Stimulatory release of hepatic lipase activity from rat hepatocytes by ruthenium red

Ruthenium Red (RuR; ruthenium oxychloride ammoniated) stimulated the release of hepatic lipase (HTGL) activity from primary cultured rat hepatocytes into medium in a time- and dose-dependent manner. The RuR-stimulated release of HTGL activity was suppressed by tyrosine kinase (TK) inhibitors (ST-638 and biochanin A). The activity of partially purified TK preparation from hepatocytes was found to be increased by incubation with RuR. In addition, treatment of the hepatocytes with H-89, a potent inhibitor of cAMP-dependent protein kinase (PKA), decreased the stimulatory release of HTGL activity by RuR. Moreover, cAMP content in RuR-incubated hepatocytes was rapidly increased, and activation of PKA was observed. The RuR-stimulated release of HTGL activity is also inhibited by uncouplers and glycosylation inhibitors. In addition, incorporation of [3H]leucine into protein was increased in the present of RuR. Under marked inhibition of protein synthesis by cycloheximide, RuR still showed a full effect on the release of HTGL activity. These results suggest that RuR stimulates the release of HTGL activity through mechanisms of action involving TK- and PKA-activating pathways, which require a metabolic energy-sensitive process rather than elevation of enzyme molecule synthesis.

Inhibition of human immunodeficiency virus type 1 replication by a bioavailable serine/threonine kinase inhibitor, fasudil hydrochloride

Replication of human immunodeficiency virus type 1 (HIV-1) is regulated by a host transcription factor, nuclear factor kappaB (NF-kappaB). NF-kappaB belongs to a group of inducible transcription factors and its activity is regulated by multiple cellular signal transduction pathways, including kinases. These kinases are known to be involved in signal-induced NF-kappaB activation and in the induction of HIV-1 gene expression from latently infected cells. In this study we have examined the effect of a newly developed serine/threonine kinase inhibitor, fasudil hydrochloride (FH), on the replication of HIV-1. Although FH was initially developed as a compound that inhibited a myosin light chain kinase (MLCK) and had been approved for clinical use in the treatment of vasospasm after subarachnoid hemorrhage, this study shows its efficacy in blocking HIV-1 replication in latently infected patients. When FH was added to monocytic cell lines latently infected with HIV-1, U1 and OM10.1, the induction of HIV-1 replication by TNF-alpha was blocked at noncytotoxic doses. The IC50 values of HIV-1 induction by FH were 9.3 and 24 microM for U1 and OM10.1, respectively. Because FH could block TNF-alpha-induced, NF-kappaB-dependent gene expression, as examined by the transient luciferase expression assay, the effect of FH was considered to be due to the blocking of the signal transduction pathway of NF-kappaB activation. Although the in vivo effect of FH in blocking HIV-1 induction is not yet known, these findings indicate the feasibility of clinical use of FH and its derivatives in decreasing viral load to prevent clinical development of acquired immunodeficiency syndrome (AIDS) among HIV-1-infected individuals.

Release of lipoprotein lipase from Ehrlich ascites tumor produced by an association with a rapid increase in cyclic AMP content

Although it is considered that the lipoprotein metabolism in tumor plays an important role in growth and multiplication, it is not clear as to the details. Lipoprotein lipase (LPL) is a key enzyme responsible for the hydrolysis of lipoprotein-triacylglyceride. In this study, we examined the regulatory step of LPL in lipoprotein metabolism of Ehrlich ascites tumor and especially the enzyme-release from the tumor cells. When LPL was stimulated to release from the tumor cells by the low molecular weight dextran sulfate (3.2 kDa), cyclic AMP content in the tumor cells was observed to increase rapidly in a time-dependent manner up to 30 s; its maximal effect was 1.5-fold higher than the basal level of cyclic AMP. The increase in cyclic AMP content was more enhanced in the presence of isobutylmethylxanthine and was never suppressed by propranolol. Moreover, cyclic AMP-dependent protein kinase (PKA) activity in the tumor cells was also recognized to elevate in a time- and dose-dependent manner. In addition, the release of LPL activity from the tumor cells was inhibited by 2',5'-dideoxyadenosine. These results suggest that LPL in the tumor cells is released through a pathway involving an activation of PKA associated with the rapid increase in cyclic AMP content.

Stimulation of nitric oxide-cyclic GMP pathway by L-arginine increases the release of hepatic lipase from cultured rat hepatocytes

The nitric oxide-cyclic GMP pathway is still undefined regarding regulation of the release of hepatic lipase (HTGL). It was found that L-arginine (Arg) stimulated the release of HTGL activity from rat hepatocytes in a time- and dose-dependent manner. L-Arg-stimulated release of HTGL activity was inhibited by N-monomethyl-L-Arg, which is a nitric oxide synthase inhibitor. L-Arg markedly increased the cyclic GMP content of hepatocytes in the presence of a cyclic GMP phosphodiesterase inhibitor. Zaprinast. The release of the enzyme activity was also suppressed by methylene blue (a guanyl cyclase inhibitor) and KT5823 (a cyclic GMP-dependent protein kinase inhibitor). These results suggest that the stimulation of nitric oxide synthesis by L-Arg increases the release of HTGL activity due to processes associated with the elevation of cyclic GMP level, probably through an activation of protein kinase.

Sodium orthovanadate increases phospholipase A2 activity in isolated rat fat pads: a role of phospholipase A2 in the vanadate-stimulated release of lipoprotein lipase activity

Phospholipase (PL) A2 activity prepared from isolated rat fat pads incubated with sodium orthovanadate (vanadate) was increased in a time- and dose-dependent manner. The increasing effect of vanadate was reduced in the presence of tyrosine kinase inhibitors. Under the inhibition of protein synthesis by cycloheximide, vanadate still showed a full effect on the increase in PL A2 activity. Various PL A2 inhibitors, such as manoalide, quinacrine and p-bromophenacyl bromide, suppressed the stimulatory release of lipoprotein lipase (LPL) activity from the fat pads by vanadate. Moreover, the vanadate-stimulated release of LPL activity was decreased by the cyclooxygenase and thromboxane synthetase inhibitors, and a thromboxane A2 receptor antagonist, but was never suppressed by a lipooxygenase inhibitor. The stimulatory release of LPL activity by vanadate was also decreased in the presence of tyrosine kinase inhibitors. These results suggest that vanadate increases PL A2 activity, and the increase in PL A2 activity is partly involved in the vanadate-stimulated release of LPL activity with an association to the membrane tyrosine kinase.

Stimulatory release of lipoprotein lipase activity with activation of protein tyrosine kinase produced by low molecular weight dextran sulfate in Ehrlich ascites tumor cells

Lipoprotein lipase (LPL), which is responsible for the hydrolysis of lipoprotein triacylglyceride, has been examined in Ehrlich ascites tumor cells. Low molecular weight dextran sulfate (DXS, M.W. 3.2 kDa) stimulates the release of the enzyme activity from the tumor cells into the incubation medium in a time-dependent manner. The stimulatory effect of DXS was markedly decreased by incubation with protein tyrosine kinase (TK) inhibitors, such as ST 638, biochanin A and amiloride. The activity of the partially purified TK preparation from the tumor cells was found to be increased following incubation with DXS in a manner which was both time- and dose-dependent. These results suggest that the stimulatory release of LPL activity by DXS is associated with the activation of TK in the tumor cells.

Stimulatory release of hepatic lipase activity from cultured rat hepatocytes by sodium orthovanadate: rapid increase in cyclic adenosine monophosphate content

The release of hepatic triacylglyceride lipase [EC 3.1.1.3] has been examined in isolated hepatocytes in primary culture. The stimulatory release of activity from the hepatocytes into the medium by sodium orthovanadate (vanadate) was observed in a time- and dose-dependent manner. However, insulin failed to have this stimulatory action. Moreover, vanadate rapidly increased the cyclic adenosine monophosphate (cyclic AMP) content in hepatocytes in a time- and dose-dependent manner. The treatment of hepatocytes with H-89, which is a potent cyclic AMP-dependent protein kinase inhibitor, decreased the stimulatory release of hepatic lipase activity by vanadate. The vanadate-stimulated release of the enzyme activity was suppressed by uncouplers. In addition, the incorporation of [3H]leucine into protein was increased in the presence of vanadate. Under the marked inhibition of protein synthesis by cycloheximide, vanadate still showed a full effect on the release of the enzyme activity. These results suggest that the vanadate-stimulated release of hepatic lipase activity from the cultured hepatocytes is associated with a rapid increase in intracellular cyclic AMP content, probably due to an activation of cyclic AMP-dependent protein kinase which requires a metabolic energy process rather than an elevation in enzyme molecule synthesis.

Stimulatory release of hepatic lipase activity from liver by epidermal growth factor

We have found that release of hepatic lipase activity is stimulated from liver slices by epidermal growth factor (EGF) into the medium in a time-dependent manner. This novel effect of EGF was markedly decreased by various tyrosine kinase inhibitors, such as alpha-cyano-3-ethoxy-4-hydroxy-5-phenyl-thiomethyl cinnamamide, amiloride and biochanin A. The stimulation by EGF was also suppressed, however, by dibutyryl cyclic adenosine monophosphate, and 3-isobutyl-1-methylxanthine, a cyclic nucleotide dependent phosphodiesterase inhibitor. These findings show that the stimulatory release of the enzyme activity by EGF is associated with the activation of tyrosine kinase activity and with the intracellular cyclic adenosine monophosphate level.

Vanadate-stimulated release of hepatic lipase activity from liver

Vanadate stimulated the release of rat hepatic lipase activity from liver slices into an incubation medium in a time- and dose-dependent manner. Insulin, however, failed to have this stimulatory action, and the release by heparin was recognized, but was not additive to that by vanadate. Amiloride, an inhibitor of tyrosine kinase in some receptors and of the Na+/H+ exchange system suppressed the vanadate-stimulated release. Biochanin A, a different type of tyrosine kinase inhibitor than amiloride, also suppressed the effect of vanadate. The stimulation by vanadate was clearly preserved in Na(+)-, K(+)-, or Ca(2+)-free medium, suggesting that neither the Na+/H+ exchange system, Na+, K(+)-adenosine triphosphatase, nor Ca(2+)-influx into cells is involved in the action of this substance. These results suggest that vanadate-stimulated release of the enzyme activity is associated with the activation of the tyrosine kinase activity.