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Biomedical subjects

Hua Liu

Publications and source records attributed to Hua Liu.

At least 37 records · Page 2Linked to original sources
PubMed2006

Genetic diversity of Acanthamoeba isolated from ocean sediments.

Genetic diversity of 18 Acanthamoeba isolates from ocean sediments was evaluated by comparing mitochondrial (mt) DNA RFLP, 18S rDNA sequences and by examining their cytopathic effects on human corneal epithelial cells versus reference strains. All isolates belonged to morphologic group II. Total of 16 restriction phenotypes of mtDNA from 18 isolates demonstrated the genetic diversity of Acanthamoeba in ocean sediments. Phylogenetic analysis using 18s rDNA sequences revealed that the 18 isolates were distinct from morphological groups I and III. Fifteen isolates showed close relatedness with 17 clinical isolates and A. castellanii Castellani and formed a lineage equivalent to T4 genotype of Byers group. Two reference strains from ocean sediment, A. hatchetti BH-2 and A. griffini S-7 clustered unequivocally with these 15 isolates. Diversity among isolates was also evident from their cytopathic effects on human corneal cells. This is the first time describing Acanthamoeba diversity in ocean sediments in Korea.

Acanthamoeba↗
PubMed2006

[The inhibitory effects of dumb-bell decoy oligodeoxynucleotides targeting NF-kappaB on the growth of multiple myeloma cells and IL-6 expression].

AIM: To investigate the inhibitory effects of dumb-bell decoy oligodeoxynucleotides(ODNs) targeting NF-kappaB on the transcriptional activity of NF-kappaB binding to its cis-elements, growth of multiple myeloma cells 8266 and the expression of IL-6 in 8266 cells. METHODS: The inhibitory effects of dumbbell decoy ODNs targeting NF-kappaB on the transcriptional activity of NF-kappaB was detected by electrophoretic mobility shift assay(EMSA). 8266 cells were randomly divided into 8266 cells of passage (control), dumb-bell decoy ODNs treatment, and cationic liposome treatment groups. Dumb-bell decoy ODNs of 2, 4 and 8 mg/L were cultured respectively into 8266 cells via cationic liposome vector. Then, the transfected 8266 cells and their supernatant were collected at 8, 12 and 18 h. IL-6 expression was measured by ELISA. Effect of decoy ODNs on the growth of 8266 cells stimulated with IL-6 was measured by MTT Colorimetry assay. RESULTS: Dumbbell decoy ODNs effectively inhibited the binding of NF-kappaB to its cis-elements in vitro. Different doses of decoy ODNs (2, 4 and 8 mg/L) had different inhibitory effects on IL-6 expression in 8266 cells. After decoy ODNs had been transfected into 8266 cells stimulated by IL-6 via cationic liposome vector, both the growth of 8266 cells and activity of IL-6 were inhibited. CONCLUSION: Dumb-bell decoy ODNs can effectively inhibit the growth of 8266 cells and decrease the expression of IL-6 in myeloma cells through the inhibiting NF-kappaB activity.

Cell Line, Tumor↗
PubMed2006

[Experiment study of tongfu huoxue decoction in the treatment of intracelebral hemorrhage].

OBJECTIVE: To investigate the effects of Tongfu Huoxue decoction on experimental intracelebral hemorrhage and the associated machenisms. METHOD: The cerebral hemorrhage model in rats was induced by local injection of type VII collagenase and they were randomly divided into four groups. The treated groups were treated with Naoxuekang and Tongfu Huoxue decoction. The control groups were only treated with water. The changes of neurological defect were observed. The content of brain water, MDA, NO and the activity of SOD were measured. RESULT: The cerebral hemorrhage rats showed hemiplegia, and the hemorrhage brains showed celebral edema, higher quotient of brain and content of brain water, suggesting the hemorrhage model was established successfully. After the treatment of Tongfu Huoxue decoction, the hemorrhage rats showed smaller hemorrhage volume, the brain tissue from the hemorrhage rats had lower MDA content and the quotient of brain, and also had higher activity of SOD and content of NO. CONCLUSION: Tongfu Huoxue decoction has treatment effects on cerebral hemorrhage.

Animals↗
PubMed2006

[Observation on therapeutic effect of blood-letting therapy on apoplectic hemiplegia numbness syndrome].

OBJECTIVE: To observe therapeutic effect of blood-letting therapy on apoplectic hemiplegia numbness syndrome and search for clinically effective therapy. METHODS: Ninety and five cases of apoplectic hemiplegia were randomly divided into a treatment group of 55 cases and a control group of 40 cases in order of visiting. The treatment group were treated with tapping Huatuo Jiaji (EX-B2) on the back by plum-blossom needle combined with blood-letting on twelve Well-points or Shixuan (EX-UE 11), once every day, 6 times constituting one course; the control group were treated with routine acupuncture at points of the four limbs, once daily, 12 times constituting one course. After they were treated for 4 courses, their therapeutic effects were observed. RESULTS: The total effective rate was 94.5% in the treatment group and 77.5% in the control group with a significant difference between the two groups (P < 0.01). CONCLUSION: Blood-letting therapy is an effective therapy for post-apoplectic hemiplegia numbness syndrome.

Acupuncture Therapy↗
PubMed2006

[Inhibited proliferation of B-lymphoma Raji cells and down-regulated expression of VEGF by arsenic trioxide].

This study was aimed to investigate the effects of As2O3 on proliferation of B lymphoma Raji cell and to study the expression changes of VEGF mRNA. The modified MTT was adopted to evaluate the effect of As2O3 on proliferation of Raji cells. Semi-quantitative RT-PCR was used to detect the expression of VEGF121 and VEGF165 mRNA in Raji cells exposed to As2O3. The results showed that the As2O3 significantly inhibited the proliferation of Raji cells, the relationship between the inhibition rate and the concentrations of As2O3 was dose- and time-dependent. The VEGF121 and VEGF165 mRNA expressions were found in Raji cells, and both were well-matched in expression levels. After treatment of As2O3 at 1 micromol/L for 48 hours, the expression levels of VEGF121 and VEGF165 mRNA were significantly down-regulated and demonstrated negative correlation with the time of exposure to As2O3. Otherwise some difference were observed in effects of As2O3 on VEGF121 and VEGF165, the expression of VEGF165 mRNA was down-regulated earlier and longer than that of VEGF121, while no similar correlation was found in selected concentration groups. It is concluded that As2O3 can significantly inhibit the growth of Raji cells and may exerted its anti-angiogenesis effects by down-regulating the VEGF mRNA expression even in a low concentration for a long term.

Antineoplastic Agents↗
PubMed2006

[Combined use of transmyocardial stents with gene therapy in the treatment of acute myocardial infarction].

OBJECTIVES: To determine the efficacy of combined use of transmyocardial stent with gene therapy to treat acute myocardial infarction in porcine model. METHODS: 24 Chinese mini swines have been divided into 4 groups randomly: group myocardial infarction (group MI n(1) = 6), group transmyocardial stent (group ST n(2) = 6), group vascular endothelial growth factor (group VEGF n(3) = 6), group transmyocardial stent and VEGF (group ST + VEGF n(4) = 6). In group MI, acute myocardial infarction animal model has been established by the ligation of the left descending coronary artery. In group ST, after the establishment of the model, 3 transmyocardial stents were implanted. In group VEGF, an expression plasmid containing the gene-encoding VEGF(165) (300 microg) was administered directly in the myocardium at 6 sites. In group ST + VEGF, both transmyocardial stents and expression plasmid containing the gene-encoding VEGF(165) are applied. 4 weeks later, the animals are sacrificed and echocardiography and pathological analysis have been done. RESULTS: The density of blood vessel in group ST, VEGF and ST + VEGF are significantly higher than group MI. And capillary density in group ST + VEGF is the highest in these groups statistically. Expression of VEGF was detected in group ST, VEGF and ST + VEGF, but in group VEGF and ST + VEGF the level of expression are higher. CONCLUSION: Combined use of transmyocardial stent with gene therapy has synthetic effect for the treatment of acute myocardial ischemia in porcine model and can significantly increase the vascular density.

Animals↗
PubMed2006

Influence of nitric oxide synthase and cyclooxygenase blockade on expression of cyclooxygenase and hemodynamics in rats with portal hypertension.

BACKGROUND: The importance of nitric oxide (NO) in the pathogenesis of portal hypertension (PHT) has been extensively studied, but whether or not prostacyclin (PGI(2)) plays a role in formation and development of hyperdynamic circutatory state in PHT has not been verified. The present study was undertaken to investigate the possible interaction between prostacyclin (PGI(2)) and nitric oxide (NO) in the hyperdynamic circulatory state of rats with chronic portal hypertension (PHT), by measuring the hemodynamic changes and expression of cyclooxygenase (COX) mRNA in vessels and small intestine after administration of N(omega)-nitro-L-arginine (L-NNA) or indomethacin (INDO) either in the short-term (7 days) or long-term (15 days). METHODS: Ninety-seven male Sprague-Dawley rats were divided into three groups: intrahepatic portal hypertension (IHPH) induced by injection of CCl(4), prehepatic portal hypertension (PHPH) induced by partial stenosis of the portal vein, and sham-operated controls (SO). Animals of each group received L-NNA or INDO either for 7 or 15 days, with saline as control. Splanchnic hemodynamics was measured by the radioactive microsphere technique. The concentration of NO in serum was determined as the nitrate; nitrite ratio (NO(2)(-)/NO(3)(-), micromol/L) by a colorometric method, and that of PGI(2) was measured by specific radioimmunoassay for its stable hydrolysis product 6-keto-PGF(1alpha) (pg/ml). The reverse transcription-polymerase chain reaction measured the levels of COX-1 mRNA in the superior mesenteric artery, thoracic aorta, and small intestine of these rats. RESULTS: Compared with SO rats, COX-1 mRNA expression and the concentrations of plasma 6-keto-PGF(1alpha) and serum NO(2)(-)/NO(3)(-) were enhanced in both IHPH and PHPH rats; splanchnic vascular resistance (SVR) decreased, but portal venous inflow (PVI) markedly increased (P<0.05). Seven or 15 days of L-NNA treatment reduced COX-1 mRNA expression in these vessels and the small intestine, concomitant with a significant decrease in the concentration of plasma PGI(2) and serum NO in IHPH and PHPH rats (P<0.05). At the same time, PVI decreased but SVR increased significantly (P<0.05). In both IHPH and PHPH rats, the COX-1 mRNA expression and the concentration of plasma PGI(2) after No synthase (NOS) blockade for 15 days were higher than those for 7 days, whereas the hyperdynamic circulatory state was improved after NOS blockade for 15 days compared with 7 days. The concentration of PGI(2) treated by INDO for 15 days was not significantly different from that after 7-day COX blockade, and hemodynamics restored hyperdynamic circulatory state. CONCLUSIONS: The hyperdynamic circulatory state in rats with PHT is correlated with the concentration of serum NO. There is a possible interaction between PGI(2) and NO in the hyperhemodynamics of PHT. PGI(2) is probably not the mediator in the formation and development of the hyperdynamic circulatory state in rats with chronic PHT.

Animals↗
PubMed2005

Loss of viability during freeze-thaw of intact and adherent human embryonic stem cells with conventional slow-cooling protocols is predominantly due to apoptosis rather than cellular necrosis.

A major challenge in the widespread application of human embryonic stem (hES) cells in clinical therapy and basic scientific research is the development of efficient cryopreservation protocols. Conventional slow-cooling protocols utilizing standard cryoprotectant concentrations i.e. 10% (v/v) DMSO, yield extremely low survival rates of <5% as reported by previous studies. This study characterized cell death within frozen-thawed hES colonies that were cryopreserved under standard conditions. Surprisingly, our results showed that immediately after post-thaw washing, the overwhelming majority of hES cells were viable (approximately 98%), as assessed by the trypan blue exclusion test. However, when the freshly-thawed hES colonies were incubated within a 37 degrees C incubator, there was observed to be a gradual reduction in cell viability over time. The kinetics of cell death was drastically slowed-down by keeping the freshly-thawed hES colonies at 4 degrees C, with >90% of cells remaining viable after 90 min of incubation at 4 degrees C. This effect was reversible upon re-exposing the cells to physiological temperature. The vast majority of low temperature-exposed hES colonies gradually underwent cell death upon incubation for a further 90 min at 37 degrees C. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end-labeling (TUNEL) assay confirmed apoptosis-induced nuclear DNA fragmentation in frozen-thawed hES cells after incubation at 37 degrees C for 90 min. Expression of active caspase-3 enzyme, which is another prominent marker of apoptosis, was confirmed by immunocytochemical staining, while transmission electron microscopy showed typical ultrastructural features of apoptosis such as chromatin condensation and margination to the nuclear membrane. Hence, our results demonstrated that apoptosis instead of cellular necrosis, is the major mechanism of the loss of viability of cryopreserved hES cells during freeze-thawing with conventional slow-cooling protocols.

Apoptosis↗
PubMed2005

Internally solvated cyclopentadienyllithium compounds: structural integrity of the Cp-Li+ moiety. NMR, dynamics, X-ray crystallography, and calculations.

[Structure: see text]. N(CH2CH2OCH3)2 are as follows: T = CHCH(CH3)2, 6; T = (CH2)2, 10; T = (CH2)3, 14. The results of NOE NMR experiments for 6, 10, and 14 together with X-ray crystallography of 14 support internally coordinated monomeric structures for all three compounds. Models have been constructed for 6, 10, and 14 from modifications of an internally solvated allylic lithium compound at the B3LYP level of theory using basis set 6-311G*. The resulting structural features are very similar to those obtained from the NMR and crystallographic data. In addition, 13C NMR shifts obtained with the GIAO procedure using the results of the B3LYP/6-311G* calculations are closely similar to the experimental shifts, which validate B3LYP as a suitable model for these compounds. The Li+ centroid distance of ca. 1.9 A to 2.0 A obtained for 6, 10, and 14 is common to most crystallographic data for externally solvated Cp-Li+ compounds as well as one which incorporates a (CpLiCp)- triple ion. It is concluded that the ligand tether and the stereochemistry around Li+ accommodate to maintain the structural integrity of Cp-Li+. NMR and crystallography show 14 to be chiral. Carbon-13 NMR line shape changes are attributed to inversion via a lateral wobble mechanism with DeltaH++ = 6 kcal x mol(-1) and DeltaS++ = -2 eu. It is also shown that a 6,6-dimethylfulvene is deprotonated at methyl by LiN(CH2CH2OCH3)3 as well as by butyllithium in the presence of PMDTA producing isopropenyl Cp-Li+ compounds 24 and 25, respectively. NMR line shape changes of the sample containing 24 have been qualitatively interpreted to result from a combination of fast transfer of coordinated ligand between faces of the carbanion plane as well as a lithium-exchange process.

Journal Article↗
PubMed2005

Acupoint-specific fMRI patterns in human brain.

Specific central nervous system (CNS) responses to acupuncture have recently attracted attention. It is important to understand the differences in fMRI images of the brain evoked by acupuncture at an acupoint and at a nearby "sham" point. Here, we report analyses of fMRI images of the brains of 37 healthy volunteers in response to acupuncture at Liv3 (Taichong) and LI4 (Hegu) versus their sham points. We found common activation areas in response to Liv3 or LI4 acupuncture in the middle temporal gyrus and cerebellum, along with deactivation areas in the middle frontal gyrus and inferior parietal lobule, compared with the effects of acupuncture at sham points. Acupuncture at Liv3 evoked specific activation at the postcentral gyrus, posterior cingulate, parahippocampal gyrus, BA 7, 19 and 41, but deactivation at the inferior frontal gyrus, anterior cingulate, BA 17 and 18, compared with acupuncture at its sham point. Acupuncture at LI4 evoked specific activation at the temporal pole, but deactivation at the precentral gyrus, superior temporal gyrus, pulvinar and BA 8, 9 and 45, compared with acupuncture at its sham point. These observations reveal that acupuncture at acupoints induces specific patterns of brain activity, and these patterns may relate to the therapeutic effects of acupuncture.

Acupuncture↗
PubMed2005

Endoplasmic reticulum stress-associated caspase 12 mediates cisplatin-induced LLC-PK1 cell apoptosis.

Reactive oxygen metabolites are important mediators in cisplatin-induced apoptosis in renal tubular epithelial cells (LLC-PK1). Mitochondria have been implicated to play a principal role in cisplatin-induced apoptosis. Caspase 12, an endoplasmic reticulum (ER)-specific caspase, participates in apoptosis under ER stress. Cytochrome P450 system is crucial to the generation of reactive oxygen metabolites and is present at high concentration in the ER. The direct role of caspase 12 in any model of renal injury has not previously been described. In this study, cleavage of procaspase 12 preceded that of caspases 3 and 9 after cisplatin treatment of LLC-PK1 cells. The active form of caspase 8 was not detected throughout the course of study. Preincubation of the LLC-PK1 cells with the caspase 9 inhibitor did not attenuate caspase 3 activation and provided no significant protection. Caspase 3 inhibitor provided only modest protection against cisplatin-induced apoptosis. LLC-PK1 cells that were transfected with anti-caspase 12 antibody significantly attenuated cisplatin-induced apoptosis. Taken together, these data indicate that caspase 12 plays a pivotal role in cisplatin-induced apoptosis. It is proposed that the oxidative stress that results from the interaction of cisplatin with the ER cytochrome P450 leads to activation of procaspase 12, resulting in apoptosis.

Antineoplastic Agents↗
PubMed2005

Oxidative cyclorelease from soluble polymeric supports.

[reaction: see text] Single electron oxidation is shown to be a viable method for effecting concomitant cyclization and cleavage (cyclorelease) of a series of polymer bound homobenzylic ethers. Soluble oligonorbornene polymers are stable toward redox chemistry and are isolable through precipitation with methanol, making them excellent supports for this process. These oxidative conditions are also shown to cleave secondary and tertiary alcohols and ethers in a new traceless approach to polymer-supported aldehyde and ketone synthesis.

Journal Article↗
PubMed2005

Temporal profiling of gene expression during neurogenesis and remodeling in the olfactory epithelium at short intervals after target ablation.

Neurogenesis in the olfactory epithelium (OE) is induced by olfactory bulbectomy (OBX), which effectively axotomizes olfactory sensory neurons (OSNs) and removes their synaptic targets, resulting in apoptosis. We used Affymetrix high-density oligonucleotide arrays to investigate changes in gene expression during initiation of signaling in pathways that regulate apoptosis and neurogenesis in the murine OE at 2, 8, 16, and 48 hr after bilateral OBX compared to that in sham-operated controls. We focused on regulation of a defined set of genes associated with apoptosis, stem/progenitor cell regulation, and cell cycle progression because of the activation of these processes in OE degeneration and remodeling after OBX. After data scrubbing and categorical analysis, one-way analysis of variance identified 72 genes (4.9% of the present known genes) as being regulated significantly (P < 0.05) at one or more points; 50 were defined as regulated differentially with the false discovery rate at 10%. Significant changes in gene expression occurred in all categories as early as 2 hr post-OBX, with the greatest number of differentially regulated genes at 16 and 48 hr. Hierarchical cluster analysis and correlation coefficients were used to identify similarities in patterns of gene expression changes within and across categories. Validation was carried out with SuperArray macroarrays and real-time RT-PCR. Our results confirmed the participation of many genes in known signaling pathways and identified changes in the expression of 42 genes not identified previously as participating in apoptosis and neurogenesis in the OE. Additionally, our analyses indicated the early involvement of genes regulating cytoskeletal reorganization and angiogenesis in the response to OBX. These studies are an important first step in defining early time-dependent changes in gene expression after target ablation that lead to neurogenesis in the olfactory sensory epithelium.

Animals↗
PubMed2005

Quadratic regression analysis for gene discovery and pattern recognition for non-cyclic short time-course microarray experiments.

BACKGROUND: Cluster analyses are used to analyze microarray time-course data for gene discovery and pattern recognition. However, in general, these methods do not take advantage of the fact that time is a continuous variable, and existing clustering methods often group biologically unrelated genes together. RESULTS: We propose a quadratic regression method for identification of differentially expressed genes and classification of genes based on their temporal expression profiles for non-cyclic short time-course microarray data. This method treats time as a continuous variable, therefore preserves actual time information. We applied this method to a microarray time-course study of gene expression at short time intervals following deafferentation of olfactory receptor neurons. Nine regression patterns have been identified and shown to fit gene expression profiles better than k-means clusters. EASE analysis identified over-represented functional groups in each regression pattern and each k-means cluster, which further demonstrated that the regression method provided more biologically meaningful classifications of gene expression profiles than the k-means clustering method. Comparison with Peddada et al.'s order-restricted inference method showed that our method provides a different perspective on the temporal gene profiles. Reliability study indicates that regression patterns have the highest reliabilities. CONCLUSION: Our results demonstrate that the proposed quadratic regression method improves gene discovery and pattern recognition for non-cyclic short time-course microarray data. With a freely accessible Excel macro, investigators can readily apply this method to their microarray data.

Algorithms↗
PubMed2005

Population genetics of complex life-cycle parasites: an illustration with trematodes.

Accurate inferences on population genetics data require a sound underlying theoretical null model. Organisms alternating sexual and asexual reproduction during their life-cycle have been largely neglected in theoretical population genetic models, thus limiting the biological interpretation of population genetics parameters measured in natural populations. In this article, we derive the expectations of those parameters for the life-cycle of monoecious trematodes, a group comprising several important human and livestock parasites that obligatorily alternate sexual and asexual reproduction during their life-cycle. We model how migration rates between hosts, sexual and asexual mutation rates, adult selfing rate and the variance in reproductive success of parasites during the clonal phase affect the amount of neutral genetic diversity of the parasite (effective population size) and its apportionment within and between definitive hosts (using F-statistics). We demonstrate, in particular, that variance in reproductive success of clones, a parameter that has been completely overlooked in previous population genetics models, is very important in shaping the distribution of the genetic variability both within and among definitive hosts. Within definitive hosts, the parameter F(IS) (a measure of the deviation from random mating) is decreased by high variance in clonal reproductive success of larvae but increased by high adult self-fertilisation rates. Both clonal multiplication and selfing have similar effects on between-host genetic differentiation (F(ST)). Migration occurring before and after asexual reproduction can have different effects on the patterns of F(IS), depending on values of the other parameters such as the mutation rate. While the model applies to any hermaphroditic organism alternating sexual and clonal reproduction (e.g. many plants), the results are specifically discussed in the light of the limited population genetic data on monoecious trematodes available to date and their previous interpretation. We hope that our model will encourage more empirical population genetics studies on monoecious trematodes and other organisms with similar life-cycles.

Animals↗
PubMed2005

[Clinical study on Zhuyu Tongfu serial recipe combined with acupuncture and massotherapy in treating hypertensive cerebral hemorrhage].

OBJECTIVE: To observe the clinical efficacy and mechanism of Zhuyu Tongfu (ZYTF) Serial Recipe combined with acupuncture and massotherapy in treating hypertensive cerebral hemorrhage (HCH). METHODS: One hundred and eighteen patients with hypertensive cerebral hemorrhage, on the basis of conventional Western medicine treatment, were randomly divided into ZYTF combined with acupuncture and massotherapy group (treated group) and simple Western medicine group (control group); the clinical efficacy, neurofunction deficit scoring (NDS) alterations and hematoma absorption rate of both groups were observed, and also the plasma superoxide dismutase (SOD) activity, plasma lipid peroxidase (LPO) content, erythrocyte glutathion peroxidase (GSH-Px) activity, hematocrit (Ht) and the whole blood viscosity (Va) change were also observed. RESULTS: In the treated group, the clinical efficacy, NDS improvement and hematoma absorption rate were superior to that of the control group; comparison between the two groups after treatment showed that plasma SOD activity and GSH-Px activity got more elevated and plasma LPO content, Ht and Va more lowered in the the treated group than those in the control group. CONCLUSION: ZYTF combined with acupuncture and massotherapy has better effect, its therapeutic mechanism was possibly correlated to the elevation of plasma SOD activity, GSH-Px activity and lowering of plasma LPO content, Ht and Va.

Acupuncture Therapy↗
PubMed2005

Transplanted human embryonic stem cells as biological 'catalysts' for tissue repair and regeneration.

Human embryonic stem cells have tremendous potential in the newly emerging field of regenerative medicine. Recently, it was demonstrated that the rescue of lethal cardiac defects in Id knockout mutant mouse embryos was not due to the transplanted cells giving rise to functional new tissues within the defective embryonic heart. Instead, there is indirect evidence that the observed therapeutic effect was due to various secreted factors emanating from the transplanted cells. This therefore, introduces the exciting prospect of utilizing human embryonic stem cells as biological 'catalysts' to promote tissue repair and regeneration in transplantation therapy. However, the immunological barrier against allogenic transplantation, as well as the teratogenic potential of human embryonic stem cells poses major technical challenges. A possible strategy to overcome the immunological barrier may be to impose a temporary regimen of immunosuppressive drugs followed by their gradual withdrawal, once adequate tissue regeneration has been achieved. Other more novel alternatives include the use of microencapsulation to block interaction with the transplant recipient's immune system, and co-transplantation with bone marrow-derived mesenchymal stem cells, which have been demonstrated to possess immuno-suppressive properties. The teratogenic potential of human embryonic stem cells could possibly be alleviated by directing the differentiation of these cells to specific lineages prior to transplantation, or through mitotic inactivation (gamma irradiation or mitomycin C exposure). Co-transplantation with autologous adult stem cells may represent a novel strategy to further enhance the 'catalytic' effects of human embryonic stem cells. The various factors secreted by human embryonic stem cells could then have a concentrated localized effect on relatively large numbers of co-transplanted autologous adult stem cells, which may in turn lead to enhanced repair and regeneration of the damaged tissue or organ. Moreover, there is also a possibility that synergistic interactions between the co-transplanted human embryonic stem cells and autologous adult stem cells, may somehow produce signals for the recruitment and migration of additional endogenous adult stem cells within the recipient (i.e. peripheral blood circulation, bone marrow), which could further enhance organ/tissue regeneration. Hence, the potential use of human embryonic stem cells as biological 'catalysts' to stimulate tissue repair and regeneration, appears to hold tremendous promise in the field of regenerative medicine. This new therapeutic strategy needs to thoroughly investigated, in view of its potentially important clinical applications.

Adult↗