Significant decrease of facial cellulitis admissions during COVID-19 lockdown in France: A multicentric comparative study

During the 2020 coronavirus pandemic, a lockdown was imposed in France during the first wave. An apparent decrease in incidence of cellulitis of odontogenic origin was noticed then. This study aimed to compare the incidence of cellulitis during this extraordinary period with the same period in 2018 and 2019, based on retrospective multicentric data. All maxillofacial surgery departments in French public hospitals were contacted. Responders were asked to include all patients admitted for the surgical drainage of a head and neck abscess of odontogenic origin during the first 2020 lockdown period, and in a similar time frame in 2018 and 2019 (control group), based on screening the French diagnostic and therapeutic classification of medical acts. We report a 44% significant nationwide decrease in the incidence of admissions for cellulitis. There were 187 patients in 2020 for 334 and 333 patients in 2018/2019 respectively. The reasons to explain this finding are hypothetical (organizational reasons leading to earlier management, patients' fear to seek for medical management, usual excess in surgical indications or concomitant decrease of non-steroidal anti-inflammatory drugs delivery). Whatever the explanation, it would be of great interest to find it out in order to improve the prevention of cellulitis.

Thrombolytic Treatment with Tissue-type Plasminogen Activator (t-PA) Containing Liposomes in Rabbits: a Comparison with Free t-PA

In this study, we aimed at improving the therapeutic index of tissue- type Plasminogen Activator (t-PA) as thrombolytic agent in the treatment of myocardial infarction. Liposome-encapsulated t-PA was tested in a rabbit jugular vein thrombosis model: administration of free t-PA (t-PA) as a bolus injection in the ear vein was compared to a similar administration of liposomal t-PA (t-PA-lip), liposomal t-PA in plasminogen-coated liposomes (Plg-t-PA-lip), a mixture of free t-PA and empty liposomes (t-PA+empty lip) and a saline-blank (blank) in terms of thrombolytic activity and side effects.

Liposomal t-PA (t-PA-lip/Plg-t-PA-lip) showed a significantly better thrombolysis efficiency than equimolar doses of free t-PA (t-PA/ t-PA+ empty lip): about 0.24 mg/kg of liposomal t-PA practically equalled the lysis-activity of a dose of free t-PA of 1.0 mg/kg (t-PAlmg/kg). On the other hand, liposome encapsulation did not affect the systemic activation of alpha2-antiplasmin and plasminogen by t-PA.

We conclude that for this model an improvement in thrombolytic efficacy of t-PA is achieved by liposome encapsulation of t-PA. As t-PA-lip and Plg-t-PA-lip -treatment induced similar results, targeting of liposomal t-PA by coupled glu-Plg remains a topic to be optimized in future studies.

Fibrin Binding of Plasminogen Coated Liposomes In Vitro

In this study, the fibrin binding properties of liposomes containing a number of plasminogen (Pig) molecules on the outside were compared to those of free (non-liposomal) Pig in an in vitro model system. Fibrin monolayer coated 96-wells plates were used, containing fibrin monomer at a density of around 3.4 to 3.9 × 10-4 nmol/cm2. These densities are similar to liposomal Plg-densities, thus allowing multivalent interactions to occur.

In the panel of experimental conditions that was chosen, binding of free Pig and liposomes with Pig showed three main differences in characteristics. Firstly, in the fibrin binding of Plg-liposomes not all Pig may be involved, but on the average 40% of the total amount of liposomal Pig. This was shown by lysing the liposomes after binding to the fibrin and estimation of truly bound Pig. With Plg-densities on the liposomes below the fibrin binding sites density, the maximal number of bound Pig molecules remains below the amount of available fibrin binding sites. Secondly, a higher binding rate by at least one order of magnitude was observed for liposomes with Pig compared to free Pig. Thirdly, liposomes with Pig exhibit a fibrin binding affinity which increases with Plg-density, because of the multivalent character of interaction. Liposomal Pig can successfully compete for fibrin binding sites with a 100 fold higher concentration of free Pig.

These in vitro findings indicate that in view of avid and rapid fibrin binding, liposomes with attached plasminogen may be suitable for in vivo targeting to fibrin based thrombi.

Clot Accumulation Characteristics of Plasminogen-bearing Liposomes in a Flow-system

In this study, the clot accumulation properties of liposome-coupled plasminogen were compared to those of free (non-liposomal) plasminogen in an in vitro, closed-loop, flow-system. After introduction of a clot into the closed system, double-radiolabelled plasminogen-liposomes were administered and the accumulation of radiolabel on the entire clot was measured.

Liposomal plasminogen showed improved accumulation over free plasminogen, on both a fibrin clot and a whole blood clot. Moreover, once liposomal plasminogen was fibrin associated, it could not be washed away with buffer, in contrast to free plasminogen. Liposomal plasminogen was able to compete successfully with an excess of free plasminogen. The plateau levels for the accumulated amount of plasminogen depended on the incubated amount of plasminogen and were influenced by partial degradation of the clot. Furthermore, it was shown that a threshold liposomal plasminogen surface-density was needed for optimum clot accumulation.

A novel method to label liposomes with 99mTc by the hydrazino nicotinyl derivative

In this study a new 99mTc labeling method for polyethyleneglycol (PEG)-coated liposomes is described. The in vitro and in vivo characteristics were compared with the conventional 99mTc-HMPAO-labeled PEG-coated liposomes.

METHODS

PEG-coated liposomes were labeled with 99mTc by the hydrazino nicotinyl (HYNIC) derivative of distearoylphosphatidyl-ethanolamine (DSPE) and compared with PEG-coated liposomes labeled with 99mTc-HMPAO. In vitro stability tests were performed. Biodistribution and imaging characteristics of both liposomal preparations were determined in rats with Staphylococcus aureus infection in the left calf muscle.

RESULTS

Per liposome, 230 hydrazine groups were incorporated. The labeling efficiency of the 99mTc-HYNIC liposomes was greater than 95%, so no postlabeling purification was required, in contrast to the 99mTc-HMPAO liposomes. The 99mTc-HYNIC liposomes showed greater in vitro stability than the conventional 99mTc-HMPAO liposomes. Abscess uptake of the 99mTc-HYNIC liposomes was significantly greater (1.74+/-0.38%ID/g versus 1.26+/-0.29%ID/g, 24 h postinjection, P < 0.03). Furthermore, kidney uptake of the 99mTc-HYNIC liposomes was one third of the uptake of the 99mTc-HMPAO liposomes (0.79+/-0.07%ID/g versus 2.47+/-0.35%ID/g, 24 h postinjection, P < 0.0001).

CONCLUSION

This new 99mTc-HYNIC-based labeling method for liposomes is rapid, efficient and easy to perform. Most importantly, the 99mTc-labeled liposomes have an improved stability and in vivo characteristics. The new labeling method is a major step forward toward a radiopharmaceutical for infection imaging that can be prepared in a one-step procedure within 15 min at room temperature and thus can be applied in every routine clinical practice.

Clot accumulation characteristics of plasminogen-bearing liposomes in a flow-system. Groningen Utrecht Institute for Drug Exploration

In this study, the clot accumulation properties of liposome-coupled plasminogen were compared to those of free (non-liposomal) plasminogen in an in vitro, closed-loop, flow-system. After introduction of a clot into the closed system, double-radiolabelled plasminogen-liposomes were administered and the accumulation of radiolabel on the entire clot was measured. Liposomal plasminogen showed improved accumulation over free plasminogen, on both a fibrin clot and a whole blood clot. Moreover, once liposomal plasminogen was fibrin associated, it could not be washed away with buffer, in contrast to free plasminogen. Liposomal plasminogen was able to compete successfully with an excess of free plasminogen. The plateau levels for the accumulated amount of plasminogen depended on the incubated amount of plasminogen and were influenced by partial degradation of the clot. Furthermore, it was shown that a threshold liposomal plasminogen surface-density was needed for optimum clot accumulation.

Fibrin binding of plasminogen coated liposomes in vitro

In this study, the fibrin binding properties of liposomes containing a number of plasminogen (Plg) molecules on the outside were compared to those of free (non-liposomal) Plg in an in vitro model system. Fibrin monolayer coated 96-wells plates were used, containing fibrin monomer at a density of around 3.4 to 3.9 x 10(-4) nmol/cm2. These densities are similar to liposomal Plg-densities, thus allowing multivalent interactions to occur. In the panel of experimental conditions that was chosen, binding of free Plg and liposomes with Plg showed three main differences in characteristics. Firstly, in the fibrin binding of Plg-liposomes not all Plg may be involved, but on the average 40% of the total amount of liposomal Plg. This was shown by lysing the liposomes after binding to the fibrin and estimation of truly bound Plg. With Plg-densities on the liposomes below the fibrin binding sites density, the maximal number of bound Plg molecules remains below the amount of available fibrin binding sites. Secondly, a higher binding rate by at least one order of magnitude was observed for liposomes with Plg compared to free Plg. Thirdly, liposomes with Plg exhibit a fibrin binding affinity which increases with Plg-density, because of the multivalent character of interaction. Liposomal Plg can successfully compete for fibrin binding sites with a 100 fold higher concentration of free Plg. These in vitro findings indicate that in view of avid and rapid fibrin binding, liposomes with attached plasminogen may be suitable for in vivo targeting to fibrin based thrombi.

Thrombolytic treatment with tissue-type plasminogen activator (t-PA) containing liposomes in rabbits: a comparison with free t-PA

In this study, we aimed at improving the therapeutic index of tissue-type Plasminogen Activator (t-PA) as thrombolytic agent in the treatment of myocardial infarction. Liposome-encapsulated t-PA was tested in a rabbit jugular vein thrombosis model: administration of free t-PA (t-PA) as a bolus injection in the ear vein was compared to a similar administration of liposomal t-PA (t-PA-lip), liposomal t-PA in plasminogen-coated liposomes (Plg-t-PA-lip), a mixture of free t-PA and empty liposomes (t-PA+ empty lip) and a saline-blank (blank) in terms of thrombolytic activity and side effects. Liposomal t-PA (t-PA-lip/Plg-t-PA-lip) showed a significantly better thrombolysis efficiency than equimolar doses of free t-PA (t-PA/ t-PA+ empty lip): about 0.24 mg/kg of liposomal t-PA practically equalled the lysis-activity of a dose of free t-PA of 1.0 mg/kg (t-PA1mg/kg). On the other hand, liposome encapsulation did not affect the systemic activation of alpha 2-antiplasmin and plasminogen by t-PA. We conclude that for this model an improvement in thrombolytic efficacy of t-PA is achieved by liposome encapsulation of t-PA. As t-PA-lip and Plg-t-PA-lip -treatment induced similar results, targeting of liposomal t-PA by coupled glu-Plg remains a topic to be optimized in future studies.

The preparation of tissue-type Plasminogen Activator (t-PA) containing liposomes: entrapment efficiency and ultracentrifugation damage

In this study, a method was developed for the efficient entrapment of active tissue-type Plasminogen Activator (t-PA) into liposomes. Experimental conditions were varied to optimize t-PA entrapment: different buffer solutions were used (pH 4 and 7.5), the effect of the incubation concentrations of phospholipid (PL) and t-PA was monitored and the influence of liposome-size was examined. Furthermore, the effect of ultracentrifugation on t-PA containing liposomes was determined in the presence and absence of Tween 80. t-PA entrapment strongly depended on experimental conditions and ranged from 30 up to 90%. Almost quantitative+ (90%) entrapment (entrapment percentage defined as absolute entrapment (IU t-PA/mumol PL) divided by total incubation ratio (IU t-PA/mumol PL), times 100%) was obtained in Hepes buffer pH 7.5, devoid of arginine, with low ionic strength. Ultracentrifugation, used for removal of non-entrapped t-PA, was shown to have a damaging effect on the liposomes (especially in the presence of 0.05% Tween 80), leading to t-PA loss. However, because acceptable alternatives were not available, ultracentrifugation was used during this study. Therefore, the encapsulation-percentage values shown in this study are in fact underestimates for the true entrapment of t-PA.

IN CONCLUSION

almost quantitative t-PA entrapment in liposomes can be achieved by selecting the proper milieu and inducing a strong interaction between t-PA and bilayer.

Impact of census error adjustments on state population projections: the case of Ohio

National undercount adjustment factors from the 1970 and 1980 U.S. censuses are used to prepare population projections for Ohio, which are in turn compared with unadjusted projections. "The findings suggest that decisions concerning adjustment factors have varying effects on short-term, long-term, and strategic forecasting. These effects are particularly salient for selected age-groups and the impact on state government budget decisions typically associated with these age-groups. We recommend that the effects of alternative adjustment possibilities be examined by state demographic centers and budget offices."