Vitamin A transport: in vitro models for the study of RBP secretion

The crosstalk effects of polybrominated diphenyl ethers on the retinoic acid and thyroid hormone signaling pathway

The toxicological and pathological influences of polybrominated diphenyl ethers (PBDEs) on the animal central nervous system have attracted worldwide attention. However, their mechanism of action has not been completely elucidated. Given that retinoic acid (RA) and thyroid hormone (TH) signaling pathway are closely related to neurodevelopment, the crosstalk between the two signaling pathways at the levels of metabolite conversion, gene expression and ligand-receptor interaction after exposure to two representative PBDE congeners (BDE-47 and BDE-209) using zebrafish larvae, dual reporter gene assay, and docking simulation was studied. Our results clarified that BDE-47 could disrupt the transport and metabolism of retinoids, induce changes in expression of key genes, bind with the seven nuclear receptors, and activate RA signaling pathway. BDE-47 exhibited more effects on the indicators of the two signaling pathways than BDE-209. Furthermore, BDE-47 may disrupt TH signaling pathway by disrupting RA signaling pathway, indicating that RA signal is priorly influenced than TH signal. This work offered a new perspective to elucidate TH signal disruption mechanism induced by PBDEs from RA signaling pathway, which is of great significance to elucidate the health effects of PBDEs.

Nutritional and Nutrition-Related Biomarkers as Prognostic Factors of Sarcopenia, and Their Role in Disease Progression

Due to the multifactorial pathogenesis of sarcopenia, it is crucial to identify biomarkers that are risk factors for sarcopenia, and which therefore have a prognostic function. Aim: This narrative review aims to define a set of biomarkers associated with nutrition and sarcopenia. These biomarkers could contribute to individualized monitoring and enable preventive and therapeutic methods. Methods: Two electronic databases, PubMed and Google Scholar, were used. The search strategy was based on a controlled vocabulary (MeSH) and includes studies published up to February 2022. Discussion: Higher levels of serum uric acid are associated with higher handgrip strength and better muscle function in elderly people and, thus, may slow the progression of sarcopenia. Leptin, an adipokine secreted by adipose tissue, promotes the production of pro-inflammatory cytokines, which in turn lead to sarcopenia. This makes leptin a significant indirect biomarker for physical disability and sarcopenic obesity. Additionally, creatinine is a reliable biomarker for muscle mass status because of its easy accessibility and cost-effectiveness. Vitamin D status acts as a useful biomarker for predicting total mortality, hip fractures, early death, and the development of sarcopenia. Therefore, there is an increasing interest in dietary antioxidants and their effects on age-related losses of muscle mass and function. On the other hand, 3-Methylhistidine is a valuable biomarker for detecting increased muscle catabolism, as it is excreted through urine during muscle degradation. In addition, IGF-1, whose concentration in plasma is stimulated by food intake, is associated with the loss of skeletal muscle mass, which probably plays a crucial role in the progression of sarcopenia. Conclusions: Many nutritional biomarkers were found to be associated with sarcopenia, and can therefore be used as prognostic indexes and risk factors. Nutrition plays an important role in the prevention and management of sarcopenia, affecting muscle mass, strength, and function in elderly people.

RNA-seq analysis of palatal transcriptome changes in all-trans retinoic acid-induced cleft palate of mice

Cleft palate is a common congenital maxillofacial malformation in newborns. All-trans retinoic acid (atRA) is an ideal exogenous stimulus to construct a mouse cleft palate model. However, the precise pathogenic mechanism remains to be elucidated. In our study, to explore the toxicity of atRA on palatal shelves during different stages of palate development, a total of 100 mg/kg atRA was administered to C57BL/6 mice at embryonic day 10.5 (E10.5). Mouse embryonic palatal shelves at E13.5, E14.5, E15.5, and E16.5 were collected for RNA extraction and histological treatment. Changes in gene expression were tested through RNA-seq. Selected differentially expressed genes (DEGs) related to metabolic pathways, such as Ptgds, Ttr, Cyp2g1, Ugt2a1 and Mgst3, were validated and analyzed by Quantitative real-time PCR (qRT-PCR). In addition, Gene Oncology analysis showed that transcriptional changes of genes from extracellular matrix (ECM) components, such as Spp1, and crystallin family might play important role in palatal shelves elevation (E13.5-E14.5). Therefore, the protein expression level of Ttr and Spp1 from E13.5 to E16.5 were tested by immunohistochemistry (IHC). Besides, the mRNA level of Spp1, were down-regulated at E16.5 and the protein were down-regulated at E15.5 and E16.5 in all-trans retinoic acid group, suggesting that atRA may involve in palatal bone formation by regulating Spp1. Overall, gene transcriptional profiles were obviously different at each time point of palate development. Thus, this study summarized some pathways and genes that may be related to palatogenesis and cleft palate through RNA-seq, to provide a direction for subsequent studies on the mechanism and targeted therapy of cleft palate.

Analysis and Screening of Reproductive Long Non-coding RNAs Through Genome-Wide Analyses of Goat Endometrium During the Pre-attachment Phase

Reproduction in goat is highly impeded by implantation failure. Of concern, the underlying mechanism leading to embryo implantation remains unclear. In this study, deep sequencing was employed through strand-specific Ribo-Zero RNA-Seq to characterize transcriptome changes in the endometrium during the maternal recognition of pregnancy. A total of 996 differential transcripts (115 lncRNAs and 881 mRNAs) existing between the pregnant and non-pregnant endometrium were revealed through bioinformatics analysis. The screening was performed on lncRNAs (XR_001918173.1, LNC_002760, and LNC_000599) and LNC_009053, to determine their potential role in regulating the synthesis of retinol and endometrium remolding through the proteasome pathway, respectively. The hypothesis of whether certain lncRNAs, namely, LNC_007223, LNC_005256, and LNC_010092 could play important roles in embryo implantation was tested. These novel findings are of paramount relevance to further elucidate the molecular mechanisms of embryo implantation and uncover new targets to improve goat reproduction.

New Insights into the Control of Cell Fate Choices and Differentiation by Retinoic Acid in Cranial, Axial and Caudal Structures

Retinoic acid (RA) signaling is an important regulator of chordate development. RA binds to nuclear RA receptors that control the transcriptional activity of target genes. Controlled local degradation of RA by enzymes of the Cyp26a gene family contributes to the establishment of transient RA signaling gradients that control patterning, cell fate decisions and differentiation. Several steps in the lineage leading to the induction and differentiation of neuromesodermal progenitors and bone-producing osteogenic cells are controlled by RA. Changes to RA signaling activity have effects on the formation of the bones of the skull, the vertebrae and the development of teeth and regeneration of fin rays in fish. This review focuses on recent advances in these areas, with predominant emphasis on zebrafish, and highlights previously unknown roles for RA signaling in developmental processes.

Sequence analysis and expression regulation of rbp4 by 9-cis-RA in Megalobrama amblycephala

Retinol-binding protein 4 (rbp4) is mainly synthesized in the liver, where it binds retinol and then enters the bloodstream, delivering retinol to cells. The full-length cDNA coding rbp4 was cloned from Megalobrama amblycephala. The amino acid sequence showed strong homology with the homologues of other vertebrates, and all structural and functional domains were highly conserved. The mRNA levels in different tissues and development stages detected by quantitative real-time PCR revealed that M. amblycephala rbp4 was highly expressed in liver (P < 0.001), but the lower levels were also detected in eyes, kidney, intestine, and spleen. During the different development stages, the rbp4 mRNA appeared until 28 hours post-fertilization (hpf), underwent a slight drop, and then gradually increased after 50 hpf. In addition, the promoter sequence of M. amblycephala rbp4 was obtained using thermal asymmetric interlaced PCR. Two single nucleotide polymorphism sites (-385A>G and -329C>T) were found in the promoter. Transfection with recombinant plasmids of two different haplotypes (GT, AC) showed that 9-cis-retinoic acid (RA) increased the promoter activity, but the AC haplotype was more sensitive to RA.

Gestational diabetes: a risk of puerperal hypovitaminosis A?

The influence of gestational diabetes on vitamin A deficiency in lactating women and, consequently, in their newborn has been verified through a cross-sectional case-control study conducted with volunteer puerperal women. The control group consisted of healthy women and the test group was composed of women with gestational diabetes. One hundred and seven women were recruited, corresponding to 71 controls and 36 cases. Personal, gestational and newborn data were collected directly from medical records during hospitalization. The retinol was determined in maternal colostrum and serum by High Performance Liquid Chromatography. Postpartum women with gestational diabetes were older, had more children and a higher prevalence of cesarean delivery. No difference was found in retinol concentration in maternal milk and serum between the groups. However, it was observed that 16.7% had vitamin A deficiency in the group of patients with diabetes and only 4.1% had such deficiency in the control group. Although no difference was found in colostrum and serum retinol concentration between women with and without gestational diabetes, the individual analysis shows that those with diabetes are at higher risk of being vitamin A deficient.

Effects of acute exposure to polybrominated diphenyl ethers on retinoid signaling in zebrafish larvae

The objectives of the present study were to investigate the effects of acute exposure to PBDEs on retinoid signaling in fish. Zebrafish embryos (2h post-fertilization, hpf) were exposed to DE-71 (0, 31.0, 68.7, and 227.6μg/L) until 120hpf. Retinoid profiles showed the content of retinal and retinoic acid was reduced significantly. While a significant up-regulation was observed in the transcription of retinal dehydrogenase (raldh2), the transcription of retinol binding protein (rbp1a), retinol dehydrogenase (rdh1), cellular retinoic acid binding protein (crabp1a and crabp2a) and retinoic acid receptor subunit (raraa) were down-regulated significantly, indicating disruption of retinoid signaling. However, the transcriptions of five opsin genes (zfrho, zfuv, zfred, zfblue, and zfgr1) were up-regulated. Furthermore, whole mount immunostaining and western blotting demonstrated increased rhodopsin protein expression in the exposure groups. Overall, the results indicated that acute exposure to PBDEs could disturb retinoid signaling and may impact on eye development of zebrafish larvae.

Retinol binding protein 4 and retinol in steatotic and nonsteatotic rat livers in the setting of partial hepatectomy under ischemia/reperfusion

Steatotic livers show increased hepatic damage and impaired regeneration after partial hepatectomy (PH) under ischemia/reperfusion (I/R), which is commonly applied in clinical practice to reduce bleeding. The known function of retinol-binding protein 4 (RBP4) is to transport retinol in the circulation. We examined whether modulating RBP4 and/or retinol could protect steatotic and nonsteatotic livers in the setting of PH under I/R. Steatotic and nonsteatotic livers from Zucker rats were subjected to PH (70%) with 60 minutes of ischemia. RBP4 and retinol levels were measured and altered pharmacologically, and their effects on hepatic damage and regeneration were studied after reperfusion. Decreased RBP4 levels were observed in both liver types, whereas retinol levels were reduced only in steatotic livers. RBP4 administration exacerbated the negative consequences of liver surgery with respect to damage and liver regeneration in both liver types. RBP4 affected the mobilization of retinol from steatotic livers, and this revealed actions of RBP4 independent of simple retinol transport. The injurious effects of RBP4 were not due to changes in retinol levels. Treatment with retinol was effective only for steatotic livers. Indeed, retinol increased hepatic injury and impaired liver regeneration in nonsteatotic livers. In steatotic livers, retinol reduced damage and improved regeneration after surgery. These benefits of retinol were associated with a reduced accumulation of hepatocellular fat. Thus, strategies based on modulating RBP4 could be ineffective and possibly even harmful in both liver types in the setting of PH under I/R. In terms of clinical applications, a retinol pretreatment might open new avenues for liver surgery that specifically benefit the steatotic liver.

Alterations in retinoid status after long-term exposure to PBDEs in zebrafish (Danio rerio)

This study examined the disruptive effect of exposure to polybrominated diphenyl ethers (PBDEs) on retinoid content in zebrafish (Danio rerio). Adult zebrafish were exposed to an environmentally relevant concentration (0.45 μg/L) and a higher concentration (9.6 μg/L) of DE-71 for 60 days. Retinoid content and gene transcription levels were examined in female zebrafish. PBDE exposure caused a significant decrease of retinyl ester content in the intestine and a downregulation of intestinal cellular retinol binding protein gene transcription (CRBP1a). In the liver, retinyl ester content was significantly decreased, while retinol content was increased. An upregulation of liver CRBP2a and retinol binding protein (RBP) gene transcription and an increased level of RBP protein were observed. In the eyes, both the retinal and retinyl ester content were increased and CRBP1a gene transcription was upregulated. However, the gene encoding for retinal dehydrogenase (RALDH2), responsible for retinoic acid synthesis, was downregulated in the eyes. CYP26a, the gene responsible for retinoic acid degradation, was upregulated, which indicated an increased level of retinoic acid. In the ovaries, the increased deposition of retinoids was also observed, while gene transcription levels of both CRBPs (CRBP1a and CRBP1b) were upregulated. An increased deposition of retinal was measured in the eggs. Overall, this study demonstrated that long-term exposure of zebrafish to environmentally relevant concentrations of DE-71 disrupted the transport, storage and metabolism of retinoid in various tissues. This study also indicated that retinoid levels in zebrafish are sensitive to PBDE exposure and highlighted the importance of liver storage, which appears to support important functions in reproduction and vision.

Co-cultures of enterocytes and hepatocytes for retinoid transport and metabolism

Dietary retinoid bioavailability involves the interplay of the intestine (transport and metabolism) and the liver (secondary metabolism). To reproduce these processes in vitro, differentiated human intestinal Caco-2/TC7 cells were co-cultured with two hepatocyte cell lines. Murine 3A cells and the more highly differentiated human HepaRG hepatocytes were both shown to respond to β-carotene (BC) and retinol (ROH) treatment by secreting Retinol Binding Protein 4 (RBP4). In co-culture experiments, Caco-2/TC7 were differentiated on filter inserts and transferred for the time of the experiment to culture wells containing confluent 3A or differentiated HepaRG cells. Functionality of the co-cultures was assayed using as endpoints the retinol-dependent secretion of RBP4 and the retinoic acid-dependent induction of CYP26A1 in hepatocytes. BC and ROH added to intestinal Caco-2/TC7 induced a reduction in intracellular RBP4 levels in the underlying hepatocytes and its secretion into the medium. HepaRG hepatocytes were also shown to up-regulate the expression of CYP26A1 mRNA in response to retinoid treatment. This in vitro model represents a useful tool to analyze the absorption and metabolism of retinoids and could be further developed to investigate other dietary compounds and molecules of pharmacological interest.

Differential changes of fat-soluble vitamins and pollutants during lactation in northern elephant seal mother-pup pairs

We investigated the changes of vitamins A and E as well as PCBs and DDTs during lactation in northern elephant seal (Mirounga angustirostris) mother-pup pairs. On average, milk vitamin A concentrations were 6 times higher during late lactation than during early lactation, a pattern that differs dramatically from terrestrial mammals. Vitamin A concentrations also significantly increased in the inner blubber throughout lactation, whereas they remained constant in the outer blubber. Similar dynamics were observed for PCBs and DDTs in maternal blubber and milk. Blubber appears to be an important storage site for vitamin A and organochlorines in seals and a direct transfer of those molecules to the mammary gland may occur. The dynamics of vitamin A, PCBs and DDTs differed from those of vitamin E. There was a significant drop in milk vitamin E concentrations between early and late lactation, which is the usual pattern observed in terrestrial mammals. The dynamics of vitamin E in the blubber layers also differed from those of vitamin A, suggesting different mechanisms of mobilization and transfer into the milk.

Molecular regulation of both dietary vitamin A and fatty acid absorption and metabolism associated with larval morphogenesis of Senegalese sole (Solea senegalensis)

The present study aimed to deepen the understanding of molecular mechanisms governing the absorption and metabolism of some nutrients, growth and development in larvae of Senegalese sole (Solea senegalensis) fed with Artemia enriched with Easy Selco (ES, INVE) or Aquagrow Gold (AGG, ABN), which mainly differed in their vitamin A (VA) content and fatty acid composition. The expression profile of genes involved in VA metabolism (crbp2, rbp, crabp1), lipid transport (i-fabp, l-fabp), nuclear receptors for VA and fatty acids (rarα1, rxrα, pparβ), growth (igf1, igf2 and their receptor igf1r) and development (bgp) was analyzed at 22, 30 and 38 days post hatching. The main results suggested that the amount of VA absorbed by larvae is controlled at the intestinal level by crbp2 in both groups, preventing excessive accumulation of this vitamin in the target tissues. The stable expression of i-fabp in the ES group with age could cause an excessive fat accumulation in the intestine inducing, in turn, the steatosis found in the liver and vascular system of these specimens. In liver, the regulation of rbp and fabp expression reflected the status of the physiological functions demanding VA and lipids. The findings revealed that dietary composition induced different strategies for VA and lipid absorption and metabolism affecting, in turn, larval development, growth and health.

High liver RBP4 protein content is associated with histological features in patients with genotype 1 chronic hepatitis C and with nonalcoholic steatohepatitis

BACKGROUND AND AIM

To investigate the hepatic expression of retinol-binding protein-4 (RBP4) in chronic hepatitis C (CHC) and nonalcoholic steatohepatitis (NASH) patients, and its association with biochemical and histological patterns of liver damage.

MATERIALS AND METHODS

Sixty-six genotype 1 CHC and 32 NASH patients were tested for hepatic RBP4 expression. Liver expression at immunostaining was scored as 0 (slight), 1 (mild), 2 (moderate), and 3 (intense). In addition, the mRNA and the quantitative protein expressions of RBP4 were tested by PCR and by western blot, respectively, in 12 NASH and 28 CHC patients. Twelve subjects undergoing elective cholecystectomy served as controls.

RESULTS

Ten (31%), 16 (50%) and 6 (19%) NASH patients, and 21 (32%), 31 (47%) and 14 (21%) CHC patients had scores of 1, 2 and 3, respectively. All control subjects scored 0. In both CHC and NASH liver RBP4 scores were directly related to western blot (p=0.001 and p=0.03), not to mRNA expression (p=0.77 and p=0.40). Older age (OR, 1.07; 95%CI, 1.01-1.13), RBP4 score (4.26; 1.27-14.21) and HOMA (2.26; 1.15-4.42) were independently associated with steatosis≥10% in CHC patients. In NASH lobular inflammation (OR, 3.77; 95%CI, 1.01-24.22) and RBP4 score (4.87; 1.003-23.65) were the only risk factors for fibrosis ≥2 at logistic regression analysis.

CONCLUSION

Hepatic storage of RBP4, unrelated to its expression, could cause liver damage both in NASH and CHC.

Retinol-binding protein-4 is decreased in patients with preeclampsia in comparison with normal pregnant women

AIMS

The aim of this study was to investigate retinol-binding protein-4 (RBP4) levels in maternal and umbilical cord serum in patients in the third trimester of pregnancy with preeclampsia in comparison to levels in normal pregnant women.

METHODS

The RBP4 levels in maternal and umbilical cord serum were measured and compared by enzyme-linked immunosorbent assay in 16 normal pregnant and 16 patients with preeclampsia.

RESULTS

Both maternal and umbilical cord serum RBP4 levels were significantly decreased in patients with preeclampsia, as compared to normal pregnant women (maternal serum, median 168.0 μg/mL vs. 202.0 μg/mL, P<0.001; umbilical cord serum, median 147.9 μg/mL vs. 193.0 μg/mL, P<0.001). Preeclampsia was independently related to RBP4 levels of maternal and umbilical cord serum.

CONCLUSION

Both maternal and umbilical cord serum RBP4 levels were lower in patients with preeclampsia than in normal pregnant women in the third trimester of pregnancy.

Serum retinol binding protein 4 level is related with renal functions in Type 2 diabetes

AIM

We aimed to evaluate the metabolic parameters and diabetes complications which would probably affect the serum retinol-binding protein 4 (RBP4) levels in Type 2 diabetic individuals. In addition to serum RBP4 concentration, the levels of its ligands, serum retinol and transthyretin (TTR) were also considered in this evaluation.

SUBJECTS AND METHODS

Serum RBP4, retinol, and TTR levels were measured in 53 Type 2 diabetic subjects and 30 body mass index (BMI)- matched controls. The molar ratios of RBP4 to retinol and RBP4 to TTR were compared.

RESULTS

While the RBP4 values were similar to those in the control group in Type 2 diabetic patients, the molar ratio of RBP4 to TTR was found to be higher than that of the control group. The serum RBP4 levels in patients who had retinopathy and macrovascular disease were similar to those in patients who did not. However, the RBP4 levels, molar ratios of RBP4 to retinol and RBP4 to TTR in micro- macroalbuminuric patients were found to be significantly higher than in normoalbuminuric subjects and controls. There was no correlation between the RBP4 levels and the patients' age, BMI, duration of diabetes, LDL, triglyceride, serum creatinine, and glycated hemoglobin values. Micro-macroalbuminuria and estimated glomerular filtration rate were independent determinants for increased serum RBP4 levels.

CONCLUSION

According to the data obtained from this study, diabetic retinopathy and cardiovascular complications do not affect the serum RBP4 level in Type 2 diabetes. Renal functions rather than the metabolic factors of diabetes determine the RBP4 level and its relation with its ligands.

Increased expression of cellular retinol-binding protein 1 in laryngeal squamous cell carcinoma

PURPOSE

To investigate the genomic alterations in larynx carcinomas (LaCa) tissues and its prognostics values in predicting survival.

METHODS

To analyse the aberrations in the genome of LaCa patients, we used array comparative genomic hybridization in 19 human laryngeal tumour samples. DNA samples were also subjected to detect human papillomavirus (HPV) sequences by polymerase chain reaction (PCR). Copy number gain was confirmed by real-time PCR. The cellular retinol-binding protein 1 (CRBP-1) gene expression was also confirmed by immunohistochemistry assay on LaCa tissues. To identify prognostic feature, CRBP-1 gene gain was correlated to patient survival.

RESULTS

The most common gains were detected for CRBP-1 and EGFR genes, while DNA lost in RAF-1 gene. Immunohistochemistry assay was revealed strong expression of CRBP1 protein in those cases with CRBP-1 gene gain. The CRBP-1 gene gain and its expression correlated significantly with survival (P = 0.003). Cox regression analysis indicated that CRBP-1 expression level was a factor of survival (P = 0.008). HPV sequences were detected in 42% of the samples, and did not show any relationship with specific gene alterations.

CONCLUSION

Our data shows that CRBP-1 gene gain can be determined by immunohistochemistry on routinely processed tissue specimens, and could support as a potential novel marker for long-term survival in laryngeal squamous cell carcinoma.

Serum concentrations of retinol-binding protein 4 in women with and without gestational diabetes

AIMS/HYPOTHESIS

Pregnancy is characterised by temporarily increased insulin resistance. Gestational diabetes occurs when pancreatic beta cell function is unable to compensate for this insulin resistance. Retinol-binding protein 4 (RBP4) could be related to insulin resistance. We hypothesised that RBP4 is elevated in gestational diabetes.

METHODS

Serum RBP4, transthyretin and retinol were cross-sectionally measured in 42 women with gestational diabetes and 45 pregnant controls. Of these, 20 women with and 22 without gestational diabetes were included in an additional longitudinal study. RBP4 was determined by enzyme immunometric assay (EIA) and western blot.

RESULTS

Women with gestational diabetes had lower RBP4 EIA and western blot levels than controls (median 6.8 [interquartile range, 3.9-14.3] vs 11.3 [7.8-19.9] microg/ml, p < 0.001 and 25.1 [21.7-29.6] vs 26.6 [23.5-32.2] microg/ml, p = 0.026). Transthyretin and the RBP4:transthyretin molar ratio were comparable between the groups. Serum retinol was lower (p < 0.001) and the RBP4 Western blot level: retinol molar ratio was higher in women with gestational diabetes (p = 0.044). RBP4 was not associated with the glucose or homeostasis model assessment of insulin resistance (HOMA-IR), but in gestational diabetes the RBP4:retinol molar ratio correlated with blood glucose and negatively with 2 h post-load insulin. The RBP4:transthyretin ratio correlated with HOMA-IR and fasting insulin in controls. In women with gestational diabetes RBP4 EIA and western blot levels increased after delivery. Retinol increased in both groups, while transthyretin and the RBP4:transthyretin ratio were not altered after parturition.

CONCLUSIONS/INTERPRETATION

RBP4 measured by two different techniques is not elevated, but the RBP4:retinol molar ratio is higher and correlates with fasting blood glucose in women with gestational diabetes. Thus, the RBP4:retinol ratio and the RBP4:transthyretin ratio are more informative than RBP4 levels alone when assessing insulin-glucose homeostasis during pregnancy.

CRBP-I in the renal tubulointerstitial compartment of healthy rats and rats with renal fibrosis

BACKGROUND

Cellular retinol-binding protein I (CRBP-I), a member of the intracellular lipid-binding protein (iLBP) superfamily, is a specific marker of quiescent stellate cells in the healthy human liver. In the diseased fibrotic/cirrhotic liver, portal and septal myofibroblasts acquire CRBP-I expression, while activated hepatic stellate cells maintain their CRBP-I expression. Here, we investigate the distribution of CRBP-I in the renal cortex of healthy rats and rats with renal fibrosis.

METHODS

Kidneys of healthy and adriamycin-treated rats were studied by immunohistochemistry, using antibodies against CRBP-I, desmin, vimentin and alpha-smooth muscle actin (alpha-SMA). Double stainings were done with immunofluorescence. Western blotting was performed to semi-quantify the expression levels of vimentin, desmin, alpha-SMA and CRBP-I.

RESULTS

In the normal rat kidney, the convoluted proximal tubular epithelial cells express CRBP-I; no expression is found in the interstitium, nor in the glomeruli. In the adriamycin-induced fibrotic rat kidney, CRBP-I expression diminishes in the convoluted proximal tubular epithelial cells, whereas peritubular myofibroblasts in the interstitium acquire CRBP-I expression.

CONCLUSIONS

In the tubulointerstitial compartment of the adriamycin-induced fibrotic rat kidney, CRBP-I is expressed in a different pattern than in the healthy rat kidney. As the convoluted proximal tubular epithelial cells dedifferentiate during fibrosis, CRBP-I expression decreases. Furthermore, de novo expression of CRBP-I is found in activated myofibroblast-like cells in the interstitium of adriamycin-treated rats. CRBP-I is therefore a useful marker to identify a subpopulation of activated/ myodifferentiated fibroblasts in the rat kidney.

Serum concentrations of retinol-binding protein 4 in women with and without gestational diabetes

AIMS/HYPOTHESIS

Pregnancy is characterised by temporarily increased insulin resistance. Gestational diabetes occurs when pancreatic beta cell function is unable to compensate for this insulin resistance. Retinol-binding protein 4 (RBP4) could be related to insulin resistance. We hypothesised that RBP4 is elevated in gestational diabetes.

METHODS

Serum RBP4, transthyretin and retinol were cross-sectionally measured in 42 women with gestational diabetes and 45 pregnant controls. Of these, 20 women with and 22 without gestational diabetes were included in an additional longitudinal study. RBP4 was determined by enzyme immunometric assay (EIA) and western blot.

RESULTS

Women with gestational diabetes had lower RBP4 EIA and western blot levels than controls (median 6.8 [interquartile range, 3.9-14.3] vs 11.3 [7.8-19.9] microg/ml, p < 0.001 and 25.1 [21.7-29.6] vs 26.6 [23.5-32.2] microg/ml, p = 0.026). Transthyretin and the RBP4:transthyretin molar ratio were comparable between the groups. Serum retinol was lower (p < 0.001) and the RBP4 Western blot level: retinol molar ratio was higher in women with gestational diabetes (p = 0.044). RBP4 was not associated with the glucose or homeostasis model assessment of insulin resistance (HOMA-IR), but in gestational diabetes the RBP4:retinol molar ratio correlated with blood glucose and negatively with 2 h post-load insulin. The RBP4:transthyretin ratio correlated with HOMA-IR and fasting insulin in controls. In women with gestational diabetes RBP4 EIA and western blot levels increased after delivery. Retinol increased in both groups, while transthyretin and the RBP4:transthyretin ratio were not altered after parturition.

CONCLUSIONS/INTERPRETATION

RBP4 measured by two different techniques is not elevated, but the RBP4:retinol molar ratio is higher and correlates with fasting blood glucose in women with gestational diabetes. Thus, the RBP4:retinol ratio and the RBP4:transthyretin ratio are more informative than RBP4 levels alone when assessing insulin-glucose homeostasis during pregnancy.

Transport properties of bovine and reindeer β-lactoglobulin in the Caco-2 cell model

Beta-lactoglobulin (betaLG) is a protein that binds ligands like fatty acids and retinol into the hydrophobic pocket. Our purpose was to study bovine and reindeer betaLG as transporter molecules and compare their transport properties across Caco-2 cell membrane. The reindeer betaLG has more valuable binder characteristics than bovine betaLG because it has only one genetic phenotype and it seems to exhibit better immunological properties. The permeation of betaLG in Caco-2 cells was evaluated by immunoblotting, and the permeation of the model substances retinol, palmitic acid and cholesterol with and without betaLG was determined using [(3)H]-labelled ligands. Both bovine and reindeer betaLG were able to pass across a Caco-2 cell monolayer similarly. Unbound and betaLG-bound [(3)H]retinol and [(3)H]palmitic acid were equally transported across the Caco-2 cell layer, whereas [(3)H]cholesterol could not pass across Caco-2 cells with or without betaLG at any of the studied circumstances. Thus, the bovine and reindeer milk betaLG is not a suitable protein to enhance transport of ligands across the Caco-2 cell membrane, used for predicting intestinal absorption.

Hydrophobic ligand binding properties of the human lipocalin apolipoprotein M

Apolipoprotein M (apoM) is a plasma protein associated mainly with HDL. ApoM is suggested to be important for the formation of prebeta-HDL, but its mechanism of action is unknown. Homology modeling has suggested apoM to be a lipocalin. Lipocalins share a structurally conserved beta-barrel, which in many lipocalins bind hydrophobic ligands. The aim of this study was to test the ability of apoM to bind different hydrophobic substances. ApoM was produced both in Escherichia coli and in HEK 293 cells. Characterization of both variants with electrophoretic and immunological methods suggested apoM from E. coli to be correctly folded. Intrinsic tryptophan fluorescence of both apoM variants revealed that retinol, all-trans-retinoic acid, and 9-cis-retinoic acid bound (dissociation constant = 2-3 microM), whereas other tested substances (e.g., cholesterol, vitamin K, and arachidonic acid) did not. The intrinsic fluorescence of two apoM mutants carrying single tryptophans was quenched by retinol and retinoic acid to the same extent as wild-type apoM, indicating that the environment of both tryptophans was affected by the binding. In conclusion, the binding of retinol and retinoic acid supports the hypothesis that apoM is a lipocalin. The physiological relevance of this binding has yet to be elucidated.

Shortcomings in methodology complicate measurements of serum retinol binding protein (RBP4) in insulin-resistant human subjects

AIMS/HYPOTHESIS

Levels of retinol binding protein (RBP4) are increased in the serum of insulin-resistant human subjects even before overt diabetes develops. RBP4 levels correlate with insulin resistance, BMI, WHR, dyslipidaemia and hypertension. Improvement of insulin sensitivity with exercise training is associated with reduction in serum RBP4 levels. Therefore serum RBP4 may be useful for early diagnosis of insulin resistance and for monitoring improvements in insulin sensitivity. We sought to determine the performance of assays for this application.

SUBJECTS AND METHODS

We compared quantitative western blotting and three commercially available multiwell immunoassays in parallel measurements of RBP4 concentrations in serum from insulin-sensitive subjects and from insulin-resistant subjects with impaired glucose tolerance or type 2 diabetes.

RESULTS

The assays yielded different absolute values and magnitudes of elevation of serum RBP4. Western blotting and a sandwich ELISA reported RBP4 concentrations that highly inversely correlated with insulin sensitivity measured by euglycaemic-hyperinsulinaemic clamp. However, western blotting yielded concentrations with a greater dynamic range and less overlap between control and insulin-resistant subjects. Two competitive enzyme-linked immunoassays undervalued serum RBP4 concentrations in insulin-resistant subjects, possibly due to assay saturation. Poor linearity of dilution also limited assay utility. All assays tested exhibited greater immunoreactivity with urinary (C-terminal proteolysed) RBP4 than with full-length RBP4, the predominant form in serum.

CONCLUSIONS/INTERPRETATIONS

These findings support the use of quantitative western blotting standardised to full-length RBP4 protein as a 'gold standard' method for measuring serum RBP4 in insulin-resistant states. Other assays should use full-length RBP4 and be extensively cross-validated using other methods.

Vitamins A and E: metabolism, roles and transfer to offspring

Vitamins A and E are essential, naturally occurring, fat-soluble nutrients that are involved in several important biological processes such as immunity, protection against tissue damage, reproduction, growth and development. They are extremely important during the early stages of life and must be transferred adequately to the young during gestation and lactation. The present article presents an overview of their biological functions, metabolism and dynamics of transfer to offspring in mammals. Among other topics, the review focuses on the biochemical aspects of their intestinal absorption, blood transport, tissue uptake, storage and catabolism. It also describes their different roles as well as their use as preventive and therapeutic agents. Finally, the mechanisms involved in their transfer during gestation and lactation are discussed.

Metabolism of retinol during mammalian placental and embryonic development

Retinol (vitamin A) is a fat-soluble nutrient indispensable for a harmonious mammalian gestation. The absence or excess of retinol and its active derivatives [i.e., the retinoic acids (RAs)] can lead to abnormal development of embryonic and extraembryonic (placental) structures. The embryo is unable to synthesize the retinol and is strongly dependent on the maternal delivery of retinol itself or precursors: retinyl esters or carotenoids. Before reaching the embryonic tissue, the retinol or the precursors have to pass through the placental structures. During this placental step, a simple diffusion of retinol can occur between maternal and fetal compartments; but retinol can also be used in situ after its activation into RA(1) or stored as retinyl esters. Using retinol-binding protein knockout model, an alternative way of embryonic retinol supply was described using retinyl esters incorporated into maternal chylomicrons. In the embryo, the principal metabolic event occurring for retinol is its conversion into RAs, the active molecules implicated on the molecular control of embryonic morphogenesis and organogenesis. All these placental and embryonic events of retinol transport and metabolism are highly regulated. Nevertheless, some genetic and/or environmental abnormalities in the transport and/or metabolism of retinol can be related to developmental pathologies during mammalian development.

Proteome analysis of chick embryonic cerebrospinal fluid

During early stages of embryo development, the brain cavity is filled with embryonic cerebrospinal fluid (E-CSF), a complex fluid containing different protein fractions that contributes to the regulation of the survival, proliferation and neurogenesis of the neuroectodermal stem cells. Using 2-DE, protein sequencing and database searches, we identified and analyzed the proteome of the E-CSF from chick embryos (Gallus gallus). We identified 26 different gene products, including proteins related to the extracellular matrix, proteins associated with the regulation of osmotic pressure and metal transport, proteins related to cell survival, MAP kinase activators, proteins involved in the transport of retinol and vitamin D, antioxidant and antimicrobial proteins, intracellular proteins and some unknown proteins. Most of these gene products are involved in the regulation of developmental processes during embryogenesis in systems other than E-CSF. Interestingly, 14 of them are also present in adult human CSF proteome, and it has been reported that they are altered in the CSF of patients suffering neurodegenerative diseases and/or neurological disorders. Understanding these molecules and the mechanisms they control during embryonic neurogenesis is a key contribution to the general understanding of CNS development, and may also contribute to greater knowledge of these human diseases.

Mammalian embryonic cerebrospinal fluid proteome has greater apolipoprotein and enzyme pattern complexity than the avian proteome

During early stages of embryo development, the brain cavity is filled with Embryonic Cerebro-Spinal Fluid, which has an essential role in the survival, proliferation and neurogenesis of the neuroectodermal stem cells. We identified and analyzed the proteome of Embryonic Cerebro-Spinal Fluid from rat embryos (Rattus norvegicus), which includes proteins involved in the regulation of Central Nervous System development. The comparison between mammalian and avian Embryonic Cerebro-Spinal Fluid proteomes reveals great similarity, but also greater complexity in some protein groups. The pattern of apolipoproteins and enzymes in CSF is more complex in the mammals than in birds. This difference may underlie the greater neural complexity and synaptic plasticity found in mammals. Fourteen Embryonic Cerebro-Spinal Fluid gene products were previously identified in adult human Cerebro-Spinal Fluid proteome, and interestingly they are altered in patients with neurodegenerative diseases and/or neurological disorders. Understanding these molecules and the mechanisms they control during embryonic neurogenesis may contribute to our understanding of Central Nervous System development and evolution, and these human diseases.

Biochemical basis for retinol deficiency induced by the I41N and G75D mutations in human plasma retinol-binding protein

Retinol-binding protein (RBP) is the retinol-specific carrier protein present in plasma, where it circulates almost entirely bound to thyroxine-binding transthyretin (TTR). Recently, depressed plasma retinol and RBP levels in carriers of the I41N and G75D RBP point mutations have been reported. We show here that although recombinant human N41 and D75 RBPs can form complexes with retinol and TTR in vitro, the retinol-mutated RBP complexes are significantly less stable than human normal holo-RBP, as revealed by the markedly facilitated retinol release by mutated holo-RBPs to phospholipid membranes, in accordance with the location of mutated residues inside the RBP retinol-binding cavity. Taken together, the data are consistent with the I41N and G75D point mutations being the cause of an altered interaction of retinol with RBP, resulting in a remarkably reduced stability of the retinol-RBP complex, which in turn can lead to the lowering of plasma retinol and RBP levels.

Retinoic acid and retinoid receptors: potential chemopreventive and therapeutic role in cervical cancer

Retinoids are natural and synthetic derivatives of vitamin A, which can be obtained from animal products (milk, liver, beef, fish oils, and eggs) and vegetables (carrots, mangos, sweet potatoes, and spinach). Retinoids regulate various important cellular functions in the body through specific nuclear retinoic-acid receptors and retinoid-X receptors, which are encoded by separate genes. Retinoic-acid receptors specifically bind tretinoin and alitretinoin, whereas retinoid-X receptors bind only alitretinoin. Retinoids have long been established as crucial for several essential life processes-healthy growth, vision, maintenance of tissues, reproduction, metabolism, tissue differentiation (normal, premalignant cells, and malignant cells), haemopoiesis, bone development, spermatogenesis, embryogenesis, and overall survival. Therefore, deficiency of vitamin A can lead to various unwanted biological effects. Several experimental and epidemiological studies have shown the antiproliferative activity of retinoids and their potential use in cancer treatment and chemoprevention. Emerging clinical trials have shown the chemotherapeutic and chemopreventive potential of retinoids in cancerous and precancerous conditions of the uterine cervix. In this review, we explore the potential chemopreventive and therapeutic roles of retinoids in preinvasive and invasive cervical neoplasia.