PubMed Health⌕ Search

Biomedical subjects

M I Naash

Publications and source records attributed to M I Naash.

25 records · Page 2Linked to original sources
PubMed1989

Glutathione-dependent enzymes in intact rod outer segments.

We have compared the specific activities of glutathione-dependent enzymes in rod outer segments (ROS) and in whole retina of rabbits and rats, using three different assays. In the first, glutathione peroxidase (GSH-Px) activity was measured as the combined activities of the Se-dependent and Se-independent forms using cumene hydroxide as a substrate. In the second, Se-dependent GSH-Px alone was measured using hydrogen peroxide (H2O2) as a substrate. In the third, the combined activities of several enzymes, collectively known as GSH-S-transferase, were measured. The latter includes the activity of the Se-independent GSH-Px. GSH-Px activity (Se-dependent and Se-independent combined) in ROS of rat and rabbit were found to be 47.7 +/- 8.2 and 72.9 +/- 11.9 nmol of GSH oxidized min-1 mg-1 soluble protein, respectively. From whole retina, values were 67.3 +/- 6.0 and 128.8 +/- 12.3, respectively. Se-dependent GSH-Px specific activities from the above tissues were 43.5 +/- 2.9 (rat ROS). 70.6 +/- 11.3 (rabbit ROS), 30.6 +/- 9.6 (rat whole retina), and 113.2 +/- 12.2 (rabbit whole retina). GSH-S-transferase activity was negligible in rabbit ROS, whereas, in rat ROS, it was 40.4 +/- 8.0, expressed as nmol of S-2,4-dinitrophenylglutathione produced min-1 mg-1 soluble protein. In contrast, the GSH-S-transferase specific activity in whole rabbit retinas was about eight times that found in the rat retina (101.5 +/- 12.3 for rat retina and 885.3 +/- 60.0 for rabbit retina). These results demonstrate that ROS contain glutathione enzymes which are important in protecting membranes from oxidative stresses by reducing hydrogen peroxide and lipid hydroperoxides at the site of their formation.

Animals↗
PubMed1988

Regional distribution of glutathione peroxidase and Glutathione-S-transferase in adult and premature human retinas.

The activities of glutathione peroxidase (GSH-Px) and glutathione-S-transferase (GSH-S-tase) were investigated in adult and premature human retinas. The measurements were done in the vascular and avascular regions of premature retinas at gestational age of 22-33 weeks and in the central, mid-peripheral, and far peripheral regions of mature retinas from the age of 1 month to 73 years. Among the premature infants, those who survived for greater than 24 hours were supplemented with alpha-tocopherol (vitamin E) on a periodic basis. The vascular and avascular regions of premature retinas had higher activities of GSH-Px when compared to the central and far peripheral regions of mature retinas. Infants surviving more than 24 hr had higher activities of GSH-S-tase in the avascular region than infants who survived less than 24 hr. Survival did not affect either enzyme activity in the vascular regions. Mature retinas showed a decrease in GSH-Px specific activity with age, but no age-related changes in GSH-S-tase were observed. These data demonstrate that premature infants are born with relatively high levels of GSH-Px and GSH-S-tase.

Adolescent↗
PubMed1988

The regional distribution of vitamins E and C in mature and premature human retinas.

Vitamin E is used to ameliorate retinopathy of prematurity, but little is known about baseline vitamin E levels in retinas of premature infants or the effect of vitamin E supplementation on these levels. Vitamin E and C levels were measured in mature retinas (1 month to 73 years) and in retinas of premature infants (22 to 33 weeks of gestation). The infants fell into two groups: (1) those who survived less than 12 hr and received no vitamin E, and (2) those who survived greater than 4 days and received vitamin E supplementation. Premature infants are born with 5 to 12 percent the vitamin E levels found in mature retinas. Vitamin E levels in vascular and avascular retina of premature infants increased with gestation. Infants born greater than 27 weeks gestation and surviving at least 4 days with vitamin E supplementation demonstrated markedly elevated vitamin E levels in vascular and avascular retina when compared to supplemented infants less than 27 weeks gestation. Premature infants possessed 35-50% higher levels of retinal vitamin C than those found in mature retinas. These data demonstrate that premature infants are born with relatively low levels of retinal vitamin E, particularly in the avascular region, but contain an abundance of retinal vitamin C. These data further suggest that vitamin E supplementation results in a rapid increase in retinal vitamin E levels, particularly in infants greater than 27 weeks gestational age.

Adolescent↗
PubMed1987

Effect of light history on retinal antioxidants and light damage susceptibility in the rat.

Albino rats were born and raised to 12 weeks of age in 12L:12D light regimes of 5, 300 or 800 lx. Upon killing, the activities of the following glutathione enzymes were measured in the neuroretina: (1) glutathione peroxidase; (2) glutathione-S-transferase; and (3) glutathione reductase. Also measured were vitamin E, ascorbic acid, and the levels of oxidized and reduced glutathione. Animals raised in 800-lx cyclic light have a significant increase in the retinal activities of the three glutathione enzymes over activities measured in animals raised in the two dimmer regimes. The retinal level of vitamin E, measured per nmol of lipid phosphorus, is directly and significantly correlated with rearing illuminance (P less than 0.05). The same is true of retinal ascorbic acid, which shows a 30% increase in the 800-lx-reared rats over the level of those raised in the intermediate light regime (300 lx). Some of the animals from each group were exposed to 2000 lx for 24 hr to determine if correlations existed between the levels of retinal antioxidants listed above and susceptibility to light damage. Animals raised in 5-lx cyclic light lost almost all of their photoreceptors as a result of the exposure. Rats raised in 300-lx cyclic light lost a small but significant number (ca. 20%), while those raised in 800 lx sustained no light damage. Electroretinographic evaluation supports these morphometrical findings.

Animals↗
PubMed1984

Characterization of glutathione peroxidase in frog retina.

The properties and kinetic parameters of glutathione peroxidase were measured in retinal homogenates from frogs (R. pipiens) using a spectrophotometric assay in which the oxidation of glutathione is coupled to the oxidation of NADPH+ by exogenous glutathione reductase. The standard assay utilized 5.0 mM glutathione and 0.6 mM cumene hydroperoxide in 50 mM sodium phosphate buffer at pH 7.0. All solutions were bubbled with argon and all reactions were carried out under an atmosphere of argon. The enzyme activity was linear with protein concentration at different concentrations of both substrates. Determination of the pH optimum was complicated by a large increase in non-enzymatic oxidation of glutathione at alkaline pH. The highest ratio of enzymatic to non-enzymatic activity was at pH 7.0. Increasing glutathione concentration showed less effect on the spontaneous reaction than increasing the cumene hydroperoxide concentration. Glutathione peroxidase Km value for glutathione was 3.86 mM and for cumene hydroperoxide was 0.55 mM. Vmax for glutathione at 0.6 mM cumene hydroperoxide was 138 nmoles glutathione oxidized/min/mg protein, while at 5.0 mM glutathione the value for cumene hydroperoxide was 146 nmoles glutathione oxidized/min/mg protein. These studies demonstrate that glutathione peroxidase is active in the retina and establish the optimal experimental conditions for determination of the enzymatic activity.

Animals↗
PubMedDate not supplied

Expression of a mutant opsin gene increases the susceptibility of the retina to light damage.

The question of whether the expression of mutant opsin predisposes the retina to light damage was addressed using transgenic mice that express rhodopsin with three point mutations near the N-terminus of the molecule. The mutations involve the substitution of histidine for proline at position 23 (P23H), glycine for valine at position 20 (V20G), and leucine for proline at position 27 (P27L). These mice express equal amounts of mutant and wild-type transcripts, and develop a progressive photoreceptor degeneration that is similar to that seen in human retinitis pigmentosa (RP). The P23H mutation is associated with the most frequently occurring form of human autosomal dominant retinitis pigmentosa (ADRP) in the United States. Transgenic and normal littermates were exposed to illuminance of 300 foot-candles (ft-c) for 24 h, then placed in darkness for either 6 h, 6 days, or 14 days. Histological and biochemical techniques were used to evaluate the outer retina in light-exposed and control animals reared on 12-h light/12-h dark cycle. The results indicate that light exposure accelerates the pathological changes associated with the transgene expression. Compared with transgenic animals reared in ambient cyclic light, retinas from light-exposed mice had a reduced rhodopsin content, fewer photoreceptor cell bodies, and less preservation of retinal structure. Data obtained from normal mice did not differ for the lighting regimens used. These findings suggest that the expression of VPP mutations in the opsin gene predisposes the transgenic photoreceptors to be more susceptible to light damage. The data also suggest that reducing photic exposure may be beneficial to any patient with RP mediated by an opsin mutation.

Animals↗