Updated assessment of occupational safety and health hazards of climate change

Workers, particularly outdoor workers, are among the populations most disproportionately affected by climate-related hazards. However, scientific research and control actions to comprehensively address these hazards are notably absent. To assess this absence, a seven-category framework was developed in 2009 to characterize the scientific literature published from 1988-2008. Using this framework, a second assessment examined the literature published through 2014, and the current one examines literature from 2014-2021. The objectives were to present literature that updates the framework and related topics and increases awareness of the role of climate change in occupational safety and health. In general, there is substantial literature on worker hazards related to ambient temperatures, biological hazards, and extreme weather but less on air pollution, ultraviolet radiation, industrial transitions, and the built environment. There is growing literature on mental health and health equity issues related to climate change, but much more research is needed. The socioeconomic impacts of climate change also require more research. This study illustrates that workers are experiencing increased morbidity and mortality related to climate change. In all areas of climate-related worker risk, including geoengineering, research is needed on the causality and prevalence of hazards, along with surveillance to identify, and interventions for hazard prevention and control.

Advancing the framework for considering the effects of climate change on worker safety and health

In 2009, a preliminary framework for how climate change could affect worker safety and health was described. That framework was based on a literature search from 1988-2008 that supported seven categories of climate-related occupational hazards: (1) increased ambient temperature; (2) air pollution; (3) ultraviolet radiation exposure; (4) extreme weather; (5) vector-borne diseases and expanded habitats; (6) industrial transitions and emerging industries; and (7) changes in the built environment. This article reviews the published literature from 2008-2014 in each of the seven categories. Additionally, three new topics related to occupational safety and health are considered: mental health effects, economic burden, and potential worker safety and health impacts associated with the nascent field of climate intervention (geoengineering). Beyond updating the literature, this article also identifies key priorities for action to better characterize and understand how occupational safety and health may be associated with climate change events and ensure that worker health and safety issues are anticipated, recognized, evaluated, and mitigated. These key priorities include research, surveillance, risk assessment, risk management, and policy development. Strong evidence indicates that climate change will continue to present occupational safety and health hazards, and this framework may be a useful tool for preventing adverse effects to workers.

Lipase-mediated stereoselective hydrolysis of stampidine and other phosphoramidate derivatives of stavudine

Enzymatic hydrolysis of stampidine and other aryl phosphate derivatives of stavudine were investigated using the Candida Antarctica Type B lipase. Modeling studies and comparison of the hydrolysis rate constants revealed a chiral preference of the lipase active site for the putative S-stereoisomer. The in vitro anti-HIV activity of these compounds correlated with their susceptibility to lipase- (but not esterase-) mediated hydrolysis. We propose that stampidine undergoes rapid enzymatic hydrolysis in the presence of lipase according to the following biochemical pathway: During the first step, hydrolysis of the ester group results in the formation of carboxylic acid. Subsequent step involves an intramolecular cyclization at the phosphorous center with simultaneous elimination of the phenoxy group to form a cyclic intermediate. In the presence of water, this intermediate is converted into the active metabolite Ala-d4T-MP. We postulate that the lipase hydrolyzes the methyl ester group of the l-alanine side chain to form the cyclic intermediate in a stereoselective fashion. This hypothesis was supported by experimental data showing that chloroethyl substituted derivatives of stampidine, which possess a chloroethyl linker unit instead of a methyl ester side chain, were resistant to lipase-mediated hydrolysis, which excludes the possibility of a direct hydrolysis of stampidine at the phosphorous center. Thus, our model implies that the lipase-mediated formation of the cyclic intermediate is a key step in metabolism of stampidine and relies on the initial configuration of the stereoisomers.

A comparative study of the hydrolysis pathways of substituted aryl phosphoramidate versus aryl thiophosphoramidate derivatives of stavudine

A comparative study of aryl phosphoramidate and aryl thiophosphoramidate derivatives of 2',3'-didehydro-2',3'-dideoxythymidine (d4T) was performed. The study focused on the nature of the substituents and the influence of a thiophosphoramidate in the structure of these derivatives. The rate of alkaline hydrolysis of these two types of d4T derivatives indicated that replacement of oxygen with sulfur decreases the rate of hydrolysis by twofold. Additionally, the activation energy (E(a)) for the sulfur analogs is comparatively higher than that of the oxygen analogs. Notably, an intermediate was formed in the hydrolysis reaction of the sulfur analogs of d4T that was absent in the case of the oxygen analog, and the tentative structure of the intermediate was proposed based on LC/mass spectroscopy data. Using both HPLC and (31)P-NMR techniques, we identified the hydrolysis product of the phosphoramidate derivatives and were able to show in in vitro studies that porcine liver esterase can hydrolyze the methyl ester portion of the phosphoramidate derivatives. Aryl phosphoramidate derivatives of d4T were 1000-fold more active than the corresponding aryl thiophosphoramidate derivatives, indicating that the energy of activation of hydrolysis of these phosphoramidate derivatives plays a significant role in their biological potency.

Effects of aryl substituents on the anti-HIV activity of the arylphosphoramidate derivatives of stavudine

We compared the anti-HIV activity of 13 phenyl phosphate derivatives of stavudine (2',3'-didehydro-2',3'-dideoxythymidine/d4T) by examining their ability to inhibit HIV-1 replication in human peripheral blood mononuclear cells. Our results show that the introduction of electron-withdrawing substituents enhances the activity of these phosphoramidate derivatives. The rate of chemical hydrolysis under alkaline conditions (but not the lipophilicity) predicted the potency of the compounds.

Health status and satisfaction with health care: a longitudinal study among patients served by the Veterans Health Administration

As the Veterans Health Administration (VHA) places high priority on becoming a performance-based organization, there is an increasing need to quantify and refine its outcome measurement system. Using panel data from VHA ambulatory care patients (1996-1998), we conducted cross-lagged correlations and ordinary least squares regression to examine the relationship between 2 VHA health care values: health status and satisfaction with care. The study results indicated that patients' health status was significantly associated with their satisfaction with care, indicating that patients with better health status were more likely to be satisfied with health care. Although satisfaction with care was both a consequence and a determinant of health status, the effects of health status on satisfaction seemed to be more important than the effects of satisfaction on health status. More research is needed for a better understanding of the dynamic relationship between health status and satisfaction with care.

N-[2-(4-methylphenyl)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea as a potent inhibitor of NNRTI-resistant and multidrug-resistant human immunodeficiency virus type 1

The composite non-nucleoside reverse transcriptase inhibitor (NNRTI) binding pocket model was used to study a number of thiourea analogues with different substitutions at the 4-phenyl position including N-[2-(4-methylphenyl)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea (compound HI-244), which inhibited recombinant RT better than trovirdine or compound HI-275 with an unsubstituted phenyl ring. HI-244 effectively inhibited the replication of HIV-1 strain HTLV(IIIB) in human peripheral blood mononuclear cells with an IC50 value of 0.007 microM, which is equal to the IC50 value of trovirdine. Notably, HI-244 was 20 times more effective than trovirdine against the multidrug-resistant HIV-1 strain RT-MDR with a V106A mutation (as well as additional mutations involving the RT residues 74V, 41L and 215Y) and seven times more potent than trovirdine against the NNRTI-resistant HIV-1 strain A17 with a Y181C mutation.

N'-[2-(2-thiophene)ethyl]-N'-[2-(5-bromopyridyl)] thiourea as a potent inhibitor of NNI-resistant and multidrug-resistant human immunodeficiency virus-1

The thiophene-ethyl thiourea (TET) compound N'-[2-(2-thiophene)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea (compound HI-443) was five times more potent than trovirdine, 1250 times more potent than nevirapine, 100 times more potent than delavirdine, 75 times more potent than MKC-442, and 50 times more potent than AZT against the multidrug resistant HIV-1 strain RT-MDR with a V106A mutation. HI-443 was almost as potent against the NNI-resistant HIV-1 strain A17 with a Y181C mutation as it was against HTLV(IIIB). The activity of HI-443 against A17 was ten times more potent than that of trovirdine, 2083 times more potent than that of nevirapine, and 1042 times more potent than that of delavirdine. HI-443 inhibited the replication of the NNI-resistant HIV-1 strain A17 variant with Y181C plus K103N mutations in RT with an IC50 value of 3.3 microM, whereas the IC50 values of trovirdine, nevirapine, and delavirdine were all >100 microM. These findings establish the novel thiophene containing thiourea compound HI-443 as a novel NNI with potent antiviral activity against NNI-sensitive, NNI-resistant and multidrug-resistant strains of HIV-1.

N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-bromopyridyl)]-thiourea and N'-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-chloropyridyl)]-thiourea as potent inhibitors of multidrug-resistant human immunodeficiency virus-1

We have replaced the pyridyl ring of trovirdine with an alicyclic cyclohexenyl, adamantyl or cis-myrtanyl ring. Only the cyclohexenyl-containing thiourea compound N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-bromopyridyl)]- thiourea (HI-346) (as well as its chlorine-substituted derivative N-[2-(1-cyclohexenyl)ethyl]-N'-[2-(5-chloropyridyl)]- thiourea/HI-445) showed RT inhibitory activity. HI-346 and HI-445 effectively inhibited recombinant RT with better IC50 values than other anti-HIV agents tested. The ranking order of efficacy in cell-free RT inhibition assays was: HI-346 (IC50 = 0.4 microM) > HI-445 (IC50 = 0.5 microM) > trovirdine (IC50 = 0.8 microM) > MKC-442 (IC5 = 0.8 microM) = delavirdine (IC50 = 1.5 microM) > nevirapine (IC50 = 23 microM). In accord with this data, both compounds inhibited the replication of the drug-sensitive HIV-1 strain HTLV(IIIB) with better IC50 values than other anti-HIV agents tested. The ranking order of efficacy in cellular HIV-1 inhibition assays was: HI-445 = HI-346 (IC50 = 3 nM) > MKC-442 (IC50 = 4 nM) = AZT (IC50 = 4 nM) > trovirdine (IC50 = 7 nM) > delavirdine (IC50 = 9 nM) > nevirapine (IC50 = 34 nM). Surprisingly, the lead compounds HI-346 and HI-445 were 3-times more effective against the multidrug resistant HIV-1 strain RT-MDR with a V106A mutation (as well as additional mutations involving the RT residues 74V,41L, and 215Y) than they were against HTLV(IIIB) with wild-type RT. HI-346 and HI-445 were 20-times more potent than trovirdine, 200-times more potent than AZT, 300-times more potent than MKC-442, 400-times more potent than delavirdine, and 5000-times more potent than nevirapine against the multidrug resistant HIV-1 strain RT-MDR. HI-445 was also tested against the RT Y181C mutant A17 strain of HIV-1 and found to be >7-fold more effective than trovirdine and >1,400-fold more effective than nevirapine or delavirdine. Similarly, both HI-346 and HI-445 were more effective than trovirdine, nevirapine, and delavirdine against the problematic NNI-resistant HIV-1 strain A17-variant with both Y181C and K103N mutations in RT, although their activity was markedly reduced against this strain. Neither compound exhibited significant cytotoxicity at effective concentrations (CC50 >100 microM). These findings establish the lead compounds HI-346 and HI-445 as potent inhibitors of drug-sensitive as well as multidrug-resistant stains of HIV-1.