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Biomedical subjects

G E Bunce

Publications and source records attributed to G E Bunce.

At least 19 recordsLinked to original sources
PubMed1997

Free amino acids reflect impact of selenite-dependent stress on primary metabolism in rat lens.

PURPOSE: A decrease in phase separation temperature, prior to nuclear cataract, has been correlated with elevated free amino acid content. Hence, we determined how selenite-induced stress alters free amino acid pools in the rat lens, following a single subcutaneous dose of sodium selenite (30 nmol g-1 body weight) in 10- to 14-day-old Sprague Dawley rats. RESULT: Oxidative stress was evident in lenses 24 h after rats were treated with selenite. Glutathione content was decreased by 60% in the lens cortex and nucleus; the flux of glucose through the pentose phosphate pathway was increased; and glycerol-3-phosphate content was elevated. Amino acid transport, evaluated as 14C-cycloleucine uptake, was not altered, although 14C-glutamine was oxidized at a slower rate. Lenses from treated animals displayed, among the free amino acids, increased glutamine, proline, serine, glycine and the branched chain amino acids, while aspartate, glutamate, and taurine were less. CONCLUSIONS: A systemic delivery of sodium selenite caused oxidative stress in the rat lens. Direct effects on primary metabolism altered free amino acid pools that may contribute to transient and permanent changes in lens transparency.

Amino Acids↗
PubMed1996

Precataractous changes affect lens transparency in the selenite cataract.

Selenite treatment of the preweanling rat stabilized the transparency of the lens nucleus to decreasing temperature. Hence, we compared properties of the cortex and nucleus from lenses of selenite-treated and age-matched control rats. A subcutaneous dose of 30 nmol Na2SeO3/g body weight was administered to 10- to 13-day-old Sprague-Dawley rats. Uninjected, age-matched littermates served as controls. As required, lenses were frozen in liquid N2 and separated into nuclear and cortical-epithelial fractions. Transparency of solutions of lens proteins (90-100 mg per ml) was monitored from 30 to 2 degrees C as percent transmittance (%T) at 490 nm. The critical phase separation temperature, Tc, was the temperature at 80%T. Protein associations were monitored with gel filtration chromatography. The nuclear 'cold cataract', in intact lenses, formed at similar temperatures at 14 and 15 days of age, but at a significantly lower temperature when the lenses were from a selenite-treated rat. The Tc, however, was greater by 1.5-2 degrees C for solutions of proteins isolated from whole lenses or lens nuclei from rats 24 and 48 h after treatment with selenite. Further, less gamma-crystallin was associated with the alpha-crystallin fraction in extracts from the nucleus of lenses from treated rats. Altered phase separation properties occurred as an early event in the etiology of selenite cataract. The different in vivo and in vitro responses to temperature indicated that properties of lens crystallins do not solely establish transparency in the intact lens.

Animals↗
PubMed1995

Causes of decreased phase transition temperature in selenite cataract model.

PURPOSE: Lenses from selenite-treated animals develop reversible "cold cataract" at a lower temperature than is required for lenses from age-matched control animals. This unexplained, stabilized phase transition is readily observed in intact lenses 36 to 48 hours after treatment and occurs in lenses before the appearance of the irreversible nuclear opacity observed 72 to 96 hours after treatment. The objective of this study was to investigate factors that may be responsible for this difference. METHODS: Preweanling rats were injected with sodium selenite. Lens extracellular water volume was measured using 14C-inulin. Free amino acids were analyzed using precolumn derivatization and high performance liquid chromatography. Soluble protein was isolated from lenses of control, and treated animals and temperature-dependent changes in light scattering were measured at 490 nm. RESULTS: Lens extracellular water was increased by the selenite treatment, with a concurrent 10% decrease in intracellular volume. Solutions of soluble protein from lenses of selenite-treated animals after postinjection hours 24 and 48 had higher critical phase transition temperatures (Tc) compared to similar proteins from control lenses. From 24 to 72 hours after injection, the free amino acid content of the lens increased 42%. Taurine levels were unchanged over the same period. The addition of 7 mM glycine and 7 mM proline to solutions of soluble protein (96 mg ml-1) decreased the phase transition temperature. Taurine (14 mM) had a similar effect. Combining taurine and the glycine plus proline solutions had an additive effect in lowering the Tc. CONCLUSIONS: Increases in free amino acid concentration occur in lenses in response to the stress imposed by a systemic dose of selenite. The altered polyion content in lenses from selenite-treated animals, before nuclear cataract formation, contributes to the greater thermal stability of transparency in these lenses, thus lowering the temperature at which "cold cataract" forms.

Amino Acids↗
PubMed1993

Selenite and Ca2+ homeostasis in the rat lens: effect on Ca-ATPase and passive Ca2+ transport.

Calcium permeability was significantly increased in lenses from rats 36 h following a single injection of a cataractogenic dose of sodium selenite (30 nmol/g body weight) and this permeability returned to control values by 72 h post-injection (PI). The greater Ca2+ permeability could be partially reversed by incubating lenses in medium containing 2 mM dithiothreitol (DTT). Estimations of Ca-ATPase activity revealed the greatest level occurred in the epithelial layer and that the nucleus had no detectable activity. By 48 h PI both Ca(2+)-pump activity and the Ca(2+)-dependent ATP hydrolytic activity were less compared to controls in membrane preparations from rat lenses. Only the hydrolytic activity could be partially restored by treatment with 5 mM DTT. Both permeability and active Ca2+ transport were affected by selenite in a manner that would lead to increased Ca2+ accumulation in lenses from rats treated with selenite. It is suggested that the oxidative damage that accompanies in vivo exposure to selenite could affect Ca2+ homeostasis in the lens by directly altering permeability and Ca-ATPase.

Animals↗
PubMed1992

Biochemical changes and cataract formation in lenses from rats receiving multiple, low doses of sodium selenite.

Nuclear cataract formed in rat lens in response to a protocol of multiple, low doses of sodium selenite. Nuclear cataract occurred, in both Wistar and Sprague-Dawley rats, following five subcutaneous injections of selenite over an 8-day period with an accumulated dose of 40-50 nmol selenite g-1 body weight. Glutathione content decreased within the first 24 hr of treatment and remained at 60% of controls. Lipid peroxidation occurred in Wistar rats prior to nuclear cataract formation. A two to three-fold increase in calcium concentration and decreased protein content accompanied nuclear cataract development. Enzyme activities were measured for glutathione peroxidase, glutathione reductase, and glutathione S-transferase, and only the peroxidase activity remained constant through the period of cataract formation. This protocol resulted in nuclear cataracts similar in appearance to those observed with a single, acute dose of selenite. The opportunity to control the rate of selenite-dependent cataract formation allows further definition of precataractous events.

Animals↗
PubMed1992

Calcium efflux in rat lens: Na/Ca-exchange related to cataract induced by selenite.

Sodium gradient-dependent 45Ca2+ transport occurred across the lens membrane both in the direction of Ca2+ uptake by inside-out vesicles and Ca2+ efflux after Ca2+ loading of right-side-out vesicles. Using the calcium ionophore, A23187, greater than 90% of the Na+ gradient-dependent Ca2+ uptake was estimated to be free Ca2+. A normal Na+ gradient was also required to maintain calcium homeostasis in the intact lens. The Na+ gradient contributed to Ca2+ efflux from lenses pre-loaded in medium containing 15 mM CaCl2. Therefore, a Na/Ca-exchange functions to control Ca efflux in rat lens, in addition to the Ca-ATPase. In the preweanling rat mature nuclear cataracts occurred by 96 h after subcutaneous injection of sodium selenite (30 nmol/g animal wt). A 3-5 fold increase of Ca2+ accompanied cataract formation. The loss of Ca2+ homeostasis can be detected by 48 h after treatment selenite treatment. At this time the initial rate of Na+ gradient-dependent Ca2+ uptake was 30% lower in lens vesicles from selenite-treated rats compared to controls. No significant reduction of Na+,K(+)-ATPase activity was detected. Altered Na/Ca-exchange may contribute directly to the loss of Ca2+ homeostasis that leads to nuclear cataract.

Animals↗
PubMed1992

Deferoxamine effect on selenite-induced cataract formation in rats.

A single subcutaneous dose of 30 nmol of sodium selenite per gram of body weight in 13-day-old rats resulted in posterior subcapsular cataract (PSC) after 24 hr and bilateral nuclear cataracts at 72-96 hr. Within 24 hr of treatment, a 60% decrease in lens glutathione was seen. A loss of calcium homeostasis observed by 48 hr resulted in increased lens calcium (4 mumol/g dry weight), which accompanied nuclear opacification. The iron chelator, deferoxamine (DF), was evaluated as a potential protective agent against these selenite-induced changes. Three doses each consisting of 1.1 mumol DF/g body weight were administered during the initial 24 hr of selenite exposure. Within 96 hr, all lenses from animals treated only with DF remained transparent, but 50% of these lenses showed cortical cataract at 3 wk postinjection. Concurrent administration of DF and selenite protected 80% of rats against PSC after 48 hr and 25% against nuclear cataract after 96 hr. No elevation in lens calcium occurred in the protected lenses. An additional 20% of animals were not protected fully but showed substantially less nuclear opacity than with selenite alone. They had a significant but moderate increase in lens calcium. After 3 wk (animal age, 35-40 d), cataract appeared in these "protected" lenses involving both the nucleus and cortex and loss of ion homeostasis. The glutathione content remained lower in lenses from animals treated with both selenite and DF compared with those from selenite-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Nutritional factors in cataract.

Age-related cataract is a condition characterized by multiple mechanisms and multiple risk factors. The mechanisms that bring about a loss in transparency include oxidation, osmotic stress, and chemical adduct formation. Risk factors for cataract include diabetes, radiation (ultraviolet B, x-ray), certain pharmaceutical substances, certain nutritional states, and possibly acute episodes of dehydration. Interaction occurs between and among mechanistic factors and risk factors. Thus nutrition must be considered as one part of a tapestry of intertwined events and responses. Certain experimental models for nutritional cataract have been useful for study of the cataractogenic process but are probably not important factors in the human disease. Little current evidence supports significant roles in human senile cataract for imbalances of tryptophan or other amino acids, deficiencies of calcium or selenium, or excessive intake of selenium. Overconsumption of galactose is likely to be hazardous only in subjects with genetic inability to metabolize this sugar. Vitamins with antioxidant potential (riboflavin, vitamin E, vitamin C, carotenoids) deserve further research scrutiny to ascertain their significance in cataract etiology. Excessive caloric intake needs to receive added emphasis as a factor contributing to cataract. Diabetes increases the likelihood of cataract three- to four-fold. Obesity, defined as more than 20% overweight, is considered a major risk factor for non-insulin-dependent, or type II, diabetes (69, 73). Weight control can be recommended as a prudent, safe, economic, and effective means of lowering risk probability for diabetes and the associated complication of cataract.

Aging↗
PubMed1990

DNA damage, repair, and replication in selenite-induced cataract in rat lens.

DNA synthesis was evaluated in vitro by measuring incorporation of 3H-thymidine in rat lens following systemic delivery of a cataractogenic dose of selenite. Among early metabolic changes observed in the lenses of rats receiving a single dose of 30 nmol Na2SeO3/g body weight was a 30% decrease in DNA replication in lens epithelium occurring between 6 and 12 h after administration of the selenite. This change was followed by an 80% increase in replication by 24 h. Thymidine incorporation in DNA remained elevated compared to controls through 96 h. Unscheduled DNA synthesis was found to be approximately 10% of the total DNA formed, but there was a 30% and 70% increase of this putative DNA repair in the lenses from selenite-treated animals at 6 and 24 h after the injection. Using the alkaline unwinding assay, the proportion of single-strand DNA in lenses from selenite-treated animals increased after 24 h. This estimate of DNA damage was greater in lenses after 96 h. Each component of DNA metabolism: damage, repair, and replication, was affected by the occurrence of selenite stress in lens. These changes both preceded and accompanied nuclear cataract formation.

Animals↗
PubMed1989

Factors influencing magnesium absorption and metabolism in ruminants.

Magnesium is a nutrient required for all animals, but it is especially critical for ruminants. A physiological deficiency of Mg results in hypomagnesemic tetany. Typically, only female ruminants are affected, and the disturbance usually occurs during the early stages of lactation. Magnesium functions at three biochemical levels, as a cofactor at the enzymatic level, at the structural level in assembly of ribosomes, and at the whole cell level as a stabilizing force in membranes. Parathyroid hormone (PTH) can affect Mg metabolism by decreasing urinary Mg excretion and stimulating bone resorption, thus releasing Mg into the extracellular fluid. Renal excretion of Mg and Mg absorption from the gastrointestinal tract both are increased by 1,25-dihydroxyvitamin D3. A number of dietary factors depress Mg absorption in ruminants. Of these, high dietary K has the greatest and most consistent effect. Feeding substantial quantities of readily digested carbohydrates increases Mg absorption, but the mode of action is not clear. High concentrations of Al in forage sometimes are associated with a high incidence of grass tetany, but this effect does not appear to be related to Mg absorption. Interrelationships of Al with Mg, Ca, P and PTH are implicated.

Absorption↗
PubMed1989

The conservative treatment of osteonecrosis of the femoral head. A comparison of core decompression and pulsing electromagnetic fields.

Once roentgenographic changes are apparent, osteonecrosis of the femoral head in the adult generally progresses to osteoarthritis within two to three years. A variety of conservative surgical procedures have been devised to conserve the femoral head with varying success. This study examines the effectiveness of pulsing electromagnetic fields and core decompression in the treatment of osteonecrosis of the femoral head. Both techniques reduce the incidence of clinical and roentgenographic progression. Exposure to pulsing electromagnetic fields appears to be more effective in hips with Ficat II lesions than in hips with more advanced lesions.

Adult↗
PubMed1987

Effect of zinc and/or pyridoxine deficiency upon oestrogen retention and oestrogen receptor distribution in the rat uterus.

A deficiency of vitamin B6 has been reported to enhance oestrogen responsiveness of the uterus in rats whereas zinc deficiency provokes a syndrome suggestive of a diminution in oestrogen sensitivity. In this study [3H]oestrogen uptake by the uterus was increased in rats deficient in either nutrient and the differences were additive in the dually deficient animals. The total number of oestrogen receptors per g tissue was unaffected by either nutrient but the proportion of the receptors recovered from the nuclear fraction increased from about 6 to 74% when both nutrients were withheld. The results are consistent with the hypothesis that both zinc and pyridoxal phosphate play important metabolic roles in end-organ responsiveness to oestrogen.

Animals↗