A Novel Polymorphism, 70Leu/Phe, Disrupts a Consensus Leu Residue within the Leucine-rich Repeat Sequence of Platelet Glycoprotein Ibα

Platelet glycoprotein (GP) Ib/IX/V complex mediates high-shear dependent platelet activation through an interaction with the von Willebrand factor (vWF). All four subunits of the complex have a structural motif, the leucine-rich repeat (LRR) sequence, with leucines in conserved positions. Here we report a new polymorphism, Leu/Phe at residue 70 of GPIbα, which disrupts the consensus sequence of the LRR in the vWF binding domain. Genotype frequencies among 142 healthy Japanese subjects were 92.3%, 7.7%, and 0.0%, for the 70Leu/Leu, 70Leu/Phe, and 70Phe/Phe genotypes, respectively.

Ristocetin-induced or shear-induced platelet aggregation was not significantly different between the 70Leu/Leu and 70Leu/Phe genotypes. In in vitro studies, a recombinant GPIbα fragment with 70Phe (L70F) as compared to that with 70Leu (WT) had low reactivity to anti-GPIbα monoclonal antibodies, GUR20-5 and Hip1, both of which recognize conformation-specific epitopes within the 45-kDa domain. Ristocetininduced 125I-vWF binding to L70F, however, did not differ from that to WT.

Antiplatelet Therapy Using Cilostazol, a Specific PDE3 Inhibitor

Cilostazol, 6-[ 4-( l-cyclohexy l-IH-tetrazol-5yl ) butoxy ]-3, 4-dihydro-2 (1H)-quinolinone, is an antiplatelet/ antithrombotic agent that has been used since 1988 in several countries, including Japan, for treatment of chronic peripheral arterial occlusion. Cilostazol was also approved by the United States Food and Drug Administration (FDA) in 1999 for the treatment of intermittent claudication. Cilostazol not only inhibits platelet activation but also increases vasodilation.1,2 In addition, it has been also shown to inhibit vascular smooth muscle cell proliferation.3 These properties of cilostazol may also improve peripheral blood flow. The mechanism of these effects is mediated through elevated cyclic adenosine monophosphate (AMP), brought about by inhibition of cyclic nucleotide phosphodiesterase (PDE3) activity.4 In this chapter, the pharmacological properties, as well as the clinical efficacy of cilostazol, are briefly discussed.

Studies on Reference Intervals for Platelet Counts in Three Cities in China and one in Japan

Hematological parameters including platelet counts, etc. were determined in 1,140 healthy subjects living in four cities: Suzhou (Jiangsu Province), Chengdu (Sichuan Province) and Harbin (Heilongjang Province) in China, and Kobe in Japan. Then, the reference intervals for platelet counts were calculated and compared. The reference interval for platelet count of subjects aged between 18 and 60 years was 60-259 × 109/L in Suzhou and 52–202 × 109/L in Chengdu, and subjects with platelet counts of 100 × 109/L or less accounted for about 30% of the subjects examined in these cities. The reference intervals in Harbin and Kobe were within the range of 150–350 × 109/L, and no subject having a platelets count of 100 × 109/L or less was detected. Mean platelet volume (MPV) determined concurrently was negatively correlated with platelet count, and the reference intervals for MPV in Chengdu and Suzhou were higher than those in Harbin and Kobe.

Thrombopoietin-Induced Signal Transduction and Potentiation of Platelet Activation

The presence of thrombopoietin, a humoral regulator of megakaryopoiesis and thrombopoiesis, had been suggested for years,1 however, some investigators were skeptical about the existence of such a factor. Modern studies of thrombopoietin begin with the cloning of c-mpl (the cellular counterpart of the v-mpl oncogene) and its cognate ligand genes. Following the cloning of the c-mpl proto-oncogene,2 Methia et al3 found that, in the presence of oligonucleotides antisense to the gene, CD34+ cells developed into megakaryocytic precursors less efficiently. As the development into other lineage was nearly intact, it was reasonably argued that the c-mpl protein may be the receptor for a thrombopoietin-like factor.3 This study inspired numerous investigations, which culminated in the cloning of the thrombopoietin gene in 1994.1, 4-8

A Heparin-coated Circuit Maintains Platelet Aggregability in Response to Shear Stress in an In Vitro Model of Cardiopulmonary Bypass

Alterations in platelet aggregability may play a role in the pathogenesis of qualitative platelet defects associated with cardiopulmonary bypass (CPB). We circulated fresh heparinized whole blood through tubing sets coated with heparin (C group, n = 10) and through non-coated sets (N group, n = 10) as a simulated CPB circuit. Shear stress (108 dyne/cm2)-induced platelet aggregation (hSIPA), plasma von Willebrand factor (vWF) activity and platelet glycoprotein (GP) Ib expression were measured, before, during, and after this in vitro set up of circulation. In the two groups, the extent of hSIPA significantly decreased during circulation and was partially restored after circulation. Decreases in the extent of hSIPA were significantly less with use of heparin-coated circuits. There was an equivalent reduction in plasma vWF activity, in the two groups. Expression of platelet surface GP Ib decreased significantly during circulation and recovered after circulation. Reduction of surface GP Ib expression during circulation was significantly less in the C group than that in the N group. Decrease in surface GP Ib expression correlated (r = 0.88 in either group) with the magnitude of hSIPA, in the two groups. The progressive removal of surface GP Ib was mainly attributed to redistribution of GP Ib from the membrane skeleton into the cytoskeleton. Our observations suggest that use of heparin-coated circuits partly blocks the reduction of hSIPA, as a result of a lesser degree of redistribution of GP Ib.

Effect of Cilostazol on Soluble Adhesion Molecules and Platelet-derived Microparticles in Patients with Diabetes

We evaluated the plasma concentrations of soluble adhesion molecules and platelet-derived microparticles (PMP) in patients with non-insulin dependent diabetes mellitus (NIDDM) and studied the effect of cilostazol on PMP generation. There were differences in the levels of soluble adhesion molecules between NIDDM patients (N = 43) and the control subjects (N = 30) (soluble thrombomodulin: 11.5 ± 5.3 vs. 7.0 ± 1.2 TU/ml, p<0.0001; soluble vascular cell adhesion molecule-1: 708 ± 203 vs. 492 ± 113 ng/dl, p<0.0001; soluble intercellular cell adhesion molecules-1: 274 ± 65 vs. 206 ± 48 ng/dl, p<0.0001; soluble P-selectin: 194 ± 85 vs. 125 ± 43 ng/dl, p<0.0001). There were also differences in the levels of PMP and platelet activation markers between NIDDM patients and the controls (PMP: 943 ± 504 vs. 488 ± 219/10 4 plt, p<0.0001; platelet CD62P: 9.2 ± 4.6 vs. 4.4 ± 4.3%, p<0.001; platelet CD63: 10.2 ± 4.5 vs. 4.5 ± 3.3%, p<0.0001; platelet annexin V: 9.1 ± 3.9 vs. 5.3 ± 3.8%, p<0.001). To study the release of PMP into plasma, a modified cone-and-plate viscometer was used. Increased release of PMP from platelets was observed in diabetic plasma compared to normal plasma under high shear stress conditions (2,672 ± 645 vs. 1,498 ± 386/104 plt, p<0.05). Therefore, one cause of PMP elevation in NIDDM may be high shear stress. The levels of PMP, activated platelets, and soluble adhesion molecules all decreased significantly after treatment with cilostazol. These results suggest that cilostazol may be useful for the inhibition of both PMP-dependent and -independent vascular damage in NIDDM.

A large deletion of the PROS1 gene in a deep vein thrombosis patient with protein S deficiency

Inherited deficiency of protein S encoded by the PROS1 gene constitutes an important risk factor for deep vein thrombosis (DVT). Nevertheless, although more than 200 deleterious genetic variations in PROS1 have been identified, causative point mutations of PROS1 gene are not detected in approximately half of protein S-deficient families. The present study investigated whether there may exist a large deletion in PROS1 that constitutes a genetic risk factor for Japanese DVT patients. A multiplex ligation-dependent probe amplification analysis was employed to identify the deletions in PROS1 in 163 Japanese patients with DVT. A large gene deletion was identified in one patient who showed 16% protein S activity and did not carry point mutations in PROS1 by DNA sequencing and it was validated by the quantitative PCR method. The deletion spanned at least the whole PROS1 gene (107 kb) and at most from the centromere located downstream of PROS1, to before the D3S3619 marker, the first heterozygous marker in the upstream of PROS1 in chromosome 3. In conclusion, a large deletion in PROS1 was shown to partly account for DVT with protein S deficiency. Screening for large deletions in PROS1 might be warranted in PROS1 causative point mutation-negative DVT patients with protein S deficiency.