Figure 4.

ARV drugs increase BACE1 processing of APP in primary neurons. Chinese hamster ovary cells stably expressing human APP were either treated with 10 μmol/L ritonavir alone for 16 hours or pretreated with increasing doses of a cell-permeable BACE1 inhibitor (BSI) for 12 hours before ritonavir treatment. Culture media were analyzed with a human/rat Aβ₄₂- or Aβ₄₀-specific sandwich enzyme-linked immunosorbent assay (ELISA; A) or a human sAPPα or sAPPβ ELISA (B and C). A: Ritonavir led to a twofold increase in Aβ₄₂ production that was dose-dependently blocked by BSI, whereas Aβ₄₀ levels were not affected by ritonavir. No statistically significant changes in sAPPβ (B) or sAPPα (C) were observed in ritonavir-treated cultures, although sAPPβ was dose-dependently decreased with BSI. D and E: Primary rat neuroglial cultures were treated with various ARV combinations [10 μmol/L ritonavir, 1 μmol/L saquinavir, and 25 μmol/L zidovudine (AZT)] for 4 or 16 hours. Culture media were analyzed with a human/rat Aβ₄₂- or Aβ₄₀-specific sandwich ELISA, as in A. At 16 hours, both Aβ₄₂ and Aβ₄₀ levels were increased in most treatment conditions. AZT appeared to blunt PI-mediated enhancement of APP processing in combination treatment. All values represent means ± SEM. n = 6 (A–C); n = 3 (D–F). ^∗P < 0.05, ^∗∗P < 0.01 (one-way analysis of variance, Dunnett post hoc), ^∗∗∗P < 0.001 (one-way analysis of variance, Newman-Keuls post hoc). UT, untreated.