SLEEP PHYSIOLOGY

Prostaglandin D Synthase (β-trace) in Healthy Human Sleep Wolfgang Jordan, MD1; Hayrettin Tumani, MD, PhD2; Stefan Cohrs, MD1; Sebastian Eggert1; Andrea Rodenbeck, DSc1; Edgar Brunner, MD, PhD3; Eckart Rüther, MD, PhD1; Göran Hajak, MD, PhD1,4

1Department of Psychiatry and Psychotherapy, University of Göttingen; 2Department of Neurology, Universitiy of Ulm; 3Department of Medical Statistics, University of Göttingen; 4Department of Psychiatry and Psychotherapy, University of Regensburg, Germany

Study Objectives: The prostaglandin D system plays an important role in Results: Serum L-PGDS concentrations showed marked time-dependent animal sleep. In humans, alterations in the prostaglandin D system have changes with evening increases and the highest values at night (P< been found in diseases exhibiting sleep disturbances as a prominent .0005). This nocturnal increase was suppressed during total sleep depri-

symptom, such as trypanosoma infection, systemic mastocytosis, bacteri- vation (P< .05), independent of external light conditions and melatonin Downloaded from https://academic.oup.com/sleep/article/27/5/867/2708439 by guest on 28 September 2021 al meningitis, major depression, or obstructive sleep apnea. Assessment secretion. Rapid eye movement sleep deprivation had no impact on cir- of this system’s activity in relation to human physiologic sleep was the tar- culating L-PGDS levels. get of the present study. Conclusions: The circadian L-PGDS pattern and its suppression by total Design: Serum concentrations of lipocalin-type prostaglandin D synthase sleep deprivation indicate an interaction of the prostaglandin D system (L-PGDS, former β-trace), and plasma levels of the pineal hormone mela- and human sleep regulation. L-PGDS measurements may well provide tonin were measured in 20 healthy humans (10 women, 10 men; aged: new insights into physiologic and pathologic sleep regulation in humans. 23.3 ± 2.39 years) at 4-hour intervals over a period of 5 days and nights, Abbreviations: CSF,cerebrospinal fluid; L-PGDS, lipocalin-type which included physiologic sleep, rapid eye movement sleep deprivation, prostaglandin-D-synthase; PGD2, prostaglandin D2; REM, rapid eye and total sleep deprivation. In addition, the serum L-PGDS and plasma movement; SWS, slow wave sleep melatonin levels of 6 subjects were determined under conditions of bright Key Words: Lipocalin-type prostaglandin D synthase (EC 5.3.99.2), β- white (10,000 lux) or dark red light (< 50 lux) in a crossover design during trace, PGD2, melatonin, human physiologic sleep regulation, sleep depri- total sleep deprivation. Nocturnal blood sampling was performed by a vation, hypersomnia through-the-wall tube system. L-PGDS was measured by an automated Citation: Jordan W; Tumani H; Cohrs S et al. Prostaglandin D synthase immunonephelometric assay, and melatonin was analyzed by direct (β-trace) in healthy human sleep. SLEEP 2004;27(5):867-874. radioimmunoassay.

INTRODUCTION Additionally, the impact of the prostaglandin D system on sleep regulation could also be demonstrated in primates.17 In humans, PROSTAGLANDINS ARE UBIQUITOUSLY DISTRIBUTED the prostaglandin D system seems to be involved in several dis- IN VIRTUALLY ALL MAMMALIAN TISSUES AND eases presenting hypersomnia as a prominent symptom, such as ORGANS.Prostaglandin D (PGD ) is unique among the 2 2 African sleeping sickness,18 systemic mastocytosis,19 or severe prostaglandins in being present in relatively high concentrations obstructive sleep apnea syndrome.20 Alterations in the in the mammalian brain. Among the 3 enzymes catalyzing the prostaglandin D system have been also associated with bacterial conversion of prostaglandin H2 to PGD2, the lipocalin-type meningitis21 or major depression,22,23 which are usually accom- prostaglandin D synthase (L-PGDS) (Enzyme Commission panied by sleep disturbances. However, the prostaglandin D sys- Number: EC 5.3.99.2) is responsible for the biosynthesis of tem has not yet been investigated in human physiologic sleep. PGD2 in the brain. L-PGDS itself is mainly synthesized in the Therefore, serum L-PGDS and plasma melatonin, a known deter- choroid plexus, leptomeninges, and oligodendrocytes of the cen- minant of the sleep-wake rhythm, were simultaneously measured tral nervous system and is secreted into the cerebrospinal fluid in healthy subjects during physiologic sleep and in conditions of (CSF).1,2 Based on the results of amino-acid sequencing, L- total and rapid eye movement (REM) sleep deprivation. PGDS has been identified as β-trace.3,4 β-trace is the second most abundant protein in human CSF after albumin, representing 8% METHODS of the total CSF protein.4 A 32:1 CSF-serum concentration gradi- ent indicates that the β-trace protein in the serum originates pre- Study Subjects 5 dominantly from the brain. The study was approved by the local Research Ethical A large number of studies has demonstrated a crucial role for Committee. A total of 20 medical students (10 women, 10 men; 2,6-16 the prostaglandin D system in rodent sleep regulation. mean age ± SD 23.3 ± 2.39 years) were included in the study after obtaining their written informed consent. All were nor- Disclosure Statement motensive and found to be healthy by medical history and phys- No significant financial interest/other relationship to disclose. ical examination. In particular, they had no history of smoking, drug intake, affective disorder, allergy, hypertension, or pul- Submitted for publication September 2003 monary, renal, neurologic, or cerebrovascular disease. Routine Accepted for publication February 2004 laboratory tests included blood cell count, coagulating properties, Address correspondence to: Dr. W. Jordan, Department of Psychiatry and electrolytes, liver enzymes, creatinine, and urea. Normal renal Psychotherapy, Georg-August-University of Göttingen, von Sieboldstr. 5, 37075 function was assessed by serum and urine creatinine and noctur- Göttingen, Germany; Tel: 49 551 396761; Fax: 49 551 393887; nal creatinine clearance. Absence of any inflammation was con- E-mail: [email protected] SLEEP, Vol. 27, No. 5, 2004 867 Prostaglandin D Synthase (β-trace) in Healthy Human Sleep—Jordan et al firmed by laboratory results. Screening of volunteers involved Behring Nephelometer Analyzer (BNA). The test kit employs blood-pressure determination, electrocardiogram, electroen- affinity-purified polyclonal rabbit antibodies coupled to latex cephalogram, and polysomnography. Subjects with more than 10 particles and is sensitive enough (analytical sensitivity of 0.05 sleep-related breathing disturbances or more than 5 periodic leg mg/L) to reliably measure serum concentrations. The interassay movements per hour were excluded from the investigation. coefficient of variation of a control sample was 4.7% at 0.262 ± During the entire study period, subjects stayed in the sleep lab- 0.012 mg/L. The validity data of the L-PGDS assay have been oratory and were given a protein-carbohydrate balanced lunch reported previously.20,21 and a light morning and evening meal, which was a standardized Plasma melatonin concentrations were measured by direct feature of the study. The mealtimes remained unchanged during radioimmunoassay using a highly specific antibody (GS 704- total sleep deprivation; this included overnight fasting until after 6483) from Guildhay antisera (Guildford, United Kingdom). The the morning blood sampling. detection limit of this assay (at which 5% of the ligand is dis- placed) was 3.33 pg/mL. Intraassay and interassay variance were Study Design 6% and 12%, respectively.26

Concentrations of serum L-PGDS and plasma melatonin were Downloaded from https://academic.oup.com/sleep/article/27/5/867/2708439 by guest on 28 September 2021 Analysis measured in 20 healthy subjects at 4-hour intervals (4:00 PM, 8:00 PM, midnight, 4:00 AM, 8:00 AM, and noon) over a period Sleep stages and arousal data were manually determined in 30- of 5 days and nights covering physiologic sleep (baseline), REM second epochs and added to the data stored on a personal com- sleep deprivation, and total sleep deprivation, as well as a recov- puter system. Standard parameters included time in bed, sleep ery night between the nights of sleep deprivation. Sleep was period time (time from sleep onset to final awakening), total polysomnographically monitored every night except for the night sleep time (sleep period time minus time spent awake), sleep effi- of total sleep deprivation. Overnight cardiorespiratory ciency (total sleep time divided by the time in bed), percentage polysomnography followed international guidelines using stan- wake of sleep period time, sleep latencies to stage 2 sleep and dard methods.24,25 All recordings were made on a polysomno- slow wave sleep (SWS), REM latency (time from first epoch of graph (Nihon Kohden; Tokyo, Japan) and simultaneously stored stage 2 sleep until the first epoch of REM sleep), percentage of on a personal computer system (Sagura Polysomnograph 2000, sleep stages (stage 1, stage 2, SWS, REM sleep) of total sleep Sagura Medizintechnik GmbH, 63165 Mühlheim, Germany). time, REM sleep duration, and total number of transitions from Each session started with an adaptation night with the complete sleep stages. In order to get more information about the efficien- montage for polysomnographic recordings, followed by baseline cy of the REM sleep deprivation induced by acoustic stimuli, sleep during which sequential blood sampling started. Nocturnal REM sleep duration per number of transitions were additionally blood sampling was performed by a through-the-wall tube sys- calculated. tem. In the process, the study group was randomly divided for the Two-tailed Student t tests were applied separately for each 2 sleep-deprivation conditions—the first group in the experimen- sleep parameter to compare 2 consecutive nights, ie, recovery tal sequence: total sleep deprivation, recovery night, and REM night versus REM sleep deprivation night in Group 1 and base- sleep deprivation (Group 1), and the second one in the sequence: line sleep night versus REM sleep deprivation night in Group 2. REM sleep deprivation, recovery night, and total sleep depriva- The statistical analysis of sleep parameters was performed such tion (Group 2). For REM sleep deprivation, acoustic stimuli (1- that they corresponded with the analysis of the L-PGDS concen- kHz tone) with increasing volume (up to 100 dB) were applied trations. when REM sleep occurred, and the effect on REM sleep termi- After excluding a difference in L-PGDS concentrations in the nation was visually controlled on line during polysomnographic baseline night for both experimental groups, the subjects could be recording. Acoustic stimulation was terminated when arousal combined to analyse L-PGDS concentrations for the entire group. occurred or as soon as the subject exhibited a transition into Subsequently, a multiple analysis of variance with repeated mea- another sleep stage or wakefulness. During the total sleep-depri- sures was performed to analyze L-PGDS concentrations across vation night, subjects were asked to remain awake and out of bed the 24-hour period during the baseline sleep state of the entire in the sleep laboratory under customary light conditions and group. In case of significance, the multiple analysis of variance restricted physical activity. The procedure was thoroughly moni- was followed by posthoc Student t tests in order to compare L- tored by the nursing staff to ensure that the subjects did not fall PGDS concentrations at different time points to the 8:00 PM asleep or become too active. Daytime naps were not allowed. In value. addition, serum L-PGDS and plasma melatonin of 6 subjects Since it is not clear whether the sequence of sleep-deprivation were determined every 2 hours during total sleep deprivation challenges has an impact on L-PGDS levels under conditions fol- under conditions of bright white (10,000 lux) or dark red light (< lowing the first baseline night, we have split the analysis for both 50 lux) in a cross-over design. The investigation of the effects of sequence groups in 2 parts with an α-adjusting for each part. We special illumination began after the 8:00 PM evening blood sam- note that classical multiple analysis of variance could not be pling and stopped after the 8:00 AM morning blood sampling. applied here because the number of time points (t = 12) per sub- ject was larger than the number of subjects within each group (n Laboratory Methods = 10). Therefore, a statistical technique has been applied as described by Brunner27 and Werner.28 The repeated measures L-PGDS in serum was concurrently determined with albumin analysis for longitudinal data compared L-PGDS concentrations as a reference protein using an immunonephelometric assay in the course of 2 consecutive nights for both experimental (Behringwerke AG, Marburg, Germany) on an automated sequences (Group 1: baseline sleep versus total sleep deprivation

SLEEP, Vol. 27, No. 5, 2004 868 Prostaglandin D Synthase (β-trace) in Healthy Human Sleep—Jordan et al and recovery night versus REM sleep deprivation; Group 2: base- summarized in Table 1. In both groups REM-sleep parameters line sleep versus REM sleep deprivation and recovery night ver- (REM duration, REM duration/number of transitions) were sig- sus total sleep deprivation, respectively). In the process, effects nificantly decreased in the REM sleep deprivation night com- of sleep conditions, times of blood sampling, and interactions pared to the preceding night. Despite a significant increase in could be investigated. The repeated measures analyses were number of transitions during REM sleep, which reflects the adjusted at the α1/2 level. Data are presented as mean ± SD. A P impact of this intervention, the efficiency with regard to relative value of < .05 was considered as significant. duration of REM sleep was rather low and exhibited a decrease of between 1.5% and 4.5%. Instead, absolute REM sleep duration RESULTS decreased between 26% and 37%, though the longer sleep period time of the preceding night in Group 1 should be noted. Sleep parameters separated for both experimental sequences Moreover, this night significantly differed from REM sleep (Group 1: baseline sleep – total sleep deprivation – recovery deprivation in most of the standard sleep parameters in that they night – REM sleep deprivation; Group 2: baseline sleep – REM predominantly describe length and quality of sleep. During the sleep deprivation – recovery night – total sleep deprivation) are REM sleep-deprivation nights the volume of the auditory stimuli applied and the number of sleep transitions required to prevent Downloaded from https://academic.oup.com/sleep/article/27/5/867/2708439 by guest on 28 September 2021 REM sleep increased in the course of the night. L-PGDS levels under baseline sleep conditions did not differ between the 2 groups. Multiple analyses of variance revealed a significant time-dependent fluctuation for the entire group (F = 4.982, df 5, P< .0005, n = 20) with the highest levels in the night and in the morning and the lowest concentration in the afternoon (Figure 1). Posthoc analysis showed significant increases at 4:00 AM and 8:00 AM, respectively, compared to the 8:00 PM values. In addition, trends were seen at midnight and 4:00 PM. The sleep onset of baseline sleep for the whole group was at 00:17 AM ± 42 minutes; awakening was at 8:13 AM ± 42 minutes. For both groups, a significant sampling time x sleep condition Figure 1—Serum lipocalin-type prostaglandin D synthase concentra- interaction (Group 1: F5.9 = 2.713, P = .013; Group 2: F5.8 = tion (mean ± SD) in 20 healthy subjects during baseline sleep. Sleep 2.648, P= .016; n = 10) in the longitudinal analysis indicated dif- onset was at 00:17 AM (± 42 minutes); awakening was at 08:13 AM (± ferent patterns of L-PGDS concentrations during total sleep 42 minutes).

Table 1—Sleep Parameters

Sleep Group 1 Group 2 parameters Baseline (1) Recovery† (3) REM sleep Statistical Baseline (1) REM sleep Recovery (3) Statistical deprivation (4) analysis deprivation (2) night analysis (3) vs (4) (1) vs (2)

Sleep onset 0.18 ± 0.36 23.22 ± 0.40 0.29 ± 0.35 P< .005 0.17 ± 0.49 0.17 ± 0.22 0.28 ± 0.32 NS Awakening 8.03 ± 0.28 9.30 ± 1.18 8.09 ± 0.47 P< .05 8.22 ± 0.52 7.54 ± 0.54 9.09 ± 0.59 P< .05 TIB, min 503.10 ± 30.78 617 ± 89.28 487.70 ± 56.44 P< .01 517.80 ± 53.92 488.25 ± 56.42 558.05 ± 64.10 NS SPT, min 464.76 ± 30.47 607.70 ± 91.01 460.03 ± 51.31 P< .005 485.65 ± 65.17 457.10 ± 66.87 521.45 ± 64.68 NS TST, min 403.35 ± 68.89 570.55 ± 76.26 394.70 ± 56.43 P< .005 426.55 ± 43.82 393.25 ± 55.20 471.50 ± 78.81 NS SE, % 80.29 ± 12.97 92.64 ± 3.23 81.21 ± 10.10 P< .01 82.50 ± 5.05 80.47 ± 5.15 84.33 ± 9.20 NS WASO, % 13.59 ± 11.73 5.86 ± 3.46 13.65 ± 8.91 P< .05 11.74 ± 5.71 13.67 ± 6.19 9.79 ± 8.39 NS S2-L, min 28.10 ± 25.29 4.50 ± 3.28 24.45 ± 18.11 P< .01 25.15 ± 27.92 17.7 ± 13.23 29.25 ± 23.58 NS SWS-L, min 16.45 ± 10.16 5.90 ± 2.23 14.65 ± 11.28 P< .05 17.05 ± 11.92 30.95 ± 39.60 29.70 ± 36.62 NS REM-L, min 137.65 ± 49.62 112.85 ± 49.77 81.40 ± 27.76 NS 114.30 ± 69.40 84.55 ± 41.13 102.40 ± 53.61 NS REM%, % 19.50 ± 6.26 19.49 ± 5.43 18.04 ± 4.13 NS 21.66 ± 7.44 17.20 ± 6.04 23.97 ± 8.06 P< .05 S1%, % 6.69 ± 3.19 4.06 ± 1.55 8.97 ± 3.29 P< .0005 6.40 ± 2.03 8.65 ± 3.42 5.87 ± 2.77 P< .05 S2%, % 55.05 ± 7.10 53.25 ± 8.43 51.42 ± 4.34 NS 56.77 ± 6.11 55.55 ± 7.38 54.15 ± 5.67 NS SWS%, % 18.68 ± 7.96 23.09 ± 6.29 21.44 ± 6.72 NS 15.17 ± 7.40 18.58 ± 9.48 15.98 ± 6.67 NS REM-D, min 82.20 ± 34.39 113.50 ± 42.60 71.45 ± 20.16 P< .05 91.50 ± 28.94 67.95 ± 26.27 117.45 ± 50.49 P< .05 REM-D/NT, no. 8.21 ± 2.26 7.76 ± 4.15 4.26 ± 1.75 P< .01 6.63 ± 3.59 2.83 ± 1.46 6.55 ± 3.56 P< .01 NT-Total, no. 164.70 ± 41.70 206.80 ± 37.47 181.40 ± 20.94 P< .05 178.70 ± 36.22 199.20 ± 42.24 177.20 ± 47.29 NS

*Data are presented as mean ± SD. † Recovery night after total sleep deprivation REM refers to rapid eye movement sleep; TIB, time in bed; SPT, sleep period time; TST, total sleep time; SE, sleep efficiency TST/TIB; WASO, percentage wake of SPT; S2-L, latency to stage 2 sleep; SWS-L, SWS latency; REM-L, REM latency; REM%, S1%, S2%, SWS%, percentage of REM sleep, sleep stage 1, stage 2, or SWS of TST; REM-D, REM sleep duration; REM-D/NT, REM sleep duration/number of transitions; NT-Total, total number of transitions from sleep stages.

SLEEP, Vol. 27, No. 5, 2004 869 Prostaglandin D Synthase (β-trace) in Healthy Human Sleep—Jordan et al deprivation and the preceding night; whereas such a difference sleep deprivation was independent of external light conditions could not be found between REM sleep deprivation and the pre- and melatonin secretion (Figure 4, Table 2). ceding night (Group 1: F3.0 = 0.263, P= .853; Group 2: F4.5 = 0.520, P= .744; n = 10) (Figure 2). In addition, the analysis of DISCUSSION longitudinal data revealed a significant time effect for the com- To our knowledge, this is the first study investigating serum L- parison of baseline sleep and REM sleep-deprivation night in PGDS in human physiologic sleep. Our results indicate a circadi- Group 2 (F = 2.291, P= .024, n = 10) and for the comparison 7.1 an pattern of serum L-PGDS concentrations with evening of sleep during recovery night and REM sleep deprivation in increases and highest values at night. This nocturnal increase was Group 1 (F = 4.289, P= .004, n = 10). Thus, time-dependent 3.3 suppressed during total sleep deprivation independently of exter- fluctuation of L-PGDS levels during baseline sleep was main- nal light conditions and melatonin secretion. In contrast, REM tained during the recovery night and REM sleep deprivation, sleep deprivation seemed to have no impact on serum L-PGDS. independent of the experimental sequence used (Group 1 or 2). In Several lines of evidence indicate that the results presented in contrast, the nocturnal increase of L-PGDS concentrations was this study are valid and reliable. The serum L-PGDS concentra- suppressed during total sleep deprivation in both experimental tions measured were in accordance with values found by other Downloaded from https://academic.oup.com/sleep/article/27/5/867/2708439 by guest on 28 September 2021 sequences. authors.5,29 Diseases known to affect serum L-PGDS values such Plasma melatonin concentrations exhibited a well-known pat- as essential hypertension,30 renal disorders,30,31 neurologic disor- tern with nocturnal increases and a marked suppression during ders,29,32 stable angina, and severe stenosis33 had been previously sleep deprivation (Figure 3). Plasma melatonin concentrations excluded. Consequently, the circadian pattern of serum L-PGDS were within the normal range for healthy subjects.26 Additionally, levels and its suppression by total sleep deprivation in our study simultaneous measurement of L-PGDS and melatonin in 6 sub- cannot be explained by any of the above-mentioned diseases. jects during total sleep deprivation with bright-white or dark-red Finally, the small quantities of L-PGDS, localized in compart- light conditions indicated that L-PGDS suppression during total ments outside the brain, such as male genital organs, retina, or

Figure 2—Serum lipocalin-type prostaglandin D synthase concentration (mean) in 20 healthy subjects at 4-hour intervals over a period of 5 days and nights covering physiologic sleep, total sleep deprivation, and rapid eye movement (REM) sleep deprivation. Group 1: baseline sleep–total sleep deprivation–recovery night–REM sleep deprivation. Group 2: baseline sleep–REM sleep deprivation–recovery night–total sleep deprivation.

SLEEP, Vol. 27, No. 5, 2004 870 Prostaglandin D Synthase (β-trace) in Healthy Human Sleep—Jordan et al cochlea, are secreted into the closed compartments of these tis- state conditions, the concentration of this leptomeningeal protein sues.6 Thus, they are unable to influence L-PGDS levels in sys- in blood could be maintained just by the CSF flow into the blood temic circulation. stream. This suggests that an additional increase in peripheral L- The circadian pattern of circulating L-PGDS in our subjects PGDS follows a prior release in the brain depending on the cir- appears to be a constant feature of sleep-wake regulation, not culation time. Whether L-PGDS levels in the periphery are relat- only found in relatively undisturbed baseline sleep and recovery ed to the functional state of the prostaglandin D system in the sleep after sleep deprivations, but also maintained in the more brain cannot be answered by this discussion or the presented data. fragmented sleep resulting from auditory stimuli to induce REM Although data from animal studies may not be completely trans- sleep deprivation. The evening increase in peripheral L-PGDS ferable to human physiology, results support the assumption that levels peaked at night and was still elevated in the morning. This increases in L-PGDS in serum of humans reflect increased avail- 2 morning elevation is most probably related to a nocturnal release ability of PGD2 in the brain. of L-PGDS in brain tissue because of the time required for this It should be noted that prostaglandins markedly enhance mela- brain-derived protein to reach the venous blood and an assumed tonin synthesis during nighttime hours.35-37 However, such an half-life of 4 hours in blood.34 The main sources of L-PGDS involvement may only be important in physiologic sleep regula- Downloaded from https://academic.oup.com/sleep/article/27/5/867/2708439 by guest on 28 September 2021 biosynthesis in the brain are the leptomeninges.1,3,5 Thus, the low tion. During total sleep deprivation, the suppression of circulat- ventricular CSF concentration of L-PGDS increases along the ing L-PGDS levels exhibited no impact on melatonin secretion. CSF flow pathway in the subarachnoid space due to a continuous Thus, an overall influence of L-PGDS or PGD2 on melatonin release by the leptomeninges. Finally, the higher concentration in synthesis seems to be unlikely. In our subjects, the nocturnal the lumbar CSF will be diluted by approximately 1:10 by the increase of L-PGDS was reliably suppressed during total sleep flow of 500 mL of CSF per day into 5 L of blood. Under steady- deprivation in both groups.Using a crossover design, we were

Figure 3—Plasma melatonin concentration (mean ± SD) in 20 healthy subjects at 4-hour intervals over a period of 5 days and nights covering phys- iologic sleep, total sleep deprivation, and rapid eye movement (REM) sleep deprivation.
Group 1: baseline sleep–total sleep deprivation–recov- ery night–REM sleep deprivation.  Group 2: baseline sleep–REM sleep deprivation–recovery night–total sleep deprivation.

Figure 4—Serum lipocalin-type prostaglandin D synthase (L-PGDS) concentrations and plasma melatonin concentrations in 1 subject every 2 hours during total sleep deprivation under conditions of bright white (10,000 lux) or dark red light (< 50 lux) in a crossover design.
L-PGDS concen- tration [mg/L]  melatonin concentration [pg/mL]

SLEEP, Vol. 27, No. 5, 2004 871 Prostaglandin D Synthase (β-trace) in Healthy Human Sleep—Jordan et al able to show that this suppression was independent of external light conditions or melatonin secretion. However, we definitely could not distinguish between the effects of complete sleep loss and specific SWS loss responsible for the L-PGDS suppression with the present data. Furthermore, the study data lack informa- tion regarding the extent to which the effects on L-PGDS con- centrations might be caused by changes in body temperature dur-

16 16.75 ± 7.96 ing total sleep deprivation. However, a direct impact of body

0.94 13.40 ± 1.18 temperature on serum L-PGDS levels has not yet been demon- strated in humans. Since the effects of sleep loss on core temper- 502 ± 0.122 0.479 ± 0.081 .477 ± 0.102 0.453 ± 0.070 ature can persist for more than 24 hours,38 an alteration in circu- lating L-PGDS levels on recovery days and nights had to be expected in our study. However, such an alteration was not observed. Therefore, we conclude that an influence of body tem- perature on L-PGDS levels during total sleep deprivation can be Downloaded from https://academic.oup.com/sleep/article/27/5/867/2708439 by guest on 28 September 2021 neglected. Moreover, it is unlikely that increased physical activi- ty during total sleep deprivation affected L-PGDS levels, even if white (10,000 lux) or dark red light (< 50 lux) a constant-routine protocol had not been implemented, because restricted activity was ensured by our nursing staff in all of our subjects. Total sleep deprivation was realized in an upright posi- tion out of bed. Since L-PGDS in blood originates primarily from CSF flow into venous blood, a change in posture could at most result in a different driving force for CSF flow, ie, an alteration of the arteriovenous pressure gradient, contributing to a larger time delay for arrival in blood. However, such a contribution of posture to circulating time has not yet been demonstrated. Altogether, total sleep deprivation decreased peripheral L-PGDS levels, thus suggesting reduced activity of the prostaglandin D system in the brain. In contrast to total sleep deprivation, REM sleep deprivation had no impact on serum L-PGDS concentrations. This might be due to the fact, that REM sleep deprivation in our subjects was not achieved consistently because a concurrent increase in time awake should be avoided to allow clear differentiation between the 2 sleep-deprivation conditions. Therefore, the results of this condition cannot be conclusively interpreted. However, recent findings in animal sleep have proposed an involvement of the L- PGDS gene in non-REM sleep regulation,15 thus supporting the 7 assumption that the effect of PGD2 on REM sleep might be the result of a prior alteration of SWS. To date, the precise involvement of the prostaglandin D system in human sleep regulation is still speculative. In an animal model, the sleep-promoting property of PGD2 seemed to be independent of the serotoninergic modulation of the sleep-wake activity,39 whereas a modulatory action on noradrenalin-induced activity of preoptic and basal forebrain neurons was found.40 It has been hypothesized that a histamine-release factor, probably inter- leukin-1, would release histamine from mast cells in the thalamus and hypothalamus, which in turn would cause phospholipase A2 to produce arachidonic acid from the phosphatidyl choline in cell membranes. PGD2 is then formed from the arachidonic acid by the action of prostaglandin H synthase and prostaglandin D syn- thase.41 Other putative sleep factors with the capacity to enhance prostaglandin production are growth hormone-releasing factor42 and muramyl dipeptide.43 However, it is questionable whether the neurobiochemical effects of L-PGDS can be restricted to its Serum L-PGDS and melatonin concentrations of 6 subjects every 2 hours during total sleep deprivation under conditions of bright enzymatic activity alone. 14.01 ± 4.83 13.26 ± 5.57 18.15 ± 11.71 14.39 ± 6.92 0.461 ± 0.132 0.466 ± 0.103 15.18 ± 6.67 0.478 ± 0.087 14.04 ± 3.3 ± 20.11 0.486 11.03 ± 0.099 14.66 0.483 ± ± 1.71 0.079 16.71 ± 5.51 0.494 ± 0.095 12.92 ± 2.26 16.59 ± 3.21 0.498 ± 0.105 24.1 ± 18.77 0.477 ± 0.084 15.45 ± 6.35 0.472 ± 0.096 41 ± 24.85 16.89 ± 7. 0 60.98 ± 40.25 93.08 ± 24.13 86.19 ± 21.68 37.84 ± 18.64 15.98 ± 4:00 PM 6:00 PM0.555 ± 0.155 0.573 ± 0.081 8:00 PM 0.533 ± 0.083 0.509 ± 0.077 0.497 ± 0.065 10:00 PM ± 0.511 0.113 0.525 ± 0.097 0.533 ± 0.118 Midnight 0.484 ± 0.131 0. 2:00 AM 4:00 AM 6:00 AMThe 8:00 AM results 10:00 AM of this Noon study have to be discussed against the back- ground of sleep-disrupting drug effects. The prostaglandin D sys- Melatonin, pg/mL Red light L-PGDS, mg/L Melatonin, pg/mL *Data are presented as mean ± SD. L-PGDS refers to lipocalin-type prostaglandin D synthase. Table 2— Table White light L-PGDS, mg/L tem and thus physiologic sleep regulation can be easily influ- SLEEP, Vol. 27, No. 5, 2004 872 Prostaglandin D Synthase (β-trace) in Healthy Human Sleep—Jordan et al enced by many drugs, eg nonsteroidal anti-inflammatory drugs, 6.Urade Y, Watanabe K, Hayaishi O. Prostaglandin D, E, and F syn- specific cyclooxygenase inhibitors, or synthetic glucocorticoids. thases. J Lipid Mediat Cell Signal 1995;12:257-73. Low doses of nonsteroidal anti-inflammatory drugs such as 7.Ueno R, Honda K, Inoue S, Hayaishi O. Prostaglandin D2, a cere- aspirin or ibuprofen given to healthy subjects for a brief period bral sleep inducing substance in rats. Proc Natl Acad Sci U S A 1983;80:1735-7. disrupt their sleep and lead to a reduction44 or a delay of SWS.45 8.Matsumura H, Takahata R, Hayaishi O. Inhibition of sleep in rats by Furthermore, the normal nocturnal decrease in body temperature inorganic selenium compounds, inhibitors of prostaglandin D syn- 46 is attenuated and melatonin synthesis is suppressed. The mech- thase. Proc Natl Acad Sci U S A 1991;88:9046-50. anisms of sleep disruption after nonsteroidal anti-inflammatory 9.Takahata R, Matsumura H, Sri Kantha S, et al. Intravenous admin- drugs ingestion have been considered to be direct or indirect con- istration of inorganic selenium compounds, inhibitors of sequences of their inhibition of prostaglandin synthesis, includ- prostaglandin D synthase, inhibits sleep in freely moving rats. Brain ing decreases in PGD2. In contrast to the situation in many tis- Res 1993;623:65-71. sues, where glucocorticoids inhibit cyclooxygenase activity and 10.Naito K, Osama H, Ueno R, Hayaishi O, Honda K, Inoue S. prostaglandin synthesis, in mouse neuronal cells, dexamethasone Suppression of sleep by prostaglandin synthesis inhibitors in unre- strained rats. Brain Res 1988;453:329-36. has been shown to induce L-PGDS gene expression,47 which pro- 11.Pandey HP, Ram A, Matsumura H, Satoh S, Hayaishi O. CircadianDownloaded from https://academic.oup.com/sleep/article/27/5/867/2708439 by guest on 28 September 2021 vides the option of direct L-PGDS gene regulation by this gluco- variations of prostaglandins D2, E2, and F2a in the cerebrospinal corticoid. As a consequence of its linkage with the immune sys- fluid of anesthetized rats. Biochem Biophys Res Commun tem as well as with human sleep regulation, the prostaglandin D 1995;213:625-9. system offers a direct access for investigating both systems, and, 12.Pandey HP, Ram A, Matsumura H, Hayaishi O. Concentration of moreover, it can be easily influenced. Therefore, assessment of prostaglandin D2 in cerebrospinal fluid exhibits a circadian alter- the prostaglandin D system, including its alteration with drugs, ation in conscious rats. Biochem Mol Biol Int 1995;37:431-7. may provide new insights into the regulation of physiologic and 13.Ram A, Pandey HP, Matsumura H, et al. CSF levels of pathologic sleep, particularly in conditions involving hypersom- prostaglandins, especially the level of prostaglandin D2, are corre- lated with increasing propensity towards sleep in rats. Brain Res nia, inflammation, or both. 1997;751:81-9. In summary, there is convincing evidence from animal studies 14.Satoh S, Matsumura H, Suzuki F, Hayaishi O. Promotion of sleep that the prostaglandin D system influences sleep regulation. The mediated by the A2a-adenosine receptor and possible involvement present data on human subjects appear to support this hypothesis. of this receptor in the sleep induced by prostaglandin D2 in rats. The physiologic significance of our findings needs to be con- Proc Natl Acad Sci U S A 1996;93:5980-4. firmed by further studies, eg, by the assessment of L-PGDS in 15.Pinzar E, Kanaoka Y, Inui T, Eguchi N, Urade Y, Hayaishi O. disorders exhibiting sleep disturbances or by testing the pharma- Prostaglandin D synthase gene is involved in the regulation of non- cologic inhibition of L-PGDS on circadian changes of the rapid eye movement sleep. Proc Natl Acad Sci U S A 2000;97:4903- prostaglandin D system and sleep. In the process, the specific 7. 16.Mizoguchi A, Eguchi N, Kimura K, et al. 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