Improvement of glucose homeostasis and hepatic insulin resistance in ob/ob mice given oral molybdate

Does the Micronutrient Molybdenum Have a Role in Gestational Complications and Placental Health?

Molybdenum is an essential trace element for human health and survival, with molybdenum-containing enzymes catalysing multiple reactions in the metabolism of purines, aldehydes, and sulfur-containing amino acids. Recommended daily intakes vary globally, with molybdenum primarily sourced through the diet, and supplementation is not common. Although the benefits of molybdenum as an anti-diabetic and antioxidant inducer have been reported in the literature, there are conflicting data on the benefits of molybdenum for chronic diseases. Overexposure and deficiency can result in adverse health outcomes and mortality, although physiological doses remain largely unexplored in relation to human health. The lack of knowledge surrounding molybdenum intake and the role it plays in physiology is compounded during pregnancy. As pregnancy progresses, micronutrient demand increases, and diet is an established factor in programming gestational outcomes and maternal health. This review summarises the current literature concerning varied recommendations on molybdenum intake, the role of molybdenum and molybdoenzymes in physiology, and the contribution these play in gestational outcomes.

The effect of exposure to MoO3-NP and common bean fertilized by MoO3-NPs on biochemical, hematological, and histopathological parameters in rats

Nanotechnologies has been used to introduce several beneficial tools in the agricultural field. Herein, the effect of molybdenum oxide nanoparticles (MoO₃-NPs) was investigated by evaluating the hematological, biochemical, and histopathological parameters in rats orally exposed to MoO₃-NPs or fed common beans (CB) fertilized by MoO₃-NPs. In the first study, 18 rats were randomly divided into 3 groups: G1 (control group) was given water orally, while G2 and G3 were administered 10 and 40 ppm MoO₃-NPs by oral gavage tube, respectively. There was a significant increase in the levels of alanine aminotransferase (ALT), albumin, and total protein; however, there was a a significant decrease in body weight change (BWC), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), creatinine, creatine kinase–MB (CK-MB), thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and testosterone levels in G3 compared to G1. In the second study, 24 rats were divided into 4 groups: the control (C) group was fed a balanced diet, and three groups were fed on a balanced diet plus 10% CB that was fertilized with 0, 10, and 40 ppm MoO₃-NPs, resulting in nCB, CB10, and CB40 groups, respectively. This revealed a significant increase in BWC and total food intake (TFI) but a significant decrease in relative kidney weight in all the CB groups compared to the control group. In CB10 and CB40 groups ALT, LDH, TSH, FT3, and testosterone levels were significantly lower than the respective levels in the control group. We concluded that high doses of MoO₃-NPs caused more side effects than low doses in both experiments.

Inverse Association of Plasma Molybdenum with Metabolic Syndrome in a Chinese Adult Population: A Case-Control Study

Molybdenum has been found to be associated with metabolic disorders. However, the relationship between molybdenum and metabolic syndrome (MetS) is still unclear. A large case-control study was conducted in a Chinese population from the baseline of Ezhou-Shenzhen cohort. A total of 5356 subjects were included with 2678 MetS and 2678 controls matched by sex and age (±2 years). Medians (IQRs) of plasma molybdenum concentrations were 1.24 μg/L for MetS cases and 1.46 μg/L for controls. After adjustment for multiple covariates, the odds ratio (OR) and 95% confidence intervals (CIs) for MetS were 1.00 (reference), 0.71 (0.59-0.84), 0.56 (0.46-0.68), and 0.47 (0.39-0.58) across quartiles of plasma molybdenum, and per SD increment of log-transformed molybdenum was associated with a 23% lower risk of MetS. In the spline analysis, the risk of MetS and its components decreased steeply with increasing molybdenum and followed by a plateau when the cutoff point was observed around 2.0 μg/L. The dose-dependent relationship of molybdenum with MetS remained consistent when considering other essential elements in the Bayesian kernel machine regression (BKMR) model. In our study, higher plasma molybdenum was significantly associated with a lower risk of MetS, as well as its components, in a dose-response manner.

Exposure to sodium molybdate results in mild oxidative stress in Drosophila melanogaster

OBJECTIVES

The study was conducted to assess the redox status of Drosophila flies upon oral intake of insulin-mimetic salt, sodium molybdate (Na₂MoO₄).

METHODS

Oxidative stress parameters and activities of antioxidant and associated enzymes were analyzed in two-day-old D. melanogaster insects after exposure of larvae and newly eclosed adults to three molybdate levels (0.025, 0.5, or 10 mM) in the food.

RESULTS

Molybdate increased content of low molecular mass thiols and activities of catalase, superoxide dismutase, glutathione-S-transferase, and glucose-6-phosphate dehydrogenase in males. The activities of these enzymes were not affected in females. Males exposed to molybdate demonstrated lower carbonyl protein levels than the control cohort, whereas females at the same conditions had higher carbonyl protein content and catalase activity than ones in the control cohort. The exposure to 10 mM sodium molybdate decreased the content of protein thiols in adult flies of both sexes. Sodium molybdate did not affect the activities of NADP-dependent malate dehydrogenase and thioredoxin reductase in males or NADP-dependent isocitrate dehydrogenase in either sex at any concentration.

DISCUSSION

Enhanced antioxidant capacity in upon Drosophila flies low molybdate levels in the food suggests that molybdate can be potentially useful for the treatment of certain pathologies associated with oxidative stress.

Herbal therapy: A review of emerging pharmacological tools in the management of diabetes mellitus in Africa

BACKGROUND

Diabetes mellitus is a chronic physiological glucose metabolic disorder. It has affected millions of people all over the world thereby having a significant impact on quality of life. The management of diabetes includes both nonpharmacological and conventional interventions. Drawbacks in conventional therapy have led to seeking alternative therapy in herbal medicine. Therefore, the need to review, elucidate and classify their mode of action in therapy for diabetes disease arises.

MATERIALS AND METHODS

Comprehensive literature reports were used to review all conventional agents and herbal therapy used in the management of diabetes. An online database search was conducted for medicinal plants of African origin that have been investigated for their antidiabetic therapeutic potentials.

RESULTS

The results showed that of the documented sixty five plants used, fourteen inhibit intestinal absorption of glucose, three exhibit insulin-mimetic properties, seventeen stimulate insulin secretion from pancreatic beta cells, twelve enhance peripheral glucose uptake, one promotes regeneration of beta-cell of islets of Langerhans, thirteen ameliorate oxidative stress and twenty induces hypoglycemic effect (mode of action is still obscure). Thirteen of these plants have a duplicate mode of actions while one of them has three modes of actions. These agents have a similar mechanism of action as the conventional drugs.

CONCLUSION

In conclusion, antidiabetic activities of these plants are well established; however, the molecular modulation remains unknown. It is envisaged that the use of herbal therapy will promote good health and improve the status of diabetic patients.

Molybdate partly mimics insulin-promoted metabolic effects in Drosophila melanogaster

Molybdenum-containing salts have been found to attenuate diabetes complications in mammals by affecting processes normally regulated by insulin and thus were believed to mimic insulin activity. In this study, we used a fruit fly model to test sodium molybdate, Na2MoO4, action in relation to insulin-promoted processes and toxicity. We studied how larval food supplementation with sodium molybdate affected levels of body carbohydrates and lipids in two-day old adult Drosophila melanogaster. Molybdate salt, in the concentrations used (0.025, 0.05, 0.5, 5, and 10mM), showed low toxicity to fly larvae and slightly influenced development and the percentage of pupated animals. Additionally, sodium molybdate decreased the level of hemolymph glucose in males by 30%, and increased the level of hemolymph trehalose in flies of both sexes. These changes were accompanied by an increase in whole body trehalose and glycogen of about 30-90%. Although total lipid levels in flies of both sexes were depleted by 25%, an increased amount of triacylglycerides among total lipids was observed. These effects were not related to changes in food intake. Taken together, the present data let us suggest that sodium molybdate may at least partly mimic insulin-related effects in Drosophila.

Effect of peripherally administered leptin antagonist on whole body metabolism and bone microarchitecture and biomechanical properties in the mouse

Leptin's in vivo effect on the rodent skeleton depends on the model used and the mode of administration. Superactive mouse leptin antagonist (SMLA) was produced and then pegylated (PEG) to prolong and enhance its in vivo activity. We blocked leptin signaling by injecting this antagonist peripherally into normal mice at various time points and studied their metabolic and skeletal phenotypes. Subcutaneous PEG-SMLA injections into 4-wk-old female C57BL/6J mice increased weight gain and food consumption significantly after only 1 mo, and the effect lasted for the 3 mo of the experiment, proving its central inhibiting activity. Mice showed a significant increase in serum glucose, cholesterol, triglycerides, insulin, and HOMA-IR throughout the experiment. Quantification of gene expression in "metabolic" tissues also indicated the development of insulin resistance. Bone analyses revealed a significant increase in trabecular and cortical parameters measured in both the lumbar vertebrae and tibiae in PEG-SMLA-treated mice in the 1st and 3rd months as well as a significant increase in tibia biomechanical parameters. Interestingly, 30 days of treatment with the antagonist in older mice (aged 3 and 6 mo) affected body weight and eating behavior, just as they had in the 1-mo-old mice, but had no effect on bone parameters, suggesting that leptin's effect on bones, either directly or through its obesogenic effect, is dependent upon stage of skeletal development. This potent and reversible antagonist enabled us to study leptin's in vivo role in whole body and bone metabolism and holds potential for future therapeutic use in diseases involving leptin signaling.

Effect of a novel biphenyl compound, VMNS2e on ob/ob mice

VMNS2e is a novel biphenyl compound, which in previous studies had showed most favourable interactions with the active site of protein tyrosine phosphatase 1B (PTP1B). The effect of acute and chronic treatment of VMNS2e (30mg/kg) was investigated in ob/ob mice. Plasma glucose was measured after acute administration of VMNS2e (30mg/kg) in both lean and ob/ob mice. In the chronic study, VMNS2e (30mg/kg) was given orally, once daily for 60days. Metformin (300mg/kg) was taken as standard therapy. Body weight, food intake and blood glucose was measured weekly while glycosylated hemoglobin A(1c) (HbA(1c)), insulin, triglyceride, total cholesterol, low density lipoprotein (LDL), fructosamine, non esterified fatty acid and organ weight were estimated after the completion of treatment period. Oral glucose tolerance test was performed on the last day of treatment. Liver and epididymal fat weights were taken. Acute dose of VMNS2e elicited an anti hyperglycemic effect. It reduced blood glucose by 14% (0.5h) and 35.6% (6h). Chronic VMNS2e treatment improved glucose tolerance by 25.3%. It decreased blood glucose levels. Hyperinsulinemia was reduced (19.6%). VMNS2e treatment had no significant effect on body weight and food consumption. VMNS2e treatment exhibited significant reduction (28.2%) in HbA(1c), plasma triglyceride (49%), LDL (24%) and fructosamine (13%) levels. VMNS2e treatment did not alter total cholesterol and non esterified fatty acid levels. Epididymal fat/body weight ratio was reduced (26.3%). VMNS2e exhibited both acute and chronic anti hyperglycemic effect, insulin sensitivity along with improvement in various lipid parameters and glycemic control.

Teucrium polium complex with molybdate enhance cultured islets secretory function

Islet transplantation has become a promising treatment in the therapy of type 1 diabetes. Its function improvement, after isolation and before transplantation, is crucial because of their loss both in number and function of islets after isolation procedures. Trace elements sodium orthovanadate (SOV) and sodium molybdate (SM), as well as medicinal plant Teucrium polium L. (TP), showed and possessed high beneficial antioxidative potential and even hypoglycemic properties via their effect on islets. We evaluated the effect of these components in combination on cultured islet function in order to improve pancreatic islet transplantation. Rat pancreatic islets were cultured for 24 h then incubated with different concentrations of TP (0.01 and 0.1 mg/mL) alone and in combination with SOV (1 mM) or SM (1 mM). Insulin concentration in buffer media was measured as islet secretory function. Administration of TP (0.01 mg/mL), SM, and SOV alone or in combination with each other significantly increased insulin secretion at high glucose concentration (16.7 mM); insulin secretion was significantly greater in the group containing both TP and SM than other treated groups (p < 0.05). The combination of the mentioned trace elements especially molybdate with TP could improve islet cells function before transplantation.

Effects of high dietary molybdenum in rabbits

To study the effects of high dietary molybdenum (Mo) content, rabbits were fed with commercial pellets and carrots containing 39 mg Mo/kg dry matter (DM) [Experiment 1] and with a commercial diet supplemented with 40 mg Mo/kg DM [Experiment 2] for 14 days. The high dietary Mo contents failed to reduce the growth performance of rabbits. Moreover, supplemental Mo given in a dose of 40 mg/kg non-significantly decreased the apparent digestibility of crude protein (CP) and crude fibre (CF) compared to the control (73.63 +/- 2.49 and 18.56 +/- 5.10 vs. 74.31 +/- 3.03 and 21.38 +/- 6.48, respectively). Molybdenum ingested with feeds was mainly excreted (57%) via the urine. The highest Mo levels were found in kidney and liver samples (3.464 +/- 0.872; 5.27 +/- 0.95 mg/kg DM [Experiment 1] and 1.878 +/- 0.283; 1.62 +/- 0.16 mg/kg DM [Experiment 2], respectively), and Mo could also be detected in limb meat (0.336 +/- 0.205 mg/kg DM). It was stated that the testes were more sensitive to Mo exposure than the female reproductive organs because the number of germ cells was reduced. Due to the high dietary Mo intake free radicals could be generated, resulting in a marked increase of creatine kinase (CK) activity.

Loss of TR4 orphan nuclear receptor reduces phosphoenolpyruvate carboxykinase-mediated gluconeogenesis

OBJECTIVE

Regulation of phosphoenolpyruvate carboxykinase (PEPCK), the key gene in gluconeogenesis, is critical for glucose homeostasis in response to quick nutritional depletion and/or hormonal alteration.

RESEARCH DESIGN/METHODS AND RESULTS

Here, we identified the testicular orphan nuclear receptor 4 (TR4) as a key PEPCK regulator modulating PEPCK gene via a transcriptional mechanism. TR4 transactivates the 490-bp PEPCK promoter-containing luciferase reporter gene activity by direct binding to the TR4 responsive element (TR4RE) located at -451 to -439 in the promoter region. Binding to TR4RE was confirmed by electrophoretic mobility shift and chromatin immunoprecipitation assays. Eliminating TR4 via knockout and RNA interference (RNAi) in hepatocytes significantly reduced the PEPCK gene expression and glucose production in response to glucose depletion. In contrast, ectopic expression of TR4 increased PEPCK gene expression and hepatic glucose production in human and mouse hepatoma cells. Mice lacking TR4 also display reduction of PEPCK expression with impaired gluconeogenesis.

CONCLUSIONS

Together, both in vitro and in vivo data demonstrate the identification of a new pathway, TR4 --> PEPCK --> gluconeogenesis --> blood glucose, which may allow us to modulate metabolic programs via the control of a new key player, TR4, a member of the nuclear receptor superfamily.

Treating insulin resistance: future prospects

Insulin resistance typically reflects multiple defects of insulin receptor and post-receptor signalling that impair a diverse range of metabolic and vascular actions. Many potential intervention targets and compounds with therapeutic activity have been described. Proof of principle for a non-peptide insulin mimetic has been demonstrated by specific activation of the intracellular B-subunit of the insulin receptor. Potentiation of insulin action has been achieved with agents that enhance phosphorylation and prolong the tyrosine kinase activity of the insulin receptor and its protein substrates after activation by insulin. These include inhibitors of phosphatases and serine kinases that normally prevent or terminate tyrosine kinase signalling. Additional approaches involve increasing the activity of phosphatidylinositol 3-kinase and other downstream components of the insulin signalling pathways. Experimental interventions to remove signalling defects caused by cytokines, certain adipocyte hormones, excess fatty acids, glucotoxicity and negative feedback by distal signalling steps have also indicated therapeutic possibilities. Several hormones, metabolic enzymes, minerals, co-factors and transcription co-activators have shown insulin-sensitising potential. Since insulin resistance affects many metabolic and cardiovascular diseases, it provides an opportunity for simultaneous therapeutic attack on a broad front.

Adiponectin downregulates its own production and the expression of its AdipoR2 receptor in transgenic mice

Adiponectin (ApN) is an adipokine whose expression and plasma levels are inversely related to obesity and insulin-resistant states. The in vivo effects of a chronic expression of exogenous ApN restricted to adipose tissue are unclear. Moreover, the regulatory effects of ApN on its own expression and on that of its receptors are still unknown. In this study, we generated transgenic (Tg) mice with moderate expression of exogenous ApN targeted to adipose tissue (native full-length ApN being placed under control of the adipocyte promoter aP2). After a transient overexpression of ApN in young pups, we intriguingly observed a reduction of ApN mRNA levels and protein content in fat depots, together with a decrease of circulating ApN in adult mice. As a result, the phenotype of these adult mice included glucose intolerance, insulin resistance, and increased adiposity. Reduced expression of ApN in fat tissue was associated with diminished expression of uncoupling protein 2 involved in energy dissipation, and higher expression of fatty acid synthase, a key enzyme of lipogenesis, and of TNFalpha implicated in insulin resistance. Concomitantly, the expression of the ApN receptor AdipoR2 that mediates action of full-length ApN was downregulated, while that of AdipoR1 was unaffected. In agreement with the in vivo studies, recombinant ApN added to the culture medium of 3T3-F442A adipocytes caused a decrease in AdipoR2 and ApN mRNA levels. This treatment did not affect the expression of AdipoR1. Eventually, we demonstrated a contrario that AdipoR2 (but not R1) was specifically upregulated in fat of ApN(-/-) mice. Our in vivo and in vitro data provide evidence for a novel regulatory feedback loop by which ApN downregulates its own production and the expression of its AdipoR2 receptor.

Inhibition of yeast growth by molybdenum-hydroxylamido complexes correlates with their presence in media at differing pH values

The effects of Mo-hydroxylamido complexes on cell growth were determined in Saccharomyces cerevisiae to investigate the biological effects of four different Mo complexes as a function of pH. Studies with yeast, an eukaryotic cell, are particularly suited to examine growth at different pH values because this organism grows well from pH 3 to 6.5. Studies can therefore be performed both in the presence of intact complexes and when the complexes have hydrolyzed to ligand and free metal ion. One of the complexes we examined was structurally characterized by X-ray crystallography. Yeast growth was inhibited in media solutions containing added Mo-dialkylhydroxylamido complexes at pH 3-7. When combining the yeast growth studies with a systematic study of the Mo-hydroxylamido complexes' stability as a function of pH and an examination of their speciation in yeast media, the effects of intact complexes can be distinguished from that of ligand and metal. This is possible because different effects are observed with complex present than when ligand or metal alone is present. At pH 3, the growth inhibition is attributed to the forms of molybdate ion that exist in solution because most of the complexes have hydrolyzed to oxomolybdate and ligand. The monoalkylhydroxylamine ligand inhibited yeast growth at pH 5, 6 and 7, while the dialkylhydroxylamine ligands had little effect on yeast growth. Growth inhibition of the Mo-dialkylhydroxylamido complexes is observed when a complex exists in the media. A complex that is inert to ligand exchange is not effective even at pH 3 where other Mo-hydroxylamido complexes show growth inhibition as molybdate. These results show that the formation of some Mo complexes can protect yeast from the growth inhibition observed when either the ligand or Mo salt alone are present.

Leptin treatment markedly increased plasma adiponectin but barely decreased plasma resistin of ob/ob mice

Adiponectin (ApN) and leptin are two adipocytokines that control fuel homeostasis, body weight, and insulin sensitivity. Their interplay is still poorly studied. These hormones are either undetectable or decreased in obese, diabetic ob/ob mice. We examined the effects of leptin treatment on ApN gene expression, protein production, secretion, and circulating levels of ob/ob mice. We also briefly tackled the influence of this treatment on resistin, another adipocytokine involved in obesity-related insulin resistance. Leptin-treated (T) obese mice (continuous sc infusion for 6 days) were compared with untreated lean (L), untreated obese (O), and untreated pair-fed obese (PF) mice. Blood was collected throughout the study. At day 3 or day 6, fat pads were either directly analyzed (mRNA, ApN content) or cultured for up to 24 h (ApN secretion). The direct effect of leptin was also studied in 3T3-F442A adipocytes. Compared with L mice, ApN content of visceral or subcutaneous fat and ApN secretion by adipose explants were blunted in obese mice. Accordingly, plasma ApN levels of O mice were decreased by 50%. Leptin treatment of ob/ob mice increased ApN mRNAs, ApN content, and secretion from the visceral depot by 50-80%. Leptin also directly stimulated ApN mRNAs and secretion from 3T3-F442A adipocytes. After 6 days of treatment, plasma ApN of ob/ob mice increased 2.5-fold, a rise that did not occur in PF mice. Plasma resistin of T mice was barely decreased. Leptin treatment, but not mere calorie restriction, corrects plasma ApN in obese mice by restoring adipose tissue ApN concentrations and secretion, at least in part, via a direct stimulation of ApN gene expression. Such a treatment only minimally affects circulating resistin. ApN restoration could, in concert with leptin, contribute to the metabolic effects classically observed during leptin administration.

Effect of sodium molybdate on the status of lipids, lipid peroxidation and antioxidant systems in alloxan-induced diabetic rats

BACKGROUND

Diabetes mellitus manifests itself in a wide variety of complications and the symptoms of the disease are multi-factorial.

METHODS

The lipid peroxidation (LPO) and antioxidant status were investigated in hemolysate, liver and kidney in alloxan-induced diabetic rats and the effect of molybdate supplementation on antioxidant defense systems.

RESULTS

Diabetic rats exhibited an increase in the levels of lipids, lipid peroxidation and decrease in antioxidant status when compared to control rats. Oral administration of molybdate to diabetic rats for 30 days significantly reduced the levels of lipids like cholesterol, triglycerides, phospholipids and lipid peroxidation whereas increased the activities of antioxidants like superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and reduced glutathione (GSH).

CONCLUSION

Molybdate prevents oxidation of lipids and protects antioxidant systems in experimental diabetic rats, and thus, may be useful for the prevention or early treatment of diabetic mellitus.

Leptin activation of corticosterone production in hepatocytes may contribute to the reversal of obesity and hyperglycemia in leptin-deficient ob/ob mice

Glucocorticoids have been implicated as pathophysiological mediators of obesity and insulin resistance and are regulated by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). This enzyme regenerates active corticosterone from inactive 11-keto forms. To assess the role of 11beta-HSD1-mediated synthesis of active corticosterone in leptin-related obesity and diabetes, we examined the peripheral effect of leptin on 11beta-HSD1 activity and gene expression in vivo and in vitro in hepatocytes from ob/ob mice and in liver of streptozotocin (STZ)-treated ob/ob mice. We observed an inverse relationship between hepatic 11beta-HSD1 expression and body weight in ob/ob mice and lean littermates. Leptin treatment of ob/ob mice markedly increased hepatic 11beta-HSD1 activity and mRNA expression. This induction of 11beta-HSD1 expression corresponded to reduced levels of circulating corticosterone and weight loss in ob/ob mice treated with leptin, indicating that impaired hepatic 11beta-HSD1 expression may contribute to the pathogenesis of obesity in ob/ob mice. In addition, leptin treatment of STZ-treated ob/ob mice caused marked increases in hepatic 11beta-HSD1 levels associated with decreased body weight and a significant reduction in hyperglycemia due to pancreatic beta-cell damage. Addition of leptin to ob/ob mouse primary hepatocytes led to a dose-dependent increase in 11beta-HSD1 mRNA expression. In contrast, leptin did not influence 11beta-HSD1 expression in primary hepatocytes from db/db mice, indicating that leptin regulation of 11beta-HSD1 expression is probably mediated by the functional leptin receptor. Thus, leptin appears to be an important metabolic signal that directly activates intrahepatic corticosterone production. These findings suggest that the liver-specific interaction of leptin with 11beta-HSD1 is involved in the development of obesity and insulin resistance in ob/ob mice.

Hepatic VLDL production in ob/ob mice is not stimulated by massive de novo lipogenesis but is less sensitive to the suppressive effects of insulin

Type 2 diabetes in humans is associated with increased de novo lipogenesis (DNL), increased fatty acid (FA) fluxes, decreased FA oxidation, and hepatic steatosis. In this condition, VLDL production is increased and resistant to suppressive effects of insulin. The relationships between hepatic FA metabolism, steatosis, and VLDL production are incompletely understood. We investigated VLDL-triglyceride and -apolipoprotein (apo)-B production in relation to DNL and insulin sensitivity in female ob/ob mice. Hepatic triglyceride (5-fold) and cholesteryl ester (15-fold) contents were increased in ob/ob mice compared with lean controls. Hepatic DNL was increased approximately 10-fold in ob/ob mice, whereas hepatic cholesterol synthesis was not affected. Basal rates of hepatic VLDL-triglyceride and -apoB100 production were similar between the groups. Hyperinsulinemic clamping reduced VLDL-triglyceride and -apoB100 production rates by approximately 60% and approximately 75%, respectively, in lean mice but only by approximately 20% and approximately 20%, respectively, in ob/ob mice. No differences in hepatic expression of genes encoding apoB and microsomal triglyceride transfer protein were found. Hepatic expression and protein phosphorylation of insulin receptor and insulin receptor substrate isoforms were reduced in ob/ob mice. Thus, strongly induced hepatic DNL is not associated with increased VLDL production in ob/ob mice, possibly related to differential hepatic zonation of apoB synthesis (periportal) and lipid accumulation (perivenous) and/or relatively low rates of cholesterogenesis. Insulin is unable to effectively suppress VLDL-triglyceride production in ob/ob mice, presumably because of impaired insulin signaling.

Murine leptin injections increase intracellular fatty acid-binding protein in green sunfish (Lepomis cyanellus)

Green sunfish (Lepomis cyanellus) were injected daily with either murine leptin, phosphate-buffered saline (PBS), or simply handled without injection for 14 days. At the end of the experiment, fish were assayed for intracellular indicators of fatty acid metabolism. Intracellular fatty acid-binding protein (FABP) expression in heart ventricle was twofold higher in the leptin treated group (87.2+/-5.6 Leptin; 47.2+/-6.8 PBS; 28.9+/-3.9 Handled; percent relative expression, Prob.>F<0.001). Two other indicators of intracellular fat metabolism, carnitine palmitoyl transferase activity (CPT) in liver and 3-hydroxyacyl-CoA dehydrogenase (HOAD) in heart were not significantly different among groups, although the trend is for higher values in the leptin treatment (CPT: 0.23+/-0.04 Leptin, 0.11+/-0.04 PBS, 0.10+/-0.03 Handled; U/gm wet weight; Prob.>F=0.08; HOAD: 1.34+/-0.28 Leptin, 0.76+/-0.12 PBS, 0.86+/-0.25 Handled; U/gm wet weight; Prob.>F=0.18). Percent change in total weight, body fat (as a percent of dry weight), cardiosomatic index, and hepatosomatic index were not significantly different among treatments. These results suggest that fish respond to murine leptin injections by increasing fat metabolism, however many of the hallmarks of leptin treatment in mammals (loss of total weight and body fat) were not observed. This lack of response may be due to incompatibility of mouse leptin with fish receptors or an inadequate dose of leptin. We also suggest that leptin's action may be slower in ectotherms due to their lower metabolic rate.

New pharmacologic agents for diabetes

New agents are being developed to address the underlying endocrinopathies and metabolic disturbances of type 2 diabetes. Stimulants of the nuclear peroxisome proliferator-activated receptor gamma (PPAR gamma) are being identified to selectively improve insulin actions, and dual agonists of PPAR gamma and PPAR alpha are being evaluated for enhanced control of hyperglycemia and dyslipidemia. Novel activators of insulin receptor phosphorylation and inhibitors of receptor dephosphorylation are offering encouraging leads for new agents. Analogues of glucagon-like peptide-1 that increase glucose-induced insulin secretion may additionally increase beta-cell neogenesis from progenitor duct cells. The amylin analogue pramlintide, which suppresses glucagon secretion and reduces weight, is advancing in clinical trial. Direct stimulants of glucose utilization and partial inhibitors of gluconeogenesis are providing useful new drug templates. Thus, new pharmacologic approaches are emerging to treat the multiple lesions of type 2 diabetes.

Effects of vanadium complexes with organic ligands on glucose metabolism: a comparison study in diabetic rats

1. Vanadium compounds can mimic actions of insulin through alternative signalling pathways. The effects of three organic vanadium compounds were studied in non-ketotic, streptozotocin-diabetic rats: vanadyl acetylacetonate (VAc), vanadyl 3-ethylacetylacetonate (VEt), and bis(maltolato)oxovanadium (VM). A simple inorganic vanadium salt, vanadyl sulphate (VS) was also studied. 2. Oral administration of the three organic vanadium compounds (125 mg vanadium element 1(-1) in drinking fluids) for up to 3 months induced a faster and larger fall in glycemia (VAc being the most potent) than VS. Glucosuria and tolerance to a glucose load were improved accordingly. 3. Activities and mRNA levels of key glycolytic enzymes (glucokinase and L-type pyruvate kinase) which are suppressed in the diabetic liver, were restored by vanadium treatment. The organic forms showed greater efficacy than VS, especially VAc. 4. VAc rats exhibited the highest levels of plasma or tissue vanadium, most likely due to a greater intestinal absorption. However, VAc retained its potency when given as a single i.p. injection to diabetic rats. Moreover, there was no relationship between plasma or tissue vanadium levels and any parameters of glucose homeostasis and hepatic glucose metabolism. Thus, these data suggest that differences in potency between compounds are due to differences in their insulin-like properties. 5. There was no marked toxicity observed on hepatic or renal function. However, diarrhoea occurred in 50% of rats chronically treated with VS, but not in those receiving the organic compounds. 6. In conclusion, organic vanadium compounds, in particular VAc, correct the hyperglycemia and impaired hepatic glycolysis of diabetic rats more safely and potently than VS. This is not simply due to improved intestinal absorption, indicating more potent insulin-like properties.