Purification and characterization of thymidine kinase from regenerating rat liver

Hepatoprotective effect of Geranium schiedeanum against ethanol toxicity during liver regeneration

AIM

To evaluate the effect of an extract of Geranium schiedeanum (Gs) as a hepatoprotective agent against ethanol (EtOH)-induced toxicity in rats.

METHODS

Male Wistar rats weighing 200-230 g were subjected to a 70% partial hepatectomy (PH); they were then divided into three groups (groups 1-3). During the experiment, animals in group 1 drank only water. The other two groups (2-3) drank an aqueous solution of EtOH (40%, v/v). Additionally, rats in group 3 received a Gs extract daily at a dose of 300 mg/kg body weight intragastically. Subsequently, to identify markers of liver damage in serum, alanine aminotransferase, aspartate aminotransferase, albumin and bilirubin were measured by colorimetric methods. Glucose, triglyceride and cholesterol concentrations were also determined. In addition, oxidative damage was estimated by measuring lipid peroxidation [using thiobarbituric-acid reactive substances (TBARS)] in both plasma and the liver and by measuring the total concentration of antioxidants in serum and the total antioxidant capacity in the liver. In addition, a liver mass gain assessment, total DNA analysis and a morpho-histological analysis of the liver from animals in all three groups were performed and compared. Finally, the number of deaths observed in the three groups was analyzed.

RESULTS

Administration of the Geranium shiedeanum extract significantly reduced the unfavorable effect of ethanol on liver regeneration (restitution liver mass: PH-EtOH group 60.68% vs PH-Gs-EtOH group 69.22%). This finding was congruent with the reduced levels of hepatic enzymes and the sustained or increased levels of albumin and decreased bilirubin in serum. The extract also modified the metabolic processes that regulate glucose and lipid levels, as observed from the serum measurements. Lower antioxidant levels and the liver damage induced by EtOH administration appeared to be mitigated by the extract, as observed from the TBARs (PH-EtOH group 200.14 mmol/mg vs PH-Gs-EtOH group 54.20 mmol/mg; P < 0.05), total status of antioxidants (PH-EtOH group 1.43 mmol/L vs PH-Gs-EtOH group 1.99 mmol/L; P < 0.05), total antioxidant capacity values, liver mass gain and total DNA determination (PH-EtOH group 4.80 mg/g vs PH-Gs-EtOH 9.10 mg/g; P < 0.05). Overall, these processes could be related to decreased mortality in these treated animals.

CONCLUSION

The administered extract showed a hepatoprotective effect, limiting the EtOH-induced hepatotoxic effects. This effect can be related to modulating oxido-reduction processes.

Development and validation of a capillary electrophoresis method for the characterization of herpes simplex virus type 1 (HSV-1) thymidine kinase substrates and inhibitors

A fast, convenient capillary electrophoresis (CE) method was developed for monitoring the enzymatic reaction of herpes simplex virus type 1 thymidine kinase (HSV-1 TK). The reaction was performed in a test tube followed by quantitative analysis of the products. The optimized CE conditions were as follows: polyacrylamide-coated capillary (20 cm effective length x 50 microm), electrokinetic injection for 30s, 50 mM phosphate buffer at pH 6.5, constant current of -60 microA, UV detection at 210 nm, UMP or cAMP were used as internal standards. Phosphorylated products eluted within less than 7 min. The limits of detection were 0.36 microM for dTMP and 0.86 microM for GMP. The method was used to study enzyme kinetics, and to investigate alternative substrates and inhibitors.

Increased thymidine kinase activity in human thyroid toxic adenomas: effects of exposure to epidermal growth factor in vitro

The activity of thymidine kinase (TK-EC 2.7.1.21)--an enzyme functioning as a part of the pyrimidine salvage pathway of DNA synthesis--is closely related to growth processes. The aim of the study was to measure TK activity in homogenates of human thyroid tissue of the following types: non-toxic nodular goiter (NTNG)--macroscopically unchanged tissue, non-toxic adenoma (NTA), and toxic adenoma (TA) (obtained from patients, who--before the surgery--had been treated with thyrostatic drugs for thyrotoxicosis). Thyroid tissue was obtained from female patients subjected to subtotal thyroidectomy at the Department of Endocrine Surgery, Medical University of Lódź. Thyroid homogenates were incubated in the presence of epidermal growth factor (EGF), used in five different concentrations (0.1 ng/ml, 1 ng/ml, 10 ng/ml, 100 ng/ml, 1000 ng/ml). TK activity was estimated by chromatographic measurements of the amount of the main reaction product--deoxythymidine monophosphate.

RESULTS

1) We did not observe any significant difference between TK activity in the homogenates of the thyroid tissue collected from NTNG and NTA; TK activity was clearly higher in the homogenates of adenomatous tissue, collected from the patients with TA; 2) EGF increased TK activity in the homogenates of the macroscopically unchanged tissue, collected--during surgery--from the patients with NTNG, as well as in homogenates of thyroid tissue from NTA; 3) In case of hyperactive thyroid tissue, obtained from TA, EGF tended to increase TK activity, however, without any statistical differences. Our results confirm TK increased activity in hyperactive thyroid tissue. At the same time, the obtained data suggest a certain role of EGF in goiter formation in humans.

Inhibition of thymidylate synthase and thymidine kinase by okadaic acid in regenerating rat liver after partial hepatectomy

The effects of okadaic acid, a potent and specific inhibitor of protein phosphatases 1 and 2A, on liver regeneration after partial (70%) hepatectomy were investigated. The injection of okadaic acid (25 micrograms/kg body weight) inhibited the increases in the activities of thymidylate synthase and thymidine kinase in regenerating rat liver at 24 hr after partial hepatectomy, with a concomitant reduction in DNA content. Northern blot analysis showed that the suppression of thymidylate synthase and thymidine kinase activities was caused by comparable decreases in their mRNA levels. The protein levels of thymidylate synthase and thymidine kinase were confirmed by immunoblotting assay to be proportional to the activity and mRNA levels. These findings suggest that okadaic acid-sensitive protein phosphatases are involved in transcriptional control of the dTMP-synthesizing enzymes during liver regeneration.