Inactivation of atrial natriuretic factor by the renal brush border.

Atrial natriuretic factor (ANF), a 28-amino-acid peptide secreted from the mammalian heart, is known to be cleared rapidly from the circulation. In vitro and in vivo studies implicate the kidney as an important site for clearance and subsequent degradation of atrial natriuretic factor. We have observed that atrial natriuretic factor is inactivated rapidly by rabbit kidney brush-border membranes. The rate of degradation of ANF measured by the loss of bioactivity followed a similar time-course to the decrease in peptide peak area measured by high-performance liquid chromatography. Interestingly, inactivation of ANF produced only a single major degradation product, which was isolated and purified. Sequence analysis revealed that the product had the same sequence of amino acids as ANF with the Cys-7-Phe-8 bond cleaved and the disulfide bridge between Cys-7 and Cys-23 remaining intact. As the renal brush border contains an abundance of proteolytic activities, it is surprising that this peptide is cleaved primarily at a single peptide bond.

Coronary blood flow in physically trained rats.

Coronary blood flow was measured using labelled microspheres (15 micrometer diameter) in sedentary and endurance trained rats during hypoxaemic conditions designed to develop coronary dilatation (Pa,O2 6.0 to 6.7 kPa [45 to 60 mmHg]). Rats that were trained for 12 to 18 weeks (26.8 m per minute, 15% gradient, 1 hour per day) had a significantly greater coronary blood flow conductance (15.3 +/- 1.0 mm3.min-1.kPa-1 aortic diastolic pressure, n = 20) than sedentary animals (10.8 +/- 0.9, n = 19). Even though cardiac hypertrophy (17%) was found in the trained animals, this increase in perfused mass accounted for only one-third of the increase in total coronary blood flow. Thus, there was a greater coronary blood flow per unit mass of the myocardium in the trained rats.

Analogues of atriopeptin(103-125)amide having high binding selectivity.

Analogues of atriopeptin(103-125)amide were prepared having a disulfide bridge at positions different from that found in the natural product. Most of these conformationally perturbed peptides were found to bind selectively to one subclass of binding sites. Binding affinity to a class of specific binding sites that is not associated with any known biological activity (nonvasorelaxant or NVR binding sites) is unaffected or even modestly improved. Affinity for the receptor subclass that is associated with vasorelaxation (VR subclass) decreases in most examples. In several cases, binding to the VR subclass is below the limits of detection for the assay used here. The data demonstrate that binding of atrial peptides to VR receptors requires rigidly defined receptor/ligand interactions. In contrast, the NVR subclass of binding sites appears to tolerate changes in peptide structure quite well.

Conformationally restricted analogues of atriopeptin(103-125)amide.

Conformationally restricted analogues of atriopeptin(103-125)amide were prepared by synthesizing novel bicyclic peptides in which a second disulfide bridge linking residues 108 and 117 was introduced. These syntheses were shown to proceed with no significant scrambling of the disulfide bonds and demonstrated that structurally defined bicyclic analogues of atrial peptides could be easily prepared. The conformationally restrained analogues described here were found to be biologically active with potencies (EC50s) ranging from 0.05 to 3 microM. In addition, these bicyclic peptides (and many of the monocyclic precursors) were found to bind selectively to a class of specific tissue binding sites that have not been shown to be associated with any known second messenger system (NVR binding sites). Since affinity for the receptor class linked to vasorelaxation was negatively affected by the conformational restrictions described here, binding of atrial peptides to this class of receptors appears to have more specific conformational requirements than does binding to the NVR sites.

Conformational restriction of angiotensin II: cyclic analogues having high potency.

Cyclic analogues of angiotensin II (AII) were synthesized by connecting the side chains of residues 3 and 5 via a disulfide bridge. Appropriate conformational constraints afforded an analogue, [Hcy3,5]AII, having high contractile activity (pD2 = 8.48 vs 8.81 for AII) and excellent binding affinity (IC50 = 2.1 nM vs 2.2 nM for AII). This type of cyclization was also used to prepare a highly potent AII antagonist, [Sar1,Hcy3,5,Ile8]AII (pA2 = 9.09 vs 9.17 for [Sar1, Ile8]AII; IC50 = 0.9 nM vs 1.9 nM for [Sar1,Ile8]AII). Model building suggests that this ring structure is consistent with a receptor-bound conformation having any of a variety of three-residue turns, including a gamma-turn. In contrast, the receptor-bound conformation of AII does not appear to accommodate a beta-turn or an alpha-helix which includes residues 3-5.

Specific inhibitors of endopeptidase 24.11 inhibit the metabolism of atrial natriuretic peptides in vitro and in vivo.

Atrial natriuretic peptides (ANPs) are degraded rapidly by renal brush border membranes in vitro. Here, we report that thiorphan, a specific inhibitor of endopeptidase 24.11, afforded almost complete protection against inactivation of ANPs by a renal brush border membrane preparation. The diastereoisomers of [3-(N-hydroxy)carboxamido-2-benzylpropanoyl]-L-alanine (HCBA) are potent inhibitors of endopeptidase 24.11 and were also tested for their abilities to inhibit ANP-(103-126) degradation. The (S,S)-diastereoisomer was more effective than the (R,S)-diastereoisomer (kelatorphan), but both were less potent than thiorphan. To determine if endopeptidase inhibitors could decrease ANP metabolism in in vivo, thiorphan and (S,S)-HCBA were given to rats with or without a continuous infusion of ANP-(103-126). Both inhibitors induced rapid increases in plasma ANP concentration in rats administered exogenous ANP-(103-126), but had no effect on endogenous ANP levels. Thus, specific inhibitors of endopeptidase 24.11 decrease the degradation of ANPs in vitro, and are effective in reducing the metabolism of ANP-(103-126) in vivo.

Treatment of cystic acne with 13-cis-retinoic acid.

13-cis-Retinoic acid (Accutane) is an effective new agent for the treatment of severe cystic acne. The most encouraging feature associated with use of this drug is the persistence of remissions even after administration has been discontinued. The cutaneous side effects are mild to moderate and are usually well tolerated. Careful monitoring of the serum lipids is necessary. In 4 of our 10 patients, the levels of triglycerides became elevated. Of these four patients, three had lowering of the high-density lipoprotein fraction. In three of our most severely affected patients, nonhealing erosions with heaped-up granulation tissue developed at the sites of large acne cysts, which healed promptly after therapy was completed. For the present, we emphasize that use of Accutane should be reserved for severe acne that is unresponsive to conventional treatment; in such cases, careful clinical and laboratory monitoring is imperative.

Chrysiasis resulting from gold therapy in rheumatoid arthritis: identification of gold by x-ray microanalysis.

A patient with blue-gray discoloration of the skin of her face, neck, and hands is described. She was a patient with rheumatoid arthritis who had received a large total cumulative dose of gold. Light microscopy of skin biopsy tissue from the forehead revealed deposits of heavy metal in macrophages. On electron microscopy, the particles were found in the lysosomes of the cell. X-ray microanalysis confirmed the presence of gold. This condition, which is called chrysiasis, may be incorrectly diagnosed as cyanosis.

Paraneoplastic pemphigus: a case of prolonged survival.

OBJECTIVE: To describe a patient with severe, recalcitrant mucous membrane erosions and chronic lymphocytic leukemia. DESIGN: We present a case report and a literature review of paraneoplastic pemphigus. MATERIAL AND METHODS: Immunofluorescence studies and immunoprecipitation confirmed the presence of autoantibodies characteristic of paraneoplastic pemphigus in the patient's serum. RESULTS: Our patient lived almost 8 years after the onset of paraneoplastic pemphigus, the longest time that anyone with this disease is known to have survived. CONCLUSION: The clinical course of paraneoplastic pemphigus tends to be rapid and fatal despite immunosuppressive therapy. Long-term survival is uncommon.

Atriopeptin regulation and renal function in conscious spontaneously hypertensive rats.

We examined the interaction of a non-guanylate cyclase-linked atriopeptin (AP) binding site ligand, SC-46542 (des[Phe106,Gly107,Ala115,Gln116]AP-(103-126], and an endopeptidase 24.11 inhibitor, thiorphan, on mean arterial pressure, urinary sodium excretion, urinary cyclic guanosine monophosphate (cGMP) excretion, plasma cGMP concentration, and plasma AP immunoreactivity (ir) in conscious spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Compared to vehicle control rats, coadministration of SC-46542 and thiorphan increased urinary sodium excretion in SHR from 2.1 +/- 0.3 to 11.6 +/- 0.7 microEq/min/100 g body weight and in WKY from 1.6 +/- 0.4 to 4.4 +/- 0.4 microEq/min/100 g body weight, and increased urinary cGMP excretion in SHR from 2.7 +/- 0.5 to 79.0 +/- 17.5 pmol/min/100 g body weight and in WKY from 7.0 +/- 3.0 to 72.4 +/- 10.6 pmol/min/100 g body weight. The change in urinary sodium excretion was greater in SHR than WKY. The coadministration of SC-46542 and thiorphan had greater effects on urinary sodium excretion and urinary cGMP excretion than administration of either compound alone. Coadministration of thiorphan and SC-46542 had no effect on glomerular filtration rate or plasma cGMP concentration, suggesting that the urinary cGMP excretion response was nephrogenous. Compared to vehicle control rats, plasma APir was increased during coadministration of SC-46542 and thiorphan in both SHR (998 +/- 76 v 5.10 +/- 116 pg/mL) and WKY (775 +/- 36 v 414 +/- 36 pg/mL).(ABSTRACT TRUNCATED AT 250 WORDS)

Gianotti-Crosti syndrome. A review of ten cases not associated with hepatitis B.

Studies of data from ten cases of infantile acrodermatitis and from eight cases reported in the North American literature disclose distinctive papular dermatosis of the face and extremities, often related to virus infection. None of our eight patients who were tested had evidence of hepatitis B infections, although transaminase values were elevated in two. All five patients who were tested had lymphocytosis. Six patients had antecedent upper respiratory tract symptoms. Data from our cases and from the other previously reported cases indicate that the eruption is a virus-related response. Although the hepatitis virus has been the most frequently encountered causative agent to date, other viruses, including Epstein-Barr virus, coxsackievirus, and parainfluenza virus, may produce a similar cutaneous response.

Evaluation of isotretinoin treatment of hidradenitis suppurativa.

Eight patients with a long-standing hidradenitis suppurativa were treated with isotretinoin, 0.71 to 1.2 mg/kg/day, as a single agent for 4 months and have had follow-up of at least 2 months. The clinical status was judged as cleared in one patient, almost cleared in three patients, improved in one patient, not changed in two patients, and worse in one patient.

A thioamide substrate of carboxypeptidase A.

Carbobenzoxythioglycyl-L-phenylalanine [CbzNHCH2C(==S)Phe, Z-Glys-Phe] was synthesized as thioamide analogue of Z-Gly-Phe, a known substrate of carboxypeptidase A (CPA). By use of a ninhydrin-based assay and Z-Gly-Gly-Phe as the substrate, Z-Glys-Phe was shown to be a weak competitive inhibitor of CPA (Ki = 1.4 mM). The L isomer (but not the D) of Z-Glys-Phe proved to be a substrate for CPA (Km = 1.1 mM and kcat = 5.3 s-1 at pH 7.5), binding with comparable affinity to, but hydrolyzing at 10% the rate of, the oxo analogue Z-Gly-Phe. The CPA-catalyzed hydrolysis of Z-Glys-Phe was shown to involve only C-N bond cleavage, to give carbobenzoxythioglycine and phenylalanine.

Sinus tracts to the chin and jaw of dental origin.

This is a report of seven patients with cutaneous sinus tracts of dental origin who were seen in the past 10 years at the Mayo Clinic. Cutaneous sinus tracts of dental origin most commonly present on the chin or the mandibular region as nodulocystic lesions with suppuration. The lesion may be confused with pyogenic granuloma, foreign body reaction, deep fungal infection, squamous cell carcinoma, or osteomyelitis. However, if the lesion is suspected of being of dental origin, the diagnosis is easily confirmed by dental examination and dental roentgenograms of the involved area. Once the correct diagnosis has been made, treatment by appropriate endodontic therapy leads to prompt resolution of the sinus tract. This is an uncommon disease but one for which a high degree of alertness must be maintained when one sees a nodulocystic or ulcerative lesion of the face.

Solid phase organic synthesis (SPOS): a novel route to diketopiperazines and diketomorpholines.

The solid phase synthesis of libraries containing a 1,3,4,6-tetrasubstituted-2,5-diketo-1,4-piperazine scaffold (DKP) or a 3,4,6-trisubstituted-2,5-diketo-1,4-morpholine scaffold (DKM) from alpha-bromocarboxylic acids and amines is described. Using a design strategy which we refer to as divergent library design, both templates were prepared from a common intermediate. The general utility of this synthetic route in creating novel, non-peptidyl chemical libraries is discussed.

Atrial peptide inactivation by rabbit-kidney brush-border membranes.

Atriopeptin (AP) 24, containing amino acids Ser103-Tyr126 of the carboxy-terminal portion of the atrial natriuretic peptide prohormone, was degraded rapidly by rabbit kidney brush border membranes. The rate of degradation of AP24 measured by the loss of vasorelaxant activity followed a similar time course to the decrease in peptide peak area measured by high-performance liquid chromatography. Inactivation of AP24 produced peptide fragments which were separated by HPLC. The major products were purified individually and their peptide sequences determined. Results indicate that AP24 was proteolytically cleaved at three peptide bonds: Ser103-Ser104, Cys105-Phe106 and Ser123-Phe124. des-Ser103-AP24 had similar vasorelaxant activity to AP24, while AP24 cleaved at Cys105-Phe106 was inactive. Regarding the proteolytic cleavage at Ser123-Phe124, there was an accumulation of the C-terminal tripeptide, Phe-Arg-Tyr, only at the later time points of the incubation. Degradation experiments were repeated with an amino- and carboxy-terminal protected peptide, acetyl-AP24-amide. Peptide sequence analysis of the major degradation products of this peptide revealed that the critical peptide bond cleaved was Cys105-Phe106. We conclude that the Cys-Phe peptide bond renders atrial peptides highly susceptible to proteolysis by renal brush border membranes, resulting in inactivation.

Retrospective analysis of an experimental high-throughput screening data set by recursive partitioning.

With the emergence of combinatorial chemistry, whether based on parallel, mixture, solution, or solid phase chemistry, it is now possible to generate large numbers of diverse or focused compound libraries. In this paper we aim to demonstrate that it is possible to design targeted libraries by applying nonparametric statistical methods, recursive partitioning in particular, to large data sets containing thousands of compounds and their associated biological data. Moreover, when applied to an experimental high-throughput screening (HTS) data set, our data strongly suggest that this method can improve the hit rate of our primary screens (about 4- to 5-fold) while increasing screening efficiency: less than one-fifth of the complete selection needs to be screened in order to identify about 75% of all actives present.

Interaction of non-guanylate cyclase-linked atriopeptin receptor ligand and endopeptidase inhibitor in conscious rats.

We examined the interaction of SC-46542 [des(Phe106, Gly107, Ala115, Gln116)-AP(103-126)], a non-guanylate cyclase-linked atriopeptin (AP) binding site ligand, with thiorphan, an inhibitor of endopeptidase 24.11, on mean arterial pressure, urine flow, urinary sodium excretion and plasma AP immunoreactivity in conscious rats. The coadministration of SC-46542 (16 micrograms/kg/min) and thiorphan (30 mg/kg i.v. bolus) produced a greater diuresis and natriuresis (but had no effect on mean arterial pressure) than administration of either compound alone; plasma APir increased 2-fold during coadministration of SC-46542 and thiorphan (from 325 +/- 46 to 676 +/- 86 pg/ml). Administration of SC-46542 or thiorphan alone had small or no effects on mean arterial pressure, urine flow, urinary sodium excretion or plasma APir. Converting enzyme inhibition did not contribute to the effects of thiorphan since coadministration of captopril plus SC-46542 produced effects similar to SC-46542 alone. When a near threshold infusion of AP(103-126) was combined with the coadministration of SC-46542 and thiorphan, there was a potentiation of the depressor, diuretic and natriuretic responses. Neither SC-46542 nor thiorphan alone had these effects. SC-46542 potentiated the depressor but not diuretic or natriuretic responses to low dose AP(103-126) infusion; thiorphan had little or no effect on the responses to low dose AP(103-126). We conclude that blockade of non-guanylate cyclase-linked AP binding sites with SC-46542 combined with inhibition of AP degradation by endopeptidase 24.11 with thiorphan increases diuresis and natriuresis more than inhibition of either system alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Thiorphan, an inhibitor of endopeptidase 24.11, potentiates the natriuretic activity of atrial natriuretic peptide.

To evaluate the role of endopeptidase 24.11 in metabolism of atrial natriuretic peptide (ANP) in vivo, we examined the effect of thiorphan, an inhibitor of this enzyme, on plasma ANP concentrations and the cardiovascular and renal actions of ANP(99-126). Thiorphan alone produced a modest increase in urinary sodium excretion in anesthetized rats; however, urine flow, arterial pressure, and basal plasma ANP concentrations were unchanged. When administered during an infusion of ANP(99-126) (330 ng/kg/min i.v.), thiorphan increased the plasma concentration of ANP and enhanced the diuretic and natriuretic activity of this hormone. The effects on urine flow and urinary sodium excretion were most pronounced immediately after the inhibitor was administered and later diminished in magnitude. Thiorphan did not alter the depressor activity of exogenous ANP(99-126). These data suggest that endopeptidase 24.11 participates in metabolism of ANP(99-126) and that thiorphan potentiates the renal actions of this hormone by inhibiting its degradation.