Figure 2.
Molecular MRI of bleomycin-induced lung fibrogenesis. Representative H&E (A) and Masson’s trichrome (B) staining of lung section from naïve and BM mice. Bleomycin-injured lung showed increased tissue density, cellularity, and collagen deposition compared with normal lungs. Lung allysine (C) and hydroxyproline (HYP) (D) content were significantly increased in BM mice compared with naïve mice. Data presented as mean ± s.d.; n = 13 for naïve mice, n = 20 for BM mice). Statistical analysis was performed using two-tailed unpaired Student’s t test, unpaired, ** p < 0.01, *** p < 0.001). E, Representative lung enhancement in naïve and BM mice. Coronal UTE images overlaid with false color image of lung enhancement generated by subtraction of the pre-injection UTE image from post-injection UTE image. MnL1, MnL2, and MnL3 produced higher signals in BM mice lungs than in naïve mice and higher signal in MnL4 injected naïve and BM mice at 60 min post-injection. F, Change of lung-to-muscle ratio (ΔLMR) as a function of time in naïve and BM mice after injection of MnL1, MnL2, MnL3, and MnL4. Data are presented as mean value with 95% simultaneous confidence bands as shaded regions; Naïve mice: n = 6 for MnL1, MnL2, and MnL3, n = 4 for MnL4; BM mice: n = 13 injected with MnL1, n = 8 injected with MnL2, n = 12 injected with MnL3, and n = 5 injected with MnL4. G, Image quantification of ΔLMR in lungs of naïve and BM mice 60 min post-injection of MnL1, MnL2, MnL3, and MnL4. Hydrazine/oxyamine bearing probes exhibited specific lung signal enhancement in the fibrotic lung. Data presented as mean ± s.d. Statistical analysis was performed using one-way ANOVA with Tukey’s post hoc test, **P < 0.01, ***P < 0.001, ns not statistically significant). H, Pair-wise analysis of ΔLMR in bleomycin-injured mice at 60 min post-injection of MnL1 and MnL3 (n = 6). Statistical analysis was performed using two-tailed paired Student’s t test, *P < 0.05. I, Washout T1/2 of MnL1, MnL3, and MnL4 in naïve and BM mice. MnL3, with higher hydrazone hydrolytic stability, exhibited longer residence time in fibrotic lungs. Data presented as mean ± s.d.; Naïve mice: n = 6 for MnL1, and MnL3, n = 4 for MnL4; BM mice: n = 13 injected with MnL1, n = 12 injected with MnL3, and n = 5 injected with MnL4. Statistical analysis was performed using one-way ANOVA with Tukey’s post hoc test, *P < 0.05, ***P < 0.001, ns not statistically significant. J, Quantification of Mn content in the left lungs of naïve and BM mice 60 min after injection of MnL1, MnL2, MnL3, and MnL4. Injection of hydrazine/oxyamine-bearing probes produced significantly higher Mn concentrations in the fibrotic lung compared with normal lung. No preferential uptake was observed in naïve or BM mice injected with MnL4. Data are presented as mean ± s.d.; Naïve mice: n = 3 for MnL1, n = 4 for MnL2, n = 3 for MnL3, n = 4 for MnL4; BM mice: n = 3 for MnL1, n = 4 for MnL2, n = 5 for MnL3, n = 3 for MnL4. Statistical analysis was performed using one-way ANOVA with Tukey’s post hoc test, *P < 0.05, **P < 0.01, ***P < 0.001, ns not statistically significant. K, The MRI lung signal enhancement in naïve and BM mice imaged with MnL1, MnL2, and MnL3 correlates well with allysine content. Compared with MnL1, MnL3 exhibited higher sensitivity in detecting fibrogenesis (slopeMnL1 = 0.011 vs. slopeMnL3 = 0.015).