Increased susceptibility to plasma lipid peroxidation in Alzheimer disease patients

Oxidative stress, linked to Abeta-lipid interactions, plays a pathogenetic role in Alzheimer's disease. We investigated modifications of lipid peroxidation products in plasma of 52 AD patients, 42 healthy controls and 16 patients with amyotrophic lateral sclerosis, a neurodegenerative disease where oxidative stress also plays a pathogenetic role. Final lipid peroxidation products were measured in plasma by thiobarbituric acid reactive substances (TBARS) assay before and after ex vivo oxidative stress catalysed by copper. There were no significant changes at basal conditions, but after copper-induced oxidation TBARS levels were higher in AD patients (19.0 microM +/- 2.2) versus both controls (5.2 microM +/- 0.8, p<0.001) and ALS patients (7.6 microM +/- 2.1, p<0.01). Stimulated TBARS levels were significantly higher in mild and moderate AD (p<0.0001) with respect to controls, but not in severe AD patients, with a significant inverse correlation between disease severity and lipid peroxidation (p<0.005, r2=0.21). Treatment of a subgroup (13) of mild and moderate AD patients with vitamin C and E for three months decreased plasma lipoperoxidation susceptibility by 60%. Thus, oxidative stress, expressed as ex vivo susceptibility to lipid peroxidation, appears to be an early phenomenon, probably related to AD pathogenetic mechanisms.

In vivo imaging of adenosine A2A receptors in rat and primate brain using [11C]SCH442416

PURPOSE

The aim of this study was to evaluate the suitability of [11C]SCH442416 for the in vivo imaging of adenosine A2A receptors.

METHODS

In rats and Macaca nemestrina, we evaluated the time course of the cerebral distribution of [11C]SCH442416. Furthermore, in rats we investigated the rate of metabolic degradation, the inhibitory effects of different drugs acting on adenosine or dopamine receptors and the modification induced by the intrastriatal administration of quinolinic acid (QA).

RESULTS

The rate of metabolic degradation of [11C]SCH442416 in rats was slow; 60 min after tracer injection, more than 40% of total plasma activity was due to unmetabolised [11C]SCH442416. At the time of maximum uptake, radioactive metabolites represented only 6% of total extractable activity in the cerebellum and less than 1% in the striatum. In the striatum, the region with the highest expression of A2A receptors, the in vivo uptake of [11C]SCH442416 was significantly reduced only by drugs acting on A2A receptors or by QA, a neurotoxin that selectively reduces the number of intrastriatal GABAergic neurons. Position emission tomography (PET) studies in monkeys indicated that the tracer rapidly accumulates in brain, reaching maximum uptake between 5 and 10 min. Twenty minutes after the injection, radioactivity concentration in the striatum was two times that in the cerebellum.

CONCLUSION

The specificity of binding, the rank order of regional distribution in the brain of rats and M. nemestrina, the good signal to noise ratios and the low amount of radioactive metabolites in brain and periphery indicate that [11C]SCH442416 is a promising tracer for the in vivo imaging of A2A adenosine receptors using PET.

Insulin resistance and endothelial function are improved after folate and vitamin B12 therapy in patients with metabolic syndrome: relationship between homocysteine levels and hyperinsulinemia

OBJECTIVE

The purpose of this study was (a) to study whether a folate and vitamin B12 treatment, aimed at decreasing homocysteine levels, might ameliorate insulin resistance and endothelial dysfunction in patients with metabolic syndrome according to the National Cholesterol Education Program-Adult Treatment Panel-III criteria and (b) to evaluate whether, under these metabolic conditions, there is a relationship between hyperhomocysteinemia and insulin resistance.

DESIGN AND METHODS

A double-blind, parallel, identical placebo-drug, randomized study was performed for 2 months in 50 patients. Patients were randomly allocated to two groups. In group 1, patients were treated with diet plus placebo for 2 months. In group 2, patients were treated with diet plus placebo for 1 month, followed by diet plus folic acid (5 mg/day) plus vitamin B12 (500 microg/day) for another month.

RESULTS

In group 2, folate treatment significantly decreased homocysteine levels by 27.8% (12.2+/-1.2 vs 8.8+/-0.7 micromol/l; P<0.01). A significant decrement was observed for insulin levels (19.9+/-1.7 vs 14.8+/-1.6 microU/ml; P<0.01) accompanied by a 27% reduction in the homeostasis model assessment levels. A positive relationship was found between the decrement of homocysteine and insulin levels (r=0.60; P<0.002). In parallel, endothelial dysfunction significantly improved in the treated group, since post-ischemic maximal hyperemic vasodilation increased by 29.8% and cGMP by 13.6% while asymmetrical dimethylarginine levels decreased by 21.7%. On the contrary, in group 1 patients, treated with placebo, no changes were shown in any of the variables.

CONCLUSIONS

Folate and vitamin B12 treatment improved insulin resistance and endothelial dysfunction, along with decreasing homocysteine levels, in patients with metabolic syndrome, suggesting that folic acid has several beneficial effects on cardiovascular disease risk factors.

Expression of heat shock protein 27 in human renal cell carcinoma

Heat shock protein 27 (HSP27, Swiss-Prot accession number P04792) is a component of the large and heterogeneous group of chaperone proteins, and its main functions are inhibition of apoptosis and prevention of aggregation of actin intermediate filament. Modified expression of HSP27 has been described in several cancers including testis, breast, and ovaric cancer. In the present work, 18 renal cell carcinoma (RCC) tissues and homologous normal kidney tissues have been investigated for HSP27 expression by combination of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) separation and Western blotting immunodetection. The results showed significant differences either in expression and in HSP27 isoform numbers in RCC compared to normal kidney. The average number of isoforms was 21 in RCC and 15 in normal tissues with 4.5-5.9 pI range and 18-29 kDa M(r) range. The overexpression was also observed by immunohistochemistry on tissue sections. Only two of RCC samples showed less isoforms than homologous normal samples. Two isoforms were not detected using anti-Ser82 phosphorylated HSP27 antibody, neither in normal nor in RCC samples. Five of all the immunodetected isoforms were confirmed by mass spectrometry as HSP27, but no evidence of post-translational modifications was pointed out. The numerous isoforms observed in RCC are not consistent with data reported in the literature so far, and they might be due to different post-translational modifications such as phosphorylation and S-thiolation. Since activation of HSP27 seems to be involved in tumor proliferation and drug resistance, it would be crucial to correlate the severity of disease with the different isoforms from RCC samples to generate diagnostic and prognostic markers.

Evaluation of three quinoline-carboxamide derivatives as potential radioligands for the in vivo pet imaging of neurodegeneration

The peripheral-type benzodiazepine receptors (PBRs) are only minimally expressed in normal brain parenchyma, where they are primarily localized in glial cells. Their basal expression rises in different neurodegenerative disorders, due to the presence of infiltrating inflammatory cells and activated microglia. [11C]PK11195, a selective PBR antagonist, has been used for the in vivo PET monitoring of neurodegeneration in clinical observations. We recently developed and labeled with carbon-11 three new carboxamide derivatives: [11C]VC193M, [11C]VC195 and [11C]VC198M. Aim of this study was to evaluate these ligands for the in vivo measuring of PBRs expression in neurodegenerations and compare their kinetic behavior with that of the reference tracer [11C]PK11195. Radioligands were evaluated in a preclinical model of Huntington's disease consisting in the monolateral striatal injection of quinolinic acid (QA). Activated microglia and astrocytic gliosis was present only within the affected striatum. A concomitant increase in radioactivity accumulation was observed for all the tracers examined (P<0.01). Among the new compounds, [11C]VC195 showed higher levels of lesioned/unlesioned striatum ratios (3.28+/-0.44), in comparison with [11C]VC193M and [11C]VC198M (2.69+/-0.53 and 1.52+/-0.36, respectively), but slightly inferior to that observed for [11C]PK11195 (3.76+/-1.41).In conclusion, the results of the study indicate that [11C]VC195 is a promising candidate for in vivo PET monitoring of neurodegenerative processes but its in vivo behavior overlap that of [11C]PK11195.

Long-term oral L-arginine administration improves peripheral and hepatic insulin sensitivity in type 2 diabetic patients

The aim of this study was to evaluate whether long-term administration of arginine acting through a normalization of NO/cyclic-guanosine-3' 5'-cyclic monophosphate (cGMP) pathway was able to ameliorate peripheral and hepatic insulin sensitivity in 12 lean type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

A double-blind study was performed for 3 months. In the first month, patients were treated with their usual diet. Then they were randomly allocated into to groups. In group 1, patients were treated with diet plus placebo (orally three times per day) for 2 months. In group 2 patients were treated for 1 month with diet plus placebo orally, three times per day) and then for 1 month with diet plus L-arginine (3 g three times per day). At the end of the first and the second month of therapy, patients underwent a euglycemic-hyperinsulinemic clamp combined with [6,6-2H2] glucose infusion. A total of 10 normal subjects underwent the same test as control subjects.

RESULTS

In group 1, no changes in basal cGMP levels, systolic blood pressure, forearm blood flow, glucose disposal, and endogenous glucose production were observed throughout. In group 2, L-arginine normalized basal cGMP levels and significantly increased forearm blood flow by 36% and glucose disposal during the clamp by 34% whereas it decreased systolic blood pressure and endogenous glucose production by 14 and 29%, respectively. However, compared with normal subjects, L-arginine treatment was not able to completely overcome the defect in glucose disposal.

CONCLUSIONS

L-Arginine treatment significantly improves but does not completely normalizc peripheral and hepatic insulin sensitivity in type 2 diabetic patients.

Mediation of the hepatic effects of growth hormone by its lipolytic activity

The aim of the study was to investigate the acute effect of GH per se, independent from its lipolytic activity, on glucose and lipid oxidation and glucose turnover in seven healthy subjects. Five tests lasting 360 min were performed. Each test consisted of a 4-h equilibration period followed by a euglycemic hyperinsulinemic (25 mU/kg x h) clamp lasting 2 h. In test 1 (control experiment) saline was infused, leaving GH and FFA at basal levels. In tests 2, 3, and 4, GH was infused (80 ng/kg x min) to increase GH levels. Whereas in test 2 FFA levels were free to increase due to GH lipolytic activity, in test 3 FFA elevation was prevented by using an antilipolytic compound (Acipimox) that allowed evaluation of the effect of GH at low FFA levels. In test 4 (GH+Acipimox+heparin) GH infusion was associated with the administration of Acipimox and heparin to maintain FFA at the basal level to evaluate the effect of GH per se independent from GH lipolytic activity. In test 5 Acipimox and a variable heparin infusion were given to evaluate possible effects of Acipimox other than the inhibition of lipolysis. During the euglycemic hyperinsulinemic clamp in the presence of high GH and FFA levels (test 2), glucose oxidation was significantly lower and lipid oxidation was significantly higher than in tests 1, 3, 4, and 5. During the same period, hepatic glucose production was completely suppressed in the control study (test 1; 94%) and in test 5 (99.6%), whereas it was significantly less inhibited (65%, 74%, and 73%) when GH was administered in tests 2, 3, and 4. In conclusion, these results suggest that GH directly mediates the reduction of insulin's effect on the liver. In addition, the effect of GH on glucose and lipid oxidation is not direct, but is mediated by its lipolytic activity.

Glucose turnover and insulin clearance after growth hormone treatment in girls with Turner's syndrome

The study was performed to elucidate, by means of a euglycemic-hyperinsulinemic clamp, whether insulin sensitivity, lipid levels, posthepatic insulin delivery, and insulin clearance are impaired in girls with Turner's syndrome in the absence of previous treatment (T0) and after 6 (T6) and 12 (T12) months of growth hormone (GH) therapy (GHT). The study was performed in six girls with Turner's syndrome and eight healthy girls. We found that previously untreated girls with Turner's syndrome had a normal insulin activity on glucose metabolism. GHT progressively and significantly decreased hepatic insulin sensitivity. In fact, residual hepatic glucose release (HGR), which was 19.6 +/- 4.7 mg/m2. min at T0, doubled at T6 (39.3 +/- 5.1 mg/m2.min) and showed a threefold increase at T12 (68.7 +/- 10.8 mg/m2.min, P < .05 v T0). On the contrary, GHT did not show an appreciable influence on peripheral insulin sensitivity. Insulin clearance was higher in girls with Turner's syndrome than in control girls at T0 (30.0 +/- 2.8 v 20.2 +/- 1.1 mL.kg-1.min-1). It decreased to normal values at T6 (18.2 +/- 2.0 mL.kg-1.min-1, P < .05 v T0) and remained at normal levels at T12 (23.8 +/- 2.9 mL.kg-1. min-1). The posthepatic insulin delivery rate significantly increased at T6 and T12, suggesting increased insulin secretion. In conclusion, we found that insulin-stimulated glucose turnover was normal in girls with Turner's syndrome before therapy. One year of GHT was successful in stimulating the growth rate, but significantly decreased the insulin suppressibility on HGR with only slight changes in peripheral insulin sensitivity. In addition, an increase in the insulin posthepatic delivery rate and a normalization of insulin clearance were present, probably to counteract hepatic insulin resistance.

Insulin regulation of glucose turnover and lipid levels in obese children with fasting normoinsulinaemia

To evaluate the early metabolic alterations induced by obesity, we studied glucose turnover and lipid levels in obese children with fasting normoinsulinaemia. Two experimental protocols were carried out. Protocol I consisted of a euglycaemic glucose clamp at two rates of insulin infusion. Protocol II was similar to protocol I except for a variable lipid infusion used to maintain basal non-esterified fatty acid (NEFA) levels. During protocol I, the glucose disappearance rates were lower in obese children, while no differences were found in hepatic glucose release. NEFA response to insulin was not substantially altered in obese children either at low or high insulin infusion. During protocol II, the NEFA clamp induced a 25% reduction in peripheral insulin sensitivity in control children whereas no changes were observed in obese children. Interestingly, lipid infusion in control children was not sufficient to reproduce the same degree of insulin resistance observed in obese children, suggesting that NEFA are only one of the determinants of insulin resistance at this stage of obesity. In conclusion, the present study provides a portrait of glucose metabolism and lipid levels in normoinsulinaemic obese children. Our results document that peripheral insulin resistance is the first alteration at this stage of obesity, whereas an increase in insulin secretion and a defect in the inhibition of hepatic glucose release by insulin may develop at a later stage. In addition, primarily receptor and post-receptor defects and some alterations of NEFA metabolism are likely to coexist in the induction of insulin resistance at this stage of obesity.

The continuous low dose insulin and glucose infusion test: a simplified and accurate method for the evaluation of insulin sensitivity and insulin secretion in population studies

In this study we investigated a simple nonlabor-intensive method to evaluate insulin sensitivity and beta-cell function which is suitable for application in population studies. The method is a refinement of the modified Harano test and consists of a continuous low dose insulin (25 mU/kg.h) and glucose (4 mg/kg.min) infusion test (LDIGIT) lasting 150 min. Insulin sensitivity was evaluated as the MCR of glucose divided by the steady state serum insulin level achieved at the end of the test. Insulin secretion was expressed as the incremental area for C-peptide concentration during the first 15 min of the test. We compared the indices of insulin sensitivity and insulin secretion yielded by LDIGIT with those derived from the euglycemic clamp and the hyperglycemic clamp, respectively. Fifty-four subjects underwent a LDIGIT (33 with normal glucose tolerance and 21 with impaired glucose tolerance); of the 54, 19 were submitted to a euglycemic clamp, 18 to a hyperglycemic clamp, and 10 to a modified Harano test (insulin infusion, 50 mU/kg.h; glucose infusion, 6 mg/kg.min). LDIGIT overcame the drawbacks associated with the modified Harano test because it resulted in more stable final glucose levels and prevented the occurrence of hypoglycemic episodes. No significant differences were found between the insulin sensitivity index (ISI) of the LDIGIT and that of the euglycemic clamp for each group of subjects. Moreover, there was a strong correlation between the ISI determined by LDIGIT and the ISI determined by clamp (r = 0.90; P < 0.0001), and the best regression line was not different from the identity line, suggesting that the two indices are equivalent. The index of insulin secretion provided by LDIGIT correlated well with that of the hyperglycemic clamp (r = 0.82; P < 0.001) and was significantly higher in overweight subjects than in normal weight subjects. In conclusion, LDIGIT is a simple and accurate method to assess insulin sensitivity and secretion. It can be useful in population studies and in situations when more complex techniques are not feasible.

Hypocaloric high-protein diet improves glucose oxidation and spares lean body mass: comparison to hypocaloric high-carbohydrate diet

The aim of the study was to investigate the effects of two hypocaloric (800-kcal) diets on body weight reduction and composition, insulin sensitivity, and proteolysis in 25 normal glucose-tolerant obese women. The two diets had the following composition: 45% protein, 35% carbohydrate (CHO), and 20% fat (HP diet, 10 subjects), and 60% CHO, 20% protein, and 20% fat (HC diet, 15 subjects); both lasted 21 days. A euglycemic hyperinsulinemic (25 mU/kg/h) clamp lasting 150 minutes combined with indirect calorimetry was performed before and after the diet. Both diets induced a similar decrease in body weight and fat mass (FM), whereas fat-free mass (FFM) decreased only after the HC diet. 3-Methylhistidine (3-CH3-HIS) excretion was reduced by 48% after the HP diet and remained unchanged after the HC diet (P < .05). A significant correlation was found between the changes in FFM and in 3-CH3-HIS excretion after the diet (rs = .50, P < .02). Blood glucose remained unchanged, while insulin decreased in both diets. Free fatty acids (FFA) significantly increased only after the HC diet (P < .05). During the clamp period, glucose disposal and glucose oxidation significantly increased after the HP diet and significantly decreased after the HC diet. Opposite results were found when measuring lipid oxidation. In conclusion, our experience suggests that (1) a hypocaloric diet providing a high percentage of natural protein can improve insulin sensitivity; and (2) conversely, a hypocaloric high-polysaccharide-CHO diet decreases insulin sensitivity and is unable to spare muscle tissue.

Insulin sensitivity and lipid levels in obese subjects after slimming diets with different complex and simple carbohydrate content

The ideal hypocaloric diet should reduce body weight, decrease fat more than muscle tissue, and ameliorate insulin sensitivity and lipid levels. The aim of this study was to investigate the effect of three hypocaloric diets with different carbohydrate (CHO) and fat contents on body weight reduction, insulin release and sensitivity, and lipid levels in patients with simple obesity. Twenty-five obese subjects with normal glucose tolerance were randomly allocated to three hypocaloric (800 kcal) diets containing: 60% high complex/high starch and fibre (HC/HSF-CHO) and 20% fat (group 1;11 subjects); 60% high simple/high natural fibre (HS/HNF-CHO) and 20% fat (group 2; 7 subjects); or 20% CHO (L-CHO) and 60% fat (group 3; 7 subjects). The remaining 20% of the diet was protein. In all cases the duration of the diet was 21 days. Before and after the diet, seven subjects from each group underwent a hyperglycemic clamp, and the other four subjects of group 1 underwent a euglycemic-hyperinsulinemic clamp, combined with a glucose turnover study. A similar decrease in body weight, fat-free mass, fat mass, total cholesterol, LDL cholesterol and apo B levels was observed in the three groups. The M/I ratio during hyperglycemic and euglycemic-hyperinsulinemic clamp and the glucose turnover rate during euglycemic-hyperinsulinemic clamp significantly decreased, and FFA levels significantly increased only after the HC/HSF-CHO diet. HDL cholesterol and apo A1 significantly increased only during the HS/HNF-CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Single dose pharmacokinetics of aminoglutethimide by a rapid SIM methodology

The kinetics of unchanged aminoglutethimide and of its major metabolite N-acetylaminoglutethimide were investigated in healthy volunteers with a new multiple selected ion monitoring (SIM) technique. This method allows a rapid detection of both the unchanged drug and of its metabolite with a single injection and after minimal handling of the samples. This rapid method provided similar kinetic findings, compared to those described with the more time consuming high pressure liquid chromatographic (HPLC) procedure. Moreover, the SIM method allowed the detection of the N-acetylamino metabolite in plasma at longer time intervals vs. the HPLC method. Some typical features of the kinetic behavior (e.g., a discontinuity in the plasma die-away curve for both unchanged drug and metabolite), attributable to partial liver extraction, could also be more clearly observed with the new procedure. This new, rapid technique confirms that aminoglutethimide and N-acetylaminoglutethimide have very similar plasma die-away curves in subjects with a normal conjugating capacity, and that kinetic patterns or individual blood levels can be readily obtained by SIM with minimal acquisition of supplementary equipment.

Lack of mutagenic activity of ademetionine in vitro and in vivo

Studies on the mutagenic activity of ademetionine (S-adenosylmethionine) tested in vitro at concentrations of 2 mg/sample and in vivo at doses up to 1500 mg/kg always gave negative responses. Moreover, a patent lack of abnormal methylated bases in the liver DNA of ademetionine-treated rats suggests that, if abnormal methylation occurs by exogenously administered ademetionine, the amount of formed methylated residues must be quite lower than that removable by the transmethylase enzymes responsible for the in vivo repair.

Transmethylation, transsulfuration, and aminopropylation reactions of S-adenosyl-L-methionine in vivo

S-Adenosylmethionine (AdoMet) is metabolized through three main pathways, i.e. (a) transfer of its methyl group to a variety of methyl acceptors, (b) decarboxylation followed by aminopropylation leading to polyamine synthesis, and (c) cleavage of the bond between the sulfur atom and carbon 4 of the amino acid chain, resulting in formation of methylthioadenosine and homoserine thiolactone. In this study the metabolism of AdoMet through these pathways was studied after intravenous administration to rats of [1-14C]-, [3,4-14C]-, [methyl-14C]-, and [35S]AdoMet at various doses. The relative utilization of AdoMet and methionine was also investigated. The results show that intravenously administered AdoMet is efficiently metabolized in vivo up to the highest tested dose (250 mumol X kg-1 body weight), about two-thirds of the metabolized compound being utilized via transmethylation and cleavage to methylthioadenosine and one-third via decarboxylation. The efficient incorporation of the methyl group of AdoMet into muscle creatine indicates unambiguously that the compound is taken up and metabolized by the liver. Moreover, intravenously administered AdoMet is shown to be a better precursor than methionine both in creatine formation and in the utilization of the sulfur atom in transsulfuration reactions.

Liquid-chromatographic monitoring of 5-methyltetrahydrofolate in plasma

The liquid-chromatographic measurement of 5-methyltetrahydrofolate in biological fluids is described. The sensitivity of the spectrophotofluorometric detector used allows direct evaluation of basal concentrations of the compound in plasma. Because it is resolved from the other common folates and from methotrexate, the procedure is suitable for monitoring it in plasma of patients receiving high-dose therapy with methotrexate.

Liquid-chromatographic monitoring of 5-methyltetrahydrofolate in plasma

The liquid-chromatographic measurement of 5-methyltetrahydrofolate in biological fluids is described. The sensitivity of the spectrophotofluorometric detector used allows direct evaluation of basal concentrations of the compound in plasma. Because it is resolved from the other common folates and from methotrexate, the procedure is suitable for monitoring it in plasma of patients receiving high-dose therapy with methotrexate.

Ethynylestradiol-induced impairment of bile secretion in the rat: protective effects of S-adenosyl-L-methionine and its implication in estrogen metabolism

Previous investigations demonstrated that S-adenosyl-L-methionine suppresses the cholestatic effect of ethynylestradiol and reduces the irreversible binding of the estrogen to rat liver microsomes, probably favoring ethynylestradiol transformation into its methyl-derivatives. Since it is not known whether SAMe also prevents the changes of bile lipid composition induced by EE and how methylation interferes with estrogen metabolism and biliary excretion, female rats have been treated with ethynylestradiol (5 mg/kg body wt, orally for 3 days) or with ethynylestradiol plus S-adenosyl-L-methionine (25 mg/kg body wt, i.m., t.i.d.). After bile duct cannulation, 5 muCi of [6,7-3H]ethynylestradiol were injected i.v. and an 8-h bile collection was started. Bile flow in ethynylestradiol + S-adenosyl-L-methionine treated rats was similar to controls, but significantly higher than in ethynylestradiol-treated animals (1.44 +/- 0.11; 1.66 +/- 0.30; 0.97 +/- 0.17 microliter/min/g liver, respectively as mean +/- SE). Cholesterol molar percentage was significnatly higher in ethynylestradiol (3.46 +/- 0.25) than in ethynylestradiol + S-adenosyl-L-methionine treated (2.16 +/- 0.41) or control rats (1.90 +/- 0.30). Total radioactivity excretion was similar in all groups, ranging from 74% to 76% of the administered dose, but radiogaschromatography showed a significant increase of methylated ethynylestradiol metabolites in S-adenosyl-L-methionine treated rats. These data indicate that in ethynylestradiol treated rats S-adenosyl-L-methionine can: (a) reverse both cholestasis and related abnormalities of biliary lipids; (b) modify the pattern but not the total amount of biliary ethynylestradiol excretion.

Studies on the 14 alpha-demethylation mechanism in cholesterol biosynthesis

Identification of radioactive 5 alpha-cholest-8(14)-ene-3 beta,7 alpha-diol in extracts obtained from incubations of 3 beta-hydroxy-5 alpha-[7-3H]cholest-7-ene-14 alpha-carbaldehyde with rat liver microsomes is reported. Levels of this diol in incubations of the 14 alpha-[32-3H]carbaldehyde were measured by multiple selected ion monitoring and were found to be of the same order of those of [3H]formate released from the substrate during the removal of the C-32 atom. The results demonstrate that the diol does not originate from known intermediates of cholesterol biosynthesis, i.e. 5 alpha-cholesta-7,14-dien-3 beta-ol, 5 alpha-cholest-7-en-3 beta-ol and from 5 alpha-cholest-8(14)-en-3 beta-ol. Functionalization at position 7 in the metabolism of 3 beta-hydroxy-5 alpha-cholest-7-ene-14 alpha-carbaldehyde suggests the direct involvement of the double bond in the elimination of the 14 alpha-formyl group in the biosynthetic pathway from lanosterol to cholesterol. 5 alpha-Cholest-8(14)-en-3 beta-ol appears not to be involved in the metabolism of the 14 alpha-carbaldehyde.

Intestinal absorption of S-adenosyl-L-methionine

The gastrointestinal absorption of S-adenosyl-L-methionine (SAMe) is demonstrated by evaluating plasma levels and gastrointestinal content of the unmodified molecule after oral administration. When [methyl-14C]SAMe is given orally, the radioactivity found in the liver is associated both with SAMe and phosphatidylcholine, a compound known to be derived from the methylation of phosphatidylethanolamine with SAMe as a methyl donor. These results and low plasma levels after the oral administration may be suggestive of a first-pass effect of SAMe characterized by an extensive uptake of the drug by the liver where it is rapidly metabolized.

Disposition of metformin (N,N-dimethylbiguanide) in man

Kinetic parameters of metformin (N,N-dimethylbiguanide), an anti-diabetic reported to be associated with a lower number of episodes of lactic acidosis than phenformin, were determined in volunteers with normal renal function and in patients with different degrees of renal impairment. Drug in body fluids was measured by a highly specific and sensitive mass fragmentographic method, after the formation of a triazine derivative, obtained with heptafluorobutyric anhydride. The half-life (t 1/2) for the elimination of drug from plasma after intravenous injection in 5 normal subjects (1.52 +/- 0.3 hr) (mean +/- SD) was shorter than that reported for phenformin by a similar assay method (7 to 15 hr). The mean t 1/2 in 5 renal patients was 4.94 +/- 1.11 hr, and a correlation was observed between t 1/2 of drug from plasma and creatinine clearance. After oral administration of metformin tablets, drug recovery in urines was only 37.6%, possibly not as a consequence of low bioavailability (a similar low recovery was found after oral administration of the metformin solution used for the intravenous studies), but of binding to the intestinal wall, as shown in animal and clinical studies with metformin and other biguanides. Metformin is rapidly eliminated through active secretion by the kidney (mean renal clearance, 440.8 ml/min)--it is neither metabolized nor protein bound in plasma. The very brief plasma t 1/2 makes significant cumulation, with a standard tid regimen, unlikely. These findings may help explain the lower incidence of toxic effects, particularly lactic acidosis, than after phenformin.