PCA and DA of normal and OA cartilage. A) The spectra of all the old and OA samples after MALDI-MSI experiments were analyzed by PCA and DA to classify peptides specific to each category using a 1 D plot. B) Loading plot of DF1 representing the peptides specific to OA given by MALDI-MSI. The OA specific peak 1366.5 is ringed. DA, discriminant analysis; MSI, MALDI, matrix assisted desorption ionization; OA, osteoarthritis; PCA, principal component analysis.