Abstract
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Objectives Acute lung injury (ALI) is one of the most frequent causes of admission to medical intensive care units. Acute Respiratory Distress Syndrome (ARDS) occurs in ~250,000 patients/yr in the US and carries a mortality rate >30%, due to lack of early detection tools and limited therapies. Recent studies have demonstrated that inhaled hydrogen gas provides protection in lung injury models of human ALI (e.g. ventilation-induced injury, transplant-induced ischemia-reperfusion injury, and hyperoxic injury), due to its potent anti-inflammatory, anti-oxidant, and anti-apoptotic properties. Previously, we demonstrated the utility of 99mTc-hexamethylpropyleneamine oxime (HMPAO) and 99mTc-duramycin (DU) imaging to detect oxidative stress and endothelial cell death in rats exposed to high concentrations of O2 (hyperoxia) as a model of human ALI/ARDS. Thus, the objective of this study is to evaluate the effectiveness of 99mTc -HMPAO and -DU to track the progression of lung injury and the effectiveness of H2 therapy in the hyperoxia rat model of ALI/ARDS.
Methods Sprague-Dawley rats (300-400 g) were continuously exposed to either 98% O2 + 2% N2 (hyperoxia) or 98% O2 + 2% H2 (O2+ H2). Rats were anesthetized and studied at 24, 48, or 60 hrs of exposure using either 99mTc-DU, or 99mTc-HMPAO (37-74 MBq), before and after i.p. treatment with the glutathione-depleting agent diethyl maleate (DEM) (n蠅5 for each group). In vivo scintigraphy images were acquired 15 min post i.v. injection and lung uptake was determined from the images as mean lung activity normalized to mean forelimb blood activity. Rat body weight and volume of pleural effusion in the chest cavity were also measured as indices of injury.
Results Lung 99mTc-HMPAO and 99mTc-DU uptake increased in hyperoxia-exposed rats in a time-dependent manner, reaching a maximum increase of ~270% and 150%, respectively, at 60 hr. This increase was reduced to ~120% and 67%, respectively, in rats exposed to O2+H2. DEM-treatment reduced the increase in 99mTc-HMPAO uptake by ~70% and 50% in the 60 hr hyperoxia and O2+H2 exposed rats, respectively. Moreover, nearly all of the difference between the uptake in the hyperoxia and O2+H2 groups was in the DEM-inhibitable portion of the lung 99mTc-HMPAO uptake. The loss in body weight measured at 60 hr in the hyperoxic rats (-6.3±0.4%) was reduced significantly to -4.5±0.5% in the O2+H2 rats. Similarly pleural effusion was reduced significantly from 8.7±1.5 ml in the hyperoxic rats to 1.3±0.4 ml in the O2+H2 rats.
Conclusions Lung uptake of 99mTc-HMPAO and 99mTc-DU can be observed early in the hyperoxic injury model and increases over the 60 hr period studied. This increase is mitigated when 2% H2 is added to the gas mixture, suggesting that H2 therapy has anti-oxidant and anti-apoptotic effects that can be detected with these SPECT agents. We also demonstrated that the O2+H2 exposed rats were better able to maintain their body weight and suffered from less pleural effusion than the hyperoxic rats. Overall these results suggest the potential utility of 99mTc-HMPAO and 99mTc-DU as a tool for detecting and monitoring early ALI, and for in vivo assessment of the anti-oxidant and anti-apoptotic effects of H2 gas therapy. Research Support: Supported by NIH1R01HL116530, NIH1R15HL129209, VA Merit Review BX001681, Alvin and Marion Birnschein Foundation (AVC, ERJ, BMR, XZ, SHJ), and NIH1S10OD016398, NIH1R01CA185214 (MZ).