Search PubMed⌕ Search

Biomedical subjects

M F Lou

Publications and source records attributed to M F Lou.

At least 55 records · Page 3Linked to original sources
PubMed1990

Phosphorus-31 NMR study of the effects of hydrogen peroxide on young and old rat lenses.

31P-NMR spectroscopy was used to study the dynamic changes in young and old rat lenses under oxidative stress with hydrogen peroxide. Control spectra were recorded for young and old rat lenses using normal media. Oxidative stress spectra were recorded under the same conditions, except that the normal media also contained hydrogen peroxide at four different concentrations. With increasing H2O2 concentration in the perfusion media there was a corresponding decrease in the observed phosphorus metabolites, phosphorylcholine and ATP. There was significant difference in the rate of depletion of metabolites between the young and old rat lenses; old rat lens showed an ATP decrease almost double that for young rat lenses. Also, the 31P control spectrum of the old rat lens was different from that of the young lens. The NMR results showed the importance of comparison of old and young rat lenses under oxidative stress as a model for senile cataractogenesis.

Adenosine Triphosphate↗
PubMed1990

The role of protein-thiol mixed disulfides in cataractogenesis.

Protein-thiol mixed disulfides in lenses have been implicated in the mechanism of protein-protein disulfide and other cross-linking leading to protein aggregation. The methodology for the detection and quantitation of protein-thiol mixed disulfides has been successfully established in our laboratory. Examination of mixed disulfides at different stages during development of a cataract may give relevant information on the mechanism of cataractogenesis, and whether oxidation is a part of that mechanism. In this study we investigated the involvement of mixed disulfides in cataract formation by using the H2O2-exposed lens as a model. Rat lenses, after being exposed to 0.5 mM H2O2 in culture showed an inverse relationship between the GSH loss and the protein-GSH formation with no effect on the protein-cysteine level. The H2O2-induced protein modification was also demonstrated indirectly by isoelectric focusing. The rate of protein-GSH production is dependent on the time of exposure and the concentration of H2O2. Age also plays some role as the lens GSH level decreases and the protein-thiol mixed disulfides increase as the animal becomes older. Lenses of older rats did not display more susceptibility to H2O2-induced mixed disulfide formation. The two protein-thiol mixed disulfides have a well-defined pattern of distribution in the rat lens. Most of the protein-GSH was found in the cortex and the water-soluble protein fraction whereas more protein-cysteine was found in the nucleus and water-insoluble protein fraction. Lens of older rat has more protein-cysteine as well as more water-insoluble proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

Micro-quantitation of lens myo-inositol by anion exchange chromatography.

A method capable of the determination of pmole quantities of myo-inositol in mgr amounts of tissue by anion exchange chromatography is detailed for use in lens and potentially other tissues. Samples were rendered protein-free through ZnSO4/Ba(OH)2 precipitation, lyophilized and reconstituted in water just prior to analysis. An aliquot of sample was injected onto an anion exchange column and eluted with a 0.045 M sodium hydroxide mobile phase. Each analysis requires 30 minutes to complete. Average recovery of myoinositol added to lens sample prior to injection was 100.6%. The coefficient of variation for repeated sample injections was 2.9%. Rabbit lens averaged 11.4 mumol/gr wet weight with epithelium containing 8.5 mumol/gr wet weight while human lens contained 20.1 mumol/gr wet weight and human epithelial cells had 17.5 nmol/mgr protein.

Animals↗
PubMed1989

The effect of an aldose reductase inhibitor on lens phosphorylcholine under hyperglycemic conditions: biochemical and NMR studies.

Phosphorylcholine (P-choline) is a precursor of the phospholipids in the lens membrane. A human lens normally contains approx. 1 mM P-choline but this is significantly lowered in some cataractous lenses. A normal rat lens contains a very high concentration (11 mM). We found that rat lens P-choline was depleted drastically when the lenses were exposed to hyperglycemic conditions either in culture, with galactose or xylose, or in vivo by streptozotocin-induced diabetes. The lens P-choline level was measured by fractionating the organic phosphates in the lens homogenate using an ion exchange column, or by quantitating the P-choline 31P NMR intensity in intact lenses. The results of both the chemical method and the noninvasive method agreed remarkably well. Besides the change in P-choline, the choline influx was also drastically reduced both in lenses from diabetic rats and in lenses incubated with 30 mM xylose. In addition, the ATP concentration was greatly diminished under similar conditions. The changes in P-choline, choline, and ATP could all be prevented in the presence of an aldose reductase inhibitor (ARI). It is thus concluded that these changes in phospholipid precursors may result from lenticular membrane defects caused by hyperglycemic stress. The effect of the lowered precursors on lipid biosynthesis was observed, and surprisingly showed a more rapid phospholipid-biosynthesis in the 2-week diabetic rat lens than in the 3-day diabetic rat lens.

Adenosine Triphosphate↗
PubMed1989

The prevention of biochemical changes in lens, retina, and nerve of galactosemic dogs by the aldose reductase inhibitor AL01576.

Normal eight month old beagle dogs were fed a diet of 30% galactose for a period of two weeks. One group of dogs was untreated while three other groups were orally dosed with 0.25, 1.0, and 5.0 mg/kg of the aldose reductase inhibitor (ARI), AL01576. No visible changes were observed in the lens but glutathione (GSH) and inositol were depleted while dulcitol was elevated. These biochemical changes closely parallel those found in the (two week) streptozotocin induced diabetic rat. In contrast with the diabetic rat model, retina and nerve inositol was not found to differ from normal in spite of significant dulcitol accumulation. Plasma AL01576 was found to be inversely correlated with lens dulcitol concentration. When plasma AL0P1576 concentration was greater than 1 microgram/mL (5 mg/kg), there was a 95% reduction in dulcitol concentration (relative to untreated), while concentrations of 0.2 to 0.2 mg/mL (1 mg/kg) of AL01576 resulted in a dulcitol reduction of at least 70%. Retina and nerve dulcitol concentrations of galactosemic dogs were similarly diminished by AL01576 treatment. The dog model exhibits a biochemical profile of change and responsiveness to ARI therapy similar to that observed in hyperglycemic rats. Changes in retina morphology in diabetic and galactosemic dogs has been shown to closely resemble those occurring in human diabetics; these early biochemical events may also parallel.

Administration, Oral↗
PubMed1989

Evidence for the presence of phosphoinositide cycle and its involvement in cellular signal transduction in the rabbit lens.

In the lens, free inositol is present at high concentrations. The lens transports inositol from the extracellular source but can also synthesize inositol from glucose via inositol-1-phosphate. The inositol containing phospholipid (phosphoinositides) constitutes only 10% of the total phospholipid in the membrane and was suggested to play some key role in the cellular differentiation. Recently, one of the phosphoinositides, PIP2, was located in the epithelial cells but not in fiber cells. Prostaglandin, which uses one of the phosphoinositide metabolites, diacylglycerol, as a precursor in its biosynthesis was also found in the lens. The evidence, although scanty, do provide some clues to the possibility that lens may contain a phosphoinositide cycle similar to retina and cornea. In this study we demonstrated that rabbit lens epithelial cells could incorporate 3H-inositol into the membrane and the label accumulated in all three phosphoinositides, PI, PIP and PIP2 with PI as the predominant form. Both PI Kinase and PIP Kinase were found in the lens epithelial homogenate which incorporated (gamma-32P) ATP into PI and PIP to form their respective product, PIP and PIP2. The membrane bound PI Synthase was also demonstrated by using a cell free system. The lens cells showed distinctive response to some agonists such as Ca2+, EGF, glucagon, serotonin but not the others such as insulin, FGF. It is therefore concluded that lens epithelium cells, like other cell types has a complete and functional phosphoinositide cycle.

1-Phosphatidylinositol 4-Kinase↗
PubMed1989

Aldose reductase in early streptozotocin-induced diabetic rat lens.

The present study investigates the status of lens aldose reductase in the early streptozotocin-induced diabetic rat. Aldose reductase protein concentration, protein synthesis, and enzyme activity was assayed at 3 days and 14 days post-streptozotocin injection. Our results indicated that there was no significant difference between normal (control) and diabetic rat lenses in these parameters during the time frame of the study. Results from whole lens analysis were supported by results of the examination of the isolated capsule-epithelium layer of these lenses. It is concluded from this study that in the initial stage of the diabetic cataract model, increase in enzyme protein or activity does not play a significant role in cataractogenesis, but rather that the hyperglycemic condition in combination with existing enzyme levels is sufficient to cause the cataractogenic changes.

Aldehyde Reductase↗
PubMed1989

Effect of opacification and pigmentation on human lens protein thiol/disulfide and solubility.

In this study, we compared the thiol/disulfide status and the protein profiles for a group of normal lenses (over 60 years old) and a group of age matched cataractous lenses. In agreement with previous reports we found that the severity of the lens opacity and the color of the nucleus correlated well with the decrease of soluble proteins and increase of guanidine insoluble proteins. However, the decrease of nonprotein thiols and protein thiols was associated only with the pigmentation of the lenses. We discovered that protein-thiol mixed disulfide profiles provided new information on the lens biochemical changes. In the normal lens, we found nearly 10% of the total nonprotein thiols bound to the protein. There were two species of protein-thiol mixed disulfides, protein-GSH and protein-cysteine with the former 3-4 times higher than the latter. In the cataractous lens the mean value of some species was elevated two-fold whereas in the noncataractous pigmented lens both protein-thiol mixed disulfides were elevated but the protein-cysteine species showed more drastic increase (three-fold in one case and 13-fold in another case). It is therefore concluded that the formation of protein-thiol mixed disulfides may play a more critical role in cataractogenesis than does protein-protein disulfide formation.

Aged↗
PubMed1988

Glutathione depletion in the lens of galactosemic and diabetic rats.

Depletion of lens glutathione (GSH) occurs quickly and drastically following induction of diabetes or galactosemia in rats as well as in lens culture. The explanation for this dramatic loss of GSH has been investigated by many laboratories but the solution has been elusive. There are several possible causes for the change in the reducing power of the lens under hyperglycemia. (a) The enzyme glutathione reductase which reduces oxidized glutathione to GSH is inhibited. (b) The cofactor NADPH which both the aldose reductase of polyol pathway and glutathione reductase require becomes depleted under hyperglycemia to the point that there is an insufficient amount for glutathione reduction. (c) Membrane permeability is increased, due to osmotic-induced lens hydration. We explored all the above possibilities in the mechanism of GSH depletion and studied the effect of aldose reductase inhibitor (ARI) on osmotic change. We found that under hyperglycemic condition, there was no change in the enzyme glutathione reductase activity. There was an initial drop in NADPH level but there was sufficient remaining for glutathione reductase use. Both NADPH and glutathione depletion could be prevented completely by ARI. In addition, ARI could also prevent any hyperglycemic-induced abnormal transport and leakage of amino acids. We have therefore concluded that only the decreased membrane transport of amino acids which are needed for glutathione biosynthesis and the simultaneous loss of GSH through leaky membrane as initiated by the polyol pathway can be responsible for the drastic GSH depletion.

Aldehyde Reductase↗
PubMed1988

Dynamic phosphorus-31 NMR study of sugar cataract and its prevention in rat lenses with aldose reductase inhibitors.

P31 NMR spectroscopy was used to study dynamic changes in rat lens phosphate metabolites under hyperglycemic conditions. NMR control spectra were collected at 37 degrees C with normal media; NMR spectra were also collected under the same conditions except the normal media was substituted for one containing 30 mM xylose. There was a significant increase in intensity of the sugar phosphate NMR signal as well as a moderate decrease in intensity for the three ATP peaks. In separate experiments normal rat lenses were pre-treated with perfusion media containing the ARIs; either Spiro-(2-fluorofluorene-9,4'-imidazolidine)-2',5'-dione (AL theta 1567) or Spiro-(2,7-difluorofluorene-9,4'-imidazolidine)-2',5'-dione (AL theta 1576) for three hours before changing to a xylose plus ARI media. After overnight perfusion, no appreciable change in the rat lens NMR spectra was found. This NMR observation indicates that lenses can be protected from hyperglycemic stress in the presence of the ARIs AL theta 1567 or AL theta 1576.

Adenosine Triphosphate↗
PubMed1987

Depletion of myo-inositol and amino acids in galactosemic neuropathy.

A depletion of not only myo-inositol (MI) but also taurine and other amino acids was observed in the sciatic nerve of a galactosemic rat. Treatment of the galactosemic rats with sorbinil, an aldose reductase (AR) inhibitor, was found to block galactitol formation and protect against the loss of MI, taurine, and other amino acids. Incubation studies of sciatic nerve have revealed that [3H]MI and [3H]taurine were actively taken up and concentrated. Incubation of the nerve in a high-galactose medium showed a decrease in the accumulation of [3H]MI and [3H]taurine whereas the galactitol level increased. Time-course studies have shown that the galactitol level reached a plateau before a substantial decrease in the accumulation of [3H]MI and [3H]taurine occurred. The addition of AR inhibitors in the galactose medium significantly protected against the loss in the capacity of the nerve to accumulate [3H]MI and [3H]taurine. Hypertonicity of the galactose medium also seemed to have a protective effect similar to that of AR inhibitors.

Amino Acids↗
PubMed1986

Quantitation of lens protein mixed disulfides by ion-exchange chromatography.

A sensitive and high resolution ion-exchange chromatographic method was employed to analyse lens protein mixed disulfides. The mixed disulfides were analysed and quantified as glutathione sulfonic acid and cysteic acid after the lens proteins were subjected to performic acid oxidation. The oxidized product was applied on a 0.9 X 15 cm column packed with BioRad Aminex A-28 resin (9 microns beads). The column was maintained at 55 degrees C and eluted with 0.3 M sodium acetate buffer, pH 5.1 at 60 ml hr-1 for 40 min before switching to 0.5 M of the same buffer. The glutathione subsequently reacted with ninhydrin and monitored for absorbance at 570 nm. The glutathione sulfonic acid emerged at 69 min, cysteic acid at 35 min, and both were clearly resolved from neighboring peaks and could be detected at less than nmol level. In the lens, both glutathione and cysteine protein mixed disulfides were only found in the TCA-insoluble protein fraction. Normal rat lens contained 0.35 nmol per lens of protein-bound glutathione but 10-fold this amount of protein-bound cysteine. The hyperglycemic condition had little effect on the protein thiol mixed disulfide level except that at a more advanced diabetic condition, equal depletion of cysteine and glutathione mixed disulfides were found. On the other hand, oxidative conditions induced a marked elevation of glutathione mixed disulfide but not of the cysteine mixed disulfide.

Animals↗
PubMed1979

Human muscular dystrophy: elevation of urinary dimethylarginines.

The amounts of the dimethylarginines NG,NG-dimethylarginine (DMA) and NG,N'G-dimethylarginine (DM'A) excreted in the urine of muscular dystrophic patients were examined and compared with the amounts excreted by normal controls, patients with other types of neuromuscular diseases, and patients with disuse muscle atrophy resulting from traumatic paralysis. The patients with muscular dystrophy excreted high concentrations of DMA and this urine showed high ratios of DMA to DM'A. This finding indicates a relation between protein methylation processes and muscular dystrophy.

Arginine↗