Albumin turnover

B19a. Bonomo, L., and D Addabbo, A., I-Albumin turnover and loss of protein into the sputum in chronic bronchitis. Clin. Chim. Ada 10, 214r-222 (1964). 

B.H. Prinsen, M.G. de Sain-van der Velden, Albumin turnover experimental approach and its application in health and renal diseases, Clin. Chim. Acta 347 (1) (2004) 1-14. 

Coleman PJ, Scott D, Ray J, Mason RM, Levick JR. Hyaluronan secretion into the synovial cavity of rabbit knees and comparison with albumin turnover. J Physiol 1997 503(3) 645-56. 

Preliminary studies on catalytic osmylation were reported by Kokubo and co-workers who used bovine serum albumin, 0s04, and t-butylhydroperoxide as the oxidant. Turnover numbers up to 40 and an e.e. for 2-phenylpropene of 68% was achieved [23], Apparently the protein binds to osmium via nitrogen donors, but as different sites may be available this may lower the e.e. 

The CSF/serum ratio of albumin during mid-adult life is less than 7 x 10. If the barrier permeability increases (as seen in purulent meningitis), the albumin ratio can increase to values greater than 100 x 10 (barrier breakdown). The albumin ratio is not dependent only on the barrier s permeability, but also on the fluid turnover, which normally is 14% per hour of the total CSF space volume. If turnover decreases, as in the presence of a spinal cord tumor, the albumin ratio can increase to values < 100 X 10-3 (CSF block). 

Between the albumin ratio (R), the barrier permeability (P), and fluid turnover (T), the following relationship exists ... 

Increasing permeability and decreasing turnover will result in the CSF concentration of albumin approaching its serum concentration because of the passive transfer of albumin through the barrier (FI). Identical concentrations (R= 1) are not quite reached, but the albumin ratio can increase to values < 100 x 10-. ... 

No alteration of protein half-life has been detected with glycosylated albumin (39) and ferritin (51). However, Jones and Peterson (45) found that fibrinogen survival, which was reduced in diabetic patients with elevated glycemia, could be increased to normal value shortly after insulin therapy. This suggests that a labile Schiff base could play a role in the regulation of fibrinogen turnover. 

The most efficient system of this type is obtained by the reduction of bovine serum albumin in the presence of molybdate. Apparently disulfide links in the peptide are broken and form thiolate groups which then bind molybdenum. In a borate buffer, this system will reduce dinitrogen and acetylene, although not using dithionite as an electron source. The turnover is similar to that of the iron-molybdenum cofactor (see Section XII), and dinitrogen reduction is inhibited by carbon monoxide and stimulated by ATP. The yield of ammonia is linearly dependent upon PN2, and the yield is also depressed in the presence of fumarate and, more surprisingly, succinate. It is calculated that the... 

The curve shown in Figure 20.26 represents the turnover of rat serum albumin when radioactive albumin is injected into the animals (curve B). Determine the required parameters from this curve in Questions 20.14 and 20.15 ... 

Figure 20.26 Turnover of rat serum albumin. (Reproduced with permission from Jeffay H, Winzler RJ. J Biol Chem 1958 231 101-116.)...

A number of studies have measured the activation of plasma transaminases by pyridoxal phosphate added in vitro however, it is difficult to interpret the results, because plasma transaminases arise largely accidentally, as a result of cell turnover, and the amount released will depend on tissue damage. Furthermore, there is a considerable amount of pyridoxal phosphate in plasma, largely associated with serum albumin, and the extent to which plasma transaminases are saturated will depend largely on the relative affinity of albumin and the enzyme concerned for the coenzyme, rather than reflecting the availability of pyridoxal phosphate for intracellular metabolism. Studies on erythrocyte transaminase activation coefficient are easier to interpret, because the extent to which the enzymes are saturated depends mainly on the availability of pyridoxal phosphate. 

In cirrhotic patients, a reduced synthesis rate of most proteins is found at an early stage, with albumin synthesis being the least compromised factor at first. Fat storage, muscle mass and protein turnover are reduced. This ultimately leads to catabolism (so-called stress metabolism) and increasing muscular atrophy (so-called wasting syndrome). The latter condition can also result from sympathicotonia with elevated catecholamine values similarly, decreased values of IGFl inhibit the formation of muscle tissue. 

Over the years, problems have arisen as a result of the presence of significant amounts of aluminium in parenteral nutrition solutions in particular they have been held responsible for hypercalciuria and its consequences (54). Parenterally administered aluminium bypasses the gastrointestinal tract, which normally serves as a protective barrier to aluminium entry into the blood. In the past, aluminium contamination of casein hydrolysate, which was used as a source of protein in parenteral nutrition solutions, was associated with low-turnover osteomalacia and with encephalopathy in uremic patients. Premature infants are still at risk of aluminium accumulation as a result of prolonged parenteral nutrition (as are patients receiving plasmapheresis with albumin contaminated in its preparation with aluminium). Metabolic bone disease can result (54). 

Fig. 4. Turnover at steady state of human albumin adsorbed on polyethylene. , [125I] Albumin, , [131I] albumin, albumin concentration, 0.8 mg ml-1 shear rate, 250 sec"1. O, mI-albumin , 131I-albumin albumin concentration, 2.0 mg ml"1 shear rate, 2500 sec"1. From Brash and Samak (1978), reproduced with permission.

Cp may transport small amounts of copper to tissue, which have separate membrane receptors for Cp- and albumin-bound copper. The importance of Cp in transport is debated, however, because turnover of Cp copper is very slow and individuals with genetic deficiency of Cp have no problems related to copper transport (see later in this chapter). Albumin and transcuprein are the major copper transport proteins, especially following absorption from the intestinal tract. 

Olesen, H., Turnover studies with iodine-labelled gamma-macroglobulin and albumin. Scand. J. Clin. Lab. Invest. 15, 497-510 (1963). 

Measurements of the levels of semm proteins such as albumin, transthyretin (also known as prealbumin), transferrin and retinol-binding protein are used as biochemical parameters in the assessment of protein energy malnutrition (Table 17-1). An ideal protein marker should have rapid turnover and present in sufficiently high concentrations in semm to be measured accurately. Transthyretin has these properties it is a sensitive indicator of protein deficiency and is effective in assessing improvement with refeeding. 

In the rat, the most often studied animal species, whose tryptophan metabolism resembles closely that of humans, acute ethanol administration, as described earlier, induces a biphasic effect on serum tryptophan levels, an initial increase followed by a later inhibition. Similarly, acute ethanol administration exerts a biphasic effect on brain serotonin synthesis and turnover, an initial enhancement followed by a later inhibition.111 The initial enhancement is caused by an increase in circulating free tryptophan availability to brain, probably secondary to a catecholamine-dependent lipolysis and a nonesteri-fied fatty acid-mediated displacement of the albumin-bound amino acid, whereas the later inhibition of serotonin synthesis and turnover is the result of a decrease in circulating free and albumin-bound tryptophan availability to the brain secondary to activation of hepatic tryptophan 2,3-dioxygenase (TP) by the earlier increase in free tryptophan to the liver. The activation of hepatic TP by acute ethanol administration, which is substrate (tryptophan) mediated, has been described in rats by Badawy and Evans.111127128... 

Johnson, R. N., R. W. Easdale, M. TatneU, and J. R. Baker. 1991. Significance of variation in turnover of glycated albumin on indices of diabetic control. Clinica ChimicaActa 198 229-238. 

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