The quantitative determination of plasmalogen by its reaction with mercuric chloride

Preferential binding of Inorganic Mercury to specific lipid classes and its competition with Cadmium

Upon uptake of Hg and Cd into living systems, possible targets for metal induced toxicity include the membranes surrounding nervous, cardiovascular and renal cells. To further our understanding of the interactions of Hg and Cd with different lipid structures under physiologically relevant chloride and pH conditions (100 mM NaCl pH 7.4), we used fluorescence spectroscopy and dynamic light scattering to monitor changes in membrane fluidity and phase transition and liposome size. The metal effects were studied on zwitterionic, cationic and anionic lipids to elucidate electrostatically driven metal-lipid interactions. The effect of Hg-catalyzed cleavage of the vinyl ether bond in plasmalogens on these aforementioned properties was studied in addition to a thermodynamic characterization of this interaction by Isothermal Titration Calorimetry. The negatively charged Hg-chloride complexes formed under our experimental conditions induce membrane rigidity in membranes containing cationic lipids and plasmalogens while this effect is heavily reduced and entirely absent with zwitterionic and anionic lipids respectively. The K_D for the interaction of Hg with plasmalogen containing liposomes was between 4-30 μM. Furthermore, the presence of Cd affected the interaction of Hg with plasmalogen when negatively charged PS was also present. In this case, even the order of the metal addition was important.

Plasmalogen degradation by oxidative stress: production and disappearance of specific fatty aldehydes and fatty alpha-hydroxyaldehydes

Plasmalogens are often considered as antioxidant molecules that protect cells from oxidative stress. Their vinyl ether bond could indeed be among the first targets for newly formed radicals. However, the long chain aldehydes released from plasmalogens were seldom studied and possible injurious or harmless effects were poorly examined. Thus, the sensitivity of the vinyl ether bond of plasmalogens was investigated in a cerebral cortex homogenate under UV irradiation- or Fe2+/ascorbate-induced peroxidation. Kinetics of aldehyde production was followed by gas chromatography/mass spectrometry. This confirmed that plasmalogens were highly sensitive to oxidative stress (70% cleavage after 90 min UV irradiation and 30% after 30 min of Fe2+/ascorbate). The aldehydes corresponding to sn-1 position 16:0, 18:0, or 18:1 were poorly detected. Conversely, oxidation of plasmalogens yielded preferentially 15:0, 17:0, and 17:1 aldehydes under UV and the alpha-hydroxyaldehydes 16:0-OH and 18:0-OH following a Fe2+/ascorbate oxidation. Kinetics showed that free aldehydes and above all free alpha-hydroxyaldehydes disappeared from the medium as soon as produced. Consequently, the behavior of these released aldehydes in the tissues has to be investigated in order to ascertain the protective effect of plasmalogens against oxidation.

Ratios of linoleic acid to alpha-linolenic acid in formulas for term infants

Commercial infant formulas with a ratio of linoleic acid (LA) to alpha-linolenic acid (ALA) of 10:1 or higher are nutritionally inadequate; the tissue levels of docosahexaenoic acid (DHA) are lower and the visual function indices are reduced in infants who are fed these formulas. All the evidence points to using LA:ALA ratios of less than 8:1, but there has been only one study in infants that used formulas with reduced LA:ALA ratios, and only biochemical indices were monitored. There is a need for both short-term studies to establish the ratios of LA to ALA that will make possible the accumulation of DHA to levels close to those in breast-fed infants and long-term trials to determine the effects of such fat blends on growth and development.

Modification of renal cortical subcellular membrane phospholipids induced by mercuric chloride

Administration of mercuric chloride (HgCl2, 6 mg/kg) to rabbits produced renal failure, with changes in serum creatinine from 1.01 +/- 1 in controls to 6.46 +/- 0.91 mg/dl 24 hr after administration. Mitochondria isolated from HgCl2-treated rabbits exhibited alterations in acceptor control ratios, with reduction to 1.9 +/- 0.2 from 3.9 +/- 1.2 in controls. Ultrastructurally, the mitochondria showed swelling and loss of inner mitochondrial membranes. Total lipids from mitochondria of control and treated rabbits were obtained by modified Folch extraction and phospholipids analyzed by TLC. Brush border membranes and basolateral membranes were prepared from control and HgCl2-treated kidneys 2 and 24 hr after HgC12 administration. At 24 hr mitochondria showed a 36% fall in phosphatidylcholine (PC), a 36% fall in phosphatidylethanolamine (PE), and a 27% fall in cardiolipin. Brush border showed a decrease in phosphatidylserine (PS) of 29% and in PE of 40%. The basolateral membranes showed a reduction only in PE of 35%. At 2 hr post HgCl2, early changes are confined to the BBM and consist of a reduction in PE in this membrane. This changes in membrane phospholipids may be important in the functional derangements that occur at the cellular level after HgCl2 administration.

HPLC of plasmalogen-containing phosphatidylcholine under reverse-phase or argentation conditions

Two approaches to the high pressure liquid chromatography (HPLC) isolation of intact plasmalogens were investigated. The first used reversed-phase HPLC and sought to take advantage of subtle differences in the hydrophobicity of the alk-1-enyl chain from the acyl counterpart. On a C-18 column, bovine heart phosphatidylcholine (PC), which was 47% plasmalogen, was separated into a number of fractions that differed in their molecular species composition. One combination of fractions amounted to a 26% yield of PC enriched to 82% plasmalogen. The second approach sought to take advantage of the uniquely electron-rich functionality of the plasmalogens, the alk-1-enyl ether double bond, and its potential to coordinate with heavy metal ions. Specifically, bovine heart PC was applied to a cation-exchange type HPLC column in the silver ion mode. Although complete exchange of all the active sites of the column with silver ion led to complete retention of PC, partial activation with silver ion resulted in the separation of the PC into fractions, according to the degree of unsaturation. Plasmalogen-rich fractions eluted last and remained intact during the process. One combination of these fractions amounted to a 49% yield of PC enriched to 72% plasmalogen. Use of a cation-exchange system in the mercuric ion mode led to on-column hydrolysis of the plasmalogen; with palladium ion, the metallic species was stripped from the column by the eluting lipid.

Biochemical changes in Cuprizone-induced spongiform encephalopathy. I. Changes in the activities of 2',3'-cyclic nucleotide 3'-phosphohydrolase, oligodendroglial ceramide galactosyl transferase, and the hydrolysis of the alkenyl group of alkenyl, acyl-glycerophospholipids by plasmalogenase in different regions of the brain

Cuprizone (biscyclohexanone oxaldihydrazone) which is known to produce a status spongiosus and demyelination in the CNS was administered in the diet of weanling male mice at a concentration of 0.4% by weight for a period of six weeks before returning animals to a normal diet. Changes in body weight but not brain weight were reversible. Based on the decline in CNP'ase activity and the concentration of galactocerebroside, the loss of myelin was around 70% in those sections of the cerebrum with a high content of white matter while the cerebellum was less affected. The activity of oligodendroglial HFA-ceramide galactosyl transferase was also reduced. These biochemical parameters of myelination were increased after withdrawal of Cuprizone. Remyelination in the cerebrum but not the cerebellum was incomplete. The activity of plasmalogenase hydrolysing the alkenyl group of alkenyl, acyl-phospholipids increased 2-fold in those sections in which myelin loss was most severe. The increase preceded the greatest loss of myelin components (3 to 6 weeks on Cuprizone). The origin of the increased phospholipase activity in demyelinating tissue is discussed. Following myelination, there was a deficit in plasmalogenase activity particularly in the frontal cortex of the cerebrum, where the plasmalogen concentration was higher than in controls.