Experimental Approaches to Tissue Injury and Repair in Advanced Age

Chlorite-Oxidized Oxyamylose (COAM) Has Antibacterial Activity and Positively Affects Skin Wound Healing

Purpose

To verify the antibacterial and immunomodulatory effects of the amylose derivative – chlorite-oxidized oxyamylose (COAM) – in a skin wound setting.

Methods

In vitro antibacterial effects of COAM against opportunistic bacterial pathogens common to skin wounds, including Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA), were determined by cultivation methods. The effects of COAM on myeloid cell infiltration into full thickness skin wounds were investigated in wild-type and in transgenic CX₃CR1-GFP mice.

Results

On the basis of in vitro experiments, an antibacterial effect of COAM against Staphylococcus species including MRSA was confirmed. The minimum inhibitory concentration of COAM was determined as 2000 µg/mL against these bacterial strains. Control full thickness skin wounds yielded maximal neutrophil influxes and no additive effect on neutrophil influx was observed following topical COAM-treatment. However, COAM administration increased local CX₃CR1 macrophage counts at days 3 and 4 and induced a trend towards better wound healing.

Conclusion

Aside from its known broad antiviral impact, COAM possesses in vitro antibacterial effects specifically against Gram-positive opportunistic pathogens of the skin and modulates in vivo macrophage contents in mouse skin wounds.

Mechanistic Studies and In Vivo Efficacy of an Oxadiazole-Containing Antibiotic

Methicillin-resistant Staphylococcus aureus (MRSA) infections are still difficult to treat, despite the availability of many FDA-approved antibiotics. Thus, new compound scaffolds are still needed to treat MRSA. The oxadiazole-containing compound, HSGN-94, has been shown to reduce lipoteichoic acid (LTA) in S. aureus, but the mechanism that accounts for LTA biosynthesis inhibition remains uncharacterized. Herein, we report the elucidation of the mechanism by which HSGN-94 inhibits LTA biosynthesis via utilization of global proteomics, activity-based protein profiling, and lipid analysis via multiple reaction monitoring (MRM). Our data suggest that HSGN-94 inhibits LTA biosynthesis via direct binding to PgcA and downregulation of PgsA. We further show that HSGN-94 reduces the MRSA load in skin infection (mouse) and decreases pro-inflammatory cytokines in MRSA-infected wounds. Collectively, HSGN-94 merits further consideration as a potential drug for staphylococcal infections.

Alcohol, aging, and innate immunity

The global population is aging: in 2010, 8% of the population was older than 65 y, and that is expected to double to 16% by 2050. With advanced age comes a heightened prevalence of chronic diseases. Moreover, elderly humans fair worse after acute diseases, namely infection, leading to higher rates of infection-mediated mortality. Advanced age alters many aspects of both the innate and adaptive immune systems, leading to impaired responses to primary infection and poor development of immunologic memory. An often overlooked, yet increasingly common, behavior in older individuals is alcohol consumption. In fact, it has been estimated that >40% of older adults consume alcohol, and evidence reveals that >10% of this group is drinking more than the recommended limit by the National Institute on Alcohol Abuse and Alcoholism. Alcohol consumption, at any level, alters host immune responses, including changes in the number, phenotype, and function of innate and adaptive immune cells. Thus, understanding the effect of alcohol ingestion on the immune system of older individuals, who are already less capable of combating infection, merits further study. However, there is currently almost nothing known about how drinking alters innate immunity in older subjects, despite innate immune cells being critical for host defense, resolution of inflammation, and maintenance of immune homeostasis. Here, we review the effects of aging and alcohol consumption on innate immune cells independently and highlight the few studies that have examined the effects of alcohol ingestion in aged individuals.