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Forages grown in temperate regions, such as alfalfa (Medicago sativa L.) and white clover (Trefolium repens L.), typically have a high nutritional value when fed to ruminants. Their high protein content and degradation rate result, however, in poor utilization of protein from the forage resulting in excessive excretion of nitrogen into the environment by the animal. Proanthocyanindins (also known as condensed tannins) found in some forage legumes such as birdsfoot trefoil (Lotus corniculatus L.), bind to dietary protein and can improve protein utilization in the animal. This review will focus on (1) the occurrence of proanthocyanidins; (2) biosynthesis and structure of proanthocyanidins; (3) effects of proanthocyanidins on protein metabolism; (4) protein precipitating capacity of proanthocyanidins and their effects on true intestinal protein adsorption by ruminants; and (5) effect on animal health, animal performance and environmental emissions.

Proanthocyanidins are oligomeric and polymeric end products of the flavonoid biosynthetic pathway. They are present in the fruits, bark, leaves and seeds of many plants, where they provide protection against predation. At the same time they give flavor and astringency to beverages such as wine, fruit juices and teas, and are increasingly recognized as having beneficial effects on human health. The presence of proanthocyanidins is also a major quality factor for forage crops. The past 2 years have seen important breakthroughs in our understanding of the biosynthesis of the building blocks of proanthocyanidins, the flavan-3-ols (+)-catechin and (-)-epicatechin. However, virtually nothing is known about the ways in which these units are assembled into the corresponding oligomers in vivo. Molecular genetic approaches are leading to an understanding of the regulatory genes that control proanthocyanidin biosynthesis, and this information, together with increased knowledge of the enzymes specific for the pathway, will facilitate the genetic engineering of plants for introduction of value-added nutraceutical and forage quality traits.

The variability in grape ( Vitis vinifera L.) proanthocyanidin content is largely attributable to viticultural and environmental conditions. However, the particular effect temperature has on proanthocyanidin biosynthesis is poorly understood. The aim of the present study was to ascertain the magnitude of the effect of temperature on proanthocyanidin biosynthesis in Cabernet Sauvignon grape berries cultured in vitro. In addition, the effects of temperature on global gene transcription were evaluated, and the microarray data were later validated by quantitative real-time PCR (qPCR). The grape berries used in this research were sampled 3–4 weeks after full bloom and cultured in vitro either under a low (20 °C) or high (30 °C) temperature treatment for 15 days (d) with sampling occurring every five days. The proanthocyanidin content was higher in the skin and seeds of grape berries cultured at a low temperature compared with a high temperature. However, overall proanthocyanidin composition between the treatments was not significantly affected. Microarray data revealed a total of 1298 genes with ≥ 3.5-fold expression differences under high temperature conditions. High temperature also inhibited the expression level of key genes involved in proanthocyanidin biosynthesis, anthocyanidin reductase ( ANR ) and leucoanthocyanidin reductase-1 ( LAR-1 ) within the berry skin. However, the transcriptomic accumulation of transcription factors, such as VvMybPAs , VvMyb5a and VvMyb5b , was barely influenced during the peak expression of ANR and LAR-1 . Thus, the present study revealed that temperature has a significant effect on proanthocyanidin biosynthesis in grape during berry development through enhancing the expression of key biosynthetic genes.

The role of bioactive tannins in browse in the postpartum performance of goats grazed under natural range conditions was studied using 40 yearling Mubende goats (20+/-0.32 kg). In a completely randomized design, goats of one group (n = 20) received a daily drench of 50 g per goat of polyethylene glycol (PEG) of molecular weight 4000 given as a condensed tannin (CT) deactivator, and goats of the other group (n = 20) acted as the control (no PEG). Mean birth weights, live weight gains, abortion and twinning rates, litter size and tissue energy retention were measured. The PEG drench resulted in lower postpartum weight gains and tissue energy retention (p < 0.05). Postpartum weekly weight loss per doe was 0.65 kg in the PEG group and 0.46 kg in the control group, while tissue energy loss was 17.7 MJ per goat in the PEG group and 10.23 MJ per goat in the control group in the first 8 weeks. Net weight gain was observed in the control group at the 11 th week but was delayed in the PEG group (15th week). The PEG group had lower birth weights and higher kids mortalities (p <0.05). Selective feeding in the Ankole rangeland exposes goats to beneficial concentrations of dietary CT with apparent cumulative effects leading to improved postpartum performance of does and kids.

Observational studies have suggested that the intake of flavonoids is associated with a decreased risk of CVD. However, the results of these studies remain controversial. The aim of the present study was to evaluate the association between dietary flavonoid intake and CVD risk by conducting a systematic review of prospective cohort studies. Electronic reference databases were searched to identify studies that met the pre-stated inclusion criteria. The studies were assessed for eligibility and data were extracted by two authors independently. For each study, relative risks (RR) and 95 % CI were extracted and pooled using either a fixed-effects or a random-effects model. Generalised least-squares trend estimation analysis was used to evaluate dose–response relationships. The inclusion criteria were met by fourteen prospective cohort studies. The intakes of anthocyanidins (RR 0·89, 95 % CI 0·83, 0·96), proanthocyanidins (RR 0·90, 95 % CI 0·82, 0·98), flavones (RR 0·88, 95 % CI 0·82, 0·96), flavanones (RR 0·88, 95 % CI 0·82, 0·96) and flavan-3-ols (RR 0·87, 95 % CI 0·80, 0·95) were inversely associated with the risk of CVD when comparing the highest and lowest categories of intake. A similar association was observed for flavonol intake and CVD risk. Sensitivity and subgroup analyses further supported this association. The summary RR for CVD for every 10 mg/d increment in flavonol intake was 0·95 (95 % CI 0·91, 0·99). The present systematic review suggests that the dietary intakes of six classes of flavonoids, namely flavonols, anthocyanidins, proanthocyanidins, flavones, flavanones and flavan-3-ols, significantly decrease the risk of CVD.

Proanthocyanidins (PAs) are major defense phenolic compounds in the leaves of poplar (Populus spp.) in response to abiotic and biotic stresses. Transcriptional regulation of PA biosynthetic genes by the MYB-basic helix–loop–helix (bHLH)-WD40 complexes in poplar is not still fully understood. Here, an Arabidopsis TT2-like gene MYB115 was isolated from Populus tomentosa and characterized by various molecular, genetic and biochemical approaches. MYB115 restored PA productions in the seed coat of the Arabidopsis tt2 mutant. Overexpression of MYB115 in poplar activated expression of PA biosynthetic genes, resulting in a significant increase in PA concentrations. By contrast, the CRISPR/Cas9-generated myb115 mutant exhibited reduced PA content and decreased expression of PA biosynthetic genes. MYB115 directly activated the promoters of PA-specific structural genes. MYB115 interacted with poplar TT8. Coexpression of MYB115, TT8 and poplar TTG1 significantly enhanced the expression of ANR1 and LAR3. Additionally, transgenic plants overexpressing MYB115 had increased resistance to the fungal pathogen Dothiorella gregaria, whereas myb115 mutant exhibited greater sensitivity compared with wild-type plants. Our data provide insight into the regulatory mechanisms controlling PA biosynthesis by MYB115 in poplar, which could be effectively employed for metabolic engineering of PAs to improve resistance to fungal pathogens.

Spine colour is an important fruit quality trait that influences the commercial value of cucumber (Cucumis sativus). However, little is known about the metabolites and the regulatory mechanisms of their biosynthesis in black spine varieties. In this study, we determined that the pigments of black spines are flavonoids, including flavonols and proanthocyanidins (PAs). We identified CsMYB60 as the best candidate for the previously identified B (Black spine) locus. Expression levels of CsMYB60 and the key genes involved in flavonoid biosynthesis were higher in black-spine inbred lines than that in white-spine lines at different developmental stages. The insertion of a Mutator-like element (CsMULE) in the second intron of CsMYB60 decreased its expression in a white-spine line. Transient overexpression assays indicated that CsMYB60 is a key regulatory gene and Cs4CL is a key structural gene in the pigmentation of black spines. In addition, the DNA methylation level in the CsMYB60 promoter was much lower in the black-spine line compared with white-spine line. The CsMULE insert may decrease the expression level of CsMYB60, causing hindered synthesis of flavonols and PAs in cucumber fruit spines.

Epidemiologic studies suggest that high flavonoid intake confers a benefit on cardiovascular outcome. Endothelial function, arterial stiffness, and wave reflections are important determinants of cardiovascular performance and are predictors of cardiovascular risk. The effect of flavonoid-rich dark chocolate (100 g) on endothelial function, aortic stiffness, wave reflections, and oxidant status were studied for 3 h in 17 young healthy volunteers according to a randomized, single-blind, sham procedure–controlled, cross-over protocol. Flow-mediated dilation (FMD) of the brachial artery, aortic augmentation index (AIx), and carotid–femoral pulse wave velocity (PWV) were used as measures of endothelial function, wave reflections, and aortic stiffness, respectively. Plasma oxidant status was evaluated with measurement of plasma malondialdehyde (MDA) and total antioxidant capacity (TAC). Chocolate led to a significant increase in resting and hyperemic brachial artery diameter throughout the study (maximum increase by 0.15 mm and 0.18 mm, respectively, P < .001 for both). The FMD increased significantly at 60 min (absolute increase 1.43%, P < .05). The AIx was significantly decreased with chocolate throughout the study (maximum absolute decrease 7.8%, P < .001), indicating a decrease in wave reflections, whereas PWV did not change to a significant extent. Plasma MDA and TAC did not change after chocolate, indicating no alterations in plasma oxidant status. Our study shows for the first time that consumption of dark chocolate acutely decreases wave reflections, that it does not affect aortic stiffness, and that it may exert a beneficial effect on endothelial function in healthy adults. Chocolate consumption may exert a protective effect on the cardiovascular system; further studies are warranted to assess any long-term effects.

Carbon-derived nanomaterials, especially carbon dots (CDs), are gaining attention for their distinct physicochemical characteristics and broad-spectrum antiviral capabilities. However, their efficacy against economically critical pathogens like porcine reproductive and respiratory syndrome virus (PRRSV), a major threat to swine health-and the molecular pathways involved remain underexplored. Here, we developed innovative proanthocyanidin-based carbon dots (PAC-CDs) to enhance their antiviral efficacy against PRRSV by targeting oxidative stress pathways and suppressing NLRP3 inflammasome-mediated pyroptosis via activation of the Nrf2/ARE antioxidant axis. PAC-CD were synthesized as uniformly dispersed spherical nanostructures averaging 5.49 nm in diameter, exhibiting exceptional aqueous solubility and biocompatibility. These nanoparticles significantly suppressed PRRSV replication in both Marc-145 and porcine alveolar macrophage (PAM) cells, while mitigating infection-induced cytopathic damage. Mechanistically, PAC-CDs exert their antiviral effects not through direct viral neutralization but by hindering viral entry and replication via Nrf2 pathway activation, which upregulates antioxidant defenses and reduces oxidative damage. Consistently, PAC-CDs impaired PRRSV-induced NLRP3 inflammasome-triggered pyroptotic cell death and downstream pro-inflammatory cytokine release. These findings advance the development of targeted antiviral therapies and highlight the translational potential of PAC-CDs against PRRSV outbreaks, offering a dual-action strategy to alleviate oxidative injury and inflammatory cascades in infected hosts.

Proanthocyanidins have received extensive attention due to their high functional value, but their sources are limited. Therefore, this experiment studied the preparation, biological activities, and characterization of proanthocyanidins from Chinese jujube (Ziziphus jujuba Mill. cv. Muzao) at different periods, aiming to explore a new source of proanthocyanidins and enhance their utilization value. Through ultrasonic-assisted enzymatic extraction, the optimal extraction conditions for PC from Muzao were determined, yielding a proanthocyanidin content of 2.01%. Purification using AB-8 macroporous resin increased the proanthocyanidin content by 11 times. The bioactivity results indicated that proanthocyanidins demonstrated significant in vitro antioxidant activity (scavenging rate ≥ 83.4%) and blood glucose-lowering activity (inhibition rate ≥ 84.7%). Both activities decreased with maturity, while the degree of polymerization also exhibited a positive effect. Mass spectrometry identified a total of 102 compounds, with cyanidin-based compounds being the most abundant, comprising 28 species. The comprehensive research results indicate that the oligomeric proanthocyanidins extracted, purified, and isolated from Muzao during the young fruit stage exhibit diverse biological activities and are abundant in content. They can be utilized for the extraction and purification of proanthocyanidins, offering a reference for the expansion of natural sources of proanthocyanidins and the development of functional foods.