Phenformin and lactic acidosis: a case report and review.

Phenformin was removed from the U.S. market 20 years ago because of a high incidence of lactic acidosis. Unfortunately, this medication is still available from foreign sources. Another biguanide, metformin, was reintroduced to the United States market for the treatment of diabetes. Biguanide-induced lactic acidosis should be included in the differential diagnosis of elevated anion gap metabolic acidosis. We present a case of phenformin-induced lactic acidosis in which we were consulted at the local poison control center. We also review its pathophysiology, presentation, and treatment. A review of the actions of phenformin illustrates the mechanism of pathology that may also occur with metformin. Risk factors for the development of lactic acidosis include renal deficiency, hepatic disease, cardiac disease, and drug interaction such as cimetidine.

Metabolic monitoring by using the rate of change of NAD(P)H fluorescene.

The amino acid fermentation by Corynebacterium glutamicum was monitored with an new technique that uses the first derivative of the NAD(P)H fluorescene signal. The rate of change of NAD(P)H pools is indicative of intracellular redox balance variations that correspond to metabolic changes. The profile of this signal showed several characteristics that coincided with major metabolic events during fermentation. We show here that the derivative fluorescence signal can accurately estimate points of threonine depletion, viable cell count, and the end of amino acid formation. Furthermore, on-line optimization strategies can be developed by using the derivative fluorescene signal. (c) 1994 John Wiley & Sons, Inc.

On-Line Detection of Substrate Exhaustion by Using NAD(P)H Fluorescence.

In this study we examined the utility of NAD(P)H fluorescence for monitoring aerobic fermentations of the threonine auxotroph Corynebacterium glutamicum ATCC 14296. Instead of attempting complicated mathematical corrections for inner-filter effects, we found that it is possible to use the information contained in the on-line NAD(P)H fluorescence signal to assess culture metabolic activities during fermentation. The first derivative of the filtered fluorescence signal, which approximates the turnover rate of the NAD(P)H pool, can be used to precisely identify the temporal points of threonine and glucose exhaustion.

On-line assessment of metabolic activities based on culture redox potential and dissolved oxygen profiles during aerobic fermentation.

We report here on the utility of on-line culture redox potential and dissolved oxygen measurements to identify metabolic changes in fermentation by Corynebacterium glutamicum under aerobic conditions. Metabolic changes were identified by observing discrepancies in the profile of culture redox potential and dissolved oxygen. On the basis of these measurements, we can identify the end of the lag phase, threonine exhaustion, and glucose exhaustion during fermentation.

Effect of reducing agents in an aerobic amino acid fermentation.

This study focuses on the effects of the reducing agents, dithiothreitol (DTT) and glutathione (GSH), on amino acid production in aerobically growing Corynebacterium glutamicum. The problem of reducing agent addition affecting the dissolved oxygen level was solved by positioning the culture at a high dissolved oxygen level and feeding the reducing agent into the fermentor. We show that it is possible to lower the redox potential even in a highly aerobic environment. The addition of DTT to the fermentation during the growth phase caused a significant increase in specific amino acid production rate and total amino acids produced, as compared with a control. In contrast, GSH had an inhibitory effect.

Utility of culture redox potential for identifying metabolic state changes in amino acid fermentation.

We investigated the relationship of dissolved oxygen and culture redox potential (CRP) on amino acid production. Corynebacterium glutamicum ATCC 14296 was used for all experiments. The fermentation can be divided into a growth phase and a production phase. Our results indicate that in order to get higher amino acid production, a lower oxygen supply during the exponential phase is favored. A higher oxygen supply rate appears to be necessary during the production phase. Culture redox potential (CRP) was used to monitor the fermentation. CRP readings were observed to drop to a characteristic minimum value as the metabolic state changed from a growth to production phase. This was evidenced by the commencement of amino acid production and a simultaneous uptake of lactate. Upon lactate exhaustion, the CRP increased abruptly. At the same time, maximal amino acid yields were observed. By the use of minimum CRP as an indication of metabolic phase changes, the agitation rate was changed to increase oxygen supply during the production phase. This significantly increased amino acid production. These results show that culture redox potential measurements can be used to monitor and optimize amino acid production by process manipulation.