Blood coagulation factors V and VIII: Molecular Mechanisms of Procofactor Activation

A hallmark of hemostasis is that cells and proteins involved in the formation of a blood clot remain in a quiescent state and are only activated following an appropriate stimulus. The homologous proteins factors V and VIII cannot participate to any significant degree in their macromolecular enzyme complexes and are thus considered procofactors. Activity is generated following limited proteolysis, indicating that the conversion of the procofactors to factor Va and factor VIIIa must result in structural changes that impart cofactor function. The proteolytic events that lead to the activation of these proteins have been extensively characterized over the past three decades. However, a fundamental understanding of the mechanism(s) by which these proteins are kept as inactive procofactors and how specific bond cleavage facilitates the conversion to the active cofactor state is only starting to become known. These molecular processes undoubtedly play critical regulatory roles, evolved to maintain normal hemostasis since factor Va and factor VIIIa have a tremendous influence on thrombin generation. This review will detail our current understanding of the molecular process of procofactor activation and highlight structural features that play a major role in factor V and factor VIII activation.

Acyl-coenzyme A:cholesterol acyltransferase inhibitor, avasimibe, stimulates bile acid synthesis and cholesterol 7alpha-hydroxylase in cultured rat hepatocytes and in vivo in the rat

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitors are currently in clinical development as potential lipid-lowering and antiatherosclerotic agents. We investigated the effect of avasimibe (Cl- 1011), a novel ACAT inhibitor, on bile acid synthesis and cholesterol 7alpha-hydroxylase in cultured rat hepatocytes and rats fed different diets. Avasimibe dose-dependently decreased ACAT activity in rat hepatocytes in the presence and absence of beta-migrating very low-density lipoproteins (betaVLDL) (by 93% and 75% at 10 micromol/L) and reduced intracellular storage of cholesteryl esters. Avasimibe (3 micromol/L) increased bile acid synthesis (2.9-fold) after preincubation with betaVLDL and cholesterol 7alpha-hydroxylase activity (1.7- and 2.6-fold, with or without betaVLDL), the latter paralleled by a similar induction of its messenger RNA (mRNA). Hepatocytes treated with avasimibe showed a shift from storage and secretion of cholesteryl esters to conversion of cholesterol into bile acids. In rats fed diets containing different amounts of cholesterol and cholate, avasimibe reduced plasma cholesterol (by 52% to 71%) and triglyceride levels (by 28% to 62%). Avasimibe did not further increase cholesterol 7alpha-hydroxylase activity and mRNA in cholesterol-fed rats, but prevented down-regulation by cholate. Avasimibe did not affect sterol 27-hydroxylase and oxysterol 7alpha-hydroxylase, 2 enzymes in the alternative pathway in bile acid synthesis. No increase in the ratio of biliary excreted cholesterol to bile acids was found, indicating that ACAT inhibition does not result in a more lithogenic bile. Avasimibe increases bile acid synthesis in cultured hepatocytes by enhancing the supply of free cholesterol both as substrate and inducer of cholesterol 7alpha-hydroxylase. These effects may partially explain the potent cholesterol-lowering effects of avasimibe in the rat.

Diagnosis and management of intrapartum fetal distress

Fetal distress is a frequent reason for obstetric intervention during labour. The final diagnosis generally is based upon the information in the cardiotocographic tracings, whether or not combined with the information from fetal scalp blood sampling. Reading, classification and interpretation of fetal heart rate (FHR) recordings is subject to considerable interobserver variation, even among experienced obstetricians. Far too often, individual decelerations in the heart rate are classified as early or late, merely on the basis of the relationship between the decelerations and the accompanying contraction. Hon's original flow sheet for classification of decelerations dictates assessment of the full tracing with, as a primary step: are decelerations uniform or not? Non-uniform decelerations should automatically be classified as variable. Comparison between the onset of the deceleration and the uterine contraction curve is the second step. Variable decelerations are the predominant type in the majority of intrapartum recordings. Features in the FHR rhythm to be assessed in case of variable decelerations include assessment of the baseline level, presence or absence of accelerations, variability in the baseline pattern and during the decelerative part of the tracing, initial and secondary acceleration, overshoot following the deceleration whether or not with smoothing, recovery from the deceleration, continuation of the baseline level and the time intervals between contractions or recurrent efforts of pushing activity. The paper further addresses pathophysiologic mechanisms of fetal distress, maternal and fetal risk factors and various alternatives in the management of intrapartum distress.