Alpha(1)-adrenoceptors (alpha(1)-AR) and vascular smooth muscle cell growth

Long-term α1B-adrenergic receptor activation shortens lifespan, while α1A-adrenergic receptor stimulation prolongs lifespan in association with decreased cancer incidence

The α1-adrenergic receptor (α1AR) subtypes, α1AAR and α1BAR, have differential effects in the heart and central nervous system. Long-term stimulation of the α1AAR subtype prolongs lifespan and provides cardio- and neuro-protective effects. We examined the lifespan of constitutively active mutant (CAM)-α1BAR mice and the incidence of cancer in mice expressing the CAM form of either the α1AAR (CAM-α1AAR mice) or α1BAR. CAM-α1BAR mice have a significantly shortened lifespan when compared with wild-type (WT) animals; however, the effect was sex dependent. Female CAM-α1BAR mice lived significantly shorter lives, while the median lifespan of male CAM-α1BAR mice was not different when compared with that of WT animals. There was no difference in the incidence of cancer in either sex of CAM-α1BAR mice. The incidence of cancer was significantly decreased in CAM-α1AAR mice when compared with that in WT, and no sex-dependent effects were observed. Further study is warranted on cancer incidence after activation of each α1AR subtype and the effect of sex on lifespan following activation of the α1BAR. The implications of a decrease in cancer incidence following long-term α1AAR stimulation could lead to improved treatments for cancer.

Repetitive hypoglycemia increases circulating adrenaline level with resultant worsening of intimal thickening after vascular injury in male Goto-Kakizaki rat carotid artery

Hypoglycemia associated with diabetes management is a potential risk for cardiovascular diseases. However, the effect of hypoglycemic episodes including a surge of sympathetic activity on the progression of neointima formation after vascular injury remains largely unknown. In this study, insulin was injected intraperitoneally into nonobese diabetic Goto-Kakizaki (GK) rats, once every 3 days for 4 weeks after balloon injury of carotid artery to induce hypoglycemia. Then, we evaluated balloon injury-induced neointima formation. Insulin treatment enhanced neointima formation and increased the number of proliferating cell nuclear antigen (PCNA)-positive cells in the carotid artery. Injection of glucose with insulin prevented hypoglycemia and abrogated intimal thickening. Also, bunazosin, an α1 adrenergic receptor antagonist, prevented intimal thickening and accumulation of PCNA-positive cells induced by insulin treatment despite the presence of concomitant hypoglycemia and high adrenaline levels. Incubation of cultured smooth muscle cells with adrenaline resulted in a significant increase in their proliferation and G0/G1 to S phase progression, which was associated with activation of extracellular signal-regulated kinase, enhanced expression of cell cycle regulatory molecules such as cyclin D1, and cyclin E, and phosphorylation of retinoblastoma protein. These adrenaline-induced effects were abrogated by bunazosin. Our data indicated that increased adrenaline induced by repetitive hypoglycemia promotes intimal thickening and smooth muscle cell proliferation after endothelial denudation in GK rats.

Mechanical stress-initiated signal transduction in vascular smooth muscle cells in vitro and in vivo

Increasing evidence has been demonstrated that hypertension-initiated abnormal biomechanical stress is strongly associated with cardio-/cerebrovascular diseases e.g. atherosclerosis, stroke, and heart failure, which is main cause of morbidity and mortality. How the cells in the cardiovascular system sense and transduce the extracellular physical stimuli into intracellular biochemical signals is a crucial issue for understanding the mechanisms of the disease development. Recently, collecting data derived from our and other laboratories showed that many kinds of molecules in the cells such as receptors, ion channels, caveolin, G proteins, cell cytoskeleton, kinases and transcriptional factors could serve as mechanoceptors directly or indirectly in response to mechanical stimulation implying that the activation of mechanoceptors represents a non-specific manner. The sensed signals can be further sorted and/or modulated by processing of the molecules both on the cell surface and by the network of intracellular signaling pathways resulting in a sophisticated and dynamic set of cues that enable cardiovascular cell responses. The present review will summarise the data on mechanotransduction in vascular smooth muscle cells and formulate a new hypothesis, i.e. a non-specific activation of mechanoceptors followed by a variety of signal cascade activation. The hypothesis could provide us some clues for exploring new therapeutic targets for the disturbed mechanical stress-initiated diseases such as hypertension and atherosclerosis.

Alpha1-and beta2-adrenoceptors in the human liver with mass-forming intrahepatic cholangiocarcinoma: density and coupling to adenylate cyclase and phospholipase C

Besides the regulation of hepatic metabolic pathways in which adrenoceptors are mainly involved, their effect on the second messenger cAMP is thought to be related to the growth and differentiation of neoplastic cells. However, few studies have been done on the status of these structures in the human liver affected by cholangiocarcinoma (CC). Thus, in this study, changes in densities of alpha1- and beta2-adrenoceptors (alpha1-and beta2-ARs) were investigated in membranes of human liver with cholangiocarcinoma, and for comparison, in membranes of non-adjacent non-tumour liver using the potent antagonists [3H]-prazosin and [1I]-iodocyanopindolol (ICYP) respectively. In addition, the activity of membrane-bound phospholipase C (PLC) and adenylate cyclase (AC) was also studied. In CC liver, the density of alpha1-and beta2-ARs was significantly reduced, compared with non-tumour liver tissues (alpha1-ARs: 23.38+/-4.69 vs 80.35+/-10.52, P=0.0002 beta2-ARs: 14.27+/-2.93 vs 33.22+/-4.32 fmol/mg protein, P=0.03), whereas the ligand affinities (KD) remained unchanged. The beta2-selective antagonist ICI 118,551 was about 100 times more potent in inhibiting ICYP binding than the beta1-selective antagonist CGP 20712A; thus, more than 98% of the beta-ARs were of the beta2-subtypes. The AC activity upon stimulants acting on beta-AR (isoprenaline), G-protein (GTP, NaF) and AC (forskolin) was decreased in CC liver. Similarly, noradrenaline-stimulated PLC activity was significantly reduced in tumour tissues. In conclusion, in CC liver the alpha1- and beta2-ARs density was down-regulated and the neoplastic invasion blunted AC and PLC activity. These quantitative changes may help to elucidate not fully understood pathogenetic mechanisms of disturbed hepatic metabolic processes, such as hypoglycemia during cancer in human liver.

Technetium-99m labeled 1-(4-fluorobenzyl)-4-(2-mercapto-2-methyl-4-azapentyl)-4-(2-mercapto-2-methylpropylamino)-piperidine and iodine-123 metaiodobenzylguanidine for studying cardiac adrenergic function: a comparison of the uptake characteristics in vascular smooth muscle cells and neonatal cardiac myocytes, and an investigation in rats

In developing technetium-99m-based radioligands for in vivo studies of cardiac adrenergic neurons, we compared the uptake characteristics of the (99m)Tc-labeled 1-(4-fluorobenzyl)-4-(2-mercapto-2-methyl-4-azapentyl)-4-(2-mercapto-2-methylpropylamino)-piperidine ((99m)Tc-FBPBAT) with those of the clinically established meta-[(123)I]iodobenzylguanidine ((123)I-MIBG) in rat vascular smooth muscle cells and neonatal cardiac myocytes. Furthermore, the cardiac and extracardiac uptake of both radiopharmaceuticals was assessed in intact rats and in rats pretreated with various alpha- and beta-adrenoceptor drugs, and adrenergic reuptake blocking agents. The uptake of (99m)Tc-FBPBAT and (123)I-MIBG into vascular smooth muscle cells and neonatal cardiac myocytes was rapid; more than 85% of the radioactivity accumulation into the cells occurring within the first 3 minutes. Radioactivity uptake after a 60-minute incubation at 37 degrees C (pH 7.4) varied from 15% to 65% of the total loaded activity per million cells. In all cases, (99m)Tc-FBPBAT showed the higher uptake, relative to (123)I-MIBG, at any given cell concentration. The cellular uptake of (99m)Tc-FBPBAT was lower at 4 degrees C and 20 degrees C than at 37 degrees C. In contrast, the (123)I-MIBG uptake was only slightly temperature dependent. Inhibition experiments confirmed that the cellular uptake of (123)I-MIBG is mediated by the uptake-I carrier, whereas alpha(1)- and beta(1)-adrenoceptors were predominantly involved in the uptake of (99m)Tc-FBPBAT into the cardiovascular tissues. Biodistribution studies in rats showed that (99m)Tc-FBPBAT accumulated in myocardium after intravenous injection. Radioactivity in rat heart amounted to 2.32% and 1.91% of the injected dose per gram at 15 and 60 minutes postinjection, compared with 3.10% and 2.21% injected dose per gram of tissue (%ID/g) in the experiment with (123)I-MIBG, respectively. Prazosin, urapidil, and metoprolol were as effective as treatment with other adrenergic drugs in lowering cardiac uptake of (99m)Tc-FBPBAT. Uptake reduction was more pronounced in myocardium than in other adrenergic-rich organs, including the lung, spleen, kidney, and adrenals, suggesting that the (99m)Tc-FBPBAT uptake in myocardium specifically reflects a high degree of alpha(1)/beta(1)-receptor binding to cardiac adrenergic neurons. In comparison, reduction of cardiac and pulmonary uptake of (123)I-MIBG was effective after pretreatment of rats with desipramine and reserpine, confirming distinct neuronal binding sites for (99m)Tc-FBPBAT and (123)I-MIBG. (99m)Tc-FBPBAT was excreted via urine and to a lower degree via feces. Urine analysis 6 hours p.i. revealed that more than 40% of the total excreted radioactivity was unmetabolized (99m)Tc-FBPBAT. In conclusion, the uptake of (99m)Tc-FBPBAT in rat myocardium specifically reflects binding to cardiac adrenergic neurons. The (99m)Tc-FBPBAT uptake appears to be predominantly mediated via the alpha(1)/beta(1)-adrenoceptor pathway. These data indicate that (99m)Tc-FBPBAT, like (123)I-MIBG, may be suitable for mapping cardiac adrenergic innervation by SPET, especially for alpha(1)/beta(1)-adrenoceptors as target in numerous heart diseases.

Stimulation of alpha2-adrenergic receptor inhibits cholangiocarcinoma growth through modulation of Raf-1 and B-Raf activities

Growth factor signaling, mediated by the mitogen-activated protein kinase (MAPK) cascade, induces cell mitosis. Adenosine 3',5'-monophosphate (cAMP) may inhibit or stimulate mitosis (depending on the cell type) through the activation of MAPK and Raf proteins. Among Raf proteins, Raf-1 and B-Raf differentially regulate mitosis. Our aims were to evaluate the role and mechanisms of action of the alpha(2)-adrenergic agonist UK14,304 in the regulation of growth of the human cholangiocarcinoma cell line Mz-ChA-1. Immunocytochemistry and immunoblotting for alpha(2A)-, alpha(2B)-, or alpha(2C)-adrenergic receptor subtypes showed positive reaction in Mz-ChA-1 cells. We found that physiological concentrations of UK14,304 increased cAMP levels and inhibited proliferation and MAPK activity in Mz-ChA-1 cells. Mz-ChA-1 cells expressed Raf-1 and B-Raf. Epidermal growth factor (EGF) immediately and transiently stimulated Raf-1 activity, whereas B-Raf activity was increased with prolonged EGF stimulation. EGF-stimulated Raf-1 and B-Raf activities were both inhibited by UK14,304. UK14,304 did not affect Ras activity. In Mz-ChA-1 cells, alpha(2)-adrenoreceptor stimulation causes up-regulation of cAMP, which inhibits EGF-induced MAPK activity through an acute increase of Raf-1 and sustained activation of B-Raf. In conclusion, because alpha(2)-AR inhibition of growth occurred downstream of Ras, adrenergic stimulation or other stimulants of cAMP may overcome the Ras mutations and offer a new therapeutic approach for patients with cholangiocarcinoma.