Highlighting the 2D-Photoacoustic Imaging Capabilities of Newly Developed PABDP1-4 Probes

A team of researchers at Nanjing Forestry University recently examined a new way to improve biomedical imaging. This study, which was published in the journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, presented new photoacoustic (PA) probes, named PABDP1–4, that were designed to monitor liver pathophysiology non-invasively (1). The results the research team achieved indicate that these probes have potential for use in therapeutic monitoring and early diagnosis.

What is oxidative stress, and what role does it play in acute liver injury?

Oxidative stress occurs when the body has an imbalance between reactive oxygen species (ROS) and antioxidant defenses (2). Oxidative stress can occur because of the body’s natural immune response and normal metabolic processes (2). During metabolic processes, the body produces free radicals, which are molecules that contain unpaired electrons (2). Normally, the body can balance the free radicals with the antioxidants. However, when it doesn’t, people can experience various symptoms, including the development of diseases like acute liver injury (ALI), which was the subject of this study.

What did the researchers develop in this study?

The research team developed new reversible probes that can help capture the process of oxidative stress in vivo. These probes, called PABDP1–4, were created based on a meso-amino-BODIPY skeleton (1). The researchers designed them to be capable of undergoing reversible and ratiometric PA signal changes in response to fluctuations in oxidative stress (1). Another important attribute to these probes is that the researchers built them to detect O_2•–, which is a primary contributor to liver damage (1).

The researchers built and tested four probes in this study with these capabilities. As part of their experimental procedure, each probe was tested and evaluated based on their effectiveness in tracking oxidative stress. Using a two-dimensional (2D) dual-channel PA imaging mode, the team tracked the dynamics of oxidative stress in real time within the livers of ALI mouse models (1).

How were these models tested?

Acetaminophen (APAP) was injected into mice to replicate acute liver injury conditions. APAP was chosen because it is known to cause liver damage at high doses (1). After systemic delivery of the PABDP4 probe, the PA signals were collected at 690 nm and 760 nm to evaluate the superoxide-related redox activity in the liver (1).

What were the results of the study?

The researchers achieved great results with the PABDP4 injection. Within minutes, a strong PA760 signal was detected in the liver region, indicating rapid probe accumulation and its specific reaction with elevated O_2•– levels (1). Another important observation was the PA760/PA690 ratio. The researchers noticed that it remained stable for 15 minutes before peaking at a value 3.7 times higher than in control mice before gradually declining. This observation is important because it suggests that the probe had the ability to track oxidative stress progression (1).

What else did the researchers test in their study?

The researchers also tested how their probes responded to different APAP dosages. In their study, the dosage levels examined were 150, 300, and 500 mg/kg. PABDP4 performed the best with all three dosage levels, as it was able to visualize dose-dependent increases in oxidative stress (1). Mice treated with the antioxidant N-acetylcysteine (NAC) alongside a high APAP dose (500 mg/kg) showed significantly reduced ratiometric signals, demonstrating the probe's sensitivity to therapeutic intervention (1).

Another thing the researchers explored was how their probes performed under specific physiological pH conditions. They found that their probes had stable, reversible signal behavior in the pH range of 7–8 (1). The signal reversibility emerged from the probes’ having the ability to interact with O_2•– and be subsequently reduced by glutathione (GSH), which is a key antioxidant in the body (1). This redox cycling mechanism adds another layer of realism and utility to the imaging approach, accurately reflecting the biological redox environment (1).

References

1. Liu, H.; Zhou, Y.; Gao, H.; Xu, H.; Liu, Z. A Small-molecular Photoacoustic Probe for Reversible and Ratiometric Imaging Oxidative Stress Dynamics in Acute Liver Injury Mice. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2025, 343, 126551. DOI: 10.1016/j.saa.2025.126551
2. Eske, J. How Does Oxidative Stress Affect the Body? Medical News Today. Available at: https://www.medicalnewstoday.com/articles/324863 (accessed 2025-06-23).