Efficacy and tolerability of a selective alpha(2C)-adrenergic receptor blocker in recovery from cold-induced vasospasm in scleroderma patients: a single-center, double-blind, placebo-controlled, randomized crossover study.

OBJECTIVE: OPC-28326 is a selective alpha-adrenergic antagonist with preferential binding to the alpha(2C)-adrenergic receptor (alpha(2C)-AR) subtype. This study observed the effect of OPC-28326 on skin temperature and digital blood flow following an acute cold challenge in patients with Raynaud's phenomenon secondary to scleroderma. METHODS: The study was designed as a single-center, double-blind, placebo-controlled, randomized, 3-period crossover study of OPC-28326 (oral doses of 10 mg or 40 mg) or placebo. The primary outcome measures were the time to recover 50% and 70% of the fall (induced by cold challenge) in baseline digital skin temperature. RESULTS: Twelve of 13 enrolled patients completed the study. The mean time to achieve 50% and 70% recovery of the change in prechallenge digital skin temperature was shorter after the OPC-28326 40-mg dose than after placebo (50% recovery at 5.8 minutes versus 10.0 minutes [P = 0.02]; 70% recovery at 13.8 minutes versus 19.5 minutes [P = 0.01]). These recovery times tended to be shorter in the 10 mg OPC-28326 group as well, but the difference versus placebo was not significant (50% recovery at 9.0 minutes versus 10.0 minutes [P = 0.65]; 70% recovery at 15.3 minutes versus 19.5 minutes [P = 0.07]). Total digital blood flow tended to be lower prior to the cold challenge and after administration of 40 mg OPC-28326, as compared with that after placebo, but the difference was not significant. Symptoms that were potentially drug-related were reported more frequently with 40 mg OPC-28326 than with 10 mg OPC-28326 or with placebo, but none were serious or sustained. CONCLUSION: OPC-28326 at doses of 10 mg and 40 mg was well tolerated during this study. The shorter time to skin temperature recovery after 40 mg OPC-28326 suggests that selective alpha(2C)-AR blockade improves digital skin perfusion during recovery from cooling in patients with Raynaud's phenomenon secondary to scleroderma.

Cilostazol and dipyridamole synergistically inhibit human platelet aggregation.

It has been previously shown that cilostazol (Pletal), a drug for relief of symptoms of intermittent claudication, potently inhibits cyclic nucleotide phosphodiesterase type 3 (PDE3) and moderately inhibits adenosine uptake. It elevates extracellular adenosine concentration, by inhibiting adenosine uptake, and combines with PDE3 inhibition to augment inhibition of platelet aggregation and vasodilation while attenuating positive chronotropic and inotropic effects on the heart. In the present study, we tested the hypothesis that cilostazol combined with a more potent adenosine uptake inhibitor, dipyridamole, synergistically inhibited platelet aggregation in human blood. In the presence of exogenous adenosine (1 microM), the combination of cilostazol and dipyridamole synergistically increased intra-platelet cAMP. Furthermore, cilostazol inhibited platelet aggregation in a washed platelet assay concentration-dependently with IC50s of 0.17 +/- 0.04 microM (P < 0.05 versus plus adenosine alone of 0.38 +/- 0.05 microM), 0.11 +/- 0.06 microM (P < 0.05), and 0.01 +/- 0.01 microM (P < 0.005) when combined with 1, 3, or 10 microM dipyridamole, respectively (n = 5). In whole blood, cilostazol (0.3 to 3 microM) and dipyridamole (1 or 3 microM) synergistically inhibited collagen- and ADP-induced platelet aggregation in vitro. Furthermore, the synergism was confirmed in an open-label, sequential study in healthy human subjects using ex vivo whole-blood collagen-induced platelet aggregation. Four hours after oral co-administration of cilostazol (100 mg) and dipyridamole (200 mg), platelet aggregation was inhibited by 45 +/- 17%, while no significant inhibition was observed from subjects treated with either drug alone. The combination may provide a potential treatment of arterial thrombotic disorders.

Expression of glycoprotein VI in vascular endothelial cells.

Glycoprotein (GP) VI, a collagen receptor, plays a important role in collagen-mediated platelet aggregation and adhesion. To date, GPVI expression has been found only in platelets and megakaryocytes. In the present studies, we have demonstrated that GPVI was also expressed in cultured human umbilical vein endothelial cells (HUVEC) at both transcript and protein levels. Using a GPVI-specific probe, a approximately 6-kb band was detected in HUVEC as well as in platelets and megakaryoblastic cell lines by Northern blotting. Using polyclonal antibodies raised against platelet GPVI peptides, the same size band (57 kDa) was labeled with convulxin (CVX) after immuo-precipitation in both HUVEC and platelet lysates. In addition, a approximately 70-kDa band was also labeled in HUVEC. Surface expression of GPVI in HUVEC was confirmed by flow cytometry with GPVI-specific IgG or by direct labeling with FITC-conjugated CVX. Since HUVEC lack FcRgamma chain that forms complex with GPVI in platelets for signaling process, the function of GPVI in vascular endothelial cells remains to be determined.

Vasopressin V2-receptor blockade with tolvaptan in patients with chronic heart failure: results from a double-blind, randomized trial.

BACKGROUND: In this study, we evaluated the effects of tolvaptan (OPC-41061), a novel, oral, nonpeptide vasopressin V2-receptor antagonist in patients with chronic heart failure (CHF). METHODS AND RESULTS: This was a double-blind study investigating the effects of three doses of tolvaptan and placebo in patients with CHF. After a run-in period, 254 patients were randomly assigned to placebo (n=63) or tolvaptan [30 mg (n=64), 45 mg (n=64), or 60 mg (n=63)] once daily for 25 days. Patients were not fluid-restricted and were maintained on stable doses of furosemide. At day 1, when compared with baseline, a decrease in body weight of -0.79+/-0.99, -0.96+/-0.93, and -0.84+/-0.02 kg was observed in the 30-, 45-, and 60-mg tolvaptan groups, respectively, and a body weight increase of +0.32+/-0.46 kg in the placebo group (P<0.001 for all treatment groups versus placebo). Although the initial decrease in body weight was maintained during the study, no further reduction was observed beyond the first day. An increase in urine volume was observed with tolvaptan when compared with placebo (3.9+/-0.6, 4.2+/-0.9, 4.6+/-0.4, and 2.3+/-0.2 L/24 hours at day 1 for 30-, 45-, and 60-mg tolvaptan groups, and placebo, respectively; P<0.001). A decrease in edema and a normalization of serum sodium in patients with hyponatremia were observed in the tolvaptan group but not in the placebo group. No significant changes in heart rate, blood pressure, serum potassium, or renal function were observed. CONCLUSIONS: In patients with CHF, tolvaptan was well tolerated; it reduced body weight and edema and normalized serum sodium in the hyponatremic patients.

Expression of glycoprotein VI in vascular endothelial cells.

Glycoprotein (GP) VI, a collagen receptor, plays an important role in collagen-mediated platelet aggregation and adhesion. To date, GPVI expression has been found only in platelets and megakaryocytes. In the present studies, we have demonstrated that GPVI was also expressed in cultured human umbilical vein endothelial cells (HUVEC) at both transcript and protein levels. Using a GPVI-specific probe, a ˜6-kb band was detected in HUVEC as well as in platelets and megakaryoblastic cell lines by Northern blotting. Using polyclonal antibodies raised against platelet GPVI peptides, the same size band (57 kDa) was labeled with convulxin (CVX) after immuno-precipitation in both HUVEC and platelet lysates. In addition, a ˜70-kDa band was also labeled in HUVEC. Surface expression of GPVI in HUVEC was confirmed by flow cytometry with GPVI-specific IgG or by direct labeling with FITC-conjugated CVX. Since HUVEC lack FcRγ chain that forms complex with GPVI in platelets for signaling process, the function of GPVI in vascular endothelial cells remains to be determined.

New mechanism of action for cilostazol: interplay between adenosine and cilostazol in inhibiting platelet activation.

Cilostazol, a potent phosphodiesterase 3 inhibitor and anti-thrombotic agent, was recently shown to inhibit adenosine uptake into cardiac myocytes and vascular cells. In the present studies, cilostazol inhibited [ H]-adenosine uptake in both platelets and erythrocytes with a median inhibitory concentration (IC ) of 7 micro M. Next collagen-induced platelet aggregation was studied and it was found that adenosine (1 micro M ), having no effect by itself, shifted the IC of cilostazol from 2.66 micro M to 0.38 micro M (p < 0.01). This shifting was due to an enhanced accumulation of cAMP in platelets and was significantly larger than that by the combination of adenosine and milrinone, which has no effect on adenosine uptake. Similarly, cilostazol, by blocking adenosine uptake, enhanced the adenosine-mediated cAMP increase in Chinese hamster ovary cells that overexpress human A receptor. Furthermore, the inhibitory effect of cilostazol on platelet aggregation in whole blood was significantly reversed by ZM241385 (100 n ), an A adenosine receptor antagonist, and by adenosine deaminase (2 U/ml). These data suggest that the inhibitory effects of cilostazol on adenosine uptake and phosphodiesterase 3 together elevate intracellular cAMP, resulting in greater inhibition of agonist-induced platelet activation.

Brain-derived neurotrophic factor is stored in human platelets and released by agonist stimulation.

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays critical roles in the survival, growth, and maintenance of brain and peripheral neurons. We report the presence of BDNF protein in human platelets and its release upon agonist stimulation. The BDNF content of washed platelets varied widely, from 3.5 to 67 ng/4 x 10(8) platelets, averaging 25.2 +/- 21.2 ng/4 x 10(8) platelets (mean+/-SD). The BDNF concentration in platelet-poor plasma was low (1.7+/-1.7 ng/ml, n = 11). Thrombin, collagen, the Ca++ ionophore A23187, and shear stress each induced a rapid release of BDNF from platelets. Up to only half of platelet BDNF was secreted upon agonist stimulation, suggesting that platelets may have a non-releasable pool of BDNF, or that the released BDNF binds to a recognition site on the platelet surface and is internalized, as occurs with serotonin. However, the cognate BDNF receptor, TrkB, was not detected in platelets. Nevertheless, the ability of BDNF to bind washed platelets was shown by FACS analysis confocal microscopy and by the binding and apparent internalization of [125I]-BDNF by platelets. A very high affinity site (Kd = 130 x 10(-15) M, approximately 80 sites/platelet) and a moderately high affinity site (Kd = 20 nM, approximately 3750 sites/platelet) were identified. The BDNF content in two megakaryocytic cell lines, DAMI and Meg-01, was only 0.1% of the content measured in platelets. No BDNF mRNA was detected by Northern blotting in these cell lines or in platelets. The pituitary gland was also ruled out as a source for platelet BDNF, since the BDNF content of rat platelets did not decrease 2 weeks after hypophysectomy. Thus, platelet BDNF is not acquired from the megakaryocyte or pituitary gland, but is probably acquired from other sources via the blood circulation. Platelets appear to bind, store and release BDNF upon activation at the site of traumatic injury to facilitate the repair of peripheral nerves or other tissues that contain TrkB.

Comparison of the effects of cilostazol and milrinone on cAMP-PDE activity, intracellular cAMP and calcium in the heart.

We investigated the basis for the difference in the cardiotonic effects of the PDE3 inhibitors cilostazol and milrinone in the rabbit heart. Cilostazol displayed greater selectivity than milrinone for inhibition of cAMP-PDE activity in microsomal vs cytosolic fractions from rabbit heart. This difference was due to the inhibition of significantly less cytosolic cAMP-PDE activity by cilostazol compared to milrinone. A combination of cilostazol (>15 microM) and the PDE4 selective inhibitor, rolipram (5 microM), inhibited levels of cytosolic cAMP-PDE activity similar to those inhibited by milrinone on its own. This suggested that milrinone inhibited PDE4 in addition to PDE3 activity. In isolated rabbit cardiomyocytes, milrinone (>10 microM) caused greater elevations in intracellular cAMP and calcium than cilostazol. In the presence of rolipram, however, the cAMP and calcium elevating effects of cilostazol and milrinone were similar. Therefore, in rabbit heart, partial inhibition of PDE4 by milrinone contributed to greater increases in cardiomyocyte cAMP and calcium levels than cilostazol. PDE4 activity in failing human heart was lower than in rabbit heart and there was no significant difference in the inhibition of human cytosolic cAMP-PDE by cilostazol and milrinone. Our results suggest that in normal rabbit heart inhibition of PDE4 by milrinone may partly contribute to the greater cardiotonic effect of milrinone when compared to cilostazol. However, the lower level of PDE4 activity in failing human heart suggests that factors other than inhibition of PDE4 by milrinone may contribute to differences in cardiotonic action when compared to cilostazol.