Low‐temperature particulate calcium phosphates for bone regeneration

Background: Low‐temperature synthesized calcium phosphates are produced by mixing calcium phosphate powders in an aqueous solution resulting in a precipitated phase. These compounds can be formulated in several forms (e.g. injectable cements and implantable blocks), and are commonly used as bone substitutes and drug delivery systems for the treatment of bone defects. As bone substitutes, calcium phosphates in general offer the advantages of being biocompatible and osteoconductive. Aims: The present work employed a machine‐based process to derive a reproducible preparation method for low‐temperature calcium phosphate particulate (LTCP). The in vivo outcomes of LTCP were compared with those of three commercially available bone substitutes by histomorphometric measurements of bone formation and material degradation in a rat femur implantation model. Materials & Methods: Specifically, LTCP, anorganic bovine bone (AB), bioactive glass (BG), and demineralized bone matrix (DBM) were implanted in defects created in the distal aspect of rat femora. Reparative bone and particulate volumes of these biomaterials were evaluated post‐operatively using micro‐computed tomography and histological analyses at 3, 6, 12, and 16 weeks. Results & Discussion: Results showed that, despite invoking bone formation, AB, BG, and DBM were found un‐resorbed in situ at 16 weeks. Conversely, LTCP showed an early increase in bone formation as well as clear evidence of complete degradation and reparative bone remodelling, resulting in the total reconstitution of the marrow cavity and marrow tissue. Conclusion: LTCP promoted increased early bone formation, associated with an improved degradation rate, compared with the other three bone‐substitute biomaterials tested. To cite this article:
Araújo MVF, Mendes VC, Chattopadhyay P, Davies JE. Low‐temperature particulate calcium phosphates for bone regeneration.
Clin. Oral Impl. Res. 21 , 2010; 632–641.     

Solution Ca/P ratio affects calcium phosphate crystal phases

Summary Previous studies on brushite formation and dissolution concluded that brushite was stable only in acidic solutions with pH<6.5. Francis in 1965 predicted that, at pH range 3.5–6.5, brushite would be the preferred phase at low solution Ca/P ratio and hydroxyapatite at high Ca/P ratio. This work presents room-temperature experimental evidence that solution Ca/P ratio affects calcium phosphate crystal phases and that brushite can be the preferred phase in certain supersaturated aqueous solutions containing Ca⁺⁺ and Pi, with or without Mg⁺⁺, even at pH 7.0. Solution mixtures were prepared containing initial [CaCl₂]=0.1−10.0 mM, [Na₂HPO₄]=0.1−100.0 mM, [MgCl₂]=0 or 3 mM. By addition of NaCl, the ionic strengths in terms of osmolarity were also varied from 100 to 800 mosM. Precipitates were isolated from solutions on the 7th, 14th and 21st days and identified by x-ray diffraction. Results indicated that in the presence of 3 mM Mg⁺⁺ and relatively high initial apparent activity products (Ca⁺⁺)(Pi), brushite, whitlockite and hydroxyapatite were obtained as transformation products of initially formed amorphous calcium phosphate when solution Ca/P ratios had low, medium and high values, respectively. In the absence of Mg⁺⁺, whitlockite was not found. However, with or without Mg⁺⁺, when (Ca⁺⁺)(Pi) was relatively low, only brushite was formed by direct crystallization. We concluded that although solutions were mixed at 23°C, pH 7.0, the results were useful in explaining the in vivo calcium phosphate crystal phases observed in renal and dental calculi.     

胫骨平台高能骨折的手术治疗

目的: 探索胫骨平台高能骨折手术治疗的临床疗效。方法: 回顾分析本院从 1997年 1月 ~2004年 3月共收治胫骨平台高能骨折即SchatzkerⅣ、Ⅴ和Ⅵ型骨折的 56例, 高能创伤造成的高能骨折均行切开复位“AO”钢板内固定治疗, 高能量创伤不仅对软组织损伤严重而且对肌肉有持续影响。结果: 随访 10个月 ~5年, 平均 1年 8个月。采用Merchant标准综合评定, 优良率达 85 .3%。结论: 胫骨平台骨折分型是高能骨折治疗的基础, 牢固可靠的内固定和早期正确处理软组织损伤是手术治疗和功能恢复的关键。     

磷酸钙骨水泥人工骨的制备及修复兔桡骨大段骨缺损的实验研究

目的制备水泥型羟基磷灰石(CPC)人工骨,并研究CPC人工骨修复兔桡骨大段骨缺损的成骨效果.方法高温法制备出磷酸四钙,然后在模拟体内环境下将其与无水磷酸氢钙发生水化固化反应,合成水泥型羟基磷灰石人工骨,将自制的CPC人工骨植入新西兰兔桡骨大段骨缺损模型中,术后4、8、12、16周取材,采用HE染色和Masson三色染色分析评价骨缺损修复效果.结果 CPC植入后4周有新生软骨形成及未成熟的骨组织,可见大量的软骨细胞、成骨细胞、胶原组织及较多的小血管.8～16周新骨继续生成,人工骨逐渐改建为成熟的板层骨、骨小梁和髓腔结构.结论 CPC人工骨制备简单,有良好的生物相容性和成骨效果,可能是一种较理想的骨移植替代材料.     

Pharmacological characterization of mitogen-activated protein kinase activation by recombinant human 5-HT<Subscript>2C</Subscript>, 5-HT<Subscript>2A</Subscript>, and 5-HT<Subscript>2B</Subscript> receptors

The type 2 serotonin (5-HT₂) receptor subfamily is known to couple to phosphoinositide hydrolysis (PI) and the subsequent mobilization of intracellular Ca²⁺, as well as the release of arachidonic acid (AA). Less is known of 5-HT₂-mediated activation of the mitogen-activated protein kinase (MAPK) or extracellular signal-regulated kinase (ERK1/2) signaling. The present study measured the relative efficacies and potencies of 5-HT agonists to activate ERK2 in non-neuronal cells expressing recombinant human 5-HT_2A, 5-HT_2B, and 5-HT_2C(ISV) receptors. 5-HT agonists stimulated ERK2 activity via all three 5-HT₂ subtypes. There were no meaningful differences in the potencies or relative efficacies of these agonists to affect ERK2 activity vs. PI accumulation or Ca²⁺ mobilization, suggesting that these pathways may be sequentially linked. Indeed, ERK2 activity was very sensitive to PKC inhibition and calcium chelation and insensitive to tyrosine kinase and PI-3-kinase inhibition. 5-HT₂ receptors efficiently couple to MAPK activation via sequential PI hydrolysis, and Ca²⁺ mobilization. This profile differs from reports of “agonist-directed trafficking of receptor stimulus” between PI/Ca²⁺ and AA pathways activated by 5-HT₂ receptors.     

在体犬急性心肌缺血再灌注31P磁共振波谱的实验研究

目的　评价 31 P磁共振频谱区分缺血再灌组心肌活力的能力。方法　建立犬缺血再灌注模型 ,用动脉夹将LAD夹闭 ,阻断血流 ,其中 7只犬夹闭 2 0min时解除动脉夹 ,使LAD再灌注为缺血再灌注顿抑心肌组 ,另外 6支犬夹闭 5h再灌注为缺血再灌注梗死组。用 31 P磁共振频谱动态观察心肌高能磷酸盐变化规律。结果　缺血再灌注梗死心肌磷酸肌酸 (Pcr)水平明显减低 ,而缺血再灌注存活心肌 (顿抑心肌 )无明显变化。缺血再灌注梗死心肌无机磷 (Pi)与磷酸肌酸的比值升高 ,而再灌注存活心肌 (顿抑心肌 )无明显变化。结论　31 P磁共振频谱能评价缺血再灌组心肌活力。这个技术临床应用方面有很大潜力     

Two repetition time saturation transfer (TwiST) with spill-over correction to measure creatine kinase reaction rates in human hearts

Background

Phosphorus saturation transfer (ST) magnetic resonance spectroscopy can measure the rate of ATP generated from phosphocreatine (PCr) via creatine kinase (CK) in the human heart. Recently, the triple-repetition time ST (TRiST) method was introduced to measure the CK pseudo-first-order rate constant k_f in three acquisitions. In TRiST, the longitudinal relaxation time of PCr while γ-ATP is saturated, T₁`, is measured for each subject, but suffers from low SNR because the PCr signal is reduced due to exchange with saturated γ-ATP, and the short repetition time of one of the acquisitions. Here, a two-repetition time ST (TwiST) method is presented. In TwiST, the acquisition with γ-ATP saturation and short repetition time is dropped. Instead of measuring T<sub>1</sub>`, an intrinsic relaxation time T₁ for PCr, T₁^intrinsic, is assumed. The objective was to validate TwiST measurements of CK kinetics in healthy subjects and patients with heart failure (HF).

Methods

Bloch equation simulations that included the effect of spillover irradiation on PCr were used to derive formulae for T₁^intrinsic and k_f measured by both TRiST and TwiST methods. Spillover was quantified from an unsaturated PCr measurement used in the current protocol for determining PCr and ATP concentrations. Cardiac TRiST and TwiST data were acquired at 3 T from 12 healthy and 17 HF patients.

Results

Simulations showed that both k_f measured by TwiST and T₁^intrinsic require spill-over corrections. In human heart at 3 T, the spill-over corrected T₁^intrinsic = 8.4 ± 1.4 s (mean ± SD) independent of study group. TwiST and TRiST k_f measurements were the same, but TwiST was 9 min faster. Spill-over corrected TwiST k_f was 0.33 ± 0.08 s⁻¹ vs. 0.20 ± 0.06 s⁻¹ in healthy vs HF hearts, respectively (p < 0.0001).

Conclusion

TwiST was validated against TRiST in the human heart at 3 T, generating the same results 9 min faster. TwiST detected significant reductions in CK k_f in HF compared to healthy subjects, consistent with prior 1.5 T studies using different methodology.

Electronic supplementary material

The online version of this article (doi:10.1186/s12968-015-0175-4) contains supplementary material, which is available to authorized users.     

生物全降解药物支架植入小型猪冠状动脉：安全性及组织相容性

背景：为解决聚左旋乳酸支架支撑力不足、代谢的酸性产物容易导致血管局部无菌性炎症等缺点,本课题组设计出新型支架,在聚左旋乳酸基础上融入无定型磷酸钙纳米颗粒。目的：评价新型生物全降解支架聚左旋乳酸/无定型磷酸钙纳米颗粒的安全性及组织相容性。方法：取16头健康西藏小型猪,随机选取左前降支、左回旋支或右冠状动脉支相同管腔大小的血管段,植入新型生物全降解支架1枚,于植入前、植入后1个月取股动脉血标本,行血液学检测。植入1,6个月后,复查冠状动脉造影后对支架段标本行苏木精-伊红染色,观察支架血管损伤、炎症及内皮化程度。结果与结论：支架植入前后血常规、血生化指标无明显变化。支架植入1,6个月后,冠状动脉造影提示冠状动脉通畅,无血栓形成,支架段血管与周围组织界限清楚,无组织粘连、坏死、贴壁不良等异常表现。与支架植入1个月时比较,植入6个月后的炎症积分降低（P 〈0.05）、内皮化积分增加（P 〈0.05）,植入部位损伤积分无明显变化;并且支架周围未见心肌梗死灶及炎性细胞浸润。结果表明新型生物全降解支架具有良好的安全性及组织相容性。     

Impaired cardiac work and oxygen uptake after reperfusion of regionally ischaemic myocardium.

Transient regional left ventricular ischaemia was produced in the isolated working perfused rat heart by ligation of the left main coronary artery and subsequent release of ligature after 15 min of acute regional myocardial ischaemia. Reperfusion restored coronary flow and the oxygen uptake to preligation values but cardiac output and peak left ventricular pressures remained impaired and tissue contents of ATP did not recover. Reperfusion also failed to restore the efficiency of the heart to pre-ligation values.