Effect of peroxides on spermine transport in rat brain and liver mitochondria

Exogenous spermine preserves mitochondrial bioenergetics via regulating Src kinase signaling in the spinal cord

Regulation of mitochondrial metabolism is becoming an important target in inhibiting necrosis and apoptosis following secondary spinal cord injury, and physiological compounds that reduce mitochondrial dysfunction are regarded as efficient protective reagents following injury. It has been demonstrated that spermine, a polyamine composed of four primary amines, may be taken up by a mitochondria‑specific uniporter and may preserve mitochondrial bioenergetics, suggesting that it may be important in the pathophysiology of mitochondria. However, the protective mechanism has not yet been definitively clarified. In the present study, isolated spinal cord mitochondria were incubated with spermine to evaluate its physiological functions and Src kinase activities. The results revealed that spermine increased oxidative phosphorylation, attenuated mitochondrial swelling and maintained the membrane potential. An inhibitor of Src kinases, amino‑5-(4‑chlorophenyl)‑7‑(t‑butyl)pyrazolo[3,4‑d]pyrimidine (PP2), markedly reduced the effects of spermine. However, inhibition of tyrosine phosphatases by vanadate led to marginal increases in the effects of spermine. Therefore, the present study hypothesized that tyrosine phosphorylation sites are present in the subunits of respiratory chains and mitochondrial permeability transition pore proteins, which may be modified via phosphorylation and dephosphorylation. Furthermore, spermine may upregulate the phosphorylation of Src kinases, and PP2 and vanadate conversely regulate Src phosphorylation. The results of the present study suggest that spermine is a strategic regulator within mitochondria that may activate Src kinases in the spinal cord, and tyrosine phosphorylation signaling is a primary regulatory pathway of mitochondrial metabolism.

Pathophysiological implications of mitochondrial oxidative stress mediated by mitochondriotropic agents and polyamines: the role of tyrosine phosphorylation

Mitochondria, once merely considered as the "powerhouse" of cells, as they generate more than 90 % of cellular ATP, are now known to play a central role in many metabolic processes, including oxidative stress and apoptosis. More than 40 known human diseases are the result of excessive production of reactive oxygen species (ROS), bioenergetic collapse and dysregulated apoptosis. Mitochondria are the main source of ROS in cells, due to the activity of the respiratory chain. In normal physiological conditions, ROS generation is limited by the anti-oxidant enzymatic systems in mitochondria. However, disregulation of the activity of these enzymes or interaction of respiratory complexes with mitochondriotropic agents may lead to a rise in ROS concentrations, resulting in oxidative stress, mitochondrial permeability transition (MPT) induction and triggering of the apoptotic pathway. ROS concentration is also increased by the activity of amine oxidases located inside and outside mitochondria, with oxidation of biogenic amines and polyamines. However, it should also be recalled that, depending on its concentration, the polyamine spermine can also protect against stress caused by ROS scavenging. In higher organisms, cell signaling pathways are the main regulators in energy production, since they act at the level of mitochondrial oxidative phosphorylation and participate in the induction of the MPT. Thus, respiratory complexes, ATP synthase and transition pore components are the targets of tyrosine kinases and phosphatases. Increased ROS may also regulate the tyrosine phosphorylation of target proteins by activating Src kinases or phosphatases, preventing or inducing a number of pathological states.

Bidirectional fluxes of spermine across the mitochondrial membrane

The polyamine spermine is transported into the mitochondrial matrix by an electrophoretic mechanism having as driving force the negative electrical membrane potential (ΔΨ). The presence of phosphate increases spermine uptake by reducing ΔpH and enhancing ΔΨ. The transport system is a specific uniporter constituted by a protein channel exhibiting two asymmetric energy barriers with the spermine binding site located in the energy well between the two barriers. Although spermine transport is electrophoretic in origin, its accumulation does not follow the Nernst equation for the presence of an efflux pathway. Spermine efflux may be induced by different agents, such as FCCP, antimycin A and mersalyl, able to completely or partially reduce the ΔΨ value and, consequently, suppress or weaken the force necessary to maintain spermine in the matrix. However this efflux may also take place in normal conditions when the electrophoretic accumulation of the polycationic polyamine induces a sufficient drop in ΔΨ able to trigger the efflux pathway. The release of the polyamine is most probably electroneutral in origin and can take place in exchange with protons or in symport with phosphate anion. The activity of both the uptake and efflux pathways induces a continuous cycling of spermine across the mitochondrial membrane, the rate of which may be prominent in imposing the concentrations of spermine in the inner and outer compartment. Thus, this event has a significant role on mitochondrial permeability transition modulation and consequently on the triggering of intrinsic apoptosis.