Here, we aimed to evaluate the in vitro and in vivo efficacy of TSEO against PSCs and hydatid cysts of
E.granulosus. We found that the monoterpenes compounds carvacrol (65.88%), γ-terpinene (9.71%), and p-cymene (7.82%) were the most abundant compounds in TSEO, respectively. Unlu et al. showed that the main compounds in Turkish TSEO were carvacrol (60.39%), γ-terpinene (12.95%), and p-cymene (9.61%), respectively (
30). Markovic et al. reported that the main compounds in Greek TSEO were carvacrol (74.5%) and γ-terpinene (11.2%) (
31). Mosleh et al. demonstrated that during the pre-flowering period, TSEO contained 7 compounds, with the main constituents being γ-terpinene (15.5%) and carvacrol (79.3%). Conversely, during full flowering, TSEO was composed of 11 compounds, with carvacrol (70.5%) and γ-terpinene (14.9%) identified as the major constituents (
32). This change in their composition and percentage can be due to the harvesting season of the plant, the part used, and the extraction methods (
32).
We found that increasing the concentration of TSEO enhanced the scolicidal effect. At a concentration of 30 µg/mL, lethality reached approximately 90%, and 100% lethality was achieved at a concentration of 50 µg/mL after 60 minutes of exposure. By conducting an in vivo assay, it was observed that treatment with TSEO led to a significant reduction in the average number, size, and weight of hydatid cysts, as supported by statistical significance. With respect to the protoscolicidal effects of
Thymus spp., Hizem et al. demonstrated that
T.capitatus essential oil, when concentrated at 2 and 3 mg/mL, led to the complete eradication of PSCs within 5 and 1 minute, respectively. Additionally, analyses conducted using GC/MS techniques revealed that carvacrol constituted the predominant component of the essential oil, accounting for 82.4% of its composition (
33). Pensel et al. showed that the essential oil derived from
T. vulgaris demonstrated a protoscolicidal effect, resulting in a significant decrease in PSC viability to 35.3% after a 60-day incubation period (
34). Fabbri et al. reported that the highest protoscolicidal effect was achieved using a concentration of 10 μg/mL of carvacrol. Upon examination at the ultrastructural level, it was observed that the germinal layer of cysts treated with carvacrol showed a loss of the characteristic multicellular structure. A decrease in cyst weight was observed after administering 40mg/kg of carvacrol over a 20-day period to mice with hydatid cysts (
35). Albani et al. demonstrated that the most significant protoscolicidal effect was observed in the combinations of carvacrol and thymol in ratios of 9:1 and 5:5, leading to a notable decrease in viability six days post-incubation, consistent with the observed ultrastructural changes. They also reported that the combination of thymol (40 mg/kg) and carvacrol (40 mg/kg) showed a tendency to reduce the weight of the cysts compared to the control group (
36). In addition, reviews have shown the high potency of carvacrol-rich plants such as
Zataria multiflora, Satureja khuzistanica, Satureja hortensis, Eucalyptus globulus, Syzygium aromaticum, and
Origanum minutiflorum against
PSCs and hydatid cysts of
E. granulosus (
37).
Today, morphological changes in the ultrastructure of microbial cells were observed using SEM (
38). Scanning electron microscopy images of the cyst treated with 50 µL/mL of TSEO for 1 hour of incubation showed ultrastructural damage, rostellar disorganization, alterations in the teguments, and deformation of the cyst structure. This indicates that TSEO leads to damage to the membrane and cell wall in hydatid cyst PSCs. It is commonly recognized that apoptosis serves a dual purpose in the interaction between the host and hydatid cysts by facilitating survival and suppression mechanisms (
39). Caspase enzymes, notably caspase-3, are essential for the progression of apoptosis, with caspase-3 specifically playing a crucial role in DNA fragmentation and the structural changes associated with cell death (
39). Our real-time PCR results showed that after exposing PSCs to TSEO, the expression level of the caspase-3 gene increased over time with increasing concentration. This indicates that apoptosis induction is one of the possible protoscolicidal mechanisms of action of TSEO.
Regarding the antimicrobial mechanisms of action of monoterpenes, studies have reported that these compounds display their efficacy by affecting cell membrane permeability, disrupting DNA synthesis, causing leakage of proteins and nucleic acids, producing reactive oxygen species, inducing oxidative stress, and triggering apoptosis (
40). Therefore, it can be suggested that the high efficacy of TSEO is probably due to the presence of monoterpene compounds such as carvacrol.
Addressing the toxicity aspects of TSEO, the analysis of biochemical parameters related to liver and kidney function revealed that after receiving TSEO at doses of 20, 30, and 40 mg/kg/day for 28 days, although there were variations in the parameters examined, no significant differences were observed compared to the control group that received normal saline. These results indicate that the administration of TSEO at these specified doses, even over 28 days, does not exhibit any harmful effects on the functionality of essential liver and kidney tissues.
5.1. Conclusions
The findings of the study confirmed the promising in vitro and in vivo effects of TSEO against hydatid cyst infection. Considering the possible mechanisms, TSEO provoked cell wall damage and induced apoptosis. However, more studies are needed to clarify these findings and accurately elucidate the mechanisms of action.