Liver delivery of NO by NCX-1000 protects against acute liver failure and mitochondrial dysfunction induced by APAP in mice

Design, synthesis and biological study of hybrid drug candidates of nitric oxide releasing cucurbitacin-inspired estrone analogs for treatment of hepatocellular carcinoma

Development of hybrid drug candidates is well known strategy for designing antitumor agents. Herein, a novel class of nitric oxide donating cucurbitacin inspired estrone analogs (NO-CIEAs) were designed and synthesized as multitarget agents. Synthesized analogs were initially evaluated for their anti-hepatocellular carcinoma activities. Among the tested analogs, NO-CIEAs 17 and 20a exhibited more potent activity against HepG2 cells (IC₅₀ = 4.69 and 12.5 µM, respectively) than the reference drug Erlotinib (IC₅₀ = 25 µM). Interestingly, NO-CIEA 17 exerted also a high potent activity against Erlotinib-resistant HepG2 cell line (HepG2-R) (IC₅₀ = 8.21 µM) giving insight about its importance in drug resistance therapy. Intracellular measurements of NO revealed that NO-CIEAs 17 and 20a showed a significant increase in NO production in tumor cells after 1 h of incubation comparable to the reference prodrug JS-K. Flow cytometric analysis showed that both NO-CIEAs 17 and 20a mainly arrested the HepG2 cells in the G0/G1 phase. Also, In-Cell Based ELISA screening showed that NO-CIEA 17 resulted in a potential inhibitory activity towards the EGFR and MAPK (25% and 29% inhibition compared to untreated control cells, respectively). This data suggests the binding ability of NO-CIEA 17 to the EGFR and ERK to be well correlated along with the docking and cellular studies. Also, treatment of HepG2-R cells with NO-CIEA 17 showed a potential reduction of MRP2 expression in a dose dependent manner providing a significant impact on the chemotherapeutic resistance. Overall, the current study provides a potential new approach for the discovery of a novel antitumor agent against HCC.

Effectiveness of vinpocetine and isosorbide-5-mononitrate on experimental schistosomiasis mansoni: Biochemical and immunohistochemical study

Schistosomiasis is one of the most important tropical and subtropical devastating diseases, where praziquantel is the sole drug of choice. Praziquantel effectively kills the adult worms, however, drug resistance has been repeatedly reported. Moreover, there is currently no efficient anti-fibrotic therapy available for chronic schistosomiasis. So, novel drugs which exert anti-fibrotic efficacy are urgently needed. This research is complementary to our previous work that evaluated the anti-schistosomal effects of the anti-inflammatory vinpocetine, as well as the vasodilator and the anti-oxidant isosorbide-5-mononitrate. In the present study, we assessed the therapeutic efficacies of drugs in Swiss albino female mice experimentally infected with an Egyptian strain of Schistosoma mansoni, using some biochemical and immunohistochemical parameters. Our results revealed that both vinpocetine and isosorbide-5-mononitrate monotherapy significantly decreased hepatic nuclear factor-kappaB, 10 weeks post infection. The best effects were seen in mice administered praziquantel combined with isosorbide-5-mononitrate, as detected by reduction in hydroxyproline and collagen contents of the liver, and significant increase in the hepatic nitric oxide content. The data provides insight into the potential effects of the assessed drugs with isosorbide-5-mononitrate being more superior to vinpocetine, hence it can be used as novel adjuvant to praziquantel to alleviate schistosomal hepatic fibrosis. However, molecular mechanism/s and clinical trials are worthy to be scrutinized.

A comparative study on the anti-schistosomal and hepatoprotective effects of vinpocetine and isosorbide-5-mononitrate on Schistosoma mansoni-infected mice

Schistosomiasis is a remarkable public health problem in developing countries. Presently, praziquantel is the optional drug for all human schistosomiasis. Owing to the increased praziquantel resistance, there is an urgent need to develop new alternatives. This study aims at determining the anti-schistosomal and/or the hepatoprotective effects of the anti-inflammatory drug; vinpocetine, and the vasodilator and the nitric oxide donor; isosorbide-5-mononitrate, in comparison to praziquantel. In the present research, the therapeutic efficacies of these drugs were assessed in Swiss albino female mice (CD-I strain) experimentally infected with an Egyptian strain of Schistosoma mansoni, using some general, parasitological, and histopathological parameters. In this work, praziquantel significantly reduced worm burden and hepatic egg load, increased the percentage of dead eggs in the small intestine and decreased granuloma count, but did not reduce granuloma diameter. While, either vinpocetine or isosorbide-5-mononitrate monotherapy did not induce significant reduction in the worm count, hepatic egg load or shift in the oogram pattern, but significantly reduced granuloma count and diameter. Moreover, isosorbide-5-mononitrate significantly reduced hepatic inflammation and necrosis. The best results were obtained in the mice groups treated with isosorbide-5-mononitrate combined with praziquantel or vinpocetine. Our results point to vinpocetine and isosorbide-5-mononitrate as a convenient and promising adjuvant to praziquantel for ameliorating schistosomal liver pathology. Further studies are recommended to reveal the actual pathways responsible for the different activities of vinpocetine and isosorbide-5-mononitrate.

Role of Nitric Oxide Pathway in Development and Progression of Chronic Kidney Disease in Rats Sensitive and Resistant to its Occurrence in an Experimental Model of 5/6 Nephrectomy

BACKGROUND Understanding the mechanisms conditioning development of chronic kidney disease (CKD) is still a challenge. The aim of this study was to evaluate the activity of the intrarenal nitric oxide (NO) pathway in the context of sensitivity or resistance of different animal strains to the development and degree of renal failure. MATERIAL AND METHODS Two rat strains were used: Wistar (WR) and Sprague-Dawley rats (SDR) in a model of CKD - 5/6 nephrectomy. We assessed parameters of renal failure and expression of nitric oxide synthase (NOS) isoforms in renal cortex and medulla. RESULTS We did not observe renal failure in WR, and CKD developed in SDR with increase of creatinine and urea concentration as well as decrease of diuresis and glomerular filtration. In the renal cortex, baseline expression of NOS2 was higher in WR than in SDR. 5/6 nephrectomy resulted in reduction of NOS2 in both strains and NOS3 in WR. In the renal medulla, baseline NOS2 expression was higher in SDR, and nephrectomy resulted in its decrease only in SDR. Although baseline NOS3 expression was higher in SDR, the NOS3 expression after nephrectomy was higher in WR rats. CONCLUSIONS In model of CKD - 5/6 nephrectomy, SDR proved to be sensitive and WR resistant to development of CKD. The intrarenal activity of the nitric oxide pathway was the factor that differentiated both strains. This mechanism may be responsible for insensitivity of WR to development of renal failure in this model of CKD.

Design and synthesis of pyrazolo[3,4-d]pyrimidines: Nitric oxide releasing compounds targeting hepatocellular carcinoma

A new series of pyrazolo[3,4-d]pyrimidines tethered with nitric oxide (NO) producing functionality was designed and synthesized. Sulforhodamine B (SRB) protein assay revealed that NO releasing moiety in the synthesized compounds significantly decreased the cell growth more than the des-NO analogues. Compounds 7C and 7G possessing N-para-substituted phenyl group, released the highest NO concentration of 4.6% and 4.7% respectively. Anti-proliferative activity of synthesized compounds on HepG2 cell line identified compounds 7h, 7p, 14a and 14b as the most cytotoxic compounds in the series of IC₅₀=3, 5, 3 and 5μM, respectively, compared to erlotinib as a reference drug (IC₅₀=25μM). Flow cytometry studies revealed that 7h arrested the cells in G0/G1 phase of cell cycle while 7p arrested the cells in S phase. Moreover, docking study of the synthesized compounds on EGFR (PDB code: 1M17) and cytotoxicity study indicated that N-1 phenyl para substitution, pyrazole C-3 alkyl substitution and tethering the nitrate moiety through butyl group had a significant impact on the activity.

Hepatoprotective effect of nitric oxide in experimental model of acute hepatic failure

AIM: To evaluate the effect of nitric oxide (NO) on the development and degree of liver failure in an animal model of acute hepatic failure (AHF).

METHODS: An experimental rat model of galactosamine-induced AHF was used. An inhibitor of NO synthase, nitroarginine methyl ester, or an NO donor, arginine, were administered at various doses prior to or after the induction of AHF.

RESULTS: All tested groups developed AHF. Following inhibition of the endogenous NO pathway, most liver parameters improved, regardless of the inhibitor dose before the induction of liver damage, and depending on the inhibitor dose after liver damage. Prophylactic administration of the inhibitor was more effective in improving liver function parameters than administration of the inhibitor after liver damage. An attempt to activate the endogenous NO pathway prior to the induction of liver damage did not change the observed liver function parameters. Stimulation of the endogenous NO pathway after liver damage, regardless of the NO donor dose used, improved most liver function parameters.

CONCLUSION: The endogenous NO pathway plays an important role in the development of experimental galactosamine-induced AHF.

U12, a UDCA derivative, acts as an anti-hepatoma drug lead and inhibits the mTOR/S6K1 and cyclin/CDK complex pathways

U12, one of 20 derivatives synthesized from ursodeoxycholic acid (UDCA), has been found to have anticancer effects in liver cancer cell lines (SMMC-7721 and HepG2) and to protect normal liver cells from deoxycholic acid (DCA) damage (QSG-7701). Its anticancer mechanism was investigated using computer-aided network pharmacology and comparative proteomics. Results showed that its anti-malignancy activities were activated by mTOR/S6K1, cyclinD1/CDK2/4 and caspase-dependent apoptotic signaling pathways in hepatocellular carcinoma cells (HCC). The action of U12 may be similar to that of rapamycin. Animal testing confirmed that U12 exerted better anti-tumor activity than UDCA and had less severe side effects than fluorouracil (5-Fu). These observations indicate that U12 differs from UDCA and other derivatives and may be a suitable lead for the development of compounds useful in the treatment of HCC.

[Hepatotoxic efects of acetaminophen. Protective properties of tryptophan-derivatives]

Rat intoxication with acetaminophen (APAP) (500-1500 mg/kg body weight intragastrically) caused a considerable dose-dependent decrease in reduced glutathione (GSH) level in both liver cellular cytoplasm and mitochondria (at the dose 1500 mg/kg body weight by 60% and 33%, respectively). The cytoplasmic GSH level decreased more pronounced by comparison with that in mitochondria. At the same time, we did not observe any inactivation of the mitochondrial enzymes: succinate dehydrogenase, alpha-ketoglutarate dehydrogenase, glutathione peroxidase despite of mitochondrial GSH consumption; also we did not observe any decrease in the respiratory activity of liver mitochondria isolated from APAP-intoxicated rats. A tryptophan derivative, melatonin (10 mg/kg body weight), did not prevent intramitochondrial GSH oxidation, but decreased the hepatoxity of APAP, diminishing the activities of AlT and AsT as well as bilirubin level in blood plasma of intoxicated rats. N-acetyl-nitrosotryptophan (a nitric oxide donor) did not exhibit any hepatoprotective effects.

NCX 1000 Alone or in Combination with Vitamin E Reverses Experimental Nonalcoholic Steatohepatitis in the Rat Similarly to UDCA

We explored the therapeutic effect of NCX 1000, a derivative of ursodeoxycholic acid (UDCA) with nitric oxide (NO) donating properties, alone or in combination with vitamin E, in an experimental model of NASH in the rat. Methods. A control group was fed a standard liquid diet (Control), and the NASH groups were fed a high-fat liquid diet for 12 weeks without (NASH) or with simultaneous daily gavage with either NCX 1000 at 15 or 30 mg/kg (N15 and N30, resp.), or N15 plus vitamin E 100 mg/kg (N15  + VitE) for the last 6 weeks; UDCA 17.2 mg/kg was used as a reference. Results. NASH rats developed all key features of the disease. Treatments with N30 improved liver histology, decreased lipid peroxidation, and completely suppressed increases in LDH release, plasma insulin, and TNF-α. It also decreased O(2) (∙-) release and returned liver weight and glutathione back to normal. All effects were similar to the reference treatment, UDCA. The N15 treatment was less efficient than the N30 group, but became comparable to the latter when combined to vitamin E. Conclusion. Our study demonstrates that NCX 1000 has potent cytoprotective, antioxidant, and hypoinsulinemic properties that can be enhanced by combination with vitamin E.

Efficacy and cytotoxicity of a liver-targeted nitric oxide-releasing drug in the treatment of liver injury in mice

AIM: To evaluate the efficacy and cytotoxicity of NO-040527, a new liver-targeted nitric oxide-releasing drug, in the treatment of liver injury induced with carbon tetrachloride, acetaminophen or D-galactosamine in mice.

METHODS: Liver injury was induced in mice by intraperitoneal injection of carbon tetrachloride, acetaminophen or D-galactosamine. NO-040527 was orally administered to animals 1 h before and 12 h after the induction of liver injury. The animals were killed 24 h after drug delivery, and blood samples were taken to determine serum ALT and AST levels using an automatic biochemical analyzer. The cytotoxicity of the targeted conjugate was determined by methyl thiazol tetrazolium (MTT) assay.

RESULTS: NO-040527 could significantly inhibit carbon tetrachloride-induced elevation of ALT and AST in mice (both P < 0.01) in a dose-dependent manner. At the same dose (55 mg/kg), NO-040527 exhibited better efficacy than control drug NCX-1000 (P < 0.05) in lowering carbon tetrachloride-induced elevation of serum ALT and AST levels. Similarly, NO-040527 could also significantly inhibit acetaminophen-induced elevation of ALT and AST (both P < 0.01) though no dose-dependent effect was noted. At the same dose (55 mg/kg), NO-040527 exhibited similar efficacy to NCX-1000 in lowering acetaminophen-induced elevation of serum ALT and AST levels. NO-040527 showed no protective effects against liver injury induced with D-galactosamine. No significant differences were noted in serum ALT and AST levels between untreated mice with D-galactosamine-induced liver injury and those treated with medium- or low-dose NO-040527. However, the levels of serum ALT and AST in mice with D-galactosamine-induced liver injury treated with high-dose NO-040527 was higher than those in untreated ones. NO-040527 at a dose of 500 μmol/L began to show cytotoxicity (cell viability rate: 45.96% ± 29.46%; P = 0.058). Significant cytotoxicity was noted when the dose of NO-040527 rose to 1000 μmol/L (P < 0.005). NO-040527 at 50 and 100 μmol/L could accelerate cell growth (cell viability rate: 137.67% ± 8.47% and 152.65% ± 10.084%, respectively; both P < 0.05).

CONCLUSION: NO-040527 has good protective effects against carbon tetrachloride- or acetaminophen-induced liver injury in mice. NO-040527 is cytotoxic when used at high dose.

Lactoferrin protects against acetaminophen-induced liver injury in mice

Acetaminophen-induced liver injury (AILI) is a significant health problem and represents the most frequent cause of drug-induced liver failure in the United States. The development and implementation of successful therapeutic intervention strategies have been demanding, due to significant limitations associated with the current treatment for AILI. Lactoferrin (Lac), a glycoprotein present in milk, has been demonstrated to possess a multitude of biological functions. Our study demonstrated a profound protective effect of Lac in a murine model of AILI, which was not dependent on its iron-binding ability, inhibition of acetaminophen (APAP) metabolism, or a direct cytoprotective effect on hepatocytes. Instead, Lac treatment significantly attenuated APAP-induced liver sinusoidal endothelial cell dysfunction and ameliorated hepatic microcirculation disorder. This protective effect of Lac appeared to be dependent on hepatic resident macrophages (Kupffer cells [KCs]).

CONCLUSION

Collectively, our data indicate that Lac, through activation of KCs, inhibited APAP-induced liver sinusoidal endothelial cell damage and improved hepatic congestion, thereby protecting against AILI. These findings reveal the significant therapeutic potential of Lac during AILI and other types of liver diseases.

Hepatoprotective effects of the nitric oxide donor isosorbide-5-mononitrate alone and in combination with the natural hepatoprotectant, silymarin, on carbon tetrachloride-induced hepatic injury in rats

The aim of this study was to investigate the effect of the nitric oxide donor isosorbide-5-mononitrate (5-ISMN) alone or in combination with the natural hepatoprotectant with anti-oxidant activity silymarin on the carbon tetrachloride (CCl(4))-induced hepatic injury in rats. 5-ISMN (1.8, 3.6 or 7.2 mg/kg), silymarin (25 mg/kg) or 5-ISMN (1.8, 3.6 or 7.2 mg/kg) combined with silymarin was given once daily orally simultaneously with CCl(4) and for 15 days thereafter. Liver damage was assessed by determining serum enzyme activities and hepatic histopathology. 5-ISMN given at the above doses conferred significant protection against the hepatotoxic actions of CCl(4) in rats, reducing serum alanine aminotransferase (ALT) levels by 31.2, 39.3 and 61.6%, respectively, when compared with controls. Serum aspartate aminotransferase (AST) levels decreased by 19.8, 22.7 and 59.4%, respectively, while alkaline phosphatase (ALP) decreased by 26.1 and 32.6% by the drug at 3.6 and 7.2 mg/kg, respectively. When silymarin was added to 5-ISMN (1.8, 3.6 or 7.2 mg/kg), ALT decreased by 32.8, 59.6, 70.2% and AST by 28.7, 50.3, 60%, when compared with CCl(4) control group levels. Silymarin in combination with 3.6 or 7.2 mg/kg 5-ISMN resulted in 37.5 and 39.2% reductions in ALP when compared with CCl(4) control group. Meanwhile, silymarin alone reduced ALT, AST and ALP levels by 65.9, 52 and 62.3%, respectively. Blood levels of reduced glutathione were markedly decreased in CCl(4)-treated rats. Reduced glutathione levels were increased by the administration of 5-ISMN and restored to near normal values by silymarin treatment. Histopathological alterations by CCl(4) were markedly reduced after treatment with 5-ISMN alone or in combination with silymarin. Histopathologic examination of the livers of CCl(4)-treated rats administered 5-ISMN at 7.2 mg/kg showed marked restoration of the normal architecture of the liver tissue and minimal fibrosis. Silymarin co-administered with 5-ISMN resulted in further improvement of the histologic picture. These results indicates that treatment with 5-ISMN protects against hepatocellular necrosis induced by CCl(4). The study suggests a potential therapeutic use for 5-ISMN in combination with silymarin in liver injury.

Signal transduction pathways involved in drug-induced liver injury

Hepatocyte death following drug intake is the critical event in the clinical manifestation of drug-induced liver injury (DILI). Traditionally, hepatocyte death caused by drugs had been attributed to overwhelming oxidative stress and mitochondria dysfunction caused by reactive metabolites formed during drug metabolism. However, recent studies have also shown that signal transduction pathways activated/inhibited during oxidative stress play a key role in DILI. In acetaminophen (APAP)-induced liver injury, hepatocyte death requires the sustained activation of c-Jun kinase (JNK), a kinase important in mediating apoptotic and necrotic death. Inhibition of JNK using chemical inhibitors or knocking down JNK can prevent hepatocyte death even in the presence of extensive glutathione (GSH) depletion, covalent binding, and oxidative stress. Once activated, JNK translocates to mitochondria, to induce mitochondria permeability transition and trigger hepatocyte death. Mitochondria are central targets where prodeath kinases such as JNK, prosurvival death proteins such as bcl-xl, and oxidative damage converge to determine hepatocyte survival. The importance of mitochondria in DILI is also observed in the Mn-SOD heterozygous (+/-) model, where mice with less mitochondrial Mn-SOD are sensitized to liver injury caused by certain drugs. An extensive body of research is accumulating suggesting a central role of mitochondria in DILI. Drugs can also cause redox changes that inhibit important prosurvival pathways such as NF-kappaB. The inhibition of NF-kappaB by subtoxic doses of APAP sensitizes hepatocyte to the cytotoxic actions of tumor necrosis factor (TNF). Many drugs will induce liver injury if simultaneously treated with LPS, which promotes inflammation and cytokine release. Drugs may be sensitizing hepatocytes to the cytotoxic effects of cytokines such as TNF, or vice versa. Overall many signaling pathways are important in regulating DILI, and represent potential therapeutic targets to reduce liver injury caused by drugs.

Acetaminophen hepatotoxicity: NO to the rescue

Severe liver injury as a result of overdose or chronic use of acetaminophen (paracetamol) remains a significant clinical problem, accounting for as much as 40% of cases of acute liver failure. The mechanisms underlying the liver injury caused by acetaminophen have become much better understood in recent years. In this issue, Fiorucci et al. report that delivery of nitric oxide (NO) in small amounts to the liver, via a novel derivative of the bile acid ursodeoxycholic acid, results in significant protection of the liver from acetaminophen-induced damage. NO appears to produce these beneficial actions through several mechanisms, including the suppression of synthesis of several proinflammatory cytokines. There is also substantial evidence that a NO-releasing derivative of acetaminophen offers several advantages over acetaminophen itself, including enhanced analgesic potency and reduced liver toxicity.

New strategy for the antifibrotic therapy with oral administration of FR260330 (a selective inducible nitric oxide synthase inhibitor) in rat experimental liver cirrhosis

Inducible nitric oxide synthase (iNOS) activity is significantly elevated in viral hepatitis, alcoholic cirrhosis, and cholestasis. However, there are few reports on the relationship between iNOS and cirrhosis. Here, we investigated the effects of a new iNOS inhibitor that has been developed for oral administration in an experimental rat liver cirrhosis model. A cirrhotic rat model was developed by long-term administration of thioacetamide injections. FR260330 is a new, rationally designed, selective iNOS inhibitor that can be administered orally. After 12 weeks of treatment with FR260330, the rats showed inhibition of progressions of cirrhosis, ascites, and splenomegaly as well as a significant reduction in the proportions of connective tissue in the liver. The expression of nitrotyrosine, which indicates the existence of peroxynitrite and nuclear factor-kappaB activation, was remarkably decreased in the FR260330 treatment group. In addition, immunohistochemical and Western blot analyses showed that the expression of transforming growth factor-beta1 was remarkably decreased in this group. The present study demonstrates that FR260330 reduces liver fibrosis by the inhibition of transforming growth factor-beta1 and retards the development of cirrhosis. This oral iNOS inhibitor will be a new strategy for the treatment of cirrhosis.

Multiple effects of acetaminophen and p38 inhibitors: towards pathway toxicology

The majority of drug-related toxicities are idiosyncratic, with little pathophysiological insight and mechanistic understanding. Pathway toxicology is an emerging field of toxicology in the post-genomic era that studies the molecular interactions between toxicants and biological pathways as a way to bridge this knowledge gap. Using two case studies--acetaminophen and p38 MAPK inhibitors--this review illustrates how a pathway-based perspective has advanced our understanding of compound and target-based toxicities. The advancement of pathway toxicology will be dependent on integrated applications of techniques from basic sciences and a fundamental understanding of the interdependence of multiple biological pathways in living organisms.

alpha(1)-Adrenoceptor antagonists prevent paracetamol-induced hepatotoxicity in mice

BACKGROUND AND PURPOSE

Paracetamol, a major cause of acute liver failure (ALF) represents a significant clinical problem. Adrenoceptor stimulation or antagonism can modulate chemical-induced hepatotoxicity. We investigated the role of endogenous catecholamines and alpha(1)-adrenoceptors in the development of paracetamol- induced hepatotoxicity.

EXPERIMENTAL APPROACH

Paracetamol (3.5 mmol kg(-1)) was administered to male CD-1 mice, with and without alpha(1)-adrenoceptor antagonists (prazosin, doxazosin, terazosin and tamsulosin; 35.7 micromol kg(-1)). Serum transaminases and hepatic glutathione (GSH) levels were assessed as markers of hepatic damage. Paracetamol bioactivation was assessed by covalent binding, hepatic and urinary conjugate formation and uridine glucuronosyltransferase activity. Plasma catecholamines levels and hepatic congestion were also analysed.

KEY RESULTS

Plasma catecholamine levels were significantly elevated 5 h post paracetamol administration. Prazosin prevented hepatotoxicity when administered 1 h before a toxic paracetamol insult and importantly, when administered up to 1 h post paracetamol injection. Prazosin had no effect on paracetamol-induced depletion of hepatic GSH, paracetamol bioactivation or paracetamol-induced transcription of defence genes. Paracetamol toxicity is associated with marked accumulation of erythrocytes within hepatic sinusoids and prazosin completely prevented this accumulation.

CONCLUSION AND IMPLICATIONS

Paracetamol-induced hepatocellular damage is associated with increased circulating catecholamines. alpha(1)-Adrenoceptor antagonists conferred complete protection from paracetamol -induced hepatotoxicity. Protection was associated with absence of hepatic erythrocyte accumulation. Increased catecholamine levels may contribute to the pathophysiology of paracetamol-induced hepatotoxicity by compromising hepatic perfusion. Protection against paracetamol toxicity by alpha(1) antagonists in mice has implications for therapeutic management of patients presenting with paracetamol overdose and ALF.

Organ systems dependent on nitric oxide and the potential for nitric oxide-targeted therapies in related diseases

Nitric oxide (NO) is a universal messenger molecule that plays diverse and essential physiologic roles in multiple organ systems, including the vasculature, bone, muscle, heart, kidney, liver, and central nervous system. NO is produced by 3 known isoforms-endothelial, neuronal, and inducible NO synthase-each of which perform distinct functions. Impairment of NO bioactivity may be an important factor in the pathogenesis of a wide range of conditions, including preeclampsia, osteoporosis, nephropathy, liver disease, and neurodegenerative diseases. Although increased levels of NO synthase or NO bioactivity have been associated with some of these disease states, research increasingly suggests that preservation or promotion of normal NO bioactivity may be beneficial in reducing the risks and perhaps reversing the underlying pathophysiology. Based on this rationale, studies investigating the use of NO-donating or NO-promoting agents in some of these diseases have produced positive results, at least to some degree, in either animal or human studies. Further investigation of NO-targeted therapies in these diverse diseases is clearly mandated.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Role of inflammation in the mechanism of acetaminophen-induced hepatotoxicity

Acetaminophen (AAP) overdose and the resulting hepatotoxicity is an important clinical problem. In addition, AAP is widely used as a prototype hepatotoxin to study mechanisms of chemical-induced cell injury and to test the hepatoprotective potential of new drugs and herbal medicines. Because of its importance, the mechanisms of AAP-induced liver cell injury have been extensively investigated and controversially discussed for > 30 years. This review highlights recent new insight into intracellular events critical for liver cell death. In addition, the relevance of the inflammatory response is addressed, including cytotoxic and inflammatory mediators generated by activated inflammatory cells, that is, resident macrophages and lymphocytes as well as newly recruited blood-derived leukocytes. Inflammation is a critical component of the overall pathophysiology, not only as a potential factor that may aggravate cell damage, but more importantly as a vital response to limit cell injury, remove cell debris and promote regeneration.

Recent pharmacological advances in paediatric analgesics

Growth and development are two linked processes that distinguish children from adults. The use of size as the primary covariate during pharmacokinetic (PK) analyses allows exploration of the effects of age. Allometric scaling models have assisted understanding of the developmental clearance changes in common analgesic drugs such as paracetamol, morphine, tramadol and local anaesthetics agents. Single nucleotide polymorphisms (pharmacogenomics [PG]) and their impact on hepatic drug metabolism for opioids, tramadol, non-steroidal anti-inflammatory drugs (NSAIDs) and drug receptor responses are increasingly reported. Altered chemical structure or formulations of common analgesics alter pharmacodynamic (PD) effects enhancing safety and efficacy for NSAIDs by stereoselectivity and the addition of nitric oxide, for intravenous paracetamol by formulation and structural difference from propacetamol and for local anaesthetics through stereoselectivity. This article focuses upon recent data for analgesics used in paediatric pain management including paracetamol, NSAIDs, morphine, tramadol, amide local anaesthetics and ketamine. It centres on PK and clinical studies in neonates, infants and children. PG studies are acknowledged as potentially allowing individual drug therapy tailoring through a decrease in between-patient population variability, although the impact of PG in the very young is less certain. There are few data describing age-related PD changes in children despite recognition that the number, affinity and type of receptors or the availability of natural ligands changes with age.

Recent developments in the pharmacological management of pain in children

PURPOSE OF REVIEW

This review explores progress in developmental pharmacokinetics, pharmacogenomics and formulations of analgesic agents, and discusses potential implications for pain therapy.

RECENT FINDINGS

Characterization of the developmental pharmacokinetics of morphine, tramadol, paracetamol and nonsteroidal anti-inflammatory drugs has improved dosing in children. Oral sugar solutions have replaced the brandy/sugar pacifier and are effective for single painful events in neonates. Intravenous paracetamol offers increased dosing accuracy, and avoids absorption and bioavailability variability. New nitric-oxide-releasing versions of paracetamol and nonsteroidal anti-inflammatory drugs offer safer alternatives to their parent drugs with enhanced potency. Ketamine has come under a cloud for its possible effects on the neonatal developing brain, but it is being used increasingly in children to supplement opioids for pain after major surgery. Hopes that morphine analgesia may improve neurological outcome in premature babies have not materialized. Reports concerning chronic pain are generally case series and controlled trials are rare and nearly nonexistent in children.

SUMMARY

Unlicensed drug use in the very young will increase as familiarity increases. Pharmacogenomic studies have the potential to tailor drug therapy to the individual and decrease between-patient variability. Unfortunately, the pharmacodynamic knowledge in children of analgesic agents remains neglected and is usually extrapolated from adult data.

Involvement of Toll-like receptor 4 in acetaminophen hepatotoxicity

The objective of this study was to determine whether Toll-like receptor 4 (TLR4) has a role in alcohol-mediated acetaminophen (APAP) hepatotoxicity. TLR4 is involved in the inflammatory response to endotoxin. Others have found that ethanol-mediated liver disease is decreased in C3H/HeJ mice, which have a mutated TLR4 resulting in a decreased response to endotoxin compared with endotoxin-responsive mice. In the present study, short-term (1 wk) pretreatment with ethanol plus isopentanol, the predominant alcohols in alcoholic beverages, caused no histologically observed liver damage in either C3H/HeJ mice or endotoxin-responsive C3H/HeN mice, despite an increase in nitrotyrosine levels in the livers of C3H/HeN mice. In C3H/HeN mice pretreated with the alcohols, subsequent exposure to APAP caused a transient decrease in liver nitrotyrosine formation, possibly due to competitive interaction of peroxynitrite with APAP producing 3-nitroacetaminophen. Treatment with APAP alone resulted in steatosis in addition to congestion and necrosis in both C3H/HeN and C3H/HeJ mice, but the effects were more severe in endotoxin-responsive C3H/HeN mice. In alcohol-pretreated endotoxin-responsive C3H/HeN mice, subsequent exposure to APAP resulted in further increases in liver damage, including severe steatosis, associated with elevated plasma levels of TNF-alpha. In contrast, alcohol pretreatment of C3H/HeJ mice caused little to no increase in APAP hepatotoxicity and no increase in plasma TNF-alpha. Portal blood endotoxin levels were very low and were not detectably elevated by any of the treatments. In conclusion, this study implicates a role of TLR4 in APAP-mediated hepatotoxicity.

Nitric oxide donor drugs: an update on pathophysiology and therapeutic potential

The discovery of the multiple physiological and pathophysiological processes in which nitric oxide (NO) is involved has promoted a great number of pharmacological researches to develop new drugs that are capable of influencing NO production directly and/or indirectly for therapeutic purposes (i.e, NO-releasing drugs, NO-inhibiting drugs, and phosphodiesterase V inhibitors). In particular, the so-called NO donor drugs could actually have an important therapeutic effect in the treatment of many diseases such as arteriopathies (atherosclerosis and its sequelae, arterial hypertension and some forms of male sexual impotence), various acute and chronic inflammatory conditions (colitis, rheumatoid arthritis and tissue remodelling), and several degenerative diseases (Alzheimer's disease and cancer). The old organic nitrates show some well-known pitfalls including the induction of tolerance and acute side effects related to abrupt vasodilation such as cephalea and hypotension, which limit their therapeutic indications. A low therapeutic index (i.e., peroxynitrite toxicity) has always characterised the sydnonimines class. A series of interesting new classes of NO donors are under intense pharmacological investigation and scrutiny (S-nitrosothiols, diazeniumdiolates and NO hybrid drugs), each characterised by a particular pharmacokinetic and pharmacodynamic profile. The most important obstacle in the field of NO donor drugs is represented by the difficulty in targeting NO release, and thereby its effects, to a particular tissue.

Morphology and regulatory mechanism of hepatocyte apoptosis in experimental fulminant hepatic failure

AIM: To study the morphological changes and the regulation of nitric oxide (NO), Fasand Bcl-2 on hepatocyte apoptosis in mouse model of experimental fulminant hepatic failure (FHF)..

METHODS: Mouse model of experimental FHF was established by combination of lipopolysaccharide (LPS) and D-galactosamin (D-GalN). The expression of Fas and Bcl-2 in the liver tissues was tested by immunohistochemistry. The level of serum NO and iNOS mRNA expression in liver were tested by nitrate reductase method and reverse transcription polymerase chain reaction (RT-PCR), respectively. The hepatocyte apoptosis was examined by TUNEL method. In addition, the changes of the above items were observed after pretreatment with L-NMMA, an inhibitor of iNOS.

RESULTS: The level of serum NO and expression of iNOS mRNA in the liver tissues were increased at 2 h in model group, reaching the peak at 4 h. There was a little Fas expression at 2 h in model group. The expression of Fas was increased significantly at 8 and 12 h, which was distinctly higher than that at 2 h (100% vs 20%, P < 0.01) and 4 h (100% vs 40%, P < 0.05). The expression of Bcl-2 started to increase at 2 h, reaching the peak at 4 h, which was markedly higher than that at 2 h (90% vs 60%, P < 0.05). The expression of Bcl-2 at 4 h was also significantly higher than that at 8 or 12 h (90% vs 20%, both P < 0.01). Typical features of hepatocyte apoptosis were observed at 8 h. The level of serum NO and liver iNOS mRNA expression were normal and the Fas, Bcl-2 expression did not change notably after L-NMMA administration in comparison with those in model group (P > 0.05). Typical hepatocyte apoptosis was also observed at 8 h after L-NMMA administration, and the pathological changes of the liver tissues were more severe.

CONCLUSION: Both expression of Fas and Bcl-2 are increased in FHF. Fas expression is consistent with hepatocyte apoptosis, while Bcl-2 expression is negatively correlated with hepatocyte apoptosis. Single administration of iNOS inhibitor can not protect hepatocytes against apoptosis and injury.

Drug-induced liver disease 2004

PURPOSE OF REVIEW

To summarize the salient reviews, studies and case reports and series that dealt with clinical, pathological, methodological, and epidemiological descriptions of drug-induced liver disease in the calendar year 2004.

RECENT FINDINGS

While no new causes of drug-induced liver injury were reported for 2004, several new reports of previously recognized hepatotoxins, including herbal products, were published. These include the antiretroviral drugs for HIV and agents to manage tuberculosis. Acetaminophen (APAP) retained its preeminent position as the leading cause of drug-induced acute liver failure, currently accounting for nearly 50% of cases according to the latest figures from the U.S. Acute Liver Failure Study Group. Not surprisingly, APAP also heads the list of drugs and toxins leading to liver transplantation for acute hepatic failure. Efforts to reduce the number of cases of intentional APAP poisonings by restricting the number of tablets sold at any one time in the UK are ongoing, but the success of the program may be lessening, as was pointed out this year. The use of potentially hepatotoxic medications in patients with underlying liver disease was examined with the statins, and they emerged as a safe class for use in this setting.

SUMMARY

Given the apparent increasing incidence of acute liver failure attributable to APAP in the US, additional efforts are still needed to better define the risks associated with its use and to further reduce the incidence of severe liver injury from this widely used agent.