Mitochondrial function and oxidative stress in isolated peripheral blood mononuclear cells and trastuzumab-induced cardiotoxicity: a prospective longitudinal study
Authors: Leemasawat K , Osataphan N , Apaijai N , Yanpiset P , Phrommintikul A , Somwangprasert A , Chattipakorn S C , Chattipakorn N 
Published: November 2023

Abstract

Introduction
Trastuzumab, a monoclonal antibody against human epidermal growth factor receptor 2 (HER2), is believed to cause cardiotoxicity through mitochondrial dysfunction and oxidative stress. Although peripheral blood mononuclear cells (PBMCs) could represent systemic oxidative stress, they are also involved in trastuzumab-mediated antibody-dependent cell-mediated cytotoxicity. The usefulness of isolated PBMCs in the assessment of trastuzumab-induced cardiotoxicity remains uncertain.

Purpose
We aimed to determine the temporal changes of mitochondrial function and oxidative stress in isolated PBMCs, and cardiac function in breast cancer patients receiving sequential doxorubin and trastuzumab treatment.

Methods
Fourteen HER-2 positive breast cancer patients with apparently normal cardiac function at baseline were recruited from September 1, 2020 to August 31, 2022. After breast surgery, all patients received doxorubicin (60 mg/m²) and cyclophosphamide (600 mg/m²) every 3 weeks for 4 cycles, followed by trastuzumab (8 mg/kg loading then 6 mg/kg) every 3 weeks for 18 cycles. Adjuvant paclitaxel (175 mg/m²) every 3 weeks for 4 cycles was an additional treatment in patients with positive lymph node(s). Echocardiography and blood samples were collected at baseline, cycle 4 of doxorubicin chemotherapy, every 3 months during trastuzumab treatment and &gt;1 month after treatment. Seahorse extracellular flux analyzer was used to determine mitochondrial oxygen consumption, and MitoSox/MitoTracker staining to determine oxidative stress in isolated PBMCs.

Results
Of 14 patients (mean age of 50.4 ±8.8 years), 2 had hypertension and 4 had hyperlipidemia. The serum troponin I levels were significantly increased during doxorubicin treatment, then gradually decreased afterward, while the serum NT-proBNP levels remained statistically unchanged (Figure 1A and B). The numerical reduction of ejection fraction was remarked during the treatment, however there was no clinical cardiac dysfunction (Figure 1C). Subclinical cardiac dysfunction, defined as a &gt;15% relative reduction in global longitudinal strain (GLS), was observed in 9 of 14 patients during trastuzumab treatment (Figure 1D). Mitochondrial oxidative stress in isolated PBMCs, although unchanged during doxorubicin treatment, was gradually increased during trastuzumab treatment (Figure 2A and B). Mitochondrial proton leak was also increased, while oxygen consumption and ATP production remained unchanged (Figure 2C and D). After treatment completion, cardiac function, as well as mitochondrial oxidative stress, tended to improve. Interestingly, there was a strong positive correlation between mitochondrial oxidative stress at baseline and maximum GLS reduction during treatment (r=0.811, p=0.001).

Conclusions
Mitochondrial oxidative stress in isolated PBMCs could be a potential marker for the evaluation and prediction of trastuzumab-induced cardiotoxicity. Further studies are warranted.Figure 1Figure 2