Analyses of the Tympanic Membrane Impulse Response Measured with High-Speed Holography

The Tympanic Membrane (TM) transforms acoustic energy to ossicular vibration. The shape and the displacement of the TM play an important role in this process. We developed a High-speed Digital Holography (HDH) system to measure the shape and transient displacements of the TM induced by acoustic clicks. The displacements were further normalized by the measured shape to derive surface normal displacements at over 100,000 points on the TM surface. Frequency and impulse response analyses were performed at each TM point, which enable us to describe 2D surface maps of four new TM mechanical parameters. From frequency domain analyses, we describe the (i) dominant frequencies of the displacement per sound pressure based on Frequency Response Function (FRF) at each surface point. From time domain analyses, we describe the (ii) rising time, (iii) exponential decay time, and the (iv) root-mean-square (rms) displacement of the TM based on Impulse Response Function (IRF) at each surface point. The resultant 2D maps show that a majority of the TM surface has a dominant frequency of around 1.5 kHz. The rising times suggest that much of the TM surface is set into motion within 50 µs of an impulsive stimulus. The maps of the exponential decay time of the IRF illustrate spatial variations in damping, the least known TM mechanical property. The damping ratios at locations with varied dominant frequencies are quantified and compared.

[Association between Lipoprotein(a) and the characteristics of left main coronary artery plaque in patients with stable angina pectoris]

Objective: To investigate the relationship between Lipoprotein (LP) (a) level and the characteristics of tissue components of left main coronary artery (LMCA) plaque. Methods: A total of 102 patients with stable angina pectoris who underwent percutaneous coronary intervention (PCI) in the People's Hospital of Henan Province from June 2010 to October 2016 were included. We performed intravascular ultrasound-virtual histology (IVUS-VH) to their LMCAs and evaluated the tissue characteristics, and the blood level of total cholesterol (TC), triacylglycerol (TG), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), ApoB, ApoA1, LP(a) were measured. According to the value of their LP(a) level they were divided into 2 groups (high LP(a) group (>300 mg/L) (n=35) and low LP(a) group (≤300 mg/L) (n=67)), then the relationship between the above lipid values and the tissue characteristics of the LMCA plaque in the patients were evaluated. Results: Patients with a high LP(a) had a larger percentage of fibrolipid volume and a smaller percentage fibrous volume compared to patients with a normal LP(a) (25%±5% vs 13%±6%, P<0.01 and 50%±8% vs 61%±9%, P<0.01). Using multivariate linear regression analysis after adjustment for the above-mentioned confounding factors, LP(a) had a significantly positive correlation with fibrolipid volume percentage (r=0.645, β=0.29, P<0.01), and had a negative correlation with fibrous volume percentage (r=-0.467, β=-0.32,P<0.01), suggesting that the LP(a) was associated with the vulnerability of the LMCA plaque. Conclusion: For the patients with stable angina pectoris, the LP(a) has a significantly positive correlation with the percentage of fibrolipid volume and a negative correlation with the percentage of fibrous volume, suggesting that the LP(a) could predict the vulnerability of the LMCA plaque.

[Effect of miR-19b on the proliferation and apoptosis of P19CL6 cells during the late-stage of cardiac differentiation]

Objective: To explore the effect of miR-19b on the function of P19CL6 cells and its molecular mechanism. Methods: Overexpression of miR-19b was carried out by transfecting miR-19b plasmid into the P19CL6 cells. MTT assay and flow cytometry were used to determine cell growth and apoptosis, respectively. Western blot was used to detect the expression level of Sox6 in P19CL6 cells. ELISA assay was used to detect the expression levels of apoptosis-related genes (Bax, Bcl-2) in P19CL6 cells at late-stage cardiac differentiation. Further online software TargetScan was used to predict the target genes of miR-19b and verified by dual luciferase reporter assay. Results: Our data showed that overexpression of miR-19b in P19CL6 cells significantly increased the cell growth rates and the apoptosis inhibition rates. The ratio of apoptosis-related proteins (Bax/Bcl-2) was significantly reduced. Results from the TargetScan and dual luciferase reporter showed that Sox6 is the direct target of miR-19b. Conclusions: We conclude that miR-19b might promote cell proliferation and inhibits cell apoptosis during the late-stage of cardiac differentiation by targeting Sox6 expression.

[Association between the ApoB/A1 ratio and the vulnerability of LMCA plaque in the patients with stable angina pectoris]

Objective: To investigate the relationship between ApoB/A1 ratio and the characteristics of tissue components of their left main coronary artery(LMCA)plaque. Methods: A total of 98 patients with stable angina pectoris who received chronic statin treatment underwentpercutaneous coronary intervention in the People's Hospital of Henan Province from June 2010 to June 2016 were included.We prospectively performed intravascular ultrasound virtualhistology (IVUS-VH) to their LMCA and evaluated the tissue characteristics, and the blood level of total cholesterol (TC) and low-density lipoprotein cholesterol(LDL-C), high-density lipoprotein cholesterol(HDL-C), triglyceride(TG), LDL-C/HDL-C ratio, ApoB, ApoA1, ApoB/A1 ratio were measured, then the association of the tissue characteristics with the aboved lipids values were analyzed. Results: According to the median value of their ApoB/A1ratios (0.80), they were divided into 2 groups [high ApoB/A1 ratio (>0.80) (n=49) and low ApoB/A1 ratio (≤0.80) (n=49)]. The patients with a high ApoB/A1 ratio had alarger fibrolipid volume and a smaller fibrous volume compared to patients with a low ApoB/A1 ratio ( 17.5%±1.2% vs 9.0%±1.0%, P=0.03 and 55.1%±2.1% vs 63.9%±1.8%, P<0.01). Using multivariate linear regression analysis after adjustment for the above-mentioned confounding factors, the ApoB/A1 ratio had a significantly positive correlation with fibrolipid volume (r=0.445, β=0.29, P=0.010)and had a negative correlation with fibrous volume (r=-0.567, β=-0.32, P=0.011), suggesting that the ApoB/A1 ratio was associated with the vulnerability of the LMCA plaque. Conclusion: For the patients with stable angina pectoris and chronic treatment of statins, a high ApoB/A1 ratio is associated with a high percentage of fibrolipid volume and a low percentage of fibrous volume in LMCA lesions, suggesting that the ApoB/A1 ratios could predict the vulnerability of the LMCA plaque.

Calcitonin alleviates hyperalgesia in osteoporotic rats by modulating serotonin transporter activity

Calcitonin may relieve pain by modulating central serotonin activity. Calcitonin partly reversed the hypersensitivity to pain induced by ovariectomy. This suggests that the anti-nociceptive effects of calcitonin in the treatment of osteoporosis may be mediated by alterations in neural serotonin transporter (SERT) activity.

INTRODUCTION

This study used a rat model of osteoporosis to evaluate the role of the cerebral serotonin system in the anti-nociceptive effect of calcitonin, a drug used to treat post-menopausal osteoporosis.

METHODS

Osteoporosis was induced in rats by ovariectomy (OVX). Rats were then randomized to the following four groups: sham operation, OVX, OVX plus calcitonin, or OVX plus alendronate.

RESULTS

OVX led to alterations in bone micro-architecture; alendronate strongly reversed this effect, and calcitonin moderately reversed this effect. OVX increased hyperalgesia (determined as the time for hind paw withdrawal from a heat source); calcitonin reduced this effect, but alendronate had no effect. OVX increased the expression of c-Fos (a neuronal marker of pain) in the thalamus; calcitonin strongly reversed this effect, and alendronate moderately reversed this effect. OVX also reduced SERT but increased 5-HT1A receptor expression and activity; calcitonin aggravated this effect, but alendronate had no effect on recovery of SERT/5-HT1A activity and expression.

CONCLUSIONS

Our study of a rat model of osteoporosis suggests that OVX-induced enhancement of the serotonergic system may protect against hyperalgesia. However, the anti-nociceptive effects of calcitonin in osteoporosis may be mediated by decreased neural SERT activity and increased activation of 5-HT1 receptors in the thalamus.

Hepatic carcinoma-associated fibroblasts induce IDO-producing regulatory dendritic cells through IL-6-mediated STAT3 activation

Although carcinoma-associated fibroblasts (CAFs) in tumor microenvironments have a critical role in immune cell modulation, their effects on the generation of regulatory dendritic cells (DCs) are still unclear. In this study, we initially show that CAFs derived from hepatocellular carcinoma (HCC) tumors facilitate the generation of regulatory DCs, which are characterized by low expression of costimulatory molecules, high suppressive cytokines production and enhanced regulation of immune responses, including T-cell proliferation impairment and promotion of regulatory T-cell (Treg) expansion via indoleamine 2,3-dioxygenase (IDO) upregulation. Our findings also indicate that STAT3 activation in DCs, as mediated by CAF-derived interleukin (IL)-6, is essential to IDO production. Moreover, IDO inhibitor, STAT3 and IL-6 blocking antibodies can reverse this hepatic CAF-DC regulatory function. Therefore, our results provide new insights into the mechanisms by which CAFs induce tumor immune escape as well as a novel cancer immunotherapeutic approach (for example, targeting CAFs, IDO or IL-6).

Cerebral klotho protein as a humoral factor for maintenance of baroreflex

The klotho protein produced by the choroid plexus is known as a humoral factor in central nervous system. Many hormones affecting the baroreflex sensitivity have been introduced in the brain. However, role of klotho in the baroreflex sensitivity is still unknown. Recently, mutations in the klotho gene have been linked to cardiovascular diseases in both animals and human subjects. Also, silencing of brain klotho has been reported to enhance cold-induced elevation of blood pressure. Thus, we investigated the role of klotho in maintenance of central cardiovascular reflex sensitivity. Male Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) were used. Either klotho shRNA or scramble shRNA was also ICV-infused into the brains of WKY rats to investigate the role of klotho in brain. Recombinant klotho or rat IgG was infused into the cerebral paraventricle (ICV) of SHRs for further understanding the role of klotho in hypertension. The baroreflex sensitivity was detected using the challenge with a depressor dose of sodium nitroprusside (SNP, 50 μg/kg) or with a pressor dose of phenylephrine (PE, 8 μg/kg). We found that silencing of klotho expression in the brain decreased the baroreflex sensitivity in WKY rats. Also, modulation of the blood pressure for one week altered the cardiovascular homeostasis and resulted in an increased expression of klotho in medulla oblongata. Moreover, the baroreflex sensitivity was restored in SHRs that received recombinant klotho through ICV brain. Thus, klotho is involved in the maintenance of baroreflex sensitivity in the brain.

Optimization of a lensless digital holographic otoscope system for transient measurements of the human tympanic membrane

In this paper, we propose a multi-pulsed double exposure (MPDE) acquisition method to quantify in full-field-of-view the transient (i.e., >10 kHz) acoustically induced nanometer scale displacements of the human tympanic membrane (TM or eardrum). The method takes advantage of the geometrical linearity and repeatability of the TM displacements to enable high-speed measurements with a conventional camera (i.e., <20 fps). The MPDE is implemented on a previously developed digital holographic system (DHS) to enhance its measurement capabilities, at a minimum cost, while avoiding constraints imposed by the spatial resolutions and dimensions of high-speed (i.e., >50 kfps) cameras. To our knowledge, there is currently no existing system to provide such capabilities for the study of the human TM. The combination of high temporal (i.e., >50 kHz) and spatial (i.e., >500k data points) resolutions enables measurements of the temporal and frequency response of all points across the surface of the TM simultaneously. The repeatability and accuracy of the MPDE method are verified against a Laser Doppler Vibrometer (LDV) on both artificial membranes and ex-vivo human TMs that are acoustically excited with a sharp (i.e., <100 μs duration) click. The measuring capabilities of the DHS, enhanced by the MPDE acquisition method, allow for quantification of spatially dependent motion parameters of the TM, such as modal frequencies, time constants, as well as inferring local material properties.

Rosiglitazone is effective to improve renal damage in type-1-like diabetic rats

A marked decrease of klotho expression was observed in the kidney of streptozotocin-induced diabetic rats (STZ rats) showing diabetic nephropathy. It has been documented that klotho is the target gene of PPARγ. However, the effect of PPARγ agonist on klotho expression in kidney of STZ rats remains obscure. Thus, we used rosiglitazone (TZD) as PPARγ agonist to investigate the effect on renal dysfunction in STZ rats. Treatment of TZD reversed the lower levels of PPARγ, klotho, and FGFR1 expressions in kidneys of STZ rats without the correction of hyperglycemia. Also, renal functions and structural defeats were improved by TZD treatment. Taken together, oral administration of TZD may improve STZ-induced diabetic nephropathy due to restoration of the expression of klotho axis through an increase in PPARγ expression without changing blood glucose in rats.

Decrease of FGF receptor (FGFR) and interstitial fibrosis in the kidney of streptozotocin-induced diabetic rats

Fibrosis is the final disorder of end-stage renal disease. Activation of fibroblast growth factor (FGF) 23-klotho axis could suppress renal fibrosis in mice. Also, a marked decrease of klotho expression was observed in the kidney of streptozotocin-induced diabetic rats (STZ rats). However, relation of FGF in renal fibrosis remained unclear. This study was aimed to screen the effect of hyperglycemia on FGF receptor (FGFR) and fibrosis in kidney of rats with diabetic nephropathy and investigate this potential mechanism in cultured Madin-Darby Canine Kidney (MDCK) epithelial cells. STZ rats were used to treat with insulin or phloridzin at the dose sufficient to correct hyperglycemia for understanding the changes of renal dysfunction. The cultured MDCK cells were also used to treat with high glucose, hydrogen peroxide, or tiron in addition to transfection of siRNA to silence the klotho. Both insulin and phloridzin reversed fibrosis and FGFR expressions in kidney of STZ rats. It was confirmed in high glucose-exposed MDCK cells. However, klotho failed to modify the level of FGFR in MDCK cells. Meanwhile, FGFR was restored by tiron in MDCK cells and in diabetic rats without changing blood glucose. In conclusion, interstitial fibrosis and decreased FGFR expression are observed in the kidney of diabetic rats. This change is reversed by tiron without the correction of blood glucose. Also, klotho has no effect on expression of FGFR. Thus, decrease of oxidative stress is useful for the recovery of FGFR expression and improvement of renal fibrosis in type-1 like diabetic rats.

Decrease of hyperglycemia by syringaldehyde in diabetic rats

Syringaldehyde is one of the active principles from the stems of Hibiscus taiwanensis (Malvaceae) that has been mentioned to lower hyperglycemia. However, the potential mechanisms for this action of syringaldehyde remain obscure. In the present study, we used streptozotocin to induce diabetic rats (STZ-diabetic rats) as type 1-like diabetic rats and fed fructose-rich chow to rats as type 2-like diabetic rats. Then, we performed the postprandial glucose test and applied the hyperinsulinemic euglycemic clamp to investigate the actions of syringaldehyde. Also, the changes of gene expressions of enzyme relating to glucose homeostasis in muscle and liver were characterized. Syringaldehyde significantly decreased the postprandial plasma glucose in rats, while the plasma insulin was not modified by syringaldehyde. The glucose infusion rate (GIR) in fructose chow-fed rats using hyperinsulinemic euglycemic clamp was markedly improved by syringaldehyde. Additionally, repeated administration of syringaldehyde for 3 days in STZ-diabetic rats resulted in a marked reduction of phosphoenolpyruvate carboxykinase (PEPCK) expression in liver and an increased expression of glucose transporter subtype 4 (GLUT 4) in skeletal muscle. Our results suggest that syringaldehyde may increase glucose utilization to lower hyperglycemia in diabetic rats.

Activation of receptors δ (PPARδ) by agonist (GW0742) may enhance lipid metabolism in heart both in vivo and in vitro

It has been documented that cardiac agents may regulate the lipid metabolism through increased expression of PPARδ in cardiac cells. However, the effect on lipid metabolism by direct activation of PPARδ is still unknown. The present study applied specific PPARδ agonist (GW0742) to investigate this point in the heart of Wistar rats and in the primary cultured cardiomyocytes from neonatal rat. Expressions of PPARδ in the heart and cardiomyocytes after treatment with GW0742 were detected using Western blots. The fatty acid (FA) oxidation and the citric acid (TCA) cycle related genes in cardiomyocytes were also examined. In addition, PPARδ antagonist (GSK0660) and siRNA-PPARδ were employed to characterize the potential mechanisms. After a 7-day treatment with GW0742, expressions of PPARδ in the heart were markedly increased. Increased expressions of FA oxidation and TCA cycle related genes were also observed both in vivo and in vitro. This action of GW0742 was blocked by GSK0660 or by siRNA-PPARδ. The obtained results show that activation of PPARδ by GW0742 is responsible for the increase of FA oxidation and TCA cycle related genes in hearts. Role of PPARδ in the regulation of lipid metabolism in heart is then established.

Insulin resistance induced by zymosan as a new animal model in mice

Insulin resistance (IR) is known as a main problem in diabetic disorders. Some animal models for research in IR have been mentioned. Each model shows merit with some disadvantages. Thus, a new animal model for IR is required. The present study used zymosan, a mixture of cell-wall particles from the yeast named Saccharomyces cerevisiae, to establish a new model of IR in mice. Also, we compared the difference of this model with fructose-rich chow-induced model and found some merits of this model. Moreover, we identified that this model induced by zymosan is reversible and IR can be reversed gradually after termination of treatment. Taken together, we suggest zymosan as a useful agent to induce IR through inflammatory pathway in mice.

Characterization of the specificity of imidazoline I-1 receptor antibody for subtype of imidazoline receptors in vitro

Specific antibodies are essential in the study of receptor protein. Gene matching shows that Nischarin (NISCH) is a mouse homologue of human imidazoline receptor antisera-selective (IRAS) protein, a viable candidate for imidazoline I-1 receptor. However, selectivity of this antibody against imidazoline I-2 or imidazoline I-3 receptors remained obscure. At first, an intracerebroventricular (ICV) injection of anti-NISCH antibody blocked the blood pressure lowering action of rilmenidine (I-1 receptor agonist) in spontaneous hypertensive rat (SHR). However, the same injection of anti-NISCH antibody showed no effect in SHR treated with clonidine (α2 agonist). In order to clarify the selectivity of anti-NISCH antibody for each subtype of imidazoline receptors, this anti-NISCH antibody was subjected to the lysate of organs isolated from Wistar rats including cortex, hippocampus, cerebellum, and brain stem as central nervous tissues, and heart, liver, pancreas, skeletal muscle, kidney, prostate, and bladder as peripheral tissues. The results show that anti-NISCH antibody positively reacted with all tissues including heart, pancreas, skeletal muscle, kidney and bladder by Western blot analysis. Also, the blotting spots for anti-NISCH antibody show a concentration-dependent manner. Moreover, anti-NISCH antibody blocked the action of glucose uptake induced by 2-BFI (I-2 receptor agonist) in L6 cells. Taken together, the obtained data suggest that anti-NISCH antibody can be used not only for imidazoline I-1 receptor but also for I-2 and I-3 subtypes in immunoassays.

Increase of peroxisome proliferator-activated receptor δ (PPARδ) by digoxin to improve lipid metabolism in the heart of diabetic rats

Increase of peroxisome proliferator-activated receptor δ (PPARδ) expression by digoxin in the heart of diabetic rats has been documented. The present study investigated the mediation of PPARδ in lipid metabolism improved by digoxin in the heart of diabetic rats and in the hyperglycemia-treated cardiomyocytes using the primary cultured cardiomyocytes from neonatal rat. The lipid deposition within the heart section was assessed in diabetic rats by oil red O staining. The fatty acid oxidation genes in cardiomyocytes were also examined. Inhibitor of calcium ions and siRNA-PPARδ were employed to investigate the potential mechanisms. After a 20-day digoxin treatment, the PPARδ expression was elevated in hearts of diabetic rats while the cardiac lipid deposition was reduced. In neonatal cardiomyocytes, digoxin also caused an increase in expressions of PPARδ and fatty acid oxidation genes. But both actions of digoxin were blocked by BAPTA-AM to chelate calcium ions and by siRNA-PPARδ in cardiomyocytes. The obtained results show that increase of PPARδ by digoxin is related to regulation of fatty acid oxidation genes in cardiac cells mediated by calcium-triggered signals.

Mediation of AMP kinase in the increase of glucose uptake in L6 cells induced by activation of imidazoline I-2 receptors

Recent work using radioactive tracer indicates that activation of imidazoline I2 receptor (I2R) by guanidinium derivatives may increase the glucose uptake in the skeletal muscle. However, the effect of I2R activation on nonradioactive glucose uptake is still unknown. The ability of glucose uptake in cultured L6 cells is then determined using 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) as a fluorescence indicator. The changes in 5'-AMP-activated protein kinase (AMPK) expression were also identified by Western blot analysis. In the present study, 2-(2-benzofuranyl)-2-imidazoline (2-BFI) is used to stimulate I2R while 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) is applied to activate AMPK directly. Both compounds can increase 2-NBDG in L6 cells in a concentration-dependent manner. Meanwhile, compound C at concentrations sufficient to inhibit AMPK blocked this increase of glucose uptake by 2-BFI or AICAR. However, only 2-BFI-induced glucose uptake action was dose-dependently blocked by BU224, a specific I2R antagonist, in L6 cells. Moreover, AMPK phosphorylation was markedly increased by 2-BFI or AICAR in L6 cells. Similarly, only the effect of 2-BFI was attenuated by BU224 in L6 cells. Thus, we suggest that AMPK is mediated in I2R activation for increase of glucose uptake in the skeletal muscle cell and I2R will be a new target for diabetic therapy.

Role of TNF-α in renal damage in mice showing hepatic steatosis induced by high fat diet

The present study was designed to investigate the role of TNF-α in renal damage observed in mice with hepatic steatosis. We induced hepatic steatosis in mice using high fat diet and treated mice with ectanercept at the dose sufficient to block TNF-α receptors or vehicle for 1 month. Plasma TNF-α, total cholesterol (TC), triglyceride (TG), LDL-cholesterol (LDL-C), and HDL-cholesterol (HDL-C) were determined at the end of this treatment. Renal damage was identified by histologic observation and the higher of serum blood urea nitrogen (BUN) and creatinine. Also, changes of PPAR-δ in kidney and renal mesangial cell (RMC) were analyzed using Western blot. Plasma TNF-α was markedly raised in mice showing hepatic steatosis. However, the levels of blood lipids (TC, TG, HDL-C, and LDL-C) and TNF-α were not modified by the treatment of etanercept although the hepatic steatosis has been improved. Etanercept shows renal protection from histological identification and recovery of serum BUN and creatinine levels. Moreover, restoration of PPAR-δ expression by etanercept was observed in mice kidney. Direct effect of TNF-α on PPAR-δ expression was also characterized in RMC cell. We suggest that renal damage in mice with hepatic steatosis is mainly induced by increase of TNF-α through the decrease of renal PPAR-δ. Etanercept could block TNF-α receptors to restore PPAR-δ and improve renal function in mice with hepatic steatosis.

Stimulatory effect of allantoin on imidazoline I₁ receptors in animal and cell line

Allantoin is known as the agonist of imidazoline receptor, especially the I₂ subtype. Effect of allantoin on imidazoline I₁ receptor (I₁R) relating to reduction of blood pressure and its merit in steatosis are still obscure. Also, farnesoid X receptor (FXR) plays an important role in lipid homeostasis related to I₁R activation. Thus, we administered allantoin into high fat diet (HFD)-fed mice showing hypertriglyceridemia and hypercholesterolemia. Allantoin significantly improved hyperlipidemia in HFD mice after 4 weeks of administration. Pretreatment with efaroxan, at a dose sufficient to inhibit I₁R activation, attenuated the action of allantoin. In addition, in cultured HepG2 cells, allantoin increased the expression of farnesoid X receptor (FXR). The allantoin-induced FXR expression was blocked by efaroxan. Similar changes were observed in the expressions of FXR-targeted genes. Otherwise, allantoin also lowered systolic blood pressure (SBP) in HFD mice that can be blocked by efaroxan. Taken together, allantoin has an ability to activate I₁R for improvement of metabolic disorders.

Treatment of gabapentin-induced myoclonus with continuous renal replacement therapy

A 56-year-old man with diabetes, hypertension, and chronic kidney disease presented to the emergency room with a complaint of pain in his right foot. He was found to have tremors. Gabapentin toxicity was suspected and the patient was found to have high gabapentin level (6.3 mcg/ml). Patient was commenced on continuous venovenous hemodiafiltration (CVVHD) and the pharmacokinetics of gabapentin was studied. The patient improved symptomatically and his tremors subsided. In this case report, we describe the successful management of gabapentin toxicity with continuous renal replacement therapy and calculate the clearance of gabapentin which will enable future treatment of gabapentin toxicity by CVVHD.

Improvement of hyperphagia by activation of cerebral I(1)-imidazoline receptors in streptozotocin-induced diabetic mice

Imidazoline I1-receptors (I1R) are known to regulate blood pressure and rilmenidine, an agonist, is widely used as antihypertensive agent in clinic. However, the role of I1R in feeding behavior is still unclear. In the present study, we used the agonist of I1R to investigate the effect on hyperphagia in streptozotocin (STZ)-induced diabetic mice. Rilmenidine decreased the food intake of STZ-diabetic mice in a dose-dependent manner. The reduction of food intake was abolished by pretreatment with efaroxan at the dose sufficient to block I1R. Intracerebroventricular (icv) administration of rilmenidine into STZ-diabetic mice also significantly reduced hyperphagia, which was reversed by icv administration of efaroxan. In addition, similar results were observed in STZ-diabetic mice, which received chronic treatment with rilmenidine 3 times daily (t.i.d.) for 7 days. Moreover, the hypothalamic neuropeptide Y (NPY) level was reduced by rilmenidine that was also reversed by pretreatment with efaroxan. In conclusion, the obtained results suggest that rilmenidine can decrease food intake in STZ-diabetic mice through an activation of I1R to lower hypothalamic NPY level.

Activation of imidazoline I-2B receptors by allantoin to increase glucose uptake into C₂C₁₂ cells

Allantoin, an active principle of the yam, belongs to the group of guanidinium derivatives and has been reported to lower plasma glucose in diabetic animals. Recent evidence indicates that activation of the imidazoline I(2B) receptor (I(2B)R) by guanidinium derivatives also increases glucose uptake; however, the effect of allantoin on I(2B)R is still unknown. Glucose uptake into cultured C₂C₁₂ cells was determined using 2-[¹⁴C]-deoxy-D-glucose as a tracer. The changes in 5'-AMP-activated protein kinase (AMPK) expression were also identified by Western blotting analysis. The allantoin-induced glucose uptake action was dose-dependently blocked by BU224, a specific I₂R antagonist, in C₂C₁₂ cells. Moreover, AMPK phosphorylation by allantoin was found to be dose-dependently increased in C₂C₁₂ cells using AICAR treatment as a reference. In addition, both actions of allantoin, the increases in glucose uptake and AMPK phosphorylation, were dose-dependently attenuated by amiloride in C₂C₁₂ cells. Moreover, compound C at concentrations sufficient to inhibit AMPK blocked the allantoin-induced glucose uptake and AMPK phosphorylation. Thus, we suggest that allantoin can activate I(2B)R to increase glucose uptake into cells, and propose I(2B)R as a new target for diabetic therapy.

Plasma glucose-lowering action of allantoin is induced by activation of imidazoline I-2 receptors in streptozotocin-induced diabetic rats

Allantoin, an active principle of yam, is documented to lower plasma glucose in diabetic rats. However, action mechanisms of allantoin remain obscure. It has been indicated that metformin shows ability to activate imidazoline I-2 receptors (I-2R) to lower blood sugar. Allantoin has also a chemical structure similar to metformin; both belong to guanidinium derivative. Thus, it is of special interest to know the effect of allantoin on I-2R. In the present study, the marked plasma glucose-lowering action of allantoin in streptozotocin-induced type-1 like diabetic rats was blocked by specific I-2R antagonist, BU224, in a dose-dependent manner. Also, the increase of β-endorphin release by allantoin was blocked by BU224 in the same manner. Otherwise, amiloride at the dose sufficient to block I-2AR abolished the allantoin-induced β-endorphin release and inhibited the blood glucose-lowering action of allantoin markedly but not completely. The direct effect of allantoin on glucose uptake in isolated skeletal muscle was also blocked by BU224. Also, the phosphorylation of AMPK in isolated skeletal muscle was raised by allantoin in a concentration-dependent manner. More-over, insulin sensitivity in diabetic rats was markedly increased by allantoin and this action was also blocked by BU224. These results suggest that allantoin has an ability to activate imidazoline I-2R while I-2AR is linked to the increase of β-endorphin release and I-2BR is related to other actions including the influence in skeletal muscle for lowering of blood glucose in type-1 like diabetic rats. Thus, allantoin can be developed to treat diabetic disorders in the future.

Urinary bladder relaxation through activation of opioid μ-receptors induced by loperamide is increased in diabetic rats

The role of opioid μ-receptor activation in the improvement of overactive bladder (OAB) remains obscure. Thus, we used loperamide to activate opioid μ-receptors for urinary bladder relaxation and compared the differences between normal and diabetic rats. Urinary bladder strips were isolated from Wistar rats that did or did not receive streptozotocin (STZ) injection for analysis of isometric tension. Samples were contracted with either acetylcholine (ACh) or KCl, and decrease of muscle tone (relaxation) was characterized after treatment with loperamide. Specific antagonists were used for pretreatment to compare the changes in loperamide-induced relaxation. As compared with normal rats, loperamide produced a more marked relaxation in bladder strips of STZ-diabetic rats in a dose-dependent manner. This relaxation by loperamide was attenuated by glibenclamide at a dose sufficient to block ATP-sensitive K(+) (K(ATP)) channels. In addition, this action of loperamide was abolished by protein kinase A (PKA) inhibitor and enhanced by the inhibitor of phosphodiesterase for cyclic AMP (cAMP). However, treatment with forskolin, an activator of adenylate cyclase, resulted in no difference in relaxation in normal and diabetic rats. The action of loperamide was abolished by cyprodime and naloxone, but was not modified by naloxonazine at a dose sufficient to block opioid μ-1 receptors. A higher expression of opioid μ-receptors in diabetic rats was observed. Our results suggest that the increase in urinary bladder relaxation in STZ-diabetic rats by loperamide is mainly induced through activation of opioid μ-receptors linked to the cAMP-PKA pathway to open K(ATP) channels.

Activation of imidazoline I-2B receptor by metformin to increase glucose uptake in skeletal muscle

Metformin (dimethylbiguanide) belongs to guanidinium-derivative and is widely used for treatment of diabetic disorders in clinic. Metformin lowers blood glucose in diabetic animals through increase of glucose uptake into skeletal muscle. Recent evidence indicates that activation of imidazoline I2B receptor (I2BR) by guanidinium-derivatives also increased glucose uptake; however, the effect of metformin on I2BR is still unknown. The blood glucose levels were determined by a glucose kit. The ability of glucose uptake into isolated skeletal muscle or cultured C2C12 cells was determined using 2-[14C]-deoxyglucose as tracer. The expressions of 5' AMP-activated protein kinase (AMPK) and glucose transporter 4 (GLUT-4) were identified by Western blotting analysis. The metformin-induced blood glucose-lowering action was dose-dependently blocked by BU224, a specific I2R antagonist, in Wistar rats. Also, similar reversion by BU224 was observed in isolated skeletal muscle regarding the metformin-induced glucose uptake. Moreover, AMPK phosphorylation by metformin was concentration-dependently reduced by BU224 in isolated skeletal muscle. In addition, signals for metformin increased glucose uptake were identified via I2R/PI3K/PKC/AMPK dependent pathway in C2C12 cells. Thus, we suggest that metformin can activate I2BR to increase glucose uptake and I2BR will be a new target for diabetic therapy.

Pharmacological activation of peroxisome proliferator-activated receptor δ improves insulin resistance and hepatic steatosis in high fat diet-induced diabetic mice

The mechanisms regarding hepatic steatosis related to hepatic insulin resistance have been well documented. However, the agents for treatment of hepatic steatosis and insulin resistance remain poorly developed. Peroxisome proliferator-activated receptors (PPARs) are transcription factors that are responsible for the regulation of glucose and/or lipid metabolism. There are 3 distinct isoforms of PPARs family: PPARα, PPARγ, and PPARδ. Both PPARα and PPARγ agonists are widely used in clinic for the treatment of hyperlipidemia and hyperglycemia. However, the therapeutic efficacy of PPARδ agonists for diabetic disorders remains obscure. In the present study, we used L-165041 as PPARδ agonist to treat the high fat diet (HFD) fed mice. Administration of L-165041 improved the hepatic steatosis and increased the insulin sensitivity in HFD-mice. In addition to the histological identification of hepatic steatosis, the improvement of insulin sensitivity was characterized by the enhanced insulin signals and the increase of hepatic glycogen content. This is the first report showing that pharmacological activation of PPARδ improves insulin resistance in diet-induced diabetic mice. Thus, we suggest that pharmacological activation of PPARδ may be a new strategy for the treatment of diabetic patients with hepatic steatosis.

A novel mechanism for decreasing plasma lipid level from imidazoline I-1 receptor activation in high fat diet-fed mice

The imidazoline I-1 receptor (I-1 R) agonists are widely used to lower blood pressure, but their effects on hyperlipidemia are still obscure. The present study is aimed to evaluate the possible mechanism(s) of I-1 R in the regulation of lipid homeostasis. Farnesoid X receptor (FXR) plays an important role in blood lipid homeostasis; however, the role of FXR in rilmenidine-induced blood lipid lowering action is still unknown. Thus, we administered rilmenidine, a selective agonist of I-1 R, into high fat diet-fed (HFD) mice showing hypertriglyceridemia and hypercholesterolemia. Rilmenidine significantly ameliorated hyperlipidemia in HFD mice after 7 days of administration. Pretreatment with efaroxan, at a dose sufficient to inhibit I-1 R activation, blocked the effects of rilmenidine. Also, in cultured HepG2 cells, rilmenidine dose-dependently induced the expression of farnesoid X receptor (FXR). The rilmenidine-induced FXR expression and FXR-related genes were blocked by efaroxan. However, rilmenidine treatment did not affect the expression of enzymes related to β-oxidation. In conclusion, activation of I-1 R may activate FXR to lower plasma lipids, suggesting I-1 R as a new target for the treatment of hyperlipidemia.

Inhibition of insulin degrading enzyme by racecadotril in the brain of Wistar rats

Racecadotril is an enkephalinase inhibitor used to treat abdominal discomfort in the clinic. The blood-glucose lowering action of racecadotril has been observed in rats; however, the mechanisms remain obscure. 8-week-old Wistar rats were intravenously injected with racecadotril and the levels of insulin in the brain were measured. Additionally, brain homogenates were co-incubated with racecadotril or thiorphan to evaluate insulin degrading enzyme (IDE) activity. Otherwise, rats were pretreated by intracerebroventricular (i. c. v.) injection of insulin antibody or glibenclamide at a dose sufficient to inhibit K (ATP) channels prior to injection of racecadotril. Moreover, rats were vagotomized to evaluate the role of the cholinergic nerve. Racecadotril significantly decreased the plasma glucose in rats; this action of racecadotril was abolished by i. c. v. pretreatment with insulin antibody or glibenclamide. Also, i. c. v. injection of thiorphan, the active form of racecadotril, lowered blood glucose, but this effect disappeared in the presence of the insulin antibody. In rat brain homogenates, racecadotril and thiorphan inhibited IDE activity and increased the cerebral insulin level. The blood-glucose lowering action of racecadotril or thiorphan was diminished in vagotomized rats. Our results suggest that racecadotril lowers blood glucose mainly through inhibition of IDE activity and increases endogenous insulin in the brain. Subsequently, the increased insulin might activate insulin receptor, which opens the K (ATP) channel and induces peripheral insulin release through the vagal nerve. Thus, we provide the new finding that racecadotril has the ability to inhibit IDE in rat brain.

Elevated retinol binding protein 4 contributes to insulin resistance in spontaneously hypertensive rats

Retinol binding protein 4 (RBP4) is an adipokine secreted by adipose tissue and liver and contributes to insulin resistance (IR) in animals. Although several human studies indicated that RBP4 is positively correlated with blood pressure and is elevated in untreated hypertensive subjects, the role of RBP4 in IR of hypertensive animals still remains obscure. In this study, spontaneously hypertensive rats (SHR) were used to investigate the relationship between RBP4 levels and IR. We found that at 7 weeks old, SHR had significantly increased plasma RBP4 levels and RBP4 expression in liver and epididymal adipose tissue accompanied by worsening of IR as compared with Wistar-Kyoto (WKY) control rats. Administration of fenretinide in SHR to increase urinary RBP4 excretion significantly decreased plasma RBP4 levels and improved IR. Moreover, treatment with valsartan markedly reduced blood pressure, circulating RBP4 and adiponectin levels, and IR in SHR. Valsartan also reversed the increase of hepatic gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) and the decrease of type 4 glucose transporter (GLUT4) in adipose tissue. In conclusion, these results suggest that RBP4 contributes, at least partly, to the pathogenesis of IR in SHR. Furthermore, the decrease of blood pressure caused by valsartan not only decreased RBP4 levels, but also improved IR in SHR.

Changes of CCAAT enhancer-binding proteins (CEBPs) in the lung of streptozotocin-induced diabetic rats

CCAAT enhancer-binding proteins (CEBPs) play key roles in the metabolic regulation, cell transformation, and inflammation. However, the expression and/or functions of CEBPs in rats with hyperglycemia are still unclear. In the present study, we investigated the changes of CEBPs protein in lung of the diabetic rats. The levels of C/EBPβ and C/EBPδ protein were decreased in the lung isolated from streptozotocin-induced diabetic rats (STZ-diabetic rats) as compared with that of normal rats. Exogenous insulin at the dose sufficient to normalize the plasma glucose of STZ-diabetic rats reversed the protein levels of C/EBPβ and C/EBPδ in lung after a 4-day treatment. Similar results were also observed in STZ-diabetic rats that received the treatment of phlorizin to reverse the plasma glucose level for 4 days. Otherwise, the protein level of C/EBPα in lung of the STZ-diabetic rats was similar as the normal rats. Also, the level of C/EBPα protein in lung of the STZ-diabetic rat was not significantly changed by correction of plasma glucose by exogenous insulin or phlorizin. In addition, we also cultured human lung cells (A-549) and rat lung cells (L2) in varies concentration of D-glucose and L-glucose to identify the effect of glucose in expression of C/EBPs. The obtained results suggest that increase of plasma glucose is related to the lower expression of C/EBPβ and C/EBPδ proteins in the lung of STZ-diabetic rats. The changes of expression of C/EBPβ and C/EBPδ are not caused by changes of osmolarity but by D-glucose itself.

Metformin can activate imidazoline I-2 receptors to lower plasma glucose in type 1-like diabetic rats

Metformin is widely used in clinic for handling the diabetic disorders. However, action mechanisms of metformin remain obscure. It has recently been indicated that guanidinium derivatives are ligands to activate type-2 imidazoline receptors (I-2 receptors) that can improve diabetes through increment in skeletal muscle glucose uptake. Also, activation of I-2 receptors can increase the release of ß-endorphin in diabetic animals. Because metformin is a guanidinium derivative, we were interested in the effect of metformin on I-2 receptors. In the present study, the marked blood glucose-lowering action of metformin in streptozotocin-induced type-1 like diabetes rats was blocked by specific I-2 receptor antagonist, BU224, in a dose-dependent manner. Also, the increase of ß-endorphin release by metformin was blocked by BU224 in same manner. A specific competition between metformin and BU224 was observed in isolated adrenal medulla. Otherwise, amiloride at the dose sufficient to block I-2A receptor abolished the metformin-induced ß-endorphin release, but only the blood glucose-lowering action of metformin was markedly reduced. In addition, the blood glucose-lowering action of metformin in bilateral adrenalectomized rats was diminished by amiloride at higher doses. These results suggest that metformin might activate imidazoline I-2 receptors while I-2A receptors link the increase of ß-endorphin release and I-2B receptors couple to the other actions for lowering of blood glucose in type-1 like diabetic rats.

Mediation of Endogenous β-Endorphin in the Plasma Glucose-Lowering Action of Herbal Products Observed in Type 1-Like Diabetic Rats

Recently, there have been advances in the development of new substances effective in managing diabetic disorders. Opioid receptors couple multiple systems to result in various biological effects, although opioids are best known for analgesia. In the present review, we used our recent data to describe the advance in plasma glucose-lowering action of herbal products, especially the mediation of β-endorphin in glucose homeostasis of insulin-deficient diabetes. In type 1-like streptozotocin-induced diabetic rats, we identified many products purified from herbs that show a dose-dependent plasma glucose-lowering action. Increase in β-endorphin secretion from the adrenal gland may activate peripheral opioid μ-receptors (MOR) to enhance the expression of muscle glucose transporters and/or to reduce hepatic gluconeogenesis at the gene level, thereby leading to improved glucose utilization in peripheral tissues for amelioration of severe hyperglycemia. It has also been observed that stimulation of α(1)-adrenoceptors (α(1)-ARs) in the adrenal gland by some herbal products is responsible for the increase in β-endorphin secretion via a phospholipase C-protein kinase dependent pathway. However, an increase in β-endorphin secretion from the adrenal gland by herbal products can function via another receptor. New insights into the mediation of endogenous β-endorphin activation of peripheral MOR by herbal products for regulation of glucose homeostasis without the presence of insulin have been established. Therefore, an increase in β-endorphin secretion and/or direct stimulation of peripheral MOR via an insulin-independent action might serve as the potential target for development of a therapeutic agent or promising adjuvant in intensive plasma glucose control.

Indomethacin activates peroxisome proliferator-activated receptor γ to improve insulin resistance in cotton pellet granuloma model

Inflammation is involved in the development of insulin resistance and diabetes. However, the effectiveness of anti-inflammatory drugs in diabetic therapy remains obscure. In the present study, the possible mechanisms of indomethacin, one of the nonsteroidal anti-inflammatory drugs, in the improvement of insulin resistance were investigated. Indomethacin treatment significantly decreased cotton pellet implantation induced white blood cell count elevation and immune cells infiltration in epididymal white adipose tissue. Also, cotton pellet implantation induced impaired glucose utilization and insulin resistance were improved by indomethacin. The decrement in phosphoinsulin receptor and phospho-Akt levels induced by cotton pellet implantation was improved by indomethacin as well. Moreover, indomethacin decreased cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expression in epididymal white adipose tissue with a marked reduction of prostaglandin 2 (PGE2) and nitrite/nitrate (NOx) levels in cotton pellet-implanted mice. Furthermore, pretreatment of peroxisome proliferator-activated receptor γ (PPARγ) antagonist, GW9662 not only reversed indomethacin-modified COX-2 and iNOS levels but also reversed indomethacin-improved insulin sensitivity determined by homeostasis model assessment-insulin resistance (HOMA-IR). Taken together, indomethacin might elevate the expression of PPARγ to decrease serum NOx and PGE2 to result in the improvement of insulin resistance.

The decreased expression of peroxisome proliferator-activated receptors delta (PPARdelta) is reversed by digoxin in the heart of diabetic rats

The present study is designed to investigate the role of peroxisome proliferator-activated receptors delta (PPARdelta) in the action of digoxin in diabetic rats showing cardiac hypertrophy. We used Wistar rats to induce diabetes by injection of streptozotocin (STZ-rat) and examined the effect of digoxin on PPARdelta expression in these hyperglycemic rats (STZ-rat) at 10 weeks later. We measured the changes of body weight, water intake, and food intake in three groups of age-matched rats; the vehicle treated normal control (Wistar rats), the vehicle treated STZ-rats, and the digoxin-treated STZ-rats. Cardiac output, heart rate, and blood pressure in addition to plasma insulin or glucose level were also determined. The mRNA and protein levels of PPARdelta were measured using Northern and Western blotting, respectively. Cardiac output, heart rate, and blood pressure were markedly reduced while food intake, water intake, and blood glucose were raised in STZ-rats showing lower body weight and plasma insulin as compared with the vehicle-treated controls. After a 20-day of digoxin treatment, cardiac output was raised in STZ-rats but the diabetic parameters were not modified. The PPARdelta expressions, both mRNA and protein, were markedly elevated in the hearts of STZ-rats by digoxin treatment. The related signals with PPARdelta, such as carnitine palmitoyltransferase 1B (CPT1B), acetyl-coenzyme A, carboxylase alpha (ACC1), fatty acid synthase (FAS), and troponin I, were also raised. The increase of cardiac output by digoxin was reversed by the combined treatment with PPARdelta antagonist GSK0660. Thus, we suggest a new finding that PPARdelta is involved in digoxin induced cardiac inrotropic action.

Increase of plasma insulin by racecadotril, an inhibitor of enkephalinase, in Wistar rats

Racecadotril is known as an inhibitor of enkephalinase. Increase of plasma insulin by racecadotril has been observed in rats while the mechanism of the action remains obscure. In the present study, intravenous injection of male Wistar rats with racecadotril significantly decreased blood glucose levels. However, this effect of racecadotril was not modified by naloxone at the dose sufficient to block opioid receptors. Thus, the blood glucose-lowering action of racecadotril might be through an endogenous opioid independent mechanism. Otherwise, we found that C-peptide content was also raised by racecadotril in parallel with the increase of insulin in Wistar rats. Thus, the blood glucose-lowering action of racecadotril was related to insulin secretion, but not through the inhibition of plasma insulin degradation. In addition, racecadotril showed no direct effect on insulin secretion in isolated islets or cultured HIT-T15 beta cells. The increase of plasma insulin and blood glucose-lowering action induced by racecadotril were reduced by pretreatment with atropine and enhanced by physotigmine. Direct inhibition of cholinesterase was not observed in brain homogenates treated with racecadotril. Moreover, actions of racecadotril were significantly reduced in rats receiving hemicholinium-3 at a sufficient dose to decrease endogenous acetylcholine. Activation of cholinergic tone is possibly involved in the blood glucose-lowering effect of racecadotril. Our results suggested that racecadotril increased insulin secretion to lower blood glucose mainly via regulation of parasympathetic tone in Wistar rats.

Opening of ATP-sensitive potassium channel by insulin in the brain-induced insulin secretion in Wistar rats

Cerebral insulin can regulate glucose homeostasis via activation of the parasympathetic nervous system, which results in the reduction of hepatic glucose output. However, the precise mechanism(s) through which cerebral insulin directly exerts an effect on insulin secretion remains unclear. In the present study, we found that cerebral administration of insulin caused an increase of plasma insulin concentration and a concomitant decrease in plasma glucose levels within one hour. These effects were blocked by vagotomy or intraperitoneal injection of 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide, a specific M (3) antagonist. The mediating influence of parasympathetic activation can thus be considered. The adenosine triphosphate-sensitive potassium (K-ATP) channel is a key mediator of the cerebral action of insulin. The plasma glucose-lowering action of insulin was abolished by cerebral administration of glibenclamide or repaglinide at concentrations sufficient to block K-ATP channels. In conclusion, our findings suggest that cerebral insulin may induce insulin release by stimulating the opening of K-ATP channels, which in turn activate parasympathetic tone in pancreatic tissue.

Decrease of bone morphogenetic protein-7 (BMP-7) and its type II receptor (BMP-RII) in kidney of type 1-like diabetic rats

Bone morphogenetic protein-7 (BMP-7) expression is known to be protective for renal damage during diabetic nephropathy and disappears early during the progression of diabetic nephropathy. However, changes in expression of BMP-7 and BMP-7 type II receptor (BMP-RII) during kidney nephropathy response to high glucose-induced oxidative stress remain unclear. In this study, we used streptozotocin-induced diabetic rats with diabetic nephropathy and treated them with insulin, phloridzin, or antioxidant tiron. The insulin, phloridzin, or tiron treatment improved the renal function and decreased fibronectin expression in the streptozotocin-induced diabetic rats. Both insulin and phloridzin could reverse the attenuation effects of hyperglycemia on BMP-7 and BMP-RII expressions in the kidneys of streptozotocin-induced diabetic rats through the correction of hyperglycemia. However, the decrease of BMP-7 and BMP-RII expressions in kidney of streptozotocin-induced diabetic rats could be reversed by tiron through decreasing the high glucose-induced oxidative stress but not through changing the levels of glucose. We further confirmed the effect on reversing the BMP-7 and BMP-RII expressions through decreasing oxidative stress by tiron treatment in high glucose exposed mesangial cells. Thus, we suggest that a decrease in oxidative stress is responsible for the improvement of renal function and recovery of renal BMP-7 and BMP-RII expression in streptozotocin-induced diabetic rats.

Insulin resistance induced by glucosamine in fructose-fed rats

Glucosamine has been widely used to treat osteoporosis in clinic and it shows an effect on hexosamine biosynthetic pathway in glucose-induced insulin resistance. However, glucosamine and chronic hyperglycemia is not correlative. Thus, we used C (2)C (12) cell line to carry out the uptake assay of 2-[14C]-deoxy-d-glucose and [3H]-glucosamine. Glucosamine inhibited the in vitro glucose uptake in a concentration-dependent manner. The glucose transporter GLUT4 prepared for [3H]-glucosamine uptake showed a concentration-dependent competition between glucose and glucosamine uptake. The effects of glucosamine on glucose tolerance and homeostasis model assessment (HOMA) were also determined in normal Wistar and fructose-fed rats. Both plasma glucose levels and/or HOMA index were not changed in normal rats treated with glucosamine as compared with the saline-treated control. However, we found that glucosamine exhibited an effect on the expression of farnesoid X receptor in liver to exacerbate the values of HOMA and accelerate the development of insulin resistance in fructose-fed rats. Thus, glucosamine should be applied with caution in type-2 diabetic patients.

Increase of adipogenesis by ginsenoside (Rh2) in 3T3-L1 cell via an activation of glucocorticoid receptor

Adipocyte plays an important role in lipid regulation in mammals. Understanding of adipocyte differentiation becomes a key issue for the development of anti-obesity agent. Glucocorticoids (GCs) regulate lipid metabolism through promoting lipogenesis in adipose tissue. Ginsenoside Rh2, with a similar chemical structure as GCs, shows antidiabetic, anti-inflammatory, and anticancer actions both in vivo and in vitro. However, effect of Rh2 on glucocorticoid receptor (GR) for an increase of adipogenesis like GCs remains unclear. In the present study, we employed ginsenoside Rh2 to investigate the changes in adipogenetic process of 3T3-L1, one of the widely used preadipocytes, through activating GR or not. In leuciferase assay, we found that ginsenoside Rh2 induced GRs transitivity in a way as dexamethasone, which was deleted by RU486 at concentrations sufficient to block GR. Moreover, 3T3-L1 preadipocytes were differentiated into adipocytes by adipogenic induction medium containing 0.01 to 1 microM of ginsenoside Rh2. Also, RU486 blocked this adipogenesis induced by ginsenoside Rh2 or dexamethasone. The obtained results suggest that ginsenoside Rh2 can promote preadipocytes differentiation through activating GR. This finding seems helpful for the understanding of ginsenosides in the regulation of lipid metabolism.

Interferon-alpha-induced serotonin uptake in Jurkat T cells via mitogen-activated protein kinase and transcriptional regulation of the serotonin transporter

Interferon (IFN)-alpha upregulates serotonin (5-HT) uptake and serotonin transporter (5-HTT) messenger ribonucleic acid (mRNA) expression in immune cells, which implies the mechanism underlying IFN-alpha-induced depression. However, the signal transduction of this effect remains unclear. We investigated whether the effects of IFN-alpha on the functions of 5-HTT were related to mitogen-activated protein kinase (MAPK). By performing Western blotting, real-time reverse transcriptase-polymerase chain reaction and [3H]5-HT labelling, we examined MAPK phosphorylation, 5-HTT mRNA expression and 5-HT uptake in Jurkat T cells. The cells had been cultured for different time periods (1) with IFN-alpha alone and (2) preincubated with either MAPK inhibitors or with the selective serotonin reuptake inhibitor, fluoxetine, and subsequently cultured along with IFN-alpha. The levels of MAPK phosphorylation, 5-HTT mRNA expression and 5-HT uptake all increased in the IFN-alpha-treated cells but were blocked in those that were pretreated with MAPK inhibitors and fluoxetine. These results appear to clarify the association of depression with IFN-alpha-induced 5-HT uptake that reduces the 5-HT levels and IFN-alpha-regulated transcription of 5-HTT; further, the results suggest the involvement of MAPK in this process.

Increase of beta-endorphin secretion by syringin, an active principle of Eleutherococcus senticosus, to produce antihyperglycemic action in type 1-like diabetic rats

We employed streptozotocin-induced diabetic rats (STZ-diabetic rats) as type 1 diabetes-like animal models to investigate the mechanism(s) of antihyperglycemic action produced by syringin, an active principle purified from the rhizome and root part S of ELEUTHEROCOCCUS SENTICOSUS (Araliaceae). Bolus intravenous (i. v.) injection of syringin dose-dependently decreased the plasma glucose of STZ-diabetic rats in 30 minutes in a way parallel to the increase of plasma beta-endorphin-like immunoreactivity (BER). Syringin enhanced BER release from the isolated adrenal medulla of STZ-diabetic rats in a concentration-dependent manner from 0.001 to 10 micromol/l. Bilateral adrenalectomy in STZ-diabetic rats eliminated the activities of syringin (1 mg/kg, i. v.) including the plasma glucose-lowering effect and the plasma BER-elevating effect. Also, syringin failed to lower plasma glucose in the presence of micro-opioid receptor antagonists and/or in the micro-opioid receptor knockout diabetic mice. In conclusion, the obtained results suggest that syringin can enhance the secretion of beta-endorphin from adrenal medulla to stimulate peripheral micro-opioid receptors resulting in a decrease of plasma glucose in diabetic rats lacking insulin.

Ginsenoside Rh2 is one of the active principles of Panax ginseng root to improve insulin sensitivity in fructose-rich chow-fed rats

Ginsenoside Rh2, one of the ginsenosides contained in the Panax ginseng root, was employed to screen the effect on insulin resistance of rats induced by a diet containing 60% fructose. Single intravenous injection of ginsenoside Rh2 decreased the plasma glucose concentrations in 60 minutes in a dose-dependent manner from 0.1 mg/kg to 1 mg/kg in rats with insulin resistance induced by fructose-rich chow. Repeated intravenous injection of ginsenoside Rh2 (1 mg/kg per injection, 3 times daily) into rats which received fructose-rich chow for 3 consecutive days decreased the value of glucose-insulin index, the product of the areas under the curve of glucose and insulin during the intraperitoneal (i.p.) glucose tolerance test. This means that ginsenoside Rh2 has an ability to improve insulin action on glucose disposal. The plasma glucose lowering action of tolbutamide, induced by the secretion of endogenous insulin, is widely used to characterize the formation of insulin resistance. Time for the loss of plasma glucose lowering response to tolbutamide (10 mg/kg, i.p.) in rats during insulin resistance induction by fructose-rich chow was also markedly delayed by the repeated treatment of ginsenoside Rh2, as compared to the vehicle-treated control. Thus, the repeated treatment of ginsenoside Rh2 delayed the development of insulin resistance in high fructose feeding rats. Increase of insulin sensitivity by ginsenoside Rh2 was further identified using the plasma glucose lowering action of exogenous insulin in streptozotocin-induced diabetic rats (STZ-diabetic rats). Repeated injection of ginsenoside Rh2 at the same dosing (1 mg/kg, 3 times daily) into STZ-diabetic rats for 10 days made an increase of the responses to exogenous insulin. Taken together, it can be concluded that ginsenoside Rh2 has an ability to improve insulin sensitivity and it seems suitable to use ginsenoside Rh2 as an adjuvant for diabetic patients and/or the subjects wishing to increase insulin sensitivity.

Mechanism for blockade of angiotensin subtype 1 receptors to lower plasma glucose in streptozotocin-induced diabetic rats

AIMS

We investigated the mechanism(s) by which valsartan, a selective antagonist of angiotensin subtype 1 (AT(1)) receptor, decreased plasma glucose in streptozotocin (STZ)-induced diabetic rats.

METHODS

The plasma glucose concentration was assessed by the glucose oxidase method. The concentration of beta-endorphin in plasma or medium incubating adrenal medulla was measured using an enzyme-linked immunosorbent assay. The mRNA levels of the subtype 4 form of glucose transporter (GLUT4) in soleus muscle and phosphoenolpyruvate carboxykinase (PEPCK) in the liver were detected by Northern blotting analysis, while the protein levels of GLUT4 in isolated soleus muscle and hepatic PEPCK were investigated using Western blotting analysis.

RESULTS

A single intravenous injection of valsartan dose-dependently increased plasma beta-endorphin-like immunoreactivity (BER) in parallel with the lowering of plasma glucose concentration in STZ-induced diabetic rats. Naloxone and naloxonazine inhibited the plasma glucose-lowering action of valsartan at doses sufficient to block opioid micro-receptors. In contrast to its action in wild-type diabetic mice, valsartan failed to modify plasma glucose in opioid micro-receptor knockout diabetic mice. Bilateral adrenalectomy in STZ-induced diabetic rats eliminated both the plasma glucose-lowering action and the plasma BER-elevating action of valsartan. In the isolated adrenal medulla of STZ-induced diabetic rats, angiotensin II (Ang II) or valsartan did not affect spontaneous BER secretion. Activation of cholinergic receptors by 1.0 micromol/l acetylcholine (ACh) enhanced BER secretion from the isolated adrenal medulla of STZ-induced diabetic rats, but not in the presence of 1.0 nmol/l Ang II, while valsartan reversed this inhibition by Ang II in a concentration-dependent manner. Treatment of STZ-induced diabetic rats with valsartan (0.2 mg/kg) three times daily for 3 days resulted in an increase in gene expression of GLUT4 in soleus muscle and impeded the reduction of elevated mRNA or protein level of hepatic PEPCK. Both of these effects were blocked by opioid micro-receptor antagonist.

CONCLUSIONS

The results suggest that blockade of AT(1) receptor by valsartan may enhance the adrenal beta-endorphin secretion induced by ACh, activating the opioid micro-receptors to increase glucose utilization and/or to decrease hepatic gluconeogenesis, resulting in the reduction of plasma glucose in STZ-induced diabetic rats.

Serotonin transporter mRNA expression is decreased by lamivudine and ribavirin and increased by interferon in immune cells

Clinical reports document that depression as a side effect is more prevalent in hepatic patients given interferon (IFN)-alpha therapy than in those given lamivudine. The mechanisms, however, are poorly understood. Serotonin transporter (5-HTT), via uptake of serotonin (5-HT) into presynaptic serotoninergic neurons, is an initial action site for antidepressants. Real-time polymerase chain reaction (PCR) was used to quantify 5-HTT mRNA expression in immune cells in order to evaluate whether 5-HTT acted as an indicator of depression. Results showed that the 5-HTT mRNA expression was much higher in T-cell and B-cell lines than that in a monocytic cell line. Treatment with either lamivudine or ribavirin reduced the 5-HTT mRNA expression, protein level and 5-HT uptake in T-cell line. Treatment with IFN-alpha, however, increased those levels in the same group. A similar effect was observed in peripheral blood mononuclear cells (PBMC). Mimicking clinical use by treating PBMC with a combination of IFN-alpha and ribavirin increased the 5-HTT mRNA expression level. Our study indicates that these therapeutic drugs regulate 5-HTT expression, which implies that 5-HTT might be a trait marker in IFN-alpha-induced depression after hepatic therapy.

Plasma glucose-lowering action of Hon-Chi in streptozotocin-induced diabetic rats

Hon-Chi was used for anti-hyperglycemic activity screening in streptozotocin-induced diabetic rats (STZ-diabetic rats) in an attempt to develop new substances for handling diabetes. Mandarin Hon-Chi is red yeast rice fermented with Monascus pilous and Monascus purpureus. Single oral administration of Hon-Chi decreased plasma glucose in STZ-diabetic rats in a dose-dependent manner from 50 mg/kg to 350 mg/kg. Similar treatment with Hon-Chi also lowered the plasma glucose in normal rats as effectively as that produced in STZ-diabetic rats. In addition, oral administration of Hon-Chi at the highest dose (350 mg/kg) attenuated the elevation of plasma glucose induced by an intravenous glucose challenge test in normal rats. Moreover, mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) in liver from STZ-diabetic rats were reversed in a dose-dependent manner by the repeated oral treatment of Hon-Chi three times daily for two weeks. Otherwise, hyperphagia in STZ-diabetic rats was markedly reversed by similar repeated treatment of Hon-Chi. The obtained results suggest that oral administration of Hon-Chi could decrease hepatic gluconeogenesis to lower plasma glucose in diabetic rats lacking insulin.

Metformin increases insulin sensitivity and plasma beta-endorphin in human subjects

Metformin has been widely used in clinical type 2 diabetes treatment and prevention. The present study was designed to explore the effect on people with a sedentary lifestyle at therapeutic doses. Twenty-two physically-inactive volunteers with normal glucose tolerance were studied. Escalating doses of metformin in low-dose (250 mg), intermediate-dose (500 mg), and high-dose (750 mg) treatment three times per day were administrated into each subject for a three-week treatment period. Fasting plasma glucose, A1C, HOMA-IR for insulin resistance, lipid profile, and plasma beta-endorphin-like immunoreactivity (BER) were measured before treatment and weekly at the end of each dosing period. Metformin significantly reduced fasting plasma glucose and HOMA-IR in healthy humans after receiving this treatment at therapeutic doses including low-dose (5 %, 17 %), intermediate-dose (6 %, 25 %) and high-dose treatment (6 %, 21 %). Plasma BER was also increased from 135.46 +/- 61.73 pg/ml to 137.52 +/- 66.11 pg/ml by low-dosing (p = 0.39), to 139.17 +/- 64.08 pg/ml by intermediate-dosing (p = 0.32), and to 149.59 +/- 63.32 pg/ml by high-dosing (p < 0.05). Also, serum cholesterol decreased significantly using metformin at therapeutic doses including low-dose (4 %), intermediate-dose (8 %) and high-dose treatment (7 %). However, metformin failed to modify levels of serum HDL-cholesterol and C-reactive protein (CRP) in healthy subjects. Also, the reduction of serum cholesterol by metformin did not correlate to the increase in insulin sensitivity. In conclusion, metformin causes a significant parallel increase in insulin sensitivity and plasma beta-endorphin level in human subjects.

Suppression of transforming growth factor-beta1 gene expression by Danggui buxue tang, a traditional Chinese herbal preparation, in retarding the progress of renal damage in streptozotocin-induced diabetic rats

Danggui buxue tang (DBT), a preparation containing Angelica sinensis (danggui) and Astragalus membranaceus (huangqi) at a ratio of 1 : 5, is used widely in China for stimulating red blood cell production and enhancing cardiovascular function. The present study was undertaken to characterize the effects of this preparation on diabetic nephropathy using streptozotocin-diabetic rats as a model. Streptozotocin-dependent alterations in renal weight/body weight ratio, urinary albumin and beta (2)-microglobulin concentrations, urinary albumin excretion rate, and creatinine clearance were ameliorated after eight weeks of treatment with either DBT or the angiotensin-converting enzyme inhibitor, benazepril. DBT, but not benazepril, partially attenuated the increases in blood glucose, triglycerides and cholesterol in STZ-diabetic rats. Additionally, the increased expression of transforming growth factor-beta (1) mRNA in the renal cortex due to streptozotocin-induced diabetes was modestly attenuated by these treatments. However, eight weeks of treatment with DBT failed to modify the concentration of angiotensin II in plasma or kidney, indicating that the ability of the preparation to retard the progression of kidney disease was not attributable to inhibition of the renin-angiotensin system. We propose that DBT alleviates renal alterations in diabetes and slows the progression of diabetic nephropathy by suppressing transforming growth factor-beta (1) mRNA expression. The preparation may therefore be useful as an adjuvant therapy for controlling diabetes and its complications.

Increase of insulin sensitivity by stevioside in fructose-rich chow-fed rats

The intake of dietary fructose has undergone a marked increase around the world, especially the developed countries, in recent times. Stevioside, a glycoside contained in the leaves of Stevia rebaudiana Bertoni (Compositae), was used to screen the effect induced by a diet containing 60% fructose on insulin resistance in rats. Single oral administration of stevioside for 90 min decreased plasma glucose concentrations in a dose-dependent manner in rats receiving fructose-rich chow for four weeks. In addition, insulin action on glucose disposal rate was measured using the glucose-insulin index, the product of the areas under the curve of glucose, and insulin during the intraperitoneal glucose tolerance test. Oral administration of stevioside (5.0 mg/kg) in rats given four weeks of fructose-rich chow for 90 min reversed the value of glucose-insulin index, indicating that stevioside has the ability to improve insulin sensitivity in this insulin-resistant animal model. Time for the loss of plasma glucose lowering response to tolbutamide (10.0 mg/kg, i. p.) in fructose-rich chow fed rats was also markedly delayed by repeated stevioside treatment three times daily compared to the vehicle-treated group. The plasma glucose-lowering activity of tolbutamide was introduced to account for varying levels of endogenous insulin secretion, and is widely used as the indicator of insulin resistance development. Thus, it provided the supportive data that repeated oral administration of stevioside delayed the development of insulin resistance in rats on a high-fructose diet. Increased insulin sensitivity by stevioside administration was further identified using the plasma glucose-lowering action of exogenous insulin in streptozotocin-induced diabetic rats (STZ-diabetic rats). Oral administration of stevioside at 0.2 mg/kg three times daily into STZ-diabetic rats for ten days increased the response to exogenous insulin. Taken together, this demonstrated that oral administration of stevioside improves insulin sensitivity, and seems suitable as an adjuvant for diabetic patients and/or those that consume large amounts of fructose.

Activation of opioid mu-receptors by loperamide to improve interleukin-6-induced inhibition of insulin signals in myoblast C2C12 cells

AIMS/HYPOTHESIS

This study investigated the role of opioid mu-receptor activation in the improvement of insulin resistance.

METHODS

Myoblast C2C12 cells were cultured with IL-6 to induce insulin resistance. Radioactive 2-deoxyglucose (2-DG) uptake was used to evaluate the effect of loperamide on insulin-stimulated glucose utilisation. Protein expression and phosphorylation in insulin-signalling pathways were detected by immunoblotting.

RESULTS

The insulin-stimulated 2-DG uptake was reduced by IL-6. Loperamide reversed this uptake, and the uptake was inhibited by blockade of opioid mu-receptors. Insulin resistance induced by IL-6 was associated with impaired expression of the insulin receptor (IR), IR tyrosine autophosphorylation, IRS-1 protein content and IRS-1 tyrosine phosphorylation. Also, an attenuated p85 regulatory subunit of phosphatidylinositol 3-kinase, Akt serine phosphorylation and the protein of glucose transporter subtype 4 were observed in insulin resistance. Loperamide reversed IL-6-induced decrement of these insulin signals.

CONCLUSIONS/INTERPRETATION

Opioid mu-receptor activation may improve IL-6-induced insulin resistance through modulation of insulin signals to reverse the responsiveness of insulin. This provides a new target in the treatment of insulin resistance.

Activation of imidazoline receptors in adrenal gland to lower plasma glucose in streptozotocin-induced diabetic rats

AIMS/HYPOTHESIS

The present study investigated the effect of agmatine, an endogenous ligand of imidazoline receptors, on plasma glucose in streptozotocin-induced diabetic rats (STZ-diabetic rats).

METHODS

Plasma glucose was assessed by the glucose oxidase method. Plasma insulin and beta-endorphin-like immunoreactivity in plasma or adrenal medulla were measured by enzyme-linked immunosorbent assay. Systolic blood pressure was determined by the tail-cuff method. The mRNA levels of glucose transporter subtype 4 (GLUT4) in soleus muscle and phosphoenolpyruvate carboxykinase (PEPCK) in liver were detected by northern blotting. Protein levels of GLUT4 in soleus muscle and hepatic PEPCK were estimated using western blotting analysis.

RESULTS

After intravenous injection into fasting STZ-diabetic rats for 30 min, agmatine decreased plasma glucose in a dose-dependent manner without changing systolic blood pressure. At the same time, plasma beta-endorphin-like immunoreactivity also increased in STZ-diabetic rats receiving the same treatment. Plasma glucose was significantly elevated in STZ-diabetic rats by an intravenous injection of clonidine at a dose sufficient to decrease systolic blood pressure. Involvement of I(1)-imidazoline receptors and/or alpha2-adrenoceptors in this effect of agmatine was thus unlikely. The lowering of plasma glucose and increase of plasma beta-endorphin-like immunoreactivity by agmatine were abolished by pretreating the rats with BU-224 at a dose sufficient to block I(2)-imidazoline receptors. Both effects of agmatine were also abolished in adrenalectomised STZ-diabetic rats. Moreover, agmatine enhanced beta-endorphin-like immunoreactivity release from the isolated adrenal medulla of STZ-diabetic rats, an effect also blocked by BU-224. Release of beta-endorphin from the adrenal glands by I(2)-imidazoline receptor activation seems responsible for the plasma glucose-lowering action of agmatine. This was supported by the fact that intravenous injection of naloxone or naloxonazine at doses sufficient to block opioid mu-receptors inhibited the action of agmatine. In addition to lowering plasma glucose, repeated intravenous injection of agmatine into STZ-diabetic rats for 4 days also increased mRNA and protein levels of GLUT4 in soleus muscle. The same treatment also reversed the higher mRNA and protein levels of PEPCK in liver of STZ-diabetic rats.

CONCLUSIONS/INTERPRETATION

Our results suggest that agmatine may activate I(2)-imidazoline receptors in the adrenal gland. This enhances secretion of beta-endorphin, which can activate opioid mu-receptors to increase GLUT4 gene expression and/or suppress hepatic PEPCK gene expression, resulting in a lowering of plasma glucose in diabetic rats lacking insulin. The results provide a potential new target for intervention in type 1 diabetes.