Reduced [14C]-methionine uptake and fecundity in Schistosoma mansoni females treated with recombinant tumor necrosis factor α in vitro

Abstract

Recombinant human TNFα (rhTNFα) has previously been shown to reduce fecundity in Schistosoma mansoni adult females maintained in vitro without males, and adversely affect the uptake of [14C]-tyrosine, an amino acid required for schistosome vitellogenesis. Here we report on the effect of rhTNFα on [14C]-methionine uptake in both separated and paired females, and the effect of three different preparations of rTNFα on schistosome oviposition in vitro. In the absence of rhTNFa, separated females incorporated only 30% of the [14C]-methionine incorporated by paired females in a dose and time-dependent manner, suggesting low metabolic activity of females in the absence of males. Separated females and worm-pairs were treated with increasing doses of rhTNFα for 2 or 4 hr and then incubated in RPMI 1640 containing 10% fetal calf serum (FCS) and 5 µCi ml-1[14C]-methionine for 1 hr. Separated females treated with rhTNFa for 4 hr incorporated less methionine than those treated for 2 hr. In contrast, paired females treated with rhTNFa incorporated significantly smaller amounts of [14C]-methionine in a TNFa dose-dependent but time-independent manner [2 hr (P = 0.001) or 4 hr (P = 0.027) One-Way ANOVA]. Worm-pairs maintained in RPMI 1640 containing 10% FCS and 100 ng ml-1 of any of the three rTNFa preparations laid significantly fewer eggs than the worms cultured without rTNFα(P = 0.001; Kruskal-Wallis Test). We also observed that among rTNFα-treated worm-pairs, females were sluggish and tended to separate from their male partners. These observations suggest that TNFa inhibits [14C]-methionine uptake and reduces fecundity in females paired with males. Since paired females incorporate substantially greater amounts of [14C]-methionine, the role of males in stimulating metabolic activity in females is affirmed. Reduced amino acid uptake, and possibly other nutrients, may contribute to the diminished fecundity observed in TNFa-treated females.