Table 1.
Overall summary of preclinical and clinical studies focused on HHcy and associated impairments
| Disease | Study design | Study participants | Results | Ref |
|---|---|---|---|---|
| Mitochondrial dysfunction | ||||
| Acute myocardial ischemia–reperfusion injury | Plasma | Male Sprague–Dawley rats and H9C2 (2–1) cells | Elevated plasma Hcy-induced mitochondrial dysfunction and oxidative stress through increased cytochrome c release, stimulation of ROS production, and ERK1/2 signaling pathway | [66] |
| Elderly frailty, skeletal muscle weakness, and fatigability | - | C57 and CBS + / − mice | HHcy caused mitochondrial dysfunction through reduced dystrophin levels along with a decrease in mtTFA and its regulator NRF-1 | [67] |
| Cerebral infarction-related disease | Hcy-treated ischemic brains | Male Sprague–Dawley rats | Elevated Hcy level inhibited the enzymatic activity of mitochondrial complex I–III that was associated with higher cytochrome c release; Hcy increased 8-Hydroxy-2′-deoxyguanosine content and mitoStat3 protein phosphorylation | [68] |
| Vascular injury | Hcy treatment | Human umbilical vein endothelial cells | Hcy treatment induced mitochondrial apoptosis through increased NOX4 expression and intracellular ROS production and decreased Bcl-2/Bax ratio and MMP, resulting in cytochrome c release and caspase-3 activation | [69] |
| PD | Hcy treatment | Male Sprague–Dawley rats | Hcy reduced activity of mitochondrial complex-I and caused oxidative stress associated with increased production of hydroxyl radicals, reduced glutathione level, and enhanced activity of antioxidant enzymes such as superoxide dismutase and catalase | [70] |
| Cellular senescence and aging | ||||
| Cellular senescence | Hcy treatment | Endothelial cells | Hcy shortened telomeres through DNA hypomethylation of human telomerase reverse transcriptase and increased acidic β-galactosidase; Hcy upregulated the markers of cellular senescence p16, p21, and p53; the administration of folic acid or SAM could reverse mentioned effect | [72] |
| Cellular senescence and atherosclerosis | Chronic exposure to Hcy | Endothelial cells | Hcy accelerated the rate of cellular senescence through a redox pathway suggesting that oxidative stress could increase the production of vascular cell senescence proven by increased expression of two surface molecules such as intracellular adhesion molecule-1 (ICAM-1) and plasminogen activator inhibitor-1 (PAI-1) | [73] |
| Coronary heart disease | Exposure to Hcy | EPC | Hcy decreased proliferation and increased EPC senescence through diminished telomerase activity and Akt phosphorylation; the treatment with atorvastatin revealed the preventive effect against Hcy-induced senescence of EPC | [74] |
| Cardiovascular diseases | ||||
| Coronary microvascular endothelial dysfunction | Serum | Patients (n = 1418) with angina pectoris and non-obstructive coronary artery disease | Increased serum Hcy levels in patients correlated with higher rates of an invasive diagnosis of coronary microvascular endothelial dysfunction | [82] |
| CAD | Plasma | Damaged coronary endothelial function and chronic HHcy patients (n = 71) | Plasma level of Hcy negatively correlates with coronary flow velocity reserve; chronic HHcy may induce the onset of coronary artery disease by causing the dysfunction of the coronary artery endothelium that could be related to the malfunction of eNOS | [83] |
| CVD associated with endothelium-dependent vasodilatation | DDAH Binding Assay | Primary bovine aortic endothelial cells | Hcy post-translationally downregulates dimethylarginine dimethylaminohydrolase enzyme activity causing asymmetric dimethylarginine to accumulate and thus inhibit NO | [84] |
| Endothelial dysfunction | Plasma | C57BL/6 J mice; L-methionine in a chow diet for 4 weeks to establish the HHcy; Human umbilical vein endothelial cells | Hcy activates the epithelial sodium channel and consequently induces endothelial dysfunction via reactive oxygen species (ROS)/COX-2-dependent activation of SGK-1/Nedd4-2 signaling | [85] |
| Endothelial dysfunction | - | Human umbilical vein endothelial cells | Hcy induced a calcium-mediated disruption of dynamics and mitochondrial function due to overexpression of the mitochondrial calcium uniporter and the IP3R-Grp75-VDAC complex in mitochondria-associated membranes | [86] |
| Heart failure | Plasma | Heart failure patients in (n = 5506) | Elevated plasma Hcy levels in patients with heart failure compared to the control individuals | [76] |
| CAD | Serum | Patients (n = 2987) of Asian population; non-obstructive CAD group (n = 1172) and obstructive CAD group (n = 1815) | Correlation of HHcy with obstructive CAD in both old (aged > 55 years) and young individuals (aged ≤ 55 years); HHcy demonstrated a higher sensitivity (93.1%), accuracy (90.0%), and specificity (86.1%) for obstructive CAD compared to non-obstructive CAD | [87] |
| CAD, coronary acute syndrome, and coronary artery stenosis | Serum | Young Chinese adults (n = 1.103, 18–35 years old); CAD patients (n = 828) and non-CAD patients (n = 275) | Young coronary acute syndrome patients showed a greater prevalence of HHcy when compared with non-CAD individuals; HHcy in young patients was linked to the severity of coronary artery stenosis, characterized by increased prevalence of multi-vessel disease, reduced value of left ventricular ejection fraction, and ST-segment elevation myocardial infarction | [88] |
| CAD | Serum | Patients (n = 3150) undergoing coronary angiography | Normal vitamin D status can suppress the deleterious effects of HHcy on coronary atherosclerosis | [89] |
| CAD and myocardial infarction | Plasma | Coronary heart disease patients (n = 184,305) and acute myocardial infarction patients (n = 181.875) | Results did not indicate a causal linkage between CAD or myocardial infarction and plasma Hcy levels | [90] |
| Acute ischemic stroke | Serum | Acute ischemic stroke patients (n = 15,636) | Elevated Hcy levels were linked with an increased risk of all-cause mortality but not poor functional outcome and recurrent stroke in subjects with acute ischemic stroke | [91] |
| Ischemic stroke | Plasma | Meta-analysis | Causal association between plasma Hcy levels and ischemic stroke induced by small artery occlusion | [92] |
| Acute ischemic stroke | Plasma | Acute ischemic stroke patients (n = 15.636) | Elevated Hcy plasma levels were linked with poorer survival of subjects; significant links between higher Hcy levels and the subject’s survival were observed only in Caucasians and Asians | [91] |
| Stroke | Plasma | Stroke patients (n = 11.061) | Hcy levels were linked with elevated risk of ischemic stroke (RR = 1.54, 95% CI 1.21–1.97, I2 = 36.4%) and stroke (RR = 1.58, 95% CI 1.25–2.00, I2 = 39.5%) | [93] |
| Stroke | Plasma | Ischemic stroke patients (n = 13.284) | Elevated Hcy plasma levels are associated with a higher risk for IS and recurrent strokes but Hcy had no distinct linkage with hemorrhagic strokes | [94] |
| Pregnancy complications | ||||
| PE | Plasma | PE (n = 32) and controls without pregnancy complications (n = 64) | Pregnant women with HHcy have a 7.7-fold risk for PE vs normal controls (Hcy and folate higher in PE vs control in third trimester) | [101] |
| Maternal blood (plasma) collected three times during pregnancy: 16th–20th weeks (T1), 26th–30th weeks (T2), at delivery (T3) | NC (n = 126) and PE (n = 62) | Higher maternal plasma Hcy level in women with PE vs normotensive women at all three time points; maternal plasma vitamin B12 higher in PE vs NC at T2 | [95] | |
| Maternal and cord blood collected at delivery | NC (n = 450) and PE (n = 350); PE women delivering at term (n = 224) and pre-term (n = 126) | Maternal and cord Hcy higher in PE vs NC (Hcy higher in the term PE group); positive association of maternal plasma Hcy with systolic and diastolic blood pressure (whole cohort) | [99] | |
| Eclampsia, PE | Serum | Healthy pregnant controls (n = 136), PE pregnant (n = 84), and eclamptic pregnant (n = 120) | Serum Hcy increased in PE and eclampsia vs control; Hcy raised more in eclampsia vs PE | [96] |
| PE, pre-term birth, low birth weight | Serum | Pregnant women with adverse outcome (n = 563) and controls (n = 600) | Upper-quartile Hcy levels associated with PE, preterm birth, and low birth weight vs lower-quartile | [97] |
| NTD | Plasma | Mothers with first NTD child or with a history of NTD child in the family (n = 96), neonates with spina bifida (n = 126), mothers with normal previous and current pregnancies (n = 84), and control neonates with no defects (n = 87) | Increased serum Hcy and decreased vitamin B12 in mothers with neonates with NTD and in neonates with NTD | [103] |
| NTD | Serum | Case women (n = 103) — diagnosis of anencephalous, spina bifida, or encephalocele and control women (n = 139) — delivering normal live births | High serum Hcy associated with NTD-affected pregnancies (even when serum B12 and RBC folate is high) | [104] |
| Abortion, pre-term birth | Serum | Patients with risk of abortion (n = 18), patients with pre-term birth (n = 22), and healthy pregnant controls (n = 14) | Higher level of Hcy and MDA (marker of oxidative stress) in women with risk of abortion or with pre-term birth | [102] |
| Oxidative stress and inflammation | ||||
| CAD | Blood | Patients with ischemic heart disease (n = 93) | Increased Iso-P (marker of lipid peroxidation and oxidative stress in CAD patients with increased tHcy; increased plasma ICAM-1 and S-AA in CAD patients with high plasma tHcy → association between homocysteinemia and low-grade inflammation | [111] |
| CVD in postmenopausal women | Serum | Healthy pre- (n = 223) and postmenopausal (n = 118) Omani women | Postmenopausal women affected by oxidative stress (independent relation to Hcy level) | [112] |
| Young adult CRVO | Plasma | Young adult CRVO (n = 23) and controls (n = 54) | Hcy induce oxidative stress | [109] |
| AD | Serum | AD patients (n = 143) and controls (n = 1553) | Higher plasma Hcy and lower antioxidant level observed in AD patients vs control | [114] |
| Panic disorder | Blood | Panic disorder patients (n = 60) and healthy individuals (n = 60) | Increased oxidative stress accompanied by elevated Hcy in patients with panic disorder vs healthy individuals | [115] |
| Rheumatoid arthritis | Serum | rheumatoid arthritis patients (n = 50) and controls (n = 50) | Increased Hcy and associated immunological-inflammatory and metabolic markers in rheumatoid arthritis patients | [117] |
| Pro-inflammatory cytokine level | Brain, heart, serum of rats | Mild hyperhomocysteinemia induced in Wistar rats by Hcy administration (0.03 μmol/g of body weight) twice a day | Hcy induced inflammation in mouse retina, brain, and cultured human monocytes (U837); mild HHcy increased brain pro-inflammatory cytokines as TNF-α, IL-1β, IL-6, and MCP-1 in Wistar rats | [116] |
| Inflammation in the dysfunction of blood-retinal barriers and blood–brain barrier and pathogenesis of diabetic retinopathy, age-related macular degeneration, and AD | Mice with HHcy (tissue lysates isolated from the brain hippocampal area), HRECs, human retinal pigmented epithelial cell line (ARPE-19) | Hcy increased pro-inflammatory and decreased of anti-inflammatory cytokines in ARPE-19; pro-inflammatory cytokines observed HRECs treated with Hcy | [106] | |
| Postmenopausal osteoporosis | Serum | Postmenopausal women (n = 252) | Hcy associated with bone mineral density, and inflammation in postmenopausal osteoporosis | [118] |
| Cancer | ||||
| BC | Plasma | BC patients (n = 35) | Increased level of plasmatic Hcy and vitamin B12 during chemotherapy while folate and platelets were decreased | [140] |
| CC and BC | Plasma | CC and BC patients (n = 47) | Increased level of Hcy in the cancer patients characterized by low-grade inflammation | [141] |
| LC | Plasma | LC patients (n = 37) and controls (n = 26) | Increased level of total Hcy, lower level of total glutathione, and folate compared to control; no significance was observed between SCLC and NSCLC patients | [143] |
| Eye disorders | ||||
| Diabetic retinopathy | Serum | Diabetic patients and mice models of diabetes | A higher level of Hcy was detected in serum, vitreous, and retina of patients and mice | [181] |
| Age-related macular degeneration | Plasma | Age-related macular degeneration patients (n = 16) and 16 matched controls | Increased level of Hcy with elevated Hcy- thiolactone, thiobarbituric acid reactive substance (TBARS); the glutathione level was reduced | [188] |
| Pseudoexfoliation glaucoma | Plasma | PEXG patients (n = 36), POAG patients (n = 40), and 40 controls (n = 40) | Plasmatic Hcy was increased in PEXG group compared to POAG group | [191] |
| Neurological disorders | ||||
| PD | Plasma | PD patients treated by L-dopa (n = 26), PD patients treated by L-dopa + COMT-I (n = 20), healthy controls (n = 32) | Increased level of plasma Hcy in PD patients. A significantly lower level of plasma Hcy in the group treated by L-dopa + COMT-I | [126] |
| Psychological symptoms of Dementia (BPSD) in AD | Serum | AD patients (n = 18) and healthy controls (n = 18) | Correlation between increased Hcy in serum and behavioral and psychological symptoms observed in patients with AD | [121] |
| AD | Hippocampal slices of rats | Male Sprague–Dawley rats injected by Hcy (400/1600 μg/kg/day). Rats (two groups) were fed with or without folate and vitamin B12 | Supplementation of folate and vitamin B12 restored Hcy plasma level and antagonized the Hcy-induced tau hyperphosphorylation | [136] |
| Healing | ||||
| Chronic bilateral, medial ankle venous ulcers | Serum | A 79-year-old white male patient with type 2 diabetes mellitus, hypertensive CVD, chronic bilateral venous insufficiency, peripheral vascular disease, elevated fasting serum Hcy (14.9 μmol/L), and lower extremity neuropathy | Normalization of Hcy level by folic acid, vitamin B6, and B12; treatment with a topical human fibroblast-derived dermal substitute led to the wound healing within 4 weeks | [194] |
| Chronic venous ulceration | Plasma | HHcy patients with chronic venous ulceration (n = 54) that underwent compression therapy and surgical procedures; non-HHcy patients who received only basic treatment (n = 33) | Hcy-lowering therapy with folic acid (1–2 mg/day for 12 months) accelerates wound healing in patients that underwent compression therapy and surgical procedures | [195] |
| Chronic leg ulcers | Plasma | A 26-year-old man with chronic leg ulcers of eight months duration | Administration of B vitamins (B1, B2, B6, and B12), trimethyl-glycine, mecobalamine, folic acid, and povidone-iodine dressings with culture-directed antibiotic therapy improved healing of ulcers over 1 month | [196] |
| Leg ulcers | Serum | A male patient (60-year-old) with HHcy and MTHFR heterozygosity (C677T and A1298C) | Six months of treatment with vitamin B complex and oral folic acid improved the Hcy level and healed the dermatological lesions | [197] |
| Femoral fracture | Serum | CD-1 mice on Hcy-supplemented diet (n = 12), control mice on standard diet (n = 13) | Elevated Hcy level was associated with the impaired/slow downed femoral fracture healing in mice on Hcy-supplemented diet | [198] |
| Femoral fracture | Serum | Folate and vitamin B12 deficient diet in CD-1 mice (n = 14), control mice with equicaloric diet (n = 13) | Folate and vitamin B12 deficiency in diet did not affect bone repair in mice | [199] |
| Tibial fracture | Plasma | Sprague–Dawley rats: sham group (n = 12), tibial fracture group (n = 12), and HHcy + fracture group (n = 12) | HHcy inhibited tibial fracture healing by suppressing PI3K/AKT signaling pathway and enhanced apoptosis and level of TNF‑α | [200] |
| Osteoporosis | Plasma | Male Sprague–Dawley rats: wild-type group (n = 10) and an HHcy group (n = 12); Hcy was supplemented (0.67 g dl-Hcy/L drinking water) for 8–12 weeks | Higher Hcy levels and decreased vitamin B12 reduced the bone's blood flow, which contributed to compromised bone biomechanical properties | [201] |
| Inflammatory bowel disease | Serum | Male Wistar rats and C57BL/6 J homozygous IL-10–deficient mice; B vitamins deficient diet or control diet | Administration of IL-10 with an ability to increase H2S synthesis ameliorated the severity of colitis, reduced serum Hcy levels and inflammation, thereby promoting healing | [202] |
Abbreviations: AD, Alzheimer’s disease; BC, breast cancer; CAD, coronary artery disease; CC, colorectal cancer; CRVO, central retinal vein occlusion; CVD, cardiovascular diseases; Hcy, homocysteine; HHcy, hyperhomocysteinemia; HREC, human primary retinal endothelial cells; IL, interleukin; Iso-P, 8-isoprostane-prostaglandin F 2; LC, lung cancer; MCP-1, chemokine monocyte chemotactic protein-1; MDA, malondialdehyde; NC, normotensive control; NTD, neural tube defects; PD, Parkinson’s disease; PE, preeclampsia; PEXG, pseudoexfoliation syndrome; POAG, primary open-angle glaucoma; RBC, red blood cell; TNF-α, tumor necrosis factor-alpha; MTHFR, methylenetetrahydrofolate reductase; H2S, hydrogen sulfide; PI3K, phosphoinositide 3-kinase; AKT; protein kinase B; TNF-α, tumor necrosis factor alpha; NO, nitric oxide; eNOS, endothelial NO synthase; NOX4, NADPH oxidase 4; MMP, mitochondrial membrane potential; mtTFA, mitochondrial transcription factor A; NRF-1, nuclear respiratory factor 1; EPC, endothelial progenitor cells