Calcium metabolism various factors

In addition to the well-known iron effects on peroxidative processes, there are also other mechanisms of iron-initiated free radical damage, one of them, the effect of iron ions on calcium metabolism. It has been shown that an increase in free cytosolic calcium may affect cellular redox balance. Stoyanovsky and Cederbaum [174] showed that in the presence of NADPH or ascorbic acid iron ions induced calcium release from liver microsomes. Calcium release occurred only under aerobic conditions and was inhibited by antioxidants Trolox C, glutathione, and ascorbate. It was suggested that the activation of calcium releasing channels by the redox cycling of iron ions may be an important factor in the stimulation of various hepatic disorders in humans with iron overload. 

Vascular calcification is a process that involves accumulation of calcium deposits in vessel walls, resulting in increased arterial wall stiffness. Extra-osseous calcification occurs in areas of chronic inflammation, as in atherosclerotic lesions, in which oxidized lipids are the inflammatory stimulus. However, nonatherosclerotic calcification can occur in metabolic disorders like end-stage renal disease, diabetes, hyperparathyroidism, and vitamin K deficiency. This involves a complex interplay of various factors such as serum calcium and phosphate levels, activity of calcification promoters and inhibitors. Vascular calcification is associated with increased morbidity and mortality, predominantly from cardiovascular causes. ... 

The reported incidence of hypercalcemia in sarcoidosis has varied from 2% to 63% in various series (180). These disparate findings may be attributable to differences in sunlight exposure, dietary calcium, skin color, and genetic factors of the populations studied. ACCESS found that a disorder in calcium metabolism from sarcoidosis was more common in men than women [17/268 (6.3%) versus 10/468 (2.1%), chi-square 7.38, p < 0.01], Caucasians compared to African Americans [20/393 (5.1%) versus 6/325 (1.8%), chi-square 223, p < 0.0001], and those diagnosed >age 40 years compared to <40 years [22/401 (5.5%) versus 5/335 (1.5%), chi-square 7.15, p < 0.01] (2). 

C20H23N7O7, Mr 473.45, pale yellow crystals +3 H2O, mp. 248 -250 °C (decomp.), [a]n +16.8° (aqueous hydrogen carbonate). F. occurs in various microorganisms in which it acts as a growth factor e. g., for the lactic acid bacterium Leuconostoc citrovorum, therefore, it is also known as citrovorum factor. F. functions as an active 1-C unit (cf. folic acid) and formyl group transfer agent in the metabolism of folic acid tetrahy-drofolic acid. F. is accessible by synthesis and its calcium salt is used therapeutically as an antidote for folic acid antagonists such as methotrexate. 

---