Studies on the physiological significance of marginal riboflavin deficiency in man with an emphasis on the metabolic role of riboflavin in red blood cell ageing

The results of a recently conducted nationwide survey in Britain indicated that a large proportion of the elderly population could be considered to be biochemically riboflavin deficient. The work presented here describes an attempt to assess the physiological significance of marginal riboflavin deficiency in man with particular emphasis on the metabolic importance of riboflavin to red blood cell (RBC) ageing. Red cells from adults and geriatrics were separated into nine fractions of different mean age by density gradient centrifugation. Haematological measurements including haematocrit, RBC count, reticulocyte count, and haemoglobin (Hb) estimation, were made on whole blood and packed cell samples from all subjects. Glutathione reductase (GR) activity (I.U./g Hb) was measured in all fractions and in unfractionated blood samples from each subject. Biochemical indices selected for study included malonyldialdehyde (MDA) production and percentage haemolysis of RBC in response to peroxidative stress; endogenous haemoglobin derivatives specifically methaemoglobin (MHb) , oxyhaemoglobin (Oxyllb) and sulphaemoglobin (SHb) ; and endogenous reduced glutathione (GSH). In addition the effect of daily riboflavin supplements on haematological and biochemical responses of RBC in two biochemically riboflavin deficient subjects was studied. Studies on RBC distribution suggested that marginal- biochemical ariboflavinosis may predispose RBC to premature lysis In vivo, particularly in the elderly. Biochemical studies showed that as RBC age GR activity, GSH, and OHb fall and peroxidative haemolysis and MHb rise. These observations implied that older cells with low GR activity are less able to resist oxidative stress than are young cells. On the other hand, more MDA was produced in peroxide stressed younger cells than in older cells which may reflect changes in RBC lipid composition as cells age. Although marginal riboflavin deficiency appeared to result in RBC with increased MHb, increased susceptibility to peroxidative haemolysis and reduced concentrations of GSH these effects were not statistically significant. Finally, a mechanism was proposed which implicated GR activity as a determinant of RBC survival and a computer programme devised to describe the mechanism. Results of the study suggested that GR activity is a determinant of RBC survival or is closely linked with the activity of another such enzyme