Effects of proteasome inhibitors MG132, ZL₃VS and AdaAhx₃L₃VS on protein metabolism in septic rats

Abstract

Proteasome inhibitors are novel therapeutic agents for the treatment of cancer and other severe disorders. One of the possible side effects is influencing the metabolism of proteins. The aim of our study was to evaluate the influence of three proteasome inhibitors MG132, ZL(3)VS and AdaAhx(3)L(3)VS on protein metabolism and leucine oxidation in incubated skeletal muscle of control and septic rats. Total proteolysis was determined according to the rates of tyrosine release into the medium during incubation. The rates of protein synthesis and leucine oxidation were measured in a medium containing L-[1-(14)C]leucine. Protein synthesis was determined as the amount of L-[1-(14)C]leucine incorporated into proteins, and leucine oxidation was evaluated according to the release of (14)CO(2) during incubation. Sepsis was induced in rats by means of caecal ligation and puncture. MG132 reduced proteolysis by more than 50% and protein synthesis by 10-20% in the muscles of healthy rats. In septic rats, proteasome inhibitors, except ZL(3)VS, decreased proteolysis in both soleus and extensor digitorum longus (EDL) muscles, although none of the inhibitors had any effect on protein synthesis. Leucine oxidation was increased by AdaAhx(3)L(3)VS in the septic EDL muscle and decreased by MG132 in intact EDL muscle. We conclude that MG132 and AdaAhx(3)L(3)VS reversed protein catabolism in septic rat muscles.

The effect of new proteasome inhibitors, belactosin A and C, on protein metabolism in isolated rat skeletal muscle

“…These data correspond with those reporting a lowering of protein synthesis in EDL following an LLnL treatment (16). Similar changes both in EDL and SOL were observed using MG132 and AdaAhx 3 L 3 VS, respectively (17,18). In contrast, LLnL has no effect on protein synthesis in incubated diaphragm (33).…”

“…A similar effect of AdaAhx 3 L 3 VS was demonstrated in both muscle types (17). We assume that this effect reflects a muscle-type-dependent response to belactosins rather than a decrease in total proteolysis.…”

“…In EDL, leucine oxidation tended to increase, however no significant changes were verified. This is partly in conflict with the findings of increase in leucine oxidation after the AdaAhx 3 L 3 VS treatment in both muscle types (18) and decrease in this parameter in EDL following an MG132 exposure (17). As the branched-chain alpha-keto acid dehydrogenase is the rate-limiting enzyme of leucine catabolism (22), one of possible explanations of increased leucine oxidation is, that the enzyme might be induced by belactosins.…”

The lumbrical muscle: a novel in situ system to evaluate adult skeletal muscle proteolysis and anticatabolic drugs for therapeutic purposes

“…In fact, the relative contribution of ATP, Ca 2ϩ -dependent, and lysosomal proteolytic systems to adult skeletal muscle proteolysis was assessed by incubation of lumbrical muscles with inhibitors of proteasome (MG132) (27), calpain (leupeptin and E64) (55), and lysosome (methylamine) systems. Our results clearly showed that the proteasome system is the major route of protein degradation in adult skeletal muscle (Fig.…”

Beta‐hydroxy‐beta‐methylbutyrate supplementation and skeletal muscle in healthy and muscle‐wasting conditions

“…In addition, the up‐regulation of autophagy and lysosomal genes has been documented at the transcript and protein levels in various catabolic conditions 76. There are reports demonstrating that muscles composed mostly by white fibres are more sensitive to catabolic stimuli, particularly to sepsis, when compared with muscles with high content of red fibres 77, 78. Also with advancing age, there is a preferential atrophy of white fibres 79.…”