Blood-brain barrier breakdown, memory impairment and neurotoxicity caused in mice submitted to orally treatment with thymol

Neuroprotective Effects of Thymol and p-Cymene in Immobilized Male rats through Alterations in Molecular, Biochemical, Histological, and Behavioral Parameters

The research was conducted to examine the neuroprotective effect of thymol and its precursor p-cymene on chronic immobility stress in adult male Wistar rats. The rats were subjected to 2.5 h of stress every day for 14 consecutive days by placing them inside a restrainer. Thymol (10 mg/kg) and p-cymene (50 mg/kg) were given to the rats during the same period. The results showed that thymol and p-cymene prevented the increase of MDA level, decline of GSH level, and decrease of SOD and GPx activity in the hippocampus of rats exposed to stress. These monoterpenes also prevented the increase in the expression of Tnfa, Il1b, Tlr4, and Nfkb, and the decrease in the expression of Nrf2, Ho1, and Bdnf. In addition, thymol and p-cymene inhibited the increase in the expression and activity of acetylcholinesterase in the hippocampus of animals exposed to immobility and enhanced the expression of A7nachr. They also reduced neuronal death in the CA1 region of stressed animals and improved their performance in the Morris water maze and elevated plus maze tests. Based on these findings, thymol and p-cymene may be effective in preventing neurodegenerative diseases as they reduce oxidative stress and neuroinflammation, strengthen ACh signaling, and stimulate Bdnf expression.

Comparative ecotoxicity assessment of highly bioactive isomeric monoterpenes carvacrol and thymol on aquatic and edaphic indicators and communities

The growing demand for sustainable natural products to replace harmful synthetic ones requires comprehensive ecotoxicity assessments to ensure their eco-friendly nature. This study explored for the first time the changes in microbial community growth and metabolic profiles from river and natural soil samples exposed to the two structural isomers, thymol (THY) and carvacrol (CARV), utilizing Biolog EcoPlate™ assays and 16S rRNA gene sequencing for taxonomic analysis. In addition, we addressed existing ecotoxicity data gaps for these two compounds by using aquatic (Daphnia magna and Vibrio fischeri) and soil (Eisenia fetida and Allium cepa) indicators. Results show acute toxicity of both CARV and THY on all indicators. V. fischeri (LC50 = 0.59 mg/L) > D. magna (4.75 mg/L) > A. cepa (6.47 mg/L) for CARV, and V. fischeri (LC50 = 1.71 mg/L) > A. cepa (4.05 mg/L) > D. magna (8.13 mg/L) for THY. E. fetida showed LC50 = 7.68 mg/kg for THY and 1.04 for CARV. River and soil microbial communities showed resilience, likely because they contain taxa capable of biodegrading these products. No significant growth inhibition effects were observed up to 100 mg/L, though substrate utilization decreased at higher concentrations, particularly for polymers and amines in soil microorganisms and polymers in aquatic communities. Soil microorganisms were more affected than aquatic ones, with CARV being more toxic than THY (EC50120h = THY 94.13 and CARV 29.79 mg/L in soil microorganisms). These findings suggest that an increase in the consumption of these products and their subsequent ecotoxicity effects from environmental discharge should still be monitored before being ruled out. However, long-term effects are unlikely due to microbial degradation of these natural products, potentially reducing risks to other target species and opening the way for their use as substitutes for commercial antibiotics.

Effects of Thymbra spicata extract and Thymol on morphine withdrawal syndrome in mice (insights to the liver function, antioxidant, and behavioral responses)

Safe chemicals for drug withdrawal can be extracted from natural sources. This study investigates the effects of clonidine and Thymbra spicata extract (TSE) on mice suffering from morphine withdrawal syndrome. Thymol, which is the active constituent in TSE, was also tested. A total of 90 mice were divided into nine groups. Group 1 was the control group, while Group 2 was given only morphine, and Group 3 received morphine and 0.2 mg/kg of clonidine. Groups 4-6 were given morphine along with 100, 200, and 300 mg/kg of TSE, respectively. Groups 7-9 received morphine plus 30, 60, and 90 mg/kg of Thymol, respectively, for 7 days. An oral naloxone challenge of 3 mg/kg was used to induce withdrawal syndrome in all groups. Improvement of liver enzyme levels (aspartate aminotransferase, alkaline phosphatase, and alanine transaminase) (p < .01) and behavioral responses (frequencies of jumping, frequencies of two-legged standing, Straub tail reaction) (p < .01) were significantly observed in the groups receiving TSE and Thymol (Groups 4-9) compared to Group 2. Additionally, antioxidant activity in these groups was improved compared to Group 2. Nitric oxide significantly decreased in Groups 4 and 6 compared to Groups 2 and 3 (p < .01). Superoxide dismutase increased dramatically in Groups 5, 8, and 9 compared to Groups 2 and 3 (p < .01). Groups 5-9 were significantly different from Group 2 in terms of malondialdehyde levels (p < .01). Certain doses of TSE and Thymol were found to alleviate the narcotics withdrawal symptoms. This similar effect to clonidine can pave the way for their administration in humans.

Thymol as a Potential Neuroprotective Agent: Mechanisms, Efficacy, and Future Prospects

Neurodegenerative diseases pose a growing global health challenge, with limited effective therapeutic options. Mitochondrial dysfunction, oxidative stress, neuroinflammation, apoptosis, and autophagy are common underlying mechanisms in these diseases. Thymol is a phenolic monoterpene compound that has gained attention for its diverse biological properties, including antioxidant, anti-inflammatory, and immunomodulatory activities. Thymol supplementation could provide potential neuroprotection and improve cognitive deficits, depressant-like effects, learning, and memory impairments in rodents. Mechanistic investigations reveal that the neuroprotective effects of thymol involve the improvement of oxidative stress, mitochondrial dysfunction, and inflammatory response. Several signaling pathways, including mitochondrial apoptotic, NF-κB, AKT, Nrf2, and CREB/BDNF pathways are also involved. In this review, the neuroprotective effects of thymol, the potential molecular mechanisms, safety, applications, and current challenges toward development as a neuroprotective agent were summarized and discussed. We hope that this review provides valuable insights for the further development of this promising natural product as a promising neuroprotective agent.

Synergistic Activity of Thymol with Commercial Antibiotics against Critical and High WHO Priority Pathogenic Bacteria

The use of synergistic combinations between natural compounds and commercial antibiotics may be a good strategy to fight against microbial resistance, with fewer side effects on human, animal and environmental, health. The antimicrobial capacity of four compounds of plant origin (thymol and gallic, salicylic and gentisic acids) was analysed against 14 pathogenic bacteria. Thymol showed the best antimicrobial activity, with MICs ranging from 125 µg/mL (for Acinetobacter baumannii, Pasteurella aerogenes, and Salmonella typhimurium) to 250 µg/mL (for Bacillus subtilis, Klebsiella aerogenes, Klebsiella pneumoniae, Serratia marcescens, Staphylococcus aureus, and Streptococcus agalactiae). Combinations of thymol with eight widely used antibiotics were studied to identify combinations with synergistic effects. Thymol showed synergistic activity with chloramphenicol against A. baumannii (critical priority by the WHO), with streptomycin and gentamicin against Staphylococcus aureus (high priority by the WHO), and with streptomycin against Streptococcus agalactiae, decreasing the MICs of these antibiotics by 75% to 87.5%. The kinetics of these synergies indicated that thymol alone at the synergy concentration had almost no effect on the maximum achievable population density and very little effect on the growth rate. However, in combination with antibiotics at the same concentration, it completely inhibited growth, confirming its role in facilitating the action of the antibiotic. The time-kill curves indicated that all the combinations with synergistic effects were mainly bactericidal.

Thymol Disrupts Cell Homeostasis and Inhibits the Growth of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a typical kind of symbiotic bacteria, which can cause human pneumonia, food poisoning, and other health problems. Nowadays, the corresponding prevention and treatment have been a hot issue of general concern in related research areas. However, the mechanism of action against S. aureus is not well understood. In order to tackle such problem, we used broth microdilution to discuss the antibacterial effect of 5-methyl-2-isopropylphenol and determine inhibitory concentration. In addition, membrane potential and lipid peroxidation levels were also measured under experimental conditions. The experimental results suggested that 300 μg/mL thymol might cause cell membrane damage and decrease of NADPH concentration and increase of NADP⁺ and lipid peroxidation level. In such condition, thymol has the potential to result in membrane rupture and disruption of cellular homeostasis. Furthermore, we also found that NOX₂ is involved in maintaining the balance of NADPH/NADP⁺ in cells. Finally, our work confirms that NOX₂ is a potential downstream target for thymol in the cell. Such target can provide specific guidance and recommendations for its application in antifungal activity. Meanwhile, our study also provides a new inspiration for the molecular mechanism of thymol's bacteriostatic action.

Thymol provokes burst of action potentials in neurons of snail Caucasotachea atrolabiata

Thymol, a phenolic monoterpene, is well known for its antimicrobial, antifungal and antioxidant properties. In spite of wide use in oral care products, pharmaceutical and cosmetic preparation and in food industry, the effects of thymol on the neuronal activity and intrinsic properties have not been well studied. We studied the effects of thymol on the spontaneous activity and action potential properties of central neurons of snail Caucasotachea atrolabiata. Thymol (1 mM) altered action potentials characteristics and provoked epileptiform burst firing in snail neurons, which were partially reversible after washout. Before burst firing, action potentials had lower amplitude and maximum rising slope, while the threshold voltage was raised. These results suggest the inhibition of ion channels underlying action potential initiation and upstroke. The maximum falling slope and afterhyperpolarization were also considerably reduced, suggesting the inhibition of potassium channels. Thymol (0.5 mM) that was not able to induce burst firing in snail neurons, synergistically acted with potassium channel blocker, tetraethyl ammonium, to induce burst firing, which also supports the importance of potassium channel inhibition, especially delayed rectifier potassium channels, to the thymol-induced alteration of firing pattern. The thymol-induced burst firing seems to be dependent on both sodium and calcium currents. Our findings provide evidences for the ability of thymol in altering the firing mode of central neurons of snail, which apparently involves the inhibition of calcium and potassium currents. These results further support the interaction of thymol with ion channels and emphasize on the vulnerability of nervous system to this compound.

Tissue oxidative damage mediates impairment on phosphotransfer network during thymol intake: Effects on hepatic and renal bioenergetics

Recent evidences demonstrated that ingestion of several monoterpenes cause hepatic and renal damage due to impairment on mitochondrial energy production, eliciting a collapse on adenosine triphosphate (ATP) synthesis and consequently impairment on bioenergetic homeostasis. Thus, the aim of this study was to evaluate whether phosphotransfer network, catalyzed by creatine kinase (CK), adenylate kinase (AK), and pyruvate kinase (PK), can be a pathway to explain hepatic and renal bioenergetics homeostasis impairment due to thymol ingestion. Daily intake of thymol (40 mg/kg) significantly cause a decreased kidney weight and relative kidney weight compared to control group. The same dose of thymol inhibited renal cytosolic and mitochondrial CK activity as well as renal PK activity compared to control group. Finally, thymol (40 mg/kg) elicited a significant increase on renal reactive oxygen species and lipid damage levels, as well as an inhibition on antioxidant capacity against peroxyl radicals and non-protein thiol levels, which did not occur liver. Doses of 10 and 20 mg/kg of thymol administered orally for 30 consecutive days non-changed these variables. Based on these evidence, the data supported that intake of a high dose of thymol severely inhibits cytosolic and mitochondrial CK activity, a crucial enzyme to maintain cellular energy homeostasis. Moreover, high dietary thymol intake impaired communication between CK isoenzymes, which inhibits the attempts to regenerate ATP or to facilitate the CK/PCr shuttle to improve the intracellular ATP utilization and consumption. Moreover, the inhibition of renal CK and PK activities appears to be mediated by the renal oxidation of lipids and thiol groups, as well as by the reduction of the renal antioxidant capacity.