Effects of arachidonic acid and docosahexaenoic acid on differentiation and mineralization of MC3T3-E1 osteoblast-like cells

Linoleic acid blunts early osteoblast differentiation and impairs oxidative phosphorylation in vitro

BACKGROUND

Linoleic acid (LNA), an essential polyunsaturated fatty acid (PUFA), plays a crucial role in cellular functions. However, excessive intake of LNA, characteristic of Western diets, can have detrimental effects on cells and organs. Human observational studies have shown an inverse relationship between plasma LNA concentrations and bone mineral density. The mechanism by which LNA impairs the skeleton is unclear, and there is a paucity of research on the effects of LNA on bone-forming osteoblasts.

METHODS

The effect of LNA on osteoblast differentiation, cellular bioenergetics, and production of oxidized PUFA metabolites in vitro, was studied using primary mouse bone marrow stromal cells (BMSC) and MC3T3-E1 osteoblast precursors.

RESULTS

LNA treatment decreased alkaline phosphatase activity, an early marker of osteoblast differentiation, but had no effect on committed osteoblasts or on mineralization by differentiated osteoblasts. LNA suppressed osteoblast commitment by blunting the expression of Runx2 and Osterix, key transcription factors involved in osteoblast differentiation, and other key osteoblast-related factors involved in bone formation. LNA treatment was associated with increased production of oxidized LNA- and arachidonic acid-derived metabolites and blunted oxidative phosphorylation, resulting in decreased ATP production.

CONCLUSION

Our results show that LNA inhibited early differentiation of osteoblasts and this inhibitory effect was associated with increased production of oxidized PUFA metabolites that likely impaired energy production via oxidative phosphorylation.

Resolvin D1 improves allograft osteointegration and directly enhances osteoblasts differentiation

Introduction

Allografts are the most common bone grafts for repairing osseous defects. However, their use is associated with an increased risk for infections, donor disease transmission and osteointegration deficiency. Resolvin D1 (RvD1) is an endogenous lipid with a scientifically proven pivotal role in inflammation resolution and osteoclastogenesis inhibition. Yet, its biological relevance as a potential bone regenerative drug has been scarcely studied. Here, we aim to investigate the RvD1 effect on allograft osteointegration in the alveolar bone regeneration (ABR) murine model.

Methods

ABR model consisted of osseous defects that were generated by the extraction of the maxillary first molar in C57BL/6 mice. The sockets were filled with allograft and analyzed via RNA sequencing. Then they were locally injected with either RvD1 or saline via single or repeated administrations. The mice were sacrificed 2W after the procedure, and regenerated sites were analyzed using µCT and histology. First, MC3T3-E1 preosteoblasts were plated with IL-17 pro-inflammatory medium, and RANKL/OPG ratio was measured. Secondly, the MC3T3-E1 were cultured w/o RvD1, for 3W. Osteoblasts' markers were evaluated in different days, using qRT-PCR and Alizarin Red staining for calcified matrix.

Results

In vivo, neither allograft alone nor single RvD1 administration promote bone regeneration in comparison to the control of spontaneous healing and even triggered an elevation in NR1D1 and IL1RL1 expression, markers associated with inflammation and inhibition of bone cell differentiation. However, repeated RvD1 treatment increased bone content by 135.92% ± 45.98% compared to its specific control, repeated sham, and by 39.12% ± 26.3% when compared to the spontaneous healing control group (n=7/group). Histologically, repeated RvD1 reduced the number of TRAP-positive cells, and enhanced allograft osteointegration with new bone formation. In vitro, RvD1 rescued OPG expression and decreased RANKL/OPG ratio in IL-17 pro-inflammatory conditions. Furthermore, RvD1 increased the expression of RUNX2, OSX, BSP and OC/BGLAP2 and the mineralized extracellular matrix during MC3T3-E1 osteoblasts differentiation.

Conclusions

Repeated administrations of RvD1 promote bone regeneration via a dual mechanism: directly, via enhancement of osteoblasts' differentiation and indirectly, through reduction of osteoclastogenesis and RANKL/OPG ratio. This suggests that RvD1 may be a potential therapeutic bioagent for osseous regeneration following allograft implantation.

Changes in Bone Marrow Fatty Acids Early after Ovariectomy-Induced Osteoporosis in Rats and Potential Functions

The aim of this study was to investigate the changes in bone marrow fatty acids early after ovariectomy-induced osteoporosis in rats, and explore the potential function of the bone marrow fatty acids. Ninety-six female Sprague Dawley rats (12 weeks) were randomly divided into an ovariectomized (OVX) group and Sham group (N = 48/group) and received ovariectomy or Sham surgery, respectively. After 3, 5, 7,14, 21 and 28 days, eight rats in each group were sacrificed to detect the composition of bone marrow fatty acids by means of gas chromatography-mass spectrometry and evaluate the trabecular bone microarchitecture by means of microCT. Bone marrow rinsing fluid and serum were collected for the detection of nitric oxide synthase/nitric oxide (NOS/NO) and bone metabolism related parameters, respectively. Our results demonstrated that the bone microstructure was damaged significantly from 14 days after OVX surgery onwards. Sample clustering and group separation were observed between the OVX group and Sham group 3 and 14 days after surgery, which suggested the role of bone marrow fatty acids in the early stage of postmenopausal osteoporosis. Palmitoleate, myristate and arachidonate were found to play an important role in classification between the OVX group and Sham group on the 3rd day after surgery (VIP > 1, p < 0.05). Palmitoleate, myristate, alpha linolenate, stearate and eicosenoate were found to play an important role in classification between the OVX group and Sham group on the 14th day after surgery (VIP > 1, p < 0.05). The levels of myristate, palmitoleate, alpha linolenate and eicosenoate were significantly decreased in the OVX group, while the levels of arachidonate and stearate were significantly increased in OVX group (p < 0.05). Additionally, myristate, palmitoleate, alpha linoleate and eicosenoate were negatively correlated with C-terminal telopeptide of type 1 collagen (CTX-1, a bone resorption marker), while arachidonate was negative correlated with osteocalcin (OCN, a bone formation marker) (p < 0.05). A significant correlation was also found between eicosenoate and NOS (p < 0.05). Profound bone marrow fatty acids changes have taken place in the early stage of post-menopausal osteoporosis. They may affect bone formation though affecting the differentiation and function of osteoclasts or osteoblasts, respectively. The NOS/NO system may mediate the influence of eicosenoate on bone formation.

Docosahexaenoic acid improves altered mineralization proteins, the decreased quality of hydroxyapatite crystals and suppresses oxidative stress induced by high glucose

Patients with type 2 diabetes mellitus (DM2) experience an increased risk of fractures and a variety of bone pathologies, such as osteoporosis. The suggested mechanisms of increased fracture risk in DM2 include chronic hyperglycaemia, which provokes oxidative stress, alters bone matrix, and decreases the quality of hydroxyapatite crystals. Docosahexaenoic acid (DHA), an omega-3 fatty acid, can increase bone formation, reduce bone loss, and it possesses antioxidant/anti-inflammatory properties. The present study aimed to determine the effect of DHA on altered osteoblast mineralisation and increased reactive oxygen species (ROS) induced by high glucose concentrations. A human osteoblast cell line was treated with 5.5 mM glucose (NG) or 24 mM glucose (HG), alone or in combination with 10 or 20 µM DHA. The collagen type 1 (Col1) scaffold, the expression of osteocalcin (OCN) and bone sialoprotein type-II (BSP-II), the alkaline phosphatase (ALP) specific activity, the mineral quality, the production of ROS and the mRNA expression of nuclear factor erythroid 2-related factor-2 (NRF2) were analysed. Osteoblasts cultured in HG and treated with either DHA concentration displayed an improved distribution of the Col1 scaffold, increased OCN and BSP-II expression, increased NRF2 mRNA, decreased ALP activity, carbonate substitution and reduced ROS production compared with osteoblasts cultured in HG alone. DHA counteracts the adverse effects of HG on bone mineral matrix quality and reduces oxidative stress, possibly by increasing the expression of NRF2.

17-β-estradiol up-regulates apolipoprotein genes expression during osteoblast differentiation in vitro

Apolipoproteins are of great physiological importance and are associated with different diseases. Many independent studies of patterns of gene expression during osteoblast differentiation have been described, and some apolipoproteins have been induced during this process. 17-β-estradiol (E2) may enhance osteoblast physiological function. However, no studies have indicated whether E2 can modulate the expression of apolipoproteins during osteoblast differentiation in vitro. The aim of the current study was to observe the regulation of apolipoprotein mRNA expression by E2 during this process. Primary osteoblasts were collected from the calvaria of newborn mice and were subjected to osteoblast differentiation in vitro with serial concentrations of E2. RNA was isolated on days 0, 5, and 25 of differentiation. Real-time PCR was performed to analyze the levels of apolipoprotein mRNA. Results showed that during osteoblast differentiation all of the apolipoprotein genes were up-regulated by E2 in a dose-dependent manner. Moreover, only ApoE was strongly induced during the mineralization of cultured osteoblasts. This result suggests that ApoE might be involved in osteoblast differentiation. The hypothesis is that E2 promotes osteoblast differentiation by up-regulating ApoE gene expression, though further study is needed to confirm this hypothesis.

Intranasal microemulsion for targeted nose to brain delivery in neurocysticercosis: Role of docosahexaenoic acid

Intranasal Microemulsions (MEs) for nose to brain delivery of a novel combination of Albendazole sulfoxide (ABZ-SO) and Curcumin (CUR) for Neurocysticercosis (NCC), a brain infection are reported. MEs prepared by simple solution exhibited a globule size <20nm, negative zeta potential and good stability. The docosahexaenoic acid (DHA) ME revealed high and rapid ex vivo permeation of drugs through sheep nasal mucosa. Intranasal DHA ME resulted in high brain concentrations and 10.76 (ABZ-SO) and 3.24 (CUR) fold enhancement in brain area-under-the-curve (AUC) compared to intravenous DHA MEs at the same dose. Direct nose to brain transport (DTP) of >95% was seen for both drugs. High drug targeting efficiency (DTE) to the brain compared to Capmul ME and drug solution (P<0.05) suggested the role of DHA in aiding nose to brain delivery. Histopathology study confirmed no significant changes. High efficacy of ABZ-SO: CUR (100:10ng/mL) DHA ME in vitro on Taenia solium cysts was confirmed by complete ALP inhibition and disintegration of cysts at 96h. Considering that the brain concentration at 24h was 1400±160.1ng/g (ABZ-SO) and 120±35.2ng/g (CUR), the in vitro efficacy seen at a 10 fold lower concentration of the drugs strongly supports the assumption of clinical efficacy. The intranasal DHA ME is a promising delivery system for targeted nose to brain delivery.

Arachidonic acid enhances turnover of the dermal skeleton: studies on zebrafish scales

In fish nutrition, the ratio between omega-3 and omega-6 poly-unsaturated fatty acids influences skeletal development. Supplementation of fish oils with vegetable oils increases the content of omega-6 fatty acids, such as arachidonic acid in the diet. Arachidonic acid is metabolized by cyclooxygenases to prostaglandin E2, an eicosanoid with effects on bone formation and remodeling. To elucidate effects of poly-unsaturated fatty acids on developing and existing skeletal tissues, zebrafish (Danio rerio) were fed (micro-) diets low and high in arachidonic acid content. Elasmoid scales, dermal skeletal plates, are ideal to study skeletal metabolism in zebrafish and were exploited in the present study. The fatty acid profile resulting from a high arachidonic acid diet induced mild but significant increase in matrix resorption in ontogenetic scales of adult zebrafish. Arachidonic acid affected scale regeneration (following removal of ontogenetic scales): mineral deposition was altered and both gene expression and enzymatic matrix metalloproteinase activity changed towards enhanced osteoclastic activity. Arachidonic acid also clearly stimulates matrix metalloproteinase activity in vitro, which implies that resorptive effects of arachidonic acid are mediated by matrix metalloproteinases. The gene expression profile further suggests that arachidonic acid increases maturation rate of the regenerating scale; in other words, enhances turnover. The zebrafish scale is an excellent model to study how and which fatty acids affect skeletal formation.

High-dose eicosapentaenoic acid and docosahexaenoic acid supplementation reduces bone resorption in postmenopausal breast cancer survivors on aromatase inhibitors: a pilot study

Postmenopausal breast cancer survivors are living longer; however, a common class of drugs, aromatase inhibitors (AI), depletes estrogen levels, promotes bone loss, and heightens fracture risk. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may offset AI effects to bone because of the known effects on cellular processes of bone turnover. Therefore, we hypothesized that 4 g of EPA and DHA daily for 3 mo would decrease bone turnover in postmenopausal breast cancer survivors on AI therapy in a randomized, double-blind, placebo controlled pilot study that included 38 women. At baseline and 3 mo, serum fatty acids, bone turnover, and inflammatory markers were analyzed. Serum EPA and DHA, total and long-chain (LC) omega (n)-3 polyunsaturated fatty acids (PUFA) increased, whereas arachidonic acid, total and LC n-6 PUFA, and the LC n-6:n-3 PUFA ratio decreased compared to placebo (all P < .05). Bone resorption was inhibited in the fish oil responders compared to placebo (P < .05). Inflammatory markers were not altered. This short-term, high-dose fish oil supplementation study's findings demonstrate that fish oil can reduce bone resorption; however, longer-term studies are needed to assess bone density preservation and to explore mechanistic pathways in this population at high risk for bone loss.

Arachidonic acid: a bridge between traumatic brain injury and fracture healing

Traumatic brain injury (TBI) is associated with enhanced osteogenesis. The aim of this study was to investigate the effect of serum from TBI rats on fracture healing. Results from this study showed that the serum from TBI rats enhanced the expression of bone gamma carboxyglutamate protein (BGLAP), and promoted in vitro proliferation of MC3T3-E1 cells, a mouse osteoblastic cell line. Furthermore, gas chromatography/mass spectrometry (GC/MS) coupled with multivariate statistical analysis was used to identify the changes in global serum metabolites after TBI. We found that arachidonic acid (AA) was significantly enhanced in serum metabolites in TBI subjects, while hydroxybutyric acid, leucine, malic acid, 5-oxyproline, isocitric acid, mannose, and uric acid were reduced. Finally, we examined the effects of AA on BGLAP expression and cell proliferation in MC3T3-E1 cells. We found that BGLAP expression and proliferation of osteoblasts were positively regulated in the presence of AA. These findings suggest that the increased AA in serum after TBI may play a key role in enhancing the speed of fracture healing.

The role of apolipoprotein E in bone metabolism

Apolipoprotein E (apoE) is a major structural apolipoprotein of several lipoprotein classes. Over the last 13 years, numerous studies have focused on the question whether human apoE affects bone phenotypes and, more recently, whether apoE regulates bone metabolism in mice. Here, we first provide a brief background introduction into the structure, established physiological and pathophysiological functions of apoE, and will then discuss the new aspects of the emerging role of apoE in bone.

Absence of glutamine supplementation prevents differentiation of murine calvarial osteoblasts to a mineralizing phenotype

Osteoblasts in vitro differentiate from a proliferating to a mineralizing phenotype upon transfer to a medium rich in beta-glycerophosphate and ascorbic acid. The nutritional requirements of the cells at different stages of this differentiation process are not known. In other cell types, nutritional supplementation during surgery can improve the outcome in terms of speed of patient recovery and prognosis. There is therefore the potential for supplementation at the site of fracture repair or bone grafting with critical osteoblast nutritional factors to potentially accelerate healing. In this study we investigate which common cell nutrients are required for the proliferating and mineralizing stages of osteoblast differentiation. Medium containing 5.5 mM glucose was sufficient to achieve maximal proliferation of primary calvarial osteoblasts and human osteoblast cell lines, with some added benefit of additional glutamine supplementation. However, when cells were stimulated to mineralize, glucose was insufficient to support their energetic requirements. Only when cells were supplemented with glucose together with glutamine were high levels of osteocalcin expression observed together with mineralized nodules in culture, suggesting that this would be a useful combination to assess in cultures of primary human osteoblasts to determine whether it may have beneficial effects during fracture surgery, bone grafting, and fixation of uncemented arthroplasty implants.

Eicosapentaenoic acid decreases expression of anandamide synthesis enzyme and cannabinoid receptor 2 in osteoblast-like cells

Anandamide (AEA) is an endogenous agonist for the cannabinoid receptor 2 (CB2) which is expressed in osteoblasts. Arachidonic acid (AA) is the precursor for AEA and dietary n-3 polyunsaturated fatty acids (PUFA) are known to reduce the concentrations of AA in tissues and cells. Therefore, we hypothesized that n-3 PUFA, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which reduce AA in cells, could lower AEA in osteoblasts by altering enzyme expression of the endocannabinoid (EC) system. MC3T3-E1 osteoblast-like cells were grown for 6, 10, 15, 20, 25 or 30 days in osteogenic medium. Osteoblasts were treated with 10 μM of AA, EPA, DHA, oleic acid (OA) or EPA+DHA (5 μM each) for 72 h prior to their collection for measurement of mRNA and alkaline phosphatase (ALP) activity. Compared to vehicle control, osteoblasts treated with AA had higher levels of AA and n-6 PUFA while those treated with EPA and DHA had lower n-6 but higher n-3 PUFA. Independent of the fatty acid treatments, osteoblasts matured normally as evidenced by ALP activity. N-acyl phosphatidylethanolamine-selective phospholipase D (NAPE-PLD), fatty acid amide hydrolase (FAAH) and CB2 mRNA expression were higher at 20 days compared to 10 days. NAPE-PLD and CB2 mRNA was lower in osteoblasts treated with EPA compared to all other groups. Thus, mRNA expression for NAPE-PLD, FAAH, and CB2 increased during osteoblast maturation and EPA reduced mRNA for NAPE-PLD and CB2 receptor. In conclusion, EPA lowered mRNA levels for proteins of the EC system and mRNA for AEA synthesis/degradation is reported in osteoblasts.

The endocannabinoid signaling system: a marriage of PUFA and musculoskeletal health

The role of diet in health and diseases related to muscle and bone has been an area of active study. Recently, endocannabinoids (EC), endogenous derivatives of arachidonic acid, an omega-6 (n-6) polyunsaturated fatty acid (PUFA), have been discovered to play regulatory roles in bone mass and muscle energy metabolism. This signaling system consists of the G-protein coupled cannabinoid receptors, CB1 and CB2, expressed in central and peripheral tissues and cells, which are variably activated by the production and on demand release of endogenous and synthetic agonists and antagonists. We propose that the balance between omega-6 and omega-3 (n-3) PUFA is an important modifier for the activation and suppression of endocannabinoid receptors and therefore, downstream signaling actions in cells. The potential of dietary PUFA to regulate this signaling system to influence the metabolic and physiological outcomes favorable to musculoskeletal health is the purpose of this review. The important role of n-3 PUFA in metabolic and physiological processes that attenuate muscle and bone loss under conditions of disease and stress is one aspect described herein. In this review, we first introduce the EC agonists (ligands) and their receptors (CB1 and CB2) and the general actions of EC signaling in various organs and systems. Second, we describe EC signaling in bone and muscle and how dietary PUFA influence the levels of endogenous agonists. Third, we discuss the potential implications of how dietary PUFA impact this system to minimize muscle atrophy and osteopenia and support healthy muscle development and bone modeling.

Inhibition of collagen fibrillogenesis by cells expressing soluble extracellular domains of DDR1 and DDR2

Collagen fiber assembly affects many physiological processes and is tightly controlled by collagen-binding proteins. However, to what extent membrane-bound versus cell-secreted collagen-binding proteins affect collagen fibrillogenesis is not well understood. In our previous studies, we had demonstrated that the membrane-anchored extracellular domain (ECD) of the collagen receptor discoidin domain receptor 2 (DDR2) inhibits fibrillogenesis of collagen endogenously secreted by the cells. These results led to a novel functional role of the DDR2 ECD. However, since soluble forms of DDR1 and DDR2 containing its ECD are known to naturally exist in the extracellular matrix, in this work we investigated if these soluble DDR ECDs may have a functional role in modulating collagen fibrillogenesis. For this purpose, we created mouse osteoblast cell lines stably secreting DDR1 or DDR2 ECD as soluble proteins. Transmission electron microscopy, fluorescence microscopy, and hydroxyproline assays were used to demonstrate that DDR ECD expression reduced the rate and quantity of collagen deposition and induced significant changes in fiber morphology and matrix mineralization. Collectively, our studies advance our understanding of DDR receptors as powerful regulators of collagen deposition in the ECM and elucidate their multifaceted role in ECM remodeling.