M. Boberg

FATTY ACID CONTENT AND CHEMICAL COMPOSITION OF FRESHWATER MICROALGAE1

Fatty acid (FA), total lipid, protein, amino acid, carbon, nitrogen, and phosphorus content was analyzed in 24 samples of freshwater microalgae. The samples originated from batch, continuous, or mass cultures in various growth phases and from net samples from lakewater. FA were analyzed quantitatively by using an internal standard in a GLC system and expressed as mg·g−1 dry weight (DW). The FA of one group of blue‐greens (e.g. Oscillatoria and Microcystis) were similar to those of the greens with higher amounts of 18C acids of the ω3 type compared to the ω6 type, whereas the other group (e.g. Anabaena and Spirulina) contained mostly ω6 acids. The flagellates, a taxonomically diverse group, were characterized by high amounts of long‐chained (20–22 C) polyunsaturated FA (PUFA), particularly of the ω3 type. The ω3/ω6 ratio appears to be highest in algae in the exponential growth phase. The increased lipid content in stressed algae was mostly due to increased saturated fatty acids and ω6 acids, whereas the valuable ω3 acids were unchanged or even decreased.

Desaturation and Elongation of Fatty Acids and Insulin Action

Abstract: Insulin resistance is characterized by specific changes of the composition of fatty acids in the serum lipids and in the skeletal muscle membranes. Impaired insulin sensitivity is associated with high proportions of palmitic (16:0) acid and low levels of linoleic (18:2 n‐6) acid in serum. In addition, there are apparent changes of the fatty acid desaturase activities, suggesting an increased activity of the Δ9 and Δ6 desaturases and a decreased activity of the Δ5 desaturase. The activity of the fatty acid desaturases is regulated by long‐chain polyunsaturated fatty acids and insulin and is probably also dependent on the degree of physical activity. A high ratio between arachidonic (20:4 n‐6) and dihomo‐gamma linolenic (20:3 n‐6) acid, as a measure of Δ5 desaturase activity, in the skeletal muscle phospholipids has been related to good insulin sensitivity. Available knowledge seems to indicate that the degree of saturation of the body lipids, and especially the proportion of palmitic acid in the lipid membranes, may be critical for insulin sensitivity. The strong relationships between the Δ5 desaturase activity, a high content of long‐chain polyunsaturated fatty acids in the skeletal muscle, and insulin sensitivity may be due to parallel effects of diet and/or physical activity on the fatty acid composition and on insulin sensitivity.

Fatty acid composition in total phospholipids of human coronary arteries in sudden cardiac death

A study was made of the fatty acid composition of the total phospholipid fraction of human coronary arteries in 30 cases of sudden cardiac death due to ischaemic heart disease (aged 40 +/- 5 years, mean +/- S.D.) and in 29 controls (mostly traffic accident victims, aged 45 +/- 6 years). The coronary arteries from cases of sudden cardiac death showed more atherosclerotic lesions than those of controls (P < 0.001). The percentages of palmitic acid (16:0) and linoleic acid (18:2(n-6)) were significantly higher and the percentage of arachidonic acid (20:4(n-6)) and of all the other major polyunsaturated fatty acids, both n-6 and n-3, was significantly lower in cases of sudden cardiac death than in controls. In conclusion, this study showed increased percentages of saturated and reduced percentages of polyunsaturated fatty acids, except linoleic acid, in total phospholipids of human coronary arteries in cases of sudden cardiac death. The results suggest an impaired metabolism of linoleic acid, possibly due to a decreased delta-6-desaturase activity in the coronary artery wall in cases of sudden cardiac death.

Supplementation with n-3 fatty acids reduces triglycerides but increases PAI-1 in non-insulin-dependent diabetes mellitus

Abstract. The effects of dietary supplementation with n‐3 fatty acids on lipid and glucose metabolism and on fibrinolysis were evaluated in 14 non‐insulin‐dependent diabetic patients who were given 10 g of MaxEPA (3 g n‐3 fatty acids) or placebo (olive oil) per day in a randomized double‐blind cross‐over study during two consecutive 8‐week periods. The serum triglyceride (TG) concentrations decreased by 27% (P < 0.01) after addition of MaxEPA with a reduction of VLDL TG by 36% (P < 0.05) while LDL cholesterol increased by 6% (P= 0.05). The fasting blood sugar and HbA1c. concentrations increased significantly after addition of MaxEPA but the changes were not significantly different from those during the placebo period. The highest glucose concentrations at fasting and after an i.v. glucose injection were seen after MaxEPA while the serum insulin concentrations were unchanged. The peripheral insulin sensitivity, as measured by a euglycaemic, hyperinsulinaemic clamp technique, did not change during the study. The mean plasminogen inhibitor‐1 (PAI‐1) activity of the patients was elevated compared with healthy controls. In spite of the reduction of the triglyceride concentrations and unchanged insulin levels, there was a significant increase of the activity of PAI‐1 (+ 21%, P < 0.01) after MaxEPA suggesting a possible impairment of the fibrinolytic capacity. In many situations there seems to be a reduction of PAI‐1 when the triglycerides are lowered. In the diabetic patients given n‐3 fatty acids this was not the case.

Fatty acid composition of platelets and of plasma lipid esters in relation to platelet function in patients with ischaemic heart disease

Serum lipoproteins, fatty acids in plasma lipid esters and in platelet phospholipids were assessed in 64 patients with ischaemic heart disease (IHD) and in 67 controls. Hyperlipoproteinemia (HLP) (VLDL triglycerides greater than 1.4 mmol/l and/or LDL cholesterol greater than 5.2 mmol/l) was found in 64% of the patients. In the plasma lipid esters the relative concentrations of saturated and monounsaturated fatty acids as well as dihomo-gammalinolenic acid were higher in the IHD patients whereas the linoleic acid concentrations were lower. The altered fatty acid pattern was apparent both in patients with and without HLP. In the platelet phospholipids there was a relative increase of oleic acid and a decrease of stearic acid. The relative content of eicosapentaenoic acid was slightly reduced whereas the linoleic acid concentrations were unchanged compared to the controls. Platelet aggregation induced by ADP and collagen was enhanced in the IHD patients. The lowest threshold value for ADP-induced aggregation was found in the normolipidemic patients. Since there were almost no differences in the relative contents of the long-chain polyunsaturated fatty acids in the platelet phospholipids between patients and controls it is concluded that mechanisms other than the prostaglandin-mediated pathway may contribute to the increased platelet aggregation in IHD patients.

Effects of an increased content of cereal fibre in the diet of Type 2 (non-insulin-dependent) diabetic patients

SummaryThe metabolic effects of an increased dietary content of cereal fibre were studied in 14 Type 2 diabetic subjects. They were given two isoenergetic diets in randomised order during two consecutive 3-week periods. A diabetic diet, containing 18.9 g dietary fibre/6.7 MJ (1600 kcal), was compared with a diet of identical composition except for an increased content of cereal fibre (42.4 g dietary fibre/6.7 MJ). The mean blood glucose level and the urinary glucose excretion were significantly lower in patients on the cereal-fibre-rich diet, while the serum insulin concentrations were similar. The mean blood glucose level was significantly reduced at 0700 h by 6% (p<0.05) and at 1100 h by 13% (p<0.01) on the highfibre diet. Consequently the insulin/glucose ratio was higher (33%, p<0.02) in patients on the fibre-enriched diet. There were only minor differences with regard to the serum lipoprotein concentrations. The lipoprotein lipase activities were similar in the two dietary groups. The reduction of blood glucose concentrations together with unchanged serum insulin concentrations is compatible with improved peripheral insulin sensitivity.

Polyunsaturated Fatty Acids May Impair Blood Glucose Control in Type 2 Diabetic Patients

Fifteen patients with Type 2 diabetes were given two diets rich in either saturated fat or polyunsaturated fat in alternate order over two consecutive 3‐week periods on a metabolic ward. Both diets contained the same amount of fat, protein, carbohydrates, dietary fibre, and cholesterol. The proportions of saturated, monounsaturated and polyunsaturated fatty acids in the saturated fat diet were 16, 10, and 5%‐energy and in the polyunsaturated fat diet (PUFA) 9, 10, and 12%‐energy. The PUFA diet contained a high proportion of n‐3 fatty acids. Metabolic control improved significantly in both dietary periods, due to both qualitative dietary changes and a negative energy balance. The serum lipoprotein concentrations decreased on both diets but the serum lipids were significantly lower after the PUFA diet (serum triglycerides −20%, p=0.001; serum cholesterol −5%, p=0.03; VLDL‐triglycerides −29%, p < 0.001; and VLDL‐cholesterol −31%, p=0.001) than after the saturated fat diet. Average blood glucose concentrations during the third week were significantly higher fasting (+ 15%, p < 0.01), and during the day at 1100 h (+18%, p < 0.001) and 1500 h (+ 17%, p=0.002) on PUFA than on the saturated fat diet. Significantly higher blood glucose levels were also recorded with a standard breakfast, while the sum of the insulin values was lower (‐19%, p=0.01). HbA1c did not differ significantly between the two dietary periods. The present study suggests that an increased content of polyunsaturated fatty acids, especially long‐chain n‐3 fatty acids, in a low fat diet may have beneficial as well as adverse effects in the management of Type 2 diabetes.

Effects of algal diets and temperature on the growth and fatty acid content of the cichlid fish Oreochromis niloticus L. – A laboratory study

The effects of different algal foods and water temperatures on the growth and fatty acid content of the Nile Tilapia, Oreochromis niloticus L., were studied. Four types of algae, given in the same amounts as the control diet, were used as food: Microcystis aeruginosa, colonial and single-celled forms; Arthrospira fusiformis; and Scenedesmus quadricauda. The control group was fed a commercial diet of cichlid pellets, while another group was left unfed. The feeding experiment was run at 25 °C. The condition factor decreased in all algal fed fish groups, except the one fed on Microcystis colonies, whereas the control group showed no significant change. Both food quantity and quality were responsible for this result. Some short-chained fatty acids in the diets could be traced in the long-chained counter-parts in the fish tissue. Both saturated fatty acids and monounsaturated fatty acids were higher in the control vs. treatment groups, whereas the polyunsaturated fatty acids displayed no significant differences amongst any of the treatment groups studied, including the unfed group. Direct quantitative comparison of individual fatty acid in the diet vs. tissue lipids in the fish proved to be difficult due to the great capacity of these tilapias to elongate and desaturate 18 carbon acids into long-chained homologues. The effect of temperature was studied by growing the fish at 16, 20 and 25 °C. All groups were fed commercial cichlid pellets. The level of saturated and monounsaturated fatty acids increased at 20 °C, whereas polyunsaturated fatty acids showed little variation. Docosahexaenoic acid, belonging to the important ‘omega 3’ group where the first double bond starts at carbon number three, was highest at 16 °C, resulting in a markedly elevated omega-3/omega-6 ratio at that temperature.

High content of dietary linoleic acid does not reduce platelet reactivity in patients with hyperlipoproteinaemia

Abstract. Seventeen patients with hypertriglyceridaemia were given a lipid‐lowering diet with a high P/S‐ratio 2·1 during a 3‐week period. The very low density lipoprotein triglycerides decreased by 43%, low density lipoprotein cholesterol by 19% and high density lipoprotein cholesterol by 12%. There was a marked increase of linoleic acid (18:2 n‐6) in all plasma lipid esters with a concomitant decrease of the saturated and monounsaturated fatty acids. There was a slight increase of the linoleic acid metabolites 18:3 n‐6, 20:3 n‐6 and 20:4 n‐6 in serum triglycerides whereas the fatty acids of the n‐3 series decreased in all plasma lipid esters. In the platelets a similar pattern was found with an increase of linoleic acid and its metabolite 22:4 n‐6 and a decrease of 18:1 n‐9 as well as of the n‐3 fatty acids. No significant differences in platelet reactivity was found. However, in a few patients there was an increased platelet aggregation after the diet period. Our results suggest that this diet based on a very high content of linoleic acid may not affect platelet reactivity in a beneficial way. The reason may be an increased turnover of arachidonic acid in the platelets or an imbalance between the n‐6 and n‐3 series of fatty acids.