Peptide 7

The renin-angiotensin system (RAS) is a key regulator of human arterial pressure. Several of its effects are modulated by angiotensin II, an octapeptide originating from the action of angiotensin-I converting enzyme (ACE) on the decapeptide angiotensin-I. ACE possess two active sites (nACE and cACE) that have their own kinetic and substrate specificities. ACE inhibitors are widely used as the first-line treatment for hypertension and other heart-related diseases, but because they inactivate both ACE domains, their use is associated with serious side effects. Thus, the search for domain-specific ACE inhibitors has been the focus of intense research. Angiotensin (1-7), a peptide that also belongs to the RAS, acts as a substrate of nACE and an inhibitor of cACE. We have synthetized 15 derivatives of Ang (1-7), sequentially removing the N-terminal amino acids and modifying peptides extremities, to find molecules with improved selectivity and inhibition properties. Ac-Ang (2-7)-NH2 is a good ACE inhibitor, resistant to cleavage and with improved cACE selectivity. Molecular dynamics simulations provided a model for this peptide's selectivity, due to Val3 and Tyr4 interactions with ACE subsites. Val3 has an important interaction with the S3 subsite, since its removal greatly reduced peptide-enzyme interactions. Taken together, our findings support ongoing studies using insights from the binding of Ac-Ang (2-7)-NH2 to develop effective cACE inhibitors.

Studies have shown that some peptides and small molecules can induce non IgE-mediated anaphylactoid reactions through mast cell activation. Upon activation, mast cells degranulate and release vasoactive and proinflammatory mediators, from cytoplasmic granules into the extracellular environment which can induce a cascade of severe adverse reactions. This study describes a lead optimization strategy to select NaV1.7 inhibitor peptides that minimize acute mast cell degranulation (MCD) toxicities. Various in vitro, in vivo, and PKPD models were used to screen candidates and guide peptide chemical modifications to mitigate this risk. Anesthetized rats dosed with peptides demonstrated treatment-related decreases in blood pressure and increases in plasma histamine concentrations which were reversible with a mast cell stabilizer, supporting the MCD mechanism. In vitro testing in rat mast cells with NaV1.7 peptides demonstrated a concentration-dependent increase in histamine. Pharmacodynamic modeling facilitated establishing an in vitro to in vivo correlation for histamine as a biomarker for blood pressure decline via the MCD mechanism. These models enabled assessment of structure-activity relationship (SAR) to identify substructures that contribute to peptide-mediated MCD. Peptides with hydrophobic and cationic characteristics were determined to have an elevated risk for MCD, which could be reduced or avoided by incorporating anionic residues into the protoxin II scaffold. Our analyses support that in vitro MCD assessment in combination with PKPD modeling can guide SAR to improve peptide lead optimization and ensure an acceptable early in vivo tolerability profile with reduced resources, cycle time, and animal use.

Glucagonlike peptide I (7-37) [GLP-I-(7-37)], encoded with glucagon and glucagonlike peptide II and intervening peptide II in the rat and human glucagon gene, is processed from proglucagon in both pancreas and intestine and is a potent stimulator of insulin secretion. Unequivocal insulin release from the isolated perfused rat pancreas is elicited by a 10(-11) M concentration of this peptide, and a weak response is found at 10(-12) M. We found that GLP-I-(7-37) is approximately 100 times more potent than glucagon in the stimulation of insulin secretion. Insulin release in response to GLP-I-(7-37) is highly dependent on the ambient glucose concentration; no response is detectable at a glucose concentration of 2.8 mM, and at 6.6 and 16.7 mM, insulin release is augmented by 4.7 and 22.8 ng/ml, respectively. The pattern of insulin secretion stimulated by GLP-I-(7-37) is biphasic, with an initial spike followed by a plateau of sustained release. The effects on insulin release of GLP-I-(7-36) amide, a GLP-I analogue, and GLP-I-(7-37) at concentrations of 10(-11) M were indistinguishable. We also found that GLP-I-(7-37) at 10(-9) M does not influence glucagon secretion and that glucagonlike peptide II and the intervening peptide II, two other peptides encoded by the glucagon gene, have no detectable effects on insulin secretion.