Extracellular matrix turnover: phytochemicals target and modulate the dual role of matrix metalloproteinases (MMPs) in liver fibrosis

Extracellular matrix (ECM) resolution by matrix metalloproteinases (MMPs) is a well-documented mechanism. MMPs play a dual and complex role in modulating ECM degradation at different stages of liver fibrosis, depending on the timing and levels of their expression. Increased MMP-1 combats disease progression by cleaving the fibrillar ECM. Activated hepatic stellate cells (HSCs) increase expression of MMP-2, -9, and -13 in different chemicals-induced animal models, which may alleviate or worsen disease progression based on animal models and the stage of liver fibrosis. In the early stage, elevated expression of certain MMPs may damage surrounding tissue and activate HSCs, promoting fibrosis progression. At the later stage, downregulation of MMPs can facilitate ECM accumulation and disease progression. A number of phytochemicals modulate MMP activity and ECM turnover, alleviating disease progression. However, the effects of phytochemicals on the expression of different MMPs are variable and may depend on the disease models and stage, and the dosage, timing and duration of phytochemicals used in each study. Here, we review the most recent advances in the role of MMPs in the effects of phytochemicals on liver fibrogenesis, which indicates that further studies are warranted to confirm and define the potential clinical efficacy of these phytochemicals.

Global, but not chondrocyte-specific, MT1-MMP deficiency in adult mice causes inflammatory arthritis

Membrane-type I metalloproteinase (MT1-MMP/MMP14) plays a key role in various pathophysiological processes, indicating an unaddressed need for a targeted therapeutic approach. However, mice genetically deficient in Mmp14 show severe defects in development and growth. To investigate the possibility of MT1-MMP inhibition as a safe treatment in adults, we generated global Mmp14 tamoxifen-induced conditional knockout (Mmp14kd) mice and found that MT1-MMP deficiency in adult mice resulted in severe inflammatory arthritis. Mmp14kd mice started to show noticeably swollen joints two weeks after tamoxifen administration, which progressed rapidly. Mmp14kd mice reached a humane endpoint 6 to 8 weeks after tamoxifen administration due to severe arthritis. Plasma TNF-α levels were also significantly increased in Mmp14kd mice. Detailed analysis revealed chondrocyte hypertrophy, synovial fibrosis, and subchondral bone remodeling in the joints of Mmp14kd mice. However, global conditional knockout of MT1-MMP in adult mice did not affect body weight, blood glucose, or plasma cholesterol and triglyceride levels. Furthermore, we observed substantial expression of MT1-MMP in the articular cartilage of patients with osteoarthritis. We then developed chondrocyte-specific Mmp14 tamoxifen-induced conditional knockout (Mmp14chkd) mice. Chondrocyte MT1-MMP deficiency in adult mice also caused apparent chondrocyte hypertrophy. However, Mmp14chkd mice did not exhibit synovial hyperplasia or noticeable arthritis, suggesting that chondrocyte MT1-MMP is not solely responsible for the onset of severe arthritis observed in Mmp14kd mice. Our findings also suggest that highly cell-type specific inhibition of MT1-MMP is required for its potential therapeutic use.

Surf4 (Surfeit Locus Protein 4) Deficiency Reduces Intestinal Lipid Absorption and Secretion and Decreases Metabolism in Mice

BACKGROUND

Postprandial dyslipidemia is a causative risk factor for cardiovascular disease. The majority of absorbed dietary lipids are packaged into chylomicron and then delivered to circulation. Previous studies showed that Surf4 (surfeit locus protein 4) mediates very low-density lipoprotein secretion from hepatocytes. Silencing hepatic Surf4 markedly reduces the development of atherosclerosis in different mouse models of atherosclerosis without causing hepatic steatosis. However, the role of Surf4 in chylomicron secretion is unknown.

METHODS

We developed inducible intestinal-specific Surf4 knockdown mice (Surf4^IKO) using Vil1Cre-ER^T2 and Surf4^flox mice. Metabolic cages were used to monitor mouse metabolism. Enzymatic kits were employed to measure serum and tissue lipid levels. The expression of target genes was detected by qRT-PCR and Western Blot. Transmission electron microscopy and radiolabeled oleic acid were used to assess the structure of enterocytes and intestinal lipid absorption and secretion, respectively. Proteomics was performed to determine changes in protein expression in serum and jejunum.

RESULTS

Surf4^IKO mice, especially male Surf4^IKO mice, displayed significant body weight loss, increased mortality, and reduced metabolism. Surf4^IKO mice exhibited lipid accumulation in enterocytes and impaired fat absorption and secretion. Lipid droplets and small lipid vacuoles were accumulated in the cytosol and the endoplasmic reticulum lumen of the enterocytes of Surf4^IKO mice, respectively. Surf4 colocalized with apoB and co-immunoprecipitated with apoB48 in differentiated Caco-2 cells. Intestinal Surf4 deficiency also significantly reduced serum triglyceride, cholesterol, and free fatty acid levels in mice. Proteomics data revealed that diverse pathways were altered in Surf4^IKO mice. In addition, Surf4^IKO mice had mild liver damage, decreased liver size and weight, and reduced hepatic triglyceride levels.

CONCLUSIONS

Our findings demonstrate that intestinal Surf4 plays an essential role in lipid absorption and chylomicron secretion and suggest that the therapeutic use of Surf4 inhibition requires highly cell/tissue-specific targeting.

Surf4, cargo trafficking, lipid metabolism, and therapeutic implications

Surfeit 4 is a polytopic transmembrane protein that primarily resides in the endoplasmic reticulum (ER) membrane. It is ubiquitously expressed and functions as a cargo receptor, mediating cargo transport from the ER to the Golgi apparatus via the canonical coat protein complex II (COPII)-coated vesicles or specific vesicles. It also participates in ER-Golgi protein trafficking through a tubular network. Meanwhile, it facilitates retrograde transportation of cargos from the Golgi apparatus to the ER through COPI-coated vesicles. Surf4 can selectively mediate export of diverse cargos, such as PCSK9 very low-density lipoprotein (VLDL), progranulin, α1-antitrypsin, STING, proinsulin, and erythropoietin. It has been implicated in facilitating VLDL secretion, promoting cell proliferation and migration, and increasing replication of positive-strand RNA viruses. Therefore, Surf4 plays a crucial role in various physiological and pathophysiological processes and emerges as a promising therapeutic target. However, the molecular mechanisms by which Surf4 selectively sorts diverse cargos for ER-Golgi protein trafficking remain elusive. Here, we summarize the most recent advances in Surf4, focusing on its role in lipid metabolism.

The role of hepatic Surf4 in lipoprotein metabolism and the development of atherosclerosis in apoE-/- mice

Elevated plasma levels of low-density lipoprotein-C (LDL-C) increase the risk of atherosclerotic cardiovascular disease. Circulating LDL is derived from very low-density lipoprotein (VLDL) metabolism and cleared by LDL receptor (LDLR). We have previously demonstrated that cargo receptor Surfeit 4 (Surf4) mediates VLDL secretion. Inhibition of hepatic Surf4 impairs VLDL secretion, significantly reduces plasma LDL-C levels, and markedly mitigates the development of atherosclerosis in LDLR knockout (Ldlr^-/-) mice. Here, we investigated the role of Surf4 in lipoprotein metabolism and the development of atherosclerosis in another commonly used mouse model of atherosclerosis, apolipoprotein E knockout (apoE^-/-) mice. Adeno-associated viral shRNA was used to silence Surf4 expression mainly in the liver of apoE^-/- mice. In apoE^-/- mice fed a regular chow diet, knockdown of Surf4 expression significantly reduced triglyceride secretion and plasma levels of non-HDL cholesterol and triglycerides without causing hepatic lipid accumulation or liver damage. When Surf4 was knocked down in apoE^-/- mice fed the Western-type diet, we observed a significant reduction in plasma levels of non-HDL cholesterol, but not triglycerides. Knockdown of Surf4 did not increase hepatic cholesterol and triglyceride levels or cause liver damage, but significantly diminished atherosclerosis lesions. Therefore, our findings indicate the potential of hepatic Surf4 inhibition as a novel therapeutic strategy to reduce the risk of atherosclerotic cardiovascular disease.

Early complementary acupuncture improves the clinical prognosis of traumatic brain edema: A randomized controlled trial

BACKGROUND

Traumatic brain edema occurs commonly brain injury, and most manifests as pericontusional edema of brain contusions. On the basis of evidence-based medicine, apart from recommending craniotomy and mannitol, there are few particularly effective measures to prevent and treat traumatic brain edema. It is uncertain whether an early complementary acupuncture treatment would improve long-term outcomes of patients with traumatic brain edema. The aim of this study is to assess the efficacy and the safety of early complementary acupuncture for patients with traumatic brain edema.

METHODS

This study is an actively accruing, single-center, single-blinded, 2-arm, randomized controlled trial. Patients with traumatic brain injury, a Glasgow Coma Scale score of 6∼12, and brain edema on computed tomography scan will be divided into 2 groups on the basis of stratified block randomization. All patients will receive conventional treatment, and the study group will undergo additional acupuncture therapy (start within 72 hours after the injury) once a day for 28 days. The primary outcome is the dichotomized Glasgow Outcome Score at 6 months and 12 months after injury, and the secondary outcomes are the Glasgow Coma Scale, the volume of traumatic brain edema, the serum levels of C-reactive protein and interleukin-6, and the Modified Barthel Index.

DISCUSSION

This study will provide data regarding the efficacy of early complementary acupuncture for traumatic brain edema. If the study yields positive results, its findings may offer insights into a valuable complementary option of acupuncture for traumatic brain edema that could provide pilot evidence for large, randomized, controlled trials.Trial registration: This trial has been published in the Chinese Clinical Trial Register, http://www.chictr.org.cn/edit.aspx?pid=141208&htm=4 (Identifier: ChiCTR2100053794, registered on December 3, 2021).

Loss of Hepatic Surf4 Depletes Lipid Droplets in the Adrenal Cortex but Does Not Impair Adrenal Hormone Production

The adrenal gland produces steroid hormones to play essential roles in regulating various physiological processes. Our previous studies showed that knockout of hepatic Surf4 (Surf4^LKO) markedly reduced fasting plasma total cholesterol levels in adult mice, including low-density lipoprotein and high-density lipoprotein cholesterol. Here, we found that plasma cholesterol levels were also dramatically reduced in 4-week-old young mice and non-fasted adult mice. Circulating lipoprotein cholesterol is an important source of the substrate for the production of adrenal steroid hormones. Therefore, we investigated whether adrenal steroid hormone production was affected in Surf4^LKO mice. We observed that lacking hepatic Surf4 essentially eliminated lipid droplets and significantly reduced cholesterol levels in the adrenal gland; however, plasma levels of aldosterone and corticosterone were comparable in Surf4^LKO and the control mice under basal and stress conditions. Further analysis revealed that mRNA levels of genes encoding enzymes important for hormone synthesis were not altered, whereas the expression of scavenger receptor class B type I (SR-BI), low-density lipoprotein receptor (LDLR) and 3-hydroxy-3-methyl-glutaryl-CoA reductase was significantly increased in the adrenal gland of Surf4^LKO mice, indicating increased de novo cholesterol biosynthesis and enhanced LDLR and SR-BI-mediated lipoprotein cholesterol uptake. We also observed that the nuclear form of SREBP2 was increased in the adrenal gland of Surf4 ^LKO mice. Taken together, these findings indicate that the very low levels of circulating lipoprotein cholesterol in Surf4^LKO mice cause a significant reduction in adrenal cholesterol levels but do not significantly affect adrenal steroid hormone production. Reduced adrenal cholesterol levels activate SREBP2 and thus increase the expression of genes involved in cholesterol biosynthesis, which increases de novo cholesterol synthesis to compensate for the loss of circulating lipoprotein-derived cholesterol in the adrenal gland of Surf4^LKO mice.

Regulation of PCSK9 Expression and Function: Mechanisms and Therapeutic Implications

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes degradation of low-density lipoprotein receptor (LDLR) and plays a central role in regulating plasma levels of LDL cholesterol levels, lipoprotein(a) and triglyceride-rich lipoproteins, increasing the risk of cardiovascular disease. Additionally, PCSK9 promotes degradation of major histocompatibility protein class I and reduces intratumoral infiltration of cytotoxic T cells. Inhibition of PCSK9 increases expression of LDLR, thereby reducing plasma levels of lipoproteins and the risk of cardiovascular disease. PCSK9 inhibition also increases cell surface levels of major histocompatibility protein class I in cancer cells and suppresses tumor growth. Therefore, PCSK9 plays a vital role in the pathogenesis of cardiovascular disease and cancer, the top two causes of morbidity and mortality worldwide. Monoclonal anti-PCSK9 antibody-based therapy is currently the only available treatment that can effectively reduce plasma LDL-C levels and suppress tumor growth. However, high expenses limit their widespread use. PCSK9 promotes lysosomal degradation of its substrates, but the detailed molecular mechanism by which PCSK9 promotes degradation of its substrates is not completely understood, impeding the development of more cost-effective alternative strategies to inhibit PCSK9. Here, we review our current understanding of PCSK9 and focus on the regulation of its expression and functions.

Membrane-type I matrix metalloproteinase (MT1-MMP), lipid metabolism and therapeutic implications

Lipids exert many essential physiological functions, such as serving as a structural component of biological membranes, storing energy, and regulating cell signal transduction. Dysregulation of lipid metabolism can lead to dyslipidemia related to various human diseases, such as obesity, diabetes, and cardiovascular disease. Therefore, lipid metabolism is strictly regulated through multiple mechanisms at different levels, including the extracellular matrix. Membrane-type I matrix metalloproteinase (MT1-MMP), a zinc-dependent endopeptidase, proteolytically cleaves extracellular matrix components, and non-matrix proteins, thereby regulating many physiological and pathophysiological processes. Emerging evidence supports the vital role of MT1-MMP in lipid metabolism. For example, MT1-MMP mediates ectodomain shedding of low-density lipoprotein receptor and increases plasma low-density lipoprotein cholesterol levels and the development of atherosclerosis. It also increases the vulnerability of atherosclerotic plaque by promoting collagen cleavage. Furthermore, it can cleave the extracellular matrix of adipocytes, affecting adipogenesis and the development of obesity. Therefore, the activity of MT1-MMP is strictly regulated by multiple mechanisms, such as autocatalytic cleavage, endocytosis and exocytosis, and post-translational modifications. Here, we summarize the latest advances in MT1-MMP, mainly focusing on its role in lipid metabolism, the molecular mechanisms regulating the function and expression of MT1-MMP, and their pharmacotherapeutic implications.

Atherosclerosis-associated hepatic secretion of VLDL but not PCSK9 is dependent on cargo receptor protein Surf4

Plasma LDL is produced from catabolism of VLDL and cleared from circulation mainly via the hepatic LDL receptor (LDLR). Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes LDLR degradation, increasing plasma LDL-C levels. Circulating PCSK9 is mainly secreted by the liver, whereas VLDL is exclusively secreted by hepatocytes. However, the mechanism regulating their secretion is not completely understood. Surfeit 4 (Surf4) is a cargo receptor localized in the ER membrane. It recruits cargos into coat protein complex II vesicles to facilitate their secretion. Here, we investigated the role of Surf4 in VLDL and PCSK9 secretion. We generated Surf4 liver-specific knockout mice and found that knockout of Surf4 did not affect PCSK9 secretion, whereas it significantly reduced plasma levels of cholesterol, triglyceride, and lipid-binding protein apolipoprotein B (apoB). In cultured human hepatocytes, Surf4 coimmunoprecipitated and colocalized with apolipoprotein B100, and Surf4 silencing reduced secretion of apolipoprotein B100. Furthermore, knockdown of Surf4 in LDLR knockout (Ldlr^−/−) mice significantly reduced triglyceride secretion, plasma levels of apoB and non-HDL-C, and the development of atherosclerosis. However, Surf4 liver-specific knockout mice and Surf4 knockdown in Ldlr^−/− mice displayed similar levels of liver lipids and plasma alanine aminotransferase activity as control mice, indicating that inhibition of Surf4 does not cause notable liver damage. Expression of stearoyl-CoA desaturase-1 was also reduced in the liver of these mice, suggesting a reduction in de novo lipogenesis. In summary, hepatic deficiency of Surf4 reduced VLDL secretion and the development of atherosclerosis but did not cause significant hepatic lipid accumulation or liver damage.

Membrane type 1 matrix metalloproteinase promotes LDL receptor shedding and accelerates the development of atherosclerosis

Plasma low-density lipoprotein (LDL) is primarily cleared by LDL receptor (LDLR). LDLR can be proteolytically cleaved to release its soluble ectodomain (sLDLR) into extracellular milieu. However, the proteinase responsible for LDLR cleavage is unknown. Here we report that membrane type 1-matrix metalloproteinase (MT1-MMP) co-immunoprecipitates and co-localizes with LDLR and promotes LDLR cleavage. Plasma sLDLR and cholesterol levels are reduced while hepatic LDLR is increased in mice lacking hepatic MT1-MMP. Opposite effects are observed when MT1-MMP is overexpressed. MT1-MMP overexpression significantly increases atherosclerotic lesions, while MT1-MMP knockdown significantly reduces cholesteryl ester accumulation in the aortas of apolipoprotein E (apoE) knockout mice. Furthermore, sLDLR is associated with apoB and apoE-containing lipoproteins in mouse and human plasma. Plasma levels of sLDLR are significantly increased in subjects with high plasma LDL cholesterol levels. Thus, we demonstrate that MT1-MMP promotes ectodomain shedding of hepatic LDLR, thereby regulating plasma cholesterol levels and the development of atherosclerosis.

Efficacy and safety of magnesium isoglycyrrhizinate injection in patients with acute drug-induced liver injury: A phase II trial

BACKGROUND

Drug-induced liver injury (DILI) is the most common reason for a drug to be withdrawn from the market. Apart from stopping the offending drug, no regimens are available for treating idiosyncratic DILI in clinical practice.

METHODS

We carried out a randomized, double-blind, multidoses, active drug controlled, multicentre phase II trial to assess the safety and efficacy of the study drug, magnesium isoglycyrrhizinate (MgIG), as compared to tiopronin, a standard therapy for DILI in China. The primary outcome was the proportion of alanine aminotransferase (ALT) normalization at week 4 after study drug administration. Logistic regression was used to examine the odds of ALT normalization between low dose (Group A) and high dose (Group B) vs active control (Group C).

RESULTS

One hundred and seventy-four eligible subjects were randomized and enrolled into three groups: 59 in group A, 56 in group B and 59 in group C. It was shown that group A and group B lowered ALT level even at early stage of study drug administration; when compared with Group C (61.02%), the proportions of ALT normalization at week 4 were significantly greater in Group A (84.75%, P = .0029) and Group B (85.71%, P = .0037) respectively. The results from the univariate logistic model showed that the odds of ALT normalized among subjects in Group A were about 3.6 times greater (OR = 3.55, 95% CI: 1.47-8.57, P = .0049) than subjects in Group C. Similar effect was observed among subjects in Group B (OR = 3.83, 95% CI: 1.54-9.55, P = .0039).

CONCLUSIONS

This trial provided preliminary evidence that MgIG is an effective and safe treatment for patients with acute DILI.

[Impact of subchronic exposure to low-dose nano-nickel oxide on the reproductive function and offspring of male rats]

OBJECTIVE

To investigate the influence of subchronic exposure to low-dose subchronic nano-nickel oxide (NNO) on the reproductive function of male rats and embryonic development of the pregnant rats.

METHODS

Fifty normal healthy male SD rats weighing 180－220 g were randomly divided into five groups of equal number, negative control, 4 mg/ml micro-nickel oxide (MNO), and 0.16, 0.8 and 4 mg/ml NNO, those of the latter four groups exposed to MNO or NNO by non-contact intratracheal instillation once every 3 days for 60 days, and then all mated with normal adult female rats in the ratio of 1∶2. After the female animals were confirmed to be pregnant, the males were sacrificed and the weights of the body, testis and epididymis obtained, followed by calculation of the visceral coefficients, determination of epididymal sperm concentration and viability and the nickel contents in the blood and semen by atomic fluorescence spectrometry. The female rats were killed on the 20th day of gestation for counting of the implanted fertilized eggs and live, dead and resorbed fetuses.

RESULTS

After 60 days of exposure, the rats of the NNO groups showed no statistically significant differences from those of the negative control and MNO groups in the weights of the body, testis and epididymis or visceral coefficients. Compared with the negative control group, the animals of the 0.8 and 4 mg/ml NNO groups exhibited markedly decreased sperm concentration (［9.36 ± 0.98］ vs ［7.49 ± 1.46］ and ［6.30 ± 1.36］ ×10⁶/ml, P < 0.05) and viable sperm (［85.35 ± 9.16］% vs ［68.26 ± 16.63］% and ［65.88 ± 14.68］ %, P < 0.05), increased morphologically abnormal sperm (［8.30 ± 2.47］% vs ［13.99 ± 4.87］% and ［15.38 ± 8.86］ %, P < 0.05), and elevated rate of dead and resorbed fetuses (1.18% vs 6.89% and 7.37%, P < 0.05), blood nickel content (［0.13 ± 0.16］ vs ［0.52 ± 0.34］ and ［0.82 ± 0.44］ mg/L, P < 0.05) and semen nickel content (［0.08 ± 0.13］ vs ［0.35 ± 0.23］ and ［0.63 ± 0.61］ mg/L, P < 0.05). The nickel level in the semen was correlated significantly with that in the blood (r = 0.912, P <0.01), negatively with the rate of viable sperm (r = －0.879, P <0.01) and positively with the percentage of morphologically abnormal sperm (r = －0.898, P <0.01).

CONCLUSIONS

Sixty-day exposure to nano-nickel oxide at 0.8 and 4 mg/ml can produce reproductive toxicity in male rats and result in fetal abnormality in the females, while that at 0.16 mg/ml has no significant toxic effect on the reproductive function of the males.

Identification of amino acid residues in the ligand binding repeats of LDL receptor important for PCSK9 binding

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes LDL receptor (LDLR) degradation, increasing plasma levels of LDL cholesterol and the risk of cardiovascular disease. We have previously shown that, in addition to the epidermal growth factor precursor homology repeat-A of LDLR, at least three ligand-binding repeats (LRs) of LDLR are required for PCSK9-promoted LDLR degradation. However, how exactly the LRs contribute to PCSK9’s action on the receptor is not completely understood. Here, we found that substitution of Asp at position 172 in the linker between the LR4 and LR5 of full-length LDLR with Asn (D172N) reduced PCSK9 binding at pH 7.4 (mimic cell surface), but not at pH 6.0 (mimic endosomal environment). On the other hand, mutation of Asp at position 203 in the LR5 of full-length LDLR to Asn (D203N) significantly reduced PCSK9 binding at both pH 7.4 and pH 6.0. D203N also significantly reduced the ability of LDLR to mediate cellular LDL uptake, whereas D172N had no detectable effect. These findings indicate that amino acid residues in the LRs of LDLR play an important role in PCSK9 binding to the receptor.

Dataset on assessment of magnesium isoglycyrrhizinate injection for dairy diet and body weight in fructose-induced metabolic syndrome of rats

The data presented herein are related to the research article entitled “Magnesium isoglycyrrhizinate blocks fructose-induced hepatic NF-κB/NLRP3 inflammasome activation and lipid metabolism disorder” (Zhao et al., 2017) [1]. This article describes the effects of magnesium isoglycyrrhizinate on 24-h food or water intake in fructose-fed rats at 15-week. In addition, this article expands the effect of magnesium isoglycyrrhizinate on the animal body weight change during 1–17 week. The field dataset is made publicly available to enable critical or extended analyzes.

Hypercholesterolemia, low density lipoprotein receptor and proprotein convertase subtilisin/kexin-type 9

Atherosclerotic cardiovascular disease is the main cause of mortality and morbidity in the world. Plasma levels of low density lipoprotein cholesterol (LDL-C) are positively correlated with the risk of atherosclerosis. High plasma LDL concentrations in patients with hypercholesterolemia lead to build-up of LDL in the inner walls of the arteries, which becomes oxidized and promotes the formation of foam cells, consequently initiating atherosclerosis. Plasma LDL is mainly cleared through the LDL receptor (LDLR) pathway. Mutations in the LDLR cause familiar hypercholesterolemia and increase the risk of premature coronary heart disease. The expression of LDLR is regulated at the transcriptional level via the sterol regulatory element binding protein 2 (SREBP-2) and at the posttranslational levels mainly through proprotein convertase subtilisin/kexin-type 9 (PCSK9) and inducible degrader of the LDLR (IDOL). In this review, we summarize the latest advances in the studies of PCSK9.

Caveolin-1 plays a key role in the oleanolic acid-induced apoptosis of HL-60 cells

Our previous study found that caveolin-1 (CAV-1) protein expression is upregulated during oleanolic acid (OA)-induced inhibition of proliferation and promotion of apoptosis in HL-60 cells. CAV-1 is the main structural protein component of caveolae, playing important roles in tumorigenesis and tumor development. It has been shown that cav-1 expression is lower in leukemia cancer cell lines SUP-B15, HL-60, THP-1 and K562 and in chronic lymphocytic leukemia primary (CLP) cells when compared with normal white blood cells, with the lowest cav-1 expression level found in HL-60 cells. To study the effects of cav-1 in HL-60 cells and the effects of cav-1 overexpression on OA drug efficacy, cav-1 was overexpressed in HL-60 cells using lentiviral-mediated transfection combined with OA treatment. The results showed that cav-1 overexpression inhibited HL-60 cell proliferation, promoted apoptosis, arrested the cell cycle in the G1 phase and inhibited activation of the PI3K/AKT/mTOR signaling pathway. Overexpression of CAV-1 also increased HL-60 cell sensitivity to OA. To further verify whether OA affects HL-60 cells via the activation of downstream signaling pathways by CAV-1, cav-1 gene expression was silenced using RNAi, and the cells were treated with OA to examine its efficacy. The results showed that after cav-1 silencing, OA had little effect on cell activity, apoptosis, the cell cycle and phosphorylation of HL-60 cells. This study is the first to show that CAV-1 plays a crucial role in the effects of OA on HL-60 cells.

ATP-binding cassette transporters and cholesterol translocation

Cholesterol, a major component of mammalian cell membranes, plays important structural and functional roles. However, accumulation of excessive cholesterol is toxic to cells. Aberrant cholesterol trafficking and accumulation is the molecular basis for many diseases, such as atherosclerotic cardiovascular disease and Tangier's disease. Accumulation of excessive cholesterol is also believed to contribute to the early onset of Alzheimer's disease. Thus, cellular cholesterol homeostasis is tightly regulated by uptake, de novo synthesis, and efflux. Any surplus of cholesterol must either be stored in the cytosol in the form of esters or released from the cell. Recently, several ATP-binding cassette (ABC) transporters, such as ABCA1, ABCG1, ABCG5, and ABCG8 have been shown to play important roles in the regulation of cellular cholesterol homeostasis by mediating cholesterol efflux. Mutations in ABC transporters are associated with several human diseases. In this review, we discuss the physiological roles of ABC transporters and the underlying mechanisms by which they mediate cholesterol translocation.

Anti-Helicobacter pylori compounds from the ethanol extracts of Geranium wilfordii

ETHNOPHARMOCOLOGICAL RELEVANCE: Geranium wilfordii Maxim has been extensively used in Chinese Herbal Medicine for treating gastrointestinal disorders, diarrhea and dysentery. In the current study we aimed to investigate the anti-Helicobacter pylori activity of ethanol extracts of Geranium wilfordii Maxim and its main active compounds, corilagin and 1,2,3,6-tetra-O-galloyl-β-D-glucose.

MATERIALS AND METHODS

The plant materials were extracted three times with ethanol and the concentrated filtrate was successively fractioned into chloroform, ethyl acetate, and n-BuOH-soluble portions which were examined in vitro for the anti-Helicobacter. pylori activity. Employing a standard strain and five clinical isolates of Helicobacter pylori, the extract, fractions and compounds of Geranium wilfordii Maxim were assessed in vitro.

RESULTS

The ethanol fraction, ethyl acetate fraction, corilagin, and 1,2,3,6-tetra-O-galloyl-β-D-glucose were found to be strongly inhibitory to Helicobacter. pylori (MICs: 40, 30, 4, and 8μg/ml respectively).

CONCLUSIONS

The results of the present study showed that the ethanol and the ethyl acetate extracts from Geranium wilfordii Maxim displayed as well the most significant inhibition to the growth of Helicobacter. pylori, of which corilagin and 1,2,3,6-tetra-O-galloyl-β-D-glucose have been identified main anti-Helicobacter pylori active constituents.

ATP-binding cassette transporters and cholesterol translocation

Cholesterol, a major component of mammalian cell membranes, plays important structural and functional roles. However, accumulation of excessive cholesterol is toxic to cells. Aberrant cholesterol trafficking and accumulation is the molecular basis for many diseases, such as atherosclerotic cardiovascular disease and Tangier's disease. Accumulation of excessive cholesterol is also believed to contribute to the early onset of Alzheimer's disease. Thus, cellular cholesterol homeostasis is tightly regulated by uptake, de novo synthesis, and efflux. Any surplus of cholesterol must either be stored in the cytosol in the form of esters or released from the cell. Recently, several ATP-binding cassette (ABC) transporters, such as ABCA1, ABCG1, ABCG5, and ABCG8 have been shown to play important roles in the regulation of cellular cholesterol homeostasis by mediating cholesterol efflux. Mutations in ABC transporters are associated with several human diseases. In this review, we discuss the physiological roles of ABC transporters and the underlying mechanisms by which they mediate cholesterol translocation. © 2013 IUBMB Life, 2013.

[Breast cancer resistance protein and diabetes]

Diabetes is a group of systematic metabolic diseases. In addition to cytochromes P450s, some ATP-binding cassette drug transporters are also under diabetic conditions. Breast cancer resistance protein (BCRP) , an important member of ATP-binding cassette drug transporters, expressed in most of the tissues, is thought to play an important protective role in normal tissues. It was reported that BCRP function and expression were impaired in intestine of diabetes rats, which affects the absorption and efflux of some drugs. Therefore, the alteration of BCRP expression and activity could be of critical importance for the treatment of diabetes mellitus. In this article, we reviewed the relationship between diabetes and

Using an abnormal increase in postexercise systolic blood pressure to diagnose coronary artery disease in gerontal patients

Data from 66 patients ≥ 60 years old with suspected coronary artery disease (CAD) were studied to determine the diagnostic value of an abnormal increase in postexercise systolic blood pressure (SBP) for detecting CAD in gerontal patients. Treadmill exercise testing (TET) and selective coronary angiography (CAG) were carried out and SBP was measured pre-TET and at each minute during a 6-min post-TET recovery phase. Abnormal increase in postexercise SBP was defined as a higher SBP compared with that measured earlier during the 6-min post-TET period. An abnormal increase of ≥ 7 mmHg in postexercise SBP had a statistically significantly better specificity, and also showed higher sensitivity and accuracy, than ST-segment depression ≥ 1 mV in identifying gerontal patients with CAD. The combination of ST-segment depression and abnormal SBP resulted in further improvement of the specificity for detecting CAD. It is concluded that measurement of abnormal increase in postexercise SBP may be a sensitive indicator of gerontal CAD.

Fraxinellone

In the title compound, C₁₄H₁₆O₃ [systematic name: (3R*,3aR*)-3-(3-furan­yl)-3a,7-dimethyl-3a,4,5,6-tetra­hydro-2-benzofuran-1(3H)-one], the pendant methyl and furan groups attached to the stereogenic centres lie to the same side of the fused ring system. The dihedral angle between the five-membered rings is 74.8 (2)°; the fused five-membered ring adopts a twisted conformation. In the crystal, mol­ecules are linked by weak C—H⋯O inter­actions, which generate [100] chains.

A Highly Stereoselective Synthesis of Stilbenes under Solvent-Free Conditions

A highly stereoselective synthesis of stilbenes ( trans-1,2-diarylethylenes) was achieved under solvent-free conditions from aryl-aldehydes and aromatic substances bearing an activated methyl group in the presence of anhydrous K2CO3 and poly(ethylene glycol). This method avoided the need for completely anhydrous condition and use of a noxious organic solvent.

[Application of apparent diffusion coefficient and fractional anisotropy in identification of tumor component and grading of brain astrocytoma]

OBJECTIVE

To evaluate the value of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in identification of tumor element and grading of brain astrocytoma.

METHODS

Thirty-three patients with histologically confirmed astrocytoma underwent diffusion weighted imaging (DWI), diffusion tensor imaging (DTI), and conventional MRI before operation. The values of ADC and FA of different regions in the same tumor and of astrocytoma of different grades were measured and compared.

RESULTS

The ADC values of the tumor parenchyma, necrotic region, peritumoral edema region were (1.28 +/- 0.44), (1.97 +/- 0.53), and (1.74 +/- 0.47) respectively, all significantly higher than that of the corresponding normal brain tissues [(0.80 +/- 0.18), P = 0.009, P = 0.000, P = 0.000] with significantly differences between the tumor parenchyma and necrotic region and peritumoral edema region (both P < 0.05), however, there was not significant difference between the necrotic region and peritumoral edema region. The FA values of the tumor parenchyma, necrotic region, and peritumoral edema region were (0.18 +/- 0.07), (0.14 +/- 0.05), and (0.16 +/- 0.05) respectively, all significantly higher than that of the corresponding normal brain tissues [(0.58 +/- 0.10), all P = 0.000], without significant differences among the former 3 groups. There were no significant differences in the ADC and FA values among the tumors at different grades, however, there was a tendency of ADC to decrease and of FA to increase along the increase of grade of tumor, although not significantly.

CONCLUSION

ADC value plays an important part in distinguishing tumor components and determining tumor boundary, and plays a certain role in judging the grade of astrocytomas. FA value is vital to determine the tumor boundary, and has certain value in differentiating high-grade from low-grade astrocytomas.

Mutational analysis of polar amino acid residues within predicted transmembrane helices 10 and 16 of multidrug resistance protein 1 (ABCC1): effect on substrate specificity

Human multidrug resistance protein 1 (MRP1) has a total of 17 transmembrane (TM) helices arranged in three membrane-spanning domains, MSD0, MSD1, and MSD2, with a 5 + 6 + 6 TM configuration. Photolabeling studies indicate that TMs 10 and 11 in MSD1 and 16 and 17 in MSD2 contribute to the substrate binding pocket of the protein. Previous mutational analyses of charged and polar amino acids in predicted TM helices 11, 16, and 17 support this suggestion. Mutation of Trp(553) in TM10 also affects substrate specificity. To extend this analysis, we mutated six additional polar residues within TM10 and the remaining uncharacterized polar residue in TM16, Asn(1208). Although mutation of Asn(1208) was without effect, two of six mutations in TM10, T550A and T556A, modulated the drug resistance profile of MRP1 without affecting transport of leukotriene C4, 17beta-estradiol 17-(beta-d-glucuronide) (E(2)17betaG), and glutathione. Mutation T550A increased vincristine resistance but decreased doxorubicin resistance, whereas mutation T556A decreased resistance to etoposide (VP-16) and doxorubicin. Although conservative mutation of Tyr(568) in TM10 to Phe or Trp had no apparent effect on substrate specificity, substitution with Ala decreased the affinity of MRP1 for E(2)17betaG without affecting drug resistance or the transport of other substrates tested. These analyses confirm that several amino acids in TM10 selectively alter the substrate specificity of MRP1, suggesting that they interact directly with certain substrates. The location of these and other functionally important residues in TM helices 11, 16, and 17 is discussed in the context of an energy-minimized model of the membrane-spanning domains of MRP1.

Transmembrane helix 11 of multidrug resistance protein 1 (MRP1/ABCC1): identification of polar amino acids important for substrate specificity and binding of ATP at nucleotide binding domain 1

Human multidrug resistance protein 1 (MRP1) is an ATP binding cassette (ABC) transporter that confers resistance to many natural product chemotherapeutic agents and can transport structurally diverse conjugated organic anions. MRP1 has three polytopic transmembrane domains (TMDs) and a total of 17 TM helices. Photolabeling and mutagenesis studies of MRP1 indicate that TM11, the last helix in the second TMD, may form part of the protein's substrate binding pocket. We have demonstrated that certain polar residues within a number of TM helices, including Arg(593) in TM11, are determinants of MRP1 substrate specificity or overall activity. We have now extended these analyses to assess the functional consequences of mutating the remaining seven polar residues within and near TM11. Mutations Q580A, T581A, and S585A in the predicted outer leaflet region of the helix had no detectable effect on function, while mutation of three residues close to the membrane/cytoplasm interface altered substrate specificity. Two of these mutations affected only drug resistance. N597A increased and decreased resistance to vincristine and VP-16, respectively, while S605A decreased resistance to vincristine, VP-16 and doxorubicin. The third, S604A, selectively increased 17beta-estradiol 17-(beta-d-glucuronide) (E(2)17betaG) transport. In contrast, elimination of the polar character of the residue at position 590 (Asn in the wild-type protein) uniformly impaired the ability of MRP1 to transport potential physiological substrates and to confer resistance to three different classes of natural product drugs. Kinetic and photolabeling studies revealed that mutation N590A not only decreased the affinity of MRP1 for cysteinyl leukotriene 4 (LTC(4)) but also substantially reduced the binding of ATP to nucleotide binding domain 1 (NBD1). Thus, polar interactions involving residues in TM11 influence not only the substrate specificity of MRP1 but also an early step in the proposed catalytic cycle of the protein.

Functional importance of polar and charged amino acid residues in transmembrane helix 14 of multidrug resistance protein 1 (MRP1/ABCC1): identification of an aspartate residue critical for conversion from a high to low affinity substrate binding state

Human multidrug resistance protein 1 (MRP1) confers resistance to many chemotherapeutic agents and transports diverse conjugated organic anions. We previously demonstrated that Glu1089 in transmembrane (TM) 14 is critical for the protein to confer anthracycline resistance. We have now assessed the functional importance of all polar and charged amino acids in this TM helix. Asn1100, Ser1097, and Lys1092, which are all predicted to be on the same face of the helix as to Glu1089, are involved in determining the substrate specificity of the protein. Notably, elimination of the positively charged side chain of Lys1092, increased resistance to the cationic drugs vincristine and doxorubicin, but not the electroneutral drug etoposide (VP-16). In addition, mutations S1097A and N1100A selectively decreased transport of 17beta-estradiol 17-(beta-d-glucuronide) (E217betaG) but not cysteinyl leukotriene 4 (LTC4), demonstrating the importance of multiple residues in this helix in determining substrate specificity. In contrast, mutations of Asp1084 that eliminate the carboxylate side chain markedly decreased resistance to all drugs tested, as well as transport of both E217betaG and LTC4, despite the fact that LTC4 binding was unaffected. We show that these mutations prevent the ATP-dependent transition of the protein from a high to low affinity substrate binding state and drastically diminish ADP trapping at nucleotide binding domain 2. Based on results presented here and crystal structures of prokaryotic ATP binding cassette transporters, Asp1084 may be critical for interaction between the cytoplasmic loop connecting TM13 and TM14 and a region of nucleotide binding domain 2 between the conserved Walker A and ABC signature motifs.

Characterization of the role of polar amino acid residues within predicted transmembrane helix 17 in determining the substrate specificity of multidrug resistance protein 3

Human multidrug resistance protein (MRP) 3 is the most closely related homologue of MRP1. Like MRP1, MRP3 confers resistance to etoposide (VP-16) and actively transports 17 beta-estradiol 17-(beta-D-glucuronide) (E(2)17 beta G), cysteinyl leukotriene 4 (LTC(4)), and methotrexate, although with generally lower affinity. Unlike MRP1, MRP3 also transports monovalent bile salts. We have previously demonstrated that hydrogen-bonding residues predicted to be in the inner-leaflet spanning segment of transmembrane (TM) 17 of MRP1 are important for drug resistance and E(2)17 beta G transport. We have now examined the importance of the hydrogen-bonding potential of residues in TM17 of MRP3 on both substrate specificity and overall activity. Mutation S1229A reduced only methotrexate transport. Mutations S1231A and N1241A decreased resistance to VP-16 and transport of E(2)17 beta G and methotrexate but not taurocholate. Mutation Q1235A also reduced resistance to VP-16 and transport of E(2)17beta G but increased taurocholate transport without affecting transport of methotrexate. Mutations Y1232F and S1233A reduced resistance to VP-16 and the transport of all three substrates tested. In contrast, mutation T1237A markedly increased VP-16 resistance and transport of all substrates. On the basis of the substrates analyzed, residues Ser(1229), Ser(1231), Gln(1235), and Asn(1241) play an important role in determining the specificity of MRP3, while mutation of Tyr(1232), Ser(1233), and Thr(1237) affects overall activity. Unlike MRP1, the involvement of polar residues in determining substrate specificity extends throughout the TM helix. Furthermore, elimination of the hydrogen-bonding potential of a single amino acid, Thr(1237), markedly enhanced the ability of the protein to confer drug resistance and to transport all substrates examined.

The role of NO and B-50 in neurotoxicity of excitatory amino acids

To investigate the direct evidence for the role which nitric oxide (NO) plays in the neurotoxicity of excitatory amino acids, we evaluated NO level by Greiss testing solution when glutamate (Glu) and kainate (KA) induced neuronal degeneration in primary cortical cultures. Glutamate-induced neurotoxicity was accompanied by a rise in NO. 5 mM hemoglobin (Hb) led to a decrease of NO content and prevented excitotoxicity induced by 1 mM glutamate. 1 mM L-arginine (L-Arg) reversed the effect of hemoglobin by raising the NO level. No change in NO content was found in KA-induced neurotoxicity, which was not affected by L-Arg, Hb or L-Arg + Hb. It is suggested that NO plays an important role in glutamate-, but not KA-induced neurotoxicity in primary cortical cultures. We also investigated the effects of glutamate on a growth-associated protein, B-50. The B-50 level declined significantly 24 h after exposure to 100 microM glutamate for 30 min and then recovered 2 days later. The effect of glutamate on B-50 was concentration-dependent. This indicates that B-50 might be involved in both glutamate neurotoxicity and the following neuronal repair process.

Nerve growth factors prevent glutamate toxicity in cortical neuronal cultures

AIM

To determine if nerve growth factors (NGF) can protect against glutamate-induced cortical neuron damage.

METHODS

Neuron viability and lactate dehydrogenase (LDH) efflux in the bathing medium in primary cultures from 17-d-old mouse fetal cortex were measured to assay NGF effect. Imaging of the calcium indicator dye Fura-2 was used to measure the [Ca2+]i.

RESULTS

The LD50 for NGF-free glutamate was 0.2 mmol.L-1 (95% confidence limits 0-1.6 mmol.L-1). In the presence of NGF 60 micrograms.L-1, 59% of the neurons survived in glutamate 1.6 mmol.L-1. The protective effect afforded by NGF was maximal at 60 micrograms.L-1, at which it prevented the elevation in [Ca2+]i.

CONCLUSION

NGF protect cortical neurons against glutamate-induced toxicity via "stabilizing" [Ca2+]i level or suppression of the rise in [Ca2+]i.

[Effects of morphine on monosodium glutamate neurotoxicity and its mechanism]

The enhancing effects of morphine on monosodium glutamate (MSG) neurotoxicity and its blocking by naloxone were studied through morphological observation, together with detection of concentrations of intracellular free Ca2+ ([Ca2+]i) by Ca2+ indicator Fura-2/AM and lactate dehydrogenase (LDH) efflux in the bathing medium in primary cultures from 14-17 d old mouse fetal cortex. It was found that 10 min pre-incubation of young cortical neurons (7 day in vitro) with morphine 10(-7) or 10(-6) mol.L-1 substantially increased LDH release from 105.7% +/- 19.0% (treated with MSG alone) to 194.5% +/- 17.7% and 214.0% +/- 9.5% respectively after exposure to MSG 0.1 mmol.L-1, but pre-incubation with morphine (10(-7) or 10(-6) mol.L-1) plus naloxone (0.1 mmol.L-1) reversed the LDH release after treatment with the same concentration of MSG. Morphine (10(-7) or 10(-6) mol.L-1) produced little elevation of [Ca2+]i. However, when combined with MSG (0.1 mmol.L-1) morphine elevated the [Ca2+]i level much more than MSG alone. These results suggest that morphine markedly enhances excitotoxic neuron damage, which can be reversed by naloxone. Overloading of intracellular Ca2+ may be a simultaneous pathological mechanism underlying the neuronal damage and death that occur in excitatory toxicity.

Characterization of the gene encoding the largest subunit of Plasmodium falciparum RNA polymerase III

We report here the isolation, sequence analysis, structure, and expression of the gene encoding the largest subunit of RNA polymerase III (RPIII) from Plasmodium falciparum. The P. falciparum RPIII gene consists of 5 exons and 4 introns, is expressed in all of the asexual erythrocytic stages of the parasite as a 8.5-kb mRNA, and is present in a single copy on chromosome 13. The predicted 2339 amino acid residue RPIII subunit contained 5 regions that were conserved between different eukaryotic RPIII subunits, and 4 variable regions that separated the conserved regions. Three of the variable regions were greatly enlarged in comparison to the corresponding variable regions in other RPIII subunits. Variable region C' represented nearly one-third of the P. falciparum RPIII subunit (750 amino acid residues), included a unique repeated decapeptide sequence, and had some homology with yeast DNA topoisomerase II. Noteworthy amino acid sequences and structures were identified in both the conserved regions and in the enlarged variable regions, and their possible role(s) as domains that regulate RPIII enzyme activity is discussed.

Mutant dihydrofolate reductase-thymidylate synthase genes in pyrimethamine-resistant Plasmodium falciparum with polymorphic chromosome duplications

We have identified dihydrofolate reductase (DHFR) gene point mutations and chromosomal changes in pyrimethamine-resistant mutants selected in vitro of Plasmodium falciparum strain FCR3. A pyrimethamine-resistant derivative of the pyrimethamine-sensitive strain FCR3, FCR3-D8, that had been grown in the absence of pyrimethamine for an extended time, was grown in two concentrations of pyrimethamine, and surviving drug-resistant parasites were subcloned. One selected mutant, FCR3-D81, that grew at 1 X 10(-6) M pyrimethamine, contained a single point mutation in the DHFR domain which caused an amino acid change (Phe to Ser) at amino acid 223, whereas another mutant, FCR3-D85, that grew at 5 X 10(-6) M pyrimethamine had that same mutation and an additional point mutation that changed amino acid 54 (Asp to Asn). The selection of FCR3-D85, whose nucleotide sequence was identical to that previously reported for FCR3-D8, confirmed that the original FCR3-D8 parasite population had changed during extended growth in vitro in the absence of drug pressure. FCR3-D81 and FCR3-D85 cells contained different pairs of polymorphic chromosomes that hybridized to a DHFR-TS probe as well as to three other chromosome 4 specific DNAs, indicating that at least part of chromosome 4 had been duplicated and that these parasites were aneuploid with 15 rather than 14 chromosomes. The mutant DHFR-TS genes were diploid. We consider the roles of the polymorphic chromosome duplications and DHFR point mutation(s) as causes of pyrimethamine resistance.

Dihydrofolate reductase mutations and chromosomal changes associated with pyrimethamine resistance of Plasmodium falciparum

The nucleotide sequence of the dihydrofolate reductase-thymidylate synthase (DHFR-TS) gene in pyrimethamine-resistant (PyrR) mutants of Plasmodium falciparum selected in vitro was examined to determine if specific mutations in DHFR were associated with drug resistance. We analysed the sequence of genomic DNA from strain FCR3, from eight previously isolated PyrR parasites derived from FCR3, and from strain Honduras-1. We found that: (1) five PyrR FCR3 mutants, FCR3-D4-D8, had an identical nucleotide change and a novel single amino acid change (Phe to Ser) at amino acid 223 of DHFR; (2) our originally reported nucleotide sequence of the DHFR-TS gene was of the PyrR strain Honduras-1, and was not of FCR3; (3) three PyrR mutants, FCR3-D1, D2, and D3, thought to have been derived from the FCR3 strain, were in fact isolates of Honduras-1. We also examined the chromosomal DNA of PyrR mutants by pulsed-field gradient gel (PFG) electrophoresis. The PyrR mutants FCR3-D1, D2, and D3 had several chromosome size polymorphisms compared to FCR3. In two of the PyrR FCR3 mutants, FCR3-D7 and D8, the chromosome 4-size DNA of FCR3 that the DHFR-TS probe normally hybridised to was not observed. Instead, in FCR3-D7, a chromosome larger than the chromosome 4-size DNA was observed to hybridise to the DHFR-TS probe. In FCR3-D8, two chromosomes that hybridised to the DHFR-TS probe were found. One of them was larger than FCR-3 chromosome 4-size DNA, and the other was smaller than FCR3 chromosome 1-size DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

An enlarged largest subunit of Plasmodium falciparum RNA polymerase II defines conserved and variable RNA polymerase domains

We have isolated the gene encoding the largest subunit of RNA polymerase II from Plasmodium falciparum. The RPII gene is expressed in the asexual erythrocytic stages of the parasite as a 9 kb mRNA, and is present as a single copy gene located on chromosome 3. The P. falciparum RPII subunit is the largest (2452 amino acids) eukaryotic RPII subunit, and it contains enlarged variable regions that clearly separate and define five conserved regions of the eukaryotic RPII largest subunits. A distinctive carboxyl-terminal domain contains a short highly conserved heptapeptide repeat domain which is bounded on its 5' side by a highly diverged heptapeptide repeat domain, and is bounded on its 3' side by a long carboxyl-terminal extension.

Premature release of Plasmodium falciparum from swollen erythrocytes induced by some antimalarials

Qinghaosu and chloroquine, but not pyrimethamine, treatment of Plasmodium falciparum cultures resulted in the formation of swollen red blood cells (RBCs) and the expulsion of degenerate trophozoites and schizonts, but not ring-stage parasites, from the infected RBCs. The parasite release resulted in the formation of RBCs with holes, that had otherwise retained their structural integrity. Membranes of swollen RBCs and their ghosts associated with parasites were efficiently visualized by Giemsa staining of thin smears for 18-24 hr but not by standard Giemsa staining for 20 min.