Carbon tetrachloride and the sorbitol pathway in the diabetic mouse

Diabetes and hypertriglyceridemia modify the mode of acetaminophen-induced hepatotoxicity and nephrotoxicity in rats and mice

Certain disease conditions can modify drug-induced toxicities, which, in turn, may cause a medication-related health crisis. Therefore, preclinical investigations into the alterations in drug-induced toxicities using appropriate disease animal models are very important. This paper reviews the reported data related to the effects of diabetes and hypertriglyceridemia, common lifestyle-related diseases in a modern society, on acetaminophen (APAP)-induced hepatotoxicity and nephrotoxicity in rats and mice. It has generally been reported that diabetes protects rats and mice from APAP-induced hepatotoxicity and there are several reports that help to speculate on the effects of diabetes on APAP-induced nephrotoxicity. In fructose-induced hypertriglyceridemic rats, hepatotoxicity of APAP becomes apparently less severe, whereas nephrotoxicity of APAP becomes significantly more severe. The mechanisms of alteration of APAP-induced hepatorenal toxicity under diabetic and hypertriglyceridemic conditions are also discussed in this paper.

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.

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.

Benfotiamine alleviates diabetes-induced cerebral oxidative damage independent of advanced glycation end-product, tissue factor and TNF-alpha

Diabetes mellitus leads to thiamine deficiency and multiple organ damage including diabetic neuropathy. This study was designed to examine the effect of benfotiamine, a lipophilic derivative of thiamine, on streptozotocin (STZ)-induced cerebral oxidative stress. Adult male FVB mice were made diabetic with a single injection of STZ (200 mg/kg, i.p.). Fourteen days later, control and diabetic (fasting blood glucose >13.9 mM) mice received benfotiamine (100 mg/kg/day, i.p.) for 14 days. Oxidative stress and protein damage were evaluated by glutathione/glutathione disulfide (GSH/GSSG) assay and protein carbonyl formation, respectively. Pro-oxidative or pro-inflammatory factors including advanced glycation end-product (AGE), tissue factor and tumor necrosis factor-alpha (TNF-alpha) were evaluated by immunoblot analysis. Four weeks STZ treatment led to hyperglycemia, enhanced cerebral oxidative stress (reduced GSH/GSSG ratio), elevated TNF-alpha and AGE levels without changes in protein carbonyl or tissue factor. Benfotiamine alleviated diabetes-induced cerebral oxidative stress without affecting levels of AGE, protein carbonyl, tissue factor and TNF-alpha. Collectively, our results indicated benfotiamine may antagonize diabetes-induced cerebral oxidative stress through a mechanism unrelated to AGE, tissue factor and TNF-alpha.

High-dose benfotiamine rescues cardiomyocyte contractile dysfunction in streptozotocin-induced diabetes mellitus

Diabetic cardiomyopathy is characterized by cardiac dysfunction. This study was designed to examine the effect of benfotiamine, a lipophilic derivative of thiamine, on streptozotocin (STZ)-induced cardiac contractile dysfunction in mouse cardiomyocytes. Adult male FVB mice were made diabetic with a single injection of STZ (200 mg/kg ip). Fourteen days later, control and diabetic (fasting plasma glucose > 13.9 mM) mice were put on benfotiamine therapy (100 mg.kg(-1).day(-1) ip) for another 14 days. Mechanical and intracellular Ca2+ properties were evaluated in left ventricular myocytes using an IonOptix MyoCam system. The following indexes were evaluated: peak shortening (PS), time to PS (TPS), time to 90% relengthening (TR90), maximal velocity of shortening/relengthening, resting and rise of intracellular Ca2+ in response to electrical stimulus, sarcoplasmic reticulum (SR) Ca2+ load, and intracellular Ca2+ decay rate (tau). Two- or four-week STZ treatment led to hyperglycemia, prolonged TPS and TR90, reduced SR Ca2+ load, elevated resting intracellular Ca2+ level and prolonged tau associated with normal PS, maximal velocity of shortening/relengthening, and intracellular Ca2+ rise in response to electrical stimulus. Benfotiamine treatment abolished prolongation in TPS, TR90, and tau, as well as reduction in SR Ca2+ load without affecting hyperglycemia and elevated resting intracellular Ca2+. Diabetes triggered oxidative stress, measured by GSH-to-GSSG ratio and formation of advanced glycation end product (AGE) in the hearts. Benfotiamine treatment alleviated oxidative stress without affecting AGE or protein carbonyl formation. Collectively, our results indicated that benfotiamine may rescue STZ-induced cardiomyocyte dysfunction but not AGE formation in short-term diabetes.

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.