Effect of a failure of energy supply on adenine nucleotide breakdown in placentae and other fetal tissues from rat and guinea pig

Placental oxygen consumption. Part II: in vitro studies--a review

The human placenta in vivo consumes large amounts of oxygen. After delivery the placenta is exposed to anoxia and under in vitro experimental conditions oxygen consumption is only a fraction of in vivo estimates. In spite of a reduced oxygen supply, structural and functional integrity of the tissue is surprisingly well preserved. Special metabolic adjustments in the sense of 'partial metabolic arrest' may be the explanation for a remarkable survival capacity of placental tissue and reduction of protein synthesis seems to be an important component of metabolic slowdown. The potential significance of this special feature of placental metabolism for the in vivo situation is discussed.

Presence of two enzymes, different from the F1F0-ATPase, hydrolyzing nucleotides in human term placental mitochondria

The hydrolysis of ATP, ADP or GTP was characterized in mitochondria and submitochondrial particles since a tightly-bound ATPase associated with the inner mitochondrial membrane from the human placenta has been described. Submitochondrial particles, which are basically inner membranes, were used to define the location of this enzyme. Mitochondria treated with trypsin and specific inhibitors were also used. The oxygen consumption stimulated by ATP or ADP was 100% inhibited in intact mitochondria by low concentrations of oligomycin (0.5 microgram/mg) or venturicidine (0.1 microgram/mg), while the hydrolysis of ATP or ADP was insensitive to higher concentrations of these inhibitors but it was inhibited by vanadate. Oligomycin or venturicidine showed a different inhibition pattern in intact mitochondria in relation to the hydrolysis of ATP, ADP or GTP. When submitochondrial particles were isolated from mitochondria incubated with oligomycin or venturicidine, no further inhibition of the nucleotide hydrolysis was observed, contrasting with the partial inhibition observed in the control. By incubating the placental mitochondria with trypsin, a large fraction of the hydrolysis of nucleotides was eliminated. In submitochondrial particles obtained from mitochondria treated with trypsin or trypsin plus oligomycin, the hydrolysis of ATP was 100% sensitive to oligomycin at low concentrations, resembling the oxygen consumption; however, this preparation still showed some ADP hydrolysis. Native gel electrophoresis showed two bands hydrolyzing ADP, suggesting at least two enzymes involved in the hydrolysis of nucleotides, besides the F1F0-ATPase. It is concluded that human placental mitochondria possesses ADPase and ATP-diphosphohydrolase activities (247).

The importance of the measurement of ATP depletion and subsequent cell damage with an estimate of size and nature of the market for a practicable method: a review designed for technology transfer

ATP is the energy currency of cells. ATP depletion is a central process in pathogenesis, in particular ischaemia, hypoxia and hypoglycaemia. ATP depletion in cells can be indirectly measured from the increased concentrations of extracellular hypoxanthine, a central intermediate in the metabolism of ATP. Cell damage secondary to ATP depletion can also be measured from extracellular hypoxanthine. The relevant biochemistry and physiology is briefly reviewed. Since market size is needed for investment decisions that would allow technology transfer, the numbers of hypoxanthine analyses that are clinically justified from the extensive published evidence are calculated per million population from UK, Norwegian and other evidence. The concentration of oxygen in blood is measured to estimate whether mitochondrial oxidative phosphorylation is adequate. Measurements of bicarbonate are used to estimate anaerobic glycolysis. Since the indirect estimation of ATP depletion is a major objective of blood gas and acid-base analyses, the number of such analyses per million population provides a good estimate of potential market size for a more direct method of estimating ATP depletion. A method is required for the rapid, dispersed emergency analyses needed clinically. Routes for method development are indicated. Competition, risks, acceptability, consumer motivation and timetables are indicated for the development phase. There are medicolegal pressures, especially in the USA, for the proposed advances to be widely used.

Characterization of the F1F0-ATPase and the tightly-bound ATPase activities in submitochondrial particles from human term placenta

In a previous study we demonstrated the existence of a tightly-bound ATPase in the human placental mitochondria (Martínez et al., 1993). The current study characterizes the ATP hydrolysis produced by the F1F0-ATPase and the tightly-bound ATPase in submitochondrial particles from the human term placenta. Both enzymes were not differentiated by pH. Inhibitors were necessary to distinguish the activity of each enzyme. The kinetic of the total ATP hydrolysis fitted into a model of two enzymes. During the characterization, it was observed that the tightly-bound ATPase activity was partially inhibited by vanadate and Mg2+, whereas the F1F0-ATPase was totally inhibited by Mg2+. Different nucleotides were hydrolyzed by the tightly-bound ATPase; the F1F0-ATPase hydrolyzed exclusively ATP. Glucose-6-phosphate, p-nitrophenylphosphate, or pyrophosphate were not hydrolyzed by the F1F0-ATPase, although some hydrolysis was observed with the tightly-bound ATPase. It is concluded that the tightly-bound ATPase activity corresponded to a 5'-nucelotidase, and that the human placental mitochondria could participate in the metabolism of nucleotides.

Lesch-Nyhan syndrome and its pathogenesis: normal nicotinamide-adenine dinucleotide but reduced ATP concentrations that correlate with reduced poly(ADP-ribose) synthetase activity in HPRT-deficient lymphoblasts

In hypoxanthine (guanine) phosphoribosyltransferase- (HPRT; EC 2.4.2.8) deficient lymphoblasts, ATP but not nicotinamide-adenine dinucleotide coenzyme concentrations are reduced by limited nutrition. Such reduced ATP concentrations are correlated with reduced poly(ADP-ribose) synthetase (polyADPRT; EC 2.4.2.30) activity; this reduces the breakdown of nicotinamide-adenine dinucleotide coenzymes and thus explains their normal intracellular concentrations. Since reductions in poly(ADP-ribose) synthetase activity reduce DNA repair, alterations in DNA could accumulate even in non-multiplying cells such as neurons, especially in the continuously active 'respiratory centre'. Our Lesch-Nyhan patients suffered respiratory deaths between 15 and 20 years of age.

Reversed-phase and ion-pair separations of nucleotides, nucleosides and nucleobases: analysis of biological samples in health and disease

Methods for the assay of nucleotides, nucleosides and nucleobases in biological samples in health and disease are reviewed, with emphasis on reversed-phase and ion-pair reversed-phase techniques for their determination. Modes of extraction from biological samples are discussed with respect of the determination of in vivo concentrations. Advantages and limitations of ion-pair reversed-phase chromatography are discussed with examples from biochemistry and clinical chemistry. The capacity of the high-performance capillary electrophoresis is compared with that of ion-pair reversed-phase chromatography.

Subcellular localization and properties of adenosine diphosphatase in human placenta

It was found that mitochondria from human placenta exhibited an ADPase activity with the following characteristics. The enzyme responsible for this activity was associated with the inner mitochondrial membrane. It was not released by treatment of the submitochondrial particles with solutions of high ionic strength. Maximal ADP hydrolysis was reached at pH 8. Specific inhibitors for alkaline phosphatase (L-phenylalanine), myokinase (P1,P5-di(adenosine-5')pentaphosphate), or 5'-nucleotidase (concanavalin A) did not decrease ADP hydrolysis. ATP synthesis from ADP by myokinase was about 13 nmol/mg/min, whereas ADP hydrolysis reached values around 500 to 550 nmol/mg/min, indicating that a myokinase-H+ATPase combination could not account for the observed rates of ADP hydrolysis. The activity was stimulated by Mg2+, but high concentrations of this cation produced inhibition. High ADP concentrations did not inhibit ADPase activity. Kinetic measurements of the activity in the submitochondrial particles showed that the true substrate was ADP-Mg. The kinetic studies showed V(app) values of 476 and 270 nmol/mg/min, and Kmapp values of 416 and 8.7 microM.

The role of the placenta in nutrition of the human fetus

Bidirectional transport across the placenta provides substrates required for fetal nutrition and prevents accumulation of metabolites in the fetal compartment. Transmission of compounds across the placental barrier occurs by diffusion and carrier-mediated transport. The technique of dual in vitro perfusion of an isolated cotyledon has provided important data for the human placenta. The high degree of permeability for hydrophilic molecules was recently confirmed by in vivo measurements that allow estimates of flux across the human placenta for a number of compounds. The bidirectional nature in transplacental exchange requires asymmetry in flux from the maternal to the fetal side or vice versa, which can be assured by a concentration gradient or an active transport system. There is increasing evidence that placental metabolism with active modification of the composition of nutrients released to the fetus in addition to transport plays an important role.

Hypoxanthine, xanthine and uridine in body fluids, indicators of ATP depletion

Measurements of hyp, xan and urd in body fluids can provide evidence of energy, ATP, depletion in the body, in organs or in cells. Such information is clinically useful in the many diseases in which cellular energy supplies cannot be maintained like perinatal asphyxia, hydrocephalus and vascular insufficiency in brain, heart, limbs, kidneys or other organs. Similar HPLC methods using reversed-phase C18 columns and quantitation by UV absorption have been employed in a variety of centres to yield almost identical results. These have been assembled in this review to form a series of reference values. The current analytical problems are reviewed. Since concentrations of hyp and xan may alter independently situations are discussed in which separate measurements rather than their summed, total oxypurine concentrations are needed. The biochemistry and physiology underlying the use of such analyses is examined to guide sampling of the appropriate body fluid at a relevant time and to avoid oversimplified interpretation of results as well as unnecessary arguments. Specifically: (1) Intracellular concentrations of hyp and xan are inversely related to adenylate energy change and therefore to the energy currency of the cell ATP. Uridine in tissues is similarly 'controlled'. (2) There is extensive evidence that large increases in hyp, xan and urd in body fluids indicate ATP depletion. (3) Small changes in hyp probably reflect alterations of ATP turnover. (4) Xanthine arises mainly from guanine and can change independently of hyp. (5) Clinically useful information is obtainable from hyp and xan concentrations in CSF, amniotic fluid, urine and plasma. Extensive clinical correlations are reviewed. At present we are in a development phase for which HPLC is ideal but the most efficient way to perform and use such analyses in routine clinical practice remains to be established.

Clinical biochemistry of the neonatal period: immaturity, hypoxia, and metabolic disease

This review attempts to provide practical information on common problems in the laboratory medicine of newborn infants and also considers unresolved problems in achieving neonatal diagnoses. A common cause of upset in the newborn--intrapartum asphyxia--can now be positively diagnosed. This leaves a small group whom it is necessary to investigate because they may have metabolic disease. The initial investigation of metabolic disease at the district general hospital should be limited to the commoner conditions.