Hit Theory Research Articles

The Emerging Battlefield: Should the Use of a Nonmonotonic, Non-Threshold Dose-Response Curve for Alleged Endocrine-Disrupting Chemicals Survive aDaubert/FryeChallenge?

IN Hormones and Endocrine-Disrupting Chemicals: Low-Dose Effects and Nonmonotonic Dose Responses, (1) authors contend that toxicological significance of alleged endocrine-disrupting chemicals (EDCs) cannot be assessed using traditional monotonic threshold dose-response curve. In contrast, they suggest that EDCs can cause adverse human biological effects at low, regulatory-approved dose levels. Although this article only focuses on biological effects per se and not on whether effect is adverse or not, they contend that it is improper to extrapolate that harmful effects cannot occur at environmentally relevant, regulatory-approved low-dose levels just because no effects are seen at much higher regulatory-accepted no observable adverse effect level (NOAEL). Plaintiffs' attorneys and their retained experts will point to Vandenberg paper in support of position that EDC at issue proximately caused their plaintiff's cancer, reproductive or developmental problem, even when plaintiff only was exposed to alleged EDC at regulatory-approved safe level. Through a weight-of-the-evidence methodology, plaintiffs' experts may attempt to use some sort of nonmonotonic, non-threshold dose-response curve to opine that health condition at issue generally and specifically was caused by exposure to very low doses of alleged EDC at regulatory approved levels. Accordingly, defendants must mount a convincing Daubert/Frye argument to defeat this theory. This article demonstrates how-to construct a successful Daubert/Frye challenge against an expert's attempted use of a nonmonotonic, non-threshold dose-response curve to support an adverse causation opinion about an alleged EDC. I. Dose-Response Curves There are three dose-response curves that come into play in any personal injury environmental toxic tort case. First, traditional monotonic, nonlinear threshold dose-response curve provides that dose has to reach a recognized threshold level before chemical likely will have any adverse human health consequences. Once chemical exerts an adverse effect, adverse effect will continue to worsen as dose increases. The generally recognized phrase the dose makes poison is associated with a monotonic, nonlinear dose-response curve. Second, monotonic, linear non-threshold dose-response curve states that a chemical can have an adverse human health effect at any dose level. Thus, there is no safe dose level and no threshold dose level. As such, exposure to even molecule of chemical at issue puts an individual at risk for development of an adverse health condition. This concept is referred to as one hit theory because allegedly just dose of chemical at any level can start disease process. Third, nonmonotonic, non-threshold dose-response curve, suggested by Vandenberg article as being particularly applicable to EDCs, provides that a chemical can have effects at regulatory approved low dose levels; have no effects at moderately higher dose levels and have effects at highest dose levels. A nonmonotonic, non-threshold dose-response curve is described as either Ushaped or inverted U-shaped. Allowing a plaintiff's expert to opine that chemical on trial should be analyzed through use of a nonmonotonic, non-threshold dose-response curve would present significant problems for a defendant. Specifically, defendant's assertion of common regulatory compliance defense that plaintiffs dose level never exceeded applicable regulatory-acceptable safe dose level would be seriously questioned and could be disregarded completely by fact finder. Moreover, plaintiff would be able to raise a significant question in jurors' minds as to whether defendant was negligent for only testing alleged EDC at regulatory-accepted high levels instead of also including in its test protocol environmentally relevant low dose levels. …

Changing paradigms in type 2 diabetes mellitus

Diabetes mellitus has been increasing in prevalence and imposes serious economic burdens on both the developed as well as the developing world. Understanding pathobiological underpinning of chronic progressive disease like diabetes is an imperative that we cannot escape. For several decades now, the focus has remained on a two hit theory which begins with insulin resistance and is followed thereafter by the β cell failure. Therapies have revolved around this concept with only limited success. Reorientation in our understanding of “islet pathology” should help rethink strategies that would yield better dividends in terms of effective therapy. Role of Glucagon needs to be revisited and incorporated to create treatment regimens addressing the concept of bi-hormonal defect rather than remaining stuck in standalone “insulinopathy.” This brief review hopes to initiate/continue that dialogue.

Therapeutic implications of disorders of cell death signalling: membranes, micro‐environment, and eicosanoid and docosanoid metabolism

Disruptions of cell death signalling occur in pathological processes, such as cancer and degenerative disease. Increased knowledge of cell death signalling has opened new areas of therapeutic research, and identifying key mediators of cell death has become increasingly important. Early triggering events in cell death may provide potential therapeutic targets, whereas agents affecting later signals may be more palliative in nature. A group of primary mediators are derivatives of the highly unsaturated fatty acids (HUFAs), particularly oxygenated metabolites such as prostaglandins. HUFAs, esterified in cell membranes, act as critical signalling molecules in many pathological processes. Currently, agents affecting HUFA metabolism are widely prescribed in diseases involving disordered cell death signalling. However, partly due to rapid metabolism, their role in cell death signalling pathways is poorly characterized. Recently, HUFA-derived mediators, the resolvins/protectins and endocannabinoids, have added opportunities to target selective signals and pathways. This review will focus on the control of cell death by HUFA, eicosanoid (C20 fatty acid metabolites) and docosanoid (C22 metabolites), HUFA-derived lipid mediators, signalling elements in the micro-environment and their potential therapeutic applications. Further therapeutic approaches will involve cell and molecular biology, the multiple hit theory of disease progression and analysis of system plasticity. Advances in the cell biology of eicosanoid and docosanoid metabolism, together with structure/function analysis of HUFA-derived mediators, will be useful in developing therapeutic agents in pathologies characterized by alterations in cell death signalling.

Tidal Volumes during General Anesthesia

Tidal Volumes during General Anesthesia

Norwalk virus: How infectious is it?

Noroviruses are major agents of viral gastroenteritis worldwide. The infectivity of Norwalk virus, the prototype norovirus, has been studied in susceptible human volunteers. A new variant of the hit theory model of microbial infection was developed to estimate the variation in Norwalk virus infectivity, as well as the degree of virus aggregation, consistent with independent (electron microscopic) observations. Explicit modeling of viral aggregation allows us to express virus infectivity per single infectious unit (particle). Comparison of a primary and a secondary inoculum showed that passage through a human host does not change Norwalk virus infectivity. We estimate the average probability of infection for a single Norwalk virus particle to be close to 0.5, exceeding that reported for any other virus studied to date. Infected subjects had a dose-dependent probability of becoming ill, ranging from 0.1 (at a dose of 10(3) NV genomes) to 0.7 (at 10(8) virus genomes). A norovirus dose response model is important for understanding its transmission and essential for development of a quantitative risk model. Norwalk virus is a valuable model system to study virulence because genetic factors are known for both complete and partial protection; the latter can be quantitatively described as heterogeneity in dose response models.

Gene Mutations, Their Interactions and Associations with Immunophenotypes of Leukemia Cells in Patients with Primary Acute Myeloid Leukemia.

The development of acute myeloid leukemia (AML) is a multistep process. Gilliland and colleagues proposed a two hit theory of leukemogenesis that requires collaboration of at least two classes of gene mutations. The Class I gene mutations activate the signal transduction pathway and confer proliferation and survival advantage to hematopoietic cells. The Class II gene mutations affect transcriptional activators or coactivators and serve to impair cell differentiation. In this study, comprehensive analyses of a panel of gene mutations, their interactions and associations with antigen expression of leukemia cells were performed in 324 patients with primary AML, including 275 adults and 49 children(≤18years). The gene mutations included FLT3/ ITD (78 cases, 24.1%), FLT/ TKD (24 cases, 7.4%), NPM(63 cases, 19.4%), CEBPA(45 cases, 13.9%), NRAS (39 cases, 12%), AML1 (31 cases, 9.6%), PTPN11 (14 cases, 4.3%), MLL/PTD(13 cases, 4%), KIT(10 cases, 3.1%), KRAS (8 cases, 2.5%), and JAK2 (3 cases, 0.9%). In addition, 33 patients had t(8;21), 24 had t(15;17), 9 had inv(16) and 13 had 11q23 translocations. Totally, the Class I gene mutations were detected in 155 patients (47.8%), and Class II gene mutations, in 228 patients (70.4%). Most Class II mutation was associated with a distinct immunophenotype of leukemic cells, such as CEBPA mutation: HLADR(+)CD7(+)CD15(+)CD19(−)CD34(+) (p<0.05), NPM mutation: HLADR(−)CD19(−)CD34(−)CD33(+)(p<0.05), AML1 mutation: HLADR(+)(p<0.05), MLL/PTD: CD7(−)(p<0.05), AML1/ETO: HLADR(+)CD7(−)CD19(+)CD33(−)CD34(+)CD56(+)(p<0.05), PML/RARA: HLADR(−)CD2(+)CD7(−)CD11b(−)CD34(−)(p<0.05), CBFB/MYH11: CD11b(+)CD14(+), and translocation 11q23: CD19(+)CD33(−)CD34(−) (p<0.05). The interactions between Class I and Class II mutations are shown in table 1. Among Class I mutations, FLT3/ ITD could interact with each subtype of Class II gene mutations, but were particularly associated with NPM mutations (p<0.001) and MLL/PTD (p=0.001). FLT3/ TKD was closely related to NPM mutations (p=0.03). Most KIT mutation were detected in the core binding factor leukemia (p<0.001). PTPN11 mutations were more frequently detected in patients with NPM mutations than in others (p=0.035). Few patients with complex cytogenetics revealed mutations of the gene panel studied (Table 1), suggesting that leukemogenesis in these patients was through mechanism other than the known Class I and Class II mutations. In this study, the cooperative gene alterations of the NUP98/HOXA9 fusion gene were demonstrated (Table1) which, to the best of our knowledge, have not been reported before. In conclusion, the development of AML requires multistep genetic changes. Most Class II mutation is closely associated with a distinct pattern of antigen expression of leukemic cells. Exploring the interactions of gene mutations may help us more understand the pathogenesis of leukemia and benefit further therapeutic strategy. [Display omitted]

Development of nonalcoholic steatohepatitis model through combination of high-fat diet and tetracycline with morbid obesity in mice

Nonalcoholic steatohepatitis (NASH) is a chronic liver disease closely associated with obesity, type 2 diabetes and hyperlipidemia. For further understanding of NASH, development and characterization of appropriate animal models with metabolic abnormalities is important. Based on the "two hit theory", we tried to develop a new murine model of NASH with metabolic abnormalities. For the first hit to achieve metabolic abnormalities, a high-fat diet (HFD: 60 cal% fat) was fed to C57BL/6 mice for 10 weeks. For the second hit, 30mg/kg tetracycline was injected intraperitoneally once daily for 10 days. The HFD-fed mice treated with tetracycline showed robust increases in triglyceride content and expression levels of proinflammatory cytokine mRNAs in the liver. In addition, plasma ALT levels were significantly elevated by this combinational treatment. Furthermore, histological examination demonstrated that combinational treatment induced multifocal inflammatory cellular infiltration in the livers of all mice, and thus caused mild steatohepatitis. The HFD-tetracycline model could be useful for further understanding NASH.

Hit and target models for DNA damage with indirect action

Hit and target theory is widely known as a method for deriving the survival probability of a cell from the number of deoxyribonucleic acid (DNA) strand breaks. Direct action and indirect action are the way of causing DNA lesion by radiation. The object of a hit and target model is dried DNA. Strictly speaking, the model does not represent the generating mechanism of lesion in vivo. The biological effect by the direct action is major affection in a high dose region. However, the influence by the indirect action is major affection in a low-dose region. Topics of modern interest concerning radiation damage are becoming the affection in the low-dose region. In this paper, we propose enhancing hit and target models which take the indirect action into consideration.

Achieving pathogenesis understanding of ocular diseases by deciphering the underlying molecular pathways

The field of ophthalmology research has experienced a revolution since the 1970's, when molecular biology techniques were gradually and widely adopted. Many of the developments generated impact that went far beyond the field of ophthalmology. A classic case was the identification and characterization of the Retinoblastoma susceptibility gene (Rb), whose impact went far beyond the rare and obscure disease, as it provides key evidence for the concept of tumor suppressor gene and the "two hit" theory of tumor formation. The identification of scores of genes involved in retinitis pigmentosum (pigmentosa), on the other hand, show cases the complexity of multi-factorial diseases. Ophthalmology researchers in China have been quick in integrating these novel tools into their research. However, the field still lags behind in the effective use of these technologies to carry out in-depth inquiries into key disease mechanisms. The advent of "omics" technologies heralded a new era in biomedical research that allows for the global and rapid survey of genetic and biochemical profiles. Effective integration of these novel technologies into ophthalmology research will have far-reaching impact for the whole field.

Track etch velocity and chemical damages induced by ions in a cellulose nitrate detector

We sum up here the results obtained on a cellulose nitrate detector (LR 115). LR 115 was irradiated with ions from proton and oxygen ions in the energy range 1–10 MeV/amu. Each irradiated sample consisted of a stack of several detectors (about 20–30) each 12 μ m thick. So chemical damages were studied according to the energy lost in each detector. Broken bonds were identified and quantified using infrared spectroscopy. In the same time we develop the same approach as proposed by Katz R. for the nuclear emulsion response. This approach is based on the hit theory, where the hits are produced by the secondary electrons removed by the incoming ion. Using this approach, neglecting any differences in the initial electron energy spectra and in the temporal aspect of energy deposition, it is surprising to simulate, with the very same parameters, the chemical cross sections from protons and oxygen ions.

Kinetics of ferrite to Widmanstätten austenite transformation in a high-strength low-alloy steel revisited

Abstract Growth kinetics of Widmanstatten austenite in ferrite in a Fe–C–Mn–Nb high strength low-alloy steel is studied. It is based on the model developed by Ivantsov, Horvay and Cahn, and Trivedi (HIT theory) that describes diffusion-controlled growth of precipitates with shapes approximating to needles or plates. The calculated results using HIT theory with experimental values of the radius of the advancing tip agree well with the experimental observations. It is found that the ratio between calculated and experimental values of the radius of the advancing tip is inversely proportional to the degree of supersaturation. The influence from transformation strain/stress and/or anisotropy of interphase energy on precipitate morphology, which was ignored in the development of HIT theory, is discussed.

Regulation of S6-kinase Activity and &lt;I&gt;Erc&lt;/I&gt; Expression in Tuberous Sclerosis 2 (&lt;I&gt;Tsc2&lt;/I&gt;) Gene-Deficient Renal Tumor Cells

Tuberous sclerosis (TSC) is an autosomal dominantly inherited disease characterized by the development of hamartomas and tumors in various organs such as kidney, brain, lung and heart. Two causative genes for TSC. TSC1 on chromosome 9q34 and TSC2 on chromosome 16p13.3, have been identified. Both genes act as tumor suppressors, and Knudson's two hit theory can be applied for the development of lesions in TSC. TSC1 encodes hamartin containing a coiled-coil domain, and TSC2 encodes tuberin showing weak Rapl-GAP homology. Recently, it was revealed that hamartin and tuberin form a complex and are involve in down-regulation of mTOR-p70 S6K pathway. However, activity of hamartin/tuberin complex and precise molecular mechanism undelying TSC disease remain to be determined.We identified a germline mutation of rat TSC2 homologue (Tsc2) as the predisposing mutation for the Eker rat model of dominantly inherited renal tumor. We also generated Tsc2 knockout mice and reported that heterozygous mutant mice develop renal tumors and hepatic hemangiomas. In addition, we generated Tsc1 knockout mice and demonstrated that phenotypes similar to Tsc2 knockout mice were developed in them. Currently, we are analyzing functions of hamartin and tuberin as well as molecular mechanism of pathogenesis of TSC using these mutant animal models. Recently, we generated renal tumor cell lines from a Tsc2 knockout mouse and analyzed mTOR-S6K signaling pathway in those cells. Tumor formation of those cells in nude mice was completely suppressed by rapamycin, a m TOR inhibitor, suggesting the involvement of mTOR-S6K pathway in tumorigenesis and potential therapeutic use of rapamycin for TSC. We are analyzing Erc/mesothelin expression, which is known to elevate in Tsc2-mutant renal tumor cells, and preliminarily found the suppressive effect of Tsc2 expression on Erc expression. Pathways other than mTOR-S6K may be regulated by tuberin. Through analyses using cell lines and animal models desribed here, molecular mechanism of TSC will be elucidated.

Clinical and genetic studies of Birt-Hogg-Dubé syndrome

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant cancer syndrome characterised by benign skin tumours, renal tumours, and spontaneous pneumothorax. The gene has been mapped to chromosome 17p11.2 and recently identified,...

Cryptosporidium dose-response studies: variation between hosts.

The issue of variation is highly important in dose-response analysis: variation among genetically related pathogens infecting the same host, but also variation among hosts, in susceptibility to infection by the same pathogen. This latter issue is addressed here for the protozoan parasite Cryptosporidium parvum, the causative agent for many outbreaks of water-borne gastrointestinal illness. In human feeding studies, infectivity has been shown to be low in subjects with high preexisting anti-Cryptosporidium IgG-levels. Here we adapt the hit theory model of microbial infection to incorporate covariables, characterizing the immune status of the susceptible host. The probability of any single oocyst in the inoculum to cause infection appears to depend on preexisting IgG-levels. This does not necessarily imply direct protection by the humoral immune system; high IgG-levels may reflect a recent episode of infection/illness, and be an epi-phenomenon associated with other protective responses. The IgG-dependence of the dose-response relation can be easily applied in quantitative risk analysis. The distribution of anti-Cryptosporidium IgG levels in the general population is accessible by analyzing serum banks, which are maintained in many Western countries. Using such an approach provides first insights into the variation of susceptibility to infection in the general population.

Chemical bonds broken in latent tracks of light ions in plastic track detectors.

When a swift ion is slowed down through a plastic detector it creates a latent track. In nuclear track detectors, this latent track can be specifically etched by an appropriate chemical solution. This enlargement process is due to a higher etch velocity (VT) along the ion's path than in the non-damaged part of the detector. The etched track velocity is definitely linked to the damage created by the incoming ion in the detector material. A relationship between the physical parameters of the energy deposition and the variation in this etched track velocity with the ion energy cannot easily be explained. We present here our study on the chemical damage created by several ions in a cellulose nitrate type detector and our first attempt to simulate them by the use of the hit theory.

Modeling the Diffusion-Controlled Growth of Needle and Plate-Shaped Precipitates

AbstractVarious theories have been developed to describe the diffusion-controlled growth of precipitates with shapes approximating needles or plates. The most comprehensive one is due to Ivantsov, Horvay and Cahn, and Trivedi (HIT theory), where all the factors that may influence the precipitate growth, i.e. diffusion, interface kinetics and capillarity, are accounted for within one equation. However, HIT theory was developed based on assumptions that transformation strain/stress and interfacial free energy are isotropic, which are not true in most of the real systems. An improved growth theory of precipitates of needle and plate shapes was developed in the present study. A new concept, the compression ratio, was introduced to account for influences from the anisotropy of transformation strain/stress and interfacial free energy on the precipitate morphology. Experimental evidence supports such compression effect. Precipitate growth kinetics were quantified using this concept. The improved HIT theory (IHIT theory) was then applied to study the growth of Widmanstatten austenite in ferrite in Fe-C-Mn steels. The calculated results agree well with the experimental observations.

Classification of the spectrum of Coats' disease as subtypes of idiopathic retinal telangiectasis with exudation.

An increasing variety of eponymous terms have been used to describe atypical cases of Coats' disease. A group of typical cases of Coats' disease and other cases of differing severity were classified as one of four subtypes of idiopathic retinal telangiectasis with exudation and compared with regard to clinical outcome. In a retrospective clinical review patients with typical and atypical Coats' disease were classified as severe, focal, juxtafoveal or associated (with another disease) forms of idiopathic retinal telangiectasis with exudation. 53 eyes in 50 patients were examined of which 62% (n=31) were male. 12 eyes were classified as severe (group 1), 22 focal (group 2), 12 juxtafoveal (group 3) and 7 associated (group 4). The mean age at diagnosis was lowest in group 1 eyes (6.8 years). The best visual acuity at presentation was 6/60 in group 1 whereas high proportions of eyes in the other groups had initial visual acuities of 6/24 or better. In group 1 only one eye was treated, the majority of eyes were blind or had been enucleated whereas 34 (79%) of eyes in the other groups were suitable for treatment and 29 eyes (67%) retained pre-treatment visual acuity or better at last follow-up. Idiopathic retinal telangiectasis with exudation is a spectrum of disease, which is synonymous with Coats' disease. In this retrospective study eyes with severe idiopathic retinal telangiectasis with exudation corresponding to typical Coats' disease, have poorer vision at presentation, are less suitable for treatment and have worse outcomes than eyes with other subtypes. The spectrum of disease severity seen in idiopathic retinal telangiectasis with exudation may be due to second somatic mutations in genes with an existing germline mutation (the two hit theory) and a mosaic phenotype.

Reconsideration of biallelic inactivation of theVHL tumour suppressor gene in hemangioblastomas of the central nervous system

OBJECTIVESCerebellar haemangioblastoma occurs sporadically or as a component tumour of autosomal dominant von Hippel-Lindau disease. Biallelic inactivation of the VHL tumour suppressor gene, which is located on chromosome 3p, has...

The Beta Poisson dose-response model is not a single-hit model.

The choice of a dose-response model is decisive for the outcome of quantitative risk assessment. Single-hit models have played a prominent role in dose-response assessment for pathogenic microorganisms, since their introduction. Hit theory models are based on a few simple concepts that are attractive for their clarity and plausibility. These models, in particular the Beta Poisson model, are used for extrapolation of experimental dose-response data to low doses, as are often present in drinking water or food products. Unfortunately, the Beta Poisson model, as it is used throughout the microbial risk literature, is an approximation whose validity is not widely known. The exact functional relation is numerically complex, especially for use in optimization or uncertainty analysis. Here it is shown that although the discrepancy between the Beta Poisson formula and the exact function is not very large for many data sets, the differences are greatest at low doses--the region of interest for many risk applications. Errors may become very large, however, in the results of uncertainty analysis, or when the data contain little low-dose information. One striking property of the exact single-hit model is that it has a maximum risk curve, limiting the upper confidence level of the dose-response relation. This is due to the fact that the risk cannot exceed the probability of exposure, a property that is not retained in the Beta Poisson approximation. This maximum possible response curve is important for uncertainty analysis, and for risk assessment of pathogens with unknown properties.

Monozygotic twins concordant for Cayler syndrome

Deletions within chromosome band 22q11.2 are associated with a variety of conditions, although a simple genotype-phenotype correlation has not been established so far. Environmental factors, chance events, or a second hit theory were supported by two observations of monozygotic twins with 22q11.2 deletions and discordant phenotypes [Goodship et al., J Med Genet 1995;32:746-748; Fryer, J Med Genet 1996;33:173]. We present monozygotic twins concordant for 22q11.2 deletion and Cayler syndrome, favoring the view that there exists a predominant genetic determination of the del 22q11.2 phenotype. As these twins are diamniotic and dichorionic, they may offer a more reliable insight in genetic phenotype determination than the other published, probably monochorionic, twins who may have a discordant malformation by twinning itself.