Heparin, one of the oldest drugs still in widespread clinical use, is a naturally occurring glycosaminoglycan whose main function is to inhibit the coagulation of blood. It was discovered almost a century ago and took many years to move from the laboratory to the bedside. There has been significant controversy regarding the distribution of credit its discovery. James Marcum has chronicled both the discovery and development (Marcum, 1990, 1997), and the dispute (Marcum, 2000).
Initial discoveries: from fat-soluble phosphatides to water-soluble heparin
In 1916, at Johns Hopkins Medical School, Baltimore, USA, a second year medical student, Jay McLean, was working under the physiologist William Henry Howell (Fig 1). Howell’s main interests were the substances controlling blood clotting; he thought there was a balance between a clotting inhibitor (termed antithrombin) and a procoagulant (termed thromboplastin). He believed that the release of cephalin (so called because it was first isolated from canine brain) from platelets and leucocytes neutralised antithrombin, permitting activation of prothrombin by calcium (Howell, 1912). McLean had come up to Baltimore the previous year and was assigned by Howell to examine the chemical purity of cephalin preparations, and to demonstrate that it was cephalin and not a contaminant in the preparation that accounted for the procoagulant activity. After finishing this work early, McLean extracted phosphatides (fat soluble compounds) from canine liver that appeared to demonstrate anticoagulant, properties in vitro and subsequently led to excessive bleeding in experimental animals. McLean then moved to the University of Pennsylvania to research cephalins further under Richard Mills Pearce. In October 1917, he returned to Baltimore but did no further research on the phosphatides he had isolated the previous year. Instead, he continued research on cephalin, feeling that work on a procoagulant rather than an anticoagulant, was better for the ongoing efforts in The Great War.
Back in Howell’s laboratories, work on anticoagulants continued. Alongside another medical student L. Emmett Holt Jr, Howell had isolated another fat soluble anticoagulant apparently distinct from that isolated by McLean 2 years previously (Howell & Holt, 1918). The term ‘heparin’ was coined by Howell from the Greek ‘hepar’, or liver, the tissue from which it was first isolated. At an annual meeting of the American Physiological Society in 1922, Howell introduced an aqueous extraction protocol for isolating heparin and, at The 12th International Physiological Congress in 1926, he presented refinements to this protocol and identified the water-soluble carbohydrate as glucuronic acid. This he correctly claimed was a compound distinct both to the entity isolated by himself and Holt in 1918 and by McLean in 1916.
This water soluble heparin began to be produced commercially by a local pharmaceutical company in Baltimore, Hynson, Westcott, and Dunning, but studies conducted at Mayo Clinic, Minnesota, by Edward Mason demonstrated that this preparation caused side effects including headaches, fevers and nausea (Mason, 1924). Howell was concerned production would cease as its toxic effects might preclude widespread use (Howell & MacDonald, 1930). However, heparin did continue to be available commercially despite these fears, although the pharmaceutical company did not advance its isolation beyond Howell’s original protocol. In 1931, Howell retired from his post at Johns Hopkins and did no further research on heparin.
Bringing heparin to the bedside
Investigators in other parts of the world were working on a way to better purify heparin and thus avoid its side effects. In 1928, the physician and physiologist Charles Best (Fig 2), most famous for his work on insulin at the Connaught Laboratories, Toronto, began to assemble a team of biochemists, physiologists and clinicians at the city’s university. He had spent the last few years in the National Institute of Medical Research (established in London in 1913 as the first institute of the Medical Research Council) and decided to develop heparin into something useful for research and clinical purposes. In 1929 he became Professor and Head of Physiology at the university and it was at this time that he and his graduate student, Arthur Charles, began work in earnest. Their aims were twofold; to further purify heparin to reduce or eliminate its side effects and to demonstrate its effects in the prevention of thrombus formation. In 1929, Erik Jorpes, a Swedish physiologist visited Best to observe the production of insulin at Toronto. Jorpes was shown around the Connaught Laboratories and introduced to the work on heparin. He subsequently returned to Stockholm and began his own attempt to isolate and characterise the substance.
It was not until 1933, four years after Best’s team had begun serious work on the project, that Charles, and his more experienced colleague David Scott, who had served as an assistant director at the Connaught Laboratories, published a series of papers on their work thus far (Charles & Scott, 1933a,b,c). In the first paper (Charles & Scott, 1933a) they outlined a protocol for isolating a crude heparin preparation from bovine liver. To increase the amount of heparin yielded, the tissue had to be autolysed but the smell of the decaying tissue was so bad that the production had to be moved from the laboratories in the city to the local Connaught Farm! Their next paper outlined a survey of extra-hepatic tissues where heparin could be identified, partly because of the high cost of liver (Charles & Scott, 1933b). They concluded that liver, muscle, and lung tissues were where heparin was most abundant. The only tissue found to have little or none isolated was the tissue considered most integral to its mode of action; blood. Almost a decade earlier Howell had claimed that heparin was responsible for the fluidity of blood, he believed that although the amount of heparin in the circulation was probably small, its overall potency was greater there (Howell, 1925). The third and final paper in the series presented a purification protocol for heparin (Charles & Scott, 1933c). As Best later clarified, the preparations were not pure in the chemical sense but rather free from toxic components. It was hoped that the preparations would be of uniform potency but, although Charles and Scott were finally able to produce a crystalline form of heparin, there were problems getting consistent results from batch to batch. This not only hampered clinical progress but also sparked complaints from researchers who had bought heparin from Connaught laboratories for their own research purposes. One such investigator was Robert Cornish who was experimenting with dogs. In 1934, he wrote a letter to the Connaught laboratories complaining that the heparin he had bought ‘caused failure of two of [their] experiments as well as damage to blood’. He went on ‘…if you intend to sell much more heparin you should avoid such serious misbranding in the future!’.
To address the clinical and physiological aspects the Canadians worked in two teams; Murray led a team at the Toronto General Hospital while Best’s team continued to work in the Department of Physiology and School of Hygiene. Their initial publication was on the application of heparin for thrombus prevention in dogs (Murray et al, 1937), where they showed that heparin prevented thrombus formation in veins traumatised by mechanical or chemical means. The first use of this newer, purer, form of the anticoagulant in a human was 16 April 1937 – a solution of heparin in saline was passed into the brachial artery resulting in a significantly increased clotting time during the 2-h infusion. There were no toxic side effects. Murray tentatively claimed during a Hunterian lecture in the same year that although its development was still in its early days, its use could potentially extend to embolectomy, splenectomy, venous grafts and pulmonary embolism.
In 1939 Jay McLean, the medical student who first isolated the anti-coagulant fat-soluble phosphatides over 20 years previously, had began to investigate the clinical efficacy of heparin (along with sulfapyridine) in patients with endocarditis (McLean et al, 1941). Unfortunately, both patients succumbed to the disease despite the treatment. More promisingly, in 1943, heparin was used to preserve a gangrenous leg from full amputation (McLean & Johnson, 1946). Following discussions with McLean, Kurt Lange from New York Medical Center reported that gangrene resulting from frostbite, and military trauma such as paratroopers landing injury might be treated with heparin (Lange et al, 1945).
After the war, Connaught Laboratories continued to produce heparin and attempted to increase its potency. However, by 1949, Drs Peter Moloney and Edith Taylor had patented a method that obtained a greater yield of heparin at lower cost, making heparin cheaper to produced elsewhere. By the early 1950s, Connaught had stopped producing the drug it had pioneered altogether (Rutty, 2000).
The distribution of credit
Before the 1940s, most researchers in the biomedical community regarded Howell as the discoverer of heparin (Murray, 1940). According to James Marcum’s account of the origin of the dispute over heparin, Jay McLean, unhappy that he had not received appropriate recognition for heparin (something he saw as his own discovery) began a campaign in the 1940s to re-dress the balance of distribution of credit (Marcum, 2000). McLean gave several national lectures and wrote a number of letters to Best claiming that he, and not Howell, was the discoverer of heparin. However, McLean kept his campaign relatively discreet until Howell’s death in 1945, largely because he wanted to avoid controversy because of his long-standing relationship with Howell. It is important to note, as Marcum points out (Marcum, 2000), that it was not the intention of McLean to deceive but rather ‘correct the perception of the biomedical community that Howell was responsible for the discovery of the anticoagulant’. Louis Jaques was irritated by McLean’s claims to be the discoverer of heparin and claimed that McLean’s contribution was part of ‘American medical folk-lore’ (Jaques, 1978) and in a letter written in 1987 he stated ‘the key person for heparin was Charles Best as he had the novel combined role of top academician and director of production of biological products’ (Marcum, 2000). McLean’s efforts in persuading the biomedical community of his discovery were largely fruitful. After his death in 1959, his obituary credited him with the accolade ‘discoverer of heparin’ and did not mention Howell at all (Marcum, 2000). In 1963, a plaque was unveiled in Johns Hopkins to commemorate the ‘major contribution [of McLean] to the discovery of heparin in 1916 in collaboration with Professor William Henry Howell’ (Ulin & Gollub, 1964).