Arphamenine B hydrochloride

The possible involvement of enzymatic degradation in the inactivation of enkephalins in the spinal cord of neonatal rats was investigated electrophysiologically and biochemically. In an isolated spinal cord-saphenous nerve preparation, electrical stimulation of the saphenous nerve evoked a slow depolarization lasting 20-30 s of the ipsilateral L3 ventral root. This slow depolarization was depressed by a mixture of peptidase inhibitors, consisting of actinonin (10 microM), thiorphan (0.6 microM), bestatin (10 microM), arphamenine B (10 microM) and captopril (10 microM). Naloxone (0.5 microM) not only reversed this effect of the mixture of peptidase inhibitors but also potentiated the slow depolarization beyond the pre-control level. In an isolated spinal cord preparation, electrical stimulation of a lumbar dorsal root evoked a slow depolarization of the contralateral ventral root of the same segment. This slow depolarization was depressed by application of [Met5]enkephalin in a dose dependent manner. This effect of [Met5]enkephalin was markedly potentiated by addition of the mixture of peptidase inhibitors. Among the five peptidase inhibitors, actinonin, thiorphan or bestatin alone potentiated the depressant effect of [Met5]enkephalin, whereas arphamenine B and captopril did not. Membrane fractions prepared from neonatal rat spinal cords showed degrading activities for [Met5]- and [Leu5]enkephalins and these activities were inhibited by the mixture of peptidase inhibitors. Among the five peptidase inhibitors, actinonin and thiorphan markedly inhibited the [Met5]enkephalin-degrading activity while bestatin was less effective. Arphamenine B and captopril were ineffective. The present results suggest that enzymatic degradation by peptidases plays a role in the termination of the transmitter action of enkephalins in the neonatal rat spinal cord. The present results, together with our previous results on the enzymatic degradation of tachykinins in a study in which we used the same preparations, suggest that similar but distinct combinations of peptidases are involved in the inactivation of enkephalin and tachykinin neurotransmitters.

We investigated the growth inhibitory activity of bestatin, an inhibitor of aminopeptidase N (CD13), on six human leukemic cell lines. Proliferation of all the cell lines except KG1 was inhibited by bestatin. P39/TSU, HL60 and U937 were highly sensitive, with 50% growth inhibitory concentrations (IC50) close to the maximum serum concentration when bestatin was orally administered at 30 mg in clinical application. All cell lines except for K562 highly expressed CD13, but a clear correlation between the sensitivity to bestatin and expression of CD13 was not observed. Other aminopeptidase inhibitors such as amastatin A, arphamenine B and WM15 antibody showed no growth inhibitory effects. To confirm the growth inhibitory effects of bestatin, we quantitatively examined DNA fragmentation in five bestatin-sensitive cell lines. Bestatin dose-dependently induced DNA fragmentation in those cell lines. In case of U937, bestatin induced DNA fragmentation quantitatively and DNA ladder and enhanced caspase-3 activity. Furthermore, the growth inhibition by bestatin was reduced by the caspase inhibitor Z-Asp-CH2-DCB. These results suggested that bestatin exhibits direct antileukemic effects against human leukemic cell lines through the induction of apoptosis.

Sperm binding to the vitelline envelope in dejellied Xenopus laevis eggs was effectively inhibited by inhibitors for trypsin (soybean trypsin inhibitor and p-toluenesulfonyl-L-lysine chloroethyl ketone) and aminopeptidase B (o-phenanthroline, bestatin, and arphamenine B). Likewise, synthetic 4-methylcoumaryl-7-amide (MCA) substrates (t-butoxycarbonyl-GlyArgArg-MCA, benzyloxycarbonyl-ArgArg-MCA, and Arg-MCA) inhibited binding. Consistently, when jellied eggs were inseminated in the presence of these substrates or inhibitors for proteases, fertilization was effectively blocked. The medium in which live sperm or the sperm membrane fraction were suspended exhibited hydrolyzing activities against the synthetic substrates mentioned above, and these activities were effectively inhibited by the protease inhibitors. Ultracentrifugal fractionation of the sperm suspension following induction of the acrosome reaction by a calcium ionophore, A23187, indicated that a considerable amount of the total tryptic and aminopeptidase B activity was released into the medium. On this occasion, part of the tryptic and aminopeptidase B activity was definitely estimated to be discharged in association with a vesiculated membrane, supporting the notion that the proteases involved in binding to the vitelline envelope are present on the sperm plasma membrane.