Table 2.

Previously reported different clinical studies to examine pharmacological potential of PQQ.

Sr. No.	Objective	Experiment Model	Produced effects	Ref.
1	Learning and memory function	Rats	Significantly improved learning ability and prevent neuron-degeneration caused by oxidative stress	(Takatsu et al., 2009; Ohwada et al., 2008)
2	Neuropsycho-logical status based on RBANS	Human	People whose RBANS scores are lower may see a more pronounced improvement after taking the PQQ•Na2-supplements	(Tamakoshi et al., 2023; Shiojima et al., 2022; Itoh et al., 2016)
3	Cognitive functions	Human	Significant improvement in task performance	Itoh et al. (2016)
4	Impacts on anxiety, fatigue, and sleeping	Human	A marked improvement in sleepiness upon awakening, the beginning of sleep, and the maintenance of sleep length	Nakano et al. (2012)
5	The impact on dry skin hydration levels, elasticity, and transepidermal water loss (TEWL)	Mice and Human	Benefits impaired skin barrier function as well as dry-skinned human female individuals and in mice model	Nakano et al. (2015a)
6	Impact on cholesterol and serum TGs levels	Human	PQQ reduce LDL-cholesterol levels	Nakano et al. (2015b)
7	Impacts on development, fertility, and markers of collagen expression and maturation	Balb/c mice	By modulating mRNA levels for Type I procollagen α1-chains, PQQ supplementation might improve growth, reproductive success, and possibly regulate indicators of the synthesis and maturation of the extracellular matrix (ECM) in neonates	Steinberg et al. (2003)
8	Nutritional essentiality of PQQ	Rats and mice	Animals fed with PQQ meals showed consistent signs of increased growth. A decrease in tendon benzylamine oxidase and an increase in cutaneous collagen solubility were seen in subjects deficient in PQQ	Rucker et al. (1989)
9	Effects on growth performance and small intestine characteristics	Weaned pigs	Reduced levels of cytokines (IL-1β, IL-2), and interferon-γ, along with improved activity of antioxidant enzymes (SOD, GSH-Px, CAT, and MDA) in the small intestine mucosa. The jejunum also showed an increase in the expression of occludin and zonula occluden protein-1 (ZO-1). Weaned piglets' growth performance and intestinal health were both significantly enhanced	(Jiang et al., 2020; Yin et al., 2019)
10	Challenged intestinal morphology, oxidative stress, and inflammatory responses to lipopolysaccharide	Broiler chickens	Incorporating PQQ•Na2 into the diet reduce IL-1β and IL-10 levels at transcriptional level in the duodenum mucosa and enhanced GSH-Px activity in serum and T-SOD and CAT activities in liver. In addition, it reduces the effects of LPS on the duodenal villus height to bulb depth ratio in broilers.	(Jiang et al., 2020; Zheng et al., 2020)