*Communication* **Heparin Administered to** *Anopheles* **in Membrane Feeding Assays Blocks** *Plasmodium* **Development in the Mosquito**

**Elena Lantero 1,2, Jessica Fernandes <sup>3</sup> , Carlos Raúl Aláez-Versón 4 , Joana Gomes <sup>3</sup> , Henrique Silveira <sup>3</sup> , Fatima Nogueira <sup>3</sup> and Xavier Fernàndez-Busquets 1,2,5,\***


Received: 2 June 2020; Accepted: 29 July 2020; Published: 1 August 2020

**Abstract:** Innovative antimalarial strategies are urgently needed given the alarming evolution of resistance to every single drug developed against *Plasmodium* parasites. The sulfated glycosaminoglycan heparin has been delivered in membrane feeding assays together with *Plasmodium berghei*-infected blood to *Anopheles stephensi* mosquitoes. The transition between ookinete and oocyst pathogen stages in the mosquito has been studied in vivo through oocyst counting in dissected insect midguts, whereas ookinete interactions with heparin have been followed ex vivo by flow cytometry. Heparin interferes with the parasite's ookinete–oocyst transition by binding ookinetes, but it does not affect fertilization. Hypersulfated heparin is a more efficient blocker of ookinete development than native heparin, significantly reducing the number of oocysts per midgut when offered to mosquitoes at 5 µg/mL in membrane feeding assays. Direct delivery of heparin to mosquitoes might represent a new antimalarial strategy of rapid implementation, since it would not require clinical trials for its immediate deployment.

**Keywords:** malaria; heparin; mosquito; *Plasmodium*; *Anopheles*; ookinete; transmission blocking; antimalarial drugs
