Pancreatic Beta-cell Dysfunction in Type 2 Diabetes

Pancreatic β-cells produce and secrete insulin to maintain blood glucose levels within a narrow range. Defects in the function and mass of β-cells play a significant role in the development and progression of diabetes. Increased β-cell deficiency and β-cell apoptosis are observed in the pancreatic islets of patients with type 2 diabetes. At an early stage, β-cells adapt to insulin resistance, and their insulin secretion increases, but they eventually become exhausted, and the β-cell mass decreases. Various causal factors, such as high glucose, free fatty acids, inflammatory cytokines, and islet amyloid polypeptides, contribute to the impairment of β-cell function. Therefore, the maintenance of β-cell function is a logical approach for the treatment and prevention of diabetes. In this review, we provide an overview of the role of these risk factors in pancreatic β-cell loss and the associated mechanisms. A better understanding of the molecular mechanisms underlying pancreatic β-cell loss will provide an opportunity to identify novel therapeutic targets for type 2 diabetes.

Lysophosphatidic Acid Induces Podocyte Pyroptosis in Diabetic Nephropathy by an Increase of Egr1 Expression via Downregulation of EzH2

Podocyte damage and renal inflammation are the main features and pathogenesis of diabetic nephropathy (DN). Inhibition of lysophosphatidic acid (LPA) receptor 1 (LPAR1) suppresses glomerular inflammation and improves DN. Herein, we investigated LPA-induced podocyte damage and its underlying mechanisms in DN. We investigated the effects of AM095, a specific LPAR1 inhibitor, on podocytes from streptozotocin (STZ)-induced diabetic mice. E11 cells were treated with LPA in the presence or absence of AM095, and the expression of NLRP3 inflammasome factors and pyroptosis were measured. A chromatin immunoprecipitation assay and Western blotting were performed to elucidate underlying molecular mechanisms. Gene knockdown by transfecting small interfering RNA was used to determine the role of the transcription factor Egr1 (early growth response protein 1) and histone methyltransferase EzH2 (Enhancer of Zeste Homolog 2) in LPA-induced podocyte injury. AM095 administration inhibited podocyte loss, NLRP3 inflammasome factor expression, and cell death in STZ-induced diabetic mice. In E11 cells, LPA increased NLRP3 inflammasome activation and pyroptosis via LPAR1. Egr1 mediated NLRP3 inflammasome activation and pyroptosis in LPA-treated E11 cells. LPA decreased H3K27me3 enrichment at the Egr1 promoter in E11 cells by downregulating EzH2 expression. EzH2 knockdown further increased LPA-induced Egr1 expression. In podocytes from STZ-induced diabetic mice, AM095 suppressed Egr1 expression increase and EzH2/H3K27me3 expression reduction. Collectively, these results demonstrate that LPA induces NLRP3 inflammasome activation by downregulating EzH2/H3K27me3 and upregulating Egr1 expression, resulting in podocyte damage and pyroptosis, which may be a potential mechanism of DN progression.

Bavachin alleviates diabetic nephropathy in db/db mice by inhibition of oxidative stress and improvement of mitochondria function

Diabetic nephropathy (DN) is a major complication of diabetes mellitus. Psoralea corylifolia L. seed (PCS) is a traditional medicine effective against various diseases. In this study, we aimed to investigate the effect of bavachin, the major active component of PCS, on DN in db/db mice. Bavachin (10 mg/kg/day) was administered orally to 12-week-old male db/db mice for 6 wk. For in vitro experiments, SV40 MES13 cells were treated with bavachin in the presence of 25 mM glucose. Food and water intake and urine mass were significantly increased in db/db mice compared to wild-type CON mice, but bavachin administration significantly reduced these increases. Urinary microalbumin, blood urea nitrogen, and creatinine clearance which were significantly increased in db/db mice, were also decreased by bavachin administration. Glomerular area and collagen deposition in the kidney were significantly decreased in db/db mice following bavachin administration. Increased renal levels of fibrotic factors, fibronectin, COL1A1, and α-SMA, were reduced following bavachin administration. Protein expressions of antioxidant enzymes, namely SOD2, catalase, and HO-1, and mitochondrial function-related factors, namely SIRT1, PGC1α, Nrf1, and mtTFA, were reduced in the kidney tissues of db/db mice compared to wild-type CON mice, and bavachin administration upregulated these protein expressions. In vitro studies also showed that bavachin decreases mitochondria ROS production, increases the expression of PGC-1α and SIRT1, and decreases the expression of α-SMA in high glucose-treated SV40 MES13 cells. Based on these results, bavachin improved DN by inhibiting oxidative stress and enhancing mitochondrial function.

Prevention of LPS-Induced Acute Kidney Injury in Mice by Bavachin and Its Potential Mechanisms

Acute kidney injury (AKI) is a serious complication of sepsis with a rapid onset and high mortality rate. Bavachin, an active component of Psoralea corylifolia L., reportedly has antioxidant, anti-apoptotic, and anti-inflammatory effects; however, its beneficial effects on AKI remain undetermined. We investigated the protective effect of bavachin on lipopolysaccharide (LPS)-induced AKI in mice and elucidated the underlying mechanism in human renal tubular epithelial HK-2 cells. Increased serum creatinine and blood urea nitrogen levels were observed in LPS-injected mice; however, bavachin pretreatment significantly inhibited this increase. Bavachin improved the kidney injury score and decreased the expression level of tubular injury markers, such as neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1), in both LPS-injected mice and LPS-treated HK-2 cells. LPS-induced oxidative stress via phosphorylated protein kinase C (PKC) β and upregulation of the NADPH oxidase (NOX) 4 pathway was also significantly decreased by treatment with bavachin. Moreover, bavachin treatment inhibited the phosphorylation of MAPKs (P38, ERK, and JNK) and nuclear factor (NF)-κB, as well as the increase in inflammatory cytokine levels in LPS-injected mice. Krüppel-like factor 5 (KLF5) expression was upregulated in the LPS-treated HK-2 cells and kidneys of LPS-injected mice. However, RNAi-mediated silencing of KLF5 inhibited the phosphorylation of NF-kB, consequently reversing LPS-induced KIM-1 and NGAL expression in HK-2 cells. Therefore, bavachin may ameliorate LPS-induced AKI by inhibiting oxidative stress and inflammation via the downregulation of the PKCβ/MAPK/KLF5 axis.

Psoralea corylifolia L. seed extract attenuates dexamethasone-induced muscle atrophy in mice by inhibition of oxidative stress and inflammation

ETHNOPHARMACOLOGICAL RELEVANCE

The seeds of Psoralea corylifolia (PCS), also called "Boh-Gol-Zhee" in Korean, have been used in traditional medicine. PCS is effective for the treatment of vitiligo, cancer, inflammatory diseases, neurodegenerative diseases, kidney diseases, and musculoskeletal diseases.

AIM OF THE STUDY

In this study, we validated the beneficial effects of PCS extract on dexamethasone (DEX)-induced muscle atrophy in mice.

MATERIALS AND METHODS

DEX (20 mg/kg/day, 10 days) was intraperitoneally injected into C57BL/6 male mice to induce muscular atrophy. Oral administration of PCS extract (200 or 500 mg/kg/day) was started 2 days before DEX injection and continued for 12 days.

RESULTS

PCS extract inhibited DEX-induced decrease in body and muscle weight, grip strength, and cross-sectional area of the tibialis anterior. PCS extract significantly increased the mRNA and protein expression levels of myosin heavy chain 1, 2A, and 2X in DEX-administered mice. DEX administration significantly increased the levels of muscle atrophy factors atrogin-1, muscle RING-finger protein-1, and myostatin, which were inhibited by the PCS extract. Additionally, PCS extract increased the expression of muscle regeneration factors, such as myoblast determination protein 1, myogenin, and embryonic myosin heavy chain, and muscle synthesis markers, such as protein kinase B and mammalian target of rapamycin signaling molecules. PCS extract also significantly decreased the DEX-induced production of 4-hydroxynonenal, an oxidative stress marker. Furthermore, PCS extract recovered superoxide dismutase 2, glutathione peroxidase, and catalase activities, which were significantly reduced by DEX administration. Moreover, DEX-induced activation of nuclear factor kappa-light-chain-enhancer of activated B cells and expression of cytokines, such as tumor necrosis factor α and monocyte chemoattractant protein-1, significantly decreased after PCS extract administration.

CONCLUSIONS

Here, we demonstrated that PCS extract administration protected against DEX-induced muscle atrophy. This beneficial effect was mediated by suppressing the expression of muscle degradation factors and increasing the expression of muscle regeneration and synthesis factors. This effect was probably due to the inhibition of oxidative stress and inflammation. These results highlight the potential of PCS extract as a protective and therapeutic agent against muscle dysfunction and atrophy.

Lysophosphatidic Acid Promotes Epithelial-Mesenchymal Transition in Kidney Epithelial Cells via the LPAR1/MAPK-AKT/KLF5 Signaling Pathway in Diabetic Nephropathy

The epithelial–mesenchymal transition (EMT) is a differentiation process associated with fibrogenesis in diabetic nephropathy (DN). Lysophosphatidic acid (LPA) is a small, naturally occurring glycerophospholipid implicated in the pathogenesis of DN. In this study, we investigated the role of LPA/LPAR1 signaling in the EMT of tubular cells as well as the underlying mechanisms. We observed a decrease in E-cadherin and an increase in vimentin expression levels in the kidney tubules of diabetic db/db mice, and treatment with ki16425 (LPAR1/3 inhibitor) inhibited the expression of these EMT markers. Ki16425 treatment also decreased the expression levels of the fibrotic factors fibronectin and alpha-smooth muscle actin (α-SMA) in db/db mice. Similarly, we found that LPA decreased E-cadherin expression and increased vimentin expression in HK-2 cells, which was reversed by treatment with ki16425 or AM095 (LPAR1 inhibitor). In addition, the expression levels of fibronectin and α-SMA were increased by LPA, and this effect was reversed by treatment with ki16425 and AM095 or by LPAR1 knockdown. Moreover, LPA induced the expression of the transcription factor, Krüppel-like factor 5 (KLF5), which was decreased by AM095 treatment or LPAR1 knockdown. The expression levels of EMT markers and fibrotic factors induced by LPA were decreased upon KLF5 knockdown in HK-2 cells. Inhibition of the extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and serine-threonine kinase (AKT) pathways decreased LPA-induced expression of KLF5 and EMT markers. In conclusion, these data suggest that LPA contributes to the pathogenesis of diabetic nephropathy by inducing EMT and renal tubular fibrosis via regulation of KLF5 through the LPAR1.

Effect of BBT-877, a novel inhibitor of ATX, on a mouse model of type 1 diabetic nephropathy

Diabetic nephropathy (DN) is one of the common microvascular complications of diabetes. Autotaxin (ATX) is an enzyme with lysophospholipase D activity, producing lysophosphatidic acid (LPA). LPA signaling has been implicated in renal fibrosis, thereby inducing renal dysfunction. BBT-877 is an orally administered small molecule inhibitor of ATX. However, its effect on DN has not been studied so far. In this study, we investigated the effect of BBT-877, a novel inhibitor of ATX, on the pathogenesis of DN in a mouse model of streptozotocin (STZ)-induced diabetes. BBT-877 treatment significantly reduced albuminuria, albumin-to-creatinine ratio (ACR), neutrophil gelatinase-associated lipocalin (NGAL), and glomerular volume compared to the STZ-vehicle group. Interestingly, BBT-877 treatment attenuated hyperglycemia and dyslipidemia in STZ-induced diabetes mice. In the liver, the expression levels of β-oxidation-related genes such as PPAR α and CPT1 were significantly decreased in STZ-induced diabetic mice. However, this effect was reversed by BBT-877 treatment. BBT-877 treatment also suppressed mRNA levels of pro-inflammatory cytokines IL-6, MCP-1, and TNF-α and protein levels of fibrotic factors (TGF-β, fibronectin, CTGF, and collagen type Ι alpha Ι (COL1A1)) in the kidneys of STZ-induced diabetic mice. In conclusion, our results indicate that BBT-877 is effective in preventing the pathogenesis of DN by reducing systemic blood glucose levels and inhibiting inflammation and fibrosis in the renal tissue of diabetes mice. These novel findings suggest that inhibition of ATX may be a potential therapeutic target for DN.

TGF-β activates NLRP3 inflammasome by an autocrine production of TGF-β in LX-2 human hepatic stellate cells

Inflammation contributes to the pathogenesis of liver disease, and inflammasome activation has been identified as a major contributor to the amplification of liver inflammation. Transforming growth factor-beta (TGF-β) is a key regulator of liver physiology, contributing to all stages of liver disease. We investigated whether TGF-β is involved in inflammasome-mediated fibrosis in hepatic stellate cells. Treatment with TGF-β increased priming of NLRP3 inflammasome signaling by increasing NLRP3 levels and activating TAK1-NF-kB signaling. Moreover, TGF-β increased the expression of p-Smad2/3-NOX4 in LX-2 cells and consequently increased ROS content, which is a trigger for NLRP3 inflammasome activation. Elevated expression of NEK7 and active caspase-1 was also shown in TGF-β-induced LX-2 cells, and this level was reduced by (5Z)-oxozeaenol, a TAK inhibitor. Finally, TGF-β-treated cells significantly increased TGF-β secretion levels, and their production was inhibited by IL-1β receptor antagonist treatment. In conclusion, TGF-β may represent an endogenous danger signal to the active NLRP3 inflammasome, by which IL-1β mediates TGF-β expression in an autocrine manner. Therefore, targeting the NLRP3 inflammasome may be a promising approach for the development of therapies for TGF-β-induced liver fibrosis.

Effects of Psoralea corylifolia L. seed extract on AGEs-induced cell proliferation and fibrotic factor expression in mesangial cells

Diabetic nephropathy is a microvascular complication of diabetes that is characterized by mesangial expansion and thickening of the glomerular basement membrane. The production of advanced glycation end products (AGEs) increases in diabetic patients. Activation of the receptor of AGE (RAGE) signaling pathway induces mesangial expansion via the reactive oxygen species (ROS)-mediated production of pro-inflammatory and extracellular matrix molecules. The Psoralea corylifolia L. seed (PCS) is a widely used herbal medicine with various biological activities. The current study investigated the effect of PCS extract on mesangial cell proliferation and the RAGE signaling pathway in SV40 MES 13 cells. SV40 MES 13 cells were harvested after treatment with various concentrations of PCS extract at 10 µg/ml AGEs for 24 h. The results revealed that the PCS extract inhibited AGEs-induced mesangial cell proliferation and cyclin protein expression in a concentration-dependent manner. In addition, the AGEs-induced expression of fibrotic factors, such as transforming growth factor β, fibronectin and collagen, was reduced in mesangial cells after exposure to the PCS extract. The PCS extract also reduced RAGE expression and inhibited the expression of its downstream signaling pathways, such as NADPH oxidase, intracellular ROS and phospho-NF-κB. In conclusion, the data suggested that the PCS extract attenuated AGEs-induced renal mesangial cell proliferation and fibrosis via the suppression of oxidative stress and the downregulation of inflammatory and fibrotic factor expression.

Ethanol Extract of Liriope platyphylla Root Attenuates Non-Alcoholic Fatty Liver Disease in High-Fat Diet-Induced Obese Mice via Regulation of Lipogenesis and Lipid Uptake

Non-alcoholic fatty liver disease (NAFLD) is a common metabolic disorder that causes excess lipid accumulation in the liver and is the leading cause of end-stage liver disease. Liriope platyphylla is a medicinal herb that has long been used to treat cough, obesity, and diabetes. However, the effect of Liriope platyphylla on NAFLD has not been studied. The aim of this study was to investigate the effect of Liriope platyphylla root ethanolic extract (LPE) on hepatic lipid accumulation in high-fat diet (HFD)-induced obese mice. Six-week-old C57BL/6 male mice were fed a HFD for 8 weeks and then treated with LPE (100 or 250 mg/kg/day) by oral gavage for another 8 weeks. Body weight gain and liver weight were significantly lower in the 250 mg/kg LPE-treated HFD group than in the vehicle-treated HFD group. Histological analysis of liver sections demonstrated that LPE treatment reduced lipid accumulation compared to the vehicle treatment. The serum total cholesterol, AST, and ALT levels significantly decreased in the LPE-treated HFD group compared to those in the vehicle-treated HFD group. The LPE significantly decreases the protein expression levels of SREBP1, ACC, p-ACC, FAS, and SCD1, which are involved in lipogenesis, and PPARγ, CD36/FAT, and FATP5, which are involved in fatty acid uptake, both in vivo and in vitro. Thus, LPE may attenuate HFD-induced NAFLD by decreasing lipid accumulation by inhibiting lipogenesis and fatty acid uptake.

Dulaglutide improves muscle function by attenuating inflammation through OPA-1-TLR-9 signaling in aged mice

Dulaglutide, a glucagon-like peptide-1 receptor (GLP-1R) agonist, is widely used to treat diabetes. However, its effects on muscle wasting due to aging are poorly understood. In the current study, we investigated the therapeutic potential and underlying mechanism of dulaglutide in muscle wasting in aged mice. Dulaglutide improved muscle mass and strength in aged mice. Histological analysis revealed that the cross-sectional area of the tibialis anterior (TA) in the dulaglutide-treated group was thicker than that in the vehicle group. Moreover, dulaglutide increased the shift toward middle and large-sized fibers in both young and aged mice compared to the vehicle. Dulaglutide increased myofiber type I and type IIa in young (18.5% and 8.2%) and aged (1.8% and 19.7%) mice, respectively, compared to the vehicle group. Peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis, decreased but increased by dulaglutide in aged mice. The expression of atrophic factors such as myostatin, atrogin-1, and muscle RING-finger protein-1 was decreased in aged mice, whereas that of the myogenic factor, MyoD, was increased in both young and aged mice following dulaglutide treatment. In aged mice, optic atrophy-1 (OPA-1) protein was decreased, whereas Toll-like receptor-9 (TLR-9) and its targeting inflammatory cytokines (interleukin-6 [IL-6] and tumor necrosis factor-α [TNF-α]) were elevated in the TA and quadriceps (QD) muscles. In contrast, dulaglutide administration reversed this expression pattern, thereby significantly attenuating the expression of inflammatory cytokines in aged mice. These data suggest that dulaglutide may exert beneficial effects in the treatment of muscle wasting due to aging.

Comparison of the Effects of Liraglutide on Islet Graft Survival Between Local and Systemic Delivery

Islet transplantation has emerged as a promising treatment for type 1 diabetes mellitus. Liraglutide, a glucagon-like peptide-1 (GLP-1) receptor agonist, protects beta cells after islet transplantation by improving glycemic control through several mechanisms. In this study, we compared the effects of local pretreatment and systemic treatment with liraglutide on islet transplantation in a diabetic mouse model. Streptozotocin (STZ)-induced diabetic C57BL/6 mice were transplanted with syngeneic islets under the kidney capsule. Isolated islets were either locally treated with liraglutide before transplantation or mice were treated systemically by intraperitoneal injection after islet transplantation. Local pretreatment of islets with liraglutide was more effective in increasing body weight, decreasing hemoglobin A1c levels, and lowering blood glucose levels in STZ-diabetic mice transplanted with islets. Local pretreatment was also more effective in increasing insulin secretion and islet survival in STZ-diabetic mice. Histological analysis of the transplantation site revealed fewer apoptotic cells following local pretreatment compared with systemic injection of liraglutide. These findings indicate that liraglutide administered once locally before transplantation might have superior effects on islet preservation than systemic administration.

5-Bromoprotocatechualdehyde Combats against Palmitate Toxicity by Inhibiting Parkin Degradation and Reducing ROS-Induced Mitochondrial Damage in Pancreatic β-Cells

Pancreatic β-cell loss is critical in diabetes pathogenesis. Up to now, no effective treatment has become available for β-cell loss. A polyphenol recently isolated from Polysiphonia japonica, 5-Bromoprotocatechualdehyde (BPCA), is considered as a potential compound for the protection of β-cells. In this study, we examined palmitate (PA)-induced lipotoxicity in Ins-1 cells to test the protective effects of BPCA on insulin-secreting β-cells. Our results demonstrated that BPCA can protect β-cells from PA-induced lipotoxicity by reducing cellular damage, preventing reactive oxygen species (ROS) overproduction, and enhancing glucose-stimulated insulin secretion (GSIS). BPCA also improved mitochondrial morphology by preserving parkin protein expression. Moreover, BPCA exhibited a protective effect against PA-induced β-cell dysfunction in vivo in a zebrafish model. Our results provide strong evidence that BPCA could be a potential therapeutic agent for the management of diabetes.

Betacellulin-Induced α-Cell Proliferation Is Mediated by ErbB3 and ErbB4, and May Contribute to β-Cell Regeneration

Betacellulin (BTC), an epidermal growth factor family, is known to promote β-cell regeneration. Recently, pancreatic α-cells have been highlighted as a source of new β-cells. We investigated the effect of BTC on α-cells. Insulin+glucagon+ double stained bihormonal cell levels and pancreatic and duodenal homeobox-1 expression were increased in mice treated with recombinant adenovirus-expressing BTC (rAd-BTC) and β-cell-ablated islet cells treated with BTC. In the islets of rAd-BTC-treated mice, both BrdU+glucagon+ and BrdU+insulin+ cell levels were significantly increased, with BrdU+glucagon+ cells showing the greater increase. Treatment of αTC1-9 cells with BTC significantly increased proliferation and cyclin D2 expression. BTC induced phosphorylation of ErbB receptors in αTC1-9 cells. The proliferative effect of BTC was mediated by ErbB-3 or ErbB-4 receptor kinase. BTC increased phosphorylation of ERK1/2, AKT, and mTOR and PC1/3 expression and GLP-1 production in α-cells, but BTC-induced proliferation was not changed by the GLP-1 receptor antagonist, exendin-9. We suggest that BTC has a direct role in α-cell proliferation via interaction with ErbB-3 and ErbB-4 receptors, and these increased α-cells might be a source of new β-cells.

Allomyrina dichotoma larva extract attenuates free fatty acid-induced lipotoxicity in pancreatic beta cells

BACKGROUD/OBJECTIVES

Allomyrina dichotoma larva (ADL), one of the many edible insects recognized as future food resources, has a range of pharmacological activities. In a previous study, an ADL extract (ADLE) reduced the hepatic insulin resistance of high-fat diet (HFD)-induced diabetic mice. On the other hand, the associated molecular mechanisms underlying pancreatic beta-cell dysfunction remain unclear. This study examined the effects of ADLE on palmitate-induced lipotoxicity in a beta cell line of a rat origin, INS-1 cells.

MATERIALS/METHODS

ADLE was administered to high-fat diet treated mice. The expression of apoptosis-related molecules was measured by Western blotting, and reactive oxidative stress generation and nitric oxide production were measured by DCH-DA fluorescence and a Griess assay, respectively.

RESULTS

The administration of ADLE to HFD-induced diabetic mice reduced the hyperplasia, 4-hydroxynonenal levels, and the number of apoptotic cells while improving the insulin levels compared to the HFD group. Treatment of INS-1 cells with palmitate reduced insulin secretion, which was attenuated by the ADLE treatment. Furthermore, the ADLE treatment prevented palmitate-induced cell death in INS-1 cells and isolated islets by reducing the apoptotic signaling molecules, including cleaved caspase-3 and PARP, and the Bax/Bcl2 ratio. ADLE also reduced the levels of reactive oxygen species generation, lipid accumulation, and nitrite production in palmitate-treated INS-1 cells while increasing the ATP levels. This effect corresponded to the decreased expression of inducible nitric oxide synthase (iNOS) mRNA and protein.

CONCLUSIONS

ADLE helps prevent lipotoxic beta-cell death in INS-1 cells and HFD-diabetic mice, suggesting that ADLE can be used to prevent or treat beta-cell damage in glucose intolerance during the development of diabetes.

Diphlorethohydroxycarmalol Attenuates Palmitate-Induced Hepatic Lipogenesis and Inflammation

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease, encompassing a range of conditions caused by lipid deposition within liver cells, and is also associated with obesity and metabolic diseases. Here, we investigated the protective effects of diphlorethohydroxycarmalol (DPHC), which is a polyphenol isolated from an edible seaweed, Ishige okamurae, on palmitate-induced lipotoxicity in the liver. DPHC treatment repressed palmitate-induced cytotoxicity, triglyceride content, and lipid accumulation. DPHC prevented palmitate-induced mRNA and protein expression of SREBP (sterol regulatory element-binding protein) 1, C/EBP (CCAAT-enhancer-binding protein) α, ChREBP (carbohydrate-responsive element-binding protein), and FAS (fatty acid synthase). In addition, palmitate treatment reduced the expression levels of phosphorylated AMP-activated protein kinase (AMPK) and sirtuin (SIRT)1 proteins, and DPHC treatment rescued this reduction. Moreover, DPHC protected palmitate-induced liver toxicity and lipogenesis, as well as inflammation, and enhanced AMPK and SIRT1 signaling in zebrafish. These results suggest that DPHC possesses protective effects against palmitate-induced toxicity in the liver by preventing lipogenesis and inflammation. DPHC could be used as a potential therapeutic or preventive agent for fatty liver diseases.

A potential therapeutic combination for treatment of COVID-19: Synergistic effect of DPP4 and RAAS suppression

COVID-19, caused by the novel coronavirus SARS-CoV-2, is an abbreviated name for coronavirus disease 2019. COVID-19 became a global pandemic in early 2020. It predominantly affects not only the upper and lower respiratory tract, but also multiple organs, including the kidney, heart, and brain. The mortality of COVID-19 patients is high in men and in elderly patients with age-related diseases such as hypertension and diabetes. The angiotensin converting enzyme-2 (ACE-2), a component in the renin–angiotensin–aldosterone system (RAAS), plays as cell surface receptors for SARS-CoV-2. A recent study proved that coronavirus SARS-CoV-2 also uses dipeptidyl peptidase-4 (DPP4, also known as adenosine deaminase complexing protein 2, CD26) as a co-receptor when entering cells. In addition, DPP4 is also implicated in the regulation of the immune response. Thus, the combination of DPP4 inhibition and suppression of ACE-2/RAAS may be a novel therapeutic strategy for combating this pandemic.

Glucosamine potentiates the differentiation of adipose-derived stem cells into glucose-responsive insulin-producing cells

Background

Islet transplantation might be a logical strategy to restore insulin secretion for the treatment of diabetes, however, the scarcity of donors poses an obstacle for such a treatment. As an alternative islet source, differentiation of stem cells into insulin-producing cells (IPCs) has been tried. Many protocols have been developed to improve the efficiency of differentiation of stem cells into IPCs. In this study, we investigated whether glucosamine supplementation during differentiation of human adipose-derived stem cells (hADSCs) into IPCs can improve the insulin secretory function.

Methods

Glucosamine was added to the original differentiation medium at different stages of differentiation of hADSCs into IPCs for 12 days and insulin secretion was analyzed.

Results

Addition of glucosamine alone to the growth medium of hADSCs did not affect the differentiation of hADSCs to IPCs. Supplementation of the differentiation medium with glucosamine at a later stage (protocol G3) proved to have the greatest effect on IPC differentiation. Basal and glucose-stimulated insulin secretion (GSIS) was significantly increased and the expression of insulin and C-peptide was increased in differentiated IPCs as compared with that in differentiated IPCs using the conventional protocol (protocol C). In addition, the expression of beta-cell specific transcription factors such as pancreatic and duodenal homeobox1 (PDX1) and neurogenin 3 (NGN3) was also increased. Furthermore, the expression of genes related to insulin secretion, including synaptotagmin 4 (Syt4), glucokinase (Gck) and glucose transporter 2 (Glut2), was also increased.

Conclusions

We conclude that glucosamine supplementation potentiates the differentiation of hADSCs into IPCs.

Polygonum multiflorum Thunb. Extract Stimulates Melanogenesis by Induction of COX2 Expression through the Activation of p38 MAPK in B16F10 Mouse Melanoma Cells

Polygonum multiflorum Thunb. (PM) root extracts have been used for treating graying hair in Oriental medicine; however, the molecular mechanisms underlying the melanogenic effects of PM root have not been fully understood. In the present study, we investigated the melanogenic effects of an ethanolic extract of PM root (PME) and the mechanisms involved. We examined the effects of PME on cell viability, cellular melanin content, and tyrosinase activity in B16F10 cells. The melanogenic mechanism of PME was explored using signaling inhibitors and examining the expression of melanogenic genes and signaling molecules by western blot and RT-qPCR analyses. PME did not exhibit any cytotoxicity in B16F10 cells compared to that in control cells. PME treatment significantly increased melanin production and tyrosinase activity. In addition, PME induced the expression of cyclooxygenase-2 (COX2) as well as that of melanogenic genes, such as microphthalmia-associated transcription factor (MiTF), tyrosinase-related protein (Trp) 1, Trp2, and tyrosinase, in B16F10 cells. PME treatment increased the level of phosphorylated p38 mitogen-activated protein kinase (MAPK), and pretreatment with SB 203580, a p38 MAPK inhibitor, significantly suppressed this PME-induced increase in the expression of COX2 and melanogenic genes. These results indicate that PME induced the expression of melanogenic genes by inducing COX2 expression via the activation of the p38 MAPK pathway, thereby contributing to the enhancement of melanogenesis.

Reduction of Secreted Frizzled-Related Protein 5 Drives Vascular Calcification through Wnt3a-Mediated Rho/ROCK/JNK Signaling in Chronic Kidney Disease

Vascular calcification (VC) is commonly associated with bone loss in patients with chronic kidney disease (CKD). The Wingless-related integration site (Wnt) regulates osteoblast activation through canonical signaling pathways, but the common pathophysiology of these pathways during VC and bone loss has not been identified. A rat model of adenine-induced CKD with VC was used in this study. The rats were fed 0.75% adenine (2.5% protein, 0.92% phosphate) with or without intraperitoneal injection of calcitriol (0.08 µg/kg/day) for 4 weeks. Angiotensin II (3 µM)-induced VC was achieved in high phosphate medium (3 mM) through its effect on vascular smooth muscle cells (VSMCs). In an mRNA profiler polymerase chain reaction assay of the Wnt signaling pathway, secreted frizzled-related protein 5 (sFRP5) levels were significantly decreased in the CKD rat model compared with the control group. The repression of sFRP5 on VSMC trans-differentiation was mediated through Rho/Rho-associated coiled coil containing protein kinase (ROCK) and c-Jun N-terminal kinase (JNK) pathways activated by Wnt3a. In a proof of concept study conducted with patients with CKD, serum sFRP5 concentrations were significantly lower in subjects with VC than in those without VC. Our findings suggest that repression of sFRP5 is associated with VC in the CKD environment via activation of the noncanonical Wnt pathway, and thus that sFRP5 might be a novel therapeutic target for VC in CKD.

Prevention of Oxidative Stress-Induced Pancreatic Beta Cell Damage by Broussonetia Kazinoki Siebold Fruit Extract Via the ERK-Nox4 Pathway

Pancreatic beta cells are vulnerable to oxidative stress, which causes beta cell death and dysfunction in diabetes mellitus. Broussonetia kazinoki Siebold (BK) is a widely used herbal medicine, but its potential effects against beta cell death-induced diabetes have not been studied. Therefore, we investigated the protective effect of an ethanolic extract of BK fruit (BKFE) against streptozotocin (STZ)-induced toxicity in pancreatic beta cells. Intraperitoneal injection of STZ in mice induced hyperglycemia; however, oral administration of BKFE significantly decreased the blood glucose level as well as HbA1c levels. BKFE treatment improved glucose tolerance and increased body weight in diabetic mice. Moreover, BKFE treatment resulted in increased serum insulin levels and insulin expression in the pancreas as well as decreased 4-hydroxynonenal levels induced by oxidative stress. Treatment with STZ decreased cell viability of mouse insulinoma cells (MIN6), which was blocked by BKFE pretreatment. BKFE significantly inhibited apoptotic cells and decreased the expression levels of cleaved-caspase-3 and cleaved-poly (ADP-ribose) polymerase (PARP) induced by STZ treatment. Production of reactive oxygen species in STZ-treated MIN6 cells was also significantly decreased by treatment with BKFE. Erk phosphorylation and Nox4 levels increased in STZ-treated MIN6 cells and the pancreas of mice injected with STZ and this increase was inhibited by treatment with BKFE. Inhibition of Erk phosphorylation by treatment with the PD98059 inhibitor or siRNA Erk also blocked the expression of Nox4 induced by STZ treatment. In conclusion, BKFE inhibits Erk phosphorylation, which in turn prevents STZ-induced oxidative stress and beta cell apoptosis. These results suggested that BKFE can be used to prevent or treat beta cell damage in diabetes.

Preventive Effects of Dulaglutide on Disuse Muscle Atrophy Through Inhibition of Inflammation and Apoptosis by Induction of Hsp72 Expression

Pathological conditions such as joint immobilization, long-time bed rest, or inactivity may result in disuse-induced muscle wasting and dysfunction. To investigate the effect of dulaglutide, a long-acting glucagon-like peptide-1 receptor agonist, on disuse muscle atrophy, disuse condition was induced by spiral wire immobilization in C57BL/6 mice and the mice were treated with dulaglutide. Dulaglutide treatment effectively improved muscle function and increased muscle mass compared with vehicle treatment. Dulaglutide inhibited the decrease of muscle fiber size and the expression of atrophic factors such as myostatin, atrogin-1/MAFbx, and muscle RING-finger protein-1 in immobilized mice. In addition, dulaglutide inhibited nuclear factor kappa B activation, leading to a decrease in the mRNA levels of proinflammatory cytokines, including tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 in muscle of immobilized mice. Dulaglutide suppressed the expression of apoptotic markers such as caspase-3, cleaved poly-ADP ribose polymerase, and Bax under immobilization condition and increased the expression of heat shock protein 72 (Hsp72), which is related to the amelioration of inflammation and apoptosis during disuse time. Further study showed that dulaglutide could induce Hsp72 expression via the regulation of 5′-AMP-activated protein kinase signaling. Our data suggest that dulaglutide could exert beneficial effects against disuse-induced muscle atrophy.

Attenuation of diabetic kidney injury in DPP4-deficient rats; role of GLP-1 on the suppression of AGE formation by inducing glyoxalase 1

Dipeptidyl peptidase 4 (DPP4) inactivates incretin hormone glucagon-like peptide-1. DPP4 inhibitors may exert beneficial effects on diabetic nephropathy (DN) independently of glycemic control; however, the mechanisms underlying are not fully understood. Here, we investigated the mechanisms of the beneficial effects of DPP4 inhibition on DN using DPP4-deficient (DPP4-def) rats and rat mesangial cells.

Blood glucose and HbA1c significantly increased by streptozotocin (STZ) and no differences were between WT-STZ and DPP4-def-STZ. The albumin level in urine decreased significantly and the albumin/creatinine ratio decreased slightly in DPP4-def-STZ. The glomerular volume in DPP4-def-STZ significantly decreased compared with that of WT-STZ. Advanced glycation end products formation, receptor for AGE (RAGE) protein expression, and its downstream inflammatory cytokines and fibrotic factors in kidney tissue, were significantly suppressed in the DPP4-def-STZ compared to the WT-STZ with increasing glyoxalase-1 (GLO-1) expression responsible for the detoxification of methylglyoxal (MGO). In vitro, exendin-4 suppressed MGO-induced AGEs production by enhancing the expression of GLO-1 and nuclear factor-erythroid 2 p45 subunit-related factor 2, resulting in decreasing pro-inflammatory cytokine levels. This effect was abolished by GLO-1 siRNA.

Our data suggest that endogenously increased GLP-1 in DPP4-deficient rats contributes to the attenuation of DN partially by regulating AGEs formation via upregulation of GLO-1 expression.

KD025 (SLx-2119) suppresses adipogenesis at intermediate stage in human adipose-derived stem cells

Rho-associated kinases (ROCKs) have been reported to antagonize adipocyte differentiation, and inhibition of ROCKs by small molecules promotes adipogenesis. Surprisingly, our recent study revealed that the ROCK2-specific inhibitor KD025 (SLx-2119), suppresses differentiation at the intermediate stage in 3T3-L1 preadipocytes. To address whether the anti-adipogenic activity of KD025 is a generalizable property, we examined the effect of KD025 in human adipose-derived stem cells (hADSCs). KD025 significantly suppressed the adipocyte differentiation of hADSCs with downregulation of the protein and mRNA expression of various adipogenic and lipogenic markers, including PPARγ, C/EBPα, SREBP-1c, Glut4 and FABP4. Notably, we observed that adipocyte differentiation is effectively suppressed by exposure to KD025 during the mid-to-late period of adipogenesis but not at the earlier stages, showing stage-specificity. Contrary to expectations, KD025 upregulated the insulin signaling, as confirmed by the increased phosphorylation levels of Akt and GSK-3α/β, and the differentiation-promoting activity of insulin signaling was observed to be overwhelmed by the inhibitory activity. In addition, we observed that other ROCK inhibitors (Y-27632, fasudil, and H-1152P) did not suppress but promoted adipocyte differentiation. These results indicate that KD025 suppresses adipocyte differentiation by modulation of key factors activated at the intermediate stage of differentiation, and not by inhibition of ROCK2.

Upregulation of caveolin-1 and its colocalization with cytokine receptors contributes to beta cell apoptosis

Caveolin-1 (cav-1), the principal structural and signalling protein of caveolae, is implicated in various signalling events, including apoptotic cell death in type 2 diabetes. However, the precise role of beta cells in apoptosis has not been clearly defined. In this study, we investigated the involvement of cav-1 in cytokine-induced beta cell apoptosis and its underlying mechanisms in the rat beta cell line, INS-1 and isolated islets. Treatment of cytokine mixture (CM, TNFα + IL-1β) significantly increased the mRNA and protein expression of cav-1, and resulting in increased formation of caveolae. We found that IL-1 receptor 1 and TNF receptor localized to plasma membrane lipid rafts in the control cells and CM treatment recruited these receptors to the caveolae domain. After cav-1 siRNA transfection, CM-dependent NF-κB activation was reduced and consequently downregulated the mRNA expression of iNOS and IL-1β. Finally, decreased cell viability by CM treatment was ameliorated in both INS-1 cells and isolated islets treated with cav-1 siRNA. These results suggest that increased cav-1 expression and recruitment of cytokine receptors into caveolae contribute to CM-induced beta cell apoptosis.

Indole-4-carboxaldehyde Isolated from Seaweed, Sargassum thunbergii, Attenuates Methylglyoxal-Induced Hepatic Inflammation

Glucose degradation is aberrantly increased in hyperglycemia, which causes various harmful effects on the liver. Glyoxalase-1 (Glo-1) is a ubiquitous cellular enzyme that participates in the detoxification of methylglyoxal (MGO), a cytotoxic byproduct of glycolysis that induces protein modification (advanced glycation end-products, AGEs) and inflammation. Here, we investigated the anti-inflammatory effect of indole-4-carboxaldehyde (ST-I4C), which was isolated from the edible seaweed Sargassum thunbergii, on MGO-induced inflammation in HepG2 cells, a human hepatocyte cell line. ST-I4C attenuated the MGO-induced expression of inflammatory-related genes, such as tumor necrosis factor (TNF)-α and IFN-γ by activating nuclear factor-kappa B (NF-κB) without toxicity in HepG2 cells. In addition, ST-I4C reduced the MGO-induced AGE formation and the expression of the receptor for AGE (RAGE). Interestingly, both the mRNA and protein expression levels of Glo-1 increased following ST-I4C treatment, and the decrease in Glo-1 mRNA expression caused by MGO exposure was rescued by ST-I4C pretreatment. These results suggest that ST-I4C shows anti-inflammatory activity against MGO-induced inflammation in human hepatocytes by preventing an increase in the pro-inflammatory gene expression and AGE formation. Therefore, it represents a potential therapeutic agent for the prevention of hepatic steatosis.

Amelioration of muscle wasting by glucagon-like peptide-1 receptor agonist in muscle atrophy

BACKGROUND

Skeletal muscle atrophy is defined as a reduction of muscle mass caused by excessive protein degradation. However, the development of therapeutic interventions is still in an early stage. Although glucagon-like peptide-1 receptor (GLP-1R) agonists, such as exendin-4 (Ex-4) and dulaglutide, are widely used for the treatment of diabetes, their effects on muscle pathology are unknown. In this study, we investigated the therapeutic potential of GLP-1R agonist for muscle wasting and the mechanisms involved.

METHODS

Mouse C2C12 myotubes were used to evaluate the in vitro effects of Ex-4 in the presence or absence of dexamethasone (Dex) on the regulation of the expression of muscle atrophic factors and the underlying mechanisms using various pharmacological inhibitors. In addition, we investigated the in vivo therapeutic effect of Ex-4 in a Dex-induced mouse muscle atrophy model (20 mg/kg/day i.p.) followed by injection of Ex-4 (100 ng/day i.p.) for 12 days and chronic kidney disease (CKD)-induced muscle atrophy model. Furthermore, we evaluated the effect of a long-acting GLP-1R agonist by treatment of dulaglutide (1 mg/kg/week s.c.) for 3 weeks, in DBA/2J-mdx mice, a Duchenne muscular dystrophy model.

RESULTS

Ex-4 suppressed the expression of myostatin (MSTN) and muscle atrophic factors such as F-box only protein 32 (atrogin-1) and muscle RING-finger protein-1 (MuRF-1) in Dex-treated C2C12 myotubes. The suppression effect was via protein kinase A and protein kinase B signalling pathways through GLP-1R. In addition, Ex-4 treatment inhibited glucocorticoid receptor (GR) translocation by up-regulating the proteins of GR inhibitory complexes. In a Dex-induced muscle atrophy model, Ex-4 ameliorated muscle atrophy by suppressing muscle atrophic factors and enhancing myogenic factors (MyoG and MyoD), leading to increased muscle mass and function. In the CKD muscle atrophy model, Ex-4 also increased muscle mass, myofiber size, and muscle function. In addition, treatment with a long-acting GLP-1R agonist, dulaglutide, recovered muscle mass and function in DBA/2J-mdx mice.

CONCLUSIONS

GLP-1R agonists ameliorate muscle wasting by suppressing MSTN and muscle atrophic factors and enhancing myogenic factors through GLP-1R-mediated signalling pathways. These novel findings suggest that activating GLP-1R signalling may be useful for the treatment of atrophy-related muscular diseases.

Allomyrina dichotoma Larva Extract Ameliorates the Hepatic Insulin Resistance of High-Fat Diet-Induced Diabetic Mice

Allomyrina dichotoma larva is a nutritional-worthy future food resource and it contributes to multiple pharmacological functions. However, its antidiabetic effect and molecular mechanisms are not yet fully understood. Therefore, we investigated the hypolipidemic effect of A. dichotoma larva extract (ADLE) in a high-fat diet (HFD)-induced C57BL/6J mice model. Glucose tolerance and insulin sensitivity in HFD-induced diabetic mice significantly improved after ADLE administration for six weeks. The levels of serum triglyceride (TG), aspartate aminotransferase (AST), alanine transferase (ALT) activity, and lipid accumulation were increased in the liver of HFD-fed mice, but the levels were significantly reduced by the ADLE treatment. Moreover, hepatic fibrosis and inflammatory gene expression in the liver from HFD-treated mice were ameliorated by the ADLE treatment. Dephosphorylation of AMP-activated protein kinase (AMPK) by palmitate was inhibited in the ADLE treated HepG2 cells, and subsequently reduced expression of lipogenic genes, such as SREPBP-1c, ACC, and FAS were observed. The reduced expression of lipogenic genes and an increased phosphorylation of AMPK was also observed in the liver from diabetic mice treated with ADLE. In conclusion, ADLE ameliorates hyperlipidemia through inhibition of hepatic lipogenesis via activating the AMPK signaling pathway. These findings suggest that ADLE and its constituent bioactive compounds are valuable to prevent or treat hepatic insulin resistance in type 2 diabetes.

Diol-ginsenosides from Korean Red Ginseng delay the development of type 1 diabetes in diabetes-prone biobreeding rats

Background

The effects of diol-ginsenoside fraction (Diol-GF) and triol-ginsenoside fraction (Triol-GF) from Korean Red Ginseng on the development of type 1 diabetes (T1D) were examined in diabetes-prone biobreeding (DP-BB) rats that spontaneously develop T1D through an autoimmune process.

Methods

DP-BB female rats were treated with Diol-GF or Triol-GF daily from the age of 3-4 weeks up to 11-12 weeks (1 mg/g body weight).

Results

Diol-GF delayed the onset, and reduced the incidence, of T1D. Islets of Diol-GF-treated DP-BB rats showed significantly lower insulitis and preserved higher plasma and pancreatic insulin levels. Diol-GF failed to change the proportion of lymphocyte subsets such as T cells, natural killer cells, and macrophages in the spleen and blood. Diol-GF had no effect on the ability of DP-BB rat splenocytes to induce diabetes in recipients. Diol-GF and diol-ginsenoside Rb1 significantly decreased tumor necrosis factor α production, whereas diol-ginsenosides Rb1 and Rd decreased interleukin 1β production in RAW264.7 cells. Furthermore, mixed cytokine- and chemical-induced β-cell cytotoxicity was greatly inhibited by Diol-GF and diol-ginsenosides Rc and Rd in RIN5mF cells. However, nitric oxide production in RAW264.7 cells was unaffected by diol-ginsenosides.

Conclusion

Diol-GF, but not Triol-GF, significantly delayed the development of insulitis and T1D in DP-BB rats. The antidiabetogenic action of Diol-GF may result from the decrease in cytokine production and increase in β-cell resistance to cytokine/free radical-induced cytotoxicity.

Lysophosphatidic Acid Signaling in Diabetic Nephropathy

Lysophosphatidic acid (LPA) is a bioactive phospholipid present in most tissues and body fluids. LPA acts through specific LPA receptors (LPAR1 to LPAR6) coupled with G protein. LPA binds to receptors and activates multiple cellular signaling pathways, subsequently exerting various biological functions, such as cell proliferation, migration, and apoptosis. LPA also induces cell damage through complex overlapping pathways, including the generation of reactive oxygen species, inflammatory cytokines, and fibrosis. Several reports indicate that the LPA–LPAR axis plays an important role in various diseases, including kidney disease, lung fibrosis, and cancer. Diabetic nephropathy (DN) is one of the most common diabetic complications and the main risk factor for chronic kidney diseases, which mostly progress to end-stage renal disease. There is also growing evidence indicating that the LPA–LPAR axis also plays an important role in inducing pathological alterations of cell structure and function in the kidneys. In this review, we will discuss key mediators or signaling pathways activated by LPA and summarize recent research findings associated with DN.

Reactive oxygen species-induced changes in glucose and lipid metabolism contribute to the accumulation of cholesterol in the liver during aging

Aging is a major risk factor for many chronic diseases due to increased vulnerability to external stress and susceptibility to disease. Aging is associated with metabolic liver disease such as nonalcoholic fatty liver. In this study, we investigated changes in lipid metabolism during aging in mice and the mechanisms involved. Lipid accumulation was increased in liver tissues of aged mice, particularly cholesterol. Increased uptake of both cholesterol and glucose was observed in hepatocytes of aged mice as compared with younger mice. The mRNA expression of GLUT2, GK, SREBP2, HMGCR, and HMGCS, genes for cholesterol synthesis, was gradually increased in liver tissues during aging. Reactive oxygen species (ROS) increase with aging and are closely related to various aging‐related diseases. When we treated HepG2 cells and primary hepatocytes with the ROS inducer, H₂O₂, lipid accumulation increased significantly compared to the case for untreated HepG2 cells. H₂O₂ treatment significantly increased glucose uptake and acetyl‐CoA production, which results in glycolysis and lipid synthesis. Treatment with H₂O₂ significantly increased the expression of mRNA for genes related to cholesterol synthesis and uptake. These results suggest that ROS play an important role in altering cholesterol metabolism and consequently contribute to the accumulation of cholesterol in the liver during the aging process.

Lysophosphatidic acid receptor 1 inhibitor, AM095, attenuates diabetic nephropathy in mice by downregulation of TLR4/NF-κB signaling and NADPH oxidase

Diabetic nephropathy (DN) is one of the major long-term complications of diabetes. Lysophosphatidic acid (LPA) signaling has been implicated in renal fibrosis. In our previous study, we found that the LPA receptor 1/3 (LPAR1/3) antagonist, ki16425, protected against DN in diabetic db/db mice. Here, we investigated the effects of a specific pharmacological inhibitor of LPA receptor 1 (LPA1), AM095, on DN in streptozotocin (STZ)-induced diabetic mice to exclude a possible contribution of LPAR3 inhibition. AM095 treatment significantly reduced albuminuria and the albumin to creatinine ratio and significantly decreased the glomerular volume and tuft area in the treated group compared with the STZ-vehicle group. In the kidney of STZ-induced diabetic mice, the expression of LPAR1 mRNA and protein was positively correlated with oxidative stress. AM095 treatment inhibited LPA-induced reactive oxygen species production and NADPH oxidase expression as well as LPA-induced toll like receptor 4 (TLR4) expression in mesangial cells and in the kidney of STZ-induced diabetic mice. In addition, AM095 treatment suppressed LPA-induced pro-inflammatory cytokines and fibrotic factors expression through downregulation of phosphorylated NFκBp65 and c-Jun N-terminal kinases (JNK) in vitro and in the kidney of STZ-induced diabetic mice. Pharmacological or siRNA inhibition of TLR4 and NADPH oxidase mimicked the effects of AM095 in vitro. In conclusion, AM095 is effective in preventing the pathogenesis of DN by inhibiting TLR4/NF-κB and the NADPH oxidase system, consequently inhibiting the inflammatory signaling cascade in renal tissue of diabetic mice, suggesting that LPAR1 antagonism might provide a potential therapeutic target for DN.

Role of Myokines in Regulating Skeletal Muscle Mass and Function

Loss of skeletal muscle mass and strength has recently become a hot research topic with the extension of life span and an increasingly sedentary lifestyle in modern society. Maintenance of skeletal muscle mass is considered an essential determinant of muscle strength and function. Myokines are cytokines synthesized and released by myocytes during muscular contractions. They are implicated in autocrine regulation of metabolism in the muscle as well as in the paracrine/endocrine regulation of other tissues and organs including adipose tissue, the liver, and the brain through their receptors. Till date, secretome analysis of human myocyte culture medium has revealed over 600 myokines. In this review article, we summarize our current knowledge of major identified and characterized myokines focusing on their biological activity and function, particularly in muscle mass and function.

Taurine-Containing Hot Water Extract of Octopus Ocellatus Meat Prevents Methylglyoxal-Induced Vascular Damage

Endothelial cell dysfunction (ECD) is a broad term, which implies dysregulation of endothelial cell functions. Several factors contribute to ECD including high blood pressure, high cholesterol levels, diabetes, obesity, hyperglycemia, and advanced glycation end products (AGEs). The highly reactive dicarbonyl methylglyoxal (MGO) is mainly formed as byproduct of glycolysis. Therefore, high blood glucose levels result in increased MGO accumulation. Taurine-rich foods are considered to protect against various diseases including vasculopathy and to exert anti-aging effects. Here, we investigated the protective effect of hot water extract of Octopus ocellatus meat (OOM), which contains high amounts of taurine, on MGO-induced cell damage in human umbilical vein endothelial cells and zebrafish embryos. Hot water extract of OOMinhibited MGO-induced cytotoxicity and DNA damage, as well as AGEs accumulation. In addition, hot water extract of OOM protected against vascular damage in zebrafish embryos. These results suggest that hot water extract of OOM possesses protective activity against MGO-induced cytotoxicity in both umbilical vein endothelial cells and zebrafish embryos. Therefore, it could be used as a dietary source of an agent for the prevention of vascular diseases.

Taurine-Rich-Containing Hot Water Extract of Loliolus Beka Gray Meat Scavenges Palmitate-Induced Free Radicals and Protects Against DNA Damage in Insulin Secreting β-Cells

The loss of pancreatic β-cells plays a central role in the pathogenesis of both type 1 and type 2 diabetes, and many studies have been focused on ways to improve glucose homeostasis by preserving, expanding and improving the function of β-cell. Elevated levels of free fatty acids such as palmitate might contribute to the loss of β-cells. A marine squid, Loliolus beka has long been used as a food in Korea, China, Japan and Europe due to its tender meat and high taurine content. Here, we investigated the protective effects of a hot water extract of Loliolus beka meat (LBM) against palmitate toxicity in Ins-1 cells, a rat β-cell line. Treatment with LBM extract protected against palmitate-induced cytotoxicity and scavenged overproduction of nitric oxide, alkyl, and hydroxyl radicals. In addition, LBM extract protected against palmitate-induced DNA damage and β-cell dysfunction. These findings suggest that LBM protects pancreatic β-cells from palmitate-induced damage. LBM could be a potential therapeutic functional food for diabetes.

Direct differentiation of insulin-producing cells from human urine-derived stem cells

The loss of pancreatic β-cells is a cause of diabetes. Therefore, replacement of pancreatic β-cells is a logical strategy for the treatment of diabetes, and the generation of insulin-producing cells (IPCs) from stem cells has been widely investigated as an alternative source for pancreatic β-cells. Here, we isolated stem cells from human urine and investigated their differentiation potential into IPCs. We checked the expression of surface stem cell markers and stem cell transcription factors, and found that the isolated human urine-derived stem cells (hUDSCs) expressed the stem cell markers CD44, CD90, CD105 and stage-specific embryonic antigen (SSEA)-4. In addition, these cells expressed octamer binding transcription factor (Oct)4 and vimentin. hUDSCs could differentiate into adipocytes and osteocytes, as evidenced by Oil-red O staining and Alizarin Red S-staining of differentiated cells, respectively. When we directly differentiated hUDSCs into IPCs, the differentiated cells expressed mRNA for pancreatic transcription factors such as neurogenin (Ngn)3 and pancreatic and duodenal homeobox (Pdx)1. Differentiated IPCs expressed insulin and glucagon mRNA and protein, and these IPCs also secreted insulin in response to glucose stimulation. In conclusion, we found that hUDSCs can be directly differentiated into IPCs, which secrete insulin in response to glucose.

Glucagon-Like Peptide 1 Increases β-Cell Regeneration by Promoting α- to β-Cell Transdifferentiation

Glucagon-like peptide 1 (GLP-1) can increase pancreatic β-cells, and α-cells could be a source for new β-cell generation. We investigated whether GLP-1 increases β-cells through α-cell transdifferentiation. New β-cells originating from non-β-cells were significantly increased in recombinant adenovirus expressing GLP-1 (rAd-GLP-1)-treated RIP-CreER;R26-YFP mice. Proliferating α-cells were increased in islets of rAd-GLP-1-treated mice and αTC1 clone 9 (αTC1-9) cells treated with exendin-4, a GLP-1 receptor agonist. Insulin⁺glucagon⁺ cells were significantly increased by rAd-GLP-1 or exendin-4 treatment in vivo and in vitro. Lineage tracing to label the glucagon-producing α-cells showed a higher proportion of regenerated β-cells from α-cells in rAd-GLP-1-treated Glucagon-rtTA;Tet-O-Cre;R26-YFP mice than rAd producing β-galactosidase-treated mice. In addition, exendin-4 increased the expression and secretion of fibroblast growth factor 21 (FGF21) in αTC1-9 cells and β-cell-ablated islets. FGF21 treatment of β-cell-ablated islets increased the expression of pancreatic and duodenal homeobox-1 and neurogenin-3 and significantly increased insulin⁺glucagon⁺ cells. Generation of insulin⁺glucagon⁺ cells by exendin-4 was significantly reduced in islets transfected with FGF21 small interfering RNA or islets of FGF21 knockout mice. Generation of insulin⁺ cells by rAd-GLP-1 treatment was significantly reduced in FGF21 knockout mice compared with wild-type mice. We suggest that GLP-1 has an important role in α-cell transdifferentiation to generate new β-cells, which might be mediated, in part, by FGF21 induction.

Synthesis of Novel FTY720 Analogs with Anticancer Activity through PP2A Activation

FTY720 inhibits various cancers through PP2A activation. The structure of FTY720 is also used as a basic structure for the design of sphingosine kinase (SK) inhibitors. We have synthesized derivatives using an amide chain in FTY720 with a phenyl backbone, and then compounds were screened by an MTT cell viability assay. The PP2A activity of compound 7 was examined. The phosphorylation levels of AKT and ERK, downstream targets of PP2A, in the presence of compound 7, were determined. Compound 7 may exhibit anticancer effects through PP2A activation rather than the mechanism by inhibition of SK1 in cancer cells. In the docking study of compound 7 and PP2A, the amide chain of compound 7 showed an interaction with Asn61 that was different from FTY720, which is expected to affect the activity of the compound.

Palmitate induces nitric oxide production and inflammatory cytokine expression in zebrafish

Inflammation markers in zebrafish embryos reflect a toxic response that is common to other animal models and humans. Free fatty acids (FFAs) are known to cause damage in various tissues by inducing inflammation. In this study, we investigated whether a FFA (palmitate) induces inflammation in zebrafish embryos. Nitrous oxide (NO) production and cyclooxygenase-2 (COX-2) mRNA expression were increased in palmitate-treated zebrafish embryos in a dose-dependent manner. mRNA expression of pro-inflammatory cytokines, interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF- α), were also increased. Additionally, the mRNA expression of p65 nuclear factor-kB and I-kB-α were significantly increased after palmitate-treatment. Increased reactive oxygen species (ROS) expression was observed in palmitate-treated zebrafish embryos as well as pericardial edema. Additionally, mRNA expression of pro-inflammatory cytokines were increased in zebrafish liver and pancreas fed with palmitate-contained diet. Taken together, these results indicated that palmitate increases pro-inflammatory mediators in zebrafish embryos, suggesting that zebrafish could be an alternative animal model for inflammatory disease including diabetes.

Effects of FGF21-secreting adipose-derived stem cells in thioacetamide-induced hepatic fibrosis

Mesenchymal stem cells (MSCs) have been investigated to treat liver diseases, but the efficiency of MSCs to treat chronic liver diseases is conflicting. FGF21 can reduce inflammation and fibrosis. We established FGF21‐secreting adipose derived stem cells (FGF21_ADSCs) to enhance the effects of ADSCs and transplanted them into thioacetamide (TAA)‐induced liver fibrosis mice via the tail vein. Transplantation of FGF21_ADSCs significantly improved liver fibrosis by decreasing serum hyaluronic acid and reducing the expression of fibrosis‐related factors such as α‐smooth muscle actin (α‐SMA), collagen and tissue inhibitor of metalloproteinase‐1 (TIMP‐1) compared with the Empty_ADSCs by inhibition of p‐JNK, NF‐κB and p‐Smad2/3 signalling. α‐lactoalbumin (LA) and lactotransferrin (LTF), secretory factors produced from FGF21_ADSCs inhibited TGF‐β1‐induced expression of α‐SMA and collagen in LX‐2 cells. These results suggest that transplantation of FGF21_ADSCs inhibited liver fibrosis more effectively than Empty_ADSCs, possibly via secretion of α‐LA and LTF.

Smad4 in T cells plays a protective role in the development of autoimmune Sjögren's syndrome in the nonobese diabetic mouse

We investigated the role of Smad4, a signaling molecule of the TGF-beta pathway, in T cells on the pathology of Sjögren's syndrome (SS) in nonobese diabetic (NOD) mice, an animal model of SS. T cell-specific Smad4-deleted (Smad4^{fl/fl,CD4-Cre}; Smad4 tKO) NOD mice had accelerated development of SS compared with wild-type (Smad4^+/+,CD4-Cre; WT) NOD mice, including increased lymphocyte infiltration into exocrine glands, decreased tear and saliva production, and increased levels of autoantibodies at 12 weeks of age. Activated/memory T cells and cytokine (IFN-γ, IL-17)-producing T cells were increased in Smad4 tKO NOD mice, however the proportion and function of regulatory T (Treg) cells were not different between Smad4 tKO and WT NOD mice. Effector T (Teff) cells from Smad4 tKO NOD mice were less sensitive than WT Teff cells to suppression by Treg cells. Th17 differentiation capability of Teff cells was similar between Smad4 tKO and WT NOD mice, but IL-17 expression was increased under inducible Treg skewing conditions in T cells from Smad4 tKO NOD mice. Our results demonstrate that disruption of the Smad4 pathway in T cells of NOD mice increases Teff cell activation resulting in upregulation of Th17 cells, indicating that Smad4 in T cells has a protective role in the development of SS in NOD mice.

Anti-adipogenic effects of KD025 (SLx-2119), a ROCK2-specific inhibitor, in 3T3-L1 cells

Adipose tissue is a specialized organ that synthesizes and stores fat. During adipogenesis, Rho and Rho-associated kinase (ROCK) 2 are inactivated, which enhances the expression of pro-adipogenic genes and induces the loss of actin stress fibers. Furthermore, pan ROCK inhibitors enhance adipogenesis in 3T3-L1 cells. Here, we show that KD025 (formerly known as SLx-2119), a ROCK2-specific inhibitor, suppresses adipogenesis in 3T3-L1 cells partially through a ROCK2-independent mechanism. KD025 downregulated the expression of key adipogenic transcription factors PPARγ and C/EBPα during adipogenesis in addition to lipogenic factors FABP4 and Glut4. Interestingly, adipogenesis was blocked by KD025 during days 1~3 of differentiation; after differentiation terminated, lipid accumulation was unaffected. Clonal expansion occurred normally in KD025-treated cells. These results suggest that KD025 could function during the intermediate stage after clonal expansion. Data from depletion of ROCKs showed that KD025 suppressed cell differentiation partially independent of ROCK’s activity. Furthermore, no further loss of actin stress fibers emerged in KD025-treated cells during and after differentiation compared to control cells. These results indicate that in contrast to the pro-adipogenic effect of pan-inhibitors, KD025 suppresses adipogenesis in 3T3-L1 cells by regulating key pro-adipogenic factors. This outcome further implies that KD025 could be a potential anti-adipogenic/obesity agent.

Infrequent Feeding of Restricted Amounts of Food Induces Stress and Adipose Tissue Inflammation, Contributing to Impaired Glucose Metabolism

Food restriction has been recommended as an effective strategy for body weight loss. However, food restriction can alter biological rhythms and leads to physiological stress. However, relatively little is known about the physiological impact of different methods of food restriction. Therefore, we investigated whether different schedules of restricted food intake induce physiological stress and then contribute to glucose metabolism disorder. C57BL/6 mice were fed a high fat diet (60% fat) for 8 weeks and then randomly divided into three groups: the control group was continuously fed the high fat diet; the two food restriction groups were fed 50% of food consumed by the control mice with one group (FR1) being fed the full amount once a day and the other group (FR2) being fed the same total amount as FR1 twice a day for 3 days. We found increased body weight loss, the serum triglyceride levels, the expression of lipolysis-related genes, and serum corticosterone levels in the FR1 group compared with the FR2 group. The immune cell population infiltrating the adipose tissue and the expression of monocyte chemoattractant protein (MCP-1) and toll-like receptor (TLR-4) mRNA were increased in the FR1 group compared with the control. To determine whether long-term dietary manipulation is associated with metabolic disorders, mice were fed a restricted diet for 3 days alternating with an unrestricted diet for the following 4 days and this was repeated for 8 weeks. The alternating FR1 group showed impaired glucose tolerance compared with the alternating FR2 group. These results indicate that infrequent feeding of restricted amounts of food could induce stress hormones, lipolysis, adipose tissue immune cell infiltration and inflammation, which in turn may promote glucose metabolism disorder.

Fatty Acid-Induced Lipotoxicity in Pancreatic Beta-Cells During Development of Type 2 Diabetes

Type 2 diabetes is caused by chronic insulin resistance and progressive decline in beta-cell function. Optimal beta-cell function and mass is essential for glucose homeostasis and beta-cell impairment leads to the development of diabetes. Elevated levels of circulating fatty acids (FAs) and disturbances in lipid metabolism regulation are associated with obesity, and they are major factors influencing the increase in the incidence of type 2 diabetes. Chronic free FA (FFA) treatment induces insulin resistance and beta-cell dysfunction; therefore, reduction of elevated plasma FFA levels might be an important therapeutic target in obesity and type 2 diabetes. Lipid signals via receptors, and intracellular mechanisms are involved in FFA-induced apoptosis. In this paper, we discuss lipid actions in beta cells, including effects on metabolic pathways and stress responses, to help further understand the molecular mechanisms of lipotoxicity-induced type 2 diabetes.

Glucagon-Like Peptide-1 Receptor Agonist and Glucagon Increase Glucose-Stimulated Insulin Secretion in Beta Cells via Distinct Adenylyl Cyclases

Diabetes mellitus is a chronic disease in which the pancreas no longer produces enough insulin. Pancreatic alpha cell mass increases in response to insufficient insulin secretion. However, the reason for this increase is not clear. It is possible that the increased alpha-cells may stimulate compensatory insulin release in response to the insufficient insulin such as insulin resistance. In this study, we investigated whether glucagon and glucagon-like peptide-1 (GLP-1), hormones produced by alpha cells, contribute to insulin secretion in INS-1 cells, a beta cell line. We confirmed that alpha cell area in the pancreatic islets and glucagon secretion were increased in HFD-induced obese mice. Co-treatment with glucagon and exendin-4 (Ex-4), a GLP-1 receptor agonist, additively increased glucose-stimulated insulin secretion in INS-1 cells. In parallel, cAMP production was also additively increased by co-treatment with these hormones. The increase of insulin secretion by Ex-4 in the presence of high glucose was inhibited by 2'5'-dideoxyadenosine, a transmembrane adenylyl cyclase inhibitor, but not by KH-7, a soluble adenylyl cyclase inhibitor. The increase of insulin secretion by glucagon in INS-1 cells was inhibited by both 2'5'-dideoxyadenosine and KH-7. We suggest that glucagon and GLP-1 produced from alpha cells additively increase cAMP and insulin secretion in the presence of high glucose via distinct adenylyl cyclases in INS-1 cells, and this may contribute to the compensatory increase of insulin secretion by an increase of pancreatic alpha cell mass under conditions of insulin resistance.

Effects of Glucagon-Like Peptide-1 on Oxidative Stress and Nrf2 Signaling

Oxidative cellular damage caused by free radicals is known to contribute to the pathogenesis of various diseases such as cancer, diabetes, and neurodegenerative diseases, as well as to aging. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and Kelch-like ECH-associated protein1 (Keap1) signaling pathways play an important role in preventing stresses including oxidative and inflammatory stresses. Nrf2 is a master regulator of cellular stress responses, induces the expression of antioxidant and detoxification enzymes, and protects against oxidative stress-induced cell damage. Glucagon-like peptide-1 (GLP-1) is an incretin hormone, which was originally found to increase insulin synthesis and secretion. It is now widely accepted that GLP-1 has multiple functions beyond glucose control in various tissues and organs including brain, kidney, and heart. GLP-1 and GLP-1 receptor agonists are known to be effective in many chronic diseases, including diabetes, via antioxidative mechanisms. In this review, we summarize the current knowledge regarding the role of GLP-1 in the protection against oxidative damage and the activation of the Nrf2 signaling pathway.

Short Synthesis of the Antidiabetic Octaketide Ethyl 2-(2,3,4-Trimethoxy-6-octanoylphenyl)acetate

A facile and practical approach for the synthesis of ethyl 2-(2,3,4-trimethoxy-6-octanoylphenyl)acetate, an antidiabetic octaketide analogue of cytosporone B, is described. Unlike known approaches for the synthesis of cytosporones and their analogues, the key step of the developed route is a Friedel–Crafts alkylation of 1-(3,4,5-trimethoxyphenyl)octan-1-one with ethyl chloro(methylthio)acetate, followed by desulfurization.