Improved Labeling of Pancreatic Islets Using Cationic Magnetoliposomes.

Pancreatic islets (PIs) transplantation is an alternative approach for the treatment of severe forms of type 1 diabetes (T1D). To monitor the success of transplantation, it is desirable to follow the location of engrafted PIs non-invasively. In vivo magnetic resonance imaging (MRI) of transplanted PIs is a feasible cell tracking method; however, this requires labeling with a suitable contrast agent prior to transplantation. We have tested the feasibility of cationic magnetoliposomes (MLs), compared to commercial contrast agents (Endorem and Resovist), by labeling insulinoma cells and freshly isolated rat PIs. It was possible to incorporate Magnetic Ressonance (MR)-detectable amounts of MLs in a shorter time (4 h) when compared to Endorem and Resovist. MLs did not show negative effects on the PIs' viability and functional parameters in vitro. Labeled islets were transplanted in the renal sub-capsular region of healthy mice. Hypointense contrast in MR images due to the labeled PIs was detected in vivo upon transplantation, while MR detection of PIs labeled with Endorem and Resovist was only possible after the addition of transfection agents. These findings indicate that MLs are suitable to image PIs, without affecting their function, which is promising for future longitudinal pre-clinical and clinical studies involving the assessment of PI transplantation.

In vivo and ex vivo 19-fluorine magnetic resonance imaging and spectroscopy of beta-cells and pancreatic islets using GLUT-2 specific contrast agents.

The assessment of the ß-cell mass in experimental models of diabetes and ultimately in patients is a hallmark to understand the relationship between reduced ß-cell mass/function and the onset of diabetes. It has been shown before that the GLUT-2 transporter is highly expressed in both ß-cells and hepatocytes and that D-mannoheptulose (DMH) has high uptake specificity for the GLUT-2 transporter. As 19-fluorine MRI has emerged as a new alternative method for MRI cell tracking because it provides potential non-invasive localization and quantification of labeled cells, the purpose of this project is to validate ß-cell and pancreatic islet imaging by using fluorinated, GLUT-2 targeting mannoheptulose derivatives (19 FMH) both in vivo and ex vivo. In this study, we confirmed that, similar to DMH, 19 FMHs inhibit insulin secretion and increase the blood glucose level in mice temporarily (approximately two hours). We were able to assess the distribution of 19 FMHs in vivo with a temporal resolution of about 20 minutes, which showed a quick removal of 19 FMH from the circulation (within two hours). Ex vivo MR spectroscopy confirmed a preferential uptake of 19 FMH in tissue with high expression of the GLUT-2 transporter, such as liver, endocrine pancreas and kidney. No indication of further metabolism was found. In summary, 19 FMHs are potentially suitable for visualizing and tracking of GLUT-2 expressed cells. However, current bottlenecks of this technique related to the quick clearance of the compound and relative low sensitivity of 19 F MRI need to be overcome. Copyright © 2016 John Wiley & Sons, Ltd.

Anoctamin 1 (Ano1) is required for glucose-induced membrane potential oscillations and insulin secretion by murine ß-cells.

Anions such as Cl(-) and HCO3 (-) are well known to play an important role in glucose-stimulated insulin secretion (GSIS). In this study, we demonstrate that glucose-induced Cl(-) efflux from ß-cells is mediated by the Ca(2+)-activated Cl(-) channel anoctamin 1 (Ano1). Ano1 expression in rat ß-cells is demonstrated by reverse transcriptase-polymerase chain reaction, western blotting, and immunohistochemistry. Typical Ano1 currents are observed in whole-cell and inside-out patches in the presence of intracellular Ca(++): at 1 µM, the Cl(-) current is outwardly rectifying, and at 2 µM, it becomes almost linear. The relative permeabilities of monovalent anions are NO3 (-) (1.83 ± 0.10) > Br(-) (1.42 ± 0.07) > Cl(-) (1.0). A linear single-channel current-voltage relationship shows a conductance of 8.37 pS. These currents are nearly abolished by blocking Ano1 antibodies or by the inhibitors 2-(5-ethyl-4-hydroxy-6-methylpyrimidin-2-ylthio)-N-(4-(4-methoxyphenyl)thiazol-2-yl)acetamide (T-AO1) and tannic acid (TA). These inhibitors induce a strong decrease of 16.7-mM glucose-stimulated action potential rate (at least 87 % on dispersed cells) and a partial membrane repolarization with T-AO1. They abolish or strongly inhibit the GSIS increment at 8.3 mM and at 16.7 mM glucose. Blocking Ano1 antibodies also abolish the 16.7-mM GSIS increment. Combined treatment with bumetanide and acetazolamide in low Cl(-) and HCO3 (-) media provokes a 65 % reduction in action potential (AP) amplitude and a 15-mV AP peak repolarization. Although the mechanism triggering Ano1 opening remains to be established, the present data demonstrate that Ano1 is required to sustain glucose-stimulated membrane potential oscillations and insulin secretion.

Sardine protein diet increases plasma glucagon-like peptide-1 levels and prevents tissue oxidative stress in rats fed a high-fructose diet.

The current study investigated whether sardine protein mitigates the adverse effects of fructose on plasma glucagon­like peptide-1 (GLP-1) and oxidative stress in rats. Rats were fed casein (C) or sardine protein (S) with or without high­fructose (HF) for 2 months. Plasma glucose, insulin, GLP­1, lipid and protein oxidation and antioxidant enzymes were assayed. HF rats developed obesity, hyperglycemia, hyperinsulinemia, insulin resistance and oxidative stress despite reduced energy and food intakes. High plasma creatinine and uric acid levels, in addition to albuminuria were observed in the HF groups. The S­HF diet reduced plasma glucose, insulin, creatinine, uric acid and homeostasis model assessment­insulin resistance index levels, however increased GLP­1 levels compared with the C­HF diet. Hydroperoxides were reduced in the liver, kidney, heart and muscle of S­HF fed rats compared with C­HF fed rats. A reduction in liver, kidney and heart carbonyls was observed in S­HF fed rats compared with C­HF fed rats. Reduced levels of nitric oxide (NO) were detected in the liver, kidney and heart of the S­HF fed rats compared with C­HF fed rats. The S diet compared with the C diet reduced levels of liver hydroperoxides, heart carbonyls and kidney NO. The S­HF diet compared with the C­HF diet increased the levels of liver and kidney superoxide dismutase, liver and muscle catalase, liver, heart and muscle glutathione peroxidase and liver ascorbic acid. The S diet prevented and reversed insulin resistance and oxidative stress, and may have benefits in patients with metabolic syndrome.

Inhibition of the glucose transporter SGLT2 with dapagliflozin in pancreatic alpha cells triggers glucagon secretion.

Type 2 diabetes (T2D) is characterized by chronic hyperglycemia resulting from a deficiency in insulin signaling, because of insulin resistance and/or defects in insulin secretion; it is also associated with increases in glucagon and endogenous glucose production (EGP). Gliflozins, including dapagliflozin, are a new class of approved oral antidiabetic agents that specifically inhibit sodium-glucose co-transporter 2 (SGLT2) function in the kidney, thus preventing renal glucose reabsorption and increasing glycosuria in diabetic individuals while reducing hyperglycemia. However, gliflozin treatment in subjects with T2D increases both plasma glucagon and EGP by unknown mechanisms. In spite of the rise in EGP, T2D patients treated with gliflozin have lower blood glucose levels than those receiving placebo, possibly because of increased glycosuria; however, the resulting increase in plasma glucagon levels represents a possible concerning side effect, especially in a patient population already affected by hyperglucagonemia. Here we demonstrate that SGLT2 is expressed in glucagon-secreting alpha cells of the pancreatic islets. We further found that expression of SLC5A2 (which encodes SGLT2) was lower and glucagon (GCG) gene expression was higher in islets from T2D individuals and in normal islets exposed to chronic hyperglycemia than in islets from non-diabetics. Moreover, hepatocyte nuclear factor 4-α (HNF4A) is specifically expressed in human alpha cells, in which it controls SLC5A2 expression, and its expression is downregulated by hyperglycemia. In addition, inhibition of either SLC5A2 via siRNA-induced gene silencing or SGLT2 via dapagliflozin treatment in human islets triggered glucagon secretion through KATP channel activation. Finally, we found that dapagliflozin treatment further promotes glucagon secretion and hepatic gluconeogenesis in healthy mice, thereby limiting the decrease of plasma glucose induced by fasting. Collectively, these results identify a heretofore unknown role of SGLT2 and designate dapagliflozin an alpha cell secretagogue.

Vitamin D supplementation ameliorates hypoinsulinemia and hyperglycemia in static magnetic field-exposed rat.

The purpose of this study is to evaluate the effects of vitamin D supplementation on glucose and lipid metabolism in static magnetic field (SMF)-exposed rats. Rats exposed to SMF (128 mT; 1 h/day) during 5 consecutive days showed an increase in plasma glucose level and a decrease in plasma insulin concentration. By contrast, the same treatment failed to alter body weight and plasmatic total cholesterol, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, and triglyceride levels. Interestingly, supplementation with vitamin D (1,600 IU/100 g, per os) corrected and restored glycemia and insulinemia in SMF-exposed rats. The same treatment had no effects on lipid metabolism.

Interdependency of selected metabolic variables in an animal model of metabolic syndrome.

In the present study, the correlation between the percentage of glycated hemoglobin, taken as representative of changes in glucose homeostasis, and selected variables was investigated. Rats were treated for 8 weeks with diets containing 64% starch and 5% sunflower oil or containing 64% D-fructose mixed with: 5% sunflower oil; 3.4% sunflower oil and 1.6% salmon oil; or 3.4% sunflower oil and 1.6% safflower oil. Positive correlations were found between glycated hemoglobin and plasma albumin, urea, creatinine, phospholipids, triglycerides and total cholesterol, liver cholesterol, triglyceride and phospholipid content, and the plasma, liver, heart, kidney, soleus muscle and visceral adipose tissue content of thiobarbituric acid reactive substances, carbonyl derivatives and hydroperoxides. Inversely, negative correlations were observed between glycated hemoglobin and plasma calcium, iron and HDL-cholesterol concentrations, liver, heart, kidney, soleus muscle and visceral adipose tissue superoxide dismutase and catalase activity; as well as plasma, liver, heart, kidney, soleus muscle and visceral adipose tissue nitric oxide content. Only the liver glucokinase activity and liver, heart, kidney, soleus muscle and visceral adipose tissue glutathione reductase activity failed to display a significant correlation with glycated hemoglobin. These findings confirm the hypothesis that there is a close association between glucose homeostasis and other variables when considering the effects of long-chain polyunsaturated ω3 and ω6 fatty acids in rats with fructose-induced metabolic syndrome.

Vitamin E prevents glucose metabolism alterations induced by static magnetic field in rats.

In the present study, we investigate the effects of a possible protective role of vitamin E (vit E) or selenium (Se) on glucose metabolism disruption induced by static magnetic field (SMF) in rats. Rats have been exposed to SMF (128 mT, 1 h/day during 5 days). Our results showed that SMF failed to alter body weight and relative liver weight. Our data demonstrated that exposure to SMF increased (+21 %) blood glucose level and caused a decrease (-15 %) in liver glycogen content. Moreover, the same treatment induced a reduction of pancreatic islet area. Interestingly, supplementation with vit E (DL α-tocopherol acetate, 150 mg/kg per os during 5 days) prevented alterations induced by SMF on glucose metabolism and liver glycogen content, whereas supplementation with Se (Na2SeO3, 0.20 mg/l, in drinking water for 4 weeks) restored only hepatic glycogen contents. By contrast, both vit E and Se failed to correct the area of pancreatic islets.

Effect of cytochalasin B on 3-O-[14C]-methyl-D-glucose or D-[U-14C]glucose handling by BRIN-BD11 cells.

The present study aimed to investigate the effects of cytochalasin B (20 µM) on the uptake of 3-O-[14C]-methyl-D-glucose or D-[U-14C]glucose (8.3 mM each) by BRIN-BD11 cells. Taking into account the distribution space of tritiated water (3HOH), which was unexpectedly increased shortly after exposure of the cells to cytochalasin B and then progressively returned to its control values, and that of L-[1-14C]glucose, used as an extracellular marker, it was demonstrated that cytochalasin B caused a modest, but significant inhibition of the uptake of D-glucose and its non-metabolized analog by the BRIN-BD11 cells. These findings resemble those observed in acinar or ductal cells of the rat submaxillary gland and displayed a relative magnitude comparable to that found for the inhibition of D-glucose metabolism by cytochalasin B in purified pancreatic islet B cells. These findings reinforce the view that the primary site of action of cytochalasin B is located at the level of the plasma membrane.

Uptake and metabolism of D-glucose in isolated acinar and ductal cells from rat submandibular glands.

The present study deals with the possible effects of selected environmental agents upon the uptake and metabolism of d-glucose in isolated acinar and ductal cells from the rat submandibular salivary gland. In acinar cells, the uptake of d-[U-(14) C]glucose and its non-metabolised analogue 3-O-[(14) C-methyl]-d-glucose was not affected significantly by phloridzin (0.1 mM) or substitution of extracellular NaCl (115 mM) by an equimolar amount of CsCl, whilst cytochalasin B (20 µM) decreased significantly such an uptake. In ductal cells, both phloridzin and cytochalasin B decreased the uptake of d-glucose and 3-O-methyl-d-glucose. Although the intracellular space was comparable in acinar and ductal cells, the catabolism of d-glucose (2.8 or 8.3 mM) was two to four times higher in ductal cells than in acinar cells. Phloridzin (0.1 mM), ouabain (1.0 mM) and cytochalasin B (20 µM) all impaired d-glucose catabolism in ductal cells. Such was also the case in ductal cells incubated in the absence of extracellular Ca(2+) or in media in which NaCl was substituted by CsCl. It is proposed that the ductal cells in the rat submandibular gland are equipped with several systems mediating the insulin-sensitive, cytochalasin B-sensitive and phloridzin-sensitive transport of d-glucose across the plasma membrane.

Expression and localization of glucose transporters in rodent submandibular salivary glands.

BACKGROUND/AIM: The submandibular gland is one of the three major salivary glands, producing a mixed secretion; this saliva is hypotonic compared to plasma. It also secretes glucose, but the mechanisms responsible for this process are poorly understood. Our study addressed the question whether glucose transporters are expressed and how are they localized within specific rodent submandibular cells, in order to estimate a possible implication in salivary glucose disposal. METHODS: Immunohistochemistry, RT-qPCR and Western blotting were performed to determine the presence/localization of glucose transporters in rodent submandibular glands. RESULTS: GLUT4 was identified in the submandibular salivary gland at both mRNA and protein level. The immunohistochemical analysis revealed its localization preponderantly in the ductal cells of the gland, near to the basolateral. SGLT1 and GLUT1 were highly expressed in submandibular tissues in both acinar and ductal cells, but not GLUT2. These results were confirmed by RT-qPCR. It was also documented that insulin stimulates the net uptake of D-glucose by ductal rings prepared from submandibulary salivary glands, the relative magnitude of such an enhancing action being comparable to that found in hemidiaphragms. CONCLUSION: At least three major glucose transporters are expressed in the rodent submandibular glands, of which GLUT4 is specifically localized near the basolateral side of ductal structures. This points-out its possible role in regulating glucose uptake from the bloodstream, most likely to sustain ductal cellular metabolism.

A tentative model for (D)-glucose turnover in human saliva.

OBJECTIVE: The aim of the present study is to propose a tentative model for d-glucose turnover in human saliva. The whole saliva and the saliva from parotid and submandibular/sublingual glands were collected by use of the Salivette™. RESULTS: The saliva glucose concentration was measured by the hexokinase method, saliva bacteria glycolysis by use of d-[5-(3)H] glucose, and the saliva ATP content by the luciferase method. The concentration of glucose amounted to 43.9±6.3 (n=29), 197.5±17.3 (n=29), 104.0±12.4 (n=27) µM in whole saliva, parotid saliva and submandibular/sublingual saliva, respectively. The rate of d-glucose utilization by oral bacteria at a physiological concentration of d-glucose in saliva (50µM) was estimated at 0.047±0.003 (n=11) nmol/min per 10(6) bacteria. Unstimulated salivary d-glucose turnover rate, as calculated from the amount of glucose secreted in saliva which comes from parotid and submandibular and sublingual glands represented 214.6±19.1%/min. In order for salivary d-glucose production to match bacterial utilization of the hexose, the total number of oral bacteria was estimated at about 2.0×10(9) bacteria, in fair agreement with previously published data. CONCLUSION: This study thus provides support for a tentative model for d-glucose turnover in human saliva.

D-glucose­ and 3-O-methyl-D-glucose-induced upregulation of selected genes in rat hepatocytes and INS1E cells: re­evaluation of the possible role of hexose phosphorylation.

The biochemical events involved in the upregulation of selected glucose­responsive genes by 3­O­methyl­D­glucose (3­MG) remain to be elucidated. The present study mainly aimed to re­evaluate the possible role of 3­MG phosphorylation in the upregulation of the thioredoxin interacting protein (TXNIP) and liver pyruvate kinase (LPK) genes in rat hepatocytes and INS1E cells. TXNIP and LPK transcription was assessed in rat liver and INS1E cells exposed to a rise in D­glucose concentration, 2­deoxy­D­glucose (2­DG), 3­MG and, when required, D­mannoheptulose. The phosphorylation of D­[U­14C]glucose and 3­O­[14C]methyl­D­glucose (14C-labeled 3-MG) was measured in rat liver, INS1E cell and rat pancreatic islet homogenates. The utilization of D­[5­3H]glucose by intact INS1E cells was also measured. In rat hepatocytes, a rise in the D­glucose concentration increased the TXNIP/hypoxanthine­guanine phosphoribosyl transferase (HPRT) and LPK/HPRT ratios, while 2­DG and 3­MG also increased the TXNIP/HPRT ratio, but not the LPK/HPRT ratio. In INS1E cells, the TXNIP/HPRT and LPK/HPRT ratios were increased in response to the addition of D­glucose, 2­DG and 3­MG. Furthermore, D­mannoheptulose abolished the response to D­glucose and 2­DG, but not to 3­MG, in these cells. Liver cell homogenates catalyzed the phosphorylation of 3­MG to a modest extent, whilst INS1E and rat pancreatic islet cell homogenates did not. Moreover, 3­MG marginally decreased D­glucose phosphorylation in INS1E cell homogenates but not in liver cell homogenates. D­[5­3H]glucose utilization by intact INS1E cells was decreased by 2­DG, but not by 3­MG. These findings reinforce the view that the upregulation of the TXNIP and LPK genes induced by 3­MG is not attributable to its phosphorylation or any favorable effect on D­glucose metabolism.

Immunocytochemistry of GLUT2, uptake of fluorescent desnitroso-streptozotocin analogs and phosphorylation of D-glucose in INS-1E cells.

The non-invasive imaging of GLUT2-expressing cells remains a challenge. As streptozotocin, and similarly alloxan, may be transported into cells by GLUT2, the major aim of the present study was to assess the possible use of fluorescent desnitroso-streptozotocin analogs for in vitro labeling of GLUT2-expressing cells. INS-1E cells, human embryonic kidney (HEK) cells, rat isolated pancreatic islets, rat hepatic cells, rat exocrine pancreatic cells and tumoral insulin-producing BRIN-BD11 cells were incubated in the presence of two distinct fluorescent desnitroso-streptozotocin analogs, probes A and B. The immunocytochemistry of GLUT2 in INS-1E cells and the phosphorylation of D-glucose by INS-1E cell homogenates were also examined. The uptake of probes A and B (12.0 µM) by INS-1E cells yielded apparent intracellular concentrations approximately one order of magnitude higher than the extracellular concentration. The two probes differed from one another by the absolute values for their respective uptake and time course, but not so by the pattern of their concentration dependency. Comparable results were recorded in HEK cells, rat isolated pancreatic islets and hepatocytes. Vastly different findings were recorded, however, in rat exocrine pancreatic cells, which do not express GLUT2. Moreover, an unusual concentration dependency for the uptake of each probe was observed in tumoral BRIN-BD11 cells. It is proposed that suitable fluorescent desnitroso-streptozotocin analogs may be used to label GLUT2-expressing cells.

Phytochemical screening and free radical scavenging activity of Citrullus colocynthis seeds extracts.

OBJECTIVE: To study the phytochemical screening of different extracts from Citrullus colocynthis (C. colocynthis ) seeds extracts and to assess their antioxidant activity on the DPPH free radical scavenging. METHODS: Phytochemical screening, total content of polyphenols and flavonoids of C. colocynthis seeds extracts, including a crude aqueous extract (E1), a defatted aqueous extract (E2), a hydromethanolic extract (HM), an ethyl acetate extract (EA) and a n-butanol extract (n-B) was carried out according to the standard methods and to assess their corresponding effect on the antioxidant activity of this plant. RESULTS: None of these extracts contained detectable amount of alkaloid, quinone, antraquinone, or reducing sugar. Catechic tannins and flavonoids were abundant in E1, HM and EA, whilst terpenoids were abundantly present in E1 and n-B but only weekly in HM. Coumarins were found in E2, EA and n-B. Polyphenols, expressed as gallic acid equivalent, amounted, per 100 g plant matter, to 329, 1002 and 150 mg in EA, HM an E1 respectively. Flavonoids, expressed as catechin equivalent, amounted, per 100 g plant matter to 620, 241 and 94 mg in EA, HM and E1 respectively. Comparable values were found in n-B and E1, with lower values in E2. Quercetin, myricetin and gallic acid were found in the EA and HM extracts by thin layer chromatography, The antioxidative effect of these extracts yielded, when tested at a concentration of 2 000 µg/mL in a 1,1-diphenyl-2-picrylhydrazyl assay, a reducing percentage of 88.8% with EA, 74.5% with HM and 66.2% with E1, and corresponding IC50 of 350, 580 and 500 µg/mL as compared to 1.1 µg/mL for ascorbic acid. CONCLUSIONS: These qualitative and quantitative analytical data document the presence in C. colocynthis extracts of such chemical compounds as flavonoids responsible for the antioxidant activity, as well as other biological activities of this plant.

Interaction between cAMP, volume­regulated anion channels and the Na+­HCO3­­cotransporter, NBCe1, in the regulation of nutrient­ and hypotonicity­induced insulin release from isolated rat pancreatic islets and tumoral insulin­producing BRIN­BD11 cells.

Soluble adenylyl cyclase (sAC) has been hypothesized to play a role in insulin secretion. The present study aimed to investigate the interaction between adenosine 3',5'­cyclic monophosphate (cAMP), volume­regulated anion channels (VRACs) and the electrogenic sodium bicarbonate (Na+­HCO3­) cotransporter, NBCe1, in the regulation of nutrient­ and hypotonicity­induced insulin release from rat pancreatic islets and tumoral insulin­producing BRIN­BD11 cells. In the islets, 5­nitro­2­(3­phenylpropylamino)benzoic acid (NPPB) and 5­chloro­2­hydroxy­3­(thiophene­2­carbonyl)indole­1­carboxamide (tenidap) reduced glucose­stimulated insulin release, however, only NPPB suppressed the enhancing action of cAMP analogs upon such a release. Insulin output from the BRIN­BD11 cells was stimulated by 2­ketoisocaproate (KIC) or extracellular hypoosmolarity. cAMP analogs and 3­isobutyl­1­methylxanthine increased the insulin output recorded in the isotonic medium to a greater relative extent than that in the hypotonic medium. The secretory response to KIC or hypotonicity was inhibited by NPPB or tenidap, which both also opposed the enhancing action of cAMP analogs. Inhibitors of mitogen­activated protein (MAP) kinase decreased insulin output in isotonic and hypotonic media. The inhibitor of sAC, 2­hydroxyestriol, caused only a modest inhibition of insulin release, whether in the isotonic or hypotonic medium, even when tested at a concentration of 100 µM. The omission of NaHCO3 markedly decreased the secretory response to KIC or extracellular hypotonicity. The omission of Na+ suppressed the secretory response to extracellular hypotonicity. The observations of the present study do not support the hypothesis of a major role for sAC in the regulation of insulin release.

Comparison of GLUT1, GLUT2, GLUT4 and SGLT1 mRNA expression in the salivary glands and six other organs of control, streptozotocin-induced and Goto-Kakizaki diabetic rats.

BACKGROUND/AIMS: The expression and localization of several distinct glucose transporters (GLUT1, GLUT2, GLUT4, and SGLT1) was recently characterized in the parotid gland of normal rats by quantitative real-time PCR analysis, immunohistochemistry and Western blotting. The major aims of the present study was to compare the mRNA expression of these glucose transporters in both the parotid gland and submaxillary gland of control rats, streptozotocin-induced diabetic rats and hereditarily diabetic Goto-Kakizaki rats. METHODS: Quantitative real-time PCR analysis was performed in the parotid and submaxillary salivary glands and, for purpose of comparison, also in the heart, kidney, liver, lung, muscle and pancreas from control animals and either streptozotocin-treated or Goto-Kakizaki rats. RESULTS: The expression of GLUT4, but not GLUT1 or SGLT1, mRNA was decreased in the diabetic rats. The results also allow comparing both the mRNA expression level of the four glucose transporters in salivary glands and six other organs, and the diabetes-induced changes in such an expression in distinct locations. CONCLUSION: The mRNA expression of the insulin-dependent GLUT4 transporter was the sole to be significantly decreased in the salivary glands of diabetic animals. The possible consequence of such a decrease in terms of the control of salivary glucose concentration requires further investigation.

Insulinotropic action of Citrullus colocynthis seed extracts in rat pancreatic islets.

The present study aimed to investigate the direct in vitro effects of several distinct Citrullus colocynthis seed extracts on glucose-stimulated insulin release from pancreatic islets isolated from rats. Six extracts were tested, a crude aqueous, defatted aqueous, ethyl acetate, H2O-methanol and n-butanol extract and an extract containing a major component (fraction A) identified by gel chromatography in the ethyl acetate, n-butanol and H2O-methanol extracts. Under selected experimental conditions, the majority of extracts exhibited a positive insulinotropic action, at least when tested in the presence of 8.3 mM D-glucose. The concentration-response correlation observed with distinct extracts revealed the participation of distinct chemical compounds, including compounds with an inhibitory insulinotropic potential, in the modulation of the insulin secretory response to D-glucose. The results of the present study are relevant for further investigations which aim to identify compounds exhibiting positive insulinotropic actions. These agents may be suitable for the treatment of human diabetic subjects.

Uptake and efflux of 3-O-methyl-D-glucose in rat parotid cells.

In the framework of recent investigations on the regulation of D-glucose production by salivary glands, the aim of the present study was to compare the uptake of 3-O-[14C]methyl-D-glucose by rat parotid cells over a 6-min incubation period at 37°C to its efflux from prelabelled parotid cells, also incubated for 6 min at 37°C. It was first assessed that the intracellular 3HOH water space, whether expressed in absolute terms or relative to the total 3HOH distribution space, is not significantly different between parotid cells obtained from either control rats or streptozotocin-induced diabetic rats. In the control rats, the uptake of 3-O-[14C]methyl-D-glucose corresponded, following correction for extracellular contamination, to a mean distribution space of 0.44±0.05 nl/103 cells, representing 29.8±3.4% of the intracellular water space. The efflux of 3-O-[14C]methyl-D-glucose from prelabelled parotid cells, expressed relative to their initial radioactive content, averaged 82.9±4.8 and 84.1±2.5% in control and diabetic rats, respectively. These findings suggest that the increased production of salivary D-glucose in diabetic subjects may be attributable to hyperglycemia, rather than to any major perturbation of the intrinsic processes involved, at least in parotid cells, in hexose handling.

The metabolic syndrome of fructose-fed rats: effects of long-chain polyunsaturated ω3 and ω6 fatty acids. V. Post-mortem findings.

The present study deals with the possible effects of dietary ω3 and ω6 fatty acids upon the metabolic syndrome found in rats exposed for 8 weeks to a diet containing 64% (w/w) D-fructose instead of starch. Fructose-fed rats were found to display a modest increase in plasma albumin and protein concentration and more pronounced increases in plasma urea, creatinine, phospholipids, triglycerides and cholesterol concentrations, glycated hemoglobin concentration and liver contents of cholesterol, triglycerides and phospholipids. The plasma concentrations of HDL-cholesterol, calcium and iron were decreased, however, in the fructose-fed rats. In general, the partial substitution of sunflower oil by either safflower oil or salmon oil opposed the metabolic perturbations otherwise associated with the fructose-induced metabolic syndrome in the fructose-fed rats, with salmon oil demonstrating particular efficacy. Consideration is given to the possible biological determinants of these perturbations and their attenuation in rats exposed to safflower or salmon oil.