Pharmacodynamics of alacepril in healthy cats

Abstract

Objectives

The aims of this study were to investigate the pharmacodynamics of alacepril and to determine the appropriate dose for clinical usage in cats.

Methods

Six experimental cats were used. Each cat received alacepril orally at a single dose of 1 mg/kg, 2 mg/kg and 3 mg/kg. Blood samples were collected before administration and at 2, 4, 6, 8, 12, 24, 36, 48 and 72 h after administration to measure serum angiotensin converting enzyme (ACE) activity. Systolic blood pressure was also measured at the same time point.

Results

Dose-dependent inhibition of ACE activity was observed. Doses of 2 mg/kg and 3 mg/kg alacepril were considered to effectively inhibit ACE activity. There were no significant differences in systolic blood pressue among groups at any time point.

Conclusions and relevance

Alacepril 2–3 mg/kg q24h may be an appropriate dosage for clinical use in cats.

Introduction

Angiotensin converting enzyme (ACE) inhibitors are most commonly used in veterinary medicine for chronic cardiovascular and kidney disease. ¹ Activation of the circulating and cardiac renin–angiotensin–aldosterone systems (RAAS) has been shown in several cardiovascular diseases and kidney disease.^2–5 Sustained increase in angiotensin II concentrations causes vasoconstriction, aldosterone-induced sodium and water retention, and sympathetic activation. Its local effects on the myocardium include myocyte hypertrophy and fibrosis. ⁶ To prevent this vicious RAAS-mediated cycle of cardiac deterioration, ACE inhibitors are used as part of the medical management. Several studies have been reported regarding ACE inhibitors in cats; for example, enalapril, benazepril and ramipril have been shown to have beneficial effects on left ventricular hypertrophy, hypertrophic cardiomyopathy, congestive heart failure and chronic kidney disease.^7–12

Alacepril is a long-acting oral ACE inhibitor used in veterinary medicine. It is deacetylated to desacetylalacepril, and then converted to captopril. Desacetylalacepril is readily transferred to the vascular wall and also has a direct effect on sympathetic nerve activity, so that alacepril has a 1.5–2 times longer antihypertensive effect than captopril in rats. ¹³ A previous report indicated that left atrial pressure was decreased by alacepril in dogs with mitral valve regurgitation. ¹⁴ Also, alacepril was useful for hypertension, chronic kidney disease and congestive heart failure in human patients.^15–17 However, clinical application of alacepril in cats has not yet been reported.

The aims of this study were to investigate the pharmacodynamics of alacepril, especially the inhibitory rate of serum ACE activity and blood pressure, and to determine the appropriate dose for clinical usage.

Materials and methods

Animals

Six experimental cats (three males and three females), aged 12 months, weighing 2.66–3.77 kg, were used. They were housed individually in cages and fed dry food in the morning and afternoon. Water was freely available. Haematology and plasma biochemistry parameters were evaluated before and after the study. No abnormalities in blood work parameters were observed throughout the study.

The studies were performed after gaining approval from the ethical committee of Azabu University (authorisation number 1207151).

Study design

All cats received a single dose of alacepril orally (1 mg/kg, 2 mg/kg and 3 mg/kg) within 30 mins before feeding. Blood samples were collected before administration, and at 2, 4, 6, 8, 12, 24, 36, 48 and 72 h after administration, to measure serum ACE activity. Systolic blood pressure (SBP) was also measured at the same time point. This was a crossover study, with a washout period of 7 days between each dose. We confirmed that plasma ACE activity had returned to the pretreatment level 6 days after administration of the last dose.

Inhibition rate of serum ACE activity

Approximately 1.0 ml of blood was collected at each time point and placed into tubes without anticoagulant. The blood was centrifuged (1000 g, 10 mins) to obtain serum. We used an ACE assay kit, ACE Color (Fujirebio), to measure ACE activity. Plasma inhibition rate of ACE activity at each time point (t) was expressed as the percentage inhibition (%), using the pretreatment value as the baseline (t₀): % inhibition of ACE (Et) = ([ACE (t₀) – ACE (t)] × 100)/ACE (t₀).

Maximum inhibition of ACE activity (E_Max) and time to maximum inhibition of ACE (TE_Max) were compared among groups.

SBP

SBP was obtained non-invasively by Doppler sphygmomanometry (Hadeco). An inflatable cuff of appropriate size was placed on the tail. ¹⁸ The hair was clipped before placing the probe. The cuff was manually inflated until the pulse signal was no longer audible and then gradually deflated. Systolic pressure was determined when the Doppler signal was re-audible. Several consecutive measurements were performed at each time point. When a stable set of five measurements was obtained, mean values of five measurements were used for statistical analyses.

Statistical analysis

Statistical analyses were performed using computer software (SPSS Statistics version 21.0; IBM). Pretreatment plasma ACE activity, E_Max, E_24h and SBP among groups were visually inspected and tested for normality by the Kolmogorov–Smirnov test. Comparisons of pretreatment plasma ACE activity, E_Max and E_24h among groups were statistically analysed by one-way ANOVA. When a significant difference was detected, multiple comparisons were evaluated by use of Bonferroni correction. Changes of SBP were statistically assessed by repeated two-way ANOVA. A significant difference was defined as P <0.05.

Results

Inhibition of serum ACE activity

The mean inhibition rate of serum ACE activity is shown in Figure 1 and Table 1. Dose-dependent inhibition of ACE activity was observed. There were significant differences in E_24h between the 1 mg/kg and 2 mg/kg groups (P = 0.001), between the 1 mg/kg and 3 mg/kg groups (P = 0.002), and in E_Max between the 1 mg/kg and 2 mg/kg groups (P <0.001), and between the 1 mg/kg and 3 mg/kg groups (P <0.001). There was no significant difference between 2 mg/kg and 3 mg/kg groups in E_24h and E_Max. In the 2 mg/kg and 3 mg/kg groups, E_Max was >90%, and inhibition was sustained 24 h after the administration. In all groups, TE_Max was 2 h after administration, and plasma ACE activity had not returned to pretreatment levels, even at E_72h.

Figure 1

Time course of inhibition rate of serum ACE activity after single doses of alacepril (1, 2 and 3 mg/kg, n = 6) in cats. Values are expressed as means ± SEM

Table 1

Inhibition of serum angiotensin converting enzyme activity following single oral administration of alacepril to cats (n = 6 cats per dose group)

Parameter	Dose of alacepril
	1 mg/kg	2 mg/kg	3 mg/kg
EMax (%)	86.7 (83.5–90.6)	96.3 (95.0–97.7)	97.1 (93.6–99.2)
E12h (%)	21.7 (2.4–49.4)	55.1 (48.7–62.2)	52.4 (43.1–61.4)
E24h (%)	23.0 (13.0–33.2)	46.0 (27.5–54.3)	44.7 (38.2–52.5)
E72h (%)	13.6 (5.8–29.4)	15.3 (8.8–30.8)	20.4 (9.7–27.2)
TEMax (h)	2.0 (2.0)	2.0 (2.0)	2.0 (2.0)

Data are median (range)

E_Max = maximum inhibition of angiotensin converting enzyme (ACE) activity; E_12h = inhibition of ACE at 12 h; E_24h = inhibition of ACE at 24 h; E_72h = inhibition of ACE at 72 h; TE_Max = time to maximum inhibition of ACE

There were not significant differences in pretreatment plasma ACE activity among groups (P >0.05).

SBP

There were no significant differences in SBP among groups at any time point (P >0.05).

Discussion

ACE activity was almost completely inhibited 2 h after alacepril administration, and more than half of the inhibition rate had been sustained for 24 h in the 2 mg/kg and 3 mg/kg groups. In previous reports, the appropriate dosage of ACE inhibitor in cats was defined using the maximum inhibition rate of serum ACE activity and inhibition rate of 24 h after treatment.^5,19 In this study, 2 mg/kg and 3 mg/kg administration q24h of alacepril was considered to effectively inhibit ACE activity in cats. Therefore, a dosage of alacepril 2–3 mg/kg may be appropriate for healthy cats. However, the serum ACE inhibition rate at 24 h after administration was lower than that of previous reports;^19,20 thus, q12h administration may be recommended.

There were no significant differences in SBP, although the efficacy of ACE inhibitors in controlling blood pressure in hypertensive and kidney disease cats has previously been described.^1,5,12,21,22 As cats used in the present study were clinically healthy and normotensive, the effect on blood pressure could not be detected. Further study is needed to assess the effects on blood pressure in cats with several diseases.

Other ACE inhibitors such as benazepril and enalapril were reportedly known to have few side effects. ¹ There were no adverse effects observed in the present study.

There were several limitations in this study. First, the sample size was small. At least 22 cats in each group was suggested as a sample size on the basis of power analysis. Second, we addressed only selected parameters, which were ACE activity and SBP. Bioavailability and elimination routes were not assessed at this time. Second, only serum ACE activity was measured and we did not measure inhibition of enzyme activity at the tissue level. Activity of the enzyme at the tissue level is responsible for its physiological effect. The serum level of inhibition and tissue level inhibition may not be equal as differences in RAAS between plasma and tissues in cats were reported. ²³ Third, it was reported that a diurnal variation of blood pressure exists in healthy cats. ²⁴ This may affect our results. Fourth, healthy cats were used in this study. Therefore, it is not possible to predict with reliability the effect of renal impairment on the disposition and actions of alacepril. ⁵

Conclusions

Alacepril 2–3 mg/kg q24h may be an appropriate dosage for clinical usage in cats.