guia do novo coronavirus
Imprimir Republish

Melatonin

Unprotected against Alzheimer’s

Inflammation associated with the neurodegenerative disease inhibits production of melatonin, a hormone that prevents cell death

Anti-inflammatory action: in the cerebellum of mice, astrocytes (yellow), microglia and neurons (green) produce melatonin in response to sign of cell damage

Luciana Pinato/UnespAnti-inflammatory action: in the cerebellum of mice, astrocytes (yellow), microglia and neurons (green) produce melatonin in response to sign of cell damageLuciana Pinato/Unesp

For Regina Markus, a pharmacologist at the University of São Paulo (USP), her days in the laboratory were much longer during the final weeks of March. Leading a team of 12 researchers, she arrived at the university early in the morning and returned home late at night. “I’m working 24 hours a day,” she wrote in an e-mail message sent on March 24, 2015 at 02:46.  Later that same day, in a telephone conversation, she recounted that during these phases of work she was accustomed to spending days with almost no sleep, and took only strategic naps. The rush was to complete drafts of eight articles that show a possible connection between the slight and persistent inflammation seen in obesity and in some cases of cancer, and the deactivation of the pineal gland, which is located in the central region of the brain and is the main source of the body’s melatonin.

In the e-mail message, Markus called attention to a study that she included as an attachment. One week before, she and her team had published in the FASEB Journal the first evidence that beta amyloid oligomers, toxic compounds that accumulate in the brain in the early stages of Alzheimer’s disease alter the functioning of the pineal gland and block the synthesis of melatonin. Produced by almost all living beings, this multifunction hormone adjusts the rhythm of physiological phenomena such as sleep, hunger and body temperature. In the late 1990s, Italian researcher Salvatore Cuzzocrea, of the University of Messina, also demonstrated that melatonin acts as an important anti-inflammatory agent. Since then, Markus and her team have been working to obtain a better understanding of how inflammation affects production of the hormone and how variations in the secretion of melatonin influence inflammation. The group’s goal is to identify specific targets on which compounds that already exist or that are still to be developed, may act in order to avoid unwanted damage from persistent inflammation.

With the Faseb Journal study, Markus’s group appears to have reached a potential explanation for the limited effects of one of the few classes of drugs available against Alzheimer’s—the cholinesterase inhibitor compounds, such as rivastigmine and galantamine. It may also have opened a new path for the development of drugs, which used in combination with the cholinesterase inhibitor compounds, may be able to improve their performance and allow lower doses to be administered, thereby reducing side effects.

Erika Cecon, a biologist and member of Markus’s team, conducted a series of experiments using mice in which she attempted to simulate the inflammation caused by beta-amyloid oligomers in Alzheimer’s. First, she injected a small dose of the oligomers into one of the chambers of the brain in mice and then analyzed what occurred at both the molecular and cellular levels.

In the pineal gland, the oligomers adhered to a molecule on the surface of cells known as toll-like receptor 4 (TLR-4), which specialize in detecting signs of damage or danger, such as the presence of dead cell fragments or pieces of invading microorganisms. Once activated, these receptors triggered a sequence of chemical reactions that in the melatonin-producing cells (pinealocytes) caused the synthesis of the hormone to stop—similar to an effect the group had already noted that had caused brain inflammation in mice using lipopolysaccharide (LPS), the molecules found in bacterial walls. “International studies suggest that people with Alzheimer’s disease do not produce melatonin,” says Markus.

The initial reduction in melatonin levels is desirable and even essential for cells of the immune system to be directed to the site of the damage, to dispose of dead cells or invading microorganisms and then eliminate their remains in a kind of cell cleaning. But if the process is prolonged, it becomes harmful because it also begins to destroy healthy tissues.

In the central nervous system, decreased melatonin levels leave cells vulnerable. In 2013 Luciana Pinato and Markus demonstrated that reduced melatonin levels killed neurons in different brain regions. Only neurons in the cerebellum were spared; this organ, which is associated with movement control, for reasons unknown, produces its own supply of the hormone.

The lack of melatonin also has another effect on brain tissue. The Markus group in partnership with French researcher Ralf Jockers have observed that neurons, the cells that transmit and store information, fail to express receptors on their surface, thus prohibiting action of the cholinesterase inhibitor drugs that are used on these receptors to treat Alzheimer’s. “Restoration of melatonin levels in the circulatory system and recovery of the melatonin receptor function may have therapeutic value, especially by administering melatonin in the advanced stages of Alzheimer,” they wrote in the FASEB Journal. This effect has yet to be proven in humans.

Project
Immune-pineal axis: integrating the biology of time in physiological, pathophysiological and pathological conditions (2013/13691-1); Grant mechanism: Thematic Project; Principal investigator: Regina Pekelmann Markus (IB/USP); Investment: R$1,833,122.85 (FAPESP – for the entire project)

Scientific articles
CECON, E. et al. Amiloid peptide directly impairs pineal gland melatonin synthesis and melatonin receptor signaling through the ERK pathway. FASEB Journal. March 10, 2015.
PINATO, L. et al. Selective protection of the cerebellum against intracerebroventricular LPS is mediated by local melatonin synthesis. Brain Structure and Function. December 22, 2013.
CECON, E. and MARKUS, R.P. Relevance of the chronobiological and non-chronobiological actions of melatonin for enhancing therapeutic efficacy in neurodegenerative disorders. Recent Patents on Endocrine, Metabolic & Immune Drug Discovery. V. 5, p. 91-9. 2011.

Republish