Importance of glycemic control on the course of glomerular filtration rate in type 2 diabetes with hypertension and microalbuminuria under tight blood pressure control.

BACKGROUND AND AIMS: To evaluate the role of glycemic control on the evolution of glomerular filtration rate (GFR) in type 2 diabetes (T2DM) with mild-moderate hypertension under tight blood pressure control, and to address the current controversy whether diabetic nephropathy worsens, independently of blood pressure, proportionally to HbA1c at any physiological level or only when HbA1c is above a 7.5-8% threshold. METHODS AND RESULTS: T2DM (N=127) during early stage diabetic nephropathy characterized by microalbuminuria were followed during a 2 year multicenter study. Individual GFR profiles were accurately obtained by (51)Cr - EDTA bolus injections and analyzed with linear statistical mixed-effects models. GFR at baseline was significantly negatively correlated with age and plasma creatinine concentration (P

Increased renal arterial resistance predicts the course of renal function in type 2 diabetes with microalbuminuria.

Type 2 diabetic patients often die because of end-stage renal failure, but no definitive reliable factor predicting long-term renal outcome has been identified. We tested whether a renal arterial resistance index (R/I) > or =80, using Doppler ultrasound technique, was predictive of worsening renal function. The primary end points of the study were 1) the course of glomerular filtration rate (GFR) and 2) the albumin excretion rate in 157 microalbuminuric, hypertensive, type 2 diabetic patients after a 7.8-year follow-up period (range 7.1-9.2). Kaplan-Meier curves for the primary end point (decrease of GFR > or = -3.0 ml/min per 1.73 m(2) per year) was two to three times more frequently observed in patients with R/I > or =80. Four- to fivefold fewer patients showed a regression to normoalbuminuria during the follow-up period from baseline microalbuminuria in the cohort with R/I > or =80. Overt proteinuria did develop in 24% of patients with R/I > or =80 and in 5% of patients with R/I <80 (P < 0.01). In conclusion, intrarenal arterial resistance appears to play a nontrivial role in deteriorating renal function in type 2 diabetic patients. R/I is a noninvasive diagnostic procedure, which strongly predicts the outcome of renal function in type 2 diabetic patients, even when GFR patterns are still normal.

Altered transcapillary escape of albumin and microalbuminuria reflects two different pathogenetic mechanisms.

We studied the following in normo- and microalbuminuric hypertensive type 2 diabetic patients: 1) transcapillary escape rate of albumin (TERalb) and 2) expression of mRNA slit diaphragm and podocyte proteins in renal biopsies. Normoalbuminuric subjects had renal cancer, and kidney biopsy was performed during surgery. TERalb was evaluated by clearance of (125)I-albumin. Real-time PCR of mRNA slit diaphragm was measured in kidney specimens. Albumin excretion rate (AER) was by definition lower in normoalbuminuric subjects than in microalbuminuric subjects with typical diabetic glomerulopathy (group 1), in microalbuminuric subjects with normal or near-normal glomerular structure (group 2), and in microalbuminuric subjects with atypical diabetic nephropathy (group 3). This classification was based on light microscopy analysis of renal tissue. TERalb (%/h) was similar in normoalbuminuric and microalbuminuric group 1, 2, and 3 diabetic patients (medians: 14.1 vs. 14.4 vs. 15.7 vs. 14.9, respectively) (ANOVA, NS). mRNA expression of slit diaphragm proteins CD2AP, FAT, Actn 4, NPHS1, and NPHS2 was higher in normoalbuminuric patients than in microalbuminuric patients (groups 1, 2, and 3) (ANOVA, P < 0.001). All diabetic patients had greater carotid artery intimal thickness than normal control subjects using ultrasound technique (ANOVA, P < 0.01). In conclusion, the present study suggests that microalbuminuria identifies a subgroup of hypertensive type 2 diabetic patients who have altered mRNA expression of slit diaphragm and podocyte proteins, even before glomerular structure shows abnormalities using light microscopy analysis. On the contrary, altered TERalb and increased carotid artery intimal thickness are shown by all hypertensive type 2 diabetic patients, both with normal and altered patterns of AER.

The angiotensin-converting enzyme DD genotype is associated with glomerulopathy lesions in type 2 diabetes.

Genetic factors are important in conferring diabetic nephropathy (DN) risk. The insertion/deletion (I/D) polymorphism of the ACE gene has been described to be associated with DN risk and progression. The renal lesions underlying DN in type 2 diabetes are heterogeneous; only a subset of patients, characterized by a faster decline of renal function, have diabetic glomerulopathy. This study explored the relations between diabetic glomerulopathy and the ACE genotype distribution in 77 type 2 diabetic patients with an albumin excretion rate > or = 20 microg/min. Using morphometric analysis of kidney biopsies, mesangial and mesangial matrix fractional volumes [Vv(mes/glom) and Vv(MM/glom)] and glomerular basement membrane (GBM) width were estimated. We found that 13 patients were II, 30 were ID, and 34 were DD. Clinical features and renal function were similar in the three groups; in contrast, the DD patients had the highest Vv(MM/glom) and GBM width. Subdividing patients in tertiles of GBM width and Vv(MM/glom), from the lowest (I) to the highest (III) values, the DD carriers had an odds ratio of 6.11 (95% CI 1.84-20.3) and 10.67 (2.51-45.36), respectively, for the likelihood of being in tertile III than I for GBM width and Vv(MM/glom). Multiple regression analysis revealed the I/D polymorphism as an independent determinant of GBM thickening in addition to diabetes duration and HbA(1c). In conclusion, the ACE DD genotype is associated with diabetic glomerulopathy lesions, making the study of this polymorphism helpful in identifying those type 2 diabetic patients at higher risk of fast DN progression.

Nitric oxide modulation of renal and cardiac hemodynamics in type 2 diabetes.

OBJECTIVE: To evaluate endothelial function in type 2 diabetic patients with and without diabetic nephropathy. METHODS: We studied the effects of systemic infusion of the nitric oxide (NO) synthase inhibitor NG-monomethyl-l-arginine (L-NMMA) on cardiovascular and renal hemodynamics in six type 2 diabetic patients with microalbuminuria (D2-MA), six type 2 diabetic patients with normoalbuminuria (D2-NA) and five control subjects. Both type 2 diabetic patients and control subjects had mild arterial hypertension. RESULTS: L-NMMA infusion decreased the cardiac index in all groups. A reduction in glomerular filtration rate (GFR) and an increase in filtration fraction were observed only in controls. Renal plasma flow decreased in controls and D2-NA patients and renal vascular resistance increased in all groups. CONCLUSIONS: The effect of L-NMMA on cardiac output was similar in controls and type 2 diabetic patients with and without diabetic nephropathy. In contrast, the effect on GFR was impaired in both diabetic groups, suggesting that glomerular NO homeostasis is altered in type 2 diabetes. Moreover the discrepancy, in diabetic patients, between cardiac and renal effects during L-NMMA infusion suggests that the modulation of glomerular hemodynamics is independent from NO-regulated cardiac output.

Blood glucose and lipid control as risk factors in the progression of renal damage in type 2 diabetes.

One of the central functions of the kidney is to excrete low molecular weight, water soluble, plasma, waste products into the urine, whereas macromolecules, the size of albumin and larger, are retained. The flow of the glomerular filtrate is thought to follow an extracellular route, passing through the endothelial fenestrae, then across the glomerular basement membrane and finally through the slit diaphragm between the foot processes of podocytes. Recently it has been hypothesized that microalbuminuria leading to proteinuria and to end stage renal disease (ESRD) is mainly due to an altered glomerular fitration barrier at podocyte level. The "conditio sine qua non" for the development of diabetic ESRD is hyperglycemia. However, arterial hypertension and abnormalities of blood lipid concentrations and structure are also an important antecedent of such complication in diabetes mellitus. Interestingly it has been suggested that hyperglycemia, arterial hypertension and dyslipidemia cause disorderes of albumin excretion rate by damaging podocyte and slit diaphragm protein scaffold with over production of and extracellular release of oxygen radical species at glomerular level. The present review will briefly discuss recent reports which describe the relationship between blood glucose and lipid abnormalities and the occurrence and progression of renal damage in diabetes mellitus. More particularly we will give evidence that the risk of a rapid decline of glomerular function abruptly increases when glycated hemoglobin is steadily higher than 7.5% and postprandial blood glucose is above 200 mg/dL. Eventually we will analyze recent reports showing that treatment with statins, the inhibitors of hydroxymethylglutaryl-coenzyme A reductase, ameliorate the course of renal function in type 2 diabetic patients. It is not yet fully understood whether this effect is due to the lowering of the circulating levels of low density lipoproteins (LDL) or to an improved endothelial function or to lower patterns of LDL oxidation.

Hypertension and renal complications in type 2 diabetes.

Diabetes mellitus and arterial hypertension are the leading causes of end-stage renal disease in industrialized countries. Although attention has focused on renal disease and insulin-dependent diabetes mellitus (type 1 diabetes), a silent epidemic of renal disease caused by type 2, noninsulin-dependent diabetes mellitus is rapidly developing. The course of renal function is heterogeneous in type 2 diabetic patients and reflects heterogeneous patterns of renal lesions. A subset of patients with microalbuminuria and proteinuria is characterized by the typical diabetic glomerulopathy usually observed in type 1 diabetic patients, with altered albumin excretion rate (AER), for example, glomerular basement membrane thickening and mesangial fractional volume expansion. These patients also have diabetic retinopathy and rapidly lose renal function despite tight blood pressure control. In contrast, a second subset of type 2 diabetic patients has normal or near-normal patterns of glomerular structure, despite abnormalities of AER comparable to those of the patients with diabetic glomerulopathy. Thus abnormalities of AER have a different renal prognostic value depending on the underlying renal structure. The patients with worse clinical prognosis and typical diabetic glomerulopathy also have diabetic retinopathy, whereas those with a better course of renal function quite often have no diabetic retinopathy. Several findings, albeit not unanimous, suggest that HbA1c levels above 7.5 to 8.0 % are closely associated with a rapid decay of renal function in type 2 diabetes. Tight blood pressure control plays a further important role in determining the progression of renal a damage in type 2 diabetes mellitus. Convincing evidence has been provided that drugs capable of inhibiting the renin-angiotensin hormonal system are quite effective in preventing and delaying the evolution of renal damage in both type 1 and 2 diabetes. Equally strong data support the view that other antihypertensive compounds such as beta-blockers and calcium antagonists also delay the progression of renal damage in diabetes mellitus. Whatever the drug used to treat hypertension, the majority of the authors conclude that blood pressure levels should be maintained below 130/85 mmHg in diabetic patients. While it is well established that uncontrolled diabetes underlies the development of diabetic nephropathy, newer evidence suggests that genetically determined susceptibility to hyperglycemia-caused glomerular injury is also necessary. More information on this issue will help to design new therapeutical approaches to treat hypertension and renal complications in type 2 diabetes.

Relationship between blood glucose control, pathogenesis and progression of diabetic nephropathy.

The present review briefly discusses evidence that the risk of a rapid decline of glomerular function abruptly increases when glycated hemoglobin is steadily higher than 7.5% and postprandial blood glucose is >200 mg/dl. The capacity to accomplish and to maintain steadily tightly controlled blood glucose levels is scanty using the currently implemented hypoglycemic drugs. Moreover, it must be highlighted that most patients with type 2 diabetes, particularly when renal damage does occur, have arterial hypertension. Several studies suggested that the development of ESRD is prevented significantly better by drugs that modulate the renin angiotensin system than by other compounds in patients with type 1 and 2 diabetes with overt diabetic nephropathy. However, a recent trial, the study Antihypertensive and Lipid Lowering Treatment to Prevent Heart Attack Trial (ALLHAT), which compared lisinopril, chlorthalidone, and amlodipine in a large population of patients with arterial hypertension, either associated or not with diabetes, demonstrated that the development of both coronary heart diseases and renal complications was equally prevented by the three drugs. One word of caveat, however, needs to be raised concerning one of the results of the ALLHAT study: the higher risk of developing new-onset diabetes among hypertensive patients who are not treated with lisinopril. Even if it is true that this latter side effect was not accompanied by a worse outcome of macrovascular and renal complications during the 5-yr follow-up period, one cannot rule out the possibility that this might be the case during more prolonged periods of follow-up in the future. Thus, the advantage of a lower cost in the treatment of hypertension with diuretics as compared with other drugs, with similar degree of success in the prevention of vascular complications, should be weighed also taking into consideration the burden of a higher rate of occurrence of new-onset diabetes.

Cardiovascular and renal protection in type 2 diabetes mellitus: the role of calcium channel blockers.

The most important factor that prevents the progression of renal damage in diabetes mellitus, beside the improvement of blood glucose control, is tight BP control. The tenet of tight BP control may be defined as the lowest BP level one can accomplish using antihypertensive therapy that is at the same time compatible with the absence of untoward side effects. In fact, both the Framingham Heart Study in nondiabetic normal subjects and the United Kingdom Prospective Diabetes Study in type 2 diabetic patients showed that systolic values as low as 108 to 111 mmHg and diastolic values as low as 70 to 71 mmHg are significantly associated with decreased cardiovascular mortality and morbidity. However, 45 to 50% of the patients with type 2 diabetes mellitus and hypertension have systolic BP levels above 140 mmHg during antihypertensive therapy, particularly when using monotherapy. Thus the issue regarding the choice of which drugs one should use to treat hypertension became critical from a clinical point of view. Pharmaceutical compounds, which inhibit the renin-angiotensin system, have become the first-choice treatment in patients with diabetes mellitus and incipient and advanced renal complications. The present brief review analyzes the effects of calcium channel blockers (CCB) on cardiovascular and renal complications in diabetes mellitus. The review discussed those studies that directly and blindly compared CCB with angiotensin-converting enzyme (ACE) inhibitors and with angiotensin II AT(1) receptor blockers (ARB). Furthermore, size of the population recruited in each trial was used as a criterion of priority in the selection of the reports from the available literature. From the point of view of cardiovascular complications, the results of these studies showed a slightly better benefit of CCB on stroke, whereas ACE inhibitors better prevented the occurrence of myocardial infarction and congestive heart failure. On the other hand, recent observations demonstrated that also ACE inhibitors and ARB are effective in the primary and secondary prevention of stroke, although these studies did not directly compare these compounds with CCB. With regard to the outcome of renal complications, both ARB and ACE inhibitors more effectively prevented the progression of renal damage among the patients with overt nephropathy than CCB. On the contrary, both CCB and ACE inhibitors were equally effective on blunting the decay of GFR in diabetic patients who do not have overt proteinuria. However, ACE inhibitors and ARB more markedly decreased the rate of albumin excretion rate in the range of both microalbuminuria and macroalbuminuria. Recent advances in the understanding of the pathogenesis of abnormalities of albumin excretion rate and of atherosclerosis are also discussed. Both mechanical stress, mainly secondary to systolic hypertension, and elevated circulating and tissue levels of angiotensin II, partially independent from each other, cause excessive generation of superoxide compounds. This chain reaction of events in turn leads to disorders of structural components of glomerular filter and to damage of the vascular wall. Systolic BP control (<130 mmHg) is not adequately accomplished in the majority of the patients treated only with ACE inhibitors and ARB, even in association with diuretics. Poor BP control may lead to excessive systemic mechanical stress at the vascular level despite satisfactory inhibition of angiotensin II effects. In conclusion, one can suggest that CCB are useful and often indispensable pharmaceutical compounds, beside ACE inhibitors and ARB, to accomplish tight BP control (<130/85 mmHg), a target that is unlikely to be successfully maintained in the overall population of type 2 diabetic patients only by ACE inhibitors or ARB, as monotherapy. However, ACE inhibitors and ARB might be considered first-choice drugs in the treatment of hypertension in diabetes mellitus, mainly because of a better renoprotection.

Insulin sensitivity correlates with glycogen synthesis rate, but not with von Willebrand factor in type 2 diabetes.

BACKGROUND: Whether insulin resistance in type 2 (non-insulin-dependent) diabetes is due to compromised endothelial insulin migration or to impaired intracellular hormone action or both is unclear. Coexistent microalbuminuria reflects possible endothelial pathogenesis in insulin resistance. METHODS: Insulin sensitivity (S(I)) was calculated from an intravenous glucose tolerance test in 23 type 2 albuminuric (AER+), 11 type 2 normoalbuminuric (AER-), and 17 control subjects. Cultured fibroblasts from skin biopsies from these subjects were used to study intracellular insulin action on glycogen synthesis. Endothelial damage in type 2 diabetes was evaluated by plasma concentrations of von Willebrand factor (vWf). Results: S(I) and glycogen synthesis in fibroblasts were lower in AER+ and AER- than in controls. Glycogen synthesis in vitro was related to S(I) in vivo (r=0.55, P<0.001). vWf was 169+/-12% in AER+ and 140+/-5% in AER-, P<0.051. No correlation was observed between vWf and S(I) or plasma insulin clearance. CONCLUSIONS: This study demonstrates that reduced insulin-mediated glucose removal in type 2 diabetes is strictly associated with a decreased glycogen synthesis of cultured skin fibroblasts in vitro, but not with markers of endothelial damage in vivo.

Cystatin C is a more sensitive marker than creatinine for the estimation of GFR in type 2 diabetic patients.

BACKGROUND: Glomerular filtration rate (GFR) is the best overall index of renal function in health and disease. Inulin and 51Cr-EDTA plasma clearances are considered the gold standard methods for estimating GFR. Unfortunately, these methods require specialized technical personnel over a period of several hours and high costs. In clinical practice, serum creatinine is the most widely used index for the noninvasive assessment of GFR. Despite its specificity, serum creatinine demonstrates an inadequate sensitivity, particularly in the early stages of renal impairment. Recently, cystatin C, a low molecular mass plasma protein freely filtered through the glomerulus and almost completely reabsorbed and catabolized by tubular cells, has been proposed as a new and very sensitive serum marker of changes in GFR. This study was designed to test whether serum cystatin C can replace serum creatinine for the early assessment of nephropathy in patients with type 2 diabetes. METHODS: The study was performed on 52 Caucasian type 2 diabetic patients. Patients with an abnormal albumin excretion rate (AER) were carefully examined to rule out non-diabetic renal diseases by ultrasonography, urine bacteriology, microscopic urine analysis, and kidney biopsy. Serum creatinine, serum cystatin C, AER, serum lipids, and glycosylated hemoglobin (HbA1c) were measured. GFR was estimated by the plasma clearance of 51Cr-EDTA. In addition the Cockcroft and Gault formula (Cockcroft and Gault estimated GFR) was calculated. RESULTS: Cystatin C serum concentration progressively increased as GFR decreased. The overall relationship between the reciprocal cystatin C and GFR was significantly stronger (r = 0.84) than those between serum creatinine and GFR (r = 0.65) and between Cockcroft and Gault estimated GFR and GFR (r = 0.70). As GFR decreased from 120 to 20 mL/min/1.73 m2, cystatin C increased more significantly that serum creatinine, giving a stronger signal in comparison to that of creatinine over the range of the measured GFR. The maximum diagnostic accuracy of serum cystatin C (90%) was significantly better than those of serum creatinine (77%) and Cockcroft and Gault estimated GFR (85%) in discriminating between type 2 diabetic patients with normal GFR (>80 mL/min per 1.73 m2) and those with reduced GFR (<80 mL/min/1.73 m2). In particular, the cystatin C cut-off limit of 0.93 mg/L corresponded to a false-positive rate of 7.7% and to a false-negative rate of 1.9%; the serum creatinine cut-off limit of 87.5 micromol/L corresponded to a false-positive rate of 5.8% and to a false-negative rate of 17.0%. CONCLUSIONS: Cystatin C may be considered as an alternative and more accurate serum marker than serum creatinine or the Cockcroft and Gault estimated GFR in discriminating type 2 diabetic patients with reduced GFR from those with normal GFR.