Irisin: The Potential Protector Against Doxorubicin-Induced Cardiotoxicity
Doxorubicin, a highly potent chemotherapy drug, plays a crucial role in treating various cancers due to its broad-spectrum efficacy. However, its use is often hampered by dose-dependent cardiotoxic side effects that can lead to irreversible heart damage. A recent study explored the potential of irisin, a hormone produced during exercise, in mitigating these adverse effects. The research, conducted on mice, provides new insights into potential treatments for heart injuries caused by doxorubicin.
The Mechanism of Doxorubicin-Induced Cardiotoxicity
The heart, a highly energy-demanding organ, houses numerous mitochondria essential for cellular energy production. Doxorubicin-induced cardiotoxicity primarily stems from the overproduction of reactive oxygen species (ROS), which disrupts the mitochondrial respiratory chain, leading to oxidative stress. This oxidative stress damages lipids, proteins, and DNA, compromising cellular membranes and causing widespread apoptosis of cardiomyocytes. Additionally, doxorubicin triggers an inflammatory response by boosting levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Combined with accumulating lipid peroxides, these factors exacerbate inflammation and oxidative damage.
The Role of Irisin in Mitigating Cardiotoxicity
Irisin, a bioactive peptide derived from the protein FNDC5, has garnered attention for its metabolic benefits, including browning of white adipose tissue and enhanced thermogenesis. Researchers hypothesize that irisin may also protect against cardiovascular damage induced by doxorubicin. Recent studies have shown that irisin preserves mitochondrial function and reduces oxidative damage in ischemic and pressure-overload heart diseases, leading them to investigate its protective effects against doxorubicin-induced heart injury.
Study Design and Key Findings
The study was conducted with male C57BL/6 mice divided into three groups: a control group, a doxorubicin (DOX)-treated group, and a DOX plus irisin-treated group. Mice were administered doxorubicin weekly for four weeks, with irisin being given three times a week for seven days prior to and during the doxorubicin treatment period. The team also used a virus (AAV9-shFNDC5) to reduce irisin levels specifically in the heart to assess its role more precisely.
Mice treated with irisin exhibited improved cardiac function and reduced myocardial fibrosis compared to those treated with doxorubicin alone. Irisin significantly decreased serum markers of myocardial injury such as lactate dehydrogenase (LDH), creatine kinase isoenzymes (CK-MB), and cardiac-specific troponin T (cTnT). Importantly, the hormone also reduced oxidative stress and inflammation in the heart muscle.
Effect on Apoptosis and Fibrosis
The study demonstrated that irisin reduced the occurrence of apoptosis in heart tissues following doxorubicin treatment. TUNEL staining and caspase-3 activity experiments both confirmed this effect. Additionally, irisin reduced the expression of pro-apoptotic genes like Bax while upregulating anti-apoptotic genes such as Bcl-2. Furthermore, irisin significantly decreased myocardial fibrosis, as evidenced by reduced collagen deposition as observed through Masson’s trichrome staining.
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Figure 2 Irisin alleviated DOX-induced myocardial fibrosis and apoptosis (n = 8 per group). (A). Representative heart sections stained with HE (upper, scale bar=50 μm; mid, scale bar =20 μm) and Masson trichrome (below, scale bar=50 μm). (B). Quantification of the fibrosis area of the heart sections. (C). Representative immunoblots (top) and the quantification (bottom) for Col1α1, α-SMA, and TGF-β expression in heart tissues. β-actin as a loading control. (D) Representative heart sections stained with DAPI (blue) and TUNEL assay kit (green), scale bar=50 μm, arrows point to TUNEL positive cells. (E) Quantification of the TUNEL positive cells of the heart sections. (F) Caspase-3 activity of heart tissues. (G) Representative immunoblots and the quantification for Bcl-2 and Bax expression in heart tissues. β-actin as a loading control. Data are expressed as mean ± SD. **P |
Impact on Oxidative Stress and Inflammation
Excessive oxidative stress is a critical factor in doxorubicin-induced cardiotoxicity, contributing to cardiomyocyte apoptosis. Irisin reduced oxidative stress in the heart by decreasing malondialdehyde (MDA) and glutathione (GSH) levels while maintaining superoxide dismutase (SOD) activity. Furthermore, irisin mitigated inflammation by reducing the levels of pro-inflammatory cytokines IL-1β and TNF-α in both serum and heart tissues.
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Figure 3 Irisin alleviated DOX-induced myocardial inflammation and oxidative stress (n = 8 per group). (A) Representative dihydroethidium (DHE) staining of heart sections, scale bar=50 μm. (B–E). MDA levels (B), SOD activity (C), NADPH activity (D), and GSH (E) content in heart tissues. (F and G). IL-1β (F) and TNF-α levels (G) in serum. (H–J). mRNA levels of IL-1β (H), IL-6 (I), and TNF-α (J) in heart tissues. Data are expressed as mean ± SD. * P |
Effect on Mitochondrial Function
Mitochondrial function is severely impaired in hearts treated with doxorubicin due to increased oxidative stress. Transmission electron microscopy revealed that irisin significantly improved the ultrastructure of mitochondria in doxorubicin-treated mice. Seahorse analysis demonstrated that irisin effectively restored mitochondrial respiration in heart tissues, which was inhibited by doxorubicin. ATP content measurements further confirmed irisin’s role in partially recovering compromised energy production in heart tissues.
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Figure 4 Irisin improved the mitochondrial function and inhibited ER stress in heart toxicity induced by DOX (n = 8 per group). (A) Representative ultrastructural images of the ventricular myocardium in mice. Yellow arrows point to fragmentation of muscle bands and white arrows point to abnormal shape of mitochondria, scale bar=1 μm. (B) Isolated mitochondria OCR from the hearts in the presence of pyruvate and malate. (C and D) Qualification of the basal OCR (C) and FCCP-stimulated maximal OCR (D). (E) ATP content in heart tissues. (F) Representative immunoblots and the quantification for protein expression of phospho- and total PERK, phospho-eIF2α, total-eIF2α, ATF4, and CHOP in heart tissues. β-actin as a loading control. Data are expressed as mean ± SD. * P |
Inhibition of the PERK-eIF2α-ATF4 Pathway
The endoplasmic reticulum (ER) stress is another critical factor in doxorubicin-induced cardiotoxicity. The unfolded protein response (UPR), specifically the PERK-eIF2α-ATF4 pathway, plays a vital role in maintaining cellular redox homeostasis. However, prolonged ER stress activation can lead to energy depletion, mitochondrial damage, and apoptosis. The study found that irisin treatment significantly downregulated the expression levels of PERK, eIF2α, ATF4, and CHOP, key components of this pathway, further indicating irisin’s role in protecting against doxorubicin-induced heart injury.
Role of Irisin in H9c2 Cells
The protective effects of irisin were also confirmed in vitro using H9c2 cells, a murine cardiomyocyte cell line. Irisin treatment restored mitochondrial respiration and reduced LDH levels in doxorubicin-induced H9c2 cell injury. Additionally, irisin reduced inflammation in these cells by lowering the levels of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α. Importantly, irisin suppressed the mitochondrial production of ROS, a critical mediator of oxidative stress.
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Figure 5 Irisin alleviated DOX-induced H9c2 cell injury and mitochondrial homeostasis disruption (n = 6 per group). (A) Cell viability of H9c2 exposure to DOX for 24 h. (B) Cell viability of H9c2 pretreatment with irisin for 24 h with or without 1 μM DOX for 24 h. (C) LDH level in the culture medium. (D) OCR curve (left) and qualification of the basal respiration (middle) and maximum respiration (right) of H9c2 cells. (E–G) IL-1β (E), IL-6 (F), and TNF-α (G) levels in the supernatants. (H) Representative fluorescence images of H9c2 cells stained with MitoSOXTM Red, scale bar=10 μm. Data are expressed as mean ± SD. **P |
Role of FNDC5 in Cardiac Defense
The study also investigated the role of FNDC5, the precursor of irisin, in defending against doxorubicin-induced cardiotoxicity. Researchers selectively knocked down FNDC5 expression in the heart using a single injection of AAV9 carrying FNDC5 short hairpin RNA (shRNA). Mice with reduced FNDC5 levels showed exacerbated cardiac dysfunction and increased activation of the PERK-eIF2α-ATF4 pathway after doxorubicin treatment. However, when exogenous irisin was supplemented, the defective cardiac function was restored, along with reduced oxidative stress and inflammation.
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Figure 6 Irisin protect against DOX-induced myocardial injury through regulating the PERK-eIF2α-ATF4 pathway (n = 6 per group). (A) Schematic diagram depicting the experimental protocol with AAV9-shFNDC5 or AAV9-shNC injection in mice. (B and C) Serum irisin level (B) and heart irisin level (C). (D) Representative echocardiography images of heart in M-mode. (E and F) Quantification of LVEF% (E) and LVFS% (F). (G) Representative immunoblots and the quantification for protein expression of phospho- and total PERK, phospho-eIF2α, total-eIF2α, ATF4, and CHOP in heart tissues. β-actin as a loading control. (H) mRNA levels of IL-1β, IL-6, and TNF-α in heart tissues. (I) Representative heart sections stained with Masson trichrome (left) and quantification of the fibrosis area (right), scale bar=50 μm. Data are expressed as mean ± SD. * P |
Conclusion and Future Directions
In conclusion, this study highlights the potential of irisin as a protective agent against doxorubicin-induced cardiotoxicity. By reducing apoptosis, oxidative stress, and inflammation, irisin enhances cardiac function while reducing myocardial fibrosis. The hormone’s regulatory effects on the PERK-eIF2α-ATF4 pathway suggest a promising therapeutic strategy for mitigating the cardiovascular side effects of doxorubicin therapy. Future research could explore the therapeutic applications of irisin in clinical settings to enhance safety and efficacy of cancer treatments.
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Figure 7 The role of irisin and the underlying mechanism in protecting against DOX-induced cardiotoxicity (Created by Figdraw (www.figdraw.com)). |
Implications for Cancer Patients
For cancer patients undergoing doxorubicin therapy, the findings of this study could be particularly important. The potential to counteract the adverse effects of doxorubicin on heart health without compromising its effectiveness as a cancer treatment could lead to better overall patient outcomes. Further clinical studies are needed to validate these findings and explore irisin’s role as a therapeutic agent in human patients.
Call to Action
If you or someone you know is undergoing cancer treatment or facing heart health concerns, these findings might bring hope. Stay informed about advancements in medical research, and don’t hesitate to discuss potential treatment options with your healthcare provider. Share this article with others who might benefit from this information. If you have comments or questions, feel free to leave them below. We encourage you to join our community and stay engaged with our latest updates on medical research and health advancements.