King-Thom Chung

Department of Microbiology and Molecular Cell Sciences

The University of Memphis

Memphis, TN 38152

Dr. Bruce N. Ames is well known for his famous Ames Salmonella/microsome mutagenicity assay which is used by more than 3,000 laboratories in the world to test chemicals for mutagenic activity in a bacterial system. His method, and also his involvement in the study of identifying mutagens/carcinogens, have influenced cancer studies for more than 30 years and will continue to influence research in the future. He is a world leader in molecular genetic toxicology, his research accomplishments having made a great impact on how we think about cancer and other degenerative diseases today.

Bruces Nathan Ames was born on December 16, 1928, in New York City. He has two younger sisters. His father Dr. M. U. Ames, was a high school chemistry teacher who also had a doctorate in law. His mother, Dorothy Andres Ames, came to the U.S. as a young child from Poland. His father was a chairman of a high school chemistry department, and later a supervisor of science for all the New York City public schools, and an Assistant Superintendent of New York City schools. They lived in the Washington Heights area of Manhattan in New York City. Every summer they rented a cabin on a lake in the Adirondack Mountains, where they enjoyed hiking, swimming, and other outdoor activities. As a child, Bruce loved the natural world and collected animal specimens. He was also an avid reader. He read many books left lying around the house by his father, and he carried a stack of books home for reading every week from the library.

At the age of 13, he attended the Bronx High School of Science. He was always interested in biology and chemistry. He did some experiments studying the effect of plant hormones on the growth of tomato root tips. [Plant hormone auxins were discovered by F. H. Went (1903-) and Kenneth V. Thimann (1905-1997) at about that time]. In 1946, he enrolled in Cornell University in Ithaca, New York, majoring in chemistry with a minor in biology. He received his B.A. degree in 1950, and went directly to the graduate school at the California Institute of Technology (Caltech), Pasadena, California, where he worked in Dr. Herschel K. Mitchell’s (1913-) laboratory. He was influenced by many distinguished scientists at Caltech. He studied biochemical genetics using mutant strains of the bread mold Neurospora. Using genetic/nutritional mutation techniques to study the biochemical pathway was pioneered by George W. Beadle (1903-1989) and Edward L. Tatum (1909-1975). George Beadle was the chairman of the genetics department from 1946 to 1959 at Caltech. Bruce’s thesis work was a cutting edge subject during those days. He completed his Ph.D. degree in 1953 at age 24. He studied the biosynthesis of the amino acid histidine using different mutant strains of Neurospora. Bruce himself said that, as a student, he was never a straight A student, but he was creative and good at solving problems. We can also see that he has a very good training; he has always been associated with top grade scientists. His innovative scientific career had been laid with a good foundation.

After completing his Ph.D. degree at Caltech, Bruce took a postdoctoral position in 1953 and worked at Bernard Horecker’s (1914-) laboratory at the National Institute of Health (NIH). From 1954, Bruce became an independent investigator and worked on histidine biosynthesis gene regulation using Salmonella typhimurium. He married Dr. Giovanna Ferro-Luzzi, a postdoctoral student from Italy in 1960. In 1961, he took a sabbatical leave from NIH in Europe. He divided the year between Dr. Francis H. C. Crick’s (1916-) laboratory in Cambridge, England, and Francois Jacob’s (1920-) laboratory at the Pasteur Institute in Paris, France. At that time, Crick was about to receive a Nobel Prize in 1962 for his earlier work on the structure of deoxyribonucleic acid (DNA). Jacob was working on how the messenger ribonucleic acid molecule (mRNA) interacts with DNA to synthesize protein, which was also a frontier research for biology at that time. Jacob, too, received the Nobel Prize in 1965. These studies were at the cutting edge of scientific progress. They impacted Ames and affected his later scientific thought.

Ames returned to the United States in 1962 to become chief of microbial genetics at the Laboratory of Molecular Biology at NIH. He focused his research on the regulation of the histidine operon—a specific group of genes involved with the biosynthesis of histidine in Salmonella and the role of transfer ribonucleic acid (tRNA) in this regulation. This work paved the way for his later development of the mutagenicity assay.

One of the special contributions during this period of time was that Ames co-authored with Dr. Robert G. Martin (1935-) a paper on sucrose gradient centrifugation, a method for determination of the molecular weights of proteins. This technique was very useful for biochemical, molecular biological, and biotechnological investigations. This technique also contributed to the development of molecular biology because the determination of the molecular weight of proteins is very important for any kind of biochemical research. Another significant contribution was the study with Martin showing that the histidine biosynthetic genes were turned

on and off as a unit and that a single mRNA was produced from the cluster of genes. This work was one of the bases for the operon theory of Jacob and Monod that led to their Nobel Prize.

Sometime in 1964, Ames read the list of ingredients on a box of potato chips, and began to wonder whether preservatives and other synthetic chemicals could cause genetic damage to human cells. It could be serious if we ingested large quantities of a mutagenic chemical. He began to develop a test for chemical mutagens. Since he mutated bacteria all the time, he used strains of Salmonella typhimurium which were mutated in a gene for synthesizing histidine (a histidine-requiring mutant). He placed about one billion cells of this bacterial culture into a petri dish with an agar medium without histidine. With such a huge number of bacteria, a few revertant colonies would appear following a short incubation time. This is called spontaneous mutation (mutation back to histidine non-requiring). Any chemical added to this test system that increases the number of such revertants is a "mutagen." A mutagen increases the rate of mutation. Later, Ames also added to the mixture a liver homogenate fraction, called the S9 fraction, from rodents. The S9 preparation contains various metabolic enzymes. Some chemicals do not cause mutation themselves, but increase mutation if this liver homogenate is also included in the assay system. This is because the enzymes in the liver homogenate can metabolize the chemical to an active form which then mutates the bacteria. Chemicals that can cause mutations in the test system without the inclusion of this homogenate are called "direct mutagens." Those chemicals that require this liver homogenate are called "indirect mutagens" that required "metabolic activation." This simulates how chemicals are metabolized in the liver system.

In 1968, Ames accepted a position as a professor of biochemistry at the University of California at Berkeley. He and his students continued to work on chemically-induced mutations. Chemicals that cause mutations in bacteria may cause mutations in human genes. He first paid attention to those chemical capable of causing human cancers—called carcinogens. His paper published in 1973 in the United States Proceedings of National Academy of Science (PNAS) was titled, "Carcinogens are mutagens." In a subsequent paper, he reported that 174 of suspected carcinogens, 80 or 90 percent of them caused mutations. His discovery thrilled the world of genetics and carcinogenesis.

Ames’s method of assaying the mutagenicity of chemicals is relatively simple, inexpensive and quick, which is in contrast to the time-consuming rodent cancer test assay. His method was quickly adapted by thousands of laboratories in the world. Ames never patented his method, he also voluntarily provided his tester bacterial strains free of charge. He was also willing to teach others how to do the test. Ames soon became world renowned and his method was widely used. His method of detecting mutagens is commonly known as the Ames test by both scientists and the public.

With his knowledge of the histidine operon, Ames continued to improve the sensitivity of the tester strains. A set of different types of histidine requiring tester strains were introduced. These strains would not only give answers to whether the test chemicals are mutagenic, they could also help interpret the types of mutations (such as base-pair mutation or frameshift mutation). In 1994, Ames and Dr. Pauline Gee developed a new set of six strains that were more sensitive than the old tester strains and diagnosed the six possible base pair mutations.

The new Ames test not only helps to identify the genotoxic nature of many chemicals, but also helps us to understand the molecular mechanism of mutagenesis. This work contributed tremendously to our broad knowledge of genetic toxicology today.

Since the publication of Ames’ work, both the public and government were concerned with the risk of hazardous chemicals released to the environment. Ames himself urged close scrutiny of possible environmental cancer hazards. He and his students demonstrated that a flame retardant, tris-BP used in children’s polyester pajamas was a mutagen. As a result of his effort, tris-BP was withdrawn from the market. He also stressed problems associated with the relative risks of various carcinogens. He noted that the potency of carcinogens could vary, well over a million fold, and a priority list was necessary to evaluate various carcinogens.

However, as the time went by, and more scientific data piled up, Ames began to change his view and came to doubt that traces of synthetic chemicals were important as causes of cancer. In the 1980s, California agriculture was threatened by the medfly. Many agricultural experts recommended use of insecticide, malathion. But Governor Jerry Brown did not agree because he sided with the environmental activitists and believed that the widely use of malathion would pose a risk to human health. Ames, however, testified that a significant hazard did not exist from using that pesticide. He suggested that the spraying of malathion would pose no more danger than pouring a can of diet soda on one’s front lawn.

Ames was not a spokesman for industry and in fact does not consult or testify in lawsuits, rather his comments were based on new scientific findings and comparative observations. His paper, "Dietary Carcinogens and Anticarcinogens," published in 1983 in Science, found that daily items such as coffee, alcohol and potatoes contain mutagens and carcinogens with possible hazards much greater than synthetic chemicals. He argued that the important thing was that many plants, vegetables and fruits we consume also contained anti-carcinogens such as vitamin C, vitamin E, beta-carotene, selenium and other natural substances. He argued that the higher incidences of cancer in certain human populations might be due to "less than optimum amounts of anticarcinogens and protective factors in the diet." Ames views pesticides as a public health advance in making produce less expensive. He strongly advocates eating more fruits and vegetables which he believes is the best way to lower risks from cancer and heart disease, other than giving up smoking. Vitamins, antioxidants, and fiber of plant source are important anticarcinogens.

The rodent test for carcinogenicity utilizes maximum tolerated doses of suspected hazardous synthetic chemicals. Therefore, Ames thought it was necessary to examine the carcinogenicity of the natural background of chemicals that humans ingest (99.9 percent of the chemicals) as a control to put synthetic carcinogens in perspective. He and his colleagues, particularly Dr. Lois Gold, had spent much time in developing a "Carcinogen Potency Database" and published a paper entitled "Ranking Carcinogenic hazards" in Science, in 1987. They created an index called HERP (Human Exposure Dose/Rodent Potency Dose) which compared the average daily dose of chemicals which humans might receive with the dose needed to induce cancer in rodents. The results of HERP show the possible cancer hazard of traces of synthetic chemicals such as pesticides, are tiny compared to natural chemicals in the diet. Even the much greater possible hazards from "rodent carcinogens" in natural chemicals should be taken with much skepticism. He and Dr. Gold have shown that half of all chemicals ever tested are "rodent carcinogens." He and his colleague Lois Gold argued that since half of natural chemicals tested were rodent carcinogens, that this finding and considerations of mechanism, suggested that high- dose tests were not relevant for low dose exposures.

Ames’s view of the relationship between cancer and pesticides received many critical attacks. The HERP was not intended to be a reliable risk indicator but "only a way of setting priorities for concern," Ames argued. However, Ames and his colleagues concluded that "we lack the knowledge to do low-dose risk assessment". Dr. Ames’ conclusion on extrapolation from high-dose to low-dose effects profoundly affected the scientific investigation of hazardous agents. Skepticism as to low-dose effects of synthetic chemical carcinogens on cancer formation has been spreading among toxicologists.

Despite the attacks and criticism on his view of cancer, Ames insisted that it is important to keep up with new scientific facts and modify one’s viewpoint, especially in the rapidly changing and difficult area of cancer causes and prevention. He also thinks there are several misconceptions on cancer which need to be clarified. He repeatedly addresses those issues to the general audience which he regards as a part of his duty as a scientist. His basic viewpoints are: (1) Concern with hundreds of minor, hypothetical risks is a distraction from major risks such as unbalanced diets and cigarette smoking; (2) Many micronutrient deficiencies are radiation mimics and are a major source of DNA damage in the U.S. population. (3) Almost half of the test chemicals are rodent carcinogens for both synthetic and natural chemicals. (4) High-dose animal testing is unreliable for low-dose extrapolation. (5) Human exposure to rodent carcinogens is almost all to natural chemicals. (6) Synthetic chemicals pose minuscule risks compared to substances found in nature. (7) Correlations does not mean causation, and "cancer clusters" mostly come about by chance alone; and (8) There are undesirable trade-offs in eliminating pesticides, as pesticides lower the cost of fruits and vegetables, a major protection against cancer.

Like many experts, Ames considers smoking and dietary imbalances the most serious causes of cancer. He also agrees with many experts that increasing dietary fruits and vegetables and ensuring adequate micronutrients are the best cancer preventive measures, other than decreasing smoking.

His work on mutagenesis and cancer led him to consider the nature of human aging. In support of the widely discussed free radical theory of aging, Ames and his students showed that many of the effects of aging may be due to oxidative damage caused by free radicals in mitochondria. There is a large amount of oxidative damage just from living. He said, "living is like getting irradiated." We are generating energy when burning fat, carbohydrates and proteins, which means pulling electrons off them. We add the electrons to oxygen in the mitochondria to generate energy. The 4 electron addition to one oxygen molecule is safe, but if one electron is added at a time, we make superoxide, hydrogen peroxide, and hydroxy radical. These radicals can cause oxidative damage which contribute to degenerated diseases such as cancer, aging, heart disease, cataract, and brain dysfunction. He estimated a very high (10⁵ hits/cell/day in the rat) endogenous oxidative DNA damage rate and a fairly high steady level of oxidative DNA damage in individuals. He has found that thymine glycol, thymidine glycol, hydroxymethyluracil, and 8-hydroxydeoxyguanidine in human urine, are probably derived mostly from repair of oxidized DNA in the tissues. These free radicals can be scavenged by various repair mechanisms and enzymes defenses and also by antioxidants such as vitamins C and E, and selenium. A major defense against cancer and other degenerative diseases is to have adequate antioxidants and other micronutrient in the diet. Many of those who get cancer or degenerative diseases may be those who are deficient in these important antioxidants and micronutrients in their diets, or those whose living style helps enhance oxidative damage such as smoking. The Ames’ laboratory recent research is focusing on the following: (a) the relationships between nutritional factors, particularly folate, vitamin B12, and B6 deficiencies, and DNA damage and cancer; (b) chronic inflammation as a risk factor for cancer formation. The lab is developing analytical methods to measure chronic inflammation in humans, and nutritional intervention to combat it; and (c) mitochondrial oxidative decay and aging. He is finding some mitochondrial metabolites reverse mitochondrial decay, which may delay degenerative processes.

In brief, Ames’s interest is in identifying the important mutagens that will damage human DNA, the defense mechanisms to protect us from damage, and studying the consequences of DNA damage for cancer formation and aging. His outstanding work not only revealed a great amount of knowledge related to molecular genetic toxicology and cancer, but also provided a lead to future investigations in human health. He has published over 400 scientific papers and is one of the most cited scientists in all fields.

Ames has often been honored for his achievements. In 1964, he received the Eli Lilly Award of the American Chemical Society. In 1966, he won the Arthur Fleming award. He received the Lewis Rosenthal Award in 1976, the Environmental Mutagen Society Award in 1977, the Cal Tech Distinguished Alumni Award in 1977, the Simon Shubitz Cancer Prize and the Felix Wankel Research Award in 1978, and the John Scott Medal in1979. In 1983, he was a recipient of the Gairdner Foundation Award from Canada and the Charles S. Mott Prize of the General Motors Cancer Research Foundation. In 1985, he won the Tyler Prize for Environmental Achievement, and in 1989, he was awarded the Roger G. Williams Award in Preventive Nutrition. In 1991, he won the Gold Medal of the American Institute of Chemists. In 1992, he was a recipient of the Glenn Foundation Award of the Gerontological Society of America. He won the Lovelace Institute Award for Excellence in Environmental Health Research in 1995 and the Achievement in Excellence Award for the Center for Excellence in Education in 1996, and the Honda Prize of the Honda Foundation (Japan) in 1996. In 1997, he received the Japan Prize. In 1998, he was a recipient of the U.S. National Medal of Science.

He is also a recipient of many honors. He is a member of the National Academy of Sciences, the American Academy of Arts and Sciences, and is a fellow of the American Association for the advancement of Science. He served as a member of The National Cancer Advisory Board from 1976 to 1982. He has received honorary degrees from Tufts University and the University of Bologna. He is a foreign member of the Royal Swedish Academy of Sciences, and an elected fellow of the Academy of Toxicological Sciences and the American Academy of Microbiology.

Ames remains at the University of California at Berkeley in the Department of Biochemistry and Molecular Biology. He served as the chairman from 1983 to 1989. Since 1979 he has been the director of the National Institute of Environmental Health Science Center at Berkeley.

Bruce Ames married Giovanna Ferro-Luzzi on August 27, 1960. Dr. Ferro-Luzzi is also a professor of biochemistry at Berkeley. They have a daughter, Sofia, and a son, Matteo. Dr. Ferro-Luzzi came from Italy, and they are enjoying a good Mediterranean diet with lot of fruits and vegetables. Ames practices what he believes in. He has a wonderful marriage and is happily living in Berkeley, California.

This author had the opportunity to listen to Dr. Ames’ seminars since 1970 as a graduate student in California. I found Ames as handsome and having a good sense of humor. He is a good and popular speaker for conferences or symposiums. One reason for his popularity is that he is always optimistic and his sense of humor, zeal, and enthusiasm, make him not likely to be an enemy of anybody, although he received many critical attacks on his work. He is successful in science as he said he is always thinking and challenging assumptions. Although he sounds like a spokesman for industry, he never obtains any funding or asks for any personal benefit from industry. Science is for science. That is the way it should be and that is the way Dr. Ames practices. He is a true leader.

Beadle, George Wells (1903-1989). American geneticist. Nobel prize in Physiology and Medicine in 1958. Researched on genetics of Indian corn and cross-over in fruit fly.

Crick, Francis Harry Compton (1916-). British biologist. Nobel Prize in Medicine and Physiology (with J. D. Watson and M. H. F. Wilkins) in 1962, proposed model for double-helix structure of DNA.

Horecker, Bernand Leonard (1914-). American biochemist. Researched on characterization and isolation of respiratory enzymes, carbohydrates metabolism, enzymology, spectrophotometry of hemoglobin and its derivatives.

Jacob, Francois (1920-). French biologist. Nobel prize in Physiology and Medicine in 1965 (with A. Lowff and J. Monod). Contribution to mechanism of information transfer and genetic basis of replicating DNA.

Mitchell, Herschel Kenworthy (1913-). American biochemist. Researched on growth factors in microorganisms, biochemical genetics of Neurospora and Drosophila.

Tatum, Edward Lawrie (1909-1975). American biochemical geneticist. Nobel prize in Physiology and Medicine in 1958. Co-discovered one-gene-one enzyme concept. Pioneered studies on genetical mutations in Neurospora.

Thimann, Kenneth V. (1905-1997). American biologist. Co-discovered plant hormone auxin and its function (with F. W. Went). Researched on plant biochemistry, effects of light and gravity in higher and lower plants.

Went, Frit Warmolt (1903-) American botanist. Studied phytohormone (with K. V. Thimann), plant tropism, effect of climate on plants, ecology of dessert plants, plant emanations as sources of atmospheric hazes.