Protein Profile of Human Perilymph: In Search of Markers for the Diagnosis of Perilymph Fistula and other Inner Ear Disease

Abstract

Recent developments in high-resolution two-dimensional polyacrylamide gel electrophoresis, combined with amino acid sequencing and computer-assisted image analysis, have allowed separation of approximately 100 proteins and identification and quantitation of some 30 proteins in human perilymph. The majority of proteins were found to be present in perilymph at levels in basic agreement with the total protein gradient between perilymph and plasma (1:35). However, several striking differences were observed: (1) β2-transferrin, known to be absent from normal plasma but present in cerebrospinal fluid, was detected in perilymph at a concentration roughly equal to that in cerebrospinal fluid; and (2) two high-density lipoprotein-associated apolipoproteins—apo D (formerly PLS:33) and apo J or NA1 and NA2 (formerly PSL:29/30), the latter showing identity with 5P40/40, or cytolysis inhibitor—were found to be present at concentrations 1 to 2 orders of magnitude higher when examined in terms of total protein and to be comparable with or higher than plasma levels when examined in terms of absolute concentrations. The functional significance of the extremely high levels of the two apolipoproteins is not known at this time. An attempt was made to use β2-transferrin, as well as apo D and apo J (NA1/NA2), as markers for the diagnosis of perilymph fistula, one of the most controversial and challenging problems for the otologist today. It was determined that the technique is indeed applicable when relatively pure fistula samples are analyzed. Limitations and potential improvements of the technique are discussed. In addition, the potential usefulness of two-dimensional polyacrylamide gel electrophoresis in other pathologic conditions of the inner ear is discussed briefly.