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.

Effect of 5-fluorouracil on branched-chain α-keto acid dehydrogenase (BCKDH) complex in rat's heart

Undisturbed branched-chain amino acids (BCAA) catabolism is necessary for normal heart function. The key enzyme in BCAA catabolism is a multienzyme branched-chain α-keto acid dehydro- genase complex (BCKDH). BCKDH activity is regulated mainly by reversible dephosphorylation (activa- tion)/phosphorylation (inactivation) cycle catalyzed by regulatory enzymes, a specific phosphatase (PPM1K) and kinase (BDK). 5-fluorouracil (5-FU) is widely used in the treatment of different types of cancer. 5-FU has the potential to cause a wide spectrum of cardiotoxicity, ranging from asymptomatic electrocardiographic changes to cardiomyopathy and subsequent cardiac failure. We hypothesize that 5-FU modifies BCKDH activity and affects cardiac muscle metabolism. The current study was aimed at the investigation of the in vivo effect of 5-FU on BCKDH activity and mRNA levels for E1, PPM1K and BDK. 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). BCKDH activity was assayed spectrophotometrically. The mRNA levels were quantified by real-time PCR. 5-FU treatment caused an increase in BCKDH activity that appears to result mainly from increased dephosphorylation of the complex and is associated with an increase of PPM1K mRNA level and reduction of BDK and E1 mRNA levels. It is conceivable that 5-FU stimulation of BCKDH is an adaptive reaction with the purpose of enhancing the BCAA catabolism and protecting from toxic effect caused by excessive accumulation of these amino acids in heart.

Effect of high carbohydrate diet on elongase and desaturase activity and accompanying gene expression in rat's liver

Background

Hepatic fatty acids (FAs) are modified through different metabolic pathways including elongation and desaturation. These processes are catalyzed by elongases and desaturases, respectively. Glucose, by transcription factors, regulates these processes. The aim of the study was to evaluate the influence of high carbohydrate diet (68%) on the expression of elongase (Elovl-2, Elovl-5, and Elovl-6) and desaturase (∆5D, ∆6D, Scd 1, Scd 2) genes and the activity of the enzymes. The changes in serum lipid profile (triglycerides (TG), total cholesterol (TC), HDL cholesterol) and glucose concentration were measured. Male Wistar rats were randomized into two study groups: animals fed with high carbohydrate diet (n = 6; HiCHO) and a control group fed with a standard diet (n = 6; ST). The expression of mRNA was determinate using reverse transcription PCR (RT-PCR). Hepatic FA composition was determined by gas chromatography, and FA ratios were used to estimate the activity of enzymes. Serum lipid profile and glucose concentration were measured using spectrophotometric methods.

Results

The mean values of transcript expression of all examined elongases and desaturases in liver HiCHO rats were higher as compared to ST. Higher expression did not always correspond to higher activity (as index). More monounsaturated FAs (MUFAs) were detected in the liver of HiCHO rats as compared to ST. Serum TG level was higher in the HiCHO than in ST.

Conclusions

These studies support the notion that the regulation of both Elovl and desaturase expression may play an important role in managing hepatic lipid composition in response to changes in dietary status.

Expression of metalloproteinases (MMP-2 and MMP-9) in basal-cell carcinoma

The aim of this study was to compare the expressions of mRNA for metalloproteinases (MMP-2 and MMP-9) and type IV collagen in two different histological types of basal-cell carcinoma (BCCs; nodular and infiltrative) and in normal tissues from the tumor interface. The study included biopsy specimens of the skin involved with BCC and normal skin adjacent the lesion. The expressions of mRNA for MMP-2, MMP-9 and type IV collagen were determined by means of RT-PCR (Reverse transcription polymerase chain reaction). The level of type IV collagen mRNA in nodular and infiltrative BCCs turned out to be significantly lower, and the expressions of MMP-2 and MMP-9 mRNA significantly higher than in normal tissues adjacent to these tumors. The expression of mRNA for MMP-9 but not for MMP-2 was significantly higher in infiltrative BCCs than in the nodular BCCs. In turn, normal tissues adjacent to nodular BCCs showed significantly higher levels of mRNA for MMP-2 and significantly lower levels of type IV collagen mRNA than the normal tissues from the interface of infiltrative BCCs. The findings suggest that MMP-2 and MMP-9 could be used as prognostic factors of BCCs.