Alterations in susceptibility to carbon tetrachloride toxicity and hepatic antioxidant/detoxification system in streptozotocin-induced short-term diabetic rats: effects of insulin and Schisandrin B treatment

Potential impact of underlying diseases influencing ADME in nonclinical safety assessment

Nonclinical studies involve in vitro, in silico, and in vivo experiments to assess the toxicokinetics, toxicology, and safety pharmacology of drugs according to regulatory requirements by a national or international authority. In this review, we summarize the potential effects of various underlying diseases governing the absorption, distribution, metabolism, and excretion (ADME) of drugs to consider the use of animal models of diseases in nonclinical trials. Obesity models showed alterations in hepatic metabolizing enzymes, transporters, and renal pathophysiology, which increase the risk of drug-induced toxicity. Diabetes models displayed changes in hepatic metabolizing enzymes, transporters, and glomerular filtration rates (GFR), leading to variability in drug responses and susceptibility to toxicity. Animal models of advanced age exhibited impairment of drug metabolism and kidney function, thereby reducing the drug-metabolizing capacity and clearance. Along with changes in hepatic metabolic enzymes, animal models of metabolic syndrome-related hypertension showed renal dysfunction, resulting in a reduced GFR and urinary excretion of drugs. Taken together, underlying diseases can induce dysfunction of organs involved in the ADME of drugs, ultimately affecting toxicity. Therefore, the use of animal models of representative underlying diseases in nonclinical toxicity studies can be considered to improve the predictability of drug side effects before clinical trials.

Schisandrin B ameliorates non-alcoholic liver disease through anti-inflammation activation in diabetic mice

Type 2 diabetes mellitus (T2DM) is a metabolic risk factor associated with non‐alcoholic liver disease (NAFLD). Schisandrin B (Sch B) is a promising agent for NAFLD. However, the actions of Sch B on diabetes‐associated NAFLD and the underlying mechanisms are not characterized. This study aimed to assess whether Sch B has beneficial effects on T2DM‐associated NAFLD. Sch B (50 mg/kg, gavage) was administrated to C57BL/KSJ db/db mice for 2 weeks. Body weight, liver weight, blood glucose, and insulin resistance were measured. Serum lipid level and liver function were detected using the biochemistry analyzer. Quantitative Real‐Time PCR assay was used to evaluate mRNA levers of lipid metabolism genes. Terminal‐deoxynucleoitidyl Transferase Mediated Nick End Labeling (TUNEL) staining was performed to measure apoptosis in the liver. Pathological analysis and immunohistochemistry assessment were used to analyze hepatic steatosis and inflammatory infiltration. Sch B supplementation significantly decrease body weight, related liver weight, blood glucose, and serum insulin, and improved insulin resistance in db/db mice. Sch B obviously corrected NAFLD phenotypes including lipid deposition, steatohepatitis, and high levels of hepatic enzymes and serum lipid. In addition, mRNA levels of Sterol response element‐bind protein 1c (SREBP‐1c), fatty acid synthetase (Fasn), and acetyl‐CoA carboxylase (ACC) were markedly downregulated by Sch B treatment. TUNEL‐positive cells were also decreased by Sch B. Furthermore, Sch B inhibited the Kupffer cells, IL‐1β, and TNF‐α infiltration to the liver. Sch B ameliorated insulin resistance and lipid accumulation under high glucose conditions, which was partly associated with its inhibition of apoptosis and anti‐inflammatory actions.

Type 2 diabetes mellitus potentiates acute acrylonitrile toxicity: Potentiation reduction by phenethyl isothiocyanate

Acrylonitrile (AN) is a known animal carcinogen and suspected human carcinogen. Recently, occupational exposure to AN has considerably increased. Previously, we demonstrated that streptozotocin-induced diabetes potentiates AN-induced acute toxicity in rats and that the induced cytochrome P450 2E1 (CYP2E1) is responsible for this effect. In the present study, we examined whether induction of CYP2E1 is also the underlying mechanism for the potentiation of AN-induced acute toxicity in type 2 diabetes in db/db mice. The effect of phenethyl isothiocyanate (PEITC) in reducing potentiation was also investigated. The mice were randomly divided into the normal control, diabetic control, AN, diabetes + AN, PEITC + AN, and diabetes + PEITC + AN groups. PEITC (40 mg/kg) was orally administered to rats for 3 days, and 1 h after the last PEITC gavage, 45 mg/kg AN was intraperitoneally injected. Time to death was observed. The CYP2E1 level and enzymatic activity, cytochrome c oxidase (CCO) activity, and reactive oxygen species (ROS) levels were measured. The survival rate was decreased in AN-treated db/db mice compared with that in AN-treated wild-type mice. The hepatic CYP2E1 level and enzymatic activity remained unaltered in db/db mice. Phenethyl isothiocyanate alleviated AN-induced acute toxicity in db/db mice as evident in the increased survival rate, restored CCO activity, and decreased ROS level in both the liver and brain. The study results suggested that CYP2E1 may not be responsible for the sensitivity to AN-induced acute toxicity in db/db mice and that PEITC reduced the potentiation of AN-induced acute toxicity in db/db mice.

Effects of Adaptogens on the Central Nervous System and the Molecular Mechanisms Associated with Their Stress-Protective Activity

Adaptogens were initially defined as substances that enhance the "state of nonspecific resistance" in stress, a physiological condition that is linked with various disorders of the neuroendocrine-immune system. Studies on animals and isolated neuronal cells have revealed that adaptogens exhibit neuroprotective, anti-fatigue, antidepressive, anxiolytic, nootropic and CNS stimulating activity. In addition, a number of clinical trials demonstrate that adaptogens exert an anti-fatigue effect that increases mental work capacity against a background of stress and fatigue, particularly in tolerance to mental exhaustion and enhanced attention. Indeed, recent pharmacological studies of a number of adaptogens have provided a rationale for these effects also at the molecular level. It was discovered that the stress-protective activity of adaptogens was associated with regulation of homeostasis via several mechanisms of action, which was linked with the hypothalamic-pituitary-adrenal axis and the regulation of key mediators of stress response, such as molecular chaperons (e.g., HSP70), stress-activated c-Jun N-terminal protein kinase 1 (JNK1), Forkhead box O (FOXO) transcription factor DAF-16, cortisol and nitric oxide.

Responses of glutamate cysteine ligase and glutathione to oxidants in deer mice (Peromyscus maniculatus)

Sensitivities of a wildlife species, deer mice, to oxidants were evaluated. A single dose (1589 mg/kg body weight by intraperitoneal injection) of carbon tetrachloride, a typical hepatotoxicant, caused changes in GCL activity and GSH content in multiple organs of deer mice. Hepatic GCL activity and GSH content were depleted substantially (P<0.01), renal GCL activity increased (P<0.05). Blood, brain and heart GCL activities increased (P<0.05), whereas GSH contents decreased significantly. Deer mice were exposed to Pb, or Pb together with Cu and Zn via drinking water for 4 weeks. GCL activities were not significantly affected by treatments. GSH contents were increased significantly by Pb alone, Pb with medium and high concentrations of Cu and Zn. Effects of multi-metal-contaminated soil were investigated via lactational, juvenile and lifelong exposure to feed supplemented with soils. Metal-contaminated soils did not lead to significant effects in pups via lactation, 50-day exposure altered GSH content marginally, while 100-day exposure resulted in marked GCL activity depletion. After 100-day exposure, GCL activities of the medium soil-, high soil- and Pb-treated deer mice were only 53%, 40% and 46% of the control, respectively (P<0.0001).

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

Healthy animals and animal models of human disease(s) in safety assessment of human pharmaceuticals, including therapeutic antibodies

Although the predictability of untoward drug effects in humans has improved in recent years, certain new drugs, with new pharmacological mechanisms, still pose a considerable challenge. This holds particularly true for biotherapeutics and their drug-related immune reactions, idiosyncratic drug hepatotoxicity and systemic toxicity. The selection of the 'right' animal models remains crucial; the species selected must be relevant (to humans) and sensitive with regard to three basic variables: pharmacodynamics, pharmacokinetics (including metabolism) and the mechanisms underlying the toxicity in the target human diseases. Furthermore, normal healthy animals might be a poor model in certain cases because the underlying disease in patients can be an important determinant of susceptibility to adverse effects. Therefore, we suggest that, where appropriate, new animal models of human disease (s) are introduced into drug safety assessment.

Mechanisms of inhibited liver tissue repair in toxicant challenged type 2 diabetic rats

Liver injury initiated by non-lethal doses of CCl(4) and thioacetamide (TA) progresses to hepatic failure and death of type 2 diabetic (DB) rats due to failed advance of liver cells from G(0)/G(1) to S-phase and inhibited tissue repair. Objective of the present study was to investigate cellular signaling mechanisms of failed cell division in DB rats upon hepatotoxicant challenge. In CCl(4)-treated non-diabetic (non-DB) rats, increased IL-6 levels, sustained activation of extracellular regulated kinases 1/2 (ERK1/2) MAPK, and sustained phosphorylation of retinoblastoma protein (p-pRB) via cyclin D1/cyclin-dependent kinase (cdk) 4 and cyclin D1/cdk6 complexes stimulated G(0)/G(1) to S-phase transition of liver cells. In contrast to the non-DB rats, CCl(4) administration led to lower plasma IL-6, decreased ERK1/2 activation, lower cyclin D1, and cdk 4/6 expression resulting in decreased p-pRB and inhibition of liver cell division in the DB rats. Furthermore, higher TGFbeta1 expression and p21 activation may also contribute to decreased p-pRB in DB rats compared to non-DB rats. Similarly, after TA administration to DB rats, down-regulation of cyclin D1 and p-pRB leads to markedly decreased advance of liver cells from G(0)/G(1) to S-phase and tissue repair compared to the non-DB rats. Hepatic ATP levels did not differ between the DB and non-DB rats obviating its role in failed tissue repair in the DB rats. In conclusion, decreased p-pRB may contribute to blocked advance of cells from G(0)/G(1) to S-phase and failed cell division in DB rats exposed to CCl(4) or TA, leading to progression of liver injury and hepatic failure.

Type 2 diabetic rats are sensitive to thioacetamide hepatotoxicity

Previously, we reported high hepatotoxic sensitivity of type 2 diabetic (DB) rats to three dissimilar hepatotoxicants. Additional work revealed that a normally nonlethal dose of CCl4 was lethal in DB rats due to inhibited compensatory tissue repair. The present study was conducted to investigate the importance of compensatory tissue repair in determining the final outcome of hepatotoxicity in diabetes, using another structurally and mechanistically dissimilar hepatotoxicant, thioacetamide (TA), to initiate liver injury. A normally nonlethal dose of TA (300 mg/kg, ip), caused 100% mortality in DB rats. Time course studies (0 to 96 h) showed that in the non-DB rats, liver injury initiated by TA as assessed by plasma alanine or aspartate aminotransferase and hepatic necrosis progressed up to 48 h and regressed to normal at 96 h resulting in 100% survival. In the DB rats, liver injury rapidly progressed resulting in progressively deteriorating liver due to rapidly expanding injury, hepatic failure, and 100% mortality between 24 and 48 h post-TA treatment. Covalent binding of 14C-TA-derived radiolabel to liver tissue did not differ from that observed in the non-DB rats, indicating similar bioactivation-based initiation of hepatotoxicity. S-phase DNA synthesis measured by [3H]-thymidine incorporation, and advancement of cells through the cell division cycle measured by PCNA immunohistochemistry, were substantially inhibited in the DB rats compared to the non-DB rats challenged with TA. Thus, inhibited cell division and compromised tissue repair in the DB rats resulted in progressive expansion of liver injury culminating in mortality. In conclusion, it appears that similar to type 1 diabetes, type 2 diabetes also increases sensitivity to dissimilar hepatotoxicants due to inhibited compensatory tissue repair, suggesting that sensitivity to hepatotoxicity in diabetes occurs in the absence as well as presence of insulin.

Potentiation of Carbon Tetrachloride Hepatotoxicity and Lethality in Type 2 Diabetic Rats

There is a need for well characterized and economical type 2 diabetic model that mimics the human disease. We have developed a type 2 diabetes rat model that closely resembles the diabetic patients and takes only 24 days to develop robust diabetes. Nonlethal doses of allyl alcohol (35 mg/kg i.p.), CCl(4) (2 ml/kg i.p.), or thioacetamide (300 mg/kg i.p.) yielded 80 to 100% mortality in diabetic rats. The objective of the present study was to investigate two hypotheses: higher CCl(4) bioactivation and/or inhibited compensatory tissue repair were the underlying mechanisms for increased CCl(4) hepatotoxicity in diabetic rats. Diabetes was induced by feeding high fat diet followed by a single dose of streptozotocin on day 14 (45 mg/kg i.p.) and was confirmed on day 24 by hyperglycemia, normoinsulinemia, and oral glucose intolerance. Time course studies (0-96 h) of CCl(4) (2 ml/kg i.p.) indicated that although initial liver injury was the same in nondiabetic and diabetic rats, it progressed only in the latter, culminating in hepatic failure, and death. Hepatomicrosomal CYP2E1 protein and activity, lipid peroxidation, glutathione, and (14)CCl(4) covalent binding to liver tissue were the same in both groups, suggesting that higher bioactivation-based injury is not the mechanism. Inhibited tissue repair resulted in progression of injury and death in diabetic rats, whereas in the nondiabetic rats robust tissue repair resulted in regression of injury and survival after CCl(4) administration. These studies show high sensitivity of type 2 diabetes to model hepatotoxicants and suggest that CCl(4) hepatotoxicity is potentiated due to inhibited tissue repair.

Streptozotocin-induced diabetic mice are resistant to lethal effects of thioacetamide hepatotoxicity

The effect of Type 1 diabetes on the toxicity of thioacetamide was investigated in a murine model. In streptozotocin-induced diabetic C57BL6 mice a LD90 dose of thioacetamide (1000 mg/kg, ip in saline) caused only 10% mortality. Alanine aminotransferase activity revealed approximately 2.7-fold less liver injury in the diabetic (DB) mice compared to the non-DB controls, at 36 h after thioacetamide (TA) administration, which was confirmed via histopathological analysis. HPLC analyses revealed lower plasma t(1/2) of TA in the DB mice. Covalent binding of [(14)C]TA to liver tissue was lower in the DB mice, suggesting lower bioactivation of TA. Compensatory hepatic S-phase stimulation as assessed by [(3)H]thymidine incorporation occurred much earlier and was substantially higher in the DB mice compared to the non-DB cohorts. Morphometric analysis of cells in various phases of cell division assessed via immunohistochemical staining for proliferating cell nuclear antigen revealed more cells in G(1), S, G(2), and M phases in the DB mice, indicating robust tissue repair in concordance with the findings of [(3)H]thymidine pulse labeling studies. The importance of tissue repair in the resistance of DB mice was further investigated by blocking cell division in the DB mice by colchicine (1 mg/kg, ip) at 40 h after TA administration, well after the bioactivation of TA. Antimitotic action of colchicine, confirmed by decreased S-phase stimulation, led to progression of liver injury and increased mortality in DB mice. These findings suggest that lower bioactivation of TA and early onset of liver tissue repair are the pivotal underpinnings for the resistance of DB mice.

Effect of some hypoglycemic herbs on the activity of phase I and II drug-metabolizing enzymes in alloxan-induced diabetic rats

Polycyclic aromatic hydrocarbons (PAHs) and N-nitrosamines (NNA) are mainly activated by cytochrome P450s, and their associated enzyme activities such as aryl hydrocarbon (benzo(a)pyrene) hydroxylase (AHH), N-nitrosdimethylamine N-demethylase I (NDMA-dI), NADPH-cytochrome C reductase, and detoxified by glutathione S-transferase (GST) and glutathione (GSH). The present study shows the influence of Cymbopogon proximus (Halfa barr), Zygophyllum coccineum L. (Kammun quaramany), Lupinus albus (Termis) as herbs capable of inducing hypoglycemia on the activity of the above mentioned enzymes in the liver of diabetic rats. Alloxan was administered as a single dose (120 mg/kg body weight) to induce diabetes and the herbs were administered to diabetic rats as repeated doses for 4 weeks. Alloxan-induced diabetes significantly increased the blood glucose level by 93% compared to the control level. On the other hand, repeated-dose treatments of diabetic rats with Cymbopogon proximus and Lupinus albus are more effective than Zygophyllum coccineum in restoring the elevated blood glucose level to the normal level. Alloxan treatment increased the hepatic activity of cytochrome P450, NADPH-cytochrome C reductase, AHH, NDMA-dI, GST and GSH by 112, 122, 82, 99, 64 and 26%, respectively. These herbs decreased the activity of above mentioned enzymes in the liver of diabetic rats compared to alloxan-treated rats. We conclude that alloxan increased the activity of cytochrome P450 system and that such herbs reduced these activities. The toxic effects of PAHs (e.g. benzo(a)pyrene) and NNA (e.g. N-nitrosdimethylamine) could be increased in the liver of diabetic rats through induction of their corresponding bioactivating enzymes. On the other hand, hypoglycemic herbs could alleviate the deleterious effects of these carcinogens in the liver of diabetic rats since these herbs reduced the hepatic content of cytochrome P450 and other associated enzyme activities compared to the diabetic group. Such alterations in the activity of phase I and II drug-metabolizing enzymes should be considered when therapeutic drugs are administered to diabetic patients since most of drugs are metabolized mainly by the cytochrome P450 system.

Altered susceptibility to ischemia-reperfusion injury in isolated-perfused hearts of short-term diabetic rats associated with changes in non-enzymatic antioxidants

The effects of short-term (2-week) diabetes on myocardial ischemia-reperfusion (I-R) injury and associated changes in myocardial non-enzymatic antioxidant level were examined. Isolated-perfused hearts prepared from control and diabetic rats were subjected to increasing periods of ischemia and reperfusion, and myocardial I-R injury was assessed by measuring the extent of lactate dehydrogenase (LDH) leakage and contractile force recovery. While a brief period (20 min) of post-ischemic reperfusion caused a smaller extent of LDH leakage, the prolonged period (40 min) of reperfusion produced a greater degree of I-R injury in diabetic hearts, as indicated by the impaired recovery of contractile force. The apparent protection against I-R injury in diabetic hearts during the early phase of post-ischemic reperfusion was associated with increases in myocardial reduced glutathione/ascorbic acid and a-tocopherol levels, with the effect on a-tocopherol being most prominent. Insulin treatment could reverse the diabetes-associated changes in susceptibility to myocardial I-R injury and antioxidant response. The ensemble of results indicates that the myocardium isolated from short-term diabetic rat can produce a beneficial antioxidant response to I-R challenge, which may, in turn, be attributable to the decreased susceptibility to I-R injury observable during the early phase of reperfusion.