DSIP Research Peptide

DSIP has one of the more unusual origin stories in neuropeptide research. A Swiss team led by Marcel Monnier and Guido Schoenenberger went looking for a sleep factor carried in the blood. They electrically stimulated the intralaminar area of the thalamus in rabbits, which produces sleep-like brain activity, and collected a dialysate of the animals’ cerebral venous blood. From that material they isolated a peptide that, when infused into the brains of other rabbits, enhanced slow-wave (delta) and spindle patterns on the EEG.

The team published its sequence in PNAS in 1977: Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu (Learn more). They synthesised it alongside five possible breakdown fragments, two altered nonapeptides and a related tripeptide, then tested all nine blind. Only the intact synthetic DSIP produced a specific effect. A follow-up paper in Pflügers Archiv put the mean rise in EEG delta activity at about 35% in both the neocortex and limbic cortex, across 61 rabbits including controls (Learn more).

DSIP was defined by what it did to the EEG, the electrical rhythm of the brain. Delta waves are the slow, high-amplitude waves of deep non-REM sleep, often called slow-wave sleep. A 1984 review summarised the first decade of findings: in rodents and humans DSIP mainly promoted slow-wave sleep, while in cats the more prominent change was in REM sleep, and responses followed a U-shaped curve, fading at both low and high concentrations (Learn more).

Human work has been small and mixed. Early double-blind studies by Schneider-Helmert and Schoenenberger reported improved sleep measures in people with disturbed sleep. A later double-blind study of 16 people with chronic insomnia did record higher sleep efficiency and shorter sleep latency, but the authors judged the effects weak and partly explained by changes in the placebo group (Learn more). In animal models the story continues: a rat study under simulated high altitude reported that a phosphorylated form, P-DSIP, increased both non-REM and REM sleep and restored spatial memory.

Some of the most consistent DSIP work has little to do with sleep. Russian physiologists, including K. V. Sudakov’s group, sorted rats by open-field behaviour into stress-resistant and stress-susceptible animals, then looked at how DSIP given before stress changed the brain’s response. In one study, DSIP reduced the number of c-Fos-positive cells, a marker of recent neuronal activation, in the paraventricular nucleus of the hypothalamus after immobilisation. That nucleus is the control hub of the hormonal stress axis. Blocking NMDA receptors abolished the effect in stress-susceptible rats, pointing to a glutamate-linked route (Learn more).

Related studies reported fewer ischaemically damaged cortical neurons in rats given DSIP before emotional stress, and shifts in liver antioxidant enzymes and lipid peroxidation under restraint and foot-shock stress. Endocrine work has linked DSIP to lower basal corticotropin (ACTH) levels, and in cultured human K562 cells it reduced the build-up of the stress protein HSP70. It is easy to see why the literature often calls DSIP a “stress-limiting factor”.

For a peptide studied for so long, DSIP keeps some remarkable secrets. Antibody tests have detected DSIP-like material in the hypothalamus, limbic system and pituitary, in the gut and pancreas, in plasma and even in human breast milk. In cerebrospinal fluid, DSIP-like immunoreactivity has been found to rise with age.

Yet no gene or precursor protein that would produce DSIP has been identified, and no dedicated receptor has been confirmed. In their review, Kovalzon and Strekalova argued that some effects credited to DSIP may belong to an as-yet-undiscovered DSIP-like peptide. There is a curious footnote too. The human gene now called TSC22D3, which encodes the glucocorticoid-induced leucine zipper (GILZ), once carried the name DSIPI, short for “DSIP immunoreactor”, because of its link to DSIP antibodies. GILZ is a separate, much larger protein switched on by glucocorticoid stress hormones, a neat echo of DSIP’s own stress-research profile.

Natural DSIP is short-lived in biological fluids: its in vitro half-life has been put at around 15 minutes, because an aminopeptidase-like enzyme trims it from the tryptophan end. That has inspired a family of analogues. P-DSIP, phosphorylated on the serine at position 7, has been measured alongside DSIP in cerebrospinal fluid and compared with it in rat temperature-regulation studies, where its effects appeared and faded more quickly. DSIP-12, with beta-alanine in place of alanine at position 2, and the shortened fragment DSIP(1–4) have both been studied in rat seizure models, where they increased delta-wave power and reduced seizure severity.

Newer work keeps the peptide in active use. In a rat model of focal stroke, DSIP was associated with faster recovery of motor coordination, although the smaller infarct size did not reach significance (Learn more). A Frontiers in Pharmacology study fused DSIP to a brain-penetrating Tat sequence and reported stronger effects than DSIP alone in a mouse model of chemically induced sleeplessness. For comparative neuropeptide work, DSIP sits naturally beside Selank and Semax.