Primitive erythropoiesis in infantile haemangioma

KIAA1429 promotes infantile hemangioma regression by facilitating the stemness of hemangioma endothelial cells

Infantile hemangiomas are common vascular tumors with a specific natural history. The proliferation and regression mechanism of infantile hemangiomas may be related to the multilineage differentiation ability of hemangioma stem cells, but the specific mechanism is not well elucidated. KIAA1429 is an N⁶ -methyladenosine methylation-related protein that can also exert its role in a methylation-independent manner. This study aims to explore the function of KIAA1429 in infantile hemangiomas. qRT-PCR, western blotting, and immunostaining were performed to verify the expression of KIAA1429. The endothelial and fibroblast-like phenotypes of hemangioma endothelial cells were detected after KIAA1429 knockdown and overexpression. The stemness properties of hemangioma endothelial cells and the underlying mechanism of KIAA1429 in hemangiomas were also investigated. Nude mouse models of infantile hemangiomas were conducted to ascertain the effects of KIAA1429 in vivo. The results showed that KIAA1429 was highly expressed in infantile hemangiomas, particularly in involuting hemangiomas. In vitro experiments confirmed that KIAA1429 inhibited the endothelial phenotype, enhanced the differentiation ability, and promoted the fibroblast-like phenotype of hemangioma endothelial cells by inducing endothelial cell transition to facultative stem cells. However, the effect of KIAA1429 on the potential target was shown to be independent of N⁶ -methyladenosine methylation modification. Mouse models further revealed that KIAA1429 could inhibit the proliferation and promote the regression of hemangiomas. In conclusion, this study found that KIAA1429 played an important role in the regression of infantile hemangiomas by enhancing the stemness of hemangioma endothelial cells and could be a potential treatment target for infantile hemangiomas.

Insights Into Vascular Anomalies, Cancer, and Fibroproliferative Conditions: The Role of Stem Cells and the Renin-Angiotensin System

Cells exhibiting embryonic stem cell (ESC) characteristics have been demonstrated in vascular anomalies (VAs), cancer, and fibroproliferative conditions, which are commonly managed by plastic surgeons and remain largely unsolved. The efficacy of the mTOR inhibitor sirolimus, and targeted therapies that block the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways in many types of cancer and VAs, further supports the critical role of ESC-like cells in the pathogenesis of these conditions. ESC-like cells in VAs, cancer, and fibroproliferative conditions express components of the renin-angiotensin system (RAS) – a homeostatic endocrine signaling cascade that regulates cells with ESC characteristics. ESC-like cells are influenced by the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways, which directly regulate cellular proliferation and stemness, and interact with the RAS at multiple points. Gain-of-function mutations affecting these pathways have been identified in many types of cancer and VAs, that have been treated with targeted therapies with some success. In cancer, the RAS promotes tumor progression, treatment resistance, recurrence, and metastasis. The RAS modulates cellular invasion, migration, proliferation, and angiogenesis. It also indirectly regulates ESC-like cells via its direct influence on the tissue microenvironment and by its interaction with the immune system. In vitro studies show that RAS inhibition suppresses the hallmarks of cancer in different experimental models. Numerous epidemiological studies show a reduced incidence of cancer and improved survival outcomes in patients taking RAS inhibitors, although some studies have shown no such effect. The discovery of ESC-like cells that express RAS components in infantile hemangioma (IH) underscores the paradigm shift in the understanding of its programmed biologic behavior and accelerated involution induced by β-blockers and angiotensin-converting enzyme inhibitors. The findings of SOX18 inhibition by R-propranolol suggests the possibility of targeting ESC-like cells in IH without β-adrenergic blockade, and its associated side effects. This article provides an overview of the current knowledge of ESC-like cells and the RAS in VAs, cancer, and fibroproliferative conditions. It also highlights new lines of research and potential novel therapeutic approaches for these unsolved problems in plastic surgery, by targeting the ESC-like cells through manipulation of the RAS, its bypass loops and converging signaling pathways using existing low-cost, commonly available, and safe oral medications.

Propranolol in the Treatment of Infantile Hemangiomas

Propranolol, as the first generation of β-blocker family, was initially introduced in the clinical application for tachycardia and hypertension in the 1960s. However, the occasional discovery of propranolol in the involution of infantile hemangiomas (IHs) brought us a new perspective. IHs are the most common infantile tumor, affecting 4–10% newborns. So far, oral propranolol is the first-line medication for IHs treatment. At the same time, local injection and topical propranolol are developing. Despite the worldwide application, the precise mechanism of propranolol of IHs has not been completely studied. In this article, we reviewed and summarized the current information on pharmacology, mechanism, efficacy, and adverse effects of propranolol. Novel design of biomaterials and bioactive molecules are needed for new treatment and ideal pathway to attain the minimal effective treatment concentration and eliminate the adverse effects.

Cell Populations Expressing Stemness-Associated Markers in Vascular Anomalies

Treatment of vascular anomalies (VAs) is mostly empirical and, in many instances unsatisfactory, as the pathogeneses of these heterogeneous conditions remain largely unknown. There is emerging evidence of the presence of cell populations expressing stemness-associated markers within many types of vascular tumors and vascular malformations. The presence of these populations in VAs is supported, in part, by the observed clinical effect of the mTOR inhibitor, sirolimus, that regulates differentiation of embryonic stem cells (ESCs). The discovery of the central role of the renin-angiotensin system (RAS) in regulating stem cells in infantile hemangioma (IH) provides a plausible explanation for its spontaneous and accelerated involution induced by β-blockers and ACE inhibitors. Recent work on targeting IH stem cells by inhibiting the transcription factor SOX18 using the stereoisomer R(+) propranolol, independent of β-adrenergic blockade, opens up exciting opportunities for novel treatment of IH without the β-adrenergic blockade-related side effects. Gene mutations have been identified in several VAs, involving mainly the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways. Existing cancer therapies that target these pathways engenders the exciting possibility of repurposing these agents for challenging VAs, with early results demonstrating clinical efficacy. However, there are several shortcomings with this approach, including the treatment cost, side effects, emergence of treatment resistance and unknown long-term effects in young patients. The presence of populations expressing stemness-associated markers, including transcription factors involved in the generation of induced pluripotent stem cells (iPSCs), in different types of VAs, suggests the possible role of stem cell pathways in their pathogenesis. Components of the RAS are expressed by cell populations expressing stemness-associated markers in different types of VAs. The gene mutations affecting the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways interact with different components of the RAS, which may influence cell populations expressing stemness-associated markers within VAs. The potential of targeting these populations by manipulating the RAS using repurposed, low-cost and commonly available oral medications, warrants further investigation. This review presents the accumulating evidence demonstrating the presence of stemness-associated markers in VAs, their expression of the RAS, and their interaction with gene mutations affecting the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways, in the pathogenesis of VAs.

β-blocker therapy for infantile hemangioma

INTRODUCTION

Fifteen percent of proliferating infantile hemangioma (IH) require intervention because of the threat to function or life, ulceration, or tissue distortion. Propranolol is the mainstay treatment for problematic proliferating IH. Other β-blockers and angiotensin-converting enzyme (ACE) inhibitors have been explored as alternative treatments.

AREAS COVERED

The demonstration of a hemogenic endothelium origin of IH, with a neural crest phenotype and multi-lineage differentiation capacity, regulated by the renin-angiotensin system, underscores its programmed biologic behavior and accelerated involution induced by propranolol, other β-blockers and ACE inhibitors. We review the indications, dosing regimens, duration of treatment, efficacy and adverse effects of propranolol, and therapeutic alternatives including oral atenolol, acebutolol, nadolol, intralesional propranolol injections, topical propranolol and timolol, and oral captopril.

EXPERT OPINION

Improved understanding of the biology of IH provides insights into the mechanism of action underscoring its accelerated involution induced by propranolol, other β-blockers and ACE inhibitors. More research is required to understand the optimal dosing and duration, efficacy and safety of these alternative therapies. Recent demonstration of propranolol's actions mediated by non-β-adrenergic isomer R-propranolol on stem cells, offers an immense opportunity to harness the efficacy of β-blockers to induce accelerated involution of IH, while mitigating their β-adrenergic receptor-mediated adverse effects.

Proliferating Infantile Hemangioma Tissues and Primary Cell Lines Express Markers Associated with Endothelial-to-Mesenchymal Transition

Supplemental Digital Content is available in the text.

Background:

We have previously shown that the endothelium of the microvessels of infantile hemangioma (IH) exhibits a hemogenic endothelium phenotype and proposed its potential to give rise to mesenchymal stem cells, similar to the development of hematopoietic cells. This endothelial-to-mesenchymal transition (Endo-MT) process involves the acquisition of a migratory phenotype by the endothelial cells, similar to epithelial-to-mesenchymal transition that occurs during neural crest development. We hypothesized that proliferating IH expresses Endo-MT–associated proteins and investigated their expression at the mRNA, protein, and functional levels.

Methods:

Immunohistochemical staining of paraffin-embedded sections of proliferating IH samples from 10 patients was undertaken to investigate the expression of the Endo-MT proteins Twist1, Twist2, Snail1, and Slug. Transcriptional analysis was performed for the same markers on proliferating IH tissues and CD34⁺ and CD34⁻ cells from proliferating IH-derived primary cell lines. Adipogenic and osteogenic differentiation plasticity was determined on the CD34-sorted fractions.

Results:

The endothelium of the microvessels and the cells within the interstitium of proliferating IH tissues expressed Twist1, Twist2, and Slug proteins. Twist1 was also expressed on the pericyte layer of the microvessels, whereas Snail1 was not expressed. Both CD34⁺ and CD34⁻ populations from the IH-derived primary cell lines underwent adipogenic and osteogenic differentiation.

Conclusions:

The expression of Endo-MT–associated proteins Twist1, Twist2, and Slug by both the endothelium of the microvessels and cells within the interstitium, and Twist1 on the pericyte layer of the microvessels of proliferating IH, suggest the presence of a process similar to Endo-MT. This may enable a tightly controlled primitive endothelium of proliferating IH to acquire a migratory mesenchymal phenotype with the ability to migrate away, providing a plausible explanation for the development of a fibrofatty residuum observed during involution of IH.

Phosphorylated Forms of STAT1, STAT3 and STAT5 Are Expressed in Proliferating but Not Involuted Infantile Hemangioma

We have recently demonstrated the expression of embryonic stem cell markers on the endothelium of infantile hemangioma, a functional hemogenic endothelium with the capacity for primitive erythropoiesis in vitro. Despite recent work characterizing stem cells within proliferating infantile hemangioma, the expression of STAT proteins, well documented for their roles in stem cell signaling, has not been investigated. 3,3-Diaminobenzidine and immunofluorescence immunohistochemical staining revealed expression of pSTAT1, pSTAT3 and pSTAT5 in proliferating infantile hemangioma samples with the strongest expression of pSTAT3. There was reduced expression of these pSTAT proteins in the involuted infantile hemangioma samples. Western blotting confirmed the identification of all these three proteins in proliferating infantile hemangioma. It is therefore not surprising that the phosphorylated/activated forms of these proteins are relatively abundantly expressed in proliferating, in comparison to involuted infantile hemangioma samples. We speculate that the reduced STAT activation, as infantile hemangioma involutes, is a reflection of the depletion of the abundant stem cells within proliferating infantile hemangioma, as the lesion involutes.

Does hypoxia play a role in infantile hemangioma?

Infantile hemangioma (IH), the most common tumor of infancy, is characterized by rapid growth during infancy, followed by spontaneous involution over 5-10 years. Certain clinical observations have led to the suggestion that IH is triggered and maintained by hypoxia. We review the literature on the possible role of hypoxia in the etiology of IH, in particular, (1) the role of hypoxia inducible factor-1α (HIF-1α) and its downstream targets including GLUT-1 and VEGF; (2) the pathophysiological link between IH and retinopathy of prematurity; (3) hypoxic events in the early life including placental insufficiency, pre-eclampsia and low birthweight that have the potential to promote hypoxic stress; and (4) the evidence supporting the development of IH independent of HIF-1α. We also discuss these observations in the context of recent evidence of the crucial role of stem cells and the cytokines niche that governs their proliferation and inevitable differentiation, offering novel insights into the biology of IH. We propose that various triggers may simultaneously up-regulate HIF-1α, which is downstream of the renin-angiotensin system, specifically angiotensin II, which promotes production of HIF-1α. These developments shed light to the understanding of this enigmatic condition.

Elevated Serum Levels of Alpha-Fetoprotein in Patients with Infantile Hemangioma Are Not Derived from within the Tumor

Aims

The embryonic-like stem cell origin of infantile hemangioma (IH) and the observed elevated serum levels of alpha-fetoprotein (AFP) in patients with hepatic IH led us to investigate if this tumor was the source of AFP.

Materials and methods

We measured serial serum levels of AFP in patients with problematic proliferating IH treated with surgical excision or propranolol treatment. We also investigated the expression of AFP in extrahepatic IH samples using immunohistochemical staining, mass spectrometry, NanoString gene expression analysis, and in situ hybridization.

Results

Serum levels of AFP normalized following surgical excision or propranolol treatment. Multiple regression analysis for curve fittings revealed a different curve compared to reported normal values in the general populations. AFP was not detected in any of the IH samples examined at either the transcriptional or translational levels.

Conclusion

This study demonstrates the association of proliferating IH with elevated serum levels of AFP, which normalized following surgical excision or propranolol treatment. We have shown that IH is not the direct source of AFP. An interaction between the primitive mesoderm-derived IH and the endogenous endodermal tissues, such as the liver, via an intermediary, may explain the elevated serum levels of AFP in infants with extrahepatic IH.

Characterisation of lymphocyte subpopulations in infantile haemangioma

Aims

Interstitial CD45+ cells and T lymphocytes have previously been demonstrated within infantile haemangioma (IH). This study investigated the expression of B and T lymphocyte markers by the CD45+ population, and the expression of Thy-1, a marker of thymocyte progenitors, which have the ability to give rise to both B and T cells.

Methods

Immunohistochemical (IHC) staining was performed on proliferating and involuted IHs for the expression of CD45, CD3, CD20, CD79a, Thy-1 and CD34. The presence of mRNA corresponding to CD45, CD3G, CD20 and Thy-1 was confirmed by reverse transcriptase-polymerase chain reaction in snap-frozen IH tissues. Cell counting of 3,3-diaminobenzidine IHC-stained slides was performed on CD45+ only cells and dually stained CD45+/CD3+ cells or CD45+/CD20+ cells and analysed statistically. In situ hybridisation and mass spectrometry were also performed to confirm the presence and abundance of Thy-1, respectively.

Results

IHC staining showed a subpopulation of CD45+ interstitial cells that expressed the T lymphocyte marker, CD3, and another subpopulation that expressed the B lymphocyte marker, CD20, in proliferating and diminished in involuted IHs. The abundant expression of Thy-1 on the endothelium of proliferating, but not involuted IH, was demonstrated by IHC staining and confirmed by in situ hybridisation and mass spectrometry.

Conclusions

Both B and T lymphocytes are present within the interstitium of proliferating and involuted IH. The expression of Thy-1 by the endothelium suggests that B and T cells in IH may have originated from within the lesion, rather than migrating from the peripheral circulation.

Biology of infantile hemangioma

Infantile hemangioma (IH), the most common tumor of infancy, is characterized by an initial proliferation during infancy followed by spontaneous involution over the next 5-10 years, often leaving a fibro-fatty residuum. IH is traditionally considered a tumor of the microvasculature. However, recent data show the critical role of stem cells in the biology of IH with emerging evidence suggesting an embryonic developmental anomaly due to aberrant proliferation and differentiation of a hemogenic endothelium with a neural crest phenotype that possesses the capacity for endothelial, hematopoietic, mesenchymal, and neuronal differentiation. Current evidence suggests a putative placental chorionic mesenchymal core cell embolic origin of IH during the first trimester. This review outlines the emerging role of stem cells and their interplay with the cytokine niche that promotes a post-natal environment conducive for vasculogenesis involving VEGFR-2 and its ligand VEGF-A and the IGF-2 ligand in promoting cellular proliferation, and the TRAIL-OPG anti-apoptotic pathway in preventing cellular apoptosis in IH. The discovery of the role of the renin-angiotensin system in the biology of IH provides a plausible explanation for the programed biologic behavior and the β-blocker-induced accelerated involution of this enigmatic condition. This crucially involves the vasoactive peptide, angiotensin II, that promotes cellular proliferation in IH predominantly via its action on the ATIIR2 isoform. The role of the RAS in the biology of IH is further supported by the effect of captopril, an ACE inhibitor, in inducing accelerated involution of IH. The discovery of the critical role of RAS in IH represents a novel and fascinating paradigm shift in the understanding of human development, IH, and other tumors in general.

Increased apoptosis and secretion of tryptase by mast cells in infantile haemangioma treated with propranolol

Propranolol is increasingly used to treat problematic infantile haemangioma (IH), although its molecular mechanisms remain unclear. A key feature of propranolol therapy is the decreased deposition of fibrofatty residuum compared with spontaneously involuting IH. This study investigated the molecular consequences of propranolol treatment for IH in vivo.Immunohistochemical and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining was performed on five age matched patients with proliferative IH. Two patients (A and B) were undergoing propranolol treatment at the time of surgical resection.Propranolol treatment increased apoptosis, and induced mast cells to degranulate and secrete tryptase into the interstitium. The microvessels of patient A were immature [weak von Willibrand Factor (vWF), and strong osteoprotegerin (OPG) staining], comparable to untreated proliferative IH, while those of patient B were mature (strong vWF staining, and no OPG staining). The perivascular CD90 mesenchymal stem cell population was preserved in both propranolol treated patients.Using rarely obtained biopsies from IH patients treated with propranolol, we show increased apoptosis by propranolol for the first time in vivo. We also suggest that mast cells, through secreted proteases, may contribute to the decreased fibrofatty residuum seen with propranolol treatment.

The modern primitives: applying new technological approaches to explore the biology of the earliest red blood cells

One of the most critical stages in mammalian embryogenesis is the independent production of the embryo's own circulating, functional red blood cells. Correspondingly, erythrocytes are the first cell type to become functionally mature during embryogenesis. Failure to achieve this invariably leads to in utero lethality. The recent application of technologies such as transcriptome analysis, flow cytometry, mutant embryo analysis, and transgenic fluorescent gene expression reporter systems has shed new light on the distinct erythroid lineages that arise early in development. Here, I will describe the similarities and differences between the distinct erythroid populations that must form for the embryo to survive. While much of the focus of this review will be the poorly understood primitive erythroid lineage, a discussion of other erythroid and hematopoietic lineages, as well as the cell types making up the different niches that give rise to these lineages, is essential for presenting an appropriate developmental context of these cells.

M2-polarised macrophages in infantile haemangiomas: correlation with promoted angiogenesis

AIMS

The pathogenesis of infantile haemangiomas (IHs) is still far from clear despite the fact that they are common vascular tumours distinctive for their perinatal presentation, rapid growth during the first year of life and subsequent slow involution.

AIMS

To determine the role of M2-polarised macrophages in IHs.

METHODS

M2-polarised macrophages were initially identified in 20 specimens of IHs by both immunochemistry and immunofluorescence for CD68 and CD163. The immunopositive M2-polarised macrophages in different phases of IHs were quantified, and further analysed for their correlations with the expression levels of Ki67, vascular endothelial growth factor (VEGF) and macrophage colony-stimulating factor (M-CSF).

RESULTS

The infiltrating macrophages in proliferative IHs were predominantly CD68/CD163, thus of the M2-polarised phenotype, whereas the density of these cells was significantly decreased in the involuting IHs. The high density of M2-polarised macrophages in proliferative IHs was closely correlated with overexpression of M-CSF, one of the cytokines considered to induce macrophages to polarise towards an M2 phenotype. The infiltrating M2-polarised macrophages probably contributed to the proliferation and angiogenesis of haemangioma endothelial cells, as evidenced by their close correlations with the immunoreactivities of Ki67 and VEGF.

CONCLUSIONS

Results indicate that the infiltrating M2-polarised macrophages may contribute to the progression of IHs by promoting the angiogenic process.

Mast cells in infantile haemangioma possess a primitive myeloid phenotype

AIMS

Recent reports on infantile haemangioma (IH) have demonstrated a primitive population of interstitial cells expressing the embryonic transcription factor, Nanog, with decreasing abundance during involution. In this report we investigated the expression of Nanog on mast cells in all three phases of IH progression.

METHODS

Paraffin-embedded sections of six proliferating, six involuting and six involuted IH lesions were used to investigate the expression of tryptase, Nanog, CD45, CD34 and GLUT-1 by immunostaining.

RESULTS

Mast cells, identified by their expression of tryptase, were located in the interstitium of IH lesions. 93%, 42% and 0% of these tryptase(+) cells also expressed Nanog, in proliferating, involuting and involuted IH, respectively.

CONCLUSIONS

The identification of an abundant population of tryptase(+)/Nanog(+) cells in IH is novel. The relative loss of Nanog expression as IH involutes may be a result of maturation and/or proliferation of these cells. This report supports the primitive nature of IH.

Verrucous hemangioma expresses primitive markers

BACKGROUND

Verrucous hemangioma (VH) presents clinically as a vascular malformation but has similar histopathologic features to infantile hemangioma. This study characterized the cell population within VH.

MATERIAL AND METHODS

Paraffin-embedded sections from two male patients with VH were processed for immunohistochemistry. The expression of SMA, CD34, glucose transporter-1 (Glut-1), D2-40, brachyury, angiotensin converting enzyme (ACE), Oct-4, hemoglobin ζ chain (HBZ), Wilms tumor protein (WT-1) and CD45 was examined.

RESULTS

The lymphatic marker, D2-40, was not expressed in VH, whereas Glut-1 was widely expressed in infantile hemangioma, it was only focally expressed by the endothelium of VH. The endothelium of VH expressed the primitive markers, Oct-4, brachyury and ACE. The primitive marker, WT-1, was expressed predominantly on the pericyte layer of both VH and infantile hemangioma. However, HBZ was only expressed in infantile hemangioma. CD45, a mature hematopoetic marker, was expressed by cells within the interstitium, away from the endothelium of VH and infantile hemangioma.

DISCUSSION

The expression of the primitive markers, Oct-4, brachyury and ACE on the endothelium, and WT-1 predominantly on the pericyte layer of VH shows a primitive microvascular phenotype similar to infantile hemangioma. However, the absence of the embryonic marker, HBZ, expressed only in first trimester placenta and in proliferating infantile hemangioma, suggests a different cellular origin. HBZ could be used to distinguish between the two conditions.

Treatment of infantile haemangioma with captopril

BACKGROUND

Infantile haemangioma (IH) has recently been reported as an aberrant proliferation and differentiation of a primitive mesoderm-derived haemogenic endothelium regulated by the renin-angiotensin system (RAS), leading us to propose angiotensin converting enzyme (ACE) as a potential therapeutic target.

OBJECTIVES

To present initial results of our open-labelled observational clinical trial using captopril, an ACE inhibitor (ACEi), in the treatment of problematic proliferating IH.

METHODS

After initial screening investigations, infants with problematic IH were admitted for initiation of captopril with a 0·1 mg kg(-1) test dose orally, followed by 0·15 8-hourly over 24 h. This was then followed by dose escalation to 0·3 mg kg(-1) 8-hourly for another 24 hours. The dosage was increased to 0·5 mg kg(-1) 8-hourly 1 week later, if a noticeable involution had not already occurred. The response of IH to captopril was documented clinically and photographically before and after treatment and any side-effect was recorded.

RESULTS

Two boys and six girls aged 5-22 weeks (mean 12·9) with problematic IH were recruited with the lesions located in nasal tip (n = 1), cervicofacial (n = 3), periorbital (n = 1) and perineal (n = 2) areas, and shoulder (n = 1). Transient mild renal impairment occurred in one subject but resolved spontaneously. No other complication was observed. The IHs in all patients responded to captopril at a dosage of 1·5 mg kg(-1) daily which led to a dramatic response in three, moderate response in two, and slow response in three patients. Continued involution of IHs was observed during the follow-up period of 8-19 months (mean 15·8) in all subjects. Treatment was ceased at 14 months of age in seven patients with no rebound growth. In the remaining patient, rapid healing occurred with ongoing gradual reduction in the size and colour of a large ulcerated retroauricular lesion following 5·5 months of treatment. The lesion was excised to address its persistent distortion of the ear.

CONCLUSIONS

The response of IH to an ACEi supports a critical role for the RAS in IH and represents a paradigm shift in the understanding and treatment of this enigmatic condition.

Pharmacologic therapies for infantile hemangioma: is there a rational basis?

BACKGROUND

Infantile hemangioma is the most common tumor of infancy. The majority of cases are managed conservatively, but intervention is necessary in approximately 10 percent of cases because of the threat to life or function or because of tissue distortion or destruction. The mainstay treatment for these problematic proliferating infantile hemangiomas is pharmacologic therapy, mostly discovered serendipitously.

METHODS

This review examines the rational basis of the hitherto empirical pharmacologic therapies for the enigmatic infantile hemangioma, in light of new knowledge regarding its biology, including the critical roles of stem cells and the renin-angiotensin system.

RESULTS

Steroids have remained the first-line therapy for problematic infantile hemangioma for over 40 years despite their known side effects and failure rates. Vincristine has emerged as an alternative to interferon for steroid-resistant cases because of interferon's adverse effects, especially neurotoxicity. β-Blockers are now the preferred first-line therapy for problematic cases. There is increasing evidence that infantile hemangioma is a disorder of aberrant proliferation and differentiation of primitive mesoderm-derived neural crest phenotypic cells. This primitive phenotype that gives rise to a hemogenic endothelium intermediate has the ability to undergo primitive erythropoiesis and terminal mesenchymal differentiation.

CONCLUSIONS

The recent discovery of the crucial role of stem cells and the inferred role of the renin-angiotensin system in the biology of infantile hemangioma underscores the possibility of even more targeted therapies, by using modulators of the renin-angiotensin system, on infantile hemangioma. The observation of the potential role of these traditional antihypertensive agents in stem cell biology may lead to better understanding of developmental biology and tumor stem cell growth.

A placental chorionic villous mesenchymal core cellular origin for infantile haemangioma

Aims

To investigate the expression of the placental cell-specific associated proteins in infantile haemangioma (IH).

Methods

Immunohistochemical staining was used to investigate the expression of human chorionic gonadotrophin (hCG), human placental lactogen (hPL), human leucocyte antigen-G (HLA-G), cytokeratin 7 (CK7) and smooth muscle actin in paraffin-embedded sections of proliferating and involuted IHs.

Results

The proteins hCG and hPL were expressed by the endothelium but not the pericyte layer of proliferating IH, but these proteins were not detected in involuted lesions. There was no expression of CK7 and HLA-G in IH.

Conclusions

The expression of hCG and hPL, but not CK7 or HLA-G, by the endothelium of proliferating IH supports a placental chorionic villous mesenchymal core cellular origin for IH rather than a trophoblast origin.