Differential scanning calorimetry of dispersions of products of oxidation of 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine

Ultraviolet light was used to promote the autoxidation of 1-stearoyl-2-linoleoyl-sn-glycero-3-phosphocholine (SLPC). The extent of oxidation was monitored by ultraviolet spectroscopy, reaction with thiobarbituric acid, fatty acid analysis, and thin-layer chromatography. Fatty acid analysis and thin-layer chromatography appeared to provide the most consistent estimates of oxidation, especially when extensive oxidation had taken place. The oxidized samples were separated by flash chromatography into fractions enriched in different oxidation products. Differential scanning calorimetry of aqueous dispersions of these fractions indicated that oxidation products had higher transition temperatures than the original SLPC.

Interactions between plasma proteins and pulmonary surfactant: pulsating bubble studies

The influence of human albumin, alpha-globulin, and fibrinogen on the actions of porcine pulmonary surfactant in a pulsating bubble surfactometer has been investigated. All three proteins detracted from the ability of the surfactant to adsorb to the air-water interface. The proteins also reduced the ability of surfactant to lower the opening pressures of bubbles cycling between different sizes in suspensions of surfactant. This was equivalent to restricting the ability of the surfactant to achieve low surface tension during compression of the surface. Of the three proteins, globulin competed most effectively with surfactant during the adsorption process, and albumin competed the least effectively. The proteins also may have interfered with the processes of surface refinement, which usually yields a monolayer enriched enough in dipalmitoyl phosphatidylcholine to achieve very low surface tension (very low opening pressures in the bubbles). Of the three proteins tested, albumin was least deleterious to surface refining whereas globulin and fibrinogen appeared to be about equally detrimental to the process.

Interactions between plasma proteins and pulmonary surfactant: surface balance studies

The influence of human fibrinogen, alpha-globulin, and albumin on the properties of monolayers of pulmonary surfactant under dynamic compression and expansion has been studied at 37 degrees C. Each of the proteins altered some of the properties of the normal compression and expansion isotherms of surfactant such that characteristics deemed desirable for proper lung function were impaired. The order of potency of these effects was fibrinogen greater than globulin greater than albumin. The proteins (a) decreased the maximum surface pressure (equivalent to the minimum surface tension) which the surfactant monolayers attained on compression, (b) decreased the areas occupied per mole of lipid phosphorus when the monolayers were at surface tensions of 20 and 12 mN.m-1, (c) reduced the areas of the hysteresis between compression and expansion isotherms, and (d) decreased the rate of change of surface tension with area at the point of initial expansion of the monolayers. The proteins might compete with surfactant lipid for available space at the interface, especially at low film compression. They might also enhance the desorption of lipid from the monolayer. The findings are consistent with the loss of pulmonary function and presence of edema that occur in adult respiratory distress syndrome being contributed to by plasma proteins interfering with surfactant function.

The effect of methylation of phosphatidylethanolamine on the behaviour of lipid monolayers at the air-water interface

Monolayers of DPPE and its N-methylated derivatives including DPPC have been investigated at 23 and 37 degrees C using a modified Langmuir-Wilhelmy surface balance. The monolayers have been subjected to dynamic compression and expansion, and some characteristics of the surfaces have been determined. The minimum surface tension attained by surfaces containing the lipids (maximum surface pressures sustained by the films) depended on the extent of methylation of the head group. Monolayers of DPPE or N-MeDPPE collapsed at surface tensions of 12-16 mN.m-1, whereas those containing N,N-diMeDPPE and DPPC could be compressed to near zero surface tension. The areas per molecule occupied by these lipids under high compression varied slightly and not systematically with head-group methylation. Monolayers containing mixtures of DPPC and DPPE were also studied under the same conditions. The monolayers showed some deviation from the behaviour expected if they were to have characteristics of ideally mixed systems. The minimum surface tensions attained suggested that monolayers containing 50 mol% or more DPPC might be further enriched during compression by some selective exclusion of the DPPE. At high surface pressures, some positive deviations in nominal areas per molecule from that expected for ideal mixing were observed in the monolayers made with 50 mol% or more DPPC. These deviations might be caused by packing disruptions associated with the explosion of lipid from the films.

Serial cultivation of epidermal keratinocytes from psoriatic plaques

Using the combined techniques of Rheinwald and Green, and Liu and Karasek, large quantities of proliferative keratinocytes from involved (PP) or uninvolved (PN) skin of psoriatic patients and from normal skin of non-psoriatic donors (NN) can be obtained. Primary cultures, initiated from a 6-mm punch biopsy, are grown on a 3T3 feeder layer seeded on a collagen surface and fed with Dulbecco's Modified Eagle's Medium containing 20% fetal calf serum, hydrocortisone, epidermal growth factor, and cholera toxin. To test the hypothesis that the mechanism(s) responsible for the abnormal proliferation of psoriatic keratinocytes may be located within the cells themselves, primary cultures are passaged onto collagen surfaces without a feeder layer and maintained with medium plus serum, but no additional supplements, and the growth profiles of the 3 cell populations compared. No difference in morphology among these cells is observed in either primary or passaged cultures. In primary cultures, PP keratinocytes, especially those isolated from active lesions, seem to initiate growth at a slower rate than do PN and NN keratinocytes. The difference in the growth rate, as determined by cell number, DNA content, and mitotic activity, is insignificant among passaged PP, PN, and NN cells. Waves observed in the mitotic index and the metabolic activity of the passaged keratinocytes from all 3 sources suggest that the cells are synchronized during subculturing. The cells have high metabolic and mitotic activities during the first week after subculturing, indicative of an initial population of actively dividing cells. We have not found the characteristic feature of hyperproliferation seen in psoriatic keratinocytes in situ, in the cultured cells; however, it is too early to reach the definite conclusion that the mechanism(s) responsible for psoriasis does not exist in the keratinocyte itself. These 3 cell types may respond differently to agents that either enhance or inhibit cell growth and, by using the culture system outlined in this report, we may study these factors and their potential role in psoriasis.

DNA repair response in human epidermal keratinocytes from donors of different age

We have compared the excision-repair and growth properties of epidermal keratinocytes from humans of different ages. Keratinocytes isolated from newborn and adult abdominal skin at autopsy were cultured on collagen gels. Repair replication was assayed by the 5-bromodeoxyuridine density-labeling method following ultraviolet (UV) irradiation (254 nm) of the cultures. The keratinocytes from newborn donors proliferated more rapidly and attained a higher concentration at confluence than did those from aged donors. Semiconservative DNA replication was inhibited by UV radiation to an equal extent in cell cultures from newborns and adults. After a UV dose of 13 J/m2, the time course of DNA repair was similar for the respective cultures. Furthermore, there were no significant differences in the time course of repair for keratinocytes in the proliferative or the plateau phase of growth. The dose-response curves for repair replication in cells from both young and old donors maximized at about 50 J/m2 but the attenuation in repair at higher doses appeared somewhat greater in cells from older donors. We conclude that no significant age-related differences exist in the rate and extent of the repair-replication response of human epidermal keratinocytes to UV-radiation damage in DNA. However, it remains to be determined whether other cellular recovery responses to damaged DNA are also relatively unrelated to age.

DNA repair responses in human skin cells

Sunlight and some environmental chemical agents produce lesions in the DNA of human skin cells that if unrepaired may interfere with normal functioning of these cells. The most serious outcome of such interactions may be malignancy. It is therefore important to develop an understanding of mechanisms by which the lesions may be repaired or tolerated without deleterious consequences. Our models for the molecular processing of damaged DNA have been derived largely from the study of bacterial systems. Some similarities but significant differences are revealed when human cell responses are tested against these models. It is also of importance to learn DNA repair responses of epidermal keratinocytes for comparison with the more extensive studies that have been carried out with dermal fibroblasts. Our experimental results thus far indicate similarities for the excision-repair of ultraviolet-induced pyrimidine dimers in human keratinocytes and fibroblasts. Both the monoadducts and the interstrand crosslinks produced in DNA by photoactivated 8-methoxypsoralen (PUVA) can be repaired in normal human fibroblasts but not in those from xeroderma pigmentosum patients. The monoadducts, like pyrimidine dimers, are probably the more mutagenic/carcinogenic lesions while the crosslinks are less easily repaired and probably result in more effective blocking of DNA function. It is suggested that a split-dose protocol that maximizes the production of crosslinks while minimizing the yield of monoadducts may be more effective and potentially less carcinogenic than the single ultraviolet exposure regimen in PUVA therapy for psoriasis.