Zinc-Deficient Rats Have More Limited Bone Recovery During Repletion Than Diet-Restricted Rats

Severe Zinc Deficiency Impairs Accrual of Bone in Rapidly Growing Rats That Is Partially Corrected Following Short-term Zinc Repletion

Zinc (Zn) deficiency impairs bone growth. However, the precise skeletal effects of varying levels of Zn deficiency and response to subsequent Zn repletion on the growing skeleton are incompletely understood. To address this gap in knowledge, we investigated the effects of dietary Zn ((severe deficiency (< 0.5 mg Zn/kg diet) and short-term Zn repletion (30 mg/kg diet), marginal deficiency (6 mg Zn/kg diet)) on bone mass, density, and cortical and cancellous bone microarchitecture in growing male Sprague Dawley rats. Marginal Zn intake for 42 days had no effect on bone mass or cortical and cancellous bone microarchitecture. Twenty-one days of severe Zn deficiency lowered serum osteocalcin and C terminal telopeptide of type I collagen (CTX-1), decreased tibial bone mineral content and density, and lowered cross-sectional volume, cortical volume, and cortical thickness in tibial diaphysis as compared to both Zn-adequate (30 mg/kg diet) and pair-fed controls. Severe Zn deficiency similarly lowered cancellous bone volume in proximal tibial metaphysis. Zn repletion (10 days) accelerated weight gain, indicative of catch-up growth, normalized CTX-1 and osteocalcin, but did not normalize bone mass (unadjusted and adjusted for body weight) or cortical and cancellous bone microarchitecture. In summary, severe but not marginal Zn deficiency in rapidly growing rats impaired acquisition of cortical and cancellous bone, resulting in abnormalities in bone microarchitecture. Zn repletion accelerated weight gain compared to Zn-adequate controls but absence of a compensatory increase in serum osteocalcin or bone mass suggests Zn repletion may be insufficient to fully counteract the detrimental effects of prior Zn deficiency on skeletal growth.

Effects of Extracellular Osteoanabolic Agents on the Endogenous Response of Osteoblastic Cells

The complex multidimensional skeletal organization can adapt its structure in accordance with external contexts, demonstrating excellent self-renewal capacity. Thus, optimal extracellular environmental properties are critical for bone regeneration and inextricably linked to the mechanical and biological states of bone. It is interesting to note that the microstructure of bone depends not only on genetic determinants (which control the bone remodeling loop through autocrine and paracrine signals) but also, more importantly, on the continuous response of cells to external mechanical cues. In particular, bone cells sense mechanical signals such as shear, tensile, loading and vibration, and once activated, they react by regulating bone anabolism. Although several specific surrounding conditions needed for osteoblast cells to specifically augment bone formation have been empirically discovered, most of the underlying biomechanical cellular processes underneath remain largely unknown. Nevertheless, exogenous stimuli of endogenous osteogenesis can be applied to promote the mineral apposition rate, bone formation, bone mass and bone strength, as well as expediting fracture repair and bone regeneration. The following review summarizes the latest studies related to the proliferation and differentiation of osteoblastic cells, enhanced by mechanical forces or supplemental signaling factors (such as trace metals, nutraceuticals, vitamins and exosomes), providing a thorough overview of the exogenous osteogenic agents which can be exploited to modulate and influence the mechanically induced anabolism of bone. Furthermore, this review aims to discuss the emerging role of extracellular stimuli in skeletal metabolism as well as their potential roles and provide new perspectives for the treatment of bone disorders.

Biomimetic trace metals improve bone regenerative properties of calcium phosphate bioceramics

The bone regenerative capacity of synthetic calcium phosphates (CaPs) can be enhanced through the enrichment with selected metal trace ions. However, defining the optimal elemental composition required for bone formation is challenging due to many possible concentrations and combinations of these elements. We hypothesized that the ideal elemental composition exists in the inorganic phase of the bone extracellular matrix (ECM). To study our hypothesis, we first obtained natural hydroxyapatite through the calcination of bovine bone, which was then investigated its reactivity with acidic phosphates to produce CaP cements. Bioceramic scaffolds fabricated using these cements were assessed for their composition, properties, and in vivo regenerative performance and compared with controls. We found that natural hydroxyapatite could react with phosphoric acid to produce CaP cements with biomimetic trace metals. These cements present significantly superior in vivo bone regenerative performance compared with cements prepared using synthetic apatite. In summary, this study opens new avenues for further advancements in the field of CaP bone biomaterials by introducing a simple approach to develop biomimetic CaPs. This work also sheds light on the role of the inorganic phase of bone and its composition in defining the regenerative properties of natural bone xenografts.

Electro-chemical deposition of nano hydroxyapatite-zinc coating on titanium metal substrate

BACKGROUND

Titanium is an inert metal that does not induce osteogenesis and has no antibacterial properties; it is proposed that hydroxyapatite coating can enhance its bioactivity, while zinc can contribute to antibacterial properties and improve osseointegration.

AIMS

A nano-sized hydroxyapatite-zinc coating was deposited on commercially pure titanium using an electro-chemical process, in order to increase its surface roughness and enhance adhesion properties.

METHODS

The hydroxyapatite-zinc coating was attained using an electro-chemical deposition in a solution composed of a naturally derived calcium carbonate, di-ammonium hydrogen phosphate, with a pure zinc metal as the anode and titanium as the cathode. The applied voltage was -2.5 for 2 h at a temperature of 85 °C. The resultant coating was characterized for its surface morphology and chemical composition using a scanning electron microscope (SEM), energy dispersive x-ray spectroscope (EDS), and Fourier transform infrared (FT-IR) spectrometer. The coated specimens were also evaluated for their surface roughness and adhesion quality.

RESULTS

Hydroxyapatite-zinc coating had shown rosette-shaped, homogenous structure with nano-size distribution, as confirmed by SEM analysis. FT-IR and EDS proved that coatings are composed of hydroxyapatite (HA) and zinc. The surface roughness assessment revealed that the coating procedure had significantly increased average roughness (Ra) than the control, while the adhesive tape test demonstrated a high-quality adhesive coat with no laceration on tape removal.

CONCLUSIONS

The developed in vitro electro-chemical method can be employed for the deposition of an even thickness of nano HA-Zn adhered coatings on titanium substrate and increases its surface roughness significantly.

Trace elements have beneficial, as well as detrimental effects on bone homeostasis

The protective role of nutrition factors such as calcium, vitamin D and vitamin K for the integrity of the skeleton is well understood. In addition, integrity of the skeleton is positively influenced by certain trace elements (e.g. zinc, copper, manganese, magnesium, iron, selenium, boron and fluoride) and negatively by others (lead, cadmium, cobalt). Deficiency or excess of these elements influence bone mass and bone quality in adulthood as well as in childhood and adolescence. However, some protective elements may become toxic under certain conditions, depending on dosage (serum concentration), duration of treatment and interactions among individual elements. We review the beneficial and toxic effects of key elements on bone homeostasis.

Implications of compromised zinc status on bone loss associated with chronic inflammation in C57BL/6 mice

Compromised zinc status and chronic inflammation are independent factors that can contribute to bone loss. However, zinc’s role in regulating lymphoid and myeloid cell populations, combined with the interplay between the immune and skeletal systems raises the question as to the extent to which a low-grade inflammatory challenge in the context of marginal zinc deficiency would exacerbate bone loss. To address this question, young adult C57BL/6 male mice (n=32) were used in a 2×2 factorial design with dietary zinc (adequate or 35 ppm vs inadequate or −Zn =5 ppm) and lipopolysaccharide (LPS, 0 or 0.1 mg/kg body weight). Mice were fed their respective diets for 10 weeks. On the 6th week, mice had a slow release pellet implanted to induce a low-grade inflammation for the final 4 weeks of the study. −Zn induced a decrease in total white cell counts and peripheral lymphocytes, whereas LPS increased blood monocytes. LPS significantly reduced spine bone mineral density and trabecular bone volume and number of the vertebral body compared with both zinc adequate and inadequate without LPS groups. Likewise, the most pronounced effects on bone strength occurred with LPS, however, −Zn also had negative effects on the bone von Mises stresses. LPS induced an increase in TNF-α and this response was further increased with −Zn. Although the marginal zinc deficiency altered immune function, bone loss was not exacerbated with low-grade chronic inflammation in marginally zinc-deficient young adult mice. These findings demonstrate that in young adult animals an immune challenge modestly increases the inflammatory response and worsens bone biomechanics in the context of a marginal zinc deficiency, but not to the extent that more severe adverse outcomes are observed on bone structural parameters.

Trace elements and bone health

The importance of nutrition factors such as calcium, vitamin D and vitamin K for the integrity of the skeleton is well known. Moreover, bone health is positively influenced by certain elements (e.g., zinc, copper, fluorine, manganese, magnesium, iron and boron). Deficiency of these elements slows down the increase of bone mass in childhood and/or in adolescence and accelerates bone loss after menopause or in old age. Deterioration of bone quality increases the risk of fractures. Monitoring of homeostasis of the trace elements together with the measurement of bone density and biochemical markers of bone metabolism should be used to identify and treat patients at risk of non-traumatic fractures. Factors determining the effectivity of supplementation include dose, duration of treatment, serum concentrations, as well as interactions among individual elements. Here, we review the effect of the most important trace elements on the skeleton and evaluate their clinical importance.

Effects of zinc-substituted nano-hydroxyapatite coatings on bone integration with implant surfaces

OBJECTIVE

The purpose of this study was to investigate the effects of a zinc-substituted nano-hydroxyapatite (Zn-HA) coating, applied by an electrochemical process, on implant osseointegraton in a rabbit model.

METHODS

A Zn-HA coating or an HA coating was deposited using an electrochemical process. Surface morphology was examined using field-emission scanning electron microscopy. The crystal structure and chemical composition of the coatings were examined using an X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). A total of 78 implants were inserted into femurs and tibias of rabbits. After two, four, and eight weeks, femurs and tibias were retrieved and prepared for histomorphometric evaluation and removal torque (RTQ) tests.

RESULTS

Rod-like HA crystals appeared on both implant surfaces. The dimensions of the Zn-HA crystals seemed to be smaller than those of HA. XRD patterns showed that the peaks of both coatings matched well with standard HA patterns. FTIR spectra showed that both coatings consisted of HA crystals. The Zn-HA coating significantly improved the bone area within all threads after four and eight weeks (P<0.05), the bone to implant contact (BIC) at four weeks (P<0.05), and RTQ values after four and eight weeks (P<0.05).

CONCLUSIONS

The study showed that an electrochemically deposited Zn-HA coating has potential for improving bone integration with an implant surface.

Enhanced effect of zinc and calcium supplementation on bone status in growth hormone-deficient children treated with growth hormone: a pilot randomized controlled trial

Reduced bone mineral content in growth hormone-deficient children (GHD) has been reported. Calcium, zinc, and vitamin D play an important role in bone formation. Hence, the aim of this pilot randomized controlled study was to evaluate the effect of calcium, vitamin D, and zinc supplementation in prepubertal GHD children treated with GH on bone health parameters. After 1 year of treatment with GH (20 mg/m(2)/week), 31 GHD (mean age 8.7 ± 2.8 years, 18 boys) prepubertal children were randomised to receive calcium (500 mg/day) and vitamin D (60,000 IU/3 months) [Group A] or a similar supplement of calcium, vitamin D, and zinc (as per Indian Recommended Allowance) [Group B] along with GH therapy for the next 12 months. The two groups were similar in anthropometric and body composition parameters at baseline (p > 0.1). After 1 year of GH therapy, height-adjusted % gain was similar in both groups, 48 % in bone mineral content (BMC) and 45 % in bone area (BA). Height-adjusted % increase in BMC was significantly (p < 0.05) higher in the second year than in the first in both the groups. This % increase in BMC and BA was greater in Group B (51 and 36 % respectively) than in Group A (49 and 34 %), although marginally (p < 0.05). Supplementation of calcium and vitamin D along with GH therapy in GHD Indian children has the potential for enhancing bone mass accrual; this effect was further enhanced through the addition of zinc supplement.

The effects of melatonin on the physical properties of bones and egg shells in the laying hen

Laying hens often experience unbalanced calcium utilization which can cause deficiencies in bone and egg mineralization. Because melatonin has been shown to affect bone mineralization in other animals, we examined whether treating hens with melatonin would affect eggshell thickness and improve skeletal performance, thereby reducing skeletal and egg shell defects. Birds were given a diet containing either low (30 µg/kg), medium (300 µg/kg), or high (3 mg/kg) concentrations of melatonin, or control feed through approximately one laying cycle. We examined the weight, length, and strength of egg, femur, tibia, and keel. Hens treated with a high concentration of melatonin showed significant strengthening in their femur and tibia, as measured by maximum force sustained and breaking force, compared to controls. Egg weights from hens treated with melatonin were significantly greater than those from hens that were not treated with melatonin. Conversely, egg shell mass of hens treated with melatonin was significantly lower than those of hens not treated with melatonin. Our data suggest that melatonin may affect the allocation of calcium to bone at the expense of egg shell mineralization.

Marginal zinc deficiency in pregnant rats impairs bone matrix formation and bone mineralization in their neonates

Zinc (Zn) deficiency during pregnancy may result in a variety of defects in the offspring. We evaluated the influence of marginal Zn deficiency during pregnancy on neonatal bone status. Nine-week-old male Sprague-Dawley rats were divided into two groups and fed AIN-93G-based experimental diets containing 35 mg Zn/kg (Zn adequately supplied, N) or 7 mg Zn/kg (low level of Zn, L) from 14-day preconception to 20 days of gestation, that is, 1 day before normal delivery. Neonates were delivered by cesarean section. Litter size and neonate weight were not different between the two groups. However, in the L-diet-fed dam group, bone matrix formation in isolated neonatal calvaria culture was clearly impaired and was not recovered by the addition of Zn into the culture media. Additionally, serum concentration of osteocalcin, as a bone formation parameter, was lower in neonates from the L-diet-fed dam group. Impaired bone mineralization was observed with a significantly lower content of phosphorus in neonate femurs from L-diet-fed dams compared with those from N-diet-fed dams. Moreover, Zn content in the femur and calvaria of neonates from the L-diet group was lower than that of the N-diet-fed group. In the marginally Zn-deficient dams, femoral Zn content, serum concentrations of Zn, and osteocalcin were reduced when compared with control dams. We conclude that maternal Zn deficiency causes impairment of bone matrix formation and bone mineralization in neonates, implying the importance of Zn intake during pregnancy for proper bone development of offspring.

Low dose parathyroid hormone maintains normal bone formation in adult male rats during rapid weight loss

A persistent negative energy balance results in bone loss. It is not clear whether the bone loss associated with chronic negative energy balance can be prevented. The objective of this study was to assess the efficacy of intermittent low dose parathyroid hormone (PTH) treatment in maintaining normal bone formation during severe energy restriction. Six-month-old male Fisher 344 rats were divided into 4 treatment groups: (1) baseline, (2) ad libitum (ad lib)-fed control, (3) energy-restricted (to consume 40% ad lib caloric intake), or (4) energy-restricted+low dose (1 μg/kg/d) PTH. Severe energy restriction for 14 d decreased body weight and serum leptin levels. Compared to ad lib-fed controls, energy-restricted rats had lower cancellous bone formation, higher osteoclast perimeter/bone perimeter and higher bone marrow adiposity in the proximal tibial metaphysis. Also, the energy-restricted rats had a lower periosteal bone formation rate at the tibia-fibula synostosis. Administration of PTH to energy-restricted rats had no effect on weight loss or osteoclast perimeter/bone perimeter. In contrast, energy-restricted rats treated with PTH had higher rates of cancellous and cortical bone formation compared to energy-restricted rats, and did not differ from the ad lib-fed control animals. Furthermore, PTH treatment maintained normal bone marrow adiposity. In conclusion, rapid weight loss in adult male rats was accompanied by decreased bone formation and increased bone marrow adiposity and these changes were prevented by low dose PTH treatment. Taken together, the results suggest that the energy cost of bone formation in adult rats is low and PTH therapy is effective in preventing the reduced bone formation associated with rapid weight loss.

Effect of different dietary zinc levels on hepatic antioxidant and micronutrients indices under oxidative stress conditions

Dietary zinc (Zn) status exerts a powerful influence on the degree of oxidative damage caused by free radicals. We examined the effect of dietary Zn variations with oxidative stress (OS) treatment on antioxidant status, liver function, and status of vitamins in male Wistar rats. Oxidative stress was generated by intraperitoneal injections of tert-butyl hydroperoxide; and dietary Zn variations done were Zn deficient, normal, and excess, with 8, 30, and 60 mg Zn per kilogram diet, respectively. After 21-day dietary regimen, the animals were killed; and plasma aspartate aminotransferase, alanine aminotransferase, hepatic antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), Zn, reduced glutathione, lipid peroxidation (LPO), and hepatic riboflavin, nicotinic acid, and ascorbic acid estimations were done. The alanine aminotransferase and aspartate aminotransferase levels were elevated in rats with OS and Zn-deficient diet, which were restored to normal levels with excess dietary Zn. Hepatic antioxidant enzymes and reduced glutathione levels were significantly decreased with concomitant increase in LPO due to OS induction in animals with Zn-deficient diet. Corresponding enhanced enzyme activities, higher hepatic Zn, and lowered LPO were observed in animals with normal- and excess-Zn diet. A dose-dependent increase in hepatic nicotinic acid accumulation was observed as the dietary Zn level increased from deficient to excess; however, there was no influence on riboflavin and ascorbic acid status. The results suggest that Zn may have a therapeutic potential in treatment of oxidative liver damage along with enhanced nicotinic acid absorption.

Dietary zinc reduces osteoclast resorption activities and increases markers of osteoblast differentiation, matrix maturation, and mineralization in the long bones of growing rats

The nutritional influence of zinc on markers of bone extracellular matrix resorption and mineralization was investigated in growing rats. Thirty male weanling rats were randomly assigned to consume AIN-93G based diets containing 2.5, 5, 7.5, 15 or 30 microg Zn/g diet for 24 days. Femur zinc increased substantially as zinc increased from 5 to 15 microg/g diet and modestly between 15 and 30 microg/g (P<.05). By morphological assessment, trabecular bone increased steadily as dietary zinc increased to 30 microg/g. Increasing dietary zinc tended to decrease Zip2 expression nonsignificantly and elevated the relative expression of metallothionen-I at 15 but not 30 microg Zn/g diet. Femur osteoclastic resorption potential, indicated by matrix metalloproteinases (MMP-2 and MMP-9) and carbonic anhydrase-2 activities decreased with increasing dietary zinc. In contrast to indicators of extracellular matrix resorption, femur tartrate-resistant acid and alkaline phosphatase activities increased fourfold as dietary zinc increased from 2.5 to 30 microg Zn/g. Likewise, 15 or 30 microg Zn/g diet resulted in maximum relative expression of osteocalcin, without influencing expression of core-binding factor alpha-1, collagen Type 1 alpha-1, or nuclear factor of activated T cells c1. In conclusion, increased trabecular bone with additional zinc suggests that previous requirement estimates of 15 microg Zn/g diet may not meet nutritional needs for optimal bone development. Overall, the up-regulation of extracellular matrix modeling indexes and concomitant decrease in resorption activities as dietary zinc increased from 2.5 to 30 microg/g provide evidence of one or more physiological roles for zinc in modulating the balance between bone formation and resorption.

Relationship between abnormal sperm morphology induced by dietary zinc deficiency and lipid composition in testes of growing rats

The present study investigated the effect of dietary Zn deficiency during sexual maturation on sperm integrity and testis phospholipid fatty acid composition. Male weanling Sprague-Dawley rats were randomised into four dietary groups for 3 weeks: Zn control (ZC; 30 mg Zn/kg); Zn marginally deficient (ZMD; 9 mg Zn/kg); Zn deficient (ZD; < 1 mg Zn/kg); pair fed (PF; 30 mg Zn/kg) to the ZD group. Morphology of cauda epididymal sperm and lipid profiles of testis phospholipids were analysed. The rats fed the ZD diet had a lower testis weight (P < 0.02). Seminal vesicles and prostate weight were also lower in the ZD and PF groups. Rats fed the ZD diet, but not the ZMD diet, had 34-35 % more abnormal spermatozoa and 24 % shorter sperm tail length than the ZC and PF rats (P < 0.001). Testis cholesterol concentration was higher in the ZD rats compared with the ZC and PF rats (P < 0.04). Testes were highly enriched with n-6 fatty acids by showing n-6 : n-3 fatty acid ratios of 27:1 in phosphatidylcholine (PC) and 23:1 in phosphatidylethanolamine (PE). The dominant fatty acid in testes was docosapentaenoic acid (22 : 5n-6), comprising 15 and 24 % of PC and PE, respectively. This fatty acid was significantly lower in the ZD rats, whereas 18 : 2n-6 was higher compared with the rats in the other diet groups. These results demonstrate that severe Zn deficiency adversely affects sperm integrity and modulates testis fatty acid composition by interrupting essential fatty acid metabolism. This suggests that Zn deficiency-associated abnormal testicular function is perhaps preceded by altered membrane fatty acid composition, especially of a major fatty acid, 22 : 5n-6.

Burn-induced oxidative stress is altered by a low zinc status: kinetic study in burned rats fed a low zinc diet

As an initial subdeficient status of zinc, considered as an essential antioxidant trace element, is frequent in burned patients, we aim to assess the effects of low zinc dietary intakes on burn-induced oxidative stress, in an animal model. After 8 weeks of conditioning diets containing 80 ppm (control group) or 10 ppm of zinc (depleted group), Wistar rats were 20% TBSA burned and sampled 1-10 days after injury. Kinetic evolutions of zinc status, plasma oxidative stress parameters, and antioxidant enzymes were also studied in blood and organs. The zinc-depleted diet induced, before injury, a significant decrease in zinc bone level and the increase of oxidative stress markers without stimulation of antioxidant enzyme activity. After burn, more markedly in zinc depleted animals than in controls, zinc levels decreased in plasma and bone, while increasing in liver. The decrease of thiol groups and GSH/GSSG ratio and the depression of GPx activity in liver are also moderately emphasized. Nevertheless, depleted zinc status could not be considered as determining for oxidative damages after burn injury. Further investigations must also be done to enlighten the mechanism of beneficial effects of zinc supplementation reported in burned patients.

Consumption of a moderately Zn-deficient and Zn-supplemented diet affects soluble protein expression in rat soleus muscle

Zinc deficiency negatively affects muscle function, but there are limited biochemical data identifying the cause of this reduction in function. The objective of the present study was to identify soluble proteins in rat soleus muscle that were responsive to different levels of dietary zinc. Rats (n=21) were fed diets containing three concentrations of zinc: 5, 30 and 200 ppm for 42 days. There was no difference in body weights of the rats consuming the 5-ppm zinc diet compared to the rats consuming the 30- or 200-ppm zinc diets; however, bone zinc levels were significantly decreased in the 5-ppm dietary zinc group. Individual soluble protein fractions were isolated from these muscles and the samples were prepared for two-dimensional polyacrylamide gel electrophoresis. The expression levels of four proteins were significantly depressed by dietary Zn depletion and supplementation, S-glutathiolated carbonic anhydrase, myosin light polypeptide 3, heat shock protein 20 and heart fatty acid binding protein. This is the first report that indicates that both Zn depletion and supplementation result in protein expression profiles that may negatively affect skeletal muscle function. These results indicate that there are specific signaling pathways that require proper Zn nutriture for maintaining optimal muscle function and suggest that the consumption of pharmacologic doses of Zn may be detrimental to muscle function.

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.

IKKbeta inhibition protects against bone and cartilage destruction in a rat model of rheumatoid arthritis

OBJECTIVE

The IKK complex regulates NF-kappaB activation, an important pathway implicated in the rheumatoid arthritis (RA) disease process. This study was undertaken to assess the efficacy of N-(6-chloro-7-methoxy-9H-beta-carbolin-8-yl)-2-methylnicotinamide (ML120B), a potent and selective small molecule inhibitor of IKKbeta.

METHODS

Polyarthritis was induced in rats by injection of Freund's complete adjuvant into the hind footpad. ML120B was administered orally twice daily, either prophylactically or therapeutically. Paw volumes and body weights were measured every 2-3 days throughout the study. We assessed bone erosions by several methods: histologic evaluation, quantitative micro-computed tomography (micro-CT) imaging analysis, and measurement of type I collagen fragments in the serum. Quantitative polymerase chain reaction was used to evaluate expression of messenger RNA for genes related to inflammation and to bone and cartilage integrity.

RESULTS

Oral administration of ML120B inhibited paw swelling in a dose-dependent manner (median effective dosage 12 mg/kg twice daily) and offered significant protection against arthritis-induced weight loss as well as cartilage and bone erosion. We were able to directly demonstrate that NF-kappaB activity in arthritic joints was reduced after ML120B administration. Also, we observed that down-regulation of the NF-kappaB pathway via IKKbeta inhibition dampened the chronic inflammatory process associated with rat adjuvant-induced arthritis.

CONCLUSION

The results of the present study suggest that IKKbeta inhibition is an effective therapeutic approach to treat both the inflammation and the bone/cartilage destruction observed in RA. Methods for the determination of serum markers for bone and cartilage destruction, as well as micro-CT analysis, may aid in predicting and evaluating the therapeutic efficacy of IKKbeta inhibition therapy in humans.

Marginal Zinc Deficiency Exacerbates Bone Lead Accumulation and High Dietary Zinc Attenuates Lead Accumulation at the Expense of Bone Density in Growing Rats

Environmental lead exposure is associated with reduced bone growth and quality, which may predispose to osteoporosis. Zinc supplementation may reduce lead accumulation; however, effects on bone development have not been addressed. Our objective was to investigate the effects of marginal zinc (MZ) and supplemental zinc (SZ) intakes on bone lead deposition and skeletal development in lead-exposed rats. In a factorial design, weanling Sprague-Dawley rats were assigned to MZ (8 mg/kg diet); zinc-adequate control (CT; 30 mg/kg); zinc-adequate, diet-restricted (DR; 30 mg/kg); or SZ (300 mg/kg) groups, with and without lead acetate-containing drinking water (200 mg Pb/l) for 3 weeks. Excised femurs were analyzed for bone mineral density (BMD) by dual-energy x-ray absorptiometry, morphometry, and mineral content. MZ had higher femur lead and lower femur zinc concentrations and impaired skeletal growth and mineralization than CT. DR inhibited growth but did not result in higher femur lead concentrations than CT. SZ had higher femur zinc and lower femur lead concentrations than the other treatments. DR and SZ had impaired BMD versus CT and MZ. Lead also retarded skeletal growth and impaired BMD, but an interaction between lead and MZ was only found for femoral knee width, which was lower in MZ exposed to lead. In summary, while MZ deficiency exacerbated bone lead concentration, it generally did not intensify lead toxicity. SZ was protective against bone lead but was detrimental to BMD, suggesting that the optimal level of SZ to reduce lead absorption, while supporting growth and bone development, requires further investigation.

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.

A graded model of dietary zinc deficiency: effects on growth, insulin-like growth factor-I, and the glucose/insulin axis in weanling rats

OBJECTIVE

Severe zinc (Zn) deficiency inhibits growth, insulin storage and release. Mild or moderate Zn deficiency may also have profound physiological effects that are not outwardly evident. We examined the effects of graded levels of low Zn intake on growth, insulin-like growth factor-I (IGF-I) and glucose homeostasis in weanling rats.

METHODS

Weanling rats were fed ad libitum for 3 weeks with diets containing different Zn levels: very low Zn, low Zn or mildly low Zn; there was also a control group and an additional group was pair-fed to very low Zn rats. Growth and food intake were recorded. Serum Zn, IGF-I, IGF binding protein-3 (IGFBP-3), serum insulin and glucose, tissue Zn and jejunal sucrase activity were measured. Relative liver IGF-I and IGFBP-3 mRNA levels were quantified.

RESULTS

Serum and tissue Zn were significantly lower in rats fed very low Zn (compared with pair-fed animals and controls) and low Zn (compared with controls). Growth was significantly lower in rats fed very low Zn and pair-fed animals (compared with controls) and in those fed very low Zn (compared with pair-fed animals). Liver IGF-I and IGFBP-3 mRNA levels were higher in low Zn animals compared with controls. Serum IGF-1 and IGFBP-3 levels were not affected by diet. Serum glucose was significantly higher in rats fed very low Zn than in pair-fed animals (191 +/- 28 vs 99 +/- 5 mg/dL, respectively). Sucrase activity was lower in rats fed very low Zn than in pair-fed animals or controls and a linear relationship was observed between serum glucose and insulin (r = 0.65, P < 0.01) in pair-fed animals and controls but not in Zn-deficient groups.

CONCLUSION

Severe Zn deficiency was associated with hyperglycemia and relative hypoinsulinemia. Mild degrees of Zn deficiency also altered glucose metabolism, suggesting that Zn intake may be a sensitive regulator of glucose homeostasis.

Exogenous recombinant human growth hormone effects during suboptimal energy and zinc intake

Background

Energy and Zinc (Zn) deficiencies have been associated with nutritional related growth retardation as well as growth hormone (GH) resistance. In this study, the relationship between suboptimal energy and/or Zn intake and growth in rats and their response to immunoreactive exogenous recombinant human GH (GHi), was determined.

Results

Rats treated with GHi and fed ad-libitum energy and Zn (100/100) had increased IGFBP-3 (p < 0.05) as compared with NSS (215 ± 23 vs. 185 ± 17 ng/ml) along with similar body weight gain. Rats treated with GHi and fed suboptimal energy and full Zn (70/100) had significantly increased weight gain (109.0 ± 18.2 vs. 73.8 ± 11.0 g) and serum IGF-I levels (568 ± 90 vs. 420 ± 85 ng/ml), along with decreased total body water (TBW; 61.0 ± 1.6 vs. 65.7 ± 2.1%) as compared to NSS controls. However, body weight gain was reduced (p < 0.05) as compared with rats fed ad-libitum energy. Growth hormone treated rats fed only suboptimal Zn (100/70), had increased weight gain (217.5 ± 13.2 vs. 191.6 ± 17.9 g; p < 0.05) compared to those given NSS. These rats gained weight in similar amounts to those fed full Zn. Rats treated with GHi and fed both suboptimal energy and Zn (70/70) showed similar results to those fed suboptimal energy with appropriate Zn (70/100), along with significant increases in IGFBP-3 levels (322 ± 28 vs. 93 ± 28 ng/ml). All restricted rats had reduced 24-h EE (kcal/100 g BW) and physical activity index (oscillations/min/kg BW) and GHi did not overcome these effects.

Conclusion

These results suggest that GHi enhances weight gain in rats with suboptimal energy and Zn intake but does not modify energy expenditure or physical activity index. Suboptimal Zn intake did not exacerbate the reduced growth or decrease in energy expenditure observed with energy restriction.