Yves Ingenbleek

Characterization of γ-linolenic acid inRibes seed

The total lipid content of fruit seeds of theRibes family ranges by weight from 18.3% in gooseberries (Ribes uva Crispa) to 30.5% in black currants (Ribes nigrum). Isolation procedures and analytical methods (gas chromatography, mass spectrometry, high performance thin layer chromatography and stereospecific analysis) demonstrate that the oils fromRibes seeds contain up to 19% by weight of γ-linolenic acid (γ-LA, C18∶3, n−6) in black currant oil. This lastRibes species thus constitutes one of the richest natural sources in γ-LA yet described. These oils appear promising for critically ill patients who seem unable to convert linoleic acid into subsequent EFA fractions.

Nutritional essentiality of sulfur in health and disease

Sulfur is the seventh most abundant element measurable in the human body and is supplied mainly by the intake of methionine (Met), an indispensable amino acid found in plant and animal proteins. Met controls the initiation of protein synthesis, governs major metabolic and catalytic activities, and may undergo reversible redox processes safeguarding protein integrity. Withdrawal of Met from customary diets causes the greatest downsizing of lean body mass following either unachieved replenishment (malnutrition) or excessive losses (inflammation). These physiopathologically unrelated morbidities nevertheless stimulate comparable remethylation reactions from homocysteine, indicating that Met homeostasis benefits from high metabolic priority. Inhibition of cystathionine-β-synthase activity causes the upstream sequestration of homocysteine and the downstream drop in cysteine and glutathione. Consequently, the enzymatic production of hydrogen sulfide and the nonenzymatic reduction of elemental sulfur to hydrogen sulfide are impaired. Sulfur operates as cofactor of several enzymes critically involved in the regulation of oxidative processes. A combination of malnutrition and nutritional deprivation of sulfur maximizes the risk of cardiovascular disorders and stroke, constituting a novel clinical entity that threatens plant-eating population groups.

Vitamin A-Deficiency Impairs the Normal Mannosylation, Conformation and Iodination of Thyroglobulin: A New Etiological Approach to Endemic Goitre

This study was undertaken in order to validate the hypothesis that vitamin A-deficiency alters the structure of thyroglobulin (Tg). For that purpose, four groups of 20 Sprague-Dawley rats were submitted during two months to varying dietary conditions, namely a control diet (C+), a vitamin A-deficient diet (A-), an iodine-deficient diet (I-) and a diet characterized by the association of both deficiencies (A-I-). Both the conventional parameters of thyroid function, the intracellular steps of Tg glycosylation and iodination were analyzed. In the A- and A-I- groups, blood levels of retinol fell to one tenth of the control mean and circulating concentrations of total and free T4 and T3 increased significantly. This biochemical hyperthyroidism contrasted with the maintenance of normal TSH plasma values, suggesting a generalized peripheral refractoriness to thyroid hormones. In both A- and A-I- groups, thyroid cytosol 3H-RPM (retinyl-phosphate-mannose) and 3H-mannose incorporation into the core of the 12S-Tg and 19S-Tg species were reduced by 40-50%. In contrast, cytosolic concentrations of 3H-DPM (dolichyl-phosphate-mannose) rose, suggesting that the N-glycosylation pathways are affected in opposite direction. The sedimentation coefficient in sucrose gradient of the purified dimeric 125I-19S-Tg after guanidine 6M and dithiothreitol denaturation showed that most of the A- Tg molecules were transformed into monomeric 12S species, implying alterations of both noncovalent and covalent bonds. Finally, the radiochromatogram of 125I-iodothyronines recovered after Tg pronase digestion revealed a significant increase in the mono- (MIT) and diiodothyronine (DIT) fractions in contrast with a significant decrease in the T3 and T4 hormonal compounds. These findings are consistent with the view that vitamin A-depletion impairs the endogenous RPM synthesis and, therefore, the normal Tg 0-mannosylation. The growing peptide is characterized by steric hindrance, leading to abnormal closure of disulphide bonds, reduced MIT-DIT coupling reactions and depressed generation of physiologically active thyroid hormones. pure iodine deficit (I-) induces no effects on the above-mentioned glycosylation reactions, but iodine shortage superimposed on preexisting vitamin A-deficit (A-I-) aggravates the Tg dysmaturation.(ABSTRACT TRUNCATED AT 400 WORDS)