Chemical Interactions and Cytotoxicity of Terpene and Diluent Vaping Ingredients

Chemical and physiological interactions between e-liquid constituents: cause for concern?

Studies of Electronic Nicotine Delivery Systems (ENDS) toxicity have largely focused on individual components such as flavour additives, base e-liquid ingredients (propylene glycol, glycerol), device characteristics (eg, model, components, wattage), use behaviour, etc. However, vaping involves inhalation of chemical mixtures and interactions between compounds can occur that can lead to different toxicities than toxicity of the individual components. Methods based on the additive toxicity of individual chemical components to estimate the health risks of complex mixtures can result in the overestimation or underestimation of exposure risks, since interactions between components are under-investigated. In the case of ENDS, the potential of elevated toxicity resulting from chemical reactions and interactions is enhanced due to high operating temperatures and the metallic surface of the heating element. With the recent availability of a wide range of e-liquid constituents and popularity of do-it-yourself creation of e-liquid mixtures, the need to understand chemical and physiological impacts of chemical combinations in ENDS e-liquids and aerosols is immediate. There is a significant current knowledge gap concerning how specific combinations of ENDS chemical ingredients result in synergistic or antagonistic interactions. This commentary aims to review the current understanding of chemical reactions between e-liquid components, interactions between additives, chemical reactions that occur during vaping and aerosol properties and biomolecular interactions, all of which may impact physiological health.

Modeling mixtures interactions in environmental toxicology

In the environment, organisms are exposed to mixtures of different toxicants, which may interact in ways that are difficult to predict when only considering each component individually. Adapting and expanding tools from pharmacology, the toxicology field uses analytical, graphical, and computational methods to identify and quantify interactions in multi-component mixtures. The two general frameworks are concentration addition, where components have similar modes of action and their effects sum together, or independent action, where components have dissimilar modes of action and do not interact. Other interaction behaviors include synergism and antagonism, where the combined effects are more or less than the additive sum of individual effects. This review covers foundational theory, methods, an in-depth survey of original research from the past 20 years, current trends, and future directions. As humans and ecosystems are exposed to increasingly complex mixtures of environmental contaminants, analyzing mixtures interactions will continue to become a more critical aspect of toxicological research.

Sesquiterpene-evoked phytochemical toxicity in PC12 neuronal cells reveals a variable degree of oxidative stress and alpha-tocopherol and glutathione-dependent protection

Phytochemicals are often promoted generally as antioxidants and demonstrate variable levels of reactive oxygen species (ROS) sequestration in vitro, which attributes to their neuroprotective bioactivity. Sesquiterpenes from cannabis and essential oils may demonstrate bifunctional properties towards cellular oxidative stress, possessing pro-oxidant activities by generating ROS or scavenging ROS directly. Sesquiterpenes can also oxidize forming sesquiterpene oxides, however the relative contribution they make to the bioactivity or cytotoxicity of complex botanical extracts more generally is unclear, while selected cannabis-prevalent terpenes such as β-caryophyllene may also activate cannabinoid receptors as part of their biological activity. In the present study, we investigated selected sesquiterpenes β-caryophyllene and humulene and their oxidized forms (β-caryophyllene oxide and zerumbone, respectively) against established antioxidants (ascorbic acid, α-tocopherol, and glutathione) and in the presence of cannabinoid receptor 1 and cannabinoid receptor 2 antagonists, to gain a better understanding of the molecular and cellular mechanisms of neuroprotection versus neurotoxicity in semi-differentiated rat neuronal phaeochromocytoma (PC12) cells. Our results demonstrate that the sesquiterpenes β-caryophyllene, humulene and zerumbone possess concentration-dependent neurotoxic effects in PC12 cells. Both β-caryophyllene- and humulene-evoked toxicity was unaffected by CB1 or CB2 receptor antagonism, demonstrating this occurred independently of cannabinoid receptors. Both glutathione and α-tocopherol were variably able to alleviate the concentration-dependent loss of PC12 cell viability from exposure to β-caryophyllene, humulene and zerumbone. During 4-hour exposure to sesquiterpenes only modest increases in ROS levels were noted in PC12 cells, with glutathione co-incubation significantly inhibiting intracellular ROS production. However, significant increases in ROS levels in PC12 cells were demonstrated during 24-hour incubation with either antioxidants or sesquiterpenes individually, and with additive toxicity exhibited in combination. Overall, the results highlight a concentration-dependent profile of sesquiterpene neurotoxicity independent of cannabinoid receptors and dissociated from the formation of reactive oxygen species as a marker or correlate to the loss of cell viability.

Evaluating Manganese, Zinc, and Copper Metal Toxicity on SH-SY5Y Cells in Establishing an Idiopathic Parkinson's Disease Model

Parkinson's disease (PD) is a neurodegenerative condition marked by loss of motor coordination and cognitive impairment. According to global estimates, the worldwide prevalence of PD will likely exceed 12 million cases by 2040. PD is primarily associated with genetic factors, while clinically, cases are attributed to idiopathic factors such as environmental or occupational exposure. The heavy metals linked to PD and other neurodegenerative disorders include copper, manganese, and zinc. Chronic exposure to metals induces elevated oxidative stress and disrupts homeostasis, resulting in neuronal death. These metals are suggested to induce idiopathic PD in the literature. This study measures the effects of lethal concentration at 10% cell death (LC10) and lethal concentration at 50% cell death (LC50) concentrations of copper, manganese, and zinc chlorides on SH-SY5Y cells via markers for dopamine, reactive oxygen species (ROS) generation, DNA damage, and mitochondrial dysfunction after a 24 h exposure. These measurements were compared to a known neurotoxin to induce PD, 100 µM 6-hydroxydopamine (6-ODHA). Between the three metal chlorides, zinc was statistically different in all parameters from all other treatments and induced significant dopaminergic loss, DNA damage, and mitochondrial dysfunction. The LC50 of manganese and copper had the most similar response to 6-ODHA in all parameters, while LC10 of manganese and copper responded most like untreated cells. This study suggests that these metal chlorides respond differently from 6-ODHA and each other, suggesting that idiopathic PD utilizes a different mechanism from the classic PD model.