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1.
The glucose uptake systems in Corynebacterium glutamicum: a review.
Ruan, H, Yu, H, Xu, J
World journal of microbiology & biotechnology. 2020;(9):126
Abstract
The phosphoenolpyruvate-dependent glucose phosphotransferase system (PTSGlc) is the major uptake system responsible for transporting glucose, and is involved in glucose translocation and phosphorylation in Corynebacterium glutamicum. For the longest time, the PTSGlc was considered as the only uptake system for glucose. However, some PTS-independent glucose uptake systems (non-PTSGlc) were discovered in recent years, such as the coupling system of inositol permeases and glucokinases (IPGS) and the coupling system of β-glucoside-PTS permease and glucokinases (GPGS). The products (e.g. lysine, phenylalanine and leucine) will be increased because of the increasing intracellular level of phosphoenolpyruvate (PEP), while some by-products (e.g. lactic acid, alanine and acetic acid) will be reduced when this system become the main uptake pathway for glucose. In this review, we survey the uptake systems for glucose in C. glutamicum and their composition. Furthermore, we summarize the latest research of the regulatory mechanisms among these glucose uptake systems. Detailed strategies to manipulate glucose uptake system are addressed based on this knowledge.
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2.
Metabolic and functional specialisations of the pancreatic beta cell: gene disallowance, mitochondrial metabolism and intercellular connectivity.
Rutter, GA, Georgiadou, E, Martinez-Sanchez, A, Pullen, TJ
Diabetologia. 2020;(10):1990-1998
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Abstract
All forms of diabetes mellitus involve the loss or dysfunction of pancreatic beta cells, with the former predominating in type 1 diabetes and the latter in type 2 diabetes. Deeper understanding of the coupling mechanisms that link glucose metabolism in these cells to the control of insulin secretion is therefore likely to be essential to develop new therapies. Beta cells display a remarkable metabolic specialisation, expressing high levels of metabolic sensing enzymes, including the glucose transporter GLUT2 (encoded by SLC2A2) and glucokinase (encoded by GCK). Genetic evidence flowing from both monogenic forms of diabetes and genome-wide association studies for the more common type 2 diabetes, supports the importance for normal glucose-stimulated insulin secretion of metabolic signalling via altered ATP generation, while also highlighting unsuspected roles for Zn2+ storage, intracellular lipid transfer and other processes. Intriguingly, genes involved in non-oxidative metabolic fates of the sugar, such as those for lactate dehydrogenase (LDHA) and monocarboxylate transporter-1 ([MCT-1] SLC16A1), as well as the acyl-CoA thioesterase (ACOT7) and others, are selectively repressed ('disallowed') in beta cells. Furthermore, mutations in genes critical for mitochondrial oxidative metabolism, such as TRL-CAG1-7 encoding tRNALeu, are linked to maternally inherited forms of diabetes. Correspondingly, impaired Ca2+ uptake into mitochondria, or collapse of a normally interconnected mitochondrial network, are associated with defective insulin secretion. Here, we suggest that altered mitochondrial metabolism may also impair beta cell-beta cell communication. Thus, we argue that defective oxidative glucose metabolism is central to beta cell failure in diabetes, acting both at the level of single beta cells and potentially across the whole islet to impair insulin secretion. Graphical abstract.
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3.
Recent progress in the structure of glycogen serving as a durable energy reserve in bacteria.
Wang, L, Wang, M, Wise, MJ, Liu, Q, Yang, T, Zhu, Z, Li, C, Tan, X, Tang, D, Wang, W
World journal of microbiology & biotechnology. 2020;(1):14
Abstract
Glycogen is conventionally considered as a transient energy reserve that can be rapidly synthesized for glucose accumulation and mobilized for ATP production. However, this conception is not completely applicable to prokaryotes due to glycogen structural heterogeneity. A number of studies noticed that glycogen with small average chain length gc in bacteria has the potential to degrade slowly, which might prolong bacterial environment survival. This phenomenon was previously examined and later formulated as the durable energy storage mechanism hypothesis. Although recent research has been warming to the hypothesis, experimental validation is still missing at current stage. In this review, we summarized recent progress of the hypothesis, provided a supporting mathematical model, and explored the technical pitfalls that shall be avoided in glycogen study.
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4.
Cellular mechanisms governing glucose-dependent insulinotropic polypeptide secretion.
Reimann, F, Diakogiannaki, E, Hodge, D, Gribble, FM
Peptides. 2020;:170206
Abstract
Glucose-dependent insulinotropic polypeptide (GIP) is a gut hormone secreted from the upper small intestine, which plays an important physiological role in the control of glucose metabolism through its incretin action to enhance glucose-dependent insulin secretion. GIP has also been implicated in postprandial lipid homeostasis. GIP is secreted from enteroendocrine K-cells residing in the intestinal epithelium. K-cells sense a variety of components found in the gut lumen following food consumption, resulting in an increase in plasma GIP signal dependent on the nature and quantity of ingested nutrients. We review the evidence for an important role of sodium-coupled glucose uptake through SGLT1 for carbohydrate sensing, of free-fatty acid receptors FFAR1/FFAR4 and the monoacyl-glycerol sensing receptor GPR119 for lipid detection, of the calcium-sensing receptor CASR and GPR142 for protein sensing, and additional modulation by neurotransmitters such as somatostatin and galanin. These pathways have been identified through combinations of in vivo, in vitro and molecular approaches.
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5.
Sodium-glucose cotransporter-2 inhibitors for diabetic kidney disease: Targeting Warburg effects in proximal tubular cells.
Morita, M, Kanasaki, K
Diabetes & metabolism. 2020;(5):353-361
Abstract
Inhibitors of sodium-glucose cotransporter 2 (SGLT2) have undoubtedly shifted the paradigm for diabetes medicine and research and, especially, diabetic kidney disease (DKD). The pharmacological action of SGLT2 inhibitors is simply the release of glucose into urine; however, precisely how SGLT2 inhibitors contribute to the health of those with diabetes has still not been completely elucidated. Towards this end, the present review provides a novel insight into the action of SGLT2 inhibitors by highlighting a neglected fuel-burning system found in proximal tubular cells-'glycolysis'. In addition, exploring the details of the molecular mechanisms and clinical biomarkers of the organ protection conferred by SGLT2 inhibitors is now required to prepare for the next stage of clinical diabetes medicine-the 'post-SGLT2 inhibitor era'.
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6.
Phosphate sugar isomerases and their potential for rare sugar bioconversion.
Kim, SJ, Kim, YS, Yeom, SJ
Journal of microbiology (Seoul, Korea). 2020;(9):725-733
Abstract
Phosphate sugar isomerases, catalyzing the isomerization between ketopentose/ketohexose phosphate and aldopentose/aldohexose phosphate, play an important role in microbial sugar metabolism. They are present in a wide range of microorganisms. They have attracted increasing research interest because of their broad substrate specificity and great potential in the enzymatic production of various rare sugars. Here, the enzymatic properties of various phosphate sugar isomerases are reviewed in terms of their substrate specificities and their applications in the production of valuable rare sugars because of their functions such as low-calorie sweeteners, bulking agents, and pharmaceutical precursor. Specifically, we focused on the industrial applications of D-ribose-5-phosphate isomerase and D-mannose-6-phosphate isomerase to produce D-allose and L-ribose, respectively.
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7.
Renal physiology of glucose handling and therapeutic implications.
Cherney, DZ, Kanbay, M, Lovshin, JA
Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association. 2020;(Suppl 1):i3-i12
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Abstract
The rationale for using sodium-glucose cotransporter 2 (SGLT2) inhibitors in patients with type 2 diabetes (T2D) has evolved over the last decade. Due to the effects on glucosuria and body weight loss, SGLT2 inhibitors were originally approved for glycemic control in T2D. Since glucosuria is attenuated in chronic kidney disease (CKD) Stages 3-5, initial regulatory approval for SGLT2 inhibitor use was limited to patients with T2D and preserved estimated glomerular filtration rate. Over time, however, it has become increasingly apparent that these therapies have a variety of important pharmacodynamic and clinical effects beyond glycemic lowering, including antihypertensive and antialbuminuric properties, and the ability to reduce glomerular hypertension. Importantly, these sodium-related effects are preserved across CKD stages, despite attenuated glycemic effects, which are lost at CKD Stage 4. With the completion of cardiovascular (CV) outcome safety trials-EMPA-REG OUTCOME, CANVAS Program and DECLARE TIMI-58-in addition to reductions in CV events, SGLT2 inhibition consistently reduces hard renal endpoints. Importantly, these CV and renal effects are independent of glycemic control. Subsequent data from the recent CREDENCE trial-the first dedicated renal protection trial with SGLT-2 inhibition-demonstrated renal and CV benefits in albuminuric T2D patients, pivotal results that have expanded the clinical importance of these therapies. Ongoing trials will ultimately determine whether SGLT2 inhibition will have a role in renal protection in other clinical settings, including nondiabetic CKD and type 1 diabetes.
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8.
Current Approaches in Diabetes Treatment and Other Strategies to Reach Normoglycemia.
Sirhan, W, Piran, R
Current topics in medicinal chemistry. 2020;(32):2922-2944
Abstract
Cells are mainly dependent on glucose as their energy source. Multicellular organisms need to adequately control individual glucose uptake by the cells, and the insulin-glucagon endocrine system serves as the key glucose regulation mechanism. Insulin allows for effective glucose entry into the cells when blood glucose levels are high, and glucagon acts as its opponent, balancing low blood glucose levels. A lack of insulin will prevent glucose entry to the cells, resulting in glucose accumulation in the bloodstream. Diabetes is a disease which is characterized by elevated blood glucose levels. All diabetes types are characterized by an inefficient insulin signaling mechanism. This could be the result of insufficient insulin secretion, as in the case of type I diabetes and progressive incidents of type II diabetes or due to insufficient response to insulin (known as insulin resistance). We emphasize here, that Diabetes is actually a disease of starved tissues, unable to absorb glucose (and other nutrients), and not a disease of high glucose levels. Indeed, diabetic patients, prior to insulin discovery, suffered from glucose malabsorption. In this mini-review, we will define diabetes, discuss the current status of diabetes treatments, review the current knowledge of the different hormones that participate in glucose homeostasis and the employment of different modulators of these hormones. As this issue deals with peptide therapeutics, special attention will be given to synthetic peptide analogs, peptide agonists as well as antagonists.
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9.
Glucose Metabolism in the Kidney: Neurohormonal Activation and Heart Failure Development.
Gronda, E, Jessup, M, Iacoviello, M, Palazzuoli, A, Napoli, C
Journal of the American Heart Association. 2020;(23):e018889
Abstract
The liver is not the exclusive site of glucose production in humans in the postabsorptive state. Robust data support that the kidney is capable of gluconeogenesis and studies have demonstrated that renal glucose production can increase systemic glucose production. The kidney has a role in maintaining glucose body balance, not only as an organ for gluconeogenesis but by using glucose as a metabolic substrate. The kidneys reabsorb filtered glucose through the sodium-glucose cotransporters sodium-glucose cotransporter (SGLT) 1 and SGLT2, which are localized on the brush border membrane of the early proximal tubule with immune detection of their expression in the tubularized Bowman capsule. In patients with diabetes mellitus, the renal maximum glucose reabsorptive capacity, and the threshold for glucose passage into the urine, are higher and contribute to the hyperglycemic state. The administration of SGLT2 inhibitors to patients with diabetes mellitus enhances sodium and glucose excretion, leading to a reduction of the glycosuria threshold and tubular maximal transport of glucose. The net effects of SGLT2 inhibition are to drive a reduction in plasma glucose levels, improving insulin secretion and sensitivity. The benefit of SGLT2 inhibitors goes beyond glycemic control, since inhibition of renal glucose reabsorption affects blood pressure and improves the hemodynamic profile and the tubule glomerular feedback. This action acts to rebalance the dense macula response by restoring adenosine production and restraining renin-angiotensin-aldosterone activation. By improving renal and cardiovascular function, we explain the impressive reduction in adverse outcomes associated with heart failure supporting the current clinical perspective.
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10.
Sleep Apnea, Obesity, and Disturbed Glucose Homeostasis: Epidemiologic Evidence, Biologic Insights, and Therapeutic Strategies.
Pugliese, G, Barrea, L, Laudisio, D, Salzano, C, Aprano, S, Colao, A, Savastano, S, Muscogiuri, G
Current obesity reports. 2020;(1):30-38
Abstract
PURPOSE OF REVIEW Obstructive sleep apnea (OSA), obesity, and disturbed glucose homeostasis are usually considered distinct clinical condition, although they are tightly related to each other. The aim of our manuscript is to provide an overview of the current evidence on OSA, obesity, and disturbed glucose homeostasis providing epidemiologic evidence, biological insights, and therapeutic strategies. RECENT FINDINGS The mechanisms hypothesized to be involved in this complex interplay are the following: (1) "direct weight-dependent" mechanisms, according to which fat excess compromises respiratory mechanics, and (2) "indirect weight-dependent" mechanisms such as hyperglycemia, insulin resistance and secondary hyperinsulinemia, leptin resistance and other hormonal dysregulations frequently found in subjects with obesity, type 2 diabetes, and/or sleep disorders. Moreover, the treatment of each of these clinical conditions, through weight loss induced by diet or bariatric surgery, the use of anti-obesity or antidiabetic drugs, and continuous positive airway pressure (CPAP), seems to positively influence the others. These recent data suggest not only that there are multiple connections among these diseases but also that treating one of them may result in an improvement of the others.