Analogs of pancreatic polypeptide and peptide YY with a locked PP-fold structure are biologically active.

Pancreatic polypeptide (PP), peptide YY (PYY) and neuropeptide Y (NPY), members of the PP-fold family share a high degree of sequence homology. Nuclear magnetic resonance (NMR) and X-ray crystallography studies have shown these peptides can adopt a tightly organized tertiary structure called the PP-fold, which has long been assumed to be the active structure of this family of peptides. To date, however, no studies have been completed with PYY and PP which confirm if the PP-fold structure is important for their physiological actions. The aim of the study was to test if PYY and PP locked into the PP-fold maintained biological activity. Therefore, we designed and produced analogs of PP and PYY in a cyclic conformation with two cysteine amino acid substitutions at the N-terminus and at position 27. These were oxidized to form a cysteine disulfide bond locking the peptides into the PP-fold structure. Studies demonstrate that the cyclic analogs have both similar in vivo activity to their parent molecules, and affinity for the Y2 and Y4 receptors. Results suggest that the proposed PP and PYY-fold is likely to be their biologically active conformation.

Pharmacokinetics, adverse effects and tolerability of a novel analogue of human pancreatic polypeptide, PP 1420.

AIMS: The objectives of this phase 1 study were to confirm the tolerability of single ascending subcutaneous doses of PP 1420 in healthy subjects, to assess its adverse effects and to investigate the drug's pharmacokinetics and dose proportionality. METHODS: This was a double-blind, placebo-controlled, randomized study. There were three dosing periods. Each subject (n= 12) was randomized to receive one dose of placebo and two ascending doses of PP 1420, given as a subcutaneous injection. Blood samples were taken over 24 h to assess pharmacokinetics. Standard safety and laboratory data were collected. The primary endpoint was the tolerability of PP 1420. The secondary endpoint was exposure to PP 1420 as assessed by C(max) and AUC(0,∞). RESULTS: PP 1420 was well tolerated by all subjects with no serious adverse effects. Following single subcutaneous doses of PP 1420 at 2, 4 and 8 mg to male subjects, C(max) was reached at a median t(max) of approximately 1 h post dose (range 0.32-2.00 h). Thereafter, plasma concentrations of PP 1420 declined with geometric mean apparent terminal elimination t(1/2) ranging from 2.42-2.61 h (range 1.64-3.95 h) across all dose levels. CONCLUSIONS: Subcutaneous PP 1420 was well tolerated in healthy human subjects at single doses between 2-8 mg, with no tolerability issues arising. Where observed, adverse events were not serious, and there was no evidence of a dose-relationship to frequency of adverse events. The results therefore support the conduct of clinical trials to investigate efficacy, tolerability and pharmacokinetics during repeated dosing.

The role of gut hormones and the hypothalamus in appetite regulation.

The World Health Organisation has estimated that by 2015 approximately 2.3 billion adults will be overweight and more than 700 million obese. Obesity is associated with an increased risk of diabetes, cardiovascular events, stroke and cancer. The hypothalamus is a crucial region for integrating signals from central and peripheral pathways and plays a major role in appetite regulation. In addition, there are reciprocal connections with the brainstem and higher cortical centres. In the arcuate nucleus of the hypothalamus, there are two major neuronal populations which stimulate or inhibit food intake and influence energy homeostasis. Within the brainstem, the dorsal vagal complex plays a role in the interpretation and relaying of peripheral signals. Gut hormones act peripherally to modulate digestion and absorption of nutrients. However, they also act as neurotransmitters within the central nervous system to control food intake. Peptide YY, pancreatic polypeptide, glucagon-like peptide-1 and oxyntomodulin suppress appetite, whilst ghrelin increases appetite through afferent vagal fibres to the caudal brainstem or directly to the hypothalamus. A better understanding of the role of these gut hormones may offer the opportunity to develop successful treatments for obesity. Here we review the current understanding of the role of gut hormones and the hypothalamus on food intake and body weight control.

Investigation of structure-activity relationships of Oxyntomodulin (Oxm) using Oxm analogs.

Oxyntomodulin (Oxm) is an intestinal peptide that inhibits food intake and body weight in rodents and humans. These studies used peptide analogs to study aspects of structure and function of Oxm, and the sensitivity of parts of the Oxm sequence to degradation. Analogs of Oxm were synthesized and studied using receptor binding and degradation studies in vitro. Their effects on food intake and conditioned taste avoidance were measured in vivo in rodents. Oxm breakdown by the enzyme dipeptidyl peptidase IV (DPPIV) was demonstrated in vitro and in vivo. In vitro degradation was reduced and in vivo bioactivity increased by inhibitors of DPPIV. Modifications to the N terminus of Oxm modulated binding to the glucagon-like peptide (GLP)-1 receptor and degradation by DPPIV. Modifications to the midsection of Oxm modulated binding to the GLP-1 receptor and degradation by neutral endopeptidase. These modifications also altered bioactivity in vivo. The C-terminal octapeptide of Oxm was shown to contribute to the properties of Oxm in vitro and in vivo but was not alone sufficient for the effects of the peptide. Elongation and acylation of the C terminus of Oxm altered GLP-1 receptor binding and duration of action in vivo, which may be due to changes in peptide clearance. An Oxm analog was developed with enhanced pharmaceutical characteristics, with greater potency and longevity with respect to effects on food intake. These studies suggest that Oxm is a potential target for antiobesity drug design.