Eisenhut M, Lehmann W D, Hull W E, Just W W, Hoffend J, Zehelein J, Zimmermann R
Department of Nuclear Medicine, and Institute for Biochemistry I, University of Heidelberg, Germany.
J Nucl Med. 1997 Dec;38(12):1864-9.
PHIPA 3-10 [13-(4'-iodophenyl)-3-(p-phenylene)tridecanoic acid] is a p-phenylene-bridged, radioiodinated omega-phenyl fatty acid that has recently been developed to study coronary artery disease or cardiomyopathies. Here, we demonstrate that PHIPA 3-10 exhibits the characteristics of a long-chain fatty acid, including its ability to be efficiently taken up by myocytes and to function as a substrate for beta-oxidation before it is trapped.
Myocardial metabolism of carrier-added and carrier-free 131I-PHIPA 3-10 preparations were investigated in rats in vivo and in isolated Langendorff rat hearts. Heart extracts were analyzed by high-performance liquid chromatography, negative-ion electrospray mass spectrometry and investigation of intracellular distribution using density-gradient centrifugation.
A single, rapidly formed metabolite was found in the heart extract and also, surprisingly, in the hydrolyzed lipids. The total amount of metabolite increased from 43% to 51% between 15 and 60 min postinjection. By high-performance liquid chromatography comparison with synthetic potential catabolites, the metabolite was assigned the name PHIPA 1-10 [11-(4'-iodophenyl)-1-(p-phenylene)undecanoic acid] and was the product of one beta-oxidation cycle. Additional proof was obtained from the mass spectrometric analysis of the metabolite formed in vivo. The formation of this metabolite could be suppressed by Etomoxir, a carnitine palmitoyl transferase I inhibitor, indicating beta-oxidation of 131I-PHIPA 3-10 in mitochondria. Final evidence for the involvement of mitochondria in the degradation of 131I-PHIPA 3-10 was obtained by density-gradient centrifugation of homogenized rat heart tissue. The position of the labeled free PHIPA 3-10 and free metabolite peaked within the fraction containing mainly mitochondria.
In spite of its bulky structure, 131I-PHIPA 3-10 is extracted by the myocardium in a manner similar to the extraction of the unmodified fatty acid analog, IPPA. The retention of PHIPA 3-10 in heart muscle results from the presence of the p-phenylene group, which prevents more than one beta-oxidation cycle. Intracellular free PHIPA 3-10 and free PHIPA 1-10 are present in the mitochondria, whereas most of the esterified metabolite was found in the cytosolic lipid pool. Hence, the rapid appearance of PHIPA 1-10 in the lipid pool must be accounted for by mitochondrial leakage or by an unknown in-out transport system.
PHIPA 3-10 [13-(4'-碘苯基)-3-(对亚苯基)十三烷酸] 是一种对亚苯基桥连的放射性碘化ω-苯基脂肪酸，最近已被开发用于研究冠状动脉疾病或心肌病。在此，我们证明PHIPA 3-10具有长链脂肪酸的特性，包括其被心肌细胞有效摄取的能力以及在被捕获之前作为β-氧化底物的功能。
在大鼠体内和离体Langendorff大鼠心脏中研究了添加载体和未添加载体的131I-PHIPA 3-10制剂的心肌代谢。通过高效液相色谱、负离子电喷雾质谱分析心脏提取物，并使用密度梯度离心法研究细胞内分布。
在心脏提取物中以及令人惊讶的是在水解脂质中发现了一种单一的、快速形成的代谢产物。注射后15至60分钟之间，代谢产物的总量从43%增加到51%。通过与合成潜在分解代谢物的高效液相色谱比较，该代谢产物被命名为PHIPA 1-10 [11-(4'-碘苯基)-1-(对亚苯基)十一烷酸]，是一个β-氧化循环的产物。从体内形成的代谢产物的质谱分析中获得了额外的证据。肉碱棕榈酰转移酶I抑制剂依托莫昔可以抑制这种代谢产物的形成，表明131I-PHIPA 3-10在线粒体中进行β-氧化。通过对匀浆的大鼠心脏组织进行密度梯度离心，获得了线粒体参与131I-PHIPA 3-10降解的最终证据。标记的游离PHIPA 3-10和游离代谢产物的位置在主要包含线粒体的部分中达到峰值。
尽管131I-PHIPA 3-10结构庞大，但心肌对其的摄取方式与未修饰的脂肪酸类似物IPPA的摄取方式相似。PHIPA 3-10在心肌中的保留是由于对亚苯基的存在，这阻止了超过一个β-氧化循环。细胞内游离的PHIPA 3-10和游离的PHIPA 1-10存在于线粒体中，而大部分酯化代谢产物则存在于细胞质脂质池中。因此，脂质池中PHIPA 1-10的快速出现必须由线粒体渗漏或未知的进出转运系统来解释。
