Endothelial cells protect Schistosoma mansoni from hydrogen peroxide-induced death

Abstract

Introduction: Schistosoma mansoni, the causative agent of intestinal schistosomiasis, thrives in the human host, particularly within the vascular system. Understanding the role of endothelial cells during infection is crucial. Currently, schistosomiasis treatment depends solely on praziquantel (PZQ), but emerging evidence suggests decreasing efficacy. This highlights the need for new therapeutic strategies, including agents that modulate the host antioxidant response, such as dapsone.

Methods: Adult S. mansoni worms were harvested from infected mice via portal perfusion. Human umbilical vein endothelial cells (HUVECs) were cultured and exposed to worm pairs and PZQ for 1, 3, or 6 hours. Post-exposure, RNA was extracted and analyzed by qPCR to assess the expression of antioxidant genes (NRF2, SOD1, GPx, GSR, CAT). Additionally, worm viability under oxidative stress was evaluated by incubating worms with hydrogen peroxide (H₂O₂), in the presence or absence of HUVECs, catalase, or dapsone hydroxylamine.

Results: Worms did not significantly alter expression of host antioxidant genes except for catalase. H₂O₂ exposure led to worm death, but co-incubation with HUVECs improved worm viability and survival, suggesting a protective role of endothelial cells against oxidative stress. Furthermore, dapsone hydroxylamine reversed the protective effect of catalase, reducing worm viability. However, worms remained viable in co-culture with HUVECs, indicating additional, unidentified mechanisms of protection.

Conclusion: Endothelial cells may play a key role in protecting S. mansoni against host oxidative defenses. Dapsone hydroxylamine interferes with this protection by inhibiting catalase activity. These findings point to potential therapeutic strategies targeting the host-parasite interface and the antioxidant environment in schistosomiasis.

Fig 1. Representative images illustrating the viability scoring system for adult Schistosoma mansoni worms cultured in vitro.

(A) Score 0 – Dead worm with fully darkened tegument and no movement. (B) Score 1 – Worm with darkened tegument, reduced motility, and impaired suckers. (C) Score 2 – Worm with partially damaged tegument and moderate motility. (D) Score 3 – Fully viable worm with intact tegument and active movement. The red circle indicates egg deposition, also used as a marker of viability. Image created by the authors.

Fig 2. Temporal expression of antioxidant genes in HUVECs exposed to adult Schistosoma mansoni.

Relative mRNA expression of antioxidant genes (SOD1, GPX, GSR, CAT, and NRF2) in human umbilical vein endothelial cells (HUVECs) after co-culture with adult S. mansoni worm pairs for 1, 3, and 6 hours.

Fig 3. Distribution of S. mansoni worm viability scores after exposure to oxidative stress with and without HUVECs.

Viability scores of adult Schistosoma mansoni worms after 24-hour exposure to increasing concentrations of hydrogen peroxide (H₂O₂), in the absence (A) or presence (B) of HUVECs. Worm viability was categorized into four scores: score 3 (intact tegument and active motility), score 2 (partial tegument damage and moderate motility), score 1 (darkened tegument and low motility), and score 0 (complete loss of motility and tegument integrity, indicating death). In the presence of HUVECs, a higher proportion of worms maintained viability (score 3), even at elevated H₂O₂ concentrations, with no deaths observed at 800 µM. In contrast, exposure to H₂O₂ alone resulted in a dose-dependent decline in viability, with complete mortality at 1600 µM.

Fig 4. Protective effect of HUVECs on S. mansoni worm survival under oxidative stress.

(A) Percentage of adult Schistosoma mansoni worms classified as high viability (scores 2–3) after exposure to increasing concentrations of hydrogen peroxide (H₂O₂), either in the absence (Sm + H₂O₂) or presence (Sm + H₂O₂ + HUVEC) of human umbilical vein endothelial cells (HUVECs). Co-culture with HUVECs significantly improved worm survival at 200, 400, and 800 µM H₂O₂, compared to exposure to H₂O₂ alone (p < 0.001, Fisher’s exact test). (B) Survival analysis of adult Schistosoma mansoni worms exposed to increasing concentrations of hydrogen peroxide (H₂O₂) in three experimental models: worms incubated with H₂O₂ alone (blue line), co-cultured with HUVECs (green line), or treated with exogenous catalase (CAT, red line). Worms cultured without HUVECs or catalase exhibited reduced survival starting at 400 µM H₂O₂. In contrast, both co-culture with HUVECs and catalase treatment preserved worm viability, with mortality observed only at the highest concentration (1600 µM). No significant difference was detected between the HUVEC and catalase models, suggesting that the protective effect of endothelial cells may be mediated, at least in part, by antioxidant enzymes such as catalase.

Fig 5. Effect of DDS-NOH on the viability of adult S. mansoni worms under oxidative stress in different experimental conditions.

The percentage of nonviable worms was assessed following exposure to H₂O₂ (400 µM), with or without the addition of catalase (CAT), DDS-NOH (50 µM), and/or HUVECs. Catalase reduced the mortality induced by H₂O₂, an effect that was reversed in the presence of DDS-NOH, suggesting catalase inhibition. Interestingly, co-culture with HUVECs preserved worm viability even in the presence of DDS-NOH, indicating that HUVECs may provide additional protective mechanisms beyond catalase activity. Bars represent the percentage of nonviable worms in each experimental condition; horizontal lines indicate statistically significant differences (p < 0.05, Fisher’s exact test).