Stages of improvement in visual fields after pituitary tumor resection.

PURPOSE: To use static threshold perimetry to examine the stages of improvement and the potential for late improvement of visual fields after surgical resection of pituitary adenomas causing visual loss from compression of the anterior visual pathways. METHODS: Retrospective review of charts of patients with pituitary tumors and abnormal static threshold perimetry before or soon after treatment who had subsequent visual fields. Quantification of the visual field mean deviation overall, superotemporally, and inferotemporally was performed and compared between visits. Postoperative visits were considered in five time periods: visit 1 (surgery to 1 week), visit 2 (1 month to 4 months), visit 3 (6 months to 1 year), visit 4 (2 years), and visit 5 (3 or more years). RESULTS: Sixty-two patients were included (33 men and 29 women; mean age 54 years [SD +/- 15 years; range, 22 to 83 years]). At visit 1, the relative improvement of the overall mean deviation for the right eye was 30.8% (P =.01) and for the left eye was 13.7% (P =.3067). At visit 2, the relative improvement of the overall mean deviation for the right eye was 30. 4% (P =.0142) and for the left eye was 32.6% (P =.0092). At visits 1 and 2, the inferotemporal quadrants were the quadrants with greatest improvement (visit 1, right eye, 37.8% [P =.0082]; visit 2, left eye, 30.8% [P =.0074]). At visits 3, 4, and 5, an overall trend toward mild improvement was observed with statistical significance only for the inferotemporal quadrant of the left eye from visit 2 to visit 3, which improved 19.7% (P =.0270). CONCLUSION: The pattern of recovery of visual function after decompression of the anterior visual pathways suggests at least three phases of improvement. The early fast phase (surgery to 1 week) of improvement may lead to normalization of visual fields in some individuals. The early slow phase (1 month to 4 months) is the period of most notable improvement. A late phase (6 months to 3 years) of mild improvement does not appear significant overall but may be marked in some individuals. Each of these phases may have one or more mechanisms underlying the observed improvement.

Xenopus IRBP, a phylogenetically remote protein, is uveitogenic in Lewis rats.

Mammalian interphotoreceptor retinoid-binding proteins (IRBPs) are highly uveitogenic in Lewis rats. Xenopus laevis IRBP resembles mammalian IRBP in its four-fold structure, and has approximately 70% amino acid sequence identity with the bovine protein. This study investigated the uveitogenicity of recombinant Xenopus IRBP and two of its derived peptides in Lewis rats. Rats immunized with Xenopus IRBP developed uveoretinitis as well as pineal inflammation. The Xenopus molecule was, however, less immunopathogenic than the bovine IRBP. Of the two Xenopus IRBP peptides tested, 1180-1191 was remarkably uveitogenic, whereas sequence 521-540 exhibited low activity. It is assumed, therefore, that as with bovine IRBP, peptide 1180-1191 is the major uveitogenic sequence in Xenopus IRBP. The role individual residues of these peptides play in the immunopathogenic process is discussed. Our data thus demonstrate that despite its being phylogenetically remote, Xenopus IRBP is uveitogenic in Lewis rats

Electronic home monitoring of congestive heart failure patients: design and feasibility.

The efficacy of electronic monitoring in the home care of heart failure (HF) patients has not been widely reported. We developed a Vital Sign System (VSS) monitoring device capable of measuring the weight, blood pressure, and heart rate of congestive heart failure (CHF) patients in the home and transmitting these measurements via modem to a World Wide Web server. In this study of 22 CHF patients, we tested the reliability of the VSS electronic measurements compared to manual measurements taken by visiting home care nurses and ease of use of the VSS units as rated by both patients and home care nurses. The correlation of electronic to manual measurements was high (weight r=0.99; systolic blood pressure [SBP] r=0.84; diastolic blood pressure [DBP] r=0.54; heart rate [HR] r=0.88). The mean difference between electronic and manual measurements was within an acceptable range for clinical surveillance and care of CHF patients (weight 1.6 lbs; SBP 8.8 mm Hg; DBP 9.2 mm Hg; HR 0.7 bpm) The devices were rated favorably by both nurses and patients. The VSS monitoring device is a reliable, feasible, and favorably rated technology for home surveillance of CHF patients. (c)1999 by CHF, Inc.

Soluble expression in E. coli of a functional interphotoreceptor retinoid-binding protein module fused to thioredoxin: correlation of vitamin A binding regions with conserved domains of C-terminal processing proteases.

The exchange of all-trans retinol and 11-cis retinal between the photoreceptors and retinal pigmented epithelium is mediated by interphotoreceptor retinoid-binding protein (IRBP). IRBP contains binding sites for retinoids, docosahexaenoic acid and probably cell surface and matrix receptors. IRBP arose through the quadruplication of an ancient protein, represented by its carboxy-terminal module (module 4 in amphibians and mammals). Module 4 has retinol binding activity and is composed of regions coded for by each of IRBP's four exons. Determining the function of the exons has been hampered by insoluble expression of module 4 in Escherichia coli. Here, we found that module 4 of Xenopus IRBP (X4IRBP), as well as its exon segments, can be expressed in a soluble form as thioredoxin fusion proteins. The recombinant proteins were purified by ion exchange and arsenical-based affinity chromatography. Liquid chromatography/mass spectrometry confirmed that the sequence of X4IRBP is correct. All-trans retinol binding was characterized by monitoring enhancement of retinol fluorescence, quenching of intrinsic protein fluorescence, and transfer of energy to the bound retinol. Retinol bound to X4IRBP at 2.20+/-0.29 sites with a KD=1.25+/-0.39. One of the two sites was localized to Exons(2+3) and had a KD=0.26+/-0.13 micron. This site, which supported protein quenching and energy transfer, probably contains at least one of the two conserved tryptophans present in this segment. The second site was localized to Exon 4. This site supported the enhancement of retinol fluorescence but not protein quenching or energy transfer and had a KD=1.94+/-0.20 micron. Exon 1 had no retinol binding activity. The location of the retinol binding regions correlated with the distribution of domains conserved between IRBPs and the newly recognized family of C-terminal processing proteases (CtpAs), proteins which bind and cleave non-polar carboxy termini.

Fourth module of Xenopus interphotoreceptor retinoid-binding protein: activity in retinoid transfer between the retinal pigment epithelium and rod photoreceptors.

PURPOSE: Interphotoreceptor retinoid-binding protein (IRBP), an extracellular protein believed to support the exchange of retinoids between the neural retina and retinal pigment epithelium (RPE) in the vertebrate eye, exhibits a modular, i.e., repeat, structure. The present study was undertaken to determine whether an individual module of IRBP has activity in retinoid transfer between the RPE and rod photoreceptors. METHODS: The retinoid transfer activity of a recombinant protein corresponding to the fourth module of Xenopus laevis IRBP (X4IRBP) was examined in two ways. First, X4IRBP was tested for its ability to support the regeneration of porphyropsin in detached/reattached Xenopus retina/RPE-eyecups. Following illumination and removal of native IRBP, Xenopus eyecups supplemented with 42 microM X4IRBP or (as a control) Ringer's solution were incubated in darkness and then analyzed for regenerated porphyropsin. Second, toad (Bufo marinus) RPE-eyecup preparations were used to evaluate X4IRBP's ability to promote the release of 11-cis retinal from the RPE. RESULTS: The regeneration of porphyropsin in X4IRBP-supplemented Xenopus retina/RPE-eyecups (0.45 +/- 0.04 nmol; mean +/- SEM, n = 11) exceeded that in controls (0.13 +/- 0.02 nmol, n = 11). For promoting the release of 11-cis retinal from the toad RPE, 42 microM X4IRBP was more effective than equimolar bovine serum albumin although considerably less than that of 26 microM native bovine IRBP. CONCLUSIONS: The results indicate a low but significant activity of IRBP's fourth module in reactions relevant to retinoid exchange.

Arginine to glutamine substitutions in the fourth module of Xenopus interphotoreceptor retinoid-binding protein.

PURPOSE: Interphotoreceptor retinoid-binding protein (IRBP) is unusual for a lipid-binding protein in that its gene is expressed uniquely by cells of photoreceptor origin and consists of four homologous repeats, each coding for a module of approximately 300 amino acid residues. All-trans retinol binding domains, which appear to be present in each module, are composed of conserved hydrophobic regions [Baer et al, Exp Eye Res 1998; 66:249-262]. Here we investigate the role of highly conserved arginines contained in these regions. METHODS: To study the arginines in an individual module without the interference of ligand-binding activity elsewhere in the protein, we expressed in E. coli the fourth module of Xenopus IRBP by itself as a soluble thioredoxin fusion protein (X4IRBP). Arginines 1005, 1041, 1073 and 1122 were separately replaced by glutamine using PCR overlap extension mutagenesis. The glutamine substitutions were confirmed by liquid chromatography-tandem mass spectrometry. The binding of all-trans retinol and 9-(9-anthroyloxy)stearic acid (9-AS) to X4IRBP and each of the mutants was evaluated by fluorescence spectroscopy. Binding was followed by monitoring the enhancement of ligand fluorescence and the quenching of protein endogenous fluorescence. The ability of the recombinant proteins to protect all-trans retinol from oxidative degradation was evaluated by monitoring absorbance at 325 nm over time. RESULTS: The substitution of Gln for Arg1005 about doubled the amount of ligand necessary to attain saturation and about doubled the level of fluorescence enhancement obtained at saturation for both all-trans retinol and 9-AS. Although there was not a significant change in the Kd, the substitution increased the calculated number of binding sites (N) from approximately 2 to approximately 4 per polypeptide. The other Arg->Gln mutants did not significantly change the Kd or N. None of the mutations compromised the ability of the module to protect all-trans retinol from degradation. CONCLUSIONS: Our data suggest that the function of the conserved arginines in IRBP is fundamentally different from that of other retinoid-binding proteins. These residues do not appear to play a role in defining the specificity of the ligand-binding domain. Rather, Arg1005 appears to play a role in defining the capacity of the domain. Our data suggest that the binding site consists of a single hydrophobic cavity promiscuous for fatty acids and all-trans retinol.

Interphotoreceptor retinoid-binding protein (IRBP): expression in the adult and developing Xenopus retina.

Apposition of the neural retina and pigment epithelium is critical to photoreceptor development and function. Interphotoreceptor retinoid-binding protein (IRBP) is a major component of the extracellular matrix separating these epithelia in the African clawed frog Xenopus laevis (Gonzalez-Fernandez et al., [1993], J. Cell Sci. 105:7-21). In the adult retina, IRBP appears to mediate the transport of hydrophobic molecules, particularly retinoids and fatty acids, within the hydrophilic extracellular domain. In this paper, we compare the distribution of IRBP and its mRNA in adult and embryonic Xenopus retina. Xenopus IRBP antisense RNA, labeled with tritium or digoxigenin, was used for in situ hybridizaton studies. For immunohistochemistry, we used an antiserum against Xenopus IRBP expressed in Escherichia coli. In the adult, we found that IRBP is synthesized at similar levels by both rods and cones. The protein is restricted to the interphotoreceptor matrix, with lesser amounts in the pigment epithelial cytoplasm. In the embryo, expression of the mRNA for IRBP is restricted to the central retina, where photoreceptor differentiation has taken place. By contrast, the protein is distributed throughout the embryonic subretinal space. Therefore, the presence of IRBP precedes photoreceptor differentiation. In summary, IRBP is synthesized by both rods and cones and may be internalized by the pigment epithelium. In the embryo, IRBP is synthesized by the central retina and diffuses through the matrix, reaching the undifferentiated peripheral retina. In view of its ligand-binding properties, diffusion of IRBP may provide the peripheral neural retina with a vehicle to transport retinoids and docosahexaenoic acid (molecules critical to normal retinal development) from the pigment epithelium.

Expression and characterization of the fourth repeat of Xenopus interphotoreceptor retinoid-binding protein in E. coli.

Interphotoreceptor retinoid-binding protein (IRBP) is an extracellular glycolipoprotein which in higher vertebrates has a 4-repeat structure and carries endogenous vitamin A and fatty acids. The location of IRBP's 1-2 binding sites for retinol is unknown. To begin to understand which repeat(s) are responsible for ligand-binding, we expressed the fourth repeat of Xenopus IRBP in E. coli to determine if it could by itself bind all-trans retinol. Our expression studies used a polyhistidine fusion domain to purify the recombinant protein directly from inclusion bodies. The fusion protein could be renatured without aggregation if refolded at a sufficiently dilute concentration (< 3 microM). The recombinant fourth repeat of Xenopus IRBP binds [3H]all-trans retinol and the fluorescence of this ligand increases 8-fold upon binding. The binding is saturable with a Kd = 0.4 microM. The expression of recombinant IRBP fragments as fusion proteins in prokaryotes will be useful for defining the structural requirements for ligand binding by this interesting protein.