Cyclic Adenosine Monophosphate Protein Kinase Research Articles

Adenosine A2 receptor stimulation protects the predamaged liver from cold preservation through activation of cyclic adenosine monophosphate-protein kinase a pathway

The shortage of organ donors has led to reconsideration for the use of non-heart-beating donors (NHBDs). However, graft injury caused by warm ischemia in livers from NHBDs strongly affects posttransplantation outcome. The aim of the present study is to investigate the role of adenosine A2 receptor with regard to hepatic viability after cold preservation of NHBD livers. Cardiac arrest was induced in Wistar rats by phrenotomy of the anesthetized nonheparinized animal. After 60 minutes, the livers were excised and flushed with 60 mL of histidine-tryptophan-ketoglutarate (HTK) and stored submerged in HTK at 4 degrees C for 24 hours. Reperfusion was performed in vitro after all livers were incubated at 22 degrees C in saline solution to account for the period of slow rewarming during surgical implantation in vivo. Addition of the selective A2-receptor agonist (CGS 21680; 30microg/100 mL) to the preservation solution resulted in a significant reduction to one quarter of the parenchymal enzyme release of alanine aminotransferase or lactate dehydrogenase on reperfusion and promoted a 2-fold increase in hepatic bile production. This salutory effect was accompanied by a significant increase (40%) in the activity ratio of protein kinase A (PKA) in the liver tissue and could be abrogated in large part by the PKA inhibitor, Rp-cAMPs. Stimulation of the adenosine A2 receptor during harvest and storage of the graft improves maintenance of tissue integrity in liver grafts. A major part of this effect, which may represent a promising approach for the use of NHBD grafts, seems to be mediated through activation of PKA.

Histamine Induces Melanogenesis and Morphologic Changes by Protein Kinase A Activation via H2 Receptors in Human Normal Melanocytes

Hyperpigmentation frequently accompanies chronic or acute inflammation. A number of inflammatory mediators have been shown to stimulate melanin synthesis in human melanocytes. Although histamine is ubiquitous as an inflammatory factor, its involvement in pigmentation remains obscure. In this work, we examined the effects of histamine on cultured human melanocytes. Treatment of human melanocytes with 0.1-10 microM histamine evoked morphologic changes and increases in tyrosinase activity. The concomitant increases in melanin content of the histamine-treated melanocytes indicated an elevation of melanin synthesis by tyrosinase activation. These stimulatory effects of histamine were completely inhibited by an H2 antagonist, famotidine, whereas H1 and H3 antagonists had no inhibitory effect whatsoever. In addition, an H2 agonist, dimaprit, induced the same degree of melanogenesis as histamine at concentrations of 0.1-10 microM. We observed an increase in the intracellular cAMP contents of human melanocytes induced by histamine via the H2 receptors. We know that this cAMP accumulation and subsequent protein kinase A activation plays a critical role in histamine-induced melanogenesis, because a specific protein kinase A inhibitor, H-89, completely suppressed these stimulatory effects of histamine, and because dibutylic cAMP, a specific protein kinase A activator, stimulated human melanocytes as potently as histamine. Taken together, we show here that histamine induces melanogenesis of human cultured melanocytes by protein kinase A activation via H2 receptors.

Elevation of intracellular cyclic adenosine monophosphate inhibits the epidermal growth factor signal transduction pathway and cellular growth in pancreatic adenocarcinoma cell lines

The epidermal growth factor (EGF) signal transduction pathway, frequently activated in pancreatic cancer, is an important regulator of cellular growth and transformation. This study examined whether activation of the cyclic adenosine monophosphate protein kinase A pathway may inhibit the EGF signal transduction pathway in pancreatic cancer cell lines. Human pancreatic cancer lines BxPC-3 and AsPC-1 were stimulated with EGF, forskolin, or both. Forskolin is a compound that increases cyclic adenosine monophosphate levels. Assays of cell lines were then obtained for cellular growth (MTT assay), anchorage-independent growth (soft agar), and EGF-induced mitogen-activated protein kinase activation as measured by an in-gel kinase assay. Treatment with forskolin resulted in inhibition of EGF-induced activation of mitogen-activated protein kinase activity (BxPC-3 78% inhibition and AsPC-1 70% inhibition, p < 0.005), diminished cellular proliferation (BxPC-3 92% inhibition and AsPC-1 86% inhibition, p < 0.001), and formation of colonies in soft agar (BxPC-3 98% inhibition and AsPC-1 76% inhibition, p < 0.001). Forskolin did not inhibit EGF receptor autophosphorylation or tyrosine kinase signaling in response to EGF. Forskolin-induced inhibition of mitogen-activated protein kinase is associated with diminished pancreatic cancer cell proliferation in vitro. Use of strategies to increase cyclic adenosine monophosphate levels may have therapeutic application in pancreatic cancer.

Effects of enprofylline, a new xanthine derivate, on human pregnant myometrium

The recently developed xanthine derivate, enprofylline, was studied in an in vitro system with human pregnant myometrium, in particular its effect on spontaneous myometrial contraction, cyclic adenosine monophosphate content, cyclic adenosine monophosphate protein kinase, and cyclic adenosine monophosphate- and cyclic guanosine monophosphate-dependent phosphodiesterase activity. Enprofylline was shown to be a rather potent smooth muscle relaxant [inhibitory concentration that decreases response by 50% (IC50) = 3 × 10−5 mol/L] and an almost equally potent cyclic adenosine monophosphate-dependent phosphodiesterase inhibitor (IC50 = 10−4 mol/L), whereas it was a less potent cyclic guanosine monophosphate-dependent phosphodiesterase inhibitor. Enzyme kinetic studies revealed that enprofylline is a competitive cyclic adenosine monophosphate phosphodiesterase inhibitor. Enprofylline increased the cyclic adenosine monophosphate content in a dose-dependent way with subsequent increased activity of cyclic adenosine monophosphate-dependent protein kinase. It is suggested that enprofylline relaxes myometrial smooth muscles and that this is at least partly the result of interference with the cyclic adenosine monophosphate system.