The use of essential fatty acid deficient rats to study pathophysiological roles of prostaglandins. Comparison of prostaglandin production with some parameters of deficiency

Pharmacological plasticity-How do you hit a moving target?

Paul Ehrlich's concept of the magic bullet, by which a single drug induces pharmacological effects by interacting with a single receptor has been a strong driving force in pharmacology for a century. It is continually thwarted, though, by the fact that the treated organism is highly dynamic and the target molecule(s) is (are) never static. In this article, we address some of the factors that modify and cause the mobility and plasticity of drug targets and their interactions with ligands and discuss how these can lead to unexpected (lack of) effects of drugs. These factors include genetic, epigenetic, and phenotypic variability, cellular plasticity, chronobiological rhythms, time, age and disease resolution, sex, drug metabolism, and distribution. We emphasize four existing approaches that can be taken, either singly or in combination, to try to minimize effects of pharmacological plasticity. These are firstly, to enhance specificity using target conditions close to those in diseases, secondly, by simultaneously or thirdly, sequentially aiming at multiple targets, and fourthly, in synchronization with concurrent dietary, psychological, training, and biorhythm-synchronizing procedures to optimize drug therapy.

Progress does not just come in giant leaps: adapting techniques for the study of inflammation to novel applications

INTRODUCTION

Discussion of the relevance of suitable experimental models for the effective translation of drug effects to clinical inflammatory diseases has a long history. Much emphasis is placed these days on genetically transformed mice, which may have developmental drawbacks. But are established models redundant?

FINDINGS

Drawn from personal experience, examples are provided of the success of tinkering with technology in the context of inflammation. These include the use of specific dietary deficiency conditions, the development of new applications for established drugs and the introduction of a variety of readouts to assess outcome in studies on established disease models. Such approaches have been used to demonstrate inflammation-modulating effects of prostaglandin E, in the development of ebselen, for the introduction of immunomodulatory macrolide drugs and in new approaches to the therapy of multiple sclerosis.

CONCLUSION

Fine tuning of experimental approaches and evaluation technologies can often still provide innovative, clinically relevant insights into the potential beneficial effects of drugs and pharmacological agents.

The inhibition of lung colonization of B16-F10 melanoma cells in EFA-deficient animals is related to enhanced apoptosis and reduced angiogenesis

Previous studies conducted in our laboratory showed that the reproduction of spontaneous and experimental metastases was reduced in host animals deprived of essential fatty acids (EFA). In the present study, we have explored the possibility whether apoptosis, proliferation, and angiogenesis might be involved in the antimetastatic effect of EFA deficiency. To this aim, in pulmonary colonies developed from B16-F10 cells in EFA-deficient animals or in animals fed a 5% corn oil diet, we performed an immunohistochemical analysis of bcl-2/bax proteins, PCNA, and VEGF and von Willebrand Factor (vWF), typical markers of apoptosis, proliferation, and angiogenesis, respectively. Apoptosis was also evaluated by detecting DNA fragments in metastatic cells. We found that the reduction of pulmonary colonies grown in EFA-deficient animals was associated with a high expression of apoptotic activity as revealed by the presence of apoptotic nuclei and a high immunoreactivity for bax. Cell proliferation seemed not to be influenced by EFA deficiency in view of the observation that PCNA was highly expressed in pulmonary colonies of control as well as EFA-deficient animals. Pulmonary colonies developed in EFA- deficient animals showed a lower expression of VEGF and a decreased microvessel density, indicating that a reduced angiogenesis contributes to the antimetastatic effects of EFA deficiency. Our analysis of the results invokes the possibility that a relationship between angiogenesis and apoptosis may account for the diminution of the development of experimental metastases in the lungs of EFA-deficient animals.

Diminution of the development of experimental metastases produced by murine metastatic lines in essential fatty acid-deficient host mice

In a previous study we found that the capacity for spontaneous metastases of tumors developed after subcutaneous transplantation of RSV-transformed Balb/c 3T3 cells was reduced in essential fatty acids (EFA)-deficient host animals. In the present study, we have extended our investigation by considering the requirement of EFA for the formation of lung colonies obtained by i.v. injection of two metastatic murine cell lines of different origin: (1) T3 cells, a highly metastatic cell line isolated from a fibrosarcoma, and (2) the F10 variant of B16 melanoma (B16-F10 cells). We found that EFA deficiency reduces the lung colonization of both T3 cells and B16-F10 cells without affecting the retention of tumor cells in the lung. NK cells did not seem to be involved in the diminution of lung colonization in EFA-deficient animals. Furthermore, by examining histologically the lung parenchyma at successive intervals after tumor cell injection, we found that, in comparison with control mice, EFA-deficient animals had fewer lung colonies and a prevalence of smaller microcolonies during the entire period of observation. This led us to conclude that the diminution in development of tumor colonies in the lungs of EFA-deficient host animals was related to a reduced growth rate of tumor cells at this site.

The effect of essential fatty acid deficiency on hepatic bile salt sulphotransferase in rats

Hepatic bile salt sulphotransferase (BSS) activity and the contents of unconjugated oestradiol-17 beta (E2) and conjugated oestrone (cE1) in liver tissue was significantly lower in young essential fatty acid (EFA) deficient female rats than in female control rats. No corresponding differences were found between male EFA deficient and control rats. A significant sex difference, with higher values in females, was found for BSS activity and E2 and cE1 contents in control rats but not in EFA deficient rats. The decrease in hepatic BSS activity in female rats caused by EFA deficiency may be mediated via a decreased estrogenic action on the liver.

Pancreatic function in the essential fatty acid deficient rat

The influence of essential fatty acid (EFA) deficiency on pancreatic endocrine and exocrine function was studied in 120-day-old rats. The plasma insulin response was determined after in vivo administration of glucose and arginine. The plasma glucagon response was assessed after infusion of arginine. Islet peptides were examined by immunocytochemistry. The exocrine function of pancreas was studied by amylase secretion in isolated pancreatic acinar cells after stimulation with the cholinergic agonist carbacholine chloride. The EFA-deficient (EFAD) rats showed higher basal plasma insulin concentrations and lower basal glucose levels than control rats (P less than .01 and P less than .01, respectively). The plasma insulin response to glucose was potentiated in the EFAD rats (P less than .001). Both insulin and glucagon responses to arginine were normal. The isolated pancreatic acinar cells showed a low basal amylase secretion, but a normal response to carbacholine chloride. There were no overt morphological changes seen in the pancreas and the immunocytochemical staining pattern of insulin, glucagon, somatostatin, and pancreatic polypeptide cells did not differ from controls. The results of the study show that the secretory function of the endocrine and exocrine pancreas is operational in EFA deficiency. The EFA deficiency was accompanied by a basal hyperinsulinemia and hypoglycemia and an exaggerated insulin response to glucose, the pathophysiology of which has to be further studied.

Increased liver lipase activity in rats with essential fatty acid deficiency

Liver lipase activity was measured in EFA-deficient rats (long-term) and in control rats and rats fed an EFA-deficient diet for two weeks (short-term). Liver lipase activity was significantly enhanced by EFA deficiency, both in long-term and short-term experiments. The enhanced liver lipase activity could be normalized by feeding these rats normal laboratory chow for 14 days. Since during EFA deficiency prostaglandin synthesis is impaired, the possible involvement of prostaglandins in the observed changes in liver lipase activity during EFA deficiency was studied. Administration of the prostaglandin synthesis inhibitor indomethacin (5 mg/kg body weight, i.p.) to normally fed rats for two days led to an increase of liver lipase activity. Prostaglandin E2 was found to inhibit the secretion of liver lipase activity by freshly isolated parenchymal liver cells in vitro. These results indicate that the increase in liver lipase activity during EFA deficiency may be due to an impairment of the prostaglandin synthesis.

Incorporation into the tissues and turnover of arachidonic acid after administration to normal and essential fatty acid deficient rats

A comparison was made of the incorporation into the tissues and metabolism of [1-14C] arachidonic acid (AA) after i.v. administration to normal and EFA-deficient rats. At different times, ultra-thin whole body sections were prepared and the distribution of the radioactivity determined by autoradiograms. After 5 min, a considerable incorporation occurs in the following organs: subcutaneous and perispinal fat, liver, heart muscle, kidney and adrenal. The EFA deficient rats show a similar distribution but the radioactivity is longer retained. The total amount of radioactivity in the heart, liver, kidney and adrenal was measured at different times. A decline occurs in the heart, and an increase in the adrenal. In the urine, the highest amount of radioactivity is excreted on the first day. The excretion is lower in the EFA-deficient rats. Small amounts of radioactive metabolites with the chromatographic characteristics of PGE2 and 13,14 dihydro-15ketoPGE2 were isolated from urine. The amounts of 14CO2 produced were determined after the administration of [1-14C] AA. Half times were: 39 +/- 2.9 min in the EFA-deficient and 28 +/- 2.8 min in the normal rats. In the heart, AA is incorporated into phospholipids and neutral lipids. The following percentages were determined: phosphatidylinositol: 6.9 +/- 0.6%, phosphatidylcholine: 44 +/- 4.1%, phosphatidylethanolamine: 10.0 +/- 1.0%, neutral lipids: 9.3 +/- 1.6%. Several explanations can be given for the higher requirements of some tissues for AA. It could be, that this substance is used in the formation of particular membranes with a high AA content. Differences in the amounts of metabolites produced may also play a role.

Quantitative relationships between dietary linoleate and prostaglandin (eicosanoid) biosynthesis

Essential fatty acid deficiency consistently depresses eicosanoid (prostaglandin E2, F2, and I2 and thromboxane) biosynthesis independent of sampling protocols. Tissue fatty acid analyses support the hypothesis that the decrease is due in part to depression of arachidonate and accumulation of eicosatrienoate (n-9). Research on the alteration of eicosanoid biosynthesis by dietary linoleate supplementation is reviewed extensively. Responses of whole blood, lung, liver and heart eicosanoid synthesis to feeding eight concentrations of dietary linoleate between 0 and 27 energy percent are reported. It is concluded that stimulation, depression and no change in eicosanoid production could be equally well documented as a response to linoleate supplementation. Evidence for the obvious mechanism that alterations in precursor fatty acid composition are a possible explanation is fragmentary and inconsistent. The appropriate sampling techniques appear not to be established at this time and most likely are species, gender and tissue specific.

Cryoglobulin-induced inflammation

Inflammation of the rat footpad followed injection of cryoglobulin in crystalline form (Type I) and injection of cryoglobulin in solution (Type II). Rats deficient in essential fatty acids responded with diminished swelling which corrected to normal levels by addition of prostaglandin E1 suggesting that this reaction is prostaglandin mediated. Addition of bradykinin produced no effect. Aggregated cryoglobulin proved more inflammogenic than non-aggregated cryoglobulin. Pre-treatment with choline salicylate and colchicine reduced swelling while pre-treatment with dipyridamole increased edema following cryoglobulin inoculation. Cryoglobulin is considered to be an acute phase reactant in inflammation.

Reduced prostaglandin synthesis by renal and aortic tissues from adult rats fed essential fatty acid-deficient diet after food deprivation

Studies were conducted to determine the efficacy of a dietary technique for reducing prostaglandin (PG) synthesis in adult rats. Rats weighing 280-318 g were fed either essential fatty acid (EFA)-deficient or EFA-adequate diets for 10-17 days after a period of food deprivation. Synthesis of renal papillary PGE2 and aortic PGI2 from endogenous precursor in vitro were estimated by liquid chromatographic and bioassay/radioimmunoassay techniques, respectively, as indices of the capacity of the technique to induce EFA deficiency. PGE synthesis and PGI2 synthesis by isolated tissues from rats fed the EFA-deficient diet were significantly decreased (ca. 50%) relative to control rats fed an EFA-adequate diet. Body and renal papillary weights were not significantly altered by the EFA-deficient diet.

Inflammatory pleuropulmonary fibrosis in essential fatty acid deficient rats and the lack of response to methysergide

In view of the association between essential fatty acid (EFA) deficiency and human cystic fibrosis, we have investigated the possible occurrence of pulmonary disease in rats fed an EFA deficient (EFAD) diet for 40 weeks. In contrast to a few slight spontaneous lesions consisting of pleural membrane hyperplasia, which were found in the lungs of control rats, a much greater incidence of fibrotic lesions was observed in the lungs of EFAD rats. These pleuropulmonary fibroses extended from the hyperplastic pleural membrane into the alveoli and were characterized by collagen deposition and marked macrophage infiltration to the extent that, in some cases, the alveolar septa were completely obstructed by inflammatory exudate. These findings lend indirect support to the contention that EFA deficiency plays a role in the aetiology of cystic fibrosis, at least with regard to pulmonary lesions. Administration of methysergide (10 mg/kg/day, p.o.) for a total of 11 weeks, did not alter the incidence of fibrosis in the lungs of EFAD rats, despite the finding that a man who had developed pleuropulmonary fibrosis as a result of chronic methysergide treatment exhibited a relative serum EFA deficiency. While a relative EFA deficiency may be a predisposing factor for the induction of fibrosis by chronic methysergide treatment, our data are not sufficient to make a decision upon this hypothesis.

Essential fatty acid deficiency: a suggestion concerning experimental design

In experiments on essential fatty acid deficiency, various strategems have been used to balance the deficient and control groups for all nutrients except essential fatty acids. We suggest the use of a single fat-free diet for both groups, with essential fatty acids administered parenterally to the control (nondeficient) group once each week.

Ethanol, essential fatty acids and prostaglandins

In the body the essential fatty acid (EFA) linoleic acid (18:2, omega-6) is desaturated and chain elongated to form homo-gamma-linoleic acid (20:3, omega-6) and arachidonic acid (20:4, omega-6). Apart from their structural function in cell membranes, the EFAs serve as precursors to the prostaglandins and related substances. The prostaglandins can, in general terms, be described as a defensive regulatory system of importance for cardiovascular, gastrointestinal and urogenital function. Acute intake of ethanol gives facial flushing, inhibition of platelet aggregation and elevation of tissue c-AMP. These effects are consistent with release of vasodilatory and antiaggregating PGs. In epidemiological studies, moderate ethanol intake offers some protection against coronary heart disease. Chronic intake high doses of ethanol is associated with damage to, e.g., liver, heart, brain, immunoregulation and various hormonal systems. Decreased tissue levels of 18:2, 20:4 and PGs have been observed both in animals and man. The conversion of 18:2 to 20:4 is inhibited by chronic ethanol exposure. It is suggested that ethanol depletes the PG precursor pool by a dual mechanism of releasing precursor acids and by inhibiting their synthesis. This would lead to a functional EFA-deficiency, manifested by a hypoactive PG system.

Eicosanoid production in rat blood as affected by fasting and dietary fat

The effects of fasting and dietary linoleate on eicosanoid production in clotting rat blood incubated 10 minutes at 37 degrees C was studied. Fasting increased eicosanoid synthesis. Dietary manipulation of eicosanoid levels was best demonstrated in the fed rat model. TXB2, PGE2, F2 alpha, and E1 synthesis increased when dietary linoleate increased from 0.0 to 0.4% calories; from 0.4 to 29% linoleate calories there was no change in PG synthesis, but a decrease in TXB2 production was apparent.

Insulin and glucagon secretion in essential fatty acid deficient rats

Insulin and glucagon secretion in response to common secretagogues were ascertained in the perfused pancreas isolated from essential fatty acid deficient rats. The pattern of insulin secretory response to glucose (16.7 mmol/L) by isolated rat pancreas perfused for 30 min was biphasic in EFA-deficient and control rat pancreas. The amplitude of glucose-stimulated acute secretion (phase I) was significantly greater (p less than 0.01) in magnitude and amplitude in EFA-deficient rats than in the control rats. There was no significant difference in the second phase of glucose-stimulated insulin secretion in the two groups. Glucagon secretion in EFA-deficient and control rats was inhibited by glucose (16.7 mmol/l). Glucagon secretion induced by L-arginine (10 mmol/l) was not significantly different in EFA-deficient and in control rat pancreata (p greater than 0.05). However, arginine (10 mmol/l)-stimulated insulin release was significantly higher in EFA-deficient than in control rats. Growth hormone (100 mumol/l)-induced glucagon and insulin secretion was variable in the two groups but significantly higher than basal secretion. The level of L-leucine (10 mmol/l)-stimulated glucagon and insulin secretion in EFA-deficient rats was minimal but significant. Our results show that isolated pancreata of rats devoid of precursors for endogenous prostaglandin synthesis secreted insulin and glucagon in response to common secretagogues. On the basis of our data, it is concluded that endogenous prostaglandins are probably not obligatory for normal secretory functions of islets of Langerhans.

Interactions between zinc, essential fatty acids and prostaglandins: relevance to acrodermatitis enteropathica, total parenteral nutrition, the glucagonoma syndrome, diabetes, anorexia nervosa and sickle cell anaemia

Many of the features of zinc deficiency and of essential fatty acid (EFA) deficiency are similar in both animals and humans. The two agents interact in various ways. EFAs are important in zinc absorption, probably after conversion to prostaglandins (PGs). Zinc seems necessary for at least two stages in EFA metabolism, the conversion of linoleic acid to gamma-linolenic acid, and the mobilisation of dihomogammalinolenic acid (DGLA) for the synthesis of 1 series PGs. Zinc may also be important in the conversion of DGLA to arachidonic acid and in arachidonic acid mobilisation for 2 series PG formation. These interactions shed considerable light on a number of clinical syndromes, including acrodermatitis enteropathica, total parenteral nutrition, diabetes mellitus, the glucagonoma syndrome and sickle cell anaemia. There is substantial evidence to suggest that anorexia nervosa is due to a combined deficiency of zinc and EFAs. Understanding of the roles of zinc and EFAs in these various clinical situations is likely to lead to improved therapy.