Plasma kinetics of tritiated d-α -tocopherol in sheep given intravenously in emulsion or ethanol

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1 Plasma kinetics of tritiated d-α -tocopherol in sheep given intravenously in emulsion or ethanol M Hidiroglou To cite this version: M Hidiroglou. Plasma kinetics of tritiated d-α -tocopherol in sheep given intravenously in emulsion or ethanol. Annales de Recherches Vétérinaires, INRA Editions, 1991, 22 (4), pp <hal > HAL Id: hal Submitted on 1 Jan 1991 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 Original article Plasma kinetics of tritiated d-α -tocopherol in sheep given intravenously in emulsion or ethanol M Hidiroglou Agriculture Canada, Animal Research Centre, Ottawa, Ontario KIA OC6, Canada (Received 13 December 1990; accepted 12 April 1991 ) Summary &horbar; Thirteen crossbred wethers were given intravenously tritiated d-a-tocopherol (2 wci/kg of bw) dissolved in emulsion or ethanol. Kinetic evaluation of the plasma specific activity versus time data was performed using either the 2- or 3-compartment model. The disappearance of the radiolabelled a-tocopherol from the plasma pool was affected by the nature of the vehicle administered. Radiotocopherol was cleared from plasma much faster when it was dissolved in ethanol than in emulsion; when radiotocopherol was injected as an emulsion concentration time curves were best described as a 2-compartment open model and in ethanol the kinetic data fitted a sum of three exponentials. The data showed higher bioavailability of the intravenously injected vitamin E in emulsion over ethanol. sheep / vitamin E / blood / vehicule / emulsion / ethanol Résumé &horbar; Cinétique plasmatique de d-a-tocophérol tritié administré par voie intraveineuse sous forme d émulsion ou dissous dans l éthanol chez le mouton. Du d-a-tocophérol tritié a été administré à 13 moutons (2 pcilkg PV) par voie intraveineuse sous forme d émulsion ou dissous dans l éthanol. La cinétique de l activité spécifique dans le plasma a été établie en utilisant un modèle bi- ou tri-compartimental. La forme sous laquelle a été administré le d-a-tocophérol tritié a influencé sa disparition de la réserve plasmatique. Le radiotocophérol a été éliminé plus vite du plasma lorsqu il était dissous dans l éthanol que lorsqu il était sous forme d émulsion. Les courbes d évolution de la concentration plasmatique étaient mieux décrites par un modèle bicompartimental ouvert quand le radiotocophérol était donné sous forme d émulsion alors que les données cinétiques correspondaient à une somme de 3 exponentielles quand le radiotocophérol injecté était dissous dans l éthanol. La vitamine E injectée par voie intraveineuse avait une plus grande biodisponibilité quand elle était sous forme d émulsion que quand elle était dissoute dans l éthanol. mouton / vitamine E / sang / excipient / émulsion / éthanol Contribution No 1712

3 INTRODUCTION At present, little is known about the absorption and disposition of vitamin E exogenously administered to sheep (Hidiroglou and Karpinski, 1987, 1988). According to Schmandke and Schmidt (1965), and Bateman and Uccelini (1984, 1985), the vehicle in which the vitamin E is dissolved dramatically affects the vitamin s uptake into the blood stream. Tokumura et al (1987) observed a difference in the bioavailability of d-a-tocopherol in dogs following the administration of this vitamin in different vehicles. In the present study, intravenous injections of tritiated-labelled tocopherol dissolved in 2 different solvents were administered to sheep and their plasma disappearance curves were compared. MATERIALS AND METHODS Animals, housing and diet Yearling crossbred wethers weighing kg were used. All animals originated from a flock born and raised in confinement. For several months before, as well as during the experiment, the animals were fed ad libitum on a single diet which consisted of grass silage (40%), hay (40%) and corn silage (20%). The sheep were placed in individual pens in a barn at controlled temperature (21 ± 1 C) and with relative humidity = 50% 10 days before dosing. A total of 13 sheep were used for this experiment. They were given intravenously tritiated d-atocopherol dissolved in emulsion (7 sheep: Group 1) or ethanol (6 sheep: Group 2). Experimental procedure Each sheep was dosed iv (2.tCi.kg- 1 bw) with d-a-[5-me- 3H]-tocopherol in emulsion in Group 1 (Hidiroglou and Karpinski, 1988) and in absolute ethanol in Group 2. Both preparation (in 1 ml) were rapidly injected via the right jugular vein. Sampling procedure Blood samples (=4 5 ml) were drawn from the left jugular vein of each wether, using disposable needles and syringes containing heparin, at various times from 0 to 56 h after the radioisotope was injected. The plasma was separated from the cellular blood components in a refrigerated centrifuge at 4 C. Materials D-a-[5-Me- 3H]-tocopherol (24 Ci/mmol) was purchased from Amersham International, Amersham, Bucks, UK. Purity was not less than 95% as determined by the supplier (thin layer chromatography). All solvents were of analytical or high-performance liquid chromatography (HPLC) grade, whereas other chemicals were high purity commercial grades. Processing of samples and counting of radioactivity Aliquots of plasma ( ) were added to 15 ml of scintillation mixture (Aquasol II, New England Nuclear, Boston, MA). Plasma radioactivities were determined in triplicate by liquid scintillation spectroscopy (LS3801 liquid scintillation spectrometer, Beckman Instruments Ltd, Palo, CA) using the external standardization method to evaluate counting efficiency (Beckman Operating Manual). Analytical procedures Quantification of vitamin E in the plasma of sheep was performed by HPLC using a fluorescence detector (McMurray and Blanchflower, 1979).

4 Mathematical analysis activity data in Group 2, where radiotocopherol intravenous injection was given in All data were fit using SAS User s Guide (1985 ) ethanol, the sum of 3 exponentials was a and the Marquardt algorithm on the logarithmic significantly better fit than the sum of 2 exscale. ponentials. These data are presented in table II. The drop-off of specific activity in the plasma was very rapid (fig 1 ). RESULTS For the two-compartment model the derived kinetic parameter estimates are given Computer modelling of the individual plas- in table III (radiotocopherol given in emulma concentration vs time data showed that sion) and those for the 3-compartment the distribution kinetic model for [3H)d-a- model are presented in table IV (radiototocopherol was variable. In Group 1, the copherol given in ethanol). The data in disappearence of plasma radiotocopherol tables III and IV were examined by a t-test given intravenously in emulsion was in a for difference between the 2 routes of adbioexponential fashion over a period of ministration. The half-lives (t!!2) in Groups 56 h. The kinetic parameters have been 1 and 2 were comparable (35 h-! vs 33 h-1). presented in table I. The plasma radioto- In the sheep dosed with the vitamin E in copherol curve displayed an initial rapid emulsion the volume of the central comdistribution (a) phase and then a slow dis- partment (VC) was higher (268 ml/kg) than appearance phase (p). The evolution of the in ethanol (164 ml/kg). There were signifispecific activities in both treatments is pre- cant differences in the transfer rate (P < sented in figure 1. For the plasma specific 0.01 ). Clearly the tracer clears out of the

5 central compartment at a much faster rate when an ethanol solution is used rather than an emulsion. If we compare area under curve (AUC) for the 2 compartment models there is a significant difference (P < 0.05). The AUC in Group 1 (emulsion) ( dpm..tg- 1.h- 1) was higher than that in Group 2 (ethanol ( dpm..tg- 1.h- 1), indicating greater availability in emulsion. DISCUSSION The mathematical models used in this study permitted a good description of the time course of radiotocopherol in the blood. In the present study, intravenous injections of radiotocopherol in different solvents were administered to sheep and the nature of the exponential plasma radiotocopherol disappearance curve compared, in an effort to identify the mechanism(s) upon which bioavailability depends. The results showed that the rate disappearance of radiolabelled a- tocopherol from the plasma pool was dependent on the nature of the vehicle administered. According to Bateman and Uccellini (1984, 1985), the vehicle in which vitamin E is dissolved dramatically affects the vitamin s uptake into the bloodstream. For Wagner (1965), the pharmacokinetic disposition of component injected iv is dependent on the vehicle used to dissolve it, and consequently, on the particle size distribution in the vehicle of the substance. Gallo-Torres and Miller (1971) reported that the rate of transfer of vitamin E from the plasma to tissues is markedly influenced by its solubility and partition coefficient between aqueous and lipid phases. Our study revealed that radiotocopherol was cleared from plasma much faster when it was dissolved in ethanol than in emulsion. When the radiotocopherol was injected in emulsion (Group 1 ) concentration-time curves were best described as a 2-compartment open model. It would appear that the plasma kinetic data in Group 2 fit a sum of 3 exponentials in a manner similar to that of the intravenous data fit in the paper published recently by Hidiroglou and Karpinski (1987), when the vehicle used was ethanol. In this open 3-compartment model

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9 (Group 2), a &dquo;shallow&dquo; and a &dquo;deep&dquo; compartment are reversibly connected to a central (plasma) compartment. The models developed provide a simple kinetic description of vitamin E absorption in sheep based on analysis of the kinetic data, when radiotocopherol is injected in emulsion or in ethanol. According to Gallo- Torres (1980) parenteral administration of commercial preparation of d-a-tocopherol in aqueous dispersions corrects the rapid decline of the free tocopherols in the blood; this also occurred with our emulsion preparation given iv in sheep (Group 1). In conclusion, this report demonstrated the usefulness of monitoring the kinetics of tocopherol administered intravenously in different dosage forms. Modelling it provided a satisfactory description of the mechanisms which regulate their distribution throughout the body by the blood and vascular network acting as a carrier system. Difference in the various kinetic parameters following intravenous (iv) administration of vitamin E dissolved in ethanol or in emulsion have implications for the parenteral supply of this vitamin in ruminants. Intravenous administration of the vitamin E in emulsion rather than in ethanol increases its bioavailability. REFERENCES Bateman NE, Uccelini DA (1984) Effect of formulation on the bioavailability of retinol d-atocopherol and riboflavine. J Pharm Pharmacol 36, Bateman NE, Uccelini DA (1985) Kinetics of d- a-tocopherol in water-soluble base in man. J Pharm P/!a/-maco/37, Gallo-Torres HE (1980) Transport and Metabolism in Vitamin E (Machlin LT, ed) Marcel Dekker, NY, Gallo-Torres HE, Miller ON (1971) Tissue uptake and metabolism of d, I-a-tocopheryl, nicotinate and d, I-a-tocopheryl-l, 2-3Hz acetate following intravenous administration. Int J Vitam Nutr Res 41, Gibaldi MD, Perrier D (1982) Pharmacokinetics. Marcel Dekker, NY Hidiroglou M, Karpinski K (1987) Vitamin E kinetics in sheep. BrJNutr58, Hidiroglou M, Karpinski K (1988) Pharmacokinetic disposition in sheep of various vitamin E preparations given orally or intravenously. Br J Nutr 59, McMurray CH, Blanchflower WJ (1979) Application of high performance fluorescence method for the rapid determination of a-tocopherol in the plasma of cattle and pigs and its comparison with direct fluorescence and high performance liquid chromatography-ultraviolet detection methods. J Chromatogr 178, SAS (1985) User s Guide. Statistics, Version 5. SAS Inc, Cary, NC Schmandke H, Schmidt G (1965) Absorption of a-tocopherol from oily and aqueous solutions.!nt J Vit Nutr Res 35, Tokumura T, Muchidu Y, Tsushima Y, Kayano M, Nagai T (1987) Intestinal absorption of tocopherol in beagle dog and effect of dosage form. Chem Pharm Bull (Tokyo) 35, Wagner IG (1965) Pharmaceutics: absorption aspects. J Pharmacol Sci 50,