Atsuo Nagamatsu

Antihypertensive substance in seeds of Areca catechu L.

Among various tannins tested, Areca II-5-C, a fraction isolated from seeds of Areca catechu L., showed the most potent angiotensin-converting enzyme (ACE) inhibitory activity in vitro. Its antihypertensive activity was therefore investigated in normotensive and spontaneous hypertensive rats (SHR) after both oral and intravenous (i.v.) administration. The activity was compared with that of captopril (D-3-mercapto-2-methylpropanoyl-L-proline), a potent ACE inhibitor. Oral administration of Areca II-5-C to SHR produced a lasting, dose-related antihypertensive effect, and the responses obtained with doses of 100 and 200 mg/kg were comparable to those of captopril at doses of 30 and 100 mg/kg. Intravenous administration of Areca II-5-C to SHR produced a rapid and marked reduction in blood pressure at doses of 10 and 15 mg/kg. The maximum antihypertensive effect of Areca II-5-C in SHR, at an i.v. dose of 15 mg/kg, was about 5 times as large as that of captopril at the same dose. Although the vasopressor response to norepinephrine and vasodepressor responses to bradykinin and acetylcholine were not appreciably changed by i.v. treatment with Areca II-5-C at a dose of 5 mg/kg, it did produce dose-related inhibition of the pressor responses to angiotensin I and II. It is suggested that Areca II-5-C has favorable properties as a hypotensive drug through its ability to inhibit the pressor responses to both angiotensin I and II.

Fibrinolytic and anticoagulant activities of highly sulfated fucoidan

A series of fucoidan [sulfated poly(L-fucopyranose)] derivatives were prepared by chemical sulfation and desulfation, and they were tested for their abilities to stimulate tissue plasminogen activator (t-PA)-catalyzed plasminogen activation, clot lysis, and the inhibition of fibrin polymer formation. The magnitude of their activities was dependent upon the degree of sulfation. A striking feature of the sulfated fucoidan was that, unlike heparin, it stimulated t-PA-induced plasma clot lysis by protecting plasmin activity from alpha 2-plasmin inhibitor and decreased the rate of fibrin polymer formation. The inhibition of hyaluronic acid-mediated enhancement of fibrin clot formation was also observed with the fucoidan derivative. We also showed that highly sulfated fucoidan prevents significantly endotoxin-induced hepatic vein thrombosis in the hyperlipemic rat model. The present results are the first to describe the fibrinolytic and anticoagulant activities of fucoidan, and thus may provide useful clues for the development of an ideal thrombolytic agent.

Tripeptidyl carboxypeptidase activity of kininase II (angiotensin-converting enzyme)

The degradation of des-Arg9-brady kinin and its analogues by highly purified preparations of hog lung and kidney kininase II (angiotensin-converting enzyme; peptidyldipeptide hydrolase, EC 3.4.15.1) was studied. The degradative peptides fragments were separated and isolated by high performance liquid chromatography and identified by amino acid analysis. Both enzymes released C-terminal tripeptides from des-Arg9-bradykinin, des-Arg9-(Leu8)-bradykinin, Pro-Pro-Gly-Phe-Ser-Pro-Phe, Pro-Gly-Phe-Ser-Pro-Phe, Gly-Phe-Ser-Pro-Phe, Bz-Gly-Ser-pro-Phe and Bz-Gly-Ala-Pro-Phe. Hydrolysis of Phe-Ser-Pro-Phe, Bz-Gly-His-Pro-Phe, Bz-Gly-Phe-Pro-Phe and Bz-Gly-Gly-Pro-Phe by both enzymes was negligible. These data indicate that kininase II can release C-terminal tripeptides of substrates having a proline residue in the penultimate position such as des-Arg9-bradykinin and its analogues, and that this enzyme is able not only to act as a dipeptidyl carboxypeptidase but also acts as a tripeptidyl carboxy-peptidase. The tripeptidyl carboxypeptidase enzyme was sensitive to inhibition by kininase II inhibitors.

Preparation of oversulfated fucoidan fragments and evaluation of their antithrombotic activities.

Oversulfated fucoidan fragments (20-40 and 40-60 kDa) were prepared, and their fibrinolytic and anticoagulant activities were compared with those of oversulfated fucoidan (100-130 kDa) reported previously [Soeda et al., Biochem. Pharmacol. 43, 1853-1858, 1992]. The results of these experiments indicated that the in vitro abilities of oversulfated fucoidan to stimulate tissue plasminogen activator (t-PA)-catalyzed plasminogen activation and to potentiate thrombin inhibition by antithrombin III or heparin cofactor II decreased with a decrease in its molecular size. However, the preventive effects of both fucoidan fragments on endotoxin-induced hepatic vein thrombosis in hyperlipemic rats were almost the same as that of oversulfated fucoidan (100-130 kDa). We also found that, unlike heparin treatment, the concentrations of serum and vascular endothelium t-PA in rats treated with oversulfated fucoidan or its fragments (1 mg each/kg/week) were maintained at normal levels. The 20-40 and 40-60 kDa fragments had an ability to decrease the elevated levels of serum cholesterol in hyperlipemic rats, whereas the 100-130 kDa fucoidan derivative did not. These results suggest that oversulfated fucoidan and its fragments have another function(s), besides the regulation of blood coagulation and fibrinolysis, and are of therapeutic benefit for the prevention of thrombus formation in hyperlipemia.

An aminopeptidase activity from porcine kidney that hydrolyzes oxytocin and vasopressin: purification and partial characterization.

An aminopeptidase from porcine kidney, hydrolyzing oxytocin and vasopressin in vitro, was purified by chromatography on hydroxyapatite, DEAE-cellulose and nickel ion chelate gel and gel filtration on Sephadex G-100. The enzyme appeared to be a high molecular mass (M(r) 105,000) monomeric protein. It was sensitive to inhibition by metal chelator, o-phenanthroline. Cobalt ion and sulfhydryl activator, 2-mercaptoethanol, had activating effects, while p-chloromercuribenzoate, amino acids with large hydrophobic side chains, L-cystine and aminopeptidase inhibitors, bestatin and amastatin, had inhibitory effects on the enzyme activity. The enzyme hydrolyzed several aminoacyl p-nitroanilides, and had the highest specificity against S-benzyl-L-cysteine p-nitroanilide. The properties of the enzyme were distinct from those of well-characterized leucyl aminopeptidase (EC 3.4.11.1), membrane alanyl aminopeptidase (EC 3.4.11.2) and primate placental cystinyl aminopeptidase (EC 3.4.11.3).

Localization of the binding sites of porcine tissue-type plasminogen activator and plasminogen to heparin

To localize the binding region of porcine tissue-type plasminogen activator (EC 3.4.21.31) (t-plasminogen activator) to heparin, functionally active A and B chains (molecular mass of each 33 kDa) were separated from the two-chain t-plasminogen activator after mild reduction and alkylation. The A chain bound to fibrin-Sepharose, but not to heparin-Sepharose. In contrast, the B chain showed amidase activity toward HD-Ile-Pro-Arg-p-nitroanilide (S-2288) and a high affinity for heparin-Sepharose, but no affinity for fibrin-Sepharose. Plasminogen activator activity of the B chain was stimulated by heparin (about 3-fold), but not by fibrin. On the other hand, the elastase digestion fragments of plasminogen, kringle 1-3 and kringle 4, had no affinity for a heparin-Sepharose column, whereas the other fragment, Val442-plasminogen, efficiently bound to the column and was eluted with 1.6 M KSCN-containing buffer. The stimulatory effect of fibrin on two-chain t-plasminogen activator-catalyzed Val442-plasminogen activation was clearly diminished by heparin. These results suggest that heparin can form a complex with both t-plasminogen activator and plasminogen molecules through their catalytic regions located in each B chain, and that the heparin connection between t-plasminogen activator and plasminogen may improve the plasminogen activation kinetics by making a situation in which t-plasminogen activator is easily approachable to plasminogen.

Effect of adjuvant-induced arthritis on hepatic drug metabolism in rats

1. Hepatic drug metabolism was investigated in normal, adjuvant-induced arthritic (AA), indomethacin-treated AA and prednisolone-treated AA rats. The contents of P450 and b5 and the activities of NADH-b5 reductase (fp2), NADPH-ferrihaemoprotein reductase, P450 mixed function oxidase, FAD-monooxygenase and several enzymes involved in conjugation were remarkably lower in AA than in normal rats. 2. Many of the decreased enzyme activities were restored to normal levels by the continuous administration (3 weeks) of indomethacin or prednisolone, which improved the arthritic states of the animals. However, the restoration of FAD-monooxygenase activity by the administration of indomethacin or prednisolone was incomplete. The P450 and b5 contents and the fp2 activity in prednisolone-treated AA rats were also significantly lower than those in normal rats. 3. These findings indicate that the ability of the liver to metabolize drugs (both oxidation and conjugation) in AA rats is greatly decreased and that a long series of the treatment of AA rats with anti-inflammatory drugs is required to restore several enzyme activities.

Regulation of prolyl oligopeptidase activity in regenerating rat liver

We have previously shown that the naturally occurring polyamines, spermidine and spermine, reverse effectively the in vitro inhibition of prolyl oligopeptidase (POPase) by its endogenous inhibitor by forming a kinetically significant complex (Soeda et al., J. Neurochem. (1986) 46, 1304-1307). In this study, we examined changes in the activities of POPase and its endogenous inhibitor and in the concentrations of polyamines during the regeneration of rat liver. POPase activity in the liver cytosol peaked 2 days after partial hepatectomy and then decreased near to control activity by 9 days, without its altered synthetic levels. Total polyamine concentrations also peaked at 2 days and remained elevated by 9 days, while cytosolic POPase inhibitor activity was minimal (56% of control) at 2 days. Treatment of the animals with a synthetic POPase inhibitor, Z-Gly-Pro-CHN2 (4 mg/kg), resulted in an obvious suppression of the liver regeneration. These results imply that the activity of POPase involved in nonlysosomal proteolytic pathway is exquisitely regulated by changes not only in its endogenous inhibitor levels but also in intracellular cationic potentials such as polyamines, and that POPase plays a crucial role for the growth and differentiation of liver cell.

Effects of experimental diabetes on aminopyrine metabolism in rats

1. The metabolism of aminopyrine has been investigated in normal, alloxan- and streptozotocin (STZ)-diabetic rats. The drug was administered i.p. and the serum concentrations of the unchanged aminopyrine and its main metabolites were measured using h.p.l.c. 2. Aminopyrine was metabolized at a slower rate in both diabetic rats, as judged from higher serum levels of the unchanged drug. Pharmacokinetic studies of aminopyrine in diabetic rats also showed a decrease in serum clearance of the drug and an increase in its serum half-life. 3. The serum concentrations of the metabolites 4-monomethylaminoantipyrine, 4-acetylaminoantipyrine and 4-formylaminoantipyrine decreased in diabetic rats. In contrast, serum levels of 3-hydroxymethyl-2-methyl-4-dimethylamino-1-phenyl-3-pyrazolin-5-on e increased over control values. Serum concentrations of 4-aminoantipyrine remained unaltered by the induction of diabetes. 4. The magnitudes of changes in serum levels of these metabolites were larger in alloxan-diabetes than in STZ-diabetes. 5. Additional support for changed metabolism of aminopyrine was obtained from the investigation of microsomal preparations from diabetic and normal rats. 6. These findings indicate that it is important to use intact animals for evaluation of the metabolism of drugs in pathological states.

Some properties of tissue-type plasminogen activator reconstituted onto phospholipid and/or glycolipid vesicles.

Porcine heart tissue-type plasminogen activator (t-PA) was reconstituted onto large multilamellar liposomes with various lipid compositions and the kinetics of plasminogen activation by free or the reconstituted t-PA were studied. Negatively charged lipids, sulfatide and phosphatidylserine (PS), lowered the Km values of t-PA for plasminogen activation (sulfatide, 20-fold; PS, 6-fold), whereas neutral lipid phosphatidylcholine raised the Km. On the other hand, these lipid environments did not affect the amidase parameters and fibrin-binding potency of t-PA. The present results suggest that t-PA could function as a cell-associated form and its plasminogen activation may be regulated by the net charge of the head group of membrane lipids.