Synergistic effects of fast-neutron dose per epithermal neutron and 10B concentration on relative-biological-effectiveness dose for accelerator-based boron neutron capture therapy.

The efficacy of accelerator-based boron neutron capture therapy was examined through relative-biological-effectiveness dose calculations with the fast-neutron dose per epithermal neutron (FNR) and the 10B concentration as parameters. In the case of a tumor 10B concentration of 65 ppm, the treatment efficacy depended more strongly on the FNR when the normal-tissue 10B concentration was 0.65 ppm, which would be brought about by the administration of an advanced chemical compound, than when the 10B concentration was 18 ppm, which is attainable by the use of boronophenylalanine.

Single oral dose of geranylgeranylacetone induces heat-shock protein 72 and renders protection against ischemia/reperfusion injury in rat heart.

BACKGROUND: Induction of heat-shock proteins (HSPs) results in cardioprotection against ischemic insult. Geranylgeranylacetone (GGA), known as an antiulcer agent, reportedly induces HSP72 in the gastric mucosa and small intestine of rats. The present study tested the hypothesis that oral GGA would induce HSP72 in the heart and thus render cardioprotection against ischemia/reperfusion injury in rats. METHODS AND RESULTS: Cardiac expression of HSPs was quantitatively evaluated in rats by Western blot analysis. Ten minutes of whole-body hyperthermia induced HSP72 expression in the rat hearts. A single oral dose of GGA (200 mg/kg) also induced expression of HSP72, which peaked at 24 hours after administration. Therefore, isolated perfused heart experiments using a Langendorff apparatus were performed 24 hours after administration of 200 mg/kg GGA (GGA group) or vehicle (control group). After a 5-minute stabilization period, no-flow global ischemia was given for 20, 40, or 60 minutes, followed by 30 minutes of reperfusion. During reperfusion, the functional recovery was greater and the released creatine kinase was less in the GGA group than in the control group. Electron microscopy findings revealed that the ischemia/reperfusion-induced damage of myocardial cells was prevented in GGA-treated myocytes. CONCLUSIONS: The results suggest that oral GGA is cardioprotective against ischemic insult through its induction of HSP72.

Effect of essential hypertension on cardiac autonomic function in type 2 diabetic patients.

OBJECTIVES: The aim of this study was to examine the effects of essential hypertension on cardiac autonomic function in type 2 diabetic patients. BACKGROUND: Hypertension is common in type 2 diabetic patients and is associated with a high mortality. However, the combined effects of type 2 diabetes and essential hypertension on cardiac autonomic function have not been fully elucidated. METHODS: Thirty-three patients with type 2 diabetes were assigned to a hypertensive diabetic group (n = 15; age: 56 +/- 8 years, mean +/- SD) or an age-matched normotensive diabetic group (n = 18, 56 +/- 6 years). Cardiac autonomic function was assessed by baroreflex sensitivity (BRS), heart rate variability (HRV), plasma norepinephrine concentration and cardiac 123I-metaiodobenzylguanidine (MIBG) scintigraphic findings. RESULTS: Baroreflex sensitivity was lower in the hypertensive diabetic group than it was in the normotensive diabetic group (p < 0.05). The early and delayed myocardial uptake of 123I-MIBG was lower (p < 0.01 and p < 0.05, respectively), and the percent washout rate of 123I-MIBG was higher (p < 0.05) in the hypertensive diabetic group. However, the high frequency (HF) power and the ratio of low frequency (LF) power to HF power (LF/HF) of HRV and plasma norepinephrine concentration were not significantly different. The homeostasis model assessment index was higher in the hypertensive diabetic group than it was in the normotensive diabetic group (p < 0.01). CONCLUSIONS: Our results indicate that essential hypertension acts synergistically with type 2 diabetes to depress cardiac reflex vagal and sympathetic function, and the results also suggest that insulin resistance may play a pathogenic role in these processes.

Noninvasive assessment of the cardiac baroreflex: response to downward tilting and comparison with the phenylephrine method.

OBJECTIVES: We studied the relation between changes in systolic blood pressure and RR interval during downward tilting in comparison with assessment of baroreflex sensitivity (BRS) measured by the phenylephrine method (Phe-BRS) and with measures of heart rate variability (HRV). BACKGROUND: The method most extensively used for assessing BRS involves bolus injections of phenylephrine. Several noninvasive methods proposed to assess BRS have not been widely applied in the clinical setting. METHODS: Sixteen healthy male volunteers were studied (mean age +/- SD 27.5+/-4.6 years). Arterial blood pressure using tonometry and electrocardiogram was simultaneously recorded. After 20 min of 70 degrees upright tilting, the table was returned to supine position at a speed of 3.2 degrees/s. Subsequently, BRS was assessed using an intravenous bolus injection of phenylephrine (2 to 3 microg/kg). Heart rate variability under resting conditions also was analyzed. RESULTS: In all subjects, a beat to beat systolic blood pressure increase associated with corresponding RR interval lengthening was observed during downward tilting as well as during phenylephrine administration. During both testing procedures, these two variables showed linear correlation, and the slope of regression line during downward tilting (DT-BRS) correlated significantly with Phe-BRS (r = 0.79, p = 0.0003). The DT- and Phe-BRS also correlated significantly with the high frequency component of resting HRV (r = 0.70, p = 0.0023 for DT-BRS; r = 0.58, p = 0.0185 for Phe-BRS). CONCLUSIONS: We conclude that in a small homogeneous group DT-BRS provided an assessment of reflex cardiac vagal function comparable to that obtained by the phenylephrine method.

Prediction of in vivo drug metabolism in the human liver from in vitro metabolism data.

As a new approach to predicting in vivo drug metabolism in humans, scaling of in vivo metabolic clearance from in vitro data obtained using human liver microsomes or hepatocytes is described in this review, based on the large number of literature data. Successful predictions were obtained for verapamil, loxtidine (lavoltidine), diazepam, lidocaine, phenacetin and some other compounds where CLint,in vitro is comparable with CLint,in vivo. On the other hand, for some metabolic reactions, differences in CLint,in vitro and CLint,in vivo greater than 5-fold were observed. The following factors are considered to be the cause of the differences: (1) metabolism in tissues other than liver, (2) incorrect assumption of rapid equilibrium of drugs between blood and hepatocytes, (3) presence of active transport through the sinusoidal membrane, and (4) interindividual variability. Furthermore, the possibility of predicting in vivo drug metabolic clearance from results obtained using a recombinant system of human P450 isozyme was described for a model compound, YM796, where the predicted metabolic clearances obtained from the recombinant system, taking account of the content of the P450 isozyme CYP3A4 in the human microsomes, were comparable with the observed clearances using human liver microsomes containing different amounts of CYP3A4. Even in the case where the first-pass metabolism exhibits nonlinearity, it appears to be possible to predict in vivo metabolic clearance from in vitro metabolic data.

Single cell analysis of CAG repeat in brains of dentatorubral-pallidoluysian atrophy (DRPLA).

Somatic mosaicism of an expanded repeat is present in tissues of patients with triplet repeat diseases. Of the spinocerebellar ataxias associated with triplet repeat expansion, the most prominent heterogeneity of the expanded repeat is seen in dentatorubral-pallidoluysian atrophy (DRPLA). The common feature of this somatic mosaicism is the difference in the repeat numbers found in the cerebellum as compared to other tissues. The expanded allele in the cerebellum shows a smaller degree of expansion. We previously showed by microdissection analysis that the expanded allele in the granular layer in DRPLA cerebellum has less expansion than expanded alleles in the molecular layer and white matter. Whether this feature of lesser expansion in granule cells is common to other types of neurons is yet to be clarified. We used a newly developed excimer laser microdissection system to analyze somatic mosaicism in the brains of two patients, one with early- and another with late-onset DRPLA, and used single cell PCR to observe the cell-to-cell differences in repeat numbers. In the late onset patient, repeat expansion was more prominent in Purkinje cells than in granule cells, but less than that in the glial cells. In the early onset patient, repeat expansion in Purkinje cells was greater than in granule cells but did not differ from that in glial cells. These findings suggest that there is a difference in repeat expansion among neuronal subgroups and that the number of cell division cycles is not the only determinant of somatic mosaicism.

Silent cortical strokes associated with atrial fibrillation.

To clarify whether silent cortical strokes (SCS) could be a predictor of symptomatic stroke in patients with atrial fibrillation (AF), 72 patients with AF (50 with chronic AF, 22 with paroxysmal AF) were studied. Patients with mitral stenosis, history of myocardial infarction, or dilated cardiomyopathy were excluded from this study. Using cranial magnetic resonance imaging (MRI), the patients were divided into those with SCS (23 patients, Group 1) and those without SCS (49 patients, Group 2). The incidence of symptomatic stroke was then compared between the two groups. Three patients (13%) in Group 1 developed symptomatic brain infarction; this is statistically significant (p < 0.05), compared with the patients in Group 2, none of whom experienced symptomatic stroke. We suggest that SCS is a predictor of symptomatic cerebral infarct in patients with AF. Therefore, it is thought to be important to diagnose SCS using cranial MRI or computed tomography and to keep patients with SCS under close surveillance.

Ibudilast, a phosphodiesterase inhibitor, in combination with low-dose aspirin potently inhibits guinea pig carotid artery thrombosis without extending bleeding time and causing gastric mucosal injury.

A combination of low-dose aspirin (ASA) and a phosphodiesterase inhibitor has been clinically tried for the secondary prevention of atherothrombotic diseases. The in vivo antithrombotic property of ibudilast (CAS 50847-11-5), a phosphodiesterase 4 (PDE4) inhibitor, was evaluated in a photochemically-induced guinea pig carotid artery thrombosis model in combination with low-dose ASA. The time required to decrease the carotid artery blood flow to the reading "zero" was defined as the time to occlusion (TTO) of the artery through thrombogenesis. Each independent use of ASA (300 mg/kg, p.o.) and ibudilast (3 and 10 mg/kg, p.o.) significantly prolonged the TTO, and ASA (300 mg/kg) significantly increased bleeding time (BT) and gastric mucosal injury. A selective PDE4 inhibitor rolipram (1 and 5 mg/kg, p.o.) tended to prolong the TTO without extending BT. ASA (100 mg/kg) plus ibudilast (3 mg/kg) and ASA (100 mg/kg) plus rolipram (5 mg/kg) markedly prolonged the TTO compared with each agent alone. Interestingly, ASA (100 mg/kg) plus ibudilast (3 mg/kg) caused a longer TTO than ASA (300 mg/kg) alone, without significant extension of BT and gastric mucosal injury as observed in ASA (300 mg/kg). These results indicate that the combination of low-dose ASA and ibudilast has a more potent antithrombotic effect than ASA alone without increasing bleeding tendency and gastric mucosal injury. The potent in vivo antithrombotic effect of this combination may be brought about by an action that is associated with PDE4 inhibition of ibudilast.

Drug-drug interactions in the metabolism of imidafenacin: role of the human cytochrome P450 enzymes and UDP-glucuronic acid transferases, and potential of imidafenacin to inhibit human cytochrome P450 enzymes.

Imidafenacin (IM), 4-(2-methyl-1H-imidazol-1-yl)-2,2-diphenylbutanamide, is a newly synthesized antimuscarinic drug developed for the treatment of overactive bladder. To predict clinically relevant drug interactions in the metabolism of IM, the paper investigated: (1) the major enzymes responsible for the metabolism of IM, (2) the effects of concomitant drugs on the inhibition of metabolism of IM, and (3) the effects of IM and its metabolites on the inhibition of human cytochrome P450 (CYP). The elimination of IM and production of oxidative metabolites were mainly catalysed by recombinant CYP3A4, and the elimination of IM by human liver microsomes (HLM) was markedly inhibited by co-incubation with ketoconazole. The production of the N-glucuronide metabolite was only catalysed by recombinant UGT1A4. Clinically established CYP3A4 inhibitors including itraconazole, ketoconazole, erythromycin and clarithromycin inhibited the elimination of IM in HLM. IM and its major metabolites did not affect the activities of CYP enzymes in vitro. The results suggest that the major enzymes responsible for the metabolism of IM are CYP3A4 and UGT1A4, and oxidative metabolism of IM is reduced by concomitant administration of CYP3A4 inhibitors. In contrast, IM and its metabolites have no inhibitory effect on the CYP-mediated metabolism of concomitant drugs.

Molecular level damages of low power pulsed laser radiation in a marine bacterium Pseudoalteromonas carrageenovora.

AIM: To study the molecular level damages in a marine bacterium, Pseudoalteromonas carrageenovora, exposed to low power pulsed laser radiation from an Nd:YAG laser. METHODS AND RESULTS: The laser damages in bacterial DNA were monitored by studying the formation of apurinic/apyrimidinic (AP) sites. Molecular probe kits were used for this purpose. Occurrence of lesions in the cell walls was monitored under a transmission electron microscope (TEM). The results showed that laser radiation significantly increased the number of AP sites in the bacterial DNA. This increase corresponded to the laser fluence (J cm(-2)) and to the duration of laser irradiation. TEM observation showed the occurrence of lesions in bacterial cell walls upon laser irradiation. CONCLUSIONS: It is concluded that bacteria exposed to laser irradiation suffers DNA damages and resulted in broken cell walls. These events led to bacterial mortality. These are in addition to the mechanisms reported earlier such as the photochemical reactions occurring inside the cells upon exposure to low power laser. SIGNIFICANCE AND IMPACT OF THE STUDY: These results help us to understand the mechanisms of bacterial mortality on exposure to low power pulsed laser irradiation and are useful in formulating a laser treatment strategy to kill bacteria.

High-performance liquid chromatographic determination of 6,8-difluoro-1-(2-fluoroethyl)-1,4- dihydro-7-(4-methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic acid and its metabolites in laboratory animals.

A simple, sensitive and specific high-performance liquid chromatographic method for a new quinolone antimicrobial agent, 6,8-difluoro-1-(2-fluoroethyl)-1,4- dihydro-7-(4-methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic acid (AM-833, I), and its metabolites in serum and urine has been developed for their simultaneous determination. This method is based on ion-pair extraction and separation by ion-pair reversed-phase chromatography with ultraviolet or fluorescence detection. The major metabolites in the serum and urine of mice, rats, dogs and monkeys were N-desmethyl I (compound II) and I N-oxide (compound III). Rabbit serum and urine contained N-desmethyl-3-oxo I (compound IV), 3-oxo I (compound V) and N-desmethyl-4-formyl I (compound VI) in addition to compounds I, II and III. Unchanged drug accounted for 80-90% of total serum concentrations in mice and more than 90% in rats, dogs and monkeys up to 6 h after dosing, whereas the fraction of compound I in rabbits was 34-67%. Unchanged drug was the most predominant in the urine of mice, rats, dogs and monkeys, whereas compound II was the most abundant in rabbit urine. Although rabbits and monkeys excreted 70-80% of dose in three-day urine, the total urinary excretion of mice, rats and dogs was relatively low, 40-50% of oral dose. The fraction of compound I in total urinary excretion was 63, 73, 27, 55 and 78% in mice, rats, rabbits, dogs and monkeys, respectively. These results suggest that there is a species difference in the metabolism and excretion pathway of compound I.

Kinetics of quinolone antibiotics in rats: efflux from cerebrospinal fluid to the circulation.

PURPOSE: An active transport system, which pumps quinolone antimicrobial agents (quinolones) from cerebrospinal fluid (CSF) to systemic blood, exists at the choroid plexus, an epithelial tissue that forms the blood-CSF barrier (BCSFB). The present study was carried out to clarify the contribution of this transport system to the disposition of quinolones in the central nervous system. METHOD: Six quinolones were administered intracerebroventricularly to rats and their elimination from the CSF was examined. The inhibitory effect of probenecid and quinolones on the efflux of fleroxacin from the CSF was also examined. Probenecid or two types of quinolone (AM-1155, pefloxacin) were co-administered intracerebroventricularly with fleroxacin. RESULTS: The elimination clearance from the CSF for norfloxacin, AM-1155, fleroxacin, ofloxacin, sparfloxacin and pefloxacin was 14, 22, 21, 20, 47 and 35 microliters/min/rat, respectively. An approximately 3.5-fold difference was thus observed between norfloxacin and sparfloxacin. These values were 4- to 14-fold larger than the [14C]mannitol clearance. Furthermore, the elimination clearance of quinolones from the CSF was 7- to 60-fold larger than the active efflux clearance at the BCSFB estimated from our previous in vitro data. Co-administration of AM-1155, pefloxacin and probenecid did not inhibit the elimination of fleroxacin from the CSF. CONCLUSIONS: The active transport system at the BCSFB plays only a small part in the elimination of quinolones from the CSF. Passive diffusion via the BCSFB and diffusion across the ependymal surface into brain extracellular fluid, followed by efflux across the blood-brain barrier, may be the predominant pathway for quinolone elimination from the CSF.

Quantitative brain microdialysis study on the mechanism of quinolones distribution in the central nervous system.

Brain interstitial fluid (ISF) concentrations, which regulate the toxicodynamic effect of quinolone antimicrobial agents (quinolones) in the central nervous system, have been determined for norfloxacin, ofloxacin, fleroxacin, and pefloxacin using a quantitative brain microdialysis technique. Steady-state brain ISF concentrations of the quinolones were 7-30 times lower than the unbound serum concentrations due to restricted distribution in the brain. Cerebrospinal fluid concentrations of the quinolones were approximately twice as high as the brain ISF concentrations, except for norfloxacin. Thus, it seems that an active efflux transport system across the blood-brain barrier is responsible for maintaining brain ISF concentrations lower than unbound serum concentrations at steady-state. A good correlation was observed for norfloxacin, ofloxacin, fleroxacin, and pefloxacin between brain ISF concentrations and total brain concentrations. Moreover, a relatively small difference was observed among the quinolones for the in vitro brain slice-to-medium concentration ratio, compared with an 11-fold difference in the in vivo brain-to-unbound serum concentration ratio after intravenous infusion. These results indicate that the different quinolones studied all exhibit similar apparent binding and/or uptake by brain parenchyma, with an average brain ISF-to-total brain concentration ratio of 0.688.

Kinetic evidence for active efflux transport across the blood-brain barrier of quinolone antibiotics.

A distributed model has been used to clarify the mechanism of the restricted and differential distribution of the quinolone antibiotics in the rat central nervous system (CNS). The symmetrical permeability clearances across the blood-brain barrier (BBB), PS(BBB), and across the blood-cerebrospinal fluid barrier (BCSFB), PS(CSF), and the active efflux clearances across the BBB, PS(BBB,eff), were obtained from a nonlinear least squares regression analysis combined with the fast inverse Laplace transforming program for in vivo data. The values of PS(BBB,eff) were 10- to 260-fold greater than those of PS(BBB), providing kinetic evidence to support the hypothesis that a significant efflux transport across the BBB is responsible for the limited distribution of quinolones in brain tissue. Moreover, by simulation studies, we could demonstrate the concentration profiles in the brain as a function of the distance from the ependymal surface. However, active efflux transport across the BCSFB has been suggested to have only a slight effect on the apparent elimination from the cerebrospinal fluid. Comparing the apparent brain tissue-to-unbound serum concentration ratio at steady state, it has been suggested that the net flux across the BBB, ie., the ratio of PS(BBB) to the sum of PS(BBB) and PS(BBB,eff), is a determinant for the differential distribution of these quinolones in brain tissue. Such a putative active efflux transport system would play a significant role in decreasing the brain interstitial fluid concentration of quinolones.

Characterization of the transport properties of a quinolone antibiotic, fleroxacin, in rat choroid plexus.

PURPOSE: It is reported that the cerebrospinal fluid (CSF) to plasma unbound concentration ratio of fleroxacin at steady-state is approximately 0.5 in experimental animals. These results can be accounted for by assuming the presence of an active transport system for the efflux of this compound across the choroid plexus. In the present study, the transport system for fleroxacin was characterized in isolated rat choroid plexus. METHODS: Choroid plexus was isolated from the lateral ventricles of rats. The accumulation of [14C] fleroxacin or [3H] benzylpenicillin by the choroid plexus was examined by the centrifugal filtration method. RESULTS: The accumulation of [14C] fleroxacin by the rat isolated choroid plexus was significantly inhibited by metabolic inhibitors (rotenone, 30 microM and carbonyl cyanide rho-trifluorometh oxyphenylhydrazone (FCCP), 100 microM) and sulfhydryl reagent (p-chloromercuribenzenesulfonic acid (PCMBS), 100 microM). This accumulation was composed of a saturable component (Vmax = 240 pmol.min-1.microliter tissue-1, Km = 664 microM) and non-saturable one (P = 0.424 min-1.microliter tissue-1). Accumulation of fleroxacin was competitively inhibited by benzylpenicillin and probenecid with Ki values of 29 microM and 51 microM, respectively. These values are comparable with the Km of benzylpenicillin transport and the Ki of probenecid for the benzylpenicillin transport at the choroid plexus, respectively. Furthermore, fleroxacin inhibited competitively the accumulation of [3H] benzylpenicillin with a Ki of 384 microM, a value comparable with the Km of [14C] fleroxacin transport. CONCLUSIONS: Fleroxacin and benzylpenicillin showed mutual competitive inhibition, suggesting that both are transported via a common transport system in the choroid plexus and are pumped out from CSF into the circulation.

Comparative distribution of quinolone antibiotics in cerebrospinal fluid and brain in rats and dogs.

The distribution of the quinolone antibiotics, norfloxacin (NFLX), AM-1155, fleroxacin (FLRX), ofloxacin, sparfloxacin (SPFX) and pefloxacin (PFLX), in the central nervous system (CNS) was investigated in dogs and rats. In dogs, the steady-state cerebrospinal fluid (CSF) to unbound serum concentration ratio (Kp,uCSF) differed widely ranging from 0.11 (NFLX) to 1.0 (PFLX). About a 10-fold difference between compounds was also observed in the Kp,uCSF in rats; however, these values were 25 to 50% smaller than those in dogs. Similarly, the brain to unbound serum concentration ratio (Kp,uBrain) of quinolones differed widely ranging from 0.15 (NFLX) to 1.5 (SPFX) in dogs and 0.04 (NFLX) to 0.33 (FLRX) in rats. The steady-state concentration ratio between CSF and brain tissue exhibited a 3-fold difference among quinolones (0.5 for PFLX to 1.6 for SPFX) in dogs, whereas, these values were all close to unity in rats. Kp,uBrain and Kp,uCSF all increased as the lipophilicity of the compound increased (except the Kp,uBrain in dogs). We also found that the quinolones inhibited the saturable accumulation of [14C]FLRX (Km 660 microM) by the isolated rat choroid plexus. About a 20-fold difference among the apparent IC50 values for FLRX transport was observed between NFLX (6000 microM) and PFLX (300 microM). The absence of a negative correlation between the affinity of the quinolones for this transport system, which in turn represents the efflux clearance from the CSF, and their in vivo distribution in rat CNS (Kp,uBrain or Kp,uCSF) suggests a minor contribution of this efflux system to the CNS distribution of quinolones.

Suppression of cesium-induced ventricular tachyarrhythmias by atrial natriuretic peptide in rabbits.

BACKGROUND: Intravenous injection of cesium chloride (Cs) causes ventricular tachyarrhythmias in rabbits. We investigated whether these tachyarrhythmias were caused by increased pressure load and whether they could be suppressed by atrial natriuretic peptide (ANP). METHODS AND RESULTS: Cs was injected in a bolus dose (1.5 mmol/kg), which was repeated 20 minutes later. Rabbits were then divided into 3 groups: control, ANP-treated, and hydralazine-treated groups. ANP or hydralazine was administered between the first and second Cs injections. The experiments were performed during intrinsic sinus rhythm (protocol A) or during ventricular pacing (protocol B). In protocol A, the second injection of Cs in the control group induced early afterdepolarizations and ventricular tachycardia, which were preceded by a marked increase in left ventricular end-diastolic pressure (LVEDP). Both ANP and hydralazine significantly suppressed Cs-induced increase in LVEDP. The arrhythmia score after the second injection of Cs was significantly lower in the ANP-treated and hydralazine-treated group compared with the control group (P < .005 and P < .05, respectively). In protocol B, the duration of left ventricular monophasic action potential and early afterdepolarization amplitude before and/or after the injections of Cs did not differ significantly between control and ANP-treated groups. CONCLUSIONS: Our results suggest that increased pressure load may play a role in the arrhythmogenic effect of Cs. The protective effect of ANP against Cs-induced ventricular tachycardia may be explained in part by a reduction in pressure overload. However, this effect might also be explained by the diverse action of ANP on the cardiovascular system.

Distributed model analysis of 3'-azido-3'-deoxythymidine and 2',3'-dideoxyinosine distribution in brain tissue and cerebrospinal fluid.

The restricted distribution of 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxyinosine (DDI) in brain tissue and cerebrospinal fluid (CSF) has been analyzed using the distributed model. The distribution volume of AZT and DDI in brain tissue (V(br)) was found to be 1.07 +/- 0.09 and 0.727 +/- 0.030 ml/g brain, respectively, in an in vitro brain slice uptake study. The pharmacokinetic parameters were obtained by fitting the concentration-time profiles of AZT and DDI in brain tissue and CSF after i.v. or i.c.v. administration taking the value of V(br), the CSF bulk flow rate (2.9 microl/min), and the surface area of the cerebroventricular ependyma (2.0 cm2), using a nonlinear least squares program combined with a fast inverse Laplace transform. The efflux transport clearance (PS(BBB,eff)) across the blood-brain barrier (BBB) and the symmetrical permeability clearance (PS(BBB)) across the BBB for AZT were calculated as 179 and 10.3 microl/min/g brain, respectively. The efflux transport clearance (PS(CSF,eff)) across the blood-cerebrospinal fluid barrier (BCSFB) and the symmetrical permeability clearance (PS(CSF)) across the BCSFB for AZT were calculated as 227 and 28.3 microl/min/ml CSF, respectively. For the distribution of DDI, the PS(BBB,eff) and PS(BBB) were 79.2 and 2.03 microl/min/g brain, respectively, while the PS(CSF,eff) and PS(CSF) for DDI were 196 and 5.88 microl/min/ml CSF, respectively. Based on simulation studies using the fitted parameters, a significant degree of efflux transport across the BBB and BCSFB has been suggested to be responsible for the restricted distribution of AZT and DDI in brain tissue and CSF, respectively.

Prediction of in vivo drug disposition from in vitro data based on physiological pharmacokinetics.

Because of the increasing availability of human liver samples we now have a greater ability to predict in vivo drug disposition and pharmacokinetics in man from in vitro metabolic and binding studies. Firstly, we review several successful attempts to predict in vivo metabolic clearances in experimental animals and humans from in vitro biochemical parameters such as plasma protein binding and hepatic metabolism, based on anatomically and physiologically realistic pharmacokinetic models. Despite the success of this approach, however, there are still some difficulties in predicting in vivo hepatic metabolism in man using in vitro human liver samples due to the large inter-individual differences arising from polymorphism (intrinsic variability) or differences in enzyme activity (extrinsic variability) due to the conditions under which liver samples have been kept. We propose a possible method to overcome these errors resulting from inter-individual differences by applying the concept of a scaling factor. In the kinetic models used in prediction, we often make a number of assumptions, e.g. rapid equilibrium between the blood and hepatocytes, availability of only the unbound drug for uptake and elimination, and homogeneous distribution of enzymes along the path taken by the blood in the liver. However, recent evidence suggests that these assumptions are not necessarily valid. As examples involving the first and second assumptions, respectively, there is the plasma-membrane-permeability-limited metabolism of a high-clearance drug, 4-methylumbelliferone, and the albumin-mediated uptake of amphiphatic drugs. The multiple-indicator dilution method (MID) is useful for estimating the membrane permeability of drugs in liver perfusion systems where the spatial organization and cell polarity of the liver are maintained. If the aforementioned factors are taken into consideration and membrane permeabilities using human hepatocytes and/or subcellular fractions such as microsomes are measured under conditions close to those in vivo, much more reliable predictions of drug hepatic clearance in man may become possible.

Beneficial effects of long-term treatment with enalapril on cardiac function and heart rate variability in patients with old myocardial infarction.

BACKGROUND: The beneficial effects of the early use of angiotensin-converting enzyme inhibitors (ACEis) in patients with acute myocardial infarction (MI) are well documented. However, the effects of ACEis in patients with an old MI and preserved cardiac function have not yet been studied. We examined the effects of 12 months of enalapril treatment in patients with previous MI. METHODS AND RESULTS: Thirteen patients with an old MI and no overt congestive heart failure (CHF), aged 70 +/- 2 years, were treated with enalapril for 12 months. We also included 13 age- and sex-matched control patients who had a similar clinical background but were not treated with enalapril. Holter electrocardiography and echocardiography were performed at entry and after 12 months of treatment. Heart rate variability, low- and high-frequency powers (LF and HF), and the ratio between LF and HF (LF/HF) were analyzed. Changes from baseline to 12 months in HF, LF/HF, left ventricular end-diastolic dimension (LVEDD), and end-systolic dimension (LVESD) were significantly different in the enalapril group (HF, 8.1 +/- 0.9 to 9.3 +/- 0.9 milliseconds: LF/HF, 1.65 +/- 0.11 to 1.53 +/- 0.16; LVEDD, 57.2 +/- 1.6 to 54.7 +/- 1.6 mm; LVESD, 40.0 +/- 2.4 to 36.3 +/- 1.9 mm) compared with the control group (HF, 8.9 +/- 0.9 to 8.5 +/- 0.7 milliseconds; LF/HF, 1.78 +/- 0.18 to 1.88 +/- 0.15; LVEDD, 52.3 +/- 2.5 to 55.9 +/- 2.2 mm; LVESD, 32.5 +/- 2.6 to 36.1 +/- 2.6 mm; P < .05). The delta change (delta) in LVESD between the end and the start of study correlated inversely with deltaHF (r = -0.56; P < .05) and positively with deltaLF/HF (r = 0.65; P < .01). CONCLUSION: Our results suggest possible ongoing structural changes in patients with old MI even in the absence of overt CHF. Enalapril seemed to prevent such changes and to restore cardiac autonomic tone toward normal. Further prospective studies using a larger sample size are warranted to confirm potential beneficial effects of ACEis in patients with previous MI and preserved left ventricular function.