Synthesis of glutathione in response to methionine load in control subjects and in patients with cirrhosis

The fasting plasma level of reduced glutathione (GSH), a methionine-derived tripeptide, is reduced in cirrhosis. There is evidence that a reduced activity of S-adenosyl-L-methionine synthetase limiting the flux of methionine along the transmethylation/transsulfuration pathway may contribute to decrease GSH levels. No studies have analyzed plasma GSH in response to a methionine load. In 6 control subjects and in 10 patients with cirrhosis, plasma sulfur amino acid and plasma and erythrocyte GSH levels were measured in response to a L-methionine load (0.1 g/kg). Blood samples were obtained throughout the day after the oral load. Urine was collected for measurement of sulfur excretion. During the study period, all subjects consumed a standard diet of 1,683 kcal containing 2% protein and virtually no methionine. Plasma methionine increased in both groups to a peak level exceeding 20 times the basal value 90 minutes after the load, and declined thereafter. Methionine clearance, calculated on the descending part of the methionine-time curve, was reduced by 50% in cirrhosis (P = .0001). Fasting GSH was higher in controls (mean +/- SD, 3.9 +/- 1.3 v 1.6 +/- 0.7 micromol/L, P = .0004). In response to a methionine load, it peaked at 10.2 +/- 7.2 and 3.2 +/- 1.3 micromol/L, respectively (P = .009). Thereafter, plasma GSH progressively declined, and after 24 hours, it returned to the fasting preinfusion values in both groups. Plasma cysteine and taurine concentrations, as well as the erythrocyte GSH time course, paralleled plasma GSH levels, with less significant differences between groups. Sulfate excretion was delayed. GSH synthesis is stimulated by a methionine load. The reduced flux of methionine along the transmethylation/transsulfuration pathway reduces GSH synthesis in cirrhosis. Defective methionine metabolism also may be responsible for reduced fasting GSH.     

Defective methionine metabolism in cirrhosis: relation to severity of liver disease.

A block in the transsulfuration pathway has previously been suggested in cirrhosis on the basis of increased fasting methionine concentrations, decreased methionine elimination and low levels of methionine end products. To date, methionine elimination has never been studied under controlled steady-state conditions, and the relation of the severity of liver disease to impaired methionine metabolism has not been clarified. We measured methionine plasma clearance in 6 control subjects and in 12 patients with cirrhosis during steady-state conditions obtained by a primed, continuous methionine infusion. In the presence of high-normal fasting methionine concentrations (range = 14 to 69 mumol.L-1 in controls and 26 to 151 mumol.L-1 in cirrhotic patients), methionine plasma clearance was reduced in cirrhotic patients (2.25 +/- S.D. 0.43 ml.sec-1 vs. 2.86 +/- S.D. 0.43 ml.sec-1 in controls; p less than 0.05), whereas methionine half-life was increased (282 +/- 90 min vs. 187 +/- 25 min in controls; p less than 0.05). Fasting methionine significantly correlated with methionine clearance. The infused methionine was not degraded to urea to any significant extent in cirrhotic patients, whereas a threefold increase in urinary urea nitrogen excretion rate was observed in controls. Similarly, taurine concentrations significantly increased both in plasma and in the urine in controls but not in cirrhotic patients. In cirrhotic patients methionine plasma clearance significantly correlated with galactose elimination capacity (r = 0.818) and with the Child-Pugh score (rs = -0.795). The study supports a major role of impaired liver cell function in the reduced metabolism of methionine and decreased formation of methionine end products that occur in cirrhosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Is the increase in serum cystathionine levels in patients with liver cirrhosis a consequence of impaired homocysteine transsulfuration at the level of gamma-cystathionase?

BACKGROUND: It has been suggested that the major metabolic block in the methionine catabolic pathway in cirrhotics exists at the level of the enzyme S-adenosylmethionine synthetase because in previous studies using conventional amino-acid analyzers, no intermediates of transmethylation/transsulfuration were found to accumulate in plasma downstream of S-adenosylmethionine synthesis. We therefore measured serum concentration intermediates of methionine transmethylation/transsulfuration using an improved gas chromatography/mass spectrometry technique. METHODS: Serum concentrations of methionine, homocysteine, cystathionine, N,N-dimethylglycine, N-methylglycine, methylmalonic acid, 2-methylcitric acid and alpha-aminobutyric acid were determined by gas chromatography/mass spectrometry in 108 consecutive patients with liver cirrhosis at Child stages A (mild cirrhosis, n = 27) and B/C (severe cirrhosis, n = 81), 18 outpatients with non-cirrhotic liver disease, and 55 healthy individuals. RESULTS: Serum levels of methionine, N,N-dimethylglycine, N-methylglycine, cystathionine, and homocysteine were significantly higher in patients at Child stages B/C compared with those of healthy controls (P < 0.01), and they were also significantly higher than in patients with non-cirrhotic liver disease (P < 0.01 and P < 0.05 for homocysteine, respectively). They also correlated with the Child-Pugh score (P < 0.01). Homocysteine, cystathionine, N,N-dimethylglycine, N-methylglycine, methylmalonic acid, and 2-methylcitric acid correlated with serum creatinine. The mean cystathionine concentration was significantly higher in patients with creatinine > or = 1.4 mg/dl than in patients with normal creatinine values (P < 0.01). However, the differences between cirrhotics and healthy controls were still significant after correcting for creatinine. CONCLUSIONS: Our data provides indirect evidence for two hitherto unrecognized alterations of methionine metabolism in cirrhotics, i.e. impairment of the transsulfuration of homocysteine at the level of cystathionine degradation and a shift in remethylation of homocysteine towards the betaine-homocysteine-methyltransferase reaction.     

Effects of insulin deprivation and treatment on homocysteine metabolism in people with type 1 diabetes

CONTEXT: Abnormal homocysteine metabolism may contribute to increased cardiovascular death in type 1 diabetes (T1DM). Amino acid metabolism is altered in T1DM. In vitro, insulin reduces hepatic catabolism of homocysteine by inhibiting liver transsulfuration. It remains to be determined whether methionine-homocysteine metabolism is altered in T1DM. OBJECTIVE: We sought to determine whether insulin deficiency during insulin deprivation or high plasma insulin concentration after insulin treatment alters homocysteine metabolism in T1DM. DESIGN: This was an acute interventional study with paired and comparative controls. SETTING: The study was conducted at a general clinical research center. PATIENTS AND INTERVENTION: We used stable isotope tracers to measure methionine-homocysteine kinetics in six patients with T1DM during insulin deprivation (I-) and also during insulin treatment (I+) and compared them with nondiabetic controls (n = 6). MAIN OUTCOME MEASURES: Homocysteine kinetics (transmethylation, transsulfuration, and remethylation) were from plasma isotopic enrichment of methionine and homocysteine and (13)CO(2). RESULTS: T1DM (I-) had lower rates of homocysteine-methionine remethylation (P < 0.05 vs. control and I+). In contrast, transsulfuration rates were higher in I- than controls and I+ (P < 0.05). Insulin treatment normalized transsulfuration and remethylation (P < 0.05 vs. I- and P > 0.8 vs. control). Plasma homocysteine concentrations were lower in T1DM (P < 0.05 vs. control during both I- and I+), which may be explained by increased homocysteine transsulfuration. Thus, significant alterations of methionine-homocysteine metabolism occur during insulin deprivation in humans with T1DM. CONCLUSIONS: Insulin plays a key role in the regulation of methionine-homocysteine metabolism in humans, and altered homocysteine may occur during insulin deficiency in type 1 diabetic patients.     

Carnitine metabolism in patients with chronic liver disease

Carnitine metabolism was studied in 79 patients with chronic liver disease, including 22 patients with noncirrhotic liver disease and 57 patients with different types of cirrhosis (22 patients with hepatitis B- or C-associated cirrhosis, 15 patients with alcohol-induced cirrhosis, 15 patients with primary biliary cirrhosis [PBC], and 5 patients with cryptogenic cirrhosis), and compared with 28 control subjects. In comparison with control subjects, patients with noncirrhotic liver disease showed no change in the plasma carnitine pool, whereas patients with cirrhosis had a 29% increase in the long-chain acylcarnitine concentration. Analysis of subgroups of patients with cirrhosis showed that patients with alcohol-induced cirrhosis had an increase in the total plasma carnitine concentration (67.8 +/- 29.5 vs. 55.2 +/- 9.9 micromol/L in control subjects), resulting from increases in both the short-chain and long-chain acylcarnitine concentration. In this group of patients, the acylcarnitine concentrations showed a close correlation with the total carnitine concentration, and the total carnitine concentration with the serum bilirubin concentration. Urinary excretion of carnitine was not different between patients with noncirrhotic or cirrhotic liver disease and control patients. However, patients with PBC showed an increased urinary excretion of total carnitine (52.5 +/- 40.0 vs. 28.0 +/- 16.7 micromol carnitine/mmol creatinine), resulting from an increase in the fractional excretion of both free carnitine and short-chain acylcarnitine. The current studies show that patients with cirrhosis are normally not carnitine deficient. Patients with alcohol-induced cirrhosis have increased plasma carnitine concentrations, which may result from increased carnitine biosynthesis because of increased skeletal muscle protein turnover. The increase in the fractional carnitine excretion in patients with primary biliary cirrhosis may result from competition of bile acids and/or bilirubin with tubular carnitine reabsorption and/or from a reduced activity of the carnitine transporter located in the proximal tubule.(Hepatology 1997 Jan;25(1):148-53)     

Oral challenge with a methionine load in patients with inflammatory bowel disease: a better test to identify hyperhomocysteinemia

BACKGROUND: Patients with inflammatory bowel disease have an increased risk of thrombosis. Hyperhomocysteinemia is one of the factors that have been related to thromboembolic complications. Patients with hyperhomocysteinemia and normal fasting homocysteine levels can be identified with an oral methionine load. We studied homocysteine levels in patients with IBD during fasting and after methionine load to determine the true prevalence of hyperhomocysteinemia and its relation with thrombotic events. METHODS: Prospective analysis of homocysteine levels in consecutive patients with IBD during fasting and 6-8 hours after an oral methionine load. Levels of folate and vitamin B12 were also determined. History of thrombotic events were recorded. RESULTS: Eighty-two patients with IBD, 56 with UC and 26 with CD were included. Eighteen patients (22%) had hyperhomocysteinemia during fasting. Mean levels of homocysteine after methionine load were 20.4 +/- 18.1 micromol/l (range, 1-79.7 micromol/l), and 43 patients (52%) had hyperhomocysteinemia (> or =20 micromol/l) after methionine load. Six patients (7.3%) had history of thrombosis. The homocysteine levels during fasting and after methionine load were significantly higher in patients with thrombotic events than in patients without thrombosis (15.5 +/- 3.7 micromol/l vs. 6.6 +/- 6.5 micromol/l; P = 0.002; 44.5 +/- 20.9 micromol/l vs. 18.4 +/- 16.5 micromol/l; P < 0.001, respectively). CONCLUSIONS: There is a higher prevalence of hyperhomocysteinemia in IBD patients than previously thought, this can be identified with an oral challenge of a methionine load. Hyperhomocysteinemia increases the risk of thromboembolic complications in patients with IBD.     

Methionine transmethylation and transsulfuration in the piglet gastrointestinal tract

Methionine is an indispensable sulfur amino acid that functions as a key precursor for the synthesis of homocysteine and cysteine. Studies in adult humans suggest that splanchnic tissues convert dietary methionine to homocysteine and cysteine by means of transmethylation and transsulfuration, respectively. Studies in piglets show that significant metabolism of dietary indispensable amino acids occurs in the gastrointestinal tissues (GIT), yet the metabolic fate of methionine in GIT is unknown. We show here that 20% of the dietary methionine intake is metabolized by the GIT in piglets implanted with portal and arterial catheters and fed milk formula. Based on analyses from intraduodenal and intravenous infusions of [1-(13)C]methionine and [(2)H(3)]methionine, we found that the whole-body methionine transmethylation and remethylation rates were significantly higher during duodenal than intravenous tracer infusion. First-pass splanchnic metabolism accounted for 18% and 43% of the whole-body transmethylation and remethylation, respectively. Significant transmethylation and transsulfuration was demonstrated in the GIT, representing approximately 27% and approximately 23% of whole-body fluxes, respectively. The methionine used by the GIT was metabolized into homocysteine (31%), CO(2) (40%), or tissue protein (29%). Cystathionine beta-synthase mRNA and activity was present in multiple GITs, including intestinal epithelial cells, but was significantly lower than liver. We conclude that the GIT consumes 20% of the dietary methionine and is a significant site of net homocysteine production. Moreover, the GITs represent a significant site of whole-body transmethylation and transsulfuration, and these two pathways account for a majority of methionine used by the GITs.     

Elevated nitric oxide and 3′,5′ cyclic guanosine monophosphate levels in patients with alcoholic cirrhosis

AIM： To evaluate whether serum levels of nitric oxide （NO^.） and plasma levels of cyclic guanosine monophosphate （cGMP） and total glutathione （GSH） are altered in patients with alcoholic cirrhosis and to examine their correlation with the severity of liver disease.
METHODS： Twenty-six patients with alcoholic liver cirrhosis were studied. Serum levels of NO^. and plasma levels of cGMP and GSH were measured in 7 patients with compensated alcoholic cirrhosis （Child-Pugh A） and 19 patients with advanced cirrhosis （Child-Pugh B and C）. The model for end-stage liver disease （MELD） score was evaluated. Sixteen healthy volunteers served as controls. Liver enzymes and creatinine levels were also tested.
RESULTS： NO^. and cGMP levels were higher in patients with Child-Pugh B and C cirrhosis than in Child-Pugh A cirrhosis or controls （NO^.： 21.70 ± 8.07 vs 11.70 ± 2.74; 21.70± 8.07 vs 7.26 ± 2.47 μmol/L, respectively; P 〈 0.001） and （cGMP： 20.12 ± 6.62 vs 10.14 ± 2.78; 20.12 ± 6.62 vs 4.95 ± 1.21 pmol/L, respectively; P 〈 0.001）. Total glutathione levels were lower in patients with Child-Pugh B and C cirrhosis than in patients with Child-Pugh A cirrhosis or controls （16.04 ± 6.06 vs 23.01 ± 4.38 or 16.04 ± 6.06 vs 66.57 ±26.23 μmol/L, respectively; P 〈 0.001）. There was a significant correlation between NO^. and cGMP levels in all patients with alcoholic cirrhosis. A significant negative correlation between reduced glutathione/glutathione disulfide and the MELD score was found in all cirrhotic patients.
CONCLUSION： Our results suggest a role for oxidative stress in alcoholic liver cirrhosis, which is more significant in decompensated patients with higher levels of NO^. and cGMP and lower GSH levels than in compensated and control patients. Altered mediator levels in decompensated patients may influence the hemodynamic changes in and progression of liver disease.     

Free Methionine Supplementation Limits Alcohol-Induced Liver Damage in Rats

Alcohol feeding to rats that were submitted to a jejunoileal bypass operation has been shown to result in liver damage being comparable with alcohol-induced liver disease in man. In the present study, a striking effect of free methionine consumption on histological liver injury, triglyceride accumulation, and energy-rich nucleoside content in the liver of rats with a jejunoileal bypass is demonstrated. The animals obtained 0, 30, and 120 mg of methionine in the control group and 0,30,120, and 240 mg in the alcohol-fed group per day and per kilogram of body weight for 12 weeks. Methionine was found to strongly improve the alcohol-induced histological changes in the liver. Triglyceride content of the liver was found to decrease in a dose-dependent manner with increasing methionine ingestion (from 255 ± 20.7 to 49.7 ± 6.1 μmol/g of protein in the control group and from 233 ± 17.3 to 42.1 ± 7.2 μmol/g of protein in the alcohol group). Hepatic adenosine triphosphate content increased significantly with higher methionine consumption (13.5 ± 0.8 vs. 26.9 ± 2.8 μmol/g of protein in the control group and 11.9 ± 1.4 vs. 20.5 ± 2.5 μmol/g of protein in the alcohol group), whereas no differences were found in the protein and DNA content of the liver. These results underscore the impairment of the transmethylation/transsulfuration pathway in the development of alcohol-induced liver diseases.     

Homocysteine and methionine metabolism in renal failure

Renal insufficiency is invariably accompanied by elevated plasma concentrations of the sulfur-containing and potentially vasculotoxic amino acid homocysteine. There is a strong relationship between glomerular filtration rate and plasma homocysteine concentration. Unlike creatinine, however, homocysteine is avidly reabsorbed in the renal tubules, and its urinary excretion is minimal. There is no evidence that homocysteine is actively removed by the human kidney. In renal insufficiency, plasma concentrations of S-adenosylmethionine, S-adenosylhomocysteine, cystathionine, cysteine, and sulfate are elevated, pointing to a remethylation or distal transsulfuration/oxidation block as the cause of hyperhomocysteinemia in renal failure. Stable isotope techniques have shown that both whole-body homocysteine remethylation and methionine transmethylation are decreased in renal failure, whereas homocysteine transsulfuration seems intact. Metabolic homocysteine clearance (i.e., transsulfuration relative to plasma homocysteine) is decreased to a major extent. These metabolic disturbances in renal failure can only be partially restored with current treatments. Folic acid treatment lowers plasma homocysteine concentration and increases remethylation and transmethylation rates. Plasma homocysteine, however, is not normalized, and metabolic homocysteine clearance by transsulfuration remains impaired. According to the currently available data, effective normalization of plasma homocysteine can only be obtained when its metabolic clearance through transsulfuration is restored.     

Rosiglitazone reduces serum homocysteine levels, smooth muscle proliferation, and intimal hyperplasia in Sprague-Dawley rats fed a high methionine diet

Homocysteine (Hcy) is a metabolite of the essential amino acid methionine. Hyperhomocysteinemia is associated with vascular disease, particularly carotid stenosis. Rosiglitazone, a ligand of the peroxisome proliferator-activated receptor gamma , attenuates balloon catheter-induced carotid intimal hyperplasia in type 2 diabetic rats. We studied 4 groups (n = 7 per group) of adult female Sprague-Dawley rats fed (a) powdered laboratory chow (control), (b) control diet with rosiglitazone (3.0 mg/kg/d), (c) diet containing 1.0% l -methionine, and (d) diet containing methionine and rosiglitazone. After 1 week on high methionine diet, the rats were administered an aqueous preparation of rosiglitazone by oral gavage. One week after initiation of rosiglitazone, balloon catheter injury of the carotid artery was carried out using established methods, and the animals continued on their respective dietary and drug regimens for another 21 days. At the end of the experimental period, blood samples were collected, and carotid arteries and liver were harvested. Serum Hcy increased significantly on methionine diet compared with controls (28.9 +/- 3.2 vs 6.3 +/- 0.04 micromol/L). Development of intimal hyperplasia was 4-fold higher in methionine-fed rats; this augmentation was significantly reduced ( P < .018) in rosiglitazone-treated animals. Rosiglitazone treatment significantly ( P < .001) suppressed Hcy levels and increased the activity of the Hcy metabolizing enzyme, cystathionine-beta-synthase in the liver samples. Hcy (100 micromol/L) produced a 3-fold increase in proliferation of rat aortic vascular smooth muscle cells; this augmentation was inhibited by incorporating rosiglitazone (10 micromol/L). After balloon catheter injury to the carotid artery of animals on a high methionine diet, there was an increase in the rate of development of intimal hyperplasia consistent with the known effects of Hcy. It is demonstrated for the first time that the peroxisome proliferator-activated receptor gamma agonist rosiglitazone can attenuate the Hcy-stimulated increase in the rate of development of intimal hyperplasia indirectly by increasing the rate of catabolism of Hcy by cystathionine-beta-synthase and directly by inhibiting vascular smooth muscle cell proliferation. These findings may have important implications for the prevention of cardiovascular disease and events in patients with hyperhomocysteinemia (HHcy).     

Folic acid lowers elevated plasma homocysteine in chronic renal insufficiency: possible implications for prevention of vascular disease

To explore interrelations between folic acid and methionine metabolism in chronic renal insufficiency, we measured plasma amino acids in 21 patients with mean serum creatinine +/- SD of 560 +/- 240 mumol/L, after a ten-hour overnight fast, before and after administration of 5 mg of oral folic acid daily for 15 +/- 6 days. Mean plasma homocysteine was 12.9 +/- 6.8 mumol/L in the patients and 4.2 +/- 0.8 mumol/L in 24 normal controls (P less than .001), and after folic acid administration it declined in the patients to 6.8 +/- 2.8 mumol/L (P less than .0001) in linear proportion (r = .92) to the prefolate homocysteine level. Methionine concentrations were normal in the patients and did not change after folate administration, nor did elevated cysteine and creatinine. Plasma serine was lower (88.3 +/- 17.2 v 121 +/- 25 mumol/L, P less than .41) and declined further to 67.8 +/- 16.4 (P less than .0001) after folate, while prefolate glycine levels increased from 273.3 +/- 61.2 to 313.2 +/- 97.5 mumol/L (P less than .01). Serum and red-cell folate levels were normal in the patients before treatment. The results show that homocysteine levels are increased in chronic renal insufficiency, but may be lowered by folate enhancement of remethylation of homocysteine to methionine. Since elevated plasma homocysteine is associated with premature vascular disease, folic acid may reduce cardiovascular risk in chronic renal insufficiency.     

Midodrine, octreotide, albumin, and TIPS in selected patients with cirrhosis and type 1 hepatorenal syndrome

Hepatorenal syndrome (HRS) is a functional renal disorder complicating decompensated cirrhosis. Treatments to date, except liver transplantation, have been able to improve but not normalize renal function. The aim of this study was to determine the efficacy of transjugular intrahepatic portosystemic stent shunt (TIPS) as a treatment for type 1 HRS in ascitic cirrhotic patients, following improvement in systemic hemodynamics with a combination of midodrine, octreotide, and albumin (medical treatment). Fourteen ascitic cirrhotic patients with type 1 HRS received medical therapy until their serum creatinine reached below 135 micromol/L for at least 3 days, followed by a TIPS if there were no contraindications. Patients were assessed before and after medical treatment, as well as at 1 week and 1, 3, 6, and 12 months post-TIPS with measurements of renal function, sodium handling, systemic hemodynamics, central blood volume, and hormonal markers. Medical therapy for 14 +/- 3 days improved renal function (serum creatinine: 233 +/- 29 micromol/L vs. 112 +/- 8 micromol/L, P =.001) and renal sodium excretion (5 +/- 2 mmol/d vs. 9 +/- 2 mmol/d, P =.002) in 10 of the 14 patients. TIPS insertion in five of the responders further improved renal function and sodium excretion, so that by 12 months post-TIPS, glomerular filtration rate (96 +/- 20 mL/min, P <.01 vs. pre-TIPS) and urinary sodium excretion (119 +/- 15 mmol/d, P <.01 vs. pre-TIPS) were normal, associated with normalization of plasma renin and aldosterone levels and elimination of ascites. In conclusion, TIPS is an effective treatment for type 1 HRS in suitable patients with cirrhosis and ascites, following the improvement of renal function with combination therapy of midodrine, octreotide, and albumin.     

A randomized controlled trial of ursodeoxycholic acid in patients with alcohol-induced cirrhosis and jaundice

The aim of our multicenter study was to assess the efficacy of ursodeoxycholic acid (UDCA) on the survival of patients with alcohol-induced cirrhosis and jaundice. We included patients with histologically proven alcohol-induced cirrhosis and serum bilirubin >50 micromol/L. After randomization, patients received either UDCA (13-15 mg/kg/d) or a placebo for 6 months. Two hundred twenty-six patients (113 in each group) were included in 24 centers. There were 139 men and 87 women, mean age of 50.3 years. Seventy-four percent had associated alcohol-induced hepatitis, and 24% received a corticosteroid therapy. At inclusion, the 2 groups were comparable for the main clinical and biologic parameters, but serum bilirubin was higher in the UDCA group than in the placebo group (163 micromol/L vs. 145 micromol/L, P <.03). The percentage of patients lost at follow-up or who resumed their alcoholism during the study was comparable in the 2 groups. During the study, 55 patients died, 35 in the UDCA group and 20 in the placebo group. In the intention to treat analysis, the probability of survival at 6 months (Kaplan-Meier method) was lower in the UDCA than in the P group (69% vs. 82%, respectively; P =.04, log-rank test). After adjustment on the bilirubin level at entry (Cox model), the independent predictive value of the treatment group did not reach the statistical level (RR = 1.64, CI 0.85-2.85; P =.077). In conclusion, UDCA administered at the dose recommended in primary biliary cirrhosis has no beneficial effect on the 6-month survival of patients with severe alcohol-induced cirrhosis. An inappropriate dosage of UDCA cannot be excluded as an explanation for the lack of therapeutic benefit.     

Cystathionine-synthase-deficient patients do not use the transamination pathway of methionine to reduce hypermethioninemia and homocystinemia

Methionine is supposed to be degraded via two known routes, the transsulfuration and the transamination pathways. In particular, patients with hypermethioninemia, due to a defect in the transsulfuration pathway, may catabolize significant amounts of methionine via the transamination pathway. In this study the relative amount of methionine degraded via the transamination pathway in 17 patients with homozygous homocystinuria, due to cystathionine synthase deficiency, was compared with 23 normal subjects, and with a patient with hypermethioninemia due to a deficiency in methionine adenosyltransferase. The homocystinuric patients and the normal subjects were studied in the fasting state as well as after methionine loading (0.1 g/kg body weight). It is concluded that in cystathionine synthase deficient patients, the transamination pathway is not quantitatively important in methionine degradation despite elevated methionine levels. This is in contrast to the patient with methionine adenosyltransferase deficiency, who catabolizes at least 20% of his dietary methionine via the transamination pathway.     

Cerebral herniation in patients with acute liver failure is correlated with arterial ammonia concentration

Cerebral edema leading to cerebral herniation (CH) is a common cause of death in acute liver failure (ALF). Animal studies have related ammonia with this complication. During liver failure, hepatic ammonia removal can be expected to determine the arterial ammonia level. In patients with ALF, we examined the hypotheses that high arterial ammonia is related to later death by CH, and that impaired removal in the hepatic circulation is related to high arterial ammonia. Twenty-two patients with ALF were studied retrospectively. In addition, prospective studies with liver vein catheterization were performed after development of hepatic encephalopathy (HE) in 22 patients with ALF and 9 with acute on chronic liver disease (AOCLD). Cerebral arterial-venous ammonia difference was studied in 13 patients with ALF. In all patients with ALF (n = 44), those who developed CH (n = 14) had higher arterial plasma ammonia than the non-CH (n = 30) patients (230 +/- 58 vs. 118 +/- 48 micromol/L; P <. 001). In contrast, galactose elimination capacity, bilirubin, creatinine, and prothrombin time were not different (NS). Cerebral arterial-venous differences increased with increasing arterial ammonia (P <.001). Arterial plasma ammonia was lower than hepatic venous in ALF (148 +/- 73 vs. 203 +/- 108 micromol/L; P <.001). In contrast, arterial plasma ammonia was higher than hepatic venous in patients with AOCLD (91 +/- 26 vs. 66 +/- 18 micromol/L; P <.05). Net ammonia release from the hepatic-splanchnic region was 6.5 +/- 6. 4 mmol/h in ALF, and arterial ammonia increased with increasing release. In contrast, there was a net hepatic-splanchnic removal of ammonia (2.8 +/- 3.3 mmol/h) in patients with AOCLD. We interpret these data that in ALF in humans, vast amounts of ammonia escape hepatic metabolism, leading to high arterial ammonia concentrations, which in turn is associated with increased cerebral ammonia uptake and CH.     

Influence of methionine synthase (A2756G) and methionine synthase reductase (A66G) polymorphisms on plasma homocysteine levels and relation to risk of coronary artery disease

BACKGROUND: Elevated plasma total homocysteine (tHcy) is increasingly being recognized as a risk factor for coronary artery disease (CAD) and other defects. Recent genetic studies have characterized molecular determinants contributing to altered homocysteine metabolism. Our objectives were therefore to confirm the relationship of tHcy with CAD and to examine the importance of genetic influence on tHcy in the coronary angiograms and conventional cardiovascular risk factors recorded in 230 subjects. We also determined the genotype frequencies distribution of the A2756G transition of the B12-dependent methionine synthase (MTR) gene and the A66G mutation of the methionine synthase reductase (MTRR) gene. RESULTS: Patients with CAD (n=151) had significantly higher tHcy concentrations than control subjects (15.49 +/- 2.75 micromol/l vs. 11.21 +/- 3.54 micromol/l, P < 0.001). Hyperhomocysteinaemia (tHcy > or =15 micromol/l) was a risk factor for CAD [RR = 4.07, 95% CI: 2.21 - 7.47, P < 0.001]. The homocysteine concentrations were significantly different between smokers and non-smokers, at 15.63 +/- 3.10 vs. 12.45 +/- 3.84 micromol/l, P < 0.05. In addition, smokers with hyperhomocysteinaemia demonstrated a markedly increased risk of CAD (OR = 2.50, 95% CI: 1.67 - 3.32, P < 0.05) compared with non-smokers with normal homocysteine.The 2756G and the 66G allele contribute to a moderate increase in homocysteine levels (P = 0.008 and P = 0.007, respectively), but not to CAD (P > 0.05). Combined MTR and MTRR polymorphisms, the 2756AG + 66AG and the 2756AG + 66GG were the combined genotypes that were a significant risk factor for having hyperhomocysteinaemia (14.4 +/- 2.8 micromol/l, OR = 2.75, IC 95% = 1.21 - 6.24, P=0.016 and 17.9 +/- 4.1 micromol/l, OR = 6.28, IC 95% = 1.46 - 12.1, P = 0.021, respectively). Statistic analysis using the UniANOVA test shows that these two polymorphisms have an interactive effect circulating homocysteine levels (P < 0.05). CONCLUSION: Our data suggest that moderately elevated tHcy levels are prevalent in our population and are associated with an increased risk for CAD. This study provides evidence that the MTR A2756G and MTRR A66G polymorphisms significantly influence the circulating homocysteine concentration. In addition, the MTR and MTRR genes may interact to increase the risk for having hyperhomocysteinaemia.     

Increased IGF-I : IGFBP-3 ratio in patients with hepatocellular carcinoma

BACKGROUND: The development of hepatocellular carcinoma in liver cirrhosis is associated with altered synthesis and secretion of several growth factors. AIM: The aim of this prospective study was to investigate the potential implication of IGF-I and its major binding protein (IGFBP-3) in the development of hepatocellular carcinoma. PATIENTS AND METHODS: IGF-I and IGFBP-3 were measured in 150 healthy subjects, 40 patients with liver cirrhosis and 63 with liver cirrhosis and untreated hepatocellular carcinoma. The ratio between IGF-I and IGFBP-3 was also calculated. RESULTS: Serum IGF-I (70 +/- 10 and 65 +/- 7 vs. 185 +/- 6.4 microg/l, P < 0.001) and IGFBP-3 levels (1225 +/- 113 and 984 +/- 67 vs. 3017 +/ -80 microg/l, P < 0.001) were lower in patients with liver cirrhosis, without or with hepatocellular carcinoma, than in controls. Age was negatively correlated with IGF-I levels in patients with liver cirrhosis (r = -0.6; P = 0.0002) as well as in controls (r = -0.8, P < 0.0001), but not in patients with hepatocellular carcinoma (r = -0.2; P = 0.2). Additionally, in patients with liver cirrhosis (r = -0.54; P = 0.0003) and more weakly in those with hepatocellular carcinoma (r = -0.24; P = 0.04) IGF-I levels were negatively correlated with liver failure measured according with Child class. Despite patients with class C hepatocellular carcinoma being older than those in the same functional class with cirrhosis (64 +/- 2 vs. 57 +/- 12 years, P < 0.01), they had a significantly increased IGF-I : IGFBP-3 ratio (0.18 +/- 0.05 vs. 0.41 +/- 0.09, P = 0.04), due mostly to increased IGF-I levels (27.1 +/- 5.6 vs. 42 +/- 6.2 microg/l) as IGFBP-3 levels were similar to patients with cirrhosis (734 +/- 81 vs. 679 +/- 83 microg/l). CONCLUSIONS: Hepatocellular carcinoma is associated with a higher IGF-I : IGFBP-3 ratio than that found in patients with liver cirrhosis and a similar degree of liver failure.     

The aminopyrine breath test does not correlate with histologic disease severity in patients with cholestasis

To determine whether the aminopyrine breath test can be used to document the presence of cirrhosis in patients with cholestatic liver disease, 19 patients (13 primary biliary cirrhosis, 4 sclerosing cholangitis and 2 chronic extrahepatic bile duct obstruction) underwent clinical and biochemical evaluations, liver biopsies and an aminopyrine breath test. Results were compared with those in 10 patients with biopsy-proven chronic active hepatitis with bridging and/or cirrhosis and in 22 healthy subjects. The aminopyrine breath test results in the 10 cholestatic patients with cirrhosis were not significantly different from the results in precirrhotic cholestatic patients (mean +/- S.D., 11.2 +/- 5.0 vs. 11.6 +/- 2.8% dose per 2 hr, p greater than 0.05) or healthy subjects (11.5 +/- 2.9% dose per 2 hr). In contrast, the results in the patients with chronic hepatitis were markedly depressed (3.2 +/- 1.9% dose per 2 hr, p less than 0.05). The aminopyrine breath test results did not correlate with results of conventional liver function tests in the cholestatic patients. These results demonstrate that the aminopyrine breath test is not clinically useful in identifying the presence of cirrhosis in patients with cholestatic liver disease, and provide further evidence that decreased microsomal enzyme function is a late feature of cholestatic liver disease.     

Plasma homocysteine after insulin infusion in type II diabetic patients with and without methionine intolerance.

BACKGROUND: A high prevalence of hyperhomocysteinemia has been reported in type II diabetic patients with documented vascular disease; hence the hypothesis that hyperhomocysteinemia may contribute to overall mortality in diabetic patients. The link between insulin and homocysteine metabolism has not been completely clarified yet; in particular, only few data are available on the effects of insulin in vivo on homocysteine metabolism in the presence of abnormalities of sulphur amino acid metabolism (methionine intolerance). MATERIALS AND METHODS: To establish whether methionine intolerance and which of its determinants could influence total plasma homocysteine in response to insulin infusion in vivo in type II diabetic patients, we submitted 18 patients (Group A) with normal and 18 patients with abnormal (hyperhomocysteinemia) (Group B) response to oral methionine load to a glucose/clamp study. At time 0, and 30, 60 and 120 minutes after hyperinsulinemia, homocysteine and methionine plasma levels were assessed. In order to evaluate the cause of methionine intolerance, all patients were assayed for fasting homocysteine-cysteine ratio (as a marker of suspected heterozygosis for cystathionine-beta-synthase deficit), MTHFR C (677)T status and homocysteine-related vitamin status (serum vitamin B (6) [PLP], vitamin B (12) and folate). RESULTS: After hyperinsulinemia, plasma methionine was reduced (by about - 30 % at 120 minutes vs. basal values) within both groups, whereas tHcy tend to decrease in group A following insulin administration (up to - 6.6 +/- 3.6 % vs. basal values at 120 minutes) with a significantly higher variability, while in patients with "methionine intolerance" (group B) tHcy tended to increase (up to + 29.05 +/- 8.3 % vs. basal values at 120 min from the clamp). Serum folic acid (7.45 +/- 2.8 vs. 4.82 +/- 2.5 nmol/L, p < 0.05), Vit. B (12) (348 +/- 78 vs. 242 +/- 65 pmol/L, p < 0.05) and PLP (84.1 +/- 23.6 vs. 50.6 +/- 32.4 nmol/L; p < 0.01) were significantly higher in group A than in group B; PLP levels significantly correlated with homocysteine after 4 h methionine load (n = 36; r = - 0.327, p < 0.05); group A showed also a significantly lower prevalence of suspected heterozygosis for cystathionine-beta-synthase deficit (1/18 [11.1 %] vs. 5/18 [33.3 %], p < 0.05) and MTHFR T allele presence (4/18 [22.2 %] vs. 11/18 [61.1 %], p < 0.01). A stepwise regression analysis with tHcy plasma level variations (event A = reduction; event B = increase) as the dependent variable showed that low serum folate and PLP levels and presence of MTHFR T allele were the variables associated with insulin-induced tHcy increase. CONCLUSIONS: Methionine intolerance may influence the effect of insulin administration on plasma homocysteine in patients affected by type 2 diabetes. To prevent a possible acute (and repeated) hyperhomocysteinemia due to insulin administration in cases of methionine intolerance, it may be useful to assess the presence of methionine intolerance (tHcy after oral methionine loading) and Hcy-related vitamin status in all patients due to be subjected to insulin therapy.