Relationships between Glucose and Mannose during Late Gestation in Normal Pregnancy and Pregnancy Complicated by Diabetes Mellitus: Concurrent Concentrations in Maternal Plasma and Amniotic Fluid†

Abstract

Enzymatic assays were modified to permit sensitive and highly reproducible simultaneous measurements of D-mannose and D-glucose in biological fluids during weeks 34-40 of human pregnancy. Plasma mannose and glucose averaged 9.8 +/- 0.4 (+/- SEM) and 790 +/- 16 micrograms/ml, respectively, after an overnight fast in pregnant women (n = 22) with normal carbohydrate metabolism. Significantly higher plasma mannose levels were found, despite only minor increases in plasma glucose, in pregnant women with relatively well controlled diabetes mellitus after an overnight fast (16.9 +/- 0.6 micrograms/ml mannose; 883 +/- 29 micrograms/ml glucose; n = 31) or 3-4 h after breakfast (15.7 +/- 1.2 micrograms/ml mannose; 1159 +/- 101 micrograms/ml glucose; n = 19). Plasma mannose correlated significantly with plasma glucose in the women with diabetes mellitus, particularly after an overnight fast. Samples of amniotic fluid were also obtained from the gravida with diabetes mellitus to provide some index of simultaneous relationships in utero. Amniotic fluid mannose and glucose averaged 5.9 +/- 0.4 and 302 +/- 24 micrograms/ml, respectively, after an overnight fast and 6.7 +/- 1.3 and 459 +/- 84 micrograms/ml 3-4 h after breakfast. In amniotic fluid, as in plasma, the concurrent levels of mannose and glucose conformed to relatively fixed relationships. Thus, both fetus and mother appear to be exposed to readily demonstrable amounts of mannose during late gestation and the absolute as well as relative abundance of mannose may be increased coincident with faulty maternal glucoregulation. However, since mannose did not exceed 3% of the concurrent concentration of glucose in any instance, it does not seem likely that endogenous levels of circulating mannose can modify glucose utilization appreciably by competing with glucose for phosphorylation via hexokinase and subsequent intracellular processing.

Enzymatic Determination of Unbound D-Mannose in Serum

“…The test subjects singled out for the present study were lean fasting females under 45 years of age and it is possible that disparities in the test subject selection and sample collection may account for at least a part of the departure. The correlation found between mannose and glucose is in compliance with earlier reports of a positive relationship between the concentrations of mannose and glucose in serum (5,20). The correlation found between mannose and glucose is in compliance with earlier reports of a positive relationship between the concentrations of mannose and glucose in serum (5,20).…”

“…However, the few studies so far conducted have produced intriguing observations on serum mannose concentrations in diabetes mellitus, Candida infection, renal disease, and hyperlipaemia associated with chronic nephritis (3,5,8,20,21). However, the few studies so far conducted have produced intriguing observations on serum mannose concentrations in diabetes mellitus, Candida infection, renal disease, and hyperlipaemia associated with chronic nephritis (3,5,8,20,21).…”

“…The concentration of free (unbound) mannose in human plasma has been measured with enzymatic methods (5,6) and by means of gas-liquid chromatography (3,(7)(8)(9)(10) or gas-liquid chromatography/mass spectrometry (11). The enzymatic methods build on the use of a chain of enzyme reactions to convert mannose to glucose phosphate and the subsequent measurement of the glucose-6-phosphate formed.…”

Mannose metabolism: More than meets the eye

“…Higher doses cause mild gastro-intestinal discomfort, but no other side effects [44]. Pregnant women with diabetes mellitus show elevated mannose levels in fasted blood and amniotic fluid which correlated with high glucose concentration [45] and several show that mannose levels are closely linked to glucose metabolism [46,47]. How this impacts glycosylation is not known.…”

A Na+-dependent D-mannose transporter in the apical membrane of chicken small intestine epithelial cells

“…Extracellular D-mannose is seldom considered as a significant source for the carbohydrate moiety of glycoproteins because, even though D-mannose can be transported by facilitative D-glucose transporters [5,13,15], its plasma concentration (30-50 µM) is at least 100 times lower than that of D-glucose [1,23]. Nevertheless, human fibroblasts transport D-mannose efficiently by D-mannosespecific transporter(s) [19].…”