Smith James R, Swift J Alan
Scanning Probe Microscopy Laboratory, School of Pharmacy and Biomedical Sciences, University of Portsmouth, St. Michael's Building, White Swan Road, Portsmouth PO1 2DT, UK.
Micron. 2005;36(3):261-6. doi: 10.1016/j.micron.2004.11.004. Epub 2005 Jan 25.
18-Methyleicosanoic acid (18-MEA) is thought to be covalently bound to the outer surface of human hair and is a major component of the outer beta-layer of the cuticular cell membrane complex (CCMC). Cuticular delamination, whether this occurs between the outer beta- and delta-layers or within the plane of the beta-layer, results in a fresh layer of 18-MEA being exposed at the newly-revealed surface. Hair from patients with Maple Syrup Urine Disease (MSUD), however, does not contain 18-MEA and here, we report on the importance this unusual fatty acid in cuticular delamination. Hair fibres were collected from 10 patients with classic (type 1A) MSUD from a Mennonite community in Pennsylvania, USA. Included amongst these were hairs from dizygotic twins (A1 and A2), one of whom had MSUD, and the other did not; it was unknown at the beginning of the study which twin had MSUD. The outer surfaces were examined using atomic force microscopy (AFM) and transverse sections imaged using transmission electron microscopy (TEM). The newly revealed intercellular surface regions from twin A2 were found to be significantly rougher than those from twin A1. TEM studies showed the trilamellar CCMC to be continuous for twin A1, but possessed discontinuities of variable length (100-1000 nm) for twin A2. In contrast with other work, TEM showed no specific defects in the outer beta-layer. The outer cuticular surfaces for most MSUD patients showed a great abundance of residual endocuticle, although in other cases this was less pronounced. These differences may be explained by some residual activity of the branched-chain alpha-ketoacid (BCKD) dehydrogenase. Cuticular delamination in MSUD-hair probably still occurs within the general plane of the CCMC, although fracture through discontinuities of this layer results in zones of endocuticle being exposed at the new surface.
18-甲基二十烷酸（18-MEA）被认为共价结合于人发的外表面，是表皮细胞膜复合体（CCMC）外β层的主要成分。角质层分层，无论是发生在外β层和δ层之间还是在β层平面内，都会导致新暴露的表面出现一层新的18-MEA。然而，枫糖尿症（MSUD）患者的头发不含18-MEA，在此，我们报告这种不寻常的脂肪酸在角质层分层中的重要性。从美国宾夕法尼亚州一个门诺派社区的10例经典（1A型）MSUD患者中收集毛发纤维。其中包括异卵双胞胎（A1和A2）的毛发，其中一人患有MSUD，另一人没有；在研究开始时，不知道哪个双胞胎患有MSUD。使用原子力显微镜（AFM）检查外表面，并使用透射电子显微镜（TEM）对横切面进行成像。发现双胞胎A2新暴露的细胞间表面区域比双胞胎A1的明显更粗糙。TEM研究表明，双胞胎A1的三层CCMC是连续的，但双胞胎A2的CCMC具有可变长度（100-1000 nm）的不连续处。与其他研究不同，TEM显示外β层没有特定缺陷。大多数MSUD患者的角质层外表面显示有大量残留的内角质层，尽管在其他情况下不太明显。这些差异可能由支链α-酮酸（BCKD）脱氢酶的一些残留活性来解释。MSUD毛发中的角质层分层可能仍发生在CCMC的总体平面内，尽管通过该层的不连续处断裂会导致内角质层区域暴露在新表面。
