Topical Pharmacokinetics of Brinzolamide Suspensions in Rabbits and Variability Analysis for Sample Size and Design Considerations

Identifying critical attributes for complex locally acting ophthalmic formulations and establishing in vitro-in vivo correlations can facilitate selection of appropriate thresholds for formulation changes that reflect lack of impact on in vivo performance. In this study the marketed antiglaucoma product Azopt® (1% brinzolamide suspension) and five other brinzolamide formulations varying in particle size distributions and apparent viscosities were topically administered in rabbits, and their ocular pharmacokinetics was determined in multiple ocular tissues. Statistical evaluation with ANOVA showed no significant differences between the formulations in the peak drug concentration (C_max) in the aqueous humor and iris-ciliary body. As a post-hoc analysis, the within animal and total variability was determined for C_max in the aqueous humor and iris-ciliary body. Based on the observed variability, we investigated the sample size needed for two types of study designs to observe statistically significant differences in C_max. For the sample size calculations, assuming both 25% and 50% true differences in C_max between two formulations, two study designs were compared: paired-eye dosing design (one formulation in one eye and another formulation in the other eye of the same animal at the same time) versus parallel-group design. The number of rabbits needed in the paired-eye dosing design are much lower than in the parallel-group design. For example, when the true difference in aqueous humor C_max is 25%, nine rabbits are required in the paired-eye design versus seventy rabbits (35 per treatment) in the parallel-group design to observe a statistically significant difference with a power of 80%. Therefore, the proposed paired-eye dosing design is a viable option for the design of pharmacokinetic studies comparing ophthalmic products to determine the impact of formulation differences.

Correction: Zvidzayi et al. A Novel Approach to Assess the Potency of Topical Corticosteroids. Pharmaceutics 2021, 13, 1456

In the original publication [...].

Fitting Pharmacodynamic Data to the Emax Model to Assess the Inherent Potency of Topical Corticosteroids

The widespread use of topical corticosteroids (TCs) in dermatotherapy requires a consideration of their potency and benefit/risk ratios. Although there are a variety of topical corticosteroid products (TCPs) available on the market and their potencies are ranked using different classification systems, to our knowledge, no classification system to rank the inherent potencies of TC active pharmaceutical ingredients (APIs) currently exists. Most of the published classification systems for TCPs are based on randomized clinical comparative studies and/or vasoconstrictor assay (VCA) data. The objective was to apply the US FDA's VCA to classify the inherent potencies of several TCs using standardized doses to make appropriate comparisons of the relevant APIs in solutions of the same molar concentrations. Six TC APIs were assessed for their relative potencies using healthy human participants. The E_max model was used to fit skin blanching data following application of the respective TCs, and the parameters, E_max and ED₅₀, were derived. E_max values were used as the metric to assess potency. Statistical analyses of the data revealed that the inherent potencies of fluticasone propionate, mometasone furoate, and hydrocortisone butyrate were similar. However, there was no significant difference between hydrocortisone butyrate and clobetasol propionate, while there was a significant difference between clobetasol propionate, fluticasone propionate, and mometasone furoate. Hence, the potency of hydrocortisone butyrate appears to overlap two potency classes. Furthermore, the potencies of betamethasone valerate and methylprednisolone aceponate were similar but lower than those of all of the other APIs. The application of the VCA to classify inherent potency provides a reliable method to establish a classification system for TCs. Inherent potency assessment of TCs provides information that will be useful when choosing an appropriate TC for the development of a TCP for a specific clinical indication.

Application of Emax model to assess the potency of topical corticosteroid products

The objective of this study was to compare the potencies of two topical corticosteroid products (TCPs) using the E_max model to fit the skin blanching responses obtained from the US FDA's vasoconstrictor assay (VCA) and to illustrate the influence of formulation on potency. The potencies of two marketed TCPs, Dermovate® cream containing clobetasol propionate (CP) and Elocon® cream containing mometasone furoate (MF), were assessed using healthy human subjects. In order to investigate the influence of formulation and associated vehicle properties, the creams were compared with their respective topical corticosteroids (TCs) from a previously published study wherein the inherent potencies of those TCs were assessed using a validated VCA method. Whereas the inherent potency of MF (E_max  = -94.45 ± 0.21) was found to be greater than CP (E_max  = -58.80 ± 15.65), when formulated as creams, the TCP containing CP had a higher potency (E_max  = -86.15 ± 0.17) than that containing MF (E_max  = -42.61 ± 26.04). This reversal of potency may be attributed to the effect of formulation factors. The comparison of the potencies of TCPs with inherent potencies of their corresponding TCs confirmed the influence of formulation parameters on the potency of those products.

Application of a dermatopharmacokinetic (DPK) method for bioequivalence assessment of topical metronidazole creams

PURPOSE

The main aim of the current research was to develop and apply a dermatopharmacokinetic (DPK) approach for the bioequivalence assessment of metronidazole (MTZ) topical cream products, indicated in the treatment of rosacea.

METHODS

A DPK methodology using tape stripping (TS) technique was developed by investigating the factors that may influence the TS results viz. tapes, dose durations, number of tapes to be used, pressure application, dose applied and gravimetric analysis of the tapes. An initial dose duration study was performed on 6 healthy participants to determine an appropriate application time duration using the Emax model. The SC thickness was normalised between participants using TEWL measurements. A pivotal study was conducted using both the arms of 10 healthy human participants to demonstrate the ability of the TS method for bioequivalence assessment by comparing the reference product to itself as a positive control and including products with higher and lower strengths of MTZ to serve as negative controls in order to confirm bioinequivalence.

RESULTS

Whereas the reference was found to be bioequivalent when compared to itself, the creams containing 0.56% and 0.95% MTZ (negative controls) were not bioequivalent (bioinequivalent). Furthermore, another product containing 0.75% MTZ was also assessed and was found to be bioequivalent to the reference product. In addition, the use of both forearms of each participant offered an important advantage of significantly reducing the number of human subjects required to demonstrate BE with a high statistical power of > 80%.

CONCLUSION

The data obtained provides compelling evidence that the developed TS method has the potential to be a cost-effective surrogate alternative for lengthy and expensive clinical trials. Consequently, its application can facilitate faster development of generic products which would, in turn, lower the economic burden of healthcare.

[Bilateral diaphragmatic palsy due to Lyme neuroborreliosis]

INTRODUCTION

Lyme disease is not uncommon and can sometimes progress to neurological complications. We report here an unusual case of bilateral diaphragmatic paralysis secondary to Lyme neuroborreliosis.

CASE REPORT

A 79-year-old man was admitted to the intensive care unit for acute respiratory distress requiring intubation and the long-term use of nocturnal non-invasive ventilation. Three months beforehand he had been bitten by a tick and developed erythema migrans which was treated with Doxycycline for 10 days. This clinical presentation became complicated a few days later by the progressive onset of severe dyspnoea. At admission, chest radiography revealed bilateral elevation of the diaphragm. Pulmonary function tests revealed a severe restrictive disorder aggravated by decubitus. A diaphragmatic electromyogram showed bilateral axonal polyneuropathy of the phrenic nerves. IgG and IgM antibodies to Borrelia burgdorferi were detectable in serum and cerebrospinal fluid, leading to the diagnosis of Lyme disease. He was treated with intravenous ceftriaxone 2g per day for 21 days, leading to a substantial improvement in symptoms.

CONCLUSION

In the presence of unilateral or bilateral diaphragmatic paralysis of undetermined aetiology, it seems relevant to perform Lyme serology in the blood and, in positive cases, to follow up with a lumbar puncture in order to detect intrathecal IgG synthesis.

Prothrombin Time Sensitivity and Specificity to Mild Clotting Factor Deficiencies of the Extrinsic Pathway: Evaluation of Eight Commercial Thromboplastins

Prothrombin-time (PT) sensitivity and specificity to mild clotting factor II, V, VII and X deficiencies have rarely been studied. We therefore carried out a prospective study, in 350 patients, of eight commercial thromboplastins (CTs) in their ability to detect mild clotting factor deficiencies, notably in factor VII. In each patient the factor II, V, VII and X clotting activities and PT performed with each CT were determined. For each CT, PT sensitivity and specificity in detecting factor deficiencies below 0.5 U/ml or below 0.4 U/ml were determined at various PTs, and then Receiver Operator Characteristic curves constructed. At optimum PT threshold level (sensitivity = specificity), exactitude varied from 0.64 to 0.74 (p < 0.01) and from 0.67 to 0.81 (p < 0.0001) in detecting deficiencies below 0.5 and 0.4 U/ml respectively. In conclusion, this study shows the limits of the PT test as performed with 8 CTs in patients with mild clotting factor deficiencies. The impact of such differences in sensitivity and specificity on monitoring certain patients subject to decrease in coagulation factor, and, in particular, of those under low-dose oral anticoagulant, remains to be determined.

Mathematical modeling and simulation in animal health. Part III: Using nonlinear mixed-effects to characterize and quantify variability in drug pharmacokinetics

A common feature of human and veterinary pharmacokinetics is the importance of identifying and quantifying the key determinants of between-patient variability in drug disposition and effects. Some of these attributes are already well known to the field of human pharmacology such as bodyweight, age, or sex, while others are more specific to veterinary medicine, such as species, breed, and social behavior. Identification of these attributes has the potential to allow a better and more tailored use of therapeutic drugs both in companion and food-producing animals. Nonlinear mixed effects (NLME) have been purposely designed to characterize the sources of variability in drug disposition and response. The NLME approach can be used to explore the impact of population-associated variables on the relationship between drug administration, systemic exposure, and the levels of drug residues in tissues. The latter, while different from the method used by the US Food and Drug Administration for setting official withdrawal times (WT) can also be beneficial for estimating WT of approved animal drug products when used in an extralabel manner. Finally, NLME can also prove useful to optimize dosing schedules, or to analyze sparse data collected in situations where intensive blood collection is technically challenging, as in small animal species presenting limited blood volume such as poultry and fish.

Pharmacokinetics and Bioequivalence of Branded and Generic Formulations of Dofetilide 0.5-mg Capsules After Single-Dose Administration in Healthy Subjects

Class III antiarrhythmics are preferred therapy for managing atrial fibrillation/flutter. Dofetilide 0.5-mg capsules were US Food and Drug Administration (FDA) approved in 1999 to treat atrial fibrillation/flutter. Bioequivalence of generic dofetilide is important for treating arrhythmias because drug concentrations must be consistent to maintain normal sinus rhythm. Generic dofetilide 0.5-mg capsule pharmacokinetics were compared with branded product in 2 open-label, 2-way crossover, single-dose studies - 1 study each in fasted and fed healthy subjects. Blood samples were collected before and up to 48 hours after dosing. Safety was assessed by tabulating adverse events and vital signs. Seventy-three subjects were enrolled; 59 completed the studies. In fasted subjects, the 90% confidence intervals (CIs) for generic dofetilide 0.5 mg versus the reference formulation were 0.996-1.026 for the area under the plasma concentration-time curve from 0 to infinity (AUC) and 0.974-1.066 for the maximum observed concentration (C_max ). In fed subjects, the 90%CIs for AUC and C_max were 0.988-1.015 and 0.928-0.992, respectively. All ratios were within the FDA-established bioequivalence range. Twenty-six subjects experienced 37 adverse events (generic, 15; reference, 22); all but 1 were mild or moderate in severity. Generic dofetilide 0.5-mg capsules can be considered bioequivalent to the reference product.

Humanized monoclonal antibody armanezumab specific to N-terminus of pathological tau: characterization and therapeutic potency

Background

The experience from clinical trials indicates that anti-Aβ immunotherapy could be effective in early/pre-clinical stages of AD, whereas at the late stages promoting the clearing of Aβ alone may be insufficient to halt the disease progression. At the same time, pathological tau correlates much better with the degree of dementia than Aβ deposition. Therefore, targeting pathological tau may provide a more promising approach for the treatment of advanced stages of AD. Recent data demonstrates that the N-terminal region of tau spanning aa 2–18 termed “phosphatase activation domain” that is normally hidden in the native protein in ‘paperclip’-like conformation, becomes exposed in pathological tau and plays an essential role in the inhibition of fast axonal transport and in aggregation of tau. Hence, we hypothesized that anti-Tau_2–18 monoclonal antibodies (mAb) may recognize pathological, but not normal tau at very early stages of tauopathy and prevent or decrease the aggregation of this molecule.

Methods

Mouse mAbs were generated using standard hybridoma methodology. CDR grafting was used for humanization of mouse mAb. Humanized mAb (Armanezumab) was characterized and tested in vitro/ex vivo/in vivo using biochemical and immunological methods (HPLC, Biacore, ELISA, IHC, FRET, etc.). Stable DG44 cell line expressing Armanezumab was generated by clone selection with increased concentrations of methotrexate (MTX).

Results

A panel of mouse mAbs was generated, clone 1C9 was selected based on binding to pathological human tau with high affinity and humanized. Fine epitope mapping revealed conservation of the epitope of human tau recognized by the parent murine mAb and Armanezumab. Importantly, Armanezumab (i) bound to tau with high affinity as determined by Biacore; (ii) bound pathological tau in brains from AD, FTD and Pick’s disease cases; (iii) inhibited seeding effect of aggregated tau from brain lysate of P301S Tg mice; (iv) inhibited cytotoxic effect of tau oligomers; (v) reduced total tau (HT7) and AT100, PHF1, AT8, AT180, p212, p214-positive tau species in brains of tau transgenic mice after intracranial injection. A stable CHO cell line producing >1.5 g/l humanized mAb, Armanezumab was generated.

Conclusion

These findings suggest that Armanezumab could be therapeutic in clinical studies for treatment of AD.

Is-it possible to distinguish irritable bowel syndrome with constipation from functional constipation?

BACKGROUND

The Rome III criteria classify patients complaining of constipation into two main groups: patients with functional constipation (FC) and patients with constipation predominant irritable bowel syndrome (IBS-C). The purpose of this study was to identify differences in the intensity of symptoms and total and segmental colonic transit time in these two types of patients.

METHODS

We performed a prospective evaluation of 337 outpatients consecutively referred for chronic constipation and classified according to the Rome III criteria as FC or IBS-C. They were asked to report symptom intensity, on a 10-point Likert scale, for diarrhea, constipation, bloating and abdominal pain. Stool form was reported using the Bristol scale, and colonic transit time was measured by using multiple-ingestion single-marker single-film technique. Statistical analysis was completed by a discriminant analysis.

RESULTS

Female gender and obstructed defecation was more frequent in IBS-C patients than in FC patients. IBS-C patients reported greater symptom intensity than FC patients, but stool form, and total and segmental colonic transit time were not different between the two groups. Multivariate logistic regression showed that only two parameters, bloating and abdominal pain, were related to the IBS-C or to the FC phenotype, and discriminant analysis showed that these two parameters were sufficient to give a correct classification of 71% of the patients.

CONCLUSIONS

Our study suggests that self-evaluation of abdominal pain and bloating is more helpful than colonic transit time in classifying patient as IBS-C or FC.

The use of an imagery mnemonic to teach the Krebs cycle

The Krebs Cycle is a highly taught biochemical pathway that is traditionally difficult to learn. Twenty-seven undergraduate students were randomized to a rote memorization arm or to a mnemonic arm. They were given a pre-test, then shown a lecture corresponding to their assigned method, and then given an immediate Week 0 post-test and a Week 4 post-test. Groups scored comparably low on the pre-test (p = 0.7113). Students in the mnemonic arm performed better on the Week 0 post-test than those using rote (p = 0.0055). By Week 4, there was evidence of knowledge decay, with both arms' having comparably low scores (mnemonic vs. rote, p = 0.3739). The mnemonic assists in rapid acquisition of knowledge but probably has to be reviewed iteratively over time to demonstrate its full potential over rote memorization. A limited number of students from only one school was used. © 2016 by The International Union of Biochemistry and Molecular Biology, 44:224-229, 2016.

Partial purification of ?-glycerotoxin, a presynaptic neurotoxin from the venom glands of the polychaete annelid glycera convoluta

The venom secreted from glands appended to the jaws of Glycera convoluta, a Polychaete Annelid, increases the spontaneous quantal release of transmitter from nerve terminals. The component that is biologically active on vertebrate cholinergic nerve terminals has recently been shown to be a high molecular weight protein. In the present work, the crude extract from the venom apparatus was shown to be toxic for mammals and crustaceans. It was fractionated by gel filtrations and ion exchange chromatographies. The biologically active component at frog neuromuscular junctions, ?-glycerotoxin, was purified more than 1,000-fold. It is distinct from the components that are toxic for crustaceans. Purified ?-glycerotoxin is a globular protein of 300,000 +/- 20,000 mol wt. It has a Stokes radius of 65 A and a sedimentation coefficient of 11 S. By its molecular properties, ?-glycerotoxin appears distinct from other neurotoxins such as ?-latrotoxin, which also trigger transmitter release.

Long-acting somatostatin analogues decrease blood transfusion requirements in patients with refractory gastrointestinal bleeding associated with angiodysplasia

BACKGROUND

Gastrointestinal angiodysplasias (GIADs) may be the cause of recurrent bleeding, despite endoscopic treatment.

AIM

To evaluate the effect of long-acting somatostatin analogues on blood transfusion requirements, in patients with refractory bleeding due to GIADs.

METHODS

Consecutive patients with recurrent bleeding from GIADs were enrolled. They received somatostatin analogue treatment for at least 6 months. The efficacy was evaluated in terms of blood transfusions, frequency of bleeding episodes and haemoglobin level during 6 months of treatment (Period During) compared to a 6-months' period before treatment (Period Before).

RESULTS

Fifteen patients were enrolled from 2007 to 2010. The median duration of somatostatin analogue treatment was 12 months (range: 6-36). The number of transfusions significantly decreased in Period During compared with Period Before [median number: 2 (0-14) vs. 10 (6-24); P < 0.001]. The percentage of patients who experienced a bleeding event was lower during somatostatin analogues treatment (20% vs. 73%; P = 0.01). The mean haemoglobin level was significantly higher when somatostatin analogues were offered [median: 10 g/dL (9-13) vs. 7 (5-8.5); P < 0.001]. None of the patients discontinued treatment due to side effects.

CONCLUSIONS

Long-acting somatostatin analogues treatment decreased transfusion needs in patients with refractory bleeding from gastrointestinal angiodysplasias. Bleeding episodes were limited and haemoglobin improved during treatment. Long-acting somatostatin analogues may represent an option for the management of patients with chronic bleeding due to gastrointestinal angiodysplasias.

Bioequivalence of topical clotrimazole formulations: an improved tape stripping method

PURPOSE

Investigations were carried out to assess the use of tape stripping (TS) for the determination of bioequivalence of topical products containing 1% clotrimazole.

METHODS

The study design involved the establishment of an appropriate application time, which was determined by conducting a dose duration study. Subsequently, two bioequivalence studies were conducted: i) using the brand (Canesten Topical - 1% clotrimazole cream) as both the test and the reference product and ii) comparing Canesten cream with a gel product containing the same concentration of clotrimazole (1%). Each tape strip was individually analyzed for clotrimazole content using an HPLC method and Transepidermal Water Loss (TEWL) measurements were used to normalize the stratum corneum thicknesses between subjects.

RESULTS

The results of the TS investigations showed that, if the study is sufficiently powered, tape stripping may be used to determine bioequivalence according to the conventional bioequivalence limits of 0.8-1.25, as well as detect formulation differences between different clotrimazole products.

CONCLUSIONS

The data from this study provided compelling evidence that tape stripping has the necessary attributes and potential to be used as a tool for the bioequivalence assessment of topical clotrimazole and/or other topical formulations, thereby circumventing the need to undertake expensive and time-consuming clinical trials for such products. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Convulxin-induced platelet adhesion and aggregation: involvement of glycoproteins VI and IaIIa

The interaction of convulxin (Cvx), a 72-kDa glycoprotein isolated from the venom of Crotalus durissus terrificus with human platelets has been studied. Cvx at low concentrations (below 100 pM) induced platelet aggregation, dense body secretion and intracellular calcium mobilization which indicates that Cvx is a potent activator of human platelets. Cvx-induced platelet aggregation and secretion was inhibited by 6Fl an anti-integrin alpha2beta1 monoclonal antibody that was without effect on calcium mobilization. Anti-GPVI Fab fragments inhibited aggregation, secretion and calcium mobilization triggered by Cvx. In addition, immobilized Cvx was found to induce divalent cation-independent platelet adhesion in a static system. Platelet adhesion to Cvx was inhibited by anti-GPVI Fab fragments but not by anti-integrin alpha2beta1 . Cvx was shown to bind to a 57,000 Dalton protein that was identified as GPVI. Altogether, these results indicate that GPVI behaves as a receptor for Cvx, while integrin alpha2beta1 could play a regulatory role in Cvx-induced platelet aggregation. Cvx and collagen interaction with platelets, thus appears to share some characteristics but to also have specific properties.

[Feto-maternal metabolism in human normal pregnancies: study of 73 cases]

From 73 normal pregnancies of gestational age between 17 and 41 weeks of gestation (WG), the concentrations of glucose, pyruvate and lactate, free fatty acids, ketone bodies (aceto-acetate and beta-hydroxybutyrate) and cholesterol were assessed on maternal venous blood (MVB) and umbilical venous blood (UVB), sampled by cordocentesis. The objective of this work was to study feto-maternal metabolism, as well as nutritional exchange between maternal blood and fetal blood during the second and third trimesters of pregnancy. Maternal and fetal glycemias, as well as maternal-fetal glucose concentration gradient, were found stable during the studied gestational period; maternal glucose is always higher than fetal glucose, with a mean concentration delta of 0.69+/-0.34 mmol/L. Maternal lactate level (1.26+/-0.38 mmol/L) is lower than fetal lactate level (1.48+/-0.46 mmol/L), whereas maternal blood pyruvate concentration (0.042+/-0.020 mmol/L) is higher than fetal blood pyruvate concentration (0.025+/-0.010 mmol/L). Consequently, mean lactate / pyruvate ratio is found twice lower in maternal blood (31.77+/-9.89) than in fetal blood (64.10+/-17.12). Free fatty acids concentration is approximately three times higher in maternal blood than in fetal blood (respectively 0.435+/-0.247 mmol/L and 0.125+/-0.046 mmol/L). Maternal venous aceto-acetate (0.051+/-0.042 mmol/L) and beta-hydroxybutyrate (0.232+/-0.270 mmol/L) concentrations are significantly lower than those in UVB (respectively 0.111+/-0.058 and 0.324+/-0.246 mmol/L) and the beta-hydroxybutyrate/aceto-acetate ratio is on average 1.7 times higher in MVB (4.75+/-2.5) than in UVB (2.82+/-1.18). Cholesterol concentration is significantly higher in maternal blood (6.26+/-1.40 mmol/L) than in fetal blood (1.66+/-0.34 mmol/L). Our results show the characteristics of oxidative metabolism of the fetus compared with that of the adult. Blood concentration in energy substrates, measured with glucose and free fatty acids levels, is low in UVB and suggests increased energy needs of the growing fetus. Mean high concentrations in aceto-acetate and beta-hydroxybutyrate in UVB, indicate probably fetal ketogenesis. UVB low cholesterolemia suggests high cholesterol consumption in the fetal compartment for cellular membrane synthesis and steroid biosynthesis.

Toxicokinetic and toxicodynamic analyses of Androctonus australis hector venom in rats: optimization of antivenom therapy

This paper reports the simultaneous determination of toxicokinetic and toxicodynamic properties of Androctonus australis hector venom, in the absence and presence of antivenom (F(ab')(2) and Fab), in envenomed rats. After subcutaneous injection of the venom, toxins showed a complete absorption phase from the site of injection associated with a distribution into a large extravascular compartment. The injection of Fab and F(ab')(2) induced the neutralization of venom antigens in the blood compartment, as well as the redistribution of venom components from the extravascular compartment to the blood compartment. Interestingly, F(ab')(2) and Fab showed distinct efficiencies depending on their route of injection. F(ab')(2) induced a faster venom neutralization and redistribution than Fab when injected intravenously. Fab was more effective than F(ab')(2) by the intramuscular route. The hemodynamic effects of Aah venom were further investigated. Changes in mean arterial pressure and heart rate were observed in parallel with an upper airway obstruction. Fab was more effective than F(ab')(2) for preventing early symptoms of envenomation, whatever their route of administration. Intraperitoneal injection of F(ab')(2) and Fab was similar for the prevention of the delayed symptoms, even after a late administration. Fab was more effective than F(ab')(2) in the inhibition of airway resistance, independent of the route and time of administration. These results show that the treatment for scorpion stings might be improved by the intravascular injection of a mixture of Fab and F(ab')(2). If antivenom cannot be administered intravenously, Fab might be an alternative as they are more effective than F(ab')(2) when injected intramuscularly.

[Biochemical profile of fetal blood sampled by cordocentesis in 35 pregnancies complicated by growth retardation]

AIM OF THE STUDY

Intra-uterine growth retardation (IUGR) is a frequent pathology in obstetrics characterized by high heterogeneity. Fetal smallness is sometimes constitutional, but can also be accompanied by fetal distress and vital risks for the infant. In 35 pregnancies complicated by IUGR of different etiologies, we measured on fetal blood obtained by cordocentesis, biochemical variables characteristic of the fetuses' respiratory and metabolic status. The aim of the study was to identify the discriminative biological alterations, related to growth retardation and fetal distress.

PATIENTS AND METHODS

The studied population includes 27 cases of severe IUGR, of gestational age 30,2+/-4,6 weeks of gestation (WG) (divided into 20 cases of isolated IUGR and 7 cases of IUGR associated with malformative syndrome), as well as 8 cases of moderate IUGR, of gestational age 26+/-4,5 WG; all fetuses had normal karyotypes. A group of 73 normal fetuses, of gestational age 26,3+/-5,7 WG, constituted a reference population. PH, pCO(2), bicarbonate concentration, pO(2) and SaO(2), as well as glucose, pyruvate, lactate, free fatty acids, aceto-acetate, beta-hydroxybutyrate and cholesterol concentrations were measured on umbilical venous blood (UVB).

RESULTS

In case of severe but isolated growth retardation, UVB analysis showed the frequency of acid-base and gasometric disturbances: acidemia and hypoxemia (65% of cases), hypercapnia (60% of cases). Metabolic abnormalities were shown: decrease in glycemia (35% of cases), increase in pyruvatemia and lactatemia (40% of cases), increased free fatty acids serum concentration; a diminution of umbilical venous cholesterol level, the most frequent abnormality, can be seen in 70% of fetuses. In case of severe IUGR associated with malformative syndrome, UVB acid-base and metabolic changes were rarely seen; however, UVB cholesterol level is low in some cases. In case of growth retardation classified as moderate, modifications are relatively not frequent and essentially gasometric.

CONCLUSION

In about 60% of cases of severe and isolated IUGR, there is a risk of fetal distress, related to an alteration of the transplacental transfer of respiratory gases and nutritional substrates; chronic fetal malnutrition can be involved, with an impact on the growth of the fetus. In case of IUGR associated with malformative syndrome, fetal smallness is probably a result of intrinsic fetal damage, without nutritional origin.

[Amniotic fluid embolism: a review]

Amniotic fluid embolism occurs rarely but is a leading cause of maternal mortality. It is a difficult and somewhat intangible diagnosis that warrants a high index of suspicion by physicians. AFE is an unpredictable, unpreventable, and, for the most part, an untreatable obstetric emergency. Management of this condition includes prompt recognition of the signs and symptoms, aggressive resuscitation efforts, and supportive therapy. Any delays in diagnosis and treatment can result in increased maternal and/or foetal impairment or death. Whereas once the invariable outcome of AFE was death of the mother, today the prognosis is somewhat brighter thanks to increased awareness of the syndrome and advances in intensive care medicine. No laboratory test is specific to attest the diagnosis and autopsy must to be realised in case of maternal death. Although non-specific, the diagnosis of AFE could be supported by the observation of amniotic fluid in the central venous blood as well as in the bronchoalveolar fluid. This easy and quick test will be helpful in decision-making. Prompt and aggressive supportive treatment is required to lessen an otherwise dismal outcome, which may include death and permanent disability. This article provides an account of the protean clinical features, pathogenesis, and principles involved in treatment.

Ultrahigh resolution drug design I: details of interactions in human aldose reductase-inhibitor complex at 0.66 A

The first subatomic resolution structure of a 36 kDa protein [aldose reductase (AR)] is presented. AR was cocrystallized at pH 5.0 with its cofactor NADP+ and inhibitor IDD 594, a therapeutic candidate for the treatment of diabetic complications. X-ray diffraction data were collected up to 0.62 A resolution and treated up to 0.66 A resolution. Anisotropic refinement followed by a blocked matrix inversion produced low standard deviations (<0.005 A). The model was very well ordered overall (CA atoms' mean B factor is 5.5 A2). The model and the electron-density maps revealed fine features, such as H-atoms, bond densities, and significant deviations from standard stereochemistry. Other features, such as networks of hydrogen bonds (H bonds), a large number of multiple conformations, and solvent structure were also better defined. Most of the atoms in the active site region were extremely well ordered (mean B approximately 3 A2), leading to the identification of the protonation states of the residues involved in catalysis. The electrostatic interactions of the inhibitor's charged carboxylate head with the catalytic residues and the charged coenzyme NADP+ explained the inhibitor's noncompetitive character. Furthermore, a short contact involving the IDD 594 bromine atom explained the selectivity profile of the inhibitor, important feature to avoid toxic effects. The presented structure and the details revealed are instrumental for better understanding of the inhibition mechanism of AR by IDD 594, and hence, for the rational drug design of future inhibitors. This work demonstrates the capabilities of subatomic resolution experiments and stimulates further developments of methods allowing the use of the full potential of these experiments.

Analgesic safety and efficacy of diclofenac sodium softgels on postoperative third molar extraction pain

PURPOSE

The purpose of this single-blind, placebo-controlled, 3-arm parallel, randomized study was to compare the analgesic efficacy and tolerability of a single dose of 100 mg diclofenac potassium (Cataflam; Novartis, Stein, Switzerland), 100 mg diclofenac sodium softgel, and placebo in patients experiencing moderate to severe postoperative pain after third molar extraction.

PATIENTS AND METHODS

Seventy-five patients (67% female with a mean age of 23, age range 18 to 34.5 years) participated in the study following removal of at least 1 impacted mandibular third molar. Patients received a single dose of study medication when their postoperative pain reached a moderate or severe intensity. Analgesic efficacy measures included the time to meaningful pain relief measured using a stopwatch and time to rescue medication. Pain relief (PR) and Pain intensity (PI) ratings were recorded at 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 8, and 24 hours postdosing. Summary analgesic measures, including Summed Pain Relief Score (TOTPAR) and Summed Pain Intensity Differences (SPID), were calculated from the 0.25- to 6-hour responses. The time between pain relief and rescue and a global evaluation for the effectiveness of the study medications were recorded at the end of the study. Seven scheduled blood samples were collected from each patient for determining plasma concentrations of diclofenac anion.

RESULTS

Both diclofenac sodium softgel and Cataflam were significantly more effective than placebo (P <.0001) for all summary analgesic measures. The average overall pain relief was substantially better from diclofenac sodium softgel than from Cataflam, but the difference was not statistically significant (P =.14). In patients taking diclofenac sodium softgel, 50% of the patients experienced a time to onset of analgesic activity within 18 minutes and the median analgesic duration was 5 hours (302 minutes). Fifty percent of the patients taking Cataflam had a time to onset of action within 38 minutes, and the median duration of analgesia was 4.5 hours (272 minutes). At the time of rescue drug administration or 6 hours, whichever was earlier, 72% of the patients given diclofenac sodium softgel rated the medication as a very good or excellent pain reliever, whereas only 45% of the patients taking Cataflam gave these ratings. No serious adverse events were observed in this study. The mean concentrations of diclofenac from the diclofenac sodium softgel formulation were significantly different from the Cataflam formulation. The mean C(max) for the softgel was almost twice that of Cataflam and C(max) was reached an hour earlier, on average.

CONCLUSIONS

More diclofenac anion was absorbed at a quicker rate using the formulation diclofenac sodium softgel 100 mg than Cataflam. The softgel provided a very rapid onset of analgesic activity, a prolonged analgesic duration, and an acceptable side-effect profile in the postoperative third molar surgery pain model. In an acute pain situation, the rapid absorption of nonsteroidal anti-inflammatory drugs from a formulation like the Softgel may positively affect the time of onset and duration of inflammatory pain compared with other commercially available nonsteroidal anti-inflammatory drug formulations.

Pharmacological and histopathological characterization of Bothrops lanceolatus (Fer de lance) venom-induced edema

OBJECTIVE

Bothrops venoms cause local edema, pain, hemorrhage and necrosis. In this study, we investigated the ability of Bothrops lanceolatus venom to cause edema in rat hind paws and examined the mediators involved.

MATERIALS AND METHODS

Hind paw edema was induced in male Wister rats by the subplantar injection of venom (12.5-100 microg/paw) in the absence and presence of antagonists. Edema was quantified by hydroplethysmometry at 0.25, 0.5, 2, 4, 6 and 24 h post-injection and was expressed as the percentage increase relative to the contralateral (control) paw. The ability of the venom to release histamine from rat peritoneal mast cells was also assessed.

RESULTS

Venom caused dose- and time-dependent edema that was maximal within 15 min but disappeared after 24 h and was accompanied by hemorrhage. Dexamethasone (1 mg/kg, s.c.), methysergide (6 mg/kg, i.p.), HOE 140 (0.6 mg/kg, i.v.) and mepyramine (6 mg/kg, i.p.) significantly ( p < 0.05) reduced edema formation, whereas indomethacin (10 mg/kg, i.p.) was ineffective. Dialysis did not affect venom-induced edema. Venom (1, 10 and 30 microg/ml) caused a concentration-dependent release of histamine (13 +/- 1%, 61.9 +/- 4.6% and 73.6 +/- 2.4%, respectively; n = 5) from rat peritoneal mast cells in vitro. Histological analysis confirmed the presence of edema, hemorrhage and neutrophil infiltration. Pretreating the venom with EDTA partially inhibited the edema and hemorrhage, but did not affect the migration of neutrophils.

CONCLUSIONS

B. lanceolatus venom produced dose- and time-dependent edema in rat paws. This edema was not dependent on low molecular weight substances in the venom, but was partially dependent on a hemorrhagin and also involved the release of arachidonic acid metabolites, bradykinin, histamine and serotonin.

Comparative evaluation of immunological and structural similarities of snake venom C-type lectin proteins

Antibodies raised against denatured and native forms of bothrojaracin were used to analyze the immunological similarities compared to the structural and biological features of five C-type lectin proteins from snake venom (bothrojaracin, botrocetin, Factor IX/X binding protein (FIX/Xbp), convulxin and Bothrops jararaca lectin). Anti-denatured-bothrojaracin antibodies, which recognize mainly linear epitopes, cross-reacted with botrocetin, FIX/Xbp and convulxin, as expected for homologous proteins. On the other hand, anti-native-bothrojaracin antibodies, which mostly interact with conformational epitopes, exhibited a higher degree of selectivity. These results show that differences exist at the surface of these proteins and that they should be related to their different biological activities, while they share a common and similar scaffold.

A model for water motion in crystals of lysozyme based on an incoherent quasielastic neutron-scattering study

This paper reports an incoherent quasielastic neutron scattering study of the single particle, diffusive motions of water molecules surrounding a globular protein, the hen egg-white lysozyme. For the first time such an analysis has been done on protein crystals. It can thus be directly related and compared with a recent structural study of the same sample. The measurement temperature ranged from 100 to 300 K, but focus was on the room temperature analysis. The very good agreement between the structural and dynamical studies suggested a model for the dynamics of water in triclinic crystals of lysozyme in the time range approximately 330 ps and at 300 K. Herein, the dynamics of all water molecules is affected by the presence of the protein, and the water molecules can be divided into two populations. The first mainly corresponds to the first hydration shell, in which water molecules reorient themselves fivefold to 10-fold slower than in bulk solvent, and diffuse by jumps from hydration site to hydration site. The long-range diffusion coefficient is five to sixfold less than for bulk solvent. The second group corresponds to water molecules further away from the surface of the protein, in a second incomplete hydration layer, confined between hydrated macromolecules. Within the time scale probed they undergo a translational diffusion with a self-diffusion coefficient reduced approximately 50-fold compared with bulk solvent. As protein crystals have a highly crowded arrangement close to the packing of macromolecules in cells, our conclusion can be discussed with respect to solvent behavior in intracellular media: as the mobility is highest next to the surface, it suggests that under some crowding conditions, a two-dimensional motion for the transport of metabolites can be dominant.

Thermal denaturation of Bungarus fasciatus acetylcholinesterase: Is aggregation a driving force in protein unfolding?

A monomeric form of acetylcholinesterase from the venom of Bungarus fasciatus is converted to a partially unfolded molten globule species by thermal inactivation, and subsequently aggregates rapidly. To separate the kinetics of unfolding from those of aggregation, single molecules of the monomeric enzyme were encapsulated in reverse micelles of Brij 30 in 2,2,4-trimethylpentane, or in large unilamellar vesicles of egg lecithin/cholesterol at various protein/micelle (vesicle) ratios. The first-order rate constant for thermal inactivation at 45 degrees C, of single molecules entrapped within the reverse micelles (0.031 min(-1)), was higher than in aqueous solution (0.007 min(-1)) or in the presence of normal micelles (0.020 min(-1)). This clearly shows that aggregation does not provide the driving force for thermal inactivation of BfAChE. Within the large unilamellar vesicles, at average protein/vesicle ratios of 1:1 and 10:1, the first-order rate constants for thermal inactivation of the encapsulated monomeric acetylcholinesterase, at 53 degrees C, were 0.317 and 0.342 min(-1), respectively. A crosslinking technique, utilizing the photosensitive probe, hypericin, showed that thermal denaturation produces a distribution of species ranging from dimers through to large aggregates. Consequently, at a protein/vesicle ratio of 10:1, aggregation can occur upon thermal denaturation. Thus, these experiments also demonstrate that aggregation does not drive the thermal unfolding of Bungarus fasciatus acetylcholinesterase. Our experimental approach also permitted monitoring of recovery of enzymic activity after thermal denaturation in the absence of a competing aggregation process. Whereas no detectable recovery of enzymic activity could be observed in aqueous solution, up to 23% activity could be obtained for enzyme sequestered in the reverse micelles.

Unusual neurotoxic envenomations by Vipera aspis aspis snakes in France

Vipera aspis aspis (V.a.a.) is the most dangerous poisonous snake in South-Eastern France. The clinical symptoms observed after V.a.a. envenomations involve mostly local signs (pain, edema) associated in the more severe cases with systemic symptoms (gastro-intestinal and cardiovascular manifestations). Since 1992, several unusual cases of moderate and severe 'neurotoxic' envenomations by V.a.a. snakes have been reported in a very localized area in South-Eastern France. Most of the human patients mainly suffered neurological signs owing to cephalic muscle paralysis. Drowsiness and dyspnea were observed for the most severe cases. Envenomed animals suffered respiratory distress and paralysis. The local signs were never as severe as observed after envenomations by vipers in other French regions. Human patients with moderate or severe clinical features received two intravenous injections of Viperfav antivenom, the first dose inducing the decrease of the neurological signs and the second reducing significantly the edema. Neurotoxic components immunologically cross-reacting with toxins from V. ammodytes ammodytes venom from Eastern Europe were detected in the blood of all patients suffering neurological symptoms after a V.a.a. bite. The protective efficacy of various antivenoms was evaluated in mice. The existence of geographical variations in the composition of V.a.a. venom emphasizes on the use of polyvalent antivenom in the treatment of viper envenomations in France.

Pharmacological characterization of the rat paw edema induced by Bothrops lanceolatus (Fer de lance) venom

The inflammatory response induced by Bothrops lanceolatus venom (BLV) in the rat hind-paw was studied measuring paw edema. Non-heated BLV (75microg/paw) caused a marked paw edema accompanied by intense haemorrhage whereas heated venom (97 degrees C, 30s; 12.5-100microg/paw) produced a dose- and time-dependent non-haemorrhagic edema. The response with heated BLV was maximal within 15min disappearing over 24h. Heated venom was then routinely used at the dose of 75microg/paw. The prostacyclin analogue iloprost (0.1microg/paw) potentiated by 125% the venom-induced edema. The histamine H(1) receptor antagonist mepyramine (6mg/kg) or the serotonin/histamine receptor antagonist cyproheptadine (6mg/kg) partially inhibited BLV-induced edema whereas the combination of both compounds virtually abolished the edema. The lipoxygenase inhibitor BWA4C (10mg/kg), but not the cyclooxygenase inhibitor indomethacin (10mg/kg), significantly inhibited the edema (35% reduction; P<0.05). Dexamethasone (1mg/kg) also markedly (P<0.001) reduced venom-induced edema. The bradykinin B(2) receptor antagonist Hoe 140 (0.6mg/kg) reduced by 30% (P<0.05) the venom induced edema, whereas the angiotensin-converting enzyme inhibitor captopril (300microg/paw) potentiated by 42% (P<0.05) the edema. Bothrops lanceolatus antivenon (anti-BLV) reduced by 28% (P<0.05) the venom-induced edema while intravenous administration of antivenom failed to affect the edema. In conclusion, BLV-induced rat paw edema involves mast cell degranulation causing local release of histamine and serotonin, a phenomenon mediated mainly by kinins and lipoxygenase metabolites. Additionally, the use of a specific Bothrops lanceolatus antivenom, given subplantarily or intravenously, revealed to be little effective to prevent BLV-induced edema.

Antagonization of TNF attenuates systemic hemodynamic manifestations of envenomation in a rat model of Vipera aspis snakebite

OBJECTIVES

Tumor necrosis factor (TNF) has been reported as a mediator of local tissue injury following snake envenomation in an intact rat model. We investigated whether systemic release of TNF occurs following Vipera aspis envenomation. We further analyzed the possible connection between envenomation-related hemodynamic depression and TNF antagonization (TNF antibodies or soluble TNF receptor).

DESIGN

A prospective, randomized, controlled experimental study using a rat model for snake envenomation.

SETTINGS

A medical university hospital research laboratory.

INTERVENTION

Eighty rats (300-400 g) were divided into four groups (n = 20): control and three experimental groups. Intramuscular injection of V. asis 500 microg/kg was administered to the three experimental groups: venom only (group 1), venom and 40 microg anti-TNF antibodies (group 2), venom and 250 microg soluble TNF receptor (p55-R; group 3). Hemodynamic parameters were monitored up to 4 h following venom injection.

MEASUREMENTS AND RESULTS

A significant hemodynamic deterioration (reduction in heart rate and blood pressure) occurred 30 min following venom injection in group 1 compared to groups 2 and 3, where hemodynamic parameters remained stable throughout the 4 h observation period. Serum levels of TNF were detected 15 min after venom injection and peaked after 2 h at 485+/-12 pg/ml.

CONCLUSIONS

The hemodynamic consequences of intramuscular injection of V. aspis venom can be blunted in a rat by systemic antagonization of TNF activity prior to venom injection. The poisonous hemodynamic effects of the V. aspis venom might be caused by systemic release of TNF.

Snake venom proteinases as tools in hemostasis studies: structure-function relationship of a plasminogen activator purified from Trimeresurus stejnegeri venom

Snake venom serine proteinases affect many steps of the blood coagulation cascade. Each of them usually acts selectively on one coagulation factor. They are therefore potentially useful components to study the mechanisms of action, the regulation and the structure-function relationships of human serine proteinase coagulation factors. This strategy is illustrated for a plasminogen activator purified from Trimeresurus stejnegeri venom.

Anticoagulant venom and mammalian secreted phospholipases A(2): protein- versus phospholipid-dependent mechanism of action

Some venom and mammalian-secreted phospholipases A(2) (sPLA(2)) have been described to exert an anticoagulant effect. This review will discuss and compare phospholipid-dependent versus protein-dependent mechanisms of action of these sPLA(2) on the coagulation cascade. The importance of venom proteins, and of the study of their pharmacological effects, to explore the physiological functions of homologous mammalian proteins is also pointed out.

Dual effect of high electric field in capillary electrophoresis study of the conformational stability of Bungarus fasciatus acetylcholinesterase

The effect of high electric field in capillary zone electrophoresis (CZE) was evaluated for the study of the thermally induced unfolding of Bungarus fasciatus acetylcholinesterase. This monomer enzyme is characterised by two interdependent uncommon structural features, the asymmetrical distribution of charged residues and a relatively low thermal denaturation temperature. Both traits were presumed to interfere in the thermal unfolding of this enzyme as investigated by CZE. This paper analyses the effect of high electric field on the behaviour of the enzyme native state. It is shown that increasing the applied field causes denaturation-like transition of the enzyme at a current power which does not induce excessive Joule heating in the capillary. The susceptibility to electric field of proteins like cholinesterases, with charge distribution anisotropy, large permanent dipole moment and notable molecular flexibility associated with moderate thermal stability, was subsequently discussed.

Thermal stability of acetylcholinesterase from Bungarus fasciatus venom as investigated by capillary electrophoresis

Previous studies on the conformation of the monomeric acetylcholinesterase (AChE) from the krait (Bungarus fasciatus) venom showed that the protein possesses a large permanent dipole moment. These studies predicted that thermal irreversible denaturation must occur via partially unfolded states. The thermal stability of Bungarus AChE was determined using capillary electrophoresis (CE) with optimized conditions. Runs performed at convenient temperature scanning rates provided evidence for an irreversible denaturation process according to the Lumry and Eyring model. The mid-transition temperature, T(m), and the effective enthalpy change, DeltaH(m) were determined at different pH. The temperature dependence of the free energy, DeltaG, of Bungarus AChE unfolding was drawn using values of T(m), DeltaH(m) and DeltaC(p) determined by CE. The thermodynamic parameters for the thermal denaturation of the monomeric snake enzyme were compared with those of different dimeric and tetrameric ChEs. It was shown that the changes in the ratio of DeltaH(cal/)DeltaH(vH) and DeltaC(p) reflect the oligomerization state of these proteins. All these results indicate that wild-type monomeric Bungarus AChE is a stable enzyme under standard conditions. However, designed mutants of this enzyme capable of degrading organophosphates have to be engineered to enhance their thermostability.

Coagulant and anticoagulant activities of Bothrops lanceolatus (Fer de lance) venom

Bothrops lanceolatus venom contains caseinolytic, phospholipase, esterase and haemorrhagic activities. We have investigated the coagulant and anticoagulant actions of B. lanceolatus venom on human citrated plasma and on purified plasma components. Although B. lanceolatus venom up to 50 microg/ml was unable to clot citrated plasma, at concentrations > or = 5 microg/ml the venom dose-dependently clotted purified human fibrinogen, indicating the presence of a thrombin-like enzyme. Human plasma (final concentration > or = 12.5%) dose-dependently inhibited the venom-induced fibrinogen clotting. This finding suggested that endogenous plasma protease inhibitors can affect the venom's action on fibrinogen. To investigate this possibility, B. lanceolatus venom was incubated with different plasma protease inhibitors and the activity on fibrinogen tested. alpha(2)-Macroglobulin and alpha(1)-antitrypsin did not interfere with the coagulant activity of the venom whereas the antithrombin-III/heparin complex partially inhibited this activity. A non-toxic, acidic phospholipase A(2) purified from B. lanceolatus venom prolonged the activated partial thromboplastin time in human plasma from 39.7+/-0.5 s (control with saline) to 60.2+/-0.9 s with 50 microg of PLA(2) (p<0.001), suggesting an anticoagulant activity associated with this enzyme. This anticoagulant activity may account for some of the effects of the venom on blood coagulation.

Interaction of linker for activation of T cells with multiple adapter proteins in platelets activated by the glycoprotein VI-selective ligand, convulxin

The snake venom toxin convulxin activates platelets through the collagen receptor glycoprotein VI (GPVI)/Fc receptor gamma-chain (FcR gamma-chain) complex leading to tyrosine phosphorylation and activation of the tyrosine Syk and phospholipase Cgamma2 (PLCgamma2). In the present study, we demonstrate that convulxin is a considerably more powerful agonist than collagen or the GPVI-selective collagen-related peptide (CRP). Confirmation that the response to convulxin is mediated solely via Syk was provided by studies on Syk-deficient platelets. The increase in phosphorylation of the FcR gamma-chain is associated with marked increases in tyrosine phosphorylation of downstream proteins including Syk, linker for activation of T cells (LAT), SLP-76, and PLCgamma2. The transmembrane adapter LAT coprecipitates with SLP-76 and PLCgamma2, as well as with a number of other adapter proteins, some of which have not been previously described in platelets, including Cbl, Grb2, Gads, and SKAP-HOM. Gads is constitutively associated with SLP-76 and is probably the protein bridging its association with LAT. There was no detectable association between Grb2 and SLP-76 in control or stimulated cells, suggesting that the interaction of LAT with Grb2 is present in a separate complex to that of LAT-Gads-SLP-76. These results show that the trimeric convulxin stimulates a much greater phosphorylation of the FcR gamma-chain and subsequent downstream responses relative to CRP and collagen, presumably because of its ability to cause a greater degree of cross-linking of GPVI. The adapter LAT appears to play a critical role in recruiting a number of other adapter proteins to the surface membrane in response to activation of GPVI, presumably at sites of glycolipid-enriched microdomains, enabling an organized signaling cascade that leads to platelet activation.

Expression of the collagen receptor glycoprotein VI during megakaryocyte differentiation

This study examined the expression of the platelet collagen receptor glycoprotein VI (GPVI) in megakaryocyte cell lines and primary megakaryocytes by reverse transcriptase-polymerase chain reaction and by flow cytometry and ligand blotting using the snake venom toxin convulxin. Expression of GPVI is increased in the megakaryoblastic cell lines HEL and CMK on differentiation with the phorbol ester phorbol 12-myristate 13-acetate (PMA), along with the Fc receptor gamma-chain (FcR gamma-chain). The increase in GPVI expression is associated with marked potentiation of tyrosine phosphorylation and Ca(++) elevation in response to convulxin. Syk, linker for activated T cells, and phospholipase C gamma 2 (PLC gamma 2) are among the proteins tyrosine phosphorylated on convulxin stimulation in PMA-differentiated HEL cells. Studies on primary murine megakaryocytes grown in vitro confirmed that GPVI is up-regulated in parallel with functional activation, assessed by measurement of [Ca(++)](i), during differentiation. The results demonstrate that expression of GPVI is up-regulated along with the FcR gamma-chain during differentiation of megakaryocytes. (Blood. 2000;96:2740-2745)

Collagen, convulxin, and thrombin stimulate aggregation-independent tyrosine phosphorylation of CD31 in platelets. Evidence for the involvement of Src family kinases

Platelet endothelial cell adhesion molecule-1 (CD31) is a 130-kDa glycoprotein receptor present on the surface of platelets, neutrophils, monocytes, certain T-lymphocytes, and vascular endothelial cells. CD31 is involved in adhesion and signal transduction and is implicated in the regulation of a number of cellular processes. These include transendothelial migration of leukocytes, integrin regulation, and T-cell function, although its function in platelets remains unclear. In this study, we demonstrate the ability of the platelet agonists collagen, convulxin, and thrombin to induce tyrosine phosphorylation of CD31. Furthermore, we show that this event is independent of platelet aggregation and secretion and is accompanied by an increase in surface expression of CD31. A kinase capable of phosphorylating CD31 was detected in CD31 immunoprecipitates, and its activity was increased following activation of platelets. CD31 tyrosine phosphorylation was reduced or abolished by the Src family kinase inhibitor PP2, suggesting a role for these enzymes. In accordance with this, each of the Src family members expressed in platelets, namely Fyn, Lyn, Src, Yes, and Hck, was shown to co-immunoprecipitate with CD31. The involvement of Src family kinases in this process was confirmed through the study of mouse platelets deficient in Fyn.

Snake venom proteins acting on hemostasis

The venoms of Viperidae and Crotalidae snakes are a rich source of proteins with activity against various factors involved in coagulation and fibrinolysis. These proteins are very specific for their molecular targets, resistant to physiological inhibitors and stable in vitro and in vivo. They have therefore proved to be useful for diagnostic tests. Based on sequence similarities, these snake venom proteins have been classified into various families, such as serine proteinases, metalloproteinases, C-type lectins, disintegrins and phospholipases A(2). The various members of a given family, although structurally similar, act selectively on different blood coagulation factors. This opens up the possibility of characterizing the structural elements involved in target molecule recognition. Thus, snake venom proteins provide excellent models for studies of structure-function relationships.