Candida Albicans & Sex Differences

The primary focus of the study is on yeast infections caused by Candida albicans, a polymorphic fungus and how sex differences effect disease susceptibility in rats

Candida Albicans: A Detailed Overview

• Candida albicans is a fungus that can change shapes depending on environmental conditions. It exists in two forms:

  • Blastoconidia (round-like shaped cells): Less pathogenic

  • Filamentous type: More pathogenic

• It is normally found on the skin, GI tract, and reproductive tracts of about 98% of the population

• It becomes pathogenic when the host is immunocompromised

Infections Caused by Candida

• Thrush: A coating of fungus on the tongue, treatable with antifungal medication

• Vaginal Yeast Infections: Common in about 95% of women, also predominantly caused by Candida albicans

• Candidemia: Occurs when the yeast enters the bloodstream, leading to mortality rates of up to 40% (It's the fourth leading cause of hospital-borne infections in the US)

Factors Influencing Susceptibility to Candida Infections

• Biological Sex is a factor

• Females are more prone to autoimmune diseases (e.g., multiple sclerosis, rheumatoid arthritis, lupus, scleroderma) compared to males

• Generally, females are less prone to bacterial, viral, and parasitic infections than males (except for worm infections)

• Fungal infections and potential sex differences require further investigation

Investigating Sex Differences in Candida Infections

• The research question: What role does sex play in susceptibility to blood infections with Candida albicans?

• Experimental design:

  • Male and female mice were infected with the yeast on day zero

  • Survival and weight change were observed over 22 days

Results of Initial Experiment

• Females showed more resistance to the infection than males

• Males experienced considerably higher weight loss compared to females

• P values indicating statistical significance were reported (reference to a 2020 publication)

Role of Sex Hormones

• Hormonal Differences: Males produce more testosterone, while females produce more estrogen

• Testes: Major producers of testosterone

• Ovaries: Major producers of estrogen

Investigating Hormonal Influence: Castration Experiments

• Male mice were castrated to assess the impact of testosterone

• Castrated males showed resistance to the infection equivalent to that of females

• Castrated females did not show a difference in resistance

Hormone Supplementation Studies

• Experimental Procedure:

  • Intact and castrated mice were implanted with pellets containing either 17 beta-estradiol (estrogen), 5 alpha-dihydrotestosterone (active form of testosterone), or a placebo

  • Mice were given Tylenol for seven days post-surgery and monitored for survival and weight change after infection

Effects of Testosterone Supplementation

• Females implanted with testosterone started succumbing to the disease, although the decrease in survival wasn't as significant as in intact males

• Castrated males supplemented with testosterone also showed decreased survival, suggesting testosterone plays a role

Effects of Estrogen Supplementation

• Intact or castrated males supplemented with estrogen succumbed readily to the infection, indicating that the presence or absence of testosterone is not the only factor

Summary of Sex Hormone Experiments

• Male mice are consistently more susceptible to systemic C. albicans infection, assessed by survival and weight loss

• Supplementation with 5 alpha-dihydrotestosterone and 17 beta-estradiol decreases survival in infected castrated male and female mice

• Sex hormones may be partially responsible, but other factors are involved

Investigating Fungal Load

• Research Question: Are male mice more infected than female mice?

• Male and female mice were infected on day zero, and tissues (liver, spleen, brain, kidney, blood) were collected on days 1, 4, and 7 to measure fungal load

• Fungal load was measured as log of colony-forming units (CFU) of C. albicans per gram of tissue

Results of Fungal Load Analysis

• The tissue fungal load in the kidneys and livers of males and females were equivalent at all time points

• Males and females are infected to the same degree, suggesting that the difference in susceptibility is not due to differences in fungal invasion

Assessment of Host Immune Response

• Focus on the host immune response to explain sex differences in susceptibility

• Key immune response components:

  • Antigen-presenting cells (APCs) activate naive T cells to differentiate into Th1, Th2, and Th17 cells

  • Th1 and Th17 responses are crucial for combating yeast infections

  • Th17 cells activate neutrophils, which are major responders to yeast infections

Cytokine and Neutrophil Analysis

• The study focused on cytokines produced by APCs that activate Th17 cells and subsequent activation of neutrophils

• Males had significantly more serum IL-6 cytokine compared to females

• IL-6 regulates neutrophil trafficking and may cause septic shock or excessive inflammation in males

Neutrophil Level Analysis

• Male mice seem to produce more neutrophils than females in the bone marrow and have higher neutrophil levels in blood

• The connection between higher neutrophil levels and susceptibility to infection is still under investigation

Summary of Immune Response Analysis

• Sex hormones are partly responsible for the worst outcome in males

• Males have higher serum IL-6 levels

• Males have higher levels of neutrophils in the blood and bone marrow

• Potential relationships between sex hormones, IL-6, and neutrophil levels are being investigated

Future Research Directions

• Wants to use testicular feminization mice (AR TFM mice) with a mutation in the androgen receptor

• Use of orchiectomized mice to confirm results regarding the impact of androgen receptor deficiency or testosterone absence on IL-6 and neutrophil levels

• Neutralizing IL-6 in the serum using anti-IL-6 antibodies to investigate the role of IL-6 further

• Assessing neutrophil levels after neutralizing IL-6

Overview of THC

• THC (tetrahydrocannabinol) is the main psychotropic component of marijuana

• Known medicinal applications:

  • Reduces pain

  • Stimulates appetite

  • Anti-inflammatory

• Affects the immune system by:

  • Impairing antigen presentation

  • Inhibiting chemotaxis of certain immune cells

  • Altering splenocyte proliferation

  • Suppressing antibody production

Medicinal Applications of THC-Based Drugs

• 1985: FDA approved Marinol and Cesamet (synthetic THC compounds) for chemotherapy-associated symptoms and appetite stimulation in AIDS patients

• 2018: FDA approved Epidiolex (CBD extracted from the plant) for treating certain forms of childhood epilepsy

• Other countries (e.g., Canada, UK): Approved Sativex (THC and CBD in a 1:1 ratio) for multiple sclerosis

The Endocannabinoid System

• Discovered after marijuana and named after cannabis plant

• Consists of:

  • Cannabinoid receptors (CB1 and CB2)

    • CB1: Mostly found in the central and peripheral nervous systems

    • CB2: Mostly found in immune cells

  • Endocannabinoids (e.g., anandamide, 2-arachidonoylglycerol)

How THC Interacts with the Endocannabinoid System

• THC can outcompete endocannabinoids like anandamide for binding to cannabinoid receptors, thereby exerting physiological effects

• Potential effects of THC on individuals with a balanced endocannabinoid system are investigated

Prior Research on THC and the Immune System

• THC affects the immune system by:

  • Impairing antigen presentation

  • Inhibiting chemotaxis of certain immune cells

  • Altering splenocyte proliferation

  • Suppressing antibody production

• THC suppresses mouse resistance to bacterial, parasitic, and viral infections

• The speaker's lab is the first to investigate the effect of THC on yeast infections caused by Candida albicans

Experiment on THC and Systemic Candida Albicans Infection

• Female and male mice were treated intraperitoneally (IP) with either vehicle control or THC on days -18 to -15 (relative to infection on day 0)

• THC or vehicle control administered in cycles (3 days treatment, 4 days rest, 3 days treatment, 4 days rest)

• Infected the animals on day 0 and monitored for up to 14 days to look at survival and morbidity

• Collected tissues including blood to measure fungi on day 3 after infection

Results of THC Treatment and Candida Infection

• Weight Change: No significant increase in weight with THC treatment

• IL-6: THC increased iL-6 in a dose-dependent manner

• Swiss Webster mice utilized, confirming males more susceptible

Overall Conclusions

• Sex hormones, serum IL-6, and neutrophil levels may be responsible for greater susceptibility to C. albicans infection in male mice compared to female mice

• Determined THC does not affect mouse susceptibility to an acute systemic C. albicans infection