Electron Microscopy

Krabbe disease (globoid cell leukodystrophy) was found with very high incidence (6/1,000 live births) in a large Druze kindred in Israel. The clinical data on 12 of the affected children demonstrated clinical variability even though these children are homozygous for the same mutation by descent from a common ancestor.

Although there has been substantial progress in the identification of diarrheal diseases in infancy and childhood, electron microscopy may be still required for establishing diagnosis, staging and response to therapy. This review describes severe conditions in which histopathology alone cannot provide a firm diagnosis needed for therapeutic decisions. Microvillus inclusion disease, in its several variants, typifies this category. In certain forms of congenital disorders of glycosylation with gastrointestinal involvement, electron microscopic diagnosis is helpful. Among disorders due to abnormal immunemediated reactions, celiac disease and cow's milk protein intolerance show fine structural changes of both diagnostic and staging value. Likewise, protein loosing enteropathies, including lymphangectasia, reveal information on the nature and extent of intestinal involvement.

Aggregated low-density lipoprotein (LDL) was shown to be present in the atherosclerotic lesion, but the mechanism responsible for its formation in vivo is not known yet. To find out whether LDL aggregation occurs in the arterial wall during atherogenesis, LDLs were extracted from the aortas of apolipoprotein E-deficient (E 0 ) mice during their aging (and the development of atherosclerosis), and were analyzed for their aggregation states, in comparison to LDLs isolated from aortas of control mice. LDL isolated from aortas of E 0 mice was already aggregated at 1 month of age and its aggregation state substantially increased with age, with 3-fold elevation at 6 months of age compared to younger, 1-month-old, mice. Only minimal aggregation could be detected in LDL derived from control mice. Electron microscopy examination revealed that LDL particles from aortas of the E 0 mice were heterogeneous in their size, ranging between 20 and 300 nm. The mouse aortic LDL contained proteoglycans (PGs) and their content increased with the age of the mice, with about 2-fold higher levels than those found in LDLs derived from aortas of control mice. Macrophage-released PGs were previously demonstrated to enhance LDL aggregation in vitro. However, their involvement in LDL aggregation in vivo has not been studied yet. Thus, we next studied the effect of arterial macrophage-released PGs on the susceptibility of plasma LDL to aggregation by Bacillus cereus sphingomyelinase (SMase). Foam cell macrophages were isolated from aortas of the atherosclerotic E 0 mice at 6 months of age and were found to be loaded with cholesterol and to contain oxidized lipids. To analyze the effect of macrophage-released PGs on LDL aggregation, PGs were prelabeled by cell incubation with [ 35 S]sulfate, followed by incubation of macrophage-released PGs with E 0 mouse plasma LDL (200 mg protein/ml) for 1 h at 37°C. [ 35 S]Sulfated PGs were found to be LDL-associated and the susceptibility of PG-associated LDL to aggregation by SMase was increased by up to 45% in comparison to control LDL. Similar results demonstrating the involvement of PGs in LDL aggregation were obtained upon incubation of LDL with increasing concentrations of PGs that were isolated from the entire aorta of E o mice (rather than the isolated macrophages). The stimulatory effect of macrophage-released PGs on LDL aggregation was markedly reduced when the PGs were pretreated with the glycosaminoglycan-hydrolyzing enzymes, chondroitinase ABC or chondroitinase AC, and to a much lesser extent with heparinase. We thus conclude that macrophage-released chondroitin sulfate PG can contribute to the formation of atherogenic aggregated LDL in the arterial wall.

Acetaminophen in large doses is well-known as hepatotoxic, and early therapy with N-acetylcysteine is frequently life-saving. However, in later stages of acetaminophen poisoning, treatment with N-acetylcysteine is not always effective. Although some of the pathways of acetaminophen toxicity and the effect of N-acetylcysteine have been elucidated, in depth information on this process is still lacking. Hepatoma-derived HepG2 cultured cells were exposed to acetaminophen (5 and 10 mM), with or without N-acetylcysteine (5 mM), for 24 and 48 hr. For the assessment of oxidative damage, apoptosis and necrosis, we followed redox status, glutathione content, nuclear fragmentation, phosphatidylserine externalization and ultrastructural changes. Variations in Ca2 π level and number of mitochondrial dense granules were also studied. Acetaminophen treatment of HepG2 cells caused oxidative damage and apoptosis. Significant decrease of cellular redox potential and glutathione content were time-and concentration-dependent. The protective effect of N-acetylcysteine was expressed by an increase of intracellular glutathione and of the level of metabolic reduction of the redox indicator Alamar Blue. The apoptogenic effect of acetaminophen was assessed by flow cytometry of annexin V binding, nuclear hypodiploidity, intracellular Ca2 π , as well as by ultrastructural examination. Beyond 24 hr of acetaminophen exposure, necrosis was also noticed. We conclude that acetaminophen-induced oxidative damage in HepG2 cultured cells can be prevented by exposure to N-acetylcysteine. However, apoptosis, either early or late, here demonstrated, is not avoided by exposure to N-acetylcysteine. N-Acetylcysteine did not prevent acetaminophen-induced plasma membrane asymmetry, nuclear damage, alterations of Ca2 π homeostasis and ultrastructural changes.

Acetaminophen overdose causes severe hepatic failure. Although the mechanisms of acetaminophen hepatotoxicity have been well investigated, little is known about the involvement of the P-glycoprotein in acetaminophen transport and toxicity. P-Glycoprotein is a membrane efflux pump, playing a significant role in regulating absorption, excretion, and tissue distribution of many drugs. To evaluate the contribution of P-glycoprotein transporter in the course of acetaminophen-induced toxicity, HepG2 and Hep3B cells with different P-glycoprotein expression and activity, were treated by acetaminophen (1-10 mM) for different time periods, with or without the P-glycoprotein inhibitor verapamil. P-Glycoprotein activity was determined by rhodamine 123 efflux assay and western blot analysis. To assess the acetaminophen-induced toxicity and effect of verapamil, we investigated cellular redox status, phosphatidylserine externalization, nuclear fragmentation and ultrastructural changes. Verapamil markedly enhanced acetaminophen-induced oxidative damage and cell death. Moreover, verapamil revealed acetaminophen toxicity even at subtoxic levels. High acetaminophen concentrations increased P-glycoprotein activity and content in both HepG2 and Hep3B cells. These observations suggest the involvement of P-glycoprotein in acetaminophen transport. Notwithstanding the differences of the investigated hepatoma cell lines in P-glycoprotein function, acetaminophen-induced toxicity was similar, possibly due to different functions of drug-metabolizing systems. We conclude that acetaminophen is a P-glycoprotein substrate and P-glycoprotein is involved in acetaminophen transport and toxicity in HepG2 and Hep3B cells. This study establishes the fact that acetaminophen can modulate P-glycoprotein in tumour cells, suggesting that its routine use in cancer patients in combination with anticancer drugs, may influence the result of chemotherapy.