Abstract
Polyamines are small polycationic alkylamines involved in many fundamental cellular processes, including proliferation, nucleic acid synthesis, apoptosis, and protection from oxidative damage. It has been proposed that in addition to these functions, elevated levels of polyamines promote longevity in various biological systems, including yeast, Drosophila, and murine models. A series of in vitro mechanistic studies by multiple investigators has led to the conclusion that addition of exogenous spermidine promotes longevity through autophagy induction; however, these experiments were confounded by the use of mammalian cell culture systems supplemented with fetal bovine serum. Using cell viability assays, LC3B immunoblots, and live-cell fluorescence microscopy, we report here that in the presence of ruminant serum, exogenously added polyamines are quickly oxidized by the copper-containing bovine serum amine oxidase. This polyamine oxidation resulted in the production of harmful byproducts including hydrogen peroxide, ammonia, and reactive aldehydes. Our data demonstrate that it is critically important to prevent confounding bovine serum amine oxidase-induced cytotoxicity in mechanistic studies of the roles of polyamines in autophagy.
Highlights
Polyamines are small polycationic alkylamines involved in many fundamental cellular processes, including proliferation, nucleic acid synthesis, apoptosis, and protection from oxidative damage
LC3B immunoblots, and livecell fluorescence microscopy, we report here that in the presence of ruminant serum, exogenously added polyamines are quickly oxidized by the copper-containing bovine serum amine oxidase
It was previously demonstrated that the addition of exogenous polyamines is toxic in cell culture systems because of bovine serum amine oxidase (BSAO) activity and that co-treatment with AG is sufficient to alleviate this toxicity [23, 24]
Summary
Polyamines are small polycationic alkylamines involved in many fundamental cellular processes, including proliferation, nucleic acid synthesis, apoptosis, and protection from oxidative damage. Considerable caution must be used when interpreting much of the published mechanistic data produced in in vitro cell culture systems because any observed autophagy included in such systems is likely the result of the toxic metabolites formed by BSAO following polyamine addition to the serum-containing medium and not a function of the polyamines themselves [25, 29,30,31,32]. It was previously demonstrated that the addition of exogenous polyamines is toxic in cell culture systems because of BSAO activity and that co-treatment with AG is sufficient to alleviate this toxicity [23, 24].
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