Design of a synthetic leptin agonist: Effects on energy balance, glucose homeostasis, and thermoregulation

We have previously reported that a synthetic peptide amide corresponding to amino acid residues 116-130 of mouse leptin, LEP(116-130), reduces body we ight gain, food intake, and blood glucose levels in ob/ob and db/db mice. I n the present study we show that the activity of LEP-(116-130) resides in a restricted sequence between amino acid residues 116-122. A synthetic pepti de corresponding to this sequence (Ser-Cys-Ser-Leu-Pro-Gln-Thr) has been na med OB3. Single point D-amino acid substitution was used to study the struc ture-function relationship of each residue in OB3. D-Amino acid analogs of OB3 were synthesized by the solid phase method, purified to 98+%, and admin istered (1 mg/day, ip) for 7 days to female C57BL/6J ob /ob mice. The effec ts of the peptides on body weight gain, food and water intake, glucose home ostasis, and thermoregulation were assessed. In most cases, the efficacy of OB3 on all parameters tested was reduced by substitution of an L-amino aci d with its corresponding D-isoform. A statistically significant increase (2 .6-fold) in the weight-reducing effect of OB3, however, was observed by inv ersion of the configuration of the leucine residue at position 4 (Leu-4) of OB3 by substitution with its D-amino acid isoform [D-Leu-4]. Com pared wit h OB3, mice treated with [D-Leu-4]-OB3 consumed 7.9% less food and 16.5% le ss water. Blood glucose was normalized to levels comparable to those in wil d-type control mice within 2 days after initiation of [D-Leu-4]-OB3 treatme nt. Unlike native leptin, however, neither OB3 nor any of its D-amino acid- substituted analogs had any apparent effect on thermogenesis. Our results i ndicate that synthetic peptide strategies may be useful in the development of potent and stabile pharmacophores with potential therapeutic significanc e in the treatment of human obesity and its related metabolic dysfunctions.