Hydrogen Peroxide Treatment of Muscle Fibres Inhibits the Formation of Myosin Cross-Bridges

Malondialdehyde as a Useful Biomarker of Low Hand Grip Strength in Community-Dwelling Stroke Patients

The assessment of muscle strength by hand grip strength (HGS) is used to evaluate muscle weakness and wasting among stroke patients. This study aimed to investigate the association of oxidative stress/oxidative damage and inflammatory biomarkers with muscle strength and wasting, as evaluated by HGS, among community-dwelling post-stroke patients. The HGS of both paretic and non-paretic limbs was negatively associated with modified Rankin scale (mRS) values. The serum levels of catalase activity and malondialdehyde (MDA), and plasma tumor necrosis factor (TNF)-α levels were significantly increased in post-stroke patients compared with non-stroke controls. Further analysis highlighted that hydrogen peroxide was positively correlated with HGS in the paretic limbs. Interestingly, an elevated MDA level, excluding advanced age and high mRS, increased the risk of low HGS in the non-paretic limbs of stroke patients. This study suggests that there is a detrimental association between MDA and muscle strength and early muscle wasting among post-stroke patients. Hence, MDA is a potentially useful biomarker of muscle weakness and wasting in post-stroke patients living in the community.

Unique functional properties of slow skeletal muscle tropomyosin

Tropomyosin (Tpm) is an α-helical coiled-coil actin-binding protein playing an essential role in the regulation of muscle contraction. The α- (Tpm 1.1) and γ- (Tpm 3.12) Tpm isoforms are expressed in fast and slow human skeletal muscles, respectively, while β-Tpm (Tpm 2.2) is expressed in both muscle types. This results in the formation of Tpm αα- and γγ-homodimers as well as αβ- and γβ-heterodimers. The properties of αα-homodimer are well studied, whereas very little is known about the functional properties of γγ-homodimer and γβ-heterodimer. We investigated interaction characteristics of Tpm γγ-homodimer and γβ-heterodimer with actin filaments and Ca²⁺-regulation of actin-myosin interaction on myosin from fast and slow skeletal muscles. The results showed that complexes formed by γγ-Tpm and γβ-Tpm with F-actin are more stable than those with αα-Tpm and αβ-Tpm. The maximum sliding speed of regulated thin filaments with either γγ-Tpm or γβ-Tpm moving over skeletal myosin was significantly less than that of the filaments with αα-Tpm or αβ-Tpm. The results indicate that isoforms of Tpm along with isoforms of myosin determine of functional properties of skeletal muscles and support an idea on the combined expression of myosin and Tpm isoforms.