Figure 3.

Functional mass spectrometry (fMSI) of human non-OA and OA knee osteochondral unit. (A) fMSI workflow. (B) Averaged MALDI mass spectrum of PC 15:0/18:1-D₇ (enzyme-substrate) and LPC 15:0 (enzyme-products) in the absence of tissue. (C) MALDI-MSI ion abundance map of LPC 15:0, PC 15:0/18:1-D₇ and LPC 15:0-to-PC 15:0/18:1-D₇ ratio from human osteochondral tissue. One non-OA and OA section from six different subjects were imaged, and one representative lesion of each type was shown. (D) The relative intensity ratio of LPC 15:0-to-PC 15:0/18:1-D₇ between non-OA and OA osteochondral units using MALDI-MSI divided according to stratigraphy. NCC: non-calcified cartilage; CCZ: calcified cartilage zone; SBP: subchondral bone plate; SB: subchondral bone; BM: bone marrow. Data are presented as means ± standard deviation (SD) for n = 6. Scale bar: 1 mm. P < 0.05 was considered significant. *P < 0.05, **P < 0.01, ***P < 0.001. The figure was created with BioRender.com.