Determination of serotonin release from platelets by enzyme immunoassay in the diagnosis of heparin-induced thrombocytopenia

Engineering protein activity into off-the-shelf DNA devices

DNA-based devices are straightforward to design by virtue of their predictable folding, but they lack complex biological activity such as catalysis. Conversely, protein-based devices offer a myriad of functions but are much more difficult to design due to their complex folding. This study combines DNA and protein engineering to generate an enzyme that is activated by a DNA sequence of choice. A single protein switch, engineered from nanoluciferase using the alternate-frame-folding mechanism and herein called nLuc-AFF, is paired with different DNA technologies to create a biosensor for specific nucleic acid sequences, sensors for serotonin and ATP, and a two-input logic gate. nLuc-AFF is a genetically encoded, ratiometric, blue/green-luminescent biosensor whose output can be quantified by a phone camera. nLuc-AFF retains ratiometric readout in 100% serum, making it suitable for analyzing crude samples in low-resource settings. This approach can be applied to other proteins and enzymes to convert them into DNA-activated switches.

A reusable neurotransmitter aptasensor for the sensitive detection of serotonin

Serotonin is one of the important neurotransmitters in human nervous system and associated with central nervous system diseases. Herein, we have prepared a novel electrochemical aptasensor for rapid and sensitive detection of serotonin by using the pre-designed and prepared DNA aptamers. In the absence of serotonin, the electron transfer rate on the aptasensor was faster than that in the presence of serotonin due to the hairpin structure of the aptamer was loose and MB could be closer to the electrode surface. While in the presence of serotonin, the hairpin structure of the aptamer was extended and MB was far away from the electrode surface. The effect of MB labeled sites on analytical performances of the proposed aptasensors was discussed by comparing sensitivity of the aptasensors that MB labeled in the intermediate of the aptamer with that MB labeled at the 3' end of the aptamer. It was found that sensitivity of the intermediate-labeled aptasensor was much higher than the terminal-labeled aptasensor due to the specific conformational changes before and after aptamer binding to serotonin. The developed aptasensors exhibits a rapid electrochemical response and high sensitivity for the determination of serotonin. Under the optimal experimental conditions, the linear range for serotonin concentrations by the intermediate-labeled aptasensor was 1 pM-10 nM with a detection limit of 0.017 fM (S/N = 3). Moreover, the proposed aptasensor is reusable and shows good reproducibility and selectivity for the detection of serotonin in 100-fold diluted rat cerebrospinal fluid, suggesting a good application prospect in the detection of serotonin in real samples.

Development and validation of a liquid chromatography/tandem mass spectrometry method for the simultaneous quantification of serotonin and thromboxane B2 from activated platelets

INTRODUCTION

Availability of a rapid and reliable platelet activation assay avoiding limitations of current techniques would be valuable to diagnose heparin-induced thrombocytopenia and platelet secretion disorders.

OBJECTIVES

The first aim was to develop and validate an ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method to quantify in a single run TxB2 synthesized and serotonin released from platelets. The second aim was to use our method in association with light transmission aggregometry (LTA) to select good platelet responders for the diagnosis of HIT.

METHODS

Electrospray ionization and chromatographic separation were optimized for the simultaneous dosage of serotonin and TxB2. The method was validated according to the European Medicines Agency (EMA) guideline for bioanalytical method validation. LTA was performed with monoclonal anti-CD9 (clone ALB6) as platelet activator to select good responders.

RESULTS

Detection was performed using a tandem mass spectrometer with alternated positive and negative electrospray ionization. The total run time was 6 minutes. The method was validated for calibration curves, precision, accuracy, lower limit of quantification, carry-over, selectivity, and matrix effect. Platelet response to ALB6 was highly variable among donors.

CONCLUSION

We developed and validated a UHPLC-MS/MS method for the simultaneous quantification of TxB2 and serotonin.

Functional Assays in the Diagnosis of Heparin-Induced Thrombocytopenia: A Review

A rapid and accurate diagnosis in patients with suspected heparin-induced thrombocytopenia (HIT) is essential for patient management but remains challenging. Current HIT diagnosis ideally relies on a combination of clinical information, immunoassay and functional assay results. Platelet activation assays or functional assays detect HIT antibodies that are more clinically significant. Several functional assays have been developed and evaluated in the literature. They differ in the activation endpoint studied; the technique or technology used; the platelet donor selection; the platelet suspension (washed platelets, platelet rich plasma or whole blood); the patient sample (serum or plasma); and the heparin used (type and concentrations). Inconsistencies in controls performed and associated results interpretation are common. Thresholds and performances are determined differently among papers. Functional assays suffer from interlaboratory variability. This lack of standardization limits the evaluation and the accessibility of functional assays in laboratories. In the present article, we review all the current activation endpoints, techniques and methodologies of functional assays developed for HIT diagnosis.

Laboratory Diagnosis of Heparin-Induced Thrombocytopenia in Asian Indians as Investigated With Functional and Immunologic Methods

Heparin-induced thrombocytopenia (HIT) was looked for in 33 Indian patients undergoing cardiovascular surgery who received unfractionated heparin (UFH). Platelet counts were performed before the initiation of UFH therapy and 5 to 16 days after administration of the therapy. A decrease in patients' platelet count >35% of the baseline value or <100,000/μL was considered to be suggestive of HIT syndrome. Heparin-induced platelet aggregation (HIPA) and enzyme-linked immunosorbent assay (ELISA) tests were performed in all the patients to detect antibodies against heparin/PF4 complex. Thrombocytopenia was found to be present in 10 (30%) patients. Of these, two patients were found to be positive as detected by HIPA and ELISA tests. These two patients were considered to have classic HIT syndrome. One of these had bleeding while the other was asymptomatic. Among the 23 non-thrombocytopenic patients and controls, HIT antibodies were not detectable by HIPA test in all but absent by ELISA in only 21 of them. Two of 23 non-thrombocytopenic patients had positive results on the ELISA test. Because the latter had negative test results on HIPA, they were considered to be false-positive results. Thus, HIT syndrome develops in approximately 6% of Indian patients treated with UFH.

Heparin-induced thrombocytopenia

Abstract A summary of heparin-induced thrombocytopenia (HIT) is presented. HIT is an adverse drug reaction characterized by thrombocytopenia and a high risk for venous or arterial thrombosis. The frequency of HIT ranges from 1 to 5% of patients receiving heparin with exact frequencies ranging between specific agents. Interestingly, this immune-mediated syndrome is ironically associated with thrombosis, not bleeding, with thrombin formation playing a major role. It is caused by heparin-dependent, platelet-activating antibodies that identifies a self-protein, PF4, bound to heparin that results in an antibody formation. The resulting platelet activation is associated with increased thrombin generation. Typically, the platelet count fall begins 5-10 days after starting heparin, although a rapid platelet count fall can occur in a patient who has antibodies from recent heparin use. Typical causes of HIT as well as the best diagnostic studies and treatment are discussed in this review. HIT was reviewed using a pubmed™ search; google scholar™ using key words: "Heparin-induced thrombocytopenia"; "heparin", and "drug AND thrombocytopenia."

Quantification of luminally released serotonin in rat proximal colon by capillary electrophoresis with laser-induced fluorescence detection

Serotonin (5-hydroxytryptamine, 5-HT) plays vital roles in regulating gastrointestinal functions. Thus, the detection of 5-HT in the gastrointestinal tract is of great importance for biomedical research, medical diagnosis, and pharmaceutical therapy. This paper presents a simple, sensitive, and fast method for the quantification of luminally released serotonin in the feces and tissues of the rat proximal colon by means of capillary electrophoresis with laser-induced fluorescence detection. 5-Carboxyfluorescein N-succinimidyl ester was used for precolumn derivatization of serotonin. The optimal separation and detection conditions were obtained with an electrophoretic buffer containing 60 mM borate (pH 8.90) and an air-cooled argon-ion laser (excitation at 488 nm, emission at 520 nm). The serotonin concentrations in the feces and tissues of proximal colons were analyzed with this method, and the average values of serotonin in the feces samples were 1.951 +/- 0.446 ng/mg (male) and 2.095 +/- 0.533 ng/mg (female) and 1.397 +/- 0.267 ng/mg in rat proximal colon tissues. The results demonstrate that this method can accurately determine luminally released 5-HT in rats.

Severe heparin-induced thrombocytopenia: when the obvious is not obvious, a case report

Thrombocytopenia commonly occurs in hospitalized patients, particularly critically ill patients. We present an exemplifying case of severe heparin-induced thrombocytopenia (HIT) in an effort to solidify its high priority in the differential diagnosis of thrombocytopenia. A 75-year-old female underwent cardiac surgery with intraaortic balloon pump (IABP) placement. A platelet count drop to 25 x 10(9)/L by the third postoperative day was attributed to the IABP, which was removed. Her thrombocytopenia remained refractory to multiple platelet transfusions over several days. Right hand cyanosis then developed, attributed to a right radial arterial catheter, which was removed. All toes and fingers then showed severe ischemic changes. Ten days after the initial platelet count drop, a critical care specialist new to the treating team suspected HIT. Heparin exposure was stopped and argatroban was initiated. A HIT antibody test was subsequently strongly positive. The patients thrombocytopenia gradually resolved. No additional thromboses occurred during a 27-day intensive care unit stay. This case underscores the need for vigilance in suspecting HIT in patients with thrombocytopenia and recent heparin exposure. To avoid catastrophic outcomes in such patients, heparin should be stopped and alternative anticoagulation should be initiated, at least until HIT is excluded.

Interaction of 5-hydroxytryptamine (serotonin) against Aspergillus spp. in vitro

This study examined the direct interaction of serotonin (5-hydroxytryptamine (5-HT)) with Aspergillus species. Accumulation of 5-HT in aspergilli was investigated by immunofluorescence staining and laser confocal scanning microscopy. The influence of 5-HT on fungal ergosterol content, cell membrane integrity, fungal growth and hyphal elongation was determined. 5-HT was localised in the cytoplasm of Aspergillus spp., as 5-HT fluorescent signals appeared after 30min at 4 degrees C and in the presence of inhibitors of oxidative phosphorylation. 5-HT treatment of Aspergillus spp. significantly affected ergosterol synthesis, fungal cell membrane integrity and hyphal elongation (P<0.05). 5-HT treatment for 4h resulted in a lag of re-growth (post-antifungal effect). In conclusion, our findings suggest that 5-HT affects hyphal growth and diminishes fungal cell membrane integrity.

Heparin-induced thrombocytopenia (an overview)

Heparin induced thrombocytopenia is a serious side effect of a drug that is widely used in clinical practice. All patients exposed to heparin, administered by any route or at any dose, are at varying risk of developing HIT and its potentially devastating thrombotic complications. There are two clinical forms of HIT, type I and type II. Type I HIT, is a non-immunologic response, while type II HIT is an immunologic response to heparin therapy. Type I HIT is not associated with an increased risk of thrombosis and is characterized by reversible thrombocytopenia. Type II HIT occurs in approximately 1 to 3% of patients receiving unfractionated heparin. Type II HIT is more severe because of the increased risk of thrombotic events. Venous and arterial thromboembolic complications may lead to amputation, stroke, myocardial infarction, and death.

Age-related changes in serum melatonin in mice: higher levels of combined melatonin and 6-hydroxymelatonin sulfate in the cerebral cortex than serum, heart, liver and kidney tissues

Age-related changes in levels of melatonin and 6-hydroxymelatonin sulfate and effects of dietary melatonin on their levels in different tissues were determined in mice. Levels of melatonin were highest in the serum followed by liver, kidney, cerebral cortex and heart as measured by a quantitative and sensitive enzyme-labeled immunosorbent assay (ELISA). Serum melatonin levels decreased with age, and were reduced by 80% in 27-month old mice relative to 12-month old mice. Levels of 6-hydroxymelatonin sulfate were measured independently in various tissues. Levels of the melatonin metabolite, 6-hydroxymelatonin sulfate were significantly higher than free melatonin in all tissues tested. Levels of 6-hydroxymelatonin sulfate were highest in the cerebral cortex followed by the serum, heart, kidney, and liver. In 12-month old mice 6-hydroxymelatonin sulfate concentration was approximately 1000-fold greater than that of melatonin in the cerebral cortex, it was only 3-fold greater than melatonin levels in the serum. Thus only 0.1% of total melatonin in the brain was present in the free and unconjugated form but the corresponding value for serum was 27.4%. The cerebral cortex had the highest levels of combined melatonin and 6-hydroxymelatonin sulfate than other tissue tested in control mice. There was no significant change in 6-hydroxymelatonin sulfate levels between young and old mice. There was also no age-dependent change in levels of serotonin or cortisol in the serum samples. Dietary supplementation with melatonin resulted in a significant increase in levels of melatonin in the serum and all other tissue samples tested. Thus, any age-related decline of tissue melatonin can be reversed by supplementation with dietary melatonin.

Comparative effects of two synthetic oligosaccharides on platelet activation induced by plasma from HIT patients

Heparin-induced thrombocytopenia (HIT) is a serious secondary event encountered in the clinical use of heparin. HIT results from the consumption of platelets that are immunologically activated by antibodies directed against complexes formed by platelet factor 4 (PF4) and sulfated polysaccharides that activate platelet aggregation, leading to paradoxical, life-threatening thrombosis. There is strong evidence that the ability of heparin and related compounds to induce HIT is closely linked to the structure of the polysaccharide, and particularly to its negative charge and to the length of the molecule. To test this hypothesis, we synthesized two sulfated oligosaccharides: SanOrg123781, a 16-mer, presenting two terminal charged domains separated by a 7-mer neutral linker, and SR121903, a highly sulfated 17-mer. Both of them displayed strong anti-factor (F) Xa and anti-FIIa activities but their affinities for PF4 were markedly different. SR121903 displaced PF4-bound heparin, whereas SanOrg123781 did not, underlining the importance of the charge of the molecule for the interaction with PF4. Platelet studies, in the presence of HIT serum, showed that SR121903 induced the secretion of platelet-dense granules (measured by the release of serotonin) whereas SanOrg123781 did not, a result in accordance with an absence of affinity of this molecule for PF4. These results were confirmed by measurements of platelet activation by flow cytometry (measured by annexin V binding, CD62 detection and activation of the GpIIb-IIIa complexes). In conclusion, we have demonstrated the importance of the charge of the polysaccharides in the HIT-induced platelet reactions measured by diverse methods, of which some are described for this purpose for the first time.

Antifungal properties of 5-hydroxytryptamine (serotonin) against Candida species in vitro

In this study the minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) of 5-hydroxytryptamine (5 HT, serotonin) against clinical isolates of Candida albicans (n = 11), Candida glabrata (n = 9), Candida tropicalis (n = 10) and Candida parapsilosis (ATCC 22019) using a broth microdilution test were investigated. In addition, it was examined whether delayed regrowth as a post-antifungal effect results following short exposure to 5 HT. 5 HT showed antifungal activity towards all isolates of Candida spp. The isolates yielded comparable MIC and MFC values of 5 HT in the range 0.91-7.34 mM and 1.83-14.68 mM, respectively. A lag in regrowth was dependent on the concentration tested. Treatment for 3 h at concentrations of 5 HT below and equipotent to the MFC resulted in a delayed regrowth of 8-12 h for isolates of Candida spp. In conclusion, these in vitro studies clearly demonstrate antifungal effects of 5 HT. Identifying the mode of action could be of great help in developing and researching new antifungal drugs.

Development of a high-pressure liquid chromatography method for diagnosis of heparin-induced thrombocytopenia

Owing to the disadvantage of radioactivity of the carbon 14 serotonin release assay and the time-consuming procedure of the enzyme immunoassay, we developed a high-pressure liquid chromatography (HPLC) method to detect serotonin released from donor platelets in the presence of heparins and serum samples from patients with heparin-induced thrombocytopenia (HIT). Samples were analyzed from 60 healthy control subjects, 19 patients with HIT, and 20 patients without HIT after incubation with heparin, low-molecular-weight heparin (LMWH), and danaparoid. Serotonin release was measured from platelets, 300 x 10(3)/microL, by HPLC. Serotonin eluted as a single peak from the HPLC column. Serum samples from patients with HIT released 5.5 to 352.5 and 6.6 to 1,533.3 ng/mL of serotonin from platelets in the presence of 0.2 IU/mL of heparin and LMWH, respectively. In the presence of 0 IU/mL of heparin, LMWH, danaparoid, and control samples, less than 2.5 ng/mL of serotonin were released. The HPLC method permits a rapid, sensitive, and quantitative determination of serotonin released from donor platelets for laboratory confirmation of HIT.

Antifungal properties of 5-hydroxytryptamine (serotonin) against Aspergillus spp. in vitro

This study shows that 5-hydroxytrypatmine (5-HT, serotonin) is fungicidal towards conidia and hyphae of clinical isolates of Aspergillus (A.) fumigatus, A. flavus and A. terreus. The minimal fungicidal concentrations for Aspergillus conidia and hyphae ranged between 14.68 to 117.5 mM and 29.37 to 235 mM during 24 and 48 h of incubation. Several serotonin receptor antagonists (5-HT2, 5-HT3) studied in vitro did not influence antifungal activity.