Altered arachidonic acid synthesis and lipid peroxidation in diabetes mellitus: possible roles in leukocyte dysfunction and other cellular defects

A preliminary report on the role of yoga asanas on oxidative stress in non-insulin dependent diabetes mellitus

Nineteen subjects of non-insulin dependent diabetes mellitus (NIDDM) between the age group of 30-60 yrs were studied to see the effect of specific yoga asanas on fasting and postprandial blood glucose (FBG, PPG), serum malondialdehyde (MDA) and glycosylated hemoglobin (HbA(1)) in addition to drug treatment and diet control. The duration of diabetes ranged from 1-10 years. Patients with renal, cardiac and proliferative retinal diseases were excluded from the study. The same patients served as their own control. Subjects were called in the morning to the cardio-respiratory laboratory and were given training by a yoga expert. Yoga asanas included Suryanamskar, Tadasan, TriKonasan, Padmasan, Pranayam, Paschimottanasan, Ardhmatsyendrasan, Pavanmukthasan, Sarpasan and Shavasan. The asanas were done every day for 40 days for 30-40 min. FBG, PPG, serum MDA and HbA(1) were estimated before and after 40 days of yoga asanas regimen. Significant reduction was seen in FBG from 220 mg/dl to 162 mg/dl, PPG from 311 mg/dl to 255 mg/dl, MDA from 6 nmol/l to 3 nmol/l and HbA(1), from 8.8% to 6.4%. Subjects felt better and were relieved of their stresses and had an improvement in their day to day performance. The decrease was statistically significant (p<0.0001 for FBG and PPG, p<0.001 for MDA and for HbA(1)).

Metabolism of arachidonic acid in neutrophils from alloxan-diabetic rabbits

The production of 5-lipoxygenase products from arachidonic acid was investigated in polymorphonuclear leukocytes (PMNL) isolated from non-diabetic and alloxan-induced diabetic rabbits: (i) production of 5-hydroxyeicosatetraenoic acid, leukotriene B4, and the two 6-trans-leukotriene B4 isomers were significantly decreased in the PMNL of diabetic rabbits when compared to non-diabetic rabbits; (ii) production of LTB4 and 5-HETE from diabetic PMNL required the addition of Ca2+ and A23187 to a greater degree than control incubations; and (iii) the availability of substrate in the PMNL of diabetics was not a limiting factor for 5-lipoxygenase product formation. Alternative pathways of arachidonic acid metabolism were also evaluated: the recovery of exogenous leukotriene B4 and 5-hydroxyeicosatetraenoic acid were identical using PMNL from control and diabetic rabbits and peptido-leukotrienes were not detected by radioimmunoassay. The data suggest that the activity of 5-lipoxygenase and the production of 5-hydroperoxyeicosatetraenoic acid in the diabetic PMNL may be limiting factors since the formation of leukotriene B4, leukotriene B4 isomers, and 5-hydroxyeicosatetraenoic acid are depressed in PMNL of diabetic rabbits. Alternative pathways do not account for the conversion of arachidonic acid to other products nor are the elimination pathways for LTB4 and 5-HETE different. Decreased formation of 5-hydroxyeicosatetraenoic acid and leukotriene B4 could predispose diabetic subjects to infection due to a decrease in mediators leading to the local accumulation of PMNL in the inflammatory response.

Oxygenation products of arachidonic acid: third messengers for insulin release

Although an association between membrane phospholipid turnover and exocytotic hormone release has long been recognized, a causal relationship has not been firmly established. Recent studies suggest that glucose (and probably other insulin secretagogues) activates phospholipases and thereby releases membrane-bound arachidonic acid (AA). AA is then converted through islet 12-lipoxygenase to mediators or modulators of insulin release (tentatively identified as peroxides and epoxides of arachidonate). These products may be critical links in stimulus-secretion coupling, since blockade of either AA release or lipoxygenation abrogates insulin release induced by glucose and many other (but not all) stimuli. Cogeneration of prostaglandins from AA through the cyclooxygenase pathway may directly or indirectly modulate the formation and/or effect of lipoxygenase products. A critical role for lipoxygenase products (and possibly metabolites of AA synthesized by other pathways, such as P-450-dependent monooxygenases) may extend to many secretory cells in addition to pancreatic beta cells. The phasic release of AA described in many cells could explain the biphasic pattern of insulin release induced by glucose. Since some phospholipases and lipoxygenases are Ca++ activated, the release of AA in conjunction with its oxygenation appears to be a concerted system generating "third messengers" for hormone release.

Is phospholipase A2 a "glucose sensor" responsible for the phasic pattern of insulin release?

The mechanisms involved in the characteristic, normal biphasic pattern of glucose-induced insulin release (which is grossly altered in type II diabetics) have not been definitely elucidated. However, the temporal pattern of arachidonic acid release induced by cellular phospholipases precisely mimics that of first-phase insulin release, both being characterized by a burst of release peaking near 2-3 minutes and followed by a "trough" or apparent refractory period most apparent at 5-10 minutes. The latter appears temporally related not only to decreased arachidonate release but also to stimulation of its re-esterification. Pancreatic islets contain a glucose-sensitive phospholipase A2, and glucose has been shown to increase the accumulation of islet lipoxygenase-derived products which appear to be "third messengers" mediating insulin release. Blockade either of islet phospholipase(s) or of islet lipoxygenase totally abrogates glucose-induced insulin release. The hypothesis is therefore proposed that phospholipase A2 could be one beta cell "glucose sensor", and that the released arachidonate is coupled to an islet lipoxygenase. Labile oxygenated metabolites (lipid peroxides and epoxides) transduce the glucose signal into insulin release. The available data (albeit incomplete) are compatible with the formulation that the biphasic pattern of glucose-induced insulin release could be explained by dynamic changes in the availability of arachidonic acid and its consequent oxygenation.