Endothelial Glycocalyx Integrity as a Prognostic Key in Sepsis: New Insights from the CLOVERS Trial

Sepsis remains one of the leading causes of mortality in critical care medicine, and its complex pathophysiology continues to challenge our therapeutic paradigms (1). Over the past 2 decades, interest in the role of the endothelium in sepsis has grown exponentially, particularly in a highly specialized and vulnerable structure: the endothelial glycocalyx (2). This glycoprotein-rich matrix, located on the luminal surface of endothelial cells, plays essential roles in regulating vascular permeability, inflammatory responses, hemostasis, and microvascular perfusion (3, 4). Its disruption not only facilitates fluid extravasation and immunothrombotic activation but also appears to precede the multiorgan dysfunction that characterizes septic shock (5).

Despite its biological relevance, the clinical translation of glycocalyx injury has been limited by the lack of evidence from controlled trials. In this issue of AnnalsATS (pp. 1382–1393), Oshima and colleagues make a significant contribution to our understanding of glycocalyx alterations in patients with sepsis, as part of a secondary analysis of the crystalloid liberal or vasopressors early resuscitation in sepsis (CLOVERS) trial (6). By incorporating precise measurements of plasma biomarkers of endothelial injury within the framework of a multicenter randomized controlled trial, the authors successfully bridge endothelial biology with hard clinical outcomes, including 90-day mortality.

The primary strength of the analysis led by Oshima and colleagues lies in its methodological anchoring within a multicenter clinical trial. CLOVERS evaluated divergent resuscitation strategies in sepsis (liberal vs. restrictive), based on early randomization and a clear therapeutic separation. Second, the combined use of heparan sulfate (via mass spectrometry) and syndecan-1 (via enzyme-linked immunosorbent assay) enhances the spectrum of endothelial injury assessment. Heparan sulfate provides high analytical precision and serves as a biomarker of endothelial activation, whereas syndecan-1 is clinically accessible and reflects specific degradation of the endothelial glycocalyx. The use of an enriched sampling strategy—including all 90-day deaths, early cases of acute respiratory distress syndrome, and a random sample—boosts statistical power without compromising representativeness. Moreover, the application of inverse probability weighting allows extrapolation of findings to the full cohort of 1,563 patients in the original trial.

In addition, the use of multivariable models adjusted for disease severity [sequential organ failure assessment score (SOFA)], comorbidities, and treatments received demonstrates that the extent of glycocalyx degradation at admission was an independent predictor of mortality. The finding that plasma heparan sulfate had greater predictive power than variables such as age, diabetes, or preexisting renal failure positions the glycocalyx as a novel axis in the prognostic stratification of patients with sepsis.

However, despite its notable methodological rigor, the study by Oshima and colleagues presents several limitations that warrant critical consideration (6). First, although a weighted sampling strategy was used, the subanalysis included only 574 of the 1,563 participants from the CLOVERS trial. Although the selection process was statistically sound, there remains a risk of bias associated with the availability of biological samples, particularly among patients who experienced early death or rapid discharge, who may represent pathophysiologically relevant extremes that are underrepresented. In addition, the biomarkers used—heparan sulfate and syndecan-1—reflect the systemic magnitude of endothelial activation and glycocalyx disruption but do not allow determination of the specific vascular bed affected (e.g., pulmonary vs. renal or splanchnic), nor do they capture temporal dynamics or responses to interventions.

In this regard, another important limitation is the lack of standardization in the type of crystalloid administered (balanced vs. unbalanced), which hinders the evaluation of their differential impact on the endothelial glycocalyx. Previous studies have suggested that unbalanced solutions may intensify glycocalyx degradation and exacerbate capillary leak (7, 8). Thus, fluid composition—rather than volume alone—may be the most critical determinant of endothelial dysfunction associated with resuscitation (8).

Finally, as the authors themselves acknowledge, the plasma quantification of glycocalyx components does not distinguish between proteolytic cleavage mechanisms (e.g., matrix metalloproteinase–mediated) and enzymatic degradation (e.g., heparanase activity), which may have divergent therapeutic implications. The absence of intracellular or gene expression markers limits, in this sense, a more refined characterization of endothelial injury.

New Contributions to Knowledge

The analysis by Oshima and colleagues provides findings that not only reaffirm the central role of the glycocalyx in the pathophysiology of sepsis but also reposition it as a dominant prognostic biomarker (9). In the adjusted multivariable model, baseline concentration of heparan sulfate exhibited greater predictive capacity for 90-day mortality than SOFA score, age, or chronic comorbidities. This observation—that the glycocalyx holds an independent and prominent statistical weight in prognosis—represents a conceptual inflection point: beyond the “clinical score,” endothelial injury now emerges as both a pathophysiological axis and a predictor.

One of the most striking—albeit negative—findings is the lack of a significant interaction between the degree of glycocalyx damage at admission and the volume of crystalloids administered, challenging the hypothesis that such injury can be modulated by fluid-restrictive strategies during the first 24 hours. This result suggests the possible existence of an early, poorly reversible endothelial injury phenotype, associated with multiple and not-yet-fully characterized pathophysiological pathways. In this context, recent studies have proposed that biomarkers such as procalcitonin could help identify early endothelial compromise in both infectious and noninfectious inflammatory settings (10, 11). The hypothesis of specific phenotypes of endothelial and microvascular injury deserves deeper exploration in future research.

Consequently, this opens the door to considering targeted interventions aimed at preserving or restoring glycocalyx integrity. Albumin, fresh frozen plasma, antioxidants such as vitamin C, and DPP4 inhibitors have been explored as potential “endothelium-protective” therapies (12–14). This study reinforces the urgency of advancing these avenues—not only from a biological rationale but also grounded in solid clinical evidence.

Conclusions and Future Directions

The CLOVERS trial subanalysis conducted by Oshima and colleagues not only expands our understanding of the role of the endothelial glycocalyx in sepsis but also redefines its clinical significance as a robust, early, and independent prognostic marker (6). These findings drive a paradigm shift—from resuscitation strategies focused solely on pressures and volumes toward an approach that considers endothelial biology as a therapeutic guide. Looking ahead, it becomes imperative to validate these biomarkers in independent cohorts, define clinically meaningful thresholds, and design studies that incorporate glycocalyx-targeted therapies as primary endpoints (12).

Furthermore, integrating syndecan-1 or other endothelial biomarkers into clinical decision-making algorithms could enable true precision medicine in sepsis (15, 16). Just as troponin is used to stratify myocardial infarction or D-dimer in thromboembolism protocols, the glycocalyx could become the first structural endothelial biomarker to guide resuscitation in patients with sepsis.

Ultimately, the study by Oshima and colleagues invites us to recognize that understanding microvascular and endothelial injury in sepsis—and advancing the search for therapeutic strategies that stabilize or repair it—represents one of the most promising frontiers in 21st-century critical care medicine.