Nuclear localization of melatonin in different mammalian tissues: Immunocytochemical and radioimmunoassay evidence

Abstract

Melatonin was detected by an improved immunocytochemical technique in the cell nuclei of most tissues studied including several brain areas, pineal gland, Harderian gland, gut, liver, kidney, and spleen from rodents and primates. Cryostat sections from tissues fixed in Bouin's fluid, formalin, or acetone/ethanol were used. The nuclear staining appeared primarily associated with the chromatin. The nucleoli did not exhibit a positive reaction. The melatonin antiserum was used in the range of 1:500 to 1:5,000. Incubation of the antibody with an excess of melatonin resulted in the complete blockade of nuclear staining. Pretreatment of the sections with proteinase K (200-1,000 ng/ml) prevented the positive immunoreaction. In a second aspect of the study, we estimated the concentration of melatonin by means of radioimmunoassay in the nuclear fraction of several tissues including cerebral cortex, liver, and gut. The subcutaneous injection of melatonin (500 micrograms/kg) to rats resulted, after 30 min, in a rapid increase in the nuclear concentration of immunoreactive melatonin which varied in a tissue-dependent manner. However, samples collected 3 h after the injection showed that melatonin levels had decreased to control values. Pinealectomy in rats resulted in a clear reduction in the nuclear content of melatonin in the cerebral cortex and liver but not in the gut. The results of these studies suggest that melatonin may interact with nuclear proteins and that the indole may have an important function at the nuclear level in a variety of mammalian tissues.

Improved mitochondrial function and increased life span after chronic melatonin treatment in senescent prone mice

“…Additionally, the lipophilicity of aMT permits that the indoleamine crosses cell membranes, reaching all intracellular structure (Costa et al, 1997;Menendez-Pelaez et al, 1993). In vitro and in vivo experiments have shown that aMT influences mitochondrial homeostasis, reducing mitochondrial hydroperoxide levels and stimulating the activity of GPx and GRd Martin et al, 2000).…”

Endogenous Melatonin Increases in Cerebrospinal Fluid of Patients after Severe Traumatic Brain Injury and Correlates with Oxidative Stress and Metabolic Disarray

“…Melatonin, being highly lipophilic, readily traverses the blood-brain barrier and the phospholipid bilayer membrane, entering the cellular cytoplasmic and nuclear compartments (Menendez-Pelaez et al, 1993)-an essential prerequisite for any efficacious neuroprotectant. Furthermore, blood-brain barrier disruption is a common consequence of TBI, with blood cells and serum components leaking into the cerebral tissue, initiating a molecular cascade that activates the immune system and inflammatory response (Morganti-Kossmann et al, 2001), providing an additional source for the generation of free radicals.…”

Aging and oxygen toxicity: Relation to changes in melatonin

“…This implies that melatonin concentrations are sufficiently high in lipid-rich membranes as well as in the aqueous cytosol and nucleoplasm to afford significant antioxidative protection. Although not frequently studied, both radioimmunoassay as well as immunocytochemical findings show high levels of melatonin in the nucleus and they generally indicate that intracellular concentrations of melatonin exceed those measured in the blood (68). The reported subcellular distribution is consistent with its high lipid solubility (69) as well as with its ability to dissolve in aqueous media (70).…”