Y. Ingenbleek

Albumin, transferrin and the thyroxine-binding prealbumin/retinol-binding protein (TBPA-RBP) complex in assessment of malnutrition

A comparative study of the level of 4 plasma proteins in malnutrition shows that albumin has low sensitivity, transferrin has intermediate and the TBPA-RBP complex has the highes sensitivity to an alteration in the nutritional status. According to protein and/or iron deficiency, the synthesis of trnasferrin seems to be submitted to contradictory impulses which partially invalidates this test as a reliable index for estimating protein depletion alone. On the contrary, the components of the TBPA-RBP complex respond together and in a parallel direction to protein deficiency. The high degree of sensitivity of TBPA and RBP to an inadequate protein intake is apparently related to their rapid turnover rate and to their unusual richness in tryptophan, which is known to play a key role in the control of protein synthesis. Measurement of TBPA (or RBP) is proposed as a method for the detection of pre-kwashiorkor and early marasmus.

MEASUREMENT OF PREALBUMIN AS INDEX OF PROTEIN-CALORIE MALNUTRITION

Abstract Measurement of prealbumin (thyroxine-binding prealbumin, T.B.P.A.) appears to be a sensitive indicator of protein deficiency and of its improvement by nutritional treatment. It also allows the detection of pre-kwashiorkor and the differential diagnosis of various forms of protein-calorie malnutrition. This sensitivity seems to be due to three factors: ( a ) biosynthesis of T.B.P.A. by the liver, which reacts promptly to protein deficiency, ( b ) the richness of T.B.P.A. in tryptophan; and ( c ) the rapid turnover-rate of this protein. Measurement by a micromethod, using radial immunodiffusion, is simple, reproducible, accurate, and inexpensive.

The role of retinol-binding protein in protein-calorie malnutrition

Plasma RBP is decreased to 1.62 mg plus or minus 0.71/100 ml, or 31.1 percent of normal, in the acute stage of kwashiorkor. RBP doubles its plasma level after 1 wk and triples after 2 wk of appropriate refeeding. The return to normal of RPB runs in close parallel with prealbumin (PA), implying that both components remain bound by 1:1 molar ratio in the PA-RBP complex. Low values recorded on admission for RBP seem to be the result of reduced liver biosynthesis. On the other hand, a high correlation persists between RBP and retinol plasma level along the successive steps of clinical recovery, suggesting that RBP acts as the limiting factor for retinol transport.

Hormonal and nutritional status: Critical conditions for endemic goiter epidemiology?

Recent advances in protein metabolism and in glycoprotein synthesis bring further insight into endemic goiter epidemiology. Retinol circulates in the blood stream in close parallelism with retinol-binding protein and prealbumin (RBP-PA), a protein complex whose liver secretory rate is dependent upon hormonal and nutritional status. On the other hand, normal glycosylation reaction occurs through the formation of a retinol-linked sugar complex. It is suggested that the relative drop of serum retinol levels, as a result of modified hormonal climate and/or declining protein status, might constitute a critical factor capable of inducing a defective incorporation of mannose into native thyroglobulin, leading to an early depression of the full glycoprotein production. This concept affords a comprehensive explanation of the following unresolved data recorded in goitrous areas: (1) clinical and biochemical discrepancies between subjects living in the same morbid territory, (2) persistence of endemicity in spite of appropriate iodine supplementation, (3) similar prevalence of goiter hypertrophy in male and female prepubertal children, (4) increased frequency of goiter enlargement in the four most vulnerable groups, namely preschool children of both sexes, adolescent girls, pregnant women, and elderly persons, (5) decreased impact of thyroid swelling accompanying improved socio-economic status, even without iodine addition, and (6) resurgence of goitrous hyperplasia as an effect of seasonal or sporadic deterioration of nutritional habits, even when iodine supply remains unchanged.

Usefulness of a prognostic inflammatory and nutritional index in pediatric clinical practice

The clinical usefulness of a prognostic inflammatory and nutritional index (PINI) was evaluated in 47 hospitalized infants and 72 age-matched controls from 1 mth to 14 yr of age. The PINI formula is a combination of two markers each of infection (C-reactive protein and orosomucoid) and of malnutrition (albumin and transthyretin). Healthy children are identified by a PINI value less than 1 whereas sick patients are characterized by a progressive rise above 1 as the conditions worsens. The PINI scoring system provides the clinician with a sensitive and universal tool, allowing the correct follow-up of both inflammatory and nutritional poles of the disease spectrum. The formula is of particular help in pediatric practice in recognising early subclinical complications and efficacy of specific therapeutic strategies. The micromethod is simple, rapid and may be regularly repeated since it requires only 46 microliters of serum.

Differences in the Retinol Circulating Complex Between Healthy Male and Female Infants

The concentration of the three components of the retinol circulating complex demonstrates in healthy male infants, but not in females, a transient elevation culminating at 5-6 months after birth. This trimolecular peak is significantly less elevated in bilateral cryptorchid babies. The rise of the retinol related parameters seems directly induced by the testosterone hypersecretion previously described in male infants at 2-3 months. The delay in the liver response in terms of retinol secretion appears to depend on a temporary functional immaturity and/or a transitory depression of the hepatic protein-synthesizing machinery. The surge of the retinol circulating complex could play a crucial role in the O-mannosylation of several glycoproteins involved in male sexual differentiation.