Covalent Linkage of Apolipoprotein E to Albumin Nanoparticles Strongly Enhances Drug Transport into the Brain

Drug delivery to the brain is becoming more and more important but is severely restricted by the blood-brain barrier. Nanoparticles coated with polysorbates have previously been shown to enable the transport of several drugs across the blood-brain barrier, which under normal circumstances is impermeable to these compounds. Apolipoprotein E was suggested to mediate this drug transport across the blood-brain barrier. In the present study, apolipoprotein E was coupled by chemical methods to nanoparticles made of human serum albumin (HSA-NP). Loperamide, which does not cross the blood-brain barrier but exerts antinociceptive effects after direct injection into the brain, was used as model drug. Apolipoprotein E was chemically bound via linkers to loperamide-loaded HSA-NP. This preparation induced antinociceptive effects in the tail-flick test in ICR mice after i.v. injection. In contrast, nanoparticles linked to apolipoprotein E variants that do not recognize lipoprotein receptors failed to induce these effects. These results indicate that apolipoprotein E attached to the surface of nanoparticles facilitates transport of drugs across the blood-brain barrier, probably after interaction with lipoprotein receptors on the brain capillary endothelial cell membranes.

In vivo conversion of norethisterone and norethisterone acetate to ethinyl etradiol in postmenopausal women

Previous studies with postmenopausal women receiving oral doses of norethisterone-containing preparations have shown that a small fraction of the dose is converted metabolically to ethinyl estradiol and may be detected in the peripheral blood. To investigate the extent and the dose dependence of this conversion in more detail, we performed a study with 24 postmenopausal women who received single oral doses of 5 mg norethisterone as well as 5 and 10 mg norethisterone acetate with a washout phase of 2 weeks between each treatment. After each treatment, blood was collected at regular intervals and the concentrations of norethisterone and ethinyl estradiol were analyzed in the serum samples by a specific radioimmunoassay and by gas chromatography/mass spectrometry, respectively. Ethinyl estradiol was present in the serum samples of all women following treatment with norethisterone acetate and, except for four cases, also after treatment with norethisterone. The conversion ratio of norethisterone acetate to ethinyl estradiol was 0.7 +/- 0.2% and 1.0 +/- 0.4% at doses of 5 and 10 mg, respectively. This corresponded to an oral dose equivalent of about 6 micrograms ethinyl estradiol per milligram of norethisterone acetate. For norethisterone, a conversion ratio of 0.4 +/- 0.4% was found at a dose of 5 mg, which corresponded to an oral dose equivalent of about 4 micrograms ethinyl estradiol per milligram of norethisterone. Although it cannot be excluded that in individual cases, even higher doses of ethinyl estradiol may be produced by conversion, it is concluded that at therapeutic doses of the progestogens, the exposure to metabolically derived ethinyl estradiol is probably of little clinical significance not only in fertile women using oral contraceptive combination preparations containing norethisterone and ethinyl estradiol, but also in postmenopausal women who receive oral doses of estradiol for estrogen replacement. The estrogenic effects of metabolically derived ethinyl estradiol on the liver (eg. synthesis of transport proteins) are very likely more than compensated due to the androgenic activity of norethisterone.

Quantitative determination of pentaerythrityl tetranitrate and its metabolites in human plasma by gas chromatography/mass spectrometry

Up to now, there has been no data available on the pharmacokinetics of pentaerythrityl tetranitrate (PETN, CAS 78-11-5) and its metabolites, pentaerythrityl-trinitrate (PE-tri-N), pentaerythrityl-dinitrate (PE-di-N), pentaerythrityl-mononitrate (PE-mono-N) in human plasma. Therefore, in order to determine PETN and its metabolites in plasma sensitive and highly selective GC/MS methods had to be developed and validated. PETN and its metabolite PE-tri-N were validated in the concentration range 50 pg/ml to 10 ng/ml. Isosorbide dinitrate (ISDN) was used as the internal standard and the analytes were extracted with dichloromethane from the plasma. The mass spectrometric tests were carried out using chemical ionization in the negative mode (NlCl) with the application of ammonia as a reagent gas. The nitrate ion m/z 62 was determined in the analytes and internal standard. The accuracy of the mean of the quality control samples during the three days (between days) was between 100 and 110% (PETN), as well as 90 and 106% (PE-tri-N). After an oral application of 100 mg PETN in a pilot study, unchanged PETN and PE-tri-N was measured in plasma. Both metabolites PE-di-N and PE-mono-N were validated at the concentration range of 0.25 ng/ml to 25 ng/ml plasma. After extraction, these analytes were derivatized with BSTFA (N,O-bis[trimethylsilyl]trifluoro-acetamide). The applied internal standard was isosorbide-5-mononitrate (IS-5-MN). The mass spectrometric tests were carried out in the same manner as for PETN and PE-tri-N with chemical ionization in the NlCl mode. The detected masses were m/z 324 for PE-di-N, m/z 351 for PE-mono-N and m/z 217 for IS-5-MN. The accuracy of the mean of the quality control samples during 5 days were between 104 and 107% (PE-di-N) and 102 and 106% (PE-mono-N). The maximum concentration of these analytes in the subject samples were on the average all over 5 ng/ml plasma after the oral administration of 100 mg PETN.

Bioequivalence evaluation of two preparations containing the highly variable compound selegiline (L-deprenyl)

Selegiline, used in the treatment of Parkinson's disease, inhibits the intracerebral degradation of dopamine and the uptake of catecholamines. Due to a high volume of distribution and also a high rate of biotransformation the concentrations of selegiline in plasma are rather low. In addition, there are indications that selegiline binds to erythrocytes. An open, randomized, 2-way cross-over study was performed in 24 healthy male volunteers to determine bioavailability and pharmacokinetic parameters of 2 oral selegiline preparations after single dose administration. Statistical tests were applied to the pharmacokinetic parameters AUCinf, AUC0-8, AUCz, Cmax and tmax. The terminal half-lives t1/2 for selegiline with geometric means of 1.69 h (n = 22) and 1.76 h (n = 21) for treatments A and B and for N-desmethyl-selegiline with geometric means of 1.98 h and 1.96 h for treatments A and B agreed very well. AUCinf of selegiline could be compared between treatments for 14 subjects only. The geometric mean ratio was 97.80% with a 90% confidence interval that ranged from 79.58%-120.17% and thus exceeded the (80%, 125%) range by a very small margin. After correction for the actual dose contained in each of the 2 preparations the geometric mean ratio was calculated to 98.39% with a 90% confidence interval that ranged from 80.06%-120.90% and thus was fully contained within the (80%, 125%) acceptance range. Treatments also agreed very well with respect to AUCinf of N-desmethyl-selegiline, the active metabolite of selegiline, with a geometric mean ratio of 96.14% with a 90% confidence interval that ranged from 92.41%-100.01% so that bioequivalence of the 2 treatments could be shown very clearly with respect to this metabolite. The AUC of N-desmethyl-selegiline in serum is about 6-fold higher than that of the parent drug. It is assessed with low variability. Thus, it is reasonable to base the judgement for or against bioequivalence primarily on the data obtained for the metabolite although "a larger acceptance range may be acceptable if inevitable and clinically acceptable" for the parent compound selegiline which certainly can be classified as a "highly variable compound".

Lack of a pharmacokinetic interaction between moexipril and hydrochlorothiazide

OBJECTIVE

To investigate the potential for pharmacokinetic interactions between moexipril, a new converting enzyme inhibitor, and hydrochlorothiazide after single dose administration.

METHODS

12 healthy male volunteers were studied by an open, randomised, three-way cross-over design, in which single doses of moexipril, hydrochlorothiazide and the two drugs together were administered. Blood and urine were collected up to 48 hours for measurement of the concentrations of moexipril and its metabolite moexiprilat. In addition, the urine samples were analysed for hydrochlorothiazide.

RESULTS

For the area under the plasma concentration-time curve calculated from time 0 to a concentration greater than zero, AUC(O-t), the study showed a mean value of moexipril 437 ng.ml-1.h-1 following administration of moexipril alone and 416 ng.ml-1.h-1 following moexipril concomitantly with hydrochlorothiazide. The corresponding values for the metabolite moexiprilat were 203 and 215 ng.ml-1.h-1, respectively. The Cmax of moexipril and the metabolite (data of the metabolite in parenthesis) were 245.4 (70.8) ng.ml-1 after administration of moexipril alone and 241.0 (69.2) ng.ml-1 after coadministration of hydrochlorothiazide. The mean total renal excretion (TUE) of hydrochlorothiazide was 15.2 mg when administered alone and 15.1 mg when given together with moexipril. The corresponding mean TUE-values for moexiprilat were 334 (1200) and 453 (1460) micrograms.

CONCLUSIONS

The coadministration of moexipril with hydrochlorothiazide had no demonstrable effect on the measured pharmacokinetic parameters of moexipril, its active metabolite moexiprilat or hydrochlorothiazide.

Pharmacokinetics and bioavailability of pentaerithrityl tetranitrate and two of its metabolites

Two preparations containing 100 mg pentaerithyrityl tetranitrate (PETN, CAS 78-11-5) each were administered to 24 healthy male volunteers in an open randomised two-way cross-over design. The test preparation was a commercially available 50 mg tablet (Pentalong 50 mg Tabletten, 2 tablets per dose), the reference preparation was an aqueous suspension prepared immediately before application from the same 25% PETN/lactose trituration as was used for manufacturing the tablets. Blood samples were withdrawn pre-dose and at 14 time points within 24 h after dosing. The resulting plasma was analysed by a GC/MS method developed on purpose. Since in a pilot study not a single one of 120 plasma samples contained concentrations of unchanged PETN or of its metabolite pentaerithrityl trinitrate (PE-tri-N, CAS 1607-17-6) above the quantification limit of 50 pg/ml, the samples of this study were assayed for the metabolites pentaerithrityl dinitrate (PE-di-N, CAS 1607-01-8) and pentaerithrityl mononitrate (PE-mono-N, CAS 1607-00-7) only. -Mean peak levels of 17 ng/ml and 7.5 ng/ml PE-di-N were reached ca. 3 h after application of tablets or trituration. The plasma elimination half-life was 4-5 h. Average maximum PE-mono-N levels of 79 ng/ml (tablets) and 35 ng/ml (trituration) were observed at 7 h p. appl. They declined with a half-life of 10-11 h. The relative bioavailability of the tablets as determined by means of the AUC of PE-di-N is 280-290%. This high value is explained by the specific properties of drug liberation and dissolution from the preparations used.

Steady state investigation of possible pharmacokinetic interactions of moxonidine and glibenclamide

The aim of the study presented here was to determine possible pharmacokinetic interactions of moxonidine and glibenclamide at steady state in 18 healthy male volunteers. Multiple oral doses of 0.2 mg of moxonidine b.i.d. (q. 12 h) and of 2.5 mg of glibenclamide o.i.d. (q. 24 h) were administered alone and in combination in an open, non-randomized, three-treatment design. The preparations were given for 5 days in each of the 3 periods. The results of this multiple dose study did not indicate substantial pharmacokinetic interactions of the drugs. Regarding the influence of glibenclamide on the pharmacokinetics of moxonidine, no significant changes were seen at all. In the presence of moxonidine, a minor decrease of bioavailability of glibenclamide was detectable, as could be derived from the AUC and clearance data. The actual differences were small and not considered to be of clinical significance.

Radioimmunological analysis of ethinylestradiol in human serum. Validation of the method and comparison with a gas chromatographic/mass spectrometric assay

The majority of combination oral contraceptives contain ethinylestradiol (EE2, CAS 57-63-6) as estrogenic component at doses between 50 and 20 micrograms/unit. Since the concentrations of EE2 in the serum of women under oral contraceptive (OC) therapy are in the lower pg-range, highly sensitive and specific analytical methods are required. Radioimmunoassay (RIA) has been the method of choice, but evidence of specificity in the presence of the coadministered progestogens and their metabolites has not always been provided. The present study compares two radioimmunological methods, which use the same antiserum but different sample volumes and standard curves (extracted vs. non-extracted), with a newly developed gas chromatographic/mass spectrometric (GC/MS) method, in order to cross-validate the methods. For that purpose, 51 serum samples obtained from women who had been taking two different combination oral contraceptives were analysed independently by all three methods. The specificity of the antiserum was further examined by submitting ex vivo serum samples obtained from OC-users to a combination of high pressure liquid chromatography (HPLC) and RIA. The results obtained by the three methods were very similar and correlation coefficients (r) obtained from linear regression analysis were about 0.7. There was no interference from the coadministered progestins on the analysis of EE2 as carried out by the three methods. There were no metabolites in the extracts of ex vivo serum samples which showed cross-reactivity with the antiserum used. Modifications of the radioimmunoassay procedure did not markedly affect the results of EE2 determination. If properly validated, radioimmunoassay can be used as an alternative to GC/MS in pharmacokinetic studies.

Influence of food on the oral bioavailability of moxonidine

Moxonidine is a new centrally acting anti-hypertensive with a very low adverse drug reaction profile. Among others, the aim of the study presented here was to determine the influence of food on the pharmacokinetics of moxonidine. Single oral moxonidine doses of 0.2 mg fasting and 0.2 mg non-fasting were administered in a randomized cross-over study. Eighteen subjects participated in the study, all of whom completed the study according to the protocol. Three sets of analytical plasma data could not be evaluated pharmacokinetically giving a total number of 15 evaluable cases. Renal excretion was evaluated for all 18 subjects. Food intake had no influence on the pharmacokinetics of moxonidine. The relative bioavailability of moxonidine administered under non-fasting conditions reached 94% of the bioavailability after fasted administration. Food intake resulted in a slight decrease of Cmax and a minimal increase of tmax as compared to the fasted treatment. The absorption half-life t1/2a showed a minor prolongation. These differences were not statistically significant in any of the parameters. For t1/2 lambda 2, CLtot and Ae(24h) no statistically significant differences were found between the fasting and non-fasting treatment. The amount of moxonidine excreted unchanged in urine accounted for about 46% of the dose administered after both treatments.

Absolute bioavailability of moxonidine

In a randomized 2-way cross-over study with eighteen healthy male volunteers, two moxonidine preparations (tablets, treatment A vs. intravenous solution, treatment B) were tested to investigate absolute bioavailability and pharmacokinetics of moxonidine. The preparations were administered as single doses of 0.2 mg; prior to and up to 24 h after administration blood samples were collected and the plasma moxonidine concentrations determined. Urine samples were collected prior to and at scheduled intervals up to 24 h after administration for the determination of unchanged moxonidine. Moxonidine plasma and urine concentrations were determined by a validated gas chromatographic/mass spectrometric method with negative ion chemical ionization. The mean areas under the plasma concentration/time curves were calculated as [mean +/- standard deviation] 3438 +/- 962 pg.h/ml (AUC(0----Tlast)) and 3674 +/- 1009 pg.h/ml (AUC(0----infinity)) for treatment A; 3855 +/- 1157 pg.h/ml (AUC(0----Tlast)) and 4198 +/- 1205 pg.h/ml (AUC(0----infinity)) for treatment B. Mean peak plasma concentrations of 1495 +/- 646 pg/ml were attained at 0.56 +/- 0.28 h after oral treatment, mean peak plasma concentrations after intravenous treatment reached 3965 +/- 1342 pg/ml at 0.17 +/- 0.01 h (= coinciding with end of infusion). The mean terminal half-lives of moxonidine were derived as 1.98 h after administration of the tablet and as 2.18 h after infusion. The amounts of moxonidine excreted in urine during the 24 h following administration (Ae(24h)) in absolute figures and as percentage of the dose administered were 102 +/- 26 micrograms or 51 +/- 13% for the tablet and 122 +/- 33 micrograms or 61 +/- 16% for the infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidermal Langerhans' cell densities influence survival in mycosis fungoides and Sézary syndrome

Because Langerhans' cells (LC) (CD1a-positive epidermal cells) have been discussed to be involved in the pathogenesis of mycosis fungoides and Sézary syndrome, the authors examined the influence of densities of Langerhans' cells and, concurrently, of other phenotypes retrospectively on survival of 35 patients. Cell densities were assessed on cryostat sections (alkaline phosphatase antialkaline phosphatase-technique) of the respective diagnostic biopsy specimens. Additionally, two clinical parameters (age, stage of disease) were evaluated. CD1a-positive epidermal cells were demonstrated to be the only cell population being significantly associated (P = 0.011) with survival. Death resulting from mycosis fungoides and Sézary syndrome was significantly (P = 0.003) less frequent in patients with epidermal CD1a-positive cell densities higher than 90 cells/mm2 (optimal break point) as compared with patients with lower numbers. These results suggest that Langerhans' cells have a significant impact on prognosis of patients with mycosis fungoides and Sézary syndrome. They play an important role in the host defense mechanisms against these lymphomas rather than to favor their progression as proposed recently.

P2-purinergic agonists stimulate phosphodiesteratic cleavage of phosphatidylcholine in endothelial cells. Evidence for activation of phospholipase D

The effects of purinergic agonists on phosphatidylcholine (PC) breakdown and prostacyclin synthesis were investigated in cultured bovine pulmonary artery endothelial cells (BPAEC) prelabeled with [3H]choline and [14C]myristic acid. Both labels were selectively incorporated into PC. In BPAEC prelabeled with [3H]choline, ATP stimulated a rapid 5-fold increase in intracellular free [3H]choline. [3H]Choline formation was associated with a concomitant loss of 3H from PC, and it was not preceded by an increase in the 3H content of other PC degradation products. In BPAEC prelabeled with [14C]myristic acid, ATP stimulated a rapid increase in [14C]phosphatidic acid and [14C]diacylglycerol. These changes were associated with a loss of 14C from PC but not from phosphatidylinositol. In permeabilized BPAEC prelabeled with [3H]choline, ATP and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) stimulated an increase in [3H]choline but not [3H]phosphocholine. The effects of ATP and GTP gamma S were synergistic at low GTP gamma S concentrations. Permeabilized BPAEC did not convert exogenous [3H]phosphocholine to [3H]choline. These data are consistent with the notion that purinergic agonists stimulate PC breakdown by a phospholipase D mechanism. This suggestion was supported by the observation that in the presence of ethanol, ATP stimulated the formation of [14C]phosphatidylethanol in BPAEC prelabeled with [14C]myristic acid. Several adenine nucleotides and related purine derivatives were compared for their effectiveness in stimulating PC breakdown and prostacyclin synthesis. The chemical specificity observed for the two responses indicated that both were mediated by the P2Y purinoceptor subtype. PC breakdown stimulated by ATP occurred prior to the maximum rate of release of prostacyclin into the medium. Taken together these data indicate that PC breakdown in endothelial cells stimulated with purinergic agonists is due, at least in part, to the activation of a phospholipase D that is coupled to purinoceptors by a guanine nucleotide-binding protein. In conjunction with previous data on the effects of bradykinin, these findings suggest an important role for PC breakdown in the mechanism of signal transduction in endothelial cells stimulated with Ca2+-mobilizing agonists.

Determination of nitrates in plasma

Because of the high efficacy of existing nitrates, alternative dosage formulations have been developed rather than new compounds. These new formulations challenge the analyst to develop analytical methods with lower sensitivity and higher precision. Isosorbide dinitrate is analysed in the presence of its major metabolites isosorbide 2-mononitrate and isosorbide 5-mononitrate. The present method is an improvement over previously published methods. It is not possible to analyse glyceryl trinitrate and its major metabolites 1,2-glyceryl dinitrate and 1,3-glyceryl dinitrate with the necessary sensitivity in one chromatogram. A 2-step procedure is therefore applied. The extraction procedures, the gas chromatographic conditions, imprecision and inaccuracy of the methods, the lower limits of quantitation, sample chromatograms and applications of all methods are described in detail. Thus, the possibilities of modern analytical methods in the determination of nitrates in the lower picogram region are demonstrated.

Pharmacokinetic evaluations with highly sophisticated analytical methods

26 patients, aged between 53 and 72 years, with chronic myocardial insufficiency of different degrees, proved radiologically by an enlargement of the heart and a mean reduction of left ventricular ejection fraction by more than 50%, were subjected to 4 weeks of treatment with 3 x 60 drops/day Miroton, (Chemische) Werke Minden GmbH), a cardioactive glycoside mixture, following a washout phase of 4 weeks. The effect on end-diastolic volume (EDV) and left ventricular ejection fraction (LVEF) was recorded and calculated by ECG-triggered radionuclide angiography both before, and after 2 and 4 weeks of medication with Miroton. On therapy with Miroton the EDV decreased by 4% after 14 days and by 18% after 4 weeks (compared to the baseline value of 126.8 ml). In contrast to this, the LVEF increased to 47.2% after 14 days and to 56% after 4 weeks (baseline value 43.7%). The inverse relation between EDV and LVEF shows a positive inotropic influence on the myocardium which was more pronounced in the last 2 weeks of treatment than in the first 2 weeks.

Relative bioavailability of two spray formulations of nitroglycerin

Twelve healthy male volunteers received two sublingual doses of 0.4-mg nitroglycerin from two metered-dose spray products, A and B. Plasma samples were collected immediately before and for up to 6 h following each dose. The samples were immediately extracted and analyzed for nitroglycerin. The results show striking differences between the two formulations. The mean AUC for preparation A, 159 +/- 66 h X pg/mL, was 2.7 times greater than for B, 59 +/- 33 h X pg/mL. The mean maximum plasma concentration for A was 1387 +/- 620 pg/mL which was 4.1 times greater than the mean maximum plasma concentration for preparation B (340 +/- 234 pg/mL). The time of maximum plasma concentration also occurred earlier for preparation A versus B, 4.3 +/- 1.6 versus 8.3 +/- 2.0 min, respectively. Such bioavailability differences may indicate therapeutic advantages for preparation A.