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Biomedical subjects

R R Wang

Publications and source records attributed to R R Wang.

At least 19 recordsLinked to original sources
PubMed1995

A brief photochemically induced oxidative insult causes irreversible lens damage and cataract. I. Transparency and epithelial cell layer.

Short-term photochemical insult of cultured rat lenses caused by the generation of H2O2, O2<--and OH. was found to lead to rapid irreversible damage to the epithelial cell layer. This irreversible damage was measured by Trypan blue staining, terminal deoxyribonucleotidyl transferase labeling, DNA laddering and morphological analyses. There appears to be an inverse relationship between the period of photochemical insult and the post-insult time required to observe epithelial cell damage. Insulting periods of a few hours require post-insult intervals of days to observe significant cell damage and weeks before complete cortical cataracts are found. Epithelial cell damage precedes the loss of transparency.

Animals↗
PubMed1995

A brief photochemically induced oxidative insult causes irreversible lens damage and cataract. II. Mechanism of action.

Using photochemically induced oxidative stress and rat lenses in organ culture with 4% O2 and 4 microM riboflavin, it has been found that the observed changes in lens parameters are, in most cases, irreversible. This has made possible the elucidation of the sequence of biological changes leading to cataract. The earliest detectable changes in lens cell biology are observed in the epithelial cell redox set point and at the DNA level in terms of DNA integrity and 3H-thymidine incorporation followed by decreased membrane transport and changes in gene expression. Significant modification in classical cataract parameters such as hydration, steady state non-protein thiol, glyceraldehyde-phosphate-dehydrogenase activity and transparency occur at later times. The data suggest a definitive pattern of lens breakdown resulting in opacity starting at the epithelial cell level and leading to subsequent fibre cell involvement.

Animals↗
PubMed1995

Lens epithelial cell apoptosis appears to be a common cellular basis for non-congenital cataract development in humans and animals.

Cataract is a major ocular disease that causes blindness in many developing countries of the world. It is well established that various factors such as oxidative stress, UV, and other toxic agents can induce both in vivo and in vitro cataract formation. However, a common cellular basis for this induction has not been previously recognized. The present study of lens epithelial cell viability suggests such a general mechanism. When lens epithelial cells from a group of 20 cataract patients 12 to 94 years old were analyzed by terminal deoxynucleotidyl transferase (TdT) labeling and DNA fragmentation assays, it was found that all of these patients had apoptotic epithelial cells ranging from 4.4 to 41.8%. By contrast, in eight normal human lenses of comparable age, very few apoptotic epithelial cells were observed. We suggest that cataract patients may have deficient defense systems against factors such as oxidative stress and UV at the onset of the disease. Such stress can trigger lens epithelial cell apoptosis that then may initiate cataract development. To test this hypothesis, it is also demonstrated here that hydrogen peroxide at concentrations previously found in some cataract patients induces both lens epithelial cell apoptosis and cortical opacity. Moreover, the temporal and spatial distribution of induced apoptotic lens epithelial cells precedes development of lens opacification. These results suggest that lens epithelial cell apoptosis may be a common cellular basis for initiation of noncongenital cataract formation.

Adult↗
PubMed1994

The redox active components H2O2 and N-acetyl-L-cysteine regulate expression of c-jun and c-fos in lens systems.

Hydrogen peroxide (H2O2) is implicated in human cataract development. At the molecular level H2O2 has been observed to cause damage to DNA, protein and lipid. It is now demonstrated, for the first time in a lens system, that H2O2 at concentrations found in cataract patients induces expression of both c-jun and c-fos. At optimal concentrations of H2O2, mRNA accumulation of c-jun and c-fos in the rat lenses is induced 20- and 18-fold above normal levels respectively, but with distinct kinetics. This induction occurs at the transcriptional level. H2O2 also induces transactivation by activating protein-1 (AP-1) in rabbit lens epithelial cells. The antioxidant N-acetyl-cysteine (NAC) has a dual effect on the induction of c-jun and c-fos. Preincubation of rat lenses with 5 mM NAC inhibits the induction by H2O2, while 30 mM and 50 mM NAC induce expression of these genes and mask the H2O2 effect. H7 (50 microM), genistein (2 microM) and okadaic acid (20 nM), all block the induction of c-jun and c-fos mRNA accumulation in the H2O2-treated rat lenses. These results suggest that H2O2 activates protein kinase and phosphatase dependent signal transduction pathways to induce c-jun and c-fos expression which may regulate lens crystallin genes and other genes containing AP-1 binding sites.

Acetylcysteine↗
PubMed1994

Manumycins E, F and G, new members of manumycin class antibiotics, from Streptomyces sp.

Three new manumycin class antibiotics, namely manumycins E, F and G, were isolated from the culture broth of Streptomyces sp. strain WB-8376. Their structures were established by spectroscopic methods, and the S configuration of C-4 in the epoxycyclohexenone moiety was determined by CD exciton chirality method for each of the three compounds. Manumycins E, F and G are active against Gram-positive bacteria, and have moderate inhibitory effects on the farnesylation of p21 ras protein. They demonstrated weak cytotoxic activity against human colon tumor cell HCT-116.

Anti-Bacterial Agents↗
PubMed1993

The prevention of cataract caused by oxidative stress in cultured rat lenses. II. Early effects of photochemical stress and recovery.

Previous work has demonstrated that photochemically induced oxidative stress generated with 4 microM riboflavin in a 4% oxygen atmosphere utilizing daylight type radiation is capable of causing cataract in cultured rat lenses. Such cataract is prevented by the GSH peroxidase type mimic, AL-3823A. Examination of the early stages of cataract formation produced by short-term oxidative stress and recovery is now reported. A 24-hr oxidative stress, under the above conditions, causes loss of transparency, particularly in the equatorial region, increased hydration, loss of glyceraldehyde-3-PO4 dehydrogenase activity, oxidation of non-protein thiol and a decrease in 86Rb and [14C]choline uptake and ATP levels. Examination of recovery of these parameters during a 72-hr period indicates, in most cases, little or no reversal of oxidative damage. Hydration and loss of non-protein thiol continued during the recovery period. The presence of AL-3823A during the stress period prevented change in all parameters. Transport systems appear to be particularly vulnerable to this type of oxidative stress losing 50% or more activity within 4 hr. Even after a 2-hr stress, choline transport did not recover even though, under these conditions, ATP levels had only decreased slightly. Cytosolic components such as non-protein thiol and glyceraldehyde-3-PO4 dehydrogenase also showed little change after a 4-hr insult. 86Rb efflux experiments indicated no change in permeability during a 24-hr stress period. The overall conclusion from these studies is that a 24-hr oxidative stress which appears to reflect physiological conditions existing during cataract development, causes extensive, irreversible damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Na,K-ATPase of cultured bovine lens epithelial cells: H2O2 effects.

Na,K-ATPase function was studied in cultured bovine lens epithelial cells under confluent and non-confluent conditions. The affinity of the Na,K-ATPase for the cardiac glycoside, ouabain, differs between the confluent and non-confluent cultures. The confluent cells have a higher affinity for ouabain than do the non-confluent cells. The ouabain affinity of the confluent cells is similar to that for the Na,K-ATPase isolated from the bovine axolemma and the bovine lens cortex. The ouabain affinity of the non-confluent cells is similar to that for the Na,K-ATPase of the renal medulla and bovine lens epithelium. Similar results are not found with confluent and non-confluent MDCK cells. H2O2 treatment of confluent and non-confluent lens epithelial cell cultures has differing effects on the Na,K-ATPase function. In the confluent cell preparations, H2O2 affects K(+)-dependent dephosphorylation of the intermediate phosphoenzyme. In the non-confluent preparations. H2O2 appears to inhibit K(+)-occlusion.

Animals↗
PubMed1992

Influence of chronic nadolol treatment on blood pressure and vascular changes in spontaneously hypertensive rats.

Chronic treatment of spontaneously hypertensive rats (SHR) and Kyoto-Wistar normotensive rats (WKY) with nadolol was carried out from gestation until 28 weeks of age. Nadolol treatment caused some lowering of blood pressure but did not prevent the development of hypertension or cardiac hypertrophy in the SHR, in spite of significant beta-blockade. The lumen of large mesenteric arteries from control SHR was smaller than from WKY, and nadolol treatment increased the lumen size in the SHR. An increased number of smooth muscle cell layers present in the control SHR as compared with WKY was reduced slightly by nadolol treatment. However, the changes produced by nadolol did not reach the levels of control and treated WKY. In the aorta, the incidence of polyploid smooth muscle cells was higher in the SHR than the WKY in the control group. Nadolol treatment reduced the percentage of polyploid cells in both SHR and WKY, so that the difference between these two groups of animals was eliminated in the treated groups. The tissue level of norepinephrine in the plasma, heart, mesenteric arteries, and adrenal glands in the SHR and WKY was not affected by the treatment. We suggest that the ineffectiveness of nadolol in preventing hypertension development may be due to its lack of effect in preventing primary changes in the resistance arteries, and that the development of polyploidy of smooth muscle cells may be mediated by beta-receptors.

Adrenal Glands↗
PubMed1990

Hydrogen peroxide-induced DNA damage in bovine lens epithelial cells.

The present investigation was undertaken to determine the types and extent of DNA damage resulting from incubation of primary cultures of bovine lens epithelial cells with hydrogen peroxide. Significant numbers of DNA single-strand breaks were detected by alkaline elution after exposure to as little as 25 microM H2O2 for 5 min at 37 degrees C. The extent of single-strand breakage was concentration dependent and linear from 25 to 200 microM H2O2. The observed single-strand breaks appear primarily due to the action of the hydroxyl radical via a Fenton reaction as both an iron chelator, 1,10-phenanthroline and OH. scavengers, including DMSO, KI and glycerol, significantly inhibited the DNA-damaging effect of H2O2. Diethyldithiocarbamate, an inhibitor of superoxide dismutase, further potentiated the DNA-damaging effects of H2O2, presumably by increasing the steady-state concentration of Fe2+. DNA-protein cross-linking was not observed. In addition, significant levels of 5,6-saturated thymine residues or pyrimidine dimers were not detected after modification of the alkaline elution methodology to allow the use of either E. coli endonuclease III or bacteriophage T4 endonuclease V, respectively. No double-strand breaks were detected after incubation of epithelial cell cultures with H2O2 concentrations of up to 400 microM for 10 min and subsequent neutral filter elution. Since, in vivo, the lens epithelium contains populations of both quiescent and dividing cells, the degree of susceptibility to oxidative damage was also studied in actively growing and plateau-phase cultures. Reduced levels of single-strand breakage were observed when plateau-phase cultures were compared to actively growing cells. In contrast, essentially no differences in repair rates were noted at equitoxic doses of H2O2. The above results suggest that lens epithelial cells may be particularly sensitive to oxidative damage and thus are a good model system in which to study the effects of oxidative stress.

Animals↗
PubMed1990

Ultraviolet light induced DNA damage and repair in bovine lens epithelial cells.

DNA damage caused by UV-B and UV-A irradiation and the rate of repair of such damage was quantitated in bovine lens epithelial cell cultures using a modified alkaline elution methodology. Two enzymes, bacteriophage T4 endonuclease V, which cleaves at the site of pyrimidine dimers, and E. coli endonuclease III, which cleaves at the site of thymine glycols, were utilized. Pyrimidine dimers were not detected after UV-A irradiation of lens cultures with up to 400 J/m2. In contrast, after exposure to as little as 2 J/m2 of UV-B irradiation, large numbers of pyrimidine dimers were observed. At higher fluences, thymine glycols were also found. Significant levels of DNA-DNA crosslinking were suggested by reduced rates of elution of DNA from cells treated with both UV-B irradiation and H2O2 in comparison to treatment with H2O2 alone. Protein-DNA crosslinks, in contrast, were not observed. The rate of repair of UV-B induced DNA damage was quantitated by harvesting cells at various times after the UV-B exposure. Single-strand breaks were never observed immediately after UV-B exposure but appeared later during the repair phase. In contrast to the repair of H2O2 induced DNA damage, which is largely completed within 30 min of exposure, more than 50% of the UV-B light induced DNA damage remained unrepaired five hours after exposure. This difference between the rate of repair of H2O2 and UV-B induced DNA damage could provide valuable insights into the nature of DNA damaging agents in the lens environment and may reflect underlying differences in the potential for epithelial cell DNA mutation in response to various DNA damaging insults.

Animals↗
PubMed1989

Repair of H2O2-induced DNA damage in bovine lens epithelial cell cultures.

H2O2 concentrations only slightly higher than normal physiological levels found in the lens and aqueous fluid produce a significant number of DNA single-strand breaks in lens epithelial cell cultures. In this investigation, the repair of DNA damaged by short-term, H2O2-induced oxidation was examined in bovine lens epithelial cell cultures. Repair was rapidly initiated and was almost completed in 30 min. A drop in NAD concentration was associated with the DNA damage. 3-Aminobenzamide inhibition of poly(ADP-ribose) polymerase, an enzyme believed to be stimulated by DNA oxidation and involved in DNA repair, prevented the loss of NAD. In contrast, a similar drop in ATP concentration was only slightly lessened by the presence of this inhibitor. Inhibition of the polymerase by 3-aminobenzamide primarily affected only the early recovery period. Overall, recovery occurred almost as effectively in the presence of the inhibitor as in its absence. Preincubation of lens cultures with o-phenanthroline, an iron chelator, prevented the drop in NAD levels associated with DNA damage. Since a hydroxyl radical is produced from H2O2 by a Fenton type reaction, this result supports the concept that the H2O2-induced oxidation of DNA is caused by hydroxyl radical. In contrast, peroxide-induced loss of activity of a cytosolic enzyme, glyceraldehyde-3-phosphate dehydrogenase, was unaffected by the presence of o-phenanthroline, suggesting direct H2O2 oxidation of this enzyme. The results of these experiments suggest that lens epithelium contains enzymes that rapidly repair single-strand DNA breaks induced by H2O2 insult.

Animals↗