A C-type lectin from Bothrops leucurus snake venom forms amyloid-like aggregates in RPMI medium and are efficiently phagocytosed by peritoneal macrophages.

Lectins are carbohydrate-binding proteins that play important roles in the immune system. Under specific conditions, lectins can form amyloids, proteinaceous aggregates rich in cross ß-strand structures. A Ca++-dependent lectin, isolated from Bothrops leucurus snake venom (BLL) has demonstrated relevant biological activities such as antibacterial and antitumor activity. In this work, we aimed to study the interaction of BLL with macrophages. The formation of amyloid structures by BLL in a cell culture medium, the effects of the lectin on macrophage morphology and cytokine production were investigated. BLL amyloid-like fibrils in RMPI medium, pH 7.2, at 37 °C was confirmed by binding of Congo Red, Thioflavin T and electron microscopy. Neither binding of amyloid markers nor fibrillar structures were found when the lectin was incubated in RPMI plus galactose, the specific BLL-binding carbohydrate. Several phagocytic compartments containing fibrillar structures were observed in BLL-treated macrophages in RPMI medium for 24 h; these compartments showed an apple-green birefringence after Congo Red staining and were positive for thioflavin S and anti-amyloid antibody, indicating the presence of amyloid-like fibrils. No fibrillar material and no labeling were observed when the macrophages were treated with BLL plus galactose or cytochalasin B, an inhibitor of phagocytosis. BLL did not affect the viability of the cells. A significant release of proinflammatory (TNF-α, IL-6, INF-ϒ and IL-1ß) and regulatory (IL-10) cytokines was observed in BLL-treated macrophages. Taken together, our results shed light on the structural organization of BLL, improving knowledge about the interaction of lectin with macrophages. The phagocytosis of amyloid-like aggregates together with the proinflammatory response induced by BLL may open new perspectives for the use of this lectin as an interesting model to study cytokines and the production of other mediators as well as understand the mechanisms occurring in human immune cells during amyloid protein deposition.

In vitro effect of Bothrops leucurus lectin (BLL) against Leishmania amazonensis and Leishmania braziliensis infection.

Leishmania amazonensis and Leishmania braziliensis are the main causative agents of American Tegumentary Leishmaniasis (ATL) in Brazil. As intracellular parasites, the infection by Leishmania species is dependent on the host immune response and the immunotherapy could be promissory for the development of new strategies to combat ATL. In this work we investigated the leishmanicidal potential of a galactose-binding lectin from the snake venom of Bothrops leucurus (BLL) during the infection with L. amazonensis and L. braziliensis. BLL inhibited the promastigote growth and viability of both species in a mechanism dependent on galactose and calcium. The treatment with BLL also decreases the survival of intracellular parasites for both species and induced profound ultrastructural changes on amastigotes without apparent damage to the host cells. The analysis of the cytokine profile revealed that BLL induced an increase in the proinflammatory cytokines IL-6 and TNF-α by infected macrophages in both species, but differed in relation to IL-1ß and IL-10 response. Future works using in vitro and in vivo models are necessary to support the use of these lectins as biotechnological tool in immunological studies.

Lectin-Carbohydrate Interactions: Implications for the Development of New Anticancer Agents.

Lectins are a large group of proteins found in animals, plants, fungi, and bacteria that recognize specific carbohydrate targets and play an important role in cell recognition and communication, host-pathogen interactions, embryogenesis, and tissue development. Recently, lectins have emerged as important biomedical tools that have been used in the development of immunomodulatory, antipathogenic, and anticancer agents. Several lectins have been shown to have the ability to discriminate between normal cells and tumor cells as a result of their different glycosylation patterns. Furthermore, the specific binding of lectins to cancer cells has been shown to trigger mechanisms that can promote the death of these abnormal cells. Here, we review the importance of lectins-carbohydrates interactions in cancer therapy and diagnosis. We examine the use of lectins in the modification of nanoparticles (liposomes, solid lipid nanoparticles and other polymers) for anticancer drug delivery. The development of drug delivery systems (liposomes, alginate/chitosan microcapsules, alginate beads) carrying some antitumor lectins is also discussed. In these cases, the processes of cell death induced by these antitumor lectins were also showed (if available). In both cases (lectin-conjugated polymers or encapsulated lectins), these new pharmaceutical preparations showed improved intracellular delivery, bioavailability and targetability leading to enhanced therapeutic index and significantly less side effects.

pCramoll and rCramoll lectins induce cell death in human prostate adenocarcinoma (PC-3) cells by impairment of mitochondrial homeostasis.

Lectins from Cratylia mollis seed have shown potential in vivo antitumor actions, however the mechanism have not yet been addressed. Here we evaluated the antitumor effects of native (pCramoll) and recombinant (rCramoll) lectins from C. mollis against human prostate adenocarcinoma (PC-3) cells. The viability of PC-3 cells was analyzed with the MTT assay and ANNEXIN V/propidium iodide staining. The actions of pCramoll or rCramoll on mitochondrial superoxide production, free cytosolic calcium concentration and mitochondrial membrane potential were evaluated using fluorescent probes (MitoSox Red, Fura 2-AM and safranin O, respectively). pCramoll and rCramoll reduced the viability of PC-3 cells in a dose-dependent manner. Both lectins increased the generation of mitochondrial superoxide as well as the concentration of cytosolic calcium. These changes led to a decrease in oxidative phosphorylation, which impaired the formation of ATP. The resulting cell death was not blocked by MPT (mitochondrial permeability transition) inhibitors (Debio 025 or bongkrekic acid). Thus pCramoll and rCramoll promote PC-3 cell death through calcium signaling, leading to mitochondrial collapse. This work provides more insights into the action of pCramoll and rCramoll against cancer cells. These lectins represent valuable tools for biomedical research.