Angiotensinogen (ANG) is the sole substrate of the renin-angiotensin system (RAS). Clinical studies have shown that RAS activation may lead to hypertension, a major cardiovascular and renal risk factor. To delineate the underlying mechanisms of hypertension-induced nephropathy, we generated transgenic mice that overexpress rat ANG (rANG) in the kidney to establish whether intrarenal RAS activation alone can evoke hypertension and kidney damage and whether RAS blockade can reverse these effects. Transgenic mice overexpressing renal rANG were generated by employing the kidney-specific, androgen-regulated protein promoter linked to rANG cDNA. This promoter targets rANG cDNA to renal proximal tubules and responds to androgen stimulation. Transgenic mice displayed kidney-specific expression of rANG, significantly increased blood pressure (BP) and albuminuria in comparison to non-transgenic littermates. Administration of losartan (an angiotensin II (type 1)-receptor antagonist) or perindopril (an angiotensin-converting enzyme inhibitor) reversed these abnormalities in transgenic animals. Renal injury was evident on examination of the kidneys in transgenic mice, and attenuated by losartan and perindopril treatment. We conclude that the overproduction of ANG alone in the kidney induces an increase in systemic BP, proteinuria, and renal injury. RAS blockers prevent these abnormalities. These data support the role of the intrarenal RAS in the development of hypertension and renal injury.

The intrarenal renin-angiotensin system (RAS) plays an important role in the progression of diabetic nephropathy. We have previously reported that mice overexpressing angiotensinogen in renal proximal tubular cells (RPTC) develop hypertension, albuminuria, and renal injury. Here, we investigated whether activation of the intrarenal RAS contributes to apoptosis of RPTC in diabetes. Induction of diabetes with streptozotocin in these transgenic mice led to significant increases in BP, albuminuria, RPTC apoptosis, and proapoptotic gene expression compared with diabetic nontransgenic littermates. Insulin and/or RAS blockers markedly attenuated these changes. Hydralazine prevented hypertension but not albuminuria, RPTC apoptosis, or proapoptotic gene expression. In vitro, high-glucose medium significantly increased apoptosis and caspase-3 activity in rat immortalized RPTC overexpressing angiotensinogen compared with control cells, and these changes were prevented by insulin and/or RAS blockers. In conclusion, intrarenal RAS activation and high glucose may act in concert to increase tubular apoptosis in diabetes, independent of systemic hypertension. Diabetic nephropathy (DN) is the leading cause of all ESRD in North America, accounting for 45% to 50% of all cases. 1,2 Intensive insulin therapy and chronic treatment with renin-angiotensin system (RAS) blockers are effective in retarding DN progression but do not provide a cure. [3][4][5] The local intrarenal RAS is well accepted. 6,7 Renal proximal tubular cells (RPTC) express all components of the RAS. 8 -10 Angiotensin II (Ang II) levels and RAS genes are elevated in the kidneys of diabetic rats and humans, 11-13 implying an important role for the intrarenal RAS in DN progression.Glomerular changes in DN first consist of hypertrophy and, later, thickening of the glomerular basement membrane, followed by expansion of the mesangial matrix and glomerulosclerosis. 14 -16 However, the gradual decline of renal function in later stages of DN is invariably associated with tubular atrophy and interstitial fibrosis, hallmarks of ESRD. 17,18 In fact, tubular atrophy and interstitial fibrosis are closely associated with loss of renal function and appear to be better predictors of renal disease progression than glomerular pathology. 15-18 Tubular atrophy in DN is incompletely understood, although apoptosis is a candidate mechanism. Indeed, apoptosis has been detected in RPTC of diabetic mouse, rat, and human kidneys. 19 -24

Increased generation of reactive oxygen species (ROS) leads to oxidative stress in diabetes. Catalase is a highly conserved heme-containing protein that reduces hydrogen peroxide to water and oxygen and is an important factor decreasing cellular injury owing to oxidative stress. Hyperglycemic conditions increase oxidative stress and angiotensinogen gene expression. Angiotensinogen conversion to angiotensin II leads to a furtherance in oxidative stress through increased generation of reactive oxygen species. In this study, we utilized mice transgenically overexpressing rat catalase in a kidney-specific manner to determine the impact on ROS, angiotensinogen and apoptotic gene expression in proximal tubule cells of diabetic animals. Proximal tubules isolated from wild-type and transgenic animals without or with streptozotocin-induced diabetes were incubated in low glucose media in the absence or presence of angiotensin II or in a high-glucose media. Our results show that the overexpression of catalase prevents the stimulation of ROS and angiotensinogen mRNA in tubules owing to elevated glucose or angiotensin II in vitro. Additionally, overexpression of catalase attenuated ROS generation, angiotensinogen and proapoptotic gene expression and apoptosis in the kidneys of diabetic mice in vivo. Our studies point to an important role of ROS in the pathophysiology of diabetic nephropathy.

It was previously demonstrated that fluid liposomal-encapsulated tobramycin, named Fluidosomes, was successful in eradicating mucoid Pseudomonas aeruginosa in an animal model of chronic pulmonary infection, whereas free antibiotic did not reduce colony-forming unit (CFU) counts (C. Beaulac et al., Antimicrob. Agents Chemother. 40 (1996) 665-669; C. Beaulac et al., J. Antimicrob. Chemother. 41 (1998) 35-41). These liposomes were also shown to be bactericidal in in vitro tests against strong resistant P. aeruginosa 64 microg/ml). The time needed to reach the maximal fusion rate was about 5 h for the resistant strain comparatively to much shorter time for the sensitive strain. The specific characteristics of Fluidosomes could help overcome bacterial resistance related to permeability barrier and even enzymatic hydrolysis considering the importance of synergy in the whole process of antibiotic resistance.