The influence of 5-fluorouracil on the α-ketoglutarate dehydrogenase complex in rat's cardiac muscle - a preliminary study.

5-fluorouracil (5-FU), which is a commonly used chemotherapy agent exerts undesired cardiac toxicity. Mitochondrial dysfunction is thought to be one of potentially important mechanisms of 5-FU- induced cardiotoxicity. α-ketoglutarate dehydrogenase (α-KGDHC) is the key regulatory enzyme of TCA cycle. The complex consists of multiple copies of three catalytic subunits: α-ketoglutarate dehydrogenase (E1), dihydrolipoamide succinyltransferase (E2) and dihydrolipoamide dehydrogenase (E3). α-KGDHC together with branched chain α-ketoacid dehydrogenase (BCKDH) and pyruvate dehydrogenase (PDH), are the members of 2-oxoacid dehydrogenases family that share some structural and functional similarities. Recently, it has been found that 5-FU stimulates BCKDH in rat's cardiac muscle. Therefore, we hypothesize that 5-FU modifies α-KGDHC activity and affects cardiac muscle metabolism. The aim of this study was to determine the effect of 5-FU on α-KGDHC activity and protein levels of E1 and E2 subunits of the complex in rat's cardiac muscle. Wistar male rats were administered with 4 doses of 5-FU, 150 mg/ kg b.wt. each (study group) or 0.3% methylcellulose (control group). α-KGDHC activity was assayed spectrophotometrically. The E1 and E2 proteins levels were quantified by Western blot. 5-FU administration resulted in stimulation of myocardial α-KGDHC activity in rats. In addition, E2 protein level increased in response to 5-FU treatment, while the E1 protein level remained unchanged. Up-regulation of α-KGDHC appears to result from change in E2 subunit protein level. However, the effect of 5-FU on factors modifying α-KGDHC activity at post-translational level cannot be excluded.

Influence of a diet rich in linoleic acid on mRNA levels for enzymes of branched chain amino acids metabolism in rat's adipose tissue: a pilot study.

White adipose tissue plays an important role in the catabolism of branched chain amino acids (BCAAs). Two initial regulatory steps in BCAAs catabolism are catalyzed by branched chain aminotransferase (BCAT) and branched chain α-keto acid dehydrogenase complex (BCKDH complex), respectively. It has been demonstrated that synthetic ligands for PPARγ receptors increased mRNA levels for enzymes involved in BCAAs catabolism. We hypothesized that feeding rats with diet rich in linoleic acid (LA), a natural PPARγ agonist modifies mRNA levels for enzymes catalyzing BCAAs degradation in adipose tissue. The current pilot study was aimed at the investigation of the effect of diet rich in LA on mRNA levels for BCATm, branched chain α-keto acid dehydrogenase (E1 component of the BCKDH), and mRNA levels for the regulatory enzymes of BCKDH complex, a specific kinase (BDK) and a specific phosphatase (PPM1K) in epididymal white adipose tissue (eWAT). Wistar male rats were fed with high unsaturated fat diet containing mainly linoleic acid (study group) or with the high saturated fat diet (control group). The relative mRNA levels were quantified by reverse transcription-PCR. We have found that in rats fed diet rich in LA mRNA level for BCATm decreased, while mRNA amount for BDK increased. There was no difference between mRNA levels for BCKDH E1 and PPM1K. It is conceivable that changes in mRNA levels for enzymes involved in BCAAs metabolism in eWAT may lead to modification of BCAAs catabolic rate. Further studies are required to fully elucidate this issue.