Dietary protein deficiency induces osteoporosis in aged male rats

Refeeding partially reverses impaired fracture callus in undernourished rats

Background

Adequate nutritional intake plays a crucial role in maximizing skeletal acquisition. The specific effects of a general food restriction and refeeding on fracture healing are yet to be fully understood. The aim of this study was to assess the impact of general food restriction and refeeding on fracture repair.

Methods

Fifty-four male Wistar Hannover rats were randomly assigned into three groups: (1) Sham: Sham rats with femoral fracture; (2) FRes: Food-restricted rats with fracture, (3) Fres+Ref: Fres rats with refeeding. Following weaning, the FRes and Fres+Ref groups received 50% of the food amount provided to the Shams. In the sixth week of the experiment, all animals underwent a mid-right femur bone fracture, which was subsequently surgically stabilized. Following the fracture, the Fres+Ref group was refed, while the other groups maintained their pre-fracture diet. Bone calluses were analyzed on the fifth-day post-fracture by gene expression and on the sixth-week post-fracture using dual-energy X-ray absorptiometry, morphometry, histomorphometry, immunohistochemistry, computed microtomography, and torsion mechanical testing. Statistical significance was determined at a probability level of less than 0.05, and comparisons were made using the ANOVA test.

Results

Food restriction resulted in significant phenotypic changes in bone calluses when compared to sham rats characterized by deterioration in microstructure (i.e., BV, BV/TV, Tb.N, and Conn.D) reduced collagen deposition, bone mineral density, and mechanical strength (i.e., torque at failure, energy, and stiffness). Moreover, a higher rate of immature bone indicated a decrease in bone callus quality. Refeeding stimulated bone callus collagen formation, reduced local resorption, and effectively restored the microstructural (i.e., SMI, BCa.BV/TV, Tb.Sp, Tb.N, and Conn.D) and mechanical changes (i.e., torque at failure, energy, and angular displacement at failure) caused by food restriction. Despite these positive effects, the density of the bone callus, collagen deposition, and OPG expression remained lower when compared to the shams. Gene expression analysis didn't evidence any significant differences among the groups.

Conclusions

Food restriction had detrimental effects on osseous healing, which was partially improved by refeeding. Based on these findings, new research can be developed to create targeted nutritional strategies to treat and improve fracture healing.

Vitamin D and Albumin Deficiency in a Swiss Orthopaedic Surgery In-Patient Cohort

Background: Vitamin D and protein deficiencies are common conditions in the general population. In Orthopaedic surgery, they can result in wound complications or poor bone healing. The goal of this study was, therefore, to determine the prevalence of vitamin D and albumin deficiencies in patients scheduled for elective Orthopaedic procedures. Methods: We performed an observational, noninterventional study using the demographic characteristics via means chart analysis of in-patients with an elective surgery in a single Swiss Orthopaedic centre. The following variables were collected and analysed: age, gender, BMI, ASA score, rate of vitamin D supplementation before surgery, and serum preoperative levels of vitamin D, albumin, Haemoglobin, calcium, and phosphate. Results: A total of 336 patients were analysed; there were 218 women (64.9%) and 118 men (35.1%). The average age was 59.4 years (17-89 years). The average BMI was 26.8 kg/m2 (17.8-37.6) and the average ASA score was II (I-III). The overall prevalence of vitamin D deficiency was 82.1%, being more common in the male (89.8%) than female patients (77.9%). Patients who received vitamin D supplements before surgery had an average vitamin D level in the normal range. Of the subgroup of 170 patients who were over 60 years of age, 78.8% of the patients were Vitamin D deficient, with deficiency once again being more common in men (93.3%) than in women (92%). Albumin deficiency was documented in 58.9% of the cases. A total of 62.8% of all the female patients were albumin deficient, and 51.7% of all male patients were. Of the subgroup of 170 patients who were over 60 years of age, 71.8% of the patients were albumin deficient, with the deficiency being practically identical in men (71.1%) and women (72%). Conclusions: Despite increased awareness in the medical community, vitamin D and albumin deficiencies remain highly prevalent in elective Orthopaedic patients. Pre/perioperative screening and addressing possible vitamin D and albumin deficiencies are of great importance for good outcomes in Orthopaedic surgery.

The multi-faceted nature of age-associated osteoporosis

Age-associated osteoporosis (AAOP) poses a significant health burden, characterized by increased fracture risk due to declining bone mass and strength. Effective prevention and early treatment strategies are crucial to mitigate the disease burden and the associated healthcare costs. Current therapeutic approaches effectively target the individual contributing factors to AAOP. Nonetheless, the management of AAOP is complicated by the multitude of variables that affect its development. Main intrinsic and extrinsic factors contributing to AAOP risk are reviewed here, including mechanical unloading, nutrient deficiency, hormonal disbalance, disrupted metabolism, cognitive decline, inflammation and circadian disruption. Furthermore, it is discussed how these can be targeted for prevention and treatment. Although valuable as individual targets for intervention, the interconnectedness of these risk factors result in a unique etiology for every patient. Acknowledgement of the multifaceted nature of AAOP will enable the development of more effective and sustainable management strategies, based on a holistic, patient-centered approach.

Effect of milk fat globules on growth and metabolism in rats fed an unbalanced diet

We assessed the effects of supplementing milk fat globules (MFG) on the growth and development of the skeleton in rats fed a Western unbalanced diet (UBD). The UBD is high in sugar and fat, low in protein, fiber, and micronutrients, and negatively impacts health. The MFG-a complex lipid-protein assembly secreted into milk-has a unique structure and composition, which differs significantly from isolated and processed dietary ingredients. Rats consuming the UBD exhibited growth retardation and disrupted bone structural and mechanical parameters; these were improved by supplementation with small MFG. The addition of small MFG increased the efficiency of protein utilization for growth, and improved trabecular and cortical bone parameters. Furthermore, consumption of UBD led to a decreased concentration of saturated fatty acids and increased levels of polyunsaturated fatty acids (PUFA), particularly omega-6 PUFA, in the serum, liver, and adipose tissue. The addition of small MFG restored PUFA concentration and the ratio of omega-6 to omega-3 PUFA in bone marrow and adipose tissue. Finally, large but not small MFG supplementation affected the cecal microbiome in rats. Overall, our results suggest that natural structure MFG supplementation can improve metabolism and bone development in rats fed an UBD, with the effects depending on MFG size. Moreover, the benefits of small MFG to bone development and metabolism were not mediated by the microbiome, as the detrimental effects of an UBD on the microbiome were not mitigated by MFG supplementation.

Gains in relative cortical area during growth and their relationship to nutrition, body size, and physical activity

OBJECTIVES

In studies of growth in the past, low percentage of cortical area (%CA) is commonly attributed to poor general health, due to factors including poor nutrition, low socioeconomic status, or other physiological stressors. What constitutes low relative cortical dimensions has not been established across a diverse range of human skeletal samples. This study examines %CA in a large immature skeletal sample to establish typical variation in humans with consideration of both body mass and subsistence strategy.

MATERIALS AND METHODS

Percentage of cortical area was calculated at the midshaft of the humerus, femur, and tibia in seven skeletal samples. Age at death was estimated from dental development, and body mass from bone dimensions. Patterns of %CA with age and log-transformed body mass were examined in the pooled sample and compared among samples using LOESS regression, Welch's ANOVA, and Kruskal-Wallis tests.

RESULTS

Across all samples, %CA displays a generally non-linear pattern, but variation in %CA with age was high, particularly in samples with lower levels of %CA. There was no relationship between %CA and age-adjusted body mass.

DISCUSSION

The lack of a relationship between %CA and body mass suggests that %CA should not be used as an indicator of mechanical loading. The variation present across samples implies that appositional bone growth is affected by physiological stress in varying ways. Without a deeper understanding of what is "typical" for long bone development, it is impossible to draw conclusions about individual or population level health.

Reduced bone formation and increased bone resorption drive bone loss in Eimeria infected broilers

Coccidiosis is an economically significant disease in the global poultry industry, but little is known about the mechanisms of bone defects caused by coccidiosis; thus, the study focused on effects of coccidiosis on the bone homeostasis of young broiler chickens. A total of 480 male Cobb500 broilers were randomly allocated into four treatment groups, including an uninfected control consuming diet ad libitum, two infected groups were orally gavaged with two different concentrations of sporulated Eimeria oocysts, and an uninfected pair-fed group fed the same amount of feed as the high Eimeria-infected group consumed. Growth performance and feed intake were recorded, and samples were collected on 6 days post infection. Results indicated that coccidiosis increased systemic oxidative status and elevated immune response in bone marrow, suppressing bone growth rate (P < 0.05) and increasing bone resorption (P < 0.05) which led to lower bone mineral density (P < 0.05) and mineral content (P < 0.05) under Eimeria infection. With the same amount of feed intake, the uninfected pair-fed group showed a distinguished bone formation rate and bone resorption level compared with the Eimeria infected groups. In conclusion, inflammatory immune response and oxidative stress in broilers after Eimeria infection were closely associated with altered bone homeostasis, highlighting the role of inflammation and oxidative stress in broiler bone homeostasis during coccidiosis.

Omega-3 fatty acid and menaquinone-7 combination are helpful for aortic calcification prevention, reducing osteoclast area of bone and Fox0 expression of muscle in uremic rats

BACKGROUND

Osteopenia, sarcopenia, and vascular calcification (VC) are prevalent in patients with chronic kidney disease and often coexist. In the absence of proven therapies, it is necessary to develop therapeutic or preventive nutrients supplementation for osteopenia, sarcopenia, and VC. The present study investigated the effect of omega-3 fatty acid (FA) and menaquinone-7 (MK-7) on osteopenia, sarcopenia, and VC in adenine and low-protein diet-induced uremic rats.

METHODS

Thirty-two male Sprague-Dawley rats were fed diets containing 0.75% adenine and 2.5% protein for three weeks. Rats were randomly divided into four groups that were fed diets containing 2.5% protein for four weeks: adenine control (0.9% saline), omega-3 FA (300 mg/kg/day), MK-7 (50 µg/kg/day), and omega-3 FA/MK-7. Von Kossa staining for aortic calcification assessment was performed. Osteoclast surface/bone surface ratio (OcS/BS) of bone and muscle fiber were analyzed using hematoxylin and eosin staining. Osteoprotegerin (OPG) immunohistochemical staining was done in the aorta and bone. Molecules related with sarcopenia were analyzed using western blotting.

RESULTS

Compared to the normal control, OcS/BS and aortic calcification, and OPG staining in the aorta and bone were significantly increased in the adenine controls. OPG staining and aortic calcification progressed the least in the group supplemented with both omega-3 FA/MK-7. In the adenine controls, the regular arrangement of muscle fiber was severely disrupted, and inflammatory cell infiltration was more prominent. These findings were reduced after combined supplementation with omega-3 FA/MK-7. Furthermore, decreased mammalian target of rapamycin and increased Forkhead box protein 1 expression was significantly restored by combined supplementation.

CONCLUSIONS

Combined nutrients supplementation with omega-3 FA and MK-7 may be helpful for aortic VC prevention, reducing osteoclast activation and improving sarcopenia-related molecules in adenine and low-protein diet induced uremic rats.

The Role of Diet in Bone and Mineral Metabolism and Secondary Hyperparathyroidism

Bone disorders are a common complication of chronic kidney disease (CKD), obesity and gut malabsorption. Secondary hyperparathyroidism (SHPT) is defined as an appropriate increase in parathyroid hormone (PTH) secretion, driven by either reduced serum calcium or increased phosphate concentrations, due to an underlying condition. The available evidence on the effects of dietary advice on secondary hyperparathyroidism confirms the benefit of a diet characterized by decreased phosphate intake, avoiding low calcium and vitamin D consumption (recommended intakes 1000-1200 mg/day and 400-800 UI/day, respectively). In addition, low protein intake in CKD patients is associated with a better control of SHPT risk factors, although its strength in avoiding hyperphosphatemia and the resulting outcomes are debated, mostly for dialyzed patients. Ultimately, a consensus on the effect of dietary acid loads in the prevention of SHPT is still lacking. In conclusion, a reasonable approach for reducing the risk for secondary hyperparathyroidism is to individualize dietary manipulation based on existing risk factors and concomitant medical conditions. More studies are needed to evaluate long-term outcomes of a balanced diet on the management and prevention of secondary hyperparathyroidism in at-risk patients at.

Effect of a high crude protein content diet during energy restriction and re-alimentation on animal performance, skeletal growth and metabolism of bone tissue in two genotypes of cattle

The objective of this study was to investigate the effect of diet crude protein (CP) content and metabolisable energy (ME) intake on skeletal growth and associated parameters of growing steers prior to and during compensatory growth in weight and catch-up growth in skeletal elongation. The experiment was a factorial design with two cattle genotypes [Brahman crossbred (BX, 178 ± 6 kg) and Holstein-Friesian (HF, 230 ± 34 kg)] and three nutritional treatments; high CP content and high ME intake (HCP-HME), high CP content and low ME intake (HCP-LME) and low CP content and low ME intake (LCP-LME) with the ME intake of HCP-LME matched to that of LCP-LME. Nutritional treatments were imposed over a 103 d period (Phase 1), and after this, all steers were offered ad libitum access to the HCP-HME nutritional treatment for 100 d (Phase 2). Steers fed the high CP content treatment with a low ME intake, showed higher hip height gain (P = 0.04), larger terminal hypertrophic chondrocytes (P = 0.02) and a higher concentration of total triiodothyronine in plasma (P = 0.01) than steers with the same ME intake of the low CP content treatment. In addition, the low CP treatment resulted in significant decreases in bone volume (P = 0.03), bone surface area (P = 0.03) and the concentration of bone-specific alkaline phosphatase in plasma (P < 0.001) compared to steers fed the HCP-HME treatment. A significant interaction between genotype and nutritional treatment existed for the concentration of thyroxine (T4) in plasma where HF steers fed LCP-LME had a lower T4 concentration in plasma (P = 0.05) than BX steers. All steers with a restricted ME intake during Phase 1 demonstrated compensatory growth during Phase 2. However, HF steers fed the LCP treatment during Phase 1 showed a tendency (P = 0.07) for a greater LWG during Phase 2 without any increase in dry matter intake. Results observed at the growth plate and hip height growth suggest that catch-up growth in cattle may also be explained by the growth plate senescence hypothesis. Contrary to our initial hypothesis, the results demonstrate that greater CP intake during ME restriction does not increase compensatory gain in cattle during re-alimentation.

Association of normalized protein catabolic rate (nPCR) with the risk of bone fracture in patients undergoing maintenance hemodialysis: The Q-Cohort Study

BACKGROUND & AIMS

Normalized protein catabolic rate (nPCR) is used as a surrogate for daily dietary protein intake and nutritional status in patients receiving maintenance hemodialysis. It remains uncertain whether the nPCR level is associated with the incidence of bone fracture.

METHODS

A total of 2869 hemodialysis patients registered in the Q-Cohort Study, a multicenter, prospective, observational study, were followed up for 4 years. The primary outcome was bone fracture at any site. The main exposure was the nPCR level at baseline. Patients were assigned to four groups based on their baseline nPCR levels (G1: <0.85, G2: 0.85≤, <0.95, G3: 0.95≤, <1.05 [reference], G4: ≥1.05 g/kg/day). We examined the relationship between the nPCR levels and the risk for bone fracture using Cox proportional hazards models.

RESULTS

During the follow-up period, 136 patients experienced bone fracture at any site. In the multivariable analyses, the risk for bone fracture was significantly higher in the lowest (G1) and highest (G4) nPCR groups than the reference (G3) group (hazard ratio [95% confidence intervals]: G1, 1.93 [1.04-3.58]; G2, 1.27 [0.67-2.40]; G3 1.00 (reference); G4, 2.21 [1.25-3.92]). The association remained almost unchanged, even when patients were divided into sex-specific nPCR quartiles, when analysis was limited to patients with a dialysis vintage ≥2 years, assumed to have lost residual kidney function, or when a competing risk model was applied.

CONCLUSIONS

Our results suggest that both lower and higher nPCR levels are associated with an increased risk for bone fracture in hemodialysis patients.

FGF21, not GCN2, influences bone morphology due to dietary protein restrictions

BACKGROUND

Dietary protein restriction is emerging as an alternative approach to treat obesity and glucose intolerance because it markedly increases plasma fibroblast growth factor 21 (FGF21) concentrations. Similarly, dietary restriction of methionine is known to mimic metabolic effects of energy and protein restriction with FGF21 as a required mechanism. However, dietary protein has been shown to be required for normal bone growth, though there is conflicting evidence as to the influence of dietary protein restriction on bone remodeling. The purpose of the current study was to evaluate the effect of dietary protein and methionine restriction on bone in lean and obese mice, and clarify whether FGF21 and general control nonderepressible 2 (GCN2) kinase, that are part of a novel endocrine pathway implicated in the detection of protein restriction, influence the effect of dietary protein restriction on bone.

METHODS

Adult wild-type (WT) or Fgf21 KO mice were fed a normal protein (18 kcal%; CON) or low protein (4 kcal%; LP) diet for 2 or 27 weeks. In addition, adult WT or Gcn2 KO mice were fed a CON or LP diet for 27 weeks. Young New Zealand obese (NZO) mice were placed on high-fat diets that provided protein at control (16 kcal%; CON), low levels (4 kcal%) in a high-carbohydrate (LP/HC) or high-fat (LP/HF) regimen, or on high-fat diets (protein, 16 kcal%) that provided methionine at control (0.86%; CON-MR) or low levels (0.17%; MR) for up to 9 weeks. Long bones from the hind limbs of these mice were collected and evaluated with micro-computed tomography (μCT) for changes in trabecular and cortical architecture and mass.

RESULTS

In WT mice the 27-week LP diet significantly reduced cortical bone, and this effect was enhanced by deletion of Fgf21 but not Gcn2. This decrease in bone did not appear after 2 weeks on the LP diet. In addition, Fgf21 KO mice had significantly less bone than their WT counterparts. In obese NZO mice dietary protein and methionine restriction altered bone architecture. The changes were mediated by FGF21 due to methionine restriction in the presence of cystine, which did not increase plasma FGF21 levels and did not affect bone architecture.

CONCLUSIONS

This study provides direct evidence of a reduction in bone following long-term dietary protein restriction in a mouse model, effects that appear to be mediated by FGF21.

Role of osteoclasts in oral homeostasis and jawbone diseases

The jawbone is a unique structure as it serves multiple functions in mastication. Given the fact that the jawbone is remodeled faster than other skeletal bones, bone cells in the jawbone may respond differently to local and systemic cues to regulate bone remodeling and adaptation. Osteoclasts are bone cells responsible for removing old bone, playing an essential role in bone remodeling. Although bone resorption by osteoclasts is required for dental tissue development, homeostasis and repair, excessive osteoclast activity is associated with oral skeletal diseases such as periodontitis. In addition, antiresorptive medications used to prevent bone homeostasis of tumors can cause osteonecrosis of the jaws that is a major concern to the dentist. Therefore, understanding of the role of osteoclasts in oral homeostasis under physiological and pathological conditions leads to better targeted therapeutic options for skeletal diseases to maintain patients' oral health. Here, we highlight the unique features of the jawbone compared to the long bone and the involvement of osteoclasts in the jawbone-specific diseases.

Increased Consumption of Plant Foods Is Associated with Increased Bone Mineral Density

OBJECTIVES

To determine the relationship between plant food consumption and bone mineral density (BMD) in a healthy population when age, gender, BMI and physical activity are accounted for.

DESIGN

Cross-sectional study.

SETTING

Participants were recruited from the Sydney Adventist hospital and the University of New South Wales, Sydney, Australia.

PARTICIPANTS

33 males and 40 females (total n=73) participated in this study. The mean age was 56.1 ± 8.5 years. All participants were non-diabetic and in general good health.

MEASUREMENTS

A principle component analysis (PCA) was performed on 12 month self-report food intake data, gathered using the Cancer Council Victoria Dietary Questionnaire for Epidemiological Studies Version 2. Dual-energy X-ray absorptiometry was used to measure total BMD. Fasting plasma total protein, calcium and 25-Hydroxy Vitamin D levels were analysed by the Sydney Adventist Hospital pathology laboratory. Anthropometric measures were obtained using a standardized protocol. Self-reported physical activity levels were assessed using the International Physical Activity Questionnaire.

RESULTS

The PCA revealed three principle components. These were termed 'Meat Based', 'Junk Food' and 'Plant Based.' After controlling for age, gender, physical activity and BMI, the Plant Based component correlated positively with BMD (p=0.054, R2=0.439) and T-score (p=0.053, R2=0.221). Using a similar model no association between the Meat Based component and BMD or T-score was found. However, when the Plant Based component was included the Meat Based component correlated positively with BMD (p=0.046, R2=0.474) and T-score (p=0.046, R2=0.279). There was no significant association between the Junk Food component and BMD or T-score. People in the third Plant (927 ± 339 vs 751 ± 255 g/day, p=0.025) and Meat Based (921 ± 270 vs 676 ± 241 g/day, p=0.002) tertile had higher calcium intakes than those in the first. People in the second Plant Based tertile had higher plasma Vitamin D levels than those in the first (63.5 ± 16.8 vs. 52.3 ± 22.1 nmol/L, p=0.053) while those in the third Junk Food tertile had lower levels than those in the first (52.4 ± 18.5 vs. 65.4 ± 19.8 nmol/L, p=0.027). No association between Plant Based tertiles and protein intake was observed, however those in the third Meat Based (99.7 ± 25.1 vs. 50.9 ± 13.8 g/day, p=0.000) and Junk Food (87.4 ± 30.7 vs. 56.6 ± 22.2 g/day, p=0.000) tertile had higher protein intake compared to those in the first tertile.

CONCLUSION

In a healthy middle aged population with normal BMD, an increase in plant food consumption, either alone or in combination with a diet containing meat, is associated with improved bone mineralisation markers. This positive relationship is most likely due to the extensive range of micronutrients and phytochemicals packaged within plants.

Egr1/p300/ACE signal mediates postnatal osteopenia in female rat offspring induced by prenatal ethanol exposure

Prenatal ethanol exposure induces developmental toxicities of multiple organs in offspring. Here, we investigate the effects of prenatal ethanol exposure on bone mass in postnatal offspring and explore its intrauterine programming mechanism. We found that prenatal ethanol exposure could induce bone dysplasia in fetuses and postnatal osteopenia in female offspring, accompanied by the sustained activation of the local renin-angiotensin systems (RAS) and inhibition of bone formation. Additionally, we also found that histone 3 lysine 9 acetylation (H3K9ac) and H3K27ac levels in the promoter region of angiotensin-converting enzyme (ACE) were increased in female offspring exposed to ethanol during pregnancy. In vitro, ethanol suppressed the formation of mineralized nodules and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), which was blocked by enalapril. Furthermore, ethanol promoted the expression and nuclear translocation of early growth response factor 1 (Egr1), which participated in the promotion of histone acetylation of ACE and subsequent RAS activation, by recruiting p300 and binding to the ACE promoter region directly. These findings indicate that the sustained activation of the local RAS might participate in bone dysplasia in fetus and postnatal osteopenia in the female offspring, while the Egr1/p300/ACE signal might be a key promoter of the sustained activation of the local RAS of the long bone.

Bone callus formation is highly disrupted by dietary restriction in growing rats sustaining a femoral fracture1

PURPOSE

To evaluate the effects of food restriction on fracture healing in growing rats.

METHODS

Sixty-eight male Wistar rats were assigned to two groups: (1) Control and (2) Dietary restriction. After weaning the dietary restricted animals were fed ad libitum for 42 days with 50% of the standard chow ingested by the control group. Subsequently, the animals underwent bone fracture at the diaphysis of the right femur, followed by surgical stabilization of bone fragments. On days 14 and 28 post-fracture, the rats were euthanized, and the fractured femurs were dissected, the callus was analyzed by dual-energy X-ray absorptiometry, micro-computed tomography, histomorphometry, mechanical tests, and gene expression.

RESULTS

Dietary restriction decreased body mass gain and resulted in several phenotypic changes at the bone callus (a delay in cell proliferation and differentiation, lower rate of newly formed bone and collagen deposition, reductions in bone callus density and size, decrease in tridimensional callus volume, deterioration in microstructure, and reduction in bone callus strength), together with the downregulated expression of osteoblast-related genes.

CONCLUSION

Dietary restriction had detrimental effects on osseous healing, with a healing delay and a lower quality of bone callus formation.

Effects of combined menaquinone-4 and PTH1-34 treatment on osetogenesis and angiogenesis in calvarial defect in osteopenic rats

PURPOSE

The aim of this study was to evaluate the effect of combining human parathyroid hormone (1-34) (PTH_1-34; PTH) and menaquinone-4 (MK-4) on calvarial bone defect repair in osteopenic rats.

METHODS

Fourteen week olds were subject to craniotomy for the establishment of osteopenic animal models fed through a chronically low-protein diet. After that, critical calvarial defect model was established and all rats were randomly divided into four groups: sham, MK-4, PTH, and PTH + MK-4. The animals received MK-4 (30 mg/kg/day), PTH_1-34 (60 μg/kg, three times a week), or PTH_1-34 (60 μg/kg, three times a week) plus MK-4 (30 mg/kg/day) for 8 weeks, respectively. Serum γ-carboxylated osteocalcin (Gla-OC) levels, histological and immunofluorescent labeling were employed to evaluate the bone formation and mineralization in calvarial bone defect. In addition, Microfil perfusion, immunohistochemical, and micro-CT suggested enhanced angiogenesis and bone formation in calvarial bone healing.

RESULTS

In this study, treatment with either PTH_1-34 or MK-4 promoted bone formation and vascular formation in calvarial bone defects compared with the sham group. In addition, combined treatment of PTH_1-34 plus MK-4 increased serum level of Gla-OC, improved vascular number and vascular density, and enhanced bone formation in calvarial bone defect in osteopenic conditions as compared with monotherapy.

CONCLUSIONS

In summary, this study indicated that PTH_1-34 plus MK-4 combination therapy accelerated bone formation and angiogenesis in calvarial bone defects in presence of osteopenia.

Smaller long bone cross-sectional size in people who died of tuberculosis: Insights on frailty factors from a 19th and early 20th century Finnish population

There is little research on how individuals suffering from tuberculosis may differ from those not infected in terms of overall skeletal morphology. Tuberculosis was endemic in 19th and early 20th century Finland making documented skeletal collections of Finns ideal to study effects of the disease on bone. The present study compares long bone cross-sectional total area between individuals who died of tuberculosis and those with another recorded cause of death in a Finnish sample. Adult male individuals (N = 105) were selected for analysis. Complete humeri (N = 56), femora (N = 66) and tibiae (N = 64) were 3D scanned using a laser scanner and total cross-sectional areas calculated with AsciiSection software. Individuals who died of tuberculosis (N = 24, 15 humeri, 14 femora, 13 tibiae) had, when standardized for body size, significantly smaller total cross-sectional femoral and humeral, but not tibial, areas. The mechanisms behind the observed relationship may reflect a combination of biological 'frailty' in terms of susceptibility to infection, reduced childhood activity and/or vitamin D deficiency, which possibly influenced both subperiosteal development during adolescence and, later, susceptibility to contracting and dying of TB. Due to the relatively small sample future studies are needed to further investigate the relationship between TB and bone cross-sectional size.

The relationship between protein quantity, BMD and fractures in older adults

BACKGROUND

Previously, no large-scale literature reviews have focussed on the relationship between dietary protein and its impact on bone mineral density (BMD) and fracture risk-as measures of bone health-in older adults and its potential impact as a primary prevention tool.

AIMS

The aim of this study was to assess the impact of varying dietary protein levels on bone health.

METHODS

A literature review of trials concerning older adults' (>50 years of age) and animals' varying protein intake in the diet and its effect on BMD (human and animal) and fracture risk (human only) was carried out. Additionally, a review of dietary assessment tools used in these studies was also analysed.

RESULTS

Ten out of fourteen trials assessing BMD and dietary protein quantity in humans and 3/4 in animal trials found a positive relationship between these two parameters. Four out of seven trials investigating the relationship between dietary protein quantity and fracture risk displayed a positive, protective effect of dietary protein levels on fracture risk. Sixty-two percent of studies used the Food-Frequency Questionnaire assessment method.

DISCUSSION

Increased protein intake in the diet is beneficial to bone health and reduces morbidity and mortality. The importance of using dietary protein, along with calcium and vitamin D, as a primary preventative strategy should be stressed, given the health and cost benefits that this would deliver, with a possible need for a higher level of protein in the diet of an elderly person than what is currently recommended.

Whey Protein Supplementation and Higher Total Protein Intake Do Not Influence Bone Quantity in Overweight and Obese Adults Following a 36-Week Exercise and Diet Intervention

BACKGROUND

Controversy exists concerning the effects of higher total protein intake (TPro) on bone health, which may be associated with reduced bone mineral density (BMD). However, whey protein (WP) may induce bone formation because of its basic component, milk basic protein.

OBJECTIVE

This study assessed the effects of WP supplementation, TPro, and change in TPro (postsupplementation - presupplementation) on BMD and bone mineral content (BMC; total body, lumbar spine, total femur, and femoral neck) in overweight and class I obese middle-aged adults following an exercise intervention.

METHODS

This analysis used data from a double-blind, randomized, placebo-controlled 36-wk WP supplementation trial, wherein participants consumed a 1.7-MJ (400-kcal) supplement (0, 20, 40, or 60 g WP/d) along with their otherwise unrestricted diet while participating in a resistance and aerobic exercise intervention (3 d/wk). TPro was the summation of WP and habitual dietary intakes (4-d food record). Statistical analyses for WP were based on group and bone data [n = 186, 108 women; mean ± SD age: 49 ± 8 y; body mass index (BMI; in kg/m²): 30.1 ± 2.8], whereas TPro was based on dietary and bone data (n = 113, 70 women; age 50 ± 8 y; BMI 30.1 ± 2.9).

RESULTS

WP supplementation, regardless of dose, did not influence BMD or BMC following the intervention. By using a multiple linear regression model, TPro (expressed as g/d or g · kg^-1 · d^-1) and change in TPro (expressed as g/d) were not associated with responses over time in total or regional BMD or BMC. By using a cluster analysis approach [<1.0 (n = 41), 1.0-1.2 (n = 28), and ≥1.2 g · kg^-1 · d^-1 (n = 44)], TPro was also not associated with responses in total or regional BMD or BMC over time.

CONCLUSION

WP supplementation and total dietary protein intake did not negatively or beneficially influence bone quantity in overweight and obese adults during a 9-mo exercise intervention. This trial was registered at clinicaltrials.gov as NCT00812409.

Nonproliferative and Proliferative Lesions of the Rat and Mouse Skeletal Tissues (Bones, Joints, and Teeth)

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) Project (www.toxpath.org/inhand.asp) is an initiative of the Societies of Toxicological Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in the skeletal tissues and teeth of laboratory rats and mice, with color photomicrographs illustrating examples of many common lesions. The standardized nomenclature presented in this document is also available on the internet (http://www.goreni.org/). Sources of material were databases from government, academic and industrial laboratories throughout the world.

The effects of combined human parathyroid hormone (1-34) and simvastatin treatment on the interface of hydroxyapatite-coated titanium rods implanted into osteopenic rats femurs

The effect of human parathyroid hormone 1-34 (PTH) and simvastatin (SIM) alone could promote bone healing in osteoporotic implant fixation, but there are no reports about the combined use of PTH and SIM for promotion of bone healing around implant in osteoporotic settings. This study aims to investigate effects of PTH + SIM on implant stabilization in osteopenic rats. Fourteen weeks after chronically fed a low protein diet, osteopenic rats randomly received implants. Subsequently, the animals were randomly divided into four groups: Control, SIM, PTH and PTH + SIM. Then all rats from groups PTH, SIM and PTH + SIM received PTH (40 μg/kg, three times a week), SIM (25 mg/kg, daily), or both for 12 weeks. The results of our study indicated that all treatments promoted bone healing around implant compared to Control, but PTH + SIM treatment showed significantly stronger effects than PTH or SIM alone in histological, micro-CT, and biomechanical tests. The results indicated additive effects of PTH and SIM on implant fixation in osteoporotic rats.

Dietary restrictions, bone density, and bone quality

Caloric restriction (CR), protein restriction (PR), and specific amino acid restriction (e.g., methionine restriction (MR)) are different dietary interventions that have been confirmed with regard to their comprehensive benefits to metabolism and health. Based on bone densitometric measurements, weight loss induced by dietary restriction is known to be accompanied by reduced areal bone mineral density, bone mass, and/or bone size, and it is considered harmful to bone health. However, because of technological advancements in bone densitometric instruments (e.g., high-resolution X-ray tomography), dietary restrictions have been found to cause a reduction in bone mass/size rather than volumetric bone mineral density. Furthermore, when considering bone quality, bone health consists of diverse indices that cannot be fully represented by densitometric measurements alone. Indeed, there is evidence that moderate dietary restrictions do not impair intrinsic bone material properties, despite the reduction in whole-bone strength because of a smaller bone size. In the present review, we integrate research evidence from traditional densitometric measurements, metabolic status assays (e.g., energy metabolism, oxidative stresses, and inflammatory responses), and biomaterial analyses to provide revised conclusions regarding the effects of CR, PR, and MR on the skeleton.

Methionine restriction alters bone morphology and affects osteoblast differentiation

Methionine restriction (MR) extends the lifespan of a wide variety of species, including rodents, drosophila, nematodes, and yeasts. MR has also been demonstrated to affect the overall growth of mice and rats. The objective of this study was to evaluate the effect of MR on bone structure in young and aged male and female C57BL/6J mice. This study indicated that MR affected the growth rates of males and young females, but not aged females. MR reduced volumetric bone mass density (vBMD) and bone mineral content (BMC), while bone microarchitecture parameters were decreased in males and young females, but not in aged females compared to control-fed (CF) mice. However, when adjusted for bodyweight, the effect of MR in reducing vBMD, BMC and microarchitecture measurements was either attenuated or reversed suggesting that the smaller bones in MR mice is appropriate for its body size. In addition, CF and MR mice had similar intrinsic strength properties as measured by nanoindentation. Plasma biomarkers suggested that the low bone mass in MR mice could be due to increased collagen degradation, which may be influenced by leptin, IGF-1, adiponectin and FGF21 hormone levels. Mouse preosteoblast cell line cultured under low sulfur amino acid growth media attenuated gene expression levels of Col1al, Runx2, Bglap, Alpl and Spp1 suggesting delayed collagen formation and bone differentiation. Collectively, our studies revealed that MR altered bone morphology which could be mediated by delays in osteoblast differentiation.

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MR affected the growth rates of males and young females, but not aged females.

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CF and MR mice had similar intrinsic strength properties.

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Low methionine media attenuated bone differentiation genes in MC3T3-E1 preosteoblast cells.

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The lower bone mass in MR mice is appropriate for its smaller body size.

Treatment study of distal femur for parathyroid hormone (1-34) and β-tricalcium phosphate on bone formation in critical-sized defects in osteopenic rats

The objective of this study was to evaluate the effect of following combined treatment with parathyroid hormone (1-34) (PTH) and β-tricalcium phosphate (β-TCP) on local bone formation in a rat 3-mm critical-sized defect at the distal femur. Fourteen weeks were allowed to pass before defect surgery for the establishment of osteopenic animal models chronically fed a low-protein diet. All animals were randomly divided into four groups: group PTH; group β-TCP, group PTH + β-TCP, and a control group. All rats then underwent a surgical procedure to create bone defects in the bilateral distal femurs, and β-TCP was implanted into critical-sized defects for the groups designated as β-TCP and group PTH + β-TCP. After the defect operation, all animals from group PTH and group PTH + β-TCP received following subcutaneous injections with PTH (60 μg/kg, three times per week) until euthanasia at 4 and 8 weeks. The distal femurs and blood were collected for evaluation. The results of study showed the strongest effect on accelerating the local bone formation with treatment β-TCP and PTH at 4 weeks and 8 weeks. The results from our study demonstrate that a combination of PTH and β-TCP had an additive effect on local bone formation in osteopenic rats chronically fed a low-protein diet.

Protein malnutrition attenuates bone anabolic response to PTH in female rats

PTH is indicated for the treatment of severe osteoporosis. Elderly osteoporotic patients frequently suffer from protein malnutrition, which may contribute to bone loss. It is unknown whether this malnutrition may affect the response to PTH. Therefore, the aim of the present study was to assess whether an isocaloric low-protein (LP) diet may influence the bone anabolic response to intermittent PTH in 6-month-old female rats. Six-month-old female rats were either pair fed an isocaloric LP diet (2.5% casein) or a normal-protein (NP) diet (15% casein) for 2 weeks. The rats continued on their respective diet while being treated with 5- or 40-μg/kg recombinant human PTH amino-terminal fragment 1-34 (PTH-[1-34]) daily, or with vehicle for 4 weeks. At the end of this period, areal bone mineral density, bone mineral content, microstructure, and bone strength in axial compression of proximal tibia or 3-point bending for midshaft tibia tests were measured. Blood was collected for the determination of IGF-I and osteocalcin. After 4 weeks of PTH-(1-34), the dose-dependent increase of proximal tibia bone mineral density, trabecular microstructure variables, and bone strength was attenuated in rats fed a LP diet as compared with rats on a NP intake. At the level of midshaft tibia cortical bone, PTH-(1-34) exerted an anabolic effect only in the NP but not in the LP diet group. Protein malnutrition was associated with lower IGF-I levels. Protein malnutrition attenuates the bone anabolic effects of PTH-(1-34) in rats. These results suggest that a sufficient protein intake should be recommended for osteoporotic patients undergoing PTH therapy.

Clinical and histological evaluation of postextraction platelet-rich fibrin socket filling: a prospective randomized controlled study

OBJECTIVES

The aims were to investigate whether the use of platelet-rich fibrin membranes (PRF) for socket filling could improve microarchitecture and intrinsic bone tissue quality of the alveolar bone after premolar extraction and to assess the influence of the surgical procedure before implant placement.

MATERIAL AND METHODS

Twenty-three patients requiring premolar extraction followed by implant placement were randomized to three groups: (1) simple extraction and socket filling with PRF, (2) extraction with mucosal flap and socket filling with PRF, and (3) controls with simple extraction without socket filling. Implant placement was performed at week 8, and a bone biopsy was obtained for histomorphometric analysis.

RESULTS

Analysis by microcomputed tomography showed better bone healing with improvement of the microarchitecture (P < 0.05) in group 1. This treatment had also a significant effect (P < 0.05) on intrinsic bone tissue quality and preservation of the alveolar width. An invasive surgical procedure with a mucosal flap appeared to completely neutralize the advantages of the PRF.

CONCLUSIONS

These results support the use of a minimally traumatic procedure for tooth extraction and socket filling with PRF to achieve preservation of hard tissue.

A Low Protein Diet Alters Bone Material Level Properties and the Response toIn VitroRepeated Mechanical Loading

Low protein intake is associated with an alteration of bone microstructure and material level properties. However, it remains unknown whether these alterations of bone tissue could influence the response to repeated mechanical loading. The authors investigated the in vitro effect of repeated loading on bone strength in humeri collected from 20 6-month-old female rats pair-fed with a control (15% casein) or an isocaloric low protein (2.5% casein) diet for 10 weeks. Bone specimens were cyclically loaded in three-point bending under load control for 2000 cycles. Humeri were then monotonically loaded to failure. The load-displacement curve of the in vitro cyclically loaded humerus was compared to the contralateral noncyclically loaded humerus and the influence of both protein diets. Material level properties were also evaluated through a nanoindentation test. Cyclic loading decreased postyield load and plastic deflection in rats fed a low protein diet, but not in those on a regular diet. Bone material level properties were altered in rats fed a low protein diet. This suggests that bone biomechanical alterations consequent to cyclic loading are more likely to occur in rats fed a low protein diet than in control animals subjected to the same in vitro cyclic loading regimen.

Species-specific responses of N homeostasis and electrolyte handling to low N intake: a comparative physiological approach in a monogastric and a ruminant species

In our former studies low crude protein (LCP) intake influenced N homeostasis and electrolyte handling in goats. We hypothesised that due to rumino-hepatic nitrogen (N) recycling adaptation of N homeostasis and adjustment of electrolyte handling to LCP intake differs between goats and monogastric animals. Therefore, an experiment similar to that with goats was conducted with rats. Two feeding groups received a diet either containing 20 or 8 % crude protein (as fed basis) for 5 weeks and intake and excretion of N, calcium (Ca) and phosphorus (P) were determined. To detect systemic and endocrine adaptation to LCP intake plasma concentrations of urea, Ca, phosphate (Pi), insulin-like growth factor 1 (IGF-1), 1,25-dihydroxyvitamin D3 (calcitriol), parathyroid hormone (PTH) and cross-linked telopeptide of type I collagen (CTX) were measured. Adjustment of renal electrolyte transport was assessed by detecting protein expression of key proteins of renal Pi transport. All data were compared with the data of the goat experiment. LCP intake decreased plasma urea concentration stronger in goats than in rats. In both species urinary N excretion declined, but faecal N excretion decreased in goats only. Furthermore, in goats urinary Ca excretion decreased, but in rats urinary Ca concentration increased. Decreased plasma IGF-1 and calcitriol concentrations were found in goats only. Thus, renal Ca excretion appears to be a common target in adaptation of electrolyte homeostasis in both species, but is regulated differently.

Mechanical testing at the whole-bone level of the femur in immature rats stunted by cornstarch consumption

Both body weight and somatic muscle forces are the main "mechanical factors" in the determination of bone strength in the "weight-bearing bones". However, other "non-mechanical factors", such as dietary proteins, also exist, which modulate bone physiology. This study was designed to explore the mechanical behavior of the femur in post-weaning female rats stunted by feeding on cornstarch. Forty female rats aged 30 days were fed freely with one of the two diets: control (CD) and experimental (ED). CD was the standard rat laboratory diet, whereas ED was cornstarch supplemented with vitamins and minerals. Control (C) and experimental (E) animals were divided into 4 groups: C40 and E40 rats were given CD and ED, respectively, for 40 days; C105 were fed the CD for 105 days; and E40-105 were given the ED for 40 days and then the CD for the remaining experimental period (65 days). Growth of rats was assessed following Parks' model. The biomechanical structural properties of the right femur middiaphysis were estimated using a 3-point bending test. The geometric properties of both the entire bone and the cross-section were determined. The left femur was ashed and both the Ca mass and the Ca concentration were determined. Rats fed the ED failed to achieve normal weight gain. Complete catch-up was observed at the end of a 65 day period of nutritional rehabilitation. The femoral weight and length were negatively affected by the ED, as were the mid-diaphyseal cross-sectional area, the mineralized cortical area, and the cross-sectional moment of inertia. All of these parameters showed incomplete catch-up. The structural bone mechanical properties indicative of strength and stiffness were seriously negatively affected. Intrinsic material bone properties, as assessed by the modulus of elasticity and the maximal elastic stress, were within normal values. In summary, the experimental bone was weaker than the control and structurally incompetent. The considered bone was smaller than the control one, showing a significant reduction in the cross-sectional area and the moment of inertia. However, material properties as well as the ash fraction and Ca concentration were similar in E and C bones. Therefore, E bone is weaker than the C one because of its smaller bone mass, which appears to have been negatively influenced by the ED in relation to its effects on overall body mass.

Low protein intake magnifies detrimental effects of ovariectomy and vitamin D on bone

Protein-induced changes in bone and calcium homeostasis could potentially be greater in the elderly and in women at risk for osteoporosis. We hypothesize that a low protein intake would magnify the negative changes in bone metabolism seen in vitamin D (vitD) insufficiency and/or estrogen deficiency. The present study was undertaken to better understand how a low protein diet along with vitD insufficiency could affect bone metabolism using a rodent ovariectomized (OVX) model. Rats (n = 60) underwent ovariectomy (OVX) or sham operation. The first 15 days after surgery, all rats were fed a standard rodent diet. Thereafter, rats (n = 10/group) were fed a low protein diet (LP; 2.5 %) or a control diet (NP; 12.5 %) with 100 IU% vitD (+D; cholecalciferol) or without vitD (-D) for 45 days. The groups were as follows: SHAM + NP + D (control); SHAM + LP + D; SHAM + LP - D; OVX + NP + D; OVX + LP + D; OVX + LP - D. Body weight (BW) of control and OVX + NP + D groups increased while those feeding the LP diet, independently of vitD feedings, decreased (p < 0.05). The OVX + LP - D group presented the lowest serum Ca, phosphorus and osteocalcin levels and the highest CTX levels (p < 0.05). At the end of the study, total skeleton bone mineral content, proximal tibia bone mineral density, bone volume and trabecular number levels decreased as follows: SHAM + NP + D (controls) > SHAM + LP + D > OVX + NP + D > SHAM + LP - D > OVX + LP + D > OVX + LP - D (p < 0.05). A low protein diet negatively affected bone mass and magnified the detrimental effects of vitD and/or estrogen deficiencies.

Dietary protein in relation to bone stiffness index and fat-free mass in a population consuming relatively low protein diets

Dietary protein has a mixed effect on skeletal health and the effect may differ by amount or source of protein. The purpose of this study was to investigate dietary protein in relation to bone density and fat-free mass in rural Korean residents consuming relatively low protein diets. Between 2008 and 2010, 3,330 participants were recruited for a baseline examination of a community-based study in Kangwha. Of those, 1,182 men and 1,393 postmenopausal women were eligible for the present study. Diet was assessed using a food-frequency questionnaire developed for Korean adults. Calcaneal bone density measured by ultrasound was expressed as the stiffness index (SI). Fat-free mass index (FFMI) was defined as fat-free mass in kilograms divided by the height in meters squared. The mean ages of men and women were 59.5 and 60.0 years, respectively. The median daily intakes of total and meat protein were 52.3 and 6.7 g in men and 45.0 and 3.0 g in women, respectively. After controlling for potential confounders, SI and FFMI showed an increasing trend with a higher meat protein intake in men (P for trend = 0.017 and 0.033, respectively), but not in women. No positive association was observed for other food sources of protein. In conclusion, our findings suggest that meat protein contributes to skeletal health in men consuming relatively low protein diets.

Chronic hyponatremia exacerbates multiple manifestations of senescence in male rats

The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is frequently responsible for chronic hyponatremia in the elderly due to age-related disruption of the inhibitory component of brain osmoregulatory mechanisms. Recent research has indicated that chronic hyponatremia is associated with gait disturbances, increased falls, and bone fragility in humans, and we have found that chronic hyponatremia causes increased bone resorption and reduced bone mineral density in young rats. In this study, we used a model of SIADH to study multi-organ consequences of chronic hyponatremia in aged rats. Sustained hyponatremia for 18 weeks caused progressive reduction of bone mineral density by DXA and decreased bone ash calcium, phosphate and sodium contents at the tibia and lumbar vertebrae. Administration of 10-fold higher vitamin D during the last 8 weeks of the study compensated for the reduction in bone formation and halted bone loss. Hyponatremic rats developed hypogonadism, as indicated by slightly lower serum testosterone and higher serum FSH and LH concentrations, markedly decreased testicular weight, and abnormal testicular histology. Aged hyponatremic rats also manifested decreased body fat, skeletal muscle sarcopenia by densitometry, and cardiomyopathy manifested as increased heart weight and perivascular and interstitial fibrosis by histology. These findings are consistent with recent results in cultured osteoclastic cells, indicating that low extracellular sodium concentrations increased oxidative stress, thereby potentially exacerbating multiple manifestations of senescence. Future prospective studies in patients with SIADH may indicate whether these multi-organ age-related comorbidities may potentially contribute to the observed increased incidence of fractures and mortality in this population.

Protein intake, calcium balance and health consequences

High-protein (HP) diets exert a hypercalciuric effect at constant levels of calcium intake, even though the effect may depend on the nature of the dietary protein. Lower urinary pH is also consistently observed for subjects consuming HP diets. The combination of these two effects was suspected to be associated with a dietary environment favorable for demineralization of the skeleton. However, increased calcium excretion due to HP diet does not seem to be linked to impaired calcium balance. In contrast, some data indicate that HP intakes induce an increase of intestinal calcium absorption. Moreover, no clinical data support the hypothesis of a detrimental effect of HP diet on bone health, except in a context of inadequate calcium supply. In addition, HP intake promotes bone growth and retards bone loss and low-protein diet is associated with higher risk of hip fractures. The increase of acid and calcium excretion due to HP diet is also accused of constituting a favorable environment for kidney stones and renal diseases. However, in healthy subjects, no damaging effect of HP diets on kidney has been found in either observational or interventional studies and it seems that HP diets might be deleterious only in patients with preexisting metabolic renal dysfunction. Thus, HP diet does not seem to lead to calcium bone loss, and the role of protein seems to be complex and probably dependent on other dietary factors and the presence of other nutrients in the diet.

Selective osteoblast overexpression of IGF-I in mice prevents low protein-induced deterioration of bone strength and material level properties

Protein deficiency is frequently observed in elderly osteoporotic patients. Undernutrition leads to decreased levels of IGF-I, an important factor in regulating bone homeostasis throughout life. IGF-I is produced in the liver and locally in the skeleton. We hypothesized that increasing IGF-I expression in the osteoblasts, the bone forming cells, would protect the skeleton from the negative effects of a low-protein diet. To test our hypothesis, we employed a mouse model in which IGF-I was overexpressed exclusively in osteoblasts and fed either a 15% (normal) or a 2.5% (low) protein isocaloric diet to the transgenic (TG) mice and their wild-type (WT) littermates for 8 weeks. Blood was collected for biochemical determinations and weight was monitored weekly. Bones were excised for microstructural analysis (μCT), as well as biomechanical and material level properties. Histomorphometric analysis was performed for bone formation parameters. A low protein diet decreased body weight, circulating IGF-I and osteocalcin levels regardless of genotype. Overexpression of IGF-I in the osteoblasts was, however, able to protect the negative effects of low protein diet on microstructure including tibia cortical thickness and volumetric density, and on bone strength. Overexpression of IGF-I in osteoblasts in these mice protected the vertebrae from the substantial negative effects of low protein on the material level properties as measured my nanoindentation. TG mice also had larger overall geometric properties than WT mice regardless of diet. This study provides evidence that while a low protein diet leads to decreased circulating IGF-I, altered microstructure and decreased bone strength, these negative effects can be prevented with IGF-I overexpression exclusively in bone cells.

Calcitropic hormones and IGF-I are influenced by dietary protein

Elderly men and women with protein deficiencies have low levels of circulating IGF-I, and it is likely this contributes to reduced bone formation and increased bone resorption. We hypothesized that calcitropic hormones are involved in this effect and are affected by dietary protein. We therefore investigated the influence of a low-protein diet on the PTH-1,25-dihydroxyvitamin D3 [1,25(OH)₂D₃] axis and IGF-I in rats, using pamidronate to block resorption that normally contributes to mineral homeostasis. We fed 6-month-old Sprague Dawley female rats isocaloric diets containing 2.5% or 15% casein for 2 wk. Pamidronate was then administered sc (0.6 mg/kg/) for 5 d. Blood samples were collected at different time points. Serum 1,25(OH)₂D₃, IGF-I, PTH, calcium, and phosphorus were determined in all rats; vertebral bone strength and histomorphometric analysis were performed in rats subject to the longest low-protein diets. We found 2 wk of low protein increased PTH levels, decreased 1,25(OH)₂D₃, calcium, and IGF-I, suggesting that increased PTH compensates for low-protein-induced decreases in 1,25(OH)₂D₃. Pamidronate augmented the increased PTH after 8 wk of low protein and prevented the 1,25(OH)₂D₃ decrease. IGF-I remained low. Protein malnutrition induced decreases in relative bone volume and trabecular thickness, which was prevented by pamidronate. Maximal load was reduced by protein restriction, but rescued by pamidronate. In summary, the low protein diet resulted in hyperparathyroidism, a reduction in circulating levels of IGF-I, and reduced 1,25(OH)₂D₃ despite hyperparathyroidism. Blocking resorption resulted in further increases in PTH and improved microarchitecture and biomechanical properties, irrespective of vitamin D status or protein intake.

Prognosis of osteopenia in chronic alcoholics

Osteoporosis is frequent among alcoholics all by a direct effect of ethanol, malnutrition, and liver failure. Therefore, it may be related to survival. The aim of this study was to assess bone mineral density (BMD), bone mineral content, hormonal status, and to determine prognostic value of these parameters in a total of 124 alcoholics followed up for a median period of 57 months. Several bone homeostasis-related hormones were measured in patients and age- and sex-matched controls. Whole-body densitometry was performed by a Hologic QDR-2000 (Waltham, MA) densitometer; nutritional status and liver function were assessed. Sixty patients underwent a second evaluation 6 months later. Patients showed lower serum insulin-like growth factor-1 (median=58, interquartile range [IQR]=33-135 vs. 135ng/mL, IQR=116-243ng/mL, P<.001), vitamin D (25.5, IQR=18.3-36.8 vs. 79.9pg/mL, IQR=59.2-107.8pg/mL, P<.001), and osteocalcin (2.1, IQR=1.1-4.5 vs. 6.5ng/mL, IQR=4.7-8.7ng/mL, P<.001) than controls, and lower BMD values, and lower Z- and T-scores at right and left legs and arms, thoracic and lumbar spine, pelvis, and right and left ribs. By multiple regression analysis, BMD mainly depends on nutritional parameters and liver function. Kaplan-Meier curves show that subtotal BMD and BMD at both arms and pelvis were significantly related with survival. Patients who had lost total hip BMD after 6 months showed a shorter survival than those who had not, but using Cox's regression, encephalopathy, ascites, and nutritional parameters displaced BMD as prognostic factor. Therefore, osteopenia ensues in chronic alcoholic patients. It mainly depends on poor nutrition and is related to survival, although surpassed in this sense by encephalopathy, ascites, and nutritional parameters.

Extrinsic mechanisms involved in age-related defective bone formation

CONTEXT

Age-related bone loss is associated with progressive changes in bone remodeling characterized by decreased bone formation relative to bone resorption. Both trabecular and periosteal bone formation decline with age in both sexes, which contributes to bone fragility and increased risk of fractures. Studies in rodents and humans revealed that, independent of sex hormone deficiency, the age-related decline in bone formation is characterized by decreased osteoblast number and lifespan and reduced bone-forming capacity of individual osteoblasts. An important clinical question is to identify the mechanisms involved in the age-related defective bone formation.

EVIDENCE ACQUISITION

The mechanisms discussed in this review are based on a PubMed search and knowledge of the authors in the field.

EVIDENCE SYNTHESIS

Available basic and clinical studies indicate that multiple mechanisms are involved in the alterations of osteoblastogenesis and the resulting decline in bone formation with aging. Notably, the age-related osteoblast dysfunctions and defective bone formation are caused by a number of extrinsic clinical factors that inhibit anabolic signaling pathways in bone. Thus, targeting these pathways can abolish age-related bone loss.

CONCLUSIONS

The identification of extrinsic mechanisms involved in osteoblast dysfunctions associated with aging improves our knowledge of age-related bone loss and provides a basis for therapeutic intervention to improve bone formation and bone mass in the aging population.

Protein deficiency and nematode infection during pregnancy and lactation reduce maternal bone mineralization and neonatal linear growth in mice

Using a 2 x 2 factorial design, we investigated the combined impact of protein deficiency (PD) and gastrointestinal nematode infection during late pregnancy and lactation on resting metabolic rate (RMR), body composition and bone mineralization, neonatal growth, and the regulatory hormones [corticosterone, leptin, and insulin-like growth factor-1 (IGF-1)] and proinflammatory cytokines [interleukin (IL)-1 beta and IL-6] that may drive these processes. Pregnant CD1 mice, fed either a protein-sufficient (PS; 24%) or protein-deficient (PD; 6%) isocaloric diet, were infected 4 times with either 0 (sham) or 100 Heligmosomoides bakeri larvae beginning on d 14 of pregnancy. Dams were killed on d 20 postpartum and pups on d 2, 7, 14, and 21. Diet and infection had largely independent effects. The PD diet elevated corticosterone and upregulated leptin concentration in maternal serum, which was associated with reduced food intake leading to lower body mass, RMR, and body temperature. Infection reduced food intake but elevated maternal serum IL-1 beta and IL-6 and did not affect corticosterone, leptin, RMR, or body temperature. The PD diet decreased maternal bone area and bone mineral content. Infection lowered maternal bone mineral density, consistent with elevated IL-1 beta and IL-6. The elevated serum IL-1 beta and lower IGF-1 in pups of PD dams and lower serum leptin and IGF-1 in pups of infected dams were both consistent with the lower pup body mass and shorter crown-rump length. This mouse model provides a novel framework to study the impact of diet and nematode infection on bone.

PTH improves titanium implant fixation more than pamidronate or renutrition in osteopenic rats chronically fed a low protein diet

SUMMARY

We evaluated the effects of parathyroid hormone (PTH), pamidronate, or renutrition on osseointegration of titanium implants in the proximal tibia of rats subject to prolonged low-protein diets. PTH improved mechanical fixation, microarchitecture, and increased pull-out strength. Pamidronate or renutrition had lesser effects. PTH can thus improve implant osseointegration in protein-malnourished rats.

INTRODUCTION

Protein malnutrition impairs implant osseointegration in rats. PTH and pamidronate prevent deleterious effects of protein restriction introduced just prior to implantation. Whether these treatments improve osseointegration after chronic protein deprivation, i.e., in osteopenic bone at time of implantation, is unknown. We evaluated effects of PTH, pamidronate, or renutrition on resistance to pull-out of titanium rods implanted into the rat tibiae following isocaloric low-protein intake.

METHODS

Forty-one adult female rats received normal or isocaloric low-protein diets. Six weeks later, implants were surgically inserted into proximal tibiae. Following implantation, rats on low-protein diets were treated with PTH (1-34), pamidronate, saline vehicle, or normal protein diets, for another 8 weeks. Tibiae were removed for micro-computerised tomographic morphometry and evaluation of pull-out strength.

RESULTS

Pull-out strength decreased in rats on isocaloric low-protein diets compared with normal protein group (-33.4%). PTH increased pull-out strength in low-protein group, even compared to controls from the normal protein group. PTH and pamidronate increased bone volume/tissue volume, bone-to-implant contact, and trabecular thickness, whilst trabecular separation was reduced, with a shift to more plate-like bone surrounding the implants.

CONCLUSIONS

PTH reversed the deleterious effects of long-term protein undernutrition on mechanical fixation and bone microarchitecture and improved implant osseointegration more than pamidronate or renutrition, likely through changes to structure model index.

Administration of growth hormone in selectively protein-deprived rats decreases BMD and bone strength

INTRODUCTION

Isocaloric protein undernutrition is associated with decreased bone mass and decreased bone strength, together with lower IGF-I levels. It remains unclear whether administration of growth hormone (GH) corrects these alterations in bone metabolism.

MATERIALS AND METHODS

Six-month-old female rats were fed isocaloric diets containing either 2.5% or 15% casein for 2 weeks. Bovine growth hormone (bGH, 0.5 or 2.5mg/kg of body weight) or vehicle was then administered as subcutaneous injections, twice daily, to rats on either diet for 4 weeks. At the proximal tibia, analysis of bone mineral density (BMD), maximal load and histomorphometry were performed. In addition, urinary deoxypyridinoline, plasma osteocalcin and IGF-I concentrations were measured. Weight was monitored weekly.

RESULTS

bGH caused a dose-dependent increase in plasma IGF-I regardless of the dietary protein content. However, bGH dose-dependently decreased BMD and bone strength in rats fed the low-protein diet. There was no significant effect of bGH on BMD in rats fed the normal protein diet within this short-term treatment period, however bone formation as detected by histomorphometry was improved in this group but not the low-protein group. Osteoclast surface was increased in the low-protein bGH-treated animals only. Changes in bone turnover markers were detectable under both normal and low-protein diets.

CONCLUSION

These results emphasize the major importance of dietary protein intake in the bone response to short-term GH administration, and highlight the need for further investigation into the effects of GH treatment in patients with reduced protein intake.

Quality of diet and potential renal acid load as risk factors for reduced bone density in elderly women

BACKGROUND

Bone mineral density (BMD) may be influenced by the general dietary pattern and the potential renal acid load (PRAL).

METHODS

We compared the dietary intake (estimated using the European Prospective Investigation into Cancer and nutrition questionnaire) of 497 community-living women (60 years of age and older) grouped according to tertiles of baseline total, trabecular and cortical BMD estimated using tibial peripheral quantitative computed tomography (pQCT), and of BMD variation over 6 years.

RESULTS

None of the nutrients taken into account nor PRAL was associated with total BMD, with the exception that the intake of polyunsaturated fatty acids (PUFA) was slightly higher among women with the highest total BMD. Similar results were found for trabecular BMD. Cortical BMD was associated with serum 25-OH vitamin D (38.8, 43.2, and 49.5 nmol/L in the first, second, and third tertiles, respectively; P=0.042). In the longitudinal analysis, a lower BMI was associated with greater loss of total BMD, while lower serum 25-OH vitamin D at baseline was associated with smaller loss of cortical BMD.

CONCLUSIONS

We found no relationship between dietary acid load and BMD. We also confirmed the role of well-recognized risk factor for osteoporosis.

Osteopenia in alcoholics: effect of alcohol abstinence

AIMS

The aims of this study were to assess bone mineral density (BMD) and content (BMC), osteocalcin, serum telopeptide, PTH and vitamin D in alcoholics, and to determine if a 6-month period of abstinence leads to changes in these parameters.

METHODS

Serum osteocalcin, insulin-like growth factor 1 (IGF-1), telopeptide (40 patients) and 1,25 dihydroxyvitamin D, were measured in 28 controls and 77 alcoholic patients, 48 of whom were evaluated again 6 months later. All patients underwent whole-body assessment of BMD by a Hologic QDR-2000 (Waltham, MA, USA) bone densitometer, at the beginning of the study and 6 months later.

RESULTS

Patients showed higher serum telopeptide levels (0.59 +/- 0.40 versus 0.19 +/- 0.10 nmol/100 ml, P < 0.001), lower IGF-1 [median = 49, interquartile range (IQR) = 31-121 ng/ml versus 135, IQR = 116-237 ng/ml, P < 0.001], vitamin D [26.5, IQR = 17.0-37.8 pg/ml versus 82.4 (IQR = 60.9-107.4 pg/ml, P < 0.001] and osteocalcin (2.1, IQR = 1.1-3.6 ng/ml versus 6.65, IQR = 4.9-8.8 ng/ml, P < 0.001) than those in controls. Patients also showed lower BMD values, Z- and T-scores at many levels of the skeleton and reduced total BMC. After 6 months, those who continued drinking showed a loss of bone mass, whereas those who abstained showed either no change or increase, differences being especially marked at pelvis, right arm and total BMD and BMC. Simultaneously, abstainers showed a significant increase in osteocalcin (versus a decrease among those who continued drinking). Serum telopeptide increased in both groups.

CONCLUSION

Ethanol consumption leads to osteopenia, and decreased serum osteocalcin, which improve with abstinence, whereas those who continue drinking show a worsening of both parameters.

Zinc increases the effects of essential amino acids-whey protein supplements in frail elderly

Protein undernutrition is frequent in the elderly. It contributes to the development of osteoporosis, possibly via lower IGF-I. Dietary zinc can influence IGF-I production.

OBJECTIVES

To determine the influence of dietary zinc addition on IGF-I and bone turnover responses to essential amino acids-whey (EAA-W) protein supplements in frail elderly.

DESIGN AND SETTING

A daily oral protein supplement was given to hospitalized patients for 4 weeks. On a randomized, double-blind basis, patients received either an additional 30 mg/day of zinc or control.

PARTICIPANTS

Sixty-one hospitalized elderly aged 66.7 to 105.8, with a mini-nutritional assessment score between 17 and 24 were enrolled.

MEASUREMENTS

Activities of daily living; dietary intakes; serum IGF-I, IGF-BP3, CrossLapsTM, osteocalcin and zinc were measured before and after 1, 2 and 4 weeks of protein supplementation.

RESULTS

Serum IGF-I rapidly increased in both groups. Zinc accelerated this increase with changes of +48.2 +/- 14.3 and +22.4 +/- 4.7% (p < .05) by 1 week, in the zinc-supplemented and control groups, respectively. Zinc significantly decreased the serum bone resorption marker CrossLapsTM by already 1 week. Activities of daily living improved by +27.0 +/- 3.1 and +18.3 +/- 4.5% in zinc-supplemented and control groups, respectively.

CONCLUSION

In the elderly, zinc supplementation accelerated the serum IGF-I response to EAA-W protein by 1 week and decreased a biochemical marker of bone resorption.

Impaired energetic metabolism after central leptin signaling leads to massive appendicular bone loss in hindlimb-suspended rats

We previously showed in rats that the leptin effects on bone were dose dependent. Positive effects were observed when serum leptin concentration was in a physiological range. In contrast, important increases in serum leptin levels led to negative effects on bone formation similar to those reported after intracerebroventricular leptin administration in mice. To clarify whether leptin effects on bone depend on administration route and/or animal model, female rats were hindlimb unloaded or not and treated either with intracerebroventricular infusion of leptin or vehicle for 14 days. By increasing cerebrospinal fluid (CSF) leptin concentration, intracerebroventricular infusion of leptin significantly reduced food intake and consequently body weight, abdominal fat, and lean mass of the animals. Leptin infusion inhibited bone elongation over the 14 days and blunted cortical bone thickening at the femoral diaphysis site. Interestingly, leptin effects were site dependent in the cancellous bone envelopes, because tibia metaphysis BMD was lower and lumbar spine BMD was higher under intracerebroventricular leptin. Treated groups showed reduced bone remodeling independently of hindlimb unloading. Multiple downstream pathways were implicated in the mediation of these negative leptin effects on bone including not only stimulation of the sympathetic nervous system but also a decrease in somatotropic axis activity. Therefore, the intracerebroventricular leptin-induced bone loss could be largely related to the concurrent alteration of energetic and metabolic status. In summary, our study supports the hypothesis of a concentration-dependent balance between peripheral and central control of leptin on bone.

Nutrition: its role in bone health

At a given age, bone mass is determined by the amount of bone accumulated at the end of skeletal growth (the so-called peak bone mass), and by the amount of bone lost subsequently. Nutritional intake is an environmental factor that influences both bone capital accumulation, which is fully achieved by the end of the second decade of life, and bone loss, which occurs during the second half of existence. Nutrients may act directly by modifying bone turnover, or indirectly via changes in calciotropic hormone secretion. The study of the association between nutrition and a bone phenotypic expression may provide inconsistent results, in part because of the low accuracy and reproducibility of the various tools used to assess dietary intakes. Sufficient dietary calcium and protein are necessary for bone health during growth as well as in the elderly.