Repurposing a tricyclic antidepressant in tumor and metabolism disease treatment through fatty acid uptake inhibition.

Fatty acid uptake is essential for cell physiological function, but detailed mechanisms remain unclear. Here, we generated an acetyl-CoA carboxylases (ACC1/2) double-knockout cell line, which lacked fatty acid biosynthesis and survived on serum fatty acids and was used to screen for fatty acid uptake inhibitors. We identified a Food and Drug Administration-approved tricyclic antidepressant, nortriptyline, that potently blocked fatty acid uptake both in vitro and in vivo. We also characterized underlying mechanisms whereby nortriptyline provoked lysosomes to release protons and induce cell acidification to suppress macropinocytosis, which accounted for fatty acid endocytosis. Furthermore, nortriptyline alone or in combination with ND-646, a selective ACC1/2 inhibitor, significantly repressed tumor growth, lipogenesis, and hepatic steatosis in mice. Therefore, we show that cells actively take up fatty acids through macropinocytosis, and we provide a potential strategy suppressing tumor growth, lipogenesis, and hepatic steatosis through controlling the cellular level of fatty acids.

Carbon monoxide releasing molecule 401 (CORM-401) modulates phase I metabolism of xenobiotics.

Next to its well-studied toxicity, carbon monoxide (CO) is recognized as a signalling molecule in various cellular processes. Thus, CO-releasing molecules (CORMs) are of considerable interest for basic research and drug development. Aim of the present study was to investigate if CO, released from CORMs, inhibits cytochrome P450-dependent monooxygenase (CYP) activity and modulates xenobiotic metabolism. CORM-401 was used as a model CO delivering compound; inactive CORM-401 (iCORM-401), unable to release CO, served as control compound. CO release from CORM-401, but not from iCORM-401, was validated using the cell free myoglobin assay. CO-dependent inhibition of CYP activity was shown by 7-ethoxyresorufin-O-deethylation (EROD) with recombinant CYP and HepG2 cells. Upon CORM-401 exposure EROD activity of recombinant CYP decreased concentration dependently, while iCORM-401 had no effect. Treatment with CORM-401 decreased EROD activity in HepG2 cells at concentrations higher than 50 µM CORM-401, while iCORM-401 showed no effect. At the given concentrations cell viability was not affected. Amitriptyline was selected as a model xenobiotic and formation of its metabolite nortriptyline by recombinant CYP was determined by HPLC. CORM-401 treatment inhibited the formation of nortriptyline whereas iCORM-401 treatment did not. Overall, we demonstrate CO-mediated inhibitory effects on CYP activity when applying CORMs. Since CORMs are currently under drug development, the findings emphasize the importance to take into account that this class of compounds may interfere with xenobiotic metabolism.

Safety evaluation of topically applied amitriptyline in porcine full-thickness wounds.

BACKGROUND AND OBJECTIVES: The tricyclic antidepressant amitriptyline is frequently used in pain clinics for management of pain. It has also been suggested that topical application of amitriptyline could be useful for the treatment of neuropathic pain. In this report we investigated the effect of amitriptyline on porcine full thickness wounds resembling excised burn wounds. We assessed if daily topical application of amitriptyline into the wound chambers for 10 days impedes wound healing as measured by (1) wound contraction and (2) histopathological findings. METHODS: Full-thickness wounds measuring 1.5 cm square were created on the dorsum of Yorkshire pigs and were enclosed in polyurethane wound chambers. Amitriptyline was applied daily at various concentrations. Bupivacaine (0.5%) or normal saline were used as controls. Daily wound serum levels were obtained and the level of amitriptyline and nortriptyline obtained. Pictures were taken daily and the wound surface analyzed for contraction. Cross-sectional, full-thickness skin biopsies were obtained at days 2, 8 and 10 and evaluated microscopically for re-epithelialization, inflammation, and necrosis. RESULTS: The high serum level of amitriptyline and nortriptyline did not affect wound healing; re-epithelialization, wound contraction, and inflammation were not significantly different between amitriptyline and control groups. CONCLUSION: Amitriptyline at the concentrations of 0.0625% and 0.125% applied daily via chambers covering wounds in a full-thickness pig excision model has no overt toxic effect on wound healing as measured by wound contraction and histological assessment.

A simplified radioimmunoassay of plasma nortriptyline in depressed patients compared with high-pressure liquid chromatography and gas-liquid chromatography.

Antiserum to nortriptyline was generated in male New Zealand rabbits innoculated with n-succinylnortriptyline-bovine serum albumin conjugates. The antiserum was used at a final dilution of 1:4000 and tritiated imipramine was used as the label antigen. An accurate, sensitive, and specific radioimmunoassay of depressed patients' plasma or serum nortriptyline is described. The accuracy was good with a recovery range of 90-100% with a mean of 94%. The method can be used to measure nortriptyline concentration in the range of 0.1 microgram/liter to 100 micrograms/liter without prior extraction and purification of plasma or serum. Results of this method correlate well with those obtained by high-pressure liquid chromatography (r = 0.979) and by gas-liquid chromatography (r = 0.98). The specificity of the antiserum was examined by studying the cross-reactivity of 20 different psychopharmacological compounds, including nortriptyline's metabolites.

Slow hydroxylation of tricyclic antidepressants--relationship to polymorphic drug oxidation.

There are marked interindividual differences in Css of tricyclic antidepressants. These are due mainly to corresponding differences in the rate of oxidative metabolism of these drugs. Twin, family, and cross-over studies with nortriptyline (NT) and desmethylimipramine (DMI) show that their kinetics and hydroxylation (Css, Kel, and Vd) are controlled mainly by genetic factors (in drug-free individuals). Slow hydroxylators are at risk of developing excessive plasma concentrations of NT and DMI when given per se or when formed from the tertiary amines amitriptyline and imipramine. Classic antidepressants have fairly well established concentration-effect curves in endogenous depression. Severe toxicity usually occurs at supratherapeutic plasma levels and might be prevented by tailoring the dosage according to the individual's drug hydroxylating capacity. Monitoring drug plasma levels is particularly relevant in slow hydroxylators (Sjöqvist et al, 1980). There is a strong association between an individual's ability to hydroxylate NT and DMI and his debrisoquine (D) hydroxylation phenotype. The D hydroxylation index will predict the patient's capacity to hydroxylate NT and DMI and hence Css during therapy. Possibly, similar hydroxylases are involved in the 4-hydroxylation of debrisoquine, in the stereospecific E-10-hydroxylation of NT, and in the 2-hydroxylation of DMI. By contrast, demethylation of AT (and probably other tertiary tricyclics) does not significantly correlate to debrisoquine hydroxylation except in non-smoking individuals. The increasing knowledge about the clinical pharmacokinetics of tricyclic antidepressants is a distinct advantage over that of the new generation of antidepressants, where little is known about concentration-effect relationships and factors governing their rate of metabolism. Possible interethnic differences in the metabolism of these essential drugs should be explored in epidemiologically sound investigations.

Tricyclic plasma levels. Effect of age, race, sex, and smoking.

Steady-state plasma tricyclic antidepressant levels were determined in 65 patients undergoing treatment for depression with either amitriptyline hydrochloride or nortriptyline hydrochloride to determine if common factors such as age, race, sex, or smoking status were predictors of steady-state drug levels that have been shown to vary up to 36-fold. Evaluation of these factors did not disclose differences in the rate of demethylation of amitriptyline to nortriptyline, or steady-state tricyclic levels in the amitriptyline-treated patients. No differences were found in the nortriptyline-treated patients except regarding race. Black patients had significantly higher (50%) nortriptyline plasma levels than did white patients, which may explain the more rapid response to tricyclic treatment demonstrated in blacks. Decreased rates of nortriptyline metabolism in blacks can result in increased side effects and treatment failure if the therapeutic plasma range is exceeded.

Drug induced biogenesis of nitrosamines.

It has been demonstrated that potentially corcinogenic nitroso compounds are readily formed when certain widely used drugs with secondary alkylaminostructures (e.g. nortriptyline and fenfluramine) or drug metabolities with such structures (e.g. norpropoxyphene) are reacted with nitrite in dilute acid aqueous medium or in human gastric juice under simulated gastric conditions. The reactions occur so readily in vitro that new quantitative procedures for the determination of these drugs have been developed and based on these principles. The potential hazards associated with the long term clinical use of such drugs are discussed.