Introduction

Recently, one of these metabolites belonging to phenolic acids, 3,5-dihydroxybenzoic acid (3,5-DHBA), has been shown to be highly bioactive in humans as an agonist of lactate receptor (HCAR1, also known as HCA1 or GPR81) and is described in the literature as a metabolic sensor. Activation of this receptor promotes multispectral effects on human cells, including modulation of the activity of neurons and intercellular brain signaling, indirect stimulation of intestinal, hematopoietic, and neural stem cells (NSCs), and promotion of drug resistance mechanisms in cancer cells. Interestingly, 3,5-dihydroxybenzoic acid is also a fruit-derived phytonutrient delivered with food from apples and some other popular fruits. However, most dietary 3,5-dihydroxybenzoic acid is the product of AR metabolism. It is digested and metabolized in the gastrointestinal tract; additionally,it can be oxidized or directly catabolized in the liver. Thus, 3,5-dihydroxybenzoic acid molecules secreted by hepatocytes can, in turn, stimulate HCAR1 receptor-bearing cells in the liver itself in an autocrine and paracrine fashion or can enter systemic circulation and affect distal organs,such as the central nervous system (CNS). A simplified flow chart illustrating the source of food enriched with ARs, the metabolism of ARs in humans, the bioactivity of the originating metabolite 3,5-dihydroxybenzoic acid and the potential impact on human organ targets is shown in Figure 1.[1]

Dietary sources of 3,5-Dihydroxybenzoic acid

Various phenolic acids, in particular derivatives of monohydroxy- and polyhydroxy-benzoic and cinnamic acids, are commonly found in fruits, vegetables, cereals, trees, and mushrooms.Surprisingly, the presence of 3,5-dihydroxybenzoic acid has been confirmed in a limited number of foods and medicinal herbs thus far.These include apples, honey, peanuts (Arachis hypogaea L.; 0.4–1.6 mg/100 g), chickpeas(Cicer arietinum L.), red sandalwood (Pterocarpus santalinusL.f.), hill raspberry (Rubus niveus Thunb.), Japanese rose (Rosa rugosa Thunb.), dog rose (Rosa canina L.), goutweed (Aegopodium podagrariaL.; 0.5 mg/100 g), two nettle species (Urtica dioica L. andUrtica urens L.; 4.3 mg/100 g), dandelion (Taraxacum officinale (L.) Weber; 0.3 mg/100 g) and chickweed (Stellariamedia (L.) Vill.; 0.2 mg/100 g).

Among these foods and herbs, apples are the most highly consumed fruits due to their worldwide availability and nutritional benefits. Recently, two glycosides of dihydroxybenzoate (dihydroxybenzoate O-hexoside, dihydroxybenzoate O-(hexoside-pentoside)), which are derivatives of DHBA, have been identified in the peel extract from apples.Low concentrations of 3,5-dihydroxybenzoic acid have also been found innutritionally valuable peanuts and popular beverages, suchas beer (0.01–0.34mg/L). Beside 3,5-dihydroxybenzoic acid derived from plant foods, other hydroxybenzoic acids aswell could also possibly be formed by gut microbiome fromingested flavonoids. Other isomers of 3,5-dihydroxybenzoic acid (pyrocatechuic, β-resorcylic, gentisic, γ-resorcylic,and protocatechuic acids) occur much more commonly in food and medicinal plants or could be end-point metabolites of particular drugs (pyrocatechuic and gentisic acid are metabolites of aspirin). Nevertheless,the process of biotransformation of 3,5-dihydroxybenzoic acid isomers into each other in potential isomerization reactions is unlikely to occur in human cells.[1]

3,5-Dihydroxybenzoic Acid-Based Selective Dopamine Detection

The selective recognition of dopamine (DA) over other neurotransmitter analogues is difficult due to the similar molecular structure and chemical reactivity. In this study,substitution-regulated chemical reactivity of the sensing substrate is utilized to explore a novel DA detection probe with satisfying selectivity. As a case study, 3,5-dihydroxybenzoic acid (carboxy-substituted resorcinol)-based probes have been explored for selective and ratiometric DA sensing. The carboxy substitution benefits the stabilization of the carbanion intermediate and the azamonardine product, which enhances the reaction kinetics and thermodynamics and subsequently facilitates selective DA recognition over other analogues and interferents. By exploring 3,5-dihydroxybenzoic acid emission as the internal reference, ratiometric fluorescence variation is realized, which contributes to sensitive DA analysis.With the combination of logic gate and fluorometric analysis, DA detection in both low and high concentrations can be readily achieved. In addition, the DA analysis in biological samples and the enzymatic transformation of DA analogues in cerebrospinal fluid samples are achieved by the proposed 3,5-dihydroxybenzoic acid probe.[2]

3,5-Dihydroxybenzoic Acid as a Potent Inhibitor

Phenol is produced by β-elimination of L-tyrosine(Tyr) catalyzed by tyrosine phenol-lyase (TPL) during intestinal bacterial metabolism. Phenol and its conjugate, phenyl sulfate(PhS), are protein-bound uremic toxins (PBUTs). Elevated levels of phenol and PhS are strongly implicated in the etiology and outcomes of uremia. Because hemodialys is is insufficient in removing phenol and PhS, novel methods are necessary for inhibiting phenol production during bacterial metabolism. Researchers explored TPL inhibitors and found that dietary polyphenols,particularly gallic acid (GA), strongly inhibited TPL-catalyzed phenol production. A GA derivative, 3,5-dihydroxybenzoic acid, competitively inhibited TPL and significantly decreased phenol levels in TPL-expressing bacteria (Morganella morganii and Citrobacter koseri) and Tyr-rich-diet-fed C57BL/6J mouse feces. These findings suggested that 3,5-dihydroxybenzoic acid was the most promising polyphenol in decreasing phenol levels. Therefore,dietary intake of 3,5-dihydroxybenzoic acid or its phenolic precursors may be useful in minimizing PBUT levels by targeting intestinal bacteria.[3]

3,5-Dihydroxybenzoic Acid Inhibits Lipolysis in Adipocytes

Niacin raises high-density lipoprotein and lowers low-density lipoprotein through the activation of the -hydroxybutyrate receptor hydroxycarboxylic acid 2 (HCA2) (aka GPR109a) but with an unwanted side effect of cutaneous flushing caused by vascular dilation because of the stimulation of HCA2 receptors in Langerhans cells in skin. HCA1 (aka GPR81), predominantly expressed in adipocytes, was recently identified as a receptor for lactate. Activation of HCA1 in adipocytes by lactate results in the inhibition of lipolysis, suggesting that agonists for HCA1may be useful for the treatment of dyslipidemia. Lactate is ametabolite of glucose, suggesting that HCA1 may also be involved in the regulation of glucose metabolism. The low potency of lactate to activate HCA1, coupled with its fast turnover rate in vivo, render it an inadequate tool for studying the biological role of lactate/HCA1 in vivo. In this article, researchers demonstrate the identification of 3-hydroxybenzoic acid (3-HBA) as an agonist for both HCA2 and HCA1, whereas 3,5-dihydroxybenzoic acid is a specific agonist for only HCA1 (EC50 150 M). 3,5-Dihydroxybenzoic acid inhibits lipolysis in wild-type mouse adipocytes but not in HCA1-deficient adipocytes. Therefore, 3,5-dihydroxybenzoic acid is a useful tool for the in vivo study of HCA1 function and offers a base for further HCA1 agonist design. Because 3-HBA and 3,5-dihydroxybenzoic acid are polyphenolic acids found in many natural products, such as fruits, berries, and coffee, it is intriguing to speculate that other heretofore undiscovered natural substances may have therapeutic benefits.[4]

References

1.Wagner W, Sobierajska K, Pu?aski ?, Stasiak A, Ciszewski WM. Whole grain metabolite 3,5-dihydroxybenzoic acid is a beneficial nutritional molecule with the feature of a double-edged sword in human health: a critical review and dietary considerations. Crit Rev Food Sci Nutr. 2024;64(24):8786-8804. doi:10.1080/10408398.2023.2203762

2.Liu Y, Cheng J, Lu F, et al. 3,5-Dihydroxybenzoic Acid-Based Selective Dopamine Detection via Subsititution-Enhanced Kinetics Differences. Anal Chem. 2023;95(40):14944-14953. doi:10.1021/acs.analchem.3c02313

3.Kobayashi T, Oishi S, Hara K, et al. 3,5-Dihydroxybenzoic Acid as a Potent Inhibitor of Tyrosine Phenol-Lyase Decreases Fecal Phenol Levels in Mice. J Med Chem. 2025;68(8):8786-8795. doi:10.1021/acs.jmedchem.5c00418

4.Liu C, Kuei C, Zhu J, et al. 3,5-Dihydroxybenzoic acid, a specific agonist for hydroxycarboxylic acid 1, inhibits lipolysis in adipocytes. J Pharmacol Exp Ther. 2012;341(3):794-801. doi:10.1124/jpet.112.192799