Microdamage in response to repetitive torsional loading in the rat tibia

Summary Tibiae from 60 male Wistar rats, aged 13 ±1 weeks, were divided into six groups for mechanical and histological testing. Bones were loaded repetitively in torsion at 90 deg.s⁻¹. Group 1 was subjected to 5,000 loading cycles at a twist angle of 3.6°, groups 2–5 to 10,000 cycles at 3.6, 5.4, 7.2, and 9.0°, respectively, and group 6 was tested to failure. Six transverse sections from the middiaphysis were then cut, bulk-stained in basic fuchsin, and hand ground to 30–50 μm to examine the presence of microcracks. Cracks were classified as running parallel to lamellae, crossing lamellae, crossing the full thickness of the cortex, or invading vascular canals. Results for fatigue testing showed that the tibiae exhibited a gradual decrease in torque (P<0.05), average stress (P<0.01), stiffness (P<0.01) and energy absorbed (P<0.01) from the initial loading cycle. Analysis of microdamage showed an increase in the variety of cracks from groups, 1–5. Analysis of deviance demonstrated a strong dependence of crack probability on the level of loading for all crack types (P<0.05) except those crossing lamellae. This study reinforces the evidence that yielding of bone observed during repetitive loading is caused by diffuse structural damage such as microcracking or debonding.     

CO2 Pneumoperitoneum modifies the inflammatory response to sepsis

OBJECTIVE: To analyze the effect of CO2 pneumoperitoneum on the inflammatory response induced by sepsis during laparoscopy. SUMMARY BACKGROUND DATA: A growing body of evidence challenges the once generally accepted notion that smaller incisions alone account for the observed benefits of the laparoscopic approach. Furthermore, laparoscopic surgery is now being applied to a broad spectrum of patients, including those in whom the inflammatory response is ignited. Delineation of the effects of CO2 pneumoperitoneum on the inflammatory response induced by sepsis is needed. METHODS: Sepsis was induced in rats by cecal ligation and puncture (CLP) performed either open or laparoscopically using CO2 or helium as insufflation gases. Animals were killed 24 hours postoperatively, at which time whole blood was collected for complete blood cell counts and livers were harvested for analysis of hepatic expression of the rat acute phase genes alpha2-macroglobulin and beta-fibrinogen. RESULTS: Laparoscopic CLP using CO2 resulted in significantly reduced hepatic expression of the rat acute phase gene alpha2-macroglobulin compared to both laparoscopic CLP using helium and open CLP. Hepatic expression of another rat acute phase gene, beta-fibrinogen, paralleled that of alpha2-macroglobulin and was significantly reduced following laparoscopic CLP using CO2 compared to laparoscopic CLP using helium. Total white blood cell and neutrophil counts following CLP were both significantly higher when CLP was performed laparoscopically using CO2 than when CLP was performed open or laparoscopically using helium. CONCLUSIONS: Intra-abdominal CO2 present during laparoscopy attenuates the acute phase inflammatory response associated with perioperative sepsis.     

Bone maturation in the vitamin D,phosphate deficient rat and the response to acid loading

Summary Vitamin D and phosphate deficiency were produced in rats in order (a) to evaluate the degree of bone mineral and matrix maturation using a bromoform/toluene density gradient technique; and (b) to compare the aforementioned bone maturational changes due to vitamin D and phosphate deprivation to those produced with superimposed severe acidosis. Rats were fed a diet deficient in vitamin D and phosphorus (0.2%) from 3 weeks through 7 weeks of age. To examine the additional contribution of dietary calcium, we gave one-half of the animals either a low (0.06%) or high (1.3%) calcium diet. Following the 4 weeks of vitamin D deficiency, one-half of each group was given 1.8% NH₄Cl in the drinking water for 4 succeeding days to induce an acute, severe acidosis. The degree of bone maturation was quantitated via bromoformtoulene density gradient fractionation; total mineral and hydroxyproline (collagen) levels were quantitated as well. The vitamin D-deficient rats deprived of adequate dietary phosphate responded by conserving phosphorus, and as a consequence total bone phosphorus levels were maintained within that level for control rats. This conservation was independent of calcium intake but was extremely sensitive to acute acid loading, where a significant reduction in total bone phosphorus was noted. The bone maturational profile obtained from the vitamin D-phosphate deficient rats, however, revealed a significant accumulation of less mature or dense bone collagen and mineral with a corresponding decrease in the most mature or dense moieties. In contrast to the reduction of the total bone phosphorus content by acute acidosis, the skeletal collagen-mineral maturational profile was not significantly affected by the short-term systemic acidosis. The observed retardations in the bone collagen and mineral maturation of the vitamin D-deficient, phosphate-deprived state provide an additional observation which may well relate to the progressive osteopenia documented in states of chronic, mild acidosis.     

Insulin enhances the bradykinin response in L8 rat skeletal myoblasts

Inhibitors of ACE/kininase II enhance insulin sensitivity, an action that is mediated in part by bradykinin (BK). We investigated whether insulin interacts with the BK receptor signaling to modulate the inositol 1,4,5-trisphosphate (IP3) response to BK in L8 rat skeletal myoblasts. Stimulation of the cultures with BK (10 nmol/l) for 15 s increased IP3 from a basal level of 75.2 +/- 7.6 to 200.2 +/- 15.7 pmol/mg protein. Treatment of the cultures with 1, 2, and 20 nmol/l of insulin for 90 min before adding BK increased IP3 formation by the same BK dose to 328.2 +/- 19, 434.5 +/- 18, and 460.8 +/-21.3 pmol/mg protein, respectively. When wortmannin was administered to inhibit phosphatidylinositol (PI) 3-kinases at lower concentration (1 nmol/l), it increased IP3 formation stimulated by BK only when insulin was present. At a higher concentration (100 nmol/l), wortmannin significantly enhanced BK-induced IP3 formation in the absence of insulin. Genistein and tyrphostin A-23, tyrosine kinase inhibitors, completely reversed the elevated IP3 formation by BK and insulin. The IP3 response to 10 nmol/l BK was 223.3 +/- 11.8 pmol/mg protein in the absence of insulin and 402.2 +/- 12.0 pmol/mg protein in the presence of 2 nmol/l insulin. However, when exposing the cultures to 1 nmol/l genistein or tyrphostin A-23, the IP3 response to BK in the presence of insulin decreased to 211.8 +/- 46.7 and 187.7 +/- 19.9 pmol/mg protein. Tyrphostin A-1, the inactive analog, was ineffective. Exposing the cells to 1 micromol/ 3,4,5-trimethoxybenzoic acid 8-[diethylamino]octyl ester, an intracellular Ca2+ antagonist, did not change the potentiation by insulin. But, exposing them to 0.1 micromol/l n-[6-aminohexyl]-5-chloro-1-naphthalene-sulfonamide, a calmodulin antagonist, resulted in enhanced IP3 response to BK alone to 292.2 +/- 18.5 pmol/mg protein and to BK in the presence of 1, 2, and 20 nmol/l insulin to 488 +/- 22.2, 625.5 +/- 11.6, and 665.2 +/- 15.9 pmol/mg protein, respectively. In conclusion, insulin potentiates BK-induced IP3 production in L8 rat skeletal myoblasts, and this action of insulin involves a tyrosine kinase. Inhibition of PI 3-kinases potentiated BK-induced IP3 formation in the presence of insulin. Calmodulin blocked the action of insulin. These results support a modulatory effect of insulin on the BK signaling system via a tyrosine kinase in L8 rat skeletal myoblasts that results in increased IP3 formation. Because BK release from skeletal muscle increases during contractions, this action of insulin is likely to play a role in the modulation of the excitation-contraction coupling process of the skeletal muscle.     

Effect of parathyroid hormone on cortical bone response to in vivo external loading of the rat tibia

Cortical bone responses following administration of parathyroid hormone (PTH) were evaluated using a four-point bending device to clarify the relationship between the effect of PTH and mechanical loading. Female Wistar rats, 36-months-old, were used. Rats were randomized into three groups (n = 10/group), namely PTH-5 (5 μg PTH/kg body weight), PTH-30 (30 μg PTH/kg body weight), and PTH-v (vehicle). PTH (human PTH (1–34)) was injected subcutaneously three times/week for 3 weeks. Loads on the right tibia were applied in vivo at 29.1 ± 0.3 N for 36 cycles at 2 Hz 3 days/week for 3 weeks using four-point bending. The administration of PTH and tibial mechanical loading were performed on the same day. After calcein double labeling, rats were killed and tibial cross-sections were prepared from the region with maximal bending at the central diaphysis. Histomorphometry was performed over the entire periosteal and endocortical surfaces of the tibiae, dividing the periosteum into lateral and medial surfaces. The in vivo average peak tibial strains (predicted) on the lateral periosteal surface were 1392.4, 1421.8 and 1384.7 μstrain in PTH-v, PTH-5 and PTH-30 groups, respectively, showing no significant difference among the three groups. Significant loading-related increases in the bone formation surface, mineral apposition rate, and bone formation rate were observed at the periosteal and endocortical surfaces. Significant differences between PTH groups were also seen. Interaction between mechanical loading and PTH was significant at both periosteal and endocortical surfaces. It is concluded that PTH has a synergistic effect on the cortical bone response to mechanical loading. Received: October 4, 2000 / Accepted: January 12, 2001     

Understanding the mechanisms by which isoflurane modifies the hyperglycemic response to surgery.

We studied the effect of anesthesia on the kinetics of perioperative glucose metabolism by using stable isotope tracers. Twenty-three patients undergoing cystoprostatectomy were randomly assigned to receive epidural analgesia combined with general anesthesia (n = 8), fentanyl and midazolam anesthesia (n = 8), or inhaled anesthesia with isoflurane (n = 7). Whole-body glucose production and glucose clearance were measured before and during surgery. Glucose clearance significantly decreased during surgery independent of the type of anesthesia. Epidural analgesia caused a significant decrease in glucose production from 10.2 +/- 0.4 to 9.0 +/- 0.4 micromol. kg(-1). min(-1) (P < 0.05), whereas the plasma glucose concentration was not altered (before surgery, 5.0 +/- 0.2 mmol/L; during surgery, 5.2 +/- 0.1 mmol/L). Glucose production did not significantly change during fentanyl/midazolam anesthesia (before surgery, 10.5 +/- 0.5 micromol. kg(-1). min(-1); during surgery, 10.1 +/- 0.5 micromol. kg(-1). min(-1)), but plasma glucose concentration significantly increased from 4.8 +/- 0.1 mmol/L to 5.3 +/- 0.2 mmol/L during surgery (P < 0.05). Isoflurane anesthesia caused a significant increase in plasma glucose concentration (from 5.2 +/- 0.1 mmol/L to 7.2 +/- 0.5 mmol/L) and glucose production (from 10.8 +/- 0.5 micromol. kg(-1). min(-1) to 12.4 +/- 1.0 micromol. kg(-1). min(-1)) (P < 0.05). Epidural analgesia prevented the hyperglycemic response to surgery by a decrease in glucose production. The increased glucose plasma concentration during fentanyl/midazolam anesthesia was caused by a decrease in whole-body glucose clearance. The hyperglycemic response observed during isoflurane anesthesia was a consequence of both impaired glucose clearance and increased glucose production. Implications: Epidural analgesia combined with general anesthesia prevented the hyperglycemic response to surgery by decreasing endogenous glucose production.The increased glucose plasma concentration in patients receiving fentanyl/midazolam anesthesia was caused by a decrease in whole-body glucose clearance. The hyperglycemic response observed during inhaled anesthesia with isoflurane was a consequence of both impaired glucose clearance and increased glucose production.     

Calciuretic response to protein loading in burn patients

The effect of dietary protein on calcium excretion has been evaluated in 6 patients with major burns. A marked calciuresis was noted when patients received more than 150g protein per day while urinary calciums approaching normal levels were noted when protein intake was less than 150 g. Excessive calcium mobilization and excretion secondary to protein loading may account for heterotopic calcium deposits and renal stones frequently seen in burn patients. Although the mechanism is not clearly defined, a primary alteration in calcium transport by the kidney seems likely.     

Site-specific skeletal response to long-term weight training seems to be attributable to principal loading modality: a pQCT study of female weightlifters

Physical training may be able to improve bone strength through site-specific changes in the composition, size and structure of the bone without notable increases in volumetric density. To address this possibility specifically, we compared 14 competitive female weightlifters with 14 female physical therapy students. Peripheral quantitative computed tomographic scans (pQCT) were taken from the distal radius, radial shaft, distal femur, and tibial midshaft of the dominant limb. Analysis of covariance (ANCOVA) was used to estimate the intergroup differences, using body weight and age as covariates. Cortical density did not differ between the weightlifters and controls at any site, whereas trabecular density was greater in the weightlifters, the benefit being 10% (P = 0.186) at the distal radius and 11% (P = 0.040) at the distal femur compared with the controls. Weightlifters' cortical cross-sectional area was 38% (P = 0.029) larger at the distal radius, 26% larger (P = 0.001) at the radial shaft, and 9% larger at the tibial midshaft (P = 0.034). Consequently, the weightlifters' forearm bone strength indices were also significantly higher, the intergroup difference being 41% (P = 0.001) at the distal radius and 43% (P = 0.004) at the radial shaft. Thus, the observed intergroup difference at the distal radius was mainly due to enlarged bone, particularly its cortex, rather than higher volumetric bone density. Findings at the radial shaft were similar. In contrast, weightlifters' trabecular tissue at the distal femur was denser but the bone per se was not clearly bigger than that of the controls' (intergroup difference 5%, P = 0.117). We suggest that bones subjected to exceptionally high bending-loading (distal radius and radial shaft) are larger than their normal counterparts while at sites experiencing axial, compressive-loading (e.g., distal femur), a denser trabecular structure (more load-carrying area) may be sufficient and any substantial enlargement in bone size may not be necessary.     

Sclerostin antibody inhibits skeletal deterioration due to reduced mechanical loading

Sclerostin, a product of the SOST gene produced mainly by osteocytes, is a potent negative regulator of bone formation that appears to be responsive to mechanical loading, with SOST expression increasing following mechanical unloading. We tested the ability of a murine sclerostin antibody (SclAbII) to prevent bone loss in adult mice subjected to hindlimb unloading (HLU) via tail suspension for 21 days. Mice (n = 11–17/group) were assigned to control (CON, normal weight bearing) or HLU and injected with either SclAbII (subcutaneously, 25 mg/kg) or vehicle (VEH) twice weekly. SclAbII completely inhibited the bone deterioration due to disuse, and induced bone formation such that bone properties in HLU‐SclAbII were at or above values of CON‐VEH mice. For example, hindlimb bone mineral density (BMD) decreased –9.2% ± 1.0% in HLU‐VEH, whereas it increased 4.2% ± 0.7%, 13.1% ± 1.0%, and 30.6% ± 3.0% in CON‐VEH, HLU‐SclAbII, and CON‐SclAbII, respectively (p < 0.0001). Trabecular bone volume, assessed by micro–computed tomography (µCT) imaging of the distal femur, was lower in HLU‐VEH versus CON‐VEH (p < 0.05), and was 2‐ to 3‐fold higher in SclAbII groups versus VEH (p < 0.001). Midshaft femoral strength, assessed by three‐point bending, and distal femoral strength, assessed by micro–finite element analysis (µFEA), were significantly higher in SclAbII versus VEH‐groups in both loading conditions. Serum sclerostin was higher in HLU‐VEH (134 ± 5 pg/mL) compared to CON‐VEH (116 ± 6 pg/mL, p < 0.05). Serum osteocalcin was decreased by hindlimb suspension and increased by SclAbII treatment. Interestingly, the anabolic effects of sclerostin inhibition on some bone outcomes appeared to be enhanced by normal mechanical loading. Altogether, these results confirm the ability of SclAbII to abrogate disuse‐induced bone loss and demonstrate that sclerostin antibody treatment increases bone mass by increasing bone formation in both normally loaded and underloaded environments. © 2013 American Society for Bone and Mineral Research.     

The osteogenic response to distant skeletal injury

We tested the hypothesis that when one bone of the skeleton is injured, others experience an osteogenic response. Although similar or related phenomena have been observed previously, the purposes of the study were to determine if this response was reproducible, to characterize it in terms of its magnitude and duration, and to show how it is related to the type of injury sustained. To obtain this information, a model was used in which an intramedullary nail was implanted in the femur and a standard closed fracture was subsequently produced. The osteogenic response was measured by histomorphometry. Eight-four nine-week-old male Sprague-Dawley rats were divided into seven groups of twelve animals each. Groups I and II consisted of control animals in which no injury was produced. In Group-III rats, cortical drilling of the intercondylar notch and piriformis fossa of the right femur was performed, without intramedullary nailing. In Groups IV through VII, half of each group received intramedullary nails only, and in the other half intramedullary nailing was done and a closed transverse diaphyseal fracture was produced. With two different fluorochrome labels, rates of mineral apposition were measured in the left and right tibiae of all animals. The labeling periods differed in each group and were designed to determine when the peak response occurred, how long it lasted, and whether aging during the course of the experiment affected the response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alendronate administration and skeletal response during chronic alcohol intake in the adolescent male rat.

Alendronate is an aminobisphosphonate that inhibits bone resorption in osteoporotic humans and rats but does not induce osteomalacia. Several bisphosphonates, including alendronate, also have direct positive actions on osteoblasts, bone formation, and mineralization. We studied the effects of alendronate on skeletal development in adolescent male rats during chronic alcohol intake. Four groups of age- and weight-matched male Sprague-Dawley rats (35 days of age) were fed the Lieber-DeCarli diet containing 36% of calories as EtOH (E), the EtOH diet plus 60 mg/kg alendronate (EA) every other day intraperitoneally (ip), an isocaloric diet (I), or the isocaloric diet plus 60 mg/kg alendronate (IA) every other day ip. Body weight, femur length, serum levels of osteocalcin (OC), insulin-like growth factor 1 (IGF-1), testosterone, and luteinizing hormone (LH); femur distal metaphyseal and middiaphyseal bone mineral density (BMD) and tibial metaphyseal gene expression for alpha-1-type I collagen (Col I), OC, and bone alkaline phosphatase (AP); and femur strength by four-point bending to failure were measured after 28 days of feeding and alendronate injections. Serum alcohol levels at death were 156 +/- 13 mg/dl (E) and 203 +/- 40 mg/dl (EA). Alendronate given to alcohol-fed rats increased metaphyseal BMD by more than 3-fold over rats fed alcohol alone. Alendronate given to isocaloric pair-fed rats increased metaphyseal BMD by more than 2.5-fold over rats fed the isocaloric diet alone. Cortical BMD was reduced by alcohol but was increased by alendronate. Alcohol consumption reduced serum IGF-1 levels, and alendronate increased IGF-1 levels in alcohol-fed rats. Serum OC, testosterone, and LH were unaffected by alcohol and alendronate. Quantitative dot blot hybridization using rat complementary DNA (cDNA) probes and normalization against 18S subunit ribosomal RNA (rRNA) levels revealed no changes in tibial metaphyseal gene expression for type I collagen, osteocalcin, or alkaline phosphatase. Alcohol significantly reduced the biomechanical properties of the femurs that were partially compensated by alendronate. Chronic alcohol consumption uncouples formation from ongoing resorption, and resorption is inhibited by alendronate. However, alendronate's positive effects on osteoblast-mediated mineralization during chronic alcohol consumption point to the potential use of bisphosphonates in the treatment of decreased bone formation secondary to alcohol-induced diminished osteoblast function.     

In vivo skeletal imaging of 18F-fluoride with positron emission tomography reveals damage- and time-dependent responses to fatigue loading in the rat ulna

The skeletal response to damaging fatigue loading is not fully understood. We used (18)F-fluoride PET to describe the time course of the skeletal response following the creation of increasing levels of in vivo, fatigue-induced damage. The right forelimbs of 40 adult rats were loaded in vivo in cyclic compression to four levels of subfracture, fatigue displacement: 30, 45, 65, or 85% of fracture displacement. Rats were injected with a bone-seeking radionuclide ((18)F-fluoride) on days 0 (4 h), 2, 4, 7, 9, 11, 18, 24, and 30, and imaged using a small animal positron emission tomography (PET) scanner. We quantified fluoride uptake in the central 50% of the right (loaded) and left (control) forelimbs. There were significant increases in fluoride uptake in loaded forelimbs compared to control on day 0 for all displacement groups. Normalized uptake (loaded/control) reached peak levels 4 to 9 days after loading. Normalized uptake depended significantly on the level of fatigue displacement. Normalized uptake increased progressively from the 30 to the 45% displacement level (P < 0.001), and from the 45 to the 65% level (P < 0.001) but did not differ between 65 and 85% (P = 0.41). Histologically, we observed a rapid periosteal response with increased vascularity as early as day 1 and abundant woven bone formation between days 3 and 7. Periosteal and woven bone thicknesses were greater in bones subjected to more fatigue displacement. We conclude that a single bout of fatigue loading leads to a transient increase in the uptake of (18)F-fluoride, that the uptake is in proportion to the level of initial damage and is associated with increased vascularity and woven bone formation in the first week after loading.     

Growth hormone is permissive for skeletal adaptation to mechanical loading.

The Lewis dwarf (DW) rat was used as a model to test the hypothesis that growth hormone (GH) is permissive for new bone formation induced by mechanical loading in vivo. Adult female Lewis DW rats aged 6.2 +/- 0.1 months (187 +/- 18 g) were allocated to four vehicle groups (DW), four GH treatment groups at 32.5 microg/100 g body mass (DWGH1), and four GH treatment groups at 65 microg/100 g (DWGH2). Saline vehicle or GH was injected intraperitoneally (ip) at 6:30 p.m. and 6:30 a.m. before mechanical loading of tibias at 7:30 a.m. A single period of 300 cycles of four-point bending was applied to right tibias at 2.0 Hz, and magnitudes of 24, 29, 38, or 48N were applied. Separate strain gauge analyses in 5 DW rats validated the selection of loading magnitudes. After loading, double-label histomorphometry was used to assess bone formation at the periosteal surface (Ps.S) and endocortical surface (Ec.S) of tibias. Comparing left (unloaded) tibias among groups, GH treatment had no effect on bone formation. Bone formation in tibias in DW rats was insensitive to mechanical loading. At the Ec.S, mechanically induced lamellar bone formation increased in the DWGH2 group loaded at 48N (p < 0.05), and no significant increases in bone formation were observed among other groups. The percentage of tibias expressing woven bone formation (Wo.B) at the Ps.S was significantly greater in the DWGH groups compared with controls (p < 0.05). We concluded that GH influences loading-related bone formation in a permissive manner and modulates the responsiveness of bone tissue to mechanical stimuli by changing thresholds for bone formation.     

Circulatory and mechanical response of skin to loading

We investigated the tolerance of skin to mechanical loading over the tibia and over the tibialis anterior muscle in 12 normal volunteers. Surface load, subcutaneous tissue pressure, skin deformation under load, and transcutaneous partial pressure of oxygen (TcPO2) were simultaneously monitored. The skin over bone showed a significantly stiffer load deformation relationship than the skin over muscle (p less than 0.001). The displacement required to reduce TcPO2 to 0 over bone, 1.1 +/- 0.3 mm (mean +/- standard deviation), was significantly less than that required over tibialis anterior muscle, 5.4 +/- 1.1 mm (p less than 0.001). The applied pressure required to reduce TcPO2 to 0 was significantly greater for skin over muscle (71 +/- 16 mm Hg) than for skin over bone (42 +/- 8 mm Hg) (p less than 0.001). However, the subcutaneous pressure required to reduce TcPO2 to 0 was not significantly different for skin over muscle (36 +/- 11 mm Hg) than for skin over bone (28 +/- 10 mm Hg) (p greater than 0.05). Our results indicate that skin over muscle tolerates greater locally applied loads and deformations because the pressure is lower within the tissue than when similar loads and deformation are applied to skin over bone. Cutaneous perfusion, as indicated by TcPO2, seems to be linked more closely to the subcutaneous tissue pressure than to the surface load or deformations. These results provide some data for predicting mechanical and physiologic response to locally applied loads such as those that may be encountered in prosthetic wear.     

力学刺激对关节软骨基质代谢的影响

关节软骨主要由软骨细胞和细胞外基质组成,软骨细胞能够感受力学环境的变化而不断调整细胞外基质的代谢活动.适当的力学刺激会促进软骨细胞外基质的代谢,不适当的力学刺激有时不但会抑制细胞外基质的代谢,而且可能引起软骨细胞的变形或破坏而导致各种骨骼疾病的发生.正常的关节软骨一直处于静态压力与动态压力交替活动的力学环境中,体外构建工程化软骨过程中必须考虑这些力学因素,选择适当的力学刺激(力的作用方式、大小、频率、持续时间等)作用于软骨基质,使之形成具有体内软骨的力学特性.认识和加深理解力学刺激的作用机制,也有助于临床骨科诊疗观念和手段的发展与进步.该文就软骨基质的功能、力学刺激对软骨基质代谢的影响及在关节软骨组织工程中的应用展望,作一综述.     

Folic acid deficiency modifies the haematopoietic response to recombinant human erythropoietin in maintenance dialysis patients.

BACKGROUND: While folic acid deficiency causes macrocytic anaemia in non-renal patients, the relevance of altered folate metabolism in anaemia of end-stage renal disease and its response to rHu-EPO is less clear. METHODS: Ten haemodialysis patients with macrocytic anaemia due to dietary folic acid deficiency were compared to 10 matched (age, duration of dialysis, degree of anaemia) patients with normocytic normochromic anaemia. Nineteen patients received erythropoietin-alpha intravenously thrice weekly. The study design was a prospective crossover (ABA) comparison of the effects of intravenously administered high doses of folic acid on haemoglobin levels and EPO doses, with 6 months active supplementation (B) and two periods of 6 months duration each without folic acid supplementation (A). RESULTS: The two patient groups did not differ at recruitment. Red blood cell folate levels were normal in patients with normocytic anaemia, but they were subnormal in all patients with macrocytic anaemia. Compared to the first period without folic acid supplementation, patients with macrocytic anaemia had significantly higher haemoglobin levels despite lower EPO doses after 6 months high-dose folic acid, and red cells had become normocytic. The removal of folic acid supplementation resulted in re-occurrence of macrocytosis and in a significantly lower response to rHu-EPO. In contrast, high-dose folic acid supplementation had no effect on response to rHu-EPO in patients with normocytic anaemia. CONCLUSIONS: Folic acid deficiency may occur in elderly haemodialysis patients with poor dietary folate intake without regular oral supplementation and may cause hyporesponsiveness to rHu-EPO. Macrocytosis is a simple and cheap indicator for folate deficiency in end-stage renal disease patients on maintenance dialysis.     

EphrinB2/EphB4 inhibition in the osteoblast lineage modifies the anabolic response to parathyroid hormone

Previous reports indicate that ephrinB2 expression by osteoblasts is stimulated by parathyroid hormone (PTH) and its related protein (PTHrP) and that ephrinB2/EphB4 signaling between osteoblasts and osteoclasts stimulates osteoblast differentiation while inhibiting osteoclast differentiation. To determine the role of the ephrinB2/EphB4 interaction in the skeleton, we used a specific inhibitor, soluble EphB4 (sEphB4), in vitro and in vivo. sEphB4 treatment of cultured osteoblasts specifically inhibited EphB4 and ephrinB2 phosphorylation and reduced mRNA levels of late markers of osteoblast/osteocyte differentiation (osteocalcin, dentin matrix protein‐1 [DMP‐1], sclerostin, matrix‐extracellular phosphoglycoprotein [MEPE]), while substantially increasing RANKL. sEphB4 treatment in vivo in the presence and absence of PTH increased osteoblast formation and mRNA levels of early osteoblast markers (Runx2, alkaline phosphatase, Collagen 1α1, and PTH receptor [PTHR1]), but despite a substantial increase in osteoblast numbers, there was no significant change in bone formation rate or in late markers of osteoblast/osteocyte differentiation. Rather, in the presence of PTH, sEphB4 treatment significantly increased osteoclast formation, an effect that prevented the anabolic effect of PTH, causing instead a decrease in trabecular number. This enhancement of osteoclastogenesis by sEphB4 was reproduced in vitro but only in the presence of osteoblasts. These data indicate that ephrinB2/EphB4 signaling within the osteoblast lineage is required for late stages of osteoblast differentiation and, further, restricts the ability of osteoblasts to support osteoclast formation, at least in part by limiting RANKL production. This indicates a key role for the ephrinB2/EphB4 interaction within the osteoblast lineage in osteoblast differentiation and support of osteoclastogenesis. © 2013 American Society for Bone and Mineral Research.     

Etomidate modifies hemodynamic response to fentanyl in patients with impaired left ventricular function]

The haemodynamic effects and the side-effects of anaesthesia using high doses of fentanyl were compared in two groups of 12 patients each. All the patients had poor left ventricular function and were scheduled for elective coronary artery bypass graft surgery or valvular replacement. Patients were randomly assigned to either group. In group EF, patients were given 5 micrograms.kg-1 of fentanyl, followed by 0.3 mg.kg-1 of etomidate. Once they had lost consciousness, they were given 15 mg of pancuronium and 25 micrograms.kg-1 of fentanyl over a 5 min period. Patients in group F received the full 30 micrograms.kg-1 dose of fentanyl over a 5 min period, followed by 15 mg of pancuronium. The patients were intubated 2 min after the end of the fentanyl infusion. They were mechanically ventilated with 100% oxygen. Anaesthesia was maintained with a continuous infusion of fentanyl (total dose 100 micrograms.kg-1). The usual haemodynamic parameters were monitored and calculated, as well as pain during injection of the drugs, myoclonia, chest wall rigidity and the time to loss of consciousness. The two groups were comparable with respect to age, weight, height and surgery. One third of the patients in group EF complained of pain during etomidate injection. The time required to loose consciousness was shorter in group EF (55 +/- 16 sec) than in group F (177 +/- 56 sec) (p < 0.001). The cardiac index decrease in group EF (2.0 +/- 0.4 l.min-1.m-2 vs. 1.9 +/- 0.4 l.min-1.m-2) (p < 0.05), respectively between the time just before tracheal intubation (T1), and 10 min after tracheal intubation (T3).(ABSTRACT TRUNCATED AT 250 WORDS)