Antipyrine metabolism during hepatic regeneration in the rat

Recovery of liver function in two-third partial hepatectomized rats evaluated by L-[1-13C]phenylalanine breath test

BACKGROUND

We have previously reported that by means of a breath test with intravenously administered L-[1-13C] phenylalanine (13Cphe), hepatopathy could be quantitatively evaluated by measuring expiratory 13CO2 levels in a short period. It is known that phenylalanine hydroxylase activity (PAHA) plays an important role in phenylalanine metabolism. We examined the relationship between changes in PAHA and the results of the 13Cphe breath test during hepatic regeneration in a rat model of 70% hepatectomy, to assess their usefulness for evaluating hepatic regeneration.

METHODS

Male Wistar rats (Shizvoka Laboratory Animal Center, Hamamatsu, Japan) weighing 230 to 290 g were subjected to 70% hepatectomy under anesthesia with sodium pentobarbital. One, 2, 3, 5, 7, and 14 days postoperatively, 30 mg/kg 13Cphe was intravenously injected into the femoral vein, and the increase in exhaled 13CO2 (Delta 13CO2) was measured for 15 minutes. Simple laparotomy was performed in control rats. After the breath test, the regenerated liver was removed and weighed. The amount of DNA, amount of hepatic tissue total protein (TP), and PAHA were determined.

RESULTS

The r between liver weight/body weight and PAHA, between DNA and PAHA, and between TP and PAHA were 0.832, 0.720, and 0.758, respectively. Breath test graphs revealed that liver weight/body weight, DNA, and TP showed the best correlations with the peak value of Delta 13CO2 (liver weight/body weight percentage, r = 0.801; DNA, r = 0.660; TP, r = 0.706), and r between PAHA and peak value was 0.638.

CONCLUSIONS

These results suggest that measurement of PAHA in regenerated liver is an effective method for following up liver function after hepatic resection. Moreover, the 13Cphe breath test may also be useful to evaluate liver function after partial hepatectomy.

Regenerative activity and liver function following partial hepatectomy in the rat using (31)P-MR spectroscopy

The aim of the present study was to determine whether alterations in hepatic energy expenditure following partial hepatectomy (PHx), as documented by in vivo hepatic (31)P-MRS, correlate with standard parameters of hepatic regeneration and/or liver function. In addition, we sought to determine whether changes in hepatic energy levels are proportional to the extent of hepatic resection. Adult male Sprague-Dawley rats (4-7 per group) underwent a 40%, 70%, or 90% PHx or sham surgeries. Magnetic resonance spectroscopy (MRS) examinations were performed on each animal 24 or 48 hours thereafter. After MRS examinations, [(3)H]thymidine incorporation into hepatic DNA, proliferating cell nuclear antigen (PCNA) protein expression, and serum bilirubin determinations were performed on each rat. Twenty-four hours following surgery, rats that had undergone 70% PHx had unchanged adenosine triphosphate (ATP) levels but significantly lower ATP/inorganic phosphate (Pi) ratios (P <.05), whereas, at 48 hours post-PHx, both ATP and ATP/Pi levels were lower than in sham- and nonoperated controls (P <.05). Hepatic regeneration and liver dysfunction mirrored these changes; correlations existed between ATP/Pi ratios and [(3)H]thymidine incorporation (r = -0.61, P <.005), PCNA protein expression (r = -0.62, P <.005), and serum bilirubin (r = -0.49, P <.05). For rats that had undergone graded resections, depleted energy levels 48 hours post-PHx were proportional to the extent of resection, degree of enhanced regenerative activity, and liver dysfunction. In conclusion, (31)P-MRS-generated ATP/Pi index is a noninvasive, robust determination that correlates with standard parameters of hepatic regeneration and function.

Evaluation of liver regeneration using the L-[1-13C]methionine breath test

BACKGROUND

We examined the relationship between changes in the liver weight/body weight percentage, amount of hepatic tissue total DNA, and the results of the [1-(13)C]methionine ((13)Cmet) breath test during hepatic regeneration in a rat model of 70% hepatectomy, to assess their usefulness for evaluating hepatic regeneration.

MATERIALS AND METHODS

Male Wistar rats (230-290 g) were subjected to 70% hepatectomy under anesthesia with Nembutal. One, 2, 3, 7, and 14 days postoperatively, 40 mg/kg (13)Cmet was intravenously injected into the femoral vein, and the increase in exhaled (13)CO(2) (Delta(13)CO(2)) was measured for 15 min. Simple laparotomy was performed in control rats. Following the breath test, the regenerated liver was removed and weighed. The amount of DNA was determined.

RESULTS

The correlation coefficients (r) between liver weight/body weight (LW/BW) and results of the (13)Cmet breath test, and between DNA and results of the (13)Cmet breath test were 0.892 and 0.800, respectively.

CONCLUSIONS

The (13)Cmet breath test is considered to be very useful for assessing liver regeneration, and total (13)CO(2) output over 15 min in the (13)Cmet breath test graph seems to be an effective indicator for evaluating liver regeneration.

Gene expression of urea cycle enzymes following two-thirds partial hepatectomy in the rat

The effect of reduction of functional liver mass on the expression of enzyme systems for hepatic urea synthesis was assessed in rats following two-thirds partial hepatectomy. Results were related to normal, fed rats and to sham-operated rats, with identical timing for surgery and feeding. Among the five urea cycle enzymes the mRNA steady-state level was higher in hepatectomized than in sham-operated rats for carbamoyl phosphate synthetase and arginino-succinate lyase. The level for albumin mRNA remained close to that of the controls. Relative transcription rates were found to be increased for carbamoyl phosphate synthetase, arginino-succinate synthase and arginase. For albumin the transcription rate was drastically reduced initially, but recovered gradually during the experimental period. The data indicate that the expression of urea cycle enzymes, in particular that of carbamoyl phosphate synthetase which is the rate-limiting step, is up-regulated by partial hepatectomy. This helps to maintain urea synthesis rate at a normal or near normal level during the period of reduced liver mass, confirming metabolic studies. In contrast, the transcription for albumin was reduced. The immediate increase in urea cycle enzyme expression during the period of acute hepatocyte loss is consistent with the view that it is vitally important that urea synthesis, in contrast to e.g. albumin synthesis, remains intact when the metabolic capacity of the liver is reduced.

Polyamine plasma levels and liver regeneration following partial hepatic resection in man

Polyamines (putrescine, spermidine, and spermine) are widely distributed in animal and vegetal tissues, where their intracellular concentration strictly correlates with normal and pathological cell growth and protein synthesis. By means of a sensitive HPLC technique, the fasting plasma concentrations of polyamines were measured serially in 11 patients who underwent partial hepatic resection because of focal liver lesions. Samples were obtained before surgery and over the next 6 months, during hepatic regeneration. Liver volume was also measured by ultrasound on the basis of the 3 maximum diameters of the liver. From 2 to 4 weeks after surgery, plasma putrescine increased by a maximum of 78%, and spermidine by approximately 50%. No changes were observed in spermine levels. The spermidine/spermine ratio nearly doubled during liver regeneration. The volume of the liver decrease from 1505 [SD 236] ml to 743 [151] ml after resection, and returned to nearly normal values after 6 months (1231 [100] ml, p < 0.05 vs. basal values). The liver regeneration rate was highest 2-4 weeks after resection, and declined thereafter, when prevailing polyamine concentrations returned to normal. These data show that liver regeneration is accompanied by a significant increase in fasting putrescine and spermidine concentrations, which might be biochemical signals of active liver cell regeneration.

Metronidazole and antipyrine metabolism in the rat: clearance determination from one saliva sample

1. The applicability of a simple, non-invasive method for assessment of metronidazole and antipyrine metabolism in rats in vivo was investigated. 2. In 48 sample pairs of blood and pilocarpine-stimulated saliva from six rats the concentration of metronidazole was almost identical (r = 0.97). 3. In 26 rats the clearance could be determined from one sample without loss of precision and accuracy compared with conventional determinations (r = 0.99). If urine was collected for 24 h the fractional clearance representing each elimination pathway could be determined. 4. Pretreatment with phenobarbitone increased the fractional clearance of metronidazole by oxidation and glucuronidation 3.8-fold and 1.6-fold, respectively, whereas 3-methylcholanthrene pretreatment increased the rate of oxidation 10-fold and decreased the rate of glucuronidation 0.5-fold. 5. The clearance and fractional clearances of metronidazole and antipyrine administered in a mixture could be determined from the same saliva sample and urine collected for 24 h without drug-drug interactions. 6. Phenobarbitone pretreatment increased the formation rate of all metabolites of metronidazole and antipyrine administered in a mixture, whereas beta-naphthoflavone increased the formation rates of only the oxidative metronidazole metabolites, norantipyrine and 4-hydroxyantipyrine, but not metronidazole glucuronide or 3-hydroxymethylantipyrine. 7. A mixture of metronidazole and antipyrine and non-invasive sampling are recommendable for the study of the differential metabolism of foreign compounds in rats in vivo.

Metronidazole and antipyrine as probes for the study of foreign compound metabolism

The aim of the present work was to develop a tool for the study of the enzyme activities relevant for the biotransformation of foreign compounds, their elimination and/or activation to toxic substances. The activity of an enzyme may be assessed by the rate of metabolism of a preferably specific probe or model compound. The cytochrome P450'ies, the key enzymes for the elimination and/or activation of most foreign compounds, exist in multiple forms with variable substrate specificity and regulation. Some cytochrome P450'ies are under genetic control, whereas the activity of others is mainly regulated by the influence from factors in the environment. Only some of the cytochrome P450'ies are relevant for the formation of harmful metabolites. Thus, the activity of as many cytochrome P450 forms as possible should be assessable, preferably simultaneously. The present work evaluated metronidazole in a cocktail with antipyrine as a tool for the study of the regulation of foreign compound metabolism in the liver. The cytochrome P450 catalyzed metabolism of metronidazole and antipyrine was studied in humans and in isolated rat hepatocytes. In humans the influence of dose, route of administration, enzyme induction and inhibition and liver disease was investigated. Rats of either sex were studied with and without pretreatment with specific enzyme inducers and incubations included specific enzyme inhibitors. Evidence was provided that the oxidative formation of the five major metabolites, two from metronidazole and three from antipyrine, depends on different cytochrome P450'ies. In humans it was demonstrated that the clearance of metronidazole and antipyrine could be determined from the same saliva sample collected 16-24 hours after their oral administration and so could the clearance for formation of each metabolite if urine was collected for 48 hours. Thus, with the cocktail of metronidazole and antipyrine and simple non-invasive sampling the activity of five different cytochrome P450'ies can be assessed in vivo. In addition, metronidazole may also be used for assessment of the glucuronidation capacity although this is a minor pathway in man. Because the variation within subjects is much less than between them, the cocktail test is particularly suited for paired designs with measurements before and after an environmental change and the subjects serving as their own control. The metronidazole/antipyrine cocktail may have many applications in the study of the regulation of foreign compound metabolism in man and in animals, in vivo and in vitro.

Metabolism of metronidazole and antipyrine in isolated rat hepatocytes. Influence of sex and enzyme induction and inhibition

The metabolism of metronidazole and antipyrine was investigated in freshly isolated hepatocytes from 7 male and 6 female control Wistar rats, 8 males and 5 females pretreated with phenobarbital (PB) and 3 males pretreated with 3-methylcholanthrene (MC). Pretreatment with PB increased the intrinsic clearance (CLi = Vmax/Km) of metronidazole to its acetic acid (MAA) and hydroxy metabolite (HM) 7- and 2.8-fold in the males and 3.2- and 3.0-fold in the females, whereas MC treatment increased the values 9- and 10-fold, respectively (P less than 0.05). The CLi of metronidazole to HM and its glucuronide conjugate was higher in the control and PB treated male than in the corresponding female groups, whereas the rank order was reversed for sulphate formation (P less than 0.05). SKF 525A was a more potent inhibitor of MAA formation than of HM formation, except in the PB treated male group. Pretreatment with MC increased the inhibitory potency of alpha-naphthoflavone and antipyrine toward MAA and HM formation. In male rats PB treatment increased the CLi of antipyrine to 3-hydroxymethyl-(HMAP), nor-(NORAP) and 4-hydroxyantipyrine (OHAP) 2.5-, 2.1- and 4.5-fold, respectively (P less than 0.05). Pretreatment with MC in male and with PB in female rats had no significant effect on antipyrine metabolism. SKF 525A was a more potent inhibitor of HMAP and OHAP formation than of NORAP formation. Treatment with MC increased the inhibitory potency of alpha-naphthoflavone toward the formation of all antipyrine metabolites. Metronidazole increased the formation rate of HMAP, but inhibited the formation of NORAP and OHAP, particularly the latter. The results suggest that the formation of MAA, HM, HMAP, NORAP and OHAP from metronidazole and antipyrine is catalyzed by different cytochrome P-450 isozymes, which may be supplemented or substituted by PB or MC induced species. The involved P-450 isozymes have more or less overlapping substrate and product specificity. Metronidazole appears to be a sensitive probe for detection and identification of PB and MC type induction.

A review of new approaches to assessing hepatic function in animals

Although a multitude of effective liver function tests are available for use in animals, a variety of modifications of currently used tests have been recently reported. In addition, newer procedures now used in human medicine may also provide unique insights into assessing and detecting acquired hepatic disorders in animals. Examples of new procedures are: assessing microsomal mixed function oxidase activity by plasma caffeine clearance; estimating the extent of active hepatic fibrogenesis through serum procollagen-III peptide levels; determining hepatic blood flow and functional mass by the galactose elimination capacity; detecting primary hepatocellular cancer through serum or urinary ligandin levels; and to estimate the liver's maximal capacity to excrete indocyanine green independent of blood flow. In evaluating drugs as to their hepatotoxicity, function tests should be included in the liver profile which measure specific metabolic alterations unique to the compound under study.

The capacity of urea-N synthesis as a quantitative measure of the liver mass in rats

The capacity of urea-N synthesis (CUNS), the galactose elimination capacity (GEC) and the antipyrine clearance (APC) were measured in rats immediately after 30, 70 and 90% partial hepatectomy and after sham operation. CUNS was assessed during alanine infusion as urea accumulation in total body water, corrected for intestinal hydrolysis, and GEC was measured during constant galactose infusion in the same animals. APC was determined by the one-sample method in a separate group of animals, treated similarily. CUNS, GEC and APC were all correlated to the liver weight with correlation coefficients (r) above 0.8 and the correlation coefficients (r) between CUNS, GEC and APC were all above 0.7. It is concluded that CUNS is a quantitative measure of the functional liver mass in the rat.