Mitochondrial changes in platelets are not related to those in skeletal muscle during human septic shock

Abstract

Platelets can serve as general markers of mitochondrial (dys)function during several human diseases. Whether this holds true even during sepsis is unknown. Using spectrophotometry, we measured mitochondrial respiratory chain biochemistry in platelets and triceps brachii muscle of thirty patients with septic shock (within 24 hours from admission to Intensive Care) and ten surgical controls (during surgery). Results were expressed relative to citrate synthase (CS) activity, a marker of mitochondrial density. Patients with septic shock had lower nicotinamide adenine dinucleotide dehydrogenase (NADH)/CS (p = 0.015), complex I/CS (p = 0.018), complex I and III/CS (p<0.001) and complex IV/CS (p = 0.012) activities in platelets but higher complex I/CS activity (p = 0.021) in triceps brachii muscle than controls. Overall, NADH/CS (r2 = 0.00; p = 0.683) complex I/CS (r(2) = 0.05; p = 0.173), complex I and III/CS (r(2) = 0.01; p = 0.485), succinate dehydrogenase (SDH)/CS (r(2) = 0.00; p = 0.884), complex II and III/CS (r(2) = 0.00; p = 0.927) and complex IV/CS (r(2) = 0.00; p = 0.906) activities in platelets were not associated with those in triceps brachii muscle. In conclusion, several respiratory chain enzymes were variably inhibited in platelets, but not in triceps brachii muscle, of patients with septic shock. Sepsis-induced mitochondrial changes in platelets do not reflect those in other organs.

Figure 1. Platelet mitochondrial biochemistry during septic shock.

Mitochondrial biochemistry was measured on platelets of ten surgical controls (white bars) and thirty patients with septic shock (<24 h from ICU admission) (black bars). Activities of nicotinamide adenine dinucleotide dehydrogenase (NADH) (p = 0.015^#) (A), complex I (CI) (p = 0.018^#) (B), complex I and III (CI+III) (p<0.001) (C), succinate dehydrogenase (SDH) (p = 0.086) (D), complex II and III (CII+III) (p = 0.672) (E) and complex IV (CIV) (p = 0.012^#) (F) are expressed as percentages of citrate synthase (CS) activity (p = 0.002) (G). Data are reported as means and standard deviations. *p<0.05 vs. controls [Student’s t or (^#) Wilcoxon rank sum tests]. Platelet count (182±83 vs. 176±63 *10³/mm³) did not differ between groups (p = 0.901).

Figure 2. Skeletal muscle mitochondrial biochemistry during septic shock.

Mitochondrial biochemistry was measured on triceps brachii muscle of ten surgical controls (white bars) and thirty patients with septic shock (<24 h from ICU admission) (black bars). Results of two patients are not available due to technical troubles. Activities of nicotinamide adenine dinucleotide dehydrogenase (NADH) (p = 0.369) (A), complex I (CI) (p = 0.021) (B), complex I and III (CI+III) (p = 0.286) (C), succinate dehydrogenase (SDH) (p = 0.432) (D), complex II and III (CII+III) (p = 0.273) (E) and complex IV (CIV) (p = 0.760) (F) are expressed as percentages of citrate synthase (CS) activity (p = 0.458) (G). Data are reported as means and standard deviations. *p<0.05 vs. controls (Student’s t test).

Figure 3. Relationship between platelet and skeletal muscle mitochondrial biochemistry.

Mitochondrial biochemistry was measured on platelets (Y-axis) and triceps brachii muscle (X-axis) of ten surgical controls (white dots) and thirty patients with septic shock (<24 h from ICU admission) (black dots). Results of skeletal muscle mitochondrial biochemistry of two patients are not available due to technical troubles. Activities of nicotinamide adenine dinucleotide dehydrogenase (NADH) (A), complex I (CI) (B), complex I and III (CI+III) (C), succinate dehydrogenase (SDH) (D), complex II and III (CII+III) (E) and complex IV (CIV) (F) are expressed as percentages of citrate synthase (CS) activity (G). r² and p values refer to Pearson product moment test.