Differentiation of pheochromocytoma and adrenal lipoid adenoma by radiomics: are enhanced CT scanning images necessary?

Purpose: To establish various radiomics models based on conventional CT scan images and enhanced CT images, explore their value in the classification of pheochromocytoma (PHEO) and lipid-poor adrenal adenoma (LPA) and screen the most parsimonious and efficient model. Methods: The clinical and imaging data of 332 patients (352 lesions) with PHEO or LPA confirmed by surgical pathology in the Affiliated Hospital of Qingdao University were retrospectively analyzed. The region of interest (ROI) on conventional and enhanced CT images was delineated using ITK-SNAP software. Different radiomics signatures were constructed from the radiomics features extracted from conventional and enhanced CT images, and a radiomics score (Rad score) was calculated. A clinical model was established using demographic features and CT findings, while radiomics nomograms were established using multiple logistic regression analysis.The predictive efficiency of different models was evaluated using the area under curve (AUC) and receiver operating characteristic (ROC) curve. The Delong test was used to evaluate whether there were statistical differences in predictive efficiency between different models. Results: The radiomics signature based on conventional CT images showed AUCs of 0.97 (training cohort, 95% CI: 0.95∼1.00) and 0.97 (validation cohort, 95% CI: 0.92∼1.00). The AUCs of the nomogram model based on conventional scan CT images and enhanced CT images in the training cohort and the validation cohort were 0.97 (95% CI: 0.95∼1.00) and 0.97 (95% CI: 0.94~1.00) and 0.98 (95% CI: 0.97∼1.00) and 0.97 (95% CI: 0.94∼1.00), respectively. The prediction efficiency of models based on enhanced CT images was slightly higher than that of models based on conventional CT images, but these differences were statistically insignificant(P>0.05). Conclusions: CT-based radiomics signatures and radiomics nomograms can be used to predict and identify PHEO and LPA. The model established based on conventional CT images has great identification and prediction efficiency, and it can also enable patients to avoid harm from radiation and contrast agents caused by the need for further enhancement scanning in traditional image examinations.

Diastereoselective and Enantioselective Hydrophosphinylations of Conjugated Enynes, Allenes and Dienes via Synergistic Pd/Co Catalysis.

Different from the reported work focusing on the construction of single P- or C-stereocenter via hydrophosphinylation of unsaturated carbon bonds, the highly diastereo- and enantioselective hydrophosphinylation reaction of allenes, conjugated enynes and 1,3-dienes is achieved via a designed Pd/Co dual catalysis and newly modified masked phosphinylating reagent. A series of allyl motifs bearing both a tertiary C- and P-stereocenter are prepared in generally good yields, >20:1 dr, >20:1 rr and 99% ee. The unprecedented diastereo- and enantioselective hydrophosphinylation of 1,3-enynes is established to generate skeletons containing both a P-stereocenter and a nonadjacent chiral axis. The first stereodivergent hydrophosphinylation reaction is also developed to achieve all four P-containing stereoisomers. The present protocol features the use of only 3-minutes reaction time and 0.1% catalyst, and with the observation of up to 730 TON. A set of mechanistic studies reveal the necessity and roles of two metal catalysts and corroborate the designed synergistic process.

Integrated multi-omics analysis reveals molecular changes associated with chronic lipid accumulation following contusive spinal cord injury.

Functional and pathological recovery after spinal cord injury (SCI) is often incomplete due to the limited regenerative capacity of the central nervous system (CNS), which is further impaired by several mechanisms that sustain tissue damage. Among these, the chronic activation of immune cells can cause a persistent state of local CNS inflammation and damage. However, the mechanisms that sustain this persistent maladaptive immune response in SCI have not been fully clarified yet. In this study, we integrated histological analyses with proteomic, lipidomic, transcriptomic, and epitranscriptomic approaches to study the pathological and molecular alterations that develop in a mouse model of cervical spinal cord hemicontusion. We found significant pathological alterations of the lesion rim with myelin damage and axonal loss that persisted throughout the late chronic phase of SCI. This was coupled by a progressive lipid accumulation in myeloid cells, including resident microglia and infiltrating monocyte-derived macrophages. At tissue level, we found significant changes of proteins indicative of glycolytic, tricarboxylic acid cycle (TCA), and fatty acid metabolic pathways with an accumulation of triacylglycerides with C16:0 fatty acyl chains in chronic SCI. Following transcriptomic, proteomic, and epitranscriptomic studies identified an increase of cholesterol and m6A methylation in lipid-droplet-accumulating myeloid cells as a core feature of chronic SCI. By characterizing the multiple metabolic pathways altered in SCI, our work highlights a key role of lipid metabolism in the chronic response of the immune and central nervous system to damage.

Exploring the protective effect and mechanism of icariside II on the bladder in a rat model of radiation cystitis based on transcriptome sequencing.

PURPOSE: Radiation cystitis (RC) is a complex and common complication after radiotherapy for pelvic cancer. Icariside II (ICAII) is a flavonoid compound extracted from Epimedium, a traditional Chinese medicine, with various pharmacological activities. The aim of the present study was to investigate the cysto-protective effects of ICAII in RC rats and its possible mechanisms. MATERIALS AND METHODS: A rat model of induced radiation cystitis using pelvic X-ray irradiation was used, and bladder function was assessed by bladder volume and bladder leakage point pressure (LPP) after ICAII treatment. HE and Masson stains were used to assess the histopathological changes in the bladder. IL-6, TNF-α, IL-10, IL-4 and IL-1ß were measured by ELISA to assess the level of inflammation. The gene-level changes in ICAII-treated RC were observed by transcriptome sequencing, and then the potential targets of action and biological mechanisms were explored by PPI, GO and KEGG enrichment analysis of the differentially expressed genes. Finally, the predicted targets of action were experimentally validated using immunohistochemistry, RT-qPCR, molecular docking and CETSA. RESULTS: ICAII significantly increased bladder volume and the LPP, ameliorated pathological damage to bladder tissues, decreased the levels of IL-6, TNF-α, and IL-1ß, and increased the levels of IL-10 and IL-4 in radiation-injured rats. A total of 90 differentially expressed genes were obtained by transcriptome sequencing, and PPI analysis identified H3F3C, ISG15, SPP1, and LCN2 as possible potential targets of action. GO and KEGG analyses revealed that these differentially expressed genes were mainly enriched in the pathways metabolism of xenobiotics by cytochrome P450, arachidonic acid metabolism, Staphylococcus aureus infection and chemical carcinogenesis - reactive oxygen species. Experimental validation showed that ICAII could significantly increase the expression of H3F3C and ISG15 and inhibit the expression of SPP1 and LCN2. ICAII binds well to H3F3C, ISG15, SPP1 and LCN2, with the best binding ability to H3F3C. Furthermore, ICAII inhibited the protein degradation of H3F3C in bladder epithelial cells. CONCLUSIONS: ICAII may alleviate the bladder inflammatory response and inhibit the fibrosis process of bladder tissues through the regulation of H3F3C, ISG15, SPP1, and LCN2 targets and has a protective effect on the bladder of radioinjured rats. In particular, H3F3C may be one of the most promising therapeutic targets.

[Arthroscopic surgery for injuries to the popliteal tendon area of the lateral meniscus].

OBJECTIVE: To investigate the mid-term effect and complications of arthroscopic popliteal tendon suture in the treatment of lateral meniscus injury. METHODS: From January 2016 to December 2020, the data of 57 patients with lateral meniscus popliteal tendon injury treated by arthroscopic popliteal tendon suture fixation were retrospectively analyzed, including 35 males and 22 females, aged from 18 to 47 years old with an average of (32.9±7.9) years old. Knee function was evaluated using the International Knee Documentation Committee (IKDC) and Lysholm scores both before the operation and at the final follow-up. Meniscus healing was evaluated according to the postoperative Barrett standard. Wound healing complications, such as vascular injury, nerve injury, and lower extremity venous thrombosis, were recorded. RESULTS: All 57 patients were followed up for 12 to 58 months with an average of (38.1±14.9) months.The incisions of the patients after the operation were all Grade A healing without infection, popliteal tendon injury, blood vessel injury, nerve injury and lower extremity venous thrombosis.The IKDC score increased from (49.7±3.6) points preoperatively to (88.5±4.4) points in the final follow-up (P<0.05). The Lysholm score increased from (48.8±4.9) points preoperatively to (91.9±3.9) points at the final follow-up (P<0.05). At 3, 6 months and 1 year after operation, according to Barrett's criteria, 54 cases were clinically healed, the healing rate was 94.7% (54/57). CONCLUSION: This study preliminarily confirmed that arthroscopic suture technique can result in clinical stability through suture and fixation of the meniscus in the injured lateral popliteal tendon area. No adverse effects on knee joint function were found in the mid-term follow-up after the operation.

Exploring machine learning applications in Meningioma Research (2004-2023).

Objective: This study aims to examine the trends in machine learning application to meningiomas between 2004 and 2023. Methods: Publication data were extracted from the Science Citation Index Expanded (SCI-E) within the Web of Science Core Collection (WOSCC). Using CiteSpace 6.2.R6, a comprehensive analysis of publications, authors, cited authors, countries, institutions, cited journals, references, and keywords was conducted on December 1, 2023. Results: The analysis included a total of 342 articles. Prior to 2007, no publications existed in this field, and the number remained modest until 2017. A significant increase occurred in publications from 2018 onwards. The majority of the top 10 authors hailed from Germany and China, with the USA also exerting substantial international influence, particularly in academic institutions. Journals from the IEEE series contributed significantly to the publications. "Deep learning," "brain tumor," and "classification" emerged as the primary keywords of focus among researchers. The developmental pattern in this field primarily involved a combination of interdisciplinary integration and the refinement of major disciplinary branches. Conclusion: Machine learning has demonstrated significant value in predicting early meningiomas and tailoring treatment plans. Key research focuses involve optimizing detection indicators and selecting superior machine learning algorithms. Future efforts should aim to develop high-performance algorithms to drive further innovation in this field.

Silica nanoparticle design for colorectal cancer treatment: Recent progress and clinical potential.

Colorectal cancer (CRC) is the third most common cancer worldwide and the second most common cause of cancer death. Nanotherapies are able to selectively target the delivery of cancer therapeutics, thus improving overall antitumor efficiency and reducing conventional chemotherapy side effects. Mesoporous silica nanoparticles (MSNs) have attracted the attention of many researchers due to their remarkable advantages and biosafety. We offer insights into the recent advances of MSNs in CRC treatment and their potential clinical application value.

Restoring energy metabolism by NAD+ supplement prevents alcohol-induced liver injury and boosts liver regeneration.

Our previous clinical metabolomics study illustrated that energy metabolism disorder is an underlying pathogenesis mechanism for the development of alcoholic liver disease (ALD). Supplementation of nicotinamide (NAM), the precursor of nicotinamide adenine dinucleotide (NAD+), may restore the energy metabolism homeostasis of ALD and thus serves as potential therapeutics to treat ALD. In this bedside-to-bench study, the protective effect of NAM against ALD was investigated by using the NIAAA mice model (chronic-plus-binge ethanol), and the liver regeneration boosting capability of NAM was evaluated by the partial hepatectomy mice model. Our results showed that NAM supplements not only protected the liver from alcohol-induced injury and improved alcohol-induced mitochondrial structure and function change, but also boosted liver regeneration in postpartial hepatectomy mice by increasing liver NAD+ content. These findings suggested that NAM, a water-soluble form of vitamin B3, can promote liver regeneration and improves liver function by alleviating alcohol-induced energy metabolism disorder.

The G932C mutation of chitin synthase 1 gene (CHS1) mediates buprofezin resistance as confirmed by CRISPR/Cas9-mediated knock-in approach in the brown planthopper, Nilaparvata lugens.

The brown planthopper (Nilaparvata lugens) is a major destructive rice pest in Asia. High levels of insecticide resistance have been frequently reported, and the G932C mutation in the chitin synthase 1 (CHS1) gene has been found to mediate buprofezin resistance. However, there has been no direct evidence to confirm the functional significance of the single G932C substitution mutation leading to buprofezin resistance in N. lugens. Here, we successfully constructed a knock-in homozygous strain (Nl-G932C) of N. lugens using CRISPR/Cas9 coupled with homology-directed repair (HDR). Compared with the background strain susceptible to buprofezin (Nl-SS), the knock-in strain (Nl-G932C) showed a 94.9-fold resistance to buprofezin. Furthermore, resistant strains (Nl-932C) isolated from the field exhibited a 2078.8-fold resistance to buprofezin, indicating that there are other mechanisms contributing to buprofezin resistance in the field. Inheritance analysis showed that the resistance trait is incomplete dominance. In addition, the Nl-G932C strain had a relative fitness of 0.33 with a substantially decreased survival rate, emergence rate, and fecundity. This study provided in vivo functional evidence for the causality of G932C substitution mutation of CHS1 with buprofezin resistance and valuable information for facilitating the development of resistance management strategies in N. lugens. This is the first example of using CRISPR/Cas9 gene-editing technology in a hemipteran insect to directly confirm the role of a candidate target site mutation in insecticide resistance.

Temporal and spatial biosonar activity of the recently established uppermost Yangtze finless porpoise population downstream of the Gezhouba Dam: Correlation with hydropower cascade development, shipping, hydrological regime, and light intensity.

Numerous dams disrupt freshwater animals. The uppermost population of the critically endangered Yangtze finless porpoise has been newly formed below the Gezhouba Dam, however, information regarding the local porpoise is scarce. Passive acoustic monitoring was used to detect the behaviors of porpoises below the Gezhouba Dam. The influence of shipping, pandemic lockdown, hydrological regime, and light intensity on the biosonar activity of dolphins was also examined using Generalized linear models. Over the course of 4 years (2019-2022), approximately 848, 596, and 676 effective monitoring days were investigated at the three sites, from upstream to downstream. Observations revealed significant spatio-temporal biosonar activity. Proportion of days that are porpoise positive were 73%, 54%, and 61%, while porpoise buzz signals accounted for 78.49%, 62.35%, and 81.30% of all porpoise biosonar at the three stations. The biosonar activity of porpoises was much higher at the confluence area, particularly at the MZ site, during the absence of boat traffic, and during the Pandemic shutdown. Temporal trends of monthly, seasonal, and yearly variation were also visible, with the highest number of porpoises biosonar detected in the summer season and in 2020. Significant correlations also exist between the hydrological regime and light intensity and porpoise activity, with much higher detections during nighttime and full moon periods. Hydropower cascade development, establishment of a natural reserve, fish release initiatives, and implementation of fishing restrictions may facilitate the proliferation of the porpoise population downstream of the Gezhouba Dam within the Yichang section of the Yangtze River. Prioritizing restoration designs that match natural flow regimes, optimize boat traffic, and reduce noise pollution is crucial for promoting the conservation of the local porpoises.

Stereoselective Synthesis of Polysubstituted Dihydropyrroles via 1,5-Addition and N-1,4-Addition Cascade.

An unprecedented 1,5-addition/N-1,4-addition cascade reaction is established via palladium hydride catalysis. A variety of polysubstituted dihydropyrrole skeletons are constructed in high yield and with exclusively >20 : 1 diastereoselectivity. An enantioselective protocol of this design is also developed to provide a novel access to enantioenriched dihydropyrroles.

Causal roles of gut microbiota in cholangiocarcinoma etiology suggested by genetic study.

BACKGROUND: Cholangiocarcinoma (CCA) is a highly malignant biliary tract cancer with poor prognosis. Previous studies have implicated the gut microbiota in CCA, but evidence for causal mechanisms is lacking. AIM: To investigate the causal relationship between gut microbiota and CCA risk. METHODS: We performed a two-sample mendelian randomization study to evaluate potential causal associations between gut microbiota and CCA risk using genome-wide association study summary statistics for 196 gut microbial taxa and CCA. Genetic variants were used as instrumental variables. Multiple sensitivity analyses assessed result robustness. RESULTS: Fifteen gut microbial taxa showed significant causal associations with CCA risk. Higher genetically predicted abundance of genus Eubacteriumnodatum group, genus Ruminococcustorques group, genus Coprococcus, genus Dorea, and phylum Actinobacteria were associated with reduced risk of gallbladder cancer and extrahepatic CCA. Increased intrahepatic CCA risk was associated with higher abundance of family Veillonellaceae, genus Alistipes, order Enterobacteriales, and phylum Firmicutes. Protective effects against CCA were suggested for genus Collinsella, genus Eisenbergiella, genus Anaerostipes, genus Paraprevotella, genus Parasutterella, and phylum Verrucomicrobia. Sensitivity analyses indicated these findings were reliable without pleiotropy. CONCLUSION: This pioneering study provides novel evidence that specific gut microbiota may play causal roles in CCA risk. Further experimental validation of these candidate microbes is warranted to consolidate causality and mechanisms.

Increased Yangtze finless porpoise presence in urban Wuhan waters of the Yangtze River during fishing closures.

Wuhan, a highly urbanized and rapidly growing region within China's Yangtze Economic Zone, has historically been identified as a gap area for the critically endangered Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) based on daytime visual surveys. However, there has been a noticeable increase in porpoise sightings since 2020. This study employed passive acoustic monitoring to investigate porpoise distribution in Wuhan between 2020 and 2022. Generalized linear models were used to explore the relationship between shipping, hydrological patterns, light intensity, and porpoise biosonar activity. Over 603 days of effective monitoring, the daily positive rate for porpoise biosonar detection reached 43%, with feeding-related buzz signals accounting for 55% of all porpoise biosonar signals. However, the proportion of minutes during which porpoise presence was detected was 0.18%, suggesting that while porpoises may frequent the area, their visits were brief and mainly focused on feeding. A significant temporal trend emerged, showing higher porpoise biosonar detection during winter (especially in February) and 2022. Additionally, periods without boat traffic correlated with increased porpoise activity. Hydrological conditions and light levels exhibited significant negative correlations with porpoise activity. Specifically, porpoise sonar detections were notably higher during the night, twilight, and new moon phases. It is highly conceivable that both fishing bans and COVID-19 pandemic-related lockdowns contributed to the heightened presence of porpoises in Wuhan. The rapid development of municipal transportation and shipping in Wuhan and resulting underwater noise pollution have emerged as a significant threat to the local porpoise population. Accordingly, it is imperative for regulatory bodies to effectively address this environmental stressor and formulate targeted protection measures to ensure the conservation of the finless porpoise.

Sagittal balance parameters measurement on cervical spine MR images based on superpixel segmentation.

Introduction: Magnetic Resonance Imaging (MRI) is essential in diagnosing cervical spondylosis, providing detailed visualization of osseous and soft tissue structures in the cervical spine. However, manual measurements hinder the assessment of cervical spine sagittal balance, leading to time-consuming and error-prone processes. This study presents the Pyramid DBSCAN Simple Linear Iterative Cluster (PDB-SLIC), an automated segmentation algorithm for vertebral bodies in T2-weighted MR images, aiming to streamline sagittal balance assessment for spinal surgeons. Method: PDB-SLIC combines the SLIC superpixel segmentation algorithm with DBSCAN clustering and underwent rigorous testing using an extensive dataset of T2-weighted mid-sagittal MR images from 4,258 patients across ten hospitals in China. The efficacy of PDB-SLIC was compared against other algorithms and networks in terms of superpixel segmentation quality and vertebral body segmentation accuracy. Validation included a comparative analysis of manual and automated measurements of cervical sagittal parameters and scrutiny of PDB-SLIC's measurement stability across diverse hospital settings and MR scanning machines. Result: PDB-SLIC outperforms other algorithms in vertebral body segmentation quality, with high accuracy, recall, and Jaccard index. Minimal error deviation was observed compared to manual measurements, with correlation coefficients exceeding 95%. PDB-SLIC demonstrated commendable performance in processing cervical spine T2-weighted MR images from various hospital settings, MRI machines, and patient demographics. Discussion: The PDB-SLIC algorithm emerges as an accurate, objective, and efficient tool for evaluating cervical spine sagittal balance, providing valuable assistance to spinal surgeons in preoperative assessment, surgical strategy formulation, and prognostic inference. Additionally, it facilitates comprehensive measurement of sagittal balance parameters across diverse patient cohorts, contributing to the establishment of normative standards for cervical spine MR imaging.

Multimodal image fusion-assisted endoscopic evacuation of spontaneous intracerebral hemorrhage.

PURPOSE: Although traditional craniotomy (TC) surgery has failed to show benefits for the functional outcome of intracerebral hemorrhage (ICH). However, a minimally invasive hematoma removal plan to avoid white matter fiber damage may be a safer and more feasible surgical approach, which may improve the prognosis of ICH. We conducted a historical cohort study on the use of multimodal image fusion-assisted neuroendoscopic surgery (MINS) for the treatment of ICH, and compared its safety and effectiveness with traditional methods. METHODS: This is a historical cohort study involving 241 patients with cerebral hemorrhage. Divided into MINS group and TC group based on surgical methods. Multimodal images (CT skull, CT angiography, and white matter fiber of MRI diffusion-tensor imaging) were fused into 3 dimensional images for preoperative planning and intraoperative guidance of endoscopic hematoma removal in the MINS group. Clinical features, operative efficiency, perioperative complications, and prognoses between 2 groups were compared. Normally distributed data were analyzed using t-test of 2 independent samples, Non-normally distributed data were compared using the Kruskal-Wallis test. Meanwhile categorical data were analyzed via the Chi-square test or Fisher's exact test. All statistical tests were two-sided, and p < 0.05 was considered statistically significant. RESULTS: A total of 42 patients with ICH were enrolled, who underwent TC surgery or MINS. Patients who underwent MINS had shorter operative time (p < 0.001), less blood loss (p < 0.001), better hematoma evacuation (p = 0.003), and a shorter stay in the intensive care unit (p = 0.002) than patients who underwent TC. Based on clinical characteristics and analysis of perioperative complications, there is no significant difference between the 2 surgical methods. Modified Rankin scale scores at 180 days were better in the MINS than in the TC group (p = 0.014). CONCLUSIONS: Compared with TC for the treatment of ICH, MINS is safer and more efficient in cleaning ICH, which improved the prognosis of the patients. In the future, a larger sample size clinical trial will be needed to evaluate its efficacy.

A multifunctional biomimetic nanoplatform for image-guideded photothermal-ferroptotic synergistic osteosarcoma therapy.

Much effort has been devoted to improving treatment efficiency for osteosarcoma (OS). However, most current approaches result in poor therapeutic responses, thus indicating the need for the development of other therapeutic options. This study developed a multifunctional nanoparticle, PDA-MOF-E-M, an aggregation of OS targeting, programmed death targeting, and near-infrared (NIR)-aided targeting. At the same time, a multifunctional nanoparticle that utilises Fe-MOFs to create a cellular iron-rich environment and erastin as a ferroptosis inducer while ensuring targeted delivery to OS cells through cell membrane encapsulation is presented. The combination of PDA-MOF-E-M and PTT increased intracellular ROS and LPO levels and induced ferroptosis-related protein expression. A PDA-based PTT combined with erastin showed significant synergistic therapeutic improvement in the anti-tumour efficiency of the nanoparticle in vitro and vivo. The multifunctional nanoparticle efficiently prevents the osteoclasia progression of OS xenograft bone tumors in vivo. Finally, this study provides guidance and a point of reference for clinical approaches to treating OS.

Asymmetric copper-catalyzed alkynylallylic monofluoroalkylations with fluorinated malonates.

The unprecedented copper-catalyzed asymmetric alkynylallylic monofluoroalkylation reaction is described via the use of 1,3-enynes and fluorinated malonates. A series of 1,4-enynes bearing a monofluoroalkyl unit are achieved in high yields, excellent regio- and enantioselectivity and high E/Z selectivity. The asymmetric propargylic monofluoroalkylation is also developed. The reliability and synthetic value of the work are highlighted by a gram-scale test and a couple of downstream transformations. Preliminary mechanistic studies unveil a negative nonlinear effect for the catalytic process.

Complex effects of testosterone level on ectoparasite load in a ground squirrel: an experimental test for the immunocompetence handicap hypothesis.

BACKGROUND: The immunocompetence handicap hypothesis suggests that males with a higher testosterone level should be better at developing male secondary traits, but at a cost of suppressed immune performance. As a result, we should expect that males with an increased testosterone level also possess a higher parasite load. However, previous empirical studies aimed to test this prediction have generated mixed results. Meanwhile, the effect of testosterone level on parasite load in female hosts remains poorly known. METHODS: In this study, we tested this prediction by manipulating testosterone level in Daurian ground squirrels (Spermophilus dauricus), a medium-sized rodent widely distributed in northeast Asia. S. dauricus is an important host of ticks and fleas and often viewed as a considerable reservoir of plague. Live-trapped S. dauricus were injected with either tea oil (control group) or testosterone (treatment group) and then released. A total of 10 days later, the rodents were recaptured and checked for ectoparasites. Fecal samples were also collected to measure testosterone level of each individual. RESULTS: We found that testosterone manipulation and sex of hosts interacted to affect tick load. At the end of the experiment, male squirrels subjected to testosterone implantation had an averagely higher tick load than males from the control group. However, this pattern was not found in females. Moreover, testosterone manipulation did not significantly affect flea load in S. dauricus. CONCLUSIONS: Our results only lent limited support for the immunocompetence handicap hypothesis, suggesting that the role of testosterone on regulating parasite load is relatively complex, and may largely depend on parasite type and gender of hosts.