Aminolaevulinic acid-induced protoporphyrin IX pharmacokinetics in central and peripheral arteries of the rat[para]

Photochemistry and Photobiology, Jul 2003 by Gabeler, Edward E E, Sluiter, Wim, van Hillegersberg, Richard, Edixhoven, Annie, Et al

Received 25 February 2003; accepted 3 April 2003

ABSTRACT

Photodynamic therapy (PDT) based on the photosensitive protoporphyrin IX (PpIX) may prevent restenosis after transluminal angioplasty. PpIX is synthesized in mitochondria, which differ in number and activity among various tissues. Therefore, we questioned whether the course of PpIX concentration after systemic aminolaevulinic acid (ALA) administration differed among various arteries. ALA was administered intravenously (200 mg/kg) to male Wistar rats (n = 21). At varying time intervals (0, 1, 2, 3, 6, 12 and 24 h) both central and peripheral arteries were isolated and homogenized, and the concentration of the various heme intermediates was determined by a fluorometric extraction method. The maximal PpIX concentration was more than two-fold higher in peripheral arteries (20.49 or - 3.0 to 24.0 or - 7.5 pmol/mg protein) than in central arteries (0-9.46 or - 0.01 pmol/mg protein) (P

Abbreviations: ALA, aminolaevulinic acid; ALA-D, ALA dehydratase; COPRO, coproporphyrin; COPROgen, coproporphyrinogen; i.v., intravenous; PBG, porphobilinogen; PBG-D, PBG deaminase; PDT, photodynamic therapy; PpIX, protoporphyrin IX; URO, uroporphyrin; UROgen, uroporphyrinogen.

INTRODUCTION

Restenosis, the chronic renarrowing of a treated stenotic artery, comprises the success rates of vascular interventions in treating symptomatic vascular disease. The incidence of this complication is between 20% and 40% within 6 months after endovascular interventions, which underlines the need for effective preventive strategies (1).

A promising tool to prevent postinterventional restenosis is vascular photodynamic therapy (PDT) using the endogenous heme intermediate protoporphyrin IX (PpIX) as the photosensitizer (2-5). To increase the synthesis of PpIX in the arterial wall, its precursor aminolaevulinic acid (ALA) is administered. Key mechanisms of ALA-PDT as an adjuvant to angioplasty are the eradication of photosensitized proliferating vascular smooth muscle cells (6) and the induction of cross-links between proteins of the sub-cellular matrix of the arterial wall (7-9).

After systemic administration, ALA is distributed to most tissues leading to PpIX production and accumulation in specific organs (10). However, no data are available on the distribution characteristics of ALA and its conversion products in the various artery types after systemic administration. Intrinsic differences between the central viscoelastic arteries and the peripheral muscular arteries could play a role in this respect. Because the products of the heme biosynthetic pathway will contribute to the photosensitization of the blood vessel, knowledge of their accumulation in the vascular wall may be of use to determine the illumination interval after ALA administration. Therefore, the aim of this study was to describe the pharmacokinetics of ALA-induced PpIX in various arteries categorized as either central (thoracic and abdominal aortas) or peripheral (carotid, renal and iliac arteries).

MATERIALS AND METHODS

Animals

Male inbred Wistar rats (Harlan CPB, Austerlitz, The Netherlands) weighing 200-300 g were used. The animals had free access to rat chow (AM II, Hope Farms, Woerden, The Netherlands) and tap water acidified to pH 4.0, while maintained in a standard 12 h light-dark cycle. The zinc content in food was 5 [mu]mol/day and in drinking water 7.2 [mu]mol/L, which is a normal daily intake.

Study design

Twenty-four rats were randomly divided into eight groups of three animals each. Each rat received intravenous (i.v.) injection of 200 mg/kg ALA (Sigma-Aldrich Chemie, Zwijndrecht, The Netherlands) dissolved in phosphate-buffered saline (pH 7.45) at 40 mg/mL and was sacrificed at 0, 1, 2, 3, 6, 12 or 24 h after administration. A control group of three rats received phosphate buffer only. The ALA solution was freshly prepared for each animal and kept away from exposure to light. The photosensitized rats were kept in the dark until sacrifice to prevent skin photocytotoxicity. The experimental protocol was approved by The Committee on Animal Research of the Erasmus University of Rotterdam and complied with Paget, G.E. (1979) Good Laboratory Practise. 204 p. Paget, G.E. (Ed). M.T.P. Press, Lancaster, UK.

Blood samples

At the end of the observation period, blood samples were collected under ether anesthesia via a cardiac puncture in plastic heparinized tubes wrapped in aluminum foil. All tubes were kept on ice. After centrifugation at 1300 g for 10 min, the plasma was collected, protected from light and stored at -70[degrees]C until use.

Arterial samples

After collecting the blood samples, all rats underwent a combined thoracotomy and medial laparotomy under ether anesthesia and subdued filtered light (acrylate yellow filter, Wientjes BV, Roden, The Netherlands) (11). Subsequently, the thoracic and abdominal aortas (central arteries) and the right renal, right common iliac and right femoral arteries (peripheral arteries) were harvested and flushed with saline, freeze dried and stored for at least 24 h in aluminum reservoirs at -70[degrees]C.