Melatonin in patients with reduced REM sleep duration: two randomized controlled trials.

Recent data suggest that melatonin may influence human physiology, including the sleep-wake cycle, in a time-dependent manner via the body's internal clock. Rapid-eye-movement (REM) sleep expression is strongly circadian modulated, and the impact of REM sleep on primary brain functions, metabolic processes, and immune system function has become increasingly clear over the past decade. In our study, we evaluated the effects of exogenous melatonin on disturbed REM sleep in humans. Fourteen consecutive outpatients (five women, nine men; mean age, 50 yr) with unselected neuropsychiatric sleep disorders and reduced REM sleep duration (25% or more below age norm according to diagnostic polysomnography) were included in two consecutive, randomized, double-blind, placebo-controlled, parallel design clinical trials. Patients received 3 mg melatonin daily, administered between 2200 and 2300 h for 4 wk. The results of the study show that melatonin was significantly more effective than placebo: patients on melatonin experienced significant increases in REM sleep percentage (baseline/melatonin, 14.7/17.8 vs. baseline/placebo, 14.3/12.0) and improvements in subjective measures of daytime dysfunction as well as clinical global impression score. Melatonin did not shift circadian phase or suppress temperature but did increase REM sleep continuity and promote decline in rectal temperature during sleep. These results were confirmed in patients who received melatonin in the second study (REM sleep percentage baseline/placebo/melatonin, 14.3/12.0/17.9). In patients who received melatonin in the first study and placebo in the second, the above mentioned effects outlasted the period of melatonin administration and diminished only slowly over time (REM sleep percentage baseline/melatonin/placebo, 14.7/17.8/16.2). Our findings show that exogenous melatonin, when administered at the appropriate time, seems to normalize circadian variation in human physiology. It may, therefore, have a strong impact on general health, especially in the elderly and in shift workers.

Perturbation of lipid metabolism by linoleic acid hydroperoxide in CaCo-2 cells.

Dietary hydroperoxides are being discussed as potential health hazards contributing to oxidative stress-related diseases. However, how food-born hydroperoxides could exert systemic effects remains elusive in view of the limited chances to be absorbed. Therefore, the metabolic fate of 13-HPODE (13-hydroperoxy octadecadienoic acid), 13-HODE (13-hydroxy octadecadienoic acid) and linoleic acid (LA) was investigated in a CaCo-2 cell monolayer as a model of the intestinal epithelium. [1-14C]-13-HPODE, up to a non-cytotoxic concentration of 100 microM, did not cross the CaCo-2 cell monolayer unreduced if applied to the luminal side. The [1 -14C]-HPODE-derived radioactivity was preferentially recovered from intracellular and released diacylglycerols (DG), phospholipids (PL) and cholesterol esterified with oxidized fatty acids (oxCE). A similar distribution pattern was obtained with 13-HODE. In contrast, LA is preferentially incorporated into triacylglycerols (TG), cholesteryl esters (CE) and PL (but mainly released as TG). 13-HPODE dose-dependently decreased the incorporation of LA into released TG, while LA accumulated in cellular and released DGs, effects similarily exerted by 13-HODE. We concluded that food-born hydroperoxy fatty acids are instantly reduced by the gastrointestinal glutathione peroxidase, which was previously shown to persist in selenium deficiency. Accordingly, modulation of the glutathione peroxidases by selenium deprivation/repletion did not modify the disturbance of the lipid metabolism by 13-HPODE. Thus, hydroperoxy fatty acids disturb intestinal lipid metabolism by being esterified as hydroxy fatty acids into complex lipids, and may render lipoproteins synthesized thereof susceptible to further oxidative modifications.

3'UTRs of glutathione peroxidases differentially affect selenium-dependent mRNA stability and selenocysteine incorporation efficiency.

Selenoprotein mRNAs are particular in several aspects. They contain a specific secondary structure in their 3'UTR, called Secis (selenocysteine inserting sequence), which is indispensable for selenocysteine incorporation, and they are degraded under selenium-limiting conditions according to their ranking in the hierarchy of selenoproteins. In the familiy of selenium-dependent glutathione peroxidases (GPx) the ranking is GI-GPx > or = PHGPx > cGPx = pGPx. This phenomenon was studied by mutually combining the coding regions of GI-GPx, PHGPx and cGPx with their 3'UTRs. HepG2 cells were stably transfected with the resulting constructs. Expression of glutathione peroxidases was estimated by activity measurement and Western blotting, the selenium-dependent mRNA stability by real-time PCR. Whereas 3'UTRs from stable PHGPx and GI-GPx could be exchanged without loss of stability, they were not able to stabilize cGPx mRNA. cGPx 3'UTR rendered GI-GPx and PHGPx mRNA unstable. Thus, cGPx mRNA contains selenium-responsive instability elements in both the translated and the untranslated region, which cannot be compensated by one of the stable homologs. Stabilizing efficiency of an individual GPx 3'UTR did not correlate with the efficiency of selenocysteine incorporation. PHGPx 3'UTR was equally effective as cGPx 3'UTR in enhancing GPx activity in all constructs, while GI-GPx 3'UTR showed a markedly lower efficacy. We conclude that different mRNA sequences and/or RNA-binding proteins might regulate mRNA stability and translation of selenoprotein mRNA.