The reversal of experimental cyclosporin A nephrotoxicity by thromboxane synthetase inhibition

Role of endoplasmic reticulum stress in drug-induced toxicity

Drug‐induced toxicity is a key issue for public health because some side effects can be severe and life‐threatening. These adverse effects can also be a major concern for the pharmaceutical companies since significant toxicity can lead to the interruption of clinical trials, or the withdrawal of the incriminated drugs from the market. Recent studies suggested that endoplasmic reticulum (ER) stress could be an important event involved in drug liability, in addition to other key mechanisms such as mitochondrial dysfunction and oxidative stress. Indeed, drug‐induced ER stress could lead to several deleterious effects within cells and tissues including accumulation of lipids, cell death, cytolysis, and inflammation. After recalling important information regarding drug‐induced adverse reactions and ER stress in diverse pathophysiological situations, this review summarizes the main data pertaining to drug‐induced ER stress and its potential involvement in different adverse effects. Drugs presented in this review are for instance acetaminophen (APAP), arsenic trioxide and other anticancer drugs, diclofenac, and different antiretroviral compounds. We also included data on tunicamycin (an antibiotic not used in human medicine because of its toxicity) and thapsigargin (a toxic compound of the Mediterranean plant Thapsia garganica) since both molecules are commonly used as prototypical toxins to induce ER stress in cellular and animal models.

A role for the thromboxane receptor in L-NAME hypertension

Actions of the lipid mediator thromboxane (Tx) A2 acting through the TP receptor contribute to the pathogenesis of cardiovascular disease. To further explore the role of TxA2 in hypertension, we examined the consequences of deficiency of the TP receptor on the course of hypertension associated with endothelial dysfunction and salt sensitivity. To this end, the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) was administered to TP-deficient (Tp-/-) and wild-type (Tp+/+) control mice in drinking water for 21 wk along with a high-salt (HS; 6% NaCl) diet. Administration of L-NAME increased urinary excretion of TxB2 to a similar extent in both Tp+/+ and Tp-/- animals. L-NAME also caused significant and sustained elevations in blood pressure that reached a maximum between weeks 3 and 6. However, the severity of hypertension was attenuated in the Tp-/- mice throughout the study period (P<0.001). At the end of the study, the wild-type mice developed significant cardiac hypertrophy (23.6+/-2% increase in heart-to-body weight ratio). The severity of cardiac hypertrophy was attenuated in the TP-deficient group (11.1+/-2.6%; P<0.05). In contrast, kidney hypertrophy was exaggerated in the Tp-/- mice compared with controls (37.1+/-5.4 vs. 12.3+/-2.3%; P<0.01). Moreover, the severity of glomerulosclerosis, tubule vacuolization, and interstitial chronic inflammation was also enhanced in the Tp-/- group (P<0.01). Thus, in L-NAME hypertension, TP receptors contribute to elevated blood pressure and cardiac hypertrophy. In this model, TP receptors also provided unexpected protection against kidney injury.

Fish oil: what the prescriber needs to know

There is a general belief among doctors, in part grounded in experience, that patients with arthritis need nonsteroidal anti-inflammatory drugs (NSAIDs). Implicit in this view is that these patients require the symptomatic relief provided by inhibiting synthesis of nociceptive prostaglandin E₂, a downstream product of the enzyme cyclo-oxygenase (COX), which is inhibited by NSAIDs. However, the concept of 'safe' NSAIDs has collapsed following a multiplicity of observations establishing increased risk for cardiovascular events associated with NSAID use, especially but not uniquely with the new COX-2-selective NSAIDs. This mandates greater parsimony in the use of these agents. Fish oils contain a natural inhibitor of COX, reduce reliance on NSAIDs, and reduce cardiovascular risk through multiple mechanisms. Fish oil thus warrants consideration as a component of therapy for arthritis, especially rheumatoid arthritis, in which its symptomatic benefits are well established. A major barrier to the therapeutic use of fish oil in inflammatory diseases is ignorance of its mechanism, range of beneficial effects, safety profile, availability of suitable products, effective dose, latency of effects and instructions for administration. This review provides an evidence-based resource for doctors and patients who may choose to prescribe or take fish oil.

Normal renal function 8 to 13 years after cyclosporin A therapy in 285 diabetic patients

BACKGROUND

Cyclosporin A (CyA) may induce acute nephrotoxicity. The question has been raised of the possible long-term unfavorable course of CyA-induced lesions. Advantage was taken of a large cohort of diabetic patients treated for several months using moderate CyA dosage to evaluate the long-term evolution of renal function in such patients.

METHODS

Two hundred and eighty five recently diagnosed type 1 diabetic patients having received CyA for a mean of 19.9 months were monitored for 13 years, in parallel with 100 similar patients treated with insulin alone.

RESULTS

In the CyA-treated group, a transient increase in creatininemia levels occurred during the first 18 months of treatment associated with a transient increase in renal vascular resistance. Both effects disappeared later on: creatininemia levels then remained normal. Inulin and p-aminohippurate (PAH) clearances remained normal throughout follow-up. Neither permanent renal failure nor progressive deterioration of renal function occurred in either group or in individual patients. A 10 to 12% increase in inulin and PAH clearance was elicited by IV amino acid infusion at 7 to 10 years, a finding consistent with a normal renal functional reserve. Patients with moderate kidney lesions on biopsy at 1 year had normal and stable clearance values at 7 to 13 years. The prevalence of arterial hypertension and retinopathy was lower in the CyA-treated group than in the control group, possibly because of the tighter metabolic control obtained in the CyA group.

CONCLUSION

These results suggest that low-dose CyA treatment combined with thorough monitoring does not result in long-term renal dysfunction.

Cyclosporine-induced interstitial fibrosis and arteriolar TGF-beta expression with preserved renal blood flow

BACKGROUND

Cyclosporine A (CsA)-induced chronic nephrotoxicity is characterized by interstitial fibrosis and afferent arteriole hyalinosis. CsA lesion has been linked to maintained renal vasoconstriction and narrowing of the afferent arteriole lumen diameter, leading to preglomerular ischemia. We investigated the role of renal hemodynamics in CsA-induced transforming growth factor (TGF-beta) expression and interstitial fibrosis.

METHODS

Groups of rats fed a low salt diet were given CsA 5 mg/kg/day (CsA) or the vehicle (olive oil, [VH]) s.c. and had the renal blood flow (RBF), glomerular filtration rate (GFR), mean arterial pressure, renal vascular resistance, renal histologic changes, and immunohistochemical features for macrophages and TGF-beta evaluated after 1, 2, and 8 weeks of treatment.

RESULTS

At week 1, despite normal renal hemodynamics and MAP, there was a significant macrophage interstitial influx in CsA-treated rats (70+/-16 vs. 29+/-4 cells+/0.5 mm2, in CsA vs. VH, P=0.02) that was progressive with treatment (80+/-13 vs. 32+/-8 cells+/0.5 mm2, P=0.016 and 197+/-36 vs. 23+/-3 cells+/0.5 mm2, P=0.0002, CsA vs. VH at 2 and 8 weeks, respectively). After 2 weeks of treatment, CsA animals developed a significant interstitial fibrosis, with preserved RBF, even when it was assessed 2 hr after CsA injection. There was a significant increase in the immunostaining for TGF-beta in the juxtaglomerular arterioles in CsA-treated rats (48.6+/-3.8 vs. 35.1+/-1.1%, CsA vs. VH at 2 weeks, P<0.05 and 59.0+/-3.2 vs. 37.0+/-2.1%, CsA vs. VH at 8 weeks, P=0.0001). A significant and progressive GFR decrease followed the renal structural injury of CsA treatment. Arteriolar and glomerular anatomic injury were not found throughout the study.

CONCLUSIONS

Low CsA doses might generate interstitial fibrosis without any decrease in RBF or structural arteriolar lesion evidence, possibly through early macrophage influx and increased TGF-beta expression. It clearly seems that CsA-induced ischemia and tubulointerstitial injury may occur independently, suggesting that chronic CsA nephrotoxicity may be very hard to prevent or even not be preventable at all.

Cyclosporine-induced coronary artery constriction--dissociation between thromboxane release and coronary vasospasm

Cyclosporine influences vascular tone, including that of coronary arteries. But its effect on myocardial prostanoid release, which may contribute to a drug-induced coronary and/or myocardial dysfunction, remains unknown. We used the isolated perfused rat heart to study the effect of cyclosporine on both the mechanical function parameters and myocardial prostanoid release into the effluent by ELISA. Cyclosporine (5 microM) induced an increase of perfusion pressure from 40 +/- 3 to 73 +/- 4 mm Hg within 60 minutes (p < 0.001), reflecting an increase of coronary tone. Cyclosporine did not affect heart rate but contractility (+dp/dtmax) tended to decrease, although not significantly. The drug's effect on coronary tone was rapidly reversible upon withdrawal. Cyclosporine perfusion resulted in an increase of thromboxane B2 liberation from 236 +/- 150 to 1321 +/- 354 pg/ml effluent (p < 0.001), whereas the 6-keto-prostaglandin F1 alpha release was unaffected. The vehicle cremophor did not change any of these parameters. Neither inhibition of myocardial prostanoid formation with acetylsalicylic acid nor thromboxane receptor blockade prevented the cyclosporine-induced increase of perfusion pressure. However, perfusion with nitroglycerin or the voltage-sensitive calcium channel antagonist nifedipine in addition to cyclosporine were able to prevent the increase of perfusion pressure. This is the first time it has been demonstrated that cyclosporine induces an acute release of the prostanoid thromboxane within the myocardium. Despite the resulting imbalance in favor of the vasoconstrictive prostanoid, a dependency of the cyclosporine-induced increase of coronary tone on this imbalance was excluded. Conversely, nitric oxide donation or calcium channel blockade were able to prevent the negative effect of the drug on coronary tone, supporting the concept of endothelium-dependent and/or myogenic mechanism of cyclosporine toxicity on the coronary vascular bed.

Cyclosporine A nephrotoxicity: role of thromboxane and reactive oxygen species

The main adverse effect of cyclosporine A (CyA) is nephrotoxicity. CyA increases urinary concentrations of thromboxane A2 (TXA2), a potent vasoconstrictor that can be involved in kidney failure induced by CyA. Furthermore, it has been postulated that a relationship exists between oxygen free radicals and the synthesis of arachidonate metabolites in experimental models of CyA nephrotoxicity. We studied the effect of vitamin E (VitE), an oxygen free radical scavenger, on renal function, on glomerular synthesis of thromboxane B2 (TXB2), and on free radicals in rats treated with CyA. Four groups of male Wistar rats were studied: (1) a control group; (2) a group given VitE at 0.05 mg/dl in drinking water for 25 days; (3) a group given CyA at 50 mg/kg body weight/day orally for 10 days; and (3) a group given Vit E + CyA, in which rats were provided with drinking water containing VitE for 15 days and afterwards were treated with VitE and CyA for 10 days. Renal function parameters and glomerular synthesis of TXB2, superoxide anion (02.-), malondialdehyde (MDA), and hydrogen peroxide (H202) were evaluated. CyA decreased body weight, caused deterioration of kidney function and increased glomerular synthesis of TXB2, O2.-, MDA, and H202. Pretreatment with VitE prevented the effects of CyA on kidney function and decreased glomerular synthesis of these mediators. In conclusion, CyA induced glomerular synthesis of reactive oxygen species (ROS) and TxB2. Pretreatment with VitE inhibited acute renal failure induced by CyA, probably by scavenging free radicals and by inhibiting the synthesis of TXB2.

Urinary excretion of 2,3-dinor-thromboxane B1, a major metabolite of thromboxane B2 in the rat

Urinary 2,3-dinor-thromboxane B2 (2,3-dinor-TXB2), an enzymatic degradation product of TXB2, is currently measured for evaluating in vivo thromboxane biosynthesis in rats. We simultaneously measured 2,3-dinor-TXB2 and 2,3-dinor-TXB1, another product of TXB2 metabolism, in the urine of rats by immunoaffinity extraction/gas chromatography negative ion chemical ionization mass spectrometry (GC-NICIMS). In rats under basal conditions, urinary excretion of 2,3-dinor-TXB1 was much higher than that of 2,3-dinor-TXB2 (19.22 +/- 4.86 and 1.64 +/- 0.29 ng/24 h, respectively). The relative abundance of the two metabolites in each animal was fairly constant (91.9 +/- 1.6 and 8.1 +/- 1.6% of their sum, respectively). Urinary excretion of both 2,3-dinor-TXB1 and 2,3-dinor-TXB2 increased in rats undergoing in vivo hepatic ischemia-reperfusion. Other thromboxane metabolites, including 11-dehydro-TXB2 and 11-dehydro-2,3-dinor-TXB2, were measured by GC-NICIMS in selected urines. The resulting profile was: 2,3,4,5-tetranor-TXB1 > 2,3-dinor-TXB1 >> 11-dehydro-TXB2 > 2,3-dinor-TXB2 = TXB2. This study shows that urinary 2,3-dinor-TXB1 is a suitable parameter of TXB2 biosynthesis in vivo in rats. The possible cross-reactivity of 2,3-dinor-TXB1 in immunoassays of urinary 2,3-dinor-TXB2 or even TXB2 in rats should be considered in future studies.