Biomedical subjects

Shijie Cai

Publications and source records attributed to Shijie Cai.

11 recordsLinked to original sources

PubMed2026

A three-metabolite microbiota-associated signature for early risk stratification of gestational diabetes mellitus.

BACKGROUND: Gestational diabetes mellitus (GDM) is associated with adverse pregnancy outcomes and long-term metabolic and cardiovascular risk. However, oral glucose tolerance testing at 24-28 gestational weeks limits early risk stratification. Gut microbiota-associated metabolites may reflect early metabolic abnormalities, including those relevant to cardiometabolic health, but robust early-pregnancy biomarkers remain limited. METHODS: We conducted a multicenter nested case-control and prospective study involving 2,693 pregnant women. Untargeted metabolomics and metagenomics were integrated to identify GDM-associated metabolites and gut microbial alterations. Three consistently dysregulated metabolites, 3-hydroxydecanoic acid, γ-Glu-Leu, and propionic acid, were quantified by targeted LC-MS/MS. Candidate algorithms were compared using repeated 10-fold cross-validation, and a final generalized linear model was externally and prospectively validated. RESULTS: Women who later developed GDM showed an adverse early-pregnancy metabolic profile, including higher BMI, triglycerides, and platelet count. Untargeted metabolomics identified 14 persistently altered metabolites enriched in energy, oxidative stress, and amino acid metabolism pathways. Metagenomics revealed taxonomic restructuring and coordinated microbiota-metabolite associations. The three-metabolite model achieved AUCs of 0.838 (95% CI, 0.791-0.885) in training, 0.840 (95% CI, 0.769-0.911) in internal validation, 0.955 (95% CI, 0.925-0.985) and 0.917 (95% CI, 0.875-0.958) in two external cohorts, and 0.969 (95% CI, 0.937-1.000) in the prospective cohort. CONCLUSION: Early microbiota-associated metabolic dysregulation is detectable before routine GDM diagnosis. This compact three-metabolite panel may support early GDM risk stratification and provides metabolic evidence relevant to broader cardiometabolic risk assessment in pregnancy.

Humans↗

PubMed2006

5-methyltetrahydrofolate rapidly improves endothelial function and decreases superoxide production in human vessels: effects on vascular tetrahydrobiopterin availability and endothelial nitric oxide synthase coupling.

BACKGROUND: The circulating form of folic acid, 5-methyltetrahydrofolate (5-MTHF), may have beneficial effects on endothelial function; however, its mechanisms of action remain uncertain. Decreased nitric oxide (NO) bioavailability and increased vascular superoxide production in vascular disease states are due in part to endothelial NO synthase (eNOS) uncoupling related to deficiency of the eNOS cofactor tetrahydrobiopterin (BH4), but whether this mechanism is important in human atherosclerosis and represents a rational therapeutic target remains unclear. We hypothesized that 5-MTHF would improve endothelial function by decreasing superoxide and peroxynitrite production and by improving eNOS coupling, mediated by BH4 availability. METHODS AND RESULTS: Vascular superoxide/peroxynitrite production and vasomotor responses to acetylcholine and bradykinin were determined in saphenous veins and internal mammary arteries from 117 patients undergoing CABG. The effects of 5-MTHF were examined ex vivo (n = 61) by incubating vessels with 5-MTHF (1 to 100 micromol/L) and in vivo by intravenous infusion of 5-MTHF or placebo before vessel harvest (n = 56). 5-MTHF improved NO-mediated endothelium-dependent vasomotor responses and reduced vascular superoxide, both ex vivo and in vivo. These changes were not explained by direct superoxide scavenging by 5-MTHF in vitro or by changes in plasma total homocysteine in vivo. Rather, 5-MTHF was a strong peroxynitrite scavenger and increased vascular BH4 and the BH4/total biopterin ratio. Furthermore, 5-MTHF reversed eNOS uncoupling, as assessed by NG-nitro-l-arginine methyl ester-inhibitable superoxide production, increased the eNOS dimer:monomer ratio, and enhanced eNOS activity. CONCLUSIONS: 5-MTHF has beneficial effects on endothelial function and vascular superoxide production in human atherosclerosis, by preventing peroxynitrite-mediated BH4 oxidation and improving eNOS coupling.

Acetylcholine↗

PubMed2005

Stoichiometric relationships between endothelial tetrahydrobiopterin, endothelial NO synthase (eNOS) activity, and eNOS coupling in vivo: insights from transgenic mice with endothelial-targeted GTP cyclohydrolase 1 and eNOS overexpression.

Endothelial dysfunction in vascular disease states is associated with reduced NO bioactivity and increased superoxide (O2*-) production. Some data suggest that an important mechanism underlying endothelial dysfunction is endothelial NO synthase (eNOS) uncoupling, whereby eNOS generates O2*- rather than NO, possibly because of a mismatch between eNOS protein and its cofactor tetrahydrobiopterin (BH4). However, the mechanistic relationship between BH4 availability and eNOS coupling in vivo remains undefined because no studies have investigated the regulation of eNOS by BH4 in the absence of vascular disease states that cause pathological oxidative stress through multiple mechanisms. We investigated the stoichiometry of BH4-eNOS interactions in vivo by crossing endothelial-targeted eNOS transgenic (eNOS-Tg) mice with mice overexpressing endothelial GTP cyclohydrolase 1 (GCH-Tg), the rate-limiting enzyme in BH4 synthesis. eNOS protein was increased 8-fold in eNOS-Tg and eNOS/GCH-Tg mice compared with wild type. The ratio of eNOS dimer:monomer was significantly reduced in aortas from eNOS-Tg mice compared with wild-type mice but restored to normal in eNOS/GCH-Tg mice. NO synthesis was elevated by 2-fold in GCH-Tg and eNOS-Tg mice but by 4-fold in eNOS/GCH-Tg mice compared with wild type. Aortic BH4 levels were elevated in GCH-Tg and maintained in eNOS/GCH-Tg mice but depleted in eNOS-Tg mice compared with wild type. Aortic and cardiac O2*- production was significantly increased in eNOS-Tg mice compared with wild type but was normalized after NOS inhibition with Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME), suggesting O2*- production by uncoupled eNOS. In contrast, in eNOS/GCH-Tg mice, O2*- production was similar to wild type, and L-NAME had no effect, indicating preserved eNOS coupling. These data indicate that eNOS coupling is directly related to eNOS-BH4 stoichiometry even in the absence of a vascular disease state. Endothelial BH4 availability is a pivotal regulator of eNOS activity and enzymatic coupling in vivo.

Animals↗

PubMed2005

Augmented BH4 by gene transfer restores nitric oxide synthase function in hyperglycemic human endothelial cells.

OBJECTIVE: Endothelial dysfunction in diabetes is characterized by decreased nitric oxide (NO) bioactivity and increased superoxide (SO) production. Reduced levels of tetrahydrobiopterin (BH4), an essential cofactor of endothelial NO synthase (eNOS), appear to be associated with eNOS enzymatic uncoupling. We sought to investigate whether augmented BH4 biosynthesis in hyperglycemic human aortic endothelial cells (HAEC) by adenovirus-mediated gene transfer of GTP cyclohydrolase I (GTPCH, the rate-limiting enzyme for the de novo BH4 synthesis), would be sufficient to rescue eNOS activity and dimerization. HAEC were cultured in media with low glucose (5 mM) or high glucose (30 mM). METHODS: After 5 days, the cells with/without GTPCH gene transfer (AdeGFP as a control) were prepared for assays of (1) NO with electron paramagnetic resonance (EPR); (2) SO with cytochrome c reduction and dihydroethidine (DHE) fluorescence; (3) BH4 with high-performance liquid chromatography (HPLC); (4) eNOS expression and dimerization with immunoblotting. RESULTS: We found that high glucose decreased HAEC NO and increased SO production, in association with reductions in both total biopterin and BH4 levels. High glucose increased total eNOS protein levels in HAEC 1.5-fold, but this was present principally in the monomeric form. GTPCH gene transfer increased cellular biopterin levels and NO production but decreased SO production. Furthermore, augmenting BH4 increased the eNOS dimer:monomer ratio 2.6-fold. CONCLUSION: This study demonstrates a critical role for BH4 in regulating eNOS function, suggesting that GTPCH is a rational target to augment endothelial BH4 and recover eNOS activity in hyperglycemic endothelial dysfunction states.

Adenoviridae↗

PubMed2005

Recognition of merged characters based on forepart prediction, necessity-sufficiency matching, and character-adaptive masking.

Merged characters are the major cause of recognition errors. We classify the merging relationship between two involved characters into three types: "linear," "nonlinear," and "overlapped." Most segmentation methods handle the first type well, however, their capabilities of handling the other two types are limited. The weakness of handling the nonlinear and overlapped types results from character segmentation by linear, usually vertical, cuts assumed in these methods. This paper proposes a novel merged character segmentation and recognition method based on forepart prediction, necessity-sufficiency matching and character-adaptive masking. This method utilizes the information obtained from the forepart of merged characters to predict candidates for the leftmost character, and then applies character-adaptive masking and character recognition to verifying the prediction. Therefore, the arbitrary-shaped cutting path will follow the right shape of the leftmost character so as to preserve the shape of the next character. This method handles the first two types well and greatly improves the segmentation accuracy of the overlapped type. The experimental results and the performance comparisons with other methods demonstrate the effectiveness of the proposed method.

Algorithms↗

PubMed2004

HSV vector-delivery of GDNF in a rat model of PD: partial efficacy obscured by vector toxicity.

Herpes simplex virus (HSV)-derived vectors have been suggested for potential use in gene therapy for Parkinson's disease (PD). HSV naturally infects adult neuronal cells and possesses a large genome for the insertion of transgenes. In the present study, we have used two different HSV constructs to deliver glial cell line-derived neurotrophic factor (GDNF) to the striatum, and to assess the neuroprotective effects of the GDNF product in an intrastriatal 6-hydroxydopamine lesion model. One construct is blocked for IE gene expression whereas the other is deleted in the thymidine kinase gene. Both constructs induced a significant protection of the dopaminergic neurons in the substantia nigra from the lesions, whereas only one induced a transient behavioural recovery in amphetamine-induced rotation. Unexpectedly, the more deleted virus caused the greater toxicity. This was found to be due to the way the vector was purified. The issue of toxicity, which might account for the variable functional effects, needs resolving prior to therapeutic application of these vectors.

Animals↗

PubMed2004

GTP cyclohydrolase I gene transfer reverses tetrahydrobiopterin deficiency and increases nitric oxide synthesis in endothelial cells and isolated vessels from diabetic rats.

Nitric oxide (NO) synthesis in endothelial cells is impaired in diabetes. We previously showed that impaired NO synthesis in the spontaneously diabetic BB (BBd) rat is due to decreased levels of tetrahydrobiopterin (BH4), secondary to decreased expression of GTP cyclohydrolase I (GTPCH). The aim of this study was to utilize adenoviral GTPCH gene transfer to reverse BH4 deficiency and repair the ability of endothelial cells to produce NO. GTPCH gene transfer increased BH4 levels in BBd endothelial cells from 0.17 +/- 0.02 (mean +/-SE) to 73.37 +/- 14.42 pmol/million cells and NO production from 0.77 +/- 0.07 to 18.74 +/- 5.52 nmol/24 h/million cells. To demonstrate a functional effect of increasing BH4 concentrations in tissues, we transferred GTPCH into aortic rings from BBd and Zucker diabetic fatty (ZDF) rats, models of human type I and type II diabetes, respectively. GTPCH gene transfer led to a dose-dependent increase in acetylcholine-induced vasorelaxation, preventable by inhibiting NO synthase. Maximal relaxation of virus-treated rings (10(10) virus particles/ml) to acetylcholine was significantly higher than sham-treated rings (BBd 64% vs. 37%, P<0.005; ZDF 80% vs. 44%, P<0.05). This study demonstrates that GTPCH gene transfer can reverse BH4 deficiency in both type I and type II diabetes and provides an experimental basis for using gene therapy to treat cardiovascular complications in diabetic patients.

Animals↗

PubMed2004

Effective multiresolution arc segmentation: algorithms and performance evaluation.

Arc segmentation plays an important role in the process of graphics recognition from scanned images. The GREC arc segmentation contest shows there is a lot of room for improvement in this area. This paper proposes a multiresolution arc segmentation method based on our previous seeded circular tracking algorithm which largely depends on the OOPSV model. The newly-introduced multiresolution paradigm can handle arcs/circles with large radii well. We describe new approaches for arc seed detection, arc localization, and arc verification, making the proposed method self-contained and more efficient. Moreover, this paper also brings major improvement to the dynamic adjustment algorithm of circular tracking to make it more robust. A systematic performance evaluation of the proposed method has been conducted using the third-party evaluation tool and test images obtained from the GREC arc segmentation contests. The overall performance over various arc angles, arc lengths, line thickness, noises, arc-arc intersections, and arc-line intersections has been measured. The experimental results and time complexity analyses on real scanned images are also reported and compared with other approaches. The evaluation result demonstrates the stable performance and the significant improvement on processing large arcs/circles of the MAS method.

Algorithms↗

PubMed2003

Adenoviral-mediated delivery of a viral chemokine binding protein blocks CC-chemokine activity in vitro and in vivo.

Chemokines are important mediators of leukocyte recruitment and activation that play critical roles in the pathology of inflammatory diseases such as atherosclerosis, rheumatoid arthritis and asthma. The vaccinia virus (strain Lister) expresses a 35 kDa soluble protein ('35K') that binds and inactivates a wide range of CC chemokines. We generated a recombinant adenovirus encoding soluble 35K (Ad35K). Ad35K-infected cell culture medium, containing recombinant 35K, potently reduced migration of CCR5-transfected 293 cells by 95% in response to the CC-chemokine RANTES, but had no effect on cells transfected with the CX3CR1 fractalkine receptor. Delivery of Ad35K to mice in vivo via tail vein injection resulted in expression of recombinant 35K in plasma and increased serum RANTES and MIP-1alpha levels when quantified by ELISA. However, chemotaxis of both CCR5-transfected cells and primary macrophages was inhibited by more than 90% by plasma from Ad35K-infected animals compared with control plasma from animals injected with AdGFP. Furthermore, 35K delivered by intra-peritoneal injection more than halved biogel-induced inflammatory cell recruitment in peritoneal exudates compared to AdGFP medium. These studies identify broad-spectrum CC-chemokine blockade using in vivo adenoviral-mediated recombinant 35K expression as a promising strategy to reduce local and systemic inflammation.

Adenoviridae↗

PubMed2003

Tetrahydrobiopterin-dependent preservation of nitric oxide-mediated endothelial function in diabetes by targeted transgenic GTP-cyclohydrolase I overexpression.

Increased production of reactive oxygen species and loss of endothelial NO bioactivity are key features of vascular disease states such as diabetes mellitus. Tetrahydrobiopterin (BH4) is a required cofactor for eNOS activity; pharmacologic studies suggest that BH4 may mediate some of the adverse effects of diabetes on eNOS function. We have now investigated the importance and mechanisms of BH4 availability in vivo using a novel transgenic mouse model with endothelial-targeted overexpression of the rate-limiting enzyme in BH4 synthesis, guanosine triphosphate-cyclohydrolase I (GTPCH). Transgenic (GCH-Tg) mice demonstrated selective augmentation of endothelial BH4 levels. In WT mice, induction of diabetes with streptozotocin (STZ) increased vascular oxidative stress, resulting in oxidative loss of BH4, forming BH2 and biopterin. Endothelial cell superoxide production in diabetes was increased, and NO-mediated endothelium-dependent vasodilatation was impaired. In diabetic GCH-Tg mice, superoxide production from the endothelium was markedly reduced compared with that of WT mice, endothelial BH4 levels were maintained despite some oxidative loss of BH4, and NO-mediated vasodilatation was preserved. These findings indicate that BH4 is an important mediator of eNOS regulation in diabetes and is a rational therapeutic target to restore NO-mediated endothelial function in diabetes and other vascular disease states.

Animals↗

PubMed2002

GTP cyclohydrolase I gene transfer augments intracellular tetrahydrobiopterin in human endothelial cells: effects on nitric oxide synthase activity, protein levels and dimerisation.

OBJECTIVES: Tetrahydrobiopterin (BH4) is an essential cofactor for endothelial nitric oxide synthase (eNOS) activity. BH4 levels are regulated by de novo biosynthesis; the rate-limiting enzyme is GTP cyclohydrolase I (GTPCH). BH4 activates and promotes homodimerisation of purified eNOS protein, but the intracellular mechanisms underlying BH4-mediated eNOS regulation in endothelial cells remain less clear. We aimed to investigate the role of BH4 levels in intracellular eNOS regulation, by targeting the BH4 synthetic pathway as a novel strategy to modulate intracellular BH4 levels. METHODS: We constructed a recombinant adenovirus, AdGCH, encoding human GTPCH. We infected human endothelial cells with AdGCH, investigated the changes in intracellular biopterin levels, and determined the effects on eNOS enzymatic activity, protein levels and dimerisation. RESULTS: GTPCH gene transfer in EAhy926 endothelial cells increased BH4 >10-fold compared with controls (cells alone or control adenovirus infection), and greatly enhanced NO production in a dose-dependent, eNOS-specific manner. We found that eNOS was principally monomeric in control cells, whereas GTPCH gene transfer resulted in a striking increase in eNOS homodimerisation. Furthermore, the total amounts of both native eNOS protein and a recombinant eNOS-GFP fusion protein were significantly increased following GTPCH gene transfer. CONCLUSIONS: These findings suggest that GTPCH gene transfer is a valid approach to increase BH4 levels in human endothelial cells, and provide new evidence for the relative importance of different mechanisms underlying BH4-mediated eNOS regulation in intact human endothelial cells. Additionally, these observations suggest that GTPCH may be a rational target to augment endothelial BH4 and normalise eNOS activity in endothelial dysfunction states.

3T3 Cells↗