Cardiovascular complications in diabetes: lessons from animal models

Production of active Exendin-4 in Nicotiana benthamiana and its application in treatment of type-2 diabetics

GLP-1 (Glucagon-like peptide-1) is a peptide that stimulates insulin secretion from the β-cell for glycemic control of the plasma blood glucose level. Its mimetic exenatide (synthetic Exendin-4) with a longer half-life of approximately 3.3-4 h is widely used in clinical application to treat diabetes. Currently, exenatide is chemically synthesized. In this study, we report that the GLP-1 analogue recombinant Exendin-4 (Exdn-4) can be produced at a high level in Nicotiana benthamiana, with an estimated yield of 50.0 µg/g fresh biomass. For high-level expression, we generated a recombinant gene, B:GB1:ddCBD1m:8xHis : Exendin-4 (BGC : Exdn-4), for the production of Exendin-4 using various domains such as the BiP signal peptide, the GB1 domain (B1 domain of streptococcal G protein), a double cellulose binding domain 1 (CBD1), and 8 His residues (8xHis) to the N-terminus of Exendin-4. GB1 was used to increase the expression, whereas double CBD1 and 8xHis were included as affinity tags for easy purification using MCC beads and Ni²⁺-NTA resin, respectively. BGC : Exdn-4 was purified by single-step purification to near homogeneity using both Ni²⁺-NTA resin and microcrystalline cellulose (MCC) beads. Moreover, Exdn-4 without any extra residues was produced from BGC : Exdn-4 bound onto MCC beads by treating with enterokinase. Plant-produced Exdn-4 (Exendin-4) was as effective as chemically synthesized Exendin-4 in glucose-induced insulin secretion (GIIS) from mouse MIN6m9 cells a pancreatic beta cell line.

Diabetes and Alzheimer's Disease: Might Mitochondrial Dysfunction Help Deciphering the Common Path?

A growing number of clinical and epidemiological studies support the hypothesis of a tight correlation between type 2 diabetes mellitus (T2DM) and the development risk of Alzheimer's disease (AD). Indeed, the proposed definition of Alzheimer's disease as type 3 diabetes (T3D) underlines the key role played by deranged insulin signaling to accumulation of aggregated amyloid beta (Aβ) peptides in the senile plaques of the brain. Metabolic disturbances such as hyperglycemia, peripheral hyperinsulinemia, dysregulated lipid metabolism, and chronic inflammation associated with T2DM are responsible for an inefficient transport of insulin to the brain, producing a neuronal insulin resistance that triggers an enhanced production and deposition of Aβ and concomitantly contributes to impairment in the micro-tubule-associated protein Tau, leading to neural degeneration and cognitive decline. Furthermore, the reduced antioxidant capacity observed in T2DM patients, together with the impairment of cerebral glucose metabolism and the decreased performance of mitochondrial activity, suggests the existence of a relationship between oxidative damage, mitochondrial impairment, and cognitive dysfunction that could further reinforce the common pathophysiology of T2DM and AD. In this review, we discuss the molecular mechanisms by which insulin-signaling dysregulation in T2DM can contribute to the pathogenesis and progression of AD, deepening the analysis of complex mechanisms involved in reactive oxygen species (ROS) production under oxidative stress and their possible influence in AD and T2DM. In addition, the role of current therapies as tools for prevention or treatment of damage induced by oxidative stress in T2DM and AD will be debated.

The Intrinsic Virtues of EGCG, an Extremely Good Cell Guardian, on Prevention and Treatment of Diabesity Complications

The pandemic proportion of diabesity—a combination of obesity and diabetes—sets a worldwide health issue. Experimental and clinical studies have progressively reinforced the pioneering epidemiological observation of an inverse relationship between consumption of polyphenol-rich nutraceutical agents and mortality from cardiovascular and metabolic diseases. With chemical identification of epigallocatechin-3-gallate (EGCG) as the most abundant catechin of green tea, a number of cellular and molecular mechanisms underlying the activities of this unique catechin have been proposed. Favorable effects of EGCG have been initially attributed to its scavenging effects on free radicals, inhibition of ROS-generating mechanisms and upregulation of antioxidant enzymes. Biologic actions of EGCG are concentration-dependent and under certain conditions EGCG may exert pro-oxidant activities, including generation of free radicals. The discovery of 67-kDa laminin as potential EGCG membrane target has broaden the likelihood that EGCG may function not only because of its highly reactive nature, but also via receptor-mediated activation of multiple signaling pathways involved in cell proliferation, angiogenesis and apoptosis. Finally, by acting as epigenetic modulator of DNA methylation and chromatin remodeling, EGCG may alter gene expression and modify miRNA activities. Despite unceasing research providing detailed insights, ECGC composite activities are still not completely understood. This review summarizes the most recent evidence on molecular mechanisms by which EGCG may activate signal transduction pathways, regulate transcription factors or promote epigenetic changes that may contribute to prevent pathologic processes involved in diabesity and its cardiovascular complications.

Antihyperglycemic Effects and Mode of Actions of Musa paradisiaca Leaf and Fruit Peel Hydroethanolic Extracts in Nicotinamide/Streptozotocin-Induced Diabetic Rats

The present study aimed to evaluate the antihyperglycemic effects of Musa paradisiaca (M. paradisiaca) leaf and fruit peel hydroethanolic extracts and to suggest their probable mode of actions in nicotinamide (NA)/streptozotocin (STZ)-induced diabetic rats. The leaf and fruit peel hydroethanolic extracts were analyzed by GC-MS that indicated the presence of phytol, octadecatrienoic acid, hexadecanoic acid, and octadecadienoic acid as major components in the leaf extract and vitamin E, octadecenamide, β-sitosterol, and stigmasterol as major phytochemicals in the fruit peel extract. Diabetes mellitus was induced by a single intraperitoneal injection of STZ (60 mg/kg body weight) dissolved in citrate buffer (pH 4.5), 15 minutes after intraperitoneal injection of NA (120 mg/kg body weight). The NA/STZ-induced diabetic rats were, respectively, treated with M. paradisiaca leaf and fruit peel hydroethanolic extracts at a dose of 100 mg/kg body weight/day by oral administration for 28 days. The treatment of NA/STZ-induced diabetic rats with leaf and fruit peel extracts significantly improved the impaired oral glucose tolerance and significantly increased the lowered serum insulin and C-peptide levels. The HOMA-IR (as the index of insulin resistance) and QUICKI (as a marker for insulin sensitivity), as well as HOMA-β cell function were significantly alleviated as a result of treatment of diabetic rats with leaf and fruit peel extracts. In association, the elevated serum-free fatty acids, TNF-α, and IL-6 levels were significantly decreased. In addition, the suppressed adipose tissue PPARγ, GLUT4, adiponectin, and insulin receptor β-subunit mRNA expressions were upregulated while the elevated adipose tissue resistin expression was downregulated in diabetic rats as a result of treatment with the leaf and peel extract. Based on these results, it can be concluded that M. paradisiaca leaf and fruit peel hydroethanolic extracts have antihyperglycemic effects which may be mediated via their insulinotropic and insulin-sensitizing effects.

Protective effects of Xinji'erkang on myocardial infarction induced cardiac injury in mice

BACKGROUND

Myocardial infarction (MI) is a major risk factor responsible for morbidity and mortality. Xinji'erkang (XJEK) has been clinically used as an effective medication in the treatment of coronary heart disease and myocarditis. The purpose of this study was to investigate the cardioprotective effect of Xinji'erkang on MI mice.

METHODS

Forty male mice were randomly assigned into four groups as follows (n = 10): sham, model, MI with administration of XJEK and fosinopril for four weeks. At the end of studies, hemodynamic parameters and electrocardiography (ECG) were recorded. Heart and body mass were measured and heart weight/body weight (HW/BW) ratio was calculated as index of hypertrophy. The hypertrophy of heart and aorta was examined using the hematoxylin and eosin (HE) staining, and the collagen deposition was evaluated using Van Gieson (VG) staining. Serum nitric oxide level (NO), superoxide dismutase (SOD) activity and malondialdehyde (MDA) concentration were assayed by colorimetric analysis. The expressions of endothelial NO synthetase (eNOS) expression in serum and cardiac tissues were determined using ELISA assay and immunohistochemistry. Angiotensin II (Ang II) in serum and cardiac tissues was measured using ELISA assay. Besides, tumor necrosis factor-α (TNF-α), interleukin1β (IL-1β) and interleukin10 (IL-10) were observed in cardiac tissues with ELISA assay as well.

RESULTS

The administration of XJEK significantly improved cardiac dysfunction and abnormal ECG with reduced HW/BW ratio and ameliorated cardiomyocyte hypertrophy and collagen deposition compared to MI, which was partly due to the decreased SOD and increased MDA in serum. Moreover, XJEK treatment also improved endothelial dysfunction (ED) with not only enhanced eNOS activities in serum and cardiac tissues and elevated NO levels in serum, but also decreased Ang II content in serum and cardiac tissues. Finally, protein expressions of pro-inflammation cytokines, TNF-α and IL-1β in the cardiac tissues with XJEK treatment were significantly decreased compared to model. On the contrary, IL-10, an anti-inflammatory cytokine concentrated in cardiac tissues was significantly enhanced compared to model.

CONCLUSION

Xinji'erkang exerts cardioprotective effect on myocardial infarction in mice, which may be due to the improvement of endothelial dysfunction and the reduction of oxidative stress and inflammation response.

Glycosylation patterns of kidney proteins differ in rat diabetic nephropathy

Diabetic nephropathy often progresses to end-stage kidney disease and, ultimately, to renal replacement therapy. Hyperglycemia per se is expected to have a direct impact on the biosynthesis of N- and O-linked glycoproteins. This study aims to establish the link between protein glycosylation and progression of experimental diabetic kidney disease using orthogonal methods. Kidneys of streptozotocin-diabetic and control rats were harvested at three different time points post streptozotocin injection. A panel of 12 plant lectins was used in the screening of lectin blots. The lectins UEAI, PHA-E, GSI, PNA, and RCA identified remarkable disease-associated differences in glycoprotein expression. Lectin affinity chromatography followed by mass spectrometric analyses led to the identification of several glycoproteins involved in salt-handling, angiogenesis, and extracellular matrix degradation. Our data confirm a substantial link between glycosylation signature and diabetes progression. Furthermore, as suggested by our findings on dipeptidyl peptidase-IV, altered protein glycosylation may reflect changes in biochemical properties such as enzymatic activity. Thus, our study demonstrates the unexplored potential of protein glycosylation analysis in the discovery of molecules linked to diabetic kidney disease.

Alteration of mevalonate pathway in proliferated vascular smooth muscle from diabetic mice: possible role in high-glucose-induced atherogenic process

The proliferation of vascular smooth muscle cells (VSMCs) is one of the main features of atherosclerosis induced by high glucose. Mevalonate pathway is an important metabolic pathway that plays a key role in multiple cellular processes. The aim of this study was to define whether the enzyme expression in mevalonate pathway is changed in proliferated VSMCs during atherogenic process in diabetic mice. Diabetes was induced in BALB/c mice with streptozotocin (STZ, 50 mg/kg/day for 5 days). Induction of diabetes with STZ was associated with an increase of lesion area and media thickness after 8 and 16 weeks of diabetes. In aorta, there were overexpressions of some enzymes, including 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), farnesyl pyrophosphate synthase (FPPS), geranylgeranyl pyrophosphate synthase (GGPPS), farnesyltransferase (FNT), and geranylgeranyltransferase-1 (GGT-1), and unchanged expression of squalene synthase (SQS) and phosphor-3-hydroxy-3-methylglutaryl-coenzyme A reductase (P-HMGR) in 8 and 16 weeks of diabetes. In vitro, VSMCs were cultured and treated with different glucose concentrations for 48 h. High glucose (22.2 mM) induced VSMC proliferation and upregulation of HMGR, FPPS, GGPPS, FNT, and GGT-1 but did not change the expressions of SQS and P-HMGR. In conclusion, altered expression of several key enzymes in the mevalonate pathway may play a potential pathophysiological role in atherogenic process of diabetes macrovascular complication.

A fusion protein derived from plants holds promising potential as a new oral therapy for type 2 diabetes

The incretin hormone glucagon-like peptide-1 (GLP-1) is recognized as a promising candidate for the treatment of type 2 diabetes (T2D), with one of its mimetics, exenatide (synthetic exendin-4) having already been licensed for clinical use. We seek to further improve the therapeutic efficacy of exendin-4 (Ex-4) using innovative fusion protein technology. Here, we report the production in plants a fusion protein containing Ex-4 coupled with human transferrin (Ex-4-Tf) and its characterization. We demonstrated that plant-made Ex-4-Tf retained the activity of both proteins. In particular, the fusion protein stimulated insulin release from pancreatic β-cells, promoted β-cell proliferation, stimulated differentiation of pancreatic precursor cells into insulin-producing cells, retained the ability to internalize into human intestinal cells and resisted stomach acid and proteolytic enzymes. Importantly, oral administration of partially purified Ex-4-Tf significantly improved glucose tolerance, whereas commercial Ex-4 administered by the same oral route failed to show any significant improvement in glucose tolerance in mice. Furthermore, intraperitoneal (IP) injection of Ex-4-Tf showed a beneficial effect in mice similar to IP-injected Ex-4. We also showed that plants provide a robust system for the expression of Ex-4-Tf, producing up to 37 μg prEx-4-Tf/g fresh leaf weight in transgenic tobacco and 137 μg prEx-4-Tf/g freshweight in transiently transformed leaves of N. benthamiana. These results indicate that Ex-4-Tf holds substantial promise as a new oral therapy for type 2 diabetes. The production of prEx-4-Tf in plants may offer a convenient and cost-effective method to deliver the antidiabetic medicine in partially processed plant food products.

Prenatal programming of obesity in a swine model of leptin resistance: modulatory effects of controlled postnatal nutrition and exercise

The main role of early nutritional programming in the current rise of obesity and associated diseases is well known. However, translational studies are mostly based in postnatal food excess and, thus, there is a paucity of information on the phenotype of individuals with prenatal deficiencies but adequate postnatal conditions. Thus, we assessed the effects of prenatal programming (comparing descendants from females fed with a diet fulfilling 100 or only 50% of their nutritional requirements for pregnancy) on gene expression, patterns of growth and fattening, metabolic status and puberty attainment of a swine model of obesity/leptin resistance with controlled postnatal nutrition and opportunity of exercise. Maternal restriction was related to changes in the relationships among gene expression of positive (insulin-like growth factors 1 and 2) and negative (myostatin) regulators of muscle growth, with negative correlations in gilts from restricted pregnancies and positive relationships in the control group. In spite of these differences, the patterns of growth and fattening and the metabolic features during juvenile growth were similar in control gilts and gilts from restricted pregnancies. Concomitantly, there was a lack of differences in the timing of puberty attainment. However, after reaching puberty and adulthood, females from restricted pregnancies were heavier and more corpulent than control gilts, though such increases in weight and size were not accompanied by increases in adiposity. In conclusion, in spite of changes in gene expression induced by developmental programming, the propensity for higher weight and adiposity of individuals exposed to prenatal malnutrition may be modulated by controlled food intake and opportunity of physical exercise during infant and juvenile development.

Leptin- and leptin receptor-deficient rodent models: relevance for human type 2 diabetes

Among the most widely used animal models in obesity-induced type 2 diabetes mellitus (T2DM) research are the congenital leptin- and leptin receptor-deficient rodent models. These include the leptin-deficient ob/ob mice and the leptin receptor-deficient db/db mice, Zucker fatty rats, Zucker diabetic fatty rats, SHR/N-cp rats, and JCR:LA-cp rats. After decades of mechanistic and therapeutic research schemes with these animal models, many species differences have been uncovered, but researchers continue to overlook these differences, leading to untranslatable research. The purpose of this review is to analyze and comprehensively recapitulate the most common leptin/leptin receptor-based animal models with respect to their relevance and translatability to human T2DM. Our analysis revealed that, although these rodents develop obesity due to hyperphagia caused by abnormal leptin/leptin receptor signaling with the subsequent appearance of T2DM-like manifestations, these are in fact secondary to genetic mutations that do not reflect disease etiology in humans, for whom leptin or leptin receptor deficiency is not an important contributor to T2DM. A detailed comparison of the roles of genetic susceptibility, obesity, hyperglycemia, hyperinsulinemia, insulin resistance, and diabetic complications as well as leptin expression, signaling, and other factors that confound translation are presented here. There are substantial differences between these animal models and human T2DM that limit reliable, reproducible, and translatable insight into human T2DM. Therefore, it is imperative that researchers recognize and acknowledge the limitations of the leptin/leptin receptor- based rodent models and invest in research methods that would be directly and reliably applicable to humans in order to advance T2DM management.

GABA tea prevents cardiac fibrosis by attenuating TNF-alpha and Fas/FasL-mediated apoptosis in streptozotocin-induced diabetic rats

GABA tea is a tea product that contains a high level of gamma-aminobutyric acid (GABA). This study investigated the effects of GABA tea on the heart in a diabetic rat model. Male Wistar rats were injected with 55mg/kg streptozotocin (STZ) to induce diabetes for 2weeks and then orally given dosages of 4.55 and 45.5mg/kg/day GABA tea extract for 6weeks. The results revealed that fasting blood glucose levels returned to normal levels in GABA tea-treated diabetic rats, but not in the untreated diabetic rats. Additionally, GABA tea effectively inhibited cardiac fibrosis induced by STZ. Further experiments showed that the STZ-induced protein levels of tumor necrosis factor-alpha (TNF-alpha), Fas, activated caspase-8 and caspase-3 were significantly inhibited by the GABA tea treatment. Therefore, our data suggest that the inhibiting effect of GABA tea on STZ-induced cardiac fibrosis in diabetic rats may be mediated by reducing blood glucose and further attenuating TNF-alpha expression and/or Fas/Fas ligand (FasL)-mediated apoptosis. These findings will provide implications for the potential anti-diabetic properties of GABA tea.

Antidiabetic agents: past, present and future

Treatment of diabetes mellitus requires, at a certain stage of its course, drug intervention. This article reviews the properties of available antidiabetic medications and highlights potential targets for developing newer and safer drugs. Antidiabetic agents are grouped in the article as parts I, II and III according to the history of development. Part I groups early developed drugs, during the 20th century, including insulin, sulfonylureas, the metiglinides, insulin sensitizers, biguanides and α-glucosidase inhibitors. Part II groups newer drugs developed during the early part of the 21st century, the past decade, including GLP-1 analogs, DPP-VI inhibitors, amylin analogs and SGLT2 inhibitors. Part III groups potential targets for future design of newer antidiabetic agents with less adverse effects than the currently available antidiabetic drugs.

Enhanced uridine adenosine tetraphosphate-induced contraction in renal artery from type 2 diabetic Goto-Kakizaki rats due to activated cyclooxygenase/thromboxane receptor axis

The dinucleotide uridine adenosine tetraphosphate (Up4A), which has both purine and pyrimidine moieties, was reported as a novel endothelium-derived contracting factor. Recently, growing evidence has suggested that Up4A plays an important role in regulation of the cardiovascular function. We previously demonstrated that Up4A-induced vasoconstrictions are altered in arteries from DOCA-salt hypertensive rats. We have assessed responses to Up4A shown by renal arteries from type 2 diabetic Goto-Kakizaki (GK) rats (42-46 weeks old) and identified the molecular mechanisms involved. Concentration-dependent contractions to Up4A were greater in renal arterial rings from the GK than age-matched control Wistar group. In both groups, the inhibition of nitric oxide synthase (with N (G)-nitro-L-arginine) increased the response to Up4A, whereas the inhibition of cyclooxygenase (COX) (with indomethacin) decreased the response. Specific inhibitors of COX-1 (valeroyl salicylate) and COX-2 (NS398), a thromboxane (TX) receptor (TP) antagonist (SQ29548), and P2 receptor antagonist (suramin) also decreased the response to Up4A. Protein expressions of COXs in renal arteries were greater in the GK than Wistar group. The production of TXB2 (a metabolite of TXA2) by Up4A did not differ between these groups. Concentration-dependent contractions to U46619, an agonist of the TP receptor, were greater in renal arteries from the GK than Wistar group. The expression of P2X1 and P2Y2 receptors did not differ between these groups. These results suggest that enhancement of the Up4A-induced contraction in renal arteries from GK rats may be attributable to the increased activation of COXs/TP receptor signaling.

Domestic animal models for biomedical research

Experimental animals in biomedical research provide insights into disease mechanisms and models for determining the efficacy and safety of new therapies and for discovery of corresponding biomarkers. Although mouse and rat models are most widely used, observations in these species cannot always be faithfully extrapolated to human patients. Thus, a number of domestic species are additionally used in specific disease areas. This review summarizes the most important applications of domestic animal models and emphasizes the new possibilities genetic tailoring of disease models, specifically in pigs, provides.

Allicin protects against myocardial apoptosis and fibrosis in streptozotocin-induced diabetic rats

To evaluate the cardioprotective effect of allicin (AL) on myocardial injury of streptozotocin (STZ)-induced diabetic rats and to further explore its underlying mechanisms. Hyperglycemia was induced in rats by single intraperitoneal injection of STZ (40 mg/kg). Three days after STZ induction, the hyperglycemic rats (plasma glucose levels ≥ 16.7 mmol/l) were treated with AL by intraperitoneal injection at the doses of 4 mg/kg, 8 mg/kg, and 16 mg/kg daily for 28 days. The fasting blood glucose levels were measured on every 7th day during the 28 days of treatment. The body weight, blood glucose, and parameter of cardiac function were detected after 4 weeks to study the cardioprotective effects of AL on diabetic rats in vivo. The apoptotic index of cardiomyocytes was estimated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. The expressions of Fas, Bcl-2, CTGF, and TGF-β(1) protein were studied by immunohistochemistry. Laser scanning confocal microscopy technique was utilized to observe the effects of AL on intracellular calcium concentration ([Ca(2+)](i)) in rat ventricular cardiomyocytes. AL at the doses of 4 mg/kg, 8 mg/kg, and 16 mg/kg significantly reduced blood glucose levels in a dose-dependent manner and increased body weight as well compared with the model group. Hemodynamic parameters including left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), and maximum rate of left ventricular pressure rise and fall (+dp/dtmax and -dp/dtmax) were significantly restored back to normal levels in AL-treated (8 mg/kg and 16 mg/kg) rats compared with diabetic model rats. AL markedly inhibited cardiomyocyte apoptosis induced by diabetic cardiac injury. Further investigation revealed that this inhibitory effect on cell apoptosis was mediated by increasing anti-apoptotic protein Bcl-2 and decreasing pro-apoptotic protein Fas. Additional experiments demonstrated AL abrogated myocardial fibrosis by blocking the expressions of CTGF and TGF-β(1) protein. AL shows protective action on myocardial injury in diabetic rats. The possible mechanisms were involved in reducing blood glucose, correcting hemodynamic impairment, reducing Fas expression, activating Bcl-2 expression, decreasing intracellular calcium overload, inhibiting the expressions of TGF-β(1) and CTGF, and further improving cardiac function.

Determinants of evolving metabolic and cardiovascular benefit/risk profiles of rosiglitazone therapy during the natural history of diabetes: molecular mechanisms in the context of integrated pathophysiology

Rosiglitazone is a thiazolidinedione, a synthetic PPARγ receptor agonist with insulin-sensitizing properties that is used as an antidiabetic drug. In addition to improving glycemic control through actions in metabolic target tissues, rosiglitazone has numerous biological actions that impact on cardiovascular homeostasis. Some of these actions are helpful (e.g., improving endothelial function), whereas others are potentially harmful (e.g., promoting fluid retention). Since cardiovascular morbidity and mortality are major endpoints for diabetes, it is essential to understand how the natural history of diabetes alters the net benefits and risks of rosiglitazone therapy. This complex issue is an important determinant of optimal use of rosiglitazone and is critical for understanding cardiovascular safety issues. We give special attention to the effects of rosiglitazone in diabetic patients with stable coronary artery disease and the impact of rosiglitazone actions on atherosclerosis and plaque instability. This provides a rational conceptual framework for predicting evolving benefit/risk profiles that inform optimal use of rosiglitazone in the clinical setting and help explain the results of recent large clinical intervention trials where rosiglitazone had disappointing cardiovascular outcomes. Thus, in this perspective, we describe what is known about the molecular mechanisms of action of rosiglitazone on cardiovascular targets in the context of the evolving pathophysiology of diabetes over its natural history.

Protein kinase C delta contributes to increase in EP3 agonist-induced contraction in mesenteric arteries from type 2 diabetic Goto-Kakizaki rats

Prostaglandin E(2) (PGE(2)), an important and ubiquitously present vasoactive eicosanoid, may either constrict or dilate systemic vascular beds. However, little is known about the vascular contractile responsiveness to and signaling pathways for PGE(2) at the chronic stage of type 2 diabetes. We hypothesized that PGE(2)-induced arterial contraction is augmented in type 2 diabetic Goto-Kakizaki (GK) rats via the protein kinase Cδ (PKCδ) pathway. Here, we investigated the vasoconstrictor effects of PGE(2) and of sulprostone (EP1-/EP3-receptor agonist) in rings cut from superior mesenteric arteries isolated from GK rats (37-44 weeks old). In arteries from GK rats (vs. those from age-matched Wistar rats), examined in the presence of a nitric oxide synthase inhibitor: 1) the PGE(2)- and sulprostone-induced vasocontractions (which were not blocked by the selective EP1 receptor antagonist sc19220) were enhanced, and these enhancements were suppressed by rottlerin (selective PKCδ inhibitor) but not by Gö6976 (selective PKCα/β inhibitor); 2) the sulprostone-stimulated phosphorylation of PKCδ (at Thr(505)), which yields an active form, was increased and 3) sulprostone-stimulated caldesmon phosphorylations, which are related to isometric force generation in smooth muscle, were increased. The protein expression of EP3 receptor in superior mesenteric arteries was similar between the two groups of rats. Our data suggest that the diabetes-related enhancement of EP3 receptor-mediated vasocontraction results from activation of the PKCδ pathway. Alterations in EP3 receptor-mediated vasocontraction may be important factors in the pathophysiological influences over arterial tone that are present in diabetic states.

Diabetes-induced birth defects: what do we know? What can we do?

Birth defects are the leading cause of infant mortality in the United States, which has one of the highest infant mortality rates in the developed world. Many of these birth defects can be attributed to pre-existing, or pregestational, diabetes in pregnancy, which significantly increases a mother's risk of having a child with a major birth defect. Strict preconceptional and early pregnancy glucose control, supplementation with multivitamins and fatty acids, and lower glycemic dietary management have been shown to reduce the incidence of birth defects in experimental and epidemiologic studies. However, because more than half of pregnancies are unplanned, these methods are not generalizable across the population. Thus, better interventions are urgently needed. Based on what we know about the molecular pathophysiology of diabetic embryopathy, our laboratory and others are developing interventions against to key molecular targets in this multifactorial disease process.

Acute and chronic animal models for the evaluation of anti-diabetic agents

Diabetes mellitus is a potentially morbid condition with high prevalence worldwide thus being a major medical concern. Experimental induction of diabetes mellitus in animal models is essential for the advancement of our knowledge and understanding of the various aspects of its pathogenesis and ultimately finding new therapies and cure. Experimental diabetes mellitus is generally induced in laboratory animals by several methods that include: chemical, surgical and genetic (immunological) manipulations. Most of the experiments in diabetes are carried out in rodents, although some studies are still performed in larger animals. The present review highlights the various methods of inducing diabetes in experimental animals in order to test the newer drugs for their anti-diabetic potential.