Systemic inflammation is a primed-status when our body fights against infection, stress or chronic disease, where many immune mediators are released in the blood. Are chronic pain and systemic inflammation linked? Many clinical studies suggest that they may be. However, it is unclear whether this type of inflammation has a role in pain, or simply a coincidence. The current preclinical study revealed that an injury to nerve could result in a systemic inflammation, which could enhance painful response.
Goal
Chronic pain patients often have a low-level and long-term systemic inflammation. Dr Zhang research team wanted to understand whether nerve injury, which is often associated with chronic pain (or also called neuropathic pain), can trigger systemic inflammation, and whether such inflammation contributes to the development of chronic pain.
Methodology
A mouse model of nerve injury was used to induce chronic pain. Researchers collected blood samples and studied the entire proteins in the serum of these nerve injured mice with proteomics, a technique that allows to not only quantify protein levels but also identify their potential functions in the body. Mouse serum from nerve injured mice were transferred to healthy mice, where pain behavior in these recipient mice was assessed. Finally, a group of nerve injured mice were treated with bone marrow-derived cell extracts (BMCE), a mixture of broadly anti-inflammatory substances, to determine if counteracting systemic inflammation can alleviate pain.
Main findings
Many inflammation-related proteins were found increased in mouse serum at both acute and chronic phase of chronic pain, i.e., 1 day and 1 month following injury. Serum from nerve injured mice transferred to normal mice caused pain in healthy mice. BMCE treatment not only alleviated nerve injury-associated systemic inflammation and improved pain experience in nerve injured mice, but also prevented the serum from these treated mice to induce pain in healthy mice.
Take home message
In this study, Sam Zhou, Ji Zhang and colleagues highlighted the potential roles of inflammatory proteins in the blood for the development of chronic pain. They demonstrated that nerve injury can cause systemic inflammation, which is able to enhance pain hypersensitivity. Anti-inflammation could be a strategy to consider in chronic pain management.
