Given the effects of AngP-2 upon lung endothelial tissue models, we evaluated relationships between plasma AngP-2 and evolving pulmonary pathophysiology as measured by spirometry. Notably, FEV1, expressed as percent predicted normal, correlated inversely and strongly with plasma AngP-2 concentrations (Spearman r = −0.78, P < 0.0001; Fig. 5). To further assess the relationships between AngP-2 and FEV1, we performed separate correlation analyses for each time point. We found that AngP-2 correlated inversely with FEV1 at baseline (Spearman r = −0. 72, P = 0.006) and penultimate (r = −0.61, P = 0.05) time points. We note that five subjects refused spirometry on the last day of HDIL-2, and thus their data were not available for this analysis. In the remaining subjects with last-day values, the correlation between AngP-2 and FEV1 fell short of significance (r = −0.43, P = 0.35). The mean plasma concentration of AngP-2 on the last day of HDIL-2 was higher in subjects who refused spirometry (22.0 [SD, 5.9]) ng/mL than in subjects who completed spirometry (14.6 [SD, 4.8 ng/mL]; P = 0.03, data not shown), suggesting that missing spirometry data are from the sickest subjects.
In this cohort of human subjects, we demonstrate that plasma AngP-2 concentrations increase throughout HDIL-2. More so, levels of AngP-2 correlate with systemic illness including inflammation, shock, and multiorgan failure. Our most interesting finding is that rising plasma AngP-2 concentrations correlate with the evolution of pulmonary pathophysiology.
Our findings have implications well beyond that of cancer therapy. Many aspects of HDIL-2 are indistinguishable from sepsis. The incidence of shock and acute renal failure in our subjects resembles reports of severe sepsis and early lung injury (3, 21). Our study provides further biochemical evidence of similar systemic inflammation during both HDIL-2 and sepsis. Specifically, both plasma IL-6 (22, 23) and AngP-2 (8, 24) concentrations during HDIL-2 are comparable to clinical studies of sepsis and ALI. Previous studies have demonstrated that AngP-2 levels were elevated in children with septic shock (25), as well as surgical patients with ARDS (26). The same study additionally demonstrated a correlation between mortality and the plasma AngP-2 concentration on the day clinical criteria for ARDS were met. More recently, studies showed that early increases in plasma AngP-2 in septic subjects predicted (a) the subsequent development of ALI subjects without lung injury present on admission (9) and (b) mortality (10). These studies enrolled subjects in the emergency room, arguably as early as possible during clinical sepsis. Thus, we know little regarding the events that led up to a rise in AngP-2 during clinical systemic inflammation. Our study provides the first clinical data to demonstrate the initiation of systemic inflammation that leads to simultaneous expression of AngP-2 and progressive organ injury.
Myriad preclinical models of sepsis demonstrate efficacy of innovative therapies that subsequently fail to improve patient outcomes, suggesting that such models do not fully recapitulate the clinical syndrome (27). In fact, a recent study demonstrated that acute inflammatory stresses from different etiologies result in highly similar responses in humans, while corresponding mouse model responses correlate poorly with the human conditions. This urges a higher priority for studies of complex human conditions rather than murine models (28). However, clinical investigations of sepsis are also challenged as heterogeneity of both subject populations, and timings of interventions make it difficult to find a signal and to identify appropriate and comparable time points for evaluation. Furthermore, unlike preclinical models, clinical investigations of sepsis are unable to capture a time 0 of systemic inflammation and thus may not be able to fully elucidate pathways that occur before organ injury occurs. Accordingly, both preclinical models and clinical investigations of sepsis face significant challenges to further our understanding of the pathogenesis of acute organ failure during sepsis.
Our results suggest that HDIL-2 may provide an important system in which to investigate the early pathogenesis of organ failure. Subjects who underwent HDIL-2 constitute a clinical population that (a) limits comorbidities that confound clinical investigations of sepsis, (b) progresses from time 0 to fulminant SIRS, and (c) demonstrates significant organ injury with direct relevance to clinical sepsis. Thus, HDIL-2 provides a unique model to detect the evolving relationships between effector molecules of systemic inflammation, such as AngP-2, and their roles in the pathogenesis of organ failure during clinical SIRS.
Previously, authors have proposed AngP-2 as a therapeutic target to prevent organ failure (29). Clinical investigations of HDIL-2 offer the potential to identify biochemical processes before secretion of AngP-2 is increased and thus identify additional targets to decrease AngP-2. Interleukin 2 directly stimulates endothelial cell secretion of AngP-2 without the circulating immune cells responsible for antitumor effects (20, 30). Because the therapeutic and injury pathways are likely distinct, studies aimed at decreasing AngP-2 may benefit treatment for renal cell carcinoma and melanoma. Such studies, performed during clinical SIRS from HDIL-2, may also serve to improve the outcomes of clinical sepsis.
Our study does have limitations. First we enrolled only a small number of subjects, as a limited number of patients are eligible for HDIL-2, given its indications and potential for toxicity (31). Next, cancer patients may display different responses to inflammation. This seems unlikely given the aforementioned similarities between our measures of AngP-2 and previous studies. Another limitation is that we elected to measure AngP-2 at only three time points. These were carefully selected in an attempt to provide the most informative evaluation of the progression of lung injury. In so doing, we demonstrated that AngP-2 continued to rise in the last 2 days of HDIL-2. This finding is also supported clinically, as most of our subjects had escalating multiorgan failure on their last day of HDIL-2 administration, consistent with systemic vascular leak syndrome.
We note that none of our subjects required supplemental oxygen, thus would not meet clinical definitions of mild acute respiratory distress syndrome (ARDS). However, noncardiogenic pulmonary edema during HDIL-2 is well documented and noted to be sudden and at times lethal, leading to a change in practice patterns to prevent fulminant ARDS (31). Furthermore, animal models demonstrate significant progression of lung injury even before gas exchange abnormalities (32). Thus, it seems likely that our subjects experienced the precursors of the clinical phenotype of ARDS.
An important limitation is that we did not directly measure lung injury; rather, we assume that decreasing FEV1 represents noncardiogenic pulmonary edema. Chest radiographs are not routinely ordered during HDIL-2. When chest radiographs are ordered, pulmonary edema is commonly found late in HDIL-2 (33), yet this imaging modality may not be sufficiently sensitive to detect the early phases of lung injury (34). Because IL-2 causes inflammation, acute bronchoconstriction is a possibility. However, FEV1 and FVC decreased in parallel with an unchanged FEV1/FVC ratio, consistent with an evolving restrictive process. This supports our belief that decreasing FEV1 in HDIL-2 patients is secondary to pulmonary edema. Certainly, the utility of FEV1 as a surrogate marker of lung injury in this population as well as further studies looking into the physiology underlying the decrease in FEV1 seen in HDIL-2 could be explored.
Plasma AngP-2 concentrations increase during HDIL-2 administration and correlate with clinical evolution of organ failure. High-dose IL-2 may serve as a clinical model of early sepsis and evolving ALI. Further investigations of the events and mechanisms leading to AngP-2 secretion may be beneficial to HDIL-2 as well as patients with sepsis.
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