Alpha lipoic is an older form. It is not all active, as it contains an inactive isomer. (there is one study showing alpha MAY suppress thyroid function--but only in rats so far)

Many of us use r-lipoic which is far more potent. This allows for much lower doses... like 100mg a day.

Now that it is economically more available, you might want to try that.

Alpha is in the literature in high dose going back almost a decade.

The r-lipoic is newer.

If you decide to try it, start at 50mg a day. It can be very stimulating, and some people don't like that effect. I used 50mg a day (I bought a tablet type--and cracked them in half) and raised to 100mg and took that for a year. I haven't continued, because I did not see much effect. For me the burning is almost gone if I avoid potatoes (nightshade veggie which triggers me).

But lipoic acid is included in "anti-aging and longevity" formulas to enhance acetyl carnitine and reduce mitochondrial decay. Biotin is often included with that mixture. Dr. Bruce Ames has a product called Juvenon, which has a website with alot of medical detail.
You might want to read that:
http://juvenon.com/
Dr. Ames is a famous biochemist in US, and has many many papers on PubMed. The site is worth reading, just for its collection of knowledge. (Our FDA still uses the Ames Test to screen new compounds for carcinogenicity.)