Related Experiment Videos
MOLECULAR MRI OF CARTILAGE SENESCENCE IN OSTEOARTHRITIS USING A BETA GAL BIORESPONSIVE CONTRAST AGENT
H E Daldrup-Link1, Y U Lokesha1, Y Tanyildizi1
1Department of Radiology, Stanford University, Palo Alto, California, USA.
Introduction:
Cellular senescence in osteoarthritis (OA) cartilage is characterized by increased beta galactosidase (Gal) activity. We developed a beta Gal bio responsive contrast agent (BCA) with a caged GdIII center. Beta Gal cleavage unmasks the central GdIII coordination site, increasing proton interaction and resulting in increased T1 signal.
Objective:
This study tested whether beta Gal BCA can detect senescent cells in human OA cartilage. We hypothesized that (i) beta Gal BCA produces greater cartilage T1 enhancement than gadobutrol as control, and (ii) that cartilage T1-enhancement on beta Gal BCA enhanced MRI correlates with histologic senescence markers.
Methods:
This IRB approved prospective study included resected knee or hip joint specimens from 20 patients with OA (n = 20, age 69 ± 11 years, 15 women, 5 men). To simulate an MR arthrography, fresh specimens were incubated with 10 ml of either beta Gal BCA (n = 10) or gadobutrol (n = 10) at 2.5 mM for 30 minutes. Pre and post contrast MRI included proton density and T2 weighted fast spin echo, T1 weighted fast spin echo, and saturation recovery T1 mapping sequences. Pre versus postcontrast cartilage T1 relaxation times within each group as well as postcontrast T1 relaxation times between contrast agent groups were compared with Wilcoxon rank sum testing. Associations of post contrast T1 with T2, Outerbridge score, and immunohistochemistry senescence markers (p16, p21, and beta Gal) were assessed using linear regression and linear mixed effects modeling. Medians and interquartile ranges are reported.
Results:
For beta Gal BCA, cartilage T1 was significantly shorter post contrast (227 [IQR 51] ms) than pre contrast (1469 [IQR 172] ms, P = 0.002). Post contrast T1 after beta Gal BCA was strongly inversely correlated with cartilage T2 (Rc2 = Rm2 = 0.77, P < 0.001). For gadobutrol, cartilage T1 was also significantly shorter post contrast (993 [IQR 440] ms) than pre contrast (1475 [IQR 88] ms, P = 0.002), but post contrast T1 showed no correlation with T2 (Rc2 = 0.34, Rm2 = 0.00, P = 0.818). Cartilage enhancement on T1 maps was higher with beta Gal BCA (delta T1 85% [IQR 5%]) than gadobutrol (delta T1 34% [IQR 32%], P < 0.001). Post contrast cartilage T1 on beta Gal BCA enhanced MRI showed strong negative correlations with p16 (Rc2 = Rm2 = 0.95, P < 0.001), p21 (Rc2 = 0.94, Rm2 = 0.92, P < 0.001), and beta Gal staining (Rc2 = Rm2 = 0.92, P < 0.001). No significant correlations were observed for gadobutrol with p16 (Rc2 = 0.26, Rm2 = 0.01, P = 0.661), p21 (Rc2 = 0.32, Rm2 = 0.01, P = 0.597), or beta Gal (Rc2 = 0.40, Rm2 = 0.03, P = 0.482). For all marker associations, slopes differed significantly between the two contrast agents (P < 0.001).
Conclusion:
Beta Gal BCA provides enzyme responsive cartilage T1 contrast on MRI that reflects senescence associated beta Gal activity in human OA cartilage, yielding substantially greater T1 shortening and strong correlations with histologic senescence markers that are not present with gadobutrol. This imaging approach supports nondestructive identification and quantification of senescent cell burden in human OA joints, enabling selection of patients for senolytic therapies and imaging-based monitoring of treatment response.
