Table 1.

Allopregnanolone (Allo) pre-clinical research translation in AD mouse models and existing clinical exposure data in healthy subjects. Allo blood plasma and brain concentrations and reported safety and efficacy by multiple routes of administration. Intravenous (IV) dose studies determine the pharmacokinetic properties. Assumed to be 100% bioavailable, the IV route of administration is the most quantitative, and useful for gauging alternative routes of administration. Our pre-clinical Allo dosing studies with subcutaneous (SC), transdermal (TD), intranasal (IN), and IV routes of administration that resulted in beneficial effects that decreased hallmarks of AD pathology and improved cognitive performance were tabulated alongside with other pre-clinical studies that tested long-term chronic continuous exposure to SC Allo that resulted in deleterious effects on AD pathology and long-term memory impairment. Human IV dosing is included to compare the mouse pharmacokinetic parameters to clinical Allo pharmacokinetics demonstrates the safety of Allo when blood levels are below the maximum tolerated dose indicated by sedation level. When bioavailability and species-specific allometric conversions are taken into account the pre-clinical studies that demonstrate neuroregenerative efficacy in an AD mouse model are within the safe range of dosage for humans. The AD mouse models were administered both chronic and acute dosing regimens. Allo treatment induced a significant increase in neurogenesis, with the latter regimen yielding the greater increase in neurogenesis. However, the 3/week/3 months (12/month) treatment induced a significant decrease in neurogenesis. Brain sections from 3xTgAD mice treated with Allo or vehicle were immunostained. Aβ immunoreactivity was detected and indicated that the 1/week/6 months (4/month) Allo treatment significantly decreased Aβ immunoreactivity. Efficacy of Aβ reduction in 4/month was comparable to the 12/month Allo treatment whereas the 1/month Allo treatment was ineffective at reducing Aβ immunoreactivity (Chen et al., 2011). Allo tested to mimic chronic stress levels associated with AD. In a series of studies, continuous subcutaneous osmotic pump infusion of Allo proved to be detrimental and decreased learning and memory performance while simultaneously exacerbating AD pathology markers (Bengtsson et al., 2012, 2013). Although not measured, neurogenesis possibly was inhibited in the continuous Allo exposure studies. From these tabulated studies we hypothesized that the dose and frequency of Allo are critical components of efficacy at neurogenic and pathological endpoints.

	Purpose	Species/Strain	Route	ALLO mg/kg	Vehicle	Frequency of exposure	Endpoint	Blood [ALLO]	Brain [ALLO]	Results	Safety	Reference
Pre-clinical	Allo pre-clinical efficacy and route of administration development in mouse model of Alzheimer’s disease	Mouse (male) 3xTgAD: APPSwe × PS1 M146V × Tau P301L	SC	10	PBS/5% EtOH	Single dose	24h	4 ng/ml (12.5 nmol/L) C24h	15 ng/g C24h	Increased neurogenesis	No adverse effects	Wang et al. (2010)
			SC	10	PBS/5% EtOH	Single dose	24 h time course	34ng/ml (107nmol/L) Cmax; 0.5h Tmax	159ng/g C0.5 h	Increased neurogenesis	No adverse effects	Irwin et al. (2013)
			IV	1.5	6% HβCD	Single dose	24 h time course	215 ng/ml (675 nmol/L) Cmax; 0.08 h Tmax	639 ng/g Cmax	Increased CREB signaling and neurodifferentiation markers	No adverse effects other than acute mild sedation	Irwin et al. (2013)
			TD	10–50	Various soluble formulations	Single dose	4h; 24h	44 ng/ml (138nmol/L) C4h	–	Increased neurogenesis	No adverse effects	Irwin et al. (2013)
			IN	3–10				–	–
			SC	10	PBS/5% EtOH	Single dose	3 wk	–	–	Increased neurogenesis and cell survival; improved hippocampal-dependent learning and memory	No adverse effects	Singh et al. (2011)
			SC	10	PBS/5% EtOH	Three/wk	3 mo	–	–	No effect on neurogenesis; decreased β-amyloid	No adverse effects	Chen et al. (2011)
			SC	10	20% HβCD	Once/wk	6 mo	–	–	Increased neurogenesis and cell survival; decreased AD pathology	No serious adverse effects; acute hyperactivity followed by brief sedation	Chen et al. (2011)
	Allo pre-clinical efficacy and regimen development in mouse model of Alzheimer’s disease	Mouse APPSwe × PS1ΔE9 (male and female, n = 6–11)	SC	1.2–2.4 mg/kg/day osmotic pump	60%SBEβCD	Continuous release	3 mo	1.3–2.2 ng/ml (4–7 nmol/L) Cmax wk 4	2.5–4.8 ng/g Cmax wk 4	Chronic treatment for three months increased soluble Aβ1–42; impaired cognitive learning assessed one month after treatment to observe long-term effects	Accelerated Alzheimer’s pathology and memory impairment	Bengtsson et al. (2012)
		Mouse APPSwe × PS1ΔE9 (male and female)	SC	2.4–4.8 mg/kg/day osmotic pump	60%SBEβCD	Continuous release	1 mo	–	–	Brief but chronic Allo for one month increased soluble Aβ1–40 and Aβ1–42 but was not sufficient to impair cognitive learning	Accelerated Alzheimer’s pathology	Bengtsson et al. (2013)
		Mouse APPSweArc (male and female)	SC	2.4mg/kg/day osmotic pump	60% SBEβCD	Continuous release	1 mo	–	–	Brief but chronic treatment for one month did not affect soluble Aβ1–40 and Aβ1–42 but impaired cognitive learning	Memory impairment	Bengtsson et al. (2013)
Clinical	Clinical trial	Human(healthy male, n = 9) Human (healthy female on oral contraceptive, n = 9)	IV	0.09	Albumin solution	Acute 1 h cumulative doses	During 1 h cumulative dosing	48 ng/ml (150nmol/L) Cmax	–	Male – decreased saccadic eye movement; decrease in contentedness	No adverse effects other than self reported sedation	van Broekhoven et al. (2007)
								32 ng/ml (100nmol/L) Cmax	–	Female – decreased saccadic eye movement; increase in contentedness
	Clinical trial	Human (healthy female, n = 10)	IV	0.09	Albumin solution	Acute 1 h cumulative doses	During 1 h cumulative dosing	22 ng/ml (70nmol/L) Cmax	–	Decreased saccadic eye movement	No adverse effects other than fatigue, mild nausea	Timby et al. (2006)
	Clinical trial	Human (healthy female, n = 28 crossover)	IV	0.07	Albumin solution	Single dose	10–55 min post-dosing	22–45 ng/ml (70–140nmol/L) Cmax	–	Acutely impaired free verbal recall episodic memory due to mild sedation with high variability; no acute effect on semantic or working memory	No adverse effects other than self reported sedation	Kask et al. (2008)
	Clinical trial	Human (healthy female, n = 12; PMDD, n = 16)	IV	0.05	Albumin solution	Single dose	0–20 min post-dosing	16–22 ng/ml (50–70 nmol/L) Cmax	–	No effect on startle response or prepulse inhibition to startle	No adverse effects other than self reported sedation	Kask et al. (2009)