Taurine Deficiency and MELAS Are Closely Related Syndromes - Advances in Experimental Medicine and Biology - page 146

Fig. 16.2 Effect of taurine deficiency on lactate/pyruvate ratio. Hearts of taurine-deficient rats
were perfused with Krebs-Hanseleit buffer containing or lacking insulin. The lactate/pyruvate
ratio of the perfusate is shown. Asterisks indicate significant difference between taurine-deficient
and control groups ( p < 0.05)

the metabolic pattern of taurine deficiency favors the metabolism of glucose to lactate
(anaerobic) at the expense of glucose oxidation (aerobic) (Fig. 16.2 ). This occurs
because the decline in respiratory chain activity leads to an elevation in the NADH/
NAD + ratio, which reduces the entry of pyruvate into the citric acid cycle and promotes
the conversion of pyruvate to lactate (Mozaffari et al. 1986 ). This pattern is nearly
identical to that seen in nondiabetic MELAS patients that present with lactic acidosis
arising from inhibition of aerobic metabolism.

16.2.3 Growth Failure in MELAS and Taurine De fi ciency

Growth failure is a widely recognized manifestation of MELAS that is often
associated with migraine headaches, learning disabilities, and exercise intoler-
ance (Sproule and Kaufmann 2008 ). Although it has been proposed that growth
failure might involve deficiencies in growth hormone, inadequate conjugation of
taurine with tRNA Leu(UUR) may be involved.
Hayes et al. ( 1980 ) found that taurine depletion of infant monkeys led to a strik-
ing depression in growth. Although the mechanism underlying this effect has not
been determined, it would be attractive to suggest that growth retardation is related
to impaired mitochondrial protein synthesis and respiratory chain dysfunction (Jong
et al. 2012 ; Kirino et al. 2004 ). Further studies are warranted to investigate the
mechanism underlying the development of this phenomenon.