Eat More Turkey (What Chic-fil-A Missed)

A study published in March of 2005 tried to determine what effect Melatonin had in Experimental Streptococcus pneumoniae Meningitis and seeing as it was Thanksgiving not too long ago and all that turkey we ate was loaded with tryptophan, I jumped right on it. The following is a cliff note version of what the study addressed.

Like most neurodegenerative diseases, bacterial meningitis causes neuronal injury through leukocyte invasion into the central nervous system; other detrimental mechanisms include stimulation of microglia and local macrophages, as well as having a direct bacterial toxicity on cerebral endothelium and neurons. Free radicals formed from such events plays a key role in the cascade leading to neuronal injury. Because of this, anti-inflammatory and antioxidative treatments have been turned to for therapeutic purposes in limiting cerebral complications in bacterial meningitis.

Melatonin is considered an antioxidant and its IUPAC name is N-acetyl-5-methoxytryptamine, a derivate of tryptophan. Melatonin is the major product of the pineal gland but is also synthesized in the retina and enterochromaffin cells of the gastrointestinal tract. As is commonly known melatonin is involved in the regulation of circadian rhythms, sleep, and reproduction. As an antioxidant, melatonin scavenges a number of oxygen and nitrogen species, including the hydroxyl radical, hydrogen peroxide, singlet oxygen, NO, and peroxynitrite. In addition melatonin has the capability of stimulating the expression of several antioxidative enzymes, such as superoxide dismutase and glutathione peroxidase. Previous studies have shown that high doses of melatonin inhibit neuronal and glial inury in various diseases, including cerebral artery occlusion and epileptic seizures. Such studies have been supported by experimental removal of the pineal gland which has shown to exaggerate the damage brought upon by free radicals. The study being discussed used a rabbit model exposed to pneumococcal meningitis and cell cultures exposed to S. pneumoniae and oxidative stress to determine the efficacy of melatonin.

Hippocampal tissue cultures were taken from six to eight day old NMRI mice and were challenged with 10⁷ cfu/mL of living unencapsulated S. pneumoniae R6 strain for 48 hours. The unencapsulated form was used because the capsule masks the cell-wall epitopes that stimulate the innate immune system. Ceftriaxone (1 ug/mL), a cephalosporin antibiotic, was administered to each culture to inhibit bacterial growth. The culture groups, each consisting of 17 hippocampal slices, were either exposed to S. pneumoniae R6 and ceftriaxone, or with S. pneumoniae R6, ceftriaxone, and melatonin. The negative controls only received melatonin and ceftriaxone. The results are shown in Figure 1 of the article.¹ Overall the cellular damage in the dentate gyrus decreased after treatment of the hippocampal tissue with melatonin.

SH-SY5Y human neuroblastoma cells were used to examine the effects of melatonin on cell viability under oxidative stress. These cells were exposed to 3-morpholinosydnonimine (SIN-1) which is known to spontaneously decay to NO and superoxide anion radicals at physiological pH. The cells were divided up into groups, each containing 6 cell culture densities, depending on which exposures they would obtain; the cells were treated with a medium that either contained SIN-1 (500 umol/L) or SIN-1 plus melatonin at concentrations of 0.1, 1, 10, 100, and 1000 ug/mL. Results of cell viability were acquired 4 hours later and are shown in figure 2A. ¹ Cell viability increased with the treatment of melatonin showing optimal results at a dose of 10 ug/mL but abolishing its neuroprotective effects at a dosage of 1 mg/mL.

Microglial cell cultures were obtained from brains of newborn C57/B16 mice that were one to three days old. There stimulation was brought upon by exposure to TLR-2 agonist tripalmitoyl-S-glyceryl-cysteine (Pam3Cys-OH) for 24 hours in the presence of IFN-gamma (100 U/mL). The cultures were either treated with Pam3Cys (0.1 ug/mL) or Pam3Cys plus melatonin at concentrations of 10, 100, 300, and 1000 ug/mL with each group containing 8 cultures. The negative control cultures only received IFN-gamma. The results were illustrated in Figure 2B.¹ Melatonin demonstrated optimal results at lower dosages in this case; its neuroprotective effects were negated at a dosage of 1 mg/mL. On a personal note, these results raised many questions for me as they conflicted with the results on cell viability (they both demonstrated that the protective effect of melatonin was abolished at a dosage of 1 mg/mL but initially an increase in dosage was good for cell viability but detrimental as well shown by an increase in nitrite concentration).

In continuation, the number of apoptotic neurons in the dentate gyrus of the hippocampal formation decreased after treatment with both melatonin and ceftriaxone compared to only treatment with ceftriaxone. The results are illustrated in Figures 3A and Figure 4.^2,3 Increased activity of SOD (superoxide dismutase) was also witnessed with the treatment of melatonin on brain homogenates of the hippocampal formation. The control group that only received ceftriaxone showed SOD concentrations of 4.29 +/- 1.65 U/10 mg of hippocampal tissue compared to those rabbits who also received melatonin which exemplified a concentration of 6.29 +/- 2.24 U/10 mg. These results are illustrated in Figure 3B.²

The study goes on to explain that melatonin can be administered in large doses in both human beings and animals without any detrimental toxic effects. It also states that other studies have looked into the therapeutic use of melatonin on acute cerebral diseases which have shown to maximize antioxidant effects. Such models, such as head trauma and cerebral ischemia, have shown reduced volume of contusions or cerebral infarction with the treatment of melatonin. However studies on melatonin’s ability to regulate the immune system have been inconsistent. Cytokine production in lipopolysaccharide-stimulated macrophage and microglial cell lines was not altered by melatonin which leads researchers to assume it has no effect in modulating macrophage and microglia function. The discussion goes on to describe other mechanisms and treatment procedures that have been studied for neuronal survival in meningitis. The study concludes with accepting that melatonin can readily penetrate the blood-brain barrier and cell membranes whilst also decreasing neuronal injury through both direct and indirect pathways qualifying it as a candidate for adjunctive therapy in bacterial meningitis. On this note I feel it would be interesting to study the effects of melatonin therapy on neurogenerative diseases discussed in class such as Alzheimer’s disease or Parkinson’s disease. Nevertheless all that turkey over break probably did us some good!

References:

Gerber, Joachim, Miriam Lotz, Sandra Ebert, Sussane Kiel, Gerald Huether, Ulrich Kuhnt, and Roland Nau. "Melatonin Is Neuroprotective in Experimental Streptococcus Pneumoniae Meningitis." The Journal of Infectious Diseases 191.5 (2005): 783-90.JSTOR. Web.

1. Figure 1 and 2 URL: http://www.jstor.org.ezproxy1.library.arizona.edu/action/showArticleImage?image=images%2Fpages%2Fdtc.148.tif.jpg&suffix=30077563

2. Figure 3 URL: http://www.jstor.org.ezproxy1.library.arizona.edu/action/showArticleImage?image=images%2Fpages%2Fdtc.149.tif.jpg&suffix=30077563

3. Figure 4 URL: http://www.jstor.org.ezproxy1.library.arizona.edu/action/showArticleImage?image=images%2Fpages%2Fdtc.150.tif.jpg&suffix=30077563