Tumor-associated primo vascular system is derived from xenograft, not host

Analysis of key pathways and genes in nodal structure on rat skin surface using gene ontology and KEGG pathway

BACKGROUND

We have previously reported anatomical, histological, and gene expression characteristics of the nodal structure of rat skin surface and suggested its potential as an acupuncture point. However, the specific characteristics of the interactions among the genes expressed in this structure remain unclear.

OBJECTIVE

We aimed to determine gene expression changes by analyzing interaction networks of genes up-regulated in nodal structures and to explore relationships with acupuncture points.

METHODS

We investigated the relationship between the nodal structures and acupuncture points by analyzing the interactions of up-regulated genes, their Gene Ontology biological functions, and the characteristics of Kyoto Encyclopedia of Genes and Genomes pathways. RNA-seq and STRING analysis provided comprehensive information on these gene groups.

RESULTS

Interactions between up-regulated genes in nodal structures were classified into three groups. The first group, which includes Wnt7b, Wnt3, and Wnt16, showed significant interactions in pathways such as Wnt signaling, Alzheimer's disease, and regulation of stem cell pluripotency. The second group, composed of Fos, Dusp1, Pla2g4e, Pla2g4f, and Fgfr3, demonstrated a notable association with the MAPK signaling pathway. Lastly, the third group, consisting of Adcy1, Pla2g4e, Pla2g4f, and Dusp1 exhibited effective interactions with the inflammatory mediator regulation of TRP channels and serotonergic synapse.

CONCLUSION

Continued research on nodal structures where these genes are expressed is needed to improve our understanding of skin anatomy and physiology as well as their potential clinical utility as acupuncture points.

Bundle structures inside the deep cervical lymphatic vessels of mice

The lymphatic system plays a crucial role in immune function and the removal of cellular waste. Recent studies have highlighted the presence of primo vessels (PVs) inside lymphatic vessels, distinct from conventional lymphatic tissues, yet their structural and functional characteristics remain poorly understood, particularly PVs inside deep cervical lymphatic vessels (dcLVs) connected to the meningeal lymphatics. We used a combination of Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Alcian Blue (AB) and H&E staining techniques to identify and characterize PVs inside the dcLVs of mice. PVs were identified inside the dcLVs, revealing distinct bundle structures composed of 3 to 5 primo subvessels (sub-PV), with diameters of 5.4 ± 2.4 μm. AFM analyses confirmed the presence of nm-sized pores on the sub-PVs, which may facilitate the absorption and retention of nanoparticles. Rod-shaped nuclei were also observed, further distinguishing PVs from other vascular structures. Our study provides new insights into the structural characteristics of PVs inside dcLVs, suggesting their potential role in targeted drug delivery. However, further research is required to explore the functional implications of these structures, especially their therapeutic applications and roles in various lymphatic regions, including the meningeal lymphatics.

Bonghan (primo vascular) system, elucidated by Bong Han Kim: Kim’s findings, later verifications, new findings, and prospective: A review

The Bonghan system (BHS) was discovered in the 1950s by Dr. Bong Han Kim in North Korea. His first report, published in 1962, revealed the identity of ‘acupuncture meridian’ as a vascular system. Kim published five reports, containing completely new facts on BHS: its distribution throughout the entire body, even in blood and lymphatic vessels and self-renovating function via a new cell cycle, demonstrating its fundamental nature in life. In about 1966, Kim’s research abruptly ceased but in about 2000, it was revived by Dr. Kwang-Sup Soh in South Korea, who later gave it another name, primo vascular system (PVS). Soh and other PVS scientists also uncovered new BHS/PVS facts: e.g., its roles in stem cell productions and in cancer metastasis. The review provides a glimpse of BHS/PVS science, which is so worthy of furthering. It includes: BHS and acupuncture meridian; BHS subtypes; sanal (산알)-cell cycle for cell-renovation and blood cell productions; sanals and stem cells; and cancer associated-PVS. The bases of BHS/PVS sciences are now laid out in front of us and it is up to us to combine our efforts together to further this important science. The review invites scientists in all fields to active debates to move forward and implement BHS/PVS sciences in healthcare.

Characterization of the primo vascular system in rabbit vagina

The primo vascular system (PVS) is observed in different parts of the body under different physiological and disease conditions. Previously, the PVS was not observed in the vagina. The vaginal samples of this study were collected from the female genitalia of healthy New Zealand white rabbits from the animal house, Faculty of Medicine, Assiut University. The vaginal samples were fixed in Bouin's solution. The sections were stained with hematoxylin and eosin and Crossmon's trichrome. Additionally, the sections were immunohistochemically stained with neuron-specific enolase (NSE) and vascular endothelial growth factor (VEGF). A primo node was observed on the lymph vessel of the vagina and has several characteristics that resemble those of the previously discovered primo nodes. The primo node in this study was surrounded by mesothelial cells that provide positive immunoreactivity to NSE and VEGF. Sinuses of different sizes, floating cells, telocyte-like cell, and primo microcells were observed as the main constituents of the primo node. Additionally, migratory cells were detected, which passed from the primo node to the enclosing lymph vessel.

Lentivirus-mediated down-regulation of CK2α inhibits proliferation and induces apoptosis of malignant lymphoma and leukemia cells

Casein kinase II subunit alpha (CK2α) is highly expressed in many malignant tumor tissues, including lymphomas and leukemia. To investigate the role of CK2α in cell proliferation and apoptosis of malignant lymphomas and leukemia, 2 lymphoma cell lines and one leukemia cell line were infected with CK2α shRNA lentivirus or negative control shRNA lentivirus, and stably infected cell lines were established. Real-time PCR and Western blot results showed that the mRNA and protein levels of CK2α were significantly reduced in CK2α knockdown cells. The tetrazolium-based colorimetric (MTT) assay found that down-regulation of CK2α inhibited the proliferation of these cells. Flow cytometry analysis showed that inhibition of CK2α induced cell cycle arrest and apoptosis of lymphoma and leukemia cells. In accordance with these, down-regulation of CK2α also reduced the protein levels of proliferating cell nuclear antigen (PCNA), cyclinD1, and bcl-2, and increased the protein expression of bax, cleaved caspase-3, cleaved caspase-9, and cleaved poly(ADP ribose) polymerase (PARP). Moreover, knockdown of CK2α impeded the growth of xenograft tumors in vivo. In summary, our study revealed that CK2α may contribute to the development of malignant lymphoma and leukemia, and serve as the therapeutic target of these malignant tumors.

Various stem cells in acupuncture meridians and points and their putative roles

Traditional Chinese and Korean medicine uses various manipulations on acupuncture points/acupoints that are located along imaginary lines on the surface of a human body, which are called 'meridians'. Acupuncture has been used from the ancient time till now to cure various diseases, including for the purpose of regenerative medicine. In various studies, meridians are alternatively called as Bong-Han ducts, primo vessels, or hyaluronic-acid rich ducts, while acupoints are called Bong-Han corpuscles, primo nodes, or hyaluronic-acid rich nodes. Meridians and acupuncture points form a system that is now called primo vascular system (PVS), which is claimed to contain various kinds of stem cells. The stem cell size is between 1-5 microns. The smallest is the primo microcells that have a putative role in regeneration. Other stem cells are adult pluripotent and hematopoietic stem cells that play a role in extra bone marrow hematopoiesis. The presence of PVS has been reproduced by many studies. However, the various stem cells need further studies to prove their existence and function, and harvesting PVS to isolate the stem cells might harm the health of the donor.

Sanal-Cell Cycle and Primo Vascular System: Regeneration via Sanals

The Primo Vascular System (PVS) is new to most scientists despite that it was discovered in the 1960s by Bonghan Kim. Out of the many physiological functions reported, one of the most important PVS functions appears to be its role in the regeneration via a small (~1 μm) subcellular body called 'sanal.' According to Kim, a cell generates multiple sanals and the sanals arriving at the primo nodes (PNs) via primo vessels (PV) eventually produce new cells, by way of the 'Sanal-Cell Cycle.' Sanals express stem cell biomarkers. Appropriately differentiated sanals have been shown to perform non-marrow hematopoiesis and repair damaged tissues. However, many questions on sanals still remain: e.g., how sanals reside in the PN; whether sanals are a new type of stem cells; and how exactly sanals produce cells and/or tissue. Our preliminary studies show that sanals reside inside the sinus formed by sub-PVs in the PNs; and in the PNs, there are more than one form of sanal-originated bodies of various sizes.

Technical Challenges in Current Primo Vascular System Research and Potential Solutions

Since Bonghan Kim's discovery of the Bonghan system (BHS) in the 1960s, numerous reports have suggested that the system is fundamental for maintaining mammalian life. The BHS is a circulatory system independent of the blood or the lymphatic system, forms an extensive network throughout the entire mammalian body, has been reported to be the acupuncture meridian, stores distinct types of stem cells, and appears to have some roles in cancer metastasis. Despite Kim's first report having been published as early as 1962, research progress has been rather slow mainly because the system is very small and translucent, making it optically difficult to distinguish it from the hemoglobin-rich surrounding tissues. Unfortunately, Kim did not describe in detail the methods that he used for identifying and harvesting the system and the components of the system. In 2000, Kwang-Sup Soh reopened the BHS research, and since then, new and important scientific findings on the system have been reported, and many of Kim's results have been verified. In 2010, the BHS was renamed the primo vascular system. Nevertheless, good tools to properly deal with this system are still lacking. In this article, we address some of the technical difficulties involved in studying the primo vascular system and attempt to discuss potential ways to overcome those difficulties.

The role of lymphangiogenesis and angiogenesis in tumor metastasis

BACKGROUND

Metastasis is the main cause of mortality in cancer patients. Two major routes of cancer cell spread are currently being recognized: dissemination via blood vessels (hematogenous spread) and dissemination via the lymphatic system (lymphogenous spread). Here, our current knowledge on the role of both blood and lymphatic vessels in cancer cell metastasis is summarized. In addition, I will discuss why cancer cells select one or both of the two routes to disseminate and I will provide a short description of the passive and active models of intravasation. Finally, lymphatic vessel density (LVD), blood vessel density (BVD), interstitial fluid pressure (IFP) and tumor hypoxia, as well as regional lymph node metastasis and the recently discovered primo vascular system (PVS) will be highlighted as important factors influencing tumor cell motility and spread and, ultimately, clinical outcome.

CONCLUSIONS

Lymphangiogenesis and angiogenesis are important phenomena involved in the spread of cancer cells and they are associated with a poor prognosis. It is anticipated that new discoveries and advancing knowledge on these phenomena will allow an improvement in the treatment of cancer patients.

Ultrastructure of a Mobile Threadlike Tissue Floating in a Lymph Vessel

Observations of the primo vascular system (PVS) floating in lymph ducts were reported by various groups. There have been, however, no studies on the ultrastructure of the entire cross section of a primo vessel (PV) inside a lymph vessel with a transmission electron microscope (TEM). In the current study we took the TEM images of a cross section of the PV inside a lymph vessel. We used the Alcian blue staining method for the finding of the target PV in a lymphatic vessel by injecting the dye into the inguinal lymph nodes. The stained PV was harvested together with the lymph vessel and some parts of the specimens were used for studying with optical microscopes. Some other parts were treated according to a standard protocol for TEM. As the results the TEM study revealed the loosely distributed collagen fibers with plenty of empty spaces and the lumens with the endothelial nuclei. It turned out to be very similar to the ultrastructure of the PVs observed on the surfaces of internal organs. It also showed how compactly the PV is surrounded with lymphocytes. In conclusion, the detailed morphological features like the distribution of fibers in the PV were revealed and shown to be similar to another kind of the PV on the surfaces of internal organs.

Primo Vascular System: A Unique Biological System Shifting a Medical Paradigm

The primo vascular system has a specific anatomical and immunohistochemical signature that sets it apart from the arteriovenous and lymphatic systems. With immune and endocrine functions, the primo vascular system has been found to play a large role in biological processes, including tissue regeneration, inflammation, and cancer metastases. Although scientifically confirmed in 2002, the original discovery was made in the early 1960s by Bong-Han Kim, a North Korean scientist. It would take nearly 40 years after that discovery for scientists to revisit Kim's research to confirm the early findings. The presence of primo vessels in and around blood and lymph vessels, nerves, viscera, and fascia, as well as in the brain and spinal cord, reveals a common link that could potentially open novel possibilities of integration with cranial, lymphatic, visceral, and fascial approaches in manual medicine.

Essential Experimental Methods for Identifying Bonghan Systems as a Basis for Korean Medicine: Focusing on Visual Materials from Original Papers and Modern Outcomes

In the 1960s, through studies on Korean Medicine, Bonghan Kim proposed the Bonghan systems (BS) as the anatomical reality of the acupuncture meridians based on various experimental data. Since 2002, several groups, mainly led by a team at Seoul National University, who renamed the BS as the primo vascular system (PVS), have published around 70 papers showing biological structures corresponding to the BS. However, it is still difficult for other researchers to find them, especially under the skin, which Bonghan Kim first reported as acupuncture points, due to similar-looking biological tissues, for example, the lymphatic vessels, and such artifacts as blood clots or fascia debris. To solve these drawbacks, we examined the main methods for identifying the BS by comparing the original papers with the modern outcomes in terms of the common physical/chemical characteristics of the BS. In addition, effective methods of staining and microscopic observations discovered by modern teams are synthetically explained using visual materials such as diagrams and photos. Through the essentially organized methods in this review paper, we suggest that one can find the BS under the skin as putative acupuncture points by tracing the intraexternal BS, from which a new Korean Medicine will be born.

A Hyaluronic Acid-Rich Node and Duct System in Which Pluripotent Adult Stem Cells Circulate

Regenerative medicine is in demand of adult pluripotent stem cells (PSCs). The "Bonghan System (BHS)" was discovered and suggested to contain cells with regenerative capacity in the early 1960s. It had been ignored for a long time due to the lack of sufficient details of experiments, but about 37 years after the initial report, the BHS was rediscovered and named as the "primo vascular system." Recently, we have discovered a similar structure, which contained a high level of hyaluronic acid, and hence, named the structure as hyaluronic acid-rich node and duct system (HAR-NDS). Here we discuss the HAR-NDS concept starting from the discovery of BHS, and findings pointing to its importance in regenerative medicine. This HAR-NDS contained adult PSCs, called node and duct stem cells (NDSCs), which appeared to circulate in it. We describe the evidence that NDSCs can differentiate into hemangioblasts that further produced differentiated blood cells. The NDSCs had a potential to differentiate into neuronal cells and hepatocytes; thus, NDSCs had a capability to become cells from all three germ layers. This system appears to be a promising alternative source of adult stem cells that can be easily delivered to their target tissues and participate in tissue regeneration.

Fascia and Primo Vascular System

The anatomical basis for the concept of acupuncture points/meridians in traditional Chinese medicine (TCM) has not been resolved. This paper reviews the fascia research progress and the relationship among acupuncture points/meridians, primo vascular system (PVS), and fascia. Fascia is as a covering, with common origins of layers of the fascial system despite diverse names for individual parts. Fascia assists gliding and fluid flow and holds memory and is highly innervated. Fascia is intimately involved with nourishment of all cells of the body, including those of disease and cancer. The human body's fascia network may be the physical substrate represented by the meridians of TCM. The PVS is a newly found circulatory system; recent increased interest has led to new research and new discoveries in the anatomical and functional aspects of the PVS. The fasciology theory provides new insights into the physiological effects of acupuncture needling on basic cellular mechanisms including connective tissue mechanotransduction and regeneration. This view represents a theoretical basis and means for applying modern biomedical research to examining TCM principles and therapies, and it favors a holistic approach to diagnosis and treatment.

Evidence for novel age-dependent network structures as a putative primo vascular network in the dura mater of the rat brain

With chromium-hematoxylin staining, we found evidence for the existence of novel age-dependent network structures in the dura mater of rat brains. Under stereomicroscopy, we noticed that chromium-hematoxylin-stained threadlike structures, which were barely observable in 1-week-old rats, were networked in specific areas of the brain, for example, the lateral lobes and the cerebella, in 4-week-old rats. In 7-week-old rats, those structures were found to have become larger and better networked. With phase contrast microscopy, we found that in 1-week-old rats, chromium-hematoxylin-stained granules were scattered in the same areas of the brain in which the network structures would later be observed in the 4- and 7-week-old rats. Such age-dependent network structures were examined by using optical and transmission electron microscopy, and the following results were obtained. The scattered granules fused into networks with increasing age. Cross-sections of the age-dependent network structures demonstrated heavily-stained basophilic substructures. Transmission electron microscopy revealed the basophilic substructures to be clusters with high electron densities consisting of nanosized particles. We report these data as evidence for the existence of age-dependent network structures in the dura mater, we discuss their putative functions of age-dependent network structures beyond the general concept of the dura mater as a supporting matrix.

Comparison of Alcian Blue, Trypan Blue, and Toluidine Blue for Visualization of the Primo Vascular System Floating in Lymph Ducts

The primo vascular system (PVS), floating in lymph ducts, was too transparent to be observed by using a stereomicroscope. It was only detectable with the aid of staining dyes, for instance, Alcian blue, which was injected into the lymph nodes. Some dyes were absorbed preferentially by the PVS than the lymph wall. It remains a standing problem to know what dyes are absorbed better by the PVS than the lymph walls. Such information would be useful to unravel the biochemical properties of the PVS that are badly in need for obtaining large amount of PVS specimens. In the current work we tried two other familiar dyes which were used in PVS research before. We found that Trypan blue and toluidine blue did not visualize the PVS. Trypan blue was cleared by the natural washing. Toluidine blue did not stain the PVS, but it did leave stained spots in the lymph wall and its surrounding tissues, and it leaked out of the lymph wall to stain surrounding connective tissues. These completely different behaviors of the three dyes were found for the first time in the current work and provide valuable information to elucidate the mechanism through which some special dyes stained the PVS preferentially compared to the lymphatic wall.

Hypothesis on the Treatment of Gliomas with Acupuncture at the Primo Node Corresponding to Zusanli (ST 36)

Background: The primo vascular system (PVS) is an anatomical structure that is a network of ducts with fluid flowing in them, which are called primo vessels and correspond to acupuncture meridians, and primo nodes that correspond to acupoints. The PVS' main function is considered to be the maintenance of regenerative homeostasis in human and animal bodies. This system is distributed throughout the bodies of normal animals and develops around and in cancer tissues. This cancer-associated PVS may be a critical metastatic path besides the blood and the lymph vessels. The author of this article proposes a hypothesis on cancer treatment: Injecting anticancer drugs into acupoints according to the pharmacopuncture method can be effective as a result of the flow channels of the PVS. The author considers the acupoint Zusanli (ST 36) and the route of the primo vessels starting from it. This specific PVS route runs along the perineurium of the sciatic nerve, the pia mater, and the arachnoid mater of the spinal cord to the brain. Thus, by injecting a suitable anticancer drug into ST 36, one can deliver the drug into the brain to treat gliomas and other brain tumors. This new drug-delivery method is just one of the new clinical applications that are possible by combining acupuncture and using the PVS. Conclusions: Anticancer drugs for glioma can be injected into the primo node at the acupoint ST 36 to reach the cancer tissue through the PVS in the sciatic nerve, spine, and brain that can avoid the blood-brain barrier.

Visualization of the primo vascular system afloat in a lymph duct

Because of the potential roles of the primo vascular system (PVS) in cancer metastasis, immune function, and regeneration, understanding the molecular biology of the PVS is desirable. The current state of PVS research is comparable to that of lymph research prior to the advent of Lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1). There is very little knowledge of the molecular biology of the PVS due to difficulties in identifying and isolating primo endothelial cells. Present investigations rely on the morphology and the use of differential staining procedures to identify the PVS within tissues, making detailed molecular studies all but impossible. To overcome such difficulties, one may emulate the explosive development of lymph molecular biology. For this purpose, there is a need for a reliable method to obtain PVS specimens to initiate the molecular investigation. One of the most reliable methods is to detect the primo vessels and primo nodes afloat in the lymph flow. The protocols for observation of the PVS in the large lymph ducts in the abdominal cavity and the thoracic cavity were reported earlier. These methods require a laparectomy and skillful techniques. In this work, we present a protocol to identify and harvest PVS specimens from the lymph ducts connecting the inguinal and the axillary nodes, which are located entirely in the skin. Thus, the PVS specimen is more easily obtainable. This method is a stepping-stone toward development of a system to monitor migration of cancer cells in metastasis from a breast tumor to the axillary nodes, where cancer cells use the PVS as a survival rope in hostile lymph flow.

Primo vascular system floating in lymph ducts of rats

An epoch-making development in the gross anatomy of the lymph system has emerged: the observation of the primo vascular system (PVS), which is a threadlike structure floating in lymph ducts. The PVS, which was proposed as the conduit for the acupuncture Qi, is a complex network distributed throughout an animal's body. The lymph-PVS, which is a subsystem of the PVS, is one of the most convincing visual demonstrations of the PVS. Because its existence is not easily demonstrated, even with a microscope, due to its transparency, in current anatomy its existence is largely unknown despite its potential significance in physiology and medicine. The lymph-PVS has been observed in rabbits, rats, and mice by several independent teams. Because the involved techniques are rather complicated, we provide detailed protocols for surgery, for injection of the staining dye, and for detection, extraction, and identification of the PVS in a rat.

50 years of bong-han theory and 10 years of primo vascular system

The primo vascular system (PVS) was first introduced by Bong-Han Kim via his five research reports. Among these the third report was most extensive and conclusive in terms of the PVS anatomy and physiology relating to the acupuncture meridians. His study results, unfortunately, were not reproduced by other scientists because he did not describe the materials and methods in detail. In 2002, a research team in Seoul National University reinitiated the PVS research, confirmed the existence of PVS in various organs, and discovered new characteristics of PVS. Two important examples are as follows: PVS was found in the adipose tissue and around cancer tissues. In parallel to these new findings, new methods for observing and identifying PVS were developed. Studies on the cell and material content inside the PVS, including the immune function cells and stem cells, are being progressed. In this review, Bong-Han Kim's study results in his third report are summarized, and the new results after him are briefly reviewed. In the last section, the obstacles in finding the PVS in the skin as an anatomical structure of acupuncture meridian are discussed.

Primo vascular system in the lymph vessel from the inguinal to the axillary nodes

The primo vascular system (PVS) in a lymph system was observed mostly in large caliber ducts around the caudal vena cava of rabbits, rats, and mice. This required a severe surgery with laparectomy and massive removal of fat tissues in the abdomen to expose the lymph vessel. In the current brief report, we presented a new method to evade these shortcomings by observing the PVS in a less large caliber duct in the skin, that is, the lymph vessel from the inguinal to the axillary nodes. The Alcian blue injection into the inguinal node revealed the desired primo vessel in the target lymph vessel. This opened a new perspective for the investigation of the lymphatic PVS without severe damage to subject animals and for monitoring of the PVS in a long period of time.

Primo vascular system in the subarachnoid space of a mouse brain

Objective. Recently, a novel circulatory system, the primo vascular system (PVS), was found in the brain ventricles and in the central canal of the spinal cord of a rat. The aim of the current work is to detect the PVS along the transverse sinuses between the cerebrum and the cerebellum of a mouse brain. Materials and Methods. The PVS in the subarachnoid space was analyzed after staining with 4',6-diamidino-2-phenylindole (DAPI) and phalloidin in order to identify the PVS. With confocal microscopy and polarization microscopy, the primo vessel underneath the sagittal sinus was examined. The primo nodes under the transversal sinuses were observed after peeling off the dura and pia maters of the brain. Results. The primo vessel underneath the superior sagittal sinus was observed and showed linear optical polarization, similarly to the rabbit and the rat cases. The primo nodes were observed under the left and the right transverse sinuses at distances of 3,763  μ m and 5,967  μ m. The average size was 155  μ m × 248  μ m. Conclusion. The observation of primo vessels was consistent with previous observations in rabbits and rats, and primo nodes under the transverse sinuses were observed for the first time in this work.

Review and Comment on the Relationship between Primo Vascular System and Meridians

This paper aims to summarize the recent progress of researches on the primo vascular system (PVS) and to analyze characteristics between PVS and traditional Chinese meridians. With the distribution, position features, identification and origin of PVS, and its function related to meridians elaborated on, we propose that there is still a lack of enough evidence to support the correlation between PVS and traditional Chinese meridians.

Differentiating Blood, Lymph, and Primo Vessels by Residual Time Characteristic of Fluorescent Nanoparticles in a Tumor Model

Fluorescent nanoparticles (FNPs) which were injected into a tumor tissue flowed out through the blood and lymph vessels. The FNPs in blood vessels remained only in the order for few minutes while those in lymph vessels remained for a long time disappearing completely in 25 hours. We found a primo vessel inside a lymph vessel near a blood vessel, and FNPs remained in the primo vessel for longer than 25 hours. In addition, we examined in detail the residual time characteristics of lymph vessels because it could be useful in a future study of fluid dynamical comparison of the three conduits. These residual time characteristics of FNPs in the three kinds of vessels may have implications for the dynamics of nanoparticle drugs for cancer chemotherapy.