Pharmacokinetics and pharmacodynamics of oral heparin solid dosage form in healthy human subjects

Current Understanding of Sodium N-(8-[2-Hydroxylbenzoyl] Amino) Caprylate (SNAC) as an Absorption Enhancer: The Oral Semaglutide Experience

Oral administration of peptide therapeutics faces challenges because of the distinct environment of the gastrointestinal tract. An oral formulation of semaglutide, a glucagon-like peptide 1 receptor agonist, was approved by the U.S. Food and Drug Administration in 2019 as a peptide therapy for the treatment of type 2 diabetes. Oral semaglutide uses sodium N-(8-[2-hydroxybenzoyl] amino) caprylate (SNAC) technology to enhance the absorption of semaglutide in the stomach and protect it from degradation by gastric enzymes. This article presents a summary of studies investigating SNAC technology as an absorption enhancer for a number of molecules and, in particular, explores how SNAC, once coformulated with oral semaglutide, facilitates increased absorption and bioavailability. Practical advice and dispensing information for pharmacists is also provided.

Efficacy and safety of oral semaglutide in type 2 diabetes mellitus: A systematic review and meta-analysis

OBJECTIVES

To investigate the efficacy and safety of oral semaglutide 7 and 14 mg, the only orally delivered glucagon-like peptide-1 (GLP-1) receptor agonist tablet approved for type 2 diabetes mellitus (T2DM) patients.

METHODS

Search several databases for randomized controlled trials (RCTs) of oral semaglutide in patients with T2DM from inception through May 31, 2021. The primary outcomes included change from baseline in hemoglobin A1c (HbA1c) and body weight. Risk ratios (RR), mean differences (MD), and 95% confidence intervals (CI) were calculated to evaluate the outcomes.

RESULTS

This meta-analysis included 11 RCTs with a total of 9821 patients. Compared with placebo, semaglutide 7 and 14 mg reduced HbA1c by 1.06% (95% CI, 0.81-1.30) and 1.10% (95% CI, 0.88-1.31), respectively. While in comparison with other antidiabetic agents, semaglutide 7 and 14 mg reduced HbA1c by 0.26% (95% CI, 0.15-0.38) and 0.38% (95%CI, 0.31-0.45). Both doses of semaglutide could significantly reduce body weight. Semaglutide 14 mg did increase the incidence of medication discontinuation and gastrointestinal events (nausea, vomiting and diarrhea).

CONCLUSION

Once-daily semaglutide 7 and 14 mg can significantly lowered HbA1c and body weight in patients with T2DM, and this effect increases with dose. Significantly, more gastrointestinal events occurred with semaglutide 14 mg.

Absolute pharmacokinetics of heparin in primates

Heparin is a commonly used anticoagulant drug, derived from the tissues of animals including pigs, cows, and sheep. Measuring heparin concentration in plasma is challenging due to its complex molecular structure. Existing methods rely on measuring heparin's anticoagulant activity, which provides pharmacodynamic (PD) data but not pharmacokinetic (PK) data, measuring concentration over time. To overcome this limitation, we used liquid chromatography-mass spectrometry (LC-MS) and the multiple reaction monitoring (MRM) method to directly measure heparin's concentration in non-human primates after administering porcine, bovine, and ovine heparin. A protocol was developed to enable an MRM method for application to small plasma volumes without purification. The PK data obtained from LC-MS are then compared with the data obtained using the Heparin Red assay and the PD data determined using biochemical clinical assays. Results showed that LC-MS and Heparin Red assay measurements closely correlated with unfractionated heparin's biological activities, supporting the use of mass spectra and dye-binding assays to determine heparin levels in plasma. This study builds a way for the measurement of heparin concentration in plasma, which could lead to an improved understanding of heparin's metabolism and dosing safety.

Gastrointestinal Permeation Enhancers for the Development of Oral Peptide Pharmaceuticals

Recently, two oral-administered peptide pharmaceuticals, semaglutide and octreotide, have been developed and are considered as a breakthrough in peptide and protein drug delivery system development. In 2019, the Food and Drug Administration (FDA) approved an oral dosage form of semaglutide developed by Novo Nordisk (Rybelsus^®) for the treatment of type 2 diabetes. Subsequently, the octreotide capsule (Mycapssa^®), developed through Chiasma's Transient Permeation Enhancer (TPE) technology, also received FDA approval in 2020 for the treatment of acromegaly. These two oral peptide products have been a significant success; however, a major obstacle to their oral delivery remains the poor permeability of peptides through the intestinal epithelium. Therefore, gastrointestinal permeation enhancers are of great relevance for the development of subsequent oral peptide products. Sodium salcaprozate (SNAC) and sodium caprylate (C8) have been used as gastrointestinal permeation enhancers for semaglutide and octreotide, respectively. Herein, we briefly review two approved products, Rybelsus^® and Mycapssa^®, and discuss the permeation properties of SNAC and medium chain fatty acids, sodium caprate (C10) and C8, focusing on Eligen technology using SNAC, TPE technology using C8, and gastrointestinal permeation enhancement technology (GIPET) using C10.

A new era for oral peptides: SNAC and the development of oral semaglutide for the treatment of type 2 diabetes

Glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1RAs) were first introduced for the treatment of type 2 diabetes (T2D) in 2005. Despite the high efficacy and other benefits of GLP-1RAs, their uptake was initially limited by the fact that they could only be administered by injection. Semaglutide is a human GLP-1 analog that has been shown to significantly improve glycemic control and reduce body weight, in addition to improving cardiovascular outcomes, in patients with T2D. First approved as a once-weekly subcutaneous injection, semaglutide was considered an ideal peptide candidate for oral delivery with a permeation enhancer on account of its low molecular weight, long half-life, and high potency. An oral formulation of semaglutide was therefore developed by co-formulating semaglutide with sodium N-(8-[2-hydroxybenzoyl]amino)caprylate, a well-characterized transcellular permeation enhancer, to produce the first orally administered GLP-1RA. Pharmacokinetic analysis showed that stable steady-state concentrations could be achieved with once-daily dosing owing to the long half-life of oral semaglutide. Upper gastrointestinal disease and renal and hepatic impairment did not affect the pharmacokinetic profile. In the phase III PIONEER clinical trial program, oral semaglutide was shown to reduce glycated hemoglobin and body weight compared with placebo and active comparators in patients with T2D, with no new safety signals reported. Cardiovascular efficacy and safety are currently being assessed in a dedicated outcomes trial. The development of an oral GLP-1RA represents a significant milestone in the management of T2D, providing an additional efficacious treatment option for patients.

Enoxaparin and Pentosan Polysulfate Bind to the SARS-CoV-2 Spike Protein and Human ACE2 Receptor, Inhibiting Vero Cell Infection

As with many other pathogens, SARS-CoV-2 cell infection is strongly dependent on the interaction of the virus-surface Spike protein with the glycosaminoglycans of target cells. The SARS-CoV-2 Spike glycoprotein was previously shown to interact with cell-surface-exposed heparan sulfate and heparin in vitro. With the aim of using Enoxaparin as a treatment for COVID-19 patients and as prophylaxis to prevent interpersonal viral transmission, we investigated GAG binding to the Spike full-length protein, as well as to its receptor binding domain (RBD) in solution by isothermal fluorescence titration. We found that Enoxaparin bound to both protein variants with similar affinities, compared to the natural GAG ligand heparan sulfate (with Kd-values in the range of 600–680 nM). Using size-defined Enoxaparin fragments, we discovered the optimum binding for dp6 or dp8 for the full-length Spike protein, whereas the RBD did not exhibit a significant chain-length-dependent affinity for heparin oligosaccharides. The soluble ACE2 receptor was found to interact with unfractionated GAGs in the low µM Kd range, but with size-defined heparins with clearly sub-µM Kd-values. Interestingly, the structural heparin analogue, pentosan polysulfate (PPS), exhibited high binding affinities to both Spike variants as well as to the ACE2 receptor. In viral infection experiments, Enoxaparin and PPS both showed a strong inhibition of infection in a concentration range of 50–500 µg/mL. Both compounds were found to retain their inhibitory effects at 500 µg/mL in a natural biomatrix-like human sputum. Our data suggest the early topical treatment of SARS-CoV-2 infections with inhaled Enoxaparin; some clinical studies in this direction are already ongoing, and they further imply an oral or nasal prophylactic inactivation of the virus by Enoxaparin or PPS for the prevention of inter-personal viral transmission.

Pharmacokinetics and Excretion Study of Lycium barbarum Polysaccharides in Rats by FITC-Fluorescence Labeling

A high-performance gel permeation chromatography fluorescence detection (HPGPC-FD) method combined with fluorescein isothiocyanate (FITC) labeling was established for the microanalysis of L. barbarum polysaccharides (LBP). The calibration curves linear over the range of 0.2–20 µg/mL in rat plasma, and 0.25–500 μg/mL in urine and feces samples with correlation coefficients greater than 0.99. The inter-day and intra-day precisions (RSD, %) of the method were under 15% with the relative recovery ranging from 84.6% to 104.0% and the RSD ranging from 0.47% to 7.28%. The concentration–time curve of LBP-FITC in plasma following intragastric administration at 100, 50 and 25 mg/kg well fitted to a nonlinear model. LBP-FITC slowly eliminated from plasma according to the long half-lives (t_1/2 = 31.39, 38.09, and 45.76 h, respectively) and mean retention times (MRT_0–t = 18.38, 19.15 and 20.07 h, respectively; AUC_0–∞ = 230.49, 236.18 and 242.57 h, respectively) after administration of LBP-FITC at doses of 100, 50, and 25 mg/kg, respectively. After intragastric administration at 50 mg/kg for 72 h, the concentration of LBP-FITC in urine and feces was 0.09 ± 0.04% and 92.18 ± 3.61% respectively; the excretion rate of urine was the highest in 0–4 h period and decreased continuously in 4–24 h period. The excretion rate of feces was the highest in 4–10 h, 48.28 ± 9.349% in feces within 4–10 h, and decreased rapidly in 10–24 h. The present study showed that LBP was absorbed as its prototype and most proportion of LBP was excreted from feces, indicating a long time remaining in intestine.

Intestinal permeation enhancers to improve oral bioavailability of macromolecules: reasons for low efficacy in humans

INTRODUCTION

Intestinal permeation enhancers (PEs) are substances that transiently alter the intestinal epithelial barrier to facilitate permeation of macromolecules with low oral bioavailability (BA). While a number of PEs have progressed to clinical testing in conventional formulations with macromolecules, there has been only low single digit increases in oral BA, irrespective of whether the drug met primary or secondary clinical endpoints.

AREAS COVERED

This article considers the causes of sub-optimal BA of macromolecules from PE dosage forms and suggests approaches that may improve performance in humans.

EXPERT OPINION

Permeation enhancement is most effective when the PE is co-localized with the macromolecule at the epithelial surface. Conditions in the GI tract impede optimal co-localization. Novel delivery systems that limit dilution and spreading of the PE and macromolecule in the small intestine have attempted to replicate promising enhancement efficacy observed in static drug delivery models.

Advanced delivery strategies facilitating oral absorption of heparins

Heparins show great anticoagulant effect with few side effects, and are administered by subcutaneous or intravenous route in clinics. To improve patient compliance, oral administration is an alternative route. Nonetheless, oral administration of heparins still faces enormous challenges due to the multiple obstacles. This review briefly analyzes a series of barriers ranging from poorly physicochemical properties of heparins, to harsh biological barriers including gastrointestinal degradation and pre-systemic metabolism. Moreover, several approaches have been developed to overcome these obstacles, such as improving stability of heparins in the gastrointestinal tract, enhancing the intestinal epithelia permeability and facilitating lymphatic delivery of heparins. Overall, this review aims to provide insights concerning advanced delivery strategies facilitating oral absorption of heparins.

Efficacy, safety and cardiovascular outcomes of once-daily oral semaglutide in patients with type 2 diabetes: The PIONEER programme

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are recommended for glycaemic management in patients with type 2 diabetes (T2D). Oral semaglutide, the first oral GLP-1RA, has recently been approved for clinical use, based on the results of the randomized, Phase 3a Peptide InnOvatioN for Early diabEtes tReatment (PIONEER) clinical trials. The PIONEER programme tested oral semaglutide in patients with T2D of duration ranging from 3.5 to 15 years, from monotherapy through to insulin add-on, in global populations and two trials dedicated to Japanese patients. Outcomes (glycated haemoglobin [HbA1c] and body weight reduction, plus other relevant efficacy and safety endpoints) were tested against both placebo and active standard-of-care medications. A separate trial evaluated the cardiovascular safety of oral semaglutide in patients with T2D at high cardiovascular risk. Over periods of treatment up to 78 weeks, oral semaglutide 7 and 14 mg once daily reduced HbA1c and body weight across the spectrum of T2D, and improved other diabetes-related endpoints, such as fasting plasma glucose. Oral semaglutide provided significantly better efficacy than placebo and commonly used glucose-lowering medications from the dipeptidyl peptidase-4 inhibitor (sitagliptin) and sodium-glucose co-transporter-2 inhibitor (empagliflozin) classes, as well as the subcutaneous GLP-1RAs liraglutide and dulaglutide. Oral semaglutide was well tolerated in line with the known safety profile of GLP-1RAs, with transient gastrointestinal events being the most common side effects reported. Cardiovascular safety was demonstrated for oral semaglutide in patients with cardiovascular disease or high cardiovascular risk. The results of the PIONEER programme suggest that oral semaglutide is efficacious and well tolerated for glycaemic control of T2D. The availability of oral semaglutide may help to broaden treatment choice and facilitate adoption of earlier GLP-1RA treatment in the paradigm of T2D management.

Inhibition of BACE1, the β-secretase implicated in Alzheimer's disease, by a chondroitin sulfate extract from Sardina pilchardus

The pharmaceutical and anticoagulant agent heparin, a member of the glycosaminoglycan family of carbohydrates, has previously been identified as a potent inhibitor of a key Alzheimer's disease drug target, the primary neuronal β-secretase, β-site amyloid precursor protein cleaving enzyme 1 (BACE1). The anticoagulant activity of heparin has, however, precluded the repurposing of this widely used pharmaceutical as an Alzheimer's disease therapeutic. Here, a glycosaminoglycan extract, composed predominantly of 4-sulfated chondroitin sulfate, has been isolated from Sardina pilchardus, which possess the ability to inhibit BACE1 (IC50 [half maximal inhibitory concentration] = 4.8 μg/mL), while displaying highly attenuated anticoagulant activities (activated partial thromboplastin time EC50 [median effective concentration] = 403.8 μg/mL, prothrombin time EC50 = 1.3 mg/mL). The marine-derived, chondroitin sulfate extract destabilizes BACE1, determined via differential scanning fluorimetry (ΔTm -5°C), to a similar extent as heparin, suggesting that BACE1 inhibition by glycosaminoglycans may occur through a common mode of action, which may assist in the screening of glycan-based BACE1 inhibitors for Alzheimer's disease.

Intestinal Permeation Enhancers for Oral Delivery of Macromolecules: A Comparison between Salcaprozate Sodium (SNAC) and Sodium Caprate (C10)

Salcaprozate sodium (SNAC) and sodium caprate (C10) are two of the most advanced intestinal permeation enhancers (PEs) that have been tested in clinical trials for oral delivery of macromolecules. Their effects on intestinal epithelia were studied for over 30 years, yet there is still debate over their mechanisms of action. C10 acts via openings of epithelial tight junctions and/or membrane perturbation, while for decades SNAC was thought to increase passive transcellular permeation across small intestinal epithelia based on increased lipophilicity arising from non-covalent macromolecule complexation. More recently, an additional mechanism for SNAC associated with a pH-elevating, monomer-inducing, and pepsin-inhibiting effect in the stomach for oral delivery of semaglutide was advocated. Comparing the two surfactants, we found equivocal evidence for discrete mechanisms at the level of epithelial interactions in the small intestine, especially at the high doses used in vivo. Evidence that one agent is more efficacious compared to the other is not convincing, with tablets containing these PEs inducing single-digit highly variable increases in oral bioavailability of payloads in human trials, although this may be adequate for potent macromolecules. Regarding safety, SNAC has generally regarded as safe (GRAS) status and is Food and Drug Administration (FDA)-approved as a medical food (Eligen®-Vitamin B12, Emisphere, Roseland, NJ, USA), whereas C10 has a long history of use in man, and has food additive status. Evidence for co-absorption of microorganisms in the presence of either SNAC or C10 has not emerged from clinical trials to date, and long-term effects from repeat dosing beyond six months have yet to be assessed. Since there are no obvious scientific reasons to prefer SNAC over C10 in orally delivering a poorly permeable macromolecule, then formulation, manufacturing, and commercial considerations are the key drivers in decision-making.

A Review on the New and Old Anticoagulants

Anticoagulants serve as the primary strategy for the prevention and treatment of both arterial and venous thromboembolism. Anticoagulants disrupt coagulation by interfering at various points in the coagulation cascade. This class of medications does not lyse clots that already exist; rather, it prevents thrombus formation and prevents or slows the extension of an existing clot. For decades, the standard therapy for patients requiring oral anticoagulation was warfarin. However, due to some of the shortcomings of warfarin, including the need for continuous routine monitoring, longtime onset and offset of anticoagulation effect, major food and drug interactions, and high incidence of bleeding, newer agents, termed direct oral anticoagulants, or DOACs were developed. This article will provide a review of clinically important information regarding the most commonly used anticoagulants and their reversal agents.

Pharmacokinetic evaluation of an oral tablet form of low-molecular-weight heparin and deoxycholic acid conjugate as a novel oral anticoagulant

This study was designed to develop a solid oral dosage form of deoxycholic acid (DOCA)-conjugated low-molecular-weight heparin (LMWH) and to evaluate its oral absorption, distribution, and metabolic stability for the prospect of providing an orally bioavailable LMWH. The LMWH derivative (LHD) was synthesised and then formulated with solubilisers and other pharmaceutical excipients to form a solid tablet. Its absorption and distribution after oral administration were evaluated in mice, rats, and monkeys. The in vitro metabolic stability of LHD was examined by liver microsome assays. More than 80% of LHD was released from the tablet within 60 minutes, guaranteeing rapid tablet disintegration after oral administration. Oral bioavailability of LHD in mice, rats and monkeys were 16.1 ± 3.0, 15.6 ± 6.1, and 15.8 ± 2.5%, respectively. After the oral administration of 131I-tyramine-LHD, most of the absorbed drug remained in the blood circulation and was eliminated mainly through the kidneys. LHD was hardly metabolised by the liver microsomes and showed a stable metabolic pattern similar to that of LMWH. In a rat thrombosis model, 10 mg/kg of orally administered LHD reduced thrombus formation by 60.8%, which was comparable to the antithrombotic effect of the subcutaneously injected LMWH (100 IU/ kg). Solid tablets of LHD exhibited high oral absorption and statistically significant therapeutic effects in preventing venous thromboembolism. Accordingly, LHD tablets are expected to satisfy the unmet medical need for an oral heparin-based anticoagulant as an alternative to injectable heparin and oral warfarin.

Antithrombotic efficacy of bivalirudin compared to unfractionated heparin during percutaneous coronary intervention for acute coronary syndrome

Bivalirudin is associated with an increased risk of acute stent thrombosis (AST) compared to unfractionated heparin (UFH) in acute coronary syndrome patients (ACS) during short-duration percutaneous coronary intervention (PCI). The mechanisms involved are unknown. We aimed to investigate the antithrombotic efficacy of bivalirudin compared to UFH during PCI. In a monocenter study, we prospectively enrolled 30 patients undergoing PCI for a non-ST elevation ACS. They were randomly assigned to a single intravenous (IV) bolus of UFH (70 IU/kg) or an IV bolus of bivalirudin 0.75 mg/kg followed by a 1.75 mg/kg/h infusion during PCI. All patients received a loading dose (LD) of 180 mg of ticagrelor at the time of PCI. The VASP index and activated partial thromboplastin time (aPTT) were used to assess the course of platelet reactivity (PR) and antithrombotic activity. The two groups were similar regarding baseline, angiographic, and interventional characteristics. There was no difference between the two groups in the course of PR following ticagrelor LD. An optimal PR inhibition was obtained 4 h after the LD of ticagrelor. The level of antithrombotic activity was significantly lower in the bivalirudin group compared to the UFH group (p < 0.001) during PCI but similar at 2 and 4 h post-PCI. We observed that, in ACS undergoing PCI, the antithrombotic efficacy of an IV bolus of bivalirudin is significantly lower than that of a 70-IU/kg UFH bolus. This could contribute to the excess in thrombotic acute events observed during short-duration PCI.

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.

Strategies to Overcome Heparins' Low Oral Bioavailability

Even after a century, heparin is still the most effective anticoagulant available with few side effects. The poor oral absorption of heparins triggered the search for strategies to achieve oral bioavailability since this route has evident advantages over parenteral administration. Several approaches emerged, such as conjugation of heparins with bile acids and lipids, formulation with penetration enhancers, and encapsulation of heparins in micro and nanoparticles. Some of these strategies appear to have potential as good delivery systems to overcome heparin’s low oral bioavailability. Nevertheless, none have reached the market yet. Overall, this review aims to provide insights regarding the oral bioavailability of heparin.

Overcoming the challenges in administering biopharmaceuticals: formulation and delivery strategies

The formulation and delivery of biopharmaceutical drugs, such as monoclonal antibodies and recombinant proteins, poses substantial challenges owing to their large size and susceptibility to degradation. In this Review we highlight recent advances in formulation and delivery strategies--such as the use of microsphere-based controlled-release technologies, protein modification methods that make use of polyethylene glycol and other polymers, and genetic manipulation of biopharmaceutical drugs--and discuss their advantages and limitations. We also highlight current and emerging delivery routes that provide an alternative to injection, including transdermal, oral and pulmonary delivery routes. In addition, the potential of targeted and intracellular protein delivery is discussed.

In situ crosslinkable heparin-containing poly(ethylene glycol) hydrogels for sustained anticoagulant release

Low-molecular weight heparin (LMWH) is widely used in anticoagulation therapies and for the prevention of thrombosis. LMWH is administered by subcutaneous injection usually once or twice per day. This frequent and invasive delivery modality leads to compliance issues for individuals on prolonged therapeutic courses, particularly pediatric patients. Here, we report a long-term delivery method for LMWH via subcutaneous injection of long-lasting hydrogels. LMWH is modified with reactive maleimide groups so that it can be crosslinked into continuous networks with four-arm thiolated poly(ethylene glycol) (PEG-SH). Maleimide-modified LMWH (Mal-LMWH) retains bioactivity as indicated by prolonged coagulation time. Hydrogels comprising PEG-SH and Mal-LMWH degrade via hydrolysis, releasing bioactive LMWH by first-order kinetics with little initial burst release. Separately dissolved Mal-LMWH and PEG-SH solutions were co-injected subcutaneously in New Zealand White rabbits. The injected solutions successfully formed hydrogels in situ and released LMWH as measured via chromogenic assays on plasma samples, with accumulation of LMWH occurring at day 2 and rising to near-therapeutic dose equivalency by day 5. These results demonstrate the feasibility of using LMWH-containing, crosslinked hydrogels for sustained and controlled release of anticoagulants.

Oral fondaparinux: use of lipid nanocapsules as nanocarriers and in vivo pharmacokinetic study

Oral anticoagulant therapy could be advanced using lipid-based nanoparticulate systems. This study examined lipid nanocapsules for their oral absorption potential as the first step in developing oral fondaparinux (Fp) novel carriers. Using phase inversion method and cationic surfactants such as hexadecyltrimethyl ammonium bromide (CTAB) or stearylamine (SA), cationic lipid nanocapsules (cLNCs), loaded with Fp on their surface, were prepared and characterized (zeta potential, size and Fp association efficiency and content). In vivo studies were conducted after single oral increasing doses of Fp-loaded cLNCs (0.5 to 5 mg/kg of Fp) in rats and the concentration of Fp in the plasma was measured by anti-factor Xa activity assay. The monodisperse, (~50 nm), positively charged Fp-cLNCs with high drug loadings demonstrated linear pharmacokinetic profiles of the drug with an increased oral absolute bioavailability (up to ~21%) compatible with therapeutic anticoagulant effect (>0.2 μg/mL).

Engineering of routes to heparin and related polysaccharides

Anticoagulant heparin has been shown to possess important biological functions that vary according to its fine structure. Variability within heparin's structure occurs owing to its biosynthesis and animal tissue-based recovery and adds another dimension to its complex polymeric structure. The structural variations in chain length and sulfation patterns mediate its interaction with many heparin-binding proteins, thereby eliciting complex biological responses. The advent of novel chemical and enzymatic approaches for polysaccharide synthesis coupled with high throughput combinatorial approaches for drug discovery have facilitated an increased effort to understand heparin's structure-activity relationships. An improved understanding would offer potential for new therapeutic development through the engineering of polysaccharides. Such a bioengineering approach requires the amalgamation of several different disciplines, including carbohydrate synthesis, applied enzymology, metabolic engineering, and process biochemistry.

Impact of autoclave sterilization on the activity and structure of formulated heparin

The stability of a formulated heparin was examined during its sterilization by autoclaving. A new method to follow loss in heparin binding to the serine protease inhibitor, antithrombin III, and the serine protease, thrombin, was developed using a surface plasmon resonance competitive binding assay. This loss in binding affinity correlated well with loss in antifactor IIa (thrombin) activity as well as antifactor Xa activity as measured using conventional amidolytic assays. Autoclaving also resulted in a modest breakdown of the heparin backbone as confirmed by a slight reduction in number-averaged and weight-averaged molecular weight and an increase in polydispersity. Although no clear changes were observed by nuclear magnetic resonance spectroscopy, disaccharide composition analysis using high-performance liquid chromatography-electrospray ionization-mass spectrometry suggested that loss of selected sulfo groups had taken place. It is this sulfo group loss that probably accounts for a decrease in the binding of autoclaved heparin to antithrombin III and thrombin as well as the observed decrease in its amidolytic activity.

Heparin mapping using heparin lyases and the generation of a novel low molecular weight heparin

Seven pharmaceutical heparins were investigated by oligosaccharide mapping by digestion with heparin lyase 1, 2, or 3, followed by high performance liquid chromatography analysis. The structure of one of the prepared mapping standards, ΔUA-Gal-Gal-Xyl-O-CH(2)CONHCH(2)COOH (where ΔUA is 4-deoxy-α-l-threo-hex-4-eno-pyranosyluronic acid, Gal is β-d-galactpyranose, and Xyl is β-d-xylopyranose) released from the linkage region using either heparin lyase 2 or heparin lyase 3 digestion, is reported for the first time. A size-dependent susceptibility of site cleaved by heparin lyase 3 was also observed. Heparin lyase 3 acts on the undersulfated domains of the heparin chain and does not cleave the linkages within heparin's antithrombin III binding site. Thus, a novel low molecular weight heparin (LMWH) is afforded on heparin lyase 3 digestion of heparin due to this unique substrate specificity, which has anticoagulant activity comparable to that of currently available LMWH.

Flavonoids with an oligopolysulfated moiety: a new class of anticoagulant agents

Polysulfated (oligo)flavonoids were synthesized and assayed for their in vitro and in vivo anticoagulant activities. The approach was based on molecular hybridization of two classes of anticoagulants, sulfated polysaccharides and sulfated flavonoids. The synthesis was optimized using microwave-assisted sulfation with triethylamine-sulfur trioxide. The obtained polysulfated flavonosides were highly effective in increasing clotting times and able to completely block the clotting process, in contrast to their corresponding aglycones. The thromboelastography proved that polysulfated flavonosides possess good whole blood anticoagulation activity. The following structure-activity relationships were found: 3-O-rutinosides (10, 13) were direct inhibitors of FXa, while 7-O-rutinosides (7, 8) showed inhibition of FXa by ATIII activation. Furthermore, compounds 7 and 13 were stable in plasma and active in vivo and preliminary toxicity studies would lead us to rule out acute side effects. From the overall results, the polysulfated flavonosides showed the potential as new effective and safe agents for anticoagulant therapy.

A sensitive and specific HPGPC-FD method for the study of pharmacokinetics and tissue distribution of Radix Ophiopogonis polysaccharide in rats

Interest in antimyocardial ischemic activity of a graminan-type fructan with a weight average molecular weight of 4.8 kDa extracted from Radix Ophiopogonis (ROP) has necessitated the study of its pharmacokinetics and tissue distribution. For that, a simple HPGPC-FD method was developed for the sensitive and specific determination of FITC-ROP (fluorescein-isothiocyanate-labeled ROP) in plasma and rat tissues (heart, liver, spleen, lung, kidney, brain and stomach). The analyte was separated on a Shodex Sugar KS-802 high-performance gel column with 0.1 M phosphate buffer (pH 7.0) as mobile phase at a flow rate of 0.5 mL/min, and fluorescence detection at lambda(ex) 495 nm and lambda(em) 515 nm. The calibration curve for FITC-ROP was linear over the range 0.25-20.0 or 50.0 microg/mL in all studied biosamples with correlation coefficients > 0.995. The inter-day and intra-day precisions of analysis were not more than 10%, and assay accuracy ranged from 93 to 105% for plasma and from 89 to 108% for tissue homogenates. This method has been confirmed here to be suitable for the study of pharmacokinetics and tissue distribution of ROP and the achieved results are highly instructive for the further pharmaceutical development of ROP, suggesting the promising application of the method to the increasingly important carbohydrate-based drugs.

Novel anticoagulant therapy: principle and practice

Currently, there are several lines of evidence supporting the interplay between coagulation and inflammation in the propagation of various disease processes, including venous thromboembolism (VTE) and inflammatory diseases. Major advances in the development of oral anticoagulants have resulted in considerable progress toward the goal of safe and effective oral anticoagulants that do not require frequent monitoring or dose adjustment and have minimal food/drug interactions. Indirect inhibitors such as low-molecular-weight heparin (LMWH) and the pentasaccharide fondaparinux represent improvements over traditional drugs such as unfractionated heparin for acute treatment of VTE, constituting a more targeted anticoagulant approach with predictable pharmacokinetic profiles and no requirement for monitoring. Vitamin K antagonist, with its inherent limitations in terms of multiple food and drug interactions and frequent need for monitoring, remains the only oral anticoagulant approved for long-term secondary thromboprophylaxis in VTE. The oral-direct thrombin inhibitor ximelagatran was withdrawn from the world market due to safety concerns. Newer anticoagulant drugs such as parenteral pentasaccharides (idraparinux, SSR126517E), novel oral-direct thrombin inhibitors (dabigatran), oral-direct factor Xa inhibitors (rivaroxaban, apixaban, YM-150, DU-176b), and tissue factor/factor VIIa complex inhibitors have been "tailor-made" to target specific procoagulant complexes and have the potential to greatly expand oral antithrombotic targets for both acute and long-term treatment of VTE, acute coronary syndromes, and for the prevention of stroke in atrial fibrillation patients.

Heparin and low-molecular weight heparins in thrombosis and beyond

Heparin and its improved version, low-molecular weight heparin (LMWH), are known to exert polypharmacological effects at various levels. Early studies focused on the plasma anti-Xa and anti-IIa pharmacodynamics of different LMWHs. Other important pharmacodynamic parameters for heparin and LMWH, including effects on vascular tissue factor pathway inhibitor (TFPI) release, inhibition of inflammation through NFkappaB, inhibition of key matrix-degrading enzymes, selectin modulation, inhibition of platelet-cancer cell interactions, and inflammatory cell adhesion, help explain the diverse clinical impact of this class of agents in thrombosis and beyond.

Recent progress and applications in glycosaminoglycan and heparin research

Heparin, the focus of this review, is a crucially important anticoagulant drug produced from animal sources, which was contaminated last year leading to a number of adverse side effects, some resulting in death. Heparin is a highly acidic polysaccharide and a member of a family of biopolymers called glycosaminoglycans. The structure and activities of heparin are detailed along with recent advances in heparin structural analysis and biological evaluation. Current state-of-the-art chemical and chemoenzymatic synthesis of heparin and new approaches for its metabolic engineering are described. New technologies, including microarrays and digital microfluidics, are proposed for high-throughput synthesis and screening of heparin and for the fabrication of an artificial Golgi.

Subchronic Oral Toxicity of Salcaprozate Sodium (SNAC) in Sprague-Dawley and Wistar Rats

Salcaprozate sodium (SNAC) (sodium 8-((2-hydroxybenzoyl) amino) octanoate, CAS RN 203787-91-1) is classified as an oral absorption promoter, and its potential therapeutic applications as a delivery agent for oral forms of heparin and insulin have been explored in a number of clinical investigations. However, limited information about its nonclinical safety is available in the published scientific literature. As part of a larger study exploring the safety of SNAC in combination with heparin, Sprague-Dawley (SD) rats (20/sex/group) received SNAC alone at 2000 mg/kg/d orally (gavage) for 13 weeks (females were terminated after 10 weeks). In a separate study assessing the safety of SNAC in combination with ibandronate, Wistar rats (10/sex/group) received SNAC alone at levels of 100, 500, or 1000 mg/kg/d orally for 13 weeks. SNAC-related mortality was evident only at the 2000-mg/kg/d level, 20% among males and 50% among females; no clear cause of death was evident. No mortality was seen in the Wistar rat study at doses up to 1000 mg/kg/d. Some differences in clinical pathology parameters, including slightly altered electrolyte levels and lower globulin levels, were seen in SD and Wistar rats. Although these differences reached statistical significance, parameters were within historical control ranges. Liver and kidney weights were slightly higher in SNAC-treated animals of both strains, with no corresponding histopathological changes. These changes may therefore constitute an adaptive response. Histopathological changes were seen in the stomach in both studies, probably secondary to irritation caused by the dosing method. Based on the results of these studies, a no-observed-adverse-effect level (NOAEL) cannot be given for SD rats. The NOAEL for SNAC in Wistar rats was considered to be 1000 mg/kg/d.

Peri- and Postnatal Developmental Toxicity of Salcaprozate Sodium (SNAC) in Sprague-Dawley Rats

Salcaprozate sodium (SNAC) (sodium 8-((2-hydroxybenzoyl) amino) octanoate, CAS RN 203787-91-1) is classified as an oral absorption promoter and may be a useful means for improving the absorption of certain nutrients and pharmaceutical agents. Presented herein is a subset of data from a larger study evaluating the potential effects of SNAC on the gestation, parturition, lactation, maternal behavior, and offspring development of rats. Pregnant Crl:CD BR VAF/Plus female rats (F0; n = 25) received SNAC at 1000 mg/kg/d orally (gavage) from implantation through lactation and weaning. F1 pups were exposed in utero and potentially through maternal milk; observations continued through sexual maturity. The study concluded with Caesarean sectioning of F1 dams for litter observations and fetal evaluations. No deaths, abortions, premature deliveries, or gross lesions occurred in (F0) dams. Excess salivation, red perivaginal substance, and slight reductions in body weights, body weight gains, and/or feed intake were noted in late gestation/early lactation. SNAC was associated with a prolonged gestation period, leading to a greater number of dams with stillborn pups, higher number of stillborn pups, and reduced live litter size. Offspring body weights/gains, feed consumption, age of sexual maturation, mating, fertility, behavioral parameters, and organ weights at necropsy were unaffected by SNAC. No gross external changes were observed in F1 or F2 pups. In summary, SNAC administered orally at 1000 mg/kg/d to pregnant rats from gestation to weaning resulted in a slight decrease in maternal body weights (−3.8%) and prolonged gestation, along with an increase in stillbirths, but had no effects on growth and development in surviving offspring.

On-line separations combined with MS for analysis of glycosaminoglycans

The glycosaminoglycan (GAG) family of polysaccharides includes the unsulfated hyaluronan and the sulfated heparin, heparan sulfate, keratan sulfate, and chondroitin/dermatan sulfate. GAGs are biosynthesized by a series of enzymes, the activities of which are controlled by complex factors. Animal cells alter their responses to different growth conditions by changing the structures of GAGs expressed on their cell surfaces and in extracellular matrices. Because this variation is a means whereby the functions of the limited number of protein gene products in animal genomes is elaborated, the phenotypic and functional assessment of GAG structures expressed spatially and temporally is an important goal in glycomics. On-line mass spectrometric separations are essential for successful determination of expression patterns for the GAG compound classes due to their inherent complexity and heterogeneity. Options include size exclusion, anion exchange, reversed phase, reversed phase ion pairing, hydrophilic interaction, and graphitized carbon chromatographic modes and capillary electrophoresis. This review summarizes the application of these approaches to on-line MS analysis of the GAG classes.

New electrophoretic and chromatographic techniques for analysis of heparin and heparan sulfate

Heparin (HE) and heparan sulfated glycosaminoglycans are well-known mediators of tissue development, maintenance and functions; the activities of these polysaccharides are depending mainly on their sulfate substitutions. The HE structure is also a very important feature in antithrombotic drug development, since the antithrombin binding site is composed by sequences of a specific sulfation pattern. The analysis of disaccharide composition is then a fundamental point of all the studies regarding HE/heparan sulfate glycosaminoglycan (and thereby proteoglycan) functions. The present work describes two analytical methods to quantify the disaccharides constituting HE and heparan sulfate chains. The use of PAGE of fluorophore-labeled saccharides and HPLC coupled with a fluorescence detector allowed in one run the identification of 90-95% of HE disaccharides and 74-100% of rat kidney purified heparan sulfate. Moreover, the protocol here reported avoid the N-sulfation disaccharides degradation, which may affect N-sulfated/N-acetylated disaccharides ratio evaluation. These methods could be also very important in clinical treatments since they are useful for monitoring the availability kinetics of antithrombotic drugs, such as low-molecular-weight HEs.

Is human placenta proteoglycan remodeling involved in pre-eclampsia?

Impaired placento-fetal communication is a coherent symptom of exaggerated pre-eclampsia. The impact of the cellular expression of different glycosaminoglycans (GAGs) in this event on the placenta in pre-eclampsia is still obscure. This is the first study aimed at discovering the relationship between structural alterations of different sulfated GAGs at the molecular level and the development of pre-eclampsia in inflicted placenta. Sulfated GAGs were isolated and purified from control and pre-eclampsia placentas. The amount and the molecular weight of GAG in each tissue sample were measured. The polydispersity of the recovered GAG samples were determined by polyacrylamide gel electrophoresis. The disaccharide composition of chondroitin sulfate, dermatan sulfate and heparan sulfate were deduced by chondroitinase and heparinase depolymerization followed by liquid chromatography-mass spectrometry. The in vivo sulfo-modulation of GAGs in pre-eclampsia and control placenta were examined using RT-PCR to determine the transcription levels of different sulfotransferases involved in GAG biosynthesis. Marked differences in GAG sulfation patterns and mRNA level of encoding selected GAG O-sulfotransferases were observed in pre-eclampsia. These data suggest a linkage between pre-eclampsia and the observed alterations in placental GAGs and could provide new insights about the modulating role of GAGs in the development and the severity of placental pre-eclampsia.