Discovery and design of novel vasopressin hypotensive peptide agonists

Six Decades of History of Hypertension Research at the University of Toledo: Highlighting Pioneering Contributions in Biochemistry, Genetics, and Host-Microbiota Interactions

PURPOSE OF REVIEW

The study aims to capture the history and lineage of hypertension researchers from the University of Toledo in Ohio and showcase their collective scientific contributions dating from their initial discoveries of the physiology of adrenal and renal systems and genetics regulating blood pressure (BP) to its more contemporary contributions including microbiota and metabolomic links to BP regulation.

RECENT FINDINGS

The University of Toledo College of Medicine and Life Sciences (UTCOMLS), previously known as the Medical College of Ohio, has contributed significantly to our understanding of the etiology of hypertension. Two of the scientists, Patrick Mulrow and John Rapp from UTCOMLS, have been recognized with the highest honor, the Excellence in Hypertension award from the American Heart Association for their pioneering work on the physiology and genetics of hypertension, respectively. More recently, Bina Joe has continued their legacy in the basic sciences by uncovering previously unknown novel links between microbiota and metabolites to the etiology of hypertension, work that has been recognized by the American Heart Association with multiple awards. On the clinical research front, Christopher Cooper and colleagues lead the CORAL trials and contributed importantly to the investigations on renal artery stenosis treatment paradigms. Hypertension research at this institution has not only provided these pioneering insights, but also grown careers of scientists as leaders in academia as University Presidents and Deans of Medical Schools. Through the last decade, the university has expanded its commitment to Hypertension research as evident through the development of the Center for Hypertension and Precision Medicine led by Bina Joe as its founding Director. Hypertension being the top risk factor for cardiovascular diseases, which is the leading cause of human mortality, is an important area of research in multiple international universities. The UTCOMLS is one such university which, for the last 6 decades, has made significant contributions to our current understanding of hypertension. This review is a synthesis of this rich history. Additionally, it also serves as a collection of audio archives by more recent faculty who are also prominent leaders in the field of hypertension research, including John Rapp, Bina Joe, and Christopher Cooper, which are cataloged at Interviews .

Vasopressin receptors in voiding dysfunction

Arginine vasopressin (AVP), also known as vasopressin or anti-diuretic hormone, is a neuropeptide produced in the hypothalamus. It is primarily responsible for osmoregulation and thus maintains body fluid homeostasis. It is also a potent vasoconstrictor, may have a role in higher cognitive functions and affects metabolism. All the biological and cellular effects of vasopressin are mediated by the interaction of this hormone with three G-protein-coupled receptors - V(1a), V(1b) and V(2).Urological applications are based on the rationale that V(2) receptors mediate water conservation and increase urine osmolality. Due to their anti-diuretic properties mediated by the V(2) receptors, synthetic vasopressin agonists, such as desmopressin, are now commonly used for the treatment of nocturnal polyuria, central diabetes insipidus and nocturnal enuresis and potentially in urinary incontinence. Desmopressin has been licenced worldwide for haematological indications of haemophilia and von Willebrand disease. Vasopressin receptor antagonists correct hyponatremia by blocking the activation of the V(2) receptor and induce a free water diuresis without an accompanying natriuresis or kaliuresis; an effect termed 'aquaresis'. Interfering with vasopressin signalling by administering vasopressin antagonists may have clinical benefits in acute and chronic heart failure.

Impact of the Merrifield solid phase method on the design and synthesis of selective agonists and antagonists of oxytocin and vasopressin: a historical perspective

This tribute to Bruce Merrifield traces the author's fortuitous path in 1964 from Vincent du Vigneaud's laboratory to the laboratory of D. W. Woolley to learn the solid phase method and then to his first faculty position in the Department of Biochemistry, McGill University, Montreal in 1965. It recalls the key roles played from early 1966 to July 1967 by Bruce Merrifield, John Stewart, Arnold Marglin, Herb Takashima, and Vincent du Vigneaud in providing key advice to the author's efforts to use the solid phase method to synthesize oxytocin; while simultaneously the du Vigneaud and Merrifield laboratories were collaborating on the solid phase synthesis of deamino-oxytocin. Both syntheses were published in the same issue of the Journal of American Chemical Society in 1968. Also described is how this breakthrough impacted the author's scientific career: by leading to highly productive collaborative studies, initially with Wilbur H. Sawyer and subsequently with others, on the design and synthesis of selective agonists, antagonists, and radioiodinated ligands for oxytocin and vasopressin receptors. These syntheses were greatly facilitated by the contributions of highly talented graduate students, research technicians, and visiting peptide chemists from Hungary, England, Poland, Bulgaria, and China. Many of these peptides have become very valuable pharmacological tools in studies on the peripheral and central effects of oxytocin and vasopressin: further attesting to the profound impact of the solid phase method as the cornerstone for all the discoveries, which he and his collaborators and coworkers have made over the past 40 years.

Design and synthesis of potent, highly selective vasopressin hypotensive agonists

We report here the solid-phase synthesis and vasodepressor potencies of a new lead vasopressin (VP) hypotensive peptide [1(beta-mercapto-beta,beta-pentamethylenepropionic acid)-2-0-ethyl-D-tyrosine, 3-arginine, 4-valine, 7-lysine, 9-ethylenediamine] lysine vasopressin, d(CH(2))(5)[D-Tyr(Et)(2), Arg(3), Val(4), Lys(7), Eda(9)]LVP (C) and 21 analogues of C with single modifications at positions 9 (1-13), 6 (14), 2 (16-20) and combined modifications at positions 6 and 10 (15) and 2 and 10 (21). Peptides 1-13 have the following replacements for the Eda residue at position 9 in C: (1) Gly-NH(2); (2) Gly-NH-CH(3); (3) Ala-NH(2); (4) Ala-NH-CH(3), (5) Val-NH(2); (6) Cha-NH(2); (7) Thr-NH(2); (8) Phe-NH(2); (9) Tyr-NH(2); (10) Orn-NH(2); (11) Lys-NH(2); (12) D-Lys-NH(2); (13) Arg-NH(2). Peptide 14 has the Cys residue at position 6 replaced by Pen. Peptide 15 is the retro-Tyr(10) analogue of peptide 14. Peptides 16-20 have the D-Tyr(Et) residue at position 2 in C replaced by the following substituents: D-Trp (16); D-2-Nal (17); D-Tyr(Bu(t))(18); D-Tyr(Pr(n)) (19); D-Tyr(Pr(i)) (20). Peptide 21 is the retro-Tyr(10) analogue of peptide 20. C and peptides 1-21 were evaluated for agonistic and antagonistic activities in in vivo vasopressor (V(1a)-receptor), antidiuretic (V(2)-receptor), and in in vitro (no Mg(2+)) oxytocic (OT-receptor) assays in the rat, and, like the original hypotensive peptide, d(CH(2))(5)[D-Tyr(Et)(2), Arg(3), Val(4)]AVP (A) (Manning et al., J. Peptide Science 1999, 5:472-490), were found to exhibit no or negligible activities in these assays. Vasodepressor potencies were determined in anesthetized male rats with baseline mean arterial blood pressure (BP) maintained at 100-120 mmHg. The effective dose (ED), in microg/100 g i.v., the dose required to produce a vasodepressor response of 5 cm(2) area under the vasodepressor response curve (AUC) during the 5-min period following the injection of the test peptide, was determined. The EDs measure the vasodepressor potencies of the hypotensive peptides C and 1-21 relative to that of A (ED = 4.66 microg/100 g) and to each other. The following ED values in microg/100 g were obtained for C and for peptides 1-21; C 0.53; (1) 2.41; (2) 1.13; (3) 1.62; (4) 0.80; (5) 1.83; (6) 1.56; (7) 2.12, (8) 2.58; (9) 1.40; (10) 0.88; (11) 0.90; (12) 0.85; (13) 0.68; (14) 0.99; (15) 1.05; (16) 0.66; (17) 0.54; (18) 0.33; (19) 0.18; (20) 0.15; (21) 0.14. All of the hypotensive peptides reported here are more potent than A. Peptides 20 and 21 exhibit a striking 30-fold enhancement in vasodepressor potencies relative to A. With a vasodepressor ED = 0.14, peptide 21 is the most potent VP vasodepressor agonist reported to date. Because it contains a retro-Tyr(10) residue, it is a promising new radioiodinatable ligand for the putative VP vasodilating receptor. Some of these new hypotensive peptides may be of value as research tools for studies on the complex cardiovascular actions of VP and may lead to the development of a new class of antihypertensive agents.

A novel vasopressin peptide lowers blood pressure through decreases in cardiac output

The changes in blood pressure, cardiac output, and total peripheral conductance evoked by the novel hypotensive arginine vasopressin (AVP) - like peptide, d(CH2)5[D-Tyr(Et)2,Arg3,Val4,Arg7,Eda9]AVP (HYPO-AVP), were recorded in conscious unrestrained Sprague-Dawley rats implanted with radiotelemetry pressure transducers and ultrasonic transit-time flowprobes. Intravenous infusions of 0.6, 1.0, 2.0, and 4.0 microg x kg(-1) x min(-1) of HYPO-AVP evoked dose-related decreases in blood pressure. At the lowest dose of 0.6 microg x kg(-1) x min(-1), the fall in blood pressure was associated with a small but significant increase in total peripheral conductance. Cardiac output was unchanged. In contrast, at the three higher doses of 1.0, 2.0, and 4.0 microg x kg(-1) x min(-1), the fall in blood pressure was related to a dramatic fall in cardiac output. Indeed, total peripheral conductance decreased, preventing blood pressure from falling further. These hemodynamic findings should help to direct future research into the mechanism of the putative hypotensive property of vasopressin, a property that attenuates the well established blood pressure elevating actions of the peptide.

Novel selective hypotensive vasopressin peptides: cardiovascular and structure–activity-relationship studies

Recently, we discovered a series of peripheral acting selective hypotensive vasopressin peptides. Whether these peptides may interact with receptors outside the vasopressin receptor family and affect cardiac function could not be excluded. Accordingly, we tested the effects of these hypotensive vasopressin peptides on blood pressure and heart rate in intact rats and on the heart rate, ventricular contractile force and coronary flow of isolated perfused rat hearts. We found that the hypotensive vasopressin peptides did not modify cardiac function, either in vivo or in vitro. The vasodepressor potency was reduced when assayed in rats with vasopressin-maintained baseline blood pressure, suggesting that vasopressin and the hypotensive peptide compete for a common vasodilating vasopressin receptor in the vasculature. We have now synthesized more potent and radioiodinatable hypotensive peptides that could serve as lead compounds for the development of a radiomarker for the putative vasodilating vasopressin receptor.

Discovery and design of novel and selective vasopressin and oxytocin agonists and antagonists: the role of bioassays

Synthetic oxytocin and vasopressin agonists and antagonists have become important tools for research and were instrumental in the identification of the four known receptor subtypes, V1a, V2, V1b (V3) and oxytocin, of these peptide hormones. However, the relative lack of receptor selectivity, particularly of the antagonists, has limited their usefulness as experimental probes and their potential as therapeutic agents. We now present some findings from our continuing studies aimed at the design of more selective oxytocin and vasopressin agonists and antagonists and a structure-activity relationship update on our recently discovered novel hypotensive vasopressin peptides. Bioassays have been, and continue to be, of critical importance in leading to the discovery of the novel agonists, antagonists and hypotensive peptides reported here. This paper highlights three main aspects of these studies. (1) Replacement of the tyrosine2 and/or phenylalanine3 residues in the V2 agonist deamino,[Val4,D-Arg8]arginine-vasopressin (dVDAVP) by thienylalanine resulted in selective V2 agonists with strikingly high potencies. However, the peptide solutions were unstable and lost activity over time. These highly potent V2 agonists, which are devoid of vasopressor activity, are promising leads for improving drugs for treating diabetes insipidus, enuresis and coagulation disorders. (2) Diaminopropionic acid and diaminobutyric acid substitution at position-5 in oxytocin and in V1a antagonists yielded, respectively, the first specific antagonist for the oxytocin receptor, desGly-NH2,d(CH2)5[D-Trp2,Thr4,Dap5]OVT and the first specific antagonist for the vasopressin V1a receptor, d(CH2)5[Tyr(Me)2,Dab5]AVP. The availability of single receptor subtype-specific or selective antagonists will enhance our ability to delineate receptor functions. Utilising these new receptor specific probes, we were able to show that the uterotonic action of vasopressin is mediated principally by oxytocin and not by V1a receptors. (3) Replacement of the phenylalanine3 residue in the V1a/V2/oxytocin antagonist, d(CH2)5[D-Tyr(Et)2,Val4]AVP, with arginine3 yielded the novel, selective, hypotensive vasopressin peptide, d(CH2)5[D-Tyr(Et)2,Arg3,Val4]AVP (Peptide I). Bioassay characterisations of Peptide I show that its vasodepressor action is independent of the peripheral autonomic, bradykinin, nitric oxide and prostaglandin systems and is not mediated by the known classical oxytocin and vasopressin receptors. These findings suggest the existence of a new vasopressin receptor subtype that may be relevant to the vasodilating action of vasopressin in regional vascular beds. Iodinatable hypotensive peptides have been synthesised and could be developed as markers for the putative new receptor. Ongoing structure-activity relationship studies on Peptide I have led to more potent and selective hypotensive peptides for use as new research tools and as leads for the development of a new class of antihypertensive agents.

Synthesis and structure-activity investigation of novel vasopressin hypotensive peptide agonists

We report the solid phase synthesis and vasodepressor potencies of the novel hypotensive peptide [1(-beta-mercapto-beta,beta-pentamethylene propionic acid)-2-O-ethyl-D-tyrosine, 3-arginine, 4-valine] arginine vasopressin, d(CH2)5[D-Tyr(Et)2, Arg3, Val4]AVP (A), its related Lys3 (B), Tyr-NH(9)2 (C), [Lys3, Tyr-NH(9)2 (D) analogs and in a preliminary structure-activity study of positions 2-4 and 7-9, 24 analogs (1-24) of A-C. Peptides 1-6, 9-14 have the following single substituents at positions 2, 3, 4, 8 and 9 in (A): 1, D-Tyr(Me)2; 2, L-Tyr(Et)2; 3, Orn3; 4, N-Me-Arg3; 5, Glu3; 6, Arg4; 9, D-Arg8; 10, Eda9; 11, Arg-NH(9)2; 12, Ala-NH(9)2; 13, desGly9; 14, desGly-NH(9)2. Peptides 15 and 16 are analogs of B which possess the following single modifications: 15, Arg-NH(9)2; 16, desGly9. Peptides 7 and 8 are analogs of (C) with the following single modification: 7, Gln4; 8, Lys8. Peptides 17-24 are analogs of A possessing the following multiple modifications: 17, [Sar7, Eda9]; 18, [Arg7, Eda9]; 19, [Arg7, Eda9<--Tyr10]; 20, [Arg4, Arg-NH(9)2]; 21, [Ile4, desGly9]; 22, [Arg4, desGly9]l; 23, [Arg7, desGly9]; 24, [Arg7, Lys8, desGly9]. All 24 new peptides were evaluated for agonistic and antagonistic activities in in vivo antidiuretic (V2-receptor), vasopressor (V1a-receptor) and in in vitro (no Mg2+) oxytocic (OT-receptor) assays and like the parent peptides (A-D) (Chan et al. Br. J. Pharmacol. 1998; 125: 803-811) were found to exhibit no or negligible activities in these assays. Vasodepressor potencies were determined in anesthetized male rats with baseline mean arterial blood pressure maintained at 110-120 mmHg. The effective dose (ED), in microg 100 g(-1) i.v., required to produce a vasodepressor response of 5 cm2, area under the vasodepressor response curve (AUC) during the 5-min period following the injection of the test peptide, was determined. Therefore, the EDs measure the relative vasodepressor potencies of the hypotensive peptides. The following ED values were obtained for A-D and for peptides 1-24: A, 4.66; B, 5.75; C, 10.56; D, 11.60; 1, approximately 20; 2, approximately 30; 3, 6.78; 4, non-detectable (ND); 5, ND; 6, approximately 32; 7, ND; 8, 8.67; 9, ND; 10, 2.43; 11, 3.54; 12, 10.57; 13, 4.81; 14, ND; 15, 4.47; 16, 9.78; 17, 5.72; 18, 1.10; 19, 1.05; 20, 10.41; 21, 9.13; 22, approximately 33; 23, 3.01; 24, 1.71. A is clearly the most potent of the four original hypotensive peptides A-D. These data provide insights to which modification of A enhance, retain or abolish hypotensive potencies. Six of the new hypotensive peptides are significantly more potent than A. These are peptides 10, 11, 18, 19, 23 and 24. Peptide 19, a radioiodinatable ligand, is ten times more potent than C or D. The Gln4 modification of C and the N-Me-Arg3, Glu3, D-Arg8 and desGly-NH(9)2 modifications of A abolished hypotensive potency. By contrast, the Eda9, Arg-NH(9)2, [Sar7, Eda9], [Arg7, Eda9<- -Tyr10], [Arg7, desGly9], [Arg7, Lys8, desGly9] modifications of A all led to enhancements of hypotensive potency. This initial structure-activity exploration provides useful clues to the design of (a) more potent vasodepressor peptides and (b) high affinity radioiodinatable ligands for the putative AVP vasodilating receptor. Some of the peptides here may be of value as pharmacological tools for studies on the complex cardiovascular actions of AVP and may lead to the development of a new class of anti-hypertensive agents.