The effect of folate analogues and vitamin B12 on provision of thymine nucleotides for DNA synthesis in megaloblastic anemia

The role of vitamin B12 in the folate dependent biosynthesis of thymidine nucleotides is controversial. In an attempt to clarify this, three methods have been used to assess the relative efficacy of vitamin B12 (hydroxocobalamin) and various folate analogues in titrated concentrations at correcting 'de novo' thymidylate synthesis by megaloblastic human marrow cells: (1) The deoxyuridine (dU) suppression test which analyses the reduction in (3H)-thymidine labeling of DNA by unlabeled dU. Marrow cells were also labeled with (6-3H)-dU with assessment of (2) its incorporation into DNA and (3) the accumulation of (6-3H)-deoxyuridine monophosphate (3H-dUMP). The three methods gave similar results. In both, N6-formyl tetrahydrofolate (formyl-FH4) was the most effective agent at correcting thymidylate synthesis in megaloblastic anemia due to vitamin B12 or folate deficiency. Vitamin B12 corrected the lesion in vitamin B12 deficiency but not in folate deficiency. Tetrahydrofolate (FH4) and folic acid were effective in deficiency of vitamin B12 or folate, although in both deficiencies they were less effective than formyl-FH4. Methyl-FH4 was effective in folate deficiency but not in vitamin B12 deficiency. These results confirm the failure of methyl-FH4 utilisation in vitamin B12 deficiency. They suggest that if vitamin B12 is needed in the formylation of FH4, this is a minor role in provision of the correct coenzyme for thymidylate synthesis compared with its major role of provision of FH4 from methyl- FH4.     

Role of ADP-ribosyl transferase in differentiation of human granulocyte- macrophage progenitors to the macrophage lineage

Nuclear adenosine diphosphate-ribosyl (ADP-ribosyl) transferase is a chromatin-bound enzyme catalyzing the transfer of ADP-ribose from NAD+ to chromatin proteins. The physiologic function of this covalent modification of chromatin has not been fully established, but roles in both DNA repair and in differentiation have been proposed. We demonstrate that three specific inhibitors of ADP-ribosyl transferase (5-methylnicotinamide, 3-methoxybenzamide, 3-aminobenzamide) inhibit differentiation of human granulocyte-macrophage progenitor cells to the macrophage lineage. Differentiation to the neutrophil-granulocyte lineage is much less affected. The inhibition of macrophage differentiation seems to relate to the ability of these compounds to inhibit ADP-ribosyl transferase. A structural analogue (3- methoxybenzoic acid), which is not inhibitory for the enzyme, did not inhibit macrophage differentiation. Additional evidence for a role of ADP-ribosyl transferase in the differentiation of granulocyte- macrophage progenitors was obtained from experiments in which enzyme activity levels were measured in permeabilized marrow cells. Marrow cell ADP-ribosyl transferase activity increased after 3-hr stimulation by the differentiation/proliferation stimulus--granulocyte-macrophage colony-stimulating activity (GM-CSA). Unstimulated marrow cells showed low or undetectable levels of enzyme activity.     

Estrogen-induced microsatellite DNA alterations are associated with Syrian hamster kidney tumorigenesis

Exposure to estrogens is associated with an increase in cancers, including malignancies of the breast and uterus in humans, and of the kidney in hamsters. DNA damage induced by metabolic activation of estrogen has been postulated to result in gene mutations critical for the development of estrogen-induced kidney tumors in hamsters. As part of our examination of the genetic consequences of estrogen-induced DNA damage, we searched for estrogen-induced alterations in microsatellite DNA, a frequent site of mutation in tumors. Genomic DNA isolated from kidney of hamsters treated with estradiol, from estrogen-induced kidney tumors and from untreated age-matched controls, was examined by Southern blot analysis with three multi-locus oligonucleotide probes: (GACA)4, (CAC)6 and (CAG)6. Alterations in DNA fragments containing GACA and CAC tandem repeats were detected in kidney DNA of hamsters treated with hormone for 3 and 4 months, whereas no such effects were seen in control animals. In estrogen-induced tumors, microsatellite alterations were observed in fragments that contain these same two repeat sequences and also CAG repeat sequences. The induction of microsatellite alterations by estradiol in kidney DNA preceding estrogen-induced renal malignancy may play a role in hormone-induced tumorigenesis.      

Peripheral and central sites of action for the non-selective cannabinoid agonist WIN 55,212-2 in a rat model of post-operative pain

Background and purpose:

Activation of cannabinoid (CB) receptors decreases nociceptive transmission in inflammatory or neuropathic pain states. However, the effects of CB receptor agonists in post-operative pain remain to be investigated. Here, we characterized the anti-allodynic effects of WIN 55,212-2 (WIN) in a rat model of post-operative pain.

Experimental approach:

WIN 55,212-2 was characterized in radioligand binding and in vitro functional assays at rat and human CB₁ and CB₂ receptors. Analgesic activity and site(s) of action of WIN were assessed in the skin incision-induced post-operative pain model in rats; receptor specificity was investigated using selective CB₁ and CB₂ receptor antagonists.

Key results:

WIN 55,212-2 exhibited non-selective affinity and agonist efficacy at human and rat CB₁ versus CB₂ receptors. Systemic administration of WIN decreased injury-induced mechanical allodynia and these effects were reversed by pretreatment with a CB₁ receptor antagonist, but not with a CB₂ receptor antagonist, given by systemic, intrathecal and supraspinal routes. In addition, peripheral administration of both CB₁ and CB₂ antagonists blocked systemic WIN-induced analgesic activity.

Conclusions and implications:

Both CB₁ and CB₂ receptors were involved in the peripheral anti-allodynic effect of systemic WIN in a pre-clinical model of post-operative pain. In contrast, the centrally mediated anti-allodynic activity of systemic WIN is mostly due to the activation of CB₁ but not CB₂ receptors at both the spinal cord and brain levels. However, the increased potency of WIN following i.c.v. administration suggests that its main site of action is at CB₁ receptors in the brain.British Journal of Pharmacology (2009) 157, 645–655; doi:10.1111/j.1476-5381.2009.00184.x; published online 3 April 2009     

Review article: increasing the dose of oral mesalazine therapy for active ulcerative colitis does not improve remission rates

BACKGROUND: Oral mesalazine (mesalamine, 5-aminosalicylic acid) formulations are effective in the treatment of active ulcerative colitis. All formulations contain the same active drug but differ with regard to mechanisms to deliver the drug to the colon. Patients who fail to respond to initial therapy are often administered higher doses of the same formulation. AIM: To review published trials of oral mesalazine formulations in treating active ulcerative colitis and to examine the effect of dose escalation on remission rates. RESULTS: Increasing the doses of oral mesalazine formulations does not result in higher remission rates, although increasing the doses of some formulations has been effective in increasing symptomatic improvement and/or response to treatment. CONCLUSIONS: Because oral mesalazine formulations do not demonstrate a significant dose response with regard to induction of remission of active ulcerative colitis, simple dose escalation may not be the most effective course for patients who fail to respond to initial mesalazine treatment.     

The effect of long term combined yoga practice on the basal metabolic rate of healthy adults

Background  

Different procedures practiced in yoga have stimulatory or inhibitory effects on the basal metabolic rate when studied acutely. In daily life however, these procedures are usually practiced in combination. The purpose of the present study was to investigate the net change in the basal metabolic rate (BMR) of individuals actively engaging in a combination of yoga practices (asana or yogic postures, meditation and pranayama or breathing exercises) for a minimum period of six months, at a residential yoga education and research center at Bangalore.