Stability and uptake of methylphenidate and ritalinic acid in nine-spine stickleback (Pungitius pungitius) and water louse (Asellus aquaticus)

Bioconcentration of carbamazepine, enalapril, and sildenafil in neotropical fish species

Sewage effluents are the main source of entry of Human Pharmaceutical Active Ingredients (HPAIs) to surface water bodies. Carbamazepine (CBZ), psychiatric drug, enalapril (ENA) antihypertensive, and sildenafil (SIL), to treat erectile dysfunction, have been frequently detected in receiving wastewater and in wild fish species from Argentina. This study aimed to assess the bioconcentration of selected HPAIs in native fish species of the Del Plata Basin. In a first trial, the bioconcentration factors of CBZ, ENA, and SIL were obtained by exposing Cnesterodon decemmaculatus, respectively, to 135, 309, and 70 μg/L during 96 h. Then the bioconcentration kinetic of SIL was comparatively assessed in C. decemmaculatus and Piaractus mesopotamicus exposed, respectively, to 44.1 and 16.2 μg/L during a one-week, followed by a four-day depuration phase. HPAIs concentrations in water and tissue were measured by HPLC-MS after 0.22 μm filtration and direct injection or solid-liquid extraction, respectively. Bioconcentration factors obtained empirically (BCFe) for C. decemmaculatus were CBZ = 1.5, SIL = 1.4, and ENA = 0.007. Parameters estimated by the SIL bioconcentration kinetic model for C. decemmaculatus were: uptake rate constant (k1) = 5.5 L/kg d, elimination rate constant during uptake phase (k2u) = 0.00175 d-1, maximum predicted tissue concentration (Ct(max)) = 138588 μg/kg, estimated bioconcentration factor (BCFm) = 3143, lag time between the exposure and the first detection in tissue (tlag) = 0 d, elimination rate constant in the depuration phase (k2d) = 0.49 d-1 and half-life in the tissue (t1/2) = 1.4 d. The model parameters for P. mesopotamicus were k1: 7.3 L/kg d, k2u: 0.0836 d-1, Ct(max): 1423 μg/kg, BCFm: 88, tlag: 3.8 d in the uptake phase and k2d: 0.31 d-1 and t1/2: 2.3 d in the depuration phase. The reached conclusions were: 1) the bioconcentration capacity of CBZ and SIL are similar but around 200 times higher than ENA, 2) the time to reach the bioconcentration equilibrium for SIL is longer than 1 week, then estimated BCFm are between 1 and 3 orders of magnitude higher than BCFe obtained after 96 h exposure, but actual values need to be verified, 3) substantial differences (≈30 fold) were observed in the estimated BCF of SIL among species, indicating the need for further studies toward understanding such diversity to improve HPAIs ecological risk assessment worldwide.

Bioconcentration of neuroactive pharmaceuticals in fish: Relation to lipophilicity, experimental design and toxicity in the aquatic environment

Uptake of contaminants is linked to their toxicity and is usually estimated through their lipophilicity (logK_ow). Here, we review current literature regarding bioconcentration, i.e. uptake of contaminants from the external environment only, and the effects of exposure to neuroactive pharmaceuticals in fish. We aim to determine if lipophilicity is a suitable predictor of bioconcentration of these compounds in fish, to identify major drivers of bioconcentration and explore the link between bioconcentration potential and toxicity, focusing on survival, growth, condition, behaviour and reproduction endpoints. Additionally, we compare concentrations known to elicit significant effects in fish with current environmental concentrations, identifying exposure risk in ecosystems. The majority of studies have focused on antidepressants, mainly fluoxetine, and encompasses mostly freshwater species. Few studies determined pharmaceuticals bioconcentration, and even a smaller portion combined bioconcentration with other toxicity endpoints. Results show that lipophilicity isn't a good predictor of neuroactive pharmaceuticals' bioconcentration in fish, which in turn is highly influenced by experimental parameters, including abiotic conditions, species and life-stage. The need for increased standardization of experimental settings is key towards improving accuracy of environmental risk assessments and application in future regulatory schemes. Still, increased fish lethality was linked to increased bioconcentration, yet no other correlations were observed when considering effects on growth, condition, behaviour or reproduction, likely as a result of insufficient and variable data. In the context of current environmental concentrations, several neuroactive pharmaceuticals were found to be potentially threatening, while data on occurrence is lacking for some compounds, particularly in brackish/marine systems. Specifically, nine compounds (fluoxetine, citalopram, sertraline, amitriptyline, venlafaxine, clozapine, carbamazepine, metamfetamine and oxazepam) were found at concentrations either above or critically close to minimum response concentrations, thus likely to affect fish in freshwater and brackish or marine environments, which supports further exploration in risk management strategies and monitoring programs in aquatic environments.

Stability of Methylphenidate under Various pH Conditions in the Presence or Absence of Gut Microbiota

Methylphenidate is one of the most widely used oral treatments for attention-deficit/hyperactivity disorder (ADHD). The drug is mainly absorbed in the small intestine and has low bioavailability. Accordingly, a high interindividual variability in terms of response to the treatment is known among ADHD patients treated with methylphenidate. Nonetheless, very little is known about the factors that influence the drug's absorption and bioavailability. Gut microbiota has been shown to reduce the bioavailability of a wide variety of orally administered drugs. Here, we tested the ability of small intestinal bacteria to metabolize methylphenidate. In silico analysis identified several small intestinal bacteria to harbor homologues of the human carboxylesterase 1 enzyme responsible for the hydrolysis of methylphenidate in the liver into the inactive form, ritalinic acid. Despite our initial results hinting towards possible bacterial hydrolysis of the drug, up to 60% of methylphenidate is spontaneously hydrolyzed in the absence of bacteria and this hydrolysis is pH-dependent. Overall, our results indicate that the stability of methylphenidate is compromised under certain pH conditions in the presence or absence of gut microbiota.

Nootropic drugs: Methylphenidate, modafinil and piracetam - Population use trends, occurrence in the environment, ecotoxicity and removal methods - A review

Pharmaceuticals which originally were designed to treat people with neurological and psychiatric conditions, e.g. Alzheimer's disease or attention deficit hyperactivity disorder (ADHD), are nowadays often misused by students as a 'brain doping' substances. These substances are known as nootropic drugs, smart drugs or cognitive enhancers, as they increase memory, attention and concentration of healthy individuals. Since they are easily available illicitly, their consumption is observed to be growing. Currently, these pharmaceuticals started gaining researchers' attention, especially since they have been recently detected in wastewater, surface water and even drinking water. This review summarises the current state of knowledge on nootropic drugs in terms of their population use trends and ethics, occurrence in the environment and detection techniques, toxicity and removal methods, in example of methylphenidate, modafinil and piracetam - three most popular nootropics. It points out that the main sources of knowledge on cognitive enhancers illicit use are often inconsistent questionnaires, which are not supported by wastewater analysis to become more veracious. Simultaneously, the studies concerning toxicity and removal methods of nootropic drugs are still limited and in many cases environmentally irrelevant. Although the prescription rules has been subjected to more strict control in developed countries, regulatory frameworks with regard to their ecosystem occurrence are still lacking and should be introduced. Moreover, the use of environmentally relevant concentrations in toxicity studies should be a standard, leading to proper ecotoxicity risk assessment. Based on this review, it is recommended to routinely monitor nootropics and their metabolites in waste- and surface waters.