Effect of carbon dioxide and various oxygen tensions on the respiratory activity of bone

Summary The present study was carried out to determine the influence of carbon dioxide and oxygen tension on the respiratory activity of bone cells in mouse calvaria in vitro. Five-day-old mouse calvaria were removed aseptically and incubated individually for 1 h at 37° C in a closed reaction chamber containing 1.5 ml of tissue culture medium made up of 60% horse serum in Gey's solution containing 100 unit/ml penicillin and 100μg/ml streptomycin. Before the calvaria were added, the medium in the incubation chamber was equilibrated with 10%, 20%, 30%, or 50% oxygen balanced with nitrogen. The effect of CO₂ on oxygen utilization by the calvaria was determined by incubating the calvaria in a medium previously equilibrated with either 50% O₂ balanced with N₂ or 50% O₂ and 5% CO₂ balanced with N₂. At each oxygen tension, the rate of oxygen utilization by the calvaria was measured polarographically by a Clark oxygen electrode. The results showed that the rate of oxygen uptake of bone increased as the oxygen tension increased and carbon dioxide stimulated significantly the rate of oxygen utilization by the bone cells. In view of the previous reports that both carbon dioxide and oxygen tension are implicated in the process of bone resorption, it is suggested that these two factors may affect bone resorption by influencing the oxygen utilization by bone cells and ultimately controlling their energy metabolism.     

The effect of ascorbic acid on the metabolism of rat calvarial bone cells in vitro

Addition of 50 micrograms/ml sodium ascorbate to confluent cultures of isolated rat calvarium bone cells resulted in a 21% increase in DNA production, a 50-60% increase in incorporation of [14C]proline into collagenous and noncollagenous proteins, and a 200% increase in alkaline phosphatase activity; under identical conditions, [35S]sulfate incorporation into proteoglycans (glycosaminoglycans) was not affected. These results suggest that ascorbate may be important in maintaining or stimulating the osteogenic phenotype of normal bone cells.     

Differentiation and mineralization in osteogenic precursor cells derived from fetal rat mandibular bone

Summary The process of mineralization in cells prepared either by neutral protease digestion (Pro I) or by collagenase digestion (fifth cycle, Col V) from fetal rat mandible was studied in vitro. Alkaline phosphatase (ALPase) activity of cells in Pro I was low on day 3, increased rapidly from day 8, and reached a maximum on day 16, whereas that in Col V was high on day 2, then declined and thereafter elevated to reach a maximum on day 13. Both cell populations synthesized type I collagen in cell matrix and medium. Type III collagen was observed in cell matrix of Pro I on day 14 and 21. There was ₂ band of type V collagen in cell matrix of Pro I on day 21. Calcium deposition could be detected from day 14 in Pro I and from day 19 in Col V. The von Kossapositive nodules were found on day 17 in Pro I and day 21 in Col V, respectively. The extracellular matrix in Pro I electron-microscopically consisted of well-banded collagen fibrils with a large number of calcified spherules. An elevation of ALPase activity, collagen synthesis, and mineral deposition occurred sequentially with a time lapse in Col V, and almost simultaneously in Pro I. The number of mineralized nodules was correlated with the density of plated cells in Pro I, but not in Col V. Dexamethasone caused an increase in the number of mineralized nodules in Pro I, but not in Col V, suggesting that Pro I contained osteoprogenitor cells. Thus, the mode of mineralization in cells derived from the mandible may differ depending on the presence of osteoprogenitor cells.     

Effect of cortisol on periosteal and nonperiosteal collagen and DNA synthesis in cultured rat calvariae

Summary The effects of cortisol on bone formation are complex and may be modulated by the presence of periosteal cells or by factors released by the periosteal tissue. To test these possibilities, cortisol was examined for its effects on the incorporation of³H-proline into collagenase-digestible protein (CDP) and noncollagen protein (NCP), on DNA synthesis and on alkaline phosphatase activity in intact and in the periosteum and nonperiosteal bone of dissected calvariae from 21-day-old fetal rats. After 24 h of treatment, cortisol increased the incorporation of³H-proline into CDP in intact bones and in the nonperiosteal bone of calvariae dissected after the culture. Cortisol inhibited the incorporation of³H-thymidine into calvarial DNA but it caused a small increase in nonperiosteal DNA content. Cortisol did not affect the incorporation of³H-proline into CDP in calvariae dissected prior to the culture if the periosteum and nonperiosteal central bone were incubated separately; the stimulatory effect was observed only if the two tissues were cultured in the same vial and were in contact. In contrast, cortisol stimulated alkaline phosphatase activity in the central nonperiosteal bone of calvariae dissected before or after the culture. After 72–96 h of treatment, cortisol inhibited the labeling of CDP, NCP, and DNA and the DNA content in intact bones and in both periosteal and nonperiosteal central bone of calvariae dissected after the culture. In contrast, when the periosteum was removed before the incubation, these inhibitory effects were observed in the periosteum and not in the nonperiosteal bone. Cortisol inhibited alkaline phosphatase activity in intact bones treated for 96 h, but removal of the periosteum resulted in a stimulatory effect in the nonperiosteal central bone. These studies indicate that 24 h treatment with cortisol stimulates collagen synthesis in nonperiosteal bone, an effect that requires the presence of periosteal tissue. Exposure to cortisol for 72–96 h inhibits collagen, noncollagen protein, and DNA synthesis, an effect that is secondary to an inhibition of periosteal cell replication. Cortisol does not cause a direct inhibition of osteoblastic function.     

Stimulation of alkaline phosphatase activity in cultured neonatal mouse calvarial bone cells by parathyroid hormone

Summary The effect of parathyroid hormone (PTH) on alkaline phosphatase activity was examined in confluent, serum-free primary cultures of neonatal mouse calvarial cells. It was found that synthetic bPTH-(1-34) caused an increase in the specific activity of skeletal alkaline phosphatase isoenzyme by 18 hours. Between 10 and 500 ng/ml, the mganitude of the change was directly related to peptide concentration. The change occurred in the absence of any effect on cell number, total cell protein, or DNA and was not the result of an effect on either proliferation or survival of a specific cell population. Results of histochemical studies indicate that bPTH-(1-34) caused an increase in the proportion of cells containing enzyme activity. The response was duplicated by intact bPTH-(1-84) and DBcAMP, but not by oxidized bPTH-(1-34) or insulin and did not require prostaglandin synthesis or hydroxylation of 25-hydroxyvitamin D₃. These results demonstrate that bPTH has a direct effect on osteoblast maturationin vitro, that the effect is specific for PTH, and suggest that it is mediated by cAMP.     

Comparative study of deflazacort,a new synthetic corticosteroid,and dexamethasone on the synthesis of collagen in different rat bone cell populations and rabbit articular chondrocytes

Summary Deflazacort is a new synthetic glucocorticoid which is an oxazoline derivative of prednisolone. In previous studies, it was shown that deflazacort, depending on the test model used, not only showed considerably more antiinflammatory potency than prednisolone in animals but also caused less deleterious effects on bone mineral metabolism than equivalent amounts of other glucocorticoids in man. In this study, we have compared the effects of deflazacort with those of dexamethasone on the synthesis of collagen in various rat bone cell populations and chondrocytes. Three bone cell populations were prepared by sequential time-dependent collagenase treatment of 1-day-old rat calvaria. Each cell population was further purified on a Percoll gradient (10–90%) yielding three populations of which two are different in alkaline and acid phosphatase and response to parathyroid hormone. A 3-day treatment of bone cell populations with deflazacort and dexamethasone (10⁻¹¹-10⁻⁵ M) revealed that both glucocorticoids, although at different concentrations, inhibited collagen synthesis. 21-desacetyl-deflazacort (5β, 11β, 16β)- 11,21-dihydroxy-2′-methyl-5-H-pregna-1-enol[17,16-d]oxazole-3,20-dione), the presumably active form of the steroid, which is formedin vivo after administration, produced nearly identical results as its precursor. Glucocorticoid concentrations at which inhibition was initially observed were 10⁻⁹ M and 10⁻⁷ M for dexamethasone and deflazacort respectively. Inhibition of collagen synthesis was significantly impaired only in cells isolated from bone during early tissue digestion, and not in those obtained during extensive collagenase treatment. Chondrocytes isolated from articular cartilage of 3-month-old rabbits and grown in primary cultures did not respond to either steroid. However, when passed and grown in secondary culture, collagen synthesis was inhibited considerably more by dexamethasone than by deflazacort. It is apparent that both deflazacort and dexamethasone, although at different concentrations, inhibit collagen synthesis in a differential manner. The lesser deterrent effect of deflazacort may be of clinical importance.     

重组BMP-4对兔骨髓基质干细胞生物学行为的影响

目的应用原核细胞基因工程方法生产出有活性的骨形态发生蛋白-4(bonemorphoge-neticprotein-4,BMP-4),观察其对骨髓基质干细胞生物学行为的影响。方法利用RT-PCR技术,从成熟的人胎盘组织中扩增出长0.34kb编码人BMP-4成熟肽的基因序列,装入表达载体pET-22b( ),转化大肠杆菌BL-21菌株,并诱导目的蛋白表达,SDS-PAGE检测表达蛋白。获得的蛋白制品经小鼠异位成骨测活证实后,诱导培养的兔骨髓基质干细胞,观测细胞形态变化、碱性磷酸酶和骨钙素的含量。结果大肠杆菌中目的蛋白表达量达菌体蛋白的15%,该蛋白可诱导骨髓基质干细胞向成骨细胞分化,形成钙结节,碱性磷酸酶和骨钙素的含量也明显增加。结论大肠杆菌可表达出有活性的BMP-4,该蛋白可诱导骨髓基质干细胞向成骨细胞分化。     

地塞米松对人牙髓细胞增殖分化影响的研究

目的观察地塞米松对体外培养的人牙髓细胞增殖和分化的影响。方法收集拔除的无龋坏、无牙周疾病的健康前磨牙及第三磨牙,获得牙髓,酶消化联合组织块法体外培养人牙髓细胞(Human dental pulp cells,hDPCs),扩增后取第4代生长状态良好的细胞用于实验。分为两组,实验组hDPCs在含2%胎牛血清(Fetal bovine serum,FBS)的αMEM培养基中加入10-8mol/L地塞米松(Dexamethasone,Dex)培养,对照组单纯使用含2%FBS的αMEM培养基培养。在细胞培养第1、3、5天检测细胞增殖情况;细胞培养的第1、5、10天分别进行ALP染色及ALP定量分析检测细胞分化情况;细胞培养第10天进行茜素红染色观察钙化结节形成情况。结果细胞增殖活性检测显示,实验组培养第3天及第5天可见hDPCs增殖活性得到显著抑制,与对照组相比有统计学差异;ALP染色及定量测定:培养10 d后,地塞米松实验组ALP活性明显高于对照组;茜素红染色结果:培养10 d后两组细胞茜素红染色均为阳性,表明实验组与对照组均有钙化结节形成,但是实验组钙化结节形成数量较多。结论酶消化联合组织块法可以成功体外培养hDPCs。10-8mol/L地塞米松可显著抑制hDPCs的增殖活性,提高hDPCs的ALP活性及矿化能力。     

Bone formation by osteoblast-like cells in a three-dimensional cell culture

Summary Cells of the clonal osteogenic cell line MC3T3-E1 were seeded onto a three-dimensional matrix of denatured collagen type 1 and cultured for a period of up to 8 weeks. Specimens were analyzed by histological, enzyme histochemical, immunocytochemical, and ultrastructural methods and byin situ hybridization between day 7 and day 56 after seeding. In 56-day cultures, the MC3T3-E1 cells were arranged in a three-dimensional network and formation of bone-like tissue was indicated by calcification of a newly synthesized collagen type I matrix resembling osteoid and surrounding osteocyte-like cells. The differentiating culture showed high expression of osteocalcin and alkaline phosphatase activity. NIH3T3 fibroblasts used as control cells passed through the network of the substrate forming a confluent monolayer underneath. This culture system offers a potentially powerful model for bone formationin vitro and for investigating the osteogenic potential of bone-derived cells.     

Effects of cyclosporin A on rat osteoblasts (ROS 17/2.8 cells) in vitro

Summary The effects of the immunosuppressive drug cyclosporin A (CsA) were evaluated on ROS 17/2.8 cells in vitro. ROS cells were treated with CsA (0, 0.5, 1.0, 5.0 g/ml) for 3 days with and without bovine parathyroid hormone (bPTH) (1–34) 10 nM. CsA at 0.5, 1.0, 5.0 g/ml without PTH and at 5.0 g/ml in the presence of PTH significantly inhibited proliferation, as determined by a tetrazolium colorimetric assay. In addition, ROS cell number was significantly reduced at 3 and 4 days with CsA (5.0 g/ml) without affecting cell viability. Incorporation of [³H]-thymidine into DNA was significantly reduced by 3.0 and 5.0 g/ml CsA after 12 and 24 hours exposure. Basal and 1,25-dihydroxyvitamin D₃-stimulated alkaline phosphatase levels in confluent ROS cells were reduced (P<0.05) with CsA (1.0 and 3.0 g/ml). Pretreatment of ROS 17/2.8 cells with CsA did not alter PTH-stimulated cAMP levels or [¹²⁵I]-PTHrP binding to ROS cells. CsA treatment of ROS 17/2.8 cells induced a spindle-shaped appearance with loss of attachment in confluent cultures. When ROS cells were cultured in CsA-containing media, cellular attachment at 6 and 12 hours was reduced (P<0.05) compared with untreated ROS cells. These findings indicate that CsA was capable of inhibiting proliferation, cell number, mitogenesis, alkaline phosphatase levels, and cell attachment of ROS cells without affecting PTH binding or cAMP levels. This direct effect of CsA on osteoblasts may be important in changes of bone remodeling observed in CsA-treated humans and animals.     

Alkaline phosphatase and ATPase activities of rat bone: Separation and characterization

Summary Extraction with Triton X-100 has proved effective in solubilizing alkaline phosphatase from rat bone particles, whereas ATPase with optimum activity at pH 8 remains attached to the bone particles. The kinetic characteristics of the ATPase activity of the Triton extracts are different from those of the same enzyme attached to bone particles, but the kinetic characteristics of the particle-bound and solubilized alkaline phosphatases are similar. The results suggest that the Triton extracts do not have true ATPase activity and provide a means of separating the ATPase and alkaline phosphatase activities.     

局部植入辛伐他汀诱导自体骨髓间充质干细胞归巢修复大鼠颅骨缺损

目的探讨局部植入辛伐他汀修复大鼠颅骨极限骨缺损的机制,即诱导自体骨髓间充质干细胞（BMSC）归巢。方法辛伐他汀5mg加聚乳酸20mg或单纯聚乳酸20mg分别溶解于200μl丙酮,制备辛伐他汀聚乳酸复合材料或单纯聚乳酸材料。16只SD大鼠尾静脉注射绿色荧光蛋白（GFP）标记的BMSC（GFP-BMSC）作为示踪细胞,48h后制作大鼠颅骨极限缺损模型,并植入辛伐他汀-聚乳酸复合材料（n=8）和单纯聚乳酸材料（n=8）进行修复。2周后经小动物活体荧光成像系统检测缺损处绿色荧光信号,冰冻切片荧光显微镜下观察辛伐他汀组（n=4）和对照组（n=4）缺损处GFP-BMSC归巢。颅骨脱钙后经免疫组化染色检测辛伐他汀组（n=4）和对照组（n=4）缺损处骨形态发生蛋白-2（BMP-2）表达。结果小动物活体荧光成像系统检测显示,辛伐他汀组缺损处有较强的绿色荧光信号,对照组缺损处绿色荧光信号较弱;冰冻切片荧光显微镜下观察发现,辛伐他汀组缺损处较对照组缺损处GFP阳性细胞数量明显增加;免疫组化检测发现,辛伐他汀组BMP-2表达增加。结论局部植入辛伐他汀可诱导自体BMSC归巢至缺损部位并参与修复,其诱导归巢过程可能与BMP-2表达上调有关。     

当归挥发油对人脐静脉内皮细胞增殖、凋亡及Ⅲ型胶原合成的影响

目的探讨当归挥发油对人脐静脉内皮细胞增殖、凋亡和胶原合成的影响。方法体外培养人脐静脉内皮细胞，用噻唑蓝比色法检测细胞增殖活性，用流式细胞术分析细胞周期及凋亡，用放射免疫法测定胶原合成。结果低浓度（≤4mg／L）当归挥发油促进细胞增殖（P〈0．05），降低G0/G1期细胞且增加S期细胞（P〈0．05），降低凋亡率（P〈0．05），而高浓度（≥16mg／L）时抑制增殖（P〈0．05），增加G0/G1期细胞且减少S期细胞（P〈0．05），增加凋亡率（P〈0．05）。当归挥发油呈剂量和时问依赖性抑制细胞合成胶原（P〈0．05或0．01）。结论当归挥发油对人脐静脉内皮细胞的增殖呈低浓度刺激高浓度抑制的双向调节作用，但对胶原合成呈抑制效应。     

Hydrolysis of pyrophosphate and ester phosphates by bone extracts

A study was conducted of the enzymatic hydrolysis of pyrophosphate and ester phosphates by extracts of bones of young rabbits. The proximal ends of humeri and distal ends of femurs were homogenized in barbital buffer (7.5 mM) at pH 7.4. The extracted pyrophosphatase activity had acid and alkaline pH optima. The acid pyrophosphatase activity at pH 5.0 was independent of magnesium up to a concentration of 3 mM and was inhibited by an excess of this ion. Pyrophosphatase activities at both pH 5.0 and 7.4 were inhibited by fluoride. The Michaelis constant of pyrophosphatase with pH 5.0 optimum activity was 1.4×10^–3 M. The bone extract, when loaded on a column of Sephadex G-200 and eluted with barbital buffer (7.5 mM) at pH 7.4 containing 1% sodium chloride, allowed a separation of the two pyrophosphatase activities; that at pH 5.0 optimum activity was associated with acid phosphatase activity. Results of experiments of the two pyrophosphatase activities and alkaline phosphatase in bones of rabbits as they aged from 5 to 60 days are presented.This investigation was supported by Grant DE-1850 from the National Institute of Dental Research, National Institute of Health, Bethesda, Maryland.The authors wish to acknowledge the help of Miss Doris Bauder in the preparation of the Sephadex columns.     

骨髓基质干细胞体外复合珊瑚材料的生长和成骨活性

目的 尝试以骨髓基质干细胞(Bone Marrow Stromal Cells,BMSCs)作为种子细胞,复合珊瑚体外培养,以发现适宜的细胞接种密度以及复合物体外共培养时间.方法 分离犬BMSCs,成骨诱导后复合珊瑚继续培养,以无诱导BMSCs复合物为对照.进行黏附率、生长曲线、扫描电镜、碱性磷酸酶(AKP)和骨钙蛋白(OCN)生物化学定量检测.结果 AKP和OCN检测均显示成骨诱导BMSCs-材料组显著高于无诱导BMSCs-材料组.复合物接种密度超过1.5×107/cm3时,黏附率显著下降;生长曲线示7天后BMSCs在材料上生长进入平台期,电镜示诱导BMSCs复合珊瑚7天后生长良好,且OCN从第7天开始表达.结论 诱导BMSCs-珊瑚复合物成骨活性高于无诱导细胞-材料复合物.复合物接种密度1.5×107/cm3,体外共培养7天较适宜.     

Impaired bone activity in aged rats: Alterations at the cellular and molecular levels

We have used a model of rapid bone induction and resorption in rats initiated by the removal of bone marrow to define age-associated deficits. Here we report the sequential expression of various genes implicated in the formation and removal of bone following marrow ablation. Significant increases in alkaline phosphatase and procollagen ₁(I) mRNA were observed by day 5, and of osteocalcin and osteopontin by day 6. At their peak, these mRNA levels were elevated three- to eight-fold and correlated with histological evidence of bone formation. No change in collagen II mRNA was observed, indicating that there was no cartilage phase. Collagenase activity increased 10-fold at day 9 and coincided with the beginning of bone resorption. Actin mRNA, a reference gene marker, remained at constant levels. Comparison of the response between adult (6 mo.) and old (24 mo.) rats showed the same temporal pattern, but a lower expression of bonerelated genes in older rats. Histological examination also showed that the bone volume and osteoblast number at day 6 were significantly lower in old rats. Furthermore, the percentage of mineralized bone was greatly reduced in the aged rat. This model system is currently being used to evaluate the effectiveness of interventions to up-regulate the bone activity in senescent rats.     

睾酮对离体胎鼠头盖骨成骨细胞影响的研究

目的 探讨雄激素对成骨细胞代谢的影响。方法 胎鼠头盖骨成骨细胞培养于含不同浓度睾酮的培养基中．观察细胞胸腺嘧啶核苷掺入、碱性磷酸薛(ALP)活性、骨钙素基因表达及骨钙素合成等细胞增殖及分化等指标的变化情况。结果 胎鼠头盖骨成骨细胞的增殖不受睾酮影响,但ALP活性、骨钙素基因表达及其合成在不同程度上受睾酮的调节。结论 雄激素对成骨细胞的分化具有促进作用,但对其增殖无影响。     

The inositol phosphate pathway as a mediator in the proliferative response of rat calvarial bone cells to cyclical biaxial mechanical strain.

Isolated newborn rat calvarial bone cells grown in monolayer on polyurethane membranes in specially constructed culture chambers and subjected to a cyclical biaxial mechanical strain of 0.17% at a frequency of 1 Hz for 30 min demonstrated a 16% increase in DNA synthesis during the subsequent 24 h. The metabolites of the inositol phosphate pathway, shown to be an important second messenger in many cell types, were shown to be elevated using high-performance liquid chromatography to separate and quantitate the various inositol polyphosphates. Inositol 1,4,5-trisphosphate, inositol 1,4-bisphosphate, and inositol 1,3,4,5-tetrakisphosphate reached peak accumulations after 20 s of mechanical strain. Inositol 1,3,4-trisphosphate reached a peak accumulation after 2 min, and inositol 1,2,3,4,5,6 phosphate reached a peak accumulation after 60 min of mechanical strain. Neomycin, an inhibitor of phospholipase C, a membrane-bound enzyme that hydrolyzes phosphatidyl inositol 4,5-bisphosphate to start the inositol phosphate cascade, completely inhibited accumulation of the above inositol phosphates during mechanical straining of the bone cells. Neomycin also completely abolished the increase in DNA synthesis that was seen after a mechanical strain of 0.17%. It is concluded from this study that the inositol phosphate pathway is activated by mechanical strain in bone cells and that this pathway is an important and primary mediator in the transduction of mechanical strain into cellular proliferation in these cells.     

Proliferation and osteoblastic differentiation of bone marrow stem cells: comparison of vertebral body and iliac crest

Bone marrow stem cells (BMSCs) can be obtained from the vertebral body (VB) and iliac crest (IC) for augmenting spinal arthrodesis. However, it is still not evaluated, which of the two sites would have a better BMSCs potential on Proliferation and osteoblastic differentiation is still not evaluated. Fourteen patients (10 men and 4 women) undergoing posterolateral lumbar arthrodesis and pedicle screw instrumentation were involved. The mean age was 54.7 years (range 31–75 years). Bone marrow aspirates were obtained from the vertebral body through the bilateral pedicle and were quantified relative to matched, bilateral aspirates from the iliac crest that were obtained from the same patient and at the same time. The mononuclear cell count and concentration of BMSCs were calculated and compared. Proliferation and osteoblastic differentiation of each of the BMSCs were characterized using biochemical and molecular biology techniques. Concentration (cells/mL) of BMSCs from VB and IC were 3.73 × 10³ and 3.19 × 10³, respectively (P > 0.05). VB and IC exhibited similar proliferation pattern at 3, 5 and 7 days, but BMSCs from the VB exhibited an increased mineralization staining with Alizarin Red S at 14 days. BMSCs from both anatomic sites expressed comparable levels of CD29, CD34, CD44, CD90 and CD105. VB and IC displayed similar levels of expression of ALP, type I collagen and osterix, but VB expressed higher level of osteocalcin and Runx-2, especially at 14 and 21 days. Our studies show that BMSCs from VB have osteogenic differentiation potential similar to IC. Based on these findings, we suggest that BMSCs from VB would be comparable candidates for osseous graft supplementation especially in spinal fusion procedures.     

Activation of serum complement inhibits collagen synthesis in fetal rat bone in organ culture

Summary Activation of rabbit serum complement caused a marked reduction in collagen synthesis but a much smaller change in noncollagen protein synthesis in fetal rat calvaria maintained in organ culture. In the periosteum of the fetal rat calvarium, both collagen and noncollagen protein synthesis were reduced, whereas in the central bone, presumably enriched in osteoblasts, only collagen synthesis was inhibited. This large decrease in bone collagen synthesis could not be attributed to enhanced degradation of newly synthesized collagen or its release into the culture medium. Activation of complement also stimulated the production of PGE in fetal rat calvaria. Antagonists of prostaglandin cyclooxygenase decreased prostaglandin synthesis but did not restore collagen synthesis in complement-treated bones, suggesting that complement decreases osteoblast collagen synthesis by a mechanism largely independent of prostaglandin production.