Extracts of pine bark (Pinus sylvestris) inhibit Cryptosporidium parvum growth in cell culture

The widespread apicomplexan parasite Cryptosporidium parvum is responsible for severe gastrointestinal disease in humans and animals. The treatment options are limited, and the efficacy of available drugs is low. Bark contains condensed tannins (CT), which are bioactive compounds previously shown to inhibit parasite development. Here, we examined the anti-cryptosporidial properties of bark extract of Scots pine (Pinus sylvestris) against C. parvum by means of an in vitro growth inhibition test. We hypothesised that bark extracts would have dose-dependent inhibitory effects on the development of C. parvum in cell culture. Bark extracts from Scots pine extracted with acetone, methanol, and water as solvents were investigated using human colorectal adenocarcinoma cells infected with C. parvum. Oocysts were inoculated onto the cell monolayer and bark extract was added at seven different concentrations. Parasite growth inhibition was quantified by qPCR. The acetone and methanol extracts demonstrated a sigmoid dose-dependent inhibition of C. parvum. The IC ₅₀ values were 244.6 and 279.1 µg dry matter extract/mL, and 25.4 and 24.1 µg CT/mL, for acetone and methanol extracts, respectively. The IC ₅₀ for both extracts were similar, both with regard to the dry matter concentration of each extract and to CT concentrations. Given the limited treatment options available for Cryptosporidium spp., the evidence generated in our study encourages further investigation into the in vitro and in vivo effects of pine bark extracts against C. parvum.