Fecundity,fertility and reproductive recovery of irradiated Queensland fruit fly Bactrocera tryoni

Pupae of the Queensland fruit fly or Q‐fly Bactrocera tryoni (Froggatt) are irradiated routinely to induce reproductive sterility in adults for use in sterile insect technique programmes. Previous studies suggest that adult sexual performance and survival under nutritional and crowding stress are compromised by the current target dose of radiation for sterilization (70–75 Gy), and that improved mating propensity and survival under stress by irradiated males may be achieved by reducing the target sterilization dose without reducing the level of induced sterility. This raises the question of the amount by which the irradiation dose can be reduced before residual fertility becomes unacceptable. The present study measures the levels of residual fertility in male and female irradiated Q‐flies at different irradiation doses (20, 30, 40, 50, 60 and 70 Gy), and investigates the possibility that fecundity and fertility increase between 10–15 and 30–35 days post emergence. Male flies require a higher dose than females to induce sterility, with no residual fertility found in females irradiated at doses of 50 Gy or above, and no residual fertility found in males irradiated at doses of 60 Gy or above. Irradiated females are more fecund at 30–35 days post emergence than at 10–15 days. However, fertility does not increase between 10 and 15 days post emergence and 30–35 days, even at doses below 50 Gy. The present study shows that there is scope to reduce the target sterilization dose for Q‐flies below that of the current dose range (70–75 Gy) at the same time as retaining an adequate safety margin above radiation doses at which residual fertility can be expected.     

Defining EMS and ENU dose-response relationships using the Pig-a mutation assay in rats

In recent years, experimental evidence has accumulated that supports the existence of sublinear dose-response relationships at low doses of DNA reactive mutagens. However, creating the in vivo data necessary to allow for a more detailed dose-response modeling with the currently available tools might not always be practical. The purpose of the current work was to evaluate the utility of the Pig-a gene mutation assay to rapidly identify dose-response relationships for direct acting genotoxicants. The induction of mutations in the peripheral blood of rats was evaluated following 28 days of exposure down to low doses of the direct acting alkylating agents ethyl methane sulfonate (EMS) and ethylnitrosourea (ENU). Using statistical modeling based on the 28-day studies, a threshold for mutation induction for EMS was estimated to be 21.9mg/kg, whereas for the more potent ENU, the threshold was estimated to be 0.88mg/kg. Comparing mutation frequencies from acute and sub-chronic dosing indicated less than additive dose-response relationships, further confirming the possibility of a threshold dose-response relationship for both compounds. In conclusion, the work presented provides evidence that the Pig-a assay might be a practical alternative to other in vivo mutation assays when assessing dose-response relationships for direct acting mutagens and that an experimental approach using fractionated dosing could be used to substantiate a biological mechanism responsible for the observation of a sublinear dose-response relationship.     

Why the concept of hormesis has not been incorporated into mainstream radiation health theory: Radiation perspective

Although adaptive and reparative responses to radiation were recognized in the early decades of this century, mutations and chromosome aberrations were subsequently observed to increase as linear‐nondireshold functions of the dose at low‐to‐intermediate levels of exposure. For certain cancers, likewise, although the dose‐response relationships in humans and laboratory animals have been observed to vary, depending on the type of neoplasm, the dose, dose rate, and LET of the radiation, the age, sex, and genetic background of the exposed population, and other variables, the existing data have been interpreted to suggest that the risks may not depart significantly from linearity at low doses and low dose rates. Hence, although the available data do not exclude alternative dose‐response relationships, the linear‐nonthreshold model has generally come to be used as a basis for assessing the risks of low‐level irradiation for purposes of radiation protection. While the use of this model has generally been considered to be prudent on the basis of the precautionary principle, the possibility that the model may grossly overestimate the risks of low‐level irradiation remains to be excluded. Therefore, especially in the light of the growing evidence that adaptive responses may protect against the effects of small doses of radiation, further research to clarify the relevant dose‐response relationships is strongly indicated.     

Differential cytotoxicity of activated lymphocytes on allogeneic and xenogeneic target cells. II. Activation by phytohemagglutinin

In the preceding paper it has been shown that human or mouse lymphocytes stimulated by a variety of agents, damaged allogeneic target cells while damage of xenogeneic target cells was weak or absent. In this study, the species specificity of the cytotoxicity of PHA activated lymphocytes has been studied in greater detail. Effector cells were purified lymphocytes either from human peripheral blood, or from spleen or lymph nodes of inbred mice. Target cells were ⁵¹Cr-labeled human Chang liver cells or mouse L cells.PHA stimulated human or mouse lymphocytes were significantly more cytotoxic to allogeneic than to xenogeneic target cells. At low PHA doses at which damage of allogeneic target cells was significant, damage of xenogeneic target cells was very weak or absent. At higher PHA doses, damage of xenogeneic target cells became also significant but always remained at a lower level than that of allogeneic target cells.Prestimulation of human lymphocytes with PHA for 3 days increased their cytotoxic efficiency. Furthermore, damage of human Chang cells by human lymphocytes had a dose-response relationship similar to that valid for stimulation of DNA synthesis. However, damage of mouse L cells by human lymphocytes increased at PHA-doses at which stimulation of DNA-synthesis declined. For mouse lymphocytes, these doseresponse relationships were less clear-cut, probably due to differences in origin and survival of the effector cells. This confirms previous observations that cytotoxicity and DNA-synthesis are different but probably interdependent expressions of lymphocyte activation.     

The suppressive effect of immunization on the proliferative responses of rat T cells in vitro. II. Abrogation of antigen-induced suppression by selective cytotoxic agents.

Rats given large i.v. doses of ovalbumin or sheep erythrocytes manifest suppressed spleen cell responses (3H-thymidine incorporation) to PHA within hours. Removal of glass wool-adherent cells totally restores responsiveness to that of normal nonadherent spleen cell cultures. Carrageenan, selectively toxic for macrophages, partially restores responses of antigen-suppressed spleen cells in culture, suggesting a supportive role for macrophages in the suppression phenomenon. Treatment of donors with low doses of cyclophosphamide (20 to 50 mg/kg) at the time of antigen injection abrogates the ability of their spleen cells to suppress the responses of normal cells to PHA. The low dose of cyclophosphamide required indicates a target other than the B cell or macrophage and suggests the possibility that cyclophosphamide eliminates the suppressor T cell component of the macrophage-T cell complex.     

Further observations on the increases in inositide phospholipids after stimulation by ACTH, cAMP and insulin, and on discrepancies in phosphatidylinositol mass and 32PO4-labeling during inhibition of hormonal effects by cycloheximide

ACTH-induced increases in adrenal polyphosphoinositides were demonstrable after extraction by acid or non-acid methods, and after purification by unidimensional or two-dimensional thin layer chromatography. ACTH-induced increases in phosphatidylinositol mass were apparent, both as increases in measurable phosphorus and inositol. ACTH and insulin also increased 32PO4 incorporation into adrenal and adipose tissue polyphosphoinositides which were acid-extracted and purified by two-dimensional chromatography. Cyclic-AMP increased the mass of phosphatidylinositol, but decreased 32PO4 incorporation into this and other phospholipids; the cause for this decrease in specific activity was not evident. Increasing doses of cycloheximide progressively inhibited ACTH- or insulin-induced increases in the mass of phosphatidylinositol, but 32PO4 incorporation therein followed a bimodal curve, with inhibition at lower doses and stimulation at higher doses; these divergent changes in phosphatidylinositol mass and 32P-labeling at higher concentrations raise the possibility that cycloheximide may activate phospholipases in hormone-stimulated tissues. These results offer further support for our contention that ACTH and insulin increase inositide phospholipid concentrations in their target tissues by a cycloheximide-sensitive mechanism.     

Interactions: Dose effect relationships and isoeffect curves

Summary Interaction from several agents, i.e., a greater or smaller effects than expected from the sum of the individual effects can be of essentially two types: a) The agents could act in paralell on the same target, and a term depending on the doses of the agents involved would have to be added to the individual dose effect relationships (parergic interaction). b) The agents could act at different points in the chain of events leading to the observed effect, and the action of the second agent, the promotor, would be, at least in part, contingent on the action of the first inducer agent so that the dose effect relationships are linked in a multiplicative manner (metergic interaction). The dose effect surfaces for interaction depend on the type of dose effect relationship of the individual agents. Formulas are given for the general cases and are exemplified in graphs. Typical isobolic diagrams are also illustrated. These formulas may be adapted to experimental data by means of non-linear regression or maximum-likelihood analysis.     

4-Thiothymidine sensitization of DNA to UVA offers potential for a novel photochemotherapy

Photochemotherapy, in which ultraviolet radiation (UVR: 280-400 nm) or visible light is combined with a photosensitizing drug to produce a therapeutic effect that neither drug or radiation can achieve alone, is a proven therapeutic strategy for a number of non-malignant hyperproliferative skin conditions and various cancers. Examples are psoralen plus UVA (320-400 nm) radiation (PUVA) and photodynamic therapy (PDT). All existing photochemotherapies have drawbacks - for example the association of PUVA with the development of skin cancer, and pain that is often associated with PDT treatment of skin lesions. There is a clear need to develop alternative approaches that involve lower radiation doses and/or improved selectivity for target cells. In this review, we explore the possibility to address this need by exploiting thionucleoside-mediated DNA photosensitisation to low, non toxic doses of UVA radiation.     

Differential sensitivity of osteoclasts and osteoblasts suggests that prostaglandin E1 effects on bone may be mediated primarily through the osteoclasts

Prostaglandin E (PGE) stimulates resorption in bone. Since osteoblast-like osteosarcoma cells secrete PGE2, the possibility that osteoclasts were the major target for PGE was considered. To study this question, it was first established that in isolated bone cells enriched for either osteoclastic (OC) or osteoblastic (OB) characteristics, PGE1 can induce biochemical effects similar to those seen with bovine parathyroid hormone 1-84 (PTH), another potent stimulator of bone resorption. These changes include increased cAMP and hyaluronate synthesis in OC cells, and increased cAMP but decreased citrate decarboxylation in OB cells. By following these markers, it is demonstrated that PGE1 can activate OC cells at doses as low as 1 nM, whereas OB cells require 250 nM. Bone cell responses to various doses of PTH and PGE1 were also compared. In OC cells the lowest effective dose of PGE1 and PTH was similar (1 nM), but increasing response to PGE1 was seen up to 1000 nM in contrast to PTH response which peaked at 20 nM. In addition, the magnitude of PGE1-induced OC cell hyaluronate was two to four times greater than that of PTH at all doses tested. In OB cells, PTH induced significant decreases in citrate decarboxylation at 0.1 nM, compared to 250 nM for PGE1. Half-maximal inhibition of citrate decarboxylation (19% of control) by PTH occurred at 0.5 nM, whereas 500 nM of PGE1 was required for an equivalent effect. Thus, (i) OC cells responded to PGE1 doses that were approximately 200 times lower than the minimum required by OB cells, and (ii) OB cells responded to 100 times lower doses of PTH than PGE1.     

Low dose effects of chemicals as assessed by the flow cytometric in vivo micronucleus assay

Using flow cytometric automation of the mouse in vivo, micronucleus assay increases the sensitivity of the test. This is achieved through a very large increase in the number of cells scored, by a factor of 100×, which in turn greatly reduces the sampling error. With this method, dose–response relationships of in vivo micronucleus induction for four model agents mitomycin C (MMC), diepoxybutane (DEB), cyclophosphamide (CPA), and colchicine (COL) were studied at low dose levels. For the three clastogens MMC, DEB and CPA, linear dose–response relationships were found over the dose ranges studied, even in the very low dose region (defined as the dose region where the frequency of micronucleated erythrocytes is less than twice the baseline frequency). This is consistent with the view that no threshold should exist for genotoxic agents which target DNA. For COL a dose range was found, in which the frequency of micronucleated erythrocytes did not increase with dose, possibly indicating an in vivo threshold. The flow cytometric in vivo micronucleus assay represents one possibility for in vivo low dose–response studies.     

Dose-response and thresholds in mutagenicity studies: a statistical testing approach

The analysis of dose-response relationships is an important objective in toxicology, and one in which both modelling and testing approaches are used. One particular question is whether a threshold exists at low doses. The concept of a pragmatic threshold is used, i.e. low doses with biologically unimportant effects are assumed to be threshold doses. "Biologically unimportant" means, in statistical terms, a lower effect than the effect of the negative control, or at least a just-tolerable margin delta higher than the effect of the negative control. Therefore, threshold doses can be tested in terms of a one-sided hypothesis of equivalence. A new approach is proposed, assuming, at the least, that the low dose is a threshold dose, and the highest dose is superior to the negative control. By analogy to the k-fold rule commonly used in mutagenicity studies, tests on ratio-to-control are used. The a priori definition of the threshold margin is inherently needed. A further approach proposes the analysis of dose-response relationships by means of order-restricted inference (the so-called trend test). A modification of a multiple-contrast test is used, in which only those contrasts are included that are sensitive for no effects at low doses. A further modification treats the complicated, but real, problem of simultaneous existence of a threshold, a monotonic increase, and a downturn effect at high dose(s). A parametric procedure is considered, together with an extension for proportions. The important problem of a priori sample size definition is discussed. The approaches are demonstrated by means of examples based on real data.     

Purified scrapie prions resist inactivation by UV irradiation.

The development of effective purification protocols has permitted evaluation of the resistance of isolated scrapie prions to inactivation by UV irradiation at 254 nm. Prions were irradiated on ice with doses of UV light ranging up to 120,000 J/m2. UV dosimetry experiments, performed with Saccharomyces cerevisiae plasmid DNA or eucaryotic cells, indicated that under these experimental conditions an incident UV dose of 10 J/m2 formed 2 thymine dimers per 5.1 X 10(6) daltons of eucaryotic cell DNA. The D37 values for scrapie prions ranged from 17,000 to 22,000 J/m2; D37 values were also determined for virus, viroid, and enzyme controls. The number of pyrimidine dimers formed was correlated with the D37 values obtained for irradiated prions and target nucleic acids. The D37 value for bacteriophage M13, 6.5 J/m2, occurred at a dose that would form 0.56 dimers per target genome; the D37 for potato spindle tuber viroid, 4,800 J/m2, occurred at a dose that would form about 24 dimers per target viroid. The D37 value for an EcoRI restriction site, a target of 12 bases, occurred at a dose that would correspond to the formation of 0.89 thymine dimers per target site. The D37 value for prions occurred at a dose that would form 1 dimer in every 4 bases of single-stranded target nucleic acid. If the putative scrapie nucleic acid were double-stranded and readily repairable after UV damage, then the prion D37 value could reflect a nucleic acid molecule of 30 to 45 base pairs. While the D37 value for prions fell within the range of pure protein targets, our experiments cannot eliminate the possibility that a prion contains a small, highly protected nucleic acid molecule.     

Enhanced mutagenic response of MNU by post-treatment with methylmercury,caffeine or thymidine in V79 Chinese hamster cells

Post-treatment with a non-toxic dose of thymidine, caffeine or methylmercury-hydroxide enhanced the mutagenic response from MNU at high doses, whereas no enhancement was observed with low doses of MNU. No mutagenic effects were found with thymidine, caffeine or methylmercury alone at the doses used. Quantitatively, the modifying effects observed were similar for the 3 agents which indicates the possibility of a similar way of action.