Regionally selective alterations in enzymatic activities and metabolic fluxes during thiamin deficiency

Abstract

To further elucidate the molecular basis of the selective damage to various brain regions by thiamin deficiency, changes in enzymatic activities were compared to carbohydrate flux through various pathways from vulnerable (mammillary bodies and inferior colliculi) and nonvulnerable (cochlear nuclei) regions after 11 or 14 days of pyrithiamin-induced thiamin deficiency. After 11 days, large decreases (-43 to -59%) in transketolase (TK) occurred in all 3 regions; 2-ketoglutarate dehydrogenase (KGDHC) declined (-45%), but only in mammillary bodies; pyruvate dehydrogenase (PDHC) was unaffected. By day 14, TK remained reduced by 58%-66%; KGDHC was now reduced in all regions (-48 to -55%); PDHC was also reduced (-32%), but only in the mammillary bodies. Thus, the enzyme changes did not parallel the pathological vulnerability of these regions to thiamin deficiency. 14CO2 production from 14C-glucose labeled in various positions was utilized to assess metabolic flux. After 14 days, CO2 production in the vulnerable regions declined severely (-46 to 70%) and approximately twice as much as those in the cochlear nucleus. Also by day 14, the ratio of enzymatic activity to metabolic flux increased as much as 56% in the vulnerable regions, but decreased 18 to 30% in the cochlear nuclei. These differences reflect a greater decrease in flux than enzyme activities in the two vulnerable regions. Thus, selective cellular responses to thiamin deficiency can be demonstrated ex vivo, and these changes can be directly related to alterations in metabolic flux. Since they cannot be related to enzymatic alterations in the three regions, factors other than decreases in the activity of these TPP-dependent enzymes must underlie selective vulnerability in this model of thiamin deficiency.

Widespread episodic thiamine deficiency in Northern Hemisphere wildlife

“…This phenomenon has been observed in numerous investigations e.g. 707879808788899091. The observed relationships between thiamine deficiency biomarkers and secondary effects are also in agreement with the scientific literature on thiamine deficiency.…”

Properties and functions of the thiamin diphosphate dependent enzyme transketolase

“…Moreover TK protein and TK mRNA are distributed unequally amongst rat brain nuclei, but their decreases in the thiamin de®cient rat brain do not correlate with the sites of brain pathology [145]. In fact, a-ketoglutarate dehydrogenase (KGDH) is the ThDPdependent enzyme whose activity varies, in thia-min de®ciency, in the closest temporal relationship with the manifestations of the disease in experimental rats [16,17,43].…”

Responses of the mitochondrial alpha-ketoglutarate dehydrogenase complex to thiamine deficiency may contribute to regional selective vulnerability

“…TD diminishes KGDHC activity in whole brain homogenates (Freeman et al, 1987;Bubber et al, 2004) or dissected brain regions such as cerebral cortex, entire thalamus or inferior colliculus (Butterworth et al, 1986;Sheu et al, 1998). For these brain regions, the changes in in vitro glucose flux reflected selective vulnerability better than KGDHC activity (Gibson et al, 1989). Immunoblotting analysis of whole thalamus and cortex from TD11 and TD13 rats reveals no changes in the immunoreactivity in any of the subunits of KGDHC compared to controls (Sheu et al, 1998).…”