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Pathogenesis of permeability barrier abnormalities in the ichthyoses: inherited disorders of lipid metabolism.

ABSTRACT: Many of the ichthyoses are associated with inherited disorders of lipid metabolism. These disorders have provided unique models to dissect physiologic processes in normal epidermis and the pathophysiology of more common scaling conditions. In most of these disorders, a permeability barrier abnormality "drives" pathophysiology through stimulation of epidermal hyperplasia. Among primary abnormalities of nonpolar lipid metabolism, triglyceride accumulation in neutral lipid storage disease as a result of a lipase mutation provokes a barrier abnormality via lamellar/nonlamellar phase separation within the extracellular matrix of the stratum corneum (SC). Similar mechanisms account for the barrier abnormalities (and subsequent ichthyosis) in inherited disorders of polar lipid metabolism. For example, in recessive X-linked ichthyosis (RXLI), cholesterol sulfate (CSO(4)) accumulation also produces a permeability barrier defect through lamellar/nonlamellar phase separation. However, in RXLI, the desquamation abnormality is in part attributable to the plurifunctional roles of CSO(4) as a regulator of both epidermal differentiation and corneodesmosome degradation. Phase separation also occurs in type II Gaucher disease (GD; from accumulation of glucosylceramides as a result of to beta-glucocerebrosidase deficiency). Finally, failure to assemble both lipids and desquamatory enzymes into nascent epidermal lamellar bodies (LBs) accounts for both the permeability barrier and desquamation abnormalities in Harlequin ichthyosis (HI). The barrier abnormality provokes the clinical phenotype in these disorders not only by stimulating epidermal proliferation, but also by inducing inflammation.

SUBMITTER: Elias PM

PROVIDER: S-EPMC2844331 | biostudies-literature | 2008 Apr

REPOSITORIES: biostudies-literature

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Pathogenesis of permeability barrier abnormalities in the ichthyoses: inherited disorders of lipid metabolism.

Elias Peter M PM Williams Mary L ML Holleran Walter M WM Jiang Yan J YJ Schmuth Matthias M

Journal of lipid research 20080202 4

Many of the ichthyoses are associated with inherited disorders of lipid metabolism. These disorders have provided unique models to dissect physiologic processes in normal epidermis and the pathophysiology of more common scaling conditions. In most of these disorders, a permeability barrier abnormality "drives" pathophysiology through stimulation of epidermal hyperplasia. Among primary abnormalities of nonpolar lipid metabolism, triglyceride accumulation in neutral lipid storage disease as a resu ...[more]

PMID: 18245815

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Project description:Disruption of the blood-brain barrier has been proposed to be important in vascular cognitive impairment. Increased cerebrospinal fluid albumin and contrast-enhanced MRI provide supporting evidence, but quantification of the blood-brain barrier permeability in patients with vascular cognitive impairment is lacking. Therefore, we acquired dynamic contrast-enhanced MRI to quantify blood-brain barrier permeability in vascular cognitive impairment. Method- We studied 60 patients with suspected vascular cognitive impairment. They had neurological and neuropsychological testing, permeability measurements with dynamic contrast-enhanced MRI, and lumbar puncture to measure albumin index. Patients were separated clinically into subcortical ischemic vascular disease (SIVD), multiple and lacunar infarcts, and leukoaraiosis. Twenty volunteers were controls for the dynamic contrast-enhanced MRI studies, and control cerebrospinal fluid was obtained from 20 individuals undergoing spinal anesthesia for nonneurological problems.Thirty-six patients were classified as SIVD, 8 as multiple and lacunar infarcts, and 9 as leukoaraiosis. The albumin index was significantly increased in the SIVD group compared with 20 control subjects. Permeabilities for the patients with vascular cognitive impairment measured by dynamic contrast-enhanced MRI were significantly increased over control subjects (P<0.05). Patient age did not correlate with either the blood-brain barrier permeability or albumin index. Highest albumin index values were seen in the SIVD group (P<0.05) and were significantly increased over multiple and lacunar infarcts. K(i) values were elevated over control subjects in SIVD but were similar to multiple and lacunar infarcts.There was abnormal permeability in white matter in patients with SIVD as shown by dynamic contrast-enhanced MRI and albumin index. Future studies will be needed to determine the relationship of blood-brain barrier damage and development of white matter hyperintensities.

Project description:Ichthyoses, including inherited disorders of lipid metabolism, display a permeability barrier abnormality in which the severity of the clinical phenotype parallels the prominence of the barrier defect. The pathogenesis of the cutaneous phenotype represents the consequences of the mutation for epidermal function, coupled with a "best attempt" by affected epidermis to generate a competent barrier in a terrestrial environment. A compromised barrier in normal epidermis triggers a vigorous set of metabolic responses that rapidly normalizes function, but ichthyotic epidermis, which is inherently compromised, only partially succeeds in this effort. Unraveling mechanisms that account for barrier dysfunction in the ichthyoses has identified multiple, subcellular, and biochemical processes that contribute to the clinical phenotype. Current treatment of the ichthyoses remains largely symptomatic: directed toward reducing scale or corrective gene therapy. Reducing scale is often minimally effective. Gene therapy is impeded by multiple pitfalls, including difficulties in transcutaneous drug delivery, high costs, and discomfort of injections. We have begun to use information about disease pathogenesis to identify novel, pathogenesis-based therapeutic strategies for the ichthyoses. The clinical phenotype often reflects not only a deficiency of pathway end product due to reduced-function mutations in key synthetic enzymes but often also accumulation of proximal, potentially toxic metabolites. As a result, depending upon the identified pathomechanism(s) for each disorder, the accompanying ichthyosis can be treated by topical provision of pathway product (eg, cholesterol), with or without a proximal enzyme inhibitor (eg, simvastatin), to block metabolite production. Among the disorders of distal cholesterol metabolism, the cutaneous phenotype in Congenital Hemidysplasia with Ichthyosiform Erythroderma and Limb Defects (CHILD syndrome) and X-linked ichthyosis reflect metabolite accumulation and deficiency of pathway product (ie, cholesterol). We validated this therapeutic approach in two CHILD syndrome patients who failed to improve with topical cholesterol alone, but cleared with dual treatment with cholesterol plus lovastatin. In theory, the ichthyoses in other inherited lipid metabolic disorders could be treated analogously. This pathogenesis (pathway)-driven approach possesses several inherent advantages: (1) it is mechanism-specific for each disorder; (2) it is inherently safe, because natural lipids and/or approved drugs often are utilized; and (3) it should be inexpensive, and therefore it could be used widely in the developing world.

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Pathogenesis of permeability barrier abnormalities in the ichthyoses: inherited disorders of lipid metabolism.

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Pathogenesis of permeability barrier abnormalities in the ichthyoses: inherited disorders of lipid metabolism.

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