Biochemical pharmacology
-
Biochemical pharmacology · Nov 1995
Comparative StudyThe antianginal agent ranolazine is a weak inhibitor of the respiratory complex I, but with greater potency in broken or uncoupled than in coupled mitochondria.
Ranolazine (RS-43285) has shown antianginal effects in clinical trials and cardiac anti-ischaemic activity in several in vivo and in vitro animal models, but without affecting haemodynamics. Its mechanism is thought to mainly involve a switch in substrate utilisation from fatty acids to glucose to, thus, improve efficiency of O2 use; however, its precise molecular target(s) are unknown. In studies to investigate its action further, using isolated rat heart mitochondria, ranolazine was found to weakly inhibit (pIC50 values > 300 microM) respiration by coupled mitochondria provided with NAD(+)-linked substrates but not with succinate. ⋯ Studies with radiolabelled ranolazine showed that it bound to mitochondrial membranes with greater affinity in the broken compared to the coupled or uncoupled conditions. Rotenone displaced radiolabelled ranolazine from its binding site. This property of ranolazine may play some role in its anti-ischaemic activity.
-
Biochemical pharmacology · Oct 1995
Enhanced biliary excretion of canalicular membrane enzymes in ethynylestradiol-induced cholestasis. Effects of ursodeoxycholic acid administration.
Cholestasis is associated with a marked increase in the release of canalicular membrane enzymes into bile. This phenomenon has been related to an increased lability of these canalicular membrane integral proteins to the solubilizing effects of secreted bile salts. To further characterize the effects of oral ursodeoxycholic acid (UDCA) administration on ethynylestradiol (EE)-induced cholestasis, the influence of this bile acid on changes in biliary excretion of membrane-bound enzymes was investigated. ⋯ UDCA also prevented the EE-induced changes in the biliary excretion of enzymes. On the contrary, UDCA did not modify either the enzyme activity in isolated membrane fractions or the morphological or ALP histochemical changes associated with EE administration. These data indicate that in EE-induced cholestasis changes occur at the canalicular membrane, enabling this portion of the plasma membrane to be more susceptible to the solubilizing effect of bile salt, and that oral administration of UDCA prevents bile secretory failure and changes in the biliary excretion of ALP and GGT in EE-treated rats.
-
Biochemical pharmacology · Jul 1994
Comparative StudyInhibitors of ribonucleotide reductase. Comparative effects of amino- and hydroxy-substituted pyridine-2-carboxaldehyde thiosemicarbazones.
A new series of alpha-(N)-heterocyclic carboxaldehyde thiosemicarbazones (HCTs) was studied for their effects on L1210 cell growth in culture, cell cycle transit, nucleic acid biosynthesis and ribonucleotide reductase activity. 3-Aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP) and 3-amino-4-methylpyridine-2-carboxaldehyde thiosemicarbazone (3-AMP) were the most active compounds tested with respect to inhibition of cell growth and ribonucleotide reductase activity. 5-Aminopyridine-2-carboxaldehyde thiosemicarbazone (5-AP) and 4-methyl-5-aminopyridine-2-carboxaldehyde thiosemicarbazone (5-AMP) were slightly less active. 3-AP, 3-AMP, 5-AP and 5-AMP inhibited the incorporation of [3H]thymidine into DNA without affecting the rate of incorporation of [3H]uridine into RNA. The uptake and incorporation of [14C]cytidine into cellular ribonucleotides and RNA, respectively, were not decreased by 3-AP or 3-AMP; however, the incorporation of cytidine into DNA via ribonucleotide reductase was inhibited markedly. Thus, a pronounced decrease in the formation of [14C]deoxyribonucleotides from radioactive cytidine occurred in the acid-soluble fraction of 3-AP- and 3-AMP-treated L1210 cells. ⋯ N-Acetylation of 3-AMP resulted in a compound that was 10-fold less active as an inhibitor of ribonucleotide reductase activity and 8-fold less active as an inhibitor of L1210 cell growth. N-Acetylation of either 5-AP or 5-AMP did not alter the inhibitory properties of these compounds. The results obtained provide an experimental rationale for the further development of the HCTs, particularly 3-AP and 3-AMP, as potential drugs for clinical use in the treatment of cancer.
-
Biochemical pharmacology · Feb 1994
Comparative StudyEffect of a new, potent, non-peptide V1a vasopressin antagonist, SR 49059, on the binding and the mitogenic activity of vasopressin on Swiss 3T3 cells.
The effects of SR 49059, a new non-peptide, selective arginine vasopressin (AVP), V1a antagonist, were investigated both on AVP's receptors and on the mitogenic effects of AVP on Swiss 3T3 fibroblasts. We characterized the AVP V1a receptors on Swiss 3T3 cell membranes using the new highly specific AVP V1a radioiodinated ligand, 125I-linear AVP antagonist. Specific binding of the 125I-linear AVP antagonist was saturable, time-dependent and reversible. ⋯ SR 49059 was even about six times more efficient than d(CH2)5Tyr(Me)AVP in inhibiting AVP-induced DNA synthesis. Moreover, SR 49059 fully inhibited Swiss 3T3 fibroblast proliferation since it completely blocked AVP-stimulated 3T3 cell growth from the G1/G0 into the S/G2M phase, as evidenced by cell cycle analysis using a cytofluorometer. In summary, SR 49059, through direct interaction at AVP V1a receptors, exerts the most potent antiproliferative effect yet described for any V1a antagonist on Swiss 3T3 cells.
-
Biochemical pharmacology · Jan 1994
Comparative Study2'-Deoxy-2'-methylene derivatives of adenosine, guanosine, tubercidin, cytidine and uridine as inhibitors of L1210 cell growth in culture.
The 2'-deoxy-2'-methylene derivatives of adenosine (MdAdo), guanosine (MdGuo), tubercidin (MdTu), cytidine (MdCyd) and uridine (MdUrd) were synthesized as mechanism-based inhibitors directed at ribonucleotide reductase. It was shown that MdCyd 5'-diphosphate irreversibly inactivated ribonucleotide reductase from Escherichia coli (Baker et al., J Med Chem 34: 1879-1884, 1991). In studies reported here, MdAdo/EHNA, MdGuo and MdCyd inhibited L1210 cell growth with IC50 values of 3.4, 10.6 and 1.4 microM, respectively. ⋯ MdAdo, MdGuo and MdCyd inhibited the incorporation of [14C]cytidine into DNA without an effect on RNA synthesis or total cellular uptake of [14C]cytidine. The conversion of [14C]cytidine to deoxycytidine nucleotides was partially inhibited by MdGuo, but not by MdAdo or MdCyd. These data show that the 2'-deoxy-2'-methylene derivatives of adenosine, guanosine and cytidine are activated via specific nucleoside kinases and that the modes of action of these compounds are not identical.