Glomerular prostaglandins, angiotensin II, and nonsteroidal anti-inflammatory drugs

Achieving clinical success with BET inhibitors as anti-cancer agents

The transcriptional upregulation of oncogenes is a driving force behind the progression of many tumours. However, until a decade ago, the concept of 'switching off' these oncogenic pathways represented a formidable challenge. Research has revealed that members of the bromo- and extra-terminal domain (BET) motif family are key activators of oncogenic networks in a spectrum of cancers; their function depends on their recruitment to chromatin through two bromodomains (BD1 and BD2). The advent of potent inhibitors of BET proteins (BETi), which target either one or both bromodomains, represents an important step towards the goal of suppressing oncogenic networks within tumours. Here, we discuss the biology of BET proteins, advances in BETi design and highlight potential biomarkers predicting their activity. We also outline the logic of incorporating BETi into combination therapies to enhance its efficacy. We suggest that understanding mechanisms of activity, defining predictive biomarkers and identifying potent synergies represents a roadmap for clinical success using BETi.

Effects of high- and low-dose aspirin on adaptive immunity and hypertension in the stroke-prone spontaneously hypertensive rat

Despite its well-known antithrombotic properties, the effect of aspirin on blood pressure (BP) and hypertension pathology is unclear. The hugely varying doses used clinically have contributed to this confusion, with high-dose aspirin still commonly used due to concerns about the efficacy of low-dose aspirin. Because prostaglandins have been shown to both promote and inhibit T-cell activation, we also explored the immunomodulatory properties of aspirin in hypertension. Although the common preclinical high dose of 100 mg/kg/d improved vascular dysfunction and cardiac hypertrophy, this effect was accompanied by indices of elevated adaptive immunity, renal T-cell infiltration, renal fibrosis, and BP elevation in stroke-prone spontaneously hypertensive rats and in angiotensin II-induced hypertensive mice. The cardioprotective effects of aspirin were conserved with a lower dose (10 mg/kg/d) while circumventing heightened adaptive immunity and elevated BP. We also show that low-dose aspirin improves renal fibrosis. Differential inhibition of the COX-2 isoform may underlie the disparate effects of the 2 doses. Our results demonstrate the efficacy of low-dose aspirin in treating a vast array of cardiovascular parameters and suggest modulation of adaptive immunity as a novel mechanism underlying adverse cardiovascular profiles associated with COX-2 inhibitors. Clinical studies should identify the dose of aspirin that achieves maximal cardioprotection with a new awareness that higher doses of aspirin could trigger undesired autoimmunity in hypertensive individuals. This work also warrants an evaluation of high-dose aspirin and COX-2 inhibitor therapy in sufferers of inflammatory conditions who are already at increased risk for cardiovascular disease.-Khan, S. I., Shihata, W. A., Andrews, K. L., Lee, M. K. S., Moore, X.-L., Jefferis, A.-M., Vinh, A., Gaspari, T., Dragoljevic, D., Jennings, G. L., Murphy, A. J., Chin-Dusting, J. P. F. Effects of high- and low-dose aspirin on adaptive immunity and hypertension in the stroke-prone spontaneously hypertensive rat.

Prostaglandins in Health and Disease: An Overview

OBJECTIVES

Prostaglandins are a group of biologically active compounds that play major roles in human physiology in both health and disease. They function in many different ways and in all major organs. This article reviews the basic physiology of prostaglandins and their application to specific effects on these systems in normal and abnormal clinical states. The critical therapeutic implications of the use of nonsteroidal antiinflammatory drugs in altering organ homeostasis are also examined.

METHODS

References were taken from Medline, Embase, and Index Medicus from 1966 to September 2005. A search was done with keywords, including prostaglandins, nonsteroidal antiinflammatory drugs, inflammation, arachidonic acid, Cox-1 (cyclooxygenase-1), and Cox-2 (cyclooxygenase-2).

RESULTS

There was a close correlation and predictability between basic prostaglandin physiology and the anticipated effects of these compounds on the heart, lungs, kidneys, gastrointestinal tract, bones and joints, brain, and male and female reproductive systems. These effects are organ and tissue specific. Despite these findings, unexplained and sometimes paradoxical physiologic responses were identified. A prime example of this is the role of prostaglandins in bone metabolism demonstrating both stimulatory and inhibitory effects. In addition all NSAIDs have the potential to impair the normal physiologic effects of prostaglandins depending primarily on the specific organ and the clinical setting.

CONCLUSIONS

Prostaglandins are regulatory compounds that play important roles in many physiologic processes in the human body. An understanding of the basic science of prostaglandins is valuable in anticipating the organ-specific biologic effects of these unique compounds in health and disease. However, at selected sites and under different physiologic conditions, unexplained and sometimes paradoxical effects are generated. Impairment of their regulatory functions can lead to significant short- or long-term organ dysfunction.

Balancing diuretic therapy in heart failure: loop diuretics, thiazides, and aldosterone antagonists

In heart failure, sodium is retained by the kidneys despite increases in extracellular volume. There is activation of renin secretion, which culminates in the production of angiotensin II, causing vasoconstriction and aldosterone secretion. These synergistically produce an increase in tubular reabsorption of sodium and water. Diuretics are the mainstay of symptomatic treatment to remove excess extracellular fluid in heart failure. Diuretics that affect the ascending loop of Henle are most commonly used. Thiazide diuretics promote a much greater natriuretic effect when combined with a loop diuretic in patients with refractory edema. Recently, spironolactone, an aldosterone receptor blocking agent, has been recommended to attenuate some of the neurohormonal effects of heart failure. Regardless of the diuretic, patients need to be counseled on the importance of avoiding sodium in their diet

Deficiency of COX-1 causes natriuresis and enhanced sensitivity to ACE inhibition

BACKGROUND

Prostanoid products of the cyclo-oxygenase (COX) pathway of arachidonic acid metabolism modulate blood pressure (BP) and sodium homeostasis. Conventional non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit both COX isoforms (COX-1 and -2), cause sodium retention, exacerbate hypertension, and interfere with the efficacy of certain anti-hypertensive agents such as angiotensin-converting enzyme (ACE) inhibitors. While a new class of NSAIDs that specifically inhibit COX-2 is now widely used, the relative contribution of the individual COX isoforms to these untoward effects is not clear.

METHODS

To address this question, we studied mice with targeted disruption of the COX-1 (Ptgs1) gene. Blood pressure, renin mRNA expression, and aldosterone were measured while dietary sodium was varied. To study interactions with the renin-angiotensin system, ACE inhibitors were administered and mice with combined deficiency of COX-1 and the angiotensin II subtype 1A (AT1A) receptor were generated.

RESULTS

On a regular diet, BP in COX-1-/- mice was near normal. However, during low salt feeding, BP values were reduced in COX-1-/- compared to +/+ animals, and this reduction in BP was associated with abnormal natriuresis despite appropriate stimulation of renin and aldosterone. Compared to COX-1+/+ mice, the actions of ACE inhibition were markedly accentuated in COX-1-/- mice. Sodium sensitivity and BP lowering also were enhanced in mice with combined deficiency of COX-1 and AT1A receptor.

CONCLUSIONS

The absence of COX-1 is associated with sodium loss and enhanced sensitivity to ACE inhibition, suggesting that COX-1 inhibition does not cause hypertension and abnormal sodium handling associated with NSAID use.

Combining salicylate and enalapril in patients with coronary artery disease and heart failure

OBJECTIVE

To study the effects of adding a salicylate to the angiotensin converting enzyme inhibitor enalapril in patients with heart failure due to coronary artery disease.

DESIGN

Double blind, crossover study for three days in hospital followed by an extended similar study outside hospital over two months of once daily enalapril plus salicylate and enalapril plus placebo.

SETTING

Tertiary referral centre.

PATIENTS

20 patients with heart failure due to myocardial infarction (New York Heart Association class II or III) and an ejection fraction less than 0.40. Twelve patients completed the two parts of the study.

MAIN OUTCOME MEASURES

Blood pressure, plasma converting enzyme activity; plasma angiotensin II and noradrenaline concentrations; excretion of metabolites of renal and systemic prostanoids.

RESULTS

The unloading effect of first and second dose of enalapril in the morning lasted only during the day; in the extended study it lasted 24 hours because of the drug's accumulation. Converting enzyme inhibitors attenuate the breakdown of bradykinin and therefore enhance prostaglandin E2 synthesis mediated by bradykinin. Evidence was found of such a prostaglandin E2 mediated contribution to ventricular unloading by enalapril, which was blocked by salicylate. The contribution, however, was small and variable, and salicylate addition had on average no significant de-unloading effect during the day. Unloading was abolished in only three of the 20 patients in the short term study and in one of the 12 in the extended study. At night, when other effects of enalapril on blood pressure had waned and the bradykinin induced effect persisted, salicylate significantly reduced the remaining small unloading effect. No effect was seen of salicylate addition on reversal of remodelling. Enalapril reduced angiotensin II induced synthesis of systemic and renal prostaglandin I2 and thromboxane A2, initially only during the day, but later also at night. It thereby masked suppression of thromboxane A2 synthesis by salicylate, which is the effect to which reinfarct prevention by salicylate is attributed.

CONCLUSION

The risk is low that salicylate will substantially reduce the benefit of enalapril in patients with heart failure by de-unloading the ventricle. Like other effects induced by bradykinin significant de-unloading occurs in only a minority of the patients. In the presence of enalapril, however, salicylate will probably not be as effective as expected in reducing reinfarction risk, because enalapril already reduces thromboxane A2 synthesis effectively in patients with heart failure and no further reduction by salicylate was found.

Indomethacin-induced renal dysfunction in patients with well-compensated cirrhosis

BACKGROUND

Patients with cirrhosis and ascites are especially sensitive to the adverse renal effects of indomethacin-induced inhibition of prostaglandin synthesis. The aim of this study was to determine whether indomethacin affects renal function in patients with well-compensated cirrhosis.

METHODS

Clearance techniques were used to assess renal hemodynamics and sodium and water homeostasis.

RESULTS

The oral administration of 50 mg of indomethacin to well-compensated patients with alcoholic cirrhosis was followed by a significant decrease in glomerular filtration rate (GFR) and effective renal plasma flow because of a preferential increase in afferent arteriolar tone. Indomethacin was both antidiuretic and antinatriuretic due principally to decreased free water clearance and increased proximal tubular reabsorption of sodium. The acute changes in renal function were not sustained. Patients with a high basal GFR were particularly sensitive to the adverse renal effects of indomethacin.

CONCLUSIONS

This study indicates that in patients with well-compensated cirrhosis renal prostaglandins are functionally active and may contribute to the pathogenesis of glomerular hyperfiltration. Nonsteroidal anti-inflammatory drugs should be used with caution in all patients with cirrhosis.

Inhibition of chloride/bicarbonate antiports in monkey kidney cells (Vero) by non-steroidal anti-inflammatory drugs

Two chloride/bicarbonate antiport mechanisms are involved in the regulation of cytosolic pH (pHi) in Vero cells, namely Na+-dependent chloride/bicarbonate antiport to normalize pHi after acidification of the cytosol, and Na+-independent Cl-/HCO3- exchange to regulate pHi back to normal after alkalinization of the cytosol. We have tested the effects of the non-steroidal anti-inflammatory drugs acetylsalicylic acid (aspirin), salicylic acid, indomethacin and piroxicam on chloride/bicarbonate exchange and on chloride self exchange in Vero cells. All these drugs were found to inhibit both the Na+-independent and the Na+-linked chloride/bicarbonate antiport in a dose dependent manner. The Na+-independent chloride/bicarbonate antiport was inhibited by lower doses of the drugs than the Na+-linked antiport. The ability of the drugs to inhibit chloride self exchange did not vary much with varying external pH, indicating that the inhibitory effect is due to the anionic form of the drugs. Inhibition occurred immediately upon addition of the drugs, and it was rapidly reversible, indicating that the inhibitory effect is due to direct interaction of the drugs with chloride/bicarbonate antiport, and not to inhibition of prostaglandin synthesis. The relevance of our findings to the clinical effects of the drugs is discussed.

Nephropathy in non-insulin-dependent diabetes mellitus

End-stage renal disease develops in about 5 percent of patients with non-insulin-dependent diabetes mellitus (NIDDM). The large majority of diabetic patients have this form of the disease. Thus, end-stage renal disease is an important clinical problem in patients with NIDDM. Moreover, hypertension and its macrovascular sequelae are significant problems in patients with NIDDM and may be linked with renal disease. A review of the problem of nephropathy in NIDDM is attempted, pointing out, where data are available, the clinical and pathophysiologic differences from its presentation in insulin-dependent diabetes. The need for further studies of the impact of renal disease in this maturity onset form of diabetes is emphasized.

Increased angiotensin II receptor binding with age in isolated rat glomeruli

The current investigation was performed to determine whether there are changes in the renin-angiotensin system with increasing age in rats. Experiments were performed on male Sprague-Dawley rats (50 to 165 days old). There were no changes in plasma renin activity or angiotensin II concentrations, but the number of angiotensin II binding sites in isolated glomeruli increased with increasing age (r = 0.87, P less than 0.01). Since rat weight varies directly with age, we studied the possibility that the increase in receptor number was due to changes in glomerular morphometrics. In a separate group of experiments the diameter of isolated glomeruli was measured, and assuming spherical shape, glomerular volume and surface area were calculated. Glomerular diameter increased with age and weight of the rats (r = 0.99, P less than 0.001). There was a strong linear correlation between the changes in angiotensin II receptor number and glomerular surface area (r = 0.99, P less than 0.001). The number of receptors per unit surface area was independent of rat weight or age (1224 receptors/micron 2). To test the hypothesis that the apparent increase in glomerular angiotensin II receptor sites with increasing age was due to the shape of the glomerulus, additional binding studies were performed on membranes prepared from isolated glomeruli. There were no differences in the number of angiotensin II receptors in membranes from 63 and 112 day-old rats (888 +/- 115 vs. 925 +/- 128 fmol/mg). In additional experiments the effects of increasing age on angiotensin modulation of renal function were studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosanoids and control of mesangial cell contraction

Contraction of glomerular mesangial cells is stimulated in vitro by the vasoconstrictor metabolite of arachidonic acid, thromboxane A2. To establish the role of mesangial prostaglandin (PG) synthesis in the modulation of contractile responses, we studied the effects of the stable thromboxane A2/endoperoxide analogue U-46619 on cultured rat mesangial cells preincubated with 1) four structurally unrelated, nonsteroidal anti-inflammatory drugs, indomethacin, acetylsalicylic acid, meclofenamate, and piroxicam, to inhibit the synthesis of PGE2, the major mesangial metabolite of arachidonic acid; 2) exogenous PGE2 and the stable analogue of PGI2, iloprost; and 3) indomethacin in the presence of exogenous PGE2. Computer-assisted image analysis microscopy demonstrated enhancement of spontaneous and agonist-induced contraction by nonsteroidal anti-inflammatory drugs in individual cells grown on a glass substrate, from 37.2 +/- 7.3% to a maximum of 75.5 +/- 6.4% of the cells with piroxicam, at 1 microM U-46619. PGE2 and iloprost dose-dependently inhibited U-46619-induced contraction, to 5.0 +/- 2.8% and 12.5 +/- 4.7% of the cells, respectively, at 1 microM U-46619. PGE2 also completely reversed the effects of indomethacin. Both PGE2 and iloprost dose-dependently stimulated intracellular cyclic AMP (cAMP) accumulation during 3-minute incubations, an effect that was blocked by the inhibitor of adenylate cyclase, 2',5'-dideoxyadenosine. The latter reversed the inhibitory action of PGE2, enhancing spontaneous and agonist-induced contractility, thus indicating a modulatory role of cAMP. We conclude that endogenous arachidonate metabolism regulates mesangial cell contraction through elevation of intracellular cAMP.

Effects of dietary fish oil on renal insufficiency in rats with subtotal nephrectomy

We studied the effects of fish oil on the progression of renal insufficiency in rats with subtotal nephrectomy. Five weeks after a 1-2/3 nephrectomy, sixteen rats were fed two different diets which differed only in fat composition. Lipid in the control diet was primarily beef tallow; that of the experimental diet, menhaden oil. Fish oil-fed rats had significant increases in plasma creatinines, decreases in urinary PGE2 and accelerated death rates. An additional twelve rats underwent 1-1/3 nephrectomies, and the same dietary manipulations, followed by renal clearance, histologic and biochemical studies after 12 weeks on the diets. Fish oil-fed rats again did worse, with decreased glomerular filtration rates and filtration fractions, more proteinuria and more glomerular sclerosis. Glomeruli and slices of cortex, medulla and papillae from rats fed fish oil produced much less PGE2 and TXB2 than dietary controls. Fish oil-induced suppression of renal PGE2 may be deleterious in this model and may outweigh the beneficial effect derived from TXA2 suppression. In contrast to fish oil's potentially therapeutic role in cardiovascular and immune-mediated renal disease, this diet is detrimental in rat renoprival nephropathy. This illustrates the importance of examining the effects of fatty acid manipulation individually for each disease entity.