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Long-term effect of epalrestat, an aldose reductase inhibitor, on the development of incipient diabetic nephropathy in Type 2 diabetic patients
Journal of Diabetes and Its Complications 15 (2001) 241 – 244
Long-term effect of epalrestat, an aldose reductase inhibitor, on the development of incipient diabetic nephropathy in Type 2 diabetic patients Kaoru Isoa,*, Hisaya Tadaa,b, Koji Kubokia, Toshiki Inokuchia a
Second Department of Internal Medicine, Toho University, School of Medicine, 6-11-1 Omori-Nishi, Ota-ku, Tokyo 143-8541, Japan Department of Internal Medicine, Shironishi Hospital, Shironishi Medical Foundation, 1-15-6 Shironishi, Matsumoto, Nagano 390-8648 Japan
b
Received 22 November 2000; accepted 30 April 2001
Abstract The aim of the present study was to elucidate the long-term effect of epalrestat, an aldose reductase inhibitor (ARI), on renal function in patients with type 2 diabetes mellitus showing microalbuminuria. Patients were allocated to two groups (cases and controls) matched for age, BMI, and the extent of urinary albumin excretion (UAE). Thirty-five type 2 diabetic patients presenting microalbuminuria were included in this study: cases were treated with epalrestat (150 mg/day) for 5 years. No significant changes were found in blood pressure, HbA1c, and total cholesterol in either group during the observation period. In the control group, UAE increased significantly ( P < .01) from 82 ± 12 mg/g Cr at the baseline to 301 ± 111 mg/g Cr at the end of the study, while UAE remained unchanged, 81 ± 15 mg/g Cr at the baseline and 87 ± 19 mg/g Cr at the end of the study, in the epalrestat-treated group. Reciprocal creatinine measured by an enzyme assay decreased significantly ( P < .01) in both groups; however, the reduction rate in the epalrestat-treated group was significantly ( P < .05) smaller than that in the control group. These results suggest the potential usefulness of ARIs in preventing the progression of incipient diabetic nephropathy in patients with type 2 diabetes mellitus. D 2001 Elsevier Science Inc. All rights reserved. Keywords: Aldose reductase inhibitor; Urinary albumin excretion; Renal function; Diabetic nephropathy
1. Introduction An accelerated polyol pathway has been implicated in the pathogenesis and development of diabetic complications including nephropathy. We and other investigators (Craven & DeRubertis, 1989; Derylo et al., 1998; Ishii, Tada, & Isogai, 1998; Kapor-Drezgic et al., 1999; Phillips et al., 1997) have demonstrated that the polyol pathway is potentially linked to diabetes-induced renal cell dysfunction through an increase in de novo synthesis of diacylglycerol (DAG), protein kinase C (PKC) activity, enhanced production of TGF-b1, extracellular matrix proteins, and prostaglandins. Studies (Bank, Mower, Aynedjian, Wilkes, & Silverman, 1989; Goldfarb, Ziyadeh, Kern, & Simmons, 1991; Itagaki et al., 1994; Mauer, Steffes, Azar, & Brown, 1989; McCaleb, McKean, Hohman, Laver, & Robinson, 1991) in rats experimentally rendered diabetic also have shown that the development of hemodynamic and morphological changes in the
* Corresponding author. Tel.: +81-3-3762-4151; fax: +81-3-37638542.
diabetic kidneys are prevented or reversed by the administration of aldose reductase inhibitors (ARIs). Furthermore, it has been reported that 6 months of aldose reductase inhibition resulted in the reduction of glomerular hyperfiltration in type 1 diabetic patients with normo- and microalbuminuria (Passariello et al., 1993; Pedersen, Christiansen, & Mogensen, 1991). However, little is known about the influence of longterm inhibition of aldose reductase on the progression of diabetic nephropathy in type 2 diabetes mellitus. Here, we report preliminary results of a case-control study designed to evaluate the therapeutic effect of epalrestat on urinary albumin excretion (UAE) and renal function in type 2 diabetic patients with microalbuminuria.
2. Methods Thirty-five type 2 diabetic outpatients were selected from the Diabetology Division of our department for this study. The patients were diagnosed as microalbuminuric with a UAE R 30, < 300 mg/g Cr (American Diabetes Association, 2000) on at least three separate occasions over a 3-month
1056-8727/01/$ – see front matter D 2001 Elsevier Science Inc. All rights reserved. PII: S 1 0 5 6 - 8 7 2 7 ( 0 1 ) 0 0 1 6 0 - X
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Table 1 Baseline clinical characteristics and laboratory data of the subjects (epalrestat-treated and control group) Characteristics
Untreated
Treated
Sex (M/F) Age (years) BMI (kg/m2) Known duration of diabetes (years) Therapy (D/OA/In) Retinopathy (N/S/Pre/Pro) Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) HbA1c (%) Serum creatinine (mg/dl) Total cholesterol (mg/dl) Triglyceride (mg/dl) High-density lipoprotein cholesterol (mg/dl) Low-density lipoprotein cholesterol (mg/dl) Urinary albumin excretion (mg/g Cr) Frequency in use of ACEIs (%)
11/11 62.8 ± 2.0 21.8 ± 0.7 12.0 ± 1.6 4/7/11 12/5/4/1 135 ± 3 78 ± 1 7.8 ± 0.3 0.61 ± 0.03 197.4 ± 7.5 114.2 ± 12.1 56.8 ± 3.3 107.1 ± 6.1 82.4 ± 12.1 40.9
7/6 63.2 ± 3.1 22.5 ± 1.0 14.1 ± 1.9 1/7/5 5/2/5/1 134 ± 4 81 ± 2 8.0 ± 0.3 0.64 ± 0.10 186.8 ± 6.5 116.8 ± 10.5 57.3 ± 3.2 116.7 ± 7.2 81.5 ± 15.0 38.5
D: diet, OA: oral agent, In: insulin, N: normal, S: simple, Pre: preproliferative, Pro: proliferative, ACEIs: angiotensin converting enzyme inhibitor.
period at the beginning and were randomly allocated to one of two groups: 13 patients (epalrestat group) were treated with epalrestat (150 mg/day) orally for 5 years, and 22 patients matched for age, BMI, duration of diabetes mellitus, blood pressure, and HbA1c did not receive epalrestat (control group; Table 1). Exclusion criteria: a history of clinically significant liver or hematological disease, the presence of any other renal disease, clinical evidence of autonomic neuropathy, and evidence of symptomatic ischemic heart disease. Their blood pressure, HbA1c, reciprocal serum creatinine, total cholesterol, and UAE were checked annually for 5 years in each group and compared between the two groups at each determination point. All the patients gave their informed consent, and the study protocol was approved by the regional scientific committee.
Fig. 1. Changes in HbA1c levels of microalbuminuric patients treated with (.) and without (6) epalrestat. No significant differences were found in both groups during the observation period. Vertical bars indicate means ± S.E.M.
HbA1c was determined by HPLC and serum creatinine was measured by an enzymatic method. UAE was determined by radioimmunoassay. Data are the mean values of three monthly measurements. Clinical data and parameters of the epalrestat group and the control group were compared by unpaired Student’s t test. The t test for paired comparison was used for analysis of possible changes during the observation period in both groups. Differences were considered statistically significant at P < .05. Data are presented as the mean ± S.E.M.
3. Results All 35 subjects completed the study and were included in the final analysis of data. Basal clinical characteristics and laboratory data are detailed in Table 1. Both groups included seven patients treated with oral hypoglycemic agents and none of them was treated with troglitazone. There were no significant differences in the levels of serum creatinine, total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and UAE between the two groups. Thus, the patients in the two groups were likely to be similar to the degree of renal lesions. In addition, no significant differences were found in the use of angiotensin-converting enzyme inhibitors (ACEIs) between the two groups. Glycemic control, as assessed by HbA1c concentration, in patients treated with epalrestat and control patients was identical during this study. In fact, no significant differences between the basal level of HbA1c and its value at 1, 2, 3, 4, and 5 years were found in either group (Fig. 1). There were no significant differences in HbA1c levels between the two groups during the observation period. Significant differences were found neither in systolic or diastolic blood pressure recorded at baseline nor during the observation period in the two groups (Fig. 2). In addition, no statistical differences were found in total
Fig. 2. Changes in systolic and diastolic blood pressure of microalbuminuric patients treated with (.) and without (6) epalrestat. No significant differences were found in both groups during the observation period. Vertical bars indicate means ± S.E.M.
K. Iso et al. / Journal of Diabetes and Its Complications 15 (2001) 241–244
Fig. 3. Changes in urinary albumin excretion of microalbuminuric patients treated with (.) and without (6) epalrestat. Vertical bars indicate means ± S.E.M. # P < .01 vs. 0 year. * P < .05 vs. patients without epalrestat.
cholesterol levels between the two groups during the study (data not shown). Of the 13 patients in the epalrestat group, 5 were treated with statins. Of the 22 patients in the control group, 6 were treated with statins. Changes in UAE are shown in Fig. 3. In the control group, UAE increased significantly ( P < .01) from 82 ± 12 mg/g Cr at baseline to 301 ± 111 mg/g Cr at 5 years. Seven out of 22 patients developed to overt proteinuria. On the other hand, UAE remained unchanged in the epalrestattreated group during the study. None of the patients in the epalrestat-treated group developed overt proteinuria. As shown in Fig. 4, renal function, expressed as reciprocal creatinine, significantly decreased from the basal value of 1.77 ± 0.12 to 1.38 ± 0.07 ( P < .01) at 5 years in the control group and from the basal value of 1.77 ± 0.11 to 1.55 ± 0.11 ( P < .01) at 5 years in the epalrestat-treated group. The reduction rate of reciprocal creatinine in the epalrestattreated group was significantly ( P < .05) smaller than that in the control group at 5 years.
Fig. 4. Changes in reciprocal creatinine of microalbuminuric patients treated with (.) and without (6) epalrestat. Vertical bars indicate means ± S.E.M. * P < .01 vs. patients without epalrestat.
243
To exclude the influence of ACEIs, the subgroups of patients who had not received ACEIs were further investigated. Thirteen patients in the control group and eight in the epalrestat group were not treated by ACEIs. No significant differences were noted regarding clinical characteristics between the two subgroups. UAE increased from 83 ± 18 mg/g Cr at baseline to 346 ± 83 mg/g Cr at 5 years ( P = .07) in the 13 patients treated without epalrestat, while UAE remained unchanged in the eight patients treated with epalrestat (79 ± 17 mg/g Cr at the baseline, 84 ± 21 mg/g Cr at 5 years). On the other hand, in the 13 patients treated without epalrestat, reciprocal creatinine significantly ( P < .01) decreased from the basal value of 1.76 ± 0.16 to 1.42 ± 0.09 at 5 years, while no significant change was observed in the eight patients treated with epalrestat.
4. Discussion Our study suggests the potential usefulness of ARIs in preventing the progression of diabetic nephropathy in type 2 diabetic patients. Concerning the expected effect of ARIs on diabetic nephropathy, changes in glycemic control, blood pressure and lipid metabolism, and use of ACEIs might act as confounding factors. In this study, HbA1c levels, total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and blood pressure did not change significantly in either group. No significant differences were found in the use of ACEIs between the two groups. In addition, the effect of ACEIs was excluded by the observation of subgroups of nonACEIs-treated patients. Thus, epalrestat administration may have contributed to suppress the increase of UAE and the deterioration of renal function, as evaluated by reciprocal creatinine. Studies in diabetic animals have shown the beneficial effects of ARIs on diabetes-associated hemodynamic and pathophysiological changes in the kidney. ARIs have been shown to prevent or reverse not only hyperperfusion and proteinuria (Bank et al., 1989; Itagaki et al., 1994; McCaleb et al., 1991) but also structural alterations, such as thickness of the glomerular basement membrane (GBM), mesangial expansion and decreased number of anionic sites on GBM in experimental diabetic rats (Isogai, Inokuchi, & Ohe, 1995; Itagaki et al., 1994; Mauer et al., 1989). Our results are consistent with those of a previous report by Passariello et al. (1993) who showed that 6 months of aldose reductase inhibition reduced the characteristic hyperfiltration and UAE rate in type 1 diabetic patients with diabetic nephropathy. Pedersen et al. (1991) have also reported a significant reduction in GFR in hyperfiltering normoalbuminuric type 1 diabetics without changes in UAE or renal vascular resistance. However, it was essential to evaluate the preventive effects of long-term ARIs supplementation on further progression of albuminuria or renal dysfunction. Our study showed that treatment with ARIs
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prevented the increase in UAE, suggesting that aldose reductase inhibition would rather protect type 2 diabetic patients from progression of diabetic nephropathy. Activation of PKC and increase in TGF-b1 by high glucose in kidney glomerular cells are considered to be closely associated with the pathogenesis of diabetic glomerulosclerosis. As to the mechanisms involved in the effect of ARIs on diabetic nephropathy, it is postulated that reduction of NAD + to NADH resulted from increased polyol pathway may be associated with an increase of de novo synthesis of DAG (Tilton et al., 1992) and that DAG activates PKC isoforms. In fact, we have provided a direct evidence of the potential link between PKC and the polyol pathway in cultured human mesangial cells (HMCs) by showing the inhibitory effect of epalrestat on the glucose-induced increase in PKC activity (Ishii et al., 1998). Furthermore, we have shown that the glucose-induced increase in TGF-b1 production from HMC is inhibited by ARIs as a consequence of the suppression of PKC activity (Ishii et al., 1998). In addition, it has been demonstrated that overproduction of extracellular matrix proteins, such as fibronectin and type IV collagen, and increase in prostaglandin synthesis by elevated glucose levels are prevented by ARIs in cultured MCs (Pugliese et al., 1994), proximal tubular cells (Phillips et al., 1997), and in glomeruli isolated from diabetic rats (Craven & DeRubertis, 1989). Thus, ARIs could ameliorate mesangial cell dysfunction induced by high ambient glucose, which may principally contribute to the pathogenesis of diabetic glomerulosclerosis. From these observations, it is conceivable that the protective effect of ARIs in the kidney may be related to changes in the extracellular matrix or prostaglandin production resulting from inhibition of the PKC-TGF-b1 pathway. However, whether aldose reductase inhibition influences the glucoseinduced increase of oxidative stress remains to be explored. In summary, the present study suggests that long-term ARIs treatment may delay or prevent the development of renal dysfunction in type 2 diabetic patients with microalbuminuria. Further prospective, double-blind studies should be performed to define the effect of ARIs on the progression of diabetic nephropathy.
References American Diabetes Association (2000). Diabetic nephropathy. Diabetes Care, 23 (Suppl. 1), S69 – S72 (Position statement).
Bank, N., Mower, P., Aynedjian, H. S., Wilkes, B. M., & Silverman, S. (1989). Sorbinil prevents glomerular hyperperfusion in diabetic rats. American Journal of Physiology, 256, F1000 – F1006. Craven, P. A., & DeRubertis, F. R. (1989). Sorbinil suppresses glomerular prostaglandin production in the streptozotocin diabetic rat. Metabolism, 38, 649 – 654. Derylo, B., Babazono, T., Glogowski, E., Kapor-Drezgic, J., Hohman, T., & Whiteside, C. (1998). High glucose-induced mesangial cell altered contractility: role of the polyol pathway. Diabetologia, 41, 507 – 515. Goldfarb, S., Ziyadeh, F. N., Kern, E. F. O., & Simmons, D. A. (1991). Effects of polyol-pathway inhibition and dietary myo-inositol on glomerular hemodynamic function in experimental diabetes mellitus in rats. Diabetes, 40, 465 – 471. Ishii, H., Tada, H., & Isogai, S. (1998). An aldose reductase inhibitor prevents glucose-induced increase in transforming growth factor-b and protein kinase C activity in cultured human mesangial cells. Diabetologia, 41, 362 – 364. Isogai, S., Inokuchi, T., & Ohe, K. (1995). Effect of an aldose reductase inhibitor on glomerular basement membrane anionic sites in streptozotocin-induced diabetic rats. Diabetes Research and Clinical Practice, 30, 111 – 116. Itagaki, I., Shimizu, K., Kamanaka, Y., Ebata, K., Kikkawa, R., Haneda, M., & Shigeta, Y. (1994). The effect of an aldose reductase inhibitor (Epalrestat) on diabetic nephropathy in rats. Diabetes Research and Clinical Practice, 25, 147 – 154. Kapor-Drezgic, J., Zhou, X., Babazono, T., Dlugosz, J. A., Hohman, T., & Whiteside, C. (1999). Effect of high glucose on mesangial cell protein kinase C-d and -e is polyol pathway-dependent. Journal of the American Society of Nephrology, 10, 1193 – 1203. Mauer, S. M., Steffes, M. W., Azar, S., & Brown, D. M. (1989). Effects of sorbinil on glomerular structure and function in long-term-diabetic rats. Diabetes, 38, 839 – 846. McCaleb, M. L., McKean, M. L., Hohman, T. C., Laver, N., & Robinson, W. G. Jr. (1991). Intervention with the aldose reductase inhibitor, tolrestat, in renal and retinal lesions of streptozotocin-diabetic rats. Diabetologia, 34, 695 – 701. Passariello, N., Sepe, J., Marrazzo, G., De Cicco, A., Peluso, A., Pisano, M. C. A., Sgambato, S., Tesauro, P., & D’Onofrio, F. (1993). Effect of aldose reductase inhibitor (tolrestat) on urinary albumin excretion rate and glomerular filtration rate in IDDM subjects with nephropathy. Diabetes Care, 16, 789 – 795. Pedersen, M. M., Christiansen, J. S., & Mogensen, C. E. (1991). Reduction of glomerular hyperfiltration in normoalbuminuric IDDM patients by 6 mo of aldose reductase inhibition. Diabetes, 40, 527 – 531. Phillips, A. O., Steadman, R., Morrisey, K., Martin, J., Eynstone, L., & Whilliam, J. D. (1997). Exposure of human renal proximal tubular cells to glucose leads to accumulation of type IV collagen and fibronectin by decreased degradation. Kidney International, 52, 973 – 984. Pugliese, G., Pricci, F., Pugliese, F., Mene, P., Lenti, L., Andreani, D., Galli, G., Casini, A., Bianchi, S., Rotella, C. M., & Di Mario, U. (1994). Mechanisms of glucose-enhanced extracellular matrix accumulation in rat glomerular mesangial cells. Diabetes, 43, 478 – 490. Tilton, R. G., Baier, L. D., Harlow, J. E., Smith, S. R., Ostrow, E., & Williamson, J. R. (1992). Diabetes-induced glomerular dysfunction: links to a more reduced cytosolic ratio of NADH/NAD + . Kidney International, 41, 778 – 788.
Long-term effect of epalrestat, an aldose reductase inhibitor, on the development of incipient diabetic nephropathy in Type 2 diabetic patients Kaoru Isoa,*, Hisaya Tadaa,b, Koji Kubokia, Toshiki Inokuchia a
Second Department of Internal Medicine, Toho University, School of Medicine, 6-11-1 Omori-Nishi, Ota-ku, Tokyo 143-8541, Japan Department of Internal Medicine, Shironishi Hospital, Shironishi Medical Foundation, 1-15-6 Shironishi, Matsumoto, Nagano 390-8648 Japan
b
Received 22 November 2000; accepted 30 April 2001
Abstract The aim of the present study was to elucidate the long-term effect of epalrestat, an aldose reductase inhibitor (ARI), on renal function in patients with type 2 diabetes mellitus showing microalbuminuria. Patients were allocated to two groups (cases and controls) matched for age, BMI, and the extent of urinary albumin excretion (UAE). Thirty-five type 2 diabetic patients presenting microalbuminuria were included in this study: cases were treated with epalrestat (150 mg/day) for 5 years. No significant changes were found in blood pressure, HbA1c, and total cholesterol in either group during the observation period. In the control group, UAE increased significantly ( P < .01) from 82 ± 12 mg/g Cr at the baseline to 301 ± 111 mg/g Cr at the end of the study, while UAE remained unchanged, 81 ± 15 mg/g Cr at the baseline and 87 ± 19 mg/g Cr at the end of the study, in the epalrestat-treated group. Reciprocal creatinine measured by an enzyme assay decreased significantly ( P < .01) in both groups; however, the reduction rate in the epalrestat-treated group was significantly ( P < .05) smaller than that in the control group. These results suggest the potential usefulness of ARIs in preventing the progression of incipient diabetic nephropathy in patients with type 2 diabetes mellitus. D 2001 Elsevier Science Inc. All rights reserved. Keywords: Aldose reductase inhibitor; Urinary albumin excretion; Renal function; Diabetic nephropathy
1. Introduction An accelerated polyol pathway has been implicated in the pathogenesis and development of diabetic complications including nephropathy. We and other investigators (Craven & DeRubertis, 1989; Derylo et al., 1998; Ishii, Tada, & Isogai, 1998; Kapor-Drezgic et al., 1999; Phillips et al., 1997) have demonstrated that the polyol pathway is potentially linked to diabetes-induced renal cell dysfunction through an increase in de novo synthesis of diacylglycerol (DAG), protein kinase C (PKC) activity, enhanced production of TGF-b1, extracellular matrix proteins, and prostaglandins. Studies (Bank, Mower, Aynedjian, Wilkes, & Silverman, 1989; Goldfarb, Ziyadeh, Kern, & Simmons, 1991; Itagaki et al., 1994; Mauer, Steffes, Azar, & Brown, 1989; McCaleb, McKean, Hohman, Laver, & Robinson, 1991) in rats experimentally rendered diabetic also have shown that the development of hemodynamic and morphological changes in the
* Corresponding author. Tel.: +81-3-3762-4151; fax: +81-3-37638542.
diabetic kidneys are prevented or reversed by the administration of aldose reductase inhibitors (ARIs). Furthermore, it has been reported that 6 months of aldose reductase inhibition resulted in the reduction of glomerular hyperfiltration in type 1 diabetic patients with normo- and microalbuminuria (Passariello et al., 1993; Pedersen, Christiansen, & Mogensen, 1991). However, little is known about the influence of longterm inhibition of aldose reductase on the progression of diabetic nephropathy in type 2 diabetes mellitus. Here, we report preliminary results of a case-control study designed to evaluate the therapeutic effect of epalrestat on urinary albumin excretion (UAE) and renal function in type 2 diabetic patients with microalbuminuria.
2. Methods Thirty-five type 2 diabetic outpatients were selected from the Diabetology Division of our department for this study. The patients were diagnosed as microalbuminuric with a UAE R 30, < 300 mg/g Cr (American Diabetes Association, 2000) on at least three separate occasions over a 3-month
1056-8727/01/$ – see front matter D 2001 Elsevier Science Inc. All rights reserved. PII: S 1 0 5 6 - 8 7 2 7 ( 0 1 ) 0 0 1 6 0 - X
242
K. Iso et al. / Journal of Diabetes and Its Complications 15 (2001) 241–244
Table 1 Baseline clinical characteristics and laboratory data of the subjects (epalrestat-treated and control group) Characteristics
Untreated
Treated
Sex (M/F) Age (years) BMI (kg/m2) Known duration of diabetes (years) Therapy (D/OA/In) Retinopathy (N/S/Pre/Pro) Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) HbA1c (%) Serum creatinine (mg/dl) Total cholesterol (mg/dl) Triglyceride (mg/dl) High-density lipoprotein cholesterol (mg/dl) Low-density lipoprotein cholesterol (mg/dl) Urinary albumin excretion (mg/g Cr) Frequency in use of ACEIs (%)
11/11 62.8 ± 2.0 21.8 ± 0.7 12.0 ± 1.6 4/7/11 12/5/4/1 135 ± 3 78 ± 1 7.8 ± 0.3 0.61 ± 0.03 197.4 ± 7.5 114.2 ± 12.1 56.8 ± 3.3 107.1 ± 6.1 82.4 ± 12.1 40.9
7/6 63.2 ± 3.1 22.5 ± 1.0 14.1 ± 1.9 1/7/5 5/2/5/1 134 ± 4 81 ± 2 8.0 ± 0.3 0.64 ± 0.10 186.8 ± 6.5 116.8 ± 10.5 57.3 ± 3.2 116.7 ± 7.2 81.5 ± 15.0 38.5
D: diet, OA: oral agent, In: insulin, N: normal, S: simple, Pre: preproliferative, Pro: proliferative, ACEIs: angiotensin converting enzyme inhibitor.
period at the beginning and were randomly allocated to one of two groups: 13 patients (epalrestat group) were treated with epalrestat (150 mg/day) orally for 5 years, and 22 patients matched for age, BMI, duration of diabetes mellitus, blood pressure, and HbA1c did not receive epalrestat (control group; Table 1). Exclusion criteria: a history of clinically significant liver or hematological disease, the presence of any other renal disease, clinical evidence of autonomic neuropathy, and evidence of symptomatic ischemic heart disease. Their blood pressure, HbA1c, reciprocal serum creatinine, total cholesterol, and UAE were checked annually for 5 years in each group and compared between the two groups at each determination point. All the patients gave their informed consent, and the study protocol was approved by the regional scientific committee.
Fig. 1. Changes in HbA1c levels of microalbuminuric patients treated with (.) and without (6) epalrestat. No significant differences were found in both groups during the observation period. Vertical bars indicate means ± S.E.M.
HbA1c was determined by HPLC and serum creatinine was measured by an enzymatic method. UAE was determined by radioimmunoassay. Data are the mean values of three monthly measurements. Clinical data and parameters of the epalrestat group and the control group were compared by unpaired Student’s t test. The t test for paired comparison was used for analysis of possible changes during the observation period in both groups. Differences were considered statistically significant at P < .05. Data are presented as the mean ± S.E.M.
3. Results All 35 subjects completed the study and were included in the final analysis of data. Basal clinical characteristics and laboratory data are detailed in Table 1. Both groups included seven patients treated with oral hypoglycemic agents and none of them was treated with troglitazone. There were no significant differences in the levels of serum creatinine, total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and UAE between the two groups. Thus, the patients in the two groups were likely to be similar to the degree of renal lesions. In addition, no significant differences were found in the use of angiotensin-converting enzyme inhibitors (ACEIs) between the two groups. Glycemic control, as assessed by HbA1c concentration, in patients treated with epalrestat and control patients was identical during this study. In fact, no significant differences between the basal level of HbA1c and its value at 1, 2, 3, 4, and 5 years were found in either group (Fig. 1). There were no significant differences in HbA1c levels between the two groups during the observation period. Significant differences were found neither in systolic or diastolic blood pressure recorded at baseline nor during the observation period in the two groups (Fig. 2). In addition, no statistical differences were found in total
Fig. 2. Changes in systolic and diastolic blood pressure of microalbuminuric patients treated with (.) and without (6) epalrestat. No significant differences were found in both groups during the observation period. Vertical bars indicate means ± S.E.M.
K. Iso et al. / Journal of Diabetes and Its Complications 15 (2001) 241–244
Fig. 3. Changes in urinary albumin excretion of microalbuminuric patients treated with (.) and without (6) epalrestat. Vertical bars indicate means ± S.E.M. # P < .01 vs. 0 year. * P < .05 vs. patients without epalrestat.
cholesterol levels between the two groups during the study (data not shown). Of the 13 patients in the epalrestat group, 5 were treated with statins. Of the 22 patients in the control group, 6 were treated with statins. Changes in UAE are shown in Fig. 3. In the control group, UAE increased significantly ( P < .01) from 82 ± 12 mg/g Cr at baseline to 301 ± 111 mg/g Cr at 5 years. Seven out of 22 patients developed to overt proteinuria. On the other hand, UAE remained unchanged in the epalrestattreated group during the study. None of the patients in the epalrestat-treated group developed overt proteinuria. As shown in Fig. 4, renal function, expressed as reciprocal creatinine, significantly decreased from the basal value of 1.77 ± 0.12 to 1.38 ± 0.07 ( P < .01) at 5 years in the control group and from the basal value of 1.77 ± 0.11 to 1.55 ± 0.11 ( P < .01) at 5 years in the epalrestat-treated group. The reduction rate of reciprocal creatinine in the epalrestattreated group was significantly ( P < .05) smaller than that in the control group at 5 years.
Fig. 4. Changes in reciprocal creatinine of microalbuminuric patients treated with (.) and without (6) epalrestat. Vertical bars indicate means ± S.E.M. * P < .01 vs. patients without epalrestat.
243
To exclude the influence of ACEIs, the subgroups of patients who had not received ACEIs were further investigated. Thirteen patients in the control group and eight in the epalrestat group were not treated by ACEIs. No significant differences were noted regarding clinical characteristics between the two subgroups. UAE increased from 83 ± 18 mg/g Cr at baseline to 346 ± 83 mg/g Cr at 5 years ( P = .07) in the 13 patients treated without epalrestat, while UAE remained unchanged in the eight patients treated with epalrestat (79 ± 17 mg/g Cr at the baseline, 84 ± 21 mg/g Cr at 5 years). On the other hand, in the 13 patients treated without epalrestat, reciprocal creatinine significantly ( P < .01) decreased from the basal value of 1.76 ± 0.16 to 1.42 ± 0.09 at 5 years, while no significant change was observed in the eight patients treated with epalrestat.
4. Discussion Our study suggests the potential usefulness of ARIs in preventing the progression of diabetic nephropathy in type 2 diabetic patients. Concerning the expected effect of ARIs on diabetic nephropathy, changes in glycemic control, blood pressure and lipid metabolism, and use of ACEIs might act as confounding factors. In this study, HbA1c levels, total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and blood pressure did not change significantly in either group. No significant differences were found in the use of ACEIs between the two groups. In addition, the effect of ACEIs was excluded by the observation of subgroups of nonACEIs-treated patients. Thus, epalrestat administration may have contributed to suppress the increase of UAE and the deterioration of renal function, as evaluated by reciprocal creatinine. Studies in diabetic animals have shown the beneficial effects of ARIs on diabetes-associated hemodynamic and pathophysiological changes in the kidney. ARIs have been shown to prevent or reverse not only hyperperfusion and proteinuria (Bank et al., 1989; Itagaki et al., 1994; McCaleb et al., 1991) but also structural alterations, such as thickness of the glomerular basement membrane (GBM), mesangial expansion and decreased number of anionic sites on GBM in experimental diabetic rats (Isogai, Inokuchi, & Ohe, 1995; Itagaki et al., 1994; Mauer et al., 1989). Our results are consistent with those of a previous report by Passariello et al. (1993) who showed that 6 months of aldose reductase inhibition reduced the characteristic hyperfiltration and UAE rate in type 1 diabetic patients with diabetic nephropathy. Pedersen et al. (1991) have also reported a significant reduction in GFR in hyperfiltering normoalbuminuric type 1 diabetics without changes in UAE or renal vascular resistance. However, it was essential to evaluate the preventive effects of long-term ARIs supplementation on further progression of albuminuria or renal dysfunction. Our study showed that treatment with ARIs
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prevented the increase in UAE, suggesting that aldose reductase inhibition would rather protect type 2 diabetic patients from progression of diabetic nephropathy. Activation of PKC and increase in TGF-b1 by high glucose in kidney glomerular cells are considered to be closely associated with the pathogenesis of diabetic glomerulosclerosis. As to the mechanisms involved in the effect of ARIs on diabetic nephropathy, it is postulated that reduction of NAD + to NADH resulted from increased polyol pathway may be associated with an increase of de novo synthesis of DAG (Tilton et al., 1992) and that DAG activates PKC isoforms. In fact, we have provided a direct evidence of the potential link between PKC and the polyol pathway in cultured human mesangial cells (HMCs) by showing the inhibitory effect of epalrestat on the glucose-induced increase in PKC activity (Ishii et al., 1998). Furthermore, we have shown that the glucose-induced increase in TGF-b1 production from HMC is inhibited by ARIs as a consequence of the suppression of PKC activity (Ishii et al., 1998). In addition, it has been demonstrated that overproduction of extracellular matrix proteins, such as fibronectin and type IV collagen, and increase in prostaglandin synthesis by elevated glucose levels are prevented by ARIs in cultured MCs (Pugliese et al., 1994), proximal tubular cells (Phillips et al., 1997), and in glomeruli isolated from diabetic rats (Craven & DeRubertis, 1989). Thus, ARIs could ameliorate mesangial cell dysfunction induced by high ambient glucose, which may principally contribute to the pathogenesis of diabetic glomerulosclerosis. From these observations, it is conceivable that the protective effect of ARIs in the kidney may be related to changes in the extracellular matrix or prostaglandin production resulting from inhibition of the PKC-TGF-b1 pathway. However, whether aldose reductase inhibition influences the glucoseinduced increase of oxidative stress remains to be explored. In summary, the present study suggests that long-term ARIs treatment may delay or prevent the development of renal dysfunction in type 2 diabetic patients with microalbuminuria. Further prospective, double-blind studies should be performed to define the effect of ARIs on the progression of diabetic nephropathy.
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