Why proof of safety is much more difficult than proof of hazard

On the basis of simple, generally accepted biostatistical and public health principles, it is shown that for environmental health hazards a proof of safety is much more difficult than a proof of hazard. The effective sample sizes required for proof of safety are orders of magnitude greater than what is feasible in biostatistical-epidemiological studies. Although many assurances of safety "in the name of science" have been issued by government agencies and others, few if any of these assurances are statistically valid.     

The role of control groups in mutagenicity studies: matching biological and statistical relevance

The statistical test of the conventional hypothesis of "no treatment effect" is commonly used in the evaluation of mutagenicity experiments. Failing to reject the hypothesis often leads to the conclusion in favour of safety. The major drawback of this indirect approach is that what is controlled by a prespecified level alpha is the probability of erroneously concluding hazard (producer risk). However, the primary concern of safety assessment is the control of the consumer risk, i.e. limiting the probability of erroneously concluding that a product is safe. In order to restrict this risk, safety has to be formulated as the alternative, and hazard, i.e. the opposite, has to be formulated as the hypothesis. The direct safety approach is examined for the case when the corresponding threshold value is expressed either as a fraction of the population mean for the negative control, or as a fraction of the difference between the positive and negative controls.     

Making new beta cells from stem cells

In 2000, Shapiro et al. provided compelling "proof of principle" data showing that the transplantation of human islets, purified from cadaveric material, could restore severely diabetic, Type 1 patients to insulin independence. This demonstration prompted renewed efforts to find an alternative and sustainable source of surrogate islet cells for cell therapy. Experiments involving adult ductal and liver "stem" cells, or embryonic stem cells, are prominent amongst these endeavors and are reviewed in this article. Whilst there are many published claims to success in converting ES cells into insulin secreting, glucose responsive cells, all require careful reinterpretation in the light of findings that cells can adsorb insulin present in growth media. It is likely that work with adult cells is less prone to this potential artifact and significant progress has been made in producing insulin-secreting cells. Assessment of in vivo function in the surrogate cells is most frequently made using cell transplantation into toxin-induced, diabetic mice, but this model is rarely used to maximal advantage. In many cases, it remains unclear whether reductions in the hyperglycemia result from insulin secretion from the transplanted cells or are due to recovery of endogenous islet function. In this latter context, experiments are reviewed where endogenous stimulation of recovery is engendered even by irradiated donor cells.     

Observed versus predicted structure of fluorescent self-quenching reporter molecules (SQRM): caveats with respect to the use of "stem-loop" oligonucleotides as probes for mRNA folding

We developed self-quenching reporter molecules (SQRMs), oligodeoxynucleotides with fluorophore and quencher moieties at the 5' and 3' ends respectively, to probe mRNAs for single-stranded, hybridization accessible sequences. SQRMs and their homologous antecedents, Molecular Beacons (MB), are designed with the assumption that they adopt a stem-loop structure thought critical for regulating their reporter function. Recently, we observed that stem-loop structures are not required for SQRM function, and on this basis proposed that these reporter molecules be classified according to whether they were stemmed (Type I) or not (Type II). This finding further stimulated us to investigate whether Type I SQRMs, and by extension MBs, actually adopt a stem-loop configuration under physiologic conditions. Accordingly, we synthesized Type I and Type II SQRMs and studied the thermodynamic characteristics of each by fluorescence melting analysis. The results of these studies suggested that the majority of stem-loop Type I SQRMs are unstructured at 37 degrees C, while some of the stemless Type II SQRMs are, surprisingly, structured. These results were not predicted by the mfold computer program. Type I and II SQRMs were then employed to "map" the mRNA secondary structure of a gene encoding a tyrosine kinase receptor, c-kit. Neither experimentally determined melting temperatures nor mfold-"predicted" thermodynamic parameters were useful in predicting the fluorescence signal-to-noise ratios obtained for SQRMs incubated with c-kit mRNA. We conclude that stem-loop reporter molecules are in fact unlikely to adopt their presumed structures at 37 degrees C, and this design consideration may be dispensed when their use is contemplated under physiologic conditions.     

Estimating the hazard of chemical substances to aquatic life

The assessment of the hazard associated with the introduction of chemical substances into the environment is receiving considerable attention in current ecological, political, and public forums. The purpose of this paper is to identify and evaluate the basic concepts involved in assessing the hazard of chemical substances to aquatic life. A conceptual framework for conducting a hazard assessment is elaborated. In addition, several proposed procedures for conducting aquatic hazard assessment are compared and contrasted. A discussion of the decision criteria currently utilized in hazard assessment procedures is included. The use of safety factors or uncertainty factors as a central concept in a sequential testing approach is presented. An assessment of the state-of-the-art in aquatic hazard assessment and recommendations for suceeding stpes in the development of procedures constitute the conclusion of the paper.     

“Periplasmic” Location of a β-Lactamase Specified Either by a Plasmid or a Chromosomal Gene in Escherichia coli

Type IIIa beta-lactamase (TEM beta-lactamase) was "periplasmic" in Escherichia coli K-12 regardless of whether its gene was chromosomal or carried on an R factor.     

Effect on pacemakers of airport weapons detectors

An investigation was carried out using a variety of pacemakers and all the types of weapons detectors in common use in Canada, to determine whether or not such detectors present a hazard to pacemaker bearers. The results indicate that only left-side implants of unipolar sensing pacemakers are likely to be affected, that ventricular fibrillation initiated by interference-induced competitive pacing is the only conceivable hazard, but that the probability of 10⁻⁹ for the occurrence of this event is so low that it may be completely disregarded. Physicians may therefore reassure pacemaker bearers of their safety in and around airport weapons detectors.     

Exact percentage points of the likelihood-ratio test for a change-point hazard-rate model

We wish to test that the hazard rate of survival or failure-time data is constant against the alternative of a change in hazard after an unspecified time. The likelihood ratio is unbounded but the exact null distribution of a restricted likelihood-ratio test statistic is found. This distribution is not affected by Type II censoring but it does depend very strongly on the interval in which the unknown change-point is assumed to lie. Some exact percentage points are given which are much larger than simulated points that have been reported in the literature.     

Histoenzymatic characterization of sub-types of type I fibres in fast muscles of rats.

The histochemical activities of succinic dehydrogenase (SDH), myofibrillar Adenosine triphosphatase (ATPase) and alpha glycerophosphate dehydrogenase were studied in serial sections of rat vastus lateralis (red) (RVL), gastrocnemius and diaphragm muscles. Three main fibre-types were distinguished. The "Type I" fibres of RVL and gastrocnemius muscles fell into two distinct groups: one category--"Type IA" showed very low ATPase activity. The second category of "Type IB" fibres displayed moderate ATPase reaction. The "Type IA" fibres were divisible into two sub-groups when tested for SDH reaction. "Type IA1" fibres possessed a homogenous distribution of diformazan granules throughout the fibre: "Type IA2" fibres displayed characteristic "moth-eaten" pattern of diformazan localization. The diaphragm muscle did not show either "Type IB" or "Type IA2" varieties. The great majority of TypeI fibres were sub-type IA1 in the three fast muscles studied. It is also demonstrated here that an inherent heterogeneity exists between Type I filores of diaphragm and leg muscles in regard to alpha-GPD localization. This histochemical data emphasizes the fact that subdivision of TypeI striated muscle fibres of mammalian animals into two sub-types is only approximate and that a further subcategorization is possible.     

Eating nanomaterials: cruelty-free and safe? the EFSA guidance on risk assessment of nanomaterials in food and feed

Nanomaterials are increasingly being added to food handling and packaging materials, or directly, to human food and animal feed. To ensure the safety of such engineered nanomaterials (ENMs), in May 2011, the European Food Safety Authority (EFSA) published a guidance document on Risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain. It states that risk assessment should be performed by following a step-wise procedure. Whenever human or animal exposure to nanomaterials is expected, the general hazard characterisation scheme requests information from in vitro genotoxicity, toxicokinetic and repeated dose 90-day oral toxicity studies in rodents. Numerous prevailing uncertainties with regard to nanomaterial characterisation and their hazard and risk assessment are addressed in the guidance document. This article discusses the impact of these knowledge gaps on meeting the goal of ensuring human safety. The EFSA's guidance on the risk assessment of ENMs in food and animal feed is taken as an example for discussion, from the point of view of animal welfare, on what level of uncertainty should be considered acceptable for human safety assessment of products with non-medical applications, and whether animal testing should be considered ethically acceptable for such products.     

Uncertainties in the risk assessment of three mycotoxins: aflatoxin, ochratoxin, and zearalenone

The risk assessment of mycotoxins is made up of two major components: an exposure assessment and a hazard assessment. There are many uncertainties in both of these components. This paper will briefly discuss the various aspects of the risk assessment process as it applies to mycotoxins and will then focus mainly on some of the uncertainties in the hazard assessment component of several carcinogenic mycotoxins. To arrive at an estimated "safe dose" (end point of the hazard assessment), we have previously used two major approaches: the no observed effect level (NOEL) divided by a safety factor approach and a mathematical (robust linear) extrapolation to a "virtual safe dose." Both of these approaches use only points from the no observed effect region of the dose-response curve and ignore valuable data from the response region. It is proposed to use the dose at which 50% of the animals would have developed tumors (the TD50) divided by a large safety factor of 50,000 as an additional estimate of "safe dose". For many studies, the TD50 lies within the observed response region of the dose-response curve and may have more validity. It is also suggested in certain cases that some of the uncertainties regarding the NOEL can be reduced if one uses a statistically derived no effect level (NEL).     

Changes in the pituitary of the migrating European eel during its journey from rivers to the sea

Summary The present studies demonstrate that, as migrating European silver eels enter the sea, important changes occur in the pars distalis of the pituitary. A decrease of Type A neurosecretory material in all nerve tracts penetrating the pars distalis was observed, as was an increased activity of Type B neurosecretion in the tracts of the proximal pars distalis.In the proximal pars distalis, gonadotropic cells show striking changes, and in the rostral pars distalis thyrotropic and prolactin cells. It is discussed whether these changes are related to migration to breeding grounds or to changes in the environment.Dedicated to Dr. Berta Scharrer on her 60th birthday.     

Reflections on the implications of thresholds of mutagenic activity for the labelling of chemicals by the European Union

During the course of the safety evaluation and regulatory control of chemicals it is important to distinguish between "potential hazard" and "actual risk" of exposure to toxins. In the case of DNA reactive chemicals, it has been prudent to assume that hazard is expressed as risk at low exposure concentrations. However, analysis of the dose-response relationships of both DNA reactive and non-DNA reactive genotoxins (e.g., aneugens) indicate that there are exposure concentrations below which protective mechanisms such as DNA repair activity and the presence of multiple targets may lead to the prediction of no risk until threshold concentrations are achieved. Current European Union management procedures for mutagenic chemicals are based predominantly upon hazard assessment rather than assessment of actual risk under likely exposure scenarios. As our knowledge of protective mechanisms increases, the time is now appropriate to undertake a re-evaluation of European Union criteria and to base the clarification mutagenic chemical more firmly upon the basis of actual risks to the human population and to the environment.     

Classification of implants with reference to safety considerations

Implants are listed both in the German Drug Law (Arzneimittelgesetz) and in the Regulations of the Safety of Medical Technical Equipment (Medizinger?teverordnung). In recent time, various guidelines concerning implants have been under discussion in Europe. It is surprising to note that more than one set of guidelines has been thought to be necessary. The present article discusses possible definitions of some of the terms employed in connection with implants, and attempts to identify the differences and common features of implants under aspects of safety, thus providing a broader base for public discussions. An analysis of the implants presently available has shown that it is useful to establish a hierarchy of possible hazards that takes into account the danger to the patient under worst-case conditions. A survey has demonstrated that in the worst case, most implants are associated with only an impairment or inconvenience for the patient, but no threat to life. In contrast, a minority of implants are of such a nature that in the case of severe failure, a life-threatening situation can develop for the patient. Such a hazard is not dependent upon whether the implant has a driving energy source or not. These findings indicate that within the framework of safery considerations, more attention need to be paid to "passive" implants than has been the case so far.     

"Red" fibres of pigeon pectoralis major muscle are "type II red".

On the basis of the histochemical activity of succinic dehydrogenase, only two fibre-types are distinguished in pigeon pectoralis major muscle. These are narrow "Red" and broad "White". The histochemical activity of myofibrillar ATPase was studied in these two distinct fibre-types. Both fibre-types showed high activity for the ATPase. "Red" fibres of pigeon pectoralis were not alkali-labile, at incubation pH 9.4, as were the "Type I" fibres of both avian and mammalian muscles. Again unlike "Type I" fibres, the "Red" fibres of pigeon pectoralis lacked the characteristic activation of acid-preincubated ATPase reaction. Pigeon pectoralis "Red" fibres are known to possess some characteristics of fast-twitch fibres (e.g. high fat, considerable phosphorylase, fibrillenstruktur myofibrillar arrangement, focal "en plaque" pattern of nerve endings). It is emphasized, therefore, that the pigeon pectoralis "Red" fibres are not equivalent to "Type I or slow-twitch", muscle fibres, but they are possibly "fast-twitch fatigue resistent or Type II Red" muscle fibres.     

Son preference and fertility in China

This paper examines the effect of son preference on the hazards of having a second and a third birth. With data from the Two-per-thousand National Sample Survey on Fertility and Contraception conducted in 1988 by the State Family Planning Commission of China, the hazard of having a second birth among 62+ thousand married women who have had a first birth, and the hazard of having a third birth among 43+ thousand married women who have had two births was examined. These two hazards (i.e. the hazard of moving from the first to the second birth, and the hazard of moving from the second to the third birth) were analysed by estimating Cox proportional hazard models. The major covariate in the first analysis is whether or not the first-born was a daughter. In the second analysis the main covariate is whether both of the first two children were girls. In both models seven covariates known to have independent effects on the transition to a second (or third) birth are controlled for, namely, whether the woman is a Han, whether she is a farmer, her age at the birth of the first (or second) child, whether she had her first (or second) birth prior to the initiation in 1979 of the one-child policy, and three dummy variables reflecting her level of education. The results show the important influence of son preference on the hazard of having another birth.     

Changes in the risk of fine-root mortality with age: a case study in peach, Prunus persica (Rosaceae)

Previous studies suggest that younger roots are more vulnerable to mortality than older roots. We analyzed minirhizotron data using a mixed-age, proportional hazards regression approach to determine whether the risk of mortality (or "hazard") was higher for younger roots than for older roots in a West Virginia peach orchard. While root age apparently had a strong effect on the hazard when considered alone, this effect was largely due to different rates of mortality among roots of different orders, diameters, and depths. Roots with dependent laterals (higher order roots) had a lower hazard than first-order roots in 1996 and 1997. Greater root diameter was also associated with a decreased hazard in both 1996 and 1997. In both years, there was a significant decrease in the hazard with depth. When considered alone, age appeared to be a strong predictor of risk: a 1-d increase in initial root age was associated with a 1.26-2.62% decrease in the hazard. However, when diameter, order, and depth were incorporated into the model, the effect of root age disappeared or was greatly reduced. Baseline hazard function plots revealed that the timing of high-risk periods was generally related to seasonal factors rather than individual root age.     

Parity models of cell proliferation

Models of the cell cycle are developed and simulated for renewing and for exponentially growing populations. Type A corresponds to the author's previous model (Barrett, 1966, Barrett, 1966). Type B incorporates a resting or regenerating phase, recurring regularly every few cycles, with an endogeneous rhythm. The parity of a cell is the number of cycles since the phase occurred in an ancestral cycle. Type C incorporates asymmetric cell division. Type B leads to novel features in calculated and simulated labelled mitoses curves, since increasing amplitudes of successive waves are permitted, and accords with certain tumour data that previously seemed anomalous. Type B leads also to correlations between cycle times for different generations, in accordance with patterns reported in bacteria. Some mathematical properties of models Type A and B are noted.     

Early Mortality and Primary Causes of Death in Mothers of Children with Intellectual Disability or Autism Spectrum Disorder: A Retrospective Cohort Study

Introduction

Mothers of children with intellectual disability or autism spectrum disorder (ASD) have poorer health than other mothers. Yet no research has explored whether this poorer health is reflected in mortality rates or whether certain causes of death are more likely. We aimed to calculate the hazard ratios for death and for the primary causes of death in mothers of children with intellectual disability or ASD compared to other mothers.

Methods

The study population comprised all mothers of live-born children in Western Australia from 1983–2005. We accessed state-wide databases which enabled us to link socio-demographic details, birth dates, diagnoses of intellectual disability or ASD in the children and dates and causes of death for all mothers who had died prior to 2011. Using Cox Regression with death by any cause and death by each of the three primary causes as the event of interest, we calculated hazard ratios for death for mothers of children intellectual disability or ASD compared to other mothers.

Results and Discussion

During the study period, mothers of children with intellectual disability or ASD had more than twice the risk of death. Mothers of children with intellectual disability were 40% more likely to die of cancer; 150% more likely to die of cardiovascular disease and nearly 200% more likely to die from misadventure than other mothers. Due to small numbers, only hazard ratios for cancer were calculated for mothers of children with ASD. These mothers were about 50% more likely to die from cancer than other mothers. Possible causes and implications of our results are discussed.

Conclusion

Similar studies, pooling data from registries elsewhere, would improve our understanding of factors increasing the mortality of mothers of children with intellectual disability or ASD. This would allow the implementation of informed services and interventions to improve these mothers'' longevity.