The effect of aldose reductase inhibitors on glomerular prostaglandin production and urinary albumin excretion in experimental diabetes mellitus

Elabela levels in patients with type 2 diabetes: can it be a marker for diabetic nephropathy?

BACKGROUND

Elabela (ELA) is a hormone that is secreted at high levels in the kidneys of a healthy adult. This study aims to investigate whether serum ELA levels of patients with Type 2 Diabetes vary with the severity of renal damage.

METHODS

Our study included 50 healthy control subjects and 100 diabetic patients, who were categorized into groups based on urine albumin/creatinine ratios (ACR). Patients included in the study were assigned to four groups: Group 1 (healthy control), Group 2 (ACR<29mg/g), Group 3 (ACR=30-299 mg/g), and Group 4 (ACR>300 mg/g normal or high serum creatinine). Physical examination findings, demographic characteristics of the study group were recorded, and serum ELA levels and other laboratory parameters were assessed using appropriate methods.

RESULTS

The results of the study indicated that ELA levels determined in healthy individuals gradually decreased through stages of normal albuminuria, microalbuminuria, and macroalbuminuria. Moreover, ELA had a significant negative correlation with LDL-C (r=-0.201, p=0.014), glucose (r=-0.437, P<0.001), retinopathy (r=-0.222, P=0.006), serum BUN (r=-0.161, P=0.049), and a positive correlation with eGFR (r=0.250, P=0.002).

CONCLUSIONS

The fact that ELA levels are higher in healthy individuals compared to diabetic patients without microalbuminuria, and higher in diabetic patients without microalbuminuria compared to patients with advanced albuminuria and kidney damage, suggests that the ELA level can be an important clinical prognostic variable and even a promising agent for the treatment of diabetic nephropathy patients.

The relationship between monocyte to high-density lipoprotein cholesterol ratio and diabetic nephropathy

Objective:

This study aims to investigate the relationship of monocyte to high-density lipoprotein cholesterol ratio (MHR) with diabetes mellitus (DM) and diabetic nephropathy.

Methods:

This study included 262 Type-2 diabetes mellitus patients, of which 60 had diabetic nephropathy and 202 did not have diabetic nephropathy who presented to the internal diseases polyclinic at Firat University Medical Faculty Hospital between May 2018 and October 2018 and 50 healthy control subjects. A retrospective scan of patient files was conducted and information relevant to nephropathy such as hemoglobin, glycated hemoglobin levels (HbA1c), hematocrit count (HCT), monocyte count, LDL, HDL, triglyceride levels, and microvascular complications were acquired.

Results:

We determined MHR values as 11.9±5.5 and 8.4±2.9 respectively for the diabetic and healthy groups. There was a statistically significant difference between the two groups in terms of MHR, with a positive correlation between diabetes and MHR (< 0.001; r: 0.241). Moreover, glucose, HDL, and triglyceride levels were different between the two groups with statistical significance (respectively, p< 0.001; p< 0.001; p< 0.001). Our study found higher MHR levels for patients with diabetic nephropathy compared to those without diabetic nephropathy (respectively, 17.1±7.9 and 10.3±3.3) and determined statistical significance and a negative correlation (p< 0.001; r: -0.512).

Conclusion:

Our results suggest that an elevated MHR can be a biomarker for diabetic nephropathy, allowing the detection of diabetic nephropathy with simple and inexpensive laboratory tests.

Aldose reductase (AKR1B3) regulates the accumulation of advanced glycosylation end products (AGEs) and the expression of AGE receptor (RAGE)

Diabetes results in enhanced chemical modification of proteins by advanced lipoxidation end products (ALEs) and advanced glycation end products (AGEs) precursors. These modifications have been linked to the development of several secondary diabetic complications. Our previous studies showed that aldose reductase (AR; AKR1B3) catalyzes the reduction of ALEs and AGEs precursors; however, the in vivo significance of this metabolic pathway during diabetes and obesity has not been fully assessed. Therefore we examined the role of AR in regulating ALEs and AGEs formation in murine models of diet-induced obesity and streptozotocin-induced diabetes. In comparison with wild-type (WT) and AR-null mice fed normal chow, mice fed a high-fat (HF) diet (42% kcal fat) showed increased accumulation of AGEs and protein-acrolein adducts in the plasma. AGEs and acrolein adducts were also increased in the epididymal fat of WT and AR-null mice fed a HF diet. Deletion of AR increased the accumulation of 4-hydroxy-trans-2-nonenal (HNE) protein adduct in the plasma and increased the expression of the AGE receptor (RAGE) in HF fed mice. No change in AGEs formation was observed in the kidneys of HF-fed mice. In comparison, renal tissue from AR-null mice treated with streptozotocin showed greater AGE accumulation than streptozotocin-treated WT mice. These data indicated that AR regulated the accumulation of lipid peroxidation derived aldehydes and AGEs under conditions of severe, but not mild, hyperglycemia and that deletion of AR increased RAGE-induction via mechanisms that were independent of AGEs accumulation.

Contribution of polyol pathway to arteriolar dysfunction in hyperglycemia. Role of oxidative stress, reduced NO, and enhanced PGH(2)/TXA(2) mediation

Hyperglycemia increases glucose metabolism via the polyol pathway, which results in elevations of intracellular sorbitol concentration. Thus we hypothesized that elevated level of sorbitol contributes to the development of hyperglycemia-induced dysfunction of microvessels. In isolated, pressurized (80 mmHg) rat gracilis muscle arterioles (approximately 150 microm), high glucose treatment (25 mM) induced reduction in flow-dependent dilation (from maximum of 39 +/- 2% to 15 +/- 1%), which was significantly mitigated by an aldose reductase inhibitor, zopolrestat (maximum 27 +/- 2%). Increasing doses of sorbitol (10(-10)-10(-4) M) elicited dose-dependent constrictions (maximum 22 +/- 3%), which were abolished by endothelium removal, a prostaglandin H(2)/thromboxane A(2) (PGH(2)/TXA(2)) receptor (TP) antagonist SQ-29548, or superoxide dismutase (SOD) plus catalase (CAT). Incubation of arterioles with sorbitol (10(-7) M) reduced flow-dependent dilations (from maximum of 39 +/- 2% to 20 +/- 1.5%), which was not further affected by inhibition of nitric oxide synthase by N(omega)-nitro-l-arginine methyl ester but was prevented by SOD plus CAT and mitigated by SQ-29548. Nitric oxide donor sodium nitroprusside-induced (10(-9)-10(-6) M) dilations were also decreased in a SQ-29548 and SOD plus CAT-reversible manner, whereas adenosine dilations were not affected by sorbitol exposure. Sorbitol significantly increased arterial superoxide production detected by lucigenin-enhanced chemiluminescence, which was inhibited by SOD plus CAT. Sorbitol treatment also increased arterial formation of 3-nitrotyrosine. We suggest that hyperglycemia by elevating intracellular sorbitol induces oxidative stress, which interferes with nitric oxide bioavailability and promotes PGH(2)/TXA(2) release, both of which affect regulation of vasomotor responses of arterioles. Thus increased activity of the polyol pathway may contribute to the development of microvascular dysfunction in diabetes mellitus.

Acetylcholine-induced vasodilation in the perfused kidney of the streptozotocin-induced diabetic rat: role of prostacyclin

Using the perfused kidneys of age-matched controls and streptozotocin (STZ)-induced diabetic rats, we previously demonstrated that endothelial dysfunction is present in STZ-induced diabetic rats and that acetylcholine (ACh) increases the level of 6-keto-prostaglandin F(1 alpha) (a metabolite of prostacyclin) in the effluent from such perfused kidneys. Here, we investigated whether the ACh-induced relaxation in the perfused kidney is modulated by prostacyclin and/or thromboxane A(2) (TXA(2)) in the STZ-induced diabetic state. ACh-induced renal vasodilatation was significantly weaker in STZ-induced diabetic rats than in age-matched controls, and it was not affected by treatment with 10 microM furegrelate (TXA(2) -synthase inhibitor) or 1 microM SQ29548 (TXA(2) -receptor antagonist) in either group. However, it was attenuated by 10 microM tranylcypromine (prostacyclin-synthesis inhibitor), but only in the diabetic group. These results suggest that the endothelium-dependent relaxation induced by ACh in the renal vascular bed of STZ-induced diabetic rats is regulated by prostacyclin, not by TXA(2). Increased prostacyclin-signaling may occur to help compensate for the impaired endothelial function seen in the kidney in long-term diabetic states.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Redox state-dependent and sorbitol accumulation-independent diabetic albuminuria in mice with transgene-derived human aldose reductase and sorbitol dehydrogenase deficiency

AIMS/HYPOTHESIS

We investigated the role played by sorbitol accumulation in the kidney in the development of diabetic albuminuria.

METHODS

We created mice ( hAR-Tg:SDH null) with transgene-derived human aldose reductase and sorbitol dehydrogenase (SDH) deficiency, and analysed (i). the contribution of accumulated sorbitol to urinary albumin excretion rate, and (ii). the effect of the aldose reductase inhibitor, epalrestat, on the diabetic redox state, including decreased renal reduced glutathione concentrations or increased lactate to pyruvate ratios in the diabetic kidney.

RESULTS

Compared to littermates, non-diabetic transgenic mice had a 2.6-fold increase in aldose reductase mRNA. In a diabetic group, aldose reductase mRNA in hAR-Tg mice was 2.7-fold higher than in littermates. In the diabetic and non-diabetic groups, hAR-Tg:SDH null mice had the highest sorbitol content among all four genetic types including hAR-Tg:SDH null, SDH null, hAR-Tg and littermates. The urinary albumin excretion rate in non-diabetic groups was similar in the four genetic types of mouse. In diabetic groups it was greater than in non-diabetic groups, but did not correlate with the sorbitol content among the four genetic types of mouse. When aldose reductase inhibitor and streptozotocin were given simultaneously at 6 weeks of age, epalrestat prevented diabetic increases in urinary albumin excretion rate and completely prevented diabetic decreases in reduced glutathione concentrations and diabetic increases in lactate to pyruvate ratios, even in the presence of transgenic aldose reductase.

CONCLUSIONS/INTERPRETATION

The degree of diabetic albuminuria in genetically modified mice is dependent on the redox state and independent of polyol accumulation; aldose reductase inhibitor can prevent diabetic albuminuria by normalising diabetic redox changes.

Suppression of 3-deoxyglucosone and heparin-binding epidermal growth factor-like growth factor mRNA expression by an aldose reductase inhibitor in rat vascular smooth muscle cells

Reactive carbonyl compounds and oxidative stress have been recently shown to up-regulate the expression of heparin-binding epidermal growth factor-like growth factor (HB-EGF), a potent mitogen for vascular smooth muscle cells (SMCs) produced by SMC themselves. Because the polyol pathway has been reported to influence the formation of carbonyl compounds and the oxidative stress in various cells, we conducted this study to investigate whether the polyol pathway affects HB-EGF expression along with the generation of carbonyl compounds and the oxidative stress in SMCs. We found that, compared with those cultured with 5.5mM glucose, SMCs cultured with 40 mM glucose showed the accelerated thymidine incorporation, elevated levels of intracellular sorbitol, 3-deoxyglucosone (3-DG), advanced glycation end products (AGEs), and thiobarbituric acid-reactive substances (TBARS) along with the enhanced expression of HB-EGF mRNA. An aldose reductase inhibitor (ARI), SNK-860, significantly inhibited all of these abnormalities, while aminoguanidine suppressed 3-DG levels and HB-EGF mRNA expression independent of sorbitol levels. The results suggest that the polyol pathway may play a substantial role in SMC hyperplasia under hyperglycemic condition in part by affecting HB-EGF mRNA expression via the production of carbonyl compounds and oxidative stress.

C-106T polymorphism of AKR1B1 is associated with diabetic nephropathy and erythrocyte aldose reductase content in Japanese subjects with type 2 diabetes mellitus

BACKGROUND

The C-106T polymorphism of AKR1B1, which encodes aldose reductase (AR), was reported to be associated with diabetic nephropathy (DN). However, this association in Japanese patients with type 2 diabetes mellitus and its potential role as a clinical marker remain unclear.

METHODS

The C-106T polymorphism was genotyped in 228 cases (microalbuminuria or overt proteinuria) and 220 controls (normoalbuminuria with diabetes duration > or =10 years) for a case-control comparison, and the association with erythrocyte AR content was investigated. In addition, a new C-11G polymorphism in the promoter region of AKR1B1 was genotyped.

RESULTS

The distribution of genotypes of the C-106T polymorphism in cases was significantly different from that in controls (P = 0.031). Carriers of the TT genotype at the C-106T polymorphism were more frequent in cases than controls, with an odds ratio of 4.7 (95% confidence interval, 1.3 to 17). Erythrocyte AR content was significantly elevated in TT carriers in comparison to non-TT carriers (13.1 +/- 1.2 versus 10.2 +/- 1.2 ng/mg hemoglobin [Hb]; P < 0.001) and in cases in comparison to controls (10.6 +/- 1.3 versus 10.1 +/- 1.2 ng/mg Hb; P = 0.041). However, distribution of genotypes of the C-11G polymorphism and estimated frequencies of haplotypes defined by these 2 polymorphisms did not differ between cases and controls.

CONCLUSION

The TT genotype of the C-106T polymorphism of AKR1B1 increases the risk for DN in Japanese subjects with type 2 diabetes mellitus, which could be linked in part to greater expression of AR.

Minalrestat, an aldose reductase inhibitor, corrects the impaired microvascular reactivity in diabetes

We demonstrated that aldose reductase inhibition corrects the impaired microvascular responses to inflammatory mediators in diabetic rats. To study the mechanism involved in the restoring effect of aldose reductase inhibition, we examined the effects of minalrestat, another aldose reductase inhibitor, on the responses of mesenteric microvessels studied in vivo to permeability-increasing agents in diabetic and galactosemic rats. The diabetic group was treated from 3 days after the alloxan injection with minalrestat (10 mg/kg/day) for 30 days and the minalrestat treatment (10 mg/kg/day/7 days) of galactosemic rats started concomitantly with the induction of galactosemia. The mesenteric microvessel reactivity was studied using intravital microscopy and changes in vessel diameters were estimated after the topical application of vasoactive agents. The impaired responses to bradykinin, histamine, and platelet-activating factor of arterioles and venules observed in diabetic and galactosemic rats were completely prevented by minalrestat. Neither diabetes nor galactosemia affected responses to acetylcholine and sodium nitroprusside. Responses to these agents were not modified by aldose reductase inhibition. The restoring effect of minalrestat was reversed by inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester, by blocking K(+) channel with tetraethylammonium but not by cyclooxygenase inhibition with diclofenac. Therefore, we concluded that NO, membrane hyperpolarization, but not cyclooxygenase products are involved in the beneficial effect of minalrestat on the microvascular reactivity in diabetes. Together, these findings led us to suggest that aldose reductase inhibition might ameliorate diabetic complications through the correction of the altered microvascular reactivity by a mechanism that involves NO and membrane hyperpolarization.

Therapeutic usefulness of Keishi-bukuryo-gan for diabetic nephropathy

Keishi-bukuryo-gan is a traditional herbal medicine, which is used clinically as a vascular system disorder-eliminating drug. In this study, its effect on the progression of diabetic nephropathy in experimental rats was investigated. The diabetic nephropathy model used in this study shows functional and morphological changes of the kidney resembling those seen in patients with diabetic nephropathy. Increased proteinuria and serum urea nitrogen and creatinine levels and decreased creatinine clearance, which are important parameters of renal function, were observed in rats with diabetic nephropathy. Pathological examination of the kidney revealed diffuse, nodular and exudative lesions and arteriolar hyalinosis. The deterioration of renal function was ameliorated in rats treated with Keishi-bukuryo-gan for 15 weeks and these results agreed with the renal histological findings. In addition, metabolic abnormalities mediated by persistent hyperglycaemia (the glycation reaction, excessive polyol pathway activity, oxidative stress and lipid metabolic abnormalities) were also observed. However, Keishi-bukuryo-gan reduced accumulation of advanced glycation end products, determined by measuring fluorescence, and serum lipid peroxidation, triglyceride and total cholesterol levels dose-dependently. Thus, this study indicates the potential therapeutic usefulness of Keishi-bukuryo-gan for retarding the progression of renal damage and suggests that its beneficial effects were due to its ability to improve metabolic abnormalities associated with diabetes.

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.

Aldose reductase and the development of renal disease in diabetic dogs

Effects of 5 years administration of an aldose reductase inhibitor (Sorbinil) on renal structure and albumin excretion were evaluated in diabetic dogs. Glycemia, estimated by frequent measurements of HbA1, glycated plasma proteins and glucosuria, was kept comparable between the placebo- and Sorbinil-treated diabetic groups. Kidney structure was evaluated using morphometric techniques by light and electron microscopy, and excretion of immunoreactive albumin was measured yearly. Placebo-treated diabetic dogs developed nephromegaly, glomerular enlargement, increased mesangial volume, and basement membrane thickening during the 5 years of study, and by the fifth year, excreted greater than normal quantities of albumin. Sorbinil treatment prevented sorbitol accumulation in erythrocytes and tended to have a similar effect in renal cortex, but had no beneficial effect on renal structure or albuminuria. Experimental galactosemia, another model of polyol over-production, failed to produce nephromegaly, glomerular enlargement, or mesangial expansion in dogs even after 5 years of galactose-feeding. The results suggest that polyol over-production and/or accumulation per se are not sufficient to account for the nephromegaly, glomerular enlargement, or increased mesangial volume observed in diabetic dogs.

Pathophysiology of diabetic nephropathy

Diabetic nephropathy (DN) is now the commonest cause of end-stage renal failure in the Western world. Recent studies examining the pathogenesis of diabetic complications have focused on the complex interaction between genetic and hemodynamic mechanisms in addition to metabolic factors such as advanced glycation, protein kinase C (PKC) activation, and polyol production. The importance of the various components, particularly with regard to the progression of DN, is currently being explored with the assistance of targeted drug intervention studies.

Spinal pharmacology of tactile allodynia in diabetic rats

1. Rats develop tactile allodynia to stimulation of the plantar surface of the hindpaw with von Frey filaments within days of the onset of streptozotocin-induced diabetes. This is prevented by insulin and alleviated by systemic lignocaine, but the aetiology is unknown. 2. Using indwelling lumbar intrathecal catheters to deliver pharmacological agents, we have investigated whether tactile allodynia in streptozotocin-diabetic rats is dependent on mechanisms associated with spinal sensitization, by assessing the efficacy of agents that inhibit specific components of spinal nociceptive processing. 3. Dose-dependent inhibition of tactile allodynia in diabetic rats was noted with the N-type calcium channel antagonist SNX 239, the alpha2-adrenoceptor agonist dexmedetomidine, the mu-opioid receptor agonist morphine, the N-methyl-D-aspartate (NMDA) receptor antagonist AP5 and the non-NMDA receptor antagonist NBQX. 4. No effect on tactile allodynia was noted after intrathecal administration of the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), the cyclo-oxygenase inhibitor ketorolac, the L-type calcium channel inhibitor diltiazem or any vehicle. 5. These data suggest that the tactile allodynia of diabetic rats involves spinal glutamatergic pathways but is not associated with spinal release of nitric oxide or prostaglandins.

Expression of constitutive cyclo-oxygenase (COX-1) in rats with streptozotocin-induced diabetes; effects of treatment with evening primrose oil or an aldose reductase inhibitor on COX-1 mRNA levels

Altered prostanoid metabolism participates in the pathogenesis of diabetic complications. The rate-limiting enzyme in the control of prostanoid metabolism is constitutive cyclo-oxygenase (COX-1). This study examined the possibility that altered prostanoid metabolism derives from altered COX-1 expression in those tissues from diabetic rats, with characteristic changes in prostanoid production and related haemodynamics. This account also describes a procedure for estimation of minute amounts of COX-1 mRNA by reverse transcription and competitive polymerase chain reaction (RT-cPCR) amplification. In streptozotocin-diabetic rats (STZ-D, 55 mg/kg body weight), compared with age-matched controls, the level of COX-1 mRNA (in attomoles/micrograms tRNA +/- 1SD) was significantly decreased in sciatic nerve (0.50 +/- 0.26 versus 0.89 +/- 0.32 in controls; P < 0.05) and thoracic aorta (3.99 +/- 1.67 versus 8.80 +/- 2.37 in controls; P < 0.05). There were no differences in COX-1 mRNA in diabetic and control rat kidney and retina, though there was a trend towards increased expression with diabetes in the latter. Evening primrose oil (EPO) treatment increased COX-1 mRNA in nerve and retina to levels in diabetic rats that were higher than those of non-diabetic controls (1.21 +/- 0.28 for nerve and 0.065 +/- 0.017 for retina, where control retinae gave 0.031 +/- 0.020-see above for nerve). Treatment of diabetic rats with an aldose reductase inhibitor was without effect on COX-1 mRNA levels in the tissues examined. This study demonstrates that the changes in COX-1 mRNA levels in diabetic rats are organ specific and suggests that altered prostanoid metabolism can, in part, be explained by altered COX-1 expression. Apart from providing arachidonate as substrate for COX, EPO stimulates COX-1 expression in some tissues.

Effect of inhibition of aldose reductase on glucose flux, diacylglycerol formation, protein kinase C, and phospholipase A2 activation

Activation of the polyol pathway under hyperglycemic conditions is proposed to contribute to the development of diabetic nephropathy. The mechanisms by which this activation may lead to functional and structural changes within the kidney are yet to be definitively established. We have examined in vitro the steps linking increased polyol pathway activity resulting from hyperglycemia to prostaglandin production. Following the demonstration of increased prostaglandin E (PGE) levels in glomeruli from diabetic rats (14.9 +/- 2.5 v 59.1 +/- 19.4 ng PGE/mg protein), a specific inhibitor of aldose reductase, HOE-843, was used in vitro to analyze the response to hyperglycemia of the steps preceding prostaglandin production. In explants of glomeruli from control animals, increasing the glucose concentration in vitro from 5.6 mmol/L to 25 mmol/L resulted in a significant increase in the flux of glucose through the pentose phosphate pathway ([PPP] 1.29 +/- 0.08 v 2.00 +/- 0.11 nmol/h), de novo diacylglycerol synthesis (2.2 +/- 0.1 v 3.1 +/- 0.2 micromol/mg protein), membrane protein kinase C (PKC) activity (18.7 +/- 0.5 v 24.3 +/- 0.75 pmol/microg protein), and in vitro phospholipase A2 (PLA2) activity (2.18 +/- 0.46 v 3.83 +/- 1.07 nmol arachidonic acid hydrolyzed/min/mg cytosolic protein). For all parameters measured, the increase resulting from the increased glucose concentration could be prevented by in vitro addition of HOE-843 for 24 hours before measurement. These findings provide evidence to suggest a mechanism linking increased polyol pathway activity and an increase in PLA2 activity to increased prostaglandin production, which is observed in diabetes of recent onset and may ultimately lead to changes associated with the development of diabetic nephropathy.

Norman MacAlister Gregg Lecture. The pathogenesis of diabetic retinopathy

Diabetic retinopathy remains a major cause of loss of vision. The Diabetes Control and Complications Trial (DCCT) has implicated hyperglycaemia as a probable major direct causative factor in the pathogenesis of diabetic retinopathy. There are several plausible mechanisms by which high glucose concentrations could lead to the functional and later structural changes characterising diabetic retinopathy. These include increased activity of the aldose reductase pathway, increase de novo synthesis of diacylglycerol from glucose, causing protein kinase C activation, increased non-enzymatic glycation and increased oxidative damage. The demonstration of the potential roles of these pathways and the subsequent effects of growth factors in enhancing angiogenesis provide potential new approaches to the prevention and treatment of diabetic retinopathy.

Diabetic nephropathy and pregnancy

Knowledge of the pathogenic mechanisms of diabetic nephropathy (by which hyperglycemia, hyperfiltration, and hypertension cause the gradual development of microproteinuria, mesangial expansion, and eventual glomerular closure) provides the basis for effective treatment. Intensified glycemic control and antihypertensive therapy that is safe for the fetus are crucial for success during pregnancy. Considered outcome measures include perinatal survival, size at birth, child development, and long-term maternal renal function.

Different effects of two aldose reductase inhibitors on nociception and prostaglandin E

This study examined the effect of two structurally dissimilar aldose reductase inhibitors, N-[[5-(trifluoromethyl)-6-methoxy-1- napthalenyl]thioxomethyl]-N-methlyglycine (tolrestat) and 4-amino-2,6-dimethylphenyl-sulphonyl nitromethane (ICI 222155), on formalin-evoked behavioural responses in control and diabetic rats and on capsaicin-evoked release of prostaglandin E from spinal cord slices in vitro. Both compounds, given orally for 4 weeks, prevented hyperalgesia in diabetic rats 5-20 min after hindpaw formalin injection. ICI 222155 also prevented hyperalgesia in diabetic rats 21-60 min after formalin, whereas tolrestat suppressed activity in diabetic rats below controls and also suppressed activity in controls when given orally or intrathecally. Capsaicin-evoked release of prostaglandin E from spinal cord slices of control rats was significantly reduced by tolrestat, but not ICI 222155. These data suggest that hyperalgesia in diabetic rats is related to glucose metabolism by aldose reductase, whereas tolrestat has specific effects on formalin-evoked nociception associated with an ability to reduce spinal prostaglandin release.

Increased phosphorylation of focal adhesion kinase in diabetic rat kidney glomeruli

Altered extracellular matrix production by the glomerular mesangium is a feature of diabetes mellitus. Matrix proteins, including fibronectin, via interaction with cell-surface receptors (the integrins) may activate intracellular pathways such as prostaglandin production, shown previously to be stimulated by addition of fibronectin to glomerular cores. However, the signalling pathways involved are unclear. An intracellular tyrosine kinase (focal adhesion kinase), associated with focal adhesions, is known to be phosphorylated after interaction with matrix proteins. We now show for the first time, in glomeruli from diabetic rats, that focal adhesion kinase has increased phosphorylation on tyrosine, when compared with non-diabetic control rats. This phosphorylation was labile and disappeared with extended time of sample preparation or digestion of glomeruli to glomerular cores. Cultured mesangial cells, from non-diabetic rats, plated onto fibronectin also showed increased tyrosine phosphorylation of focal adhesion kinase accompanied by a twofold increase in prostaglandin production. However, it may not be possible to replicate fully the diabetic ¿state¿ in vitro merely by use of raised glucose concentrations, as these conditions (for 3 weeks) resulted in decreased focal adhesion kinase phosphorylation, despite increased fibronectin and prostaglandin levels. A role for increased focal adhesion kinase phosphorylation in kidney glomeruli isolated from diabetic rats, and any linkage to intracellular signalling pathways remains to be determined.

Effect of myo-inositol supplementation on the development of renal pathological changes in the Cohen diabetic (type 2) rat

A lower concentration of intracellular myo-inositol has been implicated in the development of diabetic nephropathy. This was based on short-term studies showing that early administration of aldose reductase inhibitors or myo-inositol supplementation reduces increased glomerular filtration rate and partly reduces increased urinary albumin excretion in streptozotocin diabetic rats. We studied the effect of long-term (4 months) administration of 1% myo-inositol supplement to the Cohen diabetic (type 2) rat on the development of nephropathy and renal Na(+)-K(+)-ATPase. This treatment reduced the increased renal Na(+)-K(+)-ATPase activity but had no effect on blood glucose levels, body weight, increased kidney weight, or creatinine clearance and did not prevent or reduce the development of renal glomerular pathology. There was no correlation between the level of Na(+)-K(+)-ATPase activity and the degree of nephropathy. It is possible that the renal pathological changes are due to metabolic and humoral factors resulting from hyperglycaemia, other than myo-inositol depletion. The fact that myo-inositol treatment had no effect on the development of renal pathological changes but was shown to have a beneficial effect on restoring impaired conduction velocity and on the disruption of structural elements in the nerve indicates that the effect of the biological changes ensuing from hyperglycaemia vary in different tissues depending on local conditions.

Diabetic late complications: will aldose reductase inhibitors or inhibitors of advanced glycosylation endproduct formation hold promise?

Patients suffering from the severe complications associated with both insulin- (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM): nephropathy, retinopathy, neuropathy, and atherosclerosis are still largely left without a prospect of an efficient treatment. This is the case even if it has been assumed for decades and now finally proved by the results from the Diabetes Control and Complications Trial (DCCT) that hyperglycemia is the single main cause of these complications. Improved glycemic control as a result of intensive insulin treatment has the potential to reduce the incidence and progression of complications, but implementation and monitoring of improved glycemic control in all groups of IDDM and NIDDM patients in different communities will be difficult and expensive. Results from the recently terminated DCCT have shown that even with intensive insulin treatment, there will be a significant burden of complications on the diabetic population. It will, therefore, still be of immense importance for the long-term quality of life for the diabetic patient that additional possibilities are developed for prevention and intervention against diabetic complications. Almost two decades of research, animal model testing, and clinical trials have been conducted on various efficient aldose reductase inhibitors. Now the concept of inhibition of formation of advanced glycosylation endproducts on proteins and lipids resulting from extra- and intracellular hyperglycemia is entering the scene as an alternative or perhaps supplementary approach to reduce the occurrence of diabetic complications. An overview of the results from these two fields of research and associated drug-development programs will be presented along with thoughts on possible future developments.

The relative roles of advanced glycation, oxidation and aldose reductase inhibition in the development of experimental diabetic nephropathy in the Sprague-Dawley rat

Advanced glycation is an important pathogenic mechanism in the development of diabetic complications. However, other biochemical processes, such as the polyol pathway or lipid and protein oxidation which can interact with advanced glycation can also yield tissue fluorescence and may also be implicated in the genesis of diabetic microangiopathy. Aminoguanidine is an inhibitor of advanced glycation, but it is not known if all of its effects are mediated by this mechanism. The present study explores the relative contributions of aldose reductase, oxidative stress and advanced glycation on the development of aortic and renal fluorescence and urinary albumin excretion in streptozotocin diabetic rats. The study groups included non-diabetic (control), streptozotocin diabetic rats and diabetic rats receiving aminoguanidine, the anti-oxidants butylated hydroxytoluene and probucol and the aldose reductase inhibitor, ponalrestat. Serial measurements of glycaemic control and urinary albumin excretion were performed every 8 weeks. At 32 weeks, animals were killed, tissues removed and collagen extracted for measurement of fluorescence. Diabetic rats had increased fluorescence in aorta, glomeruli and renal tubules. Aminoguanidine prevented an increase in fluorescence at all three sites suggesting that diabetes-related tissue fluorescence is predominantly due to advanced glycation. Ponalrestat retarded fluorescence in aorta only and butylated hydroxytoluene attenuated fluorescence at the renal sites but not in the aorta. Diabetic rats had increased renal cortical sorbitol levels. Ponalrestat normalized renal cortical sorbitol levels but aminoguanidine did not affect this parameter. The only agent to decrease plasma thiobarbituric acid reactive substances was butylated hydroxytoluene. Diabetic rats developed albuminuria over the 32-week period.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

The effect of an aldose reductase inhibitor (Epalrestat) on diabetic nephropathy in rats

In order to clarify the possible contribution of the abnormal polyol pathway to the development of diabetic nephropathy, the effect of aldose reductase inhibitor on renal function and morphology was examined in streptozotocin (STZ)-induced diabetic rats. Six months after STZ injection, glomerular filtration rate and renal plasma flow showed marked decline with significant increase in nuclear-free mesangial area (MA) and relative mesangial area (RMA; MA per glomerular area) in diabetic rats. Oral administration of an aldose reductase inhibitor, Epalrestat, prevented renal hypofunction and mesangial expansion in diabetic rats without influencing the levels of blood glucose. These results suggest that the abnormal polyol pathway in diabetic rats is closely related to the development of mesangial expansion, a morphologic representative of diabetic glomerulopathy, and renal hypofunction.

Renal and microvascular effects of an aldose reductase inhibitor in experimental diabetes. Biochemical, functional and ultrastructural studies

Aldose reductase inhibitors, and particularly sorbinil, have been reported to prevent glomerular basement membrane thickening (GBMT) and albuminuria development in diabetic rats, but contradictory observations have been published. The aim of this study was to answer the following questions (i) is the corrective effect of sorbinil on GBMT, if confirmed, associated with an effect on collagen metabolism alterations? (ii) Is it associated with an effect on microvascular functional alterations? We therefore studied the influence of sorbinil on glucosyl-galactosyl-hydroxylysyl-glucohydrolase activity (GGHG; EC 3.2.1.107 which is involved in the catabolism of collagen disaccharide units), 3- and 4-hydroxyproline content and GBMT by ultrastructural morphometry in the kidney cortex of streptozotocin-diabetic rats after 5 months of disease. In parallel, the effects on albumin renal clearance and another functional alteration, the microvascular response to norepinephrine, were evaluated. We confirmed a corrective effect of sorbinil on both renal albumin clearance and GBMT. In the diabetic rats, sorbinil diminished the 3-hydroxyproline (but not the 4-hydroxyproline) content, whether expressed per mg protein or per total kidney cortex relative to body weight. Sorbinil reduced GGHG activity measured in the dialysed 10,000 g supernatant whether expressed per mg protein or per total kidney cortex; this activity has been shown to be increased in diabetes. Sorbinil also corrected the microvascular response to norepinephrine which is altered in diabetes.

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)

Effects of cilostazol, a phosphodiesterase inhibitor, on urinary excretion of albumin and prostaglandins in non-insulin-dependent diabetic patients

Microalbuminuria is characteristic in diabetic nephropathy and is thought to be influenced by renal hemodynamics, especially by the metabolism of prostaglandins (PGs) in glomruli. To reduce urinary albumin excretion in patients with non-insulin-dependent diabetes mellitus (NIDDM), we administered 100 mg of cilostazol, a phosphodiesterase inhibitor, daily for 3 months. The urinary albumin index (UAI: microgram albumin/mg creatinine) decreased significantly after 3 months of administering cilostazol. Urinary excretions of thromboxane B2 (TXB2), a stable metabolite of thromboxane A2, decreased significantly after treatment. However, it had no effects on urinary excretions of PGE2 and 6-keto PGF1 alpha (6KF), a stable metabolite of prostacyclin. The ratio 6KF/TXB2 has been known to reflect the renal metabolism of PGs. In this study, urinary 6KF/TXB2 ratio increased significantly in parallel with a significant reduction of UAI. Cilostazol had no adverse effects on the control of blood glucose and lipids. In conclusion, cilostazol has a beneficial effect on UAI in patients with NIDDM by reducing renal production of TXB2., which increases 6KF/TXB2 ratio.

Peripheral macro- and microcirculation in short-term insulin-dependent diabetes mellitus: the role of prostaglandins in early haemodynamic changes

To determine whether vasodilator prostaglandins are involved in the peripheral hyperperfusion observed in patients with short-term insulin-dependent diabetes mellitus (IDDM), forearm and skin blood flow were studied before and after cyclooxygenase inhibition. Skin nutritive (CBV: capillary blood-cell velocity) and thermoregulatory (LDF: laser-Doppler fluxmetry), and forearm (muscle) blood flow (FBF) were measured before and after 500 mg acetylsalicylic acid (ASA) infused intravenously in 14 short-term IDDM patients and 22 healthy control subjects. In the IDDM patients, baseline LDF (median: 27 (19-35); interquartile range) vs. 17 (15-23) pu) and FBF (3.4 (2.5-4.1) vs. 2.6 (2.2-2.9) ml 100 ml-1 min-1) were increased, while CBV (0.70 (0.40-1.33) vs. 0.69 (0.41-0.96) mm s-1) was unchanged compared to healthy controls. ASA infusion had similar effects on baseline CBV, LDF, and FBF in patients and controls. In eight of the control subjects the role of prostaglandins in the regulation of basal peripheral blood flow was studied before and after ASA and placebo infusion. The changes in baseline CBV, LDF, and FBF were similar after ASA and placebo infusion in healthy controls. In conclusion, in short-term IDDM patients, increased skin thermoregulatory and forearm (muscle) blood flow are probably not related to vasodilator prostaglandins. Furthermore, prostaglandins are not likely to be involved in regulating basal peripheral blood flow in healthy man.

Effect of statil on kidney structure, function and polyol accumulation in diabetes mellitus

We examined the effects of an aldose-reductase inhibitor, statil, which blocks the conversion of glucose to sorbitol, in rats rendered diabetic with streptozotocin in order to determine whether the anticipated changes in sorbitol content was associated with beneficial lack of changes in renal morphology and function. Groups of diabetic, insulin-treated and untreated rats were fed statil daily for a period of five months; each group was paired with a non-drug-treatment control group. At the conclusion of the study period, statil was not found to affect renal sorbitol concentrations nor did it effect functional or structural changes seen in the kidney. We conclude that further study, using other doses of statil and longer duration over which data is collected, must be undertaken in order to implicate the polyol pathway in the renal complications of diabetes mellitus.

Forearm arterial vascular responsiveness in insulin-dependent diabetic subjects

The vascular reactivity of forearm arterioles was measured in 16 control subjects (C) and 30 insulin-dependent diabetic (IDDM) subjects, 16 of whom were shown to have microvascular and/or neuropathic complications (DC) including 8 with autonomic neuropathy (DCa) and 14 were shown to be free of complications (DNC). Forearm blood flow was measured by strain gauge plethysmography basally, following a cold pressor stress and following a period of arterial occlusion (reactive hyperaemia). The tests were repeated 24 h later following aspirin treatment. Both C and DNC showed a significant reduction in blood flow in the cold pressor test (C 0.64 +/- 0.12, DNC 0.89 +/- 0.22 ml/100 ml forearm tissue/min reduction in flow P < 0.005), while DC showed no significant response. Reactive hyperaemia was significantly greater in C than in DNC or DC (8.37 +/- 1.14, 5.51 +/- 1.27 and 4.95 +/- 0.75 ml/100 ml tissue/min, respectively, P < 0.02). In the DC group, DCa had significantly less response than those without autonomic neuropathy. Aspirin treatment restored the response of DNC but not DC to normal, suggesting that the abnormality in the former group may have been due to overproduction of a vasoconstrictive cyclooxygenase product (such as thromboxane A2). It is concluded that the abnormalities of vasomotor responses in diabetic subjects are complex and are apparently dependent on autonomic neuropathy, humoral and perhaps structural changes.

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)

Type I diabetic nephropathy: clinical characteristics and economic impact

Approximately one-third of type I diabetic patients develop diabetic nephropathy with confounding pathogenesis--frequently manifested as heavy persistent proteinuria, fall in glomerular filtration rate, and increased arterial hypertension. There is increasing incidence and prevalence of type I diabetes, particularly in northern Europe and the United States. Increased morbidity and mortality occur in type I diabetic patients with renal disease. Among type I patients with persistent proteinuria, death occurs on the average within 5-10 years. The economic impact of endstage renal disease due to diabetic nephropathy is overwhelming, and the cost is increasing at an alarming rate.

The link between hyperglycaemia and diabetic nephropathy

A large number of experimental studies in animals and retrospective or non-randomised prospective studies in humans provide support for the concept that the microvascular complications of diabetes mellitus are dependent on hyperglycaemia. This review focuses on four potential biochemical pathways linking hyperglycaemia to changes within the kidney which can plausibly be linked to the functional and structural changes characterising diabetic nephropathy. These four pathways are the polyol pathway, non-enzymatic glycation, glucose autoxidation and de novo synthesis of diacylglycerol leading to protein kinase C and phospholipase A2 activation. Rather than being independent, there are several potential interactions between these four pathways which may explain confusing and overlapping effects observed in studies examining inhibitors of individual pathways. As many of the steps which follow on glucose metabolism are subject to modification by dietary and pharmacological means, the further delineation of the pathogenetic sequence leading to tissue damage in diabetes should allow a logical and effective approach to the prevention or treatment of the complications of diabetes.

Sorbinil does not prevent hyperfiltration, elevated ultrafiltration pressure and albuminuria in streptozotocin-diabetic rats

The effects of aldose reductase inhibition on kidney function were studied in rats with streptozotocin-induced diabetes mellitus. Diabetic rats were fed sorbinil (20 and 50 mg/kg) by daily gastric gavage and were compared with untreated diabetic rats and normal rats. The rats were under daily supervision with regard to blood glucose control, insulin administration and body weight. The aim was to promote continuous body growth and to maintain the blood glucose concentration at around 22 mmol/l without large day-to-day fluctuations. The renal functional changes observed in this well-established diabetic model closely resembled those reported in human Type 1 (insulin-dependent) diabetes mellitus. Sorbinil treatment completely prevented renal cortical sorbital accumulation, but did not abolish kidney enlargement or the increase in ultrafiltration pressure and glomerular filtration rate. Albumin excretion was increased to the same extent in the sorbinil-treated and in the untreated diabetic rats. We conclude that increased metabolism of glucose to sorbitol does not cause the hyperfiltration in rats with streptozotocin-induced diabetes.