The cardiac effects of prolonged vitamin B12 and folate deficiency in rats.

In the recent past, hyperhomocysteinemia (HHCY) has been linked to chronic heart failure. Folate and vitamin B12 deficiencies are the common causes of HHCY. The impact of these vitamins on cardiac function and morphology has scarcely been investigated. The aim of this study was to conduct an analysis of the cardiac effect of folate and vitamin B12 deficiency in vivo. Two groups of rats, a control (Co, n = 10) and a vitamin-deficient group (VitDef, n = 10), were fed for 12 weeks with a folate and vitamin B12-free diet or an equicaloric control diet. Plasma and tissue concentrations of HCY, S-adenosyl-homocysteine (SAH), S-adenosyl-methionine (SAM), and brain natriuretic peptide (BNP) were measured. Moreover, echocardiographic and histomorphometric analyses were performed. VitDef animals developed a significant HHCY (Co vs VitDef: 6.8 +/- 2.7 vs 61.1 +/- 12.8 micromol/l, P < 0.001). Fractional shortening, left ventricular dimension at end-diastole and end-systole, posterior wall thickness, perivascular collagen, mast cell number, and BNP tissue levels were comparable in VitDef and Co animals. Interstitial collagen (Co vs VitDef: 6.8 +/- 3.0 vs 4.5 +/- 2.1%, P < 0.05), plasma BNP (Co vs VitDef: 180 +/- 80 vs 70 +/- 60 ng/l, P < 0.05), and tissue HCY (Co vs VitDef: 0.13 +/- 0.07 vs 0.07 +/- 0.04 micromol/g protein, P < 0.05) were lower in VitDef animals. Folate and vitamin B12 deficiency do not affect cardiac function and morphology.

Experimental folate and vitamin B12 deficiency does not alter bone quality in rats.

Hyperhomocysteinemia (HHCY) has been linked to fragility fractures and osteoporosis. Folate and vitamin B(12) deficiencies are among the main causes of HHCY. However, the impact of these vitamins on bone health has been poorly studied. This study analyzed the effect of folate and vitamin B(12) deficiency on bone in rats. We used two groups of rats: a control group (Co, n = 10) and a vitamin-deficient group (VitDef, n = 10). VitDef animals were fed for 12 wk with a folate- and vitamin B(12)-free diet. Co animals received an equicaloric control diet. Tissue and plasma concentrations of homocysteine (HCY), S-adenosyl-homocysteine (SAH), and S-adenosyl-methionine (SAM) were measured. Bone quality was assessed by biomechanical testing (maximum force of an axial compression test; F(max)), histomorphometry (bone area/total area; B.Ar./T.Ar.], and the measurement of biochemical bone turnover markers (osteocalcin, collagen I C-terminal cross-laps [CTX]). VitDef animals developed significant HHCY (Co versus VitDef: 6.8 +/- 2.7 versus 61.1 +/- 12.8 microM, p < 0.001) that was accompanied by a high plasma concentration of SAH (Co versus VitDef: 24.1 +/- 5.9 versus 86.4 +/- 44.3 nM, p < 0.001). However, bone tissue concentrations of HCY, SAH, and SAM were similar in the two groups. Fmax, B.Ar./T.Ar., OC, and CTX did not differ between VitDef and Co animals, indicating that bone quality was not affected. Folate and vitamin B(12) deficiency induces distinct HHCY but has no effect on bone health in otherwise healthy adult rats. The unchanged HCY metabolism in bone is the most probable explanation for the missing effect of the vitamin-free diet on bone.

Hyperhomocysteinemia induces a tissue specific accumulation of homocysteine in bone by collagen binding and adversely affects bone.

BACKGROUND: Recently, hyperhomocysteinemia (HHCY) has been suggested to have adverse effects on bone. This study investigated if an experimental HHCY in rats induces an accumulation of homocysteine (HCY) in bone tissue that is accompanied by bone loss and reduced bone strength. MATERIAL AND METHODS: HHCY was induced in healthy rats by either a methionine (Meth)- or a homocystine (Homo)-enriched diet and compared with controls. Homocystine is the product of two disulfide linked HCY molecules. Tissue and plasma concentrations of HCY, S-adenosylhomocysteine (SAH) and S-adenosylmethionine (SAM) were measured. Bones were assessed by biomechanical testing, histomorphometry, microCT and the measurement of biochemical bone turnover markers in plasma. RESULTS: Meth and Homo animals developed a significant HHCY that was accompanied by a tissue specific accumulation of HCY (1300 to 2000% vs. controls). 65% of HCY in bone was bound to collagen of the extracellular matrix. The SAH / SAM-ratio in bone and plasma of Meth and Homo animals exhibited a tissue specific increase indicating a reduced methylation capacity. Accumulation of HCY in bone was characterized by a distinct reduction of cancellous bone (proximal femur: -25 to -35%; distal femur -56 to -58%, proximal tibia: -28 to -43%). Accordingly, bone strength was significantly reduced (-9 to -12%). CONCLUSION: A tissue specific accumulation of HCY in bone may be a promising mechanism explaining adverse effects of HHCY on bone. A reduced methylation capacity of bone cells might be another relevant pathomechanism.

The role of hyperhomocysteinemia as well as folate, vitamin B(6) and B(12) deficiencies in osteoporosis: a systematic review.

Hyperhomocysteinemia (HHCY) has been suggested as a new risk factor for osteoporosis. Recent epidemiological, clinical and experimental studies provide a growing body of data, which is reviewed in this article. Epidemiological and (randomized) clinical trials suggest that HHCY increases fracture risk, but has minor effects on bone mineral density. Measurement of biochemical bone turnover markers indicates a shift of bone metabolism towards bone resorption. Animal studies confirm these observations showing a reduced bone quality and stimulation of bone resorption in hyperhomocysteinemic animals. Homocysteine (HCY) has been found to accumulate in bone by collagen binding. Cell culture studies demonstrate that high HCY levels stimulate osteoclasts but not osteoblasts, indicating again a shift of bone metabolism towards bone resorption. Regarding B-vitamins, only a few in vivo studies with equivocal results have been published. However, two large cell culture studies confirm the results obtained with exogenous HCY administration. In addition, HHCY seems to have adverse affects on extracellular bone matrix by disturbing collagen crosslinking. In conclusion, existing data suggest that HHCY (and possibly B-vitamin deficiencies) adversely affects bone quality by a stimulation of bone resorption and disturbance of collagen crosslinking.

Experimental hyperhomocysteinemia reduces bone quality in rats.

BACKGROUND: Recently, hyperhomocysteinemia (HHCY) has been suggested as a new risk factor for osteoporosis. This study investigated if HHCY is a causal osteoporotic factor in vivo. METHODS: We used 3 groups of rats: a control group (n = 20), a moderate HHCY group (induced by a 2.4% methionine-enriched diet, n = 10), and an intermediate HHCY group (induced by a 2% homocystine-enriched diet, n = 10). We measured bone fragility [maximum force of an axial compression test (F(max))], bone area as percentage of total area (BAr/TAr, histomorphometry), and biochemical bone turnover markers [osteocalcin (OC) and collagen I C-terminal crosslaps (CTx)]. RESULTS: Compared with controls, 3 months of moderate or intermediate HHCY increased mean (SD) bone fragility at the femoral neck by 18% (6%) in methionine-fed (P = 0.001) and 36% (13%) in homocystine-fed rats (P <0.001). Mean (SD) BAr/TAr at the distal femur in methionine and homocystine groups was decreased by 45% (21%; P = 0.001) and 93% (9%; P = 0.001), respectively. At the femoral neck, BAr/TAr was decreased by 19% (11%; P <0.001) and 55% (19%; P <0.001). At the lumbar spine, the reduction of BAr/TAr was 17% (23%; P = 0.099) and 44% (19%; P <0.001). Plasma OC (bone formation marker) was decreased by 23% (20%; P = 0.006) and 34% (21%; P <0.001). Plasma CTx (bone resorption marker) did not differ between groups. CONCLUSION: Bone quality is consistently decreased in the presence of increased circulating homocysteine. The results provide evidence that HHCY is a causal osteoporotic factor.

Hyperhomocysteinemia--the biochemical link between a weak heart and brittle bones?

Osteoporosis, chronic heart failure (CHF) and mild to moderate hyperhomocysteinemia (HHCY) can frequently be found in elderly individuals and often occur in the same individual. Due to demographic changes in the number of elderly people the total number of individuals suffering from osteoporosis and/or CHF, and hence the cost to society, will increase dramatically over the next 50 years. Thus, prevention of these diseases by identifying and modifying risk factors is a major issue. Recent large population-based prospective studies suggested HHCY as an independent risk factor for CHF and osteoporosis. However, the mechanisms that link HHCY to CHF and osteoporosis are almost unknown. Moreover, until now both diseases have been considered as independent diseases. The finding that heart and bones share a common biochemical risk factor raises the question if there is a biochemical link between these two diseases? This manuscript reviews the existing literature about HHCY and osteoporosis, about HHCY and CHF, and about possible mechanisms that link HHCY to both diseases. Existing data suggest that HHCY could be a useful paradigm with most interesting therapeutic implications, because HCY lowering therapy could favourably influence the course in CHF and osteoporotic patients.

A review of homocysteine and heart failure.

Chronic heart failure (CHF) is a major public health problem causing considerable morbidity and mortality. Recently, plasma homocysteine (HCY) has been suggested to be increased in CHF patients potentially representing a newly recognized risk marker. This manuscript reviews the existing literature regarding hyperhomocysteinemia (HHCY) and CHF. Clinical data indicate that HHCY is associated with an increased incidence of CHF as well as with the severity of the disease. Mechanistic studies of HHCY and CHF are rare. However, preliminary results suggest that HHCY causes adverse cardiac remodelling characterized by interstitial and perivascular fibrosis resulting in increased myocardial stiffness. In addition, HHCY seems to affect the pump function of the myocardium. The mechanisms leading from an elevated HCY level to reduced pump function and adverse cardiac remodelling are a matter of speculation. Existing data indicate that direct effects of HCY on the myocardium as well as NO independent vascular effects are involved. In conclusion, HHCY might be a potential aetiological factor in CHF. Future studies need to clarify the mechanistic role of HHCY in CHF as a useful paradigm with most interesting therapeutic implications, because HCY lowering therapy could favourably influence the prognosis in CHF patients.