Characterization and quantitative determination of gangliosides and neutral glycosphingolipids in human liver

Adrenocorticotropic hormone (ACTH)-lipid interactions. Implications for involvement of amphipathic helix formation

ACTH-lipid interactions were investigated by: (1) lipid-monolayer studies using several zwitterionic and anionic phospholipids and gangliosides, (2) permeability experiments by following the swelling rate of liposomes in isotonic glycerol solutions by light scattering, using liposomes of synthetic lipids and liposomes made of lipids extracted from light synaptic plasma membranes, and (3) by steady-state fluorescence anisotropy measurements on liposomes derived from light synaptic plasma membranes employing 1,6-diphenyl-1,3,5-hexatriene as fluorescent probe. (1) The monolayer experiments demonstrated an interaction with gangliosides GT1, GM1, dioleoylphosphatidic acid and phosphatidylserine, but little or no interaction with phosphatidylcholine or sphingomyelin. The interaction with monolayers of GT1 or phosphatidic acid decreased for ACTH1-13-NH2 and ACTH1-10. (2) The liposome experiments showed that 2 X 10(-5) M ACTH1-24 increased the glycerol permeability by 20% and decreased the activation energy only when liposomes derived from light synaptic plasma membranes were used. Treatment of the liposomes with neuraminidase abolished the ACTH-induced permeability increase. (3) Steady-state fluorescence depolarization measurements revealed that ACTH1-24, ACTH1-16-NH2 and ACTH1-10 did not change the fluidity of liposomes derived from light synaptic plasma membranes as sensed by diphenylhexatriene. It is concluded that ACTH1-24 can bind to negatively charged lipids and can form an amphipathic helix aligned parallel to the membrane surface involving the N-terminal residues 1 to 12, possibly to 16. Polysialogangliosides will favorably meet the condition of a high local surface charge density under physiological circumstances. It is suggested that ACTH-ganglioside interactions will participate in ACTH-receptor interactions.

Neutral lipid precursors for gangliosides are not formed by rat liver homogenates or by purified cell fractions

As part of an ongoing investigation into the ganglioside and neutral glycosphingolipid biosynthetic pathways in rodent liver, the synthesis of ceramide, glucosylceramide and lactosylceramide was examined in homogenates and purified membrane fractions of rat liver. Ceramide synthesis and its stimulation by exogenously added D-sphingosine was demonstrated in homogenates and isolated membrane fractions, with activity concentrated in the endoplasmic reticulum. In contrast, significant D-sphingosine- or ceramide-dependent formation of glucosylceramide, or glucosylceramide-dependent formation of lactosylceramide (in the presence of labelled UDP-[14C]glucose and UDP-[14C]galactose, respectively,) could not be demonstrated. The possibility is raised that liver may be dependent on extra-hepatic sources of neutral glycosphingolipids to support ganglioside biosynthesis.

Biochemical studies in Niemann-Pick disease. I. Major sphingolipids of liver and spleen

In liver and spleen specimens of 12 patients with Niemann-Pick disease types A or B, sphingomyelin was increased 15-45-fold, total phospholipids 4-10-fold and cholesterol 3-6-fold over the normal values. The storage pattern was qualitatively similar in both types but the degree of accumulation was less in type B. In Niemann-Pick disease type C (16 cases), sphingomyelin was increased 3.5-fold in liver and 6-fold in spleen. In all forms of Niemann-Pick disease, bis(monoacylglycero)phosphate was markedly elevated. Glycosphingolipids were studied in six cases with type C, three cases with type B and two cases with type A. Glucosylceramide showed the largest increase from the normal pattern in all types of Niemann-Pick disease. Highest values were recorded in type C, 14- and 35-fold normal concentrations in liver and spleen, respectively. Other neutral glycosphingolipids, particularly lactosylceramide, were also elevated, and a 2-4-fold increase of ganglioside GM3 occurred. The fatty acid profiles of the sphingolipids showed only minor alterations. In contrast to the largely dominating sphingomyelin storage found in liver and spleen of Niemann-Pick disease types A and B, the major characteristic of the lipid storage in Niemann-Pick disease type C was the absence of any prevailing accumulation and, thus, the concept of this disorder as a primary sphingomyelin storage disease is not founded.

The occurrence of psychosine and other glycolipids in spleen and liver from the three major types of Gaucher's disease

Glycolipid changes in spleen autopsy specimens were determined in four cases of Gaucher's disease type I, three cases of type II, and twelve cases of type III. These changes were also determined in liver autopsy specimens from three cases of type II and in nine cases of type III. The concentration of glucosylceramide in spleen was of the same magnitude in all three types, 36.3 +/- 11.7 mmol/kg in type I, 32.7 +/- 8.5 mmol/kg in type II, and 32.6 +/- 6.9 mmol/kg in type III. In liver there were large differences in the glucosylceramide concentration between splenectomized and non-splenectomized cases. Thus, in the non-splenectomized type III cases it was 9.9 +/- 3.0 mmol/kg, while in the splenectomized type III cases it was 24.1 +/- 6.1 mmol/kg. The accelerated deposition of glucosylceramide in liver after splenectomy was also demonstrated by analyses of liver biopsy specimens. A 2-6-fold increase of gangliosides was found in liver and spleen from the three types, with no significant differences between the types. The increase of gangliosides was limited almost exclusively to GM3. Glucosylsphingosine, never detected in normal tissue, was demonstrated in all samples from Gaucher's livers and spleens. The concentration in spleen was in type II, 0.16 +/- 0.05 mmol/kg, in type III, 0.19 +/- 0.05 mmol/kg, while in type I it was significantly lower, 0.07 +/- 0.03 mmol/kg. In liver, the highest concentrations occurred in the splenectomized type III subjects, 0.16 +/- 0.08 mmol/kg, while in the non-splenectomized type III cases it was 0.06 +/- 0.02 mmol/kg and in type II 0.09 +/- 0.02 mmol/kg. The demonstration of high concentrations of the cytotoxic compound glycosylsphingosine may be a contributing factor behind the tissue necrosis and fibrosis commonly seen in spleens and livers from Gaucher's patients.