Dhruvesh Patel | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Dhruvesh Patel. This seminar is open to the general public to attend, either in person or via the link below:

https://ualberta-ca.zoom.us/j/95989718226?pwd=Sko4V2pqNmlsRjJObVZuRkw4SCtYQT09
Meeting ID: 959 8971 8226 Passcode: 005227

Thesis Topic: Evaluating the essentiality of dietary docosahexaenoic acid along with arachidonic acid during the development of the immune system in early life.

PhD with Dr. Catherine Field.

Seminar Abstract:

The immune system is immature at birth and the dietary fats provided during early life play an important role in the development of infant immune system. The precursor omega-3 (n-3) and n-6 polyunsaturated fatty acids (PUFAs) α-linolenic acid and linoleic acids, respectively, are essential for our body. The bioconversion of precursors into long chain polyunsaturated fatty acids (LCPUFA) such as docosahexaenoic (DHA, n-3) and arachidonic acids (ARA, n-6) is not effective and therefore dietary supply of LCPUFA is vital. It is hypothesised that the immunomodulatory properties of LCPUFA can influence the development of immune system during early life. Evidence suggest that infants with low n-3 LCPUFA status are more likely to develop atopic conditions such as asthma and food allergies. For infants with genetic predisposition to developing allergies, supplementation with fish oil (containing DHA) has been reported to reduce the T helper type-2 (Th2) dominant response promoting the prevention of food allergies also known as oral tolerance (OT). However, the effect of DHA supplementation in the presence of ARA on infant immune system development has not been fully elucidated. Thus, the aim of this thesis is to understand the essentiality of dietary LCPUFAs in the development of the immune system and oral tolerance in healthy and allergy-prone condition using pre-clinical rodent models during early life.

We conducted series of animal experiments to study the effect of LCPUFA supplementation during early life (suckling and/or weaning period) on the development of immune system and OT in offspring. OT was induced using repetitive oral-exposure to ovalbumin (ova) followed by systemic challenge with ova and adjuvant. First, using healthy Sprague Dawley rat model, we determine the effect of feeding stearidonic acid (SDA)-enriched diet (3% of total fat) on the LCPUFA status and immune functions in dams and offspring after suckling and weaning. We observed that supplementing SDA in the maternal diet during lactation increased the breastmilk levels of n-3 LCPUFAs (eicosapentaenoic (EPA) and docosapentaenoic acid (DPA) and including DHA. Providing SDA-enriched diet during suckling and weaning increased the splenocyte phospholipid levels of EPA and DPA but did not change DHA and ARA. At 6-weeks, ex-vivo cytokine response by splenocytes stimulated with lipopolysaccharide (LPS) showed that the SDA group offspring had lower levels of inflammatory cytokines; interleukin(IL)-6 and tumor necrosis factor-alpha (TNF-α) and higher IL-10 than the control group (all P’s < 0.05). Feeding SDA led to higher in-vivo biosynthesis of EPA and DHA but not DHA, which promoted an anti-inflammatory effect in 6-week offspring.

Next, we used LCPUFAs, DHA and ARA combined supplementation in allergy prone rodent model to evaluate the development of immune system and OT. Using Brown Norway rat offspring, we showed that proving DHA (0.8% in suckling period and 0.5% in weaning) along side ARA, promoted OT development (35% lower plasma ovalbumin specific (ova)-IgG levels, P = 0.04) in the offspring from DHA+ARA group compared to control. More importantly, providing DHA+ARA during weaning promoted higher Th1 specific cytokines (TNF-α and interferon(IFN)-γ) by splenocytes stimulated with phorbol-myristate-acetate and ionomycin (PMAi, non-specific lymphocyte stimulant), which may be due to higher proportion of adaptive immune cells (OX12+ and IgG+ B cells) compared to control group.

We then used suckling and weaning diets supplemented with DHA (derived from plant-based source) and ARA (each at 1% of total fat) to study immune system and OT development using a different allergy-prone model, BALB/c mouse. Dietary supplementation of DHA+ARA not only improved the DHA status in the breast milk but of dams but also splenocytes from 3-wk and 6-wk offspring, without affecting the ARA levels. Suckling period supplementation showed higher inflammatory cytokines (IL-1β, IFN-γ and TNF-α) production by LPS stimulated splenocytes from 3-week offspring in comparison to controls. In 6-week offspring, DHA supported a 3x reduction in plasma levels of ova-IgE compared to control. Furthermore, DHA resulted in higher T cell cytokines (IL-2, IFNγ and IL-1β) by splenocytes upon stimulation with anti-CD3/anti-CD28 and lower inflammatory response upon splenocyte stimulation with LPS. Last, DHA during weaning resulted in lower T helper type-2 cytokines (IL-4 and IL-6) with ova stimulation than controls, which may be beneficial for OT.

Overall, we showed that dietary supplementation of n-3 and n-6 LCPUFAs during early life can positively modulate the immune system development and the development of OT in neonates prone to developing allergies. This may be potentially through the suppression of Th2 and promotion of Th1 specific immune response.