Leptin-derived peptides that stimulate food intake and increase body weight following peripheral administration.

We previously showed that peptides containing leptin sequences 1-33 or 61-90 are taken up by the rat brain. We now report the effects of these peptides on food intake and body weight in mature rats. Peptides were infused intravenously for 4weeks, using Alzet minipumps. Dosages were 20µg/kg/day in experiment I, and 60µg/kg/day in experiment 2. In experiment 1, female rats receiving peptides 1-33 and 61-90 each underwent an approximate doubling of the weight gain of control rats. These peptides also increased food intake in female rats. Peptide 15-32, which has a lesser degree of brain uptake, gave a smaller weight gain. Peptide 83-108, which is not taken up by the brain, had no effect on weight gain or food intake. Similar results were obtained in experiment 2. In male rats, however, none of the peptides caused significant changes in food intake or body weight. This was at least partly due to the fact that all male rats underwent vigorous weight increases. We conclude that peptides 1-33 and 61-90 acted as leptin antagonists, stimulating food intake and body weight increases, at least in female rats. These peptides may lead to clinical applications in conditions such as anorexia and cachexia.

Whole body deletion of AMP-activated protein kinase {beta}2 reduces muscle AMPK activity and exercise capacity.

AMP-activated protein kinase (AMPK) ß subunits (ß1 and ß2) provide scaffolds for binding α and γ subunits and contain a carbohydrate-binding module important for regulating enzyme activity. We generated C57Bl/6 mice with germline deletion of AMPK ß2 (ß2 KO) and examined AMPK expression and activity, exercise capacity, metabolic control during muscle contractions, aminoimidazole carboxamide ribonucleotide (AICAR) sensitivity, and susceptibility to obesity-induced insulin resistance. We find that ß2 KO mice are viable and breed normally. ß2 KO mice had a reduction in skeletal muscle AMPK α1 and α2 expression despite up-regulation of the ß1 isoform. Heart AMPK α2 expression was also reduced but this did not affect resting AMPK α1 or α2 activities. AMPK α1 and α2 activities were not changed in liver, fat, or hypothalamus. AICAR-stimulated glucose uptake but not fatty acid oxidation was impaired in ß2 KO mice. During treadmill running ß2 KO mice had reduced maximal and endurance exercise capacity, which was associated with lower muscle and heart AMPK activity and reduced levels of muscle and liver glycogen. Reductions in exercise capacity of ß2 KO mice were not due to lower muscle mitochondrial content or defects in contraction-stimulated glucose uptake or fatty acid oxidation. When challenged with a high-fat diet ß2 KO mice gained more weight and were more susceptible to the development of hyperinsulinemia and glucose intolerance. In summary these data show that deletion of AMPK ß2 reduces AMPK activity in skeletal muscle resulting in impaired exercise capacity and the worsening of diet-induced obesity and glucose intolerance.

The identification of leptin-derived peptides that are taken up by the brain.

We studied the brain uptake of leptin and of a set of peptides whose combined sequences spanned the entire mature human leptin protein. We compared their uptake to that of albumin and IgG. Two of these peptides, consisting of residues 1-33 and 61-90, demonstrated brain uptake on a par with leptin protein itself, and significantly higher than the uptake of albumin and IgG. Further investigation revealed a peptide, 12-32, with higher uptake than its parent peptide 1-33. Peptide 61-90 had the highest brain uptake, and this was shown to be saturable. Comparison of these brain-permeant peptides with the published structure of the leptin:leptin receptor complex revealed a high degree of correlation. All of the leptin residues that have been identified as important receptor-binding contacts appeared to have a role in brain uptake, indicating that receptor binding is an intrinsic part of transport across the blood-brain barrier. The effect of these peptides as leptin agonists or antagonists remains to be investigated. The newly identified peptides also have a potentially large role as carrier molecules for new brain therapeutics, since peptides can be readily coupled to other molecules.