Pharmacokinetics, biological effects, and distribution of (1-->3)-beta-D-glucan in blood and organs in rabbits

The pharmacokinetics, biological effects and distribution in blood and organs of 125I-labeled (1→3)-β-D-glucan purified from Candida albicans were analyzed in rabbits during the 24-h period following an intravenous administration.The intravascular half-life of (1→3)-β- D-glucan was 1.8 min in the low-dose group (9.3 μg/kg) and 1.4 min in the high-dose group (222 μg/kg), and the mean (±SD) total body clearance was 1.12 ± 0.30 and 1.17 ± 0.16 ml/min, respectively. The rabbits remained well and (1→3)-β-D-glucan failed to alter blood cell counts. Less than 3% of the ¹²⁵I-(1→3)-β-D-glucan was initially associated with the cellular compartment, and this value decreased further during the 2-h period following administration (P = 0.0001). Over 97% of ¹²⁵I-(1→3)-β-D-glucan was associated with cell-free plasma, and the majority in plasma appeared to be present in the unbound form (not associated with lipoproteins or plasma proteins). The liver contained more than 80% of the ¹²⁵I-(1→3)-β-D-glucan detected in the six major organs analyzed.

Decreased cutaneous resonance running time in cured leprosy subjects

BACKGROUND/OBJECTIVES

Leprosy prominently involves both the skin and peripheral neural tissues and some symptoms persist after microbial cure. Because alterations in the dermis also occur in leprosy, we assessed here whether there were changes in cutaneous resonance running time (CRRT), a parameter that is influenced by collagen properties, in cured leprosy subjects.

METHODS

A reviscometer was used to measure the CRRT at various directions on the dorsal hand and the flexural forearms of 76 cured leprosy subjects aged 50-85 years and 68 age-matched normal subjects.

RESULTS

In comparison to normal subjects, CRRTs on the hands and the forearms were significantly reduced in all directions in cured leprosy, except at the 1-7, 2-8 and 3-9 o'clock directions on the forearms. CRRTs were reduced significantly at both the 4-10 and 5-11 o'clock directions on the forearm in lepromatous (73.33 +/- 4.19 at 4-10 o'clock and 67.44 +/- 2.71 at 5-11 o'clock direction) and borderline lepromatous types (77.58 +/- 5.84 at 4-10 o'clock and 79.85 +/- 6.81 at 5-11 o'clock direction) as compared with normal (143.10 +/- 7.75 at 4-10 o'clock and 125.18 +/- 8.14 at 5-11 o'clock direction). On the hand, CRRTs at all directions, except that at 4-10 o'clock direction, were also significantly reduced in lepromatous and borderline lepromatous types in comparison with normal. Significant differences in CRRT at some directions were found among the various subtypes of leprosy.

CONCLUSION

CRRTs were abnormal in the cured leprosy subjects as a whole, but varied with leprosy subtypes, which suggested that the extent of reduction of CRRTs correlates with the severity of immune alteration. These results suggest that CRRT measurements could be a useful approach to quantify the extent of some residual abnormalities in cured leprosy and perhaps could also be used to evaluate the efficacy of treatment.

Variation of skin surface pH, sebum content and stratum corneum hydration with age and gender in a large Chinese population

BACKGROUND AND OBJECTIVES

Evidence suggests the importance of skin biophysical properties in predicting diseases and in developing appropriate skin care. The results to date of studies on skin surface pH, stratum corneum (SC) hydration and sebum content in both genders and at various ages have been inconclusive, which was in part due to small sample size. Additionally, little is known about the skin physical properties of Asian, especially Chinese, subjects. In the present study, we assess the difference in skin surface pH, sebum content and SC hydration at various ages and in both genders in a large Chinese population without skin diseases.

METHODS

713 subjects (328 males and 385 females) aged 0.5-94 years were enrolled in this study. The subjects were divided by age into 5 groups, i.e., 0-12, 13-35, 36-50, 51-70 and over 70 years old. A multifunctional skin physiology monitor was used to measure SC hydration, skin surface pH and sebum content on both the forehead and the forearms.

RESULTS

In males, the highest sebum content was found on the forearm and the forehead in the age groups 36-50 (93.47 +/- 10.01 microg/cm(2)) and 51-70 years (9.16 +/- 1.95 microg/cm(2)), while in females, the highest sebum content was found on the forearm and the forehead in the age groups 13-35 (61.91 +/- 6.12 microg/cm(2)) and 51-70 years (7.54 +/- 2.55 microg/cm(2)). The forehead sebum content was higher in males aged 13-70 years than in age-matched females; the sebum content on the forehead in both males and females was higher than that on the forearm. Skin surface pH on the forehead of both males and females over the age of 70 years was higher than that in younger groups. SC hydration on the forehead in both males and females was lower above the age of 70, and the one in males aged 13-35 was higher than that in females (43.99 +/- 1.88 vs. 36.38 +/- 1.67 AU, p < 0.01). SC hydration on the forehead in both males and females did not significantly differ from that on the forearm.

CONCLUSIONS

In a large Chinese cohort, the skin surface pH, sebum content and SC hydration vary with age, gender and body site.

Abnormalities in stratum corneum function in patients recovered from leprosy

BACKGROUND AND OBJECTIVES

Leprosy involves both the skin and peripheral nervous system. Leprosy patients display an increased incidence of xerosis and altered sensory thresholds, which persist in previously active skin sites. We assessed here whether alterations in stratum corneum (SC) function persist in cured leprosy, and the relationship of epidermal functional abnormalities to each clinical subtype of leprosy.

METHODS

A total of 43 cured leprosy subjects and 29 normal control subjects were enrolled in this study. Basal skin surface pH, SC hydration, permeability barrier function as well as barrier recovery rates were measured over previously involved skin sites with a skin physiology monitor. One-way ANOVA and two-tailed Student's t test were used to determine the significance between 2 groups and 3 or more groups, respectively.

RESULTS

Competent barrier function was observed in all subtypes of cured leprosy subjects. All cured leprosy subjects except those with the borderline tuberculoid type exhibited a significantly lower SC hydration in comparison with normal subjects. Skin surface pH was significantly elevated in all cured leprosy subjects in comparison with normal subjects.

CONCLUSIONS

A varied spectrum of alterations in SC function remains in all subjects who have recovered from leprosy, but the spectrum of SC functional abnormalities varies with disease subtype.

Potassium channel openers accelerate epidermal barrier recovery

BACKGROUND

Maintenance of a competent permeability barrier in the face of external and internal stressors requires signals between the stratum corneum interface and the metabolic machinery in the underlying nucleated layers. For example, reductions in the ion gradients for Ca2+ after acute barrier disruption stimulate lamellar body (LB) secretion, a response required to restore barrier homeostasis. Although alterations in external K+ levels also regulate barrier recovery after acute insults, the mechanisms whereby K+ regulates barrier function remain unknown.

OBJECTIVES

To evaluate effects of regulators of K+ channels on barrier homeostasis in hairless mice.

METHODS

We tested a number of chemically different drugs that alter intracellular K+ levels. Results Single applications of either K+ channel openers (i.e. 1-EBIO, minoxidil, diazoxide) or the K+ ionophore, valinomycin, accelerated barrier recovery after acute insults to murine skin, paralleled by a reduction in intracellular K+ levels in cultured human keratinocytes. In contrast, applications of K+ channel blockers (i.e. gilbenclamide, dequalinium) delayed barrier recovery. Alterations in intracellular K+ regulated barrier homeostasis by either stimulating (reduced K+) or inhibiting (elevated K+) LB secretion. Finally, development of epidermal hyperplasia, a downstream consequence of barrier disruption, was also inhibited by agents that reduce intracellular K+ levels.

CONCLUSIONS

These results demonstrate that changes in K+ levels that can be presumed to occur after barrier disruption signal metabolic responses, i.e. LB secretion, which accelerates normalization of barrier function.

Extracellular pH Controls NHE1 expression in epidermis and keratinocytes: implications for barrier repair

We have previously shown that the Na+/H+ antiporter (NHE1) is an essential endogenous pathway responsible for stratum corneum (SC) acidification. Since the epidermis must re-establish its epidermal barrier after acute barrier perturbations, we asked whether the NHE1 was, in turn, regulated by changes in barrier status. We found that in vivo epidermal NHE1 expression was upregulated within hours of barrier disruption. We next asked whether NHE1 was regulated by barrier status per se, or by the SC alkalinization that accompanies barrier perturbation. NHE1 was upregulated by alkalinizing SC pH, whereas this antiporter was downregulated by acidifying SC pH, independent of changes in barrier status. Moreover, acidifying SC pH overrode the effects of barrier break in regulating NHE1 expression, suggesting that SC alkalinization is the major stimulus for increased NHE1 expression. Finally, we confirmed that the keratinocyte NHE1 antiporter is regulated by extracellular pH independent of barrier status, by demonstrating that NHE1 was upregulated in cultured keratinocytes exposed to pH 8.3 medium and downregulated in cultured keratinocytes exposed to pH 6.3 medium. These data suggest that the keratinocyte NHE1 is regulated by extracellular pH. SC barrier break also upregulates NHE1 expression, but this response seems to be mediated by concomitant changes in SC pH.

Alterations in cytokine regulation in aged epidermis: implications for permeability barrier homeostasis and inflammation. I. IL-1 gene family

Acute disruption of the cutaneous permeability barrier with either solvents or tape-stripping stimulates a homeostatic metabolic response in the subjacent nucleated layers of the epidermis that results in a rapid restoration of normal permeability barrier function. When the aged epidermal permeability barrier is stressed, it reveals a diminished capacity for recovery, in comparison to young epidermis, analogous to other organs in the aged when stressed. Although the signals that regulate this homeostatic response by the epidermis have not yet been resolved, acute permeability barrier disruption stimulates release of prestored IL-1alpha, and increased production of potentially regulatory cytokines, including IL-1alpha and TNFalpha in the epidermis. In these studies, we addressed the hypothesis that cytokine dysregulation explains the permeability barrier abnormality in aged epidermis, assessing the regulation of IL-1 and TNF signaling in aged vs young mice. To determine whether the IL-1 family of cytokines plays a key role in the permeability barrier abnormality of the aged, permeability barrier recovery rates were compared in transgenic mice lacking the functional IL-1 type 1 receptor vs wild-type mice at various ages. Knockout of the IL-1 type 1 receptor exacerbates the defect in permeability barrier homeostasis that is seen in age-matched, wild-type counterparts. Furthermore, the sluggish permeability barrier recovery in aged epidermis is associated with, and at least in part attributable to, altered expression of the IL-1 family of cytokines and receptors both under basal conditions and after acute barrier perturbations. Whereas modulations in cytokine expression with epidermal permeability barrier perturbation are qualitatively similar in aged epidermis, they greatly differ quantitatively. In contrast, examination of TNFalpha mRNA and protein basally, and following barrier perturbation revealed no alterations in aged epidermis. Together, these results show that selective alterations in the IL-1 family of cytokines occur with aging and that defects in IL-1 signaling may contribute to the epidermal permeability barrier abnormality of aged skin.

What is the 'true' function of skin?

Conventional textbook wisdom portrays the skin as an organ that literally enwraps whatever each of us stands for as a more or less functional, individual member of the mammalian species, and has it that the skin primarily establishes, controls and transmits contacts with the external world. In addition, the skin has long been recognized to protect the organism from deleterious environmental impacts (physical, chemical,microbiological), and is well-known as crucial for the maintenance of temperature, electrolyte and fluid balance. Now, ever more studies are being published that show the skin to also operate as a huge and highly active biofactory for the synthesis,processing and/or metabolism of an astounding range of e.g. structural proteins, glycans, lipids and signaling molecules. Increasingly, it becomes appreciated that the skin, furthermore, is an integral component of the immune, nervous and endocrine systems, with numerous lines of cross-talk between these systems established intracutaneously (e.g. Ann NY Acad Sci Vol 885, 1999; Endocrine Rev 21:457-487, 2000; Physiol Rev 80:980-1020, 2001; Exp Dermatol 10: 349-367, 2001). All these emerging cutaneous functions beyond the classical image of the skin as a barrier and sensory organ are immediately relevant for many of the quandaries that clinical dermatology, dermatopathology, and dermatopharmacology are still struggling with to-date, and offer the practising dermatologist attractive new targets for therapeutic intervention. Yet, many of these skin functions are not even mentioned in dermatology textbooks and await systematic therapeutic targeting. Following a suggestion by Enno Christophers, the current 'Controversies' feature brings together an unusually diverse council of biologists and clinicians, who share their thought-provoking views with the readers and allow us to peek into the future of research in cutaneous biology, not the least by reminding us of the -- often ignored -- evolutionary and embryonal origins of our favorite organ. Hopefully, this unique discussion feature will foster an understanding of the 'true' skin functions that is both more comprehensive and more profound than conventional teaching on this topic, and will stimulate more than 'skin-deep' reflections on the full range of skin functions.

Leptin regulation of the immune response and the immunodeficiency of malnutrition

Leptin is a 16 kDa protein mainly produced by adipose tissue in proportion to adipose tissue mass. Originally thought to be a satiety factor, leptin is a pleiotropic molecule. In addition to playing a role in energy regulation, leptin also regulates endocrine and immune functions. Both the structure of leptin and that of its receptor suggest that leptin might be classified as a cytokine. The secondary structure of leptin has similarities to the long-chain helical cytokines family, which includes interleukin 6 (IL-6), IL-11, CNTF, and LIF, and the leptin receptor is homologous to the gp-130 signal-transducing subunit of the IL-6-type cytokine receptors. Leptin plays a role in innate and acquired immunity. Leptin levels increase acutely during infection and inflammation, and may represent a protective component of the host response to inflammation. More important, leptin deficiency increases susceptibility to infectious and inflammatory stimuli and is associated with dysregulation of cytokine production. Leptin deficiency also causes a defect in hematopoiesis. Leptin regulates T cells responses, polarizing Th cells toward a Th1 phenotype. Low leptin levels occurring during starvation mediate the neuroendocrine and immune dysfunction of starvation.

Leptin regulation of the immune response and the immunodeficiency of malnutrition

Leptin is a 16 kDa protein mainly produced by adipose tissue in proportion to adipose tissue mass. Originally thought to be a satiety factor, leptin is a pleiotropic molecule. In addition to playing a role in energy regulation, leptin also regulates endocrine and immune functions. Both the structure of leptin and that of its receptor suggest that leptin might be classified as a cytokine. The secondary structure of leptin has similarities to the long-chain helical cytokines family, which includes interleukin 6 (IL-6), IL-11, CNTF, and LIF, and the leptin receptor is homologous to the gp-130 signal-transducing subunit of the IL-6-type cytokine receptors. Leptin plays a role in innate and acquired immunity. Leptin levels increase acutely during infection and inflammation, and may represent a protective component of the host response to inflammation. More important, leptin deficiency increases susceptibility to infectious and inflammatory stimuli and is associated with dysregulation of cytokine production. Leptin deficiency also causes a defect in hematopoiesis. Leptin regulates T cells responses, polarizing Th cells toward a Th1 phenotype. Low leptin levels occurring during starvation mediate the neuroendocrine and immune dysfunction of starvation.

Pathogenesis of the permeability barrier abnormality in epidermolytic hyperkeratosis

Epidermolytic hyperkeratosis is a dominantly inherited ichthyosis, frequently associated with mutations in keratin 1 or 10 that result in disruption of the keratin filament cytoskeleton leading to keratinocyte fragility. In addition to blistering and a severe disorder of cornification, patients typically display an abnormality in permeability barrier function. The nature and pathogenesis of the barrier abnormality in epidermolytic hyperkeratosis are unknown, however. We assessed here, first, baseline transepidermal water loss and barrier recovery kinetics in patients with epidermolytic hyperkeratosis. Whereas baseline transepidermal water loss rates were elevated by approximately 3-fold, recovery rates were faster in epidermolytic hyperkeratosis than in age-matched controls. Electron microscopy showed no defect in either the cornified envelope or the adjacent cornified-bound lipid envelope, i.e., a corneocyte scaffold abnormality does not explain the barrier abnormality. Using the water-soluble tracer, colloidal lanthanum, there was no evidence of tracer accumulation in corneocytes, despite the fragility of nucleated keratinocytes. Instead, tracer, which was excluded in normal skin, moved through the extracellular stratum corneum domains. Increasing intercellular permeability correlated with decreased quantities and defective organization of extracellular lamellar bilayers. The decreased lamellar material, in turn, could be attributed to incompletely secreted lamellar bodies within granular cells, demonstrable not only by several morphologic findings, but also by decreased delivery of a lamellar body content marker, acid lipase, to the stratum corneum interstices. Yet, after acute barrier disruption a rapid release of preformed lamellar body contents was observed together with increased organelle contents in the extracellular spaces, accounting for the accelerated recovery kinetics in epidermolytic hyperkeratosis. Accelerated recovery, in turn, correlated with a restoration in calcium in outer stratum granulosum cells in epidermolytic hyperkeratosis after barrier disruption. Thus, the baseline permeability barrier abnormality in epidermolytic hyperkeratosis can be attributed to abnormal lamellar body secretion, rather than to corneocyte fragility or an abnormal cornified envelope/cornified-bound lipid envelope scaffold, a defect that can be overcome by external applications of stimuli for barrier repair.

Regulation of scavenger receptor class B type I in hamster liver and Hep3B cells by endotoxin and cytokines

Multiple changes in HDL metabolism occur during infection and inflammation that could potentially impair the antiatherogenic functions of HDL. Scavenger receptor class B type I (SR-BI) promotes cholesterol efflux from peripheral cells and mediates selective uptake of cholesteryl ester into hepatocytes, thereby playing a pivotal role in reverse cholesterol transport. We studied the effect of endotoxin (lipopolysaccharide, LPS) and cytokines [tumor necrosis factor (TNF) and interleukin 1 (IL-1)] on hepatic SR-BI mRNA and protein levels in Syrian hamsters. LPS significantly decreased SR-BI mRNA levels in hamster liver. This effect was rapid and sustained, and was associated with a decrease in hepatic SR-BI protein levels. High cholesterol diet did not change hepatic SR-BI mRNA levels, and LPS was able to decrease SR-BI mRNA levels during high cholesterol feeding. TNF and IL-1 decreased SR-BI mRNA levels in the liver, and the effects of TNF and IL-1 were additive. TNF and IL-1 also decreased SR-BI levels in Hep3B hepatoma cells. More importantly, TNF and IL-1 decreased the uptake of HDL cholesteryl ester into Hep3B cells. In addition, we studied the effect of LPS on SR-BI mRNA in RAW 264.7 cells, a macrophage cell line. LPS rapidly decreased SR-BI mRNA levels in RAW 264.7 cells, but the effect was not sustained and did not lead to a reduction in SR-BI protein levels. Our results suggest that the decrease in hepatic SR-BI levels due to LPS and cytokines during infection and inflammation may decrease selective uptake of cholesteryl ester into the liver and result in impaired reverse cholesterol transport.

In vivo and in vitro regulation of sterol 27-hydroxylase in the liver during the acute phase response. potential role of hepatocyte nuclear factor-1

The host response to infection is associated with several alterations in lipid metabolism that promote lipoprotein production. These changes can be reproduced by lipopolysaccharide (LPS) administration. LPS stimulates hepatic cholesterol synthesis and suppresses the conversion of cholesterol to bile acids. LPS down-regulates hepatic cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the classic pathway of bile acid synthesis. We now demonstrate that LPS markedly decreases the activity of sterol 27-hydroxylase, the rate-limiting enzyme in the alternate pathway of bile acid synthesis, in the liver of Syrian hamsters. Moreover, LPS progressively decreases hepatic sterol 27-hydroxylase mRNA levels by 75% compared with controls over a 24-h treatment period. LPS also decreases oxysterol 7alpha-hydroxylase mRNA levels in mouse liver. In vitro studies in HepG2 cells demonstrate that tumor necrosis factor and interleukin (IL)-1 decrease sterol 27-hydroxylase mRNA levels by 48 and 80%, respectively, whereas IL-6 has no such effect. The IL-1-induced decrease in sterol 27-hydroxylase mRNA expression occurs early, is sustained for 48 h, and requires very low doses. In vivo IL-1 treatment also lowers hepatic sterol 27-hydroxylase mRNA levels in Syrian hamsters. Studies investigating the molecular mechanisms of LPS-induced decrease in sterol 27-hydroxylase show that LPS markedly decreases mRNA and protein levels of hepatocyte nuclear factor-1 (HNF-1), a transcription factor that regulates sterol 27-hydroxylase, in the liver. Moreover, LPS decreases the binding activity of HNF-1 by 70% in nuclear extracts in hamster liver, suggesting that LPS may down-regulate sterol 27-hydroxylase by decreasing the binding of HNF-1 to its promoter. Coupled with our earlier studies on cholesterol 7alpha-hydroxylase, these data indicate that LPS suppresses both the classic and alternate pathways of bile acid synthesis. A decrease in bile acid synthesis in liver would reduce cholesterol catabolism and thereby contribute to the increase in hepatic lipoprotein production that is induced by LPS and cytokines.

Generation of free fatty acids from phospholipids regulates stratum corneum acidification and integrity

There is evidence that the "acid mantle" of the stratum corneum is important for both permeability barrier formation and cutaneous antimicrobial defense. The origin of the acidic pH of the stratum corneum remains conjectural, however. Both passive (e.g., eccrine/sebaceous secretions, proteolytic) and active (e.g., proton pumps) mechanisms have been proposed. We assessed here whether the free fatty acid pool, which is derived from phospholipase-mediated hydrolysis of phospholipids during cornification, contributes to stratum corneum acidification and function. Topical applications of two chemically unrelated secretory phospholipase sPLA2 inhibitors, bromphenacylbromide and 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol, for 3 d produced an increase in the pH of murine skin surface that was paralleled not only by a permeability barrier abnormality but also altered stratum corneum integrity (number of strippings required to break the barrier) and decreased stratum corneum cohesion (protein weight removed per stripping). Not only stratum corneum pH but also all of the functional abnormalities normalized when either palmitic, stearic, or linoleic acids were coapplied with the inhibitors. Moreover, exposure of intact murine stratum corneum to a neutral pH for as little as 3 h produced comparable abnormalities in stratum corneum integrity and cohesion, and further amplified the inhibitor-induced functional alterations. Furthermore, short-term applications of an acidic pH buffer to inhibitor-treated skin also reversed the abnormalities in stratum corneum integrity and cohesion, despite the ongoing decrease in free fatty acid levels. Finally, the secretory-phospholipase-inhibitor-induced alterations in integrity/cohesion were in accordance with premature dissolution of desmosomes, demonstrated both by electron microscopy and by reduced desmoglein 1 levels in the stratum corneum (shown by immunofluorescence staining and visualized by confocal microscopy). Together, these results demonstrate: (i) the importance of phospholipid-to-free-fatty-acid processing for normal stratum corneum acidification; and (ii) the potentially important role of this pathway not only for barrier homeostasis but also for the dual functions of stratum corneum integrity and cohesion.

Cholesterol efflux by acute-phase high density lipoprotein: role of lecithin: cholesterol acyltransferase

HDL plays an initial role in reverse cholesterol transport by mediating cholesterol removal from cells. During infection and inflammation, several changes in HDL composition occur that may affect the function of HDL; therefore, we determined the ability of acute-phase HDL to promote cholesterol removal from cells. Acute-phase HDL was isolated from plasma of Syrian hamsters injected with lipopolysaccharide. Cholesterol removal from J 774 murine macrophages by acute-phase HDL was less efficient than that by control HDL because of both a decrease in cholesterol efflux and an increase in cholesterol influx. LCAT activity of acute-phase HDL was significantly lower than that of control HDL. When LCAT activity of control HDL was inactivated, cholesterol efflux decreased and cholesterol influx increased to the level observed in acute-phase HDL. Inactivation of LCAT had little effect on acute-phase HDL. In GM 3468A human fibroblasts, the ability of acute-phase HDL to remove cholesterol from cells was also lower than that of normal HDL. The impaired cholesterol removal, however, was primarily a result of an increase in cholesterol influx without changes in cholesterol efflux. When control HDL in which LCAT had been inactivated was incubated with fibroblasts, cholesterol influx increased to a level comparable to that of acute-phase HDL, without any change in cholesterol efflux. These results suggest that the ability of acute-phase HDL to mediate cholesterol removal was impaired compared with that of control HDL and the lower LCAT activity in acute-phase HDL may be responsible for this impairment. The decreased ability of acute-phase HDL to remove cholesterol from cells may be one of the mechanisms that account for the well-known relationship between infection/inflammation and atherosclerosis.

Regulation of sphingolipid and glycosphingolipid metabolism in extrahepatic tissues by endotoxin

The host response to infection and inflammation is associated with multiple alterations in lipid metabolism. We have shown that endotoxin [lipopolysaccharide (LPS)] stimulates hepatic sphingolipid synthesis and increases ceramide and glucosylceramide (GlcCer) content in circulating lipoproteins in Syrian hamsters. LPS also increases the activity and mRNA levels of serine palmitoyltransferase (SPT) and GlcCer synthase, the committed enzymes in sphingolipid and glycosphingolipid (GSL) synthesis, respectively, in the liver. To determine whether sphingolipid and GSL metabolism are regulated in other tissues during the host response to infection, we examined the effect of LPS on the regulation of SPT and GlcCer synthase in extrahepatic tissues in Syrian hamsters. LPS significantly increased SPT activity in spleen and kidney after 16 h of treatment, but had no effect on SPT activity in lung and brain, suggesting that the effect of LPS on sphingolipid metabolism is tissue specific. LPS also increased SPT mRNA levels in spleen and kidney by approximately 3-fold, suggesting that the increase in SPT activity is due to an increase in SPT mRNA expression. LPS significantly increased GlcCer synthase activity in spleen and kidney, and produced 4- and 15-fold increases in GlcCer synthase mRNA levels in spleen and kidney, respectively. LPS treatment increased GlcCer content by 1.3-fold in spleen and by 6.2-fold in kidney. LPS also increased the content of ceramide trihexoside by 1.7-fold in spleen. These results suggest that LPS regulates sphingolipid and GSL metabolism in spleen and kidney. An increase in GSL metabolites in spleen and kidney during the host response to infection and inflammation may be required for modulation of immune responses and regulation of cell growth. -- Memon, R. A., W. M. Holleran, Y. Uchida, A. H. Moser, C. Grunfeld, and K. R. Feingold. Regulation of sphingolipid and glycosphingolipid metabolism in extrahepatic tissues by endotoxin. J. Lipid Res. 2001. 42: 452--459.

Testosterone perturbs epidermal permeability barrier homeostasis

Although there are no known gender-related differences in permeability barrier function in adults, estrogens accelerate whereas testosterone retards barrier development in fetal skin, and male fetuses demonstrate slower barrier development than female littermates. Moreover, prenatal administration of the androgen receptor antagonist, flutamide, equalizes developmental rates in male and female fetuses. Therefore, we evaluated the effects of changes in testosterone on barrier homeostasis in adult murine and human skin. Hypogonadal mice (whether by castration or by treatment with systemic flutamide) displayed significantly faster barrier recovery at 3, 6, and 12 h than did controls, and testosterone replacement slowed barrier recovery in castrated mice. Moreover, testosterone directly effects the skin, as topical flutamide also accelerated barrier recovery in normal male mice. These findings appear to be of physiologic significance, since prepubertal male mice (age 5 wk) displayed accelerated barrier recovery in comparison with adult postpubertal (11 wk) males. These studies also appear to be relevant for humans, as a hypopituitary human subject demonstrated repeated changes in barrier recovery in parallel with peaks and nadirs in serum testosterone levels during intermittent testosterone replacement. Mechanistic studies showed that differences in epidermal lipid synthesis do not account for the testosterone-induced functional alterations. Instead, epidermal lamellar body (LB) formation and secretion both decrease, resulting in decreased extracellular lamellar bilayers in testosterone-replete animals. These studies demonstrate that fluctuations in testosterone modulate barrier function, and that testosterone repletion can have negative consequences for permeability barrier homeostasis.

Cholesterol sulfate stimulates involucrin transcription in keratinocytes by increasing Fra-1, Fra-2, and Jun D

Lipids that are synthesized de novo in the epidermis, including fatty acids, oxysterols, 1,25-dihydroxyvitamin D(3), and farnesol, can regulate the differentiation of normal human keratinocytes (NHK). Cholesterol sulfate (CS), an epidermal lipid that is produced in the upper nucleated layers of the epidermis coincident with terminal differentiation, has been shown to play a role in the regulation of the late stages of keratinocyte differentiation, including formation of the cornified envelope. In the present study, we determined i) whether CS regulates involucrin (INV), an early keratinocyte differentiation marker, and ii) the mechanism by which CS regulates differentiation. mRNA and protein levels of INV, a precursor protein of the cornified envelope, increased 2- to 3-fold in NHK incubated in the presence of CS. In contrast, cholesterol had no effect on INV protein or mRNA levels. Transcriptional regulation was assessed in NHK transfected with INV promoter-luciferase constructs. CS increased luciferase reporter activity approximately 2- to 3-fold in NHK transfected with a 3.7-kb INV promoter construct. Deletional analysis revealed a CS-responsive region of the INV promoter located between bp --2452 and --1880. A 5-base pair (bp) mutation of the AP-1 site (bp --2117 to --2111) within this responsive region abolished CS responsiveness, suggesting a role for the AP-1 complex in the regulation of INV transcription by CS. Electrophoretic mobility shift analysis demonstrated increased binding of nuclear extracts isolated from CS-treated NHK to AP-1 DNA as compared with vehicle-treated controls. Incubation of the nuclear extract with the appropriate antibodies showed that the AP-1 DNA-binding complex contained Fra-1, Fra-2, and Jun D. Western blots demonstrated that CS treatment increased the levels of Fra-1, Fra-2, and Jun D, and Northern analyses revealed that CS increased mRNA levels for these same AP-1 factors. These data indicate that CS, an endogenous lipid synthesized by keratinocytes, regulates the early stages of keratinocyte differentiation, and may do so through its ability to modulate levels of AP-1 proteins. -- Hanley, K., L. Wood, D. C. Ng, S. S. He, P. Lau, A. Moser, P. M. Elias, D. D. Bikle, M. L. Williams, and K. R. Feingold. Cholesterol sulfate stimulates involucrin transcription in keratinocytes by increasing Fra-1, Fra-2, and Jun D. J. Lipid Res. 2001. 42: 390--398.

Psychological stress perturbs epidermal permeability barrier homeostasis: implications for the pathogenesis of stress-associated skin disorders

BACKGROUND

A large number of skin diseases, including atopic dermatitis and psoriasis, appear to be precipitated or exacerbated by psychological stress. Nevertheless, the specific pathogenic role of psychological stress remains unknown. In 3 different murine models of psychological stress, it was recently shown that psychological stress negatively impacts cutaneous permeability barrier function and that coadministration of tranquilizers blocks this stress-induced deterioration in barrier function.

OBJECTIVES AND METHODS

The relationship between psychological stress and epidermal permeability barrier function was investigated in 27 medical, dental, and pharmacy students without coexistent skin disease. Their psychological state was assessed with 2 well-validated measures: the Perceived Stress Scale and the Profile of Mood States. Barrier function was assessed simultaneously with the stress measures at periods of presumed higher stress (during final examinations) and at 2 assumed, lower stress occasions (after return from winter vacation [approximately 4 weeks before final examinations] and during spring vacation [approximately 4 weeks after final examinations]).

RESULTS

The subjects as a group demonstrated a decline in permeability barrier recovery kinetics after barrier disruption by cellophane tape stripping, in parallel with an increase in perceived psychological stress during the higher vs the initial lower stress occasions. During the follow-up, presumed lower stress period, the subjects again displayed lower perceived psychological stress scores and improved permeability barrier recovery kinetics, comparable to those during the initial lower stress period. Moreover, the greatest deterioration in barrier function occurred in those subjects who demonstrated the largest increases in perceived psychological stress.

CONCLUSION

These studies provide the first link between psychological status and cutaneous function in humans and suggest a new pathophysiological paradigm, ie, stress-induced derangements in epidermal function as precipitators of inflammatory dermatoses.

Up-regulation of peroxisome proliferator-activated receptors (PPAR-alpha) and PPAR-gamma messenger ribonucleic acid expression in the liver in murine obesity: troglitazone induces expression of PPAR-gamma-responsive adipose tissue-specific genes in the liver of obese diabetic mice

Peroxisome proliferator-activated receptors (PPARs) are transcription factors that play an important role in the regulation of genes involved in lipid utilization and storage, lipoprotein metabolism, adipocyte differentiation, and insulin action. The three isoforms of the PPAR family, i.e. alpha, delta, and gamma, have distinct tissue distribution patterns. PPAR-alpha is predominantly present in the liver, and PPAR-gamma in adipose tissue, whereas PPAR-delta is ubiquitously expressed. A recent study reported increased PPAR-gamma messenger RNA (mRNA) expression in the liver in ob/ob mice; however, it is not known whether increased PPAR-gamma expression in the liver has any functional consequences. The expression of PPAR-alpha and -delta in the liver in obesity has not been determined. We have now examined the mRNA levels of PPAR-alpha, -delta, and -gamma in three murine models of obesity, namely, ob/ob (leptin-deficient), db/db (leptin-receptor deficient), and serotonin 5-HT2c receptor (5-HT2cR) mutant mice. 5-HT2cR mutant mice develop a late-onset obesity that is associated with higher plasma leptin levels. Our results show that PPAR-alpha mRNA levels in the liver are increased by 2- to 3-fold in all three obese models, whereas hepatic PPAR-gamma mRNA levels are increased by 7- to 9-fold in ob/ob and db/db mice and by 2-fold in obese 5-HT2cR mutant mice. PPAR-delta mRNA expression is not altered in ob/ob or db/db mice. To determine whether increased PPAR-gamma expression in the liver has any functional consequences, we examined the effect of troglitazone treatment on the hepatic mRNA levels of several PPAR-gamma-responsive adipose tissue-specific genes that have either no detectable or very low basal expression in the liver. The treatment of lean control mice with troglitazone significantly increased the expression of adipocyte fatty acid-binding protein (aP2) and fatty acid translocase (FAT/CD36) in the liver. This troglitazone-induced increase in the expression of aP2 and FAT/CD36 was markedly enhanced in the liver in ob/ob mice. Troglitazone also induced a pronounced increase in the expression of uncoupling protein-2 in the liver in ob/ob mice. In contrast to the liver, troglitazone did not increase the expression of aP2, FAT/CD36, and uncoupling protein-2 in adipose tissue in lean or ob/ob mice. Taken together, our results suggest that the effects of PPAR-gamma activators on lipid metabolism and energy homeostasis in obesity and type 2 diabetes may be partly mediated through their effects on PPAR-gamma in the liver.

Keratinocyte differentiation in hyperproliferative epidermis: topical application of PPARalpha activators restores tissue homeostasis

We recently showed that topically applied PPARalpha activators promote epidermal differentiation in intact adult mouse skin. In this study we determined the effect of clofibrate and Wy-14,643, activators of PPARalpha, on hyperproliferative epidermis in hairless mice, induced either by repeated barrier abrogation (subacute model) or by essential fatty acid deficiency (chronic model). The hyperproliferative epidermis was characterized by an increased number of proliferating cells expressing proliferating cell nuclear antigen. Topical treatment with PPARalpha activators resulted in a substantial decrease in epidermal hyperplasia in both the subacute and chronic models of hyperproliferation. Following topical treatment, proliferating cell nuclear antigen-expressing cells were restricted to the basal layer, similar to normal epidermis. In hyperproliferative epidermis there was decreased expression of involucrin, profilaggrin-filaggrin, and loricrin as assayed by in situ hybridization and immunohistochemistry. Following topical treatment with PPAR activators staining for these mRNAs and proteins increased towards normal levels. Finally, topically applied clofibrate also increased apoptosis. This study demonstrates that topical PPAR activators have profound effects on epidermal gene expression in hyperproliferative skin disorders. Treatment with PPARalpha activators normalizes cell proliferation and promotes epidermal differentiation, correcting the cutaneous pathology. This study identifies PPARalpha activators as potential skin therapeutic agents.

Stimulation of PPARalpha promotes epidermal keratinocyte differentiation in vivo

Our recent studies have demonstrated that PPARalpha activators stimulate differentiation and inhibit proliferation in cultured human keratinocytes and accelerate epidermal development and permeability barrier formation in fetal rat skin explants. As the role of PPARalpha activation in adult epidermis is not known, the aim of this study was to determine if topically applied PPARalpha ligands regulate keratinocyte differentiation in murine epidermis. Topical treatment with PPARalpha activators resulted in decreased epidermal thickness. Expression of structural proteins of the upper spinous/granular layers (involucrin, profilaggrin-filaggrin, loricrin) increased following topical treatment with PPARalpha activators. Furthermore, topically applied PPARalpha activators also increased apoptosis, decreased cell proliferation, and accelerated recovery of barrier function following acute barrier abrogation. Experiments with PPARalpha-/- knockout mice showed that these effects are specifically mediated via PPARalpha. Compared with the epidermis of PPARalpha+/+ mice, involucrin, profilaggrin-filaggrin, and loricrin expression were slightly decreased in PPARalpha-/- mice. Moreover, topical clofibrate treatment did not increase epidermal differentiation in PPARalpha-/- mice. Furthermore, in cultured human keratinocytes we have demonstrated that PPARalpha activators induce an increase in involucrin mRNA levels. We have also shown that this increase in gene expression requires an intact AP-1 response element at -2117 to -2111 bp. Thus, stimulation of PPARalpha stimulates keratinocyte/epidermal differentiation and inhibits proliferation.

Permeability barrier disorder in Niemann-Pick disease: sphingomyelin-ceramide processing required for normal barrier homeostasis

Prior studies have established the requirement for enzymatic hydrolysis of glucosylceramides to ceramide for epidermal barrier homeostasis. In this study, we asked whether sphingomyelin-derived ceramide, resulting from acid-sphingomyelinase activity, is also required for normal barrier function. We showed first, that a subset of Niemann-Pick patients with severe acid-sphingomyelinase deficiency (i.e., <2% residual activity) demonstrate abnormal permeability barrier homeostasis, i.e., delayed recovery kinetics following acute barrier disruption by cellophane tape-stripping. To obtain further mechanistic insights into the potential requirement for sphingomyelin-to-ceramide processing for the barrier, we next studied the role of acid-sphingomyelinase in hairless mouse skin. Murine epidermis contains abundant acid-sphingomyelinase activity (optimal pH 5.1-5.6). Two hours following acute barrier disruption by tape-stripping, acid-sphingomyelinase activity increases 1. 44-fold (p<0.008 versus vehicle-treated controls), an increase that is blocked by a single topical application of the acid-sphingomyelinase inhibitor, palmitoyldihydrosphingosine. Furthermore, both palmitoyldihydrosphingosine and desipramine, a chemically and mechanically unrelated acid-sphingomyelinase inhibitor, significantly delay barrier recovery both 2 and 4 h after acute barrier abrogation. Inhibitor application also causes both an increase in sphingomyelin content, and a reduction of normal extracellular lamellar membrane structures, in the stratum corneum. Both of the inhibitor-induced delays in barrier recovery can be overridden by co-applications of topical ceramide, demonstrating that an alteration of the ceramide-sphingomyelin ratio, rather than sphingomyelin accumulation, is likely responsible for the barrier abnormalities that occur with acid-sphingomyelinase deficiency. These studies demonstrate an important role for enzymatic processing of sphingomyelin-to-ceramide by acid-sphingomyelinase as a mechanism for generating a portion of the stratum corneum ceramides for permeability barrier homeostasis in mammalian skin.

Infection and inflammation induce LDL oxidation in vivo

Epidemiological studies have shown an increased incidence of coronary artery disease in patients with chronic infections and inflammatory disorders. Because oxidative modification of lipoproteins plays a major role in atherosclerosis, the present study was designed to test the hypothesis that the host response to infection and inflammation induces lipoprotein oxidation in vivo. Lipoprotein oxidation was measured in 3 distinct models of infection and inflammation. Syrian hamsters were injected with bacterial lipopolysaccharide (LPS), zymosan, or turpentine to mimic acute infection, acute systemic inflammation, and acute localized inflammation, respectively. Levels of oxidized fatty acids in serum and lipoprotein fractions were measured by determining levels of conjugated dienes, thiobarbituric acid-reactive substances, and lipid hydroperoxides. Our results demonstrate a significant increase in conjugated dienes and thiobarbituric acid-reactive substances in serum in all 3 models. Moreover, LPS and zymosan produced a 4-fold to 6-fold increase in conjugated diene and lipid hydroperoxide levels in LDL fraction. LPS also produced a 17-fold increase in LDL content of lysophosphatidylcholine that is formed during the oxidative modification of LDL. Finally, LDL isolated from animals treated with LPS was significantly more susceptible to ex vivo oxidation with copper than LDL isolated from saline-treated animals, and a 3-fold decrease occurred in the lag phase of oxidation. These results demonstrate that the host response to infection and inflammation increases oxidized lipids in serum and induces LDL oxidation in vivo. Increased LDL oxidation during infection and inflammation may promote atherogenesis and could be a mechanism for increased incidence of coronary artery disease in patients with chronic infections and inflammatory disorders.

Infection and inflammation-induced proatherogenic changes of lipoproteins

Epidemiologic studies suggest a link between infection/inflammation and atherosclerosis. During the acute-phase response to infection and inflammation, cytokines induce tissue and plasma events that lead to changes in lipoprotein. Many of these changes are similar to those proposed to promote atherogenesis. The changes of lipoproteins during infection and inflammation are reviewed with a focus on those that are potentially proatherogenic. Hypertriglyceridemia, elevated triglyceride-rich lipoproteins, the appearance of small dense low-density lipoproteins, increased platelet-activating factor acetylhydrolase activity, and secretory phospholipase A(2), sphingolipid-enriched lipoproteins, and decreased high-density lipoprotein (HDL) cholesterol are changes that could promote atherogenesis. Moreover, alterations of proteins associated with HDL metabolism (e.g., paraoxonase, apolipoprotein A-I, lecithin:cholesterol acyltransferase, cholesterol ester transfer protein, hepatic lipase, phospholipid transfer protein, and serum amyloid A) could decrease the ability of HDL to protect against atherogenesis through antioxidation and reverse cholesterol transport mechanisms. These proatherogenic changes of lipoproteins may contribute to the link between infection/inflammation and atherosclerosis.

The acute phase response is associated with retinoid X receptor repression in rodent liver

The acute phase response (APR) is associated with decreased hepatic expression of many proteins involved in lipid metabolism. The nuclear hormone receptors peroxisome proliferator-activated receptor alpha (PPARalpha) and liver X receptor (LXR) play key roles in regulation of hepatic lipid metabolism. Because heterodimerization with RXR is crucial for their action, we hypothesized that a decrease in RXR may be one mechanism to coordinately down-regulate gene expression during APR. We demonstrate that lipopolysaccharide (LPS) induces a rapid, dose-dependent decrease in RXRalpha, RXRbeta, and RXRgamma proteins in hamster liver. Maximum inhibition was observed at 4 h for RXRalpha (62%) and RXRbeta (50%) and at 2 h for RXRgamma (61%). These decreases were associated with a marked reduction in RXRalpha, RXRbeta, and RXRgamma mRNA levels. Increased RNA degradation is likely responsible for the repression of RXR, because LPS did not decrease RXRbeta and RXRgamma transcription and only marginally inhibited (38%) RXRalpha transcription. RXR repression was associated with decreased LXRalpha and PPARalpha mRNA levels and reduced RXR x RXR, RXR x PPAR and RXR x LXR binding activities in nuclear extracts. Furthermore, LPS markedly decreased both basal and Wy-14,643-induced expression of acyl-CoA synthetase, a well characterized PPARalpha target. The reduction in hepatic RXR levels alone or in association with other nuclear hormone receptors could be a mechanism for coordinately inhibiting the expression of multiple genes during the APR.

Reduced leptin levels in starvation increase susceptibility to endotoxic shock

Malnutrition compromises immune function, reducing resistance to infection. We examine whether the decrease in leptin induced by starvation increases susceptibility to lipopolysaccharide (LPS)- and tumor necrosis factor (TNF)-induced lethality. In mice, fasting for 48 hours enhances sensitivity to LPS. Decreasing the fasting-induced fall in leptin by leptin administration markedly reduced sensitivity to LPS. Although fasting decreases basal leptin levels, LPS treatment increased leptin to the same extent as in fed animals. Fasting increased basal serum corticosterone; leptin treatment blunted this increase. Fasting decreased the ability of LPS to increase corticosterone; leptin restored the corticosterone response to LPS. Serum glucose levels were decreased in fasted mice and LPS induced a further decrease. Leptin treatment affected neither basal glucose nor that after LPS. LPS induced a fivefold greater increase in serum TNF in fasted mice, which was blunted by leptin replacement. In contrast, LPS induced lower levels of interferon-gamma and no differences in interleukin-1beta in fasted compared to fed animals; leptin had no effect on those cytokines. Furthermore, fasting increased sensitivity to the lethal effect of TNF itself, which was also reversed by leptin treatment. Thus, leptin seems to be protective by both inhibiting TNF induction by LPS and by reducing TNF toxicity.

Farnesol stimulates differentiation in epidermal keratinocytes via PPARalpha

The isoprenoids farnesol and juvenile hormone III (JH), metabolites of the cholesterol biosynthetic pathway, have been shown to stimulate fetal epidermal development in rodents. In this study we determined whether this effect might be attributed to a direct induction of keratinocytes differentiation and examined the mechanisms responsible for these effects. Rates of cornified envelope formation, a marker of keratinocyte terminal differentiation, as well as protein and mRNA levels of two proteins required for cornified envelope formation, involucrin (INV) and transglutaminase, increased 2- to 3-fold in normal human keratinocytes (NHK) treated with either farnesol or JH, even at low calcium concentrations (0.03 mM), which otherwise inhibit differentiation. In contrast, neither cholesterol nor mevalonate affected INV or transglutaminase mRNA levels. Effects of farnesol and JH on INV and transglutaminase mRNA levels were additive with high calcium concentrations (1.2 mM) that independently stimulate keratinocyte differentiation. In contrast, keratinocyte DNA synthesis was inhibited by these compounds. Both farnesol and JH stimulated INV and transglutaminase promoter activity, suggesting regulation at the transcriptional level. A series of truncation and deletion experiments revealed a farnesol-responsive region (-2452 to -1880 base pairs (bp)) in the INV gene. This region contained an AP-1 site. A single base pair mutation of the AP-1 site at -2116 to -2110 bp abolished farnesol responsiveness, identical to effects by peroxisome proliferator-activated receptor (PPARalpha) activators. Farnesoid X-activated receptor mRNA was not detected in NHK, but farnesol treatment increased activities of both a PPAR response element and PPARalpha mRNA levels in NHK. Furthermore, the increase in PPRE activity by farnesol was dependent upon PPARalpha in CV-1 cells. Finally, topical applications of farnesol increased mRNA and protein levels of the differentiation-specific genes, profilaggrin and loricrin, determined by immunohistochemistry and in situ hybridization, in wild-type but not in PPARalpha-/- murine epidermis. These findings suggest a novel role for selected isoprenoid cholesterol intermediates in the regulation of differentiation-specific gene transcription and a convergence of PPARalpha with the cholesterol synthetic pathway.

Oxysterols induce differentiation in human keratinocytes and increase Ap-1-dependent involucrin transcription

Ligands and activators of the nuclear hormone receptor superfamily are important in the regulation of epidermal development and differentiation. Previously, we showed that naturally occurring fatty acids, as well as synthetic ligands for the peroxisome proliferator-activated receptor, induce keratinocyte differentiation in vitro. Here we asked whether oxysterols, another class of lipids formed de novo in the epidermis and that activate liver X-activated receptor, regulate keratinocyte differentiation. mRNA and protein levels of involucrin and transglutaminase 1, markers of differentiation, increased 2- to 3-fold in normal human keratinocytes incubated in the presence of 25- or 22R-hydroxycholesterol in low calcium. In high calcium, which alone induces differentiation, mRNA levels were further increased by oxysterols. Rates of cornified envelope formation, an indicator of terminal differentiation, also increased 2-fold with oxysterol treatment. In contrast, the rate of DNA synthesis was inhibited approximately 50% by oxysterols. Transcriptional regulation was assessed in keratinocytes transfected with either transglutaminase 1 or involucrin promoter-luciferase constructs. 22R-hydroxycholesterol increased transglutaminase 1 and involucrin promoter activity 2- to 3-fold. Either deletion of the -2452 bp to -1880 bp region of the involucrin promoter, or mutation of the AP-1 site within this region, abolished oxysterol responsiveness. Moreover, increased AP-1 DNA binding was observed in oxysterol-treated keratinocytes by gel shift analyses. Finally, we demonstrated the presence of liver X-activated receptor alpha and beta mRNAs, and showed that oxysterols stimulate a liver X-activated receptor response element transfected into keratinocytes. These data suggest that oxysterols induce keratinocyte differentiation, in part through increased AP-1-dependent transcription of the involucrin gene, an effect that may be mediated by liver X-activated receptor.

Oxidized cholesterol in the diet accelerates the development of atherosclerosis in LDL receptor- and apolipoprotein E-deficient mice

The aim of the current study was to determine whether oxidized cholesterol in the diet accelerates atherosclerosis in low density lipoprotein receptor- (LDLR) and apolipoprotein E- (apo E) deficient mice. Mice were fed either a control diet or a diet containing oxidized cholesterol. For LDLR-deficient mice, the control diet consisted of regular mouse chow to which 1.0% cholesterol was added. The oxidized diet was identical to the control diet except that 5% of the added cholesterol was oxidized. In apo E-deficient mice, the control diet contained 0.15% cholesterol, whereas in the oxidized diet, 5% of the added cholesterol was oxidized. LDLR-deficient and apo E-deficient mice were fed the experimental diets for 7 and 4 months, respectively. In mice fed the oxidized-cholesterol diets, the levels of oxidized cholesterol in sera were increased. At the end of the experiment, aortas were removed and atherosclerosis was assessed. We found that in LDLR-deficient mice, feeding of an oxidized-cholesterol diet resulted in a 32% increase in fatty streak lesions (15.93+/-1.59% versus 21.00+/-1.38%, P<0.03). Similarly, in apo E-deficient mice, feeding of an oxidized-cholesterol diet increased fatty streak lesions by 38% (15.01+/-0.92% versus 20. 70+/-0.86%, P<0.001). The results of the current study thus demonstrate that oxidized cholesterol in the diet accelerates fatty streak lesion formation in both LDLR- and apo E-deficient mice.

Leptin-deficient (ob/ob) mice are protected from T cell-mediated hepatotoxicity: role of tumor necrosis factor alpha and IL-18

The role of leptin was investigated in two models of T cell-mediated hepatitis: the administration of Con A or of Pseudomonas aeruginosa exotoxin A (PEA). In both models, leptin-deficient (ob/ob) mice were protected from liver damage and showed lower induction of tumor necrosis factor (TNF) alpha and IL-18 compared with their lean littermates. Neutralization of TNF-alpha reduced induction of IL-18 by either Con A (70% reduction) or PEA (40% reduction). Pretreatment of lean mice with either soluble TNF receptors or with an anti-IL-18 antiserum significantly reduced Con A- and PEA-induced liver damage. The simultaneous neutralization of TNF-alpha and IL-18 fully protected the mice against liver toxicity. However, neutralization of either IL-18 or TNF-alpha did not inhibit Con A-induced production of IFN-gamma. Thymus atrophy and alterations in the number of circulating lymphocytes and monocytes were observed in ob/ob mice. Exogenous leptin replacement restored the responsiveness of ob/ob mice to Con A and normalized their lymphocyte and monocyte populations. These results demonstrate that leptin deficiency leads to reduced production of TNF-alpha and IL-18 associated with reduced T cell-mediated hepatotoxicity. In addition, both TNF-alpha and IL-18 appear to be essential mediators of T cell-mediated liver injury.

Upregulation of uncoupling protein 2 mRNA in genetic obesity: lack of an essential role for leptin, hyperphagia, increased tissue lipid content, and TNF-alpha

Uncoupling protein 2 (UCP2) has been proposed to play a prominent role in the regulation of energy balance. UCP2 mRNA expression is upregulated in white adipose tissue (WAT) and liver, but is not altered in skeletal muscle in genetically obese ob/ob mice. The mechanisms involved in the upregulation of UCP2 in obesity have not been investigated. We have now examined the potential role of leptin, hyperphagia, increased tissue lipid content, and overexpression of tumor necrosis factor (TNF)-alpha in the upregulation of UCP2 mRNA expression in the liver and WAT in ob/ob mice. Treatment of ob/ob mice with leptin for 3 days significantly reduced their food intake but had no effect on the upregulation of UCP2 mRNA levels in the liver or WAT. To investigate the effect of feeding and higher tissue lipid content on the upregulation of UCP2 in liver and WAT, we compared UCP2 mRNA levels in ad-libitum fed and 72-h fasted control and ob/ob mice. In controls, fasting had no effect on UCP2 mRNA levels in liver, but increased UCP2 mRNA in WAT suggesting that the effects of fasting on UCP2 mRNA levels are tissue-specific. In ob/ob mice, fasting did not lower UCP2 mRNA levels in liver or WAT suggesting that the upregulation of UCP2 in ob/ob mice is not merely a direct consequence of increased food intake. 72-h fasting lowered hepatic total lipid content by 34% and 36% in control and ob/ob mice, respectively, without any corresponding decrease in hepatic UCP2 mRNA levels, suggesting that the enhanced UCP2 expression in the liver of ob/ob mice is not secondary to lipid accumulation in their livers. Although TNF-alpha has been shown to acutely increase UCP2 mRNA levels in liver and WAT, and is overexpressed in adipose tissue in obesity, deletion of the genes for both TNF receptors in ob/ob mice produces a further increase in UCP2 mRNA expression in liver and adipose tissue indicating a paradoxical inhibitory role. Taken together, these results suggest that the upregulation of UCP2 mRNA levels in the liver and WAT of ob/ob mice is not due to the lack of leptin, hyperphagia, increased tissue lipid content, or over-expression of TNF-alpha.

Stress alters cutaneous permeability barrier homeostasis

Recent studies have shown that psychological stress can influence cutaneous barrier function, suggesting that this form of stress could trigger or aggravate skin disease. In the present study, we demonstrate that transfer of hairless mice to a different cage delays barrier recovery rates. Pretreatment with a phenothiazine sedative, chlorpromazine, before transfer of animals restored the kinetics of barrier recovery toward normal, suggesting that psychological stress is the basis for this alteration in barrier homeostasis. To determine the mechanism linking psychological stress to altered barrier recovery, we first demonstrated that plasma corticosterone levels increase markedly after transfer of animals to new cages and that pretreatment with chlorpromazine blocks this increase. Second, we demonstrated that the systemic administration of corticosterone delays barrier recovery. Finally, we demonstrated that pretreatment with the glucocorticoid receptor antagonist RU-486 blocks the delay in barrier recovery produced by systemic corticosterone, change of cage, or immobilization. These results suggest that psychological stress stimulates increased production of glucocorticoids, which, in turn, adversely affects permeability barrier homeostasis.

Plasma platelet-activating factor acetylhydrolase activity in human immunodeficiency virus infection and the acquired immunodeficiency syndrome

Platelet-activating factor (PAF) acetylhydrolase (PAF-AH) catalyzes the hydrolysis of PAF, a mediator of inflammation, as well as other biologically active oxidized phospholipids. In humans, plasma PAF-AH activity is bound to low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Higher levels of plasma PAF-AH activity have been found in a variety of diseases, and are thought to be a defense mechanism against the toxic effects of PAF and oxidized phospholipids. We studied plasma PAF-AH activity in patients with human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS), a disease characterized by chronic HIV infection and a systemic host response. Plasma PAF-AH activity was significantly greater in AIDS patients compared with control subjects (25.2 +/- 2.0 v 17.0 +/- 0.8 nmol/min/mL, P < .001). The higher levels of plasma PAF-AH activity were found in LDL (28.2 +/- 2.2 v 18.3 +/- 1.0 nmol/min/mL for AIDS v controls, respectively, P = .0005), but not in HDL. Plasma PAF-AH activity in AIDS correlated with circulating interferon alfa (r = .575, P = .005) and plasma triglycerides (r = .556, P < .0025). The presence of secondary infection in AIDS did not significantly change plasma PAF-AH activity. The initiation of a new antiretroviral regimen with either a protease inhibitor or the nucleoside analog lamivudine did not significantly decrease plasma PAF-AH activity, despite successful suppression of HIV RNA levels. Plasma PAF-AH activity may be a sensitive marker of the host response to infection, and the higher levels of plasma and LDL-associated PAF-AH activity in patients with HIV infection and AIDS may be a physiological response to protect the host against oxidative injury from PAF and oxidized phospholipids.

Fetal epidermal differentiation and barrier development In vivo is accelerated by nuclear hormone receptor activators

Nuclear receptors which interact with the retinoid X receptor are involved in the regulation of epidermal differentiation and development. We have recently shown that activators of the peroxisome proliferator-activated receptor and of the farnesoid X-activated receptor accelerate epidermal barrier maturation in fetal rat skin in vitro. In this study we asked whether cutaneous development in utero was affected by peroxisome proliferator-activated receptor or farnesoid X-activated receptor activators, or by an activator of another retinoid X receptor partner, liver X receptor. Activators of the peroxisome proliferator-activated receptor (clofibrate or linoleic acid), farnesoid X-activated receptor (farnesol or juvenile hormone III), or liver X receptor (22R-hydroxycholesterol), were injected into the amniotic fluid of fetal rats on gestational day 17. Fetal epidermal barrier function and morphology was assessed on day 19. Whereas vehicle-treated fetal rats displayed no measurable barrier (transepidermal water loss > 10 mg per cm2 per h), a measurable barrier was induced by the intra-amniotic administration of all activators tested (transepidermal water loss range 4.0-8.5 mg per cm2 per h). By light microscopy, control pups lacked a well-defined stratum corneum, whereas a distinct stratum corneum and a thickened stratum granulosum were present in treated pups. By electron microscopy, the extracellular spaces of the stratum corneum in control pups revealed a paucity of mature lamellar unit structures, whereas these structures filled the stratum corneum interstices in treated pups. Additionally, protein and mRNA levels of loricrin and filaggrin, two structural proteins of stratum corneum, were increased in treated epidermis, as were the activities of two lipid catabolic enzymes critical to stratum corneum function, beta-glucocerebrosidase and steroid sulfatase. Finally, peroxisome proliferator-activated receptor-alpha and -delta and liver X receptor-alpha and -beta mRNAs were detected in fetal epidermis by reverse transcriptase-polymerase chain reaction and northern analyses. The presence of these receptors and the ability of their activators to stimulate epidermal barrier and stratum corneum development suggest a physiologic role for peroxisome proliferator-activated receptor and liver X receptor and their endogenous ligands in the regulation of cutaneous development.

Coordinate assembly of lipids and enzyme proteins into epidermal lamellar bodies

Formation of the epidermal permeability barrier requires delivery of lamellar body (LB) contents to the stratum corneum interstices. LB are enriched in a mixture of polar lipids and a family of hydrolytic enzymes, required for the extracellular processing of the secreted polar lipids into the more hydrophobic products which mediate barrier function. Prior non-quantitative studies show that acute barrier disruption leads to immediate secretion of the contents of performed LB from the outermost layer of granular cells, followed by the synthesis and accelerated secretion of newly-formed (= nascent) organelles over 0.5-4 h. We asked here whether lipids and hydrolytic enzymes are packaged into nascent organelles separately, or in a parallel, linked process. We first quantified the rate of appearance of lipids (by the content of internal lamellae within LB) and enzyme content (by cytochemistry of neutral lipase and acid sphingomyelinase); both are concentrated in LB, and in nascent organelles. Immediately after barrier disruption, the density of LB in the cytosol of the outermost granular cell decreased by > 50% reduction at 30 min, returning to near-normal densities by 4 h. Nascent organelles budded off a trans-Golgi-like reticulum, in the outermost granular cells as early as 30 min. In quantitative studies, LB progressively accumulated lipid and enzyme contents in parallel. However, when lipid/lamellae generation was inhibited with lipid synthesis inhibitors, enzymes did not accumulate in organelles. Likewise, when exogenous physiologic lipids were delivered to sites of LB generation in the face of brefeldin A blockade of organellogenesis, or when lipids were delivered in conjunction with treatment with lipid synthesis inhibitors, enzymes accumulated only in those organelles that displayed lipid content. These studies demonstrate: (a) quantitative changes in the density of LB in the outermost granular cell at various time points after acute barrier disruption; (b) the origin of nascent organelles in a trans-Golgi-like reticulum; (c) co-ordinate packaging of lipid and enzyme contents into nascent organelles; (d) that lipid deposition in nascent organelles is required for enzyme accumulation; and (e) that enzymes can be delivered to nascent organelles, even if the source of lipid is of exogenous rather than endogenous origin.

Epidermal pathogenesis of inflammatory dermatoses

It is generally assumed that dermatitis, whether of allergic or irritant origin, is primarily an immunological/inflammatory disorder. In this article, we review recent information that supports an epidermal contribution to these disorders, as well as several other dermatoses. We first review new concepts of the epidermal barrier, with recent evidence that the stratum corneum is a biosensor that regulates the epidermal lipid and DNA-metabolic responses to a variety of exogenous insults. Various signaling mechanisms, including changes in levels of epidermal cytokines and growth factors, are potential candidates to mediate these metabolic responses. Our results show that these signaling molecules may be generated not in response to permeability barrier requirements, but as an avoidable consequence of the epidermal injury that accompanies all types of acute barrier abrogation. Although the role of cytokines/growth factors as regulators of metabolic events leading to barrier recovery is still unknown, their role in initiating a cytokine cascade leading to cutaneous pathology seems more certain. We conclude that signaling molecules, released following injury to the stratum corneum, initiate a cytokine cascade that induces inflammation, which is responsible for the clinical features of specific dermatoses. Thus, 'outside-to-inside' signaling may contribute to the pathogenesis of a variety of dermatoses characterized by abnormal barrier function.

Down-regulation of liver and heart specific fatty acid binding proteins by endotoxin and cytokines in vivo

Fatty acid binding proteins (FABPs) are abundantly present in tissues that actively metabolize fatty acids (FA). While their precise physiological function is not known, FABPs have been shown to play a role in the uptake and/or utilization of FA within the cell. FA metabolism is markedly altered during the host response to infection and inflammation. Previous studies have demonstrated that endotoxin or bacterial lipopolysaccharide (LPS) enhances hepatic FA synthesis and re-esterification while inhibiting FA oxidation in liver, heart and muscle. Now, we have examined the in vivo effects of LPS and cytokines on FABPs in liver (L-FABP), heart and muscle (H-FABP). Syrian hamsters were injected with LPS, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) and the mRNA and protein content for L-FABP and H-FABP were analyzed. 16 h after administration, LPS (100 microg/100 g body weight) produced a 72% decrease in L-FABP mRNA levels in liver and this effect was sustained for 24 h. LPS also produced a 41% decrease in the protein content of L-FABP in liver after 24 h of treatment. TNF-alpha and IL-1beta decreased L-FABP mRNA levels in liver by 30 and 45%, respectively. LPS decreased H-FABP mRNA levels in skeletal muscle by 60% and in heart by 65%. LPS also produced a 49% decrease in H-FABP protein content in muscle. Neither TNF-alpha nor IL-1beta had any significant effect on H-FABP mRNA expression in heart and muscle. Taken together, these results indicate that LPS decreases FABP mRNA and protein levels in liver, heart and muscle, tissues that normally utilize FA as their primary fuel, whereas the inhibitory effect of cytokines is limited to the liver. The LPS-induced decrease in L-FABP and H-FABP may be an additional mechanism contributing to the decrease in FA oxidation that is associated with the host response to infection and inflammation.

Cutaneous barrier repair and pathophysiology following barrier disruption in IL-1 and TNF type I receptor deficient mice

Disruption of the permeability barrier elicits a homeostatic repair response which rapidly restores barrier function while repeated barrier perturbation results in cutaneous pathology. In response to barrier disruption there is a marked increase in epidermal TNF-alpha and IL-1 production. To determine the potential role of TNF and IL-1 in mediating the cutaneous changes that occur following barrier disruption we compared the kinetics of barrier recovery and the degree of epidermal hyperplasia and cutaneous inflammation in TNF type I (p55) receptor and IL-1 receptor type I (p80) deficient mice. No abnormalities in epidermal morphology were observed with light or electron microscopy in receptor deficient mice. Under baseline conditions epidermal barrier function was unchanged in receptor deficient mice. Following barrier disruption the kinetics of barrier recovery were similar in control vs TNF receptor deficient mice regardless if the barrier was disrupted by acetone treatment, SDS treatment, or tape stripping. In contrast, barrier recovery was slightly but significantly accelerated regardless of the method of barrier disruption in IL-1 receptor deficient mice. The degree of epidermal hyperplasia and cutaneous inflammation following repeated barrier disruption was similar in control, TNF receptor, and IL-1 receptor deficient mice. The present study demonstrates that barrier recovery is not delayed and the degree of epidermal hyperplasia and inflammation are not altered in either TNF receptor or IL-1 receptor deficient mice, indicating that neither TNF nor IL-1 alone are essential for either barrier repair or the cutaneous pathology induced by barrier perturbation. Whereas the increase in IL-1 following barrier disruption may delay components of the repair response, whether either TNF-alpha or IL-1 regulate aspects of the homeostatic response remains unresolved.

Regulation of glycosphingolipid metabolism in liver during the acute phase response

The host response to infection is associated with multiple alterations in lipid and lipoprotein metabolism. We have shown recently that endotoxin (lipopolysaccharide (LPS)) and cytokines enhance hepatic sphingolipid synthesis, increase the activity and mRNA levels of serine palmitoyltransferase, the first committed step in sphingolipid synthesis, and increase the content of sphingomyelin, ceramide, and glucosylceramide (GlcCer) in circulating lipoproteins in Syrian hamsters. Since the LPS-induced increase in GlcCer content of lipoproteins was far greater than that of ceramide or sphingomyelin, we have now examined the effect of LPS and cytokines on glycosphingolipid metabolism. LPS markedly increased the mRNA level of hepatic GlcCer synthase, the enzyme that catalyzes the first glycosylation step of glycosphingolipid synthesis. The LPS-induced increase in GlcCer synthase mRNA levels was seen within 2 h, sustained for 8 h, and declined to base line by 24 h. LPS-induced increase in GlcCer synthase mRNA was partly accounted for by an increase in its transcription rate. LPS produced a 3-4-fold increase in hepatic GlcCer synthase activity and significantly increased the content of GlcCer (the immediate product of GlcCer synthase reaction) as well as ceramide trihexoside and ganglioside GM3 (products distal to the GlcCer synthase step) in the liver. Moreover, both tumor necrosis factor-alpha and interleukin-1beta, cytokines that mediate many of the metabolic effects of LPS, increased hepatic GlcCer synthase mRNA levels in vivo as well as in HepG2 cells in vitro, suggesting that these cytokines can directly stimulate glycosphingolipid metabolism. These results indicate that LPS and cytokines up-regulate glycosphingolipid metabolism in vivo and in vitro. An increase in GlcCer synthase mRNA levels and activity leads to the increase in hepatic GlcCer content and may account for the increased GlcCer content in circulating lipoproteins during the acute phase response.

In vivo regulation of plasma platelet-activating factor acetylhydrolase during the acute phase response

Plasma platelet-activating factor acetylhydrolase (PAF-AH) hydrolyzes PAF and oxidized phospholipids and is associated with lipoproteins in the circulation. Endotoxin [lipopolysaccharide (LPS)], a potent inducer of the acute phase response (APR), produces marked changes in several proteins that play important roles in lipoprotein metabolism. We now demonstrate that LPS produces a 2.5- to 3-fold increase in plasma PAF-AH activity in Syrian hamsters. The plasma PAF-AH activity is found in the high-density lipoprotein (HDL) fraction and is increased threefold with LPS treatment despite a decrease in plasma HDL levels, indicating that plasma PAF-AH activity is increased per HDL particle. LPS markedly increased PAF-AH mRNA levels in liver, spleen, lung, and small intestine. The maximal increase in plasma PAF-AH activity and mRNA expression in liver and spleen is seen 24 h after LPS treatment. Both tumor necrosis factor and interleukin-1 modestly increased plasma PAF-AH activity and mRNA levels in liver and spleen, suggesting that they may partly mediate the effect of LPS on PAF-AH. Surgical removal of spleen had no effect on basal or LPS-induced plasma PAF-AH activity, suggesting that spleen per se may not contribute to plasma PAF-AH activity. Finally, LPS, turpentine and zymosan increased plasma PAF-AH activity in mice and/or rats, indicating that multiple APR inducers upregulate plasma PAF-AH and this effect is consistent across different rodent species. Taken together, our results indicate that plasma PAF-AH activity and mRNA expression is markedly upregulated during the host response to infection and inflammation. An increase in plasma PAF-AH may enhance the degradation of PAF as well as alter the structure and function of HDL during infection and inflammation.

Cloning of murine translation initiation factor 6 and functional analysis of the homologous sequence YPR016c in Saccharomyces cerevisiae

The cDNA sequence of a murine gene whose expression was up-regulated after epidermal injury was cloned utilizing differential display. The full-length cDNA was isolated by 3' and 5' rapid amplification of cDNA ends from mouse liver. The predicted protein is >97% identical to the human sequence for eukaryotic translation initiation factor (eIF) 6, thus identifying the gene as murine eIF6. Functional studies of the yeast eIF6 homolog, YPR016c, were initiated in Saccharomyces cerevisiae to determine the cellular role(s) of eIF6. Complete deletion of the YPR016c coding sequence was lethal. Viability was restored in the presence of either YPR016c or murine eIF6, when either was expressed as amino-terminal green fluorescent protein fusion protein. Moreover, both fusion proteins localized to nuclear/perinuclear compartments in their respective yeast strains. When the expression of YPR016c-green fluorescent protein was repressed, there was a dramatic reduction in the 60 S ribosomal subunit and polysome content and decreased 80S monosome content. Additionally, the YPR016c-depleted cells arrested in G1. These studies show that YPR016c, which encodes yeast eIF6, is necessary for maximal polysome formation and plays an important role in determining free 60 S ribosomal subunit content.

Induction of selected lipid metabolic enzymes and differentiation-linked structural proteins by air exposure in fetal rat skin explants

The epidermal permeability barrier of premature infants matures rapidly following birth. Previous studies suggest that air exposure could contribute to this acceleration, because: (i) development of a structurally and functionally mature barrier accelerates when fetal rat skin explants are incubated at an air-medium interface, and (ii) occlusion with a water-impermeable membrane prevents this acceleration. To investigate further the effects of air exposure on epidermal barrier ontogenesis, we compared the activities of several key enzymes of lipid metabolism and gene expression of protein markers of epidermal differentiation in fetal rat skin explants grown immersed versus air exposed. The rate-limiting enzymes of cholesterol (HMG CoA reductase) and ceramide (serine palmitoyl transferase) synthesis were not affected. In contrast, the normal developmental increases in activities of glucosylceramide synthase and cholesterol sulfotransferase, responsible for the synthesis of glucosylceramides and cholesterol sulfate, respectively, were accelerated further by air exposure. Additionally, two enzymes required for the final stages of barrier maturation and essential for normal stratum corneum function, beta-glucocerebrosidase, which converts glucosylceramide to ceramide, and steroid sulfatase, which desulfates cholesterol sulfate, also increased with air exposure. Furthermore, filaggrin and loricrin mRNA levels, and filaggrin, loricrin, and involucrin protein levels all increased with air exposure. Finally, occlusion with a water-impermeable membrane prevented both the air-exposure-induced increase in lipid enzyme activity, and the expression of loricrin, filaggrin, and involucrin. Thus, air exposure stimulates selected lipid metabolic enzymes and the gene expression of key structural proteins in fetal epidermis, providing a biochemical basis for air-induced acceleration of permeability barrier maturation in premature infants.

Lipoproteins inhibit macrophage activation by lipoteichoic acid

Regulation of lipid metabolism during infection is thought to be part of host defense, as lipoproteins neutralize endotoxin (LPS) and viruses. Gram-positive infections also induce disturbances in lipid metabolism. Therefore, we investigated whether lipoproteins could inhibit the toxic effects of lipoteichoic acid (LTA), a fragment of gram-positive bacteria. LTA activated RAW264.7 macrophage cells, stimulating production of tumor necrosis factor (TNF) in a dose-dependent matter, but produced less TNF than that seen after LPS activation. High density (HDL) or low density lipoprotein (LDL) alone inhibited the ability of LPS to stimulate TNF production, but had little effect on the activation by LTA. When a maximally effective dose of LTA was mixed with lipoproteins and 10% lipoprotein-depleted plasma (LPDP), the ability of LTA to stimulate macrophage production of TNF was inhibited. HDL, LDL, and the synthetic particle, Soyacal, when mixed with LPDP, were able to inhibit the ability of LTA to activate macrophages. Lipopolysaccharide-binding protein (LBP) substituted for LPDP in catalyzing lipoprotein neutralization of LTA by HDL. Antibody to LBP inhibited the ability of LPDP to induce LTA neutralization by HDL.Thus, lipoproteins can prevent macrophage activation by fragments from both gram-positive and gram-negative microorganisms.-Grunfeld, C., M. Marshall, J. K. Shigenaga, A. H. Moser, P. Tobias, and K. R. Feingold. Lipoproteins inhibit macrophage activation by lipoteichoic acid.