- Author: Kathy Keatley Garvey
The research involves the development of a DNA-based sensor amplification system demonstrated in a fluorescence immunoassay that can detect, both simply and rapidly, trace amounts of organophosphate pesticides (OPs) in food products.
Trace detection of such OPs as triazophos, parathion, and chlorpyrifos is “extremely important for various reasons, including food safety, environmental monitoring, and national health,” the authors pointed out.
The device is not only easier to use, more reliable, and faster than traditional methods of pesticide detection, but offers a more cost-effective alternative, said the authors, noting that their device could “address the limitations of traditional detection methods, such as liquid chromatography-tandem mass spectrometry, which are expensive, time-consuming, and require extensive training.”
The paper, “Competitive Fluorescent Immunosensor Based on Catalytic Hairpin Self-Assembly for Multiresidue Detection of Organophosphate Pesticides in Agricultural Products,” appeared in the February edition of the Food Chemistry journal and is republished in June as “Paper of the Month."
Maojun Jin, who served a year (September 2019 to September 2020) as a visiting scholar in the Hammock laboratory, UC Davis Department of Entomology and Nematology, led the research team, and is the senior author and corresponding author. He is now a professor in the Institute of Quality Standards and Testing Technology for Agro-Products, Chinese Academy of Agricultural Sciences. His doctoral student, Yuanshang Wang, is the first author.
“The immediate impact of the rapid biobar code immunoassay in reducing human and environmental exposure to three organophosphate pesticides is obvious,” said Hammock, who holds a joint appointment with the Department of Entomology and Nematology and the UC Davis Comprehensive Cancer Center. “Since Rosalyn Yalow shared the 1977 Nobel Prize for developing the immunoassay, there have been many incremental improvements to increase assay sensitivity and speed. The biobar code amplification system is more than incremental. It also allows samples to be multiplexed with several analytes monitored in one tube. This amplification technology can be applied to immunoassays in general in both the biomedical and environmental field. It is wonderful to see what Maojun and his team have accomplished. In analytical chemistry we are always striving for ‘better, faster, cheaper' and Maojun's team accomplished this.”
Hammock said that the aim is to “ensure proper use and protect human health from some commonly used and quite toxic pesticide and the development of a novel signal amplification - transduction system making the assay faster, more sensitive and allowing the assay to be multiplexed with the possibility of multiple signals in one tube with the use of DNA biobar codes.” In the paper, the co-authors point out that “The organophosphate pesticides triazophos, parathion, and chlorpyrifos are highly toxic and have been linked to adverse health outcomes, such as cancer. Although many countries have banned or restricted their use, the chemicals are still components of pesticide mixtures used in daily agricultural production around the world. The sensor contains an immunoassay, which is a type of test that uses antibodies to detect pesticide residues. This process results in a single DNA strand that then binds to a gold nanomaterial-based synthetic protein through chemical bonding.”
“Then, another DNA structure called a hairpin is added to the mix to from a double-stranded DNA structure,” they explained. “The resulting structure fluoresces upon detection of the residues so organophosphates can be quantified.”
The team then used the sensor to measure traces of OPs in contaminated fruit, vegetables, and grain and compared their results to findings from traditional liquid chromatography-tandem mass spectrometry. They found that their DNA-based sensor detected the three pesticides in the mixtures as accurately as the mass spectrometry method.
“I'm very proud of what Maoiun and his team have accomplished,” said Hammock, who directs the NIEHS-UC Davis Superfund Research Program. The research was partially funded by his Superfund grant, and his NIEHS RIVER (Revolutionizing Innovative, Visionary Environmental Health Research) Award.
In addition, the research drew financial support from the National Natural Science Foundation of China, Central Public-interest Scientific Institution Basal Research Fund, and the Central Public Interest Scientific Institution Basal Research Fund for the Chinese Academy of Agricultural Sciences.
Professor Jin is engaged in research on food safety testing technology, especially in immunoassay. “Firstly, we develop antibodies against different types of pesticides, including monoclonal antibodies, nanobodies, and recombinant antibodies,” he explained. “With these antibodies, we can specifically recognize pesticide residues in food and the environment. On the basis of preparing antibodies, we achieve quantitative detection of pesticide residues based on different labeling systems, such as colloidal gold, fluorescence, chemiluminescence, and DNA strands. This paper is based on DNA strands as marker substances, achieving the detection of very trace pesticides in food and ensuring human health.”
Yuanshang Wang is a doctoral student at Huazhong Agricultural University, specializing in food science. “My research interest is in the field of trace and rapid detection analysis of hazardous substances in food,” she said.
- Author: Kathy Keatley Garvey
Research.com just released its 2023 rankings, based on a researcher's D-index (Discipline H-index) metric, which includes only papers and citation values for an examined discipline. For chemistry, the organization singled out leading scientists with a D-index of at least 40 for academic publications.
Gee achieved a D-index of 56, 8,287 citations, and 202 publications.
“We already knew she's one of the nation's best chemists; we're so proud of her,” said Hammock, a UC Davis distinguished professor who holds a joint appointment with the Department of Entomology and Nematology and the UC Davis Comprehensive Cancer Center.
Her statistics are “better than most of the chemists in the UC Davis Department of Chemistry,” Hammock added.
“This is a pleasant surprise and I am honored,” Gee said. “But, it would not have been possible without Bruce's mentorship and all the hard work of the many graduate students and postdocs that have come through our lab. Their eagerness and creativity and the ready availability of both lab and campus wide collaborators, as well as the multidisciplinary nature of the lab let them bring many new ideas to fruition. So my deepest gratitude goes to all of them. I just tagged along for the ride!”
“In addition to her scientific leadership Shirley became the personal focus of the field with her personal encouragement and attachment for scientists internationally,” Hammock related. “She made Davis the place to come to get the latest in technology and made international introductions and fostered collaborations that continue to be productive today.”
The UC Davis toxicologist was among the first staff research associates at UC Davis to be given principal investigator status on grants. "On her own, she developed a computer-based chemical and equipment inventory system in the laboratory which could be used throughout the university," Hammock said.
Gee's work has been recognized repeatedly with achievement awards and publications in peer-reviewed journals. Her area of expertise is the development of "ELISA" (enzyme-linked immunosorbent assays) for pesticides and other environmental pollutants and their metabolites. She has trained students from around the world.
Gee was a toxicologist at SRI International in Menlo Park for three years before joining the Hammock lab in 1985. In the Hammock lab, she managed a team of researchers for more than three decades that annually included some 40 scientists: graduate students, technicians, post graduates and visiting professors from all over the world. From 2007 to 2016, she served as the director of research and founding member/manager of Synthia LLC, Davis.
“I have long been interested in human and environmental exposure to toxicants and utilizing screening methods to evaluate the presence of the toxicant as well as the potential for effects,” Gee writes in her biosketch. “Immunoassays have been used clinically for more than 50 years to detect the presence of drugs, hormones and microorganisms for human medical diagnostics.”
Hammock, a pioneer in the field that applies immunoassay and biosensor technology to environmental toxicants, noted that “Shirley led a project that extended the technology to measurement of a variety of environmental toxicants including pesticides, industrial byproducts, bioterror agents and flame retardants. It also included the application of new concepts to improve the robustness, sensitivity and high throughput that is required for environmental analysis and for the analysis of low-level exposure to toxicants in humans and animals in large scale studies.”
Gee has collaborated with investigators from the U.S. Environmental Protection Agency, Uruguay, Mexico, and Sweden using the assays for dioxins. She participated in a farmworker exposure study on the herbicide paraquat in Costa Rica and a farmer/consumer study in Thailand on exposure to pyrethroid insecticides. She is also noted for exploring novel immunoassay technologies, such as the use of nanobodies and to transfer this technology to end users throughout the world.
Four-Fold Contributions
Her major contributions to science are four-fold:
1. Her dissertation work focused on the comparative metabolism of xenobiotics in vivo and in vitro. She worked with a variety of organisms including rats, mice, monkeys, insects, and marine invertebrates. This provided a foundation for later work on the development of novel primary hepatocyte cell cultures as high throughput screening methods to assess xenobiotic toxicity and to explore mechanism of toxicity. Her colorimetric assay for monitoring cytochrome P450 assays is the basis of assays used now to monitor these enzymes in projects ranging from drug metabolism to environmental health.
2. Working with Hammock who pioneered the development of immunoassays for pesticides, Gee developed the first immunoassays for pesticides found as ground and surface waters contaminants by the California Department of Pesticide Regulation. Some of these assays were transferred to their analytical laboratory where in the early 1980s they helped end fish kills and drinking water contamination from rice herbicides. Shortly thereafter she co-authored a user's manual on assay development and use as a cooperative project with the U.S Environmental Protection Agency (EPA). The basic assay development and validation continues today and has found application to many environmental contaminants and includes the development of commercially available test kits.
3. Her interest in metabolism led her back to extending assay development from parent compounds to their metabolites. “Metabolites excreted in urine are useful biomarkers of exposure and the immunoassays developed have been used in several exposure studies,” Gee explained. “The studies have provided guidance to help reduce pesticide exposure by examining pesticide exposure patterns based on urine tests, then relaying educational information to the population.”
4. Since 1975 the gold standard of antibody reagents has been monoclonal antibodies. Touted as a better defined and continuously available reagent for immunoassays, monoclonal antibodies have applications both in analytical chemistry, including such things as home pregnancy kits and therapeutics where many new drugs are monoclonal antibodies. However, they are limited because their size does not allow penetration of the cell membrane and ‘humanizing' them for therapeutics is difficult. At 1/10th the size, single domain antibodies derived from camelids (VHH) will penetrate cell membranes, are easy to clone, express and genetically modify. Leading a team of researchers Gee explored the utility of these novel antibodies for the detection environmental contaminants and other small molecules.
In 2011, Gee received the UC Davis Staff Assembly's Citation for Excellence, presented by the chancellor. “Shirley seeks ways to help the lab and the department be successful,” the nominators wrote. “She is extremely efficient and effective” and a “can-do person skilled at anticipating and solving problems in a friendly, courteous and timely manner.”
- Author: Kathy Keatley Garvey
So wrote two Casida lab alumni, UC Davis distinguished professor Bruce Hammock and Qing X. Li, a professor at the University of Hawaii, Manoa, in their recently published biographical memoir in the Royal Society of Chemistry journal.
Casida, a UC Berkeley professor of toxicology and nutritional science for 50 years, also taught environmental science, policy and management, before becoming an emeritus professor in 2014. However, he continued to do research and mentor students until his death at age 88. He was actively involved with the UC system and often served on exam committees at UC Davis.
Casida was elected a fellow of the National Academy of Sciences in 1991 and to the London- based Royal Society in 1998. He won the first International Award for Research in Pesticide Chemistry in 1971 and the 1978 Spencer Award for Research in Agricultural and Food Chemistry by the American Chemical Society. In 1993, he was awarded the Wolf Prize in Agriculture "for his pioneering studies on the mode of action of insecticides, design of safer pesticides and contributions to the understanding of nerve and muscle function in insects.”
“John's legacy is his science, and this knowledge fostered subsequent science,” wrote Hammock and Li, longtime collaborators and friends of Casida. “A second legacy is the scientists he mentored in his career and the next generation who grew up with tales of ‘when we were in John's laboratory'. At scientific meetings, there is always a period of informal ‘Casida tales' ranging from practical jokes that extend for decades to stories of John and the charming eccentrics in his laboratory.”
“There is also a uniform awe and respect among his alumni. John set a high standard of ethics as well as work ethic in the field…What drives any of us, and particularly John Casida? Clearly wealth and fame were not important drivers, but there was a competitive spirit. The success of his many alumni brought him pleasure. We are confident John appreciated the tremendous contribution his career made to pesticide toxicology, the environment, human health and agriculture.”
Casida alumnus Sarjeet Gill, now UC Riverside distinguished professor emeritus, described him “the preeminent toxicologist in the world.”
In their abstract, the authors pointed out that Casida's “research in pesticide toxicology led to more effective agricultural chemicals that are far safer for human and environmental health. He used pesticides as probes for his fundamental studies of metabolism and mode of action, resulting in great insight into biological chemistry and the underlying mechanisms of regulatory biology, ranging from voltage-gated sodium channels, through the ryanodine receptor and calcium regulation, the gamma-aminobutyric acid (GABA)-gated chloride channel, to the nicotinic acetylcholine receptors. These discoveries, among many others, have had a profound impact on pharmacology and toxicology.”
Casida's research career “started with the introduction of DDT into agricultural practice and continued to assist in the development of many pesticides that dominate the market today,” the authors wrote, that he “trained multiple generations of toxicologists who obtained leading positions in government, industry and academics.”
Casida, born Dec. 22, 1929, spent his formative years in Madison, Wis. He received three degrees at the University of Wisconsin: his bachelor's degree in entomology in 1951; his masters in biochemistry in 1952; and a doctorate in entomology and biochemistry in 1954. He joined the faculty at the University of Wisconsin for six years, advancing to full professor, and then accepted a faculty position at UC Berkeley, where he remained active in teaching and research until his death on June 30, 2018.
His wife, Katherine “Kati” Faustine Monson, a well-known artist, died in 2021. Survivors include two sons, Eric of BeRex Corp., Berkeley, and Mark, professor of theoretical chemistry, Grenoble-Alps University, Grenoble, France. Casida “loved laboratory science and this, coupled with insatiable curiosity and a gift for finding the unexpected, led to papers from his laboratory sparkling with creativity,” the authors shared. “He similarly loved teaching at all levels and had just finished grading the final examination in his toxicology class at the time of his passing.”
“The phrase ‘long and productive career' is often used in remembrances, but this phrase is seldom more appropriately applied than when it describes J. E. Casida,” Hammock and Li wrote. “His first lead author paper was published when he was an undergraduate in Science Magazine. John was productive until his last brief illness, and even during this period of hospitalization he was planning his next works.”
Professor Casida is sorely missed by his colleagues and the broad field of toxicology and pharmacology, they said.
- Author: Kathy Keatley Garvey
Shey won the $5000 Francesca Miller Undergraduate Research Award that will fund six weeks of full-time summer research. And, judges scored her poster, “A Nanobody-Based Immunoassay for Detecting Moldy Marijuana,” as the top research poster in the undergraduate student competition.
The symposium, held recently in the UC Davis Conference Center, featured cutting-edge research in chemical biology, organic, and pharmaceutical chemistry. It memorializes Professor Miller (1940-1998) the 1985-90 chair of the Department of Chemistry and the 1997-1998 chair of the Academic Senate.
“We're very proud of Rachel,” said Hammock, who holds a joint appointment with the Department of Entomology and Nematology and the UC Davis Comprehensive Cancer Center. “Rachel winning the undergraduate research award as well as the first-place award for her poster on her research—that's no surprise. She is enthusiastic about science and has wonderful collaborations with our scientists. She is one of those rare people who can cross disciplines, and in this case, integrate molecular biology, chemistry, and analytical chemistry to address a serious problem in the world food supply. Not only that, but she makes the lab had more fun place to be.”
In her abstract, co-authored with mentor Hammock and project scientist Mark McCoy of the Hammock lab, Shey wrote:
“Have you ever forgotten about a bagel on the counter and come back a few days later to find that it has grown a thin layer of fuzzy green mold? Most people know not to eat it, but why not? Aspergillus fungus produces a toxin called aflatoxin, which is the reason moldy bread, bitter peanuts and other foods may not be safe to eat. Aspergillus grows on virtually all major crops in the world, and aflatoxin is present wherever Aspergillus grows.”
Shey related that “the first step is to optimize the concentrations of the substrate, coating antigen, and nanobody for the assay; once this is done, we can assay extracts of hemp bud samples. These samples tend to contain other reactive molecules that can create unusual signals by binding to nanobodies undesirably. This is known as the “matrix effect” and must also be controlled for, either by further diluting the sample, while paying close attention to the limit of detection, or processing the samples in a different way to reduce the amount of potential interference.”
“Cannabis is highly regulated in California,” Shey pointed out, “but batches of cannabis that fail testing are usually sold on the black market rather than at a regulated dispensary. Consumers who decide to run the risk of purchasing cannabis from an unregulated seller would also benefit from immunoassays for monitoring the levels of various pesticides and known contaminants, including aflatoxin. This immunoassay could be useful for not only commercial labs analyzing cannabis, but also consumers purchasing cannabis illegally.”
Shey also presented her poster research at two other UC Davis conferences this year: the Undergraduate Research, Scholarship and Creative Activities Conference (URSCA) and the 2023 Richard LaRock Conference.
Rachel, from Walnut Creek, and home-schooled from K-12 in the RAN Academy (RAN is an acronym for Rachel and her brothers Aaron and Nicholas), received her high school diploma in 2020. She enrolled at UC Davis in September 2020 and joined the Hammock lab in March 2022.
“I was really drawn to entomology because I've loved playing with insects ever since I was a kid,” Rachel said. “When I took organic chemistry, I fell in love with the unique style of problem solving and I grew passionate about its practical aspects as well.”
In the Hammock lab, she helps in immunoassay experiments, delivers presentations to the lab, and learns about research and science. “I am developing proficiency with ELISA (enzyme linked immunosorbent assay) and phage work,” Shey said. She is working on an independent project funded by an Innovation Institute for Food and Health Undergraduate Research Fellowship (IIFL) from the UC Davis Undergraduate Research Center. It involves the detection of aflatoxin in mouse brain tissue.
Shey also is a research assistant (since November 2022) in the lab of Cody Ross Pitt, assistant professor, UC Davis Department of Chemistry, where she is learning organic synthesis methods, including setting up air-sensitive reactions, working up reactions, using columns to purify the crude material, and operating a rotary evaporator (rotovap).
She has served a general and organic chemistry tutor or the UC Davis Academic Assistance and Tutoring Center (AATC) since September 2021. She staffs the drop-in area in the library and the online Zoom drop-in room for several hours each week. “I assist students with chemistry questions with the goal of helping my students develop study skills.”
Shey also worked part-time for almost two years as a city news reporter for the California Aggie, the UC Davis student-run newspaper.
Her career plans: to study organic chemistry and obtain a doctorate in chemistry. “I would love to work in medicinal chemistry or agrochemistry.”
“When I first talked to her she was excited over epoxides as such interesting chemical functionalities,” said Hammock, known for his expertise in chemistry, toxicology, biochemistry and entomology. Early in his career, he founded the field of environmental immunoassay, using antibodies and biosensors to monitor food and environmental safety, and human exposure to pesticides. His groundbreaking research in insect physiology, toxicology led to his development of the first recombinant virus for insect control.
“I saw Barry Sharpless last week, who like Linus Pauling, won two Nobel Prizes," Hammock said. She reminds me of Barry. The world needs more undergrads like Rachel.”
- Author: Kathy Keatley Garvey
EicOsis, based in Davis, is a leader in the clinical development of soluble epoxide hydrolase inhibitors (sEH), an innovative approach to treating chronic inflammation and pain. Hammock's pioneering work on the sEH inhibitors spans 50 years.
“Dr. McReynolds will lead EicOsis through the commercialization of its new therapeutic solution for chronic conditions that affects tens of millions of people, including those with neuropathic pain but also osteoarthritis, Alzheimer's disease, and Parkinson's disease,” said Glenn Croston, chief operating officer. “Dr. McReynolds has deep experience advancing drugs through preclinical and clinical development, including EicOsis' leading drug EC5026. In addition, she has published extensively on the science of sEH as an important new drug target.”
McReynolds, who received her doctorate in pharmacology/toxicology from UC Davis in 2021, studying with Hammock, said “it's been an amazing opportunity being involved with EicOsis as an early preclinical stage company and seeing the transition of our lead candidate to clinical
“The scientific validation of our approach supports a truly disruptive product that could provide a safe, non-addictive, and effective treatment for pain and neurodegeneration, and I look forward to leading the company as we obtain clinical validation,” she said. “We have an experienced and dedicated team that has a long history of working together, and I am excited to continue working together in this exciting next stage.”
EicOsis has “completed the human phase 1a safety trials with no adverse effects," said Hammock, who holds a joint appointment with the UC Davis Department of Entomology and Nematology and the UC Davis Comprehensive Cancer Center.
“As co-founder, Cindy has played a key role building EicOsis into a leader in therapeutics targeting sEH,” Hammock said. "Cindy's scientific insight, drive, and commitment ideally positions her to take EicOsis to the next level and builds on the vast body of science validating our approach. I know Cindy will continue to deliver great results for EicOsis and for a great many patients."
Hammock, in his role as CSO, “will continue to deliver cutting edge progress in translating soluble epoxide hydrolase inhibitors into clinical results,” Croston announced. A member of the National Academy of Sciences and the National Academy of Inventors, Hammock co-founded and built the company to translate these findings into "a revolutionary new solution for chronic inflammation and pain."
“We'd like to thank Bruce for his incredible leadership in the field and as CEO of EicOsis," said Chris Somerville, board member of EicOsis Human Health. "We're looking forward to his continued scientific leadership and to his continued support in Cindy's new role."
McReynolds, who has researched the biological activity of lipid mediators for the past 12 years, said her current efforts “focus on understanding the roles of lipid mediators in inflammation especially relating to pain and degenerative disease. My research focuses on developing tools for use in in vitro and in vivo knockout studies to understand their role in inflammation with a focus on mechanism of pharmacokinetics.”
Always aiming for a scientific career, McReynolds received a bachelor's degree (1999) in animal science from UC Davis and a master's degree (2001) in animal science from Washington State University (WSU). Her career advanced from senior research associate, Celera (formerly Axys) in South San Francisco to senior associate scientist of Miikana, Fremont, to project coordinator of Arete Therapeutics, South San Francisco, to UC Davis researcher.
At UC Davis, she served as the scientific program manager (2010-2017) for the Center for Integrative Toxicology, and as a graduate student researcher. She won a UC Davis Staff Assembly Citation of Excellence in Research in 2021. She earlier received the UC Davis 1999 Outstanding Senior Award, and several awards fromWSU: the 2000 Dr.Erb Outstanding Graduate Student Award; the 2001 Teaching Assistant of the Year, and the 2001 Outstanding Graduate Student. While a graduate student, she was supported by a National Institutes of Health Chemical Biology Training Grant.
Sarjeet Gill, now a UC Riverside distinguished emeritus professor, and Hammock co-discovered sEH in 1969 in mice when they were researching insect developmental biology and green insecticides in the UC Berkeley lab of John Casida (1929-2018). Both hold doctorates from UC Berkeley.
Hammock explained that the enzyme is a key regulatory enzyme involved in the metabolism of fatty acids. It regulates a new class of natural chemical mediators, which in turn regulates inflammation, blood pressure, pain and other key biologies. Hammock's 50-year research has led to the discovery that many regulatory molecules are controlled as much by degradation as biosynthesis. "The epoxy fatty acids rapidly degraded by the sEH," Hammock said, "control blood pressure, fibrosis, immunity, tissue growth, depression, pain, and inflammation, to name a few processes."
Approximately 50 million Americans (20 percent of the population) suffer from chronic pain, according to the Center for Disease Control and Prevention. The annual economic toll is $560 billion, encompassing direct medical expenses, lost productivity, and disability claims. Pain research is now one of the top priorities of the National Institutes of Health (NIH).
EicOsis (pronounced eye-co-sis), derives its name from eicosanoid, “the major backbone of chemical mediators in the arachidonate cascade,” said McReynolds. “It symbolizes the epoxide group in chemistry, which is key to the anti-inflammatory chemical mediators and where the biochemical target called soluble epoxide hydrolase works.”
EicOsis won the “Sacramento Region Innovator of the Year” award in the medical health/biopharmaceutical category in 2019.
