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GTS-21 alleviates oxygen-glucose deprivation/reoxygenation-induced intestinal epithelial cell injury via the PI3K/Akt pathway

This study demonstrates that GTS-21 protects rat intestinal epithelial cells from oxygen-glucose deprivation/reoxygenation-induced injury by reducing apoptosis, inflammation, and oxidative stress through the activation of the PI3K/Akt signaling pathway.

Original authors: CHEN WU, LINMEN XU, DONGMIAO CAI, YATING YANG, LIANG LIN, HAISONG WANG

Published 2026-07-02

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CC BY 4.0

Original authors: CHEN WU, LINMEN XU, DONGMIAO CAI, YATING YANG, LIANG LIN, HAISONG WANG

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Picture: A "Power Outage" and a "Fire Extinguisher"

Imagine your body's intestines are a bustling city. The cells in this city need a constant supply of electricity (oxygen) and food (glucose) to keep the lights on and the streets running.

Sometimes, due to surgery, shock, or blocked blood flow, this city experiences a sudden power outage. This is called Ischemia. When the power comes back on, it's called Reperfusion. You might think turning the power back on is a good thing, but in this specific scenario, it's like flipping a switch that causes a massive electrical surge. This surge creates chaos: fires (inflammation), rust (oxidative stress), and buildings collapsing (cell death/apoptosis). This is Intestinal Ischemia-Reperfusion (IR) Injury.

The scientists in this study wanted to find a way to protect the city's buildings (intestinal cells) from this chaotic surge. They tested a specific chemical called GTS-21.

The Experiment: Simulating the Disaster in a Lab

Since they couldn't test this on a whole human immediately, they created a "mini-city" in a petri dish using rat intestinal cells (IEC-6).

The Setup: They took these cells and cut off their oxygen and food for two hours (simulating the power outage).
The Surge: They gave the oxygen and food back for four hours (simulating the dangerous return of power).
The Test: They divided the cells into groups to see what happened:
- Group S (The Safe Zone): Cells got normal food and air.
- Group OGD/R (The Disaster): Cells got the power outage and the surge.
- Group GTS (The Hero): Cells got the power outage, but they were given GTS-21 beforehand.
- Group T (The Saboteur): Cells got the power outage and a chemical called Wortmannin (which acts like a "circuit breaker" that stops a specific safety signal).
- Group GTS+T (The Mixed Bag): Cells got the power outage, the hero (GTS-21), and the saboteur (Wortmannin).

What Happened? (The Results)

1. The Disaster Group (OGD/R):
Without help, the cells were devastated. They died in large numbers, the "buildings" collapsed (apoptosis), the city was filled with smoke and fire (inflammation), and the metal structures rusted away (oxidative stress).

2. The Hero Group (GTS-21):
When the cells were treated with GTS-21 before the disaster, they fared much better.

More Survivors: More cells stayed alive.
Less Fire: The levels of inflammatory "smoke" went down, and the "firefighters" (anti-inflammatory signals) were stronger.
Less Rust: The chemical rust (oxidative stress) was reduced, and the cells' natural rust-removers worked better.
Fewer Collapses: The cells didn't self-destruct as often.

3. The Saboteur Group (Wortmannin):
When they used the chemical that stops the safety signal, the cells suffered even more than the disaster group. It made the injury worse.

4. The Mixed Bag (GTS-21 + Wortmannin):
This was the most important clue. When they gave the cells the Hero (GTS-21) but also the Saboteur (Wortmannin), the Hero stopped working. The cells got hurt just as badly as if they never got the Hero at all.

The Secret Mechanism: The "PI3K/Akt" Safety Switch

How did GTS-21 work? The paper found that GTS-21 acts like a remote control that turns on a specific internal safety system called the PI3K/Akt pathway.

Think of PI3K/Akt as the city's emergency backup generator and repair crew.
When the power goes out, this crew usually stays off.
GTS-21 flips the switch to turn this crew ON.
Once ON, this crew rushes in to:
- Stop the buildings from collapsing (stopping cell death).
- Put out the fires (reducing inflammation).
- Clean up the rust (reducing oxidative stress).

The Proof: When the scientists used the Saboteur (Wortmannin) to cut the wire to the backup generator, GTS-21 couldn't turn the crew on. Without the crew, the damage happened anyway. This proves that GTS-21 only works because it activates this specific PI3K/Akt pathway.

The Conclusion

In simple terms, this study shows that GTS-21 is like a protective shield for intestinal cells. It works by flipping a specific internal switch (the PI3K/Akt pathway) that tells the cells to stay alive, stop the inflammation, and clean up the damage caused by a lack of oxygen and blood flow.

If you block that switch, the shield disappears, and the cells get hurt. This suggests that the PI3K/Akt pathway is the key to how GTS-21 saves these cells.

Technical Summary: GTS-21 Alleviates Oxygen-Glucose Deprivation/Reoxygenation-Induced Intestinal Epithelial Cell Injury via the PI3K/Akt Pathway

Problem Statement
Intestinal ischemia-reperfusion (IR) injury is a life-threatening clinical complication associated with acute mesenteric ischemia, hemorrhagic shock, and major abdominal surgery. The pathological process is driven by excessive inflammatory responses, oxidative stress, and apoptosis, leading to intestinal barrier dysfunction, multi-organ failure, and high mortality. While current management focuses on hemodynamic support, specific pharmacological agents targeting intestinal epithelial injury remain limited. Although the $\alpha7$ nicotinic acetylcholine receptor ( $\alpha7$ nAChR) agonist GTS-21 has demonstrated anti-inflammatory properties in other models (e.g., sepsis, lung injury), its specific protective mechanism against intestinal epithelial cell injury via the PI3K/Akt signaling pathway had not been previously investigated.

Methodology
The study utilized an in vitro model of intestinal IR injury using rat intestinal epithelial cells (IEC-6). Ischemia was simulated via oxygen-glucose deprivation (OGD) for 2 hours, followed by 4 hours of reoxygenation (R). Cells were divided into five experimental groups:

Control (Group S): Normoxic conditions.
OGD/R (Group OGD/R): Cells subjected to OGD/R without treatment.
GTS-21 + OGD/R (Group GTS): Pretreated with 200 $\mu$ M GTS-21 for 1 hour prior to OGD.
Wortmannin + OGD/R (Group T): Pretreated with 2 $\mu$ M wortmannin (WM), a PI3K inhibitor, for 1.5 hours prior to OGD.
GTS-21 + WM + OGD/R (Group GTS+T): Pretreated with both GTS-21 and WM.

Key assessments included:

Cell Viability: Measured via Cell Counting Kit-8 (CCK-8) assay.
Apoptosis: Evaluated using flow cytometry (Annexin V-FITC/PI) and Western blotting for Bax, Bcl-2, cleaved caspase-3, and cleaved caspase-9.
Inflammation: Quantification of TNF- $\alpha$ , IL-1 $\beta$ , IL-6, and IL-10 levels via ELISA.
Oxidative Stress: Measurement of Reactive Oxygen Species (ROS) via flow cytometry, and levels of malondialdehyde (MDA) and superoxide dismutase (SOD) via colorimetric assays.
Signaling Pathway: Western blot analysis of phosphorylated Akt (p-Akt) levels.

Key Results

Cell Viability and Apoptosis: OGD/R significantly reduced cell viability and increased apoptosis rates compared to the control. GTS-21 pretreatment significantly restored cell viability and reduced apoptosis. This protective effect was characterized by the downregulation of pro-apoptotic proteins (Bax, cleaved caspase-3, cleaved caspase-9) and the upregulation of the anti-apoptotic protein Bcl-2. Co-treatment with the PI3K inhibitor wortmannin abolished these protective effects, reversing the reduction in apoptosis and viability.
Inflammatory Response: OGD/R induced a significant increase in pro-inflammatory cytokines (TNF- $\alpha$ , IL-1 $\beta$ , IL-6) and a decrease in the anti-inflammatory cytokine IL-10. GTS-21 treatment significantly attenuated these changes. However, the addition of wortmannin reversed the anti-inflammatory benefits of GTS-21, leading to higher levels of pro-inflammatory cytokines and lower IL-10.
Oxidative Stress: The OGD/R group exhibited elevated ROS and MDA levels and reduced SOD activity. GTS-21 treatment significantly reduced ROS and MDA levels while restoring SOD activity. These antioxidant effects were negated by wortmannin co-treatment.
PI3K/Akt Pathway Activation: Western blot analysis revealed that OGD/R significantly decreased p-Akt levels. GTS-21 treatment markedly increased p-Akt expression. This activation was suppressed by wortmannin, confirming that GTS-21 acts through the PI3K/Akt pathway.

Significance and Claims
The authors conclude that GTS-21 alleviates OGD/R-induced intestinal epithelial cell injury by attenuating apoptosis, inflammation, and oxidative stress. The study provides evidence that these protective effects are mediated through the activation of the PI3K/Akt signaling pathway. The findings suggest that GTS-21, via its action as a selective $\alpha7$ nAChR agonist, may represent a potential therapeutic strategy for intestinal IR injury.

The paper acknowledges limitations, noting that the in vitro OGD/R model does not fully replicate the physiological complexity of in vivo IR injury and that downstream effectors such as mTOR and GSK-3 $\beta$ were not investigated. Furthermore, while changes in $\alpha7$ nAChR were observed, they were not confirmed via morphological techniques. The authors state that future studies are required to further elucidate the precise mechanisms and explore additional downstream targets within the pathway.

The Big Picture: A "Power Outage" and a "Fire Extinguisher"

The Experiment: Simulating the Disaster in a Lab

What Happened? (The Results)

The Secret Mechanism: The "PI3K/Akt" Safety Switch

The Conclusion

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