Coenzyme Q10 and key enzyme activities in papillary muscle related to left ventricle function in mitral valve disease

Coenzyme Q₁₀ (CoQ₁₀) was studied in papillary muscle from 18 patients (52–67 years, 2 females) subjected to open heart surgery due to mitral valve disease. In addition the enzyme activities of lactate dehydrogenase (LD) with its five isozymes, citrate synthase (CS) and mitochondrial CK (CK-MIT) were determined. Myocardial function was assessed by means of left ventricle (LV) angiography. CoQ₁₀ averaged 0.39 (range 0.26–0.59) g × mg^–1 dw. On an individual basis CoQ₁₀ was related to CS activity although not as closely as CK-MIT (r = 0.45, p<0.05 versus r = 0.86, p<0.001). The ratio (CoQ₁₀) × (CS activity)^–1 was calculated to represent mitochondrial quality. The level of LD₃ fraction increase was used to mark for the degree of metabolic stress in the heart. LD₃ fraction was negatively related to the quality index (r = –0.71, p<0.001). Thus, those with a low CoQ₁₀ per unit of CS activity had also a high LD₃ isozyme fraction. In a subset of 12 patients with isolated mitral regurgitation due to myxomatous valve degeneration, CoQ₁₀ and the ratio CoQ₁₀ over CS decreased with the degree of LV function impairment (r = –0.58, p<0.05 and r = –0.68, p<0.05, respectively). The quality index takes into account not only enzyme activity but also the potential for control of free oxygen radicals.