Heng Fong Seow

Candida and invasive candidiasis: back to basics

The ubiquitous Candida spp. is an opportunistic fungal pathogen which, despite treatment with antifungal drugs, can cause fatal bloodstream infections (BSIs) in immunocompromised and immunodeficient persons. Thus far, several major C. albicans virulence factors have been relatively well studied, including morphology switching and secreted degradative enzymes. However, the exact mechanism of Candida pathogenesis and the host response to invasion are still not well elucidated. The relatively recent discovery of the quorum-sensing molecule farnesol and the existence of quorum sensing as a basic regulatory phenomenon of the C. albicans population behavior has revolutionized Candida research. Through population density regulation, the quorum-sensing mechanism also controls the cellular morphology of a C. albicans population in response to environmental factors, thereby, effectively placing morphology switching downstream of quorum sensing. Thus, the quorum-sensing phenomenon has been hailed as the ‘missing piece’ of the pathogenicity puzzle. Here, we review what is known about Candida spp. as the etiological agents of invasive candidiasis and address our current understanding of the quorum-sensing phenomenon in relation to virulence in the host.

Basic fibroblast growth factor modulates cell cycle of human umbilical cord-derived mesenchymal stem cells

Mesenchymal stem cells (MSC) have great potential in regenerative medicine, immunotherapy and gene therapy due to their unique properties of self‐renewal, high plasticity, immune modulation and ease for genetic modification. However, production of MSC at sufficient clinical scale remains an issue as in vitro generation of MSC inadequately fulfils the demand with respect to patients.

Probiotic Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 exhibit strong antifungal effects against vulvovaginal candidiasis-causing Candida glabrata isolates

This study investigates the antagonistic effects of the probiotic strains Lactobacillus rhamnosus GR‐1 and Lactobacillus reuteri RC‐14 against vulvovaginal candidiasis (VVC)‐causing Candida glabrata.

Human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSC) inhibit the proliferation of K562 (human erythromyeloblastoid leukaemic cell line)

hUCB‐MSC (human umbilical cord blood‐derived mesenchymal stem cells) offer an attractive alternative to bone marrow‐derived MSC for cell‐based therapy by being less invasive a source of biological material. We have evaluated the effect of hUCB‐MSC on the proliferation of K562 (an erythromyeloblastoid cell line) and the cytokine secretion pattern of hUCB‐MSC. Co‐culturing of hUCB‐MSC and K562 resulted in inhibition of proliferation of K562 in a dose‐dependent manner. However, the anti‐proliferative effect was reduced in transwells, suggesting the importance of direct cell‐to‐cell contact. hUCB‐MSC inhibited proliferation of K562, arresting them in the G0/G1 phase. NO (nitric oxide) was not involved in the hUCB‐MSC‐mediated tumour suppression. The presence of IL‐6 (interleukin 6) and IL‐8 were obvious in the hUCB‐MSC conditioned media, but no significant increase was found in 29 other cytokines. Th1 cytokines, IFNα (interferon α), Th2 cytokine IL‐4 and Th17 cytokine, IL‐17 were not secreted by hUCB‐MSC. There was an increase in the number of hUCB‐MSC expressing the latent membrane‐bound form of TGFβ1 co‐cultured with K562. The anti‐proliferative effect of hUCB‐MSC was due to arrest of the growth of K562 in the G0/G1 phase. The mechanisms underlying increased IL‐6 and IL‐8 secretion and LAP (latency‐associated peptide; TGFβ1) by hUCB‐MSC remains unknown.

In vitro modulation of probiotic bacteria on the biofilm of Candida glabrata.

A conspicuous new concept of pathogens living as the microbial societies in the human host rather than free planktonic cells has raised considerable concerns among scientists and clinicians. Fungal biofilms are communities of cells that possess distinct characteristic such as increased resistance to the immune defence and antimycotic agents in comparison to their planktonic cells counterpart. Therefore, inhibition of the biofilm may represent a new paradigm for antifungal development. In this study, we aim to evaluate the inxa0vitro modulation of vulvovaginal candidiasis (VVC)-causing Candida glabrata biofilms using probiotic lactobacilli strains. Probiotic Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 were shown to have completely inhibited C. glabrata biofilms and the results were corroborated by scanning electron microscopy (SEM), which revealed scanty structures of the mixed biofilms of C.xa0glabrata and probiotic lactobacilli strains. In addition, biofilm-related C.xa0glabrata genes EPA6 and YAK1 were downregulated in response to the probiotic lactobacilli challenges. The present study suggested that probiotic L.xa0rhamnosus GR-1 and L.xa0reuteri RC-14 strains inhibited C.xa0glabrata biofilm by partially impeding the adherence of yeast cells and the effect might be contributed by the secretory compounds produced by these probiotic lactobacilli strains. Further investigations are required to examine and identify the biofilm inhibitory compounds and the mechanism of probiotic actions of these lactobacilli strains.

Transcriptome profiling of endothelial cells during infections with high and low densities of C. albicans cells

Systemic infections of Candida albicans, the most prevalent fungal pathogen in humans, are on the rise in recent years. However, the exact mode of pathogenesis of this fungus is still not well elucidated. Previous studies using C. albicans mutants locked into the yeast form via gene deletion found that this form was avirulent and did not induce significant differential expression of host genes in vitro. In this study, a high density of C. albicans was used to infect human umbilical vein endothelial cells (HUVEC), resulting in yeast-form infections, whilst a low density of C. albicans resulted in hyphae infections. Transcriptional profiling of HUVEC response to these infections showed that high densities of C. albicans induced a stronger, broader transcriptional response from HUVEC than low densities of C. albicans infection. Many of the genes that were significantly differentially expressed were involved in apoptosis and cell death. In addition, conditioned media from the high-density infections caused a significant reduction in HUVEC viability, suggesting that certain molecules released during C. albicans and HUVEC interactions were capable of causing cell death. This study has shown that C. albicans yeast-forms, at high densities, cannot be dismissed as avirulent, but instead could possibly contribute to C. albicans pathogenesis.

2-dodecanol (decyl methyl carbinol) inhibits hyphal formation and SIR2 expression in C. albicans.

Candida albicans is capable of undergoing yeast‐hypha transition to attain pathogenicity in humans. In this study, we investigated the differential expression of CaSIR2 via quantitative real‐time PCR (qPCR), during yeast‐hypha transition with and without the presence of 2‐dodecanol. SIR2 transcript levels were found to be significantly enhanced after hyphal induction as compared to the yeast form. This study found that 2‐dodecanol is able to inhibit hyphal development and block SIR2 up‐regulation, even in hyphal‐inducing growth conditions. We suggest that SIR2 may be involved in Candida albicans quorum‐sensing and serum‐induced yeast‐hyphae transition via the Ras1‐cAMP‐Efg1 signalling cascade. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Detection of 10 medically important Candida species by seminested polymerase chain reaction

A seminested PCR detecting ten medically important Candida species were achieved. Analytical sensitivity and specificity were not compromised.

Detection of medically important Candida species by absolute quantitation real-time polymerase chain reaction

Background: The number of invasive candidiasis cases has risen especially with an increase in the number of immunosuppressed and immunocom promised patients. The early detection of Candida species which is specific and sensitive is important in determining the correct administration of antifungal drugs to patients. Objectives: This study aims to develop a method for the detection, identification and quantitation of medically important Candida species through quantitative polymerase chain reaction (qPCR). Materials and Methods: The isocitrate lyase (ICL) gene which is not found in mammals was chosen as the target gene of real-time PCR. Absolute quantitation of the gene copy number was achieved by constructing the plasmid containing the ICL gene which is used to generate standard curve. Twenty fungal species, two bacterial species and human DNA were tested to check the specificity of the detection method. Results: All eight Candida species were successfully detected, identified and quantitated based on the ICL gene. A seven-log range of the gene copy number and a minimum detection limit of 103 copies were achieved. Conclusions: A one-tube absolute quantification real-time PCR that differentiates medically important Candida species via individual unique melting temperature was achieved. Analytical sensitivity and specificity were not compromised.

Immunomodulatory Potential of Mesenchymal Stem Cells on Microglia

It is becoming increasingly evident that inflammatory reactions of microglia contribute to the pathology of neurodegenerative diseases. Although the focus for rescuing neurones previously lied on minimising direct insult (including limiting aggregation of misfolded proteins and antagonising the effects of glutamate), therapeutic approaches now include moderating the ensuing inflammatory responses of microglia. Microglia responses in the central nervous system (CNS) are diverse and their involvement in both neuroprotection and neurotoxicity may seem paradoxical. Accordingly, management of neuroinflammation must include an understanding of conditions that trigger neurotoxic responses by microglia and deciphering strategies to maintain their neuroprotective phenotype. Mesenchymal stem cells (MSC) are stem cells with great capacity for immunomodulation on a wide range of immune cells. Evidence presented here highlights the potential of using MSC to modulate the inflammatory responses of microglia. The mechanisms underlying the ability of MSC to moderate microglia responses are also explained in this review. Although many aspects of this approach will require defined characterisation, MSC serve as a potential cell-based therapy that may slow or halt the progression of inflammatory CNS diseases.