Platelet activation in Alzheimer disease

BACKGROUND

In light of recent reports of diminished platelet serotonin concentration and increased plasma serotonin levels in patients with Alzheimer disease (AD), we hypothesized that a state of heightened platelet activation might be present in AD.

OBJECTIVE

To compare baseline activation of unstimulated platelets in patients with AD with that in control subjects.

PATIENTS AND METHODS

Flow cytometry was used to measure platelet activation in 91 patients with probable AD and 40 age-matched control subjects. Groups were compared for percentage of circulating platelet aggregates, expression of CD62p, formation of leukocyte-platelet complexes, and presence of circulating platelet microparticles, controlling for effects of demographic, clinical, physiological, and logistical factors.

RESULTS

Multiple analysis of covariance on ranked data revealed a 39.5% increase in percentage of platelet aggregates (P=.0001), a 59.3% increase in expression of CD62p (P=.001), and a 53.3% increase in leukocyte-platelet complexes (P=.0001) in the group with AD but no differences in the number of platelet microparticles, overall platelet count, plasma fibrinogen level, or plasma platelet factor 3. Activation was weakly correlated with sex, but was independent of age, severity of disease, duration of disease, depression, agitation, and family history of dementia.

CONCLUSIONS

Platelets of patients with AD exhibit greater unstimulated activation than those of controls. Potential causes of such activation include possible stimulation of platelets by damaged cerebral endothelial cells or platelet activation induced by membrane abnormalities previously reported to be present in platelets of patients with AD. In light of recent evidence that platelets are the principal source of both amyloid precursor protein and beta-amyloid peptide in human blood, it is possible that AD platelet activation may reflect or even contribute to the pathogenesis of the disease.

Platelet microparticles and calcium homeostasis in acute coronary ischemias

Elevation of free cytoplasmic calcium is the common pathway of platelet activation, leading to shape change, shedding of platelet microparticles (PMP), aggregation, and secretion of internal granules, including expression of CD62p on the surface. Platelet activation is well documented in unstable angina (UA) and acute myocardial infarction (MI). We investigated the following markers of platelet activation in 55 patients undergoing coronary angiography for suspected CAD: free cytoplasmic calcium, [Ca2+]cyt, PMP, CD62p expression, and platelet/leukocyte (P/L) interaction. [Ca2+]cyt was measured by Fluo-3 and the other measurements were by flow cytometry. Patients were classified into three groups: unstable angina (UA, n = 11), recent myocardial infarction (MI, n = 11), and patient controls (CTL, n = 33). Blood was drawn before infusion of heparin through femoral lines at the time of catheterizaton for assays. (

RESULTS

(1) PMP values were significantly higher in both UA and MI than in CTL, P < 0.05. There was no difference between UA and MI. (2) P/L interaction was significantly elevated only in UA, P < 0.05. (3) CD62p expression on free platelets did not differ significantly between any of the three groups. (4) The resting [Ca2+]cyt, thrombin-induced Ca2+ influx, and release of Ca2+ from internal stores were all significantly higher in platelets from the combined patient group (UA + MI) than in the patient control group, P < 0.001

CONCLUSIONS

Results on calcium hemostasis and PMP were significantly different in patients with acute coronary syndromes than those with stable angina or no coronary ischemia; this may reflect underlying pathophysiology of acute coronary ischemia. P/L interaction was higher only in the UA group, suggesting a role of leukocytes in UA.

Danazol for paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal stem-cell disorder in which blood cells lack complement inhibiting membrane proteins, and become susceptible to complement-mediated injury, leading to chronic intravascular hemolysis and pancytopenia. Glucocorticoids have been a mainstay of therapy. For patients refractory to glucocorticoids and requiring blood transfusions, an alternative therapy is needed. We studied danazol therapy in 5 patients refractory to other treatments. Four of the 5 benefited, showing rise in hematocrit and eventual cessation of transfusion requirements. Remissions lasted > or =2 years in 3 and 10 years in 1 patient. Danazol was well-tolerated without serious side effects. Danazol appears to be a good alternative treatment in PNH.

Activated platelet aggregates in thrombotic thromboctyopenic purpura: decrease with plasma infusions and normalization in remission

Circulating activated platelet aggregates (aPA) were assayed by flow cytometry employing mAb alpha-CD62p in eight patients with thrombotic thrombocytopenic purpura (TTP). Elevation of aPA was observed in all patients in active stages of TTP; aPA normalized in remission. Plasma infusions with plasmapheresis decreased aPA in responding patients. The rise and fall of aPA preceded relapses and improvements, respectively. These changes were seen prior to the traditional indicators, LDH, haematocrit, and platelet count. Incubation of plasma from TTP patients with normal whole blood induced formation of aPA; this effect was significantly greater than that of plasmas from ITP patient controls (P < 0.01), suggesting the presence of an aPA-promoting factor in TTP plasma. Parallel experiments using a platelet aggregometer failed to detect effect of TTP plasma on normal blood. In summary, aPA appear to be a marker of disease activity, rising with relapse, falling with plasma therapy, and normalizing in remission. The flow cytometric assay of aPA is more sensitive than aggregometry in detecting the putative aPA-promoting factor in TTP.

Danazol relieves refractory pruritus associated with myeloproliferative disorders and other diseases

Severe pruritus is frequently associated with myeloproliferative and other systemic illnesses, and often fails to respond to conventional measures. We used danazol (Danocrine), a synthetic attenuated androgen, in the treatment of severe pruritus refractory to conventional therapy. Eight patients had myeloproliferative disorders (MPD), seven had autoimmune disorders, and seven had skin diseases. Danazol at 400-800 mg/day was administered, and previous medications were tapered off. When itching was controlled with danazol alone, the dosage was reduced or discontinued, and resumed if itching recurred. Clinical responses were graded, and side effects were monitored. Overall, in 12 of 22 patients refractory to other measures, itching was controlled with danazol alone. In 10 patients itching returned when danazol was discontinued or dosage was continued for up to 5 years in responders. No serious side effects were observed. Our experience indicates that danazol is a good alternative for patients with severe pruritus associated with myeloproliferative and other systemic disorders.