According to World Health Organisation data, cardiovascular diseases (CVDs) are the leading cause of death globally, taking an estimated 17.9 million lives each year. An unhealthy diet is one of the main risk factors for CVD, as well as high blood cholesterol and high blood sugar or glucose levels. Therefore, CVDs are often accompanied by metabolic syndrome and diabetes (Han and Lean, 2016; Saklayen, 2018).

A lot of dietary patterns for the prevention of CVDs have been proposed, such as low-fat diets enriched with monounsaturated (MUFA) and polyunsaturated (PUFA) fats, low-carbohydrate diets enriched with fibres, the Dietary Approach to Stop Hypertension (DASH) diet providing more calcium, potassium, magnesium, and dietary fibre and less fat, saturated fatty acids (SFA), cholesterol, and sodium, and the Mediterranean diet characterised by a relatively high fat intake (40–50% of total daily calories), of which SFA comprises ≤8% and MUFA 15–25% of calories (Eilat-Adar et al., 2013; Anand et al., 2015; Mozaffarian, 2016).

Composition modification (fatty acids modification, sodium chloride control), fermentation (formation of bioactive compounds) and the introduction of functional additives (plant components (oils, extracts, fibres), soy protein, natural and synthetic antioxidants, lactic acid bacteria, and fish oil are successfully used in functional food processing (Mine and Shahidi, 2006; Cencic and Chingwaru, 2010; Alissa and Ferns, 2012; Hui, 2012; Griffiths et al., 2016; Lordan et al., 2018).

Peptides of animal origin released from milk and meat proteins during proteolysis, fermentation or food processing possess hypotensive, antioxidant, antimicrobial, antitumor, antithrombotic, lipid-lowering, and opioid etc. actions, and can be considered functional additives to food (Arihara, 2006; Ahhmed and Muguruma, 2010; Ryan et al., 2011; Udenigwe and Howard, 2013; Lafarga and Hayes, 2014; Bhat, Kumar and Bhat, 2015; Liu et al., 2016; Sánchez and Vázquez, 2017). However, tissue-specific proteins and peptides contained natively in slaughter by-products have still not been well-studied.

In previous studies, we confirmed the lipid-lowering effect of functional meat products derived from the porcine heart and aorta on hyperlipidaemic rats (Chernukha et al., 2018; Kotenkova and Chernukha, 2019). This paper reports the analytical results of a randomised controlled trial of meat products for specialised nutrition in patients with cardiovascular and metabolic disorders.

Meat products (MsP) for specialised nutrition were produced on ZAO "Yoshkar-Olinskiy Myasokombinat”. Porcine hearts were chopped with a particle size of 2 – 3 mm and salted for 12 h. Porcine aortas were chopped with a particle size of 2 – 3 mm and homogenised in a cutter at 3000rpm for 2 – 3 min. Minced hearts with the juice were quantitatively transferred in the cutter and homogenised at 3000rpm for 6 – 8 min (ratio of the aorta to hearts 1:3). The obtained mince was packed in cans of lamister and sterilised at 115 °C and a pressure of 0.23 MPa for 40 min. Meat products contained 17.53 ±0.95% protein, 3.82 ±0.13% fat, 0.305 ±0.015% sodium chloride, and 2.35 ±0.25% starch.

The null hypothesis about the influence of control and experimental diets on serum lipid profile inside the group were checked according to Freidman’s ANOVA for all patients and patients with a BMI below 40 kg.m^-2 (n_control = 11, n_experimental = 10) and above 40 kg.m^-2 (n_control = 9, n_experimental = 10). The results are presented in Table 1. It was shown that LCD consumption (control) for 7 – 10 days led to total cholesterol reduction by 11.2%, mainly due to its reduction in the serum of patients with a BMI below 40 kg.m^-2 by 17.7%.

The cholesterol level returned to its original level after 28–30 days of dieting. Revealed changes were not significantly reliable. LCD with MP consumption (experimental) led to a statistically significant total cholesterol reduction by 18.2% and 14.0% after 7 – 10 and 28 – 30 days, respectively, mainly due to its reduction in the serum of patients with a BMI above 40 kg.m^-2 by 28.4% and 12.8%, respectively. Despite the lack of statistical significance, it was noted that the total cholesterol level reduction was higher in patients with a BMI below 40 kg.m^-2 and equal to 15.0% compared with day 0.

In the control group, a statistically significant cholesterol LDL reduction by 13.8% was noticed after 7 – 10 days, mainly due to its reduction in the serum of patients with a BMI below 40 kg.m^-2 by 14.1%. LDL cholesterol level decline was also marked in the serum of experimental patients and was equal to 22.4% after 7 – 10 days, mainly due to its reduction in the serum of patients with a higher BMI of 40 kg.m^-2 by 36.4%. The cholesterol LDL level returned to its original level in both groups after 28 – 30 days of dieting. The same tendency was noticed concerning the cholesterol HDL level.

There were no significantly reliable changes to triglyceride levels and serum atherogenic index in both groups. However, after 7–10 days after the diets, a decrease in triglyceride levels in the control group amounted to only 3.9% and returned to its original level after 28 – 30 days, while the reduction in experimental patients was equal to 12.0% and continued to reduce until 28 – 30 days to 17.4%. The same tendency was noticed concerning serum atherogenic index (AI). Also, 7 – 10 days after the diets, the decrease in AI in the control group amounted to 16.4% and returned to its original level after 28 – 30 days, while the reduction was equal to 13.7% in experimental patients and continued to reduce until 28 – 30 days to 20.4%.

Cholesterol levels on days 0, 7 – 10 and 28 – 30 days were compared between the control and experimental groups according to the Mann-Whitney U test. There were no significantly reliable changes in cholesterol levels in the two groups for all patients and patients with a BMI higher 40 kg.m^-2. Cholesterol LDL on day 0 in the serum of experimental patients with a BMI lower than 40 kg.m^-2 was higher than in the control group by 48.3% (p < 0.05), while cholesterol HDL was lower by 15.7%; therefore, there was no difference between total cholesterol levels.

After 7 – 10 days, the cholesterol LDL in the serum of experimental patients with a BMI below 40 kg.m^-2 was still higher than in the control group by 55.4% (p <0.05), but returned to the original level in both groups after 28 – 30 days of dieting.

With such heterogeneity of groups, it is advisable to consider changes in the lipid profile in dynamics and compare changes in parameters between groups. Dynamics were evaluated between 0 day and 7 – 8 days and 0 day and 28 – 30 days and are presented in Table 2 in percentiles (P_25\75); statistical differences were calculated according to Mann-Whitney U tests.

There were no significantly reliable changes in Δ total cholesterol after 7 – 10 days of diet consumption, but after 28 – 30 days in the serum of experimental patients it was significantly lower than in the control, mainly due to LDL cholesterol reduction especially in patients with a BMI below 40 kg.m^-2. The same tendency was noticed concerning Δ triglycerides. There was still no significantly reliable changes in the Δ serum atherogenic index, despite its remarkable reduction in the experimental group by 13.7% and 20.4% at 7 – 10 and 28 – 30 days, respectively (Table 1). Nevertheless, a positive effect of MP on the serum lipid profile of patients during the trial is noticeable.

In a previous study it was shown that meat products characterised by milder hypolipidaemic action compared with native raw material or isolated active fractions; a slight effect was observed after 28 days of consumption by hyperlipidemic rats, while a significant effect was only seen after 42 days of consumption (Kotenkova and Chernukha, 2019).

The pronounced effect of meat product could be linked to the unique proteome and peptidome of the heart and aorta tissues based on organ-specific gene expression and the presence of tissue-specific substances (Fagerberg et al., 2014; Breschi et al., 2016; Guschanski, Warnefors and Kaessmann, 2017; Sonawane et al., 2017; Barbeira et al., 2018). Previously, we also observed that sterilisation led to the decomposition of most parts of the target tissue-specific proteins and peptides into active peptides with apparently similar biological actions or retained residual activity (Chernukha et al., 2016; Chernukha et al., 2018; Kotenkova and Chernukha, 2019).

On the other hand, numerous authors also considered animal proteins as abundant sources of functional peptides, including those which demonstrated a lipid-lowering effect (Bauchart et al., 2006; Ahhmed and Muguruma, 2010; Toldrá et al., 2012; Udenigwe and Howard, 2013; Lafarga and Hayes, 2014; Cicero, Fogacci and Colletti, 2017). Nakade et al. (2009) revealed that cattle heart protein hydrolysate could suppress cholesterol absorption in Caco-2 cells.

It is known that aorta tissue is enriched with collagen and elastin, while collagen-derived peptides have been better studied and are characterised by their lipid-lowering effect (Koyama and Kusubata, 2013; Hongdong and Bo, 2017; Tometsuka et al., 2017; Tomosugi et al., 2017; Yazaki et al., 2017; Arrutia et al., 2017; Wahart et al., 2019). In this regard, aorta tissue is a good source of glyproline peptides with hypolipidaemic action (Lyapina et al., 2015; Shabalina Lyapina et al., 2015; Myasoedov et al., 2016). Presumably, active peptides could be generated both during meat product processing and digestion processes.

The positive effect of developed meat products on the serum lipid profile of patients during the trial was mild but noticeable. Presumably, it is more preferable to use this as a component in a diet therapy for hyperlipidaemic humans for 28 – 30 days. Earlier, the same effect was revealed on hyperlipidaemic rodents, which confirms the lipid decreasing ability effect of innovative products and can be recommended as part of a diet to fight CVD. The pronounced effect of the product could be linked to the unique proteome and peptidome of the heart and aorta tissues based on organ-specific gene expression and the presence of tissue-specific substances.