Vascular function of MGH and MGL mice, two strains which differ by a genetic variation of magnesium metabolism

Mg deficiency is considered as a risk factor of cardiovascular disorders like hypertension and atherosclerosis. MGH and MGL mice, selected for high and low Mg status, are animal models which present variations of Mg metabolism of genetic origin. The cardiovascular functions of these mice have never been studied. In this study, the arterial blood pressure of MGH and MGL strains was measured by plethysmography. Morphology and reactivity to vasoconstrictor agents were also investigated by a pressurized and perfused system in mesenteric resistance artery. It is shown that: (1) MGH mice presented a higher plasma Mg concentration than MGL; (2) arterial blood pressure and heart rates were similar between the two groups; (3) media thickness, media cross-sectional area, and internal and external diameters were smaller in pressurized mesenteric resistance arteries from MGH mice than in those from MGL mice; (4) the vasoconstriction induced by vasopressin (but not norepinephrine) was higher in the mesenteric arteries from MGH mice than in those from MGL ones. In summary, MGH mice as compared to MGL mice present differences in arterial geometry and higher reactivity to vasopressin without repercussions on arterial blood pressure. The real repercussion of these observations on the cardiovascular system of the MGH and MGL models is at present unknown. More experiments are needed to clarify the influence of differences in Mg metabolism of genetic origin on cardiovascular function.

Effects of subchronic digestive exposure to organic or inorganic cadmium on biomarkers in rat tissues

In an experimental food chain, Wistar rats were fed cadmium (Cd) in an inorganic (CdCl(2)) or organic (mainly associated with metallothionein from Helix aspersa snail viscera) form. After 1 month of exposure to 100 microg inorganic Cd g(-1) in food, an induction of metallothionein was observed in all target tissues. In liver, glutathione peroxidase (GSH-Px) activity decreased and alanine aminotransferase (ALAT) activity increased, suggesting that Cd causes hepatotoxicity. However, lipid peroxidation as well as catalase and caspase 3 (a marker of apoptosis) activities were not modified. At a rather low exposure (2.5 microg Cd g(-1)), metallothionein level in the kidney was found to be the most sensitive biomarker of exposure for both Cd forms. In the small intestine of rats ingesting inorganic Cd, metallothionein expression was significantly higher than that observed for rats fed organic Cd. Present results allowed proposing a simple design to assess the effect of a chemical in a trophic transfer approach.

Effects of long-term dietary intake of magnesium on oxidative stress, apoptosis and ageing in rat liver

In the present study, we investigated the effect of long-term dietary Mg intake on the rate of oxidative stress, apoptosis and ageing in rat livers. To address this issue, rats were fed diets containing either a moderately deficient (0.15 g Mg/kg diet), a standard (0.8 g Mg/kg diet) or a high (3.2 g Mg/kg diet) Mg dose for two years. It is noteworthy that a higher percentage of animal mortality was observed in the lowest Mg diet, as compared to the other groups. Oxidative stress and antioxidant status were evaluated by measuring different enzyme activities, among which glutathione peroxidase activity was significantly reduced when Mg content was decreased in the diet. Moreover, we obtained an activation of caspase-3 and a higher lipid peroxidation in the Mg-deficient group, as compared to the Mg standard group, while no changes in Mg-supplemented group were observed, in accordance with our previously published data in primary cultures of rat hepatocytes (Martin et al., J Nutr 2003). Telomere shortening was measured in rat livers, as a marker of ageing. We found that telomere length was decreased in old animals, as compared to young animals confirming that telomere shortening correlated well with ageing events. Moreover, in old animals, we obtained a decrease of telomere length in the Mg-deficient group, as compared to the other groups. Taken together, our results show that a long-term chronic Mg deficiency led to oxidative stress, apoptosis and an acceleration of ageing in rat livers.

Comparison of transfer and effects of Cd on rats exposed in a short experimental snail-rat food chain or to CdCl2 dosed food

Transfer and toxic effects of two cadmium (Cd) forms, inorganic (CdCl2 dosed rat food) or organic (contaminated snail-based rat food) were studied in Wistar rat. Cd concentrations in rat food were 0 and 2.5 microg Cd g(-1) for both inorganic and organic forms and a high concentration of 100 microg Cd g(-1) was also tested for the inorganic form. Rats were exposed for four weeks to contaminated food. Both forms of Cd were bioavailable to rats, with a percentage of transfer from food to rats of around 1% for all contaminated groups. Cd concentrations in rat tissues increased with increasing Cd concentrations in the food. Rats fed with organic form of Cd accumulated significantly more Cd in the main organ for Cd toxicity, the kidney, than those eating the inorganic form. Survival was not affected for any rat group but a decrease in growth and food consumption was observed for the inorganic form. As a defence system against Cd toxicity, rats increased their metallothionein (MT) synthesis at the highest Cd concentration in the target organs (kidney, liver and small intestine) and even did the same at low Cd concentrations (2.5 microg Cd g(-1)) in the kidney. At this low Cd concentration, MT induction was lower in the small intestine of rats ingesting organic Cd than those ingesting inorganic Cd. Bioavailability of organic and inorganic forms of Cd was similar, but subsequent Cd distribution within organs was different. This quantification of the trophic transfer of both inorganic and organic forms of a toxicant is a basis for a better assessment of the fate and effects of chemicals in food webs.

Effects of aqueous hop (Humulus Lupulus L.) extract on vascular reactivity in rats: mechanisms and influence of gender and hormonal status

Phytoestrogens, naturally occurring plant compounds having oestrogenic and/or anti-oestrogenic activity, are present in many human foodstuffs including hop. Moderate intakes of isoflavonoid phytoestrogens have been associated with a reduction in cardiovascular diseases incidence. So, it is possible that hop (Humulus Lupulus L.) might similarly contribute to the reported health-beneficial effects of moderate beer consumption. Thus, the purpose of this study was to investigate in vitro effects of aqueous hop extract on thoracic vascular reactivity in Sprague Dawley male and female rats. Endothelium-intact thoracic arterial rings from male rats (MALE, n=8), sham-ovariectomized (Sham OVX) female (n=8) and ovariectomized (OVX) female rats (n=8) were used. We assessed the relaxation induced by aqueous hop extract (10(-9), 10(-2)g/l) in aortic rings precontracted with norepinephrine (10(-7)M), in the absence or in the presence of l-NAME (10(-4)M), indomethacin (10(-5)M), thapsigargin (10(-4)M), iberiotoxin (3.10(-8)M), apamin (3.10(-8)M) and TEA (3.10(-4)M). Aqueous hop extract induced relaxation of endothelium-intact thoracic arterial rings in MALE and Sham OVX rats, whereas a weak effect was observed in OVX rats. This vasorelaxation was strongly inhibited in presence of l-NAME, indomethacin and thapsigargin. These data indicated that aqueous hop extract-induced vasodilation, in male and intact female rats, is mediated by NOS activation, cyclooxygenase products and Ca(2+) pathways. Moreover, our results suggested that effect of hop in enhancing vascular reactivity was independent of gender but strongly related to hormonal status.

Effects of isometric strength training followed by no exercise and Humulus lupulus L-enriched diet on bone metabolism in old female rats

We investigated in female rats the effects on bone metabolism of a prolonged no-training period, subsequent to an isometric exercise program, performed during young adulthood and those of a long-term consumption of Humulus lupulus L-enriched diet (genistein 1.92 and daidzein 1.24 mg/kg diet) combined or not with isometric training. Forty-eight rats (4 weeks old) were randomly divided into 4 groups: trained (C-Tr) or nontrained rats (C-NTr) fed with control diet and trained (H-Tr) or nontrained rats (H-NTr) fed with Humulus lupulus L-enriched diet. The diets lasted 100 weeks. Training was followed over a 25-week period. Bone parameters were measured at week 100. Our results showed that no significant difference was observed among the 4 groups in uterine relative weight, calcium (Ca) intake, fecal Ca, urinary Ca excretion, net Ca absorption, plasma Ca, and bone Ca content. Calcium balance was significantly enhanced in H-NTr rats in comparison with C-NTr and C-Tr rats. Isometric strength training led to a significant increase in total bone mineral density (BMD), diaphyseal BMD, and osteocalcin-deoxypyridinoline ratio in C-Tr rats compared with the other groups. The main findings of the present study indicate that in female rats, a 25-week isometric strength training performed during young adulthood followed by a prolonged no-training period increases BMD values and osteocalcin-deoxypyridinoline ratio, whereas long-term consumption of Humulus lupulus L-enriched diet does not improve bone parameters. It suggests that bone gains induced by exercise do not decrease immediately after cessation of training and also confirms the importance of the practice of physical activity during puberty and young adulthood to maximize the achieved peak bone density.

Effects of long-term dietary intake of magnesium on rat liver transcriptome

In the present study we investigated the effect of a two-year treatment period with a diet containing 3.2g, 0.8 g and 0.15 g Mg/kg, on the rat liver transcriptome. At the end of the study, a treatment-dependent decrease in plasmatic Mg concentration was found (0.86 +/- 0.02 mmol/L, 0.70 +/- 0.02 mmol/L and 0.52 +/- 0.03 mmol/L for groups receiving 3.2g, 0.8 g and 0.15 g Mg/kg diet, respectively). No significant treatment-related effect on body and liver weights was observed, however a dietary Mg intake-dependent increase in mortality rate occurred in animals (11%, 25% and 38% death of animals). Mg content in the diet affected gene expression in rat livers, as assessed by rat specific DNA microarrays. We identified 11 genes up-regulated and 39 genes down-regulated by at least two-fold by a decrease in Mg content and grouped them within five functional pathways: metabolism 20%, cytoarchitecture (connective tissue/cell adhesion/cytoskeleton) 12%, channels/ transporters 20%, turn-over (nucleic acid and protein) 16%, and homeostasis (stress/DNA damage/apoptosis/ageing) 32%. The results of the present study confirm the pleiotropic effects of Mg and provide further evidence that a Mg decrease in the diet may be considered as a promoting factor for pathologies, especially in the liver, during ageing.

Immobilization of arginase and its application in an enzymatic chromatographic column: Thermodynamic studies of nor-NOHA/arginase binding and role of the reactive histidine residue

A biochromatographic approach is developed to measure for the first time changes in enthalpy, heat capacity change and protonation for the binding of nor-NOHA to arginase in a wide temperature range. For this, the arginase enzyme was immobilized on a chromatographic support. It was established that this novel arginase column was stable during an extended period of time. The affinity of nor-NOHA to arginase is high and changes slightly with the pH, because the number of protons linked to binding is low. The determination of the enthalpy change at different pH values suggested that the protonated group in the nor-NOHA-arginase complex exhibits a heat protonation of approximately -33 kJ/mol. This value agrees with the protonation of an imidazole group. Our result confirmed that active-site residue Hist 141 is protonated as imidazolium cation. Hist 141 can function as a general acid to protonate the leaving amino group of L-ornithine during catalysis. The thermodynamic data showed that nor-NOHA-arginase binding, for low temperature (<15 degrees C), is enthalpically unfavourable and being dominated by a positive entropy change. This result suggests that dehydration at the binding interface and charge-charge interactions contribute to the nor-NOHA-arginase complex formation. The temperature dependence of the free energy of binding is weak because of the enthalpy-entropy compensation caused by a large heat capacity change, DeltaC(p)=-2.43 kJ/mol/K, of arginase. Above 15 degrees C, the thermodynamic data DeltaH and DeltaS became negative due to van der Waals interactions and hydrogen bonding which are engaged at the complex interface confirming strong enzyme-inhibitor hydrogen bond networks. As well, by the use of these thermodynamic data and known correlations it was clearly demonstrated that the binding of nor-NOHA to arginase produces slight conformational changes in the vicinity of the active site. Our work indicated that our biochromatographic approach could soon become very attractive for studying other enzyme-ligand binding.

Effect of a methionine-supplemented diet on the blood pressure of Sprague–Dawley and deoxycorticosterone acetate–salt hypertensive rats

The objectives of the present study were to evaluate the effects of a methionine-supplemented diet on systolic blood pressure (BP) and vasomotor functions in Sprague–Dawley (SD) and deoxycorticosterone acetate (DOCA)–salt hypertensive rats. SD and DOCA rats were fed a normal or a methionine (8 g/kg)-supplemented diet for 10 weeks. Systolic BP was monitored and plasma homocysteine, methionine and cysteine levels were determined at the end of the experiment. Vasoconstriction and vasodilatation of aortic rings were measured. The methionine-supplemented diet induced a greater increase in homocysteinaemia concentration in DOCA rats than in SD rats and an increase in plasma cysteine concentration in DOCA rats. This diet was associated with an increase in systolic BP in SD rats and with a lesser development of DOCA–salt hypertension. An enhanced aortic constriction and a decreased responsiveness to acetylcholine, bradykinin and sodium nitroprusside in the SD rats fed the methionine-rich diet were consistent with the elevated systolic BP. In DOCA rats the increased responsiveness to bradykinin was in accordance with the systolic BP-lowering effect. In conclusion, the methionine-enriched diet cannot simply be considered as model of hyperhomocysteinaemia, since other metabolites and mechanisms seemed to be implicated in these complex interactions. The differential vasopressive effect of the methionine supplementation in SD and DOCA rats, and in particular the lowering of systolic BP obtained with a greater degree of hyperhomocysteinaemia in DOCA rats, suggest that more complex interactions exist between hyperhomocysteinaemia and BP than the simple positive association described previously.

Time course of vascular arginase expression and activity in spontaneously hypertensive rats

There is growing evidence that vascular arginase plays a role in pathophysiology of vascular diseases. We recently reported high arginase activity/expression in young adult hypertensive spontaneously hypertensive rats (SHR). The aim of the present study was to characterize the time course of arginase pathway abnormalities in SHR and to explore the contributing role of hemodynamics and inflammation. Experiments were conducted on 5, 10, 19 and 26-week-old SHR and their age-matched control Wistar Kyoto (WKY) rats. Arginase activity as well as expression of arginase I, arginase II, endothelial and inducible NOS were determined in aortic tissue extracts. Levels of L-arginine, NO catabolites and IL-6 (a marker of inflammation) were measured in plasma. Arginase activity/expression was also measured in 10-week-old SHR previously treated with hydralazine (20 mg/kg/day, per os, for 5 weeks). As compared to WKY, SHR exhibited high vascular arginase I and II expression from prehypertensive to established stages of hypertension. However, a mismatch between expression and activity was observed at the prehypertensive stage. Arginase expression was not related either to plasma IL-6 levels or to expression of NOS. Prevention of hypertension by hydralazine significantly blunted arginase upregulation and restored arginase activity. Importantly, arginase activity and blood pressure (BP) correlated in SHR. In conclusion, our results demonstrate that arginase upregulation precedes blood pressure rising and identify elevated blood pressure as a contributing factor of arginase dysregulation in genetic hypertension. They also demonstrated a close relationship between arginase activity and BP, thus making arginase a promising target for antihypertensive therapy.

Enantioselective aptameric molecular recognition material: Design of a novel chiral stationary phase for enantioseparation of a series of chiral herbicides by capillary electrochromatography

A chiral stationary phase derived from an L-RNA aptamer is evaluated for the enantiomer separation of a series of herbicide molecules (aryloxypropionic, aryloxyphenoxypropionic, and aminopropionic acid) by CEC after binding to biotin and grafting upon streptavidin-modified porous glass beads. We demonstrated that the aptamer capillary was stable in term of efficiency and retention during a long period. The influences of the mobile phase constitution and its flow-velocity on the enantioseparation were also investigated. The results suggest that the interactions of the enantiomer during CEC are solely based on chromatographic mechanisms and that the electrophoresis plays only a minor role. The separation efficiency and peak shape could be improved by Mg2+ divalent cation that stabilized the aptamer secondary structure and thus enhanced the mass transfer kinetics during the ligand-aptamer binding process. In addition, it was demonstrated that the determination of the enantiomerization barrier of flamprop was possible using this chiral stationary phase.

Beneficial effects of isometric strength training on endothelial dysfunction in rats

Using female 4-week-old Sprague–Dawley rats, we investigated the effects of 14 weeks of progressive strength isometric training on endothelium dysfunction after estrogen deficiency. We also proposed possible mechanism(s) by which such training acted on endothelium-dependent vasodilation in thoracic aortic rings. Rats were randomly divided into 4 groups of 8 rats: a sham operated group, an ovariectomized sedentary group receiving 17β-estradiol vehicle s.c. daily, an ovariectomized sedentary group receiving a daily injection of 20 µg·kg–1 17β-estradiol s.c., and an ovariectomized exercised group receiving daily s.c. vehicle. Vascular reactivity of aortic rings have been evaluated by a cumulative dose of acetylcholine (ACh), in the presence or absence of l-NAME (N-nitro-l-arginine methyl ester), indomethacin, thapsigargin, iberiotoxin, apamin, and tetraethylammonium. Ovariectomy markedly decreased the relaxation caused by ACh, whereas 17β-estradiol treatment induced a significant increase in the relaxation elicited by ACh. Isometric exercise enhanced relaxation due to ACh. This enhancement was attenuated in the presence of l-NAME, indomethacin, thapsigargin, iberiotoxin, and apamin. Our data indicated, for the first time, that the endothelium-dependent relaxant response to ACh was markedly improved in trained ovariectomized rats. This increased vasodilation is mediated by nitric oxide, cyclooxygenase, sarco-endoplasmic reticulum Ca2+-ATPase pathways, and endothelium-derived hyperpolarizing factor. Finally, this study suggested that resistance training may provide benefits in addressing vascular dysfunction consequent to a decline in estrogen levels after menopause. However, any benefits for age-related vascular dysfunction remain to be demonstrated.

N-Acetylcysteine Partially Reverses Oxidative Stress and Apoptosis Exacerbated by Mg-Deficiency Culturing Conditions in Primary Cultures of Rat and Human Hepatocytes

OBJECTIVE

The effects of magnesium (Mg) deficiency on the rate of oxidative stress and apoptosis in primary cultures of human hepatocytes were compared to cultured rat hepatocytes. The possible reversion by N-acetylcysteine (NAC) in Mg-deficient culturing conditions was evaluated.

METHODS

Incubations were conducted for up to 72 h in media containing a deficient (0-0.4 mM) or a physiological (0.8 mM) Mg concentration, and in the presence or absence of NAC after 24 h of culture in these Mg concentration conditions.

RESULTS

We obtained similar profiles in terms of apoptosis and oxidative stress in primary cultures of human hepatocytes, as compared to rat hepatocytes, i.e. a Mg concentration-dependent effect on the caspase-3 activity and GSH levels after 72 h of culture, caspase-3 activity being highest and GSH levels being lowest in Mg-free cultures. The addition of NAC to culture media after the first 24 h of culture increased GSH concentrations. This was accompanied in Mg-deficient cultures by a decrease in both the caspase-3 activity and the lipid peroxidation. However, when culturing hepatocytes with physiological Mg concentrations, an increase in both caspase-3 activity and lipid peroxidation was observed.

CONCLUSIONS

Our results indicate that Mg deficiency exacerbates the rate of apoptosis in cultured hepatocytes, associated with an increase in oxidative stress, the sensitivity of human hepatocytes being equivalent to that of rat hepatocytes. They also indicate a dual role of NAC and/or GSH, i.e. protective for hepatocytes placed in a Mg-deficient environment, while deleterious for hepatocytes placed in a Mg-physiological environment.

Long-term moderate magnesium-deficient diet shows relationships between blood pressure, inflammation and oxidant stress defense in aging rats

Epidemiological and experimental studies have indicated a relationship among aging, dietary Mg, inflammatory stress, and cardiovascular disease. Our aim in the present study was to investigate possible links between dietary Mg, oxidant stress parameters, and inflammatory status with aging in rats. We designed a long-term study in which rats were fed for 22 months with moderately deficient (150 mg/kg), standard (800 mg/kg), or supplemented (3200 mg/kg) Mg diets. Comparisons were made with young rats fed with the same diets for 1 month. Compared to the standard and supplemented diets, the Mg-deficient diet significantly increased blood pressure, plasma interleukin-6, fibrinogen, and erythrocyte lysophosphatidylcholine, particularly in aging rats, it decreased plasma albumin. The impairment of redox status was indicated by increases in plasma thiobarbituric acid reactive substances and oxysterols and an increased blood susceptibility to in vitro free-radical-induced hemolysis. We concluded that Mg deficiency induced a chronic impairment of redox status associated with inflammation which could significantly contribute to increased oxidized lipids and promote hypertension and vascular disorders with aging. Extrapolating to the human situation and given that Mg deficiency has been reported to be surprisingly common, particularly in the elderly, Mg supplementation might be useful as an adjuvant therapy in preventing cardiovascular disease.

New insights into the vascular mechanisms underlying the beneficial effect of swimming training on the endothelial vasodilator function in apolipoprotein E-deficient mice

The antiatherogenic role of exercise is poorly understood. We examined the swimming exercise-induced vascular mechanisms which enhance the endothelial vasodilator function in apoE(-/-) mice. Male apoE(-/-) mice treated for 9 weeks with a lipid-rich diet were divided into two groups: the exercise group (apoE(-/-) X), which underwent a 9-week swimming protocol (50 min/day; 5days/week) and the sedentary group (apoE(-/-) S). C57BL/6 mice were used as the control group. Atherosclerotic lesions in the aortic roots were significantly reduced in apoE(-/-) X compared to apoE(-/-) S. Relaxation to acetylcholine was improved in apoE(-/-) X as compared to apoE(-/-) S and control mice with E(max) and pD(2) values significantly higher. pD(2) values in response to papaverine were higher in apoE(-/-) X than in the other groups. Relaxation in response to A23187 and DEA-NONOate were similar. These findings suggest that swimming training may increase the sensitivity of relaxation to acetylcholine, which in turn activates acetylcholine-mediated signaling pathways leading to increased NO bioactivity. Swimming may also prolong the signaling actions of NO by stimulating the sensitivity of vascular smooth muscle cells to cyclic nucleotides. These appear to be the key mechanisms underlying the improvement of the NO-cGMP pathway in exercised apoE(-/-) mice.

A Stepwise Stoichiometric Representation To Confirm the Dependence of Pesticide/Humic Acid Interactions on Salt Concentration and To Test the Performance of a Silica Bonded Humic Acid Column

In a previous paper (André et al., in press), a novel chromatographic column was developed in our laboratory for studying the binding of pesticides with humic acid (HA), the main organic component in soil. It was demonstrated that this column supported a low fraction of organic modifier in the aqueous mobile phase (<0.25 (v/v)). To overcome this limitation for a practical use, a column in which the stationary phase was based on silica gel with chemically bonded humic acid was created. It was shown that this novel HA column supported a higher methanol fraction (<0.55 (v/v)). As well, the dependence of pesticide/humic acid interactions on salt (sodium chloride) concentration has been expressed in terms of a stepwise stoichiometric representation, which leads to a specific equation for the partition of the added salt between the pesticide molecule, the HA, and the pesticide/HA complex. Based on this novel equation, the dependence of the pesticide/humic acid association on the salt concentration can be formulated via a relation similar to the one of Tanford. In addition, for the first time, the calculation of the affinity energy distribution for different values of the salt concentration in the mobile phase confirmed the existence of several types of binding sites on the HA macromolecule.

Combined intervention of dietary soybean proteins and swim training: effects on bone metabolism in ovariectomized rats

Soybean proteins, a rich source of isoflavones, taken immediately after an ovariectomy prevent bone loss in rats. Exercise-induced stimuli are essential for bone growth. Few studies exist about the combined effects of swim training and soybean protein supplementation on bone metabolism. So, the purpose of this study was to investigate, in 48 female Sprague-Dawley rats (12 weeks old) the effects of an 8-week swim-training regimen (1 h/day, 5 days/week) and dietary soybean proteins (200 g/kg diet) on bone metabolism. Rats were randomly assigned to four groups: (1) ovariectomized fed with a semisynthetic control diet; (2) ovariectomized fed with a soybean protein-enriched semisynthetic diet; (3) ovariectomized trained to exercise and fed with control diet; (4) ovariectomized trained to exercise and fed with a soybean protein diet. Following the treatment period, body weight gain was identical in the four groups. Soybean protein supplementation increased bone calcium content, and reduced plasma osteocalcin values, without significant modification of calcium balance and net calcium absorption. Swim training enhanced plasma and bone calcium content and calcium balance and net calcium absorption. It did not modify either plasma osteocalcin values or urinary deoxypyridinoline excretion. Both exercise and soybean protein intake increased plasma on bone calcium without modifying net calcium absorption or bone markers. In conclusion, we demonstrated, in ovariectomized rats, that swimming exercise and dietary supplementation with soy proteins do not have synergistic effects on calcium metabolism and bone markers.