Tyrosine dephosphorylation and deactivation of insulin receptor substrate-1 by protein-tyrosine phosphatase 1B. Possible facilitation by the formation of a ternary complex with the Grb2 adaptor protein

Protein Tyrosine Phosphatases in Metabolism: A New Frontier for Therapeutics

The increased prevalence of chronic metabolic disorders, including obesity and type 2 diabetes and their associated comorbidities, are among the world's greatest health and economic challenges. Metabolic homeostasis involves a complex interplay between hormones that act on different tissues to elicit changes in the storage and utilization of energy. Such processes are mediated by tyrosine phosphorylation-dependent signaling, which is coordinated by the opposing actions of protein tyrosine kinases and protein tyrosine phosphatases (PTPs). Perturbations in the functions of PTPs can be instrumental in the pathophysiology of metabolic diseases. The goal of this review is to highlight key advances in our understanding of how PTPs control body weight and glucose metabolism, as well as their contributions to obesity and type 2 diabetes. The emerging appreciation of the integrated functions of PTPs in metabolism, coupled with significant advances in pharmaceutical strategies aimed at targeting this class of enzymes, marks the advent of a new frontier in combating metabolic disorders.

Neuroprotective and antidiabetic lanostane-type triterpenoids from the fruiting bodies of Ganoderma theaecolum

Eight previously undescribed lanostane triterpenoids, including five nortriterpenoids with 26 carbons, ganothenoids A-E (1-5), and three lanostanoids, ganothenoids F-H (6-8), along with 24 known ones (9-32), were isolated from the fruiting bodies of Ganodrma theaecolum. The structures of the novel compounds were elucidated using comprehensive spectroscopic methods, including electronic circular dichroism (ECD) and nuclear magnetic resonance (NMR) calculations. Compounds 1-32 were assessed for their neuroprotective effects against H2O2-induced damage in human neuroblastoma SH-SY5Y cells, as well as their inhibitory activities against protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase. Compound 4 demonstrated the most potent neuroprotective activity against H2O2-induced oxidative stress by suppressing G0/G1 phase cell cycle arrest, reducing reactive oxygen species (ROS) levels, and inhibiting cell apoptosis through modulation of B-cell lymphoma 2 protein (Bcl-2) and Bcl-2 associated X-protein (Bax) protein expression. Compounds 26, 12, and 28 exhibited PTP1B inhibitory activities with IC50 values ranging from 13.92 to 56.94 μmol·L-1, while compound 12 alone displayed significant inhibitory effects on α-glucosidase with an IC50 value of 43.56 μmol·L-1. Additionally, enzyme kinetic analyses and molecular docking simulations were conducted for compounds 26 and 12 with PTP1B and α-glucosidase, respectively.

Allosteric regulation of the tyrosine phosphatase PTP1B by a protein-protein interaction

The rapid identification of protein-protein interactions has been significantly enabled by mass spectrometry (MS) proteomics-based methods, including affinity purification-MS, crosslinking-MS, and proximity-labeling proteomics. While these methods can reveal networks of interacting proteins, they cannot reveal how specific protein-protein interactions alter protein function or cell signaling. For instance, when two proteins interact, there can be emergent signaling processes driven purely by the individual activities of those proteins being co-localized. Alternatively, protein-protein interactions can allosterically regulate function, enhancing or suppressing activity in response to binding. In this work, we investigate the interaction between the tyrosine phosphatase PTP1B and the adaptor protein Grb2, which have been annotated as binding partners in a number of proteomics studies. This interaction has been postulated to co-localize PTP1B with its substrate IRS-1 by forming a ternary complex, thereby enhancing the dephosphorylation of IRS-1 to suppress insulin signaling. Here, we report that Grb2 binding to PTP1B also allosterically enhances PTP1B catalytic activity. We show that this interaction is dependent on the proline-rich region of PTP1B, which interacts with the C-terminal SH3 domain of Grb2. Using NMR spectroscopy and hydrogen-deuterium exchange mass spectrometry (HDX-MS) we show that Grb2 binding alters PTP1B structure and/or dynamics. Finally, we use MS proteomics to identify other interactors of the PTP1B proline-rich region that may also regulate PTP1B function similarly to Grb2. This work presents one of the first examples of a protein allosterically regulating the enzymatic activity of PTP1B and lays the foundation for discovering new mechanisms of PTP1B regulation in cell signaling.

Circulating extracellular vesicle-carried PTP1B and PP2A phosphatases as regulators of insulin resistance

AIMS/HYPOTHESIS

Metabolic disorders associated with abdominal obesity, dyslipidaemia, arterial hypertension and hyperglycaemia are risk factors for the development of insulin resistance. Extracellular vesicles (EVs) may play an important role in the regulation of metabolic signalling pathways in insulin resistance and associated complications.

METHODS

Circulating large EVs (lEVs) and small EVs (sEVs) from individuals with (IR group) and without insulin resistance (n-IR group) were isolated and characterised. lEVs and sEVs were administered by i.v. injection to mice and systemic, adipose tissue and liver insulin signalling were analysed. The role of phosphatases was analysed in target tissues and cells.

RESULTS

Injection of lEVs and sEVs from IR participants impaired systemic, adipose tissue and liver insulin signalling in mice, while EVs from n-IR participants had no effect. Moreover, lEVs and sEVs from IR participants brought about a twofold increase in adipocyte size and adipogenic gene expression. EVs from IR participants expressed two types of phosphatases, phosphotyrosine 1 phosphatase (PTP1B) and protein phosphatase 2 (PP2A), IR lEVs being enriched with the active form of PTP1B while IR sEVs mainly carried active PP2A. Blockade of PTP1B activity in IR lEVs fully restored IRS1 and Akt phosphorylation in adipocytes and blunted insulin-induced Akt phosphorylation by inhibition of the macrophage secretome in hepatocytes. Conversely, blockade of PP2A activity in IR sEVs completely prevented insulin resistance in adipocytes and hepatocytes.

CONCLUSIONS/INTERPRETATION

These data demonstrate that inhibition of phosphatases carried by EVs from IR participants rescues insulin signalling in adipocytes and hepatocytes and point towards PTP1B and PP2A carried by IR EVs as being novel potential therapeutic targets against insulin resistance in adipose tissue and liver and the development of obesity.

Aerobic exercise attenuates high-fat diet-induced glycometabolism impairments in skeletal muscle of rat: role of EGR-1/PTP1B signaling pathway

OBJECTIVE

Impaired skeletal muscle glycogen synthesis contributes to insulin resistance (IR). Aerobic exercise reported to ameliorate IR by augmenting insulin signaling, however the detailed mechanism behind this improvement remains unclear. This study investigated whether aerobic exercise enhances glycogen anabolism and insulin sensitivity via EGR-1/PTP1B signaling pathway in skeletal muscle of rats.

METHODS

Sprague-Dawley rats fed a high-fat diet (HFD), and performed treadmill exercise training for 6-week. Oral glucose tolerance test was conducted to confirm the IR. Periodic Acid-Schiff (PAS) staining and anthrone colorimetry were used to assess the skeletal muscle glycogen. RT-qPCR, western blot, and immunofluorescence were used to detect the EGR-1/PTP1B pathway and associated signaling molecules.

RESULTS

We found that exercise training significantly decreased blood glucose, insulin, and homeostasis model assessment for IR (HOMA-IR) against HFD-induced elevation. Decreased muscle glycogen content due to HFD was significantly restored after exercise training. Exercise training promoted mRNA expressions of Irs1, Akt, and Glut4, while inhibited Gsk-3β expression against HFD. Next, the decreased IRS1 (phosphorylated/total), AKT (phosphorylated/total), and GLUT4, and increased GSK-3β proteins with HFD were significantly reversed by exercise. Furthermore, HFD-induced overexpression of EGR-1 and PTP1B evidenced by mRNA, protein, and immunofluorescence intensity, were substantially inhibited by exercise, which may contribute to promote insulin sensitivity and glycogen anabolism.

CONCLUSIONS

Aerobic exercise training promotes insulin sensitivity and skeletal muscle glycogen synthesis in HFD-fed rats. The beneficial effects of exercise might be mediated by EGR-1/PTP1B signaling pathway in skeletal muscle, however further studies are necessary to confirm this mechanism.

Allosteric regulation of the tyrosine phosphatase PTP1B by a protein-protein interaction

The rapid identification of protein-protein interactions has been significantly enabled by mass spectrometry (MS) proteomics-based methods, including affinity purification-MS, crosslinking-MS, and proximity-labeling proteomics. While these methods can reveal networks of interacting proteins, they cannot reveal how specific protein-protein interactions alter protein function or cell signaling. For instance, when two proteins interact, there can be emergent signaling processes driven purely by the individual activities of those proteins being co-localized. Alternatively, protein-protein interactions can allosterically regulate function, enhancing or suppressing activity in response to binding. In this work, we investigate the interaction between the tyrosine phosphatase PTP1B and the adaptor protein Grb2, which have been annotated as binding partners in a number of proteomics studies. This interaction has been postulated to co-localize PTP1B with its substrate IRS-1 by forming a ternary complex, thereby enhancing the dephosphorylation of IRS-1 to suppress insulin signaling. Here, we report that Grb2 binding to PTP1B also allosterically enhances PTP1B catalytic activity. We show that this interaction is dependent on the proline-rich region of PTP1B, which interacts with the C-terminal SH3 domain of Grb2. Using NMR spectroscopy and hydrogen-deuterium exchange mass spectrometry (HDX-MS) we show that Grb2 binding alters PTP1B structure and/or dynamics. Finally, we use MS proteomics to identify other interactors of the PTP1B proline-rich region that may also regulate PTP1B function similarly to Grb2. This work presents one of the first examples of a protein allosterically regulating the enzymatic activity of PTP1B and lays the foundation for discovering new mechanisms of PTP1B regulation in cell signaling.

Development, biological evaluation, and molecular modelling of some benzene-sulfonamide derivatives as protein tyrosine phosphatase-1B inhibitors for managing diabetes mellitus and associated metabolic disorders

Exploring new inhibitors with good bioavailability and high selectivity for managing type 2 diabetes mellitus (T2DM) and its associated complications is a major challenge for research, academia, and the pharmaceutical industry. Protein tyrosine phosphatase-1B (PTP1B) arose as an important negative regulator in insulin signaling pathways associated with metabolic disorders, including T2DM and obesity. Novel neutral compounds with a benzene-sulfonamide scaffold were designed and synthesized based on structural- and ligand-based drug design strategies for fragment growth. Promising hits against PTP1B were identified through in vitro enzymology inhibition assay. Mechanistic aspects of the compound's different inhibition activities were rigorously investigated through molecular docking coupled with explicit dynamics simulations. Four identified hits, 3c, 8, 10a, and 11, with sub-micromolar PTP-1B IC50 and significant predicted pharmacokinetic and pharmacodynamic parameters, were further biologically evaluated for their anti-diabetic, anti-obesity, anti-inflammatory, and anti-oxidant effects in a high-fat diet (HFD) + streptozotocin (STZ)-induced T2DM rat model. All these hit compounds exhibited a significant anti-diabetic and anti-obesity effect and a significant efficacy in reducing oxidative stress and increasing anti-oxidant enzymes while reducing inflammatory markers. Improving compound potency was further highlighted by improving the pharmacokinetic profile of the most active compound, 10a, through nano formulation. Compound 10a nano formulation showed the most promising anti-diabetic and anti-obesity effects and a remarkable histopathological improvement in all organs studied.

Inhibition of protein tyrosine phosphatase 1B by serratane triterpenes from Huperzia serrata and their molecular docking study

During the search for protein tyrosine phosphatase 1B (PTP1B) inhibitory compounds from the natural resources, two new serratane triterpenes, 3-O-dihydro-p-coumaroyltohogenol (1) and 21-O-acetyltohogenol (2), along with four known serratane triterpenes (3-6), were isolated from the whole plant of Huperzia serrata. The chemical structures of compounds 1 and 2 were determined by NMR study, HRMS analysis, and chemical modification. All isolates were evaluated for their PTP1B inhibitory activities. Among the isolates, compounds 1, 3, 5 and 6 exhibit moderate inhibitory activities against PTP1B. Kinetic studies demonstrated that they are competitive inhibitors. Molecular docking studies support these experimental results by showing that compounds 1, 3, 5 and 6 interact with the active site of PTP1B, clarifying the structure-activity relationship. This study suggests that serratane triterpenes from H. serrata have potential as starting skeletons for anti-diabetes or anti-obesity agents.

Protein tyrosine phosphatase 1B (PTP1B) function, structure, and inhibition strategies to develop antidiabetic drugs

Tyrosine protein phosphatase non-receptor type 1 (PTP1B; also known as protein tyrosine phosphatase 1B) is a member of the protein tyrosine phosphatase (PTP) family and is a soluble enzyme that plays an essential role in different physiological processes, including the regulation of metabolism, specifically in insulin and leptin sensitivity. PTP1B is crucial in the pathogenesis of type 2 diabetes mellitus and obesity. These biological functions have made PTP1B validated as an antidiabetic and anti-obesity, and potentially anticancer, molecular target. Four main approaches aim to inhibit PTP1B: orthosteric, allosteric, bidentate inhibition, and PTPN1 gene silencing. Developing a potent and selective PTP1B inhibitor is still challenging due to the enzyme's ubiquitous expression, subcellular location, and structural properties. This article reviews the main advances in the study of PTP1B since it was first isolated in 1988, as well as recent contextual information related to the PTP family to which this protein belongs. Furthermore, we offer an overview of the role of PTP1B in diabetes and obesity, and the challenges to developing selective, effective, potent, bioavailable, and cell-permeable compounds that can inhibit the enzyme.

Terpenoids as potential phytoconstituent in the treatment of diabetes: From preclinical to clinical advancement

BACKGROUND

Diabetes mellitus, a hyperglycemic condition associated with multitudinous organ dysfunction, is a hallmark of the metabolic disorder. This life-threatening condition affects millions of individuals globally, harming them financially, physically and psychologically in the course of therapy.

PURPOSES

The course therapy for illnesses has undergone ground-breaking transformations due to recent technical advances and insights. Alternatively, the administration of hyperglycemia-reducing agents results in several complications, including severe cardiovascular disease, kidney failure, hepatic problems, and several dermatological conditions. Consideration of alternate diabetic therapy having minimal side effects or no adverse reactions has been driven by such problems.

STUDY DESIGN

An extensive literature study was conducted in authoritative scientific databases such as PubMed, Scopus, and Web of Science to identify the studies elucidating the bioactivities of terpenoids in diabetic conditions.

METHODS

Keywords including 'terpenoids', 'monoterpenes', 'diterpenes', 'sesquiterpenes', 'diabetes', 'diabetes mellitus', 'clinical trials', 'preclinical studies', and 'increased blood glucose' were used to identify the relevant research articles. The exclusion criteria, such as English language, duplication, open access, abstract only, and studies not involving preclinical and clinical research, were set. Based on these criteria, 937 relevant articles were selected for further evaluation.

RESULTS

Triterpenes can serve as therapeutic agents for diabetic retinopathy, peripheral neuropathy, and kidney dysfunction by inhibiting several pathways linked to hyperglycemia and its complications. Therefore, it is essential to draw special attention to these compounds' therapeutic effectiveness and provide scientific professionals with novel data.

CONCLUSION

This study addressed recent progress in research focussing on mechanisms of terpenoid, its by-products, physiological actions, and therapeutic applications, particularly in diabetic and associated disorders.

Protein Tyrosine Phosphatase 1B Inhibitors of Pueraria lobata Based on the Spectrum-Effect Relationship by Q-Marker Selection

Pueraria lobata (P. lobata), a traditional anti-diabetic medicine mainly composed of flavonoids and isoflavones, has a long history in diabetes treatment in China. However, the anti-diabetic active component is still unclear. Recently, protein tyrosine phosphatase 1B (PTP1B) has been a hot therapeutic target by negatively regulating insulin signaling pathways. In this study, the spectrum-effect relationship analysis method was first used to identify the active components of P. lobata that inhibit PTP1B. The fingerprints of 12 batches of samples were established using high-performance liquid chromatography (HPLC), and sixty common peaks were identified. Meanwhile, twelve components were identified by a comparison with the standards. The inhibition of PTP1B activity was studied in vitro by using the p-nitrophenol method, and the partial least squares discriminant analysis, grey relational analysis, bivariate correlation analysis, and cluster analysis were used to analyze the bioactive compounds in P. lobata. Peaks 6, 9 (glycitin), 11 (genistin), 12 (4'-methoxypuerarin), 25, 34, 35, 36, 53, and 59 were considered as potentially active substances that inhibit PTP1B. The in vitro PTP1B inhibitory activity was confirmed by glycitin, genistin, and 4'-methoxypuerarin. The IC50s of the three compounds were 10.56 ± 0.42 μg/mL, 16.46 ± 0.29 μg/mL, and 9.336 ± 0.56 μg/mL, respectively, indicating the obvious PTP1B inhibitory activity. In brief, we established an effective method to identify PTP1B enzyme inhibitors in P. lobata, which is helpful in clarifying the material basis of P. lobata on diabetes. Additionally, it is evident that the spectrum-effect relationship method serves as an efficient approach for identifying active compounds, and this study can also serve as a reference for screening bioactive constituents in traditional Chinese medicine.

Discovery, biosynthesis, organic synthesis, and bioactivities of meroterpenoids from Rhododendron species

Meroterpenoids discovered in Rhododendrons species possess unique chemical structures and biological activities and are expected to become new drug targets for Alzheimer's disease, metabolic disorders, and chronic kidney disease, and these compounds have attracted increasing attention in recent years. In this study, Rhododendron meroterpenoids and their structures, classifications, racemate distribution, biosynthetic pathways, chemical synthesis, and bioactivities are reviewed prior to 2023.

Site-Specifically Modified Peptide Inhibitors of Protein Tyrosine Phosphatase 1B and T-Cell Protein Tyrosine Phosphatase with Enhanced Stability and Improved In Vivo Long-Acting Activity

Protein tyrosine phosphatase 1B (PTP1B) and TC-PTP can function in a coordinated manner to regulate diverse biological processes including insulin and leptin signaling, T-cell activation, and tumor antigen presentation, which makes them potential targets for several therapeutic applications. We have previously demonstrated that the lipidated BimBH3 peptide analogues were a new class of promising PTP1B inhibitors with once-weekly antidiabetic potency. Herein, we chemically synthesized two series of BimBH3 analogues via site-specific modification and studied their structure-activity relationship. The screened analogues S2, S6, A2-14, A2-17, A2-20, and A2-21 exhibited an improved PTP1B/TC-PTP dual inhibitory activity and achieved good stability in the plasma of mice and dogs, which indicated long-acting potential. In mouse models of type 2 diabetes mellitus (T2DM), the selected analogues S6, S7, A2-20, and A2-21 with an excellent target activity and plasma stability generated once-weekly therapeutic potency for T2DM at lower dosage (0.5 μmol/kg). In addition, evidence was provided to confirm the cell permeability and targeted enrichment of the BimBH3 analogues. In summary, we report here that site-specific modification and long fatty acid conjugation afforded cell-permeable peptidomimetic analogues of BimBH3 with enhanced stability, in vivo activity, and long-acting pharmacokinetic profile. Our findings could guide the further optimization of BimBH3 analogues and provide a proof-of-concept for PTP1B/TC-PTP targeting as a new therapeutic approach for T2DM, which may facilitate the discovery and development of alternative once-weekly anti-T2DM drug candidates.

Effect of Lampaya medicinalis Phil. (Verbenaceae) and Palmitic Acid on Insulin Signaling and Inflammatory Marker Expression in Human Adipocytes

BACKGROUND

Aging and obesity are associated with insulin resistance (IR) and low-grade inflammation. Molecularly, IR is characterized by a reduction in glucose uptake and insulin signaling (IRS-1/Akt/AS160 pathway), while inflammation may result from upregulated NF-κB pathway after low Tyr-IκBα phosphorylation. Upregulated phosphatase activity of PTP1B is associated with impaired insulin signaling and increased inflammation. Plasma levels of palmitic acid (PA) are elevated in obesity, triggering inflammation and disruption of insulin signaling. Traditional medicine in Northern Chile uses oral infusions of Lampaya medicinalis Phil. (Verbenaceae) to treat inflammatory conditions. Significant amounts of flavonoids are found in the hydroethanolic extract of Lampaya (HEL), which may account for its biological activity. The aim of this work was to study the effect of HEL and PA on insulin signaling and glucose uptake as well as inflammatory marker expression in human adipocytes.

METHODS

We studied HEL effects on PA-induced impairment on insulin signaling, glucose uptake and inflammatory marker content in human SW872 adipocytes. HEL cytotoxicity was assessed in adipocytes at different concentrations (0.01 to 10 g/mL). Adipocytes were incubated or not with PA (0.4 mM, 24 h) with or without HEL (2 h pre-incubation), and then stimulated with insulin (10 min, 100 mM) or a vehicle. Phospho-IRS-1, phospho-Akt, phospho-AS160, phospho-NF-κB and phospho-IκBα, as well as protein levels of PTP1B, were assessed using Western blotting, and glucose uptake was evaluated using the 2-NBDG analogue.

RESULTS

At the assessed HEL concentrations, no cytotoxic effects were observed. PA decreased insulin-stimulated phospho-Akt and glucose uptake, while co-treatment with HEL increased such markers. PA decreased phospho-IRS-1 and phospho-Tyr-IκBα. On the other hand, incubation with HEL+PA decreased phospho-AS160 and phospho-NF-κB compared with cells treated with PA alone.

CONCLUSION

Our results suggest a beneficial effect of HEL by improving PA-induced impairment on molecular markers of insulin signaling, glucose uptake and inflammation in adipocytes. Further studies are necessary to elucidate whether lampaya may constitute a preventive strategy for people whose circulating PA levels contribute to IR and inflammation during aging and obesity.

Pyrazole Scaffold: Potential PTP1B Inhibitors for Diabetes Treatment

BACKGROUND

The overexpression of the Protein Tyrosine Phosphatase 1B (PTP1B), a key role in the development of insulin resistance, diabetes (T2DM) and obesity, seems to have a substantial impact as a negative regulator of the insulin and leptin signaling pathways. Therefore, inhibiting PTP1B is a prospective therapeutic approach for the treatment of diabetes and obesity. However, the pyrazole scaffold is expected to be of significant pharmaceutical interest due to its broad spectrum of pharmacological actions. This study aims to focus on the significance of pyrazole scaffold in medicinal chemistry, the impact of PTP1B in diabetes and the therapeutic approach of pyrazole scaffold to treat T2DM.

METHODS

A comprehensive analysis of the published literature in several pharmaceutical and medical databases, such as the Web of Science (WoS), PubMed, ResearchGate, ScienceDirect etc., were indeed successfully completed and classified accordingly.

RESULTS

As reviewed, the various derivatives of the pyrazole scaffold exhibited prominent PTP1B inhibitory activity. The result showed that derivatives of oxadiazole and dibenzyl amine, chloro substituents, 1, 3-diaryl pyrazole derivatives with rhodanine-3-alkanoic acid groups, naphthalene and also 1, 3, 5-triazine-1H-pyrazole-triazolothiadiazole derivatives, octyl and tetradecyl derivative, indole- and N-phenylpyrazole-glycyrrhetinic acid derivatives with trifluoromethyl group, 2,3-pyrazole ring-substituted-4,4-dimethyl lithocholic acid derivatives with 4- fluoro phenyl substituted and additional benzene ring in the pyrazole scaffold significantly inhibits PTP1B. In silico study observed that pyrazole scaffold interacted with amino acid residues like TYR46, ASP48, PHE182, TYR46, ALA217 and ILE219.

CONCLUSION

Diabetes is a metabolic disorder that elevates the risk of mortality and severe complications. PTP1B is a crucial component in the management of diabetes and obesity. As a result, PTP1B is a promising therapeutic target for the treatment of T2DM and obesity in humans. We concluded that the pyrazole scaffold has prominent inhibitory potential against PTP1B.

Sodium orthovanadate exhibits anti-angiogenic, antiapoptotic and blood glucose-lowering effect on colon cancer associated with diabetes

BACKGROUND

The presence of type 2 diabetes mellitus increases the risk of developing the colon cancer. The main objective of this study was to determine the role of sodium orthovanadate (SOV) in colon cancer associated with diabetes mellitus by targeting the competitive inhibition of PTP1B.

METHODS

For in vivo study, high fat diet with low dose streptozotocin model was used for inducing the diabetes mellitus. Colon cancer was induced by injecting 1,2-dimethylhydrazine (25 mg/kg, sc) twice a week. TNM staging and immunohistochemistry (IHC) was carried out for colon cancer tissues. In vitro studies like MTT assay, clonogenic assay, rhodamine-123 dye assay and annexin V-FITC assay using flow cytometry were performed on HCT-116 cell line. CAM assay was performed to examine the anti-angiogenic effect of the drug.

RESULTS

Sodium orthovanadate reduces the blood glucose level and tumor parameters in the animals. In vitro studies revealed that SOV decreased cell proliferation dose dependently. In addition, SOV induced apoptosis as depicted from rhodamine-123 dye assay and annexin V-FITC assay using flow cytometry as well as p53 IHC staining. SOV showed reduced angiogenesis effect on eggs which was depicted from CAM assay and also from CD34 and E-cadherin IHC staining.

CONCLUSIONS

Our data suggest that SOV exhibits protective role in colon cancer associated with diabetes mellitus. SOV exhibits anti-proliferative, anti-angiogenic and apoptotic inducing effects hence can be considered for therapeutic switching in diabetic colon cancer.

The importance of including the C-terminal domain of PTP1B1-400 to identify potential antidiabetic inhibitors

In the present work, we studied the inhibitory and kinetic implications of classical PTP1B inhibitors (chlorogenic acid, ursolic acid, suramin) using three enzyme constructs (hPTP1B_1-285, hPTP1B_1-321, and hPTP1B_1-400). The results indicate that the unstructured region of PTP1B (300-400 amino acids) is very important both to obtain optimal inhibitory results and propose classical inhibition mechanisms (competitive or non-competitive) through kinetic studies. The IC₅₀ calculated for ursolic acid and suramin using hPTP1B_1-400 are around four and three times lower to the short form of the enzyme, the complete form of PTP1B, the one found in the cytosol (in vivo). On the other hand, we highlight the studies of enzymatic kinetics using the hPTP1B_1-400 to know the type of enzymatic inhibition and to be able to direct docking studies, where the unstructured region of the enzyme can be one more option for binding compounds with inhibitory activity.

The promising roles of medicinal plants and bioactive compounds on hepatic lipid metabolism in the treatment of non-alcoholic fatty liver disease in animal models: molecular targets

Imbalance in hepatic lipid metabolism can lead to an abnormal triglycerides deposition in the hepatocytes which can cause non-alcoholic fatty liver disease (NAFLD). Four main mechanisms responsible for regulating hepatic lipid metabolism are fatty acid uptake, de novo lipogenesis, lipolysis and fatty acid oxidation. Controlling the expression of transcription factors at molecular level plays a crucial role in NAFLD management. This paper reviews various medicinal plants and their bioactive compounds emphasising mechanisms involved in hepatic lipid metabolism, other important NAFLD pathological features, and their promising roles in managing NAFLD through regulating key transcription factors. Although there are many medicinal plants popularly investigated for NAFLD treatment, there is still little information and scientific evidence available and there has been no research on clinical trials scrutinised on this matter. This review also aims to provide molecular information of medicinal plants in NALFD treatment that might have potentials for future scientifically controlled studies.

A Descriptive Review of the Action Mechanisms of Berberine, Quercetin and Silymarin on Insulin Resistance/Hyperinsulinemia and Cardiovascular Prevention

Insulin resistance (IR) and the associated hyperinsulinemia are early pathophysiological changes which, if not well treated, can lead to type 2 diabetes, endothelial dysfunction and cardiovascular disease. While diabetes care is fairly well standardized, the prevention and treatment of IR lacks a single pharmaceutical approach and many lifestyle and dietary interventions have been proposed, including a wide range of food supplements. Among the most interesting and well-known natural remedies, alkaloid berberine and the flavonol quercetin have particular relevance in the literature, while silymarin-the active principle of the Silybum marianum thistle-was traditionally used for lipid metabolism disorders and to sustain liver function. This review describes the major defects of insulin signaling leading to IR and the main properties of the three mentioned natural substances, their molecular targets and synergistic action mechanisms. The actions of berberine, quercetin and silymarin are partially superimposable as remedies against reactive oxygen intermediates generated by a high-lipid diet and by NADPH oxidase, which is triggered by phagocyte activation. Furthermore, these compounds inhibit the secretion of a battery of pro-inflammatory cytokines, modulate intestinal microbiota and are especially able to control the various disorders of the insulin receptor and post-receptor signaling systems. Although most of the evidence on the effects of berberine, quercetin and silymarin in modulating insulin resistance and preventing cardiovascular disease derive from experimental studies on animals, the amount of pre-clinical knowledge strongly suggests the need to investigate the therapeutic potential of these substances in human pathology.

MFGE8 inhibits insulin signaling through PTP1B

The role of integrins in regulating insulin signaling is incompletely understood. We have previously shown that binding of the integrin ligand milk fat globule epidermal growth factor like 8 (MFGE8) to the αvβ5 integrin promotes termination of insulin receptor signaling in mice. Upon ligation of MFGE8, β5 complexes with the insulin receptor beta (IRβ) in skeletal muscle resulting in dephosphorylation of IRβ and reduction of insulin-stimulated glucose uptake. Here we investigate the mechanism by which the interaction between β5 and IRβ impacts IRβ phosphorylation status. We show that β5 blockade inhibits and MFGE8 promotes PTP1B binding to and dephosphorylation of IRβ resulting in reduced or increased insulin-stimulated myotube glucose uptake respectively. The β5-PTP1B complex is recruited by MFGE8 to IRβ leading to termination of canonical insulin signaling. β5 blockade enhances insulin-stimulated glucose uptake in wild type but not Ptp1b KO mice indicating that PTP1B functions downstream of MFGE8 in modulating insulin receptor signaling. Furthermore, in a human cohort, we report serum MFGE8 levels correlate with indices of insulin resistance. These data provide mechanistic insights into the role of MFGE8 and β5 in regulating insulin signaling.

Ursonic acid from Artemisia montana exerts anti-diabetic effects through anti-glycating properties, and by inhibiting PTP1B and activating the PI3K/Akt signaling pathway in insulin-resistant C2C12 cells

Artemisia is one of the largest genera in the plant family Asteraceae and has long been used in traditional medicine for its antitussive, analgesic, antihypertensive, antitoxic, antiviral, antimalarial, and anti-inflammatory properties. However, the anti-diabetic activity of Artemisia montana has not been broadly studied. The goal of this study was to determine whether extracts of the aerial parts of A. montana and its main constituents inhibit protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase activities. We isolated nine compounds from A. montana including ursonic acid (UNA) and ursolic acid (ULA), which significantly inhibited PTP1B with IC₅₀ values of 11.68 and 8.73 μM, respectively. In addition, UNA showed potent inhibitory activity against α-glucosidase (IC₅₀ = 61.85 μM). Kinetic analysis of PTP1B and α-glucosidase inhibition revealed that UNA was a non-competitive inhibitor of both enzymes. Docking simulations of UNA demonstrated negative binding energies and close proximity to residues in the binding pockets of PTP1B and α-glucosidase. Molecular docking simulations between UNA and human serum albumin (HSA) revealed that UNA binds tightly to all three domains of HSA. Furthermore, UNA significantly inhibited fluorescent AGE formation (IC₅₀ = 4.16 μM) in a glucose-fructose-induced HSA glycation model over the course of four weeks. Additionally, we investigated the molecular mechanisms underlying the anti-diabetic effects of UNA in insulin-resistant C2C12 skeletal muscle cells and discovered that UNA significantly increased glucose uptake and decreased PTP1B expression. Further, UNA increased GLUT-4 expression level by activating the IRS-1/PI3K/Akt/GSK-3 signaling pathway. These findings clearly demonstrate that UNA from A. montana shows great potential for treatment of diabetes and its complications.

Ginsenoside compound K reduces ischemia/reperfusion-induced neuronal apoptosis by inhibiting PTP1B-mediated IRS1 tyrosine dephosphorylation

Background

Ginsenoside compound K (CK) stimulated activation of the PI3K-Akt signaling is one of the major mechanisms in promoting cell survival after stroke. However, the underlying mediators remain poorly understood. This study aimed to explore the docking protein of ginsenoside CK mediating the neuroprotective effects.

Materials and methods

Molecular docking, surface plasmon resonance, and cellular thermal shift assay were performed to explore ginsenoside CK interacting proteins. Neuroscreen-1 cells and middle cerebral artery occlusion (MCAO) model in rats were utilized as in-vitro and in-vivo models.

Results

Ginsenoside CK interacted with recombinant human PTP1B protein and impaired its tyrosine phosphatase activity. Pathway and process enrichment analysis confirmed the involvement of PTP1B and its interacting proteins in PI3K-Akt signaling pathway. PTP1B overexpression reduced the tyrosine phosphorylation of insulin receptor substrate 1 (IRS1) after oxygen-glucose deprivation/reoxygenation (OGD/R) in neuroscreen-1 cells. These regulations were confirmed in the ipsilateral ischemic hemisphere of the rat brains after MCAO/R. Ginsenoside CK treatment reversed these alterations and attenuated neuronal apoptosis.

Conclusion

Ginsenoside CK binds to PTP1B with a high affinity and inhibits PTP1B-mediated IRS1 tyrosine dephosphorylation. This novel mechanism helps explain the role of ginsenoside CK in activating the neuronal protective PI3K-Akt signaling pathway after ischemia-reperfusion injury.

Discovery of Novel PTP1B Inhibitors with Once-Weekly Therapeutic Potential for Type 2 Diabetes: Design, Synthesis, and In Vitro and In Vivo Investigations of BimBH3 Peptide Analogues

Poor medication adherence in patients with type 2 diabetes mellitus has become one of the main causes of suboptimal glycemic control. Once-weekly drugs can markedly improve the convenience, adherence, and quality of life of T2DM patients; thus, they are clinically needed and preferred. PTP1B plays a negative role in both insulin and leptin signaling pathways, which makes it an important target for diabetes. Herein, we design and synthesize 35 analogues of core BimBH3 peptide via lipidation/acylation strategy based on our previous work and evaluate their PTP1B inhibitory activity, obtaining the primary structure-activity relationship. Five compounds with good PPT1B inhibitory activity, target selectivity, and significantly improved stability were selected for molecular docking study and searching candidate molecules with long-acting antidiabetic potential. The in vivo anti-T2DM evaluation validated the once-weekly therapeutic potential of analogues 19, 26, 27, 31, and 33, which were comparable with semaglutide and therefore presented as promising drug candidates.

Effect of sweet potato purple acid phosphatase on Pseudomonas aeruginosa flagellin-mediated inflammatory response in A549 cells

OBJECTIVE

The study was conducted to investigate the dephosphorylation of Pseudomonas aeruginosa flagellin (PA FLA) by sweet potato purple acid phosphatase (PAP) and the effect of the enzyme on the flagellin-mediated inflammatory response in the A549 lung epithelial cell line.

METHODS

The activity of sweet potato PAP on PA FLA was assayed at different pH (4, 5.5, 7, and 7.5) and temperature (25°C, 37°C, and 55°C) conditions. The release of interleukin-8 (IL-8) and the activation of nuclear factor kappa- light-chain-enhancer of activated B cells (NF-κB) in A549 cells exposed to PA FLA treated with or without sweet potato PAP was measured using IL-8 and NF-κB ELISA kits, respectively. The activation of toll-like receptor 5 (TLR5) in TLR5-overexpressing HEK-293 cells exposed to PA FLA treated with or without sweet potato PAP was determined by the secreted alkaline phosphatase-based assay.

RESULTS

The dephosphorylation of PA FLA by sweet potato PAP was favorable at pH 4 and 5.5 and highest at 55°C. PA-FLA treated with the enzyme decreased IL-8 release from A549 cells to about 3.5-fold compared to intact PA FLA at 1,000 ng/mL of substrate. Moreover, PA-FLA dephosphorylated by the enzyme repressed the activation of NF-κB in the cells compared to intact PA FLA. The activation of TLR5 by PA-FLA was highest in TLR-overexpressing HEK293 cells at a substrate concentration of 5,000 ng/mL, whereas PA FLA treated with the enzyme strongly repressed the activation of TLR5.

CONCLUSION

Sweet potato PAP has the potential to be a new alternative agent against the increased antibiotic resistance of P. aeruginosa and may be a new conceptual feed additive to control unwanted inflammatory responses caused by bacterial infections in animal husbandry.

The PTP1B inhibitor MSI-1436 ameliorates liver insulin sensitivity by modulating autophagy, ER stress and systemic inflammation in Equine metabolic syndrome affected horses

BACKGROUND

Equine metabolic syndrome (EMS) is a multifactorial pathology gathering insulin resistance, low-grade inflammation and past or chronic laminitis. Among the several molecular mechanisms underlying EMS pathogenesis, increased negative insulin signalling regulation mediated by protein tyrosine phosphatase 1 B (PTP1B) has emerged as a critical axis in the development of liver insulin resistance and general metabolic distress associated to increased ER stress, inflammation and disrupted autophagy. Thus, the use of PTP1B selective inhibitors such as MSI-1436 might be considered as a golden therapeutic tool for the proper management of EMS and associated conditions. Therefore, the present investigation aimed at verifying the clinical efficacy of MSI-1436 systemic administration on liver metabolic balance, insulin sensitivity and inflammatory status in EMS affected horses. Moreover, the impact of MSI-1436 treatment on liver autophagy machinery and associated ER stress in liver tissue has been analysed.

METHODS

Liver explants isolated from healthy and EMS horses have been treated with MSI-1436 prior to gene and protein expression analysis of main markers mediating ER stress, mitophagy and autophagy. Furthermore, EMS horses have been intravenously treated with a single dose of MSI-1436, and evaluated for their metabolic and inflammatory status.

RESULTS

Clinical application of MSI-1436 to EMS horses restored proper adiponectin levels and attenuated the typical hyperinsulinemia and hyperglycemia. Moreover, administration of MSI-1436 further reduced the circulating levels of key pro-inflammatory mediators including IL-1β, TNF-α and TGF-β and triggered the Tregs cells activation. At the molecular level, PTP1B inhibition resulted in a noticeable mitigation of liver ER stress, improvement of mitochondrial dynamics and consequently, a regulation of autophagic response. Similarly, short-term ex vivo treatment of EMS liver explants with trodusquemine (MSI-1436) substantially enhanced autophagy by upregulating the levels of HSC70 and Beclin-1 at both mRNA and protein level. Moreover, the PTP1B inhibitor potentiated mitophagy and associated expression of MFN2 and PINK1. Interestingly, inhibition of PTP1B resulted in potent attenuation of ER stress key mediators' expression namely, CHOP, ATF6, HSPA5 and XBP1.

CONCLUSION

Presented findings shed for the first time promising new insights in the development of an MSI-1436-based therapy for proper equine metabolic syndrome intervention and may additionally find potential translational application to human metabolic syndrome treatment.

Role of non-coding RNAs on liver metabolism and NAFLD pathogenesis

Obesity and type 2 diabetes are major contributors to the growing prevalence of non-alcoholic fatty liver disease (NAFLD), a chronic liver condition characterized by the accumulation of fat in individuals without a significant amount of alcohol intake. The NAFLD spectrum ranges from simple steatosis (early stages, known as NAFL) to non-alcoholic steatohepatitis, which can progress to fibrosis and cirrhosis or hepatocellular carcinoma. Obesity, type 2 diabetes and NAFLD are strongly associated with insulin resistance. In the liver, insulin resistance increases hepatic glucose output, lipogenesis and very-low-density lipoprotein secretion, leading to a combination of hyperglycemia and hypertriglyceridemia. Aberrant gene expression is a hallmark of insulin resistance. Non-coding RNAs (ncRNAs) have emerged as prominent regulators of gene expression that operate at the transcriptional, post-transcriptional and post-translational levels. In the last couple of decades, a wealth of studies have provided evidence that most processes of liver metabolism are orchestrated by ncRNAs. This review focuses on the role of microRNAs, long non-coding RNAs and circular RNAs as coordinators of hepatic function, as well as the current understanding on how their dysregulation contributes to abnormal metabolism and pathophysiology in animal models of insulin resistance and NAFLD. Moreover, ncRNAs are emerging as useful biomarkers that may be able to discriminate between the different stages of NAFLD. The potential of ncRNAs as therapeutic drugs for NAFLD treatment and as biomarkers is discussed.

Ameliorating Effect of the Total Flavonoids of Morus nigra L. on Prediabetic Mice Based on Regulation of Inflammation and Insulin Sensitization

Prediabetes is a critical stage characterized by insulin resistance. Morus nigra L., an edible plant, is widely used in food and nutritive supplements and exhibits various pharmacological activities; however, its therapeutic effects and mechanisms on prediabetes have rarely been reported. In this research, the major components of total flavonoids of M. nigra L. (TFM) were identified, and TFM treatment was found to reduce prediabetes progressing to type 2 diabetes mellitus (T2DM) from 93.75 to 18.75%. The microbiota and next-generation sequencing combined with western blotting in vivo and in vitro demonstrated that TFM and its components ameliorated insulin resistance mediated by the suppressor of cytokine signaling and protein tyrosine phosphatase 1B, which benefited by maintaining intestinal homeostasis and restraining plasma levels of inflammatory factors. This study confirmed the T2DM prevention effect of TFM and revealed the underlying mechanism, setting the stage for the design of functional foods for diabetes prevention.

Protein tyrosine phosphatase 1B (PTP1B) as a potential therapeutic target for neurological disorders

Protein tyrosine phosphatase 1B (PTP1B) is a typical member of the PTP family, considered a direct negative regulator of several receptor and receptor-associated tyrosine kinases. This widely localized enzyme has been involved in the pathophysiology of several diseases. More recently, PTP1B has attracted attention in the field of neuroscience, since its activation in brain cells can lead to schizophrenia-like behaviour deficits, anxiety-like effects, neurodegeneration, neuroinflammation and depression. Conversely, PTP1B inhibition has been shown to prevent microglial activation, thus exerting a potent anti-inflammatory effect and has also shown potential to increase the cognitive process through the stimulation of hippocampal insulin, leptin and BDNF/TrkB receptors. Notwithstanding, most research on the clinical efficacy of targeting PTP1B has been developed in the field of obesity and type 2 diabetes mellitus (TD2M). However, despite the link existing between these metabolic alterations and neurodegeneration, no clinical trials assessing the neurological advantages of PTP1B inhibition have been performed yet. Preclinical studies, though, have provided strong evidence that targeting PTP1B could allow to reach different pathophysiological mechanisms at once. herefore, specific interventions or trials should be designed to modulate PTP1B activity in brain, since it is a promising strategy to decelerate or prevent neurodegeneration in aged individuals, among other neurological diseases. The present paper fails to include all neurological conditions in which PTP1B could have a role; instead, it focuses on those which have been related to metabolic alterations and neurodegenerative processes. Moreover, only preclinical data is discussed, since clinical studies on the potential of PTP1B inhibition for treating neurological diseases are still required.

Phase separation of insulin receptor substrate 1 drives the formation of insulin/IGF-1 signalosomes

As a critical node for insulin/IGF signaling, insulin receptor substrate 1 (IRS-1) is essential for metabolic regulation. A long and unstructured C-terminal region of IRS-1 recruits downstream effectors for promoting insulin/IGF signals. However, the underlying molecular basis for this remains elusive. Here, we found that the C-terminus of IRS-1 undergoes liquid-liquid phase separation (LLPS). Both electrostatic and hydrophobic interactions were seen to drive IRS-1 LLPS. Self-association of IRS-1, which was mainly mediated by the 301–600 region, drives IRS-1 LLPS to form insulin/IGF-1 signalosomes. Moreover, tyrosine residues of YXXM motifs, which recruit downstream effectors, also contributed to IRS-1 self-association and LLPS. Impairment of IRS-1 LLPS attenuated its positive effects on insulin/IGF-1 signaling. The metabolic disease-associated G972R mutation impaired the self-association and LLPS of IRS-1. Our findings delineate a mechanism in which LLPS of IRS-1-mediated signalosomes serves as an organizing center for insulin/IGF-1 signaling and implicate the role of aberrant IRS-1 LLPS in metabolic diseases.

An efficient approach to angular tricyclic molecular architecture via Nazarov-like cyclization and double ring-expansion cascade

A modular and efficient method for constructing angular tri-carbocyclic architectures containing quaternary carbon center(s) from 1,3-dicycloalkylidenyl ketones is established, which involves an unconventional synergistic cascade of a Nazarov cyclization and two ring expansions. It features high selectivity, mild conditions and convenient operation, wide scope and easy availability of substrate. Substitution with R¹ and R² at the 4πe-system with electron-donating group favors this reaction, while that with electron-withdrawing group or proton disfavors. The electron-donating group as R¹ directs the initial ring expansion at its own site, while the p-π- or n-π- associated substituent as R² favors selectively the later ring expansion near its location because of the beneficial maintenance of an original conjugated system. The stereoselectivity has proved to be governed by either the steric effect of R³ and R⁴ at the expanded rings, or the migration ability of the migrating atom. Density Functional Theory calculation suggests the initial Nazarov cyclization would be the rate-determining step. A racemic total synthesis of the natural (±)-waihoensene is realized in 18 steps by use of this methodology.

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

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

Protein tyrosine phosphatases in skeletal development and diseases

Skeletal development and homeostasis in mammals are modulated by finely coordinated processes of migration, proliferation, differentiation, and death of skeletogenic cells originating from the mesoderm and neural crest. Numerous molecular mechanisms are involved in these regulatory processes, one of which is protein posttranslational modifications, particularly protein tyrosine phosphorylation (PYP). PYP occurs mainly through the action of protein tyrosine kinases (PTKs), modifying protein enzymatic activity, changing its cellular localization, and aiding in the assembly or disassembly of protein signaling complexes. Under physiological conditions, PYP is balanced by the coordinated action of PTKs and protein tyrosine phosphatases (PTPs). Dysregulation of PYP can cause genetic, metabolic, developmental, and oncogenic skeletal diseases. Although PYP is a reversible biochemical process, in contrast to PTKs, little is known about how this equilibrium is modulated by PTPs in the skeletal system. Whole-genome sequencing has revealed a large and diverse superfamily of PTP genes (over 100 members) in humans, which can be further divided into cysteine (Cys)-, aspartic acid (Asp)-, and histidine (His)-based PTPs. Here, we review current knowledge about the functions and regulatory mechanisms of 28 PTPs involved in skeletal development and diseases; 27 of them belong to class I and II Cys-based PTPs, and the other is an Asp-based PTP. Recent progress in analyzing animal models that harbor various mutations in these PTPs and future research directions are also discussed. Our literature review indicates that PTPs are as crucial as PTKs in supporting skeletal development and homeostasis.

The role of protein tyrosine phosphatase 1B (PTP1B) in the pathogenesis of type 2 diabetes mellitus and its complications

Insulin resistance, the most important characteristic of the type 2 diabetes mellitus (T2DM), is mostly caused by impairment in the insulin receptor (IR) signal transduction pathway. Protein tyrosine phosphatase 1B (PTP1B), one of the main negative regulators of the IR signaling pathway, is broadly expressed in various cells and tissues. PTP1B decreases the phosphorylation of the IR resulting in insulin resistance in various tissues. The evidence for the physiological role of PTP1B in regulation of metabolic pathways came from whole-body PTP1B-knockout mice. Whole-body and tissue-specific PTP1B-knockout mice showed improvement in adiposity, insulin resistance, and glucose tolerance. In addition, the key role of PTP1B in the pathogenesis of T2DM and its complications was further investigated in mice models of PTP1B deficient/overexpression. In recent years, targeting PTP1B using PTP1B inhibitors is being considered an attractive target to treat T2DM. PTP1B inhibitors improve the sensitivity of the insulin receptor and have the ability to cure insulin resistance-related diseases. We herein summarized the biological functions of PTP1B in different tissues in vivo and in vitro. We also describe the effectiveness of potent PTP1B inhibitors as pharmaceutical agents to treat T2DM.

A review of alpha-glucosidase inhibitors from plants as potential candidates for the treatment of type-2 diabetes

Diabetes mellitus is a multifactorial global health disorder that is rising at an alarming rate. Cardiovascular diseases, kidney damage and neuropathy are the main cause of high mortality rates among individuals with diabetes. One effective therapeutic approach for controlling hyperglycemia associated with type-2 diabetes is to target alpha-amylase and alpha-glucosidase, enzymes that catalyzes starch hydrolysis in the intestine. At present, approved inhibitors for these enzymes are restricted to acarbose, miglitol and voglibose. Although these inhibitors retard glucose absorption, undesirable gastrointestinal side effects impede their application. Therefore, research efforts continue to seek novel inhibitors with improved efficacy and minimal side effects. Natural products of plant origin have been a valuable source of therapeutic agents with lesser toxicity and side effects. The anti-diabetic potential through alpha-glucosidase inhibition of plant-derived molecules are summarized in this review. Eight molecules (Taxumariene F, Akebonoic acid, Morusin, Rhaponticin, Procyanidin A2, Alaternin, Mulberrofuran K and Psoralidin) were selected as promising drug candidates and their pharmacokinetic properties and toxicity were discussed where available.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11101-021-09773-1.

Sirtuins at the Service of Healthy Longevity

Sirtuins may counteract at least six hallmarks of organismal aging: neurodegeneration, chronic but ineffective inflammatory response, metabolic syndrome, DNA damage, genome instability, and cancer incidence. Moreover, caloric restriction is believed to slow down aging by boosting the activity of some sirtuins through activating adenosine monophosphate-activated protein kinase (AMPK), thus raising the level of intracellular nicotinamide adenine dinucleotide (NAD⁺) by stimulating NAD⁺ biosynthesis. Sirtuins and their downstream effectors induce intracellular signaling pathways related to a moderate caloric restriction within cells, mitigating reactive oxygen species (ROS) production, cell senescence phenotype (CSP) induction, and apoptosis as forms of the cellular stress response. Instead, it can promote DNA damage repair and survival of cells with normal, completely functional phenotypes. In this review, we discuss mechanisms of sirtuins action toward cell-conserving phenotype associated with intracellular signaling pathways related to moderate caloric restriction, as well as some tissue-specific functions of sirtuins, especially in the central nervous system, heart muscle, skeletal muscles, liver, kidneys, white adipose tissue, hematopoietic system, and immune system. In this context, we discuss the possibility of new therapeutic approaches.

Structural Bases for Hesperetin Derivatives: Inhibition of Protein Tyrosine Phosphatase 1B, Kinetics Mechanism and Molecular Docking Study

In the present study, we investigated the structure-activity relationship of naturally occurring hesperetin derivatives, as well as the effects of their glycosylation on the inhibition of diabetes-related enzyme systems, protein tyrosine phosphatase 1B (PTP1B) and α-glycosidase. Among the tested hesperetin derivatives, hesperetin 5-O-glucoside, a single-glucose-containing flavanone glycoside, significantly inhibited PTP1B with an IC₅₀ value of 37.14 ± 0.07 µM. Hesperetin, which lacks a sugar molecule, was the weakest inhibitor compared to the reference compound, ursolic acid (IC₅₀ = 9.65 ± 0.01 µM). The most active flavanone hesperetin 5-O-glucoside suggested that the position of a sugar moiety at the C-5-position influences the PTP1B inhibition. It was observed that the ability to inhibit PTP1B is dependent on the nature, position, and number of sugar moieties in the flavonoid structure, as well as conjugation. In the kinetic study of PTP1B enzyme inhibition, hesperetin 5-O-glucoside led to mixed-type inhibition. Molecular docking studies revealed that hesperetin 5-O-glucoside had a higher binding affinity with key amino residues, suggesting that this molecule best fits the PTP1B allosteric site cavity. The data reported here support hesperetin 5-O-glucoside as a hit for the design of more potent and selective inhibitors against PTP1B in the search for a new anti-diabetic treatment.

Interaction and Inhibition of a Ganoderma lucidum Proteoglycan on PTP1B Activity for Anti-diabetes

Protein tyrosine phosphatase 1B (PTP1B) is a key negative regulator of insulin and an effective target for the treatment of type 2 diabetes (T2D). A natural hyperbranched proteoglycan extracted from Ganoderma lucidum, namely, Fudan-Yueyang G. Lucidum (FYGL), was demonstrated capable of inhibiting the activity of PTP1B. Here, to identify the effective active components of FYGL, three different components, the polysaccharide FYGL-1, proteoglycans FYGL-2, and FYGL-3, were isolated from FYGL, and then, the protein moiety of FYGL-3 was further separated, namely, FYGL-3-P. Their abilities to enhance the glucose uptake in cells and inhibit the activity of PTP1B were compared. The inhibitory mechanisms were systematically explored by spectroscopic methods and MD simulations. The results showed that FYGL-3 and FYGL-3-P significantly enhanced the insulin-provoked glucose uptake in insulin-resistant HepG2 cells, detected by the glucose oxidase method. Also, the FYGL-3-P protein moiety in FYGL played an essential role in inhibiting the activity of PTP1B. A strong, enthalpy-driven, and multitargeted interaction by electrostatic forces between PTP1B and FYGL-3-P dramatically inhibited the catalytic activity of PTP1B. These results provided deep insights into the molecular mechanisms of FYGL inhibiting the activity of PTP1B and structurally helped researchers seek natural PTP1B inhibitors.

Insulin and Insulin Resistance in Alzheimer's Disease

Insulin plays a range of roles as an anabolic hormone in peripheral tissues. It regulates glucose metabolism, stimulates glucose transport into cells and suppresses hepatic glucose production. Insulin influences cell growth, differentiation and protein synthesis, and inhibits catabolic processes such as glycolysis, lipolysis and proteolysis. Insulin and insulin-like growth factor-1 receptors are expressed on all cell types in the central nervous system. Widespread distribution in the brain confirms that insulin signaling plays important and diverse roles in this organ. Insulin is known to regulate glucose metabolism, support cognition, enhance the outgrowth of neurons, modulate the release and uptake of catecholamine, and regulate the expression and localization of gamma-aminobutyric acid (GABA). Insulin is also able to freely cross the blood–brain barrier from the circulation. In addition, changes in insulin signaling, caused inter alia insulin resistance, may accelerate brain aging, and affect plasticity and possibly neurodegeneration. There are two significant insulin signal transduction pathways: the PBK/AKT pathway which is responsible for metabolic effects, and the MAPK pathway which influences cell growth, survival and gene expression. The aim of this study is to describe the role played by insulin in the CNS, in both healthy people and those with pathologies such as insulin resistance and Alzheimer’s disease.

Insulin signaling in health and disease

The molecular mechanisms of cellular insulin action have been the focus of much investigation since the discovery of the hormone 100 years ago. Insulin action is impaired in metabolic syndrome, a condition known as insulin resistance. The actions of the hormone are initiated by binding to its receptor on the surface of target cells. The receptor is an α2β2 heterodimer that binds to insulin with high affinity, resulting in the activation of its tyrosine kinase activity. Once activated, the receptor can phosphorylate a number of intracellular substrates that initiate discrete signaling pathways. The tyrosine phosphorylation of some substrates activates phosphatidylinositol-3-kinase (PI3K), which produces polyphosphoinositides that interact with protein kinases, leading to activation of the kinase Akt. Phosphorylation of Shc leads to activation of the Ras/MAP kinase pathway. Phosphorylation of SH2B2 and of Cbl initiates activation of G proteins such as TC10. Activation of Akt and other protein kinases produces phosphorylation of a variety of substrates, including transcription factors, GTPase-activating proteins, and other kinases that control key metabolic events. Among the cellular processes controlled by insulin are vesicle trafficking, activities of metabolic enzymes, transcriptional factors, and degradation of insulin itself. Together these complex processes are coordinated to ensure glucose homeostasis.

Multiple Leptin Signalling Pathways in the Control of Metabolism and Fertility: A Means to Different Ends?

The adipocyte-derived ‘satiety promoting’ hormone, leptin, has been identified as a key central regulator of body weight and fertility, such that its absence leads to obesity and infertility. Plasma leptin levels reflect body adiposity, and therefore act as an ‘adipostat’, whereby low leptin levels reflect a state of low body adiposity (under-nutrition/starvation) and elevated leptin levels reflect a state of high body adiposity (over-nutrition/obesity). While genetic leptin deficiency is rare, obesity-related leptin resistance is becoming increasingly common. In the absence of adequate leptin sensitivity, leptin is unable to exert its ‘anti-obesity’ effects, thereby exacerbating obesity. Furthermore, extreme leptin resistance and consequent low or absent leptin signalling resembles a state of starvation and can thus lead to infertility. However, leptin resistance occurs on a spectrum, and it is possible to be resistant to leptin’s metabolic effects while retaining leptin’s permissive effects on fertility. This may be because leptin exerts its modulatory effects on energy homeostasis and reproductive function through discrete intracellular signalling pathways, and these pathways are differentially affected by the molecules that promote leptin resistance. This review discusses the potential mechanisms that enable leptin to exert differential control over metabolic and reproductive function in the contexts of healthy leptin signalling and of diet-induced leptin resistance.

Microbially Guided Discovery and Biosynthesis of Biologically Active Natural Products

The design of small molecules that inhibit disease-relevant proteins represents a longstanding challenge of medicinal chemistry. Here, we describe an approach for encoding this challenge-the inhibition of a human drug target-into a microbial host and using it to guide the discovery and biosynthesis of targeted, biologically active natural products. This approach identified two previously unknown terpenoid inhibitors of protein tyrosine phosphatase 1B (PTP1B), an elusive therapeutic target for the treatment of diabetes and cancer. Both inhibitors appear to target an allosteric site, which confers selectivity, and can inhibit PTP1B in living cells. A screen of 24 uncharacterized terpene synthases from a pool of 4464 genes uncovered additional hits, demonstrating a scalable discovery approach, and the incorporation of different PTPs into the microbial host yielded alternative PTP-specific detection systems. Findings illustrate the potential for using microbes to discover and build natural products that exhibit precisely defined biochemical activities yet possess unanticipated structures and/or binding sites.

Discovery of Novel PTP1B Inhibitors Derived from the BH3 Domain of Proapoptotic Bcl-2 Proteins with Antidiabetic Potency

BH3 peptide analogues are generally believed to exhibit great potency as cancer therapeutics via targeting antiapoptotic Bcl-2 proteins. Here, we describe the synthesis and identification of a new class of palmitoylated peptide BH3 analogues derived from the core region (h1-h4) of BH3 domains of proapoptotic Bcl-2 proteins and as alternative PTP1B inhibitors with antidiabetic potency in vitro and in vivo. PTP1B inhibitors are attractive for treatment of type 2 diabetes. We design the analogues using a simple lipidation approach and discovered novel lead analogues with promising antidiabetic potency in vitro and in vivo. The results presented here expanded the alternative target and function for the BH3 peptide analogues from one member Bim to other members of the proapoptotic Bcl-2 proteins and emphasize their therapeutic potential in T2DM. Furthermore, our findings may provide new proof of the regulatory function of Bcl-2 family proteins in mitochondrial nutrient and energy metabolism.

Autoregulation of insulin receptor signaling through MFGE8 and the αvβ5 integrin

The role of integrins, in particular αv integrins, in regulating insulin resistance is incompletely understood. We have previously shown that the αvβ5 integrin ligand milk fat globule epidermal growth factor like 8 (MFGE8) regulates cellular uptake of fatty acids. In this work, we evaluated the impact of MFGE8 on glucose homeostasis. We show that acute blockade of the MFGE8/β5 pathway enhances while acute augmentation dampens insulin-stimulated glucose uptake. Moreover, we find that insulin itself induces cell-surface enrichment of MFGE8 in skeletal muscle, which then promotes interaction between the αvβ5 integrin and the insulin receptor leading to dampening of skeletal-muscle insulin receptor signaling. Blockade of the MFGE8/β5 pathway also enhances hepatic insulin sensitivity. Our work identifies an autoregulatory mechanism by which insulin-stimulated signaling through its cognate receptor is terminated through up-regulation of MFGE8 and its consequent interaction with the αvβ5 integrin, thereby establishing a pathway that can potentially be targeted to improve insulin sensitivity.

Insulin on the brain: The role of central insulin signalling in energy and glucose homeostasis

Insulin signals to the brain where it coordinates multiple physiological processes underlying energy and glucose homeostasis. This review explores where and how insulin interacts within the brain parenchyma, how brain insulin signalling functions to coordinate energy and glucose homeostasis and how this contributes to the pathogenesis of metabolic disease.

Insulin resistance, oxidative stress and mitochondrial defects in Ts65dn mice brain: A harmful synergistic path in down syndrome

Dysregulation of brain insulin signaling with reduced downstream neuronal survival and plasticity mechanisms are fundamental abnormalities observed in Alzheimer disease (AD). This phenomenon, known as brain insulin resistance, is associated with poor cognitive performance and is driven by the inhibition of IRS1. Since Down syndrome (DS) and AD neuropathology share many common features, we investigated metabolic aspects of neurodegeneration in DS and whether they contribute to early onset AD in DS. We evaluated levels and activation of proteins belonging to the insulin signaling pathway (IR, IRS1, BVR-A, MAPK, PTEN, Akt, GSK3β, PKCζ, AS160, GLUT4) in the frontal cortex of Ts65dn (DS model) (n = 5-6/group) and euploid mice (n = 6/group) at different ages (1, 3, 9 and 18 months). Furthermore, we analyzed whether changes of brain insulin signaling were associated with alterations of: (i) proteins regulating brain energy metabolism (mitochondrial complexes, hexokinase-II, Sirt1); (ii) oxidative stress (OS) markers (iii) APP cleavage; and (iv) proteins mediating synaptic plasticity mechanisms (PSD95, syntaxin-1 and BDNF). Ts65dn mice showed an overall impairment of the above-mentioned pathways, mainly characterized by defects of proteins activation state. Such alterations start early in life (at 1 month, during brain maturation). In particular, accumulation of inhibited IRS1, together with the uncoupling among the proteins downstream from IRS1 (brain insulin resistance), characterize Ts65dn mice. Furthermore, reduced levels of mitochondrial complexes and Sirt1, as well as increased indices of OS also were observed. These alterations precede the accumulation of APP-C99 in Ts65dn mice. Tellingly, oxidative stress levels were negatively associated with IR, IRS1 and AS160 activation as well as mitochondrial complexes levels in Ts65dn mice, suggesting a role for oxidative stress in the observed alterations. We propose that a close link exists among brain insulin resistance, mitochondrial defects and OS that contributes to brain dysfunctions observed in DS, likely favoring the development of AD in DS.

Insulin-Mimetic Dihydroxanthyletin-Type Coumarins from Angelica decursiva with Protein Tyrosine Phosphatase 1B and α-Glucosidase Inhibitory Activities and Docking Studies of Their Molecular Mechanisms

As a traditional medicine, Angelica decursiva has been used for the treatment of many diseases. The goal of this study was to evaluate the potential of four natural major dihydroxanthyletin-type coumarins—(+)-trans-decursidinol, Pd-C-I, Pd-C-II, and Pd-C-III—to inhibit the enzymes, protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase. In the kinetic study of the PTP1B enzyme’s inhibition, we found that (+)-trans-decursidinol, Pd-C-I, and Pd-C-II led to competitive inhibition, while Pd-C-III displayed mixed-type inhibition. Moreover, (+)-trans-decursidinol exhibited competitive-type, and Pd-C-I and Pd-C-II mixed-type, while Pd-C-III showed non-competitive type inhibition of α-glucosidase. Docking simulations of these coumarins showed negative binding energies and a similar proximity to residues in the PTP1B and α-glucosidase binding pocket, which means they are closely connected and strongly binding with the active enzyme site. In addition, dihydroxanthyletin-type coumarins are up to 40 µM non-toxic in HepG2 cells and have substantially increased glucose uptake and decreased expression of PTP1B in insulin-resistant HepG2 cells. Further, coumarins inhibited ONOO⁻-mediated albumin nitration and scavenged peroxynitrite (ONOO⁻), and reactive oxygen species (ROS). Our overall findings showed that dihydroxanthyletin-type coumarins derived from A. decursiva is used as a dual inhibitor for enzymes, such as PTP1B and α-glucosidase, as well as for insulin susceptibility.

Personalized Nutrition and -Omics

With change in global concern toward food quality over food quantity, consumer concern and choice of healthy food has become a matter of prime importance. It gave rise to concept of “personalized or precision nutrition”. The theory behind personalization of nutrition is supported by multiple factors including advances in food analytics, nutrition based diseases and public health programs, increasing use of information technology in nutrition science, concept of gene-diet interaction and growing consumer capacity or concern by better and healthy foods. The advances in “omics” tools and related analytical techniques have resulted into tremendous scope of their application in nutrition science. As a consequence, a better understanding of underlying interaction between diet and individual is expected with addressing of key challenges for successful implementation of this science. In this chapter, the above aspects are discussed to get an insight into driving factors for increasing concern in personalized nutrition.

The Multifaceted Actions of Curcumin in Obesity

Obesity remains a pervasive health concern worldwide with concomitant comorbidities such as cardiovascular diseases, diabetes, inflammation, and other metabolic disorders. A wealth of data validates dietary and lifestyle modifications such as restricting caloric intake and increasing physical activity to slow the obesity development. Recently, the advent of phytochemicals such as curcumin, the active ingredient in turmeric, has attracted considerable research interest in tracking down their possible effects in protection against obesity and obesity-related comorbidities. According to the existing literature, curcumin may regulate lipid metabolism and suppress chronic inflammation interacting with white adipose tissue, which plays a central role in the complications associated with obesity. Curcumin also inhibits the differentiation of adipocyte and improves antioxidant properties. In the present review, we sought to deliberate the possible effects of curcumin in downregulating obesity and curtailing the adverse health effects of obesity.

Effectiveness of cyclohexyl functionality in ugonins from Helminthostachys zeylanica to PTP1B and α-glucosidase inhibitions

Ugonins are unique flavonoids with cyclohexyl motif from Helminthostachys zeylanica. Ugonins (1-6) from the target plant displayed significant inhibitions against both PTP1B (IC₅₀s = 0.6-7.3 μM) and α-glucosidase (IC₅₀s = 3.9-32.9 μM), which are crucial enzymes associated with diabetes. A cyclohexyl motif was proved to be the key functionality for PTP1B and α-glucosidase. For example, 1 was 26-fold effective to PTP1B and 15-fold to α-glucosidase than its mother compound, luteolin. This tendency was well elucidated with distinctive differences of binding affinities (K_SV) between ugonins and mother compounds to PTP1B enzyme. Inhibitory mechanisms to PTP1B and α-glucosidase were fully characterized to be competitive, non-competitive and mixed type I according to the position of cyclohexyl functionality. In particular, the ugonin J (1) has a cyclohexyl on the B ring was estimated as a reversible, competitive and a slow binding inhibitor with parameters: K_i^app = 0.1234 μM, k₃ = 0.5713 μM^-1 min^-1, and k₄ = 0.0705 min^-1. In-depth molecular docking experiments disclosed the specific binding sites and residues of competitive inhibitor (1) and non-competitive inhibitor (4) to PTP1B enzymes. As well, all six ugonins (1-6) also inhibited α-glucosidase effectively, in which cyclohexyl motif was also the key functionality of inhibitions.

The mode of action of the Protein tyrosine phosphatase 1B inhibitor Ertiprotafib

Protein tyrosine phosphatase 1B (PTP1B) is a validated therapeutic target for the treatment of diabetes and obesity. Ertiprotafib is a PTP1B inhibitor that reached the clinical trial stage for the treatment of diabetes. Interestingly, Ertiprotafib reduces the melting temperature of PTP1B in differential scanning fluorimetry (DSF) assays, different from most drugs that increase the stability of their target upon binding. No molecular data on how Ertiprotafib functions has been published. Thus, to gain molecular insights into the mode of action of Ertiprotafib, we used biomolecular NMR spectroscopy to characterize the molecular details of the PTP1B:Ertiprotafib interaction. Our results show that Ertiprotafib induces aggregation of PTP1B in a concentration dependent manner. This shows that the insufficient clinical efficacy and adverse effects caused by Ertiprotafib is due to its tendency to cause aggregation of PTP1B.