Red blood cell Li+/Na+ exchange in patients with diabetic nephropathy and essential hypertension: therapeutic implications

The relationship between red-cell distribution width and abnormal left ventricle geometric patterns in patients with untreated essential hypertension

Abnormal left ventricle (LV) geometric patterns are associated with an increased risk of vascular complications of hypertension (HT). The association between red-cell distribution width (RDW) and HT has been recently investigated; however, the relationship between abnormal LV geometric patterns and RDW has not been studied before. The aim of this study was to investigate the relationship between RDW and abnormal LV geometric patterns in patients with untreated essential HT. Measurements were obtained from 139 patients with untreated essential HT (mean age=51.3±16.3 years). Four different geometric patterns (NG, normal geometry; CR, concentric remodeling; EH, eccentric hypertrophy; CH, concentric hypertrophy) were determined according to the LV mass index (LVMI) and relative wall thickness (RWT). RDW, lipid parameters and other biochemical markers were measured in all patients. While the highest RDW values were detected in the CH group (P<0.05, for all), it was similar among the NG, CR and EH groups (P>0.05, for all). RDW was associated with age, LVMI and LV geometry in bivariate analysis (P<0.05, for all). In a receiver operating characteristic (ROC) curve analysis, a level of RDW>14.5 predicted CH with 81% sensitivity and 59% specificity. Age (beta=0.309, P=0.001), LV geometry type (beta=0.228, P=0.01) and RWT (beta=-0.278; P=0.25) were independent predictors of high RDW in multiple linear regression analysis. In conclusion, the highest RDW values were observed in the CH group in the untreated essential HT patients. RDW seems to be a useful tool for the prediction of end-organ damage in patients with untreated essential HT.

Functional significance of cell volume regulatory mechanisms

To survive, cells have to avoid excessive alterations of cell volume that jeopardize structural integrity and constancy of intracellular milieu. The function of cellular proteins seems specifically sensitive to dilution and concentration, determining the extent of macromolecular crowding. Even at constant extracellular osmolarity, volume constancy of any mammalian cell is permanently challenged by transport of osmotically active substances across the cell membrane and formation or disappearance of cellular osmolarity by metabolism. Thus cell volume constancy requires the continued operation of cell volume regulatory mechanisms, including ion transport across the cell membrane as well as accumulation or disposal of organic osmolytes and metabolites. The various cell volume regulatory mechanisms are triggered by a multitude of intracellular signaling events including alterations of cell membrane potential and of intracellular ion composition, various second messenger cascades, phosphorylation of diverse target proteins, and altered gene expression. Hormones and mediators have been shown to exploit the volume regulatory machinery to exert their effects. Thus cell volume may be considered a second message in the transmission of hormonal signals. Accordingly, alterations of cell volume and volume regulatory mechanisms participate in a wide variety of cellular functions including epithelial transport, metabolism, excitation, hormone release, migration, cell proliferation, and cell death.

Na+/H+ exchange in hypertension and in diabetes mellitus--facts and hypotheses

An enhancement of Na+/H+ exchange (NHE) in blood cells of selected patients with essential hypertension and with diabetic nephropathy has been described by various investigators. Recent studies have shown that enhanced NHE activity persists in immortalized lymphoblasts from these patients after prolonged cell culture and, thus, appears to be under genetic control. Available evidence strongly argues against a mutation in the encoding gene or an overexpression of the NHE. Immortalized cells from hypertensive patients with enhanced NHE activity display two-fold enhanced agonist-induced rises of the cytosolic free Ca2+ concentration and the underlying reason was identified as an increased activation of pertussis toxin (PTX)-sensitive G proteins. The molecular mechanism(s) of this phenomenon have not yet been elucidated. It appears likely that similar changes contribute to the enhanced NHE activity phenotype in diabetic nephropathy, although experimental evidence for this is still lacking. An enhanced activation of PTX-sensitive G proteins could explain many of the hitherto unexplained phenomena in essential hypertension, e.g. inheritance, increased vasoconstriction, hypertrophy of remodeling of arterial blood vessels and the heart, enhanced platelet aggregation etc. In diabetes the same defect could provide the basis for the susceptibility to nephropathy, e.g. by enhancing the deleterious effects of autocrine and paracrine growth factors. Thus, the experimental approach of immortalizing blood cells from patients with essential hypertension and diabetic nephropathy has opened new horizons in the identification of genetically fixed abnormalities in intracellular signal transduction which could contribute to both pathologies and which can now be studied without the confounding influences of the diabetic or hypertensive in vivo milieu.

Therapeutic progress. III: Diabetic nephropathy

Diabetic nephropathy is a common cause of end stage renal failure. Patients ultimately require dialysis or transplantation and endure a poor quality of life in association with increased mortality. Due to the quantitative significance of this problem there is also a considerable financial burden. It has been generally accepted that once nephropathy is established it is irreversible although aggressive anti-hypertensive treatment can delay its progression. More recently there have been numerous reports proposing a specific renal protective role of certain drugs. In this article we review the current literature on the use of angiotensin converting enzyme inhibitors in diabetic nephropathy. There is strong evidence that the use of ACE inhibitors in diabetic nephropathy (in the presence or absence of hypertension) slows the progression of deterioration in renal function and may even arrest its progression if detected at the microproteinuric stage.