In the Spotlight
Botanical Dietary Supplement Safety Assessment and Challenges
The National Toxicology Program (NTP), an interagency program under the National Institutes of Environmental and Health Sciences (NIEHS) is organizing, April 26-27, 2016, the workshop, Addressing Challenges in the Assessment of Botanical Dietary Supplement Safety. The workshop will convene experts from government, industry, and other organizations to discuss the “challenges” and propose practical solutions (registration closes on April 12).
Dr. Cynthia Rider, a toxicologist at the NTP and the contact person for this event, explains that “Evaluating the safety of botanical dietary supplements can be challenging because they are often complex mixtures and the composition of products with similar labels can vary widely across the marketplace.”
As background information, this article provides a brief introduction to: the regulation of botanical dietary supplements in the U.S., the NTP Botanical Dietary Supplements Program, and some of the methods and unique challenges encountered in assessing botanical dietary supplement safety.
Botanical dietary supplements, also known as botanicals or herbal dietary supplements, are plants, parts of plants, or plant extracts that are valued for some medicinal or therapeutic property. FDA testimony to Congress noted that “Many Americans take some type of dietary supplement, and in many cases, there is either strong or suggestive evidence that many of these vitamins and minerals and other naturally occurring products have important health benefits.”
There has been an astounding growth in the U.S. dietary supplement market over the past several decades. Although data on botanicals alone was not provided, sales for all types of dietary supplements were estimated to be more than $36 billion in 2014, and more than 55,000 supplement products are in the U.S. marketplace (Akabas et al., 2016). According to three surveys conducted between 2002 and 2012, nonvitamin/nonmineral dietary supplements (which include the botanicals) are used by almost 20% of Americans (Clarke et al., 2015).
Government funding for nutrition and food safety research has also increased in recent years as researchers, government officials, and other stakeholders increasingly recognize the opportunity of improved human health and nutrition as the key to addressing many other national/global/societal problems. Overall, this appears to be an exciting time in the field with the adoption of the Food Safety and Modernization Act, increases in funding and research progress, and the release of the National Nutrition Research Roadmap 2016‒2021 by the Interagency Committee on Human Nutrition Research. Although not directly related to the NTP workshop, one of the advantages identified for the roadmap is “as a planning tool for accelerating the coordination and communication around the most effective and efficient use of federal research investments and resources supporting human nutrition research across the Government….”
Regulation of Botanical Dietary Supplements in the U.S.
In the U.S., a botanical-containing product, depending on its intended use, may be regulated under the Federal Food, Drug, and Cosmetic Act as a food (which includes the dietary supplements), drug, medical device, or cosmetic. The focus of this article and the April NTP workshop is on botanicals intended for use as dietary supplements.
The Center for Food Safety and Applied Nutrition (CFSAN) within the Food and Drug Administration (FDA) is responsible for protecting the public’s health by their regulatory oversight of the nation’s food supply and cosmetic products. One of CFSAN’s primary responsibilities in the food area is “ensuring the safety and proper labeling of dietary supplements.” One the six goals in CFSAN’s strategic plan for 2015-2018 is to “integrate and apply modern toxicological approaches to support regulatory and public health decision making on chemical hazards in foods, dietary supplements, and cosmetics.”
FDA guidance for botanicals being developed or marketed as dietary supplements can be found in two ways: 1) by searching the FDA Guidance Documents database, or 2) by consulting the list on FDA’s Dietary Supplements Guidance Documents & Regulatory Information page. The guidance provided covers current good manufacturing practice (cGMP), labeling, health claims, adverse event reporting, and the requirement to file a New Dietary Ingredient (NDI) application for any new supplement ingredient that was not marketed in the U.S. before October 15, 1994.
The Food, Drug, and Cosmetic Act was amended so that dietary supplements and their ingredients are regulated under the Dietary Supplement Health and Education Act of 1994 (DSHEA, 1994) as foods, but with additional established requirements. Under this Act, the marketing of products that are adulterated or misbranded is prohibited. Manufacturers of dietary supplements are responsible for marketing safe and correctly labeled products. The FDA’s responsibility is to take action after a mislabeled or unsafe dietary supplement reaches the market. “Under existing law …the FDA can take action to remove products from the market, but the agency must first establish that such products are adulterated (e.g., that the product is unsafe) or misbranded (e.g., that the labeling is false or misleading).”
In 1997, the Federal Food, Drug, and Cosmetic Act was amended to require a manufacturer or distributor intending to market a “new dietary ingredient” to submit “information including any citation to published articles that is the basis on which the manufacturer or distributor has concluded that a dietary supplement containing such dietary ingredient will reasonably be expected to be safe.” The Draft Guidance for Industry on New Dietary Ingredient (NDI) Notifications explains what needs to be submitted and the possible agency responses. “Congress stipulated that all dietary supplements sold before 1994 were to be considered safe and could therefore remain on the market without the manufacturer having to file an NDI notification” (Avigan et al., 2016).
The law was further amended in 2006 “to require a manufacturer, packer, or distributor whose name appears on the label of a nonprescription drug or dietary supplement marketed in the United States to: submit…within 15 business days any report of a serious adverse event….”
“The Dietary Supplement (DS) CGMP rule in 21 CFR part 111 requires persons who manufacture, package, label, or hold a dietary supplement to establish and follow current good manufacturing practice to ensure the quality of the dietary supplement and to ensure that the dietary supplement is packaged and labeled as specified in the master manufacturing record.” Implementation of this rule was phased in between 2008 and 2010, and now covers all manufacturers and distributors.
To enhance the capability of the FDA to “regulate this rapidly expanding industry,” the FDA announced the creation the Office of Dietary Supplement Program on December 21, 2015 (previously part of the Office of Nutrition Labeling and Dietary Supplements).
The Federal Trade Commission (FTC) also plays a role in regulating supplements by taking action against companies that make false or misleading health claims in advertising their product(s). “Under Federal law, dietary supplements can’t be promoted for the treatment of a disease….”
For more than a decade, the FDA and several other government programs have been advocating for further changes to the regulation of dietary supplements (Taylor, 2004). The culmination of this effort was the proposed inclusion of dietary supplements in a revised Redbook. The outcome of that action has not yet been made public.
The National Toxicology Program Botanical Dietary Supplements Program
The NTP’s Botanical Dietary Supplements Program uses an array of analytical equipment and procedures to identify and characterize the constituents, active ingredients, and contaminants (e.g., metals, molds, pesticides) in a botanical preparation. Short and long-term exposure studies in mice and rats are used to determine toxicity. Their fact sheet also mentions the use of in vitro assays to study mechanisms of action.
The NTP has been part of an Interagency Agreement since 1992 with the FDA. NTP’s role is “to support toxicology studies on FDA-regulated chemicals that have been nominated to the NTP…[and] to provide the FDA and other regulatory agencies with hazard identification and dose-response data to support risk assessment and risk management decisions that could affect public health.” The study of dietary supplements is one of the program areas covered under this NIEHS/NTP and FDA/NCTR Interagency Agreement. NTP made the observation in 2009 that “a paucity of toxicology data on available dietary supplements has resulted in the nomination of many dietary supplements to the NTP.”
Once an NTP study is complete under this agreement, the results are published as an NTP Technical Report. A 2009 summary of NTP testing at that point (for more than just botanicals) concluded the studies “have resulted in FDA regulatory decisions that will affect public health. Some of the data…led to increased understanding of the pharmacokinetics, mechanism of action, or dose-response of a chemical or substance. Other data has led to refinement of risk assessment models, while the results of some studies indicated that the chemical or substance was not toxic or carcinogenic to animals and did not pose a risk to humans.”
NTP’s Botanical Dietary Supplements Program has conducted a number of studies on botanicals using male and female mice and rats “to identify potential adverse effects of these agents after both short-term exposure and long-term exposure…. Multiple doses are given over two years, with doses that are typically higher than what humans are exposed to. These studies may be used in conjunction with other data to assess cancer and other adverse health risks to humans.” The completed and ongoing toxicology test results in rodents are provided on the NTP website. A presentation on research under the Interagency Agreement by Nigel Walker (2014) identified the need for alternative approaches for testing botanical dietary supplements.
The upcoming NTP workshop will bring together experts to consider the following challenges in the assessment of botanical dietary supplement safety:
- Developing methods and criteria for assessing phytoequivalence (i.e., similarity in chemical composition and biological activity) of botanicals
- Identifying the active constituent(s) or patterns of biological response of botanicals
- Assessing absorption, distribution, metabolism, and elimination (ADME) of botanicals
According to Rider, “the NTP has organized a workshop to focus attention on key issues related to appropriate methods for the evaluation of botanical dietary supplements in order to inform future research.”
Methods and Challenges in Evaluating Botanical Dietary Supplement Safety
Unique Features of Botanicals
Botanicals have a number of unique characteristics that add to the complexity of assessing their safety. They are complex mixtures with chemical constituents and active ingredient(s) that may or may not be defined, and their biological activity may not be well characterized. “For dietary supplements containing botanical ingredients, development of…a science base can be especially difficult because of the complexity of the chemicals that make up these products and the variability between one product and another.”
Incomplete identification of active constituents, or constituents that vary due to variations in growth and harvesting, or methods of production, can lead to inconsistent products that cannot be standardized (Avigan et al., 2016). Since most botanicals are derived from plant cultivation, testing for heavy metals, pesticides, certain microbes, and mycotoxins may be required. Many botanical products are developed using extracts of the plant materials, and different manufacturing processes can alter the chemical constituents present in the final product, and possibly its safety. Botanical ingredients are often combined in a marketed product, further complicating analytical analysis, and increasing the potential for unpredictable clinical effects. Botanical-drug interactions for the most part have not been evaluated.
Testing for and characterizing these features for the large numbers of botanical supplements in the marketplace is another challenge, not unlike the challenge of testing the large number of chemicals that are in the marketplace. Will a screening program like Tox21 for chemicals be possible for the botanical dietary supplements?
Unique also is that most botanicals in the U.S. marketplace already have a long history of safe human use as a dietary supplement. The path forward when a new study in rodents provides contradictory results is not always clear.
Analytical Testing and Standardization
Various government, industry, and quality certification programs employ advanced analytical procedures to characterize botanical products and their ingredients. Analytical testing can be used to evaluate supplement identity, purity, strength, production consistency, the presence of contaminants and adulterants, and other features. The FDA’s dietary supplement cGMP rule requires manufacturers to provide this kind of testing to ensure product quality and consistency.
As long as the active constituent(s) at the provided dose(s) have a history of safe human use, then the FDA’s dietary supplement cGMP rule, if correctly implemented by a manufacturer, can provide considerable confidence in a supplement’s safety. Testing and certification by one of the independent quality certification programs can provide further assurance to the manufacturer and consumers. Akabas, et al. (2016) provide a comparison of three of the quality certification programs for dietary supplements in the U.S.: U. S. Pharmacopeia (USP), NSF International, and ConsumerLab.com.
Betz, et al. (2007) identified a number of analytical challenges associated with botanicals, ranging from “establishing the identity of the botanical source from which an extract was derived to measuring the amount of one or more desirable or undesirable natural constituents, such as pesticides, toxic elements, natural toxins, or marker compounds.” Any method used must be reliable, accurate, precise, and specific, and a validated method needs to be “applicable throughout the manufacturing process.” Botanicals, being complex mixtures, pose unique analytical challenges such as variable chemical composition depending on geography or harvest practices. Furthermore, a marketed botanical may contain multiple botanical ingredients.
Botanical products often contain extracts, which are easier to concentrate and control dosage, but may complicate identification of the constituents. “DNA-based methods provide unique information for the identification of plant materials.” DNA testing, however, does not identify whether the active constituent of a botanical is present or at what strength. Many botanical products are developed using solvent and/or heat extraction processes to obtain the active constituent(s), and these processes may degrade the plant DNA so that detectable DNA is not present in the final product. “For this reason, the presence or absence of DNA in an extract should not be used to confirm the identity of an ingredient.”
The complexity of this basic level of characterization for a botanical is illustrated in the USP tests described in the chapter Identification of Articles of Botanical Origin. In addition to basic methods for characterizing the plant material, chemical characterization is used to ensure authenticity by detecting the presence of marker compounds. “Spectroscopic or chromatographic profiles can be used to achieve chemical identification by fingerprint comparison against that of a reference sample or standard.” Spectroscopic methods include ultraviolet (UV), infrared (IR), and Fourier transformed IR; chromatographic methods include high-pressure liquid chromatography (HPLC), thin-layer chromatography (TLC), 2-dimensional-TLC, and gas chromatography.
Changes in a manufacturing process can also result in botanical products with different properties, including their safety in humans. Avigan, et al. (2016) described the interesting example where “water extracts of kava [were found to] contain different concentrations of kavalactones than alcohol extracts,” and although the water extracted kava had a long history of safe use, the alcohol extracted kava was found to cause liver injuries.
Poor or insufficient characterization of herbal/botanical substances being evaluated in clinical trials has been proposed as one of the reasons for the variable results found in the literature regarding botanical supplement toxicity and/or efficacy. Published evaluations of herbal/botanical clinical trials found that only a minority of the trials had quantitatively characterized the evaluated botanical product, and only around half had provided a precise description the product (plant, source, processing method, etc.) (Betz et al., 2007). Such studies are said to be the genesis for NIH’s National Center for Complementary and Alternative Medicine requiring their grantees to adhere to their “natural products integrity policy,” which provides specific guidance on the characterization studies required for a botanical product to be used in research they support.
Significant progress has been made, since the report of Betz in 2007, in the development and application of advanced analytical methods for characterizing botanical dietary supplements. The summary review of methods by Kemsley (2013) describes several methods that “work particularly well for complex products and yield detailed compound fingerprint profiles for comparison to reference materials.” Avigan, et al. (2016) report “notable progress in the development of advanced methods to qualitatively and quantitatively measure ingredients and screen for contaminants and adulterants in botanical products.” They concluded that “more routine application of such methods in conjunction with the emergence of accessible product-specific fingerprint databases” will lead to better product authentication and identification of ingredients, contaminants, and adulterants.
While this is not a comprehensive review of this topic, it does illustrate the role of advanced analytical methodologies and adherence to the cGMP rule in providing consumers with safe botanical dietary supplements.
Other Testing Needs
Testing beyond what is needed to meet the dietary supplements cGMP rule is generally not required for marketing a botanical dietary supplement in the U.S.
To respond to some of the “challenges” posed at the NTP workshop, however, methods beyond analytical testing and traditional rodent toxicology may be considered. For example, chemical analysis alone has been shown to be inadequate to fully assess phytoequivalence, the first workshop “challenge.”
Phytoequivalence is defined as the “similarity in chemical composition and biological activity.” In vitro bioassays are often used to assess biological activity of botanical extracts, and can be used to standardize a product when the active constituents are not known. When the active constituents can be identified and isolated, bioassays are useful in determining mechanism of action for the botanical ingredient(s). For example, bioassays are well established for determining botanical sources of progestins and measuring relative progestegenic potency (Toh et al., 2012). Another example is that of Ye, et al. (2004) where HPLC was used to analyze authenticity and chemical composition of 10 different commercial botanical extracts and several cell-based assays were used to analyze biological potency and consistency. They found “significant variation in chemical composition and biological activities of the commercial extracts and that the amount of marker components may not reflect biological activity levels. Therefore, chemical analysis alone is inadequate for quality control, and biological assays must be included for botanical products to ensure chemical authenticity as well as pharmacological/biological potency and consistency.”
Manufacturers may need or desire additional information on a particular botanical supplement or ingredient for various reasons, including: development of a new combination product, concerns about its use in a particular consumer group, to obtain information on supplement-drug or supplement-supplement interactions, to investigate an adverse event, or to assess a change in manufacturing process or ingredient source.
One such example is the use of in vitro methods for identifying herb/botanical-drug interactions. While there is no regulatory requirement for this type of assessment for currently marketed dietary supplements, responsible industry groups find it is an issue that can and should be addressed. Dr. Amy Roe, Senior Scientist at Procter & Gamble, explains that “as herbal product usage in combination with conventional medicines continues to increase, the potential for herb-drug interactions should be evaluated. A number of well-established in vitro human metabolic systems are available; including fully-integrated primary hepatocyte systems with proven in vitro to clinical correlation.”
Inconsistencies have often been observed between in vitro and clinical studies investigating potential herb-drug interactions. Potential causes include previously mentioned issues such as poor characterization of the botanical material being evaluated. Roe, at al. (2016) also describe improved in vitro test systems, such as sandwich cultured human hepatocytes cultured under optimized conditions, as a method to improve clinically-relevant predictions. Several groups have pointed out the need for a standardized methodology, and have started to evaluate an in vitro-in silico-in vivo integrated model approach for predicting botanical-drug interactions (Brantley et al., 2014; Roe et al., 2016).
Clinical trials are the ultimate method for assessing a botanical, and can be used to determine pharmacokinetics, pharmacodynamics, and safety. However, given the large numbers of botanical products in the marketplace, and the time and cost, clinical trials will never be conducted for the majority of botanical dietary supplements. Manufacturers need other approaches to group and/or prioritize botanicals for certain types of safety assessments. Many of the safety testing needs for currently marketed botanical dietary supplements, beyond the cGMP and analytical testing, could have some achievable solution through the identification of appropriate integrated approaches based on in vitro tests, in silico modeling, and small-scale human clinical trials.