Tissue metabolism in infection. DPNase activity, DPN levels, and DPN-linked dehydrogenases in tissues from normal and tuberculous mice

NAD+ auxotrophy is bacteriocidal for the tubercle bacilli

The human tubercle bacillus Mycobacterium tuberculosis can synthesize NAD(+) using the de novo biosynthesis pathway or the salvage pathway. The salvage pathway of the bovine tubercle bacillus Mycobacterium bovis was reported defective due to a mutation in the nicotinamidase PncA. This defect prevents nicotinic acid secretion, which is the basis for the niacin test that clinically distinguishes M. bovis from M. tuberculosis. Surprisingly, we found that the NAD(+)de novo biosynthesis pathway (nadABC) can be deleted from M. bovis, demonstrating a functioning salvage pathway. M. bovisDeltanadABC fails to grow in mice, whereas M. tuberculosisDeltanadABC grows normally in mice, suggesting that M. tuberculosis can acquire nicotinamide from its host. The introduction of M. tuberculosis pncA into M. bovisDeltanadABC is sufficient to fully restore growth in a mouse, proving that the functional salvage pathway enables nicotinamide acquisition by the tubercle bacilli. This study demonstrates that NAD(+) starvation is a cidal event in the tubercle bacilli and confirms that enzymes common to the de novo and salvage pathways may be good drug targets.

NICOTINAMIDE-ADENINE DINUCLEOTIDE-GLYCOHYDROLASE ACTIVITY IN EXPERIMENTAL TUBERCULOSIS

1. The specific NAD-glycohydrolase activity is increased 70 and 50% over the normal in lung and liver tissues respectively of tuberculous mice. 2. Concomitant with the increase in the NAD-glycohydrolase activity, the NAD-isonicotinic acid hydrazide-exchange activity also is increased in infection. The isonicotinic acid hydrazide analogue of NAD formed by the lung enzyme from tuberculous mice has been isolated and identified. 3. The increased NAD-glycohydrolase activity in infection has been shown to be of host-tissue origin and not due to the activation of the bacterial enzyme on growth of the organism in vivo. 4. In addition to NAD, NMN and NADP also participate in the exchange reaction with isonicotinic acid hydrazide catalysed by NAD glycohydrolase. The interference of the drug at the nucleotide level of metabolism is therefore suggested.

Glyoxylate metabolism and adaptation of Mycobacterium tuberculosis to survival under anaerobic conditions

Tuberculosis is characterized by periods in which the disease may be quiescent or even clinically inapparent, but in which tubercle bacilli persist and retain the potential to reactivate the disease. The present study was carried out in pursuit of an in vitro model which might contribute to the understanding of the physiology of nonreplicating persisters, with oxygen limitation used as the means of inducing this state. When actively growing aerated cultures of Mycobacterium tuberculosis were suddenly placed under anaerobic conditions the bacilli died rapidly, with a half-life of 10 h. When the bacilli were grown in liquid medium without agitation, they adapted to the microaerophilic conditions encountered in the sediment; the adapted bacilli in the sediment did not replicate there but were tolerant of anaerobiosis, exhibiting a half-life of 116 h. Among the early events associated with the adaptation were the synthesis of an antigen designated URB, the function of which is not known, and a fourfold increase in isocitrate lyase activity. The bacilli later exhibited a 10-fold increase in synthesis of a glycine dehydrogenase that catalyzes the reductive amination of glyoxylate, concomitantly oxidizing NADH to NAD. Specific activities of other enzymes studied were either not affected or moderately diminished in the sedimented bacilli. It is proposed that the glyoxylate synthesis in this model serves mainly to provide a substrate for the regeneration of NAD that may be required for the orderly completion of the final cycle of bacillary replication before oxygen limitation stops growth completely. This orderly shutdown is essential to continued survival of M. tuberculosis in a quiescent form.

Hypoglycemic activity of endotoxin. II. Mechanism of the phenomenon in BCG-infected mice

The mechanism of the hypoglycemic activity of endotoxin in hyperreactive BCG mice was investigated. The mechanism was found to be an inhibition of the synthesis of glucose from noncarbohydrate sources. The possibilities of an induced hypermetabolic state and an induced release of insulin in response to endotoxin as causes for the hypoglycemic response were essentially ruled out. In addition, no clear-cut evidence of an insulin-like action by endotoxin was found in the in vivo setting.