Localization of aldose and aldehyde reductase in the kidney

Astragalin ameliorates renal injury in diabetic mice by modulating mitochondrial quality control via AMPK-dependent PGC1α pathway

Diabetic kidney disease (DKD) is a common microvascular complication of diabetes mellitus, and oxidative stress and mitochondrial dysfunction play an important role in this process. It has been shown that aldose reductase (ALR2) catalyzes NADPH-dependent reduction of glucose to sorbitol, resulting in oxidative stress and mitochondrial dysfunction in diabetic patients. Astragalin (AG), a flavonoid extracted from Thesium chinense Turcz., shows an inhibitory activity on ALR2. In this study, we investigated the therapeutic effects of AG against renal injury in streptozocin (STZ)-induced diabetic mouse model. Diabetic mice were orally administered AG (5, 10 mg·kg-1·d-1) for 4 weeks. We showed that AG treatment greatly improved the proteinuria and ameliorated renal pathological damage without affecting the elevated blood glucose in diabetic mice. Furthermore, AG treatment significantly suppressed highly activated ALR2, and reduced oxidative stress in the kidney of diabetic mice and in high glucose and lipids-stimulated HK2 cells in vitro. We demonstrated that AG treatment modulated mitochondrial quality control and ameliorated apoptosis, boosting mitochondrial biogenesis, maintaining mitochondrial dynamic homeostasis, and improving energy metabolism disorder in vivo and in vitro. In high glucose and lipids-stimulated HK2 cells, we found that AG (20 μM) restored the phosphorylation level of AMPK, and upregulated the expression and transcriptional activity of PGC1α, whereas treatment with H2O2, blockade of AMPK with Compound C or knockdown of AMPKα with siRNA abolished the protective effect of AG on mitochondrial function, suggesting that antioxidant effects and activation of AMPK-dependent PGC1α pathway might be the molecular mechanisms underlying the protective effects of AG on mitochondrial quality control. We conclude that AG could be a promising drug candidate for the treatment of diabetic renal injury through activating AMPK.

Fructose Production and Metabolism in the Kidney

Understanding fructose metabolism might provide insights to renal pathophysiology. To support systemic glucose concentration, the proximal tubular cells reabsorb fructose as a substrate for gluconeogenesis. However, in instances when fructose intake is excessive, fructose metabolism is costly, resulting in energy depletion, uric acid generation, inflammation, and fibrosis in the kidney. A recent scientific advance is the discovery that fructose can be endogenously produced from glucose under pathologic conditions, not only in kidney diseases, but also in diabetes, in cardiac hypertrophy, and with dehydration. Why humans have such a deleterious mechanism to produce fructose is unknown, but it may relate to an evolutionary benefit in the past. In this article, we aim to illuminate the roles of fructose as it relates to gluconeogenesis and fructoneogenesis in the kidney.

Fructose and uric acid in diabetic nephropathy

Clinical studies have reported associations between serum uric acid levels and the development of diabetic nephropathy, but the underlying mechanisms remain elusive. There is evidence from animal studies that blocking uric acid production protects the kidney from tubulointerstitial injury, which may suggest a causal role for uric acid in the development of diabetic tubular injury. In turn, when fructose, which is endogenously produced in diabetes via the polyol pathway, is metabolised, uric acid is generated from a side-chain reaction driven by ATP depletion and purine nucleotide turnover. For this reason, uric acid derived from endogenous fructose could cause tubulointerstitial injury in diabetes. Accordingly, our research group recently demonstrated that blocking fructose metabolism in a diabetic mouse model mitigated the development of tubulointerstitial injury by lowering tubular uric acid production. In this review we discuss the relationship between uric acid and fructose as a novel mechanism for the development of diabetic tubular injury.

Aldose Reductase Regulates Microglia/Macrophages Polarization Through the cAMP Response Element-Binding Protein After Spinal Cord Injury in Mice

Inflammatory reactions are the most critical pathological processes occurring after spinal cord injury (SCI). Activated microglia/macrophages have either detrimental or beneficial effects on neural regeneration based on their functional polarized M1/M2 subsets. However, the mechanism of microglia/macrophage polarization to M1/M2 at the injured spinal cord environment remains unknown. In this study, wild-type (WT) or aldose reductase (AR)-knockout (KO) mice were subjected to SCI by a spinal crush injury model. The expression pattern of AR, behavior tests for locomotor activity, and lesion size were assessed at between 4 h and 28 days after SCI. We found that the expression of AR is upregulated in microglia/macrophages after SCI in WT mice. In AR KO mice, SCI led to smaller injury lesion areas compared to WT. AR deficiency-induced microglia/macrophages induce the M2 rather than the M1 response and promote locomotion recovery after SCI in mice. In the in vitro experiments, microglia cell lines (N9 or BV2) were treated with the AR inhibitor (ARI) fidarestat. AR inhibition caused 4-hydroxynonenal (HNE) accumulation, which induced the phosphorylation of the cAMP response element-binding protein (CREB) to promote Arg1 expression. KG501, the specific inhibitor of phosphorylated CREB, could cancel the upregulation of Arg1 by ARI or HNE stimulation. Our results suggest that AR works as a switch which can regulate microglia by polarizing cells to either the M1 or the M2 phenotype under M1 stimulation based on its states of activity. We suggest that inhibiting AR may be a promising therapeutic method for SCI in the future.

Polyol pathway and diabetic nephropathy revisited: Early tubular cell changes and glomerulopathy in diabetic mice overexpressing human aldose reductase

Aims/Introduction:  The polyol pathway has long been involved in the pathogenesis of diabetic nephropathy. It remains still unclear, however, how the polyol pathway is implicated in this process. We explored the effects of the enhanced polyol pathway on renocortical tubular cells and glomeruli in experimentally-induced diabetes.

MATERIALS AND METHODS

  Transgenic mice (Tg) overexpressing human aldose reductase were made diabetic by streptozotocin and followed for 8 weeks. Renocortical pathology, expressions of tonicity-responsive enhancer binding protein (TonEBP) and carboxymethyllysine of advanced glycation end-products, were examined. Wild-type non-transgenic mice (Wt) were also made diabetic and served as controls.

RESULTS

  Diabetic Tg showed augmented expression of TonEBP in renocortical tubular cells with vacuolated degenerative changes. These structural changes were associated with pronounced deposition of carboxymethyllysine. There was a significant increase in kidney weight, glomerular size, and mesangial area in diabetic animals and there was a trend for more severe changes in these measures in diabetic transgenic mice compared with those in control diabetic mice. Treatment with aldose reductase inhibitor significantly prevented polyol accumulation, mesangial expansion and expressions of TonEBP and carboxymethyllysine in diabetic Tg, but its effects on the renal structure were equivocal in control diabetic Wt.

CONCLUSIONS

  Our findings suggest that tubuloglomerular change might contribute to early diabetic nephropathy under the influence of the enhanced polyol pathway. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00071.x, 2010).

The betaine/GABA transporter and betaine: roles in brain, kidney, and liver

The physiological roles of the betaine/GABA transporter (BGT1; slc6a12) are still being debated. BGT1 is a member of the solute carrier family 6 (the neurotransmitter, sodium symporter transporter family) and mediates cellular uptake of betaine and GABA in a sodium- and chloride-dependent process. Most of the studies of BGT1 concern its function and regulation in the kidney medulla where its role is best understood. The conditions here are hostile due to hyperosmolarity and significant concentrations of NH₄Cl and urea. To withstand the hyperosmolarity, cells trigger osmotic adaptation, involving concentration of a transcriptional factor TonEBP/NFAT5 in the nucleus, and accumulate betaine and other osmolytes. Data from renal cells in culture, primarily MDCK, revealed that transcriptional regulation of BGT1 by TonEBP/NFAT5 is relatively slow. To allow more acute control of the abundance of BGT1 protein in the plasma membrane, there is also post-translation regulation of BGT1 protein trafficking which is dependent on intracellular calcium and ATP. Further, betaine may be important in liver metabolism as a methyl donor. In fact, in the mouse the liver is the organ with the highest content of BGT1. Hepatocytes express high levels of both BGT1 and the only enzyme that can metabolize betaine, namely betaine:homocysteine –S-methyltransferase (BHMT1). The BHMT1 enzyme removes a methyl group from betaine and transfers it to homocysteine, a potential risk factor for cardiovascular disease. Finally, BGT1 has been proposed to play a role in controlling brain excitability and thereby represents a target for anticonvulsive drug development. The latter hypothesis is controversial due to very low expression levels of BGT1 relative to other GABA transporters in brain, and also the primary location of BGT1 at the surface of the brain in the leptomeninges. These issues are discussed in detail.

Aldose reductase, oxidative stress, and diabetic mellitus

Diabetes mellitus (DM) is a complex metabolic disorder arising from lack of insulin production or insulin resistance (Diagnosis and classification of diabetes mellitus, 2007). DM is a leading cause of morbidity and mortality in the developed world, particularly from vascular complications such as atherothrombosis in the coronary vessels. Aldose reductase (AR; ALR2; EC 1.1.1.21), a key enzyme in the polyol pathway, catalyzes nicotinamide adenosine dinucleotide phosphate-dependent reduction of glucose to sorbitol, leading to excessive accumulation of intracellular reactive oxygen species (ROS) in various tissues of DM including the heart, vasculature, neurons, eyes, and kidneys. As an example, hyperglycemia through such polyol pathway induced oxidative stress, may have dual heart actions, on coronary blood vessel (atherothrombosis) and myocardium (heart failure) leading to severe morbidity and mortality (reviewed in Heather and Clarke, 2011). In cells cultured under high glucose conditions, many studies have demonstrated similar AR-dependent increases in ROS production, confirming AR as an important factor for the pathogenesis of many diabetic complications. Moreover, recent studies have shown that AR inhibitors may be able to prevent or delay the onset of cardiovascular complications such as ischemia/reperfusion injury, atherosclerosis, and atherothrombosis. In this review, we will focus on describing pivotal roles of AR in the pathogenesis of cardiovascular diseases as well as other diabetic complications, and the potential use of AR inhibitors as an emerging therapeutic strategy in preventing DM complications.

The betaine-GABA transporter (BGT1, slc6a12) is predominantly expressed in the liver and at lower levels in the kidneys and at the brain surface

The Na+- and Cl−-dependent GABA-betaine transporter (BGT1) has received attention mostly as a protector against osmolarity changes in the kidney and as a potential controller of the neurotransmitter GABA in the brain. Nevertheless, the cellular distribution of BGT1, and its physiological importance, is not fully understood. Here we have quantified mRNA levels using TaqMan real-time PCR, produced a number of BGT1 antibodies, and used these to study BGT1 distribution in mice. BGT1 (protein and mRNA) is predominantly expressed in the liver (sinusoidal hepatocyte plasma membranes) and not in the endothelium. BGT1 is also present in the renal medulla, where it localizes to the basolateral membranes of collecting ducts (particularly at the papilla tip) and the thick ascending limbs of Henle. There is some BGT1 in the leptomeninges, but brain parenchyma, brain blood vessels, ependymal cells, the renal cortex, and the intestine are virtually BGT1 deficient in 1- to 3-mo-old mice. Labeling specificity was assured by processing tissue from BGT1-deficient littermates in parallel as negative controls. Addition of 2.5% sodium chloride to the drinking water for 48 h induced a two- to threefold upregulation of BGT1, tonicity-responsive enhancer binding protein, and sodium- myo-inositol cotransporter 1 (slc5a3) in the renal medulla, but not in the brain and barely in the liver. BGT1-deficient and wild-type mice appeared to tolerate the salt treatment equally well, possibly because betaine is one of several osmolytes. In conclusion, this study suggests that BGT1 plays its main role in the liver, thereby complementing other betaine-transporting carrier proteins (e.g., slc6a20) that are predominantly expressed in the small intestine or kidney rather than the liver.

Osmoprotective proteome adjustments in mouse kidney papilla

The papilla of the mammalian kidney must tolerate greatly varying degrees of hyperosmotic stress during urine concentration and depending on whole organism hydration state. To identify proteome adaptations supporting cell function and survival in such a harsh environment we compared the proteome of a) the hyperosmotic renal papilla with that of adjacent iso-osmotic cortex tissue and b) the renal papilla of diuretic versus that of anti-diuretic mice. Though functionally distinct the papilla is in close physical proximity to the renal cortex, an iso-osmotic region. Proteomic differences between the papilla and cortex of C57BL6 mice were identified using two-dimensional gel electrophoresis and MALDI-TOF/TOF mass spectrometry. We found 37 different proteins characteristic of the cortex and 16 proteins over-represented in the papilla. Regional specificity was confirmed by Western blot and further substantiated by immunohistochemistry for selected proteins. Proteins that are characteristic of the renal papilla include αB crystallin, Hsp beta-1, Hsp90, 14-3-3 protein, glutathione S-transferase, aldose reductase, actin and tropomyosin. Gene ontology analysis confirmed a significant increase in molecular functions associated with protein chaperoning and cell stabilization. Proteins over-represented in the cortex were largely related to routine metabolism. During antidiuresis 15 different proteins changed significantly while 18 different proteins changed significantly during diuresis relative to normally hydrated controls. Changes were confirmed by Western blot for selected proteins. Proteins that are significantly altered by diuretic state are associated with cell structure (actin, tubulin), signaling (Rho GDP dissociation inhibitor, abhydrolase domain-containing protein 14B), chaperone functioning (Hsp beta-1, αB crystallin, T complex protein-1) and anti-oxidant functions (α-enolase, GAPDH and LDH). Taken together our study reveals that specific proteins involved in protein folding, cytoskeletal stabilization, antioxidant responses, and stress signaling contribute greatly to the unique hyperosmotic stress resistant phenotype of the kidney papilla.

Autoimmunity in membranous nephropathy targets aldose reductase and SOD2

Glomerular targets of autoimmunity in human membranous nephropathy are poorly understood. Here, we used a combined proteomic approach to identify specific antibodies against podocyte proteins in both serum and glomeruli of patients with membranous nephropathy (MN). We detected specific anti-aldose reductase (AR) and anti-manganese superoxide dismutase (SOD2) IgG(4) in sera of patients with MN. We also eluted high titers of anti-AR and anti-SOD2 IgG(4) from microdissected glomeruli of three biopsies of MN kidneys but not from biopsies of other glomerulonephritides characterized by IgG deposition (five lupus nephritis and two membranoproliferative glomerulonephritis). We identified both antigens in MN biopsies but not in other renal pathologies or normal kidney. Confocal and immunoelectron microscopy (IEM) showed co-localization of anti-AR and anti-SOD2 with IgG(4) and C5b-9 in electron-dense podocyte immune deposits. Preliminary in vitro experiments showed an increase of SOD2 expression on podocyte plasma membrane after treatment with hydrogen peroxide. In conclusion, our data support AR and SOD2 as renal antigens of human MN and suggest that oxidative stress may drive glomerular SOD2 expression.

Expression and localization of rat aldo-keto reductases and induction of the 1B13 and 1D2 isoforms by phenolic antioxidants

The aldo-keto reductase (AKR) phase I drug metabolism enzyme superfamily is implicated in detoxification or bioactivation of a wide variety of carbonyl-bearing compounds. In this study, we have used antibodies raised against purified recombinant rat AKR isoforms 1A3, 1B4, 1C9, 1D2, and 7A1 to characterize the expression profile of these superfamily members in the rat and define their localization by immunohistochemistry. Western blotting showed that AKR1A3, AKR1B4, and AKR1C9 are ubiquitously expressed, whereas AKR1D2 and AKR7A1 are present in liver, adrenal gland, and kidney, with the latter also present in testis, spleen, and stomach. Immunohistochemical analysis of the kidney demonstrated the localization of AKR1A3 in proximal convoluted tubules, AKR1B4 in the loop of Henle, and AKR1C9 in the pars recta S3 segment of proximal tubules. We also report localization of AKR1B4 in the adrenal gland (parenchymal cells of the zona reticularis) and testis (Sertoli cells and late spermatids), of AKR1D2 in the liver (hepatocyte nuclei), and of AKR7A1 in the pancreatic duct and bronchiolar epithelium. Previous studies have shown that expression of AKR7A1 is induced in response to dietary administration of the phenolic antioxidants butylated hydroxyanisole and ethoxyquin. Here we identify AKR1B13 and AKR1D2 as further inducible members of the rat AKR superfamily.

Sequential expression of NKCC2, TonEBP, aldose reductase, and urea transporter-A in developing mouse kidney

This study was conducted to test the hypothesis that, during renal development, the Na-K-2Cl cotransporter type 2 (NKCC2) activates the tonicity-responsive enhancer binding protein (TonEBP) transcription factor by creating medullary hypertonicity. TonEBP, in turn, drives the expression of aldose reductase (AR) and urea transporter-A (UT-A). Kidneys from 13- to19-day-old fetuses (F13-F19), 1- to 21-day-old pups (P1-P21), and adult mice were examined by immunohistochemistry. NKCC2 was first detected on F14 in differentiating macula densa and thick ascending limb (TAL). TonEBP was first detected on F15 in the medullary collecting duct (MCD) and surrounding endothelial cells. AR was detected in the MCD cells of the renal medulla from F15. UT-A first appeared in the descending thin limb (DTL) on F16 and in the MCD on F18. After birth, NKCC2-positive TALs disappeared gradually from the tip of the renal papilla, becoming completely undetectable in the inner medulla on P21. TonEBP shifted from the cytoplasm to the nucleus in both vascular endothelial cells and MCD cells on P1, and its abundance increased gradually afterward. Immunoreactivity for AR and UT-A in the renal medulla increased markedly after birth. Treatment of neonatal animals with furosemide dramatically reduced expression of TonEBP, AR, and UT-A1. Furosemide also prevented the disappearance of NKCC2-expressing TALs in the papilla. The sequential expression of NKCC2, TonEBP, and its targets AR and UT-A and the reduced expression TonEBP and its targets in response to furosemide treatment support the hypothesis that local hypertonicity produced by the activity of NKCC2 activates TonEBP during development.

Altered expression of selected genes in kidney of rats with lithium-induced NDI

Lithium treatment is associated with development of nephrogenic diabetes insipidus, caused in part by downregulation of collecting duct aquaporin-2 (AQP2) and AQP3 expression. In the present study, we carried out cDNA microarray screening of gene expression in the inner medulla (IM) of lithium-treated and control rats, and selected genes were then investigated at the protein level by immunoblotting and/or immunohistochemistry. The following genes exhibited significantly altered transcription and mRNA expression levels, and these were compatible with the changes in protein expression. 11β-Hydroxysteroid dehydrogenase type 2 protein expression in the IM was markedly increased (198 ± 25% of controls, n = 6), and immunocytochemistry demonstrated an increased labeling of IM collecting duct (IMCD) principal cells. This indicated altered renal mineralocorticoid/glucocorticoid responses in lithium-treated rats. The inhibitor of cyclin-dependent kinases p27 (KIP) protein expression was significantly decreased or undetectable in the IMCD cells, pointing to increased cellular proliferation and remodeling. Heat shock protein 27 protein expression was decreased in the IM (64 ± 6% of controls, n = 6), likely to be associated with the decreased medullary osmolality in lithium-treated rats. Consistent with this, lens aldose reductase protein expression was markedly decreased in the IM (16 ± 2% of controls, n = 6), and immunocytochemistry revealed decreased expression in the thin limb cells in the middle and terminal parts of the IM. Ezrin protein expression was upregulated in the IM (158 ± 16% of controls, n = 6), where it was predominantly expressed in the apical and cytoplasmic domain of the IMCD cells. Increased ezrin expression indicated remodeling of the actin cytoskeleton and/or altered regulation of IMCD transporters. In conclusion, the present study demonstrates changes in gene expression not only in the collecting duct but also in the thin limb of the loop of Henle in the IM, and several of these genes are linked to altered sodium and water reabsorption, cell cycling, and changes in interstitial osmolality.

Long-term treatment with cyclosporine decreases aquaporins and urea transporters in the rat kidney

The aim of this study was to evaluate the long-term effects of cyclosporine (CsA) treatment on urinary concentration ability. Rats were treated daily for 4 wk with vehicle (VH; olive oil, 1 ml/kg sc) or CsA (15 mg/kg sc). The influence of CsA on the kidney's ability to concentrate urine was evaluated using functional parameters and expression of aquaporins (AQP1-4) and of urea transporters (UT-A-1-3, and UT-B). Plasma vasopressin levels and the associated signal pathway were evaluated, and the effect of vasopressin infusion on urine concentration was observed in VH- and CsA-treated rats. Toxic effects of CsA on tubular cells in the medulla as well as the cortex were evaluated with aldose reductase (AR), Na-K-ATPase-alpha(1) expression, and by determining the number of terminal transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells. Long-term CsA treatment increased urine volume and fractional excretion of sodium and decreased urine osmolality and free-water reabsorption compared with VH-treated rats. These functional changes were accompanied by decreases in the expression of AQP (1-4) and UT (UT-A2, -A3, and UT-B), although there was no change in AQP2 in the cortex and outer medulla and UT-A1 in the inner medulla (IM). Plasma vasopressin levels were not significantly different between two groups, but infusion of vasopressin restored CsA-induced impairment of urine concentration. cAMP levels and Gsalpha protein expression were significantly reduced in CsA-treated rat kidneys compared with VH-treated rat kidneys. CsA treatment decreased the expression of AR and Na-K-ATPase-alpha(1) and increased the number of TUNEL-positive renal tubular cells in both the cortex and medulla. Moreover, the number of TUNEL-positive cells correlated with AQP2 or UT-A3) expression within the IM. In conclusion, CsA treatment impairs urine-concentrating ability by decreasing AQP and UT expression. Apoptotic cell death within the IM at least partially accounts for the CsA-induced urinary concentration defect.

Proteomic analysis of long-term vasopressin action in the inner medullary collecting duct of the Brattleboro rat

Vasopressin regulates water and solute transport in the renal collecting duct. In addition to short-term regulation of aquaporin-2 trafficking, vasopressin also has long-term effects to regulate the abundances of aquaporins-2 and -3 and beta- and gamma-subunits of the epithelial sodium channel in collecting duct principal cells. To investigate further the direct and indirect long-term regulatory actions of vasopressin in the inner medullary collecting duct (IMCD), we used a proteomic approach [difference gel electrophoresis (DIGE) coupled with MALDI-TOF identification of differentially expressed protein spots]. DDAVP or vehicle was infused subcutaneously in Brattleboro rats for 3 days, and IMCD cells were purified from the inner medullas for proteomic analysis. Forty-three proteins were found to be regulated in response to vasopressin infusion, including 18 that were increased in abundance, 22 that were decreased, and 3 that were shifted in the gel, presumably because of posttranslational modification. Immunocytochemistry confirmed collecting duct expression of several of the proteins that were identified. Immunoblot analysis of nine of the proteins confirmed the changes seen by the DIGE method. Of these nine proteins, six were increased in response to DDAVP infusion: nitric oxide synthase-2 (NOS2), GRP78, heat shock protein-70, annexin II, glutaminase, and cathepsin D. The remaining three were decreased in response to DDAVP: aldehyde reductase I, adenylyl cyclase VI, and carbonic anhydrase II. The findings point to a role for vasopressin in the coordinate regulation of several determinants of nitric oxide levels (NOS2, arginase II, NADPH oxidase) and of proteins potentially involved in vasopressin escape (adenylyl cyclase VI and G protein-coupled receptor kinase 4).

Expression of aldose reductase in developing rat kidney

Newborn rats are not capable of producing concentrated urine. With development of the concentrating system and a hypertonic medullary interstitium, intracellular osmolytes, such as sorbitol, accumulate in the renal medulla. Sorbitol is produced from glucose in a reaction catalyzed by aldose reductase (AR). The purpose of this study was to establish the time of expression and distribution of AR in the developing rat kidney. Kidneys from 16-, 18-, and 20-day-old fetuses and 1-, 3-, 4-, 5-, 7-, 14-, and 21-day-old pups were processed for immunohistochemistry and immunoblot analysis. In adult animals, AR was expressed only in the inner medulla, in which it was localized in ascending thin limbs (ATLs), inner medullary collecting ducts (IMCDs), and interstitial cells. AR immunoreactivity was not detected in fetal kidneys but was observed in the terminal part of the descending thin limb and IMCD in the renal papilla of 1-day-old pups. At birth, all of the loops of Henle are configured as short loops and there are no ATLs. After birth, papillary thick ascending limbs are gradually transformed into ATLs by a process that involves apoptotic deletion of cells from the thick ascending limb. During this time, AR immunoreactivity appeared in the cells undergoing transformation in the ascending limb, beginning at the papillary tip and ascending to the border between the outer medulla and the inner medulla. However, there was no labeling of apoptotic cells. The expression of AR in both the ATL and the IMCD gradually increased during kidney development. We conclude that AR expression in the inner medulla coincides with the increase in medullary tonicity that is known to occur during the first 3 wk after birth. On the basis of the observation that only AR-negative cells were deleted by apoptosis in the differentiating ATL, we propose that AR may protect ATL cells against apoptosis.

The role of taurine in diabetes and the development of diabetic complications

The ubiquitously found beta-amino acid taurine has several physiological functions, e.g. in bile acid formation, as an osmolyte by cell volume regulation, in the heart, in the retina, in the formation of N-chlorotaurine by reaction with hypochlorous acid in leucocytes, and possibly for intracellular scavenging of carbonyl groups. Some animals, such as the cat and the C57BL/6 mouse, have disturbances in taurine homeostasis. The C57BL/6 mouse strain is widely used in diabetic and atherosclerotic animal models. In diabetes, the high extracellular levels of glucose disturb the cellular osmoregulation and sorbitol is formed intracellularly due to the intracellular polyol pathway, which is suspected to be one of the key processes in the development of diabetic late complications and associated cellular dysfunctions. Intracellular accumulation of sorbitol is most likely to cause depletion of other intracellular compounds including osmolytes such as myo-inositol and taurine. When considering the clinical complications in diabetes, several links can be established between altered taurine metabolism and the development of cellular dysfunctions in diabetes which cause the clinical complications observed in diabetes, e.g. retinopathy, neuropathy, nephropathy, cardiomyopathy, platelet aggregation, endothelial dysfunction and atherosclerosis. Possible therapeutic perspectives could be a supplementation with taurine and other osmolytes and low-molecular compounds, perhaps in a combinational therapy with aldose reductase inhibitors.

Relevance of aldo-keto reductase family members to the pathobiology of diabetic nephropathy and renal development

Aldo-keto reductases (AKRs) are a family of monomeric oxido-reductases with molecular weight ranging from 35-40 kDa and currently includes upwards of 60 members. They are expressed in a wide variety of tissues, where they catalyze the NADPH-dependent reduction of various aliphatic and aromatic aldehydes and ketones. The functions of most of the family members are not well defined. But two members, aldehyde reductase (AKRIA) and aldose reductase (AKRIB), have been extensively studied. The latter has received the most attention since being relevant to the complications of diabetes mellitus. It is up-regulated during hyperglycemia, and at the same time there is an increased activity of the sorbitol pathway and non-enzymatic glycation of proteins with ensuing damage in various tissues. It is developmentally regulated in the ocular lens, and is believed to modulate lens fiber morphogenesis during fetal life. Unlike the other AKR family members that are ubiquitously expressed, recently a renal-specific oxio-reductase has been described that is expressed exclusively in the proximal tubules. Although, it has no homology with other AKR members, it binds to NADPH with high affinity and is up-regulated in streptozotocin-induced diabetes in mice. It is also developmentally regulated and seems to selectively modulate renal tubulogenesis during embryonic life.

Aldose reductase and the role of the polyol pathway in diabetic nephropathy

BACKGROUND; In diabetic renal complications, hyperglycemia may cause damage at a cellular level in both glomerular and tubular locations, often preceding overt dysfunction. Our previous work has implicated aldose reductase in a pathway whereby aldose reductase-induced use of nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) drives the pentose phosphate pathway, which culminates in a protein kinase C-induced increase in glomerular prostaglandin production and loss of mesangial cell contractility as a possible cause of hyperfiltration and glomerular dysfunction in diabetes. In this model, aldose reductase inhibition in vitro redresses all aspects of the pathway proposed to lead to hyperfiltration; aldose reductase inhibition in vivo gives only a partial amelioration over the short-term or is without effect in the longer term on microalbuminuria, which follows glomerular and tubular dysfunction. In diabetes, hyperglycemia-induced renal polyol pathway activity does not occur in isolation but instead in tandem with oxidative changes and the production of reactive dicarbonyls and alpha,beta-unsaturated aldehydes. Aldose reductase may detoxify these compounds. We investigated this aspect in a transgenic rat model with human aldose reductase cDNA under the control of the cytomegalovirus promoter with tubular expression of transgene.

METHODS

Tubules (S3 region-enriched) from transgenic and control animals were prepared, exposed to oxidative stress, and analyzed to determine the cellular protein dicarbonyl content.

RESULTS

In tubules from transgenic animals, oxidative stress-induced dicarbonyls were significantly reduced, an effect not seen when an aldose reductase inhibitor was present.

CONCLUSIONS

Aldose reductase may both exacerbate and alleviate the production of metabolites that lead to hyperglycemia-induced cellular impairment, with the balance determining the extent of dysfunction.

Immunolocalization of phospholipase C isoforms in rat kidney

BACKGROUND

Phospholipase C (PLC) is an important factor in signal transduction because this enzyme is activated by several hormones and growth factors. Eight PLC isoforms have been described raising the possibility that different cells express a single isoform or activate specific isoforms in different cells. Therefore, the goal of this study was to determine which PLC isoforms are expressed in specific regions of rat kidney.

METHODS

Western blot analysis was performed in microdissected nephron segments of rat kidney, while immunohistochemical analysis was performed on whole rat kidney slices using PLC isoform-specific antibodies.

RESULTS

All three families of PLC isoforms (beta, gamma, and delta) were present throughout the cortical and medullary regions of the kidney. Only the PLC-beta1 isoform was observed in the brush border of the proximal tubule, but all isoforms were present in glomeruli and in the cytoplasm of tubular epithelial cells. In addition, only the PLC-gamma1 isoform was expressed in the internal elastic lamina of the renal artery, while vasa recta expressed PLC-beta1 most intensely. Medullary thick ascending limbs showed an intense level of expression of all three isoforms.

CONCLUSION

Multiple PLC isoforms are present in glomeruli, renal tubules, and renal vasculature in vivo, but with some segment-specific differences. These findings suggest that the response of a specific cell is not determined by expression of only one PLC isoform, with the exception of the brush border of the proximal tubule and the renal arteries. Instead, the presence of multiple PLC isoforms in specific regions of the kidney suggests that hormonal regulation in vivo involves mechanisms beyond cell-specific isoforms of PLC.

Differential expression of cytosolic proteins in the rat kidney cortex and medulla: preliminary proteomics

The rodent kidney is a target of many xenobiotics and is typified by regionally specific structure and function. This renders distinct regions of the kidney differentially susceptible to toxic exposure and effect. To characterize these differences at the proteome level, protein patterns from male rat kidney cortex and medulla cytosols were examined by two-dimensional electrophoresis (2-DE) and image analysis and prominent proteins identified immunologically or by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) and electrospray/ionization-tandem mass spectrometry (ESI-MS/MS) sequence tag identification. An average of 727 protein spots were resolved and matched to the cortex cytosol reference pattern, and 716 in the medulla. Of this total, 127 proteins were found to differ in abundance (86 higher in cortex; 41 higher in medulla) (P < 0.001). Of those proteins that were detectable in both cortex and medulla, the abundance of 97 differed significantly while 30 proteins were found to be unique to one region or the other (26 in cortex, 4 in medulla). Twenty protein spots were identified and their regional differences are discussed. These results both confirm and expand our understanding of the molecular heterogeneity characterizing structurally and functionally distinct regions of the kidney and serve as a useful foundation for future nephrotoxicologic studies.

Functional significance of cell volume regulatory mechanisms

To survive, cells have to avoid excessive alterations of cell volume that jeopardize structural integrity and constancy of intracellular milieu. The function of cellular proteins seems specifically sensitive to dilution and concentration, determining the extent of macromolecular crowding. Even at constant extracellular osmolarity, volume constancy of any mammalian cell is permanently challenged by transport of osmotically active substances across the cell membrane and formation or disappearance of cellular osmolarity by metabolism. Thus cell volume constancy requires the continued operation of cell volume regulatory mechanisms, including ion transport across the cell membrane as well as accumulation or disposal of organic osmolytes and metabolites. The various cell volume regulatory mechanisms are triggered by a multitude of intracellular signaling events including alterations of cell membrane potential and of intracellular ion composition, various second messenger cascades, phosphorylation of diverse target proteins, and altered gene expression. Hormones and mediators have been shown to exploit the volume regulatory machinery to exert their effects. Thus cell volume may be considered a second message in the transmission of hormonal signals. Accordingly, alterations of cell volume and volume regulatory mechanisms participate in a wide variety of cellular functions including epithelial transport, metabolism, excitation, hormone release, migration, cell proliferation, and cell death.

Highly selective aldose reductase inhibitors. 3. Structural diversity of 3-(arylmethyl)-2,4,5-trioxoimidazolidine-1-acetic acids

Accumulation of intracellular sorbitol, the reduced product of glucose, catalyzed by aldose reductase (AR) (EC 1.1.1.21), is thought to be the cause of the development of diabetic complications. Our attention is focused on finding compounds which inhibit AR without significantly inhibiting aldehyde reductase (ALR) (EC 1.1.1.2). The uracil or 2,4-dioxoimidazolidine skeleton having the benzothiazolyl or 4-chloro-3-nitrophenyl group as an aryl part indicated not only extremely high AR inhibitory activity but also AR selectivity. The ratio of IC50(ALR)/IC50(AR) of 3-[(5-chlorobenzothiazol-2-yl)methyl]-1,2,3,4-tetrahydro-2,4- dioxopyrimidine-1-acetic acid (47d) was more than 17 500. The uracil skeleton with the benzothiazolyl moiety seemed to be the best combination for selective AR inhibition.

Effect of hyperglycemia on the polyol pathway in rat kidney during the perinatal period

The activity of the polyol pathway was studied in developing rat kidney. For this purpose, sorbitol content, aldose-reductase activity and sorbitol-dehydrogenase activity were determined in papilla from fetuses and 24-h-old neonates. After birth, no significant difference was observed in sorbitol content, whereas sorbitol-dehydrogenase activity decreased and aldose-reductase activity doubled. Changes in aldose-reductase activity were due to an increased number of enzymatic sites but not with a change in affinity. Low levels of sorbitol were found in fetal and neonatal medulla together with low levels of urine osmolarity. In neonates, sorbitol contents were tenfold lower than in the adult, probably as a result of a lower affinity and a lower number of enzymatic aldose-reductase sites. Attempts to increase the activity of polyol pathway in fetal kidney were made by means of hyperglycemic animals; this approach resulted in an increase of aldose-reductase activity without any change in sorbitol content. Our results indicate that, in fetal and neonatal kidneys, aldose-reductase activity is probably not the limiting factor for sorbitol synthesis; another parameter, such as the availability of NADPH, might explain the low efficiency of the polyol pathway during the perinatal period.

Time-dependent aspects of osmolyte changes in rat kidney, urine, blood and lens with sorbinil and galactose feeding

Sorbitol plus myo-inositol, betaine and glycerophosphorylcholine (GPC) are cellular osmolytes in the mammalian renal medulla. Galactosemia and hyperglycemia can cause excessive levels of galactitol or sorbitol in several organs via aldose reductase (AR) catalysis. AR inhibitors can reduce these polyols. To examine osmolyte responses to polyol perturbations, male Wistar rats were fed normal diet, the AR inhibitor sorbinil (at 40 mg/kg/d), 25% galactose, or a combination, for 10, 21 and 42 days. All animals at 21 days had higher apparent renal AR activity than at 10 or 42 days, possibly providing resistance to sorbinil. Sorbinil feeding alone tended to increase urinary, plasma and renal urea levels. It reduced AR activity and sorbitol contents in renal inner medulla, though less so at 21 days; other renal osmolytes, especially betaine, were elevated. Galactose feeding caused little change in renal AR activity, and resulted in high galactose and galactitol contents in renal medulla, urine, blood and lens (and higher renal Na+ contents at 10 days). Renal sorbitol, inositol and GPC decreased, while betaine contents trended higher at all times. Sorbinilgalactose feeding reduced renal AR activities and galactitol contents (again less so at 21 days), urine, blood and lens galactitol, and further reduced renal sorbitol contents. At 10 and 21 days it tended to raise renal betaine more, and restore inositol (but not GPC) contents to control levels. At 42 days it reduced renal and urinary Na+ and galactose, and decreased renal betaine to control levels. Under most conditions, total renal (non-urea) organic osmolyte contents (presumed to be mostly intracellular) and Na+ plus galactose contents (presumed mostly extracellular) changed together such that cell volumes may have been maintained. The exception was 10 days on galactose, where total osmolytes appeared too low. In galactose-fed animals, urine/plasma ratios suggest some renal galactitol efflux, and cellular galactitol probably helps maintain osmotic balance rather than cause swelling.

Regulation of aldose reductase gene expression in renal cortex and medulla of rats

A role for aldose reductase-mediated production of polyol in the aetiology of diabetic nephropathy has been supported by both animal and clinical studies. In the renal medulla, the rate of polyol production is influenced in part by regulated changes in the level of aldose reductase gene expression. However, little is known about the expression of aldose reductase in the renal cortex. In this study, we evaluated the regulation of aldose reductase gene expression in the renal cortex and medulla in response to galactose feeding. Four groups of rats (n = 6) were treated for 9 weeks with control or galactose diet in the presence or absence of sorbinil, an aldose reductase inhibitor. In the renal medulla, galactose treatment produced a significant (p < 0.01) decrease in aldose reductase mRNA, to approximately 10% of control levels. Coadministration of sorbinil partially prevented the effect of galactose feeding on medullary aldose reductase mRNA (to 43% of control). Under basal conditions, the concentration of aldose reductase mRNA in the cortex was only 1% that of the renal medulla. Galactose feeding significantly reduced cortical aldose reductase mRNA by 29% relative to control (p < 0.01), and this was completely reversed by addition of sorbinil. Sorbinil administration to rats fed a control diet also decreased aldose reductase expression in the renal medulla and cortex. These results demonstrate that galactose feeding results in dynamic, polyol-dependent regulation of aldose reductase gene expression in the renal cortex as well as the medulla.(ABSTRACT TRUNCATED AT 250 WORDS)

Polyol pathway mediates high glucose-induced collagen synthesis in proximal tubule

The polyol pathway in diabetes is activated in tissues that are not dependent on insulin for glucose uptake. To examine the role of the polyol pathway in renal extracellular matrix accumulation, we incubated murine proximal tubule cells in either normal or high glucose concentration in the presence or absence of the aldose reductase inhibitor sorbinil. Rising medium glucose from 100 to 450 mg/dl for 72 hours increased cell sorbitol levels sevenfold. Addition of 0.4 mM sorbinil reduced sorbitol content to virtually undetectable levels as measured by gas chromatography. Sorbinil (0.1 to 0.2 mM) also reduced the secretion of collagens types IV and I in the high glucose concentration after 48 to 72 hours but had no appreciable effect in the normal glucose concentration. Concordantly, 0.1 mM sorbinil inhibited the high glucose-induced stimulation of alpha 1(IV) and alpha 2(I) mRNA levels without affecting levels in normal glucose concentration. To study the role of transcriptional activation of collagen genes, we transfected proximal tubule cells with a chloramphenicol acetyltransferase (CAT) reporter gene linked to the promoter and regulatory elements of alpha 1(IV) gene. CAT activity increased several-fold in the cells grown in the high versus normal glucose concentration; this transcriptional activation in culture media containing high glucose concentration was reduced by treatment of the cells with 0.1 mM sorbinil. Thus, high ambient glucose activates the polyol pathway in proximal tubule cells, and may mediate the high glucose-induced stimulation of gene expression for collagens types IV and I.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of NaPi-1, a Na-Pi cotransporter, in rabbit kidney proximal tubules. I. mRNA localization by reverse transcription/polymerase chain reaction

We have recently isolated from a rabbit cortex cDNA library a cDNA clone (NaPi-1), which, after in vitro transcription (cRNA) and injection into Xenopus laevis oocytes, expresses Na-dependent Pi uptake [Werner A, et al. (1991) Proc Natl Acad Sci USA 88:9608-9612]. The aim of the present work was to study the nephron location of the NaPi-1-related mRNA(s) by combining nephron microdissection procedures, reverse transcription (RT) and amplification of the resultant cDNA by the polymerase chain reaction (PCR). RT-PCR using NaPi-1-specific primers (different combinations) and either total kidney cortex RNA or microdissected proximal tubule segments resulted in two PCR products, both of approximately the expected length (but differing by about 30 base pairs). Restriction-enzyme analysis and nucleotide sequencing confirmed that both PCR products are related to NaPi-1 and that the "longer" PCR product has an insert of 26 base pairs containing an AluI restriction site. Nephron microdissection documents expression of NaPi-1-related mRNA(s) in superficial and deep proximal tubules (S1, S2 and S3 segments) and their absence in glomeruli, thin descending limb and thick ascending limbs of Henle's loop, distal convoluted tubules and cortical and inner medullary collecting ducts. These experiments suggest a "microheterogeneity" of NaPi-1-related mRNA(s) (which is not detected in Northern blot analysis) and proximal tubular expression of NaPi-1.

Human kidney aldose and aldehyde reductases

Mounting experimental evidence links increased aldose reductase activity with diabetes-related kidney functional changes. To investigate the interrelationship of NADPH-dependent reductases in the human kidney, both aldose reductase and aldehyde reductase were purified from human kidney by a series of chromatographic procedures, including gel filtration on Sephadex G-100, affinity chromatography on Matrex Gel Orange A, and chromatofocusing on Mono P. Each purified enzyme appeared as a single band on polyacrylamide gel after electrophoresis or isoelectric focusing. Aldose reductase has a pI of 5.7 and apparent molecular weight of 37 kDa, calculated from SDS-polyacrylamide gel electrophoresis, while aldehyde reductase has a pI of 5.2 and molecular weight of 39 kDa. Similar molecular weights were also obtained by gel filtration, indicating that both aldose and aldehyde reductases are present as monomers in the human kidney. Aldehyde reductase is primarily localized in the cortex, while the medulla contains aldose reductase. Both enzymes displayed properties consistent with the general characteristics of aldose and aldehyde reductases obtained from either rat or dog kidney. Purified aldose reductase utilizes aldose sugars such as D-xylose, D-glucose, and D-galactose as substrates while aldehyde reductase preferentially reduces D-glucuronate and oxidizes L-gulonate to D-glucuronate. Despite the lower apparent affinity of aldehyde reductase for aldose sugars (approximately 20- to 100-fold less) both enzymes reduced D-xylose, D-glucose, and D-galactose to their respective sugar alcohols in in vitro incubation studies where the generated sugar alcohols were identified by gas chromatography. Both enzymes were also inhibited by aldose reductase inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldose reductase expression and prostaglandin E2 production are coordinately regulated in cultured rat mesangial cells

There is increasing evidence that a link between the polyol pathway and prostaglandins is important in the pathogenesis of diabetic nephropathy. The presence of the polyol pathway in the kidneys of normal animals, the galactose-fed rat, and animals with experimental diabetes has been established. While aldose reductase (AR) immunoreactive protein (AR-IRP) and AR mRNA are expressed at high levels in renal medulla, the sites of AR synthesis and regulation and metabolic consequences of AR activity in renal cortex are uncertain. The present study was conducted to test the hypothesis that AR expression and PGE2 production are coordinately regulated in glomerular mesangial cells. To test this hypothesis, we measured AR-IRP, AR mRNA, and PGE2 production in mesangial cells isolated from rats maintained on diets containing normal chow (MC-N), 50% galactose (MC-G), and 50% dextrin (MC-D). The rank order for each parameter studied (AR-IRP, AR mRNA, PGE2) was MC-N > MC-G > MC-D. Western blot analysis demonstrated that MC-N (optical density [OD] 1.0), MC-G (OD 0.59), and MC-D (OD 0.25) express AR-IRP. Slot-blot analyses demonstrated that levels of AR mRNA were greatest in MC-N (1.0), intermediate in MC-G (0.49), and lowest in MC-D (0.31). Ribonuclease (RNase) protection analyses demonstrated a similar pattern of AR mRNA expression, with MC-N at 1.0, MC-G at 0.60, and MC-D at 0.33. PGE2 production (pg/5 x 10(4) cells/30 min) was highest in MC-N (278 +/- 29), intermediate in MC-G (110 +/- 9), and lowest in MC-D (37 +/- 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects on rat renal osmolytes of extended treatment with an aldose reductase inhibitor

1. The mammalian renal medulla uses sorbitol, myo-inositol, betaine and glycerophosphorylcholine as intracellular osmolytes. 2. Sorbitol synthesis was inhibited by feeding male Wistar rats the aldose reductase inhibitor sorbinil at 40 mg/kg/day for 71 d, and renal inner medullas were extracted for analysis. 3. Aldose reductase activities and sorbitol contents were greatly reduced in sorbinil-treated animals, while betaine contents increased significantly (with no other osmolytes changing). 4. The betaine increase compensated for the sorbitol decrease such that the total organic osmolytes maintained the same ratio to sodium contents as controls. 5. These results are identical to the pattern previously reported for sorbinil treatment of rats for 10 d, but not for 21 d.

Aldose reductase inhibitors and diabetic complications

Aldose reductase inhibitors impede flux of glucose through the sorbitol pathway in diabetes mellitus. They therefore reduce the accumulation of the pathway metabolites, sorbitol and fructose, reduce the impact of the flux on the cofactors used by the pathway and reduce other derived phenomena, such as osmotic stress and myo-inositol depletion. As drugs, their targets are the chronic complications of diabetes--neuropathy, retinopathy, nephropathy and vasculopathy. In experimental models there is proof of activity against biochemical, functional and structural defects in all of the involved tissues, but we await full clinical verification of this potential.

Localization, isolation and properties of three NADPH-dependent aldehyde reducing enzymes from dog kidney

Three kinds of NADPH-dependent aldehyde reducing enzymes were present in the dog kidney. Aldose reductase was located in the inner medulla region and aldehyde reductase in all regions of the renal cortex, outer medulla and inner medulla. In addition, a new reductase designated tentatively as high-Km aldose reductase, which was converted into an aldose reductase-like enzyme, was present in the inner medulla region of the kidney. Aldose reductase, aldehyde reductase and high-Km aldose reductase were purified to homogeneity from each region of the dog kidney. The molecular weight of aldose reductase was estimated to be 38,500 by SDS-polyacrylamide gel electrophoresis and the isoelectric point was found to be 5.7 by chromatofocusing. Aldose reductase had activity for aldo-sugars such as D-xylose, D-glucose and D-galactose as substrates and utilized both NADPH and NADH as coenzymes. Sulfate ions resulted in over 2-fold activation of aldose reductase. All aldehyde reductases from the three regions had the same properties. The molecular weights and isoelectric points of aldehyde reductases were 40,000 and 6.1, respectively. The aldehyde reductases were inactive for D-hexose, utilized only NADPH as coenzyme and were not affected by sulfate ions. High-Km aldose reductase had a molecular weight of 38,500 and an isoelectric point of 5.4. It had activity for aldo-sugars, but showed much higher Km and lower kcat/Km values than aldose reductase. Sulfate ions inhibited high-Km aldose reductase. It was converted into an aldose reductase-like enzyme by incubation in phosphate buffer at pH 7.0. The three kinds of enzymes were strongly inhibited by the known aldose reductase inhibitors. However, aldehyde reductase and high-Km aldose reductase were, in general, less susceptible than aldose reductase.

Expression of alpha B-crystallin in the developing rat kidney

The expression and cellular localization of alpha B-crystallin during rat renal development was studied by Northern blot analysis and by immunocytochemistry. Northern blotting of total RNA extracted from whole kidneys revealed that the messenger RNA for alpha B-crystallin rapidly increased after birth to reach adult levels by 20 days. At the same time, immunohistochemistry for alpha B-crystallin demonstrated that the prominent elongation of Henle's loop during the first 10 days of life was accompanied by increased alpha B-crystallin expression. Thus, the development of alpha B-crystallin expression is correlated temporally with the acquisition of tubule function in early post-natal life.

Anionic sites in diabetic basement membranes and their possible role in diffusion barrier abnormalities in the BB-rat

Basement membrane anionic sites, thought to be responsible for charge selective permeability barriers, were investigated in retinal, endoneurial, and muscle capillary basement membranes and in Bruch's membrane of diabetic, and age- and sex-matched non-diabetic BB-rats using an ultrastructural quantitative histochemical technique. Six months of diabetes was associated with significant basement membrane thickening which was linearly related to a decrease in anionic site density suggesting a relative loss of proteoglycans. Calculation of anionic sites per unit length of basement membrane, reflecting their absolute number, revealed a significant loss in basement membrane, constituting part of normal blood-tissue barrier systems such as retinal and endoneurial capillary basement membranes, and the basement membrane of the retinal pigment epithelium. The absolute number of anionic sites in normally permeable microvessels, such as those of muscle and choriocapillaries, was unaltered by diabetes. We conclude that this specific loss of anionic sites in basement membranes of tissues affected by chronic diabetic complications may in part be responsible for permeability abnormalities seen in these tissues.

The contributions of Jin H. Kinoshita to aldose reductase research

Sorbitol is a sugar alcohol formed from the aldose reductase catalyzed reduction of glucose. Mounting experimental evidence links the abnormal intracellular accumulation of sorbitol to the onset and severity of diabetes-associated pathology which results in a variety of tissue and/or functional changes in the cornea, lens, retina, iris, peripheral nerves, and kidney. Animal studies indicate that aldose reductase inhibitors, by inhibiting the formation of sorbitol in target tissues affected by diabetes, can either prevent or significantly delay the onset of many of these diabetes-associated changes. The pioneering studies of Dr Jin Kinoshita have been instrumental in defining the pathophysiological role of aldose reductase and excess sorbitol production under diabetic conditions. These studies provide a firm scientific groundwork for investigating the premise that inhibition of sorbitol formation is a new, pharmacologically direct treatment for diabetic complications that is independent of the control of blood sugar levels.