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Biomedical subjects

H M Cheng

Publications and source records attributed to H M Cheng.

At least 127 records · Page 7Linked to original sources
PubMed1989

Aqueous/vitreous tonicity in "sugar' cataracts.

We examined the aqueous/vitreous tonicity in "sugar' cataracts. Four sets of eyes and their controls were examined: diabetic human eyes, eyes from rabbits and rats fed 50% galactose for up to 1 week, and eyes from streptozotocin-diabetic rats of up to 21 days after diabetes induction. The results showed no statistically significant increase of aqueous/vitreous tonicity in the diabetic human eye and eyes from galactose-fed rats and rabbits. Diabetic rats, on the other hand, showed large tonicity increase in the vitreous, although treatment of the diabetic rats with an aldose reductase inhibitor or insulin completely normalized the tonicity. Seven days after feeding, the galactose-fed animals already showed lens opacities, while diabetic rat lenses remained clear even after 21 days after diabetes induction. These results indicate insignificant osmotic changes in the human eye. In the rat eye, the increase of lens tonicity can be offset by a concomitant increase in the vitreous tonicity. However, this phenomenon is not observed in the galactose eyes. The nature of the osmolytes in the diabetic eye is unclear, although both glucose and sorbitol have been ruled out. The presence of an osmotic regulatory mechanism in the eye is implied.

Animals↗
PubMed1989

Metabolic changes in the cornea of vitamin A-deficient rats.

We have investigated alterations of the metabolic state in vitamin A-deficient (A-) corneas using phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopy. Comparing to the control, A- corneas showed a prominent rise of phosphocreatine (PCr) as well as a total loss of glycerophosphorylcholine (GPC). Further, ATP levels were lower, and sugar phosphates (SP) and inorganic phosphate (Pi) were higher than those of the control. The accumulation of PCr and Pi, and decrease of ATP indicate that the activity of creatine kinase may be altered in vitamin A deficiency. These results suggest that vitamin A may have a role in creatine kinase activation and/or induction and that its deficiency causes a decline of energy metabolism in corneal epithelium. Moreover, disappearance of GPC implies an impaired cellular membrane metabolism. When retinyl acetate was supplied to A-rats for 5 weeks, the 31P profiles of vitamin A-repleted rat corneas recovered to normal.

Adenosine Triphosphate↗
PubMed1988

31P NMR studies of the diabetic lens.

Phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopic analyses of the crystalline lens from the experimental diabetic rat were performed. Qualitative and quantitative alterations in the phosphorus-31 NMR metabolic profile were observed over the course of 3 weeks after the induction of diabetes mellitus. Most striking was the appearance of two new, as yet unidentified, metabolites. These metabolites which resonate at 6.6 and 5.8 ppm were not detected in the normal lens. Compared to the normal lens, glycerol-3-phosphate (G3P) underwent an eightfold increase in concentration and phosphorylcholine decreased to one-third its initial level. The phosphodiesters, glycerophosphorylcholine (GPC) and glycerophosphorylethanolamine (GPE), decreased to barely detectable levels. Oral treatment of the diabetic animal with an aldose reductase inhibitor resulted in the preservation of an essentially normal lens 31P NMR spectrum. Except for the changes observed in glycerol-3-phosphate, these alterations have not been previously reported and raise new questions about the metabolic consequences of diabetes mellitus and the dependence of these alterations on the action of a single enzyme, aldose reductase.

Aldehyde Reductase↗
PubMed1988

Dynamic monitoring of corneal carbohydrate metabolism using high-resolution deuterium NMR spectroscopy.

Glucose metabolism in rabbit corneas was monitored with deuterium (D or 2H) NMR spectroscopy. The corneas were incubated in 5.5 mM deuterated glucose (glucose-6, 6-D2). A 2.5 micrograms change in lactate and a 4.1 micrograms change in glucose could be detected by the NMR method. The mean rates of glucose utilization and lactate production in intact rabbit corneas were 248- and 151 micrograms h-1, respectively. The lactate production/glucose utilization ratio of 0.60, i.e. 60% of total glucose is metabolized to lactate, confirms that glycolysis is the principal pathway for glucose catabolism. Further, based on enrichment of the HDO signal (which refers to the naturally abundant deuterium signal arising from deuterons in water), glucose oxidation through Krebs cycle and its associated pathways is estimated to be 90 micrograms h-1 or 36% of total consumption. The significant advantages of deuterium NMR spectroscopy over other NMR techniques (e.g. 13C spectroscopy) are: (1) shorter acquisition times because of the short relaxation times of deuterated metabolites; (2) the HDO signal can be used as the internal reference; and (3) significant reduction in cost and high availability of 2H-labeled compounds. Deuterium NMR spectroscopy is therefore a reliable and effective means with which the corneal glycolytic activity prior to transplantation can be readily assessed.

Animals↗
PubMed1988

Glucose flux and the redox state of pyridine dinucleotides in the rat lens.

The concentration of alpha-glycerophosphate (GP) appeared to increase and readily reached a new steady state in lenses incubated with KCN or under hyperglucosic condition. This increase can be explained by the change in NADH/NAD ratio under each condition. The relative ratio of pyridine dinucleotides (NADH/NAD) was calculated from equilibrium equations of two NAD-linked enzymes, lactate dehydrogenase (LDH) and alpha-glycerophosphate dehydrogenase (GPDH). The change in NADH/NAD ratio based on biochemical assays correlates well with that estimated from GPDH reaction. This indicates that measurements of pyridine dinucleotides (e.g. in vivo redox fluorometry) can be used to demonstrate lens metabolic status.

Animals↗
PubMed1988

Fate of primary orbital dermis-fat grafts in guinea pigs.

A year-long study was undertaken to serially evaluate the tissue changes occurring in dermis-fat graft (DFG) after orbital implantation in nine guinea pigs. Methods used to evaluate the DFGs were histology, magnetic resonance imaging, morphometric analysis, and clinical observations. The histology of a 1-year-old failed human dermis-fat graft has been included for completeness. The study reveals that clinically successful DFGs have a fibrous capsule surrounding the DFG. Minimal revascularization was present. The grafts appear to undergo continual histological changes for approximately 9 months before a steady-state condition ensues. Of interest are changes in the deep-orbital fat posterior to the DFG.

Adipose Tissue↗
PubMed1988

Ophthalmic NMR.

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Animals↗
PubMed1988

The lens's response to exogenous hydrogen peroxide.

Rat lenses treated with greater than 0.06 mM hydrogen peroxide (HP) appeared to sustain epithelial damage, particularly a loss of enzymes including hexokinase, which controls the supply of glucose-6-phosphate. This may account for the lower level of hexose monophosphate shunt activation observed in these lenses. Other alterations include a decrease of lactate production and disturbance to ionic balance. These changes occurred despite HP removal by glutathione reductase/peroxidase system, catalase and other mechanisms. This suggests an inherent weakness for the lens to resist stresses from high levels of HP. Further, competition for NADPH between aldose reductase and glutathione reductase apparently affects the lens's ability to detoxify HP. This implies a role for oxidation in diabetic cataractogenesis.

Animals↗
PubMed1987

The study of diabetic cataractogenesis in the intact rabbit lens by deuterium NMR spectroscopy.

The polyol pathway has been implicated in the process of diabetic cataractogenesis. We report the use of deuterium (2H) spectroscopy for dynamically monitoring the polyol and glycolytic pathways in the single intact rabbit lens. Using 2H labeled C-1 D-glucose, the formation of sorbitol from glucose and the metabolism of sorbitol to fructose was dynamically monitored at 5.5 mM and 35.5 mM glucose concentrations. The accumulation of sorbitol at 35.5 mM glucose concentration was prevented by the inhibition of aldose reductase using an inhibitor (Sorbinil). 2H spectra were obtained in short acquisition times because of the short T1's of deuterated metabolites. A further advantage of 2H spectroscopy is that the natural abundance resonance of water (HDO) can be used as an internal reference standard. These findings confirm previous studies and demonstrate for the first time by NMR spectroscopy activity in the polyol pathway at low glucose concentrations.

Aldehyde Reductase↗
PubMed1987

Proton magnetic resonance imaging of the ocular lens.

Several osmotic cataract models as well as human diabetic lenses were tested by nuclear magnetic resonance spectroscopy and imaging. Both longitudinal (T1) and transverse (T2) relaxation times increased with increase in lens hydration. Therefore proton magnetic resonance imaging (MRI) can be used to detect changes of the biophysical environment of water proton in the lens. T2-weighted imaging sequence (spin-echo) can be used to differentiate lenses with hydrational changes since they exhibit higher signal intensity (because of long T2) than normal lenses at the same TE (echo time). A greater contrast can be achieved with the inversion-recovery sequence, which, in addition to contribution from T2, also incorporates T1 and proton density terms. Proton MRI is potentially useful for the detection of pre-cataractous changes.

Aged↗
PubMed1987

Real-time hexose monophosphate shunt activity in light- and dark-adapted rabbit retinas.

Correlation proton nuclear magnetic resonance spectroscopy was performed on light- and dark-adapted rabbit retinas to elucidate real-time hexose monophosphate shunt (HMPS) activity. Light significantly stimulated retinal HMPS initially, which consumed 17% more glucose than that in dark-adapted retinas. The glucose consumption eventually declined to 16% of total, the baseline level, after 60 min of light exposure. In contrast, dark-adapted retinas showed an initial HMPS activity of 29% total glucose consumption, which declined to the basal level after 40 min. Lactate production appeared stable in both sets of retinas. Tert-butyl hydroperoxide (1 mM) also stimulated the shunt; however, a combination of light-adaptation and tert-butyl hydroperoxide did not stimulate the shunt additively. These data indicate that the retina has limited HMPS capacity.

Adaptation, Physiological↗
PubMed1987

Sources of variance in the objective documentation of human cataractous change with Topcon SL-45 and Neitz-CTR retroillumination photography and computerized image analysis.

In the application of Topcon SL-45 Scheimpflug slit and Neitz CTR retroillumination photography to in vivo documentation of cataractous change, several sources of variance affect the results of each technique. We have measured the between-person, between-photographer, between-focal plane (Neitz), between-photo session, replicate photograph (Topcon), between-image analyst and replicate image analysis variances encountered in in vivo documentation of human cataracts with the Topcon SL-45 and Neitz-CTR cameras and our system of computerized image analysis.

Adult↗
PubMed1986

Vitreous changes after neodymium-YAG laser photodisruption.

We investigated physicochemical changes in the vitreous body after photodisruption with a Q-switched neodymium-YAG laser. In vivo proton nuclear magnetic resonance imaging techniques were employed to assess alterations in the vitreous of irradiated rabbit eyes. Measurements of proton relaxation times (T1 and T2), viscosity, and chromatographic spectra were made in vitro on irradiated bovine and rabbit vitreous, and circular dichroism measurements were used to study changes in an irradiated sodium hyaluronate solution. Statistically significant changes in T1, were observed immediately after irradiation, but the small magnitude and reversibility of those changes, combined with the fact that the other measurements detected no changes, suggest that neodymium-YAG laser photodisruption does not have a direct deleterious effect on the structural integrity of the normal vitreous body.

Animals↗