Analysis of in vivo-derived amyloid-beta polypeptides by on-line two-dimensional chromatography-mass spectrometry.

The presence of senile plaques composed of amyloid-beta (Abeta) polypeptides within brain tissue is normally used as a definitive postmortem diagnosis for Alzheimer's Disease (AD). Therefore, these polypeptides have been investigated as potential biomarkers of the disease state. However, at present, there is a lack of a robust assay for the detection of such polypeptides derived from in vivo sources. Such an assay is essential for analysis of biological samples from model AD systems. To overcome this problem we have developed a new single-step assay utilizing two dimensional-chromatography in conjunction with mass spectrometry. The method consists of on-line size-exclusion chromatography (SEC) to provide initial separation of analytes from the sample (based on their molecular weight) coupled with sample preconcentration prior to analysis by microbore high-performance liquid chromatography-mass spectrometry (HPLC-MS). This provides an extremely versatile and powerful assay which can separate specific analytes from cell lysate in a single step without further sample handling. The use of mass spectrometry as the detection system yields much more structural information than can be obtained from traditional ELISA and sandwich ELISA antibody assays. Furthermore, the on-line sample cleanup protocol minimizes sample handling and facilitates assay automation. Utilizing this new assay we have been able to detect Abeta 1-40 and Abeta 1-42 at cellular concentration levels directly from cell lysates. Moreover, we have detected multiple peptide responses within the same analysis, some of which have been tentatively identified as other ragged C-termini Abeta polypeptides derived from Abeta 1-42, based on their molecular weight, as well as oxidized Abeta polypeptides.

Self-appraised problem-solving skills and the prediction of secondary complications among persons with spinal cord injuries.

Secondary complications following spinal cord injury (SCI) include decubitus ulcers and recurrent urinary tract infections. These conditions can significantly impair quality of life and prove life-threatening; it is also believed that these conditions are mediated by behavioral pathways. According to the social problem-solving model, persons who report effective problem-solving skills should be capable of adhering to long-term therapeutic regimens of self-care necessary to prevent these complications. We tested this assumption in the present study. Discriminant function analyses revealed self-appraised skills in approaching and defining problems contributed to the prediction of secondary complications among 53 persons with SCI. Results are discussed in light of the social problem-solving model, and the utility of problem-solving interventions in rehabilitation is explored.

Fast atom bombardment and tandem mass spectrometry for structure determination of steroid and flavonoid glycosides.

The combination of fast atom bombardment (FAB) and tandem mass spectrometry (MS-MS) was tested for its applicability to generate useful structural information for steroid and flavonoid glycosides. The following compounds were investigated: quercetin, myricitrin, apigetrin, fraxin, rutin, neohesperidin, hesperidin, naringin, apiin, cymarin, digoxin, digitoxin, xanthorhamnin, and frangulin. Upon FAB, the sample molecules are desorbed as (M + H)+, (M - H)-, or as (M + Na)+ or (M + K)+. Collisional activation of (M + H)+ or (M - H)- ions in the MS-MS experiment leads to sequential losses of glycoside moieties in a manner which permits the sequence of glycosides to be established. Some glycosides occur as mixtures of homologs. Proper interpretation of the MS-MS or collisional activation decomposition spectra often allows the homology to be located. In addition to the simple and highly selective fragmentations observed in this combined experiment, FAB and MS-MS also remove interference caused by the ubiquitous matrix ions which are desorbed by FAB.

Ribosyl-diphthamide: confirmation of structure by fast atom bombardment mass spectrometry.

Diphtheria toxin inactivates protein synthesis elongation factor 2 by attaching ADP-ribose to an unusual post-translational amino acid derivative, diphthamide, in the factor. Previously, we prepared ribosyl-diphthamide from the ADP-ribosyl-factor and proposed on the basis of NMR spectral analysis that it is 1-alpha-D-ribofuranosyl-2-[3-carboxyamido-3-(trimethylammonio++ +)propyl] histidine [N. J. Oppenheimer, and J.W. Bodley, (1981) J. Biol. Chem. 256, 8579-8581 and op. cit.]. Now, using fast atom bombardment mass spectrometry, the intact cation of ribosyl-diphthamide has been observed in the gas phase. The theoretical mass of the structure proposed for ribosyl-diphthamide uniquely agrees with the observed mass of the inact cation of the compound to within 2 ppm. Collisional activation decomposition mass spectral analysis provided additional structural confirmation. Thus, although the compound has not been synthesized, all available evidence appears uniquely consistent with the structure of ribosyl-diphthamide previously proposed.

Fast atom bombardment combined with tandem mass spectrometry for the determination of nucleosides.

The positive and negative ion fast atom bombardment (FAB) mass spectra and fast atom bombardment collisionally activated decomposition (CAD) spectra of a series of nucleosides and two dinucleotides are reported. The nucleosides studied are substituted forms of guanosine, adenosine, nebularine, tubercidin, uridine, and related pyrimidines. The FAB and CAD data both contain similar information. The CAD spectra are found to provide some structural information not found in the FAB mass spectra. Tandem mass spectrometry also allows emphasis to be put on weak fragments which are either not observed in the FAB mass spectrum or are lost in the matrix ion signals.

Resurfacing large cheek defects with rotation flaps from the neck.

A neck flap based on the midline many provide excellent cover for large cheek defects. The technical aspects of planning and replacement, with emphasis on positioning to prevent ectropion of the lower lid, are presented. Alone, or in conjunction with the multiple excision technique, this flap can produce a superior cheek surface.