The EU chemicals strategy for sustainability: in support of the BfR position

The EU chemicals strategy for sustainability (CSS) asserts that both human health and the environment are presently threatened and that further regulation is necessary. In a recent Guest Editorial, members of the German competent authority for risk assessment, the BfR, raised concerns about the scientific justification for this strategy. The complexity and interdependence of the networks of regulation of chemical substances have ensured that public health and wellbeing in the EU have continuously improved. A continuous process of improvement in consumer protection is clearly desirable but any initiative directed towards this objective must be based on scientific knowledge. It must not confound risk with other factors in determining policy. This conclusion is fully supported in the present Commentary including the request to improve both, data collection and the time-consuming and bureaucratic procedures that delay the publication of regulations.

Obesity as a Source of Endogenous Compounds Associated With Chronic Disease: A Review

In 2014, it was estimated that more than 1.9 billion adults were overweight with over 600 million classifiable as obese. Approximately two-thirds of U.S. adults over 20 years of age are currently overweight with about 35% classified as obese, a figure thought likely to reach 42% by 2030 in those over 18 years of age. Adipose cells from stored body fat secrete estrogen and a very large number (> 500) of biologically active substances termed adipokines, in addition to inducing, by other cell-driven effects, pathological alterations in insulin pathways. The U.S. National Cancer Institute reports that exposure to the hormone disrupting and proinflammatory effects of excess adipose tissue are associated with an increased risk for 11 different cancers. Obesity is also associated with a number of serious non-neoplastic conditions including metabolic syndrome and type 2 diabetes; menstrual cycle irregularities and lowered fertility (men and women); and abnormal bone morphology in a subset of female patients. In men hypogonadism, low testosterone levels, benign prostatic hyperplasia, and lowered sperm counts have been reported. In developed countries, the endogenous adverse health burden associated with obesity is only matched, quantitatively and qualitatively, by the exogenous toxicity of cigarette smoking. The investigation of possible hormonal and/or proinflammatory effects of chemicals should include an assessment of the profound endocrine alterations associated with obesity.

Bruce Nathan Ames - Paradigm shifts inside the cancer research revolution

Dr. Bruce Ames turned 92 on December 16, 2020. He considers his most recent work linking adequate consumption of 30 known vitamins and minerals with successful aging to be his most important contribution. With the passage of time, it is not uncommon for the accomplishments of a well-known scientist to undergo a parsimonious reductionism in the public mind - Pasteur's vaccine, Mendel's peas, Pavlov's dogs, Ames' test. Those of us in the research generation subsequent to Dr. Ames' are undoubtedly affected by our own unconscious tendencies toward accepting the outstanding achievements of the past as commonplace. In doing so, seminal advances made by earlier investigators are often inadvertently subsumed into common knowledge. But having followed Ames' work since the mid-1970s, we are cognizant that the eponymous Ames Test is but a single chapter in a long and rich narrative. That narrative begins with Ames' classic studies on the histidine operon of Salmonella, for which he was elected to the National Academy of Sciences. A summary of the historical progression of the understanding of chemical carcinogenesis to which Ames and his colleagues contributed is provided. Any summary of a topic as expansive and complex as the ongoing unraveling of the mechanisms underlying chemical carcinogenesis will only touch upon some of the major conceptual advances to which Ames and his colleagues contributed. We hope that scientists of all ages familiar with Ames only through the eponymous Ames Test will further investigate the historical progression of the conceptualization of cancer caused by chemical exposure. As the field of chemical carcinogenesis gradually moves away from primary reliance on animal testing to alternative protocols under the rubric of New Approach Methodologies (NAM) an understanding of where we have been might help to guide where we should go.

Human exposure to synthetic endocrine disrupting chemicals (S-EDCs) is generally negligible as compared to natural compounds with higher or comparable endocrine activity. How to evaluate the risk of the S-EDCs?

Theoretically, both synthetic endocrine disrupting chemicals (S-EDCs) and natural (exogenous and endogenous) endocrine disrupting chemicals (N-EDCs) can interact with endocrine receptors and disturb hormonal balance. However, compared to endogenous hormones, S-EDCs are only weak partial agonists with receptor affinities several orders of magnitude lower. Thus, to elicit observable effects, S-EDCs require considerably higher concentrations to attain sufficient receptor occupancy or to displace natural hormones and other endogenous ligands. Significant exposures to exogenous N-EDCs may result from ingestion of foods such as soy-based diets, green tea and sweet mustard. While their potencies are lower as compared to natural endogenous hormones, they usually are considerably more potent. Effects of exogenous N-EDCs on the endocrine system were observed at high dietary intakes. A causal relation between their mechanism of action and these effects is established and biologically plausible. In contrast, the assumption that the much lower human exposures to S-EDCs may induce observable endocrine effects is not plausible. Hence, it is not surprising that epidemiological studies searching for an association between S-EDC exposure and health effects have failed. Regarding testing for potential endocrine effects, a scientifically justified screen should use in vitro tests to compare potencies of S-EDCs with those of reference N-EDCs. When the potency of the S-EDC is similar or smaller than that of the N-EDC, further testing in laboratory animals and regulatory consequences are not warranted.

Human exposure to synthetic endocrine disrupting chemicals (S-EDCs) is generally negligible as compared to natural compounds with higher or comparable endocrine activity. How to evaluate the risk of the S-EDCs?

Theoretically, both synthetic endocrine-disrupting chemicals (S-EDCs) and natural (exogenous and endogenous) endocrine-disrupting chemicals (N-EDCs) can interact with endocrine receptors and disturb hormonal balance. However, compared to endogenous hormones, S-EDCs are only weak partial agonists with receptor affinities several orders of magnitude lower than S-EDCs. Thus, to elicit observable effects, S-EDCs require considerably higher concentrations to attain sufficient receptor occupancy or to displace natural hormones and other endogenous ligands. Significant exposures to exogenous N-EDCs may result from ingestion of foods such as soy-based diets, green tea, and sweet mustard. While their potencies are lower as compared to natural endogenous hormones, they usually are considerably more potent than S-EDCs. Effects of exogenous N-EDCs on the endocrine system were observed at high dietary intakes. A causal relation between their mechanism of action and these effects is established and biologically plausible. In contrast, the assumption that the much lower human exposures to S-EDCs may induce observable endocrine effects is not plausible. Hence, it is not surprising that epidemiological studies searching for an association between S-EDC exposure and health effects have failed. Regarding testing for potential endocrine effects, a scientifically justified screen should use in vitro tests to compare potencies of S-EDCs with those of reference N-EDCs. When the potency of the S-EDC is similar or smaller than that of the N-EDC, further testing in laboratory animals and regulatory consequences are not warranted.

Thiazopyr and Thyroid Disruption: Case Study Within the Context of the 2006 IPCS Human Relevance Framework for Analysis of a Cancer Mode of Action

Thiazopyr increases the incidence of male rat thyroid follicular-cell tumors; however, it is not carcinogenic in mice. Thiazopyr is not genotoxic. Thiazopyr exerts its carcinogenic effect on the rat thyroid gland secondary to enhanced metabolism of thyroxin leading to hormone imbalance. The relevance of these rat tumors to human health was assessed by using the 2006 IPCS Human Relevance Framework. The postulated rodent tumor mode of action was tested against the Bradford Hill criteria and was found to satisfy the conditions of dose and temporal concordance, biological plausibility, coherence, strength, consistency, and specificity that fits with a well-established mode of action for thyroid follicular-cell tumors. Although the postulated mode of action could theoretically operate in humans, marked quantitative differences in the inherent susceptibility for neoplasia to thyroid hormone imbalance in rats allows for the conclusion that thiazopyr does not pose a carcinogenic hazard to humans.

The role of toxicology in evaluating priorities in environmental health

It is easy to assume that the straightforward explanation of a rational standpoint, based on sound scientific information, will inform public debate in areas of hazard evaluation. However, although toxicology generally provides the basic data that give reassurance, it is also used as a methodology for hazard identification. Once a hazard has been identified, pressure groups will present data that suit their case and ignore those that do not. Any pretence at analysis is abandoned, as shown by the recent MMR (measles--mumps--rubella) vaccine debate in the UK. Toxicologists should not suppose that comparative evaluations of risk, based on data, will result in a rational choice about environmental interventions -- data are few and opinions are a matter of faith. Thus, we might have to be protagonists in a propaganda war for science if irrational misuse of resources is to be avoided.

A comparison of epanolol and nifedipine in stable angina patients: results of a multicentre trial

Epanolol (200 mg once daily) was compared with nifedipine (20 mg twice daily) in a multicentre, double-blind, randomised, crossover study in which 571 patients with stable angina pectoris were entered. Efficacy was assessed by anginal attack rate and short-acting nitrate consumption. Symptoms and treatment preference of the patients were assessed by questionnaires. Assessments were made at baseline and after each 4-week treatment period. Both treatments were equally efficacious as demonstrated by weekly anginal attack rates and nitrate usage. Of those patients who expressed a preference for treatment, 61% expressed a preference for epanolol compared with 39% for nifedipine. Significantly fewer patients reported experiencing flushing, pedal oedema or feeling generally unwell (p less than 0.01) during the epanolol treatment period. Patients withdrew from nifedipine treatment more often than from epanolol because of adverse effects. Hence, epanolol was found to be as efficacious as nifedipine in patients with stable angina pectoris, but exhibited a superior tolerability profile and was preferred by more patients.

Interaction of peptide boronic acids with elastase: circular dichroism studies

Boronic acid derivatives of good peptide substrates of the serine proteases cause slow-binding inhibition, manifested as biphasic binding (Kettner and Shenvi: J. Biol Chem. 259:15106-15114, 1984). These inhibitors are thought to act as reaction-intermediate analogs. Three peptide boronic acids--Ac-Pro-boro-Val-OH, DNS-Ala-Pro-boro-Val-OH, and Ac-Ala-Ala-Pro-boro-Val-OH--were chosen for far-ultraviolet circular dichroism (CD) studies in order to determine whether the second phase involves a conformational change of pancreatic elastase. The dipeptide is a simple competitive inhibitor (Ki = 0.27 microM) and the latter are slow-binding inhibitors (Ki = 16.4 and 0.25 nM, respectively). Spectral deconvolution and correction for the formation of antiparallel beta-sheet by the peptide inhibitor itself indicate that there is no significant change in the secondary structure of the enzyme in either the initial or final inhibitor complex. A kinetic experiment confirmed that the slow-binding step was not associated with a CD spectral change, and that therefore a protein conformational change was not responsible for the slow binding.

Differential effects of dextrorphan and levorphanol on the excitation of rat spinal neurons by amino acids

The effects of the stereoisomers dextrorphan and levorphanol on the excitation of spinal neurons by electrophoretically administered excitatory amino acids were studied in pentobarbitone-anaesthetised rats. Both isomers reduced responses to N-methyl-DL-aspartate (NMA), dextrorphan being both more selective and more potent than levorphanol in this respect. This observation supports the proposal that the NMA-blocking activity of a variety of drugs with psychotomimetic properties is subserved by actions at phencyclidine (PCP)/sigma opiate receptors.

Benz(F)isoquinolines as excitatory amino acid antagonists: An indication of their mechanism of action?

Using the technique of microelectrophoresis on cat and rat spinal neurones, the bridged benz(f)isoquinoline, LY154045, like ketamine and dextrorphan, was found to be a selective antagonist of N-methylaspartate, an amino acid used for characterizing excitatory amino acid synaptic receptors. The unbridged analogue, LY154005, was inactive as an amino acid antagonist. This result correlates well with the ability of LY154045, but not LY154005, to displace phencyclidine from CNS tissue and to mimic phencyclidine in behavioural tests. The potential role of N-methylaspartate antagonism in the aetiology of some of the behavioural effects of LY154045, phencyclidine and related drugs is considered.

Comparison of sigma- and kappa-opiate receptor ligands as excitatory amino acid antagonists

Using the technique of microelectrophoresis in pentobarbitone-anaesthetized cats and rats, the effects of benzomorphans, with known actions at sigma- and kappa- opioid receptors, were tested on responses of spinal neurones to amino acids and acetylcholine. The racemic mixture and both enantiomers of the sigma opiate receptor agonist, N-allylnormetazocine (SKF 10, 047), and the dissociative anaesthetic, ketamine, reduced or abolished excitation evoked by N-methyl-aspartate (NMA) with only small and variable effects on responses to quisqualate or kainate. (+)-SKF 10, 047 was 1.2 +/- 0.7 times more potent than the (-)-enantiomer in antagonizing NMA. On Renshaw cells, (+)-SKF 10, 047 enhanced responses to acetylcholine whereas the (-) enantiomer produced only a small reduction. The kappa- opiate receptor agonist, ethylketocyclazocine, had no selective effects on responses to amino acids or to acetylcholine. We conclude that actions at sigma- but not kappa-, opiate receptors are responsible for the NMA antagonism observed with benzomorphans.

The effect of the dioxolanes on amino acid induced excitation in the mammalian spinal cord

The effects of the dissociative anaesthetic, etoxadrol, and the stereoisomers of dioxadrol, dexoxadrol and levoxadrol, were examined on the excitation of spinal neurones by electrophoretically administered amino acids in pentobarbitone- or urethane-anaesthetized rats, or pentobarbitone-anaesthetized cats. Both etoxadrol and the (+)isomer of dioxadrol, dexoxadrol, administered locally or systemically, exhibited a selective antagonism of N-methyl-D,L-aspartate relative to quisqualate and kainate. This selective antagonism was not observed with the (-)isomer of dioxadrol, levoxadrol. Since such a stereoselective antagonism of the excitation of spinal neurones by N-methyl-D,L-aspartate is also displayed by the dissociative anaesthetics phencyclidine and ketamine, it is suggested that a reduced efficiency at excitatory synapses utilising N-methyl-D,L-aspartate receptors contributes to that part of the pharmacological spectrum common to both arylcyclohexylamines and dioxolanes.

Stereoselective effects of two phencyclidine derivatives on N-methylaspartate excitation of spinal neurones in the cat and rat

In pentobarbitone-anaesthetised cats and rats effects of stereoisomers of two methylated congeners of phencyclidine, GK4 and GK5, and (+)- and (-)-PCMP, were examined on the excitation of spinal neurones by electrophoretically administered excitatory amino acids and acetylcholine. GK5 and (+)-PCMP were more potent and selective antagonists of N-methylaspartate (NMA) than were GK4 and (-)-PCMP. None of these phencyclidine derivatives showed stereoselectivity in their effects on excitation of neurones by kainate, quisqualate and acetylcholine. The differences in potency between each pair of isomers as NMA antagonists correlates well with the differences reported in results from phencyclidine binding assays and behavioural tests.

The dissociative anaesthetics, ketamine and phencyclidine, selectively reduce excitation of central mammalian neurones by N-methyl-aspartate

The interaction of two dissociative anaesthetics, ketamine and phencyclidine, with the responses of spinal neurones to the electrophoretic administration of amino acids and acetylcholine was studied in decerebrate or pentobarbitone-anaesthetized cats and rats. Both ketamine and phencyclidine selectively blocked excitation by N-methyl-aspartate (NMA) with little effect on excitation by quisqualate and kainate. Ketamine reduced responses to L-aspartate somewhat more than those of L-glutamate; the sensitivity of responses to these two putative transmitters was between that to NMA on one hand and that to quisqualate or kainate on the other. On Renshaw cells, ketamine and phencyclidine reduced responses to acetylcholine less than those to NMA but more than those to quisqualate or kainate. Dorsal root-evoked synaptic excitation of Renshaw cells was reduced to a greater extent than that following ventral root excitation. Intravenous ketamine, 2.5-20 mg/kg, and phencyclidine, 0.2-0.5 mg/kg, also selectively blocked excitation of neurones by NMA. Ketamine showed no consistent or selective effect on inhibition of spinal neurones by electrophoretically administered glycine or gamma-aminobutyricacid (GABA). The results suggest that reduction of synaptic excitation mediated via NMA receptors contributes to the anaesthetic/analgesic properties of these two dissociative anaesthetics.