Advanced MRI Approaches for Evaluating Common Lower Extremity Injuries in Basketball Players: Current and Emerging Techniques

Magnetic resonance imaging (MRI) can provide accurate and non-invasive diagnoses of lower extremity injuries in athletes. Sport-related injuries commonly occur in and around the knee and can affect the articular cartilage, patellar tendon, hamstring muscles, and bone. Sports medicine physicians utilize MRI to evaluate and diagnose injury, track recovery, estimate return to sport timelines, and assess the risk of recurrent injury. This article reviews the current literature and describes novel developments of quantitative MRI tools that can further advance our understanding of sports injury diagnosis, prevention, and treatment while minimizing injury risk and rehabilitation time. Innovative approaches for enhancing the early diagnosis and treatment of musculoskeletal injuries in basketball players span a spectrum of techniques. These encompass the utilization of T2, T1ρ, and T2* quantitative MRI, along with dGEMRIC and Na-MRI to assess articular cartilage injuries, 3D-Ultrashort echo time MRI for patellar tendon injuries, diffusion tensor imaging for acute myotendinous injuries, and sagittal short tau inversion recovery and axial long-axis T1-weighted, and 3D Cube sequences for bone stress imaging. Future studies should further refine and validate these MR-based quantitative techniques while exploring the lifelong cumulative impact of basketball on players' knees. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

Deep Learning Assistance Closes the Accuracy Gap in Fracture Detection Across Clinician Types

BACKGROUND

Missed fractures are the most common diagnostic errors in musculoskeletal imaging and can result in treatment delays and preventable morbidity. Deep learning, a subfield of artificial intelligence, can be used to accurately detect fractures by training algorithms to emulate the judgments of expert clinicians. Deep learning systems that detect fractures are often limited to specific anatomic regions and require regulatory approval to be used in practice. Once these hurdles are overcome, deep learning systems have the potential to improve clinician diagnostic accuracy and patient care.

QUESTIONS/PURPOSES

This study aimed to evaluate whether a Food and Drug Administration-cleared deep learning system that identifies fractures in adult musculoskeletal radiographs would improve diagnostic accuracy for fracture detection across different types of clinicians. Specifically, this study asked: (1) What are the trends in musculoskeletal radiograph interpretation by different clinician types in the publicly available Medicare claims data? (2) Does the deep learning system improve clinician accuracy in diagnosing fractures on radiographs and, if so, is there a greater benefit for clinicians with limited training in musculoskeletal imaging?

METHODS

We used the publicly available Medicare Part B Physician/Supplier Procedure Summary data provided by the Centers for Medicare & Medicaid Services to determine the trends in musculoskeletal radiograph interpretation by clinician type. In addition, we conducted a multiple-reader, multiple-case study to assess whether clinician accuracy in diagnosing fractures on radiographs was superior when aided by the deep learning system compared with when unaided. Twenty-four clinicians (radiologists, orthopaedic surgeons, physician assistants, primary care physicians, and emergency medicine physicians) with a median (range) of 16 years (2 to 37) of experience postresidency each assessed 175 unique musculoskeletal radiographic cases under aided and unaided conditions (4200 total case-physician pairs per condition). These cases were comprised of radiographs from 12 different anatomic regions (ankle, clavicle, elbow, femur, forearm, hip, humerus, knee, pelvis, shoulder, tibia and fibula, and wrist) and were randomly selected from 12 hospitals and healthcare centers. The gold standard for fracture diagnosis was the majority opinion of three US board-certified orthopaedic surgeons or radiologists who independently interpreted the case. The clinicians' diagnostic accuracy was determined by the area under the curve (AUC) of the receiver operating characteristic (ROC) curve, sensitivity, and specificity. Secondary analyses evaluated the fracture miss rate (1-sensitivity) by clinicians with and without extensive training in musculoskeletal imaging.

RESULTS

Medicare claims data revealed that physician assistants showed the greatest increase in interpretation of musculoskeletal radiographs within the analyzed time period (2012 to 2018), although clinicians with extensive training in imaging (radiologists and orthopaedic surgeons) still interpreted the majority of the musculoskeletal radiographs. Clinicians aided by the deep learning system had higher accuracy diagnosing fractures in radiographs compared with when unaided (unaided AUC: 0.90 [95% CI 0.89 to 0.92]; aided AUC: 0.94 [95% CI 0.93 to 0.95]; difference in least square mean per the Dorfman, Berbaum, Metz model AUC: 0.04 [95% CI 0.01 to 0.07]; p < 0.01). Clinician sensitivity increased when aided compared with when unaided (aided: 90% [95% CI 88% to 92%]; unaided: 82% [95% CI 79% to 84%]), and specificity increased when aided compared with when unaided (aided: 92% [95% CI 91% to 93%]; unaided: 89% [95% CI 88% to 90%]). Clinicians with limited training in musculoskeletal imaging missed a higher percentage of fractures when unaided compared with radiologists (miss rate for clinicians with limited imaging training: 20% [95% CI 17% to 24%]; miss rate for radiologists: 14% [95% CI 9% to 19%]). However, when assisted by the deep learning system, clinicians with limited training in musculoskeletal imaging reduced their fracture miss rate, resulting in a similar miss rate to radiologists (miss rate for clinicians with limited imaging training: 9% [95% CI 7% to 12%]; miss rate for radiologists: 10% [95% CI 6% to 15%]).

CONCLUSION

Clinicians were more accurate at diagnosing fractures when aided by the deep learning system, particularly those clinicians with limited training in musculoskeletal image interpretation. Reducing the number of missed fractures may allow for improved patient care and increased patient mobility.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Incidence and Predictors of Valgus Tibiotalar Tilt after Progressive Collapsing Foot Deformity Reconstruction using Subtalar Fusion

Category:

Ankle; Ankle Arthritis; Hindfoot; Midfoot/Forefoot; Other

Introduction/Purpose:

Subtalar fusion is a powerful option for correcting hindfoot deformity in progressive collapsing foot deformity (PCFD). Despite successful correction through subtalar fusion, the development of valgus tibiotalar tilt at the ankle joint has been documented as a significant complication. This can be detrimental since abnormal forces on the ankle joint can induce cartilage wear and subsequent ankle arthritis over time. However, the incidence of valgus tilt of the ankle following subtalar fusion for PCFD reconstruction has not been extensively studied, and little is known about its etiological factors. The purpose of this study was to define the incidence of valgus tibiotalar tilt after subtalar fusion for PCFD reconstruction, and to determine if any demographic and radiographic parameters predict which patients develop this complication.

Methods:

This study reviewed 59 patients (median age: 59 years) who underwent PCFD reconstruction with subtalar fusion and had pre-and postoperative weightbearing anteroposterior radiographs of the ankle in the registry. Patients with a tibiotalar tilt prior to surgery were excluded. On standard weightbearing radiographs, the talonavicular coverage angle, talo-1st metatarsal angle, calcaneal pitch, and hindfoot moment arm (HMA), and medial distal tibial angle were measured. Weightbearing computed tomography (WBCT) was used to determine the presence of preoperative sinus tarsi or calcaneofibular bony impingement. A radiologist evaluated the superficial and deep deltoid ligaments using magnetic resonance imaging (MRI). Postoperative valgus tibiotalar tilt was defined as tilt >2 degrees. Univariate regression analysis was used to identify the factors associated with development of postoperative valgus tibiotalar tilt. These factors included age, gender, BMI, as well as concomitant procedures, radiographic parameters, lateral bony impingement on WBCT, and deltoid ligament status on MRI.

Results:

A total of 17 patients (28.8%) developed postoperative valgus tibiotalar tilt at a mean of 7.7 (range, 2-31) months. Eight (47.1%) of the 17 patients developed valgus tibiotalar tilt (mean talar tilt of 5.3 degrees, range: 4-8) on postoperative weightbearing within 3 months. In bivariate analysis, male gender and preoperative HMA were significantly associated with development of valgus tibiotalar tilt (Table 1). Univariate logistic regression demonstrated that preoperative HMA was associated with postoperative valgus tibiotalar tilt (odds ratio 1.06, P = .026), with a 6% increase in risk per millimeter of increased HMA. Deltoid ligament status on MRI and concomitant procedures on other joints including fusion did not correlate with postoperative valgus tibiotalar tilt.

Conclusion:

The incidence of valgus tibiotalar tilt after subtalar fusion in PCFD reconstruction was 28.8% in this study. Preoperative valgus hindfoot alignment rather than the condition of the deltoid ligament was a significant predictor of postoperative valgus tibiotalar tilt. Our findings indicate that surgeons should be cognizant of patients with a greater degree of hindfoot valgus and of their propensity to develop a valgus ankle deformity. Additionally, our relatively high incidence of valgus tibiotalar tilt suggests that weightbearing ankle radiographs should be included in the initial and subsequent follow-up of PCFD patients with hindfoot valgus treated with subtalar fusions.

GM-CSF Promotes Immune Response and Survival in a Mouse Model of COVID-19

COVID-19 results in increased expression of inflammatory cytokines, but inflammation-targeting clinical trials have yielded poor to mixed results. Our studies of other disorders with an inflammatory component, including Alzheimer's disease, chemobrain, Down syndrome, normal aging, and West Nile Virus infection, showed that treatment with the 'pro-inflammatory' cytokine granulocyte-macrophage colony stimulating factor (GM-CSF) in humans or mouse models alleviated clinical, behavioral, and pathological features. We proposed that human recombinant GM-CSF (sargramostim) be repurposed to promote both the innate and adaptive immune responses in COVID-19 to reduce viral load and mortality1. Here, we report the results of a placebo-controlled study of GM-CSF in human ACE2 transgenic mice inoculated intranasally with SARS-CoV2 virus, a model of COVID-19. Infection resulted in high viral titers in lungs and brains and over 85% mortality. GM-CSF treatment beginning one day after infection increased anti-viral antibody titers, lowered mean lung viral titers proportionately (p=0.0020) and increased the odds of long-term survival by up to 5.8-fold (p=0.0358), compared to placebo. These findings suggest that, as an activator of both the innate and adaptive immune systems, GM-CSF/sargramostim may be an effective COVID-19 therapy with the potential to protect from re-infection more effectively than treatment with antiviral drugs or monoclonal antibodies.

In vitro responses to platelet-rich-plasma are associated with variable clinical outcomes in patients with knee osteoarthritis

Autologous blood-derived products such as platelet-rich plasma (PRP) are widely used to treat musculoskeletal conditions, including knee osteoarthritis (OA). However, the clinical outcomes after PRP administration are often variable, and there is limited information about the specific characteristics of PRP that impact bioactivity and clinical responses. In this study, we aimed to develop an integrative workflow to evaluate responses to PRP in vitro, and to assess if the in vitro responses to PRP are associated with the PRP composition and clinical outcomes in patients with knee OA. To do this, we used a coculture system of macrophages and fibroblasts paired with transcriptomic analyses to comprehensively characterize the modulation of inflammatory responses by PRP in vitro. Relying on patient-reported outcomes and achievement of minimal clinically important differences in OA patients receiving PRP injections, we identified responders and non-responders to the treatment. Comparisons of PRP from these patient groups allowed us to identify differences in the composition and in vitro activity of PRP. We believe that our integrative workflow may enable the development of targeted approaches that rely on PRP and other orthobiologics to treat musculoskeletal pathologies.

Immunolesion of melanopsin neurons causes gonadal regression in Pekin drakes (Anas platyrhynchos domesticus)

Several light sensitive receptors have been described in the avian brain that are thought to regulate the reproductive axis independently from the eyes and pineal gland. Recently, our lab has described the presence of three of these photoneuroendocrine systems in the Pekin duck: opsin, opsin 5, & melanopsin. We set out to test the hypothesis that melanopsin receptive neurons are necessary to maintain seasonal reproductive status along with growth and development in the Pekin drake. To accomplish these goals we first investigated 50-week-old Pekin drakes that were housed in the aviary at Hope College under long day length (18h lights on) conditions in floor pens. To specifically lesion melanopsin-receptive neurons, 3μl of an anti-melanopsin-saporin conjugate (MSAP, 100ng/ul) was injected into the lateral ventricle (n=10). Control drakes were injected with 3μl of equimolar unconjugated anti-melanopsin and saporin (SAP, n=10). Reproductive behaviors were analyzed weekly in a test pen with adult hens and MSAP drakes showed a significant (p<0.01) reduction in reproductive behaviors after week 2. After 5weeks, drakes were euthanized and body weights were measured, and brains, pituitaries, and testes collected and stored for analyses. Mature MSAP-treated drakes had significantly (p<0.001) reduced relative teste weights compared to SAP controls. qRT-PCR analyses of hypothalamus showed a significant reduction (p<0.001) in GnRH and melanopsin mRNA levels, but not opsin 5, vertebrate ancient opsin, or opsin 2 (rhodopsin). Immunocytochemical analyses showed a significant reduction (p<0.01) in tyrosine hydroxylase-immunoreactivity in the PMM. These data suggest that although blue light alone is not able to maintain testicular function, the blue-light sensitive melanopsin activity is critical to maintain gonadal function.

Effects of Surgical Factors on Cartilage Can Be Detected Using Quantitative Magnetic Resonance Imaging After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Quantitative magnetic resonance (qMR) can be used to measure macromolecules in tissues and is a potential method of observing early cartilage changes in the development of posttraumatic osteoarthritis. Hypothesis/Purpose: We hypothesized that specific patient and surgical factors affecting cartilage matrix composition after anterior cruciate ligament (ACL) reconstruction (ACLR) can be detected using T1ρ and T2 relaxation times. Our purpose was to demonstrate this ability in a multicenter feasibility study.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A total of 54 patients who underwent ACLR underwent bilateral MRI at baseline before surgery and 6 months postoperatively. Operative findings were recorded. T1ρ and T2 relaxation times were calculated for 6 cartilage regions: the medial femur, lateral femur, medial tibia, lateral tibia, patella, and trochlea. A paired t test compared relaxation times at baseline and 6 months, univariate regression identified regions that influenced patient-reported outcome measures, and analysis of covariance was used to determine the surgical factors that resulted in elevated relaxation times at 6 months.

RESULTS

The injured knee had significantly prolonged T1ρ and T2 relaxation times in the tibiofemoral compartment at baseline and 6 months but had shorter values in the patellofemoral compartment compared with the uninjured knee. Prolonged T1ρ and T2 times at 6 months were noted for both the injured and uninjured knees. At 6 months, prolongation of T1ρ and T2 times in the tibial region was associated with lower patient-reported outcome measures. ACLR performed within 30 days of injury had significantly shorter T1ρ times in the tibial regions, and lateral meniscal tears treated with repair had significantly shorter T1ρ times than those treated with excision.

CONCLUSION

Prolonged relaxation times in multiple regions demonstrate how the injury affects the entire joint after an ACL tear. Changes observed in the uninjured knee may be caused by increased loading during rehabilitation, especially in the patellofemoral articular cartilage and distal femur. Relaxation times in the tibial regions may be predictive of patient symptoms at 6 months. These same regions are affected by surgical timing as early as 30 days after injury, but this may partially be reflective of the severity of the preoperative injury and the choice of treatment of meniscal tears.

Baseline cartilage quality is associated with voxel-based T1ρ and T2 following ACL reconstruction: A multicenter pilot study

In this multi-center study, voxel-based relaxometry (VBR), a novel technique to automatically quantify localized cartilage change, was used to investigate T_1ρ and T₂ relaxation times of patients with anterior cruciate ligament (ACL) tears at the time of injury and 6 months after reconstructive surgery. Sixty-four ACL-injured patients from three sites underwent bilateral 3T MR T_1ρ and T₂ mapping; 56 patients returned 6 months after surgery. Cross-sectional and longitudinal VBR comparisons of relaxation times were calculated. Noyes Score (NS) clinical grades of cartilage lesions were noted at both times and correlated with relaxation times. Lastly, patients were divided into two groups based on baseline NS grades in the injured knee. T_1ρ times of each group were assessed with VBR and compared. Results illustrate the feasibility of VBR for efficiently analyzing data from patients at different sites. Significant relaxation time elevations at baseline were observed in the injured knee compared to the uninjured, particularly in the posterolateral tibia (pLT). Longitudinally, a decrease was observed in the pLT and patella, while an increase was noted in the trochlea. Stratifying patients by baseline lesion presence revealed T_1ρ increased more 6 months after surgery in patients with lesions. Such findings propose that the presence of cartilage lesions at baseline are associated with the longitudinal progression of T_1ρ and T₂ after ACL injury, and may contribute to early cartilage degeneration. Furthermore, the speed and localized specificity of automatic VBR analysis may translate well for clinical application, as seen in this multicenter study. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:688-698, 2017.

Anterior cruciate ligament and intercondylar notch growth plateaus prior to cessation of longitudinal growth: an MRI observational study

PURPOSE

Increasing numbers of children and adolescents are being treated for ACL tears. In order for surgeons to safely optimize treatment during ACL surgery, we must better understand ACL growth and intercondylar notch patterns in the skeletally immature knee. The aim of this study is to measure ACL and intercondylar notch volume in paediatric patients and observe how these volumes change as a function of age and gender.

METHODS

Data were extracted from the picture archiving and communication systems (PACS) computer records. Sample consisted of 137 MRI knee examinations performed between January 2006 and July 2010 in patients aged 3-13. Subjects were grouped into 1-year age intervals. Patients with imaging reports including ACL tears, previous surgeries, congenital structural anomalies, or syndromes were excluded.

RESULTS

Measures of ACL volume significantly increased with age (P < 0.001). A linear increase in ACL volume was observed until the age 10, with a mean increase in volume of 148 mm(3) per age group. ACL volume plateaued at 10 years, after which minimal increase in ACL volume was observed. Sex was not found to be a significant predictor of ACL volume in the multiple linear regression (P = 0.57). Similar to ACL volume, there was a significant increase in intercondylar notch volume with age with a mean increase of 835 mm(3) per age group (P < 0.0001). Intercondylar notch volume reached a plateau at age 10, after which a minimal increase in notch volume was observed in older groups. Female patients had notch volumes that were on average 892 + 259 mm(3) smaller than male patients who were in the same age group (P = 0.0006).

CONCLUSION

The plateau in the growth of ACL and notch volume occurs at age 10, prior to the halt in longitudinal growth of boys and girls. Female patients have significantly smaller intercondylar notch volumes than their age-matched male counterparts, while no gender difference was seen in ACL volume. These results suggest that notch volume is an intrinsically sex-specific difference, which may contribute to the higher rate of ACL tears among females. These growth patterns are clinically relevant as it allows surgeons to better understand the anatomy, pathology, and risk factors related to ACL tears and its reconstruction.

LEVEL OF EVIDENCE

Observational Study, Level IV.

Lower Extremity Injury Patterns in Elite Ballet Dancers: Ultrasound/MRI Imaging Features and an Institutional Overview of Therapeutic Ultrasound Guided Percutaneous Interventions

BACKGROUND

Altered biomechanics from repetitive microtrauma, such as long practice hours in en pointe (tip of the toes) or demi pointe (balls of the feet) predispose ballet dancers to a multitude of musculoskeletal pathologies particularly in the lower extremities. Both ultrasound and magnetic resonance imaging (MRI) are radiation-sparing modalities which can be used to confidently evaluate these injuries, with ultrasound (US) offering the added utility of therapeutic intervention at the same time in experienced hands.

QUESTIONS/PURPOSES

The purposes of this paper were: (1) to illustrate the US and MRI features of lower extremity injury patterns in ballet dancers, focusing on pathologies commonly encountered at a single orthopedic hospital; (2) to present complementary roles of both ultrasound and MRI in the evaluation of these injuries whenever possible; (3) to review and present our institutional approach towards therapeutic ultrasound-guided interventions by presenting explicit cases.

METHODS

Online searches were performed using the search criteria of "ballet biomechanics" and "ballet injuries." The results were then further narrowed down by limiting articles published in the past 15 years, modality (US and MRI), anatomical region (foot and ankle, hip and knee) and to major radiology, orthopedics, and sports medicine journals.

RESULTS

Performing ballet poses major stress to lower extremities and predisposes dancer to several musculoskeletal injuries. These can be adequately evaluated by both US and MRI. US is useful for evaluating superficial structures such as soft tissues, tendons, and ligaments, particularly in the foot and ankle. MRI provides superior resolution of deeper structures such as joints, bone marrow, and cartilage. In addition, US can be used as a therapeutic tool for providing quick symptomatic improvement in these athletes for who "time is money".

CONCLUSION

Performing ballet may cause major stress to the lower extremities, predominantly affecting the foot and ankle, followed by the knee and hip. US and MRI play complementary roles in evaluating various orthopedic conditions in ballet dancers, with US allowing for dynamic evaluation and guidance for interventions.

Magnetic resonance imaging of cartilage repair techniques

Magnetic resonance (MR) imaging offers a noninvasive method to assess cartilage repair, allowing objective evaluation of the repair tissue and insight into the natural history of cartilage repair procedures. MR imaging allows assessment of the percent fill, signal morphology of the repair tissue, subchondral bone and three-dimensional geometry of the joint. The information gained from MR imaging therefore plays a valuable role in patient follow-up after cartilage repair. This article discusses the MR imaging techniques available for the assessment of articular cartilage, including quantitative imaging techniques that allow assessment of cartilage biochemistry. The MR imaging appearance and assessment of microfracture, autologous chondrocyte implantation, and osteochondral autograft and allograft transplantation is reviewed.

Effective glenoid version in professional baseball players

The pathomechanics of the throwing shoulder have yet to be fully elucidated. The focus of this study reported here was to further characterize the morphology of the glenoid in a population of elite throwing athletes. We obtained magnetic resonance imaging scans of 38 professional baseball players (dominant shoulders) and of 35 age matched nonthrowing control patients (17 dominant and 18 nondominant shoulders). Seven measurements were made by 3 blinded reviewers on 3 axial images per patient: version of superior glenoid, middle glenoid, inferior glenoid, superior capsulolabral junction, middle capsulolabral junction, inferior capsulolabral junction, and depth of concavity of glenoid in a middle slice. Mean age of the 38 players (24 pitchers, 14 fielders) was 26.8 years, and mean age of the 35 control patients was 27.6 years. Intraclass correlation coefficients ranged from .55 to .84 for the version measurements. There were no statistically significant differences between the pitchers and the fielders on any of the 7 measurements, but such differences were found between the throwers and the dominant-shoulder control patients on all 7 measurements. There were only 2 differences (version of superior glenoid, depth of concavity of glenoid in a middle slice) between dominant- and nondominant- shoulder control patients. There was significantly more retroversion in the osseous and soft tissues of the elite throwing athletes than in the nonthrowing control patients. This increased retroversion may play a role in development of internal impingement in the overhead athlete.

Association of white matter hyperintensity measurements on brain MR imaging with cognitive status, medial temporal atrophy, and cardiovascular risk factors

BACKGROUND AND PURPOSE

White matter hyperintensities (WMHs) are frequently characterized as markers of cerebrovascular disease, whereas medial temporal atrophy (MTA) is a recognized marker of Alzheimer disease (AD). Our purpose was to test the reliability of a visual rating system (VRS) in evaluating WMHs and MTA and in distinguishing healthy from cognitively impaired subjects.

MATERIALS AND METHODS

Subjects (n = 192) enrolled in the Florida Alzheimer's Disease Research Center were diagnosed with no cognitive impairment, nonamnestic mild cognitive impairment (na-MCI), amnestic MCI (a-MCI), or probable AD. The severity of WMHs was assessed on T2-weighted fluid-attenuated inversion recovery axial MR images, and the severity of MTA was evaluated on 1.5-mm-thick coronal MR images by using a computer-based visual rating system. Cardiovascular risk factor scores were calculated as the sum of 10 independent cardiovascular risk factors.

RESULTS

WMH and MTA scores were greater in subjects with probable AD, relative to those with no cognitive impairment and na-MCI. MTA scores differentiated subjects with a-MCI from those with no cognitive impairment and na-MCI. The total WMH score was significantly related to MTA (r = 0.39; P < .001) but not to cardiovascular risk factor scores (r = 0.07; P = not significant). The overall correct classification rate of probable AD versus no cognitive impairment by using MTA scores was 81.8%, improving to 86.5% when combined with WMH scores.

CONCLUSIONS

Both MTA and WMH scores distinguished subjects with no cognitive impairment and probable AD. Combining MTA and WMH scores improved the correct classification rate, whereas WMH scores were significantly related to MTA scores, but not to cardiovascular risk factor scores. This finding suggests that among subjects with a-MCI and probable AD, WMHs on MR images are primarily associated with neurodegenerative disease.

Medial temporal lobe atrophy on MRI scans and the diagnosis of Alzheimer disease

BACKGROUND

Despite convenience, accessibility, and strong correlation to severity of Alzheimer disease (AD) pathology, medial temporal lobe atrophy (MTA) has not been used as a criterion in the diagnosis of prodromal and probable AD.

METHODS

Using a newly validated visual rating system, mean MTA scores of three bilateral medial temporal lobe structures were compared for subjects with no cognitive impairment (NCI) (n = 117), nonamnestic mild cognitive impairment (MCI) (n = 46), amnestic MCI (n = 45), and probable AD (n = 53). Correlations between MTA scores and neuropsychological test scores at baseline, and predictors of change in diagnosis at 1-year follow-up were evaluated.

RESULTS

With NCI as the reference group, a mean MTA cut score of 1.33 yielded an optimal sensitivity/specificity of 85%/82% for probable AD subjects and 80%/82% for amnestic MCI subjects. MTA and Clinical Dementia Rating Sum of Boxes scores at baseline were independent and additive predictors of diagnosis at baseline, and of transition from NCI to MCI or from MCI to dementia at 1-year follow-up.

CONCLUSION

Medial temporal lobe atrophy (MTA) scores 1) distinguish probable Alzheimer disease (AD) and amnestic mild cognitive impairment (MCI) subjects from nonamnestic MCI and no cognitive impairment (NCI) subjects, 2) help predict diagnosis at baseline, and 3) predict transition from NCI to MCI and from MCI to probable AD. MTA scores should be used as a criterion in the clinical diagnosis of AD.

Transfection by electroporation

Electroporation yields a high frequency of permanent transfectants, has a high efficiency of transient gene expression, and can be easier to carry out than alternative techniques. Electroporation makes use of the fact that the cell membrane acts as an electrical capacitor which is unable (except through ion channels) to pass current. Subjecting membranes to a high-voltage electric field results in their temporary breakdown and the formation of pores that are large enough to allow macromolecules (as well as smaller molecules such as ATP) to enter or leave the cell. The reclosing of the membrane pores is a natural decay process which is delayed at decreased temperatures. This unit presents the procedures which can be used for both transient and stable transfections.

Transfection by electroporation

Electroporation--the use of high-voltage electric shocks to introduce DNA into cells--can be used with most cell types,yields a high frequency of both stable transformation and transient gene expression,and,because it requires fewer steps,can be easier than alternate techniques. In this unit,the basic protocol describes the electroporation of mammalian cells and an alternate protocol outlines modifications for preparation and transfection of plant protoplasts.

A diet high in omega-3 fatty acids does not improve or protect cognitive performance in Alzheimer’s transgenic mice

Although a number of epidemiologic studies reported that higher intake of omega-3 fatty acids (largely associated with fish consumption) is protective against Alzheimer's disease (AD), other human studies reported no such effect. Because retrospective human studies are problematic and controlled longitudinal studies over decades are impractical, the present study utilized Alzheimer's transgenic mice (Tg) in a highly controlled study to determine whether a diet high in omega-3 fatty acid, equivalent to the 13% omega-3 fatty acid diet of Greenland Eskimos, can improve cognitive performance or protect against cognitive impairment. Amyloid precursor protein (APP)-sw+PS1 double transgenic mice, as well as nontransgenic (NT) normal littermates, were given a high omega-3 supplemented diet or a standard diet from 2 through 9 months of age, with a comprehensive behavioral test battery administered during the final 6 weeks. For both Tg and NT mice, long-term n-3 supplementation resulted in cognitive performance that was no better than that of mice fed a standard diet. In NT mice, the high omega-3 diet increased cortical levels of omega-3 fatty acids while decreasing omega-6 levels. However, the high omega-3 diet had no effect on cortical fatty acid levels in Tg mice. Irrespective of diet, no correlations existed between brain omega-3 levels and cognitive performance for individual NT or Tg mice. In contrast, brain levels of omega-6 fatty acids were strongly correlated with cognitive impairment for both genotypes. Thus, elevated brain levels of omega-3 fatty acids were not relevant to cognitive function, whereas high brain levels of omega-6 were associated with impaired cognitive function. In Tg mice, the omega-3 supplemental diet did not induce significant changes in soluble/insoluble Abeta within the hippocampus, although strong correlations were evident between hippocampal Abeta(1-40) levels and cognitive impairment. While these studies involved a genetically manipulated mouse model of AD, our results suggest that diets high in omega-3 fatty acids, or use of fish oil supplements (DHA+EPA), will not protect against AD, at least in high-risk individuals. However, normal individuals conceivably could derive cognitive benefits from high omega-3 intake if it corrects an elevation in the brain level of n-6 fatty acids as a result. Alternatively, dietary fish may contain nutrients, other than DHA and EPA, that could provide some protection against AD.

The incidence of soft tissue injury in operative tibial plateau fractures: a magnetic resonance imaging analysis of 103 patients

OBJECTIVES

The goal of this study was to determine the incidence of injury to soft tissue structures of the knee in tibial plateau fractures scheduled for surgery.

DESIGN

Prospective cohort.

SETTING

Level I academic medical center.

PATIENTS/PARTICIPANTS

One hundred three consecutive patients with acute tibial plateau fractures indicated for operative intervention.

INTERVENTION

Standard x-ray examinations, including anteroposterior, lateral, and oblique views, were performed in the emergency department. Subsequently all patients had magnetic resonance imaging performed. The Schatzker and AO/OTA classifications were used to classify each fracture pattern based solely on the x-rays. Soft tissue injuries were assessed by magnetic resonance imaging.

MAIN OUTCOME MEASUREMENTS

Fifteen categories of injury were determined as positive or negative on each magnetic resonance imaging, which included tears of the cruciates, collateral ligaments, menisci, and posterolateral corner.

RESULTS

The overall incidence of injury to soft tissues was higher than previously reported. Only 1 patient (1%) in the series had complete absence of any soft tissue injury. Seventy-nine patients (77%) sustained a complete tear or avulsion of 1 or more cruciate or collateral ligaments. Ninety-four patients (91%) had evidence of lateral meniscus pathology. Forty-five patients (44%) had medial meniscus tears. Seventy patients (68%) had tears of 1 or more of the posterolateral corner structures of the knee. The most frequent fracture pattern was a lateral plateau split-depression (Schatzker II) (60%). No pure depression injuries (Schatzker III, AO/OTA 41-B2) were seen.

CONCLUSIONS

The incidence of complete ligamentous or meniscal disruption associated with operative tibial plateau fractures was higher than previously reported. Though the clinical importance of injury to each of these structures is unknown, the treating surgeon should be aware that a variety of soft tissue injuries are common in these fractures. In addition, all fractures had at least 1 cortical split visible on magnetic resonance imaging, implying that pure depression patterns are very rare or may not exist.

Environmental enrichment improves cognition in aged Alzheimer's transgenic mice despite stable β-amyloid deposition

Environmental enrichment (EE) has been shown to improve cognitive performance and brain indices of cognition in normal mice and rats. Because the therapeutic potential of intensive, long-term EE to benefit patients with Alzheimer's disease (AD) has yet to be explored, the present study evaluated the effect of long-term EE on cognition in an animal model of AD, the APPsw transgenic mouse. Beginning at 16 months of age, APPsw mice were put into EE or standard housing for 4 months and then tested in four cognitive-based tasks (Morris maze, circular platform, platform recognition, and radial arm water maze) between 20 and 22 months of age. Our results indicate that long-term EE of aged APPsw mice results in global, overall improvement in cognitive function across these tasks without decreasing brain beta-amyloid (A beta) deposition. The results suggest that long-term EE/cognitive stimulation could provide cognitive stabilization or improvement to AD patients through mechanisms independent of A beta deposition and clearance.

Temperature along the axillary nerve during radiofrequency-induced thermal capsular shrinkage

BACKGROUND

There have been reports of axillary nerve palsy after thermal capsular shrinkage with radiofrequency energy-generating devices. The exact cause of this is unknown.

HYPOTHESIS

The temperature of the axillary nerve increases during shoulder capsular shrinkage at various degrees of shoulder abduction.

STUDY DESIGN

Laboratory study.

METHODS

Fifteen cadaveric shoulders had fiberoptic thermometer probes placed at various points along the axillary nerve and major branches under the capsule. The shoulders underwent thermal capsular shrinkage with a radiofrequency energy-inducing device at various positions of abduction.

RESULTS

With the arm at the side, temperatures above 50 degrees C (56 degrees -61 degrees C) were evident along the teres minor branch of the axillary nerve in 4 of 6 specimens. The increase in temperature was noted in the middle to posterior aspect of the inferior capsule. At 45 degrees of abduction, 4 of 5 shoulders demonstrated increases in temperature greater or equal to 50 degrees. Three of 4 shoulders tested at 90 degrees of abduction revealed similar temperature increases.

CONCLUSIONS

The arthroscopic technique of thermal capsular shrinkage causes an increase in the temperature of the axillary nerve and its branches in 11 of 15 cadaveric specimens tested at various arm positions-particularly affected is the teres minor branch.

CLINICAL RELEVANCE

Orthopaedic surgeons using the radiofrequency device for thermal capsular shrinkage need to be aware of the possible increase in temperature along the axillary nerve and its branches during this procedure. The clinical effect of this type of increase on the nerve is unknown.

Effect of cytokines, dexamethasone and the A/T-signal peptide polymorphism on the expression of alpha(1)-antichymotrypsin in astrocytes: significance for Alzheimer's disease

Proinflammatory cytokines and acute phase proteins, such as alpha(1)-antichymotrypsin, are over expressed in microglia and astrocytes in brain regions with abundant mature amyloid plaques, suggesting a glial cell-led brain acute phase response in the Alzheimer neuropathology. In this paper, we show that alpha(1)-antichymotrypsin gene expression in human astrocytes is elevated by interleukin-1 and interleukin-6, and further enhanced by glucocorticoid, while the homologous contrapsin gene in rat astrocytes is unaffected by these cytokines. These distinct gene regulation mechanisms might help to explain the differential susceptibility of humans and rodents to amyloid formation of the Alzheimer's type. In addition, we demonstrate that the alpha(1)-antichymotrypsin A-allele that encodes a different signal peptide and is a suggested risk factor for Alzheimer's disease gives rise to a reduced level of immature alpha(1)-antichymotrypsin in transfected cells. The physiological result would be an enhanced ability of the A-encoded alpha(1)-antichymotrypsin protein to become secreted and promote extracellular amyloid formation. We discuss our findings in terms of a model in which cytokine-induced alpha(1)-antichymotrypsin synthesis in astrocytes constitutes a specific inflammatory pathway that accelerates the development of Alzheimer's disease and could at least partly underlie the regional specificity and species restriction of the neuropathology.

The inflammation-induced pathological chaperones ACT and apo-E are necessary catalysts of Alzheimer amyloid formation

Biochemical, genetic, and epidemiological evidence indicates that inflammation is an essential part of the pathogenesis of Alzheimer's disease. Over the last decade, we and others have focused on the mechanism by which specific inflammatory molecules contribute to the Alzheimer pathogenic pathway. In particular, we have learned that several acute phase/inflammatory molecules, specifically alpha(1)-antichymotrypsin (ACT) and apolipoprotein E (apoE) that are overproduced in the AD brain can promote the formation of, and are associated with, the neurotoxic amyloid deposits that are a key pathological hallmark of the disease. Because both of these proteins bind to the Abeta peptide and catalyze its polymerization into amyloid filaments, they have been termed "pathological chaperones".ACT, and, to a lesser extent, apoE are greatly overproduced only in areas of the AD brain that are prone to amyloid formation. This restriction suggests a local inflammatory reaction may underlie the regional specificity of amyloid deposition by inducing the production of pathological chaperones. The data that will be discussed indicate that ACT over-expression is caused by the activation of ACT mRNA synthesis in astrocytes in response to increased production of the inflammatory cytokine IL-1. IL-1 is released from microglia that become activated by pre-amyloid seeds of Abeta. Recently, this inflammatory cascade has been extended to include the amyloid precursor protein (APP), for IL-1 also upregulates the production of APP in astrocytes, but at the translational rather that the transcriptional level. Thus many of the key elements of the Alzheimer's disease pathogenic pathway are products of a local inflammatory reaction in the brain. Further support for a mechanistic role of inflammation in the Alzheimer's disease pathogenic pathway has been provided by genetic studies, which have associated an increased risk of developing AD with specific polymorphisms in the apoE, ACT, and the IL-1 genes. Most recently, transgenic mouse models of AD have demonstrated that ACT and apoE are amyloid promoters/pathological chaperones in vivo whose contribution is necessary for both amyloid formation and for amyloid-associated cognitive decline and memory loss. The importance of these findings is that they help to place inflammation at the center of the pathogenic pathway to Alzheimer's disease and identify specific steps in the pathway that may be amenable to therapeutic intervention.

The anatomy and histology of the rotator interval capsule of the shoulder

Forty-seven rotator interval regions from fetuses and 10 fresh-frozen rotator interval regions from adult cadavers were evaluated by gross dissection and light microscopy. Specimens from adults also were evaluated with ultrasound and magnetic resonance imaging. An analysis of 37 fetal specimens (> 14 weeks gestation) revealed two rotator interval types: Type I (9 of 37) was defined by a contiguous bridge of capsule consisting of poorly organized collagen fibers. A Type II rotator interval (28 of 37) had a complete defect covered by only a thin layer of synovium. Similar to the Type II rotator interval in the fetus, a rotator interval defect was present in six of eight specimens from adults. Histologically, the capsular tissue within the rotator interval consisted of poorly organized collagen fibers in specimens from the fetus and adult. Maximal opening of the rotator interval was seen by ultrasound with internal rotation and downward traction of the hyperextended arm in the coronal, oblique, and sagittal planes. Magnetic resonance imaging of the rotator interval region permitted anatomic evaluation. The complete absence of tissue in 28 of 37 fetuses suggests that the rotator interval defect is congenital. The authors recommend that surgeons carefully evaluate the integrity of the tissue within the rotator interval. When rotator interval closure is desired such as in patients with a persistent sulcus sign after arthroscopic stabilization, suturing the edges of more substantial tissue immediately adjacent to the boundaries of the rotator interval region would seem prudent.

Alpha-1-antichymotrypsin promotes beta-sheet amyloid plaque deposition in a transgenic mouse model of Alzheimer's disease

Alpha(1)-antichymotrypsin (ACT), an acute-phase inflammatory protein, is an integral component of the amyloid deposits in Alzheimer's disease (AD) and has been shown to catalyze amyloid beta-peptide polymerization in vitro. We have investigated the impact of ACT on amyloid deposition in vivo by generating transgenic GFAP-ACT-expressing mice and crossing them with the PDGF-hAPP/V717F mice, which deposit amyloid in an age-dependent manner. The number of amyloid deposits measured by Congo Red birefringence was increased in the double ACT/amyloid precursor protein (APP) transgenic mice compared with transgenic mice that only expressed APP, particularly in the hippocampus where ACT expression was highest, and the increase was preceded by elevated total amyloid beta-peptide levels at an early age. Our data demonstrate that ACT promotes amyloid deposition and provide a specific mechanism by which inflammation and the subsequent upregulation of astrocytic ACT expression in AD brain contributes to AD pathogenesis.

Ultrastructural observations on sperm storage in the ovary of the platyfish, Xiphophorus maculatus (Teleostei: poeciliidae): the role of the duct epithelium

Sperm storage is an important phenomenon occurring in viviparous and oviparous teleosts and contributes to the reproductive life history of these forms. There is a paucity of morphological studies on sperm storage in fishes. The majority of these have been confined to the light level of investigation. In this report, we describe, at the ultrastructural level, sperm storage in the viviparous platyfish, Xiphophorus maculatus. Female platyfish, as is typical of the poeciliids, are capable of storing viable sperm for up to several months within the ovary and gonoduct. We observed that sperm stored within inseminated platyfish became associated with specific epithelial cells (SACs) lining the oviduct. Two forms of association were seen: 1) sperm were found within deep surface pits and pockets, and 2) the spermatozoa were taken up and incorporated within the cytoplasm of the SACs. Junctional complexes in the form of tight junctions (zona occludens) and desmosomes at the apico-lateral surfaces of the SACs were prevalent. The junctions could have contributed to allograft survival of the haploid heterogenetic sperm cells within the female's reproductive tract. Our results shed light on the mechanism of sperm storage in the platyfish and could serve as a model for other poeciliid species and teleosts that are capable of storing sperm.

Immune response to an 18-kilodalton outer membrane antigen identifies lipoprotein 20 as a Helicobacter pylori vaccine candidate

Experiments were performed using the standardized murine model of Helicobacter pylori infection to determine the immunogenicity of H. pylori outer membrane vesicles in immune protection. These vesicles, which are naturally shed from the surface of the bacterium, induce a protective response when administered intragastrically to mice in the presence of cholera holotoxin, despite the absence of the urease enzyme and associated Hsp54 chaperonin. Immunoblotting identified a specific serum immunoglobulin G (IgG) response to an 18-kDa outer membrane protein in a significant number of immunized animals. This commonly expressed, immunodominant protein was subsequently identified as lipoprotein 20 (Lpp20). Hybridoma backpacks secreting an IgG1 subclass monoclonal antibody to Lpp20 were generated in H. pylori-infected mice and were found to significantly reduce bacterial numbers, providing evidence that this surface-exposed antigen is a true vaccine candidate and not merely an antigenic marker for successful, protective immunization.

Chromosome missegregation and trisomy 21 mosaicism in Alzheimer's disease

A connection between Alzheimer's disease (AD) and Down syndrome (trisomy 21) is indicated by the fact that all Down syndrome individuals develop Alzheimer's disease neuropathology by the 4th decade of life. Previous studies have examined the frequency of aneuploidy and other chromosomal defects in cells from familial Alzheimer's disease (FAD) patients, with varying results. To investigate the possibility that a specific type of aneuploidy--trisomy 21 mosaicism--may contribute to Alzheimer's disease, we used quantitative fluorescence in situ hybridization to measure the number of trisomy 21 cells in primary fibroblast cultures from AD and unaffected subjects. The 27 AD cultures, including 15 that were derived from individuals carrying FAD mutations in presenilin 1 or 2, exhibited a significant approximately twofold increase in the number of trisomy 21 cells compared to 13 control cultures. A small double-hybridization experiment suggested that the aneuploidy in AD cells was not limited to chromosome 21 but extended at least to chromosome 18 as well. In a parallel study, the endogenous presenilin proteins in fibroblasts were localized to the centrosomes, the nuclear envelope, and its associated interphase kinetochores. Together these results indicate that the presenilin proteins may be involved in mitosis and that FAD mutations in the presenilin genes may predispose to chromosome missegregation (nondisjunction). The data reported here also suggest that trisomy 21 mosaicism may contribute to other forms of AD that are not caused by a presenilin mutation.

Translation of the alzheimer amyloid precursor protein mRNA is up-regulated by interleukin-1 through 5'-untranslated region sequences

The amyloid precursor protein (APP) has been associated with Alzheimer's disease (AD) because APP is processed into the beta-peptide that accumulates in amyloid plaques, and APP gene mutations can cause early onset AD. Inflammation is also associated with AD as exemplified by increased expression of interleukin-1 (IL-1) in microglia in affected areas of the AD brain. Here we demonstrate that IL-1alpha and IL-1beta increase APP synthesis by up to 6-fold in primary human astrocytes and by 15-fold in human astrocytoma cells without changing the steady-state levels of APP mRNA. A 90-nucleotide sequence in the APP gene 5'-untranslated region (5'-UTR) conferred translational regulation by IL-1alpha and IL-1beta to a chloramphenicol acetyltransferase (CAT) reporter gene. Steady-state levels of transfected APP(5'-UTR)/CAT mRNAs were unchanged, whereas both base-line and IL-1-dependent CAT protein synthesis were increased. This APP mRNA translational enhancer maps from +55 to +144 nucleotides from the 5'-cap site and is homologous to related translational control elements in the 5'-UTR of the light and and heavy ferritin genes. Enhanced translation of APP mRNA provides a mechanism by which IL-1 influences the pathogenesis of AD.

Idiopathic pseudoaneurysm of the dorsalis pedis artery mimicking pigmented villonodular synovitis

Pseudoaneurysm of the dorsalis pedis artery is uncommon and is usually associated with a history of trauma to the vessel. Without such a history, the diagnosis may be challenging, because the mass may be confused with other common soft tissue masses in the foot. This case report describes a 67-year-old man with an idiopathic pseudoaneurysm of the dorsalis pedis artery that mimicked pigmented villonodular synovitis.

A general RNA-binding protein complex that includes the cytoskeleton-associated protein MAP 1A

Association of mRNA with the cytoskeleton represents a fundamental aspect of RNA physiology likely involved in mRNA transport, anchoring, translation, and turnover. We report the initial characterization of a protein complex that binds RNA in a sequence-independent but size-dependent manner in vitro. The complex includes a approximately 160-kDa protein that is bound directly to mRNA and that appears to be either identical or highly related to a approximately 1600-kDa protein that binds directly to mRNA in vivo. In addition, the microtubule-associated protein, MAP 1A, a cytoskeletal associated protein is a component of this complex. We suggest that the general attachment of mRNA to the cytoskeleton may be mediated, in part, through the formation of this ribonucleoprotein complex.

The essential role of inflammation and induced gene expression in the pathogenic pathway of Alzheimer's disease

Alzheimer's disease is among the most common diseases of advanced age affecting almost one out of ten individuals who survive beyond the age of 65 years, and an another 10% for each additional decade of the life-span. The prognosis of the disease is an inexorable decline of mental functions leading to complete dependence on caretakers in the late stages of the disease. Alzheimer's disease will become a steadily increasing financial health-care problem in the industrialized world with the increasing longevity and ageing of the population. To-date there are no effective therapeutics. However, during the last years promising findings suggest that anti-inflammatory treatment strategies might be efficient. Here, we will review the experimental and epidemiological findings which support the idea that inflammatory mechanisms play an important role in Alzheimer's disease pathogenesis. The review of the experimental findings will be focussed on the amyloid-associated proteins, alpha1-antichymotrypsin and apolipoprotein E, as well as the major cytokines. In addition, the epidemiological studies on non-steroidal anti-inflammatory drugs and traumatic head injury will be summarized. We hypothesize a pathogenic model for Alzheimer's disease in which the expression of amyloid-associated proteins/pathological chaperones, induced by inflammatory cytokines, plays an essential role in accelerating the disease progress, and suggest potential targets for drug discovery based on such a model.

Alzheimer presenilins in the nuclear membrane, interphase kinetochores, and centrosomes suggest a role in chromosome segregation

Mutations in two related genes, presenilin 1 and 2, account for most early-onset familial Alzheimer's disease. Although structural features indicate that the presenilins are membrane proteins, their function(s) is unknown. We have localized the presenilins to the nuclear membrane, its associated interphase kinetochores, and the centrosomes-all subcellular structures involved in cell cycle regulation and mitosis. The colocalization of the presenilins with kinetochores on the nucleoplasmic surface of the inner nuclear membrane, together with other results, suggests that they may play a role in chromosome organization and segregation, perhaps as kinetochore binding proteins/receptors. We discuss a pathogenic pathway for familial Alzheimer's disease in which defective presenilin function causes chromosome missegregation during mitosis, resulting in apoptosis and/or trisomy 21 mosaicism.

Cytoskeletal changes in the brains of mice lacking calcineurin A alpha

Hyperphosphorylated tau, the major component of the paired helical filaments of Alzheimer's disease, was found to accumulate in the brains of mice in which the calcineurin A alpha gene was disrupted [calcineurin A alpha knockout (CNA alpha -/-)]. The hyperphosphorylation involved several sites on tau, especially the Ser396 and/or Ser404 recognized by the PHF-1 monoclonal antibody. The increase in phosphorylated tau content occurred primarily in the mossy fibers of the CNA alpha -/- hippocampus, which contained the highest level of calcineurin in brains of wild-type mice. The CNA alpha -/- mossy fibers also contained less neurofilament protein than normal, although the overall level of neurofilament phosphorylation was unchanged. In the electron microscope, the mossy fibers of CNA alpha -/- mice exhibited abnormalities in their cytoskeleton and a lower neurofilament/microtubule ratio than those of wild-type animals. These findings indicate that hyperphosphorylated tau can accumulate in vivo as a result of reduced calcineurin activity and is accompanied by cytoskeletal changes that are likely to have functional consequences on the affected neurons. The CNA alpha -/- mice were found in a separate study to have deficits in learning and memory that may result in part from the cytoskeletal changes in the hippocampus.

Alzheimer A beta neurotoxicity: promotion by antichymotrypsin, ApoE4; inhibition by A beta-related peptides

Two inflammation-associated proteins found in the Alzheimer amyloid deposits-alpha 1-antichymotrypsin (ACT) and apolipoprotein E4 (apoE4)-have been shown to be genetic risk factors for the development of Alzheimer's disease and to promote the polymerization of the A beta peptide into amyloid filaments in vitro. In the present study, we show that ACT and apoE4 increase the neurotoxicity of the A beta peptide in parallel with their promotion of filament formation. Preincubation of ACT or apoE4 with small A beta-related peptides, or of apoE4 with apoE2, abrogated their subsequent ability to promote both the formation and the neurotoxicity of A beta filaments. These results indicate that ACT and apoE4 may play a stimulatory role in the formation of neurotoxic amyloid in Alzheimer's disease, and that their amyloid promoting activity can be blocked by inhibitory peptides.