Heparin, a highly-sulfated
glycosaminoglycanGlycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit.-Production:...
, is widely used as an injectable
anticoagulantAn anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders...
, and has the highest negative
charge densityThe linear, surface, or volume charge density is the amount of electric charge in a line, surface, or volume. It is measured in coulombs per metre , square metre , or cubic metre , respectively. Since there are positive as well as negative charges, the charge density can take on negative values....
of any known
biological moleculeA biomolecule is any organic molecule that is produced by a living organism, including large polymeric molecules such as proteins, polysaccharides, and nucleic acids as well as small molecules such as primary metabolites, secondary metabolites, and natural products.As organic molecules,...
. It can also be used to form an inner anticoagulant surface on various experimental and medical devices such as
test tubeA test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top, usually with a rounded U-shaped bottom...
s and renal dialysis machines. Pharmaceutical grade heparin is derived from mucosal tissues of
slaughteredA slaughterhouse, also called an abattoir ,or freezing works , is a facility where animals are killed and processed into meat foods...
meat animals such as porcine (pig) intestine or bovine (cow) lung.
Although used principally in medicine for anticoagulation, the true physiological role in the body remains unclear, because blood anti-coagulation is achieved mostly by
endothelialThe endothelium is the thin layer of cells that line the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. Endothelial cells line the entire circulatory system, from the heart to the smallest capillary...
cell-derived
heparan sulfateHeparan sulfate is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins...
proteoglycans. Heparin is usually stored within the secretory granules of
mast cellA mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against...
s and released only into the vasculature at sites of tissue injury. It has been proposed that, rather than anticoagulation, the main purpose of heparin is in a defensive mechanism at sites of tissue injury against invading bacteria and other foreign materials. In addition, it is preserved across a number of widely different species, including some invertebrates that do not have a similar blood coagulation system.
Heparin structure
Native heparin is a polymer with a molecular weight ranging from 3
kDaThe unified atomic mass unit or atomic mass unit , or dalton or, sometimes, universal mass unit , is a unit of mass used to express atomic and molecular masses...
to 50 kDa, although the average molecular weight of most commercial heparin preparations is in the range of 12 kDa to 15 kDa.
Heparin is a member of the
glycosaminoglycanGlycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit.-Production:...
family of carbohydrates (which includes the closely-related molecule
heparan sulfateHeparan sulfate is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins...
) and consists of a variably-sulfated repeating
disaccharideA disaccharide is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only...
unit.
The main disaccharide units that occur in heparin are shown below. The most common disaccharide unit is composed of a 2-O-sulfated
iduronic acidL-Iduronic acid is the major uronic acid component of the glycosaminoglycans dermatan sulfate and heparin. It is also present in heparan sulfate although here in a minor amount relative to its carbon-5 epimer glucuronic acid....
and 6-O-sulfated, N-sulfated glucosamine, IdoA(2S)-GlcNS(6S). For example, this makes up 85% of heparins from beef lung and about 75% of those from porcine intestinal mucosa.
Not shown below are the rare disaccharides containing a 3-O-sulfated glucosamine (GlcNS(3S,6S)) or a free amine group (GlcNH
3+). Under physiological conditions, the
esterEsters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
and
amideIn chemistry, an amide is usually an organic compound that contains the functional group consisting of an acyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds...
sulfate groups are deprotonated and attract positively-charged counterions to form a heparin salt. It is in this form that heparin is usually administered as an anticoagulant.
One unit of heparin (the "
HowellWilliam Henry Howell, Ph.D., M.D., LL.D., Sc.D. was an American physiologist. He pioneered the use of heparin as a blood anti-coagulant....
Unit") is an amount approximately equivalent to 0.002 mg of pure heparin, which is the quantity required to keep 1 mL of cat's blood fluid for 24 hours at 0°C.
Abbreviations
- GlcA = β-D-glucuronic acid
Glucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...
- IdoA = α-L-iduronic acid
L-Iduronic acid is the major uronic acid component of the glycosaminoglycans dermatan sulfate and heparin. It is also present in heparan sulfate although here in a minor amount relative to its carbon-5 epimer glucuronic acid....
- IdoA(2S) = 2-O-sulfo-α-L-iduronic acid
- GlcNAc = 2-deoxy-2-acetamido-α-D-glucopyranosyl
- GlcNS = 2-deoxy-2-sulfamido-α-D-glucopyranosyl
- GlcNS(6S) = 2-deoxy-2-sulfamido-α-D-glucopyranosyl-6-O-sulfate
Three-dimensional structure
The three-dimensional structure of heparin is complicated by the fact that
iduronic acidL-Iduronic acid is the major uronic acid component of the glycosaminoglycans dermatan sulfate and heparin. It is also present in heparan sulfate although here in a minor amount relative to its carbon-5 epimer glucuronic acid....
may be present in either of two low-energy conformations when internally positioned within an oligosaccharide. The conformational equilibrium being influenced by sulfation state of adjacent glucosamine sugars. Nevertheless, the solution structure of a heparin dodecasacchride composed solely of six GlcNS(6S)-IdoA(2S) repeat units has been determined using a combination of NMR spectroscopy and molecular modeling techniques. Two models were constructed, one in which all IdoA(2S) were in the
2S
0 conformation (
A and
B below), and one in which they are in the
1C
4 conformation (
C and
D below). However there is no evidence to suggest that changes between these conformations occur in a concerted fashion. These models correspond to the protein data bank code
1HPN.
In the image above:
- A = 1HPN (all IdoA(2S) residues in 2S0 conformation) Jmol viewer
- B = van der Waals radius
The van der Waals radius, r, of an atom is the radius of an imaginary hard sphere which can be used to model the atom for many purposes. It is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics, as he was the first to recognise that atoms had a finite size and to...
space filling model of A
- C = 1HPN (all IdoA(2S) residues in 1C4 conformation) Jmol viewer
- D = van der Waals radius space filling model of C
In these models, heparin adopts a helical conformation, the rotation of which places clusters of sulfate groups at regular intervals of about 17
angstromThe ångström or angstrom is an internationally recognized unit of length equal to 0.1 nanometre or 1 metres. It is named after Anders Jonas Ångström...
s (1.7 nm) on either side of the helical axis.
Medical use
Heparin is a naturally-occurring anticoagulant produced by basophils and
mast cellA mast cell is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against...
s. Heparin acts as an anticoagulant, preventing the formation of clots and extension of existing clots within the blood. While heparin does not break down clots that have already formed (unlike
tissue plasminogen activatorTissue plasminogen activator is a protein involved in the breakdown of blood clots. Specifically, it is a serine protease found on endothelial cells, the cells that line the blood vessels. As an enzyme, it catalyzes the conversion of plasminogen to plasmin, the major enzyme responsible for clot...
), it allows the body's natural
clot lysisFibrinolysis is the process wherein a fibrin clot, the product of coagulation, is broken down. Its main enzyme plasmin cuts the fibrin mesh at various places, leading to the production of circulating fragments that are cleared by other proteases or by the kidney and liver.-Physiology:Plasmin is...
mechanisms to work normally to break down clots that have not yet formed.
Heparin is used for anticoagulation for the following conditions:
- Acute coronary syndrome
An acute coronary syndrome is a set of signs and symptoms related to the heart. ACS is compatible with a diagnosis of acute myocardial ischemia, but it is not pathognomonic....
, e.g., NSTEMI
- Atrial fibrillation
Atrial fibrillation is the most common cardiac arrhythmia and involves the two upper chambers of the heart. Its name comes from the fibrillating of the heart muscles of the atria, instead of a coordinated contraction...
- Deep-vein thrombosis and pulmonary embolism
Pulmonary embolism is a blockage of the main artery of the lung or one of its branches by a substance that has travelled from elsewhere in the body through the bloodstream . Usually this is due to embolism of a thrombus from the deep veins in the legs, a process termed venous thromboembolism...
- Cardiopulmonary bypass for heart surgery.
- ECMO circuit for extracorporeal life support
Heparin and its derivatives (
enoxaparinEnoxaparin is a low molecular weight heparin marketed as Lovenox or Clexane.It is used to prevent and treat deep vein thrombosis or pulmonary embolism, and is given as a subcutaneous injection...
,
dalteparinDalteparin is a low molecular weight heparin. It is marketed as Fragmin by Pfizer Inc. Like other low molecular weight heparins, dalteparin is used for prophylaxis or treatment of deep vein thrombosis and pulmonary embolism....
,
tinzaparinTinzaparin is an antithrombotic drug in the heparin group. It is a low molecular weight heparin marketed as Innohep or innohep world wide. It has been approved by the U.S...
) are effective at preventing deep-vein thromboses and pulmonary emboli in patients at risk, but there is no evidence that any one is more effective than the other in preventing mortality.
Heparin binds to the enzyme inhibitor
antithrombinAntithrombin is a small protein molecule that inactivates several enzymes of the coagulation system. It is a glycoprotein produced by the liver and consists of 432 amino acids. It contains three disulfide bonds and a total of four possible glycosylation sites...
(AT) causing a conformational change that results in its activation through an increase in the flexibility of its reactive site loop. The activated AT then inactivates
thrombinThrombin also commonly called pro-thrombin is a coagulation protein in the blood stream that has many effects in the coagulation cascade...
and other proteases involved in blood clotting, most notably factor Xa. The rate of inactivation of these proteases by AT can increase by up to 1000-fold due to the binding of heparin.
AT binds to a specific pentasaccharide sulfation sequence contained within the heparin polymer
GlcNAc/NS(6S)-GlcA-GlcNS(3S,6S)-IdoA(2S)-GlcNS(6S)
The conformational change in AT on heparin-binding mediates its inhibition of factor Xa. For thrombin inhibition, however, thrombin must also bind to the heparin polymer at a site proximal to the pentasaccharide. The highly-negative charge density of heparin contributes to its very strong electrostatic interaction with
thrombinThrombin also commonly called pro-thrombin is a coagulation protein in the blood stream that has many effects in the coagulation cascade...
. The formation of a
ternary complexTernary complex refers to a complex containing three different molecules which are bound together. In structural biology ternary complex can be used to describe a crystal containing a protein with two small molecules bound, for example cofactor and substrate; or a complex formed between two...
between AT, thrombin, and heparin results in the inactivation of thrombin. For this reason heparin's activity against thrombin is size-dependent, the ternary complex requiring at least 18 saccharide units for efficient formation. In contrast anti factor Xa activity only requires the pentasaccharide binding site.
This size difference has led to the development of
low-molecular-weight heparinIn medicine, low-molecular-weight heparin is a class of medication used as an anticoagulant in diseases that feature thrombosis, as well as for prophylaxis in situations that lead to a high risk of thrombosis....
s (LMWHs) and more recently to
fondaparinuxFondaparinux is an anticoagulant medication.It is marketed by GlaxoSmithKline.-Structure and mechanism:Fondaparinux is a synthetic pentasaccharide as evident by its chemical structure on the right...
as pharmaceutical anticoagulants. Low-molecular-weight heparins and fondaparinux target anti-factor Xa activity rather than anti-thrombin (IIa) activity, with the aim of facilitating a more subtle regulation of coagulation and an improved therapeutic index. The chemical structure of fondaparinux is shown to the left. It is a synthetic pentasaccharide, whose chemical structure is almost identical to the AT binding pentasaccharide sequence that can be found within polymeric heparin and
heparan sulfateHeparan sulfate is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins...
.
With LMWH and fondaparinux, there is a reduced risk of
osteoporosisOsteoporosis is a disease of bone that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered...
and
heparin-induced thrombocytopeniaHeparin-induced thrombocytopenia without or with thrombosis is the development of thrombocytopenia due to the administration of the anticoagulant heparin, either in its "unfractionated" or "low molecular weight" form. It predisposes to thrombosis, the formation of abnormal blood clots inside a...
(HIT). Monitoring of the APTT is also not required and indeed does not reflect the anticoagulant effect, as APTT is insensitive to alterations in factor Xa.
DanaparoidDanaparoid sodium is an anticoagulant that works by inhibiting activated factor X .Danaparoid is considered a "low molecular weight heparin" by some sources, but is chemically distinct from heparin and thus has little cross-reactivity in heparin-intolerant patients.It consists of a mixture of...
, a mixture of
heparan sulfateHeparan sulfate is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins...
,
dermatan sulfateDermatan sulfate is a glycosaminoglycan found mostly in skin, but also in blood vessels, heart valves, tendons, and lungs....
, and
chondroitin sulfateChondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...
, can be used as an anticoagulant in patients that have developed HIT. Because danaparoid does not contain heparin or heparin fragments, cross-reactivity of danaparoid with heparin-induced antibodies is reported as less than 10%.
The effects of heparin are measured in the lab by the partial thromboplastin time (aPTT), (the time it takes the
blood plasmaBlood plasma is the yellow liquid component of blood, in which the blood cells in whole blood would normally be suspended. It makes up about 55% of the total blood volume. It is mostly water and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide...
to clot).
Administration
Details of administration are available in clinical practice guidelines by the
American College of Chest PhysiciansThe American College of Chest Physicians is a medical organization consisting of physicians and non-physician specialists in the field of chest medicine, which includes pulmonology, thoracic surgery, and critical care medicine....
:
Heparin dose can be effectively managed using techniques like Sonoclot
Heparin is given
parenteralParenteral is a route of administration that involves piercing the skin or mucous membrane. Parenteral nutrition refers to providing nutrition via the veins.-Etymology:...
ly, as it is degraded when taken by mouth. It can be injected intravenously or subcutaneously (under the skin). Intramuscular injections (into muscle) are avoided because of the potential for forming
hematomaA haematoma, or hematoma, is a collection of blood outside the blood vessels, generally the result of hemorrhage, or more specifically, internal bleeding....
s.
Because of its short biologic
half-lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
of approximately one hour, heparin must be given frequently or as a continuous
infusionAn infusion is the outcome of steeping plants with a desired flavour in water or oil.-History:The first recorded use of essential oils was in the 10th century by the Muslim Persian chemist Avicenna.-Preparation techniques:...
. However, the use of low-molecular-weight heparin (LMWH) has allowed once-daily dosing, thus not requiring a continuous infusion of the drug. If long-term anticoagulation is required, heparin is often used only to commence anticoagulation therapy until the oral anticoagulant
warfarinWarfarin is an anticoagulant. It was initially marketed as a pesticide against rats and mice and is still popular for this purpose, although more potent poisons such as brodifacoum have since been developed...
takes effect.
Adverse reactions
A serious side-effect of heparin is
heparin-induced thrombocytopeniaHeparin-induced thrombocytopenia without or with thrombosis is the development of thrombocytopenia due to the administration of the anticoagulant heparin, either in its "unfractionated" or "low molecular weight" form. It predisposes to thrombosis, the formation of abnormal blood clots inside a...
(HIT). HIT is caused by an immunological reaction that makes
plateletPlatelets, or thrombocytes , are small, irregularly-shaped anuclear cells , 2-3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is between 8 and 12 days...
s a target of immunological response, resulting in the degradation of platelets. This is what causes thrombocytopenia. This condition is usually reversed on discontinuation, and can generally be avoided with the use of synthetic heparins. There is also a benign form of thrombocytopenia associated with early heparin use, which resolves without stopping heparin.
There are two nonhemorrhagic side-effects of heparin treatment. The first is elevation of serum aminotransferase levels, which has been reported in as many as 80% of patients receiving heparin. This abnormality is not associated with liver dysfunction, and it disappears after the drug is discontinued. The other complication is
hyperkalemiaHyperkalemia is an elevated blood level of the electrolyte potassium. Extreme hyperkalemia is a medical emergency due to the risk of potentially fatal abnormal heart rhythms ....
, which occurs in 5 to 10% of patients receiving heparin, and is the result of heparin-induced aldosterone suppression. The hyperkalemia can appear within a few days after the onset of heparin therapy.
Rarer side-effects include
alopeciaAlopecia or hair loss is the medical description of the loss of hair from the head or body, sometimes to the extent of baldness. Unlike the common aesthetic depilation of body hair, alopecia tends to be involuntary and unwelcome, e.g., androgenic alopecia...
and
osteoporosisOsteoporosis is a disease of bone that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered...
with chronic use.
As with many drugs, overdoses of heparin can be fatal. In September 2006, heparin received worldwide publicity when 3 prematurely-born infants died after they were mistakenly given overdoses of heparin at an Indianapolis hospital.
Treatment of overdose
Protamine sulfateProtamine sulfate is a drug that reverses the anticoagulant effects of heparin by binding to it.Protamine was originally isolated from the sperm of sharks and other species of fish but is now produced primarily through recombinant biotechnology. It is a highly cationic peptide...
(1 mg per 100 Units of Heparin that had been given over 4 hours) has been given to counteract the anticoagulant of heparin.
History
Heparin is one of the oldest drugs currently still in widespread clinical use. Its discovery in 1916 predates the establishment of the Food and Drug Administration of the United States, although it did not enter clinical trials until 1935. It was originally isolated from canine
liverThe liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
cells, hence its name (
hepar or "ήπαρ" is Greek for "liver"). Heparin's discovery can be attributed to the research activities of two men, Jay McLean and
William Henry HowellWilliam Henry Howell, Ph.D., M.D., LL.D., Sc.D. was an American physiologist. He pioneered the use of heparin as a blood anti-coagulant....
.
In 1916, McLean, a second-year medical student at
Johns Hopkins UniversityThe Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university located in Baltimore, Maryland, United States. Johns Hopkins also maintains full-time campuses elsewhere in Maryland, Washington, D.C., Italy, China, and Singapore...
, was working under the guidance of Howell investigating pro-coagulant preparations, when he isolated a fat-soluble phosphatide anti-coagulant. It was Howell who coined the term
heparin for this type of fat-soluble anticoagulant in 1918. In the early 1920s, Howell isolated a water-soluble polysaccharide anticoagulant, which was also termed
heparin, although it was distinct from the phosphatide preparations previously isolated. It is probable that the work of McLean changed the focus of the Howell group to look for anticoagulants, which eventually led to the polysaccharide discovery.
In the 1930s, several researchers were investigating heparin. Erik Jorpes at
Karolinska InstitutetKarolinska Institutet is one of Europe's largest medical universities...
published his research on the structure of heparin in 1935, which made it possible for the Swedish company Vitrum AB to launch the first heparin product for intravenous use in 1936. Between 1933 and 1936, Connaught Medical Research Laboratories, then a part of the University of Toronto, perfected a technique for producing safe, non-toxic heparin that could be administered to patients in a salt solution. The first human trials of heparin began in May 1935, and, by 1937, it was clear that Connaught's heparin was a safe, easily-available, and effective blood anticoagulant. Prior to 1933, heparin was available, but in small amounts, and was extremely expensive, toxic, and, as a consequence, of no medical value.
For a full discussion of the events surrounding heparin's discovery see Marcum J. (2000).
Now the leading manufacturer of heparin is SPL a company owned by Oscar Meyer.
Novel drug development opportunities for heparin
As detailed in the table below, there is a great deal of potential for the development of heparin-like structures as
drugA drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...
s to treat a wide range of
diseaseA disease or medical condition isan abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and signs...
s, in addition to their current use as
anticoagulantAn anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders...
s.
| Disease states sensitive to heparin |
Heparins effect in experimental models |
Clinical status |
| Adult respiratory distress syndrome |
Reduces cell activation and accumulation in airways, neutralizes mediators and cytotoxic cell products, and improves lung function in animal models |
Controlled clinical trial Clinical trials are conducted to allow safety and efficacy data to be collected for new drugs or devices. These trials can only take place once satisfactory information has been gathered on the quality of the product and its non-clinical safety, and Health Authority/Ethics Committee approval is...
s |
| Allergic encephalomyelitis Encephalomyelitis is a general term for inflammation of the brain and spinal cord, describing a number of disorders:* acute disseminated encephalomyelitis or postinfectious encephalomyelitis, a demyelinating disease of the brain and spinal cord, possibly triggered by vaccination or viral...
|
Effective in animal model An animal model is a living, non-human animal used during the research and investigation of human disease, for the purpose of better understanding the disease without the added risk of causing harm to an actual human being during the process...
s |
- |
| Allergic rhinitis |
Effects as for adult respiratory distress syndrome, although no specific nasal model has been tested |
Controlled clinical trial |
| Arthritis Arthritis is a group of conditions involving damage to the joints of the body....
|
Inhibits cell accumulation, collagen Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. It is naturally found exclusively in metazoa, including sponges. In muscle tissue it serves as a major component of endomysium...
destruction and angiogenesisAngiogenesis is a physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over this, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for new blood vessel formation by...
|
Anecdotal report |
AsthmaAsthma is a predisposition to chronic inflammation of the lungs in which the airways are reversibly narrowed. Asthma affects 7% of the population of the United States, and 300 million worldwide...
|
As for adult respiratory distress syndrome, however it has also been shown to improve lung function in experimental models |
Controlled clinical trials |
CancerCancer is a class of diseases in which a group of cells display uncontrolled growth , invasion , and sometimes metastasis...
|
Inhibits tumour growth, metastasisMetastasis , or metastatic disease, sometimes abbreviated mets, is the spread of a disease from one organ or part to another non-adjacent organ or part...
and angiogenesis, and increases survival time in animal models |
Several anecdotal reports |
| Delayed type hypersensitivity reactions |
Effective in animal models |
- |
| Inflammatory bowel disease In medicine, inflammatory bowel disease is a group of inflammatory conditions of the colon and small intestine. The major types of IBD are Crohn's disease and ulcerative colitis..-Forms:...
|
Inhibits inflammatory cell transport in general. No specific model tested |
Controlled clinical trials |
| Interstitial cystitis Interstitial cystitis/painful bladder syndrome , is a urinary bladder disease of unknown cause characterised by pain associated with urination , urinary frequency , urgency, and pressure in the bladder and/or pelvis...
|
Effective in a human experimental model of interstitial cystitis |
Related molecule now used clinically |
| Transplant rejection Transplant rejection occurs when a transplanted organ or tissue is not accepted by the body of the transplant recipient. This is explained by the concept that the immune system of the recipient attacks the transplanted organ or tissue...
|
Prolongs allograft survival in animal models |
- |
- indicates no information available
As a result of heparin's effect on such a wide variety of disease states a number of drugs are indeed in development whose molecular structures are identical or similar to those found within parts of the polymeric heparin chain.
| Drug molecule |
Effect of new drug compared to heparin |
Biological activities |
| Heparin tetrasaccharide |
Non-anticoagulant, non-immunogenic, orally active |
Anti-allergic |
Pentosan polysulfatePentosan polysulfate was the first oral medication approved by the U.S...
|
Plant derived, little anticoagulant activity, Anti-inflammatory, orally active |
Anti-inflammatory, anti-adhesive, anti-metastatic |
| Phosphomannopentanose sulfate |
Potent inhibitor Something that restrains, blocks, or suppresses.Inhibitor or inhibition may refer to:* Corrosion inhibitor, a substance that decreases the rate of metal oxidation...
of heparanaseHeparanase, also known as HPSE, is an enzyme that acts both at the cell-surface and within the extracellular matrix to degrade polymeric heparan sulfate molecules into shorter chain length oligosaccharides.-Synthesis and structure:...
activity |
Anti-metastatic, anti-angiogenic, anti-inflammatory |
| Selectively chemically O-desulphated heparin |
Lacks anticoagulant activity |
Anti-inflammatory, anti-allergic, anti-adhesive |
De-polymerisation techniques
Either chemical or enzymatic de-polymerisation techniques or a combination of the two underlie the vast majority of analyses carried out on the structure and function of heparin and
heparan sulfateHeparan sulfate is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins...
(HS).
Enzymatic
The enzymes traditionally used to digest heparin or HS are naturally produced by the soil bacterium
Pedobacter heparinus (formerly named
Flavobacterium heparinum). This bacterium is capable of utilizing either heparin or HS as its sole carbon and nitrogen source. In order to do this it produces a range of enzymes such as
lyaseIn biochemistry, a lyase is an enzyme that catalyzes the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure...
s,
glucuronidaseFor α-glucuronidase, see Alpha-glucuronidaseBeta-glucuronidases are members of the glycosidase family of enzymes that catalyze breakdown of complex carbohydrates...
s, sulfoesterases and sulfamidases. It is the lyases that have mainly been used in heparin/HS studies. The bacterium produces three lyases, heparinases I , II (no
EC numberThe Enzyme Commission number is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze....
assigned) and III and each has distinct substrate specificities as detailed below.
| Heparinase enzyme |
Substrate specificity |
| Heparinase I |
GlcNS(±6S)-IdoA(2S) |
| Heparinase II |
GlcNS/Ac(±6S)-IdoA(±2S)
GlcNS/Ac(±6S)-GlcA |
| Heparinase III |
GlcNS/Ac(±6S)-GlcA/IdoA (with a preference for GlcA) |
The lyases cleave heparin/HS by a beta elimination mechanism. This action generates an unsaturated double bond between C4 and C5 of the uronate residue. The C4-C5 unsaturated uronate is termed ΔUA or UA. It is a sensitive UV chromaphore (max absorption at 232 nm) and allows the rate of an enzyme digest to be followed as well as providing a convenient method for detecting the fragments produced by enzyme digestion.
Chemical
Nitrous acidNitrous acid is a weak and monobasic acid known only in solution and in the form of nitrite salts.Nitrous acid is used to make diazides from amines; this occurs by nucleophilic attack of the amine onto the nitrite, reprotonation by the surrounding solvent, and double-elimination of water...
can be used to chemically de-polymerise heparin/HS. Nitrous acid can be used at pH 1.5 or at a higher pH of 4. Under both conditions nitrous acid effects deaminative cleavage of the chain.
At both 'high' (4) and 'low' (1.5) pH, deaminative cleavage occurs between GlcNS-GlcA and GlcNS-IdoA, all be it at a slower rate at the higher pH. The deamination reaction, and therefore chain cleavage, is regardless of O-sulfation carried by either monosaccharide unit.
At low pH deaminative cleavage results in the release of inorganic SO
4, and the conversion of GlcNS into anhydromannose (aMan). Low pH nitrous acid treatment is an excellent method to distinguish N-sulfated polysaccharides such as heparin and HS from non N-sulfated polysacchrides such as
chondroitin sulfateChondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...
and
dermatan sulfateDermatan sulfate is a glycosaminoglycan found mostly in skin, but also in blood vessels, heart valves, tendons, and lungs....
; chondroitin sulfate and dermatan sulfate being un-susceptible to nitrous acid cleavage.
Evolutionary conservation
In addition to the bovine and porcine tissue from which pharmaceutical-grade heparin is commonly extracted, heparin has also been extracted and characterised from the following species:
The biological activity of heparin within species 6–11 is unclear and further supports the idea that the main physiological role of heparin is not anticoagulation. These species do not possess any blood coagulation system similar to that present within the species listed 1–5. The above list also demonstrates how heparin has been highly
evolutionarily conservedIn biology, conserved sequences are similar or identical sequences that occur within nucleic acid sequences , protein sequences, protein structures or polymeric carbohydrates across species or within different molecules produced by the same organism...
with molecules of a similar structure being produced by a broad range of organisms belonging to many different
phylaIn biology, a phylum ["Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states.] is a taxonomic rank below Kingdom and above Class...
.
Other uses/information
- Heparin gel (topical) may sometimes be used to treat sports injuries. It is known that the diprotonated form of histamine
Histamine is a biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by basophils and by...
binds site specifically to heparin. The release of histamine from mast cells at a site of tissue injury contributes to an inflammatory response. The rationale behind the use of such topical gels may be to block the activity of released histamine, and so help to reduce inflammation.
- Heparin gains the capacity to initiate angiogenesis
Angiogenesis is a physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over this, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for new blood vessel formation by...
when its copper salt is formed. Copper-free molecules are non-angiogenic. In contrast heparin may inhibit angiogenesisAngiogenesis is a physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over this, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for new blood vessel formation by...
when it is administered in the presence of corticosteroids. This anti-angiogenic effect is independent of heparins anticoagulant activity.
- Test tubes, Vacutainer
Vacutainer is a registered brand of test tube specifically designed for venipuncture. It was developed in 1947 by Joseph Kleiner, and is currently marketed by Becton, Dickinson and company.-Principles:...
s, and capillaryCapillaries are the smallest of a body's blood vessels and are part of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
tubes that use the lithiumLithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number three. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
salt of heparin (lithium heparin) as an anticoagulant are usually marked with green stickers and green tops. Heparin has the advantage over EDTAEDTA is a widely used initialism for the chemical compound ethylenediaminetetraacetic acid . EDTA is a polyamino carboxylic acid with the formula [CH
2N
2]
2. This colourless, water-soluble solid is widely used to dissolve scale...
of not affecting levels of most ionAn ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge...
s. However, it has been shown that the levels of ionized calcium may be decreased if the concentration of heparin in the blood specimen is too high. Heparin can interfere with some immunoassayAn immunoassay is a biochemical test that measures the concentration of a substance in a biological liquid, typically serum or urine, using the reaction of an antibody or antibodies to its antigen. The assay takes advantage of the specific binding of an antibody to its antigen...
s, however. As lithium heparin is usually used, a person's lithium levels cannot be obtained from these tubes; for this purpose, royal-blue-topped Vacutainers containing sodiumSodium is a metallic element with a symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1"...
heparin are used.
- Heparin-coated blood oxygenators are available for use in heart-lung machines. Among other things, these specialized oxygenators are thought to improve overall biocompatibility
Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is used, or to more empirical clinical success of a whole device in...
and host homeostasis by providing characteristics similar to native endothelium.
- The DNA binding sites on RNA polymerase
RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
can be occupied by heparin, preventing the polymerase binding to promoter DNA. This property is exploited in a range of molecular biological assays.
- Common diagnostic procedures require PCR amplification of a patient's DNA, which is easily extracted from white blood cells treated with heparin. This poses a potential problem, since heparin may be extracted along with the DNA, and it has been found to interfere with the PCR reaction at levels as low as 0.002 U in a 50 μL reaction mixture.
- Immobilized heparin can be used as an affinity ligand
In chemistry, a ligand is either an atom, ion, or molecule that binds to a central metal-atom to produce a coordination complex. The bonding between the metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The metal-ligand bonding ranges from covalent...
in protein purificationProtein purification is a series of processes intended to isolate a single type of protein from a complex mixture. Protein purification is vital for the characterisation of the function, structure and interactions of the protein of interest. The starting material is usually a biological tissue or...
. The format of immobilized heparin can vary widely from coated plastic surfaces for diagnostic purposes to chromatography resin. Most types of immobilized heparin can be used in three ways. The first of which is to use heparin to select out specific coagulationCoagulation is a complex process by which blood forms clots. It is an important part of hemostasis , wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
factors or other types of heparin-binding proteins from a complex mixture of non-heparin-binding proteins. Specific proteins can then be selectively dissociated from heparin with the use of differing salt concentrations or by use of a salt gradient. The second use is to use heparin as a high-capacity cation exchanger. This use takes advantage of heparin's high number of anionic sulfate groups. These groups will capture common cations such as Na+ or Ca2+ in solution. The third use for immobilized heparin is group-specific purification of RNA and DNA binding proteins such as transcription factors and/or virus coat proteins. This methodology takes advantage of heparin's similar properties to RNA and DNA i.e. negatively charged sugar molecule.
- Heparin does not break up fibrin, it only prevents conversion of fibrinogen to fibrin. Only thrombolytics can break up a clot.
Contamination recalls
In December 2007, the U.S. Food and Drug Administration (FDA) recalled a shipment of heparin because of a growth of
Serratia marcescensSerratia marcescens is a species of Gram-negative, rod-shaped bacterium in the family Enterobacteriaceae. A human pathogen, S. marcescens is involved in nosocomial infections, particularly catheter-associated bacteremia, urinary tract infections and wound infections, and is responsible for...
in several unopened syringes of this product. The bacteria Serratia marcescens can lead to life-threatening injuries and/or death.
In March 2008, major
recallsIn 2008 the following exported products have been recalled from China.*Heparin made for Baxter International. -See also:*2007 Chinese export recalls*2008 Chinese milk scandal*2008 Chinese heparin contamination...
of heparin were announced by the FDA due to contamination of the raw heparin stock imported from China. According to the FDA, the contaminated heparin killed 81 people in the United States. The contaminant was identified as an "over-sulphated" derivative of
chondroitin sulfateChondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...
, a popular shellfish-derived supplement often used for
arthritisArthritis is a group of conditions involving damage to the joints of the body....
.
Use in homicide
In 2006,
Petr ZelenkaPetr Zelenka is a Czech serial killer. Zelenka, a nurse in Havlíčkův Brod, southeast of Prague, murdered seven patients by lethal injection, and attempted to kill 10 others between May and December, 2006. He killed with a hidden vial of heparin — a blood-thinning drug causing internal bleeding...
, a nurse in the
Czech RepublicThe Czech Republic is a country in Central Europe that is sometimes considered to be Eastern European. The country borders Poland to the northeast, Germany to the west and northwest, Austria to the south and Slovakia to the east. The capital and largest city is Prague...
, deliberately administered large doses to patients, killing 7, and attempting to kill 10 others.
Overdose issues
Actor
Dennis QuaidDennis William Quaid is an American actor. He became known during the 1980s after appearing in several successful films.-Early life:...
's twelve-day-old twins mistakenly were given an adult dosage, which is 1,000 times the recommended dosage for infants, in November 2007. The overdose allegedly arose because the labeling and design of the adult and infant versions of the product were easily confused. The Quaid family subsequently sued the manufacturer, Baxter Healthcare Corp., and settled with the hospital,
Cedars-Sinai Medical CenterCedars-Sinai Medical Center is a hospital located in Los Angeles, California, USA.-History:From 1906 to 1910, Dr. Sarah Vasen, the first woman doctor in Los Angeles acted as superintendent of what was then the Kaspare Cohn Hospital....
, for $750,000.
In July 2008, another set of twins born at Christus Spohn Hospital South, a hospital located in
Corpus Christi, TexasCorpus Christi is a coastal city in the South Texas region of the U.S. state of Texas. The county seat of Nueces County, it also extends into Aransas, Kleberg, and San Patricio counties.MSA population in 2008 is 416, 376. The population was 277,454 at the 2000 census; in 2006 the US Census...
, died after an accidentally administered overdose of the drug. The overdose was due to a mixing error at the hospital pharmacy and, unlike the Quaid case, was unrelated to the product's packaging or labeling. , whether the deaths were due to the overdose is under investigation.
Prior to the Quaid accident, 6 newborn babies at Methodist Hospital in Indianapolis, Indiana were given an overdose. Three of the babies died after the mistake.
Popular culture
- Heparin is featured in Dan Brown
Dan Brown is an American author of thriller fiction, best known for the 2003 bestselling novel, The Da Vinci Code. Brown's novels, which are treasure hunts set in a 24-hour time period, feature the recurring themes of cryptography, keys, symbols, codes, and conspiracy theories...
's novel Angels and DemonsAngels & Demons is a 2000 bestselling mystery-thriller novel written by American author Dan Brown and published by Pocket Books. It revolves around the quest of fictional Harvard University symbologist Robert Langdon to uncover the mysteries of a secret society called the Illuminati and to unravel...
, in which the intentional overdose of the drug is used in the murder of a significant character that is disguised to resemble a deathDeath is the termination of the biological functions that define a living organism. It refers to both a particular event and to the condition that results thereby. The true nature of the latter has for millennia been a central concern of the world's religious traditions and of philosophical...
by strokeA stroke is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by thrombosis or embolism or due to a hemorrhage...
.
- Heparin is also featured in the television film The Andromeda Strain
The Andromeda Strain is a 2008 science fiction miniseries, based on the novel published in 1969 by Michael Crichton about a team of scientists who investigate a deadly disease of extraterrestrial origin.-Plot:...
as a way to stop a mysterious alien disease from clotting people's blood.
- Heparin is used in the movie Untraceable
Untraceable is a 2008 thriller film starring Diane Lane, Joseph Cross, Billy Burke and Colin Hanks. It was directed by Gregory Hoblit and distributed by Screen Gems...
when a serial killer injects a man with an overdose of heparin live on the internet. The steady drip causes the man to bleed to death in front of millions of viewers.
- Heparin is used in the television series Dexter to prevent clotting of the blood drained from the victims of a serial killer, so it can be stored for a later purpose.
External links