Red Cell Sorbitol Research Articles

Diagnostic performance of red cell sorbitol assay in a Nigerian teaching hospital

The analytical linearity, detection limit, precision and accuracy, as well as diagnostic sensitivity, specificity and predictive values of red cell sorbitol (RCS) assay were evaluated using the fluorimetric enzymatic technique with the available laboratory facilities in a Nigerian Teaching Hospital. The assay was linear up to 40.0 nmol/ml. The detection limit was 0.55 nmol/ml. The within-assay coefficients of variation (CV) from low to high concentrations were in the range of 2.82% to 5.48% while the corresponding values for the between-assay variation were 3.60% to 6.05%. The mean recovery was 90.4%. High concentrations of some common blood constituents and drugs did not cause significant interference. An evaluation of the diagnostic sensitivity and specificity of RCS in 102 out-patients revealed a sensitivity of 94.4%, specificity of 98.8% and efficiency of 98.0%. The predictive value of a positive test was 94.4% while that of a negative test was 98.8%. The mean value of red cell sorbitol in patients confirmed to have diabetes mellitus (23.1±1.13 SE nmol/g Hb) was significantly higher ( P < 0.001) than the corresponding value (11.0±0.0.27 SE nmol/g Hb) for those without diabetes and for control subject. A similar observation was also made for plasma glucose and fructosamine. These observations demonstrate that RCS assay could be adopted in a third world laboratory for clinical applications.

Red cell sorbitol concentration in relation to short- and medium-term variation of plasma glucose.

To evaluate the time course of changes in red cell sorbitol (RCS) concentration in relation to variations of plasma glucose levels, RCS was determined in 7 normal subjects during i.v. glucose infusion (IVGTT); in 6 hyperglycemic insulin-dependent diabetic subjects while glycemia was normalized with Biostator GC 115 and in 4 diabetic patients in previously poor metabolic control, in whom normal glycemia was obtained in 8-10 days by intensive insulin therapy. During IVGTT, plasma glucose levels increased with significant differences from baseline at 5, 10, 16, 25, 60, 100 and 160 min and returned to basal levels after 3h; RCS concentration showed small and insignificant increases. During i.v. insulin infusion, plasma glucose fell to almost normal levels within roughly 3h; RCS levels showed a gradual reduction becoming significant at 180 min. In the third study, decrease in plasma glucose was always associated with a fall in RCS level which became significant between the 2nd and the 3rd day of the study. Thus, RCS levels were not affected by very short-term variations of glycemia but by a previous hyperglycemic crisis that lasted a few hours. There were therefore medium-term variations of RCS level. In conclusion, RCS determination is not useful as an index of metabolic control in diabetes.

Cone electroretinograms and visual acuities of diabetic patients on Sorbinil treatment

Photopic, 30-Hz, and foveal electroretinograms were measured in 19 diabetic patients in an experimental study of the effects of short-term Sorbinil (an aldose-reductase inhibitor) on retinal function. Patients were assigned in double-blind fashion to Sorbinil (250 mg/day) or placebo groups and were tested at the outset and after four weeks of therapy. Comparisons (t-test) between the Sorbinil and placebo groups failed to show significant effects of treatment on electroretinograms, although there was a significant correlation within the Sorbinil group between foveal recordings and red cell sorbitol at the end of treatment. Analysis showed that increased foveal electroretinograms were found in patients with low initial retinopathy but not in those with greater retinopathy. Eight patients continued Sorbinil treatment for one year. Again patients improving their foveal measurements had less initial retinopathy than those not improving. This difference was significant after one year of treatment but not at four weeks.

The Relationship between Red Cell Sorbitol and Blood Glucose Concentration in Diabetes during Hyperglycaemic Clamp Studies and in Out-Patients

The Relationship between Red Cell Sorbitol and Blood Glucose Concentration in Diabetes during Hyperglycaemic Clamp Studies and in Out-Patients

Red cell sorbitol and diabetic control.

There is a disagreement about the value of red cell sorbitol as an indicator of diabetic control. We studied 7 insulin requiring diabetics, one for 10 days and 6 for 24 hours. In the 10-day study, blood samples were obtained every 4-6 hours. Sequential analysis of plasma glucose and red cell sorbitol levels showed that simultaneous levels had the best correlation r = 0.534, P less than .001. In the 24-hour studies, blood samples were obtained at 1 to 4-hour intervals. Three of the 6 patients showed the best correlation between simultaneous plasma glucose and red cell sorbitol, with r = 0.727 to 0.957 and P less than .001 to P less than .07. When plasma glucose values were compared to red cell sorbitol levels 1, 2, 4, 8 and 12 h later, correlation coefficients were not as good as the simultaneous comparison. We conclude that the measurement of red cell sorbitol correlates well with simultaneous plasma glucose in some but not all diabetic subjects and provides no additional information to the clinician.

Plasma and red cell sorbitol assay in diabetic subjects.

Plasma and red cell sorbitol concentrations, fasting plasma glucose, glycosylated hemoglobin (GHb) were evaluated in 30 diabetic patients and 42 normal subjects. Red cell sorbitol levels were evaluated in hemolysate and non-hemolyzed samples. Mean red cell sorbitol concentrations evaluated after hemolysis were 21.5 +/- 5 nmol/ml in diabetics and 12.2 +/- 4 nmol/ml in controls (p less than 0.001). Mean values of red cell sorbitol determined in non-hemolyzed samples were 13.9 +/- 3 nmol/ml in diabetics and 8.1 +/- 3 nmol/ml in controls (p less than 0.001). Mean plasma sorbitol concentrations were 8.4 +/- 3 nmol/ml in diabetics and 5.2 +/- 1 nmol/ml in controls (p less than 0.001). The within and between run reproducibilities evaluated in plasma, hemolysate and non-hemolyzed red cells gave the lowest values for hemolyzed red cell samples. The studies on stability showed that samples neutralized and stored at -20 degrees C gave reproducible values if assayed within 3 days. A positive correlation was found between red cell hemolysate sorbitol concentrations and fasting plasma levels in both diabetics (r = 0.56; p less than 0.001) and controls (r = 0.62; p less than 0.001). Red cell hemolysate sorbitol concentrations were also positively correlated to GHb in both diabetics (r = 0.64; p less than 0.001) and controls (r = 0.36; p less than 0.05). We believe the most effective sorbitol assay to be that obtained in hemolyzed red cells and that these values related to glycemic levels could be a useful index of metabolic control and an indicator of tissue sorbitol levels in humans.

Sorbitol dehydrogenase deficiency in several pig tissues: potential implications for studies of experimental diabetes

Screening for red blood cell sorbitol dehydrogenase deficiency in 12 different mammalian species was performed. A wide inter-species variability in red cell sorbitol dehydrogenase with a virtually complete deficiency in pigs was observed. Aldose reductase and sorbitol dehydrogenase activities in 12 different pig tissues also were measured. Aldose reductase activity was present in all the tissues studied, whereas organ specificity for sorbitol dehydrogenase was observed. Sorbitol dehydrogenase activity was not detectable in lenses, among other tissues, making the pig a potential model for studies in experimental diabetes, particularly for the investigation of sorbitol dehydrogenase deficiency as a risk factor in the development of cataracts.

Sorbitol dehydrogenase deficiency in a family with congenital cataracts.

Cataract is one of the important clinical manifestations of galactosaemia due to galactokinase or galactose-1-phosphate uridyltransferase deficiency. It has been known that the accumulation of polyols, sorbitol or galactitol in a lens plays a key role in the formation of diabetic and galactosaemic cataracts (van Heyningen, 1976). It is also well established that the sorbitol pathway involving aldolase reductase (EC 1.1.1.21) and sorbitol dehydrogenase (EC 1.1.1.14) is important in cataract formation (Varma et al., 1977). Recently Vaca et al. (1982) reported the first case of red cell sorbitol dehydrogenase deficiency in a family with cataracts. Therefore we have decided to determine the sorbitol dehydrogenase activity in erythrocytes in addition to galactokinase, galactose-1-phosphate uridyltransferase and UDP-galactose epimerase activities in a selected population with congenital cataracts.KeywordsGlycogen Storage DiseaseCongenital CataractMaple Syrup Urine DiseaseSorbitol DehydrogenaseDiabetic RabbitThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Determination of sorbitol in erythrocytes of diabetic and healthy subjects by capillary gas chromatography

A gas-liquid Chromatographie method, using a fused silica capillary column, for the determination of red cell sorbitol is described. The capillary column gives complete resolution of the polyols xylitol, inositol, mannitol, sorbitol and galactitol, even when the glucose peak in the red cell chromatogram is dominating. The identity of sorbitol, and its single elution from the capillary column has been confirmed by mass spectrometry. Recovery of sorbitol from various red cell samples was 101% ± 3.2 (mean ± SD, n = 7). Precision, estimated from duplicate diabetic red cell sorbitol analyses was CV dup = 3.5% ( n = 18) and from run to run analyses CV inlerassay = 4.0% ( n = 6). Sorbitol levels determined in erythrocytes of 19 healthy subjects were 5.9 ± 1.6 nmol/ml red cells and in erythrocytes of 18 insulin-dependent diabetics 17.8 ± 8.2 nmol/ml red cells (means ± SD). The method described offers a reliable and specific tool to study in vivo polyol pathway activity in relation to some diabetes-associated complications.

Role of red cell sorbitol as determinant of reduced erythrocyte filtrability in insulin-dependent diabetics.

Erythrocyte deformability measured as filtration index is clearly diminished in diabetics, thus possibly contributing to diabetes-associated microvascular complications. Moreover, the erythrocyte sorbitol level in IDD is clearly higher than that of non-diabetics, suggesting an alteration in the polyol pathway as possible determinant of diabetes-associated complications. Following this line of research, intracellular sorbitol as well as glucose, inositol, galactitol, mannitol and 2,3-diphosphoglycerate have been studied in 21 diabetics and in 14 controls matched for age and sex. In addition to confirming the high levels of intraerythrocytic glucose and sorbitol in diabetic subjects, statistically significant correlations have been demonstrated between sorbitol and filtration index, between plasma glucose, intracellular glucose level and glycosylated hemoglobin, suggesting a relationship between metabolic control and hemorheologic alterations in diabetes.

1156 POLYOL PATHWAY HYPERKINESIS IN CHILDREN WITH DIABETES

Intracellular sorbitol accumulation has been implicated as an etiologic factor for many of the sequelae of diabetes mellitus. The human erythrocyte is a tissue that accumulates sorbitol in response to extracellular glucose concentration. Red cell sorbitol levels in children with diabetes were compared to those in red cells from non diabetics. Sorbitol was measured by a fluorometric assay utilizing sheep liver sorbitol dehydrogenase; glucose was measured by glucose oxidase. Red cell sorbitol in 140 children with diabetes (36.6±1.7nmols/gm Hb) was greater than in 50 non diabetics (10.3±.79) p<.0005. The influence of extracellular glucose was taken into account by expressing intracellular sorbitol in terms of plasma glucose concentration (S/G). The S/G ratio for red cells from diabetics was 20.6±.88 and non diabetics was 12.1±.95 p<.0005. When red cells from diabetics were exposed to non diabetic glucose concentrations for up to 14 hours the S/G ratio did not return to non diabetic levels. Non diabetic red cells exposed to elevated glucose concentrations (300 and 500 mg/dl) for 3 hours did not manifest elevated S/G ratios. Elevated S/G ratios were found in association with non diabetic hemoglobin Alc values suggesting long term exposure to near physiologic glucose levels. Increased sorbitol production was found in most, but not all individuals with diabetes and seems to be an acquired characteristic. This is the first evidence of altered polyol pathway activity not directly related to substrate availability in spontaneous human diabetes.

313 RED CELL SORBITOL AN EFFECTIVE INDICATOR OF DIABETIC CONTROL

The importance of good glycemic control is the presumed prevention of the long term sequela of diabetes. Sorbitol is the product of an insulin-independent pathway of carbohydrate metabolism that has been implicated as etiologic in the complications of diabetes. The polyol pathway producing sorbitol is active in human erythrocytes. Fasting blood samples were collected from 62 children with diabetes. Serum glucose and red cell sorbitol were measured by specific enzymatic assays. Hemoglobin Alc was measured spectrophotometrically after column separation on Bio-Rex 70. Results: The correlation of fasting glucose and sorbitol was significant. r=0.26p<.05. The correlation of fasting glucose & HbAlc was not significant r=0.1. Elevated HbAlc in vivo remains unchanged after 24 hrs. of glucose concentrations <150 mg/dl but sorbitol concentrations reflect hourly changes in glucose concentration. RBC sorbitol directly quantitates a mediator of cellular pathology in diabetes as it reflects the mean blood glucose levels. RBC sorbitol is therefore the most useful indicator of effective diabetic management

The Sorbitol Pathway of the Human Erythrocyte

The polyol pathway appears to be widely distributed in human tissues. In this pathway glucose is reduced to its polyol derivative, sorbital, by aldose reductase and the sorbitol then converted to fructose. NADPH seves as a co-factor for glucose reduction while NAD is a co-factor in the second step. The Km for glucose of aldose reductase is sufficiently high so that the intracellular glucose concentration regulates the rate of sorbitol and fructose synthesis. Our studies now demonstrate the presence of a sorbitol pathway in the red cell and its dependence on media of varying glucose concentrations (2–50 mM) and red cell and supernatant sorbitol and fructose measured after incubation. Red cell sorbitol and fructose rose as glucose concentration increased and fructose appeared in the media. Red cell sorbitol rose from 16.0 to 99.6 μmoles/ml as media glucose rose from 2 to 50 mM. Associated with this increase was a rise in the cell lactate to pyruvate ration (69:1 to 193:1), an increase in the percent of glucose metabolized to CO2, and an accumulation of triose phosphates and a fall of the DPG within the cell. These alterations appear to reflect changes in the pyrudine nuclcotide ratios within the cell secondary to the increased metabolism of glucose to fructose. AT high glucose concentration a significant fraction of all glucose metabolized traverses this pathway and is the first evidence that high plasma glucose concentration serves to regulate red cell metabolism. In vivo confirmation of the regulatory role of plasma glucose was provided by the demonstration of increased red cell sorbitol in patients with diabetes and hyperglycemia.