Swimming in metformin
Overshadowed by a green branch, Zolgensma placidly wanders through his miniature habitat in Katie Edwards’ office, fins fluttering.
His fancy moniker is an inside joke: A Binghamton University assistant professor of pharmaceutical sciences, Edwards paid a bit too much for the betta fish, so she named him after the market’s most expensive medication, used to treat spinal muscular atrophy. His predecessor, Timolol, another betta fish, had been named after a beta blocker drug.
But Zolgensma is a reminder, too, of sorts. Once medication works its way out of the human body, its chemical residue travels down sewage pipes. Sewage treatment plants aren’t geared to filter for pharmaceuticals, so another set of pipes discharges that waste into waterways — such as the nearby Susquehanna River — where fish live and breed, along with a whole chain of life that relies on those fish. What happens when those fish are exposed to this pharmaceutical residue?
It’s a question that Edwards, also a visiting professor of microbiology at Cornell University, is uniquely positioned to answer.
“My background is a little unusual for a pharmacy department,” she admits.
She worked as a synthetic organic chemist in the pharmaceutical industry, then after earning her doctorate in environmental toxicology from Cornell University, spent more than a decade in biological engineering. After that, she moved on to natural resources, then microbiology and finally a return to pharmaceutical sciences, where she investigates and teaches drug stability, drug delivery and pharmacokinetics, which deals with the timing of movement of drugs through the body.
Her environmental interests began with research into fish and vitamin B1 deficiency; also known as thiamin, it’s one of the primary cofactors involved in converting glucose to energy and it is critical to neurological and cardiovascular function. It is an essential vitamin, meaning that it must be obtained from the diet since we can’t synthesize it ourselves. Many developed countries add thiamin to breads and rice, along with other vitamins. This supplementation is usually sufficient to prevent thiamin deficiency, although it still occurs in select populations, including people with alcohol use disorders or genetic defects that restrict its uptake. It is also a vitamin that can easily be broken down during food processing. However, dietary thiamin deficiency remains a common problem in developing countries, particularly those that rely on white rice as a staple, since most of rice’s vitamin content is located in the husk, which is removed during processing.
White rice-based diets sometimes also go hand-in-hand with raw fish-based diets. The problem: Aside from insufficient amounts of thiamin in the diet, some fish are known to contain the enzyme thiaminase I, which breaks down vitamin B1. This is not only a problem for people, but the issue of thiamin deficiency in aquatic organisms has surfaced in various bodies of water, from Cayuga Lake to the Pacific coast to the Baltic Sea.
Using her bioengineering and chemistry background, Edwards developed bioanalytical assays to better understand B1 deficiency, which can be complex to detect. Through a collaboration with scientists from the University of Western Ontario, fish currently in question in her lab are lake trout from Lake Ontario. Thiamin deficiency in predator fish is usually attributed to a shift in diet to prey fish containing high levels of thiaminase. This enzyme degrades the dietarily available thiamine in the predator fish, which become thiamin deficient, a condition that reduces their reproductive success and ability to withstand disease and pollution challenges.
In this stream of research, Edwards looks at the larger picture of how thiaminase I works and how it could be inhibited. Her lab also has a project on how fishery processing steps affect thiaminase activity in Asian carp, an invasive species throughout the United States that can hopefully be increasingly harnessed by fisheries for ecological and economic benefit.
Her lab, in collaboration with colleagues at Cornell, has also been researching a purified version of this enzyme at the molecular level, recently finding what can activate and inhibit it. Thiaminase I enzymes are produced by certain bacteria pathogenic to humans and animals, including Clostridium botulinum and Paenibacillus thiaminolyticus, and can be found in certain plants, including bracken fern and horsetail. Edwards notes that “it is conceivable that thiamine depletion exacerbates the impact of C. botulinum, a bacteria yielding neurotoxic effects, on the host. Our results on its activation and inhibition at the molecular level by common dietary constituents may provide a better understanding that may benefit both human and veterinary populations.”
“I’ve been fortunate to be able to approach research challenges from different perspectives because I have applied experience in several fields, ranging from the environmental realm to engineering to pharmaceutical synthesis,” Edwards says.
From ingestion to environmental release
Edwards’ interest in fish ultimately led to a broader question: What are the side effects of our everyday medications on the environment that surrounds us?
This began with a pilot study with her collaborators in microbiology and natural resources and the environment at Cornell University, focusing on the impact of metformin at environmental levels on microbial growth. Later, partnering with Jessica Hua, a former assistant professor of biological sciences at Binghamton, Edwards has looked at the impact of metformin on the survival and growth rates of amphibians who are often vulnerable to environmental contaminants. Hua has since left for the University of Wisconsin and Edwards has expanded her focus to fish and humans, working with external fishery partners and Nannette Cowen, a clinical associate professor of nursing at Binghamton.
First introduced in 1958, metformin is the most widely prescribed medication for Type 2 diabetes in the United States and is used by approximately 150 million people worldwide every year.
“What’s interesting about metformin is that it is prescribed in very high doses,” Edwards says. “Normally, when we take medications, they’re in the microgram or milligram range: for example, for a common over-the-counter medication you’ll take, say, 325 milligrams of Tylenol to relieve an occasional headache. For metformin, a medication that is taken long-term for a chronic condition, it is common for people to take 2,000 milligrams a day.”
To have a therapeutic effect, a drug needs to reach a certain concentration in the blood plasma, called the minimum effective concentration. Often, there is a lag time between swallowing a pill and achieving that concentration, as the tablet dissolves in the GI tract. The concentration rises and then falls again as your body’s metabolic and excretion processes perform their necessary functions.
“Every drug has both a minimum and maximum effective concentration, so we want to be in a ‘sweet spot’ of that range,” Edwards says.
For many drugs, that range is narrow; take some blood thinners, for instance, in which there is a fine line between therapeutic effect and toxicity. Metformin, however, has a far larger safety window, and its dosage is measured in grams rather than micrograms or milligrams. Most patients take two large pills a day; any side effects — a sour stomach, cough and diarrhea, for example — are typically mild.
When drugs are metabolized, they typically break down into other constituent substances, often to make the drug more hydrophilic, or dissolvable in water. Metformin, however, is largely hydrophilic by nature and thus not metabolized; it exits through the urine largely intact.
“When considering the dosage, number of prescriptions and lack of metabolism, it is no surprise that various reports have found it at moderately high concentrations in water downstream of wastewater treatment plants, sometimes as much as the microgram per liter range, which is the parts per billion range. Relative to concentrations in blood used therapeutically, this is a low concentration, but as far as drugs go in environmental water, it’s comparatively high. It becomes diluted, of course, but it and other commonly used drugs remain detectable significant distances in environmental water from the point of discharge,” Edwards says of wastewater.
Concentrations are small, much lower than they would be for therapeutic effect, but they can be pervasive for creatures who literally swim in them. Additionally, the supply from human populations and veterinary use in agriculture is continually introduced into waterways so there is constant exposure. The concern isn’t just limited to metformin, of course. Virtually any pharmaceutical can pass from the human body into wastewater and ultimately into the environment, from multivitamins to antibiotics, antidepressants and cholesterol-lowering drugs. This raises questions ranging from developing antibiotic resistance by microbes to the extent to which such compounds are reintroduced into the drinking water supply. But as wide-ranging as it is, the phenomenon is difficult to research, largely because it involves so many pharmaceuticals, from prescription drugs to over-the-counter medications.
Edwards and her collaborators at Cornell University and Saint Louis University in Missouri are looking at the concentration of vitamins in wastewater, such as the multivitamins many people take every day, and she plans to look at pharmaceutical levels in the same samples.
Metformin and vitamins
Metformin has been touted in some circles for its potential to increase human longevity, but mysteries remain, even with a drug that’s more than 60 years old; researchers still don’t fully understand its mechanism of action, or what the drug is potentially doing at less than therapeutic doses, Edwards points out.
“It has been a widely successful drug, and understanding its mechanism of action more thoroughly may benefit future drug development,” she says.
To that end, she recently received a seed grant from Binghamton University’s Health Sciences Transdisciplinary Area of Excellence with nursing colleague Cowen to look at the impact of metformin on the metabolism of B vitamins, and will soon be recruiting patients for a study. Edwards’ hypothesis is that metformin’s beneficial effects, including those on diabetes management and cognitive function, may partly come from increased utilization of B1. She has seen changes in gene expression and thiamin utilization at environmentally relevant concentrations in nonhuman models and cultured cells, and this collaborative study will allow translation to effects at therapeutic concentrations in human populations.
PharmD and PhD students are also aiding this research, investigating the impact of metformin on folic acid, vitamin B12 and vitamin B6 levels, and the relationship to cognitive function in their capstone and thesis research projects using data available in the Centers for Disease Control and Prevention (CDC) National Health and Nutrition Examination Survey.
Edwards’ research on metformin began in the concentration regime that was likely to be present in aquatic environments but has led to a better understanding of its mechanism at concentrations present therapeutically.
“From a pharmacy standpoint, students learn the importance of disposing of unused drugs through community drug-take-back events or drop boxes to limit unintended ingestion and potential misuse,” Edwards says. But these practices also aid in limiting environmental contamination from flushing them down the drain. We don’t yet know the full impact of sewered medications on the environment, and while the concentrations are much lower than what we know to cause toxicity, it remains possible to modulate other properties of the aquatic environment.