Antibiotic Perturbation of Gut Microbiota Dysregulates Osteoimmune Cross Talk in Postpubertal Skeletal Development

An In Vitro Study on the Application of Silver-Doped Platelet-Rich Plasma in the Prevention of Post-Implant-Associated Infections

Implant therapy is a common treatment option in dentistry and orthopedics, but its application is often associated with an increased risk of microbial contamination of the implant surfaces that cause bone tissue impairment. This study aims to develop two silver-enriched platelet-rich plasma (PRP) multifunctional scaffolds active at the same time in preventing implant-associated infections and stimulating bone regeneration. Commercial silver lactate (L) and newly synthesized silver deoxycholate:β-Cyclodextrin (B), were studied in vitro. Initially, the antimicrobial activity of the two silver soluble forms and the PRP enriched with the two silver forms has been studied on microbial planktonic cells. At the same time, the biocompatibility of silver-enriched PRPs has been assessed by an MTT test on human primary osteoblasts (hOBs). Afterwards, an investigation was conducted to evaluate the activity of selected concentrations and forms of silver-enriched PRPs in inhibiting microbial biofilm formation and stimulating hOB differentiation. PRP-L (0.3 µg/mm2) and PRP-B (0.2 µg/mm2) counteract Staphylococcus aureus, Staphylococcus epidermidis and Candida albicans planktonic cell growth and biofilm formation, preserving hOB viability without interfering with their differentiation capability. Overall, the results obtained suggest that L- and B-enriched PRPs represent a promising preventive strategy against biofilm-related implant infections and demonstrate a new silver formulation that, together with increasing fibrin binding protecting silver in truncated cone-shaped cyclic oligosaccharides, achieved comparable inhibitory results on prokaryotic cells at a lower concentration.

Microbiota metabolites in bone: Shaping health and Confronting disease

The intricate interplay between the gut microbiota and bone health has become increasingly recognized as a fundamental determinant of skeletal well-being. Microbiota-derived metabolites play a crucial role in dynamic interaction, specifically in bone homeostasis. In this sense, short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate, indirectly promote bone formation by regulating insulin-like growth factor-1 (IGF-1). Trimethylamine N-oxide (TMAO) has been found to increase the expression of osteoblast genes, such as Runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein-2 (BMP2), thus enhancing osteogenic differentiation and bone quality through BMP/SMADs and Wnt signaling pathways. Remarkably, in the context of bone infections, the role of microbiota metabolites in immune modulation and host defense mechanisms potentially affects susceptibility to infections such as osteomyelitis. Furthermore, ongoing research elucidates the precise mechanisms through which microbiota-derived metabolites influence bone cells, such as osteoblasts and osteoclasts. Understanding the multifaceted influence of microbiota metabolites on bone, from regulating homeostasis to modulating susceptibility to infections, has the potential to revolutionize our approach to bone health and disease management. This review offers a comprehensive exploration of this evolving field, providing a holistic perspective on the impact of microbiota metabolites on bone health and diseases.

Adolescence and the Microbiome: Implications for Healthy Growth and Maturation

The gut microbiota was initially thought to develop into a stable, adult-like profile during early postnatal life. The formation of the gut microbiota during early life has been shown to contribute to healthy growth and has lifelong implications for host health. Adolescence, the developmental period between childhood and adulthood, is a critical window for healthy growth and maturation. The composition of the gut microbiota in adolescents is distinct from that of children and adults, which supports the premise that the gut microbiota continues to develop during adolescence toward an adult-like profile. Research has begun to shift its focus from understanding the gut microbiome at the extremes of the life span to evaluating the importance of the gut microbiome during adolescence and its role in healthy development. This article provides an overview of adolescent development, host-microbiota interactions, and experimental models used to discern effects of gut microbiota on health and disease. Herein, the role of the gut microbiota is reviewed as it relates to adolescent: i) brain development, cognition, and behavior; ii) metabolism and adiposity; and iii) skeletal growth and bone mass accrual. Future directions are addressed, including omics investigations defining mechanisms through which the gut microbiota influences adolescent development. Furthermore, we discuss advancing noninvasive interventions targeting the adolescent gut microbiota that could be employed to support healthy growth and maturation.

Estrogen deficiency induces bone loss through the gut microbiota

Postmenopausal osteoporosis is a common bone metabolic disease, and gut microbiota (GM) imbalance plays an important role in the development of metabolic bone disease. Here, we show that ovariectomized mice had high levels of lipopolysaccharide in serum and gut microbiota dysbiosis through increases in luminal Firmicutes:Bacteroidetes ratio. We depleted the GM through antibiotic treatment and observed improvements in bone mass, bone microstructure, and bone strength in ovariectomized mice. Conversely, transplantation of GM adapted to ovariectomy induced bone loss. However, GM depletion reversed ovariectomy-induced gene expression in the tibia and increased periosteal bone formation. Furthermore, bioinformatics analysis revealed that the G-protein-coupled bile acid receptor (TGR5) and systemic inflammatory factors play key roles in bone metabolism. Silencing TGR5 expression through small interfering RNA (siRNA) in the local tibia and knockout of TGR5 attenuated the effects of GM depletion in ovariectomized mice, confirming these findings. Thus, this study highlights the critical role of the GM in inducing bone loss in ovariectomized mice and suggests that targeting TGR5 within the GM may have therapeutic potential for postmenopausal osteoporosis.

Commensal Microbiota Effects on Craniofacial Skeletal Growth and Morphology

Microbes colonize anatomical sites in health to form commensal microbial communities (e.g., commensal gut microbiota, commensal skin microbiota, commensal oral microbiota). Commensal microbiota has indirect effects on host growth and maturation through interactions with the host immune system. The commensal microbiota was recently introduced as a novel regulator of skeletal growth and morphology at noncraniofacial sites. Further, we and others have shown that commensal gut microbes, such as segmented filamentous bacteria (SFB), contribute to noncraniofacial skeletal growth and maturation. However, commensal microbiota effects on craniofacial skeletal growth and morphology are unclear. To determine the commensal microbiota's role in craniofacial skeletal growth and morphology, we performed craniometric and bone mineral density analyses on skulls from 9-week-old female C57BL/6T germ-free (GF) mice (no microbes), excluded-flora (EF) specific-pathogen-free mice (commensal microbiota), and murine-pathogen-free (MPF) specific-pathogen-free mice (commensal microbiota with SFB). Investigations comparing EF and GF mice revealed that commensal microbiota impacted the size and shape of the craniofacial skeleton. EF versus GF mice exhibited an elongated gross skull length. Cranial bone length analyses normalized to skull length showed that EF versus GF mice had enhanced frontal bone length and reduced cranial base length. The shortened cranial base in EF mice was attributed to decreased presphenoid, basisphenoid, and basioccipital bone lengths. Investigations comparing MPF mice and EF mice demonstrated that commensal gut microbes played a role in craniofacial skeletal morphology. Cranial bone length analyses normalized to skull length showed that MPF versus EF mice had reduced frontal bone length and increased cranial base length. The elongated cranial base in MPF mice was due to enhanced presphenoid bone length. This work, which introduces the commensal microbiota as a contributor to craniofacial skeletal growth, underscores that noninvasive interventions in the gut microbiome could potentially be employed to modify craniofacial skeletal morphology. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Gut microbiota signatures and fecal metabolites in postmenopausal women with osteoporosis

BACKGROUND

Women suffer from various distress and disturbances after menopause, including osteoporosis, a risk factor associated with multiple diseases. Altered gut microbiota has been implicated in postmenopausal osteoporosis. In this study, to understand gut microbiota signatures and fecal metabolite changes in postmenopausal women with osteoporosis, 108 postmenopausal women were recruited for intestinal microbiota and fecal metabolite detection. Among these participants, 98 patients, who met the inclusion criteria, were divided into postmenopausal osteoporosis (PMO) and non-postmenopausal osteoporosis (non-PMO) groups based on bone mineral density (BMD). The compositions of gut bacteria and fungi were examined by 16 S rRNA gene sequencing and ITS sequencing, respectively. Meanwhile, fecal metabolites were analyzed using liquid chromatography coupled with mass spectrometry (LC-MS).

RESULTS

We found that bacterial α-diversity and β-diversity were significantly altered in PMO compared to non-PMO patients. Interestingly, fungi composition showed larger changes, and the differences in β-diversity were more significant between PMO and non-PMO patients. Metabolomics analysis revealed that fecal metabolites, such as levulinic acid, N-Acetylneuraminic acid, and the corresponding signaling pathways were also changed significantly, especially in the alpha-Linolenic acid metabolism and selenocompound metabolism. The screened differential bacteria, fungi, and metabolites closely correlated with clinical findings between these two groups, for example, the bacterial genus, Fusobacterium, the fungal genus, Devriesia, and the metabolite, L-pipecolic acid, were significantly associated with BMD.

CONCLUSIONS

Our findings indicated that there were remarkable changes in gut bacteria, fungi, and fecal metabolites in postmenopausal women, and such changes were notably correlated with patients' BMD ​​and clinical findings. These correlations provide novel insights into the mechanism of PMO development, potential early diagnostic indicators, and new therapeutic approaches to improve bone health in postmenopausal women.

C3a-C3aR signaling is a novel modulator of skeletal homeostasis

Osteoimmune studies have identified complement signaling as an important regulator of the skeleton. Specifically, complement anaphylatoxin receptors (i.e., C3aR, C5aR) are expressed on osteoblasts and osteoclasts, implying that C3a and/or C5a may be candidate mediators of skeletal homeostasis. The study aimed to determine how complement signaling influences bone modeling/remodeling in the young skeleton. Female C57BL/6J C3aR-/-C5aR-/- vs. wildtype and C3aR-/- vs. wildtype mice were examined at age 10 weeks. Trabecular and cortical bone parameters were analyzed by micro-CT. In situ osteoblast and osteoclast outcomes were determined by histomorphometry. Osteoblast and osteoclast precursors were assessed in vitro. C3aR-/-C5aR-/- mice displayed an increased trabecular bone phenotype at age 10 weeks. In vitro studies revealed C3aR-/-C5aR-/- vs. wildtype cultures had less bone-resorbing osteoclasts and increased bone-forming osteoblasts, which were validated in vivo. To determine whether C3aR alone was critical for the enhanced skeletal outcomes, wildtype vs. C3aR-/- mice were evaluated for osseous tissue outcomes. Paralleling skeletal findings in C3aR-/-C5aR-/- mice, C3aR-/- vs. wildtype mice had an enhanced trabecular bone volume fraction, which was attributed to increased trabecular number. There was elevated osteoblast activity and suppressed osteoclastic cells in C3aR-/- vs. wildtype mice. Furthermore, primary osteoblasts derived from wildtype mice were stimulated with exogenous C3a, which more profoundly upregulated C3ar1 and the pro-osteoclastic chemokine Cxcl1. This study introduces the C3a/C3aR signaling axis as a novel regulator of the young skeleton.

Prolonged Antibiotic Exposure during Adolescence Dysregulates Liver Metabolism and Promotes Adiposity in Mice

Antibiotic administration during early life has been shown to have lasting effects on the gut microbiota, which have been linked to sustained alterations in liver metabolism and adiposity. Recent investigations have discerned that the gut microbiota continues to develop toward an adult-like profile during adolescence. However, the impact of antibiotic exposure during adolescence on metabolism and adiposity is unclear. Herein, a retrospective analysis of Medicaid claims data was performed, which indicated that tetracycline class antibiotics are commonly prescribed for the systemic treatment of adolescent acne. The purpose of this was to discern the impact of a prolonged tetracycline antibiotic exposure during adolescence on the gut microbiota, liver metabolism, and adiposity. Male C57BL/6T specific pathogen-free mice were administered a tetracycline antibiotic during the pubertal/postpubertal adolescent growth phase. Groups were euthanized at different time points to assess immediate and sustained antibiotic treatment effects. Antibiotic exposure during adolescence caused lasting genera-level shifts in the intestinal bacteriome and persistent dysregulation of metabolic pathways in the liver. Dysregulated hepatic metabolism was linked to sustained disruption of the intestinal farnesoid X receptor-fibroblast growth factor 15 axis, a gut-liver endocrine axis that supports metabolic homeostasis. Antibiotic exposure during adolescence increased subcutaneous, visceral, and marrow adiposity, which intriguingly manifested following antibiotic therapy. This preclinical work highlights that prolonged antibiotic courses for the clinical treatment of adolescent acne may have unintended deleterious effects on liver metabolism and adiposity.

Minocycline-induced disruption of the intestinal FXR/FGF15 axis impairs osteogenesis in mice

Antibiotic-induced shifts in the indigenous gut microbiota influence normal skeletal maturation. Current theory implies that gut microbiota actions on bone occur through a direct gut/bone signaling axis. However, our prior work supports that a gut/liver signaling axis contributes to gut microbiota effects on bone. Our purpose was to investigate the effects of minocycline, a systemic antibiotic treatment for adolescent acne, on pubertal/postpubertal skeletal maturation. Sex-matched specific pathogen-free (SPF) and germ-free (GF) C57BL/6T mice were administered a clinically relevant minocycline dose from age 6-12 weeks. Minocycline caused dysbiotic shifts in the gut bacteriome and impaired skeletal maturation in SPF mice but did not alter the skeletal phenotype in GF mice. Minocycline administration in SPF mice disrupted the intestinal farnesoid X receptor/fibroblast growth factor 15 axis, a gut/liver endocrine axis supporting systemic bile acid homeostasis. Minocycline-treated SPF mice had increased serum conjugated bile acids that were farnesoid X receptor (FXR) antagonists, suppressed osteoblast function, decreased bone mass, and impaired bone microarchitecture and fracture resistance. Stimulating osteoblasts with the serum bile acid profile from minocycline-treated SPF mice recapitulated the suppressed osteogenic phenotype found in vivo, which was mediated through attenuated FXR signaling. This work introduces bile acids as a potentially novel mediator of gut/liver signaling actions contributing to gut microbiota effects on bone.

Gut microbiota can affect bone quality by regulating serum estrogen levels

Germ-free (GF) animals and animal models of the antibiotic disruption of gut microbiota are widely used to explore studies of gut microbiota-host interactions. The role of gut microbiota in bone growth and development has been well explained in studies on GF mice, indicating that changes in the gut microbiota may affect normal bone developmental processes. The mechanisms, however, are yet unclear. This study aims to clarify the effect of antibiotic treatment disrupting the gut microbiota on bone development in mice and investigate the possible causes of this effect. Our results show that long-term antibiotic feeding significantly alters gut microbiota composition in mice, reduces the bone mineral density of the spinal region, and leads to changes in trabecular microstructure. Interestingly, we found a significant decrease in the serum estrogen levels in mice treated with antibiotics, suggesting that gut microbiota may affect bone quality by regulating serum estrogen levels. These results may help understand how gut ecological dysregulation affects sex hormones and provide a new conception for the clinical treatments of osteoporosis.

Tetracyclines and bone: Unclear actions with potentially lasting effects

Tetracyclines are a broad-spectrum class of antibiotics that have unclear actions with potentially lasting effects on bone metabolism. Initially isolated from Streptomyces, tetracycline proved to be an effective treatment for Gram +/- infections. The emergence of resistant bacterial strains commanded the development of later generation agents, including minocycline, doxycycline, tigecycline, sarecycline, omadacycline, and eravacycline. In 1957, it was realized that tetracyclines act as bone fluorochrome labels due to their high affinity for the bone mineral matrix. Over the course of the next decade, researchers discerned that these compounds are retained in the bone matrix at high levels after the termination of antibiotic therapy. Studies during this period provided evidence that tetracyclines could disrupt prenatal and early postnatal skeletal development. Currently, tetracyclines are most commonly prescribed as a long-term systemic therapy for the treatment of acne in healthy adolescents and young adults. Surprisingly, the impact of tetracyclines on physiologic bone modeling/remodeling is largely unknown. This article provides an overview of the pharmacology of tetracycline drugs, summarizes current knowledge about the impact of these agents on skeletal development and homeostasis, and reviews prior work targeting tetracyclines' effects on bone cell physiology. The need for future research to elucidate unclear effects of tetracyclines on the skeleton is addressed, including drug retention/release mechanisms from the bone matrix, signaling mechanisms at bone cells, the impact of newer third generation tetracycline antibiotics, and the role of the gut-bone axis.

Commensal gut bacterium critically regulates alveolar bone homeostasis

The alveolar bone is a unique osseous tissue due to the presence of the teeth and the proximity of commensal oral microbes. Commensal microbe effects on alveolar bone homeostasis have been attributed to the oral microbiota, yet the impact of commensal gut microbes is unknown. Study purpose was to elucidate whether commensal gut microbes regulate osteoimmune mechanisms and skeletal homeostasis in alveolar bone. Male C57BL/6T germfree (GF) littermate mice were maintained as GF or monoassociated with segmented filamentous bacteria (SFB), a commensal gut bacterium. SFB has been shown to elicit broad immune response effects, including the induction of T_H17/IL17A immunity, which impacts the development and homeostasis of host tissues. SFB colonized the gut, but not oral cavity, and increased IL17A levels in the ileum and serum. SFB had catabolic effects on alveolar bone and non-oral skeletal sites, which was attributed to enhanced osteoclastogenesis. The alveolar bone marrow of SFB vs. GF mice had increased dendritic cells, activated helper T-cells, T_H1 cells, T_H17 cells, and upregulated Tnf. Primary osteoblast cultures from SFB and GF mice were stimulated with vehicle-control, IL17A, or TNF to elucidate osteoblast-derived signaling factors contributing to the pro-osteoclastic phenotype in SFB mice. Treatment of RAW264.7 osteoclastic cells with supernatants from vehicle-stimulated SFB vs. GF osteoblasts recapitulated the osteoclast phenotype found in vivo. Supernatants from TNF-stimulated osteoblasts normalized RAW264.7 osteoclast endpoints across SFB and GF cultures, which was dependent on the induction of CXCL1 and CCL2. This report reveals that commensal gut microbes have the capacity to regulate osteoimmune processes in alveolar bone. Outcomes from this investigation challenge the current paradigm that alveolar bone health and homeostasis is strictly regulated by oral microbes.

Analysis of the Associations Between the Human Fecal Microbiome and Bone Density, Structure, and Strength: The Osteoporotic Fractures in Men (MrOS) Cohort

In preclinical models, the composition and function of the gut microbiota have been linked to bone growth and homeostasis, but there are few available data from studies of human populations. In a hypothesis-generating experiment in a large cohort of community-dwelling older men (n = 831; age range, 78-98 years), we explored the associations between fecal microbial profiles and bone density, microarchitecture, and strength measured with total hip dual-energy X-ray absorptiometry (DXA) and high-resolution peripheral quantitative computed tomography (HRpQCT) (distal radius, distal and diaphyseal tibia). Fecal samples were collected and the 16S rRNA gene V4 hypervariable region sequenced. Sequences were bioinformatically processed through the DADA2 pipeline and then taxonomically assigned using SILVA. Generalized linear models as implemented in microbiome multivariable association with linear models (MaAsLin 2) were used to test for associations between skeletal measures and specific microbial genera. The abundances of four bacterial genera were weakly associated with bone density, structure, or strength (false discovery rate [FDR] ≤ 0.05), and the measured directions of associations of genera were generally consistent across multiple bone measures, supporting a role for microbiota on skeletal homeostasis. However, the associated effect sizes were small (log2 fold change < ±0.35), limiting power to confidently identify these associations even with high resolution skeletal imaging phenotypes, and we assessed the resulting implications for the design of future cohort-based studies. As in analogous examples from genomewide association studies, we find that larger cohort sizes will likely be needed to confidently identify associations between the fecal microbiota and skeletal health relying on 16S sequencing. Our findings bolster the view that the gut microbiome is associated with clinically important measures of bone health, while also indicating the challenges in the design of cohort-based microbiome studies. © 2022 American Society for Bone and Mineral Research (ASBMR).

Commensal oral microbiota induces osteoimmunomodulatory effects separate from systemic microbiome in mice

Commensal microbes critically regulate skeletal homeostasis, yet the impact of specific microbiota communities on osteoimmune response mechanisms is unknown. To discern osteoimmunomodulatory effects imparted by the commensal oral microbiota that are distinct from the systemic microbiota, osteoimmunology studies were performed in both alveolar bone and nonoral skeletal sites of specific pathogen–free (SPF) versus germ-free (GF) mice and SPF mice subjected to saline versus chlorhexidine oral rinses. SPF versus GF mice had reduced cortical/trabecular bone and an enhanced pro-osteoclastic phenotype in alveolar bone. TLR signaling and Th17 cells that have known pro-osteoclastic actions were increased in alveolar BM, but not long BM, of SPF versus GF mice. MHC II antigen presentation genes and activated DCs and CD4⁺ T cells were elevated in alveolar BM, but not long BM, of SPF versus GF mice. These findings were substantiated by in vitro allostimulation studies demonstrating increased activated DCs derived from alveolar BM, but not long BM, of SPF versus GF mice. Chlorhexidine antiseptic rinse depleted the oral, but not gut, bacteriome in SPF mice. Findings from saline- versus chlorhexidine-treated SPF mice corroborated outcomes from SPF versus GF mice, which reveals that the commensal oral microbiota imparts osteoimmunomodulatory effects separate from the systemic microbiome.

The Role of Depletion of Gut Microbiota in Osteoporosis and Osteoarthritis: A Narrative Review

Osteoporosis and osteoarthritis are common diseases in an aging society, are considered metabolic diseases, and affect the quality of life of older adults. In addition, the gut microbiome is considered an additional organ to regulate bone metabolism. In the past decade, people have been studying the relationship between gut microbiota and bone metabolism. The role and mechanism of the gut microbiota in regulating bone metabolism is very important to improve the development of osteoporosis and osteoarthritis. Depletion of the gut microbiota as a method of studying the role of the gut microbiota was provided strategies to enhance the role of the gut microbiota in regulating osteoporosis and osteoarthritis. In this review, we discuss how depletion of the gut microbiota affects osteoporosis and osteoarthritis.

Effect of Lactobacillus casei fermented milk on fracture healing in osteoporotic mice

The interaction between the gut microbiota and the host has been described experimentally by germ-free animals or by antibiotic-disturbed gut microbiota. Studies on germ-free mice have shown that gut microbiota is critical for bone growth and development in mice, emphasizing that microbiota dysbiosis may interfere with normal bone development processes. This study aimed to clarify the effect of antibiotic treatment on disturbed gut microbiota on bone development in mice and to investigate the effect of probiotic treatment on fracture healing in mice with dysbiosis. Our results showed that 4 weeks old female Kunming mice showed significantly lower abundance and diversity of the gut microbiota and significantly lower bone mineral density after 12 weeks of antibiotic treatment and significantly increased levels of RANKL and Ang II in serum (p<0.05). Mice with dysbiosis received 5 mL of Lactobacillus casei fermented milk by daily gavage after internal fixation of femoral fractures, and postoperative fracture healing was evaluated by X-ray, micro-CT scan, and HE staining, which showed faster growth of the broken ends of the femur and the presence of more callus. Serological tests showed decreased levels of RANKL and Ang II (p<0.05). Similarly, immunohistochemical results also showed increased expression of α smooth muscle actin in callus tissue. These results suggest that oral antibiotics can lead to dysbiosis of the gut microbiota in mice, which in turn leads to the development of osteoporosis. In contrast, probiotic treatment promoted fracture healing in osteoporotic mice after dysbiosis, and the probiotic effect on fracture healing may be produced by inhibiting the RAS/RANKL/RANK pathway.

Novel microbiota-related gene set enrichment analysis identified osteoporosis associated gut microbiota from autoimmune diseases

INTRODUCTION

Gut microbiota is now considered to be a hidden organ that interacts bidirectionally with cellular responses in numerous organs belonged to the immune, bone, and nervous systems. Here, we aimed to investigate the relationships between gut microbiota and complex diseases by utilizing multiple publicly available genome-wide association.

MATERIALS AND METHODS

We applied a novel microbiota-related gene set enrichment analysis approach to detect the associations between gut microbiota and complex diseases by processing genome-wide association studies (GWASs) data sets of six autoimmune diseases (including celiac disease (CeD), inflammatory bowel diseases (IBD), multiple sclerosis (MS), primary biliary cirrhosis (PBC), type 1 diabetes (T1D) and primary sclerosing cholangitis (PSC)) and osteoporosis (OP).

RESULTS

The family Oxalobacteraceae and genus Candidatus_Soleaferrea were found to be correlated with all of the six autoimmune diseases (FDR adjusted P < 0.05). Moreover, we observed that the six autoimmune diseases except PBC shared 3 overlapping features (including family Peptostreptococcaceae, order Gastranaerophilales and genus Romboutsia). For all of the six autoimmune diseases and BMDs (LS-BMD and TB-BMD), an association signal was observed for genus Candidatus_Soleaferrea (FDR adjusted P < 0.05). Notably, FA / FN-BMD shared the maximum number of overlapping microbial features (e.g., genus Ruminococcaceae_UCG009, Erysipelatoclostridium and Ruminococcaceae_UCG013).

CONCLUSION

Our study found that part of the gut microbiota could be novel regulators of BMDs and autoimmune diseases via the effects of its metabolites and may lead to a better understanding of the role played by gut microbiota in the communication of the microbiota-skeletal/immune-gut axis.

Components of the Gut Microbiome That Influence Bone Tissue-Level Strength

Modifications to the constituents of the gut microbiome influence bone density and tissue-level strength, but the specific microbial components that influence tissue-level strength in bone are not known. Here, we selectively modify constituents of the gut microbiota using narrow-spectrum antibiotics to identify components of the microbiome associated with changes in bone mechanical and material properties. Male C57BL/6J mice (4 weeks) were divided into seven groups (n = 7-10/group) and had taxa within the gut microbiome removed through dosing with: (i) ampicillin; (ii) neomycin; (iii) vancomycin; (iv) metronidazole; (v) a cocktail of all four antibiotics together (with zero-calorie sweetener to ensure intake); (vi) zero-calorie sweetener only; or (vii) no additive (untreated) for 12 weeks. Individual antibiotics remove only some taxa from the gut, while the cocktail of all four removes almost all microbes. After accounting for differences in geometry, whole bone strength was reduced in animals with gut microbiome modified by neomycin (-28%, p = 0.002) and was increased in the group in which the gut microbiome was altered by sweetener alone (+39%, p < 0.001). Analysis of the fecal microbiota detected seven lower-ranked taxa differentially abundant in animals with impaired tissue-level strength and 14 differentially abundant taxa associated with increased tissue-level strength. Histological and serum markers of bone turnover and trabecular bone volume per tissue volume (BV/TV) did not differ among groups. These findings demonstrate that modifications to the taxonomic components of the gut microbiome have the potential to decrease or increase tissue-level strength of bone independent of bone quantity and without noticeable changes in bone turnover. © 2021 American Society for Bone and Mineral Research (ASBMR).

Gut Microbiota in Bone Health and Diabetes

PURPOSE OF REVIEW

Patients with diabetes mellitus (DM) are at increased risk of developing osteopathogenesis and skeletal fragility. The role of the gut microbiota in both DM and osteopathy is not fully explored and may be involved in the pathology of both diseases.

RECENT FINDINGS

Gut microbiota alterations have been observed in DM and osteopathogenic disorders as compared with healthy controls, such as significantly lower abundance of Prevotella and higher abundance of Lactobacillus, with a diminished bacterial diversity. Other overlapping gastro-intestinal features include the loss of intestinal barrier function with translocation of bacterial metabolites to the blood stream, induction of immunological deficits and changes in hormonal and endocrinal signalling, which may lead to the development of diabetic osteopathy. Signalling pathways involved in both DM and osteopathy are affected by gut bacteria and their metabolites. Future studies should focus on gut microbiota involvement in both diseases.

Gut microbiota and bone metabolism

Osteoporosis is the most common metabolic skeletal disease. It is characterized by the deterioration of the skeletal microarchitecture and bone loss, leading to ostealgia, and even bone fractures. Accumulating evidence has indicated that there is an inextricable relationship between the gut microbiota (GM) and bone homeostasis involving host-microbiota crosstalk. Any perturbation of the GM can play an initiating and reinforcing role in disrupting the bone remodeling balance during the development of osteoporosis. Although the GM is known to influence bone metabolism, the mechanisms associated with these effects remain unclear. Herein, we review the current knowledge of how the GM affects bone metabolism in health and disease, summarize the correlation between pathogen-associated molecular patterns of GM structural components and bone metabolism, and discuss the potential mechanisms underlying how GM metabolites regulate bone turnover. Deciphering the complicated relationship between the GM and bone health will provide new insights into the prevention and treatment of osteoporosis.

The modulatory effect and implication of gut microbiota on osteoporosis: from the perspective of "brain-gut-bone" axis

Osteoporosis (OP) is a kind of systemic metabolic disease characterized by decreased bone mass and destruction of the bone microstructure. In recent years, it has become an expected research trend to explore the cross-linking relationship in the pathogenesis process of OP so as to develop reasonable and effective intervention strategies. With the further development of intestinal microbiology and the profound exploration of the gut microbiota (GM), it has been further revealed that the "brain-gut" axis may be a potential target for the bone, thereby affecting the occurrence and progression of OP. Hence, based on the concept of "brain-gut-bone" axis, we look forward to deeply discussing and summarizing the cross-linking relationship of OP in the next three parts, including the "brain-bone" connection, "gut-bone" connection, and "brain-gut" connection, so as to provide an emerging thought for the prevention strategies and mechanism researches of OP.

Gut microbiome dysbiosis alleviates the progression of osteoarthritis in mice

Gut microbiota dysbiosis has been studied under the pathological conditions of osteoarthritis (OA). However, the effect of antibiotic-induced gut flora dysbiosis on OA remains incompletely understood at present. Herein, we used a mouse (8 weeks) OA model of destabilization of the medial meniscus (DMM) and gut microbiome dysbiosis induced by antibiotic treatment with ampicillin and neomycin for 8 weeks. The results show that antibiotic-induced intestinal microbiota dysbiosis reduced the serum level of lipopolysaccharide (LPS) and the inflammatory response, such as suppression of the levels of tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6), which can lead to decreased matrix metalloprotease-13 (MMP-13) expression and improvement of OA after joint injury. In addition, trabecular thickness (Tb.Th) and osteophyte scores were increased significantly in antibiotic-induced male mice compared with female mice. We further used network correlation analysis to verify the effect of gut microbiota dysbiosis on OA. Therefore, the present study contributes to our understanding of the gut-joint axis in OA and reveals the relationship between the inflammatory response, sex and gut microbiota, which may provide new strategies to prevent the symptoms and long-term sequelae of OA. Conclusion: Our data showed that gut microbiome dysbiosis alleviates the progression of OA.

Maintaining homeostatic control of periodontal bone tissue

Alveolar bone is a unique osseous tissue due to the proximity of dental plaque biofilms. Periodontal health and homeostasis are mediated by a balanced host immune response to these polymicrobial biofilms. Dysbiotic shifts within dental plaque biofilms can drive a proinflammatory immune response state in the periodontal epithelial and gingival connective tissues, which leads to paracrine signaling to subjacent bone cells. Sustained chronic periodontal inflammation disrupts "coupled" osteoclast-osteoblast actions, which ultimately result in alveolar bone destruction. This chapter will provide an overview of alveolar bone physiology and will highlight why the oral microbiota is a critical regulator of alveolar bone remodeling. The ecology of dental plaque biofilms will be discussed in the context that periodontitis is a polymicrobial disruption of host homeostasis. The pathogenesis of periodontal bone loss will be explained from both a historical and current perspective, providing the opportunity to revisit the role of fibrosis in alveolar bone destruction. Periodontal immune cell interactions with bone cells will be reviewed based on our current understanding of osteoimmunological mechanisms influencing alveolar bone remodeling. Lastly, probiotic and prebiotic interventions in the oral microbiota will be evaluated as potential noninvasive therapies to support alveolar bone homeostasis and prevent periodontal bone loss.

The role of gut microbiota in bone homeostasis

Aims

The effect of the gut microbiota (GM) and its metabolite on bone health is termed the gut-bone axis. Multiple studies have elucidated the mechanisms but findings vary greatly. A systematic review was performed to analyze current animal models and explore the effect of GM on bone.

Methods

Literature search was performed on PubMed and Embase databases. Information on the types and strains of animals, induction of osteoporosis, intervention strategies, determination of GM, assessment on bone mineral density (BMD) and bone quality, and key findings were extracted.

Results

A total of 30 studies were included, of which six studies used rats and 24 studies used mice. Osteoporosis or bone loss was induced in 14 studies. Interventions included ten with probiotics, three with prebiotics, nine with antibiotics, two with short-chain fatty acid (SCFA), six with vitamins and proteins, two with traditional Chinese medicine (TCM), and one with neuropeptide Y1R antagonist. In general, probiotics, prebiotics, nutritional interventions, and TCM were found to reverse the GM dysbiosis and rescue bone loss.

Conclusion

Despite the positive therapeutic effect of probiotics, prebiotics, and nutritional or pharmaceutical interventions on osteoporosis, there is still a critical knowledge gap regarding the role of GM in rescuing bone loss and its related pathways.

Cite this article: Bone Joint Res 2021;10(1):51–59.

Highly efficient fluorescent chemosensor for nitro antibiotic detection based on luminescent coordination polymers with 2,6-di(4-carboxyphenyl)pyrazine

A series of isostructural porous supramolecular frameworks, {[M(DCPP)(H₂O)]·(DMF)}_n, are synthesized. The as-obtained fluorescent Zn-MOF has good recognition ability towards nitro-antibiotics with low detection limits and a wide linear range.

Association of Antibiotic Alterations in Gut Microbiota With Decreased Osseointegration of an Intramedullary Nail in Mice With and Without Osteomyelitis

Treatment of osteomyelitis requires prolonged antibiotic therapy which significantly alters the gut microbiota. While the influences on bone mass and microstructure have been extensively studied, it is poorly understood what impact the changes in gut microbiota may have on the host response to osseointegration around an intramedullary nail implanted. Here, we explored the influence of gut microbiota on the bone osseointegration process around an implant under two conditions: implantation of an intramedullary nail in the bone marrow cavity and chronic osteomyelitis (CO) induced by Staphylococcus aureus infection. Body weight, hepatorenal functions, serum levels of proinflammatory cytokines were monitored. The composition of gut microbiota was assessed via 16S rRNA sequencing, and the bone condition was analyzed via micro-computed tomography, hematoxylin and eosin staining, Safranin O-fast green and Goldner's trichrome staining. Osteoblastogenesis and osteoclastogenesis were assessed by detecting tartrate-resistant acid phosphatase and osterix expression. We found that perturbation of gut microbiota (increase in Proteobacteria and decrease in Bacteroidetes) associated with delayed osseointegration and increased levels of proinflammatory cytokines in the serum (p<0.05), lower bone mass (p<0.05), deficient endochondral ossification and bone formation, reduced osteoblastogenesis (p<0.05) and enhanced osteoclastogenesis (p<0.001). Survival rates (p=0.002) and bacterial loads (p=0.0363) in bone differed significantly between the CO and antibiotic-treated CO mice, but cytokines levels, bone mineral density, and bone formation did not differ, likely because of the severely damaged bone structure. In summary, antibiotic treatment perturbed the gut microbiota and significantly interfered with the bone osseointegration around the nail by increasing proinflammatory cytokine levels in circulation, inhibiting osteoblastogenesis, enhancing osteoclastogenesis, and thus leading to higher pathogen colonization as well as higher mortality postinfection. This report of ours is the first to demonstrate antibiotic-induced alterations in the gut microbiota affect bone osseointegration, helping us understand the role of gut microbiota disorders in osteoblastogenesis and osteoclastogenesis following implant insertion with or without infection.

New perspectives on traumatic bone infections

In this paper, we review the results of previous studies and summarize the effects of various factors on the regulation of bone metabolism in traumatic bone infections. Infection-related bone destruction incorporates pathogens and iatrogenic factors in the process of bone resorption dominated by the skeletal and immune systems. The development of bone immunology has established a bridge of communication between the skeletal system and the immune system. Exploring the effects of pathogens, skeletal systems, immune systems, and antibacterials on bone repair in infectious conditions can help improve the treatment of these diseases.

Atypical immunometabolism and metabolic reprogramming in liver cancer: Deciphering the role of gut microbiome

Hepatocellular carcinoma (HCC) is the fourth leading cause of cancer-related mortality worldwide. Much recent research has delved into understanding the underlying molecular mechanisms of HCC pathogenesis, which has revealed to be heterogenous and complex. Two major hallmarks of HCC include: (i) a hijacked immunometabolism and (ii) a reprogramming in metabolic processes. We posit that the gut microbiota is a third component in an entanglement triangle contributing to HCC progression. Besides metagenomic studies highlighting the diagnostic potential in the gut microbiota profile, recent research is pinpointing the gut microbiota as an instigator, not just a mere bystander, in HCC. In this chapter, we discuss mechanistic insights on atypical immunometabolism and metabolic reprogramming in HCC, including the examination of tumor-associated macrophages and neutrophils, tumor-infiltrating lymphocytes (e.g., T-cell exhaustion, regulatory T-cells, natural killer T-cells), the Warburg effect, rewiring of the tricarboxylic acid cycle, and glutamine addiction. We further discuss the potential involvement of the gut microbiota in these characteristics of hepatocarcinogenesis. An immediate highlight is that microbiota metabolites (e.g., short chain fatty acids, secondary bile acids) can impair anti-tumor responses, which aggravates HCC. Lastly, we describe the rising 'new era' of immunotherapies (e.g., immune checkpoint inhibitors, adoptive T-cell transfer) and discuss for the potential incorporation of gut microbiota targeted therapeutics (e.g., probiotics, fecal microbiota transplantation) to alleviate HCC. Altogether, this chapter invigorates for continuous research to decipher the role of gut microbiome in HCC from its influence on immunometabolism and metabolic reprogramming.

Helicobacter pylori Related Diseases and Osteoporotic Fractures (Narrative Review)

Osteoporosis (OP) and osteoporotic fractures (OFs) are common multifactorial and heterogenic disorders of increasing incidence. Helicobacter pylori (H.p.) colonizes the stomach approximately in half of the world's population, causes gastroduodenal diseases and is prevalent in numerous extra-digestive diseases known to be associated with OP/OF. The studies regarding relationship between H.p. infection (HPI) and OP/OFs are inconsistent. The current review summarizes the relevant literature on the potential role of HPI in OP, falls and OFs and highlights the reasons for controversies in the publications. In the first section, after a brief overview of HPI biological features, we analyze the studies evaluating the association of HPI and bone status. The second part includes data on the prevalence of OP/OFs in HPI-induced gastroduodenal diseases (peptic ulcer, chronic/atrophic gastritis and cancer) and the effects of acid-suppressive drugs. In the next section, we discuss the possible contribution of HPI-associated extra-digestive diseases and medications to OP/OF, focusing on conditions affecting both bone homeostasis and predisposing to falls. In the last section, we describe clinical implications of accumulated data on HPI as a co-factor of OP/OF and present a feasible five-step algorithm for OP/OF risk assessment and management in regard to HPI, emphasizing the importance of an integrative (but differentiated) holistic approach. Increased awareness about the consequences of HPI linked to OP/OF can aid early detection and management. Further research on the HPI-OP/OF relationship is needed to close current knowledge gaps and improve clinical management of both OP/OF and HPI-related disorders.

Crosstalk between the growth hormone/insulin-like growth factor-1 axis and the gut microbiome: A new frontier for microbial endocrinology

Both the GH/IGF-1 axis and the gut microbiota independently play an important role in host growth, metabolism, and intestinal homeostasis. Inversely, abnormalities in GH action and microbial dysbiosis (or a lack of diversity) in the gut have been implicated in restricted growth, metabolic disorders (such as chronic undernutrition, anorexia nervosa, obesity, and diabetes), and intestinal dysfunction (such as pediatric Crohn's disease, colonic polyps, and colon cancer). Over the last decade, studies have demonstrated that the microbial impact on growth may be mediated through the GH/IGF-1 axis, pointing toward a potential relationship between GH and the gut microbiota. This review covers current research on the GH/IGF-1 axis and the gut microbiome and its influence on overall host growth, metabolism, and intestinal health, proposing a bidirectional relationship between GH and the gut microbiome.

Mitigating osteonecrosis of the jaw (ONJ) through preventive dental care and understanding of risk factors

It is well established that alterations in phosphate metabolism have a profound effect on hard and soft tissues of the oral cavity. The present-day clinical form of osteonecrosis of the jaw (ONJ) was preceded by phosphorus necrosis of the jaw, ca. 1860. The subsequent removal of yellow phosphorus from matches in the early 20th century saw a parallel decline in "phossy jaw" until the early 2000s, when similar reports of unusual jaw bone necrosis began to appear in the literature describing jaw necrosis in patients undergoing chemotherapy and concomitant steroid and bisphosphonate treatment. Today, the potential side effect of ONJ associated with medications that block osteoclast activity (antiresorptive) is well known, though the mechanism remains unclear and the management and outcomes are often unsatisfactory. Much of the existing literature has focused on the continuing concerns of appropriate use of bisphosphonates and other antiresorptive medications, the incomplete or underdeveloped research on ONJ, and the use of drugs with anabolic potential for treatment of osteoporosis. While recognizing that ONJ is a rare occurrence and ONJ-associated medications play an important role in fracture risk reduction in osteoporotic patients, evidence to date suggests that health care providers can lower the risk further by dental evaluations and care prior to initiating antiresorptive therapies and by monitoring dental health during and after treatment. This review describes the current clinical management guidelines for ONJ, the critical role of dental-medical management in mitigating risks, and the current understanding of the effects of predominantly osteoclast-modulating drugs on bone homeostasis.

Specific Commensal Bacterium Critically Regulates Gut Microbiota Osteoimmunomodulatory Actions During Normal Postpubertal Skeletal Growth and Maturation

The commensal gut microbiota critically regulates immunomodulatory processes that influence normal skeletal growth and maturation. However, the influence of specific microbes on commensal gut microbiota osteoimmunoregulatory actions is unknown. We have shown previously that the commensal gut microbiota enhances T_H17/IL17A immune response effects in marrow and liver that have procatabolic/antianabolic actions in the skeleton. Segmented filamentous bacteria (SFB), a specific commensal gut bacterium within phylum Firmicutes, potently induces T_H17/IL17A‐mediated immunity. The study purpose was to delineate the influence of SFB on commensal gut microbiota immunomodulatory actions regulating normal postpubertal skeletal development. Two murine models were utilized: SFB‐monoassociated mice versus germ‐free (GF) mice and specific‐pathogen‐free (SPF) mice +/− SFB. SFB colonization was validated by 16S rDNA analysis, and SFB‐induced T_H17/IL17A immunity was confirmed by upregulation of Il17a in ileum and IL17A in serum. SFB‐colonized mice had an osteopenic trabecular bone phenotype, which was attributed to SFB actions suppressing osteoblastogenesis and enhancing osteoclastogenesis. Intriguingly, SFB‐colonized mice had increased expression of proinflammatory chemokines and acute‐phase reactants in the liver. Lipocalin‐2 (LCN2), an acute‐phase reactant and antimicrobial peptide, was substantially elevated in the liver and serum of SFB‐colonized mice, which supports the notion that SFB regulation of commensal gut microbiota osteoimmunomodulatory actions are mediated in part through a gut–liver–bone axis. Proinflammatory T_H17 and T_H1 cells were increased in liver‐draining lymph nodes of SFB‐colonized mice, which further substantiates that SFB osteoimmune‐response effects may be mediated through the liver. SFB‐induction of Il17a in the gut and Lcn2 in the liver resulted in increased circulating levels of IL17A and LCN2. Recognizing that IL17A and LCN2 support osteoclastogenesis/suppress osteoblastogenesis, SFB actions impairing postpubertal skeletal development appear to be mediated through immunomodulatory effects in both the gut and liver. This research reveals that specific microbes critically impact commensal gut microbiota immunomodulatory actions regulating normal postpubertal skeletal growth and maturation. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

A Link between the Gut and Bone: Bone Health Impacted by Changes in Gut Microbiota

This commentary highlights the article by Hathaway-Schrader et al that studies the impact of antibiotic-disruption of the gut microbiota on long-term bone development.

Depletion of Intestinal Microbiome Partially Rescues Bone Loss in Sickle Cell Disease Male Mice

Osteoporosis or osteopenia are common clinical manifestations of sickle cell disease (SCD) with unclear mechanisms. Since senescence of circulating neutrophil can be modulated by signals derived from intestinal microbiome and neutrophils are abundant in bone marrow and can regulate osteoblasts and osteoclasts, we examined whether gut microbiome contributes to bone loss in SCD mice. SCD and their littermates control mice were treated with antibiotics to deplete gut microbiome. At the end of 7 weeks treatment, serum was collected for biochemistry marker measurements. Bone mass and remodeling were evaluated by dual beam X-ray absorptiometry, micro-computed tomography, and histomorphometry. Bone-related genes in tibia and barrier marker genes in the small intestine were analyzed by quantitative PCR. Antibiotic treatment rescued increased intestinal inflammatory cytokine marker genes (Tnfα, IL17, Ifnγ) expression, rescued decreased intestinal barrier marker genes (claudin 3 and claudin 15) expression, and rescued increased serum cytokines (IFNγ, IL27, IL10) in SCD mice. Antibiotic significantly improved decreased bone mass in SCD mice mainly through enhanced osteoblast function and increased osteoblast-related genes (Runx2 and Igf1) expression in SCD mice. Our findings support that increased bacteria load augments antigenic load traversing the impaired intestinal barrier through inflammation, leading to increased inflammatory cytokines, impaired osteoblast function, and bone loss in SCD mice.

Microbiota: Overview and Implication in Immunotherapy-Based Cancer Treatments

During the last few years, the gut microbiota has gained increasing attention as a consequence of its emerging role as a modulator of the immune system. With the advent of the era of checkpoint inhibitors immunotherapy and adoptive cell transfer (ACT) in oncology, these findings became of primary relevance in light of experimental data that suggested the microbiota involvement as a plausible predictor of a good or poor response. These remarks justify the efforts to pinpoint the specific actions of the microbiota and to identify new strategies to favorably edit its composition.

Regulation of Vaginal Microbiome by Nitric Oxide

In this review, the composition and regulation of vaginal microbiome that displays an apparent microbial diversity and interacts with other microbiota in the body are presented. The role of nitric oxide (NO) in the regulation of vaginal microflora in which lactobacillus species typically dominate has been delineated from the perspective of maintaining gynecologic ecosystem and prevention of onset of bacteriostatic vaginosis (BV) and/or sexually transmitted diseases (STD) including HIV-1 transmission. The interactions between NO and vaginal microbiome and its influence on the levels of Lactobacillus, hormones and other components are described. The recent progress, such as NO drugs, probiotic Lactobacilli and Lactobacillus microbots, that can be explored to alleviate abnormality of vagina microbiome, is also discussed. An identification of Oral-GI-Vagina axis, as well as the relationship between NO and Lactobacillus regulation in the healthy or pathological status of vagina microbiome, surely offers the advanced drug delivery option against BV or STD including AIDS.