Hyperthermia exacerbates methamphetamine cardiotoxicity by promoting neutrophil-dominant inflammation and Map3k6-associated p38/ERK signaling

Methamphetamine (METH) abuse is frequently accompanied by life-threatening hyperthermia, yet the contribution of hyperthermia to METH-induced cardiac injury remains poorly defined. Here, we tested whether elevated ambient temperature amplifies METH cardiotoxicity by aggravating hyperthermia. C57BL/6 mice were exposed to different ambient temperatures (18 °C, 22 °C, or 28 °C) and treated with METH. METH rapidly increased core body temperature, whereas exposure at 28 °C further intensified hyperthermia and caused 20% mortality. In surviving mice, METH at 28 °C significantly reduced cardiac function-including heart rate, cardiac output, stroke volume, ejection fraction and fractional shortening, and induced myocardial eosinophilic degeneration, focal myofiber disruption, cardiomyocyte lysis and inflammatory cell infiltration. Cardiac transcriptomics revealed a distinct inflammatory program enriched for cytokine-cytokine receptor interaction, chemokine signaling, leukocyte chemotaxis and neutrophil migration. RT-qPCR confirmed increased cardiac expression of CCL2, CXCL1, ITGAM, ICAM-1 and MMP9, and inflammatory cytokines were also elevated. Immune-infiltration analysis identified prominent neutrophil accumulation, and gene-set enrichment analysis (GSEA) indicated activation of oxidative stress-related pathways. Among stress-related kinases, mitogen-activated protein kinase kinase kinase 6 (Map3k6, also known as ASK2) was upregulated and positively correlated with neutrophil-dominant infiltration and inflammatory markers. METH at 28 °C also increased p38 and extracellular signal-regulated kinase (ERK) phosphorylation. These findings identify elevated ambient temperature as a critical amplifier of METH-induced cardiac injury and implicate Map3k6-associated p38/ERK activation in hyperthermia-associated cardiac inflammation and functional impairment. Collectively, our results indicate that hyperthermia exacerbates METH cardiotoxicity, potentially involving Map3k6-associated p38/ERK signaling and neutrophil-dominant immune infiltration, providing new mechanistic insights into temperature-associated cardiac vulnerability following METH abuse.