Submaximal exercise training, more than dietary selenium supplementation, improves antioxidant status and ameliorates exercise-induced oxidative damage to skeletal muscle in young equine athletes

Exercise is associated with increased production of reactive oxygen species (ROS) as metabolism is upregulated to fuel muscle activity. If antioxidant systems become overwhelmed, ROS can negatively affect health and performance. Adaptation to exercise through regular training has been shown to improve defense against oxidative insult. Given selenium's role as an antioxidant, we hypothesized that increased Se intake would further enhance skeletal muscle adaptations to training. Quarter Horse yearlings (18 ± 0.2 mo; 402 ± 10 kg) were randomly assigned to receive either 0.1 or 0.3 mg Se/kg DM and placed in either an untrained or a trained (30 min walk-trot-canter, 4 d/wk) group for 14 wk. Phase 1 (wk 1 to 8) consisted of 4 treatments: trained and fed 0.1 mg Se/kg DM through wk 14 (CON-TR; n = 10), trained and fed 0.3 mg Se/kg DM through wk 14 (HIGH-TR; n = 10), untrained and fed 0.1 mg Se/kg DM through wk 14 (CON-UN; n = 5), or untrained and fed 0.3 mg Se/kg DM through wk 14 (HIGH-UN; n = 5). During Phase 2 (wk 9 to 14), dietary Se level in half of the trained horses was reversed, resulting in 6 treatments: CON-TR (n = 5), trained and fed 0.1 mg/kg Se in Phase 1 and then switched to 0.3 mg/kg Se for Phase 2 (ADD-TR; n = 5), trained and fed 0.3 mg/kg Se in Phase 1 and then switched to 0.1 mg/kg Se for Phase 2 (DROP-TR; n = 5), HIGH-TR (n = 5), CON-UN (n = 5), or HIGH-UN (n = 5). All horses underwent a 120-min submaximal exercise test (SET) at the end of Phase 1 (SET 1) and 2 (SET 2). Blood samples and biopsies from the middle gluteal muscle were collected before and after each phase of the study and in response to each SET and analyzed for markers of oxidative damage and antioxidant enzyme activity. In both phases, serum Se was higher (P < 0.0001) when horses received a diet with 0.3 than 0.1 mg Se/kg DM. Throughout the 14-wk study, resting activities of muscle glutathione peroxidase (GPx; P = 0.004) and superoxide dismutase (SOD; P = 0.06) were greater in trained horses than in untrained horses. In response to SET 1, serum creatine kinase (CK) activity was lower in trained horses than in untrained horses (P < 0.0001), indicating less muscle damage, but plasma lipid hydroperoxides (LPO) and muscle GPx and SOD activities were unaffected by training or Se. In response to SET 2, trained horses had greater muscle SOD activity (P = 0.0002) and lower serum CK activity (P = 0.003) and showed a trend for lower plasma LPO (P = 0.09) and muscle malondialdehyde (P = 0.09) than untrained horses. Muscle GPx activity did not change in response to SET 2 and was unaffected by training or Se. Results indicate that exercise training lessens muscle damage and improves antioxidant defense following an acute bout of prolonged exercise and was not further enhanced by feeding Se above the NRC requirement.

Rapid Communication: Dietary selenium improves skeletal muscle mitochondrial biogenesis in young equine athletes

Exercise is known to promote mitochondrial biogenesis in skeletal muscle as well as enhance mitochondrial function and efficiency in human and rodent models. These adaptations help to decrease exercise-associated production of reactive oxygen species, which can negatively affect health and performance if antioxidant mechanisms are overwhelmed. Little is known about the adaptations of mitochondria in response to exercise training in the growing horse or if supplementation with a dietary antioxidant can improve mitochondrial function. To evaluate the separate and combined effects of selenium (Se) supplementation, training, and an acute strenuous exercise bout on mitochondrial adaptations in young horses, 30 American Quarter Horse yearlings were randomly assigned to an exercise training group or a no-training group and, within each group, received either 0.1 or 0.3 mg Se/kg DM for 14 wk. The study was split into 2 phases (wk 0 to 8 and wk 9 to 14), with half of the trained horses switched to the opposite dietary treatment in Phase 2. At the end of each phase, all horses underwent a 120-min submaximal exercise test (SET; SET 1 and SET 2). Biopsies of the middle gluteal muscle were collected before and after each phase of the study and in response to each SET and analyzed for markers of mitochondrial number and function. At rest, horses receiving 0.3 mg Se/kg DM had higher citrate synthase activity ( = 0.021) than horses receiving 0.1 mg Se/kg DM, indicating higher mitochondrial content. In contrast, cytochrome oxidase (CCO) activity was not affected by dietary Se overall, but horses that were dropped from 0.3 mg Se/kg DM to 0.1 mg Se/kg DM during Phase 2 showed a decrease ( = 0.034) in integrated CCO activity from wk 9 to 14, suggesting impaired mitochondrial function. Mitochondrial enzyme activities were unaffected by an acute, strenuous exercise bout (SET 1 and SET 2). Our relatively low-intensity exercise training protocol did not appear to induce functional mitochondrial adaptations. However, elevated dietary Se may impart beneficial effects on mitochondrial biogenesis during growth and training. A more strenuous exercise training protocol should be investigated to determine the potential benefits of elevated dietary Se for elite equine athletes.

Dietary selenium and prolonged exercise alter gene expression and activity of antioxidant enzymes in equine skeletal muscle

Untrained Thoroughbred horses (6 mares and 6 geldings; 11 yr [SE 1] and 565 kg [SE 11]) were used to evaluate antioxidant gene expression and enzyme activity in blood and skeletal muscle in response to prolonged exercise after receiving 2 levels of dietary selenium for 36 d: 0.1 (CON; = 6) or 0.3 mg/kg DM (SEL; = 6). Horses were individually fed 1.6% BW coastal bermudagrass hay, 0.4% BW whole oats, and a mineral/vitamin premix containing no Se. Sodium selenite was added to achieve either 0.1 or 0.3 mg Se/kg DM in the total diet. On d 35, horses underwent 2 h of submaximal exercise in a free-stall exerciser. Blood samples were obtained before (d 0) and after 34 d of Se supplementation and on d 35 to 36 immediately after exercise and at 6 and 24 h after exercise. Biopsies of the middle gluteal muscle were obtained on d 0, before exercise on d 34, and at 6 and 24 h after exercise. Supplementation with Se above the NRC requirement (SEL) increased serum Se ( = 0.011) and muscle thioredoxin reductase (TrxR) activity ( = 0.051) but had no effect on glutathione peroxidase (GPx) activity in plasma, red blood cell (RBC) lysate, or muscle in horses at rest. Serum creatine kinase activity increased ( < 0.0001) in response to prolonged exercise but was not affected by dietary treatment. Serum lipid hydroperoxides were affected by treatment ( = 0.052) and were higher ( = 0.012) in horses receiving CON than SEL immediately following exercise. Muscle expression of was unchanged at 6 h but increased ( = 0.005) 2.8-fold 24 h after exercise, whereas muscle TrxR activity remained unchanged. Glutathione peroxidase activity increased in plasma (P < 0.0001) and decreased in RBC lysate ( = 0.010) after prolonged exercise. A Se treatment × time interaction was observed for RBC GPx activity (P = 0.048). Muscle and expression and GPx activity did not change during the 24-h period after exercise. Level of dietary Se had no overall effect on expression of , , , , , , or in muscle following exercise. The impact of prolonged exercise on the activities of antioxidant enzymes varied. Furthermore, changes in enzyme activity did not necessarily align with enzyme gene expression following exercise. A higher level of Se intake elevated Se status of untrained horses, increased GPx activity, and lessened lipid peroxidation following exercise, suggesting that Se may be beneficial for mitigating oxidative muscle damage and aiding in postexercise recovery.

Dietary supplements and military operations: caution is advised

We describe the case of a 32-year-old soldier who presented with acute organic psychosis during an operational tour to Iraq. This was precipitated by excessive consumption of caffeine coupled with additional use of oral nutritional stimulants. Her biochemical profile was compounded by the additional use of exogenous creatine. We present a brief overview of the issue of exercise supplementation and highlight some of the potential problems and clinical issues surrounding their use. This has important implications for both serving soldiers and the wider medical community.

Back pain in a Bangladeshi worker in Iraq

Pyogenic Spinal Infection (PSI) is an uncommon disorder encompassing a broad spectrum of diseases including septic spondylodiscitis, osteomyelitis, epidural and paravertebral abscess formation. Presentation can be vague and highly variable but usually includes back pain and fever. Whilst predisposing factors, such as trauma and diabetes can often be identified a pathogenic organism may not be identified in up to a half of all cases leading to significant delay in both accurate diagnosis and effective treatment. Precise spinal imaging is essential and includes plain X-ray, CT and preferably MRI. The treatment of PSI can be conservative (including antibiotics); however, spinal surgery may be required for the complications in up to 50% of cases, with varying degrees of success. We present a challenging case of PSI encountered in a locally-employed 42-year-old Bangladeshi civilian working in Iraq. Despite obvious resource limitations available within a Role 2 Field Hospital, clinical suspicion coupled with repeat spinal CT was pivotal in obtaining the diagnosis. The patient was repatriated to Bangladesh for MRI and definitive surgical treatment.

The Avon patellofemoral joint replacement: independent assessment of early functional outcomes

We present a prospective review of the two-year functional outcome of 37 Avon patellofemoral joint replacements carried out in 29 patients with a mean age of 66 years (30 to 82) between October 2002 and March 2007. No patients were lost to follow-up. This is the first independent assessment of this prosthesis using both subjective and objective analysis of outcome. At two years the median Oxford knee score was 39 (interquartile range 32 to 44), the median American Knee Society objective score was 95 (interquartile range 90 to 100), the median American Knee Society functional score was 85 (interquartile range 60 to 100), and the median Melbourne Knee score was 28 (interquartile range 21 to 30). Two patients underwent further surgery. Only one patient reported an unsatisfactory outcome. We conclude that the promising early results observed by the designing centre are reproducible and provide further support for the role of patellofemoral joint replacement.

Revision of Oxford medial unicompartmental knee arthroplasty to total knee arthroplasty - results of a multicentre study

The advantages of Unicompartmental Knee Replacement (UKR) over Total Knee Replacement (TKR) includes the preservation of soft tissue as well as bone stock, and better function with improved range of motion and more natural gait. It is therefore believed that the revision of failed UKR to TKR is technically easier than revision of failed TKR. In our study we tested this hypothesis by assessing the reconstruction requirements and early clinical and radiological outcome following the revision of UKR to TKR. During a 15-year period 1060 primary Oxford medial UKR procedures were performed at three centres, 36 of which underwent revision to TKR due to aseptic failure. The mean operating time for revision surgery was 113 min. Among the revision prostheses used, 28 were standard TKRs, six were constrained, and two were semi-constrained. Thirty had no intramedullary stems whereas six had intramedullary stems. In 30 cases reconstruction for bone loss was not required whereas metal augmentation was used in two knees, contained peg defects in the femur were filled with cement in two knees and contained keel defects in the tibia were grafted using the bone from revision cuts in two knees. After a mean follow-up of 2 years, the mean 'total knee score' was 86.3 and the mean functional score was 78.5. These findings suggest that the complexity of operation and complications encountered during Oxford medial UKR revision and the clinical outcome compare favorably with those of TKR revision.

Mortality and toxin bioaccumulation in Bufo marinus following exposure to Cylindrospermopsis raciborskii cell extracts and live cultures

Cylindrospermopsis raciborskii is a cyanobacterium responsible for the production of the toxin, cylindrospermopsin (CYN). Tadpoles of the cane toad Bufo marinus were exposed to freeze-thawed whole cell extracts or live cultures of C. raciborskii containing maximum CYN concentrations of 400 microg L-1 or 232 microg L-1, respectively. Exposure to live culture treatment solutions resulted in up to 66% mortality of B. marinus, whereas tadpoles exposed to whole cell extracts containing similar toxin concentrations survived. Decreases in relative growth rates and time spent for swimming were recorded from tadpoles during both types of exposure regimes. Bioconcentration of CYN was not evident following exposure to whole cell extracts containing extracellular toxin. In contrast exposure to live cultures, which contained cell-bound toxin, resulted in maximum average tissue concentrations of 895 microg free-CYN kg-1 fresh weight. This is the first investigation of C. raciborskii exposure effects and toxin bioaccumulation in the developmental stages of an amphibian.

Minimally invasive Oxford medial unicompartmental knee arthroplasty. A note of caution!

We present the peak outcome results of the Oxford medial unicompartmental arthroplasty through a minimally invasive surgical incision. This prospective study included 78 Oxford medial unicompartmental knee replacements in 68 patients. At the 2 year review the patients achieved a mean Oxford Knee Score of 38.3. This was not significantly different to the 2 year results of the phase 2 Oxford knee carried out using a standard parapatellar approach when patients achieved a mean OKS of 36.0. Four unicompartmental knee replacements required revision for unexplained pain, deep infection, aseptic loosening and bearing dislocation. Minimally invasive joint replacement is attractive to both patients and surgeons, but is technically demanding with complications inherent to limited access.

The effect of preoperative symptom severity on functional outcome of total knee replacement--patients with the lowest preoperative scores achieve the lowest marks

To determine if the functional outcome of total knee replacement (TKR) was affected by the level of preoperative symptom severity, the association between preoperative Oxford Knee Scores (OKS), and 2 year OKS, American Knee Society clinical and function scores (AKSS) was assessed. Data were prospectively collected on 45 cases who had single joint osteoarthritis and no other comorbidities. We have specifically focused on patients with single knee involvement to remove the effect of multiple joint involvement and comorbidities on the OKS. The mean preoperative OKS was 21.4, postoperative OKS 40.0 and postoperative ROM 117 degrees. The postoperative mean AKSS was 86.7 and mean function score was 85.0. The 'usual pain' and 'limp' components of the OKS had the greatest rises and the 'kneel' component had the least improvement. Rather than all patients achieving uniform results post-TKR, patients with more severe symptoms achieved poorer absolute outcomes. The Spearman correlation coefficient between pre- and postoperative OKS was r = 0.4 (p = 0.006). Although the results suggest that waiting too long before intervention compromises the final outcome, a correlation of 0.4 is not strong enough to necessitate change in current practice.

Do protein-lipid interactions determine the recognition of transmembrane helices at the ER translocon?

Membrane-protein integration, folding and assembly processes in vivo depend on complex targeting, translocation, chaperoning, and sorting machineries that somehow read the 'molecular code' built into the nascent polypeptide, ultimately producing a properly folded protein integrated into the correct target membrane. Although the main molecular constituents and the basic mechanistic principles of many of these machines are known in outline, the codes remain poorly defined and there is little quantitative information on how protein sequence affects the final structure of membrane proteins. By carefully designing model protein constructs, we have derived the first true biological hydrophobicity scale and have been able to get a first impression of how the position of a given type of residue within a transmembrane segment affects its ability to promote membrane insertion.

Influence of intracellular toxin concentrations on cylindrospermopsin bioaccumulation in a freshwater gastropod (Melanoides tuberculata)

Scant information is available regarding the bioaccumulation of cylindrospermopsin (CYN) in aquatic organisms, particularly in invertebrates. This study examined toxin bioconcentration and bioaccumulation in the aquatic snail, Melanoides tuberculata, following exposure to freeze-thawed whole cell extracts and a live Cylindrospermopsis raciborskii culture containing CYN. Both bioconcentration and bioaccumulation were evident, but exposure to toxin in the freeze-thawed solutions resulted in minor tissue contamination compared with that resulting from live C. raciborskii exposure. Thus, whilst CYN uptake resulted from both extracellular and intracellular exposures, the availability of intracellular toxin was critical in affecting tissue CYN values. M. tuberculata did not bioconcentrate CYN into the shell. Bioaccumulation of the analog deoxy-CYN was also recorded. Knowledge of intracellular toxin concentrations may be critical in evaluating the bioaccumulation, ecological and human health risks associated with contaminated systems.

Operating on patients wearing personal identity devices: a report of two cases

We report on two patients who have recently required emergency surgery and who were wearing personal identity devices at the time of presentation. The devices bear a telephone number and a message stating that, if found, the management company should be informed of the whereabouts of their owner. We discuss the issues relating to the disclosure of information to a third party in this situation and whether there is any legal obligation to do so. The conclusion of a review of the relevant literature is that the only reason to divulge information to a third party would be if a patient posed a serious risk of death or serious harm to another party. In the majority of foreseeable circumstances, this would not be the case.

Analysis of the Leeds-Keio ligament for extensor mechanism repair: favourable mechanical and functional outcome

Many techniques have been described for the challenging problem of extensor mechanism rupture, including the use of synthetic grafts. In 1994 Fujikawa et al. [J. Bone Surg. 1994:76B:200-203] reported excellent results using the Leeds-Keio polyester ligament. Patients were mobilised early, had few post operative complications and minimal extensor lag. This is the first independent assessment of this technique using both subjective and objective analysis of outcome. We reviewed 11 patients (12 knees) whose extensor mechanisms were repaired as described in the original paper. At a mean of 3 years after surgery there were no infections and no re-ruptures. Good functional recovery was observed with a mean Tegner activity score of 1.7, Lysholm score of 66 and Irrgang score of 58%. Indeed, 80% of working patients returned to their former employment. However, objective tests showed peak extensor torque recovered to only half normal strength. We conclude the results of this technique of repair compare favourably with other described techniques especially in complex cases.

Bicipetal tenodesis for anterior subluxation of the superior tibiofibular joint

A technique for stabilising the superior tibiofibular joint using an autogenous biceps graft passed through a tibial tunnel is described. The common peroneal nerve should be decompressed and the lateral inferior genicular artery protected. The technique proved to be safe and effective in two patients who were followed for at least two years.

Energetics, stability, and prediction of transmembrane helices

We show that the peptide backbone of an alpha-helix places a severe thermodynamic constraint on transmembrane (TM) stability. Neglect of this constraint by commonly used hydrophobicity scales underlies the notorious uncertainty of TM helix prediction by sliding-window hydropathy plots of membrane protein (MP) amino acid sequences. We find that an experiment-based whole-residue hydropathy scale (WW scale), which includes the backbone constraint, identifies TM helices of membrane proteins with an accuracy greater than 99 %. Furthermore, it correctly predicts the minimum hydrophobicity required for stable single-helix TM insertion observed in Escherichia coli. In order to improve membrane protein topology prediction further, we introduce the augmented WW (aWW) scale, which accounts for the energetics of salt-bridge formation. An important issue for genomic analysis is the ability of the hydropathy plot method to distinguish membrane from soluble proteins. We find that the method falsely predicts 17 to 43 % of a set of soluble proteins to be MPs, depending upon the hydropathy scale used.

'Detergent-like' permeabilization of anionic lipid vesicles by melittin

Melittin (MLT), the 26-residue toxic peptide from the European honeybee Apis mellifera, is widely used for studying the principles of membrane permeabilization by antimicrobial and other host-defense peptides. A striking property of MLT is that its ability to permeabilize zwitterionic phospholipid vesicles is dramatically reduced upon the addition of anionic lipids. Because the mechanism of permeabilization may be fundamentally different for the two types of lipids, we examined MLT-induced release of entrapped fluorescent dextran markers of two different molecular masses (4 and 50 kDa) from anionic palmitoyloleoylphosphatidylglycerol (POPG) vesicles. Unlike release from palmitoyloleoylphosphatidylcholine (POPC) vesicles, which is highly selective for the 4 kDa marker, implying release through pores of about 25 A diameter [Ladokhin et al., Biophys. J. 72 (1997) 1762], release from POPG vesicles was found to be non-selective, i.e., 'detergent-like'. Oriented circular dichroism measurements of MLT in oriented POPG and POPC multilayers disclosed that alpha-helical MLT can be induced to adopt a transbilayer orientation in POPC multilayers, but not in POPG multilayers. The apparent inhibition of MLT permeabilization by anionic membranes may thus be due to suppression of translocation ability.

Magnetic resonance imaging assessment for unicompartmental knee replacement: a limited role

The purpose of this study was to see if MRI has a role in pre-operative assessment of patients for unicompartmental knee replacement. Until now, surgeons have been unable to predict whether a patient is suitable until the operation itself when the anterior cruciate ligament is inspected. We found that 33% of patients with anteromedial osteoarthritis had a degenerate anterior cruciate ligament according to magnetic resonance imaging, compared to only 13% on surgical inspection. We conclude that MRI is too sensitive to changes of the anterior cruciate ligament to be of much practical value.

Protein chemistry at membrane interfaces: non-additivity of electrostatic and hydrophobic interactions

Non-specific binding of proteins and peptides to charged membrane interfaces depends upon the combined contributions of hydrophobic (DeltaG(HPhi)) and electrostatic (DeltaG(ES)) free energies. If these are simply additive, then the observed free energy of binding (DeltaG(obs)) will be given by DeltaG(obs)=DeltaG(HPhi)+DeltaG(ES), where DeltaG(HPhi)=-sigma(NP)A(NP) and DeltaG(ES)=zFphi. In these expressions, A(NP) is the non-polar accessible area, sigma(NP) the non-polar solvation parameter, z the formal peptide valence, F the Faraday constant, and phi the membrane surface potential. But several lines of evidence suggest that hydrophobic and electrostatic binding free energies of proteins at membrane interfaces, such as those associated with cell signaling, are not simply additive. In order to explore this issue systematically, we have determined the interfacial partitioning free energies of variants of indolicidin, a cationic proline-rich antimicrobial peptide. The synthesized variants of the 13 residue peptide covered a wide range of hydrophobic free energies, which allowed us to examine the effect of hydrophobicity on electrostatic binding to membranes formed from mixtures of neutral and anionic lipids. Although DeltaG(obs) was always a linear function of DeltaG(HPhi), the slope depended upon anionic lipid content: the slope was 1.0 for pure, zwitterionic phosphocholine bilayers and 0.3 for pure phosphoglycerol membranes. DeltaG(obs) also varied linearly with surface potential, but the slope was smaller than the expected value, zF. As observed by others, this suggests an effective peptide valence z(eff) that is smaller than the formal valence z. Because of our systematic approach, we were able to establish a useful rule-of-thumb: z(eff) is reduced relative to z by about 20 % for each 3 kcal mol(-1) (1 kcal=4.184 kJ) favorable increase in DeltaG(HPhi). For neutral phosphocholine interfaces, we found that DeltaG(obs) could be predicted with remarkable accuracy using the Wimley-White experiment-based interfacial hydrophobicity scale.

Specificity of the Oxford knee status questionnaire. The effect of disease of the hip or lumbar spine on patients' perception of knee disability

There is a need for the accurate measurement of the outcome after knee surgery. The Oxford Knee Score is being increasingly used since it is reported to be short, simple, inexpensive and validated. We sent the questionnaire to 346 patients awaiting surgery to the hip or lumbar spine. Only 11% of 141 patients with proximal pathology who denied knee problems gave a maximum score. Their mean score was substantially lower than expected at 28.7 (maximum 48), and was significantly lower than the score of 36.5 obtained from patients after total knee replacement. We therefore suggest that the frequent coexistence of hip or spinal pathology will significantly alter both the absolute score and any improvement to be expected after knee surgery. Although sensitive to disability originating from the knee the Oxford Knee Score is not sufficiently specific since it is heavily influenced by more proximal pathology.

Specificity of the Oxford knee status questionnaire

There is a need for the accurate measurement of the outcome after knee surgery. The Oxford Knee Score is being increasingly used since it is reported to be short, simple, inexpensive and validated.

We sent the questionnaire to 346 patients awaiting surgery to the hip or lumbar spine. Only 11% of 141 patients with proximal pathology who denied knee problems gave a maximum score. Their mean score was substantially lower than expected at 28.7 (maximum 48), and was significantly lower than the score of 36.5 obtained from patients after total knee replacement.

We therefore suggest that the frequent coexistence of hip or spinal pathology will significantly alter both the absolute score and any improvement to be expected after knee surgery. Although sensitive to disability originating from the knee the Oxford Knee Score is not sufficiently specific since it is heavily influenced by more proximal pathology.

Structure, location, and lipid perturbations of melittin at the membrane interface

Melittin is arguably the most widely studied amphipathic, membrane-lytic alpha-helical peptide. Although several lines of evidence suggest an interfacial membrane location at low concentrations, melittin's exact position and depth of penetration into the hydrocarbon core are unknown. Furthermore, the structural basis for its lytic action remains largely a matter of conjecture. Using a novel x-ray absolute-scale refinement method, we have now determined the location, orientation, and likely conformation of monomeric melittin in oriented phosphocholine lipid multilayers. Its helical axis is aligned parallel to the bilayer plane at the depth of the glycerol groups, but its average conformation differs from the crystallographic structure. As observed earlier for another amphipathic alpha-helical peptide, the lipid perturbations induced by melittin are remarkably modest. Small bilayer perturbations thus appear to be a general feature of amphipathic helices at low concentrations. In contrast, a dimeric form of melittin causes larger structural perturbations under otherwise identical conditions. These results provide direct structural evidence that self-association of amphipathic helices may be the crucial initial step toward membrane lysis.

MPtopo: A database of membrane protein topology

The reliability of the transmembrane (TM) sequence assignments for membrane proteins (MPs) in standard sequence databases is uncertain because the vast majority are based on hydropathy plots. A database of MPs with dependable assignments is necessary for developing new computational tools for the prediction of MP structure. We have therefore created MPtopo, a database of MPs whose topologies have been verified experimentally by means of crystallography, gene fusion, and other methods. Tests using MPtopo strongly validated four existing MP topology-prediction algorithms. MPtopo is freely available over the internet and can be queried by means of an SQL-based search engine.

Perceptions of outcomes after unicompartmental and total knee replacements

An independent measurement of the quality of outcome of 31 consecutive Oxford medial unicompartmental knee replacements in 28 patients and 130 total knee replacements in 104 patients performed between 1993 and 1997 is reported. The indications for surgery were anteromedial osteoarthritis for unicompartmental replacement and more extensive osteoarthritis for total knee replacement. All patients were treated by one surgeon. As a validated outcome measure of knee function, the Oxford 12-item knee questionnaire showed identical outcome in both groups with a mean score of 36.5 (maximum possible, 48). Neither the pain nor the functional outcomes were significantly different, although patients receiving unicompartmental replacement were better able to descend stairs. Two patients needed revision surgery in the unicompartmental replacement group compared with only one patient in the total knee replacement group. The femoral component of two unicompartmental replacements showed radiologic signs of loosening. The tibial component of one total knee replacement appeared loose, but the patient had no symptoms. In comparison with total knee replacement, implantation of meniscal bearing unicompartmental replacement technically is demanding and unforgiving. However, revision of a failed Oxford unicompartmental replacement is easier than revision of a failed total knee replacement, and the authors recommend this device for younger patients in whom one could expect a total knee replacement to fail within their lifetime.

Obturator dislocation of the hip

We describe two patients with obturator dislocation of the hip which was irreducible by described techniques of closed reduction. The first required open reduction using the iliofemoral approach with release of rectus femoris. The second was treated on a traction table which allowed disengagement of the head and, when combined with simultaneous lateral traction, adduction and gradual release of the longitudinal traction, facilitated a smooth reduction. Since the hip is stable in flexion, early mobilisation in an extension-limiting brace avoids the prolonged bed rest traditionally recommended for this injury.

How to measure and analyze tryptophan fluorescence in membranes properly, and why bother?

Tryptophan fluorescence is a powerful tool for studying protein structure and function, especially membrane-active proteins and peptides. It is arguably the most frequently used tool for examining the interactions of proteins and peptides with vesicular unilamellar model membranes. However, high light scattering associated with vesicular membrane systems presents special challenges. Because of their reduced light scattering compared to large unilamellar vesicles (LUV), small unilamellar vesicles (SUV) produced by sonication are widely used membrane models. Unfortunately, SUV, unlike LUV, are metastable and consequently unsuitable for equilibrium thermodynamic measurements. We present simple and easily implemented experimental procedures for the accurate determination of tryptophan (Trp) fluorescence in either LUV or SUV. Specifically, we show that Trp spectra can be obtained in the presence of up to 6 mM LUV that are virtually identical to spectra obtained in buffer alone, which obviates the use of SUV. We show how the widths and peak positions of such spectra can be used to evaluate the heterogeneity of the membrane conformation and penetration of peptides. Finally, we show how to use a reference fluorophore for the correction of intensity measurements so that the energetics of peptide partitioning into membranes can be accurately determined.

Formation and characterization of a single Trp-Trp cross-link in indolicidin that confers protease stability without altering antimicrobial activity

Indolicidin is a 13-residue cationic, antimicrobial peptide-amide isolated from the cytoplasmic granules of bovine neutrophils. The unique composition of indolicidin distinguishes it from alpha-helical and beta-structured cationic peptides, because five of indolicidin's 13 residues are tryptophans: H-Ile-Leu-Pro-Trp-Lys-Trp-Pro-Trp-Trp-Pro-Trp-Arg-Arg-NH(2). Solid phase synthesis of indolicidin gave rise to a minor byproduct that possessed unusual fluorescence and UV absorbance properties compared with authentic indolicidin. The byproduct was purified by combined ion exchange and reversed phase high pressure liquid chromatography steps and was shown be identical to authentic indolicidin in its microbicidal activity against Staphylococcus aureus, Escherichia coli, Candida albicans, and Cryptococcus neoformans. Mass analysis of the byproduct revealed a 2-atomic mass unit reduction compared with indolicidin, suggesting the deprotonation of two indole side chains to form an intrachain delta(1),delta(1)'-ditryptophan derivative. We confirmed the nature of the cross-linked byproduct, termed X-indolicidin, by absorbance and fluorescence spectroscopy, peptide mapping, and sequence analysis. Edman degradation revealed that Trp-6 and Trp-9 were covalently cross-linked. Compared with indolicidin, X-indolicidin was partially resistant to digestion with trypsin and chymotrypsin, suggesting that the ditryptophan stabilizes a subset of molecular conformations that are protease resistant but that are absent in the native structure.

Designing transmembrane alpha-helices that insert spontaneously

Direct measurement of the free energies of transfer of hydrophobic membrane-spanning alpha-helices from water to membranes is important for the determination of an accurate experiment-based hydrophobicity scale for membrane proteins. An important objective of such a scale is to account for the presently unknown thermodynamic cost of partitioning hydrogen-bonded peptide bonds into the membrane hydrocarbon core. We describe here the physical properties of a transmembrane (TM) peptide, TMX-1, designed to test the feasibility of engineering peptides that spontaneously insert across bilayers but that have the important property of measurable monomeric water solubility. TMX-1, Ac-WNALAAVAAAL-AAVAAALAAVAAGKSKSKS-NH(2), is a 31-residue sequence with a 21-residue nonpolar core, N- and C-caps to favor helix formation, and a highly polar C-terminus to improve solubility and to control directionality of insertion into lipid vesicles. TMX-1 appeared to be soluble in water up to a concentration of at least 1 mg/mL (0.3 mM). However, fluorescence spectroscopy, fluorescence quenching, and circular dichroism (CD) spectroscopy indicated that the high solubility was due to the formation of molecular aggregates that persisted at peptide concentrations down to at least 0.1 microM peptide. Nevertheless, aqueous TMX-1 partitioned strongly into membrane vesicles with apparent mole-fraction free-energy values of -7.1 kcal mol(-1) for phosphatidylcholine (POPC) vesicles and -8.2 kcal mol(-1) for phosphatidylglycerol (POPG) vesicles. CD spectroscopy of TMX-1 in oriented multilayers formed from either lipid disclosed a very strong preference for a transmembrane alpha-helical conformation. When TMX-1 was added to preformed vesicles, it was fully helical. A novel fluorescence resonance energy transfer (FRET) method demonstrated that at least 50% of the TMX-1 insered spontaneously across the vesicle membranes. Binding and insertion were found to be fully reversible for POPC vesicles but not POPG vesicles. TMX-1 was thus found to have many of the properties required for thermodynamic measurements of TM peptide insertion. Importantly, the results obtained delineate the experimental problems that must be considered in the design of peptides that can partition spontaneously and reversibly as monomers into and across membranes. Our success with TMX-1 suggests that these problems are not insurmountable.

Determining the membrane topology of peptides by fluorescence quenching

Determination of the topology of peptides in membranes is important for characterizing and understanding the interactions of peptides with membranes. We describe a method that uses fluorescence quenching arising from resonance energy transfer ("FRET") for determining the topology of the tryptophan residues of peptides partitioned into phospholipid bilayer vesicles. This is accomplished through the use of a novel lyso-phospholipid quencher (lysoMC), N-(7-hydroxyl-4-methylcoumarin-3-acetyl)-1-palmitoyl-2-hydroxy-sn-gly cero-3-phosphoethanolamine. The design principle was to anchor the methylcoumarin quencher in the membrane interface by attaching it to the headgroup of lyso-phosphoethanolamine. We show that lysoMC can be incorporated readily into large unilamellar phospholipid vesicles to yield either symmetrically (both leaflets) or asymmetrically (outer leaflet only) labeled bilayers. LysoMC quenches the fluorescence of membrane-bound tryptophan by the Förster mechanism with an apparent R(0) that is comparable to the thickness of the hydrocarbon core of a lipid bilayer (approximately 25 A). Consequently, the methylcoumarin acceptor predominantly quenches tryptophans that reside in the same monolayer as the probe. The topology of a peptide's tryptophan in membranes can be determined by comparing the quenching in symmetric and asymmetric lysoMC-labeled vesicles. Because it is essential to know that asymmetrically incorporated lysoMC remains so under all conditions, we also developed a second type of FRET experiment for assessing the rate of transbilayer diffusion (flip-flop) of lysoMC. Except in the presence of pore-forming peptides, there was no measurable flip-flop of lysoMC, indicating that asymmetric distributions of quencher are stable. We used these methods to show that N-acetyl-tryptophan-octylamide and tryptophan-octylester rapidly equilibrate across phosphatidylcholine (POPC) and phosphatidylglycerol (POPG) bilayers, while four amphipathic model peptides remain exclusively on the outer monolayer. The topology of the amphipathic peptide melittin bound to POPC could not be determined because it induced rapid flip-flop of lysoMC. Interestingly, melittin did not induce lysoMC flip-flop in POPG vesicles and was found to remain stably on the external monolayer.

CD spectra of indolicidin antimicrobial peptides suggest turns, not polyproline helix

Indolicidin is a 13-residue antimicrobial peptide-amide isolated from the cytoplasmic granules of bovine neutrophils that contains five Trp and three Pro residues. Falla et al. [(1996) J. Biol. Chem. 271, 19298] suggested that indolicidin forms a poly-L-proline II helix based upon the circular dichroism (CD) spectra of a closely related peptide (indolicidin methyl ester). In contrast, we found no evidence of poly-L-proline II helix formation in the CD spectra of native indolicidin in various solvents or when bound to micelles and membranes [Ladokhin et al. (1997) Biophys. J. 72, 794]. We interpreted the spectra as arising from unordered and/or beta-turn structures, but noted a sharp negative band at 227 nm arising from the tryptophan residues that would mask spectral features characteristic of poly-L-proline II helix. We have reexamined this issue by means of CD measurements of native indolicidin and several of its analogues. None of the features characteristic of a poly-L-proline helix (or alpha- or 3(10)-helix) were observed for any of the peptides studied. To eliminate artifacts associated with tryptophan, we synthesized indolicidin-L and indolicidin-F in which all five tryptophans were replaced with leucines or phenylalanines, respectively. The changes in CD spectra of these Trp-free peptides upon transfer into membrane-like environments were found to be consistent with the formation of beta-turns. For the native indolicidin in SDS micelles, temperature increases resulted in a coupled diminution of two sharp bands, a negative one at 227 nm and a positive one at 217 nm. This phenomenon, which is absent in indolicidin-L variants with single Leu-->Trp substitutions, is consistent with exciton splitting produced by the stacking of indole rings. Type VI turns in model peptides in aqueous solution are known to be promoted by stacking interactions between cis-proline and neighboring aromatic residues [Yao et al. (1994) J. Mol. Biol. 243, 754]. Molecular modeling of indolicidin with a -Trp(6)-cis-Pro(7)-Trp(8)- type VIa turn demonstrated the feasibility of this turn conformation and revealed the possibility of an accompanying amphipathic structure. We therefore suggest that turn conformations are the principal structural motif of indolicidin and that these turns greatly enhance membrane activity.

Membrane protein folding and stability: physical principles

Stably folded membrane proteins reside in a free energy minimum determined by the interactions of the peptide chains with each other, the lipid bilayer hydrocarbon core, the bilayer interface, and with water. The prediction of three-dimensional structure from sequence requires a detailed understanding of these interactions. Progress toward this objective is summarized in this review by means of a thermodynamic framework for describing membrane protein folding and stability. The framework includes a coherent thermodynamic formalism for determining and describing the energetics of peptide-bilayer interactions and a review of the properties of the environment of membrane proteins--the bilayer milieu. Using a four-step thermodynamic cycle as a guide, advances in three main aspects of membrane protein folding energetics are discussed: protein binding and folding in bilayer interfaces, transmembrane helix insertion, and helix-helix interactions. The concepts of membrane protein stability that emerge provide insights to fundamental issues of protein folding.