Nicole Pages

New data on the importance of gestational Mg deficiency

Chronic primary Mg deficiency is frequent. About 20% of the population consumes less than two-thirds of the RDA for Mg. Women, particularly, have low intakes. For example, in France, 23% of women and 18% of men have inadequate intakes. Mg deficiency during pregnancy can induce maternal, fetal, and pediatric consequences that might last throughout life. Studies of gestational Mg deficiency in animals show that Mg deficiency may have marked effects on parturition and postuterine involution. It has interfered with fetal growth and development, and caused morbidity from hematological effects and disturbances in temperature regulation, to teratogenic effects. Emphasis, here, is on effects of chronic clinical gestational Mg deficiency as it affects the infant. Premature labor, contributed to by uterine hyperexcitability caused by chronic maternal Mg deficiency, that can be intensified by stress, gives rise to preterm birth. If the only cause of uterine overactivity is Mg deficiency, its supplementation constitutes nontoxic tocolytic treatment, as an adjuvant treatment, that is devoid of toxicity and enhances efficacy and safety of tocolytic drugs such as beta-2 mimetics. Evidence is considered that Mg deficiency or Mg depletion can contribute to the Sudden Infant Death Syndrome (SIDS). SIDS may be a fetal consequence of maternal Mg deficiency through impaired control of Brown Adipose Tissue (BAT) thermoregulation mechanisms leading to a modified temperature set point. SIDS can result from dysthermias: hypo- or hyperthermic forms. Possibly, simple nutritional Mg supplements might be preventive. Various stresses in an infant can transform simple Mg deficiency into Mg depletion. For example, lying prone can be stressful for the baby, as can parental smoking. The role of chronopathological stress appears to be often neglected, as it constitutes a clinical form of primary hypofunction of the biological clock [with its anatomical and clinical stigma such as reduced production of melatonin (MT) and of its urinary metabolite: 6 Sulfatoxy-Melatonin (6 SMT)]. SIDS might be linked to impaired maturation of both the photoneuroendocrine system and BAT. Prophylaxis of this form of SIDS should include atoxic nutritional Mg therapy for pregnant women with total light deprivation at night for the infant. Consequences of maternal primary Mg deficiency have been inadequately studied. To determine ultimate outcomes of gestational Mg deficiency in infants, a long-term multicenter placebo-controlled prospective study should undertaken on effects of maternal nutritional Mg supplementation on lethality/morbidity in fetus, neonates, infants, children and adults, not only during pregnancy and the baby’s first year, but throughout life.

Experimental stroke protection induced by 4-hydroxybenzyl alcohol is cancelled by bacitracin.

Induction of protein disulfide isomerase (PDI) is validated as a main mechanism by which 4-hydroxybenzyl alcohol (4-HBA), an active principle of Gastrodia elata Blume, reduces cerebral infarct volumes in a murine model of focal brain ischemia/reperfusion. In contrast to its position isomers, i.e. 3-hydroxybenzyl alcohol (3-HBA) and 2-hydroxybenzyl alcohol (2-HBA), and to aliphatic diols (1,4-butanediol and 1,5-pentanediol), 4-HBA administered intravenously at 25 mg/kg protected mice, significantly reducing total, cortical and sub-cortical infarct volumes by 42, 28 and 55%, respectively. All compounds, 4-HBA included, were devoid of antioedematous properties. Only the stroke protective 4-HBA, but neither 3-HBA nor 2-HBA, was capable of significantly inducing PDI in intact mouse brains. Stroke protection was fully prevented by bacitracin (500 mg/kg), a known inhibitor of PDI, which, without affecting basal brain PDI levels, altered the ability of 4-HBA to induce significantly PDI in intact brains. Taken as a whole, our data indicate that stroke protection induced by 4-HBA involves PDI as a key player, making this protein a valuable target to control brain injury disorders. The fact that 4-HBA, at doses up to 200mg/kg, was devoid of neurotoxicity in the rotarod test is also a decisive element to promote the neuroprotective use of this plant compound.

Activities of α-asarone in various animal seizure models and in biochemical assays might be essentially accounted for by antioxidant properties

Anticonvulsant properties of α-asarone were studied in mice at three doses with different toxicity. The 100mg/kg dose decreased both treadmill performance and locomotor activity, caused hypothermia, and potentiated pentobarbital-induced sleep. The last two effects and no toxicity were observed at 60 and 22mg/kg, respectively. In chemical (pentylenetetrazole, picrotoxin, N-methyl-D-aspartate, pilocarpine) and electrical (maximal electroshock) seizure tests, neither seizures nor death were prevented by 60 mg/kg α-asarone which, however, exhibited protective-like effects (delay in the onset of clonic and/or tonic seizures and/or in the death of mice). Magnesium deficiency-dependent audiogenic seizures responded to non-toxic doses of α-asarone (60 mg/kg and less): 22 mg/kg protecting 50% of tested animals. Because these seizures respond to both anti-seizure and antioxidant compounds, antioxidant properties of α-asarone were studied, indicating 5 Units of superoxide dismutase-like activity per mg α-asarone. Treatment of mice by α-asarone (daily dose of 100mg/kg during 7 days) induced brain antioxidant enzymes (superoxide dismutase, glutathione peroxidase and reductase) in striatum and hippocampus and to a lesser extent in cortex. In view of recent findings about deleterious roles of chronic inflammatory/oxidant stresses in human epilepsy outcome, antioxidant and inductive properties of α-asarone are proposed to be coherent bases for traditional clinical efficacy.

The PPARγ agonist FMOC-l-leucine protects both mature and immature brain

(N-[9-fluorenylmethoxycarbonyl]-)-L-leucine (FMOC-L-leucine) and rosiglitazone, two ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), were evaluated in mature (adult mice) and immature (pups) brain injury models. In adult magnesium-deficient mice, a model responsive to both neuroprotective and anti-seizure compounds, FMOC-L-leucine, but not rosiglitazone, protected against audiogenic seizures. The protection afforded by FMOC-L-leucine was alleviated by the PPARgamma antagonist GW9662 (1-2 mg/kg) and was induced in 50% animals by 4.8+/-1.2 mg/kg. At this dose, FMOC-L-leucine modified audiogenic seizure phase durations in convulsing mice differently than prototype antiepileptic drugs did. FMOC-L-leucine (up to 100 mg/kg) was inactive in the 6 Hz seizure test, an adult animal model largely responsive to anti-seizure drugs. In a model of neonatal brain injury, FMOC-L-leucine (4 microg/kg) was neuroprotective against cerebral ibotenate toxicity. It reduced significantly the size of lesions in grey but not in white matter, while rosiglitazone (10 microg/kg) was inactive. Taken as a whole, the present data support neuroprotective potentialities of FMOC-L-leucine towards both mature and immature brain. The PPAR-based protection of immature brain is more important as it is known that classic adult brain protectants (GABA(A) activators, N-methyl-D-aspartate and sodium channel blockers) may be toxic for immature brain. The PPARgamma agonist FMOC-L-leucine is likely to be devoid of these classic protective mechanisms because of its inactivity in the 6 Hz seizure test, its activity in the audiogenic test being explained by neuroprotective rather than intrinsic anti-seizure mechanisms. Targeting PPARs might be thus a promising way to protect immature brain.

Threshold to N-methyl-D-aspartate-induced seizures in mice undergoing chronic nutritional magnesium deprivation is lowered in a way partly responsive to acute magnesium and antioxidant administrations

Magnesium deficiency may be induced by a diet impoverished in magnesium. This nutritional deficit promotes chronic inflammatory and oxidative stresses, hyperexcitability and, in mice, susceptibility to audiogenic seizures. Potentiation by low-magnesium concentrations of the opening of N-methyl-D-aspartate (NMDA) receptor/calcium channel in in vitro and ex vivo studies, and responsiveness to magnesium of in vivo brain injury states are now well established. By contrast, little or no specific attention has been, however, paid to the in vivo NMDA receptor function/excitability in magnesium deficiency. The present work reports for the first time that, in mice undergoing chronic nutritional deprivation in magnesium (35 v. 930 parts per million for 27 d in OF1 mice), NMDA-induced seizure threshold is significantly decreased (38 % of normal values). The attenuation in the drop of NMDA seizure threshold (percentage of reversal) was 58 and 20 % upon acute intraperitoneal administrations of magnesium chloride hexahydrate (28 mg magnesium/kg) and the antioxidant ebselen (20 mg/kg), respectively. In nutritionally magnesium-deprived animals, audiogenic seizures are completely prevented by these compound doses. Taken as a whole, our data emphasise that chronic magnesium deprivation in mice is a nutritional in vivo model for a lowered NMDA receptor activation threshold. This nutritional model responds remarkably to acute magnesium supply and moderately to acute antioxidant administration.

Apoptosis inhibition and ornithine decarboxylase superinduction as early epigenetic events in morphological transformation of Syrian hamster embryo cells exposed to 2-methoxyacetaldehyde, a metabolite of 2-methoxyethanol

We have conducted a study to determine the carcinogenic potential of ethylene glycol monomethyl ether (EGME), a member of the glycol ether family, as compared to its reactive metabolite 2-methoxy-acetaldehyde (MALD). Since disruption of equilibrium between cell proliferation and cell death is thought to play a key role in multistage carcinogenesis, we investigated, in Syrian hamster embryo (SHE) cells exposed to various doses of EGME and MALD, impairment in apoptosis rate and in ornithine decarboxylase (ODC) metabolism. The activity of this rate-limiting enzyme of polyamine biosynthesis is closely related to cell proliferation and cell transformation. At the end-point, comparative action of the two products on SHE cell morphological transformation frequency was evaluated. One-stage exposure of SHE cells to 2 mM EGME and 200 microM MALD for 5 h did not change basal apoptotic level, whereas 0.16 microM phorbol ester (TPA) decreased it. Using two-stage exposure protocol (1 h xenobiotic followed by 5 h TPA), MALD strongly inhibited apoptosis more than did TPA alone; the parent compound EGME did not have any effect on TPA inhibiting action. Western blotting analysis showed that sequential treatment (MALD/TPA) increased Bcl-2 oncoprotein expression, whereas Bcl-XL and Bax proteins were not changed. The same staged exposure of SHE cells to MALD/TPA strongly induced ODC activity, and the rate was higher than that obtained with TPA alone: this was accompanied by an increase of ODC protein level. This ODC superinduction was not observed with EGME/TPA treatment. In long-term SHE-cell morphological transformation assay, staged exposure to MALD (800 microM or 1 mM for 24 h) followed by TPA applications increased the number of transformed colonies at the seventh day. Such early cooperative events as apoptosis inhibition and ODC superinduction, followed by the increase of SHE-cell transformation frequency, are highly indicative of a carcinogenic potential for the metabolite, MALD.

Two-stage exposure of Syrian-hamster-embryo cells to environmental carcinogens: superinduction of ornithine decarboxylase correlates with increase of morphological-transformation frequency

As part of environmental toxicology, it is important to assess both the carcinogenic potential of xenobiotics and their mode of action on target cells. Since dysregulation of ornithine decarboxylase (ODC), a rate‐limiting enzyme of polyamine biosynthesis, is considered as an early and essential component in the process of multistage carcinogenesis, we have studied the mode of ODC induction in Syrian‐hamster‐embryo(SHE) cells stage‐exposed to carcinogens and to non‐carcinogens. One‐stage (5 hr) treatment of SHE cells with 50 μM clofibrate (CLF), a non‐genotoxic carcinogen, or with 0.4 μM benzo(a)pyrene (BaP), a genotoxic carcinogen, slightly decreased basal ODC activity. Using the 2‐stage exposure, 1 hr to carcinogen, then replacement by TPA for 5 hr, the ODC activity was higher than that obtained with TPA alone. This ODC superinduction was not observed when SHE cells were similarly pre‐treated with non‐carcinogenic compounds. Several environmental chemicals, pesticides, solvents, oxidizers and drugs were investigated with this SHE cell model. With one‐stage exposure, some xenobiotics decreased basal ODC activity, while for others ODC changes were not noticeable. With 2‐stage exposure (chemical followed by TPA), all carcinogens amplified the TPA‐inducing effect, resulting in ODC superinduction. Comparative studies of the action of carcinogens and of non‐carcinogens, using 2‐stage exposure protocols, clearly show a close relationship between ODC induction rate and morphological transformation frequency. Int. J. Cancer 75:744–749, 1998.© 1998 Wiley‐Liss, Inc.

THC aggravates rat muricide behavior induced by two levels of magnesium deficiency

A severe magnesium deprivation induces an interspecific aggressive behavior (muricidal behavior, MB) in different strains of rats. Delta9-tetrahydrocannabinol (THC) is also known to induce MB even after a single injection (11 mg/kg) in starving, isolated rats. In the present work, we investigated the MB behavior, for six successive assays 1 h delayed, of two groups of male Long-Evans rats fed 50- or 150-ppm Mg(2+)-deficient diets, for 42 days after a single injection of THC at doses (2, 4 or 8 mg/kg) that did not induce aggressiveness in control rats. This treatment led to Mg(2+) plasma levels of 5+/-0.3 and 12.3+/-0.9 mg/ml vs. 21+/-1.5 mg/ml initially. In the 50-ppm Mg-deficient rat group, all the rats were muricidal but the MB pattern was severely aggravated by THC. In the 150-ppm Mg-deficient rat group, no rat was muricidal but all doses of THC induced a 100% MB. In addition, by quantifying the three phases of MB, we showed through six consecutive hourly muricidal assays, that the two first phases (attack latency and attack on the living mouse) decreased progressively, whereas the third phase (attack on the dead mouse) increased dramatically. This indicates firstly that Mg-deprivation decreases the responsiveness threshold of rats to THC. Secondly, these very low doses of THC induced an aggravation of MB and an acquired hyper-aggressiveness in both 50- and 150-ppm Mg-deficient rats, probably involving different neurotransmitters, mainly serotonin, which is decreased by both treatments.

Practical Interest of Circulating Total and Ionized Magnesium Concentration Evaluation in Experimental and Clinical Magnesium Disorders

Magnesium (Mg) is essentially an intracellular ion, which makes it difficult to evaluate Mg status. Both circulating total (MgT) and ionized Mg2+ (MgI) are used in clinical practice but their respective interest is still debated. In the present review, we list various s tudies comparing MgT and MgI in either Mg imbalances or Mg status dysregulations. In simple Mg imbalances (either therapeutic Mg overload or Mg defi ciency), the evaluation of MgT appears a better marker than MgI because it seems that a subtle physiological homeostatic compensatory reaction modifies the proportion of MgI, the most biologically active fraction of blood Mg, in order to reduce the effects of Mg imbalance. In contrast, in Mg dysregulations (either Mg pathological overload or Mg depletion) both fractions may vary independently, depending mainly on the renal status and on the equilibrium between MgI and Mg complexed with proteins and anions. The choice of the more appropriate marker is discussed.