Abstract
Planarians of the species Dugesia tigrina are established model organisms for studying stem cell-driven tissue regeneration due to their pluripotent neoblasts and low husbandry cost. Trichosanthes kirilowii root, a herb used extensively in traditional Chinese medicine, contains bioactive compounds—including trichosanthin, flavonoids, and polysaccharides—with documented antioxidant and anti-inflammatory properties. Because oxidative stress and inflammation are known barriers to tissue repair, we hypothesized that exposure to Trichosanthes root extract would accelerate regeneration in D. tigrina. Planarians (n = 10 per group) were assigned to one of four treatment concentrations (0%, 0.01%, 0.03%, or 0.05% v/v extract) for seven days, then transversely amputated. Head and tail fragments were monitored for 11 days across two independent trials, with body length, eyespot regeneration, locomotor activity, c-shape behavior, and touch responsiveness recorded at regular intervals. Statistical analysis used one-way analysis of variance (ANOVA) followed by Tukey's honest significant difference (HSD) post hoc test. Although statistically significant between-group differences in tail regeneration length emerged at several time points (Day 1: p < 0.01; Day 3: p < 0.0001; Day 5: p < 0.02; Day 10: p < 0.0001; Day 11: p < 0.01), no dose-dependent trend was observed and no differences were detected for eyespot regeneration, locomotor activity, c-shape curling, or touch responsiveness (all p > 0.05). These results indicate that Trichosanthes root extract at the tested concentrations does not meaningfully enhance regeneration in D. tigrina, providing useful negative evidence for future screens of traditional herbal compounds in regenerative biology.
Keywords: Dugesia tigrina, Trichosanthes kirilowii, planarian regeneration, neoblasts, traditional Chinese medicine, locomotor activity
1. Introduction
1.1 Rationale and Significance
Identifying natural compounds capable of enhancing tissue regeneration represents a central challenge in translational medicine. Planarians of the species Dugesia tigrina offer an experimentally tractable model for this endeavor: when bisected, each fragment activates a population of pluripotent adult stem cells called neoblasts that proliferate and differentiate to restore the entire organism within days [1]. The neoblast-driven regenerative program shares molecular features with vertebrate stem cell systems, making planarians informative for understanding the cellular prerequisites of tissue repair [1].
Traditional Chinese medicine (TCM) has documented anti-inflammatory and antioxidant interventions for centuries, yet most of these compounds remain uncharacterized in living regeneration assays. Because inflammation and oxidative stress suppress stem cell activity and delay wound healing [2], compounds that mitigate these stressors are rational candidates for promoting regeneration. Trichosanthes kirilowii root represents one such candidate: its bioactive constituents—including the ribosome-inactivating protein trichosanthin, flavonoid antioxidants, triterpenoids, and immunomodulatory polysaccharides—are well-documented in cell-culture and clinical contexts [3,4], yet no study has examined their effect on in vivo tissue regeneration in a whole-organism model.
The present study was therefore designed to test whether continuous exposure to graded concentrations of Trichosanthes root extract (0–0.05% v/v) would accelerate regeneration in D. tigrina, as measured by body-length recovery, eyespot reformation, and indices of nervous system function. A positive result would justify further mechanistic investigation; a null result would provide valuable negative data guiding future compound selection in this growing research area.
1.2 Trichosanthes kirilowii Root
Trichosanthes kirilowii (family Cucurbitaceae) has been prescribed in TCM for respiratory inflammation, fevers, and metabolic conditions for over a millennium [3]. The root is pharmacologically complex. Trichosanthin, its most studied protein, inactivates ribosomes and has demonstrated antitumor and antiviral effects in vitro [4]. Flavonoids scavenge reactive oxygen species, protecting cells from oxidative damage that accumulates in injured tissue. Triterpenoids and polysaccharides contribute anti-inflammatory and immunoregulatory activity, respectively, collectively creating conditions proposed to be conducive to cellular repair [2]. Despite these properties, the regenerative potential of Trichosanthes root in a living, whole-organism system had not previously been evaluated.
1.3 Dugesia tigrina as a Model Organism
D. tigrina is a freshwater planarian favored in undergraduate and professional research alike for its transparent body, short regeneration timeline, and readily observable behavioral outputs. Critically, its neoblast system—the only dividing somatic cells under homeostatic conditions—underpins regeneration through mechanisms including Wnt signaling gradients and positional information cues that determine anterior-posterior identity [1]. Previous work has used D. tigrina to assess the effects of diverse exogenous compounds, including caffeine and nicotine, on regeneration rate [5], providing methodological precedents for the present study. Eyespot reformation in tail fragments and body-length recovery in both head and tail fragments serve as established proxy measures for neoblast function and nervous system reconstitution, respectively.
2. Materials and Methods
2.1 Organism Husbandry and Experimental Design
Forty Dugesia tigrina planarians (Carolina Biological Supply, catalog no. 132954) were randomly assigned to four groups (n = 10 per group) immediately upon receipt. Animals were maintained individually in loosely sealed glass jars containing Poland Spring water and stored at room temperature (~22°C) in a darkened cabinet to minimize phototactic stress. Planarians were fed ground beef liver three times per week (Monday, Wednesday, Friday); following each feeding, the jar was emptied, rinsed, and refilled with fresh water to prevent ammonia accumulation. A seven-day acclimation period preceded all experimental manipulations. All work surfaces were decontaminated with 70% isopropanol before each session. Experiments were replicated across two independent trials (Trial 1 and Trial 2) using separate cohorts to assess reproducibility.
2.2 Preparation of Treatment Solutions
Trichosanthes root extract (HerbalTerra, purchased via Amazon) was prepared as a stock and diluted to target concentrations in Poland Spring water. Working solutions (50 mL total volume) were prepared for each group according to Table 1 under sterile conditions; the appropriate volume of extract was measured with a calibrated micropipette and combined with water in a beaker, then gently swirled to homogenize. Solutions were prepared fresh on each treatment day.
Table 1. Composition of treatment solutions by group.
| Group | Extract Conc. (% v/v) | Extract Vol. (µL) | Water Vol. (mL) | n (organisms) |
| A (Control) | 0 | 0 | 50 | 10 |
| B | 0.01 | 5 | 50 | 10 |
| C | 0.03 | 15 | 50 | 10 |
| D | 0.05 | 25 | 50 | 10 |
2.3 Treatment Administration
Following the acclimation period, each group was immersed in its corresponding treatment solution for approximately 24 hours. Planarians remained in treatment solution throughout the pre-amputation period. Water quality was maintained by replacing the treatment solution at each feeding interval.
2.4 Locomotor Activity and Behavioral Assessment
Baseline locomotor activity was recorded before treatment. For each assay session, 30 mL of Poland Spring water was added to four sterile Petri dishes placed over graph paper grids. Individual planarians were transferred to their respective dishes by group, allowed a 60-second acclimation period, and then video-recorded for 30 seconds. Two behavioral measures were quantified from video: (1) the number of grid lines crossed, as a proxy for overall locomotion, and (2) the frequency of c-shape body curvature events, a stereotyped aversive response used as a stress indicator. Recordings were scored by a single observer blinded to group assignment where possible.
2.5 Transverse Amputation
Planarians were cold-anesthetized on ice for one minute to reduce movement before dissection. Each animal was transversely bisected anterior to the pharynx using a scalpel sterilized with 70% isopropanol; the scalpel was re-sterilized after every three cuts to prevent cross-contamination. Head and tail fragments from each group were placed into separate labeled containers (e.g., AH = Group A heads; AT = Group A tails) containing the appropriate treatment solution.
2.6 Regeneration Assays
Body length (mm) of both head and tail fragments was measured with a ruler every other business day for 11 days. Eyespot regeneration in tail fragments was assessed daily under a dissecting microscope using a standardized three-point scale: 0 = no visible eyespot; 0.5 = partial pigmentation or incomplete structure; 1 = fully formed, bilaterally symmetric eyespots. Touch responsiveness was evaluated in tail fragments only after pharynx regeneration was confirmed; a soft-bristle brush was lightly applied to the anterior margin of each fragment and the presence or absence of a directed avoidance response was recorded. Planarians were not fed until pharynx regeneration was complete, to avoid confounding feeding behavior with regeneration status. At the conclusion of both trials, all organisms were ethically euthanized by autoclaving at 121°C for 20 minutes under faculty supervision.
2.7 Statistical Analysis
All data were entered into Microsoft Excel. Group means and standard deviations were calculated for each measure at each time point. Differences among groups were assessed with one-way ANOVA at each time point, followed by Tukey's HSD post hoc test for pairwise comparisons when the omnibus test was significant (significance threshold: α = 0.05). Analyses were conducted using an online statistics platform.
3. Results
3.1 Locomotor Activity
Mean locomotion, quantified as grid lines crossed per 30-second recording, was similar across all treatment groups at all time points in both trials (all p > 0.05; Figs. 3 and 9). Groups began the experiment crossing approximately 4–6 lines and converged toward 7–9 lines by the end of the observation period, with no concentration-dependent pattern evident. These data indicate that Trichosanthes root extract did not detectably alter baseline locomotor function.
3.2 C-Shape Behavior
The frequency of c-shape curling events was low and variable across all groups throughout both trials, with no significant treatment effects detected at any time point (all p > 0.05; Figs. 4 and 10). This result suggests that the concentrations tested did not induce measurable aversive stress responses beyond those observed in the water-only control.
3.3 Eyespot Regeneration
Eyespot regeneration scores increased progressively over the 11-day observation period across all groups, consistent with normal neoblast-driven photoreceptor reformation. Qualitative inspection of the data suggested marginally earlier eyespot appearance in some extract-treated groups relative to controls, but these trends did not reach statistical significance in either trial (all p > 0.05; Figs. 5 and 11). By Day 11, mean eyespot scores in both trials approached 1.0 (full regeneration) across all groups.
3.4 Head Fragment Regeneration Length
Significant between-group differences in head fragment body length were detected on Day 1 of Trial 1 (p < 0.001) and Day 5 of Trial 1 (p = 0.002), and on Day 1 of Trial 2 (p < 0.001; Figs. 6 and 12). However, post hoc analysis revealed that these differences did not follow a consistent dose-response pattern, and no significant differences were observed on any other measurement day in either trial. Because Day 1 differences likely reflect variability in initial cut position rather than extract-driven growth, these transient effects are not interpreted as evidence of a treatment effect.
3.5 Tail Fragment Regeneration Length
Statistically significant differences in tail fragment body length were detected across multiple time points in Trial 1: Day 1 (p < 0.01), Day 3 (p < 0.0001), Day 5 (p < 0.02), Day 10 (p < 0.0001), and Day 11 (p < 0.01; Fig. 7). Despite the statistical significance, pairwise comparisons via Tukey's HSD did not reveal a dose-dependent ordering of groups, and the pattern was not reproduced in Trial 2. The absence of consistency across trials and the absence of a monotonic concentration-response relationship suggest that these differences reflect biological variability in fragment size rather than a true extract-mediated effect.
3.6 Touch Responsiveness
Touch responsiveness was uniformly high across all groups and time points, with all planarians exhibiting directed avoidance responses upon stimulation. No significant differences were detected between groups at any time point (all p > 0.05; Fig. 8), indicating normal peripheral and central nervous system recovery in all treatment conditions.
4. Discussion
The central hypothesis of this study—that Trichosanthes kirilowii root extract would enhance tissue regeneration in D. tigrina—was not supported. Across two independent trials, continuous exposure to extract concentrations of 0.01%, 0.03%, or 0.05% v/v produced no significant improvement in eyespot regeneration, body-length recovery, locomotor activity, c-shape behavior frequency, or touch responsiveness relative to the water-only control. Statistically significant differences in tail fragment length emerged at several time points in Trial 1, but the lack of a dose-response relationship and the failure of these effects to replicate in Trial 2 strongly suggest they reflect pre-existing size variation among fragments rather than a pharmacological effect of the extract.
Several factors may explain the null result. First, the concentrations tested (up to 0.05% v/v) may be insufficient to achieve pharmacologically relevant intracellular concentrations of trichosanthin or flavonoids in planarian tissues. The extract was an uncharacterized commercial preparation; bioactive compound concentrations were not independently verified, which limits interpretation. Second, the 24-hour treatment period prior to amputation may not have permitted adequate tissue loading. Chronic exposure throughout regeneration, beginning after rather than before amputation, represents an alternative experimental design that future studies might evaluate. Third, planarians may lack the specific molecular targets—or bioavailability pathways—through which Trichosanthes compounds exert anti-inflammatory effects in vertebrate cell lines.
Several methodological limitations should be acknowledged. Pipette cross-contamination between groups during the treatment phase was observed on at least one occasion, potentially introducing uncontrolled extract exposure to the control group. Dissection quality was variable; uneven cuts produced initial fragment-size heterogeneity that confounded early-time-point length measurements, as evidenced by the Day 1 statistical differences that were not maintained. Data collection was interrupted on multiple days due to scheduling constraints, creating gaps in the time series that reduced statistical power and the ability to detect gradual trends. Finally, water quality in some jars was not maintained at the prescribed frequency, which may have introduced osmotic or nitrogenous stress that overshadowed any extract effect.
Despite these limitations, this study makes a modest contribution to the literature by providing the first in vivo regeneration assay for Trichosanthes root extract in a whole-organism model. Negative results are informative: they establish that this extract at these concentrations does not act as a broad regenerative stimulant in planarians, narrowing the candidate-compound space for future screens. Future work should employ HPLC-characterized extract preparations, a range of concentrations extending at least an order of magnitude higher and lower than those tested here, and continuous rather than pre-treatment exposure. Genetic tools now available in related planarian species could additionally be used to determine whether specific signaling pathways downstream of Wnt or TGF-β, known to regulate neoblast activity, are modulated by trichosanthin or flavonoid fractions.
5. Conclusions
This study investigated whether Trichosanthes kirilowii root extract enhances tissue regeneration, locomotor behavior, and nervous system recovery in Dugesia tigrina across two independent trials. Despite the anti-inflammatory and antioxidant properties of its bioactive constituents, the extract did not significantly affect any measured outcome at the concentrations and exposure durations employed. Isolated statistically significant results in tail length lacked dose-response consistency and did not replicate across trials. These findings contribute to a growing evidence base evaluating traditional Chinese medicinal compounds in regenerative biology, and underscore the importance of characterized preparations, adequate concentration ranges, and replicated experimental designs in this field of inquiry.
Acknowledgements.
The authors thank [Your Institution] faculty for supervision during euthanasia procedures and laboratory access. No external funding was received for this study.
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Published on 21/01/26
Submitted on 13/01/26
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