A transmissive laser speckle imaging technique for measuring deep tissue blood flow: an example application in finger joints.

BACKGROUND AND OBJECTIVE: Laser speckle perfusion imaging (LSPI) is a minimally invasive optical measure of relative changes in blood flow, providing real-time, high resolution, two-dimensional maps of vascular structure. Standard LSI imaging uses a light-reflective geometry that limits the measurement to a thin surface layer of 0.2-1 mm. The objective of this study was to test a new LSI instrument geometry with the laser source opposed to the image capture plane (light transmissive). Captured light then travels the entire tissue thickness (10-15 mm), sampling much deeper regions of interest than conventional optical imaging techniques. STUDY DESIGN: Reflective-light (conventional) and transmissive-light LSI modes were used to measure finger joint blood flow during a timed tourniquet occlusion of the brachial artery in volunteer participants. RESULTS: There was greatly increased visibility of vessels underlying the skin in the light-transmissive mode LSI mode. Established LSI algorithms were shown to still work in the light-transmissive mode, despite decorrelation due to finite laser coherence length and the light passing through a tissue thickness of 10-15 mm. CONCLUSION: Transmissive LSI can be used to measure blood flow deep (10-15 mm) into tissues. This could be useful for non-invasive measurements of finger joint synovial blood flow in diagnosing and treating peripheral vascular disorders, such as rheumatoid arthritis.

Kinetics of blood flow during healing of excisional full-thickness skin wounds in pigs as monitored by laser speckle perfusion imaging.

BACKGROUND/PURPOSE: The laser speckle perfusion imaging (LSPI) system is a new, non-invasive technique for rapidly and reproducibly measuring tissue perfusion. The high resolution and frame rate of the LSPI overcome many of the limitations of traditional laser Doppler imaging techniques. Therefore, LSPI is a useful means for evaluating blood flow in a variety of situations. The present study investigates the ability of the LSPI system to detect temporal changes in blood flow during the healing of cutaneous wounds in a well-characterized animal model. METHODS: Full-thickness excisional skin wounds (2 x 2 cm) were created on the backs of juvenile female red Duroc pigs. Every week post-injury, the wounds were measured and photographed, and normalized blood flow values were determined using the LSPI system. RESULTS: Tissue perfusion values were available after complete re-epithelialization and removal of the eschar, at day 21. At this point, wound blood flow was significantly elevated as compared with the surrounding, uninvolved skin. Wound blood flow declined steadily during healing, and approached normal values by day 35 post-injury. CONCLUSION: The kinetics of blood flow during excisional wound healing in the red Duroc model are comparable with that previously observed in laser Doppler imaging of healing human skin wounds and hypertrophic scars. These results therefore confirm that the red Duroc is a good model of human wound healing, and further indicates that the LSPI is an excellent technique for evaluating angiogenesis and neovascularization during healing in this and other models.

Endoscopic laser speckle imaging of tissue blood flow: applications in the human knee.

This work represents the first clinical data acquired with the endoscopic laser speckle imaging (eLSPI) system, a new diagnostic tool developed for real-time imaging of tissue blood flow during endoscopic surgical procedures. eLSPI was used to image tissue perfusion in the medial compartment of the knee of five patients requiring arthroscopic knee surgery. The effectiveness of eLSPI as a diagnostic tool was tested by measuring changes in tissue perfusion resultant from tourniquet application, and intra-articular epinephrine. eLSPI produced real-time perfusion video images of tissue blood flow in the knee joint. Tourniquet applications produced consistent decreases in mean perfusion index measurements (29.3% +/- 5.1% in meniscus; 39.5% +/- 8.2% in synovium with an intra patient variability of 6%-9%). A dose-dependent vasoconstrictive response to the administration of intra-articular epinephrine was measured, with maximum dose producing a mean decrease in perfusion of 31.0%-9.3% in meniscus and 41.2%-10.9% in synovium. eLSPI consistently detects decreases in articular tissue blood flow resultant from tourniquet inflation or from the administration of increasing concentrations of epinephrine. These are the first in vivo results indicating physiologic changes in articular tissue as a function of two commonly applied practices in endoscopic joint surgery.

Bisphosphonates reduce bone mineral loss at ligament entheses after joint injury.

OBJECTIVE: To examine the effects of anterior cruciate ligament (ACL) insufficiency, and subsequent bisphosphonate (BP) antiresorptive therapy, on the bone mineral interface at the enthesis of remaining ligamentous restraints. METHODS: We measured bone mineral geometry (and subsequent adaptation) at the medial collateral ligament (MCL) origin, using micro-computed tomography (muCT). Groups of normal control, 6 and 14 wk anterior cruciate ligament transected (ACLX), and 6 wk ACLX-BP (risedronate) dosed rabbits were evaluated. Samples were then processed histologically, and the results of mineral adaptation and progression of osteoarthritis (OA) compared to joint laxity values obtained from previous biomechanical testing of the MCL-complex. RESULTS: muCT defined the MCL origin as a symmetrical, metaphyseal depression that contained soft-tissue elements, including fibrocartilage and ligament--as seen in subsequent histological sections. In contrast, the insertions from ACLX animals lost significant bone mineral, with an MCL-insertion volume 1.2 times that of normal controls at 6 wk ACLX, which further increased to 2.3 times that of normal controls at 14 wk ACLX. Significant differences were also measured between 6 and 14 wk ACLX and age-matched normal controls in volume of cortical bone containing the MCL insertion. However, there were no significant differences in the percentage of cortical bone to underlying trabecular bone at the MCL insertion. When comparing muCT mineral adaptation at the MCL-enthesis with historical MCL-complex laxity data, the values for laxity after ACLX increased proportionately as bone mineral at the insertion was lost, and subsequent use of the BP risedronate reduced both mineral loss and MCL-complex laxity. CONCLUSION: Compared to the untreated ACLX condition, administering bisphosphonate immediately after loss of the ACL conserved bone mineral at the MCL enthesis, suggesting the potential to therapeutically influence joint-complex laxity and OA progression.

A comparison of two laser-based methods for determination of burn scar perfusion: laser Doppler versus laser speckle imaging.

UNLABELLED: Laser Doppler perfusion imaging (LDI) is an established technique for early assessment of burn depth to help determine a course of treatment. Laser speckle perfusion imaging (LSPI) is an alternative laser based, non-invasive perfusion monitoring technique that offers rapid and high resolution images of tissue. We have evaluated the ability of the LSPI instrument in determining and monitoring burn scar perfusion over time and compared it with the LDI instrument as a standard. METHODS: Ten patients with hypertrophic burn scars (time since injury: 1-8 months) were recruited. Burn scars were scanned with both instruments (LSPI and LDI) monthly over a period of 11 months. Clinical grading of the burn scars was assessed on every scan date using the Vancouver burn scar scale. RESULTS: Comparison of the perfusion values determined by each instrument shows a strong positive correlation, r2=0.86 (n=63). Each instrument's output also correlated significantly with the clinical grading of the scar, indicating the expected decrease in perfusion as the clinical condition of the scars improved with time. SIGNIFICANCE: The new LSPI instrument compared favorably with the established LDI instrument, yielding similar results. The considerably faster scan time and higher resolution of the LSPI method provides a distinct clinical advantage, both in terms of patient comfort and for reliably matching perfusion characteristics to their associated anatomical features. The fast temporal response of the LSPI instrument could be used to monitor near real-time responses to mechanical or pharmacological interventions to study dynamic vascular changes to burn damaged tissues.

Antiresorptive therapy conserves some periarticular bone and ligament mechanical properties after anterior cruciate ligament disruption in the rabbit knee.

The purpose of this study was to assess, in an osteoarthritic (OA) model, whether bisphosphonate (BP) antiresorptive therapy altered periarticular bone and bone-ligament biomechanics and OA progression. We surgically transected the anterior cruciate ligament (ACLX) in two groups of rabbits; the first group was dosed with BP (risedronate, 0.01 mg/kg s.c. daily for 6 wk), the second group remained untreated, and a third group of normal (unoperated) control rabbits was also evaluated. We measured distal femoral bone mineral density (BMD, Dual Energy X-ray Absorptiometry [DEXA]), medial collateral ligament (MCL) laxity, and bone mechanical function (bone cores mechanically tested in compression). These measures were related to cartilage/joint gross morphology, histology, and measures of vascular volume (gelatin-dye perfusion) for evidence of inflammatory angiogenesis and early OA. BMD by DEXA in 6 wk ACLX animals was 18% less than normal controls (p<0.05). In contrast, BP dosing conserved periarticular BMD; risedronate-treated rabbits had distal femoral BMD only 5% less and not significantly different than normal controls. When the same bone cores were compressed to failure, both ACLX and BP-dosed animals were significantly weaker than normal controls (p<0.05). However, the bone energy to failure and elastic modulus of BP-dosed animals was conserved and not significantly different from normal controls 6 wk after ACLX. Blocking bone resorption with BP also resulted in a significantly improved bone-ligament structural complex. MCL-complex laxity was significantly less in BP-dosed animals (1.2 times that of normal controls) compared to untreated ACLX animals (1.7 times that of normal controls; p<0.05). Blocking bone resorption with risedronate did not suppress osteophytosis and inflammatory angiogenesis, which were significantly increased in the periarticular bone of both untreated and BP treated ACLX animals. Thus, administering BP immediately after ACL loss conserved some periarticular bone and MCL-complex properties in an early OA model.

Endoscopic laser imaging of tissue perfusion: new instrumentation and technique.

BACKGROUND AND OBJECTIVES: New instrumentation, based on a previously established laser speckle perfusion imaging (LSI) technique is evaluated for its ability to capture and generate blood flow images during endoscopic surgery. STUDY DESIGN/MATERIALS AND METHODS: Investigations are detailed in an in-vitro blood flow model simulating physiological properties of vascularized tissue, and in-vivo in rabbit joint capsule tissue. RESULTS: In-vitro measurements showed a linear response of the instrument to blood flow in the range of 0-800 microl/minute, where data points were significantly correlated with an r(2) value of 0.96. In-vivo measurements showed a 58.7% decrease to the medial collateral ligament during occlusion of the femoral artery. CONCLUSIONS: Blood flow images demonstrate that the endoscopic LSI technique is capable of measuring relative tissue blood flow changes at high resolutions and rapid response times and incorporates well with endoscopic surgeries.

Angiogenesis in the distal femoral chondroepiphysis of the rabbit during development of the secondary centre of ossification.

In the developing chondroepiphyses of long bones, the avascular cartilaginous anlage is invaded by numerous blood vessels, through the process of angiogenesis. The objective of this study was to investigate the chronology of this vascular invasion with the spontaneous calcification of the cartilaginous epiphysis during development of the secondary ossification centre in the rabbit distal femur. The time-course of chondroepiphyseal vascular invasion was determined histologically and standardized for eight gestational and four postnatal intervals by plotting kit body mass against crown-rump length. Similarly, microcomputed tomography (micro-CT) helped to visualize calcification at those same gestational and postnatal intervals. To confirm the angiogenic nature of the avascular chondroepiphysis, such samples were assayed on the chick chorio-allantoic membrane (CAM). Neovascular outgrowths from the CAM were apparent 48 h following introduction of an 18-day (gestational) chondroepiphyseal sample. Chondroepiphyseal samples were assayed for the potent developmental angiogenic factors bFGF and VEGF, with the mRNA expression for both these mediators being confirmed using RT-PCR. As angiogenesis and calcification during chondroepiphyseal development occur in a defined tissue environment initially devoid of blood vessels and mineral, those processes provided a unique opportunity to study their progression without complication of injury-related inflammation or extant vasculature and mineral. Furthermore, the discovery of angiogenic, angiostatic or mineral-regulating mediators specific to developing connective tissue may prove useful for analysing the regulation of vascular and mineral pathogenesis in articular tissues.

Denervation impairs healing of the rabbit medial collateral ligament.

Little is known about the contribution of innervation to ligament healing after traumatic disruption, although there is good evidence of an important role for the peripheral nervous system in the healing of fractures and skin injuries. Tissues such as ligament, with a low resting blood supply, are dependent on substantial increases in blood flow and vascular volume during the initial stages of repair. We hypothesized that this initial healing response would be strongly promoted by neurogenic inflammation. Since the saphenous nerve (a major sensory branch of the femoral nerve) supplies the medial half of the knee joint, we elected to use femoral nerve transection as a model to determine the role of sensory and autonomic innervation in the initial outcome of repair of the injured medial collateral ligament. Twelve adult, female NZW rabbits underwent right medial collateral ligament transection. Of these, six rabbits underwent right femoral nerve transection to disrupt the somatic sensory and autonomic nerve supply to the knee joint and six were kept neurologically intact (controls). At six weeks post-injury, the animals were assessed by laser Doppler perfusion imaging (LDI) to determine the local blood flow, at both the injury site and at the uninjured contralateral ligament. The animals were then killed, the knee joints were removed and the biomechanical characteristics of the healing bone-median collateral ligament (MCL)-bone complexes assessed. In a separate cohort of 16 rabbits, vascular volumes of the injured ligaments were measured by infusion of a carmine red/gelatin solution. At six weeks post-injury, in vivo measurement of perfusion with LDI revealed that normally innervated ligaments had an almost three-fold higher average blood flow. Carmine red/gelatin infusion revealed a 50% higher density of blood vessels as compared to denervated ligaments. The force required for ultimate failure was found to be 50% higher in normally innnervated MCL's as compared to denervated MCL's: 153.14 +/- 20.71 N versus 101.29 +/- 17.88 N (p < 0.05). Static creep was increased by 66% in denervated MCL's: 2.83 +/- 0.45% versus 1.70 +/- 0.12% (p < 0.05). Total creep was increased by 45% in denervated MCL's: 5.29 +/- 0.62% compared to 3.64 +/- 0.31% in innervated MCL's (p < 0.05). We conclude that intact innervation makes a critical contribution to the early healing responses of the MCL of adult rabbits.

Comparison of laser speckle and laser Doppler perfusion imaging: measurement in human skin and rabbit articular tissue.

Laser Doppler perfusion imaging (LDI) is currently used in a variety of clinical applications, however, LDI instruments produce images of low resolution and have long scan times. A new optical perfusion imager using a laser speckle measurement technique and its use for in vivo blood flow measurements are described. Measurements of human skin and surgically exposed rabbit tissue made using this instrument were compared with a commercial laser Doppler perfusion imaging instrument. Results from blood flow measurements showed that the laser speckle imager measured an 11-67% decrease in blood flow under arterial occlusion. Under similar conditions, the laser Doppler imager measured blood flow decreases of 21-63%. In comparison with LDI, it was observed that the higher temporal resolution of the laser speckle imager was more sensitive to measuring the hyperaemic response immediately following occlusion. This in vivo study demonstrated some of the several advantages laser speckle imaging has over conventional LDI, making the new instrument more versatile in a clinical environment.

Reactions of dimethylsulfoxide reductase in the presence of dimethyl sulfide and the structure of the dimethyl sulfide-modified enzyme.

The bis-molybdopterin enzyme dimethylsulfoxide reductase (DMSOR) from Rhodobacter capsulatus catalyzes the conversion of dimethyl sulfoxide (DMSO) to dimethyl sulfide (DMS), reversibly, in the presence of suitable e(-)-donors or e(-)-acceptors. The catalytically significant intermediate formed by reaction of DMSOR with DMS ('the DMS species') and a damaged enzyme form derived by reaction of the latter with O(2) (DMS-modified enzyme, DMSOR(mod)D) have been investigated. Evidence is presented that Mo in the DMS species is not, as widely assumed, Mo(IV). Formation of the DMS species is reversed on removing DMS or by addition of an excess of DMSO. Equilibrium constants for the competing reactions of DMS and DMSO with the oxidized enzyme (K(d) = 0.07 +/- 0.01 and 21 +/- 5 mM, respectively) that control these processes indicate formation of the DMS species occurs at a redox potential that is 80 mV higher than that required, according to the literature, for reduction of Mo(VI) to Mo(IV) in the free enzyme. Specificity studies show that with dimethyl selenide, DMSOR yields a species analogous to the DMS species but with the 550 nm peak blue-shifted by 27 nm. It is concluded from published redox potential data that this band is due to metal-to-ligand charge transfer from Mo(V) to the chalcogenide. Since the DMS species gives no EPR signal in the normal or parallel mode, a free radical is presumed to be in close proximity to the metal, most likely on the S. The species is thus formulated as Mo(V)-O-S(*)Me(2). Existing X-ray crystallographic and Raman data are consistent with this structure. Furthermore, 1e(-) oxidation of the DMS species with phenazine ethosulfate yields a Mo(V) form without an -OH ligand, since its EPR signal shows no proton splittings. This form presumably arises via dissociation of DMSO. The structure of DMSOR(mod)D has been determined by X-ray crystallography. All four thiolate ligands and Ogamma of serine-147 remain coordinated to Mo, but there are no terminal oxygen ligands and Mo is Mo(VI). Thus, it is a dead-end species, neither oxo group acceptance nor e(-)-donation being possible. O(2)-dependent formation of DMSOR(mod)D represents noncatalytic breakdown of the DMS species by a pathway alternative to that in turnover, with oxidation to Mo(VI) presumably preceding product release. Steps in the forward and backward catalytic cycles are discussed in relation to earlier stopped-flow data. The finding that in the back-assay the Mo(IV) state may at least in part be by-passed via two successive 1e(-) reactions of the DMS species with the e(-)-acceptor, may have implications in relation to the existence of separate molybdopterin enzymes catalyzing DMSO reduction and DMS oxidation, respectively.

Vascular response of the meniscus to injury: effects of immobilization.

Failed meniscal healing may lead to degenerative osteoarthritis of the knee. Healing is thought to be dependent upon an adequate blood supply, yet "normal" vascular changes during healing are not well understood. In this study we have quantified vasoactive and angiogenic responses to medial meniscal injury in a rabbit model under clinically relevant conditions, and related these to histological criteria of healing. Twenty-six adult rabbits were given a standardized meniscal injury; 12 of these had the hind limb immobilized by pinning. Eight normal controls and 12 sham-operated animals were also studied. After 4 weeks, animals underwent either vascular volume (vascular index) determination, or blood flow measurement using coloured microspheres. Histological analysis was also performed to assess meniscal healing. In injured animals, blood flow to the menisci was increased fivefold 4 weeks post-operative; this increase was prevented by immobilization. The vascular index of the menisci was also increased threefold by injury, but not significantly reduced by immobilization. Histological examination of injured menisci showed examples of healing and non-healing tears in both mobile and immobile groups. Meniscal injuries are associated with characteristic changes in vascularity and perfusion, and these changes likely play a significant role in the healing process. Characterization of the vascular responses to meniscal injury may lead to techniques that can promote reliable healing of meniscal tears and thereby improve clinical outcomes.

Vascular alterations in the rabbit patellar tendon after surgical incision.

Open incision of the patellar tendon (PT) is thought to promote acute vascular responses which ultimately result in an enhanced degree of tendon repair. Such a clinical procedure is commonly applied to patients with refractory tendinitis. The objective of this study was to quantify the vascular adaptations (both anatomical and physiological) to longitudinal incision of the PT, and the resultant effects on tendon organisation. Fifty-four New Zealand White rabbits were separated into 3 experimental groups and 2 control groups. Experimental groups underwent surgical incision of the right PT, and were assessed 3 d, 10 d and 42 d following injury; normal unoperated controls were evaluated at time zero, and sham-operated controls were evaluated at 3 d to control for the effects of incising the overlying skin. Quantitative measures of PT blood supply (blood flow, microvascular volume) and geometric properties of PT substance were obtained for each PT. Histomorphology was assessed to evaluate vascular remodelling and matrix organisation in the healing PT. Longitudinal open incision surgery of the PT led to rapid increases in both blood flow and vascular volume. The incision of overlying tissues alone (sham-operated) contributed to this measurable increase, and accounted for 36% and 42% of the elevated blood flow and vascular volume respectively at the 3 d interval. In the incised PT, blood flow significantly increased by 3 d compared with both time zero and sham-operated controls, and remained significantly elevated at the 10 d interval. Similarly, vascular volume of the incised PT increased at 3 d compared both with time zero and sham-operated controls. At the 10 d interval, the increase in vascular volume was greatest in the central PT substance. By 42 d both blood flow and vascular volume of the incised tendon had diminished, with only blood flow remaining significantly different from controls. In the contralateral limb, a significant neurogenically mediated vasodilation was measured in the contralateral PTs at both early time intervals, but was not seen by the later 42 d interval. With respect to PT geometric properties in the experimental animals, a larger PT results as the tendon matrix and blood vessels remodel. PT cross-sectional area increased rapidly by 3 d to 1.3 times control values, and remained significantly elevated at 42 d postinjury. Morphological assessments demonstrated the disruption of matrix organisation by vascular and soft tissue components associated with the longitudinal incisions. Substantial changes in matrix organisation persisted at 42 d after surgery. These findings suggest that open longitudinal incision of the PT increases the vascular supply to deep tendon early after injury. These changes probably arise through both vasomotor and angiogenic activity in the tissue. Since PT blood flow and vascular volume return towards control levels after 6 wk but structural features remain disorganised, we propose that vascular remodelling is more rapid and complete than matrix remodelling after surgical incision of the PT.

Evaluation of laser-Doppler perfusion imaging for measurement of blood flow in cortical bone.

Most techniques currently available to measure blood flow in bone are time consuming and require destruction of the tissue, but laser-Doppler technology offers a less invasive method. This study assessed the utility of laser-Doppler perfusion imaging (LDI) to measure perfusion in cortical bone. Twelve mature New Zealand White rabbits were assigned to one of three groups: normal control, constriction (norepinephrine), or dilatation (nitroprusside). The left and right medial tibiae were consecutively scanned at red (634-nm) and near-infrared (810-nm) wavelengths to examine the repeatability of LDI output. The pharmacological intervention groups were injected with the respective drug, and LDI measurements at 810 nm were obtained concurrently with colored microsphere-determined flow in all of the groups. LDI effectively quantified blood flow in cortical bone and detected physiologically induced changes in perfusion. A significant positive correlation was found between microsphere-determined flow and LDI output (r = 0.6, P < 0.05). Repeatability of consecutive LDI measurements was within 5%. The effectiveness of LDI to measure perfusion in bone suggests this method has potential for investigating the role of blood flow in bone metabolism and remodeling.

Physiological and mechanical adaptation of periarticular cancellous bone after joint ligament injury.

The relation between blood flow and bone mineral density (BMD) of periarticular bone was examined in an in vivo model of joint instability. Eighty mature New Zealand White rabbits were randomly assigned to experimental [anterior cruciate ligament transection (ACLX)], sham-operated control, or age-matched normal control groups. Experimental rabbits underwent unilateral transection of the right anterior cruciate ligament, and the nonoperated left [contralateral (Cntra)] limb was a within-animal control. BMD and blood flow to the periarticular bone in the femoral condyles were assessed in each group at 2, 4, 6, 14, and 48 wk postsurgery, using quantitative computed tomography scanning and entrapment of colored microspheres. BMD was significantly lower (5%) in the ACLX compared with Cntra limbs. Periarticular bone blood flow in the ACLX limbs was significantly greater than in the Cntra limb (29%) in the early stages (6 wk) after injury. Up to 48 wk post-ACLX, a significant correlation was found between increased blood flow and decreased BMD in the periarticular bone of the femoral condyles in the ACLX limbs. This correlation suggested that heightened blood flow may be linked to mechanisms of bone adaptation in joints after ligament injury.

Adaptation of post-traumatic angiogenesis in the rabbit knee by apposition of torn ligament ends.

Apposition of torn ligament ends has been shown to have a beneficial effect on healing of the medial collateral ligament; however, the mechanism underlying this improved recovery is unclear. Excessive post-traumatic angiogenesis, an inherent component of soft-tissue regeneration, may be functionally detrimental in relatively hypovascular tissues such as ligaments. The present study therefore examined the relationship between contact of transected ligament ends and vascular remodeling. Female New Zealand White rabbits were subjected to a gap injury, Z-plasty apposition, or sham operation to the midsubstance of the medial collateral ligament. Six weeks after treatment, the volume of vessels supplying the healing zone of the medial collateral ligament, as well as the ipsilateral lateral collateral ligament, posterior cruciate ligament. menisci, and medial capsule, was quantified by carmine red vascular casting. The volume of vessels supplying the neoligamentous scar formed by gap injury to the medial collateral ligament was found to be twice that of ligaments that had undergone the sham operation, and lateral collateral ligament and meniscal vascularity was also augmented in the injured joint. The medial collateral ligaments that underwent Z-plasty apposition exhibited a level of vascularity comparable with that of the control ligaments that had undergone the sham procedure, whereas meniscal and lateral collateral ligament vascularities remained elevated in this group. Capsular and posterior cruciate ligament vascularities were unaffected by gap injury or Z-plasty to the ipsilateral medial collateral ligament. These findings indicate that injury to the medial collateral ligament not only stimulates angiogenesis in the healing ligament, but other ipsilateral soft tissues also undergo vascular remodeling. Furthermore, apposition of an injured medial collateral ligament modifies these pro-angiogenic events, and this may partly explain why contact of torn ligament ends is beneficial for post-traumatic recovery of an injured joint.

Reversible dissociation of thiolate ligands from molybdenum in an enzyme of the dimethyl sulfoxide reductase family.

Much is unknown concerning the role of thiolate ligands of molybdenum in molybdopterin enzymes. It has been suggested that thiolate dissociation from molybdenum is part of the catalytic mechanism of bis-molybdopterin enzymes of the dimethyl sulfoxide reductase (DMSOR) family. For DMSOR from Rhodobacter capsulatus, thiolate dissociation has therefore been investigated crystallographically, by UV/visible spectroscopy, and by enzyme assays. When crystallized from sodium citrate, all four thiolates of DMSOR are within bonding distance of Mo, but after extended exposure to Na(+)-Hepes, a pair of thiolates dissociates, a mixture of structures being indicated after shorter exposures to this buffer. DMSOR is stable in sodium citrate and other buffers but unstable aerobically although not anaerobically in Na(+)-Hepes. Aerobically in Na(+)-Hepes, a first-order reaction (k = 0.032 hr(-)(1) at 37 degrees C) leads to loss of activity in the backward but not the forward (dimethyl sulfoxide reduction) assay and loss of absorption at lambda > approximately 450 nm. This reaction can be reversed by a cycle of reduction and reoxidation ("redox-cycling"). Slower irreversible loss of activity in the forward assay and cofactor dissociation follow. Spectral analogy with a mono-molybdopterin enzyme supports the conclusion that in the Hepes-modified DMSOR form, only two cofactor dithiolene sulfur atoms are coordinated to molybdenum. Loss of activity provides the first clear evidence that sulfur ligand dissociation is an artifact, not part of the catalytic cycle. Clearly, structural data on DMSOR samples extensively exposed to Hepes is not directly relevant to the native enzyme. The nature of the oxygen ligands detected crystallographically is discussed, as is the specificity of Hepes and the mechanism whereby its effects are achieved. DMSOR forms complexes with Na(+)-Hepes and other buffer ions. For DMSOR crystallized from Hepes, electron density in the substrate binding channel suggests that buffers bind in this site. Like the as-prepared enzyme, the modified form (DMSOR(mod)D), known to arise on extended aerobic exposure to dimethyl sulfide, is susceptible to a further degradative reaction, although this is not buffer-dependent. It involves loss of absorption at lambda > approximately 450 nm and, presumably, dissociation of thiolate ligands. Evidence is presented that, as a result of O(2) damage, DMSOR samples not submitted to redox-cycling may be contaminated with DMSOR(mod)D and with material absorbing in the region of 400 nm, analogous to the Hepes-modified enzyme. Since the latter lacks absorption at lambda > approximately 450 nm, its presence may escape detection.

Late gestational changes in sympathomimetic sensitivity in primagravid rabbit ligaments.

The adrenoceptor profile of blood vessels supplying the medial collateral ligament (MCL) of virgin and primagravid (day 29 of pregnancy) rabbit knees was examined. Topical bolus administration of the alpha1-adrenoceptor agonists methoxamine and phenylephrine, and the alpha2-adrenoceptor agonist clonidine, to exposed knee joints resulted in a dose-dependent vasoconstriction of ligamentous vessels. The rank order of potency for the alpha-agonists was found to be phenylephrine > methoxamine > clonidine. Dobutamine, which acts on beta1-adrenoceptors, and ritodrine, which is a beta2-agonist, imparted a mild vasodilatatory effect on MCL blood vessels with the efficacy of ritodrine being greater than that of dobutamine. In primagravid rabbits, the constrictor effects of methoxamine and phenylephrine were significantly attenuated compared with virgin control animals (P < 0.0001), whereas clonidine-mediated vasoconstriction was unaltered in the gravid animal (P = 0.3957). With respect to beta-adrenoceptor activity, the dilatational effect of dobutamine was the same as in controls (P = 0.5294), while ritodrine vasoactivity was completely abolished in primagravid knees (P < 0.005). These findings suggest that the adrenergic control of rabbit MCL blood flow is predominantly mediated by postjunctional alpha1 and beta2-adrenoceptors. Pregnancy leads to either downregulation and (or) desensitisation of alpha1 and beta2-adrenoceptors in the ligament which could disrupt normal joint homeostasis.

A role for calcitonin gene-related peptide in rabbit knee joint ligament healing.

Knee joint ligament healing has been shown to be improved when the torn ligament ends remain in contact, however, the rationale for these effects is unknown. The sensory neuropeptide calcitonin gene related peptide (CGRP) has potent trophic and vasodilatatory properties and as such is thought to be advantageous in wound repair. In ascertaining a role for CGRP in rabbit medial collateral ligament healing, the present study examined changes in CGRP-like immunoreactivity (CGRP-LI) and CGRP-mediated vasomotor responses in gap injured (non-contact), Z-plasty apposed (contact), and sham operated control medial collateral ligaments. At 6 weeks post-trauma, CGRP-LI decreased in the healing zone of gap injured and Z-plasty apposed medial collateral ligaments compared with controls, and non-contact ligament nerve fibres exhibited an abnormal morphology. Topical administration of CGRP (10(-13) to 10(-9) mol) caused a dose-dependent increase in ligament perfusion in each experimental group of knees. The CGRP-mediated vasodilatation associated with gap injured ligaments was not significantly different from controls (P = 0.06), whereas apposed medial collateral ligaments showed an augmented response to the peptide (P < 0.0005). These findings indicate that the beneficial effects of ligament interposition post-trauma may be related to an enhanced responsiveness to CGRP in conjunction with a more typical re-innervation profile. Conversely, the aberrant characteristics of CGRP-LI nerves occurring in gap injured tissue is suggestive of impaired CGRP release which may explain the poor functional recovery associated with these ligaments.

Aging-induced osteopenia in avian cortical bone.

Cortical bone loss contributes substantially to the degradation of skeletal integrity associated with aging. However, animal models that closely mimic age-related alterations in cortical bone are limited. The objective of this study was to determine if aged rooster cortical bone demonstrates phenotypic alterations similar to those observed in aged human cortical bone (i.e., expansion of the endocortical and periosteal envelopes and elevated cortical porosity). When compared with young adult roosters, aged roosters demonstrated significant expansion of the endocortical (16%) and periosteal (10%) envelopes, resulting in significantly increased cross-sectional moments of inertia. In addition, aged rooster bone demonstrated significantly elevated cortical porosity (51%) and average area of porosity (83%). We conclude that rooster bone demonstrates age-related adaptations similar to those of humans at both tissue and cellular levels, and may therefore represent a relatively useful, inexpensive animal model for investigating the mechanisms of age-related bone loss.