New Sakaguchi reaction

Melanin-like nanoparticles decorated with an autophagy-inducing peptide for efficient targeted photothermal therapy

Photothermal therapy efficiently ablates tumors via hyperthermia but inevitably induces serious side effects including thermal damage to normal tissues, inflammations and enhanced risk of tumor metastasis. In this study, we fabricated a dual peptide decorated melanin-like nanoparticle for tumor-targeted and autophagy-promoted photothermal therapy in pursuit of improved cancer treatment. The multifunctional nanoparticle was composed of dual peptide RGD- and beclin 1-modified and PEGylated melanin-like polydopamine nanoparticles. Beclin 1-derived peptide modified on the nanoparticle up-regulated autophagy in cancer cells and further sensitized the tumors to photothermal ablation. RGD decorated on the particle surface enhanced the selectivity and cellular uptake of polydopamine nanoparticles by breast cancer cells. In vivo therapeutic experiments revealed that the tumor-targeted and autophagy promotion-associated photothermal therapy efficiently regressed tumors at a low temperature around 43 °C. The study provides a novel and efficient strategy to improve the efficiency of photothermal therapy via the up-regulation of autophagy in tumor cells.

L-Arginine, nitric oxide, and intestinal secretion: studies in rat jejunum in vivo

BACKGROUND

L-Arginine has been shown to induce fluid secretion in human jejunum. Nitric oxide, a derivative of L-arginine is thought to have an important role as an intestinal secretagogue.

AIM

To determine the effect of L-arginine and the nitric oxide synthase inhibitor, nitro L-arginine methyl ester (L-NAME), on fluid and electrolyte movement in rat jejunum.

METHODS

A 25 cm segment of rat jejunum was perfused in situ with iso-osmotic solutions containing either (1) saline, (2) D-arginine 20, (3) L-arginine 20, (4) L-NAME 0.1, 1, or 20 mmol/l, or (5) a combination of L-arginine 20 and L-NAME 0.1, 1, or 20 mmol/l. In further groups the effect of a subcutaneous injection of L-NAME 100 mg/kg was examined in rats pretreated with either D-or L-arginine 500 mg/kg.

RESULTS

L-Arginine, unlike D-arginine, induced fluid secretion despite being better absorbed (mean -7.3 v 17.0 microliters/min/g; p < 0.01). L-NAME at 0.1 mmol/l had no effect on basal fluid movement but reversed L-arginine induced secretion (7.8; p < 0.05). L-NAME at 1 and 20 mmol/l induced fluid secretion (-15.4 and -28.4, respectively), which was enhanced by the addition of L-arginine (-30.0 and -41.0, respectively; both p < 0.05). A subcutaneous injection of L-NAME resulted in marked fluid secretion (-39.9) and histological evidence of intestinal ischaemia. These changes were attenuated or reversed by pretreatment with subcutaneous L- but not D-arginine.

CONCLUSIONS

L-arginine induces intestinal fluid secretion through production of nitric oxide. There is a delicate balance between the effect of nitric oxide as a secretagogue and its effect on maintaining blood flow and thus preventing intestinal ischaemia.

Regulation and coupling of argECBH mRNA and enzyme synthesis in cell extracts of Escherichia coli

Cell extracts from Escherichia coli were used to study both transcription and coupled translation of the argECBH gene cluster. Argininosuccinase (the argH enzyme) and N-acetylornithinase (the argE enzyme) were synthesized for 90 to 120 min, and hybridizable argECBH mRNA was synthesized for 60 min after the addition of a lambda or phi 80 dargECBH DNA template. L-Arginine (2.5 mM) repressed synthesis by argR+ extracts of argECBH mRNA 2-, to 3-fold, argE enzyme 5- to 8-fold, and argH enzyme 20- to 60-fold. Repression was specific for L-arginine, and argR extracts were insensitive to added L-arginine. The argECBH mRNA made under conditions of restricted protein synthesis had reduced ability to function in the formation of the argE and argH enzymes and was found to be predominantly 6 to 8S in sucrose density gradients. When protein synthesis was allowed, the mRNA formed was functional, and large amounts of 14 to 23S argECBH mRNA appeared on sucrose gradients. An S-100 supernatant freed of ribosomes was capable of producing hybridizable arg mRNA, but significant functional message was only produced when ribosomes were present. When purified RNA polymerase was used, the formation of short 6 to 8S argECBH mRNA was dependent upon added rho protein. The data suggest that rho-dependent sites in the argECBH operon allow early termination of mRNA synthesis when transcription is not coupled to active enzyme synthesis.

A fluorometric method for the specific determination of serum arginine with 2,3-naphthalenedicarbaldehyde

A specific and simple fluorometric method for the determination of serum arginine was developed which consists of (1) deproteinization of serum sample with 10% perchloric acid, (2) blocking thiol compounds with N-ethylmaleimide, (3) fluorescence reaction with 2,3-naphthalenedicarbaldehyde in 0.2 M borate buffer, pH 9.3, in the presence of beta-cyclodextrin (25 min at 20 degrees C, excitation wavelength: 462 nm, emission wavelength: 520 nm). Since the fluorescence reaction is highly specific for arginine, the method requires no other separation step. Linearity, recovery, and reproducibility of the method were found to be satisfactory.

Incorporation of DL-[2-14C]ornithine and DL-[5-14C]arginine in milk constituents by the isolated lactating sheep udder

1. Lactating mammary glands of sheep were perfused for several hours in the presence of dl-[2-(14)C]ornithine or dl-[5-(14)C]arginine and received adequate quantities of acetate, glucose and amino acids. 2. In the [(14)C]ornithine experiment 1.4% of the casein and 1% of the expired carbon dioxide came from added ornithine; 96% of the total radioactivity in casein was recovered in proline; 13% of the proline of casein originated from plasma ornithine. 3. In this experiment the results of chemical degradation of proline of casein as well as relative specific activities in the isolated products are consistent with the view that ornithine is metabolized, by way of glutamic gamma-semialdehyde, to proline or glutamic acid. 4. In the [(14)C]arginine experiments 3% of the casein and 1% of the expired carbon dioxide came from arginine; 84% of the arginine and 9% of the proline of casein originated from plasma arginine. 5. In these experiments the relative specific activities of arginine, ornithine and proline in plasma are in agreement with the view that arginine is metabolized by way of ornithine to proline. The conversion of arginine into ornithine is probably catalysed by arginase, so that arginase in mammary tissue may be involved in the process of milk synthesis.