Micro-PET study of 68Ga-HZ20 in the rhACE2-intraperitoneal brain model
PET imaging showed slight uptake of the probe in the brains of control mice, while significant aggregation was observed in the rhACE2 injection group (Fig. 6A, Fig. S9). SUVmax showed that within 120 min after probe injection, there were significant differences between the rhACE2 injection group and the control group, and at 15 min after probe injection, the uptake values were 0.42± 0.01, 0.44±0.01, 0.56±0.02 and 0.72±0.01, respectively (Fig. 6B). The target ratio of brain to muscle also showed consistent results, with 2.23±0.10, 2.85±0.06, 3.34±0.12, and 4.23±0.12 at 120 min, respectively (Fig. 6C). After 120 min, brain tissue ex vivo imaging was performed, and the results were consistent with the results of in vivo PET. There was almost no probe uptake in the brains of mice that were not injected with rhACE2, while the uptake of probe in brain tissue was observed in the injection group, especially in the 0.8 nmol rhACE2 group (Fig. 6D). This result also showed that the 68Ga-HZ20 probe can be applied to the quantitative monitoring of rhACE2 in brain tissue. Brain tissue % ID/g also showed that the rhACE2 injection group was significantly higher than that of the noninjection group, with the highest in the 0.8 nmol group, which was 0.004±0.001, 0.024±0.001, 0.048±0.001 and 0.123±0.002, respectively (Fig. 6E). The correlation analysis between rhACE2 and SUVmax showed the highest correlation 30 min after probe injection, and the R2 was 0.9913 (Fig. 6F). The content of rhACE2 in brain tissue was detected by western blot, and the results showed that there was a small amount of ACE2 expression in the brain tissue itself, and obvious bands and gradient relationships were visible in the injection group, indicating that rhACE2 maintained stability in structure and quantity in the brain within 120 min (Fig. 6G).