Toxicological consequences of multiple chemical interactions: a primer

Single and combined effects of cisplatin and doxorubicin on the human and mouse ovary in vitro

Chemotherapy drugs are administered to patients using combination regimens, and as such the possibility of multiplicative effects between drugs need to be investigated. This study examines the individual and combined effects of the chemotherapy drugs cisplatin and doxorubicin on the human ovary. Although cisplatin and doxorubicin are known to affect female fertility, there is limited information about their direct effects on the human ovary, and none examining the possibility of combined, multiplicative effects of co-exposure to these drugs. Here, human ovarian biopsies were obtained from 14 women at the time of caesarean section, with 38 mouse ovaries also obtained from neonatal C57Bl/6J mice. Tissue was cultured for 6 days prior to analyses, with chemotherapy drugs added to culture medium on the second day of culture only. Treatment groups of a single (5 μg/mL human; 0.5 μg/mL mouse) or double (10 μg/mL human; 1.0 μg/mL mouse) dose of cisplatin, a single (1 μg/mL human; 0.05 μg/mL mouse) or double (2 μg/mL human; 0.1 μg/mL mouse) dose of doxorubicin or a combination of a single dose of both drugs together were compared to controls without drug exposure. Exposure to cisplatin or doxorubicin significantly decreased follicle health in human and mouse, supporting the suitability of the mouse as a model for the human ovary. There was also a significant reduction of mouse follicle number. Human ovarian stromal tissue exhibited increased apoptosis and decreased cell proliferation. Crucially, there was no evidence indicating the occurrence of multiplicative effects between cisplatin and doxorubicin.

Bioavailability Enhancement of Poorly Soluble Drugs: The Holy Grail in Pharma Industry

Background:

Bioavailability, one of the prime pharmacokinetic properties of a drug, is defined as the fraction of an administered dose of unchanged drug that reaches the systemic circulation and is used to describe the systemic availability of a drug. Bioavailability assessment is imperative in order to demonstrate whether the drug attains the desirable systemic exposure for effective therapy. In recent years, bioavailability has become the subject of importance in drug discovery and development studies.

Methods:

A systematic literature review in the field of bioavailability and the approaches towards its enhancement have been comprehensively done, purely focusing upon recent papers. The data mining was performed using databases like PubMed, Science Direct and general Google searches and the collected data was exhaustively studied and summarized in a generalized manner.

Results:

The main prospect of this review was to generate a comprehensive one-stop summary of the numerous available approaches and their pharmaceutical applications in improving the stability concerns, physicochemical and mechanical properties of the poorly water-soluble drugs which directly or indirectly augment their bioavailability.

Conclusion:

The use of novel methods, including but not limited to, nano-based formulations, bio-enhancers, solid dispersions, lipid-and polymer-based formulations which provide a wide range of applications not only increases the solubility and permeability of the poorly bioavailable drugs but also improves their stability, and targeting efficacy. Although, these methods have drastically changed the pharmaceutical industry demand for the newer potential methods with better outcomes in the field of pharmaceutical science to formulate various dosage forms with adequate systemic availability and improved patient compliance, further research is required.

DNA damage exerted by mixtures of commercial formulations of glyphosate and imazethapyr herbicides in Rhinella arenarum (Anura, Bufonidae) tadpoles

Glyphosate (GLY) and imazethapyr (IMZT) are two herbicides commonly used worldwide, either alone or in mixtures. They represent key pesticides in modern agricultural management. The toxicity that results when employed as mixtures has not been characterized so far. Acute toxicity of the 48% GLY-based herbicide (GBH) Credit® and the 10.59% IMZT-based herbicide (IBH) Pivot® H alone and their binary combinations was analyzed in Rhinella arenarum tadpoles exposed in a semi-static renewal test. Lethal effects were determined using mortality as the end-point, whereas sublethal effects were determined employing the single-cell gel electrophoresis (SCGE) bioassay. Based on mortality experiments, results revealed LC5096 h values of 78.18 mg/L GBH and 0.99 mg/L IBH for Credit® and Pivot® H, respectively. An increase in the genetic damage index (GDI) was found after exposure to Credit® or Pivot® H at 5 and 10% of LC5096 h values. The combinations of 5% Credit®-5% Pivot® H LC5096 h and 10% Credit®-10% Pivot® H LC5096 h concentrations significantly enhanced the GDI in comparison with tadpoles exposed only to Credit® or Pivot® H. Thus, the effect of interaction between GBH and IBH inducing DNA damage in R. arenarum blood cells can be considered to be synergistic.

Synergism of mixtures of dicamba and 2,4-dichlorophenoxyacetic acid herbicide formulations on the neotropical fish Cnesterodon decemmaculatus (Pisces, Poeciliidae)

Dicamba (DIC) and 2,4-dichlorophenoxyacetic acid (2,4-D) are two of the most applied auxinic herbicides worldwide, both individually and as part of a mixture. However, the toxicity and interactions achieved when applied as a mixture have not yet been characterised. The equitoxic and non-equitoxic acute toxicity exerted by binary mixtures of Banvel^® (57.71% DIC) and DMA^® (58.4% 2,4-D) on the Neotropical fish Cnesterodon decemmaculatus were evaluated. Results revealed mean values of 1.02 (range, 0.96-1.08) for the toxic unit (TU) that induced 50% mortality (TU_{50 96 h}) to the fish exposed to binary equitoxic mixtures of the commercial formulations Banvel^®-DMA^®. These results suggest that the mixture is nearly concentration additive. Furthermore, results demonstrated the occurrence of synergistic interaction when non-equitoxic combinations of Banvel^®-or DMA^®-formulated herbicides were assayed. In this context and regardless of their concentrations, either Banvel^®- or DMA^®-induced toxicity were synergised by the presence of the counterpart within mixtures. The present study represents the first evidence of the lethality exerted by mixtures of two auxinic herbicides-namely, DIC and 2,4-D-reported to date for fish and other biotic matrices. When C. decemmaculatus is used as the target organism, a synergistic pattern is observed following exposure to a mixture of both herbicides.

Tumorigenesis in B6C3F1 mice exposed to ozone in combination with 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone and dietary dibutyl phthalate

Although ozone exposure has been suspected as a risk factor for the development of lung cancer, data are still inconclusive. Studies in the literature infrequently recognize that the potential toxicity of ozone could be influenced by the combined exposure with other environmental carcinogens. To evaluate the carcinogenic potential of ozone alone or in combination with other toxicants, male and female B6C3F1 mice were exposed through inhalation and diet, to 0.5 ppm of ozone, 1.0 mg/kg of 4-( N-methyl- N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 5000 ppm of dibutyl phthalate (DBP), individually and in combination for 1 year. No treatment-related death was seen, but significant differences in body and organ weights between control and treated mice were observed during the study. No tumor incidence was found in mice of either gender exposed to ozone alone. Pulmonary neoplasms were found in both, male and female mice exposed to NNK alone and in combination, ozone with NNK only or NNK plus DBP. Oviductal carcinomas were observed in females exposed to DBP alone and together with ozone plus NNK. These results indicate that ozone alone is not a lung carcinogen and in conjunction with NNK and/or DBP have no effect on tumor development in B6C3F1 mice under our experimental conditions.

Evaluation of the estrogenic activities of some pesticides and their combinations using MtT/Se cell proliferation assay

A number of pesticides are used in agricultural production with some having estrogenic activities, such as endocrine-disrupting chemicals that may affect wildlife and humans. This study aimed to detect the estrogenic effects of some mixed agricultural chemicals in agricultural production. The assay to measure estrogenic activity was evaluated by the cell proliferative activity of MtT/Se cells, which respond well to estrogen. To evaluate MtT/Se cells we went down to the molecular level of estrogen receptor (ER)-alpha and ER-beta expression. The proportion of ER-alpha to ER-beta was 3.55:1, as determined by semi-quantitative real-time PCR. These results showed that ER-alpha was dominant in MtT/Se cells on the transcriptional level, therefore implying that the estrogenic activity detected by these cells may be mainly mediated by ER-alpha. It was found that diazinon, tolclofos-methyl, pyriproxyfen, prothiofos and thiabendazole had estrogenic activity. Several pesticides are often present in agricultural products. Therefore, we evaluated the estrogenic activity of a mixture of two pesticides. The REC(10) levels of prothiofos/pyriproxyfen and thiabendazole/orthophenylphenol were increased up to 10-fold. We concluded that those two pesticide combinations showed a significantly higher estrogenic effect in comparison to the results of the respective pesticides when tested individually.

Pesticide mixtures potentiate the toxicity in murine thymocytes

The immunotoxic risks of multiple pesticide exposure were evaluated. C57BL/6 mouse thymocytes were exposed to lindane, malathion, and permethrin, either separately or in mixtures of two pesticides, in vitro. These pesticide exposures caused both apoptotic and necrotic cell death in thymocytes as evaluated by flow cytometric analysis in combination with 7-aminoactinomycin-D (7-AAD), Annexin-V/propidium iodide (PI) staining assays and lactate dehydrogenase release assays. When cells exposed to mixtures of two pesticides, a significantly greater than additive interaction was observed in both apoptotic and necrotic populations of cells. The gel electrophoresis of DNA of cells showed DNA ladder formation with limited genomic DNA and increased laddering in mixture exposures. Based on these findings, it is suggested that these pesticides are potent immunotoxicants, in vitro, and that the mechanism of cytotoxicity observed upon exposure to these pesticides may, at least in part, be due to induction of apoptosis. We also provided evidence that induction of drug metabolizing mixed function oxidase system with lindane may, in part, be responsible for the potentiation of cytotoxicity in the combined exposures. As more information is obtained on the potential immunotoxic effects of pesticides, further insights will be gained for the risk assessment of these environmental pollutants.

Chronic toxicity of a mixture of chlorinated alkanes and alkenes in ICR mice

The aim of this study was to determine the chronic toxicity of a mixture of chlorinated alkanes and alkenes (CA) consisting of chloroform, 1,1-dichloroethane, 1,1-dichloroethylene, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene. These chlorinated organic solvents were present in the underground water near an electronic appliances manufactory in Taoyuan, Taiwan. Male and female weanling ICR mice were treated with low-, medium-, and high-dose CA mixtures in drinking water for 16 and 18 mo, respectively. A significant number of male mice treated with the high-dose CA mixture developed tail alopecia and deformation, which was not prominent in CA-treated female mice. Medium- and high-dose CA mixtures induced marginal increases of liver and lung weights, blood urea nitrogen, and serum creatinine levels in male mice. In female mice, the high-dose CA mixture increased liver, kidney, and uterus and ovary total weights, without affecting serum biochemistry parameters. CA mixtures had no effects on the total glutathione content or the level of glutathione S-transferase activity in the livers and kid- neys of male and female mice. Treatments with CA mixtures produced a trend of increasing frequency of hepatocelluar neoplasms in male mice, compared to male and female controls and CA-treated female mice. The high-dose CA mixture induced a significantly higher incidence of mammary adenocarcinoma in female mice. The calculated odds ratios of mammary adenocarcinoma in female mice induced by low-, medium-, and high-dose CA mixtures were 1.14, 1.37, and 3.53 times that of the controls, respectively. The low-dose CA mixture induced a higher incidence of cysts and inflammation in and around the ovaries. This study has demonstrated that the CA mixture is a potential carcinogen to male and female mice. These animal toxicology data may be important in assessing the health effects of individuals exposed to the CA mixture.

Pesticide usage and health consequences for women in developing countries: out of sight, out of mind?

Pesticide exposures of women in developing countries are aggravated by economic policy changes associated with structural adjustment programs and globalization. Women in these countries, particularly in the agricultural sector, are increasingly exposed. Since they are concentrated in the most marginal positions in the formal and informal workforces, and production is organized in a gender-specific way, opportunities for women to control their exposures are limited. Data from developing countries show that: 1) women's exposures to pesticides are significantly higher than is recognized; 2) poisonings and other pesticide-related injuries are greatly underestimated for women; 3) for a given adverse outcome from exposure, the experience of that outcome is gender-discriminatory; 4) erroneous risk perception increases women's exposures. The hiatus in knowledge of gender-specific exposures and effects is related to gender biases in the nature of epidemiologic inquiry and in the literature, and the gendered nature of health workers' practices and surveillance. Recommendations are made for strong, independent organizations that provide opportunities for women to control their environments, and the factors affecting their health, as well as gender-sensitive research to address the particularities of women's pesticide exposures.

Suppression of arylamine toxicity in the Fischer-344 rat following ingestion of a complex mixture

The toxic effects of a mixture of 2-aminoanthracene (2-AA), benzanthracene (BA), and dinitropyrene isomers (DNP), and the toxic effects of these compounds individually, were investigated in the Fischer-344 rat following dietary exposure via a powdered basal diet. Animals were sacrificed at 14-, 30-, and 80-days of dietary exposure. Exposure to dietary 2-AA alone induced anorexia, cachexia, variable mortality, and altered serum chemistry profiles in the F-344 rat. Reduced lymphocyte counts were also shown in rats exposed to 2-AA. A temporal pattern of effect of 2-AA dietary exposure was observed in the progression of hepatic lesions in exposed animals. Dietary exposure to either DNP isomers or BA at a 10-fold higher concentration in the diet, relative to 2-AA, did not induce detectable toxic responses. However, exposure of rats to a mixture of 2-AA, BA, and DNP isomers (100 mg/kg, 1.0 g/kg, and 1.0 g/kg of diet, respectively) resulted in the attenuation of toxic effects when compared to exposure of F-344 rats to 2-AA alone. These results indicate that the toxic effects of 2-AA are suppressed by co-administration of DNP and BA and suggest that compound interactions need to be considered when predicting the toxic potential of specific environmental pollutants.

The applicability of the ADI (Acceptable Daily Intake) for food additives to infants and children

Children are not little adults. Children may respond differently from adults because they are in a state of growth and development; or because of differences in toxicokinetics or toxicodynamics. Infants and children are often assumed to be more susceptible to toxic effects, but this generalization is founded on assumptions rather than on facts. Available data are mostly concerned with toxicity and therapeutic effects of pharmaceuticals, while the effects in children of industrial chemicals are less well documented. Childhood is characterized by growth and development. Toxicants may interfere with these processes, and therefore toxic exposure may have more serious consequences for children than for adults, irrespective of sensitivity. Immature physiological functions of the foetus and young child theoretically make these age groups more vulnerable to toxicants, at least up to 1 year of age. The existing data on effects of chemical exposure in children point in the direction that susceptibility depends on the substance and on the exposure situation. For a particular compound children may be more sensitive than adults, or they may be less sensitive. Further, the sensitivity of children to a particular substance varies greatly with age. It is necessary to view premature neonates, neonates, infants, and children of different ages as separate risk groups. The long-term studies used as the basis for establishing ADIs cover lifetime for laboratory animals. Methods which have special emphasis on reproductive cells, on the foetus, and on the immature organism are used. Taken together, these studies cover exposure during all life stages. However, some specific types of effects, and delayed effects of perinatal exposure are not always included in standard toxicity test protocols. Exposure may also differ between children and adults. The food intake of children is qualitatively and quantitatively different form that of adults, and the EU Scientific Committee for Food has recommended that intake assessment of children be considered separately from that of adults because patterns of consumption are different. The ADI should cover the entire population including children. Special considerations regarding the use of food additives do apply to infants below the age of 12 weeks, who depend entirely on infant formula for nutrition.

Chemical mixtures: challenge for toxicology and risk assessment

It is now well-recognized that human environmental exposures are not to single chemicals. Rather, humans are exposed, either concurrently or sequentially, to multiple chemicals. Challenges that chemical mixtures pose for risk assessment and toxicology are presented. Challenge areas include increasing the peer-reviewed publication of human studies, improving access to peer-reviewed data and examining multiple target organs. Two difficult challenges are development of a common, consistent language and the use of appropriate and innovative experimental designs and analyses. The challenge of elucidation of mechanism(s) offers a rational basis for extrapolation across dose levels, exposure durations and exposure routes as well as to other species and to other similar chemicals. Of particular importance is focusing effort on those areas of investigation where answers have the greatest potential for reducing uncertainty in risk assessments for chemical mixtures and on those chemical mixtures and multiple chemical exposures that have the greatest potential impact on human health. A particularly fruitful area for future investigation is determination of the likelihood of nonadditive interactions in humans exposed to multiple chemicals at environmental exposure levels.

Chemical mixtures from a public health perspective: the importance of research for informed decision making

When considered from a public health perspective, the central question regarding chemical mixtures is deceptively simple: Are current approaches to risk assessment for chemical mixtures affording effective (adequate) and efficient (cost-effective) protection for members of our society? Answering this question realistically depends on an understanding of the hierarchical goals of public health (i.e. prevention, intervention, treatment) and an accurate evaluation of the extent to which these goals are being achieved. To allow decision makers to make informed judgments about the health risks of chemical mixtures, adequate scientific knowledge and understanding must be available to support risk assessment activities, which are an integral part of the regulatory decision making process. Designing and implementing relevant research depends on the existence of a feedback loop between researchers and regulators, where the information needs of regulators influence the nature and direction of research and the information and understanding generated by researchers improves the scientific basis for public health decisions. A clear, consistent, commonly accepted taxonomy for describing important mixture-related phenomena is a key factor in creating and maintaining the necessary feedback loop. Ultimately, both researchers and regulators share a common goal with regard to chemical mixtures; improving the state-of-the-science so that we can make informed decisions about protecting public health. A survey of research issues and needs that are crucial to attaining this goal is presented.