Changes in Na,K-adenosine triphosphatase (ATPase) concentration and Na,K-ATPase-dependent adenosine triphosphate turnover in human erythrocytes in diabetes

Erythrocytes express chondroitin sulphate/dermatan sulphate, which undergoes quantitative changes during diabetes and mediate erythrocyte adhesion to extracellular matrix components

Glycosaminoglycans (GAGs) such as chondroitin sulphate/dermatan sulphate (CS/DS) are complex molecules that are widely expressed on the cell membrane and extracellular matrix (ECM). They play an important role in wide range of biological activities especially during pathological conditions. Diabetes, a metabolic disorder characterized by sustained hyperglycemia, is known to affect GAGs in different tissues and affect erythrocyte adhesion. The present investigation was aimed at exploring the nature of GAGs present in erythrocytes and its role on adhesion of erythrocytes from control and diabetic rats to major extracellular matrix components. GAGs isolated from erythrocytes were demonstrated to be CS/DS and a 2-fold increase was observed in erythrocytes from diabetic rats. Disaccharide composition analysis by HPLC after depolymerization by the enzyme, chondroitinase ABC showed the presence of 4-O sulphated disaccharide units with small amounts of non-sulphated disaccharides, in both control and diabetic erythrocytes. Erythrocytes from diabetic rats, however, showed significantly increased binding to poly-l-ornithine (P-orn), type IV collagen, laminin and fibronectin, which was abrogated on treatment with chondroitinase ABC to various degrees. This study sheds new light on CS/DS in erythrocytes and its likely biological implications in vivo.

The C-peptide fragment EVARQ reduces glomerular hyperfiltration in streptozotocin-induced diabetic rats

BACKGROUND

Initially, diabetes is commonly associated with an increased glomerular filtration rate (GFR), a potential mechanism involved in the progression of diabetic nephropathy. Several studies have reported reno-protective effects of C-peptide. C-peptide reduces diabetes-induced hyperfiltration, as well as renal hypertrophy and albuminuria. In order to gain further understanding of these effects, it is very important to localize the active sites within the C-peptide molecule. This study was designed to elucidate the effects of the C-peptide fragment EVARQ on kidney function, blood pressure and blood glucose levels in diabetic rats in vivo.

METHODS

The study was performed on adult inactin-anaesthetized male Sprague-Dawley rats. Two weeks prior to the experiment, diabetes was induced by a single intravenous injection of streptozotocin (55 mg/kg BW). After recovery and recording of baseline values, vehicle, C-peptide (50 pmol . kg BW(-1).h(-1)) or EVARQ (500 pmol.kg BW(-1).h(-1)) was continuously administered for a total of 100 min.

RESULTS

Before substance administration, all diabetic groups displayed a pronounced hyperfiltration as compared to the control rats. Continuous administration of both C-peptide and EVARQ reduced the diabetes-induced hyperfiltration within an hour. Furthermore, blood pressure was only reduced in diabetic rats that were given C-peptide, whereas the blood glucose decreased in the diabetic groups that were given either C-peptide or EVARQ.

CONCLUSIONS

The present study shows that administration of the C-peptide fragment EVARQ has similar effects on GFR and blood glucose levels as the intact C-peptide molecule, suggesting at least one active site within this region.

Purine nucleotides and their metabolites in erythrocytes of streptozotocin diabetic rats

OBJECTIVES

In the present study it was tried to obtain a complete overview of purine nucleotide metabolism in erythrocytes of streptozotocin (STZ) induced diabetes mellitus rats.

METHODS

Erythrocyte levels of the main nucleotides (ATP, ADP, AMP, GTP, GDP, GMP, IMP, NAD+, NADP+), nucleosides (Ado, Guo, Ino) and the base Hyp were measured using the HPLC method. The parameters that can be deduced from their concentrations: TAN, TGN and AEC, GEC expressed by the ratio of high/low energy nucleoside phosphates were calculated. The effects of streptozotocin-induced diabetes on the concentration and metabolism of rat erythrocyte purine and pyridine nucleotides and the activity of Na+, K+-ATPase as well as Ca2+-ATPase were investigated.

RESULTS

Increased dephosphorylation of adenine nucleotides (found as the increased concentration of Ado and Hyp and the decrease in AEC value) and the decrease in ATP and TAN and the changes in the concentrations of NAD+ and NADP+ suggest serious purine and pyridine metabolism disruptions in diabetic erythrocytes and decrease in ATPases activity.

CONCLUSION

The observations suggest that purine nucleotide degradation is markedly accelerated in erythrocytes of STZ diabetic rats.

Inhibition of lipid peroxidation, protein glycation and elevation of membrane ion pump activity by taurine in RBC exposed to high glucose

BACKGROUND

Supplementation of taurine, a sulfur containing amino acid has been found to be beneficial in counteracting oxidative stress and in preventing experimental diabetic neuropathy, nephropathy and retinopathy. Taurine has its own capacity to prevent the suppression of membrane-bound Na(+)/K(+)ATPase activity and prevent Ca(2+) overload. This study was undertaken to test whether taurine can reduce lipid peroxidation and glycosylation and can increase the Na(+)/K(+)- and Ca(2+)-ATPase activities in high glucose-treated red blood cells (RBC).

METHODS

Washed normal human RBC were incubated in phosphate-buffered saline with normal (6 mmol/l) or high glucose concentrations (45 mmol/l), with and without 50-150 micromol/l taurine in a shaking water bath at 37 degrees C for 24 h. Lipid peroxidation, glycated hemoglobin, glucose utilization and Na(+)/K(+)- and Ca(2+)-ATPase activities were determined in the glucose-treated human RBC.

RESULTS

Taurine significantly lowered the level of glycated hemoglobin (GHb) and lipid peroxidation in RBC exposed to high glucose concentrations. Stimulation of glucose utilization by RBC was significant in the presence of taurine both in normal and high glucose-treated RBC. The activities of Na(+)/K(+)- and Ca(2+)-ATPases in RBC membranes were significantly lowered in high glucose-treated RBC. Taurine treatment significantly prevented the reduction in activities of Na(+)/K(+)- and Ca(2+)-ATPases activities in high glucose-treated RBC.

CONCLUSIONS

The results show that taurine is important for the physiological functions of RBCs and the effects of taurine on glucose-treated RBC may have potential therapeutic relevance in diabetes.

Islet transplantation is associated with improvement of renal function among uremic patients with type I diabetes mellitus and kidney transplants

The potential effects of islet transplantation on the renal function of 36 patients with type I diabetes mellitus and kidney transplants were studied with 4 yr of follow-up monitoring. Kidney-islet recipients were divided into two groups, i.e., patients with successful islet transplants (SI-K group) (n = 24, fasting C-peptide levels of >0.5 ng/ml for >1 yr) and patients with unsuccessful islet transplants (UI-K group) (n = 12, fasting C-peptide levels of <0.5 ng/ml). Kidney graft survival rates and function, urinary albumin excretion rates, and sodium handling were compared. Na(+)/K(+)-ATPase activity in protocol kidney biopsies and in red blood cells was cross-sectionally analyzed. The SI-K group demonstrated better kidney graft survival rates (100, 83, and 83% at 1, 4, and 7 yr, respectively) than did the UI-K group (83, 72, and 51% at 1, 4, and 7 yr, respectively; P = 0.02). The SI-K group demonstrated reductions in exogenous insulin requirements and higher C-peptide levels, compared with the UI-K group, whereas GFR values were similar. Microalbuminuria (urinary albumin index) increased significantly in the UI-K group only (UI-K, from 92.0 +/- 64.9 to 183.8 +/- 83.8, P = 0.05; SI-K, from 108.5 +/- 53.6 to 85.0 +/- 39.0, NS). In the SI-K group, but not in the UI-K group, natriuresis decreased at 2 and 4 yr (P < 0.01). The SI-K group demonstrated greater Na(+)/K(+)-ATPase immunoreactivity in renal tubular cells (P = 0.05) and higher activity in red blood cells (P = 0.03), compared with the UI-K group. The Na(+)/K(+)-ATPase activity in red blood cells was positively correlated with circulating C-peptide levels but not with glycated hemoglobin levels. Successful islet transplantation was associated with improvements in kidney graft survival rates and function among uremic patients with type I diabetes mellitus and kidney grafts.

Erythrocyte membrane glycation and NA(+)-K(+) levels in NIDDM

Although there are many investigations on protein glycation in diabetic patients, many detailed studies are needed on this subject. In this study, the correlation between red cell membrane and serum protein glycation was investigated in NIDDM. The relation of membrane glycation to intracellular Na(+) and K(+) levels was also considered. Forty patients with NIDDM and 22 healthy subjects were included in the study. The membrane proteins were isolated, and total protein (TP(m)) and fructosamine (FA(m)) levels were determined. Serum glucose, fructosamine (FA(s)) and total protein (TP(s)) levels were also measured. HbA(1C), red blood cell (RBC) and reticulocyte (RET) counts in whole blood were made in all samples. NA(+) and K(+) levels of both serum and RBC were determined. The patient group had lower levels of K(+)(RBC) (P<.001) and Na(+)(s) (P<.05) and RBC count (P<.05), and higher levels of FA(m) (P<.001), Na(+)(RBC) (P<.01), K(+)(s) (P<.01), glucose (P<.001) and HbA(1C) (P<.001) than those of controls. The ratios of FA(s)/TP(s) (P<.001) and FA(m)/TP(m) (P<.001) were higher in patients than in control. As a result, HbA(1C) levels and the ratio of FA(m)/TP(m) were high in NIDDM patients (P<.001) and these patients have slight negative correlations in FA(m)/TP(m) and FA(s)/TP(s) (P<.05). On the other hand, that there is no correlation between RBC membrane protein glycation and RBC Na(+) and K(+) levels may be caused by the fact that the membrane protein glycation is lower than that of other soluble proteins and that the membrane proteins are functional with respect to Na(+)-K(+) transport.

Linkage of the Na,K-ATPase alpha 2 and beta 1 genes with resting and exercise heart rate and blood pressure: cross-sectional and longitudinal observations from the Quebec Family Study

OBJECTIVE

To investigate whether genetic variations in the genes encoding the alpha and beta subunits of the Na,K-ATPase are linked with hemodynamic phenotypes.

DESIGN AND PARTICIPANTS

Cross-sectional data based on 533 subjects (no antihypertensive medication) were obtained from 150 families of phase 2 of the Quebec Family Study, together with longitudinal data from 338 subjects (105 families) who had been measured 12 years earlier in phase 1 of the Quebec Family Study.

MAIN OUTCOME MEASURES

Restriction fragment length polymorphisms were examined at the alpha 2 (exon 1 and exon 21-22 with BglII) and beta 1 (Msp I and Pvu II) loci of Na,K-ATPase. Hemodynamic phenotypes measured included systolic and diastolic blood pressure, heart rate and rate-pressure product at rest and during low-intensity exercise.

RESULTS

Sib-pair analysis revealed relatively strong linkages (P = 0.0003-0.002) between the resting heart rate and rate-pressure product and the alpha 2 exon 21-22 marker and alpha 2 haplotype. Moreover, the alpha 2 exon 21-22 marker showed suggestive linkages (P = 0.01 to 0.043) with resting systolic blood pressure and exercise diastolic blood pressure, heart rate and rate-pressure product, and the alpha 2 haplotype with exercise diastolic blood pressure and rate-pressure product and the 12-year change in resting systolic blood pressure (P = 0.03 to 0.05). Both the beta 1 Msp I marker and the beta 1 haplotype were linked with the resting rate-pressure product (P = 0.007 and 0.003, respectively), and all beta 1 markers showed linkage with the change in resting systolic blood pressure (P = 0.00005 to 0.024). In men, there was a significant (P = 0.01) interaction between the alpha 2 exon 21-22 genotype and the postglucose plasma insulin level with regard to resting systolic blood pressure.

CONCLUSIONS

These data suggest that the alpha 2 and beta 1 genes of Na,K-ATPase contribute to the regulation of hemodynamic phenotypes in healthy subjects.