| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Clinical Studies |
Department of Internal Medicine, University of New Mexico Health Sciences Center (V.O.S., Y.S., M.B., P.G.Z.) Albuquerque 87131; the Veterans Administration Medical Center (R.I.D.), Albuquerque, New Mexico 87108
Address all correspondence and requests for reprints to: Dr. Philip Zager, Department of Internal Medicine, University of New Mexico Health Sciences Center, Fifth Floor ACC, 2211 Lomas NE, Albuquerque, New Mexico 87131.
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
Considerable interest has focused on the enzyme aldose reductase (AR) as a candidate gene product. AR catalyzes the NADPH-dependent reduction of sugar aldehydes to their corresponding sugar polyols. The polyol pathway is present in lens (12, 13), eye (14), nerve (15), and kidney (14, 16) and has been implicated in the pathogenesis of cataract formation (17, 18), retinopathy (19), neuropathy (20), and nephropathy (21, 22, 23). In contrast, Bondy et al., using in situ hybridization histochemistry, was unable to detect AR messenger ribonucleic acid (mRNA) in renal cortex (24). However, we demonstrated significant quantities of both AR immunoreactive protein (IRP) and AR mRNA in the renal cortex, intact glomeruli, and cultured mesangial cells of rats (25, 26). Other investigators have also demonstrated the polyol pathway in mesangial cells (27). We reported the presence of polyol-dependent regulation of AR gene expression in renal cortex (25). Elevated AR levels occur in neutrophils (28), erythrocytes (29, 30), and mononuclear cells (31) isolated from patients with diabetic complications. Hamada et al. reported that diabetics who developed severe complications in less than 20 yr had the highest red blood cell (RBC) AR activity. In contrast, long standing diabetics, with no complications, had the lowest RBC AR activity (29).
The present study explores the hypothesis that AR gene expression is increased in peripheral blood mononuclear cells (PBMC) obtained from patients with KDDM compared to those from diabetics without KDDM. To test this hypothesis we studied four groups of volunteers: group I, controls (normal subjects); group II, IDDM without nephropathy; group III, IDDM with KDDM; and group IV, nondiabetic kidney disease. Volunteers were classified as having overt kidney disease if they had a serum creatinine level above 1.5 g/dL and/or a urinary protein/creatinine ratio (UPCR) above 0.3.
| Subjects and Methods |
|---|
|
|
|---|
The protocol was approved by the human subject research review committee of the University of New Mexico Health Sciences Center. Informed written consent was obtained from all volunteers. We studied four groups of volunteers (n = 81): group I, normal subjects without evidence of renal disease (n = 25); group II, IDDM with no evidence of KDDM (n = 19); group III, IDDM with overt KDDM (n = 19); and group IV, nondiabetic with renal disease (n = 18). A complete medical history and physical examination were performed on each volunteer. Three random daytime spot urine samples were obtained from each participant for determination of the UPCR. Serum creatinine and glycosylated hemoglobin (Glyc Hgb) were measured in venous blood obtained from a forearm vein. Subjects were classified into normoglycemic and diabetic categories according to WHO criteria.
Specific ribonuclease (RNase) protection assay for measuring AR-mRNA in PBMC
PBMCs were isolated by Ficoll-Hypaque density gradient centrifugation. Human AR complementary RNA (cRNA) probe was generated from the 3'-untranslated region of human AR by restriction digestion of the pGEM3 plasmid containing human placental AR complementary DNA (cDNA) with Sau3AI. A 222-nucleotide Sau3AI-EcoRI antisense cRNA was transcribed from 1 µg template DNA using the T7 RNA polymerase (Promega, Madison, WI) to a specific activity of 5 to 10 x 109 cpm/µg RNA. A second probe, derived from human ß-actin cDNA, was included in all hybridizations to control for variability in the amount of RNA loaded and the efficiency of hybridization. The human ß-actin probe was prepared by subcloning the KpnI-EcoRI fragment of human ß-actin into the SmaI site of the pTRIPLEscript vector (Ambion, Woodward, TX) in a sense orientation. The ß-actin plasmid was digested with DdeI, and the cRNA probe was transcribed with T7 RNA polymerase to yield a cRNA protecting a 129-nucleotide mRNA fragment of human ß-actin. Probe preparation was performed as described above, except that cold uridine triphosphate (20 µmol/L, final concentration) was included in the reaction to decrease the specific activity to approximately 30-fold. This reduced the differences in signal intensities that might have occurred given the large molar excess of ß-actin relative to AR mRNA in PBMC.
The DNA template was removed by the addition of 1 U RNase-free deoxyribonuclease I (Ambion, Austin, TX), followed by phenol-chloroform extraction. Free nucleotides were removed by spin chromatography with Sephadex G-50, and the probe was ethanol precipitated with 10 µg transfer RNA carrier, resuspended in formamide loading buffer, denatured at 95 C, and isolated by autoradiography on 5% denaturing PAGE containing 7 mol/L urea. AR and ß-actin probes (20,000 cpm each) and 5 µg total cellular RNA samples were coprecipitated in 70% ethanol and resuspended in hybridization buffer. RNA was denatured at 85 C for 10 min, hybridized for 16 h at 45 C, and subsequently digested in 10 mmol/L Tris-HCl (pH 7.5), 300 mmol/L NaCl, and 5 mmol/L ethylenediamine tetraacetate containing 1500 U/mL RNase T1 (Ambion, Austin, TX) at 37 C for 1 h. RNase activity was extinguished by a 15-min incubation at 37 C after the addition of 10 µL 10% SDS and 2 µL 20 mg/mL proteinase K followed by phenol-chloroform extraction. RNA was precipitated and separated on a 7 mol/L urea-PAGE gel. Gels were dried and exposed to x-ray film with Cronex intensifying screens at -70 C for autoradiography for 24 h.
Specific AR and ß-actin mRNA signals were quantitated after 3- to 6-h exposure of gels to a ß-sensitive PhosphorImager (Molecular Dynamics, Sunnyvale, CA). To facilitate direct comparison results from separate gels, RNase protection assays for each experiment were run using the same preparation of cRNA probes, thus with the same specific activity. Molar ratios were determined by correcting AR and ß-actin signals derived from the PhosphorImager for differences in specific activity and relative mass of the respective cRNA probes. In vitro transcribed AR cRNA probe was not hybridized to aldehyde reductase cDNA plasmid, confirming the specificity of the probe to AR mRNA. The interassay coefficient of variation of the AR RNase protection assay was 8.3%.
Clinical chemistry methods
Glyc Hgb was measured using an ion capture assay for quantitative measurement of the percent glycosylated hemoglobin, run on an Abbott IMX (Abbott Laboratories, North Chicago, IL). The procedure is a boronate affinity binding assay and detects all glycated hemoglobin species. The assay has a strong linear correlation with hemoglobin A1c-specific methods (32). Serum and urinary creatinine were measured on a Boehringer Mannheim/Hitachi 737 analyzer (Boehringer Mannheim, Indianapolis, IN; Hitachi, Tokyo, Japan), using a kinetic alkaline picrate modified Jaffes reaction (33). Urinary protein was measured on a Boehringer Mannheim/Hitachi 717 analyzer by a direct method that shows similar reactivities to albumin and globulin and has no interference from magnesium ions (34).
Statistical analysis
Statistical analyses were performed with SAS. To explore the hypothesis that heterogeneity of AR gene expression exists, we computed the mean, median, and 95% CI for each group. Values between groups were compared using ANOVA for normally distributed data and ANOVA for ranks (Wilcoxon rank sum test) for data that were not normally distributed. When differences were identified, we used multiple range tests to locate the differences. Multiple linear regression was used to test for the association of elevated AR/ß-actin molar ratios with KDDM. The general linear models procedure was used to test for an association between AR/ß-actin levels and age, gender, ethnicity, Glyc Hgb, serum creatinine, and UPCR. The least square mean of the AR/ß-actin molar ratio was calculated, adjusting for age, gender, and ethnicity. Results were considered statistically significant when P < 0.05.
| Results |
|---|
|
|
|---|
We studied 45 men and 36 women, aged 45 \ 12 yr (mean
\ SD), ranging from 2374 yr (Table 1
).
Although ANOVA indicated that the age difference among the four groups
attained statistical significance (P = 0.045), the
Student-Newman-Keuls test did not identify any pairwise comparisons
between groups as being statistically significant (P =
NS). However, the mean age (49 yr) for the combined groups with kidney
disease (groups III and IV) was higher than that for the combined
groups without kidney disease (groups I and II; P <
0.01). The body mass index and Glyc Hgb levels, respectively, were
similar in groups II and III (P = NS). The mean
arterial pressure was higher in group III than in group IV
(P < 0.05). The durations of diabetes were similar in
groups II and III (P = NS). Serum creatinine and UPCR,
respectively, were similar in groups III and IV (P =
NS).
|
We used serial dilutions of human kidney RNA to establish the
linearity of the AR and ß-actin assays (Fig. 1
). Data
are expressed as AR/ß-actin molar ratios to control for the amount of
RNA loaded. The molar ratio was constant (0.067 \ 0.005) over the
range of mRNA concentrations evaluated. The molar ratio in PBMC
obtained from normal subjects (0.045 \ 0.028) was approximately
30% of that in normal human kidney (P < 0.01),
consistent with the relative abundance of AR mRNA and protein (25). The
adjustment of AR mRNA for differences in ß-actin was necessary due to
differences in RNA yields between samples.
|
|
|
| Discussion |
|---|
|
|
|---|
The etiology of the higher AR mRNA levels observed in KDDM in the present study is uncertain. A selection process may be operative in vitro that favors the survival of PBMC with high or low levels of AR expression. Alternatively, changes in the stability of AR mRNA may contribute to the differences in the AR mRNA levels observed. However, recent evidence suggests that alterations in AR activity most likely reflect either heterogeneity of gene expression or the presence of significant polymorphism of the structural AR gene. Structural polymorphism could lead to alterations in protein structure and activity, which may result in a disparity between levels of AR-mRNA and AR-IRP. Ko et al. reported an association between the AR gene polymorphism and early-onset diabetic retinopathy in NIDDM patients among the Chinese population in Hong Kong (35). Specifically, they described the association of a specific allele (Z-2) of the dinucleotide repeat sequence located near the promoter region of the AR gene. We recently reported preliminary evidence that KDDM in Hispanics is associated with the Z-2 allele and high AR mRNA levels (36). Similarly, Hessom reported the association of KDDM and the Z-2 allele in Caucasians with KDDM (37). However, the results of the present investigation and other cross-sectional studies (35, 36, 37) do not establish causation. Increased AR expression may merely segregate with KDDM rather than have a role in its pathogenesis. The establishment of causation will require a prospective longitudinal study.
Absolute AR and ß-actin levels were widely variable within and between groups. Therefore, the high AR/ß-actin ratios observed in group III could reflect an increase in AR mRNA and/or a decrease in ß-actin mRNA. However, as ß-actin is constitutively expressed in PBMC, our results probably reflect increased AR expression. The duration of diabetes may modulate AR expression. Hyperglycemia increases flux through the polyol pathway; therefore, the effect of hyperglycemia on AR expression may increase with time. However, in the present study, the effects of both hyperglycemia and duration of diabetes on AR expression appear modest. AR/ß-actin ratios were similar in groups I and II, and the durations of diabetes were similar in groups II and III.
Transgenic mice, overexpressing the AR gene, may have an increased susceptibility to polyol-dependent complications (38, 39). Yamaoka et al. (40) investigated pathologic changes in transgenic mice with human AR cDNA driven by the murine MHC class I molecule promoter. Human AR mRNA was present in all tissues tested. However, as glucose feeding failed to increase renal sorbitol content, the functional integrity of the polyol pathway in this model is uncertain. Moreover, histopathological examination of the kidney revealed multiple thrombi and fibrinous deposits, but no evidence of glomerular hypertrophy or an increase in mesangial matrix. Lee et al. (39) recently demonstrated that overexpression of AR in lens epithelial cells of transgenic mice leads to polyol accumulation and the formation of sugar cataracts. When the sorbitol dehydrogenase-deficient mutation is also present in this model, there is greater accumulation of sorbitol and further acceleration of cataract formation.
Studies in rats with streptozotocin-induced diabetes (STZ-D) have linked the polyol pathway to the morphological and hemodynamic changes characteristic of KDDM (27, 41). The polyol content of glomeruli is increased 10-fold 6 weeks after the induction of STZ-D (42). Administration of AR inhibitors (ARI) decreases the glomerular hyperfiltration and mesangial expansion observed in STZ-D rats (43, 44, 45). Human studies also support a role for AR in the pathogenesis of KDDM (21, 22, 23, 39, 43, 44, 45, 46). The administration of ponalrestat (45) and tolrestat (46) to IDDM patients decreases the glomerular filtration rate and the urinary protein excretion rate. ARI administration normalizes RBC sorbitol in vivo in patients with IDDM (44).
Additional studies are necessary to assess the relationship between AR expression in PBMC and microdissected glomeruli. If there is a strong positive correlation, we will have a minimally invasive method to identify those diabetics who are at high risk for nephropathy. The presence of a strong positive correlation between AR and coll IV expression in microdissected glomeruli would provide a mechanistic link between the polyol pathway and the development of glomerulosclerosis. In summary, the present study suggests that the degree of AR gene expression in PBMC correlates with KDDM. If these observations are confirmed, an effort should be made to develop ARIs with improved tissue availability as well as AR antisense mRNAs to decrease AR expression in target tissues.
| Acknowledgments |
|---|
| Footnotes |
|---|
Received December 18, 1996.
Revised March 5, 1997.
Accepted April 2, 1997.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
M. Xu, X. Chen, L. Yan, H. Cheng, and W. Chen Association between (AC)n dinucleotide repeat polymorphism at the 5'-end of the aldose reductase gene and diabetic nephropathy: a meta-analysis J. Mol. Endocrinol., May 1, 2008; 40(5): 243 - 251. [Abstract] [Full Text] [PDF] |
||||
![]() |
B. Yang, A. D. Hodgkinson, P. J. Oates, H. M. Kwon, B. A. Millward, and A. G. Demaine Elevated activity of transcription factor nuclear factor of activated T-cells 5 (NFAT5) and diabetic nephropathy. Diabetes, May 1, 2006; 55(5): 1450 - 1455. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. R. Danielson, V. Carelli, G. Tan, A. Martinuzzi, A. H. V. Schapira, M.-L. Savontaus, and G. A. Cortopassi Isolation of transcriptomal changes attributable to LHON mutations and the cybridization process Brain, May 1, 2005; 128(5): 1026 - 1037. [Abstract] [Full Text] [PDF] |
||||
![]() |
B. F. Schrijvers, A. S. De Vriese, and A. Flyvbjerg From Hyperglycemia to Diabetic Kidney Disease: The Role of Metabolic, Hemodynamic, Intracellular Factors and Growth Factors/Cytokines Endocr. Rev., December 1, 2004; 25(6): 971 - 1010. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Wendt, N. Tanji, J. Guo, B. I. Hudson, A. Bierhaus, R. Ramasamy, B. Arnold, P. P. Nawroth, S. F. Yan, V. D'Agati, et al. Glucose, Glycation, and RAGE: Implications for Amplification of Cellular Dysfunction in Diabetic Nephropathy J. Am. Soc. Nephrol., May 1, 2003; 14(5): 1383 - 1395. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. I. Whiteside and J. A. Dlugosz Mesangial cell protein kinase C isozyme activation in the diabetic milieu Am J Physiol Renal Physiol, June 1, 2002; 282(6): F975 - F980. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Endocrinology | Endocrine Reviews | J. Clin. End. & Metab. |
| Molecular Endocrinology | Recent Prog. Horm. Res. | All Endocrine Journals |