Design, screening and biological evaluation of novel fatty acid chain-modified oxyntomodulin-based derivatives with prolonged glucose-lowering ability and potent anti-obesity effects.

Recently, oxyntomodulin (OXM) has emerged as a treatment option for type 2 diabetes mellitus and obesity. In order to develop more promising novel OXM derivatives combining glycemic effects of glucagon-like peptide-1 (GLP-1) and lipolytic properties of glucagon, six 12-mer GLP-1 receptor agonists (PP01-PP06) were screened using a phage display method and then fused to OXM (3-37) to generate hybrid OXM derivatives (PP07-PP12). PP11, as a selected starting point, was further site-specifically modified with three lengths of fatty acid chains to provide long-acting conjugates PP13-PP24, among which PP18 was found not only to retain almost the entire balanced activation potency of PP11 in GLP-1/glucagon receptors but also to enhance plasma stability and prolong hypoglycemic activity. PP18 was further confirmed as an insulin secretagogue and glycemic agent in gene knockout mice. The protracted antidiabetic effects and in vivo half-life of PP18 were further proved by hypoglycemic efficacies in diet-induced obesity (DIO) mice and pharmacokinetics tests in Sprague Dawley (SD) rats, respectively. Nevertheless, administration of PP18 once per day normalized food intake, body weight, blood biochemical indexes, insulin resistance and islet function of DIO mice. These preclinical results suggested that PP18, as a novel OXM-based dual GLP-1 and glucagon receptor agonist, may serve as a novel therapeutic approach to treat T2DM and obesity.

The mechanism of action for oxyntomodulin in the regulation of obesity.

Oxyntomodulin, a product of the proglucagon gene, is released from the enteroendocrine L-cells of the gastrointestinal tract after the digestion of food, and acts via glucagon-like peptide 1 receptors in the arcuate nucleus to induce satiety. The administration of oxyntomodulin to animals and humans causes weight loss by reducing food intake in combination with increasing energy expenditure. Thus, the development of potent and long-acting analogs of oxyntomodulin is an exciting new therapeutic avenue for addressing the global obesity epidemic. This review discusses the role of oxyntomodulin in the physiological control of appetite, and presents the currently available evidence suggesting its potential as an obesity treatment.

Hypothalamic injection of oxyntomodulin suppresses circulating ghrelin-like immunoreactivity.

Ghrelin is a gastric peptide that regulates appetite and GH secretion. Circulating ghrelin levels are elevated by fasting and suppressed postprandially. However, the mechanisms regulating circulating ghrelin levels are unclear. Oxyntomodulin is an anorexic peptide hormone released from L cells in the gut. We investigated the effects of intracerebroventricular (icv) administration of oxyntomodulin on circulating ghrelin levels. The icv administration of 1, 3, or 10 nmol oxyntomodulin reduced circulating acylated and total (acylated and des-acylated) ghrelin 60 min after icv injection. Administration of 1 nmol oxyntomodulin directly into the arcuate nucleus of the hypothalamus significantly reduced total and acylated ghrelin levels, and administration of 3 nmol oxyntomodulin into the lateral ventricle induced c-fos mRNA expression in arcuate nucleus neurons expressing the glucagon-like peptide-1 (GLP-1) receptor. In a final study, the reduction in total ghrelin observed after icv injection of 3 nmol oxyntomodulin was blocked by coadministration of the GLP-1 receptor antagonist exendin (9-39). These studies suggest oxyntomodulin reduces peripheral ghrelin levels via GLP-1 receptor-dependent hypothalamic pathways. Postprandial release of anorexic gut hormones may thus act centrally to contribute to the postprandial reduction in circulating ghrelin.

The glucagon-like peptide-1 receptor agonist oxyntomodulin enhances beta-cell function but does not inhibit gastric emptying in mice.

The proglucagon gene gives rise to multiple peptides that play diverse roles in the control of energy intake, gut motility, and nutrient disposal. Glucagon-like peptide-1 (GLP-1), a 30-amino-acid peptide regulates glucose homeostasis via control of insulin and glucagon secretion and by inhibition of gastric emptying and food intake. Oxyntomodulin (OXM) a 37-amino-acid peptide also derived from the proglucagon gene, binds to both the glucagon and GLP-1 receptor (GLP-1R); however, a separate OXM receptor has not yet been identified. Here we show that OXM, like other GLP-1R agonists, stimulates cAMP formation and lowers blood glucose after both oral and ip glucose administration, actions that require a functional GLP-1R. OXM also directly stimulates insulin secretion from murine islets and INS-1 cells in a glucose- and GLP-1R-dependent manner. Moreover, OXM ameliorates hyperglycemia and significantly reduces apoptosis in murine beta-cells after streptozotocin administration and directly reduces apoptosis in thapsigargin-treated INS-1 cells. Unexpectedly, OXM, but not the GLP-1R agonist exendin-4, increased plasma levels of insulin after oral glucose administration. Moreover, OXM administered at doses that potently lower blood glucose had no effect on inhibition of gastric emptying but reduced food intake in WT mice. Taken together, these findings illustrate that although structurally distinct proglucagon-derived peptides such as GLP-1 and OXM engage the GLP-1R, OXM mimics some but not all of the actions of GLP-1R agonists in vivo. These findings may have implications for therapeutic efforts using OXM as a long-acting GLP-1R agonist for the treatment of metabolic disorders.

PYY3-36 injection in mice produces an acute anorexigenic effect followed by a delayed orexigenic effect not observed with other anorexigenic gut hormones.

Peptide YY (PYY) is secreted postprandially from the endocrine L cells of the gastrointestinal tract. PYY(3-36), the major circulating form of the peptide, is thought to reduce food intake in humans and rodents via high-affinity binding to the autoinhibitory neuropeptide Y (NPY) receptor within the arcuate nucleus. We studied the effect of early light-phase injection of PYY(3-36) on food intake in mice fasted for 0, 6, 12, 18, 24, and 30 h and show that PYY(3-36) produces an acute anorexigenic effect regardless of the duration of fasting. We also show evidence of a delayed orexigenic effect in ad libitum-fed mice injected with PYY(3-36) in the early light phase. This delayed orexigenic effect also occurs in mice administered a potent analog of PYY(3-36), d-Allo Ile(3) PYY(3-36), but not following injection of other anorectic agents (glucagon-like-peptide 1, oxyntomodulin, and lithium chloride). Early light-phase injection of PYY(3-36) to ad libitum-fed mice resulted in a trend toward increased levels of hypothalamic NPY and agouti-related peptide mRNA and a decrease in proopiomelanocortin mRNA at the beginning of the dark phase. Furthermore, plasma levels of ghrelin were increased significantly, and there was a trend toward decreased plasma PYY(3-36) levels at the beginning of the dark phase. These data indicate that PYY(3-36) injection results in an acute anorexigenic effect followed by a delayed orexigenic effect.

Differential hypothalamic neuronal activation following peripheral injection of GLP-1 and oxyntomodulin in mice detected by manganese-enhanced magnetic resonance imaging.

The anorexigenic gut hormones oxyntomodulin (OXM) and glucagon-like peptide-1 (GLP-1) are thought to physiologically regulate appetite and food intake. Using manganese-enhanced magnetic resonance imaging, we have shown distinct patterns of neuronal activation in the hypothalamus in response to intraperitoneal injections into fasted mice of 900 and 5400 nmol/kg OXM or 900 nmol/kg GLP-1. Administration of OXM at either dose resulted in a reduced rate of signal enhancement, reflecting a reduction in neuronal activity, in the arcuate, paraventricular, and supraoptic nuclei of the hypothalamus. Conversely, GLP-1 caused a reduction in signal enhancement in the paraventricular nucleus only and an increase in the ventromedial hypothalamic nucleus. Our data show that these two apparently similar peptides generate distinct patterns of activation within the hypothalamus, suggesting that GLP-1 and OXM may act via different hypothalamic pathways.