This is one of my favourite molecules and I was surprised to find this paper when I did a search for recent papers (rather than picking it up from gerontology news services)
I have been puzzling a lot about this and looking at the detailed chemistry (in the sense of reading and using LLM searches) of Complex 1 and Complex 3. I think it may affect Reverse Electron Transport in Complex 1, but I donāt really know. I know it has a number of positive effects.
chatGPT(5.6paid):
Overall assessment
This paper presents promising early evidence that topical menaquinone-7 (MK-7, vitamin Kā) may improve visible features of skin ageing. Its strongest contribution is the randomized split-face clinical study. Its central mechanistic claimāthat MK-7 acts directly as a mitochondrial electron carrier in human skin cellsāis much less securely established.
The results justify further investigation of MK-7 as a cosmetic ingredient, but they do not yet demonstrate that the clinical effects were mediated by enhanced mitochondrial electron transport.
1. Summary
Study hypothesis
The authors propose that MK-7 improves skin ageing by supporting mitochondrial electron transport, thereby:
- increasing oxidative phosphorylation and ATP production;
- maintaining mitochondrial membrane potential;
- improving the cellular NADāŗ/NADH ratio;
- preserving mitochondrial DNA;
- reducing cellular senescence and inflammatory signalling;
- ultimately improving wrinkles, elasticity and facial sagging.
Cell experiments
Human dermal fibroblasts and immortalized HaCaT keratinocytes were treated with MK-7, generally at concentrations up to 0.002%, equivalent to 20 Ī¼g/mL or approximately 31 Ī¼M.
Different experimental systems were used:
- UVA exposure for ATP, NADāŗ/NADH and SASP measurements;
- hydrogen peroxide for mtDNA-copy-number measurements;
- CCCP-induced depolarization for membrane-potential measurements;
- unstressed cells for respiratory-complex activity measurements.
At 0.002% MK-7, the authors report:
- ATP increased by 59.1% relative to UVA-stressed control cells.
- NADāŗ/NADH ratio increased by 100.7%.
- CCCP-associated green JC-1 fluorescence decreased by 18.7%, interpreted as partial restoration of membrane potential.
- Complex I activity reached 117.5% of untreated baseline.
- Complex II reached 142.9%.
- Complex IV reached 118.0%.
- Complex V increased by 26.8% over baseline.
- Complex III was not significantly affected.
The optimal concentration for mtDNA measurements was slightly lower, 0.0015%. Relative to hydrogen-peroxide-treated controls:
- D-loop abundance increased by 46.7%.
- ND1 increased by 83.7%.
- ND5 increased by 65.3%.
Under UVA stress, 0.002% MK-7 also reduced:
- IL-8 mRNA by 75.9%;
- p21 mRNA by 33.6%;
- TNF-Ī± secretion by 18.7%;
- MMP-3 secretion by 16.4%.
Skin-permeation experiment
A 0.05% MK-7 cream was tested in Franz diffusion cells using full-thickness porcine skin.
MK-7 was retained in the skin but was not detected in the receptor fluid. The authors estimated a nominal intradermal concentration of approximately 0.78ā5.24 Ī¼g/mL, overlapping only the lower end of the concentrations used in cultured cells.
Human study
Thirty-six women aged 35ā60 entered an eight-week randomized, double-blind, split-face-and-neck study. Thirty completed it.
Each participant applied:
- 0.05% MK-7 cream to one randomized side;
- an otherwise identical vehicle cream to the other side;
- twice daily for eight weeks.
Instrumental measurements were made at baseline and weeks 2, 4 and 8.
Principal between-side findings included:
-
Facial wrinkle maximum roughness, Rz: 8.6% lower at week 4 and 5.0% lower at week 8.
-
Facial average roughness, Ra: 7.0% lower at week 4, but no longer significant at week 8.
-
Neck Ra and Rz: approximately 4.3% lower at week 4, but nonsignificant at week 8.
-
Elasticity-related parameters at week 8:
- R0 11.4% lower;
- R1 13.5% lower;
- F4 10.7% lower.
-
Mandibular plane angle: 11.5% greater than placebo at week 8, interpreted as reduced sagging.
The authors conclude that MK-7 is a mitochondrial bioenergetic activator with topical anti-ageing efficacy.
2. What is novel?
Most credible novelty
The clearest novelty is the combination of:
- multiple mitochondrial measurements in skin-relevant cells;
- an MK-7 skin-retention experiment;
- a randomized vehicle-controlled split-face human study.
Vitamin Kā had previously been linked to mitochondrial function in flies and other experimental systems, but topical MK-7 had apparently not been evaluated this comprehensively using objective human measurements of wrinkles, elasticity and facial contour.
Particularly useful new observations are:
- MK-7 increased ATP and NADāŗ/NADH under UVA stress in fibroblasts.
- It partially opposed CCCP-associated loss of membrane potential in keratinocytes.
- It reduced several UVA-induced inflammatory/senescence-associated markers.
- A 0.05% formulation produced measurable differences from an identical vehicle within eight weeks.
The split-face design is an important strength because each participant serves as her own control, substantially reducing variation caused by age, baseline skin structure, diet, genetics and general environmental exposure.
What is not established as novel
The paper repeatedly frames MK-7 as a mitochondrial electron carrier. That underlying proposition is not new: the pivotal cited evidence is the 2012 Science study in Drosophila. What is potentially new here is its proposed application to human skin cells and topical skin ageing.
Nor does the current study directly prove electron-carrier activity. It demonstrates a collection of bioenergetic associations that are compatible with several different mechanisms.
3. Critique
A. The proposed mechanism is not directly demonstrated
This is the paperās main weakness.
An increase in ATP, membrane potential or respiratory-enzyme activity does not demonstrate that MK-7 physically transports electrons in the mammalian respiratory chain. MK-7 could instead:
- reduce oxidative damage;
- alter gene expression;
- affect mitochondrial biogenesis;
- change substrate metabolism;
- modulate SIRT1 or other signalling pathways;
- influence cell number or viability;
- act through vitamin-K-dependent or membrane-related processes.
A direct electron-carrier claim would require experiments such as:
- oxygen-consumption and extracellular-acidification measurements;
- permeabilized-cell respiration with defined substrates and inhibitors;
- direct redox-state measurements of MK-7;
- rescue of electron flow across a specifically inhibited or defective ETC segment;
- mitochondrial uptake and sub-mitochondrial localization of MK-7;
- comparison with MK-7 analogues lacking redox activity;
- testing whether the effect persists when transcription and mitochondrial biogenesis are inhibited.
The complex-activity kits measure isolated enzyme-associated activities. They do not show that whole-chain electron flux increased.
B. The Complex III result conflicts with the broad claim
Complex III was not increased, whereas complexes I, II, IV and V were. The authors speculate that MK-7 might bypass Complex III, but no bypass experiment was conducted.
This is particularly problematic because conventional electron flow from Complex I or II to oxygen still requires Complex III and cytochrome c. Increasing the measured activities of I, II and IV does not establish a continuous alternative pathway.
The abstract also says MK-7 āenhanced activities of multiple respiratory complexes,ā which is technically true, but elsewhere the paper tends to imply general improvement across the chain. Complex III is an important exception.
C. The experiments do not form a unified mechanistic sequence
Different endpoints were measured in different cell types, with different stressors and different exposure schedules:
- UVA for ATP and NAD redox;
- CCCP in keratinocytes for membrane potential;
- hydrogen peroxide for mtDNA;
- no stress for complex activities.
Consequently, the paper has not shown in one experimental system that:
[
\text{MK-7 electron transfer}
\rightarrow \Delta\Psi_m
\rightarrow \text{ATP}
\rightarrow \text{reduced SASP}.
]
Instead, it assembles separate observations into this causal sequence. The observations are convergent, but the causal chain remains hypothetical.
D. Some interpretations of the mtDNA data are incorrect or overstated
The authors argue that increasing D-loop copy number could drive increases in ND1 and ND5 because the D-loop controls replication and transcription. But the PCR measurements concern regions on the same mitochondrial genome.
Higher measured abundance of D-loop, ND1 and ND5 sequences normally indicates more intact template copies or differences in lesion-dependent amplification; it does not mean that an increase in D-loop abundance caused the other regions to increase.
Furthermore:
- qPCR estimates relative amplifiable mtDNA, not necessarily fully intact functional genomes;
- oxidative lesions can inhibit PCR and masquerade as lower copy number;
- nuclear mitochondrial DNA sequences can complicate some assays;
- no mitochondrial mass, TFAM, POLG, PGC-1Ī± or citrate-synthase measurement was supplied;
- the study cannot distinguish repair, biogenesis, selective survival or simply less PCR-blocking damage.
The term āpreserved relative mtDNA abundanceā would therefore be safer than āraised mtDNA copy number.ā
E. Small and incompletely characterized in-vitro dataset
Each experiment used only three biological replicates. This is common in preliminary cell work but weak for a study making broad mechanistic claims.
Important details are absent or unclear:
- exact passage numbers;
- donor characteristics for the primary fibroblasts;
- whether the three replicates were independent cell preparations or repeated cultures from one source;
- cell viability and cell-number normalization;
- MK-7 purity and cis/trans composition;
- stability of MK-7 in DMSO, culture medium and light;
- whether the solvent control was exactly matched;
- intracellular or mitochondrial MK-7 concentrations.
The ATP assay is especially difficult to interpret without clear normalization to cell count, protein or viable-cell number.
F. The NADāŗ/NADH interpretation is too strong
A twofold increase in the total cellular NADāŗ/NADH ratio does not by itself establish improved mitochondrial ETC efficiency. The assay appears to measure whole-cell NAD pools, while cytosolic and mitochondrial NAD are separately regulated.
The same result could arise through:
- depletion of NADH;
- altered glycolysis;
- cell injury;
- changes in lactate/pyruvate metabolism;
- increased NADāŗ synthesis or consumption;
- compartment-specific effects unrelated to respiration.
Absolute NADāŗ and NADH concentrations, compartment-specific sensors and respiratory-flux measurements would be needed.
G. JC-1 provides limited evidence of restored membrane potential
JC-1 is sensitive to dye concentration, mitochondrial mass, cell density and image-analysis conditions. The paper reports a reduction in green fluorescence but does not clearly present the preferred red-to-green fluorescence ratio or normalization to mitochondrial content.
Moreover, opposing CCCP-induced depolarization does not necessarily mean MK-7 improved normal ETC function. CCCP is a protonophore that directly carries protons across the membrane; an electron carrier would not ordinarily be expected to reverse an ongoing proton leak without substantially increasing respiration.
The timing of CCCP removal and subsequent MK-7 treatment therefore matters greatly but is insufficiently clear.
H. āSASP suppressionā is an overstatement
The study measured four markers, of which:
- IL-8 and p21 were measured at RNA level;
- TNF-Ī± and MMP-3 were measured in culture medium.
This indicates attenuation of selected stress/senescence-associated markers, not comprehensive suppression of the SASP or reversal of senescence.
There was no demonstration of:
- SA-Ī²-galactosidase;
- persistent cell-cycle arrest;
- EdU incorporation;
- p16;
- Lamin B1 loss;
- senescence persistence after removal of stress;
- a broad SASP transcriptomic or proteomic profile.
UVA treatment over this short timescale may principally model acute stress rather than stable cellular senescence.
I. The permeation-to-cell-culture comparison is weak
The authors estimated āintradermal concentrationā by dividing recovered MK-7 by an assumed skin volume. This does not establish the free concentration reaching living fibroblasts or their mitochondria.
MK-7 is highly lipophilic and may remain predominantly:
- in the stratum corneum;
- within the formulation;
- in extracellular lipids;
- bound to skin proteins or membranes.
Total skin retention therefore cannot be equated with bioavailable intracellular concentration. The claim that repeated dosing would produce substantially higher local concentrations is plausible but unmeasured.
Layer-by-layer tape stripping, epidermis/dermis separation and chemical imaging would greatly strengthen this part.
J. The clinical study is encouraging but still exploratory
Strengths include randomization, an identical vehicle, within-subject comparison and objective instruments. Nevertheless:
- the trial was registered retrospectively;
- no prespecified primary endpoint is evident;
- no power calculation is reported;
- six of 36 participants dropped out;
- only the 30 completers were analysed;
- allocation concealment and the randomization procedure are not described adequately;
- blinding success was not tested;
- participants continued their routine skincare;
- numerous parameters and time points create substantial multiplicity;
- although FDR correction was used, the precise family of comparisons included in that correction needs clarification.
The lack of intention-to-treat analysis cannot simply be dismissed because dropouts were reportedly unrelated to treatment. Excluding 16.7% of recruited participants can still introduce attrition bias.
K. Some wrinkle effects weakened with continued treatment
The wrinkle results peaked at four weeks and then diminished:
- facial Ra lost significance at week 8;
- neck Ra and Rz lost significance at week 8;
- facial Rz remained significant but the effect fell from 8.6% to 5.0%.
The authors attribute this to Chinese New Year, temperature and lifestyle changes. That explanation is post hoc and unsupported by collected behavioural or environmental data.
Because both sides of the same participant experienced the same holiday and climate, these factors should largely cancel in a split-face comparisonāunless they interacted specifically with MK-7. Regression to the mean, measurement variability or a chance week-four result are equally plausible.
L. The elasticity and sagging results need independent confirmation
The elasticity findings appear more consistent than the wrinkle results and may be the most persuasive clinical outcomes. However, the reported 11.45% between-side change in mandibular plane angle over only eight weeks is surprisingly large for a topical product.
It would be useful to establish:
- testāretest reliability and minimum detectable change for MPA;
- blinded image analysis;
- predefined anatomical landmarks;
- whether changes in hydration, expression, head angle or image registration could produce the apparent lifting effect.
Representative photographs from selected responders are illustrative but not evidential.
M. No clinical mitochondrial mechanism was measured
Nothing in the human study shows that MK-7 improved mitochondrial function in vivo. The clinical and cell experiments are linked by inference.
A stronger translational study would use skin biopsies, tape-strip biomarkers or other minimally invasive measurements to assess:
- ATP or NAD redox;
- mitochondrial respiratory proteins;
- mtDNA abundance or damage;
- p21/p16;
- MMPs and inflammatory cytokines;
- collagen synthesis and degradation.
N. Commercial conflicts require caution
The sponsor supplied MK-7 and funded all testing. Several authors are employed by the sponsor, affiliated companies or a cosmetics company, and a patent application has been filed.
The clinical testing and statistical analysis were conducted by a contract research organization, which offers some separation, but the CRO was sponsor-funded. This does not invalidate the results, but it makes independent replication and access to raw data particularly important.
Bottom line
The paper provides credible preliminary evidence that a 0.05% MK-7 cream can produce modest, instrument-detectable changes in skin elasticity and some wrinkle measurements over eight weeks. The split-face vehicle-controlled design makes the human findings worth taking seriously.
However, the evidence supports the conclusion:
āTopical MK-7 is a promising cosmetic active associated with mitochondrial and anti-ageing readouts.ā
It does not yet support the stronger conclusion:
āMK-7 directly acts as a mitochondrial electron carrier in human skin and thereby causes the observed clinical improvements.ā
The next decisive experiment would combine a larger preregistered split-face trial with direct skin biomarkers and high-resolution respirometry showing that MK-7 increases integrated electron flux and ATP production at clinically achievable dermal concentrations.