Fig 1: Pharmacological inhibition of HO-1 activity with zinc protoporphyrin (ZnPP) reproduces a similar pattern to that observed in microglial HO-1 knock-out mice. (A) Scheme of the protocol followed. Mice were treated with ZnPP (25 mg/kg) 2 h prior the LPS (0.5 mg/kg) injection. ZnPP restored the iron metabolism alterations induced by LPS evidenced by a decrease in non-heme iron accumulation in the brain (B) and in the expression of DMT1 and L-ferritin in hippocampus (C and D). In a similar pattern to the genetic microglial depletion of HO-1, pharmacological inhibition reduced the inflammatory markers iNOS, p65 and CD68 in hippocampus (E and F), and was also able to revert the LPS-related increased expression of inflammasome-related proteins such as NLRP3, caspase-1 and mature IL-1 ß, (G and H). LPS-related increase in the pro-inflammatory cytokines TNF-a and IL-1ß (I) was restored in WT mice treated with ZnPP. Treatment with ZnPP partially improved social interaction (J) and a statistical trend was observed for locomotion (K). Data represent mean ± S.E.M. (N = 4–20, one-way ANOVA followed by Tukey post-hoc test). Significant differences were considered when: *p < 0.05, **p < 0.01 and ***p < 0.001 compared to aged WT saline mice or #p < 0.05, ##p < 0.01 and ###p < 0.001 compared to aged WT LPS injected mice (B–I). Data represent mean ± S.E.M. (N = 5–15, 2-way ANOVA followed by Tukey post-hoc test). Significant differences were considered when: ***p < 0.001 compared to aged WT saline mice or ###p < 0.001 compared to aged WT LPS injected mice (J-K).