Species differences and human relevance of the toxicity of 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors and a new approach method in vitro for investigation.

The mode of action (MoA) of the 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor herbicides in mammals is well described and is generally accepted to be due to a build-up of excess systemic tyrosine which is associated with the range of adverse effects reported in laboratory animals. What is less well accepted is the basis for the marked difference in the effects of HPPD inhibitors that has been observed across experimental species and humans, where some species show significant toxicities whereas in other species exposure causes few effects. The activity of the catabolic enzyme tyrosine aminotransferase (TAT) varies across species including humans and it is hypothesized that this primarily accounts for the different levels of tyrosinemia observed between species and leads to the subsequent differences in toxicity. The previously reported activities of TAT in different species showed large variation, were inconsistent, have methodological uncertainties and could lead to a reasonable challenge to the scientific basis for the species difference in response. To provide clarity, a new method was developed for the simultaneous and systematic measurement of TAT in vitro using robust methodologies in a range of mammalian species including human. The results obtained showed general correlation between high TAT activity and low in vivo toxicity when using a model based on hepatic cytosol and a very convincing correlation when using a primary hepatocyte model. These data fully support the role of TAT in explaining the species differences in toxicity. Moreover, this information should give greater confidence in selecting the most appropriate animal model (the mouse) for human health risk assessment and for key classification and labeling decision-making.

Using historical control data in bioassays for regulatory toxicology.

Historical control data (HCD) consist of pooled control group responses from bioassays. These data must be collected and are often used or reported in regulatory toxicology studies for multiple purposes: as quality assurance for the test system, to help identify toxicological effects and their effect-size relevance and to address the statistical multiple comparison problem. The current manuscript reviews the various classical and potential new approaches for using HCD. Issues in current practice are identified and recommendations for improved use and discussion are provided. Furthermore, stakeholders are invited to discuss whether it is necessary to consider uncertainty when using HCD formally and statistically in toxicological discussions and whether binary inclusion/exclusion criteria for HCD should be revised to a tiered information contribution to assessments. Overall, the critical value of HCD in toxicological bioassays is highlighted when used in a weight-of-evidence assessment.

Stratified prokaryote network in the oxic-anoxic transition of a deep-sea halocline.

The chemical composition of the Bannock basin has been studied in some detail. We recently showed that unusual microbial populations, including a new division of Archaea (MSBL1), inhabit the NaCl-rich hypersaline brine. High salinities tend to reduce biodiversity, but when brines come into contact with fresher water the natural haloclines formed frequently contain gradients of other chemicals, including permutations of electron donors and acceptors, that may enhance microbial diversity, activity and biogeochemical cycling. Here we report a 2.5-m-thick chemocline with a steep NaCl gradient at 3.3 km within the water column betweeen Bannock anoxic hypersaline brine and overlying sea water. The chemocline supports some of the most biomass-rich and active microbial communities in the deep sea, dominated by Bacteria rather than Archaea, and including four major new divisions of Bacteria. Significantly higher metabolic activities were measured in the chemocline than in the overlying sea water and underlying brine; functional analyses indicate that a range of biological processes is likely to occur in the chemocline. Many prokaryotic taxa, including the phylogenetically new groups, were confined to defined salinities, and collectively formed a diverse, sharply stratified, deep-sea ecosystem with sufficient biomass to potentially contribute to organic geological deposits.

Long-term tolerability of benazepril in dogs with congestive heart failure.

OBJECTIVES: To test the tolerability of long-term administration of benazepril in dogs with congestive heart failure (CHF). METHODS: The study was a prospective, randomized, double-blinded, placebo-controlled clinical trial. A total of 162 dogs with New York Heart Association (NYHA) class II-IV heart failure caused by chronic valvular disease (CVD) or dilated cardiomyopathy (DCM) were enrolled. Benazepril (minimum dosage, 0.25 mg/kg) or placebo were administered orally once daily for up to 34 months. In this paper, we report results of plasma alanine aminotransferase (ALT), creatinine, potassium and urea. RESULTS: The two groups were matched at baseline (p>/=0.18). Plasma creatinine concentrations were lower during treatment with benazepril versus placebo for all dogs (p=0.14) and every sub-group tested (NYHA II, III or IV; CVD; DCM; initial creatinine >124 mumol/L), although statistical significance was not reached (p=0.14-0.6). However, significantly (p=0.035) more cases of creatinine >124 mumol/L during treatment occurred with placebo (47%) as compared to benazepril (30%). Plasma ALT and urea values did not differ between groups for all dogs (p>0.5) or any sub-group (p=0.23-1.0). Plasma potassium values did not differ between groups for all dogs (p>0.5). Although differences approached statistical significance for potassium in some sub-groups (p=0.07-0.1), there were no consistent differences between groups. CONCLUSIONS: Benazepril was well tolerated during long-term therapy in dogs with CHF and no specific precautions appear to be necessary regarding plasma ALT, creatinine, potassium or urea. The possible action of benazepril in improving renal function (evidenced via lower plasma creatinine) merits further investigation.