Salivary α-amylase gene 1 (AMY1) copy number variation and association with inter-individual differences in body composition and response to carbohydrates intake

Abstract

Copy number variation has been linked to the development of several syndromes. In a 2014 publication, evidence reported the association of the copy number of salivary amylase 1 (AMY1) with obesity. Several studies confirmed these findings; however, well-powered replication studies in various populations failed to replicate this link. This controversy may be explained by the different study designs and participant populations. A significant association may still be found under specific conditions, such as gender, age, and level of physical activity. Further, if the copy number of AMY1 does influence obesity risk, its mechanisms are yet to be uncovered. We hypothesised that an increased copy number of AMY1 would be associated with body composition more strongly than body mass index (BMI) in athletes and healthy male and female adults. That led us to hypothesise that an increased copy number of AMY1 may be associated with strength athletes and muscle performance due to their lower fat mass and increased lean mass. To understand the association between AMY1 copy number and obesity from a clinical perspective, we hypothesised that healthy adults with a high copy number of AMY1 would have a healthy, controlled glycaemic response after complex CHO ingestion and a higher rate of complex CHO oxidation during rest and exercise compared to a low copy number AMY1 group. This thesis reports on three studies.

The first study (Chapter 3) investigated the association of AMY1 copy number with underlying anthropometric aspects of body composition, precisely strength and measures of muscle performance. The study included 388 young adult Lithuanian males divided into non-exercising controls (CON; n= 187, aged 23.91 ± 4) and athletes (n= 201). The latter included the subgroups of strength athletes (STP; n= 50, aged 21.06 ± 3), team sports athletes (TEA; n= 67, aged 22.31 ± 3), and endurance athletes (END; n= 84, aged 21.68 ± 4) were controls recruited between 2006 to 2009. All athletes trained a minimum of twice a week, whereas participants in the control group did not participate in any organised physical activity more than twice a week and did not compete in competitive sports. The copy number of target genes was determined using a quantitative polymerase chain reaction (qPCR). Percentage body fat (% BF) was calculated by Faulkner’s (1968) equation considering the modified Yuhasz method. We observed that the copy number of AMY1 did not differ between the athletes and the control group. Nor was it associated with athletes’ fat mass or FFM; however, a strong association was found with their height.

The second study (Chapter 4) assessed the association of increasing AMY1 copy number and body composition, including fat mass and lean mass and assessed the influence of gender differences on fat distribution among males and females. This study included 228 healthy volunteers aged 22.2 ± 3, of which 108 were male and 220 were female recruited between 2016 to 2019. Dual-energy X-ray absorptiometry (DXA) were used for BF % and FFM measurements. Participants completed a 3-day self-reported food questionnaire to assess macronutrient and energy intake and one week of physical activity level questionnaire (SPAQ). The AMY1 copy number distribution did not differ between males and females. No association was noticed between increasing copy number of AMY1 and fat mass or lean mass across the whole study sample nor in males and females. WC (cm) was negatively associated with high AMY1 in female only. The reginal body fat distribution and lean mass distribution did not correlate with AMY1 CN in either gender. Increasing Total EI was associated with decreasing AMY1 CN in males. However, physical activity level (PAL) did not associate with AMY1 CN in either gender.

The third study (Chapter 5) examined the effects of high copy number on glycaemic response after starch and glucose ingestion. This pilot study was conducted on 15 healthy young adult participants, divided into two groups, a high copy number group ≥ 9 copies (n= 10) and a low copy number group ≤ 5 copies (n= 5). We observed that the high AMY1 copy number group had higher iAUC plasma glucose concentration post starch ingestion than low CN group post glucose ingestion. However, iAUC plasma insulin concentration was post glucose ingestion higher post glucose ingestion in low CN group than high CN group. plasma lipid concentration did not differ between examined groups after glucose or starch ingestion. 60 % (n = 3) of the low CN group are insulin resistance compeered to 10% (n= 1) in the high AMY1 CN group. The total sample size of 62 adults is recommended to detect 80 % differences between the AMY1 CNV groups in the tested variables in future research.