Possible new druggable targets for the treatment of nephrosis. Perhaps we should find them in caveolea?

Nephrosis refers to a condition resulting from proteinuric kidney disease, leading to irreversible renal parenchymal damage and end-stage renal disease when left untreated. Furthermore, nephrosis appears to be a communicable disease carrying risks and complications to other organs such as the heart. Key pathophysiolgical processes involved in initiating and progressing renal damage in nephrosis and its complications may include altered glomerular hemodynamics after initial renal damage and loss of nephrons, nephrotoxicity of increased renal protein traffic enforcing intrinsic 'common pathway' mechanisms of renal scarring, and generalized endothelial dysfunction proceeding CV disease. The reader is first provided a basic overview on key mechanisms, targets and therapies in nephrosis while referred to some excellent updates hereon for more detailed information. The broader purpose of this short review, however, is to highlight caveolae/caveolins and caveolar function as central modulators in all the above key processes of nephrosis. Caveolae - little caves in the plasma membrane that are particularly abundant in endothelial cells, amongst others - are now known to be involved not only in endothelial transcytosis (e.g. of albumin) but also in cholesterol homeostasis (LDL-transport) and, importantly, in signal transduction such as insulin signalling and nitric oxide signalling in endothelial function and regulation of vasomotor tone, as well as signalling by growth factor receptors - such as TGF-beta - which may participate in renal scarring. It is suggested that caveolae may represent crucial sites where possible new druggable targets in nephrosis may be found.

The role of angiotensin(1-7) in renal vasculature of the rat.

OBJECTIVE: Angiotensin(1-7) is an active component of the renin-angiotensin-aldosterone system. Its exact role in renal vascular function is unclear. We therefore studied the effects of angiotensin(1-7) on the renal vasculature in vitro and in vivo. METHODS: Isolated small renal arteries were studied in an arteriograph system by constructing concentration-response curves to angiotensin II, without and with angiotensin(1-7). In isolated perfused kidneys, the response of angiotensin II on renal vascular resistance was measured without and with angiotensin(1-7). The influence of angiotensin(1-7) on angiotensin II-induced glomerular afferent and efferent constriction was assessed with intravital microscopy in vivo under anaesthesia. In freely moving rats, we studied the effect of angiotensin(1-7) on angiotensin II-induced reduction of renal blood flow with an electromagnetic flow probe. RESULTS: Angiotensin(1-7) alone had no effect on the renal vasculature in any of the experiments. In vitro, angiotensin(1-7) antagonized angiotensin-II-induced constriction of isolated renal arteries (9.71 +/- 1.21 and 3.20 +/- 0.57%, for control and angiotensin(1-7) pre-treated arteries, respectively; P < 0.0005). In isolated perfused kidneys, angiotensin(1-7) reduced the angiotensin II response (100 +/- 16.6 versus 72.6 +/- 15.6%, P < 0.05) and shifted the angiotensin II dose-response curve rightward (pEC50, 6.69 +/- 0.19 and 6.26 +/- 0.12 for control and angiotensin(1-7) pre-treated kidneys, respectively; P < 0.05). Angiotensin(1-7), however, was devoid of effects on angiotensin-II-induced constriction of glomerular afferent and efferent arterioles and on angiotensin-II-induced renal blood flow reduction in freely moving rats in vivo. CONCLUSION: Angiotensin(1-7) antagonizes angiotensin II in renal vessels in vitro, but does not appear to have a major function in normal physiological regulation of renal vascular function in vivo.

Losartan protects mesenteric arteries from ROS-associated decrease in myogenic constriction following 5/6 nephrectomy.

BACKGROUND: Chronic renal failure (CRF) is associated with hypertension, proteinuria, loss of myogenic constriction (MC) of mesenteric arteries and increased production of reactive oxygen species (ROS) under experimental conditions. Previous results showed that ACE (angiotensin-converting enzyme activity) inhibitor therapy is effective in slowing down the progression of disease. Therefore, we wanted to study whether the inverse AT(1) (angiotensin II type 1) receptor agonist, losartan (LOS) was effective in preventing loss of MC in a rat model of CRF and whether acute ROS scavengers could improve MC. METHODS: Rats underwent 5/6 nephrectomy (5/6 Nx) and were treated with vehicle or LOS (20 mg/kg/day; 5/6 Nx + LOS) for 12 weeks. Thereafter, the MC of the mesenteric arteries were measured in the presence and/or absence of tempol and catalase. Systolic blood pressure and proteinuria were measured weekly. RESULTS: Systolic blood pressure and proteinuria in the 5/6 Nx + LOS group were significantly lower than in the 5/6 Nx group. Moreover, the MC of 5/6 Nx + LOS arteries was significantly increased compared with the untreated 5/6 Nx group (maximum MC, 32.3 ± 6.9 vs 8.9 ± 3.8% (p < 0.01)). Tempol + catalase significantly increased the MC in the 5/6 Nx group, but not in the 5/6 Nx + LOS group (increase in MC, 59.7 ± 13.0 (p < 0.05) vs. 17.0 ± 15.1%). CONCLUSION: These results support the roles of the RAAS (renin-angiotensin-aldosterone system) and ROS in the vascular dysfunction of systemic vessels in CRF.