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Vascular Affinity of Trandolapril
AJH 1995; 8:635-675
TRANDOLAPRIL
Vascular Affinity of Trandolapril Mizuo Miyazaki, Tatsuhiko Kawamoto, and Hideki Okunishi
This article discusses the pharmacologic basis on which trandolapril exhibits a more potent and longer-lasting antihypertensive effect than its chemical prototype enalapril. Our studies have shown that 1) trandolapril and its active metabolite trandolaprilat are more lipophilic than enalapril and its active diacid enalaprilat; 2) trandolaprilat is three times more potent than enalaprilat in vitro; and 3) trandolapril is 10 times more effective and longer-acting than enalapril in lowering the blood pressure of spontaneously hypertensive rats. The long duration of action of trandolapril can be attributed to its long-lasting inhibition of the vascular tissue angiotensin converting enzyme (ACE). The long action onto the vascular tissue ACE may be due to the high lipophilicity of trandolapril
which may increase its tissue penetration and its elimination half-life from the tissue, and the unique nature of the vascular tissue which, unlike the other tissues, does not respond to trandolapril with the induction of de novo ACE that may counteract the ACE inhibition. These data imply that trandolapril is a potent ACE inhibitor with distinctively long action, which might be a result of its vascular tissue affinity and the lack of any ACE inducing ability of the vascular tissue. Am J Hypertens 1995;8:635-675 Angiotensin converting enzyme, blood vessels, lipophilicity, prolonged action, enzyme induction.
KEY WORDS:
F
ollowing the first clinical success of captopril1,2 as an orally active angiotensin converting enzyme (ACE) inhibitor, a panel of ACE inhibitors of different chemical classes have been developed. Those classes are the sulfhydrylcontaining drugs (eg, captopril and its analogs), the carboxyalkyldipeptides (eg, enalapril and its analogs) and the phosphorus-containing drugs (eg, fosinopril and its analogs).3 Although these ACE inhibitors share a common mode of action with the antihypertensives, yet they differ with each other in their pharmacokinetic properties, which may influence their oral bioavailability, tissue distribution, route and mode of excretion, and duration of action.3-5 According to previous studies by US6 •7 and others3.5,8-10 ex-
amining a number of ACE inhibitors, trandolapril (RU 44 570) appears to be the most potent and longacting. In particular, trandolapril is characteristic in its distinctively long-lasting action. 7 This article focuses on the pharmacological basis for the prolonged antihypertensive action of trandolapril as compared with its chemical prototype enalapril (MK 421), which has been to date known as a longer-acting agent than captopril. 5 Trandolapril is a prodrug-type ACE inhibitor that is biotransformed to the active diacid, trandolaprilat (RU 44 403)11 by esterase located mainly in the gastrointestinal mucosa and the liver. 12.13 This is similar to enalapril, which is deesterified to enalaprilat (MK 422). Trandolapril shares a common chemical structure with enalapril, except that trandolapril has a more lipophilic substitution (indolinecarboxylic acid) for prolyl moiety in enalapril, as is shown in Figure l. From the Department of Pharmacology, Osaka Medical College, It is conceivable that this lipophilic substitution may Takatsuki, Japan. provide trandolapril with its longer action, higher afAddress correspondence and reprint requests to Mizuo Miyazaki, MD, PhD, Department of Pharmacology, Osaka Medical finity to the ACE molecule, and higher tissueCollege, 2-7 Daigakumachi, Takatsuki 569, Japan. penetrating ability than enalapril. In this article, we C 1995 by the American Journal of Hypertension, Ltd.
0895-7061/95/$9.50
64S
MIYAZAKI ET AL
A/H-OCTOBER 1995-VOL. 8, NO. 10, PART 2
than enalaprilat. In fact, our finding that trandolapril produces brain ACE inhibition after repeated dosing, whereas enalapril does not, is a fine example demonstrating the correspondence of the lipo~hilicity of a drug to its tissue-distributing capability. The lack of brain ACE inhibition after oral enalapril treatment also has been reported by other investigators. 10 Trandolapril
IN VITRO POTENCY FOR ACE INHIBITION
Enalaprll
Trandolapril, trandolaprilat, enalapril, and enalaprilat were examined for their ACE inhibitory potency using a kinetic enzyme system 14 consisting of a synwill discuss the relationship between the high li- thetic substrate BzGly-His-Leu and purified ACE pophilicity of trandolapril and its long duration of from rabbit lung; this latter was essentially free from action in vivo. We also refer to its unique nature in esterase activity.7 Table 2 shows the K; values for relation to vascular tissue, which potentially favors these compounds, indicating that trandolaprilat is trandolapril's prolonged vascular tissue-selective three times more potent than enalaprilat. Another example indicating that the incorporation of a lipophilic action. moiety into the prolyl residue may result in an inLIPOPHILICITY OF TRANDOLAPRIL, crease in ACE-inhibiting potency is the incorporation ENALAPRIL, AND THEIR DIACIDS of a hydroxyphenyl group in rentiapril (SA 446),3,15,16 which improves the affinity of rentiapril to ACE to Table 1 summarizes the relative lipophilicity of tranthree times that of captopril. 3 Table 2 also indicates dolapril, enalapril, and their respective diacid forms, trandolaprilat and enalaprilat. Partition between the that trandolapril per se is a weak ACE inhibitor, but octanol and water phases of the respective com- once activated to trandolaprilat it has a very high afpounds was examined, as this measure is one of the finity for ACE. Its affinity for ACE is increased 2200important factors in determining tissue distribution. 3 fold. On the other hand, the affinity of enalapril to The concentration of the compounds in each phase ACE is increased by only SOD-fold after its conversion after vigorous mixing and a sufficient period for to enalaprilat. These data, together with those of liequilibration was determined by high-performance pophilicity, indicate that trandolapril could be effecliquid chromatography.7 The results indicate that tively absorbed by oral administration, as a prodrug, trandolapril is three times more lipophilic than enal- which is an only weak inhibitor, and then be bioacapril and trandolaprilat is four times more lipophilic tivated 2200-fold to trandolaprilat, which then would than enalaprilat. Trandolaprilat, although it is a di- readily distribute throughout the body, since this dicarboxylic acid, is highly lipophilic, showing half the acid is also highly lipophilic as denoted above. lipophilicity as its parent prodrug, and being one and PROLONGED ANTIHYPERTENSIVE EFFECT a half times more lipophilic than enalapril. On the OF TRANDOLAPRIL other hand, enalaprilat is eight times less lipophilic than trandolapril. These properties may be reflected Response to a Single Oral Dosing When orally adin the bioavailability upon oral dosing and tissue pen- ministered to male spontaneously hypertensive rats etration of the respective drugs. Trandolapril may be (SHR), 1 mglkg trandolapril and 10 mglkg enalapril readily absorbed from the gastrointestinal tract, and its biotransformed diacid trandolaprilat may distrib- TABLE 2. K VALUES FOR THE ACE INHIBITORS ON i ute to various tissues to a substantially higher extent PURIFIED RABBIT LUNG ACE FIGURE 1. Chemical structures of trandolapril and enalapril. Reproduced with permission from Okunishi et al. 7
ACE Inhibitor
TABLE 1. RELATIVE LIPID SOLUBILITY OF ACE INHIBITORS ACE Inhibitor Trandolapril Enalapril Trandolaprilat Enalaprilat
'70 Partition in Octanol 59.7'70 19.6'70 30.3'70 7.9'70
Prodrugs
Ratio" 7.6
2.5
3.8 1.0
-Lipophilicity relative to enalaprilat. Reproduced with permission from Okunishi et aU
Trandolapril Enalapril Active diacids Trandolaprilat Enalaprilat
7.07 ± 1.92 IlmoUL 4.89 ± 1.77 Il moUL 3.20 ± 1.18 nmaUL 9.73 ± 1.90 nmaUL
Bz Gly-His-Leu substrate used at 5 and 10 mmoliL to determine inhibition constant (K,). Values are mean ± SEM from three to five independent experiments. Data adapted from Okunishi et aU
VASCULAR AFFINITY OF TRANDOLAPRIL 65S
AJH-OCTOBER 1995-VOL. 8, NO. 10, PART 2
elicited similar hypotensive effects that lasted for more than 24 h, the results being consistent with those of Chevillard et al. 17 The duration of action, however, tended to be longer with trandolapril than enalapriI. 7 The plasma ACE activity was substantially suppressed in trandolapriI-treated SHRs 24 h after the dosing, while that of enalapril-treated rats was only minimally inhibited. This indicates the slower elimination rate for trandolapril as compared with enalapril. As stated above, the dose of trandolapril required to yield the similar antihypertensive effect is only one-tenth that of enalapril. Thus, there is some dissociation of in vivo potency ratio of trandolaprill enalapril (lOx) from that of trandolaprilatlenalaprilat in vitro (3 x ). The combination of three-fold higher affinity to ACE molecules and three- to four-fold higher lipophilicity, which may yield higher tissue penetration and the increase in elimination half-life, of trandolapril compared to enalapriI would explain the approximately ten-fold increase in the ACE inhibitory effect in vivo. Prolonged Antihypertensive Effect of Trandolapril During the Washout Phase From Repeated Dosing As depicted in Figure 2, during the 2-week period of once-daily treatment with 1 mg/kg trandolapril or 10 mglkg enalapril, the blood pressure of SHRs remained lowered to a similar extent with no statistical difference between the two groups. But the antihypertensive effect of trandolapril in SHRs continued for more than a week after the discontinuation of its repeated doses, while the hypotensive effect rapidly disappeared after the withdrawal from enalapril treatment. Further, during the washout period from
-Ol +10
trandolapril treatment, the ACE activity of the plasma, lung, heart, kidney, and brain rapidly escaped from inhibition (Figure 3). On the contrary, vascular ACE was still inhibited for more than a week. During the washout period of enalapril, the ACE activity of plasma or any tissue including blood vessels was rapidly restored toward the normal level. Thus, the changes in blood pressure paralleled concurrently the changes in vascular ACE activity for both trandolapril- and enalapril-treated SHRs, as is evident from Figure 3. This may imply that vascular tissue is the primary site in which the local ACE inhibition determines the duration and extent of antihypertensive action of ACE inhibitors. TISSULAR FACTOR THAT INFLUENCES THE PROLONGED ACE INHIBITION As mentioned above, vascular tissue is the last to recover its ACE activity from the inhibition by trandolapril. Then, what makes the difference between blood vessels and other tissues? Possible explanations are: 1) trandolapril may be more affinitive to vascular ACE than the ACE of other tissues, yielding the tight-bound complex of vascular ACE and the inhibitor; 2) trandolapril may distribute to vascular tissues more readily than other tissues; 3) trandolapril may be biodegraded by or eliminated from the vascular tissue at a slower rate; and 4) vascular tissue may be the least capable to induce de novo ACE, which might counteract the drug effect, in response to trandolapril. However, to date it is known that there is only a
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Changes in the systolic blood pressure (SBP) of spontaneously hypertensive rats (SHR) during daily dosing of the ACE inhibitors and after withdrawal from the drug treatment. Values are given as mean ± SEM. Open circles, 10 mg/kg enalapril; Solid circles, 1 mg/kg trandolapri/; Pre, pretreatment period; NS, not significantly different; "P < .05, ....p < .01 v vehicle treated SHRs. Data adapted from Okunishi et al. 7 FIGURE 2.
50
FIGURE 3. Changes in the systolic blood pressure (SBP) and ACE activities of spontaneously hypertensive rats (SHR) 1 day and 7 days after withdrawal from the repeated dosing of trandolapril and enalapril. t.S.B.P.: difference of systolic blood pressure from the mean values of vehicle-treated SHRs. ACE activities of the vehicle group are defined as 100%. "P < .05 v vehicle-treated SHRs. *P < .05 significantly different between the two groups indicated. ns: no significant difference.
66S MIYAZAKI ET AL
A]H-OCTOBER 1995-VOL. 8, NO. 10, PART 2
single gene that encodes ACE, and that all the organs there was only a minimal increase in the brain. In or tissues, except testes, have a single phenotyEe of contrast, no increase at all was seen in the vascular ACE protein with no isoform being present, 8 al- tissue. This unique nature of vascular tissue might at though differential glycosylation of ACE molecule least in part contribute to the prolonged action of may occur in different tissues. 19 Thus, it would be trandolapril preferentially onto vascular ACE. On the unlikely that an ACE inhibitor would exhibit different other hand, de novo ACE induction in other tissues affinity toward ACE in different tissues. In support may be a factor that counteracts the ACE inhibition of our assumption, a report of saturation and dis- and thus accelerates the recovery from ACE inhibiplacement studies using radiolabelled trandolaprilat tion. Although the vascular tissue did not respond to showed the similarity of ACE labeling throughout the ACE inhibitors with de novo ACE induction in our in vivo study, vascular endothelial cells in culture were body in rats. 20 The second and third possibilities might not be reportedly able to induce ACE mRNA in response to ruled out. A whole body autoradiographical study in ACE inhibition. 21 Thus, it remains to be clarified rats has shown no detectable accumulation of tran- what makes this difference between in vivo and in dolapril or trandolaprilat in the vascular tissues 48 h vitro results, and what mechanism is operating to after an oral dosing of 14C-trandolapril while there is suppress the ACE induction in the vasculature in some accumulation in the lungs (Data on file, Rous- vivo. sel-Uela£). However, the detection sensitivity might CONCLUSION not be sufficiently high, because the ACE activity measurement demonstrated the high degree of inhiTrandolapril exerts its antihypertensive action for a bition not only in the lung, but also in other tissues distinctively longer time than its chemical prototype 7 ineluding the aorta. Further studies are needed to enalapril. This is presumably due to the high lidetermine whether or not trandolapril and trandolapophilicity of trandolapril and trandolaprilat, as the prilat selectively distribute to the vascular walls, and lipophilicity may increase the vascular tissue distriwhether or not trandolapril and trandolaprilat are bution of the drug and the elimination half-life of the more slowly eliminated from the vascular tissues drug from vascular tissue. In addition to this advanthan from other tissues. tageous feature of trandolapril, vascular tissue inWe examined various tissues for their capacity to duces little de novo ACE that may counteract the induce de novo ACE during the washout period from drug effect in response to ACE inhibitors. These trandolapril treatment (unpublished data). The repharmacokinetic properties of trandolapril together sults, as illustrated in Figure 4, indicated that the total with the unique nature of the vascular tissue may be ACE activity was increased by -150% in the plasma incorporated to influence the prolonged vascular acand by -50% in the lung, heart, and kidney, while tion of trandolapril.
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Ondetti MA, Rubin B, Cushman DW: Design of specific inhibitors of angiotensin-converting enzyme: a new class of orally active antihypertensive agents. Science 1977;196:441-444. 2. Gavras H, Brunner HR, Turini GA, et al: Antihypertensive effect of the oral angiotensin converting enzyme-inhibitor SQ 14225 in man. N Engl J Med 1978; 298:991-995. 3. Ondetti MA: Structural relationships of angiotensin converting enzyme inhibitors to pharmacologic activity. Circulation 1988;77(suppl 1):1-74-1-78. 4. ACE inhibitors and tissue binding (editorial). Lancet 1.
Aorta ns
REFERENCES
1990;336:71S-nO.
5. Kelly JG, O'Malley K: Clinical pharmacokinetics of the newer ACE inhibitors. Clin Pharmacokinet 1990;19: 177-196.
VASCULAR AFFINITY OF TRANDOLAPRIL 675
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6. Okunishi H, Kawamoto T, Kurobe Y, et al: Pathogenetic role of vascular angiotensin-converting enzyme in the spontaneously hypertensive rat. Clin Exp Pharmacol PhysioI1991;18:649-659. 7. Okunishi H, Kawamoto T, Kobayashi T, et al: Prolonged and tissue-selective inhibition of vascular angiotensin-converting enzyme by trandolapril: relevance to its antihypertensive action in spontaneously hypertensive rats. Pharm Pharmacol Lett 1992;2:180183. 8. Unger T, Ganten 0, Lang RE, Scholkens BA: Is tissue converting enzyme inhibition a determinant of the antihypertensive efficacy of converting enzyme inhibitors? Studies with the two different compounds, Hoe498 and MK421, in spontaneously hypertensive rats. J Cardiovasc PharmacoI1984;6:872-880. 9. Unger T, Gohlke P, Gruber M-G: Converting enzyme inhibitors, in Ganten 0, Mulrow PJ (eds): Handbook of Experimental Pharmacology, Vol. 93, Pharmacology of Antihypertensive Therapeutics. Springer-Verlag, Berlin, 1990 pp 377-481. ML, Kurz KD: Angiotensin converting enzyme Cohen 10. inhibition in tissues from spontaneously hypertensive rats after treatment with captopril or MK421. J Pharmacol Exp Ther 1982;220:63-69. Brown NL, Badel M-Y, Benzoni F, et al: Angiotensin11. converting enzyme inhibition, antihypertensive activity and hemodynamic profile of trandolapril (RU 44570). Eur J PharmacoI1988;148:79-91. 12. Herman AG: Differences in structure of angiotensinconverting enzyme inhibitors might predict differences in action. Am J Cardiol 1992;70:102C-108C. 13. Vertes V, Haynie R: Comparative pharmacokinetics of
14. 15. 16.
17.
18.
19. 20.
21.
captopril, enalapril, and quinapril. Am J Cardiol1992; 69:8C-16C. Miyazaki M, Okunishi H, Nishimura K, Toda N: Vascular angiotensin converting enzyme in man and other species. Clin Sci 1984;66:39-45. Okunishi H, Miyazaki M, Toda N: Evidence for a putatively new angiotensin II-generating enzyme in the vascular wall. J Hypertens 1984;2:277-284. Iso T, Yamauchi H, Suda H, et al: A new potent inhibitor of converting enzyme: (2RAR)-2-(2-hydroxyphenyl)-3-(3-mercaptopropionyl)-4-thiazolidinecarboxylic acid (SA446). Jpn J PharmacoI1981;31:875-882. Chevillard C, Brown NL, Mathieu M-N, et al: Differential effects of oral trandolapril and enalapril on rat tissue angiotensin-converting enzyme. Eur J Pharmacol 1988;147:23-28. Hubert C, Houot A-M, Corvol P, Soubrier F: Structure of the angiotensin I-converting enzyme gene. Two alternate promoters correspond to evolutionary steps of a duplicated gene. J Bioi Chern 1991;266:1537715383. Soffer RL, Berg T, Sulner J, Lai CY: Pulmonary and testicular angiotensin converting isoenzymes. Clin Exp Hypertens [A] 1987;A9:229-234. Bardelay C, Mach E, Worcel M, Hunt P: Angiotensinconverting enzyme in rat brain and extraneural tissues visualized by quantitative autoradiography using 3H_ trandolaprilate. J Cardiovasc Pharmacol 1989;14:511518. King SJ, Oparil 5: Converting-enzyme inhibitors increase converting-enzyme mRNA and activity in endothelial cells. Am J Physiol 1992;263:C743-C749.
TRANDOLAPRIL
Vascular Affinity of Trandolapril Mizuo Miyazaki, Tatsuhiko Kawamoto, and Hideki Okunishi
This article discusses the pharmacologic basis on which trandolapril exhibits a more potent and longer-lasting antihypertensive effect than its chemical prototype enalapril. Our studies have shown that 1) trandolapril and its active metabolite trandolaprilat are more lipophilic than enalapril and its active diacid enalaprilat; 2) trandolaprilat is three times more potent than enalaprilat in vitro; and 3) trandolapril is 10 times more effective and longer-acting than enalapril in lowering the blood pressure of spontaneously hypertensive rats. The long duration of action of trandolapril can be attributed to its long-lasting inhibition of the vascular tissue angiotensin converting enzyme (ACE). The long action onto the vascular tissue ACE may be due to the high lipophilicity of trandolapril
which may increase its tissue penetration and its elimination half-life from the tissue, and the unique nature of the vascular tissue which, unlike the other tissues, does not respond to trandolapril with the induction of de novo ACE that may counteract the ACE inhibition. These data imply that trandolapril is a potent ACE inhibitor with distinctively long action, which might be a result of its vascular tissue affinity and the lack of any ACE inducing ability of the vascular tissue. Am J Hypertens 1995;8:635-675 Angiotensin converting enzyme, blood vessels, lipophilicity, prolonged action, enzyme induction.
KEY WORDS:
F
ollowing the first clinical success of captopril1,2 as an orally active angiotensin converting enzyme (ACE) inhibitor, a panel of ACE inhibitors of different chemical classes have been developed. Those classes are the sulfhydrylcontaining drugs (eg, captopril and its analogs), the carboxyalkyldipeptides (eg, enalapril and its analogs) and the phosphorus-containing drugs (eg, fosinopril and its analogs).3 Although these ACE inhibitors share a common mode of action with the antihypertensives, yet they differ with each other in their pharmacokinetic properties, which may influence their oral bioavailability, tissue distribution, route and mode of excretion, and duration of action.3-5 According to previous studies by US6 •7 and others3.5,8-10 ex-
amining a number of ACE inhibitors, trandolapril (RU 44 570) appears to be the most potent and longacting. In particular, trandolapril is characteristic in its distinctively long-lasting action. 7 This article focuses on the pharmacological basis for the prolonged antihypertensive action of trandolapril as compared with its chemical prototype enalapril (MK 421), which has been to date known as a longer-acting agent than captopril. 5 Trandolapril is a prodrug-type ACE inhibitor that is biotransformed to the active diacid, trandolaprilat (RU 44 403)11 by esterase located mainly in the gastrointestinal mucosa and the liver. 12.13 This is similar to enalapril, which is deesterified to enalaprilat (MK 422). Trandolapril shares a common chemical structure with enalapril, except that trandolapril has a more lipophilic substitution (indolinecarboxylic acid) for prolyl moiety in enalapril, as is shown in Figure l. From the Department of Pharmacology, Osaka Medical College, It is conceivable that this lipophilic substitution may Takatsuki, Japan. provide trandolapril with its longer action, higher afAddress correspondence and reprint requests to Mizuo Miyazaki, MD, PhD, Department of Pharmacology, Osaka Medical finity to the ACE molecule, and higher tissueCollege, 2-7 Daigakumachi, Takatsuki 569, Japan. penetrating ability than enalapril. In this article, we C 1995 by the American Journal of Hypertension, Ltd.
0895-7061/95/$9.50
64S
MIYAZAKI ET AL
A/H-OCTOBER 1995-VOL. 8, NO. 10, PART 2
than enalaprilat. In fact, our finding that trandolapril produces brain ACE inhibition after repeated dosing, whereas enalapril does not, is a fine example demonstrating the correspondence of the lipo~hilicity of a drug to its tissue-distributing capability. The lack of brain ACE inhibition after oral enalapril treatment also has been reported by other investigators. 10 Trandolapril
IN VITRO POTENCY FOR ACE INHIBITION
Enalaprll
Trandolapril, trandolaprilat, enalapril, and enalaprilat were examined for their ACE inhibitory potency using a kinetic enzyme system 14 consisting of a synwill discuss the relationship between the high li- thetic substrate BzGly-His-Leu and purified ACE pophilicity of trandolapril and its long duration of from rabbit lung; this latter was essentially free from action in vivo. We also refer to its unique nature in esterase activity.7 Table 2 shows the K; values for relation to vascular tissue, which potentially favors these compounds, indicating that trandolaprilat is trandolapril's prolonged vascular tissue-selective three times more potent than enalaprilat. Another example indicating that the incorporation of a lipophilic action. moiety into the prolyl residue may result in an inLIPOPHILICITY OF TRANDOLAPRIL, crease in ACE-inhibiting potency is the incorporation ENALAPRIL, AND THEIR DIACIDS of a hydroxyphenyl group in rentiapril (SA 446),3,15,16 which improves the affinity of rentiapril to ACE to Table 1 summarizes the relative lipophilicity of tranthree times that of captopril. 3 Table 2 also indicates dolapril, enalapril, and their respective diacid forms, trandolaprilat and enalaprilat. Partition between the that trandolapril per se is a weak ACE inhibitor, but octanol and water phases of the respective com- once activated to trandolaprilat it has a very high afpounds was examined, as this measure is one of the finity for ACE. Its affinity for ACE is increased 2200important factors in determining tissue distribution. 3 fold. On the other hand, the affinity of enalapril to The concentration of the compounds in each phase ACE is increased by only SOD-fold after its conversion after vigorous mixing and a sufficient period for to enalaprilat. These data, together with those of liequilibration was determined by high-performance pophilicity, indicate that trandolapril could be effecliquid chromatography.7 The results indicate that tively absorbed by oral administration, as a prodrug, trandolapril is three times more lipophilic than enal- which is an only weak inhibitor, and then be bioacapril and trandolaprilat is four times more lipophilic tivated 2200-fold to trandolaprilat, which then would than enalaprilat. Trandolaprilat, although it is a di- readily distribute throughout the body, since this dicarboxylic acid, is highly lipophilic, showing half the acid is also highly lipophilic as denoted above. lipophilicity as its parent prodrug, and being one and PROLONGED ANTIHYPERTENSIVE EFFECT a half times more lipophilic than enalapril. On the OF TRANDOLAPRIL other hand, enalaprilat is eight times less lipophilic than trandolapril. These properties may be reflected Response to a Single Oral Dosing When orally adin the bioavailability upon oral dosing and tissue pen- ministered to male spontaneously hypertensive rats etration of the respective drugs. Trandolapril may be (SHR), 1 mglkg trandolapril and 10 mglkg enalapril readily absorbed from the gastrointestinal tract, and its biotransformed diacid trandolaprilat may distrib- TABLE 2. K VALUES FOR THE ACE INHIBITORS ON i ute to various tissues to a substantially higher extent PURIFIED RABBIT LUNG ACE FIGURE 1. Chemical structures of trandolapril and enalapril. Reproduced with permission from Okunishi et al. 7
ACE Inhibitor
TABLE 1. RELATIVE LIPID SOLUBILITY OF ACE INHIBITORS ACE Inhibitor Trandolapril Enalapril Trandolaprilat Enalaprilat
'70 Partition in Octanol 59.7'70 19.6'70 30.3'70 7.9'70
Prodrugs
Ratio" 7.6
2.5
3.8 1.0
-Lipophilicity relative to enalaprilat. Reproduced with permission from Okunishi et aU
Trandolapril Enalapril Active diacids Trandolaprilat Enalaprilat
7.07 ± 1.92 IlmoUL 4.89 ± 1.77 Il moUL 3.20 ± 1.18 nmaUL 9.73 ± 1.90 nmaUL
Bz Gly-His-Leu substrate used at 5 and 10 mmoliL to determine inhibition constant (K,). Values are mean ± SEM from three to five independent experiments. Data adapted from Okunishi et aU
VASCULAR AFFINITY OF TRANDOLAPRIL 65S
AJH-OCTOBER 1995-VOL. 8, NO. 10, PART 2
elicited similar hypotensive effects that lasted for more than 24 h, the results being consistent with those of Chevillard et al. 17 The duration of action, however, tended to be longer with trandolapril than enalapriI. 7 The plasma ACE activity was substantially suppressed in trandolapriI-treated SHRs 24 h after the dosing, while that of enalapril-treated rats was only minimally inhibited. This indicates the slower elimination rate for trandolapril as compared with enalapril. As stated above, the dose of trandolapril required to yield the similar antihypertensive effect is only one-tenth that of enalapril. Thus, there is some dissociation of in vivo potency ratio of trandolaprill enalapril (lOx) from that of trandolaprilatlenalaprilat in vitro (3 x ). The combination of three-fold higher affinity to ACE molecules and three- to four-fold higher lipophilicity, which may yield higher tissue penetration and the increase in elimination half-life, of trandolapril compared to enalapriI would explain the approximately ten-fold increase in the ACE inhibitory effect in vivo. Prolonged Antihypertensive Effect of Trandolapril During the Washout Phase From Repeated Dosing As depicted in Figure 2, during the 2-week period of once-daily treatment with 1 mg/kg trandolapril or 10 mglkg enalapril, the blood pressure of SHRs remained lowered to a similar extent with no statistical difference between the two groups. But the antihypertensive effect of trandolapril in SHRs continued for more than a week after the discontinuation of its repeated doses, while the hypotensive effect rapidly disappeared after the withdrawal from enalapril treatment. Further, during the washout period from
-Ol +10
trandolapril treatment, the ACE activity of the plasma, lung, heart, kidney, and brain rapidly escaped from inhibition (Figure 3). On the contrary, vascular ACE was still inhibited for more than a week. During the washout period of enalapril, the ACE activity of plasma or any tissue including blood vessels was rapidly restored toward the normal level. Thus, the changes in blood pressure paralleled concurrently the changes in vascular ACE activity for both trandolapril- and enalapril-treated SHRs, as is evident from Figure 3. This may imply that vascular tissue is the primary site in which the local ACE inhibition determines the duration and extent of antihypertensive action of ACE inhibitors. TISSULAR FACTOR THAT INFLUENCES THE PROLONGED ACE INHIBITION As mentioned above, vascular tissue is the last to recover its ACE activity from the inhibition by trandolapril. Then, what makes the difference between blood vessels and other tissues? Possible explanations are: 1) trandolapril may be more affinitive to vascular ACE than the ACE of other tissues, yielding the tight-bound complex of vascular ACE and the inhibitor; 2) trandolapril may distribute to vascular tissues more readily than other tissues; 3) trandolapril may be biodegraded by or eliminated from the vascular tissue at a slower rate; and 4) vascular tissue may be the least capable to induce de novo ACE, which might counteract the drug effect, in response to trandolapril. However, to date it is known that there is only a
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Changes in the systolic blood pressure (SBP) of spontaneously hypertensive rats (SHR) during daily dosing of the ACE inhibitors and after withdrawal from the drug treatment. Values are given as mean ± SEM. Open circles, 10 mg/kg enalapril; Solid circles, 1 mg/kg trandolapri/; Pre, pretreatment period; NS, not significantly different; "P < .05, ....p < .01 v vehicle treated SHRs. Data adapted from Okunishi et al. 7 FIGURE 2.
50
FIGURE 3. Changes in the systolic blood pressure (SBP) and ACE activities of spontaneously hypertensive rats (SHR) 1 day and 7 days after withdrawal from the repeated dosing of trandolapril and enalapril. t.S.B.P.: difference of systolic blood pressure from the mean values of vehicle-treated SHRs. ACE activities of the vehicle group are defined as 100%. "P < .05 v vehicle-treated SHRs. *P < .05 significantly different between the two groups indicated. ns: no significant difference.
66S MIYAZAKI ET AL
A]H-OCTOBER 1995-VOL. 8, NO. 10, PART 2
single gene that encodes ACE, and that all the organs there was only a minimal increase in the brain. In or tissues, except testes, have a single phenotyEe of contrast, no increase at all was seen in the vascular ACE protein with no isoform being present, 8 al- tissue. This unique nature of vascular tissue might at though differential glycosylation of ACE molecule least in part contribute to the prolonged action of may occur in different tissues. 19 Thus, it would be trandolapril preferentially onto vascular ACE. On the unlikely that an ACE inhibitor would exhibit different other hand, de novo ACE induction in other tissues affinity toward ACE in different tissues. In support may be a factor that counteracts the ACE inhibition of our assumption, a report of saturation and dis- and thus accelerates the recovery from ACE inhibiplacement studies using radiolabelled trandolaprilat tion. Although the vascular tissue did not respond to showed the similarity of ACE labeling throughout the ACE inhibitors with de novo ACE induction in our in vivo study, vascular endothelial cells in culture were body in rats. 20 The second and third possibilities might not be reportedly able to induce ACE mRNA in response to ruled out. A whole body autoradiographical study in ACE inhibition. 21 Thus, it remains to be clarified rats has shown no detectable accumulation of tran- what makes this difference between in vivo and in dolapril or trandolaprilat in the vascular tissues 48 h vitro results, and what mechanism is operating to after an oral dosing of 14C-trandolapril while there is suppress the ACE induction in the vasculature in some accumulation in the lungs (Data on file, Rous- vivo. sel-Uela£). However, the detection sensitivity might CONCLUSION not be sufficiently high, because the ACE activity measurement demonstrated the high degree of inhiTrandolapril exerts its antihypertensive action for a bition not only in the lung, but also in other tissues distinctively longer time than its chemical prototype 7 ineluding the aorta. Further studies are needed to enalapril. This is presumably due to the high lidetermine whether or not trandolapril and trandolapophilicity of trandolapril and trandolaprilat, as the prilat selectively distribute to the vascular walls, and lipophilicity may increase the vascular tissue distriwhether or not trandolapril and trandolaprilat are bution of the drug and the elimination half-life of the more slowly eliminated from the vascular tissues drug from vascular tissue. In addition to this advanthan from other tissues. tageous feature of trandolapril, vascular tissue inWe examined various tissues for their capacity to duces little de novo ACE that may counteract the induce de novo ACE during the washout period from drug effect in response to ACE inhibitors. These trandolapril treatment (unpublished data). The repharmacokinetic properties of trandolapril together sults, as illustrated in Figure 4, indicated that the total with the unique nature of the vascular tissue may be ACE activity was increased by -150% in the plasma incorporated to influence the prolonged vascular acand by -50% in the lung, heart, and kidney, while tion of trandolapril.
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Ondetti MA, Rubin B, Cushman DW: Design of specific inhibitors of angiotensin-converting enzyme: a new class of orally active antihypertensive agents. Science 1977;196:441-444. 2. Gavras H, Brunner HR, Turini GA, et al: Antihypertensive effect of the oral angiotensin converting enzyme-inhibitor SQ 14225 in man. N Engl J Med 1978; 298:991-995. 3. Ondetti MA: Structural relationships of angiotensin converting enzyme inhibitors to pharmacologic activity. Circulation 1988;77(suppl 1):1-74-1-78. 4. ACE inhibitors and tissue binding (editorial). Lancet 1.
Aorta ns
REFERENCES
1990;336:71S-nO.
5. Kelly JG, O'Malley K: Clinical pharmacokinetics of the newer ACE inhibitors. Clin Pharmacokinet 1990;19: 177-196.
VASCULAR AFFINITY OF TRANDOLAPRIL 675
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6. Okunishi H, Kawamoto T, Kurobe Y, et al: Pathogenetic role of vascular angiotensin-converting enzyme in the spontaneously hypertensive rat. Clin Exp Pharmacol PhysioI1991;18:649-659. 7. Okunishi H, Kawamoto T, Kobayashi T, et al: Prolonged and tissue-selective inhibition of vascular angiotensin-converting enzyme by trandolapril: relevance to its antihypertensive action in spontaneously hypertensive rats. Pharm Pharmacol Lett 1992;2:180183. 8. Unger T, Ganten 0, Lang RE, Scholkens BA: Is tissue converting enzyme inhibition a determinant of the antihypertensive efficacy of converting enzyme inhibitors? Studies with the two different compounds, Hoe498 and MK421, in spontaneously hypertensive rats. J Cardiovasc PharmacoI1984;6:872-880. 9. Unger T, Gohlke P, Gruber M-G: Converting enzyme inhibitors, in Ganten 0, Mulrow PJ (eds): Handbook of Experimental Pharmacology, Vol. 93, Pharmacology of Antihypertensive Therapeutics. Springer-Verlag, Berlin, 1990 pp 377-481. ML, Kurz KD: Angiotensin converting enzyme Cohen 10. inhibition in tissues from spontaneously hypertensive rats after treatment with captopril or MK421. J Pharmacol Exp Ther 1982;220:63-69. Brown NL, Badel M-Y, Benzoni F, et al: Angiotensin11. converting enzyme inhibition, antihypertensive activity and hemodynamic profile of trandolapril (RU 44570). Eur J PharmacoI1988;148:79-91. 12. Herman AG: Differences in structure of angiotensinconverting enzyme inhibitors might predict differences in action. Am J Cardiol 1992;70:102C-108C. 13. Vertes V, Haynie R: Comparative pharmacokinetics of
14. 15. 16.
17.
18.
19. 20.
21.
captopril, enalapril, and quinapril. Am J Cardiol1992; 69:8C-16C. Miyazaki M, Okunishi H, Nishimura K, Toda N: Vascular angiotensin converting enzyme in man and other species. Clin Sci 1984;66:39-45. Okunishi H, Miyazaki M, Toda N: Evidence for a putatively new angiotensin II-generating enzyme in the vascular wall. J Hypertens 1984;2:277-284. Iso T, Yamauchi H, Suda H, et al: A new potent inhibitor of converting enzyme: (2RAR)-2-(2-hydroxyphenyl)-3-(3-mercaptopropionyl)-4-thiazolidinecarboxylic acid (SA446). Jpn J PharmacoI1981;31:875-882. Chevillard C, Brown NL, Mathieu M-N, et al: Differential effects of oral trandolapril and enalapril on rat tissue angiotensin-converting enzyme. Eur J Pharmacol 1988;147:23-28. Hubert C, Houot A-M, Corvol P, Soubrier F: Structure of the angiotensin I-converting enzyme gene. Two alternate promoters correspond to evolutionary steps of a duplicated gene. J Bioi Chern 1991;266:1537715383. Soffer RL, Berg T, Sulner J, Lai CY: Pulmonary and testicular angiotensin converting isoenzymes. Clin Exp Hypertens [A] 1987;A9:229-234. Bardelay C, Mach E, Worcel M, Hunt P: Angiotensinconverting enzyme in rat brain and extraneural tissues visualized by quantitative autoradiography using 3H_ trandolaprilate. J Cardiovasc Pharmacol 1989;14:511518. King SJ, Oparil 5: Converting-enzyme inhibitors increase converting-enzyme mRNA and activity in endothelial cells. Am J Physiol 1992;263:C743-C749.