Impact of removing the healthcare mask mandate on hospital-acquired COVID-19 rates.

BACKGROUND: Mandatory mask-wearing policies were one of several measures employed to reduce hospital-acquired SARS-CoV-2 infection throughout the pandemic. Many nations have removed healthcare mask mandates, but there remains a risk of new SARS-CoV-2 variants or epidemics of other respiratory viruses. AIM: To demonstrate the impact of removing the healthcare mask mandate. METHODS: SARS-CoV-2 infections were analysed in a large teaching hospital for 40 weeks in 2022 using a controlled interrupted time-series design. The intervention was the removal of a staff/visitor surgical mask-wearing policy for the most wards at week 26 (intervention group) with a subset of specific wards retaining the mask policy (control group). The hospital-acquired SARS-CoV-2 infection rate was adjusted by the underlying community infection rate. FINDINGS: In the context of a surge in SARS-CoV-2 infection, removal of the mask mandate for staff/visitors was not associated with a statistically significant change in the rate of nosocomial SARS-CoV-2 infection in the intervention group (incidence rate ratio: 1.105; 95% confidence interval: 0.523-2.334; P = 0.79) and there was no post-intervention trend (1.013; 0.932-1.100; P = 0.76) to suggest a delayed effect. The control group also showed no immediate or delayed change in infection rate. CONCLUSION: No evidence was found that removal of a staff/visitor mask-wearing policy had a significant effect on the rate of hospital-acquired SARS-CoV-2 infection. This does not demonstrate that masks were ineffective through the pandemic, but provides some objective evidence to justify the removal of healthcare mask mandates once there was widespread immunity and reduced disease severity.

STEP: simplified treatment of the enlarged prostate.

We propose a simple and practical approach to the identification, evaluation and treatment of lower urinary tract symptoms (LUTS) resulting from an enlarging and obstructive prostate. The proposed Simplified Treatment for Enlarged Prostate (STEP) plan is a logical guide to patient management by the primary care provider (PCP). Symptoms of enlarged prostate (EP) are common and may frequently progress into a condition with profound adverse effects on quality of life. Despite the high prevalence, EP is underdiagnosed and undertreated. This situation may result from patient- and provider-related issues. Assessment of symptoms of EP should be initiated with a discussion of LUTS. Evaluation includes a focused history, physical examination and selected laboratory tests. Certain factors put the symptomatic patient at risk for disease progression; however, not all factors can be readily evaluated in the PCP setting. The serum prostate-specific antigen (PSA) level acts both as an indicator of prostatic size and a screening tool for prostatic cancer, and thereby provides an important tool for PCPs. The STEP plan is a logical guide to patient management. Step 1, watchful waiting, is appropriate in patients with symptoms that are not bothersome. If symptoms cause bother, the initiation of an alpha-blocker (AB) in step 2, provides relatively rapid symptom improvement. Patients with bothersome symptoms and a PSA > or = 1.5 ng/ml are at risk for progression and consideration should be given to combination treatment with an AB and a 5alpha-reductase inhibitor (step 3). Patients with refractory symptoms should be referred to a urologist (step 4). Identification, evaluation and management of EP are within the domain of the primary care setting. The STEP approach provides a simple and practical framework for PCPs to manage most men with symptoms of EP.

Dopaquinone redox exchange with dihydroxyindole and dihydroxyindole carboxylic acid.

A pulse radiolytic investigation has been conducted to establish whether a redox reaction takes place between dopaquinone and 5,6-dihydroxyindole (DHI) and its 2-carboxylic acid (DHICA) and to measure the rate constants of the interactions. To obviate possible confounding reactions, such as nucleophilic addition, the method employed to generate dopaquinone used the dibromide radical anion acting on dopa to form the semiquinone which rapidly disproportionates to dopaquinone. In the presence of DHI the corresponding indole-5,6-quinone (and/or tautomers) was also formed directly but, by judicious selection of suitable relative concentrations of initial reactants, we were able to detect the formation of additional indolequinone from the redox exchange reaction of DHI with dopaquinone which exhibited a linear dependency on the concentration of DHI. Computer simulation of the experimental time profiles of the absorption changes showed that, under the conditions chosen, redox exchange does proceed but not quite to completion, a forward rate constant of 1.4 x 10(6)/M/s being obtained. This is in the same range as the rate constants previously established for reactions of dopaquinone with cyclodopa and cysteinyldopa. In similar experiments carried out with DHICA, the reaction more obviously does not go to completion and is much slower, k (forward) =1.6 x 10(5)/M/s. We conclude that, in the eumelanogenic pathway, DHI oxidation may take place by redox exchange with dopaquinone, although such a reaction is likely to be less efficient for DHICA.

An outbreak of wound infection in cardiac surgery patients caused by Enterobacter cloacae arising from cardioplegia ice.

This paper describes an outbreak of postoperative sternal wound infections. A cardiac surgeon noted a cluster of serious infections leading to wound dehiscence, despite the fact that none of his colleagues had noticed a rise in infection rates. The infections were predominantly with Enterobacter cloacae, and molecular typing and serotyping showed these isolates to be indistinguishable. Observation of the surgeon's practice revealed nothing untoward, and there were no infections among his patients operated on in another hospital. There appeared to be no significant difference between the modes of operation of the different surgeons. The operating theatres were screened to exclude an environmental source, with samples cultured on CHROMagar Orientation, a selective/differential medium designed for urine samples. Further questioning revealed one difference between the practices of the different surgeons; this surgeon used semi-frozen Hartmann's solution to achieve cardioplegia. The freezer used for this was swabbed and yielded E. cloacae, indistinguishable from the clinical isolates. It is hypothesized that this organism contaminated the freezer, and that the contamination was passed on to the ice/slush solution, thus infecting the patients. There have been no more cases since the freezer was replaced, a rigorous cleaning schedule instituted, and steps taken to reduce the possibility of any further contamination.

Rate constants for the first two chemical steps of eumelanogenesis.

The kinetics of the initial cyclization and redox exchange reactions involved in the eumelanogenic pathway have been studied previously but because of the difficulty of detecting the intermediate cyclodopa by optical means (because its absorbance is in the same range as dopa which is present in excess in the experimental system) no accurate value for the redox exchange reaction has so far been obtained and there is no available analytical methodology that can be applied to the successive first- and second-order reactions involved. We have synthesized cyclodopa and examined the kinetics of the formation of dopachrome following the pulse radiolytic generation of dopaquinone in its presence. From this direct measurement we determined that the rate constant of the reaction between cyclodopa and dopaquinone is 5.3 x 10(6)/M/s. Employing this value in a computational model of the combined cyclization and redox exchange reactions we calculate that the observed kinetics of dopaquinone decay and dopachrome formation are compatible with a cyclization rate constant of 3.8/s.

Pulse radiolysis studies of ortho-quinone chemistry relevant to melanogenesis.

The contributions of pulse radiolysis towards characterisation of unstable ortho-quinones relevant to melanogenesis are reviewed. The quinones discussed include dopaquinone, the precursor of both eumelanogenesis and phaeomelanogenesis, and 5-S-cysteinyldopaquinone, an early component of the phaeomelanogenic pathway. Redox exchange between dopaquinone and 5-S-cysteinyldopa is shown to be a determinant of the balance between eumelanogenesis and phaeomelanogenesis. Ortho-quinones resulting from the oxidation of tertiary N,N-dialkylcatecholamines cyclise to redox-inactive betaines which fail to autoactivate tyrosinase. This is consistent with the dopa detected during melanogenesis catalysed by tyrosinase being formed indirectly by a combination of dopaquinone intramolecular reductive addition to form leucodopachrome (cyclodopa), followed by redox exchange between remaining dopaquinone and leucodopachrome. Rapid tautomerism of the ortho-quinone of 4-cyanomethylcatechol to a redox-inactive quinomethane likewise inhibits tyrosinase autoactivation. The incorporation of trihydric phenol moieties in melanin is modelled by the reactions of several ortho-quinones with phloroglucinol, which itself is not directly oxidised by tyrosinase due to the meta-positioning of the hydroxyl groups. The importance of a susceptibility towards nucleophilic attack as well as a propensity to undergo redox-exchange, in the chemistry of melanogenic ortho-quinones, is emphasised.

Melanocyte-Directed enzyme prodrug therapy (MDEPT): development of second generation prodrugs for targeted treatment of malignant melanoma.

Evaluation of second generation prodrugs for MDEPT, by oximetry, has highlighted structural properties that are advantageous and disadvantageous for efficient oxidation using mushroom tyrosinase. In particular, a sterically undemanding prodrug bis-(2-chloroethyl)amino-4-hydroxyphenylaminomethanone 28 was synthesised and found to be oxidised by mushroom tyrosinase at a superior rate to tyrosine methyl ester, the carboxylic acid of which is the natural substrate for tyrosinase. The more sterically demanding phenyl mustard prodrugs 9 and 10 were oxidised by mushroom tyrosinase at a similar rate to tyrosine methyl ester. In contrast, tyramine chain elongation via heteroatom insertion was detrimental and the rate of mushroom tyrosinase oxidation of phenyl mustard prodrugs 21 and 22 decreased by 10 nanomol/min.

Spontaneous redox reactions of dopaquinone and the balance between the eumelanic and phaeomelanic pathways.

Eumelanogenesis and phaeomelanogenesis diverge at an early stage in pigment formation, namely at the point where dopaquinone, the initial product of tyrosine oxidation by tyrosinase, undergoes one of two types of reaction: either (1) a reductive endocyclisation in which a Michael addition of the side-chain amino group takes place; or (2) a reductive addition of cysteine to give cysteinyldopa. In the former case, the product cyclodopa, is known rapidly to undergo a redox exchange reaction with dopaquinone to yield dopachrome, the precursor of the eumelanogenic pathway. In the second instance, cysteinyldopa is regarded as leading to the formation of benzothiazoles, which are characteristic of phaeomelanin. The precursor molecule of the phaeomelanic pathway is cysteinyldopaquinone. We have examined quantitatively the role of dopaquinone in the non-enzymatic oxidation of 5-S-cysteinyldopa using pulse radiolysis and have demonstrated that the redox exchange reaction between dopaquinone and 5-S-cysteinyldopa occurs spontaneously with a rate constant of 8.8 x 10(5) M(-1) sec(-1). This study has also enabled an improved estimate of < or = 4 x 10(7) M(-1) sec(-1) to be obtained for the rate constant of the reaction of dopaquinone with cyclodopa. Calculations utilising these figures and estimates of the rate constants for the other reactions in early melanogenesis, demonstrate that, whilst similar pathways are invoked, the phaeomelanic pathway predominates in the presence of cysteine, irrespective of the availability of dopaquinone and thus independently of the rate of tyrosinase-catalysed oxidation. This suggests that the balance between the formation of eumelanin and phaeomelanin is regulated principally by the availability of cysteine at the site of melanogenesis.

Tyrosinase kinetics: a semi-quantitative model of the mechanism of oxidation of monohydric and dihydric phenolic substrates.

A mathematical model of phase I melanogenesis is described based on the differential reactivity of tyrosinase according to the redox status of the active site copper atoms shown by Lerch and co-workers (see Lerch, 1981, Metal Ions in Biological Systems (Sigel, H., ed.) Vol. 13, pp. 143-186. New York: Marcel Dekker) in combination with the indirect formation of the catecholic intermediate substrate. In this model the unusual autoactivation kinetics of tyrosinase are explained by recruitment of enzyme from the met -form, in which the active-site copper atoms are in the oxidized (Cu(II)) state, by 2-electron donation from catechol oxidation. Using estimates of the values for the rate constants of the six reactions involved, the general characteristics of the model are shown to be consistent with the kinetic behaviour of tyrosinase in vitro. These include a lag period which is sensitive to catechol addition.

Melanocyte-directed enzyme prodrug therapy (MDEPT): development of a targeted treatment for malignant melanoma.

A novel prodrug rationally designed to function as a tyrosinase substrate has been synthesised to allow targeted treatment of malignant melanoma. This agent has been evaluated for tyrosinase-mediated drug release, and has been shown to act in the desired manner. Furthermore, differential cytotoxicity has been demonstrated in cell lines which express tyrosinase and those which do not.

Comparative effect of ALA derivatives on protoporphyrin IX production in human and rat skin organ cultures.

Samples of human and rat skin in short-term organ culture exposed to ALA or a range of hydrophobic derivatives were examined for their effect on the accumulation of protoporphyrin IX (PpIX) measured using fluorescence spectroscopy. With the exception of carbobenzoyloxy-D-phenylalanyl-5-ALA-ethyl ester the data presented indicate that, in normal tissues, ALA derivatives generate protoporphyrin IX more slowly than ALA, suggesting that they are less rapidly taken up and/or converted to free ALA. However, the resultant depot effect may lead to the enhanced accumulation of porphyrin over long exposure periods, particularly in the case of ALA-methyl ester or ALA-hexyl ester, depending on the applied concentration and the exposed tissue. Addition of the iron chelator, CP94, greatly increased PpIX accumulation in human skin exposed to ALA, ALA-methyl ester and ALA-hexyl ester. The effect in rat skin was less marked.

Study of DT-diaphorase in pigment-producing cells.

DT-diaphorase is an FAD-containing enzyme capable of a two-electron reduction of ortho- and paraquinones. Nicotinamide coenzymes (NADH + H+ and NADPH + H+) serve as hydrogen sources in these reactions. The role of DT-diaphorase has been thoroughly investigated in situations when the enzyme is able to reduce exogenous and endogenous quinones, hence protecting the cells against these reactive intermediates. The enzyme has also been studied in connection with its ability to activate some quinoid cytostatics. It is surprising that DT-diaphorase has never been investigated in pigment-producing cells that are known to generate considerable amounts of ortho-quinones. Using a spectrophotometric method we could readily measure the activity of DT-diaphorase in epidermis and various cultured pigment cells. The melanocytes isolated from dark skin showed generally higher DT-diaphorase activity than those from fair skin samples. Also, darkly pigmented congenital naevus cells exhibited higher activity of this enzyme. The most striking was the high DT-diaphorase activity in melanoma cell cultures. In these cells DT-diaphorase activity could be induced by incubation of the cells with 4-hydroxyanisole. A similar effect was seen when a catechol-O-methyltransferase (COMT) inhibitor (3-(3,4-dihydroxy-5-nitrobenzylidene)-2,4-pentanedione (OR-462) was utilised. The induction was inhibited by cyclohexidine.

The great DOPA mystery: the source and significance of DOPA in phase I melanogenesis.

One of the important characteristics of tyrosinase is the autocatalytic nature of the oxidation of natural monohydric phenol substrates, such as tyrosine. In vitro tyrosinase exhibits a lag phase in which the maximum velocity of oxidation is attained after a period of induction. This acceleration contrasts with the kinetics of dihydric phenol oxidation which exhibit conventional Michaelis-Menten kinetics. It has been known for half a century that DOPA is a co-factor in the oxidation of tyrosine and addition of a small amount of catechol reduces the length of the lag period. The significance of DOPA is in this action, and DOPA is known to be formed in phase I melanogenesis. Until recently there has been controversy regarding the source of the DOPA in the in vitro reaction system. Most investigators have favoured a mechanism based on the generation of DOPA by a direct hydroxylation of tyrosine. However, recent evidence has suggested that DOPA is indirectly derived by reduction of dopaquinone. In this communication the evidence for the indirect mechanism derived from the use of analogue substrates is reviewed.

Tyrosinase autoactivation and the problem of the lag period.

Evidence is presented for the binding of the quinone oxidation product of the monohydric phenol substrate, 4-hydroxyanisole, to mushroom tyrosinase. Column chromatography and SDS-PAGE separation showed labelling of the enzyme when incubated with 14C ring-labelled 4-hydroxyanisole. It is proposed that covalent binding to the enzyme and other proteins is through reaction of accessible nucleophilic groups, including thiols and amino groups, with the anisylquinone. This reductive addition enables the indirect generation of the catecholic substrate, which acts as an electron donor for the bicupric active site of met-tyrosinase and explains the lag kinetics of tyrosinase oxidation of non-cyclizing substrates. The effects of diluting the enzyme or the addition of amino acids on the lag period was consistent with a mechanism involving indirect generation of the dihydric phenol, which acts as the met-enzyme-recruiting substrate.

Tyrosinase kinetics: failure of the auto-activation mechanism of monohydric phenol oxidation by rapid formation of a quinomethane intermediate.

When 3,4-dihydroxybenzylcyanide (DBC) is oxidized by mushroom tyrosinase, the first visible product, identified as the corresponding quinomethane, exhibits an absorption maximum at 480 nm. Pulse-radiolysis experiments, in which the o-quinone is formed by disproportionation of semiquinone radicals generated by single-electron oxidation of DBC, showed that the quinomethane (A480 6440 M-1.cm-1) is formed through the intermediacy of the o-quinone with a rate constant at neutral pH of 7.5 s-1. The oxygen stoichiometry of the formation of the quinomethane by tyrosinase-catalysed oxidation of DBC was 0.5:1. On the basis of oxygen utilization rates the calculated Vmax was 4900 nmol.min-1 and the apparent Km was 374 microM. The corresponding monohydric phenol, 4-hydroxybenzylcyanide (HBC), was not oxidized by tyrosinase unless the enzyme was pre-exposed to DBC, the maximum acceleration of HBC oxidation being obtained by approximately equimolar addition of DBC. These results are consistent with tyrosinase auto-activation on the basis of the indirect formation of the dihydric phenol-activating cofactor. The rapid conversion of the o-quinone to the quinomethane prevents the formation of the catechol by reduction of the o-quinone product of monohydric phenol oxidation from occurring in the case of the compounds studied. In the absence of auto-activation, the kinetic parameters for HBC oxidation by tyrosinase were estimated as Vmax 70 nmol.min-1 and Km 309 microM. The quinomethane was found to decay with a rate constant of 2k 38 M-1.s-1, as determined both by pulse-radiolysis and tyrosinase experiments. The second-order kinetics indicate that a dimer is formed. In the presence of tyrosinase, but not in the pulse-radiolysis experiments, the quinomethane decay was accompanied by a steady-state oxygen uptake concurrently with the generation of a melanoid product measured by its A650, which is ascribed to the formation of an oligomer incorporating the oxidized dimer.