Delta sleep-inducing peptide (DSIP): a still unresolved riddle. — VialBase Research

Summary

Kovalzon and Strekalova review the state of DSIP research nearly thirty years after its discovery, and the verdict is sharply skeptical. DSIP was isolated from rabbit cerebral venous blood by the Schoenenberger-Monnier group in Basel in 1977 and initially regarded as a candidate sleep-promoting factor. However, the authors write, the link between DSIP and sleep has never been further characterized — in part because of the failure to isolate the DSIP gene, protein, and any possible related receptor. On that basis they conclude that the hypothesis regarding DSIP as a sleep factor is extremely poorly documented and still weak, and that despite DSIP having been a focus of study for a number of researchers, its natural occurrence and biological activity still remain obscure. DSIP’s structure, they note, is different from any other known representative of the various peptide families. The review’s central proposal is that a still-unidentified DSIP-like peptide, rather than DSIP itself, is responsible at least in part for DSIP-like immunoreactivity and DSIP biological activity. Four lines of evidence support that hypothesis: (i) DSIP-like immunoreactivity shows a highly specific distribution in neurosecretory hypothalamic nuclei of various vertebrate species that are not particularly relevant for sleep regulation, per the histochemical work of the Geneva group (Charnay et al.); (ii) a large spectrum of DSIP biological activity has been revealed by biochemical and physiological in vitro studies; (iii) the authors’ own early studies found significant slow-wave sleep (SWS) promoting activity for certain artificial DSIP structural analogues — but, as they emphasize, not for DSIP itself; and (iv) a naturally occurring dermorphin-decapeptide structurally similar to DSIP in five of nine positions showed significant SWS-promoting activity in rabbits, while its optical isomer suppressed sleep. The authors outline potential future studies of the natural synthesis and release of this hypothesized DSIP-like peptide and its role in neuroendocrine regulation.

Key Findings

• The DSIP-sleep link has never been characterized beyond the original 1977 isolation, partly because the DSIP gene, protein, and any related receptor were never isolated
• The authors’ explicit judgment: the hypothesis of DSIP as a sleep factor is “extremely poorly documented and still weak,” and DSIP’s natural occurrence and biological activity remain obscure
• In the authors’ own earlier animal work, significant slow-wave sleep promoting activity was found for certain artificial DSIP structural analogues but not for DSIP itself — a distinction the review states emphatically
• DSIP-like immunoreactivity localizes to neurosecretory hypothalamic nuclei across various vertebrate species that are not particularly relevant to sleep regulation, weakening the sleep-factor interpretation of that immunoreactivity
• A naturally occurring dermorphin-decapeptide sharing five of nine positions with DSIP significantly promoted SWS in rabbits while its optical isomer suppressed sleep, supporting the authors’ hypothesis that some other DSIP-like peptide, not DSIP, carries the biological activity attributed to DSIP

Relevance to DSIP

This review is the single most important corrective for anyone researching DSIP, because it is the field turning around and auditing its own foundational claim. The title is not rhetorical flourish — nearly three decades after the peptide was named, two researchers publishing in the Journal of Neurochemistry describe it as a still unresolved riddle, state that the sleep connection was never characterized past the original report, and note that no DSIP gene, protein, or receptor was ever isolated. A compound with no identified receptor and no identified gene has no established mechanism, and the review says the sleep-factor hypothesis is extremely poorly documented and still weak in exactly those words. The most pointed detail for consumers is the authors’ own finding that certain synthetic DSIP analogues promoted slow-wave sleep in rabbits and rats while DSIP itself did not — meaning the strongest animal sleep signal in this line of work came from molecules that are not the substance sold as DSIP. The authors’ constructive hypothesis is that some other, still-unidentified DSIP-like peptide accounts for the immunoreactivity and activity historically credited to DSIP. None of this proves DSIP is inert, but it does mean that as of this review the mechanistic and evidentiary basis for using DSIP as a sleep aid had not been established, and no subsequent work of comparable prominence has resolved the question.

Citation

Kovalzon VM, Strekalova TV. Delta sleep-inducing peptide (DSIP): a still unresolved riddle. Journal of neurochemistry. 2006;97(2):303-9. doi:10.1111/j.1471-4159.2006.03693.x.

See Also

• Parent compound: DSIP