Tier 4 — mechanistic

The Identification of a SIRT6 Activator from Brown Algae Fucus distichus

Rahnasto-Rilla MK, McLoughlin P, Kulikowicz T, Doyle M, Bohr VA, Lahtela-Kakkonen M, Ferrucci L, Hayes M, Moaddel R
Marine Drugs 2017 Volume 15, issue 6, article 190

Bibliography

PubMed
PMID 28635654
PubMed Central
PMC5484140
DOI
10.3390/md15060190
Funding
Intramural Research Program of the National Institute on Aging, NIH (Bohr, Ferrucci, Moaddel). No commercial industry funding declared.
Competing interests
The authors declare no conflict of interest.

Study snapshot

DesignIn vitro biochemistry — accelerated solvent extraction of brown macroalgae, activity screening on purified SIRT6 using a synthetic H3K9-acetylated peptide substrate, mass-spectrometry identification of the active fraction, dose-response characterisation.
ModelPurified recombinant human SIRT6 protein; synthetic H3K9-acetylated peptide substrate; five brown macroalgae species — Fucus distichus, Fucus vesiculosus, Cystoseira tamariscifolia, Cystoseira nodicaulis, Alaria esculenta.
SampleTriplicate biochemistry assays; five extract species tested; eight sub-fractions of the F. distichus extract characterised.
InterventionApplication of brown-algae fraction extracts (0.5 mg/mL, 1.0 mg/mL) and purified fucoidan (25, 50, 100 μg/mL) to purified SIRT6 in H3K9 deacetylation reactions; specificity testing against SIRT1, SIRT2, SIRT3 in parallel.
DurationNot applicable — single-time-point in vitro biochemistry.
EndpointsRate of H3K9 deacetylation by purified SIRT6 with vs. without extract or purified fucoidan; Fold-activation of SIRT6 deacetylase activity vs. baseline; Sirtuin specificity — SIRT1, SIRT2, SIRT3 as controls; Structural characterisation of active fucoidan fraction by mass spectrometry

What the study showed, in plain terms

This 2017 paper began the fucoidan-SIRT6 line of research by screening extracts from five brown macroalgae species against purified human SIRT6 in a test-tube deacetylation assay.

Fucus distichus extract produced the strongest signal among the screened algae. Fractionation and mass spectrometry implicated fucoidan-rich material as the active component. An F. distichus subfraction produced roughly 140-fold SIRT6 activation at 100 μg/mL in the assay.

Because only limited F. distichus material was available, the authors used commercially purchased, >95% pure fucoidan from Fucus vesiculosus for a fuller dose-response experiment. That commercial F. vesiculosus fucoidan produced the much-cited approximately 355-fold increase in SIRT6 deacetylase activity at 100 μg/mL. The same preparation did not significantly activate SIRT1, SIRT2 or SIRT3 under the tested conditions.

The distinction matters: the approximately 355-fold result is a purified-enzyme assay result from commercial F. vesiculosus fucoidan, not a measured effect of an oral supplement in cells, animals or humans, and not the direct F. distichus subfraction result.

Key findings

  • Three of five tested brown-algae extracts significantly increased purified SIRT6 H3K9 deacetylation activity, with Fucus distichus giving the strongest crude-extract response.
  • A fucoidan-rich F. distichus subfraction produced approximately 140-fold SIRT6 activation at 100 μg/mL under the in-vitro assay conditions.
  • Commercial >95% pure Fucus vesiculosus fucoidan, used for the fuller dose-response because F. distichus material was limited, produced approximately 355-fold SIRT6 activation at 100 μg/mL.
  • The commercial fucoidan preparation did not significantly activate SIRT1, SIRT2 or SIRT3 in the parallel assays, supporting SIRT6 selectivity under these biochemical conditions.
  • No cellular uptake, oral absorption, tissue exposure, in-vivo SIRT6 target engagement or clinical outcome was measured in this study.

What this study can and cannot tell us

This is entirely an in vitro biochemistry paper — purified SIRT6 protein and a synthetic H3K9-acetylated peptide substrate in a test tube. No cellular experiments, no animal experiments, and no test of whether ingested fucoidan reaches SIRT6 inside a living cell at a bioactive concentration. The 355-fold activation number is meaningful for pharmacology, but it does not translate directly to a whole-organism effect.

Fucoidan is a large sulfated polysaccharide with typical molecular weights in the 20–200 kDa range. Oral bioavailability of intact fucoidan is limited by molecular size, and the fraction that reaches systemic circulation intact — and then the nucleus of a target cell where SIRT6 resides — is a separate question from what fucoidan does to purified SIRT6 in a tube. This paper does not address it.

The activation was tested only on SIRT6 deacetylase activity. The subsequent mono-ADP-ribosylation arm of SIRT6, later shown by Biashad 2025 and Robbins 2025 to be functionally distinct and centenarian-relevant, was not tested in 2017.

Only F. distichus fucoidan was characterised in detail. The paper flagged that structural differences between F. distichus and F. vesiculosus fucoidans exist ("A" vs "B" repeating units), foreshadowing the species-specificity finding that would become important in the 2025 preprints. But it did not systematically map structure-activity relationships across fucoidan sources — that came later.

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Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction Dr. Amr Yasser, PhDCardiometabolic, Musculoskeletal, Gut & Bioavailability Dr. Abdulla Mostafa, PhDCellular Senescence, Neurological, Mitochondrial & Brain-Ageing Biology