Glomerular capillary thrombosis and injury are characteristic of HUS. VT is cytotoxic for human glomerular cells in vitro; VT may induce apoptosis(programmed) cell death as well as cell injury through protein synthesis inhibition in susceptible cells. To further define the role of VT in glomerular cell injury, the mechanisms of VT injury were investigated in human glomerular cells and in renal tissue obtained from children with HUS.

Pure cultures of GCEC and MC were exposed to VT-1 (1 pM - 1 nM) for 6-48 hr with and without prior exposure to TNF. Apoptosis was detected by specific EM changes and TdT detection of DNA breaks in cells and in renal tissue from 4 children with HUS.

In preconfluent GCEC cultures apoptosis (8.3%) and cytotoxicity was noted after 24hr 10 pM VT-1. In MC after 24 hr 10pM VT-1, apoptosis was significantly greater in TNF pretreated cells (13.2) than in VT-1 alone(8.5%). Prior exposure to TNF increased apoptosis with VT-1 at each time period. GCEC/MC without VT-1 demonstrated little apoptosis (0.7%) with or without cytokine exposure. GCEC and MC detached from the cell monolayer after VT-1 also demonstrated apoptosis. In situ TdT labeling and EM revealed nuclear changes consistent with apoptosis after VT-1. By EM and TdT detection apoptotic changes were noted in glomerular cells (endothelial, mesangial and epithelial) in renal tissue obtained from children with HUS.

Human GCEC and MC are susceptible to VT-1 and undergo apoptosis in association with cell detachment and cell loss in vitro. Evidence for glomerular cell apoptosis in children with HUS suggests that this may be a significant mechanism in the pathogensis of glomerular injury in children with HUS.