Cathepsin L enhances angiogenesis by increasing extracellular matrix degradation 
and remodelling. This study investigated whether plasma cathepsin L could be 
used as a biomarker to predict collateral formation in patients with coronary 
heart disease (CHD). Patients with CHD (n = 218; aged 67 ± 11 years) underwent 
coronary angiography and were categorized as having either 'poor' or 'rich' 
collaterals. Plasma cathepsin L, the proangiogenic placenta growth factor (PLGF) 
and the antiangiogenic factors, cystatin C and endostatin, were measured. 
Elevated cathepsin L and PLGF levels were independently and significantly 
associated with enhanced collateral formation in patients with CHD; subgroup 
analyses also showed a significant correlation in patients with diabetes and 
acute coronary syndrome. Plasma endostatin and cystatin C levels were not 
significantly correlated with coronary collateral formation. Plasma cathepsin L 
and PLGF, acting as important modulators of angiogenesis, could be used as 
biomarkers to predict coronary collateral formation in patients with CHD.