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Biomedical subjects

D V Crabtree

Publications and source records attributed to D V Crabtree.

11 recordsLinked to original sources
PubMed2001

Tubulins in the primate retina: evidence that xanthophylls may be endogenous ligands for the paclitaxel-binding site.

The xanthophylls-lutein, zeaxanthin, and meso-zeaxanthin (L&Z)-are found in the central region of the primate retina, which is called the macula lutea (yellow spot). How they are anchored there and what their function is has been debated for over 50 years. Here, we present evidence that they may be bound to the paclitaxel (Taxol) binding site of the beta-tubulin subunit of microtubules and that a major function may be to modulate the dynamic instability of microtubules in the macula. Also, we compare nucleic acid and amino acid sequences of tubulins that are in human brain with those we have isolated from human-retina and monkey-macula cDNA libraries. In so doing, we suggest that in primates, class I beta-tubulin consists of at least two subtypes (beta(Ia) and beta(Ib)). Alignment analysis of the sequences of the genes for beta(Ia) and beta(Ib) indicates that the corresponding mRNAs may have other functions in addition to that of coding for proteins. Furthermore, we show that there are at least five different types of beta-tubulin in the macula lutea of rhesus monkey.

Alkaloids↗
PubMed1997

Retinyl palmitate in macaque retina-retinal pigment epithelium-choroid: distribution and correlation with age and vitamin E.

Retinyl palmitate (RP) and retinyl stearate (RS) are of central importance in the visual cycle because they are the major storage molecules for retinol. In some tissues (e.g. liver) the amount of vitamin A (mostly in the form of retinyl ester) is positively correlated with both the amount of alpha-tocopherol (alpha-T) and age. Furthermore, alpha-T is a noncompetitive inhibitor of the hydrolysis of RP. We measured RP, RS, alpha-T and beta+gamma-tocopherol (beta+gamma-T) as functions of distance from the foveal center (eccentricity) in the retina-RPE-choroid (NRC) of rhesus monkeys using high-pressure liquid chromatography. It was found that the central and peripheral NRC differed with respect to these parameters. The concentration (pmoles sq mm-1) of RP was higher in the central NRC than in the peripheral NRC and was at a maximum in the region of the fovea. Furthermore, although in the peripheral NRC. RP was well correlated with age and alpha-T (similar to other tissues), in the central NRC, RP per sq mm was more clearly related to photoreceptor density. These differences imply that the central NRC controls the concentration of RP within it, while the concentration of RP in the peripheral NRC is determined by its environment (e.g. nutrients available from blood) and the age of the individual.

Age Factors↗
PubMed1997

Is beta-carotene an antioxidant?

An hypothesis is presented that is opposed to the conventional viewpoint that beta-carotene is an in vivo free-radical scavenger. It is suggested that there are biochemical reasons why beta-carotene, other carotenoids, and especially their metabolites may be harmful to mammalian systems. Finally, the hypothesis that the macular pigment carotenoids, lutein and zeaxanthin, are free-radical scavengers is challenged.

Animals↗
PubMed1996

Vitamin E, retinyl palmitate, and protein in rhesus monkey retina and retinal pigment epithelium-choroid.

PURPOSE: To measure the amounts of vitamin E, retinyl palmitate, and protein in the primate retina and its supporting tissues-the retinal pigment epithelium and choroid. To compare the amounts and concentrations of these materials in the central retina with those in the peripheral retina and to compare the concentration of vitamin E in the retina with that in plasma. Finally, to compare these results in rhesus monkey with existing measurements in humans. METHODS: Ocular tissues from rhesus monkeys (Macaca mulatta) were extracted with a two-phase solvent system. Components in the extract were separated by reverse-phase high-pressure liquid chromatography. Two detectors in series monitored the effluent: Vitamin E was quantified with an internal standard and fluorescence detection, whereas retinyl palmitate was quantified with an external standard and ultraviolet light detection. RESULTS: Amounts of vitamin E, retinyl palmitate, and protein in tissues from rhesus monkey compared reasonably well with those reported for humans. The content of vitamin E in the peripheral neural retina was moderately correlated with its protein content and, to a greater extent, with the concentration of vitamin E in the plasma; however, the content of vitamin E in the central neural retina correlated only with the amount of protein in the central neural retina. CONCLUSIONS: These results are consistent with rhesus monkey as a model for the use of vitamin E by human ocular tissues. The amount of vitamin E in the central neural retina appears to be more closely regulated than the amount of vitamin E in the peripheral neural retina.

Animals↗
PubMed1996

Radial distribution of tocopherols in rhesus monkey retina and retinal pigment epithelium-choroid.

PURPOSE: To map vitamin E as a function of distance from the foveal center in the primate retina and retinal pigment epithelium (RPE)-choroid. METHODS: Eyecups from rhesus monkeys were dissected with circular trephines so that the innermost disc, centered on the fovea, was in the center of a series of concentric rings. Two different types of dissection were performed. For one type, the authors used circular trephines with diameters of 1, 4, 8, and 10 mm (1,4-D), whereas for the other type the diameters were 2, 5, 8, and sometimes 10 mm (2,5-D). When possible, the neural retina was separated from the RPE-choroid. Tissues were analyzed for vitamin E, retinyl palmitate, and protein. RESULTS: Surface area, volume, and protein were used as indexes of the amount of tissue analyzed. Distributions of vitamin E in neural retina were dependent on the tissue metric used and type of dissection performed. However, regardless of the tissue metric used, the central 1-mm disc of the 1,4-D was, on average, higher in vitamin E content than was the central 2-mm disc of the 2,5-D. This was particularly true when volume was the tissue metric. From the average values of vitamin E in a series of concentric discs, a composite plot of the vitamin E concentration in the neural retina was generated that took into consideration both types of dissection. That plot displayed a local maximum in the fovea and then precipitously declined to a minimum in the region between 0.5 and 1.0 mm eccentricity (near the foveal crest); at greater eccentricities, the vitamin E concentration rose to a value similar to that in the fovea, i.e., the composite plot indicated that vitamin E has a V-shaped distribution in the central neural retina. Vitamin E distribution in the RPE-choroid, with surface area as the tissue metric, also was measured. For this tissue, the foveal region displayed a local maximum. CONCLUSIONS: By combining the results of two different types of dissection, the authors found that in the neural retina, vitamin E displayed a minimum near the foveal crest. This minimum correlated anatomically with the site at which areolar (geographic) atrophy frequently occurs in retinal pigment epithelial cells in the human disease, age-related macular degeneration.

Animals↗
PubMed1991

Ocular toxicity of low-molecular-weight components of silicone and fluorosilicone oils.

Silicone oil (SiO) and fluorosilicone oil (FSiO) are injected into the vitreous cavity in difficult cases of retinal detachment surgery. SiO and FSiO contain linear and cyclic low-molecular-weight components (LMWC) that are thought to cause ocular toxicity. Using the purified oils (without LMWC) and some of the individual LMWC, the authors evaluated the relation of the LMWC to the short-term ocular toxicity of the oils. When octamethylcyclotetrasiloxane or other single small species of linear and cyclic LMWC of SiO were injected into the rabbit anterior chamber, severe inflammation and corneal edema were induced. The ocular responses to the single species of the LMWC of SiO decreased with an increase of the molecular weights. Cyclic LMWC of FSiO (a mixture of trimethyl-3,3,3-trifluoropropylcyclotrisiloxane and tetramethyl-3,3,3-trifluoropropylcyclotetrasiloxane) also induced inflammation and corneal edema. However, unpurified SiO and FSiO, as well as purified oils (via solvent fractionation), did not cause significant adverse ocular response, presumably because the amounts of LMWC (especially the smallest species) in the oils were relatively small. Using gas chromatography, the authors analyzed SiO and FSiO recovered from rabbit and human vitreous cavities up to 2 yr after injection. In most of the cases, the concentrations of LMWC in SiO decreased after injection. This is consistent with the possibility that LMWC diffused from the oils into the ocular tissues. The long-term effect of LMWC in intraocular SiO and FSiO has not been determined. However, diffusion of LMWC into ocular tissues may relate to the chronic ocular toxicity of the oils.

Animals↗
PubMed1990

Factors contributing to the emulsification of intraocular silicone and fluorosilicone oils.

Silicone oil (SiO) and fluorosilicone oil (FSiO) are used as vitreous substitutes during retinal detachment surgery. Emulsification of these oils causes complications in oil-injected eyes. One factor contributing to emulsification is interfacial tension (gamma i) of the oils. In general, the lower the gamma i, the more easily the oils are emulsified. We measured the gamma i of SiO and FSiO by the ring method at 37 degrees C; corrected the measured values by the Harkins-Jordan table or the Zuidema-Waters equation; and found that the gamma i between the oils and liquefied bovine vitreous was low compared with the gamma i between the oils and water (eg, gamma i of 1000 centistokes [cs]SiO against liquefied vitreous and water was 16.0 and 42.8 dyne/cm, and that of 1000 cs FSiO was 14.7 and 38.7 dyne/cm, respectively). When SiO or FSiO and liquefied vitreous were shaken in a partially filled vial, both oils were emulsified regardless of viscosity and purity. However, when the vial was filled completely (a situation in which the hydrodynamic condition of the oils may be similar to that in the eye), SiO of 1000 and 12,500 cs and FSiO of 10,000 cs did not emulsify, although FSiO of 1000 cs did emulsify. SiO was less emulsified than FSiO of the same viscosity, possibly because the smaller density difference between SiO and intraocular fluids makes agitation difficult compared with FSiO. High viscosity of the oils restricted mechanical emulsification, which was not prevented by eliminating low-molecular-weight components of the oils. Residual catalysts may relate to spontaneous emulsification, which was observed occasionally with high-viscosity SiO in water.

Animals↗
PubMed1990

Analysis and fractionation of silicone and fluorosilicone oils for intraocular use.

Silicone oil (SiO) and fluorosilicone oil (FSiO) are useful in difficult cases of retinal detachment surgery. Unidentified low-molecular-weight components (LMWC) and residual catalysts in SiO and FSiO have been implicated in the adverse reactions of the oils in the eye. The authors analyzed LMWC of SiO and FSiO using a gas chromatograph (GC) equipped with a 6-ft x 2-mm column packed with 3% SP-2250 and a flame-ionization detector. By commercially available standards and a homologous series plot, MD3M to MD23M (linear LMWC) and D4 to D30 (cyclic LMWC) were positively identified in commercial-grade 1000-centistokes (cs) SiO. Commercial-grade 12,500-cs SiO contained GC-detectable LMWC (up to MD28M and D30) at higher concentrations than commercial-grade 1000 cs SiO, although the weight percent of acetone-extractable LMWC (including those larger than MD28M and D30) was less in the former than in the latter. The GC-detectable LMWC in most medical-grade SiO were less than those in commercial-grade SiO. Tetramethylammonium siloxanolate (a residual catalyst) and tributylphosphine oxide (a heat-decomposition product of a polymerization catalyst) were tentatively identified in commercial- and medical-grade 12,500-cs SiO, respectively. Commercial-grade 1000- and 10,000-cs FSiO also contained LMWC, including F3 and/or F4 (cyclic LMWC). To eliminate LMWC from the oils, the authors developed a solvent fractionation method using acetone for SiO and hexane for FSiO. After continuous solvent extraction of SiO for 2 weeks and FSiO for 3 weeks, all measurable LMWC were eliminated from the oils.

Catalysis↗
PubMed1989

Pentafluorobenzoic anhydride as a derivatizing agent for alcohols and hydroxy fatty acid methyl esters detected by electron capture in gas chromatography.

Pentafluorobenzoate derivatives of primary and secondary alcohols have been prepared using pentafluorobenzoic anhydride. The gas chromatographic properties of the homologous series of the methyl esters of 2-hydroxycarboxylic acids from C12 to C26 have been studied on the high-temperature stationary phase Poly-S 179. The suitability of determining trace amounts of these compounds using gas chromatography with an electron-capture detector and with electron-capture negative-ion chemical-ionization mass spectrometry is discussed.

Anhydrides↗
PubMed1983

Benzo[a]pyrene-collagen interactions.

In vitro interactions of benzo[a]pyrene (BaP) with acid-soluble type I collagen from rat tail tendon have been investigated. The fluorescence of BaP increases in the presence of collagen. Bound BaP inhibits the formation of collagen fibrils in solution. When BaP-collagen complexes are irradiated in air with UV (365 nm) light, BaP rapidly undergoes photooxidation with the further inhibition of fibril formation. Viscosity and circular dichroism (CD) studies show that neither BaP nor further UV-irradiation alters the size or helical conformation of the protein. During thermal denaturation of collagen, BaP fluorescence changes. Collagen from young rat tail tendon shows a pronounced drop at about 38 degrees C, whereas that from old rat tail tendon exhibits an increase with a plateau in the same temperature range. These anomalous changes are observed when tyrosine residues, present only in the non-helical terminal telopeptides of collagen, are excited at 275 nm, but not by direct BaP excitation at 387 nm. These findings suggest that the specific hydrophobic telopeptide region, which plays an important role in fibril formation, are affected by bound BaP.

Aging↗