Molecular Structure of Human-Liver Glycogen.

Glycogen is a highly branched glucose polymer which is involved in maintaining blood-sugar homeostasis. Liver glycogen contains large composite α particles made up of linked ß particles. Previous studies have shown that the binding which links ß particles into α particles is impaired in diabetic mice. The present study reports the first molecular structural characterization of human-liver glycogen from non-diabetic patients, using transmission electron microscopy for morphology and size-exclusion chromatography for the molecular size distribution; the latter is also studied as a function of time during acid hydrolysis in vitro, which is sensitive to certain structural features, particularly glycosidic vs. proteinaceous linkages. The results are compared with those seen in mice and pigs. The molecular structural change during acid hydrolysis is similar in each case, and indicates that the linkage of ß into α particles is not glycosidic. This result, and the similar morphology in each case, together imply that human liver glycogen has similar molecular structure to those of mice and pigs. This knowledge will be useful for future diabetes drug targets.

Impairment of Liver Glycogen Storage in the db/db Animal Model of Type 2 Diabetes: A Potential Target for Future Therapeutics?

After the discovery of the db gene in 1966, it was determined that a blood-borne satiety factor was produced excessively, but was not responded to, in db/db mice. This model for type 2 diabetes is widely used since it phenocopies human disease and its co-morbidities including obesity, progressive deterioration in glucose tolerance, hypertension and hyperlipidaemia. Db/db mice, unlike their non-diabetic controls, have consistently elevated levels of liver glycogen, most likely due to hyperphagia. In transmission electron micrographs, liver glycogen usually shows a composite cauliflower-like morphology of large "α particles" (with a wide range of sizes) made up of smaller "ß particles" bound together. New studies have explored the size distribution of liver glycogen molecules and found that α particles in db/db mice are more chemically fragile than those in healthy mice, and can readily break apart to smaller ß particles. There is evidence that smaller glycogen particles have a higher association with glycogen phosphorylase, a key enzyme involved in glycogen degradation, as well as being degraded more rapidly in vitro; therefore the inability to form stable large glycogen α particles is predicted to result in a faster, less controlled degradation into glucose. The implications of this for glycaemic control remain to be fully elucidated. However, "rescuing" the more fragile diabetic glycogen to decrease hepatic glucose output in type 2 diabetes, may provide a potential therapeutic target which is the subject of this review.

Histochemical and ultrastructural analysis of hepatic glycogen and collagen fibers in alloxan-induced diabetic rats submitted to long-term physical training.

Alterations in liver functions are common among diabetic patients, and many symptoms in the liver have been reported, including changes in glycogen stores and in the amount of collagen fibers. The practice of physical training and its morphological effects in this organ, however, are scarcely studied. In order to observe the morphological effects of alloxan-induced diabetes and the alterations arising from the practice of long-term chronic physical training in the liver, samples were collected and processed, and then analyzed by means of the histochemical techniques Periodic Acid-Schiff and Picrosirius-Hematoxylin, and ultrastructural cytochemical test of Afzelius. Through evaluation of the tissue, it was observed a drastic reduction in hepatic glycogen stores of sedentary diabetics, recovered in trained diabetic rats. Furthermore, it was detected a decrease in the content of perisinusoidal collagen fibers in the diabetic liver, also recovered due to the development of a training protocol. On ultrastructural level, cytochemical analysis confirmed the loss of glycogen and the recovery obtained by training. In conclusion, the practice of a long-term chronic physical training protocol may be considered an important assistant in the treatment of diabetes, mitigating the occurrence of possible damages to liver tissue.

[Ultrastructural study of liver cells from rooks living in ecologically unfavorable areas].

The ultrastructure of liver cells was studied in rooks (Corvus frugilegus) living in radioactive and chemical contamination areas. The ultrastructure of liver cells from rook as well as jackdaw (Corvus monedula) and hooded crow (Corvus cornix) (Corvidae family) from a conventionally clean area was studied as control. Control hepatocytes proved to contain a great number of mitochondria, many of which were swollen and had clear matrix and disorganized cristae. The cristae nearly lacked glycogen and had abundant lipid droplets, which often tightly contacted mitochondria. The cytoplasm of hepatocytes in birds from both ecologically unfavorable areas had numerous mitochondria with the same ultrastructure. In contrast to control, the hepatocyte cytoplasm: (1) contained a lot of glycogen; (2) there were many lipid droplets, which directly contacted glycogen granules; and (3) had more abundant peroxisomes. In addition to normal erythrocytes, the sinusoids contained erythrocytes with mitochondria, vesicles, and lipid droplets in their cytoplasm. Analysis of many micrographs of lipid droplets contacting glycogen granules, mitochondria, peroxisomes, and cisterns of smooth endoplasmic reticulum allowed us to propose that glycogen is synthesized via gluconeogenesis from glycerol and products of fatty acid oxidation in the liver cell cytoplasm of rooks from ecologically unfavorable areas as distinct from control.

Morphometric alterations in hepatocytes and ultrastructural distribution of liver glycogen in pacu (Piaractus mesopotamicus Holmberg, 1887) during food restriction and refeeding

The morphometric alterations in hepatocytes and the ultrastructural distribution of tissue glycogen in pacu (Piaractus mesootamicus) were studied following food restriction and refeeding. Fish (200-300g) were allocated to control and experimental groups. The experimental group was sampled after 0, 2, 7, 30 and 60 days of food restriction and after 7 and 30 days of refeeding. The control group, which was fed daily, was sampled on the same days. The morphometric results were analyzed by ANOVA in a 2x7 (feeding x days) factorial design and the averages compared by the Tukey test. Transmission electron microscopy showed liver glycogen mobilization during food restriction. The levels of glycogen did not return to normal after up to 30 days of refeeding. There was a decrease in the cytoplasmic area and volume after seven days without food whereas changes in the nuclear area and volume appeared after two days of food restriction. Recovery of the nuclear and cytoplasmic area and volume occurred after 7 days and 30 days of refeeding, respectively. These results indicate tha liver glycogen supplies at least part of the energy requirement during food restriction in juvenile pacu. Thirty days of refeeding were not enough to re-establish the pre-restriction carbohydrate levels, probably because of the extra energy demand associated with the high metabolic rate that occurred during the compensatory process of refeeding at elevated ambient temperatures. However, the recovey seen in the morphometric parameters of the hepatocytes indicated a functional re-adjustment of the liver stimulated by the restored food supply.