Medina Rodolfo A, Mariotti Erika, Pavlovic Davor, Shaw Karen P, Eykyn Thomas R, Blower Philip J, Southworth Richard
Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom; and.
Centre for Cardiovascular Sciences, School of Clinical and Experimental Medicine, University of Birmingham, Birmingham, United Kingdom.
J Nucl Med. 2015 Jun;56(6):921-6. doi: 10.2967/jnumed.114.148353. Epub 2015 Apr 16.
The subtle hypoxia underlying chronic cardiovascular disease is an attractive target for PET imaging, but the lead hypoxia imaging agents (64)Cu-2,3-butanedione bis(N4-methylthiosemicarbazone) (ATSM) and (18)F-fluoromisonidazole are trapped only at extreme levels of hypoxia and hence are insufficiently sensitive for this purpose. We have therefore sought an analog of (64)Cu-ATSM better suited to identify compromised but salvageable myocardium, and we validated it using parallel biomarkers of cardiac energetics comparable to those observed in chronic cardiac ischemic syndromes.
Rat hearts were perfused with aerobic buffer for 20 min, followed by a range of hypoxic buffers (using a computer-controlled gas mixer) for 45 min. Contractility was monitored by intraventricular balloon, energetics by (31)P nuclear MR spectroscopy, lactate and creatine kinase release spectrophotometrically, and hypoxia-inducible factor 1-α by Western blotting.
We identified a key hypoxia threshold at a 30% buffer O2 saturation that induces a stable and potentially survivable functional and energetic compromise: left ventricular developed pressure was depressed by 20%, and cardiac phosphocreatine was depleted by 65.5% ± 14% (P < 0.05 vs. control), but adenosine triphosphate levels were maintained. Lactate release was elevated (0.21 ± 0.067 mmol/L/min vs. 0.056 ± 0.01 mmol/L/min, P < 0.05) but not maximal (0.46 ± 0.117 mmol/L/min), indicating residual oxidative metabolic capacity. Hypoxia-inducible factor 1-α was elevated but not maximal. At this key threshold, (64)Cu-2,3-pentanedione bis(thiosemicarbazone) (CTS) selectively deposited significantly more (64)Cu than any other tracer we examined (61.8% ± 9.6% injected dose vs. 29.4% ± 9.5% for (64)Cu-ATSM, P < 0.05).
The hypoxic threshold that induced survivable metabolic and functional compromise was 30% O2. At this threshold, only (64)Cu-CTS delivered a hypoxic-to-normoxic contrast of 3:1, and it therefore warrants in vivo evaluation for imaging chronic cardiac ischemic syndromes.
慢性心血管疾病潜在的轻微缺氧是正电子发射断层显像（PET）成像的一个有吸引力的靶点，但主要的缺氧显像剂64Cu-2,3-丁二酮双（N4-甲基硫代半卡巴腙）（ATSM）和18F-氟米索硝唑仅在极度缺氧水平时才会滞留，因此对该目的而言敏感性不足。因此，我们寻找了一种更适合识别受损但可挽救心肌的64Cu-ATSM类似物，并使用与慢性心脏缺血综合征中观察到的类似的心脏能量代谢平行生物标志物对其进行了验证。
用有氧缓冲液灌注大鼠心脏20分钟，然后使用一系列缺氧缓冲液（通过计算机控制的气体混合器）灌注45分钟。通过心室内球囊监测收缩性，通过31P核磁共振波谱监测能量代谢，通过分光光度法监测乳酸和肌酸激酶释放，通过蛋白质印迹法监测缺氧诱导因子1-α。
我们确定在缓冲液氧饱和度为30%时存在一个关键的缺氧阈值，该阈值会导致稳定且可能可存活的功能和能量代谢受损：左心室舒张末压降低20%，心脏磷酸肌酸消耗65.5%±14%（与对照组相比，P<0.05），但三磷酸腺苷水平维持不变。乳酸释放升高（0.21±0.067毫摩尔/升/分钟对0.056±0.01毫摩尔/升/分钟，P<0.05）但未达到最大值（0.46±0.117毫摩尔/升/分钟），表明存在残余氧化代谢能力。缺氧诱导因子1-α升高但未达到最大值。在这个关键阈值时，64Cu-2,3-戊二酮双（硫代半卡巴腙）（CTS）选择性沉积的64Cu比我们检测的任何其他示踪剂都显著更多（注入剂量的61.8%±9.6%对64Cu-ATSM的29.4%±9.5%，P<0.05）。
诱导可存活代谢和功能受损的缺氧阈值为30%氧气。在此阈值下，只有64Cu-CTS产生的缺氧与正常氧的对比度为3:1，因此它值得进行体内评估以成像慢性心脏缺血综合征。
