Amino acids as signaling molecules modulating bone turnover

Expression of the aryl hydrocarbon receptor in Osterix-lineage cells regulates adult skeletal homeostasis in a compartment-specific manner

Kynurenine (KYN), a tryptophan metabolite that increases with age, impairs osteoblast function. The aryl hydrocarbon receptor (AhR) has been proposed to mediate KYN's actions in bone. To test whether deletion of AhR in osteoblasts is beneficial for bone, we established an adult-onset AhR conditional knockout (CKO) model using Osx-Cre and examined the effects of AhR CKO at 4.5 and 6 mo of age (representing ~6 and 12 wk of CKO). While BMSC-derived osteoblasts from WT mice demonstrated reduced matrix formation from KYN treatment, AhR CKO osteoblasts were unaffected by KYN. Kynurenine's harmful effects were most pronounced in the middle of an osteoblastic differentiation time course, and these effects could be rescued via the AhR antagonist BAY2416964. In vivo, AhR deletion in Osx-expressing cells promoted sex- and compartment-specific skeletal phenotypes. Trabecular bone was increased in the distal femur of male and female AhR CKO mice at both 4.5 and 6 mo of age, potentially driven by a net decrease in the ratio of trabecular osteoclasts to osteoblasts despite a reduction in mineral apposition rate at 6 mo of age. In contrast, cortical bone phenotypes induced by AhR deletion depended on age and sex. In males, cortical bone volume fraction (Ct.BV/TV) was elevated in AhR CKO mice vs WT littermates at 4.5 mo of age, but differences resolved by 6 mo of age. In contrast, cortical bone was reduced in female AhR CKO as compared to WT littermates at 6 mo of age. These results underscore the complexity of AhR signaling in skeletal biology that must be considered while exploring AhR as a therapeutic target for conditions like osteoporosis and musculoskeletal frailty. Future studies will be needed to test the effects of osteoblastic AhR deletion at advanced ages, when the endogenous AhR ligand KYN is elevated in the circulation and skeletal niche.

Plasma levels of amino acids and osteoporosis: a cross-sectional study

The role of amino acids (AAs) with bone health is still controversial. We examined the association between AAs and osteoporosis in a cross-sectional study of 135 participants aged 45 years or older from the Second Hospital of Jilin University. Plasma AAs were measured with targeted quantitative methodology. We measured bone mineral density (BMD) with dual energy x-ray absorptiometry, and osteoporosis was defined as a T-score ≤ -2.5. We estimated odds ratios (OR) and corresponding 95% confidence intervals (CIs) for the associations between AAs (per 1 standard deviation increase) with osteoporosis. Approximately 18.5% of participants (n = 25) had osteoporosis. Total (adjusted β = 0.052; P = 0.002) and non-essential AA (adjusted β = 0.064; P = 0.002) levels were associated with femoral neck BMD T-scores. Greater levels of total (adjusted OR: 0.734; 95% CI: 0.655-0.821), essential (adjusted OR: 0.763; 95% CI: 0.623-0.934) and non-essential AAs (adjusted OR: 0.721; 95% CI: 0.629-0.826) were associated with lower odds of osteoporosis. Higher tryptophan (adjusted OR: 0.498; 95% CI: 0.281-0.882), cysteine (adjusted OR: 0.561; 95% CI: 0.321-0.983), glycine (adjusted OR: 0.513; 95% CI: 0.285-0.922), and ornithine levels (adjusted OR: 0.581; 95% CI: 0.345-0.978) were associated with reduced osteoporosis risk. Higher AA levels were associated with higher femoral neck BMD, and lower odds of osteoporosis.

Causal inference study of plasma proteins and blood metabolites mediating the effect of obesity-related indicators on osteoporosis

Background

Osteoporosis and obesity are both major global public health problems. Observational studies have found that osteoporosis might be related to obesity. Mendelian randomization (MR) analysis could overcome the limitations of observational studies in assessing causal relationships.

Objective

This study aims to evaluate the causal potential relationship between obesity-related indicators and osteoporosis by using a two-sample MR analysis and to identify potential mediators.

Method

A total of 53 obesity-related indicators, 3,282 plasma protein lists, and 452 blood metabolite lists were downloaded from the public data set as instrumental variables, and the osteoporosis GWAS data of the MRC IEU Open GWAS database was used as the outcome indicators. Using two-sample univariate MR, multivariate MR, and intermediate MR, the causal relationship and mediating factors between obesity-related indicators and osteoporosis were identified.

Results

The IVW model results show that 31 obesity-related indicators may have a significant causal relationship with osteoporosis (P < 0.05), except for waist circumference (id: Ieu-a-71, OR = 1.00566); the remaining 30 indicators could reduce the risk of osteoporosis (OR: 0.983-0.996). A total of 25 plasma protein indicators may have a significant causal relationship with osteoporosis (P < 0.05), and 10 of them, such as ANKED46, KLRF1, and LPO, CA9 may have a protective effect on osteoporosis (OR: 0.996-0.999), while the other 15 such as ATP1B1, zinc finger protein 175, could increase the risk of osteoporosis (OR: 1.001-1.004). For blood metabolite indicators, except for alanine (id: Met a-469, OR: 1.071), the other six blood metabolite indicators including uridine and 1-linoleoylglycerophosphoethanolaminecan may have a protective effect on osteoporosis (P < 0.05, OR: 0.961-0.992). The direction of causal relationship of MR is all correct; the heterogeneity is all not significant and not affected by horizontal pleiotropy. Using multivariate and mediated MR analysis, it was found that the protective effect of obesity-related indicators against osteoporosis may be mediated by histone-lysine N-methyltransferase in plasma proteins and alanine in blood metabolites.

Conclusion

Obesity may confer a protective effect against osteoporosis, potentially mediated by EHMT2 in plasma proteins and alanine in blood metabolites. Further empirical research is required to fully elucidate the mechanisms behind the influence of obesity on osteoporosis. Interventions on obesity-related factors to reduce the risk of osteoporosis while controlling other adverse effects associated with obesity may require further research.

Tissue-specific and spatially dependent metabolic signatures perturbed by injury in skeletally mature male and female mice

Joint injury is a risk factor for post-traumatic osteoarthritis. However, metabolic and microarchitectural changes within the joint post-injury in both sexes remain unexplored. This study identified tissue-specific and spatially-dependent metabolic signatures in male and female mice using matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) and LC-MS metabolomics. Male and female C57Bl/6J mice were subjected to non-invasive joint injury. Eight days post-injury, serum, synovial fluid, and whole joints were collected for metabolomics. Analyses compared between injured, contralateral, and naïve mice, revealing local and systemic responses. Data indicate sex influences metabolic profiles across all tissues, particularly amino acid, purine, and pyrimidine metabolism. MALDI-MSI generated 2D ion images of bone, the joint interface, and bone marrow, highlighting increased lipid species in injured limbs, suggesting physiological changes across injured joints at metabolic and spatial levels. Together, these findings reveal significant metabolic changes after injury, with notable sex differences.

Nutrition and Bone Marrow Adiposity in Relation to Bone Health

Bone remodeling is energetically demanding process. Energy coming from nutrients present in the diet contributes to function of different cell type including osteoblasts, osteocytes and osteoclasts in bone marrow participating in bone homeostasis. With aging, obesity and osteoporosis the function of key building blocks, bone marrow stromal cells (BMSCs), changes towards higher accumulation of bone marrow adipose tissue (BMAT) and decreased bone mass, which is affected by diet and sex dimorphism. Men and women have unique nutritional needs based on physiological and hormonal changes across the life span. However, the exact molecular mechanisms behind these pathophysiological conditions in bone are not well-known. In this review, we focus on bone and BMAT physiology in men and women and how this approach has been taken by animal studies. Furthermore, we discuss the different diet interventions and impact on bone and BMAT in respect to sex differences. We also discuss the future perspective on precision nutrition with a consideration of sex-based differences which could bring better understanding of the diet intervention in bone health and weight management.

Association of serum levels of phenylalanine and tyrosine with hip fractures and frailty in older adults: The cardiovascular health study

This study examined if the amino acids phenylalanine or tyrosine contribute to risk of hip fracture or frailty in older adults. We determined that neither phenylalanine nor tyrosine are important predictors of hip fracture or frailty. We suggest advice on protein intake for skeletal health consider specific amino acid composition.

PURPOSE

Protein is essential for skeletal health, but the specific amino acid compositions of protein may have differential associations with fracture risk. The aim of this study was to determine the association of serum levels of the aromatic amino acids phenylalanine and tyrosine with risk for incident hip fractures over twelve years of follow-up and cross sectional associations with frailty.

METHODS

We included 131 older men and women from the Cardiovascular Health Study (CHS) who sustained a hip fracture over twelve years of follow-up and 131 men and women without an incident hip fracture over this same period of time. 42% of this cohort were men and 95% were Caucasian. Weighted multivariable Cox hazards molecules were used to estimate the hazard ratios (HR) and 95% confidence intervals (CI) of incident hip fracture associated with a one standard deviation (SD) higher serum level of phenylalanine or tyrosine. Relative risk regression was used to determine the cross-sectional association of these amino acids with Freid's frailty index.

RESULTS

Neither serum levels of phenylalanine (HR 0.85 (95% CI 0.62-1.16) or tyrosine (HR 0.82 (95% CI 0.62-1.1) were significantly associated with incident hip fractures or cross sectionally with frailty (frail compared with prefrail/not frail) (HR 0.92 (95% CI 0.48-1.76) and HR (0.86 (95% CI 0.46-1.61) respectively.

CONCLUSION

Phenylalanine and tyrosine are not significant contributors to hip fractures or frailty in older men and women.

3D stem cell spheroids with urchin-like hydroxyapatite microparticles enhance osteogenesis of stem cells

Cell therapy (also known as cell transplantation) has been considered promising as a next-generation living-cell therapy strategy to surpass the effects of traditional drugs. However, their practical clinical uses and product conversion are hampered by the unsatisfied viability and efficacy of the transplanted cells. Herein, we propose a synergistic enhancement strategy to address these issues by constructing 3D stem cell spheroids integrated with urchin-like hydroxyapatite microparticles (uHA). Specifically, cell-sized uHA microparticles were synthesized via a simple hydrothermal method using glutamic acid (Glu, E) as the co-template with good biocompatibility and structural antimicrobial performance (denoted as E-uHA). Combining with a hanging drop method, stem cell spheroids integrated with E-uHA were successfully obtained by culturing bone marrow mesenchymal stem cells (BMSCs) with a low concentration of the E-uHA suspensions (10 μg mL-1). The resulting composite spheroids of BMSCs/E-uHA deliver a high cellular viability, migration activity, and a superior osteogenic property compared to the 2D cultured counterpart or other BMSC spheroids. This work provides an effective strategy for integrating a secondary bio-functional component into stem cell spheroids for designing more cell therapy options with boosted cellular viability and therapeutic effect.

Effects of partial replacement of red and processed meat with non-soya legumes on bone and mineral metabolism and amino acid intakes in BeanMan randomised clinical trial

The transition towards more plant-based diets may pose risks for bone health such as low vitamin D and Ca intakes. Findings for the contribution of animal and plant proteins and their amino acids (AA) to bone health are contradictory. This 6-week clinical trial aimed to investigate whether partial replacement of red and processed meat (RPM) with non-soya legumes affects AA intakes and bone turnover and mineral metabolism in 102 healthy 20-65-year-old men. Participants were randomly assigned to diet groups controlled for RPM and legume intake (designed total protein intake (TPI) 18 E%): the meat group consumed 760 g RPM per week (25 % TPI) and the legume group consumed non-soya legume-based products (20 % TPI) and 200 g RPM per week, the upper limit of the Planetary Health Diet (5 % TPI). No differences in bone (bone-specific alkaline phosphatase; tartrate-resistant acid phosphatase 5b) or mineral metabolism (25-hydroxyvitamin D; parathyroid hormone; fibroblast growth factor 23; phosphate and Ca) markers or Ca and vitamin D intakes were observed between the groups (P > 0·05). Methionine and histidine intakes were higher in the meat group (P ≤ 0·042), whereas the legume group had higher intakes of arginine, asparagine and phenylalanine (P ≤ 0·013). Mean essential AA intakes in both groups met the requirements. Increasing the proportion of non-soya legumes by reducing the amount of RPM in the diet for 6 weeks did not compromise bone turnover and provided on average adequate amounts of AA in healthy men, indicating that this ecologically sustainable dietary change is safe and relatively easy to implement.

Microplastics - Back to Reality: Impact of Pristine and Aged Microplastics in Soil on Earthworm Eisenia fetida under Environmentally Relevant Conditions

Recently, studies have highlighted the potential danger for soil organisms posed by film-derived microplastics (MPs). However, the majority of those does not accurately reflect the field conditions and the degree of MP contamination that can be found in actual settings. To fill the gap between laboratory and field scenarios, the polyethylene (PE) plastic film was made into PE-MPs and aged. Toxicity and molecular mechanisms of pristine PE-MPs (PMPs) and aged PE-MPs (AMPs) with the concentration at 500 mg/kg of dry weight were determined after 14 days of exposure by measuring the oxidative stress, osmoregulation pressure, gut microbiota, and metabolic responses in earthworms under environmentally relevant conditions. Our research showed that, when compared to PMPs (13.13 ± 1.99 items/g), AMPs accumulated more (16.19 ± 8.47 items/g), caused more severe tissue lesions, and caused a higher increase of cell membrane osmotic pressure in earthworms' intestines. Furthermore, the proportion of probiotic bacteria Lactobacillus johnsonii in the gut bacterial communities was 24.26%, 23.26%, and 12.96%, while the proportion of pathogenic bacteria of the phylum Verrucomicrobia was 2.28%, 4.79%, and 10.39% in the control and PMP- and AMP-exposed earthworms, indicating that the decrease in number of probiotic bacteria and the increase in number of pathogenic bacteria were more pronounced in the gut of AMP- rather than PMP-exposed earthworms. Metabolomic analysis showed that AMP exposure reduced earthworm energy metabolites. Consequently, the constant need for energy may result in protein catabolism, which raises levels of some amino acids, disturbs normal cell homeostasis, causes changes of cell membrane osmolarity, and destroys the cell structure. Our studies showed that aged MPs, with the same characteristics as those found in the environment, have greater toxicity than pristine MPs. The results of this study broaden our understanding of the toxicological effects of MPs on soil organisms under environmentally relevant conditions.

Plasma Levels of Branched Chain Amino Acids, Incident Hip Fractures, and Bone Mineral Density of the Hip and Spine

OBJECTIVE

Branched chain amino acids (BCAA) are building blocks for protein, an essential component of bone. However, the association of plasma levels of BCAA with fractures in populations outside of Hong Kong or with hip fractures in particular is not known. The purpose of these analyses was to determine the relationship of BCAA including valine, leucine, and isoleucine and total BCAA (SD of the sum of Z-scores for each BCAA) with incident hip fractures and bone mineral density (BMD) of the hip and lumbar spine in older African American and Caucasian men and women in the Cardiovascular Health Study.

DESIGN

Longitudinal analyses of association of plasma levels of BCAA with incident hip fractures and cross-sectional BMD of the hip and lumbar spine from the Cardiovascular Health Study.

SETTING

Community.

PARTICIPANTS

A total of 1850 men (38% of cohort) and women; mean age 73 years.

MAIN OUTCOME MEASURES

Incident hip fractures and cross-sectional BMD of the total hip, femoral neck, and lumbar spine.

RESULTS

In fully adjusted models, over 12 years of follow-up, we observed no significant association between incident hip fracture and plasma values of valine, leucine, isoleucine, or total BCAA per 1 SD higher of each BCAA. Plasma values of leucine but not valine, isoleucine, or total BCAA, were positively and significantly associated with BMD of the total hip (P = .03) and femoral neck (P = .02), but not the lumbar spine (P = .07).

CONCLUSIONS

Plasma levels of the BCAA leucine may be associated with higher BMD in older men and women. However, given the lack of significant association with hip fracture risk, further information is needed to determine whether BCAAs would be novel targets for osteoporosis therapies.

Myosin heavy chain-derived peptide of Gadus morhua promotes proliferation and differentiation in osteoblasts and bone formation and maintains bone homeostasis in ovariectomized mice

Gadus morhua is an important commercial fish rich in nutrients required for daily metabolism. However, the regulation of G. morhua peptides (GMP) on osteoblast growth remains unclear. In order to clarify the regulatory effects of GMP on osteoblasts, the effects of GMP on the growth of MC3T3-E1 cells were investigated, and the osteogenic peptides were identified and screened. The results showed that GMP promoted the proliferation and differentiation of osteoblasts by regulating the BMP/WNT signaling pathway at concentrations of 1-100 μg mL^-1. Molecular docking studies showed that a decapeptide, MNKKREAEFQ (P-GM-1), had a high affinity for integrins 3VI4 and 1L5G (-CDOCKER interaction energy: 161.30, 212.27 kcal mol^-1). Additionally, the proliferation rate of MC3T3-E1 cells was increased by 27%, and ALP activity was significantly increased under P-GM-1 treatment (100 μg mL^-1). Moreover, P-GM-1 promotes bone formation, maintains bone homeostasis, and prevents osteoporosis in ovariectomized mice by regulating the BMP/Smad signaling pathway. This study confirmed the potential of GMP in the regulation of bone mineral density and provided a certain theoretical basis for the development of anti-osteoporosis active factors from GMP.

Dietary Intake and Circulating Amino Acid Concentrations in Relation with Bone Metabolism Markers in Children Following Vegetarian and Omnivorous Diets

Scientific studies reported that most vegetarians meet the total protein requirements; however, little is known about their amino acid intakes. We aimed to assess dietary intake and serum amino acid levels in relation to bone metabolism markers in prepubertal children on vegetarian and traditional diets. Data from 51 vegetarian and 25 omnivorous children aged 4–9 years were analyzed. Dietary intake of macro- and micronutrients were assessed using the nutritional program Dieta 5®. Serum amino acid analysis was performed using high-pressure liquid chromatography technique, 25-hydroxyvitamin D and parathormone–electrochemiluminescent immunoassay, and bone metabolism markers, albumin, and prealbumin levels using enzyme-linked immunosorbent assay. Vegetarian children had a significantly lower intake of protein and amino acids with median differences of about 30–50% compared to omnivores. Concentrations of four amino acids (valine, lysine, leucine, isoleucine) in serum varied significantly by diet groups and were lower by 10–15% in vegetarians than meat-eaters. Vegetarian children also had lower (p < 0.001) serum albumin levels compared to omnivores. Among bone markers, they had higher (p < 0.05) levels of C-terminal telopeptide of collagen type I (CTX-I) than omnivores. Correlation patterns between amino acids and bone metabolism markers differed in the vegetarian and omnivore groups. Out of bone markers, especially osteoprotegerin was positively correlated with several amino acids, such as tryptophan, alanine, aspartate, glutamine, and serine, and ornithine in vegetarians. Vegetarian children consumed apparently sufficient but lower protein and amino acids compared to omnivores. In circulation these differences were less marked than in the diet. Significantly lower amino acid intake and serum levels of valine, lysine, leucine, and isoleucine as well as the observed correlations between serum amino acids and biochemical bone marker levels indicated the relations between diet, protein quality, and bone metabolism.

Sex Differences in Adipose Tissue Distribution Determine Susceptibility to Neuroinflammation in Mice With Dietary Obesity

Preferential energy storage in subcutaneous adipose tissue (SAT) confers protection against obesity-induced pathophysiology in females. Females also exhibit distinct immunological responses, relative to males. These differences are often attributed to sex hormones, but reciprocal interactions between metabolism, immunity, and gonadal steroids remain poorly understood. We systematically characterized adipose tissue hypertrophy, sex steroids, and inflammation in male and female mice after increasing durations of high-fat diet (HFD)-induced obesity. After observing that sex differences in adipose tissue distribution before HFD were correlated with lasting protection against inflammation in females, we hypothesized that a priori differences in the ratio of subcutaneous to visceral fat might mediate this relationship. To test this, male and female mice underwent SAT lipectomy (LPX) or sham surgery before HFD challenge, followed by analysis of glial reactivity, adipose tissue inflammation, and reproductive steroids. Because LPX eliminated female resistance to the proinflammatory effects of HFD without changing circulating sex hormones, we conclude that sexually dimorphic organization of subcutaneous and visceral fat determines susceptibility to inflammation in obesity.

Untargeted metabolomics reveals the effect of rearing systems on bone quality parameters in chickens

The objective of this study was to investigate the effects of rearing systems on the bone quality parameters in chickens using a metabolomics strategy. A total of 419 male one-day-old chicks were randomly allocated to two groups, a floor rearing group (FRG, n = 173) and a cage rearing group (CRG, n = 246). At 6, 8, 10, and 12 weeks of age, all chickens were radiographed by a digital X-ray machine, and body weight was recorded. At 12 weeks of age, 12 birds were selected from each group to obtain tibia and femur, and bone quality parameters of bone mineral density (BMD), mineral content (BMC), breaking strength (BBS), stiffness, Young's modulus (YM), ash content, calcium content, and phosphorus content were determined. An untargeted metabolomics assay was performed to identify changes in the serum metabolic profile (n = 8 birds/group). The results showed that cage-reared chickens had wider tibiae and greater body weight compared with floor-reared chickens. There were no significant differences in BMC or BBS between the two groups (p > 0.05), but BMD, ash content, calcium content, and phosphorus content of the tibia and femur of FRG were significantly higher than those of CRG (p < 0.05). Greater stiffness and YM of the femur were also observed in birds raised in the FRG compared with those raised in the CRG (p < 0.05). Taken together, the results suggest that rearing systems affected bone quality parameters. Furthermore, 148 and 149 differential metabolites were identified in positive and negative ion modes by LC-MS/MS analysis, among which 257 metabolites were significantly correlated with 16 bone quality parameters, including leucine, myristoleic acid, glycocholic acid, and N-phenylacetamide. KEGG analysis indicated that 15 metabolic pathways, including six pathways of amino acid metabolism, two pathways of lipid metabolism, and two pathways of carbohydrate metabolism, were responsible for bone quality. Overall, the present study demonstrated the effect of rearing systems on bone quality parameters, and identified several metabolites and metabolic pathways associated with bone quality parameters.

Metabolomic patterns, redox-related genes and metals, and bone fragility endpoints in the Hortega Study

BACKGROUND

The potential joint influence of metabolites on bone fragility has been rarely evaluated. We assessed the association of plasma metabolic patterns with bone fragility endpoints (primarily, incident osteoporosis-related bone fractures, and, secondarily, bone mineral density BMD) in the Hortega Study participants. Redox balance plays a key role in bone metabolism. We also assessed differential associations in participant subgroups by redox-related metal exposure levels and candidate genetic variants.

MATERIAL AND METHODS

In 467 participants older than 50 years from the Hortega Study, a representative sample from a region in Spain, we estimated metabolic principal components (mPC) for 54 plasma metabolites from NMR-spectrometry. Metals biomarkers were measured in plasma by AAS and in urine by HPLC-ICPMS. Redox-related SNPs (N = 341) were measured by oligo-ligation assay.

RESULTS

The prospective association with incident bone fractures was inverse for mPC1 (non-essential and essential amino acids, including branched-chain, and bacterial co-metabolites, including isobutyrate, trimethylamines and phenylpropionate, versus fatty acids and VLDL) and mPC4 (HDL), but positive for mPC2 (essential amino acids, including aromatic, and bacterial co-metabolites, including isopropanol and methanol). Findings from BMD models were consistent. Participants with decreased selenium and increased antimony, arsenic and, suggestively, cadmium exposures showed higher mPC2-associated bone fractures risk. Genetic variants annotated to 19 genes, with the strongest evidence for NCF4, NOX4 and XDH, showed differential metabolic-related bone fractures risk.

CONCLUSIONS

Metabolic patterns reflecting amino acids, microbiota co-metabolism and lipid metabolism were associated with bone fragility endpoints. Carriers of redox-related variants may benefit from metabolic interventions to prevent the consequences of bone fragility depending on their antimony, arsenic, selenium, and, possibly, cadmium, exposure levels.

One-year supplementation with Lactobacillus reuteri ATCC PTA 6475 counteracts a degradation of gut microbiota in older women with low bone mineral density

Recent studies have shown that probiotic supplementation has beneficial effects on bone metabolism. In a randomized controlled trial (RCT) we demonstrated that supplementation of Lactobacillus reuteri ATCC PTA 6475 reduced bone loss in older women with low bone mineral density. To investigate the mechanisms underlying the effect of L. reuteri ATCC PTA 6475 on bone metabolism, 20 women with the highest changes (good responders) and the lowest changes (poor responders) in tibia total volumetric BMD after one-year supplementation were selected from our previous RCT. In the current study we characterized the gut microbiome composition and function as well as serum metabolome in good responders and poor responders to the probiotic treatment as a secondary analysis. Although there were no significant differences in the microbial composition at high taxonomic levels, gene richness of the gut microbiota was significantly higher (P < 0.01 by the Wilcoxon rank-sum test) and inflammatory state was improved (P < 0.05 by the Wilcoxon signed-rank test) in the good responders at the end of the 12-month daily supplementation. Moreover, detrimental changes including the enrichment of E. coli (adjusted P < 0.05 by DESeq2) and its biofilm formation (P < 0.05 by GSA) observed in the poor responders were alleviated in the good responders by the treatment. Our results indicate that L. reuteri ATCC PTA 6475 supplementation has the potential to prevent a deterioration of the gut microbiota and inflammatory status in elderly women with low bone mineral density, which might have beneficial effects on bone metabolism.

Jin-Tian-Ge ameliorates ovariectomy-induced bone loss in rats and modulates osteoblastogenesis and osteoclastogenesis in vitro

BACKGROUND

Tiger bone, which had been one of the most famous traditional Chinese medicine for 2000 years, was originate from the skeleton of Panthera tigris L., and had the actions of anti-inflammatory, analgesic, immune-regulatory and promoting healing of bone fracture, and was used for the treatment of osteoporosis and rheumatoid arthritis. Jin-Tian-Ge (JTG), the artificial tiger bone powder, were prepared from skeletons of several farmed animals to substitute the natural tiger bone, and has been used for the treatment of osteoporosis in clinical practice. However, the characteristic and mechanism of action of JTG for the therapy of osteoporosis need to be further evidenced by using modern pharmacological methods. The aim of this work is to investigate the bone-protective effects of JTG, and explore the possible underlying mechanism.

METHODS

Ovariectomy (OVX) rats were orally administrated JTG or estradiol valerate (EV) for 12 weeks. We investigated the pharmacodynamic effects of JTG on anti-bone loss in OVX rats, and also investigated the role of JTG in promoting osteogenesis and inhibiting osteoclast differentiation.

RESULTS

JTG increased the bone mineral density (BMD), improved the bone microarchitecture and biomechanical properties in ovariectomized rast, whereas reversed the bone high turnover in OVX rats as evidenced by serum biochemical markers in OVX rats. JTG increased osteogenic differentiation of BMSCs in vitro, and up-regulated the expression of the key proteins of BMP and Wnt/β-catenin pathways. JTG also inhibited the osteoclastogenesis of BMM as evidenced by the alteration of the TRAP activity, F-actin construction and the expression of nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), c-Fos, Cathepsin K (Ctsk) and matrix metallopeptidase 9 (MMP9) of OCs induced with RANKL and LPS, reduced the expression and phosphorylation of NF-κB in OCs.

CONCLUSIONS

JTG prevented bone loss in OVX rats and increased osteogenic differentiation of BMSCs through regulation of the BMP and Wnt/β-catenin pathway, inhibited osteoclastogenesis by suppressing the NF-κB pathway, suggesting that JTG had the potentials for prevention and treatment of osteoporosis by modulating formation and differentiation of osteoblast and osteoclast.

Association of amino acid metabolites with osteoporosis, a metabolomic approach: Bushehr elderly health program

INTRODUCTION AND OBJECTIVES

Amino acids are the most frequently reported metabolites associated with low bone mineral density (BMD) in metabolomics studies. We aimed to evaluate the association between amino acid metabolic profile and bone indices in the elderly population.

METHODS

400 individuals were randomly selected from 2384 elderly men and women over 60 years participating in the second stage of the Bushehr elderly health (BEH) program, a population-based prospective cohort study that is being conducted in Bushehr, a southern province of Iran. Frozen plasma samples were used to measure 29 amino acid and derivatives metabolites using the UPLC-MS/MS-based targeted metabolomics platform. We conducted Elastic net regression analysis to detect the metabolites associated with BMD of different sites and lumbar spine trabecular bone score, and also to examine the ability of the measured metabolites to differentiate osteoporosis.

RESULTS

We adjusted the analysis for possible confounders (age, BMI, diabetes, smoking, physical activity, vitamin D level, and sex). Valine, leucine, isoleucine, and alanine in women and tryptophan in men were the most important amino acids inversely associated with osteoporosis (OR range from 0.77 to 0.89). Sarcosine, followed by tyrosine, asparagine, alpha aminobutyric acid, and ADMA in women and glutamine in men and when both women and men were considered together were the most discriminating amino acids detected in individuals with osteoporosis (OR range from 1.15 to 1.31).

CONCLUSION

We found several amino acid metabolites associated with possible bone status in elderly individuals. Further studies are required to evaluate the utility of these metabolites as clinical biomarkers for osteoporosis prediction and their effect on bone health as dietary supplements.

Immunometabolism - The Role of Branched-Chain Amino Acids

Immunometabolism has been the focus of extensive research over the last years, especially in terms of augmenting anti-tumor immune responses. Regulatory T cells (Tregs) are a subset of CD4+ T cells, which have been known for their immunosuppressive roles in various conditions including anti-tumor immune responses. Even though several studies aimed to target Tregs in the tumor microenvironment (TME), such approaches generally result in the inhibition of the Tregs non-specifically, which may cause immunopathologies such as autoimmunity. Therefore, specifically targeting the Tregs in the TME would be vital in terms of achieving a successful and specific treatment. Recently, an association between Tregs and isoleucine, which represents one type of branched-chain amino acids (BCAAs), has been demonstrated. The presence of isoleucine seems to affect majorly Tregs, rather than conventional T cells. Considering the fact that Tregs bear several distinct metabolic features in the TME, targeting their immunometabolic pathways may be a rational approach. In this Review, we provide a general overview on the potential distinct metabolic features of T cells, especially focusing on BCAAs in Tregs as well as in their subtypes.

Development of a synbiotic that protects against ovariectomy-induced trabecular bone loss

The gut microbiome has the capacity to regulate bone mass. The aim of this study was to develop a nutritional synbiotic dietary assemblage at an optimal dose to maintain bone mass in ovariectomized (Ovx) mice. We performed genomic analyses and in vitro experiments in a large collection of bacterial and fungal strains (>4,000) derived from fresh fruit and vegetables to identify candidates with the synergistic capacity to produce bone-protective short-chain fatty acids (SCFA) and vitamin K2. The candidate SBD111-A, composed of Lactiplantibacillus plantarum, Levilactobacillus brevis, Leuconostoc mesenteroides, Pseudomonas fluorescens, and Pichia kudriavzevii together with prebiotic dietary fibers, produced high levels of SCFA in vitro and protected against Ovx-induced trabecular bone loss in a dose-dependent manner in mice. Metagenomic sequencing revealed that SBD111-A changed the taxonomic composition and enriched specific pathways for synthesis of bone-protective SCFA, vitamin K2, and branched-chain amino acids in the gut microbiome.NEW & NOTEWORTHY We performed genomic analyses and in vitro experiments in a collection of bacterial and fungal strains. We identified a combination (SBD111-A) that produced high levels of SCFA in vitro and protected against ovariectomy-induced bone loss in a dose-dependent manner in mice. Metagenomic sequencing revealed that SBD111-A changed the taxonomic composition and function of the gut microbiome and enriched pathways for synthesis of bone-protective SCFA, vitamin K2, and branched-chain amino acids.

Seasonal variations and feedback from microplastics and cadmium on soil organisms in agricultural fields

Plastic film mulching is an important agricultural technology that plays a critical role in increasing crop yield and maintaining soil moisture. However, long-term coverage and untimely recovery lead to a large amount of plastic residues in soils. This decomposes into smaller plastics over time, which can reduce sowing quality, destroy the soil structure, and have adverse effects on soil organisms. In this study, the seasonal variations and correlations of microplastics and cadmium (Cd) in Wuxi farmland soils of Taihu Lake, China, were investigated in the spring and winter. The microplastics were mainly in the form of films, fibers, and debris and were mainly transparent and black in color. Microplastic abundance reached 890 particles/kg soil, with the majority of microplastics (>72.5%) being 0-500 μm. Polyethylene microplastics were the main polymers, accounting for >54.65%. In addition, the abundance of soil microplastics in the winter was significantly correlated with Cd, indicating that microplastics and heavy metals present a risk of coexposure to soil organisms. Furthermore, the response of in situ earthworms to microplastic-Cd pollution revealed that microplastics can be used as a vector to transfer heavy metals in the soil environment and may accumulate in the bodies of soil organisms. Multiomics techniques demonstrated bacterial community structure dysbiosis and metabolic changes of in situ earthworms under microplastic heavy metal-contaminated soils. The abundance of microplastics in earthworm casts and intestines was higher than that in the soil samples. These results reveal the potential risks from microplastics entering the soil environment and heavy metal pollution in soil ecosystems.

IL-18-Mediated SLC7A5 Overexpression Enhances Osteogenic Differentiation of Human Bone Marrow Mesenchymal Stem Cells via the c-MYC Pathway

Objective: To investigate the role of IL-18 in the regulation of osteogenic differentiation in human bone marrow mesenchymal stem cells (hBMSCs).

Methods: To assess whether IL-18 affects the osteogenic differentiation of hBMSCs through the c-MYC/SLC7A5 axis, IL-18 dose-response and time-course experiments were performed to evaluate its impact on osteogenic differentiation. To confirm osteogenic differentiation, alizarin red staining calcium measurement were performed. RT-qPCR and western blotting were used to determine the expression levels of bone-specific markers ALP, RUNX2, and BMP2, as well as those of SLC7A5 and c-MYC. Furthermore, SLC7A5 and c-MYC expression was evaluated via immunofluorescence. To elucidate the roles of SLC7A5 and c-MYC in osteoblast differentiation, cells were transfected with SLC7A5 or c-MYC siRNAs, or treated with the SLC7A5-specific inhibitor JPH203 and c-MYC-specific inhibitor 10058-F4, and the expression of SLC7A5, c-MYC, and bone-specific markers ALP, RUNX2, and BMP2 was assessed.

Results: Our results demonstrated that IL-18 increased calcium deposition in hBMSCs, and upregulated the expression of SLC7A5, c-MYC, ALP, RUNX2, and BMP2. Silencing of SLC7A5 or c-MYC using siRNA reduced the expression of ALP, RUNX2, and BMP2, while IL-18 treatment partially reversed the inhibitory effect of siRNA. Similar results were obtained by treating hBMSCs with SLC7A5 and c-MYC specific inhibitors, leading to significant reduction of the osteogenesis effect of IL-18 on hBMSCs.

Conclusion: In conclusion, our results indicate that IL-18 promotes the osteogenic differentiation of hBMSCs via the SLC7A5/c-MYC pathway and, therefore, may play an important role in fracture healing. These findings will provide new treatment strategies for delayed fracture healing after splenectomy.

Metabolomic biomarkers of low BMD: a systematic review

Due to the metabolic nature of osteoporosis, this study was conducted to identify metabolomic studies investigating the metabolic profile of low bone mineral density (BMD) and osteoporosis. A comprehensive systematic literature search was conducted through PubMed, Web of Science, Scopus, and Embase databases up to April 08, 2020, to identify observational studies with cross-sectional or case-control designs investigating the metabolic profile of low BMD in adults using biofluid specimen via metabolomic platform. The quality assessment panel specified for the "omics"-based diagnostic research (QUADOMICS) tool was used to estimate the methodologic quality of the included studies. Ten untargeted and one targeted approach metabolomic studies investigating biomarkers in different biofluids through mass spectrometry or nuclear magnetic resonance platforms were included in the systematic review. Some metabolite panels, rather than individual metabolites, showed promising results in differentiating low BMD from normal. Candidate metabolites were of different categories including amino acids, followed by lipids and carbohydrates. Besides, certain pathways were suggested by some of the studies to be involved. This systematic review suggested that metabolic profiling could improve the diagnosis of low BMD. Despite valuable findings attained from each of these studies, there was great heterogeneity regarding the ethnicity and age of participants, samples, and the metabolomic platform. Further longitudinal studies are needed to validate the results and confirm the predictive role of metabolic profile on low BMD and fracture. It is also mandatory to address and minimize the heterogeneity in future studies by using reliable quantitative methods. Summary: Due to the metabolic nature of osteoporosis, researchers have considered metabolomic studies recently. This systematic review showed that metabolic profiling including different categories of metabolites could improve the diagnosis of low BMD. However, great heterogeneity was observed and it is mandatory to address and minimize the heterogeneity in future studies.

A 1:1 matched case-control study on dietary protein intakes and hip fracture risk in Chinese elderly men and women

The role of protein intake in bone has been controversial. Our case-control study among Chinese elderly concluded that a higher consumption of protein, even substituted for fat, is associated with lowered hip fracture risk. Differences in protein sources, amino acids composition, gender, and calcium sufficiency may explain the inconsistency.

PURPOSE

The aim of the study was to investigate the association of dietary protein intakes with hip fracture risk among Chinese elderly.

METHODS

This was a 1:1 age and sex matched cross-sectional study of case-control design among 1070 pairs of elderly Chinese people aged 55 to 80 years. Patients who were newly diagnosed (within 2-week) hip fracture by X-ray were recruited from four hospitals in Guangdong Province of China. Dietary intakes were evaluated by a validated food frequency questionnaire for total protein, protein from different sources, amino acids profiles, and estimated renal acid load in diet.

RESULTS

Daily average intakes of total protein were 58.1±27.0 (women) and 65.7±31.8 (men) g/d for cases, and 66.8±21.5 (women) and 72.1±24.4 (men) for controls (p<0.001). Multivariable regression indicated that, compared with the lowest quartile, the highest quartile of consumption of energy adjusted total protein [OR: 0.360 (0.206~0.630) for women and 0.381 (0.153~0.949) for men] and animal protein [0.326 (0.183, 0.560) for women and 0.335 (0.136~0.828) for men] was significantly associated with the lowered risk of hip fracture in a dose-response manner (all p for trend <0.05). A significant hip fracture risk reduction was observed in women with higher intakes of sulfur amino acids [OR: 0.464 (0.286~0.753)] and aromatic amino acids [0.537 (0.326~0.884)] but not in men. Subgroup analysis suggested that these associations were more evident in elderly with lower body mass index and dietary calcium intake less than 400 mg/d.

CONCLUSIONS

A higher level of protein intake, even substituted for fat, is associated with lowered hip fracture risk.

Amino acid metabolism and autophagy in skeletal development and homeostasis

Bone is an active organ that is continuously remodeled throughout life via formation and resorption; therefore, a fine-tuned bone (re)modeling is crucial for bone homeostasis and is closely connected with energy metabolism. Amino acids are essential for various cellular functions as well as an energy source, and their synthesis and catabolism (e.g., metabolism of carbohydrates and fatty acids) are regulated through numerous enzymatic cascades. In addition, the intracellular levels of amino acids are maintained by autophagy, a cellular recycling system for proteins and organelles; under nutrient deprivation conditions, autophagy is strongly induced to compensate for cellular demands and to restore the amino acid pool. Metabolites derived from amino acids are known to be precursors of bioactive molecules such as second messengers and neurotransmitters, which control various cellular processes, including cell proliferation, differentiation, and homeostasis. Thus, amino acid metabolism and autophagy are tightly and reciprocally regulated in our bodies. This review discusses the current knowledge and potential links between bone diseases and deficiencies in amino acid metabolism and autophagy.

Metabolic Alterations in Older Women With Low Bone Mineral Density Supplemented With Lactobacillus reuteri

Osteoporosis and its associated fractures are highly prevalent in older women. Recent studies have shown that gut microbiota play important roles in regulating bone metabolism. A previous randomized controlled trial (RCT) found that supplementation with Lactobacillus reuteri ATCC PTA 6475 (L.reuteri) led to substantially reduced bone loss in older women with low BMD. However, the total metabolic effects of L. reuteri supplementation on older women are still not clear. In this study, a post hoc analysis (not predefined) of serum metabolomic profiles of older women from the previous RCT was performed to investigate the metabolic dynamics over 1 year and to evaluate the effects of L. reuteri supplementation on human metabolism. Distinct segregation of the L. reuteri and placebo groups in response to the treatment was revealed by partial least squares‐discriminant analysis. Although no individual metabolite was differentially and significantly associated with treatment after correction for multiple testing, 97 metabolites responded differentially at any one time point between L. reuteri and placebo groups (variable importance in projection score >1 and p value <0.05). These metabolites were involved in multiple processes, including amino acid, peptide, and lipid metabolism. Butyrylcarnitine was particularly increased at all investigated time points in the L. reuteri group compared with placebo, indicating that the effects of L. reuteri on bone loss are mediated through butyrate signaling. Furthermore, the metabolomic profiles in a case (low BMD) and control population (high BMD) of elderly women were analyzed to confirm the associations between BMD and the identified metabolites regulated by L. reuteri supplementation. The amino acids, especially branched‐chain amino acids, showed association with L. reuteri treatment and with low BMD in older women, and may serve as potential therapeutic targets. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Relationship Between Serum Amino Acid Levels and Bone Mineral Density: A Mendelian Randomization Study

BACKGROUND

This study aimed to explore the association between serum amino acids (AAs) levels and bone mineral density (BMD).

METHODS

We performed a two-sample Mendelian randomization (MR) analysis to analyze the associations between the levels of eight AAs and BMD values by using summary-level genome-wide association study (GWAS) data. We applied the MR Steiger filtering method and MR Pleiotropy RESidual Sum and Outlier (MR-PRESSO) global test to check for and remove single nucleotide polymorphisms (SNPs) that were horizontally pleiotropic. The associations were estimated with the inverse variance weighted (IVW), MR-Egger, weighted median and MR Robust Adjusted Profile Score (MR.RAPS) methods.

RESULTS

Our study found that genetically increased isoleucine (Ile) [IVW: effect = 0.1601, 95% confidence interval (CI) = 0.0604 ~ 0.2597, p = 0.0016] and valine (Val) levels (IVW: effect = 0.0953, 95% CI = 0.0251 ~ 0.1655, p = 0.0078) were positively associated with total body BMD (TB-BMD). The results also revealed that genetically increased tyrosine (Tyr) levels were negatively associated with TB-BMD (IVW: effect = -0.1091, 95% CI = -0.1863 ~ -0.0320, p = 0.0055).

CONCLUSIONS

In this study, associations between serum AA levels and BMD were established. These findings underscore the important role that serum AAs play in the development of osteoporosis and provide evidence that osteoporosis can be prevented and treated by the intake of certain AAs.

Protaetia brevitarsis seulensis Derived Protein Isolate with Enhanced Osteomodulatory and Antioxidative Property

The osteogenic differentiation of stem cells is profoundly affected by their microenvironmental conditions. The differentiation behavior of stem cells can be tuned by changing the niche environments. The proteins or peptides that are derived by living organisms facilitate the osteogenic differentiation of stem cells. Here, we have evaluated the osteoinductive and antioxidative potential of the Protaetia brevitarsis seulensis insect-derived protein for human bone marrow-derived mesenchymal stem cells (hBMSCs). The amino acid contents in the isolated protein were determined by an amino acid analyzer. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to analyze the extract’s functional groups and surface morphology. The extracted protein exhibited 51.08% β-sheet conformation. No adverse effects were observed in extract-treated cells, indicating their biocompatibility. The protein isolate showed an excellent antioxidative property. Besides this, an enhancement in the hBMSCs’ mineralization has been observed in the presence of treated protein isolates. Notably, osteogenic marker genes and proteins were effectively expressed in the treated cells. These results indicated that the P. brevitarsis-derived protein isolate can be used as a potential antioxidative biomaterial for bone tissue engineering applications.

A Multi-Omic Analysis for Low Bone Mineral Density in Postmenopausal Women Suggests a RELATIONSHIP between Diet, Metabolites, and Microbiota

The effect of microbiota composition and its health on bone tissue is a novel field for research. However, their associations with bone mineral density (BMD) have not been established in postmenopausal women. The present study investigates the relation of diet, the microbiota composition, and the serum metabolic profile in postmenopausal women with normal-BMD or with low-BMD. Ninety-two Mexican postmenopausal women were classified into normal-BMD (n = 34) and low-BMD (n = 58). The V4 hypervariable region was sequenced using the Miseq platform. Serum vitamin D was determined by chemiluminescence immunoassay. Serum concentrations of acyl-carnitines and amino acids were determined by electrospray tandem mass spectrometry. Diet was assessed by a food frequency questionnaire. The low-BMD group had fewer observed species, higher abundance of γ-Proteobacteria, lower consumption of lycopene, and lower concentrations of leucine, valine, and tyrosine compared with the normal-BMD group. These amino acids correlated positively with the abundance of Bacteroides. Lycopene consumption positively correlated with Oscillospira and negatively correlated with Pantoea genus abundance. Finally, the intestinal microbiota of women with vitamin D deficiency was related to Erysipelotrichaceae and Veillonellaceae abundance compared to the vitamin D non-deficient group. Associations mediated by the gut microbiota between diet and circulating metabolites with low-BMD were identified.

The Role of Tryptophan Metabolites in Musculoskeletal Stem Cell Aging

Although aging is considered a normal process, there are cellular and molecular changes that occur with aging that may be detrimental to health. Osteoporosis is one of the most common age-related degenerative diseases, and its progression correlates with aging and decreased capacity for stem cell differentiation and proliferation in both men and women. Tryptophan metabolism through the kynurenine pathway appears to be a key factor in promoting bone-aging phenotypes, promoting bone breakdown and interfering with stem cell function and osteogenesis; however, little data is available on the impact of tryptophan metabolites downstream of kynurenine. Here we review available data on the impact of these tryptophan breakdown products on the body in general and, when available, the existing evidence of their impact on bone. A number of tryptophan metabolites (e.g., 3-hydroxykynurenine (3HKYN), kynurenic acid (KYNA) and anthranilic acid (AA)) have a detrimental effect on bone, decreasing bone mineral density (BMD) and increasing fracture risk. Other metabolites (e.g., 3-hydroxyAA, xanthurenic acid (XA), picolinic acid (PIA), quinolinic acid (QA), and NAD+) promote an increase in bone mineral density and are associated with lower fracture risk. Furthermore, the effects of other tryptophan breakdown products (e.g., serotonin) are complex, with either anabolic or catabolic actions on bone depending on their source. The mechanisms involved in the cellular actions of these tryptophan metabolites on bone are not yet fully known and will require further research as they are potential therapeutic targets. The current review is meant as a brief overview of existing English language literature on tryptophan and its metabolites and their effects on stem cells and musculoskeletal systems. The search terms used for a Medline database search were: kynurenine, mesenchymal stem cells, bone loss, tryptophan metabolism, aging, and oxidative stress.

Differential modulation after feeding in different salinities and response to abscisic acid (ABA) and extracellular Ca2+ of aminopeptidase N (APN) activity in the hepatopancreas of the intertidal euryhaline crab Neohelice granulata

Modulation of aminopeptidase N (APN) activity in the digestive tract by various factors would be important to adjust digestive and absorptive processes under different physiological and (or) environmental conditions. We studied the postprandial responses at different salinities and the effect of abscisic acid (ABA) and extracellular Ca2+ on APN activity in the hepatopancreas (the main site for nutrient digestion and absorption) of the model species Neohelice granulata (Dana, 1851). Enzyme activity was determined at different times (0, 24, 48, and 72 h) after feeding in crabs acclimated either to 35 psu (osmoconformation) or 10 psu (hyper-regulation). APN activity increased around 50% at 24 h after feeding at 35 psu, whereas no changes occurred at 10 psu. Enzyme activity was also assayed in the presence of ABA (1 × 10–4 mol·L–1) or extracellular Ca2+ (1 × 10–4 mol·L–1), showing increments of 60% and 56%, respectively. The results suggest a role of APN in postprandial adjustments and its modulation by different chemical messengers by direct effect on the hepatopancreas. Moreover, to our knowledge, this work is the first to show the effect of ABA on a digestive enzyme in the digestive tract of an animal.

Circulating amino acids are associated with bone mineral density decline and ten-year major osteoporotic fracture risk in older community-dwelling adults

With aging, poor bone mineral density (BMD) and accelerated decrease in BMD are strong risk factors for fracture. Reports of the associations of dietary protein intake with bone strength are inconsistent, possibly owing to differences in protein sources and amino acid (AA) composition. We examined the associations of serum AA with 4-year hip BMD loss and subsequent fracture risk within 10 years in older community-dwelling adults, and further addressed whether lifestyle, dietary protein intake and its source, and body composition would affect the associations. In 1424 men and 1573 women (mean age 72 years), using binary logistic regression, higher serum valine, leucine, isoleucine and tryptophan concentrations were associated (or approaching a borderline significance in case of the last three ones) with less hip BMD decline (defined as BMD loss ≥ 2.8 times the precision error of the BMD measurement at femoral neck) in 4 years later, with the OR (95%CI) /SD of AA increase, ranging from 0.83 (0.75, 0.91) to 0.92 (0.87, 0.98) after multiple adjustments for baseline age, gender, BMI, BMD, estimated glomerular filtration rate (eGFR), dietary protein intake (animal- and plant-derived protein intakes), calcium intake, established lifestyles (physical activity level, smoking and alcohol drinking status), osteoporosis medications, and changes of body fat and lean muscle mass. Higher serum total homocysteine (tHcy) concentration was independently associated with BMD decline 4 years later (OR (95%CI) /SD of 1.16 (1.05, 1.27)). Using multivariate Cox regression, higher serum tryptophan concentration potentially predicted low risk of incident major osteoporotic fractures (MOFs) (HR/SD (95%CI)=0.86 (0.75, 0.98)) after multiple adjustments. Higher serum tHcy was associated with MOFs (HR/SD (95%CI)=1.29 (1.12, 1.50)) risk after multiple adjustments in men. These findings suggest that a specific AA profile correlates with greater BMD and lower subsequent fracture risk, independent of diet and lifestyle factors.

Clinical insights into the kynurenine pathway in age-related diseases

Accumulating evidence from diverse experiments, including heterochronic parabiosis-the surgical joining of two animals of different ages-has highlighted the importance of systemic factors in the progressive functional decline of various organs and tissues during aging. The major metabolic pathway of tryptophan, an essential amino acid in humans, is the kynurenine pathway (KP) in which indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) catalyze the conversion of tryptophan into kynurenine. Importantly, circulating kynurenine produced by this enzymatic breakdown, as a primary driver of the aging process, has been linked to higher mortality in humans. This review discusses the potential roles of tryptophan derivatives as biomarkers for the risk of frailty in the elderly, based on human observational studies as well as the KP as a therapeutic target for age-related diseases.

The Association of Aromatic Amino Acids with Incident Hip Fracture, aBMD, and Body Composition from the Cardiovascular Health Study

In 5187 persons from the Cardiovascular Health Study, there was no significant association of dietary intakes of aromatic amino acids (AAA) with areal BMD of the hip or body composition. However, those who had the lowest dietary intakes of AAA were at increased risk for incident hip fractures. Prior studies of the association of protein intake with osteoporosis are conflicting and have not directly examined the relationship of aromatic amino acids (AAA) with fractures, areal bone mineral density (aBMD), and body composition. We sought to determine the relationship of dietary intakes of AAA with osteoporosis parameters in elderly men and women. 5187 men and women aged ≥ 65 years from the Cardiovascular Health Study (CHS) with dietary intakes of AAA (tryptophan, phenylalanine, tyrosine) estimated by food frequency questionnaire (FFQ) were included. We examined the relationship between a one-time estimate of daily dietary AAA intake with risk of incident hip fractures over a median of 13.2 years of fracture follow-up. A subset (n = 1336) who had dual energy X-ray absorptiometry (DXA) performed were included in a cross-sectional analysis of the association of dietary AAA intake with aBMD of the total hip and measurements of body composition. In multivariable models adjusted for demographic and clinical variables, medication use, and diet, higher dietary AAA intake was not significantly associated with incident hip fractures. All hazard ratios (HR) were less than one (tryptophan, HR 0.14, 95% CI 0.01 to 1.89; phenylalanine, HR 0.60, 95% CI 0.23 to 1.55; tyrosine, HR 0.59, 95% CI 0.27 to 1.32), but confidence intervals were wide and included no difference. However, in post hoc analyses, the lowest quartile of intake for each AAA was associated with an increased risk for hip fracture compared to higher quartiles (p ≤ 0.047 for all). Dietary AAA intakes were not significantly associated with total hip aBMD or any measurements of body composition. Overall, there was no significant association of dietary AAA intake with hip fractures, aBMD of the hip, or body composition. However, there may be a subset of elderly individuals with low dietary intakes of AAA who are at increased for hip fractures.

L-Amino Acids Promote Calcitonin Release via a Calcium-Sensing Receptor: Gq/11-Mediated Pathway in Human C-Cells

Human calcitonin release is promoted by elevated extracellular Ca2+ (Ca2+o) concentration acting, at least in part, via the calcium-sensing receptor (CaSR). The CaSR is positively modulated by L-amino acids, including the aromatic amino acids L-phenylalanine (Phe) and L-tryptophan (Trp). To investigate the effect of L-amino acids on human calcitonin secretion, we selected thyroid TT cells and exposed them to various Ca2+o concentrations in the absence or presence of L-Phe, plasma-like mixtures of L-amino acids, or the clinically effective positive modulator (calcimimetic) cinacalcet. In the presence of L-Phe or plasma-like mixtures of amino acids, TT cells exhibited enhanced Ca2+o sensitivity in assays of calcitonin release and intracellular Ca2+ mobilization. Furthermore, the effect of elevated Ca2+o and L-Phe on calcitonin release was markedly suppressed by the calcilytic NPS-2143. These effects were dependent on CaSR-mediated activation of Gq/11 as revealed by the specific inhibitor YM-254890. The findings support the hypothesis that calcitonin release is stimulated by increases in plasma L-amino acid levels as well as elevated Ca2+o concentration. They also demonstrate that stimulated calcitonin release as well as basal levels of calcitonin secretion are mediated by a CaSR:Gq/11 signaling mechanism.

Human Enriched Serum Following Hydrolysed Collagen Absorption Modulates Bone Cell Activity: from Bedside to Bench and Vice Versa

Collagen proteins are crucial components of the bone matrix. Since collagen-derived products are widely used in the food and supplement industry, one may raise the question whether collagen-enriched diets can provide benefits for the skeleton. In this study, we designed an innovative approach to investigate this question taking into account the metabolites that are formed by the digestive tract and appear in the circulation after ingestion of hydrolysed collagen. Blood samples collected in clinical and pre-clinical trials following ingestion and absorption of hydrolysed collagen were processed and applied on bone-related primary cell cultures. This original ex vivo methodology revealed that hydrolysed collagen-enriched serum had a direct impact on the behaviour of cells from both human and mouse origin that was not observed with controls (bovine serum albumin or hydrolysed casein-enriched serum). These ex vivo findings were fully in line with in vivo results obtained from a mouse model of post-menopausal osteoporosis. A significant reduction of bone loss was observed in mice supplemented with hydrolysed collagen compared to a control protein. Both the modulation of osteoblast and osteoclast activity observed upon incubation with human or mouse serum ex vivo and the attenuation of bone loss in vivo, clearly indicates that the benefits of hydrolysed collagen for osteoporosis prevention go beyond the effect of a simple protein supplementation.