Effects of melatonin ingestion on cAMP and cGMP levels in human plasma

PK/PD studies on non-selective PDE inhibitors in rats using cAMP as a marker of pharmacological response

In recent years, phosphodiesterase (PDE) inhibitors have been frequently tested for the treatment of experimental inflammatory and immune disorders. It is suggested that anti-inflammatory properties of PDE inhibitors are related to their ability to increase cAMP levels. The aim of this study was to verify the hypothesis that cAMP may be a useful marker of pharmacological response following administration of non-selective PDE inhibitors (pentoxifylline and (±)-lisofylline) to endotoxemic rats. Male Wistar rats were administered LPS (1 mg kg⁻¹, i.v.) simultaneously with either compound given at two doses (40 and 80 mg kg⁻¹, i.v.). Levels of cAMP and both compounds in animal plasma were measured by the validated HPLC methods. Pharmacokinetic-pharmacodynamic analysis was performed using basic and modified indirect response (IDR) models II in Phoenix WinNonlin. The results of this study indicate that, in contrast to pentoxifylline, (±)-lisofylline demonstrates a non-linear pharmacokinetics in rats with endotoxemia. In vitro study using human recombinant PDE4B and PDE7A revealed the occurrence of additive interaction between studied compounds. Moreover, (±)-lisofylline is a more potent inhibitor of PDEs compared to pentoxifylline, as evidenced by lower IC₅₀ values. Following administration of both compounds, levels of cAMP in rat plasma increased in a dose-dependent manner. The modified IDR model II better described cAMP levels over time profiles. The validity of the proposed marker was confirmed by measuring plasma TNF-α levels in the studied animals. In conclusion, cAMP may be used in future preclinical and clinical studies of some PDE inhibitors to evaluate the drug concentration–effect relationship.

Alterations in adipocytokines and cGMP homeostasis in morbid obesity patients reverse after bariatric surgery

OBJECTIVE

Obesity-associated nonalcoholic fatty liver disease (NAFLD), covering from simple steatosis to nonalcoholic steatohepatitis (NASH), is a common cause of chronic liver disease. Aberrant production of adipocytokines seems to play a main role in most obesity-associated disorders. Changes in adipocytokines in obesity could be mediated by alterations in cyclic GMP (cGMP) homeostasis. The aims of this work were: (1) to study the role of altered cGMP homeostasis in altered adipocytokines in morbid obesity, (2) to assess whether these alterations are different in simple steatosis or NASH, and (3) to assess whether these changes reverse in obese patients after bariatric surgery.

DESIGN AND METHODS

In 47 patients with morbid obesity and 45 control subjects, the levels in blood of adipocytokines, cGMP, nitric oxide (NO) metabolites, and atrial natriuretic peptide (ANP) were studied. Whether weight loss after a bariatric surgery reverses the changes in these parameters was evaluated.

RESULTS

NO metabolites and leptin increase (and adiponectin decreases) similarly in patients with steatosis or NASH, suggesting that these changes are due to morbid obesity and not to liver disease. Inflammation and cGMP homeostasis are affected both by morbid obesity and by liver disease. The increases in interleukin 6 (IL-6), interleukin 18 (IL-18), plasma cGMP, ANP, and the decrease in cGMP in lymphocytes are stronger in patients with NASH than with steatosis. All these changes reverse completely after bariatric surgery and weight loss, except IL-18.

CONCLUSION

Altered cGMP homeostasis seems to contribute more than inflammation to changes in leptin and adiponectin in morbid obesity.

Melatonergic regulation of hemolymph sugar levels in the freshwater edible crab, Oziotelphusa senex senex

In this study, the hyperglycemic effect of melatonin in the freshwater edible crab, Oziotelphusa senex senex, is investigated. Injection of melatonin induced hyperglycemia in a dose-dependent manner. Administration of melatonin produced hyperglycemia in both intact and eyestalk-ablated crabs. Bilateral eyestalk ablation resulted in significant increase in the total carbohydrates and glycogen levels with a significant decrease in phosphorylase activity in the hepatopancreas and muscle of the crabs. Injection of melatonin resulted in significant decrease in the total carbohydrate and glycogen levels, with an increase in phosphorylase activity in hepatopancreas and muscle of both intact and eyestalk-ablated crabs. From the results, it is hypothesized that melatonin-induced hyperglycemia in the crab, O. senex senex, is not mediated by eyestalk hyperglycemic hormone.

The possible role of human milk nucleotides as sleep inducers

Breast-milk contains a potent mixture of diverse components, such as the non-protein nitrogen fraction which includes nucleotides, whose variation in levels is evident throughout lactation. In addition, these substances play an important role in sleep homeostasis. In the present study, human milk samples were analyzed using a capillary electrophoresis system. The rhythmicity of each nucleotide was studied by cosinor analysis. It was found that the nucleotides 5'AMP, 5'GMP, 5'CMP, and 5'IMP have significant (P < 0.05) circadian rhythms, the acrophases of the first two being during the night, and of the latter two during the day. While 5'UMP did not show a clear circadian rhythm, there was an increase in its levels at night. In conclusion, the rise in nocturnal levels of 5'AMP, 5'GMP, and 5'UMP could be involved in inducing the 'hypnotic' action of breast-milk at night in the infant.

Prolonged-release melatonin for the treatment of insomnia: targeting quality of sleep and morning alertness

Prolonged-release (PR) melatonin (Circadin®, Neurim Pharmaceuticals, Tel-Aviv, Israel) is a nonbenzodiazepine licensed to treat primary insomnia in patients aged 55 years and older. It exerts its effects by mimicking endogenous melatonin, a hormone which regulates sleep. PR-melatonin has been shown to be effective in improving quality of sleep and morning alertness. An oral dose of 2 mg once-daily for 3 weeks has generally been well tolerated, and does not cause ‘hangover’ effects or impair memory and psychomotor skills.

Melatonin as a hypnotic: pro

In diurnal species, nocturnal melatonin secretion coincides with the habitual hours of sleep, in contrast to nocturnal animals which are at the peak of their activity while producing melatonin. Studies in humans, diurnal non-human primates, birds and fish show that melatonin treatment can facilitate sleep initiation during the daytime or improve altered overnight sleep. Behaviorally, the sleep-promoting effects of melatonin are distinctly different from those of common hypnotics and are not associated with alterations in sleep architecture. The effects of melatonin on sleep are mediated via specific melatonin receptors and physiologic doses of the hormone, those inducing circulating levels under 200 pg/ml, are sufficient to promote sleep in diurnal species. Aging reduces responsiveness to melatonin treatment and this correlates with reduced functional potency of melatonin receptors. Since melatonin receptors are present in different tissues and organs and involved in multiple physiologic functions, using physiologically relevant doses (0.1-0.3 mg, orally) and time of administration (at bedtime) is recommended, in order to avoid known and unknown side effects of melatonin treatment.

Melatonin improves sleep in asthma: a randomized, double-blind, placebo-controlled study

Disturbed sleep is common in asthma. Melatonin has sleep-inducing activity and reportedly affects smooth muscle tone and inflammation. The aim of this study was to evaluate the effect of melatonin on sleep in patients with mild and moderate asthma. This was a randomized, double-blind, placebo-controlled study. Twenty-two consecutive women with asthma were randomized to receive melatonin 3 mg (n = 12) or placebo (n = 10) for 4 weeks. Sleep quality and daytime somnolence were assessed by the Pittsburgh Sleep Quality Index and the Epworth Sleepiness Scale, respectively. Pulmonary function was assessed by spirometry. Use of relief medication, asthma symptoms, and morning and evening peak expiratory flow rate were recorded daily. Melatonin treatment significantly improved subjective sleep quality, as compared with placebo (p = 0.04). No significant difference in asthma symptoms, use of relief medication and daily peak expiratory flow rate was found between groups. We conclude that melatonin can improve sleep in patients with asthma. Further studies looking into long-term effects of melatonin on airway inflammation and bronchial hyperresponsiveness are needed before melatonin can be recommended in patients with asthma.