THE EFFECT OF CUSHING'S SYNDROME UPON SERUM ALBUMIN METABOLISM

Review of the toxicology of beclomethasone dipropionate

This paper reviews the published toxicity of beclomethasone dipropionate (BDP). BDP is a synthetic glucocorticosteroid which has a powerful local anti-inflammatory effect but little systemic action. It has been developed for both dermatological and inhaled applications. LD50 values and other acute studies indicated low toxicity. Findings published for repeat dose and reproductive toxicity studies embraced the known range of metabolic and physiological effects of glucocorticoids. For repeat dose studies, these included reduction in body weight gains, cushingoid syndrome in dogs, reductions in the numbers of lymphocytes and the weights of the tissues connected with the immune system, and hepatic glycogen deposition and fatty liver changes. In reproductive studies, there was an increase in the prevalence of cleft palate in mice and rabbits and in the number of dead foetuses, and ossification was retarded. Despite the route of administration, there was a general similarity of effects within and between species. All observations were characteristic of synthetic glucocorticoids and related to the intrinsic effects of these drugs.

Serum albumin

The liver manufactures albumin at a massive rate and decreases production in times of environmental, nutritional, toxic and trauma stress. Osmotic pressure is a basic evolutionary regulatory factor, and hormonal control over albumin production has been demonstrated. Where and why new or old albumin is degraded are questions which have not been clarified, although the vascular endothelium may well be the degradative site. Albumin is important as a transport protein, as a measure of evolution and as a model to study secretion following synthesis without the intervening steps of glycosylation. Investigations as to how this protein enters the endoplasmic membrane may well answer some of the questions concerning signal peptide insertion (288). The role of the urea cycle intermediate ornithine and its participation in polyamine synthesis, which has a positive effect on albumin synthesis, is under study. Likewise, the inverse relation between acute-phase protein synthesis and albumin synthesis regulated by interleukin 1 and other cytokines will merit further study. These are a few of the concepts which will be tested in the future.

The effect of hydrocortisone and albumin on the synthesis and secretion of soluble proteins by isolated hepatocytes

Monolayer cultures of hepatocytes were prepared. Supplementation of the incubation medium with bovine serum albumin increasing from 150 mg% to 6% resulted in an increase in retained and total newly synthesised proteins. No clear effects on secretion of soluble proteins were observed. Hydrocortisone supplementation of the medium at 13.75 and 27.50 nmol/l resulted in both enhanced synthesis and secretion of soluble proteins, an effect found not to be a function of concentration. Serum inhibited the effect. Hydrocortisone supplementation resulted in enhanced [3H]leucine uptake by the cells, inhibited in the presence of anti-rat albumin serum. Hydrocortisone supplementation had no effect on the inhibition of synthesis and secretion that resulted from supplementation of the medium with anti-rat albumin serum.

Effects of ethanol on protein synthesis and secretion

Liver protein synthesis involves a complex series of reactions which is influenced by hormones, nutritional state and general health of an animal. The secretory processes for proteins, such as albumin, also interact with the protein synthetic machinery of the liver. Alcohol may affect synthesis and/or secretion at a number of loci and the mechanism of alcohol's action could depend on the immediate state of the experimental tissue. Ethanol was shown to interfere with albumin synthesis and the effect was shown to differ when livers from fed and fasted animals were compared. The ethanol effects were also dependent on the metabolism of ethanol rather than on the simple presence of this drug. Acetaldehyde decreased albumin synthesis but in a manner which was distinct from the ethanol effect. Acute ethanol administration under the conditions used in our studies had little effect on secretion of prelabeled proteins from hepatocytes. The implications of studies of the effects of ethanol on liver protein synthesis and secretion are discussed.

Effects of ethanol on protein synthesis

Cardiac: Cardiac protein synthesis is influenced by the state of nutrition with reduction of cardiac size in starvation. Ethanol per se may not affect this synthesis directly, but the metabolite of ethanol, acetaldehyde, profoundly decreases normal protein synthesis in the heart in vitro. The interference with the synthetic process may play a role in the ultimate cardiomyopathies of malnutrition and alcoholism. Hepatic: In vivo albumin synthesis is sensitive to environment, oncotic pressure, normal balance, nutrition, as well as toxins and state of health. Thus, to study the acute effects of alcohol alone, it was necessary to employ the isolated perfused liver. Fasting reduced albumin synthesis 50%, with loss of RNA and a disaggregation of the endoplasmic membrane bound polysome. Tryptophan, arginine and ornithine added to the perfusate at a final concentration of 10 mM reversed these findings. Alcohol likewise reduced albumin synthesis; disaggregates the bound polysome without a marked loss of RNA. Ornithine, arginine and tryptophan are able to reverse this loss in albumin synthesizing capacity. The combination of fasting and alcohol, while not lowering albumin synthesis below that seen with either stress alone, prevents the recovery from either stress.

Albumin metabolism in rabbits and rats with transplanted tumours

Albumin distributions and turnover rates have been studied using (131)I labelled tracer material in rabbits with Vx2 carcinoma and rats bearing SP7 fibrosarcoma in comparison with control animals. Albumin concentrations were reduced in the tumour bearing animals but plasma volumes increased as the tumours developed. Relative increases were seen in the extravascular distribution of albumin, due partly to albumin pooling in and around the tumours and possibly also to general increases in capillary permeability. In the rats there was a considerable increase in the catabolic rate of albumin which was not related to urinary protein loss. The tumour bearing rabbits showed evidence both of increased catabolism and of decreased synthesis and the combination of the two effects resulted in a greater lowering of albumin concentration than was seen in the rats. Possible mechanisms for these findings and their significance in human malignant disease are discussed.

Augmentation of albumin but not fibrinogen synthesis by corticosteroids in patients with hepatocellular disease

Simultaneous studies of albumin and fibrinogen metabolism have been conducted using the carbonate-(14)C method before and after a 13 day course of prednisolone in eight patients with hepatocellular disease. Initially six patients were hypoalbuminemic. The mean plasma albumin and fibrinogen concentrations and albumin and fibrinogen synthetic rates were all lower than the corresponding values in a group of control subjects. Prednisolone therapy was associated with significant increases in the plasma concentration and synthetic rate of albumin but changes in the intravascular albumin pools were not significant. It is inferred that a low synthetic rate of albumin in a patient with liver disease does not necessarily represent the maximum capacity of the diseased liver to synthesize this protein. Changes in the plasma concentration, intravascular pool, and synthetic rate of fibrinogen were small and inconsistent. The data are compatible with a selective action of corticosteroids on hepatic protein metabolism and with the existence of different mechanisms for the control of albumin and fibrinogen synthesis.

Hypercatabolism of normal IgG; an unexplained immunoglobulin abnormality in the connective tissue diseases

The metabolism of radioiodinated IgG was studied in a series of 42 patients with connective tissue diseases (16 systemic lupus erythematosus, nine rheumatoid arthritis, five polymyositis, five vasculitis, and seven miscellaneous diagnoses). Fractional catabolic rates were increased and survival half-lives were shortened in all diagnostic categories indicating hypercatabolism of IgG. This hypercatabolism was masked by increased IgG synthesis, resulting in elevated serum concentrations of IgG in patients with systemic lupus erythematosus and rheumatoid arthritis and in generally normal concentrations in the others. The metabolism of iodinated IgM was also studied in eight patients with systemic lupus erythematosus, in seven with rheumatoid arthritis, and in 12 controls. The fractional catabolic rates were normal in both groups of patients. Serum concentrations of both IgM and IgA were moderately elevated in all diagnostic categories. Serum albumin metabolism was entirely normal in the nine subjects studied who were not receiving corticosteroids; in three who were receiving them, moderate hypercatabolism was observed. The hypercatabolism of IgG could not be accounted for by factors previously known to alter IgG metabolism. It was not observed in 15 patients with other chronic, inflammatory diseases and was not explained by concomitant administration of adrenal corticosteroids to some patients. Identical results were obtained whether the IgG was obtained from a patient himself or from a normal donor, demonstrating that the hypercatabolism is a host defect and not an abnormality of the protein. Thus, patients with connective tissue disease of several different diagnostic categories have been shown to have an unexplained immunoglobulin abnormality: they catabolize normal IgG at an accelerated rate.

Albumin metabolism: effect of the nutritional state and the dietary protein intake

Nine malnourished and nine children who had recovered from malnutrition were given a single injection of albumin-(131)I and were studied during consecutive periods in which the dietary protein was changed.Malnourished children had significantly lower catabolic rates of albumin than had recovered children on the same protein intake. Both nutritional groups, however, showed a progressive fall in catabolic rate after 3-5 days on a low protein diet (0.7-1.0 g/kg per day), and the maximum effect was seen in the 2nd wk of low protein feeding. The catabolic rate could return to normal within 3 wk in a malnourished child fed 4 g of protein/kg per day. The albumin synthetic rate was measured by a computer technique suitable for nonsteady-state conditions. The synthetic rate in the malnourished groups (101 mg/kg per day) fed on a low protein diet was significantly lower than the rate in the recovered groups (148 mg/kg per day). The synthetic rate responded rapidly to a change in diet; when the rate fell, the intravascular albumin mass was maintained by two compensating mechanisms: (1) a net transfer of extravascular albumin into the intravascular pool; and (2) by a delayed fall in the catabolic rate. The net transfer of albumin into the intravascular compartment diminished as the catabolic rate fell. ADAPTATION TO A LOW PROTEIN DIET WAS ASSOCIATED WITH: (a) low synthetic and catabolic rates of albumin; (b) a reduced extravascular albumin mass; and (c) a capacity for a rapid return to normal in the synthetic rate when the dietary protein was increased.

Metabolism of human serum albumin in man during acute exposure to high altitude (14,100 feet)

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