Progressive Thinning of Retinal Nerve Fiber Layer/Ganglion Cell Layer (RNFL/GCL) as Biomarker and Pharmacological Target of Diabetic Retinopathy.

Diabetes-driven retinal neurodegeneration has recently been shown to be involved in the initial phases of diabetic retinopathy, raising the possibility of setting up a preventive strategy based on early retinal neuroprotection. To make this possible, it is crucial to identify a biomarker for early retinal neurodegeneration. To this end, in this study, we verified and confirmed that, in the Akita mouse model of diabetes, the thinning of the retinal nerve fiber layer/ganglion cell layer (the RNFL/GCL-the layer that contains the retinal ganglion cells) precedes the death of these same cells, suggesting that this dysfunction is a possible biomarker of retinal neurodegeneration. We then confirmed the validity of this assumption by starting a neuroprotective treatment (based on nerve growth factor eye drops) in concert with the first demonstration of RNFL/GCL thinning. In this way, it was possible not only to avoid the loss of retinal ganglion cells but also to prevent the subsequent development of the microvascular stage of diabetic retinopathy. In conclusion, in the case of diabetes, the thinning of the RNFL/GCL appears to be both a valid biomarker and a pharmacological target of diabetic retinopathy; it precedes the development of vascular dysfunctions and represents the ideal starting point for prevention.

Renal dysfunction and podocyturia in pre-eclampsia may be explained by increased urinary VEGF.

BACKGROUND: Pre-eclampsia has a major impact on renal function as shown by the development of proteinuria and podocyturia. How the systemic, soluble Fms-like tyrosine kinase-1 (sFlt-1)-driven inhibition of vascular endothelial growth factor (VEGF) activity detected in pre-eclampsia directly affects renal function remains unknown. The aim of the study was to clarify whether a non-canonical, renal-centred escape from VEGF inhibition in the case of pre-eclamptic pregnancy might have a direct impact on renal function. METHODS: We evaluated plasma and urinary VEGF and placental growth factor (PlGF), plasma sFlt-1 and carbonic anhydrase IX (CAIX), albuminuria and podocyturia in 18 women with uncomplicated pregnancy, 21 with pre-eclampsia and 18 non-pregnant. The three groups were matched for age and the pregnant groups also for gestational age at enrolment. RESULTS: Plasma VEGF was reduced in uncomplicated (P = 0.001) and pre-eclamptic (P = 0.0003) pregnancies when compared with controls. In uncomplicated pregnancy, the dysfunction was balanced by an increase (P = 0.009) of plasma PlGF. Increased (P = 0.0001) plasma CAIX in pre-eclampsia was in line with hypoxia. Pre-eclampsia resulted in a paradoxical increase (P = 0.0004) of urinary excretion of VEGF. Urinary concentrations of VEGF and podocytes were correlated to each other (r2 = 0.48, P < 0.0005) but also to plasma sFlt-1 (r2 = 0.56, P < 0.0001 and r2 = 0.23, P = 0.03, respectively). CONCLUSIONS: In the case of pre-eclampsia, the systemic VEGF inhibition leads the kidney, possibly the podocyte, to increase the VEGF synthesis. The mechanisms leading to local VEGF overproduction or the overproduced VEGF itself are reasonably involved in the pathogenesis of podocyturia and, as a consequence, renal dysfunction in pre-eclampsia.

Early increase in circulating carbonic anhydrase IX: A potential new predictive biomarker of preeclampsia.

Preeclampsia (PE) is a severe complication of pregnancy. The identification of a reliable predictive biomarker could help in setting up a specific preventive strategy. To this aim, we studied carbonic anhydrase IX (CAIX) as a marker of hypoxia (a pathway involved in PE pathogenesis) and compared the diagnostic accuracy of CAIX to that of the validated biomarker sFlt1/PlGF ratio. Fifteen women with overt PE and 38 women at a risk of developing PE, sampled at different time intervals during gestation (a total of 82 plasma samples collected), were enrolled and underwent the CAIX measurement. CAIX levels significantly increased (p < .001) before the onset of the disease in women (25% of the total number) who later on developed PE when compared to women who did not, starting from 28th gestational week. The best CAIX cut-off of 68.268 pg/mL yielded a sensitivity of 100%, a specificity of 81.82%, and an AUC value of .9221. In our pilot study, when compared to the sFlt1/PlGF ratio, CAIX performed better in predicting PE before the clinical onset. Furthermore when implemented as CAIX/PlGF ratio, showed up to be comparable in the identification of women with overt early PE. In conclusion, CAIX could represent an effective predictive biomarker of PE, and larger studies are mandatory to validate this finding.

Diabetes has no additional impact on retinal ganglion cell loss in a mouse model of spontaneous glaucoma.

PURPOSE: There is no valid medical treatment for diabetic retinopathy mostly because its pathogenesis remains largely unknown. Early stages of diabetic retinopathy, just like glaucoma, are characterized by the loss of retinal ganglion cells. Whether the two diseases may share a similar pathogenic background is unknown. METHODS: To clarify this issue the thickness of retinal nerve fiber layer was studied in vivo by optical coherence tomography in 10 Ins2Akita (diabetic) and 10 C57BL/6J (control) mice. The number of retinal ganglion cells and retina's surface covered by neurofilaments were quantified ex vivo in 12 normoglycemic DBA/2J (glaucoma) and 11 diabetic (alloxan-induced) DBA/2J mice (glaucoma + diabetes). RESULTS: At 16 weeks of age retinal nerve fiber layer was significantly thinner in Ins2Akita mice confirming the neurodegenerative impact of diabetes. Number of retinal ganglion cells and retina's surface covered by neurofilaments were similar in normoglycemic and diabetic DBA/2J mice with the exception of the superior quadrant where the number of retinal ganglion cells was increased in animals with glaucoma + diabetes. CONCLUSIONS: In presence of glaucoma, diabetes is unable to induce further retinal ganglion cells loss. The hypothesis that the mechanism leading to retinal ganglion cells loss may be shared by the two diseases cannot be ruled out. Whether early diabetes-driven retinal neurodegeneration could be prevented by neuroprotective treatment proven to be effective in case of glaucoma, remains to be clarified.

Topical nerve growth factor prevents neurodegenerative and vascular stages of diabetic retinopathy.

Specific and effective preventive treatment for diabetic retinopathy (DR) is presently unavailable, mostly because the early stages of the complication have been, until recently, poorly understood. The recent demonstration that the vascular phase of DR is preceded and possibly caused by the neurodegeneration of retinal ganglion cells suggests that DR could, at least theoretically, be prevented through an early neuroprotective approach. The aims of our study were to clarify the natural history of diabetes-driven retinal neurodegeneration and to verify the possibility to prevent DR using topical nerve growth factor (NGF). The results of the study show that retinal neurodegeneration, characterized by the loss of retinal ganglion cells represents a relatively early phenomenon of diabetes (between 5 and 16 weeks of age), which tends to be self-limiting in the long run. Neurodegeneration is followed by the development of DR-related vascular dysfunctions, as confirmed by the development of acellular capillaries and the loss of retinal pericytes. Both retinal neurodegeneration and subsequent vascular dysfunction can be successfully prevented by topical NGF administration. These findings suggest that: 1) The first stage of DR consists in a self-limiting retinal neurodegeneration 2) The demonstrated effectiveness of topical NGF in the prevention of DR could be rapidly translated into clinical practice.

Early renal dysfunctions in type 1 diabetes and pathogenesis of diabetic nephropathy.

Diabetic nephropathy develops in only a subgroup of patients affected by type 1 diabetes. Once established, this complication is quite difficult to control, and consequently its prevention is presently considered the first target to achieve. As hyperglycemia has immediate effects on renal function and structure, it is reasonable to say that, in predisposed individuals, the pathogenesis of diabetic nephropathy also begins with the onset of diabetes. Two major hypotheses have been put forward to explain how the renal abnormalities that characterize the first years of diabetes - i.e., hyperfiltration and hypertrophy - will later lead to the appearance of microalbuminuria and end-stage renal disease. The first hypothesis considers hyperfiltration as the driving dysfunction and hypertrophy as the consequence. Conversely, the second points to proximal tubule hypertrophy as the starting point and hyperfiltration as the result. Whatever the case, tight glucose control from the very first days of disease seems to be the only established therapy to prevent future complications in type 1 diabetes.

Inhibition of MAP-kinase cascade normalizes the proliferation rate of fibroblasts from patients with Type 1 diabetes and nephropathy.

Faster proliferation rate characterizes human skin fibroblasts from patients with Type 1 diabetes and nephropathy (DN), but the reason of this phenomenon is still unknown. Growth factors control cell proliferation through an intracellular mitogen-activated protein (MAP) kinase cascade. We have examined the effect of the inhibition of MAP kinase/ERK kinase (MEK), a key point of the MAP kinase cascade, on the proliferation rate of fibroblasts from 40 patients with Type 1 diabetes (20 with and 20 without DN) and from 10 nondiabetic participants. Proliferation rate was measured by cell count in the presence or absence of 30 mumol/l of the MEK inhibitor PD 098059. In normal cultural conditions, proliferation rate was faster in fibroblasts from patients with (0.175+/-0.009x10(5) cells day-1, mean+/-S.E.M.) than without DN (0.110+/-0.009) and in nondiabetic participants (0.094+/-0.008; ANOVA P<.0001). The inhibition of MEK induced a stronger reduction of proliferation rate in fibroblasts from patients with (0.079+/-0.006x10(5) cells day(-1); 55% of reduction) than without DN (0.068+/-0.006; 38% of reduction) and in nondiabetic participants (0.064+/-0.006; 32% of reduction), and differences among groups were lost. In parallel, PD 098059 induced a greater reduction of MEK-dependent phosphorylation in lysates of fibroblasts from patients with (73%) than without (40%) DN. In conclusion, the inhibition of MEK normalizes the proliferation rate of fibroblasts from patients with DN, suggesting that the MAP kinase cascade could be involved in this cellular dysfunction.

Dysfunction of cellular transporters and predisposition to diabetic nephropathy.

Diabetic nephropathy is presently the first reason of end stage renal failure in Europe and the USA and its worldwide prevalence is rapidly increasing. Several studies have demonstrated that diabetes per se is not sufficient to induce nephropathy and a genetic predisposition has to be present as well. Looking for genetic markers, investigators have been helped by the finding that a predisposition to hypertension facilitates the development of nephropathy in diabetic patients. Prompted by the evidence that essential hypertension is characterized by a number of defects at cellular level, similar dysfunctions have been searched also in cells obtained from diabetic patients with nephropathy. Increased Na-Li countertransport and Na-H exchange activities, slower Ca pump and faster cell proliferation rate have been found in cells obtained from patients affected by diabetic nephropathy. The definition of these intermediate phenotypes represents a necessary step toward the identification of the molecular dysfunction(s) underlying the development of diabetic nephropathy. The present review will focus on the description of the different cell dysfunctions identified in patients affected by diabetic nephropathy, their pathophysiologic meaning and will try to define an unifying hypothesis that, by linking together the different dysfunctions, will highlight a few areas "at risk", candidate to home the primitive genetic abnormality.

Increased sodium-lithium countertransport activity: a cellular dysfunction common to essential hypertension and diabetic nephropathy.

An increased activity of sodium-lithium countertransport (SLC) is a common finding in patients who have essential hypertension. The evidence that a similar dysfunction is shared also by patients with type 1 diabetes and nephropathy has suggested the hypothesis that a predisposition to essential hypertension may be the factor that, along with hyperglycemia, underlies the development of diabetic nephropathy. Despite the initial enthusiasm surrounding the potential use of SLC activity as a marker for the early detection and treatment of individuals who are predisposed to hypertension and diabetic nephropathy, its use has been so far restricted to epidemiologic studies, as specificity and sensitivity of the test are still too low to justify any clinical use. The recent finding, however, that the measurement of kinetic parameters of SLC can significantly increase the power to discriminate among individuals with and without hypertension or diabetic nephropathy could be of help toward a future clinical use of the measurement of this membrane transport. A second major point relates to the possibility that SLC per se might be directly involved in the pathogenesis of essential hypertension and diabetic nephropathy. This case has never been fully tested, as the gene responsible for this membrane transport has been, until recently, unknown. The recent identification of an alternative splicing of the first isoform of Na-H exchange that mediates SLC activity should allow for a rapid comprehension of the role of this transport in the pathophysiology of essential hypertension and diabetic nephropathy.