Tenascin-C在瘢痕疙瘩和增生性瘢痕中的基因表达研究

目的 探讨Tenascin-C基因在瘢痕疙瘩和增生性瘢痕中的表达。方法 取正常成人皮肤组织RNA，构建正义、反义Tenascin-C(Tn-C)mRNA探针，运用原位杂交技术，观测10例瘢痕疙瘩、10例增生性瘢痕和5例正常成人皮肤组织中Tn-C mRNA的表达。结果 Tn-C mRNA在正常皮肤表皮中无表达，真皮中表达稀少，局限于乳头真皮层的成纤维细胞和皮肤附属器；10例瘢痕疙瘩表皮均有表达，真皮分布较广，如成纤维细胞、血管内皮和皮肤附属器；Tn-C mRNA在3例增生性瘢痕表皮表达，7例无表达，真皮中表达与瘢痕疙瘩相同但较弱，比正常皮肤增多，但差异无显著性。结论 Tenascin-C mRNA在瘢痕疙瘩表皮和真皮中有高表达。     

Keloids and Hypertrophic Scars

BACKGROUND: Keloids and hypertrophic scars are benign fibrous growths that occur after trauma or wounding of the skin and present a major therapeutic dilemma to the dermatologist because of frequent recurrences. OBJECTIVE: The purpose of this study is to review the pertinent literature and provide updated information on keloids and hypertrophic scars that will enable the physician to better understand and treat these lesions. METHODS: A Medline literature search was performed for relevant publications. RESULTS: Traditional treatment methods which have been effective include a combination of surgery with intralesional steroids and/or radiotherapy, silicone gel sheeting, pressure, and cryotherapy. Recently newer modalities shown to be effective include pulsed dye laser, interferon alfa-2b, and cultured epithelial autografts. CONCLUSION: Keloids and hypertrophic scars present a major therapeutic dilemma to the dermatologist because of frequent recurrences. A better understanding of keloid pathogenesis may lead to improved therapies by which keloid growth and regrowth may be obviated. Although optimal treatment for keloids remains undefined, successful treatment can be obtained through a multimodality approach. Regardless of the technique employed, an observation period of at least 2 years is necessary to rule out recurrence.     

瘢痕疙瘩和增殖性瘢痕的超微结构观察

对１４例瘢痕疙瘩和７例增殖性瘢痕的超微结构进行了观察分析。该两种病变均可见到不同时期的成纤维细胞、巨噬细胞和疏密不等的胶原微纤维以及呈不同闭塞状态的微血管。多数成纤维细胞功能很活跃，胞浆内充满了大量扩张的粗面内质网和发达的高尔基复合体，胶原微纤维排列紊乱。但在瘢痕疙瘩中还常见到肌纤维母细胞。其胞质中除了粗面内质网和高尔基复合体以外，还可见大量的肌微丝、密体、密斑以及不完整的基板。该特征拟作鉴别瘢痕疙瘩和增殖性瘢痕的依据。     

细胞信号传导在激素和干扰素诱导的增殖瘢痕成纤维细胞凋亡中的作用

目的 探讨对瘢痕疙瘩和增生性瘢痕成纤维细胞在激素和干扰素α-2b(IFNα-2b)作用后是否产生凋亡,以及相关细胞信号传导通路的激活或抑制是否一致.方法 对6例瘢痕疙瘩、增生性瘢痕及6例皮肤标本,采用细胞培养、免疫组织化学、凝胶电泳及FACE ELISA方法通过检测Bax和Bcl-2蛋白表达、特异性DNA梯状条带以及激活(磷酸化)的ERK1/2和JNK的吸光度A值,对不同成纤维细胞在地塞米松(0.1 mg/ml)和干扰素α-2b(1000U/ml)作用后的细胞凋亡及相关细胞信号传导通路进行了研究.结果 地塞米松可通过激活ERK1/2和JNK细胞传导通路诱导三类不同来源成纤维细胞发生细胞凋亡;干扰素α-2b不能诱导这三类不同来源成纤维细胞发生明显细胞凋亡,且IFN α-2b抑制增殖瘢痕的ERK1/2通路,而对JNK通路无影响,其不引起正常皮肤成纤维细胞ERK1/2和JNK通路的变化.结论 激素类药物和干扰素α-2b对瘢痕疙瘩、增生性瘢痕和正常皮肤成纤维细胞的作用机制不同.     

Decreased expression of inhibitory SMAD6 and SMAD7 in keloid scarring.

Keloids are benign skin tumours occurring during wound healing in genetically predisposed patients. They are characterised by an abnormal deposition of extracellular matrix components, in particular collagen. There is evidence that transforming growth factor-beta (TGFbeta) is involved in keloid formation. SMAD proteins play a crucial role in TGFbeta signaling and in terminating the TGFbeta signal by a negative feedback loop through SMAD6 and 7. It is unclear how TGFbeta signaling is connected to the pathogenesis of keloids. Therefore, we investigated the expression of SMAD mRNA and proteins in keloids, in normal skin and in normal scars. Dermal fibroblasts were obtained from punch-biopsies of keloids, normal scars and normal skin. Cells were stimulated with TGFbeta1 and the expression of SMAD2, 3, 4, 6 and 7 mRNA was analysed by real time RT-PCR. Protein expression was determined by Western blot analysis. Our data demonstrate a decreased mRNA expression of the inhibitory SMAD6 and 7 in keloid fibroblasts as compared to normal scar (p<0.01) and normal skin fibroblasts (p<0.05). SMAD3 mRNA was found to be lower in keloids (p<0.01) and in normal scar fibroblasts (p<0.001) compared to normal skin fibroblasts. Our data showed for the first time a decreased expression of the inhibitory SMAD6 and SMAD7 in keloid fibroblasts. This could explain why TGFbeta signaling is not terminated in keloids leading to overexpression of extracellularmatrix in keloids. These data support a possible role of SMAD6 and 7 in the pathogenesis of keloids.     

Fibronectin gene expression differs in normal and abnormal human wound healing

The overproduction of fibronectin and type I collagen in keloids and hypertrophic scars implicates altered regulation of extracellular matrix components as an important aspect of these wound healing pathologies. However, little is known about the similarities and differences in extracellular matrix gene expression during normal and abnormal wound healing. This study compared the content of fibronectin messenger RNA and rates of fibronectin protein biosynthesis in fibroblasts derived from normal skin, normal scar, keloid, and hypertrophic scar. Fibronectin expression was enhanced in cells from both normal and abnormal wounds relative to cells from quiescent normal skin. Matched pairs of normal and keloid fibroblasts from the same individuals were also compared, and three of the four pairs showed higher fibronectin expression by the keloid cells at the levels of messenger RNA and protein synthesis. This was consistent with previous studies showing elevated steady state content of fibronectin in keloid cells relative to normal cells from the same individual. Fibronectin messenger RNA and protein content in the tissues from which these cells were derived was examined by in situ hybridization and immunohistochemistry. These studies revealed that in vivo, the steady state content of fibronectin messenger RNA and protein was highest in abnormal wounds, less in most normal scars, and lowest in normal skin. Thus, fibroblasts from keloids and hypertrophic scars overexpressed fibronectin in vivo relative to normal skin and normal scar and retain this characteristic in vitro relative to normal skin. Although normal scars contained little fibronectin protein and messenger RNA, cultured fibroblasts derived from these scars had contents of fibronectin messenger RNA and rates of biosynthesis in vitro similar to those of keloid fibroblasts. This indicates that the fibronectin regulatory pathway in scar fibroblasts is influenced by the tissue environment. These results are discussed with respect to the relationship of fibronectin expression in keloids, hypertrophic scars, and normal wounds in human beings.     

Study of microvascular structure in keloid and hypertrophic scars: density of microvessels and the efficacy of three-dimensional vascular imaging

We have investigated the blood vessels in keloids and hypertrophic scars, both morphologically and statistically. We also tried to construct three-dimensional images of blood vessels in a keloid and hypertrophic scar to clarify the vascular patterns. Keloids (n = 16) and hypertrophic scars (n = 12) were stained with haematoxylin and eosin, and immunostained with anti-CD31 antibody. The capillary density (number/1.0 mm(2)) and length of the major and minor axes were measured, and the major:minor axis ratio was calculated. Eighty serial sections were prepared from the preparations. Using image preparation software (Realia, INTAGE), the 80 input images were superimposed to construct a three-dimensional image of blood vessels in the tissue. We initially succeeded in constructing three-dimensional images of blood vessels in a keloid and hypertrophic scar. By statistical analysis of the vascular density and morphology, we clarified that there were fewer capillaries in keloids than in hypertrophic scars (p < 0.01), and that the vascular lumen was flattened. Capillaries in the central region of keloids tended to flat, compared with those in the marginal region. Three-dimensional images suggested that there was no microvascular communication in keloids; there was also an inadequate blood supply in keloid tissue. These findings may be a result of the growth of collagen and fibroblasts with keloid maturation.     

病理性瘢痕中原癌基因c-myc和c-fos的表达

目的　探讨原癌基因的表达与病理性瘢痕形成的相关性。方法　应用免疫组化SP法 ,检测c -myc和c -fos蛋白在增生性瘢痕、瘢痕疙瘩和正常皮肤组织中的表达和分布 ,并用图像定量分析比较其差异。结果　在增生性瘢痕和瘢痕疙瘩的成纤维细胞中c-myc、c -fos呈强阳性表达 ,两组间无明显差异 ,而与正常皮肤对照组均有显著性差异。结论　增生性瘢痕与瘢痕疙瘩中c -myc、c -fos蛋白表达升高 ,存在c -myc和c -fos原癌基因的激活 ,可能参与了成纤维细胞的分化增殖或表型转化、胶原合成与降解以及对细胞因子的调控 ,并导致瘢痕增生。     

Study of microvascular structure in keloid and hypertrophic scars: Density of microvessels and the efficacy of three-dimensional vascular imaging

Abstract

We have investigated the blood vessels in keloids and hypertrophic scars, both morphologically and statistically. We also tried to construct three-dimensional images of blood vessels in a keloid and hypertrophic scar to clarify the vascular patterns. Keloids (n = 16) and hypertrophic scars (n = 12) were stained with haematoxylin and eosin, and immunostained with anti-CD31 antibody. The capillary density (number/1.0 mm²) and length of the major and minor axes were measured, and the major:minor axis ratio was calculated. Eighty serial sections were prepared from the preparations. Using image preparation software (Realia, INTAGE), the 80 input images were superimposed to construct a three-dimensional image of blood vessels in the tissue. We initially succeeded in constructing three-dimensional images of blood vessels in a keloid and hypertrophic scar. By statistical analysis of the vascular density and morphology, we clarified that there were fewer capillaries in keloids than in hypertrophic scars (p < 0.01), and that the vascular lumen was flattened. Capillaries in the central region of keloids tended to flat, compared with those in the marginal region. Three-dimensional images suggested that there was no microvascular communication in keloids; there was also an inadequate blood supply in keloid tissue. These findings may be a result of the growth of collagen and fibroblasts with keloid maturation.     

病理性瘢痕中c-fos原癌基因的表达

目的　病理性瘢痕是创伤过度愈合的结果,以成纤维细胞的异常增殖、合成及分泌大量胶原和细胞外基质为特征,其形成机理仍不清楚。探讨原癌基因c-fos的表达与病理性瘢痕形成的相关性。方法　应用免疫组化SP法,检测c-fos蛋白在增生性瘢痕、瘢痕疙瘩及正常皮肤组织中的表达和分布,并用图像定量分析比较其差异。结果　在增生性瘢痕和瘢痕疙瘩的成纤维细胞中c-fos呈强阳性表达,两组间无明显差异,而与正常皮肤对照组均有显著性差异。结论　增生性瘢痕与瘢痕疙瘩中c-fos蛋白表达升高,存在c-fos癌基因的激活,可能参与了成纤维细胞的分化增殖、胶原合成与降解以及对细胞因子的调控,并导致瘢痕增生。     

病理性瘢痕中c-fos原癌基因的表达

目的　病理性瘢痕是创伤过度愈合的结果 ,以成纤维细胞的异常增殖、合成及分泌大量胶原和细胞外基质为特征 ,其形成机理仍不清楚。探讨原癌基因c -fos的表达与病理性瘢痕形成的相关性。方法　应用免疫组化SP法 ,检测c -fos蛋白在增生性瘢痕、瘢痕疙瘩及正常皮肤组织中的表达和分布 ,并用图像定量分析比较其差异。结果　在增生性瘢痕和瘢痕疙瘩的成纤维细胞中c-fos呈强阳性表达 ,两组间无明显差异 ,而与正常皮肤对照组均有显著性差异。结论　增生性瘢痕与瘢痕疙瘩中c -fos蛋白表达升高 ,存在c -fos癌基因的激活 ,可能参与了成纤维细胞的分化增殖、胶原合成与降解以及对细胞因子的调控 ,并导致瘢痕增生     

病理性瘢痕中c-myc、c-fos和ras原癌基因表达的实验研究

目的 探讨原癌基因的表达与病理性瘢痕形成的相关性。方法 应用免疫组化SP法及图像定量分析，检测c-myc、c-fos和ras p21蛋白在增生性瘢痕、瘢痕疙瘩和正常皮肤组织中的表达，结果 在增生性瘢痕和瘢痕疙瘩的成纤维细胞中c-myc和c-fos呈强阳性表达，而ras p21蛋白在病理性瘢痕的成纤维细胞中缺乏表达。结论 ①病理性瘢痕中c-myc和c-fos癌基因受激活，可能参与了成纤维细胞的分化增殖、胶原合成与降解以及对细胞因子的调控，并导致瘢痕增生。②ras癌基因在病理性瘢痕形成中可能不突变或不起主要作用。③病理性瘢痕只是部分原癌基因的有限制性表达，不存在多基因无限制性的共同表达可能是其较少癌变的原因。     

Effects of steroids,interferon-2B,or interluekin 1B on apoptosis of fibroblasts from keloid,hypertrophic scars,and normal skin and related signal pathway

Wound healing can lead to hypertrophic scar or keloid formation, characterized by an overabundant extracellular matrix. Current established treatment strategies include surgical resection, triamcinolone steroid injection, pressure therapy, silicone therapy, radiotherapy, etc. Cytokines also play a critical role in the regulation of cellular activities and extracellular matrix metabolism. Interferons (IFN) represent a group of antifibroproliferative agents that inhibit fibroblast proliferation and collagen production, and interleukin (IL)-1β also accelerates hypertrophic scar fibroblasts to produce collagenolytic enzymes, leading to tissue destruction. This study addressed the effects of steroid, IFN α-2b, or IL-1β on apoptosis and cell pathway of fibroblasts from keloids, hypertrophic scars, and normal skins and different responses of different fibroblasts. Six samples of keloid, six samples of hypertrophic scar, and six samples of normal skin were, respectively, collected from patients, and fibroblasts from different sources were cultured in vitro. After different fibroblasts were treated with dexamethasone (0.1 mg/ml) or IFN α-2b (1,000 μ/ml) or IL-1β (200 μ/ml), Bax and Bcl-2 were detected in situ by immunohistochemical staining; deoxyribonucleic acid ladders of different fibroblasts were observed by gel electrophoresis, and relative activated (phospho-) extracellular-signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK) pathways were detected by the method of fast activated cell-based enzyme-linked immunosorbent assay. In media containing dexamethasone, apoptosis took place in fibroblasts from keloids, hypertrophic scars, and normal skins by gel electrophoresis with increased rate of Bax/Bcl-2. Activated (phospho-) ERK1/2 and activated (phospho-) JNK expressions increased in three different fibroblasts. In media containing IFN α-2b, no apoptosis took place in three different fibroblasts without any change of expressions of Bax and Bcl-2 except for the expression of decreased Bcl-2 in fibroblasts from keloids. Activated (phospho-) ERK1/2 expression decreased in fibroblasts from keloid and hypertrophic scars without any changes of activated (phospho-) JNK expression, and IFN α-2b did not affect both activated (phospho-) ERK1/2 and activated (phospho-) JNK expressions in fibroblasts from normal skin. In media containing IL-1β, apoptosis of fibroblasts from keloids was induced by stimulating activated (phospho-) ERK1/2 and activated (phospho-) JNK pathways; IL-1β could not induce apoptosis of fibroblasts from normal skin (radio of Bax/Bcl-2 decreasing) whose activated (phospho-) ERK1/2 pathway was stimulated without any changes of activated (phospho-) JNK expression. Apoptosis in fibroblasts from hypertrophic scars was induced by activating the JNK pathway and prohibiting the ERK1/2 pathway. The effects of steroid, IFN α-2b, or IL-1β on apoptosis of different fibroblasts were different through different cell signal pathways, although all of them were effective for treatment of abnormal scars.     

Involvement of KGF in the Wound Healing Process of Tracheal Cartilage in Rat Longitudinal Tracheotomy Model

Aim:  To investigate the expression of human HtrA1 in keloid lesions, and to clarify a possible role of human HtrA1 in keloid pathogenesis.
Methods:  Total RNA was isolated from six keloids and two normal skins by single‐step method. The expression level of human HtrA1 was examined by using Northern blot analysis. Keloid and normal skin tissue samples were fixed in paraformaldehyde, and paraffin sections were obtained. Immunohistochemical analysis was performed with anti‐human HtrA1 polyclonal antibody.
Results:  The mRNA level of human HtrA1 was markedly elevated in keloid samples, compared with normal skin. Using immunohistochemical analysis, fibroblast‐like cells abundantly found in the margin of keloid lesions, were stained with anti‐human HtrA1 antibody. No human HtrA1 staining of fibroblasts in normal skin was observed. Interestingly, no significant staining was detected in hypertrophyic scar lesions, which is a similar dermal disease to keloid.
Conclusion:  Human HtrA1 expression was found to be up‐regulated in keloid lesions, especially in their margin, compared to normal skins and hypertrophic scars. Our data suggest that human HtrA1 could play a critical role in an expression of keloid specific phenotype and in the development of keloid lesions.     

A new surgical treatment of keloid: keloid core excision

Keloids and hypertrophic scars result from excessive collagen deposition, the cause of which is not yet known. Unlike hypertrophic scars, keloids frequently persist at the site of injury, often recur after excision and always overgrow the boundaries of the original wound. There have been many trials to control keloids, but most of them have been unsuccessful. The authors propose a new surgical technique to treat keloids and name it keloid core extirpation. They excise the inner fibrous core from the keloid and cover the defect with a keloid rind flap, which is arterialized by the subcapsular vascular plexus. The authors treated 24 keloids of the ear, trunk, face, and genitalia with keloid core excision. Four cases of partial rind flap congestion or necrosis occurred. Those patients who healed primarily after surgery showed no evidence of keloid recurrence as long as they were followed. The authors have found the keloid core extirpation technique to be excellent in preventing keloid recurrence, with no adjuvant therapy after surgery.     

Gene expression patterns in isolated keloid fibroblasts

Keloid scars after skin trauma are a significant clinical problem, especially in black populations, in which the incidence of keloids has been estimated at 4-16%. Keloids are abnormal dermal proliferative scars secondary to dysregulated wound healing. Despite several biochemical studies on the role of extracellular matrix proteins and growth factors during keloid formation, we still do not know what molecules and signals induce this change. Fibroblasts are thought to be the major inductive cell for keloid scar formation. The aim of this study was to identify gene expression patterns that characterize keloid fibroblasts; identifying such genetic disequilibrium may shed light on the molecular signaling events responsible for keloid formation. In this study, we performed gene expression analysis of fibroblasts isolated from keloid lesions from three individuals in comparison with the fibroblasts isolated from normal skin using the Affymetrix U133a chip (22,284 genes and expression sequence tags). We found through J5 test score expression analysis that among 22,284 genes, there were 43 genes that were overexpressed and five genes were underexpressed in keloid fibroblasts when compared with dermal fibroblasts from persons without keloids. The overexpression of three genes not previously reported as being up-regulated in keloids (annexin A2, Transgelin, and RPS18) was confirmed by real-time polymerase chain reaction. Certain overexpressed genes were similar to previous biochemical observations on the protein levels of these overexpressed genes during keloid formation. We also report for the first time that a few tumor-related genes are overexpressed in keloid fibroblasts.     

Fibrillin-1 and elastin are differentially expressed in hypertrophic scars and keloids.

Hypertrophic scars and keloids are two forms of excessive cutaneous scarring. Considering the importance of extracellular matrix elements in tissue repair, a morphological and quantitative analysis of the elastic system components (fibrillin-1 and elastin) was performed in normal skin, normal scars, hypertrophic scars, and keloids. In superficial and deep dermis, fibrillin-1 volume density was significantly higher in normal skin compared with normal scars, hypertrophic scars, and keloids. The fibrillin-1 volume density did not show differences between hypertrophic scars and keloids in superficial or deep dermis. In superficial dermis, elastin volume density was higher in normal skin compared with normal scars, hypertrophic scars, and keloids. In deep dermis, the elastin volume density was higher in keloids compared with normal skins, normal scars, and hypertrophic scars. We showed that the distribution of fibrillin-1 and elastin is disrupted in all kinds of scars analyzed, but there are two patterns: one for normal scars and another for excessive scars.     

p53 and apoptosis alterations in keloids and keloid fibroblasts

Keloids are the result of a dysregulated wound-healing process and are characterized by formation of excess scar tissue that proliferates beyond the boundaries of the inciting wound. In this study, we investigated the expression of key proteins involved in regulating apoptosis in keloids. Twenty archival paraffin-embedded keloid samples were randomly selected for an immunoperoxidase assay with antibodies against fas, p53, bcl-2, and bcl-x proteins using the target antigen-retrieval technique. Apoptosis was assessed in keloids and normal skin and in keloid and normal fibroblasts by the TdT-mediated dUTP nick-end labeling (tunel) assay on tissue sections, fibroblast cultures, and by flow cytometry for cell suspensions. We found that 18 of 20 keloids expressed p53 protein; bcl-2 was expressed by keloid fibroblasts in 19 of 20 keloids, and all specimens had prominent fas expression throughout the tissue. The distribution of these three antigens was regional within each lesion and followed a consistent pattern of p53 and bcl-2 expression colocalized to the hypercellular, peripheral areas of each keloid in a perinuclear pattern (p < .001). In contrast, an inverse distribution of fas expression was shown, with staining being more diffuse across the cell surfaces and limited to the central, more hypocellular regions in 16 of 17 keloids (p < .001). There was no specific staining pattern in these keloids with antihuman bcl-x. In vitro studies on cultured keloid fibroblasts (derived from six patients) revealed maintenance of the p53+, bcl-2+ phenotype up to passage 10. Neither neonatal nor normal adult skin fibroblasts expressed either antigen but could be induced to express p53 by exposure to adriamycin. Keloid lesions and keloid fibroblasts were found to have lower rates of apoptosis than normal controls. Keloid fibroblasts displayed enhanced apoptosis rates in response to hydrocortisone, γ interferon and hypoxia treatment as compared with normal adult fibroblasts. Focal dysregulation of p53 combined with upregulation of bcl-2 may help produce a combination of increased cell proliferation and decreased cell death in the younger hypercellular areas of the keloid. This phenotype is reversed in the older areas of the keloid and may prevent malignan degeneration, thus favoring normal apoptosis as evidenced by prominent fas expression.     

Keloids and Hypertrophic Scars: Are They Two Different Sides of the Same Coin?

Keloids and hypertrophic scars are different forms of excessive dermal fibrosis thought to be caused by regulation of cellularity increase and decrease during the wound-healing process in predisposed individuals. Differences between keloids and hypertrophic scars include distinct clinical features, histologic evidence, and cellular function in response to molecular events. Keloids and hypertrophic scars are the results of increased fibroblast density and extracellular matrix substances. Interactions between epidermal keratinocytes and dermal fibroblasts play an important role in regulating tissue homeostasis and processing scar formation. Keloids and hypertrophic scars are the two different stages of the same process that is based on separate clinical and histochemical entities. The aim of this review is to provide updated information regarding similarities and differences between keloids and hypertrophic scars as two different sides of the same coin. This article will also enable the dermatologist to better understand fundamental biology of the scarring.     

The effect of the anti-allergic agent avil on abnormal scar fibroblasts.

Abnormal wound healing in humans leads to the formation of hypertrophic scar and keloids. These abnormal scars accumulate excessive extracellular matrix proteins through increased synthesis as well as decreased degradation. In order to find a therapeutic control for scar formation, we investigated the effect of avil (pheniramine maleate) on fibroblasts cultured from abnormal scars in comparison to normal skin. We observed a decrease in the proliferation rate in cells from normal skin (39%), hypertrophic scar (44%), keloid (63%) and in DNA synthesis in cells from normal skin (50%), hypertrophic scar (55%) and keloid (63%) treated with 8 mM avil (72 h). The rate of decrease in collagen synthesis in normal skin (44%), hypertrophic scar (74%) and keloid fibroblast (73%) correlated with changes in DNA synthesis.