In vivo 1H MRS choline: correlation with in vitro chemistry/histology

We correlated the in vivo 1H Magnetic Resonance Spectroscopy (MRS) concentration of the choline peak (CHO) with in vitro chemical measures of choline-containing compounds and a histological grade of cellularity in 18 patients with neoplastic and infectious brain lesions. Gas-chromatography-mass-spectrometry (GCMS) was used to measure the concentrations of free choline (Cho), glycerophosphocholine (GPCho), phosphocholine (PCho) and phosphatidylcholine (PtdCho) from biopsies in the same area where MRS was performed. Cellular density, free Cho, PCho and GPCho were the strongest determinants of 1H MRS CHO while PtdCho was not. Just as the 1H MRS 2.0 peak reflects both the concentration of n-acetyl-l-aspartate and neuronal density, the 1H MRS 3.2 peak reflects the concentration of water-soluble choline-containing compounds and cellular density.

Betaine and inositol reduce MDCK cell glycerophosphocholine by stimulating its degradation

The amount of glycerophosphocholine (GPC) in renal medullary cells in vivo and in cultured renal [Madin-Darby canine kidney (MDCK)] cells varies with extracellular NaCl and urea. We previously showed that this is largely due to modulation of GPC degradation catalyzed by GPC:choline phosphodiesterase (GPC: PDE). GPC also varies inversely with the levels of other compatible osmolytes, the accumulation of which is induced by high tonicity. We tested whether GPC:PDE activity and GPC degradation are affected by accumulation of compatible osmolytes other than GPC. We find that MDCK cell GPC content decreases when the cells take up betaine and/or inositol from the medium. The effect is considerably greater for cells in isosmotic or high-NaCl medium than in high-urea medium. This difference is associated with suppression of betaine and inositol accumulation with high urea. We then measured GPC:PDE activity with a novel chemiluminescent assay. Addition of inositol and/or betaine to the medium greatly increases GPC:PDE activity in cells in isosmotic or high-NaCl media, but the increase is much less in high-urea medium. The increases in GPC:PDE activity, associated with the presence of betaine, are accompanied by commensurate increases in absolute rates of endogenous GPC degradation by cells in isosmotic or high-NaCl medium. We found previously that, in MDCK cells incubated for 2 days in high-NaCl medium, the rate of GPC synthesis from phosphatidylcholine is increased, correlated with an increase in phospholipase activity. However, in the present experiments, betaine accumulation has no effect on phospholipase activity under those conditions and, thus, presumably does not affect GPC synthesis. Collectively, these data support the conclusion that betaine and/or inositol reduces GPC by increasing GPC degradation catalyzed by GPC:PDE. This mechanism enables GPC to be reciprocally regulated relative to other compatible osmolytes, thus maintaining an appropriate total osmolyte content.

Hyperosmolality stimulates phospholipase A2 activity in rabbit renal medulla and in Madin-Darby canine kidney (MDCK) cells

Renal medullary cells are able to accumulate glycerophosphocholine during adaptation to the high extracellular osmolality. The aim of this study was to investigate the effect of hyperosmolality on both phospholipase A2 activity and the rate of choline incorporation into glycerophosphocholine in rabbit renal medulla and Madin-Darby Canine Kidney cells. Phospholipase A2 activity was assayed in cellular subfractions isolated from both rabbit kidney medulla and Madin-Darby Canine Kidney cells in the presence of either 1-palmitoyl-2-[1-14C]palmitoyl phosphatidylcholine or 1-stearoyl-2-[1-14C]arachidonyl phosphatidylcholine as substrate. The rate of choline incorporation into glycerolphosphocholine was measured in Madin-Darby Canine Kidney cells growing in the presence of [methyl-3H]choline in the growth medium. Water deprivation of rabbits resulted in an increase of phospholipase A2 activity from 2.7 +/- 0.4 (n = 5) and 5.7 +/- 0.7 (n = 5) to 5.0 +/- 0.8 (n = 5) and 10.8 +/- 1.3 (n = 5) pmol of fatty acid released/min per mg protein in mitochondrial and microsomal fractions, respectively, using dipalmitoyl phosphatidilcholine as substrate while the activity of cytosolic enzyme remained unchanged. Similarly, the addition of sodium chloride in order to increase growth medium osmolality (from 320 mOsm/kg to 520 mOsm/kg) resulted in an elevation of both mitochondrial (from 1.8 +/- 0.1 to 4.9 +/- 0.8 pmol of fatty acid released/min per mg protein, (n = 4) and microsomal (from 8.7 +/- 0.5 to 15.9 +/- 1.7 pmol of fatty acid released/min per mg protein, n = 4) phospholipase A2 activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal cell mutants unable to take up biologically active glycerophospholipids

We have isolated two mutant strains from the murine, macrophage-like cell line, RAW 264.7, that are resistant to the cytotoxic effects of the antineoplastic, platelet activating factor analogue, 1-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OMe). The mutants were isolated using a single round of selection to ensure that resistance was due to a single gene defect. These mutants, RAW.R1 and RAW.R23, are approximately 20 times more resistant to ET-18-OMe (ID50 = 15-17 microM) than the parent strain (ID50 = 0.7-1.0 microM). Resistance to ET-18-OMe was due to a 90-95% reduction in the ability to take up and accumulate this compound. The uptake of other choline glycerophospholipids (e.g., platelet activating factor and 1-acyl-2-lyso-sn-glycero-3-phosphocholine) was also severely affected. This defect was not limited to choline glycerophospholipids; the uptake of an ethanolamine glycerophospholipid (1-alkyl-2-lyso-sn-glycero-3-phosphoethanolamine) was reduced by 80%. The uptake of palmitic acid, an amphipathic molecule bearing no phosphate-containing head group, was unaffected in the mutants. There was little metabolism of ET-18-OMe by either the wild-type or mutant cells. Binding of ET-18-OMe appeared to be normal in the mutants, but internalization of pre-bound ET-18-OMe was reduced. Uptake of non-lipid ligands such as horseradish peroxidase, lucifer yellow, and transferrin was normal in the mutants demonstrating that fluid-phase and receptor-mediated endocytosis is functional. The ability to generate mutants displaying a lesion that affects the uptake of both choline and ethanolamine phospholipids demonstrates that these species are internalized by RAW cells through one common primary route or through pathways that share a common factor. These mutants, and this approach to their isolation, offer a system with which to study and define the mechanisms of glycerophospholipid uptake into macrophages as well as other cell types.

Phosphatidylserine exposure on the platelet plasma membrane during A23187-induced activation is independent of cytoskeleton reorganization

Modifications in cytoskeleton organization (monitored by scanning electron microscopy study of platelet shape) and cytoskeleton proteolysis were investigated for their role in phosphatidylserine exposure (measured with spin-labeled analogues of phospholipids) during A23187-induced activation of human platelets. Resting platelets treated with combinations of calpeptin and cytoskeleton-disrupting agents (nocodazole or cytochalasin D) remained discoid, and there was no dense granule release, cytoskeleton proteolysis or vesicle shedding. Spin-labeled phosphatidylserine was fully and rapidly redistributed (t1/2 approximately 5 min) from the outer to the inner leaflet of the plasma membrane through ATP-dependent aminophospholipid translocase activity. In contrast, spin-labeled phosphatidylcholine was only partially and slowly redistributed (less than 20% within 60 min) to the inner leaflet. Filopod formation, vesicle shedding, and calpain-mediated proteolysis were inhibited during activation of platelets treated with calpeptin and cytoskeleton-disrupting agents. Moreover, regardless of whether platelets were treated or not, spin-labeled phosphatidylserine was rapidly (t1/2 < 1 min) and massively (50%) exposed on the outer leaflet of the plasma membrane, while the slow and slight spin-labeled phosphatidylcholine influx did not counterbalance spin-labeled phosphatidylserine outflux. These results demonstrated that phosphatidylserine exposure was not connected to the following activation-related processes: cytoskeleton modifications (actin and tubulin polymerization, submembrane skeleton proteolysis), inhibition of aminophospholipid translocase, and filopod formation. Moreover, the redistribution kinetics of spin-labeled phospholipids during activation strongly suggested the involvement of an aminophospholipid exposure mechanism that differs from a scrambling phenomenon.

The presence of alpha-glucosidase, glycerophosphocholine and carnitine in the epididymis and ejaculate of the vervet monkey (Cercopithecus aethiops) and the Chacma baboon (Papio ursinus)

The epididymis is the site of posttesticular sperm maturation in the male genital tract. Studies on human epididymides are hampered by the practical inaccessibility of epididymides of healthy men in their reproductive years. The limited use of laboratory animals therefore seems unavoidable. The objective was to establish baseline values of the epididymal markers alpha-glucosidase, glycerophosphocholine (GPC) and carnitine in the lumen of the caput, corpus and cauda epididymidis and in the ejaculate of adult male Chacma baboons and vervet monkeys. In both primates, alpha-glucosidase was found throughout the epididymis and in the ejaculate; values did not vary significantly. In monkeys, the highest concentration of GPC was found in the cauda epididymidis, but smaller amounts were found in the other regions and the ejaculate. In baboons, GPC was absent from the caput, but present in the other regions, including the ejaculate. Carnitine concentrations increased significantly from the caput to the cauda in monkeys and from the caput to the corpus in baboons. With this study, the relative concentration ranges in which these markers are present in the epididymides of these primates have been established. In future studies, changes in concentrations of these substances would probably indicate changes in epididymal function.

Osmoregulation of GPC:choline phosphodiesterase in MDCK cells: different effects of urea and NaCl

The organic osmolyte, glycerophosphocholine (GPC), accumulates in renal cells in response to high concentrations of either NaCl or urea, despite the very different effects of these solutes on cell function and volume. Together, high levels of these solutes increase GPC amount in Madin-Darby canine kidney cells by inhibiting its enzymatic degradation. The present study tests the effects of NaCl and urea, individually, on GPC accumulation and its degradation. A technique was developed to determine the absolute rate of GPC degradation by measuring the initial rate of disappearance of [3H]GPC (pulsed into the cells by hypotonic shock) and the specific activity of GPC in the cells. The mass of GPC in the cells was measured by another newly developed method, a sensitive chemiluminescent assay. We find that exposure to high NaCl or urea decreases the absolute rate of cellular GPC degradation by approximately one-half during the first 20.5 h. Reductions in GPC degradation are accompanied by commensurate decreases in the activity of GPC:choline phosphodiesterase (GPC:PDE; EC 3.1.4.2), an enzyme that catalyzes degradation of GPC. Activity of GPC:PDE falls > 50% in cells exposed for 2 h to high osmolality. Inhibition is sustained for 7 days with high urea alone. In contrast, with high NaCl alone, GPC:PDE activity reverts to control values by 7 days, by which time synthesis of GPC is increased, accounting for sustained GPC accumulation. Collectively, these data suggest that GPC accumulation in response to either high NaCl or urea occurs initially by inhibition of its degradation but that the effect of NaCl on degradation differs, in that it is transient, while that of urea is sustained.

Glycerophosphorylcholine, a component of both Ascaris suum muscle and Caenorhabditis elegans

Studies of the muscle phospholipid metabolism of Ascaris suum suggest an effect of cholinergic drugs on the turnover of phosphatidylcholine and the generation of glycerophosphorylcholine (GPC). 31P-nuclear magnetic resonance (NMR) studies of helminths revealed the presence of a major peak that was assigned to GPC. The primary effect of the cholinergic drugs on the parasites' phosphate profile appeared to be on the level of GPC. In in vivo studies, decreases in internal GPC concentrations occurred prior to any decrease in the concentration of ATP. The importance of these studies relies on the correct identity of this major 31P-NMR resonance. More recently, the identity of this resonance as GPC was questioned by experimental data obtained from C. elegans dauer larvae using the NMR technique. Because studies from our laboratory suggested that phospholipid metabolism may be intimately connected with the parasite's responses to drugs, the identity of the assigned resonance in the 31P-NMR spectrum as GPC in Ascaris suum was reexamined and found to be correct. Similar studies with C. elegans indicate the presence of both GPC and GPE.

Molecular basis of osmotic regulation

Cells almost universally respond to the stress of long-term hyperosmolality by accumulating compatible organic osmolytes. This allows them to maintain normal cell volume without a deleterious increase in intracellular inorganic ion concentration. Cells in the renal inner medulla are exposed to variable concentrations of salt and urea that may reach molal levels. The organic osmolytes that they accumulate include sorbitol, betaine, inositol, taurine, and glycerophosphocholine (GPC). This review considers recent advances in understanding osmotic regulation of these substances. Sorbitol is synthesized from glucose catalyzed by aldose reductase. Hypertonicity elevates the abundance of this enzyme by increasing transcription of its gene. Betaine is taken up via a specialized transporter. Hypertonicity raises the number of transporters by increasing their transcription. Current studies demonstrate that the 5' regions flanking the aldose reductase and betaine transporter genes contain osmotic response elements that increase transcription in response to hypertonicity. Osmotic regulation of inositol and taurine uptake also involves increased expression of specific transporter genes. GPC is unique in that its level rises in response to high urea, as well as hypertonicity. GPC accumulation is mainly regulated by changes in its degradation to choline, catalyzed by GPC:choline phosphodiesterase. Numerous other genes, including those for heat shock proteins, are also induced by hypertonicity. Their regulation and their role in osmotic regulation are the subject of considerable ongoing research.

Organic osmolytes in the kidney of domesticated red deer, Cervus elaphus

The cortex, inner and outer medulla, and papilla of kidneys of domestic red deer were analysed. In hydrated animals the urine concentration was found to be 672 +/- 45 mOsm.l-1. The medullary and papillary regions of the kidney were rich in the osmolytes betaine, glycerophosphorylcholine (GPC), inositol and sorbitol, all of which showed a steep rise in concentration from cortex to papilla. The kidney was rich in free amino acids, in particular taurine, glutamate (+glutamine), glycine and alanine, which were present at concentrations sufficient to suggest a possible role as osmolytes.

NOE enhancements and T1 relaxation times of phosphorylated metabolites in human calf muscle at 1.5 Tesla

Nuclear Overhauser effect (NOE) enhancements and relaxation times of 31P metabolites in human calf were measured in 12 volunteers (4 men and 8 women) at 1.5 T using a dual tuned four-ring birdcage. The NOE enhancements of inorganic phosphate (Pi), phosphocreatine (PCr), gamma-, alpha-, and beta-nucleoside triphosphate (NTP) from 19 measurements were 0.51 +/- 0.10, 0.64 +/- 0.03, 0.53 +/- 0.03, 0.56 +/- 0.08, and 0.47 +/- 0.05, respectively. The relaxation times were independent of proton irradiation and from 23 measurements were 3.49 +/- 0.35, 4.97 +/- 0.58, 4.07 +/- 0.36, 2.90 +/- 0.25, and 3.61 +/- 0.25 s for Pi, PCr, gamma-, alpha-, and beta-NTP, respectively. No significant differences between gender and age were observed for either NOE enhancements or relaxation times. Also, among nine volunteers, we observed no significant differences in T1 between the coupled and decoupled cases.

Increase of GPC levels in cultured mammalian cells during acidosis. A 31P MR spectroscopy study using a continuous bioreactor system

The purpose of this study was to study the metabolic events during a slow acidosis in three different cell lines by combining 31P magnetic resonance spectroscopy and hollow fiber bioreactor technology. The rate of change in intracellular pH, glycerophosphorylcholine (GPC), phophorylcholine (PCho), and nucleoside-triphosphate (NTP) levels were measured during 8 h of acidosis and 16 h of recovery in EPO, EAT, and RN1a cells, three cultured mammalians cell lines. Our results show a significant increase in GPC levels to 330 +/- 21.540 +/- 25, and 220 +/- 21% of their initial value correlated to a decrease of PCho levels to 57 +/- 14.58 +/- 17 and 45 +/- 15% of their initial value in EAT, RN1a, and EPO cells, respectively. These changes are discussed in terms of perturbation of energetic metabolism in cells undergoing a slow acidosis.

Incorporation of a phosphonium analogue of choline into the rat brain as measured by magnetic resonance spectroscopy

A clear understanding of choline metabolism is important in our goal to modify demyelination and remyelination in multiple sclerosis. To develop a technique capable of measuring metabolic changes in the brain, we have studied the incorporation of a phosphonium analogue of choline (P-choline) in tissue extracts of rats. After feeding adult rats a choline-deficient diet supplemented with P-choline, the analogue was not detectable by in vivo volume-localized 1H spectroscopy. However, in vitro 31P measurements of brain extracts revealed an 11% incorporation of P-choline into phosphatidylcholine. We report that P-choline incorporates preferentially into the lipid pool over the lipid precursor pool and we provide evidence that the choline peak resolved by in vivo 1H spectroscopy is only composed of small molecular weight choline-containing compounds.

Choline ingestion increases the resonance of choline-containing compounds in human brain: an in vivo proton magnetic resonance study

Choline is a crucial intermediate in several clinically relevant neurochemical processes. In this study, choline-containing compounds in human brain (principally phosphocholine, glycero-phosphocholine, and choline) were measured by 1H-magnetic resonance spectroscopy, before and after the ingestion of 50 mg/kg choline in four normal control subjects. Substantial and remarkably similar increases in the brain choline resonance occurred in each subject, with a nearly two-fold rise in the choline resonance observed 3 hr following choline ingestion (p = 0.008 versus baseline). One subject also received a dose of 200 mg/kg choline, and exhibited a proportionally larger increase in the brain choline resonance. The results are consistent with animal data reporting a rise in choline-containing compounds following choline administration. This is the first study to our knowledge where an oral nutrient has been shown to produce a detectable change in human brain composition in vivo. Studying choline transport and biotransformation in human brain may have relevance to several neuropsychiatric disorders, including affective disorders and dementia.

Transfer of phospholipase A-resistant pyrene-dialkyl-glycerophosphocholine to plasma lipoproteins: differences between Lp[a] and LDL

1-O-Hexadecyl-2-O-pyrenedecanyl-sn-glycero-3-phosphocholine, a non-hydrolyzable fluorescent diether analog of phosphatidylcholine (PC), was synthesized as a probe for studying phospholipid transfer to different lipoprotein classes with potential phospholipase activities. After incubation of total human plasma with the new probe at 37 degrees C for 4.5 h, a characteristic partition between the main lipoprotein fractions was observed. The fluorescent lipid was not degraded under these conditions and, therefore, served as a measure for choline glycerophospholipid distribution between plasma lipoproteins. In low density lipoprotein (LDL) and high density lipoprotein-3 (HDL3) the fluorescent PC analog showed only monomer fluorescence, whereas in Lp[a] and HDL2 monomer and excimer fluorescence were observed, indicating that the fluorescent phosphatidylcholine analog was incorporated into the respective lipoproteins to a different extent. According to the increased pyrene excimer fluorescence in Lp[a] compared with LDL the labeled phosphatidylcholine must be enriched and/or clustered in Lp[a]. Data from phospholipid and total fluorescence analyses are compatible with the assumption of higher label concentration in Lp[a]. On the other hand, transfer rates for serum protein-catalyzed lipid transport into isolated Lp[a] were slower as compared to LDL. It is suggested that slower lipid transfer to Lp[a] under these conditions is due to the decreased lipid mobility in the Lp[a] surface, whereas the higher extent of label partition into Lp[a] as observed in total plasma might be due to the higher affinity of apolipoproteins for phosphatidylcholine in Lp[a] (Sommer, A., et al. 1992. J. Biol. Chem. 267: 24217-24222). The use of a fluorescent dialkyl- instead of diacyl-glycerophosphocholine for transfer studies was mandatory, as we found that lipoproteins contained phospholipase A2 activity toward long-chain phosphatidylcholine. The lipoprotein-associated phospholipase A2 was three times more active in Lp[a] than in LDL. The degradation products formed by the phospholipase, fatty acids, and lyso-PC may add to the high atherogenic potential of Lp[a].

Na+/myo-inositol cotransport is regulated by tonicity in cultured rat mesangial cells

Mesangial cells are considered to be faced with osmotic stress under physiological (such as extraglomerular mesangial cells) and pathophysiological (for example, diabetes mellitus) conditions. To see if mesangial cells have an osmoregulatory mechanism, like renal medullary cells, we measured the intracellular contents of organic osmolytes in isotonic and hypertonic conditions. Cultured rat mesangial cells are well tolerant of acute increase in osmolality up to 500 mOsm/kg. The myo-inositol content increased in hypertonic cells more than six-fold the value in isotonic cells. The contents of glycerophosphorylcholine and sorbitol also increased but were less than that of myo-inositol. The Na(+)-dependent myo-inositol uptake in hypertonic cells was a 12-fold uptake in isotonic cells, reaching a maximum 24 hours after the switch to a hypertonic medium. The uptake rate increased as medium osmolality increased from 300 to 500 mOsm/kg. Raffinose is the most effective solute to increase the myo-inositol uptake. NaCl, glucose and mannitol also increased the uptake rate (NaCl > glucose > mannitol). The increased uptake by hypertonicity was the result of an increase in Vmax without change in Km and was dependent on RNA and protein synthesis. These results indicate that mesangial cells respond to extracellular hypertonicity by increasing myo-inositol transport activity and accumulating myo-inositol into the cells, suggesting that myo-inositol functions as an organic osmolyte in mesangial cells.

Ca2+ dependent activation of rat uterine glycerylphosphorylcholine diesterase: presence of a positive modulator protein in uterine secretion

The rat uterine secretory enzyme glycerylphosphorylcholine (GPC) diesterase (EC 3.1.4.2) had been purified and characterized previously with respect to its mol. wt., size, amino acid, carbohydrate composition and estrogen inducible properties. This enzyme is observed to have exclusive specificity for GPC and exhibits characteristic hyperbolic kinetics with Ca2+ in an ethyleneglycolbis N'N'N'N' tetraacetic acid (EGTA) buffered system. Ca2+ reduces Km of the enzyme for GPC from 0.65 to 0.25 mM. The Km for GPC of the partially purified enzyme is found to be 0.35 mM without addition of calcium which indicates the presence of a positive modulator of the enzyme in this fraction. Based on this rationale, a protein activating factor for the enzyme was isolated from this fraction which has a native size of 18 KD as observed on Sephacryl S-200 chromatography and strikingly stimulates enzyme activity at around 0.55 microM.

Impairment of renal medullary osmolyte accumulation in potassium-depleted rats

To determine the relationship between accumulation of osmolytes and maximal urinary concentration in potassium depletion, we tested the effects of experimental water diuresis or potassium depletion on osmolytes in the renal medulla of rats. Hyperosmotic stress was imposed by 4 days of water deprivation for the purpose of establishing the maximal concentrating ability or by the infusion of sodium for the purpose of loading the equal amounts of sodium to the renal medulla. In the diuresis group, water deprivation failed to increase betaine, sorbitol, and taurine contents to the same level as the untreated group, although sodium infusion increased betaine and sorbitol. In the potassium depletion group followed by water deprivation, urine osmolality (2,490 +/- 241 vs. 3,425 +/- 268 mosmol/kgH2O) and all osmolytes were significantly lower than in the untreated group. In response to hyperosmolality with sodium infusion, myo-inositol and glycerophosphorylcholine contents rose to the level of the untreated group. Medullary betaine (67.6 +/- 6.8 vs. 99.5 +/- 8.9), taurine (44.7 +/- 2.4 vs. 61.4 +/- 6.2) and sorbitol (35.6 +/- 4.4 vs. 57.0 +/- 8.4 mmol/kg protein) contents were reduced in potassium-depleted rats when the renal medulla was as hypertonic as in the untreated group. In conclusion, the processing of betaine, taurine, and sorbitol accumulation appeared to be impaired in potassium depletion.

Loss of phospholipid asymmetry in human platelet plasma membrane after 1-12 days of storage. An ESR study

We used paramagnetic analogs of endogenous phospholipids to study modification of phospholipid distribution in platelet plasma membranes during aging. Asymmetrical distributions and translocation kinetics were very different for spin-labeled phosphatidylserine and spin-labeled phosphatidylcholine in fresh platelet plasma membranes. In freshly prepared platelets and up to day 7, spin-labeled phosphatidylserine very rapidly penetrated to the inner leaflet of the platelet plasma membrane. However, spin-labeled phosphatidylcholine was mainly retained on the external leaflet. From day 7 to day 9, the two translocation kinetics became identical with symmetrical distribution of both spin-labeled phospholipids at equilibrium. Inhibition of translocase activity and modification of membrane stability accounted for these transformations. The rapid re-exposition of spin-labeled phosphatidylserine after stimulation by the calcium ionophore A23187, measured in fresh platelet concentrates, persisted up to day 9 but disappeared between day 10 and day 12. From day 7 to day 9, a strong cytoskeleton proteolysis and marked decrease in intracellular ATP were observed. Moreover, complete suppression of beta-N-acetyl glucosaminidase secretion and vesicle formation after A23187 stimulation of aged platelets indicated that platelets could no longer be activated beyond day 9. Taken together, these results showed that during in vitro aging there are metabolic and membrane modifications in platelet similar to those described for platelet activation. In addition, all of the observed events occurred simultaneously between day 7 and day 9. These results highlight the importance of maintaining plasma membrane asymmetry to increase the hemostatic effectiveness of transfused platelet concentrates.

Glycerol phosphorylcholine (GPC) and serine ethanolamine phosphodiester (SEP): evolutionary mirrored metabolites and their potential metabolic roles

Water-soluble phosphodiesters (WSPDE) are a prominent feature of many 31P-NMR spectra; however, their role has remained somewhat of a mystery. What has been missed in almost all previous studies is the fact that two classes of WSPDE exist in vertebrates: those in mammals and those in the other (reptile-avian) line. The first is represented by glycerol phosphorylcholine and the second by serine ethanolamine phosphodiester. A further examination of the literature suggests a common role for all WSPDE as lysophospholipase inhibitors and therefore net sparers of phospholipids by decreasing phospholipid metabolic throughput.

Association of glycerylphosphorylcholine with human sperm and effect of capacitation on their metabolism

The presence and localization of glycerylphosphorylcholine (GPC) on the surface of human sperm, as well as the metabolism of its breakdown product L-glycerol 3 phosphate (G3P), were investigated. GPC was found to be associated with sperm after penetrating cervical mucus and was present after repeated washing of the sperm. GPC was partially released by treatment with 0.4 M NaCl in 0.01 M sodium phosphate buffer (pH 7.4) and localized to the head region after sperm fractionation. G3P did not increase O2 uptake of uncapacitated human sperm. However, under aerobic conditions, lactate accumulated when exogenous G3P or uterine GPC diesterase was added to sperm in suspension. The uptake of O2 by washed capacitated sperm pre-incubated with 1 unit of rat uterine GPC diesterase for 30 min was significant. This effect was inhibited by 2 microM oligomycin indicating that oxidative phosphorylation had occurred. The present study indicates that GPC may play a role in the metabolism of human sperm after capacitation.

Epididymal markers in an andrology clinic

The ability of the markers alpha-glucosidase, carnitine, and glycerylphosphorylcholine to indicate epididymal obstruction was studied. alpha-Glucosidase was found to be the best discriminant, with 93.4% correct classifications. The possible interrelationship between alpha-glucosidase activity, sperm ATP, and epididymal function was then studied. alpha-Glucosidase correlated positively with the percentage of motile sperm (p = 0.0212) and with the percentage of sperm with good forward progression (p = 0.0374), but correlated negatively with the sperm ATP (p < 0.0500). It was concluded that lower ATP and higher alpha-Glucosidase may be markers of efficient epididymal function. The possible epididymal origin of detached ciliary tufts (DCTs) was studied by determining ATP and alpha-glucosidase activity in patients with DCTs. The mean ATP in patients with DCTs was significantly higher (p = 0.009), but the alpha-glucosidase activity significantly lower (p = 0.0412) than in the control group. These results seem to support the epididymal origin of DCTs.

Activation of phospholipase D participates in signal transduction pathways responsive to gamma-radiation

Early responses of mammalian cells to ionizing radiation include the activation of a protein kinase C implicated in the regulation of gene expression, the stimulation of tyrosine kinase activities, and the enhancement of phosphatidylinositol turnover. In the present report we show that clinically relevant doses of gamma-radiation (2 Gy) stimulate phosphatidylcholine hydrolysis in human squamous carcinoma cells. Radiation induced the accumulation of intracellular [3H]choline and the simultaneous increase in [3H]myristoyl-phosphatidic acid, followed by a small increase in the levels of [3H]myristoyl-diacylglycerol. Furthermore, in the presence of ethanol, gamma-radiation stimulated the appearance of [32P]phosphatidylethanol, an indicator of phospholipase D transphosphatidylation activity. These data demonstrate for the first time that phospholipase D activation participates in signaling pathways in response to gamma-radiation.

Glycerophosphocholine and phosphocholine are the major choline metabolites in rat milk

Choline is a constituent of cell membranes, surfactant and acetylcholine and is also a major source of methyl groups for the regeneration of methionine from homocysteine. Previous analyses of rat, human and bovine milk measured only choline, phosphatidylcholine and sphingomyelin. Choline-containing compounds in milk from rats lactating for 15 d were measured by HPLC and gas chromatograph-mass spectrometry. In addition to the previously reported choline metabolites, substantial concentrations of glycerophosphocholine (3.7 mmol/L) and phosphocholine (653 mumol/L) were also detected. At 1 h after oral administration of [methyl-14C]choline to lactating rats, the major labeled metabolites were phosphocholine (91% of label in milk) and betaine (9%). Twenty-four hours after the dose, glycerophosphocholine was the major labeled metabolite (69% of label in milk). Rat mammary epithelial cells, in primary culture, synthesized and secreted phosphatidylcholine, phosphocholine, glycerophosphocholine and betaine. Thus, the mammary gland was able to synthesize the choline metabolites found in milk, but these metabolites may not be derived exclusively from uptake from maternal blood. We have established that the total choline concentration in rat milk is sevenfold higher than previously reported, with > 80% present as glycerophosphocholine and phosphocholine.