Botanical-induced toxicity: liver injury and botanical-drug interactions A report on a Society of Toxicology Annual Meeting symposium

Abstract

Botanical supplements and herbal products are widely used by consumers for various purported health benefits, and their popularity is increasing. Some of these natural products can have adverse effects on liver function and/or interact with prescription and over-the-counter (OTC) medications. Ensuring the safety of these readily available products is a crucial public health concern; however, not all regulatory authorities require premarket safety review and/or testing. To address and discuss these and other emerging needs related to botanical safety, a symposium was held at the Society of Toxicology Annual Meeting in Salt Lake City (UT) on March 11, 2024. The symposium addressed the latest research on botanical-induced liver toxicity and botanical-drug interactions, including new approach methods to screen for toxicity, challenges in assessing the safety of botanicals, and relating human adverse events to specific products. The presentations and robust panel discussion between the speakers and audience highlighted the need for further research and collaboration to improve the safety of botanical supplements and herbal products, with the ultimate goal of protecting consumer health. Although utility of many of the modern tools presented in the symposium requires further study, the synergistic efforts of diverse experts hold promise for effective prediction and evaluation of botanical-induced hepatotoxicity and botanical-drug interaction potential.

1. Introduction

Liver injury from botanical-based dietary supplements¹ remains a public health concern worldwide. This problem is complicated by the vast array of varied compositions of commercially available products and purported health benefit claims. Despite many efforts from regulatory agencies, academia, industry, and clinicians to improve expectations for safety and quality of botanical and other natural products, cases of liver injury continue to grow alongside the growth of products on the market (Gurley et al., 2022; Patel et al., 2023; Carty and Navarro, 2024; Sirois et al., 2024; Waidyanatha et al., 2024). According to the US Drug Induced Liver Injury Network (DILIN), botanical dietary supplements contribute to about 20% of drug induced liver injury (DILI) cases (American Association for the Study of Liver Diseases, 2012). The symposium held during the 2024 Society of Toxicology Annual Meeting offered the latest research on botanical-induced liver toxicity and botanical-drug interactions, including new in vitro methods to screen for toxicity, addressing the challenges in assessing the safety of botanicals, and relating human adverse events to specific products.

2. Botanical-induced liver hepatotoxicity: increase in products available on the market parallels the increase in liver injury reports.

Understanding both clinical and mechanistic aspects of botanical-induced liver injury is an important pillar when making the proper diagnosis and selecting the most effective treatment plan. Much of this work is continually addressed by the DILIN, which was established to collect and analyze cases of severe liver injury caused by prescription and OTC drugs and alternative medicines, including herbal and botanical dietary supplements. Throughout the years, the DILIN has accumulated a wealth of knowledge on liver injury from polyphenolic herbal products (e.g., green tea extract), including their clinical features and genetic susceptibility for injury. Of the newly emerging products with suspected hepatotoxicity potential, turmeric- and ashwagandha-containing products have received recent attention by the DILIN. A documented increase in turmeric-associated liver injury cases enrolled in the DILIN is of particular concern, with some data pointing to an association between the human leukocyte antigen (B35:01) and susceptibility to hepatotoxicity exerted by turmeric-containing products (Halegoua-DeMarzio et al., 2023).

One botanical on today’s market with growing attention is Withania somnifera (L.) Dunal [Solanaceae] root, commonly known as ashwagandha, and is widely used in Indian Ayurvedic medicine for its purported use by individuals experiencing stress, anxiety, and/or fatigue. Ashwagandha is also a popular dietary supplement in the United States, with tremendous sales growth during the COVID-19 pandemic and continuing as one of the top-selling botanicals (Smith et al., 2024). In 2007, the USP Admission Evaluation and Labeling Expert Committee conducted a safety review of ashwagandha root during evaluation for its suitability for monograph development (USP, 2024). A major criterion in the process deemed “USP Dietary Supplement Admission Evaluation” is an assessment of publicly available toxicology and safety information suitable to determine whether the botanical (or non-botanical) is a risk to public health (Oketch-Rabah et al., 2018). The review noted the long history of apparent safe usage in traditional Ayurvedic practices, and at that time, there were no reported serious adverse events for products containing ashwagandha. However, it should be cautioned that history of use may not be adequately reported, the scope of adverse events may not be observable, use levels may not be reported, and there can be great variability in botanical raw material, among other limitations. The USP committee admitted for USP-NF monograph development ashwagandha root, ashwagandha root powder, and ashwagandha root dry extract. The spike in usage of ashwagandha products in the Western world during the last decade has been accompanied by a spike in cases of liver injuries linked to ashwagandha exposures from those products. As of 2020, there were six cases of liver toxicity associated with the intake of products containing ashwagandha reported in the peer-reviewed literature (Inagaki et al., 2017; Bjornsson et al., 2020). However, the number of global case reports has grown, and comments of liver-like injury side effects have been reported by consumers on public websites such as Amazon (Suryawanshi et al., 2021). A recent study investigated liver biopsy samples from eight patients taking ashwagandha products, noting cholestatic injury and hepatocellular necrosis with portal-based inflammation (Philips et al., 2023). For these reasons, the USP has initiated an in-depth literature review and meta-analysis to determine whether the cases of reported hepatotoxicity are due to intrinsic factors, ashwagandha extract processing, and/or contamination. While the review is ongoing, potential causes of liver injury have been postulated, including 1) DNA damage induced by one or more of the constituents contained in ashwagandha, e.g., withanone (Siddiqui et al., 2021); 2) differential concentrations of withanolides or other constituents among roots and aerial parts of extracts; and/or 3) some other contaminant(s), including mycotoxins. Further evaluation of these various possibilities is warranted.

3. Botanical-drug interactions: old problem, new players

Botanical-drug interactions constitute another important and often neglected global problem of which aspects of polypharmacy, including co-ingestion of various drugs with botanical and other natural products, becomes overwhelmingly frequent. Of particular concern is that, despite overall popularity, scant knowledge regarding the toxicology and pharmacology of botanical products is more the norm than the exception. For instance, oral botanical products marketed as supplements prepared from the leaves of the kratom plant (Mitragyna speciosa) are increasingly used for their opioid-like effects to self-manage pain and opioid withdrawal symptoms. Calls to US poison centers involving kratom exposures increased by approximately 50-fold from 2011–2017, one-third of which reported use of kratom concurrently with drugs of abuse, including opioids and benzodiazepines (Ahmad et al., 2021). Many of these drugs are eliminated from the body through extensive metabolism by the cytochrome P450 (CYP) enzymes, particularly CYP2D6 and CYP3A, raising concerns for potential adverse pharmacokinetic kratom-drug interactions (Tanna et al., 2023a). Despite these safety concerns, rigorous fundamental knowledge about the disposition and drug interaction potential of kratom in humans remains lacking. Results from an open-label two-arm clinical study were presented during the symposium that evaluated the pharmacokinetics of a well-characterized kratom product (2 g), prepared as a tea (Arm 1), and potential interactions between the kratom tea and oral CYP2D6 probe drug dextromethorphan (30 mg) and CYP3A probe drug midazolam (2.5 mg) (Arm 2) in healthy adults. The pharmacokinetics of kratom alkaloids with the 3S configuration (mitragynine, speciogynine, paynantheine) were distinct from those with the 3R configuration (mitraciliatine, speciociliatine, isopaynantheine), which were attributed to differences in apparent intercompartmental distribution clearance, volumes of distribution, and clearance (Tanna et al., 2023a). Furthermore, kratom increased the systemic exposure to midazolam (by ~40%) but not to dextromethorphan (Tanna et al., 2023b). Results from this first comprehensive pharmacokinetic characterization and drug interaction assessment of kratom in humans filled critical knowledge gaps about the safe use of this increasingly popular botanical, thereby addressing ongoing public health concerns.

4. Efforts toward prediction of botanical-induced hepatotoxicity

It has been increasingly recognized that new approach methods may be applicable to studying complex mixtures represented by botanicals. Evaluating in silico and in vitro tools in the study of botanical safety with the intention of integrating them into a testing framework are major objectives of the Botanical Safety Consortium, a public-private partnership convened by HESI (Mitchell et al., 2022). In recent years, advances in physiologically relevant liver tissue models and assay platforms have been increasingly used to evaluate botanical and other natural products for potential human hepatotoxicity and drug interactions. Patient-derived 3D microtissue cultures of human hepatocytes were used to evaluate the hepatotoxic potential of 13 botanical mixtures, along with nine reference drugs with established clinical outcomes, using high throughput transcriptomics, assay biomarkers for liver enzyme leakage, and microtissue imaging. Results, which were generated at the U.S. National Institutes of Environmental Health Sciences, demonstrated the translational utility of this integrated omics platform in combination with benchmark concentration modeling to predict human liver injury, estimate drug interaction potential, identify mechanistic signatures of biological response similarity across botanical extracts, and estimate the potencies for in vivo liver weight increases. Ultimately, these data can be integrated with other type of toxicity data to identify efficient methods for rapidly assessing the broader safety of natural products.

Another important recent development in the field is prediction of botanical-drug interactions using a sandwich-cultured human hepatocyte (SCHH) model. The scientific literature is replete with reports of various botanical extracts and/or constituents as inhibitors of drug metabolizing enzymes and transporters. Unfortunately, most of these studies use simplistic in vitro screening-based systems without follow-up in more physiologically relevant models. Additionally, the potential for botanical extracts to induce drug metabolizing enzymes and/or transporters is rarely studied using in vitro systems. Thus, in the rare instances when clinical studies are conducted to confirm drug interaction potential, there is usually a poor correlation between in vitro studies and clinically relevant changes in the pharmacokinetics of drugs under study (Sprouse and van Breemen, 2016). Pioneering efforts by several individuals resulted in the development of a tiered approach to assess the safety of botanicals, which includes an assessment of potential drug interactions (Roe et al., 2018). Primary human hepatocyte models that maintain a fully integrated hepatic system can improve prediction of clinically relevant drug interactions and hepatotoxicity. Importantly, some of these models are capable of biliary efflux, resulting in robust models for studying complex mixtures represented by botanicals. Such a hepatocyte model has been used to model clinically relevant botanical-drug interactions using several extracts (e.g., St. John’s Wort, Schisandra chinensis, Schisandra sphenanthera, and Boswellia serrata) (Jackson et al., 2017; Roe et al., 2019). Results from these studies led the authors to propose a new paradigm to assess botanical-drug interactions using a SCHH model and an in vitro clearance approach that considers the complex botanical mixture as a single entity, regardless of the phytoconstituent profile. The proposed experimental design captures major clinically relevant hepatic pathways and data output that enable direct predictions of clinical interactions and the impact on object drug hepatic clearance. Studying botanicals in this way allows researchers to capture the overall net effect of any synergism or competing effects that might be occurring among phytoconstituents.

Conclusions

Exposures to botanicals and other natural products continue to increase globally, along with increased expectations from consumers, regulators, and industry stewards centered on quality and safety of these products. A growing botanical market also leads to higher risks of drug interactions. Synergistic efforts from government, academic, and industry experts promise to aid in the development of robust methodologies that will allow for effective prediction of botanical-induced hepatotoxicity and botanical-drug interaction potential, ensuring public health safety. The symposium brought together critical stakeholders and researchers across sectors to discuss the state of the science and continue the evolution of botanical safety research towards human translation.

Highlights.

• Botanical supplements linked to liver injury and drug interactions.

• Emerging tools improve prediction of botanical-induced hepatotoxicity.

• Ashwagandha and turmeric under scrutiny for liver injury risk.

• Cross-sector collaboration is key to improving botanical product safety.