Mass Spectrometry Based Proteomic Analysis of AL Amyloidosis: Immunoglobulin Light Chain Gene Constant Region Is an Invariable Part of Amyloid Deposits and Provides Valuable Diagnostic Target
JD Theis, JA Vrana, JD Gamez, A Dogan. Mayo Clinic, Rochester, MN
Background: AL Amyloidosis, caused by immunoglobulin light chain (LC) deposition, is a well-recognized complication of plasma cell neoplasms. So far no pan-proteomic analysis of AL amyloidosis has been performed and the real constituents of AL amyloid is not known. To understand the constituents of AL amyloidosis, we undertook a comprehensive study of AL amyloidosis using a novel mass spectrometry (MS) based proteomic approach.
Design: Paraffin embedded tissue from 100 cases of AL amyloidosis was studied. Amyloid deposits were microdissected, processed and trypsin digested into peptides. The peptides were analyzed by nano-flow liquid chromatography electrospray tandem MS. The resulting MS data were correlated to theoretical fragmentation patterns of tryptic peptide sequences from the Swissprot database using Scaffold algorithm. The identified proteins were subsequently examined for the presence or absence of amyloid related peptides.
Results: MS gave peptide profiles consistent with AL amyloidosis in each case. The analysis showed -LC deposition in 66 and -LC in 34 cases. In each case, MS confirmed the previous clinicopathological diagnosis. Peptides representing LC constant region were always present. The average coverage of the -LC and -LC constant regions were 40% and 55%, respectively. Additionally, the distribution of the peptides suggested that in most cases whole of the LC constant region was deposited. MS also identified -LC variable region peptides in 37 of 66 cases and -LC variable (V) region peptides in 29 of 34 cases studied. The V region coverage was more restricted and the peptides identified were frequently within the framework segments. It is likely that the peptides derived from CDR segments were present but not detected by the methodology due to somatic hypermutation. In the cases with the LC V region hits, it was also possible to assign V region family usage. -LC cases frequently used V region I, II and III families whereas, in -LC cases, V region I and III families dominated.
Conclusions: 1) AL amyloidosis can be accurately diagnosed MS based proteomic analysis in routine clinical specimens. 2) AL amyloidosis invariably contains LC constant region peptides and, frequently, the whole of the constant region is deposited. 3) It is possible to identify LC V region family usage using MS based proteomic analysis. In the clinical setting, this information may be helpful in predicting organ distribution and clinical outcome.
Category: Special Category for 2009 - Pan-genomic/Pan-proteomic approaches to Cancer
Tuesday, March 10, 2009 9:30 AM
Poster Session III # 223, Tuesday Morning