Pharmacotherapy of type 2 diabetes mellitus

Anti-diabetic drugs recent approaches and advancements

Diabetes is one of the major diseases worldwide and is the third leading cause of death in the United States. Anti-diabetic drugs are used in the treatment of diabetes mellitus to control glucose levels in the blood. Most of the drugs are administered orally, except for a few of them, such as insulin, exenatide, and pramlintide. In this review, we are going to discuss seven major types of anti-diabetic drugs: Peroxisome proliferator-activated receptor (PPAR) agonist, protein tyrosine phosphatase 1B (PTP1B) inhibitors, aldose reductase inhibitors, α-glucosidase inhibitors, dipeptidyl peptidase IV (DPP-4) inhibitors, G protein-coupled receptor (GPCR) agonists and sodium-glucose co-transporter (SGLT) inhibitors. Here, we are also discussing some of the recently reported anti-diabetic agents with its multi-target pharmacological actions. This review summarises recent approaches and advancement in anti-diabetes treatment concerning characteristics, structure-activity relationships, functional mechanisms, expression regulation, and applications in medicine.

Improved Insulin Resistance and Lipid Metabolism by Cinnamon Extract through Activation of Peroxisome Proliferator-Activated Receptors

Peroxisome proliferator-activated receptors (PPARs) are transcriptional factors involved in the regulation of insulin resistance and adipogenesis. Cinnamon, a widely used spice in food preparation and traditional antidiabetic remedy, is found to activate PPARgamma and alpha, resulting in improved insulin resistance, reduced fasted glucose, FFA, LDL-c, and AST levels in high-caloric diet-induced obesity (DIO) and db/db mice in its water extract form. In vitro studies demonstrate that cinnamon increases the expression of peroxisome proliferator-activated receptors gamma and alpha (PPARgamma/alpha) and their target genes such as LPL, CD36, GLUT4, and ACO in 3T3-L1 adipocyte. The transactivities of both full length and ligand-binding domain (LBD) of PPARgamma and PPARalpha are activated by cinnamon as evidenced by reporter gene assays. These data suggest that cinnamon in its water extract form can act as a dual activator of PPARgamma and alpha, and may be an alternative to PPARgamma activator in managing obesity-related diabetes and hyperlipidemia.

Targeting postprandial hyperglycemia

In healthy individuals, blood glucose levels in the fasting state are maintained by the continuous basal-level insulin secretion. After a meal, the rise in postprandial glucose (PPG) is controlled by the rapid pancreatic release of insulin, stimulated by both glucose and the intestinal production of the incretins glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1. In diabetic individuals, postprandial insulin secretion is insufficient to suppress an excessive rise in PPG. There is increasing evidence that elevated PPG exerts a more deleterious effect on the vascular system than elevation of fasting plasma glucose. In particular, individuals with normal fasting plasma glucose but impaired glucose tolerance have significantly increased risk of cardiovascular events. With the recognition of the importance of PPG and the availability of new pharmacologic options, management of diabetes will shift to greater attention to PPG levels. The prototype for such an approach is in the treatment of gestational diabetes and diabetic pregnancies where PPG is the primary target of efforts at glycemic control. These efforts have been extremely successful in improving the outlook for diabetic pregnant women. There are many approaches to reduction of PPG; dietary management and promotion of exercise are very effective. Sulfonylureas, meglitinides, metformin, thiazolidinediones, and disaccharidase inhibitors all counteract PPG elevation. The development of glucagon-like peptide 1 agonists such as exendin and dipeptidyl peptidase IV inhibitors such as vildagliptin offers a new approach to suppression of PPG elevation. New semisynthetic insulin analogues permit a more aggressive response to postprandial glucose elevation, with lower risk of hypoglycemia, than with regular insulin. Inhaled insulin also has a rapid onset of action and offers benefits in PPG control. It is proposed that an aggressive treatment approach focusing on PPG, similar to the current standards for diabetic pregancies, be directed at individuals with diabetes and impaired glucose tolerance.

Vanadium and bone development: putative signaling pathwaysThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference

Vanadium is a trace element present in practically all cells in plants and animals. It exerts interesting actions in living systems. At pharmacological doses, vanadium compounds display relevant biological actions such as mimicking insulin and growth factors as well as having osteogenic activity. Some vanadium compounds also show antitumoral properties. The importance of vanadium in bone arises from the studies developed to establish the essentiality of this element in animals and humans. Bone tissue, where the element seems to play an important role, accumulates great amounts of vanadium. This paper reviews the physiology of osteoblasts, the involvement of different growth factors on bone development, and the effects of vanadium derivatives on the skeletal system of animal models and bone-related cells. Two cellular lines are discussed in particular; one derived from a rat osteosarcoma (UMR106) and the other is a nontransformed osteoblast cell line (MC3T3-E1). The effects of different growth factors and their mechanisms of action in these cellular lines are reviewed. These models of osteoblasts are especially useful in understanding the intracellular signaling pathways of vanadium derivatives in hard tissues. Vanadium uses an intricate interplay of intracellular mechanisms to exert different biochemical and pharmacological actions. The effects of vanadium derivatives on some cellular signaling pathways related to insulin are compiled in this review. The comprehension of these intracellular signaling pathways may facilitate the design of vanadium compounds with promising therapeutic applications as well as the understanding of secondary side effects derived from the use of vanadium as a therapeutic agent.

Description and preliminary evaluation of a Multiagent Intelligent Dosing System (MAIDS) to manage combination insulin-oral agent therapy in type 2 diabetes

BACKGROUND

Computer decision support systems are potentially effective methods for adjusting insulin, but current models do not take into account simultaneous changes of more than one agent. We describe the development of the Multiagent Intelligent Dosing System (MAIDS, Dimensional Dosing Systems, Wexford, PA) for predicting glycemic outcome in response to concurrent dose adjustments in oral hypoglycemic agents and insulin.

METHODS

Retrospective data from a patient cohort with type 2 diabetes who had simultaneous changes in insulin and metformin were analyzed. Glycemic markers (fasting glucose, random glucose, or hemoglobin A1c) expected at the visit subsequent to dose changes were calculated using two methods: the previously reported Intelligent Dosing System (IDStrade mark, Dimensional Dosing Systems), which accounts for changes in only one agent, and the MAIDS. Expected results from both systems were correlated with levels actually observed.

RESULTS

We analyzed 32 patients with 40 paired visits. For fasting glucose (n = 8 paired visits), the correlation between expected and observed values was 0.07 when using the IDS but 0.78 when using the MAIDS. For random glucose (n = 16 paired visits) the correlation between expected and observed levels was 0.49 for the IDS but 0.79 for the MAIDS. With hemoglobin A1c as the marker (n = 16 paired visits), the correlation was 0.40 when using the IDS but 0.60 with the MAIDS.

CONCLUSIONS

The MAIDS allows better prediction of glycemic outcome in circumstances where both insulin and an oral hypoglycemic drug are changed concurrently. Application of the MAIDS to other clinical scenarios, such as simultaneous adjustment of insulin and carbohydrate intake, requires further study.

Effects of a novel formulation of essential oils on glucose-insulin metabolism in diabetic and hypertensive rats: a pilot study

BACKGROUND

Insulin resistance and its most severe form type 2 diabetes mellitus are rapidly increasing throughout the world. It is generally recognized that natural products with a long history of safety can increase insulin sensitivity.

AIMS

The present investigation examined the ability of various combinations of essential oils such as fenugreek, cinnamon, cumin, oregano, etc. to enhance insulin sensitivity. As a first approximation, we examined the effects of these natural products on Zucker fatty rats (ZFRs), a model of obesity and insulin resistance, and spontaneously hypertensive rats (SHRs), a model of genetic hypertension.

MATERIAL AND METHODS

Water or essential oils were given orally via droplets, and insulin sensitivity was estimated by systolic blood pressure (SBP) changes and circulating glucose and/or insulin concentrations.

RESULTS

We have found that the ability to alter SBP in rat models is the most sensitive early index of insulin sensitivity. The combined essential oils lowered circulating glucose levels and SBP in both ZFRs and SHRs, suggesting that these natural products are enhancing insulin sensitivity. The second series of studies examined two additional combinations of essential oils along with the original formula. The major differences were in the types and proportions of individual oils contributing to a given formula.

CONCLUSIONS

Although all the three formulae decreased SBP in ZFRs, one of the formulae was more effective than the others in lowering circulating glucose in the glucose tolerance testing. Accordingly, some essential oils may be added to the long list of natural products that can affect insulin sensitivity.

Effects of phenformin on the proliferation of human tumor cell lines

Phenformin is a biguanide that has been largely used in the past for its anti-diabetic activity. A large body of evidence suggests additional effects of phenformin including antitumoral activity in different animal models in vivo. Thus, the present study has been conducted in order to elucidate possible mechanisms involved in the antitumoral effects of phenformin. In various tumoral cell lines (SH-SY5Y neuroblastoma and LNCaP prostate adenocarcinoma cells), increasing concentrations of phenformin (50-500 microM) induced a concentration-dependent inhibition of cell proliferation. This effect was not dependent on the ability of the drug to reduce glucose levels and was accompanied by induction of apoptotic cell death as measured by cytofluorometric analysis. In addition, a short-time incubation of SH-SY5Y cells with phenformin induced enhanced and transient expression of the cell cycle inhibitor p21 suggesting that phenformin causes inhibition of cell cycle progression prior to induction of apoptosis. These results demonstrate an activity at the cellular level of phenformin that supports its antitumoral effect observed in vivo.

Type 2 diabetes: treat to target

Traditionally, practitioners have reserved insulin therapy for patients with type 2 diabetes until diet, exercise, and treatment with oral agents have failed to maintain glycemic control. Increasing evidence, however, supports advancing insulin therapy earlier in treating diabetes, not only to normalize glycemic control and emulate normal physiologic insulin secretion, but also to delay or prevent disease-associated comorbidity.

Phenformin suppresses calcium responses to glutamate and protects hippocampal neurons against excitotoxicity

Phenformin is a biguanide compound that can modulate glucose metabolism and promote weight loss and is therefore used to treat patients with type-2 diabetes. While phenformin may indirectly affect neurons by changing peripheral energy metabolism, the possibility that it directly affects neurons has not been examined. We now report that phenformin suppresses responses of hippocampal neurons to glutamate and decreases their vulnerability to excitotoxicity. Pretreatment of embryonic rat hippocampal cell cultures with phenformin protected neurons against glutamate-induced death, which was correlated with reduced calcium responses to glutamate. Immunoblot analyses showed that levels of the N-methyl-d-aspartate (NMDA) subunits NR1 and NR2A were significantly decreased in neurons exposed to phenformin, whereas levels of the AMPA receptor subunit GluR1 were unchanged. Whole-cell patch clamp analyses revealed that NMDA-induced currents were decreased, and AMPA-induced currents were unchanged in neurons pretreated with phenformin. Our data demonstrate that phenformin can protect neurons against excitotoxicity by differentially modulating levels of NMDA receptor subunits in a manner that decreases glutamate-induced calcium influx. These findings show that phenformin can modulate neuronal responses to glutamate, and suggest possible use of phenformin and related compounds in the prevention and/or treatment of neurodegenerative conditions.

Chronic acarbose-feeding increases GLUT1 protein without changing intestinal glucose absorption function

As alpha-glucosidase inhibitor, the antidiabetic drug acarbose reduces postprandial glucose levels by retarding the intestinal digestion of polysaccharides. However, it is unknown if acarbose also affects the expression of intestinal glucose transporters, especially the Na(+)-glucose cotransporter (SGLT1) and the glucose transporters GLUT1 and GLUT2. To unravel this question, Wistar rats received standard powdered chow either without (control) or with acarbose (40 mg acarbose/100 g chow) for 40 days. While food intake was slightly enhanced by acarbose, the drug had no influence on weight gain or plasma glucose and insulin levels. The acarbose-treatment did not alter the SGLT1 and GLUT2 gene expression in both upper and middle small intestine, whereas GLUT1 protein was increased by 75% in middle small intestine. Despite the territorial change in GLUT1 protein, the intestinal glucose absorption in an acarbose-free perfusion study was unaltered. In conclusion, the chronic use of acarbose did not alter the acarbose-free glucose absorption profile.