99MTc-Hexamethylpropyleneamine Oxime Imaging for Early Detection of Acute Lung Injury in Rats Exposed to Hyperoxia or Lipopolysaccharide Treatment

Abstract

99mTc-Hexamethylpropyleneamine oxime (HMPAO) is a clinical single-photon emission computed tomography biomarker of tissue oxidoreductive state. Our objective was to investigate whether HMPAO lung uptake can serve as a pre-clinical marker of lung injury in two well-established rat models of human acute lung injury (ALI). Rats were exposed to >95% O2 (hyperoxia) or treated with intratracheal lipopolysaccharide (LPS), with first endpoints obtained 24 hours later. HMPAO was administered intravenously before and after treatment with the glutathione-depleting agent diethyl maleate (DEM), scintigraphy images were acquired, and HMPAO lung uptake was quantified from the images. We also measured breathing rates, heart rates, oxygen saturation, bronchoalveolar lavage (BAL) cell counts and protein, lung homogenate glutathione (GSH) content, and pulmonary vascular endothelial filtration coefficient (Kf). For hyperoxia rats, HMPAO lung uptake increased after 24 hours (134%) and 48 hours (172%) of exposure. For LPS-treated rats, HMPAO lung uptake increased (188%) 24 hours after injury and fell with resolution of injury. DEM reduced HMPAO uptake in hyperoxia and LPS rats by a greater fraction than in normoxia rats. Both hyperoxia exposure (18%) and LPS treatment (26%) increased lung homogenate GSH content, which correlated strongly with HMPAO uptake. Neither of the treatments had an effect on Kf at 24 hours. LPS-treated rats appeared healthy but exhibited mild tachypnea, BAL and histological evidence of inflammation, and increased wet and dry lung weights. These results suggest the potential utility of HMPAO as a tool for detecting ALI at a phase likely to exhibit minimal clinical evidence of injury.

Protection by Inhaled Hydrogen Therapy in a Rat Model of Acute Lung Injury can be Tracked in vivo Using Molecular Imaging

“…For hyperoxia studies, age- and weight-matched rats (341±3 g, n = 77) were housed in a Plexiglass chamber and exposed to 98% O 2 + 2% N 2 (pure oxygen mixed with air) for 24 hrs, 48 hrs, or 60 hrs as previously described (12). To evaluate the therapeutic effect of 2% H 2 , age-matched rats (344±3 g, n = 62) were housed similarly but exposed to 98% O 2 + 2% H 2 (Praxair Inc., Danbury, CT) for 24 hrs, 48 hrs, or 60 hrs.…”

“…Heart and lungs from a randomly selected subset of each group of rats were isolated as previously described (12). The lungs were dissected free of the heart, trachea and mainstem bronchi and total lung wet weight was obtained.…”

“…The lungs were dissected free of the heart, trachea and mainstem bronchi and total lung wet weight was obtained. The left lung lobe was weighed and dried at 60°C for wet-to-dry weight ratio and the remaining lung lobes were used for the histological studies described below (12). …”

“…The trachea was cannulated, the chest opened, and the heart and lungs were removed from the thoracic cavity. The lungs were infused through the trachea with 3 ml of ice-cold, Ca 2+ -free phosphate-buffered saline ex vivo (12). The solution was withdrawn and saved for analysis.…”

“…Furthermore, we identified a strong correlation between 99m Tc-HMPAO uptake and glutathione tissue content (12), as an indicator of oxidative stress, and between 99m Tc-duramycin uptake and cleaved-caspase 3 as a marker of apoptosis (11,14). The objective of this study was to evaluate the potential utility of 99m Tc-HMPAO and 99m Tc-duramycin to track the effectiveness of H 2 therapy in vivo in the hyperoxia rat model of human ALI/ARDS.…”