Amelioration of cardiac function and activation of anti-inflammatory vasoactive peptides expression in the rat myocardium by low level laser therapy

Low-level laser therapy (LLLT) has been used as an anti-inflammatory treatment in several disease conditions, even when inflammation is a secondary consequence, such as in myocardial infarction (MI). However, the mechanism by which LLLT is able to protect the remaining myocardium remains unclear. The present study tested the hypothesis that LLLT reduces inflammation after acute MI in female rats and ameliorates cardiac function. The potential participation of the Renin-Angiotensin System (RAS) and Kallikrein-Kinin System (KKS) vasoactive peptides was also evaluated. LLLT treatment effectively reduced MI size, attenuated the systolic dysfunction after MI, and decreased the myocardial mRNA expression of interleukin-1 beta and interleukin-6 in comparison to the non-irradiated rat tissue. In addition, LLLT treatment increased protein and mRNA levels of the Mas receptor, the mRNA expression of kinin B2 receptors and the circulating levels of plasma kallikrein compared to non-treated post-MI rats. On the other hand, the kinin B1 receptor mRNA expression decreased after LLLT. No significant changes were found in the expression of vascular endothelial growth factor (VEGF) in the myocardial remote area between laser-irradiated and non-irradiated post-MI rats. Capillaries density also remained similar between these two experimental groups. The mRNA expression of the inducible nitric oxide synthase (iNOS) was increased three days after MI, however, this effect was blunted by LLLT. Moreover, endothelial NOS mRNA content increased after LLLT. Plasma nitric oxide metabolites (NOx) concentration was increased three days after MI in non-treated rats and increased even further by LLLT treatment. Our data suggest that LLLT diminishes the acute inflammation in the myocardium, reduces infarct size and attenuates left ventricle dysfunction post-MI and increases vasoactive peptides expression and nitric oxide (NO) generation.

Future strategies for mitigation and treatment of chronic radiation-induced normal tissue injury

Until the mid-1990s, radiation-induced normal-tissue injury was generally assumed to be solely caused by the delayed mitotic death of parenchymal or vascular cells, and these injuries were held to be progressive and untreatable. From this assumption, it followed that postirradiation interventions would be unlikely to reduce either the incidence or the severity of radiation-induced normal tissue injury. It is now clear that parenchymal and vascular cells are active participants in the response to radiation injury, an observation that allows for the possibility of pharmacologic mitigation and/or treatment of these injuries. Mitigation or treatment of chronic radiation injuries has now been experimentally shown in multiple organ systems (eg, lung, kidney, and brain), with different pharmacologic agents (eg, angiotensin-converting enzyme inhibitors, pentoxifylline, and superoxide dismutase mimetics) and with seemingly different mechanisms (eg, suppression of the renin-angiotensin system and suppression of chronic oxidative stress). Unfortunately, the mechanistic basis for most of the experimental successes has not been established, and assessment of the utility of these agents for clinical use has been slow. Clinical development of pharmacologic approaches to mitigation or treatment of chronic radiation injuries could lead to significant improvement in survival and quality of life for radiotherapy patients and for victims of radiation accidents or nuclear terrorism.

Mineralocorticoid receptor antagonists and hypertension: Is there a rationale?

Accumulating evidence indicates that aldosterone is involved in cardiovascular disease by inducing inflammation in the presence of moderate amounts of salt in the diet. Spironolactone and eplerenone are the mineralocorticoid receptor (MR) antagonists currently available for the treatment of hypertension. They have similar safety and antihypertensive efficacy. The advantage of eplerenone is the lower incidence of anti-androgenic and progestational side effects. The rationale for using MR blockade in the treatment of hypertension is threefold: the evidence of antihypertensive efficacy, the phenomenon of "aldosterone escape" occurring with angiotensin-converting enzyme inhibitor and angiotensin-receptor blockade therapy, and the compelling evidence that MR antagonism reduces target-organ damage in hypertensive patients and improves survival in patients with cardiovascular disease. Thus, blockade of the MR may be very useful in many patients with hypertension, particularly those at risk for or having evidence of target-organ damage.

[Age related features of postradiation changes of functional activity of local vascular renin-angiotensin system]

The postradiation changes of constriction effects of angiotensin II (Ang II) and angiotensin I (Ang I) on isolated preparations of thoracic aorta young and old rats which underwent gamma-irradiation in dose 1 Gy (137Cs, 9 x 10(-4) Gy/s) were investigated. It has been found, that the aging leads to the alteration of angiotensin receptors, which appears as changes in their density and/or sensitivity to action of agonist. With increase of age the activity of angiotensin-converting enzyme (ACE) in the wall of aorta is oppressed, and as a result, the level of local formation of Ang II and the constriction, caused by it are reduced. The inhibitory influence of endothelium on vasoconstriction effects of Ang II and Ang I in ontogenesis does not change. The influence of gamma-radiation in a dose of 1 Gy modifies the functional activity of the local vascular renin-angiotensin system (RAS): the sensitivity and/or density of angiotensin receptors and the activity of ACE increased the dilatation influences of endothelium were oppressed mainly for account of easing the synthesis of NO. The duration of postradiation infringements of functional activity of local vascular RAS in many respects are determined by the stage of ontogenic development of irradiated organism.

The renin-angiotensin system in experimental radiation nephropathy

Irradiation of the kidneys is followed by a well-defined sequence of changes leading eventually to kidney failure. In the rat, inhibition of angiotensin-converting enzyme or blockade of angiotensin II receptors can prevent the structural and functional changes that occur after kidney irradiation. These interventions are particularly effective between 3 and 10 weeks after irradiation. However, in a series of studies with the rat model we failed to find any evidence that the renin-angiotensin system (RAS) is activated in the first 10 weeks after kidney irradiation. First, if the RAS was activated during this interval, one would expect hypertension followed by proteinuria and azotemia. However, hypertension is significant only at the end of this period and is preceded by significant proteinuria and azotemia. This evolution is not in favor of an obviously activated RAS during the 3- to 10-week postirradiation interval that is critical for interventions aimed at the RAS. Second, plasma renin activity and active plasma renin protein concentrations are not significantly increased over the first 10 weeks after irradiation. Third, whole-blood and intrarenal angiotensin II levels are not increased and may even be decreased over this interval. This last observation is particularly important because the assay used is sensitive enough to detect the effects of dietary salt manipulation. We hypothesize that even the normal activity of the RAS contributes to injury after kidney irradiation, possibly by supporting the proliferation of cells that carry potentially lethal radiation injuries.

[APUD- and RAA- regulatory systems in acute radiation injury]

An experimental morpho-functional assessment of rat APUD and RAA systems status in acute radiation injury (cerebral form) was performed. The named regulatory systems were found to display an actual momentary post-exposure reaction, followed by subsequent functional changes of a distinct phase character. The latter were shown to determine in many respects the clinical picture and in some cases the outcome of the disease.

Angiotensin II infusion exacerbates radiation nephropathy

We hypothesized that angiotensin II will exacerbate radiation nephropathy in a time-specific manner. Experimental radiation nephropathy is treatable with angiotensin-converting enzyme inhibition or angiotensin II (AII) receptor blockers. These interventions are particularly important between 3 and 10 weeks after irradiation. We therefore undertook studies in which AII infusions were given at particular intervals after irradiation. Rats received total body irradiation (TBI) plus syngeneic bone marrow transplantation followed (or not) by AII infusion at 200 or 400 ng/kg/min. Infusions were given from 0 to 4 or 4 to 8 weeks after irradiation. An additional group was unirradiated but infused at 800 ng/kg/min for 8 weeks. Kidney function was assessed over 26 weeks, and histology was evaluated after the animals were killed. AII infusion alone did not cause azotemia. There was transient hypertension during AII infusion at 800 ng/kg/min but only minor histologic injury. Irradiation caused azotemia and hypertension, which were not exacerbated by AII infusion at 200 ng/kg/min. Irradiation plus AII infusion at 400 ng/kg/min from 4 to 8 weeks after TBI caused significantly greater azotemia than irradiation alone or irradiation with AII infusion from 0 to 4 weeks. The blood pressure was higher in irradiated rats infused with AII from 4 to 8 weeks. Arteriolar fibrinoid necrosis was a prominent feature in kidneys of rats infused with AII from 4 to 8 weeks after TBI. The worsening of radiation nephropathy by AII infusion from 4 to 8 weeks after irradiation strongly supports the idea of specific and sequential events in the pathogenesis of kidney failure in this model. Hypertension may play a role in these events in addition to the effect of AII alone. The occurrence of arteriolar fibrinoid necrosis in the irradiated, 4-to-8-week-infused animals suggests that vascular injury during that interval determines later outcome.

Angiotensin II receptor antagonists in the treatment and prevention of radiation nephropathy

PURPOSE

Angiotensin-converting enzyme (ACE) inhibitors are effective in the prophylaxis of radiation-induced renal and lung injury. Studies were designed to determine whether blocking the angiotensin II (AII) receptor, rather than blocking AII synthesis with ACE inhibitors, would also be effective.

MATERIALS AND METHODS

Rats received total body irradiation (TBI) followed by bone marrow transplantation (BMT), and were randomized to: an ACE inhibitor (captopril); an AII type 1 (AT1) receptor antagonist (L-158,809); or no treatment. Drug therapy began 9 days prior to BMT and continued for the duration of the study.

RESULTS

Analysis of renal function, histopathology and animal survival showed that the AII blocker was more effective than the ACE inhibitor in the prophylaxis of BMT nephropathy. Further studies have shown that the AII blocker is as effective as captopril in the treatment of established radiation nephropathy, and that the AII blocker is at least as effective as captopril in the prophylaxis of lung injury induced by chemo-radiation therapy.

CONCLUSIONS

These studies indicate that blockage of the AT1 receptor by itself is sufficient for the treatment of radiation-induced renal and lung injury, hence the renin-angiotensin system is fundamentally involved in the pathogenesis of these injuries. These studies provide further evidence that there is more to late radiation injuries than delayed mitotic cell death.

Brain surface exposure to CO2 and NdYag laser application: effect on pulmonary endothelium response in the rat

Pulmonary endothelial cells and the renin-angiotensin-aldosterone (RAA) system respond to different types of injury (direct or indirect) with variations in their functions. These variations influence the regulatory mechanisms of pulmonary and systemic blood pressure, electrolyte balance and fibrinolysis. Concentration changes of some components of the RAA system and lung plasminogen activator were observed following NdYag laser application to the brain surface in rats. These changes were similar to those observed in cutaneous burn and haemorrhagic hypotension. CO2 laser application did not cause the same changes.

Radiation injury in rat lung. II. Angiotensin-converting enzyme activity

To determine the role of endothelial dysfunction in the pathogenesis of radiation-induced pulmonary injury, lung angiotensin-converting enzyme (ACE) activity, arterial perfusion, and ultrastructure were examined from 1 to 150 days after a single exposure of 25 Gy of 60Co gamma rays to the right hemithorax of rats. Arterial perfusion to the irradiated right lung increased during the first 2 weeks, then decreased to approximately 80% of the left lung value at 30 days postirradiation. Perfusion of the irradiated lung continued to decline, and by 90-150 days was only 40% of that of the shielded lung. ACE activity in the irradiated right lung did not change significantly until 30 days after exposure, when it decreased to 72% of that in the left lung. ACE activity in the right lung declined steadily from 30 to 90 days postirradiation, then reached a plateau through 150 days at less than 20% of normal. Perivascular and interstitial edema was evident at 1 day after irradiation and persisted for 30 days. Endothelial cells exhibited blebbing, fragmentation, and increased basement membrane at 30 days. Mast cells were present in the septa, but interstitial collagen was not increased at that time. From 90 to 150 days postexposure, progressive obliteration of capillaries by fibrotic reactions was observed. Thus decreased ACE activity accompanies radiation-induced hypoperfusion and endothelial ultrastructural changes in rat lung. All of these reactions precede the development of pulmonary fibrosis.