The aminoguanidine carboxylate BVT.12777 activates ATP-sensitive K+ channels in the rat insulinoma cell line, CRI-G1

BVT.3531 reduces body weight and activates K(ATP) channels in isolated arcuate neurons in rats

A number of hormones, including leptin, have been shown to inhibit food intake in humans and animals. Analogues of 3-guanidinopropionic acid have also been found to reduce total food intake, but their mechanisms of action have not been well studied. The present study investigated the effects of intracerebroventricular infusion of the analogue BVT.3531 on food intake, meal pattern, and body weight in rats during 7 days. Single channel recordings from arcuate neurons and insulinoma cells were used to determine the effects of BVT.3531 on K(ATP) activity. Data analysis showed that BVT.3531 significantly decreased body weight and food intake, primarily by reducing meal size. BVT.3531 activated K(ATP) channels in cell-attached recordings from insulin-secreting cells and rat arcuate neurons but had no effect on K(ATP) channel activity in inside-out membrane patches from either cell type. BVT.3531 did not alter the firing rate or K(+) channel activity of arcuate neurons devoid of K(ATP). The study suggests that small molecules capable of mimicking the effects of leptin on food intake and body weight may utilize output mechanisms similar to those of leptin to elicit changes in arcuate neuron excitability.

Possible role of creatine concentrations in the brain in regulating appetite and weight

Cobaltic protoporphyrin IX (CoPP) is a synthetic heme analog which can elicit profound and prolonged decreases in appetite and body weight in several different animal species. Intracerebroventricular administration of CoPP in rats was found, by differential display and confirmed by Real-Time PCR, to result in an increase in expression of the creatine transporter when compared to vehicle-treated fed or vehicle-treated fasted control animals. In situ hybridization studies showed that creatine transporter mRNA concentrations were increased in several areas of the brain involved in the regulation of food intake, but creatine concentrations were decreased in hypothalamic homogenates in CoPP-treated animals compared to controls. Intracerebroventricular administration of beta-guanidinopropionic acid, a compound known to decrease intracellular creatine concentration by competition for uptake, resulted in decreased food intake and body weight and increased Fos expression in the hypothalamus. Taken together, these findings suggest that creatine concentrations in the brain may play a role in regulating food intake and body weight.

Activation of hypothalamic ATP-sensitive K+ channels by the aminoguanidine carboxylate BVT.12777

Derivatives of 3-guanidinopropionic acid, such as leptin, reduce body weight in obese, diabetic mice. We have assessed whether one of these analogues, BVT.12777 activates intracellular signalling pathways in the arcuate nucleus in a manner analogous to leptin and insulin. In addition, because these hormones have been shown to activate K(ATP) channels in a subset of arcuate neurones, we examined whether this channel is also a functional endpoint for BVT.12777 in the arcuate nucleus. BVT.12777 transiently increased phosphorylation of MAPK, STAT3, PKB and GSK3, in a manner identical to that observed for leptin and insulin. BVT.12777 also hyperpolarized glucose-responsive neurones by increasing the activity of K(ATP) channels. The increase in K(ATP) activity driven by BVT.12777 was PI3-kinase independent, unlike leptin and insulin activation of this channel, and could also be elicited in isolated patches. However, K(ATP) activity induced by BVT.12777 was dependent on actin filament dynamics, both in intact neurones and isolated patches. Thus, BVT.12777 modulates arcuate neurone K(ATP) activity by re-organization of the cytoskeleton, a mechanism that has also been ascribed to leptin and insulin. Consequently, BVT.12777 appears to act as a leptin and insulin mimetic with respect to at least some elements of arcuate neurone intracellular signalling and the activation of K(ATP) channels. Resistance to leptin and insulin, associated with obesity has, at least in part, been postulated to be due to aberrant intracellular signalling in arcuate neurones. The data presented here indicate that it may be possible to develop drugs, which by-pass up-stream signalling components associated with adiposity hormone resistance, such as PI3-kinase, but can still induce functional outputs from arcuate neurones by targeting downstream components of the leptin and insulin signalling cascades.