Ghrelin signalling in β-cells regulates insulin secretion and blood glucose

Insulin secretion from pancreatic islet β-cells is stimulated by glucose. Glucose-induced insulin release is potentiated or suppressed by hormones and neural substances. Ghrelin, an acylated 28-amino acid peptide, was isolated from the stomach in 1999 as the endogenous ligand for the growth hormone (GH) secretagogue-receptor (GHS-R). Circulating ghrelin is produced predominantly in the stomach and to a lesser extent in the intestine, pancreas and brain. Ghrelin, initially identified as a potent stimulator of GH release and feeding, has been shown to suppress glucose-induced insulin release. This insulinostatic action is mediated by Gα(i2) subtype of GTP-binding proteins and delayed outward K⁺ (Kv) channels. Interestingly, ghrelin is produced in pancreatic islets. The ghrelin originating from islets restricts insulin release and thereby upwardly regulates the systemic glucose level. Furthermore, blockade or elimination of ghrelin enhances insulin release, which can ameliorate glucose intolerance in high-fat diet fed mice and ob/ob mice. This review focuses on the insulinostatic action of ghrelin, its signal transduction mechanisms in islet β-cells, ghrelin's status as an islet hormone, physiological roles of ghrelin in regulating systemic insulin levels and glycaemia, and therapeutic potential of the ghrelin-GHS-R system as the target to treat type 2 diabetes.

Trypanocidal activity of synthetic heterocyclic derivatives of active quinones from Tabebuia sp

Continuing a program on the chemistry and biological activity of compounds from the Brazilian flora, the lytic activity against bloodstream forms of T. cruzi of nine new heterocyclic naphthooxazole and naphthoimidazole derivatives obtained from the reaction of naphtoquinones isolated from Tabebuia sp. (Tecoma) with amino-containing reagents has been studied. Also for the first time the biological activity of allyl derivatives of lawsone, a natural quinone from Lausonia alba inactive against T. cruzi, is reported. The introduction of an allyl group in lawsone gives rise to O-allyl-lawsone and C-allyl-lawsone that showed activity against the parasite, with ID50 values of 420.7 +/- 71.1 and 330.7 +/- 62.4 mumol/l, respectively. The trypanocidal activity of the naphtho heterocyclics synthesized from the original quinones showed no concordant behavior in relation to the parent compound. Six of nine of the synthesized compounds presented lower ID50 values than crystal violet, indicating a general trend of activity among naphthalenic heterocyclics of the oxazole/imidazole type. However, their chemical structures do not endow them with the capacity of free radical generation by biological reduction as the quinoidal moiety, nor do they have chemical reducible appendage like the nitro group of nifurtimox and benznidazole, responsible for such behaviour. As a hypothesis, the pattern of their biological actions should be focused in other aspects of their chemical structures. Because of their polycyclic planar topology, these derivatives are potential candidates for experimental tests as DNA intercalating agents.