Prehospital risk assessment and direct transfer to a percutaneous coronary intervention centre in suspected acute coronary syndrome.

OBJECTIVE: Prehospital risk stratification and triage are currently not performed in patients suspected of non-ST-segment elevation acute coronary syndrome (NSTE-ACS). This may lead to prolonged time to revascularisation, increased duration of hospital admission and higher healthcare costs. The preHEART score (prehospital history, ECG, age, risk factors and point-of-care troponin score) can be used by emergency medical services (EMS) personnel for prehospital risk stratification and triage decisions in patients with NSTE-ACS. The aim of the current study was to evaluate the effect of prehospital risk stratification and direct transfer to a percutaneous coronary intervention (PCI) centre, based on the preHEART score, on time to final invasive diagnostics or culprit revascularisation. METHODS: Prospective, multicentre, two-cohort study in patients with suspected NSTE-ACS. The first cohort is observational (standard care), while the second (interventional) cohort includes patients who are stratified for direct transfer to either a PCI or a non-PCI centre based on their preHEART score. Risk stratification and triage are performed by EMS personnel. The primary endpoint of the study is time from first medical contact until final invasive diagnostics or revascularisation. Secondary endpoints are time from first medical contact until intracoronary angiography (ICA), duration of hospital admission, number of invasive diagnostics, number of inter-hospital transfers and major adverse cardiac events at 7 and 30 days. RESULTS: A total of 1069 patients were included. In the interventional cohort (n=577), time between final invasive diagnostics or revascularisation (42 (17-101) hours vs 20 (5-44) hours, p<0.001) and length of hospital admission (3 (2-5) days vs 2 (1-4) days, p=0.007) were shorter than in the observational cohort (n=492). In patients with NSTE-ACS in need for ICA or revascularisation, healthcare costs were reduced in the interventional cohort (€5599 (2978-9625) vs €4899 (2278-5947), p=0.02). CONCLUSION: Prehospital risk stratification and direct transfer to a PCI centre, based on the preHEART score, reduces time from first medical contact to final invasive diagnostics and revascularisation, reduces duration of hospital admission and decreases healthcare costs in patients with NSTE-ACS in need for ICA or revascularisation. TRIAL REGISTRATION: NCT05243485.

Tissue distribution of K-vitamers under different nutritional regimens in the rat.

Two forms of vitamin K [phylloquinone (K1) and menaquinone-4 (MK-4)] were added to vitamin K-deficient rat food in varying amounts. These diets were given as the sole source of nutrition to rats for one week. The minimal dietary requirements (MDR) to attain maximal prothrombin synthesis were determined to be 0.6 and 6-10 microg/g of food for K1 and MK-4, respectively. The difference between both vitamers could be explained by the limited hepatic accumulation of MK-4. Next, vitamin K was offered to rats at concentrations ranging between 0.6 and 3000 microg/g of food, and the tissue distribution of vitamin K was investigated after one week of administration. Accumulation of K1 and MK-4 was found in all tissues investigated, but both the absolute tissue concentration and the ratio between K1 and MK-4 were tissue-dependent. Highest values were found in liver and in heart, but since the heart contains no gamma-glutamylcarboxylase, the function of vitamin K in this tissue remains obscure. High tissue concentrations of MK-4 were also found in pancreas and testis after a diet containing K1 exclusively. The data indicate that this conversion is tissue-specific, but neither the reason nor its mechanism are known.

The in vivo effects of acenocoumarol, phenprocoumon and warfarin on vitamin K epoxide reductase and vitamin K-dependent carboxylase in various tissues of the rat.

In rats the in vivo effects of a chronic low-dose treatment (+/- 60 micrograms/rat per day) with different coumarins (acenocoumarol, phenprocoumon and warfarin) on hepatic and non-hepatic vitamin K-dependent enzyme systems were compared. The plasma concentrations of the three coumarins differed largely but these differences were not reflected in the microsomal coumarin contents. The non-hepatic microsomes contained less than 20% of the coumarins found in liver microsomes. No substantial differences were observed between the following effects of the three anticoagulant treatments. The blood coagulation factor activities were about 10% of normal. The hepatic microsomal vitamin K epoxide reductase activity was diminished to about 35% of control values. The vitamin K epoxide reductase activities present in kidney, lung, spleen, testis and brain microsomes were less influenced by the coumarin treatments; activities ranged between 45 and 65% of normal. In the liver microsomes a 15-fold accumulation of non-carboxylated precursor proteins was found; in the non-hepatic microsomes this effect was less pronounced but still present. The hepatic vitamin K-dependent carboxylase activity was enhanced but the corresponding non-hepatic enzyme activities were slightly or not affected. In addition, the effects of a chronic low-dose warfarin treatment were compared with those after an acute high dose of the drug.

Intestinal flora is not an intermediate in the phylloquinone-menaquinone-4 conversion in the rat.

To elucidate the role of intestinal bacteria in the conversion of phylloquinone into menaquinone-4 (MK-4) we investigated the tissue distribution of vitamin K in germ-free rats. The rats were made vitamin K deficient by feeding a vitamin K-free diet for 13 days. In a subsequent period of 6 days, phylloquinone and menadione were supplied via the drinking water in concentrations of 10 and 50 micromol l(-1). Menadione supplementation led to high levels of tissue MK-4, particularly in extrahepatic tissues like pancreas, aorta, fat and brain. Liver and serum were low in MK-4. Phylloquinone supplementation resulted in higher phylloquinone levels in all tissues when compared with vitamin K-deficient values. The main target organs were liver, heart and fat. Remarkably, tissue MK-4 levels were also higher after the phylloquinone supplementation. The MK-4 tissue distribution pattern after phylloquinone intake was comparable with that found after menadione intake. Our results demonstrate that the conversion of phylloquinone into MK-4 in extrahepatic tissues may occur in the absence of an intestinal bacterial population and is tissue specific. A specific function for extrahepatic MK-4 or a reason for this biochemical conversion of phylloquinone into MK-4 remains unclear thus far.

Natural prenylquinones inhibit the enzymes of the vitamin K cycle in vitro.

Vitamin K belongs to a class of compounds commonly known as prenylquinones. Three other prenylquinones which are abundantly found in food are plastoquinone-9, ubiquinone-9 and ubiquinone-10. Using in vitro assay systems, it was recently found that synthetic derivatives of prenylquinones inhibit the vitamin K-dependent enzyme gamma-glutamylcarboxylase and, to a lesser extent, the vitamin K-epoxide reductase. In this paper we describe how natural prenylquinones affect the vitamin K-dependent enzymes in vitro. All three prenylquinones were found to inhibit both the vitamin K-dependent carboxylase and the K-epoxide reductase in a rat as well as in a cow liver system; 50% inhibition was obtained at concentrations in the micromolar range. On the basis of their respective standard redox potentials, a possible mechanism for the inhibitory effect of prenylquinones on the carboxylase enzyme is put forward. It is concluded that natural prenylquinones are potential antagonists of vitamin K and may interfere with vitamin K-dependent reactions in vivo.

Induction of prothrombin synthesis by K-vitamins compared in vitamin K-deficient and in brodifacoum-treated rats.

Vitamin K is a group name for a number of prenylated 2-methyl-1,4-naphtoquinones, which may differ in their ability to function as a cofactor for prothrombin biosynthesis. To quantify the bioactivity of different forms of vitamin K, two experimental animal systems are frequently used: vitamin K-deficient rats and anticoagulated rats. In this paper both models are compared, and it is shown that the results obtained depend on the model used. The main reason for this discrepancy is the difference in recycling of vitamin K-epoxide, which results in a 500 times higher vitamin K requirement in anticoagulated rats. Absorption and hepatic accumulation of long chain menaquinones seem to be restricted to a maximum, whereas also the lipophilic nature of long chain menaquinones may hamper the quinone-quinol reduction in anticoagulated animals. If these data may be extrapolated to patients, food items rich in K1 and MK-4 would be expected to influence the stability of oral anticoagulation to a much larger extent than food items primarily containing higher menaquinones.

The interaction of the prostaglandin E derivative rioprostil with oral anticoagulant agents.

The prostaglandin E1 analogue rioprostil was tested for potential interaction with oral anticoagulant therapy in healthy male volunteers. The effect of rioprostil (0.3 mg, twice a day) was investigated on acenocoumarol (10 mg per subject, n = 7) and phenoprocoumon (0.2 mg/kg, n = 6) single-dose pharmacokinetics and pharmacodynamics. Plasma levels of thrombotest, prothrombin (factor II), and factor VII activities were assayed. Rioprostil, 7 days pretreatment, did not affect control parameters of blood coagulation activity. During the rioprostil period the effect of phenprocoumon on thrombotest and factor VII activities was significantly weaker (p less than 0.02, ANOVA) compared with the control experiment. The effect of acenocoumarol on thrombotest activity was significantly weaker at 24 and 31 hours. None of the pharmacokinetic parameters tested were affected by rioprostil medication. The findings suggest that prostaglandins, at least those of the E series, attenuate the anticoagulant action of the oral anticoagulant agents by a mechanism not related to any pharmacokinetic interaction.

Altered pharmacokinetics of R- and S-acenocoumarol in a subject heterozygous for CYP2C9*3.

OBJECTIVE: Our objective was to study the pharmacokinetics of R - and S -acenocoumarol in a subject who was highly sensitive to the anticoagulant effect of acenocoumarol. The subject was found to be heterozygous for CYP2C9*3. METHODS: The plasma pharmacokinetics of the acenocoumarol enantiomers was established after an oral dose of 8 mg of racemic acenocoumarol. Urine was collected to establish the formation clearance of the 6- and 7-hydroxy metabolites of R - and S -acenocoumarol. RESULTS: The pharmacokinetics of S -acenocoumarol in this subject differed greatly (oral clearance, 6%-10%; half-life of elimination, 400%-500%) from the values of a [wt/wt] control and from population values. R -acenocoumarol clearance was at the lower level of population values. The apparent formation clearances of the metabolites were low-approximately 10% of control activity for the hydroxylations (6- and 7-) of S -acenocoumarol and for the 7-hydroxylation of R -acenocoumarol. The rate of the 6-hydroxylation of R -acenocoumarol was about 50% of control values. CONCLUSION: The presence of even one copy of CYP2C9*3 reduces profoundly the metabolic clearance of S -acenocoumarol. As a result the first-pass effect of elimination is abolished and the maintenance time is increased. S -Acenocoumarol, which is normally clinically inactive, will now exert main anticoagulant activity.

MRI in patients with suspected vascular parkinsonism.

To determine whether MRI can reveal more vascular lesions in patients clinically suspected of having vascular parkinsonism, we compared 15 such patients with 15 patients who had idiopathic Parkinson's disease and 10 hypertensive controls. Patients with suspected vascular parkinsonism had significantly more subcortical lesions than those with Parkinson's disease or hypertension. The cutoff point that best distinguished patients with suspected vascular parkinsonism from patients with Parkinson's disease was a 0.6% level of lesioned brain tissue volume. There were two types of vascular parkinsonism: one had an acute onset and lesions located in the subcortical gray nuclei (striatum, globus pallidus, thalamus); the other had an insidious onset and lesions diffusely distributed in the watershed areas.

Sjögren-Larsson syndrome: clinical and MRI/MRS findings in FALDH-deficient patients.

OBJECTIVE: To determine the spectrum of clinical and MRI/1H MRS features of patients with fatty aldehyde dehydrogenase (FALDH) deficiency. BACKGROUND: The Sjogren-Larsson syndrome (SLS) was originally defined as a clinical triad consisting of ichthyosis, spastic di- or tetralegia, and mental retardation, with autosomal recessive inheritance. By now, both the deficiency of the enzyme FALDH, and the genetic mutations on chromosome 17 responsible for this deficiency, have been identified. SLS, defined by fibroblast FALDH deficiency, seems to be a much broader syndrome. METHODS: The clinical findings of 11 FALDH-deficient patients of different ages and one patient with the characteristic SLS-like ichthyosis, but without FALDH deficiency, were evaluated in relation to their cerebral MRI, and to 1H MRS in six patients. RESULTS: The severity of neurologic symptoms showed considerable variation. Fundoscopic perifoveal glistening dots and the characteristic SLS-like ichthyosis were present in all patients. Serial MRI findings showed evidence of retarded myelination and a variable degree of dysmyelination. 1H MRS showed an accumulation of free lipids in the periventricular white matter, even before the stage of visible dysmyelination. CONCLUSIONS: The neurologic consequences of FALDH deficiency show considerable variation. The characteristic pattern of ichthyosis and retinal degeneration are seen consistently, yet they are not pathognomonic. MRI and 1H MRS findings suggest an accumulation of long-chain fatty alcohol intermediates, resulting in retarded myelination and dysmyelination.

Effects of complete renal denervation and selective afferent renal denervation on the hypertension induced by intrarenal norepinephrine infusion in conscious rats.

To test the hypothesis that continuous intrarenal norepinephrine (NE) infusions produce hypertension via activation of afferent renal nerves (ARN), rats were subjected to complete renal denervation (RN-x), selective renal deafferentation (ARN-x) or sham surgery, prior to infusion of NE. In the pre-infusion period, mean arterial pressure (MAP) was significantly lower in RN-x than in ARN-x or sham-operated rats. Plasma renin concentration (PRC) was significantly reduced following ARN-x, but not RN-x. During 5-day intrarenal infusions of 4, 12 or 36 micrograms NE/kg per h, MAP rose to similar levels in RN-x and sham-RN-x rats. However, RN-x rats exhibited significantly elevated PRC levels, suggesting that denervation supersensitivity masked the possible effects of RN-x. In sham-RN-x rats, MAP increased significantly more during intrarenal infusion of 12 micrograms NE/kg per h than during intravenous infusion of the same amount. In ARN-x rats, MAP rose to a similar degree during intravenous and intrarenal infusions. The pressor responses in the ARN-x rats, however, were not significantly smaller at any point than those in intact rats. PRC rose to comparable levels in ARN-x and intact rats. Thus, in normotensive rats, efferent renal nerves (ERN) but not ARN are of functional significance in maintaining basal blood pressure. ARN may be involved in the control of renin release. Since neither RN-x nor ARN-x attenuated the development of hypertension, renal nerves are not necessary for the full expression of hypertension in this model.

P-Aminobenzoic acid derivatives as inhibitors of the cell-free H2-pteroate synthesizing system of Escherichia coli.

A heterogeneous series of compounds, derived from p-aminobenzoic acid (PABA), has been investigated for their PABA-antagonistic potency in a cell-free H2-pteroate synthesizing system of E. coli. A prerequisite of compounds, other than sulfones or sulfonamides, to compete with PABA for the enzyme H2-pteroate synthetase appeared to be the presence of a p-aminobenzoyl moiety. Substitution of the carboxyl group of PABA by an ester, an amide, or a ketone function, however, strongly reduces the ability to interact with the PABA binding site on the enzyme. This decrease in affinity probably has to be ascribed to the inability to create a sufficient negative charge in the carbonyl part of these p-aminobenzoyl derivatives. The relatively high affinities of L-PABG (16), PABP (22), and the alpha-phenyl derivative of 22, as compared with the other substituted p-aminobenzamides and p-aminobenzene-1-alkanones, are explained by assuming that these compounds, besides interfering with the PABA receptor site, also interact with an accessory area on the enzyme.

Sensitivity of graft rejection in rats to local immunosuppressive therapy.

In this study we investigated whether allograft rejection is sensitive to local immunosuppressive therapy. In rats, cardiac transplantations (BN----Lewis) were performed with venous return on the portal vein of the recipient. For local treatment the topical steroid budesonide was infused with an osmotic minipump directly into the carotid artery of the transplant. Budesonide is rapidly cleared by the liver, and cardiac tissue binding of the drug is high. Hence, local budesonide administration, 120 micrograms/kg/day, resulted in high drug levels within the graft (29.6 ng/mg) and low systemic drug levels (0.34 ng/ml). Systemic drug levels were so low that systemic biological effects of the drug during local administration were not measurable. In contrast systemic drug delivery, via the jugular vein of recipient, resulted in similar drug levels within the graft (31.0 ng/mg), but with high systemic drug levels within the graft (31.0 ng/mg), but with high systemic drug levels (1.65 ng/ml) and important systemic side effects. Both local and systemic administration of budesonide, 120 micrograms/kg/day for 13 days, resulted in significant prolongation of graft survival; median graft survival time was respectively 19.5 days and 20.0 days, compared with 7 days in controls. These results demonstrate that allograft rejection can be treated locally without significant systemic immunosuppression.

4-Hydroxycoumarin oral anticoagulants: pharmacokinetics-response relationship.

The blood coagulating factors II and VII and prothrombin times (Thrombotest) were followed during a dosage interval (= 24 h) in patients on acenocoumarol (n = 6) and on phenprocoumon (n = 6) therapy. The patients were on stable anticoagulation (%TT: 7-13%) for at least 6 months. The study was performed to investigate the concentration-response relationship of the 4-hydroxycoumarin-type oral anticoagulants. The three parameters were stable during the 24-h interval for patients on phenprocoumon therapy. Patients on acenoumarol showed fluctuations in their factor VII levels; peak activities were observed at about 2 h, trough activities at about 16 h after acenocoumarol intake. Factor II and Thrombotest activities were stable. Plasma levels of phenprocoumon were stable during daytime whereas acenocoumarol levels declined exponentially (t1/2 about 12 h). The results indicate the oral anticoagulants to exhibit a concentration-response relationship common to drug-receptor interactions. The results also suggest that for stable and long-lasting anticoagulant therapy oral anticoagulants with half-lives beyond the dosage interval (t1/2 greater than 24 h) should be preferred.

The in vivo effects of oral anticoagulants in man: comparison between liver and non-hepatic tissues.

The in vivo effects of oral anticoagulant therapy with 4-hydroxycoumarins on various vitamin K-dependent enzyme systems in man were compared. In hepatic microsomes obtained from donors who has been treated with 4-hydroxycoumarins for more than 6 months, the vitamin K 2,3 epoxide reductase activity and the DTT-dependent vitamin K quinone reductase activity were diminished to 35% and 20% of the corresponding normal values. In the non-hepatic tissues, only a small decrease in vitamin K 2,3 epoxide reductase activity could be demonstrated, while no differences were found in the vitamin K quinone reductase activities. In none of the tissues a significant increase of noncarboxylated precursor proteins was observed, whereas also vitamin K hydroquinone-dependent carboxylase activities seemed to be unaffected by the anticoagulant treatment.

Human liver microsomal metabolism of the enantiomers of warfarin and acenocoumarol: P450 isozyme diversity determines the differences in their pharmacokinetics.

1. To explain the large differences in (the stereoselectivity of) the clearances of the enantiomers of warfarin and acenocoumarol (4'-nitrowarfarin) their human liver microsomal metabolism has been studied and enzyme kinetic parameters determined. The effects of cimetidine, propafenone, sulphaphenazole, and omeprazole on their metabolism has been investigated. 2. The 4-hydroxycoumarins follow similar metabolic routes and are mainly hydroxylated at the 6- and 7-position (accounting for 63 to 99% of the metabolic clearances). 3. Due to the lower Km values of R- and S-acenocoumarol and higher Vmax values of S-acenocoumarol, the overall metabolic clearances of R/S acenocoumarol exceed those of R/S warfarin 6 and 66 times respectively. 4. The metabolism of both compounds is stereoselective for the S-enantiomers, which is 10 times more pronounced in the case of acenocoumarol. 5. Except for the 7-hydroxylation of the R-enantiomers (r = 0.90; P < 0.025), the 6- and 7-hydroxylation rates of R/S warfarin do not correlate with those of R/S acenocoumarol. 6. Sulphaphenazole competitively inhibits the 7- and in some samples partly (up to 50%) the 6-hydroxylation of S-warfarin as well as the 7-hydroxylation of R- and S-acenocoumarol and the 6-hydroxylation of S-acenocoumarol (Kis ranging from 0.5-1.3 microM). 7. Omeprazole partly (40-80%) inhibits the 6- and 7-hydroxylation of R-warfarin (Ki = 99 and 117 microM) and of R- (Ki = 219 and 7.2 microM) and S-acenocoumarol (Ki = 6.1 and 7.7 microM) but not S-warfarin in a competitive manner. 8. Differences in the partial (up to 40%) inhibition of the metabolism of the enantiomers of the 4-hydroxycoumarins were also observed for the relatively weak inhibitors, propafenone and cimetidine.9. The results suggest that the coumarin ring hydroxylations of both compounds are catalysed by different combinations of P450 isozymes. The 7-hydroxylation of R/S acenocoumarol and the 6-hydroxylation of S-acenocoumarol are at least partly conducted by (a) P450 isozyme(s) of the 2C subfamily different from P450 2C9 (the main S-warfarin 7- and 6-hydroxylase).

The long-term effects of the rodenticide, brodifacoum, on blood coagulation and vitamin K metabolism in rats.

1. The long-term (30 days) effects of a single dose of brodifacoum (0.2 mg kg-1, orally) on blood clotting activity and on liver parameters of the vitamin K cycle were investigated in rats. Maximal effect on blood clotting activity was seen on day one. On day seven blood clotting activity had returned to normal. 2. Liver microsomal vitamin KO reductase activity was maximally suppressed (10% of control activity) on day one, steadily recovered to about 40% on day 15 to remain at that level. The same time course was seen for the number of microsomal warfarin binding sites. 3. The persistent inhibition of the vitamin K cycle was also verified in vivo; following vitamin K administration (10 mg kg-1, i.v.) on day 30, the brodifacoum-treated rats accumulated vitamin KO in the liver. 4. Although clotting factor synthesis was normal, brodifacoum-treated rats were highly sensitive to warfarin. 5. Brodifacoum rapidly accumulated in the liver until the saturation of the microsomal binding site. Brodifacoum binding to the target prevented its elimination from the liver; liver content on day 30 was not different from day 7. 6. The results show (1) an over capacity for the hepatocellular vitamin K cycle, (2) a dissociation of the vitamin K epoxidation and the vitamin K-dependent carboxylation, (3) the 'superwarfarin' rodenticides to be extremely persistent due to their binding to the target.

Vitamin K 2,3-epoxide reductase: the basis for stereoselectivity of 4-hydroxycoumarin anticoagulant activity.

1. The administration of S-warfarin (1 mg kg-1 i.v.) to rats that were pre-loaded 48 h before with tracer doses (6 micrograms) of 14C-labelled R- or S-warfarin caused the plasma levels of these compounds to increase. This is due to the substitution of the microsomal (vitamin K 2,3-epoxide (K0) reductase) bound R- or S-[14C]-warfarin by the unlabelled 4-hydroxycoumarin administered. The rate of reappearance was 3-4 fold higher for R- than for S-warfarin; t1/2 of release: 1.2 +/- 0.04 and 3.7 +/- 0.6 h, respectively. 2. Liver microsomes prepared from rats pretreated with R- or S-[14C]-warfarin, released these compounds only in the presence of dithiothreitol (DTT; 10 mM). The rate of release was higher for R- than for S-warfarin-treated microsomes. 3. Liver microsomes treated in vitro with R- or S-acenocoumarol could be reactivated by DTT (10 mM). Reactivation was higher for the R- than for the S-acenocoumarol-treated microsomes. 4. The microsomal vitamin K0 reductase activity under 'normal' assay conditions ([DTT] = 2 mM) was as sensitive for R- as for S-4-hydroxycoumarins. At elevated DTT concentrations (= 42 mM) the rate of vitamin K0 conversion was about 1.5 fold higher in the presence of the R-isomers than in the presence of the S-isomers. For instance, at 2 mM DDT the reductase activities in the presence of 2.6 microM R- and S-warfarin were about 15% of control. At 42 mM DTT the activities were 90 and 65% of control, respectively. 5. In the in vitro experiments acenocoumarol appeared to be more potent than warfarin and phenprocoumon. 6. The following mechanism is proposed: vitamin K0 reductase becomes oxidized during substrate reduction. The oxidized (i.e. inactive) form binds equally to the R- and S-enantiomers of 4- hydroxycoumarins. The attached (covalently bound?) coumarin is released by the reactivation (i.e. reduction) of the enzyme. However, the rate of reactivation is strongly attenuated by the attached coumarin. This effect is more pronounced for the S-configuration of the 4-hydroxycoumarin anticoagulants.

Renal selective N-acetyl-L-gamma-glutamyl prodrugs: studies on the selectivity of some model prodrugs.

1. In this study, a number of structurally different N-acetyl-L-gamma-glutamyl prodrugs were investigated with respect to selective uptake by the kidney in male Wistar rats. 2. All prodrugs were tested in vitro in rat kidney slices and kidney homogenate to study their uptake and conversion. It was found that the prodrugs of para-nitroaniline (agPNA), aminophenyl acetic acid (agAFA), sulphamethoxazole (agSM), sulphadimethoxine (agSDM), propranolol (agPP) and metoprolol (agMP) were accumulated by a probenecid-sensitive carrier. The prodrug of 4'-aminoantipyrine (agAAP) was not accumulated by a probenecid- or buthionine sulphoximine-sensitive carrier. Unlike all other prodrugs, agAAP and agMP were not, or only a very limited extent converted to the parent compound in vitro. 3. agPNA, agAFA and agPP were also investigated in vivo. The tissue distribution of the prodrugs and the parent drugs was established, as was their urinary excretion and pharmacokinetic behaviour. agPNA and agAFA showed selective uptake by the kidney, in contrast to agPP which accumulated in the liver. The distribution of the parent compounds following prodrug administration was as follows: agPNA was found in kidney and plasma: agAFA in kidney only; agPP in liver only. 4. The factors which determine the selectivity of N-acetyl-L-gamma-glutamyl prodrugs are discussed. The main factors are: the transport into the kidney, the conversion rate, the residence time of the prodrug in the kidney and the presence or absence of competition for uptake and conversation by other tissues, e.g. the liver. It is concluded that this prodrug approach offers the possibility of delivering drugs selectively to the kidney, but also that it is not universally applicable.

Renal selective N-acetyl-gamma-glutamyl prodrugs: a study on the mechanism of activation of the renal vasodilator prodrug CGP 22979.

1. In this study the processes underlying the renal selectivity of the vasodilator prodrug CGP 22979 (N-acetyl-L-glutamic acid-N-[N2-(5-n-butyl-2-pyridyl) hydrazide]) were studied in rats. 2. The active drug CGP 18137 (2-hydrazino-5-n-butyl pyridine) selectively accumulated in the renal tissue following administration of the prodrug. 3. The kidney concentrations of active drug following prodrug administration were significantly lower than control values when either buthionine sulphoximine, glutathione or probenecid was coadministered (29 +/- 11; 33 +/- 14 and 61 +/- 20% of control values, respectively). Inhibition of gamma-glutamyl transpeptidase by AT-125 did not cause a significant decrease of renal CGP 18137 levels. 4. In order to correlate tissue drug concentrations with pharmacological effect, the renal haemodynamic responses to CGP 22979 were measured and the effect of buthionine sulphoximine, glutathione and AT-125 on these responses evaluated. All three of the compounds attenuated the renal response to the prodrug: an approximately 50% lesser decrease in renal resistance was found. The compounds had no effect on the haemodynamic actions of CGP 18137 itself. 5. In vitro, it was found that kidney cytosol was able to convert the prodrug, whereas microsomes were not, unless acylase was added. 6. The results indicate that, upon prodrug administration, gamma-glutamyl transpeptidase is not involved in the renal accumulation of CGP 18137 but is partly responsible for the renal haemodynamic responses to CGP 22979. Active transport of the prodrug into the tubular cells appears to be the major reason for the renal selectivity. A model is proposed for the renal action of CGP 22979, in which the important parts are the uptake of the prodrug via a transport system followed by an intracellular conversion to the active drug.