Table 3.

Different species of Lactobacillus showing effectiveness in different models of AD.

Lactobacillus Species	Model Used	Effects
L. Fermentum	Transgenic mice	L. fermentum helps in the secretion of ferulic acid which has anti-AD activity. It also helps in reducing neuroinflammation and β-amyloid plaque [96].
L. Johnsonii in combination with B. Thetaiotaomicron	Transgenic mice	This combination results in the reduction of β-amyloid plaque formation. It was concluded that this combination of probiotics along with proper exercise results in the alleviation of AD progression and beneficial effects are partly mediated by microbiome alteration [97].
L. acidophilus, B. bifidum, and B. longum	Male Sprague-Dawley rats	Probiotics improved learning and memory impairment. The paired-pulse facilitation ratio was also increased. This combination also proved to reduce serum levels of total cholesterol, VLDL, and triglycerides [98].
L. acidophilus , L. fermentum, Bifidobacterium lactis, and B. longum	Rats	The findings suggested that probiotics improved behavioral impairment, reduced oxidative stress by regulating the expression of malondialdehyde and superoxide dismutase, and improved cognitive dysfunctions in the AD model [99].
Lactobacillus Plantarum MTCC1325	Wistar rats	The ATPase system was evaluated in the hippocampus and cerebral cortex. The findings showed that lactobacillus reversed all constituents of ATPase to an almost normal level in AD-induced rats with delaying neurodegeneration [100].
Lactobacillus acidophilus , Lactobacillus casei, Bifidobacterium bifidum, and Lactobacillus fermentum	Human	The current study showed that consumption of this probiotic combination positively affects metabolic status and cognitive function in AD patients. However, it had no remarkable effect on other markers like oxidative stress, inflammation, fasting plasma glucose, and other plasma profiles [101].
Calpis sour milk whey, a Lactobacillus helveticus–fermented milk product	Male ddY mice	It was concluded in a current study that scopolamine-induced cognitive impairment and object recognition memory was significantly improved by oral administration of Calpis sour milk whey powder. Hence, it was suggested that it may help prevent neurodegenerative disorders, i.e., Alzheimer’s disease, and enhance learning [102].
L. rhamnosus as curcumin adjuvant	Mice	It was concluded that probiotics in combination with curcumin reduced the cognitive dysfunction in scopolamine-induced dementia mice. The conclusion was based on an enhanced level of antioxidant enzyme level and reduction in neuronal cell loss [103].
L. pentosus var. Plantarum (C29)	20 week old mice	It was concluded that treatment with C29 significantly improved memory impairment. The conclusion was based on the reversal of BDNF level suppression, DCX expression, and activation of CREB in the D-galactose-injected mice’s brains. Senescence marker p16 was also decreased along with the reduced level of inflammation markers, i.e., p-65, COX-2, p-FOXO3a, and iNOS [104].
Lactobacillus pentosus var. Plantarum obtained from Chinese cabbage kimchi	Mice	Probiotic supplementation inhibited cognitive dysfunction in scopolamine-injected mice by enhancing BDNF expression and p-CREB expression [105].
L. acidophilus with bifidobacterium sp.	Male Wistar rats	The findings suggested that probiotics via the gut–brain axis modulate spatial cognitive abilities and synaptic dysfunction in β-amyloid induced animal models of Alzheimer’s disease [106].
Bifidobacterium bifidum TMC3115 and Lactobacillus Plantarum 45	APP/PS1 mice	The findings suggested that supplementation of probiotics resulted in the regulation of spatial memory impairment and modified gut microbiome that further is beneficial for AD patients [107].