Animal models for respiratory chain disease

Elucidation of the pathogenesis in respiratory chain diseases is of great importance for developing specific treatments. The limitations inherent to the use of patient material make studies of human tissues often difficult and the mouse has therefore emerged as a suitable model organism for studies of respiratory chain diseases. In this review, we present an overview of the field and discuss in depth a few examples of animal models reproducing pathology of human disease with primary and secondary respiratory chain involvement.     

Decreased Incorporation of [3H]Inositol and [3H]Glycerol into Glycerolipids of Sciatic Nerve from the Streptozotocin Diabetic Rat

The incorporation of [3H]myo-inositol into individual phosphoinositides and of [3H]glycerol into glycerolipids was determined in sciatic nerve obtained from normal and streptozotocin diabetic rats and incubated in vitro. The uptake of inositol into lipid was approximately linear with time. More than 80% of the label was present in phosphatidylinositol with the remainder divided about equally between phosphatidylinositol phosphate and phosphatidylinositol-4,5-bisphosphate. Labeling was unchanged 2 weeks after induction of diabetes, but was reduced by 32% after 20 weeks of the disease. Glycerol incorporation occurred primarily into phosphatidylcholine and triacylglycerol and was depressed up to 45% into major phosphoglycerides in nerves from both 2- and 20-week diabetic animals. Triacylglycerol labeling was also substantially decreased, and the reduction was comparable in intact and epineurium free nerve, suggesting that a metabolically active pool of this compound, which is sensitive to hyperglycemia and/or insulin deficiency, is located in or immediately adjacent to the nerve fibers. The considerable decline in incorporation of these lipid precursors in diabetic nerve may be related to impaired inositol transport and to decrease overall energy utilization by the tissue.     

Effect of prolactin and glucocorticoids on P-enolpyruvate carboxykinase activity in liver and mammary gland from diabetic and lactating rats

Summary The administration of 2 bromo--ergocryptine, to reduce serum prolactin decreased the activity of cytosolic P-enolpyruvatc carboxykinase (GTP) (EC4.1.1.32) about 50% in both liver and mammary gland of lactating animals. Adrenalectomy had similar effects to those of bromo-a-ergocryptine. In contrast, there was a 50% increase in enzyme activity in the mammary gland of diabetic, lactating rats and a 10-fold increase in liver as compared with normal rats. P-enolpyruvate carboxykinase activity in mammary gland as liver is coordinately regulated by prolactin, glucocorticoids and insulin.     

Neurogenic peptides and the cardiomyopathy of magnesium-deficiency: Effects of substance P-receptor inhibition

Dietary deficiency of magnesium (Mg) in rodents results in cardiomyopathic lesion formation. In our rat model, these lesions develop after 3 weeks on the Mg-deficient diet; significant elevation of several cytokines, IL-1, IL-6 and TNF also occurs. In probing the mechanisms of lesion formation, we obtained data supporting the participation of free radicals (Freedman AMet al.: Bioch Biophys Res Commun 1990; 170: 1102). Recently, we identified an early elevation of circulating substance P and proposed a role of neurogenic peptides during Mg-deficiency (Weglicki WB, Phillips TM: Am J Phys 1992; 262: R734). The present study was designed to evaluate the contribution of neurogenic peptides to the pathogenesis of Mg-deficiency. In the blood, substance-P and calcitonin gene related peptide (CGRP) are elevated during the first week on the diet. During the second week, circulating histamine, PGE₂ and TBAR-materials were elevated and red cell glutathione was reduced, all prior to the elevation of the inflammatory cytokines during the third week. When the rats were treated with the substance P-receptor blocker [CP-96,345], the levels of substance P and CGRP remained elevated; however, increases in histamine, PGE₂, TBAR-materials, and the decrease in red cell glutathione were inhibited; also, the development of cardiac lesions was inhibited significantly. These data support a central role for neurogenic peptides, especially substance P, in the development of cardiomyopathic lesions during Mg-deficiency.     

Beneficial effect of ACE inhibitor in congestive heart failure

The effects of captopril, an angiotensin-converting enzyme inhibitor, on congestive heart failure (CHF) were investigated in animal and clinical studies. Congestive heart failure was induced in rats by a combination of pressure and volume overload. Cardiac pressure overload was induced by constricting one renal artery (Goldblatt rat) and volume overload was induced by aorto-caval fistula. Captopril (100 mg/kg/day) was then administered for 14 weeks. Isometric contraction was assessed using isolated left ventricular papillary muscles. The maximum developed tension and the maximum rate of increase in tension (dT/dtmax) were decreased in untreated rats with CHF and improved in captopriltreated rats. The left ventricular myosin isoenzyme pattern was shifted towards V3 in untreated rats with CHF, and was shifted back towards V1 in the captopril-treated rats. In the clinical study, captopril (37.5–75 mg/day) was administered to patients with cardiomyopathy for 12 months. There was no effect on left ventricular mass in hypertrophic cardiomyopathy, although systolic anterior motion of the mitral valve disappeared in one patient. In dilated cardiomyopathy, however, left ventricular mass tended to decrease. These results indicate that captopril has a beneficial effect in congestive heart failure.     

Effects of glycated albumin on mesangial cells: evidence for a role in diabetic nephropathy

Nonenzymatically glycated proteins are preferentially transported across the glomerular filtration barrier, and the glomerular mesangium in diabetes is bathed with serum containing increased concentrations of glycated albumin. We investigated effects of glycated albumin on mesangial cells, which are involved in diabetic nephropathy. [³H]-thymidine incorporation was significantly inhibited when murine mesangial cells were grown in culture media containing human serum that had been nonenzymatically glycated by incubation for 4 days with 28 mM glucose. This inhibition was reversed when monoclonal antibodies that selectively react with Amadori products of glycated albumin were added to the culture media. Purified glycated albumin containing Amadori adducts of the glycation reaction induced significant inhibition of thymidine incorporation and stimulation of Type IV collagen secretion compared with cells cultured in the presence of purified nonglycated albumin. These changes were prevented when monoclonal antibodies specifically reactive with fructosyl-lysine epitopes in glycated albumin were added to the cultures. The antibodies had no effect on growth or collagen production in the presence of nonglycated albumin. The results provide the first evidence directly implicating Amadori adducts in glycated albumin in the pathogenesis of diabetic nephropathy, which is characterized by decreased cellularity in association with expansion of the mesangial matrix.     

Antihypertensive effects of captopril without adverse effects on glucose tolerance in hyperinsulinemic rhesus monkeys

The rhesus monkey (Macaca mulatta), which has been found to develop spontaneous obesity, non-insulin dependent diabetes mellitus (NIDDM; Type 2), and hypertension, was used to evaluate the potential blood pressure-lowering effects of captopril as well as the specific effects, if any, on the prediabetic state. Intravenous and oral glucose tolerance testing was carried out with oral captopril dosing. Results showed that captopril significantly decreased both systolic and diastolic blood pressure in all monkeys and significantly decreased fasting plasma glucose levels. Based on these preliminary studies in monkeys, we conclude that captopril exerted antihypertensive effects without adverse effects on glucose metabolism.     

Alterations of β-adrenoceptor-G-protein-regulated adenylyl cyclase in heart failure

Alterations of receptor-G-protein-regulated adenylyl cyclase activity have been suggested to represent an important alteration leading to contractile dysfunction in the failing human heart. Recent experiments suggest that the ₁-adrenoceptor(₁AR) density and mRNA levels are reduced, while ₂-adrenoceptors and stimulatory G-proteins are unchanged (mRNA and protein level). Functional assays demonstrated that the catalyst of the adenylyl cyclase is not different between failing and nonfailing myocardium. Inhibitory G-proteins are increased (pertussis toxin substrates, protein and mRNA) and correlate to the reduced inotropic effects of -adrenoceptor agonists and of CAMP-PDE inhibitors. Gi-coupled m-cholinoceptors and A₁-adrenergic receptors are unchanged in density and affinity. Stimulation of these receptors resulted in an unchanged antiadrenergic effect on force of contraction. In conclusion, a downregulation of ₁-AR and an increase of Gi have been observed as signal transduction alteration in failing human myocardium. These alterations are due to alterations of gene expression in the failing heart and are related to a defective regulation of force of contraction in heart failure.     

Etiologic factors and pathologic alterations in selenium-vitamin E deficiency and excess in animals and humans

The etiology of selenium-vitamin E (Se-E) deficiency diseases may be complex. Many of the syndromes involve combined deficiency of selenium and vitamin E. Selenium moves into the animal and human food chain from soil and plants, which may contain inadequate amounts of the nutrient in many areas of the world. Vitamin E may be in low concentration in many animal feeds unless supplements are added. Some syndromes, such as steatitis in cats, result from an increased requirement of vitamin E in diets that contain large amounts of polyunsaturated fatty acids, and these diseases will only respond to vitamin E administration. Deficiency syndromes in animals owing to pure Se deficiency are infrequent and have been produced mainly by laboratory studies utilizing extreme deficiency conditions. Other factors that may affect the occurrence of these deficiency diseases are concurrent dietary deficiency of S-containing amino acids, bioavailability of different forms of dietary Se, intake of compounds that antagonize Se (e.g., silver salts), and exposure to various prooxidant substances (e.g., iron compounds, oxygen, ozone, and various drugs). A wide variety of pathologic alterations occur in animals and humans with Se-E deficiency. Myocardial lesions are seen most frequently in calves, lambs, pigs, turkey poults, and ducklings. In humans, Keshan disease, an endemic cardiomyopathy in China, is attributed to Se deficiency. Necrosis of skeletal muscle is the most frequent lesion observed in animal species. Necrosis of smooth muscle of the gizzard and intestine may be a prominent lesion in turkey poults, ducklings, and quail. Other Se-E deficiency lesions include hepatic necrosis, gastric ulceration, intestinal and uterine lipofuscinosis, pancreatic damage, steatitis, exudative diathesis, encephalomalacia, and testicular necrosis. Selenium toxicosis is well characterized in animals and humans by neurological, hoof, and hair alterations.     

Alterations in the responsiveness of diabetic fibroblasts to insulin

Fibroblastic cultures from the skin of nondiabetic and diabetic (db/db) mice have been used to investigate alterations in the biological responses of diabetic cells to insulin. Confluent cultures from the skin of both nondiabetic and diabetic animals possess specific receptors for insulin. Diabetic fibroblasts exhibit only 36% as much specific binding of insulin as nondiabetic fibroblasts, because of a decrease in the total number of binding sites, without a change in binding affinity. Insulin caused a time- and dose-dependent increase in the rate of 2-deoxy D-glucose (dGlc) uptake and in ornithine decarboxylase (ODC) activity of both nondiabetic and diabetic fibroblasts. In nondiabetic cells, half-maximal increase in dGlc uptake was obtained with 0.3 nM insulin, and a maximum increase of 120% was obtained with 4.1 nM insulin. In contrast, diabetic cultures required 0.8 nM insulin for a half-maximal increase in dGlc uptake, and maximum stimulation with 4.1 nM insulin was only 50% above control levels. With 4-fold higher insulin concentrations, ODC activity of diabetic cells was only 40% that of nondiabetic cells. In nondiabetic cells, down regulation of insulin receptors by insulin abolished the ability of insulin to stimulate dGlc uptake. These results demonstrate that cells cultured from diabetic animals, which possess a decreased number of insulin receptors, also exhibit decreased stimulation of deoxy D-glucose uptake and ornithin decarboxylase activity by insulin.