[Changes in peritoneal mesothelial cells in patients on peritoneal dialysis]

Some thirty years ago peritoneal dialysis (PD) became a respectable modality of renal replacement therapy. That is why peritoneal membrane attracted interest of investigators. Certain changes, known as uremic serositis, appear in morphology of serous membranes in end stage kidney disease (ESKD). The aim of our investigation was to examine the morphology of peritoneal lining cells in control group of healthy persons and morphology of peritoneal lining cells in patients on PD.

Peritoneal biopsies were taken in 10 healthy volunteers during the kidney donation and in 15 patients on PD during clinically indicated extirpation. Biopsy samples were prepared for standard routine HE staining and for plastic embedded fine sections studying. Sections were mounted in an ultramicrotome, stained with Toluidine blue (TB) and studied by light microscope (SM), while fine sections were mounted in an ultramicrotome and studied by transmission electron microscope (TEM).

One layer mesothelium of the cuboidal or flattened lining cells were present over the lamina propria connective tissue. Mesothelial cells were overlapped like tiles on the roof. These cells were interconnected with different types of cell junctions (unpermeable, adhesion and communication junctions) positioned on lateral parts of the interdigitated cell membranes. A great number of microvilli were often present on the appical surface, as well as a kinocilia and lamellar bodies. Nuclei were euchromatic with well developed nucleoli. Many ribosomes, mitochondria, cisternae of rough endoplasmic reticulum (RER) and Golgi apparatus, lamellar bodies and lipid inclusions were present in the cytoplasm. Using TEM in analyzing fine sections of biopsies of patients on PD, characteristic ultrastructural changes including epithelial defects with only remaining parts of destroyed cells were established, as well as significantly greater number of rough endoplasmic reticulum (RER) cisternae and immature mesothelial cells in lamina propria indicating intensive regeneration of this epithelium. The cytoplasm of new mesothelial cells were of less electron density on TEM photomicrographs, whereas the nuclei of mesothelial cells in these patients were euchromatic with prominent nucleoli and numerous perichromatic granules and fibrogranular nuclear bodies, indicating cells of great activity. Cytoplasmic protrusions of different shape and content were often recognized on the apical surface of cells. Lamellar bodies were also present in this group of patients within the mesothelial cells, as well as between two mesothelial cells or on their apical surface. Mitochondria were picnotic in many of the mesothelial cells of peritoneum in this patient group. In these mesothelial cells intracytoplasmic paracrystaline inclusions were established. TEM photomicrographs showed basal lamina multiplication in this epithelium.

Our findings comply with reports of other authors. It should be stressed that TEM examination detects characteristic ultrastructural changes in mesothelial lining cells of peritoneum in patients on PD, which could compromise the function of peritoneum as a membrane for dialysis.