ESNATS Conference — The use of Human Embryonic Stem Cells for Novel Toxicity Testing Approaches

The main achievements and results of the ESNATS project (Embryonic Stem Cell-based Novel Alternative Testing Strategies) were presented at the final project conference that was held on 15 September 2013, the day before the traditional EUSAAT (European Society for Alternatives to Animal Testing) Congress in Linz, Austria. The ESNATS project was an FP7 European Integrated Project, running from 2008 to 2013, the aim of which was to develop a novel toxicity testing platform based on embryonic stem cells (ESCs), and in particular, human ESC (hESCs), to accelerate drug development, reduce related R&D costs, and propose a powerful alternative to animal tests in the spirit of the Three Rs principles. Altogether, ESNATS offered the first proof of concept that hESCs can be used to create robust, reproducible and ready-to use test assays for predicting human toxicity. In the end, essentially five test systems were developed to an adequate level for entering possible pre-validation procedures. These methods are based on hESCs, and can be combined to study the possible effects, on the human embryo, of exposure to a chemical during the early stages of development. In addition to the presentations by the main project partners, external speakers were invited to give lectures on relevant topics, both in the field of neurotoxicity and, more generally, on the applicability of hESCs in the development of advanced in vitro tests.

Alternative testing in drug research and development-The validation issue

As ECVAM (the European Centre for the Validation of Alternative Methods) intensifies its work, it is worth discussing the aspects of alternative testing in drug research and development as well as the implication of validating tests-and the possible role of ECVAM in this. Substituting animal in vivo tests with alternative testing has always been a major target in the pharmaceutical industry, for ethical and practical reasons. In vitro tests have an important role, especially in the first phase of drug discovery (the substance-finding phase) but to a lesser extent in safety testing. In the further development of a new drug, validation becomes more important for safety tests than for the initial screening and substance-finding tests. That also implies that diverse safety and toxicity testing of pharmaceuticals should be based on worldwide accepted and validated protocols. ECVAM has a role here, in informing the scientific and regulatory community about promising (validated) tests in drug discovery or development and pressing for worldwide harmonization, especially of safety testing.

Moving forward in human cancer risk assessment

BACKGROUND

The current safety paradigm for assessing carcinogenic properties of drugs, cosmetics, industrial chemicals, and environmental exposures relies mainly on in vitro genotoxicity testing followed by 2-year rodent bioassays. This testing battery is extremely sensitive but has low specificity. Furthermore, rodent bioassays are associated with high costs, high animal burden, and limited predictive value for human risks.

OBJECTIVES

We provide a response to a growing appeal for a paradigm change in human cancer risk assessment.

METHODS

To facilitate development of a road map for this needed paradigm change in carcinogenicity testing, a workshop titled "Genomics in Cancer Risk Assessment" brought together toxicologists from academia and industry and government regulators and risk assessors from the United States and the European Union. Participants discussed the state-of-the-art in developing alternative testing strategies for carcinogenicity, with emphasis on potential contributions from omics technologies.

RESULTS AND CONCLUSIONS

The goal of human risk assessment is to decide whether a given exposure to an agent is acceptable to human health and to provide risk management measures based on evaluating and predicting the effects of exposures on human health. Although exciting progress is being made using genomics approaches, a new paradigm that uses these methods and human material when possible would provide mechanistic insights that may inform new predictive approaches (e.g., in vitro assays) and facilitate the development of genomics-derived biomarkers. Regulators appear to be willing to accept such approaches where use is clearly defined, evidence is strong, and approaches are qualified for regulatory use.

Alternatives to animal experimentation: The regulatory background

The framework, in which alternatives to animal experiments can be developed, standardized, respectively formally validated, has to be seen in a global context. The ever increasing demand of testing for hazard and risk assessment in health and environment, exemplified by the EU REACH program, subsequently triggers laboratory animal testing. This holds especially true, if no valid alternative methods agreed to by the regulatory authorities and the scientific community are available. At least for regulatory toxicity testing, the global frame and network are given by institutions such as OECD, ICH, and alike. However, due to the necessity of global consent of states, organizations, and stakeholders, the time gap between availability of a novel alternative test method and its final acceptance by authorities and implementation thereafter is widening. The lack of new technologies or opportunities for alternative method application such as, for example, the broad use of transgenic animals for refinement of existing tests, adds to the problem. The bare existence of certain in vivo tests increases also the gap between public demands for testing versus availability of alternative tests. Industries operating on a worldwide basis support the alternative test development in their respective area of research and operational business. However, a more coordinating approach such as that of the ecopa-organization (European Consensus Platform on Alternatives) is needed to exploit the existing possibilities within the current regulatory framework. This will speed up the process of acceptance and challenge the political world to feel responsible for the sequels of their demanding more testing, that is, by funding alternative method development in academia and industry.

Dialogue and collaboration with ECVAM: the view of the EFPIA

An evaluation is presented of past experience of dialogue and collaboration of ECVAM with the European Federation of Pharmaceutical Industries and Associations (EFPIA) over the last nine years. Lessons learnt from the viewpoint of EFPIA company representatives are given. Also, proposals for the future ECVAM approach are made, such as support for other research areas for new methods to be validated, giving realistic statements to ECVAM's EU and external customers, and being open to any new technology development that might help in opening and establishing new alternative avenues. Finally, the need for proper publications on the implementation of alternatives is recommended, for example, through the existing national platforms and their umbrella organisation, ecopa.

Pharmacological basis for use of calcium channel antagonists in hypertension

The major mechanism of antihypertensive action of Ca2+ channel antagonists is the inhibition of Ca2+ entry into the vascular smooth muscle cell. Ca2+ channels are stabilized by these drugs in a mode unavailable for opening. The inhibition of Ca2+ entry leads to vasodilatation and lowering of arterial pressure. The advantages of Ca2+ channel antagonists in hypertension include improvement of blood supply to vital organs, diuretic activity, coronary vasodilatation, reduction in heart size and vascular cytoprotective effect.

Suppression of renin-angiotensin system in the heart of spontaneously hypertensive rats

Renin-like enzyme and angiotensin converting enzyme (ACE) were identified and their specific activities measured in cardiac tissues of spontaneously hypertensive rats (SHR) and their Wistar-Kyoto (WKY) normotensive controls. In addition, the enzyme activities were determined following administration of hypotensive drugs. The pH optima of cardiac renin-like enzymes were identical with those in vascular walls, the specific activity being higher in the heart. Cardiac ACE revealed similarities with the venous wall enzyme. The highest specific cardiac renin-like activity was found in the septum and that of ACE in atria/auricles. Both enzyme values were lower in the hearts of SHR than in those of normotensive controls. Following nifedipine treatment, specific renin-like activities increased in all cardiac structures studied (P less than 0.01); with nitrendipine and muzolimine less pronounced elevations were obtained. Administration of these three hypotensive drugs resulted in a stimulation of ACE in all the cardiac structures except in atria/auricles, where their activities were lowered.

Effect of hypotensive agents on the renin-angiotensin system in vascular walls of spontaneously hypertensive rats

Previous investigations have shown that the renin-angiotensin system (RAS) is activated in vascular walls of spontaneously hypertensive rats (SHR). The present study was undertaken to determine whether antihypertensive drugs attenuate this activation. Two calcium channel blockers, nifedipine and nitrendipine, and the diuretic muzolimine were applied to SHR for 2-4 weeks, and angiotensin (ANG) I-forming angiotensinogenase (AIFA) and ANG I converting enzyme (ACE) activities were determined. The values for both enzymes were elevated in arterial tissues of SHR (P less than 0.01), whereas in venous walls AIFA activity was decreased (P less than 0.01). All hypotensive drugs reduced arterial ACE activities in SHR (nifedipine and muzolimine: P less than 0.01; nitrendipine: P less than 0.05). Angiotensin I-forming angiotensinogenase activity was increased following treatment with nifedipine (P less than 0.01) but reduced by nitrendipine (P less than 0.05); with muzolimine, no significant alterations were observed. The results obtained indicate that in SHR, stimulation of vascular wall ACE is abolished following treatment with hypotensive agents, and the effect is independent of their mode of action. It is assumed that the activation of vascular ACE is not caused by, but rather a reaction to, elevated blood pressure.

Calcium channel blocker nisoldipine limits ischemic damage in rat kidney

The effects of the calcium channel blocker nisoldipine on renal function after 60 min. normothermic ischemia and contralateral nephrectomy were studied in male Wistar rats. Nisoldipine (300 ppm) was given in a standard diet as well as one hour prior to ischemia (10 mg./kg. orally). Survival, serum urea, serum creatinine, urine volume and creatinine clearance were used to test the effectiveness of the drug. Nisoldipine treatment resulted in the survival of all animals (compared to 66.6 per cent in the untreated group) and improved immediate and long term (14 days) renal function. The drug given post ischemia only was not effective, suggesting that nisoldipine must be present in the kidney during ischemia. The beneficial effects of the drug in postischemic acute renal failure may be attributed in part to effects on postischemic renal hemodynamics. Additional direct effects on ischemic renal epithelial cells, presumably by inhibiting transmembrane calcium fluxes, cannot be excluded.

Influence of a calcium-enriched diet on salt-induced hypertension in rats

Addition of dietary calcium exerts antihypertensive effects in spontaneously hypertensive rats (SHR), which can be intensified by a parallel increase of sodium in the diet. It was of interest to what extent calcium addition to a high salt diet might modify salt-dependent hypertension in salt-sensitive Dahl rats (S/JR). Groups of six S/JR and seven salt-resistant Dahl rats (R/JR) received, when 4 weeks old, diets containing differing sodium and calcium concentrations. A further group received a calcium-enriched diet supplemented with the calcium antagonist nitrendipine. A higher calcium content in the diet did not change the effects resulting from an 8% NaCl diet, with regard to heart weight and laboratory parameters. Salt-sensitive Dahl rats on a calcium-enriched NaCl diet had a more rapid development of hypertension than S/JR on a normal calcium/high salt diet or S/JR on a calcium-enriched diet supplemented with nitrendipine. Salt-resistant Dahl rats did not differ significantly with regard to blood pressure development on any diet. In contrast to the effect in SHR, dietary calcium has therefore no antihypertensive effect on salt-induced hypertension. A moderate increase in the calcium content of the diet does not alter blood pressure lowering effects of calcium antagonists.

Inhibition of human red blood cell Na+, K+-cotransport by various "high ceiling" diuretics

The rank order of diuretic efficacy of furosemide analogs, e.g. bumetanide and piretanide, in humans is reflected better by their ability to inhibit Na+, K+-cotransport in human red blood cells than by their natriuretic activity in rats. High ceiling diuretics which are structurally unrelated to sulfamoyl diuretics, e.g. muzolimine, tizolemide, MK 447, may be similarly effective in rat and man, but by acting via other mechanisms cannot be detected by use of the Na+, K+-cotransport system. On the other hand, a possible conversion of such compounds to metabolites active in the cotransport system cannot be ruled out. In contrast to ethacrynic acid, the weak inhibitory activity of muzolimine on the Na+, K+-cotransport was not potentiated by cysteine. These results suggest that the diuretic activity of muzolimine is not caused by inhibition of Na+, K+-cotransport.

Characteristic changes of plasma proteins in the Dahl hypertensive rat strain (DS) during the development of hypertension

Several recent studies have reported the existence of additional plasma proteins in essential hypertensive patients and strains of genetically hypertensive rats. The aim of this work was to look for similar changes in a model of salt induced hypertension, the Dahl salt sensitive (DS) rat, using the sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. No additional proteins were found when different staining techniques were employed (Coomassie, silver). However, during the development of hypertension a characteristic change in the plasma protein pattern of DS rats occurred, which could not be detected in the majority of normotensive control animals. Treatment with nifedipine inhibited both the development of hypertension and this specific change in the plasma proteins, in spite of continuous dietary salt loading. It is postulated that the plasma protein changes reflect a regulatory phenomenon of hypertension.

Chronic treatment with nifedipine prevents development of hypertension and abnormal red cell Na+ transport in Dahl-S-rats

Transmembrane Na+ transport was measured in erythrocytes of salt resistant (DR) and salt sensitive (DS) Dahl rats, fed either a standard (0.4%) or high (0.8%) NaCl diet, or a high NaCl diet containing 300 ppm of the calcium entry blocker nifedipine. Whereas salt-loaded DS became severely hypertensive, those treated with nifedipine remained normotensive. With a low NaCl diet, total Na+ efflux and Na+ pump activity was lower in DS than in DR. Cotransport was more active in DS than in DR. After excess Na+ intake, total Na+ efflux was markedly reduced in DS, but normal in nifedipine-treated DS. Cell Na+ content was increased by 52% in salt-loaded DS, but not so in DS chronically treated with nifedipine. Na+ pump was completely suppressed in salt-loaded DS, but normal in DR and rats treated with nifedipine. These results suggest that Na+ pump inhibition might be involved in the development of Dahl rat hypertension, and that prevention of salt-induced hypertension by chronic nifedipine treatment also prevents suppression of erythrocytic Na+ pump. This suggests a casual link between its biochemical and therapeutic action.

Salt-induced hypertension in the 'Sabra' rat strain: influence of nifedipine treatment

The effects of chronic dietary salt-loading and nifedipine therapy on hypertension-prone (SBH), -resistant (SBN) and parental (SB) Sabra rats were investigated. Salt diet for 12 weeks resulted in a sustained hypertension and heart hypertrophy only in SBH. Nifedipine therapy (300 p.p.m. = 300 mg/kg of food) introduced after week 7 on a salt diet, achieved small changes in salt-loaded SBN and SB rats, but resulted in a marked decrease in blood pressure in SBH rats within 1 week and in a regression of cardiac hypertrophy. Plasma renin activity rose slightly in nifedipine treated SB and SBN rats, but decreased significantly in treated SBH rats. Histopathological investigations revealed hypertensive vasculopathy in three out of nine untreated SBH rats, whereas there were no morphological changes in the treated rats.

'Calcium agonist' in salt-dependent hypertension: hints at calcium-mediated blood pressure increase

To substantiate further the hypothesized importance of increased calcium influx into vascular smooth muscle, salt-sensitive Dahl rats (DS/JR, John Rapp), on either a low or a high salt diet, were treated with 100 or 300 ppm (i.e. mg/kg food) BAY k 8644, a calcium agonist. Simultaneously, salt-resistant Dahl rats (DR/JR) on a high salt diet received 300 ppm BAY k 8644. Blood pressure rose more rapidly in the agonist-treated DS/JR rats than in the untreated DS/JR controls on high salt diet. On the low salt diet, blood pressure was only slightly higher in the agonist-treated DS/JR. Although an increased calcium influx seems to be involved in salt-induced hypertension, the presence of high sodium chloride is apparently essential for its development. In addition, since DR/JR rats remained resistant to the effect of the calcium agonist, calcium per se is not the decisive factor responsible for the sensitivity or resistance of Dahl rats to salt load.

Influence of muzolimine on arterial wall elastin

Muzolimine, 3-amino-1-(3,4-dichloro-alpha-methylbenzyl)-2- pyrazolin -5-one, an antihypertensive and diuretic drug, accumulates in the arterial tissue of rats and dogs after oral administration. Two weeks after the administration of 3 mg [14C]muzolimine, the aorta of rats contained 60-300 times more 14C-radioactivity/weight unit than the skin or tail tendon. The 14C-radioactivity was exclusively bound to the isolated aortic elastin and corresponded to 0.04% of the applied muzolimine dose. Up to ca 250 ng bound muzolimine/mg elastin was found in the aorta of dogs treated with non-labelled muzolimine for 52 weeks. The elastin-bound [14C]muzolimine was not extractable by organic solvents or by weak acids or bases but was released in a soluble form by pancreatic elastase and extracted from the elastase digest by dichloromethane. In the dichloromethane extract muzolimine was detected by HPLC and HPTLC, and was identified by mass spectrometry. Muzolimine pretreatment of rats for 2 months did not influence the elastin content of arterial tissue or [3H]glycine incorporation into aortic elastin under organ culture conditions, but after labelling the elastin with [4,5-3H]lysine, the [3H]desmosine and [3H]-isodesmosine isolated from the elastin of muzolimine-pretreated rats and incorporated under organ culture conditions was lower than that of control animals. In addition, aortic elastin of rats pretreated for 2 months with 800 ppm muzolimine in the diet was more resistant to elastase degradation. This effect might give some implications for muzolimine in the therapy of cardiovascular disorders with impaired arterial elastin metabolism.

Differential influence of the calcium antagonist nitrendipine and the vasodilator hydralazine on normal and elevated blood pressure

The relationship between pre-treatment blood pressure and its reduction by the calcium antagonist nitrendipine (NIT) and the vasodilator hydralazine (HYD) was studied in conscious normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). In SHR the correlation was linear and similar after NIT and HYD. In WKY, however, the hypotensive effect of HYD was greater than that of NIT. As revealed by the dose-response curves in SHR both drugs produce similar maximal drops in blood pressure by about 54%. In WKY, HYD also caused a similar relative reduction in blood pressure. In contrast, after NIT initial blood pressure was reduced by only 27% at maximum. The greater hypotensive effect of HYD in WKY is not caused by impaired sympathetic counterregulation since in both substrains tachycardia was more prominent after HYD. Possible mechanisms of the enhanced depressor action of NIT in hypertension are discussed.

Factors involved in the antihypertensive action of calcium antagonists

The main mechanism underlying the antihypertensive action of calcium antagonists is believed to be the vasodilation of peripheral vessels. To compare the effects of calcium antagonists with those of other vasodilators, nifedipine or its antihypertensive analog nitrendipine were tested in different normotensive and hypertensive rat strains and situations. The acute blood-pressure-lowering effect of nifedipine in the Dahl salt-sensitive rat was characterized by a rapid onset of action, the minimal effective oral dosage (0.1 mg/kg) being effective for up to 6 hours. Nifedipine was approximately 3 times more potent than hydralazine and equipotent to, but of shorter duration of action than, minoxidil. Natriuretic activity in normotensive Wistar and hypertensive Dahl salt-sensitive rats was observed with nitrendipine after an acute saline load (30 ml/kg by mouth), whereas vasodilators such as minoxidil and hydralazine decreased renal function under these conditions. Treatment of spontaneously hypertensive rats (SHR) with nifedipine in food (315 parts per million) for 60 weeks prevented the development of hypertension and resulted in decreased plasma renin activity and plasma aldosterone concentration in comparison to untreated SHR controls. Moreover, absolute and relative heart weights were reduced in the treated rats. Results suggest that the antihypertensive action of calcium antagonists, at least those of the dihydropyridine type, is not only due to peripheral vasodilation, since in contrast to other vasodilators a hyperdynamic circulation is not induced, the renin-angiotensin-aldosterone system is not activated, and sodium/volume retention cannot be expected because of a primary natriuretic effect. Therefore, a reduced volume load in addition to the decrease in afterload contributes to the antihypertensive effect of calcium antagonists and their prevention of heart hypertrophy.

Nitrendipine and other calcium entry blockers (calcium antagonists) in hypertension

Nitrendipine is a calcium antagonistic 1,4-dihydropyridine derivative with a pronounced antihypertensive activity in animal experiment. Similar to other calcium entry blockers, nitrendipine decreases blood pressure by lowering the elevated peripheral vascular resistance. However, its long-term effect differs from that of vasodilators such as hydralazine and minoxidil. In contrast to vasodilators, nitrendipine reduces heart hypertrophy in various forms of experimental hypertension in rats. Nitrendipine is highly effective in normalizing blood pressure, reducing heart hypertrophy, and preventing mortality in salt-related hypertension (two-kidney renal hypertension, salt-induced hypertension in Dahl rats), which are rather refractory to the effect of vasodilators. Nitrendipine reduces renovascular resistance in spontaneously hypertensive rats but has no effect on that of normotensive rats. In conscious renal hypertensive dogs, nitrendipine decreases blood pressure more than does hydralazine. The reflex tachycardia is more pronounced after hydralazine than after nitrendipine; blood pressure decrease is greater and the duration of the effect is longer than that of nifedipine. Nitrendipine is thus predicted as an effective drug for antihypertensive monotherapy.

Influence of nifedipine on ventricular function and myocardial hypertrophy in spontaneously hypertensive rats

We compared left ventricular (LV) hemodynamics, LV muscle mass (LVMM), and LV geometry of 13 spontaneously hypertensive rats (SHRs) treated for 20 weeks with nifedipine (30 mg/kg/day) with those of 11 age-matched untreated SHRs. LVMM, LVMM related to end-diastolic volume (LVMM/EDV), LV pressure (PLV), systolic wall stress (Tsyst), ejection fraction (EF), cardiac index (CI), and isovolumetric contractility indices (dP/dtmax, IP, t-dP/dtmax, and VCE) were determined. Nifedipine treatment lowered PLV from 170 to 136 mm Hg and Tsyst from 222 to 194 10(3) dyn/cm2. LVMM and LVMM/EDV decreased moderately from 800 to 744 mg and from 2.56 to 2.29 mg/microliter, respectively. Left ventricular ejection was markedly increased (EF from 52 to 64%; CI from 154 to 178 ml/min X kg), whereas isovolumic contractility indices remained unchanged. Thus, nifedipine reduced but did not totally prevent myocardial hypertrophy and enhanced LV function. These effects seem to result from reduction in LV afterload and not from altered myocardial contractility.

Prevention of malignant hypertension in salt loaded "S" Dahl rats with the calcium antagonist nifedipine

Female "S" Dahl rats, fed an 8% NaCl diet from the 6th week of age developed malignant hypertension and heart hypertrophy in the course of 6 weeks on the salt regimen. Simultaneous treatment with nifedipine (300 ppm in diet additional to 8% NaCl) prevented the increase in blood pressure, reduced heart hypertrophy and mortality and improved the impaired renal function in "S" rats. The decrease in hematocrit in salt loaded "S" rats was prevented by nifedipine. The prophylactic effect of the calcium antagonist nifedipine is only partly due to the prevention of increase in systemic vascular resistance. In addition an improvement of failed intrarenal hemodynamics by nifedipine can be postulated. This enables the kidney of "S" rats to excrete the salt load without increasing blood pressure and plasma volume.