Decreased oxidation of labeled glucose by dissociated brain cells in the presence of fetal bovine serum

Early metabolic alterations in edematous perihematomal brain regions following experimental intracerebral hemorrhage

OBJECT

The authors previously demonstrated, in a large-animal intracerebral hemorrhage (ICH) model, that markedly edematous ("translucent") white matter regions (> 10% increases in water contents) containing high levels of clot-derived plasma proteins rapidly develop adjacent to hematomas. The goal of the present study was to determine the concentrations of high-energy phosphate, carbohydrate substrate, and lactate in these and other perihematomal white and gray matter regions during the early hours following experimental ICH.

METHODS

The authors infused autologous blood (1.7 ml) into frontal lobe white matter in a physiologically controlled model in pigs (weighing approximately 7 kg each) and froze their brains in situ at 1, 3, 5, or 8 hours postinfusion. Adenosine triphosphate (ATP), phosphocreatine (PCr), glycogen, glucose, lactate, and water contents were then measured in white and gray matter located ipsi- and contralateral to the hematomas, and metabolite concentrations in edematous brain regions were corrected for dilution. In markedly edematous white matter, glycogen and glucose concentrations increased two- to fivefold compared with control during 8 hours postinfusion. Similarly, PCr levels increased several-fold by 5 hours, whereas, except for a moderate decrease at 1 hour, ATP remained unchanged. Lactate was markedly increased (approximately 20 micromol/g) at all times. In gyral gray matter overlying the hematoma, water contents and glycogen levels were significantly increased at 5 and 8 hours, whereas lactate levels were increased two- to fourfold at all times.

CONCLUSIONS

These results, which demonstrate normal to increased high-energy phosphate and carbohydrate substrate concentrations in edematous perihematomal regions during the early hours following ICH, are qualitatively similar to findings in other brain injury models in which a reduction in metabolic rate develops. Because an energy deficit is not present, lactate accumulation in edematous white matter is not caused by stimulated anaerobic glycolysis. Instead, because glutamate concentrations in the blood entering the brain's extracellular space during ICH are several-fold higher than normal levels, the authors speculate, on the basis of work reported by Pellerin and Magistretti, that glutamate uptake by astrocytes leads to enhanced aerobic glycolysis and lactate is generated at a rate that exceeds utilization.

Brain energy metabolism in the acute stage of experimental subarachnoid haemorrhage: local changes in cerebral glucose utilization

An experimental model was used to investigate acute alterations of cerebral metabolic activity in rats subjected to subarachnoid haemorrhage (SAH). Haemorrhages were produced in anaesthetized animals by injecting 0.3 ml of autologous, arterial nonheparinized blood into the cisterna magna. Control rats received subarachnoid injections of mock-cerebrospinal fluid to study the effect of sudden raised intracranial pressure, or underwent sham operation. Three hours after SAH rats were given an intravenous injection of [14C]-2-deoxyglucose. Experiments were terminated by decapitation, and the brains were removed and frozen. Regional brain metabolic activity was studied by quantitative autoradiography. In comparison with sham-operated controls, cerebral metabolic activity was diffusely decreased after SAH. Statistically significant decreases in metabolic rate were observed in 23 of 27 brain regions studied. Subarachnoid injections of mock-cerebrospinal fluid also produced depression of cerebral metabolic activity, but quantitatively these changes were not as pronounced and diffuse as in SAH rats. The present study shows that a widespread depression of brain metabolism occurs in the acute stage after experimental SAH and is probably secondary to the subarachnoid presence of blood itself and/or blood products.

Development modulates the serum induced effect on the incorporation of [2-3H]mannose into chick optic lobe protein: the possible role of glia

Recently, we described that serum decreases tritiated mannose incorporation into protein in the chick optic lobe at 18 days of embryonic age (Rossi et al., 1990). In this paper, we found a strikingly different response of this serum effect according to age. The data obtained showed no serum induced decrease in 6-10-day-old embryo. In addition, our results demonstrate that the differential response of the tissue to the serum is independent of the rate of sugar entry into nerve cells. Furthermore, we also report that the variation of mannose or leucine incorporation into protein coincides very closely with the pattern of protein and glycoprotein accumulation during chick optic lobe development. Finally, data were obtained to define glial cells as the cellular target of the serum induced effect. This finding may contribute to elucidate the mechanism of cellular pathogenesis of cerebral lesions that occur after the breakdown of the blood brain barrier, such as in some diseases or during bleeding after injuries.

Cerebral oxygen metabolism after aneurysmal subarachnoid hemorrhage

Previous studies of cerebral oxygen metabolism and extraction in patients with subarachnoid hemorrhage (SAH) have yielded conflicting results. We used positron emission tomography (PET) to measure the regional cerebral metabolic rate for oxygen (rCMRO2), oxygen extraction fraction (rOEF), and cerebral blood flow (rCBF) 16 times in 11 patients with aneurysmal SAH. All studies were performed preoperatively; no patient had hydrocephalus or intracerebral hematoma on brain CT. Eight patients with no arteriographic vasospasm who were studied on days 1-4 post-SAH had a significant 25% reduction in global CMRO2 compared to age-matched controls, and no significant change in global OEF, suggesting a primary reduction in CMRO2 caused by SAH. Four patients studied seven times during arteriographic vasospasm had significantly increased rOEF with unchanged CMRO2 in arterial territories affected by arteriographic vasospasm compared to territories without vasospasm, indicative of cerebral ischemia without infarction. No brain regions studied with PET were infarcted on follow-up CT. We conclude that the initial aneurysm rupture produces a primary reduction in CMRO2, and that subsequent vasospasm causes ischemia.

The impact of maternal serum on development of enolase activity in fetal rat brain cell culture

The effect of gestational age on serum-mediated changes in enolase activity was tested in a fetal rat brain cell culture. After 6 days exposure to graded concentrations (10 and 20%) of nonpregnant female rat sera, enolase activity in brain cell cultures increased from 2.83 +/- 0.03 to 3.74 +/- 0.19 mumol/min/mg protein, P less than 0.01. By contrast, similar concentrations of 20-day maternal serum progressively decreased enzyme activity from 1.52 +/- 0.14 to 1.19 +/- 0.08 mumol/min/mg protein. The inhibitory effect was apparent at 14 days gestation and became progressively greater during late gestation to reach a maximum at 20 days. Combining equal concentrations of 20-day pregnant with either nonpregnant or adult male serum neutralized the inhibitory activity. When serum from 20-day pregnant rats was partitioned by a dialysis membrane with a 50,000 MW pore size, inhibitory activity could be similarly neutralized by male or nonpregnant female serum. When 20-day maternal serum was passed successively through filters with a greater than 300,000, 100,000, and 50,000 MW exclusion, the inhibitory activity was apparent in all fractions excluded by a molecular weight of 50,000. No inhibition was apparent in fractions that were not excluded by 50,000 MW pore size. Inhibition of enolase activity was greatest in the fraction with MW greater than 300,000. Binding of IGF II could also be demonstrated in this fraction. Binding of IGF II was evident in the fraction greater than 100,000 MW but could not be demonstrated in fractions with a lower molecular weight. The presence of mRNA for IGF II in 20-day fetal rat brain cell cultures was evident when total cellular RNA was analyzed by an RNAase protection assay. It is proposed that a high-molecular-weight component of maternal serum in late gestation can bind endogenously generated IGF II. Such binding, by depleting the necessary growth factors, could inhibit in vitro growth and development of enolase activity.

Retinoid metabolism in cultured human retinal pigment epithelium

Uptake, esterification and release of all-trans-retinol in primary cultures of human retinal epithelium were studied. Cultured cells were supplemented with 3H-labelled 11,12-all-trans-retinol, using fatty-acid-free albumin as the carrier. This led to incorporation of retinal and the formation of all-trans- and 11-cis-retinyl palmitate. The metabolism of the all-trans ester was monitored in a medium containing various concentrations of foetal-bovine serum (FBS). In 20% (v/v) FBS, the ester was hydrolysed, and all-trans-retinol was released into the culture medium. In the absence of FBS, little ester was hydrolysed and no retinol was found in the medium. Dialysed or heat-inactivated FBS or fatty-acid-free albumin was as effective as FBS in provoking ester hydrolysis and retinol release. The concentration-dependency of this effect on FBS was matched by the corresponding concentrations of albumin alone. A linear relationship was also found between interphotoreceptor retinoid-binding protein and retinoid release. Haemoglobin, which does not bind retinoids, is ineffective in this capacity. It is concluded that lipid-binding substances, mainly albumin, in FBS act as acceptors for retinol and drain the cultured cells of this molecule. The release of the retinol is coupled to the hydrolysis of retinyl esters in the cell, so that there is little or no net hydrolysis of ester if there is no acceptor for retinol in the culture medium. This effect explains why cultured human retinal epithelial cells are depleted of their stores of retinoids when maintained in medium supplemented with FBS.

Serum effects on substrate oxidation by dissociated brain cells: possible sites of action

This report is an extension of recent studies indicating the presence of a factor in serum that preferentially inhibits 14CO2 production from labeled glucose. Experiments with dissociated cells revealed that the inhibitory effects of serum were only slightly changed over more than a 50-fold range in initial glucose concentration. Serum had no effect on the rate of glucose transport (uptake of 1,3[3H]2-deoxyglucose). The inhibitory effect of serum was greater on 14CO2 production from [6-14C]glucose than [1-14C]glucose. Other studies revealed that 14CO2 production from [1-14C]pyruvate was more than 5 times the rate obtained using [3-14C]pyruvate; however, the inhibitory effect of serum was much greater on the latter (20% vs 60% inhibition respectively) at 2 mM pyruvate and in the presence of 1% fetal bovine serum. Attempts to characterize the factor using Amicon filtration showed the highest inhibitory activity in a 10,000 mol. wt. fraction, although some inhibitory activity was found in commercial preparations of bovine serum albumin. Delipidation of serum had no effect. Based on these results, we postulate that the observed decrease in labeled CO2 production reflects the regulation of substrate utilization at the pyruvate carboxylase step by one or more factors in serum (with a mol. wt. of approximately 10,000).

Alterations in calcium content and biochemical processes in cultured skin fibroblasts from aged and Alzheimer donors

Aging and Alzheimer disease lead to alterations in several biochemical properties of cultured skin fibroblasts. Total bound calcium increases in fibroblasts due to normal aging (+52%) and is elevated even further with Alzheimer disease (+197%). Processes that require mitochondrial function, such as glucose and glutamine oxidation, declined in cells from aged donors (-25%) and decreased even further in Alzheimer disease (-46%). In addition, biosynthetic processes that depend upon mitochondrial function, such as glucose or glutamine incorporation into protein and lipid, paralleled the oxidative decreases. Cytosolic and nuclear processes such as leucine incorporation into protein and thymidine into DNA were depressed more by aging than Alzheimer disease. These findings suggest that calcium homeostasis and mitochondrial functions are altered more by Alzheimer disease than normal aging.