Circadian expression of pineal 5-lipoxygenase mRNA

Pharmacological Effects of Melatonin as Neuroprotectant in Rodent Model: A Review on the Current Biological Evidence

The progressive loss of structure and functions of neurons, including neuronal death, is one of the main factors leading to poor quality of life. Promotion of functional recovery of neuron after injury is a great challenge in neuroregenerative studies. Melatonin, a hormone is secreted by pineal gland and has antioxidative, anti-inflammatory, and anti-apoptotic properties. Besides that, melatonin has high cell permeability and is able to cross the blood-brain barrier. Apart from that, there are no reported side effects associated with long-term usage of melatonin at both physiological and pharmacological doses. Thus, in this review article, we summarize the pharmacological effects of melatonin as neuroprotectant in central nervous system injury, ischemic-reperfusion injury, optic nerve injury, peripheral nerve injury, neurotmesis, axonotmesis, scar formation, cell degeneration, and apoptosis in rodent models.

Melatonin and associated signaling pathways that control normal breast epithelium and breast cancer

This review article discusses recent work on the melatonin-mediated circadian regulation and integration of molecular and metabolic signaling mechanisms involved in human breast cancer growth and the associated consequences of circadian disruption by exposure to light-at-night (LAN). The anti-proliferative effects of the circadian melatonin signal are, in general, mediated through mechanisms involving the activation of MT(1) melatonin receptors expressed in human breast cancer cell lines and xenografts. In estrogen receptor-positive (ERα+) human breast cancer cells, melatonin suppresses both ERα mRNA expression and estrogen-induced transcriptional activity of the ERα via MT(1)-induced activation of G(αi2) signaling and reduction of cAMP levels. Melatonin also regulates the transcriptional activity of additional members of the nuclear receptor super-family, enzymes involved in estrogen metabolism, and the expression of core clock and clock-related genes. The anti-invasive/anti-metastatic actions of melatonin involve the blockade of p38 phosphorylation and matrix metalloproteinase expression. Melatonin also inhibits the growth of human breast cancer xenografts via MT(1)-mediated suppression of cAMP leading to a blockade of linoleic acid (LA) uptake and its metabolism to the mitogenic signaling molecule 13-hydroxyoctadecadienoic acid (13-HODE). Down-regulation of 13-HODE reduces the activation of growth factor pathways supporting cell proliferation and survival. Finally, studies in both rats and humans indicate that light-at-night (LAN) induced circadian disruption of the nocturnal melatonin signal activates human breast cancer growth, metabolism, and signaling, providing the strongest mechanistic support, thus far, for epidemiological studies demonstrating the elevated breast cancer risk in night shift workers and other individuals increasingly exposed to LAN.

N-acetylserotonin activates TrkB receptor in a circadian rhythm

Brain-derived neurotrophic factor (BDNF) is a cognate ligand for the TrkB receptor. BDNF and serotonin often function in a cooperative manner to regulate neuronal plasticity, neurogenesis, and neuronal survival. Here we show that NAS (N-acetylserotonin) swiftly activates TrkB in a circadian manner and exhibits antidepressant effect in a TrkB-dependent manner. NAS, a precursor of melatonin, is acetylated from serotonin by AANAT (arylalkylamine N-acetyltransferase). NAS rapidly activates TrkB, but not TrkA or TrkC, in a neurotrophin- and MT3 receptor-independent manner. Administration of NAS activates TrkB in BDNF knockout mice. Furthermore, NAS, but not melatonin, displays a robust antidepressant-like behavioral effect in a TrkB-dependent way. Endogenous TrkB is activated in wild-type C3H/f(+/+) mice but not in AANAT-mutated C57BL/6J mice, in a circadian rhythm; TrkB activation is high at night in the dark and low during the day. Hence, our findings support that NAS is more than a melatonin precursor, and that it can potently activate TrkB receptor.

Fetal/placental regulation of maternal melatonin in rats

We investigated how maternal melatonin is regulated in pregnant rats. To examine the involvement of the conceptus (fetus and placenta) in serum melatonin concentrations, the number of conceptuses was experimentally reduced to one on day 7 of pregnancy (1-conceptus group). Maternal circulating nighttime melatonin levels increased toward day 21 of pregnancy and rapidly decreased to the non-pregnancy levels after parturition, whereas the maternal serum nighttime melatonin levels of the 1-conceptus group on day 21 of pregnancy were significantly lower than normal pregnancy bearing dams more than 10 conceptuses. When the fetuses were removed by fetectomy (all fetuses but not the placentae) on day 12 of pregnancy, serum melatonin concentrations were not decreased. To examine the source of circulating maternal melatonin, mRNA expression of N-acetyltransferase (NAT), which is a late limiting enzyme for melatonin synthesis, was examined in the placenta and fetal pineal. NAT was not expressed in the placenta and was negligible in the pineal gland of the fetus compared with the mother's pineal gland. To examine the effect of placental hormones on maternal melatonin production, a conditioned medium, which was made by incubating placenta of day 20 of pregnancy with medium, was injected into the 1-conceptus dams from day 17 to day 20 of pregnancy. Injection of conditioned medium significantly increased serum melatonin concentrations compared with the control values whereas charcoal treatment abolished the stimulatory effect of conditioned medium. In conclusion, maternal circulating melatonin is from the maternal pineal gland and is increased by placental hormones during pregnancy.

Effects of cocaine in 5-lipoxygenase-deficient mice

5-Lipoxygenase (5-LOX), along with 12-lipoxygenase and cyclooxygenases, metabolizes arachidonic acid into eicosanoids. In rodents, 12-lipoxygenase deficiency alters behavioral responses to cocaine. We used 5-LOX-deficient mice and their controls to investigate cocaine's actions. After repeated cocaine injections, the increase in locomotor activity was greater in 5-LOX-deficient mice. Since the 5-LOX pathway may regulate the levels/metabolism of arachidonoylethanolamide (AEA) we assayed the AEA levels in the striatum, the binding of the endogenous AEA to the cannabinoid receptor CB1R, and anandamide hydrolase (FAAH) activity in the striatum, hippocampus, and cortex. Striatal AEA levels decreased after repeated cocaine injections. Cocaine also decreased CB1R binding in all brain regions studied and the only significant differences between 5-LOX-deficient and control mice was the greater hippocampal FAAH activity in 5-LOX-deficient mice. Our results demonstrated that a 5-LOX deficiency alters sensitivity to repeated cocaine. It should be investigated whether a human 5-LOX gene polymorphism affects cocaine's actions.

Antiinflammatory and neuroprotective actions of COX2 inhibitors in the injured brain

Overexpression of COX2 appears to be both a marker and an effector of neural damage after a variety of acquired brain injuries, and in natural or pathological aging of the brain. COX2 inhibitors may be neuroprotective in the brain by reducing prostanoid and free radical synthesis, or by directing arachidonic acid down alternate metabolic pathways. The arachidonic acid shunting hypothesis proposes that COX2 inhibitors' neuroprotective effects may be mediated by increased formation of potentially beneficial eicosanoids. Under conditions where COX2 activity is inhibited, arachidonic acid accumulates or is converted to eicosanoids via lipoxygenases and cytochrome P450 (CYP) epoxygenases. Several P450 eicosanoids have been demonstrated to have beneficial effects in the brain and/or periphery. We suspect that arachidonic acid shunting may be as important to functional recovery after brain injuries as altered prostanoid formation per se. Thus, COX2 inhibition and arachidonic acid shunting have therapeutic implications beyond the suppression of prostaglandin synthesis and free radical formation.

Proteomic analysis of day–night variations in protein levels in the rat pineal gland

The pineal gland secretes the hormone melatonin. This secretion exhibits a circadian rhythm with a zenith during night and a nadir during day. We have performed proteome analysis of the superficial pineal gland in rats during daytime and nighttime. The proteins were extracted and subjected to 2-DE. Of 1747 protein spots revealed by electrophoresis, densitometric analysis showed the up-regulation of 25 proteins during nighttime and of 35 proteins during daytime. Thirty-seven of the proteins were identified by MALDI-TOF MS. The proteins up-regulated during the night are involved in the Krebs cycle, energy transduction, calcium binding, and intracellular transport. During the daytime, enzymes involved in glycolysis, electron transport, and also the Krebs cycle were up-regulated as well as proteins taking part in RNA binding and RNA processing. Our data show a prominent day-night variation of the protein levels in the rat pineal gland. Some proteins are up-regulated during the night concomitant with the melatonin secretion of the gland. Other proteins are up-regulated during the day indicating a pineal metabolism not related to the melatonin synthesis.

Melatonin

Melatonin is a ubiquitous molecule and widely distributed in nature, with functional activity occurring in unicellular organisms, plants, fungi and animals. In most vertebrates, including humans, melatonin is synthesized primarily in the pineal gland and is regulated by the environmental light/dark cycle via the suprachiasmatic nucleus. Pinealocytes function as 'neuroendocrine transducers' to secrete melatonin during the dark phase of the light/dark cycle and, consequently, melatonin is often called the 'hormone of darkness'. Melatonin is principally secreted at night and is centrally involved in sleep regulation, as well as in a number of other cyclical bodily activities. Melatonin is exclusively involved in signaling the 'time of day' and 'time of year' (hence considered to help both clock and calendar functions) to all tissues and is thus considered to be the body's chronological pacemaker or 'Zeitgeber'. Synthesis of melatonin also occurs in other areas of the body, including the retina, the gastrointestinal tract, skin, bone marrow and in lymphocytes, from which it may influence other physiological functions through paracrine signaling. Melatonin has also been extracted from the seeds and leaves of a number of plants and its concentration in some of this material is several orders of magnitude higher than its night-time plasma value in humans. Melatonin participates in diverse physiological functions. In addition to its timekeeping functions, melatonin is an effective antioxidant which scavenges free radicals and up-regulates several antioxidant enzymes. It also has a strong antiapoptotic signaling function, an effect which it exerts even during ischemia. Melatonin's cytoprotective properties have practical implications in the treatment of neurodegenerative diseases. Melatonin also has immune-enhancing and oncostatic properties. Its 'chronobiotic' properties have been shown to have value in treating various circadian rhythm sleep disorders, such as jet lag or shift-work sleep disorder. Melatonin acting as an 'internal sleep facilitator' promotes sleep, and melatonin's sleep-facilitating properties have been found to be useful for treating insomnia symptoms in elderly and depressive patients. A recently introduced melatonin analog, agomelatine, is also efficient for the treatment of major depressive disorder and bipolar affective disorder. Melatonin's role as a 'photoperiodic molecule' in seasonal reproduction has been established in photoperiodic species, although its regulatory influence in humans remains under investigation. Taken together, this evidence implicates melatonin in a broad range of effects with a significant regulatory influence over many of the body's physiological functions.

Light stimulates MSK1 activation in the suprachiasmatic nucleus via a PACAP-ERK/MAP kinase-dependent mechanism

Signaling via the p42/44 mitogen-activated protein kinase (MAPK) pathway has been shown to be a key intracellular signaling event that couples light to entrainment of the mammalian circadian clock located in the suprachiasmatic nucleus (SCN). Because many of the physiological effects of the MAPK pathway are mediated by extracellular signal-regulated kinase (ERK)-regulated kinases, it was of interest to identify kinase targets of ERK in the SCN. In this study, we examined whether mitogen- and stress-activated protein kinase 1 (MSK1) is a downstream target of ERK in the SCN and whether it couples to clock gene expression. Here we show that photic stimulation during the subjective night stimulates MSK1 phosphorylation at serine 360, an event required for robust kinase activation. Activated ERK and MSK1 were colocalized in SCN cell nuclei after photic stimulation. The in vivo administration of the MAP kinase kinase 1/2 inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto) butadiene] attenuated MSK1 phosphorylation. MSK1 phosphorylation was more responsive to late-night than early-night photic stimulation, indicating that MSK1 may differentially contribute to light-induced phase advancing and phase delaying of the clock. The potential connection between pituitary adenylate cyclase-activating polypeptide (PACAP) (a regulator of clock entrainment) and MSK1 phosphorylation was examined. PACAP infusion stimulated MSK1 phosphorylation, whereas PACAP receptor antagonist infusion attenuated light-induced MSK1 phosphorylation in the SCN. In reporter gene assays, MSK1 was shown to couple to mPeriod1 via a cAMP response element-binding protein-dependent mechanism. Together, these data identify MSK1 as both a downstream target of the MAPK cascade within the SCN and a regulator of clock gene expression.

Antioxidative protection by melatonin: multiplicity of mechanisms from radical detoxification to radical avoidance

Melatonin has been shown to protect against oxidative stress in various, highly divergent experimental systems. There are many reasons for its remarkable protective potential. Signaling effects comprise the upregulation of antioxidant enzymes, such as superoxide dismutases, peroxidases, and enzymes of glutathione supply, down-regulation of prooxidant enzymes, such as nitric oxide synthases and lipoxygenases, and presumably also the control of quinone reductase 2. Other mechanisms are based on direct interactions with several reactive oxygen and nitrogen species. Among these reactions, the capacity of easily undergoing single-electron transfer reactions is of particular importance. Electron donation by melatonin is not only an aspect of direct radical scavenging, but additionally represents the basis for formation of the protective metabolites AFMK (N1-ace-tyl-N2-formyl-5-methoxykynuramine) and AMK (N1-acetyl-5-methoxykynuramine). Recent investigations on mitochondrial metabolism indicate that melatonin as well as AMK are capable of supporting the electron flux through the respiratory chain, of preventing the breakdown of the mitochondrial membrane potential, and of decreasing electron leakage, thereby reducing the formation of superoxide anions. Radical avoidance is a new line of investigation, which exceeds mitochondrial actions and also comprises antiexcitatory effects and contributions to the maintenance of internal circadian phase relationships.

Melatonin, a potent agent in antioxidative defense: actions as a natural food constituent, gastrointestinal factor, drug and prodrug

Melatonin, originally discovered as a hormone of the pineal gland, is also produced in other organs and represents, additionally, a normal food constituent found in yeast and plant material, which can influence the level in the circulation. Compared to the pineal, the gastrointestinal tract contains several hundred times more melatonin, which can be released into the blood in response to food intake and stimuli by nutrients, especially tryptophan. Apart from its use as a commercial food additive, supraphysiological doses have been applied in medical trials and pure preparations are well tolerated by patients. Owing to its amphiphilicity, melatonin can enter any body fluid, cell or cell compartment. Its properties as an antioxidant agent are based on several, highly diverse effects. Apart from direct radical scavenging, it plays a role in upregulation of antioxidant and downregulation of prooxidant enzymes, and damage by free radicals can be reduced by its antiexcitatory actions, and presumably by contributions to appropriate internal circadian phasing, and by its improvement of mitochondrial metabolism, in terms of avoiding electron leakage and enhancing complex I and complex IV activities. Melatonin was shown to potentiate effects of other antioxidants, such as ascorbate and Trolox. Under physiological conditions, direct radical scavenging may only contribute to a minor extent to overall radical detoxification, although melatonin can eliminate several of them in scavenger cascades and potentiates the efficacy of antioxidant vitamins. Melatonin oxidation seems rather important for the production of other biologically active metabolites such as N¹-acetyl-N²-formyl-5-methoxykynuramine (AFMK) and N¹-acetyl-5-methoxykynuramine (AMK), which have been shown to also dispose of protective properties. Thus, melatonin may be regarded as a prodrug, too. AMK interacts with reactive oxygen and nitrogen species, conveys protection to mitochondria, inhibits and downregulates cyclooxygenase 2.

The regional and cellular expression profile of the melatonin receptor MT1 in the central dopaminergic system

The physiological effects of pineal melatonin are primarily mediated by melatonin receptors located in the brain and periphery. Even though there are a number of studies demonstrating the regulatory role of melatonin in the development of dopaminergic behaviors, such as psychostimulant-induced diurnal locomotor sensitization or drug seeking, little is known about the contribution of melatonin receptors (i.e., MT1) to this role. Therefore, as a first step in understanding the functional role of melatonin receptors in dopaminergic behaviors, we focused on determining the expression pattern of MT1 receptors in the dopaminergic system of the human and rodent brain. Regional (e.g., nucleus accumbens shell) and cellular (e.g., tyrosine hydroxylase immunopositive cells) expression of MT1 mRNA was characterized by applying the immuno-laser capture microdissection (immuno-LCM) technique coupled with nested RT-PCR. Moreover, employing quantitative Western immunoblotting and RT-PCR, we found that the mouse MT1 receptor expression presents diurnal variations (i.e., low mRNA and high protein levels at night, ZT21). The dopaminergic system-based presence of MT1 receptor proteins was not limited to rodents; we found these receptors in postmortem human brain as well. Further research is needed to understand the regional/cellular functional role of melatonin receptors in the regulation of dopaminergic behaviors, using models such as melatonin receptor knockout mice.

Cyclooxygenase-2-specific inhibitor improves functional outcomes, provides neuroprotection, and reduces inflammation in a rat model of traumatic brain injury

OBJECTIVE

Increases in brain cyclooxygenase-2 (COX2) are associated with the central inflammatory response and with delayed neuronal death, events that cause secondary insults after traumatic brain injury. A growing literature supports the benefit of COX2-specific inhibitors in treating brain injuries.

METHODS

DFU [5,5-dimethyl-3(3-fluorophenyl)-4(4-methylsulfonyl)phenyl-2(5)H)-furanone] is a third-generation, highly specific COX2 enzyme inhibitor. DFU treatments (1 or 10 mg/kg intraperitoneally, twice daily for 3 d) were initiated either before or after traumatic brain injury in a lateral cortical contusion rat model.

RESULTS

DFU treatments initiated 10 minutes before injury or up to 6 hours after injury enhanced functional recovery at 3 days compared with vehicle-treated controls. Significant improvements in neurological reflexes and memory were observed. DFU initiated 10 minutes before injury improved histopathology and altered eicosanoid profiles in the brain. DFU 1 mg/kg reduced the rise in prostaglandin E2 in the brain at 24 hours after injury. DFU 10 mg/kg attenuated injury-induced COX2 immunoreactivity in the cortex (24 and 72 h) and hippocampus (6 and 72 h). This treatment also decreased the total number of activated caspase-3-immunoreactive cells in the injured cortex and hippocampus, significantly reducing the number of activated caspase-3-immunoreactive neurons at 72 hours after injury. DFU 1 mg/kg amplified potentially anti-inflammatory epoxyeicosatrienoic acid levels by more than fourfold in the injured brain. DFU 10 mg/kg protected the levels of 2-arachidonoyl glycerol, a neuroprotective endocannabinoid, in the injured brain.

CONCLUSION

These improvements, particularly when treatment began up to 6 hours after injury, suggest exciting neuroprotective potential for COX2 inhibitors in the treatment of traumatic brain injury and support the consideration of Phase I/II clinical trials.

Rat pineal arylalkylamine-N-acetyltransferase: cyclic AMP inducibility of its gene depends on prior entrained photoperiod

The nocturnal biosynthesis of melatonin in the rat pineal depends on strongly enhanced expression of the enzyme N-acetyltransferase [arylalkylamine N-acetyltransferase (AA-NAT); EC 2.3.1.87]. AA-NAT transcription is stimulated during darkness by adrenergic inputs to the pineal from the suprachiasmatic nucleus (SCN). Nocturnal activation of the AA-NAT promotor following stimulation of pinealocyte adrenoceptors involves cAMP-dependent stimulation of protein kinase A (PKA). The nocturnal rise in AA-NAT depends on the lighting conditions. As compared with light/dark (LD) 12:12, the delay between dark onset and the nocturnal rise in AA-NAT is shortened under long photoperiods and prolonged under short photoperiods. Here, we report that the rapidity of nocturnal AA-NAT induction depends on cAMP inducibility of the gene. Accordingly, cAMP produces a strong AA-NAT response in pineals obtained from rats housed under long photoperiods and a weak AA-NAT response under short photoperiods. Changes in AA-NAT inducibility are fully developed not earlier than after seven cycles. This observation suggests that long-term changes in the photoperiod are necessary to achieve full adjustment of cAMP inducibility of the gene. A direct relationship was found between cAMP-dependent AA-NAT inducibility and the pineal protein kinase A (PKA) activity. As compared to LD 12:12, PKA activity was increased under LD 20:4 and attenuated under LD 4:20. On the basis of the present findings, we suggest that the photoperiod determines the effectiveness of nocturnal AA-NAT induction by long-term modulation of the intrapineal pathway that transmits the cAMP signal to the AA-NAT gene.

The pineal gland is critical for circadian Period1 expression in the striatum and for circadian cocaine sensitization in mice

Sensitization to psychostimulants can be influenced by circadian rhythms. The pineal gland, the main source of circadian melatonin synthesis, may influence behavioral sensitization to cocaine; mice with normal melatonin rhythms do not get sensitized at night. Clock genes such as Period1 (Per1) show rhythmic region- and strain-dependent expression in the mouse brain, and mice mutant for the Per1 gene lack cocaine sensitization. Here, for the first time we show circadian changes of PER1 protein levels in the mouse striatum, a brain region crucial for the development of locomotor sensitization to cocaine. In male C3H/HeJ mice, we found peak striatal PER1 protein levels during the day; this was preceded by a Per1 mRNA peak 16 h earlier. Pinealectomized mice did not show this circadian pattern. We analyzed circadian cocaine sensitization at times when striatal PER1 protein levels in control mice (naive and sham-pinealectomized) were high and low, respectively. Only mice with circadian changes in striatal Per1 expression showed the night-time absence of cocaine sensitization, whereas pinealectomized mice were without circadian changes in striatal Per1 and were sensitized to cocaine regardless of diurnal rhythm. Our results indicate that both the striatal circadian Per1 expression and diurnal locomotor cocaine sensitization are strongly influenced by pineal products. Since we found evidence for the expression of melatonin receptor mRNA in the striatum, we suggest that further studies on pineal-driven mechanisms will help us better understand the mechanisms of drug abuse and identify novel targets for the prevention and/or treatment of addictions.

Neuronal expression of arylalkylamine N-acetyltransferase (AANAT) mRNA in the rat brain

The role of arylalkylamine N-acetyltransferase (AANAT) in neuronal functioning has been suggested based on biochemical assays; only scarce evidence indicates neuronal expression of the mRNA encoding for this enzyme that catalyzes the conversion of serotonin into N-acetylserotonin. Using a quantitative reverse transcriptase polymerase chain reaction (RT-PCR) assay with internal standards, and an in-situ RT-PCR hybridization assay we found evidence for the expression of AANAT in the rat brain. In the localization studies, the most prominent AANAT mRNA signal was found in the granule neurons of the hippocampus, the olfactory bulb, and the cerebellum, and in the gray matter of the spinal cord. Diurnal differences in AANAT mRNA content were observed in the pineal gland but not in the hippocampus; the content of AANAT mRNA was lower both in the pineal gland and the hippocampus of old (24 months) compared with young (2 months) rats. These data are consistent with the hypothesis that AANAT may play a physiological role in mammalian central nervous system neurons. Further studies are warranted into the possible functional significance of neuronal expression of AANAT mRNA.

Expression of 5-lipoxygenase in pulmonary artery endothelial cells

Increased expression of 5-lipoxygenase (5LO) in pulmonary artery endothelial cells (PAECs) has been observed in disease states such as pulmonary hypertension and allergen challenge. To understand the function of endothelial 5LO, we examined the expression of this enzyme in normally cultured human PAECs and its characteristics when overexpressed. A small amount of 5LO message and protein was detected by reverse-transcriptase-mediated PCR (RT-PCR) and Western blotting in PAECs. Sequencing of the RT-PCR products that overlapped the entire coding region of 5LO mRNA indicated that the sequence of PAEC 5LO was identical with that of leucocyte 5LO. Incubation of the PAECs with A23187 and arachidonic acid led to a small production of 5-hydroxyeicosatetraenoic acid (5-HETE) (46-98 pmol/4x10(6) cells) but no leukotrienes. Overexpression of 5LO in PAECs by adenovirus-mediated gene transfer revealed that the enzyme was localized in the nucleus. Incubation of the transduced cells with A23187 (5 microM) caused the production of both 5LO products and downstream leukotrienes. The proportions of the produced leukotriene A(4) (LTA(4)) hydrolates (sum of 6-trans-LTB(4) and 12-epi-6-trans-LTB(4)), LTB(4) and cysteinyl leukotriene were approx. 17:14:10. cGMP production in the 5LO-transduced PAECs was decreased by 33+/-14% on stimulation with A23187. These results show that cultured PAECs express a minimal amount of 5LO, which can generate some 5-HETE, but not leukotrienes. However, increased expression of 5LO in PAECs can lead to the production of all downstream leukotrienes, which could potentially cause endothelial dysfunction in the pulmonary vasculature.

Involvement of the 5-lipoxygenase pathway in the neurotoxicity of the prion peptide PrP106-126

Transmissible spongiform encephalopathies are characterised by the transformation of the normal cellular prion protein (PrP(C)) into an abnormal isoform (PrP(TSE)). Previous studies have shown that N-methyl-D-aspartate (NMDA) receptor antagonists can inhibit glutathione depletion and neurotoxicity induced by PrP(TSE) and a toxic prion protein peptide, PrP106-126, in vitro. NMDA receptor activation is known to increase intracellular accumulation of Ca(2+), resulting in up-regulation of arachidonic acid (AA) metabolism. This can stimulate the lipoxygenase pathways that may generate a number of potentially neurotoxic metabolites. Because of the putative relationship between AA breakdown and PrP106-126 neurotoxicity, we investigated AA metabolism in primary cerebellar granule neuron cultures treated with PrP106-126. Our studies revealed that PrP106-126 exposure for 30 min significantly up-regulated AA release from cerebellar granule neurons. PrP106-126 neurotoxicity was mediated through the 5-lipoxygenase (5-LOX) pathway, as shown by abrogation of neuronal death with the 5-LOX inhibitors quinacrine, nordihydroguaiaretic acid, and caffeic acid. These inhibitors also prevented PrP106-126-induced caspase 3 activation and annexin V binding, indicating a central role for the 5-LOX pathway in PrP106-126-mediated proapoptosis. Interestingly, inhibitors of the 12-lipoxygenase pathway had no effect on PrP106-126 neurotoxicity or proapoptosis. These studies clearly demonstrate that AA metabolism through the 5-LOX pathway is an important early event in PrP106-126 neurotoxicity and consequently may have a critical role in PrP(TSE)-mediated cell loss in vivo. If this is so, therapeutic intervention with 5-LOX inhibitors may prove beneficial in the treatment of prion disorders.

Serine/threonine phosphatase inhibitors decrease adrenergic arylalkylamine n-acetyltransferase induction in the rat pineal gland

Adrenergic regulation of the pineal enzyme serotonin N-acetyltransferase [arylalkylamine N-acetyltransferase (AA-NAT); EC 2.3.1.87] accounts for the circadian rhythm in melatonin formation. In the present study, the role of protein phosphatases in the adrenergic regulation of rat pineal AA-NAT was investigated using specific inhibitors. In cultured pineals, the serine/threonine phosphatase type 1 and type 2A inhibitors okadaic acid and calyculin A significantly decreased adrenergically or cAMP-induced AA-NAT activity, whereas the serine/threonine phosphatase type 2B inhibitor cypermethrin and tyrosine phosphatase inhibitor dephostatin were ineffective. Reverse transcriptase-polymerase chain reaction (RT-PCR) data indicate that okadaic acid exerts its effect on cAMP-dependent AA-NAT induction by downregulating the amount of AA-NAT transcript. The 'third' messengers, inducible cAMP early repressor (ICER) and Fos-related antigene-2 (Fra-2), are believed to play a negative role in pineal AA-NAT transcription. Okadaic acid increased the cAMP responsiveness of neither ICER mRNA nor Fra-2 mRNA. Therefore, the regulatory role of pineal serine/threonine phosphatases in adrenergically stimulated AA-NAT expression probably does not depend on ICER or Fra-2.

Circadian rhythm in NO synthase I transcript expression and its photoperiodic regulation in the rat pineal gland

The photoneural regulation of nitric oxide synthase type I (NOS I) expression in the rat pineal was investigated using semiquantitative RT-PCR. NOS I transcript expression exhibited a daily rhythm with peak values during the night hours. The daily rhythm in NOS I transcript expression persisted under constant dark conditions and was abolished under constant light conditions. The extent of nocturnal NOS I expression was found to be dependent on the photoperiod. It was attenuated under 20 h light and 4 h dark (L:D 20:4) compared with 12 h light and 12 h dark (L:D 12:12). The present findings indicate that, in the rat pineal, NOS I transcript expression exhibits a true circadian rhythm. Further, photoperiod-induced changes in circadian transcript expression appear to be responsible for reported changes in NOS I protein expression.

A differential role of CREB phosphorylation in cAMP-inducible gene expression in the rat pineal

In the rat pineal gland cAMP mediates nocturnal induction of the enzyme arylalkylamine N-acetyltransferase (AA-NAT) as well as of transcription factors such as inducible cAMP early repressor (ICER), Fos-related antigen-2 (Fra-2) and JunB. Cyclic AMP stimulates the phosphorylation of the DNA binding protein cAMP response element binding protein (CREB). While cAMP-induced CREB phosphorylation appears to be a prerequisite for AA-NAT and ICER gene expression, it is not known whether CREB phosphorylation accounts for the full cAMP response of the two genes. Furthermore, the significance of CREB phosphorylation in cAMP-activated Fra-2 and JunB transcription is unknown. In the present in vitro study we used the serine/threonine protein phosphatase inhibitor okadaic acid (OA) to phosphorylate CREB without altering intrapineal cAMP concentration. It was observed that OA (10(-7) M) was less effective than dibutyryl cAMP (dbcAMP; 10(-3) M) in inducing AA-NAT mRNA and ICER mRNA, respectively. On the basis of this finding, it is concluded that CREB phosphorylation alone is apparently not sufficient for the full cAMP response of the two genes. By contrast, OA and dbcAMP equally stimulated the accumulation of the mRNAs of Fra-2 and JunB. Therefore cAMP may induce Fra-2 and JunB transcripts via CREB phosphorylation. Our observations suggest that CREB phosphorylation plays a critical role in diversification of cAMP-dependent gene induction in the rat pineal.

New anti-inflammatory treatment strategy in Alzheimer's disease

Numerous reports have indicated that patients suffering from inflammatory diseases (e.g., arthritis) who take anti-inflammatory medication have a reduced risk of developing Alzheimer's disease (AD). Thus, the first generation of anti-inflammatory cyclooxygenase (COX) inhibitors, such as aspirin and indomethacin, have been tested as potential therapeutics in AD. Because the inhibition of COX-1 is also known to cause tissue damage in the gastrointestinal system from the resultant reduced cytoprotection, selective COX-2 inhibitors are being investigated and tested clinically as potentially better therapeutics for AD patients. However, such drugs may also trigger unwanted effects; for example, the COX-2 inhibitors, which reduce the production of one type of eicosanoids, the prostaglandins, may increase the production of other eicosanoids; i.e., the leukotriene B4 (LTB4), which is one of the most potent endogenous chemotactic/inflammatory factors. LTB4 production is initiated by the enzyme 5-lipoxygenase (5-LOX). The expression of the 5-LOX gene is upregulated during neurodegeneration and with aging. In spite of the fact that 5-LOX and leukotrienes are major players in the inflammation cascade, their role in AD pathobiology/therapy has not been extensively investigated. We propose that the 5-LOX inflammatory cascade may take part in the process of aging-associated neurodegenerative diseases, and we point to the role of 5-LOX in neurodegeneration and discuss its relevance for anti-inflammatory therapy of AD.