Physiology of glucose homeostasis

[Gender Disparities in Urolithiasis with a Special Focus on Oxalate Metabolism in the Liver]

The incidence and prevalence of urolithiasis are increasing in industrialized countries. In particular, an increase has been observed among young adults and women. The gender gap is closing, and gender equality (1:1) with regard to urolithiasis has already been documented for the USA. Studies have demonstrated that women have higher urine pH values than men, which promotes calcium phosphate crystallization. The tendency for men to develop calcium oxalate and uric acid stones is caused by the comparatively lower urine pH values. Malnutrition combined with a lack of exercise and the occurrence of metabolic syndrome with its underlying diseases (insulin resistance, type 2 diabetes mellitus, obesity, dyslipidaemia) are discussed as the causes of the increase in upper tract stone disease in industrialized countries. Non-alcoholic fatty liver disease (NAFLD), as the most common liver disease, is considered one of the complications of metabolic syndrome, with a prevalence of approximately 23% in Germany. Animal experiments and clinical studies have demonstrated a connection between NAFLD and increased oxalate excretion in urine. Based on the literature, NAFLD represents a possible cross-gender risk factor for kidney stone formation and is therefore considered to be a generally modifiable risk factor for recurrent urolithiasis. Simple recommendations concerning NAFLD should complement the general and metabolic workup in everyday clinical practice.

Brain glucose metabolism: Role of nitric oxide

One possible reason for failure in achieving optimal glycemic control in patients with type 2 diabetes (T2D) is that less attention has been paid to the brain, a fundamental player in glucose homeostasis, that consumes about 25% of total glucose utilization. In addition, animal and human studies indicate that nitric oxide (NO) is a critical player in glucose metabolism. NO synthesis from L-arginine is lower in patients with T2D, and endothelial NO synthase (eNOS)-derived NO bioavailability is lower in T2D. NO in the nervous system plays a role in neurovascular coupling (NVC) and the hypothalamic control of glucose sensing and energy homeostasis, influencing glucose utilization. This review explores NO's role in the brain's glucose metabolism. Literature indicates that glucose metabolism is different between neurons and astrocytes. Unlike neurons, astrocytes have a higher rate of glycolysis and a greater ability for lactate production. Astrocytes produce a greater amount of NO than neurons. NO inhibits mitochondrial respiration in both neurons and astrocytes and decreases intracellular ATP. NO-induced inhibition of mitochondrial respiration in neurons is not accompanied by compensatory glycolysis because phosphofructokinase 2.3 (PFK2.3), the most potent activator of PFK1 and thus glycolysis, is subjected to ubiquitylation and proteasomal degradation by cadherin-1 (Cdh1)-activated anaphase-promoting complex/cyclosome (APC/C), which leads to a low glycolytic rate in neurons. In astrocytes, NO inhibits mitochondrial respiration, but astrocytes display compensatory glycolysis by activating the adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathway.

Optimized MALDI2-Mass Spectrometry Imaging for Stable Isotope Tracing of Tissue-Specific Metabolic Pathways in Mice

Spatial stable isotope tracing metabolic imaging is a cutting-edge technique designed to investigate tissue-specific metabolic functions and heterogeneity. Traditional matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) techniques often struggle with low coverage of low-molecular-weight (LMW) metabolites, which are often crucial for spatial metabolic studies. To address this, we developed a high-coverage spatial isotope tracing metabolic method that incorporates optimized matrix selection, sample preparation protocols, and enhanced post-ionization (MALDI2) techniques. We employed this approach to mouse kidney, brain, and breast tumors to visualize the spatial dynamics of metabolic flow. Our results revealed diverse regional distributions of nine labeled intermediates derived from 13C6-glucose across glycolysis, glycogen metabolism, and the tricarboxylic acid (TCA) cycle in kidney tissues. In brain sections, we successfully mapped six intermediates from the TCA cycle and glutamate-glutamine (Glu-Gln) cycle simultaneously in distinct neurological regions. Furthermore, in breast cancer tumor tissues, our approach facilitated the mapping of nine metabolic intermediates in multiple pathways, including glycolysis, the pentose phosphate pathway (PPP), and the TCA cycle, illustrating metabolic heterogeneity within the tumor microenvironment. This methodology enhances metabolite coverage, enabling more comprehensive imaging of isotope-labeled metabolites and opening new avenues for exploring the metabolic landscape in various biological contexts.

Cardiac corin and atrial natriuretic peptide regulate liver glycogen metabolism and glucose homeostasis

BACKGROUND

Cardiovascular function and metabolic homeostasis are closely linked, but the underlying mechanisms are not fully understood. Corin is a protease that activates atrial natriuretic peptide (ANP), an essential hormone for normal blood pressure and cardiac function. The goal of this study is to investigate a potential corin and ANP function in regulating liver glycogen metabolism and glucose homeostasis.

METHODS

Liver glycogen and blood glucose levels were analyzed in Corin or Nppa (encoding ANP) knockout (KO) mice. ANP signaling was examined in livers from Corin and Nppa KO mice and in cultured human and mouse hepatocytes by western blotting.

RESULTS

We found that Corin and Nppa KO mice had reduced liver glycogen contents and increased blood glucose levels. By analyzing conditional KO mice lacking either cardiac or renal Corin, we showed that cardiac corin and ANP act in an endocrine manner to enhance cGMP-protein kinase G (PKG)-AKT-GSK3 signaling in hepatocytes. In cultured hepatocytes, ANP treatment stimulated PKG signaling, glucose uptake, and glycogen production, which could be blocked by small molecule PKG and AKT inhibitors.

CONCLUSIONS

Our results indicate that corin and ANP are important regulators in liver glycogen metabolism and glucose homeostasis, suggesting that defects in the corin and ANP pathway may contribute to both cardiovascular and metabolic diseases.

Gain of function mutation in K(ATP) channels and resulting upregulation of coupling conductance are partners in crime in the impairment of Ca2+ oscillations in pancreatic ß-cells

Gain of function mutations in the pore forming Kir6 subunits of the ATP sensitive K+ channels (K(ATP) channels) of pancreatic β-cells are the major cause of neonatal diabetes in humans. In this study, we show that in insulin secreting mouse β-cell lines, gain of function mutations in Kir6.1 result in a significant connexin36 (Cx36) overexpression, which form gap junctional connections and mediate electrical coupling between β-cells within pancreatic islets. Using computational modeling, we show that upregulation in Cx36 might play a functional role in the impairment of glucose stimulated Ca2+ oscillations in a cluster of β-cells with Kir6.1 gain of function mutations in their K(ATP) channels (GoF-K(ATP) channels). Our results show that without an increase in Cx36 expression, a gain of function mutation in Kir6.1 might not be sufficient to diminish glucose stimulated Ca2+ oscillations in a β-cell cluster. We also show that a reduced Cx36 expression, which leads to loss of coordination in a wild-type β-cell cluster, restores coordinated Ca2+ oscillations in a β-cell cluster with GoF-K(ATP) channels. Our results indicate that in a heterogenous β-cell cluster with GoF-K(ATP) channels, there is an inverted u-shaped nonmonotonic relation between the cluster activity and Cx36 expression. These results show that in a neonatal diabetic β-cell model, gain of function mutations in the Kir6.1 cause Cx36 overexpression, which aggravates the impairment of glucose stimulated Ca2+ oscillations.

Incretin and glucagon receptor polypharmacology in chronic kidney disease

Chronic kidney disease is a debilitating condition associated with significant morbidity and mortality. In recent years, the kidney effects of incretin-based therapies, particularly glucagon-like peptide-1 receptor agonists (GLP-1RAs), have garnered substantial interest in the management of type 2 diabetes and obesity. This review delves into the intricate interactions between the kidney, GLP-1RAs, and glucagon, shedding light on their mechanisms of action and potential kidney benefits. Both GLP-1 and glucagon, known for their opposing roles in regulating glucose homeostasis, improve systemic risk factors affecting the kidney, including adiposity, inflammation, oxidative stress, and endothelial function. Additionally, these hormones and their pharmaceutical mimetics may have a direct impact on the kidney. Clinical studies have provided evidence that incretins, including those incorporating glucagon receptor agonism, are likely to exhibit improved kidney outcomes. Although further research is necessary, receptor polypharmacology holds promise for preserving kidney function through eliciting vasodilatory effects, influencing volume and electrolyte handling, and improving systemic risk factors.

Hyperglycemia - A culprit of podocyte pathology in the context of glycogen metabolism

Prolonged disruption in the balance of glucose can result in metabolic disorders. The kidneys play a significant role in regulating blood glucose levels. However, when exposed to chronic hyperglycemia, the kidneys' ability to handle glucose metabolism may be impaired, leading to an accumulation of glycogen. Earlier studies have shown that there can be a significant increase in glucose storage in the form of glycogen in the kidneys in diabetes. Podocytes play a crucial role in maintaining the integrity of filtration barrier. In diabetes, exposure to elevated glucose levels can lead to significant metabolic and structural changes in podocytes, contributing to kidney damage and the development of diabetic kidney disease. The accumulation of glycogen in podocytes is not a well-established phenomenon. However, a recent study has demonstrated the presence of glycogen granules in podocytes. This review delves into the intricate connections between hyperglycemia and glycogen metabolism within the context of the kidney, with special emphasis on podocytes. The aberrant storage of glycogen has the potential to detrimentally impact podocyte functionality and perturb their structural integrity. This review provides a comprehensive analysis of the alterations in cellular signaling pathways that may potentially lead to glycogen overproduction in podocytes.

Diurnal Cycling of Insulin Sensitivity in Type 2 Diabetes: Evidence for Deviation From Physiology at an Early Stage

The aim of this study was to establish the contribution of insulin resistance to the morning (a.m.) versus afternoon (p.m.) lower glucose tolerance of people with type 2 diabetes (T2D). Eleven subjects with T2D (mean [SD] diabetes duration 0.79 [0.23] years, BMI 28.3 [1.8] kg/m2, A1C 6.6% [0.26%] [48.9 (2.9) mmol/mol]), treatment lifestyle modification only) and 11 matched control subjects without diabetes were monitored between 5:00 and 8:00 a.m. and p.m. (in random order) on one occasion (study 1), and on a subsequent occasion, they underwent an isoglycemic clamp (a.m. and p.m., both between 5:00 and 8:00, insulin infusion rate 10 mU/m2/min) (study 2). In study 1, plasma glucose, insulin, C-peptide, and glucagon were higher and insulin clearance lower in subjects with T2D a.m. versus p.m. and versus control subjects (P < 0.05), whereas free fatty acid, glycerol, and β-hydroxybutyrate were lower a.m. versus p.m. However, in study 2 at identical hyperinsulinemia a.m. and p.m. (∼150 pmol/L), glucose Ra and glycerol Ra were both less suppressed a.m. versus p.m. (P < 0.05) in subjects with T2D. In contrast, in control subjects, glucose Ra was more suppressed a.m. versus p.m. Leucine turnover was no different a.m. versus p.m. In conclusion, in subjects with T2D, insulin sensitivity for glucose (liver) and lipid metabolism has diurnal cycles (nadir a.m.) opposite that of control subjects without diabetes already at an early stage, suggesting a marker of T2D.

ARTICLE HIGHLIGHTS

In people with type 2 diabetes (T2D), fasting hyperglycemia is greater in the morning (a.m.) versus the afternoon (p.m.), and insulin sensitivity for glucose and lipid metabolism is lower a.m. versus p.m. This pattern is the reverse of the physiological diurnal cycle of people without diabetes who are more insulin sensitive a.m. versus p.m. These new findings have been observed in the present study in people without obesity but with recent-onset T2D, with good glycemic control, and in the absence of confounding pharmacological treatment. It is likely that the findings represent a specific marker of T2D, possibly present even in prediabetes before biochemical and clinical manifestations.

Insulin and the kidneys: a contemporary view on the molecular basis

Insulin is a hormone that is composed of 51 amino acids and structurally organized as a hexamer comprising three heterodimers. Insulin is the central hormone involved in the control of glucose and lipid metabolism, aiding in processes such as body homeostasis and cell growth. Insulin is synthesized as a large preprohormone and has a leader sequence or signal peptide that appears to be responsible for transport to the endoplasmic reticulum membranes. The interaction of insulin with the kidneys is a dynamic and multicenter process, as it acts in multiple sites throughout the nephron. Insulin acts on a range of tissues, from the glomerulus to the renal tubule, by modulating different functions such as glomerular filtration, gluconeogenesis, natriuresis, glucose uptake, regulation of ion transport, and the prevention of apoptosis. On the other hand, there is sufficient evidence showing the insulin receptor's involvement in renal functions and its responsibility for the regulation of glucose homeostasis, which enables us to understand its contribution to the insulin resistance phenomenon and its association with the progression of diabetic kidney disease.

Liver or kidney: Who has the oar in the gluconeogenesis boat and when?

Gluconeogenesis is an endogenous process of glucose production from non-carbohydrate carbon substrates. Both the liver and kidneys express the key enzymes necessary for endogenous glucose production and its export into circulation. We would be remiss to add that more recently gluconeogenesis has been described in the small intestine, especially under high-protein, low-carbohydrate diets. The contribution of the liver glucose release, the net glucose flux, towards systemic glucose is already well known. The liver is, in most instances, the primary bulk contributor due to the sheer size of the organ (on average, over 1 kg). The contribution of the kidney (at just over 100 g each) to endogenous glucose production is often under-appreciated, especially on a weight basis. Glucose is released from the liver through the process of glycogenolysis and gluconeogenesis. Renal glucose release is almost exclusively due to gluconeogenesis, which occurs in only a fraction of the cells in that organ (proximal tubule cells). Thus, the efficiency of glucose production from other carbon sources may be superior in the kidney relative to the liver or at least on the level. In both these tissues, gluconeogenesis regulation is under tight hormonal control and depends on the availability of substrates. Liver and renal gluconeogenesis are differentially regulated under various pathological conditions. The impact of one source vs the other changes, based on post-prandial state, acid-base balance, hormonal status, and other less understood factors. Which organ has the oar (is more influential) in driving systemic glucose homeostasis is still in-conclusive and likely changes with the daily rhythms of life. We reviewed the literature on the differences in gluconeogenesis regulation between the kidneys and the liver to gain an insight into who drives the systemic glucose levels under various physiological and pathological conditions.

Comparison of hepatic responses to glucose perturbation between healthy and obese mice based on the edge type of network structures

Interactions between various molecular species in biological phenomena give rise to numerous networks. The investigation of these networks, including their statistical and biochemical interactions, supports a deeper understanding of biological phenomena. The clustering of nodes associated with molecular species and enrichment analysis is frequently applied to examine the biological significance of such network structures. However, these methods focus on delineating the function of a node. As such, in-depth investigations of the edges, which are the connections between the nodes, are rarely explored. In the current study, we aimed to investigate the functions of the edges rather than the nodes. To accomplish this, for each network, we categorized the edges and defined the edge type based on their biological annotations. Subsequently, we used the edge type to compare the network structures of the metabolome and transcriptome in the livers of healthy (wild-type) and obese (ob/ob) mice following oral glucose administration (OGTT). The findings demonstrate that the edge type can facilitate the characterization of the state of a network structure, thereby reducing the information available through datasets containing the OGTT response in the metabolome and transcriptome.

Protein glycation in diabetes mellitus

Diabetes mellitus is the ninth leading cause of mortality worldwide. It is a complex disease that manifests as chronic hyperglycemia. Glucose exposure causes biochemical changes at the proteome level as reflected in accumulation of glycated proteins. A prominent example is hemoglobin A1c (HbA1c), a glycated protein widely accepted as a diabetic indicator. Another emerging biomarker is glycated albumin which has demonstrated utility in situations where HbA1c cannot be used. Other proteins undergo glycation as well thus impacting cellular function, transport and immune response. Accordingly, these glycated counterparts may serve as predictors for diabetic complications and thus warrant further inquiry. Fortunately, modern proteomics has provided unique analytic capability to enable improved and more comprehensive exploration of glycating agents and glycated proteins. This review broadly covers topics from epidemiology of diabetes to modern analytical tools such as mass spectrometry to facilitate a better understanding of diabetes pathophysiology. This serves as an attempt to connect clinically relevant questions with findings of recent proteomic studies to suggest future avenues of diabetes research.

The Mechanism of Hyperglycemia-Induced Renal Cell Injury in Diabetic Nephropathy Disease: An Update

Diabetic Nephropathy (DN) is a serious complication of type I and II diabetes. It develops from the initial microproteinuria to end-stage renal failure. The main initiator for DN is chronic hyperglycemia. Hyperglycemia (HG) can stimulate the resident and non-resident renal cells to produce humoral mediators and cytokines that can lead to functional and phenotypic changes in renal cells and tissues, interference with cell growth, interacting proteins, advanced glycation end products (AGEs), etc., ultimately resulting in glomerular and tubular damage and the onset of kidney disease. Therefore, poor blood glucose control is a particularly important risk factor for the development of DN. In this paper, the types and mechanisms of DN cell damage are classified and summarized by reviewing the related literature concerning the effect of hyperglycemia on the development of DN. At the cellular level, we summarize the mechanisms and effects of renal damage by hyperglycemia. This is expected to provide therapeutic ideas and inspiration for further studies on the treatment of patients with DN.

Recent advances of long non-coding RNAs in control of hepatic gluconeogenesis

Gluconeogenesis is the main process for endogenous glucose production during prolonged fasting, or certain pathological conditions, which occurs primarily in the liver. Hepatic gluconeogenesis is a biochemical process that is finely controlled by hormones such as insulin and glucagon, and it is of great importance for maintaining normal physiological blood glucose levels. Dysregulated gluconeogenesis induced by obesity is often associated with hyperglycemia, hyperinsulinemia, and type 2 diabetes (T2D). Long noncoding RNAs (lncRNAs) are involved in various cellular events, from gene transcription to protein translation, stability, and function. In recent years, a growing number of evidences has shown that lncRNAs play a key role in hepatic gluconeogenesis and thereby, affect the pathogenesis of T2D. Here we summarized the recent progress in lncRNAs and hepatic gluconeogenesis.

In Vitro Experimental Assessment of Ethanolic Extract of Moringa oleifera Leaves as an α-Amylase and α-Lipase Inhibitor

Methods

Phytochemical screening, antioxidant activity, α-amylase, and α-lipase inhibitory assessment were carried out on Moringa oleifera extract.

Results

The result of the phytochemical screening revealed the presence of total phenolic, flavonoid, tannin, and alkaloid contents of values 0.070 ± 0.005 mg gallic acid equivalent/g, 0.180 ± 0.020 mg rutin equivalent/g, 0.042 ± 0.001 mg tannic equivalent/g, and 12.17 ± 0.001%, respectively, while the total protein analysis was 0.475 ± 0.001 mg bovine serum albumin equivalent/g. Ferric reducing antioxidant power (FRAP) and total antioxidant capacity (TAC) values were 0.534 ± 0.001 mg gallic acid equivalent/g and 0.022 ± 0.00008 mg rutin equivalent/g, respectively. Diphenyl-2-picrylhydrazyl (DPPH), ABTS (2,2'-azino-bis (ethylbenzothiazoline-6-sulfonic acid)), and nitric oxide (NO) assays showed the extract to have a strong free radical scavenging activity. The 50% inhibitory concentration (IC₅₀) values of the lipase and amylase activities of the extract are 1.0877 mg/mL and 0.1802 mg/mL, respectively.

Conclusion

However, α-lipase and α-amylase inhibiting activity of M. oleifera could be related to the phytochemicals in the extract. This research validates the ethnobotanical use of M. oleifera leaves as an effective plant-based therapeutic agent for diabetes and obesity.

Sorafenib decreases glycemia by impairing hepatic glucose metabolism

PURPOSE

Sorafenib has been reported to reduce blood glucose levels in diabetic and non-diabetic patients in previous retrospective studies. However, the mechanism of which the hypoglycemic effects of sorafenib is not clearly explored. In this study, we investigated the effect of sorafenib on blood glucose levels in diabetic and normal mice and explored the possible mechanism.

METHODS

We established a mouse model of type 2 diabetes by a high-fat diet combined with a low-dose of streptozotocin (STZ), to identify the hypoglycemic effect of sorafenib in different mice. Glucose tolerance, insulin tolerance and pyruvate tolerance tests were done after daily gavage with sorafenib to diabetic and control mice. To explore the molecular mechanism by which sorafenib regulates blood glucose levels, hepatic glucose metabolism signaling was studied by a series of in vivo and in vitro experiments.

RESULTS

Sorafenib reduced blood glucose levels in both control and diabetic mice, particularly in the latter. The diabetic mice exhibited improved glucose and insulin tolerance after sorafenib treatment. Further studies showed that the expressions of gluconeogenesis-related enzymes, such as PCK1, G6PC and PCB, were significantly decreased upon sorafenib treatment. Mechanistically, sorafenib downregulates the expression of c-MYC downstream targets PCK1, G6PC and PCB through blocking the ERK/c-MYC signaling pathway, thereby playing its hypoglycemic effect by impairing hepatic glucose metabolism.

CONCLUSION

Sorafenib reduces blood glucose levels through downregulating gluconeogenic genes, especially in diabetic mice, suggesting the patients with T2DM when treated with sorafenib need more emphasis in monitoring blood glucose to avoid unnecessary hypoglycemia.

Comparing the responses of grain fed feedlot cattle under moderate heat load and during subsequent recovery with those of feed restricted thermoneutral counterparts: plasma biochemistry

Responses to heat stress in ruminants reflect the integration of local climatic conditions, environment/production system and the animal's homeostatic and homeorhetic capacities. Thus, the goal of ameliorating heat stress requires experimental settings that, within limits, closely resemble the target production system and cohort. We investigated the blood biochemical changes of two sequential cohorts of twelve 518 ± 23 kg grain fed Black Angus steers. Each cohort consisted of two treatments of 6 head/group: a thermally challenged (TC) treatment and a feed restricted thermoneutral (FRTN) treatment. Both groups were housed in climate controlled rooms for 19 days, with the TC group experiencing three distinct periods: PreChallenge, Challenge and Recovery. PreChallenge and Recovery delivered thermoneutral conditions, while Challenge consisted of 7 days of moderate diurnal heat load. The FRTN group was maintained in thermoneutral conditions at all times. Both groups were then relocated to outdoor pens for a further 40 days to detect any enduring change to metabolism as a consequence of the treatments. We compared blood biochemical responses of the treatments and inferred likely metabolic changes. Relative to the FRTN group, the TC animals experienced limited supply of triglycerides, cholesterol and glutamine during moderate heat load, suggesting constraints to energy metabolism. Lower blood urea during Recovery and in outdoor pens implied a requirement to capture N rather than allow its excretion. Altered liver enzyme profiles indicated a higher level of hepatic stress in the TC group. By the completion of feedlot finishing, the groups were not separable on most measures.

Integrated experimental-computational analysis of a HepaRG liver-islet microphysiological system for human-centric diabetes research

Microphysiological systems (MPS) are powerful tools for emulating human physiology and replicating disease progression in vitro. MPS could be better predictors of human outcome than current animal models, but mechanistic interpretation and in vivo extrapolation of the experimental results remain significant challenges. Here, we address these challenges using an integrated experimental-computational approach. This approach allows for in silico representation and predictions of glucose metabolism in a previously reported MPS with two organ compartments (liver and pancreas) connected in a closed loop with circulating medium. We developed a computational model describing glucose metabolism over 15 days of culture in the MPS. The model was calibrated on an experiment-specific basis using data from seven experiments, where HepaRG single-liver or liver-islet cultures were exposed to both normal and hyperglycemic conditions resembling high blood glucose levels in diabetes. The calibrated models reproduced the fast (i.e. hourly) variations in glucose and insulin observed in the MPS experiments, as well as the long-term (i.e. over weeks) decline in both glucose tolerance and insulin secretion. We also investigated the behaviour of the system under hypoglycemia by simulating this condition in silico, and the model could correctly predict the glucose and insulin responses measured in new MPS experiments. Last, we used the computational model to translate the experimental results to humans, showing good agreement with published data of the glucose response to a meal in healthy subjects. The integrated experimental-computational framework opens new avenues for future investigations toward disease mechanisms and the development of new therapies for metabolic disorders.

Microphysiological systems (MPS) are powerful tools to unravel biological knowledge underlying disease. MPS provide a physiologically relevant, human-based in vitro setting, which can potentially yield better translatability to humans than current animal models and traditional cell cultures. However, mechanistic interpretation and extrapolation of the experimental results to human outcome remain significant challenges. In this study, we confront these challenges using an integrated experimental-computational approach. We present a computational model describing glucose metabolism in a previously reported MPS integrating liver and pancreas. This MPS supports a homeostatic feedback loop between HepaRG/HHSteC spheroids and pancreatic islets, and allows for detailed investigations of mechanisms underlying type 2 diabetes in humans. We show that the computational model captures the complex dynamics of glucose-insulin regulation observed in the system, and can provide mechanistic insight into disease progression features, such as insulin resistance and β-cell dynamics. Furthermore, the computational model can explain key differences in temporal dynamics between MPS and human responses, and thus provides a tool for translating experimental insights into human outcome. The integrated experimental-computational framework opens new avenues for future investigations toward disease mechanisms and the development of new therapies for metabolic disorders.

SGLT2 Inhibitors in Chronic Kidney Disease: From Mechanisms to Clinical Practice

In recent years, sodium-glucose co-transporter 2 inhibitors (SGLT2i) have demonstrated beneficial renoprotective effects, which culminated in the recent approval of their use for patients with chronic kidney disease (CKD), following a similar path to one they had already crossed due to their cardioprotective effects, meaning that SGLT2i represent a cornerstone of heart failure therapy. In the present review, we aimed to discuss the pathophysiological mechanisms operating in CKD that are targeted with SGLT2i, either directly or indirectly. Furthermore, we presented clinical evidence of SGLT2i in CKD with respect to the presence of diabetes mellitus. Despite initial safety concerns with regard to euglycemic diabetic ketoacidosis and transient decline in glomerular filtration rate, the accumulating clinical data are reassuring. In summary, although SGLT2i provide clinicians with an exciting new treatment option for patients with CKD, further research is needed to determine which subgroups of patients with CKD will benefit the most, and which the least, from this therapeutical option.

Use of Glucose-Lowering Agents in Diabetes and CKD

Diabetes is the most common cause of kidney failure worldwide. Patients with diabetes and chronic kidney disease (CKD) are also at markedly higher risk of cardiovascular disease, particularly heart failure (HF), and death. Through the processes of gluconeogenesis and glucose reabsorption, the kidney plays a central role in glucose homeostasis. Insulin resistance is an early alteration observed in CKD, worsened by the frequent presence of hypertension, obesity, and ongoing chronic inflammation, and oxidative stress. Management of diabetes in moderate to severe CKD warrants special consideration because of changes in glucose and insulin homeostasis and altered metabolism of glucose-lowering therapies. Kidney failure and initiation of kidney replacement therapy by dialysis adds to management complexity by further limiting therapeutic options, and predisposing individuals to hypoglycemia and hyperglycemia. Glycemic goals should be individualized, considering CKD severity, presence of macrovascular and microvascular complications, and life expectancy. A general hemoglobin A1c (HbA1c) goal of approximately 7% may be appropriate in earlier stages of CKD, with more relaxed targets often appropriate in later stages. Use of sodium glucose cotransporter2 (SGLT2) inhibitors and glucagon like peptide-1 receptor agonists (GLP-1RAs) meaningfully improves kidney and heart outcomes for patients with diabetes and CKD, irrespective of HbA1c targets, and are now part of guideline-directed medical therapy in this high-risk population. Delivery of optimal care for patients with diabetes and CKD will require collaboration across health care specialties and disciplines.

Impact of Obesity on Postprandial Triglyceride Contribution to Glucose Homeostasis, Assessed with a Semimechanistic Model

The integrated glucose-insulin model is a semimechanistic model describing glucose and insulin after a glucose challenge. Similarly, a semiphysiologic model of the postprandial triglyceride (TG) response in chylomicrons and VLDL-V6 was recently published. We have developed the triglyceride-insulin-glucose-GLP-1 (TIGG) model by integrating these models and active GLP-1. The aim was to characterize, using the TIGG model, the postprandial response over 13 hours following a high-fat meal in 3 study populations based on body mass index categories: lean, obese, and very obese. Differential glucose and lipid regulation were observed between the lean population and obese or very obese populations. A population comparison revealed further that fasting glucose and insulin were elevated in obese and very obese when compared with lean; and euglycemia was achieved at different times postmeal between the obese and very obese populations. Postprandial insulin was incrementally elevated in the obese and very obese populations compared with lean. Postprandial chylomicrons TGs were similar across populations, whereas the postprandial TGs in VLDL-V6 were increased in the obese and very obese populations compared with lean. Postprandial active GLP-1 was diminished in the very obese population compared with lean or obese. The TIGG model described the response following a high-fat meal in individuals who are lean, obese, and very obese and provided insight into the possible regulation of glucose homeostasis in the extended period after the meal by utilizing lipids. The TIGG-model is the first model to integrate glucose and insulin regulation, incretin effect, and postprandial TGs response in chylomicrons and VLDL-V6.

Inflammation, Oxidative Stress, and Antioxidant Micronutrients as Mediators of the Relationship Between Sleep, Insulin Sensitivity, and Glycosylated Hemoglobin

Background

Sleep deprivation and poor sleep quality contribute to increases in oxidative stress, antioxidant imbalance, and a pro-inflammatory state which may predispose to a higher risk of diabetes. Our objective was to estimate the contributions of C-reactive protein (CRP), gamma glutamyl transferase (GGT), and micronutrient antioxidants (bilirubin, carotenoids, uric acid, vitamins A, C-E?) to the relationships between sleep-fasting insulin concentration and -glycosylated hemoglobin (HbA1c).

Methods

Data from the 2005/06 US National Health and Nutritional Examination Survey were used (N = 1,946; 20 y+). Sleep quality and quantity was assessed by the Sleep Disorders Questionnaire, and fasting blood was collected to quantify CRP, GGT, antioxidant micronutrients, insulin concentration, and HbA1c. The bootstrap method was used to estimate the amount of mediation or contribution of these mediators to the sleep-insulin concentration and -HbA1c relationships, which were quantified as large (≥0.25) or moderate (≥0.09).

Results

The sleep duration-fasting insulin relationship was mediated by GGT, carotenoids, uric acid, and vitamins C and D, whereas CRP and bilirubin were non-significant mediators of a moderate effect size. Similarly, the sleep quality-fasting insulin relationship was mediated by CRP, bilirubin and vitamin C, whereas GGT, carotenoids, uric acid, and vitamin D were non-significant large-to-moderate mediators. To a lesser degree, these micronutrients mediated for the relationship between sleep-HbA1c levels.

Conclusion

Several factors related to inflammation, oxidative stress, and antioxidant status were found to lie on the pathway of the sleep-insulin and -glycemic control relationships. Sleep hygiene, reduced systemic inflammation/oxidative stress, and optimal antioxidants intake are potentially beneficial targets for managing diabetes risk.

Diabetes Detection and Management through Photoplethysmographic and Electrocardiographic Signals Analysis: A Systematic Review

(1) Background: Diabetes mellitus (DM) is a chronic, metabolic disease characterized by elevated levels of blood glucose. Recently, some studies approached the diabetes care domain through the analysis of the modifications of cardiovascular system parameters. In fact, cardiovascular diseases are the first leading cause of death in diabetic subjects. Thanks to their cost effectiveness and their ease of use, electrocardiographic (ECG) and photoplethysmographic (PPG) signals have recently been used in diabetes detection, blood glucose estimation and diabetes-related complication detection. This review's aim is to provide a detailed overview of all the published methods, from the traditional (non machine learning) to the deep learning approaches, to detect and manage diabetes using PPG and ECG signals. This review will allow researchers to compare and understand the differences, in terms of results, amount of data and complexity that each type of approach provides and requires. (2) Method: We performed a systematic review based on articles that focus on the use of ECG and PPG signals in diabetes care. The search was focused on keywords related to the topic, such as "Diabetes", "ECG", "PPG", "Machine Learning", etc. This was performed using databases, such as PubMed, Google Scholar, Semantic Scholar and IEEE Xplore. This review's aim is to provide a detailed overview of all the published methods, from the traditional (non machine learning) to the deep learning approaches, to detect and manage diabetes using PPG and ECG signals. This review will allow researchers to compare and understand the differences, in terms of results, amount of data and complexity that each type of approach provides and requires. (3) Results: A total of 78 studies were included. The majority of the selected studies focused on blood glucose estimation (41) and diabetes detection (31). Only 7 studies focused on diabetes complications detection. We present these studies by approach: traditional, machine learning and deep learning approaches. (4) Conclusions: ECG and PPG analysis in diabetes care showed to be very promising. Clinical validation and data processing standardization need to be improved in order to employ these techniques in a clinical environment.

Unraveling Metabolite Provisioning to Offspring Through Parental Fluids: A Case Study of the Brazilian Guitarfish, Pseudobatos horkelii

Elasmobranchs have a very distinct metabolism, and many aspects related to the energetic dynamics of these animals remain poorly investigated. The reproductive period is particularly vulnerable for viviparous species, as part of the energy reserves of the parental biomass is reallocated for gamete production and embryo development. In this context, this study aimed to characterize parental metabolite provisioning to the offspring (both sperm and developing embryos) of the Brazilian Guitarfish, Pseudobatos horkelii, through glucose, β-hydroxybutyrate, triglycerides, and total cholesterol determinations in the uterine liquid (UL) and serum of pregnant females and in the seminal fluid (SF) and serum of males during the copulation period. No significant difference was observed for the analyzed markers between the UL and SF. Except for triglycerides, higher in female serum samples, all other energy markers were present at similar concentrations in the serum of both females and males. When comparing female UL and serum, significant differences were observed for triglycerides and total cholesterol. No differences were observed between SF and serum in males. The results indicate that all markers are being made available to offspring, possibly complementary to the yolk in the case of maternal liquid, and as an additional source for sperm mobilization required during egg fertilization in the case of the paternal fluid. Correlations between the markers in the parental matrices were also noted, compatible with the metabolic pathways activated during energy mobilization in vertebrates. Moreover, distinct marker predominance patterns were also noted for both UL and SF. Energy mobilization characterization directed to offspring through parental fluids aids in unraveling metabolic dynamics during the reproduction stage while also providing support for stress physiology studies to evaluate the indirect effects of parental allostatic overload in both sperm and developing embryos. Finally, energy mobilization assessments of parental fluids may also help elucidate how internal fertilization and viviparity evolved in this very distinct taxonomic group.

Calcium imaging in intact mouse acinar cells in acute pancreas tissue slices

The physiology and pathophysiology of the exocrine pancreas are in close connection to changes in intra-cellular Ca²⁺ concentration. Most of our knowledge is based on in vitro experiments on acinar cells or acini enzymatically isolated from their surroundings, which can alter their structure, physiology, and limit our understanding. Due to these limitations, the acute pancreas tissue slice technique was introduced almost two decades ago as a complementary approach to assess the morphology and physiology of both the endocrine and exocrine pancreas in a more conserved in situ setting. In this study, we extend previous work to functional multicellular calcium imaging on acinar cells in tissue slices. The viability and morphological characteristics of acinar cells within the tissue slice were assessed using the LIVE/DEAD assay, transmission electron microscopy, and immunofluorescence imaging. The main aim of our study was to characterize the responses of acinar cells to stimulation with acetylcholine and compare them with responses to cerulein in pancreatic tissue slices, with special emphasis on inter-cellular and inter-acinar heterogeneity and coupling. To this end, calcium imaging was performed employing confocal microscopy during stimulation with a wide range of acetylcholine concentrations and selected concentrations of cerulein. We show that various calcium oscillation parameters depend monotonically on the stimulus concentration and that the activity is rather well synchronized within acini, but not between acini. The acute pancreas tissue slice represents a viable and reliable experimental approach for the evaluation of both intra- and inter-cellular signaling characteristics of acinar cell calcium dynamics. It can be utilized to assess many cells simultaneously with a high spatiotemporal resolution, thus providing an efficient and high-yield platform for future studies of normal acinar cell biology, pathophysiology, and screening pharmacological substances.

Is vascular insulin resistance an early step in diet-induced whole-body insulin resistance?

There is increasing evidence that skeletal muscle microvascular (capillary) blood flow plays an important role in glucose metabolism by increasing the delivery of glucose and insulin to the myocytes. This process is impaired in insulin-resistant individuals. Studies suggest that in diet-induced insulin-resistant rodents, insulin-mediated skeletal muscle microvascular blood flow is impaired post-short-term high fat feeding, and this occurs before the development of myocyte or whole-body insulin resistance. These data suggest that impaired skeletal muscle microvascular blood flow is an early vascular step before the onset of insulin resistance. However, evidence of this is still lacking in humans. In this review, we summarise what is known about short-term high-calorie and/or high-fat feeding in humans. We also explore selected animal studies to identify potential mechanisms. We discuss future directions aimed at better understanding the ‘early’ vascular mechanisms that lead to insulin resistance as this will provide the opportunity for much earlier screening and timing of intervention to assist in preventing type 2 diabetes.

Reduced insulin signaling and high glucagon in early insulin resistance impaired fast-fed regulation of renal gluconeogenesis via insulin receptor substrate

Gluconeogenesis is one of the key processes through which the kidney contributes to glucose homeostasis. Urinary exosomes (uE) have been used to study renal gene regulation noninvasively in humans and rodents. Recently, we demonstrated fast-fed regulation of phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting enzyme for gluconeogenesis, in human uE. The regulation was impaired in subjects with early insulin resistance. Here, we studied primary human proximal tubule cells (hPT) and human uE to elucidate a potential link between insulin resistance and fast-fed regulation of renal PEPCK. We demonstrate that fasted hPTs had higher PEPCK and insulin receptor substrate-2 (IRS2) mRNA and protein levels, relative to fed cells. The fast-fed regulation was, however, attenuated in insulin receptor knockdown (IRKO) hPTs. The IRKO was confirmed by the blunted insulin-induced response on PEPCK, PGC1α, p-IR, and p-AKT expression in IRKO cells. Exosomes secreted by the wild-type or IRKO hPT showed similar regulation to the respective hPT. Similarly, in human uE, the relative abundance of IRS-2 mRNA (to IRS1) was higher in the fasted state relative to the fed condition. However, the fast-fed difference was absent in subjects with early insulin resistance. These subjects had higher circulating glucagon levels relative to subjects with optimal insulin sensitivity. Furthermore, in hPT cells, glucagon significantly induced PEPCK and IRS2 gene, and gluconeogenesis. IR knockdown in hPT cells further increased the gene expression levels. Together the data suggest that reduced insulin sensitivity and high glucagon in early insulin resistance may impair renal gluconeogenesis via IRS2 regulation.

Assessment of glycemia in chronic kidney disease

Reliable assessment of glycemia is central to the management of diabetes. The kidneys play a vital role in maintaining glucose homeostasis through glucose filtration, reabsorption, consumption, and generation. This review article highlights the role of the kidneys in glucose metabolism and discusses the benefits, pitfalls, and evidence behind the glycemic markers in patients with chronic kidney disease. We specifically highlight the role of continuous glucose monitoring as an emerging minimally invasive technique for glycemic assessment.

A Clinical Perspective of the Multifaceted Mechanism of Metformin in Diabetes, Infections, Cognitive Dysfunction, and Cancer

In type 2 diabetes, ecological and lifecourse factors may interact with the host microbiota to influence expression of his/her genomes causing perturbation of interconnecting biological pathways with diverse clinical course. Metformin is a plant-based or plant-derived medicinal product used for the treatment of type 2 diabetes for over 60 years and is an essential drug listed by the World Health Organization. By reducing mitochondrial oxidative phosphorylation and adenosine triphosphate (ATP) production, metformin increased AMP (adenosine monophosphate)-activated protein kinase (AMPK) activity and altered cellular redox state with reduced glucagon activity, endogenous glucose production, lipogenesis, and protein synthesis. Metformin modulated immune response by directly reducing neutrophil to lymphocyte ratio and improving the phagocytic function of immune cells. By increasing the relative abundance of mucin-producing and short-chain-fatty-acid-producing gut microbes, metformin further improved the host inflammatory and metabolic milieu. Experimentally, metformin promoted apoptosis and reduced proliferation of cancer cells by reducing their oxygen consumption and modulating the microenvironment. Both clinical and mechanistic studies support the pluripotent effects of metformin on reducing cardiovascular–renal events, infection, cancer, cognitive dysfunction, and all-cause death in type 2 diabetes, making this low-cost medication a fundamental therapy for individualization of other glucose-lowering drugs in type 2 diabetes. Further research into the effects of metformin on cognitive function, infection and cancer, especially in people without diabetes, will provide new insights into the therapeutic value of metformin in our pursuit of prevention and treatment of ageing-related as well as acute and chronic diseases beyond diabetes.

Effects of Diet, Lifestyle, Chrononutrition and Alternative Dietary Interventions on Postprandial Glycemia and Insulin Resistance

As years progress, we are found more often in a postprandial than a postabsorptive state. Chrononutrition is an integral part of metabolism, pancreatic function, and hormone secretion. Eating most calories and carbohydrates at lunch time and early afternoon, avoiding late evening dinner, and keeping consistent number of daily meals and relative times of eating occasions seem to play a pivotal role for postprandial glycemia and insulin sensitivity. Sequence of meals and nutrients also play a significant role, as foods of low density such as vegetables, salads, or soups consumed first, followed by protein and then by starchy foods lead to ameliorated glycemic and insulin responses. There are several dietary schemes available, such as intermittent fasting regimes, which may improve glycemic and insulin responses. Weight loss is important for the treatment of insulin resistance, and it can be achieved by many approaches, such as low-fat, low-carbohydrate, Mediterranean-style diets, etc. Lifestyle interventions with small weight loss (7-10%), 150 min of weekly moderate intensity exercise and behavioral therapy approach can be highly effective in preventing and treating type 2 diabetes. Similarly, decreasing carbohydrates in meals also improves significantly glycemic and insulin responses, but the extent of this reduction should be individualized, patient-centered, and monitored. Alternative foods or ingredients, such as vinegar, yogurt, whey protein, peanuts and tree nuts should also be considered in ameliorating postprandial hyperglycemia and insulin resistance. This review aims to describe the available evidence about the effects of diet, chrononutrition, alternative dietary interventions and exercise on postprandial glycemia and insulin resistance.

One-hundred year evolution of prandial insulin preparations: From animal pancreas extracts to rapid-acting analogs

The first insulin preparation injected in humans in 1922 was short-acting, extracted from animal pancreas, contaminated by impurities. Ever since the insulin extracted from animal pancreas has been continuously purified, until an unlimited synthesis of regular human insulin (RHI) became possible in the '80s using the recombinant-DNA (rDNA) technique. The rDNA technique then led to the designer insulins (analogs) in the early '90s. Rapid-acting insulin analogs were developed to accelerate the slow subcutaneous (sc) absorption of RHI, thus lowering the 2-h post-prandial plasma glucose (PP-PG) and risk for late hypoglycemia as comparing with RHI. The first rapid-acting analog was lispro (in 1996), soon followed by aspart and glulisine. Rapid-acting analogs are more convenient than RHI: they improve early PP-PG, and 24-h PG and A1C as long as basal insulin is also optimized; they lower the risk of late PP hypoglycemia and they allow a shorter time-interval between injection and meal. Today rapid-acting analogs are the gold standard prandial insulins. Recently, even faster analogs have become available (faster aspart, ultra-rapid lispro) or are being studied (Biochaperone lispro), making additional gains in lowering PP-PG. Rapid-acting analogs are recommended in all those with type 1 and type 2 diabetes who need prandial insulin replacement.

Glucose Metabolism in Acute Kidney Injury and Kidney Repair

The kidneys play an indispensable role in glucose homeostasis via glucose reabsorption, production, and utilization. Conversely, aberrant glucose metabolism is involved in the onset, progression, and prognosis of kidney diseases, including acute kidney injury (AKI). In this review, we describe the regulation of glucose homeostasis and related molecular factors in kidneys under normal physiological conditions. Furthermore, we summarize recent investigations about the relationship between glucose metabolism and different types of AKI. We also analyze the involvement of glucose metabolism in kidney repair after injury, including renal fibrosis. Further research on glucose metabolism in kidney injury and repair may lead to the identification of novel therapeutic targets for the prevention and treatment of kidney diseases.

Spatial-resolved metabolomics reveals tissue-specific metabolic reprogramming in diabetic nephropathy by using mass spectrometry imaging

Detailed knowledge on tissue-specific metabolic reprogramming in diabetic nephropathy (DN) is vital for more accurate understanding the molecular pathological signature and developing novel therapeutic strategies. In the present study, a spatial-resolved metabolomics approach based on air flow-assisted desorption electrospray ionization (AFADESI) and matrix-assisted laser desorption ionization (MALDI) integrated mass spectrometry imaging (MSI) was proposed to investigate tissue-specific metabolic alterations in the kidneys of high-fat diet-fed and streptozotocin (STZ)-treated DN rats and the therapeutic effect of astragaloside IV, a potential anti-diabetic drug, against DN. As a result, a wide range of functional metabolites including sugars, amino acids, nucleotides and their derivatives, fatty acids, phospholipids, sphingolipids, glycerides, carnitine and its derivatives, vitamins, peptides, and metal ions associated with DN were identified and their unique distribution patterns in the rat kidney were visualized with high chemical specificity and high spatial resolution. These region-specific metabolic disturbances were ameliorated by repeated oral administration of astragaloside IV (100 mg/kg) for 12 weeks. This study provided more comprehensive and detailed information about the tissue-specific metabolic reprogramming and molecular pathological signature in the kidney of diabetic rats. These findings highlighted the promising potential of AFADESI and MALDI integrated MSI based metabolomics approach for application in metabolic kidney diseases.

Dynamic interplay between AfadinS1795 phosphorylation and diet regulates glucose homeostasis in obese mice

KEY POINTS

Afadin is a ubiquitously expressed scaffold protein with a recently discovered role in insulin signalling and glucose metabolism. Insulin-stimulated phosphorylation of Afadin at S1795 occurs in insulin-responsive tissues such as adipose tissue, muscle, liver, pancreas and heart. Afadin abundance and Afadin^S1795 phosphorylation are dynamically regulated in metabolic tissues during diet-induced obesity progression. Genetic silencing of Afadin^S1795 phosphorylation improves glucose homeostasis in the early stages of diet-induced metabolic dysregulation. Afadin^S1795 phosphorylation contributes to the early development of obesity-related complications in mice.

ABSTRACT

Obesity is associated with systemic insulin resistance and numerous metabolic disorders. Yet, the mechanisms underlying impaired insulin action during obesity remain to be fully elucidated. Afadin is a multifunctional scaffold protein with the ability to modulate insulin action through its phosphorylation at S1795 in adipocytes. In the present study, we report that insulin-stimulated Afadin^S1795 phosphorylation is not restricted to adipose tissues, but is a common signalling event in insulin-responsive tissues including muscle, liver, pancreas and heart. Furthermore, a dynamic regulation of Afadin abundance occurred during diet-induced obesity progression, while its phosphorylation was progressively attenuated. To investigate the role of Afadin^S1795 phosphorylation in the regulation of whole-body metabolic homeostasis, we generated a phospho-defective mouse model (Afadin SA) in which the Afadin phosphorylation site was silenced (S1795A) at the whole-body level using CRISPR-Cas9-mediated gene editing. Metabolic characterization of these mice under basal physiological conditions or during a high-fat diet (HFD) challenge revealed that preventing Afadin^S1795 phosphorylation improved insulin sensitivity and glucose tolerance and increased liver glycogen storage in the early stage of diet-induced metabolic dysregulation, without affecting body weight. Together, our findings reveal that Afadin^S1795 phosphorylation in metabolic tissues is critical during obesity progression and contributes to promote systemic insulin resistance and glucose intolerance in the early phase of diet-induced obesity.

High Carbohydrate Diet Increased Glucose Transporter Protein Levels in Jejunum but Did Not Lead to Enhanced Post-Exercise Skeletal Muscle Glycogen Recovery

We examined the effect of dietary carbohydrate intake on post-exercise glycogen recovery. Male Institute of Cancer Research (ICR) mice were fed moderate-carbohydrate chow (MCHO, 50%cal from carbohydrate) or high-carbohydrate chow (HCHO, 70%cal from carbohydrate) for 10 days. They then ran on a treadmill at 25 m/min for 60 min and administered an oral glucose solution (1.5 mg/g body weight). Compared to the MCHO group, the HCHO group showed significantly higher sodium-D-glucose co-transporter 1 protein levels in the brush border membrane fraction (p = 0.003) and the glucose transporter 2 level in the mucosa of jejunum (p = 0.004). At 30 min after the post-exercise glucose administration, the skeletal muscle and liver glycogen levels were not significantly different between the two diet groups. The blood glucose concentration from the portal vein (which is the entry site of nutrients from the gastrointestinal tract) was not significantly different between the groups at 15 min after the post-exercise glucose administration. There was no difference in the total or phosphorylated states of proteins related to glucose uptake and glycogen synthesis in skeletal muscle. Although the high-carbohydrate diet significantly increased glucose transporters in the jejunum, this adaptation stimulated neither glycogen recovery nor glucose absorption after the ingestion of post-exercise glucose.

An Updated Organ-Based Multi-Level Model for Glucose Homeostasis: Organ Distributions, Timing, and Impact of Blood Flow

Glucose homeostasis is the tight control of glucose in the blood. This complex control is important, due to its malfunction in serious diseases like diabetes, and not yet sufficiently understood. Due to the involvement of numerous organs and sub-systems, each with their own intra-cellular control, we have developed a multi-level mathematical model, for glucose homeostasis, which integrates a variety of data. Over the last 10 years, this model has been used to insert new insights from the intra-cellular level into the larger whole-body perspective. However, the original cell-organ-body translation has during these years never been updated, despite several critical shortcomings, which also have not been resolved by other modeling efforts. For this reason, we here present an updated multi-level model. This model provides a more accurate sub-division of how much glucose is being taken up by the different organs. Unlike the original model, we now also account for the different dynamics seen in the different organs. The new model also incorporates the central impact of blood flow on insulin-stimulated glucose uptake. Each new improvement is clear upon visual inspection, and they are also supported by statistical tests. The final multi-level model describes >300 data points in >40 time-series and dose-response curves, resulting from a large variety of perturbations, describing both intra-cellular processes, organ fluxes, and whole-body meal responses. We hope that this model will serve as an improved basis for future data integration, useful for research and drug developments within diabetes.

Renal gluconeogenesis in insulin resistance: A culprit for hyperglycemia in diabetes

Renal gluconeogenesis is one of the major pathways for endogenous glucose production. Impairment in this process may contribute to hyperglycemia in cases with insulin resistance and diabetes. We reviewed pertinent studies to elucidate the role of renal gluconeogenesis regulation in insulin resistance and diabetes. A consensus on the suppressive effect of insulin on kidney gluconeogenesis has started to build up. Insulin-resistant models exhibit reduced insulin receptor (IR) expression and/or post-receptor signaling in their kidney tissue. Reduced IR expression or post-receptor signaling can cause impairment in insulin’s action on kidneys, which may increase renal gluconeogenesis in the state of insulin resistance. It is now established that the kidney contributes up to 20% of all glucose production via gluconeogenesis in the post-absorptive phase. However, the rate of renal glucose release excessively increases in diabetes. The rise in renal glucose release in diabetes may contribute to fasting hyperglycemia and increased postprandial glucose levels. Enhanced glucose release by the kidneys and renal expression of the gluconeogenic-enzyme in diabetic rodents and humans further point towards the significance of renal gluconeogenesis. Overall, the available literature suggests that impairment in renal gluconeogenesis in an insulin-resistant state may contribute to hyperglycemia in type 2 diabetes.

The physiological basis of insulin therapy in people with diabetes mellitus

Insulin therapy has been in use now for 100 years, but only recently insulin replacement has been based on physiology. The pancreas secretes insulin at continuously variable rates, finely regulated by sensitive arterial glucose sensing. Pancreatic insulin is delivered directlyin the portal blood to insulinize preferentially the liver. In the fasting state, insulin is secreted at a low rate to modulate hepatic glucose output. After liver extraction (50%), insulin concentrations in peripheral plasma are 2.4-4 times lower than in portal, but still efficacious to restrain lipolysis. In the prandial condition, insulin is secreted rapidly in large amounts to increase portal and peripheral concentrations to peaks 10-20 times greater vs the values of fasting within 30-40 min from meal ingestion. The prandial portal hyperinsulinemia fully suppresses hepatic glucose production while peripheral hyperinsulinemia increases glucose utilization, thus limitating the post-prandial plasma glucose elevation. Physiology of insulin indicates that insulin should be replaced in people with diabetes mimicking the pancreas, i.e. in a basal-bolus mode, for fasting and prandial state, respectively. Despite the presently ongoing limitations (subcutaneous and peripheral rather than portal and intravenous insulin delivery), basal-bolus insulin allows people with diabetes to achieve A1c in the range with minimal risk of hypoglycaemia, to prevent vascular complications and to ensure good quality of life.

Direct conversion of porcine primary fibroblasts into hepatocyte-like cells

The pig is an important model organism for biomedical research, mainly due to its extensive genetic, physiological and anatomical similarities with humans. Until date, direct conversion of somatic cells into hepatocyte-like cells (iHeps) has only been achieved in rodents and human cells. Here, we employed lentiviral vectors to screen a panel of 12 hepatic transcription factors (TF) for their potential to convert porcine fibroblasts into hepatocyte-like cells. We demonstrate for the first time, hepatic conversion of porcine somatic cells by over-expression of CEBPα, FOXA1 and HNF4α2 (3TF-piHeps). Reprogrammed 3TF-piHeps display a hepatocyte-like morphology and show functional characteristics of hepatic cells, including albumin secretion, Dil-AcLDL uptake, storage of lipids and glycogen and activity of cytochrome P450 enzymes CYP1A2 and CYP2C33 (CYP2C9 in humans). Moreover, we show that markers of mature hepatocytes are highly expressed in 3TF-piHeps, while fibroblastic markers are reduced. We envision piHeps as useful cell sources for future studies on drug metabolism and toxicity as well as in vitro models for investigation of pig-to-human infectious diseases.

Regulation of Postabsorptive and Postprandial Glucose Metabolism by Insulin-Dependent and Insulin-Independent Mechanisms: An Integrative Approach

Glucose levels in blood must be constantly maintained within a tight physiological range to sustain anabolism. Insulin regulates glucose homeostasis via its effects on glucose production from the liver and kidneys and glucose disposal in peripheral tissues (mainly skeletal muscle). Blood levels of glucose are regulated simultaneously by insulin-mediated rates of glucose production from the liver (and kidneys) and removal from muscle; adipose tissue is a key partner in this scenario, providing nonesterified fatty acids (NEFA) as an alternative fuel for skeletal muscle and liver when blood glucose levels are depleted. During sleep at night, the gradual development of insulin resistance, due to growth hormone and cortisol surges, ensures that blood glucose levels will be maintained within normal levels by: (a) switching from glucose to NEFA oxidation in muscle; (b) modulating glucose production from the liver/kidneys. After meals, several mechanisms (sequence/composition of meals, gastric emptying/intestinal glucose absorption, gastrointestinal hormones, hyperglycemia mass action effects, insulin/glucagon secretion/action, de novo lipogenesis and glucose disposal) operate in concert for optimal regulation of postprandial glucose fluctuations. The contribution of the liver in postprandial glucose homeostasis is critical. The liver is preferentially used to dispose over 50% of the ingested glucose and restrict the acute increases of glucose and insulin in the bloodstream after meals, thus protecting the circulation and tissues from the adverse effects of marked hyperglycemia and hyperinsulinemia.

Improved Glucose Intolerance through a Distinct Mouse Olfactory Receptor 23-Induced Signaling Pathway Mediating Glucose Uptake in Myotubes and Adipocytes

SCOPE

It is aimed to determine the role of mouse olfactory receptor 23 (MOR23) in regulation of glucose uptake in myotubes and adipocytes and investigate whether administration of a possible MOR23 ligand, α-cedrene, attenuates the high fat diet (HFD)-induced glucose intolerance by enhancing the OR-mediated signaling pathway in mice.

METHODS AND RESULTS

MOR23 is genetically inactivated by specific small interfering RNA in C2C12 myotubes and 3T3-L1 adipocytes and stimulated with α-cedrene under both basal and insulin-stimulated conditions. In addition, Male C57BL/6N mice are fed a normal diet, HFD, or HFD supplemented with 0.2% α-cedrene. In C2C12 myotubes and 3T3-L1 adipocytes, genetic inactivation of MOR23 significantly decrease glucose uptake and MOR23 downstream signaling under both basal and insulin-stimulated conditions. On the other hand, α-cedrene-mediated MOR23 stimulation results in increased glucose uptake and upregulation of MOR23 signaling molecules, absent in MOR23-depleted myotubes and adipocytes. Moreover, in mice, α-cedrene administration ameliorates HFD-induced glucose intolerance. Activation of MOR23 signaling cascade is also confirmed in basal and insulin stimulated skeletal muscles and adipose tissues of α-cedrene-treated mice.

CONCLUSIONS

These findings suggest that MOR23 is a novel factor for the regulation of glucose uptake and whole-body glucose homeostasis and has therapeutic potential for diabetes treatment.

IQGAP1 binds AMPK and is required for maximum AMPK activation

AMP-activated protein kinase (AMPK) is a fundamental component of a protein kinase cascade that is an energy sensor. AMPK maintains energy homeostasis in the cell by promoting catabolic and inhibiting anabolic pathways. Activation of AMPK requires phosphorylation by the liver kinase B1 or by the Ca²⁺/calmodulin-dependent protein kinase 2 (CaMKK2). The scaffold protein IQGAP1 regulates intracellular signaling pathways, such as the mitogen-activated protein kinase and AKT signaling cascades. Recent work implicates the participation of IQGAP1 in metabolic function, but the molecular mechanisms underlying these effects are poorly understood. Here, using several approaches including binding analysis with fusion proteins, siRNA-mediated gene silencing, RT-PCR, and knockout mice, we investigated whether IQGAP1 modulates AMPK signaling. In vitro analysis reveals that IQGAP1 binds directly to the α1 subunit of AMPK. In addition, we observed a direct interaction between IQGAP1 and CaMKK2, which is mediated by the IQ domain of IQGAP1. Both CaMKK2 and AMPK associate with IQGAP1 in cells. The ability of metformin and increased intracellular free Ca²⁺ concentrations to activate AMPK is reduced in cells lacking IQGAP1. Importantly, Ca²⁺-stimulated AMPK phosphorylation was rescued by re-expression of IQGAP1 in IQGAP1-null cell lines. Comparison of the fasting response in wild-type and IQGAP1-null mice revealed that transcriptional regulation of the gluconeogenesis genes PCK1 and G6PC and the fatty acid synthesis genes FASN and ACC1 is impaired in IQGAP1-null mice. Our data disclose a previously unidentified functional interaction between IQGAP1 and AMPK and suggest that IQGAP1 modulates AMPK signaling.

Greater Suppression of Glucagon, Lipolysis, and Ketogenesis with Insulin Glargine U300 as Compared with Glargine U100 in Type 1 Diabetes Mellitus

The aim of this study was to establish the effects of clinical doses of Gla-300 versus Gla-100 on suppression of glucagon, lipolysis, and ketogenesis in type 1 diabetes mellitus (T1DM). Eighteen persons with T1DM (age 40 ± 12 years, diabetes duration 26 ± 12 years, body mass index 23.4 ± 2 kg/m², A1C 7.19% ± 0.52% [55 ± 6 mmol/mol]) were studied after 3 months of titration with Gla-300 and Gla-100 (randomized, crossover design) with a 24-h euglycemic clamp (s.c. injection of individual insulin daily doses used by subjects for previous 2 weeks, Gla-300 0.35 ± 0.08 and Gla-100 0.28 ± 0.07 U/kg). Gla-300 resulted in (1) less increase in insulin concentration for 0-12 h, but greater insulin concentration in 12-24 h (no differences for 24 h); (2) greater glucagon suppression; (3) greater prehepatic insulin-to-glucagon molar ratio, primarily in 12-24 h (ratio 1.78, 90% confidence intervals [CIs] 1.5-2.1); and (4) lower 24-h free fatty acid (0.81; 90% CI 0.73-0.89), glycerol (0.78; 90% CI 0.65-0.94), and β-hydroxybutyrate (0.72; 90% CI 0.58-0.90). Over the 24 h postinjection, as compared with Gla-100, clinical doses of Gla-300 exhibit greater suppressive effects on glucagon, lipolysis, and ketogenesis, whereas the effects on glucose metabolism are equivalent.

Consuming Diet Supplemented with Either Red Wheat Bran or Soy Extract Changes Glucose and Insulin Levels in Female Obese Zucker Rats

Type 2 diabetes mellitus is characterized by the inability to regulate blood glucose levels due to insulin resistance, resulting in hyperglycemia and hyperinsulinemia. Research has shown that consuming soy and fiber may protect against type 2 diabetes mellitus. We performed a study to determine whether supplementing diet with soy extract (0.5% weight of diet) or fiber (as red wheat bran; 11.4% weight of diet) would decrease serum insulin and blood glucose levels in a pre-diabetic/metabolic syndrome animal model. In our study, female obese Zucker rats were fed either a control diet (n = 8) or control diet supplemented with either soy extract (n = 7) or red wheat bran (n = 8) for seven weeks. Compared to rats consuming control diet, rats fed treatment diets had significantly lower (p-value < 0.05) fasting serum insulin (control = 19.34±1.6; soy extract = 11.1±1.54; red wheat bran = 12.4±1.11) and homeostatic model assessment of insulin resistance values (control = 2.16±0.22; soy extract = 1.22±0.21; red wheat bran = 1.54±0.16). Non-fasted blood glucose was also significantly lower (p-value < 0.05) in rats fed treatment diets compared to rats consuming control diet at weeks four (control = 102.63±5.67; soy extract = 80.14±2.13; red wheat bran = 82.63±3.16), six (control = 129.5±10.83; soy extract = 89.14±2.48; red wheat bran = 98.13±3.54), and seven (control = 122.25±8.95; soy extract = 89.14±4.52; red wheat bran = 84.75±4.15). Daily intake of soy extract and red wheat bran may protect against type 2 diabetes mellitus by maintaining normal glucose homeostasis.

Emerging Role of SGLT-2 Inhibitors for the Treatment of Obesity

Sodium-glucose co-transporter 2 (SGLT2) inhibitors are glucose-lowering drugs that reduce plasma glucose levels by inhibiting glucose and sodium reabsorption in the kidneys, thus resulting in glucosuria. Their effects consequently include reductions in HbA1c, blood glucose levels, and blood pressure, but also reductions in body weight and adiposity. The ability to reduce body weight is consistently observed in individuals taking SGLT2 inhibitors, but this weight loss is moderate due to counter-regulatory mechanisms striving to maintain body weight. This has prompted exploration of SGLT2 inhibitors in combination with other agents acting via decreased food intake, e.g., glucagon-like peptide 1 receptor agonists (GLP1-RAs). The bodyweight effects are promising, and together with the signs of prevention of cardiovascular and renal events, such combinations including SGLT2 inhibitors are appealing. The weight loss is clinically important, as most individuals with type 2 diabetes are overweight or obese, but also because there is an unmet need for safe, effective, and durable weight loss interventions in obese individuals without diabetes.

Phosphofructokinase-1 and fructose bisphosphatase-1 in canine liver and kidney

In healthy individuals, plasma glucose levels are maintained within a normal range. During fasting, endogenous glucose is released either through glycogenolysis or gluconeogenesis. Gluconeogenesis involves the formation of glucose-6-phosphate from a variety of precursors followed by its subsequent hydrolysis to glucose. Gluconeogenesis occurs in the liver and the kidney. In order to compare gluconeogenesis in canine liver and kidney, the activity and expression of the rate limiting enzymes that catalyze the fructose-6-phosphate and fructose 1,6-bisphosphate steps, namely, phosphofructokinase-1 (PFK-1) (glycolysis) and fructose bisphosphatase-1 (FBP-1) (gluconeogenesis), were examined. Healthy male and female beagle dogs aged 1–2 years were euthanized humanely, and samples of their liver and kidney were obtained for analysis. The levels of PFK-1 and FBP-1 in canine liver and kidney were assessed by enzymatic assays, Western blotting, and RT-qPCR. Enzyme assays showed that, in dogs, the kidney had higher specific activity of PFK-1 and FBP-1 than the liver. Western blotting and RT-qPCR data demonstrated that of the three different subunits (PFK-M, PFK-L, and PFK-P) the PFK-1 in canine liver mainly comprised PFK-L, whereas the PFK-1 in the canine kidney comprised all three subunits. As a result of these differences in the subunit composition of PFK-1, glucose metabolism might be regulated differently in the liver and kidney.

Glucose and glycogen in the diabetic kidney: Heroes or villains?

Glucose metabolism in the kidney is currently foremost in the minds of nephrologists, diabetologists and researchers globally, as a result of the outstanding success of SGLT2 inhibitors in reducing renal and cardiovascular disease in individuals with diabetes. However, these exciting data have come with the puzzling but fascinating paradigm that many of the beneficial effects on the kidney and cardiovascular system seem to be independent of the systemic glucose lowering actions of these agents. This manuscript places into context an area of research highly relevant to renal glucose metabolism, that of glycogen accumulation and metabolism in the diabetic kidney. Whether the glycogen that abnormally accumulates is pathological (the villain), is somehow protective (the hero) or is inconsequential (the bystander) is a research question that may provide insight into the link between diabetes and diabetic kidney disease.

Inhibition of NF-κB Reduces Renal Inflammation and Expression of PEPCK in Type 2 Diabetic Mice

Renal gluconeogenesis is markedly promoted in patients with type 2 diabetes mellitus (T2DM); however, the underlying mechanism remains largely unknown. Renal gluconeogenesis is found to be negatively regulated by insulin. T2DM is characterized by chronic and subacute inflammation; however, inflammation has been well recognized to induce insulin resistance. Therefore, this study aimed to investigate whether the enhanced renal gluconeogenesis in T2DM was partially due to the renal inflammation-mediated insulin resistance. If so, whether inflammation inhibitor could partially reverse such change. Diabetic db/db mice and db/m mice were used in our study. Typically, diabetic db/db mice were intraperitoneally treated with 1 mg/kg NF-κB inhibitor parthenolide (PTN) or saline as control every other day. Twelve weeks after treatment, animal samples were collected for measurements. Our results suggested that the expression levels of the inflammatory factors and the gluconeogenic rate-limiting enzyme phosphoenolpyruvate carboxykinase (PEPCK) were up-regulated in renal cortex of both db/db mice and T2DM patients. Moreover, reduced insulin signaling, as well as up-regulated expression of downstream genes FOXO1 and PGC-1ɑ, could be detected in renal cortex of db/db mice compared with that of db/m mice. Consistent with our hypothesis, PTN treatment could alleviate renal inflammation and insulin resistance in db/db mice. Moreover, it could also down-regulate the renal expression of PEPCK, indicating that inflammation could be one of the triggers of insulin resistance and the enhanced renal gluconeogenesis in db/db mice. This study can shed light on the role of inflammation in the enhanced renal gluconeogenesis in T2DM, which may yield a novel target for hyperglycemia.