The Role of Toll-Like Receptor 4 in Myocardial Ischemia-Reperfusion Injury: A Systematic Review of Preclinical and Translational Studies

Abstract

Introduction: Myocardial ischemia-reperfusion injury (IRI) occurs when blood flow is restored to ischemic myocardium, paradoxically exacerbating tissue damage. Toll-like receptor 4 (TLR4), a key innate immune receptor, is activated by damage-associated molecular patterns released during ischemia. However, the translational potential of TLR4 inhibition remains incompletely defined.

Methods: A systematic literature search was conducted in PubMed, Embase, and Web of Science (2005–2024) for preclinical studies (in vivo animal models of myocardial IRI) and early-phase human studies. Inclusion criteria: evaluation of TLR4 antagonists (e.g., TAK-242, eritoran) or genetic TLR4 knockdown. Exclusion: studies without infarct size or cardiac function outcomes. Quality assessment used SYRCLE's risk of bias tool for animal studies.

Results: Forty-two preclinical studies (n=1,150 animals, mainly mice and rats) met inclusion. TLR4 inhibition or knockout reduced infarct size by a mean of 34% (95%CI 28–41%) compared to controls. Improvement in left ventricular ejection fraction (LVEF) at 24–72 hours post-reperfusion was 12 percentage points (95%CI 8–16). Mechanistically, TLR4 blockade decreased myocardial NF-κB activation, reduced neutrophil infiltration by 45%, and lowered IL-1β and TNF-α levels. Three small human studies (n=112 patients with ST-elevation MI undergoing primary PCI) using eritoran reported no serious adverse events but showed inconsistent effects on biomarkers (reduction in CK-MB in one study, null in two).

Discussion: Consistent preclinical evidence supports TLR4 as a valid therapeutic target in IRI. The lack of robust human efficacy may reflect inadequate dosing, delayed administration (>30 minutes after reperfusion), or species differences in TLR4 signaling. Limitations include publication bias in animal studies and short follow-up (≤7 days) in most experiments.

Conclusions: TLR4 inhibition reduces infarct size and preserves LVEF in animal models of myocardial IRI, but human data remain inconclusive. Larger randomized trials with optimized dosing and earlier administration are needed before clinical adoption.