The role of biofactors in the prevention and treatment of age-related diseases

The present demographic changes toward an aging society caused a rise in the number of senior citizens and the incidence and burden of age-related diseases (such as cardiovascular diseases [CVD], cancer, nonalcoholic fatty liver disease [NAFLD], diabetes mellitus, and dementia), of which nearly half is attributable to the population ≥60 years of age. Deficiencies in individual nutrients have been associated with increased risks for age-related diseases and high intakes and/or blood concentrations with risk reduction. Nutrition in general and the dietary intake of essential and nonessential biofactors is a major determinant of human health, the risk to develop age-related diseases, and ultimately of mortality in the older population. These biofactors can be a cost-effective strategy to prevent or, in some cases, even treat age-related diseases. Examples reviewed herein include omega-3 fatty acids and dietary fiber for the prevention of CVD, α-tocopherol (vitamin E) for the treatment of biopsy-proven nonalcoholic steatohepatitis, vitamin D for the prevention of neurodegenerative diseases, thiamine and α-lipoic acid for the treatment of diabetic neuropathy, and the role of folate in cancer epigenetics. This list of potentially helpful biofactors in the prevention and treatment of age-related diseases, however, is not exhaustive and many more examples exist. Furthermore, since there is currently no generally accepted definition of the term biofactors, we here propose a definition that, when adopted by scientists, will enable a harmonization and consistent use of the term in the scientific literature.

[Magnesium: Relevance for general practitioners - a position paper of the Society for Magnesium Research e. V.]

Magnesium deficiency is to be expected in the population and particularly among risk groups. Magnesium deficiency can cause numerous symptoms, is per se pathological and thus requires treatment. Diagnostics is based on clinical symptoms in conjunction with anamnestic criteria and laboratory parameters. Insufficient magnesium supply is associated with an increased risk for many diseases, e. g. metabolic syndrome, type 2 diabetes and cardiovascular diseases. Magnesium deficiency often appears as comorbidity and may exacerbate diseases. Physicians should pay more attention to magnesium in order to avoid deficits as a cause for multiple symptoms and risk factor for diseases. Optimisation of magnesium status may make an important contribution to the prevention of diseases. Oral magnesium therapy is safe and cost effective.

Platelet Aggregation Evoked In Vitro and In Vivo by Phosphatidic Acids and Lysoderivatives: Identity with Substances in Aged Serum (DAS)

In serum incubated at 36° C for 18-24 hours a factor (DAS) develops which on intravenous injection into cats evokes platelet aggregation followed by an increase in pulmonary vascular resistance (PVR). This change in PVR is mediated via the platelets since it significantly correlates with the preinjection platelet count. There is evidence that phosphatidic acids (PA) and lysophosphatidic acids (LPA) are the active components of DAS. Investigations performed on platelet-rich plasma from man, cat, pig, dog, rabbit, guinea pig, and rat demonstrate that only human and feline platelets exposed to PA or to LPA are aggregated. Feline platelets are more sensitive to either compound than are the platelets from men; however, human platelets exhibit two exceptional properties, a) the sensitivity rapidly declines with time, b) pretreatment with subthreshold concentrations of LPA or PA induces a specific tachyphylaxis.

[Zinc deficiency. Symptoms, causes, diagnosis and therapy]

Zinc is an essential trace element being required for numerous metabolic processes. The diagnosis of zinc deficiency is based on four main criteria, namely anamnesis, symptomatology, belonging to well-defined risk groups and the determination of biomarkers. The diagnosis of overt zinc deficiency is unproblematic in contrast to moderate states. The review presented here shall help to detect the latter ones. The pharmacotherapy of of zinc deficiency consists in oral administration of zinc salts.

Magnesium orotate--experimental and clinical evidence

Magnesium orotate dihydrate (MO) has the sum formula C10H6MgN4O8 x 2H2O and a MG of 370.52. The salt is poorly soluble in water and hence does not bind gastric acid nor does it exhibit noteworthy laxative effects upon oral administration in contrast to easily dissociable Mg salts. As a source of magnesium (Mg), MO is indicated for the oral treatment of extracellular Mg deficiency. Orotic acid (OA), the second active ingredient of MO, is a key intermediate in the biosynthetic pathway of pyrimidines and is shown to improve the energy status of injured myocardium by stimulating, a.o., the synthesis of glycogen and ATP. Myocardial energy-rich phosphate levels are decreased during hypoxic conditions; subsequently, intracellular Mg is depleted and lost via the urine. Since binding sites for Mg (ATP) are provided by OA it can be classified as "Mg-fixing agent". Accordingly MO is also indicated for the treatment of Mg depletion as convincingly shown in animal experiments and also in coronary heart patients undergoing e.g. aortocoronary bypass surgery.

Hohenheim consensus workshop: copper

Copper (Cu) is an essential trace element with many physiological functions. Homeostatic mechanisms exist to allow Cu to act as a cofactor in enzymatic processes and to prevent accumulation of Cu to toxic levels. The aim of this commentary is to better understand the role of dietary Cu supply in deficiency and under physiological and pathological conditions. The essentiality of Cu can be attributed to its role as a cofactor in a number of enzymes that are involved in the defence against oxidative stress. Cu, however, has a second face, that of a toxic compound as it is observed with accumulating evidence in hepatic, neurodegenerative and cardiovascular diseases. The destructive potential of Cu can be attributed to inherent physico-chemical properties. The main property is its ability to take part in Fenton-like reactions in which the highly reactive and extremely deleterious hydroxyl radical is formed. Diseases caused by dietary Cu overload could be based on a genetic predisposition. Thus, an assessment of risk-groups, such as infants with impaired mechanisms of Cu homeostasis regarding detoxification, is of special interest, as their Cu intake with resuspended formula milk may be very high. This implies the need for reliable diagnostic markers to determine the Cu status. These topics were introduced at the workshop by the participants followed by extensive group discussion. The consensus statements were agreed on by all members. One of the conclusions is that a re-assessment of published data is necessary and future research is required.

Magnesium deficiency-induced anorexia in hyperphagic obese Zucker rats

In clinical practice diabetes mellitus is the most significant cause of hypomagnesemia and Mg depletion. The obese Zucker rat approaches non-insulin-dependent type II diabetes; lean Zucker rats being suitable controls. Using this disease model the influence of dietary Mg deficiency was studied: animals received a diet providing only approximately 25 per cent of the Mg requirement; controls received drinking water fortified with Mg (16 mmol/L). During 125 days ad libitum feeding, Mg-deficient obese rats consumed nearly 50 per cent less feed pellets and gained 50 per cent less body weight than their obese counterparts. This effect was not fully reversible indicating Mg depletion. Blood glucose reflected food consumption, no glucosuria was detectable using test strips. In the heart muscle Mg was decreased and Ca increased in Mg-deficient rats indicating increased cardiac risk. When the rats were pair fed with lean Mg-deficient controls the development of obesity was prevented. Despite pronounced Mg deficiency blood glucose remained unaffected and no glucosuria was detectable. In future experiments the production of marginal Mg deficiency not inducing anorexia should be applied to study the pathogenetic role of Mg depletion in obese Zucker rats.

Organochlorine pesticide residues in human milk of a Hmong hill tribe living in Northern Thailand

In December 1998 whole breast milk samples from 25 Hmong mothers living in the village of Mae Sa Mai, 40 km north of Chiang Mai City, Northern Thailand, were collected and analysed for DDT, heptachlor, HCB and HCH residues (fat normalized data). Short questionnaires and anthropometric measurements were used to obtain information on personal characteristics, lifestyle, contact with pesticides, dietary habits and former residences. DDT was detected in all samples with a median and maximum level of 209 and 2012 ng of total DDT isomers per millilitre of milk, respectively. The median and highest percentages of p,p'-DDT were 23.2 and 44.7%. In 15 samples heptachlor was detected in the metabolized form of heptachlor-epoxide with a median value of 4.4 ng/ml. The estimated daily intakes of DDT, heptachlor and heptachlor-epoxide by the infants exceeded up to 20 times the acceptable daily intakes as recommended by the FAO and WHO. In nine samples HCB was detected with a median value of 5.4 ng/ml from which seven of the nine also had the highest values of DDT residues. The gamma-isomer of HCH was only found in one sample with 3.6 ng/ml. The mean sum-DDT residues with 14.96 mg/kg milk fat, as well as the estimated daily intakes by the infants are one of the highest reported in the 1990s. The fact that the mother breast-feeds her first child and that she originally comes from a region where DDT is still in use as a vector control agent, as well as the former use of organochlorine pesticides (OCPs) in agriculture, seem to be the main factors for high DDT and other OCP residues in the mothers' milk.

[Diagnosing magnesium deficiency. Current recommendations of the Society for Magnesium Research]

The cardiovascular risk increases with decreasing serum levels of magnesium, and this already at concentrations within the previous reference range (0.70-1.10 mmol/L). For this reason, the Society for Magnesium Research has updated its 1986 recommendations for the diagnosis of magnesium deficiency. The diagnosis is based on the patient's history, his clinical symptoms, and the results of clinical-chemical investigations of plasma/serum and urine. Further diagnostic methods used include the determination of ionized serum magnesium and the magnesium retention test. The optimal serum magnesium concentration is > 0.80 mmol/L.

The impact of diets with different magnesium contents on magnesium and calcium in serum and tissues of the rat

The impact of three different magnesium diets (70, 1,000 and 9,000 ppm) on total, ionized and bound magnesium as well as ionized calcium in serum and total calcium and magnesium in femoral bone, skeletal muscle, heart and liver of male Sprague-Dawley rats was investigated. The percentage of ionized serum magnesium was unproportionally high in rats fed a low magnesium (70 ppm) diet. Femoral magnesium was correlated with ionized and total serum magnesium. In contrast, there was generally no correlation between total serum magnesium and the magnesium fractions in skeletal muscle, heart and liver. In rats fed the magnesium deficient diet, total cardiac concentration of magnesium was even significantly increased along with total calcium content, while there were no effects on total muscle and liver magnesium. Within the single groups, ionized serum calcium was never proportional to dietary magnesium, but in all three magnesium diet groups together, it was inversely correlated with dietary magnesium. Moreover, ionized serum calcium was inversely correlated with both ionized and total serum magnesium. In all 3 groups together, the concentrations of total calcium and magnesium in heart and skeletal muscle were correlated, within the single groups correlation existed only in the 1000 ppm group. Magnesium influx via calcium channels during low magnesium intake has been seen in non cardiac tissues [35,36], but nothing similar is known about non selective channels for divalent cations in the heart [33]. Thus, magnesium uptake by cardiac cells along with calcium seems to be possible, especially at low intracellular magnesium concentrations, but is still poorly investigated. We suggest that the calcium-antagonistic effect of magnesium is related to the turnover rate of magnesium rather than to its tissue concentrations.

Prevalence of magnesium and zinc deficiencies in nursing home residents in Germany

In a multicentric study with 345 seniors over 70 years old we investigated magnesium and zinc levels in serum together with the prevalence of their typical symptoms of deficiency in nursing home residents (NHR) and non-nursing home residents (nNHR). In addition calcium, sodium and potassium levels in serum were determined as well as creatinine and albumin. Considering all seniors 33 per cent exhibited hypomagnesemia and 19 per cent hypozincemia. Zinc levels of female and male NHR were significantly lower than levels of nNHR. Hypomagnesemia was significantly associated with calf cramps and with diabetes mellitus. Hypozincemia was significantly associated with impaired wound healing.

Persistent antihypertensive effect of oral nitrite supplied up to one year via the drinking water in spontaneously hypertensive rats

The hypothesis was studied whether the chronic administration of nitrite lowers the blood pressure of spontaneously hypertensive rats (SHR) and prevents secondary hypertension-induced organ lesions. For this purpose totally 96 SHR received 50 to 75 mmol/l NaNO2 or equimolar amounts of NaHCO3 in their drinking water during 4, 8 or 12 months. At each point of time arterial blood pressure, determined with the tail cuff method, was significantly lower in the NaNO2-group in comparison to the controls indicating that no significant tolerance towards nitrite had developed. There was also a tendency towards reduced cardiac hypertrophy and renal atrophy in the NaNO2-group, however without reaching the level of significance. Drinking water containing 75 mmol NaNO2/l was not well tolerated by young rats in contrast to 50 mmol/l. Possible beneficial effects of high dietary nitrate/nitrite levels are discussed with respect to the low frequency of hypertension observed in vegetarians.

The role of magnesium in the generation and therapy of benign muscle cramps. Combined in-vivo/in-vitro studies on rat phrenic nerve-diaphragm preparations

Rats received during 3 weeks a Mg-deficient or a Mg-rich diet; Mg-deficient animals revealed hypomagnesemia, cellular K-depletion and Ca-loading. Phrenic nerve-diaphragm preparations were studied; the physiological Tyrode solution contained low or high-Mg concentrations and 0 or 12 mmol lactate/L. Electric stimulation (indirect via the nerve or direct) produced tetanic contractions and increased force at increasing stimulation frequencies. Significantly lower frequencies were needed to elicit these effects when intra- and extracellular Mg levels were low, in comparison to plentiful Mg supply. Comparing unstimulated and stimulated diaphragmatic tissue electrolyte concentrations revealed tissue losses of Mg, K Ca from stimulated tissues which were less pronounced when Mg supply was optimal. These data support the empiric finding that relief from muscle cramps is promptly offered by Mg supplements.

Bioavailability of oral vitamins, minerals, and trace elements in perspective

Bioavailability of orally administered vitamins, minerals, and trace elements is subject to a complex set of influences. Still, administrative regulation is necessary on how to quantify it. The most common approach to this problem is to determine the fraction of an oral dose that reaches the systemic circulation. For micronutrients, however, this approach has to consider the physiological plasma concentration as well as the mechanisms that regulate intestinal absorption and distribution of micronutrients between functional and storage compartments in response to the demand. The rate of exchange between these compartments has an impact on the delivery of such compounds into the plasma compartment as well as on the plasma clearance. Monitoring the area under the plasma concentration time curve after oral administration is an inadequate tool for bioavailability determination if there are substantial impacts of homeostatic mechanisms on the plasma concentration of a micronutrient. In nutritional science the term "bioavailability" encompasses the sum of impacts that may reduce or foster the metabolic utilisation of a nutrient. Bioavailability in this sense can be quantified by the rate by which deficiency symptoms are cured or by the weight gain during growth. both of these endpoints, again, are influenced by homeostatic mechanisms. To exemplify the scope of impacts on parameters that are commonly used to quantify the bioavailability of oral micronutrient preparations the basic traits of homeostatic regulation are summarised and compared for iron, magnesium, vitamin A, folic acid, and vitamin B12. The mechanisms that adapt absorption, distribution, and excretion of these five micronutrients to the demand differ to such an extent that no common approach can be derived to consider these impacts in bioavailability determination. In consequence, therefore, we recommend to define and regulate individual strategies for bioavailability testing for each micronutrient with regulated kinetics.

Evaluation of D-amino acid levels in rat by gas chromatography-selected ion monitoring mass spectrometry: no evidence for subacute toxicity of orally fed D-proline and D-aspartic acid

Sprague-Dawley rats received deionized water (controls) during 28 days or drinking water with added D-proline, L-proline, D-aspartic acid or L-aspartic acid corresponding to a mean daily load of approximately 50 mg amino acid enantiomer kg-1 body weight. Parameters indicating the physiological status (food intake and body weight, glutamic-oxalic-transaminase, glutamic-pyruvic-transaminase, alkaline phosphatase, urea and creatinine in serum, and creatine and osmomolality of urine) were determined. After 28 days the weights of the supposed target organs of toxicity (kidney, liver, brain, thymus) were determined and organs were inspected for macroscopic and microscopic alterations. No pathological changes in the organs were observed and no signs of subacute toxicity (liver, kidney) were found. In serum, homogenates of liver, kidney and brain, and in part, in urine, the amounts of D-amino acids (D-AAs) were quantitatively determined using chiral phase capillary gas chromatography-selected ion monitoring mass spectrometry. Significant levels of certain D-AAs (Ala, Pro, Ser, Asx, Glx, Orn and Lys) were already detectable in kidney and liver homogenates and serum of controls. In brain homogenates the highest amounts among the D-AAs were found for D-Ser (up to 382 nmol g-1), moderate amounts for D-Ala, D-Asx and D-Glx, and, in a few cases, trace amounts for D-Orn and D-Lys (1-2 nmol g-1). D-Pro was not detected either in the brains of controls or in the brains of animals loaded with D-Pro. Feeding with D-Pro resulted in a 20-30 fold increased renal excretion of D-Pro at the end of the experiment. Continuous feeding with D-Asp did not increase renal excretion of this enantiomer, but in the serum, higher amounts (0.8-4.0 mumol-1) were determined in comparison to the control group (0.3-0.9 mumol-1). Feeding with D-Pro led to an increase of this enantiomer in serum (1.3-10.5 mumol-1). Feeding with D-Asp did not increase its amounts in brain homogenates (38 and 43 nmol g-1) in comparison to controls.

The safety assessment of novel foods. Guidelines prepared by ILSI Europe Novel Food Task Force

The diversity of novel foods and novel ingredients covered by the scope of the EU regulation is such that a check list approach to safety evaluation is inappropriate. Rather, a case-by-case approach is required taking into account the composition of the novel food, its intake, its role in the diet and the intended target group. The SAFEST approach provides a means of targeting the safety evaluation on those aspects, nutritional or toxicological, of a novel food which are of particular concern. Using this approach, novel foods are assigned to one of three classes on the basis of certain background information. For those novel foods which can be shown to be in SAFEST class 1, namely those which are substantially equivalent to a traditional counterpart, no further information is required to demonstrate their safety. For those novel foods in SAFEST class 2, i.e. those sufficiently similar to a traditional counterpart or differing from it only in particular, well defined, characteristics, the evaluation will focus on those differences. Only in the case of novel foods which are not in class 1 or class 2 is extensive testing of the whole food likely to be required. Even in these cases, the testing should follow a scientifically-based hierarchical approach involving: literature reviews; chemical analysis; appropriate in vitro and in vivo tests; and, if necessary, confirmation of safety and nutritional value in humans. Examination of the causes of any adverse effects reported by consumers after the novel food or ingredient has been approved and is introduced into the market may provide additional reassurance of safety.

Therapeutic availability of iron administered orally as the ferrous gluconate together with magnesium-L-aspartate hydrochloride

Since in vitro experiments had excluded interactions between Fe-gluconate (Fe-gluc) and magnesium-L-aspartate hydrochloride (MAH) in aqueous solutions the present in vivo studies seemed to be justified. Animal studies: Rats were kept on magnesium-(Mg)- and iron-(Fe)- sufficient and deficient diets. The intragastral administration of Fe-gluc significantly increased plasma Fe after 3 h, either given alone, or in combination with MAH (inducing hypermagnesemia). Same results were obtained when fortified diets were offered to Fe/Mg-deficient animals. Human studies: The combination of Fe-gluc (2 x 50 mg Fe per day, per os) plus MAH (2 x 7.5 mmol Mg per day, p.o.) was well tolerated by healthy volunteers. Single dose experiments revealed that Fe-gluc alone and in combination with MAH increased plasma Fe levels during 3 h to the same extent. Two groups of pregnant women with moderately reduced hemoglobin levels either received Fe-gluc (out-patients) or its combination with MAH (at least temporarily hospitalised because of preterm labor). Treatments were well tolerated. Hemoglobin levels did not further decrease, as expected without Fe supplements, during the course of pregnancy, thus indicating the therapeutic availability of the electrolytes in both study groups. Progesterone-induced constipation is frequently observed during pregnancy; hence stool softening reported by 50% of the women receiving Fe-gluc plus MAH (versus 33% in the Fe-gluc group) can be regarded as desirable effect. It is concluded that MAH does not interfere with the enteral absorption of Fe-gluc when both electrolytes are orally administered together. Taking both electrolytes together instead of 2 to 3 h apart from each other, as actually recommended, means a less complicated dosage regimen and probably improves compliance.

Renin immunochemistry, sodium excretion and relative heart weight in cyclosporine- or alimentary-induced magnesium deficiency in rats

Rats were given a magnesium-(Mg) depleted (Mgd), or a Mg-standard (Mgst) or a Mg-enriched (Mge) diet, with 20 mg/kg/day cyclosporine (Cy) or olive oil per os for 90 days (6 groups). Anti-renin antibody was applied and the percent of renin-positive glomeruli (RI) was taken. Sodium excretion (NaU), relative heart weight (HW), as a measure of hypertension, and total femur Mg were measured. Compared to dietary controls, femur Mg was reduced under Cy and Mgd or Mgst indicating Mg deficiency. RI was higher in all Cy groups (p < 0.01), and Nau was lower in Mgd + Cy and in Mgst + Cy (p < 0.01). Correspondingly, HW was found to be significantly higher in Mgd + Cy and Mgst + Cy. In animals under Mge + Cy, there were no differences in NaU and HW compared to controls. The results indicate a relation between Cy-related hypertension and Mg status: Mg deficiency seems to enhance the hypertensive effect of Cy via sodium retention.

Magnesium metabolism: basic aspects and implications of ciclosporine toxicity in rats

In rapidly growing male Sprague-Dawley rats with an initial body weight of 100 +/- 10 g, we investigated how alimentary magnesium (Mg) supply, Mg metabolism and ciclosporine (Ci)-associated nephrotoxicity are interrelated. Food with 100 ppm Mg (1Mg) or 1,000 ppm Mg (stMg) or 10,000 ppm Mg (rMg), Ci 20 mg/kg body weight daily or olive oil were applied for 3 months (n = 10/group). Mg concentrations in various compartments were measured by atomic absorption spectrophotometry. Creatinine clearance (Jaffe), urinary N-acetyl-beta-D-glucosaminidase (NAG) activity (fluorometrically), urinary sodium excretion (flame photometry) and osmolality were measured. Histomorphological examination was done and renal renin expression was studied by monoclonal antibodies. Ci reduced the Mg concentration of the femur under 1Mg (72.6 +/- 9.7 vs. 112.6 +/- 14.3 mmol/kg dry substance, p < 0.05) and under stMg (150.6 +/- 16.6 vs. 194.1 +/- 10.2 mmol/kg dry substance, p < 0.05), thus indicating Ci-related Mg deficiency. This was due to a significant increase in Mg excretion in Ci treatment compared to dietary controls. Under rMg, there was no difference between Ci-treated and control animals. Ci treatment lowered creatinine clearance in 1Mg (1.42 +/- 0.05 vs. 3.02 +/- 0.58 ml/min) and in stMg (1.04 +/- 0.45 vs. 2.18 +/- 0.51 ml/min), NAG/creatinine and urinary sodium excretion were negatively affected by Ci under 1Mg and stMg. Histomorphology showed macrocalcifications due to Mg deficiency and Ci-specific findings, which were markedly enhanced in 1Mg and stMg. Animals with plentiful Mg supply had no functional alterations due to Ci and no or weakly expressed histomorphological lesions. Renin-positive stained cells were higher in Ci-treated animals. This seems to be functionally relevant under 1Mg and stMg, since it was associated with sodium retention and elevated relative heart weight, indicating hypertension. Alimentary or drug-induced Mg deficiency plays a relevant role in the pathophysiology of chronic Ci nephrotoxicity. Our data suggest that Mg supplementation is helpful to reduce Ci toxicity, even if there is 'normal' alimentary Mg intake.

Different effects of three high-dose oral calcium salts on acid-base metabolism, plasma electrolytes and urine parameters of rats

The oral calcium (Ca) load test has been applied to estimate the enteral absorbability of Ca salts in humans; provided that the deep bone compartments are filled up, excess Ca should be excreted in the urine. Using this "overflow model" three Ca salts were tested in rats at increasing oral doses of 0 to 14 mmol/kg body weight: CaCO3 and two other compounds containing chloride at a Ca:Cl ratio of 1:2 (CaCl2) and 1:1 (Ca-aspartate-hydrochloride). The carbonate was poorly absorbed and hence did not significantly affect acid-base metabolism nor urine pH. Both chloride-containing salts increased Ca excretion to a significantly higher degree in a dose-dependent manner; in contrast to the organic compound, the CaCl2 induced metabolic acidosis at 14 mmol/kg body weight. At decreasing base excess and urinary pH, renal excretion of Ca and of magnesium (Mg) increased, indicating that acid-base alterations must be considered when evaluating the oral load test. All Ca salts induced moderate hypomagnesemia pointing to decreased enteral absorbability of food-borne Mg in rats. Studies on volunteers reported in the literature suggest, however, that this effect is not relevant for humans.

Antihypertensive effect of oral nitrite uptake in the spontaneously hypertensive rat

The lower blood pressure of vegetarians might partly be due to the high dietary load with nitrate which--to a certain extent--is further reduced to nitrite and finally to nitric oxide. To test this hypothesis, spontaneously hypertensive rats received drinking water containing 0, 25, 50 or 100 mmol/l NO2 during 56 days. Food was offered ad libitum or was restricted by 20% (pair-feeding) to simulate the lower energy consumption of vegetarians. Blood pressure, which was monitored at regular intervals, was lowered in a dose-dependent manner by nitrite. This effect was reversible and could not be enhanced by energy restriction. In volunteers plasma nitrate levels increased by a factor of 8 to 32 following the ingestion of a nitrate-rich meal, and mean methemoglobin concentrations increased from 1.2% to 2.4% indicating the endogenous formation of nitrite under these conditions.

Influence of high and low dietary magnesium levels on functional, chemical and morphological parameters of 'old' rats

The effect of dietary magnesium deficiency has so far been studied preferentially in rapidly growing rodents or in adult animals. Since magnesium deficiency frequently occurs in elderly persons too, magnesium- and calcium-deficient diets were offered during 32 and 64 days to 'old' rats (34 months old, spontaneous mortality of 15 per cent). The calcium-deficient diet (2.5 per cent of the requirement) was well tolerated and no profound biochemical disturbances were noted. In contrast, dietary magnesium deficiency (12.5 per cent of the requirement) induced loss of body weight, formation of erythema, severe hypomagnesaemia and increase of tissue calcium levels. No seizures were noted and mortality did not increase, in contrast to growing magnesium-deficient rats. Histologically, age effects were present in bone tissues of old rats, however no additional dietary effects became visible. Tensile strength of femur and rib did not reveal treatment-related changes. Fourteen days preloading with high dietary magnesium increased plasma magnesium and also skeletal concentrations, although to an only small degree. Nevertheless, time until the appearance of erythema in 50 per cent of the rats subsequently fed the magnesium-deficient diet was significantly delayed.

Potentiation of magnesium-deficiency-induced foetotoxicity by concomitant iron deficiency and its prevention by adequate supply via drinking water

Magnesium (Mg) and iron (Fe) deficiency frequently develop during pregnancy. Therefore these factors were studied alone (Mg-L, resp. Fe-L) or in combination (Mg-L/Fe-L) on 16 female and 8 male adult fertile Sprague-Dawley rats. The animals were offered a basal diet containing 30 per cent and 17 per cent of the rat's requirement for magnesium and iron, respectively, starting 21 days before mating (2:1) until 49 days after mating. Offspring were also kept on this regimen during a 3-week lactation period and 7 days post weaning. Drinking water was either enriched with 101 ppm Fe2+ (ferrous gluconate): Mg-L, or 365 ppm magnesium (magnesium-L-aspartate hydrochloride trihydrate, MAH): Fe-L, or with any: Mg-L/Fe-L or with both electrolytes: Controls. Fertility remained unaffected under these conditions. Clinically, Fe-L induced iron deficiency and growth retardation of offspring. Pronounced reproductive toxicity was elicited by Mg-L and was even potentiated by Mg-L/Fe-L. In the parental generation, too, adverse effects of Mg-L were aggravated by Mg-L/Fe-L despite the fact that no iron accumulation occurred. Bioavailability of iron was not impaired by magnesium as MAH. With respect to human pregnancy magnesium supplementation has higher priority over iron supplements. To improve tolerance and compliance both minerals are suggested to be taken simultaneously.

Increase of streptozocin toxicity by magnesium deficiency in the diabetic rat model

To study interactions between magnesium (Mg) and diabetes mellitus, female SD-rats weighing ca. 230 g were rendered Mg-deficient by offering a diet providing only 20% of the rat's requirement. After 14 days the animals were injected 75 mg streptozocin (STZ) per kg body weight intraperitoneally. Placebo-treated controls received the same diet, however their drinking-water was enriched with 20 mmol/l Mg as the magnesium-L-aspartate hydrochloride. Mg deficiency remarkably increased STZ-induced lethality from 3.8% to 61.1% on day 35. Pronounced hyperglycemia and necrosis of pancreatic beta cells also suggest an increased effect of STZ on the pancreas during Mg deficiency. The underlying mechanisms are discussed. Food consumption was decreased in Mg-deficient animals and steeply increased 7 days following STZ treatment. Similarly consumption of drinking-water also increased. Since diabetic rats lost body weight, relative and absolute Mg intake via food or drinking-water increased. In this way further Mg depletion of diabetic rats was prevented.

Interactions between magnesium and iron. In vitro studies

In vitro experiments were performed to study the effects of magnesium (Mg) on the absorption of iron (Fe), which have been reported in the literature. Both poorly soluble Mg compounds (Mg oxide and Mg trisilicate) and a readily soluble Mg salt (Mg aspartate hydrochloride trihydrate) were studied along with ferrous gluconate. The influence of the addition of Mg aspartate hydrochloride, Mg oxide and Mg trisilicate on the pH of aqueous acidic solutions was examined initially. As expected, the Mg salts employed as antacids (Mg oxide and Mg trisilicate) were found to have a potent neutralising effect, while after the addition of Mg aspartate hydrochloride the pH value was only slightly shifted toward the alkaline side. These findings suggest that Mg aspartate hydrochloride--unlike Mg oxide and Mg trisilicate--has no appreciable influence on Fe absorption, as the availability of Fe salts in the intestinal tract is pH dependent. A procedure simulating the physiological variations of the pH value in the gastrointestinal tract was used to determine the Fe and Mg content in the supernatant after the addition of the above Fe and Mg salts to aqueous solutions. The addition of poorly water-soluble Mg compounds was shown to result in a drastic reduction in the amount of Fe contained in the supernatant. These data are in agreement with those reported in the literature. However, no decrease in the amount of dissolved Fe was noted in the presence of Mg aspartate hydrochloride. These findings confirm that poorly water-soluble Mg compounds have a high capacity to adsorb Fe and, thus, interfere with Fe absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythema formation in magnesium-deficient albino rats. A non-invasive model for the screening of anti-inflammatory agents and oral mineral supplements

The enteral bioavailability of magnesium firmly bound to a fire-proof, inert SiO2-Al2O3 matrix (ground magnesia boats) was studied in magnesium-deficient albino Sprague-Dawley rats, with and without blocking gastric hydrochloric acid secretion with omeprazole. Magnesium was absorbed, although to a small degree, also at anacidity. Pronounced erythema, developing after only some days in hypomagnesemic hypercalcemic rats, are proposed as a non-invasive model for the screening of antiinflammatory substances. Using this model significant protective effects were proven for cromoglycate, polyenthylene glycol 400, and omeprazole; the latter, however, seems more likely to act via a magnesium-sparing mechanism.

In vitro magnesium absorption and the role of intestinal motility

Magnesium (Mg) is known as an inhibitor of spontaneously contracting muscular tissues. To increase extracellular Mg in vivo, high doses of Mg must be given orally. Therefore, we investigated the effect of different doses of Mg given from the mucosal side of the small intestine of rats. According to the model of Trendelenburg, a system for the perfusion of isolated small intestine was developed, which allows the simultaneous recording of absorption and muscle contractions. Increasing doses of Mg were applied serosally or intraluminally. Intramulinal Mg did not affect intestinal motility. In contrast, increasing concentrations of serosal Mg resulted in a 50% inhibition of motility at 2.9 mmol/l Mg. This indicates no influence on intestinal motility of high doses of Mg acting from the mucosal side. In further studies, the addition of citric acid or taurocholic acid did not alter Mg absorption. Serosally applied amiloride (1 mmol/l) inhibited absorption, but also resulted in complete loss of motility. Since in this model passive diffusion is the most important mechanism of Mg transport, a direct influence of amiloride on Mg absorption can be excluded. From these data, we conclude that intestinal motility influences absorption--also of ions in aqueous solution--and should therefore be taken into account in absorption studies.

Pharmacokinetics of magnesium salts

Due to the widespread use of magnesium (Mg) in human medicine, interest in quantitative enteral absorption rates arose more than 100 years ago. The introduction of the AAS technique and of radioisotopes has stimulated research. Slowly exchanging compartments have not, however, been accessible up until now, and the exact mechanism(s) of enteral Mg absorption is still unclear; hence, the fate of orally administered Mg cannot be followed in detail. The capacity of skeletal Mg stores varies with exogenous Mg supply, consumption, excretion and age. In otherwise healthy subjects, urine Mg levels correlate with exogenous supply. Neglecting the fact that exogenous Mg exchanges with deep Mg stores to a considerable degree, it makes sense to qualitatively study the availability of Mg compounds by relating the amount administered to the amount excreted in the urine, especially after filling deep compartments. Since renal Mg excretion patterns are known to change when tubular reabsorption capacity is exceeded or when pH alterations occur, these parameters must be monitored and taken into account at the quantitative evaluation of data.

In-vivo monitoring of corticomedullary nephrocalcinosis in rats using computerized tomography

An in-vivo method, computerized tomography (CT), was used to monitor nephrocalcinosis in female rats. CT density data correlated well with renal Ca content measured by atomic absorption spectrophotometry. In-vivo CT measurements revealed that the severity of nephrocalcinosis may change spontaneously with time. Manifest calcifications may exhibit spontaneous regression and are probably affected positively by high dietary Mg, in contrast to increased Ca. It is concluded that CT is a suitable and reliable non-invasive in vivo method to follow up time-dependent alterations in kidney calcifications in rats.

Hypothesis: the effect of oral nitrite on blood pressure in the spontaneously hypertensive rat. Does dietary nitrate mitigate hypertension after conversion to nitrite?

Increasing doses of nitrite (3.7-14.8 mg/kg BW) were administered via intragastric intubation to 64 spontaneously hypertensive Sprague-Dawley rats. Systemic blood pressure, measured in conscious animals with the tail cuff method, significantly decreased in a dose-related manner 16 and 32 minutes later, and pulse rate slightly increased. Since orally ingested nitrate may be partially converted to nitrite, it seems worthwhile to study correlations between dietary nitrate and blood pressure in experimental animals and man.

Nephrocalcinosis without functional renal impairment in rats subjected to subacute moderate magnesium deficiency, and intervention studies on the mobilization of calcium deposits

Female Sprague-Dawley rats (100-120 g) were kept for 12 d on diets containing 250, 1500, or 9000 ppm Mg. Then subgroups were loaded with water, frusemide or magnesium and urine was collected over 6 h. Moderately Mg-deficient diet (250 ppm) induced moderate hypomagnesaemia (62.3% of controls), but did not result in hypercalcaemia or the formation of typical erythema. Nevertheless, pronounced nephrocalcinosis developed, as shown by increased renal wet and dry weight and elevated tissue concentrations of Ca, P and Mg, the calculous deposits probably consisting to a large extent of Ca3 (PO4)2. Despite these alterations, renal function remained unimpaired in Mg-deficient rats, as shown by normal urinary creatinine excretion and the unaffected ability of the kidneys to concentrate urine. Loading with water, frusemide or Mg increased urinary excretion of calcium in all three diet groups to a similar extent; hence no significant proof can be given that calculous deposits are mobilized under these conditions. Since comparable conditions may also be present under clinical conditions in man, special care should be given to maintain optimal Mg balance.

[The clinical importance of magnesium. 2. The indications for supplementation and therapy]

Mg deficiency is characterized by diverse secondary electrolyte alterations. Extracellularly, hypocalcemia is a particular feature, which may be explained by increased resistance of bone towards parathormone. Intracellularly, decreased concentrations of Mg and K and increased amounts of Na and Ca are found in contractile organelles. At increased Mg levels, concentration of parathormone may decrease, leading to hypocalcemia. Calcium-antagonistic effects are observed in smooth muscle, the myocardium and the end-plate of skeletal muscles. Hence, Mg may be prescribed either to correct a deficit or to utilize its pharmacologic effects. Dosaging still needs to be optimized.

[Clinical significance of magnesium. 1: Distribution in the organism, evaluation of current supply]

The most important compartments of Mg metabolism are described: Bone Mg stores correlate closely with serum Mg, which latter depends mainly on intestinal absorption and excretion, predominantly via the kidneys. Since intracellular Mg is mainly bound, the overall intracellular Mg concentration depends largely on the amount of available ligands such as ATP. Serum Mg reflects the Mg content of bone stores. The frequency at which hyper- or hypomagnesemia occurs depends largely on the precision with which the normal range is established. Recommendations for the sampling of serum are made.

Age-dependent accumulation of cadmium in rats exposed to contaminated drinking water; interactions with zinc and copper and subcellular Cd distribution in kidney cells

One of each pair of female sister rats aging 1, 4, 7 or 10 months was exposed during 3 months to 31.5 mg/L Cd (as CdCl2) in its drinking water and sacrificed immediately after Cd exposure together with its untreated sister. Concentrations of Cd, Zn and Cu were measured in the kidneys (medulla and cortex), the liver, the duodenum and the uterus. Furthermore, the subcellular distribution of Cd was measured in renal tissue. The accumulation of metal ions, defined as the difference between Cd-treated and untreated rats, was pronounced in all tissues except the uterus and was significantly decreased at increasing age. Multivariate analysis of variance revealed significant interaction with Zn and Cu. Higher Cd accumulation in the tissues of young animals probably depends on the higher consumption of contaminated drinking water per kilogram of body weight. High concentrations of Cd detected in cell nuclei may be due to the similarity between Cd2+ and Ca2+.

Magnesium in pregnant women and the newborn

In this article the importance of Mg for pregnant women and fetal outcome is reviewed. The physiological changes of Mg-containing body fluids and of tissues are discussed. Mg supplementation during pregnancy seems to be necessary and the efficacy on maternal health and on the newborn are reported. Serum Mg levels decrease during pregnancy and there is a 25% increase of renal Mg excretion. Mg supplementation has a positive effect, with reduced incidence of hospital admission and preterm labour, while the gestational age of the fetus is longer. Convulsions may occur in newborns with hypomagnesaemia. Hypermagnesaemia of the newborn following MgSO4 infusions to toxaemic mothers has been reported.

Kinetic studies on nitrite and nitrate in rats by ion-pair chromatography

A highly sensitive and specific ion-pair chromatographic method is presented for the simultaneous determination of nitrite (NO2-) and nitrate (NO3-) in plasma. The detection limits are 2 mumol NO2-/l and 8 mumol NO3-/l with recovery rates of 98-99%. The applicability of this method to clinical medicine is demonstrated using NO2- -loaded rats as a biological model: following intravenous infusion or intragastric application of NO2-, blood levels of NO2-, NO3- and methemoglobin are measured during 2-64 min. The kinetic data obtained reflect the complex metabolism of NO2- and NO3- in living organisms.

Experimental data on the problem of specific hepatosplenography with radiodense lipomicrons

Investigations into specific hepatosplenography performed with the aid of radiodense lipomicrons of different size ranges and various surface layers are presented. It is concluded that certain synthetic neutral and/or negatively charged amphiphilic substances may enhance hepatic and splenic uptake of small lipomicrons. Kinetics concerning clearance of lipid globules from the blood and hepatic concentration as well as elimination rates are studied. Furthermore, circulatory reactions following the intravenous administration of lipid emulsions and interactions between lipid globules and plasma proteins or synthetic polymeric substances are discussed.

[Magnesium therapy in pregnancy. Pharmacologic and toxicologic aspects of magnesium supplementation and use in pre-eclampsia and threatened premature labor]

The efficacy of parenteral Mg therapy for pre-eclampsia and eclampsia is due to the Mg antagonism of Ca ions. Accordingly, the Mg additional treatment of medicamentous tocolysis reduces the risk of an over-increased cardial energy consumption; at the same time Mg has an effect which inhibits uterine contractions. The favourable effects on the nocturnal calf cramps are due to the compensation of a combined Mg and Ca deficiency and/or a membrane stabilisation caused by Mg. In animal experiments all reproduction processes were negatively influenced by Mg deficiency, whilst the rate of abortions in early and late pregnancy as well as premature births decreased in pregnant women after administration of Mg. The perinatal mortality is similarly favourably influenced. Since prophylactic oral Mg application is effective and safe, it can be recommended without reservations.

Inhibition of nitrate-induced increase of plasma nitrite and methemoglobinemia in rats by simultaneous feeding of ascorbic acid or tocopherol

The formation of plasma nitrite and levels of methemoglobin (MH) were studied after oral treatment with NaNO3 in female SD rats. No effects were observed when NaNO3 was administered in aqueous solution. However, feeding of diets containing an added 5% NaNO3 daily during 1 h significantly increased plasma NO2- and MH. These effects were significantly inhibited by the addition of ascorbic acid or of tocopherol to the NaNO3-containing diet. The transplacental transfer of NO2- was demonstrated as well as fetal methemoglobinemia.

Magnesium and potassium deprivation and supplementation in animals and man: aspects in view of intestinal absorption

States of K and Mg deficiency, deprivation or depletion, are difficult to detect by determining serum concentrations, since both cations are concentrated intracellularly. The intestinal absorption of K is rather quick and complete; the uptake of Mg probably comprises two mechanisms and proceeds continuously, although incomplete. The resulting different pharmakokinetic behavior must be kept in mind when K and Mg are supplemented by the oral route. Favorable effects of oral K and Mg supplementation are reviewed, and the fact is stressed that the body cannot retain K, unless the Mg status is adequate. Therefore, K should be supplemented together with Mg. Drugs like amiloride not only spare K, but at the same time prevent renal losses of other important electrolytes, especially of chloride and Mg.

Influence of decreased and increased magnesium supply on the cardiotoxic effects of epinephrine in rats

Female Sprague-Dawley rats kept on a standard chow or on a magnesium (Mg)-deficient diet during 6 days received s.c. injections of 0, 25, 50, 100 and 200 micrograms of epinephrine (Ep). 1 h before, they were orally treated with 0, 125 or 250 mg of Mg/kg b.w. given as magnesium aspartate hydrochloride. Drug-induced changes were studied by analyzing serum and cardiac tissue samples (Mg, Ca, K, Na and in addition glucose, FFA, cholesterol and creatine kinase in serum) taken at 7 different times (15 to 420 min) after treatment with Ep; effects were evaluated by considering the respective areas under the concentration-time curves (AUC). AUCs were calculated with linear and logarithmic graduation of the time-scale and were also transformed into logarithms. In additional experiments, animals of both diet groups were treated with Mg and Ep as described above and the hearts, excised after 420 min, were prepared for histological examination. Cardiotoxic effects induced by adrenergic overstimulation were aggravated by Mg deficiency. Most pronounced electrolyte alterations and histologically detectable cardiac necroses were observed in the Mg-deficient animals at 420 min following the s. c. injection of 200 micrograms of Ep. On the other hand, oral Mg treatment induced hypermagnesemia and reduced toxic effects of Ep--especially Ca overload of the heart muscle--in controls and in Mg-deficient rats.

Failure to produce hypertension in rats by chronic exposure to cadmium

Groups of ten male and ten female Sprague-Dawley rats were exposed for 92 and 84 wk, respectively, to increasing concentrations of cadmium (as the chloride) in their drinking-water. The exposure levels of Cd used were 0, 5, 12.6 and 31.5 ppm Cd, and 5 ppm Cd plus certain trace metals. Blood pressure was measured in unanaesthetized animals at regular intervals (46 times in females, 49 times in males) by an indirect method to which the animals were kept conditioned. At the end of the experiments blood pressure was also determined directly under sodium pentobarbital anaesthesia. Although the weight of the kidneys, Cd residues and the severity of histological alterations in the kidneys increased in a dose-related manner, the blood pressure and pulse rate were not significantly affected in any of the experimental groups. There was a dose-dependent decrease in water consumption; all other parameters remained unaffected.

[Effect of the current magnesium status on the development of stress ulcers and myocardial necroses]

Depending on diverse factors, Mg-status may be deficient, normal or abundant. In animal experiments Mg-deficiency increases the sensitivity of the body against the development of stress ulcers and cardiac necroses, whereas mg-therapy offers not only protection against these alterations but also against other manifestations of acute stress.

Platelet aggregation evoked in vitro and in vivo by phosphatidic acids and lysoderivatives: identity with substances in aged serum (DAS)

In serum incubated at 36 degrees C for 18-24 hours a factor (DAS) develops which on intravenous injection into cats evokes platelet aggregation followed by an increase in pulmonary vascular resistance (PVR). This change in PVR is mediated via the platelets since it significantly correlates with the preinjection platelet count. There is evidence that phosphatidic acids (PA) and lysophosphatidic acids (LPA) are the active components of DAS. Investigations performed on platelet-rich plasma from man, cat, pig, dog, rabbit, guinea pig, and rat demonstrate that only human and feline platelets exposed to PA or to LPA are aggregated. Feline platelets are more sensitive to either compound than are the platelets from men; however, human platelets exhibit two exceptional properties, a) the sensitivity rapidly declines with time, b) pretreatment with subthreshold concentrations of LPA or PA induces a specific tachyphylaxis.