Radioimmunoassay for melatonin

Ruthenium-Anchored Carbon Sphere-Customized Sensor for the Selective Amperometric Detection of Melatonin

Melatonin (MT), a pineal gland hormone, regulates the sleep/wake cycle and is a potential biomarker for neurodegenerative disorders, depression, hypertension, and several cancers, including prostate cancer and hepatocarcinoma. The amperometric detection of MT was achieved using a sensor customized with ruthenium-incorporated carbon spheres (Ru-CS), possessing C- and O-rich catalytically active Ru surfaces. The non-covalent interactions and ion-molecule adducts between Ru and CS favor the formation of heterojunctions at the sensor-analyte interface, thus accelerating the reactions towards MT. The Ru-CS/Screen-printed carbon electrode (SPCE) sensor demonstrated the outstanding electrocatalytic oxidation of MT owing to its high surface area and heterogeneous rate constants and afforded a lower detection limit (0.27 μM), high sensitivity (0.85 μA μM -1 cm-2), and excellent selectivity for MT with the co-existence of crucial neurotransmitters, including norepinephrine, epinephrine, dopamine, and serotonin. High concentrations of active biomolecules, such as ascorbic acid and tyrosine, did not interfere with MT detection. The practical feasibility of the sensor for MT detection in pharmaceutical samples was demonstrated, comparable to the data provided on the product labels. The developed amperometric sensor is highly suitable for the quality control of medicines because of its low cost, simplicity, small sample size, speed of analysis, and potential for automation.

Role of the pineal gland in the development of malignant melanoma

The pineal gland produces many neurohormones that affect the function of the brain. One of these hormones, melatonin among other functions, shows oncostatic properties against some malignant tumors. Our investigations confirmed the oncostatic effect of this compound based on (a) the measurements of melatonin in the serum of melanoma patients, (b) 5-hydroxyindole-O-methyltransferase activity in the pineal of patients with malignant tumors, and (c) the detection of neuromelanin pigment in pineal bodies related to malignancy. Using a radioimmunoassay we have found that blood melatonin content is 4-5-fold increased in patients with the active phase of malignant melanoma. In healthy control subjects of both sexes (n = 6) between the ages 30-35 years at 10:00 a.m. serum melatonin varies between 0.47-0.65 nmol/l serum or 1.44-2.14 pg/mg serum protein. In contrast, in melanoma patients (n = 16) serum melatonin ranges from 2.07 to 6.20 nmol/l serum or 9.70-20.86 pg/mg serum protein. In another study in normal subjects (n = 24) serum melatonin level shows variations between 0.40 and 0.57 nmol/l serum or 1.75 and 2.32 pg/mg serum protein. Melanoma patients (n = 100) generally had an increased serum melatonin level ranging between 1.55 and 2.18 nmol/l serum or between 9.37 and 14.86 pg/mg serum protein. Twenty-four melanoma patients were tested several times during the duration of the disease and showed that surgical removal of the tumor resulted in a reduction of the serum melatonin level in 5 cases, remission was associated with an increase in 17 cases and in 2 cases treatment caused no change. Measurement of 5-hydroxyindole-O-methyltransferase activity in post mortem pineal glands revealed that it was significantly greater in cancer patients (n = 110) as compared to other diseases (n = 30); carcinoma of the esophagus, 12.75 +/- 2.38 nmol/h/mg protein; stomach, 9.74 +/- 1.62; colon, 14.84 +/- 3.97; lung, 9.28 +/- 1.58; kidney, 7.35 +/- 0.96; prostate, 6.02 +/- 0.93; soft palate, 0.62 +/- 0.18; leukemias, 10.96 +/- 2.80; lymphomas, 10.96 +/- 2.80; glioblastoma multiforme, 11.87 +/- 3.15; multiple myeloma, 1.46 +/- 0.42 and cardiovascular disease, 0.95 +/- 0.21. Post mortem histological examinations of isolated pineal bodies have shown that several glands contained a pigment, neuromelanin. A comprehensive study on pineals from a variety of diseases (n = 120) revealed that the pineal pigment content showed an inverse relation with the prevalence of malignancy.

The role of a thymus-pineal axis in an immune mechanism of aging

The Immune Theory of Aging cannot explain the cause of immune decline. It is hypothesized that the pineal gland acting in utero and during neonatal life in altricial mammals serves as a component of the immune system. Evidence in support of the presence of a thymus-pineal axis is presented. It is postulated that the pineal gland carries a considerable burden of immunological defense during maturation of the thymus, and also acts in the programming of the immune system. By relating thymus and immune function to the pineal and its known role as a neuroendocrine transducer for the entrainment and control of biorhythms, a consilence is developed between the role of the immune system in senescence and the pineal function in biorhythmicity. The relationships developed thus permit an extension of the immune theory as regards causative mechanisms.

Acute cerebral hemorrhage changes the nocturnal surge of plasma melatonin in humans

The diurnal rhythm of plasma melatonin was studied in 46 Chinese patients with acute cerebral hemorrhage. The state of consciousness of each patient was assessed clinically. The individual sites of lesion were determined by computerized tomography scanning. One to five days after stroke, blood samples were collected by venipuncture at 1000 and 1400 h in the daytime and 0200 and 0400 h at night. Plasma melatonin was extracted by dichloromethane and determined by radioimmunoassay. It was found that patients with lesions in the brain stem or in the third and lateral ventricles had melatonin levels significantly different from the other subjects in that these values were lower and lacking a nocturnal rise. These results are consistent with the presumptive retina-pineal pathway proposed in humans. Dramatic blunting or obliteration of the nocturnal melatonin surge in the blood was also observed in some patients with lesions in the frontal lobe, fronto-parietal lobe, parieto-temporal lobe, and basal ganglia. These brain regions are not involved in the retina-pineal pathway described in rodents or humans. Thus, our results suggest that brain regions other than the presumptive retina-pineal neural pathway may play an important role in the generation and/or regulation of the diurnal production and/or secretion of pineal melatonin in humans. However, a global functional disturbance caused by cerebral hemorrhage cannot be ruled out in some cases. It should be noted that many of the lesions leading to a change in the nocturnal rise of plasma melatonin were unilateral lesions. The significance of this finding is presently unknown. In addition, patients without a nocturnal rise of plasma melatonin were mostly comatose. They had lesions in the basal ganglion, fronto-parietal lobe, brain stem, and lateral and third ventricles. The latter findings suggest that in the brain, certain regions responsible for the state of consciousness of the individual may also be important to the dirunal rhythm of pineal melatonin secretion.

The clinical significance of melatonin serum determination in oncological patients and its correlations with GH and PRL blood levels

In order to investigate the pineal function and its relation with the hypophysis in human neoplasms, melatonin and GH serum levels were determined in 63 patients, 42 affected by solid tumours and 21 by lymphoma or leukaemia. In women with breast cancer PRL was also measured. Melatonin, GH and PRL were evaluated in 52 healthy subjects acting as controls. The oncological patients showed significantly higher mean melatonin serum levels than the control subjects. Mean melatonin values were lower in patients with solid tumours who had metastases, than in cases without metastases. Chemotherapy caused an evident decrease in melatonin levels. Surgery was followed by a fall in melatonin in patients without metastases. Mean GH serum levels observed in oncological patients were similar to those in control subjects and were not influenced by therapy. PRL levels were within the normal range in women suffering from breast cancer.

Urinary melatonin levels in human breast cancer patients

Urinary melatonin levels were measured in 10 postmenopausal Indian women suffering from advanced stages of breast cancer and in 9 well-matched women with non-endocrine complaints, mostly uterovaginal prolapse. Urines of each patient were collected over a period of 2-3 days in four 4-hourly intervals from 6 a.m. to 10 p.m. and one 8-hourly interval from 10 p.m. to 6 a.m. Serum LH, FSH, prolactin, estradiol and cortisol levels at 11 a.m. were determined as well as estrogen and progesterone receptors of the breast tumors. It was found that 24 hour urinary melatonin excretion in cancer patients was on the average 31% decreased as compared to the controls. This change was accompanied by a 33% increase in serum cortisol levels in the cancer patients. The melatonin excretion patterns of the cancer patients were not synchronized as compared to synchronized patterns of the controls. The number of tumors tested for steroid receptors does not yet allow to conclude if melatonin is different in patients with or without hormone-dependent tumors. The data suggest that pineal melatonin secretion may be modified in quantity as well as rhythmicity in breast cancer patients.

The role of the pineal gland in neuroendocrine control mechanisms of neoplastic growth

A survey of papers read during a workshop held in Vienna, 1977, is given showing that the pineal gland can be considered a model for research on neuroendocrine control mechanisms in neoplastic growth. From data obtained by different authors it can be concluded that the role of the pineal indole melatonin is very important in regard of the incidence and the development of tumours. On the basis of all the facts mentioned in this paper it is obvious that pineal gland activity should be included into the neuroendocrine factors studied in relation with oncogenic processes. For future research a number of experimental approaches, which need special emphasis, are recommended.