CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Biology. Ecology

Volume 54 No. 2 June 2005

On the mechanism of the phototoxic action of haematoporphyrin derivative towards tumour cells; 83–119

Lyudmila Chekulayeva, Igor Shevchuk, and Vladimir Chekulayev

Abstract. The aim of this study was to estimate the participation of reactive oxygen species (ROS), other than singlet oxygen (¹O₂), in the antitumour effect of photodynamic therapy (PDT) with haematoporphyrin derivative (HPD) as well as to clarify the mechanism of the potentiating influence of heating associated with photoirradiation on the efficiency of this treatment. Our studies indicated that H₂O₂ and oxygen radicals could mediate the tumouricidal action of HPD–PDT; we found that photoirradiation of Ehrlich ascites carcinoma (EAC) cells pre-incubated with HPD leads to the formation of significant amounts of H₂O₂, superoxide (O₂^–•), and hydroxyl (OH^•) radicals, which along with ¹O₂ were involved in photoinactivation of the cells in vitro. Furthermore, our experiments provided strong evidence that cell Cu/Zn superoxide dismutase, catalase, and the glutathione redox cycle can protect tumour cells against the phototoxic influence of HPD. Our data support the view that in PDT the mild hyperthermia (around 44 °C) induced by irradiation can enhance synergistically the HPD-photoinduced tumour eradication; it was found that raising the irradiation temperature from 30 to 44 °C caused a substantial (~ 1.5-fold) increase in the rate of HPD-photosensitized inactivation of EAC cells, whereas hyperthermia (44 °C) itself showed little toxic effects against the cells. Our results suggest that the potentiating effect of light-induced heating on the antitumour efficiency of HPD–PDT could be largely mediated by a heat-induced increase in the formation of cytotoxic ROS, such as H₂O₂, O₂^–•, and OH^•. Also, experiments showed that photosensitization of EAC cells by HPD caused a strong decrease in the activity of catalase and glutathione peroxidase, and that heat stress sensitized the H₂O₂-detoxifying enzymes to HPD-photoinduced inactivation; upon HPD–PDT, these events could result in loss of protection against accumulating H₂O₂. Moreover, our findings suggest that during PDT with HPD, an increase in the temperature of tumour tissues could enhance the efficiency of this therapy via the stimulation of a chlorin-type photoproduct formation.

Key words: antioxidant enzymes, heating, photodynamic therapy, reactive oxygen species, tumour.

Increase in antiplatelet effects of prostaglandins by α-tocopherol and quercetin; 120–125

Gennadi Kobzar, Vilja Mardla, and Nigulas Samel

Abstract. Prostacyclin (PGI₂) and prostaglandin E₁ (PGE₁) are effective inhibitors of platelet aggregation. Therefore, they are attractive compounds for the treatment of cardiovascular diseases. However, their use is restricted due to unwanted side effects. α-Tocopherol and quercetin are weak antiplatelet agents, which have no side effects. The aim of this work was to study possible potentiation of antiplatelet effects of PGs with α-tocopherol or quercetin. In this work, platelet-rich plasma was prepared from human blood and the inhibition of adenosine diphosphate-induced platelet aggregation by PGs in the presence and absence of α-tocopherol or quercetin was studied. At a subthreshold concentration 200 mM and 2 mM α-tocopherol and quercetin, respectively, increased the antiplatelet effects of PGI₂, PGE₁, and a synthetic analogue of PGI₂, iloprost. Thus, combination of PGs with α-tocopherol or quercetin allows using prostaglandins at lower concentrations to inhibit platelet aggregation.

Key words: platelet aggregation, α-tocopherol, quercetin, prostacyclin, prostaglandin E₁, iloprost.

Application of microwave radiation for sample preparation of pine needles for carbohydrate analysis; 126–135

Jaan Klõšeiko

Abstract. The aim of the current study was to test the suitability of microwave heating for stopping metabolism in plant material. Needles of Pinus sylvestris were treated in a microwave oven (2.45 GHz, 600 W) and compared to the reference needles treated in boiling concentrated ethanol (96%). Sucrose and its degradation products glucose and fructose were affected significantly by differences in the methods while the total content of soluble carbohydrates was not. Using the reference procedure immediately after the microwave treatment or after the drying showed the possible influence of residual enzymatic activity or impurities on the carbohydrate readings during the later stages of analysis. These tests suggest that microwave heating is suitable for the initial processing of pine needles.

Key words: carbohydrates, dielectric heating, enzymatic analysis, enzyme inactivation, Scots pine.

Annotated checklist and distribution of the true bugs (Hemiptera-Heteroptera) of Estonia; 136–165

Carl-Cedric Coulianos

Abstract. On the basis of recent fieldwork, studies of museum and private collections and faunistic literature 454 species of true bugs are listed from Estonia. Their distribution is presented by their occurrence in the 14 UTM grid 100 ´ 100 km squares covering Estonia. Faunistic remarks to 58 species are added. A list with comments on species erroneously published from Estonia is given. The following species are reported as new to Estonia: Plea minutissima (Leach), Dicyphus epilobii Reuter, and Globiceps fulvicollis Jakovlev.

Key words: Hemiptera, Heteroptera, checklist, Estonian fauna.

Instructions to authors; 166–168