Vitamin B12, Folic Acid, and Bone

Vitamin B12 and folic acid deficiency are associated with a higher serum concentration of homocysteine. A high serum homocysteine is a risk factor for fractures. Both vitamins play a role in the remethylation of homocysteine to methionine. The pathophysiology from a high serum homocysteine to fractures is not completely clear, but might involve bone mineral density, bone turnover, bone blood flow, DNA methylation, and/or physical function and fall risk. Genetic variation, especially polymorphisms of the gene encoding for methylenetetrahydrofolate reductase may play a role in homocysteine metabolism and fracture risk. It is uncertain whether supplementation with vitamin B12 and folate can decrease fracture incidence. One double blind clinical trial in post-stroke patients showed that these B vitamins could decrease hip fracture incidence, but the results of further clinical trials should be awaited before a definite conclusion can be drawn.     

BP,Cardiovascular Disease,and Death in the Folic Acid for Vascular Outcome Reduction in Transplantation Trial

The optimal BP level in kidney transplant recipients remains uncertain. This post hoc analysis of the Folic Acid for Vascular Outcome Reduction in Transplantation (FAVORIT) trial cohort assessed associations of BP with a pooled cardiovascular disease (CVD) outcome and with all-cause mortality. In 3474 prevalent kidney transplant patients, mean age was 52±9 years, 63% were men, 76% were white, 20% had a history of CVD, 40% had a history of diabetes mellitus, and the median time since transplant was 4.1 years (25th to 75th percentiles, 1.7–7.4); mean systolic BP was 136±20 mmHg and mean diastolic BP was 79±12 mmHg. There were 497 CVD events and 406 deaths. After adjustment for demographic and transplant characteristics and CVD risk factors, each 20-mmHg increase in baseline systolic BP associated with a 32% increase in subsequent CVD risk (hazard ratio [HR], 1.32; 95% confidence interval [95% CI], 1.19 to 1.46) and a 13% increase in mortality risk (HR, 1.13; 95% CI, 1.01 to 1.27). Similarly, after adjustment, at diastolic BP levels<70 mmHg, each 10-mmHg decrease in diastolic BP level associated with a 31% increase in CVD risk (HR, 1.31; 95% CI, 1.06 to 1.62) and a 31% increase in mortality risk (HR, 1.31; 95% CI, 1.03 to 1.66). However, at diastolic BP levels>70 mmHg, there was no significant relationship between diastolic BP and outcomes. Higher systolic BP strongly and independently associated with increased risk of CVD and all-cause mortality, without evidence of a J shape, whereas only lower levels of diastolic BP associated with increased risk of CVD and death in this trial.     

Effect of Homocysteine-Lowering Treatment With Folic Acid and B Vitamins on Risk of Type 2 Diabetes in Women: A Randomized, Controlled Trial

OBJECTIVE

Homocysteinemia may play an etiologic role in the pathogenesis of type 2 diabetes by promoting oxidative stress, systemic inflammation, and endothelial dysfunction. We investigated whether homocysteine-lowering treatment by B vitamin supplementation prevents the risk of type 2 diabetes.

RESEARCH DESIGN AND METHODS

The Women''s Antioxidant and Folic Acid Cardiovascular Study (WAFACS), a randomized, double-blind, placebo-controlled trial of 5,442 female health professionals aged ≥40 years with a history of cardiovascular disease (CVD) or three or more CVD risk factors, included 4,252 women free of diabetes at baseline. Participants were randomly assigned to either an active treatment group (daily intake of a combination pill of 2.5 mg folic acid, 50 mg vitamin B6, and 1 mg vitamin B12) or to the placebo group.

RESULTS

During a median follow-up of 7.3 years, 504 women had an incident diagnosis of type 2 diabetes. Overall, there was no significant difference between the active treatment group and the placebo group in diabetes risk (relative risk 0.94 [95% CI 0.79–1.11]; P = 0.46), despite significant lowering of homocysteine levels. Also, there was no evidence for effect modifications by baseline intakes of dietary folate, vitamin B6, and vitamin B12. In a sensitivity analysis, the null result remained for women compliant with their study pills (0.92 [0.76–1.10]; P = 0.36).

CONCLUSIONS

Lowering homocysteine levels by daily supplementation with folic acid and vitamins B6 and B12 did not reduce the risk of developing type 2 diabetes among women at high risk for CVD.Homocysteinemia may promote insulin resistance and β-cell dysfunction through its adverse metabolic effects, ultimately contributing to the pathogenesis of type 2 diabetes and associated complications (1–3). Several lines of evidence from both in vitro and in vivo studies support this hypothesis. First, homocysteinemia directly elicits oxidative stress by increasing reactive oxygen species production and diminishing intracellular antioxidant defense (2). Experimental studies have suggested that oxidative stress interferes with insulin signaling and impairs pancreatic β-cell insulin secretion (4,5), thereby accelerating the progression from insulin resistance to overt type 2 diabetes. Second, elevated levels of homocysteine promote systemic inflammation via the activation of a cascade of inflammatory pathways including interleukin-6, tumor necrosis factor-α, and adhesion molecules (3). Low-grade chronic inflammation, as reflected by elevated circulating levels of inflammatory cytokines, may promote insulin resistance in liver, skeletal muscle, and vascular endothelium (6,7). Last, homocysteine can exert its damaging effects on the endothelium through mechanisms involving impaired nitric oxide (NO)-dependent vasodilation, endothelial toxicity and injury, oxidative stress, and systemic inflammation (2,8). The resultant endothelial dysfunction, especially in the capillary and arteriolar endothelium, can reduce insulin delivery to insulin-sensitive peripheral tissues, which in turn impairs insulin-mediated glucose metabolism (9–11). Collectively, we speculate that elevated homocysteine levels may play an etiologic role in the development of insulin resistance and type 2 diabetes primarily by promoting oxidative stress, systemic inflammation, and endothelial dysfunction.Homocysteinemia has been recognized as a vascular risk factor for diabetic angiopathy (12), whereas few human data are currently available on the relation between homocysteine levels and risk of developing type 2 diabetes. In observational studies, homocysteine levels in nondiabetic individuals have been positively correlated with several biomarkers of insulin resistance and/or glucose intolerance in some (13–15) but not all (16–18) studies. In a 4-year prospective cohort study, elevated levels of homocysteine were independently associated with a 3.6-fold increased risk of type 2 diabetes among 170 women with a history of gestational diabetes mellitus (19). These observations not only provided suggestive evidence linking elevated levels of homocysteine to the development of type 2 diabetes but also led to the suggestion that lowering homocysteine levels may prevent or reduce risk of type 2 diabetes.Dietary folic acid and vitamins B6 and B12 are the most important modifiable determinants of homocysteine levels, and adequate intake of B vitamins may be potentially beneficial for prevention of type 2 diabetes in the general population. However, no previous prospective cohort studies have specifically examined intakes of individual B vitamins and diabetes risk. Some small and short-term randomized trials for secondary prevention of diabetes complications have been conducted but yielded inconsistent results; some reported that folic acid supplementation (5–10 mg/day) reduced oxidative stress and improved endothelial function in diabetic patients during a period of 2–12 weeks (20–23). To the best of our knowledge, there are no previous randomized clinical trials assessing the efficacy of B vitamin supplements for primary prevention of type 2 diabetes. In a large cardiovascular disease (CVD) prevention trial, the Women''s Antioxidant and Folic Acid Cardiovascular Study (WAFACS), we specifically examined the homocysteine-lowering effect by daily supplementation with folic acid, vitamin B6, and vitamin B12 on the risk of type 2 diabetes in women at high risk for CVD.     

Synthetic hydroxyapatite crystals

Apatite crystals were synthesized under approximately physiological conditions and in the presence of magnesium ions. After ageing from 4 to 21 days, the crystals were analyzed and their exchange of incorporated magnesium studied with the use of²⁸Mg.Both the kinetics and the extent of the exchange showed that magnesium ions were strongly rejected by the apatite lattice. In aged crystals, nearly 90% of the magnesium was located in readily exchangeable (surface) positions. These findings support one concept that apatitic magnesium is essentially a surface-limited ion and help to explain the ready availability of skeletal magnesium in animals on magnesium deficient diets.This work was supported in part by the U. S. Public Health Service Training Grant No. 1 T1 DE-175 and in part by the U. S. Atomic Energy Commissio Contract No. AT (30-1)-49 and has been assigned Report No. UR-49-1308.     

Synthetic facial implants

This article presents a range of synthetic implant materials for use in facial plastic surgery. The authors discuss alternatives to autogenous tissue transfer in terms of biocompatibility, technique, complications, controversies, and cautions. The reader is presented information about a range of synthetic implant materials such as silicone, polyester fiber, polyamide mesh, metal, polyethylene, polyacrylamide gel, hydroxyapatite, polylactic acid, collagen, and others.     

Synthetic hydroxyapatite crystals

Synthetic hydroxyapatite crystals were produced under approximately physiological conditions both in the absence and presence of 0.025 M HCO ₃ ^– .X-ray diffraction studies and solubility data established that the crystals formed from the bicarbonate medium were essentially a single phase, carbonate-apatite. These crystals were extremely minute, of composition comparable to bone mineral, and, on aging, showed very little increase in crystallinity in comparison with CO₂-free preparations.Exchange studies with C¹⁴O₂ established that about 60% of the CO₂, presumably as CO ₃ ⁼ , residedwithin the crystal lattice and 40%, presumably as HCO ₃ ^– , resided in the hydration shells of the crystals. Of the latter, approximately 50% was lost on drying.Preliminary experiments with bones of young rats labelled with C¹⁴O₂ in vivo suggested that the model experiments are biologically applicable. Approximately 47% of the C¹⁴O₂ in the bones was lost on drying.

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Zusammenfassung Synthetische Hydroxyapatitkristalle wurden unter annähernd physiologischen Bedingungen mit und ohne Zusatz von 0,025 M HCO ₃ ^– hergestellt.Untersuchungen mit Röntgenstrahlendiffraktion sowie Löslichkeitsbestimmungen ergaben, daß die in der Bicarbonatlösung entstandenen Kristalle vorwiegend aus einer einzigen Phase, nämlich Karbonatapatit, bestanden. Diese Kristalle waren äußerst klein, und ihre Zusammensetzung war derjenigen des Knochenminerals vergleichbar; beim Altern zeigten sie eine sehr kleine Kristallinität zunahme im Vergleich zu CO₂-freien Präparaten.Austauschversuche mit C¹⁴O₂ ergaben, daß sich ungefähr 60% des CO₂, wahrscheinlich als CO ₃ ⁼ ,im Kristallgitter befanden, und 40%, wahrscheinlich als HCO ₃ ^– , in der Hydratationsschicht der Kristalle vorkamen. Von letzteren gingen ungefähr 50% beim Trocknen verloren.Vorversuche an Knochen von jungen Ratten, diein vivo mit C¹⁴O₂ markiert wurden, ließen vermuten, daß diese Modellversuche biologisch anwendbar sind. Ungefähr 47% des C¹⁴O₂ in den Knochen ging beim Trocknen verloren.

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Résumé Des cristaux d'hydroxylapatite synthétique sont préparés dans des conditions presque physiologiques en présence et en l'absence de 0.025 M HCO ₃ ^– .Des études par diffraction aux rayons X et les résultats de solubilité indiquent que les cristaux formés à partir du milieu bicarbonaté constituent essentiellement une phase unique, carbonateapatite. Ces cristaux sont très petits et de composition voisine de celle du minéral osseux. En vieillisant, ils présentent une très faible augmentation de la «cristallinité», si on les compare à des préparations sans CO₂.Des études d'échanges avec C¹⁴O₂ démontrent qu'environ 60% du CO₂ est contenu dans la maille cristalline vraisemblablement sous forme de CO ₃ ⁼ , alors que 40% du CO₂ est réparti dans l'enveloppe d'hydratation des cristaux, vraisemblablement sous forme de HCO ₃ ^– : environ 50% de ce dernier est perdu par dessication.Des recherches préliminaires effectuéesin vivo sur des os de jeunes rats, marqués avec du C¹⁴O₂ indiquent que ces expériences témoins sont biologiquement valables. Environ 47% du C¹⁴O₂ des os est perdu par dessication.

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This work was supported in part by the United States Public Health Service training grant no. 1 T1 DE 175-01, and in part by the United States Atomic Energy Commission, contract no. W-7401-ENG-49.     

4-1BB-mediated Signals Confer Protection Against Folic Acid-induced Nephrotoxicity

Background : The role of co-stimulatory molecules in renal diseases has been previously examined, however, little is known about the role of 4-1BB in the context of renal diseases resulting from nonimmune-mediated tubulointerstitial fibrosis. Folic acid induced Nephrotoxicity (FAN) in mice was used to explore the role of 4-1BB in this setting. Methods : CD1 mice were treated with folic acid and kidneys subsequently examined using histochemistry, in addition to defining T cell profiles and evaluating renal function. Increased CD3+ and CD4+ T lymphocytes present in blood and spleen at day 3 suggested immunopathological reactions during the early stages of FAN and decreased CD3+ and CD4+ T lymphocytes on day 14 were characteristic of an immunocompromised state observed during the late stages of FAN. Results : After 14 days of co-treatment with agonistic anti-4-1BB monoclonal antibodies, renal tubulointerstitial lesions were reduced. Renal function was improved, with Bun scores decreasing (p<0.01) and sCr levels decreasing (p<0.01). CD3+ and CD4+ T lymphocytes levels were increased during the early stages of disease in FA treated mice and reduced to the normal level in the 4-1BB-treated mice. CD3+ and CD4+ T lymphocytes levels were decreased in FA treated mice and returned to baseline in the 4-1BB-treated mice during later stages. Conclusions : Data presented in this report demonstrated that 4-1BB signals had immunoregulatory effects that attenuated early immune-mediated pathology and reversed the immunocompromised state observed during the later stages of disease.     

Folic acid inhibits homocysteine-induced proliferation of human arterial smooth muscle cells

PURPOSE: An elevated plasma homocysteine level has been identified as an independent risk factor for atherosclerosis. Whether this represents a marker for vascular disease or a direct effect on the vasculature remains unclear. Because vascular smooth muscle cells (VSMCs) play an integral role in the atherosclerotic process, we studied the effect of homocysteine on human infragenicular VSMC proliferation and the role of folic acid in reversing the homocysteine effect. METHODS: Human infragenicular VSMCs harvested from amputation specimens were studied. Various cell groups were exposed to physiologic (6.25 micromol/L and 12.5 micromol/L) and pathologic (25 micromol/L to 500 micromol/L) concentrations of homocysteine. Similar groups were simultaneously exposed to 20 nmol/L of folic acid. Cell counts and DNA synthesis, as reflected by [methyl-(3)H]-thymidine incorporation, were performed at 6 days and 24 hours, respectively. Additional groups were exposed to various combinations of folic acid (20 nmol/L), vitamin B(6) (145 nmol/L), and vitamin B(12) (0.45 nmol/L) in the presence of homocysteine (25, 50, and 250 micromol/L). RESULTS: Homocysteine resulted in a dose-dependent increase in DNA synthesis and cell proliferation. Cell counts increased significantly at homocysteine concentrations ranging from 25 micromol/L to 500 micromol/L (P <.05), with a maximal increase of 98% at 500 micromol/L of homocysteine. The addition of 20 nmol/L folic acid resulted in significant inhibition of cell proliferation at all homocysteine concentrations studied (P <.001). Maximal inhibition of 70% occurred in the cells exposed to 50 micromol/L of homocysteine. The increases in [methyl-(3)H]-thymidine incorporation ranged from 36% at 6 micromol/L homocysteine to a maximum of 247% at 500 micromol/L homocysteine. All increases were statistically significant (P <.05). The addition of 20 nmol/L folic acid resulted in significant inhibition of DNA synthesis (P <.002). Vitamins B(6) and B(12) did not demonstrate significant antiproliferative properties. CONCLUSION: A possible role of homocysteine in the formation of atherosclerotic lesions is through a direct proliferative effect on VSMCs in a dose-dependent fashion. Folic acid intake at levels available in dietary supplements may prove protective in hyperhomocysteinemia-induced atherosclerosis. Vitamins B(6) and B(12) alone do not appear to exhibit a substantial inhibitory effect in the setting of elevated homocysteine levels.     

Synthetic biliary bypass.

A method for the bypass of high biliary strictures using a Dacron velour prosthesis is discussed. This has been employed in 24 patients with obstructive jaundice caused by malignant disease which could not be relieved by conventional means.     

Synthetic bone graft substitutes

Replacement of extensive local bone loss is a significant clinical challenge. There are a variety of techniques available to the surgeon to manage this problem, each with their own advantages and disadvantages. It is well known that there is morbidity associated with harvesting of autogenous bone graft and limitations in the quantity of bone available. Alternatively allografts have been reported to have a significant incidence of postoperative infection and fracture as well as the potential risk of disease transmission. During the past 30 years a variety of synthetic bone graft substitutes has been developed with the aim to minimize these complications. The benefits of synthetic grafts include availability, sterility and reduced morbidity. The present article examines the relevance of synthetic bone graft substitutes, their mechanical properties and clinical application.     

Folic acid status of patients with chronic renal failure maintained by dialysis

Twenty-five uremic patients on chronic hemodialysis were followed over a period of 9 months with regard to hemoglobin, mean corpuscular volume and folate concentration in serum and erythrocytes. The daily dietary intake of folic acid was estimated at 80-90 microgram, and no folic acid supplements were given. None of the patients developed macrocytic anemia. At the end of the period all patients had a normal erythrocyte folate content. Serum folate was normal in 17 and below normal in 8 patients. These 8 patients were in a negative folate balance at the time of investigation. In 7 patients dialyzed with a RP VI dialyzer the maximum loss of folic acid was 75 microgram/dialysis, and in 6 patients on chronic intermittent peritoneal dialysis the maximum loss was 13 microgram/dialysis. Thus there is no need for oral folic acid supplementation in uremic patients on chronic dialysis provided that daily dietary intake of folic acid is adequate.     

Synthetic biomaterials for spinal fusion

Calcium hydroxylapatite (HAP), tricalcium phosphate (TCP), and Bioglass (BG) were implanted in the spines of dogs to determine their potential in augmenting and enhancing spinal fusion. HAP and TCP showed continuous bone to biomaterial interfaces of varying degrees. Trabecular bone surrounded and incorporated the particulate hydroxylapatite. Tricalcium phosphate ceramic showed little evidence of resorption. The glass particulate, BG, showed a thin, fibrous encapsulation with some adjacent bony trabeculae. Decortication and autogenous bone enhanced incorporation. This multivariant initial study showed that trends found for the biomaterials implanted independently were similar to those used in combination. No adverse tissue reactions were noted for the combination of materials.     

Synthetic ligaments. Current status

Many techniques for ligamentous reconstruction have been developed in recent years. In the United States, injuries of the knee have been increasingly treated with innovative methods of surgical reconstruction, most of which have used normal structures. There are obvious theoretic advantages in using synthetic materials that might simplify surgery, spare normal tissues, and possibly facilitate stronger repairs. To these ends, several synthetic substances have been used experimentally and clinically. This is a brief summary of eight of the materials that have been or are being investigated in the United States. Some are no longer in use, others are currently being used in clinical trials. As of this writing, only the Gortex ligament has received a general device release from the Food and Drug Administration (FDA).