The role of homocysteine in multisystem age-related problems: a systematic review

The relation of plasma homocysteine to radiographic knee osteoarthritis

OBJECTIVE

Homocysteine has been implicated in multiple diseases that involve changes in structural tissue. In vitro studies have found that it alters the structure of collagen cross-linking thus affecting stability and mineralization such as that occurring in bone tissue. In the present study we considered the possible relationship between plasma homocysteine levels and the development and progression of knee osteoarthritis (OA).

METHODS

The study question was posed in 691 men and 966 women from the original and offspring cohorts of the Framingham Osteoarthritis Study. We divided individuals into three groups according to plasma homocysteine levels and compared their risk for the development of new and progression of existing OA. We adjusted for potential confounders including age, body mass index, weight change, and physical activity.

RESULTS

In the crude analysis, men in the middle homocysteine tertile were found to be at a greater risk than men in the lowest tertile for incident OA [odds ratios of 1.9 (1.1-3.5)]. This result persisted after adjusting for covariates [odds: 2.0, (1.1-3.8)]. No significant correlation was seen in women for the development of OA. In the evaluation of progression no significant trends were seen for both men and women.

CONCLUSIONS

Although cellular and molecular studies of homocysteine-related pathophysiology suggest a possible correlation between plasma homocysteine levels and OA, the present clinical study did not conclusively demonstrate such an association. However, further research is needed to explore the role of homocysteine in specific aspects of OA etiopathogenesis.

Chronic glucocorticoid hypersecretion in Cushing's syndrome exacerbates cognitive aging

Cumulative exposure to glucocorticoid hormones (GC) over the lifespan has been associated with cognitive impairment and may contribute to physical and cognitive degeneration in aging. The objective of the present study was to examine whether the pattern of cognitive deficits in patients with Cushing's syndrome (CS), a disorder characterized by chronic exposure to elevated levels of glucocorticoids (GC), is similar to that observed in older individuals. Ten subjects with CS were compared to sex-, age-, and education-matched healthy controls and older subjects (age of CS subjects+15 yr). All participants were administered tests to assess attention, visuospatial processing, learning and memory, reasoning, concept formation and verbal fluency. MANCOVAs with depression scores as covariate and polynomial contrasts revealed that the age-matched control group performed better than the CS and older subject groups in visual target detection, trail making test, stroop task, digit symbol substitution, block design, object assembly, visual reproduction, spatial memory and similarities. The CS and older subjects performed similarly on these tasks. Further, a principal component analysis revealed two significant factors, representing general cognitive function and verbal memory explaining 39.9% and 10.0% of the variance, respectively. Additional MANCOVAs with depression as a covariate revealed that CS and older control subjects showed impaired performance on general cognitive function compared to age-matched controls. These results suggest that hypersecretion of GCs has "aging-like" effects on cognitive performance in individuals with CS.

Clinical utility of genotyping the 677C>T variant of methylenetetrahydrofolate reductase in humans is decreased in the post-folic acid fortification era

Moderate hyperhomocysteinemia is associated with many diseases. Major factors affecting plasma total homocysteine (tHcy) concentrations include folate concentrations and polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene. Because U.S.-mandated fortification of grain products with folic acid has improved folate and tHcy status in Americans, we investigated the effect of the MTHFR 677C>T variant before and after fortification. We determined tHcy and folate concentrations in sera from 844 Caucasian and 587 African American participants in the Coronary Artery Risk Development in Young Adults study before and after fortification and we genotyped the MTHFR 677C>T variant. MTHFR 677TT homozygotes had higher (P < 0.01) tHcy concentrations both before and after fortification compared with MTHFR 677CC homozygotes. However, the difference between these 2 genotypes decreased from 2.5 micromol/L before fortification to <0.7 micromol/L postfortification (P < 0.01). In addition, the prevalence of moderate hyperhomocysteinemia (tHcy > 13 micromol/L) in 677TT homozygotes decreased from 33% before fortification to 12% postfortification (P < 0.01). Using a cutoff value of 13 micromol/L to define moderate hyperhomocysteinemia, the sensitivity of the MTHFR 677TT genotype to predict elevations in homocysteine was low (approximately 30%) both before and after folic acid fortification. Increasing the cutoff from 13 to 19 micromol/L increased the sensitivity of the assay before fortification to 62% but decreased the sensitivity to 17% postfortification. We conclude that after folic acid fortification in the US, measurement of tHcy rather than genotyping of MTHFR 677TT should be used as the primary assay for the diagnosis and monitoring of moderate hyperhomocysteinemia.

Ageing of the conduit arteries

Conduit arteries become stiffer with age due to alterations in their morphology and the composition of the their major structural proteins, elastin and collagen. The elastic lamellae undergo fragmentation and thinning, leading to ectasia and a gradual transfer of mechanical load to collagen, which is 100-1000 times stiffer than elastin. Possible causes of this fragmentation are mechanical (fatigue failure) or enzymatic (driven by matrix metallo proteinases (MMP) activity), both of which may have genetic or environmental origins (fetal programming). Furthermore, the remaining elastin itself becomes stiffer, owing to calcification and the formation of cross-links due to advanced glycation end-products (AGEs), a process that affects collagen even more strongly. These changes are accelerated in the presence of disease such as hypertension, diabetes and uraemia and may be exacerbated locally by atherosclerosis. Raised MMP activity, calcification and impaired endothelial function are also associated with a high level of plasma homocysteine, which itself increases with age. Impaired endothelial function leads to increased resting vascular smooth muscle tone and further increases in vascular stiffness and mean and/or pulse pressure. The effect of increased stiffness, whatever its underlying causes, is to reduce the reservoir/buffering function of the conduit arteries near the heart and to increase pulse wave velocity, both of which increase systolic and pulse pressure. These determine the peak load on the heart and the vascular system as a whole, the breakdown of which, like that of any machine, depends more on the maximum loads they must bear than on their average. Reversing or stabilising the increased arterial stiffness associated with age and disease by targeting any or all of its causes provides a number of promising new approaches to the treatment of systolic hypertension and its sequelae, the main causes of mortality and morbidity in the developed world.

Relationship of homocysteine levels to quadriceps strength, gait speed, and late-life disability in older adults

BACKGROUND

Elevated homocysteine, causing tissue injury by such mechanisms as oxidative stress, endothelial damage, and protein homocysteinylation, is associated with multiple age-related problems including cardiovascular diseases, dementia, and osteoporotic fracture. Disability is one of the most common features in older adults. However, little is known about the role of homocysteine in physical disability among older adults.

METHODS

Participants (>60 years, N = 1677) were from the National Health and Nutrition Examination Survey (NHANES) 1999-2002. Nineteen questionnaires in five major domains were administered to assess the level of difficulty in performing various tasks: activities of daily living (ADL), instrumental ADL (IADL), leisure and social activities (LSA), lower extremity mobility (LEM), and general physical activities (GPA). Peak quadriceps strength was obtained by using an isokinetic dynamometer. Habitual gait speed was obtained from a 20-foot timed walk. Homocysteine levels were measured by the Abbott homocysteine assay, an automated fluorescence polarization immunoassay (FPIA).

RESULTS

Elevated homocysteine was associated with disability in ADL, IADL, LSA, and GPA after multivariate adjustment. The odds ratios (ORs) for disability in these domains comparing participants in the highest quartile of homocysteine to those in the lowest were 2.18 (95% confidence interval [CI], 1.32-3.59) for ADL; 1.62 (95% CI, 1.02-2.57) for IADL; 2.00 (95% CI, 1.14-3.51) for LSA; and 1.52 (95% CI, 1.05-2.21) for GPA. The strength of associations weakened somewhat after additional adjustment of quadriceps strength and/or gait speed, suggesting a mediating role of quadriceps strength and gait speed in the association between homocysteine and disability. Homocysteine had an inverse relationship to quadriceps strength and gait speed. Likewise, quadriceps strength seemed to mediate the inverse association between homocysteine and gait speed.

CONCLUSIONS

Elevated homocysteine is associated with multiple domains of disability mediated in part by muscle strength and gait speed. The results suggest that homocysteine levels may be important indicators of performance status in older adults.

Oxidative stress: A bridge between Down's syndrome and Alzheimer's disease

Besides the genetic, biochemical and neuropathological analogies between Down's syndrome (DS) and Alzheimer's disease (AD), there is ample evidence of the involvement of oxidative stress (OS) in the pathogenesis of both disorders. The present paper reviews the publications on DS and AD in the past 10 years in light of the "gene dosage" and "two-hit" hypotheses, with regard to the alterations caused by OS in both the central nervous system and the periphery, and the main pipeline of antioxidant therapeutic strategies. OS occurs decades prior to the signature pathology and manifests as lipid, protein and DNA oxidation, and mitochondrial abnormalities. In clinical settings, the assessment of OS has traditionally been hampered by the use of assays that suffer from inherent problems related to specificity and/or sensitivity, which explains some of the conflicting results presented in this work. For DS, no scientifically proven diet or drug is yet available, and AD trials have not provided a satisfactory approach for the prevention of and therapy against OS, although most of them still need evidence-based confirmation. In the future, a balanced up-regulation of endogenous antioxidants, together with multiple exogenous antioxidant supplementation, may be expected to be one of the most promising treatment methods.

Diabetes mellitus in older men

Most persons with diabetes mellitus are over the age of 60 years. Males develop diabetes more commonly than females. Older diabetics tend to have both impaired insulin release as well as insulin resistance. In older persons diabetes mellitus is associated with decreased functional status and cognitive dysfunction. In general, older persons with diabetes are inclined to be underdiagnosed and undertreated. Managing diabetes in older persons requires special considerations because of their differences in pathophysiology of diabetes and strong association with functional, cognitive impairments and comorbidities. The use of strict therapeutic diets is not recommended in older persons. Treatment of hypertension and hyperglycemia can improve outcomes in older persons. The interdisciplinary team approach is important for care of older diabetic persons.

The Hordaland Homocysteine Study: a community-based study of homocysteine, its determinants, and associations with disease

The Hordaland Homocysteine Study (HHS) is a population-based study of more than 18,000 men and women in the county of Hordaland in Western Norway. The first investigation (HHS-I) took place in 1992-93, when the subjects were aged 40-67 y. In 1997-99, a follow-up study (HHS-II) of 7,053 subjects was carried out. In this large population, plasma levels of total homocysteine (tHcy) are associated with several physiologic and lifestyle factors and common diseases. Increasing age, male sex, smoking, coffee consumption, high blood pressure, unfavorable lipid profile, high creatinine, and the MTHFR 677C > T polymorphism are among the factors associated with increased tHcy levels; physical activity, moderate alcohol consumption, and a good folate or vitamin B-12 status are associated with lower tHcy levels. Subjects with raised tHcy levels have increased risk of cardiovascular morbidity, cardiovascular and noncardiovascular mortality, and are more likely to suffer from depression and from cognitive deficit (elderly). Among women, raised tHcy levels are associated with decreased bone mineral density and increased risk of osteoporosis. Women with raised tHcy levels also have an increased risk of having suffered from pregnancy complications and an adverse pregnancy outcome. Significant associations between tHcy and clinical outcomes are usually observed for tHcy levels > 15 micromol/L, but for most conditions, there is a continuous concentration-response relation with no apparent threshold concentration. Overall, the findings from HHS indicate that a raised tHcy level is associated with multiple clinical conditions, whereas a low tHcy level is associated with better physical and mental health.