Accelerated Cytotoxic Mechanism Screening of Hydralazine Using an in Vitro Hepatocyte Inflammatory Cell Peroxidase Model

Drug-induced organ injury in coronavirus disease 2019 pharmacotherapy: Mechanisms and challenges in differential diagnosis and potential protective strategies

The world is currently facing an unprecedented pandemic caused by a newly recognized and highly pathogenic coronavirus disease 2019 (COVID-19; induced by SARS-CoV-2 virus), which is a severe and ongoing threat to global public health. Since COVID-19 was officially declared a pandemic by the World Health Organization in March 2020, several drug regimens have rapidly undergone clinical trials for the management of COVID-19. However, one of the major issues is drug-induced organ injury, which is a prominent clinical challenge. Unfortunately, most drugs used against COVID-19 are associated with adverse effects in different organs, such as the kidney, heart, and liver. These side effects are dangerous and, in some cases, they can be lethal. More importantly, organ injury is also a clinical manifestation of COVID-19 infection. These adverse reactions are increasingly recognized as outcomes of COVID-19 infection. Therefore, the differential diagnosis of drug-induced adverse effects from COVID-19-induced organ injury is a clinical complication. This review highlights the importance of drug-induced organ injury, its known mechanisms, and the potential therapeutic strategies in COVID-19 pharmacotherapy. We review the potential strategies for the differential diagnosis of drug-induced organ injury. This information can facilitate the development of therapeutic strategies, not only against COVID-19 but also for future outbreaks of other emerging infectious diseases.

Flutamide-induced cytotoxicity and oxidative stress in an in vitro rat hepatocyte system

Flutamide (FLU) is a competitive antagonist of the androgen receptor which has been reported to induce severe liver injury in some patients. Several experimental models suggested that an episode of inflammation during drug treatment predisposes animals to tissue injury. The molecular cytotoxic mechanisms of FLU in isolated rat hepatocytes using an in vitro oxidative stress inflammation system were investigated in this study. When a nontoxic hydrogen peroxide (H₂O₂) generating system (glucose/glucose oxidase) with peroxidase or iron(II) [Fe(II)] (to partly simulate in vivo inflammation) was added to the hepatocytes prior to the addition of FLU, increases in FLU-induced cytotoxicity and lipid peroxidation (LPO) were observed that were decreased by 6-N-propyl-2-thiouracil or deferoxamine, respectively. N-Acetylcysteine decreased FLU-induced cytotoxicity in this system. Potent antioxidants, for example, Trolox ((±)-6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), resveratrol (3,5,4′-trihydroxy-trans-stilbene), and DPPD (N,N′-diphenyl-1,4-phenylenediamine) also significantly decreased FLU-induced cytotoxicity and LPO and increased mitochondrial membrane potential (MMP) and glutathione (GSH) levels in the H₂O₂ generating system with peroxidase. TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl), a known reactive oxygen species (ROS) scavenger and superoxide dismutase mimetic, also significantly decreased toxicity caused by FLU in this system. These results raise the possibility that the presence or absence of inflammation may be another susceptibility factor for drug-induced hepatotoxicity.

Advances pertaining to the pharmacology and interactions of irreversible nonselective monoamine oxidase inhibitors

Recent advances clarifying the pharmacology and interactions of irreversible nonselective monoamine oxidase inhibitors that have not been considered in depth lately are discussed. These new data elucidate aspects of enzyme inhibition and pharmacokinetic interactions involving amine oxidases, cytochrome P450 enzymes, aminotransferases (transaminases), and decarboxylases (carboxy-lyases) and the effects of tyramine. Phenelzine and tranylcypromine remain widely available, and many publications have data relevant to this review. Their effect on CYP 450 enzymes is less than many newer drugs. Tranylcypromine only inhibits CYP 450 2A6 (selectively and potently). Phenelzine has no reported interactions, but, like isoniazid, weakly and irreversibly inhibits CYP 450 2C19 and 3A4 in vitro. It might possibly be implicated in interactions (as isoniazid is). Phenelzine has some clinically relevant inhibitory effects on amine oxidases, aminotransferases, and decarboxylases, and it lowers pyridoxal phosphate levels. It commonly causes pyridoxal deficiency, weight gain, sedation, and sexual dysfunction, but only rarely causes hepatic damage and failure, or neurotoxicity. The adverse effects and difficulties with monoamine oxidase inhibitors are less than previously believed or estimated, including a lower risk of hypertension, because the tyramine content in foods is now lower. Potent norepinephrine reuptake inhibitors have a strong protective effect against tyramine-induced hypertension. The newly discovered trace amine-associated receptors probably mediate the pressor response. The therapeutic potential of tranylcypromine and L-dopa in depression and Parkinson disease is worthy of reassessment. Monoamine oxidase inhibitors are not used to an extent proportionate with their benefits; medical texts and doctors' knowledge require a major update to reflect the evidence of recent advances.

Hepatocyte or serum albumin protein carbonylation by oxidized fructose metabolites: Glyceraldehyde or glycolaldehyde as endogenous toxins?

Excessive sugar intake in animal models may cause tissue damage associated with oxidative and carbonyl stress cytotoxicity as well as inflammation. Fructose became a 100-fold more cytotoxic if hepatocytes were exposed to a non-toxic infusion of H(2)O(2) so as to simulate H(2)O(2) released by Kupffer cells or infiltrating immune cells. In order to determine the molecular mechanisms involved, protein carbonylation of fructose and its metabolites were determined using the 2,4-dinitrophenylhydrazine method. In a cell-free system, fructose was found to carbonylate bovine serum albumin (BSA) only if low concentrations of FeII/H(2)O(2) were added. Protein carbonylation by the fructose metabolites glyceraldehyde or glycolaldehyde was also markedly increased by FeII/H(2)O(2). The protein carbonylation may be attributed to glyoxal formation by hydroxyl radicals as the glyoxal trapping agent aminoguanidine or hydroxyl radical scavengers prevented protein carbonylation. Glyoxal was also much more effective than other carbonyls at causing protein carbonylation. When BSA was replaced by isolated rat hepatocytes, fructose metabolite glyceraldehyde in the presence of non-toxic 2 microM FeII:8-hydroxyquinoline (HQ) and a H(2)O(2) generating system (glucose/glucose oxidase) markedly increased cytotoxicity, protein carbonylation and reactive oxygen species (ROS)/H(2)O(2) formation. Furthermore this was prevented by hydroxyl radical scavengers or aminoguanidine, a glyoxal scavenger. CuII: 8-hydroxyquinoline increased H(2)O(2) induced hepatocyte protein carbonylation less but was prevented by aminoguanidine. However, cytotoxicity and protein carbonylation induced by glyceraldehyde/CuII:HQ/H(2)O(2) were not affected by hydroxyl radical scavengers. Although fatty liver induced by an excessive sugar diet in animal models has been proposed as the first hit for non-alcoholic steatohepatitis (NASH) we propose that oxidative stress induced by the oxidation of fructose or fructose metabolites catalysed by Fenton FeII/H(2)O(2) could be a 'second hit'. A perpetual cycle of oxidative stress in hepatocytes could lead to cytotoxicity and contribute to NASH development.

Hepatocyte inflammation model for cytotoxicity research: fructose or glycolaldehyde as a source of endogenous toxins

Insulin resistance and hepatotoxicity induced in high fructose fed rats may involve fructose derived endogenous toxins formed by inflammation. Thus fructose was seventy-fold more toxic if hepatocytes were exposed to non-toxic levels of hydrogen peroxide (H(2)O(2)) released by inflammatory cells. This was prevented by iron (Fe) chelators, hydroxyl radical scavengers, and increased by Fe, copper (Cu) or catalase inhibition. Fructose or glyceraldehyde/dihydroxyacetone metabolites were oxidized by Fenton radicals to glyoxal. Glyoxal (15 microM) cytotoxicity was increased about 200-fold by H(2)O(2). Glycolaldehyde was enzymically formed from glyceraldehyde, the fructokinase/aldolase B product of fructose. Glycolaldehyde cytotoxicity was increased 20-fold by H(2)O(2). The oxidative stress cytotoxicity induced was attributed to the Fenton oxidation of glycolaldehyde forming glycolaldehyde radicals and glyoxal, since cytotoxicity was prevented by aminoguanidine (glyoxal trap) or Fenton inhibitors. Glyoxal was also the Fenton product responsible for glycolaldehyde protein carbonylation as carbonylation was prevented by aminoguanidine or Fenton inhibitors.

Fructose and carbonyl metabolites as endogenous toxins

Dietary fructose consumption is one of the environmental factors contributing to the development of obesity and a fatty liver (hepatic steatosis). A two-hit hypothesis has been proposed for progression of hepatic steatosis to the more serious non-alcoholic steatosis (NASH), with the first hit being hepatic steatosis, and the second hit being inflammation and associated oxidative stress caused by reactive oxygen species (ROS) formation. As well, fructose-fed rats develop insulin resistance and serum levels of methylglyoxal, a glycolytic metabolite, are increased. Previously we reported that glyoxal-induced hepatocyte cytotoxicity could be attributed to mitochondrial toxicity as mitochondrial membrane potential was decreased and cytotoxicity was increased several orders of magnitude by low non-cytotoxic doses of H(2)O(2) (hepatocyte inflammation model). In this study, we have assessed the toxicity of fructose towards hepatocytes and investigated the molecular cytotoxic mechanisms involved. Fructose itself was only toxic at 1.5M, whereas 12 mM caused 50% cell death in 2h if the hepatocytes were exposed to a non-cytotoxic dose of H(2)O(2) continuously generated by glucose and glucose oxidase. The cytotoxic mechanism involved oxidative stress as ROS and H(2)O(2) formation preceded cytotoxicity, and cytotoxicity was prevented by radical scavengers, lipid antioxidants and ROS scavengers. It is proposed that the highly potent Fenton derived ROS catalyse the oxidation of fructose and particularly its carbonyl metabolites glycolaldehyde, dihydroxyacetone, glyceraldehyde. The carbon radicals and glyoxal formed compromise the cell's resistance to H(2)O(2).