Any CA19-9 decline at week 8 and radiologic response by week 8 each predicted longer OS in both treatment arms. In the nab-P + Gem arm, the higher proportion of patients with week 8 CA19-9 decrease [82% (206/252); median OS 13.2 months] than a RECIST-defined response [16% (40/252); median OS 13.7 months] suggests that CA19-9 decline is a predictor of OS applicable to a larger population.

The ethanol-induced increase in urinary folate excretion has been shown to decrease plasma folate levels and may contribute to the development of folate deficiency associated with alcoholism. The mechanism for this effect remains to be elucidated. The present studies were designed to examine the direct effect of ethanol on the renal handling of 5-methyltetrahydrofolate (5-CH3-H4PteGlu), the physiological folate. Rats were given four consecutive hourly doses of ethanol (1 g/kg) or isocaloric doses of glucose solution orally. This treatment generated an average plasma ethanol level of 305 mg/dl. Kidneys from male Sprague-Dawley rats were removed 5 hr after initial treatment and perfused in vitro to eliminate any extrarenal effects that could confound interpretation of results. Ethanol was not added to the perfusate. These treatments had no effect on 5-CH3-H4PteGlu conservation by the isolated perfused rat kidney in comparison to experiments in which the animal received no treatment. Ethanol was then added directly to the perfusate to generate average concentrations of 293 mg/dl. The in vitro addition of ethanol significantly decreased the percentage reabsorption and increased the fractional excretion of 5-CH3-H4PteGlu in comparison to controls (kidneys perfused with or without an isocaloric dose of glucose). This effect did not become significant until the renal tissue was exposed to these levels of ethanol for 1 hr. These results indicate that ethanol directly impairs the renal conservation of 5-CH3-H4PteGlu.

The renal regulation of folate excretion is an important component in maintaining the body burden of folate. The tubular processes for folate disposition have been examined by a variety of methods to elucidate the mechanism by which renal folate excretion is regulated. Accordingly, the isolated perfused rat kidney technique was evaluated by investigating the clearance and metabolic patterns of 5-methyltetrahydrofolate (5-CH3-H4PteGlu). Kidneys from male Sprague-Dawley rats were perfused in vitro with [3H]5-CH3-H4PteGlu (1-2000 nmol/L). Linear regression analysis of 5-CH3-H4PteGlu excretion vs. filtered load revealed a tubular transport maximum of 7.5 pmol x min-1.g-1. A dual component system for tubular transport of 5-CH3-H4PteGlu was found: a high capacity, nonsaturable system and a low capacity, saturable system represented by the transport maximum. Furthermore, HPLC analysis of urine demonstrated renal uptake and metabolism of the labeled tracer. Tetrahydrofolate was identified as one metabolic product that indicated secretion of this compound. Additional metabolites were identified from kidney samples. Results suggest that 5-CH3-H4PteGlu undergoes net reabsorption by a dual component transport system; some of the reabsorbed 5-CH3-H4PteGlu is metabolized to other products that may be secreted in the urine.

The reabsorption of 5-methyltetrahydrofolic acid (5-CH3-H4PteGlu) by the renal proximal tubule has an important role in the maintenance of plasma folate concentrations. However, the mechanism by which this vitamin traverses the renal epithelium remains to be determined. Studies in cultured cells have suggested that the folate receptor in association with a probenecid-sensitive anion carrier may be involved in the transmembrane transport of the vitamin. Because 5-CH3-H4PteGlu is reabsorbed and metabolized in the isolated perfused rat kidney (IPRK) in a smaller manner to in vivo models, the IPRK was used to evaluate pathways involved in folate reabsorption. Reabsorption of 5-CH3-H4PteGlu could not be saturated in the isolated perfused rat kidney, even at concentrations up to 2 mumol/L. Folic acid (PteGlu) was used as a competitive inhibitor of FR-dependent reabsorption of 5-CH3-H4PteGlu. When 5-CH3-H4PteGlu was maintained at 1 nmol/L (a concentration at which receptor-mediated transport should be maximal), PteGlu (up to 100 nmol/L) had no effect on reabsorption. The addition of probenecid (1 mmol/L) did not affect the reabsorption of 5-CH3-H4PteGlu but inhibited the fractional excretion of the anion para-aminohippurate. Probenecid also inhibited the urinary excretion of 5-CH3-H4PteGlu metabolites, indicating that reabsorbed 5-CH3-H4PteGlu was metabolized to products that were subsequently secreted into the urine by anion exchange pathways. The physiological importance of a folate receptor-mediated reabsorption of 5-CH3-H4PteGlu appears to be minor in the isolated perfused rat kidney, whereas nonspecific pathways appear to play a major role in the renal folate reabsorption.