Experimental Thiamine Deficiency TRENDS OF KETO ACID FORMATION AND DETECTION OF GLYOXYLIC ACID BY CHI-CHIN LIANG

Thiamine deficiency leads to a well-defined biochemical lesion of carbohydrate metabolism with increase in pyruvate and lactate in the blood (Peters, 1936). Since Lohmann & Schuster (1937) showed that thiamine in the ester form of pyrophosphate is the coenzyme for the decarboxylation of pyruvic acid, it has been found to participate in several important reactions of carbohydrate metabolism, in the phosphogluconate oxidative pathway, the transaldolation and transketolation between ketoses and aldoses and the newly recognized oxidative decarboxylation of glyoxylic acid (Nakada & Sund, 1958). Peters (1948, 1953) emphasized that absence of thiamine does not affect the metabolic change of glucose or glycogen to pyruvate, but that it interferes selectively with the degradation of pyruvate to carbon dioxide and water by the pyruvateoxidase system, thereby inhibiting the liberation of the energy required to maintain the tissue in its living state. Pyruvic acid itself has not been found to be toxic, even when injected intravenously. Therefore the raised pyruvate is only a sign of thiamine deficiency and not necessarily the cause of the associated syndrome. Methylglyoxal was considered non-toxic and was assigned a key part in carbohydrate metabolism (Dakin & Dudley, 1913), until Strohr (1932) demonstrated its toxicity. Findlay (1921) reported that pigeons suffering from polyneuritis were deficient in liver glyoxylase and that this increased after feeding with thiamine. Vogt-Moller (1931) described thiamine deficiency as methylglyoxal intoxication caused by a decreased tissue-glyoxalase activity. Methyglyoxal was reported to be present in the urine of polyneuritic dogs and in the urine and cerebrospinal fluid of infants suffering from apparent thiamine deficiency (Geiger & Rosenberg, 1933), in the blood and urine of man with beri-beri (Platt & Lu, 1939) and in the milk of women with beri-beri (Chiba, 1932; Takamatsu & Sato, 1934; Suzuki & Takamatsu, 1934; Orimo, 1939; Fehily, 1944). Since glutathione was the coenzyme of glyoxalase (Lohmann, 1932), Stannus (1942) suggested that absence of glutathione resulted in an accumulation of methylglyoxal. But Johnson (1936) was unable to detect any preformed methylglyoxal in the tissues of polyneuritic pigeons, and Hopkins & Morgan (1945) have pointed out the absence of satisfactory evidence for the occurrence of a substrate for glyoxalase in the cells and tissues. Kun (1950) found that methylglyoxal inhibited the succinic-oxidase system and Salem (1954) described a possible route of formation of methylglyoxal in thiamine-deficient rats. This again raised the problem of methylglyoxal in thiamine deficiency. Though disorders resulting from lack of thiamine, in functional derangement of muscles, nerves and cardiac system, have been shown, the mechanisms underlying these abnormalities are still unknown. Liang (1960) reported that an aldehyde acid, glyoxylic acid, was found in the urine and blood of thiamine-deficient rats and that its formation depends on the interaction of the metabolism of carbohydrate, fat and protein. Its effect on cellular functions in various organs would merit further investigation in the hope of elucidating the cause of the multiple syndromes of B1-avitaminosis. This paper presents a hitherto unobserved but characteristic fluctuation in pyruvic acid concentration as well as changes in the total keto acid. Furthermore, chromatographic study did not reveal the formation of methylglyoxal in experimental thiamine deficiency; nevertheless, significant amounts of glyoxylic acid were discovered in the urine, blood and tissues of thiamine-deficient rats (Liang, 1960).