic scale with accompanying syndemic health problems, including glucose intolerance, insulin resistance (IR), and diabetes. Impaired tissue sensitivity to insulin or IR paradoxically leads to diseases with an inflammatory component despite hyperinsulinemia. Therefore, an excess of visceral AT in obesity initiates chronic low-grade inflammatory conditions that interfere with insulin signaling via insulin receptors (INSRs). Moreover, in response to IR, hyperglycemia itself stimulates a primarily defensive inflammatory response associated with the subsequent release of numerous inflammatory cytokines and a real threat of organ function deterioration. In this review, all components of this vicious cycle are characterized with particular emphasis on the interplay between insulin signaling and both the innate and adaptive immune responses related to obesity. Increased visceral AT accumulation in obesity should be considered the main environmental factor responsible for the disruption in the epigenetic regulatory mechanisms in the immune system, resulting in autoimmunity and inflammation.

Sleeve Gastrectomy-Induced Weight Loss Increases Insulin Clearance in Obese Mice

Sleeve gastrectomy (SG) successfully recovers metabolic homeostasis in obese humans and rodents while also resulting in the normalization of insulin sensitivity and insulinemia. Reduced insulin levels have been attributed to lower insulin secretion and increased insulin clearance in individuals submitted to SG. Insulin degradation mainly occurs in the liver in a process controlled, at least in part, by the insulin-degrading enzyme (IDE). However, research has yet to explore whether liver IDE expression or activity is altered after SG surgery. In this study, C57BL/6 mice were fed a chow (CTL) or high-fat diet (HFD) for 10 weeks. Afterward, the HFD mice were randomly assigned to two groups: sham-surgical (HFD-SHAM) and SG-surgical (HFD-SG). Here, we confirmed that SG improves glucose-insulin homeostasis in obese mice. Additionally, SG reduced insulinemia by reducing insulin secretion, assessed by the analysis of plasmatic C-peptide content, and increasing insulin clearance, which was evaluated through the calculation of the plasmatic C-peptide:insulin ratio. Although no changes in hepatic IDE activity were observed, IDE expression was higher in the liver of HFD-SG compared with HFD-SHAM mice. These results indicate that SG may be helpful to counteract obesity-induced hyperinsulinemia by increasing insulin clearance, likely through enhanced liver IDE expression.

In Vitro Insulin Resistance Model: A Recent Update

Insulin resistance, which affects insulin-sensitive tissues, including adipose tissues, skeletal muscle, and the liver, is the central pathophysiological mechanism underlying type 2 diabetes progression. Decreased glucose uptake in insulin-sensitive tissues disrupts insulin signaling pathways, particularly the PI3K/Akt pathway. An in vitro model is appropriate for studying the cellular and molecular mechanisms underlying insulin resistance because it is easy to maintain and the results can be easily reproduced. The application of cell-based models for exploring the pathogenesis of diabetes and insulin resistance as well as for developing drugs for these conditions is well known. However, a comprehensive review of in vitro insulin resistance models is lacking. Therefore, this review was conducted to provide a comprehensive overview and summary of the latest in vitro insulin resistance models, particularly 3T3-L1 (preadipocyte), C2C12 (skeletal muscle), and HepG2 (liver) cell lines induced with palmitic acid, high glucose, or chronic exposure to insulin.

Pathogenesis of (smoking-related) non-communicable diseases-Evidence for a common underlying pathophysiological pattern

Non-communicable diseases, like diabetes, cardiovascular diseases, cancer, stroke, chronic obstructive pulmonary disease, osteoporosis, arthritis, Alzheimer's disease and other more are a leading cause of death in almost all countries. Lifestyle factors, especially poor diet and tobacco consumption, are considered to be the most important influencing factors in the development of these diseases. The Western diet has been shown to cause a significant distortion of normal physiology, characterized by dysregulation of the sympathetic nervous system, renin-angiotensin aldosterone system, and immune system, as well as disruption of physiological insulin and oxidant/antioxidant homeostasis, all of which play critical roles in the development of these diseases. This paper addresses the question of whether the development of smoking-related non-communicable diseases follows the same pathophysiological pattern. The evidence presented shows that exposure to cigarette smoke and/or nicotine causes the same complex dysregulation of physiology as described above, it further shows that the factors involved are strongly interrelated, and that all of these factors play a key role in the development of a broad spectrum of smoking-related diseases. Since not all smokers develop one or more of these diseases, it is proposed that this disruption of normal physiological balance represents a kind of pathogenetic "basic toolkit" for the potential development of a range of non-communicable diseases, and that the decision of whether and what disease will develop in an individual is determined by other, individual factors ("determinants"), such as the genome, epigenome, exposome, microbiome, and others. The common pathophysiological pattern underlying these diseases may provide an explanation for the often poorly understood links between non-communicable diseases and disease comorbidities. The proposed pathophysiological process offers new insights into the development of non-communicable diseases and may influence the direction of future research in both prevention and therapy.

Progression from prediabetes to type 2 diabetes mellitus induced by overnutrition

Prediabetes has developed into a global pandemic, its prevalence increasing year by year. Although lifestyle changes are advocated as the basis for prediabetes treatment, some patients fail to choose or adhere to appropriate interventions. The basis for selecting an appropriate intervention is determining the stage and cause of the disease. In this review, we aimed to examine the various types and disease processes of prediabetes caused by overnutrition, the present review supporting the hypothesis that overnutrition-induced hyperinsulinemia precedes insulin resistance (IR) and independently causes β-cell dysfunction. Tissue insulin resistance is the main feature of prediabetes with the crosstalk between tissues promoting the formation of systemic insulin resistance. Finally, both β-cell dysfunction induced by hyperinsulinemia or IR and reduced β-cell mass can lead to abnormal insulin secretion and contribute to development of type 2 diabetes mellitus (T2DM). Hence, overnutrition can cause multiple prediabetes phenotypes resulting in development of T2DM through different trajectories. Future diagnosis and treatment should therefore more carefully consider the disease phenotype and stage of development in patients with prediabetes to reduce the incidence of T2DM.

Incorporation of Oxidized Phenylalanine Derivatives into Insulin Signaling Relevant Proteins May Link Oxidative Stress to Signaling Conditions Underlying Chronic Insulin Resistance

A link between oxidative stress and insulin resistance has been suggested. Hydroxyl free radicals are known to be able to convert phenylalanine (Phe) into the non-physiological tyrosine isoforms ortho- and meta-tyrosine (o-Tyr, m-Tyr). The aim of our study was to examine the role of o-Tyr and m-Tyr in the development of insulin resistance. We found that insulin-induced uptake of glucose was blunted in cultures of 3T3-L1 grown on media containing o- or m-Tyr. We show that these modified amino acids are incorporated into cellular proteins. We focused on insulin receptor substrate 1 (IRS-1), which plays a role in insulin signaling. The activating phosphorylation of IRS-1 was increased by insulin, the effect of which was abolished in cells grown in m-Tyr or o-Tyr media. We found that phosphorylation of m- or o-Tyr containing IRS-1 segments by insulin receptor (IR) kinase was greatly reduced, PTP-1B phosphatase was incapable of dephosphorylating phosphorylated m- or o-Tyr IRS-1 peptides, and the SH2 domains of phosphoinositide 3-kinase (PI3K) bound the o-Tyr IRS-1 peptides with greatly reduced affinity. According to our data, m- or o-Tyr incorporation into IRS-1 modifies its protein–protein interactions with regulating enzymes and effectors, thus IRS-1 eventually loses its capacity to play its role in insulin signaling, leading to insulin resistance.

Insulin Clearance in Obesity and Type 2 Diabetes

Plasma insulin clearance is an important determinant of plasma insulin concentration. In this review, we provide an overview of the factors that regulate insulin removal from plasma and discuss the interrelationships among plasma insulin clearance, excess adiposity, insulin sensitivity, and type 2 diabetes (T2D). We conclude with the perspective that the commonly observed lower insulin clearance rate in people with obesity, compared with lean people, is not a compensatory response to insulin resistance but occurs because insulin sensitivity and insulin clearance are mechanistically, directly linked. Furthermore, insulin clearance decreases postprandially because of the marked increase in insulin delivery to tissues that clear insulin. The commonly observed high postprandial insulin clearance in people with obesity and T2D likely results from the relatively low insulin secretion rate, not an impaired adaptation of tissues that clear insulin.

Amino Acid-Induced Impairment of Insulin Signaling and Involvement of G-Protein Coupling Receptor

Amino acids are needed for general bodily function and well-being. Despite their importance, augmentation in their serum concentration is closely related to metabolic disorder, insulin resistance (IR), or worse, diabetes mellitus. Essential amino acids such as the branched-chain amino acids (BCAAs) have been heavily studied as a plausible biomarker or even a cause of IR. Although there is a long list of benefits, in subjects with abnormal amino acids profiles, some amino acids are correlated with a higher risk of IR. Metabolic dysfunction, upregulation of the mammalian target of the rapamycin (mTOR) pathway, the gut microbiome, 3-hydroxyisobutyrate, inflammation, and the collusion of G-protein coupled receptors (GPCRs) are among the indicators and causes of metabolic disorders generating from amino acids that contribute to IR and the onset of type 2 diabetes mellitus (T2DM). This review summarizes the current understanding of the true involvement of amino acids with IR. Additionally, the involvement of GPCRs in IR will be further discussed in this review.

Plasma Branched-Chain Amino Acids Are Associated With Greater Fasting and Postprandial Insulin Secretion in Non-diabetic Chinese Adults

Background: Plasma branched-chain amino acids (BCAA) are consistently elevated in subjects with obesity and type 2 diabetes (T2DM) and correlate with insulin resistance. The association of BCAA with insulin secretion and clearance rates has not been adequately described. Objective: To evaluate the relationships between fasting and postprandial plasma BCAA, insulin secretion and insulin clearance. Design: Ninety-five non-diabetic Chinese subjects (43 females) underwent a mixed-meal tolerance test; blood biomarkers including BCAAs (leucine, isoleucine, valine) were measured for 6 h. Fasting and postprandial insulin secretion rates (ISR) and insulin clearance were determined by oral minimal modeling of glucose and C-peptide. Results: Fasting and postprandial plasma BCAA correlated strongly with each other (ρ = 0.796, P < 0.001), and both were positively associated with basal ISR (ρ = 0.45/0.36, P < 0.001), total postprandial ISR AUC (ρ = 0.37/0.45, P < 0.001), and negatively with insulin clearance (ρ = -0.29/-0.29, P < 0.01), after adjusting for sex and body mass index. These relationships largely persisted after adjusting further for insulin resistance and postprandial glucose. Compared with subjects in the middle and lowest tertiles for fasting or postprandial plasma BCAA, subjects in the highest tertile had significantly greater postprandial glucose (by 7-10%) and insulin (by 74-98%) concentrations, basal ISRs (by 34-53%), postprandial ISR AUCs (by 41-49%), and lower insulin clearance rates (by 17-22%) (all P < 0.05). Conclusions: Fasting and postprandial plasma BCAA levels are associated with greater fasting and postprandial insulin secretion and reduced insulin clearance in healthy Chinese subjects. These observations potentially highlight an additional layer of involvement of BCAA in the regulation of glucose homeostasis.

LEAP-2: An Emerging Endogenous Ghrelin Receptor Antagonist in the Pathophysiology of Obesity

Liver-expressed antimicrobial peptide 2 (LEAP-2), originally described as an antimicrobial peptide, has recently been recognized as an endogenous blocker of growth hormone secretagogue receptor 1a (GHS-R1a). GHS-R1a, also known as ghrelin receptor, is a G protein-coupled receptor (GPCR) widely distributed on the hypothalamus and pituitary gland where it exerts its major functions of regulating appetite and growth hormone (GH) secretion. The activity of GHS-R1a is controlled by two counter-regulatory endogenous ligands: Ghrelin (activation) and LEAP-2 (inhibition). Ghrelin activates GHS-R1a on the neuropeptide Y/Agouti-related protein (NPY/AgRP) neurons at the arcuate nucleus (ARC) to promote appetite, and on the pituitary somatotrophs to stimulate GH release. On the flip side, LEAP-2, acts both as an endogenous competitive antagonist of ghrelin and an inverse agonist of constitutive GHS-R1a activity. Such a biological property of LEAP-2 vigorously blocks ghrelin's effects on food intake and hormonal secretion. In circulation, LEAP-2 displays an inverse pattern as to ghrelin; it increases with food intake and obesity (positive energy balance), whereas decreases upon fasting and weight loss (negative energy balance). Thus, the LEAP-2/ghrelin molar ratio fluctuates in response to energy status and modulation of this ratio conversely influences energy intake. Inhibiting ghrelin's activity has shown beneficial effects on obesity in preclinical experiments, which sheds light on LEAP-2's anti-obesity potential. In this review, we will analyze LEAP-2's effects from a metabolic point of view with a focus on metabolic hormones (e.g., ghrelin, GH, and insulin), and discuss LEAP-2's potential as a promising therapeutic target for obesity.

Remodeling of whole-body lipid metabolism and a diabetic-like phenotype caused by loss of CDK1 and hepatocyte division

Cell cycle progression and lipid metabolism are well-coordinated processes required for proper cell proliferation. In liver diseases that arise from dysregulated lipid metabolism, hepatocyte proliferation is diminished. To study the outcome of CDK1 loss and blocked hepatocyte proliferation on lipid metabolism and the consequent impact on whole-body physiology, we performed lipidomics, metabolomics, and RNA-seq analyses on a mouse model. We observed reduced triacylglycerides in liver of young mice, caused by oxidative stress that activated FOXO1 to promote the expression of Pnpla2/ATGL. Additionally, we discovered that hepatocytes displayed malfunctioning β-oxidation, reflected by increased acylcarnitines (ACs) and reduced β-hydroxybutyrate. This led to elevated plasma free fatty acids (FFAs), which were transported to the adipose tissue for storage and triggered greater insulin secretion. Upon aging, chronic hyperinsulinemia resulted in insulin resistance and hepatic steatosis through activation of LXR. Here, we demonstrate that loss of hepatocyte proliferation is not only an outcome but also possibly a causative factor for liver pathology.

Effect of growth hormone on insulin signaling

Growth hormone (GH) is a pleiotropic hormone that coordinates an array of physiological processes, including effects on bone, muscle, and fat, ultimately resulting in growth. Metabolically, GH promotes anabolic action in most tissues except adipose, where its catabolic action causes the breakdown of stored triglycerides into free fatty acids (FFA). GH antagonizes insulin action via various molecular pathways. Chronic GH secretion suppresses the anti-lipolytic action of insulin and increases FFA flux into the systemic circulation; thus, promoting lipotoxicity, which causes pathophysiological problems, including insulin resistance. In this review, we will provide an update on GH-stimulated adipose lipolysis and its consequences on insulin signaling in liver, skeletal muscle, and adipose tissue. Furthermore, we will discuss the mechanisms that contribute to the diabetogenic action of GH.

In vitro characterization of the effects of chronic insulin stimulation in mouse 3T3-L1 and human SGBS adipocytes

Hyperinsulinemia is the hallmark of the development of insulin resistance and precedes the diagnosis of type 2 diabetes. Here we evaluated the effects of prolonged exposure (≥4 days) to high insulin doses (150 nM) in vitro in two adipose cell types, mouse 3T3-L1 and human SGBS. Chronic insulin treatment significantly decreased lipid droplet size, insulin signalling and insulin-stimulated glucose uptake. 3T3-L1 displayed an increased basal glucose internalization following chronic insulin treatment, which was associated with increased GLUT1 expression. In addition, both cells showed increased basal lipolysis.

In conclusion, we report the effects of prolonged hyperinsulinemia in 3T3-L1 and SGBS, highlighting similarities and discrepancies between the cell types, to be considered when using these cells to model insulin-induced insulin resistance.

Effect of antioxidant-rich propolis and bee pollen extracts against D-glucose induced type 2 diabetes in rats

The present study was designed to investigate the preventive effect of propolis, bee pollen and their combination on Type 2 diabetes induced by D-glucose in rats. The study was carried out by feeding daily two concentrations (100 and 200 mg/Kg BW) of propolis or bee pollen (or their combination to normal (non-diabetic) and diabetic rats for a period of 16 weeks. In vivo biochemical changes associated to diabetes are induced by drinking a solution containing 10% of D-glucose (diabetic rats). The in vitro antioxidant activity was also evaluated and the chemical composition of propolis and bee pollen extracts was determined by UHPLC-DAD. Phytochemical composition of propolis and bee pollen revealed the presence of several natural antioxidants, such as hydroxycinnamic acids, hydroxybenzoic acids, flavonoids, flavan-3-ols and stilbens. The major antioxidant compound present in propolis was Naringin (290.19 ± 0.2 mg/Kg) and in bee pollen was apigenin (162.85 ± 17.7 mg/Kg). These results have been related with a high antioxidant activity, more intense in propolis extract. In rats, the administration of D-glucose had induced hyperglycemia (13.2 ± 0.82 mmol/L), increased plasmatic insulin levels (25.10 ± 2.12 U/L) and HOMA-IR index (14.72 ± 0.85) accompanied with dyslipidemia, elevation of hepatic enzyme levels, and a change in both serum renal biomarkers and plasmatic calcium. The co-administration of propolis and bee pollen extracts alone or in combination restored these biochemical parameters and attenuated the deleterious effects of D-glucose on liver and kidney functions. Furthermore, these effects were better attenuated in the combined therapy-prevented diabetic rats. Hence, it is possible to conclude that propolis and bee pollen can be used as a preventive natural product against diabetes induced dyslipidemia and hepato-renal damage.

Clinical implications, diagnosis, and management of diabetes in patients with chronic liver diseases

Diabetes mellitus (DM) negatively affects the development and progression of chronic liver diseases (CLD) of various etiologies. Concurrent DM and CLD are also associated with worse clinical outcomes with respect to mortality, the occurrence of hepatic decompensation, and the development of hepatocellular carcinoma (HCC). Unfortunately, early diagnosis and optimal treatment of DM can be challenging, due to the lack of established clinical guidelines as well as the medical complexity of this patient population. We conducted an exploratory review of relevant literature to provide an up-to-date review for internists and hepatologists caring for this patient population. We reviewed the epidemiological and pathophysiological associations between DM and CLD, the impact of insulin resistance on the progression and manifestations of CLD, the pathogenesis of hepatogenic diabetes, as well as the practical challenges in diagnosis and monitoring of DM in this patient population. We also reviewed the latest clinical evidence on various pharmacological antihyperglycemic therapies with an emphasis on liver disease-related clinical outcomes. Finally, we proposed an algorithm for managing DM in patients with CLD and discussed the clinical and research questions that remain to be addressed.

Insulin: too much of a good thing is bad

BACKGROUND

Insulin shares a limited physiological concentration range with other endocrine hormones. Not only too low, but also too high systemic insulin levels are detrimental for body functions.

MAIN BODY

The physiological function and clinical relevance of insulin are usually seen in association with its role in maintaining glucose homeostasis. However, insulin is an anabolic hormone which stimulates a large number of cellular responses. Not only too low, but also excess insulin concentrations are detrimental to the physiological balance. Although the glucoregulatory activity of insulin is mitigated during hyperinsulinemia by dampening the efficiency of insulin signaling ("insulin resistance"), this is not the case for most other hormonal actions of insulin, including the promotion of protein synthesis, de novo lipogenesis, and cell proliferation; the inhibition of lipolysis, of autophagy-dependent cellular turnover, and of nuclear factor E2-related factor-2 (Nrf2)-dependent antioxidative; and other defense mechanisms. Hence, there is no general insulin resistance but selective impairment of insulin signaling which causes less glucose uptake from the blood and reduced activation of endothelial NO synthase (eNOS). Because of the largely unrestricted insulin signaling, hyperinsulinemia increases the risk of obesity, type 2 diabetes, and cardiovascular disease and decreases health span and life expectancy. In epidemiological studies, high-dose insulin therapy is associated with an increased risk of cardiovascular disease. Randomized controlled trials of insulin treatment did not observe any effect on disease risk, but these trials only studied low insulin doses up to 40 IU/day. Proof for a causal link between elevated insulin levels and cardiovascular disease risk comes from Mendelian randomization studies comparing individuals with genetically controlled low or high insulin production.

CONCLUSIONS

The detrimental actions of prolonged high insulin concentrations, seen also in cell culture, argue in favor of a lifestyle that limits circadian insulin levels. The health risks associated with hyperinsulinemia may have implications for treatment regimens used in type 2 diabetes.

Serum Dipeptidyl peptidase-4 level is related to adiposity in type 1 diabetic adolescents

BACKGROUND

Insulin resistance (IR) plays a great role in type 1 diabetes (T1DM) disease process than is commonly recognized. Dipeptidyl peptidase-4 (DPP-4) is an enzyme that deactivates many bioactive peptides involved in glucose regulation.

AIMS

This study evaluates DPP-4 level in adolescent patients with T1DM compared to controls and investigates the relationship between DPP-4 level and IR in these patients.

MATERIALS AND METHODS

We measured serum DPP-4 level in 50 patients with T1DM recruited from the Diabetes Endocrine Metabolism Pediatric Unit, and in 80 healthy controls. IR was assessed by the equation for estimated glucose disposal rate (eGDR). Biochemical evaluation including glycated haemoglobin (HbA1C) and lipid profile were included.

RESULTS

IR was found in 80% of patients with T1DM. DPP-4 was significantly higher in control group than patients with T1DM. Patients with T1DM were classified into 3 groups according to DPP-4 tertiles showing significant increase in BMI SDS and total cholesterol across the 3 groups. Significant correlation was found between DPP-4 levels and insulin dose. DPP-4 was significantly higher in patients with T1DM with good glycemic control.

CONCLUSION

In sample of individuals researched by us, serum DPP-4 was related to adiposity and not to the hyperglycemia in patients with T1DM. Larger sample should be researched to make firm conclusions.

Optimizing Adult Protein Intake During Catabolic Health Conditions

The DRIs define a range of acceptable dietary intakes for each nutrient. The range is defined from the minimum intake to avoid risk of inadequacy (i.e., the RDA) up to an upper limit (UL) based on a detectable risk of adverse effects. For most nutrients, the minimum RDA is based on alleviating a clear deficiency condition, whereas higher intakes are often recommended to optimize specific health outcomes. Evidence is accumulating that similar logic should be applied to dietary recommendations for protein. Although the RDA for protein of 0.8 g/kg body weight is adequate to avoid obvious inadequacies, multiple studies provide evidence that many adults may benefit from protein quantity, quality, and distribution beyond guidelines currently defined by the RDA. Further, the dietary requirement for protein is a surrogate for the constituent amino acids and, in particular, the 9 considered to be indispensable. Leucine provides an important example of an essential amino acid where the RDA of 42 mg/kg body weight is significantly less than the 100-110 mg/kg required to optimize metabolic regulation and skeletal muscle protein synthesis. This review will highlight the benefits of higher protein diets to optimize health during aging, inactivity, bed rest, or metabolic dysfunction such as type 2 diabetes.

Serum Androgens Are Independent Predictors of Insulin Clearance but Not of Insulin Secretion in Women With PCOS

CONTEXT/OBJECTIVE

In insulin-resistant individuals, hyperinsulinemia is a key compensatory mechanism, aimed at maintaining glucose homeostasis. Increased secretion and reduced clearance of insulin may both potentially contribute to this phenomenon. Insulin resistance and hyperinsulinemia are common findings in women with polycystic ovary syndrome (PCOS). While there is some information on insulin secretion, very few studies have investigated metabolic clearance rate of insulin (MCRI) in these women. Moreover, there is paucity of data on the relationships between MCRI and the pathophysiological characteristics of PCOS. The aim of the study was to explore these issues.

PATIENTS

One hundred ninety women with PCOS, diagnosed according to the Rotterdam criteria, with normal glucose tolerance.

DESIGN

Assessment of MCRI and clinical, hormonal, and metabolic characteristics of subjects. MCRI and insulin sensitivity were measured by the hyperinsulinemic euglycemic clamp. Serum androgens were assessed by liquid chromatography-mass spectrometry and equilibrium dialysis. A historical sample of healthy women was used to define the corresponding reference intervals.

RESULTS

MCRI was impaired in about two-thirds of women with PCOS. Subjects with low MCRI differed from those with normal MCRI for a number of anthropometric, metabolic, and endocrine features. In multivariate analysis, the degree of adiposity, estimates of insulin secretion, and serum androgen concentrations were independent predictors of MCRI. Conversely, age, adiposity, MCRI, and insulin sensitivity, but not serum androgens, were independent predictors of insulin secretion.

CONCLUSIONS

In women with PCOS, metabolic clearance of insulin is reduced, contributing to generating hyperinsulinemia. Serum androgens are independent predictors of this phenomenon.

Impact of high-intensity interval training and sprint interval training on peripheral markers of glycemic control in metabolic syndrome and type 2 diabetes

Glycemic control is essential to reduce the risk of complications associated with metabolic syndrome (MetS) and type 2 diabetes (T2D). Aerobic and resistance exercise performed alone or in combination improve glycemic control in both conditions. However, perceived lack of time and commitment are considered principal barriers to performing exercise regularly. High intensity interval training (HIIT) and sprint interval training (SIT) can be performed in a fraction of the time required for continuous aerobic exercise. A substantial scientific evidence indicates that HIIT/SIT improve glycemic control to a similar or greater extent than aerobic exercise in populations without MetS or T2D. Likewise, growing evidence suggest that HIIT/SIT improve the glycemic control during MetS and T2D. The aim of this review is to discuss the effects of interval training protocols on peripheral markers of glucose metabolism in patients with MetS and T2D.

Intermittent Fasting for Twelve Weeks Leads to Increases in Fat Mass and Hyperinsulinemia in Young Female Wistar Rats

Fasting is known to cause physiological changes in the endocrine pancreas, including decreased insulin secretion and increased reactive oxygen species (ROS) production. However, there is no consensus about the long-term effects of intermittent fasting (IF), which can involve up to 24 hours of fasting interspersed with normal feeding days. In the present study, we analyzed the effects of alternate-day IF for 12 weeks in a developing and healthy organism. Female 30-day-old Wistar rats were randomly divided into two groups: control, with free access to standard rodent chow; and IF, subjected to 24-hour fasts intercalated with 24-hours of free access to the same chow. Alternate-day IF decreased weight gain and food intake. Surprisingly, IF also elevated plasma insulin concentrations, both at baseline and after glucose administration collected during oGTT. After 12 weeks of dietary intervention, pancreatic islets displayed increased ROS production and apoptosis. Despite their lower body weight, IF animals had increased fat reserves and decreased muscle mass. Taken together, these findings suggest that alternate-day IF promote β -cell dysfunction, especially in developing animals. More long-term research is necessary to define the best IF protocol to reduce side effects.

Reducing Type 1 Diabetes Mortality: Role for Adjunctive Therapies?

Individuals with type 1 diabetes (T1D) frequently fail to achieve glycemic goals and have excess cardiovascular risk and premature death. Adjunctive agents may play a role in reducing morbidity, mortality, and the adverse sequelae of insulin treatment. A surge in type 2 diabetes drug development has revealed agents with benefits beyond glucose lowering, including cardiovascular risk reduction. Could these benefits translate to T1D? Specific trials for T1D demonstrate substantial hemoglobin (Hb)A1c reductions with sodium glucose cotransporter inhibitors (SGLTis) and glucagon-like peptide (GLP)1 agonists, and modest improvements with metformin, dipeptidyl peptidase-4 inhibitor (DPP4i), and pramlintide. Studies exploring cardiovascular risk reduction are warranted. This review synthesizes the emerging literature for researchers and clinicians treating people with T1D. Challenges in T1D research are discussed.

Origins and History of the Minimal Model of Glucose Regulation

It has long been hoped that our understanding of the pathogenesis of diabetes would be helped by the use of mathematical modeling. In 1979 Richard Bergman and Claudio Cobelli worked together to find a "minimal model" based upon experimental data from Bergman's laboratory. Model was chosen as the simplest representation based upon physiology known at the time. The model itself is two quasi-linear differential equations; one representing insulin kinetics in plasma, and a second representing the effects of insulin and glucose itself on restoration of the glucose after perturbation by intravenous injection. Model would only be sufficient if it included a delay in insulin action; that is, insulin had to enter a remote compartment, which was interstitial fluid (ISF). Insulin suppressed endogenous glucose output (by liver) slowly. Delay proved to be due to initial suppression of lipolysis; resultant lowering of free fatty acids reduced liver glucose output. Modeling also demanded that normalization of glucose after injection included an effect of glucose itself on glucose disposal and endogenous glucose production - these effects were termed "glucose effectiveness." Insulin sensitivity was calculated from fitting the model to intravenous glucose tolerance test data; the resulting insulin sensitivity index, SI, was validated with the glucose clamp method in human subjects. Model allowed us to examine the relationship between insulin sensitivity and insulin secretion. Relationship was described by a rectangular hyperbola, such that Insulin Secretion x Insulin Sensitivity = Disposition Index (DI). Latter term represents ability of the pancreatic beta-cells to compensate for insulin resistance due to factors such as obesity, pregnancy, or puberty. DI has a genetic basis, and predicts the onset of Type 2 diabetes. An additional factor was clearance of insulin by the liver. Clearance varies significantly among animal or human populations; using the model, clearance was shown to be lower in African Americans than Whites (adults and children), and may be a factor accounting for greater diabetes prevalence in African Americans. The research outlined in the manuscript emphasizes the powerful approach by which hypothesis testing, experimental studies, and mathematical modeling can work together to explain the pathogenesis of metabolic disease.

Vitamins D and E Stimulate the PI3K-AKT Signalling Pathway in Insulin-Resistant SK-N-SH Neuronal Cells

This study investigated the effects of vitamins D and E on an insulin-resistant model and hypothesized that this treatment would reverse the effects of Alzheimer’s disease (AD) and improves insulin signalling. An insulin-resistant model was induced in SK-N-SH neuronal cells with a treatment of 250 nM insulin and re-challenged with 100 nM at two different incubation time (16 h and 24 h). The effects of vitamin D (10 and 20 ng/mL), vitamin E in the form of tocotrienol-rich fraction (TRF) (200 ng/mL) and the combination of vitamins D and E on insulin signalling markers (IR, PI3K, GLUT3, GLUT4, and p-AKT), glucose uptake and AD markers (GSK3β and TAU) were determined using quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA). The results demonstrated an improvement of the insulin signalling pathway upon treatment with vitamin D alone, with significant increases in IR, PI3K, GLUT3, GLUT4 expression levels, as well as AKT phosphorylation and glucose uptake, while GSK3β and TAU expression levels was decreased significantly. On the contrary, vitamin E alone, increased p-AKT, reduced the ROS as well as GSK3β and TAU but had no effect on the insulin signalling expression levels. The combination of vitamins D and E only showed significant increase in GLUT4, p-AKT, reduced ROS as well as GSK3β and TAU. Thus, the universal role of vitamin D, E alone and in combinations could be the potential nutritional agents in restoring the sensitivity of neuronal cells towards insulin and delaying the pathophysiological progression of AD.

Hypothesis: Role of Reduced Hepatic Insulin Clearance in the Pathogenesis of Type 2 Diabetes

There is wide variance among individuals in the fraction of insulin cleared by the liver (20% to 80%). Hepatic insulin clearance is 67% lower in African Americans than European Americans. Clearance is also lower in African American children 7-13 years of age. Lower hepatic insulin clearance will result in peripheral hyperinsulinemia: this exacerbates insulin resistance, which stresses the β-cells, possibly resulting in their ultimate failure and onset of type 2 diabetes. We hypothesize that lower insulin clearance can be a primary cause of type 2 diabetes in at-risk individuals.

Mild Physiologic Hyperglycemia Induces Hepatic Insulin Resistance in Healthy Normal Glucose-Tolerant Participants

CONTEXT

Chronic hyperglycemia worsens skeletal muscle insulin resistance and β-cell function. However, the effect of sustained physiologic hyperglycemia on hepatic insulin sensitivity is not clear.

OBJECTIVE

To examine the effect of sustained physiologic hyperglycemia (similar to that observed in patients with type 2 diabetes) on endogenous (primarily reflecting hepatic) glucose production (EGP) in healthy individuals.

DESIGN

Volunteers participated in a three-step hyperinsulinemic (10, 20, 40 mU/m2 per minute) euglycemic clamp before and after a 48-hour glucose infusion to increase plasma glucose concentration by ∼40 mg/dL above baseline. EGP was measured with 3-3H-glucose before and after chronic glucose infusion.

PARTICIPANTS

Sixteen persons with normal glucose tolerance [eight with and eight without a family history (FH) of diabetes] participated in the study.

MAIN OUTCOME MEASURE

EGP.

RESULTS

Basal EGP increased following 48 hours of glucose infusion (from a mean ± SEM of 2.04 ± 0.08 to 3.06 ± 0.29 mg/kgffm⋅ min; P < 0.005). The hepatic insulin resistance index (basal EGP × fasting plasma insulin) markedly increased following glucose infusion (20.1 ± 1.8 to 51.7 ± 6.6; P < 0.005) in both FH+ and FH- subjects.

CONCLUSION

Sustained physiologic hyperglycemia for as little as 48 hours increased the rate of basal hepatic glucose production and induced hepatic insulin resistance in health persons with normal glucose tolerance, providing evidence for the role of glucotoxicity in the increase in hepatic glucose production in type 2 diabetes.

Impact of hyperinsulinemia and hyperglycemia on valvular interstitial cells - A link between aortic heart valve degeneration and type 2 diabetes

Type 2 diabetes is a known risk factor for cardiovascular diseases and is associated with an increased risk to develop aortic heart valve degeneration. Nevertheless, molecular mechanisms leading to the pathogenesis of valve degeneration in the context of diabetes are still not clear. Hence, we hypothesized that classical key factors of type 2 diabetes, hyperinsulinemia and hyperglycemia, may affect signaling, metabolism and degenerative processes of valvular interstitial cells (VIC), the main cell type of heart valves. Therefore, VIC were derived from sheep and were treated with hyperinsulinemia, hyperglycemia and the combination of both. The presence of insulin receptors was shown and insulin led to increased proliferation of the cells, whereas hyperglycemia alone showed no effect. Disturbed insulin response was shown by impaired insulin signaling, i.e. by decreased phosphorylation of Akt/GSK-3α/β pathway. Analysis of glucose transporter expression revealed absence of glucose transporter 4 with glucose transporter 1 being the predominantly expressed transporter. Glucose uptake was not impaired by disturbed insulin response, but was increased by hyperinsulinemia and was decreased by hyperglycemia. Analyses of glycolysis and mitochondrial respiration revealed that VIC react with increased activity to hyperinsulinemia or hyperglycemia, but not to the combination of both. VIC do not show morphological changes and do not acquire an osteogenic phenotype by hyperinsulinemia or hyperglycemia. However, the treatment leads to increased collagen type 1 and decreased α-smooth muscle actin expression. This work implicates a possible role of diabetes in early phases of the degeneration of aortic heart valves.

Evaluating the Impact of Different Hypercaloric Diets on Weight Gain, Insulin Resistance, Glucose Intolerance, and its Comorbidities in Rats

Animal experimentation has a long history in the study of metabolic syndrome-related disorders. However, no consensus exists on the best models to study these syndromes. Knowing that different diets can precipitate different metabolic disease phenotypes, herein we characterized several hypercaloric rat models of obesity and type 2 diabetes, comparing each with a genetic model, with the aim of identifying the most appropriate model of metabolic disease. The effect of hypercaloric diets (high fat (HF), high sucrose (HSu), high fat plus high sucrose (HFHSu) and high fat plus streptozotocin (HF+STZ) during different exposure times (HF 3 weeks, HF 19 weeks, HSu 4 weeks, HSu 16 weeks, HFHSu 25 weeks, HF3 weeks + STZ) were compared with the Zucker fatty rat. Each model was evaluated for weight gain, fat mass, fasting plasma glucose, insulin and C-peptide, insulin sensitivity, glucose tolerance, lipid profile and liver lipid deposition, blood pressure, and autonomic nervous system function. All animal models presented with insulin resistance and dyslipidemia except the HF+STZ and HSu 4 weeks, which argues against the use of these models as metabolic syndrome models. Of the remaining animal models, a higher weight gain was exhibited by the Zucker fatty rat and wild type rats submitted to a HF diet for 19 weeks. We conclude that the latter model presents a phenotype most consistent with that observed in humans with metabolic disease, exhibiting the majority of the phenotypic features and comorbidities associated with type 2 diabetes in humans.

Akebia Saponin D Regulates the Metabolome and Intestinal Microbiota in High Fat Diet-Induced Hyperlipidemic Rats

Hyperlipidemia is a major component of metabolic syndrome, and regarded as one of the main risk factors causing metabolic diseases. We have developed a therapeutic drug, akebia saponin D (ASD), and determined its anti-hyperlipidemia activity and the potential mechanism(s) of action by analyzing the metabolome and intestinal microbiota. Male Sprague-Dawley rats were fed a high fat diet to induce hyperlipidemia, and then given ASD orally for 8 weeks. Lipid levels in serum were determined biochemically. Metabolites in serum, urine and feces were analyzed by UPLC-Q/TOF-MS, and the structure of the intestinal microbiota was determined by 16S rRNA sequencing. The ASD treatment significantly decreased the levels of TC, TG and LDL-c and increased the serum level of HDL-c. Metabolomics analysis indicated that the ASD treatment mainly impacted seven differential metabolites in the serum, sixteen differential metabolites in the urine and four differential metabolites in feces compared to the model group. The ASD treatment significantly changed eight bacteria at the genus level compared to the model group. In conclusion, ASD treatment can significantly alleviate HFD-induced hyperlipidemia and the hypolipidemic effect of ASD treatment is certainly associated with a systematic change in the metabolism, as well as dynamic changes in the structure of the intestinal microbiota.

Atmospheric PM2.5 aspiration causes tauopathy by disturbing the insulin signaling pathway

Epidemiological and toxicological studies have shown that ambient fine particulate matter (PM_2.5) is a healthy risk factor for neurodegenerative diseases. Hyperphosphorylated tau is the common feature of numerous neurodegenerative diseases known as tauopathy, which could be inhibited by insulin stimulation. However, the effects of PM_2.5 on tau protein injury by disturbing the insulin signaling pathway still need to be illuminated. In present study, male C57BL/6 J mice were administered with PM_2.5 to determine whether PM_2.5 inhalation can induce tauopathy via the insulin resistance (IR) related pathway (IRS-1/AKT/GSK-3β signaling pathway). The results showed that PM_2.5 treatment induced the generation of phosphorylated tau (P-tau) and contributed to the development of tauopathy because of the insulin signaling disorders in insulin targeting organs. As expected, the occurrence of central and peripheral IR and accompanying hyperinsulinemia aggravated the disturbance of the IRS-1/AKT/GSK-3β signaling pathway. These observations indicated that PM_2.5 exposure led to neurodegenerative tau lesion, and insulin signaling pathway might be a potential therapeutic target for tauopathy.

How Western Diet And Lifestyle Drive The Pandemic Of Obesity And Civilization Diseases

Westernized populations are plagued by a plethora of chronic non-infectious degenerative diseases, termed as "civilization diseases", like obesity, diabetes, cardiovascular diseases, cancer, autoimmune diseases, Alzheimer's disease and many more, diseases which are rare or virtually absent in hunter-gatherers and other non-westernized populations. There is a growing awareness that the cause of this amazing discrepancy lies in the profound changes in diet and lifestyle during recent human history. This paper shows that the transition from Paleolithic nutrition to Western diets, along with lack of corresponding genetic adaptations, cause significant distortions of the fine-tuned metabolism that has evolved over millions of years of human evolution in adaptation to Paleolithic diets. With the increasing spread of Western diet and lifestyle worldwide, overweight and civilization diseases are also rapidly increasing in developing countries. It is suggested that the diet-related key changes in the developmental process include an increased production of reactive oxygen species and oxidative stress, development of hyperinsulinemia and insulin resistance, low-grade inflammation and an abnormal activation of the sympathetic nervous system and the renin-angiotensin system, all of which play pivotal roles in the development of diseases of civilization. In addition, diet-related epigenetic changes and fetal programming play an important role. The suggested pathomechanism is also able to explain the well-known but not completely understood close relationship between obesity and the wide range of comorbidities, like type 2 diabetes mellitus, cardiovascular disease, etc., as diseases of the same etiopathology. Changing our lifestyle in accordance with our genetic makeup, including diet and physical activity, may help prevent or limit the development of these diseases.

Integrated metabolomic profiling for analysis of antilipidemic effects of Polygonatum kingianum extract on dyslipidemia in rats

AIM

To identify the effects and mechanism of action of Polygonatum kingianum (P. kingianum) on dyslipidemia in rats using an integrated untargeted metabolomic method.

METHODS

A rat model of dyslipidemia was induced with a high-fat diet (HFD) and rats were given P. kingianum [4 g/(kg•d)] intragastrically for 14 wk. Changes in serum and hepatic lipid parameters were evaluated. Metabolites in serum, urine and liver samples were profiled using ultra-high performance liquid chromatography/mass spectrometry followed by multivariate statistical analysis to identify potential biomarkers and metabolic pathways.

RESULTS

P. kingianum significantly inhibited the HFD-induced increase in total cholesterol and triglyceride in the liver and serum. P. kingianum also significantly regulated metabolites in the analyzed samples toward normal status. Nineteen, twenty-four and thirty-eight potential biomarkers were identified in serum, urine and liver samples, respectively. These biomarkers involved biosynthesis of phenylalanine, tyrosine, tryptophan, valine, leucine and isoleucine, along with metabolism of tryptophan, tyrosine, phenylalanine, starch, sucrose, glycerophospholipid, arachidonic acid, linoleic acid, nicotinate, nicotinamide and sphingolipid.

CONCLUSION

P. kingianum alleviates HFD-induced dyslipidemia by regulating many endogenous metabolites in serum, urine and liver samples. Collectively, our findings suggest that P. kingianum may be a promising lipid regulator to treat dyslipidemia and associated diseases.

Dissection of hepatic versus extra-hepatic insulin clearance: Ethnic differences in childhood

AIMS

Adult African American (AA) women have one third of the hepatic insulin clearance of European American (EA) women. This lower hepatic (but not extra-hepatic) insulin clearance in AA individuals is associated with higher plasma insulin concentrations. This study aims to understand whether impairment of hepatic insulin clearance is seen in AA individuals since childhood, possibly suggesting that genetic/epigenetic factors, rather than lifestyle only, contribute to this.

MATERIALS AND METHODS

A total of 203 children (105 male and 98 female (55 AA, 88 EA and 60 Hispanic American [HA]; ages, 7-13 years; mean BMI, 19 kg/m² )) underwent the frequently applied intravenous glucose tolerance test (FSIGT) at the University of Alabama at Birmingham, General Clinical Research Center and Department of Nutrition Sciences. Glucose, insulin and C-peptide levels were measured and hepatic and extra-hepatic insulin clearances were calculated using mathematical modelling.

RESULTS

Fractional hepatic insulin extraction (FE_L ) was lower in AA than in EA children (mean (SD), 19% (20%) vs 33% (20%); P = 0.0007). Adjusting for age, Tanner stage and body fat, FE_L was lower in AA than in EA children (P = 0.0012), and there was a slight sex-related difference (FE_L, 24% (10%) vs 29% (10%) in boys vs girls; P = 0.04). Extra-hepatic insulin clearance did not differ with ethnicity (27 (12), 21 (12) and 24 (28) mL/kg/min for AA, HA and EA children, respectively; P > 0.05).

CONCLUSIONS

At a young age, FE_L is lower in AAs than in EAs, which does not rule out genetic/epigenetic factors. These differences are related to hyperinsulinaemia and, over time, could possibly contribute to metabolic disorders in AA individuals.

Sexually dimorphic metabolic responses mediated by CRF2 receptor during nutritional stress in mice

BACKGROUND

Chronic stress is a major contributor in the development of metabolic syndrome and associated diseases, such as diabetes. High-fat diet (HFD) and sex are known modifiers of metabolic parameters. Peptide hormones corticotropin-releasing factor (CRF) and urocortins (UCN) mediate stress responses via activation and feedback to the hypothalamic-pituitary-adrenal (HPA) axis. UCN3 is a marker of pancreatic β-cell differentiation, and UCN2 is known to ameliorate glucose levels in mice rendered diabetic with HFD. CRF receptor 2 (CRF₂) is the only known cognate receptor for UCN2/3. Here, we ascertained the role of CRF₂ in glucose clearance, insulin sensitivity, and other parameters associated with metabolic syndrome in a mouse model of nutritional stress.

METHODS

Wild-type (WT) and Crhr2^-/- (null) mice of both sexes were fed either normal chow diet or HFD. After 8 weeks, blood glucose levels in response to glucose and insulin challenge were determined. Change in body and fat mass, plasma insulin, and lipid profile were assessed. Histological evaluation of liver sections was performed.

RESULTS

Here, we show that genotype (Crhr2), sex, and diet were all independent variables in the regulation of blood glucose levels, body and fat mass gain/redistribution, and insulin resistance. Surprisingly, CRF₂-deficient mice (Crhr2^-/-) male mice showed similarly impaired glucose clearance on HFD and chow. HFD-fed female Crhr2^-/- mice redistributed their fat depots that were distinct from wild-type females and male mice on either diet. Blood cholesterol and low-density lipoprotein (LDL) levels were elevated significantly in male Crhr2^-/- mice; female Crhr2^-/- mice were protected. Male, but not female Crhr2^-/- mice developed peripheral insulin resistance. HFD, but not chow-fed wild-type male mice developed hepatic macrovesicular steatosis. In contrast, livers of Crhr2^-/- male mice showed microvesicular steatosis on either diet, whereas livers of female mice on this 8-week HFD regimen did not develop steatosis.

CONCLUSIONS

CRF₂ receptor dysregulation is a sexually dimorphic risk factor in development of pre-diabetic and metabolic symptoms.