DSIP (Delta Sleep-Inducing Peptide)

What Is DSIP?

DSIP, or delta sleep-inducing peptide, is a nonapeptide first isolated from rabbit cerebral venous blood and named for its ability to enhance delta (slow-wave) EEG activity in early experiments. Its sequence is Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu.^[1]

DSIP was one of the first proposed sleep factors to be purified and characterized. A 1984 review noted that it was one of only two sleep peptides purified to homogeneity at that time and that it induced mainly delta sleep in rabbits, rats, mice and humans.^[2]

Its standing has since become less clear. A 2006 review called DSIP a still unresolved riddle: its link to sleep was never further characterized, and its natural occurrence and biological activity remain obscure.^[3]

Although named for sleep, DSIP was also investigated in early research for possible roles in pain and in drug withdrawal, reflecting the wide range of effects reported in animal studies.^[4]

Chemical Structure and Molecular Identity

DSIP is a linear nine-residue peptide with the molecular formula C35H48N10O15 and a molecular weight of 848.8. Its one-letter sequence is WAGGDASGE, with free amino and carboxyl termini, and early reviews reported its molecular weight as 849.^[2]

The 1978 characterization paper established the sequence by amino-acid analysis and sequence determination, then confirmed activity with synthetic peptide. Only the pure alpha-aspartyl form was highly active; the beta-aspartyl isomer was not.^[1] That distinction matters for synthesis, because aspartic acid residues can rearrange to the beta form.

Identifiers

• CAS: 62568-57-4 (PubChem also lists 69431-45-4)
• InChIKey: ZRZROXNBKJAOKB-GFVHOAGBSA-N
• INN: emideltide
• Three-letter sequence: H-Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu-OH

A 2006 review noted that the DSIP structure differs from every other known peptide family.^[3] With three acidic groups (the Asp and Glu side chains and the C-terminal carboxyl) and no basic side chains, DSIP is highly polar; PubChem lists a computed XLogP of -7.1.

Research History and Development

DSIP was discovered by the Schoenenberger-Monnier group in Basel, Switzerland, which isolated it in 1977 and published its sequence and synthesis in 1978. It was initially regarded as a candidate sleep-promoting factor.^[3][1] A 1986 review dated the isolation and characterization work from 1963 to 1977, reflecting a long search for a humoral sleep factor.^[4]

The peptide was isolated from the dialysate of cerebral venous blood collected from rabbits whose intralaminar thalamic area was electrically stimulated to induce sleep.^[1] Interest grew quickly. A 1986 update reported that, within two years of the first review, much new literature had accumulated, including work on insomnia, pain and withdrawal.^[4][2]

Human studies followed in the early 1980s, mainly small trials in people with chronic insomnia.^[5][6] Researchers also mapped DSIP-like immunoreactivity in tissues, finding it in brain, peripheral organs and plasma.^[2] Immunohistochemical and radioimmunoassay studies were interpreted as suggesting possible links between the peptide and certain diseases, though these were not established.^[4]

Momentum later slowed. By 2006, reviewers noted that no DSIP gene, precursor protein or receptor had been isolated, and they described the sleep-factor hypothesis as extremely poorly documented and still weak.^[3]

Mechanisms Studied in Research

No receptor or signaling pathway for DSIP has been confirmed; its mechanism of action remains unknown. Proposed mechanisms have included modulation of adrenergic transmission, which a 1986 review said remained to be established.^[4]

Broad biological activity

Beyond sleep, early studies reported effects on electrophysiological activity, brain neurotransmitter levels, circadian and locomotor patterns, hormone levels, psychological performance and responses to neuropharmacological drugs, including withdrawal.^[2] Its activity followed a U-shaped curve for both dose and infusion time, meaning intermediate conditions produced the largest effects.^[2]

The DSIP-like peptide hypothesis

The 2006 review proposed that an as-yet-unidentified DSIP-like peptide may account for DSIP immunoreactivity and activity. Its authors cited four lines of evidence: DSIP-like immunoreactivity concentrated in neurosecretory hypothalamic nuclei not closely tied to sleep, broad in-vitro activity, slow-wave-sleep promotion by certain synthetic DSIP analogs but not DSIP itself in their rabbit and rat studies, and sleep-promoting activity of a dermorphin decapeptide that matches DSIP at five of nine positions. The optical isomer of that decapeptide suppressed sleep in rabbits.^[3]

Key Findings From Published Studies

DSIP research includes animal EEG studies, small human sleep studies and tissue-distribution work, with results that later reviewers found difficult to build on. Most primary studies date from 1978 to 1992.

Animal studies

In the original rabbit study, which included 61 animals, synthetic DSIP infused into the brain ventricles under double-blind conditions increased EEG delta activity by a mean of 35% in the neocortex and limbic cortex compared with controls given CSF-like solution or eight related peptides.^[1] Those comparison peptides included five possible DSIP metabolic fragments, two nonapeptide analogs with one or two amino acids exchanged, and the tripeptide Trp-Ser-Glu, none of which reproduced the effect.^[1] Effects on REM sleep were more pronounced than delta effects in cats.^[2]

Human studies

• In six middle-aged adults with chronic insomnia, intravenous synthetic DSIP was followed by longer and less interrupted sleep and slightly more REM sleep, without daytime sedation. Sleep-promoting effects began in the second hour, after a slight arousing effect in the first hour, and the authors reported no side effects.^[5]
• A 1984 summary of insomnia studies reported improved sleep, with progressive normalization of sleep structure on repeated administration. It also described a case of insomnia associated with organic brain disease that responded well.^[6]
• In 15 drug-free men with schizophrenia, cerebrospinal fluid DSIP-like immunoreactivity correlated with stage 3 and delta sleep during the first NREM period and negatively with the percentage of stage 2 sleep. The authors cautioned that the finding needed testing in people without psychiatric illness.^[7]

Tissue distribution

DSIP-like immunoreactivity has been found in brain neurons, pituitary and adrenal medulla endocrine cells, and gut endocrine cells of humans, pigs and rats. The human gut was the richest source, and chromatography showed material resembling the fragment DSIP 3-9.^[8] In human gut, the immunoreactivity sat in cells that also contain gastrin/CCK, secretin and PYY/glicentin.^[8]

Summary of evidence

Because only the alpha-aspartyl form of DSIP was highly active, researchers typically confirm identity and isomeric purity with HPLC and mass spectrometry certificates of analysis.

Regulatory and Research Status

DSIP is not approved by the FDA for any use. It has an assigned international nonproprietary name, emideltide, but no approved product is described in the literature reviewed here.

The human evidence consists of small studies from the 1980s and early 1990s, without large controlled trials.^[5][6] A 2026 review of therapeutic peptides listed DSIP among recovery-oriented peptides and noted that clinical trials are lacking across that group.^[9]

The central open questions are basic ones: whether DSIP is produced naturally from a specific precursor, what receptor it acts on, and whether its reported effects reflect DSIP itself or a related peptide.^[3] DSIP is supplied for laboratory research only.