Cephalosporinase and penicillinase activities of a β-lactamase from Pseudomonas pyocyanea

1. Pseudomonas pyocyanea N.C.T.C. 8203 produces a beta-lactamase that is inducible by high concentrations of benzylpenicillin or cephalosporin C. Methicillin appeared to be a relatively poor inducer, but this could be attributed in part to its ability to mask the enzyme produced. Much of the enzyme is normally cell-bound. 2. No evidence was obtained that the crude enzyme preparation consisted of more than one beta-lactamase and the preparation appeared to contain no significant amount of benzylpenicillin amidase or of an acetyl esterase. 3. The maximum rate of hydrolysis of cephalosporin C and several other derivatives of 7-aminocephalosporanic acid by the crude enzyme was more than five times that of benzylpenicillin. Methicillin, cloxacillin, 6-aminopenicillanic acid and 7-aminocephalosporanic acid were resistant to hydrolysis, and methicillin and cloxacillin were powerful competitive inhibitors of the action of the enzyme on easily hydrolysable substrates. 4. Cephalosporin C, cephalothin and cephaloridine yielded 2 equiv. of acid/mole on enzymic hydrolysis, and deacetylcephalorsporin C yielded 1 equiv./mole. Evidence was obtained that the opening of the beta-lactam ring of cephalosporin C and cephalothin is accompanied by the spontaneous expulsion of an acetoxy group and that of cephaloridine by the expulsion of pyridine. 5. A marked decrease in the minimum inhibitory concentration of benzylpenicillin and several hydrolysable derivatives of 7-aminocephalosporanic acid was observed when the size of the inoculum was decreased. This suggested that the production of a beta-lactamase contributed to the factors responsible for the very high resistance of Ps. pyocyanea to these substances. It was therefore concluded that the latter might show synergism with the enzyme inhibitors, methicillin and cloxacillin, against this organism.     

Hepato- and pneumotoxicity of pyrrolizidine alkaloids and derivatives in relation to molecular structure.

62 pyrrolizidine alkaloids and derivatives have been screened for acute and chronic hepato- and pneumotoxicity by the single dose method previously described. This procedure is satisfactory for the compounds of medium to high hepatotoxicity but failed to detect toxicity in certain other compounds of known, low hepatotoxicity. New findings significant in relation to hepatotoxicity are as follows: (i) On a molar basis, diesters of heliotridine and retronecine are about 4 times as toxic as the respective mono-esters and heliotridine esters are 2-4 times as toxic as retronecine esters. (ii) Crotanecine esters are less toxic than retronecine esters, and the 6,9-diester madurensine, 2-4 times less toxic than the 7,9-diester anacrotine (the difference being ascribed to there being only one reactive alkylating centre in the toxic metabolite from madurensine). (iii) Hepatotoxicity was confirmed for 7-angelylheliotridine but not observed for 9-angelyheliotridine and 7- and 9-angelylretronecine. (iv) Other significant compounds failing to induce hepatotoxicity were 9-pivalyl- and 7,9-dipivalyheliotridine, the alpha- and beta-epoxides of monocrotaline, 7-angelyl-1-methylenepyrrolizidine and the methiodides of monocrotaline and senecionine. The following compounds are readily converted by rat liver microsomes in vitro into dehydroheliotridine (or dehydroretronecine): 7- and 9-angelyheliotridine, 7- and 9-angelylretronecine, 7,9-dipivalylheliotridine and otosenine. 7,9-Divalerylheliotridine, the alpha- and beta-epoxides of monocrotaline, and retusamine yield pyrrolic metabolites more slowly. The preparation and characterisation of several alkaloid derivatives are described. Chronic lung lesions were produced by most compounds which gave chronic liver lesions, although a higher dose was required in some instances. This requirement may sometimes mean that chronic lung lesions cannot be induced because of the intervention of acute or peracute deaths. Apart from this factor, structure activity requirements for pneumotoxicity are the same as for hepatotoxicity, consistent with their being both caused by the same toxic metabolites.     

Localization in the cell cycle of the antimitotic action of the pyrrolizidine alkaloid,lasiocarpine and of its metabolite,dehydroheliotridine

The antimitotic action of the pyrrolizidine alkaloid lasiocarpine on rat liver parenchyma was investigated using as the experimental model the wave of mitosis produced in liver by a single dose of thioacetamide. A single low dose of lasiocarpine administered two weeks before the thioacetamide, almost completely inhibited the mitotic wave without inhibiting to the same extent the preceding wave of DNA synthesis. By the use of selective inhibitors and radioisotope labelling, the location of the mitotic block was found to be either in the latter half of the DNA synthetic phase, S, or early in G₂, the post-synthetic phase. The mitotic wave was similarly inhibited by pretreatment of the rats with a single injection of dehydroheliotridine, a pyrrolic metabolite of heliotridine-based pyrrolizidine alkaloids.     

Can fossil fuel energy be recovered and used without any CO2 emissions to the atmosphere?

Reviews in Environmental Science and Bio/Technology - The world’s energy system is still dominated by fossil fuels. While there is a rapid reduction in the cost of renewable energy and the...     

Longitudinal associations between BMI,waist circumference,and cardiometabolic risk in US youth: Monitoring implications

Objective:

This study examined whether change in body mass index (BMI) or waist circumference (WC) is associated with change in cardiometabolic risk factors and differences between cardiovascular disease specific and diabetes specific risk factors among adolescents. We also sought to examine any differences by gender or baseline body mass status.

Design:

The article is a longitudinal analysis of pre‐ and post‐data collected in the HEALTHY trial. Participants were 4,603 ethnically diverse adolescents who provided complete data at 6th and 8th grade assessments.

Methods:

The main outcome measures were percent change in the following cardiometabolic risk factors: fasting triglycerides, systolic and diastolic blood pressure, high density lipoprotein cholesterol, and glucose as well as a clustered metabolic risk score. Main exposures were change in BMI or WC z‐score. Models were run stratified by gender; secondary models were additionally stratified by baseline BMI group (normal, overweight, or obese).

Results:

Analysis showed that when cardiometabolic risk factors were treated as continuous variables, there was strong evidence (P < 0.001) that change in BMI z‐score was associated with change in the majority of the cardiovascular risk factors, except fasting glucose and the combined risk factor score for both boys and girls. There was some evidence that change in WC z‐score was associated with some cardiovascular risk factors, but change in WC z‐score was consistently associated with changes in fasting glucose.

Conclusions:

In conclusion, routine monitoring of BMI should be continued by health professionals, but additional information on disease risk may be provided by assessing WC.     

Similar hypotensive responses to resistance exercise with and without blood flow restriction

Low intensity resistance exercise (RE) with blood flow restriction (BFR) has gained attention in the literature due to the beneficial effects on functional and morphological variables, similar to those observed during traditional RE without BFR, while the effects of BFR on post-exercise hypotension remain unclear. The aim of the present study was to compare the blood pressure (BP) response of trained normotensive individuals to RE with and without BFR. In this cross-over randomized trial, eight male subjects (23.8 ± 4 years, 74 ± 3 kg, 174 ± 4 cm) completed two exercise protocols: traditional RE (3 x 10 repetitions at 70% one-repetition maximum [1-RM]) and low intensity RE (3 x 15 repetitions at 20% 1-RM) with BFR. Blood pressure measurements were performed after 15 min of seated rest (0), immediately after and 10 min, 20 min, 30 min, 40 min, 50 min and 60 min after the experimental sessions. Similar hypotensive effects for systolic BP (SBP) were observed for both protocols (P < 0.05) after exercise, with no differences between groups (P > 0.05) and no statistically significant difference for diastolic BP (P > 0.05). These results suggest that in normotensive trained individuals, both traditional RE and RE with BFR induce hypotension for SBP, which is important to prevent cardiovascular disturbances.     

Long-term treadmill exercise improves spatial memory of male APPswe/PS1dE9 mice by regulation of BDNF expression and microglia activation

Increasing evidence suggests that physical activity could delay or attenuate the symptoms of Alzheimer''s disease (AD). But the underlying mechanisms are still not fully understood. To investigate the effect of long-term treadmill exercise on the spatial memory of AD mice and the possible role of β-amyloid, brain-derived neurotrophic factor (BDNF) and microglia in the effect, male APPswe/PS1dE9 AD mice aged 4 months were subjected to treadmill exercise for 5 months with 6 sessions per week and gradually increased load. A Morris water maze was used to evaluate the spatial memory. Expression levels of β-amyloid, BDNF and Iba-1 (a microglia marker) in brain tissue were detected by immunohistochemistry. Sedentary AD mice and wildtype C57BL/6J mice served as controls. The results showed that 5-month treadmill exercise significantly decreased the escape latencies (P < 0.01 on the 4th day) and improved the spatial memory of the AD mice in the water maze test. Meanwhile, treadmill exercise significantly increased the number of BDNF-positive cells and decreased the ratios of activated microglia in both the cerebral cortex and the hippocampus. However, treadmill exercise did not significantly alleviate the accumulation of β-amyloid in either the cerebral cortex or the hippocampus of the AD mice (P > 0.05). The study suggested that long-term treadmill exercise could improve the spatial memory of the male APPswe/PS1dE9 AD mice. The increase in BDNF-positive cells and decrease in activated microglia might underpin the beneficial effect.