No abstract

The increasing levels and frequencies at which active pharmaceutical ingredients (APIs) are being detected in the environment are of significant concern, especially considering the potential adverse effects they may have on nontarget species such as fish. With many pharmaceuticals lacking environmental risk assessments, there is a need to better define and understand the potential risks that APIs and their biotransformation products pose to fish, while still minimizing the use of experimental animals. There are both extrinsic (environmentand drug-related) and intrinsic (fish-related) factors that make fish potentially vulnerable to the effects of human drugs, but which are not necessarily captured in nonfish tests. This critical review explores these factors, particularly focusing on the distinctive physiological processes in fish that underlie drug absorption, distribution, metabolism, excretion and toxicity (ADMET). Focal points include the impact of fish life stage and species on drug absorption (A) via multiple routes; the potential implications of fish's unique blood pH and plasma composition on the distribution (D) of drug molecules throughout the body; how fish's endothermic nature and the varied expression and activity of drug-metabolizing enzymes in their tissues may affect drug metabolism (M); and how their distinctive physiologies may impact the relative contribution of different excretory organs to the excretion (E) of APIs and metabolites. These discussions give insight into where existing data on drug properties, pharmacokinetics and pharmacodynamics from mammalian and clinical studies may or may not help to inform on environmental risks of APIs in fish.

Over the past few years, great progress has been made in the development of high-affinity adenosine A 1 and/or A 2A receptor antagonists-promising agents for the potential treatment of Parkinson's disease. Unfortunately, many of these compounds raise structure-related concerns. The present study investigated the effect of ring closures on the rA 1 /A 2A affinity of compounds containing a highly reactive α,βunsaturated carbonyl system, hence providing insight into the potential of heterocycles to address these concerns. A total of 12 heterocyclic compounds were synthesised and evaluated in silico and in vitro. The test compounds performed well upon qualitative assessment of drug-likeness and were generally found to be free from potentially problematic fragments. Most also showed low/ weak cytotoxicity. Results from radioligand binding experiments confirm that heterocycles (particularly 2-substituted 3-cyanopyridines) can replace the promiscuous α,βunsaturated ketone functional group without compromising A 1 / A 2A affinity. Structure-activity relationships highlighted the importance of hydrogen bonds in binding to the receptors of interest. Compounds 3c (rA 1 K i = 16 nM; rA 2A K i = 65 nM) and 8a (rA 1 K i = 102 nM; rA 2A K i = 37 nM), which both act as A 1 antagonists, showed significant dual A 1 /A 2A affinity and may, therefore, inspire further investigation into heterocycles as potentially safe and potent adenosine receptor antagonists.

The affiliation of the authors (C. Matthee and H.D. Janse van Rensburg) has been published incorrectly in the original publication. The correct affiliation of authors is updated in this correction.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.