Surface and biological evaluation of hydroxyapatite-based coatings on titanium deposited by different techniques.

Hydroxyapatite coatings have been deposited on titanium cp by plasma spray, sol-gel, and sputtering techniques for dental implant applications. The latter two techniques are of current interest, as they allow coatings of micrometer dimensions to be deposited. Coating morphology, composition, and structure have been investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). All coatings were homogeneous and exhibited a rough morphology suitable for implant applications. The sputtered (after annealing), plasma spray, and sol-gel coatings all showed diffraction peaks corresponding to hydroxyapatite. The surface contaminants were observed to be different for the different coating types. The sputtered coatings were found to have a composition most similar to hydroxyapatite; the sol-gel deposits also showed a high concentration of hydroxyl ions. A discrepancy in the Ca/P ratio was observed for the plasma spray coatings, and a small concentration of carbonate ions was found in the sputter-deposited coatings. The in vitro cell-culture studies using MG63 osteoblast-like cells demonstrated the ability of cells to proliferate on the materials tested. The sol-gel coating promotes higher cell growth, greater alkaline phosphatase activity, and greater osteocalcin production compared to the sputtered and plasma-sprayed coatings.

Defective high-affinity thiamine transporter leads to cell death in thiamine-responsive megaloblastic anemia syndrome fibroblasts.

We have investigated the cellular pathology of the syndrome called thiamine-responsive megaloblastic anemia (TRMA) with diabetes and deafness. Cultured diploid fibroblasts were grown in thiamine-free medium and dialyzed serum. Normal fibroblasts survived indefinitely without supplemental thiamine, whereas patient cells died in 5-14 days (mean 9.5 days), and heterozygous cells survived for more than 30 days. TRMA fibroblasts were rescued from death with 10-30 nM thiamine (in the range of normal plasma thiamine concentrations). Positive terminal deoxynucleotide transferase-mediated dUTP nick end-labeling (TUNEL) staining suggested that cell death was due to apoptosis. We assessed cellular uptake of [3H]thiamine at submicromolar concentrations. Normal fibroblasts exhibited saturable, high-affinity thiamine uptake (Km 400-550 nM; Vmax 11 pmol/min/10(6) cells) in addition to a low-affinity unsaturable component. Mutant cells lacked detectable high-affinity uptake. At 30 nM thiamine, the rate of uptake of thiamine by TRMA fibroblasts was 10-fold less than that of wild-type, and cells from obligate heterozygotes had an intermediate phenotype. Transfection of TRMA fibroblasts with the yeast thiamine transporter gene THI10 prevented cell death when cells were grown in the absence of supplemental thiamine. We therefore propose that the primary abnormality in TRMA is absence of a high-affinity thiamine transporter and that low intracellular thiamine concentrations in the mutant cells cause biochemical abnormalities that lead to apoptotic cell death.

Expression of selenium-dependent glutathione peroxidase in human breast tumor cell lines.

In estrogen receptor (ER)-positive breast cancer cell lines, very low expression of glutathione peroxidase-1 (GPX-1) activity and hgpx1 mRNA has been observed. Such cell lines have been used as models in studies of resistance to redox cycling anticancer drugs. In particular, large increases in GPX-1 activity levels by expression of transfected GPX-1 cDNA have been shown to confer some resistance to such drugs. It has never been determined that such low GPX-1 expression is a common feature of breast cancer. Based on previous limited surveys of breast cancer cell lines, it has been suggested that there may be an inverse correlation between ER status and GPX-1 production. Here we report the results from a larger survey of breast cancer cell lines, including six recently isolated cell lines. A near absence of hgpx1 mRNA expression was observed in 3 of 13 ER-negative cell lines; 1 of 4 ER-positive cell lines had high production of GPX-1. Both observations weaken the proposed inverse correlation between ER status and GPX-1 production. We have evidence to suggest that one cell line, COH-BR-5 (ER-negative), lacked hgpx1 gene expression prior to culture. This is based on the finding of stable hgpx1 gene expression during serial culture of ER-negative breast cancer cell lines newly isolated from malignant effusion and absence of hgpx1 mRNA expression in COH-BR-5. Expression of hgpx2 mRNA (producing GPXGI, the GI tract GPX) was detected in several long and newly established, ER-negative breast cancer cell lines. Cell lines, COH-BR-5 and MDA-MB-175, expressed only hgpx2 mRNA. The hgpx2 mRNA was detected in COH-BR-5 and COH-BR-7 at low passage number, suggesting that hgpx2 gene expression occurs in breast cancer malignant effusion. Thus, studies of the role of GPX in redox drug resistance may account for changes in hgpx2 gene expression. Phospholipid hydroperoxide GPX activity was not found to be generally elevated above normal tissue levels in newly established breast cancer-derived cell lines.

Effect of gold on selenium and glutathione peroxidase activities in rat tissues.

Gold (Au) thioglucose, used to treat inflammatory diseases such as rheumatoid arthritis, inhibits the selenium (Se)-dependent glutathione peroxidase. The present study examines the ability of Au to act either as a Se antagonist or as a GSH peroxidase inhibitor in vivo. The effects of gold thioglucose loading on Se distribution, and on Se-dependent GSH peroxidase and GSH S-transferase, were examined in rats fed three dietary levels of Se (0, 0.2, and 2.0 ppm), and with or without adjuvant-induced inflammation. Kidney, liver, spleen, testes, and erythrocytes were selected for study based upon their high Se content and their ability to concentrate Au. Au loading increased kidney, liver, and spleen Se concentrations, and this effect was dependent upon dietary Se levels. Rats fed Se-supplemented diets had higher levels of Au in kidney, liver, and spleens than did rats fed a Se-deficient diet. Au loading decreased GSH peroxidase activity in kidney, liver, and erythrocytes. The decrease in GSH peroxidase in kidney and liver, and the increase in Se concentration in these tissues, suggest that Au-Se complexes may have limited the biosynthesis of the enzyme. Au affects Se distribution, and Se concentrates Au in tissues with a high lysosomal content.

Effect of dietary selenium and injected gold thioglucose on adjuvant-treated rats.

Gold (Au) thioglucose, which has been used in the treatment of rheumatoid arthritis, inhibits selenium (Se)-glutathione peroxidase. Since Au and Se play roles in inflammation, the effects of dietary Se (0, 0.2, and 2.0 ppm for 10 weeks) and injected gold thioglucose (5 mg Au/day/kg body weight for 28 days) in adjuvant-treated rats were investigated. Au toxicity was evidenced by lower body weights and higher tissue weight/body weight ratios for kidneys and spleens of Au-treated rats. Adjuvant-induced inflammation, measured by paw thickness, was not influenced by dietary Se, although Au decreased inflammation in Se-deficient rats. Liver glutathione peroxidase activity was depressed by Se deficiency and by Au. Sulfhydryl levels in liver soluble fraction and plasma were highest for Se-deficient rats. Among liver, kidney, spleen, and plasma, thiobarbituric acid reactants were highest in kidneys of Au-treated rats and lowest in plasma of rats fed 2 ppm Se. gamma-Glutamyltranspeptidase activity in plasma indicated liver damage in Se-deficient rats. Kidney PGE2 output in 24-hour urine samples was unaffected by Au, Se, or adjuvant. Au-Se interactions in vivo are complex, but decreased glutathione peroxidase activity in Au-injected rats suggests that Se nutrition of Au-treated rheumatoid arthritis patients may be a practical concern.

Control of evaporative heat loss during changes in plasma osmolality in the cat.

1. The effects of intravenous infusion of hypertonic saline and distilled water into normally hydrated and dehydrated cats have been examined at both high and neutral ambient temperatures.2. In hydrated cats measurements of body temperature (T(b)) and evaporative heat loss (e.h.l.) show that infusion of 30% saline (1.5 ml./kg) at an ambient temperature of 38 degrees C, lowers e.h.l. by an average of 0.21 W/kg (P < 0.001) and elevates T(b) by 0.43 degrees C (P < 0.01).3. At 25 degrees C alterations in these two parameters were in the same direction, though not statistically different from pre-infusion levels (P > 0.05).4. Infusion of distilled water (15 ml./kg) into dehydrated animals produced significant increases in e.h.l. (+0.35 W/kg, P < 0.001) and reductions in T(b) (-0.45 degrees C, P < 0.001) at 38 degrees C. No significant effects were observed at 25 degrees C.5. Infusion of water into normally hydrated animals at 38 degrees C also significantly increased e.h.l. (+0.13 W/kg, P < 0.05) and insignificantly lowered T(b) (-0.03 degrees C, P > 0.05).6. Local heating of the preoptic hypothalamic area in four animals indicated that hypertonic saline infusion into normally hydrated animals caused a reduction in the slope and displacement to the right of the relationship between hypothalamic temperature and e.h.l.7. Conversely, water infusion into dehydrated animals increased the slope and shifted this relationship to the left.8. These experiments provide evidence for an osmotic interaction in body temperature regulation which acts to alter the responsiveness of the hypothalamus to increasing temperature. This osmotic component may be an important factor in the alterations in thermoregulation seen in dehydrated animals.

Intracranial osmoreceptors control evaporation in the heat-stressed cat.

During heat stress, most mammals regulate body temperature by evaporating body water. Dehydrated mammals reduce their evaporative water losses and allow body temperature to rise. The physiological mechanism underlying this inhibition of evaporative cooling in dehydration have remained unclear. We now report that the rate of evaporation in dehydrated, heat-stressed cats is controlled by intracranial osmoreceptors and suggest that these receptors are part of a common central neural osmoreceptive mechanism regulating evaporative heat loss, renal water loss and thirst.

Effect of dehydration on hypothalamic control of evaporation in the cat.

1. Cats were surgically prepared with intracranial thermodes for heating of the hypothalamic thermosensitive area or with venous cannulae for measurement of blood volume and plasma osmolality. They were kept in an environmental chamber in which the ambient temperature was cycled between 25 and 38 degrees C on an 18:6 hr diurnal schedule. 2. Measurements of blood volume and plasma osmolality and of the evaporative response to hypothalamic heating were made during the 38 degrees C phase of the diurnal temperature cycle in animals when they were hydrated ad lib and in the same animals after 72--96 hr of water deprivation. 3. Water deprivation produced a loss of 10% of the body weight, a significant rise in plasma osmolality and a significant fall in blood volume. 4. Hypothalamic heating in hydrated animals generated a highly significant, positive, linear relationship between hypothalamic temperature and evaporative heat loss in every case. 5. In dehydrated animals, the evaporative response to hypothalamic heating was reduced. Rates of evaporation at a given hypothalamic temperature were lower and the slopes of the lines relating evaporative heat loss to hypothalamic temperature were significantly reduced. 6. It is concluded that dehydration reduces the thermal responsiveness of central neural structures controlling evaporation in the cat.

Hypothalamic control of thermoregulation during dehydration.

Hypothalamic control of thermoregulatory evaporation has been examined in hydrated and dehydrated cats exposed to warm ambient temperatures. Reduction in evaporative cooling during dehydration is associated with increased hypothalamic temperature. Local thermal stimulation of the hypothalamus indicates that the thermosensitivity of hypothalamic systems controlling evaporation is reduced by dehydration. These findings are discussed in relation to control system models of thermoregulation.

Variability of skin temperature in the waking monkey.

Temperatures of the brain, skin, and nasal mucosa were recorded along with the cortical electroencephalogram (EEG) in chaired, conscious pigtail monkeys at 25 degrees C air temperature. In undisturbed animals, skin temperatures ranged from 34 to 37 degrees C. When the animal was alerted by visual or auditory stimuli, temperatures on the extremities, tail, nose, ears, and nasal mucosa dropped rapidly to 22-29 degrees C. Temperatures on the proximal limbs and trunk and most of the head remained steady at all times. Average hypothalamic temperature was 0.91 degrees C higher when the extremities, tail, nose, ears, and nasal mucosa were cool than when they were warm, the brain temperature change beginning 80-120 s after the change in peripheral temperatures. A slight decrease in EEG frequency, but no change in amplitude, occurred during skin warming. Anesthetic doses of barbiturate led to a rapid rise in temperature of the extremities, tail, nose, ears, and nasal mucosa and a drop in brain temperature. These large changes in skin temperature in conscious monkeys reflect changes in cutaneous blood flow, the resulting alteration in heat loss leading to a rapid change in deep body temperature. The experiments demonstrate the importance of the state of arousal on autonomic nervous control of peripheral vasomotor tone in the monkey.

Influence of the carotid rete on brain temperature in cats exposed to hot environments.

1. Thermocouples were chronically implanted in various intracranial and extracranial structures in adult cats. Temperature of arterial blood on the proximal and distal sides of the carotid rete was determined by measuring temperature in the aortic arch and at the anterior cerebral arteries. Temperatures of brain stem regions supplied by the carotid rete and by the vertebral-basilar system were determined by measuring temperature in the anterior hypothalamus and the caudal medulla. Nasal mucosal temperature was measured with a thermocouple implanted in the nasal cavity.2. In a cool environment (25 degrees C), the temperature of anterior cerebral arterial blood was lower than aortic arterial temperature. Anterior cerebral temperature showed shifts which were not present in central (aortic) arterial blood and which were clearly associated with changes in heat loss from the nasal mucosa and with the behaviour of the animal. When the cats were relaxed or in e.e.g. slow-wave sleep, the nasal mucosal temperature was high and the temperature at the anterior cerebral arteries was as much as 0.30 degrees C less than aortic temperature. During behavioural arousal and paradoxical sleep, the nasal mucosal temperature fell and the anterior cerebral arterial temperature rose toward central arterial temperature. Shifts in hypothalamic temperature followed the changes in anterior cerebral arterial temperature. Medullary temperature was higher than aortic temperature and showed shifts which suggested that blood from the rostral circle of Willis mixed with vertebral blood in the basilar artery.3. When the ambient temperature was raised to 40-45 degrees C the cooling of cerebral arterial blood and brain increased as the rate of thermal panting increased. Respiratory rate increased tenfold and aortic temperature rose by 2.0-2.5 degrees C. Anterior cerebral arterial temperature fell below aortic temperature by as much as 1 degrees C, hypothalamic temperature dropping in parallel with cerebral arterial temperature. Medullary temperature cooled below aortic temperature during heat exposure, but the temperature drop in the medulla was not as high as in the rostral brain stem.4. Blowing air into the nasal cavity of anaesthetized cats produced a large, rapid temperature drop at the anterior cerebral arteries and in the hypothalamus, with little effect on central arterial temperature. The same experiments in a dead animal cooled the brain after a longer period of time, suggesting that an active process is involved in the brain cooling observed in living animals.5. It is concluded that the cooling of the rostral cerebral arterial blood and brain which occurs in cats in a cool environment and is accelerated during thermal panting, is a result of countercurrent heat exchange between arterial blood in the carotid rete and venous blood draining the evaporative surfaces of the upper respiratory passages. Such direct brain cooling during thermal panting has now been demonstrated in the cat, the sheep and the gazelle, and probably explains the high heat tolerance of the carnivores and hoofed mammals in which a rete is present.

The influence of the nasal mucosa and the carotid rete upon hypothalamic temperature in sheep.

1. In chronically-prepared sheep, intracranial temperatures were measured in the cavernous sinus among the vessels of the carotid rete and at the circle of Willis extravascularly, and in the preoptic area and in other brain stem regions. Extracranial temperatures were measured intravascularly in the carotid or internal maxillary arteries and on the nasal mucosa and the skin of the ear.2. At 20 degrees C ambient temperature, shifts in temperature of the hypothalamus and of other brain sites paralleled temperature shifts in the cerebral arterial blood which was cooler than central arterial blood. During periods of arousal and of paradoxical sleep, vasoconstriction of the nasal mucosa and the ear skin occurred and temperatures at the cerebral arteries and in the brain rose without a comparable rise in central arterial blood temperature.3. Anaesthetic doses of barbiturate abolished the temperature oscillations in the cerebral arterial blood and the brain. When air was blown rapidly over the nasal mucosa in anaesthetized animals, temperatures dropped precipitously in the cavernous sinus, at the cerebral arteries, and in the brain, while central arterial temperature fell only slightly. Injections of latex into the facial venous system demonstrated a venous pathway from the nasal mucosa to the cavernous sinus.4. When sheep were exposed to 45-50 degrees C ambient temperature, respiratory rate increased 5-10 times and the temperature gradient between central and cerebral arterial blood widened.5. It is concluded that venous blood returning from the nasal mucosa and the skin of the head to the cavernous sinus cools the central arterial blood in the carotid rete. This is an important factor in the maintenance of hypothalamic temperature in the wool-covered, long-nosed, panting sheep and undoubtedly affects hypothalamic thermoreceptors and temperature regulation in artiodactyls.