Barbara E Golden

Free radicals and malnutrition

A free radical is simply an atom or molecule with an unpaired electron. This confers very considerable reactivity on the molecule. As the unpaired electron seeks to be paired, it may either abstract an electron from a donor molecule, leaving a new radical in its place, or attach itself to a second molecule, forming an adduct: the position of the unpaired electron may then change to form a new radical. Only when two molecules react, both of which have unpaired electrons, will the radical reaction terminate without a radical product. The single electron step may be an intermediate in an essential biological process that incorporates a safe mechanism to provide the pairing electron. It is important to emphasize that these reactions are common to many of the normal transformations and energy producing metabolic steps of the body: free radicals are common and normal intermediates in metabolism. All the monooxygenases, several dehydrogenases, cytochrome-P450 and b6, prostaglandin synthetase, leucotriene synthetase, vitamin K-dependent enzymes, the mitochondrial respiratory chain, and many other enzymes normally generate radicals. Photochemical production of radicals occurs on exposure to sunlight, and the production of radicals in the retina leads to changes in molecular configuration that are perceived as light. There is nothing esoteric or unusual about radical reactions: they are commonplace.

Malnutrition: trials and triumphs

Severe malnutrition is uncommon but often fatal, particularly in very young infants or when oedema is present. Another major contributor to mortality is undiagnosed infection. Three pilot studies have recently been performed in severely malnourished patients in therapeutic feeding centres in sub-Saharan Africa. In each, a practical management problem was addressed and a potential solution tested. Three conclusions were reached: young breastfeeding infants were best managed using a supplemented suckling technique; routine antibiotics from admission reduced mortality; and in adults with oedematous malnutrition, therapeutic diets with a lower-than-usual protein:energy ratio were effective in reducing mortality and permitting catch-up weight gain.

Calprotectin is raised in endogenous posterior uveitis

Calprotectin, the L1 leucocyte protein, is found in large quantities in the cytosol of granulocytes and monocytes. Plasma calprotectin levels are increased in infections, malignant tumours, vascular insults and various other pathogenic conditions. The authors have investigated plasma calprotectin and ANCA levels in 27 patients with endogenous posterior uveitis (EPU) and six healthy volunteers. Compared to the control values, the mean levels of plasma calprotectin were raised in patients with active uveitis (p<0.005 (ANOVA)). Raised serum ANCA titres, which are also associated with neutrophil activation, were also detected in some patients with EPU but the level of ANCA did not correlate with that of calprotectin. The authors suggest that measurement of plasma calprotectin may be a sensitive indicator of disease activity in patients with endogenous posterior uveitis.

ZINC ABSORPTION IN AND DURING RECOVERY FROM SEVERE MALNUTRITION IN CHILDHOOD

Severely malnourished Jamaican children have evidence of both malabsorption and zinc (Zn) deficiency, especially when they are oedematous. However, on high energy feeds, they are able to gain weight at greatly accelerated rates. By labelling their feeds with the stable isotope, 70Zn, and measuring their intake and faccal output of total and isotopic Zn over 3 days, we calculated total absorption, net absorption and, by difference, endogenous loss of Zn in groups of children, 8 to 19 months old, wiih marasmus (n 4), with oedematous malnutrition (n 3), during rapid weight gain following severe malnutrition (n = 11) and after their recovery to reference weight-for-length (‘controls’, n = 8).Results are expressed as percentages of Zn intake, group means 1 SEM. In the Jamaican ‘controls’, total absorption Zn (25 ± 2%) and net absorption Zn (19 ± 3%) were similar to values in healthy U.S. children of similar age. However, compared with the controls total absorption Zn was lower in the children with oedematous malnutrition (12 ± 4 %) while in both the marasmic and oedematous children, endogenous loss was higher (24 ± 3 vs 9 ± 2% in the controls): two of the 3 oedematous children had negative net absorption Zn. During rapid weight gain, net absorption Zn (27 ± 2%) was higher than in the controls and correlated positively with their rate of weight gain (r 0.74, p < 0.01): their endogenous loss was low (5 ± 2%).The results suggest that Zn malabsorption occurs particularly in oedematous malnutrition but resolves rapidly during recovery.