"Much ado about nothing": monoamine oxidase inhibitors, drug interactions, and dietary tyramine

Testosterone Replacement Therapy in the Treatment of Depression

BACKGROUND

Depression is a common disorder that affects millions globally and is linked to reduced quality of life and mortality. Its pathophysiology is complex and there are several forms of treatment proposed in the literature with differing side effect profiles. Many patients do not respond to treatment which warrants augmentation with other treatments and the investigation of novel treatments. One of these treatments includes testosterone therapy which evidence suggests might improve depressed mood in older patients with low levels of testosterone and helps restore physical impairments caused by age-related hormonal changes.

OBJECTIVE

The objective of this review is to synthesize information regarding clinical depression, its treatment options, and the efficacy and safety of testosterone treatment for the treatment of depression.

METHODS

This review utilized comprehensive secondary and tertiary data analysis across many academic databases and published work pertaining to the topic of interest.

RESULTS

Within some subpopulations such as men with dysthymic disorder, treatment resistant depression, or low testosterone levels, testosterone administration yielded positive results in the treatment of depression. Additionally, rodent models have shown that administering testosterone to gonadectomized male animals reduces symptoms of depression. Conversely, some studies have found no difference in depressive symptoms after treatment with testosterone when compared with placebo. It was also noted that over administration of testosterone is associated with multiple adverse effects and complications.

CONCLUSION

The current evidence provides mixed conclusions on the effectiveness of testosterone therapy for treating depression. More research is needed in adult men to see if declining testosterone levels directly influence the development of depression.

The trace amine theory of spontaneous hypertension as induced by classic monoamine oxidase inhibitors

The classic monoamine oxidase inhibitors (MAOIs) tranylcypromine (TCP) and phenelzine (PLZ) are powerful antidepressants that come with an equally powerful stigma, and are thus rarely prescribed-despite their well-established effectiveness. Some of these preconceptions appear to stem from unclarity, as the etiology of a rare but important side effect, 'spontaneous hypertension' (SH)-a significant increase in blood pressure absent dietary tyramine ingestion-remains improperly elucidated. This paper aims at uprooting some of the stigma surrounding MAOIs by advancing the trace amine (TA) theory as the causative underpinning of SH. This theory posits that SH results from the considerable influx of TAs observed following TCP- or PLZ-administration. TAs are known, albeit at greatly supraphysiological levels, to raise blood pressure on account of their propensity to exert potent indirect sympathomimetic effects; additionally, some research posits that TAs may induce vasoconstrictive effects partly or wholly separate therefrom, which would then constitute a second hypertensive mechanism. TAs are endogenous to the human body in low quantities. Both TCP and PLZ cause marked elevations of 2-phenylethylamine (PEA), meta- and para-tyramine (m-/p-TYR), octopamine (OA), and tryptamine (TRYP), following both acute and (sub)chronic administration. This paper holds that TYR plays a pivotal role in causing SH, due to its strong pressor effect. Cautious treatment of SH is advised, given its typically self-limiting nature. The risk of hypotensive overshoots must be taken into account. For severe cases, this paper urges reconsideration, following suitable confirmation trials, of antipsychotics (notably risperidone) as these agents may reduce striatal p-TYR levels.

Selected Food/Herb-Drug Interactions: Mechanisms and Clinical Relevance

BACKGROUND

Food/Herb-drug interactions have become a major problem in health care. These interactions can lead to loss of therapeutic efficacy or toxic effects of drugs.

AREAS OF UNCERTAINTY

To probe the clinical relevance of such interactions, the impact of food/herb intake on the clinical effects of drug administration has to be evaluated. Failure to identify and efficiently manage food-drug interactions can lead to serious consequences. A comprehensive knowledge of the mechanisms that underpin variability in disposition will help optimize therapy.

DATA SOURCES

Electronic search of literatures from relevant databases were conducted. A total of 58 original scientific reports/review articles were obtained with the search strategy; of which 25 were found eligible to be included in the present review. Required data were extracted from these studies, and their methodologies were assessed.

RESULTS AND CONCLUSIONS

This review updates our knowledge on clinical food-drug interactions with emphasis on mechanism and clinical implications. Results obtained from literature search identified interactions with selected foods/herbs generated from in vivo and in vitro studies. For example, interaction studies in humans revealed a reduction in the bioavailability of mercaptopurine when taken concurrently with substances containing xanthine oxidase (eg, cow milk); a reduction in the bioavailability of quinine with Garcinia kola; increased bioavailability/toxicity of felodipine, nifedipine, saquinavir, sildenafil with grape juice; increased bioavailability of felodipine, cisapride with red wine and diminished bioavailability of fexofenadine with apple. Pharmacokinetic and/or pharmacodynamic mechanisms are implicated in many of these interactions. By evaluating the dietary patterns of patients and use of prescribed medications, health professionals will be well informed of potential interactions and associated adverse effects.

A reassessment of the safety profile of monoamine oxidase inhibitors: elucidating tired old tyramine myths

This review appraises over 150 recent original papers reporting data that demonstrate the greatly reduced tyramine content of modern-day 'foods', about which the medical literature has a paucity of information. It discusses the cardiovascular pharmacology of tyramine and the characteristics, extent, risks, and treatment of the blood pressure increases that sometimes result from tyramine ingestion (the pressor response). In past decades, cheese was the only food associated with documented fatalities resulting from hypertension. Today, few foods contain problematically high tyramine levels, which is a result of changes in international food production techniques (especially the use of starter cultures), and hygiene regulations. Nowadays, even 'matured' cheeses are usually safe in healthy-sized portions. The mechanism by which tyramine may be produced in foods (by certain micro-organisms) is explained and hundreds of recent estimations of cheeses are reviewed. Numerous other previously inadequately documented foods are reviewed, including fish and soy sauces, salami-type sausages, dried meats, beers, wines, and various condiments. Evidence that the risk of harm from the pressor response has previously been overstated is reviewed, and the iatrogenic harms from hasty and aggressive treatment of hypertensive urgency are re-evaluated. Evidence now suggests that MAOIs are of comparable safety to many newer drugs and are straightforward to use. Previously held concerns about MAOIs are misplaced and some are of over-estimated consequence. The variability of pressor sensitivity to tyramine between individuals means that the knowledge and judgement of doctors, and some care, are still required.

Mechanisms of the antilipolytic response of human adipocytes to tyramine, a trace amine present in food

Tyramine is found in foodstuffs, the richest being cheeses, sausages, and wines. Tyramine has been recognized to release catecholamines from nerve endings and to trigger hypertensive reaction. Thereby, tyramine-free diet is recommended for depressed patients treated with irreversible inhibitors of monoamine oxidases (MAO) to limit the risk of hypertension. Tyramine is a substrate of amine oxidases and also an agonist at trace amine-associated receptors. Our aim was to characterize the dose-dependent effects of tyramine on human adipocyte metabolic functions. Lipolytic activity was determined in adipocytes from human subcutaneous abdominal adipose tissue. Glycerol release was increased by a fourfold factor with classical lipolytic agents (1 μM isoprenaline, 1 mM isobutylmethylxanthine) while the amine was ineffective from 0.01 to 100 μM and hardly stimulatory at 1 mM. Tyramine exhibited a partial antilipolytic effect at 100 μM and 1 mM, which was similar to that of insulin but weaker than that obtained with agonists at purinergic A1 receptors, α₂-adrenoceptors, or nicotinic acid receptors. Gi-protein blockade by Pertussis toxin abolished all these antilipolytic responses save that of tyramine. Indeed, tyramine antilipolytic effect was impaired by MAO-A inhibition. Tyramine inhibited protein tyrosine phosphatase activities in a manner sensitive to ascorbic acid and amine oxidase inhibitors. Thus, millimolar tyramine restrained lipolysis via the hydrogen peroxide it generates when oxidized by MAO. Since tyramine plasma levels have been reported to reach 0.2 μM after ingestion of 200 mg tyramine in healthy individuals, the direct effects we observed in vitro on adipocytes could be nutritionally relevant only when the MAO-dependent hepato-intestinal detoxifying system is overpassed.