Systemic Administration of the TRPV3 Ion Channel Agonist Carvacrol Induces Hypothermia in Conscious Rodents

Increased Activity of β-Lactam Antibiotics in Combination with Carvacrol against MRSA Bacteremia and Catheter-Associated Biofilm Infections

β-Lactam antibiotics are the mainstay for the treatment of staphylococcal infections, but their utility is greatly limited by the emergence and rapid dissemination of methicillin-resistant Staphylococcus aureus (MRSA). Herein, we evaluated the ability of the plant-derived monoterpene carvacrol to act as an antibiotic adjuvant, revitalizing the anti-MRSA activity of β-lactam antibiotics. Increased susceptibility of MRSA to β-lactam antibiotics and significant synergistic activities were observed with carvacrol-based combinations. Carvacrol significantly inhibited MRSA biofilms and reduced the production of exopolysaccharide, polysaccharide intercellular adhesin, and extracellular DNA and showed synergistic biofilm inhibition in combination with β-lactams. Transcriptome analysis revealed profound downregulation in the expression of genes involved in two-component systems and S. aureus infection. Mechanistic studies indicate that carvacrol inhibits the expression of staphylococcal accessory regulator sarA and interferes with SarA-mecA promoter binding that decreases mecA-mediated β-lactam resistance. Consistently, the in vivo experiment also supported that carvacrol restored MRSA sensitivity to β-lactam antibiotic treatments in both murine models of bacteremia and biofilm-associated infection. Our results indicated that carvacrol has a potential role as a combinatorial partner with β-lactam antibiotics to address MRSA infections.

Neuroprotective Potential and Underlying Pharmacological Mechanism of Carvacrol for Alzheimer's and Parkinson's Diseases

The phytochemicals have antioxidant properties to counter the deleterious effects of oxidative stress in the central nervous system and can be a promising drug candidate for neurodegenerative diseases. Among various phytochemicals, constituents of spice origin have recently received special attention for neurodegenerative diseases owing to their health benefits, therapeutic potential, edible nature, and dietary accessibility and availability. Carvacrol, a phenolic monoterpenoid, has garnered attention in treating and managing various human diseases. It possesses diverse pharmacological effects, including antioxidant, anti-inflammatory, antimicrobial and anticancer. Alzheimer's disease (AD) and Parkinson's disease (PD) are major public health concerns that place a significant financial burden on healthcare systems worldwide. The global burden of these diseases is expected to increase in the next few decades owing to increasing life expectancies. Currently, there is no cure for neurodegenerative diseases, such as AD and PD, and the available drugs only give symptomatic relief. For a long time, oxidative stress has been recognized as a primary contributor to neurodegeneration. Carvacrol enhances memory and cognition by modulating the effects of oxidative stress, inflammation, and Aβ25-35- induced neurotoxicity in AD. Moreover, it also reduces the production of reactive oxygen species and proinflammatory cytokine levels in PD, which further prevents the loss of dopaminergic neurons in the substantia nigra and improves motor functions. This review highlights carvacrol's potential antioxidant and anti-inflammatory properties in managing and treating AD and PD.

TRPV3 enhances skin keratinocyte proliferation through EGFR-dependent signaling pathways

Transient receptor potential vanilloid 3 (TRPV3) is highly expressed in skin keratinocytes where it forms Ca2+-permeable nonselective cation channels to regulate various cutaneous functions. TRPV3 expression is upregulated in many skin disorders. Here, we examined how TRPV3 affects keratinocyte proliferation and investigated the underlying mechanism. Topical application of TRPV3 agonist, carvacrol, increased skin thickness in wild type (WT) mice but not in TRPV3 knockout (KO) mice. Carvacrol promoted proliferation of human keratinocytes HaCaT cells at concentrations ≤ 100 μM, but at 300 μM, it decreased cell viability, suggesting a nonmonotonic proliferative effect. Suppression of TRPV3 expression abolished carvacrol-induced cell proliferation while overexpression of TRPV3 enhanced HaCaT cell proliferation. Carvacrol also stimulated Ca2+ influx and proliferation of primary keratinocytes prepared from WT but not TRPV3 KO mice, suggesting that carvacrol-stimulated cell proliferation was dependent on TRPV3-mediated Ca2+ influx. Mechanistic investigation demonstrated that carvacrol stimulated TGFα release and increased phosphorylation levels of EGFR, PI3K, and NF-κB, effects abolished by suppression of TRPV3 expression and CaMKII inhibition. Moreover, inhibition of CaMKII, EGFR, PI3K, or NF-κB diminished carvacrol-induced cell proliferation. We conclude that while strong activation of TRPV3 may cause cell death, moderate activation of TRPV3 promotes cell proliferation in keratinocytes through Ca2+/CaMKII→TGFα/EGFR→PI3K→NF-κB signaling. Graphical abstract Headlights 1. Carvacrol induces epidermal hyperplasia and keratinocyte proliferation. 2. TRPV3 mediates carvacrol-induced epidermal hyperplasia and keratinocyte proliferation. 3. TRPV3 acts through Ca2+/CaMKII→TGFα/EGFR→PI3K→NF-κB signaling to promote keratinocyte proliferation.

Effect of treatment with carvacrol and aerobic training on cardiovascular function in spontaneously hypertensive rats

NEW FINDINGS

What is the central question of this study? Can two non-drug therapies, carvacrol and aerobic physical training, together have additive effects on the reduction of cardiovascular risks and control of arterial hypertension? What is the main finding and its importance? The oral use of carvacrol (20 mg/kg/day) can control sustained hypertension in spontaneously hypertensive rats, and when this use is associated with aerobic physical training, there is a more pronounced effect on the reduction of blood pressure values, making these therapies an adjunct option in the drug treatment of hypertension.

ABSTRACT

Systemic arterial hypertension is considered the foremost cardiovascular risk factor, and it is important to examine different therapies that help prevent and treat it, especially when associated with other cardiovascular risk factors. In this context, it is known that both carvacrol and aerobic physical training benefit the cardiovascular system. This study investigated the effects of treatment with carvacrol combined with aerobic exercise on hypertensive rats with cardiovascular risk parameters. We used an experimental design with six groups: normotensive control (Wistar rats); hypertensive control (spontaneously hypertensive rats, SHR); positive control rats treated with amlodipine (Aml-20 mg); rats treated with carvacrol (Carv-20 mg); rats trained with exercise (Exer); and rats treated with carvacrol and exercise (ExerCarv). The treatment lasted for 4 weeks, monitoring heart rate and systolic blood pressure (SBP). At the end of the treatment, vascular reactivity tests were performed in addition to biochemical measurements of urea, creatinine, aspartate aminotransferase, alanine aminotransferase, triglycerides, total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, very low density lipoprotein cholesterol, atherogenic indexes, relative heart weight and histopathological analysis of cardiac perivascular tissue. Significant reductions in SBP were observed after the training period, with the ExerCarv group showing a greater magnitude of reduction (∆SBP = 88 ± 10.0 mmHg, 42%). This group also experienced reductions in atherogenic indices and improvement in all analysed lipid parameters, with no differences observed in the Exer group. The findings indicated that the interaction between aerobic exercise and carvacrol offers a greater BP reduction. Exercise is particularly effective for controlling biochemical parameters of cardiovascular risk, regardless of carvacrol use.

Tocolytic effect of the monoterpenic phenol isomer, carvacrol, on the pregnant rat uterus

Despite the wide application of carvacrol (CAR) in different biological and medical areas, there is still insufficient electrophysiological data on the mechanisms of action of CAR, particularly in the pregnant uterine function. The aim of this study was to evaluate the in vitro tocolytic effect of CAR on the contractility of isolated pregnant rat uterus in the presence of a calcium channel antagonist (nifedipine) and a cyclooxygenase inhibitor (indomethacin). The uteri were isolated from pregnant Wistar rats at 16-18 days of pregnancy and suspended in an isolated organ bath chamber containing a Ringer's physiological solution and aerated with 95% O₂and 5% CO₂. Samples were used in functional tests to evaluate the inhibitory effect of CAR at increasing concentrations on the rhythmic spontaneous, oxytocin-induced phasic, K⁺-induced tonic, and Ca²⁺-induced contractions. The differences in inhibitory concentration-50 and E_maxamong the compounds were determined using the one-way ANOVA followed by a post hoc Student-Newman-Keuls or Bonferroni test, in all casesP < 0.05 was considered statistically significant. Nifedipine was used as positive controls where required. CAR caused a significant concentration-dependent inhibition of the uterine contractions induced by the pharmaco- and electro-mechanic stimuli. We showed that the inhibitory effects of CAR depends on the type of muscle contraction stimuli, and that it acts stronger in spontaneous rhythmic activity and in contractions of isolated rat uterus induced by Ca²⁺. Nifedipine was more potent than CAR and indomethacin on the uterine contractility (P < 0.05), but none of them was more effective than nifedipine. Therefore, the tocolytic effect induced by CAR was associated with the blockade of the calcium channels in the pregnant rat uterus. This property placed CAR as a potentially safe and effective adjuvant agent in cases of preterm labor, an area of pharmacological treatment that requires urgent improvement.

Identification of Essential Oils with Strong Activity against Stationary Phase Borrelia burgdorferi

Lyme disease is the most common vector borne-disease in the United States (US). While the majority of the Lyme disease patients can be cured with 2–4 weeks antibiotic treatment, about 10–20% of patients continue to suffer from persisting symptoms. While the cause of this condition is unclear, persistent infection was proposed as one possibility. It has recently been shown that B. burgdorferi develops dormant persisters in stationary phase cultures that are not killed by the current Lyme antibiotics, and there is interest in identifying novel drug candidates that more effectively kill such forms. We previously identified some highly active essential oils with excellent activity against biofilm and stationary phase B. burgdorferi. Here, we screened another 35 essential oils and found 10 essential oils (Allium sativum L. bulbs, Pimenta officinalis Lindl. berries, Cuminum cyminum L. seeds, Cymbopogon martini var. motia Bruno grass, Commiphora myrrha (T. Nees) Engl. resin, Hedychium spicatum Buch.-Ham. ex Sm. flowers, Amyris balsamifera L. wood, Thymus vulgaris L. leaves, Litsea cubeba (Lour.) Pers. fruits, Eucalyptus citriodora Hook. leaves) and the active component of cinnamon bark cinnamaldehyde (CA) at a low concentration of 0.1% have strong activity against stationary phase B. burgdorferi. At a lower concentration of 0.05%, essential oils of Allium sativum L. bulbs, Pimenta officinalis Lindl. berries, Cymbopogon martini var. motia Bruno grass and CA still exhibited strong activity against the stationary phase B. burgdorferi. CA also showed strong activity against replicating B. burgdorferi, with a MIC of 0.02% (or 0.2 μg/mL). In subculture studies, the top five essential oil hits Allium sativum L. bulbs, Pimenta officinalis Lindl. berries, Commiphora myrrha (T. Nees) Engl. resin, Hedychium spicatum Buch.-Ham. ex Sm. flowers, and Litsea cubeba (Lour.) Pers. fruits completely eradicated all B. burgdorferi stationary phase cells at 0.1%, while Cymbopogon martini var. motia Bruno grass, Eucalyptus citriodora Hook. leaves, Amyris balsamifera L. wood, Cuminum cyminum L. seeds, and Thymus vulgaris L. leaves failed to do so as shown by visible spirochetal growth after 21-day subculture. At concentration of 0.05%, only Allium sativum L. bulbs essential oil and CA sterilized the B. burgdorferi stationary phase culture, as shown by no regrowth during subculture, while Pimenta officinalis Lindl. berries, Commiphora myrrha (T. Nees) Engl. resin, Hedychium spicatum Buch.-Ham. ex Sm. flowers and Litsea cubeba (Lour.) Pers. fruits essential oils all had visible growth during subculture. Future studies are needed to determine if these highly active essential oils could eradicate persistent B. burgdorferi infection in vivo.

TRP Channels as Drug Targets to Relieve Itch

Although acute itch has a protective role by removing irritants to avoid further damage, chronic itch is debilitating, significantly impacting quality of life. Over the past two decades, a considerable amount of stimulating research has been carried out to delineate mechanisms of itch at the molecular, cellular, and circuit levels. There is growing evidence that transient receptor potential (TRP) channels play important roles in itch signaling. The purpose of this review is to summarize our current knowledge about the role of TRP channels in the generation of itch under both physiological and pathological conditions, thereby identifying them as potential drug targets for effective anti-itch therapies.

Precise Control of Target Temperature Using N6-Cyclohexyladenosine and Real-Time Control of Surface Temperature

Targeted temperature management is standard of care for cardiac arrest and is in clinical trials for stroke. N⁶-cyclohexyladenosine (CHA), an A₁ adenosine receptor (A₁AR) agonist, inhibits thermogenesis and induces onset of hibernation in hibernating species. Despite promising thermolytic efficacy of CHA, prior work has failed to achieve and maintain a prescribed target core body temperature (T_b) between 32°C and 34°C for 24 hours. We instrumented Sprague-Dawley rats (n = 19) with indwelling arterial and venous cannulae and a transmitter for monitoring T_b and ECG, then administered CHA via continuous IV infusion or intraperitoneal (IP) injection. In the first experiment (n = 11), we modulated ambient temperature and increased the dose of CHA in an attempt to manage T_b. In the second experiment (n = 8), we administered CHA (0.25 mg/[kg·h]) via continuous IV infusion and modulated cage surface temperature to control T_b. We rewarmed animals by increasing surface temperature at 1°C h^-1 and discontinued CHA after T_b reached 36.5°C. T_b, brain temperature (T_brain), heart rate, blood gas, and electrolytes were also monitored. Results show that titrating dose to adjust for individual variation in response to CHA led to tolerance and failed to manage a prescribed T_b. Starting with a dose (0.25 mg/[kg·h]) and modulating surface temperature to prevent overcooling proved to be an effective means to achieve and maintain T_b between 32°C and 34°C for 24 hours. Increasing surface temperature to 37°C during CHA administration brought T_b back to normothermic levels. All animals treated in this way rewarmed without incident. During the initiation of cooling, we observed bradycardia within 30 minutes of the start of IV infusion, transient hyperglycemia, and a mild hypercapnia; the latter normalized via metabolic compensation. In conclusion, we describe an intravenous delivery protocol for CHA at 0.25 mg/(kg·h) that, when coupled with conductive cooling, achieves and maintains a prescribed and consistent target T_b between 32°C and 34°C for 24 hours.

Optimization of Thermolytic Response to A1 Adenosine Receptor Agonists in Rats

Cardiac arrest is a leading cause of death in the United States, and, currently, therapeutic hypothermia, now called targeted temperature management (TTM), is the only recent treatment modality proven to increase survival rates and reduce morbidity for this condition. Shivering and subsequent metabolic stress, however, limit application and benefit of TTM. Stimulating central nervous system A₁ adenosine receptors (A₁AR) inhibits shivering and nonshivering thermogenesis in rats and induces a hibernation-like response in hibernating species. In this study, we investigated the pharmacodynamics of two A₁AR agonists in development as antishivering agents. To optimize body temperature (T_b) control, we evaluated the influence of every-other-day feeding, dose, drug, and ambient temperature (T_a) on the T_b-lowering effects of N⁶-cyclohexyladenosine (CHA) and the partial A₁AR agonist capadenoson in rats. The highest dose of CHA (1.0 mg/kg, i.p.) caused all ad libitum-fed animals tested to reach our target T_b of 32°C, but responses varied and some rats overcooled to a T_b as low as 21°C at 17.0°C T_a Dietary restriction normalized the response to CHA. The partial agonist capadenoson (1.0 or 2.0 mg/kg, i.p.) produced a more consistent response, but the highest dose decreased T_b by only 1.6°C. To prevent overcooling after CHA, we studied continuous i.v. administration in combination with dynamic surface temperature control. Results show that after CHA administration control of surface temperature maintains desired target T_b better than dose or ambient temperature.

Neuroactive and Anti-inflammatory Frankincense Cembranes: A Structure-Activity Study

An expeditious isolation method for the cembrane diterpene alcohols incensol (1a) and serratol (2) has been developed from respectively African and Indian frankincense. The two native alcohols and a series of semisynthetic derivatives of incensol were evaluated for transient receptor potential vanilloid 3 (TRPV3) activation and the inhibition of NF-κB, the putative molecular targets underlying the psychotropic and anti-inflammatory activities of incensol acetate (IA, 1b). Serratol (2) was the most potent TRPV3 activator, outperforming by 2 orders of magnitude the reference agonist thymol and by 1 order of magnitude incensol acetate (1b). Acylation, epimerization, and oxidation did not significantly improve the affinity of incensol for TRPV3, while NF-κB inhibition, marginal for both natural alcohols, could be improved by esterification of incensol (1a) with lipophilic acids. Interestingly, incensol (1a) but not IA (1b) was a potent inhibitor of STAT3, raising the possibility that hydrolysis to incensol (1a) might be involved in the in vivo biological activity of IA (1b). Serratol was not amenable to chemical modification, but some marine cembranoids related to the frankincense diterpenoids showed a certain degree of TRPV3-activating properties, qualifying the aliphatic macrocyclic cembrane skeleton as a selective chemotype to explore the pharmacology of TRPV3, a thermo-TRP otherwise resistant to modulation by small molecules.