An exploration of the effects of L- and D-tetrahydroisoquinoline-3-carboxylic acid substitutions at positions 2, 3 and 7 in cyclic and linear antagonists of vasopressin and oxytocin and at position 3 in arginine vasopressin

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 .

Design of Oxytocin Analogs

The neurohypophyseal hormone oxytocin (OT) and related modulators of the oxytocin receptor (OTR) have been the subject of intensive research for nearly seven decades. Despite having rather poor drug-like properties, OT is used as a treatment for labor induction, postpartum hemorrhage, and lactation support. The potential use of OT in the treatment of central nervous system (CNS)-related diseases has recently renewed interest in the pharmacology of OT. Oxytocin is one of the most extensively studied cyclic peptides and since the elucidation of its structure in 1953 thousands of peptidic OT analogs with antagonistic and agonistic properties have been synthesized and biologically evaluated. Among them are atosiban, a mixed oxytocin receptor (OTR)/vasopressin 1a receptor (V_1aR) antagonist used as a tocolytic agent approved (in certain countries), and carbetocin, a longer acting OTR agonist on the market for the treatment of postpartum hemorrhage. Many other OT analogs with improved pharmacological properties (e.g., barusiban, Antag III) have been identified. These peptides have been tested in clinical trials and/or used as pharmacological tools. In this chapter, the modifications of the OT molecule that led to the discovery of these compounds are reviewed.

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.

Highly Potent 1-Aminocyclohexane-1-Carboxylic Acid Substituted V2 Agonists of Arginine Vasopressin

The synthesis and some pharmacological properties of two sets of analogues, one consisting of six peptides with 1-aminocyclohexane-1-carboxylic acid (Acc) in position 2 and the other with the amino acid in position 3, have been described. All the peptides were tested for their pressor, antidiuretic, and uterotonic in vitro activities. The Acc(2) modification has been shown to selectively modulate the activities of the analogues. Four of the compounds were highly potent antidiuretic agonists with different pressor and uterotonic activities. On the other hand, the 3-substituted counterparts failed to exhibit any of the activities. One exception was provided by the [Mpa(1),Acc(3),Val(4),D-Arg(8)]VP analogue, which exhibited antidiuretic activity matching that of AVP, yet, unlike AVP, it was fairly selective.

Influence of 1-aminocyclohexane-1-carboxylic acid in position 2 or 3 of AVP and its analogues on their pharmacological properties

In this study we describe the synthesis and some pharmacological properties of seven new analogues of arginine vasopressin (AVP) substituted in position 2 or 3 with 1-aminocyclohexane-1-carboxylic acid (Acc). All peptides were tested for the pressor, antidiuretic and uterotonic in vitro activities. The Acc3 modifications of AVP, dAVP, [d-Arg8]VP and [Cpa1]AVP have been found to be deleterious for interaction with all three neurohypophyseal hormone receptors, as judged from the several orders of magnitude decreased biological activities, whereas Acc2 substitution selectively altered the interaction with the receptors. Two of the new analogues, [Acc2]AVP and [Acc2, d-Arg8]AVP, are potent antidiuretic agonists. [Acc2]AVP exhibits moderate pressor agonistic activity and weak antiuterotonic properties. [Acc2, d-Arg8]AVP has been found to be a weak antagonist in the pressor and uterotonic tests. Another analogue - [Cpa1, Acc3]AVP - turned out to be a highly selective V2 agonist. This is an unexpected effect, as its parent peptide, [Cpa1]AVP is a very potent V1a receptor antagonist. This is the first Cpa1 modification to have resulted in V2 agonism enhancement. Besides providing useful information about structure-activity relationships, our results could open up new possibilities in the design of highly potent and selective V2 agonists.

Noncompetitive nature of oxytocin antagonists with general structure Mpa(1)Xxx(2)Sar(7)Arg(8)

Eight oxytocin (OT) antagonists with general structure Mpa(1)Sar(7)Arg(8), substituted at position 2 with conformationally constrained and bulky amino acids, were synthesized and pharmacologically tested. Binding affinities and selectivities of compounds for OT, and vasopressin receptor subtypes were investigated. In vitro effects of antagonists were evaluated via inhibition of OT-induced contractions of isolated guinea-pig uterus. The abilities of OT antagonists to inhibit spontaneous contractility in 24 h postpartum rat uterus were investigated. These peptides exhibited pseudoirreversible pharmacological properties, and comprise a novel group of OT antagonists for potential clinical use. Their noncompetitive pharmacological nature can be of therapeutic benefit through a sustained effect on myometrium.

Preparation and investigation of tumor affinity, uptake kinetic and transport mechanism of iodine-123-labelled amino acid derivatives in human pancreatic carcinoma and glioblastoma cells

In developing radioiodinated agents for pancreatic and brain tumor imaging by single photon emission tomography (SPET), we prepared p-amino-3-[123I]iodo-l-phenylalanine (IAPA), p-[123I]iodo-l-phenylalanine (IPA), L-8-[123I]iodo-1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid (ITIC) and L-3-[123I]iodo-alpha-methyl-tyrosine (IMT) in radiochemical yields up to 95%, and we investigated their uptake in human pancreatic carcinoma and glioblastoma cells as well as the mechanisms promoting the tumor uptake. The radiopharmaceutical uptake into tumor cells was rapid (t(1/2) < or = 5 min) and temperature- and pH-dependent. The radioactivity concentration in tumor cells varied from 10 to 33% of the total activity (105-310 cpm/1000 cells) following a 30-min incubation at 37 degrees C (pH 7.4). In comparison, accumulation of the radiopharmaceuticals into normal brain and pancreatic tissue remained relatively low. Depolarizing the plasma membrane potential in high K+ buffer significantly altered the radioactivity concentration in the tumor cells, suggesting that membrane potential plays a certain role in the cellular uptake. Competitive inhibition experiments with specific amino acid transport inhibitors indicated that the uptake of IAPA, IPA and IMT into human pancreatic carcinoma and glioblastoma cells is predominantly mediated by the L and ASC transport systems, while no substantial involvement of the transport system A in their tumor uptake could be demonstrated. In contrast, results of the present investigation indicated that ITIC is not taken up into tumor cells via the common neutral amino acid carrier systems, including the A, L and ASC system. Furthermore, preloading with naturally occurring L-amino acids failed to stimulate the cellular uptake of the radiopharmaceuticals. These data indicate that the investigated radiopharmaceuticals exhibit interesting characteristics with promise for in vivo tumor investigations to ascertain their potential as radioligands for glioma and pancreatic carcinoma imaging by SPET.

Theoretical conformational analysis of six arginine vasopressin analogs with the L-naphthylalanine in position 3

Introduction of the naphthylalanine residue into either position 3 of arginine vasopressin (AVP), or its analogs results in peptides with interesting pharmacological properties. The single substituted analog of AVP with L-2-Nal in position 3 causes moderate antiduretic activity, whereas [Mpa1, (L-1-Nal)3, (D-Arg)8] VP and [Mpa1, (L-2-Nal)3, (D-Arg)8] VP are potent and selective V2 agonists. Moreover [(L-2-Nal)3, (D-Arg)8] VP is among the most potent and selective antagonists of V1a receptors. In this study we carried out conformational calculations on [(L-1-Nal)3] AVP, [(L-2-Nal)3] AVP, [(L-1-Nal)3, (D-Arg)8] VP, [(L-2-Nal)3, (D-Arg)8] VP, [Mpa1, (L-1-Nal)3, (D-Arg)8] VP, [Mpa1, (L-2-Nal)3, (D-Arg)8] VP, using the ECEPP/3 force field with and without including hydration to simulate aqueous and nonpolar environments. It was found that in all six compound studied, the low-energy conformations have common geometry and relative energies. Therefore, the modifications of the Phe in position 3 influence the binding to the receptor by changing the size of the third residue, rather than by changing the conformational space. The lowest-energy conformations in the presence and absence of water had beta-turns at residues Phe3-Gln4 and Gln4-Asn5 and Gln4-Asn5, respectively. The conformation at the Gln4-Asn5 turn was most similar to the crystal structure of the pressinoic acid (the cyclic moiety of vasopressin).

Synthesis of oxytocin antagonists containing conformationally constrained amino acids in position 2

Analogues of oxytocin containing D-Trp, 2-amino-1,2,3,4-tetrahydronaphthalene-1-carboxylic acid (Atc) or 1,2,3,4-tetrahydro-beta-carboline-1-carboxylic acid (Car) with R or S configurations in position 2 were synthetized, and their receptor bindings were tested on isolated guinea-pig uterus, rat liver and rat kidney inner medulla plasma membranes. The peptides were synthetized in the solid phase by using racemates of Car and Atc. The resulting diastereomeric mixtures were separated by means of RP-HPLC. The binding to the oxytocin receptor was somewhat decreased for the Atc isomers and dramatically decreased for both R- and S-Car, while the D-Trp-containing analogue displayed a relatively high receptor affinity. However, the V1 receptor affinities were almost the same as those of the parent peptide for the Car-containing analogues and dramatically decreased for the S-Atc substituted analogue, which has a relatively high OT/V1 receptor selectivity of 44.5.

An investigation of position 3 in arginine vasopressin with aliphatic, aromatic, conformationally-restricted, polar and charged amino acids

We report the solid-phase synthesis and some pharmacological properties of 23 new analogs of arginine vasopressin (AVP) which have the Phe3 residue replaced by a broad variety of amino acids. Peptides 1-9 have at position 3: (1) the mixed aromatic/aliphatic amino acid thienylalanine (Thi) and the aliphatic amino acids; (2) cyclohexylalanine (Cha); (3) norleucine (Nle); (4) Leu; (5) norvaline (Nva); (6) Val; (7) alpha-aminobutyric acid (Abu); (8) Ala; (9) Gly. Peptides 10-23 have at position 3: the aromatic amino acids, (10) homophenylalanine (Hphe): (11) Tyr; (12) Trp; (13) 2-naphthylalanine (2-Nal); the conformationally-restricted amino acids (14) Pro; (15) 2-aminotetraline-2-carboxylic acid (Atc); the polar amino acids (16) Ser; (17) Thr; (18) Gln; and the charged amino acids (19) Asp; (20) Glu; (21) Arg; (22) Lys; (23) Orn. All 23 new peptides were evaluated for agonistic and, where appropriate, antagonistic activities in in vivo antidiuretic (V2-receptor) and vasopressor (V1a-receptor) assays and in in vitro (no Mg2+) oxytocic assays. The corresponding potencies (units/mg) in these assays for AVP are: 323+/-16; 369+/-6 and 13.9+/-0.5. Peptides 1-9 exhibit the following potencies (units/mg) in these three assays: (1) 379+/-14; 360+/-9; 36.2+/-1.9; (2) 294+/-21: 73.4+/-2.7; 0.33+/-0.02; (3) 249+/-28; 84.6+/-4.3; 4.72+/-0.16; (4) 229+19; 21.4+/-0.6; 2.1+/-0.2; (5) 134+/-5; 31.2+/-0.9; 28.4+/-0.2; (6) 114+/-9; 45.3+2.3; 11.3+/-1.6; (7) 86.7+/-2.5; 4.29+/-0.13; 0.45+/-0.03; (8) 15.5+/-1.5; 0.16+/-0.01; approximately 0.02: (9) 3.76+/-0.03; < 0.02; in vitro oxytocic agonism was not detected. These data show that the aliphatic amino acids Cha, Nle, Leu, Nva and Val are well-tolerated at position 3 in AVP with retention of surprisingly high levels of antidiuretic activity. Peptides 2-9 exhibit significant gains in both antidiuretic/vasopressor (A/P) and antidiuretic/oxytocic (A/O) selectivities relative to AVP. [Thi3]AVP appears to be a more potent antidiuretic and oxytocic agonist than AVP and is equipotent with AVP as a vasopressor agonist. The antidiuretic potencies of peptides 10-23 exhibit drastic losses relative to AVP. They range from a low of 0.018+/-0.001 units/mg for the Lys3 analog (peptide 22) to a high of 24.6+/-4.6 units,mg for the Hphe3 analog (peptide 10). Their vasopressor potencies are also drastically reduced. These range from a low of < 0.002 units/mg for peptide 22 to a high of 8.99+0.44 units/mg for the Atc3 analog (peptide 15). Peptides 10-23 exhibit negligible or undetectable in vitro oxytocic agonism. The findings on peptides 10-23 show that position 3 in AVP is highly intolerant of changes with aromatic, conformationally-restricted, polar and charged amino acids. Furthermore, these findings are in striking contrast to our recent discovery that position 3 in the potent V2/V1a/OT antagonist d(CH2)5D-Tyr(Et)2VAVP tolerates a broad latitude of structural change at position 3 with many of the same amino acids, to give excellent retention of antagonistic potencies. The data on peptides 1-4 offer promising clues to the design of more potent and selective AVP V2 agonists.

Discovery and design of novel vasopressin hypotensive peptide agonists

This presentation will trace the serendipitous discovery of novel vasopressin (VP) hypotensive agonists d(CH2)5[D-Tyr(Et)2,X3]VAVP (where X = Arg, Lys). These peptides were uncovered as part of an ongoing program aimed at the design of potent and selective VP antidiuretic (V2 receptor) antagonists. We will also present highlights of our subsequent preliminary studies seeking (i) to design high affinity radioiodinatable ligands for the localization and characterization of the putative VP vasodilatory (V1c?) receptor; (ii) to identify the structural features of selective and non-selective cyclic and linear VP and oxytocin (OT) antagonists of the V2 receptor, the vascular (V1a) receptor and of the uterine (OT) receptor required for hypotensive agonism and; (iii) to enhance hypotensive potency. These novel VP hypotensive agonists could serve as valuable research tools in studies on the roles of VP in blood pressure regulation and may also lead to the development of a new class of therapeutically useful antihypertensives.

Position three in vasopressin antagonist tolerates conformationally restricted and aromatic amino acid substitutions: a striking contrast with vasopressin agonists

We report the solid-phase synthesis and some pharmacological properties of 12 position three modified analogues (peptides 1-12) of the potent non-selective antagonist of the antidiuretic (V2-receptor), vasopressor (V1a-receptor) responses to arginine vasopressin (AVP) and of the uterine contracting (OT-receptor) responses to oxytocin (OT), [1(-beta mercapto-beta,beta-pentamethylenepropionic acid)-2-O-ethyl-D-tyrosine 4-valine] arginine vasopressin [d(CH2)5D-Tyr(Et)2VAVP] (A) and two analogues of (B) (peptides 13,14), the 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid3 (Tic3) analogue of (A). Peptides 1-12 have the following substituents at position three in (A): (1) Pro; (2) Oic; (3) Atc; (4) D-Atc; (6) D-Phe; (7) Ile; (8) Leu; (9) Tyr; (10) Trp; (11) Hphe; (12) [HO]Tic; Peptide (13) is the Tyr-NH2(9) analogue of (B): Peptide (14) is the D-Cys(6) analogue of (B). All 14 new peptides were evaluated for agonistic and antagonistic activities in in vivo V2 and V1a assays and in vitro (no Mg2+)n oxytocic assays. With the exception of the D-Phe3 peptide (No. 6), which exhibits very weak V2 agonism (approximately 0.0017 U/mg), none of the remaining 13 peptides exhibit any agonistic activities in these assays. In striking contrast to their deleterious effects on agonistic activities in AVP, the Pro3, Oic3, Tyr3 and Hphe3 substitutions in (A) are very well tolerated, leading to excellent retention of V2, V1a and OT antagonistic potencies. All are more potent as V2 antagonists than the Ile3 and Leu3 analogues of (A). The Tyr-NH2(9) and D-Cys(6) substitutions in (B) are also well tolerated. The anti-V2 pA2 values of peptides 1-5 and 7-14 are as follows (1) 7.77 +/- 0.03; (2) 7.41 +/- 0.05; (3) 6.86 +/- 0.02; (4) 5.66 +/- 0.09; (5) approximately 5.2; (7) 7.25 +/- 0.08; (8) 6.82 +/- 0.06; (9) 7.58 +/- 0.05; (10) 7.61 +/- 0.08; (11) 7.59 +/- 0.07; (12) 7.20 +/- 0.05; (13) 7.57 +/- 0.1; (14) 7.52 +/- 0.06. All analogues antagonize the vasopressor responses to AVP, with anti-V1a pA2 values ranging from 5.62 to 7.64, and the in vitro responses to OT, with anti-OT pA2 values ranging from 5.79 to 7.94. With an anti-V2 potency of 7.77 +/- 0.03, the Pro3 analogue of (A) is surprisingly equipotent with (A), (anti-V2 pA2 = 7.81 +/- 0.07). These findings clearly indicate that position three in AVP V2/V1a antagonists, in contrast to position three in AVP agonists, is much more amenable to structural modification than had heretofore been anticipated. Furthermore, the surprising retention of V2 antagonism exhibited by the Pro3, Oic3, Tyr3, Trp3 and Hphe3 analogues of (A), together with the excellent retention of V2 antagonism by the Tyr-NH2(9) and D-Cys6 analogues of (B) are promising new leads to the design of potent and possibly orally active V2 antagonists for use as pharmacological tools and/or as radioiodinatable ligands and for development as potential therapeutic agents for the treatment of the hyponatremia caused by the syndrome of the inappropriate secretion of the antidiuretic hormone (SIADH).