Effects of zinc supplementation on vertebral and femoral bone mass in rats on strenuous treadmill training exercise

Does Physical Exercise Always Improve Bone Quality in Rats?

For decades, the osteogenic effect from different physical activities on bone in rodents remained uncertain. This literature review presents for the first time the effects on five exercise models (treadmill running, wheel running, swimming, resistance training and vibration modes) in three different experimental rat groups (males, females, osteopenic) on bone quality. The bone parameters presented are bone mineral density, micro-architectural and mechanical properties, and osteoblast/osteocyte and osteoclast parameters. This review shows that physical activities have a positive effect (65% of the results) on bone status, but we clearly observed a difference amongst the different protocols. Even if treadmill running is the most used protocol, the resistance training constitutes the first exercise model in term of osteogenic effects (87% of the whole results obtained on this model). The less osteogenic model is the vibration mode procedure (31%). It clearly appears that the gender plays a role on the bone response to swimming and wheel running exercises. Besides, we did not observe negative results in the osteopenic population with impact training, wheel running and vibration activities. Moreover, about osteoblast/osteocyte parameters, we conclude that high impact and resistance exercise (such jumps and tower climbing) seems to increase bone formation more than running or aerobic exercise. Among the different protocols, literature has shown that the treadmill running procedure mainly induces osteogenic effects on the viability of the osteocyte lineage in both males and females or ovariectomized rats; running in voluntary wheels contributes to a negative effect on bone metabolism in older male models; whole-body vertical vibration is not an osteogenic exercise in female and ovariectomized rats; whereas swimming provides controversial results in female models. For osteoclast parameters only, running in a voluntary wheel for old males, the treadmill running program at high intensity in ovariectomized rats, and the swimming program in a specific ovariectomy condition have detrimental consequences.

Disruption of Bone Zinc Metabolism during Postnatal Development of Rats after Early Life Exposure to Cadmium

This current study was conducted to investigate whether bone tissue impairment induced by early life exposure to cadmium (Cd) during postnatal development could result from disruption to zinc (Zn) metabolism. For this reason, the offspring from mothers receiving either tap water, Cd, Zn or Cd + Zn during gestation and lactation periods were euthanized at PND21 and PND70. At the end of the lactation period (PND21), our results showed that exposure to Cd increased Cd accumulation and Zn depletion in the femur. Furthermore, calcium (Ca) level was reduced. At the molecular level, Cd induced an increase of MT-1 expression and caused an upregulation of ZIP2 accompanied with a down-regulation of ZnT5. Runx2, ALP, colα-1 and Oc mRNA levels were also decreased. In plasma, IGF-1 and osteocalcin concentrations were decreased. Further, Cd altered femoral growth by generating changes in the growth plate. Consequently, the toxic effect of Cd persisted at adult age (PND70) by decreasing bone volume (%BV/TV), bone mineral density (BMD) and Ca content and by increasing trabecular separation (Tb.Sp) in the distal femur. Interestingly, Zn supply provided total or partial corrections of several toxic effects of Cd. These data suggest that the increases of Zn bioavailability as well as the reduction of Cd accumulation in the femur following the changes in ZIP2 and ZnT5 expression are part of the mechanism involved in Zn protection against Cd toxicity on bone tissue.

Zinc supplementation inhibits the increase in osteoclastogenesis and decrease in osteoblastogenesis in streptozotocin-induced diabetic rats

Zinc (Zn) has been shown to stimulate bone formation and inhibit osteoclastic bone resorption and osteoclastogenesis. However, the effects of Zn on bone metabolism in diabetic animals remain to be clarified in vivo. Here, the effects of Zn supplementation on bone metabolism, including osteoclastogenesis and osteoblastogenesis, were investigated using streptozotocine (STZ)-induced diabetic rats. Zn-supplemented water (7.5 mg/L) was given for 1 week to diabetic rats injected with STZ (30 mg/kg body weight) 1 week earlier. The Zn supplement prevented a decrease in the activity and mRNA of alkaline phosphatase (ALP), osteocalcin mRNA, and hydroxyproline and calcium levels, and an increase in the activity and mRNA of tartrate-resistant acid phosphatase (TRAP) and cathepsin K in the proximal tibia of diabetic rats. Histological analysis revealed that the Zn supplement inhibited the diabetes-induced increase and decrease in the number of osteoclasts and osteoblasts, respectively, in the metaphysis of the proximal tibia. The increase in mRNA levels of receptor for activation of NF-κB (RANK), c-fos, c-jun, TRAP, and cathepsin K and decrease in the expression of Runx2, Dlx5, osterix, ALP, osteocalcin, and collagen were prevented by the supplement. The decrease in β-catenin, phosphorylated GSK3β, phosphorylated Akt, insulin-like growth factor 1 (IGF-1), and IGF-1 receptor (IGF-1R) protein levels in diabetic rats was also inhibited, although Zn did not affect the diabetes-increased gene and protein expression of Sost and Dkk1. These results suggested that Zn prevented the diabetes-induced increase in osteoclastogenesis and decrease in osteoblastogenesis by inhibiting RANK expression and stimulating IGF-1/IGF-1R/Akt/GSK3β/β-catenin signaling, respectively.

Zinc modifies the effect of phyto-oestrogens on osteoblast and osteoclast differentiation in vitro

Osteoblast and osteoclast activity is disrupted in post-menopausal osteoporosis. Thus, to fully address this imbalance, therapies should reduce bone resorption and promote bone formation. Dietary factors such as phyto-oestrogens and Zn have beneficial effects on osteoblast and osteoclast activity. However, the effect of combinations of these factors has not been widely studied. We therefore examined the effect of coumestrol, daidzein and genistein in the presence or absence of zinc sulphate (Zn) on osteoclast and osteoblast activity. Osteoclast differentiation and bone resorption were significantly reduced by coumestrol (10- 7 m), daidzein (10- 5 m) and genistein (10- 7 m); and this direct anti-osteoclastic action was unaffected by Zn (10- 5 m). In addition, Zn augmented the inhibitory effect of phyto-oestrogens on the osteoblast-derived stimulus for osteoclast formation, significantly reducing the ratio of receptor activator of NF-κB ligand (RANKL)-to-osteoprotegerin mRNA expression in human osteoblast. We then examined the effect of these compounds on osteoblast activity. Mineralisation was enhanced by coumestrol (10- 5 to 10- 7 m), daidzein (10- 5 to 10- 6 m) and genistein (10- 5 m); and Zn significantly augmented this response. Zn and phyto-oestrogens also significantly enhanced alkaline phosphatase activity and Runt-related transcription factor 2 (Runx2) mRNA expression. On the other hand, Zn blunted phyto-oestrogen-induced type I collagen and osteocalcin expression and suppressed coumestrol and daidzein-stimulated osterix expression. Zn may therefore modify the anabolic action of phyto-oestrogens, promoting characteristics associated with early rather than late stages of osteoblast differentiation. Our data suggest that while Zn enhances the anti-osteoclastic effect of phyto-oestrogens, it may limit aspects of their anabolic action on bone matrix formation.

Zinc deficiency decreases osteoblasts and osteoclasts associated with the reduced expression of Runx2 and RANK

The effects of Zinc(Zn)-deficiency on the function and differentiation of osteoblasts and osteoclasts were investigated in vivo using rats, which were fed a Zn-adequate (control) or Zn-free diet (ZD) or pair-fed a Zn-adequate diet (PF) for 3 weeks. Levels of Zn, insulin, insulin-like growth factor I (IGF-I), and osteoclacin in serum and the activities and numbers of osteoblasts and osteoclasts in bone decreased in ZD rats compared with the control and PF rats. The frequency analyses showed that the precursors of osteoblasts and osteoclasts decreased in bone marrow of ZD, but not PF, rats. The expression of receptor for activation of NF-κB (RANK) decreased with the Zn-deficiency, although RANK ligand, osteoprotegerin, macrophage colony-stimulating factor, and c-fms levels were unaltered. The protein level of a transcription factor MITF, but not PU.1, decreased. The expression of Runx2 decreased associated with the decrease in β-catenin protein and the suppression of glycogen synthase kinase 3β (GSK3β) inhibition and Akt activation. The gene expression of the insulin receptor, IGF-I and the IGF-I receptor was decreased with a reduced level of transcription factor SP-1. These results suggested that a deficiency of Zn decreased osteoclastogenesis associated with the reduced expression of RANK through a decrease in MITF protein, and osteoblastogenesis associated with the reduced expression of Runx2 through the inhibition of Wnt/β-catenin signaling via the suppression of GSK3β inhibition and Akt activation preceded by the reduced level of SP-1 protein.

Administration of zinc inhibits osteoclastogenesis through the suppression of RANK expression in bone

Zinc (Zn) has been known to inhibit osteoclastic bone resorption and stimulate osteoblastic bone formation. However, the mechanisms responsible for these effects have not been well characterized in vivo. Here, the effects of a dietary administration of Zn on osteoclastogenesis and osteoblastogenesis were investigated in Zn-adequate rats. The administration of Zn decreased the activities of bone tartrate-resistant acid phosphatase (TRAP) and cathepsin K, without affecting the serum osteocalcin level. Histological analysis showed a decrease in the number of osteoclasts with a normal number of osteoblasts in the metaphysis of the proximal tibia. The mRNA levels of receptor for activation of NF-κB (RANK), c-fos, c-jun, TRAP and cathepsin K were significantly decreased, although those of RANK ligand, macrophage colony-stimulating factor and c-fms were unaltered. The gene expression of bone morphogenic protein-2, Runx2, Dlx5, osterix, alkaline phosphatase, osteocalcin and collagen was not affected. The level of the RANK protein decreased, while the levels of the Runx2 and β-catenin proteins were unchanged. Further, the osteoclastic differentiation of precursor cells in vitro was suppressed. The suppressed osteoclastogenesis was associated with decreased levels of reactive oxygen species, extracellular signal-regulated kinase (ERK) activation and RANK expression. A lower lipid peroxide level and a higher glutathione level were also observed. These results suggested that Zn-administration did not affect osteoblastogenesis but decreased osteoclastogenesis by inhibiting RANK expression through suppression of the production of reactive oxygen species and ERK activation in Zn-adequate rats.

Zinc deficiency suppresses matrix mineralization and retards osteogenesis transiently with catch-up possibly through Runx 2 modulation

A characteristic sign of zinc deficiency is retarded skeletal growth, but the role of zinc in osteoblasts is not well understood. Two major events for bone formation include osteoblast differentiation by bone marker gene expression, which is mainly regulated by bone-specific transcription factor Runx2 and extracellular matrix (ECM) mineralization by Ca deposits for bone nodule formation. We investigated whether zinc deficiency down-regulates bone marker gene transcription and whether this might occur through modulation of Runx2. We also investigated whether zinc deficiency decreases ECM mineralization in osteoblastic MC3T3-E1 cells. In the presence of 5 mumol/L TPEN as zinc chelator, zinc deficiency (ZnD: 1 micromol Zn/L) decreased bone marker gene (collagen type I, osteopontin, alkaline phosphatase, osteoclacin and parathyroid hormone receptor) expression, as compared to normal osteogenic medium (OSM) or zinc adequate medium (ZnA: 15 micromol/L) (P<0.05) both at 5 days (proliferation) and 15 days (matrix maturation). Decreased bone marker gene transcription by zinc deficiency could be caused by decreased nuclear Runx2 protein (P=0.05) and transcript (P<0.05) levels in ZnD. Furthermore, within the first 24 h of differentiation when Runx2 expression is induced, maximal Runx2 mRNA and nuclear protein levels were delayed in ZnD compared to OSM and ZnA. ECM Ca deposition was also lower in ZnD, which was also indirectly confirmed by detection of decreased cellular (synthesized) and medium (secreted) ALP activity as well as matrix ALP activity. Taken together, zinc deficiency attenuated osteogenic activity by decreasing bone marker gene transcription through reduced and delayed Runx2 expression and by decreasing ECM mineralization through inhibition of ALP activity in osteoblasts. Decreased and delayed bone marker gene, Runx2 expression and ECM mineralization in osteoblasts by zinc deficiency can be a potential explanation for the retarded skeletal growth which is the major zinc deficiency syndrome.

Zinc deficiency negatively affects alkaline phosphatase and the concentration of Ca, Mg and P in rats

Zn is an essential nutrient that is required in humans and animals for many physiological functions, including immune and antioxidant function, growth, and reproduction. The present study evaluated whether Zn deficiency would negatively affect bone-related enzyme, ALP, and other bone-related minerals (Ca, P and Mg) in rats. Thirty Sprague Dawley rats were assigned to one of the three different Zn dietary groups, such as Zn adequate (ZA, 35 mg/kg), pair fed (PF, 35 mg/kg), Zn deficient (ZD, 1 mg/kg) diet, and fed for 10 weeks. Food intake and body weight were measured daily and weekly, respectively. ALP was measured by spectrophotometry and mineral contents were measured by inductively coupled plasma-mass spectrophotometer (ICP-MS). Zn deficient rats showed decreased food intake and body weight compared with Zn adequate rats (p<0.05). Zn deficiency reduced ALP activity in blood (RBC, plasma) and the tissues (liver, kidney and small intestine) (p<0.05). Also, Zn deficiency reduced mineral concentrations in rat tissues (Ca for muscle and liver, and Mg for muscle and liver) (p<0.05). The study results imply the requirement of proper Zn nurture for maintaining bone growth and formation.

Effects of dietary phytase on body weight gain, body composition and bone strength in growing rats fed a low-zinc diet

Phytic acid, a major phosphorous storage compound found in foodstuffs, is known to form insoluble complexes with nutritionally essential minerals, including zinc (Zn). Phytases are enzymes that catalyze the removal of these minerals from phytic acid, improving their bioavailability. The objective of the present study was to determine the ability of dietary phytase to affect body weight, body composition, and bone strength in growing rats fed a high phytic acid, low Zn diet. Rats (n = 20) were fed either a control (AIN-93) or phytase supplemented (Natuphos, BASF, 1,500 phytase units (FTU)/kg) diet for a period of 8 weeks. Phytase supplementation resulted in increased (P<.05) bone and plasma Zn, but no change in plasma inorganic phosphorous or bone levels of Ca, Fe, or Mg. The addition of phytase to the diets resulted in a 22.4% increase (P<.05) in body weight at the end of the study as compared with rats fed a control diet. Dual x-ray absorptiometry (DXA) revealed that phytase supplementation resulted in increase lean body mass (LBM, P<.001) and increased bone mineral content (BMC, P<.001) as compared with feeding the control diet. Bone studies indicated that femurs and tibias from phytase supplemented rats had greater mass (P<.05) and were stronger (P<.05) than rats fed the control diet. This data suggest that the addition of phytase to low Zn diets results in improved Zn status, which may be responsible for beneficial effects on growth, body composition, and bone strength.

Influence of boron supplementation on vertebral and femoral bone mass in rats on strenuous treadmill exercise. A morphometric, densitometric, and histomorphometric study

We studied the effect of boron supplement on experimental osteopenia caused by strenuous exercise in 93- d-old female Wistar rats. A control group of 15 rats was not manipulated. The exercise group of 30 rats was divided into 2 groups of 15 rats each, one that was fed a diet supplemented with 50 mg/kg of boron in the form of Na(2)B(4)O(7), and other that, did not receive a boron supplement. The length and weight were determined in the femur and fifth lumbar vertebra and the bone mineral content and density were assessed through densitometry, and trabecular bone volume, trabecular number, trabecular thickness, and trabecular separation with histomorphometry. The femur length and weight, and vertebra weight, and femur and vertebra bone mineral content and density were significantly lower and the trabecular separation was higher in the exercise group than in the others (p < 0.005 in all). The femur weight, bone mineral content and density, trabecular bone volume and trabecular thickness, were significantly higher in the exercise plus boron group (p < 0.005 to 0.0001). It was concluded that boron preserves bone mass in rats that have been exposed to intense exercise.

The positive effects of zinc on skeletal strength in growing rats

The aim of the present study was to assess the skeletal effects of alimentary zinc depletion and supplementation in an animal model of intact, growing rats. The study was planned as a dose-response study. Thirty-six male Wistar rats, 4 weeks old, were divided into three groups of 12 rats each. The rats had free access to a semisynthetic diet with different amounts of zinc added. Group 1 was given a zinc-free diet containing 2 mg zinc/kg, group 2 was given a normal-zinc diet containing 47 mg zinc/kg; and group 3 was given a zinc-supplemented diet containing 60 mg zinc/kg. All animals were killed 4 weeks after initiation of the experiment and the right femora were removed. The biomechanical effects were measured at the following skeletal sites: femoral diaphysis; femoral neck; and distal femoral metaphysis. In addition, static histomorphometry was performed at the middiaphyseal region. Biomechanical testing revealed a significant zinc-induced increase in bone strength at all sites investigated. It also showed that zinc influenced bone strength in a dose-dependent manner except at the distal metaphysis, where there was no significant difference between the group fed normal-zinc diet and the group fed a hyper-zinc diet. Zinc also improved the rates of growth in the rats. The body weights and length of femora increased dose-dependently. Static histomorphometry showed that zinc exerted its main effect on the periosteal envelope, thereby increasing bone area, tissue area, and axial moment of inertia. We conclude that alimentary zinc supplementation in growing rats induces an increase of bone strength in both the femoral neck and the femoral diaphysis. These results further support the view that zinc has a positive effect on bone metabolism which mimics that of growth hormone (GH) or insulin-like growth factor 1 (IGF-1).

Do ultrasound measurements reflect bone microarchitecture rather than bone mass?: An in vitro study of the rat femur with the use of ultrasound, densitometry, and histomorphometry

RATIONALE AND OBJECTIVES

In an experimental study in 40 rat femurs, the authors correlated the amplitude-dependent speed of bone ultrasound (Ad-SOS) with the bone mineral content and density and with the bone trabecular connectivity: trabecular bone volume, trabecular number, trabecular thickness, and trabecular separation to evaluate and compare the usefulness of the Ad-SOS to determine bone quantity and/or quality.

METHODS

Bone mineral content and density were determined with dual-energy x-ray absorptiometry. Trabecular connectivity was determined with histomorphometric techniques.

RESULTS

There was a strong correlation between the Ad-SOS and the other parameters studied, with a particularly high positive correlation with trabecular bone volume and trabecular thickness, and an inverse correlation with trabecular separation. The correlation was weaker with the bone mineral content and bone mineral density and with the trabecular number. For the trabecular separation, the correlation was significant in all cases, but it was negative.

CONCLUSIONS

Bone ultrasound, in this case Ad-SOS, defines the quality of the bone in terms of trabecular architecture rather than bone density; however, this conclusion is valid only for the rat femur model that the authors used.

The effect of supplemental copper on osteopenia induced by ovariectomy in rats

OBJECTIVE

The effect of a copper supplement on preventing bone mass loss induced by ovariectomy in rats was investigated.

DESIGN

Three groups of fifteen 100-day-old female Wistar rats, each with a mean initial weight of approximately 260 g per animal, were selected for a 30-day experiment. One group of 15 ovariectomized rats was fed a diet supplemented with 15 mg of copper per kilogram of feed. The other two groups: 15 ovariectomized and 15 Sham- ovariectomized rats did not receive the supplement. Morphometric (weight and length) and densitometric studies with dual-energy x-ray absorptiometry were performed on the whole femur and the fifth lumbar vertebra of each animal at the end of the 30-day period.

RESULTS

The ovariectomized rat group fed a diet supplemented with copper did not show the bone mass loss at the axial (fifth lumbar vertebra) or peripheral (femur) level that was evidenced in the ovariectomized group.

CONCLUSIONS

The results of the measurement of axial and peripheral bones show that a supplement of copper may have a potential therapeutic application in the treatment and prevention of involutional osteoporosis.

Nutrition in bone health revisited: a story beyond calcium

Osteoporosis is a complex, multi-factorial condition characterized by reduced bone mass and impaired micro-architectural structure, leading to an increased susceptibility to fractures. Although most of the bone strength (including bone mass and quality) is genetically determined, many other factors (nutritional, environmental and life-style) also influence bone. Nutrition is important modifiable factor in the development and maintenance of bone mass and the prevention and treatment of osteoporosis. Approximately 80-90% of bone mineral content is comprised of calcium and phosphorus. Other dietary components, such as protein, magnesium, zinc, copper, iron, fluoride, vitamins D, A, C, and K are required for normal bone metabolism, while other ingested compounds not usually categorized as nutrients (e.g. caffeine, alcohol, phytoestrogens) may also impact bone health. Unraveling the interaction between different factors; nutritional, environmental, life style, and heredity help us to understand the complexity of the development of osteoporosis and subsequent fractures. This paper reviews the role of dietary components on bone health throughout different stages of life. Each nutrient is discussed separately, however the fact that many nutrients are co-dependent and simultaneously interact with genetic and environmental factors should not be neglected. The complexity of the interactions is probably the reason why there are controversial or inconsistent findings regarding the contribution of a single or a group of nutrients in bone health.

Effects on bone loss of manganese alone or with copper supplement in ovariectomized rats. A morphometric and densitomeric study

OBJECTIVE

The aim of this study was to examine the effect of manganese (Mn) alone and with the addition of copper (Cu) in the inhibition of osteopenia induced by ovariectomy (OVX) in rats. STUDY CONDITIONS: Four lots of 100-day-old female Wistar rats were divided into experimental groups of 15 each. One group received a diet supplemented with 40 mg/kg of Mn per kilogram of feed (OVX+Mn). The second group received the same diet as the first, but with an additional 15 mg/kg of copper (OVX+Mn+Cu). The third group of 15 OVX and the fourth group of 15 Sham-OVX received no supplements. At the conclusion of the 30-day experiment, the rats were slaughtered and their femurs and fifth lumbar vertebrae were dissected. Femoral and vertebral length were measured with caliper and bones were weighed on a precision balance. The bone mineral content (BMC) and bone density (BMD) of the femur (F-BMC, mg and F-BMD, mg/cm(2)) and the fifth lumbar vertebra (V-BMC, mg and V-BMD, mg/cm(2)) were measured separately with dual energy X-ray absorptiometry.

RESULTS

The F-BMD, mg/cm(2) was lower in the OVX than in the Sham-OVX group (P<0.0001) and in the other two groups receiving mineral supplements (P<0.005 in both). F-BMC, mg was significantly lower in the OVX group than in the other three (P<0.0001 in all cases). Calculations for V-BMC, mg and V-BMD, mg/cm(2) are similar to findings in the femur.

CONCLUSIONS

These data show that a Mn supplement is an effective inhibitor of loss of bone mass after OVX, both on the axial and the peripheral levels, although this effect is not enhanced with the addition of Cu.

Physical activity, diet and skeletal health

Diet and physical exercise concur in the determination of skeletal mass at the end of adolescence and in the conservation of it during adult life. The functional demand imposed on bone is a major determinant of its structural characteristics. Stress applied to a skeletal segment affects the geometry of the bone, the microarchitecture and the composition of the matrix. The stimulatory effect occurs when the skeleton is subjected to strains exceeding habitual skeletal loads, and the intensity of load is more important than the duration of the stimulus. Physical activity leads to greater bone density in children and adolescents and, to a minor extent, in adults. Weight bearing activities, such as walking, have a greater effect than non weight bearing activities, such as cycling and swimming. Reduction of loads as in bed resting or in space flights leads to bone loss. Intense training may cause damage, promptly repaired, as in stress fractures observed in army recruits. Female athletes may experience oligo-amenorrhea, though they still have a positive bone balance. There is an important interaction between the mechanical demands and the availability of nutrients to manufacture bone tissue. The increase in bone density in post-menopausal women is positively related to calcium intake when calcium supplementation is accompanied by exercise. When mechanical demands are low, such as during immobilisation, the intestinal calcium absorption is reduced. Calcium intake should also be analysed in the light of other dietary factors affecting the balance between absorption and excretion, and in combination with a number of other minerals, trace elements and bioactive substances with an impact on bone metabolism.