Regulation of alpha 1-acid glycoprotein plasma concentration by sex steroids and adrenal-cortical hormones during experimental inflammation in the rat

Treatment of adult intact rats with sex steroids (estradiol-17 beta, ethynylestradiol, dihydrotestosterone) raises the concentration of serum acute-phase alpha 1-acid glycoprotein (AGP). Estrogens are more effective than dexamethasone, and experimental inflammation causes an additive effect on AGP synthesis when ethynylestradiol is given simultaneously. Adrenaline is also able to increase the AGP level. Experiments with adrenalectomized and adrenalectomized plus castrated rats result in a 50% reduction in the serum level of AGP as compared with that in normal and hypophysectomized rats. Although ethynylestradiol is the strongest inducer of AGP synthesis in intact animals, it is unable to enhance significantly the AGP level in adrenalectomized rats, contrary to dexamethasone. Adrenalectomized rats are incapable of undergoing a substantial increase in plasma AGP level following experimental inflammation, and ethynylestradiol or adrenaline cannot take the place of dexamethasone in inducing high levels of AGP in these inflamed rats. These results indicate that glucocorticoids play an obligatory role in modulating AGP synthesis either by directly regulating the AGP gene or in modulating AGP synthesis by increasing the stability of AGP mRNA. Finally, it is suggested that glucocorticoids may also act in unmasking receptor binding sites at the AGP gene level for other mediators such as sex steroids and putative inflammatory factors.

Long-term biosynthesis of complement component C3 and alpha-1 acid glycoprotein by adult rat hepatocytes in a co-culture system with an epithelial liver cell-type

We used a system of co-culture of adult rat hepatocytes with another epithelial cell type from rat liver to study the synthesis of two acute-phase reactants, alpha-1 acid glycoprotein (alpha 1AGP) and the third component of complement (C3), and we have obtained long-term secretion of these two proteins. After a period of adaptation corresponding to the first 2-4 days of the co-culture, hepatocytes secreted C3 and alpha 1AGP for at least 2 weeks at a mean level higher than that observed in the first days of a pure culture of hepatocytes. When pulse-chase analysis was performed on day 6 of co-culture, kinetics of synthesis of alpha 1AGP and C3 were the same as those observed on day 1 of a conventional culture of pure hepatocytes. Furthermore, intracellular and extracellular alpha 1AGP had Mr values respectively of 39,000 and of 42,000-52,000, identical with those observed in pure cultures of hepatocytes. Similarly, the molecular size and subunit structures of C3 were the same in co-culture and in cultures, indicating an identical processing of this protein. C3 produced in co-culture was also haemolytically active. Therefore, the system of adult hepatocytes co-cultured with this liver epithelial cell provides a physiological system in vitro which permits long-term synthesis of the two acute-phase reactants C3 and alpha 1AGP. This model opens the possibility to study the modulation of the synthesis of these two proteins during a long period by inflammatory agents or by hormones.

The effects of 17 alpha-ethynyloestradiol and of acute inflammation on the plasma concentration of rat alpha 1-acid glycoprotein and on the induction of its hepatic mRNA

We measured the serum concentration of alpha 1-acid glycoprotein (alpha 1-AGP) and we evaluated the content of its hepatic mRNA in rats after 17 alpha-ethynyloestradiol treatment or after turpentine-induced acute inflammation, or after both treatments performed simultaneously. We have also studied the affinity of serum alpha 1-AGP for concanavalin A under these conditions. Both types of stimuli induce a marked retention of the glycoprotein on free concanavalin A. The serum concentration of alpha 1-AGP is increased about 14-fold compared with that in control rats when a single pharmacological dose (50 micrograms) or multiple injections of 17 alpha-ethynyloestradiol are administered. This increase is greater in turpentine-oil-injected rats (about 21-fold) and reaches a maximum (about 32-fold) in rats injected with 17 alpha-ethynyloestradiol plus turpentine oil; this increase in alpha 1-AGP corresponds to the addition of the effects of the two inducing agents. Similar changes are also observed either in the alpha 1-AGP mRNA content as estimated by using an alpha 1-AGP-specific cDNA probe, or in the amount of translatable alpha 1-AGP mRNA. The results indicate that: after a high dose of 17 alpha-ethynyloestradiol and after acute inflammation, the increase of the alpha 1-AGP serum concentration is due to an accumulation of the alpha 1-AGP mRNA; different mechanisms and/or pathways are probably involved in regulating the synthesis of alpha 1-AGP under various stimuli; 17 alpha-ethynyloestradiol as well as acute inflammation seem to control the glycosylation process of alpha 1-AGP in an identical manner.

Evidence for alpha-1-acid glycoprotein populations of different pI values after concanavalin A affinity chromatography. Study of their evolution during inflammation in man

Isoelectric focusing in polyacrylamide gel was used to reveal the two alpha 1-acid glycoprotein populations separated by affinity chromatography on Con A-Sepharose from human purified alpha 1-acid glycoprotein, whole normal serum and sera from patients undergoing an acute inflammatory process. The concanavalin A non-reactive peak had a lower isoelectric point than did the concanavalin A reactive peak. Moreover, crossed immunoaffinity electrophoresis with free concanavalin A revealed three alpha 1-acid glycoprotein populations (concanavalin A reactive, weakly and non-reactive). A significant difference was observed between the patterns of normal and of inflammatory sera, since the concanavalin A reactive fraction was enhanced during the inflammatory process. These results suggest a variation in relative ratios of the different types of peripheral oligosaccharide branches in the alpha 1-acid glycoprotein populations.