Application of the Cellular Thermal Shift Assay (CETSA) to validate drug target engagement in platelets

Small molecule drugs play a major role in the study of human platelets. Effective action of a drug requires it to bind to one or more targets within the platelet (target engagement). However, although in vitro assays with isolated proteins can be used to determine drug affinity to these targets, additional factors affect target engagement and its consequences in an intact platelet, including plasma membrane permeability, intracellular metabolism or compartmentalization, and level of target expression. Mechanistic interpretation of the effect of drugs on platelet activity requires comprehensive investigation of drug binding in the proper cellular context, i.e. in intact platelets. The Cellular Thermal Shift Assay (CETSA) is a valuable method to investigate target engagement within complex cellular environments. The assay is based on the principle that drug binding to a target protein increases that protein's thermal stability. In this technical report, we describe the application of CETSA to platelets. We highlight CETSA as a quick and informative technique for confirming the direct binding of drugs to platelet protein targets, providing a platform for understanding the mechanism of action of drugs in platelets, and which will be a valuable tool for investigating platelet signaling and function.

Utilizing orthodontic appliances to retain and disguise a pediatric maxillary obturator throughout growth

Unique challenges are encountered when providing an obturator for an adolescent patient. Challenges include the need to modify the obturator throughout growth, engaging the mixed dentition or partially erupted teeth with minimal undercuts, the psychosocial challenges of an actively maturing patient, and the possible need for coincidental orthodontic therapy. This clinical report describes the ongoing rehabilitation of a patient who presented at the age of 10 with a biopsy-confirmed palatal mucoepidermoid carcinoma. Incorporating orthodontic brackets for retention of innovative adjustable obturator clasps allowed for the favorable function of the obturator prosthesis and the ability to alter the prosthesis over time.

Human soluble CD39 displays substrate inhibition in a substrate-specific manner

CD39 (ectonucleoside triphosphate diphosphohydrolase-1; ENTPD1) metabolizes extracellular ATP and ADP to AMP. AMP is subsequently metabolized by CD79 to adenosine. CD39 activity is therefore a key regulator of purinergic signalling in cancer, thrombosis, and autoimmune diseases. In this study we demonstrate that soluble, recombinant CD39 shows substrate inhibition with ADP or ATP as the substrate. Although CD39 activity initially increased with increasing substrate concentration, at high concentrations of ATP or ADP, CD39 activity was markedly reduced. Although the reaction product, AMP, inhibits CD39 activity, insufficient AMP was generated under our conditions to account for the substrate inhibition seen. In contrast, inhibition was not seen with UDP or UTP as substrates. 2-methylthio-ADP also showed no substrate inhibition, indicating the nucleotide base is an important determinant of substrate inhibition. Molecular dynamics simulations revealed that ADP can undergo conformational rearrangements within the CD39 active site that were not seen with UDP or 2-methylthio-ADP. Appreciating the existence of substrate inhibition of CD39 will help the interpretation of studies of CD39 activity, including investigations into drugs that modulate CD39 activity.

Accuracy of Digital Impressions at Varying Implant Depths: An In Vitro Study

PURPOSE

Implants placed at variable depths may vary the amount of visible scannable surface of a scan body. Intraoral scanner technology uses advanced optical principles to record the surface of the scan body to accurately capture the implant position. The purpose of this study is to investigate the effect implant placement depth has on the accuracy of digital implant impressions using an intraoral scanner.

MATERIALS AND METHODS

A partially edentulous gypsum master model was fabricated to allow the positioning of a single implant analog at different depths. Four groups were created based on the planned implant depths of 7, 6, 3, and 0 mm and corresponding visibility of the scan body at 2, 3, 6, and 9 mm. The model was digitized with a laboratory scanner for the reference scan and with an intraoral scanner to generate 15 test scans per group, with a total of 60 scans. The test scans were superimposed onto the reference scan using the best fit algorithm to analyze and measure the positional (dXYZ) and angular deviation (d⍬) of the scan body using three-dimensional metrology software. Statistical analysis was performed using a one-way ANOVA and pairwise comparison was done with a Tukey-Kramer HSD test (α = 0.05).

RESULTS

The one-way ANOVA of the groups for the dXYZ and dθ parameters was statistically significant (F_3,56 = 11.45, p < 0.001, F_3,56 = 24.04, p < 0.001). Group D (9 mm) showed the least positional deviation at 38.41 μm (95% CI 30.26; 46.56) and the least angular deviation of 0.17° (95% CI 0.12; 0.21). Group A (2 mm) showed the greatest positional deviation of 77.17 μm (95% CI 65.23; 89.11) and greatest angular deviation of 0.84° (95% CI 0.65; 1.03). The positional and angular deviation increased with increased implant depth.

CONCLUSIONS

The accuracy of digital impressions is influenced by the implant depth and the amount of visibility of the scan body. The trueness and precision are highest when the implant is placed at 0 mm depth with complete visibility of the scan body and decreases with subgingival implant placement.

Platelet-Derived Extracellular Vesicles in Arterial Thrombosis

Blood platelets are necessary for normal haemostasis but also form life-threatening arterial thrombi when atherosclerotic plaques rupture. Activated platelets release many extracellular vesicles during thrombosis. Phosphatidylserine-exposing microparticles promote coagulation. Small exosomes released during granule secretion deliver cargoes including microRNAs to cells throughout the cardiovascular system. Here, we discuss the mechanisms by which platelets release these extracellular vesicles, together with the possibility of inhibiting this release as an antithrombotic strategy.

Endothelial inflammation and neutrophil transmigration are modulated by extracellular matrix composition in an inflammation-on-a-chip model

Inflammatory diseases are often characterised by excessive neutrophil infiltration from the blood stream to the site of inflammation, which damages healthy tissue and prevents resolution of inflammation. Development of anti-inflammatory drugs is hindered by lack of in vitro and in vivo models which accurately represent the disease microenvironment. In this study, we used the OrganoPlate to develop a humanized 3D in vitro inflammation-on-a-chip model to recapitulate neutrophil transmigration across the endothelium and subsequent migration through the extracellular matrix (ECM). Human umbilical vein endothelial cells formed confluent vessels against collagen I and geltrex mix, a mix of basement membrane extract and collagen I. TNF-α-stimulation of vessels upregulated inflammatory cytokine expression and promoted neutrophil transmigration. Intriguingly, major differences were found depending on the composition of the ECM. Neutrophils transmigrated in higher number and further in geltrex mix than collagen I, and did not require an N-formyl-methionyl-leucyl-phenylalanine (fMLP) gradient for transmigration. Inhibition of neutrophil proteases inhibited neutrophil transmigration on geltrex mix, but not collagen I. These findings highlight the important role of the ECM in determining cell phenotype and response to inhibitors. Future work could adapt the ECM composition for individual diseases, producing accurate models for drug development.

Q94 is not a selective modulator of proteinase-activated receptor 1 (PAR1) in platelets

Thrombin is a potent platelet activator, acting through proteinase-activated receptors -1 and -4 (PAR1 and PAR4). Of these, PAR-1 is activated more rapidly and by lower thrombin concentrations. Consequently, PAR-1 has been extensively investigated as a target for anti-platelet drugs to prevent myocardial infarction. Q94 has been reported to act as an allosteric modulator of PAR1, potently and selectively inhibiting PAR1-Gαq coupling in multiple cell lines, but its effects on human platelet activation have not been previously studied. Platelet Ca²⁺ signaling, integrin α_IIbβ₃ activation and α-granule secretion were monitored following stimulation by a PAR1-activating peptide (PAR1-AP). Although Q94 inhibited these responses, its potency was low compared to other PAR1 antagonists. In addition, α_IIbβ₃ activation and α-granule secretion in response to other platelet activators were also inhibited with similar potency. Finally, in endothelial cells, Q94 did not inhibit PAR1-dependent Ca²⁺ signaling. Our data suggest that Q94 may have PAR1-independent off-target effects in platelets, precluding its use as a selective PAR1 allosteric modulator.

Maintaining flippase activity in procoagulant platelets is a novel approach to reducing thrombin generation

BACKGROUND

During thrombosis, procoagulant platelets expose phosphatidylserine (PS), which enhances local thrombin generation. Reducing platelet PS exposure could be a novel anti-thrombotic approach. PS is confined to the inner leaflet of the plasma membrane in unstimulated platelets by ATP-dependent "flippase" activity. Ca2+ ionophores trigger all platelets to expose a high level of PS by activating a scramblase protein and inactivating the flippase. Although R5421 was previously shown to reduce Ca2+ ionophore-induced PS exposure, its mechanism of action is unknown.

OBJECTIVES

To determine the mechanism by which R5421 reduces platelet PS exposure.

METHODS

Washed human platelets were stimulated with the Ca2+ ionophore, A23187, to induce procoagulant platelet formation while bypassing proximal receptor signalling. Platelets PS exposure was detected using annexin V or lactadherin in flow cytometry. NBD (7-nitro-2-1,3-benzoxadiazol-4-yl)-PS was used to assess scramblase and flippase activity. Thrombin generation was monitored using a fluorogenic substrate.

RESULTS AND CONCLUSIONS

R5421 reduced the extent of A23187-stimulated platelet PS exposure, as demonstrated with annexin V or lactadherin binding. R5421 also maintained flippase activity in procoagulant platelets. Although R5421 appeared to inhibit scramblase activity in procoagulant platelets, it did not once the flippase had been inhibited, demonstrating that scramblase activity is not directly inhibited. Furthermore, R5421 inhibited the contribution of A23187-stimulated platelets to thrombin generation. Together these data demonstrate that R5421 reduces the extent of PS exposure in procoagulant platelets by maintaining flippase activity. Maintaining flippase activity in procoagulant platelets is a novel and effective approach to reducing thrombin generation.

Protease-activated receptor antagonists prevent thrombosis when dual antiplatelet therapy is insufficient in an occlusive thrombosis microfluidic model

Background

Platelet activation and arterial thrombosis on a ruptured atherosclerotic plaque is a major cause of myocardial infarction. Dual antiplatelet therapy (DAPT), the combination of platelet aggregation inhibitors, aspirin and a P2Y12 antagonist, is used to prevent arterial thrombosis. However, many people continue to have arterial thrombosis and myocardial infarction despite DAPT, indicating that additional therapies are required where DAPT is insufficient.

Objectives

To determine whether antagonists of protease-activated receptors (PARs) can prevent occlusive thrombosis under conditions where DAPT is insufficient.

Methods

We used human whole blood in a microfluidic model of occlusive thrombosis to compare conditions under which DAPT is effective to those under which DAPT was not. Cangrelor (a P2Y12 antagonist) and aspirin were used to mimic DAPT. We then investigated whether the PAR1 antagonist vorapaxar or the PAR4 antagonist BMS 986120, alone or in combination with DAPT, prevented occlusive thrombosis.

Results and Conclusions

A ruptured plaque exposes collagen fibers and is often rich in tissue factor, triggering activation of platelets and coagulation. Occlusive thrombi formed on type I collagen in the presence or absence of tissue factor (TF). However, although DAPT prevented occlusive thrombosis in the absence of TF, DAPT had little effect when TF was also present. Under these conditions, PAR antagonism was also ineffective. However, occlusive thrombosis was prevented by combining DAPT with PAR antagonism. These data demonstrate that PAR antagonists may be a useful addition to DAPT in some patients and further demonstrate the utility of in vitro models of occlusive thrombosis.

Epigenetic Regulation of F2RL3 Associates With Myocardial Infarction and Platelet Function

BACKGROUND

DNA hypomethylation at the F2RL3 (F2R like thrombin or trypsin receptor 3) locus has been associated with both smoking and atherosclerotic cardiovascular disease; whether these smoking-related associations form a pathway to disease is unknown. F2RL3 encodes protease-activated receptor 4, a potent thrombin receptor expressed on platelets. Given the role of thrombin in platelet activation and the role of thrombus formation in myocardial infarction, alterations to this biological pathway could be important for ischemic cardiovascular disease.

METHODS

We conducted multiple independent experiments to assess whether DNA hypomethylation at F2RL3 in response to smoking is associated with risk of myocardial infarction via changes to platelet reactivity. Using cohort data (N=3205), we explored the relationship between smoking, DNA hypomethylation at F2RL3, and myocardial infarction. We compared platelet reactivity in individuals with low versus high DNA methylation at F2RL3 (N=41). We used an in vitro model to explore the biological response of F2RL3 to cigarette smoke extract. Finally, a series of reporter constructs were used to investigate how differential methylation could impact F2RL3 gene expression.

RESULTS

Observationally, DNA methylation at F2RL3 mediated an estimated 34% of the smoking effect on increased risk of myocardial infarction. An association between methylation group (low/high) and platelet reactivity was observed in response to PAR4 (protease-activated receptor 4) stimulation. In cells, cigarette smoke extract exposure was associated with a 4.9% to 9.3% reduction in DNA methylation at F2RL3 and a corresponding 1.7-(95% CI, 1.2-2.4, P=0.04) fold increase in F2RL3 mRNA. Results from reporter assays suggest the exon 2 region of F2RL3 may help control gene expression.

CONCLUSIONS

Smoking-induced epigenetic DNA hypomethylation at F2RL3 appears to increase PAR4 expression with potential downstream consequences for platelet reactivity. Combined evidence here not only identifies F2RL3 DNA methylation as a possible contributory pathway from smoking to cardiovascular disease risk but from any feature potentially influencing F2RL3 regulation in a similar manner.

An "occlusive thrombosis-on-a-chip" microfluidic device for investigating the effect of anti-thrombotic drugs

Cardiovascular disease remains one of the world's leading causes of death. Myocardial infarction (heart attack) is triggered by occlusion of coronary arteries by platelet-rich thrombi (clots). The development of new anti-platelet drugs to prevent myocardial infarction continues to be an active area of research and is dependent on accurately modelling the process of clot formation. Occlusive thrombi can be generated in vivo in a range of species, but these models are limited by variability and lack of relevance to human disease. Although in vitro models using human blood can overcome species-specific differences and improve translatability, many models do not generate occlusive thrombi. In those models that do achieve occlusion, time to occlusion is difficult to measure in an unbiased and objective manner. In this study we developed a simple and robust approach to determine occlusion time of a novel in vitro microfluidic assay. This highlighted the potential for occlusion to occur in thrombosis microfluidic devices through off-site coagulation, obscuring the effect of anti-platelet drugs. We therefore designed a novel occlusive thrombosis-on-a-chip microfluidic device that reliably generates occlusive thrombi at arterial shear rates by quenching downstream coagulation. We further validated our device and methods by using the approved anti-platelet drug, eptifibatide, recording a significant difference in the "time to occlude" in treated devices compared to control conditions. These results demonstrate that this device can be used to monitor the effect of antithrombotic drugs on time to occlude, and, for the first time, delivers this essential data in an unbiased and objective manner.

Epigallocatechin gallate inhibits release of extracellular vesicles from platelets without inhibiting phosphatidylserine exposure

Arterial thrombosis triggers myocardial infarction and is a leading cause of death worldwide. Procoagulant platelets, a subpopulation of activated platelets that expose phosphatidylserine (PS), promote coagulation and occlusive thrombosis. Procoagulant platelets may therefore be a therapeutic target. PS exposure in procoagulant platelets requires TMEM16F, a phospholipid scramblase. Epigallocatechin gallate (EGCG) has been reported to inhibit TMEM16F but this has been challenged. We investigated whether EGCG inhibits PS exposure in procoagulant platelets. PS exposure is often measured using fluorophore-conjugated annexin V. EGCG quenched annexin V-FITC fluorescence, which gives the appearance of inhibition of PS exposure. However, EGCG did not quench annexin V-APC fluorescence. Using this fluorophore, we show that EGCG does not inhibit annexin V binding to procoagulant platelets. We confirmed this by using NBD-labelled PS to monitor PS scrambling. EGCG did not quench NBD fluorescence and did not inhibit PS scrambling. Procoagulant platelets also release PS-exposing extracellular vesicles (EVs) that further propagate coagulation. Surprisingly, EGCG inhibited EV release. This inhibition required the gallate group of EGCG. In conclusion, EGCG does not inhibit PS exposure in procoagulant platelets but does inhibit the EV release. Future investigation of this inhibition may help us further understand how EVs are released by procoagulant platelets.

Dietary supplementation with rumen-protected capsicum during the transition period improves the metabolic status of dairy cows

In ruminants, it has been observed that capsicum oleoresin can alter insulin responses and that high-intensity artificial sweetener can increase glucose absorption from the small intestine. Because glucose metabolism and insulin responses are critical during early lactation, these supplements might have an effect on the metabolic status of dairy cows during the transition period. The objective of this experiment was to evaluate the effects of rumen-protected capsicum oleoresin fed alone or in combination with artificial sweetener during the transition period on lactational performance and susceptibility to subclinical ketosis in dairy cows. Fifteen primiparous and 30 multiparous Holstein cows (a total of 39 cows finished the study) were arranged in a randomized complete block design during d -21 to 60 relative to parturition. Cows within block were randomly assigned to one of the following treatments: no supplement (CON), supplementation with 100 mg of rumen-protected capsicum/cow per day (RPCap), or RPCap plus 2 g of high-intensity artificial sweetener/cow per day (RPCapS). For both the RPCap and RPCapS treatments, only rumen-protected capsicum was fed during the dry period. From d 8 to 11 of lactation, intake was limited to 70% of predicted dry matter intake to induce subclinical ketosis. Production variables were recorded daily, samples for milk composition were collected on wk 2, 4, 6, and 8, and blood samples were collected on wk -2, 1, 2, and 4 of the experiment for analysis of metabolic hormones and blood cell counts. Supplementation with rumen-protected capsicum increased serum insulin and decreased β-hydroxybutyrate concentrations precalving, indicating a decrease in lipolysis. During the lactation period, RPCap was associated with a trend for increased milk production and feed efficiency following the ketosis challenge. Supplementation with RPCapS appeared to negate the response to rumen-protected capsicum. All cows developed subclinical ketosis during the challenge, and this was not affected by treatment. We conclude that treatments did not decrease susceptibility to subclinical ketosis; however, dietary supplementation with rumen-protected capsicum was effective at improving energy status precalving and tended to increased milk production and feed efficiency. The mechanism underlying these responses is unclear.

Establishing an Analogue Based In Silico Pipeline in the Pursuit of Novel Inhibitory Scaffolds against the SARS Coronavirus 2 Papain-Like Protease

The ongoing coronavirus pandemic has been a burden on the worldwide population, with mass fatalities and devastating socioeconomic consequences. It has particularly drawn attention to the lack of approved small-molecule drugs to inhibit SARS coronaviruses. Importantly, lessons learned from the SARS outbreak of 2002-2004, caused by severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1), can be applied to current drug discovery ventures. SARS-CoV-1 and SARS-CoV-2 both possess two cysteine proteases, the main protease (Mpro) and the papain-like protease (PLpro), which play a significant role in facilitating viral replication, and are important drug targets. The non-covalent inhibitor, GRL-0617, which was found to inhibit replication of SARS-CoV-1, and more recently SARS-CoV-2, is the only PLpro inhibitor co-crystallised with the recently solved SARS-CoV-2 PLpro crystal structure. Therefore, the GRL-0617 structural template and pharmacophore features are instrumental in the design and development of more potent PLpro inhibitors. In this work, we conducted scaffold hopping using GRL-0617 as a reference to screen over 339,000 ligands in the chemical space using the ChemDiv, MayBridge, and Enamine screening libraries. Twenty-four distinct scaffolds with structural and electrostatic similarity to GRL-0617 were obtained. These proceeded to molecular docking against PLpro using the AutoDock tools. Of two compounds that showed the most favourable predicted binding affinities to the target site, as well as comparable protein-ligand interactions to GRL-0617, one was chosen for further analogue-based work. Twenty-seven analogues of this compound were further docked against the PLpro, which resulted in two additional hits with promising docking profiles. Our in silico pipeline consisted of an integrative four-step approach: (1) ligand-based virtual screening (scaffold-hopping), (2) molecular docking, (3) an analogue search, and, (4) evaluation of scaffold drug-likeness, to identify promising scaffolds and eliminate those with undesirable properties. Overall, we present four novel, and lipophilic, scaffolds obtained from an exhaustive search of diverse and uncharted regions of chemical space, which may be further explored in vitro through structure-activity relationship (SAR) studies in the search for more potent inhibitors. Furthermore, these scaffolds were predicted to have fewer off-target interactions than GRL-0617. Lastly, to our knowledge, this work contains the largest ligand-based virtual screen performed against GRL-0617.

Cytosolic and mitochondrial Ca2+ signaling in procoagulant platelets

Platelets are the major cellular contributor to arterial thrombosis. However, activated platelets form two distinct subpopulations during thrombosis. Pro-aggregatory platelets aggregate to form the main body of the thrombus. In contrast, procoagulant platelets expose phosphatidylserine on their outer surface and promote thrombin generation. This apparently all-or-nothing segregation into subpopulations indicates that, during activation, platelets commit to becoming procoagulant or pro-aggregatory. Although the signaling pathways that control this commitment are not understood, distinct cytosolic and mitochondrial Ca²⁺ signals in different subpopulations are likely to be central. In this review, we discuss how these Ca²⁺ signals control procoagulant platelet formation and whether this process can be targeted pharmacologically to prevent arterial thrombosis.

Novel Small-Molecule Scaffolds as Candidates against the SARS Coronavirus 2 Main Protease: A Fragment-Guided in Silico Approach

The ongoing pandemic caused by the novel coronavirus has been the greatest global health crisis since the Spanish flu pandemic of 1918. Thus far, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in over 1 million deaths, and there is no cure or vaccine to date. The recently solved crystal structure of the SARS-CoV-2 main protease has been a major focus for drug-discovery efforts. Here, we present a fragment-guided approach using ZINCPharmer, where 17 active fragments known to bind to the catalytic centre of the SARS-CoV-2 main protease (SARS-CoV-2 M^pro) were used as pharmacophore queries to search the ZINC databases of natural compounds and natural derivatives. This search yielded 134 hits that were then subjected to multiple rounds of in silico analyses, including blind and focused docking against the 3D structure of the main protease. We scrutinised the poses, scores, and protein-ligand interactions of 15 hits and selected 7. The scaffolds of the seven hits were structurally distinct from known inhibitor scaffolds, thus indicating scaffold novelty. Our work presents several novel scaffolds as potential candidates for experimental validation against SARS-CoV-2 M^pro.

Short communication: Short-term effect of 3-nitrooxypropanol on feed dry matter intake in lactating dairy cows

The objective of this study was to investigate the effect of 3-nitrooxypropanol (3-NOP), an enteric methane inhibitor under investigation, on short-term dry matter intake (DMI) in lactating dairy cows. Following a 1-wk adaptation period, 12 multiparous Holstein cows were fed a basal total mixed ration (TMR) containing increasing levels of 3-NOP during 5 consecutive, 6-d periods. The experiment was conducted in a tiestall barn. Feed bins were split in half by a solid divider, and cows simultaneously received the basal TMR supplemented with the following: (1) a placebo without 3-NOP or (2) 3-NOP included in the TMR at 30, 60, 90, or 120 mg/kg of feed dry matter (experimental periods 2, 3, 4, and 5, respectively). Cows received the control diet (basal TMR plus placebo premix) during experimental period 1. A premix containing ground corn grain, soybean oil, and dry molasses was used to incorporate 3-NOP in the ration. Cows were fed twice daily as follows: 60% of the daily feed allowance at 0800 h and 40% at 1800 h. Feed offered and refused was recorded at each feeding. During the morning feedings, each cow was offered either control or 3-NOP-treated TMR at 150% of her average intake during the previous 3 d. After collection of the evening refusals, cows received only the basal TMR without the premix until the next morning feeding. The test period for the short-term DMI data collection was defined from morning feeding to afternoon refusals collection during each day of each experimental period. Location (left or right) of the control and 3-NOP diets within a feed bin was switched every day during each period to avoid feed location bias. Dry matter intake of TMR during the test period was quadratically increased by 3-NOP compared with the control. Inclusion of 3-NOP at 120 mg/kg of feed dry matter resulted in decreased 10-h DMI compared with the lower 3-NOP doses, but was similar to the control. There was no effect of feed location (left or right) within feed bin on DMI. Data from this short-term study suggests that 3-NOP does not have a negative effect on DMI in lactating dairy cows.

High extracellular phosphate increases platelet polyphosphate content

Platelet-derived extracellular polyphosphate (PolyP) is a major mediator of thrombosis. PolyP is a linear chain of inorganic phosphate (P_i) and is stored in platelet dense granules. P_i enters cells from the extracellular fluid through phosphate transporters and may be stored as PolyP. Here we show that high extracellular P_i concentration in vitro increases platelet PolyP content, in a manner dependent on phosphate transporters, IP6K and V-type ATPases. The increased PolyP also enhanced PolyP-dependent coagulation in platelet-rich plasma. These data suggest a mechanistic link between hyperphosphatemia, PolyP and enhanced coagulation, which may be important in pathologies such as chronic kidney disease.

Dose-response effect of 3-nitrooxypropanol on enteric methane emissions in dairy cows

This experiment was designed to test the effect of inclusion rate of 3-nitrooxypropanol (3-NOP), a methane inhibitor, on enteric methane emissions in dairy cows. The study was conducted with 49 multiparous Holstein cows in a randomized complete block design in 2 phases; phase 1 was with 28 cows, and phase 2 with 21 cows. Cows were fed a basal total mixed ration ad libitum and were blocked based on days in milk, milk yield, and enteric methane emissions during a 14-d covariate period. Treatments were control (no 3-NOP) and 40, 60, 80, 100, 150, and 200 mg of 3-NOP/kg of feed dry matter. Following a 14-d adaptation period, enteric gaseous emissions (methane, carbon dioxide, and hydrogen) were measured using the GreenFeed system (C-Lock Inc., Rapid City, SD) over a 3-d period. Compared with the control, inclusion rate of 3-NOP quadratically decreased daily enteric methane emissions from 22 to 40%. Maximum mitigation effect was achieved with the 3 highest 3-NOP doses (with no statistical difference among 100, 150, and 200 mg/kg). The decrease in methane emission yield and emission intensity ranged from 16 to 36% and from 25 to 45%, respectively. Emissions of hydrogen quadratically increased 6- to 10-fold, compared with the control; the maximum increase was with 150 mg/kg 3-NOP. Treatment did not affect daily emissions of carbon dioxide, but a linear increase in carbon dioxide emission yield was observed with increasing 3-NOP doses. Dry matter intake and milk yield of the cows was not affected by 3-NOP. Milk fat concentration and yield were increased by 3-NOP due to increased concentration of de novo synthetized short-chain fatty acids in milk. Inclusion of 3-NOP also tended to increase milk urea nitrogen but had no other effects on milk components. In this short-term experiment, 3-NOP decreased enteric methane emissions without affecting dry matter intake or milk yield and increased milk fat in dairy cows. Maximum mitigation effect was achieved at 100 to 200 mg/kg of feed dry matter.

2-Aminoethoxydiphenylborate (2-APB) inhibits release of phosphatidylserine-exposing extracellular vesicles from platelets

Activated, procoagulant platelets shed phosphatidylserine (PS)-exposing extracellular vesicles (EVs) from their surface in a Ca2+- and calpain-dependent manner. These PS-exposing EVs are prothrombotic and proinflammatory and are found at elevated levels in many cardiovascular and metabolic diseases. How PS-exposing EVs are shed is not fully understood. A clearer understanding of this process may aid the development of drugs to selectively block their release. In this study we report that 2-aminoethoxydiphenylborate (2-APB) significantly inhibits the release of PS-exposing EVs from platelets stimulated with the Ca2+ ionophore, A23187, or the pore-forming toxin, streptolysin-O. Two analogues of 2-APB, diphenylboronic anhydride (DPBA) and 3-(diphenylphosphino)-1-propylamine (DP3A), inhibited PS-exposing EV release with similar potency. Although 2-APB and DPBA weakly inhibited platelet PS exposure and calpain activity, this was not seen with DP3A despite inhibiting PS-exposing EV release. These data suggest that there is a further target of 2-APB, independent of cytosolic Ca2+ signalling, PS exposure and calpain activity, that is required for PS-exposing EV release. DP3A is likely to inhibit the same target, without these other effects. Identifying the target of 2-APB, DPBA and DP3A may provide a new way to inhibit PS-exposing EV release from activated platelets and inhibit their contribution to thrombosis and inflammation.

Comparison of putative BH3 mimetics AT-101, HA14-1, sabutoclax and TW-37 with ABT-737 in platelets

Platelet lifespan is regulated by intrinsic apoptosis. Platelet apoptosis can be triggered by BH3 mimetics that inhibit the pro-survival Bcl-2 family protein, Bcl-xL. Here, we investigated several small molecules that are reported to act as BH3 mimetics and compared their effects to the well-established BH3 mimetic, ABT-737. Platelet phosphatidylserine (PS) exposure was determined by flow cytometry. Changes in cytosolic Ca²⁺ signaling were detected using Cal-520. Plasma membrane integrity was determined by calcein leakage. The roles of caspases and calpain in these processes were determined using Q-VD-OPh and calpeptin, respectively. As previously reported, ABT-737 triggered PS exposure in a caspase-dependent manner and calcein loss in a caspase and calpain-dependent manner. In contrast, AT-101 and sabutoclax triggered PS exposure independently of caspases. HA14-1 also triggered PS exposure in a caspase-independent but calpain-dependent manner. There were also significant differences in the pattern and protease-dependency of cytosolic Ca²⁺ signaling in response to these drugs compared to ABT-737. Since there are clear differences between the action of ABT-737 and the other putative BH3 mimetics investigated here, AT-101, HA14-1 and sabutoclax cannot be considered as acting as BH3 mimetics in platelets. Furthermore, the platelet death caused by these drugs is likely to be distinct from apoptosis.

Elevated intracellular cAMP concentration mediates growth suppression in glioma cells

Supressed levels of intracellular cAMP have been associated with malignancy. Thus, elevating cAMP through activation of adenylyl cyclase (AC) or by inhibition of phosphodiesterase (PDE) may be therapeutically beneficial. Here, we demonstrate that elevated cAMP levels suppress growth in C6 cells (a model of glioma) through treatment with forskolin, an AC activator, or a range of small molecule PDE inhibitors with differing selectivity profiles. Forskolin suppressed cell growth in a PKA-dependent manner by inducing a G₂/M phase cell cycle arrest. In contrast, trequinsin (a non-selective PDE2/3/7 inhibitor), not only inhibited cell growth via PKA, but also stimulated (independent of PKA) caspase-3/-7 and induced an aneuploidy phenotype. Interestingly, a cocktail of individual PDE 2,3,7 inhibitors suppressed cell growth in a manner analogous to forskolin but not trequinsin. Finally, we demonstrate that concomitant targeting of both AC and PDEs synergistically elevated intracellular cAMP levels thereby potentiating their antiproliferative actions.

Effects of ensiling time on corn silage neutral detergent fiber degradability and relationship between laboratory fiber analyses and in vivo digestibility

Accurate analysis of degradability of silage neutral detergent fiber (NDF) is important for diet formulation and to predict lactational performance of dairy cows. In this study, 5 corn silage hybrids ensiled for 0 (unfermented), 30, 60, 120, and 150 d were used to determine the effects of ensiling time on silage neutral detergent fiber degradability (NDFD) and to assess the relationships between near-infrared reflectance spectroscopy (NIR) NDF-related analyses and in situ NDFD variables. In addition, the relationships between dietary concentration of indigestible NDF, 288-h incubation (iNDF288), or undegraded NDF, 240-h incubation (uNDF240), and in vivo total-tract apparent organic matter and NDF digestibility were studied in total mixed ration samples from 16 experiments with lactating dairy cows. Ensiling time had no effect on silage NDF concentration; however, the ratio of acid detergent fiber ÷ NDF increased, and estimated hemicellulose concentration decreased quadratically with ensiling time. Also, concentration of NDF-bound protein decreased, and that of lignin increased linearly with ensiling time. These changes in silage fiber composition resulted in a linear decrease in in situ effective degradability of silage NDF with increasing ensiling time. The indigestible fraction of NDF and concentration of structural carbohydrates were not affected by ensiling time. Correlations of in situ NDFD variables with laboratory NIR NDFD analyses were weak to moderate. The relationship of corn silage uNDF240 with lignin concentration or 30-h NDFD (all NIR analyses) was remarkably good (R² = 0.73 and 0.88, respectively). The relationship between in situ iNDF288 concentration (but not uNDF240) and in vivo total-tract apparent digestibility of dietary organic matter and NDF was good (R² = 0.72 and 0.80, respectively). In conclusion, in situ degradability of silage NDF linearly decreased from 0 to 150 d ensiling time, primarily caused by a decrease in concentrations of hemicellulose and NDF-bound protein. In situ NDF degradability measurements and common laboratory NIR NDF-related analyses were generally poorly correlated. We found a good relationship between in vivo NDF digestibility and dietary concentration of iNDF288 determined in situ, but the relationship with uNDF240 was poor.

Effects of 3-nitrooxypropanol on rumen fermentation, lactational performance, and resumption of ovarian cyclicity in dairy cows

This study examined the effect of 3-nitrooxypropanol (3-NOP), a substance under investigation, on enteric methane (CH₄) emission, rumen fermentation, lactational performance, sensory properties of milk, and the resumption of ovarian cyclicity in early-lactation dairy cows. Fifty-six multi- and primiparous Holstein cows, including 8 that were rumen cannulated, were used in a 15-wk randomized complete block design experiment. Cows were blocked based on parity and previous lactation milk yield (MY) or predicted MY, and within each block were randomly assigned to one of 2 treatments: (1) control (CON), administered no 3-NOP, or (2) 3-NOP applied at 60 mg/kg of feed dry matter (3-NOP). Enteric CH₄ emission was measured during experimental wk 2, 6, 9, and 15, using the GreenFeed system. Dry matter intake (DMI) and MY data were collected daily throughout the experiment, and milk composition samples were collected 7 times during the experiment. Milk samples were collected from 14 to 60 (±2) d after calving, 3 d per week, and assayed for progesterone concentration to determine resumption of ovarian activity. Compared with CON, 3-NOP decreased daily CH₄ emission by 26%, CH₄ yield (CH₄ per kg of DMI) by 21%, and CH₄ emission intensity [CH₄ per kg of MY or energy-corrected milk (ECM)] by 25%. Enteric emission of carbon dioxide was decreased by 5%, and hydrogen emission was increased 48-fold by 3-NOP. Inclusion of 3-NOP decreased concentration of total volatile fatty acids (by 9.3%) and acetate but increased butyrate molar proportion, ethanol, and formate concentrations in ruminal fluid. Dry matter intake was lower for 3-NOP compared with CON, but DMI expressed as a percentage of body weight was not different between treatments. Treatment had no effect on milk and ECM, body weight change, or body condition score. Milk composition and milk fat and protein yields were not affected by treatment, except that concentrations of short-chain fatty acids in milk were increased by 3-NOP. Nutrient digestibility and blood metabolites and hormones were not affected by 3-NOP, except that insulin was decreased by 3-NOP. There was no effect of 3-NOP on postpartum resumption of ovarian activity, including days to first and second luteal phases, length of first and second luteal phases, and interval from first to second luteal phase. Sensory properties of milk from cows fed 3-NOP and cheese made from that milk were not affected by treatment. In this experiment, 3-NOP decreased daily enteric CH₄ emission, emission yield, and emission intensity, improved feed efficiency, and did not affect lactational performance or onset of ovarian activity in early-lactation dairy cows.

Production effects of feeding extruded soybean meal to early-lactation dairy cows

The objective of this experiment was to evaluate productive and reproductive effects of replacing solvent-extracted soybean meal (SSBM) with extruded soybean meal (ESBM) in a total mixed ration for early-lactation dairy cows. Thirty-four Holstein cows (12 primiparous and 22 multiparous) were used in a randomized complete block design experiment with 17 cows per treatment. Feeding was ad libitum for 5 to 10% refusals. A fresh-cow diet was fed the first 21 d in milk followed by a lactation diet from 22 to 60 d in milk. Milk and dry matter intake data were collected throughout the experiment, and samples were collected for blood chemistry and amino acid profile, nutrient digestibility, nitrogen utilization, and enteric methane emission using the GreenFeed system (C-Lock Inc., Rapid City, SD). Dry matter intake, milk yield, and feed efficiency were not different between SSBM and ESBM. Energy-corrected milk yield and efficiency were also not different between diets. Diet had no effect on milk composition, except that milk true protein yield was decreased by ESBM. Enteric methane emission, yield, and intensity were not different between SSBM and ESBM. Because of its greater fat content, ESBM triggered expected changes in milk fatty acid (FA) profile: decreased sum of C16, saturated, and odd- and branched-chain FA and increased sum of preformed FA, polyunsaturated, and trans FA. The ESBM diet increased or tended to increase some essential amino acids in plasma. In this study, ESBM did not affect dry matter intake and did not improve lactational performance or onset of ovarian function in early-lactation dairy cows, and it decreased milk protein yield, possibly due to greater unsaturated FA intake compared with SSBM.

Platelet P-selectin triggers rapid surface exposure of tissue factor in monocytes

Tissue factor (TF) plays a central role in haemostasis and thrombosis. Following vascular damage, vessel wall TF initiates the extrinsic coagulation cascade. TF can also be exposed by monocytes. Inflammatory or infectious stimuli trigger synthesis of new TF protein by monocytes over the course of hours. It has also been suggested that monocytes can expose TF within minutes when stimulated by activated platelets. Here, we have confirmed that monocytes rapidly expose TF in whole blood and further demonstrate that platelet P-selectin exposure is necessary and sufficient. Monocyte TF exposure increased within five minutes in response to platelet activation by PAR1-AP, PAR4-AP or CRP-XL. PAR1-AP did not trigger TF exposure on isolated monocytes unless platelets were also present. In whole blood, PAR1-AP-triggered TF exposure required P-selectin and PGSL-1. In isolated monocytes, although soluble recombinant P-selectin had no effect, P-selectin coupled to 2 µm beads triggered TF exposure. Cycloheximide did not affect rapid TF exposure, indicating that de novo protein synthesis was not required. These data show that P-selectin on activated platelets rapidly triggers TF exposure on monocytes. This may represent a mechanism by which platelets and monocytes rapidly contribute to intravascular coagulation.

ABT-737 Triggers Caspase-Dependent Inhibition of Platelet Procoagulant Extracellular Vesicle Release during Apoptosis and Secondary Necrosis In Vitro

Platelet lifespan is limited by activation of intrinsic apoptosis. Apoptotic platelets are rapidly cleared from the circulation in vivo. ABT-737 triggers platelet apoptosis and is a useful tool for studying this process. However, in vitro experiments lack clearance mechanisms for apoptotic platelets. To determine whether apoptotic platelets progress to secondary necrosis, apoptosis was triggered in human platelets with ABT-737, a BH3 mimetic. Platelet annexin V (AnV) binding, release of AnV⁺ extracellular vesicles (EVs), and loss of plasma membrane integrity were monitored by flow cytometry. ABT-737 triggered AnV binding, indicating phosphatidylserine exposure, release of AnV⁺ EVs, and a slow loss of plasma membrane integrity. The latter suggests that apoptotic platelets progress to secondary necrosis in vitro. These responses were dependent on caspase activation and Ca²⁺ entry. Surprisingly, although intracellular Ca²⁺ concentration increased, AnV⁺ EV release was not dependent on the Ca²⁺-dependent protease, calpain. On the contrary, ABT-737 downregulated the ability of the Ca²⁺ ionophore, A23187, to trigger calpain-dependent release of AnV⁺ EVs. This was dependent on caspase activity as, when caspases were inhibited, ABT-737 increased the ability of A23187 to trigger AnV⁺ EV release. These data suggest that apoptotic platelets progress to secondary necrosis unless they are cleared. This may affect the interpretation of ABT-737-triggered signaling in platelets in vitro. Ca²⁺-dependent AnV⁺ EV release is downregulated during apoptosis in a caspase-dependent manner, which may limit the potential consequences of secondary necrotic platelets.

Acceptance of flavored concentrate premixes by young ruminants following a short-term exposure

Three cafeteria feeding design experiments were conducted to test whether young ruminants have flavor preferences. Experiment 1 was with 11 Dorset × Suffolk weaned lambs of both sexes, aged 5 mo and averaging 47.5 (standard deviation = 5.8) kg of body weight. The lambs were offered a choice of 5 flavored concentrate premixes (FCP) and an unflavored control for 5 min 4 times over 10 d. The FCP were prepared by mixing 200 to 300 g/t (as-is basis) of synthetic flavors (vanilla, milky, spicy/fenugreek, red summer fruits, and molasses) into a basal diet. The unflavored control and the milky flavor were consumed in greater amounts than all other flavors at 83.9 and 65.8 g/test, respectively. The consumption rate of FCP (g/min) was similar among treatments. Lambs spent more time consuming the milky flavor and the control at 123 and 144 s/test, respectively, compared with all other FCP (average of 65 s/test). In experiment 2, 12 weaned female Holstein Friesian calves (56-68 d of age) averaging 75.8 kg (standard deviation = 8.45) of body weight were offered a choice of 4 FCP (vanilla, milky, spicy/fenugreek, and red summer fruits) at an inclusion rate of 150 to 200 g/t (as-is basis) and the unflavored control for 5 min 4 times over 10 d. The average consumption rate was 27.8 g/min, and there were no differences among FCP. In experiment 3, a choice of 4 FCP with 2 different flavor combinations (vanilla-fenugreek and milky-vanilla) included at 75 g/t (as-is basis; low) or 150 g/t (high) was offered to a total of 12 weaned female Holstein Friesian calves (47-62 d of age) with an average body weight of 65.3 kg (standard deviation = 7.91). The FCP were offered daily for 14 d for 30 to 60 min/d. Vanilla-fenugreek (low) was consumed less at 57.5 g/test per calf compared with the other FCP (average of 87.5 g/test per calf). There were no other differences among FCP in experiment 3. Overall, compared with the control, flavors used in the present experiments did not affect feed intake of weaned lambs and calves. Other factors, such as taste, sight, texture of the feed, effect of the dams as previous experience (via maternal ingestion, which influences neonatal feeding), and their interactions, may also play a role in flavor preferences of young ruminants.

Rapid kinetics of changes in oxygen consumption rate in thrombin-stimulated platelets measured by high-resolution respirometry

Platelet activation plays a key role in normal haemostasis and pathological thrombosis. Platelet activation is rapid; within minutes of stimulation, platelets generate bioactive phospholipids, secrete their granule contents, activate integrins and aggregate together to form a haemostatic plug. These events are dependent on ATP synthesis. Mitochondrial function in platelets from healthy volunteers and patients with a range of diseases indicate an important role for oxygen consumption in oxidative phosphorylation in normal and pathological function. Platelets also consume oxygen during oxidation reactions, such as cyclooxygenase-dependent thromboxane A₂ synthesis. In this study, we used high-resolution respirometry to investigate rapid changes in oxygen consumption during platelet activation. We demonstrated a rapid, transient increase in oxygen consumption rate within minutes of platelet stimulation by the physiological activator, thrombin. This was partly inhibited by aspirin and by oligomycin. This shows that high resolution respirometry can provide information regarding rapid and dynamic changes in oxygen consumption during platelet activation.

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High resolution respirometry can be used to investigate the rapid kinetics of changes in platelet oxygen consumption rate.

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Thrombin triggers a rapid, transient increase in platelet oxygen consumption rate.

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Aspirin and oligomycin partially inhibit the increased oxygen consumption rate.

Lipid rafts are essential for release of phosphatidylserine-exposing extracellular vesicles from platelets

Platelets protect the vascular system during damage or inflammation, but platelet activation can result in pathological thrombosis. Activated platelets release a variety of extracellular vesicles (EVs). EVs shed from the plasma membrane often expose phosphatidylserine (PS). These EVs are pro-thrombotic and increased in number in many cardiovascular and metabolic diseases. The mechanisms by which PS-exposing EVs are shed from activated platelets are not well characterised. Cholesterol-rich lipid rafts provide a platform for coordinating signalling through receptors and Ca2+ channels in platelets. We show that cholesterol depletion with methyl-β-cyclodextrin or sequestration with filipin prevented the Ca2+-triggered release of PS-exposing EVs. Although calpain activity was required for release of PS-exposing, calpain-dependent cleavage of talin was not affected by cholesterol depletion. P2Y12 and TPα, receptors for ADP and thromboxane A2, respectively, have been reported to be in platelet lipid rafts. However, the P2Y12 antagonist, AR-C69931MX, or the cyclooxygenase inhibitor, aspirin, had no effect on A23187-induced release of PS-exposing EVs. Together, these data show that lipid rafts are required for release of PS-exposing EVs from platelets.

Cross-reactivity of anti-HMGB1 antibodies for HMGB2

HMGB1 and HMGB2 are DNA-interacting proteins but can also have extracellular actions during inflammation. Despite their relatively high homology, they may have distinct roles, making it essential to be able to differentiate between the two. Here we examine the specificity of five commercially-available anti-HMGB1 antibodies. By Western blotting of recombinant proteins and HMGB1−/− mouse embryonic fibroblasts, we identified only one HMGB1 antibody that, under our experimental conditions, did not also detect HMGB2. Selecting specific antibodies for HMGB1 and HMGB2 allowed identification of distinct HMGB1 and HMGB2 subcellular pools in primary neutrophils.

Auranofin, a thioredoxin reductase inhibitor, causes platelet death through calcium overload

Platelets are central to normal hemostasis and must be tightly controlled to prevent thrombosis. However, drug treatments that also affect platelets could lead to unwanted side effects on hemostasis or thrombosis. In this study, the effect of auranofin on platelets was tested. Auranofin, a gold-based thioredoxin reductase (TRXR) inhibitor, has been previously used in arthritis. Recently, auranofin and other inhibitors of the thioredoxin system have been proposed as novel anti-cancer therapies. TRXR is an important part of the antioxidant defenses in many cells that maintain intracellular proteins in their reduced state. TRXR activity in platelets could be completely inhibited by auranofin. Auranofin-treated platelets showed several features of cell death, including the inability to aggregate in response to thrombin, leakage of cytosolic lactate dehydrogenase, and surface exposure of procoagulant phosphatidylserine. Auranofin increased platelet reactive oxygen species production and intracellular calcium concentration. DTT, a sulfydyl reducing agent, and BAPTA-AM, which chelates intracellular calcium, prevented auranofin-induced phosphatidylserine exposure. These data suggest that TRXR is an important part of the platelet antioxidant defense. TRXR inhibition by auranofin triggers oxidative stress and disrupts intracellular calcium homeostasis, leading to platelet necrosis. The use of auranofin or other TRXR inhibitors could therefore lead to unwanted side effects.

Extracellular chloride is required for efficient platelet aggregation

Anion channels perform a diverse range of functions and have been implicated in ATP release, volume regulation, and phosphatidylserine exposure. Platelets have been shown to express several anion channels but their function is incompletely understood. Due to a paucity of specific pharmacological blockers, we investigated the effect of extracellular chloride substitution on platelet activation using aggregometry and flow cytometry. In the absence of extracellular chloride, we observed a modest reduction of the maximum aggregation response to thrombin or collagen-related peptide. However, the rate of aggregation was substantially reduced in a manner that was dependent on the extracellular chloride concentration and aggregation in the absence of chloride was noticeably biphasic, indicative of impaired secondary signaling. This was further investigated by targeting secondary agonists with aspirin and apyrase or by blockade of the ADP receptor P2Y12. Under these conditions, the rates of aggregation were comparable to those recorded in the absence of extracellular chloride. Finally, we assessed platelet granule release by flow cytometry and report a chloride-dependent element of alpha, but not dense, granule secretion. Taken together these data support a role for anion channels in the efficient induction of platelet activation, likely via enhancement of secondary signaling pathways.

Effect of high-oleic-acid soybeans on production performance, milk fatty acid composition, and enteric methane emission in dairy cows

The objective of this study was to investigate the effect of 3 soybean sources differing in fatty acid profile and processing method on productivity, milk composition, digestibility, rumen fermentation, and enteric methane emission in lactating dairy cows. The soybean sources were conventional, high-linoleic-acid variety extruded soybean meal (ESBM; 8.7% ether extract with 15% oleic and 54% linoleic acids); extruded Plenish (DuPont Pioneer, Johnston, IA), high-oleic-acid variety soybean meal (EPSBM; 8.4% ether extract with 73% oleic and 8% linoleic acids); and whole, heated Plenish soybeans (WPSB; 20.2% ether extract). The study involved 15 Holstein cows in a replicated 3 × 3 Latin square design experiment with three 28-d periods. The inclusion rate of the soybean sources in the diet was (dry matter basis) 17.1, 17.1, and 7.4% for ESBM, EPSBM, and WPSB, respectively, which resulted in ether extract concentration of the diets of 3.99, 3.94, and 4.18%, respectively. Compared with ESBM, the Plenish diets tended to increase dry matter intake and decreased feed efficiency (but had no effect on energy-corrected milk feed efficiency). The Plenish diets increased milk fat concentration on average by 5.6% and tended to increase milk fat yield, compared with ESBM. The WPSB diet tended to increased milk true protein compared with the extruded soybean meal diets. Treatments had no effect on rumen fermentation and enteric methane or carbon dioxide emissions, except pH was higher for WPSB versus EPSBM. The Plenish diets decreased the prevalence of Ruminococcus and increased that of Eubacterium and Treponema in whole ruminal contents. Total-tract apparent digestibility of organic matter and crude protein were decreased by WPSB compared with ESBM and EPSBM. Compared with the other treatments, urinary N excretion was increased by EPSBM and fecal N excretion was greater for WPSB. Treatments had marked effects on milk fatty acid profile. Generally, the Plenish diets increased mono-unsaturated (mostly cis-9 18:1) and decreased polyunsaturated, total trans-, and conjugated linoleic fatty acids concentrations in milk fat. In this study, compared with conventional, high-linoleic-acid variety extruded soybean meal, the Plenish soybean diets increased milk fat concentration and tended to increase fat yield, decreased feed efficiency, and modified milk fatty acid profile in a manner expected from the greater concentration of oleic acid in Plenish soybean oil.

Histidine deficiency has a negative effect on lactational performance of dairy cows

A 10-wk randomized complete block design experiment with 24 Holstein cows was conducted to investigate the long-term effects of feeding a His-deficient diet on lactational performance of dairy cows. Cows were blocked by days in milk, milk yield, and parity, and randomly assigned to 1 of the following 2 treatments: (1) His-adequate diet [HAD; providing +166 g/d over metabolizable protein (MP) requirements, according to the National Research Council (2001) and digestible His (dHis) supply of 68 g/d, or 2.5% of MP requirements] and (2) His-deficient diet (HDD; +37 g/d over MP requirements and dHis supply of 49 g/d, or 1.9% of MP requirements). Both HAD and HDD were supplemented with rumen-protected (RP) Met and Lys supplying digestible Met and digestible Lys at 2.4 and 2.4% and 7.2 and 7.1% of MP requirements, respectively. At the end of the 10-wk experiment, HDD was supplemented with RPHis (HDD+RPHis; total dHis supply of 61 g/d, or 2.4% of MP requirements) for an additional 9 d. Dry matter intake (DMI; 25.4 and 27.1 kg/d, standard error of the mean = 0.41), yields of milk (37.6 and 40.5 kg/d, standard error of the mean = 0.62), protein and lactose, energy-corrected milk, and milk and plasma urea-N were decreased by HDD compared with HAD. Feed and energy-corrected milk feed efficiencies, milk fat, protein and lactose concentrations, body weight, and body condition score of the cows were not affected by treatment. Apparent total-tract digestibility of dry and organic matter, crude protein, and neutral detergent fiber, and excretion of urinary N and urea-N were decreased by HDD compared with HAD. Concentration of plasma leptin tended to be decreased for HDD compared with HAD. Plasma concentrations of EAA (His, Leu, Lys, Val) and carnosine decreased and total EAA tended to be decreased in cows fed HDD compared with HAD. Muscle concentrations of free His, Leu, and Val decreased and Gly and β-alanine tended to be increased by HDD compared with HAD. Cows fed HDD had a lower blood hemoglobin concentration than cows fed HAD. At the end of the 10-wk study, the 9-d supplementation of HDD with RPHis (i.e., HDD+RPHis) increased DMI and plasma His, and tended to increase energy-corrected milk yield and plasma carnosine, compared with HDD. In conclusion, feeding a diet deficient in dHis supplying adequate MP, digestible Met, and digestible Lys affected negatively lactational performance of dairy cows. These results confirm our previous findings that low dietary His supply can impair DMI, yields of milk and milk protein, and blood hemoglobin in dairy cows.

Thioredoxin Inhibitors Attenuate Platelet Function and Thrombus Formation

Thioredoxin (Trx) is an oxidoreductase with important physiological function. Imbalances in the NADPH/thioredoxin reductase/thioredoxin system are associated with a number of pathologies, particularly cancer, and a number of clinical trials for thioredoxin and thioredoxin reductase inhibitors have been carried out or are underway. Due to the emerging role and importance of oxidoreductases for haemostasis and the current interest in developing inhibitors for clinical use, we thought it pertinent to assess whether inhibition of the NADPH/thioredoxin reductase/thioredoxin system affects platelet function and thrombosis. We used small molecule inhibitors of Trx (PMX 464 and PX-12) to determine whether Trx activity influences platelet function, as well as an unbiased proteomics approach to identify potential Trx substrates on the surface of platelets that might contribute to platelet reactivity and function. Using LC-MS/MS we found that PMX 464 and PX-12 affected the oxidation state of thiols in a number of cell surface proteins. Key surface receptors for platelet adhesion and activation were affected, including the collagen receptor GPVI and the von Willebrand factor receptor, GPIb. To experimentally validate these findings we assessed platelet function in the presence of PMX 464, PX-12, and rutin (a selective inhibitor of the related protein disulphide isomerase). In agreement with the proteomics data, small molecule inhibitors of thioredoxin selectively inhibited GPVI-mediated platelet activation, and attenuated ristocetin-induced GPIb-vWF-mediated platelet agglutination, thus validating the findings of the proteomics study. These data reveal a novel role for thioredoxin in regulating platelet reactivity via proteins required for early platelet responses at sites of vessel injury (GPVI and GPIb). This work also highlights a potential opportunity for repurposing of PMX 464 and PX-12 as antiplatelet agents.

Short communication: Preference for flavored concentrate premixes by dairy cows

Flavor preferences may be used to stimulate feed intake in dairy cows, which may improve use of robotic milking systems and increase feed intake of sick cows. A cafeteria-design experiment was used to determine if dairy cows have flavor preferences. Sixteen lactating Holstein cows averaging 197±32d in milk, 1.9±0.8 lactations, 27.8±4.2kg/d of dry matter intake, and 41.5±7.4kg/d of milk yield were involved in the experiment. Cows were offered 7 flavored concentrate premixes (FCP) and 1 control premix. The FCP flavors were anise, fenugreek, honey, orange, thyme, molasses, and vanilla; the absence of flavor, neutral, acted as a control. The inclusion rate of the flavors in FCP was 250 to 300g/t on an as-is basis. Cows were not adapted to the flavors before the experiment. Cows were housed in a tiestall barn and offered, on each day, 4 different FCP (1kg each) in plastic bins placed in front of each cow. The experiment lasted 6 consecutive days. Each FCP was presented to each cow once every 2d, 2h after the morning feeding. Flavors and position of the bins in front of the cows were randomized. As a result, each flavor was presented to each cow 3 times during the experiment, at 3 different bin locations. Each cow had access to the FCP for 5min from the time they started eating. Eating time and amount eaten were recorded. The vanilla and fenugreek FCP were consumed the most, at 408 and 371g/5-min offering, respectively, whereas the orange and anise FCP were consumed the least, at 264 and 239g/5-min offering, respectively. Similarly, cows spent the most time eating the vanilla and fenugreek FCP at 99 and 75 s/offering, respectively, and the least amount of time eating the orange and anise FCP at 49 and 50 s/offering, respectively. We detected an effect of bin position: the 2 center FCP were consumed more than the outer 2 FCP. Flavor had no effect on consumption rate. In conclusion, relative to the control, concentrate intake was not affected by flavor, but dairy cows may prefer vanilla or fenugreek flavors when offered a novel choice.

Effect of 3-nitrooxypropanol on methane and hydrogen emissions, methane isotopic signature, and ruminal fermentation in dairy cows

The objective of this crossover experiment was to investigate the effect of a methane inhibitor, 3-nitrooxypropanol (3NOP), on enteric methane emission, methane isotopic composition, and rumen fermentation and microbial profile in lactating dairy cows. The experiment involved 6 ruminally cannulated late-lactation Holstein cows assigned to 2 treatments: control and 3NOP (60 mg/kg of feed dry matter). Compared with the control, 3NOP decreased methane emission by 31% and increased hydrogen emission from undetectable to 1.33 g/d. Methane emissions per kilogram of dry matter intake and milk yield were also decreased 34% by 3NOP. Milk production and composition were not affected by 3NOP, except milk fat concentration was increased compared with the control. Concentrations of total VFA and propionate in ruminal fluid were not affected by treatment, but acetate concentration tended to be lower and acetate-to-propionate ratio was lower for 3NOP compared with the control. The 3NOP decreased the molar proportion of acetate and increase those of propionate, butyrate, valerate, and isovalerate. Deuterium-to-hydrogen ratios of methane and the abundance of (13)CH3D were similar between treatments. Compared with the control, minor (4‰) depletion in the (13)C/(12)C ratio was observed for 3NOP. Genus composition of methanogenic archaea (Methanobrevibacter, Methanosphaera, and Methanomicrobium) was not affected by 3NOP, but the proportion of methanogens in the total cell counts tended to be decreased by 3NOP. Prevotella spp., the predominant bacterial genus in ruminal contents in this experiment, was also not affected by 3NOP. Compared with the control, Ruminococcus and Clostridium spp. were decreased and Butyrivibrio spp. was increased by 3NOP. This experiment demonstrated that a substantial inhibition of enteric methane emission by 3NOP in dairy cows was accompanied with increased hydrogen emission and decreased acetate-to-propionate ratio; however, neither an effect on rumen archaeal community composition nor a significant change in the isotope composition of methane was observed.

Identification of roles for the SNARE-associated protein, SNAP29, in mouse platelets

Platelets are critical for maintaining vascular hemostasis, but also play a major role in the formation of occlusive cardiovascular and cerebrovascular thrombi under disease conditions. Secretion of platelet alpha and dense granules is a requirement for efficient thrombus formation. Understanding and targeting the mechanisms of secretion is important to aid the development of effective antithrombotics. SNAP29 is a tSNARE found in platelets, but whose role has not been defined. Using a platelet-specific SNAP29 knockout mouse model, we assessed the role of SNAP29 in platelet secretion and function under standardized conditions and also in in vitro and in vivo thrombosis. The data showed no major defects in SNAP29-null platelets, but revealed a minor defect in α-granule secretion and a significant increase in embolization rate of thrombi in vivo. These data suggest that SNAP29 contributes to the regulation of platelet α-granule secretion and thrombus stability, possibly partially masked by functional redundancy with other tSNAREs, such as SNAP23.

Leukemia-associated Rho guanine-nucleotide exchange factor is not critical for RhoA regulation, yet is important for platelet activation and thrombosis in mice

BACKGROUND

RhoA is an important regulator of platelet responses downstream of Gα13 , yet we still know little about its regulation in platelets. Leukemia-associated Rho guanine-nucleotide exchange factor (GEF [LARG]), a RhoA GEF, is highly expressed in platelets and may constitute a major upstream activator of RhoA. To this end, it is important to determine the role of LARG in platelet function and thrombosis.

METHODS AND RESULTS

Using a platelet-specific gene knockout, we show that the absence of LARG results in a marked reduction in aggregation and dense-granule secretion in response to the thromboxane mimetic U46619 and proteinase-activated receptor 4-activating peptide, AYPGKF, but not to adenosine diphosphate. In a ferric chloride thrombosis model in vivo, this translated into a defect, under mild injury conditions. Importantly, agonist-induced RhoA activation was not affected by the absence of LARG, although basal activity was reduced, suggesting that LARG may play a housekeeper role in regulating constitutive RhoA activity.

CONCLUSIONS

LARG plays an important role in platelet function and thrombosis in vivo. However, although LARG may have a role in regulating the resting activation state of RhoA, its role in regulating platelet function may principally be through RhoA-independent pathways, possibly through other Rho family members.

Loss of the insulin receptor in murine megakaryocytes/platelets causes thrombocytosis and alterations in IGF signalling

Aims

Patients with conditions that are associated with insulin resistance such as obesity, type 2 diabetes mellitus, and polycystic ovary syndrome have an increased risk of thrombosis and a concurrent hyperactive platelet phenotype. Our aim was to determine whether insulin resistance of megakaryocytes/platelets promotes platelet hyperactivation.

Methods and results

We generated a conditional mouse model where the insulin receptor (IR) was specifically knocked out in megakaryocytes/platelets and performed ex vivo platelet activation studies in wild-type (WT) and IR-deficient platelets by measuring aggregation, integrin α_IIbβ₃ activation, and dense and α-granule secretion. Deletion of IR resulted in an increase in platelet count and volume, and blocked the action of insulin on platelet signalling and function. Platelet aggregation, granule secretion, and integrin α_IIbβ₃ activation in response to the glycoprotein VI (GPVI) agonist collagen-related peptide (CRP) were significantly reduced in platelets lacking IR. This was accompanied by a reduction in the phosphorylation of effectors downstream of GPVI. Interestingly, loss of IR also resulted in a reduction in insulin-like growth factor-1 (IGF-1)- and insulin-like growth factor-2 (IGF-2)-mediated phosphorylation of IRS-1, Akt, and GSK3β and priming of CRP-mediated platelet activation. Pharmacological inhibition of IR and the IGF-1 receptor in WT platelets recapitulated the platelet phenotype of IR-deficient platelets.

Conclusions

Deletion of IR (i) increases platelet count and volume, (ii) does not cause platelet hyperactivity, and (iii) reduces GPVI-mediated platelet function and platelet priming by IGF-1 and IGF-2.

Syntaxin 8 regulates platelet dense granule secretion, aggregation, and thrombus stability

Platelet secretion not only drives thrombosis and hemostasis, but also mediates a variety of other physiological and pathological processes. The ubiquitous SNARE machinery and a number of accessory proteins have been implicated in regulating secretion in platelet. Although several platelet SNAREs have been identified, further members of the SNARE family may be needed to fine-tune platelet secretion. In this study we identified expression of the t-SNARE syntaxin 8 (STX8) (Qc SNARE) in mouse and human platelets. In mouse studies, whereas STX8 was not essential for α-granule or lysosome secretion, Stx8^−/− platelets showed a significant defect in dense granule secretion in response to thrombin and CRP. This was most pronounced at intermediate concentrations of agonists. They also showed an aggregation defect that could be rescued with exogenous ADP and increased embolization in Stx8^−/− mice in vivo consistent with an important autocrine and paracrine role for ADP in aggregation and thrombus stabilization. STX8 therefore specifically contributes to dense granule secretion and represents another member of a growing family of genes that play distinct roles in regulating granule release from platelets and thus platelet function in thrombosis and hemostasis.

SDF-1α is a novel autocrine activator of platelets operating through its receptor CXCR4

Platelets store and secrete the chemokine stromal cell-derived factor (SDF)-1α upon platelet activation, but the ability of platelet-derived SDF-1α to signal in an autocrine/paracrine manner mediating functional platelet responses relevant to thrombosis and haemostasis is unknown. We sought to explore the role of platelet-derived SDF-1α and its receptors, CXCR4 and CXCR7 in facilitating platelet activation and determine the mechanism facilitating SDF-1α-mediated regulation of platelet function. Using human washed platelets, CXCR4 inhibition, but not CXCR7 blockade significantly abrogated collagen-mediated platelet aggregation, dense granule secretion and thromboxane (Tx) A₂ production. Time-dependent release of SDF-1α from collagen-activated platelets supports a functional role for SDF-1α in this regard. Using an in vitro whole blood perfusion assay, collagen-induced thrombus formation was substantially reduced with CXCR4 inhibition. In washed platelets, recombinant SDF-1α in the range of 20–100 ng/mL^− 1 could significantly enhance platelet aggregation responses to a threshold concentration of collagen. These enhancements were completely dependent on CXCR4, but not CXCR7, which triggered TxA₂ production and dense granule secretion. Rises in cAMP were significantly blunted by SDF-1α, which could also enhance collagen-mediated Ca(2 +) mobilisation, both of which were mediated by CXCR4. This potentiating effect of SDF-1α primarily required TxA₂ signalling acting upstream of dense granule secretion, whereas blockade of ADP signalling could only partially attenuate SDF-1α-induced platelet activation. Therefore, this study supports a potentially novel autocrine/paracrine role for platelet-derived SDF-1α during thrombosis and haemostasis, through a predominantly TxA₂-dependent and ADP-independent pathway.

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Collagen-induced platelet aggregation, TxA₂ production and dense granule secretion require CXCR4 signalling.

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CXCR4 regulates platelet thrombus formation.

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SDF-1α-induced changes in cAMP and Ca(2 +) signalling require CXCR4.

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SDF-1α, via CXCR4, enhances platelet activation responses to collagen, primarily through a TxA₂-dependent and ADP-independent pathway.

Chloride channels are necessary for full platelet phosphatidylserine exposure and procoagulant activity

Platelets enhance thrombin generation at sites of vascular injury by exposing phosphatidylserine during necrosis-like cell death. Anoctamin 6 (Ano6) is required for Ca(2+)-dependent phosphatidylserine exposure and is defective in patients with Scott syndrome, a rare bleeding disorder. Ano6 may also form Cl(-) channels, though the role of Cl(-) fluxes in platelet procoagulant activity has not been explored. We found that Cl(-) channel blockers or removal of extracellular Cl(-) inhibited agonist-induced phosphatidylserine exposure. However, this was not due to direct inhibition of Ca(2+)-dependent scrambling since Ca(2+) ionophore-induced phosphatidylserine exposure was normal. This implies that the role of Ano6 in Ca(2+-)dependent PS exposure is likely to differ from any putative function of Ano6 as a Cl(-) channel. Instead, Cl(-) channel blockade inhibited agonist-induced Ca(2+) entry. Importantly, Cl(-) channel blockers also prevented agonist-induced membrane hyperpolarization, resulting in depolarization. We propose that Cl(-) entry through Cl(-) channels is required for this hyperpolarization, maintaining the driving force for Ca(2+) entry and triggering full phosphatidylserine exposure. This demonstrates a novel role for Cl(-) channels in controlling platelet death and procoagulant activity.

RhoG protein regulates platelet granule secretion and thrombus formation in mice

Rho GTPases such as Rac, RhoA, and Cdc42 are vital for normal platelet function, but the role of RhoG in platelets has not been studied. In other cells, RhoG orchestrates processes integral to platelet function, including actin cytoskeletal rearrangement and membrane trafficking. We therefore hypothesized that RhoG would play a critical role in platelets. Here, we show that RhoG is expressed in human and mouse platelets and is activated by both collagen-related peptide (CRP) and thrombin stimulation. We used RhoG(-/-) mice to study the function of RhoG in platelets. Integrin activation and aggregation were reduced in RhoG(-/-) platelets stimulated by CRP, but responses to thrombin were normal. The central defect in RhoG(-/-) platelets was reduced secretion from α-granules, dense granules, and lysosomes following CRP stimulation. The integrin activation and aggregation defects could be rescued by ADP co-stimulation, indicating that they are a consequence of diminished dense granule secretion. Defective dense granule secretion in RhoG(-/-) platelets limited recruitment of additional platelets to growing thrombi in flowing blood in vitro and translated into reduced thrombus formation in vivo. Interestingly, tail bleeding times were normal in RhoG(-/-) mice, suggesting that the functions of RhoG in platelets are particularly relevant to thrombotic disorders.