HIT-T15 Cells Research Articles

Isoquinoline alkaloids from Corydalis edulis Maxim. Exhibiting insulinotropic action

Eleven undescribed isoquinoline analogues, namely edulisines A–K, along with sixteen known alkaloids, were isolated from the whole plants of Corydalis edulis. The structures of the isolated alkaloids were established on the basis of extensive spectroscopic data (1D and 2D NMR, UV, IR, and HRESIMS). Their absolute configurations were determined by single-crystal X-ray crystallographic analysis and ECD. Compounds (+)-1 and (−)-1 are a pair of undescribed isoquinoline alkaloids bearing a unique coupled pattern of coptisine and ferulic acid via Diels-Alder [4 + 2] cycloaddition, while compounds (+)-2 and (−)-2 feature benzo [1,2-d:3,4-d]bis [1,3]dioxole moiety. Compounds (+)-2, (−)-2, (−)-5, 10, 13, 15, 20, 22, and 23 significantly triggered the secretion of insulin in the HIT-T15 cells at a concentration of 40 μM.

Evolution of Nrf2 Gene Expression in HIT-T15 β-Cells During Chronic Oxidative Stress and Glucose Toxicity.

Chronic exposure of pancreatic islets to elevated glucose levels causes progressive declines in beta cell Pdx-1 and insulin gene expression, and glucose-induced insulin secretion. This has been shown to be associated with excessive islet reactive oxygen species and consequent damage to beta cell function, a process termed glucose toxicity. In short-term rodent in vivo studies, Nrf2 (Kelch-like ECH-associated protein 1:nuclear factor erythroid-derived-2 related factor complex) has been shown to play a central role in defending beta cells from oxidative damage via activation of antioxidant gene expression. The current studies were primarily designed to examine the behavior of Nrf2 gene expression during longer term exposure of beta cells to glucose toxicity. We provide evidence that gene expression of Nrf2 in HIT-T15 cells, an insulin-secreting beta-cell line, undergoes a biphasic response characterized by an initial decrease followed by increased expression during prolonged culturing of these cells in a physiologic (0.8 mM) but not a supraphysiologic (16.0 mM) glucose concentration. This was associated with a slight rise in HO-1 gene expression. Pdx-1 and insulin mRNA levels also decreased but then stabilized in late passages of cells that had been cultured in low glucose concentrations. These complex events support the concept that Nrf2 gene expression plays an important regulatory role in defending beta cells during prolonged exposure to oxidative stress.

Antidiabetic compounds 8a, 8b, 8k, and 9h enhance insulin secretion: activity and mechanism.

This study primarily investigated the effects of hypoglycemic compounds (Imeglimin derivatives) on insulin secretion in type 2 diabetes mellitus (T2DM), and further explored the possible mechanism underlying these effects. Firstly, Metformin was used as the initiating compound to synthesize three sets of derivatives which contained Imeglimin structure core. At the cellular level, we screened compounds with better effect on the activity of insulin receptor tyrosine protein kinase (IFcTPK) after the islet β cells were treated with the compounds of different concentrations. The insulin secretion was assessed using radioimmunoassay and the cytotoxicity to islet β cells was evaluated by means of MTT assay following treatment with the compounds. The Ca2+-related mechanism by which these compounds promote insulin secretion was elucidated with whole cell recordings from current-clamp mode. Totally, 48 synthesized compounds were generated, wherein 10 compounds could increase the activity of IFcTPK in HIT-T15 cells better among these compounds. The modified Imeglimin, especially in the structure of hydrophilic hydroxyl or piperidine rings, could improve the activity of the compound to promote insulin secretion. Furthermore, the compounds 8a, 8b, 8k, and 9h revealed high insulin secretion-promoting activity. These compounds enhanced insulin secretion in islet β cells by repressing the ATP-sensitive K(+) and voltage-gated K+ pathway. Our findings indicate that the hypoglycemic compounds 8a, 8b, 8k, and 9h confer better promotive effect on insulin secretion, which provides a reference for the development of drugs with better hypoglycemic activity.

Silk Fibroin Promotes the Regeneration of Pancreatic β-Cells in the C57BL/KsJ-Leprdb/db Mouse.

Diabetes mellitus is a chronic metabolic disease, and its progression leads to serious complications. Although various novel therapeutic approaches for diabetes mellitus have developed in the last three decades, its prevalence has been rising more rapidly worldwide. Silk-related materials have been used as anti-diabetic remedies in Oriental medicine and many studies have shown the effects of silk fibroin (SF) in both in vitro and in vivo models. In our previous works, we reported that hydrolyzed SF improved the survival of HIT-T15 cells under high glucose conditions and ameliorated diabetic dyslipidemia in a mouse model. However, we could not provide a precise molecular mechanism. To further evaluate the functions of hydrolyzed SF on the pancreatic β-cell, we investigated the effects of hydrolyzed SF on the pancreatic β-cell proliferation and regeneration in the mouse model. Hydrolyzed SF induced the expression of the proliferating cell nuclear antigen (PCNA) and reduced the apoptotic cell population in the pancreatic islets. Hydrolyzed SF treatment not only induced the expression of transcription factors involved in the pancreatic β-cell regeneration in RT-PCR results but also increased neurogenin3 and Neuro D protein levels in the pancreas of those in the group treated with hydrolyzed SF. In line with this, hydrolyzed SF treatment generated insulin mRNA expressing small cell colonies in the pancreas. Therefore, our results suggest that the administration of hydrolyzed SF increases the pancreatic β-cell proliferation and regeneration in C57BL/KsJ-Leprdb/db mice.

Blockade of multiple monoamines receptors reduce insulin secretion from pancreatic \u03b2-cells

Clinical use of olanzapine frequently causes severe hyperglycemia as an adverse effect. In this study, we elucidated mechanisms by which olanzapine reduced insulin secretion using the hamster pancreatic β-cell line HIT-T15. Reverse transcriptional-PCR analysis revealed expression of dopamine (D2, D3 and D4), serotonin (5-HT2A, 5-HT2B, 5-HT2C, and 5-HT6), and histamine (H1 and H2) receptors in HIT-T15 cells. Olanzapine decreased insulin secretion from HIT-T15 cells at clinically relevant concentrations (64–160 nM). A dopamine D2 agonist, D3 antagonist, and D4 antagonist suppressed insulin secretion, whereas a D2 antagonist and D3 agonist increased it. A serotonin 5-HT2B agonist slightly increased insulin secretion, while a 5-HT2C antagonist slightly decreased it. Other agonists and antagonists for serotonin receptors did not affect insulin secretion. A histamine H1 agonist increased insulin secretion, whereas an H1 antagonist and H2 agonist suppressed it. Our results suggest that dopamine (D2, D3 and D4), serotonin (5-HT2B and 5-HT2C), and histamine (H1 and H2) receptors, which are expressed on pancreatic β-cells, directly modulate insulin secretion from pancreatic β-cells. Thus, olanzapine may induce hyperglycemia in clinical settings by suppressing insulin secretion from pancreatic β-cells through inhibition of dopamine D3, serotonin 5-HT2B and 5-HT2C, and histamine H1 receptors.

Repression of insulin gene transcription by indirect genomic signaling via the estrogen receptor in pancreatic beta cells

The mechanism whereby 17β-estradiol (E2) mediates insulin gene transcription has not been fully elucidated. In this study, exposure of hamster insulinoma (HIT-T15) cells to 5 × 10−9 to 1 × 10−7 M E2 led to a concentration-dependent decrease of insulin mRNA levels. Transient expression of the estrogen receptor (ER) in HIT-T15 cells revealed that estrogen receptor α (ERα) repressed transcription of the rat insulin II promoter in both ligand-dependent and ligand-independent manners. The N-terminal A/B domain of ERα was not required for either activity. However, the repression was absent with mutated ER lacking the DNA-binding domain. Moreover, introducing mutations in the D-box and P-box of the zinc finger of ER (C227S, C202L) also abolished the repression. Deletion of the insulin promoter region revealed that nucleotide positions − 238 to − 144 (relative to the transcriptional start site) were needed for ER repression of the rat insulin II gene. PDX1- and BETA2-binding sites were required for the repression, but an estrogen response element-like sequence or an AP1 site in the promoter was not involved. In conclusion, we found that estrogen repressed insulin mRNA expression in a beta cell line. In addition, the ER suppressed insulin gene transcription in a ligand-independent matter. These observations suggest ER may regulate insulin transcription by indirect genomic signaling.

LC-MS-Guided Isolation of Insulin-Secretion-Promoting Monoterpenoid Carbazole Alkaloids from Murraya microphylla.

Fifteen new structurally unique monoterpenoid carbazole alkaloids, including two pairs of epimers (1/2 and 3/4), three pairs of enantiomers (6a/6b, 7a/7b, and 8a/8b), and five optically pure analogues (5, 9-12), were obtained from a 95% aqueous EtOH extract of Murraya microphylla by a combination of bioassay- and LC-MS-guided fractionation procedures. Their structures were established based on NMR and HRESIMS data interpretation. The absolute configuration of compound 1 was determined via X-ray crystallographic data analysis and for all compounds by comparison of experimental and calculated ECD data. Compounds 1-5 were assigned as five new thujane-carbazole alkaloids, and compounds 6-12 as 10 new menthene-carbazole alkaloids linked through an ether or carbon-carbon bond. Compounds 1-12 promoted insulin secretion in the HIT-T15 cell line, 1.9-3.1-fold higher than the gliclazide control at 100 μM.

Bioactive carbazole and quinoline alkaloids from Clausena dunniana

Nine undescribed carbazole and quinoline alkaloids, named dunnines A–E, and 14 known analogues were isolated from the leaves and stems of Clausena dunniana. Their structures were elucidated on the basis of comprehensive analysis of NMR and HRMS spectroscopic data, and the absolute configurations were assigned via comparison of their specific rotations and calculated and experimental ECD data. (±)-Dunnines A–C and (±)-clausenawalline A are four pairs of biscarbazole atropisomers and (±)-dunnine D is a pair of dihydropyranocarbazole enantiomers. They were separated by chiral HPLC to obtain the optically pure compounds. Three compounds showed weak inhibitory effects on nitric oxide production stimulated by lipopolysaccharide in BV-2 microglial cells (IC50 > 50 μM); five compounds could significantly promote insulin secretion in HIT-T15 cell line (1.9–3.1-fold of the control, p < 0.01) at 40 μM, and nine compounds could inhibit the apoptosis of PC12 cell induced by 6-hydroxydopamine with IC50 values in the range of 10.9–47.2 μM.

YH18968, a Novel 1,2,4-Triazolone G-Protein Coupled Receptor 119 Agonist for the Treatment of Type 2 Diabetes Mellitus.

G protein-coupled receptor 119 (GPR119) is expressed in the pancreas and gastrointestinal tract, and its activation promotes insulin secretion in the beta cells of the pancreatic islets as well as the secretion of glucagon-like peptide-1 (GLP-1) in intestinal L cells, consequently improving glucose-stimulated insulin secretion. Due to this dual mechanism of action, the development of small-molecule GPR119 agonists has received significant interest for the treatment of type 2 diabetes. We newly synthesized 1,2,4-triazolone derivatives of GPR119 agonists, which demonstrated excellent outcomes in a cyclic adenosine monophosphate (cAMP) assay. Among the synthesized derivatives, YH18968 showed cAMP=2.8 nM; in GLUTag cell, GLP-1secretion=2.3 fold; in the HIT-T15 cell, and insulin secretion=1.9 fold. Single oral administration of YH18968 improved glucose tolerance and combined treatment with a dipeptidyl peptidase 4 (DPP-4) inhibitor augmented the glucose lowering effect as well as the plasma level of active GLP-1 in normal mice. Single oral administration of YH18968 improved glucose tolerance in a diet induced obese mice model. This effect was maintained after repeated dosing for 4 weeks. The results indicate that YH18968 combined with a DPP-4 inhibitor may be an effective therapeutic candidate for the treatment of type 2 diabetes.

207 - Mechanism Underlying 2-Deoxy-D-Ribose-Induced Oxidative Damage in a Pancreatic Beta-Cell Line

2-Deoxy- d -ribose (dRib) is known to induce oxidative damage and apoptosis by depleting GSH content in several types of cells. However, little is known about how dRib depletes intracellular GSH content. We hypothesized that dRib would deplete GSH content through inhibition of cystine uptake via system χc-. HIT-T15 cells were incubated with various concentrations of dRib, 2-mercaptoethanol (2-ME), Sulfasalazine (SASP), and homocysteic acid (HCA). We measured intracellular uptake of l -[14C]cystine, GSH content, and cell viability. Stimulation with dRib dose- and time-dependently decreases intracellular l -[14C]cystine uptake and GSH content. The addition of 2-ME, a cystine uptake enhancer, fully recovered the dRib-induced decreases in l -[14C]cystine uptake, GSH content, and cell viability. The 2-ME promoted the l -[14C]cystine uptake even in the absence of extracellular Na+, probably suggesting the involvement of the system χc-. SASP and HCA, system χc- inhibitors, significantly reduced l -[14C]cystine uptake and GSH content like dRib did, and 2-ME also restored the reductions. These findings suggest that dRib depletes intracellular GSH content through inhibition of cystine transport, and this inhibition may be mediated by system χc-. Additional experiments using a gene overexpression technique is necessary to further clarify the mechanism.

Protein kinase- and lipase inhibitors of inositide metabolism deplete IP7 indirectly in pancreatic β-cells: Off-target effects on cellular bioenergetics and direct effects on IP6K activity

Inositol pyrophosphates have emerged as important regulators of many critical cellular processes from vesicle trafficking and cytoskeletal rearrangement to telomere length regulation and apoptosis. We have previously demonstrated that 5-di-phosphoinositol pentakisphosphate, IP7, is at a high level in pancreatic β-cells and is important for insulin exocytosis. To better understand IP7 regulation in β-cells, we used an insulin secreting cell line, HIT-T15, to screen a number of different pharmacological inhibitors of inositide metabolism for their impact on cellular IP7. Although the inhibitors have diverse targets, they all perturbed IP7 levels. This made us suspicious that indirect, off-target effects of the inhibitors could be involved. It is known that IP7 levels are decreased by metabolic poisons. The fact that the inositol hexakisphosphate kinases (IP6Ks) have a high Km for ATP makes IP7 synthesis potentially vulnerable to ATP depletion. Furthermore, many kinase inhibitors are targeted to the ATP binding site of kinases, but given the similarity of such sites, high specificity is difficult to achieve. Here, we show that IP7 concentrations in HIT-T15 cells were reduced by inhibitors of PI3K (wortmannin, LY294002), PI4K (Phenylarsine Oxide, PAO), PLC (U73122) and the insulin receptor (HNMPA). Each of these inhibitors also decreased the ATP/ADP ratio. Thus reagents that compromise energy metabolism reduce IP7 indirectly. Additionally, PAO, U73122 and LY294002 also directly inhibited the activity of purified IP6K. These data are of particular concern for those studying signal transduction in pancreatic β-cells, but also highlight the fact that employment of these inhibitors could have erroneously suggested the involvement of key signal transduction pathways in various cellular processes. Conversely, IP7’s role in cellular signal transduction is likely to have been underestimated.

Corydalis edulis Maxim. Promotes Insulin Secretion via the Activation of Protein Kinase Cs (PKCs) in Mice and Pancreatic \u03b2 Cells

Corydalis edulis Maxim., a widely grown plant in China, had been proposed for the treatment for type 2 diabetes mellitus. In this study, we found that C. edulis extract (CE) is protective against diabetes in mice. The treatment of hyperglycemic and hyperlipidemic apolipoprotein E (ApoE)−/− mice with a high dose of CE reduced serum glucose by 28.84% and serum total cholesterol by 17.34% and increased insulin release. We also found that CE significantly enhanced insulin secretion in a glucose-independent manner in hamster pancreatic β cell (HIT-T15). Further investigation revealed that CE stimulated insulin exocytosis by a protein kinase C (PKC)-dependent signaling pathway and that CE selectively activated novel protein kinase Cs (nPKCs) and atypical PKCs (aPKCs) but not conventional PKCs (cPKCs) in HIT-T15 cells. To the best of our knowledge, our study is the first to identify the PKC pathway as a direct target and one of the major mechanisms underlying the antidiabetic effect of CE. Given the good insulinotropic effect of this herbal medicine, CE is a promising agent for the development of new drugs for treating diabetes.

Effect of protein kinase C on glucose-mediated insulin secretion in HIT-T15 cells.

To clarify the regulation of protein kinase C on glucose-mediated insulin secretion. We examined the effect of protein kinase C on the cytosolic free Ca(2+) concentration ([Ca(2+)]i) and the activity of Ca(2+)-activated K(+) channels (K(Ca)-channel) in the insulinoma cell line, HIT-T15. Glucose at a concentration of 10 mmol/L increased the secretion of insulin. This increase was partly inhibited by 1 nmol/L staurosporine, a protein kinase C inhibitor. Staurosporine (1 nmol/L) also attenuated the glucose-induced elevations in [Ca(2+)]i. On the contrary, glibenclamide (100 nmol/L) specifically blocked ATP-sensitive K(+) channels, and increased both [Ca(2+)]i and insulin secretion, but staurosporine had no effect on them. Patch clamp studies showed that 10 mmol/L glucose almost completely blocked K(Ca) channel activity, an effect that was reversed by 1 nmol/L staurosporine. Phorbol 12-myristate 13-acetate (1 mmol/L), a protein kinase C activator, also decreased K(Ca) channel activity. These results indicate that the activation of protein kinase C is involved in the glucose-induced release of insulin by modulating K(+) channel function in HIT-T15 cells.

The effect of gliquidone on KATP channels in pancreatic β-cells, cardiomyocytes, and vascular smooth muscle cells

AimsSulfonylurea drugs exert an insulinotropic effect through ATP-sensitive potassium (KATP) channel inhibition in pancreatic islet cells. These channels are also expressed in cardiomyocytes and vascular smooth muscle cells (VSMCs), suggesting potential for adverse cardiovascular effects. We evaluated the effects of Gliquidone (Glq) on sulfonylurea receptors in HIT-T15 cells (SUR1), cardiomyocytes (SUR2A), and VSMCs (SUR2B). MethodsThe concentration-dependent effects of Glq (0.001–500μM) on KATP channels were assessed using whole-cell patch clamp in HIT-T15 cells, rat cardiomyocytes, and VSMCs. Parallel studies using Glibenclamide (Glb) (0.001–10μM) and Gliclazide (Glc) (0.01–500μM)were conducted as controls. ResultsIn HIT–T15 cells, Glb exhibited the lowest IC50 (0.03μM), as compared to Glq (0.45μM) and Glc (1.21μM). However, Glq had higher IC50 in cardiomyoctes and VSMCs, as compared to Glb (119.1 vs. 0.01 and 149.7 vs. 0.09μM, respectively), suggesting that Glq is more selective to β-cells than Glb. Thus, Glq may have fewer side effects in cardiomyoctes and VSMCs. ConclusionsGlq is a highly selective SUR secretagogue with moderate affinity to β-cells, but low affinity to cardiomyocytes and VSMCs. Our data also reveal the non-selective nature of Glb, as evidenced by high binding affinity to KATP channels in all the three cell types examined.

153: The effect of Gelam honey on the oxidative stress induced inflammatory pathways in pancreatic hamster cells

Type 2 diabetes consists of progressive hyperglycemia, insulin resistance, and pancreatic β cell dysfunction which could result from glucose toxicity, inflammatory cytokines and oxidative stress. In the present study we investigated the effect of gelam honey and quercetin, on the oxidative stress induced inflammatory pathways and the proinflammatory cytokines. Methods: HIT-T15 cells were cultured in 5% CO 2 and then preincubated with gelam honey extract (20, 40, 60 and 80 μg/ml., as well as quercetin (20,40, 60 and 80 μM), prior to stimulation by 20 and 50 mM glucose. Cell lysates were collected to determine the effect of honey extracts and quercetin on JNK and IKkβ inflammatory pathways and the proinflammatory cytokines TNFα, IL-6 and IL-1β. Results: HIT-T15 cells cultured under hyperglycemic condition showed a significant increase in the inflammatory pathways by phosphorylating JNK, IKkβ and IRS-1at ser 307 ( p p p p In conclusion our data suggest the potential use of the extract from gelam honey and quercetin in modulating the inflammation induced insulin signaling pathways. It is also possible that JNK and IKkβ pathways could be a therapeutic target for Type 2 diabetes.

Pancreatic and duodenal homeobox-1 nuclear localization is regulated by glucose in dispersed rat islets but not in insulin-secreting cell lines

The transcription factor Pancreatic and Duodenal Homeobox-1 (PDX-1) plays a major role in the development and function of pancreatic β−cells and its mutation results in diabetes. In adult β−cells, glucose stimulates transcription of the insulin gene in part by regulating PDX-1 expression, stability and activity. Glucose is also thought to modulate PDX-1 nuclear translocation but in vitro studies examining nucleo-cytoplasmic shuttling of endogenous or ectopically expressed PDX-1 in insulin-secreting cell lines have led to conflicting results. Here we show that endogenous PDX-1 undergoes translocation from the cytoplasm to the nucleus in response to glucose in dispersed rat islets but not in insulin-secreting MIN6, HIT-T15, or INS832/13 cells. Interestingly, however, we found that a PDX-1-GFP fusion protein can shuttle from the cytoplasm to the nucleus in response to glucose stimulation in HIT-T15 cells. Our results suggest that the regulation of endogenous PDX-1 sub-cellular localization by glucose is observed in primary islets and that care should be taken when interpreting data from insulin-secreting cell lines.

Oral delivery of glucagon like peptide-1 by a recombinant Lactococcus lactis.

To develop a live oral delivery system of Glucagon like peptide-1 (GLP-1), for the treatment of Type-2 Diabetes. LL-pUBGLP-1, a recombinant Lactococcus lactis (L. lactis)) transformed with a plasmid vector encoding GLP-1 cDNA was constructed and was used as a delivery system. Secretion of rGLP-1 from LL-pUBGLP-1 was characterized by ELISA. The bioactivity of the rGLP-1 was examined for its insulinotropic activity on HIT-T15 cells. Transport of rGLP-1 across MDCK cell monolayer when delivered by LL-pUBGLP-1 was studied. The therapeutic effect of LL-pUBGLP-1 after oral administration was investigated in ZDF rats. DNA sequencing and ELISA confirmed the successful construction of the LL-pUBGLP-1 and secretion of the active form of rGLP-1. In vitro insulinotropic studies demonstrated that LL-pUBGLP-1 could significantly (p < 0.05) stimulate HIT-T15 cells to secrete insulin as compared to the controls. When delivered by LL-pUBGLP-1, the GLP-1 transport rate across the MDCK cell monolayer was increased by eight times (p < 0.01) as compared to the free solution form. Oral administration of LL-pUBGLP-1 in ZDF rats resulted in a significant decrease (10-20%, p < 0.05) in blood glucose levels during 2-11h post dosing and a significant increase in insulin AUC0-11h (2.5 times, p < 0.01) as compared to the free solution. The present study demonstrates that L. lactis when genetically modified with a recombinant plasmid can be used for the oral delivery of GLP-1.

Macrophage migration inhibitory factor is overexpressed in pancreatic cancer tissues and impairs insulin secretion function of β-cell

BackgroundUnderstanding the pathogenic mechanism of pancreatic cancer associated diabetes (PCDM) might help yield biomarkers for the early diagnosis of pancreatic cancer (PC) from population with new-onset diabetes. In the current study, we sought to determine the role of macrophage migration inhibitory factor (MIF) in PCDM pathogenesis.MethodsThe protein and mRNA levels of MIF in paraffin-embedded human PC samples, chronic pancreatitis specimens, and normal pancreas were measured by immunohistochemistry and quantitative reverse-transcriptase polymerase chain reaction. We measured serum levels of MIF in PC patients and controls. The biologic impacts of MIF overexpression on insulin secretion function of mice islets and β cells (HIT-T15) were investigated in vitro.ResultsMIF expression was significantly increased in pancreatic cancer tissues compared with chronic pancreatitis or normal pancreas specimens. The insulin secretion function of both islets and HIT-T15 cells was impaired by indirect co-cultured with PC cells or treated with conditioned media from them. Stable MIF knock-down significantly decreased the diabetogenic effect of PC cells, while MIF knock-in HPDE6 cells demonstrated a strong inhibitory effect on insulin secretion function of islets and HIT-T15 cells. MIF impaired βcell function by depressing the Ca2+ currents, decreasing L-type Ca2+ channel α1 subunit protein expression level, and enhancing p-Src activity. Mean serum level of MIF was significant higher in new-onset diabetes associated PC patients in comparison with other groups.ConclusionsMIF is up-regulated in patients with pancreatic cancer and causes dysfunction of insulin secretion in β-cells.

Anti-Diabetic Potential of the Essential Oil ofPinus koraiensisLeaves toward Streptozotocin-Treated Mice and HIT-T15 Pancreatic β Cells

The metabolic syndrome creates risk factors for coronary heart disease, diabetes, fatty liver, obesity and several cancers. Our group has already reported that the essential oil from leaves of Pinus koraiensis SIEB (EOPK) exerted antihyperlipidemic effects by upregulating the low-density lipoprotein receptor and inhibiting acyl-coenzyme A, cholesterol acyltransferases. We evaluated in the current study the anti-diabetic effects of EOPK on mice with streptozotocin (STZ)-induced type I diabetes and on HIT-T15 pancreatic β cells. EOPK significantly protected HIT-T15 cells from STZ-induced cytotoxicity and reduced the blood glucose level in STZ-induced diabetic mice when compared with the untreated control. EOPK consistently and significantly suppressed the α-amylase activity in a dose-dependent manner and enhanced the expression of insulin at the mRNA level in STZ-treated HIT-T15 cells, while the expression of insulin was attenuated. EOPK also significantly abrogated the population of reactive oxygen species when compared to the untreated control in STZ-treated HIT-T15 cells. Furthermore, EOPK significantly reduce nitric oxide production, suppressed the phosphorylation of endothelial nitric oxide (NO) synthase and suppressed the production of vascular endothelial growth factor (VEGF) in STZ-treated HIT-T15 cells, implying its potential application to diabetic retinopathy. Overall, our findings suggest that EOPK had hypoglycemic potential by inhibiting reactive oxygene species (ROS), endothelial NO synthase (eNOS) and VEGF in STZ-treated mice and HIT-T15 pancreatic β cells as a potent anti-diabetic agent.

Antidiabetic and Beta Cell-Protection Activities of Purple Corn Anthocyanins

Antidiabetic and beta cell-protection activities of purple corn anthocyanins (PCA) were examined in pancreatic beta cell culture and db/db mice. Only PCA among several plant anthocyanins and polyphenols showed insulin secretion activity in culture of HIT-T15 cells. PCA had excellent antihyperglycemic activity (in terms of blood glucose level and OGTT) and HbA1c-decreasing activity when compared with glimepiride, a sulfonylurea in db/db mice. In addition, PCA showed efficient protection activity of pancreatic beta cell from cell death in HIT-T15 cell culture and db/db mice. The result showed that PCA had antidiabetic and beta cell-protection activities in pancreatic beta cell culture and db/db mice.