Structural features of prostanoid analogues involved in hepatocytes protection against CCl4-induced injury.

The ability of natural prostaglandins (PGs) and synthetic prostanoids of B, H and E(1)-types to prevent CCl(4)-induced liver injury in vitro was examined. Seven analogs of PGB, 3 derivatives of PGH and two 11-deoxy-analogs of PGE(1) decreased cytotoxic index of CCl(4) by 2-fold and were more effective then such well-known hepatoprotectors as silymarin, curcumin and PGI(2). These prostanoids reduced trien conjugates formation by 25-95% and strongly prevented LDH leakage through plasma membrane. The results from the structure-activity relationship (SAR) analysis can be summarized as follows: (1) the presence of 2-pyridyl at the 15 position of ω-chain plays the main role in cytoprotection for synthetic analogs of PGH; (2) among 11-deoxy-analogs of PGE(1) the most active substances possess the phenyl residue at C-15 connected with C-13 isoxazolin or C-13 isoxazol; (3) C-13 cyclohexylamine or C-15 phenyl groups in ω-chain and metoxy-group in α-chain are important for protective activity of PGB analogs; (4) synthetic analogs of PGB demonstrate more pronounced cytoprotective properties than prostanoids of H and E-types. This information suggests paths for further exploration in the area of hepatoprotection and the design of novel therapeutic agents.

The mechanism of the rat liver cytochrome P4502E1 inhibition by the synthetic prostanoids of A-type.

AIM: The elucidation of mechanism of A-type synthetic prostanoids inhibitory action on microsomal cytochrome P(450)2E1 (CYP2E1) from rat liver activity was carried out. RESULTS: Analogs U-34 and U-26 in a final concentration of 1 x 10(-5)M inhibited CYP2E1 activity by 93% and 46%, respectively; however natural prostaglandins had no effect. These synthetic prostanoids of A-type (5 x 10(-8) to 10(-4)M) inhibited chlorzoxazone hydroxylation in a dose-dependent manner while IC(50)=7.1 x 10(-7)M and 8.0 x 10(-7)M for U-26 and U-34, respectively. The curves of CYP2E1 activity in the presence of different concentrations of chlorzoxazone and varying concentration of prostanoids were hyperbolic. Double-reciprocal plots of these results 1/V=f(1/S) indicated that prostanoids inhibit CYP2E1 through a competitive mechanism with particular effect. CONCLUSION: CYP2E1 is a target for A-type prostanoids, possessing 2-oxo-4-amino-oct-3(E)-enyl in alpha- or omega-chain, which are able to inhibit its action through a competitive mechanism.

Biochemistry of prostaglandins A.

This review considers modern concepts on the structural-functional properties and antiproliferative, antitumor, and antiviral effects of cyclopentenone prostaglandins A and mechanisms underlying their actions. Possible directions of pharmacological application of these compounds and their analogs are discussed.

Synthetic heteroprostanoids of A- and E-types as novel non-comprehensive inhibitors of adenylyl cyclase in rat hepatocytes.

Treatment of rat hepatocyte plasma membranes with five novel synthetic heteroprostanoids of A- and E-types significantly decreased basal activity of adenylyl cyclase. Inhibition of forskolin-stimulated activity of the enzyme was seen as well. The maximal effective concentration for all substances tested was found at approximately 5x10(-6)-1x10(-5) M. The values of half maximal concentration (IC50) for all prostanoids were at the region of 0.7-1.1 microM. Prostanoids belonging to cyclopentenone group A (U-39, U-26) were less active than analogs of 11-deoxy-PGE1 (TA-227, TA-280, and TA-239). The strongest inhibitory effect of adenylyl cyclase activity (more than 3 times) was determined in the presence of prostanoid TA-227 possessing hydrophobic 15-phenyl ring and isoxazol group in omega-chain. The investigation of AC activity in the presence of different concentrations of prostanoids and varying concentrations of Mg x ATP has demonstrated that a non-comprehensive mechanism with particular effect takes place in case of AC inhibition by the heteroprostanoids.

[Functional interactions of components of the adenylate cyclase system in the rat liver after prenatal exposure to gamma irradiation]. / Funktsional'noe vzaimodeistvie komponentov adenilattsiklaznoi sistemy pecheni krys posle prenatal'nogo vozdeistviia gamma-izlucheniia.

The effects of long-term prenatal gamma-radiation (0.5 Gy) on the glucagon signalling through adenylyl cyclase in adult rat liver have been investigated. The coupling of receptor/Gs-protein/adenylyl cyclase was tested using kinetic constants for stimulation of adenylyl cyclase by GTP, Gp(NH)pp, AlF4- and glucagon. The estimated data suggests that prenatal chronic gamma-radiation prompted (i) a decrease in rate of GTP hydrolysis on Gs-protein; (ii) a reduction of glucagon potency to accelerate the exchange GDP for GTP on Gs-protein.

Influence of plasma membrane depolarization on cAMP level in rat brain synaptosomes.

We studied the influence of plasma membrane depolarization on cAMP content in presynaptic nerve endings (synaptosomes) isolated from brain hemispheres (HS) and cerebellum (CS). Depolarization by elevated [K+]o decreased basal cAMP level in both types of synaptosomes; reduced cAMP content in HS and increased cAMP in CS in the presence of IBMX; and lowered forskolin-stimulated cAMP accumulation in both the HS and the CS. Similar results were obtained when depolarization was induced by veratrine or when [Ca2+]i was elevated by treatment of the synaptosomes with the ionophore A23187. In Ca2+-free media, depolarization was not able to affect the synaptosomal cAMP levels. These data suggest that in brain synaptosomes intracellular cAMP pathway is modulated by alterations in [Ca2+]i.

[Effect of prenatal gamma-irradiation on functional properties of rat liver adenylate cyclase]. / Vliianie vnutriutrobnogo gamma-oblucheniia na funktsional'nye svoistva adenilattsiklazy pecheni krys.

In the present work the effects of long-term prenatal gamma-irradiation (0.5 Gy) on the glucagon signalling through adenylyl cyclase have been investigated. In utero gamma-irradiation resulted in the increase of basal and GTP-stimulated adenylyl cyclase activity, whereas, the adenylyl cyclase response to glucagon was essentially reduced. The comparison of kinetic constants estimated from dose-response data for GTP and glucagon suggests that prenatal chronic irradiation prompted (i) the decrease in rate of GTP hydrolysis on Gs-protein; (ii) the reduction of glucagon potency to accelerate the exchange GDP for GTP on Gs-protein.

[Purification and biochemical characteristics of myosin from rat malignant sarcoma-45]. / Ochistka i biokhimicheskaia kharakteristika miozina iz zlokachestvennoi opukholi krys sarkoma-45.

Myosin was purified from rat tumour sarcoma-45 whose properties (effects of cations on ATPase activity, substrate specificity, temperature- and pH-optima, thermal stability, sensitivity of Mg2(+)-ATPase to F-actin, molecular mass, subunit composition) are similar to those of fast skeletal muscle myosin. Some parameters of the protein, namely, the levels of Ca2(+)- and K+, EDTA-ATPase activity, relative content of myosin light chains with Mr 16500 and the degree of tumoural myosin Mg2(+)-ATPase activation by F-actin, were significantly lower than those of skeletal muscle myosin.

[Effect of vincristine on Mg2+-ATPase activity of actomyosin-like protein from sarcoma-45 and actomyosin from rat skeletal muscle]. / Vliianie vinkristina na Mg2+-ATFaznuiu aktivnost' aktomiozinopodobnogo belka iz sarkomy-45 i aktomiuzina iz skeletnoi myshtsy krys.

Kinetic parameters of the inhibitory effect of vincristine on Mg2+ATPase activity containing in the actomyosin-like protein from rat sarcoma 45 and in actomyosin from rat skeletal muscle was studied. The alkaloid decreased the VM value for the reaction catalyzed by ATPase in presence of Mg2+ and EGTA and did not alter Km value for both contractile proteins. Inhibitory constants, calculated for the actomyosin from skeletal muscles and for the actomyosin-like protein from sarcoma 45, constituted 520 mcM and 250 mcM, respectively. Vincristine appears to inhibit Mg2+-ATPase containing in these contractile proteins studied by the non-competitive type, simultaneously with lowering of the activating effect of actin on the myosin-derived ATPase.

Transport and intracellular localization of cortisol-asialotranscortin complexes in rat liver.

The influence of desialylation of human transcortin on transport of the transcortin-cortisol complex into the liver cells and its intracellular distribution was investigated in perfused rat liver. Under experimental conditions used the half-time of cortisol in perfusion medium was decreased more than 200 times in presence of asialotranscortin compared to that of native transcortin. Experiments with [3H]cortisol and [131I]asialotranscortin demonstrated a simultaneous uptake of cortisol and asialotranscortin by the hepatocytes. Distribution of [3H]cortisol and [131I]asialotranscortin in subcellular fractions showed the following pathway of cortisol-asialotranscortin complex: cell membrane, lysosomes, cytoplasm. The complex dissociates in lysosomes.

[Role of adrenoreceptors in regulating aspartate aminotransferase isoenzyme activity in albino rat hearts]. / Rol' adrenoretseptorov v reguliatsii aktivnosti izofermentov aspartat-aminotransferazy serdtsa belykh krys.

Cytoplasmic (c) and mitochondrial (m) isoenzymes of aspartate aminotransferase (AAT, EC 2.6.1.1.) were isolated from rat heart extracts by electrophoresis in agar gel. Their pH optima and Km values were estimated; optimal conditions for estimation of the enzymatic activities are reported. Isadrine activated and adrenaline inhibited the cAAT activity. Noradrenaline did not affect the activity of both isoenzymes. Phentolamine, as contrary to obsidane which decreased the activity of both isoenzyme, activated the isoenzymes; the effect was partially decreased by obsidane. Phentolamine did not alter the noradrenaline effect on either mAAT or cAAT; it decreased significantly the free form of the mAAT activity only. Results of the experiments with administration of adrenomimetic drugs suggested that adrenaline and noradrenaline-isadrine had different sites of attachment through which they mediated their action on aspartate aminotransferase in rat heart mitochondria.

[Role of adrenergic mechanisms in the regulation of aspartate aminotransferase isoenzyme activity in the liver of white rats]. / Rol' adrenergicheskikh mekhanizmov v reguliatsii aktivnosti izofermentov aspartat-aminotransferazy pecheni belykh krys

Cytoplasmic (c) and mitochondrial (m) isozymes of aspartate aminotransferase (AAT) (EC 2.6.1.1) were isolated from white rat liver tissue by means of electrophoresis in agar gel. For the enzymes Km values, pH optima were estimated and conditions, suitable for the reaction, were studied. On the basis of activating effectiveness on c-AAT the catecholamines were arranged in decreasing order as follows: adrenaline, isadrine, noradrenaline. Towards the m-AAT the series was: noradrenaline, isadrine, adrenaline. Obsidane decreased the action of adrenaline more effectively than it did isadrine. Phentholamine did not alter the effect of noradrenalin on c-AAT, but distinctly decreased the m-AAT activity. Beta-adrenergic receptor, but not alpha-receptor, participated in regulation of the AAT isozymes activity. Adrenaline promoted and isadrine inhibited the penetration of m-AAT into cytoplasma. Obsidane increased the effect of these catecholamines. After administration of phentholamine an increase in the AAT activity was caused by an increase in content of catecholamines in the organism.