In this study, we aimed to determine whether the plasma levels of glycocalyx components are indicative of influenza A (H1N1) severity. We found that SDC-1, HS, and HA levels were significantly higher in patients with severe influenza A (H1N1) than in patients with mild disease. In addition, the severity of endothelial glycocalyx shedding was closely associated with disease severity, and facilitated the identification of patients with severe influenza A (H1N1). Furthermore, we found that the level of SDC-1 was an independent risk factor for mortality among patients with influenza A (H1N1). To our knowledge, this study is the first to compare plasma glycocalyx components in patients with mild and severe influenza A (H1N1).
Pandemic 2009 influenza A (H1N1) viral infections continue to be a public health threat . Influenza A (H1N1)-infected patients most often have a mild clinical course; only 6–31% of hospitalized patients with influenza A require treatment in the ICU [19–21]. However, this study observed a higher proportion (71.7%) of hospitalized patients with influenza A (H1N1) requiring treatment in the ICU. We considered that a large number of patients with mild influenza A (H1N1) received oseltamivir in the early stages of upper respiratory tract infection, thus reducing the positive rate of influenza A (H1N1) virus testing, and the inclusion of patients with mild influenza A (H1N1). In this study, the proportion of patients with a history of smoking and chest pain was significantly higher in the severe group than in the mild group. Furthermore, we found that approximately 21% of patients with severe H1N1 had no underlying disease. Several studies have found that both young subjects and adults may develop a severe clinical course of H1N1 infection without having any known risk factors [19, 22]. The underlying pathogenic mechanisms have not been fully elucidated. In the ICU, patients with influenza A (H1N1) often present with viral pneumonia, severe hypoxemic respiratory failure, and ARDS. Currently, treatment for patients with severe influenza A (H1N1) is limited to antiviral drugs and symptomatic treatment, and which mainly consists of the optimization of oxygen supply and transfer through ventilation.
The severity of influenza A has been attributed to a systemic and inflammatory process that damages not only the lungs, but also multiple organs, including the central nervous system and cardiovascular disease [23, 24]. In our study, we found that patients with severe influenza A (H1N1) had increased levels of ALT, AST, and D-dimer, indicating injuries to multiple organs, including the liver, and coagulation disorders. This systemic form of influenza A may be due to inflammation and vascular endothelial cell injury . The cytokine storms caused by influenza have been associated with proinflammatory response disorder, which may lead to significant immunosuppression and poor prognosis [5, 26, 27]. The levels of pro-inflammatory cytokines are closely related to outcomes in patients with severe influenza infections [26–28]. This is consistent with our observation of significantly higher levels of inflammatory cytokines (IL-6 and IL-10) in non-survivors compared to survivors.
The levels of endothelial glycocalyx components, including SDC-1, HS, and HA, are useful biomarkers for sepsis [14, 15], ARDS [12, 16], and COVID-19 [13, 29]. Further, the APACHE II and SOFA scores may be used to assess the risk of death in critically ill patients, regardless of the primary disease. We found that plasma levels of SDC-1 and HA were significantly higher in patients with severe H1N1 than in patients with mild H1N1, and were positively correlated with the APACHE II and SOFA scores. Furthermore, at a cutoff point of > 173.9 ng/ml, SDC-1 showed a specificity of 81.3% and sensitivity of 70.3% for predicting 28-day mortality. Thus, SDC-1 is a simple and reliable predictor of severity and mortality among hospitalized patients with influenza A (H1N1).
The importance of platelets in the regulation of hemostasis and blood coagulation is well-known. Chappell et al. reported that protection of glycocalyx shedding reduces platelet adhesion in ischemia/reperfusion injury . In addition, Fraser et al. reported that endothelial glycocalyx degradation in critically ill COVID-19 patients had implications for microvascular platelet aggregation . We previously found that increasing levels of SDC-1 can be used as a biomarker for predicting DIC development with sepsis , and that non-anticoagulant heparin can improve coagulation by inhibiting the activity of heparinase and reducing the shedding of glycocalyx in sepsis rats . In the present study, we found that the levels of SDC-1 and HA were negatively correlated with the platelet count in patients with influenza A (H1N1). It is well known that a sharp increase in D-dimer, a secondary fibrinolytic specific molecular marker, typically indicates the existence of a thrombus. Wang reported that abnormally increased D-dimer at the preliminary diagnosis is a general predictor of respiratory failure or even ARDS in patients with 2009 novel influenza A (H1N1) . Our study found that the D-dimer level was significantly higher in non-survivors than in survivors, and was positively correlated with SDC-1 and HA levels.
Albumin has multiple biological activities including antioxidant effects, and maintains vessel wall integrity. Although albumin has a net negative charge, its amphoteric nature promotes tight binding to the glycocalyx, with the net effects of reducing hydraulic conductivity across the vascular barrier, resisting glycocalyx degradation (i.e., protecting against shedding), and contributing to the maintenance of vascular integrity and normal capillary permeability [34, 35]. In this study, we observed a significant negative correlation (r = -0.639) between the plasma albumin level and SDC-1 level. Although reduced albumin was not identified as an independent risk factor for disease development in the multivariate logistic regression analysis, there was a strong correlation between the albumin level and glycocalyx function.
Our study has several limitations. First, this study was conducted at a single center and involved a relatively small number of patients with influenza A (H1N1); our findings require large-scale clinical validation in order to be generalized. Therefore, our data should be interpreted with caution. Second, the data presented here were based on single time-point measurements and were not consecutive. Although decreased SDC-1 was observed to be an independent risk factor for 28-day mortality in patients with influenza A (H1N1), the dynamic change was unknown, and the predictive value needs further evaluation. Despite the above limitations, we believe that our study has yielded important and novel findings regarding the prediction of mortality in hospitalized patients with influenza A (H1N1).