Mn-deficient diet

One interpretation of the above results is that the Wistar rat has a better ability to adapt to a Mn-deficient diet than does the Sprague-Dawley. Thus we hypothesized that this differential response to Mn deficiency between the strains would allow us to better identify metabolic responses to the consumption of Mn-deficient diets. In our initial study, weanling Sprague-Dawley and Wistar rats were fed diets containing either 45 or 1 ug Mn/g for 6 weeks. After this period, the rats were fasted overnight and then jLijtubated with 1 g of the 1 ug Mn/g diet which was labeled with Mn. The diet was given as a 50% slurry made with deionized water. Six hours after intubation the animals were killed and tissues were collected and counted. 

Mineral levels in serum and bone from rats on the 3 different diets are shown in Table I. Serum Ca was significantly higher in deficient rats at six months. Serum Cu and Mn were significantly lower in L and D rats respectively. The mineral concentrations of Ca in the femur as well as Mn were affected by the Mn-deficient diets. Ca concentrations of the femur was inversely correlated with the serum Ca concentrations in the L and D rats. Radiographic observations of isolated humeri indicated that osteopenic-like lesions were associated with the L and D regimens (31). 

A dietary deficiency of Mn has been shown to result in a reduction of MnSOD activity in rats, mice, and chickens. In adult mice fed diets deficient in Mn (1 ug Mn/g diet) prenatally and postnatally, the activity of this enzyme was significantly lower in liver, brain, heart, and lung than in tissues of animals fed control diets (45 ug Mn/g diet) (11). In chickens, there was lower activity of MnSOD in liver after only 7 days of feeding a Mn-deficient diet (1 ug Mn/g diet) to hatchlings compared to controls. The activity of the enzyme was quickly elevated to normal by the feeding of Mn-adequate diets. Concomitant with the decline in activity of MnSOD, the activity of copper-zinc SOD (CuZnSOD) was increased, suggesting a compensatory response to 0 which was not dismutated due to the lower MnSOD activity. Paynter (12) has reported that a reduction in heart and kidney MnSOD can also occur in rats when the deficient diets are initiated at weaning. 

Pyruvate carboxylase is a well-known Mn metalloenzyme. The enzyme is a tetramer and contains one biotin cofactor per subunit and one divalent cation per subunit. The enzyme from calf liver, for example, contains four tightly boimd Mn atoms. The enzyme from chicken liver contains two Mn atoms and two Mg atoms. Raising chickens on an Mn-deficient diet results in the production of an Mn-free enzyme, where magnesium ions replace the usually occurring manganese ions. The Mg-containing enzyme is catalytically active, leaving the requirement of the enzyme for Mn in question (Scrutton et al, 1972). 

Chondroitin 4-sulphate ig the principal proteoglycan found in the media of cultured B16 mouse melanoma cells. The epiphysial cartilage of four-week-old chickens that had been fed a Mn " -deficient diet contained low levels of glycosaminoglycans, owing to a decrease in the D-xylosylation of core proteins and an increase in the degradation of glycosaminoglycans. ... 

There have been relatively few studies on Mn bioavailability from various types of diets as well as from individual factors in the diet. However, to better understand the requirement of Mn in humans it is essential to obtain such information. While Mn deficiency in humans appears to be rare (see Chapter by Keen et al.), our knowledge about the signs of human Mn deficiency as well as our means to clinically assess Mn status is very limited. The physiological requirement of Mn, i.e., the amount that must be absorbed to balance the daily excretion and retention in growing subjects, is not known. The observed whole body turnover rate in human adults (a half-life of about 40 days) and available estimates of total body Mn content (20 mg) (26) speaks for a daily turnover of about 0.25 mg. With a low degree of absorption, the dietary requirement will be much higher. 

The essentiality of manganese (Mn) for animals was established in 1931 by Orent and McCollum (3) and Kemmerer and co-workers (4j who demonstrated poor growth in mice and abnormal reproduction in rats fed diets deficient in the element. Today it is known that under rigidly controlled laboratory conditions, Mn deficiency results in a wide variety of structural and metabolic defects. 

Despite increasing recognition that Mn deficiency may be a factor underlying several human pathologies, the metabolism of this element is poorly understood. In our opinion, the recent report by Friedman and co-workers (14) concerning the relatively rapid induction of Mn deficiency in male subjects fed diets low in this element further underscores the need to understand the metabolism of this element in humans. 

Mean Mn concentrations were similar in Sprague-Dawley and Wistar rats fed the control diet (2.3 and 2.2 ug Mn/g wet weight, respectively). Manganese concentrations were markedly lower in the rats fed the deficient diets compared to the controls. Liver Mn concentrations were slightly lower in the deficient Sprague-Dawley rats than in the deficient Wistar rats (0.4 and 0.7 ug/g, respectively). ... 

This increase reflects the edematous and inflammatory response of the lung to 0 exposure. Neither lung CuZnSOD nor MnSOD activity was affected By diet in air-breathing groups. In marked contrast, exposure to O resulted in an increase in total lung SOD activity in the Mn-sufricient group this increase was a function of higher activities of both MnSOD and CuZnSOD in these animals. Exposure to 0 also resulted in an increase in total SOD activity in Mn-deficient mice however, in these animals the increase occurred as a result of a selective increase in CuZnSOD activity. 

We have evaluated the biochemical response of mice to ADR treatment when fed either Mn-sufficient or -deficient diets. In addition we varied the level of vitamin E to assess the influence of a combined deficit of dietary antioxidants on ADR toxicity (33). 

Results from this study showed that SOD activity was not affected by acute ADR treatment. A second finding was that acute ADR toxicity did not promote cardiac lipid peroxidation. However, it was observed that mitochondrial lipid peroxidation was highest in mice fed diets low in both antioxidants. Ultrastructural examination revealed mitochondrial abnormalities in cardiac tissue from ADR-treated animals (Figures 3 and 4). There were large vacuoles within the mitochondria and condensation of the inner and outer membranes of the mitochondria. The ultrastructural effects of ADR treatment were most severe in the low E, Mn-deficient mice. It is reasonable to suggest that a higher than normal level of lipid peroxidation may predispose the animal to tissue damage from ADR. Consistent with this concept, Meyers et al. (34) have reported that pretreatment with supplemental vitamin E can reduce the toxicity of ADR in mice. 

Weanling, Wistar and RICO (genetically hypercholesterolemic) rats were placed on manganese-deficient (0.12 pg Mn/g) or manganese-sufficient (100.12 pg Mn/g) diets. Plasma total, VLDL- and HDL-cholesterol levels, and liver cholesterol and lipid concentrations were not affected by the treatment used. These results suggest that dietary manganese deficiency does not result in significant alterations in cholesterol and lipid metabolism in the rat (8). 

The need to include a variety of minerals in experimental diets has already been mentioned this was especially stressed (1920-1930) by Boyd-Orr, the director of the Rowett Institute for Animal Nutrition in Scotland. Increasingly refined food sources led to the identification of large numbers of trace elements (e.g., Cu, Mn, Mo, Zn) whose importance in the diet was suggested from hydroponic experiments with plant seedlings. Cobalt is an example of such a trace element. Vitamin Bj2 is synthesized by bacteria in the rumens of sheep and cattle but is absent from their fodder. In Australia, sheep feeding on cobalt-deficient pastures failed to thrive because vitamin B12 could no longer be made. 

In contrast to the estimated dietary requirement of approximately 35 ug/kg/day in adults, the requirement of infants has been estimated to be 0.2-0.6 ug/kg/day (35). This difference is likely explained by the differences in degree of absorption or in excretion rates and susceptibility to Mn at different ages. Because of the vulnerability of the newborn to deficiency and excess of Mn, we have investigated Mn in various infant diets and the extent to which it is absorbed. The concentration of Mn in human milk is very low, 4-8 ug/L, as compared to 20-50 ug/L in cow s milk and 50-1300 ug/L in U.S. infant formula (6,36,37). Thus, Mn intake of breast-fed infants will be 0.5-0.9 ug/kg/day, while the intake of formula-fed infants will be considerably higher and highly variable depending on the formula used. 

An interaction also exists between Fe and Mn at the gut level in rats (30), and it has been established numerous times that excess supplemental Mn adversely affects Fe status of mammals and chicks (2,18,21). Halpin (24) recently investigated the mutual interrelationship between Mn and Fe in chicks. In a casein-dextrose diet containing either 14 or 1014 ppm Mn, Fe ranging from deficient to a 2000 ppm excess had little or no effect on chick gain or on tissue Mn concentration. The 1000 ppm Mn addition, however, reduced hemoglobin and hematocrit levels when dietary Fe was at or below the chick s requirement. These data indicate that the interrelationship between Fe and Mn is unidirectional in chicks ie., excess Mn affects Fe status of chicks, but excess Fe does not affect Mn status of chicks. Therefore, this interaction appears to be similar to the unidirectional interactions between Fe and Zn (33) and between Zn and Cu (34-35). 

Our interest in the role of trace elements in bone metabolism developed in a rather bizarre fashion. Ve became interested in the orthopedic problems of a prominent professional basketball player. Bill Walton. Several years ago he was plagued by frequent broken bones, pains in his joints and an inability to heal bone fractures. We hypothesized that he might be deficient in trace elements as a result of his very limited vegetarian diet. In cooperation with his physician, we were able to analyze Walton s serum. We found no detectable manganese (Mn). His serum concentrations of copper (Cu) and zinc (Zn) were below normal values. Dietary supplementation with trace elements and calcium (Ca) was begun. Over a period of several months his bones healed and he returned to professional basketball (1,2). In cooperation with several other orthopedic physicians, we analyzed serum from other patients with slow bone healing. Several of these patients also had abnormally low Zn, Cu and Mn levels. 

It comes as no great surprise that trace elements may affect the growth and development of bone. Trace element deficiences profoundly alter hone metabolism in animals either directly or indirectly (3). The absence of a trace element in the diet can lead to inefficient functioning of a specific enzyme or enzymes that require the transition element as a cofactor. An example of this is the role of Cu and iron (Fe) in the cross-linking of collagen and elastins (4-9). The participation of Mn in the biosynthesis of mucopolysaccharides (10-12) is another example. Zn deficiency causes a reduction in osteoblastic activity, collagen and chondroitin sulfate synthesis and alkaline phosphatase activity (13-16). 

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