Carotenoid modifying enzymes in metazoans

Effect of carotenoid supplementation on blood pressure in adults: a GRADE-assessed systematic review and dose-response meta-analysis of randomized controlled trials

CONTEXT

Hypertension (HTN) is regarded as a serious public health issue throughout the world. High blood pressure (BP) may be improved by carotenoid supplementation; however, randomized controlled trials (RCTs) provide conflicting evidence.

OBJECTIVE

The aim of this study was to evaluate the effects of carotenoid supplementation on BP in RCTs by systematically review and meta-analysis.

DATA SOURCES

A comprehensive literature search was performed in the Scopus, PubMed, and Web of Science databases until October 2023, with no limitation on the date or language of publication.

DATA EXTRACTION

Studies that evaluated the net effects of carotenoids in the form of supplements on BP in adults were selected. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) were calculated on the basis of a fixed or random-effects model. Sensitivity analysis, meta-regression, publication bias, and heterogeneity were assessed using standard methods. Cochrane quality assessments were used to evaluate the included studies' bias risks. Evidence certainty was calculated using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework).

DATA ANALYSIS

Reports on a total of 19 RCTs involving 1151 participants were included in this review. Carotenoid supplementation significantly reduced the systolic BP (SBP) (WMD, -2.492 mmHg; 95%CI, -4.52, -0.47; P = 0.016) and diastolic BP (DBP) (WMD, -1.60 mmHg; 95%CI, -2.73, -0.47; P = 0.005). Greater effects were observed in Asian participants, those aged >50 years, nonhealthy participants, and participants with a baseline SBP ≥130 mmHg and DBP ≥80 mmHg, at dose >10 mg. Dose-response analysis showed that carotenoid supplementation decreased SBP and DBP levels at doses of, respectively, 0-25 and 0-20 mg/d. Evidence for all SBP, DBP, and heart rate values was high quality.

CONCLUSIONS

Carotenoid supplementation had a beneficial effect on BP parameters, especially in nonhealthy study participants with high BP baseline levels.

PROSPERO REGISTRATION NO

CRD42023402740.

Carotenoids: resources, knowledge, and emerging tools to advance apocarotenoid research

Carotenoids are a large class of isoprenoid compounds which are biosynthesized by plants, algae, along with certain fungi, bacteria and insects. In plants, carotenoids provide crucial functions in photosynthesis and photoprotection. Furthermore, carotenoids also serve as precursors to apocarotenoids, which are derived through enzymatic and non-enzymatic cleavage reactions. Apocarotenoids encompass a diverse set of compounds, including hormones, growth regulators, and signaling molecules which play vital roles in pathways associated with plant development, stress responses, and plant-organismic interactions. Regulation of carotenoid biosynthesis indirectly influences the formation of apocarotenoids and bioactive effects on target pathways. Recent discovery of a plethora of new bioactive apocarotenoids across kingdoms has increased interest in expanding knowledge of the breadth of apocarotenoid function and regulation. In this review, we provide insights into the regulation of carotenogenesis, specifically linked to the biosynthesis of apocarotenoid precursors. We highlight plant studies, including useful heterologous platforms and synthetic biology tools, which hold great value in expanding discoveries, knowledge and application of bioactive apocarotenoids for crop improvement and human health. Moreover, we discuss how this field has recently flourished with the discovery of diverse functions of apocarotenoids, thereby prompting us to propose new directions for future research.

ASTER-B regulates mitochondrial carotenoid transport and homeostasis

The scavenger receptor class B type 1 (SR-B1) facilitates uptake of cholesterol and carotenoids into the plasma membrane (PM) of mammalian cells. Downstream of SR-B1, ASTER-B protein mediates the nonvesicular transport of cholesterol to mitochondria for steroidogenesis. Mitochondria also are the place for the processing of carotenoids into diapocarotenoids by β-carotene oxygenase-2. However, the role of these lipid transport proteins in carotenoid metabolism has not yet been established. Herein, we showed that the recombinant StART-like lipid-binding domain of ASTER-A and B preferentially binds oxygenated carotenoids such as zeaxanthin. We established a novel carotenoid uptake assay and demonstrated that ASTER-B expressing A549 cells transport zeaxanthin to mitochondria. In contrast, the pure hydrocarbon β-carotene is not transported to the organelles, consistent with its metabolic processing to vitamin A in the cytosol by β-carotene oxygenase-1. Depletion of the PM from cholesterol by methyl-β-cyclodextrin treatment enhanced zeaxanthin but not β-carotene transport to mitochondria. Loss-of-function assays by siRNA in A549 cells and the absence of zeaxanthin accumulation in mitochondria of ARPE19 cells confirmed the pivotal role of ASTER-B in this process. Together, our study in human cell lines established ASTER-B protein as key player in nonvesicular transport of zeaxanthin to mitochondria and elucidated the molecular basis of compartmentalization of the metabolism of nonprovitamin A and provitamin A carotenoids in mammalian cells.