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Boon Chin Heng

Publications and source records attributed to Boon Chin Heng.

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

Alternative solutions to the current situation of oocyte donation in Singapore.

The rising incidence of age-related female infertility in Singapore, coupled with the prohibition on commercialized oocyte donation and egg sharing, has resulted in a severe shortage of donor oocytes. Infertile women are routinely encouraged by fertility doctors here to seek their close relatives and friends as prospective oocyte donors, which does not alleviate the shortage. A number of alternative solutions are discussed. The use of substantial financial remuneration to encourage oocyte donation is rejected as being legally, ethically and morally incompatible with present day Singaporean society. Egg sharing in return for subsidized fertility may have a strong case for ethical justification, but implementation would need amendment of the current legislation in Singapore. Cross- and mirror-exchange oocyte donations face less of a legal challenge in Singapore and also have a strong case for ethical justification. However, special consideration must be given to the unique socio-cultural values of Singaporean society, i.e. traditional Chinese culture. Finally, if no changes are made to restrictive regulations governing oocyte donation in Singapore, and shortage of donor oocytes still persists, then reproductive tourism abroad may be the solution for some patients; referrals by local fertility doctors are unlikely to be allowed in Singapore.

Humans↗
PubMed2006

Delayed motherhood through oocyte and ovarian tissue cryopreservation - a perspective from Singapore.

Recent advances in oocyte and ovarian tissue cryopreservation technology have brought hope not only to women facing premature loss of ovarian function, but also to healthy women seeking delayed motherhood. This is a major issue of contention in healthcare ethics. Proponents of this new technology argue that this enables women to pursue educational and career goals in their youth, so that they have greater financial security for children in later life. Nevertheless, this argument may be flawed by the reality that even if the cryopreservation of oocytes and ovarian tissue were optimized in the future, this would in no way be a guaranteed route for women to have biological children later in life. Moreover, because only a limited amount of autologous reproductive material can be cryopreserved and stored for a single healthy woman, there is a risk of material depletion before reproductive success is attained. Another prime consideration is the increased morbidity and mortality associated with clinical assisted reproduction in older women. Hence, it is imperative that delayed motherhood through the cryopreservation of oocytes and ovarian tissues be viewed with extreme caution, and mandatory counselling should be given to all patients if such a medical procedure ultimately finds approval for widespread application.

Cryopreservation↗
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

The egg-sharing model for human therapeutic cloning research: managing donor selection criteria, the proportion of shared oocytes allocated to research, and amount of financial subsidy given to the donor.

Recent advances in human therapeutic cloning made by Hwang and colleagues have opened up new avenues of therapy for various human diseases. However, the major bottleneck of this new technology is the severe shortage of human donor oocytes. Egg-sharing in return for subsidized fertility treatment has been suggested as an ethically justifiable and practical solution to overcome the shortage of donor oocytes for therapeutic cloning. Because the utilization of shared oocytes in therapeutic cloning research does not result in any therapeutic benefit to a second party, this would necessitate a different management strategy compared to their use for the assisted conception of infertile women who are unable to produce any oocytes of their own. It is proposed that the pool of prospective egg-sharers in therapeutic cloning research be limited only to younger women (below 30 years of age) with indications for either male partner sub-fertility or tubal blockage. With regards to the proportion of the shared gametes being allocated to research, a threshold number of retrieved oocytes should be set that if not exceeded, would result in the patient being automatically removed from the egg-sharing scheme. Any excess supernumerary oocyte above this threshold number can be contributed to science, and allocation should be done in a randomized manner. Perhaps, a total of 10 retrieved oocytes from the patient may be considered a suitable threshold, since the chances of conception are unlikely to be impaired. With regards to the amount of subsidy being given to the patient, it is suggested that the proportion of financial subsidy should be equal to the proportion of the patient's oocytes being allocated to research. No doubt, the promise of future therapeutic benefit may be offered to the patient instead of financial subsidy. However, this is ethically controversial because therapeutic cloning has not yet been demonstrated to be a viable model of clinical therapy and any promises made to the patient might turn out to be illusionary. Hence, it is proposed that a tangible financial subsidy on the medical fees might be the better option for the patient's welfare.

Cloning, Organism↗
PubMed2005

Modulating gene expression in stem cells without recombinant DNA and permanent genetic modification.

Future therapeutic applications of stem cells in regenerative medicine require efficient techniques for modulating gene expression. Conventionally, this is achieved through the use of recombinant DNA, which invariably leads to permanent genetic alteration to the cell. Overwhelming safety and ethical concerns are likely to preclude the application of genetically modified stem cells in human clinical therapy for the foreseeable near future. An alternative may be to adopt a "milieu-based" approach to influence gene expression, by exposing stem cells to a cocktail of exogenous cytokines, growth factors, and extracellular matrix. Nevertheless, the non-specific pleiotropic effects exerted by various cytokines, growth factors, and extracellular matrix would make this a relatively inefficient approach. Moreover, a "milieu-based" approach is likely to require extended durations of in vitro culture, which might delay autologous transplantation of adult stem cells to the patient and might alter their immunogenicity through prolonged exposure to xenogenic proteins within the culture milieu. The obvious solution would be to deliver proteins, RNA, or their synthetic analogs, such as peptide nucleic acid, directly into the cell to modulate gene expression. Currently, two promising delivery platforms are available: (1) protein transduction domains, and (2) immunoliposomes. Because such molecules have a limited active half-life in the cytosol and are obviously not incorporated into the genetic code of the cell, these would only exert a transient modulatory effect on gene expression. Nevertheless, a transient effect may be preferable for clinical therapy, since this would ultimately avoid permanent genetic alteration to the cell.

Animals↗
PubMed2005

Reprogramming autologous skeletal myoblasts to express cardiomyogenic function. Challenges and possible approaches.

Cell transplantation therapy is emerging as a promising mode of treatment following myocardial infarction. Of the various cell types that can potentially be used for transplantation, autologous skeletal myoblasts appear particularly attractive, because this would avoid issues of immunogenicity, tumorigenesis, ethics and donor availability. Additionally, skeletal myoblasts display much higher levels of ischemic tolerance and graft survival compared to other cell types. There is some evidence for improvement in heart function with skeletal myoblast transplantation. However, histological analysis revealed that transplanted myoblasts do not transdifferentiate into functional cardiomyocytes in situ. This is evident by the lack of expression of cardiac-specific antigens, and the absence of intercalated disc formation. Instead, there is differentiation into myotubes that are not electromechanically coupled to neighboring cardiomyocytes. This could in turn limit the clinical efficacy of treatment. This review would therefore examine the various challenges faced in attempting to reprogram autologous skeletal myoblast to express cardiomyogenic function, together with the various possible strategies that could be employed to achieve this objective.

Cell Differentiation↗
PubMed2005

Incorporating protein transduction domains (PTD) within recombinant 'fusion' transcription factors. A novel strategy for directing stem cell differentiation?

Application of embryonic and adult stem cells in regenerative medicine will require efficient protocols for directing stem cell differentiation into well-defined lineages. The use of exogenous cytokines, growth factors, or extracellular matrix substratum, will obviously require extended durations of in vitro culture. With autologous adult stem cells, this could delay transplantation to the patient, as well as alter the immunogenicity of the cultured autologous cells. Genetic modulation to direct stem cell differentiation would obviate prolonged durations of in vitro culture; but there are overwhelming safety concerns with regards to the application of recombinant DNA technology in human clinical therapy. A novel alternative would be to incorporate protein transduction domains (PTD) into recombinant transcription factors that play important roles in somatic differentiation. Such protein-engineered transcription factors will then have the ability to translocate across the cell membrane and be internalized within the cytosol, thereby acting as paracrine signaling molecules. Upon internalization, the recombinant transcription factors would only have a limited active half-life, so that their effects are only transient. However, this could provide sufficient stimulus for initiating stem cell differentiation into a required lineage.

Cell Differentiation↗
PubMed2005

Incorporating protein transduction domains (PTD) within intracellular proteins associated with the 'stemness' phenotype. Novel use of such recombinant 'fusion' proteins to overcome current limitations of applying autologous adult stem cells in regenerative medicine?

Adult stem cells originating from post-natal tissues hold tremendous promise in regenerative medicine. Nevertheless, there are several deficiencies of adult stem cells that would limit their application in transplantation therapy, in particular their relative scarcity, restricted multi-potency and limited proliferative capacity in vitro. A possible approach to overcome these limitations would be to genetically modulate adult stem cells to strongly express genes that are closely associated with the 'stemness' phenotype. Overwhelming safety concerns would preclude the direct application of recombinant DNA technology in genetic modulation. Moreover, constitutive expression of 'stemness' genes would prevent adult stem cells from participating in tissue/organ regeneration upon transplantation. A novel alternative would be to incorporate protein transduction domains within intracellular proteins (i.e. transcription factors) that are associated with the 'stemness' phenotype. Such recombinant fusion proteins would then have the ability to translocate across the cell membrane and be internalized within the cytosol, thereby enabling them to exert a gene-modulatory effect on the cell, without any permanent genetic alteration. This would be particularly useful for maintaining the 'stemness' of adult stem cell populations during extensive ex vivo proliferation, to generate adequate cell numbers for transplantation therapy.

Adult↗