Blood S-adenosylmethionine concentrations and lymphocyte methylenetetrahydrofolate reductase activity in diabetes mellitus and diabetic nephropathy.

The erythrocyte concentrations of the body's chief physiologic methyl donor S-adenosylmethionine (SAM) and of its metabolite and inhibitor S-adenosylhomocysteine (SAH), the plasma concentrations of total homocysteine (tHcy), and the activity of N(5,10) methylenetetrahydrofolate reductase (MTHFR) in lymphocytes were determined in healthy subjects and patients with diabetes mellitus without complications and at various stages of diabetic nephropathy, categorized according to the degree of progression of the disease. These groups were as follows: 1, control; 2, diabetics with no complications; 3, patients with albuminuria; 4, patients with an elevated plasma creatinine; and 5, patients on dialysis. No parameter studied exhibited significant differences between the type 1 and the type 2 diabetics. In control subjects, the blood concentrations of SAM were proportional to the activity of MTHFR; in diabetics, it was not. Consistent with previous observations, progression of nephropathy was accompanied by increased concentrations of tHcy. Increased erythrocyte concentrations of SAH, decreased erythrocyte concentrations of SAM, SAM/SAH ratios, and lymphocyte MTHFR activity also accompanied disease progression. The blood concentrations of SAH paralleled those of tHcy, while the concentrations of SAM showed a bimodal relationship with those of tHcy. These results provide further evidence that alterations in the blood concentrations of SAM and related compounds are abnormal in patients with diabetes, particularly in those with nephropathy. The deficiency of SAM may lead to methyl deficiencies, which may contribute to the high morbidity and mortality in patients with diabetic nephropathy. We have also demonstrated a decrease in lymphocyte MTHFR activity in patients with advanced nephropathy, suggesting that hyperhomocysteinemia in these patients may be due to a generalized metabolic abnormality. Further studies are needed to determine the pathogenesis of these abnormalities and whether they are present in renal failure due to causes other than diabetes or whether they are specific to diabetic nephropathy.

Blood determinations of S-adenosylmethionine, S-adenosylhomocysteine, and homocysteine: correlations with diet.

An increasing number of both clinical and experimental studies have shown an association between deficiencies of the dietary sources of physiological methyl groups and cancer formation. The critical metabolic intermediate in a determination of methylation status is S-adenosylmethionine (SAM), the body's chief physiological methyl donor. The present study examined the erythrocyte levels of SAM and of its demethylated metabolite S-adenosylhomocysteine (SAH) in 66 normal subjects (33 men and 33 women), whose blood had been drawn at days 0, 7 and 14 of an experimental period during which they were fed a fixed diet. The plasma levels of homocysteine (HCys) were also determined in the same individuals at the same time points. In addition, the subjects had completed a food frequency questionnaire (FFQ) describing their usual dietary habits before being placed on the dietary regimen. The blood levels of SAM, SAH, and HCys were compared with the dietary intakes of folate, vitamin B(6), fats, and calories, both prior to using the FFQ and during the experimental period. The results indicated that the intraindividual differences were very low, but the interindividual differences were large for the values of SAM, SAH, SAM:SAH ratios, and HCys. Interestingly, the blood levels of SAM and HCys were higher in men than in women and generally showed the expected correlations with folate intake i.e., positive for SAM and negative for HCys. The intakes of folate (276 microg/days) and B(6) (1.87 mg/days) during the 2-week experimental period were relatively low compared with the usual intakes of these vitamins (375 and 2.06 mg/day for folate and B(6), respectively) but correlated well with each other during both periods of the study. Surprisingly, both men and women showed a significant rise in erythrocyte SAM:SAH ratios as a function of age. In addition, the combined results from men and women, even adjusted for gender, showed significant correlations between HCys and both weight and body mass index. On the other hand, during the experimental period of the study, blood SAM levels were inversely correlated with the intakes of both fat and calories when the data for both men and women were combined and adjusted for gender. The blood determinations of SAM and related compounds showed a high degree of reproducibility over time and thus appear to provide a practical marker of methylation status for the assessment of cancer risk from dietary, environmental, and genetic factors.

Butylated hydroxytoluene modulates DNA methylation in rats.

The major observation of this investigation is that a single intraperitoneal injection of butylated hydroxytoluene (BHT, 60 mg/kg body mass) results within a few hours in a strong increase in nuclear DNA(cytosine-5)-methyl transferase (methyl transferase) activity in the liver, kidneys, heart, spleen, brain and lungs of male rats. In most organs, the rise in methyl transferase activity is observed as early as 4 h after BHT injection, it reaches a maximum at 8 h and then, except for lungs and brain, gradually decreases to its initial level at 16 h. At the maximum induction times, the methyl transferase activity in liver, kidney and spleen increases by about 16-, 3- and 5-fold, respectively. A second BHT injection at 96 h results in a secondary rise in hepatic methyl transferase activity. Isoelectric focusing electrophoresis of control rat liver nuclear extracts showed methyl transferase activity in the pI 4.7 and 7.4 protein fractions. Both fractions methylate calf thymus DNA better than they do Drosophila melanogaster DNA. In similar extracts from BHT-treated rats, the methyl transferase activity is found in three protein fractions with pI values equal to 4.0, 6.2 and 9.5, respectively. Most of the methyl transferase fractions from the livers of BHT-treated rats methylate the completely unmethylated D. melanogaster DNA better than they do calf thymus DNA. Thus, BHT induces methyl transferase activity that preferably provides de novo DNA methylation. BHT injection had no significant effect on the hepatic contents of S-adenosylmethionine (AdoMet), S-adenosylhomocysteine (AdoHcy) and AdoMet/AdoHcy ratios. While BHT injection did not alter the 5-methyldeoxycytidine content in liver DNA, it did appear to alter such content in other organs. BHT appears to cause the reversible changes in the methylation status of an internal cytosine residue in some CCGG sites of the rat liver cytosine DNA-methyl transferase gene. BHT induces also hypomethylation of the renal methyl transferase gene and the hepatic c-Ha-ras gene. While BHT also increases the hepatic mRNA transcripts for the S-adenosylmethionine synthetase and the p53 genes, it had no detectable effects on the corresponding mRNA transcripts for methyl transferase homologous to murine methyl transferase. Thus, BHT induces tissue-specific reversible changes in methyl transferase activity and methylation of total DNA and various genes in rats. A strong increase in methyl transferase activity in rat liver is accompanied with BHT-induced change in the methyl transferase set observed in this organ.

Methamphetamine treatment affects blood and liver S-adenosylmethionine (SAM) in mice. Correlation with dopamine depletion in the striatum.

Methamphetamine (METH) is a major drug of abuse which causes neurotoxicity by depleting dopamine, its metabolites, high-affinity dopamine uptake sites and tyrosine hydroxylase activity in the striatum. Dopamine depletion and reduced dopamine transit are associated with depression. S-Adenosylmethionine (SAM) is the chief methyl donor used in dopamine and other neurotransmitter metabolism in mammals. Low SAM is associated with depression and other psychological and neurological disorders in humans. SAM is used to treat depression and some other neurological and psychiatric disorders. The present study was designed to determine if single or multiple doses of METH induce alterations in blood or liver SAM in mice and if these correlate with dopamine levels in the striatum. Adult male C57 mice were injected intraperitoneally with either single (1 x 40 mg/kg) or multiple (4 x 10 mg/kg) doses of METH. Animals were sacrificed at various intervals. A single injection of METH resulted in slightly higher blood SAM levels at 4 hr. Multiple doses of METH resulted in decreased hepatic and blood SAM levels at 72 hr. Blood SAM returned to control levels by 1 wk. Published work shows that dopamine levels increase hours after a single injection of METH, whereas dopamine decreases days after multiple injections of METH. These present data clearly demonstrate that METH dosing leads to significant alterations in liver and blood SAM and that these changes in SAM levels correlate with changes in striatal dopamine levels.

Measuring S-adenosylmethionine in whole blood, red blood cells and cultured cells using a fast preparation method and high-performance liquid chromatography.

The physiological methyl donor S-adenosylmethionine (SAM) plays a key role in the maintenance of human health and in the prevention of disease. A convenient clinical test for blood SAM does not exist, even though blood SAM is increasingly seen as an important indicator of health. We have developed a simple procedure to extract SAM from small amounts of blood or cells. The extracted SAM is then measured by high-performance liquid chromatography (HPLC). This measurement is sensitive, precise and uses as little as 200 microliters of blood or 0.5-10(6) cultured cells per determination. SAM, as tested with this method, under acidic conditions, is stable for hours and can be frozen for later analysis. The method has been used to show that blood SAM varies with species, sex and treatment. We have also measured the SAM levels in cultured cells, and have been able to detect wide variations depending upon treatments administered during the growth of those cells. In conclusion, this is a very rapid and easy method to measure SAM in biological fluids and cell culture and which could be adapted to the clinical setting.

DNA adduct levels in congenic rapid and slow acetylator mouse strains following chronic administration of 4-aminobiphenyl.

4-Aminobiphenyl (4-ABP) is a human and mouse bladder carcinogen. Epidemiological studies have shown that individuals with a slow acetylator phenotype, especially those exposed to high levels of carcinogenic aromatic amines, show an increased susceptibility to bladder cancer. In order to determine if a slow acetylator phenotype results in increased DNA damage, congenic mouse strains C57BL/6J and B6.A-Nat(s), which differ genetically at the acetyltransferase (EC 2.3.1.5) locus as homozygous rapid (Natr/Natr) and homozygous slow (Nat(s)/Nat(s)) acetylators respectively, were continuously administered 4-ABP.HCl (55-300 p.p.m.) in their drinking water for 28 days. The levels of covalently bound N-(deoxyguanosin-8-yl)-4-ABP-DNA adducts, which are believed to be critical for the initiation of tumors, were quantitated in the liver and bladder by 32P-postlabeling analysis. The levels of the hepatic DNA adduct increased with dose in both sexes, but were independent of the mouse acetylator genotype. At comparable doses, however, the levels of DNA adducts were 2-fold higher in the liver of the female as compared to the male animals. The DNA adducts also increased with dose in bladder of the male mice, but in contrast to the liver, the adduct levels were approximately 2-fold lower in the bladder DNA of the female mice. Also in contrast to the liver, the levels of bladder DNA adducts were significantly higher (P < or = 0.03) in the phenotypic rapid acetylator females compared to the slow acetylators at both 75 and 150 p.p.m. doses; the median levels of adducts were 10-20% higher in the phenotypic slow acetylator male bladders compared to their rapid acetylator counterparts. The results of these studies are consistent with the increased carcinogenicity of 4-ABP to the liver of female mice and the bladder of male mice. They further suggest that factors other than acetylator phenotype limit the extent of DNA adduct formation from 4-ABP in these mice.