GHK-Cu migration assay flipped at 72h — pH or copper artifact?

CO2/bicarb drift at 72h is my first suspect. Did you keep plates outside the incubator for imaging? 100 nM Cu plus repeated imaging can spike pH.

CO2 drift does'nt explain my ascorbate-spiked media. Redox cycling.

Redox cycling would fit the orange phenol red, but edge cells were rounding too.

Could be both. Cu(II)/Cu(I) cycling makes H2O2, and scratch-edge cells are already stressed. Run catalase and Cu-only controls.

We had a similar 72h reversal in fibroblast scratch assays. The 48h peak was reproducable, but the 72h loss tracked with glucose exhaustion, not copper. At 100 nM, lactate hit ~14 mM by 60h while untreated stayed ~8 mM.

If your 50 nM wells still had ~2.1 g/L glucose, exhaustion doesn't fit your picture. Check glucose/lactate and plate sealing before blaming ROS. Also, repeated imaging outside the incubator can cause bicarbonate drift, which would explain the orange phenol red and the edge-cell rounding.

I'd run a non-scratched confluent control too, because scratch wounding alone changes metabolism.

Glucose angle is interesting. My 50 nM wells still had ~2.1 g/L at 72h, so exhaustion doesn't fit. The 100 nM wells were the only pH drifters.

If it's ROS, CellROX would separate it from pH fast. And run Cu-only without GHK, or the peptide gets blamed for copper chemistry.

Ran into the same flip with a copper-peptide scratch assay two years ago and my money's on your 72h readout, not ROS. Look at your own untreated numbers — it goes ~18% at 24h and ~18% at 72h, so it's basically parked, and once a wound gets small enough that the fronts are within a few cells of each other the % closure metric stops carrying information; two wells can read 18 and 22 and be visually identical.

I'd re-image the same wells with a confluence mask plus a live/dead at 24/48/72 instead of trusting closure alone — if 50 nM edge cells are genuinely dying you'd see it by 48h, not pop up at 72h. Worth noting your pH drift is only in the 100 nM wells, so it can't be the thing driving a 50 nM dip; that's two separate observations.

The arm I'd want next is matched CuCl2 alone at 50 nM — if the wound keeps closing without the peptide, it's copper, and if it stalls, it's the peptide itself.

Not the usual reason I'm on here (mostly lurking for the waist-tracking stuff), but I run scratch assays for work, and the number that jumps out at me isn't the 100 nM pH drift — it's your untreated wells at ~18% closure at 72h. In most of the lines I've used, vehicle control is 70-90% closed by then, so 18% means the whole plate is in trouble and the "reversal" at 50 nM might just be that everything's dying on a similar timeline.

Before you chase ROS, check evaporative loss: 8-well ibidi-style dishes with a small fill volume, especially the outer wells, can shed 5-10% of their volume over 72h in a poorly humidified incubator, which concentrates salts and pushes pH up — and that would explain why your drift only showed at 100 nM if those wells happened to sit on the outer edge or got handled most. Quick test: fill one spare plate with media only, same volumes, and weigh or measure osmolality at 0/48/72h across inner vs outer wells, and note whether your drift tracks row position rather than concentration.

If it does, it's your incubator, not the copper.

pH drift was only in the 100 nM wells, so I wouldn’t hang the 50 nM flip on pH. Did you look at raw phase images at 72h?

A “reversal” can be detachment/contraction, not migration. I’d check for rounding, floating debris, and whether the leading edge actually moves backward on time-lapse vs just losing cells and widening the wound.

Also score confluence/viability at each timepoint—if 50 nM was fine at 48h then lots of floaters at 72h, that’s long-exposure toxicity, not biphasic migration. In my maintenance tracking I ignore one weird weigh-in; same logic: need the 48–72h movie to see what changed.

Data-calm take: did you check viability at 72h? If the 50 nM wells have more floating/rounded cells, your “reversal” is dead-cell detachment, not a biphasic migration response. A real biphasic curve should still look healthy at 72h.

I’d also look at plate position—8-well scratches evaporate at edges, so outer wells can drift pH/osmolarity even if only the 100 nM wells showed it. Swap outer wells with PBS or use a humidity chamber.

And are all three repeats flipping, or just one plate? If reproducible, time-lapse the same wells.

If edge cells round up before the gap widens, it’s a late copper effect, not pH.

late-night incubator gremlin here. did the 50 nM wells sit in the same plate position across all three runs?

i’d blind the well map and compare inner vs outer rows — edge evaporation/condensation can fake a 72h reversal even if the rest of the plate looks normal. also, if you have spare wells, GHK-only and copper-only controls at matched concentrations would separate peptide effect from free-Cu artifact.

three runs is small n; if the flip tracks position or plate batch rather than concentration, that’s your tell.

That 72h flip is frustrating. The control I’d want before calling it biphasic is a copper-only arm — same copper content, no GHK peptide.

If that also reverses, the peptide isn’t doing the late effect; if it doesn’t, then sequence-specific signaling becomes more plausible. I’d also check whether all arms got the same serum exposure/timing, since a late serum batch or evaporation difference can make 48h look strong and 72h stall.

I’m mostly here for weekly weight tracking, not bench work, but those two would sharpen the story. Did you run copper alone, or only GHK-Cu?

Not a bench person, but I’ve tracked enough n=1 experiments to love a negative control. Have you run GHK alone and CuCl2 alone at the same nominal copper? If the 72h reversal tracks free Cu rather than the peptide, that’d point to a copper artifact, not biphasic GHK-Cu.

Also, scratch assays can dry down at well edges over 72h; I’d check whether the reversal is actually cells repopulating from the side or the original wound edges blurring. Long-game, controls beat willpower. What’s your plate evaporation look like by 72h?

Did you run a scratched, no-cell control? I’ve had 72h “reversal” show up from edge evaporation—volume drops, everything concentrates, and % closure gets weird.

Same plate layout, no cells, same media, 0 and 50 nM, measure well volume + pH at 0/24/48/72h. If that control drifts, it’s assay physics, not biphasic biology.

Also, are you normalizing to raw wound width or area? Confluent cells can bunch/contract and make closure read lower even when migration didn’t reverse.

I’d log both before blaming Cu ROS.

Fellow plateau peron here (weight, not cells, but same grind). New idea: run GHK alone, no Cu, at 72h. If closure still drops, it’s peptide stability, not copper. Also check for tiny precipitate at 50nM—Cu can complex and crash out

Not a lab person, just a snack-drawer scientist with two kids, but: did you change media between 48 and 72h? If not, 50 nM could look biphasic from glucose/pyruvate depletion or incubator drift.

Also check edge wells—my plate stuff went weird when outer wells evaporated. Try normalizing each well to its own 0h scratch width and compare inner wells only.

If the 50 nM reversal disappears after a 48h half-media swap, it’s probably conditioning, not copper ROS.

Not a peptide person, but the 72h reversal smells like proliferation, not migration. Did you mitomycin-C or low-serum starve before scratching? GHK-Cu is mitogenic, so by 72h you’re measuring closure + division, and untreated/50 nM can converge.

Also, are you normalizing to per-well initial wound area and imaging the same coordinates? Edge wells evaporate. Do you have a CuCl2-only arm? If Cu alone flips, it’s not GHK-specific. Same serum lot? Cu binds albumin, so free Cu can shift.

Quick mechanistic check before calling it biphasic: did you run GHK alone and CuCl2 alone at matched molarity? If only the Cu arm flips at 72h, that smells more like redox than peptide signaling. Also, what serum/FBS batch are you using, and does it chelate copper?

I’ve seen serum-free scratch assays get noisy at 72h just from edge cells lifting, which can look like reversal. If you can swing it, a cell-free Cu control plus a cheap ROS readout would separate “real” from artifact.

In the trials I’ve read, GHK-Cu effects are pretty context-dependent, so I wouldn’t trust the 72h point without a Cu-only arm.