Sumegi B, Butwell N B, Malloy C R, Sherry A D
University Medical School Pecs, Department of Biochemistry, Hungary.
Biochem J. 1994 Jan 1;297 ( Pt 1)(Pt 1):109-13. doi: 10.1042/bj2970109.
We investigated whether lipoamide and diacetyl-lipoamide are able to change the substrate selection in post-ischaemic myocardium. This can be important, because shifting heart metabolism from fatty acid to carbohydrate oxidation can decrease ischaemic injury. Studying the metabolism of [1,2-13C]diacetyl-lipoamide in situ in perfused rat heart by 13C n.m.r., we found intense 13C labelling in glutamate and aspartate, showing that acetyl groups from diacetyl-lipoamide are effectively transferred to CoA and metabolized in heart tissue. From analysis of glutamate C-3 and C-4 isotopomers, we determined the [1,2-13C]acetate/[3-13C]lactate utilization ratio in normoxic and post-ischaemic hearts, where under our experimental conditions the acetate/lactate utilization ratios were 1.2 +/- 0.2 and 2.4 +/- 0.3 in normoxic and post-ischaemic hearts respectively. When 0.25 mM lipoamide was added to the perfusate the acetate/lactate utilization ratio decreased to 1.4 +/- 0.1, which is almost equal to that found for normoxic hearts, showing that lipoamide increased the lactate utilization. In accordance with these data, we found that lipoamide activated pyruvate dehydrogenase by 50% in post-ischaemic myocardium. Competition between [3-13C]lactate and unlabelled octanoate was also studied in post-ischaemic hearts, and we found that lipoamide increased lactate utilization by 100% and increased the rate of the tricarboxylic acid cycle by 64%. Under the same experimental conditions, lipoamide significantly promoted the recovery of post-ischaemic unpaced hearts, showing the positive effect of increased lactate oxidation in post-ischaemic myocardium.
我们研究了硫辛酸和二乙酰硫辛酸是否能够改变缺血后心肌的底物选择。这可能很重要，因为将心脏代谢从脂肪酸氧化转变为碳水化合物氧化可以减少缺血损伤。通过¹³C核磁共振原位研究灌注大鼠心脏中[1,2-¹³C]二乙酰硫辛酸的代谢，我们发现谷氨酸和天冬氨酸中有强烈的¹³C标记，表明二乙酰硫辛酸的乙酰基有效地转移到辅酶A并在心脏组织中代谢。通过分析谷氨酸C-3和C-4异构体，我们测定了常氧和缺血后心脏中[1,2-¹³C]乙酸盐/[3-¹³C]乳酸盐的利用比率，在我们的实验条件下，常氧和缺血后心脏中的乙酸盐/乳酸盐利用比率分别为1.2±0.2和2.4±0.3。当向灌注液中加入0.25 mM硫辛酸时，乙酸盐/乳酸盐利用比率降至1.4±0.1，这几乎与常氧心脏中的比率相等，表明硫辛酸增加了乳酸的利用。根据这些数据，我们发现在缺血后心肌中硫辛酸使丙酮酸脱氢酶活性提高了50%。我们还研究了缺血后心脏中[3-¹³C]乳酸与未标记辛酸之间的竞争，发现硫辛酸使乳酸利用率提高了100%，三羧酸循环速率提高了64%。在相同的实验条件下，硫辛酸显著促进了缺血后未起搏心脏的恢复，表明缺血后心肌中乳酸氧化增加具有积极作用。
