RESEARCH
Prostaglandin research intensifies Successful induction of abortion spurs studies on potent lipids; vast medical potential foreseen They are the new frontier in medical science. Among the most potent naturally occurring compounds in ani mals, they may become the most im portant new drugs of this decade. They are prostaglandins, and drug companies have been scrambling to in tensify research efforts on them. Late last month, preliminary results from some of the first clinical trials were made public: Prostaglandins have been successfully used to induce abor tions in humans. At present, 16 prostaglandins have been discovered. A family of lipid acids, they are found in a variety of body tissues and biological fluids in ex tremely minute amounts. They are be lieved to be regulators of myriad body functions, including smooth muscle ac tivity, lipid metabolism, and central nervous system, cardiovascular, and re productive physiology. As little as 10" 9 gram per ml. of prostaglan din will affect smooth muscle tissue. Effects in man have been observed when 10 - 1 1 gram per kg. of body weight per minute was infused. Research scientists are hopeful that prostaglandins can be used to regulate menstruation and fertility, prevent con ception, induce childbirth, lower blood pressure, prevent blood clots, treat asthmatics, and act as long-lasting nasal decongestants. One prosta glandin has been reported to control gastric secretions in dogs and rats and prevent formation of experimentally induced stomach ulcers in rats. Clinical studies. In the latest clin ical studies, two research groups have reported successfully inducing abor tions in humans with prostaglandins, without serious side effects [Lancet, 1, 157, 190 (1969)]. One team is made up of pharmacologist S. M. M. Karim, Makerere University, Kampala, Uganda, and house surgeon G. M. Filshie, King's College, London. The other group, at Karolinska Institutet, Stockholm, includes Dr. M. Bygdeman, Dr. N. Wiqvist, and Dr. S. Bergstrom. Dr. Karim had previously found that a prostaglandin can be used to induce labor and childbirth in pregnant women who are at or near term. The intravenous dose was 4 micrograms per minute. The prostaglandin stimulated uterine contractions in women whose bodies produced less than the normal 42 C&EN FEB. 16. 1970
"Primary" Prostagladins Have Been Identified
amount of the lipid. The current preliminary report by Dr. Karim and Dr. Filshie shows suc cess in inducing abortions in 14 of 15 consecutive cases, with only minor side effects of vomiting and diarrhea in some patients. These side effects indi
cate that prostaglandin also stimulates the muscles of the digestive system. Using about a 50 microgram-perminute intravenous injection of the F 2 a-type prostaglandin, abortions oc curred from four to 27 hours later. One trial failed after 48 hours. The treatment was used on women who were from nine to 22 weeks pregnant and ranged in age from 16 to 36. The Stockholm group used subcu taneous injection as well as intravenous methods to give the prostaglandins in doses from 1 to 50 micrograms per minute. Both P G F 2 a and PGEj pros taglandins were used. P G F 2 a seems to cause fewer side effects, the sci entists note. Exactly how prostaglandins work at the molecular level is still largely spec ulative. However, what they are has been known for some time. In 1947 Dr. Sune Bergstrom of Sweden's Karo linska Institutet identified them as un saturated hydroxy fatty acids. All 16 have the same basic 20-carbon-atom skeleton: prostanoic acid (see illustration, this page). The first two prostaglandins isolated in pure crystalline form-in 1957 at the Karo linska Institutet—are now known as PGEj and FGFxa. Their empirical formulas are C 2 0 H 3 4 O 5 and C 2 0 H 3 6 O 5 , respectively. All Ε-type prosta glandins have 11-alpha-hydroxy and 9-keto groups in a five-membered ring. In the F-types, the 9-keto group is re duced to a hydroxyl. These modulators of cellular meta bolism are separated into four cate gories—E, F, A, and B—depending on the arrangements of double bonds, hydroxyl, and ketone groups. All the "primary" prostaglandins contain the 13:14-trans double bond. The E1 and F x compounds contain only this one double bond; the E 2 and F 2 molecules have an additional 5:6-cis double bond. History. The history of prostaglan din research started about four decades ago. In 1930 two New York gynecolo gists, Dr. R. Kurzrok and Dr. C. C. Lieb, reported that fresh human semen could cause strong contractions or re laxation when applied to strips of the human uterus. A few years later, Dr. M. W. Goldblatt in England and Dr. U. S. von Euler in Sweden, working independently, studied the properties of seminal plasma, using partially puri-
Upjohn's C. F. Lawson checks blood pressure of rat given prostaglandin
fied lipid fractions. Dr. Goldblatt used extracts of human seminal plasma, and Dr. Von Euler used the seminal fluid of the monkey, sheep, and goat, and extracts of the vesicular glands of sheep. They collected extensive data on the smooth-muscle-stimulating and the vasodepressor (blood-pressure-lowering) properties of the lipids. It was Dr. von Euler who in 1935 gave the name "prostaglandin" to the active principle of his mixtures. After a hiatus during World War II, progress in prostaglandin research was slow because of lack of material and the difficulty of separating and identifying minute amounts of a sensitive molecule with the conventional tools available at the time. However, in 1956 Dr. Sune Bergstrom of Karolinska Institutet returned to the problem with a team of experts in chromatography, ultramicro analysis, and mass spectrometry, and produced the first crystalline pure compounds the following year. Dr. Bergstrom obtained financial support from Upjohn Co., through Dr. David I. Weisblat, now vice president for pharmaceutical research and development. Production. In 1962, more than 25 years after the discovery of prostaglandin activity, Dr. Bergstrom and colleagues at the Karolinska Institutet elucidated the structures of two prostaglandins. Recent developments in analytical methods had finally made possible the structure determination. In 1964, prostaglandin research received a huge boost when techniques were perfected for in vitro production of the material in relatively large quantities. The method, developed independently by U.S. (Upjohn Co.), Swedish, and Dutch scientists, used fatty acid precursors incubated with sheep vesicular glands.
Upjohn holds the patent on the process and supplies material to laboratories throughout the world. The firm also serves as an informal clearinghouse for information and publishes a revised bibliography quarterly. In 1966, Upjohn scientists, led by Dr. John E. Pike and Dr. Philip F. Beal, developed a synthetic route to a metabolite of prostaglandin (C&EN, July 4, 1966, page 3 2 ) . Two years later, independently and by different routes, scientists at Upjohn and Dr. E. J. Corey's group at Harvard synthesized primary prostaglandins. With the chemical and biochemical synthesis established, knowledge of prostaglandin action in humans is starting to accumulate rapidly. Most of the work has been and is being done in the U.S., Sweden, the Netherlands, and England. Scientific papers on all phases of prostaglandin research are currently appearing at the rate of more than one a day. The race to discover the role of prostaglandins in physiology and medicine is almost unprecedented. The lipids have been found in the greatest amount in human and sheep seminal plasma. They are also present in lesser amounts in uterus, lung, brain, iris, thymus, pancreas, and kidney tissue, besides being discharged in human menstrual blood. Many observers believe they exist in almost all, if not all, tissues. In addition, prostaglandins have been found in such simple animals as a marine coral, Plexaura homomalL·, by University of Oklahoma scientists A. J. Weinheimer and R. L. Sproggins. The prostaglandins differ in their physiological action, both qualitatively and quantitatively. Besides being smooth muscle stimulants and dilators or constrictors of blood vessels, they
Dr. A. Raz separates prostaglandins on chromatographic column at Upjohn
are inhibitors of lipolysis, of platelet aggregation, and of gastric secretion. Major fields of interest now undergoing animal studies include the cardiovascular system, renal and reproductive physiology, gastric secretion, cellular metabolism, and the nervous system. Research workers hope to find a prostaglandin useful in the treatment of hypertension and vascular diseases. These diseases of the heart, kidney, and blood vessel·, together pose the greatest single threat to the lives, health, and well-being of the U.S. population as a whole. Precursors. Several investigators have shown that prostaglandins are formed in the body by cyclization and oxygenation of essential fatty acids. Polyunsaturated fatty acids are termed "essential" when their restriction in a person's diet causes a deficiency syndrome—including scaly skin, stunted growth, impaired fertility, and increased water loss through the skin— which is cured by refeeding small amounts of the acids. Hence, the role of essential fatty acids can be partially explained as precursors of prostaglandins. Two of these unsaturated fatty acids, dihomo-gamma-linolenic acid and arachidonic acid, have been converted to PGEx and PGE 2 , respectively, with crude enzyme preparations from sheep seminal vesicular glands. In this enzyme reaction, three atmospheric oxygen atoms are incorporated into the polyunsaturated fatty acid. Both oxygen atoms attached to the five-memFEB. 16, 1970 C&EN 43
bered ring come from the same oxygen molecule. Response to prostaglandins in the presence of a wide variety of pharmacological blocking agents and in depolarized muscles has led some research workers to suggest a nonneural mechanism for the fatty acids, involving interaction of prostaglandin with a specific discrete receptor in the cell membrane. Furthermore, hydroxy fatty acids might provide chelating sites and carry Ca+ + ions through cell membranes, causing smooth muscle contraction. However, many of the effects demonstrated using prostaglandins, although occurring at very low concentrations, may be quite unrelated to their true physiological function. One explanation of prostaglandin action is that they are control substances regulating cell function, possibly acting by influencing a cell-membrane enzyme, adenyl cyclase. This enzyme, which varies from one cell type to another, converts adenosine triphosphate to cyclic-AMP, which is formed inside the cell and activates metabolic enzymes. In cases where a prostaglandin blocks adenyl cyclase, it has been suggested that the prostaglandin buffers the effects of other hormones or acts as a "counterhormone." The medical area where prostaglandins might first be used as drugs for humans is in controlling stages of the reproductive cycle. Besides the recent clinical abortion studies, Upjohn scientists have been able to prevent conception in mated Rhesus monkeys by prostaglandin treatment. The hypothesis is that the prostaglandin restricts outflow of ovarian blood, which causes the corpus luteum to regress and cease supplying progesterone to the uterine wall. Implantation of the fertilized ovum is thus prevented, and, without a supply of progesterone, menstruation occurs. In Sweden, a prostaglandin is being tested on infertile couples. Since some infertile men have a low prostaglandin level in their sperm, it is possible that the man's semen mixed with a prostaglandin could be successfully used in artificial insemination. The prostaglandin can cause uterine contractions that move sperm to the Fallopian tubes where fertilization takes place. There are also other ways prostaglandins might be used for fertility control. Upjohn Co., a prime mover of prostaglandin research, has been saying for years that "prostaglandins may be as important to medical progress as the steroid hormone discoveries of two decades ago." By the middle of this decade, the Kalamazoo, Mich.based firm probably will have been proved either right or wrong. 44 C&EN FEB. 16, 1970
Data link alcoholism and opiate addiction Acetaldehyde from ethanol alters dopamine pathway, resulting in formation of morphinelike alkaloids There's substantial biochemical evidence to show that addiction to alcohol (ethanol) is very similar to, if not identical to, addiction to opiates (morphine and related compounds). Distinctions between the two drugs in addiction may be only in the length of time and dosage required to develop a dependence. That's what scientists working at the Veterans Administration Hospital in Houston, Tex., believe. Those working on this research include biochemist Virginia Eischen Davis and pharmacologist Michael J. Walsh (both of whom also hold appointments at Baylor University college of medicine), and Dr. Yasumitsu Yamanaka, a visiting pharmacologist from the Hiroshima (Japan) University school of medicine. Ethanol and morphine alkaloids are not only chemically but structurally unrelated. However, a now-acknowledged similarity in addiction to the two drugs could mean that some material that ultimately interacts with the central nervous system is the same, or so nearly the same, for both drugs that the same symptoms of addiction result.
A biochemical explanation for the similarity, developed by Dr. Davis and coworkers, is based on the effect that ethanol has on the metabolism of a biogenic amine, dopamine. The Texas group has for some time studied changes in the metabolism of biogenic amines caused by alcohol: The research team recently demonstrated that acetaldehyde derived from alcohol in the human body is responsible for altering the metabolism of biogenic amines. Abnormal. According to the scientists, the oxidation of ethanol to acetaldehyde is the first step in forming an alkaloid similar to morphine. Subsequently, metabolism of dopamine is altered by acetaldehyde. Acetaldehyde inhibits an enzyme thus diverting dopamine metabolism along a normally unused pathway. The product of this reaction is tetrahydropapaveroline (THP or norlaudanosoline). To form THP, which is formed in tissues rich in biogenic amines, dopamine is first converted to 3,4-dihydroxyphenyl acetaldehyde, a product of oxidation at the juncture of the amine group of dopamine.
inhibition of normal pathway by alcohol leads to complex alkaloid
