Tolerance of isolated rabbit hearts to short ischemic periods is affected by increased LV mass fraction.

Hypertrophied hearts are known for increased risk of arrhythmias and are linked with reduced ischemic tolerance. However, still little is known about state characterized only by increased left ventricle (LV) mass fraction. Seventeen isolated rabbit hearts with various LV mass were divided into two groups according to LV weight/heart weight ratio (LVW/HW ratio), namely group H and L (with higher and lower LVW/HW ratio, respectively) and underwent three short cycles of global ischemia and reperfusion. The differences in electrogram (heart rate, QRS(max), mean number, onset and dominant form of ventricular premature beats) and in biochemical markers of myocardial injury (creatine kinase, lactate dehydrogenase - LDH) and lipid peroxidation (4-hydroxy-2-nonenal - 4-HNE) were studied. As compared to group L, hearts in group H exhibited lower tolerance to ischemia expressed as higher incidence and severity of arrhythmias in the first ischemic period as well as increase of LDH and 4-HNE after the first reperfusion. In the third cycle of ischemia-reperfusion, the preconditioning effect was observed in both electrophysiological parameters and LDH release in group H. Our results showed consistent trends when comparing changes in electrograms and biochemical markers. Moreover, 4-HNE seems to be good potential parameter of moderate membrane alteration following ischemia-reperfusion injury.

Different doxorubicin formulations affect plasma 4-hydroxy-2-nonenal and gene expression of aldehyde dehydrogenase 3A1 and thioredoxin reductase 2 in rat.

Increased oxidative stress is indisputably an important mechanism of doxorubicin side effects, especially its cardiotoxicity. To prevent impairment of non-tumorous tissue and to improve the specificity in targeting the tumor tissue, new drug nanotransporters are developed. In many cases preclinical therapeutic advantage has been shown when compared with the administration of conventional drug solution. Three forms of doxorubicin--conventional (DOX), encapsulated in liposomes (lipoDOX) and in apoferritin (apoDOX) were applied to Wistar rats. After 24 h exposition, the plasma level of 4-hydroxy-2-nonenal (4-HNE) as a marker of lipoperoxidation and tissue gene expression of thioredoxin reductase 2 (TXNRD2) and aldehyde dehydrogenase 3A1 (ALDH3A1) as an important part of antioxidative system were determined. Only conventional DOX significantly increases the level of 4-HNE; encapsulated forms on the other hand show significant decrease in plasma levels of 4-HNE in comparison with DOX. They also cause significant decrease in gene expression of ALDH3A1 and TXNRD2 in liver as a main detoxification organ, and a mild influence on the expression of these enzymes in left heart ventricle as a potential target of toxicity. Thus, 4-HNE seems to be a good potential biomarker of oxidative stress induced by various forms of doxorubicin.

[Activation of the ribosomal gene during blast transformation of human lymphocytes]. / Aktivace ribozomálního genu v prubehu blastické transformace lidských lymfocytu.

BACKGROUND: Natural lectin, phytohemagglutinin, initiates the transformation of normally quiescent T lymphocytes into proliferating lymphoblast-like cells. Recently we have shown that the transformation is accompanied by strong promotion of ribosomal RNA synthesis and by phosphorylation of its activator, initiating factor UBF, both culminating in a synthetic phase of the first cell division cycle. In contrast we have revealed that the UBF gene was activated and its transcription culminated in the early G1 phase. We examined three possible delaying mechanisms: the kinetics of unwinding of rDNA chromatin, the kinetics of transcription of genes coding for the second initiating factor, SL1 complex, and the kinetics of the translation of UBF protein product. METHODS AND RESULTS: Up to 48 hrs following the addition of phytohemagglutinin to the growth medium, we monitored structural changes in the rDNA chromatin using indirect antiUBF immunofluorescence. The data indicated an increased number of separated transcriptional units during the G1 phase of the first cycle. In a time interval of up to 70 hrs we measured the mRNA levels of four constituents of SL1 complex: TAF110, TAF63, TAF48 and TBP using the RT-PCR method. We found a close correlation between the kinetics of the transcription of UBF and SL1 genes and the maximal rate in the early G1 phase. Using metabolic labelling with 35S methionine/cysteine we monitored the translation of UBF protein in PHA stimulated lymphocytes. The data suggested that UBF translation, starting in the S phase, paralleled chromosomal DNA replication. CONCLUSIONS: During the transformation of normal T lymphocytes into proliferating blast-like cells, the multicopy rDNA gene unwinds in the G1 phase of the first cycle forming individual transcriptional units. Genes coding for factors which initiate synthesis of ribosomal precursors are activated in the early G1 phase. The G1 synthesis of ribosomal RNA is accelerated by phosphorylation of the hypophosphorylated UBF pool. As blastic transformation develops UBF translation is triggered in the S phase and neosynthesized UBF, activated by phosphorylation, pushes the synthesis of ribosomal precursors to maximal efficiency. The process of blastic transformation interferes throughout the entire prolonged G1 phase of the first cell division cycle.