Paediatric heart transplantation in Australia comes of age: 21 years of experience in a national centre.

BACKGROUND: Heart transplantation (HT) is established therapy for end-stage heart failure in children with cardiomyopathy or congenital heart disease. AIMS: This review summarises experience at a national referral centre since the first local transplant. METHODS: Medical records of children referred for HT between 1 April 1988 and 1 January 2010 were retrospectively reviewed. All patients listed for HT were included. Survival analysis was used to summarise wait-list time to death/transplant, and separately, time to death in HT patients. RESULTS: One hundred and thirty-nine children were accepted on to the HT waiting list during the study (median age 7.7 (interquartile range (IQR) 2.5, 13.6) years), of whom 93 underwent HT (median age 10.9 (IQR 4.4, 14.6) years). Wait-list mortality was 32% (45 of 139 patients), lowest among children aged >10 years at listing (P < 0.001). Median time to HT was 69 days (range 29-146). Survival post-transplantation was 90% (95% confidence interval 82-95) at 1 year, 82% (72-89%) at 5 years and 68% (50-80%) at 10 years. Increasing case complexity over the study period included pre- and post-transplant circulatory support, management of pulmonary hypertension and introduction of ABO-incompatible HT for infants. Post-transplant survival did not vary according to age, pre-transplant diagnosis or use of pre-transplant circulatory support (all P > 0.05). CONCLUSIONS: Results of paediatric HT in Australia are comparable with international results, despite limitations of geographic isolation, small population and low organ donation rate. Increasing case complexity has not impacted on post-transplant survival.

Lessons and insights from ABO-incompatible lung transplantation.

With ABO blood group incompatibility (ABOi) between donor and recipient becoming a part of mainstream living-donor renal transplantation, the applicability of ABOi to other areas of transplantation is being reconsidered. Here we present a case of inadvertent ABOi lung retransplantation managed successfully with initial plasmapheresis, antithymocyte globulin and intravenous immunoglobulin; and subsequently with oral cyclophosphamide and sirolimus in addition to tacrolimus and prednisolone. Interestingly, in the setting of solid levels of tacrolimus and sirolimus, the patient developed a fatal thrombotic microangiopathy of uncertain origin subsequent to the cessation of cyclophosphamide at 9 years posttransplant. It is apparent that ABOi lung transplantation can result in surprisingly successful long-term outcomes. Low pretransplant antibody titers likely aid this and, in pediatric neonatal or infant cases, this may not be uncommon. We must proceed cautiously as there are significant risks. Understanding the monitoring, prevention and treatment of lung transplant antibody-mediated rejection, while avoiding the long-term complications of overimmunosuppression, will be the keys to the success of future cases.

Acrylamide: review of toxicity data and dose-response analyses for cancer and noncancer effects.

Acrylamide (ACR) is used in the manufacture of polyacrylamides and has recently been shown to form when foods, typically containing certain nutrients, are cooked at normal cooking temperatures (e.g., frying, grilling or baking). The toxicity of ACR has been extensively investigated. The major findings of these studies indicate that ACR is neurotoxic in animals and humans, and it has been shown to be a reproductive toxicant in animal models and a rodent carcinogen. Several reviews of ACR toxicity have been conducted and ACR has been categorized as to its potential to be a human carcinogen in these reviews. Allowable levels based on the toxicity data concurrently available had been developed by the U.S. EPA. New data have been published since the U.S. EPA review in 1991. The purpose of this investigation was to review the toxicity data, identify any new relevant data, and select those data to be used in dose-response modeling. Proposed revised cancer and noncancer toxicity values were estimated using the newest U.S. EPA guidelines for cancer risk assessment and noncancer hazard assessment. Assessment of noncancer endpoints using benchmark models resulted in a reference dose (RfD) of 0.83 microg/kg/day based on reproductive effects, and 1.2 microg/kg/day based on neurotoxicity. Thyroid tumors in male and female rats were the only endpoint relevant to human health and were selected to estimate the point of departure (POD) using the multistage model. Because the mode of action of acrylamide in thyroid tumor formation is not known with certainty, both linear and nonlinear low-dose extrapolations were conducted under the assumption that glycidamide or ACR, respectively, were the active agent. Under the U.S. EPA guidelines (2005), when a chemical produces rodent tumors by a nonlinear or threshold mode of action, an RfD is calculated using the most relevant POD and application of uncertainty factors. The RfD was estimated to be 1.5 microg/kg/day based on the use of the area under the curve (AUC) for ACR hemoglobin adducts under the assumption that the parent, ACR, is the proximate carcinogen in rodents by a nonlinear mode of action. When the mode of action in assumed to be linear in the low-dose region, a risk-specific dose corresponding to a specified level of risk (e.g., 1 x 10-5) is estimated, and, in the case of ACR, was 9.5 x 10-2 microg ACR/kg/day based on the use of the AUC for glycidamide adduct data. However, it should be noted that although this review was intended to be comprehensive, it is not exhaustive, as new data are being published continuously.

Comparison of the EU T25 single point estimate method with benchmark dose response modeling for estimating potency of carcinogens.

The T25 single-point estimate method of evaluating the carcinogenic potency of a chemical, which is currently used by the European Union (EU) and is denoted the EU approach, is based on the selection of a single dose in a chronic bioassay with an incidence rate that is significantly higher than the background rate. The T25 is determined from that single point by a linear extrapolation or interpolation to the chronic dose (in mg/kg/day), at which a 25% increase in the incidence of the specified tumor type is expected, corrected for the background rate. Another method used to obtain a carcinogenic potency value based on a 25% increase in incidence above the background rate is the estimation of a T25 derived from a benchmark dose (BMD) response model fit to the chronic bioassay data for the specified tumor type. A comparison was made between these two methods using 276 chronic bioassays conducted by the National Toxicology Program. In each of the 2-year bioassays, a tumor type was selected based on statistical and biological significance, and both EU T25 and BMD T25 estimates were determined for that end point. In addition, simulations were done using underlying cumulative probability distributions to examine the effect of dose spacing, the number of animals per dose group, the possibility of a dose threshold, and variation in the background incidence rates on the EU T25 and BMD estimates. The simulations showed that in the majority of cases the EU T25 method underestimated the true T25 dose and overestimated the carcinogenic potency. The BMD estimate is generally less biased and has less variation about the true T25 value than the EU estimate.

Determination of a site-specific reference dose for methylmercury for fish-eating populations.

Environmental risk-management decisions in the U.S. involving potential exposures to methylmercury currently use a reference dose (RfD) developed by the U.S. Environmental Protection Agency (USEPA). This RfD is based on retrospective studies of an acute poisoning incident in Iraq in which grain contaminated with a methylmercury fungicide was inadvertently used in the baking of bread. The exposures, which were relatively high but lasted only a few months, were associated with neurological effects in both adults (primarily paresthesia) and infants (late walking, late talking, etc.). It is generally believed that the developing fetus represents a particularly sensitive subpopulation for the neurological effects of methylmercury. The USEPA derived an RfD of 0.1 microg/kg/day based on benchmark dose (BMD) modeling of the combined neurological endpoints reported for children exposed in utero. This RfD included an uncertainty factor of 10 to consider human pharmacokinetic variability and database limitations (lack of data on multigeneration effects or possible long-term sequelae of perinatal exposure). Alcoa signed an Administrative Order of Consent for the conduct of a remedial investigation/feasibility study (RI/FS) at their Point Comfort Operations and the adjacent Lavaca Bay in Texas to address the effects of historical discharges of mercury-containing wastewater. In cooperation with the Texas Natural Resource Conservation Commission and USEPA Region VI, Alcoa conducted a baseline risk assessment to assess potential risk to human health and the environment. As a part of this assessment. Alcoa pursued the development of a site-specific RfD for methylmercury to specifically address the potential human health effects associated with the ingestion of contaminated finfish and shellfish from Lavaca Bay. Application of the published USEPA RfD to this site is problematic; while the study underlying the RfD represented acute exposure to relatively high concentrations of methylmercury, the exposures of concern for the Point Comfort site are from the chronic consumption of relatively low concentrations of methylmercury in fish. Since the publication of the USEPA RfD, several analyses of chronic exposure to methylmercury in fish-eating populations have been reported. The purpose of the analysis reported here was to evaluate the possibility of deriving an RfD for methylmercury, specifically for the case of fish ingestion, on the basis of these new studies. In order to better support the risk-management decisions associated with developing a remediation approach for the site in question, the analysis was designed to provide information on the distribution of acceptable ingestion rates across a population, which could reasonably be expected to be consistent with the results of the epidemiological studies of other fish-eating populations. Based on a review of the available literature on the effects of methylmercury, a study conducted with a population in the Seychelles Islands was selected as the critical study for this analysis. The exposures to methylmercury in this population result from chronic, multigenerational ingestion of contaminated fish. This prospective study was carefully conducted and analyzed, included a large cohort of mother-infant pairs, and was relatively free of confounding factors. The results of this study are essentially negative, and a no-observed-adverse-effect level (NOAEL) derived from the estimated exposures has recently been used by the Agency for Toxic Substances and Disease Registry (ATSDR) as the basis for a chronic oral minimal risk level (MRL) for methylmercury. In spite of the fact that no statistically significant effects were observed in this study, the data as reported are suitable for dose-response analysis using the BMD method. Evaluation of the BMD method used in this analysis, as well as in the current USEPA RfD, has demonstrated that the resulting 95% lower bound on the 10% benchmark dose (BMDL) represents a conservative estimate of the traditional NOAEL, and that it is superior to the use of "average" or "grouped" exposure estimates when dose-response information is available, as is the case for the Seychelles study. A more recent study in the Faroe Islands, which did report statistically significant associations between methylmercury exposure and neurological effects, could not be used for dose-response modeling due to inadequate reporting of the data and confounding from co-exposure to polychlorinated biphenyls (PCBs). BMD modeling over the wide range of neurological endpoints reported in the Seychelles study yielded a lowest BMDL for methylmercury in maternal hair of 21 ppm. This BMDL was then converted to an expected distribution of daily ingestion rates across a population using Monte Carlo analysis with a physiologically based pharmacokinetic (PBPK) model to evaluate the impact of interindividual variability. The resulting distribution of ingestion rates at the BMDL had a geometric mean of 1.60 microg/kg/day with a geometric standard deviation of 1.33; the 1st, 5th, and 10th percentiles of the distribution were 0.86, 1.04, and 1.15 microg/kg/day. In place of the use of an uncertainty factor of 3 for pharmacokinetic variability, as is done in the current RfD, one of these lower percentiles of the daily ingestion rate distribution provides a scientifically based, conservative basis for taking into consideration the impact of pharmacokinetic variability across the population. On the other hand, it was felt that an uncertainty factor of 3 for database limitations should be used in the current analysis. Although there can be high confidence in the benchmark-estimated NOAEL of 21 ppm in the Seychelles study, some results in the New Zealand and Faroe Islands studies could be construed to suggest the possibility of effects at maternal hair concentrations below 10 ppm. In addition, while concerns regarding the possibility of chronic sequelae are not supported by the available data, neither can they be absolutely ruled out. The use of an uncertainty factor of 3 is equivalent to using a NOAEL of 7 ppm in maternal hair, which provides additional protection against the possibility that effects could occur at lower concentrations in some populations. Based on the analysis described above, the distribution of acceptable daily ingestion rates (RfDs) recommended to serve as the basis for site-specific risk-management decisions at Alcoa's Point Comfort Operations ranges from approximately 0.3 to 1.1 microg/kg/day, with a population median (50th percentile) of 0.5 microg/kg/day. By analogy with USEPA guidelines for the use of percentiles in applications of distributions in exposure assessments, the 10th percentile provides a reasonably conservative measure. On this basis, a site-specific RfD of 0.4 microg/kg/day is recommended.

Evaluation of the uncertainty in an oral reference dose for methylmercury due to interindividual variability in pharmacokinetics.

An analysis of the uncertainty in guidelines for the ingestion of methylmercury (MeHg) due to human pharmacokinetic variability was conducted using a physiologically based pharmacokinetic (PBPK) model that describes MeHg kinetics in the pregnant human and fetus. Two alternative derivations of an ingestion guideline for MeHg were considered: the U.S. Environmental Protection Agency reference dose (RfD) of 0.1 microgram/kg/day derived from studies of an Iraqi grain poisoning episode, and the Agency for Toxic Substances and Disease Registry chronic oral minimal risk level (MRL) of 0.5 microgram/kg/day based on studies of a fish-eating population in the Seychelles Islands. Calculation of an ingestion guideline for MeHg from either of these epidemiological studies requires calculation of a dose conversion factor (DCF) relating a hair mercury concentration to a chronic MeHg ingestion rate. To evaluate the uncertainty in this DCF across the population of U.S. women of child-bearing age, Monte Carlo analyses were performed in which distributions for each of the parameters in the PBPK model were randomly sampled 1000 times. The 1st and 5th percentiles of the resulting distribution of DCFs were a factor of 1.8 and 1.5 below the median, respectively. This estimate of variability is consistent with, but somewhat less than, previous analyses performed with empirical, one-compartment pharmacokinetic models. The use of a consistent factor in both guidelines of 1.5 for pharmacokinetic variability in the DCF, and keeping all other aspects of the derivations unchanged, would result in an RfD of 0.2 microgram/kg/day and an MRL of 0.3 microgram/kg/day.

Calculation of benchmark doses for reproductive and developmental toxicity observed after exposure to isopropanol.

Reproductive, including developmental, toxicity risk assessment has typically relied on estimation of toxicity criteria values derived from no-observed-adverse-effect levels (NOAELs). The benchmark dose (BMD) approach has been proposed as an alternative that avoids problems with NOAELs. In this analysis of the reproductive and developmental toxicity observed in a multigeneration study of rats exposed to isopropanol, the BMD approach has been applied to all effects exhibiting significant dose-response relationships. The BMD estimates were very consistent across models and across end points; they were within the range of doses (100 to 500 mg/kg/day) that has been suggested as being the NOAEL. The use of the BMD approach for analysis of isopropanol reproductive toxicity is shown to avoid the experiment-specific argument of whether a particular treatment has induced statistically significant differences, compared to controls, in favor of the estimation of experiment-independent doses corresponding to risk levels of interest. The consistency of the BMD estimates, with values of about 420 mg/kg/day, suggests that, for isopropanol, the available multigeneration study data may provide a suitable basis for considering safe exposure.

Influence of prenatal mercury exposure upon scholastic and psychological test performance: benchmark analysis of a New Zealand cohort.

This paper presents benchmark (BMD) calculations and additional regression analyses of data from a study in which scores from 26 scholastic and psychological tests administered to 237 6- and 7-year-old New Zealand children were correlated with the mercury concentration in their mothers' hair during pregnancy. The original analyses of five test scores found an association between high prenatal mercury exposure and decreased test performance, using category variables for mercury exposure. Our regression analyses, which utilized the actual hair mercury level, did not find significant associations between mercury and children's test scores. However, this finding was highly influenced by a single child whose mother's mercury hair level (86 mg/kg) was more than four times that of any other mother. When that child was omitted, results were more indicative of a mercury effect and scores on six tests were significantly associated with the mothers' hair mercury level. BMDs calculated from five tests ranged from 32 to 73 mg/kg hair mercury, and corresponding BMDLs (95% lower limits on BMDs) ranged from 17 to 24 mg/kg. When the child with the highest mercury level was omitted, BMDs ranged from 13 to 21 mg/kg, and corresponding BMDLs ranged from 7.4 to 10 mg/kg.

Gingival overgrowth in pediatric heart and heart-lung transplant recipients.

BACKGROUND: Gingival overgrowth is a recognized side effect of cyclosporine therapy with cosmetic and functional sequelae. This study examines the incidence and severity of gingival overgrowth in pediatric heart and heart-lung transplant recipients. METHODS: Thirty-one pediatric heart and heart-lung transplant recipients underwent a comprehensive dental evaluation. The severity of gingival overgrowth was scored by use of dental plaster casts. Parameters of dental hygiene in each patient included both a plaque index and a gingival inflammation index. The mean cyclosporine level and daily dose (mg/kg/day) at 3 and 12 months after transplantation and at latest follow-up were determined. RESULTS: The mean (+/- SD) patient age at transplantation was 10.5 (+/- 5.5) years, and the mean duration of posttransplantation follow-up was 3.2 (+/- 2.1) years. In all 30/31 (97%) of the cohort had some degree of overgrowth, with children aged less than 10 years at time of transplantation the most severely affected. By univariate analysis gingival overgrowth was inversely related to age at time of transplantation (r = -0.67, p < 0.001). With multiple regression analysis, only age at transplantation was significantly related to gingival overgrowth. CONCLUSIONS: Gingival overgrowth occurs in most pediatric heart and heart-lung transplant recipients treated with cyclosporine and is most severe in the younger patients. Attention to oral hygiene may improve gingival health parameters; however, the daily weight-adjusted dose of cyclosporine is not related to the severity of overgrowth.

Capturing the promise of science in medical schools.

To gain a better understanding of the effects on medical schools of transformations in medical practice, science, and public expectations, the Association of American Medical Colleges (AAMC) constituted the Advisory Panel on the Mission and Organization of Medical Schools (APMOMS) in 1994. APMOMS created six working groups to address the issues deemed by panel members to be of highest priority. This article is a report of the findings of the Working Group on Capturing the Promise of Medical Research, which addressed questions concerning the direction of research and the integration of scientific developments in medical education and practice. The working group explored a broad panorama of issues, including those related to sustaining the accomplishments, momentum, and progress of medical research. A dominant theme emerged: the central importance of an environment of discovery to the core missions of medical schools. The present article consists of the group's comments and recommendations on the main topic-the promise of biomedical research in relation to medical education-and their comments and recommendations on five other topics that have important relationships to the main topic and to the group's central charge. These are ethics; academia-industry relations; the administrative structure of medical schools; university-medical school relations; and research funding.

Reanalysis of dose-response data from the Iraqi methylmercury poisoning episode.

Applying a hockey stick parametric dose-response model to data on late or retarded development in Iraqi children exposed in utero to methylmercury, with mercury (Hg) exposure characterized by the peak Hg concentration in mothers' hair during pregnancy, Cox et al. calculated the "best statistical estimate" of the threshold for health effects as 10 ppm Hg in hair with a 95% range of uncertainty of between 0 and 13.6 ppm. A new application of the hockey stick model to the Iraqi data shows, however, that the statistical upper limit of the threshold based on the hockey stick model could be as high as 255 ppm. Furthermore, the maximum likelihood estimate of the threshold using a different parametric model is virtually zero. These and other analyses demonstrate that threshold estimates based on parametric models exhibit high statistical variability and model dependency, and are highly sensitive to the precise definition of an abnormal response. Consequently, they are not a reliable basis for setting a reference dose (RfD) for methylmercury. Benchmark analyses and statistical analyses useful for deriving NOAELs are also presented. We believe these latter analyses--particularly the benchmark analyses--generally form a sounder basis for determining RfDs than the type of hockey stick analysis presented by Cox et al. However, the acute nature of the exposures, as well as other limitations in the Iraqi data suggest that other data may be more appropriate for determining acceptable human exposures to methylmercury.

Crown reduction--disarming of biting pets.

Crown reduction is a sterile endodontic procedure indicated for reducing the crown height of teeth. The procedure is used primarily on canine teeth as a disarming technique in aggressive biting pets or to treat traumatic occlusion. Recommendations for using this technique for biting pets are described.

Cytotoxicity of three novel fluoropyrimidines in cultured L1210 murine lymphocytic leukemia cells.

Cultured L1210 murine lymphocytic leukemia cells were used to compare metabolic activation and cytotoxicity of 5-fluorouracil (FU), Ftorafur (FT), and three novel FU-sulfur analogues. These analogues, 1-(2'-tetrahydrothienyl)-5-fluorouracil (FUS), 1-(2'-tetrahydrothienyl)-5- fluorouracil-1'-oxide (FUSO), and 1-(2'-tetrahydrothienyl)-5-fluorouracil-1'-1'-dioxide (FUSO2), have yet to be fully evaluated for potential therapeutic value based on in vitro cytotoxicity. The role of these FU analogues as prodrugs was evaluated by comparing metabolism of normal pyrimidine pathways and activation by hepatic mixed function oxidases (MFO). Significant differences in biochemical activity and cytotoxicity were measured between FU and FU analogues. FU and FU analogues were cytotoxic to L1210 cells (63-92% growth inhibition of 100 microM concentrations after 72 hr of incubation). However, at equimolar concentration cytotoxicity of the FU analogues after MFO activation (56-66% growth inhibition) was greater than FU (47% growth inhibition). Hypoxanthine, a purine precursor, did not significantly alter fluoropyrimidine cytotoxicity with or without MFO. Thymidine and uridine, pyrimidine precursors, reduced FT and FUS cytotoxicities in the presence (27, 40%) and absence (25, 15%) of MFO but did not modify FU, FUSO, or FUSO2 cytotoxicities.

Evaluation of uncertainty in input parameters to pharmacokinetic models and the resulting uncertainty in output.

Physiologically-based pharmacokinetic (PBPK) models may be used to predict the concentrations of parent chemical or metabolites in tissues, resulting from specified chemical exposures. An important application of PBPK modeling is in assessment of carcinogenic risks to humans, based on animal data. The parameters of a PBPK model may include metabolic parameters, blood/air and tissue/blood partition coefficients, and physiological parameters, such as organ weights and blood flow rates. Uncertainty in estimates of these parameters results in uncertainty regarding tissue concentrations and resulting risks. Data are reviewed relevant to the quantification of these uncertainties, for a PBPK model-based risk assessment for tetrachloroethylene. Probability distributions are developed to express uncertainty in model parameters, and uncertainties are propagated by a sequence of operations that simulates processes recognized as contributing to estimates of human risk. Distributions of PBPK model output and human risk estimates are used to characterize uncertainty resulting from uncertainty in model parameters.

Choice of dose measure for extrapolating carcinogenic risk from animals to humans: an empirical investigation of 23 chemicals.

When estimating carcinogenic risk in humans from animal data, animal to human extrapolation is often accomplished by assuming that humans and animals are equally sensitive when dose is measured appropriately in common units in both species. This paper reports on an empirical investigation of several dose units, based on data from 23 chemicals for which both animal and human data were available. The dose units were evaluated using a measure called "bias," which represents roughly the factor by which the TD25 calculated from animal data must be multiplied to correspond, on average, to the TD25 calculated from human data. (A TD25 is the average human dose rate per unit of body weight in mg kg-1 d-1, administered between ages 20 and 65, that would cause an extra lifetime cancer risk of 25%.) Biases of greater than one mean that estimates of human risk from animal data exceeded estimates made from human data. Five dose measures are evaluated in this paper; they are based on several risk assessment methods. The resulting ranges of biases are: dose rate per surface area in mg m-2 d-1, 2.1 to 12; dose rate per unit of body weight in mg kg-1 d-1, 0.36 to 1.6; parts per million in diet, 1.1 to 6.2; cumulative dose per unit of body weight in mg kg-1 per lifetime, 13 to 84; parts per million in air, 1.1 to 4.5. These findings suggest that all of these measures of dose except dose rate per unit of body weight tend to result in overestimation of human risk.

Correlation between carcinogenic potency of chemicals in animals and humans.

Twenty-three chemicals were selected for comparison of the carcinogenic potencies estimated from epidemiological data to those estimated from animal carcinogenesis bioassays. The chemicals were all those for which reasonably strong evidence of carcinogenicity could be found in humans or animals and for which suitable data could be obtained for quantifying carcinogenic potencies in both humans and animals. Many alternative methods of analyzing the bioassay data were investigated. Almost all of the methods yielded potency estimates that were highly correlated with potencies estimated from epidemiological data; correlations were highly statistically significant (p less than 0.001), with the corresponding correlation coefficients ranging as high as 0.9. These findings provide support for the general use of animal data to evaluate carcinogenic potential in humans and also for the use of animal data to quantify human risk.