Oxidation of the ß-blocker propranolol by UV/persulfate: Effect, mechanism and toxicity investigation.

In this study, the degradation of propranolol (PRO) by UV/persulfate process was systematically investigated. Direct photolysis of PRO was limited due to its low quantum yield, while the PRO degradation efficiency can be greatly promoted by the combination of persulfate and UV irradiation. Radical scavenging tests showed that both SO4- and OH contributed to the removal of PRO, with SO4- playing a more important role. The degradation rate of PRO was improved by increasing the persulfate dose and initial solution pH consistent with pseudo-first-order reaction kinetics. The effects of common water constituents were species dependent. HCO3- and Cl- promoted PRO degradation. By contrast, NO3- and HA were found to inhibit PRO degradation. A total of nine degradation products were identified by LC/MS/MS, which mainly derived from the ring-opening attack on the naphthalene group or oxidation of the amino moiety by SO4- and OH. Finally, the toxicity of the reaction mixtures was also assessed using luminescent bacteria Vibrio fischeri, and the results indicated that UV/persulfate is capable of controlling the toxicity of PRO degradation.

Assessing the potential of pharmaceuticals and their transformation products to cause mutagenic effects: Implications for gene expression profiling.

The selection and prioritization of pharmaceuticals and their transformation products for evaluating effects on the environment and human health is a challenging task. One common approach is based on compounds (e.g., mixture composition, concentrations), and another on biology (e.g., relevant endpoint, biological organizational level). Both of these approaches often resemble a Lernaean Hydra-they can create more questions than answers. The present study embraces this complexity, providing an integrated approach toward assessing the potential effects of transformation products of pharmaceuticals by means of mutagenicity, estrogenicity, and differences in the gene expression profiles. Mutagenicity using the tk kinase assay was applied to assess a list of 11 priority pharmaceuticals, namely, atenolol, azithromycin, carbamazepine, diclofenac, ibuprofen, erythromycin, metoprolol, ofloxacin, propranolol, sulfamethoxazole, and trimethoprim. The most mutagenic compounds were found to be ß-blockers. In parallel, the photolabile pharmaceuticals were assessed for their mixture effects on mutagenicity (tk assay), estrogenicity (T47D- KBluc assay), and gene expression (microarrays). Interestingly, the mixtures were mutagenic at the µg/L level, indicating a synergistic effect. None of the photolysed mixtures were statistically significantly estrogenic. Gene expression profiling revealed effects related mainly to certain pathways, those of the p53 gene, mitogen-activated protein kinase, alanine, aspartate, and glutamate metabolism, and translation-related (spliceosome). Fourteen phototransformation products are proposed based on the m/z values found through ultra-performance liquid chromatography-tandem mass spectrometry analysis. The transformation routes of the photolysed mixtures indicate a strong similarity with those obtained for each pharmaceutical separately. This finding reinforces the view that transformation products are to be expected in naturally occurring mixtures. Environ Toxicol Chem 2016;35:2753-2764. © 2016 SETAC.

Enhancement of Fenton and photo-Fenton processes at initial circumneutral pH for the degradation of the ß-blocker metoprolol.

The need for acidification in the Fenton and photo-Fenton process is often outlined as one of its major drawbacks, thus in this work the acidification of the Metoprolol (MET) is avoided by the addition of resorcinol (RES), which is used to simulate model organic matter. The experiments were carried out at natural pH (6.2) with different Fe(2+) (1, 2.5, 5, and 10 mg/L) and H2O2 (25, 50, 125 and 150 mg/L) concentrations. The performance of MET and RES degradation was assessed along the reaction time. Working with the highest concentrations (5 and 10 mg/L of ferrous iron and 125 and 150 mg/L of H2O2) more than 90% of MET and RES removals were reached within 50 and 20 min of treatment, respectively, by Fenton process. However a low mineralization was achieved in both cases, likely, due to by-products accumulation. Regarding to photo-Fenton process, within 3 min with the highest iron and hydrogen peroxide concentrations, a complete MET degradation was obtained and 95% of RES conversion was achieved. Parameters such Total Organic Carbon, Chemical Oxygen Demand, and AOS were measured. Intermediates were identified and MET degradation path was proposed in the presence of resorcinol. Finally, a comparison between Fenton and photo-Fenton processes at acid pH and at initial circumneutral pH was discussed. The positive effect of RES on Fenton and photo-Fenton systems has been confirmed, allowing the work at circumneutral pH.

Ultraviolet light converts propranolol, a nonselective ß-blocker and potential lupus-inducing drug, into a proinflammatory AhR ligand.

UV light and some medications are known to trigger lupus erythematosus (LE). A common mechanism underlying the immunopathologic effect, resulting from exposure to these two seemingly unrelated factors, remains unknown. The aryl hydrocarbon receptor (AhR) plays a key role in the regulation of IL-22 production in humans and can be activated by both xenobiotics and naturally occurring photoproducts. A significant expansion of Th17 and Th22 cells was observed in the peripheral blood of active systemic LE (SLE) patients, compared to inactive patients and controls. We also show that propranolol, a potential lupus-inducing drug, induced stronger AhR activation in PBMCs of SLE patients than in those of controls. AhR agonist activity of propranolol was enhanced by UV light exposure. MS analysis of irradiated propranolol revealed the generation of a proinflammatory photoproduct. This compound behaves like the prototypic AhR ligand 6-formylindolo[3,2-b]carbazole, a cutaneous UV light-induced tryptophan metabolite, both promoting IL-22, IL-8, and CCL2 secretion by T-cells and macrophages. Finally, LE patients exhibit signs of cutaneous AhR activation that correlate with lesional expression of the same proinflammatory cytokines, suggesting a role for photometabolites in the induction of skin inflammation. The AhR might therefore represent a target for therapeutic intervention in LE.

Photodegradation kinetics, products and mechanism of timolol under simulated sunlight.

The photodegradation of ß-blocker timolol in fulvic acid (FA) solution was investigated under simulated sunlight. The triplet excited state of FA ((3)FA(*)) and singlet oxygen ((1)O2) were the main reactive species responsible for the degradation of timolol in the aerated FA solutions. Both dissolved oxygen and iodide ions (I(-)) are the efficient quenchers of (3)FA(*). The photodegradation was drastically accelerated after removing the dissolved oxygen. The presence of I(-) inhibited the photosensitized degradation of timolol in the deoxygenated FA solutions, whereas the role of I(-) in the reaction was concentration-dependent in the aerated solutions. The other halide ions such as chloride (Cl(-)) and bromide (Br(-)) exhibited less effect on the photodegradation of timolol in both aerated and deoxygenated solutions. By LC-DAD/ESI-MS/MS analysis, the photoproducts of timolol in both aerated and deoxygenated FA solutions were identified. Electron transfer interaction occurred between (3)FA(*) and amine moiety of timolol, leading to the cleavage of C-O bond in the side chain and oxidation of the hexatomic ring. These findings suggest the photosensitized degradation was a significant pathway for the elimination of timolol in natural waters.

The effect of ionizing radiation on metoprolol.

The influence of ionising radiation on physico-chemical properties of metoprolol tartrate (MT) in solid phase was studied. The compound was irradiated by radiation produced by a beam of high-energy electrons in an accelerator, in doses from 25 to 400 kGy, and the possible changes in the samples were detected by organoleptic analysis (colour, forms, clarity), chromatographic and spectrometric methods. Already at the standard sterilisation dose of 25 kGy, the presence of free radicals (0.3764 × 10(16) spin/g) and a decrease in the melting point by 1°C were noted. At higher doses of irradiation products of radiolysis appeared (100 kGy) and the colour was changed from white to pale cream (200 kGy). Our observation was that with increasing mass loss of MT after irradiation with 100, 200 and 400 kGy, the concentration of free radicals increased from 1.0330 to 1.6869 × 10(16) spin/g. The radiolytic yield of total radiolysis was 4.54 × 10(7) mol/J for 100 kGy, 7.42 × 10(7) mol/J for 200 kGy and 4.74 × 10(7) mol/J for 400 kGy. No significant changes were observed in the character of FT-IR spectra, but in UV an increase in intensity of the band at the analytical wavelength was noted. As follows from the results MT shows high radiochemical stability for the typical sterilisation doses 25-50 kGy, and will probably be able to be sterilised by radiation in the dose of 25 kGy.

UV-C radiation based methods for aqueous metoprolol elimination.

The endocrine disruptor metoprolol has been oxidised in aqueous solution by means of the systems UV-C, UV-C/H(2)O(2), UV-C/percarbonate, UV-C/monopersulfate, UV-C/TiO(2), UV-C/H(2)O(2)/TiO(2) and photo-Fenton. From simple photolysis experiments the quantum yield of metoprolol has been calculated (roughly 5x10(-3) mol Einstein(-1) at circumneutral pH). Addition of free radicals promoters significantly enhanced the metoprolol depletion rate. Mineralization degree was negligible when no promoter was added, while low values were achieved in the presence of either inorganic peroxides or titanium dioxide. The combination of radiation, hydrogen peroxide and TiO(2) increased the mineralization level up to values in the proximity of 45-50% under the best conditions investigated. The photo-Fenton process was the best system in terms of total oxidation (mineralization degree 70%) when optimum conditions were applied.

Photodegradation products of propranolol: the structures and pharmacological studies.

Recently, single-dose drug packaging systems, allowing the administration of multiple drugs in a single pill, have become popular for the convenience of the patient. The quality of drugs and an accurate measurement of their photostabilities within this system, however, have not been carefully addressed. Drugs that are unstable in light should be carefully handled to protect their potency and ensure their safety. Propranolol (1), a beta-adrenergic receptor antagonist, is widely used for angina pectoris, arrhythmia, and hypertension. Due to its naphthalene skeleton, this drug may be both light unstable and a photosensitizing agent. In this study, we isolated three photodegraded products of propranolol (1): 1-naphthol (2), N-acetylpropranolol (3), and N-formylpropranolol (4). The structures of these compounds were determined by spectroscopic methods and chemical syntheses. We also examined the acute toxicities of these substances in mice and their binding to beta-adrenergic receptors using rat cerebellum cortex membranes. Although the photoproducts isolated in this study did not exhibit any acute toxicity or significant binding to beta-adrenergic receptors, these results serve as a warning to single-dose packaging systems, as propranolol (1) must be handled carefully to protect the compound from light-induced degradation.

HPLC detection and quantification of radiolytic products of eight beta-blockers irradiated in the solid state and hypotheses on their origins.

PURPOSE: The radiolytic products of eight beta-blockers were studied in order to understand the mechanisms of irradiation of drugs in the solid state. METHODS: The drugs were analyzed by high-performance liquid chromatography coupled to a diode array detector in order to observe the degradation of the main compound after irradiation and in order to study the nonvolatile final products on more concentrated solutions of irradiated drugs. RESULTS: The first test assessed that the main compound was not significantly degraded after gamma irradiation for any of the eight beta-blockers. A more complete study, which consisted on separating the nonvolatile products and on quantifying them, indicated first that the radiolytic products could reach the number of 14 and moreover that some could exceed the 0.1% threshold at 30 kGy. Eventually, radiolytic yields were compared with radical yields previously determined. CONCLUSIONS: The sensitivity of the first test can be discussed. It seems that, to study the feasibility of the radiosterilization, a complete study of the products of degradation is needed. Moreover, no correlation between radical and final products could be established, which denies that the former would be the precursors of the latter.

The use of multi-frequency EPR techniques to identify the radicals produced in irradiated beta-blockers.

The identification of radicals trapped in irradiated drugs can be very intricate. A multi-frequency electron paramagnetic resonance (EPR) study is proposed to resolve this problem. The Q-band (ca. 34 GHz) comparison with X-band (ca. 9 GHz) did not show significant differences for the four beta-blockers studied (atenolol, esmolol, nadolol and propranolol). The use of a higher frequency (285 GHz) was required. It enabled us to determine the g-tensor values of the radicals present in atenolol and esmolol, respectively, g1 = 2.0086, g2 = 2.0059 and g3 = 2.0021 and g1 = 2.0066, g2 = 2.0044 and g3 = 2.0021. The latter was assigned as a phenoxyl radical, which can not be the case for the former. Therefore, radicals produced in esmolol may result from a more complex mechanism than the abstraction followed by the diffusion of an H atom inside the solid. In addition, two molecules as similar as atenolol and esmolol hydrochloride do not contain the same radicals after irradiation. These two conclusions drawn from the EPR results on beta-blockers show clearly the importance of continuing the investigations on radiolytic mechanisms in solid-state drugs.

Determination of radical yields in solid-state drugs as one technique to identify drugs that will withstand radiosterilization: radioresistance of beta blockers.

This article describes a simple preliminary test to determine whether a drug is sufficiently radioresistant to withstand radiosterilization. The test is based on the electron spin resonance (ESR) detection of radicals produced after irradiation of a solid-state drug, assuming that these radicals are the precursors of the final products detected after dissolution of the drug. A calibration curve has therefore been established by measuring ESR spectra of l-alanine irradiated at different doses. The response factor to quantify the radicals is the normalized double integration (DI) of the whole first-derivative ESR spectrum. The curve gives the relationship between the normalized DI and the number of radicals. Eight beta blockers have been chosen and their radical yield determined. This is the first time that several different drugs of the same pharmacological group have been studied and compared. The results obtained are similar for seven of the eight beta blockers; the mean G value (excepted for nadolol) is 3 x 10(-9) mol/J. This means that beta blockers are radioresistant. The two most radiosensitive drugs (nadolol and esmolol hydrochloride) were also studied by high-performance liquid chromatography (HPLC). No significant loss of the active compound was detected, which confirms this radioresistant property. Moreover, no change in color or smell was observed. Using ESR and HPLC, beta blockers were identified as potential candidates for radiosterilization.

Radical mechanisms in the radiosterilization of metoprolol tartrate solutions.

PURPOSE: Study of the radical mechanisms in the radiosterilization of metoprolol tartrate aqueous solutions in order to determine the parameters governing its radiostability. METHODS: Pulse radiolysis with pseudo-first-order kinetics to measure Ihe reaction rate constants of hydrated electrons and hydroxyl radicals with metoprolol tartrate. Chemsimul was used to solve the decay kinetics of transients and to simulate the radiolysis of metoprolol tartrate solutions. RESULTS: Hydrated electrons react with metoprolol and the tartrate ion with rate constants of 6.8 x 10(7) M(-1) s(-1) and 1.7 x 10(7) M(-1) s(-1), respectively. Hydroxyl radicals react with metoprolol and the tartrate ion with rate constants of 5.2 x 10(9) M(-1) s(-1) and 5.5 x 10(8) M(-1) s(-1), respectively. The hydroxyl-metoprolol transients are found to scavenge the superoxide anion (5.5 x 10(10) M(-1) s(-1)), react with oxygen (1.0 x 10(8) M(-1) s(-1)), and follow a biradical decay (2.0 x 10(8) M(-1) s(-1). A simplified radical mechanism is used to simulate the loss of potency of metoprolol tartrate aqueous solutions during radiosterilization. CONCLUSIONS: To decrease the loss of potency of metoprolol tartrate. the sterilization dose must be lowered and very high dose rates used.

Singlet molecular oxygen generation and quenching by the antiglaucoma ophthalmic drugs, Timolol and Pindolol.

The dye sensitized photooxidation in water (pH 6), of the pharmaceutical topical antiglaucoma drugs, Timolol and Pindolol, which act as beta-adrenergic receptor antagonists, were studied by means of static and time-resolved spectroscopic methods and polarographic determinations. O2(1delta(g))-mediated photooxidation of Timolol and Pindolol takes place with quantum efficiencies of 0.035 and 0.16, respectively, which raises concern about the possible daylight-mediated photodamaging of the drugs, in the presence of sensitizing agents. Pindolol behaves kinetically as a typical indole derivative, for which the intermediacy of a polar complex is proposed. Solvent effects on the kinetics of photooxidation suggests that the same mechanism could operate for the case of Timolol. Upon direct ultraviolet-light irradiation Timolol and Pindolol generate O2(1delta(g)), with quantum yields of 0.027 and 0.11 respectively. The former comprises three desirable properties for an external-use ocular drug: a reduced efficiency of O2(1delta(g)) photooxidation, a relatively high power as O2(1delta(g)) physical deactivator and a relatively low propensity to O2(1delta(g)) generation upon direct light irradiation.

Studies on the photostability and in vitro phototoxicity of Labetalol.

The purpose of this study was to obtain information on the photochemical and phototoxic properties of Labetalol, a beta-blocker drug. Preliminary information on the drug photoreactivity was achieved using a flow system with a photochemical reactor on-line with a diode array detection system. Photophysical and photochemical investigations on the drug were performed in aqueous solutions at different pH values using spectrophotometric and fluorimetric methods; the photodegradation quantum yield was found to be 2.7 x 10(-3) at pH 5.8 and 1.5 x 10(-2) at pH 11.5. Forced photodegradation of labetalol solutions under exposure to UVA--UVB radiations (xenon arc lamp) was monitored by reversed-phase liquid chromatography. The main photodegradation products were isolated and characterized by NMR and mass spectrometry; labetalol was found to give 3-amino-1-phenylbutane and salicylamide-4-carboxaldehyde as the main photoproducts. Preliminary phototoxic testings on human keratinocyte cultures were performed evaluating the viability of the cells by the neutral-red uptake assay; mutagenic and photomutagenicity tests were also carried out based on Salmonella typhimurium strains. As a result, labetalol was found to be photolabile,mainly in alkaline medium, but evidences of significant phototoxic and photomutagenic effects by the drug were not observed.