Specific binding of melatonin by immunocompetent cells in humans and rodents. Modifications during postnatal development

Ototoxicity caused by aminoglycosides is ameliorated by melatonin without interfering with the antibiotic capacity of the drugs

The production of free radicals seems to be involved in the mechanisms of ototoxicity. Aminoglycosides produce ototoxicity, which can be determined through distortion product otoacoustic emissions (OAEs) that measure the activity of the outer hair cells of the organ of Corti. An ototoxic chart was obtained in rats using gentamicin or tobramycin. Together with this treatment, the animals ingested melatonin in the drinking water, or melatonin was injected subcutaneously or intramuscularly. The distortion product OAEs were determined over a prolonged period of time for each of the groups. The effect of melatonin on the antibiotic capacity of the aminoglycosides used was also studied. Antibiograms inoculated with Escherichia coli or Pseudomonas aeruginosa and treated with gentamicin or tobramycin in the presence or absence of melatonin at quantities from pharmacological to physiological doses were performed. The ototoxicity produced by gentamicin and tobramycin was maximal from days 3 to 5 post-treatment, returning to normal values in 2 wk. When melatonin was present, the recovery was at day 5 post-treatment, independently of the means of administration of the pineal product. The antibiograms showed that melatonin had no effect on the antibiotic capacity. It is concluded that the ototoxicity caused by gentamicin and tobramycin is ameliorated by melatonin and that the pineal hormone does not interfere with the antibiotic capacity of these antibiotics.

Melatonin and other antioxidants prolong the postmortem activity of the outer hair cells of the organ of Corti: its relation to the type of death

The outer hair cells of the organ of Corti transform sound into electrical signals, beginning the nervous auditive process. These cells produce acoustic emissions when working routinely, known as otoacoustic emissions. Otoacoustic emissions (OAEs) are recorded from the hearing duct through a probe which incorporates a sound source and a sensitive microphone. On the other hand, the cochlea produces oxygen-derived free radicals and nitric oxide, in addition, melatonin is present in the cochlea. The authors have studied the influence of melatonin or an antioxidant mixture (alpha-tocopherol acid succinate, ascorbic acid, glutathione, and N-acetylcysteine) on the postmortem activity of the outer hair cells of the organ of Corti of the rat, measuring distortion product otoacoustic emissions. Control rats showed postmortem distortion product otoacoustic emissions for about 2 min when sacrificed by decapitation, and for about 3 min when sacrificed by chloroform inhalation. Melatonin prolonged the postmortem activity 3.5 times when the animals were sacrificed by decapitation, and 7 times when animals were sacrificed by chloroform inhalation. Similar results were obtained with the antioxidant mixture. Results show that melatonin and other antioxidants have, in general, a protective role on the postmortem activity of the outer hair cells of the organ of Corti.

Melatonin restores and enhances the human type B tonsillar lymphocyte subset in recurrent acute tonsillitis

Tonsils have a privileged situation in the immune system in that they are in touch with the environment. Melatonin is a hormone that is influenced by the circadian environmental variations of dark-light and is a modulator of the immune system. We have studied a group of thirty five children with recurrent acute tonsillitis that were submitted for tonsillectomy. Tonsillar lymphocyte subsets were determined before and after culture through flow cytometry in a tonsillar mononuclear suspension. After the culture, the lymphocyte subsets of type B suffered a decrease that was restored in the presence of melatonin or phytohemaglutinin, and even increased above the values of the control when the culture was accomplished in the presence of both substances. This process was specific for B cells, no occurrence for T lymphocytes or natural killer cells. Melatonin is found in the crossroads of the interaction of the microorganisms, pollens or inert substances with the tonsillar lymphocytes in the production of the immune defences. Further study is required on tonsillar pathology to explain its physiopathology and its possible therapeutic role.

Melatonin induces hyporeactivity caused by type II collagen in peripheral blood lymphocytes from patients with autoimmune hearing losses

We have studied the behavior of peripheral blood lymphocytes in healthy controls and in patients with various hearing losses. These hearing losses were of an autoimmune origin in which type II collagen and melatonin were either present or absent, activated or not with concanavalin A (Con A). In patients with autoimmune hearing losses, the results showed lymphocytes that displayed hyporeactivity to type II collagen in terms of their proliferative activity in the presence of Con A. The hyporeactivity is specially relevant in those cells which are melatonin incubated. When different nosologic entities were studied, we observed similar lymphocyte hyporeactivity to type II collagen in bilateral sensorineural hearing loss, Ménière's disease and otosclerosis. We conclude that in the lymphocytes of patients with autoimmune hearing losses, there is hyporeactivity to type II collagen when compared to the hyporeactivity of lymphocytes in control groups. This hyporeactivity is revealed when the lymphocytes are activated in the presence of melatonin.

Melatonin site and mechanism of action: single or multiple?

By affecting the entrainment pathways of the biologic clock, melatonin has a major influence on the circadian and seasonal organization of vertebrates. In addition, a number of versatile functions that far transcend melatonin actions on photoperiodic time measurement and circadian entrainment have emerged. Melatonin is a free radical scavenger and antioxidant and it has a significant immunomodulatory activity, being presumably a major factor in an organism's defense toxic agents and invading organisms. Besides affecting specific receptors in cell membranes to exert its effects, the interaction of melatonin with nuclear receptor sites and with intracellular proteins, like calmodulin or tubulin-associated proteins, as well as the direct antioxidant effects of melatonin, may explain many general functions of the pineal hormone.

Ageing as upregulation failure

This paper investigates similarities in physiological senescent changes in various mammalian organ systems and relates these to postulated mechanisms of age modulation. It proposes that the observed decline in homeostasis with age is due to an inability of target cells, of neural, endocrine and other forms of control, to upregulate after their downregulation. The well-documented flattening of circadian rhythms with age, particularly the loss of the sustained diurnal hypothermic phase, is described as integral to such change, and maintenance or induction of certain youthful circadian patterns is proposed as a means of restoring homeostasis in senescence and other conditions.