Erythrocyte morphologic features and serum chemistry studies in ovine pregnancy-induced hypertension treated with thromboxane synthetase inhibitors

Microscopic schistocyte determination according to International Council for Standardization in Hematology recommendations in various diseases

INTRODUCTION

Recently, a consensus report for microscopic schistocyte determination was prepared by International Council for Standardization in Hematology (ICSH). ICSH focused on diagnosis of thrombocytopenic purpura (TTP)/hemolytic uremic syndrome (HUS). We aimed to reanalyze schistocytes according to ICSH recommendations, to study diseases other than TTP/HUS related to the schistocytes, and to compare the percentage of schistocytes among the various diseases.

METHODS

We retrieved all reported cases of peripheral blood (PB) smear in a single institution during 6 years. Schistocytes on 282 PB smears showing previous peripheral schistocytes and hemoglobin ≤10 g/dL were recounted according to ICSH recommendations.

RESULTS

The schistocytes were frequently observed in patients with microangiopathic hemolytic anemia (MAHA), metastatic carcinoma, sepsis, chronic renal failure, preterm infant, and infection. Only two among 34 patients categorized as MAHA were diagnosed as TTP/HUS. Schistocytes were observed with other morphological changes in 169 of 170 cases with schistocyte ≤1% and in 102 of 112 with schistocyte >1%. The median schistocyte percentages of patients with hematologic malignancy, megaloblastic anemia, acute renal failure, and preterm infant were 1.20%, 1.30%, 1.35%, and 1.70%, respectively.

CONCLUSION

Schistocytes were observed above 1% in many diseases other than TTP /HUS. Therefore, it is important to understand that schistocytes could be seen in various diseases, and in these cases, schistocytes were usually detected together with other red blood cell morphologic changes. These data support ICSH recommendation that a schistocyte count should be considered clinically meaningful if schistocytes represent the main morphological abnormality in the PB smear.

Morphologic diagnosis of thrombotic thrombocytopenic purpura

The diagnosis of thrombotic thrombocytopenic purpura (TTP) rests on evidence of microangiopathic hemolytic anemia and thrombocytopenia in the absence of disseminated intravascular coagulation and other known causes of thrombotic microangiopathy. Highly specific diagnostic tools such as serum levels of ADAMTS13 are not routinely available for immediate clinical diagnosis. The presence of schistocytes on a blood smear is the morphologic hallmark of the disease, but no guidelines exist as to the number of schistocytes required to differentiate TTP from other thrombotic microangiopathies. We studied 6 patients with TTP and compared their schistocyte counts with those of 40 normal subjects, 28 patients with chronic renal disease, 5 with preeclampsia, and 5 with normal functioning mechanical heart valves. The mean schistocyte count for the TTP patients was 8.35% versus 0.05% for normal subjects, 0.2% for renal patients, 0.25% for preeclamptic patients, and 0.18% for patients with mechanical valves (P < 0.001). Schistocytes were found on 100% of blood films of TTP patients and ranged from 1.0% to 18.4% of red cells. Schistocytes are found on the smears of 58% of normal individuals and on 80-100% of the other patient groups studied, but always comprise less than 0.5% of the red cell population. An initial schistocyte count of greater than 1% strongly suggests a diagnosis of TTP in the absence of other known causes of thrombotic microangiopathy.

The Na+/K+ co-transport system in erythrocytes from pregnant patients

In erythrocytes, the extrusion of a cellular sodium level load is accomplished by the Ouabain--sensitive Na+/K+ pump and by the furosemide-sensitive Na+/K(+)--cotransport, which operates against the passive sodium permeability. An abnormal low rate of net sodium extrusion by the Na+/K+ cotransport was observed in pre-eclamptic patients. At the molecular level the cotransport abnormality seems to be the consequence of an apparent diminished affinity for intracellular Na+. Normal pregnancy is characterized by a strong increase of Na+/K+ cotransport efflux. No difference could be detected between the passive sodium permeability of erythrocytes from normotensive pregnant patients and from normotensive non-pregnant controls. Pre-eclampsia seems to be associated with a low passive sodium and potassium permeability. The abnormalities of cotransport and red cell deformability in patients with pre-eclampsia might be interpreted as an early sign of impaired microcirculation and increased vascular reactivity.

Thromboxane synthetase inhibition as a new therapy for preeclampsia: animal and human studies minireview

The role of the eicosanoids in the pathophysiology of preeclampsia is reviewed, and the results of animal model and human studies with thromboxane synthetase inhibitors in preeclampsia are described. Potential benefits and limitations of therapy are discussed.

Effects of a 48 hour continuous intravenous infusion of CGS 13080-primagrel, a selective thromboxane synthetase inhibitor, on the perinatal and early postnatal period in the guinea pig

CGS 13080, imidazo[1,5-a]pyridine-5-hexanoic acid, was evaluated for perinatal and postnatal effects in third trimester pregnant guinea pigs and their offspring. The compound was administered via 48 hour continuous intravenous infusion to a group of pregnant guinea pigs (n = 16) at a dose of 3 mg/kg/hr starting on gestational day 52 (via chronically implanted indwelling jugular venous cannulas). A saline control group (n = 12) received equivalent volumes of normal saline 0.5 ml/kg/hr throughout the dosing period. A third group (surgery-sham, n = 16) was subjected to cannulation but not infused. A gross examination of each dam and piglets was conducted at necropsy on day 5 of lactation. The neonatal brains and all gross lesions (maternal and neonatal) were removed and fixed for histopathological examination. Compound-related clinical signs were noted in dams during the dosing phase of gestation. Six guinea pigs developed cephalic lymphatic swelling during the infusion. This observation may be correlated to the reported redistribution of fluid volume to the thorax of guinea pigs given intravenous injections of CGS 13080. There were no compound-induced effects on labor, delivery, or any of the examined reproductive parameters. There were no compound-related clinical signs, or effects on survival, body weight and developmental parameters in the F1 generation. Histopathological examination of the brains and other organs did not reveal any compound-related abnormalities. Based on these results, it was concluded that CGS 13080 did not elicit adverse perinatal and postnatal effects in guinea pigs.

Fetal and maternal response to intravenous infusion of a thromboxane synthetase inhibitor

Pharmacologic inhibition of thromboxane synthetase activity has reversed the clinical manifestations of toxemia in the ovine model. To investigate placental transfer and fetal effects of a selective thromboxane synthetase inhibitor, CGS13080 (Ciba-Geigy, Summit, N.J.) was intravenously infused into eight singleton- or twin-bearing ewes near term. During CGS 13080 infusion (0.1 mg/kg/hr), maternal steady-state CGS 13080 levels of 102 +/- 18 ng/ml were achieved within 30 minutes and maternal serum thromboxane generation decreased significantly (13 +/- 3 to 4 +/- 1 ng/ml). However, fetal serum levels of CGS 13080 were only 4% of peak maternal concentrations and fetal serum thromboxane generation did not change. There was no evidence of change in uterine blood flow, maternal or fetal blood pressure, heart rate, blood gas values, or fetal or maternal metabolites of prostacyclin or prostaglandin E2 during the study. We speculate that CGS 13080 may be efficacious in the treatment of human pregnancy-induced hypertension.

Effects of thromboxane synthetase inhibition on maternal-fetal homeostasis in gravid ewes with ovine pregnancy-induced hypertension

Simultaneous maternal indirect blood pressure measurements, electronic fetal heart rate monitoring, and ultrasonographic biophysical profile testing were used to assess maternal-fetal homeostasis in gravid ewes during gestational days 127 to 134 (term 146), during a 72-hour fast, and during treatment with thromboxane synthetase inhibitors CGS13080 and CGS12970. Seventy-five percent of the ewes (12 of 16) developed clinical signs of ovine pregnancy-induced hypertension, including maternal hypertension and fetal depression. In three untreated hypertensive ewes, pregnancy was terminated by spontaneous premature delivery, and one maternal death occurred after an eclamptic seizure. All nine ewes treated with one of the two thromboxane synthetase inhibitors responded to therapy with decreases in blood pressure and resolution of fetal depression. These nine ewes completed gestation, and were delivered at term. These data indicate that therapy with thromboxane synthetase inhibitors in this animal model of preeclampsia results in profoundly beneficial effects and suggest that further studies of thromboxane synthetase inhibitors are warranted in preeclampsia.