Nicotinamide excess/toxicity

Neurotoxins produced by the body. Some normal body constituents are neurotoxic in excess. These incluse quinolinic acid (Fig. 25-11),889 3-hydroxykynurenine (Fig. 25-11 p. 1444),890 and homocysteine.891 Elevated levels of homocysteine are also associated with vascular disease and stroke (Chapter 24). 3-Hydroxykynurenine is a precursor to ommochrome pigments of insects and an intermediate in conversion of tryptophan into the nicotinamide ring of NAD in humans (Fig. 25-11). 6-Hydroxydopamine (Fig. 30-26), which may be formed in the body, is severely toxic to catecholaminergic neurons.892... 

Toxicity. Toxic effects of nicotinamide Include (Table 9) flushing, pruritus, skin rash, heartburn, nausea, vomiting, diarrhea, ulcer activation, abnormal liver function, hypertension, and hyperglycemia (Ban, 1974 Berge, 1961 Berge et al, 1961 DlPalma and Ritchie, 1977). The doses used are often greater In excess of... 

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