Physiologic role of the peripheral enkephalinergic system in regulating cardiovascular homeostasis: evidence of interactions with the renin-angiotensin and kallikrein-kinin systems

On isolated heart preparation, it was found that Leu5-Enkephalin (Leu5-ENK) did not influence the cardiac function. On the other hand, Leu5-ENK induced a specific dose-related inhibition, in the cardiac perfusate, of the activities of kininase II (KII) and angiotensin converting enzyme (ACE) (but not of kininase I-KI). Instead no detectable alterations of the above enzymatic activities with the used concentrations of Leu5-ENK were observed in vitro. This opioid also increased specifically the effects induced by some of the autacoids, related to both renin-angiotensin and kallikrein-kinin systems, on the KII and ACE activities. A specific correlation between these Leu5-ENK-induced modifications and the functional responses of the heart to the same autacoids was observed. Naloxone (NAL) and more significantly ICI 174864 (ICI) opposed or reversed the inhibitory effect of the used opioid whereas they had neither inhibitory nor synergic effect on both KII and ACE activity by themselves. The possible physiologic role of the enkephalins in regulating cardiovascular function by acting peripherally on some humoral systems through modulatory mechanism was discussed.

Formation of angiotensin II and other angiotensin peptides from des-leu 10-angiotensin I in rat lung and kidney

The formation of AII from a metabolite of AI, des-leu10-angiotensin I [A(1-9)] has been studied in centrifugal fractions of rat lung and kidney using gradient elution HPLC to monitor the formation of peptide products. AII-forming activity was present in kidney S2 (22.3 nmol/mg protein/min) but not in kidney P2 centrifugal fractions. Lung S2 fractions showed relatively weak AII-forming activity (0.34 nmole/mg protein/min) whilst no activity was observed in lung P2. Carboxypeptidase N-like activity measured using both Hipp-Arg and Hipp-Lys as synthetic substrates did not parallel AII-forming activity, since this activity was highest in the P2 fractions of both lung and kidney, as were ACE and aminopeptidase activities. Whilst the major peptide produced in kidney S2 was AII (71%) significant amounts of both AIII (23%) and A(2-9) (6%) were also observed. In lung the amounts of these peptides produced as a percentage of the A(1-9) degrading activity were 2.9%, 2.4% and 21% respectively. The AII-forming activity in kidney S2 was not inhibited by enalaprilat, bestatin, amastatin, phosphoramidon or Pro-Phe but was inhibited (31%) by 1 mM cobalt (II). 1,10-Phenanthroline, iodoacetic acid, EDTA and puromycin significantly enhanced the formation of AII and increased the rate of degradation of the substrate, A(1-9). These results support the concept of a sequential carboxypeptidase pathway operating, particularly in kidney, to produce AII from AI. These results provide further evidence of an alternative metabolic pathway for the formation of AII not involving angiotensin converting enzyme.

Characterization of the carboxypeptidase N secreted by Hep G2 cells

Human hepatoma (Hep G2) cells secrete nanogram quantities of carboxypeptidase enzymes which are capable of hydrolyzing COOH-terminal lysine and arginine residues. A carboxypeptidase with a neutral pH optimum (greater than pH 7.0) was partially purified from the conditioned medium and compared with pure plasma carboxypeptidase N. The two enzymes behaved in a similar manner on gel filtration (apparent Mr = 280,000), DE52 ion exchange chromatography, and concanavalin A-affinity chromatography and were indistinguishable enzymatically and immunologically. Immunoblots of the Hep G2 and plasma carboxypeptidase N before and following deglycosylation with peptide-N4-[N-acetyl-beta-glucosaminyl]asparagine amidase F revealed a similar, if not identical, multimeric structure. A second carboxypeptidase with a lower molecular weight and a pH optimum of 5.0 was also detected in the Hep G2 medium.

Nature of kininase activity in the exudate in kaolin-induced inflammation of the air pouch type in rats

Experimental inflammation was induced by injection of a suspension of kaolin in carboxymethylcellulose solution into a subcutaneous air pouch preformed on the back of rats. Endogenous bradykinin generated in the inflammatory pouch declined quickly unless kininase inhibitors were administered into the pouch. Bradykinin injected into the pouch brought about no significant increase in plasma exudation in the pouch unless kininase inhibitors were administered simultaneously. Although kininase I and II activities were present in normal rat serum, kininase II rather than kininase I was mainly responsible for the degradation of bradykinin in rat serum. In the pouch challenged with the kaolin suspension and vehicle, kininase II originating from the pouch wall tissue played a predominant role in the degradation of bradykinin while the role of kininases derived from the blood and inflammatory cells was minor.

A new type of ultrasensitive bioluminogenic enzyme substrates. I. Enzyme substrates with D-luciferin as leaving group

Derivatives of D-luciferin, D-luciferin methyl ester, D-luciferin O-sulfate, D-luciferin O-phosphate, D-luciferyl-L-N alpha-arginine and D-luciferyl-L-phenylalanine were used as highly sensitive substrates for carboxylic esterase, arylsulfatase, alkaline phosphatase and carboxypeptidases A, B and N. Enzymatic cleavage of the compounds by enzymes leading to the release of D-luciferin was demonstrated. Kinetic constants have been determined for D-luciferin methyl ester and carboxylic esterase, for D-luciferin O-sulfate and arylsulfatase, for D-luciferin O-phosphate and alkaline phosphatase, for D-luciferyl-L-phenylalanine and carboxypeptidase A, and for carboxypeptidases B and N and D-luciferyl-L-N alpha-arginine. All compounds proved to be highly sensitive substrates for the respective enzymes, permitting a limit of detection for enzymes between 10 and 500 fg per assay.

Role of bradykinin in the vascular permeability response induced by carrageenin in rats

1 Bradykinin in carrageenin-induced inflammatory pouch fluid was measured by an enzyme immunoassay method. 2 The bradykinin showed a single peak in the 30-60 min period after the challenge and then decreased quickly, and there was a correlation between the bradykinin level and exudation of fluorescein-labelled bovine serum albumin in the first 60 min period. 3 Captopril (an inhibitor of kininase II) elevated both the bradykinin level in the inflammatory pouch fluid and vascular permeability, while DL-2-mercaptomethyl-3- guanidinoethylthiopropanoic acid (an inhibitor of kininase I) had no effect. 4 Soybean trypsin inhibitor (SBTI) inhibited the vascular permeability response in parallel with the decrease in the bradykinin level. 5 A bradykinin-degrading activity appeared in the pouch fluid within 1 h after the challenge and increased with time. 6 In the period of 3.5-4 h, bradykinin levels were suppressed below the sensitivity limit of the assay, i.e. 0.07 nm ml-1, in spite of active generation. This was because degradation of bradykinin was very rapid in this late stage. Nevertheless, bradykinin still played a definite role in sustaining a high level of vascular permeability response in the late stage in conjunction with prostaglandins.

High performance liquid chromatographic quantitation of carboxypeptidase activity secreted by human hep G2 cells

A new high performance liquid chromatographic method has been developed for the determination of carboxypeptidase N activity which quantitates the furylacryloyl-alanine released by enzymatic cleavage of furylacryloyl-alanyl-lysine or furylacryloyl-alanyl-arginine. A short isocratic gradient elutes the substrate and product in less than 7 min and multiple analyses are facilitated by an automatic sample injector. The microassay readily detects and quantitates carboxypeptidase N activity secreted into culture medium. It was determined that approximately 1 X 10(6) Hep G2 cells at early confluence secreted 1 ng of carboxypeptidase N in 24 h. The microassay will also detect as little as 51 pg of purified carboxypeptidase N or 8 pg of carboxypeptidase B.

Estradiol stimulates a uterine plasma membrane protease activator

An estrogen-regulated arginine esteropeptidase is present in the immature rat uterus. The enzymatic complex consists of a membrane-bound activator and a soluble proenzyme. The activator is under strong estrogen control; its activity increases 10-fold 3 h after a single dose of 17 beta-estradiol. The subcellular localization of the activator is determined by a radioactive assay of fractions prepared by sucrose density centrifugation. The distribution of activity parallels the distribution of two plasma membrane markers, Mg2+-ATPase and 5'-nucleotidase. Electron micrographic visualization of the gradient fractions containing the activator reveals a population of vesicles 0.2-0.5 micron in diameter.

Macrophage colony-stimulating factor in nerve growth factor preparations

Following a report that nerve growth factor preparations have granulocyte-colony-stimulating activity, we investigated the presence of colony-stimulating factors in 7s mouse submaxillary nerve growth factor and its subunits. Macrophage colonies were formed in mouse bone marrow cultures after exposure to preparations of 7s nerve growth factor, the gamma subunit, and, to a small extent, the alpha subunit; the beta subunit, which is responsible for the nerve growth function, did not stimulate colony growth. Furthermore, the esteropeptidase activity of the gamma subunit was not detected in preparations of macrophage colony-stimulating factor purified from the giant cell tumor (GCT) cell line. Immunoprecipitation of radiolabeled gamma subunit with a polyclonal antibody to L-cell macrophage colony-stimulating factor showed a protein band that could represent the gamma subunit of nerve growth factor. Separation of the macrophage activity from the esteropeptidase activity of the gamma subunit was accomplished on the basis of molecular size. Thus, macrophage colony-stimulating factor was a contaminant of nerve growth factor produced by the mouse submaxillary gland and copurified with the gamma subunit.

Carboxypeptidase N (kininase I) activity in blood and synovial fluid from patients with arthritis

Carboxypeptidase N (CPN, kininase I) and kininase II (angiotensin converting enzyme) activities were measured simultaneously in blood plasma and synovial fluid in patients suffering from rheumatoid arthritis (RA), psoriatic arthritis (PA) and osteoarthritis (OA) and in the plasma of normal volunteers. CPN levels (defined as the rate of hydrolysis of furylacryloyl-Ala-Lys) in blood were modestly increased and correlated with erythrocyte sedimentation rate in RA and PA. Based on the hydrolysis of synthetic substrates, CPN activity was much higher than kininase II activity in synovial fluid (SF). SF kininase activities were always inferior to the blood levels in all patients and were correlated with the logarithm of SF leukocyte counts, an indicator of the intensity of inflammation. In addition, CPN and albumin levels in SF were highly correlated when expressed as a percent of the plasma concentrations. Biochemical properties of CPN in crude SF confirmed its similarity to blood CPN. Polymorphonuclear leukocytes derived from inflammatory SF did not release CPN. It is concluded that kininases diffuse from the blood into SF through increased vascular permeability and that CPN could be a major metabolic pathway for kinins in this form of exudate. CPN leads to the formation of des-Arg kinins, selective agonists of the B1 receptors for kinins.

Metabolism of bradykinin and angiotensin I by human basilar artery and rabbit aorta

The role of angiotensin converting enzyme in the metabolism of bradykinin and angiotensin I by in vitro human basilar artery and rabbit aorta was studied. On both human basilar artery and rabbit aorta concentration-effects curves to angiotensin I were significantly attenuated by captopril at a concentration which had no effect on bradykinin responses on both tissues. The metabolism of bradykinin and angiotensin I was studied using high performance liquid chromatography. Both peptides were broken down by human basilar artery and rabbit aorta in a similar fashion. The breakdown of angiotensin I but not bradykinin was significantly attenuated by captopril. 1,10-phenanthroline did attenuate breakdown of bradykinin but this was found not to be significant compared with controls. The results confirm that angiotensin converting enzyme is present in both these tissues and is important for the conversion of angiotensin I to angiotensin II. It appears that other peptidases are important in the breakdown of kinins by these tissues and should be taken into account when investigating the mechanism of action of such peptides on these vascular preparations.

Growth-promoting activity in serum-free medium of kallikreinlike arginylesteropeptidases from rat submaxillary gland

The characterization and purification of the growth-promoting activity present in rat submaxillary gland extracts, known to be required for the proliferation of adipose precursor cells in serum-free medium, have been undertaken. Fractionation of the extracts by ion-exchange chromatography, gel filtration, and affinity chromatography on immobilized benzamidine allowed the copurification of the mitogenic activity with two distinct arginylesteropeptidases of apparent molecular weight 25,000; one of these enzymes has been purified to homogeneity and shown to be immunologically related to tonin, a well-characterized kallikreinlike protease from submaxillary gland. The specificity of both enzymes was similar to that of plasma and glandular kallikreins, as indicated by the relative rates of hydrolysis of peptide p-nitroanilide substrates. Prior treatment of the kallikreinlike proteases with phenylmethylsulfonylfluoride or aprotinin abolished completely both mitogenic and arginylesteropeptidase activities, indicating that enzymatic activity was essential for the manifestation of their growth-promoting ability. The kallikreinlike proteases from rat submaxillary gland were able to replace thrombin to support the proliferation of Chinese hamster lung fibroblasts in serum-free medium. These results underline the role of proteases in controlling cell growth and are discussed in light of adipose tissue development.

Assessment of kininases in rheumatic diseases and the effect of therapeutic agents

Bradykinin is degraded in human plasma by a carboxypeptidase to yield desArg9-bradykinin (DBK) which is then digested by angiotensin-converting enzyme (ACE) to the pentapeptide Arg-Pro-Pro-Gly-Phe and the tripeptide Ser-Pro-Phe. We have studied the rate of kinin degradation by each of these enzymes in patients with rheumatoid arthritis (RA) and with systemic lupus erythematosus (SLE), compared with the degradation rate in degenerative joint disease and normal subjects. Carboxypeptidase activity was the same in all individuals, but ACE activity was increased in the RA and SLE patients. We examined the effects of aspirin, sodium salicylate, auranofin, penicillamine, and corticosteroids on kinin metabolism, and all of these were marked inhibitors of ACE; however, only penicillamine had any demonstrable inhibition of carboxypeptidase. These observations suggest rapid degradation of DBK in patients with untreated RA and SLE, whereas drugs utilized in therapy have the opposite effects. Studies to examine the role of DBK in disease manifestations are in progress.

Kininase I activity in human fluids and tissues of the urogenital tract

Kininase I (EC 3.4.17.3) activity has been determined in human fluids and tissues of the urogenital tract. Benzoyl-glycyl-L-arginine and benzoyl-glycyl-L-lysine were used as substrates. The cleaved benzoyl-glycine was measured by means of high performance liquid chromatography. Results obtained showed a high enzymatic activity for kidney cortex. Normal prostate, benign prostatic hyperplasia and prostatic adenocarcinoma showed similar enzymic values. The activity of kininase I was higher in normal serum than in the tissues studied.

Carboxypeptidase activity in human mycoplasmas

Mycoplasma salivarium produced citrulline, ammonia, and ATP from N-benzoylglycyl-L-arginine. The activity was inhibited by EDTA and was therefore concluded to be due to an arginine-specific carboxypeptidase. The activity was also found to exist in M. orale, M. buccale, M. faucium, and M. hominis.

Inactivation of kallikrein and kininases and stabilization of whole rat brain kinin levels following focused microwave irradiation

Focused microwave irradiation was employed to stabilize endogenous whole rat brain bradykinin levels prior to a simple extraction procedure. Skull microwave exposure (2450 MHz, 3.8 kW., 2.45 sec) resulted in inactivation to less than 5% of control of whole brain kallikrein and kininase activity. Using this adequate exposure duration whole rat brain kinin levels as measured by a sensitive radioimmunoassay were approximately 0.6 pmol/g (wet weight). Further purification of irradiated brain extracts using HPLC revealed that immunoreactive kinin eluted as a single peak that co-chromatographed with authentic bradykinin. Microwave fixation duration of 1.25 sec yielded greatly increased levels of immunoreactive kinin which following HPLC purification eluted in two peaks, corresponding to authentic bradykinin and T-kinin, respectively. The tissue injury resulting from incomplete microwave fixation resulted in the release of kinins. This excess immunoreactive kinin may be derived from cerebral blood, since the predominant form of kinin-generating protein in plasma is T-kininogen.

Localization of renal kallikrein-kinin system components in the kidney

In a study using a stop-flow technique in dog kidney, the existence of kallikrein and kinin was recognized in distal tubules. The presence of kininase I was seen in both distal and proximal tubules, and also partly in the distal tubules. The presence of kininase II in the distal tubules was again confirmed by pretreatment with SQ14225. No evidence of kinin formation, however, was obtained in the proximal nephrons in stop-flow method. From these results, it was suggested that kininase I and II localized in proximal tubules may destroy the kinin filtered from glomeruli at the proximal level, while kallikrein and kininogen and also kininase I and II in the distal tubules may regulate the activity of the renal kallikrein-kinin system in the distal nephrons.

Comprehensive studies on the renal kallikrein-kinin system in essential hypertension

In order to investigate the role of the renal kallikrein-kinin (K-K) system in normal (NRH) and low renin (LRH) subgroups of essential hypertension (EHT), daily urinary excretions of renal K-K system components including kallikrein (KAL), total KAL, pre-KAL, kinin (KIN) and kininase (total, I and II), were measured in 21 normotensives (NT) and 45 patients with EHT (NRH: 29, LRH: 16). Urinary KAL and KIN quantities, KAL activity, total and pre-KAL, and kininase (total, I and II) were measured by direct RIA, kininogenase assay, direct RIA of KAL after trypsin treatment, and KIN destroying capacity, respectively. The daily excretions of KAL quantity and activity, total and pre-KAL, and KIN were significantly lower in EHT than in NT. That of total kininase and kininase I were significantly higher in EHT than in NT while no significant difference was found in kininase I between EHT and NT. In comparing NRH and LRH, the urinary KAL activity and KIN were lower in LRH than in NRH, and kininase I was higher in LRH than in NRH. No significant difference, however, was found in total and pre-KAL, KAL quantity and kininase II between NRH and LRH. The ratio of KAL quantity/total KAL which reflects the conversion rate from pre-KAL in the kidney, did not show any significant difference among NT, NRH and LRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Sexual difference in kininase activity in the mouse submandibular gland

A marked sexual difference in kininase activity was found in the adult mouse submandibular gland. The activity was over 3-fold higher in females than in males between 10 and 12 weeks of age. Castration of male mice increased kininase activity up to the level of females. Testosterone administration to castrated males restored enzyme activity to about the normal level. Moreover, testosterone administration to normal females decreased enzyme activity to about the level of normal male mice, while ovariectomy had no effect. These results suggest that kininase activity in the mouse submandibular gland is suppressively regulated by endogenous androgen.

Nerve growth factor biosynthesis: isolation and characterization of a guinea pig prostate kallikrein

Guinea pig prostate contains one major soluble esteropeptidase activity. The protein has been purified and characterized and found to be a glycoprotein comprised of a single polypeptide chain. The molecular has a similar Km for lysine and arginine synthetic substrates, although the Vmax for arginine is much greater than that for lysine. Amino-terminal sequence analysis has also revealed a marked degree of homology to mouse gamma-nerve growth factor (NGF) and the kallikrein family of serine proteases. In contrast to gamma-NGF, however, the guinea pig enzyme does not appear to form stable complexes with beta-NGF.

Molecular mechanism for the production of multiple forms of MM creatine kinase

Incubation of human, canine or rabbit MM creatine kinase with carboxypeptidase-N or B resulted in the production of 2 additional enzyme forms with increased anodal migration on polyacrylamide gels. The C-terminal amino acid of tissue MM creatine kinase from all 3 species was shown to be lysine, a specific substrate for carboxypeptidase-N and B.

Cell biology of pulmonary endothelium

Since the late 1960s, understanding of the cell biology of endothelium has been transformed. Endothelium is not merely a metabolically inert, semipermeable barrier separating blood from parenchyma; rather, it is a layer of metabolically active cells. In lungs, even gas exchange may be assisted by reactions occurring on the endothelial surface. Endothelial cells synthesize specific proteins (some for export); these cells have receptors and enzymes capable of reacting with certain hormones and other excitatory substances as they pass in circulating blood. Endothelium is antithrombogenic unless injured; when injured, endothelium becomes thrombogenic and then thrombolytic. Endothelium may sometimes retard the development of inflammation and at other times may facilitate it. In addition to providing sites for exchange of nutrients and metabolites, endothelium interacts with prohormones and hormones to determine the composition of blood moving downstream. The latter is a key function of pulmonary endothelium: its venous effluent is systemic arterial blood. Efforts to understand how endothelium accomplishes its wide range of metabolic activities have motivated parallel efforts to define the fine structure of the endothelial cell. Thus it has become feasible to visualize habitats of two surface enzymes, angiotensin-converting enzyme and carboxypeptidase N. Efforts to visualize surface enzymes required development of means of replicating cell surfaces, a methodology that in turn provided the first en face view of the glycocalyx. Given the ubiquity of vascular endothelium and its activities, it is difficult to imagine an area of medical practice that can safely ignore requirements for appropriately functioning endothelium.