Na+-K+-ATPase Pumping Activity Is Not Directly Linked to <i>myo</i>-inositol Levels After Sorbinil Treatment in Lenses of Diabetic Rats

Bitensky

Proc. Natl. Acad. Sci. U.S.A.

et al. 1989

We have found a defect in the ouabain-sensitive Na+,K+-ATPase (Na+ pump, EC 3.6.1.37) oferythrocytes from streptozotocin diabetic rats. This defect was accompanied by an increase in cell volume and osmotic fragility and a decrease in the cytosolic K+/Na+ ratio. There was also a doubling in the time needed for diabetic erythrocytes to pass through 4.7-jim channels in a polycarbonate filter. Our data are consistent with a primary defect in the erythrocyte Na+ pump and secondary changes in cell volume, osmotic fragility, K+/Na+ ratio, and cell ifiterability. All were reversed or prevented in vivo by insulin or the aldose reductase inhibitor Sorbinil. Protein kinase C agonists (phorbol ester and diacylglycerol) and agonist precursor (myoinositol) reversed the Na+ pump lesion, suggesting that protein kinase C-dependent phosphorylation of the 100-kDa subunit regulates Na+ pump activity and that insulin can influence erythrocyte protein kinase C activity. Ouabain inhibition of the erythrocyte Na+ pump also produced increases in cell size and reductions in rates of ifitration. Theoretical treatment of the volume changes also predicts reduction in ifiterability as a consequence of cell swelling. We suggest that enlarged erythrocytes could play a role in the evolution of the microvascular changes of diabetes mellitus.A decrease in ouabain-sensitive Na',K+-ATPase (Na' pump, EC 3.6.1.37) activity has been found in diabetic lens, nerve, and glomerulus (1-3). This Na' pump impairment was corrected by aldose reductase inhibitors or by normalization of blood sugar with insulin. In contrast, Na' pump activity in diabetic erythrocytes (RBCs) is a subject of controversy, with reports of increases (4, 5) and decreases (6, 7). We therefore initiated a study of the Na' pump in erythrocytes of rats rendered diabetic with streptozotocin. The streptozotocin diabetic rat provided a reliable source ofRBCs whose time-integrated exposure to hyperglycemia was determined by measurement of glycated albumin. Since nondiabetic RBCs must deform considerably to pass through small capillaries, we were especially interested in learning whether such a putative Na' pump lesion would influence the volume and hence filterability of affected RBCs. MATERIALS

Section: Appendixmentioning

confidence: 99%

“…A decrease in ouabain-sensitive Na',K+-ATPase (Na' pump, EC 3.6.1.37) activity has been found in diabetic lens, nerve, and glomerulus (1)(2)(3). This Na' pump impairment was corrected by aldose reductase inhibitors or by normalization of blood sugar with insulin.…”

mentioning

confidence: 99%

Reversible sodium pump defect and swelling in the diabetic rat erythrocyte: effects on filterability and implications for microangiopathy.

Bitensky

Proc. Natl. Acad. Sci. U.S.A.

et al. 1989

“…Although an increase of lens weight could indicate osmotic stress caused by polyol accumulation within lens tissue, the cataractogenic effects of CIG do not seem to be involved using the present approach. Despite the documented ability of the aldose reductase inhibitor SORB to effectively inhibit sugar-induced cataract formation in vivo (Kador et al, 1986;Yeh et al, 1987;Yeh and Ashton, 1990) and in vitro (Kador et al, 1986;Yeh et al, 1986), both in terms of adverse changes in lens weight and clarity and lenticular ATP and GSH content, SORB did not attenuate the toxicity of CIG to rat lenses either in terms of lens clarity or on the same biochemical markers of toxicity under the present culture conditions ( Table 2). The concentration of SORB used in this study was 5 times higher than the concentration that has been shown to effectively inhibit aldose reductase (Ͼ90%) and sorbitol accumulation (Ͼ80%) in rat lenses exposed to 35 mM glucose (Yeh et al, 1986).…”

Section: Discussionmentioning

confidence: 73%

“…In some cases, such as acetaminophen, the compound that penetrates the lens and causes the damage is a reactive metabolite that is formed via the cytochrome P450 system found in the ciliary body of the eye (Zhao and Shichi, 1995) or liver (Lubek et al, 1988). In other cases, such as S-(1,2-dichlorovinyl)-L-cysteine (Walsh Clang and Aleo, 1997), naphthalene (Lou et al, 1996), or glucose (Yeh et al, 1986(Yeh et al, , 1987Yeh and Ashton, 1990), the compound seems to require metabolic activation within the lens itself.…”

mentioning

confidence: 99%

Ciglitazone-Induced Lenticular Opacities in Rats: In Vivo and Whole Lens Explant Culture Evaluation

Aleo¹,

Doshna²,

Navetta³

2004

J Pharmacol Exp Ther

The cataractogenic potential of the thiazolidinedione ciglitazone (CIG) was investigated in vivo and in vitro. In the rat, CIG caused a dose-dependent (30 -300 mg/kg/day) increase in incidence and severity of nuclear cataract formation during a 3-month nonclinical safety assessment study. Potential mechanisms of toxicity were surveyed using whole rat lens explants exposed to CIG with or without various inhibitors of cataract formation. In vitro, CIG caused a concentration-(0.375-30 M) and time-dependent (3-24 h) change in biochemical [ATP content or mitochondrial reduction of the tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) and reduced glutathione (GSH) content] and morphometric (lens wet weight and clarity) markers of damage. Within 3 h of exposure, 7.5 M CIG decreased lens ATP content 37 Ϯ 7% (percentage of difference from control, p Ͻ 0.05). After 24 h of exposure, lens ATP content, MTT reduction, and GSH content declined 57 Ϯ 5, 30 Ϯ 28, and 42 Ϯ 8%, respectively. Lens wet weight increased 17 Ϯ 4% with a concomitant decrement in lens clarity. Pretreating lenses with the mitochondrial calcium uniport inhibitor ruthenium red (RR) partially or fully protected lenses from toxicity. In contrast, the antioxidant dithiothreitol, aldose reductase inhibitor sorbinil, and selective cell-permeable calpain inhibitors [calpain II inhibitor and (2S,3S)-trans-epoxysuccinyl-L-leucylamido-3-methylbutane ethyl ester (E64d)] were ineffective in providing protection under the present testing conditions. Early and selective changes in lenticular ATP content and the partial or full protective effect of RR suggest that alterations in lens bioenergetics may play an important role in CIG-induced cataract formation. Lens explant cultures were successfully used to select two thiazolidinediones that lacked cataractogenic activity when evaluated in 3-month rat safety assessment studies.

“…• Reduction in cell-membrane phosphatidyl-inositol [7] leads to changes in membrane fluidity and a reduction in DAG production, which leads to reduction in protein kinase C activity. However, Yeh et al [27] found that the drug Sorbinil restores Na + /K + -ATPase activity at a lower concentration than that required for restoration of cell myo-inositol levels.…”

Section: Introductionmentioning

confidence: 99%

Na/K-ATPase Activity and Ketone Body Metabolism in Long-term Diabetic Rats

Buxbaum

2019

Preprint

The long-term (34 weeks) effect of streptozotocin induced diabetes was assessed in Wistar rats.Na + /K + -ATPase activity was measured by ouabain inhibitable 86 Rb + -uptake into erythrocytes. No difference in the rate of Rb + -uptake, the K m for Rb + or the K i for ouabain was detected between normal and diabetic rats. Thus, the change in Na + /K + -ATPase activity repeatedly described in short-term studies may not translate into a long term physiologically relevant change in ion flux through the sodium pump.Rats excrete ketone bodies mainly as β-hydroxybutyrate. This compound does not show up with nitroprusside sodium based test sticks, it can however be detected by coupled spectrophotometric assay with hydroxybutyrate dehydrogenase.Almost half of the diabetic animals reverted to a non-diabetic state during the experiment, followed by at least partial reversal of secondary diabetic damage.