Prostaglandins Leukotrienes and Essential 0 Longman Group UK Ltd 1991
(1991) 43, 197-201
Fatty Acid and Prostaglandin Metabolism in Children with Diabetes Mellitus. II. - The Effect of Evening Primrose Oil Supplementation on Serum Fatty Acid and Plasma Prostaglandin Levels M. Arisaka, 0. Arisaka and Y. Yamashiro Department of Pediatrics, Juntendo University School and Medicine, 2-l-l Tokyo 113, Japan (Reprint requests to MA)
Our previous study demonstrated that levels of dihomo-gamma-linolenic acid (DGLA) and arachidonic acid in serum total lipids decreased in association with increased plasma levels of prostaglandins E, (PGEJ and F, (PGF,,) in patients with insulin-dependent diabetes mellitus. In this study, 11 children with insulin-dependent diabetes mellitus completed a double-blind, placebo-controlled study to assess the effect of dietary supplementation with gamma-linolenic acid (GLA) on serum essential fatty acid and plasma PGE, and PGF,, levels. GLA was given as the seed oil from the evening primrose (EPO) and all patients received either EPO capusles (containing 45 mg of GLA and 360 mg of linoleic acid) or indistinguishable placebo capsules for 8 months. Initially patients took 2 capsules daily for 4 months then 4 capsules daily for a further 4 months. AlI patients were assessed at the start of the study, after 4 months and at the end of the study, by measuring serum essential fatty acid and plasma PGE, and PGF, levels. After administration of 4 capsules daily the DGLA levels increased and PGE, levels decreased significantly (p < 0.01) in the EPO compared with the placebo group. Neither fatty acid nor PGE, and PGF, levels were altered by administration of 2 EPO capsules daily. This suggests that the altered essential fatty acid and PG metabolism in diabetes may be reversed by direct GLA supplementation.
INTRODUCTION Evidence that there are abnormalities of serum, platelet, and red cell n-6 polyunsaturated essential fatty acids (EFAs) in diabetes mellitus, in experimental animals and humans, is growing. In particular, the conversion of linoleic acid to gammalinolenic acid (GLA) is impaired passibly because insulin deficiency or reductions in insulin action may inhibit 6-desaturase activity (l-9). Most of the biological effects of linoleic acid depend on its conversion to 6-desaturated metabolites, which act as key components of membrane structure and also as precursors of the prostaglandins (PGs) and other eicosanoids (10-12). The altered EFA and/or PG metabolism appears to be related to the development of various diabetic vascular complications (1, 3, 9, 13-17). In a previous study we demonstrated that levels of dihomo-gamma-linolenic acid (DGLA) and arach-
Date received 13 December 1990 Date accepted 25 February 1991
idonic acid in serum total lipids were decreased, in association with increased plasma levels of prostaglandin E2 (PGE2) and prostaglandin Fz~ (PGFz,). in children with insulin-dependent diabetes mellitus compared with those in normal controls. These findings indicate that EFA and PG metabolism is deranged in diabetes (1). In diabetes, the dietary EFAs, linoleic acid and alpha-linoleic acid, may not be utilized normally: thus direct administration of derived EFA which have undergone 6-desaturation and which are usually synthesized within the body but are not normally present in important amounts in the diet may be necessary (9-11). Very high doses of linoleic acid given to patients with type 2 diabetes were associated with a reduced risk of progression to microvascular complications (14). Another recent study suggested that administration of the 6-desaturated linoleic metabolite, gammalinolenic acid (GLA as evening primrose oil) to diabetic patients was useful for preventing and treating polyneuropathy (18). It is possible that the high levels of linoleic acid or GLA provided by such supplements overcome the partial block of 6desaturation in diabetes (14, 18). This study was 197
and Essential Fatty Acids
designed to investigate whether altered EFA and PG metabolism in diabetic children could be reversed by direct supplementation of GLA, which was given as seed oil from the evening primrose.
MATERIALS AND METHODS 11 patients (6 girls and 5 boys, age range 8-18 years) with insulin-dependent diabetes mellitus were admitted to the study. All patients were receiving human NPH insulin injection (0.7-1.4 U/kg per day) and routine funduscopic examination showed no diabetic retinopathy.
These normal controls were children aged 8-15 years. All values are expressed as mean + SD. Statistical analysis The unpaired, two-tailed Student’s t-test was used to compare the mean baseline fatty acid and PG levels in the placebo and EPO groups and to compare mean changes in these measurements from the baseline after treatment with 2 and 4 placebo or EPO capsules. Differences showing P values of less than 0.05 were considered to be significant.
RESULTS Trial design
The trial was a double-blind, placebo-controlled study of 8 months duration. During this period, patients received either evening primrose oil (EPO) or indistinguishable placebo capsules; one EPO capsule (Efamol Ltd, Guildford, UK) contained 360 mg of linoleic acid and 45 mg of GLA. Initially the 6 patients in the EPO group took 2 capsules daily for 4 months then 4 capsules daily for a further 4 months. The 5 patients in the placebo group took matching placebo capsules according to the same regimen. There were no significant differences between the placebo and EPO groups with respect to mean age (13 years vs 12 years), duration of the illness (5.3 years vs 5.0 years) or hemoglobin Ai value (11.4 f 1.8% vs 11.7 < 2.2% [normal, 4.58.0%]). All patients were assessed at the beginning of the study, 4 months later and at the end of the trial (8 months later) by measuring the levels of serum fatty acids and plasma PGE2 and PGF2,. Blood was collected while the patients were fasting. The patients’ caloric intake remained unchanged and hemoglobin Al values, assessed every month, showed no significant change during the study. Informed consent was obtained from all patients.
The results of serum fatty acid analyses before and following placebo and EPO administration are shown in Figure 1. The level of each fatty acid is expressed as a percentage of the total fatty acid level. There were no significant differences in the levels of the fatty acids between the placebo and EPO groups of diabetic children before starting the study. However, the DGLA and arachidonic acid levels in the placebo and EPO groups were significantly lower than ‘.ose in the normal controls (p < 0.005 in each case). The values in the normal controls were: linoleic acid 34.0 * 3.0%; DGLA 1.6 + 0.4%; arachidonic acid: 7.1 f 0.8%. There were no significant differences between the placebo and EPO groups with respect to levels of linoleic acid (before: 36.9 * 5.0% [placebo] vs 35.6 + 4.6% [EPO]; 4 months: 33.7 + 2.5% vs 35.3 + 4.5%; 8 months 33.5 f 3.3% vs 34.6 It 2.8%) and arachidonic acid (before: 5.8 * 1.5% [placebo] vs 5.5 & 1.1% [EPO]; 4 months: 5.2 f 0.9% vs 5.9 + 1.3%; 8 months: 4.7 * 2.0% vs 7.6 + 1.8%). However at 8 months there was a non-significant trend for arachidonic acid levels to rise in the EPO group compared with the placebo group; the arachidonic acid levels at 8 months in the EPO group showed no statistically significant difference compared with those in normal controls. With respect to DGLA levels, there were no significant differences between the placebo and EPO groups at the start or after 4 months (before: 0.7 + 0.4% [placebo] vs 0.8 + 0.3% [EPO]; 4 months: 0.8 f 0.4% vs 0.8 f 0.3%). However DGLA levels increased significantly at 8 months (0.7 + 0.4% [placebo] vs 1.7 + 0.5% [EPO], p < O.Ol), these levels were within the range of normal controls.
Measurement of fatty acids and prostaglandins The methods of measurement of serum fatty acids and plasma PGE2 and PGF,, are described elsewhere (1). Briefly, fatty acids in the total lipid fraction were extracted from serum total lipids by Folch’s method (19) and analyzed by gas chromatography. Seven fatty acids, namely, palmitic, palmitoleic, stearic, oleic, linoleic, dihomo-gamma-linolenic (DGLA), and arachidonic acids were determined. Prostaglandin Ez and PGF,, were assayed by radioimmunoassay, according to a slightly modified version of the method of Dray et al (20). Normal serum fatty acid composition values were obtained from 7 normal controls and levels of PGE2 and PGFZ,, were obtained from 27 normal controls (1).
Prostaglandins The results of plasma PGEz and PGF2, assays before and following the placebo and EPO ad-
Fatty Acid and Prostaglandin in Children with Diabetes