Takanori Shinjo

DPP-IV inhibitor anagliptin exerts anti-inflammatory effects on macrophages, adipocytes, and mouse livers by suppressing NF-κB activation

Dipeptidyl peptidase IV (DPP-IV) expression in visceral adipose tissue is reportedly increased in obese patients, suggesting an association of DPP-IV with inflammation. In this study, first, lipopolysaccharide (LPS)- or palmitate-induced elevations of inflammatory cytokine mRNA expressions in RAW264.7 macrophages were shown to be significantly suppressed by coincubation with a DPP-IV inhibitor, anagliptin (10 μM), despite low DPP-IV expression in the RAW264.7 cells. Regarding the molecular mechanism, LPS-induced degradation of IκBα and phosphorylations of p65, JNK, and p38, as well as NF-κB and AP-1 promoter activities, were revealed to be suppressed by incubation with anagliptin, indicating suppressive effects of anagliptin on both NF-κB and AP-1 signaling pathways. Anagliptin also acted on 3T3-L1 adipocytes, weakly suppressing the inflammatory cytokine expressions induced by LPS and TNFα. When 3T3-L1 and RAW cells were cocultured and stimulated with LPS, the effects of anagliptin on the suppression of cytokine expressions in 3T3-L1 adipocytes were more marked and became evident at the 10 μM concentration. Anti-inflammatory effects of anagliptin were also observed in vivo on the elevated hepatic and adipose expressions and serum concentrations of inflammatory cytokines in association with the suppression of hepatic NF-κB transcriptional activity in LPS-infused mice. Taking these observations together, the anti-inflammatory properties of anagliptin may be beneficial in terms of preventing exacerbation of diabetes and cardiovascular events.

Mosapride citrate improves nonalcoholic steatohepatitis with increased fecal lactic acid bacteria and plasma glucagon-like peptide-1 level in a rodent model

Several lines of evidence have suggested a role of gut microbiota in the etiology of nonalcoholic steatohepatitis (NASH). NASH subjects reportedly showed a prolonged orocecal transit time coexistent with small intestinal bacterial overgrowth. We considered the possibility that enhanced gastrointestinal motility would influence gut microbiota and thus investigated the effects of the gastroprokinetic agent mosapride citrate (MC) on gut microbiota and the development of NASH using a methionine-choline deficient (MCD) diet-fed rodent model. Mice were divided into three groups, given the normal chow diet (NCD), the MCD diet, or the MCD diet containing 10 mg·kg(-1)·day(-1) of MC (MCD plus MC) for 6 wk. NASH development was evaluated based on hepatic histochemical findings, serum parameters and various mRNA and/or protein expression levels. MC treatment suppressed MCD diet-induced NASH development, with reduced serum lipopolysaccharide and increased plasma glucagon-like peptide-1 (GLP-1) concentrations. Calculation of the relative abundance of each strain based on gut microbiota analyses indicated lactic acid bacteria specifically, such as Bifidobacterium and Lactobacillus, in feces to be decreased in the MCD, compared with the NCD group. Interestingly, the reduction in lactic acid bacteria in the MCD diet group was reversed in the MCD plus MC group. In addition, colon inflammation observed in the MCD diet group was reduced in the MCD plus MC group. Therefore, MC showed a protective effect against MCD diet-induced NASH development in our rodent model, with possible involvements of increased fecal lactic acid bacteria, protection against colon inflammation and elevated plasma GLP-1.

Protection from diet-induced obesity and insulin resistance in mice lacking CCL19-CCR7 signaling

Several chemokines play important roles in recruiting the monocyte/macrophage lineage into adipose tissues. We previously found CCL19 was highly expressed in adipocytes cocultured with macrophages stimulated by endotoxin. This study aimed to evaluate the role of CCL19‐CCR7 axis on obesity and insulin resistance.

Par14 protein associates with insulin receptor substrate 1 (IRS-1), thereby enhancing insulin-induced IRS-1 phosphorylation and metabolic actions.

Background: Par14 is a parvulin-type peptidyl-prolyl cis/trans isomerase homologous with Pin1, but its functions remain largely unknown. Results: Par14 markedly enhanced insulin signaling by associating with IRS-1, and hepatic overexpression of Par14 normalized hyperglycemia in diabetic mice. Conclusion: Par14 exhibits an insulin-sensitizing effect. Significance: This is the first report showing the roles of Par14 in metabolism and signal transduction. Pin1 and Par14 are parvulin-type peptidyl-prolyl cis/trans isomerases. Although numerous proteins have been identified as Pin1 substrates, the target proteins of Par14 remain largely unknown. Par14 expression levels are increased in the livers and embryonic fibroblasts of Pin1 KO mice, suggesting a compensatory relationship between the functions of Pin1 and Par14. In this study, the association of Par14 with insulin receptor substrate 1 (IRS-1) was demonstrated in HepG2 cells overexpressing both as well as endogenously in the mouse liver. The analysis using deletion-mutated Par14 and IRS-1 constructs revealed the N-terminal portion containing the basic domain of Par14 and the two relatively C-terminal portions of IRS-1 to be involved in these associations, in contrast to the WW domain of Pin1 and the SAIN domain of IRS-1. Par14 overexpression in HepG2 markedly enhanced insulin-induced IRS-1 phosphorylation and its downstream events, PI3K binding with IRS-1 and Akt phosphorylation. In contrast, treating HepG2 cells with Par14 siRNA suppressed these events. In addition, overexpression of Par14 in the insulin-resistant ob/ob mouse liver by adenoviral transfer significantly improved hyperglycemia with normalization of hepatic PEPCK and G6Pase mRNA levels, and gene suppression of Par14 using shRNA adenovirus significantly exacerbated the glucose intolerance in Pin1 KO mice. Therefore, although Pin1 and Par14 associate with different portions of IRS-1, the prolyl cis/trans isomerization in multiple sites of IRS-1 by these isomerases appears to be critical for efficient insulin receptor-induced IRS-1 phosphorylation. This process is likely to be one of the major mechanisms regulating insulin sensitivity and also constitutes a potential therapeutic target for novel insulin-sensitizing agents.

The inflammation–lipocalin 2 axis may contribute to the development of chronic kidney disease

BACKGROUND Chronic kidney disease (CKD) is an important risk factor for coronary heart disease, and previous studies indicated the involvement of low-grade inflammation in the pathogenesis of CKD. METHODS The study was designed to (i) identify and confirm genes and their products upregulated in mesangial cells cocultured with endotoxin-stimulated macrophages and (ii) determine the clinical relevance of genes and proteins upregulated in mesangial cells under inflammatory conditions by an epidemiological approach. RESULTS DNA microarray analysis revealed upregulated expression of many genes and their products including several cytokines and chemokines, as well as the inflammatory marker, lipocalin 2 gene. The gene expression and protein upregulation of lipocalin 2 were synergistically affected by endotoxin and tumor necrosis factor (TNF)-α stimulation. In human studies, lipocalin 2 level was significantly associated with creatinine (r = 0.419, P < 0.001) and negatively associated with eGFR (r = -0.365, P < 0.001). Multiple logistic regression analysis revealed a significant association between lipocalin 2 and soluble tumor necrosis factor receptor 2 (sTNF-R2), eGFR and uric acid in general subjects attending regular annual medical check-up (n = 420). When subjects with diabetes were excluded from the analysis, lipocalin 2 remained associated with sTNF-R2, eGFR and uric acid. CONCLUSIONS Since an activated TNF system, as demonstrated by elevated sTNF-R2, and elevated uric acid were recently implicated in an elevated CKD risk, we conclude that inflammation could play an important role in the pathogenesis of CKD, and that lipocalin 2 is a potential universal marker for impaired kidney function. Furthermore, the results obtained by the current microarray analysis could improve the understanding of gene profiles associated with the pathophysiology of CKD under inflammatory conditions.

Valsartan restores inflammatory response by macrophages in adipose and hepatic tissues of LPS-infused mice.

Inflammation involving adipose tissue is regarded as one of the major molecular mechanisms underlying obesity-related insulin resistance. Recent studies have suggested a series of angiotensin II receptor blockers (ARBs) to improve insulin resistance or protect against the development of diabetes mellitus. We previously demonstrated that valsartan suppresses the inflammatory response of macrophages. Interestingly, however, this effect did not occur via peroxisome proliferator-activated receptor (PPAR) γ or the AT1a receptor. This suppression appears to secondarily lead to amelioration of insulin resistance and reductions in abnormal gene expressions in adipocytes. In addition to these in vitro findings, we herein demonstrate the in vivo effects of valsartan, using mice constitutively infused with lipopolysaccharide (LPS) for 4 weeks. Oral administration of valsartan to LPS-infused mice normalized the increased expressions of inflammatory cytokines in adipose and liver tissues. These results raise the possibility that valsartan not only contributes to normalization of obesity-related insulin resistance, but is also beneficial for the treatment of other diseases with inflammation related to the metabolic syndrome such as atherosclerosis and non-alcoholic steatohepatitis. Further study is necessary to clarify these issues.

Angiopoietin-like protein 2 is a positive regulator of osteoblast differentiation

INTRODUCTION AND AIMS Several studies have reported that angiopoietin-like protein 2 (Angptl2) is expressed abundantly in adipocytes and is associated with adipose tissue inflammation. In the present study, we found that osteoblasts and mesenchymal stem cells also expressed Angptl2 at high levels. The aim of this study was to understand the role of Angptl2 in osteoblastic cell differentiation. METHODS Angptl2 expression was examined during osteoblast and adipocyte differentiation. The role of Angptl2 on cell differentiation and associated signaling was analyzed by gene knockdown using Angptl2 small interfering ribonucleic acid (siRNA). RESULTS Angptl2 was highly expressed in MC3T3-E1 cells, ST2 cells and primary osteoblasts, but not in RAW264 cells. Inhibition of Angptl2 expression using siRNA markedly inhibited alkaline phosphatase (ALP) expression and osteoblastic differentiation in MC3T3-E1, ST2 cells and primary osteoblasts. Angptl2 siRNA also inhibited adipocyte differentiation in ST2 cells. Treatment of MC3T3-E1 cells with Angptl2 siRNA led to the down-regulation of the activities of several cell signaling pathways, including extracellular signal-regulated kinase (ERK), Jun amino-terminal kinase (JNK), Akt, and nuclear factor kappa B (NF-κB) signals. It also down-regulated the expression of Osterix, but not that of runt-related transcription factor 2 (Runx2), suggesting that Angptl2 is a positive activator of Osterix and its down-stream signals. Treatment of MC3T3-E1 cells with anti-Angptl2 antibodies suppressed ALP gene expression. In addition, treatment of Angptl2 siRNA-treated cells with culture supernatants of normal MC3T3-E1 cells restored ALP gene expression, indicating that Angptl2 acts in an autocrine manner. CONCLUSIONS The results suggest that Angptl2 is an autocrine positive regulator of cell differentiation. Thus, it is suggested that Angptl2 regulates not only adipose tissue metabolism but also bone metabolism.

High-fat diet feeding significantly attenuates anagliptin-induced regeneration of islets of Langerhans in streptozotocin-induced diabetic mice

BackgroundDPP-4 inhibitors reportedly exert effects on both alpha and beta cells, and promote the proliferation and survival of beta cells. We investigated the effects of anagliptin on structurally-impaired islets of Langerhans in streptozotocin (STZ)-treated mice, fed either a normal or a high-fat diet. Pdx-1 expression in the pancreas and serum insulin/glucagon concentrations were also examined.FindingsAnagliptin treatment significantly up-regulated pancreatic Pdx-1 expression, with elevated serum glucagon-like peptide-1 concentrations, regardless of whether the diet was normal or high-fat. However, interestingly, the beta cell regeneration, structural normalization of islets of Langerhans including alpha cell: beta cell area ratios, and serum insulin elevation, all observed with anagliptin administration in the animals fed a normal diet, were markedly suppressed in the high-fat fed group.ConclusionsHigh-fat diet feeding clearly weakened the regenerative effects of anagliptin on the islets of Langerhans in STZ-treated mice. Our findings suggest the importance of normalizing lipid metabolism for full manifestation of DPP-4 inhibitor effects on the islets of Langerhans.

Exogenous Insulin Infusion Can Decrease Atherosclerosis in Diabetic Rodents by Improving Lipids, Inflammation, and Endothelial Function

Objective— The objective of this study is to evaluate whether exogenously induced hyperinsulinemia may increase the development of atherosclerosis. Approach and Results— Hyperinsulinemia, induced by exogenous insulin implantation in high-fat fed (60% fat HFD) apolipoprotein E–deficient mice (ApoE−/−) mice, exhibited insulin resistance, hyperglycemia, and hyperinsulinemia. Atherosclerosis was measured by the accumulation of fat, macrophage, and extracellular matrix in the aorta. After 8 weeks on HFD, ApoE−/− mice were subcutaneously implanted with control (sham) or insulin pellet, and phlorizin, a sodium glucose cotransporters inhibitor (1/2)inhibitor, for additional 8 weeks. Intraperitoneal glucose tolerance test showed that plasma glucose levels were lower and insulin and IGF-1 (insulin-like growth factor-1) levels were 5.3- and 3.3-fold higher, respectively, in insulin-implanted compared with sham-treated ApoE−/− mice. Plasma triglyceride, cholesterol, and lipoprotein levels were decreased in mice with insulin implant, in parallel with increased lipoprotein lipase activities. Atherosclerotic plaque by en face and complexity staining showed significant reductions of fat deposits and expressions of vascular adhesion molecule-1, tumor necrosis factor-&agr;, interleukin 6, and macrophages in arterial wall while exhibiting increased activation of pAKT and endothelial nitric oxide synthase (P<0.05) comparing insulin-implanted versus sham HFD ApoE−/− mice. No differences were observed in atherosclerotic plaques between phlorizin-treated and sham HFD ApoE−/− mice, except phlorizin significantly lowered plasma glucose and glycated hemoglobin levels while increased glucosuria. Endothelial function was improved only by insulin treatment through endothelial nitric oxide synthase/nitric oxide activations and reduced proinflammatory (M1) and increased anti-inflammatory (M2) macrophages, which were inhibited by endothelial nitric oxide synthase inhibitor. Conclusions— Exogenous insulin decreased atherosclerosis by lowering inflammatory cytokines, macrophages, and plasma lipids in HFD-induced hyperlipidemia, insulin resistant and mildly diabetic ApoE−/− mice.

Metabolic Endotoxemia-Activated Macrophages Promote Pancreatic β Cell Death via IFNβ-Xaf1 Pathway

Metabolic endotoxemia has been implicated in the pathogenesis of type 2 diabetes. In addition to adipose tissue inflammation, inflammatory cell infiltration is also observed in islets, although its effect on islets is largely unknown. We hypothesized that macrophage infiltration into islets leads to impairment of α or β cell function, which ultimately act to exacerbate the pathophysiology of diabetes. Gene expression in a murine α cell line, αTC1, and β cell line, βTC6, was investigated by DNA microarray after co-culturing the cells with a murine macrophage cell line, RAW 264.7, in the presence or absence of bacterial endotoxin. Among the genes showing highly upregulated expression, genes specifically upregulated only in β cells were evaluated to determine the roles of the gene products on the cellular function of β cells. In both α and β cells, expression of type I interferon-responsive genes was highly upregulated upon endotoxin stimulation. Among these genes, expression of the X-linked inhibitor of apoptosis (Xiap)-associated factor 1 (Xaf1) gene, which is associated with the induction of apoptosis, was specifically enhanced in β cells by endotoxin stimulation. This upregulation appeared to be mediated by macrophage-derived interferon β (IFNβ), as endotoxin-stimulated macrophages produced higher amounts of IFNβ, and exogenous addition of IFNβ into βTC6 cultures resulted in increased Xaf1 protein production and cleaved caspase 3, which accelerated β-cell apoptosis. Macrophages activated by metabolic endotoxemia infiltrated into islets and produced IFNβ, which induced β-cell apoptosis by increasing the expression of Xaf1.