Conny Edlund

Fatty acid composition of brain phospholipids in aging and in Alzheimer’s disease

The two major phospholipid classes, namely, phosphatidylethanolamines (PE) and phosphatidylcholines (PC), were studied in four different regions of human brain,i.e., in frontal gray matter, frontal white matter, hippocampus and in pons. The fatty acid (FA) compositions of these phospholipids were found to be specific for the different regions. PC contains mostly saturated and 18∶1 FA, while PE is rich in polyunsaturated FA. Aging has no influence on the FA compositions, while in Alzheimer’s disease (AD) PE is modified in all four regions, particularly in frontal gray matter and in hippocampus. The abundance of the major monounsaturated FA of PE, 18∶1, is not significantly altered in Alzheimer’s disease, but there is a substantial increase in the relative amounts of the saturated components 14∶0, 16∶0 and 18∶0. This is paralleled by a decrease in the polyunsaturated FA 20∶4, 22∶4 and 22∶6. It is not clear whether the changes observed are specific for AD. Changes in saturated/polyunsaturated FA ratio are likely to influence cellular function, which in turn may cause certain neural deficiencies. The findings do not support the hypothesis that AD reflects an accelerated aging process.

Lipid Compositions of Different Regions of the Human Brain During Aging

The neutral and phospholipid compositions of various regions of the human brain were analyzed using autopsy material covering the life period between 33 and 92 years of age. The protein content was also measured and, on a weight basis, this content is unchanged in the cerebellum, pons, and medulla oblongata, whereas in the 90‐year‐old group it decreases in the hippocampus, gray matter, and nucleus caudatus. In white matter, the protein content decreases continuously with age. The phospholipid composition is characteristic of the region investigated, but remains unchanged during aging. The total phospholipid content exhibits only a 5–10% decrease in the oldest age group. The content of dolichol and its polyisoprenoid pattern are also characteristic of the region analyzed. Between 33 and 92 years of age, the amount of dolichol in all portions of the brain increases three‐to fourfold, but the isoprenoid pattern remains constant. The level of dolichyl‐P varies between different regions, but only a moderate increase is seen with age. Ubiquinone content is highest in the nucleus caudatus, gray matter, and hippocampus, and in all areas this content is decreased to a great extent in the oldest age groups. All regions of the human brain are rich in cholesterol, but alterations in the amount of this lipid are highly variable during aging, ranging from no change to a 40% decrease.

Lipid composition in different regions of the brain in Alzheimer's disease/senile dementia of Alzheimer's type

Abstract: The lipid compositions of 10 different brain regions from patients affected by Alzheimers disease/senile dementia of Alzheimers type were analyzed. The total phospholipid amount decreased somewhat in nucleus caudatus and in white matter. The cortical areas that are morphologically affected by Alzheimers disease, i.e., frontal and temporal cortex and the hippocampus, showed elevated contents of lipid solvent‐extractable phosphatidylinositol. Sphingomyelin content was decreased in regions rich in myelin. There was a 20–50% decrease in dolichol amount in all investigated parts of the brain, but no change was seen in the polyisoprenoid pattern. Levels of α‐unsaturated polyprenes were decreased in Alzheimer brains. Dolichyl‐phosphate content increased in most regions, up to 100%. In both control and Alzheimer tissue almost all of the dolichyl‐phosphate was covalently bound, apparently through glycosylation. Cholesterol amounts were highly variable but mostly unchanged, whereas ubiquinone concentrations increased by 30–100% in most regions in brains affected by Alzheimers disease. These results demonstrate that both phospholipids and neutral lipids are modified in brains affected by Alzheimers disease/senile dementia of Alzheimers type.

CD8 is critically involved in lymphocyte activation by a T. brucei brucei-released molecule

T. brucei brucei released a lymphocyte triggering factor (TLTF), which triggered purified CD8+, but not CD4+, T cells to interferon gamma (IFN-gamma) mRNA expression and secretion and to [3H]thymidine incorporation. TLTF also induced mRNA for transforming growth factor beta, but not for interleukin-4. The action of this TLTF on mononuclear cell (MNC) cultures was blocked by anti-CD8 antibodies and by soluble CD8. MNCs from a mutant mouse strain lacking CD8 expression were not triggered by TLTF. IFN-gamma provides a growth stimulus for T. brucei brucei, and infected CD8- mice had much lower parasitemia and survived longer than CD8+ mice. The host-parasite interaction in experimental African trypanosomiasis thus involves parasite release of TLTF, which by binding to CD8 triggers CD8+ cells to produce the parasite growth-promoting cytokine IFN-gamma.

Rates of cholesterol, ubiquinone, dolichol and dolichyl-P biosynthesis in rat brain slices

Slices from the brain and liver of rats were prepared and upon incubation exhibited a continuous and high capacity for incorporation of radioactive precursors into proteins and lipids. Using [3H]mevalonate as precursor, the rates of biosynthesis of cholesterol, ubiquinone, dolichol and dolichyl‐P in brain slices were determined and found to be 5.5,0.25,0.0093 and 0.0091 nmol/h/g, respectively. Dolichol and dolichyl‐P accumulate to a limited extent, but almost all of these lipids in the brain originate from de novo synthesis. The calculated half‐lives for cholesterol, ubiquinone, dolichol and dolichyl‐P were 4076, 90, 1006 and 171 h, respectively. The results indicate that lipids formed via the mevalonate pathway in the brain have an active and independently regulated biosynthesis.

A Trypanosoma brucei brucei-Derived Factor that Triggers CD8+ Lymphocytes to Interferon-γ Secretion: Purification, Characterization and Protective Effects In Vivo by Treatment with a Monoclonal Antibody against the Factor

A protein factor that stimulates CD8+ lymphocytes to produce and secrete IFN‐γ has been purified from Trypanosoma brucei brucei (T.b. brucei). This was accomplished by raising monoclonal antibodies (MoAbs) against a fraction of T.h. brucei obtained by gel filtration, whieh contained high levels of material inducing rat mononuelear cells (MNC) to IEN‐y production. MoAbs from four hybridomas strongly inhibited trypanosome‐induced IFN‐γ production. One of them (MO1) was used for purification of the trypanosome‐derived lymphocyte triggering factor (TLTF) by affinity chromatography, SDS electrophoresis of the purified TLTF displayed a band of 42‐45 kDa MW. Gel filtration of homogenates of whole parasites yielded several peaks of IFN‐γ‐inducing activity with a lowest MW of 41 46 kDa. Bioactivity of all peaks was blocked by MO1. suggesting that a single molecule, or a single epitope of additional molecules, is responsible for the different peaks with IFN‐γ‐indueing activity. IFN‐γ released from MNC stimulates T.b. brucei growth. Blocking of TLTF in vitro with MO1 inhibited MNC‐supported growth of the parasites. To study the in vivo relevance of TLTF in the course of experimental African trypanosomiasis, MO1 was used to treat rats and mice at different times after infection. Treatments instituted at different time‐points after infection suppressed parasite growth, abrogated the IFN‐γ production by splenocytes indueed by the infection and prolonged survival of the animals. The data support the hypothesis that TLTF and IFN‐γ have a erueial regulatory function in the parasite host interactions and that these moleeules influence the disease eourse during experimental African trypanosomiasis.

Effects of mevinolin treatment on tissue dolichol and ubiquinone levels in the rat

Rats were treated with mevinolin by intraperitoneal injection (15 days) or dietary administration (30 days). The cholesterol, dolichol, dolichyl phosphate and ubiquinone contents of the liver, brain, heart, muscle and blood were then investigated. The cholesterol contents of these organs did not change significantly, with the exception of muscle. Intraperitoneal administration of the drug increases the amount of dolichol in liver, muscle and blood and decreases the dolichyl-P amount in muscle. The same treatment increases the level of ubiquinone in muscle and blood and decreases this value in liver and heart. Oral administration decreases dolichol, dolichyl-P and ubiquinone levels in heart and muscle, while in liver the dolichol level is elevated and ubiquinone level lowered. In brain the amount of dolichyl-P is increased. Intraperitoneal injection of mevinolin also modifies the liver dolichol and dolichyl-P isoprenoid pattern, with an increase in shorter chain polyisoprenes. The levels of dolichol and ubiquinone in the blood do not follow the changes observed in other tissues. Incorporation of [3H]acetate into cholesterol by liver slices prepared from mevinolin-treated rats exhibited an increase, whereas in brain no change was seen. Labeling of dolichol and ubiquinone was increased in both liver and brain, but incorporation into dolichyl phosphate remained relatively stable. The results indicate that mevinolin affects not only HMG-CoA reductase but, to some extent, also affects certain of the peripheral enzymes, resulting in considerable effects on the various mevalonate pathway lipids.

Content and fatty acid composition of cardiolipin in the brain of patients with alzheimer's disease

The frontal, temporal and occipital cortex from human brains affected by Alzheimers disease were analyzed for their contents and fatty acid compositions of cardiolipin. Phospholipids were purified using an HPLC system and cardiolipin was found to be present in the same amount (on a protein basis) as in age-matched controls. One-third of the total fatty acyl moieties of this phospholipid were saturated, one-third monounsaturated and one-third polyunsaturated. In affected brain regions the levels of certain polyunsaturated fatty acids displayed moderate decreases, not exceeding 10-15%. However, the total amount of polyunsaturated fatty acids decreased by only 9%. These results demonstrate that the amount and structure of brain cardiolipin are not modified to any great extent in connection with Alzheimers disease.

Effects of inhibitors of hydroxymethylglutaryl coenzyme A reductase on coenzyme Q and dolichol biosynthesis

SummaryInhibitors of hydroxymethylglutaryl coenzyme A reductase are used clinically to decrease blood levels of low-density lipoprotein cholesterol in hypercholesterolemic patients. However, little is known about the possible effects of these inhibitors on dolichol and cholesterol synthesis. Oral administration of mevinolin to rats was found here to decrease dolichol, dolichyl-P and coenzyme Q levels in the heart and skeletal muscle and to increase the hepatic dolichol level while decreasing the coenzyme Q content in this same organ. The amounts of dolichyl-P decreased in heart and muscle and increased in brain. Intraperitoneal administration also affected the levels of these lipids. The concentrations of blood lipids were not modified in the same manner as tissue lipids. Analysis of individual enzyme activities and of incorporation of [3H]acetate into various lipids of liver and brain slices demonstrated that both up- and down-regulation of different proteins occur in various tissues, resulting in modifications in lipid synthesis. Hypercholesterolemic patients were found to have high blood coenzyme Q levels, which are decreased upon pravastatin treatment, although they are still above control values. It appears that these HMG-coenzyme A reductase inhibitors do not selectively lower cholesterol levels, but that they also modify the dolichol and coenzyme Q content and synthesis both in the liver and various other tissues.

Isoprenoids in aging and neurodegeneration

During aging the human brain shows a progressive increase in levels of dolichol, a reduction in levels of ubiquinone, but relatively unchanged concentrations of cholesterol and dolichyl phosphate. In a neurodegenerative disease, Alzheimers disease, the situation is reversed with decreased levels of dolichol and increased levels of ubiquinone. The concentrations of dolichyl phosphate are also increased, while cholesterol remains unchanged. This study shows that the isoprenoid changes in Alzheimers disease differ from those occurring during normal aging and that this disease cannot, therefore, be regarded as a result of premature aging. The increase in the sugar carrier dolichyl phosphate may reflect an increased rate of glycosylation in the diseased brain and the increase in the endogenous anti-oxidant ubiquinone an attempt to protect the brain from oxidative stress, for instance induced by lipid peroxidation.