Progression of diabetic nephropathy: role of plasma homocysteine and plasminogen activator inhibitor-1

Homocysteine and diabetes: Role in macrovascular and microvascular complications

Diabetes mellitus (DM) can lead to the development of macro- and microvascular complications. Homocysteine (Hcy) may play a role in the development of cardiovascular (CV) diseases (CVDs). The role of Hcy in the development of the vascular complications associated with DM is not clearly defined. Despite a strong initial assumption regarding the importance of Hcy in DM and its complications, over time "enthusiasm has waned" because several studies showed unconvincing and occasionally contradictory results. A universal conclusion is not easy to draw given the diversity of studies (e.g. number of patients, design, folic acid and vitamin B status, ethnic differences, genetic background). For some complications, most results encourages further investigation. Impaired renal function is a major independent determinant of high total Hcy (tHcy) levels. However, the role of hyperhomocysteinaemia (HHcy) in the development of diabetic kidney disease (DKD) has yet to be determined. Hcy-lowering therapies can significantly decrease Hcy levels but their effects on CVD risk reduction are conflicting. Further studies are needed to determine the influence of Hcy-lowering therapy on CVD risk reduction, especially in patients with DM.

Genetically elevated circulating homocysteine concentrations increase the risk of diabetic kidney disease in Chinese diabetic patients

Diabetic kidney disease (DKD) is a devastating and frequent complication of diabetes mellitus. Here, we first adopted methylenetetrahytrofolate reductase (MTHFR) gene C677T polymorphism as an instrument to infer the possible causal relevance between circulating homocysteine and DKD risk in a Chinese population and next attempted to build a risk prediction model for DKD. This is a hospital‐based case‐control association study. Total 1107 study participants were diagnosed with type 2 diabetes mellitus, including 547 patients with newly diagnosed and histologically confirmed DKD. MTHFR gene C677T polymorphism was determined using the TaqMan method. Carriers of 677TT genotype (14.55 μmol/L) had significantly higher homocysteine concentrations than carriers of 677CT genotype (12.88 μmol/L) (P < 0.001). Carriers of 677TT genotype had a 1.57‐fold increased risk of DKD (odds ratio: 1.57, 95% CI: 1.21‐2.05, P = 0.001) relative to carriers of 677CT genotype after adjusting for confounders. Mendelian randomization analysis revealed that the odds ratio for DKD relative to diabetes mellitus per 5 μmol/L increment of circulating homocysteine concentrations was 3.86 (95% confidence interval: 1.21‐2.05, P < 0.001). In the Logistic regression analysis, hypertension, homocysteine and triglyceride were significantly associated with an increased risk of DKD and they constituted a risk prediction model with good test performance and discriminatory capacity. Taken together, our findings provide evidence that elevated circulating homocysteine concentrations were causally associated with an increased risk of DKD in Chinese diabetic patients.

Hyperhomocysteinemia Causes Chorioretinal Angiogenesis with Placental Growth Factor Upregulation

Hyperhomocysteinemia is a risk factor for atherosclerosis, which may also be associated with retinal vascular disease, diabetic retinopathy, retinal vein occlusion, and glaucoma. For this study, we established a hyperhomocysteinemia animal model to explore homocysteine (hcy)-related choroidal angiogenesis and possible related factors. We injected Sprague Dawley (SD) rats with different concentrations of hcy and performed color fundus imaging, fluorescein angiography, image-guided optical coherence tomography, and retinal histology to observe the retinal and choroidal changes. Subsequently, we observed prominent choroidal vasculature with congested and tortuous retinal and choroidal vessels in fundus angiographies of the hyperhomocysteinemia animal model. In the histological study, the choroidal capillaries proliferated in the hcy-treated eyes, mimicking choroidal neovascularization. Disrupted retinal pigment epithelium (RPE), abnormal branching vascular network (BVN), and polyp-like structures were also observed in the hcy-treated eyes. Furthermore, we found that placental growth factor (PlGF), but not vascular epithelial growth factor (VEGF), was the key mediating factor of this phenomenon. Our findings suggest that hyperhomocysteinemia might cause choroidal angiogenesis.

Clinical value of inflammatory urinary biomarkers in overt diabetic nephropathy: a prospective study

AIMS

The evolution of diabetic nephropathy is incompletely accounted by current clinical tools. New biomarkers may refine patient assessment and help monitor therapy. We compared the added predictive value of 7 candidate inflammatory urinary biomarkers to known risk factors of progression.

METHODS

We prospectively followed 83 patients with overt diabetic nephropathy for a median 2.1 years and obtained repeated measurements of proteinuria, IL-1β, IL-6, IL-8, MCP-1, TNF-α, TGF-β1, and PAI-1.

RESULTS

Patients had an initial estimated glomerular filtration rate of 25 ± 9 mL/min/1.73 m(2), blood pressure of 142/69 mmHg and used a median of 4 anti-hypertensive medications over the course of the study. The observed rate of renal function decline was 2.9 ± 3.0 mL/min/1.73 m(2)/year. All urinary biomarkers levels were collinear and for each one except IL-1β, elevated levels predicted a more rapid progression. MCP-1 was the only biomarker increasing during follow-up, which also correlated with a worst outcome. Using multivariate linear regression adjusting for clinical risk factors of progression, urinary MCP-1 and TGF-β1 predicted progression independently and additively to the degree of proteinuria. We dichotomized these 3 biomarkers and observed a renal function decline with 0, 1, 2 or 3 elevated biomarkers of -0.8 ± 1.4, -2.1 ± 2.1, -4.2 ± 2.8 and -6.0 ± 2.8 mL/min/1.73 m(2)/year, respectively (p<0.001).

CONCLUSIONS

Multiple urinary biomarkers predict outcome in overt diabetic nephropathy. However, urinary MCP-1 and TGF-β1 are also independent and additive to proteinuria in predicting the rate of renal function decline and could serve as useful clinical tools in patient risk stratification.

Plasminogen activator inhitor-1 associates with cardiovascular risk factors in healthy young adults in the Cardiovascular Risk in Young Finns Study

AIMS

Hypofibrinolysis displayed by elevated serum plasminogen activator inhibitor 1 (PAI-1) level has been associated with cardiovascular disease (CVD) and its risk factors such as obesity and insulin resistance. However, no studies have examined associations between PAI-1 and CVD risk factors in healthy subjects. We examined associations between serum PAI-1, ultrasound markers of atherosclerosis and CVD risk factors and whether PAI-1 improves prediction of atherosclerosis over known risk factors in a cohort of asymptomatic adults.

METHODS

We analyzed PAI-1 and CVD risk factors and assessed carotid intima-media thickness (cIMT), distensibility (CDist) and the presence of a carotid atherosclerotic plaque and flow-mediated dilation (FMD) ultrasonographically for 2202 adults (993 men and 1,209 women, aged 30-45 years) participating in the ongoing longitudinal cohort study, The Cardiovascular Risk in Young Finns Study. High cIMT was defined as >90th percentile and/or carotid plaque and low CDist and low FMD as <20th percentile.

RESULTS

In bivariate analyses, PAI-1 correlated directly with cIMT and the risk factors: blood pressure, BMI, waist and hip circumference, alcohol use, total and LDL-cholesterol, triglycerides, glomerular filtration rate, high-sensitivity CRP and glucose (all P<0.005). PAI-1 was higher in men and increased with age. Inverse correlation was observed with CDist, HDL-cholesterol and adiponectin in both sexes, with testosterone and sex hormone binding globulin in men and with creatinine and oral contraceptive use in women (P<0.005). Independent direct associations were observed between PAI-1 and waist circumference, serum triglycerides, insulin, alcohol use and age and inverse with serum creatinine, HDL-cholesterol and adiponectin. PAI-1 did not improve estimation of high cIMT, low CDist and low FMD over conventional risk factors (P for difference in area under curve ≥ 0.37).

CONCLUSION

PAI-1 was independently associated with several known CVD risk factors, especially obesity markers, in both men and women. However, addition of PAI-1 to known risk factors did not improve cross-sectional prediction of high cIMT, low CDist and low FMD suggesting that PAI-1 is not a clinically important biomarker in early atherosclerosis.

Plasma homocysteine is adversely associated with glomerular filtration rate in asymptomatic black and white young adults: the Bogalusa heart study

That plasma homocysteine is elevated markedly in renal dysfunction is well recognized. But whether the increased homocysteine is an independent correlate of glomerular filtration rate, a marker of renal function, in asymptomatic younger individuals is not clear. The aim of this study was to determine the association between plasma homocysteine and renal function in a biracial (black-white) community-based cohort of asymptomatic young adults. Plasma homocysteine along with cardiovascular disease risk factor variables were measured in 805 white and 330 black subjects, ages 24-44 years, enrolled in the Bogalusa Heart Study. Modification of Diet in Renal Disease Study equation was used to calculate the estimated glomerular filtration rate (eGFR) from serum creatinine level. Males versus females showed higher homocysteine levels (8.83 +/- 3.16 vs. 7.35 +/- 2.84 micromol/L, p < 0.0001) and lower eGFR (99.1 +/- 17.6 vs. 102.5 +/- 21.0 mL/min/1.73 m(2), p = 0.024). Whites versus blacks had lower eGFR (97.3 +/- 18.0 vs. 110.0 +/- 20.6 mL/min/1.73 m(2), p < 0.0001). In a multivariate regression analysis that included age, race, sex, body mass index, blood pressure, lipoprotein variables, insulin resistance index and homocysteine, white race, age and homocysteine, in that order, were independently and negatively associated with eGFR. The odds ratio (95% confidence interval) of individuals in the homocysteine quintiles II, III, IV and V vs. I for having the risk of impaired eGFR defined as <10th percentile was 2.28 (0.95-5.50, p = 0.065), 2.97 (1.24-7.12, p = 0.015), 3.32 (1.45-7.60, p = 0.005) and 6.99 (3.06-15.94, p < 0.0001), respectively. Homocysteine is an independent correlate of renal function in asymptomatic black and white young adults.

The Lipid lowering and Onset of Renal Disease (LORD) Trial: a randomized double blind placebo controlled trial assessing the effect of atorvastatin on the progression of kidney disease

Background

There is evidence that dyslipidemia is associated with chronic kidney disease (CKD). Experimental studies have established that lipids are damaging to the kidney and animal intervention studies show statins attenuate this damage. Small clinical trials, meta-analyses, observational studies and post-hoc analyses of cardiovascular intervention studies all support the concept that statins can reduce kidney damage in humans. Based on this background, a double blind randomized placebo controlled trial was designed to assess the effectiveness of atorvastatin 10 mg on slowing the progression of kidney disease in a population of patients with CKD.

Method/Design

The Lipid lowering and Onset of Renal Disease (LORD) trial is a three-year, single center, multi-site, double blind, randomized, placebo controlled trial. The primary outcome measure is kidney function measured by eGFR calculated by both Modification of Diet in Renal Disease (MDRD) and Cockcroft and Gault equations. Secondary outcome measures include kidney function measured by 24-hour urine creatinine clearance and also 24-hour urinary protein excretion, markers of oxidative stress, inflammation and drug safety and tolerability.

Discussion

The results of this study will help determine the effectiveness and safety of atorvastatin and establish its effects on oxidative stress and inflammation in patients with CKD.

Trial Registration

ANZCTRN012605000693628

Plasminogen Activator Inhibitor-1 Deficiency Has Renal Benefits but Some Adverse Systemic Consequences in Diabetic Mice

BACKGROUND

Elevated plasma levels of plasminogen activator inhibitor-1 (PAI-1) are observed in patients with obesity, hypertension and diabetes, and several observations suggest that PAI-1 mediates diabetic vascular complications. Although increased intrarenal expression of PAI-1 is also a feature of diabetic nephropathy, evidence that PAI-1 plays a primary pathogenetic role in the renal pathology is lacking.

METHODS

This study was designed to investigate the renal effects of genetic PAI-1 deficiency in db/db mice with obesity, hyperinsulinemia and hyperglycemia. For comparison the effects of PAI-1 deficiency were also examined in a cohort of mice with insulin-deficient streptozotocin (STZ)-induced diabetes. The findings are reported for 4 study groups at 8 months of age: PAI-1+/+ controls, PAI-1+/+ diabetics, PAI-1-/- controls and PAI-1-/- diabetics.

RESULTS

PAI-1 deficiency had an unexpected negative impact on the db/db mice. Overall 33% of the diabetic mice died prematurely, and 63% of the db/db PAI-1-/- males had an obese body habitus but were runts. The final analyses were limited to the female db/db mice. Several nephropathy parameters were improved in the db/db PAI-1-/- group compared to the db/db PAI-1+/+ group including: albumin-to-creatinine ratios (57 +/- 45 vs. 145 +/- 71 microg/mg x10), change in glomerular extracellular matrix (ECM) area (decrease of 10% compared to controls vs. an increase of 31%) and increased total kidney collagen (47% increased vs. 96% in the PAI-1+/+ diabetics). The serum glucose levels were 15-25% lower in the PAI-1-/- nondiabetic control groups and remained lower in the db/dbPAI-1-/- mice. The STZ study was performed in males. None of the mice developed a runted phenotype or died prematurely. After diabetes of 6 months' duration changes in glomerular ECM area (-15 vs. +64%) and total kidney collagen (+8 vs. +40%) were lower in the PAI-1-/- mice compared to the PAI-1+/+ mice. The serum cholesterol levels were significantly lower in the PAI-1-/- mice, both controls (47 +/- 3 vs. 53 +/- 10 mg/dl) and diabetics (48 +/- 3 vs. 74 +/- 9 mg/dl).

CONCLUSION

These data suggest a direct role for PAI-1 in renal matrix expansion and metabolic control in diabetes, but they also highlight important adverse outcomes that include male runting and premature death in mice with diabetes due to an inactive leptin receptor.

Relationship between homocysteine and mortality in chronic kidney disease

BACKGROUND

The relationship between total homocysteine (tHcy) and outcomes has not been investigated in patients with chronic kidney disease stages 3 to 4.

METHODS AND RESULTS

The Modification of Diet in Renal Disease Study was a randomized, controlled trial of 840 patients. Serum tHcy was measured in frozen samples collected at baseline (n=804). Survival status and cause of death were obtained from the National Death Index. To evaluate its association with all-cause and cardiovascular disease (CVD) mortality, tHcy was evaluated both as tertiles (<14.7, 14.7 to 19.5, > or =19.6 micromol/L) and as a continuous variable (per 10/micromol/L). Participants had a mean age of 52+/-12 years and glomerular filtration rate (GFR) of 33+/-12 mL/min per 1.73 m2; 60% were male, and 85% were white. During a median follow-up of 10 years, 195 (24%) died from any cause, and 118 (15%) from CVD. The level of GFR was lower and proteinuria higher in the highest tHcy tertile. There was no association between the highest tertile of tHcy and all-cause (hazard ratio [HR]; 95% confidence interval [CI[, 1.32, 0.94 to 1.85) or CVD (HR; 95% CI, 1.50, 0.96 to 2.34) mortality in univariate analyses; this association was further attenuated by adjustment for GFR (HR; 95% CI all-cause, 1.04, 0.72 to 1.51; CVD, 1.20, 0.73 to 1.95). There was no association between tHcy as a continuous variable and all-cause (0.98, 0.83 to 1.16) or CVD (1.04, 0.85 to 1.27) mortality.

CONCLUSIONS

Hyperhomocystinemia does not appear to be a risk factor for all-cause or CVD mortality in the Modification of Diet in Renal Disease Study. Prior studies demonstrating an association between tHcy and CVD risk may have inadequately adjusted for the confounding effects of kidney function.

Homocysteine and vascular disease in diabetes: a double hit?

Cardiovascular disease is a major problem in diabetes, and risk factors presumably unrelated to diabetes, such as hyperhomocysteinaemia, may be related to the development of cardiovascular complications in diabetic individuals. Plasma homocysteine levels are usually normal in diabetes, although both lower and higher levels have been reported. Homocysteine levels in diabetes are modulated by hyperfiltration and renal dysfunction, as well as low folate status. Insulin resistance does not appear to be a major determinant of plasma homocysteine level. Hyperhomocysteinaemia has been associated with microalbuminuria and retinopathy in type 1 and type 2 diabetes. In patients with type 2 diabetes, plasma homocysteine concentration is a significant predictor of cardiovascular events and death. This relation seems to be stronger in subjects with diabetes than without. The underlying pathophysiological mechanism of this increased vascular risk remains unexplained, but may be related to worsening of endothelial dysfunction and/or structural vessel properties induced by oxidative stress. Because homocysteine and diabetes have apparent synergistic detrimental vascular effects, patients with diabetes are candidates for screening and treatment with folic acid until the results of ongoing clinical trials are available.

Smoking and progression of diabetic nephropathy in type 1 diabetes

OBJECTIVE

Cigarette smoking contributes to development of diabetic nephropathy. However, long-term studies on the effect of smoking on decline in kidney function in diabetic nephropathy are lacking. We assessed the impact of smoking on progression of diabetic nephropathy in type 1 diabetic patients enrolled in a prospective observational cohort study started in 1983.

RESEARCH DESIGN AND METHODS

We identified all albuminuric type 1 diabetic patients (n = 301) followed for at least 3 years, median (range) 7 years (3-14), who underwent at least yearly measurement of glomerular filtration rate (GFR) by the (51)Cr-EDTA plasma clearance technique (n = 8, range 3-24). In total, 192 men and 109 women were included (age [mean +/- SD] 36 +/- 11 years, duration of diabetes 22 +/- 8 years); 271 patients were treated with antihypertensive drugs, predominantly ACE inhibitors in 179 patients. Patients were classified as smokers if they smoked more than one cigarette per day during a portion of or the entire observation period. Blood pressure, albuminuria, HbA(1c), and serum cholesterol were measured every 3-4 months during the study.

RESULTS

In all 301 patients, the mean (SE) rate of decline in GFR (deltaGFR) was 4.0 (0.2) mlx min(-1) x year(-1) during the investigation period. No difference in Delta GFR was demonstrated between nonsmokers (n = 94), deltaGFR 4.5 (0.4), ex-smokers (n = 31), deltaGFR 3.1 (0.7), and smokers (n = 176), deltaGFR 3.9 (0.3) ml x min(-1) x year(-1), respectively (NS). Adjustment for other risk factors for progression of diabetic nephropathy did not alter the results: smoking was not associated with deltaGFR, whereas blood pressure, albuminuria, HbA(1c), and serum cholesterol were demonstrated to be independent progression promoters.

CONCLUSIONS

In our study, smoking was not associated with decline in kidney function in type 1 diabetic patients with diabetic nephropathy.