METABOLISM OF D-GLUCURONOLACTONE IN MAMMALIAN SYSTEMS. 3. FURTHER STUDIES OF D-GLUCURONOLACTONE DEHYDROGENASE OF RAT LIVER

Glycosidases in cancer and invasion

Glycosidases have been demonstrated to be elevated in the interstitial fluid of tumors, sera of animals and patients with tumors, and in some tumor tissue as compared to normal adjacent tissue. Elevations of serum beta-N-acetylglucosaminidase and beta-glucuronidase most commonly have been found to occur and these enzymes have been shown to be secreted into the extracellular medium by many different tumor cell types in vitro. The mechanism of cellular release of these hydrolytic enzymes probably involves tumor lysosomal exocytosis. Increased tumor glycosidase levels may promote increased tumor cell shedding from primary tumors, local invasion and perhaps be responsible directly, or indirectly for structural changes in tumor cell surface glycoconjugates. These cell surface changes could facilitate tumor cell thrombus formation, secondary site implantation and attachment in the microcirculation to endothelial cells and/or subendothelial basement membrane components. Other studies have demonstrated a correlation between metastatic cell potential and increased endoglycosidase and polysaccharide lyase activity. Generally, metastatic tumor cell variants have been found to be more invasive and capable of degrading proteoglycan basement membrane components, in part due to these increased levels of degradative enzymes. Hence, it is of considerable interest to develop inhibitors against these enzymes. Initial studies with glucuronidase inhibitors in the therapy of bladder tumors have been promising and with the advent of better agents and the use of appropriate in vitro metastatic models it may be possible to design and develop agents which interfere in various metastatic events and limit tumor progression.

Liver cytosolic aldehyde dehydrogenases in rats with different predisposition to induction by phenobarbital. Partial purification and characterization of the enzymes at basal state

Liver cytosolic aldehyde dehydrogenases were partially purified from rats with different genetic predisposition to induction of aldehyde dehydrogenase activity by phenobarbital. The enzymes were studied at basal state without any pretreatment with an inducer. The main aldehyde dehydrogenases from the non-, high- and intermediate reactor animals could not be differentiated by substrate specificity or thermostability. The enzyme from the non-reactor rats was more resistant to changes of pH and to the inhibitory effects of disulfiram than the enzymes from the high- or intermediate reactors. Immunochemical studies suggested a dissimilarity of these enzymes.

Investigation of accelerated metabolic function in small for gestational age infants

Small for gestational age (SGA) infants are known to develop relatively mild transient hyperbilirubinaemia, especially in comparison with premature infants. This may be interpreted as an index of accelerated maturation of particular vital functions. In the present study 12 SGA infants, 12 appropriate for gestational age (AGA) infants, and 12 premature infants had 24 h urine collections under standardized conditions on the third day of life. Urinary excretion of D-glucaric acid and creatinine, which can be increased by drugs (e.g. phenobarbital), were estimated. Haematocrit and bilirubin were determined at the age of 72h. In the 3 groups, the SGA infants had the highest mean haematocrit (SGA = 0.58, AGA = 0.5, Prem = 0.561/1) and the lowest mean bilirubin (SGA = 6.3, AGA = 8.6, Prem = 11.1 mg/dl). Despite a comparatively small urine volume (SGA = 19.6, AGA = 28.3, Prem = 37.3 ml/kg), excretion of D-glucaric acid (SGA = 0.18, AGA = 0.11, Prem = 0.06 mumol/kg) and creatinine (SGA = 101.6, AGA = 79.6, Prem = 80.2 mumol/kg) was significantly higher in the SGA infants. While the results do not provide conclusive evidence, the increased excretion of glucaric acid and creatinine associated with mild transient hyperbilirubinaemia can be considered an indicator of metabolic differences in SGA infants.

Metabolism of D-glucuronolactone in mammalian systems. Inhibitory properties of the products of D-glucuronolactone-dehydrogenase action

1. d-Glucuronolactone was converted into d-glucaro-(1-->4)-lactone, a beta-glucuronidase inhibitor, probably via the intermediate d-glucaro-(1-->4)-(6-->3)-dilactone, by a dehydrogenase in human-liver extracts. 2. Similar experiments with mouse-liver extracts appeared to yield only d-glucaric acid or a non-inhibitory lactone. 3. A strong beta-glucuronidase inhibitor was present in mouse liver after the intraperitoneal administration of d-glucuronolactone. 4. d-Glucarodilactone decomposed spontaneously in aqueous solution to give 25% of d-glucaro-(1-->4)-lactone; the percentage conversion was unaffected by human-liver homogenates. but considerably increased by mouse-liver or pig-liver fractions.