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Biomedical subjects

D G Hwang

Publications and source records attributed to D G Hwang.

33 records · Page 2Linked to original sources
PubMed1993

Combination antibiotic supplementation of corneal storage medium.

Gram-positive cocci frequently contaminate donor corneal tissue and represent the most common cause of postkeratoplasty endophthalmitis. Although gentamicin is currently added to corneal storage medium in an effort to decrease bacterial contamination of donor tissue, it has poor or variable in vitro activity against many strains of streptococci and staphylococci. To investigate whether the antibiotic supplementation of corneal storage media could be improved, we surveyed 11 antibiotics for antimicrobial efficacy under simulated storage conditions against gentamicin-resistant strains of Staphylococcus aureus, S. epidermidis, Streptococcus pneumoniae, and St. viridans. All antibiotics showed markedly reduced activity at 4 C as compared to their predicted activity at 37 C. Bactericidal activity of streptomycin and tobramycin was enhanced by preceding 4 C storage with a three-hour period at room temperature (23 C). Under these conditions, streptomycin showed the best antimicrobial activity of the 11 antibiotics tested. Addition of gentamicin to streptomycin resulted in further improvement of activity against S. aureus and S. epidermidis, whereas the addition of penicillin G to streptomycin enhanced the activity against St. viridans. Optimal antibiotic activity (99% or more killing) against all four isolates of gentamicin-resistant gram-positive cocci was best achieved with the combination of gentamicin, streptomycin, and penicillin G, coupled with a three-hour period at room temperature before 4 C storage.

Cornea↗
PubMed1993

Lamellar flap corneal biopsy.

A modified technique of corneal biopsy is described that allows a lesion in the deep corneal stroma to be accessed for scraping or biopsy while sparing the stromal tissue anterior to the lesion. This technique may be especially valuable in cases of deep corneal pathology in which traditional methods of corneal biopsy risk excessive removal of tissue, which, in turn, can lead to complications such as thinning or perforation.

Anti-Bacterial Agents↗
PubMed1992

Computer-assisted study of diurnal variation in corneal topography after penetrating keratoplasty.

Diurnal changes in corneal topography have been documented to be greater in eyes following radial keratotomy that in normal eyes. To determine whether substantial changes of this nature result from corneal incisions in general or are a specific complication of radial keratotomy, we examined 12 corneas (10 patients) after penetrating keratoplasty for diurnal changes, using a computerized corneal topographic analysis system. Diurnal changes in keratometry readings, central corneal thickness, intraocular pressure, and refraction also were analyzed. From morning to evening, central corneal curvature flattened by an average of 0.74 +/- 0.18 diopters in eight eyes (67%), and steepened by an average of 2.00 +/- 0.53 D in four eyes (33%). Diurnal changes in central corneal thickness were correlated with diurnal changes in central corneal curvature (r = 0.63, P less than .05). These data suggest that changes in corneal thickness over the course of the day may partially account for the changes in corneal curvature demonstrated to occur following penetrating keratoplasty.

Adult↗
PubMed1989

Collagen shield enhancement of topical dexamethasone penetration.

Collagen corneal shields were investigated as a vehicle for enhancing the ocular penetration of topical 0.1% dexamethasone alcohol in rabbit eyes. Four protocols were compared: a single dexamethasone drop, hourly drops, a 24-hour collagen shield presoaked in 0.1% dexamethasone, and a presoaked collagen shield followed by hourly drops. Dexamethasone concentrations in the cornea, aqueous, iris, and vitreous were measured by radioassay at six time intervals, and cumulative drug delivery over 6 hours was calculated for each tissue. Treatment with a presoaked collagen shield plus hourly drops resulted in peak and cumulative drug delivery to the cornea, aqueous, iris, and vitreous that was twofold to fourfold higher than delivery achieved with hourly drops alone. A presoaked shield by itself yielded equivalent or superior peak and cumulative drug delivery compared with a regimen of hourly drops. Collagen shields significantly enhance topical dexamethasone penetration and may be useful for maximizing the intraocular delivery of dexamethasone and for decreasing the required frequency of topical dexamethasone administration.

Animals↗
PubMed1987

Applications of liquid chromatography-mass spectrometry in metabolic studies of explosives.

Liquid chromatography-mass spectrometry was used for the detection and identification of metabolites of 2,4,6-trinitrotoluene (TNT) in urine and blood. The metabolites were found in the urine of rats and in the blood of rabbits fed with TNT, in the urine of rats exposed to TNT by skin absorption and in the urine of TNT munition workers. The detected metabolites, formed by reduction processes, included 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,4-diamino-6-nitrotoluene and 2,6-diamino-4-nitrotoluene, in addition to untransformed TNT.

Animals↗
PubMed1986

Metabolic studies of explosives. 5. Detection and analysis of 2,4,6-trinitrotoluene and its metabolites in urine of munition workers by micro liquid chromatography/mass spectrometry.

Metabolites of 2,4,6-trinitrotoluene (TNT) were found in the urine of a group of TNT munition workers. The urine extracts were analysed by micro liquid chromatography/mass spectrometry. The metabolites found included 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene, 2,4-diamino-6-nitrotoluene, 2,6-diamino-4-nitrotoluene and untransformed TNT. The detection limit of the metabolites in urine was 0.1 ng/ml for 20 ml urine samples.

Chromatography, High Pressure Liquid↗
PubMed1985

Metabolic studies of explosives. II. High-performance liquid chromatography-mass spectrometry of metabolites of 2,4,6-trinitrotoluene.

A series of metabolites of 2,4,6-trinitrotoluene were studied by combined high-performance liquid chromatography-mass spectrometry. These metabolites are formed mainly by oxidation and reduction processes. Separations were done on a C8 reversed-phase column, using acetonitrile-water at various relative concentrations as mobile phases, followed by ultraviolet and on-line mass spectrometry with a direct liquid insertion probe liquid chromatograph-mass spectrometer interface. The mass spectra obtained were chemical-ionization spectra with the mobile phase as reagent. Mass spectra obtained included mainly reduced ions, adduct ions and typical fragment ions. The combination of high-performance liquid chromatographic separation with on-line mass spectrometry was found to be a suitable method for the identification of the investigated metabolites.

Animals↗
PubMed1985

Identification of urinary metabolites of 2,4,6-trinitrotoluene in rats by liquid chromatography-mass spectometry.

Metabolites of 2,4,6-trinitrotoluene (TNT) were found in the urine of rats fed with TNT. The urine extracts were analysed by liquid chromatography-mass spectrometry (LC-MS). Metabolites found included TNT itself as well as 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene and 2,4-diamino-6-nitrotoluene, indicating that reduction processes are responsible for the formation of these metabolites.

Aniline Compounds↗
PubMed1984

Metabolic studies of explosives. 1--EI and CI mass spectrometry of metabolites of 2,4,6-trinitrotoluene.

A series of metabolites of trinitrotoluene (TNT) have been synthesized and analysed by electron impact (EI) and chemical ionization (CI) mass spectrometry. Identification characteristics of these metabolites by their mass spectra have been determined. Differentiation of isomers is made possible by EI ions which are characteristic of the position of the methyl with regard to the nitro groups.

Aniline Compounds↗
PubMedDate not supplied

Expression of matrix metalloproteinases 2 and 9 and tissue inhibitors of metalloproteinase 1 and 2 in inflammation-induced corneal neovascularization.

PURPOSE: Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase (TIMPs) have been linked to the angiogenic process in general. In order to understand the potential roles of MMP-2, MMP-9 and TIMPs in the corneal neovascularization process, we examined the expression and activities of MMP-2, MMP-9 and TIMPs during the course of cauterization-induced corneal neovascularization in a rat model. METHODS: Neovascularization of rat corneas was induced by silver nitrate cauterization. The expression of MMP-2, MMP-9, TIMP-1 and TIMP-2 was examined by immunohistochemistry and RT-PCR. The protein activities of MMPs and TIMPs were compared in pre- and postcauterization corneas by gelatin zymography and reverse zymography, respectively. RESULTS: MMP-2, TIMP-1 and TIMP-2 immunoreactivities were expressed in normal corneas, predominantly in the corneal epithelium. After injury, immunoreactivities of both MMPs and TIMPs were increased, notably in the healing corneal epithelium, infiltrating inflammatory cells, stromal fibroblasts and ingrowing vascular endothelial cells. The increase in gross MMP-2 enzymatic activity paralleled the maximal vascular ingrowth on day 4, while the gross MMP-9 enzymatic activity rose immediately on day 1, then decreased steadily, which paralleled the magnitude of inflammatory cell infiltration. The immunoreactivity of MMPs/TIMPs decreased significantly 2 weeks after cauterization. On day 35, MMP-2, TIMP-1 and TIMP-2 staining was seen only in corneal epithelium and vascular endothelial cells. Both the RT-PCR and reverse zymography results revealed a more constant expression of TIMP-2, while the TIMP-1 expression appeared to be more inducible. CONCLUSION: MMPs as well as TIMPs were upregulated in cauterization-induced corneal neovascularization, suggesting that both may participate in extracellular matrix remodeling in the corneal wound healing, inflammation and neovascularization processes.

Animals↗
PubMedDate not supplied

Corneal complications of cataract surgery.

The intraoperative and postoperative complications of cataract surgery that affect the cornea vary in etiology and severity. Principal complications include epithelial disruption, infections, sterile corneal ulceration, stromal melt, mechanical or toxic injury of the endothelium, vitreous touch, stripped Descemet's membrane, and epithelial and fibrous downgrowth. Meticulous cataract surgery with careful attention to protecting the cornea can prevent most serious corneal complications. Certain clinical situations warrant special note; patients with rheumatoid arthritis and dry eyes require extra lubrication to the epithelium to prevent disruption during surgery; patients with low endothelial cell counts benefit from the least possible surgical trauma to minimize cell loss; surgical clean-up of vitreous from the anterior segment remains an important principle; clinically significant Descemet's membrane tears or areas of stripping should be repaired at the time of cataract surgery. The clinical judgment and skills of the cataract surgeon should be equal to the type of cataract operation performed.

Cataract Extraction↗