In vivo effects of leptin-related synthetic peptides on body weight and food intake in female ob/ob mice: Localization of leptin activity to domains between amino acid residues 106-140

In C57BL/6J ob/ob mice, a single base mutation of the ob gene in codon 105 results in the replacement of arginine by a premature stop codon and production of a truncated inactive form of leptin. These observations suggest that leptin activity may be localized, at least in part, to domains distal to amino acid residue 104. To investigate this possibility, we synthesized six overlapping peptide amides corresponding to residues 106-167 of leptin, and examined their effects on body weight and food intake in female C57BL/6J ob/ob mice. When compared with vehicle-injected control mice, weight gain by mice receiving 28 daily 1-mg ip injections of LEP-(106-120), LEP-(116-130), or LEP-(126-140) was significantly (P < 0.01) reduced with no apparent toxicity. Weight gain by mice receiving LEP-(136-150), LEP-(146-160), or LEP-(156-167) was not significantly different from that of vehicle-injected control mice. The effects of LEP-(106-120), LEP-(116-130), or LEP-(126-140) were most pronounced during the first week of peptide treatment. Within 7 days, mice receiving these peptides lost 12.3%, 13.8%, and 9.8%, respectively, of their initial body weights. After 28 days, mice given vehicle alone, LEP-(136-150), LEP-(146-160), or LEP-(156-167) were 14.7%, 20.3%, 25.0%, and 24.8% heavier, respectively, than they were at the beginning of the study. Mice given LEP-(106-120) or LEP-(126-140) were only 1.8% and 4.2% heavier, respectively, whereas mice given LEP-(116-130) were 3.4% lighter. Food intake by mice receiving LEP-(106-120), LEP-(116-130), or LEP-(126-140), but not by mice receiving LEP-(136-150), LEP-(146-160), or LEP-(156-167), was reduced by 15%. The results of this study indicate 1) that leptin activity is localized, at least in part, in domains between residues 106-140; 2) that leptin-related peptides have in vivo effects similar to those of native leptin; and 3) offer hope for development of peptide analogs of leptin having potential application in human or veterinary medicine.