Different in vitro toxicity of ribosome-inactivating proteins (RIPs) on sensory neurons and Schwann cells

Objective: To study the neurotoxicity induced by Ricinus communis agglutinin (RCA), ricin A chain (RTA), and trichosanthin (TCS) in vitro. Methods: Rat neurons and Schwann cells were cultured and real-time up-take of RIPs was traced. TUNEL, Annexin V and DAPI were employed to study the mechanism. Results: The purity of both primary neuronal and Schwann cell cultures attained 80–90%. In neuritis, transport of FITC-RCA was demonstrated, but RTA and TCS were not detected. RCA elicited the strongest TUNEL and annexin V signals in both cultures. RTA evoked a stronger apoptotic signal than TCS in neurons. In contrast, compared with TCS, RTA elicited an attenuated apoptotic reaction in Schwann cells. All internalized RIPs were concentrated in the cytoplasm of the cells and their nuclei were not stained by DAPI. Conclusion: The toxicity of these RIPs on neurons is different from that on Schwann cells. Although they enter cells by different mechanisms they all induce apoptosis. These results may find application in in vivo neural lesioning studies and clinical therapy.