Effect of hydrazine exposure on hepatic triacylglycerol biosynthesis

Protective effect of picroliv against hydrazine-induced hyperlipidemia and hepatic steatosis in rats

The protective effect of picroliv (PIC) obtained from Picrorhiza kurroa (family: Scrophulariaceae) against hydrazine (Hz)-induced hyperlipidemia was evaluated in rats. Hz administration (50 mg/kg, i.p.) caused an increase in triglyceride (TG), cholesterol (CHO), free fatty acids (FFA), and total lipids (TL) in both the plasma and liver tissue of rats accompanied by a fall in phospholipids (PL) in the liver tissue 24 h after its administration, indicating its hyperlipidemic property. The above abnormality was prevented by simultaneous treatment of PIC (50 mg/kg, p.o.) with Hz. Hz treatment also caused an increase in the mobility of TG and TL from adipose tissue, and these results indicate that Hz administration could cause hepatic steatosis by nonhepatocellular factors (such as mobilization of depot fats). This effect was also prevented by simultaneous treatment of PIC with Hz. PIC-alone treatment, however, did not produce any change in the status of all the lipid parameters evaluated in plasma, liver, and adipose tissues. These results indicate that increased mobilization of depot fats from adipose tissue may contribute to the development of hepatic steatosis in addition to decreased lipoprotein secretion, increased hepatic TG biosynthesis, and increased hepatic uptake of FFA. These have been reported as the mechanism responsible for the development of Hz-induced hepatic steatosis. PIC prevents Hz-induced hyperlipidemia, hepatic steatosis, and mobilization of lipids from depot fats, but the mechanism behind the protective effect of PIC remains to be elucidated.

Triglyceride disposition in isolated hepatocytes after treatment with hydrazine

Treatment of animals with hydrazine causes the accumulation of triglycerides in the liver but the mechanism remains unclear. Therefore, the effect of hydrazine on hepatic triglyceride synthesis and subsequent transport was studied in a hepatocyte model, in vitro in order to isolate liver cells from extrahepatic influences. Hepatocytes were isolated and either incubated in suspension with [14C]palmitate in the presence of hydrazine (2-12 mM) or pre-incubated with [14C]palmitate, washed free of the fatty acid and then incubated with hydrazine (2-12 mM). Hydrazine resulted in a significant reduction in the incorporation of [14C]palmitate into triglycerides and reduction in the transportation of triglycerides out of cells. When [14C]palmitate was in the incubation medium, ATP levels were reduced by lower concentrations of hydrazine than have previously been reported. None of the concentrations of hydrazine used affected cell membrane integrity (viability) as measured by LDH leakage. The 14CO2 produced by the beta-oxidation of [14C]palmitate was also measured in short term incubations (30 min) carried out in sealed vessels. There was a dose dependent increase in 14CO2 produced by very low concentrations of hydrazine (0.01-0.1 mM) after which the effect was maximal and concentrations above 8 mM hydrazine decreased 14CO2 production. The data suggest that the inhibition of transportation of triglycerides out of cells by hydrazine may have a more important role in the accumulation of triglycerides in the liver than has been previously recognised. However, the model was not able to mimic the accumulation of triglycerides in hepatocytes seen in vivo.

Determination of hydrazine in biofluids by capillary gas chromatography with nitrogen-sensitive or mass spectrometric detection

Plasma and liver levels of hydrazine were determined at 10, 30, 90 and 270 min in rats given 0.09, 0.27, 0.84 and 2.53 mmol of hydrazine per kg body weight orally by capillary gas chromatography-mass spectrometry of its pentafluorobenzaldehyde adduct (DFBA, m/z 388) using selected ion monitoring with 15N2-labelled hydrazine as the internal standard (adduct, m/z 390). The mean half-life for hydrazine in the plasma was approximately 2 h but varied with dose. Urinary excretion (0-24 h) of hydrazine and its metabolite acetylhydrazine were determined employing nitrogen-phosphorus detection of the adducts utilising a novel internal standard, pentafluorophenylhydrazine, the adduct of which structurally resembles DFBA. The fraction of the original dose excreted as hydrazine (and acetylhydrazine) declined with increasing dose.

Effect of subacute administration of isoniazid and pyridoxine on lipids in plasma, liver and adipose tissues in the rabbit

The effect of subacute intraperitoneal administration of Isoniazid (INH) on various lipid parameters was studied in liver and adipose tissue in addition to plasma. In the liver, its effect on various phospholipid fractions was also assessed. The changes in lipid profile reflected INH-induced hepatic steatosis. While pyridoxine alone did not alter any of these lipid parameters, its concurrent administration with INH prevented almost all the INH-induced lipid changes. The enhanced lipid mobilization into liver, and a fall in phosphatidylcholine with a concomitant rise in phosphatidylethanolamine in liver impeding lipoprotein synthesis, might be responsible for the hepatic steatosis. Pyridoxal, a pyridoxine metabolite, might have trapped the primary amine functional group of acetylhydrazine and thus prevented the steatosis.

Course of ATP depletion in hydrazine hepatotoxicity

The effect of hydrazine on ATP levels has been investigated in rats in vivo and in hepatocytes in vitro. Hydrazine was found to cause a dose-dependent depletion of hepatic ATP in vivo 3 h after dosing. In isolated hepatocytes in vitro hydrazine also caused a concentration-dependent depletion of ATP which preceded cytotoxicity as indicated by loss of cell viability. The ATP depletion in isolated hepatocytes was also significant at a concentration of hydrazine which was not cytotoxic. Attempts to determine hepatic ATP depletion in vivo over time using topical 31P NMR were confounded by the effects of the thiopentobarbitone used to anaesthetise the animals. This was found to ameliorate the effects of hydrazine on ATP depletion but potentiate the lethality of hydrazine. Consequently, although ATP depletion was detected in some hydrazine-treated animals, this was only observed in animals which subsequently died. The results indicate that ATP depletion may underlie the hepatotoxicity of hydrazine.

The effects of hydrazine on the phosphatidate phosphohydrolase activity in rat liver

Injection of hydrazine (0.7 mmole/kg) in the male fasting rats caused an increase in phosphatidate phosphohydrolase (PAP) activity in the soluble fraction of the liver. The increased PAP activity was parallel with a rise in hepatic triacylglycerol (TG) (3.5-fold) and in the catecholamine concentration (3.4-fold) in adrenal glands. Hydrazine also increased serum glucose. The hydrazine-induced increase in PAP activity and TG accumulation was completely prevented by adrenalectomy. The data suggest that increased PAP activity is at least partly responsible for hydrazine-induced fatty liver and that adrenal hormones may take part in the mechanism by which hydrazine exerts its effects on the liver.

The effect of fatty acid exposure on the biosynthesis of glycerolipids by cultured hepatocytes

Incubation of hepatocyte monolayers with oleate or palmitate (1.0 mM) for 2-48 h, increased (20 to 80%) the incorporation of [1,3-14C]glycerol and palmitate into triacyglycerol but not phosphatidylcholine. The effect of fatty acids on liver cell triacylglycerol formation correlated well (r = 0.990) with a simultaneous rise (2-4-fold) in phosphatidate phosphatase (EC 3.1.3.4) activity. Phosphatidate phosphatase activity and triacylglycerol biosynthesis are also increased (2-fold) after hepatocyte monolayers are incubated for 24 h with cyclic GMP in the absence of fatty acids. Fatty acid-dependent increases in liver cell triacylglycerol formation and phosphatidate phosphatase activity are not blocked by cycloheximide. Phosphatidylcholine biosynthesis was also elevated in homogenates of liver cells exposed (24-48 h) to 1.0 mM oleate when exogenous CDPcholine was added to the incubation mixture. Apparently, the phosphatidate phosphatase-dependent rise in diacylglycerols that occurs after fatty acid exposure is primarily shunted into triacylglycerols because liver cell CDPcholine content is not correspondingly increased, and high levels of diacylglycerol acyltransferase (EC 2.3.1.20) and fatty acyl-CoA derivatives are present.

Studies on hydrazine hepatotoxicity. 2. Biochemical findings

Hydrazine causes a dose-related increase in liver triglycerides and in liver weight and causes a decrease in hepatic glutathione. The threshold dose for the toxic effect is around 10 mg/kg, and the optimal effect is seen after a dose of 40 mg/kg. The effect of hydrazine on liver weight and glutathione was detectable within 30 min of dosing, but the elevation of hepatic triglycerides was not detectable until 4 h after dosing. At 24 h after a dose of 60 mg hydrazine/kg, hepatic reduced glutathione was approximately 50% of the control value and triglycerides were about 7 times the normal level. In vitro studies indicated that hydrazine is metabolized by rat liver microsomal enzymes, this being dependent on NADPH and oxygen. Pretreatment of animals with phenobarbital or piperonyl butoxide respectively decreases and increases the hepatotoxicity. Prior depletion of hepatic glutathione by administration of diethyl maleate had no effect on the toxicity. Pyruvate azine, a probable metabolite of hydrazine, is much less toxic than hydrazine itself on a molar basis. These and other results suggest that although hydrazine is metabolized via several routes, the hepatotoxicity may well be due to the parent compound rather than a metabolite.

The acute effects of streptozotocin-induced diabetes on rat liver glycerolipid biosynthesis

Streptozotocin-induced diabetes produced a significant rise in rat serum and liver triacylglycerol content and hepatic triacylglycerol biosynthesis measured in vivo. Microsomes, isolated from the livers of streptozotocin-exposed animals (2-72h), exhibited an increased capacity to incorporate sn-[1,3-(14)C]glycerol 3-phosphate into neutral lipid (diacylglycerol and triacylglycerol) in the presence of ATP, CoA and palmitate. The streptozotocin-induced elevation of microsomal neutral lipid production was accompanied by a corresponding rise in the activity of microsomal phosphatidate phosphohydrolase (4-fold after 72 h of streptozotocin exposure). Diabetic-dependent increases in acylglycerol formation, phosphatidate phosphohydrolase activity and serum triacylglycerol and fatty acid levels were reversed by administering insulin (10 units protamine zinc/kg) at 16-h intervals (three separate doses( beginning 24 h after streptozotocin exposure. However, the diabetic-related rise in hepatic triacylglycerol content was only partially corrected by insulin administration. Streptozotocin-relate increases in liver triacylglycerol biosynthesis and phosphatidate phosphohydrolase activity we associated with alterations in plasma factors, since homogenates of hepatocyte monolayers exposed (18h) to plasma isolated from diabetic (72 h exposure to streptozotocin) animals exhibit an increased capacity to incorporate sn-[1,3-(14)C]glycerol 3-phosphate into triacylglycerol compared to homogenates of cells exposed to plasma from control (non-fasted) animals. The importance of these plasma factors in altering hepatic acylglycerol formation was also supported by the observation that hepatocyte monolayers exposed to a mixture of plasma isolated from normal (non-fasted) animals and plasma components elevated in diabetes (glucagon, glucose, oleate and ketones) showed increases in triacylglycerol formation which were similar to those produced by exposure to diabetic plasma. Additional studies demonstrated that fatty acids (oleate) appeared to be the agent primarily responsible for the diabetic plasma-induced rise in monolayer triacylglycerol biosynthesis and phosphatidate phosphohydrolase activity.

Triacylglycerol metabolism in the phenobarbital-treated rat

1. Various aspects of triacylglycerol metabolism were compared in rats given phenobarbital at a dose of 100mg/kg body wt. per day by intraperitoneal injection; controls were injected with an equal volume of 0.15m-NaCl by the same route. Animals were killed after 5 days of treatment. 2. Rats injected with phenobarbital demonstrated increased liver weight, and increased microsomal protein per g of liver. Other evidence of microsomal enzyme induction was provided by increased activity of aminopyrine N-demethylase and cytochrome P-450 content. Increased hepatic activity of gamma-glutamyltransferase (EC 2.3.2.2) occurred in male rats, but not in females, and was not accompanied by any detectable change in the activity of this enzyme in serum. 3. Phenobarbital treatment increased the hepatic content of triacylglycerol after 5 days in starved male and female rats, as well as in non-starved male rats; non-starved females were not tested in this regard. At 5 days after withdrawal of the drug, there was no difference in hepatic triacylglycerol content or in hepatic functions of microsomal enzyme induction between the treated and control rats. 4. After 5 days, phenobarbital increased the synthesis in vitro of glycerolipids in cell-free liver fractions fortified with optimal concentrations of substrates and co-substrates when results were expressed per whole liver. The drug caused a significant increment in the activity of hepatic diacylglycerol acyltransferase (EC 2.3.1.20), but did not affect the activity per liver of phosphatidate phosphohydrolase (EC 3.1.3.4) in cytosolic or washed microsomal fractions. A remarkable sex-dependent difference was observed for this latter enzyme. In female rats, the activity of the microsomal enzyme per liver was 10-fold greater than that of the cytosolic enzyme, whereas in males, the activities of phosphohydrolases per liver from both subcellular fractions were similar. 5. The phenobarbital-mediated increase in hepatic triacylglycerol content could not be explained by a decrease in the hepatic triacylglycerol secretion rate as measured by the Triton WR1339 technique. Since the hepatic triacylglycerol showed significant correlation with microsomal enzyme induction functions, with hepatic glycerolipid synthesis in vitro and with diacylglycerol acyltransferase activity, it is likely to be due to enhanced triacylglycerol synthesis consequent on hepatic microsomal enzyme induction. 6. In contrast with rabbits and guinea pigs, rats injected with phenobarbital showed a decrease in serum triacylglycerol concentration in the starved state; this decrease persisted for up to 5 days after drug administration stopped, and did not occur in non-starved animals. It seems to be independent of the microsomal enzyme-inducing properties of the drug, and may be due to the action of phenobarbital at an extrahepatic site.