Sepsis associated acute kidney injury (SA-AKI) is a prevalent and severe complication among critically ill patients, contributing to elevated morbidity and mortality rates (Peerapornratana et al., 2019). Notably, the mortality rate in SA-AKI patients significantly exceeds that of sepsis patients without acute kidney injury (AKI) (Bagshaw et al., 2007). This heightened mortality is attributed to the unclear pathogenesis of SA-AKI, the absence of highly sensitive and specific biomarkers for early diagnosis, and the lack of effective, specific treatment modalities (Peerapornratana et al., 2019). Presently, neutrophil gelatinase-associated lipocalin (NGAL) stands as the most extensively studied biomarker for SA-AKI (Shang and Wang, 2017). Despite NGAL’s potential in SA-AKI diagnosis and prediction, prior studies have indicated that the combination of multiple biomarkers yields superior effects and predictive value compared to a single biomarker (Grover et al., 2014). Further investigation is needed to explore whether biomarkers with heightened sensitivity and specificity or combined detection can enable earlier SA-AKI diagnosis.

Fibroblast growth factors (FGF), also recognized as heparin-binding growth factors (HBF), comprise a protein family consisting of approximately two dozen heparin-binding proteins (HBP) (Ornitz and Itoh, 2001), including aFGF and bFGF. Within the FGF family, proteins signal through at least one of four tyrosine kinase receptors and interact with heparan sulfate proteoglycans (HSPGs). In adults, FGFs serve as homeostatic factors involved in tissue repair and responses to injury (Beenken and Mohammadi, 2009). Previous studies have demonstrated that HBP predicts septic infection-induced organ dysfunction and disease severity. Tapper, H., et al. (Tapper et al., 2002) emphasized the predictive value of HBP for SA-AKI. HBP emerges as a pathogenic biomarker and a potential target for heparin treatment of human SA-AKI (Lee et al., 2012). Heparin inhibits HBP-induced inflammation and reduces interleukin (IL) −6 production (Lee et al., 2012). Studies have indicated that low molecular weight heparin (LMWH) blocks HBP-induced inflammation in renal tubular cells, suggesting a potential avenue for SA-AKI treatment (Fisher et al., 2017).

Studies have indicated that heparanase (HPA) mediates septic AKI (Chen et al., 2017). HPA disrupts the structural integrity of extracellular matrix (ECM) and basement membrane, releasing and activating active substances attached to side chains (Lerolle et al., 2010; Teixeira and Götte, 2020), which leads to the release of heparin-binding molecules promoting pro-inflammatory factors such as IL-2, IL-8, bFGF, and transforming growth factor (TGF)-β within the ECM. These inflammatory factors regulate the interaction between the surface of white blood cells (WBC) and endothelial cells, thereby affecting the recruitment, migration and extravasation of WBC (Carter et al., 2003; Axelsson et al., 2012; Higashi et al., 2020). Heparin can alleviate SA-AKI by inhibiting HPA activity (Hirsh and Levine, 1992; Chen et al., 2015).LMWH has been shown to inhibit HPA-mediated HS degradation (Achour et al., 2016). Therefore, it is speculated that LMWH may inhibit HPA activity, reduce the degradation of ECM, decrease the release of HBP, and improve the renal function and clinical prognosis of SA-AKI.

Our study primarily demonstrated a significant association between elevated plasma HPA and HBP levels and the presence as well as progression of AKI in sepsis, thereby indicating that HPA and HBP exert a pivotal role in the pathophysiology of SA-AKI, which aligns with previous research findings (Fisher et al., 2017; Poston and Koyner, 2019; Liu et al., 2023). Clearance correlation analysis revealed a positive association between HPA and NGAL, HBP, creatinine, and syndecan-1. Consequently, we integrated NGAL, HBP, and HPA to conduct ROC curve analysis and observed that this combination exhibited superior predictive ability for early SA-AKI diagnosis. Additionally, we found that LMWH effectively inhibited HPA and HBP-induced inflammation in renal cells, indicating the potential of targeting HPA and HBP for SA-AKI treatment. Furthermore, through MR analysis, we established a direct association between HBF and renal tubular injury, consistent with findings from clinical observational studies. Finally, we hypothesized that the potential mechanism underlying the beneficial effects of LMWH in ameliorating SA-AKI may involve attenuation of HPA activity, inhibition of ECM degradation, and subsequent reduction in FGF release, thereby leading to improved renal function in SA-AKI.

Previous in vitro and in vivo studies have shown increased activation of the HPA axis in glomerular and interstitial vascular endothelial cells during sepsis. However, renal function improved with the use of HPA inhibitors (Chen et al., 2015). Based on these findings, we hypothesised that HPA inhibitors may improve renal function in patients with SA-AKI, suggesting HPA may be a therapeutic target for SA-AKI. Consequently, we categorized SA-AKI patients into control and LMWH groups to investigate the impact of LMWH on renal function and clinical prognosis by modulating HPA activity. Our study represented a pioneering investigation into elucidate the role of HPA in patients with SA-AKI, unequivocally demonstrating that pharmacological inhibition of HPA exerts a beneficial effect on renal function in SA-AKI.

The findings from murine sepsis models have demonstrated that HPA promotes the shedding of endothelial glycocalyx, leading to vascular leakage and decreased blood volume, consequently contributing to increased sepsis related mortality (Song et al., 2017). Glycocalyces, mainly composed of HSPGs and glycosaminoglycans, cover the surface of the endothelium and play a crucial role in regulating vascular permeability, coagulation, platelet and white blood cell adhesion, as well as anti-inflammatory and antioxidant processes (Sieve et al., 2018; Lupu et al., 2020). Syndecan-1 serves as a biomarker of glycocalyx degradation (Rehm et al., 2007) and is released into the blood under stressful conditions such as AKI, chronic kidney disease, and cardiovascular disease (Puskarich et al., 2016). Consistent with our study, inhibiting HPA reduced syndecan-1 levels.

In addition, we observed that HPA can exert an influence on inflammation, immune response, and coagulation function in patients with SA-AKI. During sepsis, HPA is activated by pathogen-associated molecular patterns and inflammatory cytokines. In our study, LMWH was employed, which exerted anti-inflammatory effects by inhibiting HPA activity, thereby safeguarding renal function and ameliorating renal inflammation, consistent with previous studies (Achour et al., 2016; Mayfosh et al., 2019). Evidence also indicates that HPA mediates interactions among various immune cell types, including T cells, B cells, natural killer cells, macrophages, neutrophils, and dendritic cells (Mayfosh et al., 2019). LMWH has the capability to prevent activation of the complement system, and the inhibition of C5a prevents the release of inflammatory and prothrombotic molecules such as TNF-α and tissue factor (Rao et al., 1993). In our study, we observed improved immune function in the LMWH group compared with the control group, suggesting that LMWH may also enhance renal immune function in patients with SA-AKI. The anticoagulant effect of LMWH is related to its binding to antithrombin III, which inhibits coagulation and platelet aggregation, leading to alterations in APTT. Consistent with these mechanisms, we observed that APTT was significantly prolonged in the LMWH group. Previous studies have reported that LMWH has anti-inflammatory properties independent of its anticoagulant effects (Luan et al., 2014). With the progress of treatment, the platelet count gradually recovered. The platelet level of patients with SA-AKI in the LMWH group was significantly increased, and the coagulation function was improved. The effects of LMWH on platelet recovery also could be due to reduced platelets bound to the vessel wall.

In terms of clinical outcomes, no significant differences were noted between the two groups concerning 28-day mortality, 90-day survival, and duration of ICU stay. Several plausible explanations underlie these findings. Firstly, patients with SA-AKI typically present with a constellation of comorbidities, and the length of their hospitalization is subject to a multitude of influencing factors. Secondly, the current usage of LMWH primarily as an anticoagulant may not wield sufficient impact on mortality and survival rates in SA-AKI patients. Moreover, the LMWH employed in our investigation lacked specificity as an HPA inhibitor, as safe clinical-grade HPA inhibitors remain elusive. Furthermore, owing to the constrained sample size in our study, the potential impact of LMWH on the mortality and survival rates of patients with SA-AKI by inhibiting HPA activity may not have been comprehensively elucidated. Nonetheless, our study unearthed noteworthy disparities in SA-AKI grade post-treatment between the two cohorts, with HPA inhibitor utilization correlating with diminished requirements for RRT and reduced hospitalization costs, thus alleviating the financial burden on patients. Notably, to the best of our knowledge, such findings have not been previously documented in SA-AKI patients. Our study disclosed a 28 days mortality rate of approximately 70% among patients with an average SOFA score of 9, markedly surpassing previously reported rates (Raith et al., 2017). The patients included in this study were generally older and frequently presented with severe infections. Owing to economic constraints, many patients were discharged upon symptomatic improvement, albeit without complete disease control, potentially contributing to escalated mortality rates. Additionally, the study sample was robust but exhibited inherent biases, alongside elevated mortality rates.

In conclusion, our study supports previous findings indicating a higher incidence of SA-AKI compared to septic patients without AKI. We have identified plasma HPA as a promising biomarker for early diagnosis of SA-AKI. Furthermore, our findings suggest that inhibiting HPA could potentially improve renal function in patients with SA-AKI. The correlation we observed between HPA levels and biomarkers of renal damage, including NGAL, HBP, creatinine, and syndecan-1, further strengthens the link between HPA and renal structural injury. In addition, our study highlights the potential of LMWH in reducing HPA levels, thereby enhancing renal function, mitigating inflammation and immune response, and modulating coagulation in SA-AKI patients. Although no significant differences in clinical outcomes were observed, the improvements in renal function grading, reduced need for RRT, and lower hospitalization costs among SA-AKI patients suggest potential advantages of HPA inhibition in SA-AKI management. However, comprehensive investigations with larger cohorts and specific HPA inhibitors are warranted to fully elucidate the therapeutic efficacy of targeting HPA in SA-AKI treatment.

Our study possesses several notable strengths:

1. Clinical Relevance: Unlike previous investigations primarily conducted on cellular and animal models, our study is pioneering in directly observing the effects of inhibiting HPA on renal function in SA-AKI patients, thus enhancing its clinical relevance.

Our study also exhibits certain limitations:

1. Lack of Urine Samples for HPA Detection: HPA emanates from various sources, with platelets being notably significant (Eustes et al., 2021). Consequently, the kidney may not singularly serve as the origin of HPA, rendering plasma-based measurements insufficient for an accurate depiction of renal HPA levels. Due to instances where patients presenting with oliguria or anuria upon admission, the acquisition of urine specimens was unattainable, necessitating our reliance on plasma HPA assessments predominantly. Additionally, assays for syndecan-1 and NGAL were conducted on plasma samples rather than urine, potentially compromising the sensitivity and specificity of HPA in the diagnosis of SA-AKI. Furthermore, the assessment of HPA enzyme activity, typically involving complex techniques, was not performed in our study.

LMWH can improve renal function in critically ill patients with SA-AKI, and the potential mechanism may be that LMWH reduces the release of HBP by inhibiting the activity of HPA, as suggested by potential mechanisms. Moreover, MR Analysis underscores a corresponding causal link. These results also highlight the necessity for future randomized controlled trials to corroborate these observations.