Tau filaments are tethered within brain extracellular vesicles in Alzheimer's disease

The abnormal assembly of tau protein in neurons is the pathological hallmark of multiple neurodegenerative diseases, including Alzheimer's disease (AD). In addition, assembled tau associates with extracellular vesicles (EVs) in the central nervous system of patients with AD, which is linked to its clearance and prion-like propagation between neurons. However, the identities of the assembled tau species and the EVs, as well as how they associate, are not known. Here, we combined quantitative mass spectrometry, cryo-electron tomography and single-particle cryo-electron microscopy to study brain EVs from AD patients. We found filaments of truncated tau enclosed within EVs enriched in endo-lysosomal proteins. We observed multiple filament interactions, including with molecules that tethered filaments to the EV limiting membrane, suggesting selective packaging. Our findings will guide studies into the molecular mechanisms of EV-mediated secretion of assembled tau and inform the targeting of EV-associated tau as potential therapeutic and biomarker strategies for AD.

P62 accumulates through neuroanatomical circuits in response to tauopathy propagation

In Alzheimer's disease and related tauopathies, trans-synaptic transfer and accumulation of pathological tau from donor to recipient neurons is thought to contribute to disease progression, but the underlying mechanisms are poorly understood. Using complementary in vivo and in vitro models, we examined the relationship between these two processes and neuronal clearance. Accumulation of p62 (a marker of defective protein clearance) correlated with pathological tau accumulation in two mouse models of tauopathy spread; Entorhinal Cortex-tau (EC-Tau) mice where tau pathology progresses in time from EC to other brain regions, and PS19 mice injected with tau seeds. In both models and in several brain regions, p62 colocalized with human tau in a pathological conformation (MC1 antibody). In EC-Tau mice, p62 accumulated before overt tau pathology had developed and was associated with the presence of aggregation-competent tau seeds identified using a FRET-based assay. Furthermore, p62 accumulated in the cytoplasm of neurons in the dentate gyrus of EC-Tau mice prior to the appearance of MC1 positive tauopathy. However, MC1 positive tau was shown to be present at the synapse and to colocalize with p62 as shown by immuno electron microscopy. In vitro, p62 colocalized with tau inclusions in two primary cortical neuron models of tau pathology. In a three-chamber microfluidic device containing neurons overexpressing fluorescent tau, seeding of tau in the donor chamber led to tau pathology spread and p62 accumulation in both the donor and the recipient chamber. Overall, these data are in accordance with the hypothesis that the accumulation and trans-synaptic spread of pathological tau disrupts clearance mechanisms, preceding the appearance of obvious tau aggregation. A vicious cycle of tau accumulation and clearance deficit would be expected to feed-forward and exacerbate disease progression across neuronal circuits in human tauopathies.

PAC1 receptor-mediated clearance of tau in postsynaptic compartments attenuates tau pathology in mouse brain

Accumulation of pathological tau in synapses has been identified as an early event in Alzheimer's disease (AD) and correlates with cognitive decline in patients with AD. Tau is a cytosolic axonal protein, but under disease conditions, tau accumulates in postsynaptic compartments and presynaptic terminals, due to missorting within neurons, transsynaptic transfer between neurons, or a failure of clearance pathways. Using subcellular fractionation of brain tissue from rTg4510 tau transgenic mice with tauopathy and human postmortem brain tissue from patients with AD, we found accumulation of seed-competent tau predominantly in postsynaptic compartments. Tau-mediated toxicity in postsynaptic compartments was exacerbated by impaired proteasome activity detected by measuring lysine-48 polyubiquitination of proteins targeted for proteasomal degradation. To combat the accumulation of tau and proteasome impairment in the postsynaptic compartments of rTg4510 mouse brain, we stimulated the pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1R) with its ligand PACAP administered intracerebroventricularly to rTg4510 mice. We observed enhanced synaptic proteasome activity and reduced total tau in postsynaptic compartments in mouse brain after PACAP treatment. The clearance of tau from postsynaptic compartments correlated with attenuated tauopathy and improved cognitive performance of rTg4510 transgenic mice on two behavioral tests. These results suggest that activating PAC1R could prevent accumulation of aggregate-prone tau and indicate a potential therapeutic approach for AD and other tauopathies.

Music Perception and Speech-in-Noise Skills of Typical Hearing and Cochlear Implant Listeners

Purpose Adult cochlear implant (CI) users rate music as one of the most important auditory stimuli, second to speech perception. However, few studies simultaneously examine music perception and speech-in-noise perception in adult CI recipients. This study explores the effect of auditory status on music perception and speech-in-noise perception recognition in noise as well as the relationship among music engagement, music perception, and speech-in-noise perception. Method Participants include 10 adults with typical hearing (TH) and 10 adults with long-term CI use. All participants completed the Music-Related Quality of Life Questionnaire, which assesses subjective music experiences and their importance; the Pitch Direction Discrimination, Familiar Melody Recognition, and Timbre Recognition subtests of the Clinical Assessment of Music Perception for Cochlear Implants; the Unfamiliar Melody Recognition subtest of the Profile of Music Perception Skills; and the Bamford-Kowal-Bench Speech-in-Noise Test. Results The TH group significantly outperformed the CI group for speech-in-noise perception and on all four music perception tasks. The CI group exhibited not only significantly poorer mean scores but also greater variability in performance compared to the TH group. Only Familiar Melody Recognition and Unfamiliar Melody Recognition subtests significantly correlated with speech-in-noise scores. Conclusions Patients and professionals should not assume speech perception and music perception in adult CI users derive from the same auditory or cognitive foundations. The lack of significant relationships among music engagement, music perception, and speech-in-noise perception scores in adult CI users suggests this population enjoys music despite poor and variable performance in discrete music tasks.

Identification of pannexin 1-regulated genes, interactome, and pathways in rhabdomyosarcoma and its tumor inhibitory interaction with AHNAK

Rhabdomyosarcoma (RMS), the most common soft tissue sarcoma in children, is an aggressive cancer with a poor prognosis. Despite current management, the 5-year survival rate for patients with metastatic RMS is ∼30%; underscoring the need to develop better treatment strategies. We have recently reported that pannexin 1 (PANX1) levels are downregulated in RMS and that restoring its expression inhibits RMS progression. Here, we have surveyed and characterized the molecular changes induced by PANX1 re-expression in RMS. We cataloged transcriptomic changes in this context by RNA sequencing. At the protein level, we unveiled PANX1 interactors using BioID, complemented by co-immunoprecipitation coupled to high-performance liquid chromatography/electrospray ionization tandem mass spectrometry performed in PANX1-enriched fractions. Using these data, we generated searchable public databases for the PANX1 interactome and changes to the RMS transcriptome occurring when PANX1 expression is restored. STRING network analyses revealed a PANX1 interactome involving plasma membrane and cytoskeleton-associated proteins including the previously undescribed interactor AHNAK. Indeed, AHNAK knockdown abrogated the PANX1-mediated reduction in RMS cell viability and migration. Using these unbiased approaches, we bring insight to the mechanisms by which PANX1 inhibits RMS progression, identifying the cell migration protein AHNAK as a key modifier of PANX1-mediated changes in RMS malignant properties.

A tau homeostasis signature is linked with the cellular and regional vulnerability of excitatory neurons to tau pathology

Excitatory neurons are preferentially impaired in early Alzheimer's disease but the pathways contributing to their relative vulnerability remain largely unknown. Here we report that pathological tau accumulation takes place predominantly in excitatory neurons compared to inhibitory neurons, not only in the entorhinal cortex, a brain region affected in early Alzheimer's disease, but also in areas affected later by the disease. By analyzing RNA transcripts from single-nucleus RNA datasets, we identified a specific tau homeostasis signature of genes differentially expressed in excitatory compared to inhibitory neurons. One of the genes, BCL2-associated athanogene 3 (BAG3), a facilitator of autophagy, was identified as a hub, or master regulator, gene. We verified that reducing BAG3 levels in primary neurons exacerbated pathological tau accumulation, whereas BAG3 overexpression attenuated it. These results define a tau homeostasis signature that underlies the cellular and regional vulnerability of excitatory neurons to tau pathology.

Using Technology to Improve Adherence to HIV Medications in Transitional Age Youth: Research Reviewed, Methods Tried, Lessons Learned

In transitional age youth living with HIV or AIDS, non-adherence (<80%) to anti-retroviral medication is associated with viral resistance, disease progression, and an increased risk of death. This feasibility study investigated the Maya MedMinder electronic pillbox and cell phone texting with personalized motivational interviewing strategies to improve medication adherence in non-adherent youth. Twenty patients out of 30 identified as non-adherent by the Pediatric HIV team at the Medical University of South Carolina were approached, and 15 were recruited (Ages 12 to 20; 13.3% male, 86.7% female; 100% African-American). Following baseline MedMinder monitoring, subjects were randomized to intervention groups with reminder signals on or off. The time medications were taken was collected by the MedMinder, resulting in adherence scores. All were interviewed for readiness to change utilizing the Motivational Interviewing (MI) Stages of Change scores. Viral load and CD4 labs were scheduled every 6 weeks. Despite monetary incentives and personalized support, recruitment and adherence to the protocol was a challenge. Only 6/15 subjects completed the entire study scheduled for 6-months .Stages of change scores revealed that those that transitioned to making changes had higher CD4 percentages midway through the study. Challenges included missed appointments and labs despite efforts by text and phone to schedule convenient appointment times with participants. Device challenges included the large size of the MedMinder and faulty electronic signaling, especially from rural areas. The methodology was feasible with these patients. This small feasibility study highlights that technological tools to promote adherence and motivational enhancement strategies in teens and young adults who are non-adherent to HIV medication regimens can enhance biomarker outcomes associated with medication adherence.

Adolescent Physical Activity: Moderation of Individual Factors by Neighborhood Environment

INTRODUCTION

Less than a third of U.S. adolescents meet federal physical activity (PA) guidelines. Understanding correlates of PA at multiple levels of the Social Ecological Model could improve PA interventions among youth. This study examines (1) associations between factors across the Social Ecological Model including psychosocial factors, perceived neighborhood physical and social environment characteristics, and adolescent moderate to vigorous PA (MVPA) and (2) whether perceived neighborhood characteristics moderate associations between psychosocial factors and MVPA.

METHODS

A national sample of adolescents (aged 12-17 years) in the 2014 Family Life, Activity, Sun, Health, and Eating Study was used to examine associations between psychosocial characteristics, perceived neighborhood social and physical characteristics, and self-reported weekly minutes of MVPA. Analyses were conducted in 2015. Interaction terms between psychosocial and neighborhood variables were added to multiple linear regression models to examine moderation hypotheses.

RESULTS

Significant two-way interactions revealed that neighborhoods with features perceived as supportive of PA strengthened several psychosocial-MVPA associations. The positive associations between MVPA and friend norms, friend support, and attitudes were strengthened for adolescents living in neighborhoods with high versus low PA resource availability (all p<0.05). Furthermore, the association between controlled and autonomous motivation and MVPA was strengthened under conditions of shops/stores near (versus distant from) adolescents' homes (p<0.05).

CONCLUSIONS

The association between some psychosocial factors and adolescent MVPA may be environment dependent. Neighborhood physical and social environments supportive of PA are important to consider when developing targeted PA interventions and may strengthen the association between psychosocial-level factors and adolescent MVPA.

Using an Internet-Based Breast Cancer Risk Assessment Tool to Improve Social-Cognitive Precursors of Physical Activity

BACKGROUND

Internet-based cancer risk assessment tools might serve as a strategy for translating epidemiological risk prediction research into public health practice. Understanding how such tools affect key social-cognitive precursors of behavior change is crucial for leveraging their potential into effective interventions.

PURPOSE

To test the effects of a publicly available, Internet-based, breast cancer risk assessment tool on social-cognitive precursors of physical activity.

METHODS

Women (N = 132) aged 40-78 with no personal cancer history indicated their perceived risk of breast cancer and were randomly assigned to receive personalized ( www.yourdiseaserisk.wustl.edu ) or nonpersonalized breast cancer risk information. Immediately thereafter, breast cancer risk perceptions and physical activity-related behavioral intentions, self-efficacy, and response efficacy were assessed.

RESULTS

Personalized information elicited higher intentions, self-efficacy, and response efficacy than nonpersonalized information, P values < 0.05. Self-efficacy and response efficacy mediated the effect of personalizing information on intentions. Women who received personalized information corrected their inaccurate risk perceptions to some extent, P values < 0.05, but few fully accepted the information.

CONCLUSION

Internet-based risk assessment tools can produce beneficial effects on important social-cognitive precursors of behavior change, but lingering skepticism, possibly due to defensive processing, needs to be addressed before the effects can be maximized.

Comparing the Maryland Comprehensive Cancer Control Plan With Federal Cancer Prevention and Control Recommendations

INTRODUCTION

Since the introduction of the Affordable Care Act (ACA) in 2012, 11 million more Americans now have access to preventive services via health care coverage. Several prevention-related recommendations issued by the US Preventive Services Task Force (USPSTF), Centers for Disease Control and Prevention (CDC), and Advisory Committee on Immunization Practices (ACIP) are covered under the ACA. State cancer plans often provide prevention strategies, but whether these strategies correspond to federal evidence-based recommendations is unclear. The objective of this article is to assess whether federal evidence-based recommendations, including those covered under the ACA, are included in the Maryland Comprehensive Cancer Control Plan (MCCCP).

METHODS

A total of 19 federal recommendations pertaining to cancer prevention and control were identified. Inclusion of federal cancer-related recommendations by USPSTF, CDC, and ACIP in the MCCCP's goals, objectives, and strategies was examined.

RESULTS

Nine of the federal recommendations were issued after the MCCCP's publication. MCCCP recommendations corresponded completely with 4 federal recommendations and corresponded only partially with 3. Reasons for partial correspondence included specification of less restrictive at-risk populations or different intervention implementers. Three federal recommendations were not mentioned in the MCCCP's goals, objectives, and strategies.

CONCLUSION

Many cancer-related federal recommendations were released after the MCCCP's publication and therefore do not appear in the most current version. We recommend that the results of this analysis be considered in the update of the MCCCP. Our findings underscore the need for a periodic scan for changes to federal recommendations and for adjusting state policies and programs to correspond with federal recommendations, as appropriate for Marylanders.

Dispositional and comparative optimism interact to predict avoidance of a looming health threat

Research indicates that when confronted with a health threat, individuals high in both dispositional and comparative optimism employ a more avoidant style of coping than individuals high in dispositional but low in comparative optimism. We examined the hypothesis that threat distance moderates this interactive optimism association. In two studies, participants were randomly assigned to a looming or distant threat condition. Study 1 revealed that in the looming threat condition, participants high in both forms of optimism were more likely to minimise the threat and less inclined to seek additional health information relative to participants high in dispositional but low in comparative optimism. In Study 2, the same interaction pattern emerged on a measure of psychological abstraction suggesting these variables combine to alter broad information processing strategies. Implications for considering multiple forms of optimism when delivering health status information are discussed.

Patient Involvement in Treatment Decision Making Can Help or Hinder Placebo Analgesia

Experiments have found that choosing between placebo analgesics can reduce pain more than being assigned a placebo analgesic. Because earlier research has shown prior experience moderates choice effects in other contexts, we tested whether prior experience with a pain stimulus moderates this placebo-choice association. Before a cold water pain task, participants were either told that an inert cream would reduce their pain or they were not told this information. Additionally, participants chose between one of two inert creams for the task or they were not given choice. Importantly, we also measured prior experience with cold water immersion. Individuals with prior cold water immersion experience tended to display greater placebo analgesia when given choice, whereas participants without this experience tended to display greater placebo analgesia without choice. Prior stimulus experience appears to moderate the effect of choice on placebo analgesia.

Comparative and dispositional optimism as separate and interactive predictors

Comparative optimism and dispositional optimism are typically studied separately and little is known regarding their unique and combined predictive abilities. We examined how these two types of optimism predict cognitive and affective reactions following unpleasant dental health feedback (Studies 1 and 2) and neutral feedback (Study 2). In Study 1, dispositional optimism and a measure of dental health comparative optimism interacted to predict appraisals of dental health feedback. In Study 2, dispositional optimism and dental health comparative optimism interacted to predict appraisals of new dental health information following negative dental health feedback - but not following neutral feedback. Individuals scoring high in dispositional optimism and low in dental health comparative optimism were more interested in and receptive to the dental health feedback than those scoring high in both types of optimism. Finally, greater dental health comparative optimism was associated with less negative affect following the dental health feedback, whereas dispositional optimism was associated with greater positive affect under all conditions. The results indicate that comparative and dispositional optimism are unique as well as interactive predictors.

Placebo expectations and the detection of somatic information

In a laboratory study we examined the hypothesis that placebo expectations enhance the initial identification of placebo-relevant sensations over placebo-irrelevant sensations. Participants (N = 102) were randomly assigned to one of three expectation groups. In the first group, participants ingested a placebo capsule and were told it was caffeine (deceptive expectation). In a second group, participants ingested a placebo capsule and were told it may be caffeine or it may be a placebo (double-blind expectation). Participants in the third group were given no expectation. All participants then tallied the placebo-relevant and placebo-irrelevant sensations they experienced during a 7-min period. Participants in the deceptive expectation group identified more placebo-relevant sensations than placebo-irrelevant sensations. No-expectation participants identified more placebo-irrelevant sensations than placebo-relevant sensations. Participants given the double-blind expectation identified an equal amount of placebo-relevant and irrelevant sensations. The amount of both placebo-relevant and placebo-irrelevant sensations detected mediated the relationship between the expectation manipulation and subsequent symptom reports. These data support the position that expectations cause placebo responding, in part, by altering how one identifies bodily sensations.

Dispositional optimism predicts placebo analgesia

Based on prior research identifying dispositional optimism as a predictor of placebo responding, the present study tested the hypothesis that individuals high in optimism would be more likely to respond to a placebo analgesic. Optimists and pessimists were randomly assigned to a placebo expectation condition or a no expectation condition before a cold pressor task. Blood pressure and heart rate were recorded before and during the cold pressor task, and participant ratings of pain and expectations were obtained immediately after the task. Analysis of the expectation manipulation revealed that the placebo instruction was successful in altering participant expectancy during the cold pressor. Supporting the main hypothesis, dispositional optimism was associated with lower pain ratings in the placebo condition but not in the control condition. Because dispositional optimism can alter placebo responding to laboratory pain, future studies should examine the potential role that this individual difference factor may play in patient responsivity to pharmacological and nonpharmacological treatments for clinical pain.

PERSPECTIVE

This study examined the possibility that individual differences can predict placebo analgesia. Participants were randomly assigned to receive either a placebo expectation or no expectation before a cold pressor task. Dispositional optimism was related to less cold pressor pain in the placebo condition as compared with the control condition.

Tissue-specific cross-reactivity of connexin32 antibodies: problems and solutions unique to the central nervous system

Gap junction proteins are a highly homologous family of 21 connexins. Here, the authors describe a tissue-specific technical artifact complicating analysis of connexin32 protein expression in the central nervous system. The authors show that in brain, but not liver, eight commonly employed antibodies exhibit a higher affinity for a cross-reactive protein that masks the detection of connexin32. Cross-reactivity is evident in Western blot analyses when proteins are subjected to reducing/denaturing conditions but not immunoprecipitation or immunofluorescent applications. Through bioinformatic analyses, tested by sucrose gradient fractionation and immunoblotting of lysates from connexin null-mutant mice, the authors show that the cross-reactive protein is not found in the same cellular compartments as connexin32 and is likely not a member of the connexin family. These findings are presented with the intent of helping to reduce the amount of time laboratories currently expend in validating changes in connexin32 expression in the central nervous system.

Assessment of adherence with medications in human immunodeficiency virus-infected children

The purpose of this study was to determine the reliability of screening for medication adherence in HIV-infected children. The results suggest that caregivers who are unable to describe the medication regimen or who are nonadherent with appointments are unlikely to adhere to the medication regimen. Adherence with at least 90% of medication doses was associated with a virologic response.

Evidence for person-to-person transmission of Candida lusitaniae in a neonatal intensive-care unit

Candida lusitaniae is an increasingly important nosocomial bloodstream pathogen. Epidemiological investigation and molecular typing techniques identified three neonates infected with identical strains of C lusitaniae that were distinguished readily from epidemiologically unrelated strains from other locations in the hospital. The results of this study provide evidence for nosocomial transmission of C lusitaniae in a neonatal intensive-care unit and suggest that these infants are at increased risk for infection with this agent.

Oral famciclovir for suppression of recurrent genital herpes simplex virus infection in women. A multicenter, double-blind, placebo-controlled trial. Collaborative Famciclovir Genital Herpes Research Group

OBJECTIVE

To evaluate the efficacy and safety of oral famciclovir in the suppression of genital herpes.

METHODS

In this randomized, double-blind, placebo-controlled trial that was performed at 11 university and 9 private ambulatory care referral centers, 375 women who were 18 years of age or older and had a history of 6 or more episodes of genital herpes during 12 of the last 24 months in the absence of suppressive therapy were treated for 4 months with oral famciclovir, 125 mg once daily or twice daily, 250 mg once daily or twice daily, 500 mg once daily, or placebo. The primary outcome measures included the time to first clinically and virologically confirmed recurrences, and safety as measured by clinical laboratory tests and adverse experiences.

RESULTS

The median time to first recurrence was 82 days in the placebo group, 114 days in those receiving famciclovir, 125 mg once daily, and more than 120 days in the other treatment groups. When compared with placebo recipients, the time to the first clinical recurrence was significantly prolonged in subjects who received famciclovir, 125 mg twice daily (hazard ratio, 1.8; 95% confidence interval, 1.0-3.0; P = .03), and in those who received famciclovir, 250 mg twice daily (hazard ratio, 3.6; 95% confidence interval, 1.9-6.9; P < .001). Treatment was well tolerated, and there was no evidence of emergence of resistance during or after suppressive famciclovir therapy.

CONCLUSIONS

Oral famciclovir, 250 mg, given twice daily for 4 months is an effective, well-tolerated treatment for the suppression of genital herpes in women with frequent recurrences, but single daily doses produced less complete suppression of genital herpes.

Herpes simplex virus-1 replication in histiotypic rotation-mediated reaggregated murine brain

Inbred mouse strains exhibit varying susceptibilities to severe herpes simplex virus (HSV)-1-related neurologic disease. HSV-1 replication was examined in neural tissue obtained from mouse strains susceptible (A/J, SJL), moderately resistant (Balb/c), or resistant (C57BL/6) to severe HSV-1 disease. Reaggregated brain cultures were prepared from mechanically dissociated fetal mouse brains maintained with constant rotation. The resulting aggregates each contain neurons, astrocytes, oligodendrocytes, and microglia. These were inoculated with 10(-2)-10(4) plaque-forming units (pfu) HSV-1 MacIntyre/aggregate. Aggregates and media were harvested at 24, 48, 72, and 96 hr post-inoculation (p.i.) and assayed for virus production by plaque titration. Brain cultures prepared from A/J, SJL, Balb/c, and C57BL/6 mice supported HSV-1 replication equally well: by 96 hr p.i., titers of 10(6) pfu/ml were produced by each strain at each inoculum. ID50s were similar for A/J and C57BL/6 cultures. There was no increased capacity for HSV-1 replication or for permissiveness for HSV-1 infection in histiotypic brain cultures from mouse strains susceptible to severe HSV-1 disease.

Outcome of herpes simplex virus type 2 infection in guinea pigs

Factors that influence the outcome of genital herpes simplex virus (HSV) infection were explored in a guinea pig model. The viral inoculum required to establish infection in 50% of animals (ID50) was similar for inbred (strain 2) and outbred (Hartley) guinea pigs. However, the viral inoculum required to produce clinical disease in 50% of the animals (CD50) was 10 times greater for strain 2 compared to Hartley animals. HSV infection of both inbred and outbred animals was more likely to result in death of weanling than adult animals. The duration and severity of genital disease and the magnitude of vaginal viral replication were similar for strain 2 and Hartley animals in both young and adult animals. The lethal dose for 50% of animals (LD50) was 100-fold greater than the CD50 for Hartley animals, but the LD50 and the CD50 were equal in strain 2 guinea pigs. Viral cultures of homogenized neural tissues from infected animals revealed that HSV ascended to the level of the temporal cortex in strain 2 guinea pigs while virus was never recovered above the lumbar spinal cord in Hartley animals. Endogenous peripheral blood mononuclear cell-mediated cytolytic activity against HSV-infected targets was greater prior to HSV inoculation in survivors compared to animals that died. A fatal outcome of genital HSV-2 may relate to the failure to limit CNS viral replication. Death is more common among guinea pigs that have low endogenous HSV-directed natural killer activity, such as occurs among strain 2 and young animals whether inbred or outbred.

A double-blind randomized clinical study of the safety, tolerability and efficacy of Hexabrix in pediatric angiocardiography

Hexabrix, a low-osmolality radiographic contrast agent consisting of the meglumine and sodium salt of ioxaglic acid (600 mOsm/kg), was evaluated in 50 children undergoing cardiac catheterization in a randomized double-blind manner. In comparison with a conventional radiographic contrast agent (Renografin-76), Hexabrix produced a marked reduction in the pain or discomfort after the injection. Neither agent produced any significant change in pulse or respiratory rates or blood pressure. Changes in left and right ventricular pressures were small and comparable for both groups. Significant dysrhythmias were not noted. There was no evidence of deterioration in renal or hepatic function in either group. Serum LDH and CPK increased comparably with both contrast agents but without any definite evidence of myocardial injury. Postinjection increases in serum osmolality were slightly, but not significantly, higher with Renografin. In the first few hours following the procedure there was an increase in circulating segmented neutrophils and a reciprocal decrease in lymphocytes; this was transient and gone by 24 hours. Radiographic image quality was judged good or excellent in almost all cases. Hexabrix is a contrast agent that is significantly better tolerated than conventional agents and is associated with no greater incidence of side-effects while producing radiographic images of equivalent quality.