Chronic effects of SQ29,852, a new angiotensin converting enzyme (ACE) inhibitor with a phosphonic acid group, in experimental hypertensive rats

Gen. Pharmac. Vol. 24, No. 4, pp. 863-866, 1993 Printed in Great Britain. All rights reserved

0306-3623/93 $6.00 + 0.00 Copyright © 1993 Pergamon Press Ltd

CHRONIC EFFECTS OF SQ29,852, A NEW ANGIOTENSIN CONVERTING ENZYME (ACE) INHIBITOR WITH A PHOSPHONIC ACID GROUP, IN EXPERIMENTAL HYPERTENSIVE RATS KOICHIRO KISHI a n d MASATO IKEDA Department of Pharmacology, Jichi Medical School, Minamikawachi-machi, Tochigi-ken 329-04, Japan [Fax 81-285-44-5541]

(Received 22 January 1993.) Abstract--1. Chronic effects on blood pressure of SQ29,852 administered daily for 21 consecutive days were compared to those of captopril and enalapril in spontaneously hypertensive (SHR) and two-kidneyone-clip renal hypertensive (CLIP) rats. 2. SQ29,852 showed significant chronic anti-hypertensive effects at 30 mg/kg in SHR and at 10 mg/kg in CLIP rats. Chronic anti-hypertensive effects of SQ29,852 were in-between those of enalapril and captopril. 3. Significant anti-hypertensive effects lasted in enalapril-treated SHR for 7 days after discontinuation of treatment, while only a tendency toward persistence of anti-hypertensive effects was noted in all animals treated with SQ29,852 and captopril.

INTRODUCTION

afternoon using a rat tail manometer-tachometer system (KN-210; Natsume Seisakusho). Rats were pre-warmed in the rat holders [KN-325(B); Natsume Seisakusho] on the hot plate, surface temperature of 40°C for 30~0 min (Kubota et al., 1985). All drugs were dissolved in sterile distilled water and they were administered everyday in the morning by gavage at a volume of 5 ml/kg body weight. Sterile distilled water was administered to the solvent control group. Captopril and enalapril were used as reference drugs. Treatment was continued daily for 21 consecutive days. Effects of the discontinuation of treatment were evaluated for 7 subsequent days. Animals were assigned to one of the following groups:

SQ29,852 is a newly synthesized angiotensin converting enzyme ( A C E ) inhibitor of a new type containing a p h o s p h o n i c acid function as the zinc-binding moiety ( K a r a n e w s k y et al., 1988). The efficacy o f A C E i n h i b i t o r in hypertension is now firmly established by m a n y A C E inhibitors containing sulfhydryl moiety (captopril) or carboxyl group (enalapril). Like other A C E inhibitors, SQ29,852 is also expected to be effective as a n anti-hypertensive drug. It is also interesting to see how this drug's characteristics compare with those o f o t h e r A C E inhibitors ( O k a m o t o et al., 1991). It has been already reported t h a t SQ29,852 showed acute anti-hypertensive effects in spontaneously hypertensive (SHR) a n d two-kidney-oneclip renal hypertensive (CLIP) rats ( D e F o r r e s t et al., 1990). In the present study, we evaluated its characteristics a n d chronic anti-hypertensive effects in rats with experimental hypertension to c o m p a r e with those o f o t h e r A C E inhibitors.

Group Control SQ29,852 SQ29,852 Captopril Enalapril

Doses 3 mg/kg 30 mg/kg 30 mg/kg 30 mg/kg

Number of rats 10 I0 I0 I0 I0

3. Chronic effects in two-kidney-one-clip renal hypertensive rats (CLIP) The left renal artery was constricted with a silver ribbon (slit width: 0.2 mm) in female Donryu rats aged 9-10 weeks. The other kidney was left intact. Animals which had hypertension 10-11 weeks after surgery were used for experiments. Treatment was made daily for 21 consecutive days. Effects of discontinuation of the treatment were observed for subsequent 7 days. Other conditions were similar to those used in the experiments in SHR. Animals were assigned to one of the following groups:

MATERIALS AND METHODS 1. Test drugs SQ29,852, captopril and enalapril were used in this study. All drugs were dissolved in sterile distilled water and administered orally to the animals.

2. Chronic effects in spontaneously hypertensive rats (SHR) All experiments were carried out under SPF conditions (room temperature, 23°C; relative humidity, 50%; 12hr light,lark cycle) using male SHR at 10 weeks old. Sterile diet (Labo MR Stock; Nihon Nosan Kogyo) and sterile water were supplied ad libitum. Systolic blood pressure and heart rate were determined in unanesthetized animals in the 863

Group Control SQ29,852 SQ29,852 Captopril Enalapril

Doses 3 mg/kg 10 mg/kg 3 mg/kg 3 mg/kg

Number of rats 7 7 7 7 7

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Days Fig. I. Chronic effects on systolic blood pressure in SHR rats.

4. Statistics

SHR and of the discontinuation of administration are shown in Figs 1 and 2, respectively. Significant decreases in blood pressure occurred compared to the control in animals treated with 30 mg/kg of SQ29,852 and those given captopril and enalapril on the 3rd day of treatment. These effects lasted until the 21st day of treatment. Significant hypotension was also seen in animals given 3 mg/kg of SQ29,852 on and after the 17th day of treatment. Chronic anti-hypertensive effects of SQ29,852 were in-between those of

All data were shown as the means + SE. Differences in means between the treated and control groups were analyzed by Bonferroni's multiple comparison test after one-way layout variance analysis (Wallenstein et al., 1980). RESULTS

1. Chronic effects in S H R rats

Effects of daily administration of SQ29,852 on systolic blood pressure (caudal arterial pressure) in

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Days Fig. 2. Effects of the discontinuation of treatment on systolic blood pressure in SHR rats.

SQ29,852--an ACE inhibitor

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Days Fig. 3. Chronic effects of daily administration (21 days) and effects of the discontinuation of treatment (7 days) on systolic blood pressure in CLIP rats.

captopril and enalapril when compared at the same dose. After discontinuation of treatment, significant antihypertensive effects were maintained for 7 days in animals treated with enalapril, while anti-hypertensive effects showed a tendency to be maintained in other drug treated groups. As a whole, body weight or heart rate showed no significant change in any group during and after discontinuation of treatment. 2. Chronic effects in C L I P rats

Chronic effects of daily administration of SQ29,852 (21 consecutive days) on systolic blood pressure (caudal arterial pressure) and effects of discontinuation of the treatment (7 days) observed in CLIP rats are shown in Fig. 3. Blood pressure decreased significantly in animals treated with 10 mg/kg of SQ29,852 and those treated with enalapril starting the 7th day of treatment, with the effects lasting until the 21st day of treatment in the SQ29,852 group. Chronic antihypertensive effects of 10 mg/kg of SQ29,852 were comparable to those of 3 mg/kg of enalapril. After discontinuation of treatment, a tendency toward decreases in blood pressure was noted in the treated groups compared to the control, but differences between the treated and control groups were not significant and decreased gradually. Body weight or heart rate showed no significant change in any group during and after discontinuation of treatment.

DISCUSSION

In this study, SQ29,852 showed a significant chronic anti-hypertensive effect at 30 mg/kg in SHR and at 10 mg/kg in CLIP rats. This chronic effect of SQ29,852 in SHR seemed to be in-between those of enalapril and captoprii. In CLIP rats, the effect at 10 mg/kg of SQ29,852 were almost parallel with that of enalapril at 3 mg/kg. On the other hand, it was reported that repetitive dosing of SQ29,852 caused a chronic anti-hypertensive effect in conscious dogs and it was somewhat more marked than the same dose of enalapril (Ohara et al., 1992). However, the in vitro inhibiting activity of SQ29,852 is far less potent than that of enalapril on ACE of rabbit's lung and human kidney (Karanewsky et al., 1988; Hiwada et al., 1990). It can not be interpreted by the discrepancy of the potency between the inhibition of ACE activity in vitro and the anti-hypertensive effect in vivo, although generally the ACE activity inhibition is considered the major mechanism of anti-hypertensive effect of ACE inhibitots. Currently, it is believed that ACE-inhibition in certain tissues (e.g. blood vessels) plays an important role for the anti-hypertensive effects. Cushman et al. (1989) conducted a comparative study on the inhibitive effects of seven ACE inhibitors on tissue ACE activity and showed that the inhibitory efficacy of SQ29,852 was not so strong comparing with other ACE inhibitors. However, this result was obtained from the rats administered single dose of each ACE

866

KOICHIROKISHI and MASATOIKEDA

inhibitor, therefore, it might change by the difference of the affinity in each ACE inhibitors when given multiple doses. It was also reported in a dog study that AI/AII value raised after single administration of either SQ29,852 or enalapril, nevertheless, the repetitive administration of SQ29,852 had no effect on AI/AII value but enalapril raised it in contrast (Ohara et al., 1992). This finding suggested that the negative feedback reaction might differ in multiple dosing of ACE inhibitors and this difference may affect the anti-hypertensive potency of each ACE inhibitors. In conclusion, the difference of efficacy of ACE inhibitors between the inhibition of ACE in vitro and anti-hypertensive effect in vivo remain unexplained. However, the results of the present animal studies suggest that SQ29,852 is anticipated to show a long lasting antihypertensive effects also in human.

REFERENCES

Cushman D. W., Wang F. L., Fung W. C., Harvey C. M. and DeForrest J. M. (1989) Differentiation of angiotensin-converting enzyme (ACE) inhibitors by their selective inhibition of ACE in physiologically important target organs. AJH 2, 294-306. DeForrest J. M., Waldron T. L., Harvey C. and Scalese R. (1990) Ceranapril (SQ29,852), an orally active inhibitor of

angiotensin converting enzyme (ACE). J. Cardiovasc. Pharmac. 16, 121-127. Hiwada K., Inoue Y. and Kokubu T. (1990) Effect of SQ29,852, a new angiotensin converting enzyme (ACE) inhibitor with a phosphonic acid group, on the activity of angiotensin converting enzyme from human kidney. Gen. Pharmac. 21, 555-558. Karanewsky D. S., Badia M. C., Cushman D. W., DeForrest J. M., Dejneka T., Loots M. J., Perri M. G., Petrillo E. W. Jr and Powell J. R. (1988) (Phosphinyloxy) acyl amino acid inhibitors of angiotensin converting enzyme (ACE). 1. Discovery of (S)- 1-[6amino-2[[hydroxy (4-phenyl-butyl) phosphinyl]-l-oxohexyl]-Lproline, a novel orally active inhibitor of ACE. J. Med. Chem. 31, 204-212. Kubota N., Kishi K., Sokabe H., Kawashima K., Ishii Y. and Kawase S. (1985) Chronic effects ofa fl-adrenoceptor blocking drug, 4-[3-(tert-butylamino)-2-hydroxypropoxy]-N-methylisocarbostyril hydrochloride (N-696), in hypertensive rats. J. Pharmacobio-Dyn. 8, 134-141. Ohara N., Takizawa M., Yokota S., Ogawa N. and Katumura H. (1992) Hypotensive effect of a phosphorus-converting novel angiotensin converting enzyme inhibitor, (s)-l-[6-amino-2[[hydroxy(4-phenylbutyl)phosphinyl]oxy]- 1-oxohexyl]-L-proline (SQ29,852) in conscious hypertensive dogs. J. Pharmacobio-Dyn. 15, 267-276. Okamoto K., Ohta Y., Chikugo T., Shiokawa H. and Morita N. (1991) Chronic treatment with captopril, SQ29,852, Hydralazine and 33% fish meal diet in malignant stroke-prone spontaneously hypertensive rats. J. Hypertension 9, 1105-1117. Wallenstein S., Zucker C. L. and Fleiss J. L. (1980) Some statistical methods useful in circulation research. Circ. Res. 47, 1-9.