In a recent paper, researchers from McGill University in Canada have investigated how a combination of two senolytics, RG-7112 and o-Vanillin, influences the intervertebral disc cells of back pain patients [1].
Back pain is a widespread issue
An overwhelming majority of people, a full 80%, have suffered from back pain at some point in their lives or will in the future. It is the main reason why people spend time living with a disability [2].
The pain is often the result of intervertebral disc degeneration. Intervertebral discs are structures in the spine that serve as cushions between the vertebrae of the spinal column. While this is a common problem, there is only limited understanding of its cellular and molecular mechanisms.
Researchers have found that the pain associated with intervertebral disc degeneration is associated with inflammation. One of the contributors to this inflammation and pain is the senescence-associated secretory phenotype (SASP), the collection of molecules that senescent cells are known to produce in excess.
Since previous research suggests that the accumulation of senescent cells plays a role in the onset and progression of intervertebral disc degeneration, some researchers are exploring whether targeting senescent cells can help in low back pain treatment.
In this paper, the researchers targeted senescent cells with senolytics, specifically RG-7112 and o-Vanillin, which have been previously described as having senotherapeutic activity in degenerated intervertebral disc cells [3, 4]. These senolytic compounds work on different cellular pathways.
This paper’s hypothesis is that targeting different cellular pathways and processes simultaneously will have a better effect on the senescent, degenerated intervertebral disc cells than a single drug. This might also allow for a lower dose of each drug, thus also limiting side effects.
RG-7112 and o-Vanillin combination therapy
This paper’s authors aimed to reproduce the environment in which degenerated intervertebral disc cells exist in the human body. They received cells from patients who suffer from degenerated intervertebral discs and lower back pain. They used a 3D culture model to grow these cells in the lab and stimulated them to enter senescence.
First, they established that both RG-7112 and o-Vanillin, when used separately, reduce the expression of SASP factors and other senescence-associated molecules. Subsequently, they tested whether their effect would be additive. They tested a few combinations of different RG-7112 and o-Vanillin concentrations and found a combined concentration that outperformed each molecule separately.
Their subsequent experiments showed that senolytic treatments reduced the number of senescent cells. Combined RG-7112 and o-Vanillin treatment resulted in the highest increase in programmed death of the senescent cells but were not toxic to the healthy, non-senescent cells. Additionally, this combination led to a reduction in the SASP.
Researchers also tackled the expression of factors responsible for disc innervation. Painful, degenerating intervertebral discs were observed to have increased levels of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), markers associated with the sprouting and growth of neurites, which project from the bodies of neurons. Such innervation is a feature of painful and degenerated discs, as healthy intervertebral discs mostly lack nervous tissue and blood vessels [5].
Researchers tested RG-7112 and o-Vanillin, combined and separately, on those factors and on neurites. They observed that the combination decreased NGF and BDNF as well as neurite growth.
Therefore, the authors suggest that removing senescent cells through senolytics results in reduced NGF and BDNF, thereby leading to decreased neurite sprouting and a subsequent reduction in back pain.
Senolytic therapies for disc degeneration
All in all, combining RG-7112 and o-Vanillin was better in reducing senescence and SASP when compared to a single treatment. Additionally, it resulted in an increased number of proliferating non-senescent cells and a higher number of senescent cells that underwent programmed cell death.
However, since this research is done in cells grown in the laboratory, it is essential to follow up with research in live, vertebrate animals that have discs that can be examined.
RG-7112 and o-Vanillin are not the only senolytics that are currently being tested for intervertebral disc degeneration. A combination of dasatinib and quercetin has been tested in mice. Elderly animals given multiple injections of this combination were found to have reduced SASP in their intervertebral discs [6].
Dasatinib and quercetin, in combination with fisetin, are also currently being tested in a human clinical trial that is targeting senescent cells with the aim of improving older adults’ skeletal health. If proven effective, these therapies could potentially help millions of people suffering from back pain.
Literature
[1] Mannarino, M., Wu-Martinez, O., Sheng, K., Li, L., Navarro-Ramirez, R., Jarzem, P., Ouellet, J. A., Cherif, H., & Haglund, L. (2023). Senolytic Combination Treatment Is More Potent Than Single Drugs in Reducing Inflammatory and Senescence Burden in Cells from Painful Degenerating IVDs. Biomolecules, 13(8), 1257.
[2] Global Burden of Disease Study 2013 Collaborators (2015). Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet (London, England), 386(9995), 743–800.
[3] Mannarino, M., Cherif, H., Li, L., Sheng, K., Rabau, O., Jarzem, P., Weber, M. H., Ouellet, J. A., & Haglund, L. (2021). Toll-like receptor 2 induced senescence in intervertebral disc cells of patients with back pain can be attenuated by o-vanillin. Arthritis research & therapy, 23(1), 117.
[4] Cherif, H., Bisson, D. G., Jarzem, P., Weber, M., Ouellet, J. A., & Haglund, L. (2019). Curcumin and o-Vanillin Exhibit Evidence of Senolytic Activity in Human IVD Cells In Vitro. Journal of clinical medicine, 8(4), 433.
[5] Krock, E., Rosenzweig, D. H., Chabot-Doré, A. J., Jarzem, P., Weber, M. H., Ouellet, J. A., Stone, L. S., & Haglund, L. (2014). Painful, degenerating intervertebral discs up-regulate neurite sprouting and CGRP through nociceptive factors. Journal of cellular and molecular medicine, 18(6), 1213–1225.
[6] Novais, E. J., Tran, V. A., Johnston, S. N., Darris, K. R., Roupas, A. J., Sessions, G. A., Shapiro, I. M., Diekman, B. O., & Risbud, M. V. (2021). Long-term treatment with senolytic drugs Dasatinib and Quercetin ameliorates age-dependent intervertebral disc degeneration in mice. Nature communications, 12(1), 5213.
