Recently, 750 chemical compounds including 150 cannabinoids have been identified in Cannabis plants^1,2. Cannabinoids are the active constituents of the Cannabis plant. Due to their potential, significant therapeutic and medicinal properties, cannabinoids have been addressed in various disease indications since ancient times^3–9. More recently, the antiviral activities of cannabinoids against SARS-CoV-2, HIV, and COVID-19 have been demonstrated, and the demand for research on their medical effects has urgently emerged^10–14.

The biosynthesis of cannabinoids has been elucidated over the past decades^15–17. Cannabinoids exist in two forms: the prevalent carboxylated form, commonly referred to as acidic cannabinoids, and the decarboxylated form, neutral cannabinoids primarily derived from the transformation of acidic cannabinoids¹⁸. Further, more than 60 cannabinoids are formed by non-enzymatic modification reactions like decarboxylation, isomerization, and oxidation¹⁹.

The decarboxylation reaction of acidic cannabinoids occurs naturally in plants. The term ‘decarboxylation’ is a widespread organic chemistry reaction, which is the loss of carboxylic acid in the form of carbon dioxide²⁰. Consequently, acidic cannabinoids are called ‘pre-cannabinoids’ by some researchers¹⁸. The converted cannabinoids such as Δ⁹-THC and CBD are pharmacologically more active in the human body than their acidic counterpart^21,22. On the other hand, Rock et al.²³ reported that THCA is 10 times more potent than Δ⁹-THC²⁴, and CBDA may be 100-1000 times more potent than CBD in reducing nausea and vomiting in animal model²⁵.

Currently, clinical interest in THCA and CBDA have been growing due to the lack of psychoactivity, however, their decarboxylation reaction remains a challenging issue. If acidic cannabinoid stability is solved with the stabilizing matrix, cannabis products of acidic cannabinoids will increase dramatically in the market.

In Cannabis, heating, drying, or combustion initiate the transformation reaction of cannabinoids, and these processes can alter the profile of cannabinoids²⁶. For example, these phenomena often lead to the decarboxylation of acidic cannabinoids and the eventual formation of neutral cannabinoids such as cannabidiol (CBD), cannabigerol (CBG), and Δ⁹-tetrahydrocannabinol (Δ⁹-THC)^27–29.

Cannabidiolic acid (CBDA) and tetrahydrocannabinolic acid (THCA) are the primary components of Cannabis inflorescence, along with minor components such as cannabichromenic acid (CBCA), cannabigerolic acid (CBGA), and cannabinolic acid (CBNA)³⁰. While these compounds have been detected to a lesser extent in other parts of the plants, CBDA and THCA predominantly accumulate in the secretory cavities of capitate-stalked and sessile glandular trichomes^31,32. In particular, the capitate-stalked glandular trichomes produce the highest concentrations of cannabinoids in the secretory cavities^33,34.

Acidic cannabinoids including CBDA and THCA have been reported to induce apoptosis in both plant cells and insect cells, suggesting their cytotoxic properties and potential role as plant defence compounds³⁵. THCA has been associated with hydrogen peroxide formation, potentially contributing to the self-defence mechanism of Cannabis³⁶. Nonetheless, cannabinoids have been observed to cause mitochondrial permeability transition, DNA degradation, and cell necrosis in plants and cancer^37,38.

Cannabinoids are deposited and stored in the extracellular cavity called a secretory cavity of glandular trichomes to prevent cellular damage, which has been suggested as the site of the final step in cannabinoid biosynthesis^39,40. The cannabinoid biosynthesis process is initiated in the cytosol of disc cells and concludes with oxidocyclization in the apoplastic space, at or outside the plasma membrane^41,42.

The plastids of disc cells are recognized as the primary site for acidic cannabinoid biosynthesis in glandular trichomes and subsequent accumulation in the secretory cavity^43,44. However, the exact areas of cannabinoid conversion remain unclear.

In this study, the secretory cavity contents and the air-dried inflorescence extracts were examined to compare the cannabinoid profiles and to track the progress of acidic cannabinoid decarboxylation. Given that the conversion of acidic cannabinoids into neutral or transformed cannabinoids yields significantly different pharmacological effects, these findings will contribute crucial insights into the control of manufacturing processes for the pharmaceutical and industrial applications of cannabinoids.