[Scintigraphic study of gastric emptying and intragastric distribution of a solid meal: gender differences]

Gender-related differences in gastric emptying are still controversial. The aims of this study were: to confirm the sex-related difference in gastric emptying of a solid meal and to investigate its association with different patterns of meal distribution between the proximal and distal gastric compartments. Eighteen healthy volunteers (nine males, mean age 35 +/- 9 years; nine females, mean age: 41 +/- 11 years) were studied in the morning, after ingestion of the solid test-meal (an omelette labeled with 185MBq of 99mTc-sulfur colloid). Simultaneous anterior and posterior images of the stomach were acquired immediately after ingestion of the meal and every 10 minutes for 120 minutes. Time versus activity curves were obtained for the whole, proximal and distal stomach. Gastric T1/2 was longer in women (96.1 +/- 17.2 min) than in men (79.9 +/- 17.8 min; P = 0.02). The analysis of the meal distribution inside the stomach showed no differences between males and females in proximal gastric emptying, but the meal retention in the distal compartment was significantly increased among women (P = 0.04). In conclusion, gastric emptying of a solid meal is slower in pre-menopausal women than in age-matched men, probably due to an increased retention of the meal in the distal compartment. This should be taken into consideration to avoid misleading diagnosis of gastroparesis for female patients.

In vitro and post-transplantation differentiation of human keratinocytes grown on the human type IV collagen film of a bilayered dermal substitute

Using human type IV and type I + III collagens and a new, nontoxic cross-linking procedure, we have developed a cell-free bilayered human dermal substitute for organotypic culture and transplantation of human skin keratinocytes. We have studied the formation of the basement membrane, and the differentiation of keratinocytes grown on the type IV collagen layer of this dermal substitute, in vitro and after grafting onto nude mice. These studies demonstrated the formation of essential constituents of the basement membrane in culture: hemidesmosomes and deposition of extracellular matrix on the top of the type IV collagen were observed as early as 6 days after plating of human keratinocytes. Although the keratinocytes formed a well-organized multilayered epithelium, they exhibited limited differentiation when grown submerged in liquid medium. However, the multilayered sheet obtained after 14 days in submerged culture was composed of a regular basal cell layer, several nucleated suprabasal cell layers containing granular cells, and several dense, anucleated cell layers. The grafting experiments have shown a good biocompatibility of the dermal substitute. It is repopulated by fibroblasts, newly synthesized collagen, vessels, and a few mononuclear cells. At Day 14 after grafting, the type IV collagen layer was still present and very dense, and the basement membrane appeared as in culture, with numerous well-structured hemidesmosomes and deposition of extracellular matrix resembling lamina densa. At Day 55 after transplantation, even if the epidermal graft did not exhibit all the characteristics of the normal epidermis in vivo, it was very close to it. At this stage, the basement membrane was complete, with structures clearly indicative of anchoring fibrils. This new dermal substitute offers many advantages. It is stable and easy to handle. Its production is standardized. The oxidation induced by periodic acid led to a nontoxic cross-linked matrix. This dermal substitute is the first one entirely composed of human collagens. The type I + III collagen underlayer is reorganized when grafted. It supports a type IV collagen top layer which offers an excellent substrate for keratinocytes, favors their anchorage, and favors the formation of the basement membrane in vitro. This dermal substitute could be useful for wound coverage or as an in vitro model for toxicological and pharmacological studies.

Cultured keratinocyte grafts are recognized, but not rejected by CD8+ T cells in vivo

It has been shown in the mouse that cultured keratinocyte allografts [fully major histocompatibility complex (MHC) mismatched] survive for at least 100 days without evidence of rejection. In an attempt to analyze the immune mechanisms underlying this phenomenon we have investigated the induction of tolerance to such grafts. Primary cultures of BALB/c keratinocytes were prepared using irradiated 3T3 feeder cells, and the cultured cell sheets were grafted, using a silicone transplantation chamber, onto CBA recipients. After the cultured grafts had been in place for 4-6 weeks full-thickness tail skin from BALB/c donors was grafted onto the dorsal flank opposite the cultured graft. The median graft survival time of these full-thickness allografts was 15.5 days compared to 13 days in the control group. These data show that in the absence of Langerhans cells and MHC class II expression, keratinocytes expressing class I and minor histocompatibility antigens induce a prolonged survival of full-thickness skin allografts. The results from experiments in which T cell subsets were depleted in vivo suggest that CD8+ cells (a) recognize the class I alloantigens of the cultured graft, (b) do not reject the cultured graft and (c) do not progress further in their maturation pathway. We propose that these CD8+ T cells might have been partially primed by receiving only the first signal of activation and that they may be equivalent to "poised" cytotoxic T cells. These CD8+ cells can reject non cultured full-thickness skin grafts, and do so more effectively after removing CD4+ cells.

Epithelial differentiation of human skin equivalents after grafting onto nude mice

Human skin equivalents were developed in vitro with a unidimensionally retracted dermal equivalent made of human type I + III collagen and human MRC5 fibroblasts, and a multilayered epithelium grown in liquid medium from normal human keratinocytes in suspension. We investigated the degree of epidermal differentiation that could be achieved after in vivo grafting onto nude mice by means of light and electronmicroscopy as well as by immunohistochemistry. All transplanted grafts showed a primary take. The grafts formed an epidermis with a stratum corneum and from day 7 to 14 after transplantation a distribution of a 56.5 Kd keratin protein, involucrin, profilaggrin/filaggrin, and MHC-I antigens that was similar to what is noted in normal human epidermis. These data indicate that a full terminal differentiation was only achieved after in vivo transplantation of the cultured epithelium. Pigmentation was present, but no marker of Langerhans cells was seen at 4 weeks. Although there was no evidence of the dermal equivalent after 2 weeks, we noted a strong adherence of the graft to the wound bed, with the presence of type-IV collagen, laminin, and bullous pemphigoid antigen at the dermo-epidermal junction (day 7) and hemidesmosomes, a lamina lucida and a lamina densa (day 30). No epithelial damage was noted in spite of an inflammatory infiltrate in the underlying tissue. This represents a preliminary step in the use of such a skin-equivalent in the treatment of human patients with wounds.

Growth and differentiation of human keratinocytes on extracellular matrix

Extracellular matrices (ECM) have been reported to enhance epithelial cell attachment and proliferation as well as to induce differentiation in vitro. Since ECM components are physiological constituents of the dermoepidermal basement membrane, we studied the growth and differentiation of human keratinocytes on ECM in order to determine the benefits of culturing epidermal epithelial cells (keratinocytes) on reconstituted basement membranes. Disaggregated epidermal cells were grown in primary and subcultures in liquid medium; the attachment of the cells was greatly enhanced by ECM and noted within the first few hours after seeding; cells formed small islets that reached confluence within 2-12 days depending upon the plating density and the type of culture (primary or passages). Histological and ultrastructural cross-sections of the cultures clearly indicated that a multilayered epithelium can be obtained including a basal cell layer, several intermediate cell layers with cytoplasmic organelles, intermediate size filaments, desmosomes, and keratohyaline granules, and an upper layer of anucleated cells. Using immunofluorescence, both pemphigus and pemphigoid (basal membrane zone) antigens were expressed. The keratin pattern noted indicated that these epithelia differentiate and keratinize but do not express a complete program of keratinization, a finding usually noted when cells are grown submersed. These data show that ECM favor epidermal cell proliferation and differentiation and suggest that they may be used to obtain large amounts of epidermal equivalent suitable for grafting and/or in vitro studies.